IMAGE TRANSFER DEVICE

Abstract: A device for transferring image information from a belt (1), driven at a first speed, to a medium (14) driven at a second speed, comprising - a pressing element (28), that can be brought in a first position in which it keeps the belt (1) free from the medium (14), and in a second position in which it keeps the belt (1) in a small zone in pressure contact with the medium to transfer the image, in which zone the belt (1) under the influence of frictional forces assumes the speed of the medium (14), - two guide rollers (27,29) disposed at either side of said zone, being movable along predetermined paths and excerting a tightening force on the belt (1), - as well as means to position one (27) of the guide rollers in a predeter­ mined position when said pressing element (28) is in said first position. In such a device the guide rollers (27, 29) still are in a relatively undefined position, when the pressing element (28) is in its first position. This unstable situation can cause vibrations in the movement of the image forming medium (14) and disadvantageously influence the image forming medium (14). Therefore the positioning means comprise a latching device (112) that keeps the guide rollers (27, 29) in a defined position when the pressing element (28) is free from the image forming medium (14).

Description: This invention relates to a device for transferring image information from a belt, driven at a first speed, to a medium driven at a second speed, comprising a pressing element, that can be brought in a first position in which it keeps the belt free from the medium, and in a second position in which it keeps the belt in a small zone in pressure contact with the medium to transfer the image, in which zone the belt under the influence of frictional forces assumes the speed of the medium. two guide rollers disposed at either side of said zone, being movable along predetermined paths and exerting a tightening force on the belt, as well as means to position one of the guide rollers in a predetermined position when said pressing element is in said first position. A device of this kind is known from US patent 4.183.658. The disadvantage of this known device is that when the pressing element is in the first position in which it keeps the belt free from the intermediate support the guide rollers on either side of the pressing element still are in a relatively undefined position. This can cause displacements of these guide rollers due to small speed variations in the drive of the image forming belt. These displacements of the guide rollers in turn result in vibrations which propagate in the movement of the image forming belt thereby disadvantageously influencing the image forming stations placed alongside said image forming belt. The object of the invention is to provide a device according to the preamble without the above disadvantage. According to the invention this object is attained in that said positioning means comprise a latching device co-operating with said one guide roller, said latching device allowing said one guide roller to move when said pressing element is in said second position or is moving to said position, and in that means are provided which exert a force on the latching device, when said pressing element has left the second position, the latching device, under influence of that force, causing said one guide roller to take up said predetermined position and latching it at that position. By means of this latching device the guide rollers are kept in a defined position when the pressing element is free from the intermediate support, so the movement of the image forming belt is in no way influenced by unwanted displacements of said guide rollers. In a further embodiment according to the invention, the latching device comprises a plate which is provided with a V-shaped excision, the edges of which cooperate with one end of the shaft of said one guide roller, and which plate is movable along a predetermined path, by which movement the V-shaped excision crosses the path of said end of the shaft of said guide roller, and the exerting means exert the force on the plate in order to keep the edges of the V-shaped excision in pressure contact with the said end of the shaft. The invention and its further advantages will be described in detail hereinafter with reference to the accompanying drawings wherein: Fig. 1 represents a cross-section of part of an electrophotographic apparatus in the form of a copying machine, Fig. 2 represents the image transfer section of the copying machine in detail, Fig. 3 represents a control device for controlling the copying machine, Fig. 4 represents a number of tables used for controlling the copying machine, Fig. 5 represents the block schematic of the servo-system for driving the intermediate support, Fig.6 represents in detail the correction circuit used in the servo system of Fig. 5, Fig. 7 represents a number of signals against time as generated in the servo system and delivered to the servo system of Fig. 5, and Fig.8 represents against one another a number of variables occurring in the servo system of Fig. 5. The copying machine Fig. 1 represents a cross-section of part of a copying machine. An original can be fed via drive rollers 44 along an entry path 52 into an endless path 54. A stop 49 is provided just past the drive rollers 44 and can be lifted by an electrically controllable actuating means. An original supplied along entry path 52 can be retained by means of stop 49. Drive rollers 45A - 45I are disposed along path 54 and take the original along path 54, the original being taken at uniform speed past an exposure slit 55. A switch 61 is disposed just past rollers 45H and can be set to a first and a second position. In the first position, the original is deflected