JPH0437972B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for correcting the position of a projection lens in a scanning exposure type copying machine that changes the copying magnification by changing the position of the projection lens and changing the scanning speed.

PRIOR ART In a copying machine having a plurality of magnifications, the positioning of the variable magnification system is often performed by providing means for detecting the position of the variable magnification system according to each magnification. In addition, when there are many magnifications, providing a large number of detection means complicates the apparatus, and this is especially impossible for a copying machine that can be set steplessly. In such a case, a method is known in which a detector is provided only at the position of the reference magnification and the other positions are controlled by relative distances from that position. In such a configuration, magnification accuracy is largely dependent on the position of the detector. However,
The positioning of the detector is delicate and manual adjustment is extremely difficult. Conventionally, as a countermeasure, a method has been used in which the deviation of the detector is measured as a magnification error and corrected. This method requires manual magnification measurement, which requires complicated work. Furthermore, automation using a jig or the like is extremely difficult in this method.

Purpose The present invention has been made in view of the above circumstances, and its purpose is to enable accurate positioning of the projection lens of a variable magnification system with simple operations without requiring highly accurate positioning of the detector. An object of the present invention is to provide a method for correcting the position of a projection lens.

Summary The present invention is a method for positioning a projection lens in a scanning exposure type copying machine that moves the projection lens when changing the copying magnification, comprising: a detection means for detecting the position of the projection lens; The amount of movement when the lens is moved from a position corresponding to the reference magnification determined by the detection means until it is detected by the detection means is stored as a correction value, and based on the stored correction value, the projection lens is moved to a position corresponding to the reference magnification. The position when the projection lens is moved to is set as the reference magnification position for controlling the movement of the projection lens.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 schematically shows an example of a scanning exposure type copying machine according to the present invention. A photoreceptor drum 1 that can be rotated counterclockwise is disposed approximately in the center of the copying machine body, and around it are a main eraser lamp 2, a sub-charger 3, a sub-eraser lamp 4, and a main charger 5. , a microtoning type developing device 6, a transfer charger 7, a copy paper separation charger 8, and a blade type cleaning device 9 are provided. Photoreceptor drum 1 is on the surface
A Cds/nCdCO ₃ resin binder photoreceptor is provided, and this photoreceptor is sensitized and charged by passing through the eraser lamps 2 and 4 and charging chargers 3 and 5, and receives image exposure from an optical system 10.

The optical system 10 is installed below the original glass 16 so that the original image can be scanned, and includes a light source (not shown).
Movable mirrors 11, 12, 13 and projection lens 14
and a mirror 15. The light source and the movable mirror 11 have a circumferential velocity v of the photosensitive drum 1.
(constant regardless of magnification or variable magnification) vs. (v/
The movable mirrors 12 and 13 move to the left at a speed of (v/2n). Note that changing the copy magnification involves moving the projection lens 14 on the optical axis and moving and swinging the mirror 15, but such a variable magnification system will be described in detail later.

Reference numeral 60 denotes a DC motor incorporating an encoder (not shown), and a scanning system 61 including movable mirrors 11, 12, 13 and a light source is driven by this DC motor 60 to reciprocate. A home switch 62 detects whether the scanning system 61 is at the home position, that is, the scanning start position. A brake switch 63 determines the braking timing when the scanning system 61 moves backward.

On the other hand, paper feed units 20 and 22 each having paper feed rollers 21 and 23 are installed on the left side of the copying machine body, and the copy paper conveyance path includes a pair of rollers 24 and 25, a pair of timing rollers 26, and a conveyor belt 27. , a fixing device 28, and a pair of discharge rollers 29.

Next, a variable magnification system for changing the copy magnification will be explained with reference to FIG. This variable magnification system allows you to select stepless magnification from enlargement to reduction, specifically from enlargement (×1.4) to normal magnification (×1).
The magnification can be selected as appropriate up to reduction (×0.64).

The variable power system generally includes a lens moving mechanism 35, a mirror moving mechanism 40, a mirror swinging mechanism 55, and a stepping motor 30 that drives these.

