GB1458210A - Determining accuracy of form of surfaces - Google Patents

Abstract

1458210 Measurement of surfaces electrically RANK ORGANISATION Ltd 4 Dec 1974 [19 Dec 1973] 58701/73 Heading GIN The accuracy of form of a workpiece surface 18 may be determined by means of a sensing head 11 in the form of an array of elements which are electrically insulated from one another, a circuit being provided for determining the capacitance or inductance between the surface 18 and each element to produce, when sequentially coupled to each element, a plurality of signals representative thereof. The elements are shaped and arranged so as to substantially lie in a surface which represents at least part of the desired form of surface 18. As described, the circuit includes an oscillator 23 for applying an oscillating electric signal to the workpiece, a switch unit 19 for sequentially switching each element into the circuit, and a measuring unit 20 for producing an analogue output signal representative of the inductance or capacitance. A digital computer 25 may also be provided to store the received signals and to produce control signals to actuate the switch means. Each element may be fixed so that one face of each thereof define together a cylindrical surface for determining the accuracy of a cylindrical hole, as shown, or an external cylindrical surface, or define a planar surface for checking a planar surface. Alternatively, each element may be mounted on a member 34, Figure 3, resiliently biased so that a range of workpiece diameters may be accommodated by a single sensor head. A reference surface may also be provided too so as to allow comparison of the measured signals therewith.