in the direction of an exit path 62 so that the original leaves the path 54. In the second position the original is deflected in the direction of the rollers 45I, so that the original again passes the exposure slit 55. The portion of the original behind slit 55 is exposed by lamps 56. The image of this exposed portion is projected, by means of a lens 57 and mirrors 58, 59 and 60, onto a photoconductive belt 1 at an exposure place 59A. Belt 1 is advanced in the direction of arrow 77 at a speed which is in synchronism with the speed of the original. The path covered by the belt 1 comprises an image-forming section 2, in which a powder image is formed on the belt electrophotographically, a first belt drive section 6 in which belt 1 is driven by a drive roller 7 and a synchronous motor 8 connected to the mains supply, an image transfer section 3 in which the powder image can be transferred to an intermediate support 14, a cleaning section 4 in which any powder residues remaining on belt 1 are removed, a second belt drive section 9 in which belt 1 is driven by a drive roller 10 and a servo system 11, a meander 12 and a third belt drive section 13 in which belt 1 is driven by a drive roller 47 and a servo system 15. In the image-forming section 2, belt 1 is drawn by synchronous motor 8 over a freely rotatable guide roller 16 and the stationary guide rollers 17,18,19 and 20 at a uniform speed. Guide roller 16 is freely movable vertically. A displacement pick-up 21 is secured to the shaft of roller 16 and delivers a voltage VL3 which indicates the displacement of roller 16 with respect to a predetermined position. The displacement pick-up is so constructed that the magnitude of the voltage VL3 falls when roller 16 is displaced downwardly. Voltage VL3 is delivered via a signal line 22 to servo-system 15. Servo system 15 drives belt 1 at a speed proportional to the voltage VL3. Servo system 15 and displacement pick-up 21 together torn a feed-back control system by means of which roller 16 is kept in a state of equilibrium by adjusting the speed of belt 1. Disposed along the path of the belt 1 inside the image-forming section 2 are a corona charging device 23, projections means 57-60, and a magnetic brush developing device 25. Belt 1 is uniformly charged by means of corona charging device 23. Belt 1 is locally discharged by projection means 57 - 60 by projecting a light image of the original moving along the exposure slit 55, so that a charge image corresponding to the original is formed on belt 1. A powder image is formed by the magnetic brush developing device 25 by applying powder to the charge image. In the image transfer section 3, the belt 1 is taken along the freely rotatable guide rollers 26 -31. Roller 28 is secured to a horizontally movable block 32. Intermediate support 14 is disposed opposite roller 28. Intermediate support 14 consists of an endless belt, made from silicone rubber, trained over a drive roller 36 and a guide roller 34. Roller 36 is driven in the direction of arrow 76 by a servo system 35. A heating element 46 is disposed inside roller 34 to heat intermediate support 14 via the surface of roller 34. Roller 28 can be brought into three positions by displacement of block 32, viz.: a position of rest in which roller 28 is distant from the intermediate support 14 an auxiliary position in which roller 28 is situated in the direct vicinity of intermediate support 14 but in which the belt 1 is not in contact with the intermediate support 14, and a transfer position in which belt 1 is pressed by roller 28 against intermediate support 14 and the powder image is transferred from belt 1 to intermediate support 14. Hereinafter in the description, the actuating means for moving the block 32 will be described in detail. The rollers 27 and 29 are secured to a block 33. Block 33 is so coupled to block 32 mechanically that if block 32 is moved horizontally over a specific distance block 33 is moved in the same direction over half the distance. Consequently, the distance between the exposure place 59A and roller 28, as measured along the path covered by the belt 1, does not change as a result of displacement of roller 28. Roller 27 and roller 29 are freely movable horizontally with respect to block 33. If the roller 28 is in the position of rest or the auxiliary position, however, roller 27 is locked in a predetermined position. A displacement pick-up, in the form of a potentiomter 37, is secured to block 33. The slider of potentiometer 37 is secured to the shaft of roller 27. A spring (not shown) is also secured to the shaft of roller 27 to press roller 27 away from roller 28. Potentiometer 37 is connected to a voltage source. On displacement of roller 27, the slider of potentiometer 37 is driven by the shaft of roller 27, so that the voltage at the slider of potentiometer 37 changes (this slider voltage will hereinafter be denoted by VL1). This voltage change is an indication of the displacement of roller 27 with respect to block 33. The voltage source is so connected that the voltage VL1 drops off when roller 27 is moved towards roller 28. Voltage VL1 is delivered via a signal line 38 to servo system 35. By means of voltage VL1, servo system 35 controls the speed of roller 36 in such a way that the speed of belt 14 is kept equal to the speed of belt 1. Servo system 35 will be described in detail hereinafter in the description. A second displacement pick-up in the form of a potentiometer 39 is also secured to block 33. The slider of potentiometer 39 is secured to the shaft of roller 29. A spring (not shown) is also secured to the shaft of roller 29 to press roller 29 away from roller 28. Potentiometer 39 is connected to a voltage source. On displacement of roller 29 with respect to block 33, the slider of potentiometer 39 is driven by