Patent Description:
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.

<CIT> describes a solution by retracting the printhead in the shuttle or by lowering the receiver table. The relative scanning movement of the printhead may be stopped by halting the shuttling printhead or stopping the feeding of the receiver.

A different approach is described in <CIT>, wherein the inkjet heads are raised sequentially.

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 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 a plurality of 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 <NUM> 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.

<FIG> shows a substrate height sensing assembly <NUM> according to an embodiment of the invention. The sensors are mechanically assembled in a unique support <NUM> such that vertical movement and their relative vertical position remains constant, i.e. relative sensor positions (y<NUM>, y<NUM>,. , y(n-<NUM>), yn) on the support are not adjustable. The height sensing arrangement is mounted at the entry of the printer and before the printheads <NUM>, where a substrate <NUM> entering printer's transport <NUM> is considered totally flattened. In embodiments, the height sensing assembly is a mechanical assembly that is vertically movable <NUM>, such that its position may be adjusted by, for example tenth millimeter's, via a mechanical transmission system composed of a spindle, a gearbox, and a motor (not shown).

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 <NUM> 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 <NUM> offset and faulty media trigger sensor. All these parameters are configured by the user through a user interface application (see <FIG>).

Sensor <NUM> 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 <NUM> through Sensor n-<NUM>) are used to detect substrate thickness deviations and correct the printhead position to avoid media jams.

<FIG> shows an alignment plate <NUM> for plurality of height sensors according to an embodiment of the invention. All sensors are positioned to project their light beam parallel to printer's transport surface, and consequently, parallel to substrate's surface. This calibration process is done mechanically. Prior to the printing process the printer's control system executes an alignment checking routine. The alignment plate is a template that is used for this purpose. It is located at a certain height on the reflector side. The template is a mechanical plate with mechanized holes that match the distances defined for each sensor on the mechanical support (y<NUM>, y<NUM>,. y(n-<NUM>), yn).

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 <NUM>.

Detection system position depends on the substrate's thickness. When starting the printing process, the sensor's support is moved vertically to set Sensor <NUM> a certain distance (offset) below nominal substrate's thickness defined in printer's user interface: <MAT>.

The printing process starts once Sensor <NUM> is positioned in y<NUM> and the printheads are positioned in printing position (ypp), which depends on substrate's thickness and the jetting gap (Jp) defined in printer's user interface. It is calculated following the formula: <MAT>.

While the printing process is going on, the detection system monitors sensor status and executes printhead position corrections when any of sensors from Sensor <NUM> to Sensor n-<NUM> 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: <MAT>.

The control system then sets the printhead position by selecting the highest position between ypp and ycp: <MAT>.

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.

<FIG> is a flow diagram showing the operation of a printer with high productivity media scanning according to an embodiment of the invention. In embodiments, media height measurement is performed by a plurality of digital sensors to detect the thickness of the media (<NUM>).

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 (<NUM>), 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 (<NUM>), operation of the printer is stopped (<NUM>), 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 + y<NUM>). 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 (<NUM>) and stack zones (<NUM>). 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 (<NUM>). 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 (<NUM>), and sends the printed media to the stacker (<NUM>). 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 (<NUM>). 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 (<NUM>); and bad media are not printed but are routed through the printer directly to the reject facility (<NUM>).

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 (<NUM>). Here, the media are all printed and routed to the stacker, and none of the media are routed to the reject facility.

In <FIG>, the following parameters are observed:.

<FIG> shows a printer with high productivity media scanning according to an embodiment of the invention in which media having a thickness with risk of crash is presented for printing.

In <FIG>, media <NUM>, such as a sheet of corrugated cardboard, is presented to a printer <NUM> which, in this embodiment, is a sheet-to-sheet single pass digital inkjet printer. In the example of this embodiment, the media has a nominal thickness (ySus) while the printer has an offset from the nominal substrate's thickness of <NUM> (y1) and a highest printhead position (yPh). The media thickness in <FIG> exceeds the highest printhead position, which creates the risk of the media crashing into the printheads.

The upstream printer path also includes several thickness sensors <NUM>. For example, stop laser (Sensor n) is positioned upstream from the printer. The stop laser in this embodiment has a height detection threshold of <NUM>. In this embodiment, additional sensors (Sensor n-<NUM>, Sensor <NUM>, and Sensor <NUM>) 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 <NUM> to the printer to control the height of the printheads <NUM> by raising or lowering <NUM> the print bars <NUM> 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 <NUM>) measures media thickness of <NUM> and a last measuring sensor (Sensor n-<NUM>) measures media thickness of <NUM>. These sensors define the range of acceptable media thickness within which printhead height is adjustable to produce acceptable prints.

In the embodiment of <FIG>, the stop sensor senses that the media has a thickness that is greater than the detection threshold of <NUM> and, accordingly signals the printer to stop operation <NUM>.

<FIG> shows a printer with high productivity media scanning according to an embodiment of the invention in which media having a thickness of <NUM> (ySus) is presented for printing.

In <FIG>, media <NUM>, such as a sheet of cardboard, is presented to the printer <NUM>. In this example, the media has a thickness of <NUM> (ySus).

In the embodiment of <FIG>, the printer has a media clearance of <NUM> relative to the printer carriage. Because the media height is such that a decent quality print may be made, the media is printed <NUM> and routed <NUM> to a stacker <NUM>.

<FIG> shows a printer with high productivity media scanning according to an embodiment of the invention in which media having a thickness of <NUM> is presented for printing.

