Head driving method and printing system

Abstract

To provide a technique for suppressing lowering of quality of a printed image caused by change of conveyance speed of a recording medium.SOLUTION: A printer 1 includes a plurality of heads 11 and a plurality of head controllers 270 connected to each of the plurality of heads 11, a conveyance mechanism including two conveyance rollers 5A and 5B for conveying a recording medium 4, an encoder 5M for outputting an encoder signal according to conveyance speed of the recording medium 4, and a main controller 70 connected to the encoder 5M and the head controller 270. The main controller 70 detects the conveyance speed of the recording medium 4 from the encoder signal, generates packet data P1 including discharge timing information FT and packet data P2 including speed identification information FS according to the conveyance speed, and transmits the packet data to the head controller 270.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a head driving method and a printing system.

Background Art

[0002] A certain known printing apparatus includes a plurality of ejection units provided for each color, a conveyance mechanism that conveys a recording medium such as printing paper in a conveyance direction, and a plurality of head control units respectively corresponding to the plurality of ejection units. Note that the conveyance mechanism has an encoder, and each head control unit detects the conveyance speed of the recording medium by receiving encoder pulses from the encoder.

[0003] In a plurality of portions of an image to be printed, the time required for generating drawing data may vary. Therefore, in the above printing apparatus, the conveyance speed of the recording medium is adjusted according to the time required for generating the drawing data. If the ejection amount and ejection timing of the ink are not adjusted even though the conveyance speed of the recording medium is adjusted, the ink density of the printed image may become non-uniform in the conveyance direction, and the quality of the printed image may deteriorate. Thus, in the above printing apparatus, each head control unit detects the conveyance speed of the recording medium from the encoder pulses received from the encoder. Then, each head control unit determines ejection parameters for the corresponding ejection unit according to the detected conveyance speed, and gives an instruction to change the ejection parameters to the corresponding ejection unit.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above-described printing apparatus, a plurality of head control units each detect the conveyance speed of a recording medium and issue an instruction to change the ejection parameters of the corresponding ejection unit according to the detected conveyance speed. At this time, the detection timing of the conveyance speed and / or the timing of the instruction to change the ejection parameters may shift for each head control unit. If the detection timing of the conveyance speed and / or the timing of the instruction to change the ejection parameters shifts, the ejection parameters and ejection timing used may differ for each ejection unit, and the image quality may differ for each ejection unit.

[0006] An object of the present invention is to provide a technique for suppressing a decrease in the quality of a printed image due to a change in the conveyance speed of a recording medium.

Means for Solving the Problems

[0007] According to an aspect of the present invention, there is provided a head driving method executed by a printing system including a head bar having a plurality of heads and a plurality of head controllers respectively connected to the plurality of heads, a conveyance mechanism configured to convey a recording medium, an encoder that outputs an encoder signal corresponding to the conveyance speed of the recording medium, and a main controller connected to the encoder and the plurality of head controllers. The driving method includes: the main controller detecting the conveyance speed of the recording medium from the encoder signal; the main controller determining ejection timing information based on the encoder signal, generating packet data including the ejection timing information, and transmitting the packet data to the plurality of head controllers; the main controller determining speed identification information according to the detected conveyance speed, generating packet data including the speed identification information, and transmitting the packet data to the plurality of head controllers; the plurality of head controllers determining ejection parameters based on the speed identification information. The plurality of head controllers transmit the ejection timing information and the ejection parameters to the plurality of heads, and drive the plurality of heads based on the ejection timing information and the ejection parameters.

Advantages of the Invention

[0008] In the above configuration, the main controller connected to the plurality of head controllers detects the conveyance speed of the recording medium from the encoder signal of the encoder. Then, the main controller transmits packet data including ejection timing information and packet data including speed identification information corresponding to the conveyance speed of the recording medium to the plurality of head controllers. Note that the packet data including ejection timing information and the packet data including speed identification information corresponding to the conveyance speed of the recording medium may be grouped as one packet data or may be separate packet data. According to the above configuration, the detection entity for detecting the conveyance speed of the recording medium is the main controller, and since there are not a plurality of detection entities, there is no possibility that the detected conveyance speeds vary. Also, the main controller transmits packet data including ejection timing information and packet data including speed identification information corresponding to the conveyance speed of the recording medium to the plurality of head controllers. Therefore, it is suppressed that the timing at which the plurality of head controllers receive the packet data including ejection timing information and the packet data including speed identification information corresponding to the conveyance speed of the recording medium is shifted for each head controller. As a result, since the detection timing of the conveyance speed of the recording medium and / or the timing of the change instruction of the ejection parameters do not shift for each of the plurality of head controllers, even when the conveyance speed of the recording medium changes, it is suppressed that the quality of the printed image deteriorates due thereto.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

MODE FOR CARRYING OUT THE INVENTION

[0010] Hereinafter, the printing apparatus 1 according to an embodiment of the present invention will be described with reference to the drawings. The printing apparatus 1 is an example of the printing system of the present invention. In FIG. 1, the conveyance direction of the recording medium 4 corresponds to the front-rear direction of the printing apparatus 1. Further, the width direction of the recording medium 4 corresponds to the left-right direction of the printing apparatus 1. Further, the direction orthogonal to the front-rear direction and the left-right direction, that is, the direction perpendicular to the paper surface in FIG. 1 corresponds to the up-down direction of the printing apparatus 1.

