Sheet transporting apparatus

Abstract: A sheet transporting apparatus, for transporting a sheet-form article along a feeding path between first and second locations that are spaced apart horizontally, comprises two parallel endless-loop conveyors (10a) having respective horizontal portions extending along opposite sides of the said feeding path, a sheet-gripper (10e, 10f) having opposite ends mounted respectively on the two parallel conveyors (10a), so as to extend therebetween across the said feeding path, for gripping a leading edge of such a sheet-form article (P) and pulling it along the said path, and an auxiliary endless conveyor belt (22) arranged so as to have a horizontal upper operative portion extending along the said feeding path, between the said two parallel conveyors, for supporting such a sheet-form article rearward of the said gripper. The support surface of the auxiliary conveyor belt (22) is formed with a recess (22d) which, when the apparatus in use, accommodates the said gripper (10e, 10f) so as to enable the sheet-form article gripped thereby to extend horizontally therefrom onto the said support surface rearward of the said recess as that article is pulled along the said feeding path. Such a sheet transporting apparatus may be used, for example, in a printer or photocopier for feeding a sheet, on which an image is to be printed, between toner printing units arranged along the feeding path, and can enable the sheet to be delivered to these units reliably and in a desirably accurate horizontal disposition.

Description: The present invention relates to a sheet transporting apparatus, for example for feeding a printing medium, such as a sheet of paper on which an image is to be printed, to a color printer having a plurality of toner printing units arranged along a feeding path of the sheet to transfer, in turn, color images of yellow (Y), magenta (M), cyan (C), and black (B), respectively, to the sheet. A printer including a plurality of toner printing units, used for printing, in turn, various colors, for example yellow (Y), magenta (M), cyan (C), and black (B), respectively, and arranged along a feeding path of the printing sheet to obtain a full color image on the printing sheet is known, and such a printer is disclosed, for example, in Japanese Unexamined Patent Publication (Kokai) No. 62-145262, in which a plurality of toner printing units are arranged along a sheet feeding path. Each of the toner printing units comprises a rotatable photoconductor drum, and around this photoconductor drum are arranged, in turn, a charger unit for charging the photoconductor drum, an optical depositing unit for forming a latent image on the photoconductor drum, a developing unit for changing the latent image to a toner image, a transferring unit for transferring the toner image on the photoconductor drum onto the printing sheet, and a cleaner for removing remaining toner from the photoconductor drum. The printing sheet is fed along a horizontal sheet feeding path by grippers mounted on a gripper feeding chain for gripping a leading edge of the printing sheet, and a plurality of air suction belts are arranged between the toner printing units to support the printing sheet in a horizontal state when the printing sheet is fed in the feeding direction, for example as also described in JP-A-59-62879. In such a sheet feeding apparatus however, the air suction belts must be arranged lower than the photoconductor drum by at least a thickness of the grippers. Therefore, the printing sheet may be easily bent or deformed while it is fed along the sheet feeding path. Namely, an exact horizontal state of the printing sheet cannot be guaranteed, and thus the transferring or printing positions of the printing sheet do always coincide in the respective toner printing units. It is desirable to provide an apparatus, for feeding a printing sheet in a printer having a plurality of toner printing units arranged in series along a sheet feeding path, which is capable of substantially avoiding any bending or deformation of the printing sheet and of stably supporting the printing sheet in a horizontal state, so that a desired image can be transferred on the printing sheet reliably and with satisfactory accuracy. According to the present invention there is provided sheet transporting apparatus, for transporting a sheet-form article along a feeding path between first and second locations that are spaced apart horizontally, which apparatus comprises at least one endless-loop conveyor having a horizontal portion extending along the said feeding path, a sheet-gripper mounted on the conveyor for gripping a leading edge of such a sheet-form article and pulling it along the said feeding path, and an