Heat protected position transducer in an electric motor

Details Heat protected position transducer in an electric motor Heat protected position transducer in an electric motor

1997-01-14

1999-12-07

Allen, Stephone

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

318565, 99468, H02P 800, A23B 700

Patent

active

059987839

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The invention relates to position and/or velocity transducers for providing signals in regard of the position or velocity of a movable part, in particular of a rotor of an electric motor or generator.


BACKGROUND

There is an increasing need for stiff and compact servo motor systems. To be stiff, a servo motor system must be able to give a fast response to large and unexpected external torques. A fast response requires a very high resolution and a very low delay in the speed signal.
Analog electrodynamic tachometer generators offer a solution providing high resolution but it is difficult to build them so as to give a low delay. The generator adds a not negligible inertia to the rotor. The torsional stiffness in the mechanic coupling of the tachogenerator to the motor rotor is limited, and this gives a resonance frequency that limits the possible bandwidth of the servo motor control loop. Torsionally very stiff designs require mechanically very compact assemblies of the motor and the tacho generator. However, high resolution tacho generators should not be attached close to the motor as the stray flux from the motor windings might affect the output voltage of the tacho generator in the case where the two units are located too close to each other. Tachos also adds considerable cost and increase the size of the motor system.
Transducers that detect or sense rotary or linear motion by using at least two periodic primary signals having a phase difference in the order of magnitude of 90 degrees such as a resolver or an optical incremental encoder have been used for many decades of years. Resolvers and synchros can be made with very high resolutions but the costs of high resolution units are very high. The time delay from a motor speed change to the corresponding change of the detector output signal is not negligible since the torsional stiffness of mechanical coupling of the resolver to the motor rotor is limited, and this gives a resonance frequency that limits the possible bandwidth of the motor control loop. Torsionally very stiff designs require mechanically very compact assemblies of the motor and the resolver. High resolution resolvers should however not be mounted close to the motor as the stray flux from the motor windings might affect the output voltage of the resolver in the case where the two units are located too close to each other.
Incremental transducers are commonly used to give angular position information. By reading position data repetitively at known time intervals, an approximate value of the velocity can be obtained. The primary signal from optical incremental transducers are normally processed in one of two ways. In the first way the analog primary signals are compared to a reference level thus converting the basic sinus signal to a square wave binary signal that is fed to a counter chain that is readable from a computer.
In the second way, the signal is fed to a "multiplying" network that digitalizes the data based on the assumption that the analog signals have a constant amplitude and are sinusoidal. Such converters can for example convert one period of a sinusoidal input signal to 5 or 100 periods of the square wave output signals.
At low speeds, the limited resolution of a digital incremental encoder gives very high quantification errors in the speed estimate. With standard decoding electronics that gives 4 count pulses per period, even a 5000 line encoder gives only 20000 positions per turn. At a relatively high speed like 15 rpm and a test interval of 200 .mu.s, the change in position is approximately 15/60*20000*0.0002=1 unit, which due to quantification errors can give either 0, 1 or 2 units as a speed estimate input signal to a control algorithm.
The resolution problem can be reduced by using encoders comprising more lines or by using interpolation circuits that generate for example 100 counts for every period of the basic encoder signal. Hardware interpolation requires a very high signal quality; the amplitude of the primary signals must be constant over one full

REFERENCES:
patent: 3400275 (1968-09-01), Trump
patent: 4554451 (1985-11-01), Kirstein
patent: 4779031 (1988-10-01), Arends et al.
patent: 4794251 (1988-12-01), Scholian
patent: 5365137 (1994-11-01), Richardson et al.
patent: 5456164 (1995-10-01), Bang
patent: 5605294 (1997-02-01), Migaki et al.

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