JP2000211761A - Image forming device and conveying speed control method of recording sheet in the image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device and a conveying speed control method of a recording sheet in the image forming device capable of shortening a required processing time per one sheet of the recording sheet while ensuring a fixing property of a toner even if the recording sheet (specialty paper) having a large heat capacity such as a thick film and a film sheet for OHP is used. SOLUTION: A specialty paper sent out from any one of paperfeeding cassettes 15-19 is conveyed at a system speed (first conveying speed) until a rear end thereof is passed through a transfer position immediately below a photosensitive body drum 9 except for the time when it is abutted to a resist roller 37 and is once waited. When the rear end of the specialty paper is passed through the transfer position, a motor, i.e., a driving source of a conveying belt 10 is braked by a brake to reduce a speed to a second conveying speed slower than a first conveying speed before a tip end thereof enters into a fixing device 11. A fixing upper roller 11a of the fixing device is rotated at a revolution speed corresponding to the second conveying speed.

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 such as a copying machine, and more particularly, to a technique for controlling a conveying speed of a recording sheet.

[0002]

2. Description of the Related Art In a copying machine, a recording sheet taken out of a paper feed cassette by a pickup roller is
Unless the printer is temporarily stopped to synchronize with the image forming operation of the image forming unit including the photosensitive drum until reaching the discharge tray,
Generally, it is transported at a constant transport speed (hereinafter, referred to as “system speed”).

During this time, a toner image is transferred from the photosensitive drum to the recording sheet, and the toner on the recording sheet is fixed by a fixing device. This fixing device is composed of a pair of fixing rollers having a built-in heater on one or both sides.
The toner on the recording sheet is nipped by the fixing roller pair and transported by the rotational force of the fixing roller.
The image is fixed by heat supplied from the heater.

[0004] By the way, in addition to recording sheets which are usually used and have a thickness of about 100 to 150 μm (hereinafter, referred to as “plain paper”), postcards and other thick papers and OHP (over head projector) Film sheet or the like may be used. Because this type of recording sheet has a larger heat capacity than plain paper due to its thickness and the like (hereinafter, such a recording sheet having a larger heat capacity than plain paper is referred to as “special paper”), toner is used. In order to reliably fix, more heat is required.

For this purpose, a method of increasing the heating temperature by the heater is conceivable. However, since the temperature of the heater does not rise immediately, there arises a problem that the waiting time for copying increases. It is not preferable from the viewpoint of energy saving. Therefore, conventionally, a method has been devised in which when the recording sheet is special paper, the system speed is made slower than when the recording sheet is plain paper. By reducing the system speed, a sufficient amount of heat is supplied to the recording sheet, so that the toner is reliably fixed.

[0006]

However, according to the above-mentioned conventional method, although the fixing property of the toner is ensured, the productivity of the copy is reduced by the decrease in the system speed. That is, the processing time required for one recording sheet increases. SUMMARY OF THE INVENTION In view of the above-described problems, the present invention provides an image forming apparatus and a recording sheet in an image forming apparatus capable of shortening a processing time required for one recording sheet while securing toner fixing property when special paper is used. It is an object of the present invention to provide a transport speed control method.

[0007]

In order to achieve the above object, an image forming apparatus according to the present invention comprises a conveying means for conveying a recording sheet, and a toner image forming apparatus for forming a toner image on the conveyed recording sheet. Means, fixing means for fixing the formed toner image on the recording sheet, and the conveying means after the trailing edge of the recording sheet has passed through the toner image forming means and before the leading end of the recording sheet reaches the fixing means. And a speed-reducing means for reducing the transport speed of the vehicle.

The conveying means includes a motor, a conveying force acting portion for receiving a power transmitted from the motor and applying a conveying force to the recording sheet, and transmitting the power of the motor to the conveying force acting portion. And a deceleration unit that includes a brake device that acts on the power transmission unit to brake the motor. Furthermore, the image forming apparatus further includes a target rotation speed of the motor,
Motor control means for controlling switching between a first rotation speed corresponding to a first transfer speed and a second rotation speed corresponding to a second transfer speed lower than the first transfer speed; Detecting means for detecting the number of rotations, wherein the motor control means switches the target number of rotations from the first number of rotations to the second number of rotations almost simultaneously with the start of braking by the brake device, and the deceleration means The braking by the brake device is released before the rotation speed detected by the detection means reaches the second rotation speed.

