GB1571095A - Variable magnification photocopier - Google Patents

Description

(54) A VARIABLE MAGNIFICATION PHOTOCOPIER We, CANON KABUSHIKI KAISHA, a Japanese Company of 30-2, 3-chome, Shimomaruko, Ohta-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a variable magnification line-by-line photocopier.

Photocopiers are of two types. One is of the type in which the entire area of the original is exposed at once, which is called "full illumination type".

The other is of the so called "scanning type" in which the original is successively exposed line-by-line from one edge to the other. Practically the latter is more widely employed than the former.

In the case of the latter, it is known that a preliminary operation of the optical system is required which is usually called "prerunning". This is because at the starting time of movable optical members such as mirror and original table, there occur vibrations that give adverse effects to the image, for example, make the produced image unclear.

To prevent such adverse effects caused by vibration of mirror or original table when they begin to move, they are preliminarily moved by a predetermined distance or prerun distance to allow them to reach the desired running speed. This additional running is what is called "pre-running".

This has been troublesome in the past.

Notwithstanding, however, the scanning type of apparatus has been widely employed and preferred.

This is because it has various advantages which outweigh the above mentioned disadvantage. For example, it permits miniaturization of optical system assembly and use of a small light source for exposure.

But, if a variable magnification mechanism, for example, to reduce the image of an original is incorporated into a scanning type of optical system, another problem arises. The problem is that images are produced in which the fore edge portion is missing. This is caused by the fact that when a reduced copy image is formed, the running speed cf the movable optical members is increased, and since a photosensitive body on which the image is received moves always at the same speed given for copying at 1:1 magnification, prerunning of the optical system finishes prematurely and transmission of the image to the photosensitive body begins too soon.

The opposite occurs when a magnified image is formed and the scanning speed is reduced.

To solve the problem, it is known that the photosensitive sheet (for FAX type copying apparatus) or the transfer sheet (for transfer type copying apparatus) may be fed and conveyed with a suitabie time delay enough to obtain coincidence. However, there are arranged along the path of the photosensitive copy sheet or the transfer sheet various elements and members such as control means for the sheet feeding and conveying device, control means for the transfer sheet separator and a blocking detector at the fixing station. Due to this, control of the necessary time delay mentioned above becomes very complicated and troublesome.

The present invention provides a variable magnification line-by-line photocopier, comprising means for moving a photosensitive member at a constant speed past a position at which it receives an image of an original produced by optical scanning means, the scanning means including a member movable at a scanning speed variable in accordance with the selected magnification, and control means for varying the starting position of the movable member in accordance with the selected magnification such that the time required for the movable member to move from the starting position to the position at which scanning of the fore edge of the original is commenced remains substantially constant regardless of the selected magnification.

The pre-running or pre-scan distance of the scanning member may be adjusted in accordance with a selected magnification (m) at a rate of lim and its speed at v/m, where v is the speed when m equals 1 and 1 the pre-scan distance when m equals 1.

Thus, the time required for the optical means to move through the pre-scan distance is constant irrespective of the selected magnification. The scanning member thus reaches the fore edge of the original at substantially the same time as the exposure of the photosensitive member to the image starts.

The scanning member may comprise a mirror movable at a speed v/m, with a stationary original carrier, or the scanning member may comprise the original carrier itself movable at the speed v/m. Where the scanning member comprises a scanning mirror, a second mirror may be provided in the scanning means which moves at half the speed of the first.

For the case of a scanning speed of 150 mm/sec., for example, the pre-running length may be about 40-60 mm.

Some preferred embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic view of an arrangement of copying apparatus having a stationary original table and movable illuminating means and reflecting means showing one embodiment of the invention.

Fig. 2 shows one example of scanning method by a reflecting means in the same type of the apparatus as shown in Fig. 1.

Fig. 3 is a schematic view of essential part of a copying apparatus as shown in Fig. 2 illustrating in particular the operation of optical means.

Fig. 4 is a schematic view of positioning mechanism in the apparatus as shown in Fig. 3 showing in particular how to position the first mirror for variable magnification copying.

Fig. 5 shows an electric circuit for controlling the scanning system in the copying apparatus shown in Fig. 4.

Figs. 6 and 7 show an electric circuit for automatically setting back a scanning optical system from its position for variation copy to the position for unit copy after one operation of variation copy has been completed.

Fig. 8 is a schematic view of the essential part of an apparatus having movable original table showing another embodiment of the invention.

Fig. 9 is a similar view as Fig. 8 but showing another type of copying apparatus in which first latent image is formed at first and then second latent image is formed and a stationary original table is provided.

Fig. 10 is a schematic view of a driving mechanism for lens member in the variable magnification photocopier illustrating the manner how to move and stop the lens member, and Fig. I I shows a circuit for operating the mechanism shown in Fig. 10.

Referring to Fig. 1, there is shown in a schematic sectional view a transfer type of electronic copying apparatus with a stationary original supporting plate. The apparatus includes a photosensitive body I in the shape of a drum which is known, for example, by U.S.P. 3,666,363 and comprises three layers, namely an electric conductive substrate, a photoconductive intermediate layer and an insulating top layer on the substrate. Around the drum 1 are positioned a first corona discharge device 2, a second corona discharge device 3 having the function of simultaneous exposure, a developing device 4, a cleaning device 5, a stack of transfer sheets 6, a sheet feed roller 7, registering roller 8, a transfer corona discharge device 9, a conveyor belt 10, a heat roller fixing device 12 and a sheet discharge tray 13.An original 15 to be copied, for example, a document, is placed on an original supporting plate 14. The original 15 is illuminated by a lamp 16 and the reflected image of the original is exposed on the surface of the photosensitive drum 1 by means of a first mirror 17, a second mirror 18, a lens 19 having a driving mechanism, a third mirror 20 and a fourth mirror 21. To form a copy of the original with said apparatus, the photosensitive drum 1 rotating in the direction indicated by the arrow at the rate of Vr is charged by the first corona discharge device 2 and then the image of the document is exposed on the drum while being discharged by the second corona discharge device 3.

