This application claims priority based on 35 USC 119 from prior Japanese Patent Application No. P2009-122481 filed on May 20, 2009, entitled “Drive transmission Device and Image Forming Apparatus”, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The invention relates to a drive transmission technique to transmit a rotational driving force to a rotator in a device such as an image forming apparatus configured to form an image on a medium.
2. Description of Related Art
A conventional image forming apparatus, such as a printer, a copy machine, a facsimile machine, or a MFP (Multi-Function Peripheral), configured to form an image on a recording medium, includes a drive transmission device for an image forming unit. The drive transmission device includes: a driven member, which is a drum flange provided at an axial end of a photosensitive drum (image carrier) and having a conical concave gear; a driving member, which is a drive shaft flange provided at an axial end of a drive shaft and having a conical convex gear configured to interlock with the conical concave gear of the drum flange; and a coupling mechanism configured to couple the conical convex gear with the conical concave gear with a biasing member such as a spring to drive the photosensitive drum to rotate with the drive shaft (for example, see Japanese Patent Application Laid-Open No. 09-134094).
In the coupling mechanism in the conventional drive transmission device, the axis of the driving member may be misaligned with the axis of the driven member because of a mesh error and/or clearance between the conical concave gear and the conical convex gear. Such a misalignment causes an eccentric rotation of the photosensitive drum and this may cause an image-forming failure.
An first aspect of the invention is a drive transmission device including: a driving member configured to rotate by a first electric current and having an attracting portion configured to generate magnetic force by a second electric current; a driven member having an attracted portion, the attracted portion facing the driving member and configured to be attached to the attracting portion by the magnetic force, so that the driven member integrally rotates with the driving member when the attracting portion is coupled to the attracted portion; and a controller configured to control the first electric current and the second electric current, the controller configured to apply the first electric current and then the second electric current.
A second aspect of the invention is an image forming apparatus including the drive transmission device according to the above aspect.
A third aspect of the invention is a method of controlling a drive transmission device, including the steps of: rotating a driving member by applying a first electric current; magnetically attaching a driven member to the driving member by applying a second electric current, after the driving member starts rotating.
In the third aspect of the invention, the second electric current may be first applied intermittently and then applied continuously at a constant level.
According to the aspect of the invention, a misalignment between the axis of the driving member and the axis of the driven member is prevented so as to eliminate eccentric rotation of the driven member.
Descriptions are provided herein below for embodiments based on the drawings. In the respective drawings referenced herein, the same constituents are designated by the same reference numerals and duplicate explanation concerning the same constituents is omitted. All of the drawings are provided to illustrate the respective examples only.
Note that although a color electrophotographic printer is described as an example of an image apparatus in the following embodiments, an image forming apparatus according to the invention may be another type of an image forming apparatus such as a printer, a copy machine, a facsimile machine, a MFP (Multi-function peripheral), or the like having a printing function.
The image forming apparatus of the first embodiment includes image forming units 11y, 11m, 11c and 11k of the respective colors. Exposure heads 14y, 14m, 14c, and 14k are disposed adjacent to image forming units 11y, 11m, 11c and 11k, respectively, with a space therebetween.
The image forming apparatus has therein a medium transporting path extending from medium tray 15 to stacker cover 25. Media tray 15 contains therein stacked media 16 and has separation rollers 17 for separating media 16 and to feed medium 16 one by one to the medium transporting path. Disposed along the medium transporting path are conveying rollers 18; image forming units 11y, 11m, 11c and 11k; image transfer belt 19 provided opposite to the image forming units and configured to transfer, to medium 16, toner images formed by the image forming units; fixing unit 20 configured to fix the toner images to medium 16; and discharging rollers 21 and 22. Printed medium 16 is discharged from the medium transport path onto stacker cover 25.
Image forming unit 11y, 11m, 11c, and 11k contain therein toner 30y, 30m, 30c, and 30k of the respective colors. Each image forming unit 11y, 11m, 11c, and 11k includes: photosensitive drum 13y, 13m, 13c, and 13k in contact with image transfer belt 19; developing roller 12y, 12m, 12c and 12k; and charging roller 23y, 23m, 23c, and 23k in contact with photosensitive drum 13y, 13m, 13c, 13k.
