GB2078902A

GB2078902A - Feedscrew device

Info

Publication number: GB2078902A
Application number: GB8110368A
Authority: GB
Original assignee: Mitutoyo Manufacturing Co Ltd
Current assignee: Mitutoyo Manufacturing Co Ltd
Priority date: 1980-04-25
Filing date: 1981-04-02
Publication date: 1982-01-13
Also published as: DE3114440A1; JPS56153148A; GB2078902B; DE3114440C2

Abstract

A feedscrew device comprises a movable member (29) which is slidably supported by a guide member (16) and is moved by a nut member (23) threaded onto a feedscrew 14. The nut member is connected to the movable member by means of a connecting member (34) capable of accommodating a dimension variation in the radial direction of the feedscrew and tiltable with respect to a direction perpendicularly intersecting the axis of the feedscrew. Complicated movements of the nut member due to a sweep of the feedscrew, eccentricities of bearings and the like can thus be accommodated, without affecting smooth movement of the movable member. <IMAGE>

Description

SPECIFICATION Feed screw device The invention relates to feedscrew devices wherein a movable member is moved along a guide member by a nut member which is threaded on a feedscrew and more particularly to improvements in a connec tion between the nut member and the movable member.

In a previous device of this type, the connection between the nut member and the movable member has involved direct bolting or an integral formation.

However, in the case of such a fixed connection, there has been the disadvantage that it becomes impossible to perform the feeding operation unless the parallelism between the feedscrew and the direction of movement of the movable member is finished with high precision.

To obviate this disadvantage, there has been proposed a device as shown in Figure 1 of the accompanying drawings, which will be described hereinafter. In Figure 1 a nut member 2 is threaded on a feedscrew 1, and a slider 4 constituting a movable member is slidably supported on a guide shaft 3 constituting a guide member provided in parallel to the feedscrew 1. This slider 4 is rigidly secured to a connecting plate 5, having a hole 6, through which in turn is non-rotatably inserted the outer periphery of the nut member 2. The dimension of the hole 6 in the direction between the axes of the feedscrew 1 and the guide shaft 3 is larger than the outside dimension of the nut member 2, and conse quently, a clearance is formed between the hole 6 and the nut member 2.The connecting plate 5 can thus move at the outer periphery of the nut member 2 in the direction between the feedscrew 1 and the guide shaft 3. Furthermore, the connecting plate 5 is clamped between a flange 7 formed at one end of the nut member 2 and a fixing plate 8 fixed on the outer periphery of the nut member 2, whereby the feed movement of the nut member 2 is imparted to the slider 4. Secured to this slider 4 is a member to be moved, such as a measuring instrument, not shown.

With the abovedescribed arrangement, rotation of the feedscrew 1 causes the nut member 2, which has been locked against rotation by the connecting plate ,5, to move in the axial direction of the feedscrew.

This movement is imparted to the slider 4 constitut gng the movable member through the connecting plate 5, whereby the slider 4 is moved along the guide shaft 3 constituting the guide member.

However, with the abovedescribed arrangement, during movement of the nut member 2, dimensional variations resulting from imperfect parallelism be tween the two shafts, a sweep of the feedscrew 1, eccentricities of bearings for supporting the feeds crew 1 and such like, can be accommodated only so far as dimensional variations in the direction be tween the shaft axes are concerned, i.e. by the clearance formed between the hole 6 and the nut member 2. Dimensional variations or components of dimensional variations in other directions cannot be accommodated, so that the slider 4 can not move smoothly. Because of this, in the case of a feeding mechanism in a precision measuring instrument such as a contour measuring instrument, utilising the conventional feedscrew device of Figure 1, irregular movements of the slider 4 result in errors in measurement.Consequently, in applying the feedscrew to the measuring instrument, it is vital that the parallelism between thefeedscrew 1 and the guide shaft 3 is precisely adjusted, and bearings, not shown, for supporting opposite ends of the feedscrew 1 have to be replaced with new ones many times during operation so as to enable the slider 4 to move smoothly and the bearings to rotate in unison with the feedscrew 1 at the rate of 1 to 1. The adjustment as described above requires a very long period of time thus resulting in a bottleneck in the manufacturing process of the device and increased cost of manufacture.

In accordance with the invention, a feedscrew device comprises a nut member threaded on a feedscrew and a member movable by the nut member along a guide member, wherein the nut member and the movable member are connected to one another through a connecting member capable of accommodating a dimensional variation in the radial direction of the feedscrew and tiltable with respect to a direction perpendicularly intersecting the axis of the feedscrew.

