JP2007178591A - Drive transmission apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the rotating variation of a drive transmission apparatus causing color smear or density unevenness without raising cost caused by upsizing an apparatus or increasing the number of components. <P>SOLUTION: A driving unit 103 for transmitting a driving force to a photoreceptor drum is provided with: the intermediate stage gear 47 with two gears different in diameter on the same shaft; a drum driving gear 48 engaging with the intermediate stage gear 47 at a first engaging position and having driving force transmitted from the intermediate stage gear 47; and a pinion 46 engaging with the intermediate stage gear 47 at a second engaging position and transmitting the driving force to the intermediate stage gear 47. Each gear above is installed according to rotational phase of the pinion 46 and the number of gates or the number of ribs in the intermediate stage gear 47 so that variation in quick action due to cumulative error in a gate pitch for the intermediate stage gear 47 occurring in the first engaging position is in a relationship of steadily canceling out a speed variation component due to eccentricity in the pinion 46 occurring in the second engaging position. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a drive transmission device having a gear train composed of three or more gears and transmitting a driving force to a rotating body, and an image forming apparatus having the drive transmission device.

  In recent years, there has been an increasing demand for electrophotographic image forming apparatuses capable of forming color images. Color image formation that can achieve six items of (1) low running cost, (2) space saving, (3) low power, (4) high image quality, (5) high speed, and (6) improved operability. The introduction of equipment is expected.

  Under such circumstances, the conventional (6) easy-to-operate, (5) high speed, and (4) high quality color image can be provided. A device has been proposed. For example, a so-called tandem (or four-drum) image forming apparatus that performs image formation by arranging four photosensitive drums in parallel using process cartridges of four colors of yellow, magenta, cyan, and black.

  In this method, four color images are independently formed to form one color image. For this reason, when the image forming point formed by each drum is displaced from the target (ideal) position, the relative positional deviation between the colors is the color deviation between the colors (for example, the color deviation between black and cyan) or the pitch unevenness. There is a problem that (stepped density unevenness) appears on an actual image.

  In particular, the drive motor of the drive transmission device that transmits the rotation to the photosensitive drums of each color is likely to cause uneven speed of the motor rotation cycle due to fluctuations such as the coaxiality between the shaft and the rotor and the coaxiality between the motor positioning portion and the shaft. It is easy to cause positional deviation from the target (ideal) position.

  Further, a color image forming apparatus having a structure in which a resin gear is attached to the shaft of the drive motor is known in order to prevent noise (harmful sound) due to the meshing frequency of the gear. However, in this configuration, the speed irregularity of the rotation cycle of the motor is more likely to occur due to the gear accuracy such as the accumulated pitch error of the resin gear and the shake such as the coaxiality of the shaft and the resin gear. For this reason, even with the above-described configuration, there is a high possibility that pitch unevenness (stepped density unevenness) will occur on an actual image.

  Therefore, a technique for reducing the speed fluctuation of the drive transmission device that causes the above-described color misregistration and density unevenness has been conventionally proposed. In Japanese Patent Laid-Open No. 2000-330449 (hereinafter referred to as Patent Document 1), a flywheel is provided on each of drum drive gear shafts for rotating and transmitting four photosensitive drums, and the inertia amount is increased to increase the amount of inertia. Techniques for reducing the speed fluctuations of this are disclosed.

  In Japanese Patent Laid-Open No. 2000-162846 (hereinafter referred to as Patent Document 2), detection devices each including a wheel and an encoder are provided on drum drive gear shafts for rotationally transmitting four photosensitive drums. Further, a feedback control technique is disclosed in which a rotation fluctuation of the drum drive gear is detected by these detection devices, and a drive motor that rotates the photosensitive drum is rotated by a drive signal that cancels the rotation fluctuation.

JP 2000-330449 A JP 2000-162846 A

  However, the technique as described in Patent Document 1 may increase the size of the flywheel depending on the required amount of inertia, and is difficult to apply in consideration of downsizing and space saving of the image forming apparatus. In particular, in a tandem type four-drum type color image forming apparatus, a flywheel is required for each color, which may further increase the size of the apparatus.

  Further, in the technique as described in Patent Document 2, although the possibility of occupying space is smaller as in the flywheel system, the number of parts increases and a detection device for four drums is required. For this reason, an increase in cost is inevitable, and it is particularly difficult to apply to a low-end small-sized image forming apparatus.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to reduce rotational fluctuations of a drive transmission device that cause color misregistration and density unevenness without increasing costs due to an increase in the size of the device or an increase in the number of parts.

  In order to achieve the above object, a typical configuration of the present invention includes an intermediate gear having two gears having different diameters on the same axis, meshed with the intermediate gear at a first meshing position, and driving force transmitted from the intermediate gear. A downstream transmission gear, and an upstream gear that meshes with the intermediate gear at a second meshing position and transmits the driving force to the intermediate gear, and transmits the driving force to the rotating body, The reduction gear ratio between the upstream gear and the intermediate gear is N (N is a natural number), the number of gates of the intermediate gear is the same N (N is a natural number), and the accumulated pitch error of the upstream gear is h1. The cumulative pitch error of the intermediate gear meshing with the gear is h2, the cumulative pitch error of the intermediate gear meshing with the downstream gear is mh2 (m is a positive real number), and the radius ratio of the two gears of the intermediate gear is k: 1 ( k is Of course, when the meshing angle of the three gears formed by the first meshing position and the second meshing position is θ, according to the rotational phase of the upstream gear and the gate position of the intermediate gear, When the relationship of accumulated pitch error is 0 <h2 ≦ | h1 / km |, the meshing angle of the gear satisfies the relationship of θ = π × (2i−1) / N1 (i is a natural number) and the accumulated When the relationship between pitch errors is | h1 / km | ≦ h2, the gears are arranged such that the meshing angle of the gears satisfies θ = π × 2i / N1.

  According to the present invention, since the speed fluctuation due to the eccentricity of the upstream gear is offset with the speed fluctuation of the gate period of the intermediate gear, in the rotational fluctuation on the downstream gear shaft, Speed fluctuation can be reduced. Thereby, the rotation fluctuation of the drive transmission device causing the rotation unevenness of the rotating body can be reduced without increasing the cost due to the increase in the size of the device or the number of parts.

