GB2213949A

GB2213949A - "Image forming apparatus with controlled magnification"

Info

Publication number: GB2213949A
Application number: GB8900145A
Authority: GB
Inventors: Hideshi Oushiden; Akihiko Kida; Norio Imada
Original assignee: Toshiba Corp; Toshiba Intelligent Technology Co Ltd
Current assignee: Toshiba Corp; Toshiba Intelligent Technology Co Ltd
Priority date: 1988-01-14
Filing date: 1989-01-05
Publication date: 1989-08-23
Also published as: DE3900903A1; FR2626126A1; GB8900145D0; JPH01182867A

Description

w C-2139 49 "IMAGE FORMING APPARATUS HAVING FUNCTION FOR CONTROLLING

SCANNING START POSITION" The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus having a function for controlling a scanning start position in accordance with an image forming magnification.

As well known, an image forming apparatus, for example, an electronic copying machine, has a 100 % magnification function to copy an original image on paper with the size of the original image, or another function to copy a original image in an enlarged form or a reduced form. An image is formed through movement of an exposure/scanning means along the surface of a is document.

In the electronic copying machine capable of copying the original image with the enlarged size or the reduced size, an exposure/scanning means is moved for exposing and scanning the original. A moving speed of the exposure/scanning means is different between the operation modes of the copying machine, an enlargement mode and a reduction mode. Specifically, a speed of the movement of the exposure/scanning means in a reduction mode is set to be higher than that for the 100 % magnification. The moving speed in an enlargement mode is lower than that in a 100 % magnification mode.

In such a conventional copying machine, the starting position of the exposurelscanning means is set at the same position for the 100 % magnification mode and the enlargement or reduction mode. That is to say, the starting position is set at the position for the maximum reductionmagnification, which requires the longest acceleration distance, in those copy modes, 100 % magnification, enlargement and reduction. In addition, the scanning means is accelerated at the minimum reduction-magnification. Therefore, in a 100 magnification mode, for example, the exposure/scanning means reaches a scanning speed required for the 100 % magnification before the starting position of exposing the forward end of an original. The time interval is between the position that the necessary scanning speed is reached and the exposure starting position, is unnecessary for the exposure and scanning operation of the original to light. This fact implies that in the conventional copying machine, the exposure/scanning means moves an excessive distance when the exposure and the scanning are performed, and that particularly when the copying operation is successively performed, much time is taken for the exposure and scanning operation of the original image.

Accordingly, an object of the present invention is to provide an image forming apparatus in which a magnification of the copied image is readily set and 0- 1 - 3 changed, and reduction is made of the time taken for the exposure and scanning operation of an original image particularly in the successive copying operation.

According to an aspect of the...-,resent invention, there is provided an apparatus for forming an image on an image forming medium, said apparatus comprising means for optically scanning an original, means for setting one of a plurality of magnifications with respect to an image obtained by scanning the original, means for initializing the optical scanning means at an initial position, and means for controlling a distance for which the optical scanning means is moved from an initial position to a start position where the optical scanning means starts operating, in accordance with an image forming magnification set by the magnification setting means, the optical scanning means being accelerated from the initial position to the start position and reaching the start position in an accelerated condition.

According to another aspect of the present invention, there is provided a scanning apparatus, comprising means for optically scanning an original, means for setting one of a plurality of magnifications with respect to an image obtained by scanning the.original, means for initializing the optical scanning means at an initial position, means for photoelectrically is 1 converting the image to an electrical signal at the one of a plurality of magnifications based on the image, and means for controlling a speed, which is selected from a plurality of speeds and at which the optical scanning means is moved from the initial position to a start position where the optical scanning means starts operating, in accordance with a scanning magnification set by the magnification setting means, the optical scanning means being accelerated from the initial position to the start position and reaching the start position in an accelerated condition.

