GB2057688A - Calliper gauge machine - Google Patents

Abstract

Linear dimension measuring apparatus (10) comprising two arms (30, 39) adapted by means of weight biasing to engage the workpiece (34) to be measured and pivotally mounted on translatable carriages (17, 18). Motors (19, 20) operated by electrical transducers when the arms are not horizontal translate the carriages (17, 18) until the arms (30, 39) are horizontal. Digital measuring units such as 23 measure the distances moved by the carriages (17, 18) and hence the arms (30, 39) from a datum so that the linear dimension may be determined. <IMAGE>

Description

SPECIFICATION Measuring apparatus This invention relates to measuring apparatus and in particular to measuring apparatus suitable for measuring linear dimensions.

When grinding a cylindrical workpiece, it is convenient to continuously monitor the workpiece diameter. This is usually achieved by providing the grinding machine with a measuring device which comprises opposed short range transducers adapted to engage the workpiece. Whilst such devices provide an adequate continuous indication of workpiece diameter, they are very restricted in their applications. Thus transducers are only effective over comparatively small ranges.

Consequently if a grinding machine is required to machine a range of different diameters on a workpiece, a different measuring device is required for each diameter.

It is an object of the present invention to provide a measuring apparatus which is effective over a wide range of dimensions.

According to the present invention, apparatus suitable for measuring a linear dimension of a workpiece comprises support means having two carriages mounted for translation thereon, drive means adapted to translate said carriages and measuring means adapted to provide an output representative of the distances of said carriages from a datum, each of said carriages being provided with a workpiece engaging arm and mounted for translation on said support means in such a manner that said arms are maintained in opposed relationship, each of said arms being movable relative to its respective carriage, biassed towards the workpiece to be measured and associated with means adapted to provide an output representative of its position relative to its respective carriage, said arm position indication means and said drive means being interconnected in a closed loop circuit in such a manner that in operation each carriage is translated by said drive means to bring its respective arm into engagement with the workpiece to be measured, translation being maintained until each arm is urged by said workpiece against said arm bias into a predetermined position relative to its respective carriage whereupon translation of said carriage is discontinued.

Each of said arms may be pivotally mounted on its respective carriage.

Said means adapted to provide an output representative of the position of each arm relative to its respective carriage is preferably a linear displacement transducer.

Said arms may be weight biased towards the workpiece to be measured.

Said carriages are preferably each provided with drive means so as to be independently translatable on said support means.

Said carriages are preferably mounted for vertical translation on said support means.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a side view of measuring apparatus in accordance with the present invention.

Figure 2 is a view on arrow A of Figure 1.

With reference to Figure 1, the measuring apparatus generally indicated at 10 comprises a bed 11 which carries a vertical, generally rectangular support member 12. The support member 12 is of plate form and provided on opposite faces 1 3 and 14 with vertical roller slides 1 5 and 16 respectively as can be seen in Figure 2.

Carriages 1 7 and 18 are respectively mounted on the roller slides 1 5 and 16.

Electric moton 19 and 20 mounted on the support frames 1 3 and 14 are adapted to translate the carriage 17 and 1 8 via ball screws 21 and 22.

Thus each of the carriages 17 and 18 may be independently translated along its corresponding roller slide 1 5 and 16.

Digital measuring units 23 and 24 are mounted on the support member faces 13 and 14 respectively. The moving portions 25 and 26 of the digital measuring units 23 and 24 are adapted to engage extension pieces 27 and 28 provided on the carriages 1 7 and 18. Thus the output of the digital measuring unit 23 indicates the distance moved by the carriage 17 along the roller slide 1 5 and the output of the digital measuring unit 24 indicates the distance moved by the carriage 1 8 along the roller slide 1 6.

The carriage 17 is provided with a boss 29 on which an arm 30 is pivotally mounted. The right hand end 31 of the arm 30 when viewed in Figure 1 is provided with a weight 32 which is sufficient to exert a moment upon the arm 30 to bring its opposite end 33 into engagement with a cylindrical workpiece 34, the diameter of which is to be determined by the apparatus 10. A short range linear transducer 35 is mounted on the carriage extension piece 27 so that its movable portion 36 engages the right hand end 31 of the arm 30. The transducer 35 is arranged so that its electrical output is zero when the arm 30 is horizontal. However when the arm 30 departs from the horizontal, the transducer 35 provides an electrical output of appropriate sense which is fed to the electric motor 19 via an amplifier 37 of suitable gain.The electric motor 1 9 then translates the carriage 1 7 in the appropriate direction to return the arm 30 to a horizontal position. The transducer 35, amplifier 37, electric motor 1 9 and carriage 1 7 thus constitute a closed loop servo system which tends to maintain the arm 30 in a horizontal position.

