BACKGROUND

[0001] Some print apparatus apply print agents such as inks or toners directly to a substrate such as paper, card, plastic metal and the like in a pattern to form an image (which may comprise any combination of text, pictures, patterns and the like) on the substrate. Other print apparatus form patterns of print agents, such as printing fluids on an image forming member and apply the formed patterns of print agents to a substrate. In electrophotographic printing, which may include Liquid Electrophotographic Printing (LEP), an image is first formed in toner (or in the case of LEP, electronic ink) on an electrostatic plate bearing a charge pattern corresponding to the image to be formed. The pattern may then be transferred to an intermediate transfer member in a first transfer, and then transferred to a substrate in a second transfer. In some examples, the pattern may be transferred to the intermediate transfer member under an applied voltage. The pattern may then be transferred from the intermediate transfer member to the substrate by application of pressure between the intermediate transfer member and the substrate by an impression drum.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Non-limiting examples will now be described with reference to the accompanying drawings, in which:

[0003] Figure 1 shows a simplified schematic representation of an example print apparatus;

[0004] Figure 2a shows a simplified schematic representation of part of the example print apparatus of Figure 1 ; [0005] Figure 2b shows another simplified schematic representation of part of the example print apparatus of Figure 1 ;

[0006] Figure 3 shows a simplified schematic representation of another example print apparatus;

[0007] Figure 4 shows a flowchart of an example method of printing with a print apparatus;

[0008] Figure 5 shows an example of a machine readable medium in association with a processor.

DETAILED DESCRIPTION

[0009] In an electrophotographic (e.g. LEP) print apparatus, a pattern to be printed may first be formed as an electrostatic pattern of charges on a photoconductive surface (which may be curved around a cylinder). Print agent is attracted to the photoconductive surface according to the charge pattern to form an image.

[0010] In some examples, during a printing operation, an image may be transferred from an image forming photoconductive surface to an intermediate transfer member. In some examples, the intermediate transfer member may comprise a ‘blanket’, for example formed of rubber. In some examples, the image is transferred under a voltage or mechanical pressure. In some examples, the image may be at least partially dried or cured while on the intermediate transfer member. In some examples, the image may be heated while on the intermediate transfer member. In some examples, a number of ‘separations’, i.e. images formed of different (e.g. different color) print agents, may be built up on the intermediate transfer member before being further transferred to a substrate. In other examples, separations may be transferred from the intermediate transfer member to a substrate individually.

[0011] When printing, the image on the intermediate transfer member may then be transferred to a substrate. This transfer may be effected by urging the substrate against the intermediate transfer member. For a sheet-fed printer, pressing a sheet substrate against the intermediate transfer member during the transfer, over and over again, can cause mechanical fatigue damage in the form of indentations which form on the intermediate transfer member at locations where edges of the sheet substrate (e.g. a sheet of paper) have been pressed onto the intermediate transfer member, due to a high- pressure gradient at the edges of the print substrate.

[0012] If paper of a certain size is always placed at the same location relative to the intermediate transfer member (e.g. so that the paper is in a predictable location to align with the image during transfer of the image to the substrate) the edges of the substrate may be located in the same place on the intermediate transfer member for multiple pages of print substrate. The indentations therefore deepen and become more pronounced over time. These indentations cause damage to the intermediate transfer member, which reduces the lifespan of the intermediate transfer member. In addition, these indentations can cause print defects (e.g. if a smaller size paper is used for printing followed by a larger size of paper which will then overlap with the indentations). Printer users often need to plan workflows to account for this, determining a sequence in which to print substrates of different sizes in order to prevent print defects. The indentations on the intermediate transfer member can also cause damage to the photoconductive surface which engages with the intermediate transfer member during the printing process.

