JPH02131231A - Magnification varying mechanism for copying machine - Google Patents

Abstract

PURPOSE:To remove the backlash of a power transmission mechanism and to accurately position a lens unit by driving a driving source with such low torque that the lens unit can not be moved before the lens unit is moved to another positioning position. CONSTITUTION:When the lens unit 51 is moved to reach one of positioning holes 44a - 44e corresponding to set copying magnification, a positioning pin 57 is inserted into the positioning hole. Then when the lens unit 51 is moved to another position because of the copying magnification is varied, the driving source 82 is driven for a slight time in the moving direction of the lens unit 51 with such low torque that the lens unit 51 can not be moved before the movement. Therefore, the backlash of the power transmission mechanism 81 coupled with the driving source 82 is removed while the lens unit 51 is stopped. Consequently, the positioning between the positioning pin 57 and positioning holes 44a - 44e is accurately performed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a variable magnification mechanism for reducing or enlarging a document in a copying machine for copying, and in particular to a variable magnification mechanism for moving and positioning a lens unilateral to a position according to the copying magnification. Regarding the improvement of the mechanism for

[Conventional technology]

You can reduce or enlarge the original to a specified magnification and copy it.
In a copying machine having a variable magnification function, the variable magnification mechanism is comprised of a lens unit, a mirror unit, a drive source for driving these units, and a control circuit.

The lens unit and mirror unit 1 are both assembled so as to be movable in the optical axis direction.

In other words, the lens unit moves to a position corresponding to a predetermined copying magnification with respect to the document, and the mirror unit changes according to the copying magnification (in a copying machine where the document position and exposure position on the light beam remain unchanged). It is moved to optimize the optical path length from the document position to the exposure position.

Conventionally, when moving and positioning a lens unit to a position corresponding to a copying magnification, the following method has been used.

That is, the lens unit is provided with a positioning pin driven by a solenoid, and the frame of the copying machine is provided with a positioning hole at each lens unit position corresponding to each of a plurality of copying magnifications. When the copying magnification is changed, the lens unit is moved by a driving source such as a pulse motor through a transmission mechanism such as a gear train, and the lens unit is moved to the approximate center position of the positioning hole corresponding to the changed magnification. When the positioning pin reaches the positioning pin, the positioning pin is pushed out by the solenoid and inserted into the positioning hole.

The inner diameter of the positioning hole is made slightly larger than the outer diameter of the positioning pin to create play. When the positioning pin is inserted into the positioning hole, the lens unit is further moved by the amount of play described above until the positioning pin contacts a reference end that is predetermined at either the front or rear end of the positioning hole, and then the lens unit is moved further by the amount of play described above, and the contact is made. At this point, positioning ends.

[Problem to be solved by the invention]

In the conventional lens unit positioning process described above, backlash always occurs because a gear train or the like is used as a power transmission mechanism from the drive source to the lens unit, and it is difficult to accurately align the positioning pin and the positioning hole. The problem is that there is no. In other words, the position of the lens unit is usually determined based on how many steps the valsmotor as a driving source is rotated from a predetermined origin position, but the position of the positioning pin and the positioning hole may shift due to the backlash of the gear train. There is a problem in that when the positioning pin is pushed out, it collides with the outer periphery of the positioning hole, making it impossible to insert the positioning pin smoothly.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a variable magnification mechanism for a copying machine that eliminates such backrun of a power transmission mechanism and allows accurate positioning of a lens unit.

[Means to solve the problem]

To achieve the above object, a variable magnification mechanism for a copying machine according to the present invention includes a lens unit that is driven by a drive source via a power transmission mechanism and linearly moves within a predetermined range in the optical axis direction, and a plurality of copying magnifications. a plurality of positioning holes provided on the frame corresponding to each positioning position of the lens unit according to each of the positions; and a plurality of positioning holes provided in the lens unit corresponding to the set copying magnification by movement of the lens unit. and a positioning pin that is inserted into the positioning hole when the lens unit reaches the position, when the lens unit is moved to another position by changing the copying magnification, the drive source is activated prior to the movement of the lens unit to another position.
The present invention is characterized in that it includes a control circuit that drives the lens unit with a torque so low that it cannot be moved by an amount sufficient to eliminate backlash in the power transmission groove.

