Patent GB-601241-A (GB)
Title: Improvements in electric couplings control apparatus
IPC: H02P29/00
Filed: 1946-01-08
Abstract: 601,241. Automatic control systems for clutches. WINTHER, M. P. Jan. 8, 1946, No. 655. Convention date, Jan. 26, 1944. [Class 38 (iv)] [Also in Group XIX] An electric clutch and brake are controlled by means responsive to the speed of an associated driven shaft. In the embodiment shown, the grinding-wheel W is mounted on shaft SH and driven from motor M through eddy-current clutch C in which the flux generated in coil L on polar member F interlinks with armature A. Rotor RO-2 of brake BR is mounted on shaft SH and rotates in the magnetic field produced by coil B in fixed polar member ST. Winding L is energized through slip-rings SR and the output of permanent magnet generator GN is responsive to the shaft speed. The grid-controlled gas-discharge rectifier valves 3 and 1 supply, respectively, the clutch winding L and brake winding B in conjunction with separate phase windings of a mains transformer. To energize the clutch winding and thereby to commence rotation of the driven shaft, the arm PA of potentiometer PT is rotated clockwise from point T-16 to point T-17. With arm PA at T-16 the grid G-4 of triode valve 5b is negative relative to the cathode K-2 and the potential of point T-5 is raised due to the absence of or very small valve current. The potential of point T-6 is fixed relative to that of the lines W-6, W-11, resulting in the potential of line W-10 being now above that of line W-9, and grids G-1 and G-2 of valves 3 and 1 are biassed negatively and positively respectively. Full brake excitation and minimum clutch excitation are thereby produced. As arm PA is rotated clockwise, the potential of grid G-4 rises and the consequent increase in anode current flow lowers the potential of point T-5 relative to that of point T-6. A reversal of the bias conditions at grids G-1 and G-2 occurs as arm PA is rotated to point T-17 and excitation is transferred from the brake to the clutch. The consequent rotation of shaft SH causes generator GN to produce a voltage which is rectified by double diode 7 and applied as a negative bias to grid G-4 of valve 5b in opposition to the positive potential from arm PA, the position of which sets the speed of shaft SH. Fluctuations in the speed of shaft SH above or below the datum, due to variations in load are reflected in the output from rectifier valve 7 and ultimately in the relative magnitudes of the excitations of windings L and B which are rapidly adjusted to render the fluctuations substantially zero. At low speeds of shaft SH, instability of the governing circuit may be produced by the lightness of the load and this is prevented by the application of an artificial load through the brake. With arm PA turned to a low-speed setting, the grid G-3 of valve 5a is sufficiently positive to permit current flow. This lowers the potential of cathode K-6 of valve 1 which conducts and causes energization of the brake windings. In the complete circuit (not shown) valves 1, 3 are respectively connected in parallel with diode gas-discharge valves which improve the wave-form of the current through windings L, B and relieve the circuit of high inductive voltages. Valves 5a, 5b are combined in one envelope and a coldcathode valve is employed in parallel with potentiometer PT as a voltage stabilizer. In a modification (not shown), the speed of transfer of excitation between the coils L and B is raised by the insertion of a common resistor in series with both. In a further embodiment (not shown), comprising a combined absorbing and motoring dynamometer, the excitations of the fields of the parts are controlled manually to enable the friction losses of a prime-mover under test to be estimated immediately following a load test.