Work position adjusting apparatus and adjusting method

An apparatus for adjusting the position of a work mounted on a machine tool. A base is fixed to a work table of the machine tool, and the position of a mounting member is adjusted with respect to the base. The work is mounted on a mounting surface of the mounting member. The positions in the Z-axis direction of central portions of the four sides of the mounting member are adjusted by first driving and fixing members so that a work surface of the work is along an X-Y plane. The position where the mounting member is rotated around the Z-axis is then adjusted by second driving and fixing members arranged in the central portions of the pair of opposite sides of the mounting member so that a plane of the work is parallel to an X-Z plane. Each of the driving and fixing members includes piezoelectric displacement elements for adjusting an amount of displacement in response to an applied voltage so as to fix the mounting member in a state where the amount of displacement is adjusted.

CROSS REFERENCE TO RELATED APPLICATION
 This application claims priority benefits under 35 USC .sctn.119 of
 Japanese Patent Application Serial No. 9-197265 filed on Jul. 23, 1997,
 the disclosure of which is incorporated by reference.
 BACKGROUND OF THE INVENTION
 1.Field of the Invention
 The present invention relates to a work position adjusting apparatus and a
 work position adjusting method for correcting an error in inclination of a
 work surface of a work, for example, and an error in rotation along the
 work surface on a work table of a machine tool.
 2. Description of Related Arts
 Referring to FIGS. 21 and 22, reference numeral 30 denotes a machine tool
 such as an NC milling machine. Reference numeral 31 denotes a work table
 on which a work is carried. An upper surface 32 of the work table 31 is
 basically parallel to an X-Y motion plane (hereinafter merely referred to
 as an X-Y plane) of a machine. In the case of FIG. 21, the work table 31
 is movable upon being guided by an X-axis guide rail 37 and a Y-axis guide
 rail 38 on the X-Y plane of the machine. A work 33 is carried and fixed on
 the upper surface 32 of the work table 31 directly or through a work
 supporting device 34 such as a vice. A cutting tool 35 is mounted on a
 spindle and is rotated around a pindle center M to cut the work 33.
 Referring to FIG. 22, at the time of working, a work surface 39 of the work
 33 must be set in a correct positional relationship with the X-Y plane of
 the machine. In order to simplify the description, a case where the work
 surface 39 of the work 33 should be parallel to the X-Y plane will be
 hereafter premised. In this case, in such working that precision on the
 order of microns is required, the work surface 39 is not always completely
 parallel to the X-Y plane only by merely mounting the work 33 directly or
 through the work supporting device 34.
 Specifically, the work surface 39 is not always completely parallel to the
 X-Y plane by accumulating various errors such as an error in inclination
 of a surface of the work table 31 itself and an error caused by the work
 supporting device 34, and generally, has an error in inclination on the
 order of microns (an error in the degree of parallelization). The work 33
 has an error in rotation around an axis perpendicular to the X-Y plane. In
 either case, it is preferable that the error in inclination and the error
 in rotation are brought as close to zero as possible.
 In the prior art, the error in inclination of the work surface 39 is
 measured prior to the working, and then the inclination is adjusted by
 lightly tapping a part of the work surface 39 of the work 33 or spreading
 a thin metal foil between a part of the bottom of the work 33 and a base
 metal 40, for example. The error in inclination on the order of microns is
 brought close to zero by repeating such operations of measuring and
 correcting the error.
 The error in the degree of parallelization related to the above-mentioned
 error in rotation is measured, and is measured again after slightly
 loosening a bolt 41 for mounting the work supporting device 34 on the work
 table 31 and lightly tapping a side part of the work supporting device 34,
 thereby finely adjusting the degree of parallelization of the work
 supporting device 34. The error in the degree of parallelization on the
 order of microns is brought close to zero by repeating such an operation
 as mentioned above.
 The operations are very troublesome, and the efficiency of the operations
 significantly depends on the skill of a worker.
 Furthermore, human intervention is always required for the operations,
 which presents a large problem in the case of unmanned automation of the
 working including a set-up operation such as replacement of the work and
 fine adjustment of the inclination and the degree of parallelization.
 SUMMARY OF THE INVENTION
 An object of the present invention is to provide a work position adjusting
 apparatus and a work position adjusting method for adjusting the position
 of a work with high precision simply and in a short time without depending
 on the skill of a worker, which method is adapted to cope as required with
 unmanned automation.
 In order to attain the above-mentioned object, in one mode of the present
 invention, a work position adjusting apparatus for adjusting the position
 of a work having first and second surfaces crossing each other, on the
 basis of mutually perpendicular first, second and third axes are set in a
 machine tool with respect to a relative motion between a tool head and a
 work table, comprises a base, a mounting member on which the work is
 mounted, and supporting means interposed between the base and the mounting
 member for supporting the mounting member. The supporting means comprises
 first correcting means for correcting the inclination of the first surface
 relative to a plane including the first and second axes, by driving the
 mounting member in a direction parallel to the third axis, and second
 correcting means for correcting the inclination of the second surface
 relative to the first axis by rotating the mounting member around an axis
 parallel to the third axis. The work position adjusting apparatus further
 comprises coordinate value detecting means for detecting coordinate values
 related to the inclination of the first surface relative to the plane
 including the first and second axes and a coordinate value inclination of
 the second surface relative to the first axis, and controlling means for
 controlling the operation of each of the correcting means in response to a
 signal from the coordinate value detecting means.
 In the present embodiment, it is possible to detect the coordinate values
 related to the inclinations of the first and second surfaces of the work,
 control the operation of each of the correcting means depending on the
 detected coordinate values, and automatically correct the work to a
 desired mounting position. Further, the surface of the work is corrected
 on the basis of a motion axis of the machine tool, so that the correction
 can be made with high precision without being affected by an error in
 mounting between the base and the work table.
 The correction of the inclination of the first surface relative to the
 plane including the first and second axes, means the correction is to
 assure that an angle between both the plane and the first surface is a
 required angle. The required angle includes zero (that is, a case where
 both the surfaces are parallel to each other). Further, the correction
 according to the invention could be a case where the angle is so corrected
 as to fall within an allowable range including the required range, or a
 case where it is strictly corrected to the required angle. The same are
 true for the correction of the inclination of the second surface of the
 work. When the machine tool is an electric discharge machine, an electrode
 head for mounting an electrode shall correspond to a tool head.
 The base may be or may not be shared by components such as a work table of
 the machine tool.
 The foregoing and other objects, features, aspects and advantages of the
 present invention will become more apparent from the following detailed
 description of the present invention when taken in conjunction with the
 accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Preferred embodiments of the present invention will be described with
 reference to accompanying drawings.
 FIG. 1 is a perspective view of a machine tool equipped with a work
 position adjusting apparatus according to one embodiment of the present
 invention. A work position adjusting apparatus 100 according to the
 present invention (hereinafter merely referred to as a position adjusting
 apparatus 100 ) comprises as a principal part a position adjusting device
 1 serving as an adjusting unit fixed to an upper surface 32 serving as a
 reference surface of a work table 31 of a machine tool 30 using a fixed
 member such as a bolt. The position adjusting apparatus 100 further
 comprises a probe-type touch sensor 46 serving as signal outputting means
 mounted on a tool head 44, displacement sensors 47, 48 and 49 (see FIG. 8)
 for detecting respective displacements on three reference axes previously
 provided in the machine tool 30, and a controller C serving as controlling
 means for controlling operations of driving and fixing members as
 described later provided in the position adjusting device 1.
 FIG. 2 is a perspective view of the position adjusting device 1, FIG. 3 is
 a plan view of the position adjusting device 1, FIG. 4A is a side view
 showing the position adjusting device 1 as viewed along the Y-axis, and
 FIG. 4B is a side view showing the position adjusting device 1 as viewed
 along the X-axis. Referring to the drawings, the position adjusting device
 1 comprises a base 2 in a rectangular plate shape fixed to the work table
 31, and a mounting member 3 in a rectangular plate shape having a mounting
 surface 3a approximately parallel to an upper surface 2a of the base 2.
 The X-axis, the Y-axis and the Z-axis in the drawings are reference axes
 of the machine tool 30, which are the same in the following description.