According to another aspect of the present invention, there is provided a method for controlling a conveyance speed of a recording sheet in an image forming apparatus, comprising: A method for controlling a conveying speed of a recording sheet by said conveying means in an image forming apparatus which forms a toner image by forming a toner image by a toner image forming means and fixing the toner image by a fixing means. A first step of setting the number of revolutions to a first number of revolutions, a second step of detecting passage of the toner image forming means at the trailing end of the recording sheet, and detecting passage of the toner image forming means at the trailing end of the recording sheet Then, the third step of switching the target rotational speed of the motor to a second rotational speed lower than the first rotational speed, and the switching of the motor speed substantially simultaneously with the switching of the rotational speed. A fourth step of initiating braking and a fifth step of detecting that the number of rotations of the motor reaches a third number of rotations having a value between the first number of rotations and the second number of rotations. And a sixth step of releasing the braking on the motor when the third rotational speed is detected.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an image forming apparatus according to the present invention applied to a digital copying machine will be described. FIG. 1 is a diagram showing an overall configuration of the digital copying machine (hereinafter, simply referred to as “copying machine”).

As shown in FIG. 1, the copying machine includes a document reading unit 100, a printer unit 200, and a paper feeding unit 300. The document reading unit 100 converts the reflected light from the document into an electric signal once, performs necessary image processing such as density conversion and edge enhancement, and outputs the signal to the printer unit 200. The printer unit 200 forms an image by a known electrostatic copying method. In the exposure scanning unit 1, a laser diode (not shown) emits a laser beam in response to an output signal from the document reading unit 100, The light is reflected and deflected by a mirror surface of a polygon mirror (not shown) driven to rotate at a constant speed. The light path of the deflected laser beam is changed by the mirror 2 and the surface of the photosensitive drum 3 is exposed and scanned.

Around the photosensitive drum 3, a charging charger 4, a developing device 5, a transfer charger 6, a separation charger 7, a cleaning device 8, and an eraser lamp 9 are arranged in this order along the drum rotation direction a. The toner image of the read document is transferred onto the recording sheet fed from the sheet feeding unit 300 by a known electrostatic copying process such as charging, exposure, development, transfer, and separation. The recording sheet onto which the toner image has been transferred is sent to a fixing device 11 by a transport belt 10, where it is fixed, and then discharged onto a tray 13 via a discharge roller 12.

The paper feed section 300 holds the paper feed cassettes 15 to 19 in a cabinet 14 provided in two upper and lower stages by guide rails (not shown) so as to be slidable toward the front of the drawing, and is mounted on the right side wall of the cabinet. A transport path 20 for transporting recording sheets from each of the paper feed cassettes 15 to 19 is formed along the transport path. The starting end of the transport path 20 is branched by the number of paper feed cassettes 15 to 19, and the branch paths 21 to 2 are provided.
Sheet feed mechanisms 26 to 30 for taking out recording sheets from a sheet feed cassette are arranged at the end of the branch road 5. Also,
The paper feed mechanisms 26 to 30 are driven by a paper feed motor M1 composed of a pulse motor, and are driven by a known electromagnetic micro clutch (not shown) provided for each of the paper feed mechanisms 26 to 30 to drive the paper feed motor M1. And the five paper feed mechanisms 26
One of the paper feed mechanisms out of .about.30 is selectively driven.

In the transport path 20, each paper feed mechanism 26-
Vertical transport rollers 31 to 35 are disposed at a predetermined distance from the downstream side from 30 to constitute a vertical transport mechanism. This vertical transport mechanism is driven to rotate by a vertical transport motor M2 composed of a pulse motor via a power transmission mechanism (not shown), and transports the recording sheet fed from the paper feed cassette further downstream. .

The recording sheet taken out of the paper feed cassette by the paper feed mechanism and conveyed by the vertical conveyance roller is conveyed further downstream through the conveyance path 20 by the intermediate roller 36 and once abuts on the registration roller 37 to contact the registration roller 37. After waiting, the conveyor belt 1 is fed out by the registration roller 37 which rotates in synchronization with the above-described image forming operation of the photosensitive drum 3, and stretched by a driving roller 38 and a driven roller 39.
By 0, the photosensitive drum 3 is transported to the transfer position.