[0013] Figure 1 shows a schematic representation of print apparatus 100, which may be an electrophotographic (e.g. LEP) printer. Print apparatus 100 comprises a sheet-fed printer, to print on a plurality of separate sheets of print substrate. Print apparatus 100 comprises an intermediate transfer member 102 also referred to as a ‘blanket’, which may be formed from a deformable substance e.g. rubber. The intermediate transfer member 102 is to receive a pattern of print agent 104 from a photoconductive surface 106 also called a photo imaging plate or ‘PIP’, to form a pattern of print agent 104 on the intermediate transfer member 102.

[0014] Print apparatus 100 also comprises an impression drum 108 to exert pressure on a sheet of print substrate 110 as it passes between the intermediate transfer member 102 and the impression drum 108 in order to transfer the pattern of print agent 104 to the sheet of print substrate 110. The impression drum 108 may comprise a rotating drum or roller.

[0015] Print apparatus 100 also comprises a substrate feed mechanism 112 which is to feed a plurality of separate sheets of print substrate 110 between the impression drum 108 and the intermediate transfer member 102, one at a time,. In some examples, the substrate feed mechanism 112 may include a set of grippers 116 to clamp the substrate 110 and guide it along the print path. In other examples, another substrate feed mechanism, such as a set of rollers may be used. In some examples, the substrate feed mechanism 112 may comprise a gripper-to-gripper substrate transport system in which the substrate 110 (e.g. a sheet of paper) is held by one or a plurality of sets of grippers, which are to clamp together on either side of the substrate 110 to hold the substrate 110 between the grippers 116 as it passes along the print path to the impression drum 108, which may include a further set of grippers (not shown) which grip the paper to position it as it is fed between the impression drum 108 and the intermediate transfer member 102. The substrate feed mechanism 112 may be to rotate about an axis parallel to the rotation axis of the impression drum 108 after gripping the substrate 110 in order to pick up the substrate 110 and feed it into contact with the impression drum 108. Providing the substrate feed mechanism 112 with a gripper system may ensure correct positioning of the substrate during the feed and provides high registration repeatability.

[0016] In addition, print apparatus 100 comprises a controller 114, wherein the controller 114 is to control the print apparatus 100 to apply an offset to a position of the pattern of print agent 104 on the intermediate transfer member 102. For example, the controller 114 may be to control a first transfer of the pattern of print agent 104 from a photoconductive surface 106 to the intermediate transfer member to apply an offset to the pattern of print agent 104 on the intermediate transfer member 102. In some examples, as described in more detail below, the controller may be to control a writing head of the print apparatus 100 to apply an offset to the pattern of print agent 104 by applying an offset to the pattern of electrostatic charges written on the photoconductive surface 106. The controller 114 is further to control the print substrate feed mechanism 112 to apply a corresponding offset to a position of the sheet of print substrate 110 relative to the intermediate transfer member 102. Furthermore, the controller 114 is to adjust the offset of a subsequent sheet of print substrate. The controller 114 may adjust the offset for each sheet of print substrate 110 that passes between the intermediate transfer member 102 and the impression drum 108.

[0017] Therefore, in the example of Figure 1 , the placement of the sheet of print substrate 110 relative to the intermediate transfer member 102 is controlled by adding an offset to the print substrate 110 position so that the edge indentations caused by pressing the print substrate 110 against the intermediate transfer member 102 for image transfer do not occur in the same location each time. This reduces the depth of the indentations that form on the intermediate transfer member and increases the lifetime of the intermediate transfer member, the blanket and PIP foil before replacement is needed, while also reducing the likelihood of print defects.

[0018] In some examples the controller 114 is to apply both a horizontal and a vertical offset to the pattern of print agent 104 and the position of the print substrate 110, wherein the vertical offset modifies a contact position of leading and trailing edges of the print substrate 110 on the intermediate transfer member 102 and the horizontal offset modifies a contact position of side edges of the print substrate 110 on the intermediate transfer member 102. The vertical (y) offset is therefore an offset applied in the print substrate feed direction, i.e. an offset along the same direction as the print substrate feed path. The horizontal (x) offset is an offset applied in a scan direction, across the substrate feed path, i.e. in the plane of the print substrate in a direction orthogonal to the print substrate feed direction.

