Drive transmission mechanism

Abstract: A drive transmission mechanism comprising a drive wheel (24) fixed to a drive shaft, a plurality of inter­ mediate wheels (27,28,29) supported by a support shaft and each having a first transmission wheel (27a,28a,29a) and a second trans­ mission wheel (27b,28b,29b) different from each other in diameter and rotatable together, and a driven wheel (26) fixed to a driven shaft, the drive wheel being coupled to the first transmission wheel of the first intermediate wheel counted from the drive side, the second transmission wheel of the (n - 1)th intermediate wheel as counted from the drive side being coupled to the first transmission wheel of the nth intermediate wheel as counted similarly, n being an optional integer of not smaller than 2, the second transmission wheel of the last intermediate wheel as counted from the drive side being coupled to the driven wheel, at least two of the drive wheel, the intermediate wheels and the driven wheel being mounted on the same shaft and rotatable relative to each other.

Description: The present invention relates to a drive transmission mechanism for transmitting the rotational driving force of a drive shaft connected to a motor or like drive source to a driven shaft on speed reduction or increase. A gear mechanism, transmission mechanism comprising a pair of toothed pulleys and a timing belt, or the like is most widely used for transmitting the rotation of a drive shaft to a driven shaft. When a great reduction ratio or increase ratio is required for the transmission, mechanisms comprising, for example, a plurality of idle gears each having two spur gears and different from one another in gear ratio are generally used. Fig. 3 shows an example of such mechanism. With reference to the drawing, indicated at 101 and 101′ are upright inside plates provided in the interior of an apparatus. A motor 102 serving as a drive source is mounted on the inside plate 101. A specified number of intermediate shaft 103 are fixed, each at its one end, to the inside plate 101′, which also supports a driven shaft 105 by a bearing 104 rotatably. The drive shaft 102a of the motor 102 fixedly carries a drive gear 106 to rotate the gear therewith. Similarly, a driven gear 107 is fixed to the driven shaft 105. An intermediate gear 108 is mounted on each of the intermediate shafts 103 and is rotatable relative to the shaft 103. The intermediate gear 108 comprises a large gear ring 108a and a small gear ring 108b integral with the gear ring 108a and different therefrom in diameter. The large gear ring 108a of the intermediate gear 108 most proximate to the drive shaft 102a is in mesh with the drive gear 106, and the small gear ring 108b of this intermediate gear 108 is in mesh with the large gear ring 108a of the second intermediate gear 108. Through similar meshing engagement between the other gears including the small gear ring 108b of the last intermediate gear 108 in mesh with the driven gear 107, the drive shaft 102a is coupled to the driven shaft 105. With the above mechanism, the rotation of the drive shaft 102a of the motor 102 is transmitted via the drive gear 106, the plurality of intermediate gears 108 and the driven gear 107 to the driven shaft 105 upon a great reduction. However, the mechanism of Fig. 3 has the problem that the intermediate gears 108 need to be supported by the respective intermediate shafts 103, so that a larger space is required with an increase in the number of gears, making it difficult to include the mechanism compactly in the body of an apparatus. The mechanism has the further drawback of being complex in construction, necessitating many shafts and therefore being costly. FR-A-1448923 discloses another drive transmission mechanism in which meshing intermediate gears are stacked on extended driving arid driven shafts to transmit the drive with a required speed change between the shafts. The arrangement described here have an intermediate wheel on one shaft sandwiched between preceding and succeeding wheels on the other shaft so that there is rubbing contact between the end faces of adjacent wheels giving rise to large friction forces. Furthermore, although the mechanism is more compact than that shown in Fig. 3, the locations of the driving and driven shafts are closely constrained by the requirements for the gears. According to the present invention, a drive transmission mechanism wherein the mechanism comprises a drive wheel fixed to a drive shaft, a plurality of intermediate wheels comprising wheels supported by a shaft and each having a first transmission ring and a second transmission ring different from each other in diameter and rotatable together, and a driven wheel fixed to a driven shaft, the drive wheel being coupled to the first transmission ring of the first intermediate wheel counted from the drive side, the second transmission ring of the (n - 1)th intermediate wheel as counted from the drive side being coupled to the first transmission ring of the nth intermediate wheel as counted similarly, n being an optional integer of not smaller than 2, the second transmission ring of the last intermediate wheel as counted from the drive side being coupled to the driven wheel, at least two wheels of the drive, intermediate and driven wheels being mounted on the same shaft and rotatable relative to each other, at least two of said intermediate wheels being mounted on a shaft intermediate said driving and driven shafts, said at least two intermediate wheels being rotatable with respect to each other, at least one of the intermediate wheels having a stepped portion between the first transmission ring and the second transmission ring, with a diameter less than the larger of the two associated transmission rings, said stepped portion contacting an end face of a further intermediate wheel coupled to said one intermediate wheel adjacent the periphery of said further intermediate wheel for determining the axial