Abstract:
A printer or copier has a toner transfer belt which is moved into an out of engagement with a transfer printing area. The toner transfer belt is carried on an arrangement of rollers that maintain a constant tension on the toner transfer belt. Rigid linking levers extend between the rollers of the roller arrangement so that belt tension is maintained by movement of compensation rollers, outward while moving a transfer roller upward, for example.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a device for transferring at least one toner image from a toner carrier belt onto a carrier material, whereby the toner carrier belt carries the toner image to be transferred and has a predetermined belt tension, and whereby the toner carrier belt, in a first operating status, is arranged close to the carrier material in the transfer area in order to transfer the toner image and, in a second operating status, is arranged at a predetermined distance from the carrier material in the transfer area in order to prevent a transfer of the toner image. 
     2. Description of the Related Art 
     Published PCT Application No. WO 98/39691 of the same applicant discloses a printer or copier for the performance-adapted monochromous printing and/or colored one-sided or two-sided printing of a recording medium. The device uses a transfer belt onto which toner images of different hues are superimposed onto one another in a first operating status. The overall toner image arising in this way by superimposition is subsequently transferred to the recording medium. In the collecting operating phase, the toner carrier belt is distanced from the carrier material so that a transfer of the sub-toner images is prevented. The transfer belt is arranged close to the recording medium when the collected overall toner image is transferred for transferring the overall toner image. The content of Published Application WO 98/39691, therefore, is incorporated by reference into the present patent application as disclosure content. 
     In the aforementioned device concept, the transfer belt therefore is removed from the carrier material at the transfer location given a stoppage of the printing operation and is moved again toward the carrier material when the printing continues. This back and forth motion must be smooth given the operating mode for multicolor printing, in particular, since a transfer printing process occurring at the same time between a photoconductor belt and the transfer belt for transferring a toner image is otherwise impaired—the toner image is blurred, for example. Traditional devices with belt tension devices are not without jerky movements in the toner carrier belt, however, so that belt tension changes lead to a lower printing quality. 
     German Patent A 42 10 077 discloses an image generation device having an electrostatic transfer device for a latent print image. A roller that can be pivoted via a mechanism serves the purpose of optionally causing contact between a transfer belt and a photoconductor drum. 
     German Patent A 41 39 409 describes a further image generation device having an electrostatic transfer printing device. A transport belt led via at least two rollers guides a print medium along a photoconductor drum. A latent print image thereby is transferred from the photoconductor drum onto the print medium. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a device for transferring at least one toner image from a toner carrier belt onto a carrier material, whereby a high printing quality is obtained even given a back and forth motion of the toner carrier belt in the transfer printing area. 
     This object is achieved by a device for transferring at least one toner image from a toner carrier belt onto a carrier material, wherein the toner carrier belt carries the toner image to be transferred and has a predetermined belt tension, the toner carrier belt is held by a belt drive guiding the toner carrier belt through a roller device in the transfer printing area in which the toner image is transfer-printed onto the carrier material, the toner carrier belt, in a first state, is arranged close to the carrier material in the transfer printing area in order to transfer the toner image and, in a second state, is arranged at a predetermined distance from the carrier material in the transfer printing area in order to prevent a transfer of a toner image, and wherein the belt tension in the toner carrier belt is essentially the same in the first and second operating state. 
     Further advantages of the invention are realized by the belt tension also being the same in the transitional phase from the first operating state to the second operating state. In a preferred embodiment, the roller device is moved back and forth at least approximately perpendicular relative to the carrier material given a change of the operating states. 
     Preferably, the roller device has one single transfer printing roller which is moved back and forth at least approximately perpendicular given a change of the operating states, the belt drive has a stationary roller with a stationary rotational axis at both sides of the transfer printing roller, a movable compensation roller is respectively arranged between the stationary roller and the transfer printing roller, the respective distance between the rotational axes of the transfer printing roller and the compensation roller and the respective distance between the rotational axes of the compensation roller and the stationary roller remains constant in every operating state, and the diameters of the transfer printing roller, the compensation rollers and of the stationary rollers are of the same size. Specifically, the centers of the rotational axes of the transfer printing roller and the compensation rollers, as well as the centers of the rotational axes of the compensation rollers and the stationary rollers are connected to one another by rigid connecting-rod levers. The surface areas of the stationary rollers and of the compensation rollers may have contact with the toner carrier belt in both operating states and in the transitional phases. A movable cleaning roller of equal diameter may be arranged between the transfer printing roller and at least one of the compensation rollers, and the distance between the rotational axes of the transfer printing roller and of the cleaning roller, as well as the distance between the rotational axes of the cleaning roller and of the compensation roller remains constant in every operating state. The centers of the rotational axes of the transfer printing roller and of the cleaning roller, as well as the rotational axes of the cleaning roller and of the compensation roller are connected by rigid coupling elements. 