This exposure of the original is effected by the lamp 16 and the first mirror 17 moving at the rate of V1 relative to the original 15 on the stationary supporting plate 14 made of glass, the second mirror 18 moving at the rate of V1/2 in the same direction as the first mirror 17, the lens 19 and the mirrors 20 and 21.

By this exposure step there is formed on the photosensitive drum 1 an electrostatic latent image which is then developed by the developing device 4. The developed image is transferred onto the transfer sheet 6 under the action of the electric field produced by corona discharge from the transfer corona discharge device 9. The developed image on the transfer sheet 6 is fixed by the fixing device 12 and finally the sheet 6 is discharged into the sheet discharge tray 13.

When the original has to be copied at a selected magnification which is not 1:1 magnification with the apparatus, the first and second mirrors 17 and 18 are shifted so that their scanning starting positions come to 17' and 18' respectively. At the same time, in order to change the imaging magnification, the lens 19 is displaced to the position indicated by the dotted line and also the third and fourth mirrors 20 and 21 are shifted to the positions indicated by the reference numerals 20' and 21' respectively.

Provided that the pre-running length for 1:1 magnification is 1, and that for the selected magnification m is 12, then 12 will become l1/m. Therefore. the shift of the first mirror 17 is increased by the distance 12. lj compared with that for 1:1 magnification so as to give a lengthened pre-running length in accordance with the magnification change.

This makes it possible to form the image of the fore edge position 0 of the original document at the correct position as in case of 1:1 magnification. To form the image of the fore edge of the document always at the same position on the photosensitive drum 1 rotating at the rate of V1 irrespective of the magnification change, it is required that the scanning time t of the original 15 viewed from the drum side should be the same as that for 1:1 magnification. In other words, the requirement for this purpose is only that the relation t=11/V1=12/V2 (V2 is the velocity of the first mirror 17 for the given magnification) should be satisfied and the pre-running length 12 for the selected magnification m should be 11/m.With the change in the position of the lens 19, the third and fourth mirrors 20 and 21 are shifted to focus the image of the original on the photosensitive drum 1. A conventional transmission mechanism (not shown) may be employed to give the first and second mirrors 17 and 18 the required velocity V2 corresponding to the selected magnification. For example, the mirrors may be connected with a wire cord moving around a pulley rotating at a variable rotational speed in accordance with the given magnification.

Fig. 2 illustrates the manner how to set the various pre-running positions may be set in accordance with magnification as well as the corresponding operation of the first mirror in a copying apparatus equipped with a variable magnification system as described above. The copying apparatus shown in Fig.

1 allows to select one of two copy sizes. In contrast with the apparatus of Fig. 1, the copying apparatus of Fig. 2 has a wider selection range. It allows the selection of magnification from four degrees of magnification, that is, 1:1, 1:0.8, 1:0.82 and 1:0.71 Now referring to Fig. 2, four operational examples A-D of the first mirror will be explained. The first mirror 22 corresponds to the first mirror 17 of the apparatus shown in Fig. 1. The first mirror 22 is integrally formed with a support 23 on which a cam '4 is fixedly mounted. The first mirror moves in the direction indicated by the arrow at a given velocity to scan the original. A second mirror which scans the original at a rate of 1/2 velocity of that of the first one is not shown in Fig. 2 for clarity.Microswitches M1--M6 are opened and closed by the above mentioned cam 24 through the action of the corresponding actuator to detect the position of the first mirror and control the scanning. The position 0 is the position of the fore edge of the document and L in Fig.

2 corresponds to the pre-running length 11 in Fig. 1 and indicates the pre-running length for copying at 1:1 magnification.

The starting position of the first mirror 22 is determined by the cooperation of one of the microswitches M1--M4 and a magnification control means (not shown).

The microswitches M1--M4 are selectively used to detect and determine the starting position of the first mirror 22 and Ml is selected for 1:1, M2 for 1:0.87, M3 for 1:0.82 and M4 for 1:071 magnification. The operational example A shows the case where the original is to be copied at 1:0.87 magnification after the first mirror 22 has been in its position for 1:1 magnification. In this case, for example, the operator pushes the operation button for 1:0.87 magnification (not shown) arranged on an operation panel (not shown) so as to move the cam 24 of the first mirror in the direction indicated by the arrow.When the cam 24 reaches the microswitch M5, the corresponding actuator is actuated to operate the microswitch M5 which, in turn, causes the reversal of the movement of the mirror 22 as indicated by the arrow. The movement in the reversed direction of the cam 24 with the mirror 22 continues until the cam 24 reaches the microswitch M2 and actuates it to stop the mirror 22. After the pre-running length has been adjusted in this manner, the apparatus is now ready for copying at 1:0.87 magnification.

In the same manner, the apparatus can be shifted from the position for copying at 1:0.71 magnification to that for 1:1 magnification as shown by the arrow in the example B. The arrow in the example C indicates the movement of the cam 24 for the case where the operator cut off the power source due to some cause during the scanning of the original by the first mirror 22 and some time after again switched on the apparatus and pushed the operation button for 1:0.82 magnification (not shown).

As illustrated. the current from the source makes the cam 24 with the mirror 22 continue scanning until the cam 24 reaches the microswitch M6. The microswitch M6 actuated by the cam 24 reverses the movement of the mirror 22 and now the cam 24 is moved toward the microswitch M3.

When the cam 24 contacts with the microswitch M3, it will stop the mirror 22 as ordered by the above mentioned operation button. The apparatus is then ready for copying at 1:0.82 magnification and the mirror 22 can start scanning the original.

