OPTICAL SYSTEM MOVING APPARATUS FOR DUPLICATING MACHINE

Abstract: An optical system moving apparatus for a duplicat­ ing machine which is so arranged as to effect a scanning operation of document images through the movement of two units of mirror platforms (1,2) respectively at a scanning speed and at a speed half as fast as the scanning speed. The stator (9,12)for the polyphase brushless motor is provided along the moving direction on both the side portions of the moving region of each mirror platform, and two sets of rotors by the core-less coil (U,V,W)of the polyphase brushless linear motor are disposed on these stators, and may drive the respective gravity center positions through the support of both the end portions of two units of mirror platforms.

Description: BACKGROUND OF THE INVENTION The present invention generally relates to an optical system moving apparatus for driving an optical system in a duplicating machine by a linear motor. Generally, recent duplicating machines often move the optical system, instead of moving a document platform, so as to scan the document images. A mechanical transmission gear such as wire, pulley or the like is required to convert the revolving power of the motor into rectilinear movements for transmitting it to an optical system when such optical system movement is effected by the use of a rotary motor. However, it is difficult for a transmission apparatus such as wire, pulley or the like to move the optical system with high accuracy and speed, because an elastic member is used. Therefore, an optical moving apparatus for a duplicating machine using a linear motor, which does not require such a transmission apparatus, is already known. An invention disclosed in Japanese Patent Publication (unexamined) Tokkaisho No. 60-136731 is provided as an arrangement for using a linear pulse motor (LPM) in a linear motor. A stator with uneven-shaped teeth being provided on the top face of the long yoke plate is mounted on the side of the main body of a duplicating machine along the moving direction, so that a rotor supporting an optical system is shaped to linearly move on it. The rotor has a coil-wound -shaped yoke mounted on both the NS polarity ends of a permanent magnet, and has the uneven-shaped teeth on both magnetic poles of each yoke, with the teeth being disposed to opposite the teeth on the side of the stator. Accordingly, a pulse current properly flows to each coil to sequentially generate such magnetic force as absorb the forward teeth on the side of the stator for driving the rotor. Also, an invention disclosed in Japanese Patent Publication (unexamined) Tokkaisho No. 56-87065 is provided as an arrangement for using a voice coil motor (VCM) in a linear motor. A stator has a long yoke rod mounted on the main body of the duplicating machine along the moving direction, with a long permanent magnet being mounted sideways of the yoke rod, so that a rotor for supporting the optical system is engaged into the yoke rod to be linearly slid. The rotor is provided with a coil slidably wound with respect to the yoke rod. A current for flowing in the coil of the rotor and a magnetic flux in the direction always normal to be moving direction of the rotor are adapted to be formed by the permanent magnet on the side of the stator. Accordingly, a DC current is flowed into the coil, so that the rotor is driven through an electromagnetic force received. The optical system of a duplicating machine is required to keep constant an optical distance from the document surface to the exposure position of an exposure member regardless of the scanning position. Thus, the optical system is adapted to move a first mirror platform, which reflects the light from the document surface into the horizontal direction, together with a light source at a scanning speed, and to move a second mirror platform, which reverses the direction of the reflected light by the first mirror platform in the same direction at half of the scanning speed. The conventional optical system moving apparatus is driven with a linear motor provided on the first mirror platform only. The second mirror platform is moved at half of the scanning speed upon coupling to the first mirror platform through a mechanical coupling apparatus such as a moving pulley or the like. Therefore, conventionally, the driving force can not be considered as acting on the center of gravity of the whole optical system, so that the stable movement may not be effected. Also, when a linear pulse motor is used for the linear motor, a permanent magnet and a coil-wound yoke are placed on a rotor for supporting the optical system, thus resulting in heavier weight on the side of the rotor. Also, the linear pulse motor becomes larger in coil inductance, because the coil is wound around the yoke. Besides, the linear pulse motor is