JPH09249342A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent pulling out of paper which stands by in a condition in which it is nipped by paper discharge rollers. SOLUTION: This image forming device consists of an image forming means 18 which forms an image on paper, a paper discharge roller 36 which discharges the paper on which the image is formed by the image forming means 18 to the outside and can be inverted, and conveyance means 34a, 40, 42, 44, 48, 26a which convey the paper to the image forming means 18 to form an image on a rear surface of the paper which is switched back in the inside due to the inversion of the paper discharge roller 36. In this case, the paper discharge roller 36 is stopped while paper is nipped and rotation load is applied in this condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming images on both sides of paper.

[0002]

2. Description of the Related Art Conventionally, there has been proposed an image forming apparatus capable of double-sided printing, in which an image is formed on the front surface of a sheet, and then the sheet is switched back to form an image on the rear surface and discharged. In this image forming apparatus, a compact and inexpensive structure is adopted by using the paper discharge roller as the switchback means. In order to speed up double-sided printing, first, an image is formed on the front surface of the first sheet of paper, and the first sheet of paper is switched back to wait inside. After the image is formed on the front surface of the first sheet, the second sheet is held by the sheet ejection roller in a state of being held by the sheet ejection roller until the preparation for printing (data development, etc.) on the back side of the first sheet is completed. An image is formed on the back side of the first sheet, and at the same time, the second sheet is switched back to wait inside, so that the first sheet is ejected and then the second sheet is image-formed. There is.

[0003]

However, while the second sheet of paper is held by the discharge rollers while waiting, the second sheet of paper is almost output to the outside while being caught by the discharge rollers. Since the printing has been stopped, the user may mistakenly consider that the printing has been completed and pull out from the paper discharge roller. The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus in which a standby sheet cannot be pulled out while being held by a discharge roller.

[0004]

To solve the above problems, the present invention provides an image forming means for forming an image on a sheet,
A reversible paper discharge roller for discharging the paper on which the image is formed by the image forming means to the outside, and the paper for forming an image on the back surface of the paper switched back inside by the reverse rotation of the paper discharge roller. In the image forming apparatus including a conveying unit that conveys the sheet to the image forming unit, the sheet discharge roller is stopped while holding the sheet, and a rotational load is applied in that state.

According to the configuration of the above invention, since the rotational load is applied when the paper discharge roller is stopped, the paper discharge roller does not rotate even if the paper held by the paper discharge roller is pulled,
I can't withdraw.

In a preferred aspect of the present invention, the sheet discharging roller is driven by a stepping motor, and a current is supplied to the stepping motor when the sheet discharging roller is stopped so that a rotational load is applied to the sheet discharging roller. May be. With this configuration, when the user pulls the sheet that is still held by the paper ejection roller and the user applies an external force to the paper ejection roller, a static torque is applied to the paper ejection roller and the paper cannot be pulled out. . This mode has an advantage that control becomes easy because it is only necessary to stop the stepping motor and hold the current. In this aspect, in order to prevent the stepping motor from being loaded with a load for a long time and causing a failure due to heat generation, the holding of the current flowing through the stepping motor is released after a fixed time when the discharge roller is stopped. Is preferred.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a printer 10 which is an image forming apparatus of the present invention. The printer 10 includes a printer main body 12 having an apparatus necessary for image formation, a double-sided printing unit (hereinafter referred to as a double-sided printing unit detachably attached to the printer main body 12 and used when the printer 10 performs double-sided printing).
It is simply called a double-sided unit. ) 14 and.

An image forming unit 18 containing a photoconductor 16 is removably mounted on the printer body 10, and a laser device 20 is arranged adjacent to the image forming unit 18. The laser device 20 includes the photoconductor 16
A laser corresponding to print information is exposed on the outer peripheral surface of to form an electrostatic latent image. The image forming unit 18 develops the electrostatic latent image formed on the photoconductor 16 to form a toner image. A tray 22 for accommodating sheets is provided on the bottom of the printer body 10. Above the end of the tray 22,
A paper feed roller 24 that feeds the paper one by one is provided. A paper feed path 26 is formed between the paper feed roller 24 and the photoconductor 16 of the image forming unit 18. Also,
A transfer roller 28 is disposed at a position facing the photoconductor 16, and at a portion (transfer unit 30) where the transfer roller 28 and the photoconductor 16 face each other, the photoconductor 16 is placed on the sheet conveyed from the paper feed path 26. The toner image is transferred.