The lens moving mechanism 35 has the projection lens 14 movably mounted on a guide rail 36 installed parallel to the optical axis, and a drive wire 37 wound around a drive pulley 32 fixed to the output shaft 31 of the stepping motor 30. is stretched around rotatable pulleys 38, 38, and the intermediate portion of the drive wire 37 is fixed to the side of the projection lens 14. Therefore,
By rotating the stepping motor 30 in the forward and reverse directions at a predetermined rotation speed, the drive wire 37 is rotated in the forward and reverse directions via the drive pulley 32, and the projection lens 14 is rotated along the guide rail 36 on the optical axis as shown in FIG. It moves left and right and stops at a position according to the magnification. A light shielding plate 64 is attached to the projection lens 14 , and this light shielding plate 64 blocks the light transmitted from the light emitting part to the light receiving part of the photo interrupter 65 for detecting the position of the projection lens 14 .
4 position is detected.

The mirror moving mechanism 40 has a guide shaft in which the mirror 15 is fixed on the back side to a shaft 43 rotatably supported by a moving body 41, and side pieces 42 of the moving body 41 are set parallel to the optical axis. 45, and a rotatable roller 44 provided at the end of the shaft 43 is placed on an auxiliary guide rail 46. Further, the periphery of the movable drive cam 53 comes into contact with a pin 50 provided on the movable body 41 via a bracket 49, and the movable body 41 is attached to the cam 53 side by a coil spring 48 whose one end is fixed to the pin 47. Forced. Output shaft 31 of the stepping motor 30
A gear 33 fixed to is engaged with a gear 52 fixed to one end of a support shaft 51, and the cam 53 is fixed to the other end of the support shaft 51.

Therefore, the rotation of the stepping motor 30 is transmitted from the gear 33 to the cam 5 via the gear 52 and the support shaft 51.
3, the movable body 41, that is, the mirror 15 moves back and forth on the optical axis according to the peripheral surface shape of the cam 53,
Correct the path length due to the change in magnification. That is, the projection lens 14 and mirror 15 are driven in conjunction with each other by the stepping motor 30 as the magnification is changed. In the embodiment of the present invention, the rotation amount of the stepping motor 30 can be continuously adjusted in order to perform stepless magnification, but if this is done step by step, a mechanism for selecting several types of magnification will be required. can do.

On the other hand, the mirror swinging mechanism 55
The circumferential surface of a swing drive cam 57 fixed to a rotatable support shaft 56 provided in the coil spring 5 is brought into contact with the back surface of the mirror 15, and the mirror 15 is wound around the shaft 43.
A pinion gear 59 fixed to a support shaft 56 is engaged with a rack 60 attached to the main body of the copying machine, and the rack 60 extends parallel to the guide shaft 45. . This mirror swinging mechanism 55 corrects the deviation of the exposure point where the optical axis of the light beam reflected by the mirror 15 hits the photoreceptor drum 1 by simply moving the mirror 15 when changing the magnification. At this time, the mirror 15 is also swung so that the optical axis is directed to the same exposure point. That is, when the movable body 41 moves back and forth in accordance with the change in magnification, the pinion gear 59 rolls on the rack 60 and the cam 57 rotates together with the support shaft 56.
The mirror 15 is attached to the shaft 43 according to the circumferential shape of the cam 57.
The exposure point is corrected by swinging around the fulcrum.

In this case, the swing angle of the mirror 15 is positioned such that the optical axis of the light beam reflected by the mirror 15 is directed toward the center of the photoreceptor drum 1 at maximum magnification (in this embodiment, at the time of magnification), and at smaller magnifications. The optical axis is adjusted so that it points to the same exposure point as the exposure point at maximum magnification. Since the slit-shaped image is enlarged and projected, the optical axis at the maximum magnification, where the distortion of the exposed image appears most conspicuously, is incident perpendicularly to the photoreceptor drum 1, thereby reducing the overall deviation of the angle of incidence. This makes distortion of the exposed image less noticeable.

Note that if there are three types of magnification (×1), (×0.8), and (×0.7), the maximum magnification is at the same magnification (×1), so the optical axis at the same magnification is perpendicular to the photoreceptor drum 1. Inject it into the In this case, distortion is most likely to occur when the magnification is changed to (×0.7), but the slit width in the exposed area is narrowed and the image itself is also reduced, so the distortion is hardly noticeable.

Further, the driving of the stepping motor 30 is controlled by a digital signal, and the amount of change in magnification per step is a value divisible by an integer. In addition,
It is also possible to perform analog control using a normal motor as the motor.

FIG. 3 shows a control circuit for controlling only the scanning system and variable magnification system.

