GB2302588A

GB2302588A - Changeable probes for co-ordinate measuring machines

Info

Publication number: GB2302588A
Application number: GB9609990A
Authority: GB
Inventors: Peter Aehnelt; Kurt Brenner; Klaus Herzog; Roland Roth; Karl Seitz
Original assignee: Carl Zeiss AG
Current assignee: Carl Zeiss AG
Priority date: 1995-06-21
Filing date: 1996-05-14
Publication date: 1997-01-22
Anticipated expiration: 2016-05-14
Also published as: GB2302588B; DE19623600A1; GB9609990D0

Abstract

A changeable probe for a co-ordinate measuring machine is held in a sleeve by a clamping lever 16 and three bearing points 22,23,24. Two of the bearing points 22,23 are situated at the entrance of the sleeve and each comprises an inclined cylinder which engages with a pair of balls 12a, 13b on the probe shaft 5. The lines g1, g2 which connect the pairs of balls are parallel and in the same horizontal plane. The third bearing point 24 is located at the other end of the sleeve and comprises two cylinders 24a, 24b which engage a larger ball 14 held inside the end of the probe shaft 5. The line g3 connecting the cylinders is also horizontal but perpendicular to lines g1 and g2. The clamping lever 16 is a spring loaded lever and carries a rotatably mounted roll (18, figure 3) which bears against the ball 14, hence drawing the shaft 5 into the sleeve. The probe is inserted or released from the sleeve by moving the lever 16 away from the shaft 5 by pressing an activating button (33, figure 3).

Description

Specification Probe Chanaina Svstem A multitude of different changing systems is known for quickly exchanging the probe styluses on coordinate measuring machines, systems which are partly manually operated and partly automatically controlled. In general, these changing systems contain a three-point bearing which clearly defines the position of the probe stylus and in which three bearing points with two supporting points each are arranged on the circumference of a circle, i.e., in one plane at 1200 from each other. One example of a manually operated probe changing system of the described type is outlined in GB 1 599 751. An electromagnetically operated probe changing system of this type is disclosed in European Patent 0 128 464.

In the described probe changing systems, the rigidity of the changing points and the reproducibility of the spatial probe position are a function of the circle diameter on which the bearing points are arranged. If very high demands are made on rigidity and reproducibility, the result is frequently a design which is bulky and protruding in an undesirable manner perpendicularly to the probe shaft. The same applies to the probe changing systems illustrated in Figures 7 and 8 of DE 38 24 549, in which the six supporting points of the bearing are located on the surface of a truncated pyramid. Here, too, rigidity and reproducibility depend on the size of the pyramid base.

The invention is based on the task of creating a probe changing system which takes up as little room as possible perpendicularly to the probe shaft, but which still provides an adequately rigid and reproducible bearing for the probe.

This problem is solved by the measures specified under claim 1.

According to the invention, at least one bearing point of the bearing is offset with respect to the other bearing points by an amount which is noticeably larger than the interspacing between the other bearing points. This makes it possible to meet the two otherwise contradictory demands for a slim design of the probe changing system and rigid and reproducible bearing of the probe. The probe changing system can therefore be installed in a sleeve which is only minimally wider than the diameter of the actual probe shaft.

Ideally, the bearing should feature three bearing points with two supporting points each, and the lines which interconnect the supporting points of the respective bearing points should lie in two different planes offset in the direction of the probe shaft. In this manner, two of the bearing points can use their supporting points to hold the probe in the direction of the probe shaft, and the supporting points of the bearing point in the second plane offset with respect to the first one can hold the probe more or less perpendicularly to the probe shaft.

Although the bearing points of this bearing have then two different supporting directions, the probe shaft can still be very simply clamped, provided the clamping device is designed in such a way that it introduces a clamping force in the probe shaft which provides force components in the direction of the probe shaft as well as perpendicularly to it.

It is of special advantage if the probe changing system is equipped with sensors for code identification and the probes to be exchanged are provided with corresponding codes. The computer of the coordinate measuring machine can then automatically identify the type of probe which has been brought in and take its dimensions into account in the subsequent coordinate measurement.

Further benefits of the invention are disclosed in the following description of an embodiment of the invention using Figures 1 - 3 of the annexed drawings as examples.

Figure 1 is a simplified schematic showing a slim probe held by a probe changing system on the probe head of a coordinate measuring machine; Figure 2 is a detailed perspective illustration of the bearing of probe shaft (5) in sleeve (10) of the probe changing system of Fig. 1 at a magnified scale; Figure 3 is a sectional view of the probe changing system magnified yet again, with the probe shaft inserted in one of the planes containing the linear probe axis.

The probe head according to the simplified illustration in Figure 1 features a carrying component (2) deflectable in the direction of arrow (z). Via a spring parallelogram this component is mounted with its two parallelogram legs (4a and 4b) on the coordinate measuring machine's measuring arm (1) which is displaceable within the measuring range Carrying component (2) is angular and, on its horizontal leg (3) and via flexible waistline (8), carries a cylindrical sleeve (10) in which the exchangeable probe with its shaft (5) drawn in hatched lines is inserted. The actual probe (6) with ball tip (7) is screwed on the bottom end of shaft (5).When probing movements are performed perpendicularly to the linear shaft direction in the direction of the bow-shaped arrows marked (x) and (y), sleeve (10) which is pivotable about waistline (8) can yield so that deflectability is provided in all three spatial directions.