 An X-Y plane is a plane including the X-axis and the Y-axis, and a Z-X
 plane is a plane including the Z-axis and the X-axis.
 In FIG. 1, reference numeral 42 denotes a Y-axis moving table so supported
 that it can freely travel along the Y-axis by a main body 30A of the
 machine tool 30, and reference numeral 43 denotes an X-axis moving table
 so supported that it can freely travel along the X-axis by the Y-axis
 moving table 42. The X-axis moving table 43 and the Y-axis moving table 42
 are respectively driven by an X-axis servo motor and a Y-axis servo motor
 (which are not illustrated in FIG. 1 but are respectively illustrated as
 B1 and B2 in FIG. 8). The displacements of the X-axis moving table 43 and
 the Y-axis moving table 42 are respectively detected by the corresponding
 displacement sensors 47 and 48 (see FIG. 8). The position of each of the
 moving tables 42 and 43 is controlled on the basis of the detected
 displacement.
 On the other hand, the tool head 44 for mounting a tool and a supporting
 member 45 for supporting the tool head 44 are so supported that they can
 freely travel along the Z-axis by the main body 30A, and the supporting
 member 45 is driven by a Z-axis servo motor (which is not illustrated in
 FIG. 1 but is illustrated as B3 in FIG. 8). Further, the direction in the
 Z-axis direction of the supporting member 45 is detected by the
 displacement sensor 49 (see FIG. 8), and the position of the supporting
 member 45 is controlled on the basis of the detected displacement.
 As shown in FIG. 1, the controller C for adjusting the position of the
 mounting member 3 is mounted at a predetermined position of the machine
 tool 30. An operation panel C1 is arranged on the surface of the
 controller C, and a microcomputer C2 as described later for carrying out
 control of the position and the moving speed of each of the moving tables
 42 and 43 and the supporting member 45, control of the number of
 revolutions of the tool, adjustment of the position of the work before
 working, and the like is mounted inside the controller C. A lead wire from
 each of piezoelectric displacement elements as described later is
 connected to the controller C, which is not illustrated.
 A rolling bearing 8 for rotatably supporting the mounting member 3 around
 an axis 20 along the Z-axis is arranged between the center of the mounting
 member 3 and the base 2. The upper surface 2a and a lower surface of the
 base 2 are reference surfaces of the base 2, and the lower surface serving
 as the reference surface is fixed along the upper surface of the work
 table 31. Therefore, the upper surface 2a serving as the reference surface
 of the base 2 is almost properly positioned.
 Referring to FIG. 5 which is a cross-sectional view along the X-axis in
 FIG. 3, the rolling bearing 8 is composed of a radial ball bearing, for
 example, and has a supporting main unit 8a in an approximately cylindrical
 shape fixed to the upper surface 2a of the base 2 by a screw 2c. A groove
 18 having an inner raceway surface 18a is formed on a peripheral surface
 of the supporting main unit 8a, and a plurality of balls 15 made of steel,
 for example, held in the groove 18 are fitted in a receiving portion 14
 composed of a circular hole formed on the lower surface of the mounting
 member 3. The balls 15 are revolved while being rolled using an inner
 peripheral wall of the receiving portion 14 as an outer raceway surface
 19. Further, the balls 15 are so set as to be rolled in a state where a
 clearance is zero with the inner raceway surface 18a and the outer raceway
 surface 19.
 On the other hand, a predetermined clearance S is provided between an upper
 surface 16 of the supporting main unit 8a and a bottom surface 17 of the
 receiving portion 14, and the rolling bearing 8 does not support the
 mounting member 3 in the Z-axis direction but supports only the rotation
 of the mounting member 3 along the X-Y plane. Consequently, the movement
 of the mounting member 3 in the direction along the X-axis and in the
 direction along the Y-axis is regulated by the rolling bearing 8. Further,
 the mounting member 3 can be also displaced in an inclined shape in the
 Z-axis direction, with the center of revolution of the ball 15 used as a
 support, by the above-mentioned clearance S.
 In the present embodiment, description is made of a case where a work W is
 directly mounted on the mounting surface 3a of the mounting member 3. A
 reference guide rail 3c in an angle shape, for example (see FIG. 2. The
 illustration of the reference guide rail 3c is omitted in the other
 drawings) is arranged in a required position of the mounting surface 3a of
 the mounting member 3. The work W is put on the mounting surface 3a in a
 state where it is along the reference guide rail 3c, so that the work W is
 roughly positioned. As means for fixing the work W to the mounting surface
 3a, means for inserting a screw for work fixing into a tapped hole formed
 on the mounting surface 3a and pressing and fixing the work W to the
 mounting surface 3a can be illustrated. Further, in a case where a load is
 hardly applied to the work W by an electric discharge machining, for
 example, it is also possible to bond and fix the work W to the mounting
 surface 3a using an adhesive such as an instantaneous adhesive.
 There is a system for indirectly fixing the work W through a mounting vice
 (for example, one which is the same as that shown in the conventional
 example in FIG. 21) fixed to the mounting surface 3a, in addition to a
 system of directly fixing the work W to the mounting surface 3a. Further,
 the work W may be fixed to the mounting member 3 through an attachment
 such as an automatic centering device suitable for unmanned automatic
 working.
 Referring to FIG. 3, recesses 3b are formed in respective central portions
 of the four sides of the mounting member 3, and driving projections 12 and
 13, which are rectangular in cross section, are so formed as to project
 outward from respective central portions of the recesses 3b. The driving
 projections 12 respectively extend in the Y-axis direction and a reversed
 Y-axis direction, and the driving projections 13 respectively extend in
 the X-axis direction and a reversed X-axis direction and are so set as to
 be longer than the driving projections 12. The driving projections 12 and
 13 are respectively supported in the Z-axis direction by first driving and
 fixing members 4 serving as first correcting means. Further, the longer
 driving projections 13 are respectively supported in the direction of
 rotation around the axis 20 parallel to the Z-axis by second driving and
 fixing members 6 serving as second correcting means.
 The first driving and fixing members 4 are so arranged as to divide the
 circumference centered around the axis 20 into equal divisions. The paired
 second driving and fixing members 6 are arranged in positions which are
 symmetrical with respect to the axis 20 interposed therebetween. The first
 driving and fixing members 4 respectively adjust the heights in the
 central portions of the four sides of the mounting member 3 through the
 driving projections 12 or 13, to adjust the inclinations of the mounting
 surface 3 relative to the X-axis and the Y-axis, and adjust the
 inclination of a work surface Wa of the work W through the adjustment. On
 the other hand, the second driving and fixing members 6 respectively
 adjust the position where the mounting member 3 is rotated, and therefore
 the work W is rotated around the axis 20 through the driving projections
 13.
 Each of the first driving and fixing members 4 includes piezoelectric
 displacement elements 9a and 9b which are paired with each other. The
 piezoelectric displacement elements 9a and 9b are supported on the upper
 surface 2a of the base 2 by a fixed frame 5 having a channel shape, fixed
 to the upper surface 2a of the base 2 by a screw 11. The fixed frame 5
 comprises a transverse bar 5a parallel to the upper surface 2a of the base
 2 and a pair of legs 5b connected to both ends of the transverse bar 5a.
 The driving projection 12 penetrates a space defined by the fixed frame 5
 and the upper surface 2a of the base 2, and the piezoelectric displacement
 elements 9a and 9b are respectively arranged above and below the driving
 projection 12 in the space.
 The piezoelectric displacement element in the present embodiment is
 constructed by laminating a plurality of piezoelectric elements having the
 property of expanding and contracting if a voltage is applied thereto,
 where it is possible to obtain an amount of displacement corresponding to
 the applied voltage and obtain an arbitrary amount of displacement
 corresponding to the number of piezoelectric elements laminated. That is,
 when a large amount of displacement is required, a piezoelectric
 displacement element formed of a large number of laminated piezoelectric
 elements, may be selected and used. On the other hand, when a required
 amount of displacement is small, a piezoelectric displacement element
 having a small number of laminated piezoelectric elements, may be selected
 and used. The piezoelectric displacement element has sufficiently high
 rigidity to withstand a load of several hundred kilograms, and has a fast
 displacement response to the applied voltage, although the size thereof is
 generally very small, for example, approximately 10 mm.times.10
 mm.times.18 mm. When it is necessary to receive a larger load, a
 piezoelectric displacement element having a large load area may be used.
