Browse Prior Art Database

Voice Coil Motor Drive

IP.com Disclosure Number: IPCOM000034662D
Original Publication Date: 1989-Mar-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Hanson, CC: AUTHOR [+2]

Abstract

A hard disk drive actuator for moving transducer heads is typically positioned by a voice coil motor. The voice coil is a coil of wire attached to the mechanism that moves the heads and located in a magnetic field generated by fixed permanent magnets. When current flows in the coil, a force is generated. The magnitude and direction of the force are controlled by the magnitude and direction of the current in the coil. (Image Omitted) In a file where seeking and track following are controlled by a digital signal processor, the position error signal is generated in digital form and sent to the processor. The desired value of the current is presented to a digital-to-analog converter (DAC) in digital form and converted to an analog voltage applied to the voice coil motor driver circuit.

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Voice Coil Motor Drive

A hard disk drive actuator for moving transducer heads is typically positioned by a voice coil motor. The voice coil is a coil of wire attached to the mechanism that moves the heads and located in a magnetic field generated by fixed permanent magnets. When current flows in the coil, a force is generated. The magnitude and direction of the force are controlled by the magnitude and direction of the current in the coil.

(Image Omitted)

In a file where seeking and track following are controlled by a digital signal processor, the position error signal is generated in digital form and sent to the processor. The desired value of the current is presented to a digital-to-analog converter (DAC) in digital form and converted to an analog voltage applied to the voice coil motor driver circuit. The driver circuit must sense the polarity and magnitude of this analog voltage and convert it to a proportional current. The driver has typically been a completely analog circuit with a power output stage which is within the closed analog loop (Fig. 1). This requires that the analog circuit control the polarity of an H-type bridge driver which has built-in delays and complexity to perform the current switching, current sensing and regulation. In some cases, these circuits have been designed so that the analog drivers are constantly conducting idle current to speed up response. This increases power dissipation. The output of the DAC is centered about a voltage reference which is exactly half the full scale output of the DAC. The driver circuit senses the polarity and magnitude of the DAC output relative to the reference and converts the voltage to a current of proportional magnitude and proper polarity. Fig. 2 shows the block diagram of a simplified driver. Instead of all eight bits of the digital input to produce an analog voltage, the eighth bit is used as a digital polarity b...