Patent Application
20230271433
Various of the disclosed embodiments concern increasing the productivity of inkjet printers when using materials of poor or inconsistent quality.
Various print media present a challenge for efficient print production. This is especially true for such media as corrugated cardboard, where tolerances for such factors as height can vary widely and where such media due to their nature are subject to warping and other deformation. When confronted with such variability in media height a printer may print some such media in a satisfactory manner because the height of such media is optimal for the printer while other such media may result in a low-quality print or, in some cases, may be of such thickness as to collide with the printheads or other portions of the printer mechanism, thus jamming and potentially damaging the printer. As a result, printer efficiency is impacted.
Embodiments of the invention maintain consistent operation of a digital inkjet printer by reducing the requirements for media flatness. This prevents out of tolerance, warped, or damaged substrates from stopping the printing process in an inkjet printer and thus enhances robustness and productivity in real world conditions. To achieve the foregoing, several actions are executed when media thickness is measured at the printer and is determined to be out of specification. For example, when the media is of sufficient height to jam or damage the printer the print signal to the printheads is disabled, immediately stopping the printing process; the printheads are lifted to a safe position to avoid collision with the media; and when the media is of not of sufficient height to jam or damage the printer media but are sufficiently out of specification that they should not printed such media are rejected and routed to a reject facility instead of being stacked in line.
Embodiments of the invention provide a method and apparatus in which a digital inkjet printer processes media that are warped, deformed, and/or that have a variable thickness beyond that acceptable for quality printing. Operating the printer during production to manage a wide range of media height variations maximizes printer productivity by avoiding production stoppages that are due to warped or damaged media or media that otherwise does not conform to thickness tolerances.
Embodiments of the invention use one or several sensors to determine the highest point of each sheet of incoming media over a reference surface of the media transportation system, e.g. the upper surface of the conveyor belt of the printer and, based on the difference between the read value and the nominal media thickness, a control system determines if it is possible to keep the printer working.
If the media is too warped and there is physical risk for the printer, embodiments stop operation of the printer. If there is no collision risk, the system evaluates if adequate printing can be achieved or not.
If the media can be printed, embodiments adjust the height of the printheads to prevent interference with the media and thus keep the printheads within acceptable limits for adequate print quality relative to upper media surface distance.
If the media is too warped to be printed, the media is rejected without printing in a seamless manner after passing through the printer, without stopping or slowing down the production process. This results in maximum productivity for non-ideal media without negatively affecting the safety or productivity of the printer.
These actions avoid stacking substrates that have printing quality issues, save ink when the printheads are lifted, and reduce printer downtime. For example, by cancelling a print order when the detection system detects faulty media, the printheads stop the printing process. This means the printheads stop transferring ink through their ink nozzles. This avoids using ink for media that are inside the printer or that are just about to enter the printer, and that to be rejected subsequently due to low quality issues.
Print quality is related to the distance between the printheads and the substrate when the printheads are jetting the ink onto the substrate. The more distance between them, the lower the quality of the print. If the printheads are moved while printing, the quality can be affected and reduced. Because of that, the more common strategy is to allocate the printheads at a jetting gap distance with a balance between the quality and the need to move it because of a jam risk.
In embodiments, a print height detection system may be compounded by several photoelectric sensors, depending on the application this number varies from 3 to “n.” Photoelectric sensors use light sensitive elements to detect objects and are made up of an emitter (light source) and a receiver.
There are many distinct types of light sensitive sensors:
For this application only Thru-Beam and Retroreflective sensors are valid, so performance does not depend on object’s reflectivity properties for detection.
Sensor light beams are parallel to the printer transport belt surface, so it is possible to detect the highest thickness of the substrate whenever its position all along the width of the substrate as the substrate passes below the sensor block.
In embodiments detection with one sensor is also possible using CCD emitter-receiver sensors with a range of detection bigger than the maximum thickness of substrates admitted to the printer.
Due to its reduced dimensions and the low quantity of elements that the height sensing assembly requires, it may be retrofitted printers that are already in operation and working in the field. In such case, an easy mechanical refurbishment and an update of the industrial controller program is required.
There is a control system embedded in a programmable logic controller, henceforth called PLC, which manages all physical processes in the printer. Some of these physical processes are the electrical signals sent by sensors when they detect the substrate. Signals from each sensor are mapped into the embedded program. Connected to some of the digital inputs of the controllers, the information of the sensors arrives at the control system and actions can be taken with that information.
Each sensor relative position referenced to Sensor 1 is parameterized in the control system. The PLC adjusts the position of the motors, i.e. both the motor of the sensor block and the motor of the printhead assembly. The detection system is adjusted by the user with three main parameters: nominal board thickness, jetting gap distance, Sensor 1 offset and faulty media trigger sensor. All these parameters are configured by the user through a user interface application (see
Sensor 1 is the sensor that is used to detect the substrate entering the printer; the sensor defined as the faulty media trigger (Sensor n) is used to stop printing process immediately. The rest of sensors (Sensor 2 through Sensor n-1) are used to detect substrate thickness deviations and correct the printhead position to avoid media jams.