These and other features and advantages of the present invention will become more apparent from the following detailed description of exemplary embodi- ments as illustrated in the accompanying drawings, in which:

Fig. 1 is a block diagram showing a control system of an electronic copying machine according to an embodiment of the present invention; Fig. 2 is a perspective view showing appearance of the copying machine; Fig. 3 shows a longitudinal sectional view showing an internal structure of the copying machine; Fig. 4 is a diagram showing a layout of controls on an operation panel of the copying machine; Fig. 5 is a perspective view schematically showing a drive mechanism of an optical system in the copying - S - machine; Fig. 6 is a perspective view schematically showing the drive mechanism of an optical system in the copying machine, the illustration being for explaining a movement of the optical system; Fig. 7 is a flowchart showing the operation of the copying machine; Fig. 8 is a graph showing a relationship between moving speed and distance of a first carriage; Fig. 9 is a graph showing a relationship between moving speed and time of a first carriage; and Fig. 10 is a sectional view showing a structure of a scanner, which is another embodiment of the present invention.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.

Figs. 1 through 5 schematically illustrate an arrangement of an image forming apparatus, for example, a copying machine, according to the present invention. A document table (transparent glass plate) 14 for supporting an original 0 is secured to the central portion of top panel 12 on the top surface of main body 10 of a copying machine. Table 14 is provided with fixed scale 16 providing a reference when original 0 is set on table 14. Further, cover 18, which may be open and close, and work table 20 are located near table 14. original - 6 0 placed on table 14 is exposed to light and scanned when an optical system including exposure lamp 22, and mirrors 24, 26 and 28, is reciprocately moved along the bottom surface of table 14 in the directions of arrow "all. In this case, to maintain an optical path, mirrors 26 and 28 are moved at the half speed of that of mirror 24. The reflecting light from original 0 during the scanning operation by the optical system, namely, the reflecting light from the original resulting from the illumination by lamp 22, is reflected by mirrors 24, 26 and 28, passes through magnification varying lens block 30, reflected again by mirror 32, and led to photoconductive drum 34. In this way, an image on original 0 is formed on the surface of drum 34.

Drum 34 is rotatable in the direction of arrow "b", as shown in Fig. 3. In the copying operation, main charger 36 first charges the surface of drum 34. Then, the reflected light containing an original image is applied through a slit onto the surface of drum 34, so that an electrostatic latent image is formed on the drum surface. Developer 38 applies toner onto the latent image on the drum surface, thereby to visualize that imalce.

Paper P as sheet on which an image is to be copied is set in upper feed cassette 40, and lower feed cassette 402. These cassettes 40, and 402 are removably set in the lower part of the right side of main body 10.

1 Paper P is picked up sheet by sheet from either of the cassettes 401 or 402 by pick up roller 421 or 42 2 The picked-up paper P is guided through paper guide path 441 or 442 to regist roller pair 46. Roller pair 46 further guides paper P to transfer unit 48. Cassette 401 or 402 is manually selected by operating a related key on operation panel 80 to be described later. Cassette size detecting switch 501 and 502 are for selecting the cassette size of cassette 401 and 402, which depends on the size of paper P placed in the cassettes. These switches 501 and 502 each includes a plurality of micro switches which are turned on and off upon insertion of the cassettes of different size.

Paper P transported to transfer unit 48 is made to closely contact the surface of photoconductive drum 34 in the portion of transfer charger 52, so that the toner image on the surface of drum 34 is transferred onto paper P by transfer charger 52. Paper P bearing the transferred toner image is electrostatically separated from the surface of drum 34 by separation charger 54.

The separated paper is transported to fixing roller pair 58 as a fixing means provided downstream of the fixing roller. Paper P emanating from the fixing roller pair is discharged into receiving tray 62 by exit roller pair 60.