In case of the last example D, a copy is made at the same magnification as that for the previous copy cycle. The arrow indicates the movement of the cam 24 for this purpose. When the scanning of the original supporting plate has been completed, the microswitch M6 is actuated to reverse the movement of the mirror 22 as in the case of the example C. The reversed cam 24 is again stopped at the same starting position. The function of the microswitch M5 is to shorten the time required for changing the starting position of the first mirror 22. As understood from the foregoing, when the first mirror is positioned in a given starting position, the mirror is stopped always when moving in the same direction following its reversal by the microswitch M5 or M6. Because of this errors in operation of the microswitches can be reduced.The distance moved by the first mirror 22 and the speed of its movement are determined in accordance with the selected magnification as described above and the pre-running length for the selected magnification can be calculated by the method as described above referring to Fig.

1.

A substantial increase in copying speed can be attained if the first mirror 22 is moved to a given starting position, after reversal by the microswitch M6, at a higher speed than that during scanning by changing the speed of the mirror at its reversal point.

In the embodiments described above, a cam is used to actuate microswitches and actuators to position the mirror. However, it should be noted that the use of such a cam is by no means essential for the invention. This is one example of means for determining the pre-running starting position of the mirror.

In copying apparatus equipped with a variable magnification system, it is a common practice to position the scanning mirror and the focusing lens for copying at a selected magnification with mechanical positioning means such as cam and microswitch. As is well known, in the production of copies with this type of apparatus, misalignment of optical system often occurs due to inertia forces of the operational members and limited operational accuracy of cam and switch members. When such misalignment has once occurred, copy quality is reduced for example, because of marginal image difference between the original and the copy thereof, obscurity of the copied image and extraordinary distortion of the copied image crosswise or lengthwise.One solution to this problem is that the stopping of the optical system is always effected at a given position only when it is moved toward the position from one direction. This reduces the risk of misalignment of the optical system in its stop position. Thus the image quality of the copy is improved and also the manufacturers have no worries above the size of operational members, cam members and the like.

The manufacture and adjustment of these members becomes very easy.

Control of the optical system in the above mentioned type of copying apparatus will now be explained. In the following examples, the apparatus used comprises the same photosensitive body as the photosensitive drum in Fig. 1 embodiment and has three different magnifications.

Referring to Fig. 3, there is shown an arrangement of lens system, mirrors and the like of the apparatus mentioned above. The apparatus is an electrophotography copy machine which comprises a stationary original supporting plate and in which the image of the original document is exposed on a rotating photosensitive body b-slit exposure.

In the drawing of Fig. 3, the photosensitive body is designated by la, and the direction of its rotation is indicated by the arrow. An original 15a placed on an original supporting plate 14a is illuminated by a lamp 25 and exposed onto the surface of the photosensitive drum la by means of a first mirror 26, a second mirror 27, a lens system 28 having a driving mechanism, a third mirror 29 and a fourth mirror 30. To form a copy image with the apparatus, discharge devices are provided around the drum la and corona discharge therefrom is used for exposure in the conventional manner. The original supporting plate is made of glass and the lamp 25 illuminating the original 15a placed on the glass plate is moved at the rate of V, together with the first mirror 26. The second mirror 27 is moved at the rate of V,/2 in the same direction as the first mirror 26.

The exposure of the original is effected by these mirrors 26, 27, the lens system 28 and the mirrors 29 and 30.

When the magnification is changed, the pre-running length of the first mirror 26 is changed in accordance with the magnification change, as shown in Fig. 1. Simultaneously, the pre-running length of the second mirror 27 is changed one half of the pre-running length change of the mirror 26. Thus, the first and second mirrors 26 and 27 are shifted and also the lens system 28 is shifted to the position 28', the third mirror 29 and 29' and the fourth mirror 30 and 31' respectively.

The shift of the mirrors 29 and 30 is effected as follows: The mirrors 29 and 30 are supported by a supporting block 31 which is slidingly movable along a pair of guide rails 32. The supporting block 31 is under the action of a pair of springs 33, 34 which pull the supporting block 31 toward the left-hand side of the plane of the drawing. The positioning of the supporting block 31 is effected by a rotary eccentric cam 35 abutting on the block and keeping it in its position against the pulling force of the springs 33, 34. The eccentric cam 35 is rotated together with its rotary shaft 36.

Therefore, by controlling the amount of the rotational motion of the shaft 36 in accordance with the selected magnification, the positions of the mirrors 29 and 30 can be adjusted as desired.

The control of the operation of the scanning optical system in the above described apparatus is explained referring to Fig. 4.

The lamp 25 and the first mirror 26 are supported by a supporting block 37. Fixed on the underside of the supporting block there is a cam 38 to actuate microswitches 39 through 43. The photosensitive drum la, the supporting block 37 and the second mirror 27 are driven by a motor 47. During the operation time for copying, the motor is rotating at a uniform speed and the operational speed of the scanning optical system is changed by a set of clutches 45.To copy the original, for example, at 1:1 magnification, one of the clutches, namely the clutch 45a is energized so that the scanning optical system is moved leftwards by the motor 44 at the same speed as the peripheral speed of the drum la. For copying at a selected magnification m other than 1:1 magnification, the first mirror scans the original at a speed of (the peripheral speed of the drum la) x (I/m). The changing in the speed of the scanning optical system is effected by changing the rotational frequency of the motor 44 by the clutch 45.

