EP0468962A1 - Procede et dispositif de positionnement d'une memoire a disque magnetique - Google Patents

Procede et dispositif de positionnement d'une memoire a disque magnetique

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Publication number
EP0468962A1
EP0468962A1 EP19890910619 EP89910619A EP0468962A1 EP 0468962 A1 EP0468962 A1 EP 0468962A1 EP 19890910619 EP19890910619 EP 19890910619 EP 89910619 A EP89910619 A EP 89910619A EP 0468962 A1 EP0468962 A1 EP 0468962A1
Authority
EP
European Patent Office
Prior art keywords
positioning
current
positioning unit
nominal
value
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP19890910619
Other languages
German (de)
English (en)
Inventor
Heinz-Dieter Maier
Werner Spengler
Heriberto Unger
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
Siemens Corp
Original Assignee
Siemens AG
Siemens Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens AG, Siemens Corp filed Critical Siemens AG
Publication of EP0468962A1 publication Critical patent/EP0468962A1/fr
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
    • G11B5/54—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head into or out of its operative position or across tracks
    • G11B5/55—Track change, selection or acquisition by displacement of the head
    • G11B5/5521—Track change, selection or acquisition by displacement of the head across disk tracks
    • G11B5/5526—Control therefor; circuits, track configurations or relative disposition of servo-information transducers and servo-information tracks for control thereof
    • G11B5/553—Details
    • G11B5/5547—"Seek" control and circuits therefor

Definitions

  • the invention relates to a method for positioning a positioning unit of a magnetic disk memory according to the preamble of claim 1 and to a device for performing this method.
  • the average access time is known to be one of the essential performance criteria in addition to the storage capacity.
  • the track density and the average access time which may include the pure positioning time and the settling time on a selected track, determined the structure of the positioning unit and the positioning method.
  • the conventional positioning methods are similar in that a speed profile dependent on the track distance, ie a specific speed as a function of the distance traveled during the positioning process, is specified as a setpoint curve and the sequence of the positioning process is then regulated
  • An analysis of the positioning process on this basis is described, for example, in "Magnetic Recording", Vol. II, published by CDMee and EDDaniel, Mc Graw Hill Verlag, 1988 in Section 2.3.5. With this setpoint specification in the form of a speed profile, access times are around 20 ms still controllable.
  • the positioning unit In this known positioning method, three groups of positioning processes are distinguished depending on the track distance that occurs. In the case of positioning operations below a certain track distance, the positioning unit does not yet reach the maximum predetermined acceleration. In this case, the positioning unit is linearly accelerated in the first quarter of the positioning time, then the change in the acceleration reverses its direction, so that with three quarters of the positioning time the greatest deceleration occurs, which then occurs near drops again until the end of the positioning process.
  • the course of acceleration over time therefore corresponds to two triangles which are symmetrical to the time axis and are placed directly next to one another.
  • the acceleration profile therefore also contains sections with constant acceleration or deceleration and corresponds to two trapezoids that are symmetrical with respect to one another with respect to the time axis and are placed directly next to one another.
  • the acceleration profile then corresponds to two trapezoids lying symmetrically to the time axis, which are spaced apart from one another in time.
  • the acceleration component of the overall profile with the opposite sign is identical to the deceleration component, i. H. the setpoint curve is point symmetrical. This symmetry considerably facilitates the determination of the respective setpoint profile under real-time conditions, as does the requirement that the acceleration or deceleration change linearly with a predetermined gradient in all positioning processes.
  • Each of the described acceleration profiles contains more or less discontinuities in the temporal derivation of this acceleration function, which are still the reason for the excitation of mechanical vibrations and thus for the generation of operating noises, although due to the gradual increase and decrease in the acceleration or deceleration, an extension of the positioning time is accepted.
  • the present invention is therefore based on the object of creating a method of the type mentioned which, with a further reduction in the average access time, eliminates the causes of the generation of undesired mechanical vibrations even more than hitherto, and also to provide a device for carrying out this method which inexpensive structure has a high flexibility to adapt to the respective application.
  • a major advantage of the solution according to the invention is that it succeeds in "smoothing" the acceleration for driving the positioning unit throughout the course of the setpoint curve, i. H. in other words, without specifying rounded points of discontinuity.
  • a linear increase in the acceleration or deceleration is not accepted, but rather the aim is to optimize the time, to achieve maximum acceleration or deceleration values as quickly as possible by means of a corresponding current specification.
  • This helps to reduce the average access time as well as the Rounding of the acceleration profile at the end of a positioning process, which allows the positioning unit to enter the target track as precisely as possible with an optimized settling behavior.
  • the positioning method is based on a setpoint curve which, apart from the rounding, is preset in a time-optimized manner and is nevertheless also optimized with regard to the settling on the target track.
  • Another important advantage of the method according to the invention is that it is also able to use the reserves in the control for driving the positioning unit, ie. H. make full use of the influence of the back EMF.
