GB2043254A - Measuring machine - Google Patents

Abstract

In co-ordinate measuring machines having a sensor comprising a ball 2 mounted on a shaft 1, the shaft is connected to one or more resilient rods 8, of which the free ends are spring- loaded. In one embodiment, the upper end of the rod 8 carries a cylinder 9 with a bore 12 in its upper face. A similar but inverted cylinder 11 is placed coaxially above it, with a ball 14 resting in the bores. The springs 10 and 13 guide the assembly. <IMAGE>

Description

SPECIFICATION System for the adjustment of sensers Field of use of the invention The invention relates to a system for the adjustment of position, measuring force and free movement of sensers, for multi-axial path measurement in applications of length-measuring techniques, preferably for coordinate-measuring machines and for open and closed-loop control purposes, for instance, in multi-axially controlled measuring and milling machines, the contour to be measured being sensed by a senser shaft which can be deflected measurably in space in one or more directions and at whose end a sensing ball is disposed.

Characteristics of the known technical methods Sensers are known for multi-axial path measurement which, with a view to non-frictional operation, are guided orthogonally (e.g.., German Auslegeschrift 2242 355) or cardan-fashion (e.g., German Auslegeschrift 24 40 692) in resilient (sprung) bearings.

A number of sensing head constructions have pre-guiding elements, to ensure that the sensing ball bears reliably, even in the spatial zero position.

However, since the measuring process makes it difficult to adjust the spatial zero point of the senser deflection, clamping elements are also provided which can block one or usually two degrees of freedom at choice (e.g. East German Patent 92 567).

However, in that case there is the disadvantage that in the sensing of inclined surfaces the measuring force, which is adjusted at an inclination, causes considerable errors of measurement due to transverse deformation of the senser shaft. Moreover, the workpieces to be measured must be well secured, since if the senser deflection is accidentally increased, the measuring force rises very sharply, resulting in possible displacements or deformations of the workpieces, leading to errors.

Object of the Invention The object of the invention is to increase the quality of measurement.

Statement of the Essential Nature of the Invention The invention solves the problem of adjusting a senser for multi-axial path measurement, using a system for adjusting position, measuring force and free movement.

To this end according to the invention connected to the senser shaft is at least one resilient rod whose free end is retained spring-pre-stressed in the zero position in the casing.

Preferably, at least one resilient rod bears at the end a cylindrical member having an end-face bore and an edge and attached to the casing for each resilient rod is a matching abutment, which is constructed similarly to the cylindrical member and is disposed coaxially and laterally inverted in relation thereto and is guided in parallel springs parallel with the resilient rod axis and is pre-stressed by an end-face spring and if a plurality of resilient rods are used, a parallelepipedic member having a longitudinal groove and a longitudinal edge on both sides is substituted for at least one cylindrical member, a ball being disposed in each case betwen the matching abutment and the cylindrical or parallelepipedic member.

In a preferred embodiment of the invention, a first resilient rod with a cylindrical member is attached to the senser shaft of a resiliently mounted senser, and a second resilient rod having a parallelepipedic member is attached to its matching abutment in prolongation of the parallel springs.

In a further preferred embodiment, attached to the senser shaft are three resilient rods which are disposed in a plane, off-set by 120 , and of which two bear a cylindrical member, the third bearing a parallelepipedic member.

In another preferred embodiment, attached to the senser shaft are three rsilient rods which are disposed in a plane, off-set by 120 , and are borne spring-pre-stressed on cutting edges; preferably, at each resilient rod end a spring is pre-stressed over the cutting edges.

In the range of very small deflections, the preferred measuring range, the resilient rod ends remain fixed in the zero position.

The measuring force increases proportionally with the deflection of the senser shaft. The resilient rod end moves out of its zero position only when the forces become greater than the pre-stressing forces.

In the construction using balls, the balls roll out of the bores as far as the edge, without the measuring force substantially changing as a result. Without balls, the measuring force continues to increase.

However, the characteristic curve can be kept significantly less steep. In both variants the zero position, the measuring range and the free movement are adjusted using one system. In principle, measurement can even be performed in the free movement range if required, and with somewhat lower demands on accuracy. Under the return force of the springs, the senser is automatically guided back to the zero position, even from its greatest possible deflection.

Exemplary Embodiments In the drawings: Figure 1 shows a construction according to the invention having two resilient rods and balls, Figure 2 shows a detail of Figure 1, to an enlarged scale, Figure 3 is a front elevation of a construction according to the invention having three resilient rods and balls, Figure 4 is a plan view of the construction shown in Figure 3, and Figure 5 shows a construction according to the invention having three resilient rods without balls.

Three constructions according to the invention are illustrated. The first one has two resilient rods, the second has three resilient rods and balls, and the third has three resilient rods, but no balls. They all share the feature that the workpiece can be sensed in the x, y and z directions. In each case the senser consists of a senser shaft 1, a sensing ball 2, a plate 5, and three inductive path-measuring transformers, which have ferrite cores 6 and coils 7 and which are disposed in the plane of the plate, off-set by 120 .

