Positioning control method and apparatus

Abstract: A positioning control method and apparatus in which a fine movement mechanism can be always moved without exceeding a movable area so that positioning of a large amount of displacement can be attained with high accuracy and high-speed positioning from a point to a point can be attained with the same control method are disclosed. The positioning control apparatus including a coarse movement mechanism 101 having a large amount of movement and low positioning accuracy and a fine movement mechanism 102 having a small amount of movement and high positioning accuracy supplies to the fine movement mechanism 101 a signal E4 based on a difference signal C4 of a movement command signal A4 and a displacement signal B4 representative of a displacement of an object to be positioned with respect to a fixed position detected by absolute position detecting means 105 and supplies to the coarse movement mechanism 101 a coarse movement command signal M4 produced by adding a signal representative of a relative displacement of the fine movement mechanism 102 with respect to the coarse movement mechanism 101 detected by relative position detecting means 133 to the difference signal C4 to thereby control respective movements.

Description: FIELD OF THE INVENTION AND RELATED ART STATEMENT The present invention relates to a positioning control method and apparatus for use in a movement apparatus for effecting positioning with high accuracy for a large amount of movement. Figs. 8, 9 and 10 are block diagrams of a conventional controller of a positioning apparatus for positioning for a large amount of movement with high accuracy in combination with a coarse movement mechanism and a fine movement mechanism. In the conventional controller of Fig. 8, a coarse movement mechanism 1 is moved with respect to an apparatus and a fine movement mechanism 2 is moved with respect to the coarse movement mechanism 1. The coarse movement mechanism 1 has low positioning accuracy but can be moved in a wide area, while the fine movement mechanism 2 can be moved in a narrow area with high positioning accuracy. When it is assumed that an absolute displacement of a reference point of the coarse movement mechanism 1 with respect to a fixed point of the apparatus is a displacement F and a relative displacement of the fine movement mechanism 2 with respect to the reference point of the coarse movement mechanism 1 is a displacement G, a displacement H of an object on the fine movement mechanism 2 with respect to the fixed point of the apparatus is a sum of G and F. A signal generator 4 constituted by a computer or the like prepares a movement command A for designating a position of the object on the fine movement mechanism 2 with respect to the fixed point of the apparatus. The displacement H of the object on the fine movement mechanism 2 with respect to the fixed point of the apparatus is detected as a displacement B by position detecting means 5 such as, for example, a laser measuring device or the like. A difference signal C which is equal to a value obtained by subtracting the displacement B from the movement command A is supplied to the coarse movement mechanism 1 and the fine movement mechanism 2 through input switching means 3. In brief, in the controller shown in Fig. 8, the movement command A is prepared by the signal generator 4 constituted by a computer or a signal generator. The absolute displacement H of the object to be positioned with respect to the fixed position which is a sum of the relative displacement G of the fine movement mechanism 2 with respect to the coarse movement mechanism 1 and the absolute displacement F of the coarse movement mechanism 1 with respect to the fixed point is detected as the displacement B by means of the position detecting means such as, for example, a laser measuring device or the like. The difference signal C between the movement command A and the displacement B is supplied to the input switching means 3 constituted by a computer or an analog circuit, for example. When the difference signal C is larger as compared with a movable area of the fine movement mechanism 2, the input switching means is connected to a and a coarse movement command signal D is supplied to the coarse movement mechanism 1. The coarse movement mechanism 1 is controlled to be moved within the movable area of the fine movement mechanism by means of the difference signal C. When the difference signal C falls within the movable area of the fine movement mechanism 2, the input switching means 3 is connected to b and a fine movement command signal E is supplied to the fine movement mechanism 2. By moving the fine movement mechanism 2 so that the difference signal C is substantially equal to zero, the absolute displacement H of the object to be positioned with respect to the fixed position is caused to coincide with the movement command signal A. A conventional controller shown in Fig. 9 controls a coarse movement mechanism and a fine movement mechanism having the same configuration as that of the controller of Fig. 8. When it is