Correction of asynchronous timing utilizing a phase control loop

Claim 2

In a magnetic storage and retrieval system wherein input information is recorded on a moving magnetic medium as transitions in magnetization between two saturation states occurring at multiples of a nominal time interval corresponding to a minimum spacing and the transitions are detected by a magnetic readhead having a gap of predetermined length, the method of reducing the effective spacing between the transitions on the recording medium to a maximum value at least as large as the minimum spacing, the method comprising the steps of: sensing when the spacing between successive data transitions in response to the input information is greater than the maximum value; recording at least one pair of control transitions in between successive data transitions on the recording medium whenever successive data transitions are spaced in excess of the maximum value; sensing the variations in the speed of the medium during recording; and adjusting the time of occurrence of the pair of control transitions as the speed of the medium varies to maintain a predetermined spacing relative to the successive data transitions between which the pair of control transitions is recorded.

Claim 3

The method of claim 1, in which the maximum value is substantially the same as the minimum spacing.

Claim 4

The method of claim 1, in which the spacing on the medium between each pair of control transitions is smaller than half the gap length of the associated readhead.

Claim 5

The method of claim 1, in which the minimum spacing on the medium is defined by continuously spaced clock transitions recorded on the medium, the step of sensing variations in the speed of the medium comprises the step of sensing variations in the time of occurrence between the clock transitions, and the step of adjusting the time of occurrence of the pair of control transitions adjusts the time of occurrence of the pair of control transitions to maintain a constant relationship to the time of occurrence of the clock transitions.

Claim 6

In a magnetic storage and retrieval system wherein input information is recorded on a magnetic medium as transitions in magnetization between two saturation states spaced at multiples of a nominal interval and the transitions are detected by a magnetic readhead having a gap of predetermined length, the method of reducing the effective spacing between the transitions on the recording medium to a maximum value at least as large as the nominal interval, the method comprising the steps of: sensing when the spacing between successive data transitions in response to the input information is greater than the maximum value; recording at least one pair of control transitions in between successive data transitions on the recording medium whenever successive data transitions are spaced in excess of the maximum value, the spacing between the pair of control transitions being substantially smaller than the nominal interval; sensing variations in the nominal interval; and adjusting the position of the pair of control transitions recorded on the recording medium to correspond to the variations in the nominal interval.

Claim 7

In a magnetic storage and retrieval system wherein input information is recorded on a magnetic medium as transitions in magnetization between two saturation states spaced at multiples of a nominal interval and the transitions are detected by a magnetic readhead having a gap of predetermined length, the method of reducing the effective spacing between the transitions on the recording medium to a maximum value at least as large as the nominal interval, the method comprising the steps of: sensing when the spacing between successive data transitions in response to the input information is greater than the maximum value; recording at least one pair of control transitions in between successive data transitions on the recording medium whenever successive data transitions are spaced in excess of the maximum value, the spacing between the pair of control transitions being substantially smaller than the nominal interval; sensing variations in the nominal interval; and adjusting the position of the pair of control transitions recorded on the recording medium to correspond to the variations in the nominal interval.

Claim 8

The method of claim 5, in which the maximum value is substantially the same as the nominal interval.

Claim 9

ThE method of claim 5, in which the spacing on the medium between each pair of control transitions is smaller than half the gap length of the associated readhead.

Claim 10

A magnetic recording system comprising: a movable magnetic storage medium; a source of binary data to be recorded; means responsive to the source for recording the binary data on the storage medium as data transitions in magnetization between two saturation states occurring at multiples of a nominal time interval; means for recording at least one pair of control transitions in between successive data transitions on the storage medium whenever successive data transitions occur at some given multiple of the nominal time interval that is larger than one, the time interval between the pair of control transitions being substantially smaller than the nominal time interval; means for sensing variations in the speed of the storage medium during the recording of the transitions; and means responsive to the sensing means for adjusting the time of occurrence of the data and control transitions as the speed of the medium varies to maintain a predetermined spacing between the successive data transitions and between the data transitions and the control transitions.

Claim 11

A magnetic recording system comprising: a movable magnetic storage medium; a source of binary data to be recorded; means responsive to the source for recording the binary data on the storage medium as data transitions in magnetization between two saturation states occurring at multiples of a nominal time interval; means for recording at least one pair of control transitions in between successive data transitions on the storage medium whenever successive data transitions occur at some given multiple of the nominal time interval that is larger than one, the time interval between the pair of control transitions being substantially smaller than the nominal time interval; means for sensing variations in the speed of the storage medium during the recording of the transitions; and means responsive to the sensing means for adjusting the time of occurrence of the data and control transitions as the speed of the medium varies to maintain a predetermined spacing between the successive data transitions and between the data transitions and the control transitions.

