An actuator driving circuit is provided for a positive feedback amplification, through an amplifier, of a counter electromotive force generated in a stator coil of a linear actuator, for continuating a reciprocating movement of a moving element by self-oscillation of the linear actuator, and for an application of a periodic voltage to the stator coil, while the voltage is made sinusoidal if required, so as to render the driving circuit to be high in the driving efficiency and small in dimensions.
A driving device for an oscillatory actuator in which a FLL (Frequency Locked Loop) is employed for detecting an electromotive force generated in a driving coil resulting from mechanical oscillation during a period in which no driving current is supplied to the oscillatory actuator, and for controlling an oscillation frequency on the basis of a relative time ratio between positive and negative polarities of the electromotive force to thereby pull a driving frequency into a neighborhood of a self-resonance frequency of the oscillatory actuator.
An apparatus for controlling an electromagnetic parts feeder comprises a vibrating unit provided with an electromagnet that vibrates at a predetermined frequency, a bowl adapted to discharge parts accommodated therein by means of the vibrating unit, a driving circuit for driving the electromagnet, and a control unit for outputting a driving signal to the driving circuit to cause a predetermined driving. The control is performed by idling the driving of the electromagnet temporarily at every predetermined driving cycles thereof and controlling the vibration of the electromagnet based on a signal obtained from a coil of the electromagnet by its electromagnetic induction during the idling period, for instance, based on a phase difference between a waveform of this signal and the driving signal of the driving circuit.
An improved self-oscillation system for a linear oscillatory actuator composed of a stator and a reciprocator. The stator carries a winding to which an electric current is periodically supplied for making a resonant oscillation of the reciprocator. The system includes a self-oscillation circuit for continuing the resonant oscillation of the actuator by a positive feedback manner based upon a back electromotive force (Vbemf) appearing across the winding. The system further includes a PWM control for increasing the electric current in response to a decreasing oscillation amplitude due to an increasing load applied to the reciprocator. A detector circuit is included to monitor the oscillation amplitude of the reciprocator and provides a corresponding detector output in response to which the self-oscillation circuit provides a drive pulse of varying pulse width for making the PWM control. The detector circuit is connected to monitor Vbemf of the winding in the absence of the electric current and to judge the instant oscillation amplitude of the reciprocator based upon the monitored Vbemf. Thus, the system can eliminate an external sensor, yet assuring the PMW control reliably based upon Vbemf correctly reflecting the actual oscillation of the reciprocator.
A drive apparatus for an electromagnetic drive type actuator, which includes a movable element, a fixed element, a connection element, a magnetic field generation element, and a drive coil, such that the movable element is caused to oscillate by an interaction between a current flowing through the drive coil and a magnetic field generated by the magnetic field generation element, comprises a drive signal supply element, which supplies to the drive coil a current signal with a periodic waveform that has a frequency substantially equal to a resonance frequency of the movable element and whose current value is zero in a fixed period in one cycle, and an oscillation detection element, which detects an oscillation state based on a timing of a zero-cross point of a voltage waveform between both ends of the drive coil in a period corresponding to the period in which the current value is zero.
A dual sided self-oscillation circuit for driving an oscillatory actuator with high efficiency and high response speed. The actuator has a winding to receive a periodical supply current from a power source and oscillates in a predetermined resonant frequency. The self-oscillation circuit includes a bandpass filter for receiving a back electromotive force voltage (Vbemf) developed across the winding and producing a sine wave output signal, a comparator for comparing the sine wave output signal with a threshold voltage and producing two drive pulses per cycle of the resonant frequency, and a switch connected in series with the winding to connect or disconnect the power source to the winding in response to the drive pulses, thereby flowing electric current in two directions at each cycle.