The fixing roller 3 is located above the transfer section 30.
A paper discharge path 34 is formed which is curved through 2 and extends slightly in the horizontal direction. The fixing roller 32 fixes the toner image on the sheet conveyed through the sheet discharge path 34. At the end of the paper discharge path 34, a paper discharge roller 36 that discharges the paper to a tray 38 provided on the upper surface of the printer body 10 is provided. A switchback path 34a is formed in a horizontal portion of the paper discharge path 34 so as to branch in a direction opposite to the direction of the paper discharge roller 36.

A transport path 40 continuous with the switchback path 34a is formed in the double-sided unit 14 in the vertical direction, and transport rollers 42 for transporting a sheet are provided in the transport path 40.
44 and 48 are arranged at a predetermined interval. The lower end of the transport path 40 of the double-sided unit 14 is a re-feed path 26a formed so as to merge with the paper feed path 26 of the printer body 10.
And is continuous.

The paper discharge roller 36 can be driven in the normal and reverse directions by a paper discharge motor M1. In addition, the transport roller 4
2, 44 and 48 are configured to be rotationally driven in a fixed direction by the transport motor M2. A sensor SE1 for detecting the arrival of the sheet is provided slightly upstream of the branch point of the discharge path 34 of the printer body 12 from the switchback path 34a. In addition, the conveyance path 4 of the double-sided unit 14
A sensor SE2 for detecting the arrival of the sheet is also provided on the slightly downstream side of the 0 transport roller 44.

FIG. 2 shows a control circuit for controlling the printer 10 having the above-described structure, particularly a drive circuit for the paper discharge motor M1. The central processing unit (CPU) 50 receives paper size and counter inputs, paper detection signal inputs from the sensors SE1 and SE2, and other inputs. Also,
The CPU 50 includes an image forming unit 18 and a paper discharge motor M.
1 and output of control signals to the carry motor M2 and other outputs. The paper discharge motor M1 is a two-phase excitation type stepping motor having four phases.

The CPU 50 outputs pulse signals φ1 and φ2 for driving the paper discharge motor M1. These pulse signals φ1 and φ2 are inverted by the gate ICs 52 and 54, and four-phase signals φ1, φ1 ′, φ2 and φ2 ′ (here,
φ1 ′ and φ2 ′ are inverted signals of φ1 and φ2, respectively. ) Is input to the discharge motor driving IC 56. The discharge motor driving IC 56 generates four-phase motor drive signals A, A ', B, B' (where A'and B'are inverted signals of A and B, respectively) and the discharge motor. M1
A signal (CW) for driving the sheet in the forward direction, a signal (CCW) for driving the sheet in the reverse direction, and a signal (STOP) for stopping the sheet are output to the paper discharge motor M1.

The CPU 50 also outputs an enable signal for disabling the current to the paper discharge motor M1. When the enable signal is "high (H)", no current flows through the paper discharge motor M1 regardless of the states of the pulse signals φ1 and φ2. When the enable signal is "low (L)", the current to the discharge motor M1 is allowed and the pulse signal φ
The paper discharge motor M1 rotates and stops according to the states of 1 and φ2. This will be described in more detail with reference to FIG. That is, when the enable signal is “L”, the pulse signal φ
When 1 is "H", the phase difference between the pulses output from the pulse signals φ1 and φ2 is + 90 °, so the CW motor drive signal is output to the paper ejection motor M1, and the paper ejection motor M1 Drive forward. In addition, the pulse signal φ2
Is “H”, the phase difference becomes −90 °, and CC
A W motor drive signal is output to the paper discharge motor M1, and the paper discharge motor M1 is driven in reverse. Furthermore, pulse signals φ1, φ
If both output states of 2 are kept at the same state by setting both to "H", the discharge motor M1 stops rotating. In this rotation stopped state, a current is flowing through the paper discharge motor M1, and therefore, when a rotational torque due to an external force acts on the paper discharge motor, a torque for stopping the motor, that is, a maximum stationary torque is generated.

The discharge motor M1 has four phases,
It is not limited to the two-phase excitation method. Also, the gate IC5
It is also possible to directly output the number of signals corresponding to the number of phases of the discharge motor M1 to the discharge motor driving IC 56 from the CPU 50 without using 2, 54. Furthermore, without using the enable signal, the four-phase signals are maintained in the same phase to generate the maximum stationary torque, and the four-phase signals are all set to "L" to reduce the stationary torque. You may use differently.

