Browse Prior Art Database

Automated Servo Motor/ Encoder Tester

IP.com Disclosure Number: IPCOM000050243D
Original Publication Date: 1982-Sep-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 4 page(s) / 60K

Publishing Venue

IBM

Related People

Cavill, BR: AUTHOR [+3]

Abstract

This describes a complete automated DC Motor/Encoder Testing system which tests the motor and attached encoder to obtain test data, evaluate motor and encoder performance, and then determines if performance is of an acceptable level.

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Automated Servo Motor/ Encoder Tester

This describes a complete automated DC Motor/Encoder Testing system which tests the motor and attached encoder to obtain test data, evaluate motor and encoder performance, and then determines if performance is of an acceptable level.

Motor data to be used to determine motor parameters is obtained by driving a motor and an analog computer simulated motor model with the same excitation and then adjusting several parameters in the simulated motor until the motor and motor model responses match. A block diagram of the motor tester is shown in Fig. 1. Both the real motor and the motor model are driven by a DC drive voltage with a riding AC excitation voltage. The motor resonant AC frequency is determined by varying the frequency of the generator until there is zero phase shift between the motor current and the driving voltage. The motor "capacitance" value is obtained by setting the applied AC excitation frequency well below resonance and adjusting the model variable "CA" until the demodulator is nulled using the simulator current as the demodulator excitation. The motor inductance is measured by varying the model variable "LA" until there is zero phase shift between the simulator current and the resonant driving AC voltage. Finally, the resistance value is determined by adjusting the model variable "RA" until the demodulator is nulled with an excitation signal of the applied voltage. The process is similar to adjusting an AC bridge circuit, and several iterations must be made to achieve satisfactory nulls. The motor parameters can then be calculated from the resulting data.

The motor test system described above has been automated and enhanced in many unique ways to allow improved testability and ease of use. Also, testing of the attached encoder has been added to permit testing of the motor and encoder as a unit.

An automated motor test system, shown in Fig. 2, is driven by the "control and motor test microcomputer". This microcomputer responds to command buttons from an operator panel and initiates the motor test procedures. It controls motorstart, stopping, and the frequency of the excitation AC signal. The microcomputer performs the phase detector function in software, responding to the excitation voltage and the motor and simulator model current trigger sense lines. The microcomputer measures the phase difference between the desired inputs and then modifies the output (L or FREQ) until obtaining zero phase shift. The microcomputer also performs the synchronous demodulation function in software. It measures the difference in motor and simulator currents as the output of a hardware analog to digital converter (ADC). This value is used by the microcomputer to change the output (R(A) or C(A)) until the input ADC value is zero. The sampling of the ADC output is synchronized to the excitation input of either the motor voltage or simulator current trigger sense input depending on the desired output....