Control apparatus and method for digital printing system

Abstract

To reduce or eliminate distortion of an image.SOLUTION: Embodiments of the present invention relate to a control apparatus and method for a printing system, for example, comprising an intermediate transfer member (ITM). Some embodiments relate to regulation of a velocity and / or tension and / or length of an endless belt or a blanket 102 functioning as the ITM. Some embodiments relate to regulation of deposition of ink on the moving ITM. Some embodiments relate to an apparatus configured to alert a user of one or more events related to operation of the ITM. The invention is configured to stretch an upper travel part of the ITM, maintain the stretched state, and substantially isolate an upper travel part from mechanical vibrations in a lower travel part so as to reduce or eliminate distortion of an image.SELECTED DRAWING: Figure 1B

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims priority to the following patent applications: U.S. Provisional Patent Application No. 61 / 606,913, filed Mar. 5, 2012; U.S. Provisional Patent Application No. US61 / 611,547, filed Mar. 15, 2012; U.S. Provisional Patent Application 61 / 624,896, filed Apr. 16, 2012; U.S. Provisional Patent Application US61 / 641,288, filed May 1, 2012; U.S. Provisional Patent Application 61 / 642445, filed May 3, 2012; International Application PCT / IB2012 / 056100, filed Nov. 1, 2012; and International Application PCT / IB2013 / 050245, filed Jan. 10, 2013, all of which are hereby incorporated by reference in their entirety.

[0002] The present invention relates to a control apparatus and method for a digital printing system. In particular, the present invention is suitable for an indirect printing system using an intermediate transfer member.

Background Art

[0003] Digital printing techniques have been developed that allow a printer to receive commands directly from a computer without the need to prepare a printing plate. Among these, there are color laser printers that use an electrophotographic process. Color laser printers that use dry toner are suitable for certain applications, but they do not produce photo - quality images acceptable for publications such as magazines.

[0004] A process more suitable for short - run high - quality digital printing is used in HP - Indigo printers. In this process, an electrostatic image is created on an image - receiving cylinder charged by exposure to laser light. The electrostatic charge attracts an oily ink to form a color ink image on the image - receiving cylinder. The ink image is then transferred onto paper or any other substrate by a blanket cylinder.

[0005] Inkjet and bubble jet (registered trademark) processes are commonly used in home and office printers. In these processes, ink droplets are sprayed onto a final substrate in an image pattern. Generally, the resolution of such processes is limited by the uptake of ink into a paper substrate. Thus, substrates are generally selected or adapted to suit the particular characteristics of the inkjet printing mechanism being used. Fibrous substrates such as paper generally require special coatings designed to absorb liquid ink in a controlled manner or to prevent its penetration beneath the surface of the substrate. However, using specially coated substrates is an expensive option that is not suitable for certain printing applications, particularly commercial printing. Moreover, the use of coated substrates creates problems of its own in that the surface of the substrate remains wet and additional costly or time-consuming steps are required to dry the ink so that it is not later soiled when the substrate is handled, for example stacked or wound onto a roll. Moreover, excessive wetness of the substrate causes wrinkling and, if possible, makes printing on both sides of the substrate (also called duplex printing) difficult.

[0006] Moreover, direct inkjet printing onto porous paper or other fibrous materials results in poor image quality due to variations in the distance between the printhead and the surface of the substrate.

[0007] The use of indirect or offset printing techniques overcomes many of the problems associated with direct inkjet printing onto a substrate. It allows the distance between the surface of the intermediate image transfer member and the inkjet printhead to be maintained constant and reduces wetness of the substrate so that the ink can be dried on the intermediate image member before being applied to the substrate. As a result, the final image quality on the substrate is less affected by the physical properties of the substrate.

[0008] Also, various printing devices that use an indirect inkjet printing process have been previously proposed. This process is one in which an inkjet printhead is used to print an image onto the surface of an intermediate transfer member, and the intermediate transfer member is then used to transfer the image onto a substrate. The intermediate transfer member can be a rigid drum or a flexible belt (e.g., induced on a roller or attached to a rigid drum), which is also referred to as a blanket in this specification. SUMMARY OF THE INVENTION

[0009] The present disclosure relates to a control method and apparatus for a digital printing system, such as a digital printing system having a moving intermediate transfer member (ITM), such as a flexible ITM (e.g., a blanket) attached to a plurality of rollers (e.g., belts) or a flexible ITM (e.g., a blanket attached to a drum) attached to a rigid drum.

[0010] An ink image is formed on the surface of the moving ITM (e.g., by droplet deposition at an image forming station) and then transferred to a substrate. To transfer the ink image to the substrate, the substrate is pressed between at least one impression cylinder and the region of the moving ITM where the ink image is located, at which point the transfer station (also referred to as the impression station) is said to be engaged.

[0011] In the case of a flexible ITM mounted on a plurality of rollers, the impression station typically comprises, in addition to the impression cylinder, a pressure cylinder or roller, the outer surface of which can optionally be compressible. A flexible blanket or belt typically passes between two such cylinders that can be selectively engaged or disengaged, typically when the distance between the two is decreased or increased. One of the two cylinders may be in a fixed position in space and the other may move towards or away from it (e.g., the pressure cylinder is movable or the impression cylinder is movable), or the two cylinders may each move towards or away from the other. In the case of a rigid ITM, a drum (on which a blanket can optionally be mounted) constitutes a second cylinder that engages or disengages from the impression cylinder.

[0012] In the case of a flexible ITM, the movement of the ITM can be linear in the intermediate section of the roller or can rotate when passing over such a roller. In the case of a rigid ITM having a drum shape or a support, the movement of the ITM is rotational. In either case, the movement of the ink image from the imaging station to the impression station defines the printing direction. Unless the context clearly indicates otherwise, terms such as upstream and downstream as may be used below relate to the position with respect to the printing direction.

[0013] Some embodiments relate to a method of controlling the temporal variation of the surface speed of an ITM to (i) maintain a constant surface speed of a portion of the intermediate transfer member at a position aligned with the imaging station and (ii) locally accelerate and decelerate only a portion of the intermediate transfer member at a position spaced from the imaging station to obtain a variable speed at least for a portion of the time at a position spaced from the imaging station.

[0014] In one example, each of the ITM and the impression cylinder includes a discontinuity in its circumference. For example, (i) the ITM may include a seam position where the ends of a flat, flexible, elongated blanket piece are fixed to each other to form an endless belt, and (ii) the impression cylinder may include a cylinder gap that interrupts the circumference of the impression cylinder (e.g., for receiving a gripping portion). In some embodiments, it is desirable to avoid situations where the ITM engages the impression cylinder when (i) the seam position of the ITM is aligned with the impression cylinder and / or (ii) the gap in the impression cylinder is aligned with the ITM. Instead, it is preferable to operate such that (i) the seam position of the ITM is aligned with the impression cylinder gap and / or (ii) the gap in the impression cylinder is aligned with the ITM during a disengaging period.

[0015] Generally speaking, this result can be achieved if the system is configured such that (i) the circumference of the ITM and (ii) the circumference of the impression cylinder are fixed and equal to a positive integer. In a printing system where the impression cylinder can receive n sheets of a substrate, the circumference of the ITM can be set to a positive integer that is 1 / n of the circumference of the impression cylinder.

[0016] However, in certain situations, the circumference or "length" of the ITM can vary over time, for example, due to temperature changes or material fatigue or for any other reason.

[0017] As described above, in some embodiments, it is possible to locally accelerate and decelerate only a portion of the intermediate transfer member at a position spaced from the image forming station in order to obtain a variable speed only at positions spaced from the image forming station for at least a portion of the time. Thus, the local acceleration and deceleration to temporarily and locally correct the surface speed of the portion of the ITM can be performed (i) to correct for a deviation of the circumference / length of the ITM from a desired value or setpoint value (e.g., equal to a positive integer multiple of the circumference of the ITM), and / or (ii) to avoid alignment of the seam of the ITM or the gap of the impression cylinder with the nip between the ITM and the impression cylinder during the period of engagement.

[0018] Such temporary and local correction of the surface speed of the portion of the ITM is typically performed when the ITM is not engaged with the impression cylinder. Once the ITM is engaged again with the impression cylinder, it is possible to resume operation such that the surface speed of the ITM matches the surface speed of the rotating impression cylinder once again, at which point they can be said to move "in tandem".

[0019] If the ITM includes a flexible belt mounted on a plurality of rollers, increasing or decreasing the rotational speed of one or more of the roller(s) temporarily when the ITM is disengaged from the impression cylinder can accelerate (e.g., locally accelerate) or decelerate the ITM.

[0020] Alternatively or in addition, in some embodiments, powered tension rollers or dancers are disposed on both sides of the nip between the ITM and the impression cylinder. If the temporary acceleration or deceleration of the roller accumulates slack on one side of the nip, the tension accumulates on the other side of the nip. It is possible to compensate for that slack by moving the dancer in the opposite direction.

[0021] As described above, in some embodiments, during the period of disengagement between the ITM and the impression cylinder, when the seam passes through the nip between the ITM and the impression cylinder, it is desirable for the circumference of the ITM to be an integer multiple of the circumference of the impression cylinder so that the seam is aligned with the cylinder gap of the impression cylinder. If the circumference of the ITM increases or decreases, it is possible to maintain the phase synchronization between the seam of the ITM and the cylinder gap by accelerating or decelerating the entire ITM or some of them (e.g., the part including the seam).

[0022] Alternatively or in addition, for example, by moving one or more rollers to which the ITM is attached relative to each other, it may be possible to stretch the ITM (e.g., including a flexible belt) or contract the belt. Therefore, some embodiments of the present invention relate to a control method and apparatus, whereby (i) the length of the circumference of the ITM is not fixed and varies with time, and (ii) this circumference length is adjusted to a setpoint length equal to an integer multiple of the circumference of the impression cylinder. The adjustment of the circumference length of the ITM can be done by increasing or decreasing the distance between any set of rollers to which the ITM is attached.

[0023] As described above, some embodiments relate to a digital printing system in which the ITM comprises a flexible belt. In some embodiments, the length of the flexible belt or a part thereof may vary with time, where the magnitude of the variation may depend on the physical structure of the flexible belt. In some embodiments, the stretching and contraction of the belt may be non-uniform.

[0024] In a system in which an ink image is formed on an ITM with a flexible belt by depositing ink droplets onto the ITM, it is disclosed herein that it is advantageous to (i) monitor temporary variations in the non-uniform stretching of the ITM with the flexible belt and (ii) adjust the timing of ink droplet deposition according to the monitored temporary variations.

[0025] It is disclosed herein that non-uniform stretching of the ITM can distort the ink image formed thereon. By measuring and compensating for this phenomenon, it is possible to reduce or eliminate this image distortion.

[0026] A method of operating a printing system, wherein an ink image is formed on an intermediate transfer member moving at an image forming station and transferred from the intermediate transfer member to a substrate at a printing pressure station, the method comprising: (i) maintaining a constant surface speed of a portion of the intermediate transfer member at a position aligned with the image forming station; and (ii) controlling a temporal change in the surface speed of the intermediate transfer member by locally accelerating and decelerating only a portion of the intermediate transfer member at a position spaced from the image forming station to obtain a variable speed at least partially over time at a position spaced from the image forming station. A method is disclosed herein.

[0027] In some embodiments, i. the moving intermediate transfer member is periodically engaged with a rotating printing cylinder at the printing pressure station and disengaged from the printing cylinder to transfer the ink image from the intermediate transfer member to the substrate, and ii. the acceleration and deceleration are performed to (i) prevent a predetermined section of the intermediate transfer member from being aligned with the printing cylinder during the engagement period and / or (ii) improve the synchronization between a predetermined section of the intermediate transfer member and a predetermined position of the printing cylinder.

[0028] In some embodiments, the predetermined section of the intermediate transfer member is a blanket seam and / or the predetermined section of the printing cylinder is a gap in the printing cylinder that receives the substrate gripping portion.

[0029] In some embodiments, the acceleration and deceleration are performed by upstream and downstream powered dancers arranged upstream and downstream of the printing pressure station where the ink image is transferred.

[0030] In some embodiments, only portions of the intermediate transfer member within regions downstream of the upstream dancer and upstream of the downstream dancer are accelerated or decelerated.

[0031] In some embodiments, i. the moving intermediate transfer member comprises a flexible belt mounted (e.g., firmly mounted) on upstream and downstream rollers arranged upstream and downstream of the image forming station, the upstream and downstream rollers defining upper and lower running portions of the flexible belt, ii. the lower running portion of the flexible belt includes one or more slack portions, and iii. the torque applied to the belt by the rollers holds the upper running portion taut so as to substantially isolate the upper running portion from mechanical vibrations in the lower running portion.

[0032] In some embodiments, i. the moving intermediate transfer member is periodically engaged with and disengaged from a rotating impression cylinder at the impression station for transferring an ink image from the intermediate transfer member to a substrate, and ii. the surface speed of the intermediate transfer member at the impression station matches the linear surface speed of the rotating impression cylinder during the engagement period, and the acceleration and deceleration of the intermediate transfer member are performed only during the disengagement period.

[0033] In some embodiments, i. the moving intermediate transfer member is periodically engaged with and disengaged from a rotating impression cylinder at the impression station for transferring an ink image from the intermediate transfer member to a substrate, ii. the method further includes monitoring a phase difference between (i) a locator point attached to the moving intermediate transfer member and (ii) the phase of the rotating impression cylinder, and iii. local acceleration of only a portion of the intermediate transfer member is performed in response to the result of the phase difference monitoring.

[0034] In some embodiments, the locator point corresponds to the position of a marker on or a lateral formation of the intermediate transfer member.

[0035] A printing system comprising: a. an intermediate transfer member; b. an image forming station configured to form an ink image on the surface of the intermediate transfer member when the intermediate transfer moves, such that the ink image is transferred to a printing station thereon; and c. a speed controller configured to control the temporal change of the surface speed of the intermediate transfer member such that: (i) a constant surface speed of the intermediate transfer member is maintained at a position aligned with the image forming station, and (ii) a variable speed is obtained at least in part of the time at a position spaced from the image forming station by locally accelerating and decelerating only a portion of the intermediate transfer member at a position spaced from the image forming station. The printing system is disclosed herein.

[0036] In some embodiments: i. the moving intermediate transfer member is periodically engaged with and disengaged from a rotating printing cylinder at the printing station to transfer the ink image from the intermediate transfer member to a substrate; and ii. the speed controller is configured to perform acceleration and deceleration such that: (i) a predetermined section of the intermediate transfer member is prevented from being aligned with the printing cylinder during the engagement period, and / or (ii) the synchronization between a predetermined section of the intermediate transfer member and a predetermined position of the printing cylinder is improved.

[0037] In some embodiments, the predetermined section of the intermediate transfer member is a blanket seam and / or the predetermined section of the printing cylinder is a gap within the printing cylinder that receives a substrate gripper.

[0038] In some embodiments, the acceleration and deceleration are performed by upstream and downstream powered dancers arranged upstream and downstream of the printing station where the ink image is transferred.

[0039] In some embodiments, only portions of the intermediate transfer member within the region downstream of the upstream dancer and upstream of the downstream dancer are accelerated or decelerated.

[0040] In some embodiments, i. the moving intermediate transfer member comprises a flexible belt attached (e.g., firmly attached) to upstream and downstream rollers arranged upstream and downstream of the image forming station, the upstream and downstream rollers defining upper and lower running portions of the flexible belt, ii. the lower running portion of the flexible belt includes one or more slack portions, and iii. the torque applied to the belt by the rollers holds the upper running portion taut so as to substantially isolate the upper running portion from mechanical vibrations in the lower running portion.

[0041] In some embodiments, i. the moving intermediate transfer member is periodically engaged with and disengaged from a rotating impression cylinder at the impression station to transfer an ink image from the intermediate transfer member to a substrate, ii. the system and / or speed controller further comprises an electronic circuit configured to monitor a phase difference between (i) a locator point attached to the moving intermediate transfer member and (ii) the phase of the rotating impression cylinder, and iii. the speed controller is configured to perform local acceleration of only a portion of the intermediate transfer member in response to the result of the monitoring of the phase difference. In some embodiments, the locator point corresponds to the position of a marker on or a lateral formation of the intermediate transfer member.

[0042] A printing system comprising: a. an intermediate transfer member having a flexible belt (e.g., an endless belt); b. an image forming station configured to form an ink image on the surface of the intermediate transfer member as the intermediate transfer moves and to transfer the ink image onto a substrate at a printing station; c. upstream and downstream rollers arranged upstream and downstream of the image forming station to define an upper running portion passing through the image forming station and a lower running portion passing through the printing station; and d. a printing cylinder at the printing station that is periodically engaged with and disengaged from the intermediate transfer member to transfer the ink image from the moving intermediate transfer member to a substrate passing between the intermediate transfer member and the printing cylinder, wherein the system is configured such that: i. the periodic engagement induces mechanical vibrations within a slack portion in the lower running portion of the belt, and ii. the torque applied to the belt by the upstream and downstream rollers holds the upper running portion taut to substantially isolate it from the mechanical vibrations in the lower running portion. A printing system is disclosed herein.

