|
(11) | EP 2 949 476 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
|
|
|
|
|||||||||||||||||||||||||||
| (54) | IMAGE FORMING APPARATUS AND METHOD TO COMPENSATE WOBBLE OF A ROLL IN AN IMAGE FORMING APPARATUS |
| (57) The invention relates to an image forming apparatus (36) to print an image on an
image receiving member (2), wherein the image forming apparatus comprises: a printing assembly (3) configured to print the image on the image receiving member, when the image receiving member is arranged in a printing position, and an image receiving member transport system (41) to transport the image receiving member towards and/or away from the printing position, wherein the transport system comprises: a roll (28), rotatable about an axis of rotation (48) and comprising an outer surface (46), wherein the roll comprises a first end and a second end, and a wobble compensation system to compensate for wobble of the roll; According to the invention at least a part of the outer surface (46) of the roll is movable in a first direction substantially perpendicular to the axis of rotation, and in that wobble compensation system comprises: a sensor system (53,54) configured to determine a wobble signal representative for wobble of said roll, a controller (55) to provide an actuator signal on the basis of the wobble signal, and an actuator (52) configured to move on the basis of the actuator signal at least the movable part of the outer surface to compensate for wobble of the roll. |
Field of the Invention
[0001] The present invention relates to an image forming apparatus and a method to compensate wobble of a roll of a transport system configured to transport an image receiving member in an image forming apparatus.
Background of the Invention
[0002] An image forming apparatus is used to print images on an image receiving member, such as paper or any other suitable media. Such image forming apparatus comprises a printing assembly to print images on the image receiving member, when the image receiving member is held in a printing position associated with the printing assembly. An image receiving member transport system is provided to transport the image receiving member from a supply towards the printing assembly and away from the printing assembly to a delivery tray or roll.
[0003] In embodiment of the image forming apparatus, the image receiving member may be wound on a support roll to form a roll comprising the image receiving member. Such roll may for example be an infeed roll comprising a quantity of image receiving member to be fed to the printing position or an outfeed roll comprising a quantity of image receiving member which is received after passing the printing position.
[0004] The outer surface of such roll is formed by the image receiving member. The image receiving member may however be wound unevenly on the support roll, i.e. the radii of the outer surface of the roll with respect to the axis of rotation may not be constant over the roll in longitudinal and/or tangential direction. Winding or unwinding of such roll may cause wobble of the roll and therewith of the image receiving member. This is generally undesirable.
[0005] Known prior art devices use correction rollers to correct wobble of the roll in order to provide a constant flow of image receiving member towards or away from the printing assembly. A drawback of the use of correction rollers is that extra space is required to accommodate the correction rollers.
Summary of the Invention
[0006] It is an object of the present invention to provide an image forming apparatus comprising an effective roll wobble compensation.
[0007] The present invention provides an image forming apparatus to print an image on an image receiving member, wherein the image forming apparatus comprises: a printing assembly configured to print the image on the image receiving member, when the image receiving member is arranged in a printing position, and an image receiving member transport system to transport the image receiving member towards and/or away from the printing position, wherein the transport system comprises:
a roll, rotatable about an axis of rotation and comprising an outer surface, wherein the roll comprises a first end and a second end, and
a wobble compensation system to compensate for wobble of the roll, characterized in that at least a part of the outer surface of the roll is movable in a first direction substantially perpendicular to the axis of rotation, and in that wobble compensation system comprises:
a sensor system configured to determine a wobble signal representative for wobble of said roll,
a controller to provide an actuator signal on the basis of the wobble signal, and an actuator configured to move on the basis of the actuator signal at least the movable part of the outer surface to compensate for wobble of the roll.
[0008] In the image printing apparatus of the present invention wobble may be corrected by changing a position of at least a part of the outer surface of the roll in the first direction, typically the transport direction of the image receiving member away from or towards the roll. By using the roll itself to compensate for wobble of the roll, in particular by actively controlling the position of the roll, no separate correction rolls are required for wobble compensation. This provides the possibility to create a more compact construction of the image receiving member transport system.
[0009] The wobble of the roll may be caused by a non-constant radius of the outer surface in a longitudinal direction, i.e. substantially parallel to the axis of rotation, or may be caused by a non-constant radius of the outer surface in the tangential direction, i.e. substantially in the circumferential direction of the roll, or a combination thereof. Both the unevenness in longitudinal direction and in tangential direction may be compensated by the image forming apparatus of the invention.
