Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B21/00—Head arrangements not specific to the method of recording or reproducing
  • G11B21/02—Driving or moving of heads
  • G11B21/08—Track changing or selecting during transducing operation
  • G11B21/081—Access to indexed tracks or parts of continuous track
  • G11B21/083—Access to indexed tracks or parts of continuous track on discs
• • 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

Definitions

• the invention relates to a method for adjusting an access arm of a disk storage system with at least one disk on which. data is stored along a multiplicity of tracks, the access arm carrying at least one transducer head which generates a position signal from continuously read position data and which is positioned on the respective track by the access arm being actuated by a servo drive which ent ⁇ a drive coil holds which electrical current is supplied as a function of the output signal of a controller, which determines the deviation of the position signal from a target value indicating the target position and regulates it.
• the invention further relates to a circuit arrangement for performing the method.
• Such a method is e.g. used in the positioning control of a magnetic disk memory.
• the access arms of several plates of a plate stack are mechanically connected to one another to form an access comb.
• Each access arm carries at least one transducer head, which can be designed as a read / write head or only as a write head or read head.
• the transducer heads of an access comb are arranged in such a way that they point to traces of the same radial position on the various plate surfaces at every position of the access comb.
• a storage surface of a disk is exclusively described with a pattern of position information, which define locations of concentric tracks on the disk surfaces.
• a specially designed read head which is also referred to as a servo head, continuously scans this position information, and an evaluation unit uses this information to generate a position signal which can be used to determine whether the servo head is pointing to a predetermined track and whether there is a deviation from the position Target track exists.
• a servo drive is used to adjust the position of the servo head, which moves the access arm or the access comb in the radial direction transverse to the traces of the plate surfaces.
• the servo drive contains a drive coil on which a static magnetic field acts. If a current flows through the drive coil, it is deflected in the magnetic field in a direction dependent on the current direction as a result of the force acting on a conductor through which current flows, and thereby adjusts the relevant access arm or the entire access chamber "
• a continuous current is applied to the drive coil, the amount and sign of which depend on the output signal of the controller, which detects the deviation of the position signal from a setpoint and regulates it to zero.
• the power amplifier of the controlled system required for the continuous supply of current to the drive coil is inevitably also operated in a state in which it generates a high electrical power loss.
• the power loss is converted into heat and must be dissipated to the environment by complex cooling measures. The result of this heat is that the electronic components of the servo drive are exposed to a high thermal load. Furthermore, the device dimensions must be large in order to create space for adequate cooling.
• This object is achieved for a method of the type mentioned above in that the position signal is sampled at a constant sampling frequency and converted into digital values which are fed to the controller working digitally and at a constant operating frequency by supplying voltage pulses of constant pulse frequency to the drive coil.
• the polarity and / or duration of which is set as a function of the output signal of the controller, and that the pulse frequency, the sampling frequency and the working frequency are in an integer relationship to one another.
• the invention is based on the knowledge that the discontinuous or digital processing of variables in a control loop compared to continuous or analog processing leads to greater accuracy and better reproducibility of the control result. Accordingly, in the case of the invention, the controller is not realized by resistors, capacitors and amplifiers, but rather by digitally working assemblies which can be controlled by a microprocessor. The result of a controller operating in this way is independent of critical component parameters such as temperature and component tolerance, so that the. Sturgeon p i ⁇ dige against external interference verrin ⁇ siege and Schwi ⁇ gneist of Regelk r ice is reduced. The digital control concept is consequently also applied to the actuator in that the drive coil is supplied with voltage pulses.
• a method of modulation of the voltage pulses consists of the fact to alternately switch "positive and negative voltage to the drive coil.
• the duty cycle of the voltage pulses is adjusted according to the output of the digital controller, which in turn according to the detected deviation of the digital values of the position signal by a digital setpoint
• the duty cycle of the voltage pulses can be varied between the values 0 and 100%, the value 100% corresponding to a DC voltage without pulse change and the value 0% having the reverse DC voltage.
• This type of modulation the voltage pulse is referred to as pulse width modulation.
• modulating the voltage pulses is to switch only pulses of one polarity to the drive coil, the polarity depending on the polarity of the output signal of the digital controller, the duration, however, depending on the amount.
• the control range here is ⁇ 100 %, whereby 100% corresponds to a DC voltage again, with 0% the voltage impulse is missing ⁇
• This type of modulation can be called modified pulse width modulation.
• the power stage supplying the drive coil with electrical power is only operated in two operating states, in the switching mode and in the blocking mode. In both states, the power loss arising in the final stage is lower than in continuous operation using the known method. This is due to the fact that the switching stage is supplied with a large current in the switching mode, but with a small voltage drop. In contrast, in the blocking operation of the output stage its voltage drop is large, but the current flow is small. The respective product from the two electrical quantities, i.e. the electrical power loss is minimal in both cases. In this view, the dynamic power losses generated when switching between the operating states of blocking and switching are neglected. This is permissible since these power losses do not count in relation to the current-related static power loss of the output stage.