With this arrangement, complex movements of the nut member due to a sweep of the feedscrew, eccentricities of the bearings and such like can be accommodated, so that the movement of the movable member can be made smooth, without requiring much time for adjustment and utilising without appreciable modification to parts available on the market.

In one construction, the connecting member comprises a shaft provided on one of the nut member and the movable member, and a spherical bearing provided on the other of said two members for supporting the shaft in a manner to allow relative movement in the axial direction of the shaft.

In another construction, the connecting member comprises a shaft on one of the nut member and the movable member, the shaft being provided at its distal end with a part spherical portion; and a bearing on the other of said two members for supporting the part spherical portion in a mannerto allow relative rotation and relative sliding movement in the axial direction of the shaft.

In a further construction, the movable member is a slide shaft disposed on the same axis as that of the feedscrew and having an axial bore, into and out of which the feedscrew can move linearly; and the connecting member comprises a spherical member provided on one of the nut member and the slide shaft, and a guide hole provided in the other of said two members for supporting the spherical member in a manner to allow relative rotation and relative movement in the radial direction of the feedscrew.

The nut member may be elongate in the axial direction of the feedscrew and be formed over its full length with a slot extending inwardly from its outer periphery to its internally screw threaded bore; means being provided for reducing the width of the slot to tighten the nut about the feedscrew. This allows backlash between the feedscrew and the nut member to be minimised. The flexibility of the nut member may be increased if the nut member has a central portion which lies with a clearance from the feedscrew.

Some examples of devices constructed in accordance with the invention, and a comparative prior art device, are illustrated in the accompanying drawings, in which: Figure 1 is a partially sectional elevation showing a feedscrew device of the prior art; Figure 2 is a vertical sectional view showing the general construction of a feedscrew device according to the present invention as applied to a contour measuring instrument; Figure 3 is a section taken on the line Ill-Ill in Figure 2; l Figure 4 is a partially sectional elevation of another device in accordance with the present invention; Figure 6 is a partially sectional elevation of a further device in accordance with the present invention; Figure 6 is a section taken on the line VI-VI in Figure 5; and, Figure 7 is an enlarged sectional view of the essential portions of Figure 5.

As shown in Figures 2 and 3, there are mounted on a base 11, at a predetermined interval, support plates 12 and 13, between which a feedscrew 14 is rotatably supported through bearings 15, and by which a guide shaft 16 acting as a guide member, is also supported. The right end portion of the feedscrew 14 as shown in the drawing projects through the support plate 13. This projecting end portion is connected to an output shaft of a motor 20 through a pulley 17, a belt 18 and a pulley 19, and adapted to be rotated in unison with the rotation of the motor 20.This motor 20 is supported by the support plate 13 at a position out of abutting contact with any movable component such as a slider to be described hereinafter as a movable member. Furthermore,the left end portion of the feedscrew 14 as shown in the drawings is connected to a rotary encoder 22 through a joint 21 and rotation of the feedscrew 14 is sensed by this rotary encoder 22.

A nut member 23 is threaded on the intermediate portion of the feedscrew 14 and adapted to be moved to the left and right upon rotation of the feedscrew 14. This nut member 23 is elongate in the axial direction of the feedscrew 14 and is provided at its central portion with an internal enlarged bore 24, whereby the nut member 23 engages only at its opposite ends with the feedscrew 14 and the central portion lies with a clearance from the feedscrew. A slot 25 extends to the internal screwthreaded bore from the upper surface of the nut member 23 over the full length thereof. This slotted portion can be drawn together by two bolts 26 to reduce the width of the slot, thereby eliminating backlash between the feedscrew 14 and the nut member 23. A shaft 27 projects downwardly from the centre of the bottom portion of the nut member 23.

A slider 29, acting as the movable member is axially slidably supported on the guide shaft 16 through a bush 28. Secured to the upper portion of this slider 29 through a mounting plate 33 is a spherical bearing 32 including a part spherical member 30, the upper and lower ends of which are cut away in parallel to each other and which is provided at its centre with a hole; and a seat 31 for the member 30 in a manner to be universally rotatable. The shaft 27 projecting from the nut member 23 is rotatably and axially slidably inserted into the hole 30A of the member 30 of the spherical bearing 32.The shaft 27 and spherical bearing 32 constitute a connecting member 34, by which an axially sliding movement between the shaft 27 and - the hole 30A of the member 30 can accommodate a dimensional variation in the direction between the axes of the feedscrew 14 and the guide shaft 16, i.e. a dimensional variation in the radial direction of the feedscrew 14, and the connecting member 34 can tilt in all directions with respect to a direction perpendicularly intersecting the axes of the feedscrew 14 and guide shaft 16 through the turning of the part spherical member 30 relatively to the seat 31 and the rotation of the shaft 27 relative to the part spherical member 30.