Claim 12

The recording system of claim 8, in which the medium has recorded on it a plurality of clock transitions spaced at substantially constant intervals along its length; the means for recording control transitions comprises a binary counter capable of assuming a plurality of states responsive to successive trigger pulses, a source of trigger pulses occurring at a frequency that is a multiple of the reciprocal of the nominal time interval, means for coupling the source of trigger pulses to the counter to advance the state of the counter at the frequency of the trigger pulses, and means for recording the pair of control transitions at points in time defined respectively by first and second given states of the counter; the sensing means comprises means for sensing the clock transitions as the medium moves during recording; and the adjusting means comprises means responsive to the variations in phase between the clock transitions and a third given state of the counter for changing the frequency of the trigger pulses from the source so as to synchronize the third given state of the counter to the clock transitions.

Claim 13

The recording system of claim 9, in which the means for recording data transitions records the data transitions at points in time defined by a fourth state of the counter.

Claim 14

The recording system of claim 10, in which the third state of the counter precedes the first and second states of the counter.

Claim 15

The recording system of claim 11, in which the fourth state of the counter lies between the first and second states of the counter.

Claim 16

The recording system of claim 12, in which the counter has eight states, the control transitions being defined by the third and sixth states, the data transition being defined by the fifth state.

Claim 17

An information storage and retrieval system comprising: a movable magnetic storage medium on which information is stored as transitions in magnetization between two saturation states, the medium having stored on a portion of it a plurality of clock transitions spaced at substantially constant intervals along its length and having a portion reserved for the storage of data as data transitions; means for sensing the clock transitions as the medium moves; means responsive to each sensed clock transition during data retrieval for generating a group of successive strobe pulses, the sum of the durations of the group of strobe pulses equaling the period between clock transitions; means for adjusting the durations of the strobe pulses as the period between clock transitions varies; means responsive to one of the strobe pulses of each group during data retrieval for sensing the data transitions on the medium; a source of binary data to be stored on tHe medium; means responsive to the source of binary data and to one of the strobe pulses of a group during data storage for recording the binary data on the storage medium as data transitions between two saturation states occurring at multiples of the period between clock transitions; and means responsive to the source of binary data and to two of the strobe pulses of a group during data storage for recording at least one pair of control transitions in between successive data transitions on the storage medium whenever successive data transitions occur at some given multiple of the period between clock transitions that is larger than one, the time interval between the pair of control transitions being substantially smaller than the time interval between the clock transitions.

Claim 18

An information storage and retrieval system comprising: a movable magnetic storage medium on which information is stored as transitions in magnetization between two saturation states, the medium having stored on a portion of it a plurality of clock transitions spaced at substantially constant intervals along its length and having a portion reserved for the storage of data as data transitions; means for sensing the clock transitions as the medium moves; means responsive to each sensed clock transition during data retrieval for generating a group of successive strobe pulses, the sum of the durations of the group of strobe pulses equaling the period between clock transitions; means for adjusting the durations of the strobe pulses as the period between clock transitions varies; means responsive to one of the strobe pulses of each group during data retrieval for sensing the data transitions on the medium; a source of binary data to be stored on tHe medium; means responsive to the source of binary data and to one of the strobe pulses of a group during data storage for recording the binary data on the storage medium as data transitions between two saturation states occurring at multiples of the period between clock transitions; and means responsive to the source of binary data and to two of the strobe pulses of a group during data storage for recording at least one pair of control transitions in between successive data transitions on the storage medium whenever successive data transitions occur at some given multiple of the period between clock transitions that is larger than one, the time interval between the pair of control transitions being substantially smaller than the time interval between the clock transitions.

Claim 19

The system of claim 14, in which the means for generating a group of successive strobe pulses comprises an oscillator having a frequency that is nominally a multiple of the frequency at which the clock transitions are sensed as the medium moves, a counter that has a number of states equal to the frequency multiple of the oscillator, and means for coupling the oscillator to the counter to advance the state of the counter at the frequency of the oscillator and the adjusting means comprises means for sensing the phase difference between the clock transitions and one of the strobe pulses to generate a control signal and means responsive to the control signal for changing the frequency of the oscillator.

Claim 20

The system of claim 15, in which the means for sensing the data transitions includes a magnetic readhead having a gap length that is too small to resolve the recorded pair of control transitions.