Low vibration pulse drive device for an electric motor

A switching control circuit for an electric motor having a start-up phase and a subsequent running state comprising, a pair of input terminals for connection to a source of voltage, an output terminal for connection to the motor, and a control device coupling at least one input terminal to the output terminal and comprising, first and second controlled switching devices for selectively coupling at least said one input terminal to the output terminal to produce a drive signal for the motor during the motor running state having a waveform with at least one edge that varies stepwise from a first level to a second level at a first instant of time and varies stepwise to a third level at a second instant of time with said second level being intermediate in value said first and third levels, and means for controlling the operation of said first and second switching devices so that the time interval between the first and second time instants is approximately equal to half a period of a mechanical resonance vibration which otherwise would be produced in the motor drive if said drive signal varied stepwise from the first to the third level.

A pulsed drive device for an electric motor having a start-up phase and a subsequent running state comprising, a pair of input terminals for connection to a source of supply voltage, means coupled between the input terminals and the motor for deriving a drive signal during the running state of the motor, said drive signal comprising a sequence of pulses at least some of which have at least one edge that varies substantially stepwise from a first level to a second level at a first time instant and that varies substantially stepwise to a third level at a second time instant, said second level being intermediate in value between the first and third level, and means for setting the time interval between the first and the second time instants to a value so as to compensate at least one mechanical resonance vibration produced by the motor drive.

A method of driving an electric motor having a start-up phase and a subsequent running state wherein a switching device is coupled between a source of supply voltage and an input terminal of the motor, the method comprising:

• operating said switching device during the running state of the motor so as to apply a drive signal to the motor input terminal having a waveform with a leading edge that varies stepwise from a first level to a second level at a first instant of time, and then operating the switching device to vary the leading edge of the waveform from the second level to a third level at a second instant of time and with said second level being intermediate in amplitude said first and third levels, the time interval between the first and second time instants being approximately equal to half a period of mechanical resonance vibration of the motor drive otherwise produced by a stepwise variation of the drive signal waveform.