This application is a U.S. National Stage Application of and claims priority to International Patent Application No. PCT/EP2014/066561, filed on Jul. 31, 2014, and entitled “DEVELOPING SECTIONS FOR DIGITAL PRINTING PRESSES, CONTROLLERS AND METHODS,” which is hereby incorporated by reference in its entirety.
Digital printing presses allow a hardcopy image to be produced on a substrate directly from digital data, such that no “analogue” intermediate media is required. Offset printing presses make use of an intermediate member to transfer an image from a plate member to a substrate. Offset printing may reduce wear on the plate member and may improve image quality by providing a transfer member that is able to conform to the topology of the substrate.
Examples of the invention are further described hereinafter with reference to the accompanying drawings, in which:
Each development unit 118 may contain a single ink, but the different development units 118 may contain inks of different colors. For example, the seven development units 118 of
The digital printing press 100 may produce a print as follows. The surface 110 of the photo imaging member 112 is charged by a charging assembly 114, such as a Scorotron assembly. As the photo imaging member 112 is rotated, a writing head 116 produces a laser beam that discharges specific areas on the surface 110 of the photo imaging member 112. These discharged areas define a latent image.
One development unit 118 applies ink to the foil 110 during each rotation of the photo imaging member 112. A development unit 118 is engaged with (e.g. moved near to or into contact with) the surface 110 of the photo imaging member 112. The development unit 118 may include a developer that is charged to a lower potential than the charged areas on the surface 110 of the photo imaging member 112, and a larger potential than the discharged areas on the surface 110 of the photo imaging member 112. Charged ink in the development unit 118 is attracted to the discharged areas on the surface 110 of the photo imaging member 112. Ink is transferred from the developing unit 118 (e.g from a developer roller 119 of the developing unit 118) to the discharged areas. Ink should not be transferred to those areas of surface 110 having higher potential than the developer roller 119. In this manner, ink is selectively deposited on the surface 110 of the photo imaging member 112. As the surface 110 of the photo imaging member 112 is rotated, a color plane of the image is formed on the surface 110 of the photo imaging member 112.
With each additional rotation of the photo imaging member 112, the writing head 116 discharges specific areas on the surface 110, and another development unit 118 applies ink to the discharged areas. In this manner, a developed image is formed on the foil 110.
The developed image is transferred from the surface 110 of the photo imaging member 112 to an Intermediate Transfer Member (ITM) 122. The ITM 122 may include a blanket 120 wrapped around the drum of the ITM 122, such that the image is transferred to the blanket 120. The transfer of the developed image may be achieved through electrical and mechanical forces. The blanket 120 may be charged and heated to raise the temperature of the ink on the blanket 120. The increase in temperature causes the ink to swell and acquire a gelatin-like form. With the help of another drum 124, the developed image is transferred from the blanket 120 to a substrate 126 (i.e., a print medium).
A controller 128 may be provided to control one or more of the elements of
In some arrangements, development units 118 that are not currently intended to transfer ink to the photo imaging member 112 may be disengaged (e.g. moved away) from the surface 110 of the photo imaging member 112 to prevent (or reduce) transfer of ink to the photo imaging member 112 from those development units 118. Accordingly, during a period in which only a single development unit 118 is to transfer ink to the surface 110 of the photo imaging member 112 (e.g. during a single rotation of the photo imaging member), the remaining development units 118 may be withdrawn away from the surface 110 of the photo imaging member 112.
The surface 110 of the photo imaging member 112 may include a seam, for example running along the surface 110 of the photo imaging member 112 parallel with an axis of the photo imaging member 112. In some examples, the seam is not appropriate for carrying a latent image, and a development unit 118 applying ink to the surface 110 of the photo imaging member 112 may be disengaged from the surface 100 of the photo imaging member 112 when the seam passes the development unit.