[Effect]

In the magnification changing mechanism of the copying machine of the present invention having the above configuration, when the lens unit is moved to a different position by changing the copy magnification, the driving source is turned to a low torque such that the lens unit cannot be moved, prior to the movement. to drive the lens unit in the direction of movement for a short period of time. Here, by driving the drive source at low torque for a short period of time, backlash in the power transmission mechanism connected to the drive source can be removed while the lens unit is stopped. Thereafter, the movement of the lens unit is started by high torque. Therefore, the positioning pin and the positioning hole can be accurately aligned.

〔Example〕

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

Overall configuration and operation of a copying machine Figure 2 is a schematic cross-sectional view of a copying machine that uses a photosensitive pressure-sensitive method and has a variable magnification function that allows for full-color copying and allows for setting of 5 levels of magnification, including 1:1 magnification. show. Incidentally, a photosensitive paper (consisting of microcapsule paper and color developer paper) that enables such copying has been proposed in Japanese Patent Application Laid-Open No. 58-88739, and will not be described in detail here.

The copying machine 40 is composed of an original platen glass 2 whose top plate is a transparent glass having a substantially rectangular shape, and an original platen cover 1. A desired original can be placed face down on the original platen glass 2. Can be done.

A light source consisting of a halogen lamp 3 extending in a direction perpendicular to the direction of movement of the original platen glass 2 and a semi-cylindrical reflecting mirror 4 disposed to surround it is fixed to the upper right side of the copying machine 40. Light is irradiated in a line toward the document table glass 2. Therefore, the light emitted from the halogen lamp 3 can sequentially illuminate the entire surface of the document table glass 2 from the left end to the right end by moving the document table glass 2 in the left-right direction. The light emitted from the light source passes through the transparent original platen glass 2 and is reflected by the original placed on it. A document table cover 1 that covers the upper surface of the document document table 2 is provided.

In addition, in order to use the light emitted from the halogen lamp 3 to irradiate the original with high efficiency, a reflector 5 is provided on the left side of the light source to reflect light that is not directed directly toward the original and use it to irradiate the original. .

A fan 6 and a louver 7 are provided to the right of the halogen lamp 3 to take in air from the outside, so that air can be efficiently applied to the document table glass 2.

Light emitted from the halogen lamp 3 and reflected by the document placed on the document table glass 2 passes through the filter 8 and enters the lens 9 . The filter 8 is for changing the light transmission characteristics according to the sensitivity characteristics of the microcapsule paper 37 and adjusting the tone of the copied image. Lens 9 is
The lens unit 51 is attached to the lens frame 52 so as to allow minute angle adjustment with respect to the optical path.

The light focused by the lens 9 is turned 180° by two reflecting mirrors 11, and is imaged on the microcapsule paper 37 closely positioned below the exposure stage 19. The two reflecting mirrors 11 are fixed to two mirror mounting plates 12a and 12b to form a mirror unit 61.

On the other hand, a long microcapsule paper 37 is wound around a cartridge holder 14 and housed in a removable cartridge 13 disposed below the platen glass 2. It reaches the winder 25 via the developing device 20.

That is, the microcapsule paper 37 coming out from the lower part of the cartridge 13 is guided by the feed roller 15 and the tie roller 17, passes below the exposure table 19, and is then co-fed to the pressure developing device 20. Thereafter, the microcapsule paper 37 that has passed through the pressure developing device 20 is guided to a peeling roller 23 and a meandering adjustment roller 24, and then wound onto a winding member 25.

The unexposed microcapsule paper 37 after leaving the cartridge 13 is maintained in an unexposed state by the light shielding cover 16.

The conveyance speed of the microcapsule paper 37 is controlled to be constant by the capsule paper feed roller 22 and is made to correspond to the moving speed of the document platen glass 2, so that the microcapsule paper 37 is Latent images of predetermined lines of the document are sequentially formed.

Further, a developer paper cassette 32 containing cut paper type developer paper 38 is provided below the pressure developing device 20, and the developer paper 38 is taken out one by one by a half-moon roller 33, and then transferred to the developer paper roller 34 and the resist. After the leading end is aligned by the gate 35, the paper is transported to the paper entrance of the pressure developing device 20.

Therefore, the pressure developing device 20 includes the microcapsule paper 37.
The color developer paper 38 and the color developer paper 38 are supplied in a state where they are in close contact with each other and are integrated. The pressure developing device 20 is composed of a small diameter roller 21 and a hack up roller 31. Microcapsule paper 3
Microcapsule surface and color developer paper 38 on which latent image No. 7 is formed
The color developer-applied surface of the roller 21 is sandwiched between the small diameter aperture roller 21 and the back amp roller 31 so that pressure is applied thereto. This pressure destroys the unexposed microcapsules and forms an image on the developer paper 38.