  • the detachment from point symmetry practically results in a deceleration interval that is shorter with respect to the acceleration interval and thus uses a further influencing variable that contributes to reducing the average access time.
  • this method using a commercially available signal processor is able to carry out the control process under real-time conditions without that of the respective track distance-dependent courses of the setpoint profile are already predetermined, for example in a setpoint memory. For this reason, a device for carrying out this method does not require any specialized integrated circuits that were previously not available on the market. Rather, the method can be implemented solely with the aid of conventional components, with a conventional signal processor with its properties being optimized with regard to certain addition and multiplication processes.
  • FIG. 1 shows schematically in a block diagram a control unit for a magnetic disk memory with an actual value generator and a setpoint generator, in which setpoints are generated for the positioning for each positioning process
  • FIGS. 2a to 2c schematically in the form of pulse diagrams the principle of a speed profile, a corresponding current profile for driving the positioning unit and a profile for the terminal voltage on a drive coil of the positioning unit
  • FIG. 5 shows the equivalent circuit diagram for an FIR filter
  • FIG 6 in the form of pulse diagrams a step function and a filter response of an FIR filter corresponding to this step function
  • FIG. 7 shows a block diagram for a setpoint generator according to FIG. 1,
  • FIG. 9 shows an embodiment for a setpoint generator in hard-wired circuit technology
  • FIG. 11 shows schematically in a block diagram a further embodiment of a device for carrying out the positioning method using a signal processor
  • FIG. 12 shows schematically in a block diagram the processes under control of the signal processor for converting the acceleration or current profile shown in FIG. 8 into a profile according to FIGS. 10a and
  • FIG. 13 shows a flowchart for the control or computing processes carried out by the signal processor.
  • a device control 1 is shown schematically in a block diagram, via which the magnetic disk memory contacts its environment.
  • the device controller controls the data transfer from and to the magnetic disk storage and - which is of more important interest in the present case - also triggers a lane change if one Writing or reading in another track of the magnetic disk memory is to be continued.
  • Such device controls are generally known. There is therefore no need for any further explanation here, because when a lane change is to be carried out, this device control merely provides a distance address ADR which outputs a corresponding jump distance in the form of the number of recording tracks to be overflowed and the respective direction, and a start signal START which defines the start of the lane change operation.
  • FIG. 1 also schematically shows a positioning unit 2 for the magnetic disk memory, which is to be designed as a rotary positioner.
  • Rotary positioners for magnetic disk storage are particularly common for 5 1/4 "or 3 1/2" disk storage, so that no detailed description appears necessary for this unit. Therefore, it should only be pointed out here that conventional rotary positioners have a swivel piece which is rotatably mounted in the disk storage housing.
  • the swivel piece carries, via a plurality of radially projecting support arms, a corresponding plurality of magnetic head systems which are exactly aligned with one another and which, when the swivel piece swivels, pivot in together over the surfaces of the storage disks of the magnetic disk storage assigned to them.
  • the swivel is driven by a magnetic drive coil, to which a corresponding coil current is fed via a controlled power controller.
  • the magnetic drive coil is surrounded by a system of permanent magnets so that it moves depending on the coil current and thus deflects the swivel piece.
  • Such a drive device 201 of the positioning unit 2 is only indicated schematically in FIG.
  • read / write electronics 202 which contains, in particular, write or read amplifiers assigned to the magnetic head systems, are also axially arranged in the positioning unit 2. It is assumed here that this read / write electronics 202 additionally also has an evaluation electronics for recording riding, rectification and selective comparison of servo signals.
  • phase-locked loop 3 which is used to derive a dependent internal clock pulse sequence CLK from these read signals RS in magnetic disk memories, which forms the time basis for all internal control processes and, for reasons of simplicity, for example also for the control of the control processes when positioning is used.
  • this read / write electronics 202 in the form of the evaluation electronics should also have switching devices which generate position error signals PES from the read servo signals. These usually form the control signals for tracking in magnetic disk memories. As indicated schematically, the position error signals here have a sawtooth-shaped course, the zeros of which occur when the positioning unit 2 continuously crosses recording tracks in the course of a track change.
  • the magnetic disk memory is a memory with random access, ie the positioning system must be adjustable to any track on the magnetic memory disks each time a track is changed. Furthermore, every positioning process should always run optimally, since the average positioning time is a key performance criterion in magnetic disk storage.
  • One projects in the drive device 201 of the positioning unit 2 given supply voltage V is available, which is to be used optimally, in principle in the acceleration phase of the magnetic drive coil of the positioning device 2 to supply maximum acceleration current until the predetermined maximum speed of the positioning unit 2 is reached.
  • the braking phase begins, in which the positioning unit 2 is braked with the maximum braking current, until it enters the target track as precisely as possible.
