Abstract: A variable motor speed control arrangement of the tachogenerator feedback loop type comprises a triac (5) connected in series with the motor (M). The triac is fired in each half cycle of the AC mains supply. The firing angle of the triac is varied to provide the required control. The arrangement employs a single cycling counter (CT) to time the interval between two output pulses of the tachogenerator (T) in order to determine the current motor speed and also to provide a count-down from the beginning of each half cycle to the required firing instant. The control processes are carried out in periods beginning at each counter overflow instant. This breaking up of the processing, together with the use of the single counter allows a microcomputer (1), which is running other programs to provide the speed control in addition.

Abstract: A duplex copying apparatus is provided in the space therebelow with a duplex copying auxiliary means for returning a sheet having an original copied thereon to a sheet feed path extending from a sheet discharge station of the copying apparatus to an image formation station of the apparatus. A support unit for exclusive use in the copying apparatus is detachably provided with a copied sheet return station of the duplex copying auxiliary means.

Abstract: A counter (24) increments several times during the duty cycle of a microprocessor (10), and a comparator (30) connected to both outputs a High signal when the microprocessor output exceeds the counter output and outputs a Low signal when the counter output is at least the microprocessor output. The microprocessor output is proportional to desired motor speed for an elevator door drive motor according to a velocity profile stored in a ROM (18). Thereby, the High:Low ratio of the comparator output is a pulse width modulation signal, which is amplified (34) for the motor (12), at a much higher frequency than the microprocessor duty cycle.

Abstract: In a motor control system for a DC motor, a modulation circuit provides a plurality of pulse width modulated signals to control the current applied to the motor. The motor is coupled to a current sensing resistor and a plurality of switches responsive to the pulse width modulated control signals. The output of the current sensing resistor is summed with an input current command to provide an error signal. A modulation circuit which includes a waveform generator generates a plurality of interposed triangular waves adjustably offset by a predetermined amount. The triangular waves are compared to the error signal to provide pulse width modulated control signals which cause a "dither" current to be applied to the motor when there is substantially no input command and currents having substantially decreasing form factors to be applied as the input command increases.

Abstract: Emergency braking device for a brushless motor comprising damping means connected through a switch to the windings of the brushless motor in case of emergency to dissipate the energy stored in the inductance of the windings of the brushless motor. The impedance characteristics of the damper means are optimized by selecting a capacitance which has a predetermined relationship to the inductance of the motor winding.