[0043] In some embodiments, the downstream roller is configured to sustain a torque on the belt that is significantly stronger than that of the upstream roller.

[0044] A method of operating a printing system having a moving intermediate transfer member that is periodically engaged with and disengaged from a rotating printing cylinder such that during the engagement period, an ink image is transferred from the surface of the moving intermediate transfer member to a substrate positioned between the printing cylinder and the intermediate transfer member, the method comprising: (i) during the engagement period, moving the intermediate transfer member at the same surface speed as the rotating printing cylinder to prevent a predetermined section of the intermediate transfer member from aligning with the printing cylinder and / or (ii) during the disengagement period, increasing or decreasing the surface speed of the moving intermediate transfer member or a portion thereof to improve synchronization between a predetermined section of the intermediate transfer member and a predetermined position of the printing cylinder. A method is disclosed herein.

[0045] In some embodiments, a predetermined section of the intermediate transfer member is a seam of the blanket, and / or a predetermined section of the impression cylinder is a gap within the impression cylinder that receives the substrate gripper.

[0046] In some embodiments, (i) the intermediate transfer member comprises a flexible belt mounted on a plurality of rollers, (ii) at least one of the plurality of rollers is a drive roller, and (iii) acceleration or deceleration of the intermediate transfer member is effected by increasing or decreasing the rotational speed of one or more of the drive rollers during a disengagement period.

[0047] In some embodiments, the surface speed of only a portion of the intermediate transfer member is increased or decreased during a disengagement period.

[0048] In some embodiments, i. the intermediate transfer member comprises a flexible belt, ii. the printing system includes upstream and downstream powered dancers arranged upstream and downstream of the nip between the belt and the impression cylinder, and iii. during a disengagement period, the movement of the upstream and downstream dancers locally accelerates and then decelerates only a portion of the intermediate transfer member within a region that includes the nip that is downstream of the upstream dancer and upstream of the downstream dancer, thereby accelerating and decelerating a predetermined section of the intermediate transfer member.

[0049] In some embodiments, the overall surface speed of the intermediate transfer member is increased or decreased during a disengagement period.

[0050] In some embodiments, the method further includes monitoring a phase difference between (i) a locator point attached to the moving intermediate transfer member and (ii) the phase of the rotating impression cylinder, and increasing or decreasing the surface speed of the intermediate transfer member during a disengagement period is performed in response to the result of the monitoring of the phase difference.

[0051] In some embodiments, the locator point corresponds to the position of a marker on or a lateral formation of the intermediate transfer member.

[0052] In some embodiments, (i) the intermediate transfer member comprises a flexible belt, (ii) the method further comprises monitoring a varying length of the flexible belt, and (iii) increasing or decreasing the speed of the intermediate transfer member during a disengaging period is performed in response to the results of the length monitoring.

[0053] A printing system comprising: a. an intermediate transfer member; b. an image forming station configured to form an ink image on a surface of the intermediate transfer member while the intermediate transfer member is moving; c. a rotating impression cylinder configured to be periodically engaged with and disengaged from the rotating intermediate transfer member such that during an engaging period, the ink image is transferred from the surface of the rotating intermediate transfer member to a substrate located between the impression cylinder and the intermediate transfer member; and d. a controller configured to adjust the movement of the intermediate transfer member such that: i. during an engaging period, the intermediate transfer member moves at the same surface speed as the rotating impression cylinder, and ii. during a disengaging period, the surface speed of the intermediate transfer member, or a portion thereof, is increased or decreased. The controller is further configured to prevent a predetermined section of the intermediate transfer member from aligning with the impression cylinder during the engaging period and / or to improve synchronization between a predetermined section of the intermediate transfer member and a predetermined position of the impression cylinder. In some embodiments, the predetermined section of the intermediate transfer member is a blanket seam and / or the predetermined section of the impression cylinder is a gap in the impression cylinder that receives a substrate gripper.

[0054] In some embodiments, (i) the intermediate transfer member comprises a flexible belt mounted on a plurality of rollers, (ii) at least one of the rollers is a drive roller, and (iii) the controller is configured to accelerate or decelerate the intermediate transfer member by increasing or decreasing the rotational speed of one or more of the drive rollers during a disengaging period.

[0055] In some embodiments, the controller is configured to increase or decrease the surface speed of only a portion of the intermediate transfer member during the disengaging period.

[0056] In some embodiments, i. the intermediate transfer member comprises a flexible belt mounted on a plurality of rollers, ii. the printing system further comprises upstream and downstream powered dancers arranged upstream and downstream of the nip between the belt and the impression cylinder, and iii. the controller is associated with the dancers such that during the disengaging period, the upstream and downstream dancers are moved to locally accelerate and then decelerate a portion of the belt that includes a pre-determined segment.

[0057] In some embodiments, the controller is configured to increase or decrease the surface speed of the entire intermediate transfer member during the disengaging period.

[0058] In some embodiments, the system further comprises an electronic circuit configured to monitor the phase difference between (i) a moving locator point attached to the moving intermediate transfer member and (ii) the phase of the rotating impression cylinder, and the controller increases or decreases the surface speed of the intermediate transfer member during the disengaging period in response to the result of the phase difference monitoring.

[0059] In some embodiments, the locator point corresponds to the position of a marker on or a lateral formation of the intermediate transfer member.

[0060] In some embodiments, (i) the intermediate transfer member is a flexible belt, (ii) the system further comprises an electronic circuit configured to monitor the varying length of the flexible belt, and (iii) the controller increases or decreases the surface speed of the intermediate transfer member or a portion thereof during the disengaging period in response to the result of the length monitoring.

[0061] In some embodiments, the rotating impression cylinder is driven independently of the moving intermediate transfer member.

[0062] In some embodiments, an ink image is formed by deposition of ink (e.g., ink droplets) onto a moving flexible blanket, which is then transferred from the blanket to a substrate, and the method includes: a. monitoring a temporary variation in non-uniform stretching of the moving blanket; and b. adjusting the deposition of ink (e.g., ink droplets) onto the blanket in response to the result of the monitoring so as to eliminate or reduce the severity of distortion of the ink image formed on the moving blanket caused by non-uniform stretching of the blanket.

[0063] In some embodiments, the timing of deposition of ink (e.g., ink droplets) is adjusted in response to the result of the monitoring.

[0064] In some embodiments, the flexible blanket is mounted on a plurality of rollers.

[0065] In some embodiments, the method further includes c. predicting future non-uniform blanket stretching from past stretching data obtained by monitoring the temporary variation, and the adjustment of ink deposition (e.g., droplet deposition) is performed in response to the result of the prediction.

[0066] In some embodiments, A. the operation of the printing system defines at least one of the following operating cycles, namely, (i) a blanket rotation cycle, (ii) an impression cylinder rotation cycle, and (iii) an engagement cycle of the blanket and the impression cylinder, and B. non-uniform blanket stretching is predicted according to a mathematical model that assigns high weight to past data describing the stretching of the blanket at past times corresponding to a cycle defined according to one of the operating cycles.

[0067] A printing system comprising: a. a flexible blanket; b. an imaging station configured to form an ink image on the surface of the blanket by deposition of ink droplets onto the surface of the blanket while the blanket is moving; c. a transfer station configured to transfer the ink image from the surface of the moving blanket to a substrate; and d. an electronic circuit configured to monitor temporary variations in non-uniform stretching of the blanket and to adjust the deposition of ink droplets onto the blanket so as to eliminate or reduce the severity of distortion of the ink image formed on the moving blanket according to the results of the monitoring. The printing system is disclosed herein.

[0068] In some embodiments, the timing of deposition of ink (e.g., ink droplets) is adjusted by the electronic circuit in response to the results of the monitoring.

[0069] In some embodiments, the flexible blanket is mounted on a plurality of rollers.

[0070] In some embodiments, the electronic circuit is operable to predict future non-uniform stretching of the blanket from past stretching data obtained by monitoring the temporary variations, and the electronic circuit adjusts the deposition of ink droplets in response to the results of the prediction.

[0071] In some embodiments, A. the operation of the printing system defines at least one of the following operating cycles: (i) a blanket rotation cycle, (ii) an impression cylinder rotation cycle, and (iii) an engagement cycle of the blanket and the impression cylinder; and B. the electronic circuit is configured to predict non-uniform stretching of the blanket according to a mathematical model that assigns high weights to past data describing the stretching of the blanket at past times corresponding to cycles defined according to one of the operating cycles.

[0072] In some embodiments, monitoring transient variations in non-uniform stretching of the blanket involves detecting the passage of one or more markers formed laterally thereon past a print bar or attached to the blanket by a marker detector within, on, or attached to the blanket. A printing system is disclosed herein that includes: a. an intermediate transfer member having one or more markers at different respective positions thereon; b. an image forming station including one or more print bars configured to deposit ink on the intermediate transfer member as the intermediate transfer member rotates; and c. one or more marker detectors positioned to detect the passage of the markers on the rotating intermediate transfer member, each print bar being associated with a respective marker detector arranged at a position fixed relative to the print bar and configured to detect movement of the marker(s).

[0073] In some embodiments, one or more of the marker(s) are attached to the blanket.

[0074] In some embodiments, one or more of the marker(s) are formed laterally on the blanket.

[0075] In some embodiments, (i) the image forming station includes a plurality of print bars spaced from each other in the direction of movement of the intermediate transfer member, and (ii) the one or more marker detectors include a plurality of marker detectors such that each print bar of the plurality of print bars is associated with a respective marker detector arranged at a position fixed relative to the print bar.

[0076] In some embodiments, the marker detector is arranged (i) adjacent to the respective associated print bar and / or (ii) below the respective associated print bar and / or (iii) within and / or on the housing of the respective associated print bar.

[0077] In some embodiments, the marker detector includes at least one of (i) a photodetector, (ii) a magnetic detector, (iii) a capacitance sensor, and (iv) a mechanical detector.

[0078] Disclosed herein is a method of operating a printing system having a moving intermediate transfer member of non-constant length, wherein the length of the moving intermediate transfer member is adjusted to a setpoint length.

[0079] In some embodiments, (i) an image is transferred to a substrate at a printing station by an engagement between the intermediate transfer member and a rotating impression cylinder, and (ii) the setpoint length is equal to an integer multiple of the circumference of the impression cylinder.

[0080] In some embodiments, the ratio of the setpoint length of the intermediate transfer member to the circumference of the impression cylinder is at least 2 or at least 3 or at least 5 or at least 7 and / or between 5 and 10.

[0081] In some embodiments, adjusting the length of the intermediate transfer member includes operating a linear actuator to increase or decrease the length of the moving intermediate transfer member.

[0082] In some embodiments, (i) the intermediate transfer member is guided over a plurality of rollers, and (ii) adjusting the length of the intermediate transfer member includes modifying the distance between the rollers to stretch or contract the moving intermediate transfer member for one or more sets of rollers.

[0083] In some embodiments, the movement of one or more markers attached to the one or more intermediate transfer members or the movement of one or more formations from the intermediate transfer member is tracked by one or more detectors, and the length of the intermediate transfer member is adjusted according to the results of the tracking.

[0084] A printing system is disclosed herein that comprises: a. an intermediate transfer member of non-uniform length; b. an image forming station configured to deposit ink on the surface of the intermediate transfer member while the intermediate transfer member is moving so as to form an ink image on the surface of the intermediate transfer member; c. a transfer station configured to transfer the ink image from the surface of the moving intermediate transfer member to a substrate passing between a transfer member and a printing cylinder during a period of engagement; and d. an electronic circuit configured to adjust the length of the intermediate transfer member to a setpoint length.

[0085] In some embodiments, the setpoint length is equal to an integer multiple of the circumference of the printing cylinder.

[0086] In some embodiments, the ratio of the setpoint length of the intermediate transfer member to the circumference of the printing cylinder is at least 2 or at least 3 or at least 5 or at least 7 and / or between 5 and 10.

[0087] In some embodiments, the adjustment of the length of the intermediate transfer member includes the operation of a linear actuator to increase or decrease the length of the moving intermediate transfer member.

[0088] In some embodiments, (i) the intermediate transfer member is guided over a plurality of rollers, and (ii) the adjustment of the length of the intermediate transfer member includes modifying the distance between the rollers for one or more sets of rollers so as to stretch or contract the moving intermediate transfer member.

[0089] In some embodiments, the movement of one or more markers attached to the one or more intermediate transfer members or the movement of one or more formations from the intermediate transfer member is tracked by one or more detectors, and the length of the intermediate transfer member is adjusted according to the result of the tracking.

[0090] A method for monitoring the performance of a printing system in which an ink image is formed by deposition of ink on a moving intermediate transfer member of variable length and is then transferred from the moving intermediate transfer member to a substrate, the method comprising: a. monitoring an indication of the length of the moving intermediate transfer member of variable length; and b. generating an alarm or warning signal based on the length of the intermediate transfer member deviating from a set point by more than an acceptable threshold, is disclosed herein.

[0091] In some embodiments, the acceptable threshold is between 0.1% and 1%.

[0092] A method for monitoring the performance of a printing system in which an ink image is formed by deposition of ink on a moving blanket mounted on one or more rollers, the method comprising: a. measuring an indication of blanket slip on one or more of the guide rollers; and b. in response to the blanket slip measurement, (i) generating an alarm or warning signal based on the magnitude of the blanket slip exceeding a threshold and / or (ii) displaying an indication of the magnitude of the blanket slip on a display device, is disclosed herein.

[0093] In some embodiments, the indication of blanket slip is the rotational speed difference between two rotational speeds of the guide roller on which the blanket is guided above.

[0094] A method for monitoring the performance of a printing system in which an ink image is formed by deposition of ink on a moving intermediate transfer member having a seam and is then transferred from the moving intermediate transfer member to a substrate by repeated engagement between the intermediate transfer member and a printing cylinder, the method comprising: i. predicting an indication of the likelihood of an aligned engagement of the seam between the intermediate transfer member and the printing cylinder when the seam of the intermediate transfer member is aligned with the printing cylinder; and ii. generating a warning or alarm signal based on the result of the prediction if the prediction indicates a high likelihood of an aligned engagement of the seam between the intermediate transfer member and the printing cylinder, is disclosed herein.

[0095] A method of monitoring the performance of a printing system in which an ink image is formed by deposition of ink on a moving intermediate transfer member of variable length and is then transferred from the moving intermediate transfer member to a substrate, the method comprising: a. monitoring an indication of the length of the intermediate transfer member; and b. indicating a predicted remaining life of the intermediate transfer member according to a deviation of the length of the intermediate transfer member from a predetermined length of the intermediate transfer member, is disclosed herein.

[0096] In some embodiments, a warning or alert signal is provided by at least one of: i. sending an email message; ii. generating an audio signal; iii. generating a visual signal on a display screen; and iv. sending an SMS message to a phone.

[0097] In some embodiments, the warning or alert signal is provided immediately.

[0098] In some embodiments, the warning or alert signal is provided after a time delay.

[0099] A printing system comprising: a. an intermediate transfer member of non-constant length; b. an imaging station configured to deposit ink on a surface of the intermediate transfer member as the intermediate transfer member moves so as to form an ink image on the surface of the intermediate transfer member; c. a transfer station configured to transfer the ink image from the surface of the moving intermediate transfer member to a substrate; and d. an electronic circuit configured to: (i) monitor an indication of the length of the rotating intermediate transfer member of variable length; and (ii) generate a warning or alert signal depending on the length of the intermediate transfer member deviating from a set point value by more than a tolerance threshold, is disclosed herein.

[0100] In some embodiments, the tolerance threshold is between 0.1% and 1%.

[0101] A printing system, comprising: a. a blanket mounted on one or more impression cylinders; b. an imaging station configured to deposit ink on the surface of the blanket while the blanket is moving so as to form an ink image on the surface of the blanket; c. a transfer station configured to transfer the ink image from the surface of the moving blanket to a substrate; and d. an electronic circuit configured to (i) measure an indication of blanket slip on one or more of the impression cylinders and (ii) in response to the measurement of the blanket slip, perform at least one of (A) generating an alarm or warning signal depending on the magnitude of the blanket slip exceeding a threshold and / or (B) displaying an indication of the magnitude of the blanket slip on a display device. The printing system is disclosed herein.

[0102] In some embodiments, the indication of blanket slip is the rotational speed difference between two rotational speeds of the impression cylinder.

[0103] A printing system, comprising: a. a blanket including a seam; b. an imaging station configured to deposit ink on the surface of the blanket while the blanket is moving so as to form an ink image on the surface of the blanket; c. a transfer station configured to transfer the ink image from the surface of the moving blanket to a substrate passing between the blanket and an impression cylinder during a period of engagement; and d. an electronic circuit configured to (i) predict an indication of the likelihood of an aligned engagement of the seam between the blanket and the impression cylinder when the seam of the blanket is aligned with the impression cylinder and (ii) generate an alarm or warning signal according to the result of the prediction if the prediction indicates a high likelihood of an aligned engagement of the seam between the blanket and the impression cylinder. The printing system is disclosed herein.

