GB2167187A

GB2167187A - Device for driving a measuring sleeve in a tailstock-type length measuring device

Info

Publication number: GB2167187A
Application number: GB08523869A
Authority: GB
Inventors: Wilfried Tanzer; Horst Metzig; Hans-Joachim Sommer
Original assignee: Carl Zeiss Jena GmbH
Current assignee: Jenoptik AG
Priority date: 1984-10-01
Filing date: 1985-09-27
Publication date: 1986-05-21
Also published as: GB8523869D0; JPS6190001A; DD248421A1; DE3524437A1; GB2167187B; CH669036A5

Abstract

A device for driving a measuring tailstock sleeve in a length measuring apparatus, comprises a motor-driven drive (7) for the controlled displacement of the measuring sleeve (5) relative to a test object (3) to be measured. The drive (7) is coupled to the sleeve (5) by way of a carrier (8) on the drive, a first arm (9) connected to the sleeve (5), a second arm (11) pivotally mounted on the first arm (9) by means of a pivot (10), and a stop (12) carried by the second arm (11). A weighted cable (14) is arranged to urge the stop (12) into engagement with the carrier (8). Thus, when the measuring sleeve is driven into contact with the test object 3 the pressure of contact is limited to that generated by the weight 13 acting by way of the cable 14 on the second arm 11. <IMAGE>

Description

SPECIFICATION Device for driving a measuring sleeve in a tailstock-type length measuring device The invention relates to a device for driving a measuring sleeve in a tailstock-type measuring apparatus, in particular for generating and enabling reversal of the measuring force in instruments for measuring length whose measuring principle is based on the two-arm method of measurement.

In known machines for measuring length in which horizontal or vertical sensing of a test object is carried out by means of a sensor disposed in a movable tailstock-type measuring sleeve, during measurement, the sleeve is subjected to a force in the direction of the test object by means of a weight which is connected to the measuring sleeve by way of a cable guided across a guide pulley fixed to the frame. To reverse the direction of force, as required when changing from internal to external measurements, the weight and cable are hung over a pulley at the opposite end of the measuring machine.This principle is used in the instruments described in Lehmann's "Linear Measurement Manual" published by VEB Verlag Technik Berlin, 1960, pages 45 and 46, wherein it is disadvantageous that there is a direct correlation between the effective range of the tailstock sleeve and the range of movement of the weight. The dynamics of the measuring force are not controlled.

In the measuring device in CH-PS 611015, a measuring tailstock sleeve is driven by an electromotor by way of a pinion and gear wheel with the aid of a cable drive, wherein, when the measuring device is disposed horizontally, the motor is used to generate the measuring force.

This operation is controlled by a complicated electric device for controlling the size and direction of the motor current.

The latter device does not provide for the drive unit to be disengaged from the measuring tailstock sleeve when the test object is being sensed, so that additional measures, such as a frictional coupling, must be provided to avoid damage. The size of the measuring force is thus dependent on the friction ratios in the coupling.

The object of the present invention is to eliminate the disadvantages of the known arrangements and to achieve a high level of safety during sensing of the test object using a construction which is technically simple.

According to the present invention, there is provided a device for driving a measuring tailstock sleeve in a length measuring apparatus, comprising a motor-driven drive arrangement for the controlled displacement of the measuring sleeve relative to a test object to be measured, a carrier disposed on the drive arrangement, a first arm connected to the measuring sleeve, a second arm pivotally mounted on the first arm, a stop member carried by the second arm, and a weighted cable coupled to the second arm for urging the stop carried by the second arm into abutment with said carrier.

It is advantageous if the carrier on the drive unit and the pivot for the second arm are disposed in alignment with one another.

Preferably, one end of the cable is connected to the carrier and the other end carries a weight, the cable passing over a pulley carried by said second arm such as to subject the second arm to a turning moment urging said stop into abutment with the carrier.

Alternatively, one end of the cable is connected to said second arm and the other end carries a weight, the cable passing over a pulley carried by said drive arrangement such as to subject the second arm to a turning moment urging said stop into abutment with the carrier.

When the measuring sleeve is moved by the drive unit towards the object to be tested, the tailstock sleeve stops as soon as the test object is touched, although the drive unit continues to operate until stopped. The engagement between the carrier and the stop is then broken and the measuring force generated by the weight is applied to the test object by the weighted cable by way of the second and the first arms. The drive unit may be stopped at any point, although it is advantageous to stop the drive unit at the time of breaking of the connection between the carrier and the stop.

For this purpose, the carrier and stop can be provided with electric switching contacts which may open and close an electric circuit.

To reverse the measuring force direction, the second arm is pivoted by 180 at its pivot disposed on the first arm. This is necessary for carrying out internal measurements on the object being measured.

