MOVABLE TABLE

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and claims priority to Japanese patent application no. 2007-224889 filed on Aug. 30, 2007, in the Japan Patent Office, and incorporated by reference herein.

BACKGROUND

Field

The present invention relates to a movable table for retaining and positioning, and more particularly to a movable table on which a measurement workpiece is mounted, and which positions the workpiece with respect to a measurement base of a measuring machine to assist measurement of the workpiece.

SUMMARY

The disclosed movable table is mounted on a base made of steel or iron, is positioned to a desired position with respect to the base through manual movement, and is fixed to the base after the positioning. The moveable table may include a top plate, a magnet bonded to a bottom surface of the top plate, where the magnet attracts the base to fix the top plate to the base.

The disclosed lift mechanism includes releasing the top plate from a fixed state and lifting the top plate from the base against an attraction force of the magnet, or against the attraction force and the gravity of the magnet, and a mechanism that lowers the top plate from a desired lifted position with either or both the attraction force or the gravity of the magnet, and fixes the top plate to the base with an action of the attraction force of the magnet.

The lift mechanism includes at least two operation levers, each operation lever being rotatable between a free position and a movement position around a supporting point, shafts integrally arranged with the operation levers, where the shafts are oppositely rotated within rotation angle ranges of the operation levers in accordance with the rotation of the operation levers.

The disclosed lift mechanism may also include cams integrally formed with shafts, where the cams come into contact with a top plate mount surface of the base, the surface on which the top plate is mounted, and are operable to be located at a position in which the top plate is lifted from the base or at a position in which the top plate is lowered to the base in accordance with rotation of the shafts.

Additional aspects and/or advantages will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 illustrates a movable table for positioning according to a related art example;

FIG. 2A is a plan view of a movable table for positioning according to another related art example;

FIG. 2B is a front view of a movable table for positioning according to another related art example;

FIG. 2C is a side view of a movable table for positioning according to another related art example;

FIG. 3A is a plan view of a movable table.

FIG. 3B is a front view of a movable table.

FIG. 3C is a side view of a movable table.

FIG. 3D is a plan view of a shaft and cams provided integrally with the shaft, these parts being extracted from FIG. 3A.;

FIG. 4A is a plan view of a movable table according to a modification thereto.

FIG. 4B is a front view of a movable table according to a modification thereto.

FIG. 4C is a side view of a movable table according to a modification thereto.

FIG. 4D is a plan view of a shaft and cams provided integrally with the shaft, these parts being extracted from FIG. 4A.

FIG. 4E is an enlarged view showing a positional relationship between a base and a magnet of a movable table according to a modification thereto.

FIG. 4F is a partially enlarged view of FIG. 4C.

FIG. 5 illustrates a movable table;

FIG. 6 illustrates a movable table;

FIG. 7 illustrates an exemplary lift mechanism applied to a movable table;

FIG. 8 illustrates an exemplary lift mechanism applied to a movable table; and

FIG. 9 is an illustration showing an exemplary lift mechanism applied to a movable table.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.

A movable table is generally used for positioning a small and light measurement workpiece with respect to a measurement base of a measuring machine.

FIG. 1 shows a movable table for positioning according to a related art example. As shown in FIG. 1, a movable table 1 for positioning has an X-axis moving stage 2 that can move in an X-axis direction relative to a measurement base of a measuring machine (not shown), and a Y-axis moving stage 3 that can move in a Y-axis direction relative to the X-axis moving stage 2 and serves as a workpiece stage.

The X-axis moving stage 2 is slidably attached to an X-axis fixed stage 4 that is fixed to the measurement base of the measuring machine. The above-mentioned X-axis moving stage 2 slides along the X-axis direction when a screw 5 arranged at the X-axis fixed stage 4 is rotated left and right with operator's fingers.

The Y-axis moving stage 3 is slidably attached to a Y-axis fixed stage 6 that is fixed to the X-axis moving stage 2. The Y-axis moving stage 3 slides along the Y-axis direction when a screw 7 arranged at the Y-axis fixed stage 6 is rotated left and right with the operator's fingers.

The movable table 1 for positioning can reliably and accurately position a workpiece. After the positioning, the workpiece can be retained at a position.

However, in the movable table 1, the screws have to be rotated, which is a time-consuming, troublesome work, and causes quick positioning a workpiece difficult.

