GB2042732A

GB2042732A - Height Measuring Device

Info

Publication number: GB2042732A
Application number: GB8002026A
Authority: GB
Original assignee: Eley & Warren Precision Engs C
Current assignee: Eley & Warren Precision Engs C
Priority date: 1979-02-07
Filing date: 1980-01-22
Publication date: 1980-09-24
Also published as: GB2042732B

Abstract

A height measuring device comprising a base 10 having an air bearing support, a vertical pillar 13 channel shaped in cross section and extending from the base, a counterbalanced carriage movable along said pillar, said carriage 15 having at least one probe holder 17 extending therefrom, a scale mounted on the vertical pillar and an electrical contact for the scale mounted on the carriage, the scale being mounted on the front wall within said channel and the probe holder being mounted on the carriage outside the channel at a position adjacent the front wall. The carriage may be provided with a friction drive Figures 3 and 4 (not shown) which engages a locking bar whereby the carriage may be moved along the pillar. The friction drive may be engageable and disengageable so that the carriage may be moved for coarse adjustment when the friction drive is disengaged and moved for fine adjustment when the friction drive is engaged. <IMAGE>

Description

SPECIFICATION Height Measuring Device This invention relates to height measuring devices.

Height measuring devices are known which comprise a base, a vertical pillar extending from the base and a carriage movable along said pillar, said carriage being provided with a probe holder and means for contacting the position of the carriage on the pillar. Thus by moving the carriage between two positions as determined by the position of a probe in the probe holder the distance moved can be measured; the distance moved by the probe between its first and second positions is then known accurately.

It is also known to utilise for measuring the carriage movement in said height measuring devices a scale with a pick-up mounted on the carriage for contact with the scale so that a readout of the distance moved can be obtained. Such a read-out may for example, be a digital read-out provided with a re-set facility so that a reference position of the probe can be set to zero on the read-out and then the distance moved will be shown n directly.

According to the present invention a height measuring device comprises a base, a vertical pillar extending from the base, a carriage movable along said pillar, said carriage having at least one probe holder extending therefrom, a scale mounted on the vertical pillar and an electrical contact for the scale mounted on the carriage, the vertical pillar being of channel section, such as, generally U-shaped cross section, including a front wall and two side walls, the scale being mounted on the front wall within said channel and the probe being mounted on the carriage outside the channel at a position adjacent the front wall.

The applicants have found that the use of such a pillar provides for a much more accurate measurement than is obtained with conventional solid pillars. The distance between the probe and the scale on which the measurement is taken is relatively small and this is found to be extremely advantageous where carriage measurements e.g.

to .0001 of an inch are being made.

The device is preferably provided with a digital read-out which is mounted separate from the height measuring device and connected to the pick-up by means of flexible connecting means.

This has the advantage that the device can be used in a restricted space which is not possible where the read-out is mounted on the carriage or column.

In order to permit lateral adjustment of the position of the height measuring device on a reference bed it is desirable to provide an air bearing for the base. Conveniently, the air supply to the bearing is controlled by control means mounted on the device.

In a preferred form of the invention the carriage is provided with a friction drive whereby it may be moved along the pillar. Preferably, the friction drive is engageable and disengageable so that the carriage may be moved for coarse adjustment when the friction drive is disengaged and moved for fine adjustment when the friction drive is engaged. It is advantageous that such friction drive should be self-centring when it is engaged in order to avoid any transverse force on the pillar or guide member with which the drive is associated since such transverse force could lead to inaccuracy of measurement.

Reference is now made to the accompanying drawings in which: Figure 1 is a perspective view of a height measuring device according to the invention with the casing removed; Figure 2 is a side elevation of the height measuring device shown in Figure 1; Figure 3 is a section through a friction drive arrangement shown in the engaged position; and Figure 4 is a section similar to that of Figure 3 with the drive shown in the disengaged position.

The device comprises a base 10 which is mounted on an air bearing for easy movement, the air bearing being supplied by air line 11 and controlled by control button 12.

The base 10 carries a vertical pillar 13 of channel section and each vertical edge of said column is provided with slideways 14.

