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

The invention relates to a method and an apparatus for determining a state of a filter unit in an ink circuit of a printer. Starting from an initial fill level of an ink container, ink is pumped from an ink reservoir through the filter unit into the ink container with the aid of an ink pump. With the aid of a sensor unit, at least one first fill level value in the ink container is detected, wherein the initial fill level is below the first fill level value. With the aid of the ink pump, ink is pumped into the ink container until the first fill level value is reached, so that at least a predefined volume between the initial fill level and the first fill level value is filled.In high performance ink jet printers having 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 particulates and / or solids from the ink before it is fed to the print heads of the printer. Without an efficient filter unit, these particulates and / or solids would clog the nozzles of the printhead and affect print quality. The filters of the filter unit of a printer are wear-resistant parts and must be replaced in the event of dirt. A printing device with a filter unit is known, for example, from the document DE 10 2020 129 787 A1.Document EP 3 335 884 A1 discloses an ink supply system with a counter which counts the printed ink drops and determines a printed ink volume and a delivery rate of an ink pump on the basis of the number of printed ink dots.Depending on the state and quality of the ink, filter units in high performance printers are often clogged. They then cause sudden downtime of the printer and require unscheduled service operations by service technicians to change the filter of the filter unit only. This is a complicated and costly process. This can also cause long downtime of the printer.To avoid this, all filters can be proactively replaced when only one filter is clogged. Alternatively or additionally, it is also conceivable that, independently of the state of the filters, all the filters of the printer or all the printers of a customer are proactively exchanged after a predetermined time and / or predetermined operating hours and / or predetermined ink consumption quantity. Thus, the filters of a printer can be replaced every month, regardless of the actual fouling of the filters.The proactive switching of the filters solves the problem of surprising downtime of the printer, but is not resource-saving and expensive.The object of the invention is to specify methods and apparatus for determining a state of a filter unit in an ink circuit of a printer.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.The contamination state of the filter unit can be easily determined by the method having the features of claim 1 before the filter unit is so contaminated or is so clogged with dirt particles that sufficient ink can no longer be pumped through the filter unit. The method does not require a proactive replacement of the filters of the printer, but also prevents failures of the printer by clogged filters in that the contamination of the filter can be informed in good time and replacement of the filter can be initiated in good time and not prematurely. In particular, the filter unit has an exchangeable filter. The filter information determined can be output in particular in order to inform an operator or a service technician about the filter state, in particular about a required filter change.It is advantageous if the ink container 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. As a result, the initial fill level can be determined easily and reliably.Furthermore, the initial level of the ink container can be achieved by pumping ink from the ink container with the aid of the ink pump or a further ink pump. As a result, the initial fill level can be easily reached even if, due to the process, a higher fill level is present in the ink container.It is particularly advantageous if the ink pump is controlled with a control voltage in such a way that a pump rotor for driving the pump is prestressed at rest and the pump rotor drives the ink pump at a setpoint rotational speed when the control voltage is raised abruptly and ink is thereby pumped at a constant delivery rate with the aid of the ink pump. This achieves a more rapid attainment of the setpoint rotational speed of the ink pump, with the result that the nominal delivery quantity of the ink pump is achieved relatively quickly. Alternatively, the rotational speed of an electric drive of the ink pump can be increased along an acceleration ramp up to the nominal rotational speed after the ink pump is switched on, wherein as a result, a volume flow reduced by the starting of the ink pump can be determined and can be easily taken into account in the determination of the volume flow by the filter unit. This increases the accuracy in determining the volume flow through the filter unit.It is particularly advantageous if the ink pump is an electrically driven gear pump. This achieves an exact and constant delivery rate. Furthermore, gear pumps are cost-effective and low-maintenance.It is furthermore advantageous if the method is carried out in a print pause and / or every 1 to 2 days and / or every 24 to 48 operating hours. As a result, the filter state is determined sufficiently often to cause a filter exchange in the case of a contaminated filter.It is also advantageous if a value in the range from 60% to 80% of the volume flow with new filter is preset as the limit value. This ensures a sufficient remaining volume