Method and device for determining a state of a filter unit in an ink circuit of a printer

Abstract

In a method and device for determining a state of a filter unit (41) in an ink circuit of a printer (10), starting from an initial fill level of an ink container (48), ink is pumped from an ink reservoir (48) through the filter unit (41) into the ink container (48) with the aid of an ink pump (42) until the first fill level is reached, so that at least a predetermined volume between the initial fill level and the first fill level is filled. The time it takes for the ink pump (42) to be activated until the first fill level is reached is recorded. Based on the predetermined volume and the recorded time, the volume flow of the ink through the filter unit (41) is determined. The determined volume flow is compared with a volume flow limit value, wherein filter status information is generated at least when the volume flow limit value is reached or undershot.

Description

[0001] The invention relates to a method and a device for determining the status of a filter unit in an ink circuit of a printer. Starting from an initial fill level of an ink container, an ink pump is used to pump ink from an ink reservoir through the filter unit into the ink container. A sensor unit detects at least a first fill level value in the ink container, wherein the initial fill level is below the first fill level value. The ink pump pumps ink into the ink container until the first fill level value is reached, so that at least a predetermined volume between the initial fill level and the first fill level value is filled.

[0002] In high-performance inkjet printers with print speeds of greater than 1 m / s up to currently 3 m / s, filter units are used to filter the ink to remove unwanted suspended matter and / or solids from the ink before it is fed to the printer's print heads. Without an efficient filter unit, these suspended matter and / or solids would clog the print head nozzles and impair print quality. The filters in a printer's filter unit are wear parts and must be replaced when dirty. A printing device with a filter unit is known, for example, from document DE 10 2020 129 787 A1.

[0003] Document EP 3 335 884 A1 discloses an ink supply system having a counter that counts the printed ink drops and, based on the number of printed ink drops, determines a printed ink volume and a feed rate of an ink pump.

[0004] Depending on the condition and quality of the ink, filter units in high-performance printers often become clogged. This causes sudden printer downtime and requires unscheduled service calls from service technicians just to change the filter unit's filter. This is a time-consuming and costly procedure. It can also cause long printer downtimes.

[0005] To avoid this, all filters can be proactively replaced if only one filter is clogged. Alternatively, or additionally, it is also conceivable that all filters of the printer or all of a customer's printers are proactively replaced after a specified time and / or specified operating hours and / or specified ink consumption, regardless of the filter condition. This way, the filters of a printer can be replaced every month, regardless of the actual filter contamination.

[0006] While proactively changing filters solves the problem of unexpected printer downtime, it is not resource-efficient and is expensive.

[0007] The object of the invention is to provide a method and device for determining a state of a filter unit in an ink circuit of a printer.

[0008] This object is achieved by a method having the features of claim 1 and by a device having the features of the independent device claim. Advantageous further developments are specified in the dependent claims.

[0009] Using the method having the features of claim 1, the contamination level of the filter unit can be easily determined before the filter unit becomes so dirty or clogged with dirt particles that sufficient ink can no longer be pumped through the filter unit. The method eliminates the need for proactive replacement of the printer's filters, but also prevents printer failures caused by clogged filters by providing timely information about filter contamination and allowing the filter to be replaced in a timely manner and not prematurely. In particular, the filter unit has a replaceable filter. The determined filter information can be output, in particular, to inform an operator or service technician about the filter status, in particular about a required filter change.

[0010] It is advantageous if the ink tank is empty at the initial fill level. Alternatively or additionally, the sensor unit can detect a second fill level value, and the initial fill level corresponds to the second fill level value. This allows the initial fill level to be determined easily and reliably.

[0011] Furthermore, the initial fill level of the ink tank can be reached by pumping ink from the ink tank using the ink pump or another ink pump. This makes it easy to reach the initial fill level, even if the ink tank is at a higher level due to process-related reasons.