auxiliary endless conveyor including at least one auxiliary endless conveyor belt arranged so as to have a horizontal upper operative portion extending along the said feeding path for supporting such a sheet-form article rearward of the said gripper, characterised in that the support surface of the said auxiliary endless conveyor belt is formed with a recess which, when the apparatus is in use, accommodates the said sheet-gripper so as to enable the sheet-form article gripped thereby to extend horizontally therefrom onto the said support surface rearward of the said recess as that article is pulled along the said feeding path. In an embodiment of the invention, for transporting such a sheet-form article along a feeding path having a series of at least three such horizontally spaced-apart locations, the apparatus has a plurality of such sheet-grippers mounted equidistantly on the endless-loop conveyor, and also has a plurality of such auxiliary endless conveyors, each including at least one such auxiliary endless conveyor belt, arranged respectively between successive locations of the said series. Such an embodiment is suitable for use in image forming apparatus in which a plurality of toner image-forming devices are arranged respectively at the said locations for transferring a toner image to the said sheet-form article as it passes through the device concerned. The auxiliary endless conveyor belts are preferably driven in synchronization with the endless-loop conveyor, in such a manner that the grippers are received, in turn, in the recesses of the auxiliary endless conveyor belts. Therefore, no interference of the grippers is caused by the auxiliary endless conveyor belts when supporting the sheet-form article in the horizontal state, and thus the auxiliary endless conveyor belts can be arranged at the same level as a lower portion of a photoconductor drum included in each toner image-forming device. Accordingly, the sheet-form article is kept substantially in the horizontal state without any bending or deformation thereof, so that the transferring or printing positions are substantially the same for all the different toner image-forming devices. Reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a front view of internal components of a color printer including a printing sheet feeding apparatus embodying the present invention; Figure 2 shows a perspective view, to a larger scale, of part of the feeding apparatus of Fig. 1; Figure 3 shows a front view, to a larger scale, of part of the sheet feeding apparatus of Fig. 1; Figure 4 is a view, corresponding to Fig. 3, of a further feeding apparatus embodying the invention; Figures 5A, 5B, and 5C are front, plan, and cross-sectional views, respectively, of an endless belt assembly for use in apparatus embodying the invention; Figure 6 is a perspective view of the endless belt assembly of Fig. 5; Figures 7A, 7B, and 7C are schematic views illustrating a sheet releasing operation in the apparatus of Figure 1; and, Figures 8A, 8B, and 8C are views corresponding to Figs. 7A, 7B, and 7C, respectively, but illustrating a sheet gripping operation in the apparatus of Figure 1. Referring now to Figs. 1 to 4, a color printer has a sheet feeding apparatus, generally indicated by a reference numeral 10, for feeding printing media, i.e., printing sheets or papers, one by one along a sheet feeding path located between a sheet supply unit 12 and a fuser unit 14. Along the sheet feeding path, four toner image-forming devices (printing or transferring units) 16Y, 16M, 16C, and 16B are arranged in series, at successive locations, in the sheet feeding direction for transferring different color images of, e.g., yellow (Y), magenta (M), cyan (C), and black (B), respectively. Each of these toner printing units 16Y, 16M, 16C, and 16B has basically the same structure and operates in the same manner. Each of the toner printing units 16Y, 16M, 16C, and 16B comprises a rotatable photoconductor drum 16a which rotates in the clockwise direction in Fig. 1, and around this photoconductor drum 16a and along the direction of rotation thereof, are arranged a charger unit 16b for charging the peripheral surface of the photoconductor drum 16a, an optical depositing unit 16C including a LED array consisting of a number of light-emitting-diodes for exposing onto the surface of the photoconductor drum 16a to form a latent image on the charged surface of the photoconductor drum 16a, a toner developing unit 16d for attaching toner onto the latent image on the photoconductor drum 16a to form a toner image, a transfer/discharge unit 16e for transferring the toner image on the photoconductor drum 16a to a printing sheet (sheet-form article) P and then discharging the peripheral