The microcapsule paper 37 and the color developer paper 38 that have come out of the pressure developing device are conveyed by the capsule paper feed roller 22, and the microcapsule paper is moved upward by the peeling roller 23, and the color developer paper 3 is transported by the peeling roller 23.
8 are orthogonally separated.

The developing paper 38 is accelerated in color development by the heat fixing device 39 to form an image, and is then delivered to the paper discharge tray 27 with the image side facing up. The heat fixing device 39 includes a hollow heat roller 29 having a heater 30 therein, and a developing paper feed roller 28.

The separated microcapsule paper passes through a meandering adjustment roller 24 and is wound around a winding shaft 25.

The operation of the device configured as described above will be explained below.

First, open the document platen cover 1 and place the original on the document glass 2, and then press the start button (not shown).The document glass 2 will move to the right and the left edge of the document glass 2 will become the light source. Stop at a position facing the

Thereafter, with the halogen lamp 3 turned on, the document table glass 2 is moved to the left. halogen lamp 3
After being reflected by the original, the light irradiated from the filter 8 passes through the filter 8.
After passing through the lens 9 and being reflected by the two reflecting mirrors 11, the microcapsule paper 3 is placed below the exposure table 19.
7.

At this time, the microcapsule paper 37 is placed on the document table glass 2.
Since the lower part of the exposure table is moved to the left at a speed corresponding to the moving speed of , the image on the document is formed on the microcapsule paper 37 as a latent image.

As the document platen glass 2 moves to the left, the half-moon roller 3
3, the color developer paper 38 is taken out from the color developer paper cassette 32, and is supplied to the pressure developing device 20 in a superimposed state with the exposed microcapsule paper 37, and the latent image on the microcapsule paper 37 is developed. The image is then transferred onto the color developing paper 38.

Thereafter, the developing paper 38 is thermally fixed by a thermal fixing device 39 and then discharged from the copying machine 40 . On the other hand, pressure developing device 2
The microcapsule paper 37 that has passed through zero is sequentially wound around the winding shaft 25.

When the right end of the document platen glass 2 finishes moving to a position facing the light source, copying of the document is completed and the halogen lamp 3 is turned off.

Structure and operation of the variable magnification mechanism FIG. 3(a) shows the details of the lens unit 51 and mirror unit 61 in the schematic cross-sectional view of the copying machine 40 shown in FIG. The plan view and FIG. 3(C) show the lens unit 51 and mirror unit 61.
This shows the link body that links the .

The lens frame 52 that constitutes the lens unit 51 is
As shown in FIG. 3(b), it is formed into a substantially U-shape, and a rack 54 and a cam body 55 are attached to one end edge 52a.
A rack 54 is fixed to each of the other end edges 52b.

A substantially V-shaped groove 58 is provided in the center of the lens frame 52.
Two positioning plates 58 having a diameter a are fixed in the optical direction, upper and lower, and the outer periphery of the lens 9 is brought into contact with the groove 58a, and the lens 9 is fixed by the lens band 53 between the two positioning plates 58. ing.

Two sets of positioning pins 57 and a solenoid 56 for driving the positioning pins 57 are fixed to the lens frame 52 through a support member 60 slightly toward the center of both end edges.

On the one edge 52a side of the lens frame 52, as shown in FIG.
a) As shown in the figure, vertically extending guide portions 52c and 52d are provided, and the frame 4
A lens arbor 45 fixed to the frame 44 is inserted through the lens arbor 45, and the lens unit 51 is supported to be movable up and down with respect to the frame 44 by this lens arbor 45 and a rotation prevention mechanism 59 provided at the other end edge 52b. ing.

As shown in FIG. 3(a), as the lens unit 51 moves in the vertical direction, the cam body 55 moves its contact portion with a contactor, which will be described later, in a direction perpendicular to the optical axis direction, corresponding to the copying magnification. It has cam surfaces 558 to 55e that change in five stages.

The frame 44 has a positioning pin 5 of the S lens unit 51 at a position determined in design depending on each copying magnification.
Positioning holes 44a to 44e, through which the positioning pins 57 are inserted, are provided in accordance with the position 7.

A drive section 81 that drives such a lens unibody 51 includes a pulse motor 82 and a gear train.

A pinion 83 of a pulse motor 82 fixed to the frame 44 causes . First, rotation is transmitted to the spur gear 84 fixed to a gear shaft 85 rotatably supported by the frame 44. Two small gears 86 are further fixed to the gear shaft 85, and these small gears 86 are connected to two idle gears 8 rotatably supported by the frame 44.
7 rotates, and the lens unit 51 is moved in the vertical direction by two rasoks 54 that mesh with this.