FIG. 2 shows a schematic configuration of a driving mechanism of the conveyor belt 10. The drive mechanism includes a motor M3 as a drive source and a power transmission mechanism. The power transmission mechanism transmits the power of the motor M3 to the rotation shaft 38s of the drive roller 38 by the reduction gear 40 and the shaft joint 41 formed of a gear train. A known electromagnetic clutch / brake 43 (hereinafter, simply referred to as “brake 43”) is attached to an output shaft 42 of the motor M3, which is a part of the power transmission mechanism. Is braked. The motor M3 is a motor with an FG (frequency generator). As will be described later, the FG detects the number of rotations of the motor and controls the rotation speed of the motor.
A rotary encoder 44 (hereinafter, simply referred to as “encoder 44”) for controlling the rotation speed of the motor M3 is attached to one end of the rotating shaft 38s. In consideration of the speed reduction ratio of the speed reducer 40, the FG and the encoder 44 generate pulse signals having the same period if the rotation speed of the motor M3 is the same, assuming that there is no loss in power transmission by the power transmission mechanism. Is used. Alternatively, adjustment may be performed by passing one or both pulse signals through a frequency divider to obtain pulse signals having the same period. The use of the FG and the encoder 44 will be described later.

Returning to FIG. 1, the toner image formed on the photosensitive drum 3 is transferred to the recording sheet conveyed by the conveyor belt 10, and the toner image is fixed by the fixing device 11. The fixing device 11 has an upper fixing roller 11u having a built-in heater and a lower fixing roller 11d provided in pressure contact with the upper fixing roller 11u. The upper fixing roller 11u is rotated in the direction of arrow b by the motor M4, and the lower fixing roller 11d is driven by the rotation. The toner image on the recording sheet is fixed by the heat supplied from the heater while the recording sheet held between the rollers 11u and 11d is conveyed to the discharge roller 12. Note that the conveyance speed of the recording sheet by the fixing device 11 is switched between a system speed and a second speed lower than the first speed when the system speed is the first speed. The switching of the speed is performed by a main control unit 90 described later.
By controlling the number of revolutions of the motor M4, the speed is controlled at a first speed (system speed) when plain paper is used as a recording sheet, and at a second speed when special paper is used. By doing so, a sufficient amount of heat required for fixing is supplied even to special paper, and the toner image is reliably fixed.

A sensor 46 is provided between the fixing device 11 and the photosensitive drum 3 for detecting the leading and trailing ends of the conveyed recording sheet. An operation panel 45 is provided at a position on the upper surface of the copying machine where the operation is easy. The operation panel 45 includes a copy start key for instructing a copy start, a numeric keypad for setting the number of copies, a paper size designation key for designating a recording sheet size, and a paper type selection for selecting one of plain paper and special paper. In addition to various input keys such as keys, a display unit 45a (FIG. 3) for displaying the set contents and the like is provided. The original reading unit 100, the printer unit 200, and the paper feeding unit 300 are controlled by the main control unit 90,
A smooth copy operation is realized.

FIG. 3 mainly shows a motor M3 and a brake 4
FIG. 3 is a diagram illustrating a schematic configuration of a control unit 50 that controls the control unit 3; The control unit 50 is connected to the main control unit 90. The main control unit 90 includes the CPU 91
ROM 91, RAM 93 and interface 9
CPU 91 is connected to ROM 9
The control is performed according to the program stored in the second program. Further, the CPU 91 (main control unit 90) is connected to the control unit 50, the operation panel 45, the sensor 46, and other components via the interface 94.

A start (L) signal and a stop (H) signal for instructing start or stop of the motor M3 are output from the main control unit 90 to the control unit 50 via a connection line 81.
The signal is input to the controller 51 of the control unit 50. The controller 51 includes FV converters 52 and 53, a comparator 54, a driver 55, and the like.

One FV converter 52 has a selector 56
, A pulse signal of either the encoder 44 or the FG is input, and the FV converter 52 converts the frequency of the pulse signal into a voltage and outputs the voltage to the comparator 54. The other FV converter 53 is connected to a crystal oscillator 58 via a frequency divider 57, and the FV converter 53 is generated by the crystal oscillator 58 and divided by the frequency divider 57. The frequency of the clock signal is converted into a voltage and output to the comparing unit 54.

The crystal oscillator 58 generates a reference clock signal, and the frequency divider 57 divides the frequency of the reference clock signal to generate a clock signal of two different frequencies, high and low, which serves as a reference for controlling the rotation speed of the motor M3. Generate. The main controller 9 determines which of the high and low frequency clock signals is generated.
It is determined by a speed setting signal input from 0 through the connection line 82. When the speed setting signal is H, the clock signal of the frequency F1 corresponding to the first reference rotation speed X1 is:
When the speed setting signal is L, a clock signal having a frequency F2 corresponding to a second reference rotation speed X2 lower than the first reference rotation speed is generated.