  In particular, when the present invention is applied to a drive transmission device that transmits a driving force to an image carrier in an image forming apparatus, the speed fluctuation caused by the eccentricity of the upstream gear is the speed fluctuation of the gate (or rib) cycle of the intermediate gear. Is offset by For this reason, in the rotational fluctuation on the axis of the image carrier that forms the actual image, it is possible to reduce the speed fluctuation of the rotational period component of the upstream gear, and the color shift and pitch unevenness (stepped shape) generated on the actual image. It is possible to reduce density unevenness.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated otherwise, the scope of the present invention is not intended to be limited thereto.

  FIG. 1 is a sectional view schematically showing a color image forming apparatus according to an embodiment of the present invention. The color image forming apparatus shown in FIG. 1 includes four photosensitive drums 1 (1a, 1b, 1c, 1d) arranged in parallel in the vertical direction. The photosensitive drum 1 as an image carrier is rotated by a driving force transmitted from a driving unit described later. Around each photosensitive drum 1, there are charging means 2 (2a, 2b, 2c, 2d), developing means 4 (4a, 4b, 4c, 4d), cleaning means 6 (6a, 6b, 6c, 6d), etc. Is arranged. Here, the charging means 2 is for uniformly charging the surface of the photosensitive drum 1. The developing means 4 is for developing a toner image by attaching a developer (hereinafter referred to as toner) to the electrostatic latent image. The cleaning unit 6 removes transfer residual toner remaining on the surface of the photosensitive drum 1 after transfer. In FIG. 1, reference numeral 3 (3a, 3b, 3c, 3d) denotes exposure means for irradiating a laser beam based on image information to form an electrostatic latent image on the photosensitive drum 1. Reference numeral 5 denotes transfer means for transferring the toner image on the photosensitive drum 1 to a recording material. These constitute image forming means.

  Here, the photosensitive drum 1, the charging unit 2, the developing unit 4, and the cleaning unit 6 are integrally formed into a cartridge, and a process cartridge 7 (7a, 7b, 7c, 7d) that is detachable from the main body of the image forming apparatus is provided. Forming.

  The recording material fed from the feeding unit 8 is conveyed to the image forming unit by a conveying unit 9 constituted by a conveying belt, and each color toner image is sequentially transferred to record a color image. Thereafter, the recording material S to which the color image has been transferred is image-fixed by the fixing unit 10 and discharged to the discharge unit 13 by the discharge roller pair 12.

  In double-sided recording, before the recording material is fixed by the fixing unit 10 and discharged by the discharge roller pair 12, the discharge roller pair 12 is reversed to be conveyed to the double-sided conveyance path (in the direction of arrow A). ). The recording material conveyed to the double-sided conveyance path is conveyed again to the image forming unit by the registration roller 8 c of the feeding unit 8.

  FIG. 2 is a diagram showing a state in which the process cartridge is mounted on the main body of the image forming apparatus and the photosensitive drum 1 in the process cartridge is positioned on the main body side plate. The process cartridge is a cartridge in which the photosensitive drum 1 and process means (charging means, developing means, and cleaning means) that act on the photosensitive drum 1 are integrated into a cartridge, and can be attached to and detached from the image forming apparatus main body by the user. It has become. Inside the image forming apparatus main body, a guide rail portion (not shown) is provided along the attaching / detaching direction of the process cartridge, and the user inserts the process cartridge along the guide rail portion. At this time, the outer peripheries of the bearing portions 130 and 131 that rotatably support the photosensitive drum 1 in the process cartridge are the end surfaces 133a, 133b, and 134a and 134b of the edge notches 133 and 134 of the main body right side plate 101 and the main body left side plate 102, respectively. I hit it. As a result, the photosensitive drum 1 and the process cartridge are positioned and fixed with respect to the image forming apparatus main body with high accuracy.

  A drive unit 103 (see FIG. 3) for driving the plurality of photosensitive drums 1 is positioned and fixed outside the right frame (main body right side plate) 101 of the main body of the image forming apparatus on the right side in the process cartridge insertion direction.

  FIG. 3 is a diagram for explaining the drive unit 103. In the driving unit 103, driving units 103Y, 103M, 103C, and 103Bk for driving the photosensitive drums 1 of Y, M, C, and Bk colors are positioned and fixed on the driving frame 104 with high accuracy. Here, Y is yellow, M is magenta, C is cyan, and Bk is black. Each drive unit of the drive unit 103 has a drum motor 45 as a drive source fixed to the drive frame 104. Further, a pinion 46 as an upstream gear fixed to the motor shaft of the motor 45, an intermediate gear 47 as an intermediate gear that meshes with the pinion 46 and the drum drive gear 48 and is rotatably supported, and a drum drive as a downstream gear. A gear 48 is provided. Further, it has a bearing 51 that supports the drum driving gear 48 and a triangular coupling portion 52 formed at the tip of the drum driving gear 48.

  Next, a connection configuration between the photosensitive drum 1 and the drive unit 103 will be described with reference to FIGS. 4 and 5.

  After the user mounts the process cartridge on the main body of the image forming apparatus, the rotary cam 128 rotates in conjunction with the rotating operation of bringing the recording material carrying / conveying unit (not shown) into contact with the photosensitive drum 1. Then, the mating rotary cam 129 connected to the rotary cam 128 thrusts in the axial direction of the photosensitive drum 1 by the urging force of the return spring 62 together with the drum drive gear 48. As a result, the triangular coupling recess 52 formed at the tip of the drum drive gear 48 is connected to and fitted with the triangular coupling protrusion 37 formed in the drum coupling 57 at the end of the photosensitive drum unit. Thereby, the drum driving gear 48 is positioned and fixed with respect to the photosensitive drum 1, and the axis of the drum driving gear 48 is arranged on the same straight line with respect to the photosensitive drum 1.

  The triangular coupling concave portion 52 has a hole that becomes a twisted regular triangular prism, and is engaged with and disengaged from the triangular coupling convex portion 37 in the axial direction. When the triangular coupling convex part 37 and the triangular coupling concave part 52 are fitted, the ridge line of the twisted regular triangular prism of the triangular coupling convex part 37 contacts the twisted triangular prism surface of the triangular coupling concave part 52. Thereby, the triangular coupling convex part 37 and the triangular coupling concave part 52 are aligned, and the rotation centers coincide. In the above description, the drum drive gear 48 during image formation has its thrust position determined at the position most moved to the process cartridge side when the bottom surface of the triangular coupling concave portion 52 and the end surface of the triangular coupling convex portion 37 abut against each other. The drum drive gear 48 has a fixed thrust and is supported along the bearing 51 so as to be able to move back against the urging force of the return spring 62.