Next, the printer 10 by the CPU 50
The above control operation, particularly the control operation of the discharge motor M1 relating to the present invention, will be described with reference to the flowcharts of FIGS.

FIG. 3 is a main routine of the control operation of the printer 10 by the CPU 50. When the power is turned on, first, various initial settings are made (# 1) and an internal timer is started (# 2). Next, a discharge motor control (# 3) for controlling the drive of the discharge motor M1, a transport motor control (# 4) for controlling the drive of the transport motor M2 of the duplex unit 14, and an abnormality for avoiding an abnormal state. control(#
5), print control for image formation (# 6) is sequentially performed, and after waiting for the end of the internal timer (# 7), step # 2
Return to and repeat the same steps.

FIG. 4 is a subroutine for controlling the discharge motor. When the on-edge of the sheet detection signal by the sensor SE1 is detected (# 31), a CW signal for driving the sheet discharge motor M1 to rotate in the forward direction is output, and at the same time, an enable signal is output.
L "(# 32). As a result, the discharge motor M
1 is driven in the normal direction, and the paper is sent out in the discharge direction. Next, the flag F ₂ indicating that double-sided printing has been completed is "0".
It is determined whether or not (# 33). Since the flag F ₂ has entered "0" as an initial value, a F ₂ = 0 That sided printing when the first sheet of the print.

When the flag F ₂ is "0" and single-sided printing is performed, a timer T until the trailing edge of the sheet is clamped by the discharge roller 36 is set and started (# 34). The set time T of this timer depends on the system speed S, sensor SE
When the distance of the paper discharge path 34 from the position 1 to the paper discharge roller 36 is 1, the size of the paper in the feeding direction is L, and the trailing edge margin of the paper, that is, when the paper is stopped while being held by the paper discharge roller 36 The distance from the paper ejection roller 36 to the rear edge is α
Then, it is expressed by the equation 1.

## EQU1 ## T = (l + L-α) / S

When the flag F ₂ is "1" and double-sided printing is performed, a timer T'is started until the trailing edge of the paper leaves the paper discharge roller 36 (# 35). The set time T'of this timer is the sheet drop margin, that is, the distance from the trailing edge of the sheet to the sheet discharge roller 36 when it is assumed that the sheet leaves the sheet discharge roller 36 and continues to move at the current speed. Is expressed as α '.

## EQU2 ## T '= (l + L-α') / S

Next, it is judged whether or not the timer T or T'has timed out (# 36), and if it has not timed out, the process returns as it is to the subroutine (Fig. 5) for the next conveyance motor control. Transition. If the time is up, the type of the timer, that is, T or T'is determined (# 37).

If the timer is the timer T until the trailing edge of the sheet is clamped by the sheet discharge roller 36, is the flag F ₁ indicating the standby state for back side printing "0"? It is determined whether or not (# 38). Here, since "0" is entered as an initial value for this flag F ₁ , F ₁ = 0 at the time of printing the first sheet, that is, it is not in a standby state for back side printing.

When the flag F ₁ is "0" and it is not in the standby state for the back side printing, at the same time as outputting the CCW signal for driving the paper discharge motor M1 in the reverse direction, the enable signal is set to "L" ( # 39). As a result, the discharge motor M1 is driven in the reverse direction, and the paper is switched back in the direction opposite to the discharge direction, and the switchback path 3
4a is conveyed.

When the flag F ₁ is "1" and the printer is in the standby state for printing on the back side, the STOP signal for stopping the paper discharge motor M1 is output and at the same time the enable signal is set to "L". (# 42). As a result, the paper discharge motor M1 is stopped, and the paper is stopped while being held by the paper discharge roller 36. At this time, although the paper discharge motor M1 is stopped, the state in which current is flowing by the inversion signals A'and B'is maintained. As a result, even if a rotational external force acts on the paper discharge motor M1, a stationary torque acts to prevent it. Therefore, the user mistakenly recognizes that the printing is completed by looking at the sheet that is almost outside the sheet while being bitten by the sheet ejection roller 36, and even if the user pulls it, the sheet cannot be pulled out. Therefore, there is no possibility that the sheet waiting in the single-sided print state is pulled out. Next, in order to prevent the malfunction of the discharge motor M1 and its driving IC 56 from rising in temperature in the state where the static torque acts on the discharge motor M1 in this way, the counter is started (# 43). ), And resets after a predetermined time.