The microswitches 39, 40 and 41 correspond to the magnification selector buttons 47a 47b and 47c respectively and are used to determine the starting position of the first mirror 26. When the original is copied at a selected magnification, the speed at which the scanning optical system is moved will change in accordance with the selected magnification, which may cause the copying apparatus to produce a defective copy in which the image of the fore edge portion of the original is missing. The pre-running of the first mirror 26 eliminates this problem. Usually prior to scanning the original, the scanning system is preliminarily moved by some distance, which is called "pre-running". By this pre-running, the adverse effect of the vibration occurring at the start motion of the scanning system can be prevented.However, when variable magnification copying process is carried out, the speed of pre-running changes in accordance with the selected magnification. Therefore it is necessary to compensate the change in pre-running speed by changing the distance of the pre-running (pre-running length) to prevent the produced copy from lacking the image of the fore edge portion of the original due to early exposure.

The microswitches M39, M40 and M41 are provided to adjust the above mentioned pre-running length.

The microswitch M42 is a switch for reversing the direction of the movement of the scanning system, and is equivalent to the microswitch M5 shown in Fig. 2. The microswitch M43 is also a switch for reversing the direction. This microswitch M43 detects the scanning of the original supporting plate and produces a signal to reverse the movement of the scanning system when the end of the original supporting plate is detected. When the microswitch M43 is actuated, the clutch 45d reverses the motor 44 which, in turn, reverses the scanning system. A control circuit part 46 is provided for controlling the operation of the scanning system and a selector button 47 selects magnification d.

The second mirror 27 is not shown in Fig. 4.

The mirror 27 corresponds to the first mirror 26 and is driven by the same driving mechanism as that for the first mirror.

Now referring to the electric circuit shown in Fig. 5, the operation of every part at the time when one of the selector buttons 47a - 47c shown in Fig. 4 is pushed for a desired magnification will be explained.

Starting from the position of the apparatus shown in Fig. 4 in which the cam 38 is actuating the microswitch M42, if the selector button 47a is depressed, the relay 48 will be thrown in the circuit and hold its position. Thereby the relay 51 is energized by power source A through NC (normal closed) relay contact 48-b of the microswitch M41 and NO (normal open) relay contact 52-e of the microswitch M42. The clutch 45--d is operated through the contact 51-b and the motor 44 is operatively connected with the supporting block 37 supporting the mirror 26. As a result, the supporting block 37 starts moving toward the right-hand side as viewed in Fig.

4. The shift of the supporting block 37 makes the cam 38 release the microswitch M42, but the contact 51-a of the relay 51 holds it. When the microswitch Ml related to the selector button 47a is actuated, the relays 48 and 51 are opened so that the optical system may stop.

If the cam 38 is in a position to the right of the microswitch M42 shown in Fig. 4, the depressing of the selector button 47b, after one operation cycle has been complete, will close the relay 49. Then, the electric current flows through NC contact 49-b of the microswitch M40, NC contact of the microswitch M42 and NC contact of the microswitch M43, and energizes the relay 52, which actuates the clutch 45-a through the contact 52-d. As a result, the optical system moves rightwards on the drawing of Fig. 4 and when the cam 38 actuates the microswitch M42, the relay 52 opens, the clutch 45-a is released and the optical system stops.When NO relay 51 of the microswitch M42 is energized to actuate the clutch 45-d, the optical system moves rightwards and the actuation of the microswitch M40 stops it. Where the cam 38 is in a ,)position between the microswitches M42 and M43, the action of the apparatus will be understood by substituting the microswitch M43 for the microswitch M42 in the above explanation.

As seen from the foregoing, it is important to shift the cam 38 to the position of M42 or M43 whenever the cam 38 is in a position on the right-hand side of the microswitch M42 or M43. The scanning of the original by the optical system must be started after it has been shifted to M42 or M43 and also after it has been stopped at the position of one of the microswitches M39 -- M41 corresponding to the switch selected by the selector button 47. Furthermore the stop position must be the position in which the selected switch is actuated by the right side cam surface of the cam 38. In this way it is assured that the scanning optical system always takes a definite starting position and that coincidence of scanning system and the fore edge portion of the original can be obtained irrespective of the width of the cam which actuates the microswitch.

In practical use of the variable magnification copying apparatus, the apparatus is usually used more often for copying at 1:1 magnification than for copying at any other magnification. Therefore, it is preferable for the apparatus to be set at its position for 1:1 magnification after it has been used to copy at another selected magnification.

When the apparatus has not been set back to 1:1 magnification, it is possible that the next time the apparatus is used this will not be noticed and copies at incorrect magnifications may be made. This can cause considerable loss of copy sheets, in particular in a high speed copying apparatus.

According to the preferred embodiment as shown in Figs. 6 and 7, the problem is solved by providing the apparatus with means for automatically setting back the apparatus to its position for copying at 1:1 magnification after copying at a selected magnification other than 1:1. The apparatus of this embodiment is essentially the same in arrangement of the optical system as that shown in Fig. 3, and, for simplification, the control of the lens system 28 will not be explained again. The difference between this embodiment and the above described embodiments is that a set of selector buttons 47 does not include the button 47a corresponding to 1:1 magnification. Instead of the button 47a, the electric circuit shown in Figs. 6 and 7 contains a timer T the output of which is used in a similar way to the output of the above mentioned button 47a.When a voltage is supplied to terminal XY, the timer T is actuated after a definite time delay and the output of the timer T is lost after a definite actuation time has elapsed. Therefore by applying a voltage to terminal XY, a signal essentially equal to the signal of the above described selector button 47a can be obtained. After the signal has been generated, the apparatus operates in the same manner as that described above.