assumed that an absolute displacement of a reference point of a coarse movement mechanism 11 with respect to a fixed point of an apparatus is a displacement F1 and a relative displacement of a reference of a fine movement mechanism 12 with respect to the reference point of the coarse movement mechanism 11 is a displacement G1, a displacement H1 of an object on the fine movement mechanism 12 with respect to the fixed point of the apparatus is a sum of G1 and F1. A signal generator 13 constituted by a computer or the like prepares a movement command A for designating a position of the object on the fine movement mechanism 12 with respect to the fixed point of the apparatus. A displacement H1 of the object on the fine movement mechanism 12 with respect to the fixed point of the apparatus is detected as a displacement B1 by means of position detecting means 15 such as, for example, a laser measuring device or the like. A difference signal C1 equal to a value obtained by subtracting the displacement B1 from the movement command A is supplied to the coarse movement mechanism 11 and the fine movement mechanism 12 through a compensation circuit 16, a limiter circuit 17 and a insensitive band circuit 18. In brief, in the controller shown in Fig. 9, the movement command signal A1 is prepared by the signal generator 14. The absolute displacement H1 of the object to be positioned with respect to the fixed position which equal to a sum of the absolute displacement G1 of the fine movement mechanism 12 with respect to the coarse movement mechanism 11 and the absolute displacement F1 of the coarse movement mechanism 11 with respect to the fixed position is detected as the displacement B1 by means of the position detecting means 15. The difference signal C1 between the movement command A1 and the displacement B1 is supplied to the compensation circuit 16 for compensating a gain characteristic and a phase characteristic of the object to be positioned to thereby obtain a compensation difference signal J1. The compensation difference signal J1 is supplied to the coarse movement mechanism 11 and the fine movement mechanism 12 simultaneously. The compensation difference signal J1 supplied to the fine movement mechanism 12 passes through the limiter 17 and the compensation difference signal J1 supplied to the coarse movement mechanism 11 passes through the insensitive band circuit 18. The fine movement mechanism 12 responds to a specific difference area of -α to α within the movable area of the fine movement mechanism 12 and the coarse movement mechanism 11 responds to the outside of the difference area or the external area larger than α and smaller than -α . The limiter 17 produces an output signal proportional to an input signal when the input signal is within the specific difference area and produces an output signal having a fixed value when the input signal is outside of the specific reference area. The insensitive circuit 18 does not produce any output signal when an input signal is smaller than a specific difference value and produces an output signal proportional to a difference of the input signal and the specific difference value when the input signal is not smaller than the specific difference value. When the difference signal C1 is outside of the specific difference area, the coarse movement mechanism 11 is moved a long distance, and when the difference signal C1 comes within the specific difference area, the fine movement mechanisms 12 is moved so that the difference C1 is substantially equal to zero. Accordingly, the absolute displacement H1 of the object to be positioned with respect to the fixed position substantially coincides with the movement command signal Al to effect the positioning (refer to Nakagawa, Torii and Kubota; "Development of Combined Fine and Coarse Movement Super-Precision Servo Technique - Trial Manufacture and Estimation", 1990, Collected Treatises of Lectures of Autumn Scientific Lecture Meeting of The Japan Society for Precision Engineering, pp. 1055). In a conventional control of Fig. 10, a coarse movement mechanism 21 is moved with respect to a fixed point of an apparatus and a fine movement mechanism 22 is moved with respect to the coarse movement mechanism 21. The fine movement mechanism 22 and the coarse movement mechanism 21 include measuring devices 25a and 25b for measuring displacement with respect to the fixed point of the apparatus, respectively. In the controller shown in Fig. 10, a signal generator 24 supplies to the fine movement mechanism 22 a fine movement command signal A3 having a fine movement step hm as a resolution as shown in Fig. 11 as a movement command signal. Further, the signal generator 24 supplies to the coarse movement mechanism 21 a coarse movement command signal A2 for generating a coarse movement step hc (=3×hm) as a movement command signal as shown in Fig. 12 each time three fine movement steps hm of Fig. 11 are generated. The coarse movement command signal A2 to the coarse movement mechanism 21 is not produced until time tl that the fine movement steps hm of the fine movement command signal