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# DC Motor Start Algorithm

IP.com Disclosure Number: IPCOM000060774D
Original Publication Date: 1986-May-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 34K

IBM

## Related People

Collins, DW: AUTHOR [+3]

## Abstract

The DC brushless spindle motor of a rigid magnetic disk data file requires efficient acceleration control to provide high initial acceleration to quickly fly the transducer heads for minimal head-disk wear while using a limited amount of power supply current. The average power supply current delivered to the motor increases with speed if the current flowing in the motor is held at a constant value. In a typical motor a motor current may be set to a value such as five amperes and maintained until the transducer heads are flying safely above the disk surfaces. In a typical case, a speed of about 80 radians per second is required and a speed of 120 radians per second can be attained without exceeding a safe motor current value.

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DC Motor Start Algorithm

The DC brushless spindle motor of a rigid magnetic disk data file requires efficient acceleration control to provide high initial acceleration to quickly fly the transducer heads for minimal head-disk wear while using a limited amount of power supply current. The average power supply current delivered to the motor increases with speed if the current flowing in the motor is held at a constant value. In a typical motor a motor current may be set to a value such as five amperes and maintained until the transducer heads are flying safely above the disk surfaces. In a typical case, a speed of about 80 radians per second is required and a speed of 120 radians per second can be attained without exceeding a safe motor current value. The motor current is then periodically reduced by a value such as one-third ampere, causing the supply current to drop immediately and gradually ramp back up as the motor continues to gain speed. As shown in the figure, a microprocessor uses the velocity of the motor to determine when the motor current should be reduced. This process of reducing the motor as the motor accelerates continues until the desired velocity is reached to thereby maintain the supply current within a narrow band of values. The microprocessor controls four input bits of a spindle predrive module. This predrive module controls six power transistors. The predrive module monitors the motor current and adjusts such current to be equal to the value s...