As shown in FIG. 3(a), the mirror unit 61 has two reflecting mirrors 11 fixed at both ends to two mirror mounting plates 12a and 12b. Of these two mirror mounting plates, the mirror mounting plate 12a on the near side shown in FIG.
The end edge 6 through which the mirror arbor 46 fixed to 4 is inserted
263a is provided. Further, the mirror mounting plate 12b on the other side of the illustration in FIG. 3(a) is provided with a rotation prevention mechanism (not shown) and an edge portion 63b that matches the lower edge portion 63a of the mirror mounting plate 12a. There is. This mirror unit 61 is biased downward by biasing means such as a spring (not shown).

In the link body 71, as shown in FIG. 3(C), an L-shaped link 72 and a sub-am 73 are fixed to a link member 74, and a contact 75 is attached to one end of the L-shaped link 72. A push-up roller 76 is rotatably supported at the other end and the tip of the sub-arm 73.

As shown in FIGS. 3(a) and 3(b), the link body 71
is attached to the frame 44 so as to be rotatable about the link shaft 74. As shown in FIG. 3(a), the link body 71 is moved counterclockwise around the link 74 by the two push-up rollers 76 coming into contact with the end edges 63a, 63b of the mirror unit 61. The contact 75 is urged to rotate and is always in contact with the cam body 55.

FIG. 3(a) shows a state in which the contact 75 is in contact with the cam member 55c of the cam body 55 due to the set copying magnification. At this time, the positioning pin 57 shown in FIG. 3(b) is pushed out by the solenoid 56 and inserted into the positioning hole 44c of the frame 44, and
is positioned securely in the vertical direction.

From this state, the copy magnification is changed to, for example, one of the five copy magnifications set in the copying machine according to this embodiment.
When the copying magnification is set such that the lens unit 51 descends the lowest, the positioning pin 57 is first pulled out from the positioning hole 44c by the solenoid 56 to enable the lens unit 51 to move in the vertical direction, and then the control circuit not shown in FIG. The lens unit 51 is moved downward to a predetermined position by the rack 54 via the gear train by the controlled pulse motor 82, and the positioning pin 57 is pushed out by the solenoid 56 and inserted into the positioning hole 44a. is fixed at a position corresponding to a predetermined copying magnification.

Positioning pin 57 at the time when this positioning is completed
FIG. 4 shows the relationship between the positioning holes 44'a and 44b. Here, each positioning hole 44a. It is assumed that the reference end of 44b is determined to be the lower end of each hole. When the positioning is completed, the positioning pin 57 is inserted into the positioning hole 44.
It is in contact with the reference end (lower end) of a. Positioning hole 44a
The size of ~44e is formed to be somewhat larger than the size of the positioning pin 57 (for example, 1 to 2+ nm both vertically and horizontally), and there is a gap of 2Δd between the upper end of the positioning pin 57 and the upper end of the positioning hole 44a when they are in contact with each other. .

In this state, it is assumed that the copying magnification is set such that the next movement is to the positioning hole 44b. Then, the lens unit 51 is moved upward again as described above, and the positioning pin 57 is inserted into the positioning hole 44b to complete the positioning.The process will be explained in more detail as follows.

First, the lens unit 51 is raised by Δd, and the positioning pin 57 comes to the center position 57a of the positioning hole 44a. At this time, the positioning pin 56 is
moves backward and is pulled out from the positioning hole. Subsequently, the lens unit 51 is raised by a distance d to the positioning hole 44b, and the positioning pin 57 comes to the center position 57b of the positioning hole 44b. At this time, the positioning pin 57 is pushed out by the solenoid 56 and inserted into the positioning hole 44b. Thereafter, the lens unit 51 is lowered by Δd, and positioning is completed at a position 57c where the positioning pin 57 contacts the reference end (lower end) of the positioning hole 44b.

In this way, the lens unit 51 descends to the positioning hole 44a at the first copy magnification change, and rises to the positioning hole 44b at the next magnification change, but when the positioning at the first positioning hole 44a is completed, the drive unit 81 The gear train is in an engaged state when descending, and the next time the gear train is moved up, the pulse motor 82 rotates extra by the amount of pack rush, and the gear train is in an engaged state when ascending, and then the actual ascending operation begins. .