[0012] It is particularly advantageous if the ink pump is controlled by a control voltage in such a way that a pump rotor is pre-tensioned to drive the pump at rest and, when the control voltage is suddenly increased, the pump rotor drives the ink pump at a set speed, thereby pumping ink with the help of the ink pump at a constant feed rate. This ensures that the set speed of the ink pump is reached more quickly, so that the nominal feed rate of the ink pump is reached relatively quickly. Alternatively, the speed of an electric drive of the ink pump can be increased along an acceleration ramp up to the nominal speed after the ink pump has been switched on. This allows the reduced volume flow caused by the start-up of the ink pump to be determined and easily taken into account when determining the volume flow through the filter unit. This increases the accuracy when determining the volume flow through the filter unit.

[0013] It is particularly advantageous if the ink pump is an electrically driven gear pump. This ensures a precise and consistent flow rate. Furthermore, gear pumps are cost-effective and low-maintenance.

[0014] Furthermore, it is advantageous if the process is performed during a printing break and / or every 1 to 2 days and / or every 24 to 48 operating hours. This ensures that the filter condition is determined frequently enough to prompt a filter replacement if it becomes contaminated.

[0015] It is also advantageous to preset the limit value to a value in the range of 60% to 80% of the flow rate with the new filter installed. This ensures sufficient remaining flow rate for continued printing operations.

[0016] In particular, a warning message can be issued when the limit is reached or exceeded, preferably to a service center. This ensures that a filter change can be easily arranged.

[0017] A printer for carrying out the method comprises, in particular, at least one ink pump for pumping ink, an ink container for providing ink for the printer's print heads, an ink reservoir for providing ink, and at least one filter unit for filtering the ink. Ink is supplied to the printer with the aid of the ink reservoir, with a full ink reservoir being inserted into the printer for this purpose. After the ink has been pumped out of the ink reservoir with the aid of the ink pump, the empty ink reservoir is removed from the printer, and another full ink reservoir is inserted into the printer.

[0018] The printer may further comprise at least one sensor unit configured to detect at least a first fill level value in the ink container.

[0019] The device with the features of the independent device claim has the same advantages as the claimed method. In particular, the device can be further developed with the features of the dependent claims directed to the method and the aforementioned developments.

[0020] Embodiments of the invention are explained in more detail below with reference to the schematic drawings, in which: Fig. 1 a schematic plan view of a printing device, Fig. 2 a block diagram of an arrangement for determining a state of a filter unit in the ink circuit of the printing device, Fig. 3 a flow chart for determining a state of a filter unit in the ink circuit, and Fig. 4 a diagram showing an exemplary course of the volume flow through the filter unit as a function of the operating time of the pressure device.

[0021] Fig. Figure 1 shows a schematic plan view of a printing device 10 for printing on a web-shaped recording medium 12. In the exemplary embodiment, the printing device 10 is embodied as a known inkjet printing device. Such a printing device is known, for example, from document DE 10 2014 106 424 A1. The printing device 10 is also generally referred to as printer 10 in this application.

[0022] The printing device 10 has at least one printing bar 18 to 24 per primary color with one or more illustrated print heads 26, which are arranged transversely to a transport direction T1 of the continuously drivable, web-shaped recording medium 12. The recording medium 12 can be made of paper, cardboard, paperboard, textile, a combination thereof, and / or other suitable and printable media.

[0023] As an alternative to continuously fed web-shaped recording media 12, individual sheets can also be fed to the printing device 10.

[0024] The recording medium 12 is guided through the printing device 10 and is guided past the printing bars 16 to 24 with at least one print head 26 by means of several guide rollers, wherein the print head 26 applies a print image 28 to the recording medium 12 in the form of print dots. The print image 28 is in Fig. 1 is shown as an example as two parallel bars printed across the printable width of the recording medium 12.

[0025] The recording medium 12 is then fed to a drying device (not shown) and, if necessary, to a subsequent printing device, in which, in particular, the reverse side of the recording medium 12 can then be printed. Subsequently, or alternatively, the recording medium 12 can be fed to a post-processing stage in which the recording medium 12 is cut, folded, and / or finished in other processing steps.