Following the image transfer, photoconductive drum 34 is discharged by discharging charger 64, and then the residual toner on the drum surface is removed by cleaning unit 66. Drum 34 is moved under discharge lamp 68 by which an afterimage,on the drum surface is removed, and is restored to the initial state. Reference numeral 70 designates a cooling fan for preventing excessive temperature rise within main body 10. Reference numeral 72 is a sensor for sensing an initial position of first carriage 100 to be given later.

Fig. 4 shows operation panel 80 installed on the top surface of main body 10. Reference numeral 82 designates a copy key for instructing start of a copying operation; 84, numerical keys for instructing the number of copies; 86, an indicator section for indicating various operation states of the necessary portions in the copying machine, and jamming; 88, cassette select keys for selecting upper and lower feed cassettes 401 and 402; 90, indicators each for indicating the selected cassette; 92, magnification setting keys for stepwise setting reduction and enlargement magnifications depending on a predetermined relationship; 94, smooth keys for continuously setting enlargement and reduction magnifications; 96, a display window for displaying a set magnification; and 98, a density setting section for setting a density of the copied image.

Fig. 5 shows a drive mechanism for reciprocately move the optical system. As shown, exposure lamp 22 and mirror 24 are supported by a first carriage 100, and mirrors 26 and 28 are supported by second carriage 102. These first and second carriages 100 and 102 are respectively guided by guide rails 104 and 106, and those carriages arranged in parallel are movable bidirectionally as indicated by arrows "all. Scale 108, which will be described later, is secured on the top surface of first carriage 100. Scanning motor (4-phase stepping motor) 110 drives pulley 112. Timing belt 116 is wound around pulley 112 and idle pulley 114 located separately from the former. one end of first carriage 100 supporting mirror 24 is secured to this belt 116. Two pulleys 120 and 122 are rotatably secured to both end portions c-F guide 118 of second carriage 102 supporting mirrors 26 and 28, which extends along guide rail 106.

Wire 124 is wound around pulleys 120 and 122. One end of wire 124 is fixed to L-shaped member 126, while the other end to the same through coil spring 1'28.

one end of first carriage 100 is fixed to an appropriate portion of wire 124. with such an arrangement, when scanning motor 110 is driven, belt 116 is turned to move first carriage 100 and in turn second carriage 102. In this operation, these pulleys 120 and 122 serve as running pulleys. Therefore, second carriage 102 turns at the half speed of that of first carriage 100, and in the same direction as that of the first carriage. The directions of the first and second carriages 100 and 102 may be controlled by switching the rotating direction of scanning motor 11o.

Fig. 1 shows a control circuit for executing an overall control of the copying-machine.

Main processors 130 constructed with a one-chip microcomputer, for example, is coupled with operation panel 80, and input device 132 including various switches and sensors, such as cassette size detecting switches 501 and 502, and detects the output signals of those switches and sensors. Main processors 130 is further c,-Upled with high-voltage transformer 134 for driving the respective chargers, discharging lamp 68, and blade solenoid 660 of clee.. r-.-irkg unit 66. Main pro- cessors 130 is additionally coupled with heater 580 of fixing roller pair 58 via heater control unit 136, expo sure lamp 22 through lamp regulator 138, and through motor driver 140 to developing motor 380, toner motor 382, fixing motor 582, and fan motor 700. Developing motor 380 is a motor for driving the developing roller, for example, in developer 38, and toner motor 382 is for supplying toner to developer 38. Fixing motor 582 drives paper transport path 56, fixing roller pair 58 and exit roller pair 60. Fan motor 700 is a motor for driving cooling fan 70.

Main processors 130 coupled with first and second subprocessors 142 and 144, and controls these sub processors. First subprocessors 142 is coupled with scanning motor 110, shutter motor 148 and lens motor 300 If which will be described later, through stepping motor driver 146, and further coupled with a motor position sensor 150. These motors are controlled by first subprocessors 142. Second subprocessors 144 is coupled with drum motor 340, feed motor 420, and regist motor 460, which will be described later, and controls them.