[0010] A non-constant radius in the longitudinal direction, may for example at least partially be compensated by changing orientation of the outer surface, for example by changing the orientation of the axis of rotation of the roll with respect to the first direction.
[0011] A non-constant radius in tangential direction may be at least partly compensated by moving the axis of rotation of the roll in the first direction. For example, when the radius of the roll decreases during rotation of the roll, the axis of rotation may be moved in the first direction of rotation, and vice versa.
[0012] It is remarked that although the image printing apparatus may be used to compensate the wobble at any position of the roll, the wobble is advantageously compensated at the contact line where the image receiving member transport path through the image forming apparatus contacts the roll, i.e. leaves or first touches the roll.
[0013] The wobble of the roll may be determined by a sensor system that measures a location/position of the outer surface of the roll. The controller may be any controller suitable to determine an actuator signal on the basis of the wobble signal of the sensor system. The controller may be a separate controller, or may be combined with other functions of the image forming apparatus.
[0014] In an embodiment, the roll comprises a support roll and image receiving member wound on the support roll, wherein the outer surface is formed by the image receiving member. Wobble of the roll may in particular be caused by an image receiving member, such as paper, that is wound on a support roll.
[0015] In an embodiment, the first end of the roll is movable in the first direction to move the outer surface of the roll in the first direction, wherein the actuator is configured to move the first end of the roll in the first direction to compensate for wobble of the roll. The outer surface of the roll may be moved in a direction perpendicular to the axis of rotation by moving the first end of the roll in the first direction in dependence of the output of the controller.
[0016] The second end of the roll may be arranged at a fixed position and pivotally mounted to allow movement of the first end in the first direction.
[0017] By moving the first end of the roll in the first direction, while maintaining the other end of the roll at a fixed position, the orientation of the axis of rotation, and therewith the outer surface may be changed to compensate for wobble of the roll.
[0018] In a further embodiment, the second end of the roll is movable in the first direction to move the outer surface of the roll in the first direction, wherein the wobble compensation system comprises a second actuator configured to move the second end of the roll in the first direction to compensate for wobble of the roll. In this embodiment, the roll can be moved in the first direction at the first end and at the second end.
[0019] By identical movement of both ends the roll can be moved in the first direction without a change in the orientation of the roll. Such movement can be used to compensate wobble in the tangential direction of the outer surface of the roll. Alternatively, or at the same time, the first and the second end may be moved by non-identical movements to change the orientation of the roll with respect to the first direction in order to compensate wobble of the outer surface in the longitudinal direction of the roll.
[0020] In an embodiment, a radius of the outer surface with respect to the axis of rotation over at least a part of the length of the roll is adaptable by said actuator in dependence of the actuator signal. Instead of moving the complete roll by one or more actuators at one or more ends of the roll, the outer surface of the roll may also be moved in the first direction, when the outer surface of the roll is moveable with respect to the axis of rotation. For example, the roll may comprise an inner support roll and an outer support roll arranged around the inner support roll. The inner support roll may be rotatably mounted on a frame, while the outer surface is formed or carried by the outer support roll, for instance by image receiving member wound on the outer support roll. One or more actuators may be provided between the inner support roll and the outer support roll to actively move the outer support roll with respect to the inner support roll to compensate for wobble of the roll.
[0021] In an embodiment, the sensor system comprises a first sensor to determine a location of the outer surface at the first end of the roll and a second sensor to determine a location of the outer surface at the second end of the roll. The first and second sensors may for example be an optical sensor capable of measuring a distance between the optical sensor and the outer surface.
[0022] In an embodiment, the sensor system comprises an array of three or more sensors arranged along the roll in a longitudinal direction thereof, wherein each of the three or more sensors is configured to determine in a direction substantially perpendicular to the axis of rotation a location of the outer surface of the roll. By providing three or more sensors over the length of the outer surface in longitudinal direction, information can be obtained over the non-uniformity of the roll over the length thereof.
[0023] The sensor data obtained by the three or more sensors can be used to calculate an optimum position of the outer surface of the roll to compensate for the wobble. For example the roll may have a small radius at the first and second end of the roll, but may have a relatively large radius at the middle. When sensors are only provided at the ends of the roll the middle of the roll will not be taken into account during determination and compensation of the wobble of the roll. Thus, by measuring at the middle of the roll the determination and compensation of the wobble may be improved.