[0104] A printing system comprising: a. a blanket of non-uniform length; b. an imaging station configured to deposit ink onto the surface of the blanket while the blanket is moving so as to form an ink image on the surface of the blanket; c. a transfer station configured to transfer the ink image from the surface of the moving blanket to a substrate; and d. an electronic circuit configured to monitor an indication that (i) indicates the length of the blanket and (ii) indicates the predicted remaining life of the blanket according to a deviation of the length of the blanket from a predetermined length of the blanket, is disclosed herein.

[0105] In some embodiments, a warning or alarm signal is provided by at least one of the following: i. sending an email message; ii. generating an audio signal; iii. generating a visual signal on a display screen; and iv. sending an SMS message to a phone.

Brief Description of the Drawings

[0106] Herein, the invention will be further described, by way of example, with reference to the accompanying drawings, in which the dimensions of the components and features shown in the drawings are chosen for the sake of convenience and clarity of explanation and are not necessarily to scale.

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DETAILED DESCRIPTION OF THE INVENTION

[0107] For the sake of brevity, various terms are presented herein in the context of the description in this specification. To the extent that definitions are provided explicitly or implicitly herein or elsewhere in this application, such definitions are understood to be consistent with the use of terms defined by those of ordinary skill in the art. Moreover, such definitions will be construed in the broadest possible sense that is consistent with such use. In the case of the present disclosure, "electronic circuit" is broadly intended to describe any combination of hardware, software, and / or firmware.

[0108] An electronic circuit may include any executable code module (i.e., one stored on a computer-readable medium), and / or, without limitation, field programmable logic array (FPLA) element(s), wired logic element(s), field programmable gate array (FPGA) element(s), and also application specific integrated circuit (ASIC) element(s), including firmware and / or hardware element(s). Any instruction set architecture may be used, including, without limitation, reduced instruction set computer (RISC) architecture and / or complex instruction set computer (CISC) architecture. The electronic circuit may be located in a single location or distributed among multiple locations where various circuit elements may communicate with each other via wired or wireless electronic communication.

[0109] In various embodiments, an ink image is first deposited on the surface of an intermediate transfer member (ITM) and transferred from the surface of the intermediate transfer member to a substrate (i.e., a sheet substrate or web substrate). In the case of the present disclosure, the terms "intermediate transfer member", "image transfer member", and "ITM" are synonymous and may be used interchangeably. The location where ink is deposited on the ITM is referred to as the "image formation station".

[0110] In the case of the present disclosure, the terms "substrate transfer system" and "substrate handling system" are synonymous and refer to a mechanical system for moving a substrate from an input stack or roll to an output stack or roll.

[0111] An "indirect" printing system or indirect printer includes an intermediate transfer member. An example of an indirect printer is a digital press. Another example is an offset printer.

[0112] The location where the ink image is transferred to the substrate is defined as the "image transfer location" or "image transfer station", and the terms are also referred to as the "impression station" or "transfer station". It is recognized that for some printing systems, there can be multiple "image transfer locations". In some embodiments of the invention, the image transfer member comprises a belt having a reinforcing or support layer coated with a release layer. The reinforcing layer can consist of a fabric reinforced with fibers such that it is substantially non-extensible in the longitudinal direction. By being "substantially non-extensible", it means that during any cycle of the belt, the distance between any two fixed points on the belt does not vary to an extent that would affect the image quality. However, the length of the belt can vary with temperature, or over a long period, with aging or fatigue. In its lateral direction, the belt can have some degree of elasticity to help keep it taut and flat as it is pulled through the image forming station. A suitable fabric can, for example, have glass fibers in its longitudinal direction and cotton fibers woven, sewn, or otherwise held in the vertical direction.

[0113] "Improving synchronization" is defined as reducing the phase difference and / or mitigating its increase.

[0114] For an endless intermediate transfer member, the "length" of the ITM / blanket / belt is defined as the circumference of the ITM / blanket / belt.

[0115] A "blanket marker" or "ITM marker" or "marker" is a detectable feature of the ITM or blanket that indicates the longitudinal position of the ITM or blanket. Typically, the longitudinal thickness or length of the marker is much less than the circumference of the blanket or ITM (e.g., at most a few percent or at most 1% or at most 0.5% of that circumference). The marker can be attached to the blanket or ITM (e.g., attached to its outer surface), or can be a lateral formation of the blanket or ITM. A "marker detector" can detect the absence or presence of a "marker" as the marker passes by a fixed position at a specific interval.

[0116] The spaced and fixed positions are positions in an inertial reference frame rather than in a moving reference frame of the ITM or blanket.

[0117] In the context of the present disclosure, "impression station" and "transfer station" are synonymous.

[0118] In some embodiments, the ITM or belt or blanket intermittently or repeatedly "engages" a pressing cylinder. When (i) the ITM or belt or blanket and (ii) the pressing cylinder are "engaged", the nip therebetween undergoes a pressing between the ITM or belt or blanket and the pressing cylinder. For example, when a substrate is present in the nip, when the ITM or belt or blanket is "engaged" with the pressing cylinder, the substrate is pressed between at least one pressing cylinder and the rotating region of the ITM. "Engagement" is to bring about an engagement between the ITM or belt or blanket and the pressing cylinder. "Disengagement" is to end the engagement between the ITM or belt or blanket and the pressing cylinder.

[0119] There is no limitation as to how "engagement" is performed. In one example, the ITM or belt or blanket area can be moved towards the impression cylinder (e.g., by a pressure cylinder). In these embodiments, there is no requirement that the entire ITM or belt or blanket be moved towards the impression cylinder, or alternatively, a portion of the whole can be moved towards the impression cylinder. Alternatively or in addition, the impression cylinder can be moved towards the ITM or belt or blanket area, and the nip is pressed between the impression cylinder and the ITM or belt or blanket.

[0120] General Overview The printers shown in FIGS. 1A and 1B essentially comprise three separate, interacting systems, namely a blanket system 100, an image forming system 300 above the blanket system 100, and a substrate transfer system 500 below the blanket system 100.

[0121] The blanket system 100 acts as an ITM and includes an endless belt or blanket 102 guided over two rollers 104, 106. An image composed of dots of ink is applied by the image forming system 300 to the upper run of the blanket 102 at a location herein referred to as the image forming station. The lower run selectively interacts with two impression cylinders 502 and 504 of the substrate transfer system 500 at two impression or image transfer stations to print the image onto a substrate compressed between the blanket 102 and respective pressure rollers 140, 142 during the engagement period. As will be explained below, the purpose of having two impression cylinders 502, 504 is to enable duplex printing. In the case of a simplex printer, only one image transfer station would be required. The printers shown in FIGS. 1A and 1B can print single-sided prints at twice the speed of printing double-sided prints. In addition, a number of single-sided and double-sided mixed prints can also be printed.

[0122] During operation, an ink image, which is a mirror image of the images that will each be pressed onto the final substrate, is printed by the image forming system 300 onto the upper run of the blanket 102. In this context, the term "run" is used to mean the length or section of the blanket between any two given rollers over which the blanket is guided. While being transported by the blanket 102, the ink is heated to dry it by evaporation of all but a small portion of the liquid carrier. The ink image is further heated to make tacky the film of ink solids remaining after evaporation of the liquid carrier, which film is referred to as the residual film to distinguish it from the liquid film formed by the flattening of each ink droplet. By the impression cylinders 502, 504, the image is pressed onto the individual sheets 501 of the substrate, which substrate is transported by the substrate transport system 500 via the impression cylinders 502, 504 from the input stack 506 to the output stack 508.

[0123] Although not shown in the drawings, the blanket system may further comprise a cleaning station that can be used to periodically "refresh" the blanket during or between print jobs. In some embodiments, the control systems and devices according to the invention further synchronize the cleaning of the ITM with any desired steps included in the operation of the printing system.

[0124] Image forming system As best shown in FIG. 3, the image forming system 300 comprises print bars 302 that are each slidably mounted on a frame 304 positioned at a height fixed above the surface of the blanket 102. Each print bar 302 may comprise a print head section approximately the width of the printing area on the blanket 102 and may comprise individually controllable print nozzles. The image forming system can have any number of bars 302, each of which may contain a different color of ink.

[0125] Since some print bars may not be required during a particular printing job, the heads can be moved between an operable position and an inoperable position, where in the operable position they overlap the blanket 102. A mechanism is provided to move the print bar 302 between its operable and inoperable positions, but that mechanism is not illustrated herein and need not be described as it is not relevant to the printing process. It should be noted that the bars remain stationary during printing.

[0126] When moved to their inoperable positions, the print bars are covered for protection to prevent the nozzles of the print bars from drying out or clogging. In certain embodiments of the invention, the print bars are stopped above a liquid reservoir (not shown) that aids in this task. In another embodiment, the print heads are cleaned, for example, by removing residual ink deposits that may form around the nozzle edges. Such maintenance of the print heads can be achieved by any suitable method from contact wiping of the nozzle plate to remote spraying of cleaning solution onto the nozzles and the removal of ink deposits washed by positive or negative air pressure. The print bars in the inoperable position can be easily changed and accessed for maintenance even while the printing job is proceeding using other print bars. In some embodiments, the control system and apparatus according to the invention further synchronize the cleaning of the print heads of the image forming station with any desired steps included in the operation of the printing system.

[0127] Within each print bar, the ink can be continuously recirculated, filtered, degassed, and maintained at a desired temperature and pressure. Since the design of the print bars can be conventional or at least similar to those used in other inkjet printing applications, their structure and operation will be apparent to those skilled in the art without the need for more detailed description.

[0128] Since the different print bars 302 are spaced from each other along the length of the blanket, of course, it is essential that their movements be precisely synchronized with the movement of the blanket 102.

[0129] As illustrated in FIG. 4, it is possible to provide a blower behind each print bar 302 so as to blow a slow flow of hot gas, preferably air, onto the ITM to initiate drying of the ink droplets deposited by the print bars 302. This helps to fix the droplets deposited by each print bar 302, i.e., to resist their shrinkage, prevent their movement on the ITM, and also prevent them from melting into the droplets subsequently deposited by other print bars 302.

[0130] Blanket and Blanket Support System In one embodiment of the invention, the blanket 102 has a seam. In particular, the blanket is formed from an initially flat elongate piece, the ends of which are releasably or permanently fastened to each other to form a continuous loop. A releasable fastening can be a zipper or hook and loop fastener that is substantially parallel to the axes of the rollers 104 and 106 over which the blanket is guided. A permanent fastening can be achieved by the use of an adhesive or tape.

[0131] To avoid a sudden change in the tension of the blanket as the seam passes over these rollers, it is desirable to make the seam as close as possible to the same thickness as the rest of the blanket. It is also possible to tilt the seam with respect to the axis of the roller, but this would be at the expense of an enlarged non-printable image area.

[0132] The primary purpose of the blanket is to receive an ink image from an imaging system and transfer that image, while dried but not disturbed, to a printing station. To enable easy transfer of the ink image at each printing station, the blanket has a thin top release layer that is hydrophobic. The outer surface of the transfer member, on which ink can be applied, may comprise a silicon material. Under suitable conditions, polydialkylsiloxane materials and aminosilicons modified or terminated with silanol, silyl or silane have been found to function well. Suitably, the material forming the release layer can be made non-absorbent.

[0133] The strength of the blanket can be derived from a support or reinforcement layer. In one embodiment, the reinforcement layer is formed from a fabric. When the fabric is woven, the warp and weft of the fabric may have different compositions or physical structures so that the blanket has greater elasticity in its transverse direction (parallel to the axes of rollers 104 and 106) than in its length direction for reasons that will be described below.

[0134] The blanket may comprise an additional layer between the reinforcement layer and the release layer, for example, to provide compliance or compressibility of the release layer to the surface of a substrate. Other layers provided on the blanket may act as a heat reservoir or a thermally partial barrier and / or may act to allow an electrostatic charge to be applied to the release layer. An internal layer may be further provided to control drag due to friction on the blanket as the blanket is rotated on its support structure. Other layers may be included to adhere or connect one of the above layers to another or to prevent molecular movement between them.

[0135] The structure supporting the blanket in the embodiment of FIG. 1A is shown in FIGS. 2A and 2B. Two elongated overhangs 120 are interconnected by a plurality of crossbars 122 to form a horizontal ladder-shaped frame on which the remaining components are mounted.

[0136] Roller 106 is pivotally supported by a bearing that is directly attached to the overhang member 120. However, at the opposite end, roller 104 is pivotally supported by a support base 124 that is guided for sliding movement relative to the overhang member 120. An electric motor 126, such as a stepper motor, moves through a suitable transmission to move the support base 124 so as to change the distance between the axes of rollers 104 and 106 while maintaining them parallel to each other.

[0137] The thermally conductive support plates 130 are attached on the crossbars 122 to form continuous flat support surfaces on both the top and bottom sides of the support frame. The joints between the individual support plates 130 are intentionally offset (e.g., made zigzag) from each other to avoid creating lines running parallel to the length of the blanket 102. The electric heating elements 132 are inserted into transverse holes in the plates 130 and apply heat to the upper running portion of the blanket 102 in and through the plates 130. Other means for heating the upper running portion will be apparent to those skilled in the art and may include heating from below the blanket itself, from above the blanket itself, or within the blanket itself. The heating plates may also serve to heat the lower running portion of the blanket at least until transfer is performed.

[0138] Also attached to the blanket support frame are two pressure or nip rollers 140, 142. The pressure rollers are located on the lower surface of the support frame in the gap between the support plates 130 that cover the lower surface of the frame. Pressure rollers 140, 142 are aligned with the impression cylinders 502, 504 of the substrate transfer system, respectively, as most clearly shown in FIGS. 1B and 3. Each impression cylinder and the corresponding pressure roller form an image transfer station when engaged as described below.

[0139] Each of the pressure rollers 140, 142 is preferably mounted such that it can be raised or lowered relative to the lower running portion of the blanket. In one embodiment, each pressure roller is mounted on an eccentric that is rotatable by respective actuators 150, 152. When it is raised by its actuator to an upper position within the support frame, each pressure roller is spaced from the opposing impression cylinder, allowing the blanket to pass by the side of the impression cylinder while not contacting either the impression cylinder itself or the substrate carried by the impression cylinder. On the other hand, when moved downward by its actuator, each of the pressure rollers 140, 142 projects downward beyond the plane of the adjacent support plate 130, bending a portion of the blanket 102 and pressing it against the opposing impression cylinders 502, 504. In this lower position, it presses the lower running portion of the blanket against the final substrate being carried on the impression cylinder (or the web of the substrate in the embodiment of FIG. 3).

[0140] Rollers 104 and 106 are connected to respective electric motors 160, 162. Motor 160 is more powerful and serves to drive the blanket clockwise as seen in FIGS. 2A and 2B. Motor 162 can be used to provide a torque reaction and adjust the tension in the upper running portion of the blanket. The motors can operate at the same speed in certain embodiments, in which the same tension is maintained in the upper and lower running portions of the blanket.

[0141] In an alternative embodiment of the invention, motors 160 and 162 are operated in such a way as to maintain a higher tension in the upper running portion of the blanket where the ink image is formed and a lower tension in the lower running portion of the blanket. The lower tension in the lower running portion can help absorb sudden disturbances caused by abrupt engagement and disengagement of the blanket 102 with the impression cylinders 502 and 504. Further details are provided below with reference to FIGS. 20A - 20B.

[0142] In certain embodiments of the invention, it should be understood that the pressure rollers 140 and 142 can be independently lowered or raised such that either, both, or only one of the rollers is in a lower position engaging its respective impression cylinder and the blanket passing therebetween.

[0143] In certain embodiments of the invention, a blower or air blower (not shown) is mounted on the frame to maintain near atmospheric pressure in the volume 166 enclosed by the blanket and its support frame. The negative pressure acts to keep the blanket flat against the support plate 130 on both the upper and lower sides of the frame to achieve good thermal contact. When the lower running portion of the blanket is relatively loosely fixed, the negative pressure also helps to keep the blanket out of contact with the impression cylinder when the pressure rollers 140, 142 are not actuated.

[0144] In certain embodiments of the invention, each of the overhangs 120 also supports a continuous track 180 that engages formations on the side edges of the blanket and holds the blanket taut in its width direction. The formations can be spaced protrusions, such as the teeth of half of a zipper sewn or otherwise attached to the side edges of the blanket. Alternatively, the formations can be continuous flexible beads of greater thickness than the blanket. The lateral track guiding channels can have any cross-section suitable for receiving and holding the lateral formations of the blanket and keeping it taut. To reduce friction, the guiding channels can have rotary bearing elements for holding protrusions or beads within the channels.

