GB2187289A

GB2187289A - Determining charactistic of a curved surface

Info

Publication number: GB2187289A
Application number: GB08704628A
Authority: GB
Inventors: Rudolf Diem
Original assignee: SKF GmbH
Current assignee: SKF GmbH
Priority date: 1986-03-01
Filing date: 1987-02-27
Publication date: 1987-09-03
Also published as: GB8704628D0; FR2595138A1; SE8700756D0; IT8719424A0; SE8700756L; DE3606725A1

Abstract

A measuring instrument for determining diametral values on a stationary machine part 10 is provided with at least three pairs of linear measuring sensors 11, 12 and 13 which measure the diameter at three angularly spaced locations on the circumference. A device connected thereto selects and calculates characteristic values, such as the maximum, mean, and minimum diameters and the out of roundness of the machine part. The instrument may be arranged to measure internal diameters. <IMAGE>

Description

SPECIFICATION Determining characteristic values of the curved surface of a machine part The invention relates to a method of and apparatus for determining the characteristic values of the curved surface of a machine part.

For the measurement of curved surfaces and recesses such as the cylindrical outer surface and bore of a machine part there are used, among other things, linear measuring sensors which are disposed radially at the required location of a machine part and indicate the diameter of the machine part. In this case the machine part is situated within a prismatic device which forms the support and the reference position for the linear measuring sensor.

If such a support for the machine part cannot be provided, two diametrically opposed linear measuring sensors are used, as disclosed by DE patent specification No.

902,556, in which by way of a device the sum of the starting signals is formed, which represents a value proportional to the diameter of the machine part. In this case, within predetermined limits, the radial position of the machine part in relation to the linear measuring sensors no longer enters into the measurement result. A method of this type is suitable not only for the outer surfaces but also to the same extent for measuring bore surfaces. If further characteristic values of the machine part, for example out of roundness, minimum and maximum diameters and the like, are to be measured the machine part, for example, has to be rotated relative to the linear measuring sensors. In a device for evaluating diametral values in this case the maximum and minimum values have to be stored.Subsequently, the necessary characteristic values can be calculated or deduced therefrom and displayed. Both the rotation of the machine part and the necessary storage of the measured values necessitate a laborious and expensive mode of operation which entails serious disadvantages, particularly in respect of measurement in series production. If relatively small machine parts occurring in large batches are to be measured, the automatic measurement frequently reaches the limit of its capacity and can thereby substantially affect the rate of production. Moreover, the drive necessitates complicated handling of the machine parts and this, together with the rotary sensing of the measured values, can result in surface damage.

A method according to the invention involves simultaneously measuring the diameter at at least three angularly spaced locations lying in a common diametral plane while the machine part is stationary. For this purpose an apparatus can be used comprising a fixture for receiving the machine part, a measuring instrument co-operating therewith and a device for calculating the characteristic values, the measuring instrument having three angularly spaced pairs of diametrically opposed linear measuring sensors in a summation circuit.

The diameter of the machine part is measured, for example, at three angularly spaced locations and simultaneously the readings are fed into the device for calculating the characteristic values. These three measurements take place simultaneously and while the machine part is completely stationary, so that its surface cannot be damaged even under a high measuring load originating from the linear measuring sensors. Moreover, the tips of the linear measuring sensors are also protected.The determination of the diametral values at the indicated three locations on the machine part is generally sufficient to provide an individually reconstructible diametral value, the latter being formed as an arithmetic average of the three measured values and thus providing the mean diameter of the machine part in this plane.If further characteristic values of the machine part are to be calculated, for example out of roundness, only the iargest and smallest of the three diametral values has to be selected for example. The difference in the two extreme values is thus representative of the out of roundness of the machine part.

All the indicated characteristic values can be calculated and displayed in the device without being stored. Accordingly, all the characteristic values are quickly available after introducing the machine part and applying the measuring instrument. Furthermore, in an automatically operating apparatus, all the control functions in respect of the drive for the machine part are dispensed with, which enables a considerably more rapid measuring operation to be achieved. Inner and outer cylindrical surfaces can be measured. Where necessary, the accuracy of determination of the measured values can be improved by increasing the number of pairs of linear measuring sensors. Moreover, by moving the measuring instrument into another diametral plane of the machine part, additional characteristic values, such as degree of taper, convexity and so on can be determined or calculated and displayed.Of course, advantages can be gained in sorting or classifying machine parts with cylindrical surfaces.