Each image forming unit 11y, 11m, 11c, and 11k also includes: supply roller 24y, 24m, 24c, and 24k in contact with developing roller 12y, 12m, 12c and 12k to supply toner 30y, 30m, 30c and 30k to developing roller 12y, 12m, 12c and 12k; and development blade 29y, 29m, 29c, and 29k to form a thin layer of toner 30y, 30m, 30c, and 30k on developing roller 12y, 12m, 12c and 12k.
Regarding the control system in the image forming apparatus, as shown in
The configuration of a part of image forming unit 11 is illustrated in
Drive flange 32 is formed with convex-shaped projection 32a at the center of the drive flange 32, and bobbin 33 is disposed such that there is a gap between bobbin 33 and drive shaft 31, as shown in
When supplied with the second electric current, coil 34 wound around drive shaft 31 generates an electromagnetic field through drive shaft 31 and drive flange 32, so that drive flange 32 magnetically attracts drum flange 35 which is opposite to drive flange 32.
Drum flange 35 is formed integrally with photosensitive drum 13 at an end of photosensitive drums 13 and made of a material, such as iron, that is attracted by a magnetic attraction. Conical recess 35a is formed on the center of drum flange 35 and faces projection 32a of drive flange 32. Accordingly, drive flange 32 and drum flange 35 form a coupling mechanism.
Note that drive flange 32 functions as an attracting portion, drive shaft 31 and drive flange 32 form a driving member, drum flange functions as attracted portion, and drum flange 35 and photosensitive drums 13 form a driven member.
The magnetic attraction of drive flange 32 varies depending on the value of the current flowing through coil 34. The current is set to a certain value at which coil 34 generates a magnetic attraction that is sufficient to cause the drive torque required to drive image forming unit 11 (required to rotate photosensitive drum 13).
For example, the magnetic attraction Fq is set to satisfy the formula ηFq>αFd, wherein Fd represents the rotational load for rotating the photosensitive drum including loads for other rollers and/or gears upon rotating the photosensitive drum; η represents a friction coefficient between drum flange 35 and drive flange 32; Fq represents the magnetic attraction; α (about 1.1 to 1.2, for example) represents a margin coefficient; and thus ηFq is the drive torque for frictionally driving the drum flange. Note that, for an A3-size color electrophotographic printer, the rotational load Fd may be about 0.5 N-m (that is, 5 kg-cm).
(Operation)
In the above configuration, the image forming apparatus of the first embodiment operates as described below. The operation of the image forming apparatus will be described in detail referring to
First, upon receiving a print instruction from an un-illustrated external apparatus or host apparatus, image forming apparatus 1 separates media 16 one by one with separation roller 17 to feed medium 16 to the medium transporting path and then conveys medium 16 to image transfer belt 19 with conveying rollers 18 (see
At the same time, in image forming units 11y, 11m, 11c, and 11k, supply rollers 24y, 24m, 24c, and 24k are rotationally driven by image drum driving motor 65 (not shown in
Toners 30y, 30m, 30c, and 30k are charged and metered to a thin layer onto developing rollers 12y, 12m, 12c, and 12k by development blades 29y, 29m, 29c, and 29k. Each exposure head 14y, 14m, 14c, and 14k forms a latent image on the charged surface of photosensitive drum 13y, 13m, 13c, and 13k, which were charged by charging rollers 23y, 23m, 23c, and 23k, by irradiating with light the charged surface of photosensitive drums 13y, 13m, 13c, and 13k. The latent images are developed with toners 30y, 30m, 30c, and 30k supplied respectively from developing rollers 12y, 12m, 12c, and 12k to form toner images on photosensitive drum 13y, 13m, 13c, and 13k.
The respective toner images on photosensitive drums 13y, 13m, 13c, and 13k are transferred to medium 16 by image transfer belt 19 and then fixed to medium 16 in fixing unit 20. Such medium 16 with toner images fixed thereon are discharged to stacker cover 25 with discharging rollers 21 and 22.
Hereinafter, referring to the time chart in
In the state at time T0, as shown in
At time T0 driving controller 63 starts driving image drum driving motor 65 of image forming unit 11 to start rotating drive shaft 31, in order to form an image on medium 16. At time Ta a time interval Δt1 after a time point when the driving current of image drum driving motor 65 reached a constant value, the rotation of image drum driving motor 65 becomes stable.