the shaft of roller 29 50 that the voltage at the slider of potentiometer 39 changes (this slider voltage will hereinafter be referred to as VL2). This voltage change is an indication of the displacement of roller 29 with respect to block 33. The voltage source is so connected that the voltage VL2 falls off when roller 29 is moved towards roller 28. Voltage VL2 is delivered via a signal line 40 to servo system 11. Servo system 11 drives belt 1 at a speed directly proportional to voltage VL2. Servo system 11 and potentiometer 39 together form a feedback control system by means of which roller 29 is kept in a position of equilibrium with respect to block 33 by adjustment of the speed of belt 1. A light source 70 is also disposed above the section of the belt 1 between the rollers 27 and 28 in order to reduce the adhesion of the powder image to the belt 1. Disposed opposite roller 34 is a pressure roller 68 which can be pressed against intermediate support 14 by actuating means (not shown). A sheet of paper can be fed between the rollers 34 and 68 along a paper conveying path 69 by means of a conveyor roller 48. Just past conveyor roller 48 there is disposed a stop 50 which can be raised or lowered by actuating means (not shown). In the low position, any sheet of paper fed via path 69 is retained by stop 50. A cleaning brush 72 is provided in the cleaning section 4 opposite a roller 73 to remove any powder residues remaining on the belt 1. Before belt 1 reaches brush 72 the belt is exposed by a lamp 71, by means of which any charge residues on belt 1 are removed. After roller 73 belt 1 is fed via a roller 74 to drive section 9 and then to meander 12. Meander 12 consists of a number of rollers 41A - 41K and a vertically freely movable roller 75 over which the belt 1 is taken. A number of detectors are also provided to control the copying process, namely a detector 64 which detects the presence of an original in the entry path 52, a detector 66 disposed at a predetermined distance from slit 55 to detect the presence of an original passing, and a detector 67 in the meander 12. Detector 67 is disposed at a predetermined distance from exposure place 59A and detects a marker 43 applied on belt 1. Marker 43 is disposed at a predetermined distance from a seam 42 present in the belt 1. Fig. 2 represents the image transfer section 3 in detail. Freely rotatable rollers 100A - 100C are secured to block 32 and rest on a guide 101 secured to the frame of the copying machine, so that block 32 can be displaced horizontally with little friction. A first rack 103 is secured to guide 101. A gearwheel 102, the shaft of which is mounted in block 33, engages rack 103. Gearwheel 102 also engages a second rack 104 secured to block 32. When block 32 is displaced a specific distance with respect to guide 101, gearwheel 102 and hence block 33 are displaced over half the distance as a result of the displacement of rack 104. Shafts 107 and 108 of rollers 27 and 29 respectively are freely movable horizontally in slots 105 and 106 respectively in block 33. A force is exerted in the direction of arrow 110 at each end of the shafts 107 and 108 by means of a torsion spring 109. Each torsion spring 109 is freely rotatable about a shaft 133 secured to block 33 midway between the ends of the shafts 107 and 108. The tension in the belt 1 before and after roller 28 is substantially identical as a result of the above steps. A latch 112 is secured to a shaft 113, the latter being mounted in block 33 so as to be freely rotatable. Latch 112 is formed with a notch by means of which shaft 107 can be set at a predetermined place with respect to block 33. A pawl is secured to the frame of the copying machine and co-operates with an inclined portion of latch 112. When block 33 is moved to the left pawl 114 presses against the inclined portion so that latch 112 is pressed up. Shaft 107 is thus unlocked so that it becomes freely movable in slot 105. A toggle lever 115 is pivotable about a shaft 116 secured to the frame of the copying machine. One side of the toggle lever 115 is coupled to block 32. The other side of toggle lever 115 is connected via a rod to a piston 117 freely movable in a cylinder 118. The end of cylinder 118 is secured to the frame of the copying machine. Either the bottom part 119 or the top part 120 of cylinder 118 can be pressurised by means of electrically controllable actuating means 123. A rod 121 is also connected to lever 115. A shaft 126 about which a roller 122 is freely rotatable is secured to the end of rod 121. Aside of roller 122 is a roller 125 freely rotatable about a shaft 127 secured to the frame of the copying machine. A wedge 128 is located between the rollers 122 and 125 and rests against roller 125 on one side. A piston 129 is secured to the wedge and co-operates with a cylinder 130 secured to the frame of the copying machine. Either the top part 131 or the bottom part 132 of cylinder 130 can be pressurised by means of an electrically controllable actuating means 124. Cylinder part 119 and cylinder part 131 respectively are pressurised by the actuating means 123 and 124 in the position represented in Fig. 2. Roller 28 is then in the position of rest. As soon as pressure is applied to cylinder part 120 by actuating means 123, piston 117 is pressed out of cylinder 118 so that pivoting of the toggle lever 115 causes block 32 and hence also block 33 to be displaced to the loft with respect to Fig. 2. When the roller 122 driven by lever 115 and rod 121 reaches wedge 128, any further pivoting of the toggle lover 115 is counteracted. The roller 28 secured to block 32 is then in the auxiliary position. In this position block 32 has not yet been moved to the loft to such an extent that latch 112 is pressed up by pawl 114, so that roller 27 remains locked. When