Swing-gear mechanism and image forming apparatus having multiple speed modes

An image forming apparatus has a high-speed mode and a low-speed mode and includes a speed switch unit configured to select the high-speed mode or the low-speed mode by switching a rotation direction of a drive source. The speed switch unit includes a drive gear attached to a rotating shaft of the drive source; a first drive gear series transmitting a rotating power of the drive source upon rotation in a first direction to an image carrier; and a second drive gear series transmitting a rotating power of the drive source upon rotation in a second direction to the image carrier, the second drive gear series having a larger reduction ratio than the first drive gear series. The speed switch unit causes the drive gear to be selectively connected to the first drive gear series or the second drive gear series depending on the rotating direction of the drive source.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to image forming apparatuses, such as copy machines, printers, facsimile machines, plotters, and multifunction peripherals (MFP) incorporating multiple image forming functions, such as copying and printing functions. More particularly, the present invention relates to an image forming apparatus having multiple image formation speed modes.

2. Description of the Related Art

An image forming apparatus is known in which a low-speed mode or a high-speed mode can be selected by a user. In the low-speed mode, image quality may be given priority, while in the high-speed mode, speed (productivity) may be given priority. In this type of an image forming apparatus, a drive source, such as a motor, may be connected to an image carrier, such as a photosensitive drum, via a series of drive gears. When the gear ratio of the series of drive gears is fixed, the high-speed mode and the low-speed mode may be switched by varying the number of rotations of the drive source.

In this type of an image forming apparatus, noise may increase in the high-speed mode. The noise during an image formation operation is known to be largely due to the noise level of the gear meshing frequency of drive source gears. The gear meshing frequency is the number of times two gears mesh with each other per second. For example, the gear meshing frequency of a drive source is the number of times a motor gear and a transmission gear mesh with each other per second. Thus, the gear meshing frequency, and hence the noise level, can be reduced by decreasing the number of rotations of the motor in the drive source. Desirably, the gear meshing frequency should be lowered below 100 Hz because the sound of such frequencies is difficult for humans to hear.

The drive source in this type of image forming apparatus may include a so-called FG (frequency-generating) output motor equipped with a frequency generator. Typically, the FG output motor has a pattern of frequency-generating pulse shapes (“FG pattern”) disposed opposite a magnet of a rotating part of the motor. As the motor rotates, electromagnetic induction is caused between the magnet and the FG pattern, thereby producing a pulse current. Based on the pulse current, a feedback control is performed so that the rotating speed of the motor can be controlled (see Japanese Laid-Open Patent Application No. 09-46995, for example). The FG output motors are frequently used as a drive source for image forming apparatuses because of their inexpensive rotation control mechanism.

As mentioned above, the high-speed mode and the low-speed mode may be switched by changing the number of rotations of the drive source when the gear ratio the series of drive gears is fixed. In this case, when the rotation speed of the drive source in the high-speed mode is lowered in order to reduce the noise level of the gear meshing frequency of the drive source gears, the number of rotations for the low-speed mode also decreases because of the fixed gear ratio. As a result, the frequency generator may not be able to produce a sufficient level of pulse signal for the feedback control of the rotation speed of the motor.

Japanese Laid-Open Patent Application No. 2002-089638 discusses a drive apparatus including various motors, a simple planetary gear mechanism as an intermediate speed-reduction mechanism, and various speed-reduction units. In this drive apparatus, the motors and the speed-reduction units can be selectively engaged with the simple planetary gear mechanism on an input and an output end, respectively, in order to reduce vibration and noise.

Japanese Laid-Open Patent Application No. 2007-212806 discusses a rotating drive apparatus including a drive source, a series of gears, and a driven member. The gears are coupled via planetary gears for increasing accuracy of rotation of an output shaft and reducing the size in the shaft axial direction, while allowing the detachment of the driven member from the rotating drive apparatus.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a swing gear mechanism includes a frame having a first and a second arch-shaped guide opening having a first end and a second end; a first swing gear supported by the frame with a shaft of the first swing gear being guided in the first arch-shaped guide-opening; a second swing gear supported by the frame with a shaft of the second swing gear being guided in the second arch-shaped guide opening; and a drive gear meshed with the first and the second swing gears and configured to rotate in a first or a second direction. The first swing gear and the second swing gear are displaced to the first end of the corresponding arch-shaped guide openings upon rotation of the drive gear in the first direction, or to the second end of the corresponding arch-shaped guide openings upon rotation of the drive gear in the second direction.

In another aspect of the present invention, an image forming apparatus includes the swing gear mechanism.