[0011] As shown in FIGS. 1 and 2, the printing apparatus 1 includes a platen 3 housed in a housing 2, three head bars 10, two conveyance rollers 5A and 5B, an arch frame 6, a controller 7 (see FIG. 5), three ink reservoirs 8 for the head controller, and the like. In FIGS. 1 and 2, only one ink reservoir 8 is shown for simplifying the drawing.

[0012] As shown in FIGS. 1 and 2, the recording medium 4 passes over the upper surface of the platen 3. The three head bars 10 are positioned above the platen 3 so as to face the platen 3. Ink is supplied to each head bar 10 from the ink reservoir 8. The structure of the head bar 10 will be described later. The three head bars 10 are fixed to the arch frame 6 in a state of being arranged along the front-rear direction (the conveyance direction of the recording medium 4). As shown in FIG. 2, the arch frame 6 has an arch shape, and the three head bars 10 are inclined with respect to the horizontal plane at different angles.

[0013] As shown in FIGS. 1 and 2, the two conveyance rollers 5A and 5B are respectively positioned behind and in front of the platen 3. The two conveyance rollers 5A and 5B are driven by a motor (not shown). As shown in FIG. 2, the recording medium 4 is sent out from the supply roll 4A wound in a roll shape and wound around the take-up roll 4B. For example, the recording medium 4 is roll paper. Rotating shafts 4C and 4D that rotate by motors (not shown) are respectively fixed to the supply roll 4A and the take-up roll 4B. These two rotating shafts 4C and 4D and the two conveyance rollers 5A and 5B cooperate so that the recording medium 4 is sent out from the supply roll 4A, conveyed downstream (forward) in the conveyance direction so as to pass over the platen 3, and wound around the take-up roll 4B. An encoder 5M is arranged between the two conveyance rollers 5A and 5B. The encoder 5M outputs an encoder signal corresponding to the conveyance speed of the recording medium 4. The encoder 5M may be a contact type or a non-contact type. The encoder 5M is connected to the encoder unit 71 of the main controller 70 described later. The two rotating shafts 4C and 4D and the two conveyance rollers 5A and 5B are an example of the conveyance mechanism of the present invention.

[0014] As shown in FIG. 3, each head bar 10 includes a head group 20 having a plurality of heads 11 (for example, 12 heads 11). In FIG. 1, for the sake of simplicity of the drawing, the number of heads 11 is reduced for illustration. As shown in FIG. 3, the plurality of heads 11 form two head rows arranged in the front-rear direction. Each head row includes six heads 11 arranged in the left-right direction. The positions of the six heads 11 arranged in the left-right direction in one head row are the same in the front-rear direction. However, in the following description, the statement that the positions are the same does not strictly mean that the positions are exactly the same, but is intended to mean that the positions are the same within the range of manufacturing errors and mounting errors. Note that the left-right positions of the respective heads 11 included in the two head rows are shifted from each other. That is, the 12 heads 11 of the head group 20 are positioned in a staggered manner.

[0015] The lower surface of each head 11 is a nozzle surface 41b (see FIG. 4) on which a plurality of nozzles 42 are formed. In the present embodiment, as shown in FIG. 3, the head 11 includes two rows of nozzle rows, but this is merely an example, and the head 11 may include two or more rows of nozzle rows. Also, in FIG. 3, for the sake of simplicity of the drawing, the number of nozzles 42 included in each nozzle row is reduced for illustration, but the number of nozzles 42 included in each nozzle row can be any number. For example, each nozzle row may include 1000 or more nozzles 42. Although an internal head flow path is formed inside the head 11, the shape and the like of the internal head flow path will be described later.

[0016] As described above, the 12 heads 11 of each head bar 10 (head group 20) form two head rows, and each head 11 has two rows of nozzle arrays. Yellow ink is supplied from one of the three ink reservoirs 8 to the 12 heads 11 of the head bar 10 located at the rearmost (uppermost stream in the conveyance direction). Magenta ink is supplied from one of the three ink reservoirs 8 to the 12 heads 11 of the second head bar 10 from the rear (second from the upstream in the conveyance direction). Cyan ink is supplied from one of the three ink reservoirs 8 to the 12 heads 11 of the head bar 10 located at the foremost (lowermost stream in the conveyance direction). Thus, in this embodiment, light-colored to dark-colored inks are ejected in order from upstream to downstream in the conveyance direction from the three head bars 10 arranged in the conveyance direction. Note that in this embodiment, the printing apparatus 1 has three head bars 10, but may further have two head bars 10. Then, white ink and black ink may be ejected from the two head bars 10, respectively. Note that the white ink, yellow ink, magenta ink, cyan ink, and black ink are all, for example, UV-curable inks.