Here, the first reference rotation speed X1 is a rotation speed corresponding to the system speed (first speed). That is, when the motor M3 rotates at the reference rotation speed X1, the transport belt 10 runs around at the system speed. The second reference rotation speed X2 is a rotation speed corresponding to the second speed. That is, when the motor M3 rotates at the second reference number of revolutions, the transport belt 10 runs around at the same speed as the second speed when the fixing device 11 transports the special paper.

The comparator 54 compares the voltage input from the FV converter 53, ie, the reference rotation speed, with the voltage input from the FV converter 52, ie, the detected rotation speed. The difference is output to the driver unit 55. The driver unit 55
Based on the difference input from the comparing unit 54, the energization width (duty) to the motor coil of the motor M3 is increased or decreased, and energization control to the motor M3 is performed so that the detected rotation speed always approaches the reference rotation speed. The energization of the motor coil of the driver unit 55 is started by the input of the start signal (H), and is stopped by the input of the stop signal (L).

The controller 51 outputs a lock signal to the selector 56 and the main controller 90 based on the comparison result of the comparator 54. The lock signal of (L) is output while the detected rotation speed is within the tolerance ± 6.25% with respect to the reference rotation speed for a predetermined time Ta or more, and otherwise the lock signal of (H) is output. Here, the fact that the detected rotation speed is within the tolerance ± 6.25% with respect to the reference rotation speed is defined as “the detected rotation speed is within the target range”. Further, the predetermined time Ta refers to a time sufficient for determining that the detected rotation speed is stable within the target range. Further, when the detected rotation speed is out of the target range and continues within the tolerance for a predetermined time period Ta or more, it is defined as "the detected rotation speed converges to the reference rotation speed". Needless to say, the value of the tolerance is not limited to the above.

When the lock signal is an H signal, the selector 56 selects a pulse signal from the FG and outputs it to the FV conversion unit 52. When the lock signal is an L signal, the selector 56 selects a pulse signal from the encoder 44. The signal is selected and the FV converter 52
Output to That is, when the motor M3 is started or when the set speed is switched, feedback control of the rotation speed of the motor M3 is performed using the FG until the convergence to the target reference rotation speed is performed. After converging to, during steady rotation (while the detected rotation speed is within the target range),
The feedback control of the rotation speed of the motor M3 is performed using the encoder 44.

The lock signal is also input to the main control unit 90 via the connection line 83 as described above, and the pulse signal from the encoder 44 is amplified by the transistor 59, and then the main control unit 90 Is also entered. After starting the motor M3 (after transmitting the start signal (H) and the H signal of the speed setting signal), or after switching the speed setting signal from the L signal to the H signal,
When the lock signal switches from the H signal to the L signal,
When the control of the rotation speed of the motor M3 is switched from the control by the FG to the control by the encoder 44, the detection abnormality determination processing of the encoder 44 is performed.

This detection abnormality determination processing will be described with reference to FIG. FIG. 4A shows a waveform of a pulse signal input from the encoder 44 to the main control unit 90 when the motor M3 is rotating at a steady speed. Since the pulse signal is detected during the steady rotation, if there is no abnormality in the encoder 44 and the like, the pulse signal has a waveform of a substantially constant period P [sec] as shown in FIG.
It goes without saying that the value of P differs between the case where the control is performed at the first reference rotation speed and the case where the control is performed at the second reference rotation speed). When the lock signal changes from the H signal to the L signal, the main control unit 90 sets the reference time to the time t2 after P / 4 from the time t1 (0V → 5V) of the pulse, and the P / 2 interval from the time t2. (T3, t4, t5
…) Sampling of pulse signals. As a result, 0V
And 5 V are alternately detected while the encoder 44
Are determined to be operating normally. On the other hand, if only 0 V is detected during the predetermined time Ti (during the predetermined number of samplings), or if only 5 V is detected as shown in FIG. It is determined that there has been any abnormality in 44 or the like, and that fact (for example, a corresponding trouble code) is displayed on the display unit 45a. The above-mentioned display is also performed when the rise of the pulse is not detected even after a predetermined time has elapsed after the lock signal changes from the H signal to the L signal. When an abnormality occurs in the encoder 44 and a normal pulse signal cannot be obtained from the encoder 44, the detected number of revolutions (voltage) and the reference number of revolutions (voltage) input to the comparing unit 54 (FIG. 3) are used. Greatly changes, the lock signal switches from the L signal to the H signal, and as a result, the motor M
Since the rotation control of the motor M3 is continued, abnormal rotation of the motor M3 due to the abnormality of the encoder 44 is prevented.