In <FIG>, media <NUM>, such as a sheet of cardboard, is presented to the printer <NUM>. In this example, the media has a thickness of <NUM> (ySus). As noted, the stop laser (Sensor n) positioned upstream from the printer has a detection threshold of <NUM>; and the upstream printer path includes several additional thickness sensors <NUM> which, in this embodiment, detect various media thicknesses.

In the embodiment of <FIG>, the printer has a printhead position of <NUM> (yPh). Media that exceed this clearance in height trigger the stop sensor to stop operation of the printer. The media thickness in this embodiment is greater than the height of the highest sensor, i.e. <NUM> but less than the stop sensor height, i.e. <NUM>. In such case a good quality print may not be made but it is not necessary to stop operation of the printer. As such, the media is not printed, and it is routed <NUM> directly to the reject facility <NUM>.

<FIG> are screenshots that show operation of a printer with high productivity scanning according to an embodiment of the invention. In <FIG> the photocells are shown as photocells A-F. For purposes of the discussion herein, these photocells approximately correspond respectively to Sensor <NUM> to Sensor n in <FIG>. Those skilled in the art will appreciate that the spacing and number of photocells/sensors is determined by the application to which the invention is put, e.g. the media, media variations in height, printer and printhead clearance, etc. Photocells A-F are mounted on the substrate height sensing assembly such that photocell A detects media, which nominally has a thickness of <NUM>. Photocells B-F are spaced from photocell A as follows: photocell B <NUM>, photocell C <NUM>, photocell D <NUM>, photocell E <NUM>, and photocell F <NUM>. These values may be adjusted by raising or lowering the substrate height sensing assembly, e.g. with the homing photocell motor in this embodiment, for example to adapt the printer to accept media having a different nominal substrate thickness or tor use of the invention on printers having a different printhead clearance and/or print bar arrangement.

<FIG> is a block diagram illustrating an example of a processing system <NUM> in which at least some operations described herein can be implemented. For example, components of the processing system <NUM> may be hosted on a computing device that includes a threat detection platform. As another example, components of the processing system <NUM> may be hosted on a computing device that is queried by a threat detection platform to acquire emails, data, etc..

The processing system <NUM> may include a central processing unit (also referred to as a "processor") <NUM>, main memory <NUM>, non-volatile memory <NUM>, network adapter <NUM>, e.g. a network interface, video display <NUM>, input/output device <NUM>, control device <NUM>, e.g. a keyboard or pointing device, drive unit <NUM> including a storage medium <NUM>, and signal generation device <NUM> that are communicatively connected to a bus <NUM>. The bus <NUM> 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 <NUM>, 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 (I2C) bus, or an Institute of Electrical and Electronics Engineers (IEEE) standard <NUM> bus (also referred to as "Firewire").

The processing system <NUM> 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 <NUM>.

While the main memory <NUM>, non-volatile memory <NUM>, and storage medium <NUM> 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 <NUM>. 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 <NUM>.

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 <NUM>, <NUM>, <NUM>, set at various times in various memory and storage devices in an electronic device. When read and executed by the processors <NUM>, the instructions cause the processing system <NUM> 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 <NUM>, 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 <NUM> enables the processing system <NUM> to mediate data in a network <NUM> with an entity that is external to the processing system <NUM> through any communication protocol supported by the processing system <NUM> and the external entity.

The network adapter <NUM> 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.

Claim 1:
A printer (<NUM>), comprising:
a plurality of sensors (<NUM>) positioned within a print path before a printhead location (<NUM>), said sensors (<NUM>) generating a signal indicative of a highest point of incoming media (<NUM>; <NUM>; <NUM>) relative to a reference surface of the printer (<NUM>);
a control system (<NUM>) in communication with said sensors (<NUM>) configured to, in response to receiving said sensors signals, determine when the height of the highest point of the incoming media (<NUM>; <NUM>; <NUM>) relative to the reference surface of the printer (<NUM>) poses a collision or damage risk to the printer (<NUM>);
said control system (<NUM>) being configured to generate a signal that stops operation of the printer (<NUM>) when the height of the highest point of said incoming media (<NUM>; <NUM>; <NUM>) relative to the reference surface of the printer (<NUM>) poses a collision or damage risk to the printer (<NUM>);
characterised in that the control system (<NUM>) is configured as follows: when said control system (<NUM>), in response to receiving said sensors signals, determines that the height of the incoming media (<NUM>; <NUM>; <NUM>) relative to the reference surface of the printer (<NUM>) does not pose a collision or damage risk to the printer (<NUM>) and said control system (<NUM>) determines that the height of the incoming media (<NUM>; <NUM>; <NUM>) relative to the reference surface of the printer (<NUM>) does not allow printing of the media (<NUM>; <NUM>; <NUM>), said control system (<NUM>) generates
a signal that rejects the media (<NUM>; <NUM>; <NUM>) after the media (<NUM>; <NUM>; <NUM>) is passed through the printer (<NUM>) without being printed and without stopping or slowing down printer operation; and
when said control system (<NUM>), in response to receiving said sensors signals, determines that the height of the incoming media (<NUM>; <NUM>; <NUM>) allows printing of the media (<NUM>; <NUM>; <NUM>), said control system (<NUM>) generates a signal that adjusts printhead height relative to an upper media surface distance to prevent interference with the media (<NUM>; <NUM>; <NUM>) while allowing the printheads (<NUM>) to print.