GB2154324A

GB2154324A - Improvements to dynamic measuring system

Info

Publication number: GB2154324A
Application number: GB08431851A
Authority: GB
Inventors: Derek Harry Graddon Redman
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-02-15
Filing date: 1984-12-17
Publication date: 1985-09-04
Also published as: GB8404007D0; GB8431851D0

Abstract

The measuring system comprises a movable machine tool table (16), a machine tool (12) (such as a grinding wheel), positioned at a location above the table, a non-contact sensor (18) e.g. of the electromagnetic or capacitance type positioned above the table at a second location A spaced from the machine tool, the sensor being mounted on a slide unit (17) maintaining constant height over the workpiece W by use of a sample and hold circuit as the workpiece passes under the sensor (18), and thereby measuring the height of the workpiece by signal means from the slide unit, or by use of a similar sample and hold circuit to compare a signal from the sensor (18) when it passes over a datum surface (19) with the sample and hold signal obtainable from the workpiece. <IMAGE>

Description

SPECIFICATION Improvements to dynamic measuring system This invention relates to a dynamic measuring system and particularly applicable to accurate measurement of workpieces on a moving machine tool table.

According to the invention, there is provided a dynamic measuring system comprising a movable machine tool table, a machine tool positioned at one location above the table, a non-contact measuring sensor positioned above the table at a second location spaced from said first location, the sensor being able to detect or measure a dimension of a workpiece on the table as it passes under the sensor and by use of a slide unit to keep this dimension constant, and a sample and hold circuit operable to sample and hold a signal from the sensor indicative of the workpiece dimension, with reference to a datum surface.

An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawing, in which: Figure 1 is a side view of a grinding machine incorporating a dynamic measuring system according to the present invention, and Figure 2 is an electrical circuit diagram of the measuring system of Fig. 1.

Referring to the drawings, a conventional grinding machine 10 includes a grinding wheel 1 2 rotating about a horizontal axis, a horizontally movable table 14 and an upper table 1 6 carried by table 1 4 and rotational about the vertical axis. Workpieces W to be ground to a given thickness are secured to the upper surface of table 1 6 and are brought into engagement with grinding wheel 1 2 by the rotational movement of table 1 6 and the horizontal movement of table 14.

Positioned above the table 1 6 at a location A diametrically opposite the grinding wheel is a measuring sensor 1 8 of the non-contact type such as an electromagnetic or capacitive sensor having a highly stable output and giving an output representative of the distance between the sensor face and an upper face of a workpiece as it passes beneath the sensor 18 and of a datum surface 1 9 of required thickness, sensor 1 8 is also mounted on a slide unit 1 7 which is driven by motor reducer 13.

Also positioned at location A are two trigger sensors 20, 22, the purpose of which will become apparent in the following description of the electrical circuit of the present system.

Associated with the trigger 20 is a magnet 24, and a magnet 26 is positioned alongside one of the workpieces to be measured on the table and is positioned to pass under trigger 22.

Referring to the electrical circuit of Fig. 2, two sample and hold amplifiers 28, 30 are each fed at one of their inputs with the output of the measuring sensor 18 through its own amplifier 23, the other input of amplifier 28 being fed with the output of sensor 20, and that of amplifier 30 being fed with the output of sensor 22. Power for the sensor is provided from supply 32. Sample and hold amplifier 30 feeds power amplifier 25 and in conjunction with reference signal 25 drives motor 1 3.

As the datum surface passes the measuring sensor 18, magnet 24 triggers sensor 20 which causes amplifier 28 to sample the output of sensor 1 8 and to display the output on indicator 34. Similarly, as workpiece W passes the measuring sensor 18, magnet 26 triggers sensor 22 which causes amplifier 30 to sample the output of sensor 18 and electronic control 23 to drive control motor 1 3 through amplifier 25. The reference signal 24 is algebraically summed with output of amplifier 30 so that motor 1 3 and slide 1 7 maintains sensor 1 8 a constant height above workpiece.

The outputs of the amplifiers are compared in scanning amplifier 38 which when the inputs are substantially equal is operative to actuate relay 40 to stop the grinding machine.

The operation of the system using sensor 1 8 mounted on slide unit 1 7 is to keep the sensor 1 8 a constant distance from workpiece W. Thus a small sensor with restricted surface area can be used to sense small areas of the workpiece, this also allows greater accuracy of sensor 1 8 and by use of the slide 1 7 a greater working distance can be obtained between sensor 1 8 and workpiece W.

Depending on working distance the reference datum surface 1 9 will not always show an output, but as the work-piece W is machined reference datum surface 1 9 will come into range of sensor 1 8 and show dimensional difference and reading at which operation is to be terminated.

In a modification sensor 20, magnet 24 and datum surface 1 8 are omitted and are replaced by a signal producing means (not shown) indicative of slide unit movement which can be used to give the deserved representation of the workpiece thickness.

In a further modification an additional measuring sensor (not shown) can be mounted alongside sensor 1 8 and laterally offset. This additional measuring sensor can be used to sense a datum surface 1 9 which may be away from the workpiece location. In this case both measuring sensors would be zeroed together over a datum surface before commencing machinning, and the operation would be similar to the system already described.

It will be appreciated that the above system enables workpieces to be measured dynamically while the machine tool is in operation, which operation is not terminated until the workpieces are of the desired thickness.

Claims

1. A dynamic measuring system for measuring a workpiece dimension whilst the workpieces are moving on a machine tool table, the system comprising a movable table, a machine tool positioned at one location above the table, a non-contact measuring sensor mounted on a vertical slide positioned above the table at a second location spaced from said first location, the sensor being able to detect or measure a dimension of a workpiece on the table as it passes under the sensor, and a sample and hold circuit operable to sample and hold a signal from the sensor indicative of the workpiece dimension and to hold this dimension constant by movement of the vertical slide.

2. The system of Claim 1, including a trigger sensor positioned at the second location and operable to cause an amplifier of the sample and hold circuit to sample the output of the non-contact measuring sensor and to maintain this distance substantially constant by virtue of the movement of the vertical slide and to cause an indicator to display the movement of the slide.

3. The system of Claim 2, including a summing amplifier for comparing a signal representative of the slide unit movement with a required dimension signal and operable to stop the machine tool when the slide movement signal and required dimension signal are equal.

4. The system of any one of the preceding Claims, wherein the required dimension signal represented by the movement of the slide is provided by a datum surface positioned on the table.

5. The system of Claim 4, including a second trigger sensor positioned at the second location and operable to cause a second amplifier of the sample and hold circuit to sample a second output of the non-contact measuring sensor as the datum surface passes underneath.

6. The system of Claim 5, including a second indicator to display the difference in output of the non-contact measuring sensor when measuring using the first and second trigger sensors.

7. A dynamic measuring system substantially as herein described with reference to the accompanying drawings.