  As shown in FIGS. 6 and 7, the triangular coupling recess 52 is provided with a key groove 65 in one side 52 a of a hole serving as a twisted regular triangular prism, and one side 37 a of the regular triangular prism of the triangular coupling convex portion 37. It is configured to be fitted with a phase positioning rib 66 provided on the surface. The phase positioning rib 66 is engaged only in one rotation and one phase so that the ridge line of one side 52a of the regular triangular prism hole of the triangular coupling recess 52 and the surface of one side 37a of the regular triangular prism of the triangular coupling convex portion 37 are always in contact with each other. It is configured so that it can be removed. Until the phases of the phase positioning rib 66 and the key groove 65 coincide with each other, the triangular coupling convex portion 37 and the triangular coupling concave portion 52 are not fitted to each other even when the rotation starts.

  In a state where the phase positioning rib 66 and the keyway 65 are out of phase and the triangular coupling convex portion 37 and the triangular coupling concave portion 52 are not connected, the end face of the triangular coupling convex portion 37 is at the mouth of the triangular coupling concave portion 52. The edge is pushed, and the drum drive gear 48 is retracted to the outside of the image forming apparatus against the urging force of the return spring 62. Then, after the process cartridge 7 is mounted, the connection is instantaneously made when the phase of the phase positioning rib 66 and the key groove 65 coincide with each other when the image forming apparatus main body is rotated forward.

  As described above, in the drum driving gear 48 and the photosensitive drum 1, the phases of the phase positioning rib 66 and the key groove 65 coincide with each other, and the triangular coupling concave portion 52 and the triangular coupling convex portion 37 are engaged with each other. For the first time, positioning and fixing are performed. Along with this positioning and fixing, a rotational driving force by the drum motor 45 as a driving source is transmitted to the triangular coupling convex portion 37.

  Also, as shown in FIGS. 4, 5, and 6, the drum drive gear 48 is provided with a phase detection rib 72 so that the rotational phase can be detected. The phase detection rib 72 is provided with slit portions 72 a and 72 b having different slit widths, and the detection portion 71 separately installed in the image forming apparatus main body passes through the slit portions 72 a and 72 b while the drum drive gear 48 is rotating. Detect. Thereby, the rotational phase of the drum drive gear 48 is instantaneously detected. Then, when the pre-rotation is stopped when the image forming apparatus is activated, the detection unit 71 detects the rotation phases of the drum driving gears 48 for the four colors. Then, the rotation of the motor 45 is controlled so that each drum drive gear 48 is stopped at a position shifted in advance by a predetermined angle so that the rotation phases of each drum drive gear 48 coincide with each other at the time of printing. Thereby, when the next print job is started, the rotational phases of the photosensitive drums 1 for the four colors are not shifted at all, and the color shift of the drum period in the sub-scanning direction due to the phase shift does not occur.

  Here, the gear phase arrangement configuration of the pinion 46, the intermediate gear 47, and the drum drive gear 48 constituting the drive transmission device will be described with reference to FIGS.

  As shown in FIG. 8, the number of teeth of the gear train that drives the photosensitive drum 1 in the drive unit 103 is such that the rotation period of each gear is an integral fraction of the rotation period of the drum drive gear 48. It is configured like this. Specifically, in this embodiment, the drum drive gear 48 has 128 teeth, the intermediate gear 47 has a large gear 47a and a small gear 47b of 64 teeth and 32 teeth, and the pinion 46 has 16 teeth, respectively. . Further, the reduction ratio between the pinion 46 and the intermediate gear 47 located at the uppermost stream is 4, and each gear is manufactured by injection molding using a resin member. FIG. 9 is an example of a graph showing the accumulated pitch error of the pinion 46, which can be approximately represented by a sine curve of one rotation period having a size of about 60 μm. A marking 150 that can manage the phase of the accumulated pitch error of the pinion 46 is provided at a position corresponding to the maximum value of the accumulated pitch error at the gear end of the pinion 46.

  As shown in FIG. 8, the number of gates used when molding the intermediate gear 47 is configured with the same four points as the reduction ratio with the pinion 46, and the marking 151 is such that the phase can be managed at the gate position. Is given. The four markings 151 are provided on the gears 47 a and 47 b of the intermediate gear 47. Specifically, the large gear 47a is provided with a marking 151a (one of which is not shown), and the small gear 47b is provided with a marking 151b. FIG. 10 is an example of a graph showing the accumulated pitch error of the large gear 47 a of the intermediate gear 47. Normally, a gear formed by injection molding of a multipoint gate generates an accumulated pitch error of the gate pitch separately from the eccentric component of one rotation cycle. Although the accuracy of the pitch error varies depending on the mold accuracy and molding conditions, cost increases and advanced techniques are required to improve mold accuracy and optimize molding conditions. It is difficult to make the error zero. FIG. 11 is an example of a graph showing the accumulated pitch error of the small gear 47 b of the intermediate gear 47. Since the intermediate gear 47 is a four-point gate, in FIG. 10 and FIG. 11, a composite of a sine curve of one rotation cycle having a cumulative pitch error of about 80 μm and a sine curve of a gate pitch of ¼ cycle. Approximately represented by a wave. Note that the amplitude of each cycle varies depending on the gear accuracy, and also varies depending on the outer diameter of the gear. Therefore, the graphs shown in FIGS. 10 and 11 are cumulative pitches that are easily approximated to explain the present embodiment. The state of error is shown. Each gate position to which the marking 151 of the intermediate gear 47 is applied coincides with the peak phase of the accumulated pitch error curve. This is because the pressure of the resin flowing from the gate during molding differs in the vicinity of each gate and in the center between each gate, so the transferability to the mold changes and affects the gear accuracy such as cumulative pitch error. is there.