A microcomputer 70 plays a central role in control, and a microcomputer 80 (hereinafter referred to as master) controls other processes of the copying machine.
operates in sync with. SCAN is a signal for synchronizing the microcomputer 70 with the master 80, and is output by the master 80 at the timing of document scanning in synchronization with other processes of the copying machine. MAG is a signal representing the copying magnification, and the microcomputer 70 drives the scanning system at a speed corresponding to the copying magnification MAG. An encoder 71 is arranged on the rotating shaft of the DC motor 60 and generates pulses with a period corresponding to the number of rotations of the DC motor 60. The pulses from the encoder 71 are waveform-shaped by a waveform shaping circuit 72 and input to the microcomputer 70, and the speed of the scanning system is detected from the pulse interval of the encoder pulses. A reference oscillator 73 emits fixed frequency pulses to the microcomputer 70 for measuring the pulse interval of the pulses from the encoder 71. The microcomputer 70 uses an internal counter to count the fixed frequency pulses generated within the pulse interval of the encoder pulses, and uses the counted value to control the DC motor 6.
0 rotation speed, that is, the speed of the scanning system 61 is calculated. 74 is a D/A converter and an amplifier circuit that converts the digital amount of electricity calculated by the microcomputer 70 into an analog amount and supplies it to the DC motor 60. 75 is a stepping motor 30
This is the drive circuit. The switch LADJ 76 is a switch for setting a correction value for the position of the photo interrupter 65 for detecting the position of the projection lens, and is composed of a plurality of dip switches.

Here, a stepping motor 30 for driving the projection lens of the variable magnification system and a DC motor 60 for driving the scanning system are used.
An overview of the control method will be explained below.

Stepping motor 30 that drives the projection lens
The control system is an open type, as shown in Figure 3.
The stepping motor 30 rotates by an angle proportional to the number of pulses output from the microcomputer 70. The stepping motor follows external pulses within a range called a self-starting region, and as the frequency of the pulses increases, the torque of the stepping motor decreases.
Therefore, as shown in Figure 4, a method is generally used in which the pulse frequency is gradually increased at a constant rate when starting up, and the pulse frequency is gradually lowered at a constant rate when stopping. . This method is also used in this embodiment, and the pulse frequency is changed as shown in FIG. 5 according to the total number of steps, so that driving of the projection lens is completed in the shortest possible time.

FIG. 6 shows a timing chart during constant speed control of the DC motor 60 for driving the scanning system. The encoder 71 is rotated by the DC motor 60 for driving the scanning system.
A pulse corresponding to the number of rotations of the motor 60 is outputted from the motor 60 , and this pulse is waveform-shaped by a waveform shaping circuit 72 and inputted to an external interrupt terminal INT of the microcomputer 70 . When the microcomputer 70 detects the rising edge of this encoder pulse, it executes an external interrupt processing routine.
INT-E is activated. In the external interrupt processing routine INT-E, the reference time T inside the microcomputer is sampled and the current time is
Get Tc. This time Tc is compared with the time T _E when the rising edge of the previous encoder pulse occurred, and the current encoder pulse interval T _I is calculated. Once the pulse interval T _I is calculated, the time
T _C is stored in register T _E as the updated time T _E. On the other hand, the pulse interval T _I is compared with the pulse interval T _S of the encoder corresponding to the set rotational speed of the motor, and the sum of the difference multiplied by a constant and the bias value Po proportional to the friction of the mechanical system is the motor 60
The amount of current P is output to the terminal Pout. By performing the above processing every rising edge of the encoder pulse, the motor 60 is maintained at the set rotational speed. What you need to be careful about here is that
The pulse interval cannot be measured unless the rising edge of the encoder pulse occurs at least twice.
Unable to calculate difference. Therefore, in this embodiment, it is assumed that the motor is stopped at this time, and the energization amount is outputted as a difference with the maximum value Pmax.

The microcomputer 7 is shown in FIGS. 7 to 16.
0 shows a flowchart of the program. below,
The details of the processing procedure of the microcomputer 70 will be explained with reference to this flowchart.