[0145] According to one embodiment of the invention, an entry point is provided along track 180 for attaching a blanket onto its support frame. One end of the blanket is extended laterally and formations on its edge are inserted through the entry point into track 180. Using a suitable instrument to engage the formations on the edge of the blanket, the blanket is advanced along track 180 until it surrounds the support frame. Then, both ends of the blanket are fastened to each other to form an endless loop or belt. Then, rollers 104 and 106 can be moved apart to apply tension to the blanket and to stretch it to a desired length. The section of track 180 is collapsible in a nested fashion to allow the length of the track to vary as the distance between rollers 104 and 106 is varied.

[0146] In one embodiment, the ends of the elongated blanket piece are advantageously shaped to facilitate the guidance of the blanket through a lateral track or channel during introduction. The initial guidance of the blanket into place can be done, for example, by first securing the leading edge of the blanket piece introduced into the middle of the lateral channel 180 to a cable that can be moved manually or automatically to introduce the belt. For example, one or both lateral ends of the leading edge of the blanket can be releasably attached to a cable within each channel. Advancing the cable(s) advances the blanket along the channel path. Alternatively or in addition, the edges of the belt in the region where the seam is ultimately formed when both edges are secured from one to the other may have less flexibility than those in regions other than the seam. This local "rigidity" can facilitate the insertion of the lateral protrusions of the blanket into their respective channels.

[0147] After introduction, the blanket pieces can be edge-to-edge adhered by soldering, gluing, taping (e.g., using Kapton® tape, RTV liquid adhesive or PTFE thermoplastic adhesive using connecting pieces that partially overlap both edges of the piece), or any other generally known method, to form a continuous belt loop. Any method of joining the ends of the belt can result in a discontinuity, herein referred to as a seam, and it is desirable to avoid an increase in thickness or a discontinuity in the chemical and / or mechanical properties of the belt at the seam.

[0148] Further details regarding the formation of an exemplary blanket and its derivation, which can serve to implement control in accordance with the present teachings, are disclosed in co-pending PCT application No. PCT / IB2013 / 051719 (Attorney Docket No. LIP7 / 005PCT).

[0149] For the image to be properly formed on the blanket and transferred to the final substrate, and also for alignment of the front and back images in duplex printing to be achieved, many different components of the system must be properly synchronized. To properly position the image on the blanket, both the position and speed of the blanket are known and must be controlled. In certain embodiments of the invention, the blanket is marked at or near its edge with one or more markings spaced in the direction of the blanket's movement. One or more sensors 107 detect the timing of these markings as they pass by the sensors. The speed of the blanket and the speed of the surface of the impression roller should be the same for proper transfer of the image from the transfer blanket to the substrate. Signals from the sensor(s) 107 are sent to a controller 109, which also receives indications of the rotational speed and angular position of the impression roller, for example, from encoders on one or both of the shafts of the impression roller (not shown). A sensor 107, or another sensor (not shown), also determines the time when the seam of the blanket passes by the sensor. For maximum utility of the available length of the blanket, it is desirable for the image on the blanket to start as close as possible to the seam.

[0150] The controller controls electric motors 160 and 162 to ensure that the linear speed of the blanket is the same as the speed of the surface of the impression roller.

[0151] Since the blanket contains the resulting unusable area from the seam, it is important to ensure that this area always remains in the same position relative to the images printed in successive cycles of the blanket. Also, whenever the seam passes by the impression cylinder, it is preferable to ensure that it is simultaneous with the time when the discontinuity on the surface of the impression cylinder (which receives the substrate gripper described below) faces the blanket.

[0152] Preferably, the length of the blanket is set to an integral multiple of the circumferences of the impression cylinders 502, 504. Since the length of the blanket 102 can vary with time, the position of the seam relative to the impression roller is preferably changed by instantaneously changing the speed of the blanket. When synchronization is achieved again, the speed of the blanket is readjusted to match the speed of the impression roller when it is not engaged with the impression cylinders 502, 504. The length of the blanket can be determined from a shaft encoder that measures the rotation of one of the rollers 104, 106 during one detected revolution of the blanket.

[0153] The controller also controls the timing of the flow of data to the print bar.

[0154] This control of speed, position, and data flow ensures synchronization among the image forming system 300, the substrate transfer system 500, and the blanket system 100, and ensures that the image is formed at the correct position on the blanket for proper positioning on the final substrate. The position of the blanket is monitored by markings on the surface of the blanket detected by a number of sensors 107 attached at different positions along the length of the blanket. The output signals of these sensors are used to indicate the position of the image transfer surface to the print bar. Analysis of the output signals of the sensors 107 is further used to control the speed of motors 160 and 162 to match the speed of the impression cylinders 502, 504.

[0155] Since its length is a factor in synchronization, in some embodiments, the blanket can be configured to resist substantial elongation or creep. On the other hand, in the transverse direction, only maintaining the blanket flat and taut without causing excessive dragging due to friction with the support plate 130 is required. For this reason, in certain embodiments of the invention, the extensibility of the blanket is intentionally made anisotropic.

[0156] Pre - treatment of the blanket Figure 1A schematically shows a roller 190 positioned outside the blanket immediately prior to the roller 106, according to an embodiment of the invention. Such a roller 190 can optionally be used to apply a thin film of a pretreatment solution containing a chemical agent, e.g., a dilute solution of a charged polymer, to the surface of the blanket. Although not shown in the drawings, a series of rollers can be used for this purpose, one, for example, receiving a first layer of such a conditioning solution, transferring it to one or more subsequent rollers, and the last one optionally contacting the ITM at the engagement position. The film is preferably completely dried by the time it reaches the print bar of the imaging system in order to leave a very thin layer on the surface of the blanket that helps the ink droplets retain their film-like shape after they hit the surface of the blanket.

[0157] While one or more rollers can be used to apply a flat film, in an alternative embodiment, the pretreatment or conditioning material is sprayed or otherwise applied onto the surface of the blanket and spread more evenly, e.g., by undulating application that creates intermittent contact with a solution from a jet from an air knife, fine droplets from spraying, or an ejection source operated by pressure or vibration. Independent of the method used to apply the optional conditioning solution, the location where such pre-print treatment can be performed, as needed, can be referred to herein as a conditioning station and, as described, it can be engaged or disengaged.

[0158] In some embodiments, the applied chemical agent counteracts the effect of the surface tension of the aqueous ink after contact with the hydrophobic release layer of the blanket. In one embodiment, the conditioning agent is a polymer containing amine nitrogen atoms (e.g., primary, secondary, tertiary amines or quaternary ammonium salts) having a relatively high charge density and an MW (e.g., greater than 10,000).

[0159] In some embodiments, the control system and apparatus according to the invention further synchronize any desired steps involved in the operation of the printing system with the conditioning of the ITM. In one embodiment, the application of the conditioning solution is set to occur following the transfer of the ink image at the image transfer station and / or before and / or after any optional cooling of the ITM and / or before the deposition of the ink image onto the ITM at the image forming station.

[0160] Heating of the ink image 132 inserted into the support plate 130 is used to heat the blanket to a temperature suitable for the rapid evaporation of the ink carrier and compatible with the composition of the blanket. In various examples, the blanket can be heated within a range from 70 °C to 250 °C, depending on various factors such as the composition of the ink and / or the blanket and / or the conditioning solution as required.

[0161] A blanket containing amino silicone can generally be heated to a temperature between 70 °C and 130 °C. When using the bottom heating of the transfer member exemplified previously, it is desirable for the blanket to have a relatively high heat capacity and low thermal conductivity so that the temperature of the body of the blanket 102 does not change significantly as it moves between any optional pre-treatment or conditioning station, image forming station, and image transfer station(s). An external heater or energy source (not shown) can be used to locally apply additional energy, for example, before reaching the impression station to make the residual ink sticky, before the image forming station to dry the conditioning agent as required, and at the image forming station to start the evaporation of the carrier from the ink droplets as soon as possible after the ink droplets hit the surface of the blanket.

[0162] The external heater can be, for example, a high-temperature gas or air blower 306 (as schematically represented in FIG. 1A), or, for example, a radiant heater that focuses infrared radiation onto the surface of the blanket, which can reach temperatures exceeding 175°C, 190°C, 200°C, 210°C, or even exceeding 220°C.

[0163] When the ink contains components sensitive to ultraviolet light, the ultraviolet light source can be used to help cure the ink as it is transferred by the blanket.

[0164] In some embodiments, the control system and apparatus according to the invention can further monitor and control the heating of the ITM at various stations of the printing system and take corrective steps (e.g., decreasing or increasing the applied temperature) in response to the monitored temperature.

[0165] Substrate transfer system Substrate transfer can be designed to transfer individual sheets of the substrate to the printing station, as in the embodiments of FIGS. 1A - 1B, or to transfer a continuous web of the substrate, as shown in FIG. 3.

[0166] In the case of FIGS. 1A - 1B, for example, individual sheets are advanced by reciprocating an arm to a first transfer roller 520 that feeds the sheet from the top of the input stack 506 to the first printing cylinder 502.

[0167] Although not shown in the drawings, various transfer rollers and printing cylinders, which are known per se, can incorporate gripping portions that are cam-operated to open and close at the appropriate time in synchronization with their rotation to hold the leading edge of each sheet of the substrate. In certain embodiments of the invention, the tips of the gripping portions of at least the printing cylinders 502 and 504 are designed not to protrude beyond the outer surface of the cylinders to avoid damage to the blanket 102. In some embodiments, the control system and apparatus according to the invention further synchronize the gripping of the substrate.

[0168] As the image passes between the impression cylinder 502 and the blanket 102 applied thereon by the pressure roller 140 and is pressed onto one side of the substrate sheet, the sheet is then fed by the transfer roller 522 to a double-sided brushing cylinder 524 having a circumference twice that of the impression cylinders 502, 504. The leading edge of the sheet is transferred by the double-sided brushing cylinder past the transfer roller 526, and the gripping portion of the transfer roller is timed to catch the trailing edge of the sheet carried by the double-sided brushing cylinder and feed the sheet to the second impression cylinder 504 such that a second image is pressed onto the opposite side thereof. The sheet, now printed on both sides thereof, can be advanced from the second impression cylinder 504 to the output stack 508 by the belt conveyor 530.

[0169] In further embodiments not illustrated in the drawings, the printed sheet is subjected to one or more final finishing steps either before being delivered to the output stack (inline final finishing) or after being so delivered to output (offline final finishing) or in a combination where two or more final finishing steps are performed. Such final finishing steps include, but are not limited to, gluing, pasting, sheeting, folding, shining, metallizing, coating for protection or decoration, cutting, trimming, punching, embossing, debossing, perforating, creasing, sewing, and binding, and two or more can be combined. Since the final finishing steps can be performed using appropriate conventional equipment or at least similar principles, the integration of those in each final finishing station in the process and in the inventive system will be apparent to those skilled in the art without the need for more detailed explanation. In some embodiments, the control system and apparatus according to the invention further synchronize any desired steps and final finishing steps included in the operation of the printing system, typically following the transfer of the image to the substrate.

[0170] The images printed on the blanket are always spaced from each other by a distance corresponding to the circumference of the impression cylinder, so the distance between the two impression cylinders 502 and 504 should also be equal to the circumference of the impression cylinders 502, 504 or a multiple of this distance. The length of the individual images on the blanket depends, of course, not on the size of the impression cylinder, but on the size of the substrate.

[0171] In the embodiment shown in FIG. 3, the web 560 of the substrate is drawn from a supply roll (not shown) and passes over a number of guide rollers 550 having fixed axes and a stationary cylinder 551 that guides the web past a single impression cylinder 502.

[0172] Some of the rollers over which the web 560 passes do not have fixed axes. In particular, a roller 552 that can move vertically is provided on the feed side of the web 560. Thanks to its weight alone, or with the help of a spring acting on its axis if desired, the roller 552 serves to maintain a constant tension in the web 560. If for some reason the supply roller provides temporary resistance, the roller 552 will rise, and conversely, the roller 552 will automatically move down to take up the slack in the web drawn from the supply roll. In some embodiments, the control system and apparatus according to the invention further monitor and control the tension of the web substrate.

[0173] At the impression cylinder, the web 560 is required to move at the same speed as the surface of the blanket. Unlike the above-described embodiment where the position of the substrate sheet is fixed by the impression roller to ensure that all sheets are printed when they reach the impression roller, if the web 560 is permanently engaged with the blanket 102 at the impression cylinder 502, much of the substrate between the printed images would need to be discarded.

[0174] To reduce this problem, two motorized powered dancers 554 and 556 spanning the impression cylinder 502 are provided, which can be moved in different directions, for example, in synchronization with each other. After the image is pressed onto the web, the pressure roller 140 is disengaged so that the web 560 and the blanket can move relative to each other. Immediately after the disengagement, dancer 554 moves downward while dancer 556 is moved upward. The rest of the web continues to move forward at its standard speed, but the movement of dancers 554 and 556 has the effect of moving the short length of web 560 backward through the gap between the impression cylinder 502 and the blanket 102, after which it is disengaged. This is done by taking up the slack from the running section of the web after the impression cylinder 502 and transferring it to the running section preceding the impression cylinder. The movement of the dancers is then reversed to return them to their illustrated positions so that the section of the web in the impression cylinder is accelerated again to the speed of the blanket. Next, the pressure roller 140 can be re-engaged to print the next image onto the web without leaving a large blank area between the images printed on the web. In some embodiments, the control system and apparatus further monitor and control taking up the slack of the web substrate to reduce the blank area between the printed images.

[0175] Figure 3 shows a printer having only a single impression roller for printing on only one side of the web. For printing on both sides, a tandem system can be provided with two impression rollers, and a web inverter mechanism can be provided between the impression rollers to enable turning the web over for double-sided printing. Alternatively, if the width of the blanket exceeds twice the width of the web, it is possible to use two halves of the same blanket and impression cylinder to print simultaneously on both sides of different sections of the web.

[0176] Alternative embodiments of the printing system Although operating on the same principle as FIG. 1A, a printing system employing an alternative architecture is shown in FIG. 4A. The printing system of FIG. 4A includes an endless belt 210 that circulates through an image forming station 212, a drying station 214, and a transfer station 216. The image forming station 212 of FIG. 4A is similar to the previously described image forming system 300, exemplified in FIG. 1A for example.

[0177] At the image forming station 212, four separate print bars 222 incorporating one or more print heads using, for example, inkjet technology deposit aqueous ink droplets of different colors onto the surface of the belt 210. The illustrated embodiment has four print bars capable of depositing one of the typical four different colors (i.e., cyan (C), magenta (M), yellow (Y), and black (K)) respectively, but the image forming station can have a different number of print bars, the print bars can deposit different shades of the same color (e.g., various shades of gray including black), and two or more print bars can deposit the same color (e.g., black). In further embodiments, the print bars can be used for a pigment-free liquid (e.g., a decorative or protective varnish) and / or for special colors (e.g., achieving visual effects such as a metallic, shiny, glittery or sparkling appearance, or even a scented effect). Some embodiments relate to the control of the deposition of such inks and other printing liquids onto the ITM. Next to each print bar 222 at the image forming station, an intermediate drying system 224 is provided to blow hot gas (usually air) onto the surface of the belt 210 to partially dry the ink droplets. This hot gas flow helps prevent clogging of the inkjet nozzles and also prevents the droplets of different colors of ink on the belt 210 from melting into each other. At the drying station 214, the ink droplets on the belt 210 are exposed to radiation and / or hot gas to more thoroughly dry the ink, driving off most but not all of the liquid carrier and leaving only a layer of resin and colorant that is heated to the extent that it becomes sticky.

[0178] In the transfer station 216, the belt 210 passes between the impression cylinder 220 and the blanket cylinder 218 having a compressible blanket 219. The length of the blanket is equal to or greater than the maximum length of the substrate sheet 226 on which printing is performed above. The impression cylinder 220 has a diameter twice that of the blanket cylinder 218 and can support two sheets 226 of the substrate simultaneously. The substrate sheet 226 is conveyed from the supply stack 228 by a suitable transfer mechanism (not shown in FIG. 4A) and passed through the nip between the impression cylinder 220 and the blanket cylinder 218. In the nip, the surface of the belt 220 carrying the adhesive ink image is firmly pressed against the substrate by the blanket on the blanket cylinder 218 so that the ink image is pressed onto the substrate and separated properly from the surface of the belt. The substrate is then transferred to the output stack 230. In some embodiments, a heater 231 may be provided immediately before the nip between the two cylinders 218 and 220 of the image transfer station to help make the ink film sticky to facilitate transfer to the substrate.

[0179] In the example of FIG. 4A, the belt 210 moves in the clockwise direction. The direction of movement of the belt defines the upstream and downstream directions. The rollers 242, 240 are positioned upstream and downstream of the image forming station 212 respectively, and thus the roller 242 may be called the "upstream roller" while the roller 240 may be called the "downstream roller". In the example of FIG. 1B, the rollers 106 and 104 are arranged upstream and downstream of the image forming station 300 respectively.