  • the braking phase begins with short distances, ie short track distances, before the maximum speed is reached.
  • FIG. 2a A speed profile v i (t) is shown in FIG. 2a
  • FIG. 2b shows a corresponding current curve i (t), ie a curve which corresponds to the time profile of the current supplied to the magnetic drive coil in the drive device 201 as a control variable
  • FIG. 2c illustrates the corresponding one Course of the terminal voltage V (t) on the drive device 201 of the positioning unit 2.
  • FIG. 3 shows a series circuit of a current source 203 and a magnetic drive coil 204 of the drive device 201 arranged between the supply voltage V s and ground.
  • the current source 203 is implemented by a power amplifier, to which a control voltage for setting the coil current i (t) is supplied.
  • This power amplifier has a predetermined own requirement, which is effective as a voltage drop. You also need a certain span to be able to regulate during the positioning process reserve.
  • V 1 partial voltage
  • the equivalent circuit diagram of the magnetic drive coil 204 clarifies the ohmic resistor 205 and the inductive resistor 206 of the magnetic drive coil, which are predetermined by the dimensioning of the coil 204.
  • the influence of the back emf is indicated in the form of a voltage source 207, which builds up as a voltage contribution that is linearly dependent on the speed and the motor constant K of the magnetic drive coil 204.
  • I o (V s - V 1 ) / R
  • K is the motor constant
  • R is the ohmic resistance of the magnetic drive coil 204
  • V s is the supply voltage
  • V 1 is the partial voltage which corresponds to the self-consumption of the controlling power amplifier 203 and the control reserve.
  • the back EMF has a braking effect when accelerating, but can then be used to support the braking phase.
  • the setpoint curve for the coil current i (t) becomes asymmetrical, ie that the braking phase becomes shorter than the acceleration phase.
  • FIGS. 2a to 2c also illustrate, as an example, that in order to control the positioning process, a specific profile must be specified for each possible track distance in order to carry out the positioning process in a time-optimized manner.
  • Velocity profile v i (t) is used. But if, for example, with 5 1/4 "magnetic disk storage media today you are aiming for average positioning times of less than 15 ms, this means speeds that can only be mastered by control technology with considerable effort due to the additional constraint that the target track should be approached as precisely as possible.
  • a path profile x n (t) is used in connection with a current specification in (t) for the control of the positioning process, the latter determining the acceleration of the positioning unit 2 in the initial phase or its deceleration in the final phase of a positioning process.
  • FIG. 4c A current curve i (t) or the corresponding acceleration curve a (t) is shown schematically in FIG. 4c, which has a linear course pieced together.
  • the associated amplitude spectrum A shown in FIG. 4d with the same transfer function shows a significantly more favorable course compared to the illustration in FIG. 4b, but always appreciable amplitude values even at frequencies above 5 kHz.
  • a current and acceleration curve i (t) or a (t) is shown in FIG. 4e, the edges of which rise or fall relatively steeply, but which is rounded, for example, according to a cosine function in the transition regions.
  • the associated amplitude spectrum A shown in FIG. 4f shows the best values in a comparison of all FIGS. 4b, 4d and 4f. This shows convincingly that it is very important to design the current curve i (t) in such a way that all transitions run as smoothly as possible in order to avoid the excitation of mechanical vibrations, thus disturbances in the positioning process, such as long settling times and high operating noises.
  • x is the deflection related to the servo head
  • ⁇ the moment of inertia of the positioning unit 2
  • 0 the speed proportional friction
  • d is a restoring force of the positioning unit, which can be attributed, for example, to the flexible cable feeds.
  • This approximate relationship corresponds to the fact that the displacement of the positioning unit 2 is proportional to the double integration of the current in the magnetic drive coil 204, as long as the coil is not oversaturated.
  • an analog control variable i s (t) fed to the drive device 201 of the positioning unit 2 is linearly proportional to the current curve i (t).
  • this control variable is based on an already rounded current profile with the matching path x or whether one first specifies a hard current profile i (t), as indicated for example in FIG. 2b, with the associated path and then both in electrical Sends functions expressed by signals through the same filter and thus rounded.
  • FIR filters finite impulse response filters
  • a circuit design of such a filter is such. B. in IEEE Journal of Solid-State Circuits, Vol. 23, No. 2, April 1988, pages 536 to 542 and discussed in detail. Knowledge of this type of filter can therefore be assumed here.
  • FIG. 5 an equivalent circuit diagram for such an FIR filter is therefore shown schematically only for better understanding. Since the rules of the z-transformation are to be applied to digital filters, each block z in this equivalent circuit diagram means the shift of the input signal SI by one sampling period
  • FIG. 6 schematically illustrates this filter function for a 5th order FIR filter.
  • a broken line pulse is shown with broken lines as the input signal SI.
