Electricity: motive power systems – Positional servo systems
Patent
1991-05-24
1993-07-06
Ip, Paul
Electricity: motive power systems
Positional servo systems
318800, 318808, 318803, 187119, 187114, H02P 540, B66B 130, H03K 1700
Patent
active
052257541
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a control system for a motor and, in particular, to a synchronous servo motor controller for controlling a synchronous servo motor used to raise and lower lift cars in a lift well.
The invention in a first aspect may be said to reside in a controller for a motor for raising and lowering a lift car in a lift well, said controller comprising drive circuit means for providing power to said motor,
first processing means for receiving data relating to the state of said motor and for processing that data, second processor means for receiving information from said drive means concerning the state of said drive means and for processing that information and main processing means for receiving information from the first and second processing means and for analyzing the information provided by the first and second processing means and controlling said drive circuit and/or said motor in accordance with that information.
Preferably the drive means includes a plurality of transistor bridge circuits.
Preferably the first processor means comprises switch means for passing one of a plurality of signals containing data relating to the state of said transistor bridge circuits to an analog to digital converter for converting analog signals to digital signals and providing said digital signals to said main processor, a polar conversion circuit for receiving said signals from said transfer bridge circuits and for converting the signals into signals having a magnitude and a phase component and an overcurrent sensor for sensing whether the current supplied by the transistor bridge circuits is too high, said overcurrent and sensor circuit being coupled to a pulse modulator circuit for controlling the pulse width of the signal applied to the transistors in said transistor bridge circuits.
Preferably the second processing circuit comprises a multiplexer arrangement for receiving data relating to the status of said motor or the power supplied by said drive circuit and for converting streams of parallel data signals into a serial stream of data signal and then reconstructing the original parallel data signals for application to said main processing means.
Preferably the main processing means comprises a central processor coupled to a control circuit which ensures that the central processor operates correctly.
The invention also provides a circuit to convert from rectangular to polar co-ordinates for use in a controller to control a motor for raising and lowering a lift car, said circuit comprising at least two inputs for receiving signals indicative of the angular position of currents and/or voltages applied to said motor, or of the angular position of a motor shaft, circuit means for comparing said two signals for performing arithmetic operations upon said signals based upon said comparison to convert the signals to polar signals having a magnitude and a phase component.
The conversion of the signals from rectangular co-ordinates to polar co-ordinates decreases the amount of time consumed by the main processor during input signal processing and also assists in scaling of the values to be processed by the processor.
Preferably, the comparing circuit determines which is the greater of the modules of the two input signals and converts the input signals into a single current vector in polar co-ordinates which have said magnitude and said phase components and expresses said phase component as an inverse tangent of the quotient of the two input signals by dividing the smaller of the input signals by the larger of the signals.
Another aspect of the invention concerns isolating signals representing voltages produced by the drive circuit and applied to the motor from the processing circuitry in the controller. Although the controller is mainly concerned with difference between voltages, the absolute voltages which are involved are high and could damage the processing circuitry if applied directly to the processing circuitry.
The present invention therefore also includes an isolator for use in a control circuit for co
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Boral Johns Perry Industries Pty. Ltd.
Ip Paul
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