[0180] Referring to FIG. 4A again, note that due to the clockwise direction of movement of the belt 210, the dancers 250 and 252 are positioned upstream and downstream of the transfer station 216 respectively, and thus the dancer 250 may be called the "upstream dancer" while the dancer 252 may be called the "downstream dancer".

[0181] The above of the embodiment of FIG. 4A is provided and simplified only for the purpose of enabling an understanding of the present invention. In various embodiments, the physical and chemical properties of the ink, the chemical composition and possible treatments of the release surface of the belt 210, and the various stations of the printing system can each play an important role.

[0182] In order for the ink to be properly separated from the surface of the belt 210, the back surface may include a hydrophobic release layer. In the embodiment of FIG. 1A, this hydrophobic release layer is formed as part of a thick blanket that also includes a compressible compliant layer necessary to ensure proper contact between the release layer and the substrate at the transfer station. The resulting blanket is very heavy and costly and needs to be replaced in case of any impairment of the many functions it performs.

[0183] In the embodiment of FIG. 4A, the release layer forms part of an element separate from the thick blanket 219 required to press it against the substrate sheet 226. In FIG. 4A, the release layer is preferably formed on a flexible thin inextensible belt 210 reinforced with fibers for enhancing the tensile strength in its longitudinal dimension.

[0184] As schematically shown in FIGS. 4C-4D, the lateral edges of belt 210 are provided in some embodiments of the invention with spaced lateral formations or protrusions 270, and those lateral formations or protrusions on each side are received into respective guiding channels 280 (shown in cross-section in FIG. 4D and also as track 180 in FIGS. 2A-2B) to hold the belt taut in its lateral dimension. The protrusions 270 can be half teeth of a zipper sewn or otherwise fixed to the lateral edges of the belt. As an alternative to the spaced protrusions, a continuous flexible bead of greater thickness than the belt 210 can be provided along each side. The protrusions need not be the same on both sides of the belt. To reduce friction, the guiding channels 280 can have rotary bearing elements 282, as shown in FIG. 4D, to hold the protrusions 270 or beads within the channels 280.

[0185] The protrusions can be made of any material capable of withstanding the operating conditions of the printing system, including high speeds of the belt. Suitable materials can withstand high temperatures in the range of about 50° C. to 250° C. Advantageously, such materials are also resistant to friction and do not produce chips of a size and / or amount that would adversely affect the movement of the belt during its operable life. For example, the lateral protrusions can be made of polyamide reinforced with molybdenum disulfide.

[0186] The guiding channels within the image forming station ensure precise placement of ink droplets onto the belt 210. In other areas, such as within the drying station 214 and the transfer station 216, lateral guiding channels are desirable but not critical. In areas where the belt 210 has slack, there are no guiding channels.

[0187] All steps taken to guide the belt 210 are equally applicable to the guiding of the blanket 102 in the embodiments of FIGS. 1-3, where the guiding channels 280 were also referred to as track 180.

[0188] In some embodiments, since any hesitation or vibration will affect the targeting of ink droplets of different colors, it may be important for the belt 210 to move through the imaging station 212 at a constant speed. To assist in the smooth guidance of the belt, friction is reduced by passing the belt over rollers 232 adjacent to each print bar 222, rather than sliding the belt over a stationary guide plate. The rollers 232 do not need to be precisely aligned with their respective print bars. They may be located slightly (e.g., a few millimeters) downstream of the print head jet positions. The frictional force holds the belt taut and maintains it substantially parallel to the print bar. Thus, the lower surface of the belt may have high friction properties since it is in rolling contact only with those surfaces on which the belt is guided and which are all surfaces. The lateral tension applied by the guide channels is sufficient to keep the belt 210 flat as long as it is in contact with the rollers 232 as it passes under the print bars 222. Apart from the non-extensible reinforcement / support layer, the hydrophobic release surface layer and the high friction lower surface, the belt 210 is not required to perform any other function. Thus, it can be a thin, light and inexpensive belt that is easy to remove and replace if it wears out.

[0189] In some embodiments, the control system and apparatus according to the invention further monitor and control the lateral tension applied by the guide channels.

[0190] To achieve intimate contact between the release layer and the substrate, the belt 210 passes through a transfer station 216 that includes a printing cylinder 220 and a blanket cylinder 218. A replaceable blanket 219, releasably fastened on the outer surface of the blanket cylinder 218, provides the required compliance to urge the release layer of the belt 210 into contact with the substrate sheet 226. Rollers 253 on each side of the transfer station ensure that the belt is maintained in the desired orientation as it passes through the nip between cylinders 218 and 220 of the transfer station 216.

[0191] As described above, temperature control is of utmost importance to the printing system when high-quality printed images are achieved. This is considerably simplified in the embodiment of FIG. 4A in that the heat capacity of the belt can be lower or considerably lower than that of the blanket 102 in the embodiments of FIGS. 1-3.

[0192] Also, it has been proposed above in connection with embodiments that use a thick blanket 102 such that, considering that the blanket is heated from below, it includes an additional layer that affects the heat capacity of the blanket. The separation of the belt 210 from the blanket 219 in the embodiment of FIG. 4A allows the temperature of the ink droplets heated to the softening temperature of the dried resin to use considerably lower energy in the drying section 214. Moreover, the belt can be cooled before returning to the imaging station, which reduces or avoids problems caused by attempts to spray ink droplets onto a hot surface running very close to the inkjet nozzles. Alternatively, in addition, a cooling station can be added to the printing system to reduce the temperature of the belt to a desired value before the belt enters the imaging station. Cooling can be effected by passing the belt 210 over a roller, the lower half of which sprays a coolant onto the belt by passing the belt 210 over a coolant source, immersing the belt in the coolant, which can be water or a cleaning / processing solution. In some embodiments, the control system and apparatus according to the invention further monitor and control the cooling of the ITM.

[0193] In some embodiments of the invention, the release layer of the belt 210 has hydrophobic properties to ensure that the sticky ink residue image is cleanly peeled off therefrom at the transfer station. The control devices and methods according to the teachings herein can be applied to any type of ITM, regardless of the release layer and / or the type of ink adapted. In addition, they can be applied to any moving member of a system that requires a similar alignment, or lack thereof, between the moving member and any other part of such a system.

[0194] The belt 210 can be seamless, in other words, it has no discontinuities anywhere along its length. Such a belt can always be operated so that it runs at the same surface speed as the circumferential speeds of the two cylinders 218 and 220 of the image transfer station, which will considerably simplify the control of the printing system. Any stretching of the belt due to aging does not affect the performance of the printing system and will simply require further slack take-up by applying tension to the rollers 250 and 252, as will be explained in detail below.

[0195] However, it is inexpensive to initially form the belt as a flat elongate strip, and the two ends of the elongate strip are fixed to each other, for example, by a zipper, or optionally, by elongate strips of hook and loop tape, or optionally, by soldering the edges together, or optionally, by using a tape (e.g., Kapton® tape, RTV liquid adhesive or PTFE thermoplastic adhesive using a connecting piece that partially overlaps both edges of the elongate strip). In such a structure of the belt, it may be advantageous to ensure that printing is not performed on the seam or in the surrounding area immediately adjacent thereto (the "non-printing area") and that the seam is not flattened against the substrate 226 at the transfer station 216.

[0196] The impression cylinder 218 and the blanket cylinder 220 of the transfer station 216 can be configured in the same manner as the blanket cylinder and the impression cylinder of a conventional offset litho press. In such cylinders, there are circumferential discontinuities on the surface of the blanket cylinder 218 in the regions where the two ends of the blanket 219 are fastened. There are also discontinuities (i.e., "cylinder gaps") on the surface of the impression cylinder that serve to grip the substrate sheets and help transfer them through the nip. In the illustrated embodiment of the invention, the circumference of the impression cylinder is twice that of the blanket cylinder such that the discontinuities align twice per cycle of the impression cylinder, and the impression cylinder has two sets of gripping portions.

[0197] If the belt 210 has a seam, it can be useful to ensure that the seam always coincides with the gap between the cylinders of the transfer station 216. For this reason, it is desirable for the length of the belt 210 to be equal to an integer multiple of the circumference of the blanket cylinder 218.

[0198] However, even if the belt has such a length when new, its length can change during use, for example with fatigue or temperature, and if this change occurs, the phase of the seam passing through the nip will change from cycle to cycle.

[0199] To compensate for such changes in the length of the belt 210, it can be driven at a slightly different speed from the cylinders of the transfer station 216. The belt 210 is driven by two separate powered rollers 240 and 242. By applying different torques through the rollers 240 and 242 that drive the belt, the running portion of the belt passing through the image forming station is maintained under a controlled tension. The speeds of the two rollers 240 and 242 can be set to be different from the surface speeds of the cylinders 218 and 220 of the transfer station 216.

[0200] Two powered tension rollers, or dancers 250 and 252, are provided, one on each side of the nip between the cylinders of the transfer station. These two dancers 250, 252 are used to control the slack length in the belt 210, before or after the nip, and their movement is schematically represented by the two-sided arrows adjacent to each dancer. In some embodiments, a control device monitors and controls the movement of the dancers.

[0201] When the belt 210 is slightly longer than an integer multiple of the circumference of the blanket cylinder, if the seam aligns with the increased gap between cylinders 218 and 220 of the transfer station in one cycle, then in the next cycle the seam will be shifted to the right as seen in FIG. 4A. To compensate for this, the belt is driven at high speed by rollers 240 and 242 such that slack accumulates to the right of the nip and tension accumulates to the left of the nip. To maintain the belt 210 at the correct tension, the upstream 250 and downstream 252 powered dancers can be moved simultaneously in different (e.g., opposite) directions. When the discontinuities of the cylinders of the transfer station face each other and a gap is created between them, dancer 252 is moved down and dancer 250 is moved to accelerate the running portion of the belt passing through the nip and introduce a seam into the gap.

[0202] The speed of the ITM and / or the belt and / or the blanket at a position away from the image forming station can vary (e.g., and hence the seam passes through the gap during the time the ITM disengages from impression cylinder 220), but it is possible to operate the system such that the speed at the ITM speed at a position aligned with the image forming station 212 (see 398 in FIG. 20B) is maintained substantially constant without temporal or spatial variations. This constant speed at the aligned position 398 can be important to avoid image distortion caused by speed variations at these positions.

[0203] Accordingly, some embodiments relate to a method of operating a printing system in which an ink image is formed on an intermediate transfer member moving at an image forming station and transferred from the intermediate transfer member to a substrate at a pressing station. The method includes controlling a temporal change in the surface speed of the intermediate transfer member such that (i) a constant surface speed of the intermediate transfer member is maintained at a position aligned with the image forming station and (ii) a variable speed is obtained only at positions spaced from the image forming station for at least a portion of the time, by locally accelerating and decelerating only a portion of the intermediate transfer member at positions spaced from the image forming station.

[0204] To reduce drag on the belt 210 as it is accelerated through the nip, the blanket cylinder 218 may be provided with rollers 290 within a discontinuous region between the ends of the blanket, as shown in FIG. 3.

[0205] The need to correct the phase of the belt in this way can be detected by measuring the length of the belt 210 or by monitoring the phase of one or more markers on the belt relative to the phase of the cylinders of the transfer station. The marker(s) can be attached to the surface of the belt, for example, and magnetically or optically detected by a suitable detector. Alternatively, the marker can take the form of an irregularity, such as a missing tooth, in a lateral projection used to apply tension to the belt and maintain it under tension, and thus serves as a mechanical position indicator.

[0206] Marker detector In the context of the present disclosure, the terms “marker” and “marking” are interchangeable and have the same meaning.

[0207] As illustrated in FIG. 5, in some embodiments, the ITM 102 (e.g., a blanket or a belt) may include one or more markings 1004 thereon, e.g., in a direction 1110 defined by the ITM movement. As will be described below, a number of markings respectively positioned at different locations may be useful when it is desired to reduce or eliminate image distortion due to non-uniform blanket stretch.

[0208] The nature of the markings typically differs from the nature of the adjacent unmarked positions. For example, the color(s) of the markings may differ from the color of the adjacent positions. Other optical properties of the markings may be in the non-visible range.

[0209] In some embodiments, the markings are numerous N such that at least 50, or at least 100, or at least 250, or at least 500 distinct markings are on the ITM, a situation where the markers are also said to be "dense on the ITM". In one non-limiting example, for an ITM having a circumference length of at least 1 meter or at least 2 meters or at least 3 meters, there are approximately 500 equally spaced markings on an ITM having a length between 5 meters and 10 meters such that the average separation distance between the markings is at most 5 cm or at most 3 cm or at most 2 cm or at most 1 cm.

[0210] An ITM having a relatively high "marker density" may be useful for many purposes, e.g., for tracking local ITM speed or local ITM stretch at various locations on the ITM.

[0211] In the examples of FIGS. 6A - 6B and 7, a plurality of optical sensors 990 configured to detect the presence of markers are spaced from each other along the direction of movement of the rotating ITM. These optical sensors are, therefore, an example of a "marker detector". Each of the optical sensors is aimed onto the surface of the ITM and is configured to read the ITM markings 1004 thereon as they pass by.

[0212] The N different markers can have a width along the direction of movement 1100 that is at most 1 cm or at most 5 mm, and / or at most 5% or at most 2.5% or at most 1% or at most 0.5% or at most 0.1% of the length of the ITM102.

[0213] In the case of an endless ITM, the "length" of the ITM is defined as the circumference of the ITM.

[0214] In some embodiments, the number of markers is such that, from one of the N different ITM markers, along the direction of rotational movement 1100, positions of substantially most (i.e., at least 75% of the area of its surface) or substantially all (i.e., at least 90% of the area of its surface) of the surface of the ITM102 are not displaced over the entire ITM, exceeding 10% or exceeding 5% or exceeding 2.5% or exceeding 1% or exceeding 0.5% of the ITM length. In some embodiments, the markings are located on one or two lateral edges of the ITM, outside the seam area for a seamed belt, at a position that does not significantly affect the printing area as defined by the length of the print bar and the length of the ITM. The markings do not have to be the same on both edges of the blanket.

[0215] In the example of FIG. 5, the marker is visible to the naked eye. This is not limiting. In some embodiments, the marker can be distinguished from the rest of the blanket based on any optical property, including, but not limited to, the visible spectrum or other wavelengths or optical emissions or any other kind of electromagnetic radiation. Additionally and / or alternatively, the lateral protrusions of the belt can be unevenly spaced in a manner that can serve as a mechanical marking. In some embodiments, the ITM can comprise markings having different kinds of signals. For example, different suitable detectors can be used to monitor combinations of optical, mechanical, and magnetic signals.

[0216] FIGS. 6A-6B illustrate an intermediate transfer member 102 disposed on a plurality of rollers 104, 106. A plurality of optical sensors 990 are aimed at the ITM. In one non-limiting example, the optical sensors are used to detect a marker 1004 on the rotating ITM. For example, the optical sensors 990 can detect the presence or absence of the marker 1004 at a position aligned with the optical sensors 990. In the example of FIG. 8A, sensors 990A-990J are oriented downward, and thus the fixed position at an “aligned” interval with the optical sensors 990 is directly below the sensors. However, the optical sensors can be aimed in different orientations, and the position “aligned” with the optical sensors 990 is not required to be directly below the sensors 990.

[0217] In the context of the present disclosure, the terms “sensor” and “detector” are used interchangeably. Sensors capable of detecting optical, magnetic, or mechanical markers, or any other suitable kind of signal, are known and need not be described in detail.

[0218] In the context of the present disclosure, a “fixed interval” position is a position fixed via a gap. This is a position attached to the ITM and contracted to a “fixed intermediate transfer member” or “fixed blanket” position that rotates with the ITM.

[0219] As described above, markings on the intermediate transfer member 102 are not required to be visible to the naked eye or optically detectable. As such, the optical sensor 990 can be operable to detect optical signals of any wavelength. Alternatively, the marker detector 990 is not required to be an optical sensor, and any "marker detector" operable to detect the presence or absence of ITM markers can be utilized. Examples of the "marker detector" 990 include, but are not limited to, magnetic detectors, optical detectors, and capacitance sensors.

[0220] In the non-limiting example of FIGS. 6A-6B, several "roller-aimed" marker detectors 990, individually exemplified as 990A-990J, are each aimed at a fixed-spaced position on the upper run of the blanket when mounted on rollers 104, 106. As will be described below with reference to FIG. 10, the roller-aimed marker detector 990 can be used to detect the presence or absence of slip between the ITM 102 and either of the rollers 104, 106, or can be used to measure the "slip speed".