Preferably the device has a circuit for comparing the deviation in the diametral values from one another in relation to a reference value. In this case a datum or limit value is fed into the device as a reference, which value is higher than the expected variations in the diametral values, which provide an indication of the out of roundness. This enables machine parts, having a defective surface, to be readily selected and for any accumulation of dirt between the linear measuring sensors or other defects in the measuring system to be indicated.

In the accompanying drawings: Figure 1 is a partial cross-section through a measuring instrument with three pairs of linear measuring sensors; and Figure 2 is a block diagram of a device for calculating characteristic values of a machine part measured in accordance with Fig. 1.

Fig. 1 shows a measuring instrument for determining three diametral values of the circumferential surface of a stationary cylindrical machine part 10 in a radial plane. The measuring implement is provided with three diametrically opposed pairs 11, 12 and 13 of known electric linear measuring sensors which are uniformly angularly spaced apart on the periphery and which are connected respectively to an electronic device illustrated in Fig. 2. Each of the three pairs 11, 12, 13 of linear measuring sensors is connected to a respective matching amplifier 14 in a summation circuit so that the actual diameter is measured, irrespective of the relative position of the machine part 10 in relation to the measuring instrument.The output signals from the matching amplifiers 14 are then fed into an analyser 15 which from the three diametral values selects the maximum value Dmax and the minimum value Drain and then feeds these two values, separately from the third diametral value, to a differential amplifier 16. These two values Dmax and Dm,n are then displayed on units 17 and 18. In addition, the analyser 15 derives from the three diametral values the arithmetic average which appears as a mean diameter Dm on an individual display unit 19.The differential amplifier 16 calculates the difference between the maximum diametral value Dniax and the minimum diametral value Admin. This differential value, which is displayed on a fourth unit 20 is in indication of the out of roundness of the machine part 10. The analyser incorporates a further detector stage which derives the relative variation in the diametral values from one another and compares it with a set limit or reference value. When this limit value is exceeded, a fault indication is displayed on a fifth display unit 21. This adduitional facility selects machine parts 10 which have surface damage, which have an extremely wide variation in diametral values, and/or if dirt particles are present between the linear measuring feelers 11, 12 and 13 and the surface of the machine part 10 and/or if a defect occurs at any point in the measuring system.

Of course, the diametral values may also be determined with other types of sensors or detectors for linear measurement values and further computer controlled characteristic values of the machine part can be determined, calculated or statistically evaluated. This is particularly associated with the additional sequential or parallel measurement of further diametral planes of the machine part or with an increase in the number of the pairs of linear measuring sensors so as to afford even greater accuracy.

The method can be applied in like manner to bore diameters.

Claims

1. A method of determining characteristic values of the curved surface of a machine part, such as out of roundness and maximum, mean and minimum diameters, derived from diametral values of a cylindrical surface of the machine part, by measuring the diameter at a plurality of locations and subsequently calculating and further processing the characteristic values, the method including simultaneously measuring the diameter at at least three angularly spaced locations lying in a common diametral plane while the machine part is stationary.

2. A method substantially as herein described with reference to and as shown in the accompanying drawings.

3. An apparatus for carrying out the method as claimed in Claim 1 or 2, comprising a fixture for receiving the machine part, a measuring instrument co-operating therewith and a device for calculating the characteristic values, wherein the measuring instrument has three angularly spaced pairs of diametrically opposed linear measuring sensors in a summation circuit.

4. An apparatus as claimed in Claim 3, wherein the relative axial position of the machine part in relation to the measuring instrument is adjustable.

5. An apparatus as claimed in Claim 3 or 4, wherein the device has a circuit for comparing the deviation in the diametral values from one another in relation to a reference value.

6. Apparatus substantially as herein described with reference to and as shown in the accompanying drawings.