JPH1010806A - Paper inversion device for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paper inversion device capable of suppressing vibration noise and using an inexpensive stepping motor by detecting the leading edge and the thickness of a paper, increasing the output torque of the stepping motor when the paper is inverted and changing the output torque of the stepping motor according to the thickness of the paper. SOLUTION: When the leading edge of the paper P is detected by a paper edge detection part 3, the output torque of the stepping motor 2 can be increased by a motor control part 4 before the leading edge of the paper P arrives at a paper inversion roller 1. Besides, when the thickness of the paper P is detected by a thickness detection part 5, the output torque of the motor 2 can be changed according to the thickness of the paper P. Thus, the insufficiently of the torque is eliminated at a maximum load time and the motor 2 is not actuated in a state where the output torque thereof is always increased. Besides, the vibration noise is suppressed and the inexpensive stepping motor can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic copying machine,
The present invention relates to an image forming apparatus such as a laser printer and a facsimile apparatus, and more particularly, to an improvement in a sheet reversing apparatus for enabling double-sided printing.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus having a double-sided printing function for forming images on both sides of a transfer sheet, an image forming section first forms an image on one side and then does not discharge the sheet. Then, the image is formed on the back surface by temporarily reversing the sheet on a double-sided tray or the like and holding it, and when an image corresponding to the image on the back surface is formed on the photosensitive member, re-feeding the paper to the transfer position in a timely manner. In the above-mentioned double-sided tray, a single-sided printed transfer sheet is inverted using a sheet reversing device having a sheet reversing roller. However, a conventional sheet reversing device that drives a sheet reversing roller by a stepping motor is used. In this case, a large load torque is generated only when the sheet is reversed by the sheet reversing roller, and the load torque at other times is very small as compared with the time of the reversal. In addition, when using sheets of various thicknesses, the load torque is small for thin sheets and large for large sheets. Therefore, the output torque of the conventional stepping motor is set to exceed the value of the maximum load torque when reversing thick paper.

[0003]

However, in the above prior art, since the output torque of the stepping motor is uniformly set so as to exceed the maximum load torque for thick paper, the load torque can be small. When using paper, the output torque of the stepping motor becomes an unnecessarily large value, and the vibration noise increases,
Since the output torque decreases due to the temperature rise of the stepping motor and the motor loses synchronism at the maximum load and becomes inoperable, an inexpensive stepping motor such as a PM type motor cannot be used. It was in a situation where a simple stepping motor had to be used. Therefore, the present invention detects the leading edge of the paper and the thickness of the paper before the single-sided printed transfer paper reaches the paper reversing roller, and increases the output torque of the stepping motor when the paper is reversed. By changing the output torque of the stepping motor according to the thickness of the
Provided is a sheet reversing device that can use an inexpensive stepping motor.

[0004]

In order to solve the above-mentioned problems,
According to a first aspect of the present invention, a sheet reversal for an image forming apparatus in which a single-sided printed sheet that has been printed on one side in an image forming unit is turned upside down and re-fed to the image forming unit to print on the opposite side. In the apparatus, a sheet reversing roller for reversing the sheet by rotating forward, stopping at a predetermined position, and re-feeding the image forming unit by reversing the rotation, and a stepping motor for driving the sheet reversing roller And sheet edge detection means for detecting the leading and trailing edges of the sheet before the single-side printed sheet reaches the sheet reversing roller,
A motor control unit for increasing the output torque of the stepping motor when the sheet is reversed by the sheet reversing roller. According to a second aspect of the present invention, in the sheet reversing device according to the first aspect, the sheet reversing device further includes a thickness detecting means for detecting the thickness of the sheet before one-side printed sheet reaches the sheet reversing roller. The magnitude of the output torque of the motor control means is changed according to the value detected by the means.

[0005]