[0019] Applying an offset in both the horizontal and the vertical directions reduces the overlap between contact positions of both leading and trailing and side edges of the print substrate. Applying different horizontal and vertical offsets for a plurality of sheets of print substrate during image transfer therefore increases the lifetime of the intermediate transfer member 102 and reduces print defects as it reduces the depth of indentations formed on the intermediate transfer member 102 over time.

[0020] In some examples, the vertical offset may be an offset of between 0 and ± 5mm. In some examples the vertical offset may be an offset of between 0 and ±18mm. In some examples, the horizontal offset may be an offset of between 0 and ± 10mm. In some examples the horizontal offset may be an offset of between 0 and ± 25mm. In some examples, the size of the horizontal offset applied may depend on the sheet size of the substrate. For example, for smaller sheet sizes a larger offset may be applied, whereas for a larger substrate, the maximum offset applied may be less due to the size of the substrate.

[0021] Figure 2a shows a flattened view of a transfer surface of intermediate transfer member 102 and an example position at which a first pattern of print agent 104a is to be applied to the intermediate transfer member 102. Figure 2a also shows an example position of a second pattern of print agent 104b that is to be applied to the intermediate transfer member 102 after the first pattern of print agent 104a has been transferred to a first print substrate 110a. The second pattern of print agent 104b is positioned on the intermediate transfer member 102 with an offset applied in both the horizontal and vertical directions. Figure 2a also shows an example position of a third pattern of print agent 104c that is to be applied to the intermediate transfer member 102 after the second pattern of print agent 104b has been transferred to a second print substrate 110b. The example position of the third pattern of print agent 104c has an offset applied in both the horizontal and vertical directions relative to the position of the first pattern of print agent 104a. The offset applied to the third pattern of print agent 104c is different from the offset applied to the second pattern of print agent 104b so that there is also a relative offset between the third pattern of print agent 104c and the second pattern of print agent 104b. Each of the first second and third patterns of print agent 104a-c are applied to the intermediate transfer member at different positions.

[0022] Figure 2b shows a flattened view of the transfer surface of intermediate transfer member 102 and a contact position of a first print substrate 110a, i.e. the position where the first print substrate contacts the intermediate transfer member 102 during transfer of the pattern of print agent 104 from the intermediate transfer member 102 to the print substrate 110. The contact position of the first print substrate 110a corresponds to the position of the first pattern of print agent 104a so that the print agent 104a and substrate 110a are correctly aligned relative to each other. Figure 2b also shows a contact position of a second print substrate 110b to which an offset has been applied in both the horizontal and vertical directions. As can be seen from Figure 2b, the edge positions of substrate 110a and substrate 110b are located at different locations on the intermediate transfer member 102. Figure 2b also shows a contact position of a third print substrate 110c to which an offset has been applied in both the horizontal and vertical directions. The offset that has been applied to the third print substrate 110c is different from the offset that has been applied to the second print substrate 110b in both the horizontal and vertical directions, so that the edges of the third print substrate 110c are located at different locations on the intermediate transfer member 102. The contact positions of the second and third substrate 110b and 110c correspond to the positions of the second and third patterns of print agent 104b and 104c respectively. Subsequent print substrates may have further different offsets applied such that a plurality of print substrates contact the intermediate transfer member at a plurality of different positions during image transfer, to minimise or reduce the amount of overlap between edge positions of the print substrates on the intermediate transfer member. Depth of indentations formed on the intermediate transfer member are therefore minimised or reduced since occurrences of co-located edge impressions are reduced for all edges of a substrate.

