Disk drive system controller

Abstract: A method and apparatus of controlling an actuator of disk drive apparatus having an actuator controller arranged to move said actuator to seek a selected disk track. The control signals applied to the actuator controller are determined to cause the actuator to follow the desired velocity profile. Substantial coincidence with the desired profile can be achieved by utilising Fuzzy rules. Specifically, the control signals are determined for deceleration in dependence upon a deceleration constant, the actual velocity of the actuator, and a value determined by Fuzzy rules in dependence upon the difference between the actual velocity of the actuator and the desired velocity of the profile. This enables the track seeking time to be reduced with minimal overshoot at the target track. The said difference between actual and desired velocities is compared with a function of said actual velocity in order to initially cause a switch from acceleration to deceleration.

Description: The present invention relates to a method and apparatus for controlling an actuator of a disc drive apparatus. A disk drive system controller has a sensor, such as the head of a disk drive system or the optical sensor of a pickup apparatus, for recording and reproducing data to and from a disk. In general, a hard disk drive system, an opto-magnetic disk drive system, an optical disk drive system or a floppy disk drive system for recording and reproducing required data to and from a mass information storage media, such as a hard disk, an opto-magnetic disk, an optical disk or a floppy disk, is gradually being enhanced in its precision and functions with the advanced design techniques. Such a disk drive system generally establishes tracks and sectors on a disk to efficiently manage data stored on it. That is, a disk drive system records or reproduces data stored on the tracks and sectors established on a disk by a head mounted in it. A positioning control is performed by a microcontroller in order for the head to move to a target track (track seeking operation) and to exactly follow the target track (track following operation). In the track seeking operation, a locus for the movement control of the head is calculated in advance by a velocity profile method for the proximate optimal time. And also, during the head movement, the track seeking operation is performed by controlling the head position based on a velocity error which is a difference between a calculated head velocity and a predetermined velocity profile. One of such prior art is disclosed in U.S. Patent No. 4,979,055 granted to John P. Squires era., entitled " Disk Drive System Controller architecture utilizing embedded real-time diagnostic monitor " The disk drive system controller disclosed in U.S. Patent No. 4,979,055 provides for the storage and retrieval of data with respect to a rotating media and transfer of data with respect to a host in response to host commands, wherein the data is read and written by a sensor with respect to the rotating media, comprising a microcontroller and a memory containing a control program including a sensor positioning control process executed by the microcontroller. In the disclosed controller, the control algorithm used for the control of the sensor is as follows. O=K Tgain (P o -j x P -1 )+I t O S =K Sgain (S schd - (Save + S ff )) + I t where, K Tgain : a predetermined gain constant, P o : the off-track error of a current sector with respect to the sensor P -1 : the off-track error of a previous sector with respect to the sensor j x : a constant (o < j x < 1) I t : predetermined initialization data value K sgain : a seek gain constant S schd : the scheduled Velocity S ave : average of the calculated actual velocity of the sensor and the predicted velocity for a next sector S ff : the product of a gain constant times s schd In the control by means of the disclosed algorithm, the control input in a head acceleration portion is different from that in a head deceleration portion. That is, a velocity error between a velocity profile and an actual head velocity is used as the control input in the head acceleration portion, whereas an addition velocity of the error velocity and an actual head velocity is used as the control input in the head deceleration portion. The agitation, such as pressure caused by FPCB (Flexible Printed Circuit board) or an air flow, acting evenly on the head at every track is calculated in advance at every track just after an application of power to a disk drive system and considered to be compensated in a separate manner for the control input when performing a track seeking operation. Namely, a head velocity must be coincident with a given velocity profile in a velocity profile control method. However, in the head position control by the disclosed algorithm, an actual head velocity will exceed a given velocity profile by acceleration and imperfection of an acceleration/deceleration commutation method for preventing an abrupt variation of current in case that there is a change from a head acceleration portion to a head