The scanning motor 110, as stated earlier, is for moving first carriage 100 supporting exposure lamp 22 and mirror 24 for scanning an original, and second carriage 102 supporting mirrors 26 and 28. Shutter motor 148 is a motor for moving a shutter (not shown) to adjust a width of an area on photoconductive drum 34 to be changed by charger 36 when a magnification of the copied image is varied. Lens motor 300 is a motor for shifting magnification varying lens block 30 for varying the magnification. Drum motor 340 is a motor for driving drum 34. Feed motor 420 is a motor for driving pickup rollers 42, and 422- Regist motor 460 is a motor for driving regist roller pair 46.

Main processors 130 sends commands to drive and stop the motors to first and second subprocessors 142 and 144. These subprocessors send status signals repre senting status of the motors, e.g., driven and stopped status. First processors 142 receives position data from motor position sensor 150 for sensing the initial positions of scanning motor 110, shutter motor 148, and lens motor 300.

These subprocessors 142 and 144 are each made up of, for example, a microcomputer, and a programmable Interval timer for controlling a phase switching inter val of the stepping motor by counting a reference clock pulse according to a set value supplied from the micro computer.

Reference numeral 154 designates a power source for driving the necessary devices and components in the copying machine.

The operation of main processors 130 and first carriage 100 in the copying machine thus arranged when an image is formed, will be described with reference to Figs. 6 through 9.

After power source 154 of copying machine main frame 10 is turned on, first carriage 100 is returned to the original position. Specifically, main processors drives scanning motor 110 through subprocessors 142 and then stepping motor driver 146. With the driven motor, first carriage 100 is moved along guide rails 104 and 106 toward the exit side (to the left in the drawing of Fig. 6) of main body 10, to turn on first carriage position sensor 72 installed in the portion under top panel 12 and closer to the exit side than fixed scale 16. The position of the first carriage sensed by first carriage position sensor 72 is loaded into a data register in first subprocessors 142, as operation start z 1 k f position SO to be treated as an initial position of first carriage 100. The start position SO as is stored as the initial position of first carriage 100, is a reference position to determine, for example, the start position of first carriage 100 to be moved in accordance with an enlargement/reduction magnification.

The position data, which is the operation start position stored as SO in first subprocessors 142, is used to determine, for example, start position S1 for the maximum reduction-magnification, start position S2 for 100 % magnification and exposure start position S3 of the forward end of original 0. The "exposure start Position" (S3) indicates a position of the first carriage when the light emitted from exposure lamp 22 is is applied to original 0 through document table 14 and the copying machine is ready for the exposure/scanning operation. These start positions, such as S1, S2 and S3, are determined by the number of pulses derived from stepping motor driver 146. In response to the applied pulse, scanning motor 110-is driven to move first carriage 100 by timing belt 116 to those start positions S1, S2 and S3.

Before the copying operation starts, in a stand-by state, first carriage 100 is set at a position, called a home position, indicating a copying range defined by, for example, the cooperation of fixed scale 16 and scale 108 of first carriage 100 on the basis of a current copying magnification and the size of original o. For example, in Fig. 6, SIi is called a home position, and the copying range exits between exposure start position S3 and home position SH.

After first carriage 100 is initialized in this way, if copy key 82 on operation panel 80 is operated, control checks if the current magnification is 100 % in step ST1. llf it is a copying magnification other than the 100 % magnification, e.g., reduction magnification or enlargement magnification, control goes to step ST2. In this step, the copying operation is performed in a normal reduction or enlargement mode.

