| 摘要 |
<p>1,270,701. Control of D.C. motors. A. K. LITTWIN. 21 April, 1969 [1 May, 1968], No. 20240/69. Heading H2J. While a D.C. motor is dynamically braked from a high speed to a lower speed the supply is disconnected (to protect supply rectifiers from overvoltage); braking is terminated, and the supply re-connected, by means sensitive to the armature voltage during braking. The motor is a compound machine and the reduced speed is obtained by short circuiting a rheostat in series with the shunt field. A complete sequence of full speed-slow speed-full speed again is effected by programmed relays, and the means sensitive to the armature voltage comprises a relay winding connected across the armature and which is in opposition to another winding connected across the supply. While braking is taking place the supply is held disconnected by relays controlled by an electronic valve which is switched by the voltage on a chain of resistors across the armature. During acceleration a second valve is controlled by further resistors responsive to the motor current; if this becomes excessive the valve operates relays which short circuit the shunt field rheostat. This is thus inserted intermittently until full speed is reached. The circuit diagram (not shown) has many elements not relevant to the invention; they concern the operation of a grinding machine, which the motor drives, to grind and dress threads, but this is not fully described.</p> |