A3 are generated three times and the coarse movement mechanism is not moved. On the contrary, the fine movement mechanism 22 is moved in response to the fine movement command signal A3 as follows. A difference signal C3 obtained by subtracting a displacement signal B3 produced from the position detecting means 25a for detecting an absolute displacement value H2 with respect to the fixed point of the apparatus of the object on the fine movement mechanism 22 from the fine movement command signal A3 is supplied to a compensation circuit 29 constituted by a computer or an analog circuit for compensating a gain characteristic and a phase characteristic of the object to be positioned. The fine movement mechanism 22 receives fine movement compensation difference signal E2 produced by the compensation circuit 29 and is moved to be substantially coincident with the fine movement command signal A3. When the fine movement steps hm for the fine movement command signal A3 are generated three times and the time t1 comes, the coarse movement command signal A2 generates a coarse movement step corresponding to three times of the fine movement steps hm. A difference signal C2 obtained by subtracting from the coarse movement command signal A2 a displacement signal B2 produced by the position detecting means 25b for detecting the absolute displacement value of the coarse movement mechanism with respect to the fixed position is supplied to the compensation circuit C2. The coarse movement mechanism 21 receives a coarse displacement compensation difference signal D2 and is moved to be coincident with the coarse movement command signal A2. On the other hand, the fine movement mechanism 22 continues the same movement as that made until the time t1. Accordingly, movement value G2 of the fine movement mechanism at the time t1 is G2=3hm, and movement value F2 of the coarse movement mechanism is F2=hc=3hm. Accordingly, the absolute displacement value H2 of the object to be positioned with respect to the fixed position is H2=F2+G2=6hm. At this time, the displacement signal B3 produced by the position detecting means 25 is subtracted from the fine movement command signal A3. Accordingly, the fine movement mechanism 22 is supplied with a difference C3=A3-B3=3hm-6hm=-3hm=-F3 and is moved back by the movement value F2 of the coarse movement mechanism. The controller shown in Fig. 10 performs the above operations repeatedly to perform positioning over a long distance with high accuracy (refer to Sakuta, Ogawa and Ueda; "Study Concerning Super-Precision Position Control - Interlocked Control of Coarse and Fine Movement", Collected Treatises of Lectures of Spring Scientific Lecture Meeting of Precision Engineering Society, 1990, pp. 795 and Sakuta, Ogawa and Ueda; "Position Control by Interlocked Coarse and Fine Movement", Collected Treatises of Lectures of Spring Scientific Lecture Meeting of The Japan Society for Precision Engineering, 1991, pp. 229). In a prior art control method and apparatus disclosed in Patent Abstracts of Japan, vol. 9, no. 311 (M-436)[2034] 7 December 1985 & JP-A-60 146 650, the difference between a command position of an object to be positioned and its actual position is fed back to the controller of the fine movement mechanism. The sum of said difference and a signal E, which is related to the displacement of the fine movement mechanism, is fed back to the controller of the coarse movement mechanism. The difference between the signal E and the actual displacement of the fine movement mechanism is neglected. This results in impaired accuracy as there is a great difference between them. The signal E is not always exactly proportional to the displacement of the fine movement mechanism because of the hysteresis of the movement of the mechanism, a change of temperature, and an external force. In general, a piezoelectric element has a limited frequency range of response and some resonance frequencies. As a result, the input signal E and the actual displacement of the fine movement mechanism is not identical from a low frequency range to a high frequency range. Especially in a resonance region, the difference is substantial. OBJECT AND SUMMARY OF THE INVENTION In order to perform continuous positioning control in which an object to be positioned traces the locus to be targeted with high accuracy over a long distance, a positioning apparatus including a coarse movement mechanism having a large amount of movement and low positioning accuracy and a fine movement mechanism having a small amount of movement and high positioning accuracy and on which an object to be positioned is mounted is employed. In this case, a movement command having accuracy corresponding to that of the fine movement mechanism is inputted. Since the input to the fine movement mechanism 2 and the coarse movement mechanism 1 is switched by the input switching means 3 in accordance with a magnitude of the difference signal C in the controller shown in Fig. 8, the absolute displacement value H of the object to be positioned with the fixed position is substantially coincident with the movement