larger in thrust ripple. In this case, the response speed becomes lower, with a problem that the controlling of higher speed movement and accuracy is hard to effect. When a voice coil motor is used for the linear motor, the magnetic flux to be formed in the entire sliding portion of the rotor is concentrated on both end portions of the yoke rod, so that the sectional area of the end yoke for forming a magnetic path here is required to be made larger. Also, as the permanent magnets on the side of the stator magnetically attract the opposite yoke rods or the like in the entire long portions, the mechanical strength of the entire stator is required to be increased. Therefore, in this case, it is difficult to make the liner motor lighter in weight. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical system moving apparatus for a duplicating machine, which is capable of stably moving an optical system, because two sets of rotors for the polyphase brushless linear motor may drive the respective gravity center of the mirror units due to the support of both the end portions of two units of mirror platforms. Another important object of the present invention is to provide an optical system moving apparatus for a duplicating machine, which is capable of quickening the response speed of the optical system movement and simplifying the control of the high speed and high accuracy, because the coil inductance may be made smaller as the rotor of the polyphase brushless linear motor uses the core-less coil, and the permanent magnet and the coil-winding yoke are not required on the rotor. Still another object of the present invention is to provide an optical system moving apparatus for a duplicating machine, which is capable of easily making the optical system moving apparatus smaller, because the yoke of large sectional area is not required as the permanent magnet for the polyphase brushless linear motor is dispersed in its magnetic path, and the force with which the permanent magnet magnetically attracts the yoke may be made smaller. In accomplishing these and other objects, according to the embodiments of the present invention, there is provided an optical system moving apparatus for a duplicating machine arranged to scan document images, said apparatus comprising two elongated mirror units extending in a direction perpendicular to the scanning direction, one unit moving at the scanning speed, the other unit moving at half the scanning speed, the light from the illuminated document being reflected by the mirror of said one unit to a mirror of the other unit so that the optical path length between the document and a member to be exposed is kept constant during sacnning, and which apparatus is characterized in that two elongated stators of a polyphase brushless motor extend along the scanning direction, one stator being adjacent to one end portion of of each unit, the other stator being adjacent to the other end portion of each unit, and that each unit has in each of its two end portions a rotor, made of coreless coils of a polyphase brushless motor, which rotor coacts with one of said stators, said rotors driving the corresponding end portions during scanning such that the combined driving force can be considered as acting on the center of gravity of the unit. Furthermore, the rotors are mounted to the units with yoke plates and yokes directed to the yoke plates mounted on the units. The permanent magnet and the yoke with coil to be wound around it are not mounted on the rotor as in the conventional linear pulse motor. Thus, the response speed of the operation is made faster and the control of the higher speed movement and accuracy is made easier. As the stator of the polyphase brushless linear motor does not require the yoke of large sectional area, because the permanent magnets have alternating north and south poles, equally arranged along the scanning direction. Also, as a yoke rod is not required in opposition to the permanent magnet of the stator, the mechanical strength is not required to be made excessive, because the permanent-magnet force for magnetically attracting the yoke of the other portion becomes smaller. When the yoke of proper size is arranged to form the magnetic path on the side of the stator, the permanent magnet on the side of the stator may be added to the support portion of the mirror platform through the magnetic attraction of the yoke by the permanent magnet on the side of the stator. Therefore, a roller or the like for supporting the rotor is prevented from being played so as to stabilize the movement. When the other mirror unit is coupled by mechanical means to said one mirror unit moving at a scanning speed so that it may move at a speed half as fast as it, the speed difference between them may be forced to be fixed at 1:2. Thus, the feedback controlling by the linear scale is to be effected only through the position detection of one of mirror units, thus simplifying the control system. In this case, in order not to apply an unnecessary force to the mechanical means, the ratio F₂:F₁ of the thrust of two sets of rotors is required to be set for conformity to m₂:2m₁, with the mass of the respective movable portions composed of the mirror unit and both the rotors being respectively m₁, m₂. