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Step Error Measurement Using Back EMF

IP.com Disclosure Number: IPCOM000062550D
Original Publication Date: 1986-Dec-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 5 page(s) / 30K

Publishing Venue

IBM

Related People

Hamilton, DC: AUTHOR

Abstract

A variable reluctance step motor used for positioning a daisy wheel so that a correct character petal thereon is struck against a platen by a hammer is tested to determine the extreme value of absolute position error occurring in a revolution of the daisy wheel. This is obtained through using hardware of U.S. Patent 4,422,040 to Raider et al without changing the hardware or increasing its test time by changing the program of a microprocessor of Raider et al.:AB 6 p.

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Step Error Measurement Using Back EMF

A variable reluctance step motor used for positioning a daisy wheel so that a correct character petal thereon is struck against a platen by a hammer is tested to determine the extreme value of absolute position error occurring in a revolution of the daisy wheel.

This is obtained through using hardware of U.S. Patent 4,422,040 to Raider et al without changing the hardware or increasing its test time by changing the program of a microprocessor of Raider et al.:AB 6 p. In moving a daisy wheel by a step motor so that the correct character petal on the daisy wheel is captured by the hammer and struck against the platen, the error in the location of each stable detent in the step motor, known as the absolute position error, has a significant effect on whether the hammer will capture the correct character petal on the daisy wheel. For the step motor to be satisfactory, the absolute position error of the step motor must be below a specified limit.

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The hardware of Raider et al only measures the distance between adjacent stable detent back EMF zero crossovers whether these back EMF zero crossovers result from sensing the back EMF of each phase (this corresponds to commutating the step motor by full stepping with one phase on) or sensing the summed back EMF of each possible combination of two phases (this corresponds to commutating the step motor by full stepping with two phases on). The measured distance between adjacent stable detent back EMF zero crossovers, which is called back EMF step length error, is employed to determine the extreme value of the step motor absolute position error occurring in a revolution. The back EMF step length error one phase on commutation is used to find the extreme value of the absolute position error for one phase on commutation. Similarly, the back EMF step length error for two phase on commutation is utilized to find the extreme value of the absolute position error for two phase on commutation. In determining the absolute position error for one phase on commutation or two phase on commutation, the same method is used with the only difference being the input data to the method. Furthermore, the back EMF step length error must be measured at a current, which is the nominal current producing the maximum back EMF, to accurately determine the extreme value of the absolute position error of the step motor. The zero-crossover detecting circuit of Raider et al is the portion of its hardware containing the signals used to measure the distance between adjacent stable detent EMF zero crossovers for either one phase on full stepping or two phase on full stepping. Fig. 1 shows the signals used to measure the distance between adjacent stable back EMF zero crossovers for both one-phase and two-phase energized commutation. Because the step motor has its rotor turning at a constant speed, the distance between adjacent stable back EMF zero crossovers is measured in time u...