Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Magnetic Tape Unit Capstan Servomechanism

IP.com Disclosure Number: IPCOM000078745D
Original Publication Date: 1973-Mar-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Mitchell, JO: AUTHOR [+3]

Abstract

This capstan velocity servomechanism is a hybrid digital-analog sample-data type system. Its function is to quickly accelerate capstan motor 10 from a rest position to running velocity and to thereafter maintain a constant run velocity.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

Magnetic Tape Unit Capstan Servomechanism

This capstan velocity servomechanism is a hybrid digital-analog sample-data type system. Its function is to quickly accelerate capstan motor 10 from a rest position to running velocity and to thereafter maintain a constant run velocity.

During acceleration, a high-magnitude motor current is maintained until the motor velocity increases to approximately 70% of its eventual run velocity. At this point, and during the run interval, the motor current is controlled to be proportional to speed error; see Fig. 2.

The GO command, Fig. 1, sets a large digital number into register 11. The register is connected to the input of digital-to-analog converter (DAC) 12. This number indicates the command magnitude for motor accelerate current. The analog DAC output remains constant from 0% velocity, until the motor reaches approximately 70% of the desired steady-state run velocity.

The above-mentioned large digital number can be reduced in three steps as the motor speed increases from 0% to 70%. These steps can be triggered, based on distance-traveled information from the motor's digital tachometer.

From 0% to 70% velocity (the accelerate interval) the motor's digital tachometer period is measured by an oscillator driven counter 13. At each tachometer pulse the counter is reset and begins counting (measuring) a new tachometer period. So long as the motor speed is less than 70%, the second section 14 of the counter increments to the large digital number and is then degated from high-frequency oscillator 15. The counter holds this static number until the next tachometer pulse, whereupon the number is transferred to the resister. This maintains the DAC's large digital number constant for the acceleration interval.

The GO command also sets the large digital number into the second section 14 of the counter, to insure that the counter will contain this number when the first tachometer pulse occurs. Thereafter, so long as the motor speed is less than 70%, the counter will always increment to this number between tachometer pulses.

When a count lower than the large digital number coincides with the occurrence of the next tachometer pulse, the end of the acceleration interval has arrived.

The DAC output is modified by second-order filter 16 prior to being summed with motor current feedback 17. The fu...