The carriage 1 5 is mounted for vertical movement on the pillar 13 and the carriage is provided with roller bearings 1 6 each of which run on a respective slideway 14 and maintain the carriage accurately in position relative to the pillar 13.

As can be seen from Figure 2 the carriage 1 5 is provided with a pair of probe holders 1 7 one of which is shown with a probe 1 8 in position in Figure 2.

The carriage 1 5 is counterbalanced by means of a cable 19 which passes over a pulley 20 and is attached to a counterbalance weight 21 movable vertically along the guide 22.

The adjustment of the carriage 1 5 relative to the pillar 1 3 therefore be readily made by sliding the carriage 1 5 manually to the desired position.

Fine adjustment of the position of the carriage is then effected by means of the friction drive arrangement shown in detail in Figures 3 and 4 of the accompanying drawings.

The friction drive arrangement comprises a casing 23 which is integral with or secured to the carriage 1 5. Mounted within said casing 23 is a friction drive roller 26 and a pair of jockey rollers 27 arranged so that when the friction drive is in the engaged position the friction roller 26 and jockey rollers 27 are disposed in engagement with, and on opposite sides of, the locking bar 28 which extends vertically along the front of column 13 as shown in Figure 2. The crown wheel 25, and hence the friction roller 26 which is driven thereby, is in turn driven by the worm 29 carried on shaft 30 rotatable in a bush 47. The adjusting knob 31 is fixed to a driving part 45 by means of set screws 43 and the driven part 46 is fixed to the shaft 30 by means of set screw 44.The coil spring 32 urges the driving part 46 into contact with friction washer 33 and the latter into contact with the driven part 46 so that the assembly constitutes a slipping clutch arrangement for rotating the shaft 30 by means of the adjusting knob 31.

The friction drive is capable of moving into and out of engagement by virtue of the fact that the jockey rollers 27 are mounted on jockey carrier 34 and the crown wheel 25 and friction roller 26 are mounted on crown wheel carrier 35. The crown wheel carrier 35 can slide in a slot (not shown) in the casing 23 and is integral with the shaft 39 which is journalled in the casing 23.

The jockey carrier is urged away from the locking bar 28 by a coil spring 44 which engages with the extension 45 of the crown wheel carrier 35 which can slide in the bore 43 in the jockey carrier 34.

The slidable member 42 can slide relative to the casing 23 and is constrained against rotation by pin 57 in the bore 58 which locates in a groove in the member 42. The shaft 53 extends from the extension 45 through a bore in the slidable member 42 and carries at its outer end a locking assembly.

The locking assembly 40 includes a locking element 41 having a radially extending lever 36 which can rotate relative to the shaft 53 and relative to control element 49 which is held on the shaft 53 by a set screw 51. The assembly is completed by a cover 52 and a pair of shims 48.

The control element has an axially projecting peg 50 which engages in an arcuate slot in the element 41 to limit the rotation thereof between two extreme positions.

When the friction drive is in the disengaged condition as shown in Figure 4 the friction roller 26 and the jockey rollers 27 are spaced from the locking bar 28. The friction drive is engaged by turning the knob 40 to the position shown in Figure 3 in which cam surfaces 41a and 41b cause the slidable member 42 to move to the right thereby compressing spring 37 which overcomes the force exerted by the spring 44 and urges the jockey carrier 34 to the right and thus the rollers 27 into contact with the locking bar 28.

The arrangement is self-centring by virtue of the fact that the crown wheel carrier 35 can slide relative to the jockey carrier 34 and both can move relative to the casing 23; thus the pressure applied to the locking bar 28 is equalised on both sides of the locking bar 28 due to the pressure exerted by the spring 37. The carriage can then be driven by rotation of the knob 31.

When it is desired to disengage the friction drive the locking assembly 40 is returned to the position shown in Figure 4 causing the slidable member 42 to move to the left. This reduces the pressure applied by the spring 37 and thus spring 44 causes the jockey carrier 34 to move to the left and disengage jockey rollers 27 from the locking bar 28.

It will be appreciated that such an arrangement is self-centring when in the engaged position and the only force which will be applied to the locking bar 28 is a balanced force between the jockey rollers 27 and friction roller 26 and there will be no tendency to twist the carriage or the locking bar relative to the pillar 13.

