JPH0220090B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a variable magnification image forming apparatus.

In a variable magnification image forming apparatus, such as a variable magnification electrophotographic copying machine, an original image is formed by changing the position of optical members such as lenses and/or mirrors that constitute an optical system that projects and forms an original image on a photosensitive surface. It is common to change the magnification of the image. One conceivable method is to control the amount of movement of the optical member as described above by counting the pulses generated by the pulse train generating means when changing the magnification, but even if the driving means is stopped after counting a predetermined number of pulses, , the optical member may deviate from its normal position corresponding to the selected magnification due to the inertial force of the optical member and stop, or the discrepancy between the number of pulses and the amount of rotation of the drive means may occur due to uneven rotation of the drive means, etc. A deviation from a predetermined relationship may occur, causing the optical member to deviate from the normal position and stop. In this way, as the magnification changing operation is repeated many times, the deviations described above accumulate, and it becomes impossible to form an original image of the required magnification on the photosensitive surface, or the focus state of the image goes out of the permissible range. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a variable magnification image forming apparatus that solves the above-mentioned disadvantages.

In order to achieve the above object, the present invention includes a lens that focuses an original image on a photoreceptor, and a pulse train generating means that generates pulses, and the number of pulses generated by the pulse train generating means is adjusted according to a change in magnification. In a variable magnification image forming apparatus that controls the movement of a lens by counting with a counter, a detection element that detects that the lens has reached a reference position, a magnification changing means that changes the magnification, and detection by the above-mentioned detection element. measuring means for measuring the time from time to input of a change signal by the magnification changing means; and comparing means for comparing a predetermined time set in advance with the time measured by the measuring means, the comparing means If it is determined that the time measured by the measuring means is longer than the predetermined time, the lens is moved to the reference position and the counter is set to a new pulse based on the detection signal from the detection element. The lens is reset to a new number of pulses, and by counting this new number of pulses, the lens is moved from a reference position to a predetermined position determined by a magnification changing means.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram of a variable magnification electrophotographic copying machine to which the present invention can be applied. In the figure, reference numeral 1 denotes a photosensitive drum having an electrophotographic photosensitive member on its circumferential surface, which rotates in the direction of the arrow. As the drum 1 rotates, it is first uniformly charged by a corona discharger 2, and then an optical image of a document O at a selected magnification is slit-exposed through a slit 3 by an optical system to be described later. The electrostatic latent image thus formed on the drum 1 is developed by the developing device 4, and a toner image is obtained. This toner image is then transferred under the action of a transfer corona discharger 5 to a transfer paper P that is conveyed in the direction of the arrow. This transfer paper P is then sent to a fixing device 6, and the transferred toner image is fixed on the paper P. On the other hand, the drum 1 after the transfer is cleaned by a cleaning device 7 and used again for the image forming process.

The original O is placed on a fixed transparent original table 8. This original O is illuminated by a lamp 9, and the light reflected from the original is reflected by mirrors 10, 11, 1.
2 are sequentially reflected and incident on the zoom lens 13.
The imaging light beam from the document exiting the zoom lens 13 exits the mirror 14 and enters the photosensitive drum 1 as described above, forming an optical image of the document O at a selected magnification. When the lens 13 is at the solid line position 13 ₁ in the figure, an m ₁ times image of the document is formed on the drum 1, and when the lens 13 is moved to the 13 ₂ position, an m ₂ times image is formed.
When moved to the ₁₃₃ position, an _m3 magnification image is formed.
Here, it is assumed that m ₁ > m ₂ > m ₃ . For convenience, in the example
Although the description will be made assuming that m ₁ =1, the present invention can also be applied to an apparatus that can copy an enlarged image of a document. Note that 13 ₄ is the reference position of the lens 13.

When the position of the zoom lens 13 is changed as described later, zooming is performed in conjunction with this, and the lens focal length is changed to a value corresponding to the new lens position, in other words, a value corresponding to the selected copy magnification. Ru.