[0221] In some embodiments, the optical sensor or other marker detector 990 can be used to measure the local speed of the ITM 102 at the fixed-spaced positions at which the marker detector 990 is aimed. In the example of FIGS. 6A-6B, a number of marker detectors 990B-990I are spaced from each other along the direction 1100 of the surface speed of the upper run of the ITM, and the upper run is defined as the section of the ITM located directly under the imaging station between the rollers 104, 106. In the non-limiting example of the drawing, a total of eight marker detectors are arranged, but this is not limiting, and any number of marker detectors can be used.

[0222] In some embodiments, the local ITM speed may vary depending on the position on the ITM (i.e., in the blanket reference frame that rotates with the blanket) and / or the position in the “inertial reference frame” or “fixed interval reference frame”, “fixed interval reference frame”. For example, the ITM speed close to rollers 104, 106 can be very close to being equal to the speed of the drive roller(s) due to the “no-slip” condition of the ITM on the roller(s). However, the ITM speed further away from rollers 104, 106 can deviate from the speed of the roller depending on the position (e.g., depending on the distance from one of the drive rollers). As will be described below, ITM marker 1004 and marker detector 990 can be used to detect the local speed of the ITM at a fixed position of the interval through which the marker of the intermediate transfer member will pass.

[0223] Therefore, in one example, the local ITM speed at the position targeted at detector 990B can be different from the local ITM speed at positions targeted at any of detectors 990C - 990I. In some embodiments, spacing the multiple marker detectors apart can, among other things, enable “profiling” the local ITM speed for multiple fixed positions of the interval by monitoring the specific local ITM speed at each marker.

[0224] Also, illustrated in FIGS. 6A - 6B are multiple rotary encoders 88A - 88C that measure the angular displacement of either rollers 104, 106 or impression cylinder 502. The presence of rotary encoders is not essential. Some embodiments may be lacking such encoders.

[0225] Alternatively or in addition, as illustrated in FIG. 6B, one or more tandem rollers 982 or 984 can rotate at the same surface speed as rollers 104, 106 and can be equipped with rotary encoders to measure the rotation of rollers 104 or 106.

[0226] A rotary encoder can be used to measure rotational displacement(s) or rotational speed(s) of any roller(s).

[0227] FIGS. 7 and 8 relate to embodiments in which for each of one or more of a plurality of print bars 302 (e.g., two or more “adjacent” print bars, or three or more print bars, or three or more “adjacent print bars”), respective different marker detectors 990 are arranged (i) on or within the print bar housing and / or on or within the housing of each print bar 302, and / or (ii) on the track on which the print bar 302 slides (e.g., on the track that can slide in a direction parallel to the local surface of the blanket 102 but perpendicular to the surface speed direction 1100), and / or (iii) between the print bar 302 and the blanket 102, and / or (iv) adjacent to the print bar 302 (i.e., closer to a given print bar 302 than any adjacent print bar, so that marker detector 990C is adjacent to print bar 320B and thus closer to it than either of the adjacent print bars 320A, 320C).

[0228] In the example of FIG. 7, the “neighbors” of print bar 320B are 320A and 320C, and the “neighbors” of print bar 320C are 320B and 320D, etc.

[0229] In one non-limiting example related to ink image registration (e.g., when “printing” an ink image on the blanket 102 by depositing ink droplets thereon), the marker detector 990 is used to detect local speed at a specific position below the marker detector 990 in a “fixed reference frame of intervals” (i.e., as opposed to a blanket reference frame that rotates with it).

[0230] In some embodiments, the rate at which ink droplets are deposited onto the ITM102 by the print bar 302 (e.g., a variable rate that varies over time) is determined according to the bias from the desired local velocity below a given print bar 302 to minimize and / or eliminate the resulting image distortion by determining the deposition rate of the droplets, and may be determined according to the "local intermediate transfer member velocity" of the ITM below the print bar 302. Since the marker detector can be used to measure the local velocity, for example, to precisely measure the local ITM velocity at a fixed position of a given print bar pitch, the marker detector is (i) on the print bar housing or within the print bar housing and / or on the print bar housing of each print bar 302 or within the print bar housing, and / or (ii) on the track on which the print bar 302 can slide (e.g., in a direction parallel to the local surface of the ITM102 but perpendicular to the surface velocity direction 1100), and / or (iii) between the print bar 302 and the ITM102, and / or (iv) adjacent to the print bar 302 (i.e., closer to a given print bar 302 than any adjacent print bar, so the marker detector 990C is adjacent to the print bar 320B and thus closer to it than either of the adjacent print bars 320A, 320C). As described above and in more detail below, the local ITM velocity can vary at fixed positions of different pitches, and it would be desirable to measure the local ITM velocity as close as possible to the position (e.g., the print bar position) where the droplets are deposited on the rotating ITM102.

[0231] Measurement of the local velocity of the intermediate transfer member In some embodiments, it is possible to measure the time required for the ITM marker 1004 in order to measure the local ITM velocity, and the marker has a known width in the plane of motion that intersects a "vertical plane" (not shown) that is perpendicular to the direction of the rotational motion 1100. For example, the marker detector 990 is aimed at the ITM102 within the "vertical plane".

[0232] In this case, the local speed can be inversely proportional to the time required for the marker to cross the "vertical plane" and can be directly proportional to the marker width.

[0233] In another example, for adjacent ITM markers, MARKER FIRST and MARKER SECOND the local ITM speed can be measured by measuring the time difference TIME_DIFF(FIRST,SECOND) between (i) the first time TIME FIRST when the leading edge of MARKER FIRST crosses the "vertical plane" and (ii) the second time TIME SECOND when the leading edge of MARKER SECOND crosses the "vertical plane", where the "leading edge" is defined according to the direction of ITM rotation. In the case of a non-limiting example of a light marker(s) on a dark ITM, this time difference TIME_DIFF(FIRST,SECOND) can be the "between-peak" time delta_t as illustrated in FIG. 8B.

[0234] Measurement of Slip Speed As described above, in some embodiments, the rotary encoder can measure the angular displacement of any of the roller(s). For example, a relatively large number (e.g., at least 500 or at least 1,000 or at least 5,000 or at least 10,000 or at least 50,000 or at least 100,000) of markings within any of the rollers 104, 106 (or cylinders 982, 984 that rotate tandemly therewith) can be present to measure relatively small angular displacements and / or any angular displacement with relatively high precision. In one non-limiting example, it is also possible to measure the angular velocity of the rollers 104, 106 using a rotary encoder, for example, by measuring the time required for the roller to rotate at a predetermined angle.

[0235] ​​​​​​​​As described above, in some embodiments, the ITM speed at the location of the roller (104 or 106) can be determined by the speed of the roller resulting from the "slip-free" condition of the ITM around the roller.

[0236] However, there may be some situations contrary to the "slip-free" condition, for example, when the ITM is "stretched" beyond its initial length and is "too long" as the running section defined by the roller(s). In this case, the ITM guided around the rollers 104, 106 may exhibit a certain "slip speed" at one or more rollers.

[0237] The procedure for measuring the ITM slip speed is described in FIG. 9A, that is, the speed difference between (i) the local ITM speed at the induction or drive roller and (ii) the roller speed of that roller is described below. The procedure includes three consecutive steps, namely steps S811, S815, and S819, where S811 is the first step, S815 is the second step, and S819 is the third step.

[0238] In step S811, the ITM speed is detected at the contact position where the ITM 102 contacts the roller. For example, the local ITM speed can be detected using any marker detector 990, such as marker detector 990A for roller 106 or marker detector 990J for roller 104, as illustrated in FIG. 7.

[0239] In step S815, the roller rotation speed is detected, and in step S819, it is possible to (i) compare the roller rotation speed with the local ITM speed and / or (ii) calculate the difference between them to calculate the slip speed.

[0240] Measurement and indication of the length of the intermediate transfer member As described above, in the case of an endless ITM, the "length" of the ITM is defined as the circumference of the ITM.

[0241] In some embodiments (e.g., a continuous loop belt), the length of the endless ITM can vary over time during the operation of the printing system as the ITM 102 rotates.

[0242] Figure 9B is a flowchart of a procedure for measuring the length of the intermediate transfer member 102 while the ITM rotates. The procedure includes three consecutive steps, namely steps S831, S835, and S839, where S831 is the first step, S835 is the second step, and S839 is the third step.

[0243] In step S831, the circumference ROLLER_CIRC of the roller (104 or 106) is determined. This can be a pre-determined value. In some embodiments, it is possible to incorporate small variations in the circumference of the roller due to, for example, its temperature dependence such as that resulting from thermal expansion. In some embodiments, a look-up table may be provided.

[0244] In some embodiments, the ITM includes N ITM markers {MARKER1, MARKER2, ··· MARKER N}, where N is a positive integer (e.g., at least 10 or at least 50 or at least 100).

[0245] In step S835, for a given one of the ITM markers MARKER I (where I is a positive integer having at most the value of N), it is possible to determine (e.g., by using any one of the marker detectors) when a given marker MARKER I starts and completes one rotation. This "marker rotation measurement" can be performed with respect to a fixed position of the interval (i.e., the position aimed at one of the marker detectors 990). Since the speed of the ITM can vary slightly over time depending on the position on the ITM (e.g., due to the stretching or contraction of the ITM as it rotates), the "marker rotation measurement" is performed for a plurality of ITM markers (i.e., a single MARKER INot only about but also) and / or can be repeated at a plurality of "measurement positions" (i.e., the first measurement can be performed about the position targeted at sensor 990A, the second measurement can be performed about the position targeted at sensor 990B, etc.).

[0246] For each marker, the "start" and "completion" of one rotation define a time interval. It is possible to measure the rotational displacement of the roller (i.e., having the circumferential ROLLER_CIRC) for this time interval (e.g., in radians or degrees, or in any angular unit), which explains how much of the roller rotates during the time interval.

[0247] In step S831, it is possible to determine the length or circumference of the ITM based on (i) the rotational displacement of roller 104 (or 106) during one rotation of the ITM marker and (ii) the circumference of the roller. For example, for ITM marker MARKER I if the roller having ROLLER_CIRC rotates 900 degrees during the time required to complete one rotation, the length of the ITM can be estimated to be 2.5 times that of ROLLER_CIRC.

[0248] This measurement can be repeated and averaged for a number of ITM markers.

[0249] Some features related to the spliced intermediate transfer member Although not a requirement, in some embodiments, it was described above that endless ITM102 can be a spliced ITM. For example, ITM102 can include releasable fastening such as a zipper or hook and loop fastener, or permanent fastening achievable by adhesiveness of the blanket ends, and such seams lie substantially parallel to the axes of rollers 104 and 106, on which the ITM is guided.

[0250] The following description refers to one seam, but the teachings disclosed herein may be applicable to ITMs having multiple seams.

[0251] In some embodiments, it may be desirable to directly or indirectly track the position of the seam 1130 during rotation of the ITM. FIG. 10 illustrates four frames of the rotational movement of the seam 1130 (i.e., those at times t1, t2, t3, and t4) for a non-limiting example of rotation of the ITM clockwise.

[0252] In some embodiments, it is useful to track the relative phase difference (or lack thereof) between the seam 1130 and a predetermined position 1134 of the rotating impression cylinder 502.

[0253] In the non-limiting example of FIG. 13 (i.e., related to a particular case of a sheet substrate), there are integer ink images on the ITM 102 (i.e., each of them is defined as a "page image" 1302). The ink images do not exist on the seam 1130. In this example, the ink images are not formed by deposition of droplets onto the position of the seam 1130.

[0254] In some embodiments, the ITM can engage with the impression cylinder 502 repeatedly and disengage from the impression cylinder 502 by at least a portion of the movement of the ITM 102 towards the cylinder 502 (e.g., downward movement), and / or by the movement of the cylinder 502 towards at least a portion of the ITM 102 (e.g., upward movement), or by any other means.

[0255] As illustrated in FIGS. 12A - 12B, in some embodiments, it may be desirable to operate the printing system so as to avoid engaging the ITM 102 with the impression cylinder 502 when the seam 1130 is aligned with the impression cylinder 502 as illustrated in FIG. 12A (e.g., by the pressure roller 140 or by any other means). Instead, as illustrated in FIG. 12B, it may be desirable for the seam 1130 to be able to pass by the impression roller 502 during the "disengagement portion" of the engagement cycle between the ITM and the impression cylinder.

[0256] In some embodiments, this can be achieved by (i) adjusting the length of the ITM to the length of an appropriate set point and / or (ii) temporarily modifying the speed of at least a portion of the ITM (e.g., where the seam is located).

[0257] In some embodiments, it may be useful to utilize an endless ITM having a length that is an integer multiple of the circumference of the impression cylinder 502. In the example of FIG. 13, there are eight print areas of a page, each of which is associated with a different page image having (i) a height that matches the height of the substrate sheet on which the page image is transferred to the substrate sheet and / or (ii) a height equal to the circumference of the cylinder of the impression cylinder 502.

[0258] In the non-limiting example of FIG. 11, the length of the ITM 102 is equal to eight times the circumference of the impression cylinder 502.

[0259] First Procedure for Operating a Printing System with a Non-Constant ITM Length In some embodiments, the length of the ITM 102 can vary over time or "vary slightly (e.g., by at most 2% or at most 1% or at most 0.5%)".

[0260] FIGS. 13-14 relate to an apparatus and method for operating a printing system having an ITM with a non-constant length that varies over time. In one non-limiting example, the ITM 102 can be exposed to mechanical noise caused by repeated engagement with a rotating impression cylinder 502. In yet another example, over the life of the ITM, the ITM can be "stretched" by use. In yet another example, temperature variations or any other operating or environmental parameter can cause the ITM to expand or contract.

[0261] In some embodiments (see step S101), to detect length variations, it may be useful to monitor the length indicator of ITM 102, for example, by actually measuring the ITM length or by monitoring a parameter that indicates the ITM length without actually measuring the ITM length. An example of a parameter that indicates the ITM length is the "rotational displacement" during the period required for one of the ITM markers to complete one rotation.

[0262] If the monitored length is less than the "target" or "setpoint" length (e.g., the target is equal to an integer multiple of the circumference of the impression cylinder 502), this may increase the risk of pressing the seam 1130 against the impression cylinder or may be associated with any other set of adverse effects (if any). In this case, it may be advantageous to (i) extend the ITM 102 (see, for example, the apparatus of FIG. 13 or the procedure of FIG. 14), and / or (ii) decelerate the ITM 102 (e.g., when the ITM 102 is disengaged from the impression cylinder 502). In some situations, during the disengagement time, the surface speed of the ITM 102 is different from the surface speed of the impression cylinder 502.

[0263] It is not required to accelerate or decelerate the entire ITM 102. For example (see FIG. 4A), it is possible to locally accelerate or decelerate a portion of the ITM 102 that extends upstream 250 and downstream 252 by means of powered dancers.

[0264] Reference is made to FIGS. 13 and 14. In FIG. 14, instead of the length between the fixed rollers 104, 106, the length between them is variable and controllable. For example, a motor (not shown) and / or any linear actuator can increase or decrease the distance between the rollers 104, 106. In some embodiments, the motor for modifying the distance between the guide rollers is different from the motor used to cause the rotation of the ITM 102. Various procedures are illustrated in FIG. 14.

[0265] The reference is made to FIG. 14. This drawing provides an example of monitoring and adjusting ITM characteristics such as length or speed. There is constant monitoring of the length of the ITM (S101). In one example, the length of the ITM is compared to the maximum allowable setpoint length (S109). An example of the setpoint length can be an integer multiple of the circumference of the impression cylinder or can be (2 * n - 1) times the circumference of the pressure cylinder, where n is an integer. The setpoint length can have upper and lower tolerance levels. If the length of the ITM exceeds the setpoint length, it may be possible to contract the ITM (S111). In one example, to contract the ITM length, it may be possible to reduce the distance between rollers 104 and 106. If the length of the ITM does not exceed the setpoint length, the length can be compared to the minimum setpoint length (S115). If the monitored length is less than the value being compared, the length of the ITM can be increased (S119). In one non - limiting example, the length can be increased by separating rollers 104 and 106. Steps S111 and S119 can be performed by any other means.

[0266] Second procedure for operating a printer in which the length of the intermediate transfer member is non - uniform In the previous section, a procedure for responding to bias in the ITM length by modifying the ITM length was described.

[0267] Alternatively or in addition, as described above, at least a portion of the ITM 102 can respond by accelerating or decelerating as it moves between the "disengagement portion" of the engagement cycle of the ITM and the impression cylinder. Refer to FIGS. 16A - 16B.

[0268] In some embodiments, to complete one rotation of the ITM (i.e., at a position aligned with the impression cylinder 502), there may be a fixed relationship between (i) the engagement cycle of the ITM and the impression cylinder, and (ii) the timing parameters (e.g., period) of the ITM rotation cycle or a predetermined position (e.g., seam 1130). In this case, the ITM rotation cycle can be said to be "synchronized" with the engagement cycle of the ITM and the impression cylinder.

