BACKGROUND

[0001 ] In many printing systems the distance between a print engine, and the media which is to be printed on is an important parameter in ensuring high quality printing. In inkjet printing systems, for example, the distance between the lower surface of an inkjet printhead from which drops of printing fluid are ejected, and the top surface of a media is often referred to as the pen to paper spacing (PPS).

[0002] Some printing systems enable the height of the print engine to be modified such that an optimal PPS may be maintained when printing on media of different thicknesses. BRIEF DESCRIPTION

[0003] Examples will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0004] Figure 1 is a simplified side view of a printer according to one example;

[0005] Figure 2 is a simplified plan view of the printer of Figure 1 according to one example;

[0006] Figure 3 is a block diagram of a print support structure controller according to one example;

[0007] Figure 4 is a flow diagram outlining a method of operating a printer according to one example;

[0008] Figure 5 is a flow diagram outlining a method of operating a printer according to one example; and

[0009] Figure 6 is a flow diagram outlining a method of operating a printer according to one example.

DETAILED DESCRIPTION

[00010] In inkjet printing systems a print engine may comprise one or multiple inkjet printheads. Depending on the printer configuration, the type of print engine support structure may differ. For example, in scanning inkjet printers, one or multiple inkjet printheads may be insertable into a carriage that is moveable bi-directionally over one or multiple carriage bars to define a print zone. In page-wide array printers, multiple inkjet printheads may form a static, or substantially static, print bar that defines a print zone.

[0001 1 ] Some large format printers are able to print on media up to and over 1 meter in length. Accordingly, the weight of print engine support structures, including the weight of anything supported by the support structure, may be quite considerable. For example, in some printers the print engine support structure may weight in excess of several hundred kilos.

[00012] To allow the PPS of such print engine support structures to be accurately adjusted, it is common to provide at least one controllable height adjustor at each end of the print engine support structure. A controllable height adjustor may, for example, comprise a motorized screw mechanism.

[00013] To provide optimal print quality, the print engine support structure should be positioned parallel to a printer platen, such that the plane of the printhead nozzle plates is parallel with the printer platen. This ensures that the PPS spacing along the whole length of the platen is constant.

[00014] However, where each controllable height adjustor is controllable independently, it may be difficult, or costly, to accurately synchronize the movement of each height adjustor and hence difficult to ensure that the print engine support structure and platen remain parallel. In wide-format printers, the large length of the print engine support structures (which may be in excess of 1 m in length) exacerbates the problem. For example, the large distance between each of end of the print engine support structure makes it largely unfeasible to have utilize mechanically coupled height adjustors.

[00015] Referring now to Figure 1 there shown a simplified side view of a printing system 100 according to one example. Figure 2 shows a corresponding plan view of the printing system 1 00. [00016] The printing system 100 comprises a print engine support structure 102 to support one or multiple print engines, such as inkjet printheads 104a to 104n. As described above, in one example the print engine support structure 1 02 may comprise a printhead carriage (not shown) to receive one or multiple inkjet printheads in a scanning inkjet printer configuration. In another example the print engine support structure 102 may comprise multiple inkjet printheads, or may receive multiple inkjet printheads, in a page-wide array printer configuration. [00017] The printing system 100 may print on media of different thicknesses, such as a media 202 shown in Figure 2, whilst maintaining an optimal PPS height by appropriately adjusting the height of the support structure 102 above a printer platen 106. [00018] The print engine support structure 102 is positioned above the printer platen 1 06 via height adjustors 108. In the example shown four height adjustors 108a to 1 08d are provided, although in other examples a smaller or greater number of height adjustors may be provided. As shown in Figure 2, one height adjustor 1 08 is provided in the region of each corner of the print engine support structure 102. In one example each height adjustor 1 08a to 108d is a screw mechanism, although in other examples other suitable mechanisms may be used, such as rack and pinion mechanisms.

[00019] Each height adjustor 108a to 108d is coupled to a respective drive mechanism 1 10a to 1 1 Od. In one example each drive mechanism is an electric motor, although in other examples other suitable drive mechanisms may be provided, such as hydraulic drive mechanisms or the like.