 Each of side surfaces 22 of each of the piezoelectric displacement elements
 9a and 9b is fixed to the leg 5b through a layer 21 of an adhesive having
 elasticity, such as an adhesive including silicone interposed between the
 side surface 22 and an opposite inner surface of the leg 5b. Each of an
 upper surface 23a and a lower surface 23b of each of the piezoelectric
 displacement elements 9a and 9b is not fixed to a surface opposite
 thereto. Even if the mounting member 3 is rotated by the second driving
 and fixing member 6, so that the driving projection 12 is subjected to a
 displacement in the horizontal direction, no excessive stress is applied
 to the piezoelectric displacement elements 9a and 9b. In the drawings,
 reference numerals 24 and 25 denote lead wires for applying a driving
 voltage to the piezoelectric displacement elements 9a and 9b.
 As described in the foregoing, each of the piezoelectric displacement
 elements 9a and 9b expands and contracts by application of a voltage. The
 lower piezoelectric displacement element 9b is caused to contract while
 the upper piezoelectric displacement element 9a is expanded, so that the
 driving projection 12 is pressed and displaced downward in a state where
 it is interposed from above and below. On the contrary, the upper
 piezoelectric displacement element 9a is caused to contract while the
 lower piezoelectric displacement element 9b is expanded, so that the
 driving projection 12 is pressed and displaced upward in a state where it
 is interposed from above and below.
 The inclination of the mounting member 3 relative to the X-axis can be
 adjusted by the pair of first driving and fixing members 4 arranged along
 the X-axis, while the inclination of the mounting member 3 relative to the
 Y-axis can be adjusted by the pair of first driving and fixing members 4
 arranged along the Y-axis. The inclination of the mounting surface 3a of
 the mounting member 3 is adjusted in two crossing directions, thereby
 making it possible to adjust the inclination of the work surface Wa
 corresponding to a first surface of the work W mounted on the mounting
 surface 3a. That is, the work surface Wa of the work W can be so adjusted
 as to be parallel to the X-Y plane.
 On the other hand, referring to FIG. 3, the longer driving projections 13
 extending in the X-axis direction and the reversed X-axis direction are
 also received by the second driving and fixing members 6, respectively.
 The second driving and fixing member 6 is arranged at an end of the
 driving projection 13. Referring to FIG. 7 which is a side view of the
 second driving and fixing member 6 as viewed along the X-axis, each of the
 second driving and fixing members 6 comprises a pair of piezoelectric
 displacement elements 10a and 10b, and the piezoelectric displacement
 elements 10a and 10b are supported by a fixed frame 7 in a trapezoidal
 shape. FIG. 7 illustrates a state where the driving projection 13 is in
 its initial position, which is the center in the lateral direction of a
 through hole 7a, as described later with respect to the fixed frame 7. In
 FIG. 7, a position indicated by a broken line is the position of an end
 surface of each of the piezoelectric displacement elements 10a and 10b in
 a state where no voltage is applied thereto.
 The fixed frame 7 is fixed to the upper surface 2a of the base 2 by the
 screw 11, and has a rectangular through hole 7a. The driving projection 13
 penetrates the center of the through hole 7a. The piezoelectric
 displacement elements 10a and 10b are respectively arranged on the right
 and the left of the driving projection 13 in the through hole 7a. The
 paired piezoelectric displacement elements 10a and 10b press the driving
 projection 13 in opposite directions, and rotate the mounting member 3 in
 cooperation with each other. Each of upper and lower surfaces 26 of each
 of the piezoelectric displacement elements 10a and 10b is fixed to the
 fixed frame 7 through a layer 21 of an adhesive having elasticity such as
 an adhesive including silicone between the surface 26 and an opposite
 inner upper or inner bottom surface of the through hole 7a. On the other
 hand, left and right side surfaces 27a and 27b of each of the
 piezoelectric displacement elements 10a and 10b are not fixed to left or
 right side surfaces of the driving projection 13 and the through hole 7a.
 Even if the driving projection 13 is displaced in the Z-axis direction by
 the first driving and fixing member 4, therefore, the fixed frame 7 and
 the piezoelectric displacement elements 10a and 10b fixed thereto do not
 restrict the displacement, and the piezoelectric displacement elements 10a
 and 10b receive no excessive force.
 FIG. 8 is a block diagram showing the electrical construction of the
 position adjusting apparatus 100 according to the present embodiment.
 Referring to FIG. 8, in the present embodiment, a signal from an X-axis
 displacement sensor 47 for detecting the displacement of the X-axis moving
 table 43, a signal from the Y-axis displacement sensor 48 for detecting
 the displacement of the Y-axis moving table 42, a signal from the Z-axis
 displacement sensor 49 for detecting the displacement in the Z-axis
 direction of the supporting member 45, and a signal from a touch sensor 46
 (to be a trigger signal) are inputted to the microcomputer C2.
 The touch sensor 46 is mounted on the tool head 44 in place of a tool, and
 emits a signal upon detecting the contact with the work W. An end of a
 contact of the touch sensor 46 is formed in a spherical shape, and allows
 the contact in all directions.
 On the other hand, the microcomputer C2 controls voltages applied to
 piezoelectric displacement elements 9a, 9b, 10a and 10b through driving
 circuits A each of which includes a D/A converter. Further, the
 microcomputer C2 controls the driving of X-axis, Y-axis and Z-axis servo
 motors B1, B2 and B3 through driving circuits B, respectively.
 The voltage to be applied to each of the piezoelectric displacement
 elements 9a, 9b, 10a and 10b will hereafter be described.
 FIG. 6A illustrates a state where the voltages respectively applied to the
 piezoelectric displacement elements are zero volt wherein a total
 clearance between the piezoelectric displacement elements and the driving
 projection 12 is .DELTA.t1.times.2. That is, the driving projection 12 of
 the mounting member 3 can be displaced by a maximum of .DELTA.t1.times.2
 in the vertical direction. Each of the piezoelectric displacement elements
 9a and 9b must be one in which the displacement of at least
 .DELTA.t1.times.2 is obtained. When an applied voltage in a case where the
 displacement of .DELTA.t1.times.2 is obtained is taken as V1 volts, both
 the piezoelectric displacement elements 9a and 9b in the first driving and
 fixing member 4 extend by .DELTA.t1 vertically and in opposite directions
 upon application of a voltage of V1/2 in a normal state where the
 inclination of the work surface Wa is not corrected, thereby interposing
 the driving projection 12 of the mounting member 3 from above and below
 and just fix the driving projection 12 in a central position in the range
 of displacement (the above-mentioned initial position).
 Similarly, when a total clearance between both the piezoelectric
 displacement elements 10a and 10b of the second driving and fixing member
 10 and the driving projection 13, in a case where both voltages V10a and
 V10b applied to the piezoelectric displacement elements 10a and 10b are
 zero volt is taken as .DELTA.t2.times.2, the piezoelectric displacement
 elements 10a and 10b extend by .DELTA.t2 horizontally and in opposite
 directions upon application of a voltage of V2/2 volts in a normal state
 where the degree of parallelization is not corrected when an applied
 voltage required to obtain a displacement of .DELTA.2/2.times.2 is taken
 as V2 volts, thereby interposing the driving projection 13 from the right
 and the left and just fix the driving projection 13 in a central position
 in the range of displacement (the above-mentioned initial position).
 If a voltage is applied once to the piezoelectric displacement elements 9a
 and 9b, a residual displacement .delta. actually occurs even after the
 voltage is removed. Therefore, the displacement of the driving projection
 12 or 13 interposed between the piezoelectric displacement elements 9a and
 9b may deviate from its proper position, as shown in FIG. 9A. In FIG. 9A,
 the displacement of the driving projection 12 or 13 may be one in an
 intermediate position between the voltage-displacement characteristics of
 the lower piezoelectric displacement element 9b and the
 voltage-displacement characteristics of the upper piezoelectric
 displacement element 9a (indicated by a one-dot and dash line).
