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# Digital Control of Spindle Motor

IP.com Disclosure Number: IPCOM000037064D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 3 page(s) / 46K

IBM

## Related People

Kisaka, M: AUTHOR

## Abstract

Disclosed is an algorithm for enabling design for spindle motor control easier than classical control design by the feedback of both system input and system output. It utilizes a modern control design algorithm so that the start-up time of the motor speed can be faster than the time obtained by classical control. But the algorithm is simpler than the modern control design algorithm.

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Digital Control of Spindle Motor

Disclosed is an algorithm for enabling design for spindle motor control easier than classical control design by the feedback of both system input and system output. It utilizes a modern control design algorithm so that the start-up time of the motor speed can be faster than the time obtained by classical control. But the algorithm is simpler than the modern control design algorithm.

A servo system for a spindle motor rotates the motor at constant velocity. To measure rotational speed, one or more pulses are generated per revolution. The servo system compares an interval of the pulses with a target value, calculates a velocity error and feeds back the proper value. In a classical control design, a term proportional to the velocity error, an integrator term, and a differential term are used for getting a feedback value. These terms are derived from only the velocity error, and feedback coefficients for these terms are determined experimentally. The control algorithm will be described in detail.

The average velocity at n'th sample is described as follows:

AV(n) = C /Ti(n) (1) where AV(n) : average velocity at n'th sample C : angle between pulses

Ti(n) : n'th interval of pulses

The rotational accuracy of the spindle motor is within +/- 0.1%. Thus, the average velocity can be approximated as follows: AV(n) NN ( r(n) - r(n)-1) /Ts (2) where r(n) = rotational angle at n'th sample Ts = target interval

Using a transfer function from a motor control input ( U(n) ) to a rotational angle, the following equation can be derived. r(n+1) = 2*r(n) - r(n-1) + K*{ (1-q)2*U(n)

+ (1+2q-2q2)*U(n-1) + q2*U(n-2) }

(3)

where K : (torque constant)*Ts2 .(2*inertia)

q : t/Ts

t is delay time (see the figure)

By using Equations (2) and (3), we o...