In Fig. 6, CB designates a copying operation button. When the button CB is depressed, relays 53 and 54 are actuated and the contact 53-a is closed, which makes the terminal XY cut out from the power source. According to the rotational position of the photosensitive drum, switch HP is cut in to align the fore edge of the original to a given position on the photosensitive body. Then relay 54 is actuated and held through the contact 54-a. Relay 48' is held through the contact 48-c of the relay 48 as soon as DC power source is cut in. Because of the contact 48'-d being closed, the clutch 45-a is brought into operation and the lamp L is switched on for exposure.The first mirror is shifted and thereby the microswitch M43' is actuated, which microswitch M43' is arranged in parallel with the above described microswitch M43 arranged at the reversal position. With the actuation of the microswitch M43', the relay 55 is closed and the relays 53 and 54 are deenergized. Also, by the contact 54-b, the clutch 45-a, is released from its operation and the clutch 54-d is brought into operation by the contact 55-c. As a result the direction of the movement of the optical system is reversed. Thereafter, movement of the optical system in the reversed direction continues until the microswitch M42' arranged in parallel the above described microswitch M42 is actuated. With the actuation of the microswitch M42', the relay 55 is opened and simultaneously the clutch 45--d is released so that the optical system stops. At the same time, the relay 56 is opened to connect terminal XY with the source so that the timer T (see Fig. 7) may start operating. The output of the timer T actuates the relay 48. At the time when the relay 48 is closed and one copy cycle has been completed, the scanning part including the first mirror is in a position in which it actuates the microswitch M42. Therefore, the scanning optical system must be shifted until it closes the relay 51 and actuates the microswitch M41.In this manner. the lens system as well as the optical system of the scanning part can be set back to the position for copying at 1:1 magnification upon the completion of a copying operation even when the copying operation was that for a selected magnification other than 1:1.

As described above, when the optical elements of the apparatus such as lens system, mirrors and lamp are moved to make different magnification copies the determination of their set position must be made by stopping the optical elements only when they are moving in one direction. By doing so, any possible operational error caused by switch actuating members such as the cam may be eliminated to a great extent.

This requires reversal of the movement of the optical part whenever it comes from a direction different from that direction. The switch means arranged for copying at 1:1 magnification may also serve as means for reversal and, therefore, the cost involved in such reversal will be compensated by the advantage of the resultant smooth operation in view of the frequency of the use of 1:1 magnification. Also, as mentioned above, the loss caused by possible operator's mistakes can be reduced by automatically setting back the optical elements to their position for copying at 1:1 magnification. It should be noted that the concept of automatic setting back and the concept of undirectional stop setting for the optical system described above are independent of each other.

All of the above explanations have been made of variable magnification copying apparatus having a stationary original supporting plate or table. In particular, coincidence by "pre-running" for different magnification copies which is an important feature of the present invention. has been explained referring to Fig. 1 showing the apparatus in which mirror scanning is adopted. The method for adjusting the position of the mirror for selected magnification copies and the mechanism for carrying it out have been explained referring to Fig. 2. Referring to Figs. 3 and 4, a more detailed concrete apparatus embodying the invention has been explained and an electric control mechanism for the optical system illustrated in Fig. 4 has been explained in detail referring to Figs. 5 through 7.

Fig. 8 shows an apparatus having a movable original supporting plate, in which coincidence by "pre-running" for different magnification copies is provided.

In the drawing reference numeral 57 designates an original supporting plate made of glass, 58 is an original, 59 is a stationary mirror, 60 is a first movable mirror, 61 is a second movable and 62 designates a third movable mirror. These movable mirrors are shifted to the positions indicated by phantom line respectively when the original is copied at a selected magnification other than 1:1 magnification.

63 designates a lens having a driving mechanism, 64 is a lamp for illuminating the original and 65 is a cam firmly attached to the under side of the original supporting plate. Microswitches M7 - M10 are opened and closed by this cam 65.

A photosensitive body in the shape of a drum 66 rotates at a peripheral speed of V1 ;in the direction indicated by arrow. The original supporting plate is shown in its position for copying at 1:1 magnification.

The image of the original is exposed on the photosensitive drum 66 while the original plate is moving in the direction indicated by arrow at a speed of V1. In this drawing, position 0 indicates the position of the fore edge of the original and 11 is pre-running length for 1:1 magnification. Microswitch M9 functionally corresponds to the microswitch M5 shown in Fig. 2 and M10 corresponds to M6 also shown in Fig. 2. When an operator wishes to make a copy at 1 :m magnification after copying at 1:1 magnification, he pushes an operation button for l:m variation copy (not shown).

Then the original supporting plate 57 moves in the direction of arrow until the cam 52 actuates the microswitch M9 to reverse the movement. After reversal the plate 57 comes back and at the moment when the cam 65 actuates the microswitch M8, it stops. The apparatus is then ready to start copying at l:m magnification. Pre-running length in this step is Im and the speed of the original supporting plate is V2. The value of Im is l1/m and V2 is Vl/m.

The speed V2 may be obtained by changing the driving force. A driving means the rotational frequency of which varies in accordance with the selected magnification and a wire rope for driving the original supporting plate may be used to change the speed of the original supporting plate.

In the above described embodiments, the copying apparatus comprises a photosensitive body on which the image of copy is developed.

Fig. 9 shows another type of copying apparatus to which the present invention is applicable. In the apparatus of Fig. 9, a first electrostatic latent image is formed on a photosensitive body and from the latent image a second electrostatic latent image is formed on another insulating material.

The apparatus of Fig. 9 includes a screen photosensitive body 67 (hereinafter referred as screen) composed, for example, of core electric conductive member, photoconductive material on the core and surface insulating material. It has a plurality of fine openings. A detailed explanation of structure and latent image forming process of such a kind of screen has been made in U.S. Serial No. 480,280 by the applicant of this application.

The screen 67 rotates in the direction of arrow and the first electrostatic latent image is formed on the surface of the rotary screen by first and second corona discharge devices 68 and 69 and a full illumination lamp 70. In the screen 67, there is provided a corona discharge device 71. After the first latent image has been formed, the screen is subjected to ion modulation at the position of the corona discharge device 71 and fos-ms a second electrostatic latent image on the surface of the insulating drum 72 which rotates in the direction of arrow at the same peripheral speed as that of the screen 67.