 In order to correct a deviation in displacement caused by the residual
 displacement .delta. and improve the linearity of the voltage-displacement
 characteristics, overdrive voltages having bias voltages Vc and Vd added
 thereto are respectively applied to the piezoelectric displacement
 elements 9a and 9b, so that the displacement of the driving projection 12
 or 13 almost passes through the origin (see FIG. 9B).
 The bias voltage for overdriving is not a predetermined voltage, and is so
 applied that it is increased in proportion to an amount of displacement of
 the piezoelectric displacement element. That is, in the embodiment shown
 in FIG. 9B, the bias voltage is zero when the amount of displacement of
 the piezoelectric displacement element is zero (only the residual
 displacement .delta.), is increased as the amount of displacement is
 increased, and becomes Vc at the time of the maximum displacement.
 Operations in a case where the position of the work W is controlled using
 the above-mentioned position adjusting apparatus 100 will be described on
 the basis of a flow chart shown in FIG. 10.
 The inclination of the work surface Wa serving as a reference surface is
 first corrected with respect to the work W coarsely positioned using the
 above-mentioned reference guide rail (steps S1 to S3). The work surface Wa
 must be along an X-Y plane whose inclination is zero by correcting an
 error in inclination of the work surface Wa relative to the X-Y plane.
 A plane in an three-dimensional XYZ coordinate space can be expressed by
 the following equation:
EQU aX+bY+c=Z (1)
 In this equation, a represents the inclination in the X-axis direction, and
 b represents the inclination in the Y-axis direction. The inclination in
 the X-axis direction means the inclination of the line at which the Z-X
 plane intersects the plane, for example the work surface Wa, with respect
 to the X-axis. The inclination in the Y-axis direction means the
 inclination of the line at which the Z-Y plane intersects the plane, for
 example the work surface Wa, with respect to the Y-axis. The coordinates
 of three arbitrary points are taken as (X1, Y1, Z1), (X2, Y2, Z2), and
 (X3, Y3, Z3). When the inclinations a and b of a cubic equation obtained
 by substituting the coordinates into the foregoing equation (1) are found,
 a and b are expressed by the following equations (2) and (3):
 ##EQU1##
 The coordinates (x1, y1, z1), (x2, y2, z2) and (x3, y3, and z3) of three
 arbitrary points P.sub.1, P.sub.2 and P.sub.3 on the work surface Wa of
 the work W are first measured. In the microcomputer C2, the actual degree
 of inclination in each of the X-axis direction and the Y-axis direction of
 the work surface Wa serving as a reference surface is found on the basis
 of the coordinates and the foregoing equations (2) and (3) (step S1).
 Specifically, in the microcomputer C2, the X-axis moving table 43 and the
 Y-axis moving table 42 are driven to coincide with the X and Y coordinates
 of the point P.sub.1, for example, after which the supporting member 45 is
 slowly lowered to stop being lowered at the time point where the touch
 sensor 46 is brought into contact with the work surface Wa thereby a
 trigger signal is inputted thereto, and the Z coordinates of the point
 P.sub.1 at this time point are detected so as to obtain the
 three-dimensional coordinates of the point P.sub.1. The same is true for
 the points P.sub.2 and P.sub.3.
 When the found degree of inclination is not within an allowable range (for
 example, not more than 0.5 .mu.m with respect to a span of 100 mm), the
 inclination is corrected, and the corrected inclination is fixed (steps S2
 and S3).
 When the pitch between the two first driving and fixing members 4 in the
 X-axis direction is taken as d1 mm (see FIG. 3), relative amounts of
 correction of the inclination in the Z-axis direction of the mounting
 member 3 in the two first driving and fixing members 4 are a total of
 a.times.d1.times.1000 .mu.m. That is, a displacement of
 a.times.d1.times.1000/2 .mu.m may be corrected with respect to the center
 of the mounting member 3 by one of the first driving and fixing members 4.
 On the other hand, a displacement of a.times.d1.times.1000/2 .mu.m may be
 corrected in the opposite direction with respect to the other first
 driving and fixing member 4.
 An applied voltage required for a displacement per 1 .mu.m of the
 piezoelectric displacement element is previously found. When the applied
 voltage is taken as K1 volts, therefore, the following correction voltages
 are respectively applied to the piezoelectric displacement elements 9a and
 9b in one of the pair of first driving and fixing members 4 arranged along
 the X-axis:
EQU V.sub.9a =V1/2+(K1.times.a.times.d1.times.1000/2) (4)
EQU V.sub.9b =V1/2-(K1.times.a.times.d1.times.1000/2) (5)
 The following correction voltages are respectively applied to the
 piezoelectric displacement elements 9a and 9b in the other first driving
 and fixing member 4:
EQU V.sub.9a =V1/2-(K1.times.a.times.d1.times.1000/2) (6)
EQU V.sub.9b =V1/2+(K1.times.a.times.d1.times.1000/2) (7)
 The foregoing value a may positive or negative.
 The inclination of the work surface Wa in the X-axis direction which is
 thus found by measuring the degree of inclination once, can be corrected
 at a time. The inclination in the Y-axis direction can be also corrected
 simultaneously with the correction of the inclination in the X-axis
 direction in the same manner as that in the X-axis direction.
 The coordinates of two points P.sub.4 and P.sub.5 on a plane Wb are
 measured in a state where the correction is so made that the work surface
 Wa is along the X-Y plane, that is, in a state where the axis 20
 perpendicular to the work surface Wa is along the Z-axis. Although the
 manner of the measurement is basically the same as that in a case where
 the coordinates of the three points P.sub.1, P.sub.2 and P.sub.3 on the
 work surface Wa are measured, it differs in that the X-axis moving table
 43 and the supporting member 45 are driven to set the X and Z coordinates
 of the point P.sub.4, for example, after which the Y-axis moving table 42
 is driven to abut the touch sensor 46 against the plane Wb.
 The inclination of the plane Wb relative to the X-axis (the degree of
 parallelization between the plane Wb and the X-axis) is measured on the
 basis of the coordinates of the two points P.sub.4 and P.sub.5 which are
 thus measured and the following equation (4) (step S4). When the measured
 inclination is not within an allowable range (within 0.5 .mu.m with
 respect to a span of 100 mm, for example), the fixing of the inclination
 of the work surface Wa is released once, after which the correction of the
 inclination of the work surface Wa (the same correction as that in the
 step S3) and the correction of the inclination (that is, the correction of
 the degree of parallelization) of the plane Wb are simultaneously made,
 and fix the corrected inclination of the work surface Wa (steps S5, S6,
 and S7).
 Consider a case where the inclination of the plane Wb had already been
 within the allowable range when it was corrected. In this case, the degree
 of parallelization is fixed by the second driving and fixing members 6 as
 it is (that is, in a state where the inclination of the work surface Wa is
 fixed by the first driving and fixing members 4) (steps S5 and S8).
 Specifically, an error in the direction of rotation of the work surface Wa
 within the X-Y plane is adjusted by using the plane Wb corresponding to a
 second surface perpendicular to the work surface Wa as a reference surface
 and adjusting the degree of parallelization in the X-axis direction
 between the plane Wb serving as the reference surface and the Z-X plane.
 The degree of parallelization in the X-axis direction between the Wb and
 Z-X planes means the degree of parallelization between X-axis and the line
 at which the X-Y plane intersects the plane Wb. When the X and Y
 coordinates of the two arbitrary points P.sub.4 and P.sub.5 are measured
 on the plane Wb serving as the reference surface of the degree of
 parallelization, and the found coordinates of the two points P.sub.4 and
 P.sub.5 are respectively taken as (x4, y4) and (x5, y5), the inclination e
 in the direction of rotation within the X-Y plane is expressed by the
 following equation:
EQU e=(y4-y5)/(x4-x5) (8)
 When the distance between the second driving and fixing member 6 and the
 axis of rotation 20 is taken as d3 mm, therefore, the second driving and
 fixing member 6 may displace the mounting member 3 in the direction of
 rotation by an amount of correction of d3.times.e.times.1000 .mu.m. An
 applied voltage required for a displacement per 1 .mu.m of each of the
 piezoelectric displacement elements 10a and 10b in the second driving and
 fixing member 6 is previously found. When the applied voltage is taken as
 K2 volts, therefore, the following correction voltages are respectively
 applied to the piezoelectric displacement elements 10a and 10b:
 V.sub.10a =V2/2+(K2.times.e.times.d3.times.1000) (9)
EQU V.sub.10b =V2/2-(K2.times.e.times.d3.times.1000) (10)
 An error in the degree of parallelization, which is thus found by measuring
 the degree of parallelization once, can be corrected at a time. The
 foregoing value e may be either of positive or negative.