Here, the optical path length l ₁ between the original and the lens, and the lens,
The sum of the optical path lengths l ₂ between the photoreceptors is 1 (l is constant),
If the imaging magnification of the original image (that is, the selected copying magnification) is m and the lens focal length is f, then l ₁ = l/m+1 l ₂ = ml/m+1 f=ml/(m+1) ² . The position and focal length of the lens may be changed in accordance with the selected magnification m.

The position shown in FIG. 1 is of the document scanning type. In order to scan the original, the mirror 10 is integrated with the lamp 9 in the direction of the arrow, and the circumferential speed of the drum 1 is multiplied by the reciprocal of the selected copying magnification, 1/m, in order to set the copying magnification in the direction of rotation of the drum to m. Moving forward at speed, mirrors 11 and 12
moves in the direction of the arrow at half the speed of the mirror 10 in order to keep the intersection length between the original and the lens constant. The original O is thus scanned, and its image is slit-exposed onto the drum 1. When scanning of the original is completed, members 9~
12 moves backward and returns to their respective forward movement starting positions.

FIG. 2 shows the movement and zooming mechanism of the lens 13. In the figure, 15 is the zoom lens 13.
It is a lens barrel with a built-in. This lens barrel 15 is fixed to a lens stand 16. Slide bearings 17 and 18 are fixed to the lens stand 16, and these bearings 17 and 18 are slidably fitted into a linear guide rail 19 fixed to a substrate 20. Therefore, the lens stand 16 on which the lens 13 is mounted can reciprocate under the guidance of the guide rail 19 in directions parallel to the guide rail (direction A, direction B). Note that the direction of the rail 19 and, therefore, the direction of movement of the lens 13 is inclined with respect to the optical axis This is to align the image of the document side edge to the reference position of the photoreceptor side edge. Therefore, in a copying machine in which the center of the document is placed at the center of the document table when copying at any magnification, and the image of the center of the document is formed at the center of the photoreceptor, the rail 19 is placed parallel to the optical axis X. You may.

Both ends 21' of the wire 21 are attached to the lens stand 16,
21'' is locked. The wire 21 is connected to the board 20
It is hung around pulleys 22 and 23 that are rotatably supported by shafts 22' and 23' fixed to the drive pulley 24, and is wound around a drive pulley 24 several times between the pulleys 22 and 23. This drive pulley 24 is connected to the shaft 2 through a torque limiter 25, an example of which is shown in FIG.
It is attached to 6. A worm wheel 27 is fixed to this shaft 26, and is engaged with a worm gear 28 fixed to an output shaft 30 of a motor 29. When the motor 29 rotates forward, the shaft 26 is rotated clockwise by the worm gear 28 and the worm wheel 27, and the torque limiter 25 rotates between the shaft 26 and the pulley 24.
When fixedly connected, this pulley 24 rotates counterclockwise, so the lens stand 16 on which the lens 13 is mounted is indexed by the wire 21 and moves in the direction of arrow A. Similarly, when the motor 29 reverses, the pulley 2
4 is rotated counterclockwise, and the lens stand 16 is indexed by the wire 21 and moved in the direction of arrow B.