In yet another aspect of the present invention, an image forming apparatus has a high-speed mode and a low-speed mode and includes a drive source configured to be rotated in a first direction or a second direction; an image carrier configured to be rotated by the drive source; an optical scanning unit configured to scan the image carrier with a beam of light in order to form an electrostatic latent image on the image carrier; a developing unit configured to develop the electrostatic latent image on the image carrier into a visible image; a transfer unit configured to transfer the visible image onto a recording medium directly or indirectly; and a speed switch unit configured to select the high-speed mode or the low-speed mode by switching a rotation direction of the drive source. The speed switch unit includes a drive gear attached to a rotating shaft of the drive source; a first drive gear series configured to transmit a rotating power of the drive source upon rotation in the first direction to the image carrier; and a second drive gear series configured to transmit a rotating power of the drive source upon rotation in the second direction to the image carrier, the second drive gear series having a larger reduction ratio than the first drive gear series. The speed switch unit is configured to cause the drive gear to be selectively connected to the first drive gear series or the second drive gear series depending on the rotating direction of the drive source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1illustrates a laser color printer100as an image forming apparatus according to an embodiment of the present invention. In the laser color printer100, photosensitive drums (image carriers)20Y (yellow),20M (magenta),20C (cyan), and20K (black) are disposed side by side along an extended surface of an intermediate transfer belt50which is supported by support rollers102a,102b, and102c. The laser color printer100further includes an optical scan unit105(exposure unit); charging units (not shown), developing units106Y,106M,106C and106K; a primary transfer roller (not shown) disposed inside the intermediate transfer belt50; a cleaning unit (not shown); and a neutralizing unit (not shown).

The optical scan unit105is configured to emit laser beams L1, L2, L3, and L4in accordance with image information signals for the various colors. The laser beams L1, L2, L3, and L4hit the photosensitive drums20Y,20M,20C, and20K, thereby forming electrostatic latent images of the various color components on the photosensitive drums20Y,20M,20C, and20K. The latent images are thereafter rendered into visible toner images by the developing units106Y,106M,106C, and106K, as well known in the art.

The toner images of the various colors are successively transferred onto the intermediate transfer belt50, forming an overlaid color image. The overlaid image is then transferred onto a transfer sheet120(recording medium) by the secondary transfer roller102d. The transfer sheet120is fed from the sheet-feeding cassette111at a predetermined timing. Thereafter, the intermediate transfer belt50is cleaned by the cleaning unit. The transfer sheet120with the color image transferred thereon is transported to the fusing unit114where the color image is fused onto the transfer sheet120using heat and pressure. The fused transfer sheet is then ejected onto an ejected sheet tray110.

FIG. 2illustrates a drive mechanism1for the image forming apparatus100. InFIG. 2, the intermediate transfer belt50(indicated by broken lines) is supported across belt gears36and15, which are integrally formed with the support rollers102aand102b, respectively. The drive mechanism1includes a drive gear3for driving the photosensitive drum20K and a drive gear5for driving the color photosensitive drums20Y,20M, and20C. The drive gears3and5are fixed to rotating shafts6aof FG-output-type motors6(drive source), as will be described below.

The drive gear3is meshed with a speed-reduction gear7. The speed-reduction gear7is meshed with a drum gear9that is integral with the photosensitive drum20K. The speed-reduction gear7is also meshed with a speed-reduction gear11. The speed-reduction gear11is coupled with a belt gear15via an idler gear13. The belt gear15is integral with the support roller102b. Rotation of the motor6for the drive gear3in counter-clockwise direction (“second direction”) causes the drum gear9to rotate in a direction indicated by the corresponding arrow (counter-clockwise direction) via the speed-reduction gear7. At the same time, the belt gear15is caused to rotate in a direction indicated by the corresponding arrow (clockwise direction).

The drive gear5for driving the color photosensitive drums20Y,20M, and20C is meshed with swing gears17and19. The swing gear17is engageable with a speed-reduction gear21. The other swing gear19is engageable with a speed-reduction gear22meshed with the speed-reduction gear21. The speed-reduction gear21is also meshed with a drum gear23that is integral with the photosensitive drum20M. Idler gears25and27are meshed with the speed-reduction gear21on an input end. The idler gear25is further engaged with a drum gear31via a speed-reduction gear29. The drum gear31is integral with the photosensitive drum20Y. The idler gear27is also engaged with a drum gear35via a speed-reduction gear33. The drum gear35is integral with the photosensitive drum20C.