     As a preferred development, the rotational axis of the transfer printing roller is connected to a driving device which, in a linear motion, moves the rotational axis back and forth in an approximately perpendicular manner relative to the carrier material. The driving device may contain a switching eccentric. Alternatively, the rotational axis of the cleaning roller is connected to a further driving device moving the cleaning roller back and forth in a linear motion. 
     The toner carrier belt may be constructed to engage with a cleaning station or be removed from the cleaning station when the cleaning roller is moved back and forth. 
     The roller device of one embodiment is driven during its back and forth motion by the control surface of a rotating radial cam, at least one compensation roller is moved back and forth during the rotation of the radial cam, and the difference in length of a belt backlash, given the motion of the roller device, is compensated by the motion of the compensation roller. The roller device may contain two transfer printing rollers which are simultaneously moved back and forth by the control surface of a radial cam, each transfer printing roller having one compensation roller allocated to it, which is moved back and forth by the control surface of a radial cam. The transfer printing rollers and the compensation rollers that are respectively allocated to them are driven by the same radial cam. The radial cams are symmetrically rotated in preferred embodiments, or the radial cams can be asymmetrically rotated. 
     In one embodiment, the roller device can be moved in the direction of a guide bar, two tension rollers are symmetrically arranged relative to the guide bar, whereby the tension rollers are respectively connected by swivel arms to one end of the guide bar and by respectively one connecting rod to a sliding piece, which can be moved back and forth on the guide bar, and the tension rollers are charged with equal forces for pressing against the toner carrier belt. 
     A spring pressing against the sliding piece can be arranged on the guide bar. The roller device contains two transfer printing rollers that are symmetrically arranged relative to the guide bar. The belt drive may have two stationarily arranged deviation rollers for the toner carrier belt at both sides symmetrically relative to the center line of the guide bar, and the deviation rollers are of equal diameter. The belt drive of the preferred development does not contain additional tension elements apart from the two tension rollers. 
     In the first and second operating states, the belt tension in the toner carrier belt is inventively kept constant. The length of the toner carrier belt does not change as a result and belt tension spikes are prevented. Given simultaneous transfer printing of a toner image onto the toner carrier belt at a second transfer area, the environmental conditions in this transfer area remain constant and a high printing quality can be obtained as a result of the constant belt tension. 
     Advantageously, the belt tension in the toner carrier belt also remains the same in the transitional phase from the first operating state to the second operating state and vice versa. This means that the transport motion of the belt can also be maintained during this transitional phase without reducing the quality given simultaneous transfer printing of a toner image onto the toner carrier belt. 
     A transfer belt is to be preferably provided as a toner carrier belt, whereby a toner image is transferred, in a transfer printing process, from a toner image generation device, such as a photoconductor drum or a photoconductor belt, onto the transfer belt. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are subsequently explained on the basis of the drawings. Further advantages and features of the invention are described on the basis of these exemplary embodiments. 
     FIG. 1 is a side view which schematically shows a connecting-rod lever movement mechanism. 
     FIG. 2 shows a connecting-rod lever movement mechanism in a simplified perspective representation. 
     FIGS. 3 a  and  3   b  are schematic side views which show a movement mechanism with radial cams. 
     FIGS. 4 a  and  4   b  are schematic side views which show the radial cams according to FIGS. 3 a  and  3   b  in a different movement phase. 
     FIG. 5 is a side view which shows a further exemplary embodiment with tension rollers. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a first exemplary embodiment of the invention in a simplified schematic representation. A toner carrier belt fashioned as a transfer belt  10  is guided around rollers of a belt drive, which is generally referred to as  12 . FIG. 1 only shows one part of the belt drive  12  and of the transfer belt  10 . The transfer belt  10  is guided around a roller device  13  with one single transfer printing roller  14 , whose rotational axis  16 , with the assistance of a longitudinal guide  18  and a driving device, can execute back and forth motions approximately perpendicular relative to a carrier material  22 , generally single sheets or belt material composed of paper. The driving device  20  contains a switching eccentric  24 , for example, whereby the rotational axis  16  moves back and forth in the direction of the arrow P 1  when the switching eccentric is rotated. 