The ferrite cores 6 are disposed parallel with one another and with the axis of the senser shaft. The coils are connected to an electronic computer.

In the first embodiment, the plate 5 is suspended resiliently from the casing 4 in three radially stressed helical springs 3 disposed off-set by 120 . On the end face a first resilient rod 8 is attached to the plate 5 in prolongation of the senser shaft 1. The end of the resilient rod 8 bears a cylindrical member 9 having at the end face a bore 12 and a collar 17. A similarly constructed matching abutment 11 is disposed coaxially and laterally inverted in relation to the cylindrical member. The matching abutment 11 is guided parallel with the resilient rod axis by two parallel springs 10 connected to the casing. Disposed between the cylindrical member 9 and the matching abutment 11 is a ball 14. It is disposed in bores 12, A spring 13 keeps the members pre-stressed.

In the zone of very small deflections in the x, y direction, the ball remains lying in the bores. The measuring force at the sensing ball is substantially determined by the spring characteristic of the first resilient rod 8 and in this zone increases linearly with deflection. Only with larger deflections does the ball roll out of the bores, at the furthest as far as the edge 17. The springs are sa adjusted to one another that the measuring force does notsubstantialy change in this free movement (stroke) zone. The edge diameter is so adapted to the diameters of the balls and bores, that even after the maximum deflection, the force of the springs automatically returns the senser to the zero position.

For precise measurements in the z direction a second resilient rod 8 is attached to the matching abutment 11 in the prolongation of the parallel springs 10. The resilient rod 8 bears at its end a parallelepipedic member 15 with a horizontal longitudinal groove 16 and a longitudinal edge 18 on both sides. Stressed against the parallelepipedic member is a further matching abutment 11. A further ball 14 is disposed between these two members.

In the second embodiment three resilient rods 8 are attached to the plate 5. They are disposed in the plane of the plate and off-set by 120 in relation to one another. Attached to each of the two resilient rods is a cylindrical member 9, a parallelepipedic member 15 being attached to the third resilient rod.

Bearing is provided in three pre-stressed matching abutments 11. A ball 14 is disposed in each case between the matching abutment and the cylindrical or parallelepipedic members, as described hereinbefore. In this embodiment the system according to the invention for the adustment of position, measuring force and free stroke at the same time provides the resilient bearing of the sensor.

In the third embodiment, just as in the second embodiment, three resilient rods 8 off-set by 1200 are attached to the plate 5. Their ends bear against cutting edges 19. A pre-stressed spring 20 is disposed above each resilient rod end and each cutting edge. The resilient rod ends lift off only with relatively large measuring forces, which overcome the spring pre-stressing. Until then the measuring force is proportional to the deflection and is determined exclusively by the spring characteristic of the resilient rods. Moreover, a proportionality is again established which, however, is now also partly determined by the springs 20. This characteristic line can be kept less steep so that the measuring force must not substantially increase even in this free stroke zone. Instead of the three outer springs 20, the pre-stressing might also be exerted by a prestressed spring acting centrally on the plate 5.

Claims (7)

1. A system for the adjustment of sensers, having a casing, path-measuring transformers, a senser shaft and sensing ball, characterised in that connected to the senser shaft is at least one resilient rod (8) whose free end is retained spring-pre-stressed in the zero position in the casing.

2. A system according to claim 1, characterised in that at least one resilient rod (8) bears at the end a cylindrical member (9) having an end-face bore (12) and an edge (17) and attached to the casing for each resilient rod is a matching abutment (11), which is constructed similarly to the cylindrical member and is disposed coaxially and laterally inverted in relation thereto and is guided in parallel springs (10) parallel with the resilient rod axis and is pre-stressed by an end-face spring (13) and if a plurality of resilient rods are used, a parallelepipedic member (15) having a longitudinal groove (16) and a longitudinal edge (18) on both sides is substituted for at least one cylindrical member, a ball (14) being disposed in each case between the matching abutment and the cylindrical or parallelepipedic member.

3. A system according to claims 1 and 2, char acterised in that a first resilient rod with a cylindrical member is attached to the sensor shaft of a resiliently mounted sensor, and a second resilient rod having a parallelepipedic member is attached to its matching abutment in prolongation of the parallel springs.

4. A system according to claims 1 and 2, characterised in that attached to the senser shaft are three resilient rods which are disposed in a plane, off-set by 120% and of which two bear a cylindrical member, the third bearing a parallelepipedic member.

5. A system according to claim 1, characterised in that attached to the senser shaft are three resilient rods which are disposed in a plane, off-set by 1200, and are borne spring-pre-stressed on cutting edges.

6. A system according to claims 1 to 6, characterised in that at each resilient rod end a spring is pre-stressed over the cutting edges.

7. Asystomfortho adjustment of sensers substantially as herein described with reference to the accompanying drawings.