[0269] When the two cycles are synchronized, it is possible to operate the printing system such that the seam 1130 (or any other predetermined position on the ITM 102) passes by the impression cylinder simultaneously within each cycle of the engagement cycle of the ITM and the impression cylinder. Therefore, it can be arranged that the seam 1130 always passes by the impression cylinder 502 during the "disengagement" part of the engagement cycle of the ITM and the impression cylinder.

[0270] If the impression cylinder 502 rotates at a period that is an integer multiple of the period of the engagement cycle of the ITM and the impression cylinder, this means that each time the seam 1130 (or any other predetermined position on the ITM 102) passes by the impression cylinder 502, the seam 1130 is aligned with a predetermined position 1134 of the rotating impression cylinder (e.g., the position of the impression cylinder gap 1138, see FIGS. 15C - 15D). Refer to FIG. 12. Here, the seam 1130 always passes by the rotating impression cylinder when the position 1134 (i.e., the circumferential discontinuity) of the rotating impression cylinder 502 directly faces the ITM 102.

[0271] However, in the case of an increase or decrease in the rotational speed of the ITM, or in the case of an increase or decrease in the length of the ITM that would modify the linear speed of a position on the ITM 102 (e.g., the seam 1130) for a fixed rotational speed, this can rotate the ITM in a manner that is "phase shifted" with respect to the engagement cycle of the ITM and the impression cylinder. For example, unlike the situation of the previous paragraph where the seam 1130 passes by the impression cylinder simultaneously within each cycle of the engagement cycle of the ITM and the impression cylinder, this can pass the seam 1130 by the impression cylinder 502 at different parts of the engagement cycle of the ITM and the impression cylinder. Even if the seam 1130 passes by the impression cylinder 502 during the "disengagement part" of the cycle during the "first pass", it is easy for it to pass by the impression cylinder 502 during the "engagement part" of the impression cycle when passing by the impression cylinder 502 later.

[0272] (i) When the rotation cycle of the impression cylinder 502 is synchronized with the engagement cycle of the ITM and the impression cylinder, and (ii) when the rotation cycle of the ITM 102 is not synchronized therewith (e.g., because the length of the ITM 102 deviates from the setpoint length), this can create the situation of FIG. 15D. In contrast to FIG. 15C where the seam 1130 always passes by the rotating impression cylinder 502 when the position 1134 of the rotating impression cylinder 502 directly faces the ITM 102, in FIG. 15D, the seam can "drift" while being aligned with the position 1134. This drift can indicate a situation where there is a high risk of the ITM rotating "out of sync" with the engagement cycle of the ITM and the impression cylinder, and / or the ITM 102 engaging the cylinder 502 when the seams 1130 are aligned between them.

[0273] Here, reference is made to FIG. 16A. In this drawing, it is possible to detect a printing risk (S121) at a length bias (S103) or at a predetermined position (e.g., seam position 1130) on the ITM102, and / or an undesirable phase difference (S123) between the ITM rotation cycle and (i) the engagement cycle of the ITM and the impression cylinder and / or (ii) the impression cylinder rotation cycle.

[0274] In order to bring the ITM rotation cycle back into phase with (i) the engagement cycle of the ITM and the impression cylinder and / or (ii) the impression cylinder rotation cycle, it is possible to accelerate or decelerate the ITM102 (i.e., the entire intermediate transfer or a part thereof) when the ITM is disengaged from the impression cylinder 502 (S129).

[0275] In some embodiments, the approach of FIGS. 16A-16B may be useful but may give rise to other problems, e.g., it may distort one or more of the ink images. Thus, it may be preferable to rely on accelerating or decelerating the rotation speed of the ITM102 only after the ITM length has been corrected and after the reasonable options for correcting the ITM length have been exhausted.

[0276] As illustrated in FIG. 17, in the case of a "small positive length bias" from the target length, a shrinkage or expansion approach of the ITM (see FIG. 16) may be suitable. For example, if the ITM102 is extended beyond a certain length, this may cause or increase the risk of "slip of the intermediate transfer member" on the roller(s) 104 and / or 106).

[0277] Therefore, in some embodiments, the acceleration or deceleration of the ITM may depend on the length of the ITM deviating from the target length beyond a certain threshold value, and only then will this approach be relied upon. Alternatively or in addition, the acceleration or deceleration of the ITM may depend on the detected or predicted slip between the ITM102 and the roller(s) 104 and / or 106).

[0278] A person skilled in the art is guided by FIGS. 18 to 19.

[0279] Reference is made to FIG. 18A. In step S101, the length of the ITM is monitored. In step S109, it is determined whether the length exceeds the setpoint length. If so, in step S151, it is determined whether the bias length exceeds Up_tolerance I If it exceeds, the ITM is contracted in step S111; if not, the ITM is accelerated in step S131.

[0280] Reference is made to FIG. 18B. In step S101, the length of the ITM is monitored. In step S109, it is determined whether the length exceeds the setpoint length. If so, in step S151, it is determined whether there is a high risk of slip of the ITM on the roller(s). If it exceeds, the ITM is contracted in step S111; if not, the ITM is accelerated in step S131.

[0281] Reference is made to FIG. 19. In step S101, the length of the ITM is monitored. In step S115, it is determined whether the length is less than the setpoint length. If so, in step S151, it is determined whether the bias length exceeds Down_tolerance I If it exceeds, the ITM is extended in step S119; if not, the ITM is decelerated in step S135.

[0282] The first technique for reducing or eliminating image distortion FIGS. 20A to 20B illustrate an ITM or blanket mounted on upstream and downstream rollers, where the tension in its upper running part 910 exceeds the tension in its lower running part 912.

[0283] The system of FIG. 20A is the same as the system of FIG. 4A, where upper 910 and lower 912 running parts are illustrated and defined by upstream 242 and downstream 240 rollers. FIG. 20B is somewhat more schematic and can be applied to the system of FIG. 4A or any other system. In FIG. 20B, the nomenclature of FIG. 1A is adopted, and the upstream and downstream rollers are called 106 and 104, respectively.

[0284] As illustrated in FIG. 20B, the torque applied by the downstream roller 106 significantly exceeds the torque of the upstream roller 104. When the torque received by the downstream roller 104 exceeds the torque applied by the upstream roller 106, this can maintain the upper running part 910 of the belt 102 at a higher tension than the tension of the lower running part 912. In the example of FIGS. 20A - 20B, the torque of the downstream roller 104 applies a horizontal force F2 on the upper running part 912 of the belt 102 that exceeds the horizontal force F1 applied by the upstream roller 106 on the upper running part 912 of the belt 102. In that way, the rollers 104, 106 can be said to stretch the upper running part 912 to keep the upper running part taut.

[0285] In different embodiments, the ratio of the torque applied by the downstream roller to the torque applied by the upstream roller, and / or the ratio of the magnitude of the horizontal force applied by the downstream roller 106 to the magnitude of the horizontal force applied by the upstream roller 104 is at least 1.1 or at least 1.2 or at least 1.3 or at least 1.5 or at least 2 or at least 2.5 or at least 3.

[0286] As described above, in some embodiments, the impression cylinder 210 in the impression station 216 is periodically engaged with and disengaged from the intermediate transfer member 210 to transfer the ink image from the moving intermediate transfer member to the substrate 226 passing between the intermediate transfer member and the impression cylinder. This repeated or intermittent engagement can induce mechanical vibrations within the slack portion in the lower run of the belt 912.

[0287] By pinning and maintaining the upper run 910, it is possible to substantially isolate the upper run 912 from the mechanical vibrations in the lower run 912. In one non-limiting example, the upper run 910 is pinned and maintained as described above, but this should not be construed as limiting.

[0288] A second technique for reducing and eliminating image distortion In the previous section, techniques for reducing distortion were described, whereby the upper run 910 was pinned and maintained and substantially isolated from the mechanical vibrations of the lower run 912. These mechanical vibrations can non-uniformly stretch the belt 102. If these mechanical vibrations are allowed to propagate to the portion 398 of the belt 102 (see FIG. 20B) aligned with the image forming station 300, the mechanical vibrations and the resulting non-uniform stretching of the belt 102 can cause image distortion of the ink image formed on the outer surface of the belt 102 at the image forming station 300.

[0289] Therefore, instead of or in addition to taking measures to prevent (or reduce the magnitude of) non-uniform stretching in the portion 398 of the belt 102 (see FIG. 20B) aligned with the image forming station 300, it is possible to cancel or eliminate image distortion by (i) measuring the magnitude of the non-uniform stretching and (ii) adjusting the timing of ink droplet deposition on the rotating blanket according to the measured non-uniform blanket stretching and / or blanket shape variation.

[0290] To more fully explain the concepts related to non-uniform stretching of a rotating blanket, it is useful to explain the concepts of "fixed-spacing" and "fixed-blanket" positions.

[0291] In the example of FIG. 21, a number of "fixed-spacing" positions (i.e., positions in a stationary or non-rotating reference frame as opposed to, e.g., ITM and a rotating ITM-fixed position) SL1 - SL8 are illustrated. They are not evenly spaced.

[0292] In the examples of FIGS. 22 - 24, in addition to the fixed-spacing positions SL1 - SL8, a number of fixed-blanket positions BLANKET_LOCATION1 - BLANKET_LOCATION4 (not evenly spaced) that rotate with the blanket or ITM are illustrated. In FIGS. 22 - 24, the fixed-blanket position BLANKET_LOCATION i (where i is a positive integer between 1 and 4) is located at the fixed-spacing position SL i at time t1 and the fixed-spacing position SL i+4 at a later time t2, and, for example, the ITM rotates in a clockwise direction.

[0293] In some embodiments, each blanket position BLANKET_LOCATION i corresponds to the i-th blanket marker of the ITM marker 1004 (see FIG. 8A).

[0294] In some embodiments, the ITM 102 is stretchable at least in the longitudinal direction. Some embodiments of the present invention relate to temporary variations in the distance between fixed-blanket positions. The "distance" between two positions on the ITM surface refers to the distance along the ITM surface along the direction of the surface velocity of the ITM.

[0295] In a situation where the ITM is completely rigid, the "distance between" the ITM fixed positions remains fixed. However, in the case of a flexible and / or stretchable blanket, the distance between positions can vary (e.g., vary slightly). This is illustrated in FIGS. 22 - 24, where, for example, depending on the fixed positions of the intervals, the distance between adjacent blanket positions varies over time. Thus, when BLANKET_LOCATION1 is located at SL1 (see FIG. 23A), the distance between BLANKET_LOCATION1 and BLANKET_LOCATION2 is the first value (see FIG. 23A) DIST(BL1, BL2, SL1). When BLANKET_LOCATION1 is located at SL5 (see FIG. 23B), the distance between BLANKET_LOCATION1 and BLANKET_LOCATION2 is a second value (see FIG. 23B) DIST(BL1, BL2, SL5) that is greater in FIG. 23B than DIST(BL1, BL2, SL1) in FIG. 23A.

[0296] When BLANKET_LOCATION2 is located at SL2 (see FIG. 23A), the distance between BLANKET_LOCATION2 and BLANKET_LOCATION3 is the first value (see FIG. 23A) DIST(BL2, BL3, SL2). When BLANKET_LOCATION2 is located at SL6 (see FIG. 23B), the distance between BLANKET_LOCATION2 and BLANKET_LOCATION3 is a second value (see FIG. 23B) DIST(BL2, BL3, SL6) that is smaller in FIG. 23B than DIST(BL2, BL3, SL2) in FIG. 23A.

[0297] In some embodiments, the blanket 102 is stretched over rollers 104, 106 or a rotating drum (not shown). As the blanket rotates, the stretching force thereon can be non-uniform, for example, due to the presence of mechanical noise (e.g., from repeated engagement and disengagement between a pressure roller and an ITM). As such, the blanket can stretch non-uniformly, where the non-uniform stretching of the blanket varies over time and / or over the blanket position and / or at fixed positions of the spacing. In an example relevant to the latter case, the stretching force on the blanket can vary with position, for example, in the upper running portion of the blanket 102, and the blanket 102 closer to the rollers 104, 106 can have more tension than the central portion further away from the rollers.

[0298] In the previous paragraph, it was mentioned that non-uniform stretching forces can cause non-uniform stretching of the blanket 102 and changes in the distance between fixed positions of the spacing.

[0299] Alternatively or in addition, in some embodiments, the material properties (e.g., related to material elasticity) and / or the mechanical stretching force applied to the blanket 102 (or any other ITM property) can vary depending on the position on the ITM. For example, since the blanket 102 can be a blanket with seams, the elasticity or rigidity or thickness or any other physical or chemical property can be different or different from near the seam 1130.

[0300] Note that when the separation distance between adjacent ITM fixed positions varies depending on time and / or fixed positions of the spacing (see FIGS. 23A - 23B), the local surface velocity of the ITM fixed positions can also vary. For example, during the period between t1 and t2, the average velocity of the blanket at BLANKET_LOCATION2 exceeds the average velocity of BLANKET_LOCATION3, reducing the distance between them (comparing FIG. 23A with FIG. 23B).

[0301] Obviously, as demonstrated in FIGS. 22-24, the ITM (e.g., flexible and / or longitudinally extensible) can deform as it rotates.

[0302] Therefore, in some embodiments, the speed of the ITM at different positions is different from the average speed because the ITM deforms.

[0303] In FIGS. 24A-24B, local speeds are illustrated, and the speed DIST(BL i SL j ) is the position of the fixed position of the i-th blanket when it is arranged at the fixed position of the j-th interval.

[0304] Consideration of FIG. 25 In some embodiments, ink droplets are deposited on the ITM102 at a position below the print bar 302 and / or aligned with and / or closest to the print bar 302. Since the rate at which ink droplets are deposited on the ITM102 can depend on the local speed of the ITM102 at the "deposition position" (i.e., where the ink droplets are deposited), and since even the speed at the fixed position of the blanket can vary as the ITM102 rotates, it may be useful to arrange a respective (e.g., including a photodetector) marker detector for each print bar 302 in order to precisely measure the local ITM speed at the "deposition position".

[0305] Therefore, it is possible to measure the local speed under each print bar.

[0306] As described above, in some embodiments, the rate at which droplets need to be deposited to form a given image on the ITM102 depends on the speed and the desired dot pattern of the image to be created on the rotating ITM. When the speed is constant, there is no need to consider speed variations.

[0307] However, in some embodiments, the fixed position BL of a given blanket or (e.g., SL in FIG. 25)A or SL I at a position below one of the rollers as in or SL of FIG. 25 B ~SL H The local speed at a fixed position SL corresponding to another position of the print bar as in is variable according to at least one of (i) shape fluctuations of the ITM due to non-uniformity of the interval or non-constancy of time dilation or deformation, (ii) temporary increase or decrease in the distance between positions (e.g., neighboring positions separated by less than a few centimeters), and / or (iii) mechanical noise, e.g., due to the printing cycle of the ITM and the printing cylinder, and / or (iv) non-uniform tension on the ITM 102 that can vary with time or interval.

[0308] FIGS. 26A - 26B illustrate a method for depositing ink droplets on a rotating blanket 102. Referring to FIG. 26A, note that in step S201, properties related to the local speed (or indicating that speed), e.g., properties related to temporary variations in non-uniform stretching and / or temporary variations in the shape of the blanket 102, e.g., properties that then indicate speed variations, are monitored. In step S205, the ink droplets are deposited on the rotating blanket according to the monitored parameters that indicate speed variations.

[0309] Reference is made to FIG. 26B. Step S221 includes monitoring and / or predicting details of the non-uniform blanket speed such that the locally fixed speed on the surface of the intermediate transfer member (e.g., the blanket) deviates from its average or representative speed by only a non-zero local bias speed. The ink image is formed on the rotating blanket 102 in step S225 by depositing ink droplets thereon in a manner determined according to what is monitored, e.g., and thus determined.

[0310] Several examples of performing step S225 are illustrated in FIG. 27. Refer to steps S205, S209, and S213. In particular, several examples of performing step S225 include: (i) adjusting the rate, timing, or frequency of ink deposition; (ii) providing color alignment by a number of print bars led to the ITM; and (iii) providing image overlay by a number of print bars led to the ITM.

[0311] Referring to FIG. 28, note that the mathematical model used to predict non-ITM stretch and / or to adjust the deposition of ink onto the rotating ITM can be a “programmable” mathematical model that is repeatedly updated. Refer to steps S301, S305, S309, S313, S317, S321, S325, and S329.

[0312] As illustrated in FIG. 29, the mathematical model can incorporate data about the operating cycle of the printing system, for example, by assigning a greater weight to data from the early past corresponding to the cycle than would otherwise be assigned.

[0313] Embodiments of the present invention relate to techniques for adjusting the rate, timing, or frequency at which ink droplets are deposited onto a rotating ITM in accordance with monitored variations in local velocity at a location (s) on the ITM and / or in accordance with monitored variations in ITM shape and / or in accordance with monitored non-uniform ITM stretch. By monitoring and compensating for variations in the property (s) of the ITM, it is possible to reduce or eliminate distortion in the resulting ink image.