[0024] In an embodiment, the sensor system comprises a first edge sensor configured to determine a position of a first edge of the image receiving member, and a second edge sensor configured to determine a position of an opposite second edge of the image receiving member. As an alternative or in addition to the first and second sensor measuring a position of the outer surface, a first and second edge sensor may be provided to determine the position of opposite edges of the image receiving member. These first and second edge sensor may be provided to measure the location of the edges of the image receiving member on the roll, but also in an image receiving member path from the roll towards or from the printing assembly. Wobble of the roll may have the effect that the image receiving member in the image receiving member path will move sideways. By measuring the position of the edges this sideways movement can be determined and used as input for compensation of the wobble of the roll.
[0025] The wobble compensation system of the invention can in particular be used to compensate wobble of a roll supporting a quantity of image receiving member, such as paper or other printing media, since such image receiving member may be non-uniformly wound on the supporting roll supporting the image receiving member.
[0026] The roll may for example be an infeed roll comprising a quantity of image receiving member to be transported towards the printing position or an outfeed roll comprising a quantity of image receiving member received after the image receiving member has passed the printing position.
[0027] In a further embodiment, multiple rolls in the image printing apparatus, in particular the infeed roll and the outfeed roll, may be provided with a wobble compensation systems according the invention. The wobble compensation systems may function independently of each other, or be combined in a single wobble compensation system.
[0028] In an embodiment, the controller is configured to determine on the basis of the wobble signal of the sensor system a linear surface line approximation of the outer surface, wherein the controller is configured to provide an actuator signal in order to bring the linear surface line approximation in a direction perpendicular to the first direction and/or to maintain the linear surface line approximation at a constant distance from the printing assembly.
[0029] In an embodiment, the controller is configured to determine the linear outer surface line approximation by determining a line through a first location of the outer surface at the first end of the roll and a second location of the outer surface at the second end of the roll. The first location and the second location may be determined by a first sensor and a second sensor, respectively. Three or more sensors may be used to obtain further information on the unevenness of the outer surface. On the basis of this information also second or higher order approximations may be determined and used for wobble compensation.
[0030] The invention further provides a method to compensate wobble of a roll of a transport system configured to transport an image receiving member in an image forming apparatus, wherein the method comprises:
determining, by a sensor system, a wobble signal representative for wobble of the outer surface of the roll,
providing, by a controller, an actuator signal to actuate one or more actuators on the basis of the wobble signal, and
moving, by the one or more actuators, at least a part of the outer surface of the roll to compensate for the wobble of the roll.
[0031] In an embodiment, the step of providing an actuator signal comprises calculating a linear outer surface approximation of the outer surface, and calculating the actuator signal to bring the linear outer surface approximation in parallel with the axis of rotation of the roll.
[0032] In an embodiment determining the linear outer surface approximation comprises determining a line through a first location of the outer surface at the first end of the roll measured by a first sensor of the sensor system and a second location of the outer surface at the second end of the roll, measured by a second sensor of the sensor system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:
- Figure 1A depicts an image forming apparatus according to an embodiment of the invention;
- Figure 1B shows an ink jet printing assembly applied in the image forming apparatus;
- Figure 2A depicts schematically a side view of an image forming apparatus according to an embodiment of the invention;
- Figure 2B depicts schematically a top view of an image forming apparatus according to an embodiment of the invention loading of a flat substrate on a substrate support; and
- Figures 3A, 3B and 3C show an alternative embodiment for actively controlling the position of the infeed roll of an image forming apparatus.
DETAILED DESCRIPTION OF EMBODIMENTS
[0034] The present invention will now be described with reference to the accompanying drawings, wherein the same reference numerals have been used to identify the same or similar elements throughout the several views.
[0035] Fig. 1A shows an image forming apparatus 36, wherein printing is achieved using a wide format inkjet printer. The wide-format image forming apparatus 36 comprises a housing 26, wherein the printing assembly, for example the ink jet printing assembly shown in Fig. 1B is placed. The image forming apparatus 36 also comprises a storage means for storing image receiving member 28, 30, a delivery station to collect the image receiving member 28, 30 after printing and storage means for marking material 20. In Fig. 1A, the delivery station is embodied as a delivery tray 32. Optionally, the delivery station may comprise processing means for processing the image receiving member 28, 30 after printing, e.g. a folder or a puncher. The wide-format image forming apparatus 36 furthermore comprises means for receiving print jobs and optionally means for manipulating print jobs. These means may include a user interface unit 24 and/or a control unit 34, for example a computer.