  As shown in FIG. 12, when the marking position 150 of the pinion 46 is in the meshing position with the large gear 47a of the intermediate gear 47, the phase where the accumulated pitch error of the pinion 46 whose meshing position is upstream is large. It corresponds to. For this reason, in the vicinity of the meshing position, the intermediate gear 47 is rotated ahead of the normal time, and the rotational position error of the intermediate gear 47 increases in the rotational direction. Further, as shown in FIG. 13, when the marking position (gate position) 151a of the intermediate gear 47 is in the meshing position with the pinion 46, the meshing position of the large gear 47a of the intermediate gear 47 that is on the downstream side is This corresponds to a phase in which the accumulated pitch error increases. For this reason, in the vicinity of the meshing position, the intermediate gear 47 is delayed in the advance of rotation than usual, and the rotational position error of the intermediate gear 47 is increased in the counter-rotating direction. Similarly, as shown in FIG. 14, when the marking position 151b of the intermediate gear 47 is in the meshing position with the drum drive gear 48, the small gear 47b of the intermediate gear 47 whose upstream meshing position is the meshing position. This corresponds to a phase in which the accumulated pitch error increases. For this reason, in the vicinity of the meshing position, the drum drive gear 48 is rotated ahead of the normal time, and the rotational position error of the drum drive gear 48 increases in the rotation direction. At this time, the large / small gear tooth ratio of the intermediate gear 47 in this embodiment is 2. Therefore, as shown in FIGS. 10 and 11, when the accumulated pitch error is the same value (80 μm in FIGS. 10 and 11), the magnitude of the rotational position error exerted on the counterpart driven gear by the same accumulated pitch error is The small gear 47b corresponds to twice the large gear 47a.

  Therefore, as shown in FIG. 8, the meshing phases of the pinion 46, the intermediate gear 47, and the drum drive gear 48 are set to 180 ° opposite to the pinion 46 marking position 150 and the large gear 47a of the intermediate gear 47. It meshes with the marking position 151a. At the same time, the marking position 151 b of the small gear 47 b of the intermediate gear 47 and the drum driving gear 48 are engaged with each other. Thereby, the rotational position error of one rotation period of the pinion 46 on the axis of the drama driving gear 48 can be minimized. That is, as shown in FIG. 16, at the second meshing position of the pinion 46 and the large gear 47a, the speed fluctuation caused by the accumulated pitch error of the pinion 46 and the speed fluctuation caused by the accumulated gate pitch error of the large gear 47a. The influences will build up. For this reason, a pitch circumferential error on the large gear 47a corresponding to about 70 μm occurs on the intermediate gear 47 axis. Further, since one rotation period of the pinion 46 and the gate pitch period of the intermediate gear 47 are the same, the speed fluctuations of both of them constantly increase at the second meshing position. However, the speed fluctuation caused by the gate pitch accumulated error of the small gear 47b generated at the first meshing position between the small gear 47b and the drum driving gear 48 is the speed variation component generated at the second meshing position. There is a constant offset relationship. For this reason, as shown in FIG. 17, the speed fluctuation in one rotation cycle of the pinion 46 on the drum drive gear 48 which is the most downstream gear is minimized. 18 removes the rotation period components of the intermediate gear 47 and the drum drive gear 48 from the state of FIG. 17, and shows the speed fluctuation state of only one rotation component of the pinion 46 as a single unit of the pinion 46 shown in FIG. This is compared with the accumulated pitch error. As shown in FIG. 18, here, the pitch circumferential error of one rotation period of the pinion 46 on the drum drive gear 48 due to the cumulative pitch error of the pinion 46 alone is about 30 μm. In contrast, the pitch circumferential error of one rotation period of the pinion 46 on the drum driving gear 48 was reduced to about 10 μm.

  Here, it is assumed that the cumulative pitch error of the pinion 46 is 60 μm, and the cumulative pitch error of the gate gear 47 of the intermediate gear 47 is 80 μm for both the large gear 47a and the small gear 47b. It is not a thing. If the accumulated pitch error of the gate pitch of the intermediate gear 47 is 60 μm, a pitch circle of one rotation period of the pinion 46 on the drum drive gear 48 is obtained by the effect of canceling the rotation error as described above. The circumferential error can be reduced to about zero. That is, the effect of reducing the pitch circumferential error of one rotation period of the pinion 46 on the drum drive gear 48 due to the magnitude of the cumulative pitch error of the pinion 46 and the cumulative pitch error of the gate pitch of the intermediate gear 47. Will be different.

  Therefore, the rotational phase of the pinion 46, the meshing angle of the three gears of the pinion 46 and the intermediate gear 47 and the drum drive gear 48, the accumulated pitch error of the pinion 46, and the gate pitch of the intermediate gear 47 Each parameter is uniquely determined based on a certain relationship in the mutual relationship with the numerical value of the accumulated pitch error. As a result, it is possible to reduce the speed fluctuation of one rotation period component of the pinion 46 on the drum drive gear 48 axis that is the most downstream, and to surely reduce the accumulated pitch error of the pinion 46 alone.

  Next, a specific gear train configuration that makes it possible to realize the effect of reducing the speed fluctuation in one rotation cycle of the pinion 46 as described above will be described in detail.

  First, as shown in FIG. 15, the pinion is such that the marking position of the small gear 47b is in the meshing position with the drum drive gear 48 and the marking position of the pinion 46 is in the meshing position with the large gear 47a. 46 and the drum drive gear 48 are arranged. Here, the reduction ratio between the pinion 46 and the intermediate gear 47 is N1, and the number of gates of the intermediate gear 47 is the same N1 (N1 is a natural number). The reduction ratio between the intermediate gear 47 and the drum drive gear 48 is N2 (N2 is a natural number). The angle formed by the meshing position (second meshing position) between the pinion 46 and the large gear 47a and the meshing position (first meshing position) between the small gear 47b and the drum drive gear 48 is defined as θ. Further, the accumulated pitch error of one rotation period of the pinion 46 is h1, the accumulated pitch error of the gate pitch of the large gear 47a is h2, and the accumulated pitch error of the gate pitch of the small gear 47b is mh2 (m is a coefficient). . The radius ratio of the intermediate gear 47 is k: 1 (k is a natural number).