[0023] The controller 114 may be to adjust a timing control of the substrate feed mechanism 112 to apply the vertical offset to the position of the print substrate 110 relative to the intermediate transfer member 102. The substrate feed mechanism 112 may include a controlled motor such as a servomotor and the controller 114 may adjust a speed or timing of the motor to adjust a timing at which the substrate feed mechanism 112 feeds a print substrate 110 between the intermediate transfer member 102 and the impression drum 108. The intermediate transfer member 102 of Figure 1 comprises a moving surface e.g. a curved surface of a rotating drum, so adjusting a timing of the substrate feed mechanism 112 therefore also adjusts a location on the intermediate transfer member 102 at which the substrate 110 contacts the intermediate transfer member 102.

[0024] The controller 114 may also be to control a horizontal offset of the substrate contact position. In some examples, the substrate feed mechanism 112 is moveable in a lateral direction relative to the intermediate transfer member 102 (i.e. in the scan/horizontal/x direction) and the controller is to control a lateral alignment between the substrate feed mechanism 112 and the intermediate transfer member 102 by adjusting the lateral position of the substrate feed mechanism 112, in order to apply the horizontal offset. The substrate feed mechanism 112 may include a linear motor that is to adjust the lateral position of the substrate feed mechanism 112, for example a motor that is to rotate a lead screw to move the whole substrate feed mechanism 112 from side to side. In some examples, the horizontal offset may be controlled by moving the intermediate transfer member 102 laterally relative to the substrate feed mechanism 112.

[0025] Figure 3 shows a schematic representation of another print apparatus 200, which may include the print apparatus 100 described above. The print apparatus 200 may be an electrophotographic printer (e.g. a LEP). Print apparatus 200 includes a photoconductive surface 106, also called a photo imaging plate or ‘PIP’ which may be formed around a rotatable electrostatic imaging cylinder.

[0026] The intermediate transfer member 102 is to receive a pattern of print agent 104 from the photoconductive surface 106 by engaging the photoconductive surface 106 with a surface of the intermediate transfer member 102. The print apparatus 200 also includes a writing head 202, to form a pattern of electrostatic charges on the photoconductive surface 106, in order to define the pattern of print agent 104 that will form the image. The writing head 202 may receive image data from controller 114 representing an image to be formed on the print substrate 110 and may form the pattern of electrostatic charges according to the received image data. A photo charging unit (not shown) may deposit a uniform static charge on the photoconductive surface 106. The writing head 202 may comprise e.g. a laser imaging system, or LED imaging system, which can dissipate the static charges in selected portions of the image area on the photoconductive surface to leave a latent electrostatic image comprising the pattern of electrostatic charges.

[0027] The apparatus 200 also includes a print agent dispenser 204, which is to transfer/apply print agent onto the photoconductive surface 106 at locations defined by the pattern of electrostatic charges, in order to form a pattern of print agent 104 on the photoconductive surface 106. The print agent may be e.g. any substance that can be applied upon a substrate by a printing system during a printing operation, including but not limited to inks, electro-inks, primers, and overcoat materials (such as a varnish), water, and solvents. The print agent dispenser 204 may comprise a Binary Ink Developer (BID) unit. The print agent may be electrically charged by virtue of an appropriate potential applied to the print agent. The charged print agent, by virtue of an appropriate potential on the electrostatic image areas, is then attracted to the latent electrostatic image on the photoconductive surface 106. In some examples, the print apparatus 200 may include a number of print agent dispensers, for example with each to dispense ink of a different color to form a number of color separations on the photoconductive surface 102.

[0028] In the example of print apparatus 200, controller 114 is to apply an offset to a position of the pattern of print agent 104 on the intermediate transfer member 102 by controlling the writing head 202 to apply an offset to the position of the pattern of electrostatic charges formed on the photoconductive surface 106. For example, the controller 114 may apply an offset to the image data representing the image to be formed on the print substrate 110. In this way, the controller applies an offset to a position of the pattern of print agent 104 on the intermediate transfer member 102. The offset applied to the pattern of print agent 104 corresponds to the offset applied to the position of the print substrate 110 so that the pattern of print agent 104 is correctly aligned with the print substrate 110 during transfer of the image from the intermediate transfer member 102 to the print substrate 110. The writing head 202 and substrate feed mechanism 112 are therefore synchronized with the print job in order to write the image relative to the current substrate position so that the image is in a constant position relative to the substrate 110 and in a changing position relative to the photoconductive surface 106.