For example, if the current magnification is the maximum reductionmagnification, e.g., 65 %, first carriage 100 is moved from home position SH to operation start position SO, and subprocessors 142 count the number of pulses supplied from stepping motor driver 146. Then, carriage 100 is moved from position SO to start position S1 for the maximum reductionmagnification, which position is determined in accordance with the counted pulse number. When a predetermined number of pulses has been counted, carriage 100 is accelerated at a predetermined acceleration in the distance from start position S1 to exposure start position S3 by controlling the rotational frequency of stepping motor 110. When the speed of first carriage 100 reaches a scanning speed (at exposure start position S3 of the forward end of original 0), original 0 is exposed and scanned at a uniform rate, or a constant speed. The above sequence of the copying operation is repeated a predetermined number of times as set by numerical keys 84 on operation panel 80. Then, first carriage 100 is returned to the home position SH, and is placed in a stand-by state.

In step ST1, when control decides that the 100 % magnification has been set, controls jumps to step ST3. In this step ST3, first carriage 100 is moved from home position SH to 100 % magnification start position S2, through operation start position So. This start position S2 is set in the following way. First carriage 100 is made to move at the acceleration which 12 equal to the predetermined acceleration for the maximum reduction-magnification. That is to say, the acceleration of first carriage 100 in the acceleration section from the start position to the exposure start position in the same for every magnifying operation. In this case, the scanning speed for the 100 % magnification can be obtained at the exposure start position S3 of original 0. The distance between start positions S1 and S2 is set at 3.93 (mm), for example.

When first carriage 100 is moved to start position S2, a copying operation is started in step ST4.

This will be described with reference to Fig. 9 showing a speed vs. distance relationship during the one-stroke operation of first carriage 100 when the i % magnification is set up. In Fig. 9, curves indicated by solid lines show speed variations of the first carriage in the copying machine according to the present invention, while a curve indicated by dotted line shows a variation of a speed of first carriage 100 in the conventional copying machine.

First carriage 100 is accelerated from start position S2 for the 100 % magnification and its speed reaches the predetermined scanning speed at exposure start position S3 of the forward end of original 0 (acceleration time T1). From exposure start position S3, it is moved at a constant speed to expose and scan original 0 (scanning time T2'i. An image is formed by the exposure and scanning operation of original 0 in the following way.

An operator places original 0 on document table 14. Then, he sets a desired number of copies by numerical keys 84, with the above copying magnification, and pushes copy key 82. Upon depression of the copy key, exposure lamp 22 illuminates original 0, while first and second carriages 100 and 102 are moved along guide rails 104 and 106, as described above. In this way, the exposure and scanning operation of original 0 progresses. The reflecting light from original 0 is led through magnification varying lens block 30 and mirror 32 to photoconductive drum 34, which has been charged by main charger 36, so that an image of original 0 is formed on R j the drum 34. Subsequently, developer 38 makes the formed image visible. The visible image is transferred onto paper P by transfer unit 48. The paper has been transported to transfer unit 48 from upper or lower paper supply cassette 401 or 402. Paper P with the transferred image is separated from the surface of drum 34, and moved to fixing roller 58. The fixing roller 58 fixes the transferred image on the paper. Then, it is discharged to tray 62.

Following the exposure and scanning of original 0, first carriage 100 is decelerated (deceleration time T3) and temporarily stopped (switching time T4). This switching time T4 is a time required for reversing rota tion of scanning motor 110 to return first carriage 100 to start position S2. With the reversed rotation of the scanning motor, first carriage 100 is accelerated and moved in the reverse direction (acceleration time TS), and is returned to the start position S2 for the 100 % magnification at a higher speed than it is moved for the exposure and scanning (return time T6, acceleration time T7). First carriage 100 returned to start position S2 is temporarily stopped there in preparation for the copies not yet to be processed which may exist (switching time T8). In step ST5, control checks if the copying operation has completed. If it is not yet completed, and the copies not yet to be processed exist, first carriage 100 is moved from start position S2 again, and the above sequence of the copying operation is performed, and repeated till the copying operation is completed in step ST5.