In the paper reversing device for an image forming apparatus constructed as in the first aspect, before the single-side printed paper reaches the paper reversing roller, the leading edge of the paper is detected by the paper edge detecting means. By dividing the distance between the sheet edge detecting means and the sheet reversing roller by the sheet conveying speed, it is possible to determine at which timing the sheet leading edge reaches the sheet reversing roller after the sheet edge detecting means detects the leading edge of the sheet. Immediately before reaching the paper reversing roller, the output torque of the stepping motor can be increased by the motor control means, so that the output torque can be increased in accordance with the maximum load at which the paper is reversed. In the sheet reversing device for an image forming apparatus configured as described in the second aspect, the thickness of the sheet can be detected by the thickness detecting means before the single-side printed sheet reaches the sheet reversing roller. Before the leading edge of the paper reaches the paper reversing roller, the output torque of the stepping motor is made smaller than the standard if the paper thickness is thinner than the standard, and the output torque of the stepping motor if the paper thickness is thicker than the standard. Can be made larger than the reference, and the output torque of the stepping motor can be changed by the motor control means in accordance with the thickness of the paper. Therefore, it is possible to provide a paper reversing device capable of giving an optimum output torque according to the load. Was.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a side view showing a main part of a sheet reversing device (double-sided tray) for an image forming apparatus of the present invention. A sheet P on which only the upper surface is printed on one side is conveyed from an image forming unit (not shown) located on the left side of the drawing in the direction of arrow A by a conveying roller (not shown). Paper P
Before the sheet reaches the sheet reversing roller 1, the leading edge of the sheet is detected by the sheet edge detecting unit 3 which detects the leading edge and the trailing edge of the sheet. The paper edge detection unit 3 includes a detection lever 3a, an optical unit (photo interrupter) 3b having a surface facing light emission and light reception, and a processing unit (control unit) 3c for processing the output of the optical unit 3b. I have. Further, the sheet edge detecting section 3 of the present example also serves as a thickness detecting section 5 for detecting the thickness of the sheet. The sheet reversing device is configured to apply a single-sided printed sheet P to a sheet reversing roller 1.
And a reversing path 21 for reversing the outer peripheral surface of the sheet reversing roller 1 and temporarily holding the sheet for reversal, and the insertion auxiliary roller 11 and the insertion and discharge auxiliary roller 12 The contact with the outer peripheral surface of the reversing roller 1 assists in carrying in and reversing the sheet P. The single-sided printed paper P once entering the reversing path 21 is re-fed at a predetermined timing toward the transfer position of the image forming unit (not shown) with the trailing edge leading. Reference numeral 13 denotes a direction control plate for switching the transport direction. The direction control plate 13 is used to smoothly carry the sheet into the reversing path 21 and discharge the sheet from the reversing path (feeding the sheet to the re-feeding path 22 indicated by the arrow G). It is configured to be able to advance and retreat between a solid line position and a dotted line position around the axis 13a.

Hereinafter, a detection method by the detection units 3 and 5 will be described with reference to FIG. When the leading end of the sheet P reaches the sheet end detecting unit 3 during the conveyance toward the sheet reversing roller 1, one end (operating piece) of the detection lever 3a (which is rotatable around the shaft 3A).
Is pushed up, the one end is lifted upward as shown by the dotted line in the figure. Since the detection lever 3a rotates around the central shaft 3A as a fulcrum, the detection lever 3a
Is further lowered to further block light from the optical unit 3b, and the input to the processing unit 3c is reduced. FIG. 2 is a diagram illustrating a change state of the output level from the processing unit 3c before and after the insertion of the sheet P. In FIG. 2, the fully open level indicated by the dotted line indicates the output level of the processing unit 3c in a state where the light of the optical unit 3b is not blocked. Output level (V-
O) indicates the output level of the processing unit 3c before the sheet P is inserted, where the light of the optical unit 3b is partially blocked by the detection lever 3a. When the sheet P is inserted and one end of the detection lever 3a is lifted, the output level becomes (VL) or (V) according to the thickness of the sheet.
−H). The output level of (V-H) is (V-
This is a case where a sheet P thicker than L) is inserted. That is, if the output level of the processing unit 3c is checked, the thickness of the inserted sheet P can be determined.

The output level (threshold level) (VT)
H) is a level for determining whether or not the sheet P has been inserted. If the output level is higher than (V-TH) (in the direction of the fully open level), it is determined that the sheet P has not been inserted, and (VT)
If the output level is lower than H) (in the direction opposite to the fully open level), it indicates that the paper P has been inserted. In the figure, the output level (V-L) or (V-H) exceeds the threshold level (V-TH) at the time t1, and the leading end of the sheet P is applied to the detection lever 3a at the time t1. It can be determined that it has been reached. At time t2, the output level (VL) and (VH) return to the initial output level (VO), so that at time t2, the rear end of the sheet P is detected by the detection lever. It can be understood that 3a has escaped. Therefore, the length from time t1 to t2 changes according to the length of the sheet P. As described above, by processing the change in the output level of the processing unit 3c, the operation is performed both as the detection of the thickness of the sheet P and the detection of the leading edge and the trailing edge.

Returning to FIG. 1, after the sheet P has passed through the sheet edge detecting section 3, the sheet P advances in the direction of arrow B by the driving force of the sheet reversing roller 1 and the insertion auxiliary roller 11 rotating in the direction of arrow C. . Further, the direction control plate 13 for controlling the transport direction depending on whether the sheet P is inserted into the reversing path 21 or discharged from the reversing path is inclined in the direction of the solid line, and the sheet P is It is fed in the direction of arrow E by the driving force. Then, the rear end of the sheet P is moved to the position l.
The rotation of the sheet reversing roller 1 and the insertion / ejection auxiliary roller 12 is stopped so as to be between (L) (to be nipped by the rollers 1 and 12). Paper P at this time
In the figure, the surface on which one side is printed is inverted and is on the lower side. Next, at the time of discharging from the reversing path 21, the rotations of the paper reversing roller 1 and the insertion / discharging auxiliary roller 12 are in the opposite directions (the paper reversing roller 1 is rotating in the D direction), and the direction control plate 13 Turns into. Therefore, the paper P that has advanced to the rear end portion at the time of insertion advances in the direction of the arrow G indicated by the dotted line by the direction control plate 13. Thereafter, the sheet proceeds with the lower side as a printed surface opposite to the direction of insertion in the advancing direction of the sheet, receives printing on the upper surface in an image forming unit (not shown), and ends double-side printing.