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: Fig. 1 through Fig. 7 show one embodiment of the present invention; Fig. 1 is a plan view of an optical system moving apparatus; Fig. 2 is a sectional front-face view taken along a line II-II of Fig. 1; Fig. 3 is a side view of an optical system moving apparatus; Fig. 4 is a front face view of a core-less coil in a rotor; Fig. 5 is a partial back view of a permanent magnet in a stator; Fig. 6 is a circuit diagram showing the connection of a core-less coil; Fig. 7 is a block diagram of a driving control circuit in the optical system moving apparatus; Fig. 8 through Fig. 10 show another embodiment of the present invention; Fig. 8 is a plan view of an optical moving apparatus; Fig. 9 is a sectional front-face view showing a coupling apparatus for a mirror unit and Fig. 10 is a block diagram of a driving control circuit in the optical system moving apparatus. DETAILED DESCRIPTION OF THE INVENTION Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. Referring now to the drawings, there is shown in Fig. 1 through Fig. 7 an optical system moving apparatus according to one preferred embodiment of the present invention. An optical system which is moved by the optical system moving apparatus includes a first mirror unit 1 and a second mirror unit 2. The first mirror unit 1 moves at a scanning speed in its scanning direction (X-direction in the drawing). Also, the second mirror unit 2 follows after the first mirror unit 1 at a speed half as fast as the scanning speed in the scanning direction. An inclined mirror 1a is provided on the first mirror unit 1 so that the inclined mirror may reflect the light A from the document surface (not shown) into a direction opposite to the scanning direction as shown in Fig. 2. A right-angled mirror 2a is provided on the second mirror unit 2 so that the light A reflected by the mirror 1a (not shown) is reflected once downwardly (in Z-direction), and furthermore, is reflected in the scanning direction. The light A reflected in the scanning direction is again reflected by a conventional fixed mirror and is applied onto the exposure portion of an exposure member (not shown). The inclined mirror 1a and the right-angled mirror 2a are formed long in the scanning width direction (in Y-direction), thus allowing the duplicating operation to be effected up to the document approximately as wide as the length of the document. A long guide shaft 3 is disposed along the scanning direction (in the X-direction) on one end side (on the Y-direction side) of the first mirror unit 1 and the second mirror unit 2, and is secured on the duplicating-machine main body (not shown). Three rollers 4 which are rotatably disposed on the one end side of the first mirror unit 1 are disposed so that they may be rotated on the upper peripheral face and the lateral peripheral face of the guide shaft 3. Also, the three rollers 4 are rotatably disposed, likewise, even on one end side of the second mirror unit 2 so that they may be rotated on the upper peripheral face and the lateral peripheral face of the guide shaft 3. A long guide yoke 5 is disposed along the scanning direction on the other end side of the first mirror unit 1 and the second mirror unit 2, so that it may be secured to the duplicating-machine main body. Two rollers 6 disposed rotatably on the other end side of the first mirror unit 1 are disposed so that they may be rotated on the top face of the guide yoke 5. Also, two rollers 6 are rotatably provided similarly even on the side of the other end of the second mirror unit 2, so that they may be rotated on the top face of the guide yoke 5. Accordingly, first mirror unit 1 and the second mirror unit 2 may be reciprocated freely in the scanning direction under the control of the guide shaft 3 and the guide yoke 5. In the present embodiment, a three-phase brushless linear motor is provided on the first mirror unit 1 and the second mirror unit 2, each being constructed as described hereinabove. Each of the three-phase core-less coils U 1a , V 1a , W 1a is secured respectively in the Y-direction through a yoke plate 7 onto the end face of one end side (the side of the Y-direction) of the first mirror unit 1. Also, each of the three-phase core-less coils U 2a , V 2a , W 2a is secured respectively in the Y-direction through the yoke plate 7 even onto the end face on the one end side of the