command signal A when the fine movement mechanism 2 is within the movable area. However, when the fine movement mechanism 22 is moved to the movable area, the difference signal C is increased gradually since the fine movement mechanism 2 can not be moved. When the difference signal C reaches a magnitude in which the input switching means is switched to the coarse movement mechanism 1, the coarse movement mechanism 1 is moved in response to the difference signal C. Accordingly, in the continuous positioning control, since the fine movement mechanism 2 can not be moved and only the coarse movement mechanism 1 is moved in accordance with the above procedure, the continuous positioning control with high accuracy is not attained. Further, in the controller of Fig. 9, the compensation difference signal J1 obtained by supplying the difference signal C1 to the compensation circuit 16 is selectively supplied to the limiter 17 or the insensitive band circuit 18 in accordance with the magnitude of the compensation difference signal J1 to produce the fine movement compensation difference signal El or the coarse movement compensation difference signal D1. At this time, as described above, when the continuous positioning control with high accuracy is made, since the movement command signal Al is inputted with accuracy corresponding to that of the fine movement mechanism 12, the fine movement mechanism 12 is moved to the movable area of the fine movement mechanism 12 and the absolute displacement amount H1 of the object to be positioned is substantially coincident with the movement command signal A1. However, when the movement command signal A1 is a command signal that the movable area of the fine movement mechanism 12 is exceeded, the fine movement mechanism 12 can not be moved although the compensation difference signal J1 is supplied to the fine movement mechanism 12. Thus, since the compensation signal C1 is increased gradually, the compensation difference signal J1 is also increased. When the compensation difference signal J1 exceeds the difference area of -α to α set by the limiter 17 and the insensitive band circuit 18, the compensation difference signal J1 is supplied to the coarse movement mechanism 11 and the coarse movement mechanism is moved. Thus, since the fine movement mechanism 12 already exceeds the movable area, the fine movement mechanism 12 can not be moved for the subsequent locus control and only the coarse movement mechanism 11 is moved, so that the continuous positioning control with high accuracy is not attained. Further, in the controller of Fig. 10, when the control with high accuracy is made, the fine movement command A3 having the fine movement step hm corresponding to the accuracy of the fine movement mechanism 22 is supplied to the fine movement mechanism 22 as shown in Fig. 11. The coarse movement step he having a resolution or more with which the coarse movement mechanism 21 can be moved and having an integral multiple, for example three times of the fine movement step hm is supplied to the coarse movement mechanism 21 as shown in Fig. 12 at the same time as the time tl or t2 that the fine movement command signal A3 generates the fine movement steps hm three times. At this time, as described above, the fine movement mechanism 22 is moved back by the movement amount F2 of the coarse movement mechanism to attain positioning. Since the coarse movement mechanism 21 generally has low positioning accuracy, a positioning error necessarily occurs in the coarse movement mechanism movement amount F2 for the coarse movement command signal A2. Accordingly, since the fine movement mechanism 22 is moved to correct the positioning error, the positioning error of the coarse movement mechanism is accumulated for each repetition of the above control method. Thus, the movable area of the fine movement mechanism 22 is exceeded and the fine movement mechanism can not be moved. Accordingly, the continuous positioning control with high accuracy can be not be made thereafter. As described above, even in any controller shown in Figs. 8 to 10, when the object to be positioned is positioned with high accuracy over a long distance, the fine movement mechanism necessarily exceeds the movable area and can not be moved, so that the positioning with high accuracy can not be made for the continuous movement command signal. Further, even in any apparatus, it is impossible to control the continuous positioning in a large amount of movement with high accuracy and movement of a point to a point that high-speed movement is made between two points of a starting point of the object to be positioned and a final positioning point to effect positioning to the final positioning point by means of the same control method, and accordingly control methods must be selectively used in accordance with movement to be made. It is an object of the present invention to be able to move a fine movement mechanism of a movement apparatus including a coarse movement apparatus which is moved with respect to an apparatus and a fine movement apparatus which is moved with respect to the