FIG. 7 is a flowchart of the main routine.
First, when the power is turned on, the internal parameters are initialized in steps, and then the subroutine
The variable magnification system is returned to the reference position (in this embodiment, the same magnification position) by LREST (step). next,
It is checked whether there is a magnification input from the master 80 (step), and if there is a magnification input, the magnification is read into the magnification register M (step). Then, the variable magnification system is set according to the magnification register M by subroutine LSET(M). (step). After setting the variable magnification system, test the scanning timing signal SCAN from the master 80 (step, if the signal SCAN is "1", start scanning,
If SCAN is "0", the process returns to checking the magnification input. When the signal SCAN is "1", first, the pulse interval of the encoder at the scanning speed corresponding to the magnification set in the magnification register M is set in the pulse interval reference register T _S (step). This pulse interval T _S is a value obtained by multiplying the pulse interval T _O of the encoder at the same scanning speed by the magnification M.
After setting the scanning speed, subroutine START executes two interrupt processing routines for speed control.
INT-T and INT-E are activated (step). As a result, from now on, the scanning speed is kept constant by the interrupt processing routine, regardless of the main routine. Then, in the main routine, SCAN
A check is performed (step). When the scanning end timing is reached, the master 80 sends the SCAN
is set to "0". In the main routine, the signal
When it is detected that SCAN is "0", the interrupt processing routine for speed control is stopped by the subroutine STOP, and the scanning is ended (step).

When the scanning is completed, control is performed to return the scanning system to the scanning starting position. In return control, the scanning system is returned at the maximum speed without performing speed control, so the negative maximum value is set as the amount of current to the motor.
Output Pmax (step). Thereafter, the scanning system performs a return operation at maximum speed, and when it returns to the position of the brake switch 63, which determines the timing of starting the side, the main routine detects that the brake switch is "1" (step).
The scanning system starts decelerating operation. The deceleration is performed by the acceleration in the scanning direction obtained by outputting (stepping) a positive output _PBRK as the amount of current applied to the motor. The output of _PBRK continues until the scanning system returns to the scanning start position and the home switch 62 becomes "1" (step). The position of the brake switch 63 and the amount of energization _PBRK are set to maintain a certain speed even when the scanning system returns to the scanning start position, and the energization is cut off when the scanning system returns to the scanning start position. (Step) The scanning system is smoothly stopped by a damper (not shown) provided at the scanning start position.

Then, the process returns to waiting for magnification input (step).

As described above, the main routine controls a series of operations such as receiving data from the master 80, setting the variable magnification system, and scanning.

Below, a subroutine for actually performing lens movement and speed control and an interrupt processing routine will be explained.

FIG. 8 is a flowchart of the subroutine STEP for controlling the driving of the stepping motor 30. This subroutine STEP requires the number of steps L of the stepping motor, the acceleration A of the step speed, and the step direction D as arguments. The subroutine STEP first checks the number of steps L (step 〓〓), and ends if the remaining number of steps L is zero. If the step number L is not zero, 1 is subtracted from the step number L (step 〓〓). Depending on the step direction D (step 〓〓), the phase of the current stepping motor drive pulse is
PHASE is phase-shifted (Step 〓〓, 64'), and the phase PHASE of the current drive pulse is determined and outputted to the drive circuit 75 (Step 〓〓). Then, the step interval corresponding to the current step speed RATE is tabled.
Determine it from DELAY and set it in temporary memory register REG ₁ (Step 〓〓). And the register
1 is subtracted from register REG ₁ until REG ₁ becomes zero, and the process waits for a time corresponding to the step interval (steps 〓〓, 〓〓). After the waiting time is over, the next step speed is determined by adding the acceleration A to the step speed RATE (step 〓〓), and the process returns to the beginning.

By repeating the above procedure, the stepping motor rotates in the step direction D by the number of steps L, with acceleration, deceleration, or constant speed depending on the acceleration A.
Drives the variable magnification system. The acceleration or deceleration pattern is set in the table DELAY. In this embodiment, a speed pattern as described in FIG. 5 is set.