In embodiments, a motor (not shown) moves the sensor support to the known template position and checks that light signals are detected by sensor’s receivers, checking that the light beams are completely parallel all along the width of the printer and are at their predefined distance in vertical direction from Sensor 1.
Detection system position depends on the substrate’s thickness. When starting the printing process, the sensor’s support is moved vertically to set Sensor 1 a certain distance (offset) below nominal substrate’s thickness defined in printer’s user interface:
The printing process starts once Sensor 1 is positioned in γ1 and the printheads are positioned in printing position (γpp), which depends on substrate’s thickness and the jetting gap (Jp) defined in printer’s user interface. It is calculated following the formula:
While the printing process is going on, the detection system monitors sensor status and executes printhead position corrections when any of sensors from Sensor 2 to Sensor n-1 detects substrate deviations.
When one of the mentioned sensors detects substrate deviations, the required position to avoid a jam is defined (ycp) by setting the height of the sensor immediately above the highest sensor of those that have detected the substrate, i.e. sensor “i” detects the substrate:
The control system then sets the printhead position by selecting the highest position between ypp and ycp:
In case Sensor n detects the substrate, the printer’s transport is stopped immediately to prevent the substrate from reaching the printheads. At the same time, printheads are raised to their highest position.
In some embodiments, media detection is integrated into printers that have preexisting height detection systems and no additional sensor/reject mechanism is required over what is needed for machine protection/printing quality rejection. The individual sensors also allow the detection of the quality of the media. In embodiments, detecting the presence of media with one sensor indicates that the media is a perfectly or near perfectly flat media (1030), whereas detecting a media with all but one sensor other than the stop sensor indicates that the media is a least acceptable printable media. If the stop sensor detects media entering the printer (1010), operation of the printer is stopped (1020), and the print bars are raised to prevent the media from crashing into the printer mechanism.
Information gathered by the detection system is not only used by the control system to adjust printhead position, reducing stop cases and therefore reducing downtime, or to stop the printing process when required to avoid the printheads getting damaged. It also serves to optimize the entire printing process by filtering unprinted and inferior quality printed boards (media) by switching them from a stacking flow, which ends with the boards being stacked and packed as valid product at the stacker zone, to the reject flow, which ends with boards being stacked at reject zone, where printer user may reuse the unprinted boards.
This process occurs in case the higher positioned of sensors configured to detect substrate thickness deviations detects a substrate, in which case the printheads then are positioned to the highest corrected position allowed (ycp = yn + y1). At this position where the printheads are positioned too far from substrate’s nominal thickness, printing quality is not decent enough to be considered to yield a valid final product and the media is rejected and routed to a reject facility.
To perform this process the PLC executes a board tracking process by detecting the board when it enters the printer, and then tracks the board along the line until it is finally rejected or stacked. The PLC calculates the board’s position considering the printer’s transport speed, the board’s length, and the distance from the printer gate until the reject (1080) and stack zones (1050). Thus, if the last measuring sensor detects media and the stop sensor does not detect media, the printing bar is raised to a safe height above the stop sensor height. This allows the media to be routed through the printer to the reject facility without being printed and without damaging the printheads. In this way ink is saved because the printheads stop transferring ink through their ink nozzles. This avoids using ink for media that are inside the printer or that are just about to enter the printer, and that to be rejected subsequently due to low quality issues. In this way, interruption of printer operation is avoided, and potential damage to the printer is prevented.
If it is determined that the media can be printed properly, the printhead height is automatically adjusted to maintain the print quality of the production (1060). If the media is to be rejected, the print heads are moved to a safe position to avoid any crash with the media while it is rejected. When media that is not too warped to print is presented to the printer after media has been previously rejected, the printer automatically returns to production, positions the printheads for printing, starts printing the media (1040), and sends the printed media to the stacker (1050). In this way, every piece of media is examined for printability and potential to damage the printer. Printer operation is only stopped if the media has the potential to damage the printer. Otherwise, the printer continues to process media, whether the media is of printable quality, although only media of printable quality are printed.
In addition to assisting the thickness measurement sensors in determining the height of the media, the stop sensor also allows the printer to keep producing despite bad or warped media that have been introduced into the printer as long as the media would not damage the printer. If the stop sensor detects the potential for damage to the printer, it stops the printer (1020). If the other thickness measurement sensors detect media but the stop sensor does not, the printer continues to print on good media and reject bad media. Good media are printed and then routed to the stacker (1050); and bad media are not printed but are routed through the printer directly to the reject facility (1080).
When media is fed to the printer and the height of the media is determined by the thickness measurement sensors, the print bar adapts the printhead gap to maintain good image quality (1060). Here, the media are all printed and routed to the stacker, and none of the media are routed to the reject facility.