cylinder part 132 is then pressurised, wedge 128 is raised by piston 129. Consequently, roller 122 is no longer retained by wedge 128 so that toggle lever 115 is pivoted further in the clockwise direction as a result of the pressure in cylinder part 120, until roller 28 is pressed by block 32 against intermediate support 14. Roller 28 is then in the transfer position. Block 33 is displaced in these conditions to an extent such that pawl 114 presses up latch 112 so that shaft 107 becomes freely movable in slot 105. Belt drive In the above-described copying machine, the path covered by the belt 1 is divided up into three sections. In each section the belt 1 is advanced by a separate drive system. These sections are as follows: the section between roller 16 and roller 7, in which belt 1 is advanced by synchronous motor 8, the section between roller 26 and drive roller 10, in which belt 1 is advanced by servo system 11, and the section between roller 41A and drive roller 47, in which belt 1 is driven by servo system 15. The tension in belt 1 in the section between roller 16 and roller 7 is determined by the force with which the roller 16 is pressed down. In the example described here, roller 16 is a roller moving freely in the vertical direction, so that the belt tension in this section, except for a small deviation due to friction, is determined by the weight of roller 16. The tension of belt 1 in meander 12 is determined by the weight of the roller 75, which is freely movable in the vertical direction. In the section between roller 26 and roller 10, if belt 1 is not in contact with belt 14 and if roller 27 is locked, the tension of belt 1 is determined by the force with which the ends of torsion springs 109 press against the ends of shaft 108 of roller 29. If roller 28 has been brought to the transfer position so that belt 1 is pressed against belt 14 and roller 27 is unlocked, the bolt tension between roller 28 and roller 10 is still determined by the force with which torsion springs 109 press against the shaft 108 of roller 29. However, in that case, the belt tension in the section between roller 26 and roller 28 is determined by the force with which torsion springs 109 press against the shaft 107 of roller 27. Since the torsion springs are disposed freely rotatable in the middle between the slots 105 and 106, the belt tension in the transfer position before and after the roller 28 is substantially identical. One of the results of this is that the frictional force required to advance the belt 1 and exerted thereon by belt 14 at the transfer zone is very low, so that the wear on the belts is low and any vibrations in belt 1 at the transfer zone, which would have an adverse effect on the quality of the transferred image, are avoided. As a result of the above steps, the belt tensions in the separate sections are independent of one another. It is thus possible to select optimum belt tension for each section. Also, vibrations in the belt in one section have hardly any effect, if any, on the other section. This is important particularly in respect to the image-forming part 2, where belt 1 has to be advanced at a very uniform speed at exposure place 59A since speed variations (due to vibrations) result in an unsharp copy. The average speed in the sections between the roller 26 and the roller 47 is made equal to the speed of the belt 1 in the image-forming part 2 by means of servo systems 11 and 15. Servo system 15 controls the speed of belt 1 at roller 16 in such a manner that roller 16 is held in a predetermined position. This means that belt 1 is taken to roller 16 by servo system 15 at a speed equal to the speed with which belt 1 is moved by motor 8. Similarly, servo system 11 keeps the speed at which belt 1 is taken away from roller 29 equal to the speed at which belt 1 is taken to roller 29. Image forming Copies of an original fed past the exposure slit 55 can be made by means of the above-described copying machine. To this end, to form one copy, a powder image is formed on belt 1 by successively charging, exposing and applying powder to belt 1. When the powder image approaches roller 28, the latter is brought into the transfer position so that belt 1 is pressed against belt 14. When the powder image then passes through the pressure zone between rollers 28 and 36, it is transferred to belt 14. The transferred powder image is heated while it is driven by the intermediate support 14. In these conditions the powder particles soften so that the image has become tacky when it approaches the roller 34. In the meantime, a cutting means (not shown) has cut a sheet of paper to the length of the powder image from a reel. The length of the sheet is derived from the length of the original which is in turn determined in the path 54. The cut-off sheet is taken along path 69 where it is retained by stop 50. As soon as the softened powder image approaches the roller 34, stop 50 is raised so that the sheet of paper lying in readiness is fed between the rollers 34 and 68. Also, roller 68 is pressed against belt 14. When the sheet and the powder image on belt 14 subsequently pass through the pressure zone between the rollers 34 and 68 the softened (and tacky) image material is pressed into the paper. After cooling the image will be firmly bonded to the paper and thus fixed. Control of copying machine The actuating means for displacing the rollers 28 and 68 and raising and lowering stop 50 and switching the corona device on and off are controlled by a control device 150 which will be described in detail hereinafter with reference to Fig. 3. The times at which rollers 28 and 68 have to be displaced, stop 50 has to be raised or lowered, and the corona device has to be switched on or off, are related to the location of the copy under formation on belt 1 or