deceleration portion. In this known system there is a problem in that overshooting occurs since a head fails to exactly follow a velocity profile until it reaches to a target track. There is another problem in that a long transient response time exists since a head reaches to a target track without time for lessening the velocity error when the head travels to its adjacent track. There is still another problem in that two or three velocity profiles must be used according to the number of tracks for a head to be travelled. JP-A-2079274 describes a method of controlling an actuator of a disk drive apparatus, wherein, in response to control signals, an actuator controller is arranged to move said actuator to seek a selected disk track and to position a actuator head thereof relative to said selected disk track, and wherein said controller is arranged to accelerate and then decelerate said actuator. EP-A-0481492 relates to feedback control of a variable in general. After having approached the target value to within a settling range, fuzzy control is added so as to prevent overshoot. The present invention extends to a method of controlling an actuator as defined above, characterised in that during deceleration of said actuator said method comprises the steps of determining the control signals applied to said actuator controller during deceleration such that said actuator substantially follows a desired velocity profile, and in that said control signals are determined in dependence upon a predetermined deceleration constant, the actual velocity of the actuator, and a value determined by Fuzzy rules in dependence upon the difference between the desired velocity of the profile and the actual velocity of the actuator, fuzzy rules not being applied during acceleration A disk drive system controlled by a method of the invention enables its sensor, such as the head of a disk drive system or the optical sensor of a pickup apparatus for recording and reproducing data to and from a disk, to exactly follow a velocity profile by means of Fuzzy rules and compensation constants in a deceleration portion, thereby to reduce the track seeking time by minimizing overshoot at a target track. The present invention also extends to disk drive system controller comprising a microcontroller; a data recording/reproducing apparatus having a sensor for recording and reproducing data to and from a disk; an actuator; the microcontroller being arranged to control the actuator; and a memory containing a control program including head positioning control processes executed by the microcontroller; wherein said control program incorporates control processes for causing the actuator to undertake a track seeking operation and a track following operation, the controller being characterised in that said track seeking operation is executed according to: V error = Vprof - V actual V actual =(V cal + V pred )/2 V pred =V cal + K pred ·V cal F(V error , V error ')=-V actual + K decel + f (V error , V error ') Where, V error : a velocity error of a head, V error ' : a derivative value of a velocity error V prof : a head velocity at a given current track V actual : a head velocity which a calculation time delay is compensated PES n : a position error signal notifying of the off-track error of a head from a track. I pes : an integral value of PESn K switching : an acceleration/deceleration communtation constant F(V error , V error ') : a fuzzy function K p : a proportional gain constant K D : a derivative gain constant P error : the number of remaining track to be travelled K following : a communtation constant from a track seeking operation to a track following operation V cal : a head velocity calculated by a difference between the number of for tracks to be travelled at present and the number of tracks to have been travelled at a previous sampling time V pred : a predicted velocity of a next sampling time K pred : a constant obtained from a trial-and-error method K decel : a compensation constant t trans : a transient response time E permit : a predetermined transient response time. A head is accelerated and decelerated according to Eq. 1 and Eq. 2 of the above control algorithm, and the controller determines that the head has reached to a target track in case that the P error is smaller than the commutation constant K following , and the controller has the head to follow the current track by means of the PID control (Proportional Integral/Differential control) according to the algorithm as shown in Eq. 3. Since the commutation from head acceleration to head deceleration is performed by comparing V actual /K switching with a velocity error V error in every sampling, it has no relation to the number of tracks. The acceleration/deceleration commutation constant K switching is determined in a trial-and-error manner in order for a variation of a current to be minimized. By the head deceleration according to the control algorithm Eq. 2, an actual head velocity V actual becomes coincident with a given head velocity V prof . Accordingly, a control input for the head velocity decreases to zero in the