GB1082877A - Improvements in or relating to controlled velocity drives - Google Patents

Abstract

1, 082, 877. Automatic speed control. HEENAN and FROUDE Ltd. April 6, 1965 [May 6, 1964], No. 14569/65. Heading G3R. In a system for maintaining constant the speed of a shaft driven through an electromagnetic coupling, the energization of the coupling is automatically controlled by means of a switching device operated in dependence on the difference between the actual and desired speeds of the shaft and the integral of the difference. As described, the speed of a shaft driven through an eddy-current clutch is measured by a tachometer alternator the output of which is rectified and compared with an adjustable reference voltage. Any difference, representing a speed error, is applied through a transistor amplifier to control the charging rate of a capacitor associated with a trigger circuit so that the mark-space ratio of the trigger circuit output is varied. This output is applied to control a half-wave or fullwave silicon-controlled rectifier energizing the clutch winding so that the speed of the shaft is corrected. The error signal is also applied through an integrator circuit formed by an amplifier having capacitative feedback to provide an additional, integral, component of control for the trigger circuit. A second transistor amplifier, matched to the first and sharing a common heat sink, cancels the effect of temperature variations. Temperature compensation, limiting, filtering, smoothing and protection is also provided elsewhere in the circuit. Adjustable potentiometers are provided for setting maximum and minimum speed limits. A push button switch may be operated in one manner to actuate a relay energizing the clutch momentarily through the silicon-controlled rectifier to inch the shaft or may be operated in a different manner to make the relay self-holding so that the speed control system is operative until a stop button is operated.