  • the filter response, ie the output signal SO of the FIR filter is the step-shaped signal curve which, after a number n of sampling periods corresponding to the order n of the filter, corresponds exactly to the end value of the input signal SI.
  • Using an FIR filter it is therefore possible to specify the current profile "hard” and still achieve a "soft” setpoint value with an adjustable rounding curve while observing the described boundary conditions.
  • the block diagram shows an actual value transmitter 4, to which the sawtooth-shaped position error signal PES is fed.
  • This signal has a period that is identical to the track grid and has a stroke that fully utilizes the available supply voltage for a single track distance.
  • the device address 1 supplies this actual value transmitter 4 with the distance address ADR, which defines the jump distance for the upcoming lane change.
  • the START signal START which is also supplied by the device controller 1, the actual value transmitter 4 evaluates the supplied position error signal PES in such a way that it reduces the distance address ADR by the value "1" for each detected track crossing.
  • the respectively remaining current remainder is output as the actual path value x a for the deflection of the positioning unit 2 which is still to be covered.
  • FIG. 7 A possible implementation for this actual value transmitter 4 is shown in FIG. 7. Thereafter, it has a loadable counter 41 designed as a down counter, at whose data inputs DI the distance address ADR is present and is loaded when the start signal START occurs.
  • a zero crossing detector 42 is provided for the signal PES. This derives a rectangular pulse sequence from the position error signal, which is supplied to the counter 41 as a clock signal. After each leading edge of this clock signal, the counter 41 thus outputs a distance address reduced by "1" via data outputs DO. This is fed to an adder 43, at whose second inputs the position error signal PES converted into a binary value via an analog-digital converter 44 is present.
  • the actual path value xa output by the adder 43 is therefore composed of the distance still to be covered, expressed in the number of tracks still to be crossed, and a fine adjustment value which corresponds to the current offset from the middle of the track of the last crossed track.
  • FIG. 1 also schematically indicates a setpoint generator 5, the nominal values. x n and in for the still to be covered
  • This setpoint generator 5 is - as a possible embodiment - constructed in hard-wired circuit technology and has a function generator 51 which, depending on the value of the distance address ADR supplied to it after the start signal START has been supplied, continuously generates the non-rounded current specification curve i (corresponding to the respective positioning process) t) generated.
  • This unrounded current specification curve is fed to a FIR filter 52 in the form of binary values.
  • This filter should be of a sufficiently high order, for example 20th order, in order to generate a filter response which is rounded in the desired manner, preferably cosine, and which is output in binary form as the nominal current specification i n .
  • the nominal current specification i n corresponds linearly to a nominal acceleration tion, ie the second derivative of the remaining nominal
  • the braking phase begins with a current value -i 2 and at time t3 the braking phase ends with a current value -i 3 , which in turn jumps to zero.
  • the linear sections of the current specification curve i (t) during the time intervals ⁇ t1 and ⁇ t3 are described as gradients m 1 and m 3 by the current drop di / dt approximating the back emf.
  • the parameters i 0 , i 3 , m 1 and m 3 are each independent of the respective track distance, ie they are device constants. This makes it clear that the individual positioning processes differ only in the length of the time intervals ⁇ t1 to ⁇ t3.
  • FIG. 9 shows an embodiment for the function generator 51 which is embodied in a hard-wired circuit and is shown as a block diagram on which this calculation basis is based.
  • the variable parameters are stored in a programmable read-only memory 510 for all track distances and can be selected by the distance addresses ADR.
  • the current start value i 0 is loaded into a first counter 511.
  • This counter is designed as a down counter, which is controlled by the internal clock pulse sequence CLK. Its counter reading decreases in time with this control signal and is continuously read out to a multiplexer 512. Set by the START signal, this multiplexer switches this variable current value during the time interval
  • a first digital comparator 513 is also provided The current value i 1 is supplied to the first inputs from the programmable read-only memory 510 and the second inputs of the current value are also connected to the outputs of the first counter 511.
  • This comparator thus continuously compares the counter reading of the first counter 511 with the final value of the current at the end of the first time interval ⁇ t1 of the unrounded current specification curve i (t).
  • the first comparator thus determines the expiry of the first time interval ⁇ t1 when the signals supplied to it are identical.
  • the multiplexer 512 is switched by the output signal of this first comparator 513 and at the same time a second counter 514 is loaded with a value that corresponds to the length of the second time interval ⁇ t2.
  • the outputs of this second counter 514 are connected to inputs of a second digital comparator 515.
  • This digital comparator is also supplied with a value "0", preferably from the programmable read-only memory 510, so that it determines when the second time interval ⁇ t2 has expired.
  • the second comparator 515 outputs an output signal which switches the multiplexer 512 and at the same time controls the loading of a third counter 516 with the braking current value -i 2 at the beginning of the third time interval ⁇ t3.
  • this third comparator 517 is also offered the final value -i 3 for the braking current from the read-only memory 510.