[0029] Figure 4 shows a method, which may be a method of printing. Method 400 may be performed by a print apparatus, e.g. print apparatus 100 or print apparatus 200.

[0030] Block 402 of method 400 comprises applying, by a print apparatus, a first image onto an intermediate transfer member. Applying the first image onto the intermediate transfer member may comprise transferring print agent forming the first image from a photoconductive surface to the intermediate transfer member by engaging the photoconductive surface with the intermediate transfer member. Block 402 may also include writing, by a writing head, a first pattern of electrostatic charges on a photoconductive surface; and dispensing, by a print agent dispenser, print agent at locations defined by the first pattern of electrostatic charges to form the first image.

[0031] Block 404 of method 400 comprises feeding, by a substrate feed mechanism, a first print substrate between the intermediate transfer member and an impression roller to transfer the first image onto the first print substrate.

[0032] Block 406 of method 400 comprises controlling, by a controller (e.g. controller 114), the print apparatus to apply an offset to a second image. Block 406 may comprise controlling a writing head of the printing apparatus to write a second pattern of electrostatic charges at an offset position on a photoconductive surface; and dispensing print agent at locations defined by the second pattern of electrostatic charges to form the second image. Block 406 may comprise applying, by the controller, an offset to image data defining the position of the second pattern of electrostatic charges to be written on the photoconductive surface.

[0033] Block 408 of method 400 comprises applying, by the print apparatus, the second image with the offset onto the intermediate transfer member, which may comprise transferring print agent forming the second image from a photoconductive surface to the intermediate transfer member by engaging the photoconductive surface with the intermediate transfer member.

[0034] Block 410 of method 400 comprises controlling, by the controller, the substrate feed mechanism to apply a corresponding offset to a second print substrate, wherein applying the corresponding offset to the second print substrate comprises feeding, by the substrate feed mechanism, the second print substrate between the intermediate transfer member and an impression roller at an offset position relative to the position of the first print substrate. The offsets applied to the second image and the second print substrate correspond in the sense that the alignment between each image and each print substrate remains consistent so that the image is aligned and centred correctly on the print substrate, even though the print substrate contacts a different part of the intermediate transfer member during image transfer. The offset in x and y position on the intermediate transfer member is applied to both the pattern of print agent and the print substrate. The offset position of the second print substrate may be set by the controller to a position in which each edge of the second print substrate contacts the intermediate transfer member at a different location relative to the locations of each edge of the first print substrate as described in more detail above in relation to Figure 2b.

[0035] The intermediate transfer member may comprise a rotating drum, and feeding the second print substrate between the intermediate transfer member and the impression roller at the offset position may comprise controlling a timing of the substrate feed mechanism such that leading and trailing edges of the second print substrate contact the intermediate transfer member at different locations compared with leading and trailing edges of the first print substrate. Controlling the timing of the substrate feed mechanism may comprise controlling a motor of the substrate feed mechanism. In some examples, the motor may be a servomotor. In some examples the motor may be another type of actuator.

[0036] Figure 5 shows an example of a non-transitory machine readable medium 400 in association with a processor 402. The machine-readable medium 400 may be part of a print apparatus such as print apparatus 100 or 200, or may be in communication with a print apparatus. In some examples, controller 114 may comprise the machine-readable medium 400 and the processor 402. The machine-readable medium may be to control a print apparatus, such as print apparatus 100 or 200, to perform the method 400.