In the determination of the type of timer in step # 37, the timer that has timed out is not the timer T until the trailing edge of the sheet is clamped by the discharge roller 36,
If the trailing edge of the sheet is the timer T'until the sheet passes through the sheet discharge roller 36, the sheet has already been discharged. Therefore, at the same time as outputting the STOP signal for stopping the sheet discharge motor M1, the enable signal is set to "H". Set (# 40). As a result, no current flows through the paper discharge motor M1, and the paper discharge roller 36 becomes free.

FIG. 5 is a subroutine for carrying motor control of the duplex unit 14. When the paper that has been switched back to the transport path 40 of the duplex unit 14 through the switchback path 34a detects the on edge by sensor SE2 (# 44), the flag F ₂ indicating that you have two-sided printing "1 "it is set to (# 45), the flag F ₂ to be detected on-edge Details" remains 0 ".

Next, if the flag F ₂ indicating that double-sided printing has been completed is "1"(# 46), whether or not the preparation for printing the back side data has been completed (this judgment is made from the image forming unit 18). This is done by the print ready signal.)
Judge. If you are ready to print,
Outputs a drive signal of the conveying motor M2 (# 48), the flag F ₁ indicating the standby state for the back surface printing is reset to "0". As a result, the paper is re-fed to the image forming unit 18 along the re-feed path 26a, and the back side printing operation is performed. If the print preparation is not completed, a stop signal of the carry motor M2 is output (# 50),
Set the flag F ₁ indicating the standby state for back side printing
1 ". This causes the paper to wait until it is ready to print.

FIG. 6 shows an abnormal control subroutine.
It is determined whether or not the counter in step 43 of the discharge motor control subroutine has counted up. If the counter has counted up, the enable signal is set to "H". As a result, current does not flow to the paper discharge motor M1 in a state where the paper is held while being pinched and the static torque is applied, and the paper discharge motor M1 and its driving IC 56 rise in temperature and malfunction occurs. To be prevented.

The flow of paper by the operation of the paper discharge roller 36 and the transport rollers 42, 44, 48 described in the above flow chart will be described in more detail below with reference to the schematic diagrams of FIGS. 7 to 9 and the time chart of FIG. .

In FIG. 7A, when the first sheet is fed by the sheet feed roller 24 and the image of the second page is printed on the sheet by the image forming unit 18 and the transfer roller 28, the sheet is fixed. It is conveyed toward the discharge roller 36 via the roller 32. At this time, the leading edge of the sheet is detected by the sensor SE1, and the sheet discharge roller 36 rotates in the CW direction based on the signal from the sensor SE1.

In FIG. 7B, the paper is the paper discharge roller 3.
6 is conveyed in the discharge direction, but the rotation of the discharge roller 36 is switched to the CCW direction before being completely discharged from the discharge roller 36. As a result, the sheet is switched back to the switchback path 34a.

In FIG. 7 (c), the switched-back paper is fed from the switchback path 34a to the duplex unit 1
4 is conveyed to the conveyance path 40 and stopped. At this time, the paper discharge roller 36 stops rotating and current is not held.

In FIG. 8D, when the second sheet of paper is fed and the image of the fourth page is printed, the sheet of paper is conveyed toward the discharge roller 36. At this time, the leading edge of the sheet is detected by the sensor SE1, and the sheet discharge roller 36 rotates in the CW direction based on the signal from the sensor SE1.

In FIG. 8 (e), the second sheet is conveyed in the ejection direction by the sheet ejection roller 36, but the sheet ejection roller 36 holds the sheet before it is completely ejected from the sheet ejection roller 36. While still doing, stop once. At this time, the current of the paper discharge motor M1 is held so that the paper held by the paper discharge roller 36 is not pulled out. When the preparation for printing on the back surface of the first sheet is completed, the transport motor M2 of the duplex unit 14 rotates, and the first sheet waiting in the transport path 40 forms an image on the re-feed path 26a. Unit 1
It is re-fed to 8. At the same time, the paper discharge roller 36 rotates in the CCW direction. As a result, the second sheet is switched back and moves toward the switchback path 34a.