[00020] Each drive mechanism 1 10a to 1 1 0d is controlled by a print engine support structure controller 1 12, which is shown in more detail in Figure 3. The controller 1 12 comprises a processor 302, such as a microprocessor or microcontroller, coupled to a non-transitory computer readable memory 304, for example through a communications bus (not shown). The memory 304 stores print engine support structure control instructions 306 which are machine readable instructions that, when executed by the processor 302, cause the controller 1 12 to control the height of the print engine support structure 102 as described herein in various examples. [00021 ] The print engine support structure controller 1 1 2 enables the height of the print engine support structure 1 02 to be varied by sending appropriate drive signals to each of the drive mechanisms 1 10a to 1 10d. In one example a drive signal may comprise an electrical signal having a predetermined electrical voltage and lasting for a predetermined duration. However, since each drive mechanism may have subtly different characteristics, it is not possible to guarantee that sending the same drive signal to each of the drive mechanisms 1 10a to 1 10d will result in the same change in height to be achieved by each respective height adjustor. As previously mentioned, however, ensuring uniform PPS height along the length of the support structure 102 is key to maintaining high print quality.

[00022] To ensure uniform PPS height along the length of the support structure 102 a spatial orientation sensor 1 14 is coupled to the support structure 102. In one example the spatial orientation sensor 1 14 is an accelerometer. In the example shown the accelerometer is shown coupled to an upper surface of the support structure, although in other examples it may be coupled to any appropriate portion of the support structure, either directly or indirectly.

[00023] The accelerometer 1 14 supplies signals or data that enable the orientation of the accelerometer 1 14 to be determined in three-dimensional space. For example, in one example the accelerometer 1 14 supplies signals or data that enable its orientation in the x-axis, the y-axis, and the z-axis to be determined. Although shown in Figure 1 as a single device, in one example separate spatial orientation sensors may be used to determine an orientation of each of the x-axis, the y-axis, and the z-axis.

[00024] A height sensor 1 16 is also provided that provides appropriate signals to the controller 1 12 to enable the controller 1 12 to determine when a predetermined PPS height has been achieved. The height sensor, may for example, be any electronic device to suitable for measuring distance, and may include, without limitation, a laser, an ultrasound module, a mechanical or optical encoders, or the like. [00025] Each height adjustor 108a to 108d is associated with a reference position 1 18. In one example the reference position 1 18 may be a mechanical reference position, such as the upper surface of the printer platen 106. In other examples the mechanical reference position may be provided, for example, by a plurality of mechanical barriers provided at or in proximity to each of the height adjustors 108a to 108d.

[00026] During manufacture of the printer 1 00 the height adjustors 108 are assembled to a high degree of accuracy such that when the support platform 102 is positioned against the reference position 1 1 8 the support structure 1 02 is substantially parallel to the upper surface of the printer platen 106, and has hence the same orientation as the printer platen 106.

[00027] Operation of the printing system 1 00 according to one example is described below with reference to the flow diagram of Figure 4.

[00028] At block 402, the controller 1 12 obtains reference orientation data from the accelerometer 1 14 when the support platform 1 02 is in the reference position 1 18. The orientation data defines the orientation of the accelerometer, and hence indirectly defines the orientation of the support platform 102, at the reference position.

[00029] In one example, the controller 1 12 individually controls each of the height adjustors 108a to 1 08d, by sending individual drive signals thereto, to move the support structure 102 to the reference position 1 18 to enable the reference orientation data to be determined.

[00030] In one example the controller 1 12 may determine that the support structure 102 is against the reference position by sensing an appropriate change in electrical current in each of the drive mechanisms, for example as each drive mechanism experiences an increase in torque as the support structure 102 is positioned against the reference position 1 18. In other examples the controller 1 12 may determine that the support structure 102 is against the reference position by using a suitable configuration of switches, pressure sensors, or other appropriate sensing devices.

[00031 ] It is important to obtain the orientation data whilst the support platform 102 is in the reference position, since the printer 100 may be installed such that it is not perfectly level. Accordingly, it is not appropriate to assume that the support platform 102 is completely level whilst it is in the reference position 1 18.

[00032] At block 404, the controller 1 12 individually controls each of the height adjustors 108a to 108d to adjust the height of the support structure 102 to a predetermined height above the printer platen 106. The controller 1 12 may individually control each of the height adjustors 108a to 108d to adjust the height of the support structure 102 until the controller 1 12 determines from the height sensor 1 16 that the support platform has been adjusted to the predetermined height. [00033] At block 406, the controller 1 12 obtains orientation data from the accelerometer 1 14 to determine the orientation of the support platform at the predetermined height. If the controller 1 1 2 determines that the orientation of the support platform 102 at the predetermined height matches (within an acceptable degree of tolerance) the reference orientation this indicates that the support platform 1 02 is parallel to the platen 106 and that the PPS height is uniform.