Returning to FIG. 3, a portion relating to the timing control of turning on / off the brake 43 will be described. F
The voltage (corresponding to the detected rotation speed) output from the -V conversion unit 52 is input to the non-inverting input terminal of the comparator 60. On the other hand, when the voltage input to the non-inverting input terminal becomes a voltage indicating a rotation speed equal to or lower than the reference rotation speed X3, the output signal of the comparator 60 becomes an H signal (Vre).
f) is entered. That is, the comparator 60 outputs an H signal when the detected rotation speed is equal to or less than the reference rotation speed X3, and outputs an L signal when the detected rotation speed exceeds the reference rotation speed X3. The reference rotation speed X3 is a rotation speed that takes an intermediate value between the reference rotation speed X1 and the reference rotation speed X2.

The output signal of the comparator 60 is supplied to an OR gate 61
Is input to one of the input terminals. The other input terminal of the OR gate 61 receives the speed setting signal (H) / (L). The OR gate 61 outputs an L signal only when both input signals are L signals, and otherwise outputs an H signal. When the output signal of the OR gate 61 is an L signal, the brake 43 is turned on via the buffer 62 and
In the case of a signal, the brake 43 is turned off.

Next, a control operation of the motor M3 realized by the above configuration will be described with reference to FIG. (A) of FIG.
FIG. 5B shows a timing chart of switching of various signals, and FIG. 5B shows a change in the number of revolutions of the motor M3 corresponding to the timing chart.
When a start (L) signal (not shown) for instructing activation of the motor M3 is output from the main control unit 90 and the speed setting signal is set to an H signal (b1), the motor M3 sets the reference rotation speed X1 to It is started as the target rotation speed (e1). Until the detected rotation speed converges to the reference rotation speed X1, the lock signal from the controller 51 becomes an H signal.
2), the selector 56 selects the pulse signal from the FG and outputs it to the FV converter 52. As a result of the control by the FG,
When the detected rotation speed converges to the reference rotation speed X1, the lock signal changes from the H signal to the L signal (d2), and accordingly, the control of the motor M3 shifts from the FG to the encoder 44.
During this time, the signal output from the comparator 60 switches from the H signal to the L signal when the rotation speed of the motor M3 passes through X3 (e2) (a2).

Next, the main control unit 90 sets the reference rotational speed X
When the speed setting signal is switched from the H signal to the L signal at a predetermined timing (this timing will be described later) in order to reduce the speed from 1 to X2 (b2), both the input signals to the OR gate 61 become the L signal. Therefore, the output signal of the OR gate 61 is switched to the L signal (c1). As a result, the brake 43 is turned on, and the forcible deceleration of the motor M3 by the brake 43 is started (e4).

By the forcible deceleration by the brake 43 and the deceleration by the energization control of the driver unit 55, the motor M
When the rotation speed of No. 3 falls below the reference rotation speed X3 (e5), the output signal of the comparator 60 switches from the L signal to the H signal (a3). As a result, the output signal of the OR gate 61 is switched from the L signal to the H signal (c2), and accordingly, the brake 43 is turned off, and thereafter the deceleration until reaching the reference rotational speed X2 is exclusively performed by the driver 55 Is performed by the energization control.

As described above, when decelerating from the reference rotational speed X1 to X2, the brake 43 is turned off before the detected rotational speed reaches the target X2 (when the detected rotational speed falls below X3), and forced deceleration is performed. It is canceled for the following reasons. That is,
Assuming that the deceleration by the brake 43 is performed until the detected rotational speed reaches X2, the detected rotational speed changes as indicated by a dashed line in FIG. It takes extra time to converge on. Therefore, by performing the above, excessive deceleration is reduced, as a result, the convergence of the rotational speed is improved, and the time required from the start of deceleration to stabilization at the target rotational speed X2 is reduced as much as possible. is there.

When the speed setting signal switches from the H signal to the L signal (b2), the lock signal switches from the L signal to the H signal (d3). Accordingly, the control of the motor M3 is controlled by the encoder 44 to the FG. Move to When the detected rotation speed converges to the reference rotation speed X2 (e6), the lock signal switches from the H signal to the L signal (d4), and accordingly, the control of the motor M3 shifts from the FG to the encoder 44.