surface of the photoconductor drum 16a, and a cleaner 16f for removing the remaining toner from the photoconductor drum 16a. The transfer/discharge unit 16e comprises a pair of corotron units 16e₁ and 16e₂ operating as a transferring unit and a discharge unit, respectively. Namely, the transferring unit 16e₁ applies an electric charge opposite to that of the charged toner image, to the printing sheet P, so that the toner image on the surface of the photoconductor drum 16a is transferred to the printing sheet P. On the other hand, the discharge unit 16e₂ is energized with an alternate current to remove the electric charge on the printing sheet P, to prevent the printing sheet P from becoming attached or flattened against the photoconductor drum 16a by the static charge, and to make it possible to easily separate the printing sheet P from the photoconductor drum 16a. As shown in Figs 1 and 3, the transfer/discharge unit 16e, comprising the pair of corotron units 16e₁ and 16e₂, and the photoconductor drum 16a are arranged on opposite sides of the sheet feeding path and, therefore auxiliary endless conveyors 20, as mentioned later, are arranged between the transfer/decharger units 16e of adjacent toner printing units 16. As shown in Fig. 2, the printing sheet feeding apparatus 10 comprises a pair of endless-loop conveyors (endless belts or chains 10a) extended in parallel to each other from a pair of drive pulleys 10b supported on a transverse shaft 10d and a pair of driven pulleys 10c (Fig. 1). The endless-loop conveyor 10a may be a toothed belt driven by a suitable drive means, not illustrated, via the transverse shaft 10d and the toothed drive pulley 10b. Transverse plates 10e are mounted on and between the pair of endless-loop conveyors 10a by mounts 10g attached to the respective ends of the transverse plate 10e, which are equidistantly arranged along the sheet feeding direction. Each of the transverse plates 10e is provided with four gripping pieces or grippers 10f spaced apart from one another and together serving to grip a leading end of a printing sheet P. The gripper 10f is made of a thin piece pivotally mounted on the transverse plates 10e and always urged toward the transverse plates 10e by a spring means (not illustrated) to hold the leading end of the printing sheet P therebetween. The operation of the gripper 10f will be described later in detail. The sheet supply unit 12 comprises a hopper 12a for accommodating a stack of printing sheets P and a pickup roller 12b for picking up the printing sheets P one by one from the hopper 12a to supply the sheets P to the sheet feeding apparatus. Therefore, when a printing sheet P is picked up by the pickup roller 12b, the leading end of the printing sheet P is gripped by the grippers 10f and then the printing sheet P is fed along the sheet feeding path to pass in turn, through the toner printing units 16Y, 16M, 16C, and 16B. Namely, when the transverse plate 10e carrying the grippers 10f for holding the printing sheet P is detected by a sensor 16g arranged in front of the first toner printing unit 16Y, operation of the LED array 16c of this unit 16Y is started so that a latent image is formed on the peripheral surface of the photoconductor drum 16a. The latent image is then changed to a charged toner image by the toner developing unit 16d. When the toner image on the photoconductor drum 16a arrives at the charger unit 16e₁ , the leading end of the printing sheet P is introduced into the transfer unit 16e₁ and the toner image on the photoconductor drum 16a is transferred to the printing sheet P. After the transferring operation is finished in the first toner printing unit 16Y and a color image of yellow is transferred onto the printing sheet P, the latter is then fed to the second toner printing unit 16M, in which the same operation is repeated, so that a color image of magenta is transferred onto the same printing sheet P. Namely, the toner images of different colors, i.e.; yellow, magenta, cyan, and black are superimposed, in turn, on the printing sheet P. Then the printing sheet P is released from the grippers 10f, as will be described later in detail, and fed into the fuser 14, where the transferred image on the printing sheet P is fixed. The fuser 14 comprises a pair of heat and backup rollers 14a and 14b between which the printing sheet P passes through and the toner image is fixed. Then, the printing sheet P is unloaded on a tray 18 and stacked thereon. In the printer of Figure 1, a plurality of auxiliary endless conveyors 20 are provided between the toner printing units 16Y, 16M, 16C, and 16B, to support the printing sheet P and maintain a horizontal state thereof, to prevent a tailing end of the printing sheet P from