second mirror unit 2. These core-less coils U a , V a , W a , which are the core-less coils of each phase in the three-phase brushless linear motor, are disposed side by side in the sequential order on the yoke plate 7 as shown in Fig. 4. Also, Hall elements H u , H v , H w are respectively disposed in the air-core central portions of the respective core-less coils U a , V a , W a . The Hall elements H u , H v , H w are magnetic-field detecting elements for detecting the excitation change-over in the three-phase brushless linear motor. A detector 8 of a reflection type is provided on the bottom portion of the yoke plate 7. A permanent magnet 9 and a yoke 10 for retaining it to form a magnetic path are disposed sideways of another one end side of the first mirror unit 1 and the second mirror unit 2, as shown in Fig. 5, and are secured to the duplicating machine main body. The permanent magnet 9 is so arranged as to confront the respective core-less coils U a , V a , W a of the first mirror unit 1 and the second mirror unit 2, with a slight interval being provided with respect to the core-less coils. As shown in Fig. 5, the permanent magnet 9 is alternately magnetized, with the N polarity and the S polarity in the face opposite to the core-less coils U a , V a , W a . The magnetized pitch is set to 3/5 times as big as the pitch among the respective core-less coils U a , V a , W a shown in Fig. 4. Also, a linear scale 10a with black and white patterns being repeatedly drawn thereon is formed on the side face of the yoke 10 located in the lower portion (in a Z-direction) of the magnetized face of the permanent magnet 9. The linear scale 10a is adapted to detect the position and speed of the first mirror unit 1 and the second mirror unit 2 by the photodetector 8. The linear scale 10a is used in common by the photodetectors 8, 8 in the first mirror unit 1 and the second mirror unit 2. The respective three-phase core-less coils U 1b , V 1b , W 1b are respectively secured downwardly (in the Z-direction) through the yoke plate 11 onto the side of the other end of the first mirror unit 1. Also, the respective three-phase core-less coils U 2b , V 2b , W 2b are respectively secured downwardly through the yoke plate 11 on the side of the other end of the second mirror unit 2. These core-less coils U b , V b , W b are core-less coils of each phase in the three-phase brushless linear motor, and are secured on the yoke plate 11 in the arrangement similar to that of the core-less coils U a , V a , W a shown in Fig. 4, with no Hall elements H u , H v , H w being provided. Also, no photo-detector is disposed on the side of the other end of the first mirror unit 1 and the second mirror unit 2. A permanent magnet 12 to be retained by the guide yoke 5 is disposed downwardly of the other end sides of the first mirror unit 1 and the second mirror unit 2, and is secured onto the duplicating-machine main body. The permanent magnet 12 is so arranged as to confront the respective core-less coils U b , V b , W b of the first mirror unit 1 and the second mirror unit 2, with a slight interval with respect to the coils. The permanent magnet 12 is alternately magnetized to the N pole and the S pole as in the permanent magnet 9 as shown in Fig. 5 in the face opposite to the core-less coils U b , V b , W b , with no linear scale being formed on the guide yoke 5. The two pairs of the permanent magnet 9 and yoke 10, and the guide yoke 5 and permanent magnet 12 respectively constitute a stator of the three-phase brushless linear motor. Also, the core-less coils U 1a , V 1a , W 1a , and yoke plate 7, and the core-less coils U 1b , V 1b , W 1b , and yoke plate 11 in the first mirror unit 1, and the core-less coils U 2a , V 2a , W 2a , and yoke plate 7, and the core-less coils U 2b , V 2b , W 2b , and yoke plate 11 in the second mirror unit 2 respectively constitute the rotor of the three-phase brushless linear motor. The core-less coils U 1b , V 1b , W 1b and the core-less coils U 2b , V 2b , W 2b are equally arranged in the position of the X-direction as in the respective corresponding core-less coils U 1a , V 1a , W 1a and the core-less coils U 2a , V 2a , W 2a . Also, the magnetized pitch and the magnetization polarity of the permanent magnet 12 are made equal in the X-direction arrangement as in those of the permanent magnet 9. The core-less coils U 1a , V 1a , W 1a , and the core-less coils U 1b , V 1b , W 1b for constituting both the rotors of the first mirror unit 1 are intended to equalize the thrust by Y-connection of the three phase with connection in series for each phase. The same thing can be adapted, also, about the core-less coils U 2a , V 2a , W 2a and the core-less coils U 2b , V 2b , W 2b for constituting both the rotors of the second mirror unit 2. Accordingly, as the thrust at both the end