FIG. 9 is a flowchart of the subroutine LREST for determining the reference position of the variable magnification system when the power is turned on. Here, a photo interrupter for detecting the position of the projection lens is placed at the temporary same-magnification position as the reference position.
LHOME is provided. subroutine
At the beginning of LREST, the step speed RATE of the stepping motor and the phase PHASE of the drive pulse are initialized (step). Next, the photo interrupter LHOME is used to check whether the variable power system is currently located on the reduction side or the enlargement side from the reference position (step). If the photo interrupter LHOME is "L" and the variable magnification system is on the reduction side, the stepping motor is driven in the enlargement direction (step). At this time, since the number of steps to the reference position is unknown, the stepping motor is driven one step at a time at a low and constant speed, and the photo interrupter LHOME is set to "H" to move the projection lens.
Move it to the enlarged side. When the projection lens moves to the enlargement side, it is moved one step at a time at a slow and constant speed toward the reduction side until it reaches the same magnification position on the reduction side (step). If the variable magnification system is on the enlargement side when the power is turned on, only the step to the reduction side is performed. This is because in position control using a stepping motor, the set positions are discrete, so the next position when the photo interrupter LHOME changes from "H" to "L" (step 〓〓) is used as the reference position. be. It also has the effect of eliminating the effects of mechanical system hysteresis such as gear backlash.

Through the above processing, the projection lens is set to a temporary 1x position. Next, the predetermined position correction value LADJ is input as the number of steps L (Step 〓〓), and the projection lens is moved to the true same-magnification position (Step 〓〓). That is, a correction value LADJ is set for the installation position of the photo interrupter LHOME, and the projection lens is moved in accordance with this correction value LADJ to position the projection lens at the true 1:1 magnification position. Here, it is assumed that the correction value LADJ is always determined to be a correction toward the reduction side.

Finally, the absolute position of the projection lens corresponding to the standard magnification of equal magnification is determined by the function f of the magnification and the position of the projection lens, and is substituted into the register LPOS indicating the current position of the projection lens (Step 〓〓). .
Thereafter, the projection lens is positioned by moving it relative to this position LPOS.

The above-mentioned position correction value LADJ can be easily obtained as follows. First, the projection lens is set to the true 1x position using the image back-projected from the photosensitive drum 1 onto the document surface. Other jigs may be used for this purpose. Next, the photo interrupter LHOME for detecting the position of the projection lens is set at an appropriate position on the magnification side. This position may be a completely fixed position as long as it is on the magnification side of the range of variation in the position of the projection lens 14 adjusted to the true 1:1 magnification position. next,
The projection lens 14 is moved to the magnification side by the stepping motor 30 for driving the projection lens, the number of steps up to the photo interrupter 65 is measured, and this value is set in the switch LADJ 76.

This measurement is performed in an extremely short time.

Normally, if the projection lens position shifts by 0.1mm, it will be approximately 1/1
This results in a magnification error of 000. Manual position adjustment of 0.1 mm is extremely difficult, but according to the present invention, there is no need for highly accurate positioning of the photo interrupter, and by setting the correction value, magnification accuracy can be adjusted extremely quickly and easily. It becomes possible to guarantee the following.

FIG. 10 shows a program for a jig for determining the position correction value LADJ. First, the step speed RATE of the stepping motor and the phase of the drive pulse are
PHASE and temporary correction value C are initialized (steps 100 and 101). Next, the lens is driven one step toward the enlargement side (step 102), and it is checked whether the level of the photo interrupter LHOME has become "H" (step 103). photo interrupter
If LHOME is not "H", 1 is added to the temporary correction value C (step 105), and the drive is driven one step again (step 102). Photo interrupter LHOME
If the value is "H", the provisional correction value C is displayed (step 104). This displayed provisional correction value C is set with the dip switch (LADJ). The jig includes a microcomputer (not shown) that processes a jig program separately from the copying machine main body. Incidentally, in step 104, the correction value C may be directly set in the register LADJ that stores the position correction value.

11 and 12 are subroutines for moving the projection lens to a specified magnification.
First, the absolute position corresponding to the specified magnification M
Find LDIST (step). Then, from the difference between the current position LPOS and the absolute position LDIST, the amount of movement is
Find SL3 as a relative value (step). At this time, if the difference is zero, the process ends. If the difference is not zero, the moving direction, ie, the stepping direction D of the stepping motor, is set depending on the sign of the difference (step 35'). At the same time, take the absolute value of the difference (Step 〓〓). Next, from this difference SL ₃ , subtract twice the maximum number of steps SL ₁ max in the acceleration region of the speed pattern of the stepping motor (step 〓〓, 〓〓), and if the current movement is a motion pattern with a constant speed region. Check if there is one (Step 〓〓).
If not, the number of steps in the constant speed region
SL ₂ is set to zero (Step 〓〓), half of the total number of steps is set as the number of steps in the acceleration region SL ₁ (Step 〓〓), and considering the case where the total number of steps is an odd number, the number of steps in the deceleration region SL ₃ is set. Find (step 〓〓).
Steps in the angular region of acceleration, constant speed, and deceleration SL ₁ , SL ₂ ,
When SL ₃ is determined, the subroutine STEP sequentially changes the acceleration of the step speed and moves the variable magnification system (steps 〓〓, 〓, 〓). lastly,
The absolute position LDIST after the movement is completed is substituted into the current position LPOS, and the current position of the projection lens is updated (Step 〓〓).