dropping or trailing down, particularly when the printing sheet P passes between the toner printing units 16Y, 16M, 16C, and 16B. In the sheet feeder apparatus of Fig. 2, each of the auxiliary endless conveyors 20 comprises four individual endless belt assemblies 22 arranged in parallel to each other and between the above-mentioned pair of endless belts 10a. Each of the belt assemblies 22 comprises a drive timing pulley 22a, a driven pulley 22b, and an endless toothed conveyor belt (timing belt) 22c extended between these pulleys. These endless belt assemblies 22 are driven in synchronization with the above-mentioned pair of endless-loop conveyors 10a, as will be described below. These belt assemblies 22 can be driven in such a manner that the circumferential speed thereof is matched to the speed of the grippers 10f attached to the endless-loop conveyors 10a. Also, the endless conveyor belt 22c has at least one recess 22d for receiving the transverse plate 10e carrying the grippers 10f. Thus, when the recess 22d comes to the upper path of this endless conveyor belt 22c, the transverse plate 10e is received in the recess 22d so that the upper path of the endless conveyor belt 22c can be located at the same level as the thin gripping pieces 10f, i.e., grippers 10f, and at the same level as the lower portion of the photoconductor drum 16a. Therefore, the printing sheet P can be supported on these endless conveyor belts 22c in a desirably precise horizontal state and, therefore, the tailing end of the printing sheet P is not bent or deformed while moved along the feeding path. Figure 3 shows such an auxiliary endless conveyor 20 in more detail. In the Fig. 3 embodiment, the endless conveyor belt 22c is extended over one drive pulley 22a and three driven pulleys 22b to form a substantially rectangular loop. The endless conveyor belt 22c has two recesses 22d, either of which can receive the transverse plate 10e carrying the grippers 10f, and therefore, the circumferential length of the endless conveyor belt 22c between recesses is exactly equal to the distance between the adjacent transverse plates 10e (i.e., grippers 10f). The distance between the adjacent grippers 10f should be determined so as to securely hold the printing sheet P; Namely, it should be larger than a maximum length of the printing sheet P. The endless conveyor belt 22c can be provided with one, two or more recesses 22d provided equidistantly along the circumferential direction of the endless conveyor belt 22c, but if the circumferential speed of the endless conveyor belt 22c is equal to the speed of the grippers, the circumferential length Lb of the endless conveyor belt 22c should be determined as Lg× n/m , wherein Lg: the distance between adjacent grippers 10f, n: number of recesses in the endless conveyor belt 22c, and m: an integral number. Thus, in one embodiment, n = 2, and m = 3. In this case, while the grippers 10f move a distance equal to their pitch, i.e., the subsequent grippers 10f move to positions at which the preceding grippers 10g were located, the endless conveyor belt 22c is turned 1.5 times around the pulleys 22a and 22b. Note, the endless conveyor belt 22c is driven at the same speed as the grippers 10f. Alternatively, the circumferential speed of the endless conveyor belt 22c in the respective belt assembly 20 can be set to be less than the speed of the grippers, by a few or several percent. In this case, the endless belt 10a for carrying the grippers 10f and the endless belt 22c for supporting the printing sheet P should be driven as follows. Tg = Lg/Vg = Lb/Vb X m/n Vg > Vb where: Tg: the duration of a feeding cycle of the gripper 10f, Lg: distance between adjacent grippers 10f, Vg: speed of the grippers, Lb: the circumferential length of the endless conveyor belt 22c, Vb: the circumferential speed of the endless conveyor belt 22c, n: the number of recesses in the endless belt 22c, and, m: an integral number. In such an arrangement, while the printing sheet P is fed by the grippers 10f at a speed of Vg, a slight back tension is given to the printing sheet P by a friction force with respect to the endless conveyor belt 22c, since the speed of the latter (Vb) is slightly less than the gripper speed (Vg). Therefore, even if the printing sheet P is bent or deformed for any reason, the problem is automatically resolved and the printing sheet P returned to the original horizontal flat state. Figure 4 shows another embodiment of the printing sheet feeding apparatus according to the present invention, in which the circumferential speeds of the endless conveyor belts 22c in the respective auxiliary endless conveyors 20 are different from one another. Namely, the endless-loop conveyors 10a, for carrying the