coarse movement apparatus without exceeding a movable area always. It is another object of the present invention to control positioning in a large amount of movement with high accuracy and high-speed positioning from a point to a point by the same control method. The above objects are attained by the positioning control method and controller as defined in appendent claims 1 and 2. The relative displacement of the fine movement mechanism with respect to tile coarse movement mechanism is detected by the relative position detecting means. The coarse movement mechanism is moved in accordance with the coarse movement command signal obtained by adding the difference signal to the relative displacement. The coarse movement mechanism is moved while always observing the movement amount of the fine movement mechanism. When the fine movement mechanism reaches a specific movement amount, since the coarse movement mechanism is moved by a movement amount substantially corresponding to that of the fine movement mechanism, the fine movement mechanism is moved back by the movement amount of the coarse movement mechanism. The fine movement mechanism is moved to compensate a difference of the movement command signal and the displacement amount of the object to be positioned occurring by movement of the coarse movement mechanism with respect to the fixed position. Accordingly, positioning can be always attained with high accuracy. By repeating the above operation, a large amount of movement can be made with high accuracy while always maintaining the fine movement mechanism within the movable area. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a first embodiment of the present invention; Fig. 2 is a graph showing a movement characteristic of a coarse movement mechanism and a fine movement mechanism with respect to a movement command signal of the embodiment shown in Fig. 1; Fig. 3 is a graph showing a positioning characteristic (an absolute movement to a movement command signal when going and returning a distance of 500 µm at steps of 5nm) of the embodiment shown in Fig. 1; Fig. 4 is a graph showing an extracted and enlarged portion of Fig. 3; Fig. 5 is a graph showing a movement characteristic of an object to be positioned (movement of the object to be positioned with respect to the movement command signal having a step of 1mm) in the embodiment shown in Fig. 1; Fig. 6 is a block diagram showing a second embodiment of the present invention; Fig. 7 is a graph showing a movement characteristic similar to that of Fig. 5 of the object to be positioned in the embodiment shown in Fig. 6; Fig. 8 is a block diagram showing a first conventional positioning controller; Fig. 9 is a block diagram showing a second conventional positioning controller; Fig. 10 is a block diagram showing a third conventional positioning controller; Fig. 11 is a waveform diagram showing a movement command signal to a fine movement mechanism of the controller shown in Fig. 10; and Fig. 12 is a waveform diagram showing a movement command signal to a coarse movement mechanism of the controller shown in Fig. 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention are now described in detail with reference to the accompanying drawings. Fig. 1 is a block diagram showing a first embodiment of the present invention. A coarse movement mechanism 101 uses as its driving source an actuator such as, for example, a DC servo motor or a stepping motor and uses as its guide element, for example, rolling friction. The coarse movement mechanism 101 has relatively slow response speed and positioning accuracy but has large movement amount. A fine movement mechanism 102 uses as its driving source an actuator such as, for example, a piezoelectric element or a magnetostrictive element having high-speed response, high positioning resolution and large force generation capability and uses as its guide element, for example, a hinged spring or a leaf spring. The fine movement mechanism 102 has high speed response capability and high positioning accuracy but has as small movement amount as about several tens µm. A signal generator 104 generates a movement command signal A4 for an object to be positioned. The generator is constituted by a computer or an analog circuit. An absolute position detecting means 105 is a sensor formed by, for example, a laser interferometer and detects an absolute displacement H4 which is a displacement of an object to be positioned on the fine movement mechanism with respect to a fixed point of the apparatus to produce the displacement amount at this time as a displacement signal B4. Relative position detecting means 133 is a sensor formed by, for example, a capacitance type displacement measuring device and detects a relative displacement of the fine movement mechanism 102 with respect to the coarse movement mechanism 101 to supply its output signal K4 to a control operation unit 134. The control operation unit 134 is constituted by, for example, an integrator and adjusts a gain and a frequency characteristic to produce an output signal L4. The displacement signal B4 is subtracted from