  • this comparator 517 establishes the identity of the input signals fixed and emits a corresponding output signal.
  • This control signal STOP indicates the end of the unrounded current specification for the positioning process and is supplied to the device controller 1 and the integrator 53 shown in FIG. An embodiment for this integrator 53 is also shown in FIG.
  • the output signal emitted by the FIR filter 52 represents the second derivative of the nominal path specification x n . Since the nominal current specification i n is available as a digital value, the integration of this value can be attributed to a continued addition. Therefore, the integrator 53 is composed of two adders 530 and 531. The first adder is connected to the FIR filter 52 with first signal inputs. Its outputs are both connected to first inputs of the second adder 531 and also fed back to its second inputs. The second adder 531 is connected in a corresponding manner, so that both adders carry out continuous additions of the input signals supplied in each case and together double integration of the output signals of the FIR filter
  • the integrator 53 thus generates the nominal one
  • Path specification x n . 10a to 10c show pulse diagrams which exemplify the effect of the FIR filter arrangement 52.
  • a current or acceleration profile a (t), i (t) is shown with broken lines in FIG. 10a, which corresponds to the unrounded specification of FIG. With solid lines, the associated filtered default curve is a (t); i n (t) shown.
  • the rounding effect of the FIR filter 52 can be seen in particular. It is particularly important that the defined final state is reached exactly after a finite delay predetermined by the order of the FIR filter 52 is. In FIGS.
  • speed profiles v (t), v n (t) and path profiles x (t) are analogous to the acceleration profile of FIG. 10a; x n (t) not rounded and filtered.
  • the three time segments of the setpoint curve are illustrated there analogously by the times t 0 , t 1 , t 2 and t 3 .
  • the essential reference variable for the positioning process is the nominal current specification i n , to which, delayed by the delay element 54, the output signal of the digital comparator 6 is added in an adder 7.
  • the delay element 54 compensates for transit times in the integrator 53 and in the digital comparator 6, so that the input variables offered to the adder 7 are phase-synchronized.
  • the output signal of this adder 7 thus represents the actual reference variable for the positioning process, which is converted in a digital / analog converter 8 into the analog control variable i s (t).
  • This control variable is supplied to the drive device 201 of the positioning unit 2 as a control signal for the power amplifier 203 forming the switched current source.
  • a first exemplary embodiment has been described above which allows the positioning method on which the underlying method is based to be carried out in hard-wired circuit technology. Despite all the optimization of the method steps described, such a hard-wired solution is always relatively complex and also not very flexible with regard to adaptations, for example changing the device constants. A way out is a programmable controller. Today, digital signal processors are available that are suitable for this application, since they are optimized for filter calculations in which multiplications and additions predominate.
  • the A person skilled in the art is, for example, known from the publications "Digital Signal Processing Applications With The TMS 320 Family", 1986 and “First Generation TMS 320 User's Guide”, 1987, both published by Texas Instruments, an extensive range of instruments, such as how to use the TMS 320 CIO signal processor ® can be used in a wide variety of applications.
  • the processor mentioned has a cycle time of 200 ns with a word length of 16 bits, the accumulator being 32 bits wide and the multiplier delivering a 32 bit result with a thickness of 16 x 16 bits.
  • an explanation of the performance of this signal processor is given here by way of example to an instruction sequence MPY and LTD, which is described there on pages 4/49 and 4/41.
  • this command sequence results in a 16 x 16-bit multiplication, a 32-bit addition to the accumulator, the loading of a RAM cell into the multiplier and the shifting of the contents of this RAM cell to the next higher address.
  • an intelligent positioning control unit 9 is shown schematically in a block diagram, which is connected to the device controller 1.
  • an 8-bit wide analog / digital converter 92 and a 10-bit wide digital / analog converter 93 are provided in this positioning control unit.
  • the above-mentioned units are connected to one another via an interface 94 which, as in many conventional microprocessor applications, has simple logic circuits which enable the signal processor 91 to exchange data with the connected units.
  • the analog / digital converter 92 and the digital / analog converter 93 can be implemented by an AD7569 module from Analog Devices®, which has an 8-bit analog / digital converter and two 8-bit digital / analog converters and corresponding inputs /Output and contains selection logic.
  • This module can be used in such a way that its two digital / analog converters together form the digital / analog converter 93. For this purpose, they are switched in such a way that one only outputs the signal corresponding to the current specification curve i n during a positioning process and the other outputs the actual control signal for tracking.
  • the gain of the first digital / analog converter is four times higher than that of the second. The result is that the resolution for the nominal current command i n corresponds to a 10-bit value. Because of the availability of a corresponding fast module, this division is more cost-effective and possibly also more expedient in view of the real-time conditions than a correspondingly broad individual digital / analog converter, as is indicated schematically in FIG. 10.