[00034] If, however, the controller 1 12 determines that the orientation of the support platform 102 at the predetermined height does not match (within an acceptable degree of tolerance) the reference orientation, the controller 1 12 may further control one or more of the height adjustors 108a to 108d to bring the orientation of the support platform 102 into the same orientation as the reference orientation. The determination of which height adjustor(s) to adjust may be made based on the determined orientation data. [00035] Once this has been achieved, the controller 1 12 may verify, using the height sensor, that the support platform is still at the predetermined height, and if not the controller 1 12 may make further control appropriate ones of the height adjustors 108a to 108d to bring the height of the support platform 102 to the predetermined height.

[00036] The controller 1 1 2 may perform multiple iterations of adjusting the orientation and adjusting the height of the support platform 102 until the orientation and height are within acceptable tolerances.

[00037] In the above-described example the orientation of the support platform 102 may not be maintained whilst the height of the support platform 102 is being adjusted. This may occur, for example, if one of the drive mechanisms 1 1 0a to 1 10d operates at a different speed for a given drive signal.

[00038] In some circumstances, however, it may be beneficial, or even critical, to maintain the orientation of the support platform 1 02 in its reference orientation whilst it is being raised or lowered. For example, this may help reduce the risk of the support platform 102 become bent or distorted when the PPS height is adjusted.

[00039] Operation of the printing system 100 according to a further example is described below with reference to the flow diagram of Figure 5.

[00040] At block 502 the controller 1 12 individually controls each of the height adjustors 108a to 108d to move the support structure 102 to the reference position 1 18 to enable the reference orientation data to be determined. [00041 ] At block 504, the controller 1 12 obtains reference orientation data from the accelerometer 1 14 when the support platform 1 02 is in the reference position 1 18. [00042] At block 506 the controller 1 1 2 sends individual drive signals to each height adjustor 108a to 108d to individually adjust the height of the support structure 102. As the height of the support structure 102 is being adjusted, at block 508 the controller 1 12 obtains orientation data from the support structure 102 from its current position.

[00043] At block 510 the controller 1 12 determines whether any modification to the drive signals being sent to each height adjustor 108a to 108d should be made to ensure that the support platform is maintained in the same orientation as the reference orientation whilst the height of the support structure 102 is being adjusted. If any modifications are deemed appropriate the controller 1 12 adjusts the appropriate drive signals being sent.

[00044] At block 512 the controller 1 12 determines whether the support platform 102 has been adjusted to the predetermined height. If not, the above described process continues until the predetermined height is reached and the process stops at block 514.

[00045] In a further example, shown in Figure 6, the controller 1 12 performs the operations shown in blocks 602 to 61 0 in place of the operation shown in block 502 of Figure 5.

[00046] Thus, at block 602, the controller 1 12 obtains orientation data from the accelerometer 1 14 when the support platform 102 is in its current position.

[00047] At block 504 the controller 1 1 2 sends individual drive signals to each height adjustor 108a to 108d to individually adjust the height of the support structure 102 to move the support structure 102 to the reference position 1 18. [00048] As the height of the support structure 102 is being adjusted, at block 606 the controller 1 12 obtains orientation data from the support structure 102 from its current position. [00049] At block 608 the controller 1 12 determines whether any modification to the drive signals being sent to each height adjustor 108a to 108d should be made to ensure that the support platform is maintained in the same orientation whilst the height of the support structure 102 is being adjusted. If any modifications are deemed appropriate the controller 1 12 adjusts the appropriate drive signals being sent.

[00050] At block 610, the controller 1 1 2 determines when the support structure 102 is in the reference position 1 18. In some circumstances the orientation of the support platform 102 may have to be adjusted in order to align the support platform 102 with the reference position 1 18.

[00051 ] The controller 1 12 then continues with performing the operations shown in blocks 504 to 514 as shown in Figure 5 and as described above.

[00052] In this way, the controller 1 12 may adjust the height of the support structure 102 whilst ensuring that the orientation the support structure 102 remains substantially constant. [00053] It will be appreciated that some examples of the present invention can be realized in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are examples of machine-readable storage that are suitable for storing a program or programs that, when executed, implement examples described herein. Accordingly, some examples provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine readable storage storing such a program. [00054] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[00055] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.