  At this time, when the intermediate gear 47 is arranged so that the marking position of the intermediate gear 47 is in the meshing position with the pinion 46, the pitch circumferential error curve P on the drum drive gear 48 axis is as follows. The pitch circumference error curves P1, P2 and P3 shown in FIG. That is, when the meshing position of the drum drive gear 48 is θ = π × 2i / N1 (i is a natural number) and each gear arrangement is expressed, the pitch circumferential error curve P on the drum drive gear 48 is as shown in FIG. 19, the pitch circumferential error curve P1 on the drum driving gear 48 due to the accumulated pitch error of the pinion 46, and the pitch circumferential error on the drum driving gear 48 due to the accumulated gate pitch error of the large gear 47a. The curve P2 and the sum of error curves of the pitch circumferential error curve P3 on the drum drive gear 48 due to the accumulated gate pitch error of the small gear 47b can be approximated and expressed.

Pitch circumferential error curve on the drum drive gear 48 due to the accumulated pitch error of the pinion 46 P1 = h1 × sin [N1 × N2 × θ + π] / (2 × k)
Pitch circumferential error curve on the drum drive gear 48 due to the accumulated pitch error of the large gear 47a P2 = h2 × sin [N1 × N2 × θ + π] / (2 × k)
Pitch circumferential error curve on the drum drive gear 48 due to the accumulated pitch error of the small gear 47b P3 = mh2 × sin [N1 × N2 × θ] / 2
That is,
P = P1 + P2 + P3
= H1 × sin [N1 × N2 × θ + π] / (2 × k) + h2 × sin [N1 × N2 × θ + π] / (2 × k) + mh2 × sin [N1 × N2 × θ] / 2
= (− H1 + (km−1) h2) × sin [N1 × N2 × θ] / (2 × k)
From the above equation, it can be seen that the pitch circumferential error on the drum drive gear 48 is | (−h1 + (km−1) h2) |.

FIG. 20 shows the transition of the pitch circumferential error on the drum drive gear 48 when the accumulated pitch error h2 of the gate pitch of the large gear 47a is plotted on the horizontal axis. As shown in FIG. 20, when the gear meshing position is θ = π × 2i / N1, the pitch circumferential error of the one rotation period of the pinion 46 on the drum driving gear 48 can be surely reduced. The range of the value of the accumulated pitch error h2 is
0 <h2 <| 2 × h1 / (mk−1) |
It turns out that it is.

  Next, as shown in FIG. 21, when the intermediate gear 47 is arranged so that the intermediate point of the two gate positions of the intermediate gear 47 is in the meshing position with the pinion 46, the drum driving gear 48 is provided. The pitch circumference error curve P on the axis can be approximated and expressed as the sum of error curves of pitch circumference error curves P1, P2 and P3 shown below. That is, when the meshing position of the drum drive gear 48 is θ = π × (2i−1) / N1 (i is a natural number) and the gear arrangement is expressed, the pitch circumferential error curve on the drum drive gear 48 As shown in FIG. 22, P is a pitch circumferential error curve P1 on the drum drive gear 48 due to the accumulated pitch error of the pinion 46, and on the drum drive gear 48 due to the accumulated gate pitch error of the large gear 47a. The pitch circumference error curve P2 and the gate pitch accumulated error curve P3 of the small gear 47b can be approximated and expressed as a sum of pitch circumference error curves on the drum drive gear 48 due to errors.

Pitch circumferential error curve on the drum drive gear 48 due to the cumulative pitch error of the pinion 46 P1 = h1 × sin [N1 × N2 × θ + π] / (2 × k)
Pitch circumferential error curve on the drum drive gear 48 due to the accumulated pitch error of the large gear 47a P2 = h2 × sin [N1 × N2 × θ] / (2 × k)
Pitch circumference error curve on the drum drive gear 48 due to the accumulated pitch error of the small gear 47b P3 = mh2 × sin [N1 × N2 × θ] / 2
That is,
P = P1 + P2 + P3
= H1 × sin [N1 × N2 × θ + π] / (2 × k) + h2 × sin [N1 × N2 × θ] / (2 × k) + mh2 × sin [N1 × N2 × θ] / 2
= (− H1 + (km + 1) h2) × sin [N1 × N2 × θ + γ1] / (2 × k)
However, cos [γ1] = − h1 / (h1 ² + h2 ² (km−1) ² ) ^(1/2)
From the above equation, it can be seen that the pitch circumferential error on the drum driving gear 48 is | (−h1 + (km + 1) h2) |.

FIG. 23 shows the transition of the pitch circumferential error on the drum drive gear 48 when the accumulated pitch error h2 of the gate pitch of the large gear 47a is plotted on the horizontal axis. 23, when the gear meshing position is θ = π × (2i−1) / N1, the large gear 47a can reliably reduce the pitch circumferential error of one rotation period of the pinion 46 on the drum driving gear 48. The range of the accumulated pitch error h2 of the gate pitch of
0 <h2 <| 2 × h1 / (mk + 1) |
It turns out that it is.

Therefore, from FIG. 24 in which the graphs of FIGS. 20 and 23 are integrated, the meshing position θ that can most reduce the pitch circumferential error of one rotation period of the pinion 46 on the axis of the drum drive gear 48 is
If 0 <h2 ≦ | h1 / km |, θ = π × (2i−1) / N1 (1)
When | h1 / km | ≦ h2, θ = π × 2i / N1 (2)
It can be seen that

  As described above, the rotational phase of the pinion 46, the meshing angle of the three gears of the pinion 46 and the intermediate gear 47 and the drum drive gear 48, the accumulated pitch error of the pinion 46 and the intermediate gear 47 The gears are arranged so as to satisfy the relationship of the expressions (1) and (2) in relation to the numerical value of the accumulated pitch error of the gate pitch. As a result, it is possible to reduce the speed fluctuation of one rotation period of the pinion 46 on the drum drive gear 48 axis, and to reliably reduce the accumulated pitch error of the pinion 46 alone.

  Next, the phase alignment accuracy of each gear will be described in detail. Ideally, it is desirable to ensure that the marking position of each gear matches the meshing position by the mutual relationship as described above. However, in reality, there may be an angle between the marking position of each gear and the ideal position due to errors in assembling the gear and other restrictions. Even in such a case, if the other gears are arranged at the ideal position, the above-described reduction effect can be ensured without changing depending on the size of the angle deviation between the marking position of each gear and the ideal position. Can do.