• the pulse frequency, the sampling frequency and the working frequency are chosen so that they are in an integer relationship to each other. If this is the case, there are also fixed phase relationships between the signals of the various modules, for example when scanning the position signal, when regulating and when driving the drive coil.
• the position signal is sampled at the sampling frequency, those spectral components in the position signal whose frequency is an integer multiple of the sampling frequency are hidden.
• the interference amplitudes with the pulse frequency or their harmonics therefore do not reach the digital controller, so that no positive feedback effect can arise which excites the control circuit to oscillate. This measure ensures that the control loop operates very stably and effectively suppresses control vibrations.
• the pulse frequency of the voltage pulses is an integral multiple of the sampling frequency with which the position signal is sampled. This ensures that the drive coil is supplied with high-frequency voltage pulses even at a low sampling frequency, so that a current smoothed by the inductance flows in it, causing a smooth, jerk-free movement of the access arm.
• a formwork arrangement which is characterized in that four controllable switching elements arranged in a bridge circuit are provided, the one bridge diagonal being connected to the supply voltage and the other bridge diagonal being the Contains drive coil, and that the switching elements can be controlled so that, depending on the direction of the deviation of the transducer head from the target track, two diagonally opposite switching elements are not conductive and the other two switching elements can be switched on during the pulse duration.
• This circuit arrangement makes it possible to supply the drive coil with voltage pulses with an optionally adjustable sign, which are derived from only one operating voltage. These voltage pulses of different signs cause currents of opposite polarity to flow in the coil. These generate forces which cause the access arm to accelerate or brake in opposite directions.
• field effect transistors are provided as switching elements. These semiconductor components are particularly well suited for the rapid switching of voltages without high power losses occurring in them. As a result, the electrical losses in the servo drive are further reduced.
• Fig. 2 is a schematic representation of the
• Control circuit for digital control of the position of a servo head in a block diagram
• FIG. 3 shows a circuit arrangement for controlling a drive coil with voltage pulses
• Fig. 4 curves of the voltage and current of the drive coil and the position signal over time.
• FIG. 1 schematically shows a disk storage system with a plurality of disks 10, 12, 14 which rotate about a spindle axis 16.
• a plurality of tracks in which information can be magnetically recorded are provided on an annular section of the respective disk 10, 12, 14.
• This information is written or read by read / write heads 30, 32 arranged on access arms.
• the access arms are mechanically fixed to an access comb 18. This ensures that all read / write heads 30, 32 can be positioned on the same track of the respective disk 10, 12, 14 in a single positioning operation.
• the access comb 18 is rotatably mounted on bearings 20, 22 and can carry out pivoting movements about the pivot axis 24. With the help of these swiveling movements, the read / write heads 3.0,: -32 are moved radially to the plates - surfaces 10, 12, 14 and across the tracks.
• the swiveling movement is brought about by a servo drive 36, which contains, as the drive coil, a plunger coil 40 through which an electric current I flows with an alternating sign.
• the plunger coil 40 is located in a magnetic field of a permanent magnet 38. Depending on the strength of the current I and on its direction, the coil 40 and thus the access comb 18 are pivoted by the force effect on a conductor through which current flows.
• Position information in the form of magnetic flux changes is stored on the underside of the magnetic plate 14 and is read by a special read head or servo head 32. With the help of this position information, individual tracks on the disk 14 can be identified.
• the servo drive 36 is now adjusted so that the servo head 32 is positioned on a desired target track so that data can be written and read on the tracks of the disks 10 and 12 with the same radial positions.
• the control required for positioning the servo head 32 is shown schematically in a block diagram in FIG. 2.
• the position information on the magnetic disk 14 which is continuously read by the servo head 32 is fed to a signal generating module 42, which generates a position signal from this information, which indicates the current position or actual position of the servo head 32.
• the track with a specific track number, on which the servo head 32 is to be positioned is counted down by that of the servo head in the radial direction Saving averaged starting with a starting lane.
• Another way of reaching one Determining the desired track consists in storing an absolute address characterizing it in the respective track as position information and evaluating this address for the track positioning.
• the read / write heads of the storage disks After positioning on the desired track, which is also referred to as rough positioning, the read / write heads of the storage disks must be positioned in the center of the respective data track.
• magnetic position marks are stored on the servo surface in accordance with a known pattern using the known 4-servo signal method.
• the position of the position marks relative to one another define center lines of data tracks.
• the position signal 43 is sampled by an analog / digital converter 44 with a constant sampling frequency fa and converted into digital values. These are fed to a digital controller 48, which generates a digital output signal that controls a pulse width modulator 52.
• the digital controller 48 has PID behavior and is designed for optimum control speed and minimal control deviation. It works with a fixed operating frequency fr, ie the system deviation is only determined at certain times and its output signal can also only be changed at such times.
