Patent GB-1288449-A (GB)
IPC: G01C19/5691
Filed: 1970-10-01
Abstract: 1288449 Turn-sensitive devices GENERAL MOTORS CORP 1 Oct 1970 [6 Oct 1969] 46764/70 Heading H4D [Also in Division Gl] A device for detecting rotation about a predetermined axis comprises a high-Q resilient bell-shaped member having a centre region supported along said axis by a platform and having side regions depending over and encircling a post carried by the platform, a forcer for imparting first radial vibrations to the side regions, and a sensor located adjacent one of the nodal regions of the resulting radial vibration pattern for detecting second radial vibrations induced at the node (by Coriolis forces) as a result of rotation of the platform about the axis, at least one of the forcer and sensor being fixed to the post within the confines of the bell-shaped member. In the Fig. 1 embodiment the high-Q member is a bell 10 with a stem 16 adjustably supported on a platform 12 having a raised central post 24. A housing 80 is clamped to platform 12 by a ring 260. The first radial vibrations are maintained electrically by a feedback loop including (a) two diametrically opposed forcer electrodes 48, 56 (acting by electrostatic forces on the bell lip) resin-bonded in bores in platform 12 and disposed adjacent vibration anti-nodes, (b) two diametrically opposed sensor electrodes (responsive to changes of capacitance between the bell lip and each sensor electrode) similarly bonded in bores in housing 80 adjcaent vibration antinodes and (c) an oscillator circuit driving the forcer electrodes with a modulated D.C. voltage and synchronized by the sensor electrode outputs. The vibration amplitude is sensed by a level detector coupled to the sensor electrodes and is kept below a selectable maximum value by controlling the modulated D.C. voltage with a signal derived from the level detector. The second radial vibrations, indicative of rotation, are sensed by two diametrically opposed electrodes disposed in housing 80 adjacent the nodes of the first vibrations and provide a rotation-rate output which may be integrated to indicate rotation angle. A signal derived from the latter electrodes is applied with appropriate amplitude and phase to a further pair of forcer electrodes at the said nodes or other nodes of the first vibrations in order to null the second radial vibrations. Air damping of the bell vibrations is reduced by providing cut-outs 255 and 97 in the side walls of post 24 and housing 80, and by partially evacuating the housing and possibly back-filling it with helium. 0-rings 265 and 269 seal the housing while allowing relative angular adjustment of bell 10, platform 12 and housing 80 for optimum positioning of the various electrodes. Electrostatic shielding between the electrodes is provided by bell 10 and by guard sleeves 96, 256 partially surrounding each electrode. Details are given of a method of constructing the apparatus, comprising resinbonding the electrodes and sleeves in bores in material intended to form the platform 12 or housing 80 so that they are insulated from each other and from the bore walls, then machining off the material plus electrodes plus sleeves to conform to the contours of the bell lip.