[0036] Images are printed on an image receiving member, for example paper, supplied by a roll 28, 30. The roll 28 is supported on the roll support R1, while the roll 30 is supported on the roll support R2. Alternatively, cut sheet image receiving members may be used instead of rolls 28, 30 of image receiving member. Printed sheets of the image receiving member, cut off from the roll 28, 30, are deposited in the delivery tray 32.
[0037] Each one of the marking materials for use in the printing assembly are stored in four containers 20 arranged in fluid connection with the respective print heads for supplying marking material to said print heads.
[0038] The local user interface unit 24 is integrated to the print engine and may comprise a display unit and a control panel. Alternatively, the control panel may be integrated in the display unit, for example in the form of a touch-screen control panel. The local user interface unit 24 is connected to a control unit 34 placed inside the printing apparatus 36. The control unit 34, for example a computer, comprises a processor adapted to issue commands to the print engine, for example for controlling the print process. The image forming apparatus 36 may optionally be connected to a network N. The connection to the network N is diagrammatically shown in the form of a cable 22, but nevertheless, the connection could be wireless. The image forming apparatus 36 may receive printing jobs via the network. Further, optionally, the controller of the printer may be provided with a USB port, so printing jobs may be sent to the printer via this USB port.
[0039] Fig. 1B shows an ink jet printing assembly 3. The ink jet printing assembly 3 comprises supporting means for supporting an image receiving member 2. The supporting means are shown in Fig. 1B as a platen 1, but alternatively, the supporting means may be a flat surface. The platen 1, as depicted in Fig. 1B, is a rotatable drum, which is rotatable about its axis as indicated by arrow A. The supporting means may be optionally provided with suction holes for holding the image receiving member in a fixed position with respect to the supporting means. The ink jet printing assembly 3 comprises print heads 4a - 4d, mounted on a scanning print carriage 5. The scanning print carriage 5 is guided by suitable guiding means 6, 7 to move in reciprocation in the main scanning direction B. Each print head 4a - 4d comprises an orifice surface 9, which orifice surface 9 is provided with at least one orifice 8. The print heads 4a - 4d are configured to eject droplets of marking material onto the image receiving member 2. The platen 1, the carriage 5 and the print heads 4a - 4d are controlled by suitable controlling means 10a, 10b and 10c, respectively.
[0040] The image receiving member 2 may be a medium in web or in sheet form and may be composed of e.g. paper, cardboard, label stock, coated paper, plastic or textile. Alternatively, the image receiving member 2 may also be an intermediate member, endless or not. Examples of endless members, which may be moved cyclically, are a belt or a drum. The image receiving member 2 is moved in the sub-scanning direction A by the platen 1 along four print heads 4a - 4d provided with a fluid marking material.
[0041] A scanning print carriage 5 carries the four print heads 4a - 4d and may be moved in reciprocation in the main scanning direction B parallel to the platen 1, such as to enable scanning of the image receiving member 2 in the main scanning direction B. Only four print heads 4a - 4d are depicted for demonstrating the invention. In practice an arbitrary number of print heads may be employed. In any case, at least one print head 4a - 4d per color of marking material is placed on the scanning print carriage 5. For example, for a black-and-white printer, at least one print head 4a - 4d, usually containing black marking material is present. Alternatively, a black-and-white printer may comprise a white marking material, which is to be applied on a black image-receiving member 2. For a full-color printer, containing multiple colors, at least one print head 4a - 4d for each of the colors, usually black, cyan, magenta and yellow is present. Often, in a full-color printer, black marking material is used more frequently in comparison to differently colored marking material. Therefore, more print heads 4a - 4d containing black marking material may be provided on the scanning print carriage 5 compared to print heads 4a - 4d containing marking material in any of the other colors. Alternatively, the print head 4a - 4d containing black marking material may be larger than any of the print heads 4a - 4d, containing a differently colored marking material.
[0042] The carriage 5 is guided by guiding means 6, 7. These guiding means 6, 7 may be rods as depicted in Fig. 1B. The rods may be driven by suitable driving means (not shown). Alternatively, the carriage 5 may be guided by other guiding means, such as an arm being able to move the carriage 5. Another alternative is to move the image receiving material 2 in the main scanning direction B.