A second boss 38 provided on the carriage 18 vertically above the first boss 29 is adapted to pivotally support a second arm 39. The second arm 39 is not provided with a biassing weight but instead relies on its own weight and the position of its pivotal attachment to the boss 38 to bias its left hand end 41 (when viewed in Figure 1) into engagement with the cylindrical workpiece 34. A short range linear transducer 40 is mounted on the extension piece 28 on the carriage 1 8 in a similar manner to the transducer 35 on the carriage extension piece 31 but is inverted.

A suitable amplifier (not shown) similar to the amplifier 37 interconnects the transducer 40 with the electric motor 20 so that the arm 39 is maintained in a horizontal position in the same manner as is the arm 30.

it will be seen therefore that the arms 30 and 39 are driven by the electric motors 19 and 20 into engagement with the workpiece 34 with drive being maintained until the arms 30 and 39 are horizontal, whereupon the drive is discontinued.

Since the drive to the electric motors 19 and 20 is discontinued only when the arms 30 and 39 are horizontal, then the sum of the distances of the carriages 17 and 18 from a datum will be equal to the diameter of the workpiece. Thus if the digital measuring units 23 and 24 are set to register the distances of the carriages 1 7 and 18 from a common datum, then the sum of their outputs will be equal to the diameter of the workpiece 34.

In order that diameter of the workpiece 34 may be accurately determined, the arms 30 and 39 are cranked in opposite directions in the region of their pivotal positions so that their left hand ends (when viewed in Figure 1)33 and 41 are aligned.

The measuring apparatus 10 in accordance with the present invention may be used for measuring a linear dimension on a static workpiece.

However it is particularly suitable for monitoring the diameter of a workpiece whilst that diameter is altering as a result of the workpiece being machine. Thus for instance if the workpiece 34 is rotated and then machined by a grinding wheel 42, the left hand ends 33 and 41 of the arms 30 and 39 will be biassed against the workpiece 34 and remain in contact with it as its diameter decreases. Hardened faces 43 and 44 on the arm ends 33 and 41 ensure that arm wear by the workpiece is minimal. As the diameter of the workpiece 34 decreases, so the diameter is continually indicated by the outputs of the digital measuring units.

The outputs from the digital measuring units 23 and 24 may be fed to a control unit which automatically reduces the feed rate of the grinding wheel 42 at pre-set distances from the finished diameter of the workpiece 34 until the feed is discontinued when the finished diameter is reached.

Although the present invention has been described with reference to a measuring apparatus 10 which measures linear dimensions in a vertical plane, it is also suitable for operation in other planes if suitable means such as springs are used to bias the arms towards the workpiece.

The direction of bias could be reversed in certain cases so that, for instance, internal diameters could be measured.

Moreover it will be appreciated that whilst the arms 30 and 29 have been described as being pivotally mounted on the carriages 1 7 and 18, they could in fact be mounted by other means which provide suitable relative movement such as for instance slides.

Claims (7)

1. Apparatus suitable for measuring a linear dimension of a workpiece comprising support means having two carriages mounted for transmission thereon, drive means adapted to translate said carriages and measuring means adapted to provide an output representative of the distances of said carriages from a datum, each of said carriages being provided with a workpiece engaging arm and mounted tor translation on said support means in such a manner that said arms are maintained in opposed relationship, each of said arms being movable relative to its respective carriage, biassed towards the workpiece to be measured and associated with means adapted to provide an output representative of its position relative to its respective carriage, said arm position indication means and said drive means being interconnected in a closed loop circuit in such a manner that in operation, each carriage is translated by said drive means to bring its respective arm into engagement with the workpiece to be measured, translation being maintained until each arm is urged by said workpiece against said arm bias into a predetermined position relative to its respective carriage whereupon translation of said carriage is discontinued.

2. Apparatus suitable for measuring a linear dimension as claimed in claim 1 wherein each of said arms is pivotally mounted on its respective carriage.

3. Apparatus suitable for measuring a linear dimension as claimed in claim 1 or claim 2 wherein said means adapted to provide an output representative of the position of each arm relative to its respective carriage is a linear displacement transducer.

4. Apparatus suitable for measuring a linear dimension as claimed in any one preceding claim wherein said arms are weight biassed towards the workpiece to be measured.

5. Apparatus suitable for measuring a linear dimension as claimed in any one preceding claim wherein said carriages are each provided with drive means so as to be independently translatable on said support means.

6. Apparatus suitable for measuring a linear dimension as claimed in any one preceding claim wherein said carriages are mounted for vertical translation on said support means.

7. Apparatus suitable for measuring a linear dimension substantially as hereinbefore described with reference to and as shown in Figures 1 and 2 of the accompanying drawings.