When all of the remaining copies have been processed, first carriage 100 is moved to home position SH, and placed in a stand-by state (step ST6).

in the present embodiment, as shown in Fig. 8, a period that first carriage 100 is accelerated, viz., an approach period, for the 100 % magnification is shorter than that for the maximum reductionmagnification. Therefore, as seen from Fig. 9, a time taken for one stroke of first carriage 100 is reduced when comparing with that of the conventional copying machine. This implies that a time taken for the operation to make one is copy can be reduced.

In Fig. 9, the respective time periods are as follows:

Acceleration time Tl = 29.6 (ms) Scanning time T2 = 1939.0 (ms) Deceleration time T3 29.6 (ms) Switching time T4 54.6 (ms) Acceleration time T5 96.8 (ms) Return Time T6 699 (ms) Deceleration time T7 96.8 (ms) Switching time T8 54.6 (ms) Accordingly, the time consumed by one copying operation reaches 3000 (ms). This time amounts to j time for copying 20 sheets/minute of A4 size in a successive mode.

In the copying operation of the 100 % magnification with the fixed start position as by the conventional copying machine, if the first carriage 100 is accelerated from start position S1 for the maximum reducltionmagnification, a distance between start posi tions S1 and S2 is added to both the going and return distances of first carriage 100. If the scanning speed is 121 (mm/s) and the return speed is 292.86 (mm/s), a time taken for first carriage 100 to shift between start positions S1 and S2 is (3.93/121 + 3.93/292.86) x 103 = 45.9 (ms) In this instance, the distance first carriage 100 moves is elongated 45.9 (ms), and hence a time of one copying operation is 3000 + 45.9 = 3045.9 (ms) This time corresponds to the time required for copying 19.7 sheets/minute of A4 size in a successive mode.

These figures indicate that if the shifted start position is used, the copying speed may be improved by 0.3 sheets/minute. This means that a required copying time will be greatly reduced when the number of copied sheets is large, or a large number of copied sheets will be obtained within a fixed period of time, in compared with the conventional copying machine.

In the above-mentioned embodiment, the start position of first carriage 100 is shifted only for the copying operation of 100 % magnification. it is evident that the technical idea of shifting the start position of first carriage 100 is correspondingly applicable for the copying operation of the enlargement magnification. Also in this case, the time for the enlargement copying operation may be reduced. More specifically, first carriage 100 is made to move at the acceleration equal to the predetermined one for the maximum reduction- magnification. In this case, the start position S4 for the maximum enlargement-magnification (e.g., 154 %), for example, may be set on the basis of exposure start positiOn S3 of original 0 (Fig. 8). The copying operation of the maximum enlargement-magnification is similar to that of the maximum reduction-magnification, and hence description of it will be omitted.

In the above-mentioned embodiment, the home position of first carriage 100 is set at the position (position SH in Fig. 6) indicating a copying range depending on a copying magnification as set. Alternatively, it may be set at the operation start position (position SO in the same figure) or the start position for the maximum reduction-magnification (S1 in the same figure), for example.

While the present invention has been described by using the embodiment in which the invention is applied for a copying machine, it may be applied to a scanner, c - 21 for example.

Reference is made to rig. 10 illustrating a structure of a,,canner incorporating the present invention. As shown, document table (transparent glass plate) 14 for supporting original 0 is secured to the central portion of top panel 12 laid on the top scanner main body 101. Table 14 is provided with fixed scale 16 providing a reference when original 0 is set on table -14. Further, cover 18, which may be open and close, is located near table 14. original 0 placed on table 14 is exposed to light and scanned when an optical system including exposure lamp 22, and mirrors 24, 26 and 28, is reciprocately moved along the bottom surface of table 14 in the directions of arrow "a, ". In this case, to maintain an optical path, mirrors 26 and 28 are moved at the half speed of that of mirror 24. The refl'--cting light from the original resulting from the illumination by lamp 22, is reflected by mirrors 24, 26 and 28, passes through magnification varying lens block 30, reflected again by mirror 32, and led to photoelectric converter 160. Photoelectric converter 160 converts the reflected light into an electrical signal representing an image of theoriginal, and supplies the electrical signal to an output device (not shown).

