GB1282579A - Angular velocity sensors - Google Patents

Abstract

1282579 Measuring angular velocity electrically HONEYWELL Inc 12 Dec 1969 [19 Dec 1968] 60711/69 Heading G1N An arrangement for measuring angular velocity about an axis (axis 1) comprises an accelerometer sensitive to angular acceleration about an axis (axis 11) and means for moving, e.g. oscillating or rotating, the accelerometer so that the angle between the two axes varies whereby the accelerometer gives an output dependent on the angular velocity about axis 1. Consider an accelerometer, shown as a disc 7, sensitive to acceleration about an axis 11 perpendicular to the disc. Now consider rotation about an axis in space 1 at a constant angular velocity w m , which it is desired to measure. In the position shown in Fig. 1A the accelerometer would give no output since w m is constant. Now consider rotation of the disc about an axis 10 at some angular velocity w, say 8000r.p.m. The disc rotates through the positions shown in Fig. 1B, 1C, 1D. In Fig.1C the "heads" side of the disc is now lowermost instead of uppermost as in 1A. The rotation w m is now anti-clockwise with respect to this "heads" side i. e. to the sensitive axis 11, instead of clockwise in Fig. 1A. The change in rotation indicates that the accelerometer has been subject to acceleration about the axis 11, and it will therefore yield an output as the disc rotates. 'This output therefore has a sinusoidal form, Fig. 1E, whose frequency depends on the rotational velocity and whose maximum amplitude depends on the rotational velocity w m . It will be clear that the axis M about which angular velocity is to be measured could lie along the direction 2 instead of the direction 1, or indeed in any direction in the plane of 1 and 2 since these are all scanned by the axis 11 during rotation about 10. Similarly since any other direction can be resolved into one input in this plane and one component in the direction 10, it is possible to obtain a measure of angular velocity about any axis except direction 10. The accelerometer which is shown in Fig.2 functions on the principle of an MHD generator. A radially magnetized annular magnet 22 produces flux which passes radially through an annulus of mercury 25 in a casing, and returns through ferromagnetic slugs 22. Movement of the mercury develops an emf resulting in a current which links a toroidal pick-up coil 19 in which the associated output current is developed. The casing has a projection 31 on which is mounted the rotor 30 of an induction motor which rotates the casing about the axis 10. In operation acceleration about the axis 11 will cause the magnet to rotate while under idealized conditions (such as arise when the rotational speed w r is above 1000r.p.m.) the mercury remains stationary in its plane. An output of sinusoidal form is thereby obtained whose maximum amplitude is a measure of the angular velocity about an axis within the plane of 1 and 2. A demodulating arrangement is provided to extract from this output signal components representative of the components of this velocity about the axes 1 and 2. As shown a pair of coils 33 aligned parallel with the axis 1 and a second pair (not shown) as right angles thereto are influenced by a permanent magnet on the projection 31. The output signals are fed, together with the output from coil 20 to demodulators 41, 42, to provide outputs indicative of the two components on calibrated meters 3, 4. If the mercury cannot be considered as stationary i.e. if the rotational speed w, is less than say 1000 r. p. m. the output voltage is not directly proportional to the angular velocity being measured and correction must be made for the rotational speed w,. A further form of accelerometer is disclosed, Figs. 4 and 5 (not shown) in which an annulus of mercury is again provided but the arrangement of magnets and pick-up coils is different.