Sheet inverting apparatus

Abstract: The present invention relates to a sheet inverting apparatus having an inverting rotary member (22) having a sheet clamping hole (22a) which clamps and inverts the sheet (S) and being arranged orthogonal to a sheet carrying route of the apparatus.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention is related to a sheet inverting apparatus, or to be more specific, a sheet inverting apparatus equipped with an inverting roll to turn over the sheet on which an image is formed on the route of carrying the sheet. Related Background Art The conventional image forming apparatus is explained hereunder by taking a compact laser printer used as the output device of a data processing system as an example. As illustrated in Fig. 1, a laser printer is provided with a process cartridge 3 which is removably attached to the main body 2 of the apparatus, wherein the process cartridge 3 accomodates the conventional processing apparatus having a photosensitive drum 4, an electric charger 5, a developing apparatus 6, a cleaner 7 etc. At the upper part of the main body 2 of the apparatus are provided a scanner unit 8 and a mirror 9 which irradiate the laser beam and execute scanning, wherein a latent image corresponding to the specified image data is formed on the photosensitive drum 4 which is electrically charged by the charger 5 and the latent image is developed by the developing apparatus 6 to form a toner image. At the lower part of the main body 2 of the apparatus is arranged a sheet feeding cassette 10 which holds a plurality of sheets S and a sheet feeding roll 11 is arranged at the sheet feeding cassette 10, wherein the sheets S housed in the sheet feeding cassette 10 are delivered sheet by sheet to a regist or registration roller 12 by the sheet feeding roller 11, which regist roller 12 adjusts the timing of delivering the sheet to a location between the photosensitive drum 4 and transfer charger 13, where the toner image is transferred from the photosensitive drum 4. The sheet S on which the toner image has been transferred is delivered to a fixing apparatus 15 by a conveyor belt unit 14, the toner image is fixed thereon and the sheet is discharged to the outside of the main body 2 of the apparatus. The laser printer 1 has two systems for discharging the sheets S, one being the system for discharging the sheets S in face up posture, i.e. the image plane facing upwardly, and for discharging the sheets via face up discharge rollers 16 into a face up discharge tray 17; the other being the system for discharging the sheets S in the order of the pages in face down posture, i.e. with the image plane facing downwardly, wherein the sheet S is turned over after being guided upwardly from the face up discharge rollers 16, via the sheet delivery direction change-over system such as flapper and sheet guide etc., and discharged via face down discharge rollers 18 into a face down discharge tray 19. Maintenance of the laser printer, i.e. prevention of jamming, exchange of the process cartridge 3 etc., is executed as illustrated by the two dotted lines in Fig. 1 by turning an upper part 2a of the main body 2 of the apparatus upwardly around a fulcrum shaft P in relation to a lower part 2b of the main body 2, thus opening the inside of the apparatus, and introducing the hand in the direction of the arrow A. In the case of a conventional double face copying machine as illustrated in Figure 2, the image is transcribed by the photosensitive drum 4 and fixed by the fixing apparatus 15 on the 1st face of the sheet delivered from the sheet feeding cassette 10, and the sheet is delivered in S-letter shape by the rollers 16, 51 and 52. Then, after inverting the sheet S at a pass 53, the timing is adjusted by carrying rollers 54 and 55 and regist rollers 12, and the image is formed on the 2nd face of the sheet S by the photosensitive drum 4. In the case of a rolled sheet discharge section of a conventional facsimile machine, a rolled sheet 57 on which an image has been formed by an image forming section 56 is further carried forwardly and cut by a cutter 58. Thus, the cut sheet 57 hangs down from the discharge outlet and the front end of the sheet 57 enters into a inverting hole 59 (Fig. 3A). Due to the bending strength of the sheet, a loop 57a is formed (Fig. 3B), the rolled sheet is cut at a specified length (Fig. 3C) and discharged onto the face down discharge tray 17 to be piled up (Fig. 3D). According to the conventional case as illustrated in Fig. 1, it was necessary to have two kinds of discharge systems, i.e. a face up system and a face down system. Consequently, it has the following drawbacks: (i) Since the apparatus has two discharge trays 17 and 19, it is necessary to have two kinds of discharge rollers, namely, the face up discharge rollers 16 and the face down discharge rollers 18. Besides, the discharge trays 17 and 19 must be set at two places, namely, the face up tray 17 at one place and the face down tray 19 at another place. (ii) Since the discharging point differs between the face up discharge and the face down discharge, the operability of the system is inferior. (iii) The sheet carrying route of the face down discharge is long and, thus, there is a higher probability of jamming, wherein