 In the present embodiment, the correction of the inclination of the work
 surface Wa of the work W and the correction of the degree of
 parallelization of the plane Wb can be made without human intervention
 very simply, in a short time and with high precision. As a result, it is
 also possible to automate the preparation of the adjustment.
 The driving and fixing members 4 and 6 serving as correcting means are also
 used as locking means for fixing positions, so that the construction of
 the position adjusting apparatus can be simplified.
 Particularly, the mounting member 3 is supported so as to be rotatable
 around the axis 20 which is perpendicular to the mounting surface 3a, so
 that a deviation in rotation can be corrected only by providing the second
 driving and fixing member 4 in one position on the circumference. In this
 case, the construction of the position adjusting apparatus can be
 simplified, and a supporting structure including the driving and fixing
 member 4 can sufficiently withstand a cutting stress exerted on the X-Y
 plane. In the above-mentioned embodiment, a pair of second driving and
 fixing members 4 is arranged in positions which are symmetrical with the
 axis 20 interposed therebetween in order to improve rigidity corresponding
 to a higher driving force and a stronger cutting stress.
 Since the piezoelectric displacement elements 9a, 9b, 10a and 10b are used,
 the following advantages are obtained. That is, the piezoelectric
 displacement element makes it possible to significantly miniaturize the
 driving and fixing members 4 and 6 serving as correcting means and to bear
 a sufficient fixing load. Further, the piezoelectric displacement element
 has an amount of displacement which is stabilized against an applied
 voltage as well as a good response function, so that a displacement can be
 quickly adjusted to be the desirable one. On the other hand, a
 piezoelectric displacement element having an arbitrary amount of
 displacement can be obtained depending on the number of laminated layers
 of piezoelectric elements. Therefore, a piezoelectric displacement element
 has flexibility in terms of a desirable amount of displacement since it
 can be selected and used depending on an amount of adjustment required.
 Further, the reproducibility of applied voltage-displacement amount
 characteristics are good, so that the correction can be made with high
 precision by performing setting only once.
 The paired piezoelectric displacement elements constituting each of the
 driving and fixing members are sufficient if they can drive the mounting
 member 3 in opposite directions. The form of arrangement thereof is not
 particularly limited. For example, the paired piezoelectric displacement
 elements may be arranged a distance away from each other. Further, the
 paired piezoelectric displacement elements may be one element arranged on
 each side with a rotating support such as a spherical bearing interposed
 therebetween, and rotating the mounting member 3 in opposite directions by
 pressing the mounting member 3 in the same opposite directions.
 Furthermore, the mounting member 3 is displaced while interposing each of
 the driving projections 12 and 13 of the mounting member 3 between the
 piezoelectric displacement elements 9a and 9b ( 10a and 10b) on both sides
 thereof upon pressing the driving projection, so that the displacement can
 be adjusted with high precision, and the stability in a case where the
 displacement is fixed is improved. The reason for this is that the
 piezoelectric displacement element is not so formed that it can bear a too
 large tensile load but is so formed that it can bear a compressive load.
 The mounting member 3 may be integrally formed by including the driving
 projections 12 and 13, or the driving projections 12 and 13 may be
 separately formed. The pairs of piezoelectric displacement elements 9a and
 9b and 10a and 10b are respectively provided in the fixed frames 5 and 7,
 so that the driving and fixing members 4 and 6 can be made compact as
 correcting means.
 In the step of correcting the plane Wb serving as a second surface which is
 carried out after the inclination of the work surface Wa serving as a
 first surface relative to the X-Y plane is corrected, the mounting member
 3 is rotated around the Z-axis. Particularly when the work surface Wa is
 corrected to be approximately parallel to the X-Y plane, therefore, the
 correction of the work surface Wa already adjusted is not affected by the
 correction of the plane Wb. Even if the correction is affected, the effect
 is at a level which can be substantially ignored, thereby making it
 possible to make highly precise corrections.
 The correction of the work surface Wa previously made is released once to
 return the work surface Wa to a state before the correction, after which
 the plane Wb is corrected and, at the same time, the work surface Wa is
 returned to the above-mentioned previously corrected state. Since at the
 time of making the correction by one of the driving and fixing members 4
 and 6, no unnecessary force is exerted on the other driving and fixing
 members, therefore, it is possible to make the correction in a state where
 the effect of the correction of one of the driving and fixing members on
 the correction of the other driving and fixing member is reliably avoided.
 As a result, it is possible to make more highly precise corrections and to
 lengthen the life of the driving and fixing members 4 and 6 serving as
 correcting means.
 In the above-mentioned embodiment, after the inclination and the degree of
 parallelization are corrected through the step S7 or S8, the coordinates
 of each of the points P.sub.1 to P.sub.5 may be measured once again to
 confirm that the inclination of the work surface Wa and the degree of
 parallelization of the plane Wb are within the allowable ranges.
 In the above-mentioned embodiment, corrections are made in two steps such
 that after correcting the inclination of the work surface Wa, the degree
 of parallelization of the plane Wb is corrected upon measuring the degree
 of parallelization, however, both the corrections can be simultaneously
 made by collectively measuring the coordinates of the five points P.sub.1
 to P.sub.5 before the corrections. Strictly speaking, highly precise
 correction of the degree of parallelization cannot be made until the
 inclination of the work surface Wa is corrected, therefore the precision
 of the former correction is higher. On the other hand, the amount of
 correction itself is at a significantly low level. The effect of the
 correction of the inclination of the work surface Wa on the degree of
 parallelization of the plane Wb is at a level that may be substantially
 ignored; therefore, the latter simultaneous correction can be made.
 Furthermore, the structures including the base 2, the driving and fixing
 members 4 and 6, and the mounting member 3 are formed into a unit as a
 position adjusting device 1, so that the unit can be easily applied to
 various types of machine tools, thereby improving versatility.
 In the above-mentioned embodiment, the measurements of the coordinates for
 measuring an error in inclination and an error in the degree of
 parallelization are made using certain types of sensors provided in the
 machine tool 30 to simplify the construction of the position adjusting
 apparatus; however, the present invention is not limited to the same. For
 example, the coordinates may be measured using a known three-dimensional
 measuring device or the like apart from the machine tool, processed using
 a personal computer or the like, and inputted to a controller of the
 machine tool.
 The roller bearing 8 in the above-mentioned embodiment can be replaced with
 a spherical bearing 80 as shown in FIG. 11A, to support a load in the
 Z-axis direction. In this case, as shown in FIG. 11B, the first driving
 and fixing members 4 may be arranged in at least two positions which are
 different from the position where the spherical bearing 80 is arranged,
 thereby making it possible to simplify the construction of the position
 adjusting apparatus. Further, the mounting member 3 can be supported by
 the spherical bearing 80 more stably. It is necessary that the positions
 where all the first driving and fixing members 4 are arranged and the
 position where the spherical bearing 80 is arranged are not on the same
 straight line.
 As the form of arrangement of the first driving and fixing members 4, the
 first driving and fixing members 4 can be arranged at four corners of the
 mounting member 3, as shown in FIGS. 12A and 12B. In this case, pairs of
 first driving and fixing members 4 are respectively arranged on a pair of
 diagonal lines of the mounting member 3 in FIG. 12A, while pairs of first
 driving and fixing members 4 extending in the Y-axis direction and the
 reversed Y-axis direction are respectively arranged in FIG. 12B. In FIGS.
 12A and 12B, the second driving and fixing members 6 are respectively
 arranged in central portions of a pair of opposite sides of the mounting
 member 3.
 As shown in FIG. 12C, the first driving and fixing members 4 may be
 respectively provided in such positions as to divide the circumference
 centered around the center of the circular mounting member 3 into three
 approximately equal divisions, for example, and the second driving and
 fixing member 6 may be provided in one position on the circumference.