Next, the operation process described with reference to FIGS.
An embodiment corresponding to claim 1 will be described based on the block diagram of FIG. First, when the leading edge of the paper P is detected by the paper edge detection unit 3, a detection signal is passed from the processing unit 3 c of the paper edge detection unit 3 to the motor control unit 4. The motor driver of the motor control unit 4 receives the signal from the processing unit 3c immediately or
Alternatively, the output torque of the stepping motor 2 for driving the sheet reversing roller 1 in the normal rotation direction is increased after a predetermined time from the reception of the signal. For this purpose, the motor driver can increase the motor current value for a predetermined time. The timing for increasing the output torque of the stepping motor 2 is set to be immediately before the sheet reaches the sheet reversing roller 1. With this operation, it is possible to prevent a torque shortage when the sheet is reversed by the sheet reversing roller 1 from the direction of arrow B to the direction of arrow E. According to this embodiment, the output of the stepping motor before the leading edge of the sheet reaches the sheet reversing roller 1 can be reduced, so that the current can be saved and the durability of the motor can be improved.

Next, a second embodiment of the present invention will be described with reference to FIGS. 1 and 2 and the block diagram of FIG. When the thickness of the sheet P is detected by the thickness detection unit 5, the thickness information is sent from the processing unit of the thickness detection unit 5 to the motor control unit 4. The motor driver of the motor control unit 4 changes the magnitude of the output torque of the stepping motor 2 according to the thickness information immediately after receiving the signal from the processing unit or after a predetermined time from the signal.
Here, the motor control unit 4 stores in a storage unit (not shown) such as a ROM a correspondence table storing correspondence values for changing the drive current of the motor driver in multiple stages according to the thickness information. When the detected thickness information is received, the corresponding motor driver is switched from the correspondence table to the corresponding stage. That is, if the thickness of the paper P is thicker than the reference, the magnitude of the output torque is made larger than the reference accordingly, and if the thickness of the paper P is thinner than the reference, the magnitude of the output torque is made smaller. Is controlled to be smaller than the reference in accordance with. By this operation, even if the thickness of the paper P changes, the output torque when the paper is reversed from the direction of arrow B to the direction of arrow E by the paper reversing roller 1 is optimized, and torque shortage is prevented. it can. In addition, in the example of FIG. 1, the sheet end detecting unit 3 and the thickness detecting unit 5 are shared, but a completely separate detecting unit may be used. Further, in the above embodiment, an example in which the sheet reversing device is applied to an electrophotographic image forming apparatus has been described, but this is only an example. Therefore, for example, the present invention can be applied to a case where two-sided printing is performed in a printing apparatus that does not use an electrophotographic system. Accordingly, in the claims, printing is a concept including electrophotographic image formation and other printing and printing.

[0012]

According to the first aspect of the present invention, if the leading edge of the paper is detected by the paper edge detecting means, the output torque of the stepping motor is increased by the motor control means before the leading edge of the paper reaches the paper reversing roller. As a result, the shortage of torque at the maximum load is eliminated, the stepping motor does not always operate with the output torque increased, the vibration noise is suppressed, and an inexpensive stepping motor is used. It is possible to provide a sheet reversing device for an image forming apparatus that can be used.

According to the second aspect of the present invention, the output torque of the stepping motor can be changed in accordance with the thickness of the sheet, and an appropriate output torque can be adjusted following the change in the thickness of the sheet. As a result, the shortage of torque at the time of maximum load is eliminated, the motor is not always operated in a place where the output torque of the stepping motor is large, the vibration noise is suppressed, and an inexpensive stepping motor can be used. It is possible to provide a sheet reversing device for an image forming apparatus.

[Brief description of the drawings]

FIG. 1 is a side view of a main part of a sheet reversing device for an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a detection operation of a sheet edge detection unit and a thickness detection unit of the sheet reversing device according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating the operation of claim 1 in the sheet reversing device according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram illustrating the operation of claim 2 in the sheet reversing device according to the embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 paper reversing roller 2 stepping motor 3 paper end detection unit 4 motor control unit 5 thickness detection unit

Claims (2)

[Claims] 1. A sheet reversing device for an image forming apparatus, in which a single-sided printed sheet that has been printed on one side in an image forming unit is turned upside down and re-fed to the image forming unit to print on the opposite side. A sheet reversing roller that reverses the sheet by rotating forward, stops at a predetermined position, and re-feeds the sheet to the image forming unit by further rotating in reverse.
A stepping motor for driving the sheet reversing roller, sheet edge detecting means for detecting the leading and trailing edges of the sheet before the one-side printed sheet reaches the sheet reversing roller, and the sheet is reversed by the sheet reversing roller At that time,
A sheet reversing device for an image forming apparatus, comprising: a motor control unit for increasing an output torque of the stepping motor. 2. The sheet reversing device for an image forming apparatus according to claim 1, further comprising: a thickness detecting unit configured to detect a thickness of the single-sided printed sheet before the sheet reaches the sheet reversing roller. A sheet reversing device for an image forming apparatus, wherein the magnitude of the output torque of the motor control unit is changed according to a value detected by the detecting unit.