In FIG. 8F, the image of the first page is printed on the first sheet re-fed to the image forming unit 18 through the re-feeding path 26a. Further, the switched-back second sheet is conveyed from the switchback path 34a to the conveyance path 40 of the duplex unit 14 and stopped.
Then, the printed first sheet is ejected by the paper ejection roller 36.
Conveyed toward. At this time, the leading edge of the paper is the sensor S
Detected by E1, the paper discharge roller 36 rotates in the CW direction based on the signal of this sensor SE1.

In FIG. 9G, when the first sheet is ejected by the ejection roller 36, the ejection roller 36 stops. At this time, the paper discharge roller 36 does not hold the paper, and therefore current is not held.

In FIG. 9 (h), the second sheet is re-fed and the image of the third page is printed. The printed paper is conveyed toward the paper discharge roller 36. At this time, the leading edge of the sheet is detected by the sensor SE1, and the sheet discharge roller 36 rotates in the CW direction based on the signal from the sensor SE1.

In FIG. 9 (i), when the second sheet of paper is ejected by the paper ejection roller 36, the paper ejection roller 36 stops. At this time, the paper discharge roller 36 does not hold the paper, and therefore current is not held. Thus, (a) ~
By repeating the operation of (i), double-sided printing is performed at high speed.

In the case of a small size sheet, a plurality of sheets can be built in the conveying path 40 of the double-sided unit 14, so that when the second built-in sheet is sent to the conveying path 40, that is, the sheet is discharged. When the roller 36 is switched back, whether the first sheet is in the standby state or not can be switched to be stopped in the state of being held by the discharge roller 36. However, in the case of a large size as shown in FIG. 11, since only one sheet can be built in, double-sided printing is completed for each sheet. Therefore, instead of switching whether to stop in a state of being held by the paper discharge roller 36 when switching back by the paper discharge roller 36, whether to wait when the switched back paper comes to SE2, that is, It suffices to switch whether or not to stop with the electric current applied to the paper discharge roller 36.

In the above embodiment, the double-sided unit 14 is detachable from the printer main body 12. However, the same structure as the double-sided unit 14 is integrally incorporated in the printer main body 12 to form an image forming apparatus. It goes without saying that the present invention can also be applied to the above.

[0042]

As is apparent from the above description, according to the present invention, the paper discharge roller is stopped while holding the paper, and a rotational load is applied in that state. The paper stopped while being bitten is no longer accidentally pulled out by the user. As a result, the double-sided printing operation is smoothly performed without being disturbed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a printer that is an image forming apparatus of the present invention.

FIG. 2 is a control circuit diagram of the printer of FIG.

3 is a flowchart showing a main routine of a control operation of the printer of FIG.

FIG. 4 is a flowchart of a discharge motor control subroutine.

FIG. 5 is a flowchart of a subroutine for carrying motor control.

FIG. 6 is a flowchart of an abnormal control subroutine.

FIG. 7 is a schematic diagram that sequentially shows a sheet conveyance state.

FIG. 8 is a schematic diagram sequentially showing the conveyance state of the paper following FIG.

FIG. 9 is a schematic diagram sequentially showing the conveyance state of the paper following FIG.

FIG. 10 is a time chart of each of phase output and enable output to the paper discharge motor.

FIG. 11 is a schematic diagram showing a sheet conveyance state in another embodiment.

[Explanation of symbols]

10 ... Printer (image forming apparatus), 18 ... Image forming unit (image forming means), 26a ... Refeed path (conveying means), 34a ... Switchback path (conveying means), 36 ...
Paper discharge rollers, 40 ... Conveying paths (conveying means), 42, 44,
48 ... Conveying roller (conveying means), M1 ... Paper ejection motor.

Claims (3)

[Claims] 1. An image forming unit for forming an image on a sheet,
A reversible paper discharge roller for discharging the paper on which the image is formed by the image forming means to the outside, and the paper for forming an image on the back surface of the paper switched back inside by the reverse rotation of the paper discharge roller. In the image forming apparatus including a conveying unit that conveys the sheet to the image forming unit, the sheet discharge roller is stopped while holding the sheet, and a rotational load is applied in that state. Forming equipment. 2. A discharge load is applied to the discharge roller by driving the discharge roller with a stepping motor and holding a current flowing through the stepping motor when the discharge roller is stopped. The image forming layer apparatus according to claim 1. 3. The image forming apparatus according to claim 2, wherein the holding of the current flowing through the stepping motor is released after a fixed time when the paper discharge roller is stopped.