A disk 31 as shown in FIG. 3 is fixed to the output shaft 30 of the motor 29. As shown in FIG. Therefore, this disc 31 rotates in synchronization with the shaft 26, and therefore, when the shaft 26 and the pulley 24 are fixedly connected by the torque limiter 25, as is clear from the above, the disc 31 rotates in synchronization with the shaft 26. rotates in synchronization with the movement of the lens stand 16 on which the lens 13 is mounted. Disk 31
As shown in FIG. 3, a large number of light-transmitting slits 31'' of equal width are provided at equal intervals on an opaque disk 31'. 32 is a photocoupler fixed to the substrate 20, and its light emitting The element section 32' and the light receiving element section 32'' are arranged with the slit forming area of the disk 31 sandwiched therebetween. Therefore, as the disc 31 rotates due to the operation of the motor 29, the emitted light from the light emitting element 32' periodically passes through the slit 31'', so the light receiving element 32'' periodically generates electric pulses. do. Therefore, the rotation angle of the shaft 26 that rotates during one pulse period of this pulse train is the same at any time, and therefore, the amount of movement of the lens stand 16 on which the lens 13 is mounted during the one pulse period is the same at any time. be. When the motor 29 is driven during the magnification changing operation, the lens 1
3 starts moving, and in synchronization with this, the above pulse train starts to be generated.As will be described later, the number of pulses is counted, and when the number of pulses corresponding to the selected magnification is counted, the motor 29 is started. This deenergizes and stops the lens movement. The lens 13 is thus moved by a distance corresponding to the selected magnification.

As mentioned above, the lens 13 is a zoom lens,
In the embodiment shown in FIG. 2, zooming of the lens is performed in conjunction with the lens movement. That is, the lens barrel 15 is provided with a cam hole 15'.
A pin 33 fixed to a focal length changing lens holding cylinder movably provided in the lens barrel 15 in the optical axis direction is engaged with and protrudes from the cam hole 15'. A zoom ring 34 is attached to the lens barrel 15 so that it does not move relative to the lens barrel 15 in the optical axis direction, but is rotatable about the optical axis X.
The zoom ring 34 is provided with a long hole 34'.
The pin 33 is engaged with this elongated hole 34'. Therefore, when the zoom ring 34 is rotated, the pin 33 moves along the cam hole 15', thereby changing the distance between predetermined lens elements within the lens barrel 15. The focal length also changes. The mechanism for rotating the zoom ring 34 is as follows.

That is, the wire 34 is wound around the zoom ring 34 once to several times. 36 is a wire support member slidably attached to the lens stand 16, one end 35' of the wire 35 is locked to one end of the support member 36, and the other end 35'' of the wire 35 is used to prevent loosening. Support member 36 via tension spring 37
is connected to the other end. A linear guide rod 38 extending perpendicular to the optical axis X is fixed to this support member 36, and this rod 38 is slidably inserted into slide bearings 39, 40 fixed to the lens stand 16. ing. Therefore, the wire support member 36 moves relative to the lens stand 16 in a direction perpendicular to the optical axis X, and this movement drives the wire 35, so that the zoom ring 34 rotates. Here, a cam follower 41 is fixed to the wire support member 36, and this follower 41 is a cam groove that is provided in a cam plate 43 fixed to the substrate 20 and has a long cam groove in a direction inclined with respect to the lens movement direction. 42. Therefore, if the lens stand 16 on which the lens 13 is mounted is moved as described above, the wire support member 36 will move relative to the lens stand 16 under the control of the cam 42 as described above, and the zoom ring 34 will thereby move. Since it rotates, the focal length of the lens 13 is changed. As can be seen from the above, the amount of lens movement and the amount of lens zooming correspond. The shapes and installation directions of the cams 15' and 42 are set so that the three equations described above hold between the lens position and focal length.

Now, 44 is a stopper fixed to the board 20. In FIG. 2, this stopper 44 is provided at one end of the lens moving path. When the lens stand 16 moves in the direction of arrow A and reaches its end position, the side surface 18' of the bearing 18 mentioned above is
comes into contact with the side surface 44' of the stopper 44, and further movement of the lens stand 16 in the direction of arrow A is prevented. The position of the lens stand 16 stopped with the bearing 18 of the lens stand 16 in contact with the stopper 44 as described above is the reference position of the lens stand 16. In other words, the position of the lens 13 in this state (the 1) is the reference position of the lens ₁₃ . A micro switch 45 is fixed to the stopper 44, and the actuator of the micro switch 45 has a side surface of the bearing 18 when the bearing 18 comes into contact with the stopper 44.
8' comes into contact. In other words, when the lens stand 16 comes to the reference position, the lens 13 moves to the reference position 1.
3 When it reaches ₄ , the micro switch 45 outputs a signal.

