Patent GB-1431141-A (GB)
Title: Linear electromagnetic actuator
IPC: H02K7/065
Filed: 1974-02-13
Abstract: 1431141 Electromagnets; electromagnetic and electrostatic holding devices PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 13 Feb 1974 [2 March 1973] 6478/74 Heading H1P An electromagnet linear actuator comprises a magnetizable gapped ring 1, of e.g. soft iron with energizing winding 2 and pole faces 3, 31. Retaining elements comprising electromagnets 4, 5 are rigidly connected to the ring and have energizing windings 6, 7 whereby the electromagnets may be clamped on a guide rail 9 of, e.g. soft iron. In operation the electromagnet 5 is energized and clamped to the rail and winding 2 is energized so that magnetic forces between the pole faces 3, 3<SP>1</SP> deform the ring so that electromagnet 4 and drive rod 8 carried by the ring move leftward. Electromagnet 4 is energized and electromagnet 5 de-energized while winding 2 is de-energized so that electromagnet 5 moves leftward one step on release of the inter-polepiece forces. The stepping may be progressive and rightward stepping may be produced by energizing electromagnet 4 before electromagnet 5. The displacement per step is variable with the exciting current of coil 2 and the magnetizable ring may be rectangular. The ring may have inserts of elastic material, e.g. rubber therein with separate exciting polar windings (Fig. 2, not shown). The poles may be of L- shape with separate windings separated by a common elastic block (Fig. 3, not shown). In a modification to reduce any displacement of drive rod 8 normal to its longitudinal axis the magnet poles 41, 41<SP>1</SP> separated by gap 43 are secured to thin magnetizable plates 44, 45 magnetically interconnected by cross pieces 46, 47 and the poles are surrounded by winding 42 energizable to cause the poles to magnetically attract or repel each other along a straight line (Fig. 4). The magnetizable material may itself be made of elastic, e.g. by loading a synthetic plastic with magnetizable particles. Remanent magnetic forces and wear on the guide rail may be reduced by applying a non- magnetic wear resistant material (e.g. Cr, Ni or an organic plastic layer) to a surface thereof to furnish an artificial gap. The electromagnets retaining the guide rail may be replaced by electrostatic retaining elements. In application to apparatus (Fig. 5) for optically reading a record carrier disc 51 having plural concentric tracks or a continuous spiral track 60 rotated by shaft 52, a read beam 61, e.g. from a laser 54 is reflected on to the carrier by mirror 55 and focused to a spot by lens 56. The emergent read-out beam pulse modulated by the tracked and untracked portions of the record to convey information is focused by lens 57 and mirror 8 on radiation detector 59 producing electrical pulses therefrom. Radial motion of the scanning spot relatively to the record carrier is produced, e.g. by rotation of mirror 55 in response to predetermined electrical signals from a photo-electronic source, e.g. a detector on which an image of the tracked structure contiguous to the scanning spot is projected. Further movement of the scanning spot over the surface of the record carrier is also produced by movement of the entire reading head assembly 63 by the actuator described. Alternatively the disc and its rotary axis may be displaced relatively to the scanning head. The actuator may also displace a pick-up arm over a mechanically or magnetically recorded disc, or operate micromanipulators. The retaining electromagnets are replaceable by electrostructure elements whose length varies to clamp the guide rail in response to a central voltage.