Patent GB-1062783-A (GB)
Title: Means for monitoring the surface of an object
IPC: G01B7/28
Filed: 1965-01-28
Abstract: 1,062,783. Surface testing. F. MAYER. Jan.28, 1965, No.3839/65. Heading G1N. The shape and/or orientation of a surface 3, Fig. 1, rotating relatively to a probe 1, varies the capacitance between the surface and the probe, and an amplifier 9 supplies a transformer 10 with a signal the amplitude of which depends upon the capacity; two of the transformer secondaries are connected to two synchronous rectifier circuits 12X, 12Y, the reference signals 31X, 31Y for which are in synchronism with the rotation and are relatively displaced by 90 degrees; and a third transformer secondary winding 14 supplies a signal proportional to the capacitance variation to the rotor winding 32 of a rotary transformer of which the rotor rotates at the speed of the surface, and of which the two 90 degrees spaced secondary windings consequently give signals representing variations in the surface in two orthogonal directions. The outputs of the two stator windings 33X, 33Y are respectively added to a manually adjustable fraction of the output of the reference signal generators 31X, 31Y, and applied at 36X, 36Y to orthogonal plates of an oscilloscope in order to trace the actual shape of the surface. The outputs of the synchronous rectifier circuits 12X, 12Y are averaged at 13X, 13Y and used to operate meters 15X, 15Y, which may indicate for example the displacement in two orthogonal directions of the axis of a disc, of which the edge is the test surface, from the axis of rotation, or the angular deviation of the perpendicular axis of the flat face of a disc from its axis of rotation. The outputs 36X, 36Y, may respectively be combined with the meter signals 15X, 15Y to indicate simultaneously on the oscilloscope the shape of the surface and the eccentricity thereof Fig. 2 (not shown). The orientation of the axis of a bore hole (3A, Fig. 4, not shown) relative to the axis of rotation of two spaced rotating probes (1<SP>1</SP>, 1<SP>2</SP>) is determined by subtracting the outputs of the X-direction averaging synchronous rectifier circuits associated respectively with the two probes, and similarly for the Y circuits. The angular position of dynamic unbalance of a rotating body may be determined using a refinement of the arrangement of Fig. 1 wherein Fig. 5 (not shown) the two average outputs from the X and Y synchronous detectors are fed respectively to each of the two-phase windings of a resultant field indicating device (59). The surface of a body (3, Fig. 6, not shown) may be oriented in required mutually orthogonal X, Y, and Z directions by rotating the probe (1) in the X-Y plane and about the Z axis over a portion of the surface, and using the X and Y synchronous detector outputs to indicate the displacement of the surface from the plane containing the X and Y axes; and by further determining the angular displacement of the surface about the Z axis by comparing (at 63) pulses generated as the probe passes over studs (G1<SP>1</SP>, G1<SP>2</SP>, G1<SP>3</SP>, G1<SP>4</SP>) arranged on orthogonal axes in the surface, with pulses generated (at 62) as the rotational reference signal (31Y) passes through zero, a meter (64) giving a maximum reading when alignment is complete. In a curve-following device Fig. 7 (not shown), the probe (1) rotates in the vicinity of the curve (3), and the output of each synchronous detector (13X, not shown, and 13Y) is compared (at 72), with a signal, (from 70), representing a given distance between the curve and the probe, any error signal being used to drive a motor (66), to reposition the probe in each of the X and Y directions. A cosine potentiometer (71), is included to improve the accuracy of the device.