belt 14. These times will hereinafter be referred to as action times and the operation required to be carried out at a time will hereinafter be referred to as an action. In order to determine these action times, the control system for each copy under formation registrates the positions of the leading edge and the trailing edge of the part of belt 1 or belt 14 on which a copy is being formed. These parts will hereinafter be termed imaging sections. As soon as the leading or trailing edge of an imaging section reaches a location at which an action is required to be carried out (hereinafter referred to as the action location), the control system will deliver the necessary signals to the actuating means or actuating circuits so that the action is carried out through the agency of said means or circuits. For example, by means of control device 150: the corona device 23 is switched on when the leading edge of an imaging section reaches location V1 (see Fig. 1), corona device 23 is switched off when the trailing edge of an imaging section reaches location B1, the light intensity of the lamps 56 is adjusted as soon as the leading edge of an imaging section reaches location V3, roller 28 is brought into the transfer position as soon as the leading edge of an imaging section reaches location V4, roller 28 is brought into the auxiliary position as soon as the trailing edge of an imaging section reaches location B3, stop 50 is raised as soon as the leading edge of an imaging section reaches location V5, stop 50 is lowered again as soon as the trailing edge of an imaging section reaches location B4, roller 68 is pressed against belt 14 as soon as the leading edge of an imaging section reaches location V6, roller 68 is lowered again as soon as the trailing edge of an imaging section passes location B5. Before an image is formed a check is made to determine whether seam 42 comes within the imaging section intended for the formation of the image. The way in which this is determined will be described in detail hereinafter. If seam 42 comes within an imaging section, a so-called dummy copy is formed. Upon forming a dummy copy, the imaging section, after being charged, is again discharged by a lamp 51 (see Fig. 1) which is disposed between corona device 23 and exposure place 59A along the path traversed by the belt 1. Also, upon forming of a dummy copy, stop 50 is not raised so that no sheet of paper is fed between rollers 34 and 68. Upon forming of a dummy copy, lamp 51 is switched on at the time that the leading edge of the imaging section reaches location V2 and is switched off at the time that the trailing edge reaches location B2. Hereinafter, the control device 150 will be described in detail with reference to Fig. 3. In Fig. 3, reference 151 denotes a central processing unit (CPU) of a conventional type. The central processing unit 151 is connected via a data bus 152, an address bus 153 and a control bus 154, to a read-only memory (ROM) 155, a random access memory (RAM) 156, a control panel 157 for inputting data and displaying the input data in respect of a required copying order, and an interface circuit 158. Interface circuit 158 comprises a number of input gates 160, 161 and 162 and a number of output registers 163 - 173. Via address bus 153 the central processing unit 151 can select one of the input gates 160, 161 or 162 or one of the output registers 163- 173. Via data bus 152 the central processing unit 151 can read the input signals of the selected input gate or load a selected output register. The loading or reading process is controlled by central processing unit 151 via control bus 154. The inputs of input gates 160, 161 and 162 are connected to detectors 64, 66 and 67 respectively. The outputs of output registers 163, 166, 167, 168, 169 and 173 are connected to the control inputs of actuating means 123, an actuating means 175 for raising stop 50, an actuating means 174 for raising roller 68, an actuating means 177 for switching lamp 51 on and off, an actuating means 176 for raising stop 49, an actuating means 182 for actuating switch 61, respectively. The output of output register 172 is connected to the control inputs for switching servo systems 11 and 15 on and off and an actuating circuit 179 for switching synchronous motor 8 on and off. The outputs of output registers 164 and 165 are connected to the first and second input respectively of a two-input AND gate 190. The output of AND gate 190 is connected to the input of actuating means 124 for bringing roller 28 into the transfer position. Roller 28 is held in the transfer position when the output signal of AND gate 190 is 1, i.e. when both output register 164 and output register 165 is loaded with a 1. The outputs of output registers 170 and 171 are connected to the first and second input respectively of a two-input AND gate 191. The output of AND gate 191 is connected to the input of an actuating circuit 178 for switching the corona device 23 on and off. Corona device 23 is switched on when the output signal of AND gate 191 is 1, i.e. when both register 170 and register 171 is loaded with a 1. A pulse generator 180 is connected to the program interrupt input 181 of central processing unit 151. Pulse generator 180 delivers pulses P at a frequency proportional to the speed of belt 1 so that a period of the pulse signal corresponds to a constant displacement of belt 1. In order to control the copying process, the central processing unit 151 carries out a program stored in the read-only memory 155. Depending upon the copying order input via the control panel, the signals delivered by detectors 64, 66 and 67, and the stages of the various copies under formation, central processing unit 151 switches the means and devices required to form the copy on or off. For the purpose of performing each