The bedding of probe shaft (5) into the bearing of the probe changing system integrated in sleeve (10) has been implemented in the form of two pairs of balls (12a and 12b) (the second ball is invisible) and (13a and 13b) (the first ball is invisible) mounted on a conical shoulder (11) on the probe carrying side of probe shaft (5), in two places offset by 1800 with respect to the probe axis. These ball pairs support probe shaft (5) on two inclined cylinders (22 and 23) embedded in sleeve (10).

The other end of probe shaft (5) carries a ball (14) with a larger diameter than balls (12) and (13). With one side ball (14) touches two further rolls (24a and 24b) which are mounted on the inside of sleeve (10) with their axes aligned parallel to probe shaft (5).The illustration given in Figure 2 also shows the fork-shaped end of clamping lever (16) protruding at the top. This lever clamps the probe shaft against the described bearing in sleeve (10), as can be seen in Figure 3.

As apparent from the illustration, the distance between the bearing points (12/22) and (13/23) arranged on either side of probe shaft (5) on the conical shoulder (11) is noticeably smaller than the distance of these bearing points from bearing point (14/24) at the upper end of probe shaft (5). The straight lines (gl) and (g2), which connect the contact points of the two bearing points (12/22) and (13/23), are therefore located in one plane, and straight line (g3), which connects the contact points of ball (14) with rolls (24), is located in a second plane displaced with respect to the first one in the direction of the probe shaft.

The sectional view of Figure 3 is shown with respect to Figure 2 in such a way that it illustrates the upper bearing (14/24) but not the two bearing points on the conical shoulder (11) of probe shaft (5). At the bottom of the probe shaft, reference mark (17) indicates the threaded bore via which probes of different geometries can be firmly screwed on probe shaft (5).

At the lower end of sleeve (10) which is deflectable in the (x) and (y) directions, clamping lever (16) is mounted pivotally about axis (20). The pivoting direction has been selected so that the upper end of pivot lever (16) is mobile in the direction of roll pair (24a/b). There, at the upper end, clamping lever (16) carries a rotatably mounted roll (18) whose outside circumference touches ball (14) inside the probe shaft at an angle from below on the side facing away from rolls (24).

The fork-shaped upper end (26) of clamping lever (16) is pressed against ball (14) by shoulder (31) of a spring-loaded pin (32) in such a manner that the clamping device's clamping force (FS) applied to ball (14) provides a component (F1) which pulls probe shaft (5) into sleeve (10), and also another component (F2) which presses ball (14) against roll pair (24a/b), thus preventing tilt against the probe shaft. Pin (32) is mounted on both sides of sleeve (10) inside the cylindrical inserts (30) and (35) to enable sliding movement, and on one end carries activating button (33) against which spring (34) is supported. In the illustrated position, shaft (5) of the probe is clamped by the force of spring (34). To insert or remove it, activating button (33) is pressed, following which the shaft can be pulled out of sleeve (10) from below.Activating bolt (32) for clamping lever (16) is designed in such a way as to retain the force flow within the probe changing device when button (33) is activated (which might happen when the entire probe is encircled with one hand), thus preventing any reaction forces being applied to the other parts of the probe head.

At one point of its circumference probe shaft (5) features several bores located one above the other, in which magnets (19a-c) are installed for the purpose of identifying which probe has been brought in. These magnets form a digital code which can be detected by Hall sensors (19a,b,c) located opposite the magnets and connected with the control system of the coordinate measuring machine not shown here in detail.

It is possible, of course, to use other code readers, for example, optical or mechanical ones, for probe identification instead. It is also possible without any problem to replace the manually operated clamping device described here by an electrical or pneumatic clamping device, for example, which can be automatically activated by the control system of the coordinate measuring machine.

To protect the probe against damage or excessive wear, another sleeve (21) encloses sleeve (10). Stops (39a,b) on the outside of the deflectable sleeve (10) restrict its motion range with respect to sleeve (21).

Claims

Patent claims:

1. Probe changing system, in particular for coordinate measuring machines, with a clamping device (30-35) which pulls the interchangeable probe (5-7) against a bearing (22-24) providing unambiguous definition of its position, with at least one of the bearing points (14/24) of the bearing being offset against the other bearing points (12/22, 13/23) in the direction of the slim probe shaft (5), by an amount which is clearly higher than the interdistances between them.

2. Probe changing system according to claim 1, with the bearing system featuring three bearing points (22,23,24) with two supporting points each, and with the straight lines (gl-g3), which connect the supporting points, being located in at least two different planes displaced in the direction of the probe shaft (5).

3. Probe changing system according to claim 2, with the supporting points (12a/b, 13a/b), which are located in a first plane, supporting the probe in the direction of the probe shaft (5), and with the supporting points (24a,b), which are located in a second plane displaced with respect to the first plane, supporting the probe primarily perpendicularly to the probe shaft (5).

4. Probe changing system according to claim 3, with the clamping device (30-35) applying a clamping force (FS) on the probe shaft, which at the same time asserts a force component (F1) in the direction of the probe shaft and a force component (F2) perpendicularly to it.

5. Probe changing system according to claim 1, with the clamping device being manually operable.

6. Probe changing system according to claim 5, with the clamping device featuring a spring-loaded clamping lever (16).

7. Probe changing system according to claim 1, with the clamping device being automatically controllable and electrically or pneumatically operable.

8. Probe changing system according to claim 1, with the probes (5-7) to be brought into the probe changing system being provided with a code (9a-c), and the changing system including sensors (19a-c) for code identification.