track following portion which is a next control portion. In case of controlling an error compensation valve by a velocity error V error alone as in accelerating a head, a control input becomes small. Therefore, an actual head velocity fails to exactly follow a given velocity profile V prof and fluctuates around the given velocity profile V prof . This means that the actual head velocity V actual has to follow the given velocity profile V prof in a deceleration portion rather than follow the entire given velocity profile V prof . Since this is a matter on whether more or less deceleration is required to the head, deceleration has to be considered as a factor to control the head. As a result, a control input in a track following portion increases due to the foregoing matter. Accordingly, Fuzzy rules, which reduce a velocity error and fluctuation, are applied. Eq. 7 in the control algorithm, which describes Eq. 2 in detail, determines a control input in terms of-V actual , a compensation constant K decel and a fuzzy function f (V error , V error '). In case of applying a large control input for a fast reduction of the velocity error V error , in order to make an actual head velocity V actual to exactly follow a given head velocity profile V prof without fluctuation of the head velocity by preventing an occurrence of a velocity error V error in an opposite sign caused when the actual head velocity V actual exceeds the given head velocity profile V prof , the fuzzy function in Eq. 7 empolys a derivative value V error ' of the velocity error V error that notifies of the velocity error V error and the changed state of the velocity error V error . Language variables of the velocity error V error and its derivatie value V error ' are respectively defined in terms of language values, that is, PB (positve big), PM (positive medium), PS (positive small), Z (zero), NS (negative small), NM (negative medium), NB (negative big), which constitute 49 rules. The fuzzy rules are constructed with a trial-and-error method and experiences obtained from phenomena occurred in conventional control methods. A look-up table is formed by inferring the possible cases according to the constructed Fuzzy rules. On performing an actual control, a control input is determined with reference to the look-up table in accordance with a velocity error V error and its derivative value V error '. Since the control input by means of the Fuzzy rules to controls an actual head velocity by predicting a velocity error V error , the actual head velocity can follow a given velocity profile V prof exactly in a less head velocity fluctuation. And also, without using any separate velocity profile in order to prevent variation of transient response time in accordance with a change of the number of tracks to be travelled, a constant response appears at any number of tracks to be travelled by compensating for a control input in a deceleration control portion of the head using a compensation constant K decel calculated by Eq. 8 and Eq. 9 according to the number of tracks to be travelled. Since the method for determining a compensation constant is constructed together with Fuzzy rules, a rising time lengthened by a critical damping to appear when using the Fuzzy rules can be improved. As described above, by means of Fuzzy rules and compensation constants, the head of a disk drive system can exactly follow a velocity profile in a deceleration portion, thereby reducing the track seeking time by minimizing overshoot at a target track. Embodiments of the present invention will hereinafter be described, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 is a schematic block diagram of a general disk drive system controller, Fig. 2 is a graph showing a method for determining a velocity profile, Fig. 3 shows a chart of Fuzzy rules in language variables, Fig. 4 shows a look-up table according to the Fuzzy rules of Fig. 3, and Fig. 5 is a block diagram of a control algorithm. Fig. 1 shows a schematic block diagram of a general disk system controller as illustrated and described in US 4,979,055. The general arrangement of the disk system controller of the present invention may be as described in the above identified US Patent, and the description in US Patent No. 4,979,055 is specifically included herein by reference. The disk drive system controller comprises a controller (µc), an actuator assembly having an actuator, an arm and a head; and an actuator assembly controller (ACT CTL) connected to the microcontroller (µc) for controlling the actuator assembly. A memory (ROM) containing a control program is provided and includes head positioning control process for execution by the microcontroller. The memory is arranged to contain a control program which includes a head positioning control process according to the control algorithm as follows: V error = V prof - V actual V actual = (V cal + V pred )/2 V pred = V cal + K pred ·V cal F (V error , V error ') = -V actual + K decel + f(V error , V error ') Where, V error : a velocity error of a head, V error ' : a derivative value of a velocity error V prof : a head