The reason for selectively using the encoder 44 and the FG is as follows. A speed reducer 4 is provided between a motor M3 as a driving source and a driving roller 38 to be driven.
Therefore, even if the motor M3 is rotated at a constant speed, vibration caused when the gears of the speed reducer 40 mesh with each other and machining accuracy errors of the components of the power transmission mechanism including the gears are reduced even if the motor M3 is rotated at a constant speed. As a result, rotation unevenness occurs in the drive roller 38. Therefore, when it is necessary to rotate the drive roller 38 at a constant speed, that is, when the transfer of the toner image to the recording sheet and the fixing of the toner image by the fixing device 11 are performed, the drive is performed. Rotary shaft 3 of roller 38
The rotation speed of the drive roller 38 is directly detected using the encoder 44 that detects the rotation speed of 8 s, and the detection result is fed back to control the rotation speed of the motor M3.

On the other hand, if the encoder 44 is used to control the acceleration or deceleration of the motor M3, such as when the motor M3 is started or when the speed is changed, the motor M3 to be controlled and the encoder serving as detection means are used. 44, the response of the detection means to the control amount is delayed. As a result, the motor M3 does not over-accelerate or over-decelerate once it reaches the target rotational speed. It repeats, and it takes time to converge to the reference rotational speed.

Therefore, when the motor M3 is controlled to be accelerated or decelerated, such as when the motor M3 is started or when the speed is switched, the rotation speed of the output shaft of the motor M3 to be controlled is detected. Therefore, an FG having a small delay in response to the control amount is used. as a result,
The time from the start of the motor M3 or the switching of the set speed to the convergence to the target reference rotational speed is shorter than in the case where the encoder 44 is used.

Next, the control contents of the motor M3 of the main control unit 90 will be described based on the flowchart shown in FIG.
This will be described with reference to FIG. The flowchart shown in FIG. 6 is a flowchart of a program executed when special paper is selected by the paper type selection key on the operation panel 45. When the copy start key is pressed (Yes in step S1), the main control unit 90 outputs a start signal (L), turns on the motor M3 (step S2), and sets the speed setting signal to an H signal. (Step S3). As a result, the motor M3 rotates at the reference rotation speed X1, and the transport belt 10 runs around at the system speed. In this state, when the leading end of the recording sheet conveyed by the conveyance belt 10 is detected by the sensor 46 (Yes in step S4), the main control unit 90
An internal timer (not shown) is started after resetting (step S5).

When the timer counts the predetermined time p1 (Yes in step S6), that is, when it is determined that the rear end of the recording sheet has passed through the transfer position immediately below the photosensitive drum 3, the main control unit 90 The speed setting signal is switched to the L signal (step S7). Accordingly, the deceleration of the motor M3 by the brake 43 is started. Subsequently, when the trailing edge of the recording sheet is detected by the sensor 46 (Yes in step S8), the internal timer is reset and started (step S9).

When the timer counts a predetermined time p2 (Yes in step S10), that is, when it is determined that the rear end of the recording sheet has passed through the fixing device 11, the main control unit 90 operates the operation panel 45 and the like. It is determined whether or not copying of the number of sheets designated from has been completed (step S1)
1). Thereafter, until the specified number of copies have been completed,
Steps S3 to S10 are repeated, and when the specified number of copies have been completed (Yes in step S11), a stop signal (H) is output to turn off the motor M3 (step S12), and the program ends.

When plain paper is selected with the paper type selection key on the operation panel 45, another program for controlling the motor M3 is started. In that case, the copy start key is pressed. Until the designated number of copies is completed after the completion, the motor M3 is controlled to the reference rotation speed X1, and the conveyor belt 10 runs around at the system speed throughout.

The conveyance speed of the recording sheet by the fixing device 11 is the system speed (first speed) throughout when the plain paper is selected by the paper selection key, and when the special paper is selected. , Is controlled to the second speed throughout.
Therefore, when the special paper is selected, the recording sheet fed out from the registration roller 37 at the system speed is first conveyed by the conveying belt 10 which runs around at the system speed, and the conveyed sheet includes:
At the transfer position immediately below the photoconductor drum 3, a toner image is transferred from the photoconductor drum 3. The recording sheet is transported at the system speed even during the period from the sheet cassette to the registration rollers 37.

