Patent GB-830407-A (GB)
Title: Inductive control device
IPC: C01B17/12
Filed: 1956-04-26
Abstract: 830,407. Correspondence control transducers. CONTRAVES ITALIANA S.p.A. April 26, 1956 [May 3, 1955], No. 12870/56. Class 40 (1). [Also in Group XXXV] An inductive control device comprises a magnetic core having a central polepiece 12 and at least one pair of outer polepieces, the or each pair of outer polepieces being symmetrically disposed on each side of the central polepiece and aligned therewith, a primary winding 21 on the central polepiece, secondary windings on each outer polepiece, said secondary windings for the or each pair of outer polepieces being connected in series opposition and an armature 20 movable in relation to the polepieces by a control member 19, the armature, projecting in its central neutral position beyond each outer polepiece. The winding 21 on the central polepiece is fed from an A.C. source and for small movements of the control member the sensitivity of the device is low. As shown, the core is adjustable and has four outer polepieces 13, 13, (not shown), and 14, 14 and two sets of secondary windings 22, 22 (not shown), on the poles 13, 13 and 23, 23 on the poles 14, 14; the device can thus control two independent follow up systems, i.e. the azimuth and elevation control systems of an anti-aircraft gun. The armature 20 and control member are mounted for universal movement and the armature is of square shape in plan and its inner and outer faces are part-spherical in shape and have a common centre at the mounting centre so' that the armature is of uniform thickness, the surfaces of the polepieces are also part spherical in shape and concentric with the armature surfaces in the centrally-adjusted position of the core; movement of the control handle in alignment with one pair of polepieces does not therefore cause any voltage to be induced into the windings on the other pair of polepieces. The control member 19 is mounted by means of two pairs of bearings the axes of which are at right angles to each other and the control member is retained in its neutral position by providing a re-setting system for each axis of rotation each re-setting system comprises two stirrup members 24, 25 which are freely pivoted for rotation about the axis and which are urged together by a spring 28. An abutment 27 is attached to the frame which contains the core and armature and a second abutment 26 is fixed to the control member; thus movement of the control member moves one of the stirrup members and stresses the spring 28 since the other stirrup member is prevented from movement by the fixed abutment. Release of the control member causes the spring to return the control member to the neutral position. The core is made adjustable by being mounted on a ball-bearing 32 and its position is changed by means of four screws 33; this enables the air gaps between the armature and the outer polepieces to be made equal. The winding on the central polepiece is fed from an A.C. supply through a phase-shifting device consisting of a condenser and resistance, to compensate for the iron losses and bring the output voltage into phase with the supply voltage. Any residual voltage in the secondary windings at the neutral position of the control member is balanced out; for the in-phase component this is achieved by adjustment of the air gap but for the quadrature component this is achieved by feeding into the secondary windings a voltage of the same amplitude and opposite phase from a circuit connected to the supply voltage. Since the windings on opposite pairs of outer polepieces are connected in series opposition the voltages induced into these windings from the central winding oppose each other and movements of the control member from the neutral position which do not move the outer edge of the armature beyond the outer face of one of the polepieces will only produce a very small output voltage since such movement will only produce a very small change in the reluctances of the magnetic circuits linking the two windings with the central winding. Immediately however the edge of the armature passes the outer edge of one of the polepieces the difference in the reluctances of the two magnetic circuits is stated to increase rapidly and hence the output voltage similarly increases rapidly; thus the sensitivity is small for small movements of the control member and large for large movements. The sensitivities can be made different for the two pairs of outer polepieces by making the armature of rectangular shape instead of square shape, by varying the shape of the pairs of polepieces or by varying the number of turns in the windings. If desired the device can have only a single pair of outer polepieces in which case the faces of the armature and polepieces are part cylindrical in shape, and coaxial in the centrally-adjusted position of the core.