action, depending on whether it is a switching-on or switching-off action, the program comprises a switch-on action routine or a switch-off action routine. During the performance of a switch-on action routine or a switch-off action routine, the output register in question is loaded with a 1 or a 0 respectively. To determine the action times, central processing unit uses a leading edge action table 200, a trailing edge action table 201 and a copy table 202 (see Fig. 4). Central processing unit 151 also uses a seam position register 203 for registering the position of seam 42, and an order table 204 storing the data of the copy orders in progress (Fig. 4). Seam position register 203 consists of a memory location in the random accesss memory 156. Seam position register 203 contains a number which indicates the distance between marker 43 and detector 67. This distance is expressed as a number of periods of pulses P. Order table 204 consists of a number of memory locations with consecutive addresses in random access memory 156. The order table is used for storing the data of copying orders. A copying order of this kind comprises making a set number of copies of an original with a set exposure intensity. The order table is divided up into a number of rows 205 - 208 and a number of columns 209 - 213. Each row can be used to store the data of one copying order, viz.: in column 209 the required number of copies in column 210 the number of times that the original still has to be taken past exposure slit 55 in column 211 the number of copies still to be finished in column 212 the length of the copies to be made in column 213 the exposure intensity. Hereinafter, the memory locations in the columns 209, 210, 211, 212 and 213 will respectively be termed AT, OT, KT, LG and BG. Order table 204 also comprises an order row pointer (ORW) denoted by reference 254 and an order row counter (ORT) denoted by reference 255. ORW 254 points to the row containing the data of the latest copy order. The AT, OT, KT, LG, BG pointed to by ORW 254 will hereinafter be respectively designated AT (ORW), OT(ORW), KT(ORW), LG(ORW) and BG(ORW). ORT 255 points to the number of orders for which copies are still being formed. ORT 255 is increased by 1 when the data of a new copying order to be executed are input to order table 204, and ORT 255 is reduced by 1 when all the copies of a copying order have been finished. When a new copying order is introduced, the contents of ORW 254 are first increased by 1 and then the data of the new copying order are stored in the row pointed to by the adjusted ORW 254. However, if, before the increase, ORW 254 points to the last row 208 of order table 204, the data of the new copying order are stored in the first row 205 and ORW 254 is so adjusted that it points to the first row after the adjustment. The order table obtained in the manner described above thus always contains the data for those copying orders for which copies are under formation. Leading edge action table 200 consists of a number of memory locations with consecutive addresses in read-only memory 155. The table is divided up into a number of rows 215 - 221 and two columns 222 and 223. In leading edge action table 200 the distances between, respectively, the locations V1 and V2, V2 and V3, V3 and V4, V4 and V5, and V5 and V6 are fixed in column 222 in the rows 216, 217, 218, 219 and 220. The distance between location V1 and a location 0 situated at a distance from exposure place 59A corresponding to the distance covered by the belt 1 during the interval of time when the leading edge of an original covers the distance between the detector 66 and the slit 55, is also fixed in column 222 in row 215. The above distances are expressed as a number of periods of pulses P. In column 223, in the rows 215, 216, 217, 218, 219 and 220, are stored the initial addresses of the action routines for performing the actions associated with the locations V1, V2, V3,V4, V5 and V6. In column 222, row 211, is stored a stop code SC indicating the end of leading edge action table 200. Similarly, the distances between, respectively, the locations 0 and B1, B1 and B2, B2 and B3, B3 and B4, and B4 and B5 are fixed in the trailing edge action table 201 in column 244 in rows 246, 247, 248, 249 and 250. In column 245, rows 246, 247, 248, 249 and 250, are stored the initial addresses of the action routines for performing the actions associated respectively with the locations B1, B2, B3, B4 and B5, and related to the position of the trailing edge of an imaging section. In column 244, row 251, stop code SC indicates the end of the trailing edge action table. Copy table 202 consists of a number of memory locations with consecutive addresses in random access memory 156. Copy table 202 is divided up into a number of rows 226 - 231 and a number of columns 232 - 235. In copy table 202, the position of the leading and the trailing edge of the associated imaging section is kept for each copy under formation. Each row in copy table 202 can be used to indicate the position of one leading edge or the position of one trailing edge. By means of the so-called leading edge / trailing edge bit (hereinafter referred to as VAB) it is indicated in the memory location of a row in column 234 (hereinafter referred to as SG), whether the position of a leading or trailing edge is stored in the associated row. A row fro: the action table indicated by VAB is indicated by the memory location in column 233 (hereinafter referred to as AW). The memory location in column 232 (hereinafter referred to as AG) stores a number which indicates the distance that the associated edge of an imaging section still has to cover before calling on that action routine of which the initial address is stored in the row pointed to by AW in the action table indicated