Data storage device having a drive mechanism for rotating a data storage medium

Abstract

A data medium is driven by a brushless direct current motor and possesses control signals on a track which can be picked up by a sensing device and supplied to a switch arrangement for activation of the motor winding. The control signals on the track characterize at least those angular positions of the rotor with respect to the stator in which commutation is to be initiated.

Description

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 depicts the principles of an exemplary embodiment having an external-rotor brushless d.c. motor 1. The four-pole stator 2 is provided with a winding made up of four coils 3-6 and is, in a known fashion, encircled by a permanent-coils magnet rotor 7.

For the sake of a simple illustration of inventive principles there is shown an external-rotor d.c. motor having an annular air gap; self-evidently, however, one can use any other motor type that would be suitable, in the sense of reduced axial length, a disk-rotor motor having a planar air gap being also preferred.

Rigidly connected to shaft 8 of motor 1 is a hub 9 on which a data carrier 10 is arranged. The data carrier 10 is constituted by a rigid or flexible computer data-storage platter carrying data signals on concentric tracks. A write/read head 11 is arranged to be movable in radial direction over the data carrier 10; by means of head 11 data signals on the concentric tracks of data carrier 10 can be written, read, or erased. In known manner via a connection here shown as line 12, these signals are transmitted from a non-illustrated processing unit to the write/read head 11 or, as the case may be, are transmitted from the head to the processing unit. As shown in FIG. 1, hub 9, data carrier 10, motor 1, write/read head 11, and a read head 16 are positioned in a generally enclosed space 100. In magnetic hard disk storage devices, data carrier 10 is a magnetic hard data storage disk and space 100 is a clean chamber, as readily apparent to those of ordinary skill in the art.

Depending on the type of data carrier 10 or, as the case may be, depending upon the employed data storage method, the read/write head 11 may comprise a magnetic head, an optical device, a laser head or a device for some other read/write principle. The orientation of the read/write head 11 relative to the concentric data signal tracks can be such that, instead of a radial shifting occurring, even a tilting motion takes place.

In order to produce a magnetic field that effects rotary movement of the rotor, the coils 3 to 6 of the stator winding must be energized by current in a certain succession, for example one after the other in the sequence of their arrangement. Here, note should be taken that the expression "winding coils" is also to be understood to apply to the special case of a stator having only one coil which is energized by current pulses in dependence upon rotor position, being energized either by current pulses all of which have the same direction of flow, or else being energized by current pulses each successive one of which has a direction of flow opposite to that of the preceding current pulse; however, an arbitrary number of separately energizable coils, all belonging to the stator winding, likewise falls under this expression. The switching-on and switching-off of the energizing current flowing to the winding, or as the case may be the switchovers in the feeding of energizing current to the winding coils 3-6 (commutation), is controlled by a circuit unit 13, which in the exemplary embodiment of FIG. 1 essentially contains a switching unit 14 for the fed current.

Control signals for the switchover of the winding's energizing current are recorded on a radially outward concentric storage track 15 of data carrier 10, the latter being read by a read head 16 that corresponds to the write/read head 11 for the data signals. Control signals read by read head 16 are transmitted via a connection shown as conductor 17 to the circuit unit 13, whose switching arrangement 14 for fed current switches the operating current over from the energized one of the winding coils 3-6 to the winding coil that is to follow next in the energization sequence. In the simplest case, for each angular position at which a switchover is to occur, there is recorded on the storage track 15 a single control signal; after sensing such signal the circuit unit 13, i.e., its switching unit 14 for fed current, switches off the supply of current for the energized coil and switches on the supply of current for the next-following coil. In order to avoid a damaging overlap of electrical or magnetic effects, it is frequently advantageous to enforce a pause between the switching-off and renewed switching-on of the fed current; for this reason, for each angular position at which a commutation is to occur, advantageously two control signals can be arranged on the storage track 15 with definite spacing relative to each other. The reading of the first control signal that pertains to an angular position at which a commutation is to occur then causes the switching unit 14 for fed current to interrupt the supply of current to the presently energized winding coils of the motor winding along a connection here shown as line 19, whereas the reading of the second control signal effects establishment of current feed to the winding coils 3-6 that are next in the energization sequence. The spacing of the con control signals that are provided on the data carrier for each angular position at which a commutation is to occur accordingly determines the length of the energizing-current pause.