[0026] For full-color printing, four primary colors are typically used: CMYK (cyan, magenta, yellow, and black). Additional primary colors, such as green, orange, or violet, can expand the color gamut of the printing device 10. Furthermore, other colors or special inks, such as MICR ink (Magnetic Ink Character Recognition), can be present. Each primary color is printed onto the recording medium 12 using the print heads 26 of a single printing bar 18 to 24. It is also possible for transparent special liquids, such as primers or drying enhancers, to be digitally applied before or after printing the printed image 28, also using a separate printing bar, in order to improve the print quality or the adhesion of the ink to the recording medium 12. In the embodiment according to Fig. 1, a primer fluid is printed onto the recording medium 12 using the printing bar 16. The primer fluid is thus printed onto the recording medium 12 before the print image 28 is printed.

[0027] The printing bars 16 to 24 form a printing unit 34. Each of the printing bars 16 to 24 of the printing device 10 can perform line-width printing. For this purpose, each printing bar 16 to 24 comprises several print heads 26 arranged in two rows, spaced apart from one another.

[0028] In Fig. 1, each printing bar 16 to 24 comprises five print heads 26 to apply the print image 28 in several columns 38 onto the recording medium 12. Each print head 26 comprises a plurality of print nozzles 36 (in Fig. 1, only ten print nozzles are shown for the sake of simplicity), whereby each print nozzle 36 can apply ink drops of a variable volume to the recording medium 12 in the form of print dots. In practice, each print head 26 can comprise several hundred to several thousand print nozzles 36 directed onto the recording medium 12. The print nozzles 36 are arranged in a row transversely to the transport direction T1. With the help of the print nozzles 36 of a print head 26, a print image 28 can be printed over part of a line along the printable width of the recording medium 12 and in the form of one of the columns 38 over the length of the recording medium 12 in the transport direction T1. Each print head 26 prints an area of the recording medium 12 below the print head 26.

[0029] In other embodiments, each print head 26 has multiple rows of print nozzles 36. In this case, an area with multiple lines is printed simultaneously on the recording medium 12 below the print head 26.

[0030] Each print dot along a line across the printable width of the recording medium 12 is printed by the corresponding print nozzle 36 of the print bar 18 to 24. The print resolution in the print line direction (transverse to the transport direction T1) is thus determined by the distances between the print dots printed by the print nozzles 36 on the recording medium 12. The print resolution in the transport direction T1, however, is determined for single-line print heads by the transport speed of the recording medium 12 and the line timing of the print heads 18 to 24 during line-clocked printing. With multiple rows of print nozzles, the print resolution in the transport direction T1 depends on the distance between the rows of print nozzles.

[0031] In the printing device 10 according to Fig. 1, the print heads 16 to 24 are arranged stationary. In other embodiments, the print heads 16 to 24 can also be arranged to be movable, preferably transverse to the transport direction T1.

[0032] With the aid of a control unit 40, the individual print heads 26 of the printing bars 18 to 24 are controlled based on rasterized print data, so that the individual ink drops are applied to the position of the recording medium 12 defined by the print data. The individual ink drops form individual print dots on the recording medium 12, which, as a whole, form the print image 28 on the recording medium 12.

[0033] The area coverage of the printing dots in a region of the recording medium 12 determines the inking intensity in that region. When the recording medium 12 is completely inked with a primary color, the inking intensity is 100%. When the recording medium 12 is only half inked, the inking intensity is 50%. If the recording medium 12 is not inked in that region, the inking intensity is 0%.

[0034] Fig. Figure 2 shows a block diagram of an arrangement 30 for determining the status of a filter unit 41 in the ink circuit of the printing device 10. An ink pump 42 pumps ink from an ink reservoir 44 via an ink line 46 through the filter unit 41 into an ink container 48. For example, the ink pump 42 is a hose pump, peristaltic pump, and / or gear pump, each of which preferably has a brushless DC drive with a signal output for a tachometer signal. This optional tachometer signal can then contain at least one pulse per revolution.

[0035] The filter unit 42 removes unwanted suspended matter and / or solids from the ink. The filter unit 42 comprises, in particular, a filter that can be replaced with a new filter when it becomes dirty.