The photo imaging member 112 is illustrated in
In the arrangement of
As shown schematically in
In some applications, it may be desirable for consecutive image regions 230, 235 of the substrate 240 to be continuous, without a non-image region 250 between them. In order to avoid, or reduce, the non-image region 250, the substrate 240 may be rewound, such that after the substrate 240 has been advanced by an amount equal to the circumference CPIM of the photo image member (or more generally by an amount equal to the length of the photo image member 112 in a direction of the relative motion between the photo image member 112 and the development unit 118) the substrate feed direction may be reversed, and the substrate moved back, or rewound, such that the next image region 230, 235 will begin immediately after the end of the previous image region 230, 235. This is shown schematically in
In
In principle, electrical forces should block transfer of ink into unexposed areas of the photo imaging member, e.g. outside the borders of the latent image. However, in practice a small amount of ink may be transferred into these unexposed areas, due to some ink particles not being fully charged, for example. Herein, unexposed areas of the photo imaging member that are not intended to receive a particular ink may be referred to as the background, and particles of that ink in these regions may be referred to as background ink.
In an arrangement as illustrated in
In some examples, a repeat length, Lrepeat, may be defined for a print job. The repeat length may be defined as the separation between onsets of two subsequent images 230, 235 on the substrate (measured along a feed direction of the substrate 240). Typically, the repeat length is equal to the image length, Limage, such that subsequent images are immediately adjacent, without overlapping, so as to form a continuous series of images. However, this is not necessarily the case, and the repeat length may be greater or less than the image length. In the example of
According to some examples, background ink associated with a non-image region 250 of the substrate 240 (or a non-image portion 220 of the surface 110 of the photo imaging member 112) may be reduced or eliminated. The development unit 118 may be arranged to change between a first state and a second state depending on whether an image portion 210 or a non-image portion 220 of the surface 110 of the photo imaging member 112 is presented to the development unit 118 for development. When the image portion 210 is presented to the development unit 118, the development unit 118 is in the first state, in which ink may be transferred to the surface 110 of the photo imaging member 112 as normal. When the non-image portion 220 is presented to the development unit 118, the development unit 118 is in the second state, in which ink is prevented from being transferred to the surface 110 of the photo imaging member 112. Accordingly, the amount of ink transferred to the surface 110 of the photo imaging member 112 in the non-image region 220 will be reduced or eliminated, such that the amount of background ink in the overlap region 260 of the substrate 240 is reduced. According to these examples, prevention of ink transfer in the non-image portion 220 of the surface 110 of the photo imaging member 112 does not rely only on the electrostatic forces (such as may be used on to prevent unwanted ink transfer within the borders of the image), but also (or alternatively) changes a state of the development unit 118 based on whether an image portion 210 or a non-image portion 220 of the surface 110 of the photo imaging member 112 is presented to the developing unit 118. Accordingly, these examples may provide improved image quality in an overlap region of a substrate 240.
Controller 128 may control a configuration of the development unit 118 such that the development unit 118 is in a first state when the controller 128 determines that an image area of the surface 110 of the photo imaging member 112 is presented to the development unit for development, and such that the configuration of the development unit 118 is in a second state when the controller 128 determines that a non-image area of the surface 110 of the photo imaging member 112 is presented to the development unit. In some examples the controller 128 may be configured to control the development unit 118 to be in a first or second state based on a determination comparing a location of the portion of the surface 110 of the photo imaging member 112 presented to the development unit 118 with a location of a transition between the image portion 210 and the non-image portion 220.
Controller 128 may be arranged to determine an image portion of the surface 110 of the photo imaging member 112 corresponding with an extent of the image to be developed, with the extent being measured in the direction of motion of the photo imaging member 112 relative to the development unit 118. The extent of the image is the extent along the surface 110 of the photo imaging member 112 in the direction of movement of the photo imaging member 112 relative to the development unit 118.
The controller 128 may be further arranged to control the development unit, such that a configuration of the development unit is in a first state when the controller 128 determines that the portion of the surface 110 of the photo imaging member 112 presented to the development unit 118 is in the image portion
According to some examples, the controller may receive data describing the image to be developed, and may determine whether an image portion or a non-image portion is presented to the development unit 118 based on the received data.
In some examples, the received data may describe a repeat length associated with the image to be developed, and the determination of whether an image portion or non-image portion is presented to the development unit 118 may be based on the repeat length. In some examples, the determination may assume that the repeat length is equal to an image length (i.e. a length of the image to be developed). In some arrangements, the image length may not be readily available to the controller 128, and where the repeat length is available to the controller 128, approximation of the image length by the repeat length permits the reduction of background ink in the overlap region without requiring further information (e.g. provided by a user).