portions becomes uniform, the first mirror unit 1 and the second mirror unit 2 may effect the stable movement. The yoke plates 7, 7 for forming the magnetic paths of the core-less coils U a , V a , W a are absorbed in the Y-direction by the magnetic force of the permanent magnet 9. Also, the yoke plates 11, 11 for forming the magnetic paths of the core-less coils U b , V b , W b are sucked in the downward direction (in the Z-direction) by the magnetic force of the permanent magnet 12. Thus, each roller 4 which rolls on the sideward peripheral face of the guide shaft 3 is previously pressed towards the Y-direction by the magnetic force. Also, the roller 6 is pressed downwardly by the self-weight on the side of the other ends of the first mirror unit 1 and the second mirror unit 2 and by the magnetic forces thereof. Accordingly, the play and so on to be caused by these rollers 4 and the roller 6 are prevented, thus allowing the first mirror unit 1 and the second mirror unit 2 to effect their smooth movements. As a small pressure force will do, the yoke plate 7 and the yoke plate 11 may be smaller and lighter, which does not increase the weight of the rotor considerably. Also, the core-less coils U, V, W are used, and the coil inductance becomes smaller. Accordingly, the rotor becomes better in response property. The optical system moving apparatus constructed as described hereinabove is driven by a driving control circuit shown in Fig. 7. The outputs of the respective Hall elements H u1 , H v1 , H w1 in the core-less coils U 1a , V 1a , W 1a of the first mirror platform 1 are inputted into the first three-phase driver circuit 21. The three-phase driver circuit 21 switches the three-phase exciting current by a signal from the Hall elements H u1 , H v1 , H w1 so as to respectively feed it into the core-less coils U₁, V₁, W₁ of both ends of the first mirror platform 1. Thus, the first mirror platform 1 is driven in the scanning direction (in the X-direction). Also, the microcomputer 23 feeds into the three-phase driver circuit 21 a speed signal PWM₁ corresponding to the scanning speed. In the three-phase driver circuit 21, the speed signal PWM₁ is inputted into a switching regulator so as to feed the exciting current corresponding to the duty ratio. Accordingly, the moving speed of the first mirror unit 1 is controlled by the speed signal PWM₁ into the scanning speed. To the microcomputer 23 is input the signal PG₁ coming from a photodetector 8 in the first mirror unit 1 so as to generate the speed signal PWM₁ by the PLL servo-control. Thus, the first mirror unit 1 may move stably and positively at a scanning speed. The output of the respective Hall elements H u2 , H v2 , H w2 in the core-less coils U 2a , V 2a , W 2a of the second mirror unit 2 is inputted into the second three-phase driver circuit 22. The three-phase driver circuit 22 switches the three-phase exciting current by signals coming from the Hall elements H u2 , H v2 , H w2 so as to respectively feed them to the core-less coils U₂, V₂, W₂ of both the ends of the second mirror unit 2. The second three-phase driver circuit 22 is composed of a circuit similar to the first three-phase driver circuit 21. Also, the microcomputer 23 feeds into the three-phase driver circuit 22 a speed signal PWM₂ corresponding to the speed-half as fast as the scanning speed. To the microcomputer 23 is input a signal PG₂ coming from the photodetector 8 in the second mirror platform 2 so as to generate the speed signal PWM₂ by the PLL servo-control. Accordingly, the second mirror unit 2 may move stably and positively at a speed half as fast as the scanning speed. In a case where the optical system has completed its scanning, the driving direction is reversed by the driving control circuit, and it is needless to say that the first mirror unit 1 and the second mirror unit 2 return to the given position. As the first mirror unit 1 and the second mirror unit 2 obtain the thrust by the core-less coils U a , V a , W a and the core-less coils U b , V b , W b disposed on the side of both the ends, the gravity-center positions of the movable portions are respectively driven so as to prevent unnecessary vibrations or the like from being caused in the moving. Referring now to the drawings, there is shown in Fig. 8 through Fig. 10 another embodiment of the present invention. The photodetector 8 is provided, as shown similarly in embodiment 1, in the lower portion of the yoke plate 7 on the side of one end of the first mirror unit 1. However, no photodetector is provided in the lower portion of the yoke plate 7 on the side of one end of the second mirror unit 2. Accordingly, detection of the position and the speed by the linear scale 10a are effected only on the side of the first mirror platform 1. As shown in Fig. 8, the other end side of the first mirror