it also causes a cost increase of the motor due to the increase of the carrying torque, and a cost increase due to the necessity of the guide plate. (iv) Because of the presence of the face down carrying route (part surrounded by the one dotted line in Fig. 1), it is impossible to make the body compact and to reduce the area occupied by the apparatus. The conventional apparatus as illustrated in Fig. 2 has the drawback that an extremely large space in S-letter shape is required at the part where the sheet S turns over and, thus, it is difficult to make the equipment compact. The conventional apparatus as illustrated in Fig. 3 has the drawback that the system is effective only for a rolled sheet 57 having a low bending strength, whereas, in the case of a sheet having a high bending strength, such as a cut sheet S, the front end of the sheet S does not enter into the inverting hole, and a sufficient inverting performance cannot be obtained. Further, from the document US-A-4 810 120, a sheet inverting apparatus for an image forming apparatus is known, which comprises an inverting rotatable member for inverting a sheet received from a sheet discharging means, said inverting rotatable member being rotatably supported on a shaft and driven by means of a pulse motor. When a sheet reaches the inverting rotatable member, the top edge of the sheet is inserted between the inverting rotatable member and an endless belt as well as between the inverting rotatable member and associated pawls. This condition is detected by a sensor which generates a signal to start the pulse motor, thereby moving the belt to rotate the inverting rotatable member. With the top edge of the sheet inserted between the above members, the sheet is forcibly pulled round the inverting rotatable member by the rotation thereof and completely turned over when it has passed between the inverting rotatable member and the belt. Thus, the sheet is inverted. Although this sheet inverting apparatus exhibits a compact construction, it suffers from the fact that a bulky pulse motor is provided, which needs to have a relatively large output torque for turning over the sheets having a high bending strength. SUMMARY OF THE INVENTION Therefore, the object of the present invention is to provide a sheet inverting apparatus which can easily turn over and discharge the sheet by using an inverting mechanism with simple and low cost design. This object is solved by the features indicated in claim 1. According to the present invention, an inverting rotatable member has a counterweight for maintaining it stationary in a waiting position, and a sheet clamping recess opposing a sheet discharge roller when the inverting rotatable member is in the waiting position, wherein the inverting rotatable member is rotated by the sheet discharging force together with the counterweight against the weight of the counterweight when the leading end of the sheet discharged from the sheet discharge roller has been introduced into the sheet clamping recess. Thereafter, the inverting rotatable member is rotated to a position where the weight of the counterweight acts in a direction promoting rotation of the inverting rotatable member. Then, it is rotated by the weight of the counterweight to wind and thereby tip over the sheet, whereupon the leading end of the sheet is dropped when the sheet clamping recess is directed downwardly. Finally, the inverting rotatable member is returned to the waiting position by the weight of the counterweight. According to the present invention, the inverting rotatable member is turned over by the resisting force of the sheet against bending, and by the weight of the counterweight, whereby the sheet is turned over, as well. Therefore, a driving source is not necessary for inverting the sheet. Thus, the construction of the inverting mechanism is simpler and the manufacturing costs are reduced. Further, the inverting rotatable member is turned over not only by utilizing the stiffness of the sheet against bending but also by the friction force and, therefore, the inverting performance of the inverting rotatable member is improved. According to claim 3, since the inverting rotatable member can be retreated from the carrying route by a retreating means upon necessity, it is possible for the user to freely select the timing of invertion of the sheet, thus providing a large freedom of operation for the users. Besides, according to claim 5, by turning the inverting rotatable member by an additional driving source, the rotation is executed with certainty, and inversion can be made with certainty. According to claim 2, by providing a guide, the sheet is inserted into the inverting rotatable member with certainty. Further advantageously developed embodiments are subject-matters of the remaining dependent claims. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a longitudinal side view of a conventional laser printer. Fig. 2 is a longitudinal side view of a conventional double face copying machine. Figs. 3A - 3D are explanatory drawings of the performance of a conventional facsimile machine. Fig. 4 is a diagonal view of the laser printer according to an embodiment of the present invention. Fig. 5A is a longitudinal side view thereof; Fig. 5B is an enlarged side view of the part near the inverting rotatable member of Fig. 5A. Figs. 6A - 6H are explanatory drawings of the performance of the sheet invertion. Fig. 7 is a longitudinal sectional view of a double face copying machine in which the present invention is embodied. Fig. 8 is a diagonal view of an inverting apparatus which turns over a sheet whilst receiving a driving force. Figs. 9A and 9B are sectional side views of the inverting section of Fig. 8. Fig. 10 is a side view showing the relation between the inverting guide and the inverting rotatable member. Figs. 11A, 11B and 11C are side views showing the shape of the inverting rotatable member. Figs. 12A - 12D indicate other shapes of the inverting rotatable member, wherein Fig. 12A is a diagonal view, Fig. 12B is the X view thereof, Fig. 13C is a side view, Fig. 13D is the Y view thereof. Fig. 13 is a side view of an inverting rotatable member to which a friction member is added. Fig. 14 is a diagonal view of an inverting mechanism which can retreat. Fig. 15 is a side view showing the supporting arm of the retreating mechanism. Figs. 16A and 16B are side views indicating the states of retraction of the inverting mechanism. Fig. 17 is a diagonal view of a further inverting mechanism which can retreat. Fig. 18 is a side view showing the fulcrum shaft of the retreating mechanism. Figs. 19A and 19B are side views showing the states of retraction. Fig. 20 is a diagonal view showing still another inverting mechanism which can retreat. Figs. 21A and 21B are front views showing the retreated mechanism. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereunder, preferred embodiments of the present invention are explained with reference to the drawings. The 1st embodiment is explained with reference to Figs. 4, 5A and 5B. The members having the same construction and performance as those of Fig. 1 which have been explained above, are provided with the same numbers and their explanations are omitted. An inverting guide 20 is installed substantially horizontally below the discharge outlet of the face up discharge rollers 16, and adjacent thereto, an inverting rotatable member or roller 22 is supported by a shaft 21 which is installed horizontally at the outside of the main body 2a. At the lower part of the inverting roller 22 a weight (or counterweight) 22b such as a metallic plate is fixed, and at the upper part a bent sheet clamping hole or recess 22a is provided which faces the upper surface of the inverting guide 20. The weight of the weight 22b is adjusted such that, when the sheet S is inserted into the sheet clamping hole 22a and pushed forward, the inverting roller 22 turns anticlockwise. The inverting roller 22 may be made integral with or separate from the inverting shaft 21, as long as it is freely rotatable. With reference to Figs. 6A - 6H, the performance of the present embodiment will be explained in the following. A sheet S is moved on the inverting guide 20 and inserted into the sheet clamping hole 22a (Figs. 6A - 6B). When the sheet S is further delivered by the face up discharge rollers 16, the roller 22 is pushed due to the resistance of the sheet S against bending, and revolves anticlockwise resisting against the force given by the weight 22b (Figs. 6C - 6D). Then, the sheet S rubs against the section B of the roller 22 whilst forming a loop, wherein its frictional force further turns the roller 22 (Figs. 6E and 6F). When the sheet S is kicked out, the upper part of the loop moves leftward and the sheet S is piled up into the face up discharge tray 17 in a face down state. The roller 22 returns to the original position due to the force of the weight 22b (Figs. 6G and 6H). Next, with reference to Fig. 7 an embodiment will be explained according to which the present invention is applied to a double face copying type copying machine. The sheet S is brought down from the rollers 16 and carried rightward at the downstream of carrying rollers 23, wherein, by the action of the inverting roller 22 of the present invention which is rotatably attached to the carrying route at a location more than a sheet length apart from a tray 24, the sheet S is inverted onto the tray 24 and carried again by a carrying roller 54. By the above mechanism, the height of the sheet inverting section of the double face copying machine can be made smaller than in the case of the S-letter-shaped pass according to Fig. 2. As explained above, only by rotatably attaching the inverting roller 22 at the discharge outlet for the sheets S, it is possible to easily invert the sheet S. By employing the face down mechanism using such a sheet inverting system, the main body 2 is made compact and measurable, and cost reduction is also realized. Besides, this construction requires a smaller number of constituent members, the unit costs of parts are lower and the system requires no driving force. Therefore, it can easily be connected as an optional device to the conventional face up discharge apparatus which has no face down discharge outlet. Besides, since the sheet discharge outlets for face up and face down discharge are not different in type, for the users the operability of the system is superior to other systems. As aforementioned, when the present invention is used, it is possible to invert the sheet S by a