The following advantages result from a comparison with the known devices: Only a single-stage measuring system is required, wherein a motor-driven drive unit may be used.

A high level of measuring force constancy is achieved independently ofsthe position of the drive unit. The dynamics of the drive do not influence the measuring force, so that fault and brake paths for the drive unit may be selected within broad limits independently of the position of the measuring sleeve.

In the event of the measuring tailstock sleeve itself, and not the sensor pin, touching the object to be measured, or in the event of the measuring tailstock sleeve reaching its end position, the drive unit is decoupled from the measuring tailstock sleeve so that no additional damage prevention systems are necessary.

Reversal of the measuring force direction is ensured using a simple construction.

The search for the reversal point during measurement is not influenced by the drive unit.

The range of movement of the weight is independent of the effective range.

As a result of the drive unit being simultaneously decoupled from the measuring sleeve at the commencement of sensing, vibration problems caused by the moving system of the measuring sleeve and the drive unit do not affect the acquisition of measurement data, as the coupling between the carrier and the stop has already been broken. Measurement data acquisition occurs in a "quasi-static" state, although the drive unit does not yet have to be stopped.

The present invention thus enables the provision of a drive unit for a measuring tailstock sleeve in an instrument for measuring length in which a constant measuring force and decoupling of the drive unit from the measuring tailstock sleeve at the moment of sensing are achieved in a technically simple manner and independently of the direction of measurement.

The invention is described further hereinafter, by way of example only, with reference to the accompanying schematic drawing, which shows one embodiment of an apparatus in accordance with this invention.

In a measuring machine 1, a test object 3 is disposed between an adjustable sleeve 4 and a measuring sleeve 5 on a measuring table 2.

The measuring sleeve 5 is located displaceably in a tailstock-type holder 6 which is disposed on the base of the measuring machine 1 and which may also be displaceable or be fixed.

The position of the measuring sleeve 5 is ascertained by a measuring system not shown in the drawing.

A drive arrangement 7 having a carrier 8 is provided on the tailstock holder 6 and may be moved in the direction of measurement (shown by the arrow in the drawing). A first arm 9 is fastened to the measuring sleeve 5 and has a pivot 10 on which a second arm 11 is pivoted. The arm 11 carries a stop 12 frictionally abutting against the carrier 8 and having a guide pulley 15 guiding a cable 14 loaded with a weight 13. The other end of this cable is fastened to the carrier 8 of the drive arrangement 7. The carrier 8 and the pivot 10 of the second arm 11 on the first arm 9 are advantageously disposed in alignment one with the other.

The device shown for driving the measuring sleeve 5 ensures that the stop 12 is always abutting against the carrier 8 when the measuring sleeve 5 is not sensing the test object 3, thus ensuring frictional connection of the drive arrangement 7 to the measuring sleeve 5. As soon as the measuring sleeve 5 senses the test object 3, this connection is broken and the measuring sleeve 5 is under the effect of a measuring force generated by the weight 13.

In a variant (not shown) having the same effect, the guide pulley 15 is disposed on the drive arrangement 7 and the free end of the cable 14 on the second arm 11.

If the direction of the measuring force is to be reversed, as is required when carrying out internal measurements on the test object 3, the second arm 11 is pivoted on its pivot 10 together with the cable 14, the guide pulley 15 and the stop 12 by 180 . This position is indicated by the dash-dotted line in the drawing.

Claims

1. A device for driving a measuring tailstock sleeve in a length measuring apparatus, comprising a motor-driven drive arrangement for the controlled displacement of the measuring sleeve relative to a test object to be measured, a carrier disposed on the drive arrangement, a first arm connected to the measuring sleeve, a second arm pivotally mounted on the first arm, a stop member carried by the second arm, and a weighted cable coupled to the second arm for urging the stop carried by the second arm into abutment with said carrier.

2. A device as claimed in claim 1, wherein the carrier on the drive arrangement and the pivot for the second arm are disposed in alignment with one another.

3. A device as claimed in claim 1, wherein the carrier on the drive arrangement and the pivot for the second arm are disposed in vertical alignment with one another.

4. A device as claimed in claim 1, 2 or 3, wherein one end of the cable is connected to the carrier and the other end carries a weight, the cable passing over a pulley carried by said second arm such as to subject the second arm to a turning moment urging said stop into abutment with the carrier.

5. A device as claimed in claim 1, 2 or 3, wherein one end of the cable is connected to said second arm and the other end carries a weight, the cable passing over a pulley carried by said drive arrangement such as to subject the second arm to a turning moment urging said stop into abutment with the carrier.

6. A device for driving a measuring tailstock sleeve in a length measuring apparatus, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.