• a signal 50 is supplied to the digital controller 48, in which the number of the target track is digitally encoded as the setpoint.
• Another signal 51 contains, as information, the setpoint for fine positioning on the center line of a data track.
• the signals 50 and 51 are provided by a higher-level controller (not shown).
• the pulse width modulator 52 generates pulse-shaped control signals S1, S2 with a constant pulse frequency fp, the respective pulse duty factor of which can be varied between 0% and 100%.
• the duty cycle here is the ratio of the pulse duration tp to the time T between two pulses.
• the control signals S1, S2 are fed to a power output stage 54, which generates voltage pulses U of a defined magnitude with different signs.
• the voltage pulses dependent on the control signal S 1 serve to accelerate a moving coil in a predetermined direction, while the voltage pulses dependent on the control signal S2 accelerate this moving coil in the opposite direction.
• the voltage pulses U are fed to a servo drive 36 which contains a moving coil which is deflected by the current in the coil caused by the voltage pulses in the radial direction x and thereby adjusts the servo head 32.
• a servo drive 36 which contains a moving coil which is deflected by the current in the coil caused by the voltage pulses in the radial direction x and thereby adjusts the servo head 32.
• the direction of adjustment depends on the current direction and thus on the sign of the voltage pulses U with which the coil is applied.
• a clock generator 46 generates synchronous clock pulses with the frequency fe and twice the frequency fp. These clock pulses are made by frequency division Mother impulses derived with a higher frequency. The pulses with the frequency fa are fed to the digital controller 48 and the analog / digital converter 44 and determine the operating cycle of these modules. The pulse width modulator 52 is controlled with clock pulses of the higher frequency fp.
• the mode of operation of the control loop according to FIG. 2 is explained below.
• the target position to be approached by the servo head 32 is communicated to the digital controller 48 via the signals 50, 51. If the actual position of the servo head 32 shown in the position signal 43 deviates from this target value, the digital controller 48 generates an output signal which controls the pulse width modulator 52 and consequently the power output stage 54 in such a way that the voltage pulses U output to the servo drive 36 drive the servo head 32 in Move towards the target track.
• the digital controller 48 switches over to the fine positioning mode and regulates the position of the servo head 32 exactly on the center line of the data track.
• the voltage pulses U output by the power output stage 54 represent a disturbance variable with an interference frequency equal to the pulse frequency fp with which the control loop is acted upon. If this disturbance variable is fed back in the control loop so that it fulfills the oscillation conditions for control loops in terms of phase and amplitude, this can become unstable.
• the sampling frequency fa and the control frequency fr ha> are as large as the pulse frequency "fp, ie the frequencies are in each case in an integer relationship to one another discontinuous sampling of the position signal 43 and in the discontinuous processing of the signals in the control loop, each with a constant frequency, it is known to suppress those spectral components in the signals which oscillate with the fundamental frequency or with an integral multiple of this frequency. This means that the amplitude values of such vibrations are not amplified in the control loop and thus cannot trigger a positive feedback effect which could set the control loop in vibration.
• the disturbance variable caused by the voltage pulses U therefore has no negative influence on the stability of the entire control loop.
• FIG. 3 shows an exemplary embodiment of the power output stage 54, which outputs the voltage pulses U to a plunger coil 62 with different signs.
• Four field effect transistors 64, 66, 68, 60 are connected in a bridge circuit and are supplied with the positive supply voltage V from a voltage source.
• the voice coil 62 is arranged in the bridge diagonal. If the diagonally opposed field effect transistors 66 and 60 are switched into the blocking state and the transistors 64 and 68 are driven at their gate electrodes with the pulse-shaped control voltage S1, the plunger coil 62 is made up of supply voltage via the current path V, field effect transistor 64, plunger coil 62, field effect transistor 68, measuring resistor 63 and ground, negative voltage pulses supplied.
• a voltage U3 proportional to the current I through the plunger 62 drops across the measuring resistor 63.
• This voltage U3 can be used to improve the timing behavior of the control loop, in that it is also scanned by the digital controller and a current control loop is subordinate to the position control in a manner known per se. This makes it possible to detect interference on the control circuit even earlier and to increase the positioning speed for the servo head 32.
• control pulses S1 are emitted to the power end stage 54 and thus voltage pulses U with a negative sign are transmitted to the plunger coil 62 starting at the time t2.
• the servo head 32 is braked and reaches the target track 65 at time t3.
• the rough positioning process is thus completed and the digital controller switches over to the fine positioning mode.
• the control pulses 70, 72, 74 required for this have correspondingly small duty cycles tp / T.

Landscapes

• Moving Of The Head To Find And Align With The Track (AREA)
• Moving Of Head For Track Selection And Changing (AREA)
• Moving Of Heads (AREA)
• Fixed Capacitors And Capacitor Manufacturing Machines (AREA)

Applications Claiming Priority (2)

Publications (1)

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ID=6397902

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• 1990
  • 1990-01-11 DE DE4000663A patent/DE4000663C1/de not_active Expired - Lifetime
  • 1990-12-14 EP EP91901750A patent/EP0510031A1/de not_active Ceased
  • 1990-12-14 JP JP3502050A patent/JPH05501935A/ja active Pending
  • 1990-12-14 WO PCT/EP1990/002187 patent/WO1991010991A1/de not_active Application Discontinuation
  • 1990-12-14 KR KR1019920701632A patent/KR920704271A/ko not_active Withdrawn

Non-Patent Citations (1)

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