 FIGS. 13A and 13B respectively illustrate still another embodiment of the
 present invention. The embodiment shown in FIG. 13A differs from the
 embodiment shown in FIG. 12A in that second driving and fixing members 6
 are respectively arranged in central portions of the sides of the mounting
 member 3. The second driving and fixing members 6 are arranged in such
 positions as to divide the circumference centered around the center of the
 mounting member 3 into approximately equal divisions. The mounting member
 3 can be rotatably supported equivalently by the second driving and fixing
 members 6. Rigidity which can withstand a cutting load in the horizontal
 direction is ensured by the second driving and fixing members 6 even if
 bearings are omitted, so that the mounting member 3 can be maintained in a
 stable position. Consequently, the structures of the roller bearing 8 and
 the spherical bearing 80 can be omitted, so that the construction of the
 position adjusting apparatus can be simplified.
 The embodiment shown in FIG. 13B differs from the embodiment shown in FIG.
 12C in that the second driving and fixing members 6 are respectively
 provided in such positions as to divide the circumference of the mounting
 member 3 into three equal divisions. Even if the second driving and fixing
 members 6 are thus arranged only in such positions as to divide the
 circumference of the mounting member 3 into three equal divisions, a
 position stabilized against the cutting load in the horizontal direction
 can be maintained. As a result, the construction of the position adjusting
 apparatus can be simplified by omitting the roller bearing 8 and the
 spherical bearing 80.
 FIG. 14 illustrates still another embodiment. Referring to FIG. 14, in the
 present embodiment, one of a pair of piezoelectric displacement elements
 9a and 9b with a driving projection 12 or 13 interposed therebetween is
 replaced with an elastic member, for example, a compressive coil spring
 50. In this case, a voltage of only one of the piezoelectric displacement
 elements 9a and 9b may be controlled, so that the control thereof is
 simplified. The fabrication cost can be made low by reducing the number of
 piezoelectric displacement elements. Any elastic member can be used,
 provided that it can bear a required amount of displacement and a required
 load. For example, an elastic member of rubber or resin or the like can be
 used. Further, a spring made of a metal can be also used. A tensile coil
 spring can be used in addition to the above-mentioned compressive coil
 spring as a spring.
 FIG. 15 illustrates still another embodiment. Referring to FIG. 15, in the
 present embodiment, each of pairs of first and second driving and fixing
 members 4 and 6 with a driving projection 13 interposed therebetween are
 arranged in a cross shape in one fixed frame 51 having a cross-shaped
 through hole 51a. In this case, the number of fixed frames 51 and the
 length of the driving projection 13 can be reduced, so that the entire
 position adjusting apparatus 100 can be made compact.
 FIG. 16 illustrates still another embodiment. Referring to FIG. 16, the
 present embodiment differs from the embodiment shown in FIG. 2 in that an
 intermediate member 60 in a rectangular plate shape arranged parallel to a
 base 2 is provided between the base 2 and a mounting member 3, so that the
 position where the intermediate member 60 is rotated about the base 2 is
 adjusted by second driving and fixing members 6, and the inclination of a
 work surface Wa is adjusted by first driving and fixing members 4 for
 supporting the mounting member 3 on the intermediate member 60 (whose
 construction is the same as that in the embodiment shown in FIG. 2). The
 intermediate member 60 may be directly put on an upper surface 2a of the
 base 2, or may be supported on the base 2 through a slide bearing such as
 a needle roller bearing. Further, a fixed frame 5 of the first driving and
 fixing member 4 is fixed to the intermediate member 60, and a fixed frame
 7 of the second driving and fixing member 6 is fixed to the base 2.
 In the present embodiment, the inclination of the mounting member 3 is
 adjusted with respect to the relationship between the mounting member 3
 and the intermediate member 60, and the position where the mounting member
 3 is rotated is adjusted with respect to the relationship between the
 intermediate member 60 and the base 2, so that respective adjustments by
 the driving and fixing members 4 and 6 can be made in a state where they
 are completely independent of each other.
 Referring now to FIGS. 17 to 19, another embodiment of the present
 embodiment will be described. Referring to FIG. 17, a work W is carried on
 a work table 31 of a machine tool 30 through a position adjusting device 1
 in a work position adjusting apparatus 101 (hereinafter merely referred to
 as a position adjusting apparatus 101). First driving and fixing members 4
 are provided in such positions as to divide the circumference of a
 circular mounting member 3 into three approximately equal divisions.
 Similarly, second driving and fixing members 6 are provided in such other
 positions as to divide the circumference of the mounting member 3 into
 three approximately equal divisions.
 The form of arrangement of each of the driving and fixing members in the
 present embodiment corresponds to that in the above-mentioned embodiment
 shown in FIG. 13B. Each of the first and second driving and fixing members
 4 and 6 is constituted by a pair of piezoelectric displacement elements
 arranged opposite to each other with a predetermined portion of the
 mounting member 3 interposed therebetween. The form of arrangement of the
 piezoelectric displacement elements in each of the driving and fixing
 members 4 and 6 is the same as that in the embodiment shown in FIG. 1.
 The work W is carried on the mounting member 3 through a centering
 positioning jig J serving as a work position adjusting device. Referring
 to FIG. 17, and to FIG. 18 that is a side view of the position adjusting
 device 1, an upper surface 32 of the work table 31 is parallel to an X-Y
 motion plane, that is, an X-Y plane 52 of a machine. Further, an upper
 surface 2a of the base 2 in the position adjusting device 1 located on the
 work table 31 is also parallel to the X-Y plane 52.
 A main body J1 of the centering positioning jig J is clamped and fastened
 to an approximately central portion of the mounting member 3 by a bolt 50,
 and a work base J2 on which the work W is put is inserted into a fitting
 hole (not shown) of the main body J1 by a fitting axis (not shown), so
 that the work W is in a predetermined position with respect to the
 mounting surface 3a of the mounting member 3. Since the other structures
 are the same as those in the embodiment shown in FIG. 1, the same
 reference numerals are assigned to the structures and hence, the
 description thereof is not repeated.
 The procedure for processing in the present embodiment will be described on
 the basis of a flow chart shown in FIG. 19.
 When processing is started, the first and second driving and fixing members
 4 and 6 are first reset to their initial positions and are fixed to the
 positions (step S1). The initial positions are respectively set in central
 positions within the respective maximum ranges of correction made by the
 driving and fixing members 4 and 6. By resetting the first driving and
 fixing members 4, a reference surface of the degree of inclination Zw
 which is composed of an upper surface Wa of the work W or a virtual plane
 parallel thereto (see FIG. 18) and a work mounting surface 3a of the
 mounting member 3 are approximately parallel to a virtual plane to be a
 target, for example, the X-Y plane 52. Further, a reference surface of the
 degree of parallelization Wb of the work W is approximately parallel to a
 target axis, for example, to the X-axis by resetting the second driving
 and fixing members 6.
 The three-dimensional coordinates of three arbitrary points on the
 reference surface of the degree of inclination Zw of the work W are then
 measured and are stored in a memory (step S2). The degree of inclination
 in the X-axis direction a1 and the degree of inclination in the Y-axis
 direction b1 of the reference surface of the degree of inclination Zw are
 operated using the measured three-dimensional coordinates of the three
 points, whereby the following linear equation of the reference surface of
 the degree of inclination Zw is found (step S3):
EQU Z=a1.multidot.X+b1.multidot.Y+c1 (11)
 The following deviation equation (13) between the following linear equation
 (12) of a virtual plane Zr previously set to be a target for correcting
 the reference surface of the degree of inclination Zw and the foregoing
 equation (11) of the reference surface of the degree of inclination Zw is
 then found:
EQU Z=a2.multidot.X+b2.multidot.Y+c2 (12)
EQU .DELTA.Z=(a1-a2)X+(b1-b2)Y+(c1-c2) (13)
 The X and Y coordinates (x1n, y1n) of a position 53 (see FIG. 18) where
 each of the first driving and fixing members 4 is arranged are substituted
 into the deviation equation (13), to find an amount of deviation in
 displacement .DELTA.Zn indicating how much the plane Zw deviates from the
 plane Zr in the Z-axis direction in an XY coordinate position of the first
 driving and fixing member 4 (step S4):
EQU .DELTA.Zn=(a1-a2)x1n+(b1-b2)y1n+(c1-c2) (14)
 If the virtual plane Zr which is previously set to be a target is an X-Y
 plane (a plane where a linear equation Z=0), a value of .DELTA.Zn is given
 by the following equation (15) because a2, b2 and c2 are zero in the
 equation (14):
EQU .DELTA.Zn=a1.multidot.x1n+b1.multidot.y1n+c1 (15)
 When an absolute value .vertline..DELTA.Zn.vertline. of at least one of the
 found amounts of deviation in displacement .DELTA.Zn (.DELTA.Z1,
 .DELTA.Z2, .DELTA.Z3) exceeds an allowable value m, that is, at least one
 of the amounts of deviation in displacement .DELTA.Zn departs from an
 allowable range (.DELTA.Zn&lt;-m, or m&lt;.DELTA.Zn), the fixing of all the
 first and second driving and fixing members 4 and 6 is released once (step
 S6), after which only the first driving and fixing member 4 in which the
 amount of deviation in displacement departs from the allowable range is
 driven to correct the inclination of the reference surface of the degree
 of inclination Zw and fix the corrected inclination (step S7). At this
 time, an amount of correction Hn required in the Z-axis direction is
 expressed by the following equation (16):
EQU Hn=-.DELTA.Zn (16)
 That is, the first driving and fixing member 4 to be corrected is driven in
 a direction opposite to the direction in which a deviation in displacement
 occurs so that the deviation in displacement is eliminated to fix the
 first driving and fixing member 4 to the corrected position.