  • the design of the positioning control unit 9 is based on the principles which have already been explained in detail in connection with the first exemplary embodiment. A significant difference in the implementation here is, however, that the default values, made possible by the performance of the digital signal processor 91, are determined in real time during a positioning process, which is particularly advantageous with regard to a possible adaptability in this embodiment for carrying out the positioning method . Since the calculation methods for determining the time intervals ⁇ t1 to ⁇ t3 are optimized with regard to the properties of the digital signal processor 91 used, they are explained below. Here, too, it is assumed that the following basic conditions apply to each positioning process.
  • the relationship (6) gives an estimated positioning range xs', which must be smaller than because of the requirements ⁇ t 1 ' ⁇ t 1 and ⁇ t 3 ' ⁇ t 3 the full positioning range xs.
  • the difference between the actual positioning range xs and the estimated positioning range xs' is compensated for by introducing the time interval ⁇ t 2 .
  • the positioning unit 2 is constantly moved at the speed v, at the end of the time period ⁇ t 1 '.
  • this velocity v 1 is calculated according to the following relationship (8):
  • (8) v 1 a 0 ⁇ t 1 '+ (1/2) m 1 ⁇ t 1 ' 2
  • the derivation described above initially has the advantage that the estimate for the time interval ⁇ t 1 'is based on a simple relationship which, in contrast to an exact calculation, requires considerably less programming effort, computing time and storage space requirement. Since the time interval ⁇ t 1 'is estimated anyway, it can always be selected as an integer value of sampling periods ⁇ t, thereby avoiding correction calculations of the specification curve in the transition area between the time intervals ⁇ t 1 and ⁇ t 2 . Another very important advantage is that, regardless of the track distance, a time interval ⁇ t 2 is introduced with each positioning process or, in other words, there is no need to distinguish between positioning processes over short or long track distances.
  • This maximum value for the first time interval ⁇ t1 is an operating constant which is calculated once during a restart of the magnetic disk storage in a start-up routine.
  • the current specification was used as an example and the path specification was obtained from it by integration.
  • a path specification is used, from which the rounded nominal current specification is determined by double differentiation after the filtering.
  • the non-rounded default curve is to be shaped by filtering in such a way that it specifies the current for exciting the magnetic drive coil of the positioning unit 2 as harmless as possible.
  • This goal can only be adequately achieved with a higher order FIR filter.
  • the basis here is an FIR filter, for example of the 20th order, which is implemented by a filter program of the signal processor 91. Because of the high order of the FIR filter, a corresponding amount of computing time arises, which should be minimized as far as possible, since the determination of the default values for current and distance takes place in a time-critical area.
  • the last term from relationship (11), namely m i ⁇ t 3, is constant within these time intervals.
  • the relationship (11) thus corresponds formally to a filter operation that can be processed by the signal processor 91 in a time-optimized manner. In this extrapolation routine it should be noted that when moving from a period, e.g. B. ⁇ t 1 for the next period, e.g. B.
  • ⁇ t 2 does not have any corresponding previous travel setpoints per se.
  • these three previous path setpoints must therefore be simulated, ie calculated before the actual execution of the positioning process and made available in a memory.
  • the path information for example a current path setpoint x k, is absolute information which relates to the width of the entire data band on the magnetic storage disks.
  • a data format of 32 bit positions for the x-variables is therefore advisable for a 5 1/4 "magnetic disk memory. This format corresponds to two data words for a 16-bit signal processor. This extrapolation from three previous setpoint values could also be avoided.
  • the corresponding rounded quantity is filtered using Using the FIR filter to determine. It has already been indicated above that this filter should be of the 20th order. 5 and 6 it has already been explained that the filter order results from the ratio of smoothing time to the sampling period. If the sampling period is 60 ms and a 20 th order filter is used, the result is a smoothing time of 1.2 ms, which is still acceptable in the present application.
  • the selected high-performance digital signal processor 91 would still result in an excessively long computing time despite the algorithms described.
  • One solution to this problem is not to filter the absolute value for the current travel setpoint x k , but only to use its travel increment ⁇ x k to the previous travel setpoint x k-1 .
  • This path increment can be represented with sufficient accuracy in a 16-bit format. In other words, one forms the path increment ⁇ x k before filtering and then filters it.
  • the filtered path increment thus obtained is added to the previous absolute value of the nominal path specification x nk -1 and thus the absolute size for the filtered path specification, ie the nominal path specification x nk for the current sampling period.
  • the rounded current specification i n is derived from the nominal path specification x n by double differentiation. In the present case, this can be reduced to the formation of the second difference according to the following relationship (12):
  • i nk (x nk - 2x nk-1 + x nk-2 ) / ⁇ t 2
  • i nk ( ⁇ x nk - ⁇ x nk-1 ) + ⁇ 0 + ⁇ 1 . x nk + ⁇ 2 . ⁇ x nk
  • the expansion term ⁇ 0 corresponds to a constant acceleration, which compensates for an unbalance of the positioning unit 2, for example.