by VAB. These distances are expressed as a number of periods of pulses P. The copy table is updated after each pulse P. The manner in which this takes place will be described hereinafter. A row from order table 204 is pointed to by each memory location in column 235 (hereinafter referred to as OW). Copy table 202 also contains a copy table row pointer (KRW) indicated by 236, a copy table row counter (KRT) indicated by 237, an auxiliary pointer (HW) indicated by 238, and an auxiliary counter (HT) indicated by 239. The row taken into use the latest from copy table 202 is pointed to by means of KRW 236. The AG, AW, SG and OW pointed to by KRW 236 are hereinafter referred to respectively as AG (KRW), AW (KRW), SG (KRW) and OW (KRW). KRT 237 indicates the number of rows in copy table 202 which is in use. For each copy requiring to be formed, two rows are taken into use in the copy table 202. The position of the leading edge of the imaging section is registered in one row and the position of the trailing edge of the imaging section is registered in the other row. When a row is put into use, the contents of KRW 236 are first increased by 1 and then the row indicated by the adjusted KRW 236 is filled with the necessary data. However, if KRW 236 indicates the last row before the increase, the first row 226 is taken into use and KRW 236 is so adjusted that the first row 226 is indicated after the adjustment. Also, each time a row is taken into use, KRT 237 is increased by 1. KRT 237 is reduced by 1 if the leading or trailing edge passes location V6 or B5 respectively. The way in which this is performed will be described in detail hereinafter. In addition to the abovementioned tables 200, 201, 202 and 204 and register 203, a number of memory locations in the random access memory 156 (hereinafter referred to as the input memory) are also used to store data for the last copy order input via control panel 157 but not yet started. In the example described here, these data are the number of copies to be made and the required exposure intensity. Fig. 5 represents the block schematic of the servo system 35 for controlling the speed of belt 14. The voltage VL 1 at the slider of potentiometer 37 is fed via signal line 38 to a first input 400 of a summation circuit 401 and to an input 402 of a correction circuit 403, the latter being described in detail hereinafter. Output 404 of correction circuit 403 is connected to a second input 405 of summation circuit 401 The control signal 419 originating from AND gate 190 is fed not only to actuating means 124 for bringing roller 28 into the transfer position, but also to an input 409 of correction circuit 403 and to the input of a delay circuit 406. Delay circuit 406, in response to a 1-0 changeover of signal 419, generates a signal 408 of fixed pulse width which is delayed with respect to the 1-0 changeover. Both signal 419 and signal 408 are represented against time in Fig. 7. Output 411 of summation circuit 401 is connected to a first input 412 of a controller 413. A servo motor 415 is energized by a signal originating from an output 414 of controller 413. Servo motor 415 is connected to the shaft of drive roller 36 for driving belt 14. A tachogenerator 416 is also connected to the shaft of servo motor 415. Output 417 of tachogenerator 416 delivers a voltage proportional to the revolutions per second of motor 415. This voltage is fed to a second input 418 of controller 413. By means of this controller 413 the revolutions per second of motor 415 and hence the speed of belt 14 are so controlled in a manner known in control theory that the voltage at the inputs 412 and 418 of controller 413 remain equal to one another. The speed of belt 14 controlled in this way is thus proportional to the voltage Vref at the input 412 of controller 413. Fig.6 represents the correction circuit 403 in detail. Voltage VI 1 is fed to the input 402 of an operational amplifier 420 connected as a voltage follower. The output Of amplifier 420 is connected, via an electronic switch 421 actuated by signal 419, to an analog memory ciruit 422. The output of amplifier 420 is also connected to the positive input of a subtraction circuit 423. The negative input of subtraction circuit 423 is connected to the output of memory circuit 422. The output of subtraction circuit 423 is connected to the negative input of a second subtraction circuit 424. The output of subtraction circuit 424 is connected, via an electronic switch 425 actuated by signal 408, to a second memory circuit 426. The output of memory circuit 426 acts as the output 404 of correction switch 403. Output 404 is connected, via an electronic switch 427 actuated by signal 419, to the input of a third memory circuit 428. The output of memory circuit 428 is connected to the positive input of subtraction circuit 424. The operation of servo system 15 will be described hereinafter with reference to Fig. 7 and Fig. 8. Fig. 7 represents the signals 419 and 408, voltage VL 1, voltage Vref, voltage - U at the output of subtraction circuit 423, and voltage VG at output 404 against time. Fig.8 represents the speed Vt of belt 14 against the voltage Vref and, for a number of values of VG, the voltage Vref as a function of the position XR of roller 27 with respect to block 32. Line F denotes Vref as a function of XR for VG = 0. In that case Vref is equal to VL 1. Assuming that the output of output register 164 is equal to 1 at time TO, and the output signal for register 166 is equal to 0, then signal 419 will be equal to 0, roller 28 will be in the auxiliary position and roller 27 will thus be locked. XRA in Fig.8 denotes the position in which the roller 27 is locked. G denotes the voltage VL1A associated with XRA at the slider of potentiometer 37. The voltage VG at the output 404 of correction