High stability digital head servo for video recorders

Claim 2

A servo system for regulating an operating time variable of a driven load comprising: means responsive to the driven load for providing a feedback signal at a rate that is proportional to the operating time variable of the load; means responsive to a first standard rate signal for providing a reference signal of a rate which is equal in rate to that of said feedback signal, said first standard rate signal being related to the desired rate of rotation of the load; first means for comparing said reference signal and said feedback signal and providing a first error signal indicative of the time difference between the rates of the compared signals; means electrically coupling said first error signal provided by said comparing means to the load for driving the load such that said reference signal and said feedback signal are in locked synchronism; and control means responsive to said feedback signal and a second standard rate signal for incrementally adjusting the rate of said reference signal in accordance with time variations in said feedback signal, and said second standard rate signal having a rate substantially lower than said first standard rate signal and having a timing related to the desired position of the angular position of the load.

Claim 3

A servo system as defined in claim 1 wherein: said reference signal providing means further includes means for generating a high rate pulse train clock signal that is phase locked to said first standard source rate signal and is at a substantially higher rate than said reference signal and dividing means operatively connected to the output of said clock signal generating means for providing a pulse of said reference signal in response to a predetermined number of pulses being received at the input thereof; and said control means further includes means coupled to said load responsive means for converting the feedback signal to a lower rate nominally equal to the rate of said second standard rate signal, second means for comparing the time difference between said converted feedback signal with said second standard rate signal and providing a second error signal at the output thereof that is coupled to said dividing means for incrementally altering the number of pulses in said pulse train of said clock signal applied to said dividing means, whereby said reference signal is phase corrected relative to said second standard rate signal.

Claim 4

A servo system as defined in claim 2 wherein said clock signal generating means comprises a voltage controlled oscillator connected in a phase locked loop, and said first standard rate signal is the horizontal sync component of a television signal.

Claim 5

A servo system as defined in claim 2 wherein said second comparing means further includes means for adding a pulse in said pulse train signal whereby the predetermined count occurs at a time earlier than its normal time; and means for subtracting a pulse from said pulse train clock signal so that the predetermined count occurs at a time later relative to its normal time, said pulses being added or subtracted as determined by said second error signal.

Claim 6

A servo system as defined in claim 4 wherein said second comparing means includes means for adding a pulse in said pulse train clock signal whereby the predetermined count occurs at a time earlier than its normal time and means for subtracting a pulse from said pulse train clock signal so that the predetermined count occurs at a time later relative to its normal time, said pulses being added or subtracted as determined by said second error signal.

Claim 7

A servo system as defined in claim 4 wherein each of said pulses that are added or subtracted from said pulse train represent a time increment of about 200 nanoseconds.

Claim 8

A servo system as defined in claim 4 wherein said second standard rate signal comprises the vertical sync component of a television signal.

Claim 9

A servo system as defined in claim 4 wherein said control means further includes delay means interconnected between said converting means and said second comparing means for introducing a delay corresponding to the lead introduced by said presetting means.

Claim 10

A servo as defined in claim 2 wherein said control means further includes means for presetting said dividing means with a preselected count immediately following said predetermined count, said preselected count corresponding with a preselected phase lead with respect to said second standard rate signal.

Claim 11

A servo system for a capstan drive motor for use in a television recording and reproducing apparatus comprising: drive means for providing power to said drive motor; tachometer means operatively connected to a drive motor and providing train of pulses having a rate indicative of the speed of operation thereof; discriminator means operatively connected to said tachometer means and providing an error signal to said drive means, said error signal decreasing as the speed of said motor increases to a predetermined operating speed during start-up thereof; means for disconnecting said discriminating means when said drive motor has reached said predetermined operating speed; means for providing a reference train of pulses whose rate is nominally equal to a multiple of the vertical rate of the television signal; said reference producing means including a clock signal producing means for producing a train of pulses related in time to the horizontal synchronizing pulses of the television signal and having a rate that is a multiple of the horizontal rate of the television signal, and means coupled to said clock signal producing means for dividing the rate of clock pulses to the nominal rate of the reference signal; first comparing means operatively connected to said tachometer means for comparing the rate of said tachometer pulses and said reference pulses and providing a first error signal indicative of the time difference therebetween; means electrically coupling said first error signal of said comparing means to said drive means for providing a motor speed such that the reference pulses and the tachometer pulses are locked in synchronism; second comparing means coupled to said tachometer means for comparing the timing of said tachometer pulses with the timing of the vertical pulses in the television signal and providing a second error signal in response to time variations between the two signals, and means coupled to said dividing means for adding or subtracting clock pulses therein in accordance with said second error signal to thereby adjust the timing of said reference pulses whereby said head motor phase errors that can be caused by temperature variation, drift, loading of the drive motor and the like are corrected.

Claim 12

A servo system for a capstan drive motor for use in a television recording and reproducing apparatus comprising: drive means for providing power to said drive motor; tachometer means operatively connected to a drive motor and providing train of pulses having a rate indicative of the speed of operation thereof; discriminator means operatively connected to said tachometer means and providing an error signal to said drive means, said error signal decreasing as the speed of said motor increases to a predetermined operating speed during start-up thereof; means for disconnecting said discriminating means when said drive motor has reached said predetermined operating speed; means for providing a reference train of pulses whose rate is nominally equal to a multiple of the vertical rate of the television signal; said reference producing means including a clock signal producing means for producing a train of pulses related in time to the horizontal synchronizing pulses of the television signal and having a rate that is a multiple of the horizontal rate of the television signal, and means coupled to said clock signal producing means for dividing the rate of clock pulses to the nominal rate of the reference signal; first comparing means operatively connected to said tachometer means for comparing the rate of said tachometer pulses and said reference pulses and providing a first error signal indicative of the time difference therebetween; means electrically coupling said first error signal of said comparing means to said drive means for providing a motor speed such that the reference pulses and the tachometer pulses are locked in synchronism; second comparing means coupled to said tachometer means for comparing the timing of said tachometer pulses with the timing of the vertical pulses in the television signal and providing a second error signal in response to time variations between the two signals, and means coupled to said dividing means for adding or subtracting clock pulses therein in accordance with said second error signal to thereby adjust the timing of said reference pulses whereby said head motor phase errors that can be caused by temperature variation, drift, loading of the drive motor and the like are corrected.