The belt gear36is integral with the support roller102a(FIG. 1). Toner supply units38Y,38M,38C, and38K are configured to supply the various colors of toner to the developing unit106Y,106M,106C, and106K. The speed-reduction gear22is disposed above a center line of the photosensitive drum20M (magenta); namely, the drum gear23. In this way, the space between the photosensitive drums20M and20C and additionally defined by the toner supply unit38C, for example, can be effectively utilized for a structure (including the swing gears17and19and guide openings43and45) for enabling the switching between the high-speed mode and the low-speed mode, as will be described later.

FIG. 3Aillustrates a swing-gear mechanism, andFIG. 3Billustrates an assembly of the FG-output-type motor6, the drive gear5, and the swing gears17and19. The FG-output-type motor6to which the drive gear5is fixed may include a frequency generator for detecting a rotation speed by an electromagnetic pattern generating method. The electromagnetic pattern generating method may involve generating a pulse signal using an electromagnetic pattern (rotation speed detecting unit) disposed between a rotating part and a fixed part (which are not illustrated) of the motor6when the motor6rotates by a predetermined angle. The time interval of generation of such pulse signals may be detected as a speed and supplied for a feedback control.

Referring toFIG. 3B, the motor6is supported on a motor circuit board37(drive source fixing unit) and a frame39. On the motor circuit board37, there may be formed the FG pattern as a part of the aforementioned electromagnetic pattern. The swing gears17and19are supported between the frame39and another frame41having the guide openings43and45in them. The swing gears17and19are movable in the guide openings43and45. The swing gears17and19are pressurized in a thrust direction by thrust springs47and49. The gears17and19are integral with shafts that are movable in the guide openings43and45. The guide openings43and45have a smooth arc shape so that the shafts of the gears17and19can smoothly move therein. The ends of the guide openings43and45have a shape conforming to the circumferential surface of the shafts of the swing gears17and19.

When the motor6rotates in one direction or the other, the swing gears17and19are displaced in the guide openings43and45by a pressing force provided by the rotation of the motor6, so that the swing gears17and19rotate with their shafts abutted against one or the other end of the guide openings43and45.FIG. 3Aillustrates the case where the swing gear17is displaced to the right while the swing gear19is displaced to the left with reference to the drawing in a swinging motion when the motor6rotates in counter-clockwise direction (“second direction”) in the low-speed mode.

On the other hand, in the high-speed mode, the motor6rotates in clockwise direction (“first direction”) with reference toFIGS. 2 and 3, for example. In this case, the swing gear17is displaced to the left and meshed with the speed-reduction gear21as illustrated inFIG. 2, so that the color photosensitive drums20M,20Y, and20C are rotated at high speed. In this case, the swing gear17, the speed-reduction gear21, and the drum gear23constitute a first drive gear series for the high-speed mode, the swing gear17being the most upstream gear. The swing gear19, the speed-reduction gear22, the speed-reduction gear21and the drum gear23constitute a second drive gear series (for the low-speed mode), with the swing gear19being the most upstream gear.

When the motor6rotates in the first (clockwise) direction with reference toFIG. 2, for example, the swing gear19is disengaged from the speed-reduction gear22, so that the second drive gear series is rendered incapable of transmitting drive power. Referring toFIG. 4, when the motor6rotates in the second (counter-clockwise) direction for the low-speed mode, the swing gear19is meshed with the speed-reduction gear22, so that the color photosensitive drums20M,20Y,20C are rotated at a low speed. In the low-speed mode, the swing gear17is disengaged from the speed-reduction gear21, thus rendering the first drive gear series incapable of transmitting drive power. The structure including the drive gear5, the first drive gear series, the second drive gear series, and the swing-gear mechanism may be hereafter referred to as a “speed switch unit”.

Table 1 below illustrates a specification of the drive mechanism1according to an embodiment of the present invention.

TABLE 1Torque of photosensitive drum and roller0.5 N · m102bNumber of photosensitive drums driven by3drive gear 5Gear transmission efficiency0.95Rotation speed (rpm) of photosensitive94.03drum (high-speed mode)Rotation speed (rpm) of photosensitive47.02drum (low-speed mode)Rotation speed (rpm) of support roller117.00102b (high-speed mode)Rotation speed (rpm) of support roller58.50102b (low-speed mode)Number of teeth of drive gear 58*The number of teeth of drive gear 5 may be selected depending on the cost of bar material prior to formation of teeth in it.