When the trailing edge of the recording sheet passes through the transfer position, the brake M 43 is braked by the brake 43 in order to reduce the transport speed of the transport belt 10 to the second speed. When the trailing edge of the recording sheet has passed the transfer position, the distance from the leading edge of the recording sheet to the fixing device 11 is small. Since the transport speed of the transport belt 10 does not decrease to the second speed before the leading end enters the fixing device 11, the brake 43 is forcibly decelerated. That is, the transport belt 1
When the recording sheet rushes into the fixing device 11 without the conveyance speed of 0 being completely reduced to the second speed, the recording sheet bends due to a speed difference between the conveyance speed by the fixing device 11 and the conveyance speed by the conveyance belt, and is undetermined. There is a risk that unstable toner may be peeled off from the recording sheet due to adhesion,
This is to avoid this. With the recent miniaturization of image forming apparatuses, the distance between the transfer position and the fixing position tends to be reduced, and the present invention is particularly effective for such an image forming apparatus.

By the braking of the brake 43, the fixing device 11
The recording sheet (special paper), which has been decelerated to the second speed before reaching, is supplied with heat while being conveyed by the fixing device 11 at the second speed, and the toner image on the recording sheet is fixed. As described above, according to the present embodiment, when special paper is used as a recording sheet, the recording sheet taken out from the paper supply cassette by the paper feeding mechanism is transferred to the transfer end immediately below the photosensitive drum 3. Until the sheet passes through the position, the sheet is conveyed at the system speed except when the sheet is temporarily stopped by contacting the registration roller 37. After that, the conveyance speed of the recording sheet is the second speed lower than the system speed (first speed) until the leading end of the recording sheet enters the fixing device 11.
(The transport speed of the recording sheet by the fixing device 11 when the recording sheet is special paper) is forcibly decelerated by the brake 43. Therefore, the fixing of the toner image on the special paper is reliably performed.

Further, the processing time required for one recording sheet can be reduced as compared with the case where the recording sheet is conveyed at the second speed immediately after being fed out of the sheet feeding cassette as in the related art. Further, since the braking by the brake 43 is released shortly before reaching the second speed which is the target transport speed, the motor M which is the drive source of the transport is released.
3, the convergence to the target rotation speed is accelerated, and as a result, the time from the start of deceleration to the arrival at the target speed (convergence) is reduced.

Although the present invention has been described based on the embodiment, it goes without saying that the present invention is not limited to the above embodiment. (1) In the above embodiment, the driving source (motor M3) of the transport belt 10 and the driving source (motor M4) of the fixing device 11
Are provided separately, but a single power source may be commonly used by using an appropriate power transmission mechanism. (2) In the above embodiment, the sensor 4 detects that the trailing edge of the recording sheet has passed the transfer position.
It was determined that a predetermined time had passed since the detection in step 6. This is a method adopted because the leading edge of the recording sheet cannot be directly detected due to a short distance from the leading edge of the recording sheet to the fixing device 11 when the trailing edge of the recording sheet has passed the transfer position. . Therefore, if there is a sufficient distance from the leading edge of the recording sheet when the trailing edge of the recording sheet has passed the transfer position to the fixing device 11, the leading edge of the recording sheet at that time is detected. In such a case, the rear end of the recording sheet may be regarded as passing through the transfer position. (3) In the above embodiment, the FG is used as the tachometer for directly detecting the rotation speed of the motor M3, and the rotary encoder is used as the tachometer for detecting the rotation speed of the drive roller 38. The invention is not limited to this, and another type of tachometer may be used. (4) In the above embodiment, the electromagnetic clutch / brake is used to decelerate the motor M3. However, the deceleration means is not limited to this, and other band brakes, disk brakes, energy recovery brakes, etc. may be used. Further, in the above embodiment, the output shaft of the motor M3 is braked. However, other parts of the power transmission mechanism may be braked, or the drive roller 38 may be braked. .

[0048]

As described above, according to the image forming apparatus of the present invention, when special paper is used as a recording sheet, for example, after the rear end of the recording sheet has passed through the toner image forming means, After the toner image is formed on the recording sheet and before the leading edge of the recording sheet reaches the fixing unit, the transport speed is reduced. As compared with the case where the recording sheet is conveyed, the processing time required for one recording sheet can be reduced. In addition, since the fixing of the toner image can be performed at the reduced conveyance speed, the fixing property of the toner image can be secured.

