Patent GB-1021336-A (GB)
Abstract: 1,021,336. Measuring dimensions electrically. LABORATOIRE D'ELECTRONIQUE ET D'AUTOMATIQUE DAUPHINOIS-L.E.A.D. July 1,1963 [July 3, 1962], No. 26041/63. Heading G1N. Variations in the distance between at least one object 2 and a rotary member, using a probe 1 mounted on the object or member, are monitored by combining a measuring signal from the probe with a selected one of a plurality of reference signals each having a different waveform. The probe may be magnetic and in Fig. 1 rotates about an axis OZ. The measuring signal is applied to a transformer primary 5, having two secondary windings 7, 8 associated with it and connected in respective X and Y synchronous detector circuits DSX, DSY. Each includes an RC circuit so that an indicator connected to SX or SY indicates the average current. Rotating with the probe is a two phase alternator 20 with a permanent magnet rotor. The sinusoidal reference signals generated are 90 degrees out of phase with each other,and are in phase with the passage of probe 1 past axes OX and OY. These signals S1, C1 are fed directly to contacts I of selectors KX, KY. The reference signals are also applied to Schmitt trigger circuits BX, BY which supply square waves S2, C2 to contacts II. The square waves are also differentiated at DX, DY and the pulses S3, C3 produced control monostable multivibrators MX, MY. The pulses S4 from MX are fed to contact III of selector KY and those, C4, from MY to contact III of KX. The selectors are connected to the synchronous detectors. Reference signals S4, C4 cause the indicators at SX and SY to indicate the distance between object and probe only when the probe is aligned with OX and OY. S2 and C2 allow the average value of distance d to be registered while the probe traverses an arc of 180‹ symmetrical with OY and OX, respectively. Reference signals S1 and C1 have a similar effect, except that more weight is given to signals corresponding to the direction of one or other axis OX, OY. Other reference signal waveforms are suggested, including a pulse waveform at an integral multiple or fraction (e.g. a half) of the probe rotation frequency,or pulses at 120 degree intervals If the object 2 has irregularities such as depressions or projections a reference signal having zero amplitude at angles corresponding to the irregularities may be used. The reference signals may be produced photo-electrically and detectors DSX, DSY may comprise triodes or transistors, and the transformer may be replaced by symmetrical amplifier stages. A face 31 of an object 32 may be aligned with the direction of movement of a table on which it is mounted, by means of a probe 33 in conjunction with a pulsed reference signal. A plate 34 may be provided at a known distance from the probe to provide a reference amplitude, or a voltage equal in amplitude but opposite in polarity to the average measuring signal may be injected into the system. The probe may be made to follow the contour of a workpiece at a fixed distance by mounting the probe on a support driven by two motors fed with X and Y outputs. A shaft may be centred in a square hole or between four parallel rods by mounting the probe for rotation about the shaft. In the former case reference signals S2, C2 are used, and in the latter case S4, C4. An object may also be centred for a machining operation (Fig. 5 not shown). The probe is fixed and the rotatable object is mounted in resilient bearings. The sinusoidal reference signals are used, their ratio giving the angular position of the unbalance.