Thus, when it is desired to adjust the position of the carriage 15 on the pillar 13, the coarse adjustment is made by hand with the friction drive in the disengaged position as shown in Figure 4.

The lever 36 is then rotated to the position shown in Figure 3 to bring the friction drive into its engaged condition and the carriage 1 5 is then moved by rotation of the adjusting knob 31. Since this is provided with a slipping clutch arrangement a constant force is applied to the probe in contact with a surface to be measured.

In Figure 2 the device is shown in contact with a surface 42 on an object 51 to be measured. If it is desired to measure the distance between surface 50 and surface 52, for example, the carriage must be moved until the probe 1 8 is in contact with surface 52. This is effected by disengaging the friction drive, raising the carriage 15, operating the air bearing by means of control button 1 2 to move the device forward, releasing the button 12, lowering the carriage 1 5 until the probe 1 8 is almost in contact with surface 52, applying the friction drive by means of roller 36 and then adjusting the position of probe 1 8 by means of the fine adjustment knob 31.

This distance moved by the probe 1 8 between surface 50 and surface 52 will be the same distance as that moved by the carriage 1 5.

Movement of the carriage 15 is measured by means of scale 53 disposed on the inside of the pillar 13 and readable by means of a pick-up device (not shown) mounted on the carriage 1 5.

Such a scale and pick-up device may be of any suitable type but it is preferred that it is of the kind which generates an output for a digital readout, such as a differential capacitor measuring strip. The read-out conveniently has a zero setting so that it may be set at zero for the position of surface 50 and then the distance between surface 50 and surface 52 can be directly read from the digital read-out.

The height measuring device of the present invention is very convenient to use in that it is readily movable over a plane surface by means of the air bearing and is capable of very accurate height measurements. This is particularly so by virtue of the provision of the U-shaped pillar which enables the scale 53 to be situated as near as possible to the probe and thereby reduces errors due to twisting of the carriage 1 5 relative to the pillar 13.

The provision of the self-centring friction drive also represents a considerable advantage in that is provides for easy and reproducable fine adjustment of the position of the probe and selfcentring arrangement eliminates any twisting applied to the carriage or locking bar.

We have found that the use of a carriage which is engaged to a digital read-out by means of flexible cable (not shown) is preferable to the provision of a read-out on the carriage since this tends to be bulky and hinders advancement and manipulation of the carriage during height measurement.

Claims

1. A height measuring device comprising a base, a vertical pillar extending from the base, a carriage movable along said pillar, said carriage having at least one probe holder extending therefrom, a scale mounted on the vertical pillar and an electrical contact for the scale mounted on the carriage, the vertical pillar being of channel section including a front wall and two side walls, the scale being mounted on the front wall within said channel and the probe holder being mounted on the carriage outside the channel at a position adjacent the front wall.

2. A device according to Claim 1 provided with a digital read-out which is mounted separate from the height measuring device and connected to the pick-up by means of flexible connecting means.

3. A device according to Claim 1 or 2 in which the base is provided with an air bearing.

4. A device according to Claim 3 in which the air supply to the bearing is controlled by control means mounted on the device.

5. A device according to any of claims 1 to 4 in which the carriage is provided with a friction drive which engages a locking bar whereby the carriage may be moved along the pillar.

6. A device according to claim 5 in which the friction drive is engageable and disengageable so that the carriage may be moved for coarse adjustment when the friction drive is disengaged and moved for fine adjustment when the friction drive is engaged.

7. A device according to claim 6 in which the friction drive is self-centring when it is engaged.

8. A device according to claim 6 or 7 in which the friction drive exerts a predetermined pressure derived from a coil spring on the locking bar.

9. A device according to claim 6, 7 or 8 in which the friction drive is operable by a rotatable knob which incorporates a slipping clutch.

10. A height measuring device substantially as herein described with reference to Figures 1 and 2 of the accompanying drawings.

11. A height measuring device substantialiy as herein described and incorporating a friction drive arrangement as described with reference to Figures 3 and 4 of the accompanying drawings.