At such time Ta, attraction controller 64 starts applying a constant voltage to coil 34 and continues applying it from time Ta to time Tb. Thereby the coil current gradually increases from time Ta to time Tb. At time Tb, the coil current reaches a value (attractable current level Iq+a predetermined margin) sufficiently strong to cause magnetic attraction of drum flange 35 to drive flange 32 in the direction of arrow A in
From time Tb to time Tc, attraction controller 64 continues turning on and off the voltage applied to coil 34 in a predetermined cycle so that the magnetic attraction of drive flange 32 gradually increases. Such on-off control is continued until the coil current value becomes stable after the coil current value reaches a certain value (driving current level Id) such that the coil generates a sufficiently-strong magnetic attraction to cause drum flange 35 to be coupled to drive flange 32 in a manner that drive shaft 31 and photosensitive drum 13 rotate integrally.
In this operation, drive flange 32 and drum flange 35 are in contact with each other and projection 32a and recess 35a are in contact with each other, as show in
As described above, drum flange 35 is gradually pulled to drive flange 32 by the on-off control of the current flowing through coil 34 and is intermittently coupled to drive flange 32. In this state (a half coupled state), slipping occurs between drum flange 35 and drive flange 32 while drum flange 35 rotates such that the rotation speed of drum flange 35 is slower than the rotation speed of drive flange 32.
In the half-coupled state, projection 32a of drive flange 32 and recess 35a of drum flange 35 are in slide contact with each other, and thus the axis of drive flange 32 and the axis of drum flange 35 are aligned with each other. This ensures that drive shaft 31 and photosensitive drums 13 are coaxially coupled with each other while rotating together.
By going through the half coupled state (intermittent coupled state), sudden impact to drum flange 35 is prevented. This operation between time Tb and time Tc can be referred to as a fitting operation (axial alignment operation) to execute the axial alignment.
After executing the on-off control until time Tc, attraction controller 64 controls the current flowing through coil 34 to a continuous constant value that causes drive flange 32 and drum flange 35 to be completely-coupled, so that drive flange 32 and drum flange rotate together. After that, the image forming operation is executed.
Note that, although the first embodiment controls the current flowing through coil 34 by continually turning on and off the applied voltage in the predetermined cycle, a modification shown in
Although, in the first embodiment, projection 32a is formed on the center portion of drive flange 32 and recess 35a is formed on the center portion of drum flange 35, a recess may be formed on the center portion of drive flange 32 whereas a projection may be formed on the center portion of drum flange 35.
Although there is an initial gap between drive flange 32 and drum flange 35 before the start of driving image forming unit 11 in the first embodiment, drive flange 32 and drum flange 35 may be fit to each other with a bias member such as a spring before the start of driving image forming unit 11. This modification achieves the same effect as the first embodiment if the biasing force of the bias member is fixed to a value that is negligibly-smaller than the attraction force caused by attraction controller 64.
In the first embodiment the start of the pre-attraction operation (
For example, the following operation may be used although preparation time before the image forming operation is longer than that of the first embodiment. First, after the pre-attraction operation for drum flange 35 is executed by applying the predetermined voltage to coil 34, image drum driving motor 65 starts to be driven. Then, after the rotation of drive flange 32 becomes stable, drum flange 35 is gradually pulled by intermittently applying the voltage to coil 34 to fit drive flange 32 to drum flange 35.
Although the pre-attraction operation in the first embodiment continuously applies the voltage from time Ta to time Tb until the coil current reaches attractable current level Iq, a modified operation may intermittently apply the voltage to supply the current from time Ta to time Tc to fit drive flange 32 to drum flange 35.
According to the image forming apparatus of the first embodiment as described above, a drive transmission device includes; a driving body fixed at an axial end of a drive shaft, a driven body fixed at an axial end of a rotator and facing the driving body; a concave portion provided at one of the driving body and the driven body; a convex portion provided at the other of the driving body and the driven body wherein the convex portion and the concave portion are configured to fit to each other; a rotational drive controller operable to control rotation of the driving body by a first electric current; and an attraction controller operable to intermittently control a second electric current to generate a magnetic field to attract and fit the driven body to the driving body. Accordingly, the drive transmission device can correct a misalignment between the axis of the driving side (the drive shaft) and the axis of the driven side (the rotator). This eliminates eccentric rotation and absorbs a sudden load change at the beginning of rotation.