According to the recording sheet conveying speed control method of the present invention, for example, when special paper is used as the recording sheet, when the passage of the toner image forming means at the rear end of the recording sheet is detected, When the formation of the toner image on the recording sheet is completed, the target rotation speed of the motor that is the drive source of the recording sheet conveying means is switched from the first rotation speed to a second rotation speed lower than the second rotation speed. Approximately at the same time, the braking of the motor is started. This makes it possible to reduce the transport speed of the recording sheet to the second speed before the recording sheet reaches the fixing unit. Therefore, as before,
Even when the recording sheet is conveyed at the second conveyance speed during the formation of the toner image, the required processing time per recording sheet can be reduced. In addition, since the braking of the motor is released when the third rotation speed takes a value between the first rotation speed and the second rotation speed, excessive deceleration due to the braking is prevented, and the second rotation speed of the motor is prevented. Converges quickly to the rotation speed of the motor, and as a result, the time from the start of deceleration to the end of deceleration (convergence to the second rotation speed) can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a digital copying machine according to an embodiment.

FIG. 2 is a diagram showing a schematic configuration of a driving mechanism of a transport belt in the copying machine.

FIG. 3 is a diagram schematically illustrating a configuration of a control unit that mainly controls a conveyance belt driving motor and a brake in the copying machine.

FIG. 4 is a diagram illustrating a detection abnormality determination process of an encoder in the copying machine.

FIG. 5 is a diagram for explaining a control operation of a transport belt driving motor in the copying machine.

FIG. 6 is a flowchart of a control program for a conveyance belt driving motor of a main control unit in the copying machine.

[Explanation of symbols]

 Reference Signs List 3 photosensitive drum 6 transfer charger 10 transport belt 11 fixing device 38 drive roller 39 driven roller 43 electromagnetic clutch / brake 44 rotary encoder 46 sensor 50 control unit 90 main control unit M3 motor

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 2H027 DA16 DC04 DC05 ED16 EE03 EE04 2H033 AA20 BA08 CA22 CA36 2H072 AA16 AA24 AB09 CA05 HA07 HA08 3F049 EA04 EA10 EA13 EA14 EA24 LA02 LB03 9A001 HH34 JJ35 KK35

Claims (4)

[Claims] A conveying unit configured to convey the recording sheet; a toner image forming unit configured to form a toner image on the conveyed recording sheet; a fixing unit configured to fix the formed toner image to the recording sheet; An image forming apparatus comprising: a decelerating unit that reduces a conveying speed of the conveying unit before a leading end of the recording sheet reaches the fixing unit after a rear end of the recording sheet passes through the toner image forming unit. . 2. The apparatus according to claim 1, wherein the conveying unit receives a power from the motor, applies a conveying force to the recording sheet and applies a conveying force to the recording sheet, and transmits the power of the motor to the conveying force operating unit. The image forming apparatus according to claim 1, further comprising: a power transmission unit configured to perform the power transmission, wherein the deceleration unit includes a brake device that acts on the power transmission unit and brakes the motor. 3. The image forming apparatus according to claim 1, further comprising: setting the target rotation speed of the motor to a first rotation speed corresponding to a first transfer speed and a second transfer speed lower than the first transfer speed. Motor control means for switching control between a second rotation speed and a detection means for detecting the rotation speed of the motor, wherein the motor control means sets a target at almost the same time as the start of braking by the brake device. The rotation speed is changed from the first rotation speed to the second rotation speed.
And the speed reducing means detects that the number of rotations detected by the detecting means is the second number.
3. The image forming apparatus according to claim 2, wherein the braking by the brake device is released shortly before the rotation speed of the image forming apparatus reaches the rotation speed. 4. A recording sheet is conveyed by conveying means using a motor as a drive source, a toner image is formed on the conveyed recording sheet by a toner image forming means, and the toner image is fixed by a fixing means to form an image. A method for controlling a transport speed of a recording sheet by said transport means in an image forming apparatus to be formed, wherein a target rotational speed of said motor is set to a first rotational speed.
And a second step of detecting the passage of the toner image forming means at the rear end of the recording sheet. If the passage of the toner image forming means at the rear end of the recording sheet is detected, the target rotation speed of the motor is set to the first. A third step of switching to a second rotation number lower than the rotation number of the motor; a fourth step of starting braking of the motor at substantially the same time as the switching of the rotation number; A fifth step of detecting reaching a third rotation speed that takes a value between the rotation speed and the second rotation speed, and, when the third rotation speed is detected, releasing the braking on the motor. A method for controlling a conveyance speed of a recording sheet in an image forming apparatus, comprising: a sixth step.