     The belt drive  12  contains two stationary rollers  26  and  28  whose rotational axes  30  and  32  are stationarily anchored at the frame of the belt drive  12 . Compensating rollers  34  and  36 , whose rotational axes  38  and  40  are mobile and can be moved in the direction of the arrows P 2  and P 3 , for example, are arranged between the transfer printing roller  16  and the stationary rollers  26  and  28 . 
     A mobile cleaning roller  42 , whose rotational axis  44  can be moved back and forth in the direction of the arrow P 4  by a further driving device  46  having a switching eccentric, is arranged between the transfer printing roller  14  and the compensating roller  34 . During this back and forth motion, the movable cleaning roller  42  with the transfer belt  10  is engaged or disengaged with respect to a cleaning roller  48 . This cleaning roller  48  serves the purpose of removing residuary toner material which is still present after the transfer printing on the transfer belt  10 . 
     The rotational axis  32  of the stationary roller  28  and the rotational axis  40  of the movable roller  36  are connected to one another by a rigid coupling element  50 , which can execute swivelling motions on the rotational axes  32  and  40 . This rigid coupling element  50  serves the purpose of keeping the distance between the rotational axes  32  and  40  in all operating phases constant. A rigid, pivotable coupling element  52  is also arranged between the rotational axis  40  of the movable roller  36  and the rotational axis  16  of the transfer printing roller  14 . A further rigid coupling element  54  is provided between the rotational axis  16  of the transfer printing roller  14  and the rotational axis  44  of the cleaning roller  42 . The rotational axis  44  of the cleaning roller  42  and the rotational axis  38  of the movable roller  34  are connected via a rigid coupling element  56 . Finally, the rotational axis  38  of the movable roller  34  is also connected to the rotational axis  30  of the stationary roller  26  via a rigid, pivotable coupling element  58 . The coupling elements  50 ,  52 ,  54 ,  56  and  68  can be of different length. A critical feature of the invention is that the diameter of the rollers  26 ,  28 ,  34 ,  36 ,  42  and  14  is the same. The rotational axes  16 ,  30 ,  32 ,  38 ,  40  and  44  are arranged parallel to one another and reside perpendicular relative to the paper plane in FIG.  1 . 
     The transfer belt  10  is generally composed of a plastic material. A slight change in length of the transfer belt  10 , e.g. within the mm range, can arise as result of changes in humidity or temperature, for example. For compensating this change in length, a separate tension roller (not shown) can be provided. The roller  28  can also assume the function of a tension roller and can have an excursion of approximately 1 mm. The roller  28 , however, can still be considered stationary, since this excursion at the transfer printing location or, respectively, at the transfer printing locations, does not cause a change in location of the toner picture elements to be transferred with respect to the carrier material  22  or a photoconductor belt. 
     The functions of the arrangement are subsequently explained according to FIG.  1 . In the illustrated state of FIG. 1, the transfer belt  10  is kept in immediate proximity of the carrier material  22  given its forward motion in the direction of the arrow P 0  or, respectively, is in contact with this carrier material  22 . In this operating state, toner images, which are present on the transfer belt  10  in a relatively loose form and have not yet been fixed, can be transfer-printed onto the carrier material  22 . Given activation of the driving device  20 , a second operating state is adjusted, wherein the transfer printing roller  14  is upwardly moved in the direction of the arrow P 1 . The motion is transferred, by the coupling elements  50 ,  52 ,  54 ,  56  and  58 , onto the movable rollers  34 ,  36  and  42  when the transfer printing roller  14  is lifted. The stationary rollers  26  and  28  do not move. As it has already been mentioned, the coupling elements  50 ,  52 ,  54 ,  56  and  58  are pivotably borne on the rotational axes  32 ,  40 ,  16 ,  44 ,  38  and  30 . The movable rollers  36 ,  42  and  34  are predominately moved in the direction of the arrows P 2  and P 3 , since the cleaning roller is stopped and does not execute a movement in the direction of the arrow P 4 . Since the connecting-rod levers  50 ,  52 ,  54 ,  56  and  58  extend exactly parallel to the corresponding sections of the transfer belt  10 , the diameters of the allocated rollers  28 ,  36 ,  14 ,  42 ,  34  and  26  are identical, a change in length in the transfer belt  10  does not arise, regardless of how large the stroke is by which the transfer printing roller  14  is lifted by the driving device  20 . This means that the belt tension in the transfer belt  10  is independent of this stroke and therefore remains constant. A spike or an additional force does not occur when the transfer printing roller  14  moves. Therefore, the belt tension also remains constant in the transitional phase between both operating states of the transfer printing roller  14 . 