grippers 10f,and the endless conveyor belts 22c for supporting the printing sheet P are driven as follows. Tg = Lg/Vg = Lb₁/Vb₁ x m1/n1 = Lb₂/Vb₂ x m2/n2 = Lb₃/Vb₃ x m3/n3, and Vg > Vb₁ > Vb₂ > Vb₃ provided that Tg: the duration of a feeding cycle of the gripper 10f, Lg: distance between adjacent grippers 10f, Vg: speed of the grippers, Lb: the circumferential length of the endless conveyor belt 22c, Vb: the circumferential speed of the endless conveyor belt 22c, Lb₁ , Lb₂ , Lb₃: circumferential lengths of the endless conveyor belts 22c in the first, second and third auxiliary endless conveyors 20, the auxiliary endless conveyors being numbered according to their position from upstream to downstream along the sheet feeding path, Vb₁ , Vb₂ , Vb₃: circumferential speeds of the endless conveyor belts 22c in the auxiliary endless conveyors 20 n1, n2, n3: number of recesses in the endless conveyor, belts 22c in the auxiliary endless conveyors 20, and m1, m2, m3: integral numbers. In this embodiment, while the printing sheet P is fed by the grippers 10f at a speed of Vg, a slight back tension is given to the printing sheet P by a friction force with respect to the endless conveyor belts 22c, since the speeds of the latter (Vb₁ , Vb₂ , Vb₃) are slightly less than the gripper speed (Vg). In practice, Vb₃ is less than Vg by a few percent. In addition, Vb₂ if less than Vb₃ and Vb₁ is less than Vb₂ , by a few percent, respectively, and therefore, such a back tension is also given to the printing sheet P between the respective auxiliary endless conveyors 20. Therefore, even if the printing sheet P is bent or deformed for any reason, the printing sheet P is perfectly extended and returned exactly to the original horizontal flat state. In Figs. 5A, 5B, and 5C, each individual endless belt assembly 22 comprises a toothed timing drive pulley 22a, a toothed driven pulley 22b, and an endless toothed conveyor belt (timing belt) 22c extended therebetween. This endless conveyor belt 22c has two recesses 22d for receiving the grippers 10f. The endless conveyor belt 22c consists of a relatively thin base portion 22c₁ made of a hard rubber material and provided with a plurality of teeth, to thereby constitute the timing belt, and a relatively thick peripheral pertion 22c₂ made of a relatively soft rubber material, such as sponge, adhered to the former portion. The thin portion 22c₁ , not having the thick portion 22c₂ , defines the above-mentioned two recesses 22d. The thick peripheral portion 22c₂ is divided by a plurality of transverse cuts extending from the outer periphery thereof toward the thin base portion 22c₁ to form a plurality of cut sections 22c₂. These cut sections 22c₂ make it possible to reduce stress imposed on this endless conveyor belt 22c when turning around the drive pulley 22a or the driven pulley 22b. If such cut sections were not provided, an unfavorable excess stress would be exerted on the belt, particularly when the leading parts D (Fig. 5A) of the belt 22c2 next to the recesses 22d reach the pulley 22a or 22b and start to turn theraround. In such a case, the speed of this endless conveyor belt 22c would become unstable. In this embodiment, however, when the endless conveyor belt 22c turns around the pulley 22a or 22b, the cut sections 22c₂ are separated from each other and, therefore, the endless conveyor belt 22c turns more easily around the pulley 22a or 22b to reduce the stress exerted thereon. The endless conveyor belt 22c is further provided with a plurality of air suction holes 22e arranged over an entire circumferential length of the belt 22c except for the recess portions 22d. Between the upper and lower paths of the endless conveyor belt 22c there is disposed, as shown in Fig 6, a box-like air suction duct member 24 along the longitudinal or sheet feeding direction of the endless conveyor belt 22c. The member 24 has an upper opening 24a, which is communicated with the air suction holes 22e when they are at the upper path of the belt 22c, and a side air duct 24b connected to a vacuum source, such as a vacuum pump not shown. The printing sheet P can thus be absorbed and stably supported by the air suction force available over the upper path of the endless belt 22c, even if the photoconductor drum 16a is not completely decharged by the transfer/discharge unit 16e, so that the printing sheet P is not subjected to a static electric charge. Figures 7A-C and 8A-C illustrate the operations of the grippers 10f for releasing and picking up the printing sheet P, respectively. As shown in Figs. 7A-C, a drive shaft 10d on which the drive pulleys 10b are rigidly mounted is provided with a cam member 101 having a projection 10m. The drive shaft 10d is rotated in such a manner that