[0017] Next, with reference to FIGS. 3 and 4, the flow path unit 40 and the actuator unit 50 that constitute each head 11 will be described. Note that since the structures of the flow path unit 40 and the actuator unit 50 are common to the 12 heads 11, the flow path unit 40 and the actuator unit 50 in one head 11 will be described.

[0018] As shown in FIG. 4, the flow path unit 40 is formed by a plurality of metal plates laminated in the vertical direction and a nozzle plate 41. Ink flow paths such as the individual flow paths 12 including the pressure chambers 12a, the supply manifold 13a, and the return manifold 13b are formed in the plurality of metal plates by etching. The nozzle plate 41 is formed of a polymer synthetic resin material such as polyimide, for example, and is joined to the lower surface of the laminated metal plates with an adhesive. The lower surface of the nozzle plate 41 is the above-described nozzle surface 41b. Note that the nozzle plate 41 may also be formed of a metal material such as stainless steel.

[0019] As shown in FIG. 4, inside the flow path unit 40, individual flow paths 12 communicating with the respective nozzles 42, a supply manifold 13a, and a return manifold 13b communicating with the individual flow paths 12 are formed. Although not shown in the figure, the supply manifold 13a and the return manifold 13b extend in the left-right direction (the direction perpendicular to the plane of the paper in FIG. 4). The supply manifold 13a is connected to a tank 400 located outside the head 11 via an ink supply port (not shown) formed in the flow path unit 40. The return manifold 13b is connected to the tank 400 (see FIG. 2) located outside the head 11 via an ink discharge port (not shown) formed in the flow path unit 40. Thereby, an ink circulation path is formed in which the ink discharged from the tank 400 passes through the supply manifold 13a, the individual flow paths 12, and the return manifold 13b and returns to the tank 400.

[0020] Although not shown in the drawings, corresponding to the fact that a plurality of nozzles 42 are positioned to form two rows of nozzle rows extending in the left - right direction as described above, in the flow path unit 40, a plurality of individual flow paths 12 corresponding to the nozzles 42 are positioned to form two rows of individual flow path rows extending in the left - right direction. Also, twelve supply manifolds 13a and twelve return manifolds 13b are respectively formed in the flow path unit 40, and each supply manifold 13a and each return manifold 13b communicate with a plurality of individual flow paths 12 that constitute two rows of individual flow path rows. As a result, inside the flow path unit 40, a plurality of ink flow paths are formed that lead from the supply manifold 13a through the pressure chambers 12a of the plurality of individual flow paths 12 to the nozzles 42 and the return manifold 13b. Note that the number of supply manifolds 13a and return manifolds 13b formed in the flow path unit 40 is adjusted according to the number of nozzles 42. Also, the number of individual flow paths 12 communicating with each supply manifold 13a and each return manifold 13b is adjusted according to the number of nozzles 42.

[0021] As shown in FIG. 4, a pressure chamber 12a is formed in each individual flow path 12, and above the pressure chamber 12a, an actuator unit 50 is positioned. The actuator unit 50 includes a diaphragm 51 positioned on the upper surface of the flow path unit 40 so as to cover all the pressure chambers 12a, a plurality of piezoelectric bodies 52 respectively positioned at positions on the upper surface of the diaphragm 51 facing the pressure chambers 12a, and a plurality of individual electrodes 53 respectively positioned on the upper surfaces of the plurality of piezoelectric bodies 52. As will be described later, the diaphragm 51 functions as a common electrode. The diaphragm 51 as the common electrode, the individual electrodes 53, and the piezoelectric bodies 52 form one drive element 55. That is, the actuator unit 50 includes a plurality of drive elements 55 respectively corresponding to the plurality of nozzles 42.

[0022] The diaphragm 51 is a metal plate that is substantially rectangular in plan view and is made of, for example, an iron-based alloy such as stainless steel, a copper-based alloy, a nickel-based alloy, or a titanium-based alloy. The upper surface of the conductive diaphragm 51 is located below the piezoelectric body 52. Therefore, the upper surface of the diaphragm 51 can also serve as a common electrode. The diaphragm 51 as the common electrode is connected to the ground wiring of a driver IC (not shown) that drives the actuator unit 50 and is always held at the ground potential. Note that the diaphragm 51 does not necessarily have to be a metal plate. For example, it may be formed of the same piezoelectric material as the piezoelectric body 52, and a metal film may be formed on its upper surface as a common electrode.

[0023] The piezoelectric body 52 is formed of a piezoelectric material mainly composed of lead zirconate titanate (PZT), which is a solid solution of lead titanate and lead zirconate and is a ferroelectric. The piezoelectric body 52 is polarized in the thickness direction (vertical direction) at least in a region facing the pressure chamber 12a (the portion sandwiched between the individual electrode 53 and the diaphragm 51). In the present embodiment, there are a plurality of piezoelectric bodies 52 corresponding to the plurality of pressure chambers 12a, but the piezoelectric body 52 may be a layer of piezoelectric body (piezoelectric layer) continuously formed across the plurality of pressure chambers 12a on the upper surface of the diaphragm 51. In this case, the diaphragm 51 as the common electrode, the individual electrode 53, and the portion sandwiched between the individual electrode 53 of the piezoelectric body 52 and the diaphragm 51 form one driving element 55.

