Electricity: motive power systems – Open-loop stepping motor control systems
Patent
1983-09-28
1986-05-06
Shoop, Jr., William M.
Electricity: motive power systems
Open-loop stepping motor control systems
318685, H02K 2904
Patent
active
045874735
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a stepper motor control circuit.
In known stepper motor control circuits, control of the current by means of a chopper operating at a frequency an order of magnitude higher than the maximum stepping rate has already been proposed. The circuits employed in the prior art have, however, been extremely complex and have usually employed output stages containing a large number of high power semi-conductor components.
In addition, although the problem of shock loading of the rotor by the stepping pulses to it has been considered previously, no completely satisfactory solution has been proposed.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention a stepper motor control circuit comprises a waveform generator circuit arranged to generate a pair of substantially stepless symmetrical periodic waveforms of constant amplitude and of frequency determined by a variable step rate demand signal received thereby, the waveforms being 90.degree. out of phase, a pair of pulse width modulation circuits arranged to drive the motor windings, each modulation circuit receiving one waveform as a current demand signal and a feedback signal related to the instantaneous current in the associated one of the motor windings.
The term "substantially stepless" is used herein to mean a waveform in which any step changes which occur are of very small magnitude compared with the amplitude of the waveform. Thus, for example, the waveform could be generated utilizing digital techniques, wherein the waveform amplitude is represented by a digital signal of at least 7 bits, so that a change in the digital signal represents a step in the wave form of only one one hundred and twenty eight of the waveform amplitude.
Preferably, each modulation circuit includes an output stage comprising a pair of semi-conductor switch elements which are transformer coupled to a driving stage of the modulation circuit. The output stage is preferably arranged as a push-pull stage operating between positive and negative power supply rails with the windings connected to an earth return through a current sensing resistor which provides the current feedback signal.
Preferably, the pulse width modulating circuits are arranged to operate at a fixed frequency at least an order of magnitude higher than the maximum stepping frequency.
BRIEF DESCRIPTION OF THE DRAWINGS
Four examples of the invention are shown in
FIGS. 1 to 4 respectively of the accompanying drawings which are electrical circuit diagrams of the stepper motor control circuits.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring firstly to FIG. 1, the stepper motor which is being controlled has four windings, two of which, 10 and 11 are shown in the accompanying drawing. These windings are connected in parallel with one another, via a current sensing resistor R.sub.1 to ground at one end and to the junction of two inductors L.sub.1, L.sub.2 at the other end. The inductors L.sub.1, L.sub.2 are connected in series between the collector of a pnp transistor Q.sub.1 and the collector of an npn transistor Q.sub.2. Transistor Q.sub.1 has its emitter connected to a positive power supply rail 12 and transistor Q.sub.2 has its emitter connected to a negative power supply rail 13. The inductor L.sub.1 is magnetically linked to a winding L.sub.3 which is connected between ground and the anode of a diode D.sub.1, the cathode of which is connected to rail 12. Similarly inductor L.sub.2 is linked to a winding L.sub.4 connected between ground and the anode of a diode D.sub.2 which has its cathode connected to the rail 13. A capacitor K.sub.3 is connected between the junction of inductors L.sub.1 and L.sub.2 and ground.
Transistor Q.sub.1 is biased off by a resistor R.sub.3 connecting its base to the rail 12. The base of transistor Q.sub.1 is also connected to the anodes of two diodes D.sub.3 and D.sub.4 the cathodes of which are connected to opposite ends of two series connected secondary windings TRA.sub.1 and TRA.sub.2, the common point of
REFERENCES:
patent: 3909693 (1975-09-01), Yoshitake
patent: 4255693 (1981-03-01), Keidl
Electronic Engineering, vol. 52, No. 636, Apr. 1980 (London, GB) E. Davies.
Stepping Motors and Their Microprocessor Controls; T. Kenjo; pp. 105-106; 138-139; 141-143.
Bergmann Saul M.
Lucas Industries Public Limited Company
Shoop Jr. William M.
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