  • the second expansion term ⁇ 1 . x nk corresponds to a path-proportional acceleration that takes into account a force that acts proportionally on the positioning unit 2 and compensates, for example, a restoring force caused by connecting lines.
  • the third extension term ⁇ 2 . ⁇ x nk corresponds to an acceleration proportional to speed and thus takes into account, for example, a friction in the positioning unit 2. This shows that with the help of the relationship (12b) it is also possible to control a positioning unit 2 which deviates to a considerable extent from the quantities on which the ideal mechanics are based.
  • Block 110 shows an equivalent circuit diagram for the path extrapolation described.
  • Line 111 shows basic values x k-2 , x k-2 and x k-3 or m i ⁇ t 3 , each of which begins at the beginning of a new time interval ⁇ t 1 , ⁇ t 2 and ⁇ t 3 are loaded into registers of the signal processor 91 in order to suitably initialize the path extrapolation.
  • the current path setpoint x k can already be loaded in a register 112 and the simulated previous path setpoints x k and x k-2 in corresponding registers.
  • the three path parameters for one of the time intervals ⁇ t i result from the parameters a 0 , v 0 and x 0 of this time interval according to the following relationships (13), (14) and (15):
  • the first time interval ⁇ t 1 is always an integer multiple of the sampling period. With that lies the
  • x e3 x 1 + v 1 ( ⁇ t 2 + ⁇ t f ) + (1/2) a 3 ⁇ t f 2 + (1/6) m 3 ⁇ t f 3
  • the equivalent circuit diagram 114 reproduces the path increment described, in which the path setpoints x k and x k-1 of the current or the previous sampling period are subtracted from one another and result in the path increment ⁇ x k loaded in a register 115.
  • Block 116 represents an equivalent circuit diagram for the FIR filter, in which path increments x ki , evaluated with corresponding filter coefficients c i , are added up.
  • i means an integer value from 0 to n, where n indicates the order of the FIR filter.
  • Block 119 thus designates the equivalent circuit diagram for the described two-fold differentiation of the path increments, so that the current value i nk for the nominal current specification i n results therefrom.
  • the value temporarily stored in the register 117 for the rounded path increment ⁇ x nk is - as indicated by a delay element 121 - added to the content of a register 120 with a delay, which contains the absolute value for the path specification x nk-1 of the previous sampling period.
  • the current absolute value x nk for the nominal path specification x n is thus continuously output in synchronism with the current value for the current specification i n .
  • FIG. 12 shows a flow chart for the entire positioning routine.
  • the values for the time intervals ⁇ t 1 , ⁇ t 2 and ⁇ t 3 are first calculated in method step 1201. With these values obtained in this way, the basic parameters for each time interval, as indicated in method step 1202, are determined before the actual positioning process is carried out. With zeroing the values for the time interval ⁇ t and the
  • Time lapse t in method step 1203 the positioning control unit 9 and thus its signal processor 91 is set to a defined initial state at the beginning of the actual positioning process. Then, in order to initiate the first time interval ⁇ t 1 in accordance with method step 1204, the value for the current time interval is incremented by "1". After the initiation of this new time interval, the basic values assigned to it are first loaded in accordance with method step 1205. In the course of the first time interval ⁇ t 1 , the path increments ⁇ x k are then successively calculated in accordance with method step 1206 and filtered in accordance with method step 1207.
  • the current path increment output at the output of the FIR filter is, generally considered, added to the absolute size of the previous path setpoint and the current absolute size x nk of the nominal path specification x n is thus specified in method step 1208.
  • step 1209 this is followed by the calculation of the corresponding current variable i nk for the nominal current specification i n .
  • the absolute values x nk thus calculated for the
  • the path specification and i nk for the current specification are output, ie fed to the comparator 6 according to FIG. 1 or to the digital / analog converter, as indicated in method step 1210.
  • the time sequence is then incremented by the value "1" in method step 1211 and, according to branch 1212, the condition is queried as to whether t is already greater than the calculated total time for the positioning process. If this is the case, the positioning process is finished. Otherwise, a further condition is queried in method step 1213 as to whether the current time interval ⁇ t 1 , ⁇ t 2 or ⁇ t 3 has expired. If this is not the case, the current setpoint value x k for the applicable time period is calculated in accordance with method step 1214 and the program sequence continues with the calculation of the next path increment ⁇ x k in accordance with method step 1206. However, if the branching condition in method step 1213 is fulfilled, ie the current time interval has been completed, then the program flow continues according to method step 1204 with the incrementing of the time interval.
  • two variables namely the actual travel value x a and the nominal travel specification x n, are managed as absolute values in the memory of the signal processor 91.
  • the control process only the difference between these two variables is evaluated, each of which has a 32-bit format.