As described above, when the motor 29 is rotated in the forward direction to continue moving the lens in the direction of arrow A, the microswitch 45 issues a signal after a certain period of time has elapsed. This signal is a signal indicating that the lens 13 has reached the reference position as described above, but if the motor 29 is deenergized and the driving of the lens stand 16 is stopped at the same time as this signal is generated, the lens 13 There is a possibility that the robot stops at a position deviated from the reference position ₁₃₄ . This may be due to an error in the mounting position of the switch 45, an error in the operating timing of the switch 45, or the table 16 being displaced in the direction B due to the reaction of the collision between the bearing 18 and the stopper 44. Because it is possible. In any case, if the lens 13 stops at a position deviated from the reference position ₁₃₄ , when the lens 13 is moved from this position a distance corresponding to the number of pulses corresponding to the selected magnification, the new lens position will be Position 13 ₁ or 13 ₂ or 13 ₃ corresponding to the selected magnification
As a result, a copy with the required magnification cannot be obtained. Therefore, in the embodiment shown in FIG.
5 continues to operate the motor 29 until some time after the signal formed by the bearing 1.
8 is firmly pressed against the stopper 44 (that is, after the lens 13 is securely stopped and held at the reference position ₁₃₄ ), the motor 29 is deenergized. As the lens position detection means, in addition to the switch 45 shown in the illustrated example, it is also possible to use one in which a magnet is attached to one of the lens stand 16 and the stopper 44, and a Hall element is attached to the other.
The signal generated by the Hall element when the magnets face each other can be used in the same way as the signal from the microswitch 45.

Figure 4 shows an example of a torque limiter. Fourth
In the figure, a shaft 26 to which a worm wheel 27 is fixed is rotatably supported by bearings 46 and 47 fixed to the substrate 20. A flange 26' is integrally provided on this shaft 26. Also, the shaft 26
A perforated disk 48 is loosely fitted in the . The base of the pulley 24, the shaft 26, the flange 26', and the disc 4
8, spacers 49, 50, and 51 are interposed between them. And another one on the disk 48 and the shaft 26.
A compression spring 53 is interposed between the perforated discs 52 that are loosely fitted. Numeral 54 is a nut screwed onto a screw provided on the shaft 26 to receive the disc 52. By adjusting the nut 54, the spring 53
The pressing force applied to the disc 48 can be adjusted. In any case, due to the elastic pressing force of the spring 53, the disk 48 and the spacer 51, the spacer 51 and the base of the pulley 24,
Base of pulley 24 and spacer 50, spacer 50
and flange 26' are pressed together. Therefore, unless a load exceeding a predetermined value is applied to the wire 21, the shaft 26 and the pulley 24 are fixedly connected, and the wheel 27
When the pulley 24 is rotated, the pulley 24 also rotates integrally with the shaft 26, and the lens is moved in the A direction and the B direction as described above. However, when the motor 29 is rotated in the forward direction with the bearing 18 of the lens stand 16 in contact with the stopper 44 as described above, that is, when the lens stand 16 is further moved in the direction of arrow A, the load applied to the wire 21 is Since the above predetermined value is exceeded, slippage occurs between the spacers 49, 50, 51 and the shaft 26, flange 26', and disk 48 that are in contact with each other, and the pulley 24 remains stopped rotating while the worm wheel 27 simply rotates integrally with the shaft 26. In other words, the motor 29 idles. Accurate positioning of the lens 13 at the reference position 13 ₄ is thus guaranteed.