 As a result, when the amount of deviation in displacement .DELTA.Zn is
 positive, it is corrected by an amount of correction
 .vertline..DELTA.Zn.vertline. in a reversed Z-axis direction. When the
 amount of deviation in displacement .DELTA.Zn is negative, it is corrected
 by an amount of correction .vertline..DELTA.Zn.vertline. in the Z-axis
 direction.
 In making the correction in the step S7, the fixing of all the driving and
 fixing members 4 and 6 is released in the previous step S6. That is, the
 fixing of the second driving and fixing members 6 and the first driving
 and fixing members 4 requiring no correction (the amount of deviation in
 displacement .DELTA.Zn is within the allowable range) is released once,
 and the second driving and fixing members 6 and the first driving and
 fixing members 4 requiring no correction are set again to states before
 the release and are fixed simultaneously with the correction of the first
 driving and fixing member 4 to be corrected.
 On the other hand, when all amounts of deviation in displacement .DELTA.Zn
 are within the allowable range (that is, -m.ltoreq..DELTA.Zn.ltoreq.m),
 the program proceeds to the subsequent step S8 without passing through the
 steps S6 and S7 for correcting the degree of inclination.
 In the step S8, two-dimensional X and Y coordinates (x4, y4) and (x5, y5)
 of two arbitrary points P.sub.4 and P.sub.5 on the reference surface of
 the degree of parallelization Wb of the work W are measured, and the
 measured coordinates are stored. An inclination (corresponding to the
 degree of parallelization) ex of the reference surface of the degree of
 parallelization Wb with respect to the target axis, for example, the
 X-axis is then operated using the measured two-dimensional coordinates
 using the following equation (17) (step S9):
EQU ex=(y4-y5)/(x4-x5) (17)
 Letting D2 be the distance between each of the second driving and fixing
 members 6 and the rotation center of the mounting member 3, a displacement
 in the direction of rotation Uw of the work which is converted to the
 position of the second driving and fixing member 6 is as follows:
EQU Uw=ex.multidot.D2 (18)
 Letting Ur be a displacement in a target position, an amount of deviation
 in displacement in the direction of rotation .DELTA.U is as follows:
EQU .DELTA.U=Uw-Ur (19)
 If the position is so adjusted that the reference surface of the degree of
 parallelization Wb is parallel to the X-axis, the amount of deviation in
 displacement in the direction of rotation .DELTA.U is Uw since Ur=0.
 An absolute value .vertline..DELTA.U.vertline. of the found amount of
 deviation in displacement in the direction of rotation .DELTA.U exceeds an
 allowable value n, that is, the amount of deviation in displacement in the
 direction of rotation .DELTA.U departs from an allowable range
 (.DELTA.U&lt;-n, or n&lt;.DELTA.U), the fixing of all the first and second
 driving and fixing members 4 and 6 is released once, after which the
 degree of inclination and the degree of parallelization are simultaneously
 corrected to fix the second driving and fixing members 4 and 6 to the
 corrected inclination (steps S11, S12, and S13).
 At this time, in order to correct the degree of parallelization, an amount
 of correction in the direction of rotation L required in a clockwise
 direction centered around the Z-axis is expressed by the following
 equation:
EQU L=-.DELTA.U (20)
 That is, each of the second driving and fixing members 6 is driven in a
 direction opposite to the direction in which a deviation in displacement
 in the direction of rotation occurs so as to eliminate the deviation in
 displacement in the direction of rotation and fix the displacement, after
 which the processing is terminated.
 As a result, when the amount of deviation in displacement in the direction
 of rotation .DELTA.U is positive, it is corrected by the amount of
 correction in the direction of rotation .vertline..DELTA.U.vertline. in a
 clockwise direction. When the amount of deviation in displacement in the
 direction of rotation .DELTA.U is negative, it is corrected by the amount
 of correction .vertline..DELTA.U.vertline. in a counterclockwise
 direction.
 On the other hand, when the amount of deviation in displacement in the
 direction of rotation .DELTA.U is within the allowable range (that is,
 -n.ltoreq..DELTA.U.ltoreq.n), the processing is terminated without making
 the correction in the steps S12 and S13.
 In correcting the degree of parallelization (the correction of the
 displacement in the direction of rotation) in the step S13, the fixing of
 all the driving and fixing members 4 and 6 is released once in the
 previous step S12. That is, the fixing of the first driving and fixing
 members 4 already set is released once, and the first driving and fixing
 members 4 are set again to states before the release and are fixed
 simultaneously with the correction of the degree of parallelization by the
 second driving and fixing members 6.
 In the present embodiment, the work can be corrected to a desirable
 mounting position with high precision, quickly and automatically and
 therefore, the necessity of human intervention for adjustment can be
 eliminated as in the embodiment shown in FIG. 1. As a result, it is
 possible to cope with the automation of the preparation of the adjustment.
 Further, the following advantages are obtained.
 The correction is always started from a predetermined position already
 known by first resetting each of the driving and fixing members 4 and 6 to
 its initial position before starting the correction. The present position
 need not be examined every time the correction is started, so that the
 correction can be made more quickly. Moreover, the initial position is the
 central position within the maximum range of correction (a so-called
 dynamic range) made by each of the driving and fixing members 4 and 6, so
 that the control of the correction is simplified. As a result, the
 correction can be made more quickly.
 In the embodiment shown in FIG. 1, the correction is so made that the
 reference surface of the degree of inclination which is composed of the
 work surface Wa conforms to the X-Y plane which is a target, and the
 reference surface of the degree of parallelization which is composed of
 the plane Wb conforms to the Z-X plane which is a target. On the other
 hand, in the present embodiment, the targets need not necessarily be the
 X-Y plane and the Z-X plane. For example, the present embodiment can be
 carried out using planes inclined at predetermined angles from the planes
 as targets, so that the versatility is high from this point of view.
 In the embodiment shown in FIG. 1, the first and second driving and fixing
 members 4 and 6 are respectively arranged along the X-axis and the Y-axis,
 the present embodiment can be carried out even if the driving and fixing
 members 4 and 6 respectively deviate from the axes; therefore, the
 versatility is high also from this point of view.
 Furthermore, an amount of correction required by the first driving and
 fixing member 4 can be quickly found without executing a complicated
 operation using the deviation equation between the linear equations and
 the X and Y coordinates in the position where the first driving and fixing
 member 4 is arranged. Further, the position where the first driving and
 fixing member 4 is arranged may be any position, so that the degree of
 freedom of the arrangement is increased.
 In the foregoing step S3, the amount of deviation in displacement .DELTA.Zn
 of the reference surface of the degree of inclination Zw from the target
 plane Zr in the position of the first driving and fixing member 4 may be
 found by substituting the coordinates of the first driving and fixing
 member 4 into the deviation equation between the equations of both the
 planes Zw and Zr, or may be found by substituting the coordinates of the
 first driving and fixing member 4 into the respective linear equations of
 the planes Zw and Zr to find respective Z values, and then calculating the
 difference therebetween.