flow for the further pressure operation.In particular, when the limit value is reached or undershot, a warning message can be output, preferably to a service center. This ensures that a filter change can be easily initiated.A printer for carrying out the method comprises in particular at least one ink pump for pumping ink, an ink container for providing ink to print heads of the printer, and an ink reservoir for providing ink and at least one filter unit for filtering the ink. Ink is supplied to the printer by means of the ink reservoir, a full ink reservoir being inserted into the printer for this purpose. After the ink is pumped from the ink reservoir by the ink pump, the empty ink reservoir is removed from the printer again and another full ink reservoir is inserted into the printer.The printer can further comprise at least one sensor unit which is designed to detect at least one first fill level value in the ink container.The apparatus having the features of the subordinate apparatus 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 previously mentioned developments.Exemplary embodiments of the invention are explained in more detail below with reference to the schematic drawing. Shown therein are: FIG. 1 is a schematic plan view of a printing device, FIG. 2 shows a block diagram of an arrangement for determining a state of a filter unit in the ink circuit of the printing device, FIG. 3 shows a flow chart for determining a state of a filter unit in the ink circuit, and FIG. 4 shows a diagram in which an exemplary profile of the volume flow through the filter unit is shown as a function of the operating time of the printing device.Fig. 1 is a schematic plan view of a printing apparatus 10 for printing on a web-shaped recording medium 12. Such a printing device is known, for example, from the document DE 10 2014 106 424 A1. The printing apparatus 10 is also generally referred to in this application as a printer 10.The printing device 10 has per primary color at least one printing bar 18 to 24 with one or more illustrated print heads 26 which are arranged transversely to a transport direction T 1 of the continuously drivable, here web-shaped recording medium 12. The recording medium 12 can be produced from paper, cardboard, cardboard, textile, a combination thereof and / or other suitable and printable media.Alternatively to continuously supplied web-shaped recording media 12, individual sheets can also be supplied to the printing apparatus 10.The recording medium 12 is guided through the printing device 10 and in the process is guided past the printing bars 16 to 24 by at least one print head 26 with the aid of a plurality of guide rollers, wherein the print head 26 applies a printed image 28 to the recording medium 12 in the form of printing dots. The printed image 28 is shown in FIG. 1 by way of example as two parallel bars printed over the printable width of the recording medium 12.The recording medium 12 is then further guided to a drying process, not shown, and optionally to a subsequent further printing device, in which the rear side of the recording medium 12 can then be printed. Subsequently or alternatively, the recording medium 12 can be supplied to post-processing, in which the recording medium 12 is cut, folded and / or finally processed in other working steps.For full color printing, four primary colors are typically used, namely CMYK (cyan, magenta, yellow and black). Additional primary colors, such as green, orange or violet, may extend the color gamut of the printing device 10. In addition, still further colors or special inks, such as MICR ink (magnetic ink character recognition=magnetically readable ink), can be present. Each primary color is printed on the recording medium 12 by means of the print heads 26 of a single printing bar 18 to 24. It is likewise possible for transparent special liquids, such as primers or drying improvers, to be applied digitally before or after printing of the printed image 28 likewise with the aid of 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 liquid is printed onto the recording medium 12 with the aid of the printing bar 16. The primer liquid is thus printed onto the recording medium 12 before the printing of the printed image 28.The printing bars 16 to 24 form a printing unit 34. For this purpose, each printing bar 16 to 24 comprises a plurality of print heads 26 which are arranged side by side in two rows in a gap.In FIG. 1, each printing bar 16 to 24 comprises five print heads 26 in order to apply the printed image 28 in a plurality of columns 38 to the recording medium 12. Each print head 26 comprises a plurality of print nozzles 36 (for the sake of simplicity only ten print nozzles are shown in FIG. 1 ), wherein each print nozzle 36 can apply ink droplets of a variable volume to the recording medium 12 in the form of print dots. In practice, each print head 26 may comprise several hundred to several thousand print nozzles 36 directed onto the recording medium 12. The printing nozzles 36 are arranged in a row transversely to the transport direction T 1. With the aid of the printing nozzles 36 of a print head 26, a printed image 28 can be printed over a part of a row 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 T 1. In this case, each print head 26 prints a region of the recording medium 12 beneath the print head 26.In other embodiments, each printhead 26 has multiple rows of print nozzles 36, in which case a region of multiple lines is simultaneously printed on the record carrier 12 beneath the printhead 26.Each printing dot along