The configuration of an image forming apparatus of a second embodiment will be described with reference to
The image forming apparatus of the second embodiment has drum fixed flange 45 and movable flange 46, instead of drum flange 35 of the first embodiment. Like drum flange 35 of the first embodiment, drum fixed flange 45 is made of a material, such as an iron, that is attracted by a magnetic field. Drum fixed flange 45 is integrally formed with photosensitive drums 13 and has conical recess 45a at the center portion.
Like drum fixed flange 45, movable flange 46 is made of a material, such as an iron, that is attracted by a magnetic field. Movable flange 46 is provided between drum fixed flange 45 and photosensitive drums 13. Movable flange 46 is axially movable with respect to drum fixed flange 45 within a predetermined gap and is rotationally fixed to drum fixed flange 45.
Note that like the first embodiment, in the second embodiment drive flange 32 functions as an attracting portion, drive shaft 31 and drive flange 32 form a driving member, movable flange 46 and drum fixed flange 45 function as an attracted portion, and movable flange 46, drum fixed flange 45, and photosensitive drums 13 form a driven member.
(Operation)
In this configuration, the image forming apparatus of the second embodiment operates as described below. Note that controller 61 operates in the same way as the operation shown in the timechart of
In the image forming apparatus of the second embodiment, a fitting operation (coaxial-aligning operation) between time Tb and Tc is executed by causing drum fixed flange 45 to be in contact with drive flange 32; and the coupling operation after time Tc is executed by causing drum fixed flange 45 and movable flange 46 to be in contact with drive flange 32 so as to couple drive flange 46 with the drum flange (45, 46) in a manner that photosensitive drum 13 rotates integrally with drive shaft 31.
That is, a magnetic attraction of drive flange 32 in the fitting operation (axial-aligning operation) between time Tb and time Tb is set to such a sufficient value that drum fixed flange 45 is attracted to and attached to drive flange 32 but movable flange 46 is not attached to drive flange 32 so that drive shaft 31 and photosensitive drum 13 do not rotate integrally with each other.
First, attraction controller 64 starts executing a pre-attraction operation at time T0 when the drive transmission mechanism is in the initial state shown in
After the pre-attraction operation, attraction controller 64 executes a fitting operation (axial alignment operation) between time Ta and time Tb. In the fitting operation of applying variable current caused by the intermittent voltage to coil 34, recess 45a of drum fixed flange 45 is in contact with projection 32a of drive flange 32 as shown in
Next, at Time Tc, attraction controller 64 controls the current flowing through coil 34 to a predetermined value to completely couple drive flange 32 and the drum flange (45, 46). With this operation, movable flange 46 as well as drum fixed flange 45 are coupled to drive flange 32 as shown in
Note that although movable flange 46 is configured to be axially movable with respect to drum fixed flange 45 between drum fixed flange 45 and photosensitive drums 13 before the start of driving image forming unit 11 in the second embodiment, movable flange 46 may be biased by a bias member such as a spring. In this case, a bias force of the bias member should be set to a value negligibly-weaker than the attraction force generated by attraction controller 64.
As described above, the image forming apparatus of the second embodiment includes: a drive flange having a projection at the center portion of the drive flange; a drum fixed flange made of magnetic material and formed integrally with a photosensitive drum and having a conical recess at the center portion of the drum fixed flange; and a movable flange made of magnetic material and provided around the drum fixed flange and rotationally fixed with respect to the drum fixed flange and axially movable with respect to the drum fixed flange within a predetermined range, wherein the drum fixed flange and the movable flange separately contact with the drive flange. Accordingly, the second embodiment further improves the axial alignment to high accuracy.
In the image forming apparatus of the third embodiment, the drive flange is divided into drive flange projection 52 and drive flange planar portion 53. Drive flange projection 52 and drive flange planar portion 53 are fixed to each other with nonmagnetic sleeve 54 provided therebetween.
Bobbin 55, around which coil 53 is wound, is provided around an external cylinder of drive flange planar portion 53 with a gap therebetween. Coil 56 is electrically connected to attraction controller 64 such that an electric current flowing through coil 56 is controlled by attraction controller 64. When electric current flows through coil 56, coil 56 around drive flange planar portion 53 generates an electromagnetic field such that drive flange planar portion 53 attracts movable flange 46.