unit 1 is projected sideways of the other end side so as to form a wire mounting portion 13. A moving pulley 14 is rotatably mounted on the side of the end face on the other end side of the second mirror unit 2. In addition, fixed pulleys 15, 16 are respectively mounted rotatably on the duplicating-machine main body near both the ends of the scanning direction (in the X-direction) in the guide yoke 5 which is a stator on the side of the other end. One end of a first wire 17 and a second wire 18 are respectively secured to the wire mounting portion 13 of the first mirror unit 1. The moving pulley 14, the fixed pulleys 15, 16, the first wire 17 and the second wire 18 constitute a coupling apparatus for the first mirror unit 1 and the second mirror unit 2. As shown in Fig. 9, the coupling apparatus is reversed in direction, with the first wire 17 being wound around the moving pulley 14, the first wire 17 being secured to one end onto a face facing the direction opposite to the scanning direction (in the X-direction) in the wire mounting portion 13, and is secured on its other end side to the duplicating-machine main body. When the first mirror unit 1 forming the wire mounting portion 13 moves at the scanning speed in its scanning direction, the second mirror unit 2 mounted with the moving pulley 14 is to be forced to move at a speed half as fast as the speed in the same direction. Also, the second wire 18 with its one end being secured to a face directed at the scanning direction in the wire mounting portion 13 is wound around the fixed pulley 15 on the side of the scanning direction so as to be reversed in the direction, further is wound around the moving pulley 14 so as to be reversed again in the direction, with the other end side being secured to the duplicating-machine main body. When the first mirror unit 1 is moved in the direction opposite to the scanning direction, the second mirror unit 2 is to be forced to move in the same direction at half speed. The assembling operation is effected, with a proper tension amount being given previously to the first wire 17 and the second wire 18 so as to prevent the deflection. The optical system moving apparatus constructed as described hereinabove is driven by a driving control circuit shown in Fig. 10. The outputs of the respective Hall elements H u , H v , H w in the core-less coils U a , V a , W a of the first mirror unit 1 and the second mirror unit 2 are respectively inputted into the first three-phase driver circuit 21 and the second three-phase driver circuit 22 , and the exciting current to be fed to the core-less coils U, V, W is switched in a manner similar to that of the first embodiment. The speed signal PWM common to the three-phase driver circuit 21 and the three-phase driver circuit 22 is fed from the microcomputer 23. The first three-phase driver circuit 21 receives the speed signal PWM to drive the first mirror unit 1 at the scanning speed. However, the second three-phase driver circuit 22 receives the same speed signal PWM so as to be driven at a speed half as fast as the speed in the first three-phase driver circuit 21. Thus, the second mirror unit 2 is driven at a speed half as fast as the scanning speed. Accordingly, the speed of the first mirror unit 1 and the second mirror unit 2 results the same as that of the first embodiment. To the microcomputer 23 is input a signal PG from the photodetector 8 in the first mirror unit 1 so as to generate the speed signal PWM by the PLL servo-control. Accordingly, the first mirror unit 1 is capable of effecting the stable and positive movement at a scanning speed. Also, as the second mirror unit 2 is also coupled to the first mirror unit 1 by the coupling apparatus, it may be moved stably and positively at a speed half as fast as the scanning speed. In the second embodiment as described hereinabove, as the first mirror unit 1 is coupled to the second mirror unit 2 by a coupling apparatus, a speed signal PWM is generated only by a signal PG from the photodetector 8 in the first mirror unit 1. As the speed signal PWM may be used in common in the driving control of the first mirror unit 1 and the second mirror unit 2, the control system may be simplified. The ratio F₂:F₁ of the thrust caused by the core-less coils U₁, V₁, W₁ and the core-less coils U₂, V₂, W₂ is required to be set to conform to m₂:2m₁, so that unnecessary force may not be applied upon the respective first wire 17 and the second wire 18 of the coupling apparatus which couples the first mirror unit 1 to the second mirror unit 2. Here, the masses including the rotor and so on of the first mirror unit 1 and the second mirror unit 2 are respectively assumed to be m₁, m₂. However, if the three-phase brushless linear motor to be used in the second embodiment is set to generate proper exciting current respectively