simple mechanism. In the case of the 1st embodiment as explained above, the sheet is inverted without employing a driving source, but as illustrated in Figs. 8 and 9, the sheet may be inverted by attaching an additional drive force to the inverting shaft 21. At the inlet of the sheet clamping hole 22a of the sheet inverting roller 22 a sheet passage sensor 25 (Fig. 9A) is provided, wherein, when the sheet S tries to enter into the sheet clamping hole 22a, a sensor lever 27 which can rotate about a fulcrum shaft 26 is turned by the sheet S to make the sheet passage sensor 25 respond and turn ON a solenoid 28 (Figs. 8 and 9B). On the inverting shaft 21 a clutch mechanism such as a spring clutch 29 is provided and, thus, the inverting shaft 21 starts to rotate. The inverting action of the sheet S is the same as that of the aforementioned 1st embodiment and as soon as the inversion of sheet S completes, an actuator stopper 30 of the solenoid 28 turns until the stopper 30 is caught by a stopper 31 of an one turn control hub of the spring clutch 29, whereby the sheet clamping hole 22a waits for the sheet S at a specified position. Next, the 2nd embodiment will be explained with reference to Figs. 10 - 12. As illustrated in Fig. 10, by arranging the discharge guide 20 moderately inclined upwards as against the sheet S to be discharged, the sheet S discharged from the discharge rollers 16 is smoothly guided into the sheet clamping hole 22a of the inverting roller 22 as the sheet S is discharged in such a manner that the front end of the sheet S is always in contact with the inverting guide 20. In order to improve and to make the performance of inserting of the sheet S into the sheet clamping hole 22a smooth, the shape of the sheet clamping hole 22a of Fig. 11A may be modified in such a manner as illustrated in Fig. 11B. When it is formed in such a shape, the rear end of the sheet S does not separate from the sheet clamping hole 22a, when the sheet S forms a loop as it turns over. As shown in Fig. 11C, instead of attaching a weight 22b, the part where it is attached may be made larger and heavier. The inverting roller 22 with the shape as illustrated in Fig. 12A and its X view (Fig. 12B) may be used instead, and by properly expanding the inlet of the sheet clamping hole 22a upwards and downwards or also in right and left directions as illustrated in Fig. 12C and its Y view (Fig. 12D), it is possible to smoothly insert the sheet S which may be curled by the heat of the fixing, or a sheet S having a large thickness. To explain the weight of the inverting roller 22, the inverting roller 22 is turned by the torque of the stiffness of bending the sheet S as illustrated in Figs. 6B - 6E. Since such a torque is not large at all, the inertia moment of the inverting roller 22 including the weight of the counterweight 22b must be made small. Therefore, it is necessary to use plastic etc. with a small specific gravity for the inverting roller 32, and the weight 22b must be of the minimum weight necessary for restituting the posture to the original state. Next, the 3rd embodiment will be explained with reference to Fig. 13. As shown in Fig. 6F, the sheet S rubs the section B of the inverting roller 22 while forming a loop. Therefore, a friction member 22c having a large friction coefficient is attached to the section B, i.e. the periphery of the part substantially opposite to the sheet clamping hole 22a. By doing so, the inverting roller 22 may be turned not only by the resisting force of bending the sheet S, but also by the frictional force given by sheet S. Thus, the sheet inverting performance is improved. The friction member 22c may be a rubber piece etc. attached to the surface, or a material having a large friction coefficient and being coated on the surface. Alternatively, a weight 22b made of a material having a large friction coefficient may be attached to the periphery. Next, the 4th embodiment will be explained with reference to Figs. 14 - 21. If the inverting roller 22 is always located at the carrying route of the sheet S, the sheet S is always discharged in face down posture, and it is impossible to discharge it in face up posture. In the present embodiment, the inverting roller 22 can be retreated from the carrying route of the sheets S so that the sheet S is discharged in face up posture, or the roller 22 may not be retreated so that the sheet S is discharged in face down posture. According to Fig. 15, a fulcrum shaft 32 is fixed to the outer plane of the sheet discharge hole of the main body 2, side plates 33a and 33b are fixed to the fulcrum shaft 32 to form one unit, the inverting shaft 21 is fixed to the side plates 33a and 33b, and the inverting roller 22 is rotatably fixed to the inverting shaft 21. As illustrated in Fig. 15, at the lower end of the side plates 33a and 33b, the fulcrum arm 34 is supported centrally by a shaft 35 which is fixed to the main body 2. A compression spring 36 pushes up or down the fulcrum arm 34 from the dead point, wherein one end of the spring is fixed to a pin 36a which is fixed to the body 2, the other end thereof being fixed to the front end of the fulcrum arm 34. When the arm is pushed upwardly, it stops by pressing the fulcrum arm 34 against a fixed pin 37a, whereas, when the arm is