In addition, in the case where accurate positioning and accurate operation timing of the micro switch 45 as a lens position detection means are guaranteed, and there is no reaction displacement when the table 16 collides with the stopper 44, the above-mentioned The torque limiter may be omitted and the transmission of the driving force to the lens stand 16 may be stopped immediately when the micro switch 45 issues a signal.

Next, the operation of the above mechanism will be explained. A microcomputer is used for operation control. That is, as shown in FIG. 5, the microcomputer CPU instructs the copying machine to perform a copying operation. copy key
SWC, command the copy magnification m _{1x1 key} SW1,
Specify the copy magnification m ₂ m _2x key SW2, specify the copy magnification m ₃ m _3x key SW 3, signals from the pulse train generator 32 and lens position detector 45 are applied, and the motor 29 is driven to rotate in the normal direction. Signal to energize circuit DA, drive circuit to reverse motor 29
Outputs signals that activate the DB and signals that cause the copier to perform copying operations. When the signal is at H level, the circuit DA is energized, and the lens 13 moves in the direction of arrow A in Fig. 2.
move in the direction. Also, when the signal is at H level, the circuit
DB is energized, and the lens 13 moves in the direction of arrow B in FIG. When the signal is at L level, the circuit
DA and DB are not energized and the lens 13 is stopped. In addition, by outputting a signal, the driving means for the photosensitive drum 1, the driving means for the chargers 2 and 5, the driving means for the developing device 4, the driving means for the fixing device 6, the driving means for the lamp 9, and the driving means for the mirrors 10, 11, and 12 are driven. means, paper P
transport drive means (all the above drive means together)
(hereinafter referred to as a CD) is energized according to a predetermined sequence, and the copying process described in FIG. 1 is performed to form a copy image from the original O onto the paper P.
Since the sequence of the copying process in which each driving means CD operates can be a known one, the description thereof will be omitted in this specification to avoid complexity. The microcomputer CPU also has a counter (TN1) function that counts the number of pulses generated by the pulse train generator 32, and a timer (T2) that measures the time immediately after the copying process is completed by changing the magnification.
It is equipped with functions.

Furthermore, as shown in Fig. 7, the lens is at the reference position 1.
The pulse train generator 32 generates P ₁ pulses when moving from _{3 4} to position 13 ₃ when copying m 3 times, and when moving from position 13 ₃ to position 13 ₂ when copying m ₂ times. P generates ₂ pulses, position 13 ₂
P ₃ to move from m to position 13 ₁ when copying at _1x
It is assumed that pulses are generated.

Now, what is shown in FIGS. 6A, B, and C is a flowchart of the control software by the microcomputer CDU. In FIG. 6A, when the power is connected to the copying machine (power ON), first the timer T2 is cleared (step _S1 ), and then the lens is 13 is located at the reference position ₁₃₄ (step _S2 ). If yes, jump to step _S5 , but if no, set the signal to H level and move the lens 13 in the direction of arrow A. direction (step _S3 ). When it is determined from the signal from the micro switch 45 that the lens 13 has reached the reference position ₁₃₄ (step S ₄ ), the number of count pulses P ₄ is set in the counter TN1 (step S ₅ ). This means that the motor 29 continues to rotate in the normal direction from the time when the bearing 18 acts on the micro switch 45 until a time point corresponding to the number of pulses P ₄ , and as described above, the lens 13 is accurately held at the reference position ₁₃₄ . It is for this purpose. Therefore, P ₄ does not need to be a very large value, and the lens 13 is placed at position 13 ₄
The value is selected to be as small as possible within the range that allows accurate positioning. This is because the larger this value is, the longer the total lens movement time will be, resulting in the disadvantage that the time required for copying will be longer.

After that, the pulse train generator 3 is placed on the counter TN1.
It is determined whether or not a pulse input from 2 is received (step S ₆ ), and the counter TN1 is decremented each time a pulse is input to the counter TN1 (step S ₇ ). In this way, it is determined whether TN1 has become 0 or not (step _S8 ), that is, it is determined whether a time corresponding to the number of P4 pulses has elapsed since the microswitch ₄₅ generated the signal. Yes
If so, set the signal to L level and motor 29
(Step _S9 ).