[0036] Via a printing bar ink line 50, one of the printing bars 18 to 24 is supplied with ink, or the ink is transported to one of the printing bars 18 to 24, to then be printed onto the recording medium 12. The printing device 10 comprises at least four of the assemblies 30, each of which supplies a printing bar 18 to 24 with ink. Thus, an assembly 30 is provided for each of the primary colors CMYK.

[0037] Furthermore, the primer pressure bar 16 can be supplied with a primer fluid using an additional assembly 30. In this case, the primer fluid is pumped by the ink pump 42 instead of ink. When ink is mentioned in the description in connection with the assembly 30, the term also includes the primer fluid.

[0038] Furthermore, the ink pump 42 comprises, in particular, a so-called BLDC drive, which can be controlled via the control unit 40 of the printing device 10 to pump ink. The control unit 40 can determine the drive speed of the ink pump drive with the aid of a rotation sensor (tachometer). The rotation sensor is, for example, a Hall sensor that generates at least one pulse per rotation of a drive shaft and, in the case of multiple pulses per rotation, can even determine a fraction of a rotation. Furthermore, the ink pump 42 can be controlled with a control voltage such that a magnetic field is created in the electric pump drive and the ink pump 42 is already preloaded without moving the drive shaft. This preload overcomes the existing mechanical play in the pump, thus avoiding further inaccuracies.When the pump starts, the control voltage is then abruptly increased according to a target speed to bring the drive shaft to the target speed. The preloaded pump drive allows the drive shaft to accelerate to its target speed with a significantly shortened acceleration phase. Fluctuations in the pumping efficiency during start-up of ink pump 42 can thus be reduced.

[0039] The ink container 48 of the arrangement 10 comprises at least one sensor unit with a first signal generator 52 and a second signal generator 54. The sensor unit detects a fill level of the ink container 48. The first signal generator 52 detects a first fill level value when ink in the ink container 48 reaches at least the first signal generator 52. In Fig. In Figure 2, the ink container 48 is shown filled with ink such that the ink has reached the first signal transmitter 52, thus determining a first fill level value. The second signal transmitter 54 correspondingly determines a second fill level value, which is below the first fill level value.

[0040] The ink volume of the ink container 48 between the first and second fill level values is predetermined. This means that there is a predetermined volume between the first and second fill level values. The ink container 48 is precisely manufactured and the sensor unit is precisely positioned, so that the corresponding volume across the various ink containers can be calculated very accurately.

[0041] Alternatively, the sensor unit of the ink container 48 may comprise only one signal transmitter, which either determines only one fill level value or determines the continuous fill level value of any fill level within a sensor range. For example, the sensor unit may be an ultrasonic sensor.

[0042] The control unit 40 is designed to determine the switching-on time of the pump 41 for pumping ink into the ink container 48, which is required starting from the second fill level value until the first fill level value is reached.

[0043] Based on the determined switch-on time and the specified volume, the control unit 40 determines the volume flow through the filter unit 41. The volume flow depends in particular on the filter condition, i.e. on the contamination level, of the filter unit 41. The determined volume flow is compared with a preset, stored limit value. If the determined volume flow reaches and / or falls below the limit value, a certain degree of contamination has been reached. This makes it possible to determine filter condition information before the ink supply to the ink container 48 is impaired, which can be used to initiate filter replacement at an early stage. A preventative replacement of the filter is therefore no longer necessary, which saves resources and therefore costs.

[0044] Furthermore, in other embodiments, a degassing unit can be provided before and / or after the filter unit 41. Such a degassing unit removes gas inclusions, in particular air bubbles and / or gases dissolved in the ink, from the ink. Furthermore, in alternative embodiments, a heat exchanger can be provided in the ink line 46, with the aid of which the temperature of the ink can be adjusted or regulated. Furthermore, the filter unit 41 can also be arranged after the pump 42 in the ink line 46.

