GB2072357A

GB2072357A - Photocopying

Info

Publication number: GB2072357A
Application number: GB8009507A
Authority: GB
Original assignee: Fuji Xerox Co Ltd
Current assignee: Fujifilm Business Innovation Corp
Priority date: 1980-03-21
Filing date: 1980-03-21
Publication date: 1981-09-30
Also published as: GB2072357B

Abstract

A variable magnification line-by-line photocopier employs a drum 2 for feeding an original past an illumination station, drum 2 having drive means 4 and speed detector 8; a photoconductive drum 16 rotated at constant speed by drive means 12; projection optics comprising a zoom lens 22 having drive means 28 and speed detector 30; and magnification setting means, which determine the magnification of the zoom lens 22 and the speed of drive means 4. Fine adjustment of lateral and longitudinal magnification may be made. <IMAGE>

Description

SPECIFICATION Variable Magnification Copying Machines The invention relates to variable magnification copying machines capable of producing enlarged or reduced copies from originals, which may themselves of course be copies, for example of drawings or text.

In conventional variable magnification copying machines having an optical system including a lens and mirrors, the lens and/or the mirrors are moved to satisfy following equations in order to change the conjugate length of the optical system.

a=f(1+ M b=f(l +M1 where a is the distance between the centre of a lens and an object; b is the distance between an image and the centre of the lens; M is magnification; and f is the focal length.

Magnification means either enlargement or reduction ratio in producing an image.

Hitherto it has been difficult to attain target values of the magnification with less than +0.5% error by adjusting the optical system. The type of copy paper (plain paper or tracing paper, for example) and the environment, especially humidity in the atmosphere, make it difficult to attain a target magnification value because they cause expansion or contraction of the copy paper.

Another factor for affecting the magnification is any irregularity in the scanning of the original.

Also, for ordinary copy paper, the expansion and contraction ratios in the longitudinal direction is different from that in the lateral direction.

The invention provides a variabiemagnification copying machine comprising means for feeding an origianl for copying, a variable speed first drive means for the feeding means, first means for detecting the speed of the first drive means, a photosensitive drum rotatable at constant speed, a zoom lens for forming an electrostatic image on the drum, a second drive means for varying the magnification of the zoom lens, a second means for detecting the speed of the second drive means, magnification-setting means, first means for controlling the second drive means in response to a set magnification value, and second means for controlling the first drive means in response to the set magnification value.

The magnification-setting means preferably includes a main-magnification setting means, a fine adjustment lateral-magnification setting means and a fine adjustment longitudinalmagnification setting means. As the magnification is separately corrected and adjusted in longitudinal and lateral directions, a preset target magnification value can be precisely obtained.

Drawings Figure 1 is a schematic view of a variable magnification copying machine according to the invention; Figure 2 is a partial elevation of a front panel of the copying machine of Figure 1 showing magnification setting dials; Figure 3 is a block diagram of a control system for lateral magnification in the machine of Figure 1;and Figure 4 is a block diagram of a control system for longitudinal magnification in the machine of Figure 1.

Referring to Figure 1, a feed drum 2 for originals to be copied is rotated by a DC motor 4 through a belt 6. The rate of revolution of the DC motor 4 is detected by a revolution detecting encoder 8. A mirror 10 is fixedly but adjustably mounted above the feed drum 2 so as to receive and reflect an image. Rotatably supported and driven at a constant speed by a synchronous motor 1 2 through a belt 14 is a photosensitive selenium drum 1 6. Fixedly but adjustably mounted above the drum 1 6 is another mirror 1 8.

Between the mirrors 10 and 18 is an optical system 20 for varying the magnification of the image. The optical system 20 comprises a zoom lens 22 adapted to move along a screw rod 24 by engaging a screw-threaded sleeve 26 fixedly secured to the zoom lens 22, and a DC motor 28 for rotating the screw rod 24.

The screw rod 24 is arranged in paraliel with the optical axis of the zoom lens 22. The rate of rotation of the DC motor 28 is detected by a revolution detector 30 coupled with the DC motor 28 and the variable position of the zoom lens 22 is detected by a potentiometer 32 disposed along the screw rod 24. Although not specifically illustrated in the drawing, by rotating the DC motor 28, not only the position of the zoom lens 22 is varied but also the focal length of the zoom lens 22 is changed so as to focus an image on the drum 1 6. Therefore, when an original is placed around the feed drum 2, an enlarged or reduced electrostatic latent image is formed on the drum 1 6 by adjusting and controlling the optical system 20. The image is subsequently developed and transferred to copy paper by means not shown.

Referring to Figure 2, mounted on a front panel 34 of the copying machine is a main magnification-setting dial 36, a fine adjustment lateral magnification-setting dial 38 and a fine adjustment longitudinal magnification-setting dial 40. When the main magnification-setting dial 34 can ivy turned in either direction, and the magnification value selected is displayed on a digital display panel 42 as a percentage.

Referring now to Figure 3, which shows a control system for the optical system 20, when the main magnification-setting dial 36 is turned and the magnification value is displayed on the digital display panel 42, a magnification-setting signal A is generated from a variable resistor 44 interlocked with the main magnification-setting dial 36. The signal A passes through a low pass filter 46 and a buffer 48 and is fed into an adder 50. On the other hand, if and when the fine adjustment lateral magnification-setting dial 38 is manipulated, a fine adjustment signal B is generated from a variable resistor 52 which is interlocked with the fine adjustment lateral magnification-setting dial 38.The fine adjustment signal B is fed into the adder 50 where it is added to the magnification-setting signal A from the variable resistor 44 and an added signal C is generated from the adder 50 and fed into a comparator 52.