In accordance with the present embodiment, the number of rotations of the motor6in the high-speed mode may be set at 700 rpm, as illustrated in Table 2. 700 rpm is a relatively low speed that can be controlled by a FG-output-type motor and that satisfies the condition that the gear meshing frequency be below 100 Hz, which corresponds to the low-frequency sound that is hard for humans to hear. In this case, the gear meshing frequency is 93.3 Hz, indicating a sufficient decrease in noise.

In accordance with the present embodiment, in order to switch to the low-speed mode, the motor6is rotated in the second direction so that the motor6is engaged with the speed-reduction gear21via the swing gear19and the speed-reduction gear22. Thus, a lower rotation speed is achieved by increasing the reduction ratio compared to the case where the motor6is rotated in the first direction.

Thus, the difference in the number of rotations of the photosensitive drums between the high-speed mode and the low-speed mode is provided by varying the reduction ratio of the drive gear series while the number of rotations of the motor6is set at a constant value of 700 rpm, for example. In this way, two or more speed modes can be realized without changing the rotation speed of the motor6, so that the rotation speed of the motor6can be set to a low speed at all times that contributes to a decrease in noise. Thus, the gear meshing frequency of the drive gear5can be made lower than the low-frequency sound of 100 Hz in any of the multiple speed modes.

TABLE 2Drive gear5 (for color drums)3 (for (K) drum)3 (for belt 50)Gear5→17→5→19→22→3→7→93→7→93→11→3→11→sequence21→2321→2313→1513→15Speed modeHighLowHighLowHighLowRpm of700.0700.01400.0700.01400.0700.0drivesourceGear ratio7.414.914.914.912.012.0Output (W)189136136Shaft0.1260.2520.0890.0890.0890.089torque(N · m)Sound50.049.053.049.053.049.0pressurelevel(dBA)Meshing93.393.3186.793.3186.793.3frequency(Hz)*Reduction ratio is the ratio of the numbers of rotation of the drive source to the photosensitive drum or the support roller.

Table 2 corresponds to a case where the aforementioned speed switch unit (including the drive gear, the first and the second drive gear series, and the swing-gear mechanism) is not applied to the drive gear3for the photosensitive drum20K (for black). However, in another embodiment of the present invention, the speed switch unit may be applied to the drive gear3for the photosensitive drum20K in the same way as for the color photosensitive drums20Y,20M, and20C for enhanced noise reduction purposes.

FIG. 5is a graph indicating torque and sound pressure level with respect to the number of rotations (rpm). The initial rpm of “700” is the number of rotations in the high-speed mode. The second rpm of “700” is the number of rotations in the low-speed mode. In the low-speed mode, torque increases due to the increased reduction ratio. The corresponding values are shown in Table 3.

FIG. 6illustrates a conventional drive mechanism in which the speed switch unit according to the foregoing embodiment of the present invention is not used. As illustrated, the drive gear5is directly meshed with the speed-reduction gear21. Thus, drive power from the drive source is transmitted by a series of drive gears including the drive gear5, the speed-reduction gear21, and the drum gear23in a fixed manner, so that the rotation direction of the motor6is fixed to the second direction (counter-clockwise direction).

In this conventional example, the number of rotations of the motor6in the low-speed mode may be fixed at 700 rpm while the high-speed mode may be provided by doubling the rotation speed of the motor6to 1400 rpm. In this case, in the high-speed mode, the gear meshing frequency of the drive gear5is 186.7 Hz as illustrated in Table 4 below, which is far above the low-frequency sound threshold of 100 Hz, resulting in a large noise level. If the rotation speed in the high-speed mode is lowered in order to reduce the noise, the decrease in rotation speed is directly reflected in the low-speed mode because of the fixed reduction ratio of the drive gear series. As a result, the rotation speed in the low-speed mode greatly decreases, making it impossible to control the FG-output-type motor6.

TABLE 4Drive gear5 (for color drums)3 (for (K) drum)3 (for belt 50)Gear5→21→235→21→233→7→93→7→93→11→3→11→sequence13→1513→15Speed modeHighLowHighLowHighLowRpm of1400.0700.01400.0700.01400.0700.0drivesourceGear ratio14.914.914.914.912.012.0Output (W)189136136Shaft0.1260.1260.0890.0890.0890.089torque(N · m)Sound53.049.053.049.053.049.0pressurelevel(dBA)Meshing186.793.3186.793.3186.793.3frequency(Hz)*Reduction ration values may be in integers so that an image position error due to motor vibration can be cancelled.

Although this invention has been described in detail with reference to certain embodiments, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.

The present application is based on Japanese Priority Application No. 2009-198660 filed Aug. 28, 2009, the entire contents of which are hereby incorporated by reference.