EP0097208A1 — Head positioning system with automatic gain contr…

Claim 1

Independent Claim 288 words

A head positioning system with automatic gain control, for use in disk information storage apparatus, comprising:- a head positioning actuator (72) for moving at least one transducing head transversely of concentric information storage tracks on one of the disk surfaces (70); position reference information (25-30) on one of the disk surfaces for defining the radial position of the information storage tracks (0-3), the position reference information having a circumferentially extending and radially repeated pattern including at least two radially offset subsets (25,26,27) of elements; a transducing head (39;40), movable by the actuator (72), for detecting the position reference information and producing signals representative thereof; a variable gain amplifier (75) for amplifying the signals from the transducing head; position error signal generating means (80) arranged to receive the amplified signals from the variable gain amplifier and to generate from them, corresponding to each subset (25,26,27) of the position reference information, a respective phase of radial position error signal (A,B,C) whose variation with radial displacement is cyclical and related to the pitch of the tracks (0-3); and feedback means (99,100) for feeding back a composite position error signal, derived from the multi-phase position error signals, to control the head positioning actuator; the system being characterised by:- a gain function generating means (190,200,207-211) arranged to combine portions of the different phase position error signals (A,B,C) to provide, at any position of the head, a gain function (63) which is a measurement of the rate of change of the position error signals (A,B,C) per track of displacement; and a gain control loop (212,110-115,102) for controlling the gain of the variable gain amplifier (75) in dependence on the gain function so as to tend to keep the measured rate of change substantially constant.

Claim 2

Dependent Claim 288 words

A head positioning system with automatic gain control, for use in disk information storage apparatus, comprising:- a head positioning actuator (72) for moving at least one transducing head transversely of concentric information storage tracks on one of the disk surfaces (70); position reference information (25-30) on one of the disk surfaces for defining the radial position of the information storage tracks (0-3), the position reference information having a circumferentially extending and radially repeated pattern including at least two radially offset subsets (25,26,27) of elements; a transducing head (39;40), movable by the actuator (72), for detecting the position reference information and producing signals representative thereof; a variable gain amplifier (75) for amplifying the signals from the transducing head; position error signal generating means (80) arranged to receive the amplified signals from the variable gain amplifier and to generate from them, corresponding to each subset (25,26,27) of the position reference information, a respective phase of radial position error signal (A,B,C) whose variation with radial displacement is cyclical and related to the pitch of the tracks (0-3); and feedback means (99,100) for feeding back a composite position error signal, derived from the multi-phase position error signals, to control the head positioning actuator; the system being characterised by:- a gain function generating means (190,200,207-211) arranged to combine portions of the different phase position error signals (A,B,C) to provide, at any position of the head, a gain function (63) which is a measurement of the rate of change of the position error signals (A,B,C) per track of displacement; and a gain control loop (212,110-115,102) for controlling the gain of the variable gain amplifier (75) in dependence on the gain function so as to tend to keep the measured rate of change substantially constant.

Claim 3

Dependent Claim 82 words

A system as claimed in claim 1 in which each of the position error signals (A,B,C) is substantially linear within a portion of each cycle and deviates from linearity over the remainder of the cycle, the system further including correction means (120,210,211) for providing a correction signal to the gain function generating means (190,200,207-211) for combination with the different phase position error signals whenever one of the position error signals which is being combined is in a non-linear portion of a cycle.

Claim 4

Dependent Claim 90 words

A system as claimed in claim 2 in which the transducing head for detecting position reference information is one of a plurality of such heads whose sensitive widths in a direction transverse to the tracks may vary from head to head, the system further including a store (117) responsive to head address information to provide a first output signal whose value is related to the width of the selected head, the correction means (120,210,211) being responsive to the first output signal to vary the correction signal by a predetermined amount.

Claim 5

Dependent Claim 26 words

A system as claimed in claim 3 in which the first output signal from the store (117), is also applied directly to the gain control loop.

Claim 6

Dependent Claim 59 words

A system as claimed in claim 3 or claim 4 in which the plurality of heads are divided into inner (39) and outer (40) groups, the store being responsive to the head address information to provide a second output signal, indicative of whether the selected head is an inner or an outer head, directly to the gain control loop.

Claim 7

Independent Claim 135 words

A system as claimed in any preceding claim in which the position reference information is located in servo sectors (10) on the disk, the servo sectors being interspersed with data sectors (11,12) in which the information storage tracks are located, each servo sector comprising gain reference information (22) preceding the position reference information and detectable by the transducing head (39,40) and in which the gain control loop (212,110-115,102) is of relatively low bandwidth, the system comprising a further gain control loop (101,102) of higher bandwidth, a gain reference information amplitude detector (152,155,156,157) whose output is a measure of the full width response of the transducing head (39,40) to information signals on the disk, and combining means (102) for combining the output signals from both loops to control the gain of the variable gain amplifier (75).

Claim 8

Independent Claim 35 words

A system as claimed in any preceding claim in which the gain function generating means includes at least one modulus circuit (207,209) and combines only the modulus values of the different phase position error signals.

Claim 9

Dependent Claim 108 words

A system as claimed in claim 7 in which there are three phases of position reference information, the corresponding position error signals (A,B,C) each having nominally linear and non-linear regions such that two of the three are nominally linear when the third is non-linear the system including phase comparison means (194-196) for comparing the magnitudes of the three phase position error signals (A,B,C) and selection logic (193) responsive to the outputs of the phase comparison means to generate selection signals, the gain function generating means (190,200,207-211) being responsive to the selection signals to combine only those pairs of position error signals which are in their nominally linear regions.

Claim 10

Dependent Claim 76 words

A system as claimed in claim 8 in which the gain function generating means includes two switching circuits (190,200) to each of which the three phase position error signals are applied, the switching circuits each being responsive to selection signals from the selection logic (193) to output different respective ones of the three phase signals, the selection logic being arranged to select sequentially a different one of the three phase signals at each quarter track position.

Claim 11

Dependent Claim 92 words

A system as claimed in claim 9 in which the output of one of said switching circuits (190) is the composite position error signal (62), and in which the correction means includes a maximum value selection circuit (211) to which a constant amplitude correction signal and the modulus of the composite position error signal are applied, the maximum value selection circuit (211) passing whichever is the greater of these two signals to the gain function generating means for combination with the phase position error signal selected by the other switching circuit (200).

Head positioning system with automatic gain control

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