Also, two sets of double-layer stages, each of which is composed of the fixed stage and the moving stage sliding thereon, are stacked to correspond to the X- and Y-axis directions. The position of a workpiece mounted may be markedly higher than the position of the measurement base of the measuring machine.

In a case where the measuring machine is a coordinate measuring machine using a laser beam, a measurement base may be typically a turntable.

If a workpiece stage of a movable table, which is positioned at the measurement base of the turntable, is located markedly higher than the position of the measurement base, an eccentricity error generated during rotation of the measurement base may affect measurement accuracy of a workpiece mounted on the workpiece stage.

Also, the above-mentioned movable table for positioning has a complicated mechanism, thereby increasing a size of the entire device. Such a large device may restrict the choice of the measuring machine to be used. The complicated mechanism may increase the cost.

Further, such a movable table is heavy and its center of gravity is located at a high position. When the turntable is used as the measurement base, a large couple is applied to a bearing of the turntable, and hence, an eccentricity error may increase over time.

FIG. 2A is a plan view of the movable table for positioning according to another related art example. FIG. 2B is a front view of the movable table. FIG. 2C is a side view of the movable table. A movable table 8 shown in FIGS. 2A to 2C has a top plate 9a and a magnet 9b bonded to the lower side of the top plate 9a.

A retainer 9d is attached to the top plate 9a through a retainer attachment screw hole 9c. A measurement workpiece is placed between the retainer 9d and a measurement workpiece retaining screw 9e. The measurement workpiece retaining screw 9e is held with operator's fingers to move the movable table 8 in a horizontal direction and then to move it downward. The workpiece is retained on the measurement base with a force caused by the magnet 9b.

This configuration can solve problems of the above-discussed art example including high expense associated with the movable table, the mount position of the workpiece is higher than the position of the measurement base, and that the movable table is heavy and its center of gravity is located at a high position.

However, when the movable table, which has been fixed to the measurement base, has to be moved to adjust a measurement position, a measurement workpiece retaining screw 9e is held, pulled up, and then moved.

This does not cause any problem when the measurement workpiece can be completely retained at the movable table 8. In many cases, a part of the measurement workpiece may not be retained although a container or a frame may be retained. The attraction force of the magnet increases as the movable table is fixed firmly.

It is difficult to smoothly detach the movable table 8, and the measurement workpiece may be unintentionally moved due to the detachment. Accordingly, currently obtained measurement data may not match previously obtained measurement data, and hence, measurement workability may deteriorate.

Sometimes, the movable table 8 may seriously incline and drop the measurement workpiece.

For example, Japanese Unexamined Patent Application Publication No. 2004-022538 discloses a cover and a base of a socket connector. The cover and the base are two thin-plate objects. When the cover slides relative to the base, mechanisms prevent a lateral deflection from being generated in a direction perpendicular to the sliding direction. One of the mechanisms includes an operation lever, and a driving cam perpendicularly connected to the operation lever.

In the technique, the mechanism restricts the lateral deflection in the direction perpendicular to the sliding direction when the two thin-plate objects relatively slide. However, the two objects are merely fitted to predetermined positions. The objects are not positioned at desired positions with the operation lever and the driving cam.

FIG. 3A is a plan view of the movable table. FIG. 3B is a front view. FIG. 3C is a side view. FIG. 3D is a plan view of a shaft and cams provided integrally with the shaft, these parts being extracted from FIG. 3A.

A movable table 10 shown in FIGS. 3A to 3C is an exemplary movable table mounted on a measurement base made of steel or iron and provided at a measuring machine (not shown) that measures a workpiece.

The movable table 10 includes a top plate 11, a magnet 12 fixed to a bottom surface of the top plate 11 so as to fix the top plate 11 to the measurement base in parallel by attracting the measurement base of the measuring machine, and a lift mechanism 13 that lifts or lowers the top plate 11 from or to the measurement base of the measuring machine in a direction indicated by an arrow a or b. The lift mechanism 13 as described herein refers to components and/or operations described in association with the disclosed movable table.

The top plate 11 is mounted on the measurement base of the measuring machine and is used as a stage for a measurement workpiece, for example, when a denturist or the like, who makes a denture on the basis of a denture mold that is taken from a patient by a dentist, accurately measures a denture mold to make a precise denture.