position of said further wheel, said stepped portion also locating an outer rim portion of said larger transmission ring at a clearance from said further intermediate wheel. The above and other optional features and advantages of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings. Fig. 1 is a plan view in section of a drive transmission mechanism embodying the invention; Fig. 2 is a front view in section of an automatic duplex document feeder including the transmission mechanism; and Fig. 3 is a plan view in section of a conventional drive transmission mechanism. Referring firstly to Fig. 2, this shows the interior construction of an automatic feeder for duplex (double-faced) documents which includes a drive transmission mechanism according to the present invention. The feeder has the function of feeding the document onto a contact glass plate 1 of a copying machine and discharging the document, and the function of reversing the fed document and feeding the document onto the glass plate 1 again. The feeder has a feed assembly including a document tray 2, a feed roller 3, a pair of register rollers 4, etc. A conveyor belt 6 is provided above the glass plate 1. Disposed downstream from the belt is a mechanism 7 for reversing the document. The document reversing mechanism 7 comprises a guide member 9 and a reversing roller 10 having transport rollers 11, 12 in pressing contact with the roller 10. A switch guide plate 13 is disposed downstream from the roller 12. The switch guide plate 13 is shiftable between a first position as illustrated and a second position to which the plate 13 is slightly rotated counterclockwise in Fig. 2 from the first position. When in the first position, the switch guide plate 13 forms with the reversing roller 10 a return passage 14 through which the document is returned onto the glass plate 1. When in the second position, the plate 13 provides a document discharge passage for guiding the document to a discharge tray 15. The drive transmission mechanism (speed reduction mechanism) of the present invention is installed in the feeder for driving the shaft (driven shaft) 10a of the reversing roller 10. The transmission mechanism will be described with reference to Fig. 1. The drawing shows upright inside plates 20, 20′ provided in the feeder, and a motor 21 fixed to the inside plate 20 and having a drive shaft 21a projecting toward the inside plate 20′. An intermediate shaft 22 is fixed at its one end to the inside plate 20′. The shaft 10a of the reversing roller 10 is positioned in alignment with the drive shaft 21a and rotatably supported by a bearing 23 on the inside plate 20′. A drive gear 24 having a pitch circle of small diameter is fixed to the drive shaft 21a with a screw 25. A driven gear 26 having a pitch circle of large diameter is mounted on the roller shaft 10a and held to the shaft 10a against rotation. More specifically, a pin 10b extends through the shaft 10a, with opposite ends of the pin 10b projecting outward from the roller shaft periphery. A groove 26a formed in the driven gear 26 has the pin ends fitted therein. The drive gear 24 is coupled to the driven gear 26 by three intermediate gears 27 to 29 which are all identical in shape. Each of the intermediate gears 27 to 29 comprises a large gear (first transmission wheel) 27a (28a, 29a) having the same pitch circle as the driven gear 26, and a small gear (second transmission wheel) 27b (28b, 29b) integral with the large gear and having the same pitch circle as the drive gear 24. A stepped portion 27c (28c, 29c) is formed between the large gear 27a (28a, 29a) and the small gear 27b (28b, 29b). The gears mesh with one another in the following relationship. (1) The drive gear 24 and the large gear 27a of the intermediate gear 27. (2) The small gear 27b of the intermediate gear 27 and the large gear 28a of the intermediate gear 28. (3) The small gear 28b of the intermediate gear 28 and the large gear 29a of the intermediate gear 29. (4) The small gear 29b of the intermediate gear 29 and the driven gear 26. Thus, with the present mechanism, the meshing pairs of gears 24, 27 to 29 and 26 are all equal in speed transmission ratio. The mechanism is further characterized in that the intermediate gears 27, 29 are supported by the intermediate shaft 22 rotatably relative to each other, and that the intermediate gear 28 is supported by the roller shaft 10a rotatably relative to the shaft 10a and also to the driven gear 26. Stated more specifically, the intermediate gears 27, 29 as arranged in superposed layers (in series) are mounted on the intermediate shaft 22 rotatably relative to the shaft 22 and positioned in place by a retaining ring 30 axially of the shaft. The intermediate gear 28 mounted on the roller shaft 10a is positioned closer to the motor 21 than the driven gear 26 and held in this position axially thereof by the contact of one side face of its large gear 28a with the stepped portion 27c of the intermediate gear 27. With the mechanism described above, suppose the gear-to-gear speed transmission ratio is i (i < 1), and the angular velocity of the drive shaft 21a rotated by the operation of the motor 21 is ω. The intermediate gear 27 in mesh with the drive gear 24 fixed to the drive shaft 21a then rotates at an angular velocity of ωi. Further the intermediate gear 28 meshing with this intermediate gear 27 rotates at an angular velocity of ωi², the intermediate gear 29 meshing with the gear 28 rotates at an angular velocity of ωi³, and the driven gear 26 meshing with the gear 29 rotates with the roller shaft 10a at an angular velocity of ωi⁴. Thus, the mechanism transmits the rotation of the drive shaft 21a to the roller shaft 10 at a reduction ratio of i⁴. The present mechanism requires five gears like the mechanism of Fig. 5, whereas these gears can be supported by three shafts, i.e., the drive shaft 21a, roller shaft 10a and single intermediate shaft 22. This serves to greatly reduce the