pushed down, it stops by pressing against a fixed pin 37b. As illustrated in Fig. 16A, when the side plates 33a and 33b are located at the position indicated by solid lines in Fig. 15, the inverting roller 22 orientates the sheet clamping hole 22a towards the inverting guide 20, whereas, when the side plates 33a and 33b are located at the position indicated by the dotted line of Fig. 15 as illustrated in Fig. 16B, the inverting roller 22 retreats to the position below the inverting guide 20. When the operator turns a knob 32a at one end of the fulcrum shaft 32, the sheet S is inverted and discharged in face down posture in the case of Fig. 16A, and discharged in face up posture in the case of Fig. 16B. As illustrated in Fig. 17, when the inverting roller 22 is supported by the inverting shaft 21 provided at the outside plane of the sheet discharge hole of the main body 2, the inverting guide 20 is fixed to and integral with a shaft 39 supported by the main body 2, and the operator turns a knob 39a at the end of the shaft 39, the inverting guide 20 is supported at an upper or a lower position by the fulcrum arm 34 as illustrated in Fig. 18. As shown in Fig. 19A, when the inverting guide 20 is orientated towards the sheet clamping hole 22a of the inverting roller 22, the sheet S is discharged in face down posture, whereas, if the inverting guide 20 retreats to the position above the inverting roller 22 as illustrated in Fig. 19B, the sheet S is discharged in face up posture. As illustrated in Fig. 20, the inverting guide 20 and the inverting shaft 21 are fixed to the main body 2 and the inverting roller 22 is attached to the inverting shaft 21 such that sliding and free rotation are possible. A roller position restricting plate 40 is attached to both sides of the roller 22 below the inverting shaft 21 such that free sliding is possible. The restricting plate 40 is attached to the upper part of a wire 41 which is applied to pulleys 42a and 42b, wherein the pulleys 42a or 42b are driven by a driving power source (not shown). When the pulley 42a or 42b is driven by the driving power source, and the inverting roller 22 retreats to the side of the discharge hole for the sheet S via the wire 41 and the restricting plate 40, the sheet S is discharged in face up posture (Fig. 21B). When the inverting roller 22 is located substantially at the center of the discharge hole, the sheet S is discharged in face down posture. The present inventing may be utilized as a manuscript or an original inverting apparatus. Instead of the roller, a disc-shaped rotary member may be used.

Claims: A sheet inverting apparatus, comprising a sheet discharge roller (16) and an inverting rotatable member (22) which is rotatably supported on a shaft (21), characterized in that said inverting rotatable member (22) has a counterweight (22b) for maintaining it stationary in a waiting position, and a sheet clamping recess (22a) opposing said sheet discharge roller (16) when said inverting rotatable member is in said waiting position, wherein said inverting rotatable member is rotated by the sheet discharging force together with said counterweight against the weight of said counterweight when the leading end of the sheet (S) discharged from said sheet discharge roller has been introduced into said sheet clamping recess, thereafter is rotated to a position where the weight of said counterweight acts in a direction promoting rotation of said inverting rotatable member, then is rotated by the weight of said counterweight to wind and thereby tip over the sheet, whereupon the leading end of the sheet is dropped when said sheet clamping recess is directed downwardly, and, finally, is returned to said waiting position by the weight of said counterweight. A sheet inverting apparatus according to claim 1, characterized by a discharge guide (20) which is disposed upstream of and adjacent to said inverting rotatable member (22) and which is adapted to guide the sheet (S) gradually upwards to said sheet clamping recess (22a) of said inverting rotatable member. A sheet inverting apparatus according to claim 1, characterized by a retreating means (32 - 39) for selectively retracting said inverting rotatable member (22) from the sheet discharge path when the discharged sheet (S) is not to be inverted. A sheet inverting apparatus according to claim 1, characterized by a friction member (22c) attached to said inverting rotatable member (22) at its outer circumferential surface, opposing said sheet clamping recess (22a). A sheet inverting apparatus according to claim 1, characterized in that an additional driving source can be attached to said shaft (21). An image forming apparatus comprising an image forming portion, characterized by a sheet inverting apparatus according to one of the preceding claims. An image forming apparatus according to claim 6, characterized by a sheet re-supplying path for introducing the sheet on which an image has been formed to said image forming portion (3 - 7, 13) again, wherein said sheet discharge roller (16) and said inverting rotatable member (22) are disposed in said sheet re-supplying path.

Inventors: YASHIRO MASAHIKO, YASHIRO, MASAHIKO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1990
Main classification: B41J13
IPC codes: B41J3