For this purpose, the above-mentioned top plate 11 has a workpiece retaining device on which a measurement workpiece such as a denture mold is mounted and retained. Although a container or a frame can be retained, the entire workpiece may not be retained. This may be a problem.

As shown in FIG. 3A, the workpiece retaining device includes retainer attachment screw holes 14, retainer attachment auxiliary screw holes 15, measurement workpiece retainers 16, and a measurement workpiece retaining screw 17. The screw holes 14 and 15 are respectively formed at two corners of a rear portion in an upper surface of the top plate 11 (left side in FIG. 3A). The measurement workpiece retainers 16 (FIG. 3B) are screwed and fixed to the screw holes 14 and 15. The measurement workpiece retaining screw 17 is provided at a front surface of the top plate 11.

The measurement workpiece mounted on the top plate 11 is supported by three points of the two measurement workpiece retainers 16 (fixed to the screw holes 14 or 15) and the measurement workpiece retaining screw 17. Hence, the measurement workpiece is retained on the top plate 11.

In this embodiment, the magnet 12 is made of a ferrite magnet plate having a size substantially similar to a size of the top plate 11. The arrangement and shape of the magnet 12 is not limited thereto, and for example, a small-size ferrite magnet plate may be used if an attraction force of the magnet is too large.

In this embodiment, while the ferrite magnet plate comes into contact with the measurement base, the invention is not limited thereto. For example, as a modification of this embodiment, the top plate 11 may come into contact with the measurement base through a guide groove plate and a pressing plate, and the ferrite magnet plate may be arranged slightly distant from the measurement base as shown in FIGS. 4A, 4B, 4C, 4E and 4F.

FIG. 4A is a plan view showing a movable table of the above-mentioned modification. FIG. 4B is a front view. FIG. 4C is a side view. FIG. 4D is a plan view of a shaft and cams provided integrally with the shaft, these parts being extracted from FIG. 4A. FIG. 4E is an enlarged view (enlarged cross-sectional view taken along a line A-A′ in FIG. 4A) showing a positional relationship between a base and a magnet. FIG. 4F is a partially enlarged view of FIG. 4C.

It is noted that numerals in FIGS. 4A to 4F different from those in FIGS. 3A to 3D refer different and new components. If components and/or functions in FIGS. 4A to 4F are similar to those in FIGS. 3A to 3D, like numerals are applied to FIGS. 3A to 3D briefly for the convenience and understanding.

As shown in FIGS. 4E to 4F, in this modification, a guide groove plate 34 is closely attached to a bottom surface of the top plate 11. A pressing plate 35 is arranged below the guide groove plate 34 to hold a shaft 21 by pressing the shaft 21 from below.

The guide groove plate 34 has rotation shaft guide grooves 23 (FIG. 3A). Clearances 24 for the cams 22 are formed at the guide groove plate 34 and the pressing plate 35.

The magnet 12 is composed of a north pole 38 and a south pole 39 provided at a magnet housing 37. As shown in FIG. 4E, the magnet 12 is configured to come away from a measurement base 36 (i.e., to be retracted from a lower surface of the pressing plate 35) by an extremely small distance h when the top plate 11 comes into contact with the measurement base 36 through the guide groove plate 34 and the pressing plate 35, and fixed to the measurement base 36.

With the modification shown in FIGS. 4A to 4F, the shape durability of the magnet may increase although the manufacturing cost may increase.

Referring back to FIGS. 3A to 3D (which is substantially similar to FIGS. 4A to 4F except for the modification part as described above), the lift mechanism 13 has at least two operation levers 18. The two operation levers 18 each are rotated between a free position F and a movement position M at an end 19 thereof used as a supporting point, as shown in FIG. 3C.

Each of the operation levers 18 is integrally arranged with the shaft 21 at the end 19. The shafts 21 are rotated within rotation angle ranges of the operation levers 18 in accordance with the rotation of the operation levers 18.

In this embodiment, the shaft 21 may be made of a hard steel wire. The shaft 21 is integrally formed with the cams 22.

As shown in FIGS. 3A and 3D, the plurality of cams 22 (in this embodiment, two cams) are formed at each shaft 21 including by bending the shaft 21 made of the hard steel wire.

The cams 22 protrude toward an inside (a center) of the top plate 11 from each shaft 21.