Secured to the slider 29 is a fulcrum member 35, which rotatably supports an arm 37 through a fulcrum shaft 36. Secured to one end of this arm 37 is a stylus 39 for contacting the outer surface of an object 38 to be measured and rotating the arm 37 upon tracing the shape of the outer surface, i.e., the contour in a predetermined section of the object 38 to be measured. Furthermore, secured to the other end of the arm 37, in a manner to be adjustable in position, is a balance weight 40, which is fixed at a position in such a manner that the stylus side of the arm 37 from the fulcrum shaft 36 is slightly heavier than the balance weight side. Further, a differential transformer 43 including a core 41 and a coil 42 is provided between the arm 37 and the fulcrum member 35, so that rotation of the arm 37 can be detected.

With the abovedescribed arrangement, in measuring the contour of the outer surface of the object 38 to be measured in a predetermined section, the arm 37 is stopped with the side of the stylus 39 raised means of clamp means, not shown, the motor 20 is driven to rotate the feedscrew 14 in the abovedescribed condition, the nut member 23 being moved'to the left in Figure 2, the arm 37 is moved to the left, along with the movement of the nut member 23 through the connecting member 34, slider 29 and fulcrum member 35, and the stylus 39 is disposed at a position for measurement at the left end of the object 38 to be measured.

Then, the clamp means, not shown, is released to lower the stylus 39 into abutting contact with the outer surface of the object 38 to be measured.

Thereafter, the motor 20 is rotated in a direction opposite to the abovementioned direction to move the nut member 23 to the right, and the arm 37 is also moved to the right. The number of rotations of the feedscrew 14 is sensed by the rotary encoder 22, while the vertical movement of the stylus 39 tracing the irregularities on the outer surface of the object 38 to be measured, and the corresponding vertical movement of the arm 37, is detected by the differential transformer 43. The rotation of the arm 37, the feed in the lateral direction and the vertical movement are recorded based on the data detected as described above, and the contour of the outer surface of the object 38 to be measured is indicated by an X-Y recorder or the like.Furthermore, when the arm 37 is moved, even if the nut member 23 performs complex vertical, longitudinal and rotational movements in addition to the movement in the direction of feed due to a sweep of the feedscrew 14, eccentricities of the bearings 15 and such like, all of these movements are accommodated by the connecting member 34, with the result that only the movement in the direction of feed is transmitted to the slider 29 constituting the movable member, so that the slider 29 can be moved smoothly without any unsteadiness. Consequently, any unnecessary movement due to the sweep of the feedscrew 14 and such like is not imparted to the arm 37, so that errors in measurement due to the movements of the feedscrew 14 can be eliminated.

A spherical bearing available on the market can be used as the spherical bearing 32, thus enabling the spherical bearings to be obtained inexpensively.

Furthermore, the nut member 23, being comparatively long in the axial direction of the feedscrew 14, provided with the enlarged bore 24, and engaged at its opposite ends with a comparatively long span along the feedscrew 14, has little backlash due to the presence of the slot 25 and the bolts 26, whereby the nut member 23 is reliably fed by the rotation of the feedscrew 14. Rotation of the feedscrew 14 detected by the rotary encoder 22 thus correctly corresponds with the movement of the arm 37, thereby eliminating errors in measurement in the direction of feed.

In the Figure 4 example, a connecting member 44 is integrally formed at its distal end thereof with a part spherical portion 45 and comprises a shaft 46 whose proximal end is fixed on the nut member 23.

A cylindrical bearing 47 with a flange for slidably, rotatably supporting the portion 45 of the shaft 46 extends in the axial direction of the shaft 46 and is embedded in the slider 29.

This example operates similarly to the Figures 2 and 3 example and similar parts have the same reference numerals.