A feature of the present invention is that a compensation operation is added to the control of the pulse motor 82 to substantially nullify the extra rotation of the pulse motor 82 corresponding to this pack rush. FIG. 1 shows the configuration of an embodiment of a control circuit for realizing this and its characteristics.

In FIG. 1(a), this control circuit includes a control section 100
, a drive pulse generator 101 , a changeover switch 102 , a frequency dividing circuit 103 , and a drive amplifier 104 . The control section 100 drives and controls the drive pulse generation circuit 101 to perform the movement and positioning operations of the lens unit 51 as described above when the copying magnification is changed.

At this time, the control circuit 100 determines the current position of the lens unit 51 based on the origin signal that is emitted when the lens unit 51 is at a predetermined origin position and the number of rotation steps of the pulse motor 82 after the manual input point of this origin signal. The location can be recognized. This control circuit 100 is also capable of sending a switching command to the changeover switch 102 as necessary. The drive pulse generator 101 outputs pulses at a predetermined rate for driving the pulse motor 82. The changeover switch 102 is configured to apply the output pulse from the drive pulse generator 101 to the frequency dividing circuit 103 in a first state, and to send the drive pulse as it is to the drive amplifier 104 in the second state. This switching between the first and second states is performed by a switching command from the control unit 100. The frequency dividing circuit 103 divides the frequency of the manually inputted drive pulse at a predetermined rate (for example, 1/2) and sends the divided frequency to the drive amplifier 104. Drive amplifier 1
04 amplifies the power of the input drive pulse and supplies it to the pulse motor 82 to drive it.

In FIG. 1(b), the drive pulse generator 101 outputs relatively high-rate pulses as shown in B. In FIG. When the selector switch 102 is in the first state, the high rate pulse B is sent to the frequency divider circuit 103 and is converted to A in FIG. 1(b).
The signal is converted into a low-rate pulse as shown in FIG. 1 and sent to the drive amplifier 104. FIG. 1(C) shows the relationship between the torque of the pulse motor 82 and the pulse rate, and the rate of the low rate pulse A corresponds to point X in FIG. 1(C). Therefore, the pulse motor 82 is driven with high torque, and the lens unit 51 is moved.

On the other hand, when the selector switch 102 is in the second state, the high rate pulse B from the drive pulse generator 101 is sent as is to the drive amplifier 104. This pulse rate corresponds to point Y in FIG. 1(C).

Therefore, the pulse motor 82 is switched to low torque drive.

The torque generated by the pulse motor 82 at this time is
This value is set to such a low value that it is possible to move the gear train, but it is not possible to move the lens unit 51.

Lens unit 5 realized by such a control circuit
The operation process of movement and positioning of No. 1 will be explained with reference to the flowchart of FIG. 5, taking as an example the upward movement from the positioning hole 44a to the positioning holes 4, 4b.

First, referring to FIG. 4, in the initial state, the positioning pin 57 is in contact with the reference end of the positioning hole 44H. In this state, when the copy magnification corresponding to the positioning hole 44b is selected, the control circuit 100
is brought into the second state, and the pulse motor 82 is rotated in the upward direction at low torque for a short period of time to remove the backlash of the gear train (step Sl). Then, the drive unit 81 is rotated in the gear train upward direction to eliminate backlash (step S2).

When the backlash is removed and the gear train is brought into engagement during upward movement, the load of the lens unit 51 is applied to the pulse motor 82, so the low-torque driven pulse motor 82 cannot withstand this load and steps out. Step S3). Therefore, although the backlash is removed, the lens unit 51 does not move at all.

Next, the control unit 100 switches the changeover switch 102 to the first state and rotates the pulse motor 82 in the upward direction with high torque (step S4). As a result, the lens unit 51 starts to move for the first time, and when it has risen by Δd, that is, when the positioning pin 57 reaches the center position 57a of the positioning hole 44b, the positioning pin 5
7 is retreated and pulled out from the positioning hole 44a (steps S5, S6). Subsequently, the control section 100 further rotates the pulse motor 82 while maintaining the high torque drive to raise the lens unit 51 by a distance d (step S7).

Thereby, the positioning pin 57 is accurately located at the center position 57b of the positioning hole 44b.

Next, the control unit 100 switches the rotation direction of the pulse motor 82 and rotates the pulse motor 82 downward by a distance Δd+α that is somewhat larger than the distance Δd plus the backlash (step S8).

As a result, after the backlash of the gear train is removed and the gear train engages downward, the positioning pin 57 descends to the reference end of the positioning hole 44b, and at the position 57c where it contacts the reference end, the pulse motor 82 steps out and the positioning is completed. (Step S9). This final lowering operation may be performed with a high torque, but may also be performed with a slightly lower torque to facilitate tax adjustment and soften the contact impact.