In this embodiment, the cams 22 are usually in contact with a top plate mount surface, on which the top plate 11 is mounted, of the measurement base of the measuring machine because of gravity. Hence, the cams 22 can prevent a shake from occurring during operation.

As shown in FIG. 3C, the cams 22 are rotated between positions U in which the top plate 11 is lifted in a direction indicated by the arrow a and positions D in which the top plate 11 is lowered in a direction indicated by the arrow b, relative to the measurement base of the measuring machine, in accordance with an rotation of the shafts 21, caused by the rotation of the operation levers 18 between the movement positions M and the free positions F.

The lift mechanism 13 has a rotation shaft guide groove 23 that guides a rotation of each shaft 21, and a clearance 24 for each cam 22.

The rotation shaft guide groove 23 houses the shaft 21 and guides the rotation of the shaft 21 so that the shaft 21 is not deviated when being rotated.

The clearance 24 provides a space for the cam 22 when the cam 22 is rotated to a retracted position that is the position D in which the top plate 11 is lowered.

The rotation shaft guide groove 23 and the clearance 24 may be formed at either the top plate 11 or the magnet 12, or at both the top plate 11 and the magnet 12. Alternatively, the rotation shaft guide groove 23 and the clearance 24 may be provided at other component that is integrally formed with the top plate 11.

The above-described operation lever 18 has a forced stop mechanism that defines a movement limit at the movement position M to forcibly stop the operation levers 18.

Referring to FIGS. 3A and 3C, when the two operation levers 18 move toward the movement positions M, the two operation levers 18 come into contact with sides of the measurement workpiece retaining screw 17, and hence, the operation levers 18 are forcibly stopped. As shown in FIG. 3C, opposite sides of the measurement workpiece retaining screw 17 come in contact with the operation levers 18 to forcibly stop the operation levers.

As described above, when the operation levers 18 are located at the forced stop positions (movement positions M), the top plate 11 is located at an upper end position.

Although the magnetic force of the magnet 12 decreases as it comes away from the measurement base, when the top plate 11 is located at the upper end position, the top plate 11 keeps a magnetic force against the measurement base such that the top plate 11 can move relative to the measurement base in any direction.

That is, even when the top plate 11 is located at the upper end position, the magnet 12 continuously provides a weak magnetic force against the measurement base such that an operator can easily move the top plate 11 by moving the operation levers 18 located at the forced stop positions (movement positions M). As shown in FIG. 3C, for example, an operator may move the operation levers 18 towards each other and the retaining screw 17

As described above, in the lift mechanism 13, the cams 22 are rotated from the downward-movement positions D to the upward-movement positions U in accordance with the rotation of the operation levers 18 from the free positions F to the movement positions M with the operator's fingers. Accordingly, the lift mechanism 13 lifts the top plate 11 from the measurement base in a direction indicated by the arrow a, against an attraction force caused by the magnetic force of the magnet 12 toward the measurement base.

Since the cams 22 generate a lift movement, the movable table 11 can move smoothly and horizontally. Thus, unlike the configuration in which the movable table is manually detached, a position of the workpiece is prevented from unintentionally being changed due to the detachment.

The magnetic force acting between the magnet 12 and the measurement base has a strength such that the top plate 11 does not fall from the measurement base. At the same time, the magnetic force is small such that the top plate 11 can be moved in any direction by moving or adjusting the operation levers 18 that are fixed to the movement positions M with the operator's fingers.

The magnetic force generated between the magnet 12 and the measurement base can be easily adjusted by increasing or decreasing a protrusion amount of the cams 22.

If the operation levers 18 are longer, the top plate 11 can be easily moved to an upper end position against a strong attraction force of the top plate 11 toward the measurement base because of the magnet 12, with a small force generated by a user (operator).

In this state, the top plate 11 is moved in any direction while the operation levers 18 are held at the fixed positions of the movement positions M. Accordingly, tip ends of the cams 22 slide on a surface of the measurement base.

The top plate 11 can be freely moved by a user while a lower surface of the top plate 11 is parallel to the upper surface of the measurement base.

Thus, the measurement workpiece on the top plate 11 can be arranged at a desired measurement position. After the positioning, the operation levers 18 are released.

The top plate 11 is lowered toward the measurement base from a predetermined lifted position because of gravity and an attraction force of the magnet 12. When the top plate 11 comes into contact with the measurement base, the magnetic force caused by the magnet 12 has a maximum value, and hence, the top plate 11 is firmly fixed to the measurement base.