[0314] An example of the ITM is, for example, a rotatable drum having a round shape. Another example of the ITM is a flexible blanket or belt that is guided, for example, onto a drum or onto a plurality of guide rollers attached to the drum. For example, the blanket or belt can follow a path defined by drive and guide rollers mounted on a support frame, and the nip roller can be arranged on the support frame on the opposite side of the impression cylinder, and the nip roller is selectively movable relative to the support frame so as to compress the substrate between the blanket or belt and the impression cylinder.

[0315] In one non-limiting example related to a varying rotational speed, n external sources of mechanical noise affect the surface speed of the ITM (e.g., due to the "cycle of the ITM and the impression cylinder" described below or due to any other cause(s)). Otherwise, when superimposed on a uniform, constant surface speed, the mechanical noise can cause a "rattling surface motion" of the rotating ITM rather than the "smooth motion" that would be observed in the hypothetical absence of mechanical noise. In one non-limiting example related to shape variations of the ITM, the ITM can locally alternately stretch and contract as it progresses, such that, for example, the distance between two neighboring points on the ITM alternately (e.g., slightly and / or at high speed) increases and decreases. The local shape of the ITM can vary differently at different positions on the ITM. For example, the distance between fixed points A and B of the neighboring blanket at a first location of the ITM can vary differently from the distance between fixed points C and D of the neighboring blanket at a second location of the ITM.

[0316] Embodiments of the present invention relate to apparatuses and methods in which the above-described speed variations (i.e., temporary and / or position-dependent speed variations) and / or shape variations of the ITM are monitored and / or quantified and / or mathematically modeled.

[0317] The ITM can be determined in accordance with (i) the content of the image to be formed on the transfer surface and (ii) the speed of the ITM.

[0318] Consider an "unfeatured" image that will be formed by droplet deposition on an ITM consisting only of evenly spaced dots. In a conventional system, in order to form an "unfeatured image" on the ITM by droplet deposition, ink droplets can be deposited at a constant rate on the rotating ITM. This constant rate of ink droplet deposition can depend only on a constant surface speed of the rotating ITM and a desired uniform distance between the dots.

[0319] In contrast to the "unfeatured image", when using a conventional system to form an image on the ITM by droplet deposition that has non-uniform (i.e., non-uniform along the direction of rotation of the ITM) features or dot patterns, the rate of droplet deposition can vary according to the features of the image to be printed.

[0320] Once again, consider the above-mentioned "unfeatured" image. In contrast to a conventional system, when determining the rate (e.g., a rate that itself varies, for example, at high speed) at which droplets will be deposited on the rotating ITM to print an unfeatured image on the ITM by droplet deposition, it can be useful to consider variations in the surface speed of the ITM (e.g., relatively high and / or slight variations). According to some embodiments of the present invention, when printing the above-mentioned unfeatured image consisting only of evenly spaced dots, the rate at which ink droplets are deposited on the rotating ITM is not constant and varies according to variations in the surface speed of the ITM.

[0321] It is also disclosed that, according to some embodiments, the need to compensate for and / or incorporate variations in the local surface speed of the ITM is not limited to the special case of an image consisting of evenly spaced dots. Therefore, the rate at which ink droplets are deposited on the ITM to form an ink image thereon can vary according to both (i) the image features and (ii) variations in the local speed of the ITM.

[0322] In some embodiments, “rapid” shape or speed variations occur over a time scale that is at most a few seconds or at most one second or at most 0.5 seconds or at most a few tenths of a second and / or at most the time required for the ITM to complete a single revolution or at most the time required for the ITM to complete 50% of a revolution or at most the time required for the ITM to complete 25% of a revolution or at most the time required for the ITM to complete 10% of a revolution. In the context of the present disclosure, when the speed variation is “slight”, the local speed deviates from the representative or average speed of the ITM by at most 5% or at most a few percent or at most 1% or at most 0.5% or at most a few tenths of a percent. When the ITM undergoes “slight” shape variations, the distance between fixed positions of a predetermined blanket on the ITM can vary by at most 5% or at most a few percent or at most 0.5% or at most a few tenths of a percent.

[0323] In some embodiments, the printing system has a number of print bars separated from each other along the direction of the surface speed of the ITM. The ink image can be formed on the rotating ITM as follows. That is, (i) first, a relatively “low” resolution ink image (or a portion thereof) is formed on the rotating ITM below the first print as ink droplets are deposited thereon to form “dots” of the image thereon, and (ii) thereafter, the resolution of the low resolution ink image on the rotating ITM can be increased by superimposing additional image dots on the low resolution ink image on the ITM. The additional image dots are added to the ink image on the rotating ITM by deposition of ink droplets below the second print bar at a position “downstream” from the first print bar along the direction of ITM rotation. In this case, the droplets can be deposited on the ink ITM below the second print bar (i.e., to increase the image resolution of the ink image on the rotating ITM) in a manner determined according to the results of monitoring and / or quantification and / or modeling.

[0324] For example, (i) the time at which an image dot at a given position within the ink image is formed by droplet deposition by a first print bar, and (ii) the time delay between the time at which an image dot at a substantially same given position within the ink image is formed by droplet deposition by a second print bar to increase the image resolution can be adjusted according to the results of monitoring and / or quantification and / or modeling.

[0325] In some embodiments, ink droplets of a first color are deposited by a first print bar, and ink droplets of a second color are deposited by a second print bar to effect a "color registration" operation. In some embodiments, the color registration operation can be performed according to the results of monitoring and / or quantification and / or modeling. For example, (i) the time at which an image dot at a given position within the ink image is formed by droplet deposition by a first print bar, and (ii) the time delay between the time at which an image dot at a substantially same given position within the ink image is formed by droplet deposition by a second print bar to effect color registration can be adjusted according to the results of monitoring and / or quantification and / or modeling.

[0326] As described above, embodiments of the present invention relate to an image transfer surface of an ITM whose ITM speed and / or shape vary over time. As such, the local speeds at different positions on the ITM can deviate from the average or representative ITM speed. Ink droplets can be deposited according to the magnitude of the speed bias between the local speed and the average speed. In non-limiting examples, variations in the speed and / or shape of the ITM can be associated with one or more of a number of causes (i.e., any combination thereof). In one example, the ITM can engage and disengage from a printing cylinder repeatedly, and an ink image is transferred to a substrate by the printing cylinder, defining an "engagement cycle of the ITM and the printing cylinder". This "engagement cycle of the blanket and the printing cylinder" can generate mechanical noise that is transmitted to different positions on the ITM away from the engaging cylinder. This mechanical noise can be superimposed on a generally uniform and constant speed to cause a certain "rattling" motion on the ITM. If the blanket is flexible and / or stretchable, this mechanical noise can affect the local shape of different ITM positions differently.

[0327] Alternatively or in addition, in another non-limiting example, the mechanical or material properties of the blanket can vary at different locations on the ITM. For example, if the endless blanket is a so-called spliced blanket, where the two ends are joined together (e.g., by a zipper) at a splice to form an endless belt, the ITM can be more elastic at positions further away from the splice than at positions closer to the splice. Alternatively or in addition, the local mechanical properties of the ITM can be affected by an apparatus outside the ITM having a fixed position, for example, in a so-called "fixed-spacing" reference frame (as opposed to a "blanket-fixed" rotating reference frame that rotates with the blanket). For example, the belt can be guided or driven along a suitable roller. At a position close to the drive roller, the local ITM speed can be strongly affected by the "no-slip" condition at the ITM-roller interface, i.e., the ITM is required to have the same local speed as the local speed of the drive roller. Further away from the drive roller, this no-slip condition may not affect the local ITM speed as much, and its local speed can exhibit a greater deviation from the speed that would be defined by the roller. In yet another example, mechanical noise (e.g., from an engagement cycle with an impression cylinder) can have a greater impact on the local ITM speed at positions closer to the impression cylinder than at positions further away.

[0328] It is further possible to incorporate into the belt a microchip similar to those found in electronic circuits, for example, "chip and pin" credit cards, in which data can be stored. The microchip can comprise only read-only memory, in which case it can be used by the manufacturer to record data such as the place and time where the belt was manufactured and details of the physical or chemical properties of the belt. The data can be related to a catalog number, batch number, and any other identifier that enables information related to the use of the belt and / or its user to be provided. This data can be read by the controller of the printing system during introduction or during operation and used, for example, to determine calibration parameters. Alternatively, or in addition, the chip can include random access memory to enable data to be stored on the microchip by the controller of the printing system. In this case, the data can include information such as the number of printed pages or the length of the web printed using belt parameters such as the belt or the previously measured belt length to assist in recalibrating the printing system when starting a new printing run. Reading and writing on the microchip can be achieved by making direct electrical contact with the terminals of the microchip, in which case contact conductors can be provided on the surface of the belt. Alternatively, the data can be read from the microchip using a wireless signal, in which case the microchip can be powered by an induction loop printed on the surface of the belt.

[0329] The present invention and its embodiments can be used, inter alia, with respect to the printing systems described in the co-pending PCT applications International Application No. PCT / IB2013 / 051716 (Agent's Reference No. LIP5 / 001PCT), International Application No. PCT / IB2013 / 051717 (Agent's Reference No. LIP5 / 003PCT) and International Application No. PCT / IB2013 / 051718 (Agent's Reference No. LIP5 / 006PCT), which are incorporated by reference as fully defined herein.

[0330] The present invention is described using detailed descriptions of embodiments thereof provided by way of example, and is not intended to limit the scope of the invention. The above embodiments have different features, and not all of them are required in all embodiments of the invention. Some embodiments of the present invention utilize only some of the features or possible combinations of the features. Variations of the described embodiments of the present invention and embodiments of the present invention having different combinations of the features mentioned in the above embodiments will be apparent to those skilled in the art related to the invention.

[0331] In the description and claims of the present disclosure, each of the verbs "comprise", "include" and "have", and their cognates, are used to indicate that the object or the object of the verb is not necessarily a complete list of the members, components, elements or parts of the object or the object of the verb. As used herein, the singular forms "a", "an" and "the" include plural meanings unless the context clearly dictates otherwise. For example, the term "marking" or "at least one marking" may include a plurality of markings.

Claims

1. a. An intermediate transfer member (ITM) including a flexible belt; b. An image forming station configured to form an ink image on the surface of the intermediate transfer member when the intermediate transfer member moves so that the ink image is transferred to a pressing station on the intermediate transfer member; c. An upstream roller and a downstream roller arranged upstream and downstream of the image forming station to define an upper running portion passing through the image forming station and a lower running portion passing through the pressing station; d. A pressing cylinder provided at the pressing station, which is periodically engaged with the intermediate transfer member and disengaged from the intermediate transfer member in order to transfer the ink image from the moving intermediate transfer member to a substrate passing between the intermediate transfer member and the pressing cylinder. A printing system comprising: i. The periodic engagement is configured to induce mechanical vibration in the slack portion in the lower running portion of the belt; ii. Each of the upstream roller and the downstream roller is configured to apply torque to the belt. The magnitude of the torque applied by the upstream roller is defined as the upstream roller torque amount, and the magnitude of the torque applied by the downstream roller is defined as the downstream roller torque amount; iii. The downstream roller is configured to maintain a torque on the belt that is significantly stronger than that of the upstream roller; A printing system configured to maintain the upper running portion taut and isolate the upper running portion substantially from mechanical vibrations in the lower running portion by maintaining a torque amount ratio, which is the ratio of (A) the upstream roller torque amount to (B) the downstream roller torque amount, at 1.2 or more.

2. The printing system according to claim 1, wherein the printing system is configured to maintain the torque amount ratio at 1.3 or more.

3. e. A controller configured to: A. prevent a predetermined section of the intermediate transfer member from being aligned with the impression cylinder during the engagement period and / or B. improve the synchronization between a predetermined section of the intermediate transfer member and a predetermined position of the impression cylinder, i. during a certain period, move the intermediate transfer member at the same surface speed as the impression cylinder that rotates the intermediate transfer member, and ii. during other periods, adjust the movement of the intermediate transfer member such that the surface speed of the intermediate transfer member is increased or decreased. The printing system according to claim 1 or 2, further comprising the controller.

4. The printing system according to claim 3, wherein the predetermined section of the intermediate transfer member is a seam of the blanket.

5. The printing system according to claim 4, wherein the predetermined section of the impression cylinder is a gap within the impression cylinder that receives the substrate gripping portion.

6. (i) At least one of the rollers is a drive roller, and (ii) the controller is configured to accelerate or decelerate the intermediate transfer member by increasing or decreasing the rotational speed of one or more of the drive rollers during the disengagement period. The printing system according to any one of claims 1 to 5.

7. The printing system according to any one of claims 1 to 6, further comprising: (i) a moving locator point attached to the moving intermediate transfer member and (ii) an electronic circuit configured to monitor a phase difference between the moving locator point and the phase of the rotating impression cylinder, and the controller is configured to accelerate or decelerate the intermediate transfer member during the disengagement period in response to the result of the monitoring of the phase difference.

8. (i) An intermediate transfer member (ITM) including a flexible belt (ii) An image forming station (iii) An impression station (iv) An upstream roller and a downstream roller arranged upstream and downstream of the image forming station to define an upper running portion passing through the image forming station and a lower running portion passing through the impression station A method of operating a printing system comprising: At the image forming station, forming an ink image on the surface of the intermediate transfer member while the intermediate transfer member is moving. In the printing station, a step of periodically engaging the printing cylinder with the moving intermediate transfer member and transferring an ink image from the moving intermediate transfer member to a substrate passing between the intermediate transfer member and the printing cylinder is included. The periodic engagement induces mechanical vibration within the slack portion of the lower running portion of the belt. Torque is applied to the belt by each of the upstream roller and the downstream roller. The magnitude of the torque applied by the upstream roller is defined as the upstream roller torque amount, and the magnitude of the torque applied by the downstream roller is defined as the downstream roller torque amount. The downstream roller sustains a torque on the belt that is significantly stronger than that of the upstream roller. A method of operating a printing system that maintains the upper running portion taut and substantially isolates the upper running portion from mechanical vibrations in the lower running portion by maintaining a torque amount ratio, which is the ratio of (A) the upstream roller torque amount to (B) the downstream roller torque amount, at 1.2 or more.

9. The method according to claim 8, wherein the upstream roller and the downstream roller are controlled to maintain the torque amount ratio at 1.3 or more.

10. a. An intermediate transfer member of non-constant length; b. An image forming station configured to deposit ink on the surface of the intermediate transfer member while the intermediate transfer member moves so as to form an ink image on the surface of the intermediate transfer member; c. A transfer station configured to transfer an ink image from the surface of the moving intermediate transfer member to a substrate passing between the intermediate transfer member and the printing cylinder during the engagement period; d. An electronic circuit configured to adjust the length of the intermediate transfer member to a setpoint length; A printing system comprising: The printing system, wherein the setpoint length is equal to an integer multiple of the circumference of the printing cylinder.

11. a. An intermediate transfer member (ITM) having a blanket seam; b. An image forming station configured to form an ink image on the surface of the intermediate transfer member when the intermediate transfer member moves, transfer the ink image on the intermediate transfer member to the printing station, and transfer the ink image from the intermediate transfer member to a substrate; c. A sensor configured to detect the time when the blanket seam of the intermediate transfer member passes through the sensor; A printing system comprising:

12. The printing system according to claim 11, wherein formation of the ink image is controlled to start as close as possible to near the seam of the blanket on the surface of the intermediate transfer member.

13. The printing system according to claim 12, wherein formation of the ink image is controlled such that the position of the seam of the blanket is held at the same position with respect to the printed image in a continuous cycle of the intermediate transfer member.

14. a. An intermediate transfer member having a seam of the blanket; b. An image forming station configured to form an ink image on the surface of the intermediate transfer member when the intermediate transfer member moves, transfer the ink image to a pressing station on the intermediate transfer member, and transfer the ink image from the intermediate transfer member to a substrate; A printing system comprising: A printing system, wherein formation of the ink image is controlled such that the position of the seam of the blanket is held at the same position with respect to the printed image in a continuous cycle of the intermediate transfer member.

15. (i) The pressing station includes a rotating pressing cylinder having a discontinuous portion on its surface; (ii) The relative movement between the intermediate transfer member and the pressing cylinder is controlled such that whenever the seam of the blanket passes through the pressing cylinder, the discontinuous portion on the surface of the pressing cylinder faces the intermediate transfer member at the same time. The printing system according to claim 14.

16. The printing system according to claim 14, wherein formation of the ink image is controlled to start as close as possible to near the seam of the blanket on the surface of the intermediate transfer member.

17. The printing system according to claim 16, further comprising a sensor configured to detect the time when the seam of the blanket passes through the sensor.

18. The printing system according to claim 15, wherein the length of the intermediate transfer member is equal to an integral multiple of the circumference of the pressing cylinder.

19. The printing system according to claim 14, wherein the ends of the intermediate transfer member are fastened to each other by adhesion at the position of the seam of the blanket.

Images