[0024] Next, the operation of the drive element 55 of the actuator unit 50 during ink injection will be described. When a predetermined drive potential is applied from a driver IC (not shown) to a certain individual electrode 53, a potential difference is generated between the individual electrode 53 to which the drive potential is applied and the diaphragm 51 serving as a common electrode held at the ground potential. As a result, an electric field in the thickness direction acts on the piezoelectric body 52 sandwiched between the individual electrode 53 and the diaphragm 51. The direction of this electric field is parallel to the polarization direction of the piezoelectric body 52. Therefore, the piezoelectric body 52 in the region (active region) facing the individual electrode 53 contracts in the plane direction orthogonal to the thickness direction. Here, the diaphragm 51 below the piezoelectric body 52 is fixed to the flow path unit 40. Therefore, as the piezoelectric body 52 located on the upper surface of the diaphragm 51 contracts in the plane direction, the portion of the diaphragm 51 covering the pressure chamber 12a deforms so as to protrude toward the pressure chamber 12a (unimorph deformation, see FIG. 4). At this time, since the volume in the pressure chamber 12a decreases, the ink pressure in the pressure chamber 12a rises, and ink is ejected from the nozzle 42 communicating with this pressure chamber 12a.

[0025] As shown in FIG. 5, the controller 7 includes a main controller 70 that controls each part of the printing apparatus 1 except for the head bar 10, a plurality of sub-controllers 170 corresponding to the plurality of head bars 10 respectively, and a plurality of head controllers 270 corresponding to the plurality of heads 11 (see FIG. 3) respectively. The controller 7 (main controller 70, sub-controller 170, and head controller 270) includes an FPGA (Field Programmable Gate Array), an EEPROM (Electrically Erasable Programmable Read-Only Memory), a RAM (Random Access Memory), and the like. Note that the controller 7 may include a CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit) instead of or in addition to the FPGA.

[0026] The main controller 70 is connected to an external device 9 such as a PC (see FIG. 1) so as to be capable of data communication, and controls each part of the printing apparatus 1 based on the print data sent from the external device 9. For example, the main controller 70 controls the motors that drive the rotary shafts 4C and 4D and the motors that drive the conveyance rollers 5A and 5B, and conveys the recording medium 4 in the conveyance direction by the two conveyance rollers 5A and 5B. As shown in FIG. 5, the main controller 70 includes an encoder unit 71. The encoder unit 71 is connected to an encoder 5M, and the encoder 5M outputs an encoder signal corresponding to the rotational speed of at least one of the conveyance rollers 5A and 5B or the conveyance speed of the medium conveyed by the conveyance rollers 5A and 5B. The encoder unit 71 detects the conveyance speed of the recording medium 4 based on the encoder signal output from the encoder 5M.

[0027] As described above, the plurality of sub-controllers 170 respectively correspond to the plurality of head bars 10. Each sub-controller 170 is communicably connected to the main controller 70. At the same time, each sub-controller 170 is communicably connected to a plurality of head controllers 270 arranged corresponding to the plurality of heads 11 (see FIG. 3) included in the corresponding head bar 10. In FIG. 5, for the sake of simplicity of the drawing, only one head controller 270 is shown for each head bar 10. In the present embodiment, the main controller 70 can transmit a packet signal described later to the plurality of head controllers 270 included in the head bar 10 corresponding to the sub-controller 170 via each sub-controller 170.

[0028] Next, the printing process will be described. As shown in FIG. 6, when a print start instruction from a user of the printing apparatus 1 is input to the main controller 70 (S301), the main controller 70 transmits a print instruction to each sub-controller 170 (S302). The sub-controller 170 that has received the print instruction transmits the print instruction to the head controller 270 and, at the same time, requests the main controller 70 to transmit print data (S303), and receives the print data (S304). The sub-controller 170 transmits the received print data to the head controllers 270 corresponding to the plurality of heads 11 (S305). The printing apparatus 1 repeats the processes from S302 to S305 until printing is completed. Note that after receiving the print instruction, the head controller 270 can transmit initial parameters for initializing ejection parameters, which will be described later, to the plurality of heads 11 before driving the plurality of heads 11 to start printing.

[0029] The conveyance speed of the recording medium 4 can be detected based on the encoder signal output from the encoder 5M. In the prior art, the encoder signal from the encoder 5M was input to each of a plurality of sub-controllers 170 corresponding to the plurality of head bars 10, or to each of a plurality of head controllers 270 corresponding to the plurality of heads 11 (see FIG. 3) respectively. Then, each sub-controller 170 (or each head controller 270) detected the conveyance speed of the recording medium 4, and based on the detected conveyance speed, the head controller 270 (or each head controller 270) adjusted the ejection timing. However, in this case, due to the difference in the timing at which each sub-controller 170 (or each head controller 270) detected the conveyance speed of the recording medium 4, the magnitudes of the conveyance speeds of the recording medium 4 detected by each sub-controller 170 (or each head controller 270) might vary. When variations occurred in the magnitudes of the conveyance speeds of the recording medium 4 detected by each sub-controller 170 (or each head controller 270), even when ink droplets were ejected from the heads 11 of the plurality of head bars 10 toward a predetermined position, the landing positions of the ink droplets ejected from the heads 11 of each head bar 10 might shift from each other.