The second electrostatic latent image formed on the insulating drum 72 is developed and transferred to a transfer material in the same manner as the photosensitive drum of Fig. 1 embodiment.

Above the screen 67, there is a stationary original supporting plate 73 which is the same as the stationary original supporting plate of Fig. I embodiment. An original 74 placed on the supporting plate 73 is exposed on the screen 67 through first mirror 75, lamp 76, second mirror 77, lens 78 having a driving mechanism, third mirror 79, fourth mirror 80 and fifth mirror 81. The first mirror 75 moves in the direction of arrow at a speed of V, and the second mirror 77 moves by a distance equal to 1/2 of the distance the first mirror moves, and at a speed of V,/2.

In order to make a variation (different magnification) copy, the optical system is shifted to the position indicated by phantom line. For the apparatus in which ion modulation system or conventional latent image transfer method (TESI method) is adopted, the number of mirrors to be used must be an odd number. In the drawing, position 0 indicates the position of the fore edge of the original, Ii is pre-running length for 1:1 copy and Im is pre-running length for a different magnification copy.

As described above, in Fig. 9 the prerunning length is adjusted in accordance with the selected magnification to prevent the image of the fore edge portion from being out off in the produced copy.

Therefore, the invention allows production of a relatively high quality copy with a scanning type of variable magnification electronic copying apparatus.

A further advantage of the present invention is that there is no need for the speed of the photosensitive body to be controlled or for complicated control elements of copy sheet or transfer sheet feeding and conveying members. This ib because according to the invention, copying at a selected magnification can be done only by changing the speed of the moving original table or the speed of the moving scanning optical system.

In addition to the above advantages, the present invention reduces the trouble caused by unstable motion of the movable part of the apparatus at its starting time.

This is of importance in particular for the case where an original to be copied as a reduced image. According to the present invention, in this case, the pre-running length is lengthened so that the unstable motion caused by the increase in scanning speed may be dissipated by the time the fore-edge of the original is reached.

In the above described embodiments, only a photosensitive body in the form of a drum rotating at a constant speed has been shown and explained. However, the present invention is applicable to copying apparatus provided with other types of photosensitive body such as photosensitive web moving round at a constant speed or a photosensitive sheet or plate being moved at a constant speed.

In the described embodiments, microswitches for detecting the position of the optical system, e.g. mirror and original supporting glass plate, along its path. But it is also possible to use photoconductive cell in the apparatus so that driving means may be braked with the detection signal from the cell. Position detecting means may be located at any suitable position allowing the detection of movement of the optical system. An optical system moving mechanism such as pulley may be used for this purpose. The above described embodiments relate only to cases where reduced copies of the original are made. But the present invention is not limited only to reductions and magnified copies.

Also, the means for carrying the original is not limited to a glass plate on which the original is placed as shown in the drawings.

A sheet of an original document itself may constitute original carrying means. Further, it is not always necessary to transmit the image of the original to the photosensitive body in the form of reflected light. The light transmitted through the original also may be used.

The advantage of unidirectional stop setting and the practical arrangement and operational manner for it have been described as applied to positioning of reflecting means for varying the start position. This unidirectional stop setting method can be applied not only for reflecting means but also for positional control of other optical means such as the lens system.

Now referring to Fig. 10, a method for moving and stopping a lens system in a variable magnification copying apparatus and a practical arrangement for carrying out the method will be explained.

In the drawing, reference numeral 82 designates a reversible motor. The motor 82 turns a driving screw 87 connected with the output shaft of the motor. The driving screw 87 is formed as a male screw and engaged with a driven screw 88 formed as a female screw. The driven screw 88 is provided in a portion of a lens supporting member 90 supporting a lens system 89. The upper portion of the supporting member 90 is fitted on a guide rail 91 so that the supporting member 90 may slide along the guide rail when the driving screw is turned by the motor. The slide motion of the supporting member is made in the direction of the optical axis. On the under side of the supporting member 90, there is firmly attached a cam 92 by which three microswitches M84, M85, M86 are opened and closed. Reference numeral 93 designates a magnification selector button.In this embodiment, three selector buttons are provided, selector button 93a for 1:1 magnification, 93b for 1:0.86 and 93c for 1:0.71.

Signals produced by the selector buttons 93a-93c as well as by the microswitches M84--M86 are converted, in a control circuit part 83, into signals for effecting normal rotation, reversion and stopping of the motor 82. A detailed explanation of control circuit part 83 will be given later with reference to Fig. I 1.

The operation of the lens system driving mechanism is as follows: For convenience it is assumed that by pushing the selector button 93b, the lens system 89 has been located in the position shown in the drawing. Now, if an operator pushes the selector button 93a, the motor will be started by a signal from the control circuit part 83 to turn the driving screw 87 which, in turn, will drive the supporting member 90 through the driven screw 88. As a result, the lens system 89 begins to move to the right in Fig. 10. The cam 92 is also moved in the same direction and eventually the cam actuates the microswitch M84 with its right side cam surface B.

A signal generated by the microswitch M84 is introduced in the control circuit 83 so as to stop the motor 82. When the motor is stopped, an electric brake is actuated to prevent the motor from over-running by inertia force. The lens system 89 is thus stopped at a definite position. Here it should be noted that when the selector button 93a is pushed, the lens system 89 and the cam 92 are always moved until the cam 92 actuates the microswitch M84 and that the actuation of the microswitch M84 is always effected by the right side cam surface B. This is very important so that the lens system is always stopped accurately at a definite position and a well focussed image may normally be obtained.

If the selector button 93c is pushed after the above operation, the motor 82 is started through the control circuit 83 but in reversed direction. Therefore, the lens system 89 moves to the left together with the cam 92 starting from the position corresponding to the microswitch M84. The lens system 89 passes over the position of the microswitch M85 and continues moving until the cam 92 actuates the microswitch M85. The motor 82 is then stopped and, therefore, the lens system is accurately positioned.