the movement command signal A4 to prepare a difference signal C4, which is supplied to a fine movement compensation circuit 131 and a coarse movement compensation circuit 132. The output signal L4 of the control operation unit 134 based on the output signal K4 from the relative position detecting means 133 for detecting the relative displacement of the fine movement mechanism 102 with respect to the coarse movement mechanism 101 is added to the difference signal C4 supplied to the coarse movement compensation circuit 132 to prepare a coarse movement command signal M4 (=C4+L4). Thereafter, the coarse movement command signal M4 is changed to a coarse movement compensation command signal D4 through the coarse movement compensation circuit 132. The coarse movement compensation circuit 132 prepares the coarse movement compensation command signal D4 on the basis of the coarse movement command signal M4 prepared by adding the output signal L4 based on the relative displacement G4 to the difference signal C4 which is a difference of the movement command signal A and the displacement signal B4. The coarse movement mechanism 101 is moved by the coarse displacement F4 with respect to the apparatus on the basis of the coarse movement command signal D4 produced by the coarse movement compensation circuit 132. On the other hand, the difference signal C4 supplied to the fine movement compensation circuit 131 is changed to a fine movement compensation command signal E4 by means of the fine movement compensation circuit 131. The fine movement compensation circuit 131 produces the fine movement compensation command signal E4 on the basis of the difference signal C4. The fine movement mechanism 102 is moved by the fine displacement on the basis of the fine movement compensation command signal E4 produced by the fine movement compensation circuit 131. The fine displacement is a relative displacement G4. Thus, the coarse movement mechanism 101 and the fine movement mechanism 102 are moved by the coarse displacement F4 and the fine displacement G4 in response to the coarse movement compensation command signal D4 and the fine movement compensation command signal E4. The coarse movement mechanism is to be moved always by the coarse displacement F4 to coincide with the movement command signal A4 in response to the coarse movement compensation signal D4. However, since the coarse movement mechanism 101 has low accuracy, the coarse movement mechanism 101 can not reduce the difference signal C4 between the movement command signal A4 and the displacement signal B4 to zero. In order to reduce the left difference to zero, the fine movement mechanism 102 is moved by the fine movement amount G4. Consequently, the absolute displacement amount H4 of the object to be positioned with respect to the fixed position is H4=F4+G4. The absolute displacement amount H4 is detected by the absolute position detecting means 105 again. The displacement signal B4 detected at this time is subtracted from the movement command signal A4 of the signal generator 104 to prepare the difference signal C4, so that the closed feedback control is attained. Consequently, positioning in large amount of movement with high accuracy is attained. The fine displacement amount G4 accumulated by movement of the fine movement mechanism 102 is detected by the relative position detecting means as a relative displacement of the fine movement mechanism 102 and the coarse movement mechanism 101. An output signal K4 of the relative position detecting means 133 is supplied to the control operation unit 134, which produces output signal L4, and the output signal L4 is added to the difference signal C4 to produce the coarse movement command signal M4, which is supplied to the coarse movement compensation circuit 132. The coarse movement mechanism 101 is moved by the coarse movement compensation command signal D4. In this manner, the coarse movement mechanism 101 always monitors the fine movement amount G4. Thus, when the fine movement mechanism 102 is moved to a specific displacement, the coarse movement mechanism is moved so that the fine movement mechanism 102 can be always moved within a specific area. The movable area of the fine movement mechanism 102 is set by gain adjustment of the control operation unit 132. Thus, the fine movement mechanism can be always moved within the movable area. Fig. 2 is a characteristic diagram showing displacements of the coarse movement mechanism 101 and the fine movement mechanism 102 when a stepwise movement command signal A4 having accuracy of 5nm is inputted. Referring to Fig. 2, it would be understood that the coarse movement mechanism 101 is moved not to exceed the movable area of the fine movement mechanism 102 and the fine movement mechanism 102 corrects an error of the coarse movement mechanism 101. Fig. 3 is a graph showing the absolute displacement amount H4 of the object to be positioned with respect to the fixed position when the signal for going and returning a distance of 500 µm by steps of 5nm is applied as the movement command signal A4. Fig. 4 is a graph showing an