The flowcharts in FIGS. 13 to 16 are subroutines for controlling the DC motor 60 that drives the scanning system.

FIG. 13 shows a subroutine for starting constant speed control. First, in order to synchronize the encoder pulses of the motor 60 with the external interrupt processing routine, the number of encoder pulses required until the control of the amount of current supplied to the motor is started is set in the register SYNC (step <<>). Next, assuming that the motor is initially stopped, set the maximum amount of current to start it.
Output Pmax to the motor. Then, interrupts are enabled (step 〓). As a result, constant speed control is thereafter performed by the interrupt processing routine.

FIG. 14 shows a subroutine for stopping, which prohibits interrupts and sets the amount of current to zero.

Figure 15 shows the timer interrupt processing routine INT-
This is a flowchart of T. This timer interrupt processing routine INT-T is activated when the 8-bit hardware counter C of the microcomputer counts the reference oscillation pulses input to the external clock terminal ECK. In the timer interrupt processing routine INT-T, the count number 256 (=2 ⁸ ) of the counter C is added to the reference time T for measuring the pulse interval of encoder pulses, and the reference time T is updated. As a result, the current time, expressed as a reference oscillation pulse, is the reference time T plus the value of the counter C.

Figure 16 shows the external interrupt processing routine INT-E.
This is a flowchart. The external interrupt processing routine INT-E is activated when an encoder pulse is input to the external interrupt terminal INT of the microcomputer.

In INT-E, first, the current value of the counter C is added to the reference time T to find the current encoder pulse generation time Tc (step 〓〓). Then check the register SYNC and check the encoder pulse and
Check whether synchronization of INT-E is completed (step 〓〓). If the synchronization is not complete,
Subtract 1 from SYNC (step 〓〓) and store the time Tc at which the current encoder pulse occurred in register _TE (step 〓〓).

If synchronization has been completed, the pulse interval _TI is calculated by subtracting the previous encoder pulse generation time _TE from the encoder pulse generation time Tc (step 〓〓). Then, multiply the error between the pulse interval T _I and the encoder pulse interval T _S corresponding to the current set speed by a constant K to obtain the bias value according to the friction.
Add Po and calculate the amount of current P to the motor (Step 〓〓). After outputting the energization amount P (step 〓〓), the time _Tc at which the current encoder pulse was generated is stored in the register _TE (step 〓〓).

Effects As explained above, in the present invention, the projection lens positioned at the reference magnification position is moved to the position detected by the position detector, and this movement amount is used as a correction value to adjust the mounting position of the position detector. However, since the projection lens is positioned at the position that corresponds to the standard magnification, the projection lens does not require the complicated work of positioning the position detector with high precision by simply correcting the position using an electrical signal. can be accurately positioned at a position corresponding to a predetermined copying magnification.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic configuration of a copying machine according to the present invention, FIG. 2 is a plan view showing a variable magnification system of the copying machine, and FIG.
The figure is a block diagram showing the configuration of the control circuit that controls the scanning system and the variable magnification system. Figures 4 and 5 are graphs showing the drive pattern of the stepping motor that drives the variable magnification system. Figure 6 is a graph showing the drive pattern of the stepping motor that drives the variable magnification system. A timing chart showing the relationship between the amount of current applied to the DC motor to be driven and the encoder pulse, and FIGS. 7 to 16 are flowcharts of the microcomputer program. 14... Projection lens, 65... Photo interrupter.

Claims (1)

[Claims] 1. A method for positioning a projection lens in a scanning exposure type copying machine that moves the projection lens when changing the copying magnification, comprising: providing a detection means for detecting the position of the projection lens; The amount of movement from a position corresponding to a predetermined reference magnification until it is detected by the detection means is stored as a correction value, and the projection lens is moved to a position corresponding to the reference magnification based on the correction value. A method for positioning a projection lens, characterized in that the position when the lens is moved is set as a reference magnification position for controlling the movement of the projection lens.