Bobbin 33 and drive shaft 31 are provided inside the external cylinder of drive flange planar portion 53, as in the first and second embodiments. Bobbin 33, around which coil 34 is wound, is provided around drive shaft 31. Coil 34 is electrically connected to attraction controller 64 such that an electric current flowing through coil 34 is controlled by attraction controller 64. When electric current flows through coil 34, coil 34 around drive shaft 31 generates an electromagnetic field such that drive flange projection 52 attracts drum fixed flange 45.
Note that in the third embodiment, drive flange projection 52 and drive flange planar portion 53 function as an attracting portion, drive shaft 31, drive flange projection 52, and drive flange planar portion 53 function as a driving member. Also in the third embodiment, like the second embodiment, movable flange 46 and drum fixed flange 45 function as an attracted portion, and movable flange 46, drum fixed flange 45, and photosensitive drums 13 function as a driven member.
With this configuration, the magnetic attraction of movable flange 46 caused by supplying current through coil 56 and attraction of drum fixed flange 45 caused by supplying current through coil 34 are separately controlled.
(Operation)
With this configuration, the image forming apparatus of the third embodiment operates as described below. The operation will be described with reference to
First, attraction controller 64 executes a pre-attraction operation from time Ta to Tb by applying predetermined constant voltages to coil 34 and coil 56, respectively. With this operation, the current flowing through coil 34 and the current flowing through external coil 56 gradually increase, respectively, so that a magnetic attraction force of drive flange projection 52 and a magnetic attraction force of drive flange planar portion 53 gradually increase, respectively. Accordingly, drum fixed flange 45 and movable flange 45 are gradually attracted in the direction of arrow A in
Next, attraction controller 64 executes a fitting operation (axial-aligning operation) between time Tb to Tc by stopping to apply the voltage to external coil 56 while starting to apply a periodic intermittent voltage to coil 34. In the fitting operation between time Tb to Tc, since no voltage is applied to external coil 56, a magnetic attraction force between the drive flange (52, 53) and the drum flange (45, 46) does not couple the drive flange (52, 53) with the drum flange (45, 46) to integrally rotate photosensitive drum 13 and drive shaft 31, so that slipping occurs between the drive flange (52, 53) and the drum flange (45, 46) in the rotational direction in a manner that the rotational speed of photosensitive drum 13 is slower than the rotational speed of drive shaft 31. In such a fitting operation, the periodic intermittent voltage application to coil 34 causes variation of the magnetic attraction force between the drive flange (52, 53) and the drum flange (45, 46), so that a misalignment between the axis of drive shaft 31 and the axis of photosensitive drum 13 are removed while the state shown
Then, attraction controller 64 executes a coupling operation at time Tc. Specifically, at time Tc, attraction controller 64 applies constant voltages to external coil 56 and coil 34 to generate the magnetic attraction force of drive flange planar portion 53 as well as the magnetic attraction force of drive flange projection 52. With this operation, movable flange 46 is further pulled in the direction of arrow A as shown in
According to the image forming apparatus of the third embodiment as described in detail above, contact between projection 52 of the drive flange and recess 45a of drum fixed flange 45 and contact between drive flange planar portion 53 and movable flange 46 are separately controlled. Accordingly, the misalignment between the axises is corrected with higher accuracy.
[Other Modification]
Although the invention is applied to the drive of photosensitive drums 13 in the above embodiments, the invention may be applied to the drive of developing roller 12 of image forming unit 11.
Also, the invention may be applied to the drive of image transfer belt flange 72 of image transfer belt 71 in image transfer belt unit as shown in the C portion in
Also, drive flange 32 and image transfer belt flange 72 may have the same configuration as those shown in
As described above, the invention can be widely applied to an image forming apparatus, such as a printer, a copy machine, a facsimile machine or a MFP (Multi-functional Peripheral), which is configured to rotationally drive a roller member and execute printing on a recording medium.
The invention includes other embodiments in addition to the above-described embodiments without departing from the spirit of the invention. The embodiments are to be considered in all respects as illustrative, and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description. Hence, all configurations including the meaning and range within equivalent arrangements of the claims are intended to be embraced in the invention.
Number | Date | Country | Kind |
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2009-122481 | May 2009 | JP | national |