[0045] Fig. 3 shows a flowchart for determining a state of the filter unit 41 in the ink circuit or in the ink line 46. The method starts in step S100. In step S102, the ink pump 42 and / or the ink pump 43 arranged in line 50 is activated in order to lower the fill level in the ink container 48 below the second fill level value, if such a value exists. If the second signal generator 54 is not present or not in use, the ink container 48 can be completely emptied. In this case, the ink supply 46' and / or discharge 50' can preferably be arranged at the lowest point of the ink container 48 (see lines 46', 50' shown in dashed lines). The ink pump 42 and / or 43 is controlled by the control unit 40 such that ink is pumped from the ink container 48 into the ink reservoir 44.When the control unit 40 detects the second fill level value using the second signal generator 54, the ink pump 42 (and / or 43) is stopped during emptying when the second fill level value is no longer detected. This ensures that the fill level is reliably below the second fill level value after step S102. If the ink container 48 is already empty, for example, during maintenance, step S102 can be skipped. With other measurement methods, such as ultrasonic level measurement, the ink pump 42, 43 can also be stopped when the second fill level value is reached.

[0046] In step S104, the ink pump 42 is controlled so that ink is pumped from the ink reservoir 44 into the ink container 48.

[0047] In step S106, the time required to pump the ink into the ink container 48 until the first fill level is reached is recorded with the help of the control unit 40. When the second signal generator 54 is used, the second (lower) fill level is recorded before the first (higher) fill level. The control unit 40 records the time from the activation of the ink pump 42 from the moment the second fill level is reached until the first fill level is reached. This determines the time required to fill the specified volume between the second fill level and the first fill level. If the second signal generator 54 remains unused or is not present, the second fill level is zero.

[0048] In step S108, the flow rate, ie the volume flow, through the filter unit 41 is determined with the aid of the control unit 40 based on the determined time and the predetermined volume.

[0049] Subsequently, in step S110, the determined volume flow is compared with a preset, stored volume flow limit value using the control unit 40. In step S112, the status of the filter unit 41 is then determined with the help of the control unit 40. If the comparison of the determined volume flow value with the preset, stored volume flow limit value shows that the determined volume flow value does not fall below the volume flow limit value, the volume flow through the filter unit 41 is OK and it can be assumed that the filter unit 41 is not or only slightly contaminated. However, if the determined volume flow value is equal to or less than the preset, stored volume flow limit value, the filter is at least significantly contaminated. The preset, stored volume flow limit value is selected such that the printing device 10 can still be operated safely.The volume flow limit can, in particular, be selected such that the pressure device 10 can continue to operate safely for at least a predetermined number of operating hours, leaving sufficient time to perform an orderly replacement of the filter of the filter unit 41 or to schedule a service call by a service technician to replace the filter. The process then ends in step S114.

[0050] Fig.4 shows a diagram illustrating an exemplary curve 60 of the volume flow through the filter unit 41 as a function of the operating time of the printing device 10. Time t indicates the operating hours of the printing device 10. The volume flow is specified in milliliters per minute. For a new, uncontaminated filter in the filter unit 41, the volume flow is 700 milliliters per minute. As the filter unit 41 becomes increasingly contaminated, the volume flow through the filter unit 41 decreases. Relevant contamination is detected from a volume flow of 650 milliliters per minute. The preset, stored volume flow limit value in this exemplary embodiment is 650 milliliters per minute.When this volume flow limit is reached or undershot, a service order to replace the filter of the filter unit 41 is preferably automatically generated and / or information regarding the contamination of the filter of the filter unit 41 is issued to an operator of the printing device 10. This occurs before a failure of the printing system 10 occurs. A failure of the printing system 10 due to insufficient ink supply is imminent at a volume flow of 500 milliliters per minute or more. Thus, sufficient time remains within the period 62 to replace the filter of the filter unit 41.

[0051] It is advantageous to determine the flow rate, ie the volume flow, of the ink pump 42 at intervals of several days and to use the determined volume flow as an indicator of the condition of the filter of the filter unit 41.