     Independently of the motion of the transfer printing roller  14 , the driving device  46  can move the cleaning roller  42  back and forth in the direction of the arrow P 4 . The connecting-rod levers  58 ,  56  and  54  then perform compensating motions assuring that the transfer belt does not become loose, so that the belt tension therefore also remains the same within the transfer belt  10 . 
     A number of advantages are achieved by the arrangement of FIG.  1 . Each time the transfer printing roller  14  moves, the arrangement of the connecting-rod levers  50 ,  52 ,  54 ,  56  and  58  assures an exact allocation of the compensating rollers  36  and  34  to the transfer printing roller  14 . Mechanically complicated parts are not necessary; the effective mechanism of the arrangement is clear. The connecting-rod levers  50 ,  52 ,  54 ,  56  and  58  assume the driving and guiding of the compensating rollers  36  and  34 . Only the transfer printing roller  14  and the cleaning roller  42  must be moved by a separate drive. The connecting-rod lever movement mechanism makes it possible to include a further swivelling motion of neutral length at a different location of the transfer belt  10 , as is shown in the example of the movable cleaning roller  42  which is separately driven by a drive  46 . 
     FIG. 2 shows a perspective representation of the movement mechanism of FIG. 1, whereby the same parts are referred to by the same reference character. In the arrangement of FIG. 2, the connecting-rod levers  54  and  56  are combined to one single connecting-rod lever  55 . It can be seen in FIG. 2 that connecting-rod levers are arranged on both sides of the rollers. The arrangement in FIG. 2 has corresponding connecting-rod levers  50 ′,  52 ′,  55 ′ and  58 ′ that are arranged in the back. 
     FIGS. 3 a  and  3   b  show another exemplary embodiment, wherein control cams are used. Parts that correspond to previous exemplary embodiments are referred to by the same reference characters. The transfer belt  10  is moved in the direction of the arrow P 0  by the belt drive  12 . At a first transfer printing location  60 , the toner image on a photoconductor belt  62  is transferred onto the transfer belt  10 . The transfer belt  10  is deviated at a deviation roller  64  and is guided past a first compensating roller  66 , which can be moved in the indicated arrow directions. The transfer belt  10  subsequently arrives at a second transfer printing area  68 , in which the toner image situated on the transfer belt  10  or the collected overall color toner image is transferred onto the carrier material  22 . The roller device  13 , which can be moved back and forth in perpendicular direction relative to the carrier material  22 , is arranged in the transfer printing area  68 . The roller device  13  has two transfer printing rollers  70  and  72 , which can be moved in the direction of the shown arrows. Subsequently, the transfer belt  10  is guided past a second compensating roller  74 , which can be moved in the direction of the shown arrows. The belt drive  12  contains a second transfer printing roller  76  at which the transfer belt  10  is deviated. 
     The deviation rollers  70  and  72  and the compensation rollers  66  and  74  are driven by control cams  78  and  80 , as can be seen in greater detail in FIG. 3 b  on the basis of the control cam  78 . The control cam  78  has an elliptic control surface  82  and can be rotated around a rotational axis  84 . In the shown state, the deviation roller  70  is maximally downwardly excused, whereas the compensation roller  66  is maximally excused to the left. Given a clockwise rotation of the control cam  78 , the compensating roller  66 , in FIGS. 3 a  and  3   b,  is excused to the right due to the elliptic control surface  82 , whereas the deviation roller  70  moves upward given a corresponding pretension. If the compensating roller  66  was stationary, the transfer belt  10  wrapping around the two rollers  66  and  70  would become loose by a difference of length when the transfer printing roller  70  moves upward. The control surface  82  of the control cam  78  is arched such that the difference of length resulting from the upward motion of the transfer printing roller  70  is precisely compensated by the motion of the compensating roller  66  to the right. The resulting control surface  82  must not necessarily be elliptical but can also assume a different cam shape. 