in the first three-phase driver circuit 21 and the second three-phase driver circuit 22 in accordance with the speed signal PWM, with the thrust thereof being proportional to the exciting current, the ratio of the thrust may be easily provided. Accordingly, unrequired tension is added to the respective first wire 17 and second wire 18 of the coupling apparatus so as to prevent the excessive vibration from being caused in the movement of the first mirror unit 1 and the second mirror unit 2. As is clear from the foregoing description, according to the optical system moving apparatus for the duplicating machine in accordance with the present invention, when the scanning operation of document images is effected by the movement of two mirror units at the respective scanning speeds and the speeds half as fast as the scanning speeds, the stator of a polyphase brushless linear motor is provided along the moving direction on both the side portions of the moving region of each mirror platform and two units of rotors by the core-less coil of the polyphase brushless linear motor are disposed on these stators, with the respective units of both the rotors being adapted on both elongated mirror units. The present invention has an effect in that the optical system may be stably moved, because two units of rotors for the polyphase brushless linear motor may drive the respective gravity-center positions through the support of both the end portions of two mirror units. Also, as the rotor of the polyphase brushless linear motor is composed of a core-less coil, the coil inductance may be made smaller. In addition, the yoke is not required to mount a yoke on the rotor so as to wind the permanent magnet and coil. Thus, the present invention has a combined effect of speed up the response speed of the optical system movement and simplifying the control of the high speed movement and high accuracy. As the permanent magnets for the polyphase brushless linear motor have alternating north and south poles, equally arranged along the scanning direction, the yoke of large sectional area is not required. Also, the force with which the permanent magnet magnetically attracts the yoke may be made smaller. Therefore, the present invention has an effect in that the optical system moving apparatus may be easily made smaller. Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.

Claims: An optical system moving apparatus for a duplicating machine arranged to scan document images, said apparatus comprising two elongated mirror units (1,2) extending in a direction perpendicular to the scanning direction, one unit (1) moving at the scanning speed, the other unit (2) moving at half the scanning speed, the light from the illuminated document being reflected by the mirror of said one unit (1) to a mirror of the other unit (2) so that the optical path length between the document and a member to be exposed is kept constant during scanning, characterised in that two elongated stators (9,12) of a polyphase brushless motor extend along the scanning direction, one stator being adjacent to one end portion of each unit, the other stator being adjacent to the other end portion of each unit, and that each unit has in each of its two end portions a rotor, made of coreless coils (U,V,W) of a polyphase brushless motor, which rotor coacts with one of said stators, said rotors driving the corresponding end portions during scanning such that the combined driving force can be considered as acting on the center of gravity of the unit. The apparatus as defined in claim 1, wherein the rotors are mounted to the units (1, 2) with yoke plates (7, 11) and yokes (5, 10) directed to the yoke plates (7, 11) are mounted on the units (1,2). The apparatus as defined in claim 1, wherein the stators are permanent magnets (9, 12). The apparatus as defined in claim 3, wherein the permanent magnets have alternating north and south poles, equally arranged along the scanning direction. The apparatus as defined in any of the preceding claims, wherein the rotor coils (U, V, W) of each phase provided in both ends of a unit are connected in series. The apparatus as defined in any of the preceding claims, wherein a linear scale (10a) extending along the scanning direction is provided at one (9) of the stators, which scale can be read by a photodetector (8) provided on a rotor associated to said stator to detect the position of the unit in the scanning direction. The apparatus is defined in claim 6, wherein said photodetector (8) is provided in both units (1, 2). The apparatus is defined in claim 1, wherein said one unit (1) is coupled by mechanical means (13-18) to the other unit (2).

Inventors: ISHII, HIROSHI, SAWAI, HIROYUKI, UEDA, TETUYUKI
Applicants: SHARP KABUSHIKI KAISHA
Application year: 1988
Main classification: G03G15
IPC codes: G03B27, H04N1, G03G15