Figures 5 to 7 show a further example in which the movable member is a slide shaft 48, which is slidably supported at opposite ends (only the left end is shown in Figure 5) by a pair of bearings 49 (onlythe left one is shown in Figure 5) and prevented from rotating by a stop member 50 fixed onto this slide shaft 48. This rotational stop member 50 has a guide shaft 51, which slides on a groove-shaped guide surface 52 provided on a body of device, not shown, whereby the slide shaft 48 can move in the axial direction without rotating. Furthermore, the slide shaft 48 is disposed on the same axis as that of the feedscrew 14 and is provided with an internal axial bore 53, into and out of which the feedscrew 14 can move linearly. The axial bore 53 has a large diameter inlet portion 54, in which is disposed the nut member 23 threaded on to the feedscrew 14.As shown in Figure 6, the nut member 23 has an eccentric octagonal peripheral surface with respect to its screw threaded bore, and has a spherical member 55, fixed to the upper surface thereof in the drawing by soldering or bonding. This spherical member 55 is adapted to be rotatable and movable in the radial direction of the feedscrew 14 in a guide hole 56 formed at a portion adjacent an end of the slide shaft 48, and inserted in the axial direction of the feedscrew 14 with no looseness. Furthermore, the top portion of the spherical member 55, which would otherwise project from the slide shaft 48 when inserted in the guide hole 56, is cut away, whereby a portion of the slide shaft 48 where the guide hole 56 is formed is not hampered when the portion is inserted into the bearing 49. Further, the spherical member 55 and guide hole 56 constitute a connecting member 57.

In addition, the reason why the peripheral surface of the nut member 23 is made eccentric is that, when the spherical member 55 fixed on the nut member 23 is to be inserted into the guide hole 56, the nut member 23 can be offset to one side in the large diameter inlet portion 54 of the axial bore 53.

Even with the abovedescribed arrangement, the complex movements of the nut member 23 due to the sweep of the feedscrew 14, eccentricities of the bearings and such like are accommodated by rotation of the spherical member 55 relative to the guide hole 56 and the movement of the feedscrew 14 in the axial direction thereof, so that the movement of the slide shaft 48 forming the movable member can be smooth, thereby providing substantially the same functional effects as in the preceding examples in accordance with the invention.

In the example shown in Figures 2 and 3, the shaft 27 may be provided on the slider 29 and the spherical bearing 32 may be provided on the nut member 23, and similarly, in the example shown in Figure 4, the shaft 46 may be provided on the slider 29 and the bearing 47 may be provided on the nut member 23. Further, in the example shown in Figures 5 to 7, the spherical member 55 may be provided on the slide shaft 48 and the guide hole 56 may be formed in the nut member 23, Furthermore, the connecting member is not limited to the specific forms of the connecting member 34,44 and 57 in the preceding examples, but any other type of connecting member may be adopted. In short, it suffices only if the connecting member can accommodate the dimensional variation in the radial direction of the feedscrew 14 and accommodate the inclination of the nut member 23 in all directions, i.e. as tiltable with respect to a direction perpendicularly intersecting the axis of the feedscrew 14. The present invention is applicable not only to the feeding mechanism of the contour measuring instrument as described above but also to the feeding mechanism of other measuring instruments or those in the equipment and machines in general.

Claims

1. A feedscrew device comprising a nut member threaded on a feedscrew and a member movable by the nut member along a guide member, wherein the nut member and the movable member are connected to one another through a connecting member capable of accommodating a dimensional variation in the radial direction of the feedscrew and tiltable with respect to a direction perpendicularly intersecting the axis of the feedscrew.

2. A device according to claim 1, wherein the connecting member comprises a shaft provided on one of the nut member and the movable member, and a spherical bearing provided on the other of said two members for supporting the shaft in a manner to allow relative movement in the axial direction of the shaft.

3. A device according to claim 1, wherein the connecting member comprises a shaft on one of the nut member and the movable member, the shaft being provided at its distal end with a part spherical portion; and a bearing on the other of said two members for supporting the part spherical portion in a manner to allow relative rotation and relative sliding movement in the axial direction of the shaft.

4. A device according to claim 1, wherein the movable member is a slide shaft disposed on the same axis as that of the feedscrew and having an axial bore, into and out of which the feedscrew can move linearly; and the connecting member comprises a spherical member provided on one of the nut member and the slide shaft, and a guide hole provided in the other of said two members for supporting the spherical member in a mannerto allow relative rotation and relative movement in the radial direction of the feedscrew.

5. A device according to claim 4, wherein the nut member has an eccentric polygonal peripheral surface with respect to its internal screw thread which engages the feedscrew.

6. A device according to claim 5, wherein the polygonal peripheral surface of the nut member is octagonal.

7. A device according to any one of the preceding claims, wherein the nut member is elongate in the axial direction of the feedscrew and is formed over its full length with a slot extending inwardly from its outer periphery to its internally screw threaded bore; and means being provided for reducing the width of the slot to tighten the nut about the feedscrew.

8. A device according to claim 7, wherein the nut member has a central portion which lies with a clearance from the feedscrew.

9. A device according to claim 7 or claim 8, wherein the reducing means comprises bolts connecting portions of the nut member across the slot.

10. A device according to claim 1, substantially as described with reference to any one of the examples illustrated in Figures 2 to 7 of the accompanying drawings.