a line across the printable width of the record carrier 12 is printed by the corresponding print nozzle 36 of the print bar 18-24. The print resolution in the print line direction (transversely to the transport direction T1) is thus determined by the distances of the print dots printed by the print nozzles 36 onto the recording medium 12 to one another. The printing resolution in the transport direction T1, on the other hand, is determined in the case of single-line print heads by the transport speed of the recording medium 12 and the line timing of the print heads 18 to 24 in the case of line-clocked printing. In the case of a plurality of printing nozzle rows, the printing resolution in the transport direction T 1 is dependent on the distance of the printing nozzle rows from one another.In the printing device 10 according to FIG. 1, the print heads 16 to 24 are arranged in a stationary manner. In other embodiments, the print heads 16 to 24 can also preferably be arranged movably transversely to the transport direction T 1.With the aid of a control unit 40, the individual print heads 26 of the printing bars 18 to 24 are controlled on the basis of rastered 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 droplets form individual print dots on the recording medium 12 which, in their entirety, form the print image 28 on the recording medium 12.The area coverage of the printing dots in an area of the recording medium 12 determines the inking intensity in this area. When the recording medium 12 is completely colored with a base color, the coloring intensity is 100%. In the case of half the inking of the recording medium 12, the inking intensity is 50%. In the case where no coloring of the recording medium 12 occurs in the area, the coloring intensity is 0%.Fig. 2 shows a block diagram of an arrangement 30 for determining a state of a filter unit 41 in the ink circuit of the printing device 10. an ink pump 42 delivers ink from an ink reservoir 44 via an ink line 46 through the file unit 41 into an ink container 48. for example, the ink pump 42 is a peristaltic pump, peristaltic pump and / or gear pump, wherein the pumps each preferably have a brushless DC drive with a signal output for a tacho signal. This optional tacho signal can then contain at least one pulse per revolution.The filter unit 42 removes unwanted particulates and / or solids from the ink. The filter unit 42 comprises in particular a filter which can be exchanged for a new filter in the event of contamination.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 in order then to be printed on the recording medium 12. The printing device 10 comprises at least four of the assemblies 30, each supplying a printing bar 18 to 24 with ink. Thus, an array 30 is provided for each of the primary colors CMYK.Furthermore, the primer pressure bar 16 can be supplied with a primer liquid with the aid of an additional arrangement 30. In this case, instead of ink, the primer liquid is supplied from the ink pump 42. When ink is referred to in the description in the context of the assembly 30, the term also includes the primer liquid.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 in order to pump ink. In this case, the control unit 40 can determine the drive speed of the drive of the ink pump with the aid of a rotation sensor (tachometer). The revolution sensor is, for example, a Hall sensor which generates at least one pulse per revolution of a drive shaft and can even determine the fraction of a revolution in the case of a plurality of pulses per revolution. Furthermore, the ink pump 42 can be controlled with a control voltage in such a way that a magnetic field is built up in the electric pump drive and the ink pump 42 is already prestressed without moving the drive shaft. The biasing overcomes the mechanical play present in the pump so as to avoid further inaccuracies. Upon a pump start, the control voltage is then increased abruptly corresponding to a setpoint rotational speed in order to bring the drive shaft to the setpoint rotational speed. By means of the prestressed pump drive, the drive shaft can be accelerated to its desired rotational speed with a greatly shortened acceleration phase. Variations in the discharge efficiency at the start-up of the ink pump 42 can thus be reduced.The ink container 48 of the arrangement 10 comprises at least one sensor unit with a first signal transmitter 52 and a second signal transmitter 54. The sensor unit detects a fill level of the ink container 48. The first signal transmitter 52 detects a first fill level value when ink in the ink container 48 reaches at least the first signal transmitter 52. In FIG. 2, the ink container 48 is shown filled with ink such that the ink has reached the first signal transmitter 52 and thus determines a first fill level value. The second signal transmitter 54 correspondingly determines a second fill level value that lies below the first fill level value.The ink volume of the ink container 48 between the first and second fill level values is predetermined. That is, a predefined volume is located between the first and the second fill level value. The ink container 48 is precisely manufactured and the sensor unit is precisely arranged, so that the corresponding volume can be calculated very precisely over the different ink containers.Alternatively, the sensor unit of the ink container 48 can 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 can be an ultrasonic sensor.The control unit 40 is designed to determine the switch-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.On