the projection 10m cooperates with the gripper 10f. Namely, the transverse plate 10e carrying the grippers 10f, which now hold the leading end of the printing sheet P, approaches the drive pulley 10b (Fig. 7A) and is then wound therearound (Fig. 7B). Then the projection 10m engages with the gripper 10f (Fig. 7C), so that the gripper 10f is pivotably moved against the spring means to release the leading end of the printing sheet P. When the transverse plate 10e comes away from the drive pulley 10b, the gripper 10f is returned to its initial position by the spring means. In Figs. 8A-C, a driven shaft 10q on which the driven pulleys 10c are rigidly mounted is provided with a cam member 10p having a projection 10r, which cooperates with the gripper 10f, in the same manner as Figs. 7A-C. Namely, the transverse plate 10e (the grippers 10f) approaches the driven pulley 10c (Fig. 8A) and then is wound therearound (Fig. 8B). Then the projection 10r engages with the gripper 10f (Fig. 8C), so that the gripper 10f is pivotably moved against the spring means to open, and at this time, the printing sheet P is picked up by the pickup roller 12b (Fig. 1) and the leading end of the printing sheet P is inserted between the gripper 10f and the transverse plate 10e. Then the projection 10r disengages from the gripper 10f, so that the leading end of the printing sheet P is gripped between the gripper 10f and the transverse plate 10e. As mentioned above, in a sheet feeder apparatus embodying the invention, the printing sheet P is prevented from being bent or deformed while fed along the sheet feeding path, and therefore an accurate feeding and horizontal state of the printing sheet can be obtained, so that the transferring or printing positions of the printing sheet P always coincide in the respective toner printing units 16Y, 16M, 16C, and 16B, and thus the quality of the printing can be significantly improved. As will be apparent, the present invention is also applicable to a copying machine.

Claims: Sheet transporting apparatus, for transporting a sheet-form article along a feeding path between first and second locations that are spaced apart horizontally, which apparatus comprises at least one endless-loop conveyor [10a] having a horizontal portion extending along the said feeding path, a sheet-gripper [10e, 10f] mounted on the conveyor [10a] for gripping a leading edge of such a sheet-form article (P) and pulling it along the said feeding path, and an auxiliary endless conveyor [20] including at least one auxiliary endless conveyor belt [22c] arranged so as to have a horizontal upper operative portion extending along the said feeding path for supporting such a sheet-form article rearward of the said gripper, characterised in that the support surface of the said auxiliary endless conveyor belt [22c] is formed with a recess [22d] which, when the apparatus is in use, accommodates the said sheet-gripper [10e, 10f] so as to enable the sheet-form article gripped thereby to extend horizontally therefrom onto the said support surface rearward of the said recess as that article is pulled along the said feeding path. Sheet transporting apparatus as claimed in claim 1, having two such endless-loop conveyors [10a] arranged in parallel such that the respective horizontal portions thereof extend along opposite sides of the said feeding path, the sheet-gripper [10e, 10f] having opposite ends mounted respectively on the two parallel endless-loop conveyors [10a] so as to extend therebetween across the said feeding path. An apparatus as claimed in claim 2, wherein each of the said endless-loop conveyors [10a] is a toothed belt. Sheet transporting apparatus as claimed in claim 1, 2 or 3, for transporting such a sheet-form article along a feeding path having a series of at least three such horizontally spaced-apart locations, which apparatus has a plurality of such sheet-grippers [10e, 10f] mounted equidistantly on the conveyor or conveyors [10a], and also has a plurality of such auxiliary endless conveyors [20], each including at least one such auxiliary endless conveyor belt [22c], arranged respectively between successive locations of the said series. Apparatus as claimed in claim 4, wherein the said endless-loop conveyor(s) [10a] and the said auxiliary endless conveyor belts [22c] are driven such that: Tg = Lg/Vg = Lb i /Vb i x m i /n i where: i = 2, 3, ....k, k being the total number of auxiliary endless conveyors [20] in the said plurality, and i denoting the ordinal number of the auxiliary endless conveyor in the said plurality and increasing in the downstream direction of the said feeding path, and where: Tg: the duration of a gripper feeding cycle, Lg: the distance between mutually-adjacent sheet-grippers [10e, 10f], Vg: the circumferential speed of the endless-loop conveyor(s) [10a], Lb i : the circumferential length of the or each auxiliary endless conveyor belt [22c] of the i th auxiliary endless conveyor [20], Vb i : the circumferential speed of the or each auxiliary endless conveyor belt [22c] of the i th auxiliary endless conveyor [20], n i : the number of such recesses [22d] in the or each auxiliary endless conveyor belt [22c] of the i th auxiliary endless conveyor [20], and m i : an integer. Apparatus as claimed in claim 5, wherein the said endless-loop conveyer(s) [10a] and the said auxiliary endless conveyor belts [22c] are driven such that: Vg ≧ Vb k ≧ .... ≧ Vb i ≧ .... ≧ Vb₂ ≧ Vb₁. Apparatus as claimed in any one of claims 4 to 6, wherein each of the said sheet-grippers comprises a transverse plate [10e] and a plurality of thin gripping pieces [10f] each pivotably mounted on the said transverse plate [10e] and urged towards that plate by spring means so that the said leading edge of such a sheet-form article [P] is gripped between the said gripping pieces and the said transverse plate. Apparatus as claimed in claim 7, wherein the said gripping pieces [10f] are pivotably moved towards and away from the said transverse plate [10e] to grip and release the said sheet-form article at an inlet and an outlet, respectively, of the said feeding path. Apparatus as claimed in any one of claims 4 to 8, wherein each of the said auxiliary endless conveyors [20] includes a plurality of the said auxiliary endless conveyor belts [22c], each formed with such a recess [22d], arranged in parallel to one another and in parallel to the or each endless-loop conveyor [10a]. Apparatus as claimed in any one of claims 4 to 9, wherein each of the said auxiliary endless conveyor belts [22c] is a toothed belt. Apparatus as claimed in any one of claims 4 to 10, wherein each of the said auxiliary endless conveyor belts [22c] is provided on its outer circumferential periphery with a plurality of transverse cut sections [22c₂] over the entire circumferential length of the belt except for the said recess(es) [22d]. Apparatus as claimed in any one of claims 4 to 11, wherein each of the said auxiliary endless conveyor belts [22c] is provided on its outer circumferential periphery with a plurality of vacuum absorbing means for absorbing the said sheet-form article to the belt [22c] concerned. Apparatus as claimed in claim 12, wherein the said vacuum absorbing means [22e] comprises a plurality of air holes arranged along the entire circumferential length of the belt except for the said recess(es) [22d]. Image forming apparatus including sheet transporting apparatus as claimed in any one of claims 4 to 13 and also including a plurality of toner image-forming devices [16] arranged respectively at the said locations for transferring a toner image to the said sheet-form article [P] as it passes through the device concerned. Image forming apparatus as claimed in claim 4, wherein the said plurality of toner image-forming devices comprises four such devices [16Y, 16M, 16C, 16B] which are used respectively for transferring yellow [Y], magenta [M], cyan [C], and black [B] colour toner images in turn onto the said sheet-form article [P]. Image forming apparatus as claimed in claim 14 or 15, wherein each of the said toner image-forming devices [16] includes a rotatable photoconductor drum [16a], a charger unit [16b] for charging the said photoconductor drum [16a], an optical unit [16c] for forming a latent image on the said photoconductor drum [16a], a developing unit [16d] for changing the said latent image to a toner image, a transferring unit [16e] for transferring the said toner image on the said photoconductor drum onto the said sheet-form article [P], and a cleaner [16f] for removing residual toner from the said photoconductor drum. Image forming apparatus as claimed in claim 16, wherein the said charger unit [16b], the said optical unit [16c], the said developing unit [16d], the said transferring unit [16e], and the said cleaner [16f] are arranged one after the next around the periphery of the said photoconductor drum [16a]. Image forming apparatus as claimed in claim 17, wherein the said transferring unit [16e] and the said photoconductor drum [16a] of each toner image-forming device [16] are arranged to face each other from opposite sides respectively of the feeding path, and the said auxiliary endless conveyors [20] are arranged respectively between the transferring units [16e] of successive toner image-forming devices [16].

Inventors: INOUE HIROYUKI, TANAKA NOBUYUKI, INOUE, HIROYUKI, TANAKA, NOBUYUKI
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1990
Main classification: B65H5
IPC codes: G03G15, B65H5