enlarged portion of Fig. 3. As shown in Figs. 3 and 4, it would be understood that the object to be positioned is moved over the area of 500 µm by steps of 5nm without the fact that the fine movement mechanism 102 does not exceed the movable area. Fig. 5 is a graph showing movement of the object to be positioned when the stepwise movement command of 1mm is applied. It would be understood from Fig. 5 that although residual oscillation is left, the object to be positioned can be moved to coincide with the movement command signal A4 for movement for a long distance from a point to a point. Fig. 6 is a block diagram showing a second embodiment of the present invention. This embodiment is an improvement of the embodiment of Fig. 1. In the embodiment of Fig. 6, the output signal K4 of the relative position detecting means 133 is subtracted from an output signal N5 of a gain adjusting device 135 for adjusting a gain of the difference signal C5 to produce a difference signal P5, which is supplied to the fine movement compensation circuit 131. Other configuration is the same as that of the first embodiment shown in Fig. 1. The same elements as those of Fig. 1 are given by the same numerals and duplicate description is omitted. The output signal G4 of the fine movement mechanism 102 is fed back to the input of the fine movement compensation circuit 131 through the relative position detecting means 133. Accordingly, the transient response of the fine movement mechanism is improved. According to the embodiment, the moving speed of the object to be positioned for the movement command signal A4 for going and returning a distance of 500 µ m with accuracy of 5nm can be improved about five times as compared with the first embodiment. Fig. 7 shows a movement of the object to be positioned in the case where a stepwise movement command signal A4 of 1mm is inputted. It is apparent from Fig. 7 that the residual oscillation shown in Fig. 5 is removed and accordingly the transient response can be improved by the embodiment. As described above in detail in conjunction with the embodiments, according to the present invention, the relative displacement amount of the fine movement mechanism with respect to the coarse movement mechanism is detected by the relative position detecting means and the signal representative of the detected result is added to the difference signal which is a difference of the movement command signal and the displacement signal based on the absolute displacement amount of the object to be positioned with respect to the fixed position, so that the cnarse movement mechanism is moved by the signal representative of the added result. Accordingly, movement with high accuracy can be always attained for the continuous positioning control for a large amount of movement requiring high accuracy without exceeding the movable area of the fine movement mechanism. Further, the object to be positioned can be positioned with high accuracy even for the movement command for moving between two points.

Claims: A positioning control method of an object to be positioned, wherein the object to be positioned is mounted on a fine movement mechanism which can move relative to a coarse movement mechanism, said coarse movement mechanism can move in a wide range with low positioning accuracy, whereas said fine movement mechanism can move in a small range with high positioning accuracy, a signal corresponding to the difference between a commanded position of the object and its actual position is fed back to a controller for fine movement of said fine movement mechanism characterized in that a signal corresponding to the sum of said difference and an actual displacement of said fine movement mechanism is fed back to a controller for coarse movement of said coarse movement mechanism. A positioning controller comprising a coarse movement mechanism (101) which can move in a wide range with low positioning accuracy, and a fine movement mechanism (102) which can move in a small range with high positioning accuracy and on which the object to be positioned is mounted, said fine movement mechanism (102) is controlled by a controller (131) for fine movement, and said coarse movement mechanism (101) is controlled by a controller (132) for coarse movement, a signal corresponding to the difference between a commanded position of the object and its actual position is fed back to said controller (131) of the fine movement mechanism, characterized in that a signal corresponding to the sum of said difference and an actual displacement of said fine movement mechanism (102) is fed back to said controller (132) of the coarse movement mechanism (101).

Inventors: ASANO SHIN, GOTO TAKAYUKI, OKAZAKI YUICHI, ASANO, SHIN, GOTO, TAKAYUKI, OKAZAKI, YUICHI, Asano, Shin, c/o Advanced Technological Res. Cent., Goto, Takayuki, c/o Advanced Technological Res., Okazaki, Yuichi, c/o Mechanical Eng. Lab. Agency
Applicants: AGENCY IND SCIENCE TECHN, MITSUBISHI HEAVY IND LTD, AGENCY OF INDUSTRIAL SCIENCE AND TECHNOLOGY, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: G05B19
IPC codes: G05B19, B23Q15, G05D3