In some examples the controller may receive an adjustment value, representing an adjustment to the repeat length. In such arrangements the image length may be determined (or approximated) based on the repeat length and the adjustment value. The adjustment value may be a manually supplied adjustment.
According to some examples, the image portion of the surface 110 of the photo imaging member 112 corresponds with a portion of the surface 110 bearing a latent image.
The photo imaging member 112 moves relative to the developing unit 118 in order to present different portions of the surface 110 of the photo imaging member 112 for development by the development unit.
An actuator 410 may be provided to cause the movement of the development unit 118 between the engaged and disengaged states.
According to some examples, not all of the development units apply ink to the surface 110 at the same time; for example, there may be one active development unit applying ink to the surface 110 at a particular time, and the remaining development units may be inactive, and not applying ink to the surface 110. When the active development unit has completed applying ink to the photo imaging member (e.g. the active development unit has applied ink through a complete cycle of the photo imaging member), the active development unit may become inactive, and one of the inactive development units may become active. In some examples, inactive development units may be moved away from the surface 110 to prevent undesirable ink transfer. In some examples, in the second state the development unit may be in the same state as another development unit that is not currently to apply ink to the surface 110 of the photo imaging member 112. That is, in the second state, an active development unit may be moved away from the surface 110 in the same or similar manner as an inactive development unit. Accordingly, in some examples, this arrangement may be implemented by making use of functionality that may be provided in the device for another purpose, providing additional functionality while reducing or avoiding the need for structural modifications.
In some printing presses, the development unit may be positioned away from the surface 110 when a seam portion of the surface 110 is presented to the development unit, the seam portion being a region around a seam in the surface 110. According to some examples, the second state may correspond to the development unit being positioned away from surface 110, using the same or a similar mechanism to the mechanism for positioning the development unit away from the seam portion of the surface 110, such that the development unit 118 is withdrawn from the surface 110 in the second state. Accordingly, in some examples, this arrangement may be implemented by making use of functionality that may be provided in the device for another purpose, and may reduce or eliminate the need for structural modifications.
The development unit 518 of
The selective transfer of charged ink from the development unit 518 to the surface 110 of the photo imaging member 112 is achieved electrically, with the latent image (defined by discharged portions of the surface 110 of the photo imaging member 112) being attractive to the charged ink particles and areas not corresponding to the latent image (being defined by charged portions on the surface 110 of the photo imaging member 112, either within the image region 230 or the non-image region 250) presenting a repulsive, or rejecting, vector to the charged ink, substantially preventing transfer of ink.
In some arrangements, the charges on the developer roller 119 and squeegee roller 520 are intended to control the charged ink (e.g. by electrostatic attraction) and do not significantly change the charge carried by the ink.
According to the arrangement of
By increasing the repulsive vector in the second state (i.e. when the photo imaging member 112 presents a non-image region 250 of its surface 110 to the development unit 518), the transfer of ink may be reduced in the non-image region 250, leading to a reduction of background ink in the overlap region.
In some examples, the portion of the surface 110 of the photo imaging member 112 that is presented to the development section 518 may be the portion of the surface 110 that is in the nip 525, or at the start of the nip 525 (this may also be the case in examples in accordance with
According to some examples, the first state is a normal printing state, and the second state is a state associated with the non-image region 250 being in the nip 525. The following table gives exemplary voltages of components in the development unit 118 in the first state. Voltage 1 gives the voltage relative to an exposed portion of the photo imaging member (abbreviated as PIP in Table 1), and Voltage 2 gives the voltage relative to the developer roller 119. Exposed and Unexposed denote the portions of the surface 110 of the photo imaging member 112 that have been exposed nor not exposed, respectively.
The transition between the first and second state need not occur at when the boundary between the image region 230 and the non-image region 250 is in the nip 525. For example, the transition between the first and second state may occur at time T1-2=TNIR−ΔTe-d, where T1-2 is the time of the transition between the first and second states, TNIR is the time at which the boundary between the image region 230 and the non-image region 250 is at the start of the nip 525, and ΔTe-d is the time taken for ink at the end of the electrode (i.e. at the point of transfer from the electrode to the developer roller 199) to reach the start of nip 525. This example, the second state may differ from the first state by applying a different voltage to the electrode 510, e.g. by reducing the voltage on the electrode 510 (that is, increasing the absolute voltage difference between the electrode and the developer roller), such that the ink on the electrode 510 in the second state is more strongly charged. The more strongly charged ink will arrive at the nip 525 at approximately the same time as the boundary between the image region 230 and the non-image region 250. The more strongly charged ink will be repelled more strongly (have a greater repulsion vector), relative to ink charged in the first state, from the unexposed portions of the surface 110 of the photo imaging member 112. Accordingly, less ink will be transferred to the photo imaging member 112 in the non-image region 250.