The basic structure of the scanner is the same as that of the copying machine described in the first embodiment. only the difference between them is that in the former, the reflecting light by exposure lamp 22 is led to photoconductive drum 34, but in the latter, it is led to photoelectric converter 160. Therefore, the drive mechanism for the scanner is the same as that for the optical system in the first embodiment. The mechanism shown in Figs. 5 and 6 is available for the scanner drive mechanism. Hence, no description of the scanner drive mechanism will be given.

1 4

Claims

Claims:

1. An apparatus for forming an image on an image forming medium, said apparatus comprising: means for optically scanning an original; means for setting one of a plurality of magnifications with respect to an image obtained by scanning the original; means for initializing said optical scanning means at an initial position; and means for controlling a distance for which said optical scanning means is moved from an initial position to a start position where said optical scanning means starts operating, in accordance with an image forming magnification set by said magnification setting means, is said optical scanning means being accelerated from the initial position to the start position and reaching the start position in an accelerated condition.'

2. An apparatus according to claim 1, wherein said - control means controls the movement of said optical scanning means such that said optical scanning means is accelerated from the initial position to the start position in accordance with a smallest one of at least two different image forming magnifications and is moved at a constant speed after passing the start position.

3. An apparatus according to claim 2, wherein said control means controls the distance for which optical scanning means is moved to the start position so 1 that the start position is fixed at the same position independent of said at least two different image forming magnifications.

4. An apparatus according to claim 1, wherein said optical scanning means includes an exposure lamp for illuminating said original with light, a scanning motor for driving said optical scanning means per se in said predetermined direction, and a motor driving means for driving said scanning motor and for determining the ini- tial position and the start position.

5. An apparatus according to claim 1, wherein said magnification setting means includes a means for selecting a desired image forming magnification from among said at least two different image forming magni- fications.

6. An apparatus according to claim 1, wherein said optical scanning means is set by said control means at an initial position which indicates an image forming range based on both the image forming magnification set by said magnification setting means and the size of said image forming medium.

7. An apparatus according to claim 6, wherein said control means controls the movement of said optical scanning means such that said optical scanning means is accelerated from the initial position to the start position in accordance with a smallest one of at least two different image forming magnifications and is moved h at a constant speed after passing the start position.

8. An apparatus according to claim 7, wherein said control Means controls the distance for which said optical scanning means is moved to the start position so that the start position is fixed at the same position independent of said at least two different image forming magnifications.

9. An apparatus according to claim 6, wherein said optical scanning means includes an exposure lamp for illuminating said original with light, a scanning motor for driving said optical scanning means per se in said predetermined direction, and a motor driving means for driving said scanning motor and for determining the initial position and the start position.

10. An apparatus according to claim 6, wherein said magnification setting means includes a means for selecting a desired image forming magnification from among said at least two different image forming magnifications.

11. An apparatus according to claim 1, wherein said optical scanning means is set by said control means at an initial position which is located away from the start position in a direction opposite to the direction in which the scanning operation is performed.

12. An apparatus according to claim 11, wherein said control means control's the movement of said optical scanning means such that said optical scanning means is 1 1 accelerated from the initial position to the start position in accordance with a smallest one of at least two different image forming magnifications and is moved at a constant speed after passing the start position.

13. An apparatus according to claim 12, wherein said control means controls the distance for which said optical scanning means is moved the start position so that the start position is fixed at the same position irrespective of said at least two different image forming magnifications.

14. An apparatus according to claim 11, wherein said optical scanning means includes an exposure lamp for illuminating said original with light, a scanning motor for driving said optical scanning means per se in said predetermined direction, and a motor driving means for driving said scanning motor and for determining the initial position and the start position.

15. An apparatus according to claim 11, wherein said magnification setting means includes a means for selecting a desired image forming magnification from among said at least two different image forming magnifications.

