Rodime Plc

Other

David S Ruxton

Alec Donald Stewart

James N White

Kenneth L Miller

Nigel Macleod

Brian D Chalmers

In a disc data store, wherein a read/write head is radially positionable by a feedback servomechanism to interact with a selectable one out of a plurality of radially equispaced data storage tracks on a rotary disc, the positioning errors resultant from phase errors between the plural signals available as the output of an optical grating head position transducer are eliminated by replacing one of the data storage tracks with a servo track by arranging that the period of the recursive, triangular wave position indicating signals from the transducer is equal to twice the radial spacing between tracks on the disc, by selecting as the exclusively-used position indicating signal that one of the plurality of transducer signals which brings the head to the center of the servo track with least offset, and, while employing that selected signal or its generated inverse as the feedback signal to the servomechanism applying that least offset as a correction when positioning the head over data storage tracks.

Head positioning system for a disc data store

A data disk storage system utilizing a bipolar stepper motor for use in conjunction with the controlling of the operation of the storage system. The stepper motor imparts a drive force for moving a control arm to which a read/write head is coupled. The operation of the stepper motor through driving of the control arm causes the read/write head to move across the various tracks of the data disk within the data storage system during operation of such system. The stepper motor includes a stator and a rotor coupled to an output shaft of the motor which output shaft in turn is coupled to the read/write head through the control arm. A first drive mechanism within the stepper motor generates a first phase signal within the stator for creating a first drive force for rotating a rotor. A second drive mechanism of the stepper motor generates a second phase signal within the stator for creating a second drive force for rotating the rotor. These first and second drive forces are out of phase with each other, normally by 90.degree. when both signals are positive or both are negative or by multiples of 90.degree. when one of the signals is positive and the other is negative. A control mechanism selectively provides positive and negative phase current signals to the first and second drive mechanisms for generating 8 stable step positions for the rotor during each motor cycle. This control mechanism controls the current supplied to the first and second drive mechanism so that the resulting holding torque on the rotor generated by the first and second drive mechanisms is substantially the same at each step position.

Stepper motor control for data disk system

A method and apparatus for controlling a stepper motor and a disk drive is described for minimization of stepper motor oscillations for a single step, minimizing the time taken for the stepper motor to move between tracks for multi-track seeks, and reduction of angular hysteresis due to the mechanical and magnetic properties of the stepper motor construction. This control is achieved using a microprocessor-based circuit adapted to drive the stepper motor in accordance with predetermined programs. Oscillations of the stepper motor are damped by controlling, using one program, the current applied to the stepper motor during the last step of its motion by switching this current on and off within small predetermined time intervals. The time taken to move between tracks is controlled by another program in which the non-linear torque speed characteristics of a particular stepper motor are matched by a non-linear pulse rate which is determined by data held in the memory of the microprocessor circuit. This data can be modified to suit the requirements of the stepper motor and load. Another program controls minimization of hysteresis by ensuring that each track on the disk is approached from the same direction and from the same previously energized set of windings. The microprocessor controls the direction of motion of the stepper motor and hence decides whether or not the read/write head should cross the desired track and return it to ensure uniformity of approach.

Method and apparatus for controlling a stepper motor

In a disk drive system which uses as stepper motor, overshooting of the desired final position is reduced by short-circuiting the windings of the stepper motor which normally remain open-circuit or are switched off. This short-circuiting provides a current path for any EMF induced in the unused windings. This effect is achieved by connecting a pair of transistors in parallel with each other and with each respective winding. The transistors are connected in opposite polarity to provide a short-circuit regardless of the polarity of the EMF across the windings. The transistors are connected to a microprocessor which is programmed such that the windings are selectively short circuited and the short circuits are applied at a predetermined time with regard to the step so that `damping` is optimized. The microprocessor may be programmed to switch the transistors on and off as desired giving flexible timing to suit different conditions. One or more stepper motor steps may be treated in this manner.

Growing community of inventors

Crieff, United Kingdom

David S Ruxton