Other Embodiments FIG. 6 shows the configuration and characteristics of a second embodiment of the control circuit. As shown in FIG. 6(a), this embodiment is applicable to the first and second selector switches 102 in the circuit of FIG. 1(a).
In addition to reversing the connection of the output in the state of
3 is changed to a chopper circuit 105, and the driving pulse generating section 101 is further changed to a circuit 106 that generates a low rate pulse as shown at A in FIG. 1(b). Therefore, when the low rate pulse from the drive pulse generator 106 shown in A in FIG. and is sent to the drive amplifier 104. Therefore, the amount of current supplied to the pulse motor 82 is reduced and the pulse motor 82 is driven with low torque.

FIG. 7 shows a third embodiment of the control circuit.

In this circuit, as shown in FIG. 7(a), the current amplification factor is supplied from the drive pulse generator 106 via the drive amplifier 107 whose current amplification factor is switched from a high value to a low value by a switching command from the control unit 100 etc. The low rate pulse A is supplied to the pulse motor 82. The simplest configuration for switching the amplification factor is, for example, a circuit as shown in FIG. 7(b) connected to the drive amplifier 1.
It is conceivable to provide it at the output stage of 07. That is, the output resistance is switched from the low resistance 109 to the high resistance 110 by the switch 108 which is switched in response to a switching command from the control unit 100. As a result, as shown in FIG. 7(C), the current waveform of the pulse supplied to the pulse motor 82 is switched from the high current value D to the low current value E, and the pulse motor 8
2 switches to low torque drive.

Therefore, even if a control circuit as shown in FIG. 6 or 7 is used, backrun removal as shown in FIG.
It is possible to perform moving and positioning operations.

Although some preferred embodiments have been described above, the present invention is not limited only to these embodiments, and the present invention will not be limited to the timing of torque switching, the specific circuit configuration of the control circuit for torque switching, etc. Various variations can be made without departing from the gist of the invention.

〔Effect of the invention〕

As explained above, according to the present invention, before moving the lens unit to another positioning hole position, the pulse motor is driven with low torque to eliminate backlash in the power transmission mechanism without moving the lens unit. This allows for accurate positioning.

[Brief explanation of drawings]

FIGS. 1(a) to (C) are diagrams showing the configuration and characteristics of an embodiment of a control circuit used in a variable magnification mechanism according to the present invention, and FIG. 2 is a diagram showing a copying machine in which an embodiment of the present invention is used. A schematic sectional view showing an example, FIGS. 3(a) to 3(c) are views showing a variable magnification mechanism and its link unit in an embodiment of the present invention, and FIG. 4 is a view showing the relationship between a positioning pin and a positioning hole. , FIG. 5 is a flowchart showing the process of moving and positioning the lens unit according to the embodiment of the present invention, FIGS. 6(a) and 6(b) are diagrams showing the configuration and characteristics of the second embodiment of the control circuit, and FIG. 7(a) to (C) are diagrams showing the configuration and characteristics of a third embodiment of the control circuit. 40... Copying machine, 44a to 44e... Positioning hole,
51... Lens unit, 57... Positioning pin,
81... Drive unit, 82... Valse motor, 100...
・Control unit, 101, 106... Drive pulse generation unit, 1
02... Selector switch, 103... Frequency divider circuit, 10
4,107...Drive amplifier, 105...Chopper circuit, 108...Switch, 109,110...Resistor. Applicant's representative Yasuo Ishikawa (b) -+-t Figure 1 Figure 2 Figure (C) Figure (a) ->t (b) Figure (a) (b) (C) 1- t figure

Claims (1)

[Claims] A lens unit is driven by a drive source via a power transmission mechanism and linearly moves within a predetermined range in the optical axis direction, and a lens unit is mounted on the frame corresponding to each positioning position of the lens unit according to each of a plurality of copying magnifications. a plurality of positioning holes provided in the lens unit, and a positioning pin provided in the lens unit and inserted into the positioning hole when the lens unit reaches a position corresponding to the set copy magnification by movement of the lens unit. In the apparatus, when the lens unit is moved to another position by changing the copying magnification, the drive source is activated by an amount sufficient to remove backlash of the power transmission mechanism before moving the lens unit to another position. A variable magnification mechanism for a copying machine characterized by having a control circuit that is driven with a torque so low that it cannot be moved.