  • the higher-order data word contains the information about the track number in whole numbers
  • the lower-order data word on the other hand, the deviation from the track center in the form of fractions of a track.
  • this format the entire width of the data tape on the magnetic storage disks can be represented linearly with high accuracy.
  • any nominal track and additionally a selectable deviation from this track can thus be specified via the nominal path specification x n .
  • the actual path value x a is continuously updated via the position error signals PES which are read in, track crossings being automatically taken into account.
  • the next expected value is extrapolated from the course of this path actual value in the past and the corresponding edge of the position error signal PES is selected.
  • adjacent information tracks are distinguished by the track type which is defined in the servo cells containing the track information on the servo surface of the magnetic disk memory.
  • the described method can ensure correct track selection even if, at the limit speed of the positioning unit 2 of, for example, more than 1.5 m / s, up to six tracks are "blindly" flown over in a sampling period ⁇ t. Due to the separate management of the actual path value x a and the nominal path specification x n , any path errors are permitted in principle, this applies both to the positioning process and when settling onto a selected track. This principle also allows, if expedient, positioning operations over short track distances to be brought about solely by the sudden change in the nominal path specification x n , although a corresponding settling time must be expected. Reference list

Landscapes

  • Control Of Position Or Direction (AREA)
  • Moving Of Head For Track Selection And Changing (AREA)
  • Moving Of The Head To Find And Align With The Track (AREA)

Abstract

Afin de positionner une unité de positionnement (2), la position momentanée (xa) de l'unité de positionnement, sous forme de valeur réelle, est comparée en continu avec la position voulue (xn), sous forme de valeur de consigne. A cet effet, on utilise une courbe des valeurs de consigne dépendante de la distance entre la piste de départ et la piste cible. Le courant fourni à l'entraînement (201) de l'unité de positionnement est réglé en fonction de cette comparaison. La courbe des valeurs de consigne est tracée de manière optimale dans le temps sous forme de fonction progressive, prenant en considération la force contre-électromotrice de l'entraînement. Des valeurs de balayage (ik ou xk) correspondantes à cette courbe des valeurs de consigne sont transmises en continu avec une période prédéterminée de balayage (DELTAt) à un agencement FIR de filtrage (par exemple 52). Les coefficients de filtrage (c0... cn) sont sélectionnés de sorte que les points d'inflexion de la courbe des valeurs de consigne soient arrondis de préférence en cosinus. Les valeurs de balayage (ink ou xnk) ainsi filtrées sont converties en une valeur de commande (is(t)) de l'entraînement de l'unité de positionnement. Ce procédé est mis en oeuvre en temps réel de préférence au moyen d'un processeur de signaux.
EP19890910619 1989-04-27 1989-09-20 Procede et dispositif de positionnement d'une memoire a disque magnetique Ceased EP0468962A1 (fr)

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EP89107624 1989-04-27
EP89107624 1989-04-27

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WO1995025327A1 (fr) * 1994-03-14 1995-09-21 Seagate Technology, Inc. Deverrouillage d'un actionneur a boucle fermee sans capteur
US5600219A (en) * 1994-03-14 1997-02-04 Seagate Technology, Inc. Sensorless closed-loop actuator unlatch
US6324030B1 (en) 1995-05-02 2001-11-27 International Business Machines Corporation Digital pes demodulation for a disk drive servo control system using synchronous digital sampling
DE19523885A1 (de) * 1995-06-30 1997-01-02 Zeiss Carl Fa Verfahren zur Filterung von Meßwertkurven
WO2000003389A1 (fr) * 1998-07-13 2000-01-20 Seagate Technology, Llc. Formation de profil courant visant a reduire les variations du temps de recherche de lecteur de disque et le bruit acoustique genere
US6449117B1 (en) 1998-07-13 2002-09-10 Seagate Technology Llc Reducing acoustic noise using a current profile during initial stages of a disc drive seek
US6320721B1 (en) 1998-09-21 2001-11-20 Texas Instruments Incorporated Method and apparatus for controlling a voice control motor in a hard disk drive
DE50207999D1 (de) 2002-05-07 2006-10-12 Ems Chemie Ag Gewellter Mehrschicht-Polymer-Schlauch- oder Rohrleitung mit reduzierter Längenänderung

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JPH0833771B2 (ja) * 1985-11-26 1996-03-29 日本電信電話株式会社 アクチユエ−タのアクセス制御方法
FR2594586B1 (fr) * 1986-02-14 1988-04-29 Bull Sa Procede pour deplacer un systeme mobile par rapport a un support d'informations et dispositif pour le mettre en oeuvre
US4775903A (en) * 1986-10-14 1988-10-04 Hewlett-Packard Company Sampled servo seek and track follow system for a magnetic disc drive
WO1988002913A1 (fr) * 1986-10-14 1988-04-21 Maxtor Corporation Procede et appareil de commande de la position d'un assemblage de tete mobile

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