[0043] Each print head 4a - 4d comprises an orifice surface 9 having at least one orifice 8, in fluid communication with a pressure chamber containing fluid marking material provided in the print head 4a - 4d. On the orifice surface 9, a number of orifices 8 are arranged in a single linear array parallel to the sub-scanning direction A. Eight orifices 8 per print head 4a - 4d are depicted in Fig. 1B, however obviously in a practical embodiment several hundreds of orifices 8 may be provided per print head 4a - 4d, optionally arranged in multiple arrays. As depicted in Fig. 1B, the respective print heads 4a - 4d are placed parallel to each other such that corresponding orifices 8 of the respective print heads 4a - 4d are positioned in-line in the main scanning direction B. This means that a line of image dots in the main scanning direction B may be formed by selectively activating up to four orifices 8, each of them being part of a different print head 4a - 4d. This parallel positioning of the print heads 4a - 4d with corresponding in-line placement of the orifices 8 is advantageous to increase productivity and/or improve print quality. Alternatively multiple print heads 4a - 4d may be placed on the print carriage adjacent to each other such that the orifices 8 of the respective print heads 4a - 4d are positioned in a staggered configuration instead of in-line. For instance, this may be done to increase the print resolution or to enlarge the effective print area, which may be addressed in a single scan in the main scanning direction. The image dots are formed by ejecting droplets of marking material from the orifices 8.
[0044] Upon ejection of the marking material, some marking material may be spilled and stay on the orifice surface 9 of the print head 4a - 4d. The ink present on the orifice surface 9 may negatively influence the ejection of droplets and the placement of these droplets on the image receiving member 2. Therefore, it may be advantageous to remove excess of ink from the orifice surface 9. The excess of ink may be removed for example by wiping with a wiper and/or by application of a suitable anti-wetting property of the surface, e.g. provided by a coating.
[0045] Figures 2a and 2b show schematically a side view and a top view of an image forming apparatus 36 comprising a printing assembly 3 configured to print an image on the image receiving member 2 when the image receiving member 2 is arranged in a printing position 40 associated with the printing assembly 3.
[0046] The image forming apparatus 36 further comprises an image receiving member transport system 41 to transport the image receiving member 2 towards and away from the printing position 40.
[0047] The transport system 41 comprises an infeed roll 28 and an outfeed roll 42. The infeed roll 28 comprises an infeed support roll 43 and a quantity of image receiving member 2 supported by the infeed support roll 43 and, correspondingly, the outfeed roll 42 comprising an outfeed support roll 44 and a quantity of image receiving member 2 supported by the outfeed support roll 44.
[0048] When the image receiving member 2 is transported by the transport system 41 through the image forming apparatus 36, image receiving member 2 to be fed to the printing position 40 is unwound from the infeed roll 28 and image receiving member 2 on which an image has been printed is wound on the outfeed roll 42. The transport direction 45a, 45b of image receiving member 2 is indicated by arrows in Figures 2a and 2b. The transport direction 45a associated with the infeed roll 28 is the direction in which the image receiving member 2 is moved away from the infeed roll 28, and the transport direction 45b is the direction in which the image receiving member 2 is received by the outfeed roll 42.
[0049] It is remarked that instead of an outfeed roll 42, also a sheet cutting device and a delivery tray as shown in Figure 1A may be provided to receive printed image receiving member from the printing position 40.
[0050] The infeed roll 28 comprises an outer surface 46 and the outfeed roll 42 comprises an outer surface 47. It is remarked that since these outer surfaces 46, 47 are formed by the image receiving member 2 wound on the infeed roll 28 and the outfeed roll 42, respectively, the radius of the outer surfaces 46, 47 may change in dependency of the amount of image receiving member wound on the respective infeed roll 28 and outfeed roll 42.
[0051] The infeed roll 28 is rotatable about an axis of rotation 48 and the outfeed roll 42 is rotatable about an axis of rotation 49. The image receiving member 2 may not be wound completely even on the infeed support roll 41 and/or the outfeed support roll 42, which may result in wobble of the infeed roll 28 and/or outfeed roll 42 when image receiving member 2 is wound from the infeed roll 28 or on the outfeed roll 42. This wobble is undesirable as it may have a negative effect on the printing quality and/or may damage the image receiving member 2.
[0052] The first end of the infeed support roll 28 is pivotably mounted at a fixed position at mounting location 50. The second end of the infeed support roll 43 is pivotably mounted at a movable mounting location 51. The movable mounting location 51 is movable by an actuator 52 configured to move the movable mounting location 51 in the transport direction 45a, as indicated by a double headed arrow in Figure 2B.