space required to compact the body of the apparatus (i.e. the automatic document feeder), further making the mechanism simplified in construction and less costly. When the intermediate gears 27 to 29 are shaped identically as in the present embodiment, a further cost reduction can be achieved. If the intermediate gear 28 is positioned in place by the stepped portion 27c of the intermediate gear 27 as stated above, a positioning member such as a retaining ring can be dispensed with. This leads to a further cost reduction and also makes it possible to position, for example, the drive shaft 21a very close to the roller shaft 10a end-to-end as illustrated for a greater reduction in the space needed. Although the intermediate gears 27 to 29 need not always be made common according to the present invention, the gear arrangement shown in Fig. 1 requires that the pairs of meshing gears be definite in the axis-to-axis distance, more specifically in the sum of diameters of the pitch circles (the sum of tooth numbers in the case of equal modules). The advantages of the invention can be obtained insofar as at least two gears or the like are supported by the same shaft and made rotatable relative to each other. With the mechanism of Fig. 1, for example, the intermediate gears 27, 29 may be supported by individual support shafts. The single roller shaft 10a supporting both the intermediate gear 28 and the driven gear 26 still serves to reduce the space by a corresponding amount. The intermediate gears 27, 29 need only to be rotatable relative to each other. For example, the intermediate gear 27 may be fixed to the intermediate shaft 22 and made rotatable with the shaft 22, with the intermediate gear 29 mounted on the shaft 22 rotatably relative thereto. A plurality of gears may be mounted on the drive shaft 21a. Alternatively, the drive shaft 21a and the roller shaft 10a may be provided with the drive gear 24 and the driven gear 26 only, respectively, with at least two of the intermediate gears mounted on one shaft. With these arrangements, the drive side and the driven side may be replaced by each other to use the arragement as a speed increasing mechanism. The terms "drive shaft" and "driven shaft" as used herein have relative meanings; the "drive shaft" need not always be connected directly to the drive source, nor is it always required that the "driven shaft" be connected directly to the member to be driven. In other words, these shafts may be connected to the drive source or driven member by another drive transmission means. The present invention can be embodied with use of drive transmitting wheels which include not only gears but also frictional wheels. The foregoing embodiment has been described as a drive transmission mechanism for use in automatic duplex document feeders, but the invention is not limited thereto and is also applicable to various devices or apparatus which require speed reduction or increase.

Claims: A drive transmission mechanism wherein the mechanism comprises: a drive wheel (24) fixed to a drive shaft (21a), a plurality of intermediate wheels comprising wheels (27,29) supported by a shaft (22;10a) and each having a first transmission ring (27a,29a) and a second transmission ring (27b,29b) different from each other in diameter and rotatable together, and a driven wheel (26) fixed to a driven shaft (10a), the drive wheel being coupled to the first transmission ring of the first intermediate wheel counted from the drive side, the second transmission ring of the (n - 1)th intermediate wheel as counted from the drive side being coupled to the first transmission ring of the nth intermediate wheel as counted similarly, n being an optional integer of not smaller than 2, the second transmission ring of the last intermediate wheel as counted from the drive side being coupled to the driven wheel, at least two wheels of the drive, intermediate and driven wheels being mounted on the same shaft and rotatable relative to each other, characterised by: at least two of said intermediate wheels being mounted on a shaft intermediate said driving and driven shafts, said at least two intermediate wheels being rotatable with respect to each other, at least one of the intermediate wheels having a stepped portion (27c,29c) between the first transmission ring and the second transmission ring, with a diameter less than the larger of the two associated transmission rings, said stepped portion contacting an end face of a further intermediate wheel coupled to said one intermediate wheel adjacent the periphery of said further intermediate wheel for determining the axial position of said further wheel, said stepped portion also locating an outer rim portion of said larger transmission ring at a clearance from said further intermediate wheel. A mechanism of claim 1, wherein the drive shaft (21a) is positioned in alignment with the driven shaft (10a). A mechanism as defined in claim 1 or claim 2 preceding claims wherein all the intermediate wheels are identical in shape. A mechanism as defined in any one of claims 1 to 3 wherein each of the drive, driven and intermediate wheels comprises a gear. A mechanism as defined in any one of claims 1 to 3 wherein each of the drive, driven and intermediate wheels comprises a friction wheel. A mechanism as defined in any one of the preceding claims wherein at least one intermediate wheel (28) is rotatable on the driven shaft (10a). A mechanism as defined in any one of the preceding claims having intermediate wheels in which the first transmission ring has a larger diameter than the second transmission ring. A mechanism as defined in any one of claims 1 to 6 having intermediate wheels in which the first transmission ring has a smaller diameter than the second transmission ring.

Inventors: TAKIMOTO KAZUSHI, TAKIMOTO, KAZUSHI
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO. LTD.
Application year: 1989
Main classification: F16H1
IPC codes: F16H35, F16H57, F16H7, F16H1