  As shown in FIG. 25, the case where the intermediate gear 47 and the drum drive gear 48 are arranged at ideal positions and the rotational phase of the pinion 46 is shifted by an angle α from the ideal position will be described in detail. When the intermediate gear 47 is arranged so that the gate position of the intermediate gear 47 is in the meshing position with the pinion 46, the pitch circumferential error curve P on the drum drive gear 48 axis is the pitch shown below. It can be approximated and expressed as the sum of the error curves of the circumferential error curves P1, P2 and P3. That is, when the meshing position of the drum driving gear 48 is θ = π × 2i / N1 (i is a natural number) and the gear arrangement is expressed, the pitch circumferential error curve P on the drum driving gear 48 is Pitch circumferential error curve P1 on the drum drive gear 48 due to the accumulated pitch error of the pinion 46, Pitch circumference error curve P2 on the drum drive gear 48 due to the accumulated gate pitch error of the large gear 47a, and the small gear 47b can be approximated as the sum of the error curves of the pitch circumferential error curve P3 on the drum drive gear 48 due to the accumulated gate pitch error.

Pitch circumference error curve on the drum drive gear 48 due to the accumulated pitch error of the pinion 46 P1 = h1 × sin [N1 × N2 × θ + π + α] / (2 × k)
Pitch circumferential error curve on the drum drive gear 48 due to the accumulated pitch error of the large gear 47a P2 = h2 × sin [N1 × N2 × θ + π] / (2 × k)
Pitch circumferential error curve on the drum drive gear 48 due to the accumulated pitch error of the small gear 47b P3 = mh2 × sin [N1 × N2 × θ] / 2
That is,
P = P1 + P2 + P3
= H1 × sin [N1 × N2 × θ + π + α] / (2 × k) + h2 × sin [N1 × N2 × θ + π] / (2 × k) + mh2 × sin [N1 × N2 × θ] / 2
= (((− H1) ² + (km−1) ² × h2 ² + 2 × (−h1) × (km−1) × h2 × cos [α]) ^(1/2) ) × sin [N1 × N2 × θ + γ2] / (2 × k)
However, cos [γ2] = − h1 / (h1 ² + h2 ² (km + 1) ² ) ^(1/2)
From the above equation, the pitch circumferential error on the drum drive gear 48 axis when the rotational phase of the pinion 46 is shifted by the angle α is
| (((− H1) ² + (km−1) ² × h2 ² + 2 × (−h1) × (km−1) × h2 × cos [α]) ^(1/2) ) / k | (3)
It turns out that it becomes.

FIG. 26 shows the transition of the pitch circumferential error on the drum drive gear 48 when the rotational phase deviation angle α of the pinion 46 is set on the horizontal axis. 26, when the gear meshing position is θ = π × 2i / N1, even if the rotational phase deviation of the pinion 46 is the angle α, one rotation period of the pinion 46 on the drum driving gear 48 is within a certain range. It can be seen that the pitch circumference error can be reliably reduced. The range of the angle α at which this reduction effect can be obtained is between the two intersections of the expressions (3) and (h1 / k), that is,
−h2 × (km−1) / (2 × h1) <cos [α] <h2 × (km−1) / (2 × h1)
It is.

  Next, when the intermediate gear 47 is arranged so that the intermediate point of the two gate positions of the intermediate gear 47 is in the meshing position with the pinion 46, the pitch circumferential error on the drum drive gear 48 axis is determined. The curve P can be approximated and expressed as the sum of error curves of pitch circumferential error curves P1, P2, and P3 shown below. That is, when the meshing position of the drum drive gear 48 is θ = π × (2i−1) / N1 (i is a natural number) and the gear arrangement is expressed, the pitch circumferential error curve on the drum drive gear 48 P is a pitch circumferential error curve P1 on the drum driving gear 48 due to the accumulated pitch error of the pinion 46, and a pitch circumferential error curve P2 on the drum driving gear 48 due to the accumulated gate pitch error of the large gear 47a. And an approximate sum of error curves of the pitch circumferential error curve P3 on the drum drive gear 48 caused by the gate pitch accumulated error of the small gear 47b.

Pitch circumference error curve on the drum drive gear 48 due to the accumulated pitch error of the pinion 46 P1 = h1 × sin [N1 × N2 × θ + π + α] / (2 × k)
Pitch circumferential error curve on the drum drive gear 48 due to the accumulated pitch error of the large gear 47a P2 = h2 × sin [N1 × N2 × θ] / (2 × k)
Pitch circumferential error curve on the drum drive gear 48 due to the accumulated pitch error of the small gear 47b P3 = mh2 × sin [N1 × N2 × θ] / 2
That is,
P = P1 + P2 + P3
= H1 × sin [N1 × N2 × θ + π + α] / (2 × k) + h2 × sin [N1 × N2 × θ] / (2 × k) + mh2 × sin [N1 × N2 × θ] / 2
= (((− H1) ² + (km + 1) ² × h2 ² + 2 × (−h1) × (km + 1) × h2 × cos [α]) ^(1/2) ) × sin [N1 × N2 × θ + γ3] / (2 × k)
Where cos [γ3] = − h1 / (h1 ² + h2 ² (km + 1) ² ) ^(1/2)
From the above equation, the pitch circumferential error on the drum drive gear 48 when the rotational phase of the pinion 46 is shifted by the angle α is
| (((− H1) ² + (km + 1) ² × h2 ² + 2 × (−h1) × (km + 1) × h2 × cos [α]) ^(1/2) ) / k | (4)
It turns out that it becomes.

FIG. 27 shows the transition of the pitch circumferential error on the drum drive gear 48 when the rotational phase deviation angle α of the pinion 46 is set on the horizontal axis. From FIG. 27, when the gear meshing position is θ = π × (2i−1) / N1, even when the rotational phase shift of the pinion 46 is the angle α, the range of the angle α that can obtain the reduction effect is expressed by the equation (4). ) And (h1 / k) between the two intersections,
−h2 × (km + 1) / (2 × h1) <cos [α] <h2 × (km + 1) / (2 × h1)
It is.

  Finally, as shown in FIG. 28, when the intermediate gear 47 and the drum drive gear 48 are arranged at ideal positions and the rotational phase of the pinion 46 is at the correct position, the drum drive gear 48 and A state where the angle θ formed by the pinion 46 is shifted from the ideal position by the angle φ will be described in detail. The pitch circumference error curve P on the drum drive gear 48 axis is caused by the pitch circumference error curve P1 on the drum drive gear 48 caused by the accumulated pitch error of the pinion 46 and the gate pitch accumulated error caused by the large gear 47a. The pitch circumference error curve P2 on the drum drive gear 48 and the pitch circle error curve P3 on the drum drive gear 48 due to the accumulated gate pitch error of the small gear 47b are approximated and expressed as approximations. I can do things.