As an alternative to the above described embodiment the circuit unit 20 shown in FIG. 2 can be employed as a variant upon the circuit unit 13 of FIG. 1, with again only one control signal needing to be provided on data carrier 10 for each angular position at which a commutation is to occur. In addition to the switching arrangement 21 for fed current, which in principle performs the same functions as described above, there is furthermore provided a delay unit 22. Delay unit 22 can, e.g., be constituted by a clock-controlled counter that is pre-set to a certain value, started by an input signal, counts with a fixed clock frequency, and, upon the issuance of an end signal, stops. The value to which the counter is pre-set is in that event advantageously adjustable.

As can be seen from the simplified flowchart of FIG. 3, a control signal--read from rotating data carrier 10 and transmitted, via the connection shown as line 17, to the switching unit 21 for fed current--causes the feeding of current via the connection shown as conductor 19 to become switched off and the delay arrangement 22 to become started. After elapse of the pre-set delay time, delay unit 22 is reset to its starting setting, and an output signal is transmitted to the switching circuit 21 for fed current, which latter thereupon establishes a feed of energizing current to the next-following winding coil of motor 1. In this exemplary embodiment, the magnitude of the current pause between the switching-off and renewed switching-on of the energizing current for the winding is accordingly determined by the delay unit 22.

In the case of the exemplary embodiments described up to this point, regulating circuits such as known and used in the prior art can of course be connected in the current-supply circuit of the motor, the regulating circuit implementing a constant rpm by adjusting, for example, the amplitude of the energizing current pulses.

The circuit unit 23 of FIG. 4, besides a switching unit 24 for fed current and a delay unit 25, furthermore comprises a time-measuring unit 26, which likewise can be formed by a counter which is started by a first input signal and, beginning from zero, counts upward with a fixed clock frequency until the counting operation is ended by a second input signal. For each switchover-operation the data carrier 10 has two control signals which are spaced from each other and are, via the connection represented by line 17, transmitted from the read head 16 to the time-measuring unit 26 to be input signals to the latter. According to the simplified flowchart of FIG. 5, the arrival of the first one of such a pair of control signals has the effect that the time-measuring arrangement 26 becomes started. The second control signal, arriving at the now counting time-measuring unit 26, stops the time-measuring operation and causes the switching unit 24 for fed current to interrupt the flow of energizing current along conductor 19 to the winding of motor 1. Simultaneously, the measured time value is transmitted from the time-measuring unit 26 to the time-delay unit 25, whose delay time value is decreased by the amount of the measured time value. If a counter is used as the delay unit 25, a base value to which the counter becomes set would accordingly be decreased by the amount of the measured time value. If the delay unit 25 set and started with the corrected value is reached at the end of the delay time, then a signal is transmitted to the switching unit 24 for fed current, whereupon flow of energizing current is initiated for the next-following winding coil of the d.c. motor 1. With the configuration of this exemplary embodiment, a very quick rpm regulation is thus implemented using only two signals for each angular position at which a commutation is to occur; due to the relatively large diameter of data carrier 10 a speed measurement, achieved by measuring the length of a distance, can be had over an angular distance of only small extent. The first control signal of each such pair is provided to initiate the measuring operation, whereas the second control signal initiates the commutation. The current pause, which is dependent upon the deviation of the measured rpm from the desired rpm is, in contrast, determined by the delay unit 25.