the basis of the determined switch-on time and the predefined volume, the control unit 40 determines the volume flow through the filter unit 41. the volume flow is dependent in particular on the filter state, i.e. on the contamination state, of the filter unit 41. The volume flow determined is compared with a preset stored limit value. If and / or if the ascertained volume flow reaches and / or falls below the limit value, a certain degree of contamination is reached. As a result, filter state information can be determined already before the ink supply to the ink container 48 is impaired, by means of which filter state information can be initiated at an early stage. Preventive replacement of the filter is thus no longer required, whereby resources and thus costs can be saved.Furthermore, in other embodiments, a degassing unit may 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 adapted or regulated. Further, the filter unit 41 may be disposed after the pump 42 in the ink conduit 46.FIG. 3 shows a flow chart for ascertaining a state of the filter unit 41 in the ink circuit or in the ink line 46, and the method starts in step S 100. In step S 102, 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 is present. If the second signaling device 54 is not present or not in use, the ink container 48 can be emptied completely. In this case, the ink supply 46' and / or discharge 50' may preferably be located at the deepest point of the ink container 48 (see dotted lines 46', 50'). In this case, the ink pump 42 and / or 43 is controlled by the control unit 40 in such a way that ink is pumped from the ink container 48 into the ink reservoir 44. If the control unit 40 detects the second fill level value with the aid of the second signal transmitter 54, the ink pump 42 (and / or 43) is stopped during the idle pumping if the second fill level value is no longer detected. This ensures that the fill level after step S 102 is reliably below the second fill level value. If the ink container 48 is already empty, for example, at maintenance, step S102 may be skipped. In other measuring methods, such as an ultrasonic fill level measurement, the ink pump 42, 43 can also be stopped when the second fill level value is reached.In step S104, the ink pump 42 is driven to pump ink from the ink reservoir 44 into the ink container 48.In step S 106, the time required to pump the ink into the ink container 48 until the first fill level value is reached is recorded with the aid of the control unit 40. When using the second signal transmitter 54, the second (lower) fill level value is detected in advance before the first (higher) fill level value. The control unit 40 detects the time of activation of the ink pump 42 from reaching the second fill level value to reaching the first fill level value. The time required to fill the predefined volume between the second fill level value and the first fill level value is thus determined. If the second signal transmitter 54 remains unused or is not present, the second fill level value is zero.In step S 108, the flow rate, i.e. the volume flow, is determined by the filter unit 41 with the aid of the control unit 40 starting from the determined time and the predefined volume.Subsequently, in step S 110, the ascertained volume flow is compared with a preset stored volume flow limit value with the aid of the control unit 40. In step S 112, the state of the filter unit 41 is then determined with the aid of the control unit 40. If the comparison of the ascertained volume flow value with the preset stored volume flow limit value reveals that the ascertained volume flow value does not fall below the volume flow limit value, the volume flow through the filter unit 41 is okay and it can be assumed that the filter unit 41 is not contaminated or is only contaminated to a slight extent. However, if the volume flow value determined is equal to or less than the preset stored volume flow limit value, the filter is at least considerably contaminated. The preset stored volume flow limit value is selected in such a way that the printing device 10 can still be safely operated further. The volume flow limit value can be selected in particular such that the printing device 10 can still continue to be operated safely for at least a predefined number of operating hours, so that sufficient time remains to carry out an orderly replacement of the filter of the filter unit 41 or to plan a service use of a service technician for replacing the filter. Then, in step S 114, the flow is ended.FIG. 4 shows a diagram in which an exemplary profile 60 of the volume flow through the filter unit 41 is illustrated as a function of the operating time of the printing device 10. The time t indicates the hours of operation of the printing apparatus 10. The volume flow is given in milliliters per minute. In the case of a new, non-dirty filter of the filter unit 41, the volume flow is 700 milliliters per minute. As the fouling of the filter unit 41 increases, the volume flow through the filter unit 41 falls. A relevant fouling is established starting from a volume flow of 650 milliliters per minute. The preset stored volume flow limit value is 650 milliliters per minute in this exemplary embodiment. When this volume flow limit value is reached or undershot, a service request for replacing the filter of the filter unit 41 is preferably automatically generated and / or an item of information for contamination of the filter of the filter unit 41 is output to an operator of the printing apparatus 10. This occurs before failure of