Pitch circumferential error curve on the drum drive gear 48 due to the accumulated pitch error of the pinion 46 P1 = h1 × sin [N1 × N2 × θ + π] / (2 × k)
Pitch circumference error curve on the drum drive gear 48 due to the accumulated pitch error of the large gear 47a P2 = h2 × sin [N1 × N2 × θ + π + N2 × φ] / (2 × k)
Pitch circumferential error curve on the drum drive gear 48 due to the accumulated pitch error of the small gear 47b P3 = mh2 × sin [N1 × N2 × θ] / 2
That is,
P = P1 + P2 + P3
= H1 × sin [N1 × N2 × θ + π] / (2 × k) + h2 × sin [N1 × N2 × θ + π + N2 × φ] / (2 × k) + mh2 × sin [N1 × N2 × θ] / 2
= ((− H1 + h2 × km) ² + (− h2) ² + 2 × (−h1 + h2 × km) × (−h2) × cos [N2 × φ]) ^(1/2) ) × sin [N1 × N2 × θ + γ4 ] / (2 × k)
However, cos [γ4] = − h1 / (2 × h1 ² −h1 × h2 + h2 ² × k ² × m ² ) ^(1/2)
From the above equation, the pitch circumferential error on the drum drive gear 48 axis when the angle θ formed by the drum drive gear 48 and the pinion 46 deviates from the ideal position by the angle φ is:
| ((− H1 + h2 × km) ² + (− h2) ² + 2 × (−h1 + h2 × km) × (−h2) × cos [N2 × φ]) ^(1/2) ) / k | (5) )
It turns out that it becomes.

  FIG. 29 shows the transition of the pitch circumferential error on the drum drive gear 48 axis when the angle θ formed by the drum drive gear 48 and the pinion 46 deviates from the ideal position by the angle φ from the above equation (the horizontal axis is Angle φ). 29, even if the angle θ formed by the drum driving gear 48 and the pinion 46 is deviated from the ideal position by an angle φ, the pitch circumference of the rotation of the pinion 46 on the drum driving gear 48 axis is within a certain range. It can be seen that the error can be reliably reduced.

The range of the angle φ at which the reduction effect can be obtained is between two intersections of the expressions (5) and (h1 / k), that is, − (− 2 × h1 × km + h2 (k ² × m ² +1)) / (− 2 × h1 + 2 × h2 × km) <cos [N2 × φ] <(− 2 × h1 × km + h2 (k ² × m ² +1)) / (− 2 × h1 + 2 × h2 × km)
It is.

  At this time, if the range of the accumulated pitch error h2 of the gate pitch of the large gear 47a is | h1 / (km + 1) | ≦ h2 <| h1 / (km−1) |, the drum driving gear 48 and the The angle θ formed by the pinion 46 has a reduction effect in the entire range. However, the precondition is that the intermediate gear 47 and the drum drive gear 48 are arranged at ideal positions and the rotational phase of the pinion 46 is at a correct position.

  In this way, if the phase arrangement of each gear is determined in the manner described above, the speed fluctuation due to the eccentricity of the pinion 46 is offset with the speed fluctuation of the gate period of the intermediate gear 47. Speed fluctuation on 48 axes can be reduced. At this time, even when the phase arrangement of each gear is slightly deviated from the ideal position, the reduction effect can be similarly exerted within the above-described angle deviation. As a result, the rotational fluctuation of the drive transmission device, which causes uneven rotation of the photosensitive drum, can be reduced without increasing the cost due to the increase in the size of the device or the number of parts, and the color generated on the actual image can be reduced. Deviation and pitch unevenness (stepwise density unevenness) can be reduced.

  In the above-described embodiment, the case where the number of gates of the intermediate gear 47 is N has been described, but the present invention is not limited to this. For example, as shown in FIG. 30, the number of ribs 153a, 153b of the intermediate gear 47 is N, and the phase arrangement of each gear may be determined in the same manner as in the above-described embodiment. Also with this configuration, as in the above-described embodiment, the speed fluctuation due to the eccentricity of the pinion 46 is offset with the speed fluctuation of the rib period of the intermediate gear 47, and therefore, on the axis of the drum driving gear 48. Speed fluctuation can be reduced. At this time, even when the phase arrangement of each gear is slightly deviated from the ideal position, the reduction effect can be similarly exhibited within the above-described angle deviation.

  In the above-described embodiment, four image forming units are used. However, the number used is not limited, and may be set as needed.

  In the above-described embodiment, as a process cartridge that is detachable from the main body of the image forming apparatus, a process that integrally includes a photosensitive drum and a charging unit, a developing unit, and a cleaning unit as a process unit that acts on the photosensitive drum. A cartridge was illustrated. However, the present invention is not limited to this. For example, in addition to the photosensitive drum, a process cartridge that integrally includes any one of a charging unit, a developing unit, and a cleaning unit may be used.

  Further, in the above-described embodiment, the configuration in which the process cartridge including the photosensitive drum is detachable from the main body of the image forming apparatus is illustrated, but the present invention is not limited to this. For example, an image forming apparatus in which each constituent member is incorporated independently, or an image forming apparatus in which each constituent member can be independently attached and detached may be used.

  In the above-described embodiment, the printer is exemplified as the image forming apparatus. However, the present invention is not limited to this, and other image forming apparatuses such as a copying machine and a facsimile machine, or a combination of these functions. Other image forming apparatuses such as multifunction peripherals may also be used. Furthermore, in the above-described embodiment, the image forming apparatus that uses the recording material carrier and sequentially transfers the toner images of the respective colors onto the recording material carried on the recording material carrier is exemplified as the image forming apparatus. It is not limited to this. For example, an image forming apparatus that uses an intermediate transfer member, sequentially superimposes and transfers toner images of each color on the intermediate transfer member, and collectively transfers the toner images carried on the intermediate transfer member onto a recording material. Also good. The same effect can be obtained by applying the present invention to these image forming apparatuses.