As described above, with the movable table 10 according to an embodiment, the movable table 10 firmly fixed to the measurement base can be easily and smoothly lifted from the measurement base by moving or adjusting the operation levers 18. Also, the top plate 11 can be moved by a user and positioned in a short time while maintaining the attraction force to the measurement base caused by a weak magnetic force.

In the movable table 10 according to an embodiment, a height of the upper surface of the top plate 11, on which the measurement workpiece is mounted and fixed, from the measurement base is defined by only the thickness of the top plate 11 and the thickness of the magnet 12. Accordingly, the approach state to the surface of the measurement base can be kept.

Thus, even when the measurement base of the measuring machine has a rotation function, an eccentricity error in the rotation of the measurement base hardly increases. The measurement workpiece can be measured with high accuracy.

The configuration of this embodiment is light and the center of gravity is located at a lower position as compared with the movable table in FIG. 1 of the related art. A couple applied to the rotation shaft of the measurement base noticeably decreases.

This can reduce an error with time of a rotation driving system for the measurement base, thereby reliably keeping the accuracy of measurement data.

FIG. 5 is an illustration showing a movable table according to an embodiment. Numerals in FIG. 5 similar to those in FIGS. 3A to 3D refer to like components and functions. In FIG. 5, the workpiece retaining device is not shown.

As shown in FIG. 5, in a movable table 25 according to an embodiment, the operation levers 18 shown in FIGS. 3A to 3C have substantially spherical grips 26 that are integrally provided with the operation levers 18.

With the grips 26, when the operator adjusts the two operation levers 18 to move the operation levers 18 in movement directions indicated by arrows c and d, the grips 26 can prevent the user from unintentionally releasing the operation levers 18.

Also, the grips 26 allow the user adjusting the operation levers 18 to be reliably fixed to the operation levers 18 at the lower portions of the grips 26. Accordingly, when the top plate 11 is lifted from the measurement base of the measuring machine (not shown) and is positioned, the positioning can be easily performed.

The grips 26 also serve as a forced stop mechanism according to an embodiment. When the two grips 26 come into contact with each other at a center in a front surface of the top plate 11, the operation levers 18 are forcibly stopped.

FIG. 6 is an illustration showing a movable table according to an embodiment. Numerals in FIG. 6 similar to those in FIGS. 3A to 3D or 5 refer like components and functions. In FIG. 6, the workpiece retaining device is not shown.

Operation levers 18 of a movable table 27 in this embodiment intersect with each other in an X-form at release positions shown in FIG. 6.

Also, cams 22 formed at shafts 21 integrally formed with the operation levers 18 protrude toward an outside of the top plate 11 from the shafts 21.

When the operation levers 18 are adjusted by a user and moved in movement directions indicated by arrows e and f, the shafts 21 integrally formed with the operation levers 18 rotate reversely to the configuration of the movable table 10 or 25 of the above discussed embodiments.

The cams 22 are rotated with the rotation of the operation levers 18, press a surface of the measurement base, and lift the top plate 11 from the measurement base.

Since the operation levers 18 in this embodiment intersect with each other in an X-form at the free positions, fingers of a user for moving or adjusting the tip ends of the two operation levers 18 are usually located at the outer side of the operation levers 18, and thus, the operation levers 18 are pressed obliquely downward toward the outside.

When tip ends of the operation levers 18 are moved with fingers of a user and the operation levers 18 are moved in the movement directions indicated by the arrows e and f, the fingers would not be released from the operation levers 18.

The fingers for moving the tip ends of the two operation levers 18 are usually located at outer sides of the operation levers 18, and hence the fingers define the movement limit of the operation levers 18. Stoppers for forced stop in the direction of the shaft 21 or in the direction opposite thereto do not have to be provided at the operation levers 18.

Since the cams 22 protrude toward an outside of the top plate 11 from the shafts 21, the cams 22 press the surface of the measurement base at the outer sides of the shafts 21, that is, with an area larger than that of the shafts 21, to lift the top plate 11 from the measurement base.

The four cams 22 come into contact with the measurement base at the outer sides of the shafts 21, that is, with a large area as compared with the configuration of the movable table 10 or 25 of the above discussed embodiments. Accordingly, supporting points provided by the four cams 22 can be spread as compared with the above discussed embodiments.