[0053] To reduce the wobble of the infeed roll 28 and/or the outfeed roll 42, or at least substantially reduce the negative effects caused by the wobble of the infeed roll 28 or the outfeed roll 42, a wobble compensation system is provided.
[0055] The wobble compensation system comprises a sensor system comprising a first sensor 53 and a second sensor 54. The first sensor 53 is configured to measure a distance between the first sensor 53 and the outer surface 46 at the first end of the infeed roll 28 and at the contact line where the image receiving member 2 leaves the infeed roll 28 towards the printing position 40. The measurement direction is substantially radially with respect to the axis of rotation 48. As a result, the radius at the first end of the infeed roll 28 is determined.
[0056] Correspondingly, the second sensor 54 is configured to measure a distance between the second sensor 54 and the outer surface 46 at a second end of the infeed roll 28 and at the contact line where the image receiving member 2 leaves the infeed roll 28 towards the printing position 40. The measurement direction of the second sensor 54 is also substantially radially with respect to the axis of rotation 48 such that the radius of the outer surface 46 of the infeed roll 47 at the second end of the infeed roll 28 is measured.
[0057] The first sensor 53 and the second sensor 54 may be optical sensors that emit light in the measurement direction and receive light reflected on the outer surface 46, whereby on the basis of the emitted light and the reflected light, the distance between the respective sensor 53, 54 and the outer surface 46 may be determined.
[0058] Since the location of the first sensor 53 and the second sensor 54 is known, the position of each of the first end and the second end of the outer surface 46 can be determined. The combination of the position of the outer surface 46 at the first end and at the second end of the infeed roll 46 is representative for the wobble of the roll. A perfectly even wound up image receiving member 2 on the infeed roll 28 will have the same radius of the outer surface 46 at the first end and the second end of the infeed roll 28. An uneven radius measured at opposite ends of the infeed roll indicates the presence of wobble in at least the longitudinal direction of the outer surface 46.
[0059] The output of the first sensor 53 and the second sensor 54 is fed into a controller 55. The controller 55 is configured to determine an actuator signal that is fed to the actuator 52 to actively position the second end of the infeed support roll 43 to compensate for any wobble determined in the longitudinal direction of the outer surface 46.
[0060] The actuator 52 is capable of moving the second end of the infeed support roll 43, and therewith the outer surface 46 at the second end of the infeed roll 42 in the transport direction 45a. With this movement, the orientation of the outer surface at the contact line can be adapted. Wobble may be compensated by adapting the orientation of the outer surface in such a way that the orientation of the outer surface at the contact line where the image receiving member leaves the infeed roll 28 remains substantially perpendicular to the transport direction 45a of the image receiving member 2.
[0061] It is remarked that three or more sensors may be arranged in the longitudinal direction (one shown in Figure 2B in dashed lines between the first sensor 53 and the second sensor 54) to determine the radius of outer surface 46 of the infeed roll 28 in the longitudinal direction of the infeed roll 28. This may provide further information on the unevenness of the outer surface 46 of the infeed roll 28 and therewith on the wobble of the infeed roll 28.
[0062] Further, in addition to the first sensor 53 and the second sensor 54, the wobble compensation system shown in Figures 2A and 2B comprises a first edge sensor 56 and a second edge sensor 57. Each of the first edge sensor 56 and the second edge sensor 57 is configured to determine the position of one of opposite edges of the image receiving member 2 in an image receiving member path from the infeed roll 28 towards the printing assembly 3. By determining the position of the edges of the image receiving member 2 any sidewards movements, i.e. movements transverse to the transport direction 45a, of the image receiving member 2 can be determined.
[0063] These sidewards movements are also representative for the wobble of the infeed roll 28, and are fed into the controller 55 and used by the controller 55 to determine an actuator signal that is fed to the actuator 52 to compensate the wobble of the infeed roll 28. In the shown embodiment, the first edge sensor 56 and the second edge sensor 57 are used in addition to the first sensor 53 and the second sensor 54.
[0064] In alternative embodiments only the first edge sensor 56 and the second edge sensor 57 may be used to provide a measurement signal representative for wobble of the infeed roll 28, i.e. providing measurement signals on the basis of which wobble of the infeed roll 28 may be determined.
[0065] Any other type of sensor that can be used to determine an uneven radius of the infeed roll 28 or more generally wobble of the infeed roll 28 may also be applied.