velocity at a given current track V actual : a head velocity which a calculation time delay is compensated PES n : a position error signal notifying of the off-track error of a head from a track. I pes : an integral value of PESn K switching : an acceleration/deceleration communtation constant F(V error , V error ') : a fuzzy function K p : a proportional gain constant K D : a derivative gain constant P error : the number of track to be travelled K following : a communtation constant from a track seeking operation to a track following operation V cal : a head velocity calculated by a difference between the number of tracks to be travelled at the present time and the number of tracks to have been travelled at a previous sampling time V pred : a predicted velocity of a next sampling time K pred : a constant obtained from a trial-and-error method K decel : a compensation constant t trans : a transient response time E permit : a predetermined transient response time. An integral value of PES n Ipes, is too small to exert influence on a control input in a track seeking operation, but the value is a predominent control input for lessening a velocity error V error in a track following operation, that is, in the normal state in the PID control. A velocity profile V prof plays a dominant role in determining a performance of a disk drive controller system. As shown in Fig. 2, since overshoot occurs when a head velocity exceeds a proximate-optimal time curve, that is, a given velocity profile, the slope of a velocity profile is determined to be low for switching as earlier as the changed velocity difference during the time period of two sampling in a maximum acceleration of a head on the basis of the proximate-optimal time curve. The reason of the two sampling time period is established for preventing a head velocity from being switched over the proximate-optimal time curve by a sampling time delay and to keep the head velocity steady against an external disturbance. A head is accelerated and decelerated according to Eq. 1 and Eq. 2 of the above control algorithm, and the controller determines whether the head has reached to a target track in case that the number of track to be travelled P error is smaller than the commutation constant K following , and the controller has the head to follow the current track by means of the PID control (Proportional Integral/Differential Control) according to the algorithm as shown in Fig. 3. The head is accelerated with the highest acceleration or linearly by using a velocity error V error as a control input according to Eq. 1. When a head is to travel a number of tracks. the head is accelerated to the highest acceleration, but an abrupt change of current does not occur as in the proximate-optimal time control since the magnitude of acceleration gets smaller when the velocity error V error becomes smaller. The commutation from head acceleration to head deceleration is performed by comparing V actual /K following with a velocity error V error . In case there are a number of tracks for a head to be travelled, since the head reaches to a velocity profile at a very high speed due to a long acceleration time, the shorter timing of commutation to deceleration is required than that of a few tracks. Otherwise, the head velocity continues to increase, so that the head velocity exceeds a velocity profile due to acceleration. In this case, it is difficult to decelerate the head as well as to avoid an abrupt current change. However, the commutation in the proposed commutation method is not implemented by comparison of a specific reference with an actual head velocity V atual or a velocity error V error or the number of track P error , but by comparison of V actual /K switching with a velocity error V error , the commutation reference varies in proportion to an actual head velocity. Therefore, the actual head velocity can be used as a commutation reference regardless of the number of tracks for the head to be travelled. In fact, since the commutation is accomplished before a head velocity reaches up to a velocity profile, the head is not immediately decelerated due to a small quantity of the velocity error remained, but kept with a small quantity of acceleration which is not decelerated yet. Since the head starts to be decelerated when a velocity error V error in an opposite sign appears just after a head velocity reaches to a velocity profile, a smooth commutation from acceleration to deceleration can be obtained. At this point, the commutation constant K following are to be chosen in a trial-and -error method in order to make the variation of current minimized. The seeking time becomes longer when the timing of the commutation becomes shorter. If the timing of the commutation gets later, a sudden variation of the current appears. The head deceleration is controlled to be on the line of a velocity profile V prof according to Eq. 2. The object of the head deceleration according to Eg. 2 is to reduce the control for the head input in a track following portion to zero. In case of controlling an error compensation value by a velocity