[0030] In this embodiment, as shown in FIG. 5, the encoder signal from the encoder 5M is input to the encoder unit 71 of the main controller 70. As shown in FIG. 7, the main controller 70 detects the conveyance speed of the recording medium 4 based on the encoder signal (S101). As described above, in the prior art, a plurality of sub-controllers 170 or a plurality of head controllers 270 each detected the conveyance speed of the recording medium 4. That is, in the prior art, there were a plurality of detection entities for detecting the conveyance speed of the recording medium 4. Therefore, the detected conveyance speeds may vary among the plurality of detection entities (that is, the plurality of sub-controllers 170 or the plurality of head controllers 270). However, in this embodiment, since the main controller 70 detects the conveyance speed of the recording medium 4 and there is only one detection entity, it is impossible for the detected conveyance speeds to vary among a plurality of detection entities as in the prior art. After the main controller 70 detects the conveyance speed of the recording medium 4 based on the encoder signal, the main controller 70 determines the ejection timing information FT based on the encoder signal and generates packet data P1 (see FIG. 8(b)) including the ejection timing information FT (S102). Further, the main controller 70 determines the speed identification information FS according to the detected conveyance speed and generates packet data P2 (see FIG. 8(b)) including the speed identification information FS (S103). The main controller 70 transmits the generated packet data P1 and P2 to the plurality of head controllers 270 via the sub-controller 170 (S104).

[0031] Each head controller 270 determines the ejection parameters based on the received speed identification information (S105). As an example of the ejection parameters, the voltage value of the drive voltage applied to the drive element 55 of the head 11 can be mentioned. Each head controller 270 drives the head 11 based on the received ejection timing information FT and the ejection parameters (S106).

[0032] In this embodiment, the packet data P1 including the ejection timing information FT is processed as packet data with a higher priority than other packet data. For example, the packet data P1 including the ejection timing information FT may have the highest priority among the packet data transmitted from the main controller 70 to the head controller 270. Alternatively, the packet data P1 including the ejection timing information FT may be processed as packet data with a higher priority than the packet data P2 including the speed identification information FS. Note that the speed identification information FS does not necessarily have to be transmitted as different packet data P2 from the packet data P1. For example, as shown in FIG. 8(a), the packet data P1 may include both the ejection timing information FT and the speed identification information FS. In this case, the packet data P1 may be fixed-length data including the data area of the ejection timing information FT and the data area of the speed identification information FS. Inside the packet data P1, either the data area of the ejection timing information FT or the data area of the speed identification information FS may be in the front. In the following description, the case where the packet data P1 including the ejection timing information FT and the packet data P2 including the speed identification information FS are different packet data will be described as an example (see FIG. 8(b)). In this case, the transmission frequency of the packet data P2 including the speed identification information FS can be made lower than the transmission frequency of the packet data P1 including the ejection timing information FT.

[0033] In this embodiment, the main controller 70 can generate packet data P2 including speed identification information FS in response to a change in the conveyance speed of the recording medium 4 and transmit it to the head controller 270. Whether there is a change in the conveyance speed of the recording medium 4 can be determined, for example, as follows. After the rotational speeds of the feeding roll 4A and the take-up roll 4B reach the target speed, the speed fluctuation range that may occur due to variations in the roll diameters of the feeding roll 4A and the take-up roll 4B and the roll diameters of the conveyance rollers 5A and 5B is stored in advance in a memory such as the EEPROM of the main controller 70. The main controller 70 determines that there is a change in the conveyance speed of the recording medium 4 when the change in the conveyance speed of the recording medium 4 exceeds the speed fluctuation range stored in the memory. For example, the main controller 70 calculates a value of the conveyance speed assumed at a predetermined time (referred to as the speed average value) based on the speed fluctuation range, and determines that there is a change in the conveyance speed when the conveyance speed of the recording medium 4 deviates from the speed average value by more than the speed fluctuation range. Thereby, when there is a change in the conveyance speed caused by variations in the roll diameters of the feeding roll 4A and the take-up roll 4B and the roll diameters of the conveyance rollers 5A and 5B, this can be excluded. Alternatively, the main controller 70 determines that there is a change in the conveyance speed when the difference (speed difference) between the conveyance speed measured immediately before and the conveyance speed at the time of measurement exceeds a predetermined value. As an example of the predetermined value, the above-described speed fluctuation range can be mentioned. In addition, the main controller 70 may generate packet data P2 including speed identification information FS at a predetermined cycle and transmit it to the head controller 270 even when it is determined that the conveyance speed has not changed, in addition to the case where it is determined that the conveyance speed of the recording medium 4 has changed.

[0034] When the main controller 70 generates packet data P2 including speed identification information FS in response to a change in the conveyance speed of the recording medium 4 and transmits it to the head controller 270, each head controller 270 can update the ejection parameters determined based on the speed identification information in response to receiving the packet data P2 including the speed identification information FS, and transmit the updated ejection parameters to the head 11.