As in the example above, the transition between the first and second state may occur before the boundary between the image region 230 and non-image region 250 meets the nip 525. The transition may occur when the boundary between the image region 230 and non-image region 250 is a predetermined temporal or spatial separation from the nip 525. In the above example, the transition occurs at a temporal separation of ΔT=ΔTe-d.
The second state may include multiple states. In some examples each of the multiple states is arranged to transfer less ink to a non-exposed area than the first state.
In the above example, the reduced (e.g. more negative, leading to a greater difference between the electrode voltage and the developer roller voltage) electrode voltage may relate to a first sub-state of the second state, and a second sub-state of the second state may follow the first sub-state. For example, a transition between the first and second sub-states may occur at time T21-22=TNIR−ΔTnip. Where T21-22 is the time of the transition between the first and second sub-states of the second state, and ΔTnip is the time taken for ink to pass from the start of the nip 545 to the end of the nip 545. In the second sub-state, the electrode voltage may be increased (relative to the first sub-state) and the voltage of the developer roller 119 may be increased, such that the repulsive vector is further increased, and ink transfer to the photo imaging member 118 is further inhibited. In some examples, the voltage difference between the electrode 510 and developer roller 119 may be the same in the first and second sub-states, such that the change in voltage of the electrode 510 (e.g. relative to a fixed potential, such as ground) between the first and second sub-states is the same as the change in voltage of the developer roller 119 (e.g. relative to a fixed potential, such as ground) between the first and second sub-states.
According to some examples, the electrode voltage does not influence the repulsion vector. In some arrangements the electrode voltage may be changed with the developer roller voltage, such that the difference between the electrode voltage and the developer roller voltage is the same in the first and second states. In other arrangements the electrode voltage and/or developer roller voltage may be changed independently.
In some arrangements, the transition to the second sub-state may occur at a time T21-22=TNIR−ΔT21-22, where ΔT21-22 is a specified time interval that may be greater or smaller than ΔTnip. By initiating the transition a short time before TNIR, the transition may be complete, or essentially complete before the non-image region 250 is in the nip 525, avoiding an initial portion of the non-image region 250 (neighboring the image region 230) from receiving a higher level of background ink before the transition to the second sub-state is complete (or sufficiently complete). In some examples, a reduction in image quality due to the transition to the second sub-state while the image region 230 is in the nip 525 may be avoided where ΔT21-22 is sufficiently short.
The voltages of the electrode 510 and/or squeegee 530 relative to the voltage of developer roller 119 may be controlled to make the ink on the developer roller 119 thinner, tackier and/or more highly charged. These properties of the ink at the nip 525 can reduce the background development on the photo imaging member. Moreover, in the non-image region 250, it is not necessary to ensure that ink can be transferred to the photo imaging member 112, since there is no image to develop in that region 250. This relaxes constraints on the properties of the ink.
The voltage of the developer roller 119 relative to the surface 110 of the photo imaging member 119 affects the electrical rejection vector of the non-image (charged) photo imaging member 112. In the non-image region 250, reducing the voltage of the developer roller 119 (increasing the difference between the voltage of the developer roller 119 and the voltage of the photo imaging member 119) will reduce background ink transfer to the development roller 119.
Table 2 gives examples of component voltages in the second state. As with table 1, voltage 1 is the voltage relative to an exposed portion of the photo imaging member. The second column gives the change in voltage between the first and second states, with the voltages measured relative to an exposed portion of the photo imaging member. Without the loss of generality, the voltage relative to the photo imaging member may be considered as an absolute voltage if we consider the exposed (latent image portion) of the photo imaging member to be 0V.
Table 2 additionally gives voltage 3, the voltage relative to the developer roller 119 in the second state. The fourth column in Table 2 gives the voltage difference between the first and second states, with the voltages measured relative to the developer roller 119 in the respective state.