[0037] The machine readable medium 400 stores instructions 404 to cause the processor to, at block 406, control a print apparatus to apply a first offset to a first image which is applied to an intermediate transfer member. At block 408, the instructions are to control a timing of a substrate feed mechanism to apply a corresponding first offset to a position of a first print substrate relative to the intermediate transfer member during transfer of the first image from the intermediate transfer member to the print substrate. At block 410, the instructions are to control a print apparatus to apply a second offset to a second image which is applied to the intermediate transfer member. At block 412 the instructions are to control a timing of a substrate feed mechanism to apply a corresponding second offset to a position of a second print substrate relative to the intermediate transfer member during transfer of the second image from the intermediate transfer member to the print substrate. The second offset applied at blocks 410 and 412 is different from the first offset applied at blocks 406 and 408 such that leading and trailing edges of the second print substrate contact the intermediate transfer member at different locations compared with leading and trailing edges of the first print substrate. In some examples, the instructions may be to apply a third offset to a third image and a third print substrate, wherein the third offset is different from the second and first offsets. In some examples, the instructions are to print a plurality of sheets of print substrate and to adjust the offset applied to each sheet and each corresponding image, to print a plurality of sheets at a plurality of different contact positions on the intermediate transfer member.

[0038] In blocks 408 and 412, controlling the timing of the substrate feed mechanism may comprise controlling a motor of the substrate feed mechanism to delay or advance a timing of the second print substrate passing between the intermediate transfer member and an impression drum. The motor may be a servomotor.

[0039] In some examples, the instructions 404 include instructions to apply both a horizontal and a vertical offset to the second image and the position of the second print substrate, wherein the vertical offset modifies a contact position of leading and trailing edges of the second print substrate on the intermediate transfer member and the horizontal offset modifies a contact position of side edges of the second print substrate on the intermediate transfer member.

[0040] In some examples, instructions 404 also include instructions to control a lateral alignment of the substrate feed mechanism relative to the intermediate transfer member to apply the horizontal offset to the second print substrate.

[0041] Instructions 404 may include instructions to determine an offset to be applied. For example, the instructions may be to, from a plurality of different possible offset positions, select a least frequently used offset position and/or a least recently used offset position as the offset position for the second print substrate. In some examples, determining the offset to be applied may comprise determining a plurality of synchronized x and y displacements to provide a plurality of different possible substrate positions with minimal overlap between edge positions.

[0042] The present disclosure is described with reference to flow charts and/or block diagrams of the method, devices and systems according to examples of the present disclosure. Although the flow diagrams described above show a specific order of execution, the order of execution may differ from that which is depicted. Blocks described in relation to one flow chart may be combined with those of another flow chart. It shall be understood that each flow and/or block in the flow charts and/or block diagrams, as well as combinations of the flows and/or diagrams in the flow charts and/or block diagrams can be realized by machine readable instructions.

[0043] It shall be understood that some blocks in the flow charts can be realized using machine readable instructions, such as any combination of software, hardware, firmware or the like. Such machine readable instructions may be included on a computer readable storage medium (including but is not limited to disc storage, CD-ROM, optical storage, etc.) having computer readable program codes therein or thereon.

[0044] The machine readable instructions may, for example, be executed by a general purpose computer, a special purpose computer, an embedded processor or processors of other programmable data processing devices to realize the functions described in the description and diagrams. In particular, a processor or processing apparatus may execute the machine readable instructions. Thus functional modules of the apparatus and devices may be implemented by a processor executing machine readable instructions stored in a memory, or a processor operating in accordance with instructions embedded in logic circuitry. The term ‘processor’ is to be interpreted broadly to include a CPU, processing unit, ASIC, logic unit, or programmable gate array etc. The methods and functional modules may all be performed by a single processor or divided amongst several processors.

[0045] Such machine readable instructions may also be stored in a computer readable storage that can guide the computer or other programmable data processing devices to operate in a specific mode. Further, some teachings herein may be implemented in the form of a computer software product, the computer software product being stored in a storage medium and comprising a plurality of instructions for making a computer device implement the methods recited in the examples of the present disclosure. [0046] The word “comprising” does not exclude the presence of elements other than those listed in a claim, “a” or “an” does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the claims.

[0047] The features of any dependent claim may be combined with the features of any of the independent claims or other dependent claims.