  Further, the drive transmission device constituted by the above-described gear arrangement can be used as a drive part for rotationally driving not only the photosensitive drum but also another image carrier such as a recording material carrier or an intermediate transfer member. It may be provided. Also with this configuration, the speed variation due to the eccentricity of the upstream gear is offset with the speed variation of the gate (or rib) cycle of the intermediate gear. It is possible to reduce the speed fluctuation of the rotation period component. As a result, it is possible to reduce the level of color misregistration (for example, color misregistration between black and cyan) and pitch nonuniformity (stepped density nonuniformity) occurring on an actual image.

  In the above-described embodiment, the image carrier in the image forming apparatus is exemplified as the rotating body. However, the rotating body is not limited thereto. For example, the present invention can be applied not only to an image forming apparatus but also to a drive transmission device that transmits a driving force to a rotating body in order to eliminate a problem caused by rotation unevenness of the rotating body.

A longitudinal sectional view showing the overall configuration of the image forming apparatus A perspective view illustrating the configuration of an image forming apparatus Unit configuration diagram showing configuration of drive unit in image forming apparatus Configuration diagram for explaining a connection form of a drive unit and a photosensitive drum in an image forming apparatus Configuration diagram for explaining a connection form of a drive unit and a photosensitive drum in an image forming apparatus The perspective view which shows the coupling shape of the drive unit in an image forming apparatus The perspective view which shows the coupling shape of the image carrier unit in an image forming apparatus Configuration diagram illustrating an example of a drive gear train configuration in an image forming apparatus A graph for explaining the cumulative pitch error of the pinion gear in the image forming apparatus A graph for explaining the accumulated pitch error of the intermediate gear (large gear) in the image forming apparatus Graph for explaining the accumulated pitch error of the intermediate gear (small gear) in the image forming apparatus Configuration diagram for explaining a drive gear train configuration in an image forming apparatus Configuration diagram for explaining a drive gear train configuration in an image forming apparatus Configuration diagram for explaining a drive gear train configuration in an image forming apparatus Configuration diagram for explaining a drive gear train configuration in an image forming apparatus Graph explaining speed fluctuation on intermediate gear shaft in image forming apparatus Graph for explaining speed fluctuation on photosensitive drum gear shaft in image forming apparatus A graph for explaining the effect of reducing the speed fluctuation on the photosensitive drum gear shaft in the image forming apparatus A graph for explaining the effect of reducing the speed fluctuation on the photosensitive drum gear shaft in the image forming apparatus A graph for explaining the effect of reducing the speed fluctuation on the photosensitive drum gear shaft in the image forming apparatus Configuration diagram for explaining a drive gear train configuration in an image forming apparatus A graph for explaining the effect of reducing the speed fluctuation on the photosensitive drum gear shaft in the image forming apparatus A graph for explaining the effect of reducing the speed fluctuation on the photosensitive drum gear shaft in the image forming apparatus A graph for explaining the effect of reducing the speed fluctuation on the photosensitive drum gear shaft in the image forming apparatus Configuration diagram for explaining a drive gear train configuration in an image forming apparatus A graph for explaining the effect of reducing the speed fluctuation on the photosensitive drum gear shaft in the image forming apparatus A graph for explaining the effect of reducing the speed fluctuation on the photosensitive drum gear shaft in the image forming apparatus Configuration diagram for explaining a drive gear train configuration in an image forming apparatus A graph for explaining the effect of reducing the speed fluctuation on the photosensitive drum gear shaft in the image forming apparatus Configuration diagram for explaining another example of the drive gear train configuration in the image forming apparatus

Explanation of symbols

1 ... Photosensitive drum (rotating body)
45 ... Motor (drive source)
46 ... Pinion (upstream gear)
47 ... Intermediate gear (intermediate gear)
47a ... large gear 47b ... small gear 48 ... drum drive gear (downstream gear)
103 ... Drive unit 150 ... Marking 151, 151a, 151b ... Marking (gate)
153a, 153b ... ribs

Claims (4)

An intermediate gear having two gears having different diameters on the same axis, a downstream gear that meshes with the intermediate gear at a first meshing position, and a driving force transmitted from the intermediate gear, and an intermediate gear and a second meshing position. An upstream gear that transmits a driving force to the intermediate gear, and a drive transmission device that transmits the driving force to a rotating body,
The reduction gear ratio between the upstream gear and the intermediate gear is N (N is a natural number), and the number of gates or ribs of the intermediate gear is the same N (N is a natural number).
Cumulative pitch error of the upstream gear is h1, cumulative pitch error of the intermediate gear meshing with the upstream gear is h2, cumulative pitch error of the intermediate gear meshing with the downstream gear is mh2 (m is a positive real number), and the intermediate gear When the radius ratio of the two gears is k: 1 (k is a natural number), and the meshing angle of the three gears formed by the first meshing position and the second meshing position is θ,
Depending on the rotational phase of the upstream gear and the gate position of the intermediate gear, when the relationship of the accumulated pitch error is 0 <h2 ≦ | h1 / km |, the meshing angle of the gear is θ = π × (2i− 1) / N1 (i is a natural number), and if the cumulative pitch error is | h1 / km | ≦ h2, the gear meshing angle satisfies θ = π × 2i / N1. Further, the drive transmission device characterized in that the gears are arranged.   If the angle of the rotational phase shift of the upstream gear with respect to the second meshing position is α, the range of the angle α is −h2 × when the meshing angle of the gear is θ = π × 2i / N1. (Km−1) / (2 × h1) <cos [α] <h2 × (km−1) / (2 × h1) is satisfied, and the meshing angle of the gear is θ = π × (2i−1) / N1 In this case, the range of the angle α is −h2 × (km + 1) / (2 × h1) <cos [α] <h2 × (km + 1) / (2 × h1). 2. The drive transmission device according to 1. When the meshing angle of the three gears formed by the first meshing position and the second meshing position is deviated from the meshing angle θ by an angle φ, the range of the angle φ is − (− 2h1km + h2 (k ² × m is 2 × h1 + 2 × h2 × km) - 2 +1)) / (- 2 × h1 + 2 × h2 × km) <cos [N2φ] <(- 2 × h1 × km + h2 (k 2 × m 2 +1)) / ( The drive transmission device according to claim 1.   4. An image forming apparatus that forms an image on a recording material using a rotating body, wherein the driving body transmits a driving force to a rotating body related to the formation of an actual image among the rotating bodies. An image forming apparatus using the drive transmission device according to claim 1.