     FIGS. 4 a  and  4   b  show the relationships when the radial cams  78  and  80  have rotated by 90° in a clockwise direction. The transfer printing roller  70  and the compensation roller  66  moved from the position which is shown in broken lines in FIG. 4 b  to the position shown with solid lines. It can be seen in FIG. 4 a  that the transfer belt  10  is lifted from the carrier material  22  in the shown state. In this state, a transmission of toner images onto the carrier material  22  is prevented; the transfer belt  10  and the carrier material  22  can have different speeds, whereby this is advantageous for starting the printing operation and for stopping the printing operation, since a relative motion can occur in these operating statuses. The control surface  82  of the radial cam  78  is preferably arched such that a length compensation for the transfer belt  10  ensues such that the difference in length of the transfer belt  10 , in the entire motion phase of the deviation rollers  70  and  72  and of the compensation rollers  66  and  74 , is compensated as a result of the back and forth motion of the deviation rollers  70  and  72 . In this case, belt tension modifications do not arise in the transfer belt  10 , so that a transfer printing can continue at the transfer printing location  60  without blur effects. 
     In the exemplary embodiment according to the FIGS. 3 a,    3   b,    4   a  and  4   b,  the two radial cams  78  and  80  are symmetrically rotated, whereby a symmetric motion process also results and the two deviation rollers  70  and  72  are swivelled in a parallel fashion. This exemplary embodiment according to the FIGS. 3 a  to  4   b  can be multiply varied. The radial cams  78  and  80  can be asymmetrically rotated, so that different asymmetrical swivel courses are obtained. For operating the roller pair deviation roller  70  and appertaining compensation roller  66  or, respectively, the roller pair deviation roller  72  and compensation roller  74 , a common radial cam  78  or, respectively,  80  or separate radial cams can be arranged on common or separate axes. 
     FIG. 5 shows a further exemplary embodiment of the invention, wherein spring-loaded tension rollers are used. The belt drive  12  transporting the transfer belt  10  has stationary deviation rollers  90 ,  92  and  94 , two tension rollers  96  and  98  and a roller device  13 , which is composed of two transfer printing rollers  100  and  102  and which can be moved back and forth. The tension rollers  96  and  98 , by swivel arms  104 ,  106 , are pivotably attached to a rigid rotational axis  108  at the end of a guide bar  110 . The rotational axes  112  and  114  of the tension rollers  96  and  98 , via connecting rods, are pivotally borne on a pivot  120 , which is attached to a sliding piece  122 . The sliding piece  122  can be moved along the guide bar  110 . The roller device  13  with the two deviation rollers  100  and  102  can also be moved along the guide bar  110 . The guide bar is stationarily fastened with respect to the belt drive  12  at the upper end in a rigid manner. A pressure spring  124  generates a pretension onto the sliding piece  122 . If the roller device  13  is now upwardly moved along the center line  126 , a belt backlash would occur in the transfer belt  10  given stationary belt rollers  96 ,  98 . The pressure spring  124  downwardly pushes the sliding piece  122  along the guide bar  110 , whereby the connecting rods  116  and  118  symmetrically move the tension rollers  96  and  98  to the outside along an orbit, which is defined by the swivel arms  104  and  106 . It is thus prevented that a belt backlash arises. The transfer belt  10  is equally tensioned on both sides of the roller device  13  as a result of the symmetrical arrangement of the tension rollers  96  and  98 , the connection by the connecting rods  116 ,  118  and the central spring  124 . Assuming that the transfer belt does not stretch itself, the actual belt length cannot change. It results therefrom that the individual picture elements on the transfer belt  10  move along the center line  126  and therefore perpendicular to the carrier material  22  at the transfer printing location  68 . It is thus ensured that the toner image is not blurred. Given swivelling-to and swivelling-from the roller device  14  onto the carrier material  22 , the printing image cannot become blurred. In order to obtain a symmetrical behavior, the two deviation rollers  92  and  94  are to be symmetrically arranged relative to the center line  126 . Due to the spring excursion, the belt tension can be slightly different in the printing transfer belt  10  in both operating modes; however, it is assured that the length of the transfer belt remains constant in both operating states with swivelled-to and swivelled-from roller device  13 . 
     Although other modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.