As described above, since the supporting points of the four cams 22 are spread, a posture of the top plate 11 during the positioning in a state where the top plate 11 is lifted from the measurement base can become further stable.

With this embodiment, shapes of the levers and cams and the positions of the shafts can be appropriately designed, and hence, the positions of the levers relative to the top plate can be lower as compared with the configuration in FIG. 5. Thus, a blind spot in measurement can be reduced.

FIG. 7 is an illustration showing a movable table according to an embodiment. Numerals in FIG. 7 similar to those in FIGS. 3A to 3C or 5 refer like components and functions. FIG. 7 shows only one of arrangements to define a lift mechanism.

As shown in FIG. 7, in the lift mechanism of an embodiment, an operation lever 18 and a shaft 21 fixed to a lower end portion of the operation lever 18 are made of a hard steel member.

Two cams 22 are made of a hard steel member, and are integrally formed with the shaft 21 in a longitudinal direction. The number of cams 22 may be three or more.

Since the entire lift mechanism of this embodiment is made of the hard steel member, the lift mechanism can be applied to a larger movable table.

FIG. 8 is an illustration showing a movable table according to an embodiment. Numerals in FIG. 8 similar to those in FIG. 7 refer like components and functions. FIG. 8 shows only one of arrangements to define a lift mechanism.

In the lift mechanism of this embodiment shown in FIG. 8, an operation lever 18, a shaft 21 fixed to a lower end portion of the operation lever 18, and a cam 22 integrally formed with the shaft 21, are made of a hard steel member.

The number of cams 22 is one, and the cam 22 extends along a longitudinal direction of the shaft 21.

Although the number of cams 22 is one, the cam 22 extends along the longitudinal direction of the shaft 21. Accordingly, the function of the cam 22 is similar to that of the lift mechanism shown in FIG. 7.

That is, the lift mechanism of this embodiment is strong because the entire lift mechanism is made of the hard steel member. Thus, the lift mechanism is applied to a larger movable table.

If a movable table is a table extending horizontally, it may be difficult to design an operation lever to have a size that allows an operator to adjust the operation lever with fingers according to the above discussed embodiments.

This can be overcome with a link mechanism. The link mechanism is described below as a sixth embodiment.

FIG. 9 shows an exemplary lift mechanism applied to a movable table according to an embodiment. FIG. 9 shows the movable table in this embodiment as viewed in a direction similar to the side view of the FIG. 3C.

Numerals in FIG. 9 similar to those in FIGS. 3A to 3C or 5 refer like components and functions. In FIG. 9, the workpiece retaining device is not shown.

A lift mechanism 13 shown in FIG. 9 includes three operation levers 18, and a link mechanism coupled to the three operation levers 18 to interlock them. While the three operation levers are provided in this embodiment, two operation levers are enough to provide smooth operation if the movable table is small.

The link mechanism has a coupling bar 28 and a supporting member 29. The supporting member 29 slidably supports an end portion of the coupling bar 28 at a supporting portion 31 located at an upper end of the supporting member 29. The coupling bar 28 is supported by the supporting portion 31 and moves in a horizontal direction indicated by a double-head arrow g in FIG. 9.

The position of the coupling bar 28 in FIG. 9 is a position when the coupling bar 28 moves from a free position to a movement position. The coupling bar 28 has engagement portions 32. The three operation levers 18 engage with the engagement portions 32 of the coupling bar 28. The operation levers 18 are rotated rightward in FIG. 9 in accordance with the rightward movement of the coupling bar 28 in FIG. 9.

The cams 22 formed at the shaft 21 are rotated downward from clearances (refer to the plan view in FIG. 3A), and the tip ends of the cams 22 protrude from the lower surface of the magnet 12 to press the surface of the measurement base of the measuring machine (not shown). Accordingly, the top plate 11 is lifted from the surface of the measurement base.

If a movable table is a large table extending horizontally, at least three (the number is three in this embodiment in FIG. 9, however, the number may be four or larger) of evenly arranged operation levers 18, a shaft 21, and cams 22 are provided at the movable table.

With this embodiment, advantages similar to the above embodiments can be provided. In particular, easy operation can be provided, and high accuracy can be provided such that an eccentricity error would not increase because a top plate is located at a lower position, as compared with a typical configuration, with respect to a position of a surface of a measurement base.

Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.