error V error alone as in accelerating a head, a control input becomes smaller. Therefore, an actual head velocity fails to exactly follow a given head velocity-profile V prof and fluctuates around the given velocity-profile V prof . This is a problem occurred since the actual head velocity V actual has to follow the given velocity-profile V prof in a deceleration state rather than follow the given velocity-profile V prof . Even though the sign of a velocity error V error changes, the sign of a control input does not change, and its magnitude changes. Since this is a matter on whether more or less deceleration is required to the head, deceleration has to be considered as a factor to control the head. As a result, a control input in a track following portion increases due to the foregoing matter, so that overshoot is caused. Accordingly, Fuzzy rules, which reduces a velocity error and fluctuation, are applied. Eq. 7 in the control algorithm, which describes Eq. 2 in detail, determines a control input in terms of - V actual , a compensation constant K decel which will be described later and a fuzzy function f(V error , V error '). In case of applying a large control input for a fast reduction of the velocity error V error , in order to make the actual head velocity V actual exactly follow the given velocity profile V prof without fluctuation of the head velocity with preventing an occurrence of a velocity error V error in an opposite sign caused when the actual head velocity V actual exceeds the given velocity profile V prof , the fuzzy function in Eq. 7 employs a derivative value V error ' of the velocity error V error that notifies of the velocity error V error and the changed state of the velocity error V error . Language variables of the velocity error V error and its derivative value V error ' are respectively defined in terms of language values, that is, PB (positive big), PM (positive medium), PS (positive small), Z (zero), NS (negative small), NM (negative medium), NB (negative big), which constitute 49 rules as shown in Fig. 3. The Fuzzy rules are constructed with a trial-and-error method and experiences obtained from phenomena occurred in conventional control methods. A look-up table, as shown in Fig. 4, is formed by inferring the possible cases according to the constructed Fuzzy rules. On performing an actual control, a control input is determined with reference to the look-up table in accordance with a velocity error V error and its derivative value V error '. Since the control input by means of the Fuzzy rules controls an actual head velocity by predicting a velocity error V error , the actual head velocity can follow a given velocity profile V prof exactly in a less head velocity fluctuation. And also, without using any seperate velocity profile in order to prevent variation of transient response time in accordance with a change of the number of tracks to be travelled, a constant response appears at any number of tracks to be travelled by compensating for a control input in a deceleration control portion of the head using compensation constant K decel calculated by Eq. 8 and Eq. 9 according to the number of travelled tracks to be travelled. Since the method for compensation constant is constructed together with Fuzzy rules, a rising time lengthened by a critical damping to appear when using the Fuzzy rules can be improved. Eq. 8 and Eq. 9 are applied for determining a compensation constant K decel . The compensation constant K decel satisfying a predetermined transient response time E permit at every number of tracks to be travelled is determined in an off-line manner, and compensates for a control input when a head travels tracks. where, t trans denotes a transient response time. Fig. 5 shows a block diagram of control algorithm. A reference numeral ref is a track movement command which is to be given as a target track number. The P error is determined by the number of track to be travelled on the basis of a current track number. The track seeking operation, reference numeral (3) in Fig. 5, is constructed with a head acceleration process and a head deceleration process, reference numeral (4) in Fig. 5. An actual head velocity, an output value of Fuzzy rules and a compensation constant are generated as a control input. When a head reaches to a target track, the number of tracks to be travelled P error becomes smaller, and a commutation is performed from a track seeking operation in reference numeral (2) of Fig. 5 to a track following operation in reference numeral (1) of Fig. 5. A commutation constant K following is used as a commutation reference and the commutation is made by comparison of the number of tracks to be travelled P error with the commutation constant K following . The track following operation is accomplished by the PID control in reference numeral (2) of Fig. 5. As described above, by means of Fuzzy rules and compensation constants, the head of a disk drive system can exactly follow a velocity profile in a deceleration portion, so that the track seeking time can be reduced with minimizing overshoot at a target track.