the printing system 10 occurs. Failure of the printing system 10 due to insufficient ink supply threatens from a volumetric flow rate of 500 milliliters per minute. In the period 62, sufficient time therefore remains to change the filter of the filter unit 41.It is advantageous to determine the flow rate, i.e. the volume flow, of the ink pump 42 at a distance of several days and to use the determined volume flow as an indicator for the state of the filter of the filter unit 41.The invention is based on the general knowledge that the state of the filter of the filter unit 41 has a strong influence on the delivery rate of the ink pump 42, so that the delivery rate of the ink pump 42 can be used as an indicator for the degree of contamination of the filter of the filter unit 41.The invention allows a planned filter change to be carried out. The change can then be planned in particular when the printer is not in operation. Then, all filters showing signs of clogging and no other unstained filters can be changed at the proper time. The downtime of the printing device 10 is thereby reduced.List of reference characters10 Printing device 12 16, 18, 20, 22, recording medium 24 printing bar 26 print head 28 print image 30 arrangement for determining a state of a filter unit 34 printing unit 36 printing nozzle 38 column 40 control unit 41 filter unit 42 ink pump 44 ink reservoir 46 ink line 48 ink container 50 printing bar ink line 52 first signal transmitter 54 second signal transmitter 60 graph 62 exchange period T 1 transport directionReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2020 129 787 A1

[0002] EP 3 335 884 A1

[0003] DE 10 2014 106 424 A1

[0021]

Claims

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) by means of an ink pump (42) into the ink container (48) through the filter unit (41), in which at least one first fill level value in the ink container (48) is detected by means of a sensor unit (52, 54), wherein the initial fill level is below the first fill level value, in which ink is pumped into the ink container (48) by means of the ink pump (42) until the first fill level value is reached, such that at least one predefined volume is filled between the initial fill level and the first fill level value, in which the time of the activated ink pump (42) until the first fill level value is detected, and in which the volume flow is determined by the filter unit (41) on the basis of the predetermined volume and the detected time, and in which the determined volume flow is compared with a volume flow limit value, wherein filter state information is generated at least when the volume flow limit value is reached or undershot.The method of claim 1, wherein the ink container (48) is empty at the initial fill level.Method according to one of the preceding claims, in which the sensor unit (52, 54) detects a second fill level value and the initial fill level corresponds to the second fill level value.Method according to one of the preceding claims, in which the initial filling level of the ink container (48) is achieved by ink being pumped out of the ink container (48) by means of the ink pump (42) or a further ink pump (43).Method according to one of the preceding claims, in which the ink pump (42) is controlled with a control voltage in such a way that a pump rotor is prestressed at rest and the pump rotor drives the ink pump (42) at a setpoint rotational speed when the control voltage is raised abruptly, and ink is thereby pumped at a constant delivery rate with the aid of the ink pump (42).The method of any preceding claim, wherein the ink pump (42) is an electrically driven gear pump.Method according to one of the preceding claims, wherein the method is carried out in a print pause and / or every 1 to 2 days and / or every 24 to 48 operating hours.Method according to one of the preceding claims, in which a value in the range from 60% to 80% of the volume flow with new filter is preset as the limit value.Method according to one of the preceding claims, in which, when the limit value is reached or undershot, a warning message is issued, preferably to a service centre.Device for determining a state of a filter unit in an ink circuit of a printer (10), the device comprising at least one ink pump (42) for pumping ink, an ink container (48) for supplying ink to print heads (26) of the printer (10), and an ink reservoir (44) for supplying ink and at least one filter unit (41) for filtering the ink, having at least one sensor unit (52, 54) which is designed to detect at least one 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 to pump ink from the ink reservoir (44) through the filter unit into the ink container (48) starting from an initial fill level of the ink container (48) until the first fill level value is reached, so that at least one predefined volume between the initial fill level and the first fill level value is pumped by the filter unit (41), with a control unit (40) which is designed to record at least the time of the activated ink pump (42) until the first fill level value is reached, wherein the control unit (40) is furthermore designed to determine the volume flow through the filter unit (41) on the basis of the predefined volume and the recorded time, and wherein the control unit (40) is furthermore designed to compare the determined volume flow with a volume flow limit value, wherein the control unit (40) is designed to generate filter state information at least when the volume flow limit value is reached or undershot.

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