Abstract: A metrological instrument includes an inductive transducer having a stylus, all being disposed within a protective housing. Upon initiation of the measuring operation, the transducer is moved so that the stylus moves round an endless path such that the stylus is first projected at a high speed from the housing, is thereafter moved to engage the workpiece surface, is then moved at relatively slow speed across the workpiece surface for performing the measurements, and, following completion of the latter movement, is retracted at a high speed into the housing. These movements are effected by a series of cams driven by a single motor. Such an instrument may be located next to a production line without risk of damage and may used for the checking of each of a multiplicity of identical components produced in a mass production process.

Abstract: In a position encoder an interpolator derives from quadrature input signals a series of sine waves equispaced in phase. These are applied to respective comparators which output a binary zero or a binary one according to whether the respective sine wave is above or below the zero crossing point. Interpolation is achieved by identifying an adjacent pair of said sine waves of which one has a value above and the other a value below zero and a counter stores a number indicative of this pair of signals.

Abstract: Metrological apparatus, particularly for measuring form, has a turntable 4 and a transducer 14 and associated stylus 12 mounted so that the tip 12a of the stylus is displaceable radially and vertically relative to the turntable 4. The problem of obtaining both high resolution and large range of operation is solved by using a transducer/stylus 12,14 having a resolution of 12 nanometers and a range of only 0.4 mm and mounting the transducer 14 on an arm 10 which is driven radially and/or vertically by a computer 30 in response to the output from the transducer 14 to cause the stylus 12 to follow the workpiece surface. High resolution data defining the rotary position of the turntable 4 and the radial and vertical position of the transducer 14 is provided by a photodetector/optical grating arrangement 23, 21, 31; 27, 19, 43 and associated interpolators 42, 44, 46.

Abstract: Apparatus for measuring velocity utilizes quadrature input signals provided by a transducer and divides the derivative of one of the signals by the magnitude of the other to obtain a measure of velocity. The apparatus may be digital or analog. It is particularly suitable for the measurement of velocity where the quadrature signals are provided by an optical grating and transducer arrangement.

Abstract: In a metrological or other sensitive apparatus, the transducer or other operative member (22) is mounted on a support structure (14 to 18) which is carried on a chassis (2) by a first set of dampers or isolating means (10) and the chassis (2) is mounted on the floor by a second set of dampers or isolating means (6). The two sets (10, 6) have different natural frequencies and the first set (10) is arranged so that any vibration of the support structure tends to be rotational centered in the zone of operation (21) of the transducer or other member. This is achieved by arranging that the stiffness of the first set of dampers (10) is higher in the direction (24) passing through the zone of operation (21) than in the transverse direction.

Abstract: A bearing structure, preferably for supporting a rotary table (4) in metrological apparatus, includes both a journal bearing (34,36,38) and a thrust bearing (56,66). The journal bearing is made up of three dry pads (34,36,38), one (38) of which is radially adjustable, and the thrust bearing (56,66) comprises first and second air bearings. The axis of rotation of the bearing is vertical, and the lower (66) of the air bearings is less stiff than the upper one (56).

Abstract: To measure distances, light from a flash tube is plane polarized by a polarizing filter, then polarization modulated by an electro-optical crystal, then passed along a `wobbling` light path, then subjected to a relative retardation of about a quarter wavelength by a rhomb and then passed through a calibrated variable light path before being projected to a distant target reflector. The reflected light returns along the same path and is detected by a photomultiplier after passing through the polarizing filter. Adjustment of the variable light path until a null is obtained at the photomultiplier indicates that the length travelled by the light from the crystal to the reflector and back is an integral number of modulation wavelengths, possibly plus one half-wavelength. The quality of the null is adjustable by adjusting the orientation of the rhomb. Temperature correction may be provided by constructing a reference resonator defining the modulation wavelength of the same material as a structure being measured.

Abstract: Metrological apparatus is provided with a turntable (4) which is movable horizontally and pivotally for centering and levelling. The turntable (4) is supported at three points (A,B,P), one (P) of which is fixed and the other two (A,B) of which are vertically movable by motorized jacks. Centering and levelling is achieved automatically by means of a computer (72) which calculates the required horizontal and pivotal movements of the turntable (4) from data obtained by sensing the workpiece surface with a transducer (12).