Next, the number of counting pulses (P ₁ +P ₂ +P ₃ ) required to move the lens 13 from the reference position 13 ₄ to the position 13 ₁ for forming a same-magnification image is set (step S ₁₀ ). Next, the signal is set to H level and the lens 13 starts moving in the direction of the arrow from position ₁₃₄ (step _S11 ).

Then, it is determined whether the lens is at position ₁₃₄ (step _S12 ), and whether or not there is an input from the pulse generator 32 to the counter TN1 (step S12).
_S13 ), and when there is this input, the counter TN1 is decremented (step _S14 ),
Next, the number of pulses (P ₁
+P ₂ +P ₃ ) are all counted. (Step _S15 ) TN1=0 at this step _S14
When it is determined that the lens has reached the ₁₃₁ position, the signal is set to L level and the motor 29
to stop moving the lens. (step
_S16 ) Then, at the same time as step _S16 ends, timer T2 is started. (Step _S17 ) Thus, after the power of the copying machine is turned on, the lens 13 is once positioned at the reference position ₁₃₄ , and then moved from that position to the position ₁₃₁ for full-size copying and stopped. (
) Therefore, the next time you turn on the copy key SWC, you can copy an accurate, same-size image of the original. (Note that the highest copying frequency is same-size copying.) Now, the operator presses the aforementioned keys SW1, SW2, SW3.
Turn on the desired magnification key. Therefore, in step _S18 , the microcomputer CSU
It is determined whether or not there is a magnification specification key input, and if No, the process goes to step _S20 described later, but if Yes, in step _S19 , the current position of the lens is input to the selected magnification specification key. In other words, it is determined whether it is necessary to move the lens to a position corresponding to the selected magnification, and if No, the process returns to step _S18 . Again in step _S18 , it is determined whether or not the magnification specifying key has been input, but at this time, since this input information has already been determined and deleted, the determination is No, and the process proceeds to step _S20 .

In step _S20 , it is determined whether or not the copy key SWC has been turned on, and if yes, the above-mentioned copying step _S21 is carried out based on the signal. Then, the printer jumps when the copying process is completed the number of times corresponding to the set number of copies. Meanwhile, in step S ₂₀
If No, the process returns to step _S18 , and steps _S18 and _S20 are repeated until the copy key SWC is turned on or the magnification designation key is turned on. On the other hand, if it is determined in step _S19 that it is necessary to move the lens 13, in step _S22 the time of timer T2 and a preset time t (described later) are compared by a comparison means (not shown). If the time of is greater than t, the process moves to the flowchart; otherwise, the process moves to the flowchart. If the time of T2 is less than or equal to t, that is, if not much time has passed since the power was turned on, or if not much time has passed since the transition to the flowchart, which will be described later, it is assumed that the number of magnification changes is small. It is determined that the accumulation of lens movement errors will be small even if the lens 13 is not returned to the reference position, and the lens is directly moved to the desired lens position. Also, if the time of T2 is greater than or equal to t,
Assuming that the number of magnification changes is large, the lens 13 is temporarily returned to the reference position ₁₃₄ , and then moved from that position to the position designated by the magnification designation key.