As clearly seen from the drawing, the actuation of the microswitch M86 is effected by the left side cam surface A of the cam 92. In this manner, when the selector button 93c is pushed, the lens system is stopped always at a same definite position.

Pushing of the selector button 93b will cause the microswitch 93c to return back and through the control circuit 83 the motor to start in its reversed rotational direction.

The lens system 84 moves now from the position of the microswitch M86 towards the microswitch M84. In the course of this movement, the cam 92 actuates the microswitch M85. But the motor 82 continues rotating and when the cam 92 actuates the microswitch M84, the motor is reversed by a signal from the microswitch M84. The lens system 83 is then moved to the left and stopped when the cam 92 actuates the microswitch M85 corresponding to switch 93b with its left side cam surface A, so as to stop the motor 82. Thus, when an operator pushes the selector button 93b, the lens system can be stopped only when the left side cam surface A actuates the microswitch M85. This unidirectional stop setting of optical system such as focusing lens system is very useful for variable magnification copying.Errors in positioning caused by the configuration of a switch actuating member such as a cam as well as by the operational error of the switch itself are almost eliminated and it is assured that a clear and high quality image can normally be obtained even when optical system is displaced for different magnifications.

Now referring to Fig. I I, the control circuit 83 will be explained.

The motor 82 is a reversible motor. When the contact a of a relay 98 is closed, the motor 82 rotates clockwise, which causes the lens system 89 to move rightwards.

When the contact b of a relay 97 is closed, the motor 82 rotates counterclockwise and then the lens system 89 is moved leftwards.

Reference numeral 101 designates a transformer which has an input of 100V and an output of 18V, and which serves as a power source for the control circuit, with its DC voltage of 24V taken from a bridge diode 100.

For the purpose of explanation it is assumed that starting from the position shown in Fig. 10, the selector button 93a is now pushed. In the starting position, the microswitch M84 is on its NC (normal closed) side. Therefore, by pushing the selector button 93a, relays 94--a and 9Pb are closed and relay 94 is held in operation.

At this point, relay 98 is also energized to close the contact 98-a. The motor 82 rotates clockwise and the cam 92 is moved to the right as viewed in Fig. 10.

When the cam 92 actuates the microswitch M84, the relays 94 and 98 are deenergized and therefore the motor 82 stops. The lens system 89 comes to a halt at the position in which the right side cam surface B (Fig. 10) actuates the microswitch.

If the selector button 93b is depressed, relay 95 is actuated and it is held in operation by relay 95-b, now closed. As long as the microswitch M84 is not actuated by the cam 92, relay 98 is actuated through the microswitch M85 and the relays 95-b and 99-a. As a result the motor starts rotating clockwise and the lens system is moved to the right in Fig. 10 until the cam actuates the microswitch M84. Upon the actuation of M84, relay 99 is thrown in the circuit and the relay 99-a is actuated so that the relay 99 is turned over from NC to NO (normal open) side. As the relay 98 opens and the relay 97 is thrown in the circuit, the motor 82 reverses its rotational direction to rotate counter-clockwise. Therefore, the lens system 89 is now moved leftwards.At this time, the microswitch 84 is turned over from NO to NC side. But, through the contact 97-a and the microswitch M85, the relay 97 is maintained in its closed position and therefore the motor continues rotating counterclockwise, and the lens system is further moved leftwards. When the microswitch M85 is actuated by the cam 92, the relay 97 opens so as to stop the motor 82 and the relay 95 is also opened.

When the selection button 93c is pushed following the above operation, the relays 98 and 96 are actuated so that the contact 98-a closes and the motor 82 starts rotating clockwise. Thereby the cam 92 accompanied by the lens system 89 is moved rightwards until the cam actuates the micro switch M84. Upon the actuation of the microswitch M84, the relay 99 is closed so that the motor 82 is reversed. Now the cam 92 is moved leftwards until it actuates the microswitch M86. By the actuation of the microswitch M86, the relay is opened, the motor 82 is stopped and the relay 97 is also opened.

The variation of the magnification of the original image in the optical scanning direction and in the vertical direction is usually effected by changing the position of the lens system and, if it is required, also by changing the optical length. In such a case, the unidirectional stop setting of the optical system described above has various advantages. It permits accurate positioning of the lens system since errors caused by the width of a switch actuating member such as a cam are prevented. The problems over the accuracy of focussed image are reduced and the width of cam and the like does not cause errors. Therefore, manufacture and adjustment of the actuating member is relatively easy.

WHAT WE CLAIM IS: 1. A variable magnification line-by-line photocopier. comprising means for moving a photosensitive member at a constant speed past a position at which it receives an image of an original produced by optical scanning means, the scanning means including a member movable at a scanning speed variable in accordance with the selected magnification, and control means for varying the starting position of the movable member in accordance with the selected magnification such that the time required for the movable member to move from the starting position to the position at which scanning of the fore edge of the original is commenced remains substantially constant regardless of the selected magnification.

2. A photocopier according to claim 1, in which, if the scanning speed is v/m, the prescan run distance is l/m, where m is the magnification selected, v is the speed of the photosensitive member when the magnification is 1, and 1 is the pre-scan run distance when the magnification is 1.

3. A photocopier according to claim 1, in which said control means moves the scanning member to its starting position which corresponds to the magnification selected and the control means stops the scanning member at its starting position only when the scanning member reaches the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (16)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   be obtained even when optical system is displaced for different magnifications.

   Now referring to Fig. I I, the control circuit 83 will be explained.

   The motor 82 is a reversible motor. When the contact a of a relay 98 is closed, the motor 82 rotates clockwise, which causes the lens system 89 to move rightwards.

   When the contact b of a relay 97 is closed, the motor 82 rotates counterclockwise and then the lens system 89 is moved leftwards.