Claims: A method of controlling a actuator of a disk drive apparatus, wherein, in response to control signals, a actuator controller is arranged to move said actuator to seek a selected disk track and to position an actuator head thereof relative to said selected disk track, ad wherein said controller is arranged to accelerate and then decelerate said actuator, the method being characterised in that during deceleration of said actuator said method comprises the steps of determining the control signals applied to said actuator controller during deceleration such that said actuator substantially follows a desired velocity profile, and in that said control signals are determined in dependence upon a predetermined deceleration constant, the actual velocity of the actuator, ad a value determined by Fuzzy rules in dependence upon the difference between the desired velocity of the profile and the actual velocity of the actuator, fuzzy rules not being applied during acceleration. A method as claimed in Claim 1, wherein a look-up table constructed in accordance with Fuzzy rules is provided, and said value determined by Fuzzy rules is determined by inputting said difference between the desired and actual velocities, and the derivative of said differences, to said look-up table. A method as claimed in Claim 1 or Claim 2, wherein said predetermined deceleration constant is selected in dependence upon the number of tracks to be travelled by said actuator. A method as claimed in any preceding claim, further comprising the step of causing said controller to switch from acceleration to deceleration of the actuator if it is determined that the difference between the desired velocity of the profile and the actual velocity of the actuator is substantially equal to the value of the actual velocity divided by a predetermined commutation constant. Apparatus for controlling an actuator of a disk drive utilising the control method as claimed in any preceding claim, said apparatus comprising an actuator controller arranged to move said actuator to seek a selected disk track and to position an actuator head thereof relative to said disk track, and programmable control means programmed for determining and generating the control signals according to the method as defined in any of the preceding claims and for applying them to said actuator controller to cause track seeking movement of said actuator. A disk drive system controller comprising a microcontroller; a data recording/reproducing apparatus having a sensor for recording and reproducing data to and from a disk; an actuator; the microcontroller being arranged to control the actuator; and a memory containing a control program including head positioning control processes executed by the microcontroller; wherein said control program incorporates control processes for causing the actuator to undertake a track seeking operation and a track following operation, the controller being characterised in that said track seeking operation is executed according to: a) in an acceleration portion, U = V error + I pes (V actual /K switching < V error ) b) in a deceleration portion, U = f(V error , V error ') - V actual + K decel c) said track following operation is executed according to: U = K p .PES n + K D . (PES n-1 - PES n ) + I pes (P error < K following ) Where, V error : a velocity error of the head, V error ': a derivative value of a velocity error, V prof : a head velocity at a given current track, V actual : a head velocity which a calculation time delay is compensated, PES n : a position error signal notifying of the off-track error of a head from a track, I pes : an integral value of PES n , K switching : an acceleration/deceleration communtation constant, F(V error , V error '): a fuzzy function, K p ; a proportional gain constant, K D : a derivative gain constant, P error : the number of track to be travelled, K following : a communtation constant from a track seeking operation to track following operation, V cal : a head velocity calculated by a difference between the number for tracks to be travelled at present and the number of tracks to have been travelled at a previous sampling time, V pred : a predicted velocity of a next sampling time, K pred : a constant obtained from a trial-and-error method, K decel : a compensation constant, t trans : a transient response time, E permit : a predetermined transient response time. A disk drive system controller as claimed in claim 6, wherein said data recording/reproducing apparatus is an actuator assembly constituted with an actuator, an arm and a head. A disk drive system controller as claimed in claim 6, wherein said data recording/reproducing apparatus is a pickup apparatus having at least one travelling unit and at least one optical sensor.

Inventors: CHANG WOOSEOG, CHOI HYEONTAEK, KIM GOONJIN, LEE CHANGHEE, SEO ILHONG, CHANG, WOOSEOG, CHOI, HYEONTAEK, KIM, GOONJIN, LEE, CHANGHEE, SEO, ILHONG
Applicants: DAEWOO ELECTRONICS CO LTD, DAEWOO ELECTRONICS CO., LTD
Application year: 1993
Main classification: G11B21
IPC codes: G05B19, G11B21, G11B7