If Yes at step S ₂₂ (T2≦t), Figure 6B
Go to step S ₂₃ and now set the lens to position 13 ₁ .
It is determined whether or not to move the lens from position 13 ₂ to position 13 2. If No, it is further determined at step S ₂₄ whether or not to move the lens from position 13 ₁ to position 13 _2. If No, the lens is moved from position 13 ₂ to position 13. It is determined in step _S25 whether or not to move to ₃ . Steps S ₂₃ , S ₂₄ and S ₂₅ are all for determining whether or not to move the lens in the A direction. Then, if Yes in step _S23 , count pulse number _P3 , if Yes in step _S24 , count pulse number ( _P3 + _P2 ), and if step _S25 Yes, count pulse number _P2. are set in the counter TN1, respectively (steps _S26 , _S27 , _S28 ). Next, set the signal to H level and start moving the lens 13 in the direction A from the position where it is currently located (step
S ₂₉ ), steps similar to steps S ₆ , S ₇ , S ₈ , S ₉
S ₃₀ , S ₃₁ , S ₃₂ and S ₃₃ are executed to move the lens 13 a distance corresponding to the number of pulses set in the counter TN1. That is, the lens 13 is moved and stopped at a position corresponding to the magnification specified by the magnification specifying key. Once this is complete, jump to Figure 6A.

On the other hand, if the result in step _S25 is NO, it means that the lens 13 is to be moved in the direction B, and step S25 is NO.
In _S34 , it is determined whether or not to move the lens from the ₁₃₂ position to ₁₃₁ , and if No, it is determined whether or not to move the lens from ₁₃₃ to ₁₃₁ (step _S35 ).
If No here, change the lens position from 13 ₃ to 1
Since it is requested to move to ₃₂ , the count pulse number _P2 is set in the counter TN1 (step _S38 ). On the other hand, if the answer is Yes in step _S34 , the number of counted pulses _P3 is counted, and if the answer is Yes in step _S35 , the number of counted pulses ( _P2 + _P3 ) is counted.
Set to TN1 (steps _S36 , _S37 ). Next, in step _S39 , the signal is set to H level and the lens 13 starts moving in the direction of arrow B from the current position. Then, steps S ₄₀ , S ₄₁ , S ₄₂ , and S ₄₃ similar to steps S ₁₃ , S ₁₄ , S ₁₅ , and S ₁₆ are executed to move the lens 13 a distance corresponding to the number of pulses set in the counter TN1. . That is, the lens 13 is moved and stopped at a position corresponding to the magnification specified by the magnification specifying key. When this is completed, the program jumps to the location shown in FIG. 6A.

Next, if No at step _S22 in Figure 6A (T2
>t), move to step _S44 in Fig. 6C, and set lens 1.
3 in the A direction, and the following steps S ₂ ,
Steps similar to S ₃ , S ₄ , S ₅ , S ₆ , S ₇ , S ₈ , S ₉
S ₄₄ , S ₄₅ , S ₄₇ , S ₄₈ , S ₄₉ , S ₅₀ , and S ₅₁ are executed to accurately position the lens at the reference position ₁₃₄ , and timer T2 is cleared (step S ₄₆ ). In step _S47 , the new number of pulses is set again, ie reset to the new number of pulses.
Incidentally, step _S46 may be performed after the lens 13 reaches the reference position ₁₃₄ , for example, at a time point between step _S51 and step _S52 . Next, in step _S52 , it is determined whether or not to move the lens to the ₁₃₃ position, and if no, in step S53, the lens is moved to _{the 133} position.
It is determined whether or not to move the lens to the ₃₂ position, and if the answer is No, the lens is to be moved to the ₁₃₁ position, so in step _S56 , the number of counted pulses (P ₁ + P ₂ +
_P3 ). On the other hand, if Yes in step _S52 and Yes in step _S53 , each step
At S ₅₄ and S ₅₅ , count pulse number P ₁ is sent to counter TN1,
Set (P ₁ + P ₂ ). Then, in step _S57 , the signal is set to H level to start moving the lens 13 from the reference position ₁₃₄ in the direction B.
Steps S ₅₈ , S ₅₉ , similar to S 13 , S ₁₄ , S _{15 ,} S ₁₆ ,
Execute S ₆₀ and S ₆₁ and set lens 13 to the above counter.
Move from the reference position ₁₃₄ by a distance corresponding to the number of pulses set in TN1. And the steps
At S ₆₂ , start timer T2 anew,
Jump to point A in Figure 6. In addition, step
_S62 may be performed before or during movement of the lens 13 to a position corresponding to the set magnification. For example, it may be performed between steps S ₅₄ , S ₅₅ , S ₅₆ and S ₅₇ . Naturally, this makes it possible to substantially set the time when the reference position of the lens is detected as the time when the timer T2 starts. If you jump to a location after steps S ₃₃ , S ₄₃ , or S ₆₃ , the step will continue unless the magnification designation key is turned on during the lens movement operation.
_S18 and step _S20 are repeated.