Also introduced into the comparator 52 through a buffer 54 is a voltage divided position signal H generated from the potentiometer 32 for detecting the position of the zoom lens 22. The signals C and H are compared in the comparator 52 and a signal D for rotating the motor 12 in forward or reverse direction is generated therefrom. The signal D is fed into a speed control circuit 56 through a limiter 55. Also introduced into the speed control circuit 56 is a speed signal G from the revolution detector 30. A speed control signal E is generated from the speed control circuit 56 and amplified by a preamplifier 58 before entering into a drive circuit 60. The drive circuit 60 then sends out an output signal F for driving the motor 28 in forward or reverse direction.Accordingly, the screw rod 24 is rotated thereby moving the zoom lens 22 in either direction along its optical axis and the focal length of the zoom lens 22 is simultaneously changed.

The revolutional speed of the DC motor 28 is detected by the revolution detector 30 and the speed signal G therefrom is fed back into the speed control circuit 56 for attaining a desirable moving speed of the zoom lens 22. When the zoom lens 22 approaches a preset target stop position, the output signal D from the comparator 52 is reduced and therefore the speed control circuit 5Q generates a signal for reducing the speed of the motor 28 as output signal E corresponding to the input signals thereto. As a result, the speed of the motor 28 is reduced and the moving speed of the zoom lens 22 is also reduced.

When the zoom lens 22 reaches the preset target stop position which is detected by the potentiometer 32, the output signal D from the comparator 52 becomes zero which brings the motor 28 to a halt. Therefore the zoom lens 22 is stopped at the preset target stop position set by the main magnification-setting dial 36 and the fine adjustment lateral magnification-setting dial 38. When a target magnification value is obtained by manipulating only the main magnificationsetting dial 36, it is not necessary to manipulate the fine adjustment lateral magnification-setting dial 38.

We now refer to Figure 4. Since not only the variable resistor 44 in Figure 3 but also a variable resistor 62 is interlocked with the main magnification-setting dial 36, when the main magnification-setting dial 36 is turned in either direction a magnification-setting signal A' is generated from the variable resistor 62. The signal A' passes through a buffer 64 and enters into an adder 66. On the other hand, if and when the fine adjustment longitudinal magnificationsetting dial 40 is manipulated, a fine adjustment signal B' is generated from a variable resistor 68 interlocked with the fine adjustment longitudinal magnification-setting dial 40. The fine adjustment signal B' is fed into the adder 66 where it is added to the magnification-setting signal A' from the variable resistor 62 and an added signal J is generated from the adder 66 and fed into a voltage control oscillator 70.

The oscillator 70 sends out a rectangular wave K corresponding to the input signal J and the rectangular wave J is fed into a phase comparator 72. Also introduced into the phase comparator 72 is a signal L from the revolution detector 8 as a feedback circuit. The phase comparator 72 compares the phase of both the signals K and L and sends out a signal M to a loop filter 74 where it is proportionally integrated before sending out a signal N as an output signal. The signal N is fed into a drive circuit 78 after being amplified by a preamplifier 76. The drive circuit 78 generates a drive signal P for rotating the motor 4 and the speed of the DC motor 4 is controlled in such a way that phases of both the signals K and L synchronize with each other. Accordingly, the drum 2 feeds an original at a speed corresponding to a magnification value set by the main magnification-setting dial 36 and the fine adjustment longitudinal magnification-setting dial 40 is manipulated. By feeding an original at a speed corresponding to a magnification value set as mentioned above, an enlarged or reduced image is formed on the drum 1 6. The image is developed, transferred to copy paper, and fixed.

Should an image not exactly correspond to a preset magnification value, either the fine adjustment lateral magnification-setting dial 38 or the fine adjustment longitudinal magnificationsetting dial 40 should be manipulated to correct it.

Claims

1. A variable-magnification copying machine comprising means for feeding an original for copying, a variable speed first drive means for the feeding means, first means for detecting the speed of the first drive means, a photosensitive drum rotatable at constant speed, a zoom lens for forming an electrostatic image on the drum, a second drive means for varying the magnification of the zoom lens, a second means for detecting the speed of the second drive means, magnification-setting means, first means for controlling the second drive means in response to a set magnification value, and second means for controlling the first drive means in response to the set magnification value.

2. A copying machine according to claim 1 in which the magnification setting means includes a main magnification-setting means, a fine adjustment lateral magnification-setting means and a fine adjustment longitudinal magnificationsetting means.

3. A copying machine according to claim 2 in which the first control means comprises a first adder for adding signals from the main magnification-setting means and the fine adjustment lateral magnification-setting means, a third means for detecting the position of the zoom lens, a first comparator connected with the first adder and third detector for comparing signals therefrom, and a first drive circuit connected at the input side with the first comparator to receive signals therefrom, the first drive circuit being connected at the output side thereof with the second drive means and adapted to send out drive signals for driving the second drive means.

4. A copying machine according to claim 3 in which the first control means further includes speed control circuit means disposed between said first comparator and the first drive circuit for controlling the speed of the second drive means, the speed control circuit being further connected with the second detector as a feedback circuit.

5. A copying machine according to claim 3 or claim 4 in which the third detector is a potentiometer.

6. A copying machine according to any of claims 2 to 5 in which the second control means comprises a second adder for adding signals from the main magnification-setting means and the fine adjustment longitudinal magnification-setting means, a second comparator connected at the input side thereof with the second adder and the first detector for comparing signals therefrom, and a second drive circuit connected at the input side with the second comparator to receive signals therefrom and at the output side with the first drive means and adapted to send out signals for driving the first drive means.

7. A copying machine according to claim 6 wherein the second control means includes a voltage control oscillator between the second adder and the second comparator for sending out rectangular wave signals in response to input signals from the second adder.

8. A copying machine as herein described with reference to the drawings.