[0035] Also, in the present embodiment, the main controller 70 can generate packet data P2 including speed identification information FS and transmit it to the head controller 270 regardless of whether the conveyance speed of the recording medium 4 is changing. For example, the main controller 70 can generate packet data P2 including speed identification information FS at a fixed period and transmit it to the head controller 270. Alternatively, the main controller 70 can generate packet data P2 including speed identification information FS at the same period as the drive period of a motor (not shown) that drives the conveyance rollers 5A and 5B, and transmit it to the head controller 270. In this case, the main controller 70 can generate and transmit the packet data P2 including the speed identification information FS at a frequency higher than the change in the conveyance speed of the recording medium 4 to the head controller 270.

[0036] When the main controller 70 generates packet data P2 including speed identification information FS regardless of whether the conveyance speed of the recording medium 4 is changing and transmits it to the head controller 270, each head controller 270 detects from the received speed identification information that there is a speed difference (not zero) in the conveyance speed of the recording medium 4. Then, in response to detecting that there is a speed difference in the conveyance speed of the recording medium 4, each head controller 270 can update the ejection parameters determined based on the speed identification information and transmit the updated ejection parameters to the head 11. In this case, after the rotational speeds of the feeding roll 4A and the take-up roll 4B reach the target speed, the speed fluctuation range that may occur due to variations in the roll diameters of the feeding roll 4A and the take-up roll 4B and the roll diameters of the conveyance rollers 5A and 5B is stored in advance in a memory such as the EEPROM of the head controller 270. And similar to the above-mentioned main controller 70, when the head controller 270 detects that there is a speed difference in the conveyance speed of the recording medium 4, the head controller 270 can determine that there has been a change in the conveyance speed of the recording medium 4 when the change in the conveyance speed of the recording medium 4 exceeds the speed fluctuation range stored in the memory. Alternatively, the head controller 270 can determine that there has been a change in the conveyance speed when the speed difference between the conveyance speed measured immediately before and the conveyance speed at the time of measurement exceeds a predetermined value (speed fluctuation range).

[0037] <Operation and Effect of Embodiment> In the above embodiment, the printing apparatus 1 includes a plurality of heads 11, a plurality of head controllers 270 respectively connected to the plurality of heads 11, a conveyance mechanism including two conveyance rollers 5A and 5B for conveying the recording medium 4, an encoder 5M that outputs an encoder signal corresponding to the conveyance speed of the recording medium 4, and a main controller 70 connected to the encoder 5M and the head controller 270.

[0038] The main controller 70 detects the conveyance speed of the recording medium 4 from the encoder signal. Further, the main controller 70 determines ejection timing information FT based on the encoder signal, generates packet data P1 including the ejection timing information FT, and transmits the packet data P1 to the head controller 270. Furthermore, the main controller 70 determines speed identification information FS according to the detected conveyance speed and transmits the speed identification information FS to a plurality of head controllers 270. Each head controller 270 determines ejection parameters based on the received speed identification information FS. Also, each head controller 270 transmits the ejection timing information FT and the ejection parameters to the plurality of heads 11, and drives the plurality of heads 11 based on the ejection timing information FT and the ejection parameters.

[0039] Suppose that a plurality of head controllers 270, or a plurality of sub-controllers 170 provided corresponding to a plurality of head bars 10, each detect the conveyance speed of the recording medium 4 and determine ejection timing information FT and ejection parameters according to the detected conveyance speed. In this case, since the number of detection entities (the plurality of sub-controllers 170 or the plurality of head controllers 270) that detect the conveyance speed of the recording medium 4 is plural, the detected conveyance speeds may vary among the plurality of detection entities. Alternatively, the detection timing of the conveyance speed and / or the timing of the instruction to change the ejection parameters may shift for each head controller 270 (or sub-controller 170). When there are variations in the detected conveyance speed, or when the detection timing of the conveyance speed and / or the timing of the instruction to change the ejection parameters shifts, the ejection parameters and ejection timing used may differ for each head 11, and the quality of the printed image may deteriorate. On the other hand, in the above-described embodiment, the main controller 70 detects the conveyance speed of the recording medium 4 from the encoder signal, generates packet data P1 including ejection timing information FT and packet data P2 including speed identification information FS corresponding to the conveyance speed, and transmits them to the head controller 270. In this case, since one detection entity (i.e., the main controller 70) detects the conveyance speed of the recording medium 4, there is no possibility that the detected conveyance speed varies. Further, the main controller 70 transmits the packet data P1 including the ejection timing information FT and the packet data P2 including the speed identification information FS corresponding to the conveyance speed of the recording medium 4 to the plurality of head controllers 270. Therefore, the timing at which the plurality of head controllers 270 receive the packet data P1 including the ejection timing information FT and the packet data P2 including the speed identification information FS corresponding to the conveyance speed of the recording medium 4 is suppressed from shifting for each head controller 270. As a result, since the detection timing of the conveyance speed of the recording medium 4 and / or the timing of the instruction to change the ejection parameters do not shift for each of the plurality of head controllers 270, even when the conveyance speed of the recording medium 4 changes, a decrease in the quality of the printed image due thereto is suppressed.