[0052] The invention is based on the general finding that the condition of the filter of the filter unit 41 has a strong influence on the delivery capacity of the ink pump 42, so that the delivery capacity of the ink pump 42 can be used as an indicator of the degree of contamination of the filter of the filter unit 41.

[0053] The invention enables a scheduled filter change. The change can then be scheduled, especially when the printer is not in operation. Then, all filters showing signs of clogging, and no other uncontaminated filters, can be changed at the right time. This reduces downtime of the printing device 10. List of reference symbols 10 Printing device 12 recording media 16, 18, 20, 22, 24 pressure bars 26 Print head 28 Print image 30 Arrangement for determining a condition of a filter unit 34 printing unit 36 pressure nozzle 38 column 40 Control unit 41 Filter unit 42 Ink pump 44 ink reservoirs 46 Ink line 48 ink tanks 50 printing bar ink line 52 First signal generator 54 Second signal generator 60 graphs 62 Exchange period T1 transport direction

Claims

[1] Method for determining a state of a filter unit in an ink circuit of a printer, in which, starting from an initial fill level of an ink container (48), ink is pumped from an ink reservoir (44) through the filter unit (41) into the ink container (48) by means of an ink pump (42), in which at least a first fill level value in the ink container (48) is detected with the aid of a sensor unit (52, 54), the initial fill level being below the first fill level value, in which ink is pumped into the ink container (48) with the aid of the ink pump (42) until the first fill level is reached, so that at least a predetermined volume between the initial fill level and the first fill level is filled, in which the time of the activated ink pump (42) until the first fill level value is reached is recorded, and in which the volume flow through the filter unit (41) is determined on the basis of the predetermined volume and the recorded time, and in which the determined volume flow is compared with a volume flow limit value, wherein filter status information is generated at least when the volume flow limit value is reached or undershot. [2] The method of claim 1, wherein the ink container (48) is empty at the initial fill level. [3] Method according to one of the preceding claims, wherein the sensor unit (52, 54) detects a second fill level value and the initial fill level corresponds to the second fill level value. [4] Method according to one of the preceding claims, in which the initial fill level of the ink container (48) is achieved by pumping ink out of the ink container (48) with the aid of the ink pump (42) or a further ink pump (43). [5] Method according to one of the preceding claims, in which the ink pump (42) is controlled by a control voltage in such a way that a pump rotor is pretensioned at rest and the pump rotor drives the ink pump (42) at a desired speed when the control voltage is suddenly increased and ink is thereby pumped by means of the ink pump (42) at a constant feed rate. [6] Method according to one of the preceding claims, wherein the ink pump (42) is an electrically driven gear pump. [7] Method according to one of the preceding claims, wherein the method is carried out during a printing break and / or every 1 to 2 days and / or every 24 to 48 operating hours. [8] Method according to one of the preceding claims, in which a value in the range of 60% to 80% of the volume flow with a new filter is preset as the limit value. [9] Method according to one of the preceding claims, in which a warning message is issued, preferably to a service center, when the limit value is reached or undershot. [10] Device for determining a state of a filter unit in an ink circuit of a printer (10), wherein the device comprises at least one ink pump (42) for pumping ink, an ink container (48) for providing ink for print heads (26) of the printer (10), and an ink reservoir (44) for providing ink and at least one filter unit (41) for filtering the ink, with at least one sensor unit (52, 54) which is designed to detect at least a first fill level value in the ink container (48), wherein the initial fill level is below the first fill level value, wherein the ink pump (42) is designed, starting from an initial fill level of the ink container (48), to pump ink from the ink reservoir (44) through the filter unit into the ink container (48) until the first fill level value is reached, so that at least a predetermined volume between the initial fill level and the first fill level value is pumped through the filter unit (41), with a control unit (40) which is designed to detect at least the time of the activated ink pump (42) until the first fill level value is reached, wherein the control unit (40) is further designed to determine the volume flow through the filter unit (41) based on the predetermined volume and the detected time, and wherein the control unit (40) is further designed to compare the determined volume flow with a volume flow limit value, wherein the control unit (40) is designed to generate filter status information at least when the volume flow limit value is reached or undershot.

Images