[0066] The first edge sensor 56 and the second sensor 57 may for instance be optical sensors or cameras capable of monitoring the position of the respective edge of the image receiving member 2.
[0067] Furthermore, it is remarked that the controller 55 may also be used to actively position the outfeed roll 42 to compensate for wobble of the outfeed roll 42. The wobble compensation system of the outfeed roll 42 further comprises optical sensors 58, 59, edge sensors 60, 61 and an actuator 62.
[0068] The optical sensors 58, 59 are configured to measure a position of the outer surface 47 of the outfeed roll 42 at its first and second end, respectively, and the edge sensors 60, 61 are configured to determine a position of opposite edges of the image receiving member path moving towards the outfeed roll 42. The actuator 62 is provided to actively position a movable pivotable mounting location 63 of the outfeed support roller 44 in the transport direction 45b on the basis of an actuator signal of the controller 55. A mounting location 64 at the first end of the outfeed roll 42 pivotably supports the outfeed support roll 44 at a fixed position.
[0069] Figures 3A, 3B and 3C show an alternative embodiment of actively controlling the position of the infeed roll 28 in order to compensate wobble of the infeed roll.
[0070] In this embodiment, the pivotable mounting location 70 at the first end of the infeed support roll 43 and the pivotable mounting location 51 at the second end of the infeed support roll 43 are both mounted movably in the transport direction 45a. At the first end of the infeed support roll 43 a first actuator 71 configured to move the first mounting location is provided and at the second end of the infeed support roll 43 a second actuator 52 configured to move the second mounting location 51 is provided.
[0071] The presence of the first actuator 71 and the second actuator 52 provides further possibility to actively control the position of outer surface 46 the infeed roll 28 in order to compensate wobble of the infeed roll 28.
[0072] On the basis of the sensor information obtained by a sensor system as shown in Figures 2A and 2B, a linear surface line approximation of the outer surface 46 can be determined. This linear surface line approximation is shown schematically by line 72 as the effect of an uneven radius at the contact line 73; more length of image receiving member 2 is provided at the second end of the infeed roll 28 than at the first end of the infeed roll 28.
[0073] This linear surface approximation can be obtained by estimating a line through a first location of the outer surface 46 at the first end of the infeed roll 28 as measured by the first sensor 53 and a second location of the outer surface 46 at the second end of the roll as measured by the second sensor 54. To compensate the uneven feed of image receiving member at opposite ends of the infeed roll 28, the controller 55 may be configured to provide actuator signals to actively position the feed roll 28 in such a way that the line 72 is directed perpendicular to the transport direction 45a. This can be achieved by actuating the first actuator 71 to move the movable mounting location 70 towards the printing assembly 3, in the shown embodiment to the right, as shown in Figure 3B. Alternatively, the second actuator 52 may be activated to move the mounting location 51 in the opposite direction, or both movements can be made.
[0074] In this way the unevenness of the outer surface 46 in longitudinal direction of the infeed roll 28 and the resulting wobble may be compensated. However, wobble may also be caused by an unevenness of the radius of the outer surface 46 in the tangential direction. For example, the cross section of the infeed roll 28 may be oval instead of circular. Such unevenness may not be compensated by adapting the orientation of the infeed roll 28 as shown in Figure 3B.
[0075] Figure 3C shows how compensation of wobble caused by unevenness in tangential direction. When such unevenness in tangential direction is determined by the sensor system, the controller 55 can be configured to provide actuator signals to the first actuator 71 and the second actuator 52 to carry out identical movements of the first mounting location 70 and the second mounting location 51. The identical movements of the first mounting location 70 and the second mounting location 51 does not result in a change in the orientation of the infeed roll 28 with respect to the transport direction 45a, but in a translation of the complete infeed roll 28 with respect to the printing assembly 3.
[0076] By controlling this translation in line with the unevenness of the outer surface 46 in tangential direction wobble can be compensated, therewith effectively maintaining a constant distance between the infeed roll 28 and the printing assembly 3. Alternatively the wobble compensation system comprises a sensor to measure the disturbances caused by the wobble on the printed image or on the image receiving member substantially under the printing assembly to be able to correct for errors on the transport of the image receiving member at the error-sensitive location at the print assembly. At this position transport errors are most visible in the end-product, i.e. the produced image on the image receiving member.
[0077] In practice, the controller 55 may be configured to simultaneously compensate wobble caused by unevenness of the outer surface of the infeed roll 28 in the longitudinal direction and the tangential direction.