In the above example, by creating a sequence, the lens will move directly to the specified position when changing the magnification within a certain period of time after the copying machine power is turned on, but after a certain period of time, the instruction to change the magnification will not be issued. If so, be sure to return to the reference position once and then move to the position corresponding to the selected magnification.

This assumes that there is a proportional relationship between time and the number of magnification changes, and within a certain time, the number of lens movements is small, so the accumulation of lens movement errors is small, but after that time, the number of lens movements increases. Since the number of errors will increase and the cumulative error will no longer be negligible, the idea is to temporarily return to the standard.

The certain time t may be made variable, and may be set to about 10 minutes, for example, in the case of an operator who frequently changes the magnification. In addition, in the case of an operator who does not operate frequently, t may be set to 1 hour or 2 hours.

Also, the process of starting timer T2 for the first time after turning on the power is to press the copy key first after turning on the power.
It may be performed at a time such as when the SWC is turned on or when the lens is moved for the first time after the power is turned on.

In any case, according to the present invention, when the lens is moved by counting pulses, it is possible to prevent lens movement amount errors from accumulating and causing deviations in magnification and focus.

Note that the present invention can be applied to devices that can change the magnification steplessly or in many steps, and can be applied not only to electrophotographic copying machines but also to devices that form an original image on a solid-state image sensor and read this image. It can also be applied to an apparatus that does not scan an original but forms an image of the entire original onto a photosensitive surface at once. The present invention can also be applied to moving mirrors.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an example of a variable magnification electrophotographic copying machine to which the present invention is applied, FIG. 2 is an explanatory diagram of an example of a lens moving mechanism of the apparatus shown in FIG. 1, and FIG. 3 is an explanatory diagram of an example of a slit disk. Fig. 4 is an explanatory diagram of an example of a torque limiter, Fig. 5 is a block diagram of a control system according to an embodiment of the present invention, and Figs. 6A, B, and C explain software of the control system of Fig. 5. The flowchart, FIG. 7, is an explanatory diagram of the number of pulses for lens movement. O is a document, 1 is a photosensitive drum, 13 is a zoom lens, 15 is a lens barrel, 16 is a lens stand, 19 is a guide rail, 21 is a drive wire, 24 is a drive pulley, 25 is a torque limiter, 26 is a drive shaft,
27 is a worm wheel, 28 is a worm gear,
29 is a motor, 31 is a slit disk, 32 is a photocoupler, 34 is a zoom ring, 44 is a stopper,
45 is a micro switch, CPU is a microcomputer, and SW1, SW2, and SW3 are magnification designation keys.

Claims (1)

[Claims] 1. A lens that forms an original image on a photoreceptor, and a pulse train generating means that generates pulses, and a counter counts the number of pulses generated by the pulse train generating means in accordance with a change in magnification. In a variable magnification image forming device that controls the movement of a lens by A measuring means for measuring the time until a change signal is input by the magnification changing means, and a comparing means for comparing a predetermined time set in advance with the time measured by the measuring means. If it is determined that the time measured by the above measuring means is longer, the lens is moved to the reference position once and the counter is reset to a new number of pulses based on the detection signal from the detection element. A variable magnification image forming apparatus characterized in that the lens is moved from a reference position to a predetermined position determined by a magnification changing means by counting this new number of pulses.