[0040] In the above embodiment, the packet data P1 including the ejection timing information FT is the packet data with the highest priority among the packet data transmitted from the main controller 70 to the head controller 270. In this case, the main controller 70 can surely transmit the packet data P1 including the ejection timing information FT to the head controller 270 while suppressing the delay.

[0041] In the above embodiment, the main controller 70 can generate packet data P2 including speed identification information FS in response to a change in the conveyance speed of the recording medium 4 and transmit it to the head controller 270. In this case, since the amount (traffic volume) of the packet data transmitted from the main controller 70 to the head controller 270 can be reduced, it is possible to suppress the occurrence of communication delays and the like due to an increase in the traffic volume. Note that due to the influence of noise, a value of a certain bit in the packet data P2 may be inverted, or a value held in the FPGA of the head controller 270 may change, so that the head controller 270 may recognize the conveyance speed of the recording medium 4 as an incorrect value. In the present embodiment, in addition to the case where the main controller 70 determines that the conveyance speed of the recording medium 4 has changed, even when it is determined that the conveyance speed has not changed, for example, the main controller 70 can generate packet data P2 including the speed identification information FS at a predetermined cycle and transmit it to the head controller 270. Thereby, even when the head controller 270 recognizes the conveyance speed of the recording medium 4 as an incorrect value, the head controller 270 can grasp the latest speed identification information FS and surely correct it.

[0042] In the above-described embodiment, the main controller 70 can generate packet data P2 including speed identification information FS in response to a change in the conveyance speed of the recording medium 4 and transmit it to the head controller 270. In this case, each head controller 270 can update the ejection parameters determined based on the speed identification information in response to receiving the packet data P2 including the speed identification information FS, and transmit the updated ejection parameters to the head 11. In this case, since the head controller 270 updates the ejection parameters in response to the main controller 70 detecting a speed difference in the conveyance speed of the recording medium 4, the update frequency of the ejection parameters can be suppressed, and the communication volume between the head controller 270 and a driver IC (not shown) can be reduced.

[0043] In the above-described embodiment, the main controller 70 can generate packet data P2 including speed identification information FS and transmit it to the head controller 270 regardless of whether the conveyance speed of the recording medium 4 is changing. Also in this case, even when the head controller 270 recognizes the conveyance speed of the recording medium 4 as an incorrect value, the head controller 270 can grasp the latest speed identification information FS and surely correct it.

[0044] In the above-described embodiment, the main controller 70 can generate packet data P2 including speed identification information FS and transmit it to the head controller 270 regardless of whether the conveyance speed of the recording medium 4 is changing. In this case, each head controller 270 detects from the received speed identification information that there is a speed difference (non-zero) in the conveyance speed of the recording medium 4. Then, in response to detecting that there is a speed difference in the conveyance speed of the recording medium 4, each head controller 270 can update the ejection parameters determined based on the speed identification information and transmit the updated ejection parameters to the head 11. In this case, since the head controller 270 updates the ejection parameters in response to detecting that there is a speed difference in the conveyance speed of the recording medium 4, the update frequency of the ejection parameters can be suppressed, and the communication volume between the head controller 270 and a driver IC (not shown) can be reduced.

[0045] In the above-described embodiment, after receiving a printing instruction, before starting printing by driving a plurality of heads 11, the head controller 270 can transmit initial parameters for initializing the ejection parameters described later to the plurality of heads 11. In this case, since the ejection parameters can be initialized before starting printing, it is possible to secure time for recovery in case of failure in initialization as compared with the case where the ejection parameters are initialized immediately before ejection.

[0046] In the above embodiment, the packet data P1 may include both the ejection timing information FT and the speed identification information FS. In this case, the packet data P1 may be fixed-length data including the data area of the ejection timing information FT and the data area of the speed identification information FS. In this case, since the byte length of the packet data P1 is fixed, the process of the destination of the packet data P1 checking the byte length can be omitted. Also, in the above embodiment, the packet data P1 including the ejection timing information FT and the packet data P2 including the speed identification information FS may be different packet data. In this case, the transmission frequency of the packet data P2 including the speed identification information FS can be made smaller than the transmission frequency of the packet data P1 including the ejection timing information FT. In this case, the communication volume between the head controller 270 and the main controller 70 can be reduced.

[0047] The embodiments disclosed this time are illustrative in all respects and not restrictive. Not all of the components shown in the above embodiments are essential, and the configuration can be changed or omitted as needed.

[0048] In the above embodiment, the number of the head bars 10 was three. However, the present invention is not limited to such an aspect, and the number and position of the head bars 10 can be changed as appropriate. Similarly, the number and position of the heads 11 included in one head group 20 can be changed as appropriate. Also, the number and position of the nozzles 42 included in each head 11 can be changed as appropriate.