 Even if the reference surface of the degree of inclination Zw is so
 corrected as to conform to the target plane inclined at a predetermined
 angle (for example, 1.degree. to 2.degree.) relative to the X-Y plane 52,
 and is then so corrected as to match the degree of parallelization upon
 being rotated around the Z-axis, the degree of inclination previously
 matched is hardly affected practically. When it is desired to also
 eliminate a significantly small amount of deviation which may be caused by
 the affect, it can be reliably eliminated by repeating the steps S2 to S13
 a plurality of numbers of times in the flow chart shown in FIG. 19.
 Examples of a case where the reference surface is inclined from the X-Y
 plane 52 as described above include a case where a surface having a draft
 angle of a molding die is worked.
 Meanwhile, description is made of a case where the position of the
 apparatus according to the embodiment shown in FIG. 2 is adjusted using
 the flow chart in the present embodiment. In the apparatus shown in FIG.
 2, the first driving and fixing members 4 are arranged along the X-axis
 and the Y-axis, respectively. That is, the respective X and Y coordinates
 of the first driving and fixing members 4 are represented by (x11, 0),
 (x12, 0), (0, y11), and (0, y12). Therefore, amounts of deviation in
 displacement .DELTA.Zn in the positions where the first driving and fixing
 members 4 are arranged are obtained by substituting the coordinates of the
 first driving and fixing members 4 into a linear equation Z=aX+bY, as
 follows:
EQU .DELTA.Z1=ax11, .DELTA.Z2=ax12, .DELTA.Z3=by11, .DELTA.Z4=by12 (21)
 It is assumed that the Z-axis penetrates the center of the mounting member
 3. In this case, letting D1 be the distance between each of the first
 driving and fixing members 4 and the central axis of the mounting member
 3, the following equation holds:
EQU .vertline.x11.vertline.=.vertline.x12.vertline.=.vertline.y11.vertline.=.ve
 rtline.y12.vertline.-D1 (22)
 Consequently, the amounts of deviation in displacement are as follows:
 .DELTA.Z1=-aD1, .DELTA.Z2=aD1, .DELTA.Z3=-bD1, .DELTA.Z4=bD1 (23)
 As a result, the operation is simplified.
 In this case, in the step S4 in the flow chart shown in FIG. 19 (the step
 of finding the amount of deviation in displacement .DELTA.Zn), the degree
 of inclination in the X-axis direction a1 and the degree of inclination in
 the Y-axis direction b1 of the plane Zw and the distance D1 between each
 of the first driving and fixing members 4 and the rotation center of the
 mounting member 3 are multiplexed instead of substituting the X and Y
 coordinates of each of the first driving and fixing members 4 into the
 linear equation of the plane Zw. At this time, a positive sign is added to
 D1 with respect to the first driving and fixing member 4 which is positive
 on the X-axis and the Y-axis, while a negative sign is added to D1 with
 respect to the first driving and fixing member 4 which is negative on the
 X-axis and the Y-axis.
 FIG. 20 shows the flow of processing in still another embodiment of the
 present invention. Referring to FIG. 20, the present embodiment differs
 from the embodiment shown in FIG. 19 in that the coordinates of a
 reference surface of the degree of inclination and a reference surface of
 the degree of parallelization are measured (steps S2 and S3), and each of
 amounts of deviation in displacement .DELTA.Zn and .DELTA.U is then
 determined (steps S4 to S7), after which the inclinations of the reference
 surface of the degree of inclination and the reference surface of the
 degree of parallelization are collectively corrected (steps S8 to S10).
 The steps S1, S2, S3, S4, S5, S6, and S7 in the present embodiment
 respectively correspond to the steps S1, S2, S8, S3, S4, S9, and S10 in
 the embodiment shown in FIG. 19. The steps S9 and S10 in the present
 embodiment respectively correspond to the steps S12 and S13 in the
 embodiment shown in FIG. 19.
 In the present embodiment, both the corrections are collectively made, so
 that the corrections can be quickly made. When the corrections are
 simultaneously made, an affect of each of the corrections of the degree of
 inclination and the degree of parallelization on the other correction is
 at a level which can be almost ignored practically. It can be said that
 the precision of the corrections is hardly affected. Further, the steps S2
 to S10 are repeated a plurality of times, so that the precision of the
 adjustment can be improved.
 The present invention is not limited to each of the above-mentioned
 embodiments. The present invention is applicable to not only a machine
 tool for performing cutting work such as an NC milling cutter but also all
 machine tools requiring highly precise setting of the position of a work,
 for example, an electrical discharge machine.
 As the first and second driving and fixing members 4 and 6, piezoelectric
 displacement elements can be replaced with supermagnetostrictive elements.
 Examples of the supermagnetostrictive elements include a rare earth
 magnetic material having large magnetostriction, for example, a Tb-Dy-Fe
 alloy. The supermagnetostrictive element can be used without any cable
 because it produces a displacement in non-contact depending on the change
 in an external magnetic field. Further, the supermagnetostrictive element
 has a larger output and a larger displacement, as compared with a
 piezoelectric displacement element, and the weight thereof per unit stress
 is small. When the supermagnetostrictive elements are used, therefore, a
 sufficiently large amount of displacement can be ensured even if they are
 made small in size, and the position of the work can be stably maintained
 upon withstanding a larger cutting load.
 Furthermore, it is also possible to replace the piezoelectric displacement
 elements with fluid pressure cylinders using fluid pressure such as oil
 pressure. Further, it is also possible to use elements capable of
 controlling an amount of displacement by adjusting the temperature.
 In the embodiments shown in FIGS. 19 and 20, each of the driving and fixing
 members 4 and 6 is first reset to a central position in the maximum range
 of correction which is its initial position before the position of the
 work is adjusted. That is, although a work mounting surface is so set as
 to be approximately parallel to an X-Y plane with the degree of
 inclination thereof taken as approximately zero, it is not limited to the
 same. It may previously have a predetermined degree of inclination as
 required. Further, when the correction allowable range of the driving and
 fixing member is sufficiently larger than the amount of displacement, for
 example, the adjustment of the position may be started from an arbitrary
 position without determining a predetermined initial position as in the
 embodiment shown in FIG. 10, for example.
 Furthermore, in each of the above-mentioned embodiments, in performing each
 of the corrections of the degree of inclination and the degree of
 parallelization, the fixing of the driving and fixing member requiring no
 correction is also released once, and the driving and fixing member is
 reset to a state before the release and is fixed simultaneously with the
 correction. This is for the following reason. That is, each of the driving
 and fixing members is constructed using piezoelectric displacement
 elements. Unless the fixing of the driving and fixing member which is not
 related to the correction is released once, therefore, an excessive
 external force may be applied to the piezoelectric displacement element,
 to shorten the structural life thereof. When the structural life may not
 be shortened by the characteristics of the driving and fixing member used,
 the conditions of specifications, and the like, the fixing of the driving
 and fixing member which is not related to the correction need not
 necessarily be released once.
 In each of the embodiments, a series of adjusting steps may be carried out
 a plurality of times in order to increase the accuracy of an adjusted
 position.
 Although the touch sensor is used for measuring coordinates in each of the
 embodiments, the present invention is not limited to the same. For
 example, an electric micrometer can be also used. Further, the present
 invention is not limited to a sensor of a contact type. It is also laser
 or the like provided outside a machine tool.
 Although the controller C of the machine tool carries out the control of
 the position adjusting apparatuses 100 and 101 in each of the embodiments,
 the present invention is not limited to the same. Each of the position
 adjusting apparatuses 100 and 101 may include a personal computer for
 inputting a signal from signal outputting means such as a touch sensor,
 determining an amount of correction, and controlling the driving of each
 of driving and fixing members. In this case, signals are exchanged between
 the personal computer and the controller of the machine tool in order to
 measure coordinates.
 In addition thereto, various changes can be made in the range of the
 present invention.
 Although the present invention has been described and illustrated in
 detail, it is clearly understood that the same is by way of illustration
 and example only and is not to be taken by way of limitation, the spirit
 and scope of the present invention being limited only by the terms of the
 appended claims.