   Reference numeral 101 designates a transformer which has an input of 100V and an output of 18V, and which serves as a power source for the control circuit, with its DC voltage of 24V taken from a bridge diode 100.

   For the purpose of explanation it is assumed that starting from the position shown in Fig. 10, the selector button 93a is now pushed. In the starting position, the microswitch M84 is on its NC (normal closed) side. Therefore, by pushing the selector button 93a, relays 94--a and 9Pb are closed and relay 94 is held in operation.

   At this point, relay 98 is also energized to close the contact 98-a. The motor 82 rotates clockwise and the cam 92 is moved to the right as viewed in Fig. 10.

   When the cam 92 actuates the microswitch M84, the relays 94 and 98 are deenergized and therefore the motor 82 stops. The lens system 89 comes to a halt at the position in which the right side cam surface B (Fig. 10) actuates the microswitch.

   If the selector button 93b is depressed, relay 95 is actuated and it is held in operation by relay 95-b, now closed. As long as the microswitch M84 is not actuated by the cam 92, relay 98 is actuated through the microswitch M85 and the relays 95-b and 99-a. As a result the motor starts rotating clockwise and the lens system is moved to the right in Fig. 10 until the cam actuates the microswitch M84. Upon the actuation of M84, relay 99 is thrown in the circuit and the relay 99-a is actuated so that the relay 99 is turned over from NC to NO (normal open) side. As the relay 98 opens and the relay 97 is thrown in the circuit, the motor 82 reverses its rotational direction to rotate counter-clockwise. Therefore, the lens system 89 is now moved leftwards.At this time, the microswitch 84 is turned over from NO to NC side. But, through the contact 97-a and the microswitch M85, the relay 97 is maintained in its closed position and therefore the motor continues rotating counterclockwise, and the lens system is further moved leftwards. When the microswitch M85 is actuated by the cam 92, the relay 97 opens so as to stop the motor 82 and the relay 95 is also opened.

   When the selection button 93c is pushed following the above operation, the relays 98 and 96 are actuated so that the contact 98-a closes and the motor 82 starts rotating clockwise. Thereby the cam 92 accompanied by the lens system 89 is moved rightwards until the cam actuates the micro switch M84. Upon the actuation of the microswitch M84, the relay 99 is closed so that the motor 82 is reversed. Now the cam

   92 is moved leftwards until it actuates the microswitch M86. By the actuation of the microswitch M86, the relay is opened, the motor 82 is stopped and the relay 97 is also opened.

   The variation of the magnification of the original image in the optical scanning direction and in the vertical direction is usually effected by changing the position of the lens system and, if it is required, also by changing the optical length. In such a case, the unidirectional stop setting of the optical system described above has various advantages. It permits accurate positioning of the lens system since errors caused by the width of a switch actuating member such as a cam are prevented. The problems over the accuracy of focussed image are reduced and the width of cam and the like does not cause errors. Therefore, manufacture and adjustment of the actuating member is relatively easy.

   WHAT WE CLAIM IS: 1. A variable magnification line-by-line photocopier. comprising means for moving a photosensitive member at a constant speed past a position at which it receives an image of an original produced by optical scanning means, the scanning means including a member movable at a scanning speed variable in accordance with the selected magnification, and control means for varying the starting position of the movable member in accordance with the selected magnification such that the time required for the movable member to move from the starting position to the position at which scanning of the fore edge of the original is commenced remains substantially constant regardless of the selected magnification.
2. 2. A photocopier according to claim 1, in which, if the scanning speed is v/m, the prescan run distance is l/m, where m is the magnification selected, v is the speed of the photosensitive member when the magnification is 1, and 1 is the pre-scan run distance when the magnification is 1.
3. 3. A photocopier according to claim 1, in which said control means moves the scanning member to its starting position which corresponds to the magnification selected and the control means stops the scanning member at its starting position only when the scanning member reaches the

   starting position from a predetermined direction.
4. 4. A photocopier according to claim 3, in which said control means includes a plurality of position detecting devices located along a moving path of said scanning member, each position detecting device corresponding to a respective magnification, and means for actuating the detecting devices mounted on the scanning member.
5. 5. A photocopier according to claim 4, in which the detecting devices include microswitches and the actuating means includes a cam.
6. 6. A photocopier according to any one of the preceding claims, in which the scanning member is a scanning mirror movable at a speed v/m, where m is the magnification selected and v is the speed of said photosensitive member.
7. 7. A photocopier according to claim 6, in which said scanning means further includes a second mirror movable at one half of the speed of said first mentioned mirror and in the same direction as said first mentioned mirror.
8. 8. A photocopier according to claim 7, in which said control means changes the prescan run distance of said second mirror by 1/2 of the distance change of the first mirror pre-scan run.
9. 9. A photocopier according to any one of claims 1 to 5, wherein said scanning member includes an original carrier movable at a speed v/m. where m is the magnification selected, and v is the speed of said photosensitive member.
10. 10. A photocopier according to any one of the preceding claims, including means for changing the position of a lens of said scanning means for selecting the magnification.
11. 11. A photocopier according to claim 10, wherein said lens position changing means, upon its position changing operation, stops said lens only when said lens reaches a predetermined position from a predetermined direction.
12. 12. A variable magnification photocopier substantially as herein described with reference to Figures 1 to 5 of the accompanying drawings.
13. 13. A variable magnification photocopier substantially as herein described with reference to Figures 6 and 7 of the accompanying drawings.
14. 14. A variable magnification photocopier substantially as herein described with reference to Figure 8 of the accompanying drawings.
15. 15. A variable magnification photocopier substantially as herein described with reference to Figure 9 of the accompanying drawings.
16. 16. A variable magnification photocopier substantially as herein described with reference to Figures 10 and 11 of the accompanying drawings.