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The upstream printer path also includes several thickness sensors 106. For example, stop laser (Sensor n) is positioned upstream from the printer. The stop laser in this embodiment has a height detection threshold of 20 mm. In this embodiment, additional sensors (Sensor n-1, Sensor 2, and Sensor 1) detect various media thicknesses as determined when the detector assembly is built. Each of these sensors is arranged to provide signals via a control system 120 to the printer to control the height of the printheads 108 by raising or lowering 115 the print bars 110 up to the highest printhead position (yPh). Thus, when one or more sensors detect the presence of media a height adjustment signal is sent by the control system to the printer engine, where the height of the sensors relative to a reference surface, such as the printer transport belt, determines how much to raise the printheads when media is detected. Those skilled in the art will appreciate that both the stop sensor and the thickness sensors may be set to detect other thicknesses as desired and as appropriate for the media that are to be printed. In this embodiment, a first measuring sensor (Sensor 1) measures media thickness of 3.5 mm and a last measuring sensor (Sensor n-1) measures media thickness of 9.5 mm. These sensors define the range of acceptable media thickness within which printhead height is adjustable to produce acceptable prints.
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The processing system 1800 may include a central processing unit (also referred to as a “processor”) 1802, main memory 1806, non-volatile memory 1810, network adapter 1812, e.g. a network interface, video display 1818, input/output device 1820, control device 1822, e.g. a keyboard or pointing device, drive unit 1824 including a storage medium 1826, and signal generation device 1830 that are communicatively connected to a bus 1816. The bus 1816 is illustrated as an abstraction that represents one or more physical buses or point-to-point connections that are connected by appropriate bridges, adapters, or controllers. The bus 1816, therefore, can include a system bus, a Peripheral Component Interconnect (PCI) bus or PCI-Express bus, a HyperTransport or industry standard architecture (ISA) bus, a small computer system interface (SCSI) bus, a universal serial bus (USB), inter-integrated circuit (12C) bus, or an Institute of Electrical and Electronics Engineers (IEEE) standard 1394 bus (also referred to as “Firewire”).
The processing system 1800 may share a similar processor architecture as that of a desktop computer, tablet computer, mobile phone, game console, music player, wearable electronic device, e.g. a watch or fitness tracker, network-connected (“smart”) device, e.g. a television or home assistant device, virtual/augmented reality systems, e.g. a head-mounted display, or another electronic device capable of executing a set of instructions, sequential or otherwise, that specify actions to be taken by the processing system 1800.
While the main memory 1806, non-volatile memory 1810, and storage medium 1826 are shown to be a single medium, the terms “machine-readable medium” and “storage medium” should be taken to include a single medium or multiple media, e.g. a centralized/distributed database and/or associated caches and servers, that store one or more sets of instructions 1828. The terms “machine-readable medium” and “storage medium” shall also be taken to include any medium that can store, encoding, or carrying a set of instructions for execution by the processing system 1800.
In general, the routines executed to implement the embodiments of the disclosure may be implemented as part of an operating system or a specific application, component, program, object, module, or sequence of instructions, collectively referred to as “computer programs.” The computer programs typically comprise one or more instructions, e.g. instructions 1804, 1808, 1828, set at various times in various memory and storage devices in an electronic device. When read and executed by the processors 1802, the instructions cause the processing system 1800 to perform operations to execute elements involving the various aspects of the present disclosure.
Moreover, while embodiments have been described in the context of fully functioning electronic devices, those skilled in the art will appreciate that some aspects of the technology are capable of being distributed as a program product in a variety of forms. The present disclosure applies regardless of the machine- or computer-readable media used to effect distribution.
Further examples of machine- and computer-readable media include recordable-type media, such as volatile and non-volatile memory devices 181810, removable disks, hard disk drives, and optical disks, e.g. Compact Disk Read-Only Memory (CD-ROMS) and Digital Versatile Disks (DVDs), and transmission-type media, such as digital and analog communication links.
The network adapter 1812 enables the processing system 1800 to mediate data in a network 1814 with an entity that is external to the processing system 1800 through any communication protocol supported by the processing system 1800 and the external entity. The network adapter 1812 can include a network adaptor card, a wireless network interface card, a router, an access point, a wireless router, a switch, a multilayer switch, a protocol converter, a gateway, a bridge, a bridge router, a hub, a digital media receiver, a repeater, or any combination thereof.
The network adapter 1812 may include a firewall that governs and/or manages permission to access/proxy data in a network. The firewall may also track varying levels of trust between different machines and/or applications. The firewall can be any number of modules having any combination of hardware, firmware, or software components able to enforce a predetermined set of access rights between a set of machines and applications, machines and machines, or applications and applications, e.g. to regulate the flow of traffic and resource sharing between these entities. The firewall may additionally manage and/or have access to an access control list that details permissions including the access and operation rights of an object by an individual, a machine, or an application, and the circumstances under which the permission rights stand.
The language used in the specification has been principally selected for readability and instructional purposes. It may not have been selected to delineate or circumscribe the subject matter. It is therefore intended that the scope of the technology be limited not by this Detailed Description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of various embodiments is intended to be illustrative, but not limiting, of the scope of the technology as set forth in the following claims.