Relative to the values in table 1, in table 2 the electrode has a larger voltage difference relative to the developer roller, leading to the ink being more highly charged in the second state. The squeegee roller has an increased voltage difference relative to the developer roller, leading to the ink being tackier in the second state. The developer voltage is increased relative to the photo imaging member, leading to an increased repulsion vector in the second state.
In some examples, the first state may have voltages as set out in table 1, and the second state may have one or more voltages as set out in table 2.
According to some examples, relative to the first state, the second state involves a change of only one or two of the developer roller 119, squeegee roller 520, and electrode 510. In other examples, all three voltages may be changed.
Where the second state has two or more sub-states, one or more of the voltages in table 2 may be used in one or more of the sub-states.
In some examples, the second state may include a gradual change from starting voltages (e.g. the voltages in the first state) to a target voltages (such as those in table 2).
The above examples described the transition from an image region 230 to a non-image region 250. However, similar approaches may be adopted for a transition from a non-image region 230 to an image region 250.
In the examples above, certain assumptions were made regarding the polarity of charges and voltages of the various elements. However, in other examples, the polarities may be reversed.
If the determination in 720 is positive, the method proceeds to 730 and the development unit 118 selectively develops the image on the photo imaging member 112 at 740. The method then proceeds to 760. Where the determination at 720 depends on a portion of the surface 110 of the photo imaging member 112 that is not currently presented to the development unit 118, the developing in 740 may be delayed until that portion of the surface 110 is presented to the development unit 118.
Where the determination in 720 is negative, the method proceeds to 750, and the development unit 118 is set in the second state. Where the determination at 720 depends on a portion of the surface 110 of the photo imaging member 112 that is not currently presented to the development unit 118, the developing unit 118 may continue to develop the photo imaging member. The method then proceeds to 760.
At 760 it is determined whether or not the cycle of the photo imaging member 112 is complete. Where the cycle is not complete, the photo imaging member 112 is advanced (e.g. rotated) at 770, and the method returns to 720.
Where it is determined at 760 that the cycle is complete, the method terminates at 780.
It is to be understood that the method may be performed continuously, with various stages occurring simultaneously, or substantially simultaneously. For example, advancing 770 the photo imaging member 112 may include be moving the photo imaging member 112 continuously, and as the photo imaging member 112 moves, determining 720 if an image portion 230 is presented to the development unit 118.
Herein, unless otherwise specified or another meaning is apparent, references to lengths and distances in relation to the photo imaging member 112 (such as the length of the surface 110 of the photo imaging member 112 and the length of the latent image) relate to a length measured along the surface 110 of the photo imaging member 112 in a direction parallel to the direction of motion of the photo imaging member 112 (relative to the development unit 118 in order to present different portions of the surface 110 of the photo imaging member 112 to the development unit 118. As is clear from the example of
Herein, a spread is used to describe a portion of the substrate 240 that has been printed as a result of one transfer cycle of the photo imaging member. A transfer cycle of the photo imaging member is used herein to describe one cycle of the photo imaging member to transfer ink to the ITM 122 from the whole useable surface 110 of the photo imaging member 112. For example, in the arrangement of
Herein, references to a portion of the surface 110 of the photo imaging member 112 being presented to a development unit 118 mean that that portion of the surface 110 of the photo imaging member 112 would receive ink from the active development unit 118 if the development unit 118 were engaged and if that portion of the surface 110 were to bear a part of the latent image that is to be developed. That is, a portion of the surface 110 of the photo imaging member 112 may be considered to be presented to the development unit 118 regardless of whether the development unit is engaged or disengaged, and regardless of whether or not the voltages applied to the components would cause transfer of ink to the photo imaging member 112. For example, the portion exposed to the development section 118 may be the portion in the nip 525 between development roller 119 and photo imaging member 112.
For simplicity, the examples of
Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.
Features, integers or characteristics described in conjunction with a particular aspect or example of the invention are to be understood to be applicable to any other aspect or example described herein unless incompatible therewith. 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. The invention is not restricted to the details of any foregoing examples. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2014/066561 | 7/31/2014 | WO | 00 |
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WO2016/015777 | 2/4/2016 | WO | A |
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