[0078] Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. In particular, features presented and described in separate dependent claims may be applied in combination and any advantageous combination of such claims are herewith disclosed.
[0079] Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. The terms "a" or "an", as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly.
[0080] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
1. An image forming apparatus to print an image on an image receiving member, wherein
the image forming apparatus comprises:
a printing assembly configured to print the image on the image receiving member, when the image receiving member is arranged in a printing position, and
an image receiving member transport system to transport the image receiving member towards and/or away from the printing position, wherein the transport system comprises:
a roll, rotatable about an axis of rotation and comprising an outer surface, wherein the roll comprises a first end and a second end, and
a wobble compensation system to compensate for wobble of the roll,
wherein at least a part of the outer surface of the roll is movable in a first direction substantially perpendicular to the axis of rotation, and in that wobble compensation system comprises:a sensor system configured to determine a wobble signal representative for wobble of said roll,
a controller to provide an actuator signal on the basis of the wobble signal, and
an actuator configured to move on the basis of the actuator signal at least the movable part of the outer surface to compensate for wobble of the roll.
2. The image forming apparatus of claim 1, wherein the roll comprises a support roll
and image receiving member wound on the support roll, wherein the outer surface is
formed by the image receiving member.
3. The image forming apparatus of claim 1 or 2, wherein the first end of the roll is
movable in the first direction to move the outer surface of the roll in the first
direction, and wherein the actuator is configured to move the first end of the roll
in the first direction to compensate for wobble of the roll.
4. The image forming apparatus of claim 3, wherein the second end of the roll is movable
in the first direction to move the outer surface of the roll in the first direction,
and wherein the wobble compensation system comprises a second actuator configured
to move the second end of the roll in the first direction to compensate for wobble
of the roll.
5. The image forming apparatus of claim 1 or 2, wherein a radius of the outer surface
with respect to the axis of rotation over at least a part of the length of the roll
is adaptable by said actuator in dependence of the actuator signal.
6. The image forming apparatus of any of the preceding claims, wherein the sensor system
comprises a first sensor to determine a location of the outer surface at the first
end of the roll and a second sensor to determine a location of the outer surface at
the second end of the roll.
7. The image forming apparatus of claim 6, wherein the sensor system comprises an array
of three or more sensors arranged along the roll in a longitudinal direction thereof,
wherein each of the three or more sensor is configured to determine in a direction
substantially perpendicular to the axis of rotation a location of the outer surface
of the roll.
8. The image forming apparatus of any of the claims 1-7, wherein the sensor system comprises
a first edge sensor configured to determine a position of a first edge of the image
receiving member, and a second edge sensor configured to determine a position of a
opposite second edge of the image receiving member.
9. The image forming apparatus of any of the claims 1-8, wherein the first direction
is substantially parallel to a transport direction of the image receiving member towards
or from the printing assembly.
10. The image forming apparatus of any of the claims 1-9, wherein the roll is an infeed
roll comprising a quantity of image receiving member to be transported towards the
printing position.
11. The image forming apparatus of any of the claims 1-9, wherein the roll is an outfeed
roll comprising a quantity of image receiving member received after the image receiving
member was moved passed the printing position.
12. The image forming apparatus of any of the claims 1-11, wherein the controller is configured
to determine on the basis of the wobble signal a linear surface line approximation
of the outer surface, wherein the controller is configured to provide an actuator
signal to bring the linear surface line approximation in a direction perpendicular
to the first direction and/or to maintain the linear surface line approximation at
a constant distance from the printing assembly.
13. The image forming apparatus of claim 12, wherein the controller is configured to determine
the linear outer surface line approximation by determining a line through a first
location of the outer surface at the first end of the roll and a second location of
the outer surface at the second end of the roll.
14. A method to compensate wobble of a roll of a transport system configured to transport
an image receiving member in an image forming apparatus, wherein the method comprises:
determining, by a sensor system, a wobble signal representative for wobble of the outer surface of the roll,
providing, by a controller, an actuator signal to actuate one or more actuators on the basis of the wobble signal, and
moving, by the one or more actuators, at least a part of the outer surface of the roll in a first direction substantially perpendicular to the axis of rotation of the roll to compensate for the wobble of the roll.
15. The method of claim 14, wherein the step of providing an actuator signal comprises
calculating a linear outer surface approximation of the outer surface, and calculating
the actuator signal to bring the linear outer surface approximation in a direction
perpendicular to the first direction.