16. A scanning apparatus, comprising:

means for optically scanning an original; means for setting one of a plurality of magnifications with respect to an image obtained by scanning the original; 1 44 j % 11 27 - means for initializing said optical scanning means at an initial position; means for photoelectrically converting the image to an electrical signal at the one of a plurality of magnifications based on the image; and means for controlling a speed, which is selected from a plurality of speeds and at which said optical scanning means is moved from the initial position to a start position where said optical scanning means starts operating, in accordance with a scanning magnification set by said magnification setting means, said optical scanning means being accelerated from the initial position to the start position and reaching the start position in an accelerated condition.

17. An apparatus according to claim 16, wherein said control means controls the movement of said optical scanning means such that said optical scanning means is accelerated from the initial position to the start position-in accordance with a smallest one of ci... least two different scanning magnifications and is moved at a constant speed after passing the start position.

18. An apparatus according to claim 17, wherein said control means controls the distance for which said optical scanning means is moved to the start position so that the start position is fixed at the same position irrespective of said at least two different scanning magnifications.

z. %

19. An apparatus according to claim 16, wherein said optical scanning means includes an exposure lamp for illuminating said original.with light, a scanning motor for driving said optical scanning means per se in said predetermined direction, and a motor driving means for driving said scanning motor and for determining the initial position and the start position.

20. An apparatus according to claim 16, wherein said magnification setting means includes a means for selecting a desired scanning magnification from among said at least two different scanning magnifications.

21. An apparatus according to claim 16, wherein said optical scanning means is set by said control means at an initial position which indicates a scanning range based on the scanning magnification set by said magnification setting means.

22. An apparatus according to claim 21, wherein said control means controls the movement of said optical scanning means such that said optical scanning means is accelerated from the initial position to the start position in accordance with a smallest one of at least two different scanning magnifications and is moved at a constant speed after passing the start position.

23. An apparatus according to claim 22, wherein said control means controls the distance for which said optical scanning means is moved to the start position so 4 i that the start position is fixed at the same position irrespective of said at least two different scanning magnifications.

24. An apparatus according to claim 21, wherein said optical scanning means includes an exposure lamp for illuminating said original with light, a scanning motor for driving said optical scanning means per se in said predetermined direction, and a motor driving means for driving said scanning motor and for determining the initial position and the start position.

25. An apparatus according to claim 21, wherein said magnification setting means includes a means for selecting a desired scanning magnification from among said at least two different scanning magnifications.

26. An apparatuL according to claim 16, wherein said optical scanning means is set by said control means at an initial position which indicates a scanning range based on the scanning magnification set by said magni fication setting means.

27. An apparatus according to claim 26, wherein said control means controls the movement of said optical scanning means such that said optical scanning means is accelerated from the initial position to the start position in accordance with a smallest one of at least two different scanning magnifications and is moved at a constant speed after passing the start position.

28. An apparatus according to claim 27, wherein 4 said control means controls the distance for which said optical scanning means is moved to the start position so that the start position is fixed at the same position irrespective of said at least two different scanning magnifications.

29. An apparatus according to claim 26, wherein said optical scanning means includes an exposure lamp for illuminating said original with light, a scanning motor for driving said optical scanning means per se in said predetermined direction, and a motor driving means for driving said scanning motor and for determining the initial position and the start position.

30. An apparatus according to claim 26, wherein said magnification setting means includes a means for selecting a desired scanning magnification from among said at least two different scanning magnifications.

31. An image forming apparatus having function for controlling scanning start position, substantially as hereinbefore described with reference to the accompany- ing drawings.

Pubhshed 1988 at The Patent Office. State House. 66 71 High Ho'born. London WC1R 4TP_ F_,rther copies may be obtained from The Patent Office. Sales Branch, St Mary Cray. Orpington. Kent BR,5 3RD Printed by Multiplex techniques Itd. St Mary Cray. Kent. Con 1,87- 1