[0049] The printing apparatus 1 of the above embodiment includes three head bars 10 and is configured to eject three colors of ink, cyan ink, magenta ink, and yellow ink. The present invention is not limited to such an aspect, and the printing apparatus 1 can be configured to eject ink of an appropriate color. Also, in the present embodiment, UV curable ink was used. However, the present invention is not limited to such an aspect, and ink other than UV curable ink (for example, water-based ink, pigment ink, etc.) can also be used.

[0050] Moreover, the present invention is not necessarily limited to a head bar including a line head, and can be widely applied to a head bar including a plurality of heads. Further, the present invention is not limited to an inkjet printing apparatus that ejects ink. Also, the present teachings can be applied to printing apparatuses used for various purposes other than printing images and the like. For example, it is also possible to apply the present teachings to a printing apparatus that ejects a conductive liquid onto a substrate to form a conductive pattern on the substrate surface. The scope of the present invention is intended to include all modifications within the scope of the claims and the scope equivalent to the claims.

Explanation of Reference Numerals

[0051] 1 Printing apparatus 10 Head bar 11 Head 42 Nozzle 7 Controller 70 Main controller 71 Encoder section 170 Sub-controller 270 Head controller

Claims

1. A head driving method executed by a printing system, wherein the printing system includes a head bar having a plurality of heads and a plurality of head controllers respectively connected to the plurality of heads, a conveyance mechanism configured to convey a recording medium, an encoder that outputs an encoder signal corresponding to the conveyance speed of the recording medium, and a main controller connected to the encoder and the plurality of head controllers, and the driving method includes the main controller detecting the conveyance speed of the recording medium from the encoder signal, the main controller determining ejection timing information based on the encoder signal, generating packet data including the ejection timing information, and transmitting the packet data to the plurality of head controllers, the main controller determining speed identification information according to the detected conveyance speed, generating packet data including the speed identification information, and transmitting the packet data to the plurality of head controllers, the plurality of head controllers determining ejection parameters based on the received speed identification information, and the plurality of head controllers transmitting the ejection timing information and the ejection parameters to the plurality of heads and driving the plurality of heads based on the ejection timing information and the ejection parameters.

2. The head driving method according to claim 1, wherein the packet data including the ejection timing information is the packet data with the highest priority among the packet data transmitted from the main controller to the plurality of head controllers.

3. The head driving method according to claim 1, wherein the main controller generates packet data including the speed identification information and transmits the packet data to the plurality of head controllers in response to a change in the conveyance speed of the recording medium.

4. The head driving method according to claim 1, wherein the main controller generates packet data including the speed identification information and transmits the packet data to the plurality of head controllers regardless of whether the conveyance speed of the recording medium is changing.

5. The head driving method according to claim 3, wherein the main controller generates packet data including the speed identification information and transmits the packet data to the plurality of head controllers even when the conveyance speed of the recording medium has not changed.

6. The head driving method according to claim 4, wherein the plurality of head controllers update the ejection parameters determined based on the speed identification information in response to detecting a speed difference in the conveyance speed from the speed identification information, and transmit the updated ejection parameters to the plurality of heads.

7. The head driving method according to claim 3, wherein the plurality of head controllers transmit the ejection parameters determined based on the speed identification information to the plurality of heads in response to receiving packet data including the speed identification information transmitted from the main controller.

8. The head driving method according to claim 1, wherein the plurality of head controllers transmit initial parameters for initializing the ejection parameters to the plurality of heads after receiving packet data including a printing instruction from the main controller and before driving the plurality of heads.

9. The head driving method according to claim 1, wherein the main controller generates packet data including the ejection timing information and packet data including the speed identification information as one fixed-length packet data including the ejection timing information and the speed identification information.

10. The printing system includes a plurality of head bars, The main controller is connected to the plurality of head controllers respectively included in the plurality of head bars, The head driving method according to claim 9, wherein the main controller determines the speed identification information for each of the plurality of head bars, generates packet data including the speed identification information, and transmits the packet data to the plurality of head controllers.

11. The main controller generates the packet data including the ejection timing information and the packet data including the speed identification information as separate packet data, The frequency at which the main controller transmits the packet data including the speed identification information to the plurality of head controllers is lower than the frequency at which the packet data including the ejection timing information is transmitted to the plurality of head controllers. The head driving method according to claim 1.

12. A head bar having a plurality of heads and a plurality of head controllers respectively connected to the plurality of heads, A conveyance mechanism configured to convey a recording medium, An encoder that outputs an encoder signal corresponding to the conveyance speed of the recording medium; A main controller connected to the encoder and the plurality of head controllers; and The main controller is configured to: Detect the conveyance speed of the recording medium from the encoder signal; Determine ejection timing information based on the encoder signal, generate packet data including the ejection timing information, and transmit the packet data to the plurality of head controllers; Determine speed identification information according to the detected conveyance speed, generate packet data including the speed identification information, and transmit the packet data to the plurality of head controllers; The plurality of head controllers are configured to: Determine ejection parameters based on the speed identification information; Transmit the ejection timing information and the ejection parameters to the plurality of heads, and drive the plurality of heads based on the ejection timing information and the ejection parameters. A printing system is configured as such.

Images