circuit 403 is equal to VG1. The voltage Vref (VRA) associated with XRA is accordingly equal to the sum of VL1A and VG1. The speed of belt 14 associated with the voltage VRA is denoted by VTB. In the case under examination here, the speed VTB of belt 14 is not equal to the speed VB1 of belt 1. If at time T1 roller 28 has to be brought into the transfer position, signal 419 will become equal to 1. As a result, the electronic switches 421 and 427 are closed. Also, belt 1 is pressed against belt 14. In these conditions, belt 1 assumes the speed VTB of belt 14 at the pressure zone. Since the speed at which belt 14 carries off belt 1 is lower than the speed VB1 at which the synchronous motor 8 supplies the belt 1, roller 27 will move towards potentiometer 37. As a result of this movement, the voltage VL1 and hence also the speed VT of belt 14 will increase. The speed VT will continue to increase until roller 27 has moved to such an extent that the voltage Vref has reached a value at which the speed of belt 14 has become equal to the speed VB1. The position associated with this speed is denoted by XRC in Fig.8. At time T2 signal 419 again becomes 0 so that switches 421 and 427 are opened. The voltage at the outputs of memory circuits 422 and 428 are thus fixed at a value equal to the value of the output at tee T2. This voltage is equal to VG1 for circuit 428 and this voltage is equal to slider voltage VL1C at time T2 for circuit 422. Also, as a result of the 1-0 changeover of signal 419, roller 28 is brought into the auxiliary position and roller 27 is brought back to position XRA in which it is locked. As a result, the voltage VL1 will fall off again. The voltage - Δ U at the output of subtraction circuit 423 now indicates the difference between the slider voltage VL1A in the case of a looked roller 27 and the voltage at the output of memory circuit 422, which latter voltage is representative of the slider voltage VL1C as it was at time T2. The voltage at the output of subtraction circuit 424 is now equal to VG1 +ΔU. At time T3 signal 408 becomes equal to 1 and the voltage at the output of memory circuit 426 becomes equal to the value VG1 +ΔU. Consequently, the voltage Vref increases by a value ΔU, so that Vref again becomes equal to the value of Vref at time T2, at which value the speed VT of belt 14 was equal to the speed VB1. This voltage is denoted by VRE in Fig. 8. At time T4 signal 408 again becomes 0, so that switch 425 is again opened. Consequently, the voltage at output 404 is fixed at the value VG2. If signal 419 again becomes 1 at time T5, belt 1 will again be brought into contact with belt 14. As a result, belt 1 will again be driven by belt 14. Since the speeds of belt 1 and belt 14 before being brought into contact were already equal to one another, the speed of belt 1 at the pressure zone will not change. In the way described hereinbefore, if, as a result of a change in the system parameters or for any other reason, the speeds of belt 1 and belt 14 are no longer equal to one another during the interval of time when the belts are disengaged from one another, the output voltage at output 404 will always be so adjusted that after adjustment the speeds of the belts are again equal to one another in the free-running condition. This results in reduced wear on belts 1 and 14. Also, the distance over which an image is entrained by belts 1 and 14 remains always the same, so that the time required to bring an image from exposure place 59A to roller 68 remains always the same and hence the time at which copy material has to be introduced between the rollers 34 and 68 is always known.

Claims: A device for transferring image information from a belt (1), driven at a first speed, to a medium (14) driven at a second speed, comprising a pressing element (28), that can be brought in a first position in which it keeps the belt (1) free from the medium (14), and in a second position in which it keeps the belt (1) in a small zone in pressure contact with the medium to transfer the image, in which zone the belt (1) under the influence of frictional forces assumes the speed of the medium (14), two guide rollers (27,29) disposed at either side of said zone, being movable along predetermined paths and exerting a tightening force on the belt (1), as well as means to position one (27) of the guide rollers in a predetermined position when said pressing element (28) is in said first position, characterised in that said positioning means comprise a latching device (112) co-operating with said one guide roller (27), said latching device (112) allowing said one guide roller (27) to move when said pressing element (28) is in said second position or is moving to said position, and in that means are provided which exert a force on the latching device (112), when said pressing element (28) has left the second position, the latching device (112), under influence of that force, causing said one guide roller (27) to take up said predetermined position and latching it at that position. A device according to claim 1, characterised in that, the latching device comprises a plate (112) which is provided with a V-shaped excision, the edges of which cooperate with one end (107) of the shaft of said one guide roller (27), and which plate is movable along a predetermined path, by which movement the V-shaped excision crosses the path (105) of said end of the shaft of said guide roller (27), and in that the exerting means exert the force on the plate in order to keep the edges of the V-shaped excision in pressure contact with the said end of the shaft.

Inventors: EERTINK, BASTIAAN BERNARD BOELE, GEURTS, PETRUS ANTONIUS MARIE, ROELOFS, JOHANNES CHRISTIANUS HENRICUS
Applicants: OCE-NEDERLAND B.V.
Application year: 1985
Main classification: G03G15
IPC codes: G03G21, G03G15, G03B15