Capstan control system for a tape drive

Claim 2

In a high performance magnetic tape drive comprising a magnetic head, a capstan for driving tape past said magnetic head, a capstan motor for driving said capstan, and a capstan control system for controlling said capstan motor comprising: a tachometer means for generating a series of tachometer pulses having a frequency representing the capstan velocity; a clock pulse means for generating clock pulses between said tachometer pulses; a counter means for counting the number of said clock pulses generated between said tachometer pulses; a digital-to-analog converter means for generating an analog signal representing the count accumulated in said counter means; a means for generating an error signal having a component substantially proportional to the difference between said analog signal and a reference signal; and a power amplifier means having an input and an output, said error signal generating means being coupled to said input and said capstan motor being coupled to said output to provide linear control of said capstan motor.

Claim 3

The capstan control system of claim 1 wherein the output of said power amplifier means provides high power substantially fixed control below a predetermined capstan velocity independent of said error signal and low power substantially linear control above said predetermined capstan velocity responsive to said error signal.

Claim 4

The capstan control system of claim 2 wherein said error signal also comprises a component substantially proportional to the integral of said difference between said analog signal and said reference signal.

Claim 5

The capstan control system of claim 3 wherein said means for generating an error signal comprises: a comparison means having an input and an output, said analog signal and said reference signal being coupled to the input of said comparison amplifier; and an integrating means having an input connected to the output of said comparison means, said counter means being preset to a count greater than the count representing desired steady-state velocity for a particular operation to prevent accumulation of a large error signal at said integrating means while the capstan velocity is below said predetermined velocity.

Claim 6

The capstan control system of claim 1 further comprising a source of said reference signal providing a reference signal having a first substantially constant signal level during read and write operations and a linearly increasing signal level to a second substantially constant signal level higher than said first signal level during a rewind of operation.

Claim 7

The capstan control system of claim 1 wherein said source of said reference signal supplies said digital-to-analog converter means generating an error signal during the read and write of operations so as to render any deviations in said reference signal self-cancelling.

Claim 8

The capstan control system of claim 6 wherein said digital-to-analog converter comprises a ladder network having a plurality of transistors and associated output resistors connected to and controlled by said register means, said transistors associated with smaller resiStors corresponding to higher counts so as to be in the nonconductive state as said capstan motor approaches the steady state velocity thereby eliminating the effect of saturated transistor voltage drops on said error signal.

Claim 9

In a high performance magnetic tape drive comprising a magnetic head, a capstan for driving tape past said magnetic head, a capstan motor for driving said capstan, and a capstan control system for driving said capstan motor comprising: a power amplifier capable of operating in a linear region and a saturated region; a means for generating an analog signal representing the instantaneous velocity of said capstan; a signal source for generating a reference signal representing a reference capstan velocity; a means for comparing said analog signal and said reference signal and generating an error signal applied to said power amplifier and having a component proportional to the difference between said instantaneous capstan velocity and a reference capstan velocity and a component proportional to the integral of said difference; a means for operating said power amplifier in said saturated power region thereby driving said motor independently of said error signal when said instantaneous capstan velocity is below a predetermined level; and a means for operating said power amplifier in said linear region in response to both said proportional and integral components thereby driving said motor in response to said error signal when the instantaneous capstan velocity is equal to or above said predetermined level.

Claim 10

In a high performance magnetic tape drive comprising a magnetic head, a capstan for driving tape past said magnetic head, a capstan motor for driving said capstan, and a capstan control system for driving said capstan motor comprising: a power amplifier capable of operating in a linear region and a saturated region; a means for generating an analog signal representing the instantaneous velocity of said capstan; a signal source for generating a reference signal representing a reference capstan velocity; a means for comparing said analog signal and said reference signal and generating an error signal applied to said power amplifier and having a component proportional to the difference between said instantaneous capstan velocity and a reference capstan velocity and a component proportional to the integral of said difference; a means for operating said power amplifier in said saturated power region thereby driving said motor independently of said error signal when said instantaneous capstan velocity is below a predetermined level; and a means for operating said power amplifier in said linear region in response to both said proportional and integral components thereby driving said motor in response to said error signal when the instantaneous capstan velocity is equal to or above said predetermined level.

Claim 11

The capstan control system of claim 8 wherein said means for comparing said analog signal and said reference signal comprises: a comparison amplifier means having an input coupled to said means for generating an analog signal and said signal source; and an integrating amplifier means having an input connected to the output of said comparison amplifier means.

Claim 12

The capstan control system of claim 9 wherein said signal source comprises: a means for generating a reference signal of constant amplitude during the read and write modes for said tape drive; and a means for generating a linearly increasing reference signal when said tape drive is switched from the read or write mode to the rewind mode, said reference signal increasing linearly to a constant level.