The exemplary embodiment of FIG. 6 offers a still more convenient solution, whose manner of operation is explained in connection with the simplified flowchart of FIG. 7. The circuit unit 27, besides containing a switching unit 28 for fed current and a time-measuring unit 29, further comprises a comparator 30 and a delay unit 31 with several different delay times or a variable delay time. For such purpose, there can be provided a tabulation having individually addressable, differing delay values which can be used to set a counter in the manner described further above. Comparator 30 furnishes a reference or desired value, which can be fixedly pre-set, or else can receive such a value at a desired-value signal input 33 from a source 32 that is provided with a set of desired-value or preset-value data. In this exemplary embodiment too, for each angular position at which a commutation is to occur, there are arranged on the storage track 15 of data carrier 10 two mutually spaced control signals, read one after the other by read head 16 when data carrier 10 is rotating.

As already described above in connection with FIGS. 4 and 5, in each instance the first one of a pair of control signals starts the time-measuring unit 29, whereas the second control signal causes the time measuring unit 29 to again stop (FIG. 7). The ending of the time measurement causes a signal to be transmitted to the switching unit 28 for fed current, which latter thereupon interrupts the feeding of current to the motor winding. The value determined by the time-measuring unit 29 is transmitted to comparator 30, which compares it against the desired value. The result of the comparison is transmitted to delay unit 31 and constitutes a criterion for the selection of a pulse pause of suitable magnitude between the interruption and re-establishment of flow of energizing current to the winding, for example constituting an address for a delay-times tabulation. If for example the result of the comparison indicates a deviation from the desired value such that the desired value is smaller than the value measured by the time-measuring unit 29, then the delay unit 31 must generate a time value for the pulse pause correspondingly below the normal pulse-pause duration, in order in that way to increase the pulse breadth of the energizing pulses for the winding and accelerate the too-slowly-turning rotor 7 of motor 1. In the opposite situation, i.e. when the result of the comparison indicates a deviation from the desired value such that the desired value exceeds the measured value, the delay unit 31 must correspondingly generate a time value for a longer pulse, in order in that way to decrease the pulse breadth of the energizing pulses for the winding and decelerate the too-fast-turning rotor 7 of motor 1 pause. Subsequent to the selection of the deviation-dependent time-delay, or after elapse thereof, the time-measuring unit 29 is again brought to its starting setting; and, by means of the switching unit 29 for fed current, flow of energizing current is established for the coil of stator winding 2 that is next in the energization sequence.

Establishment of a desired value (for example taken from a tabulation of desired values, or else computable) makes possible open-loop or closed-loop control of the rpm of the motor and data carrier in accordance with desired speed profiles, e.g. to implement a desired acceleration behavior or braking behavior. Furthermore, depending upon the stringency of the requirements of a particular situation, a more or less complicated configuration of the delay unit 31 can be used to establish a dimensionally coarse or very fine correction of speed deviation, implemented on the basis of a short angular distance and performed immediately. Instead of varying the pulse pause in the energization of the winding, it is of course also possible to have the amplitude of the energizing pulses be varied in corrective fashion or, in the event of successions of energizing pulses produced by some keying method, to have the number of individual pulses per cycle of energization of the winding be varied in corrective fashion.

The described exemplary embodiments indicate only a small selection of the possibilities opened up by the concepts of the invention, which the person of routine skill can vary within wide limits and adapt to special requirements or desires. For example, it is thinkable that the signal-storing track for the control signals be provided with further motor-control data, such as perhaps a direction-of-rotation indication. For a more complex motor control system, even a second data storage track, or yet further tracks, could be utilized. Finally, for the motor-control action, the storage track, or the control signals thereon, can even be encoded with incremental values.

Also, it is not absolutely necessary to provide two separate write and/or read heads for the control signals and the data signals or to provide the control signals on a concentric data track. On the contrary, for the person of routine skill, it is self-evident that one single read/write head can, in each instance at the correct moment in time, seek out the actual data track; or that, when writing data in accordance with any particular data-formatting scheme, the motor-operation control signals, too, and in correspondence therewith, are written at another location and arranged in some other manner.

Also, the following should additionally be mentioned: It may be that the data storage device has its flow of data controlled and/or evaluated by means of a microcomputer. In that event, the functions of the circuitry required for implementation of the concepts of the invention are advantageously performed by the microcomputer of the data storage device, so that a further cost reduction results.