Method and apparatus for detecting motion of a motor for a disk drive system

1. Technical Field of the Invention

This invention relates to improvements in circuitry for driving polyphase motors, and more particularly to a method and apparatus for relatively rapidly driving a polyphase motor for a disk drive from an inactive state to an operable state for performing a memory access, and still more particularly to a circuit and method for detecting motion of a polyphase motor for a disk drive system.

2. Background of the Invention

Although the present invention pertains to polyphase and/or polyphase dc motors, in general, it finds particular application in conjunction with three phase dc motors, particularly of the brushless, sensorless type which are used for rotating data media, such as found in computer related applications, including hard disk drives, CD ROM drives, floppy disks, and the like. In computer applications, three phase brushless, sensorless dc motors are becoming more popular, due to their reliability, low weight, and accuracy.

Motors of this type can typically be thought of as having a stator with three coils connected in a “Y” configuration, although actually, a larger number of stator coils are usually employed with multiple motor poles. Typically, in such applications, eight pole motors are used having twelve stator windings and four N-S magnetic sets on the rotor, resulting in four electrical cycles per revolution of the rotor. The stator coils, however, can be analyzed in terms of three “Y” connected coils, connected in three sets of four coils, each physically separated by 90 degrees. In operation, the coils are energized in sequences, in each of which a current path is established through two coils of the “Y”, with the third coil left floating. The sequences are arranged so that as the current paths are changed, or commutated, one of the coils of the current path is switched to float, and the previously floating coil is switched into the current path. Moreover, the sequence is defined such that when the floating coil is switched into the current path, current will flow in the same direction in the coil which was included in the prior current path. In this manner, six commutation sequences are defined for each electrical cycle in a three phase motor.

In the past, during the operation of a polyphase dc motor for a disk drive system, such as a spindle motor for spinning the disk media upon which data is stored, it has been recognized that maintaining a known position of the rotor of the motor is an important concern. There have been various ways by which this was implemented. The most widely used way, for example, was to start the spindle motor in a known position, then develop information related to the instantaneous or current position of the rotor. One source of such instantaneous position information was developed as a part of the commutation process, and involved identifying the floating coil, and monitoring its back emf, that is, the emf induced into the coil as it moves through the magnetic field provided by the stator.

Oftentimes, a spindle motor of a disk drive system is slowed due to a relatively prolonged absence of requests to access the disk drive. During these periods of inactivity, the spindle motor may be slowed considerably or stopped altogether. Conventional disk drive systems attempted to quickly spin up the spindle motor from an inactive state by initially determining whether the spindle motor was moving. This determination was accomplished by tri-stating the phase windings of the motor for a sufficient period of time to detect at least two consecutive zero crossings of the back emf signals associated with the phase windings. In the event the rotor is spinning very slowly, the amount of time necessary to detect consecutive zero crossings may undesirably approach several hundred milliseconds. Once consecutive zero crossings of the back emf signals are detected, thereby indicating a spinning rotor, a resynchronization procedure is executed to synchronize to the rotor spin the application of drive signals to the motor's phase windings. In the event successive zero crossings of the back emf signals are not detected even after the lapse of several hundred milliseconds, an inductive sense routine is initiated to determine the position of the rotor, followed by executing a spin-up procedure to bring the spindle motor to the desired operable speed. Consequently, the delay related to returning rotor spin to operable levels may be excessive.

Based upon the foregoing, there is a need for a controller and method for controlling the motor of a disk drive to efficiently increase motor spin to operable spin speeds following periods of disk drive inactivity, and particularly for initially determining whether or not the disk drive motor is spinning.

The present invention overcomes shortcomings in prior and existing disk drive systems and satisfies a significant need for high speed disk drive operation. According to an embodiment of the present invention, a controller for a polyphase motor, such as the spindle motor of a disk drive, initially senses current on a single selected phase winding of the motor. A period of time is measured until the sensed current reaches and/or surpasses a predetermined threshold current level. The measured period of time is then selectively stored in memory. Current is sensed on the selected phase winding a number of times and time period measurements are taken corresponding thereto. Minimum and maximum measured time periods are thereafter compared with each other. The rotor of the disk drive motor is determined to be spinning if the minimum measured time period and the maximum measured time period are not within a predetermined percentage of each other. Alternatively, the rotor of the disk drive motor is determined to be stopped if the minimum measured time period and the maximum measured time period are within the predetermined percentage of each other.

Having determined whether or not the rotor of the motor is spinning, the controller is capable of relatively quickly bringing the motor to an operable speed for performing a memory access operation. Specifically, in the event the rotor is determined to be spinning, the controller then executes a resynchronization operation to synchronize the application of the drive signals to the already spinning rotor. In the event the controller determines that the motor's rotor is not spinning, a spin-up operation is executed by the controller to spin up the motor from the inactive state to an operable state. Because the time to execute the current sensing operations is substantially less than the time to execute the initial resynchronization operation in prior systems for a slowly moving rotor, the time to bring the rotor up to a spin level to suitably access the disk is markedly reduced.

A more complete understanding of the system and method of the present invention may be obtained by reference to the following Detailed Description when taken in conjunction with the accompanying Drawings wherein:

FIG. 1 is a function block diagram of a system having a disk drive according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of the controller for the spindle motor of the disk drive of FIG. 1, in conjunction with the spindle motor's phase windings, according to an embodiment of the present invention; and

FIG. 3 is a flow chart illustrating the operation of the controller shown in FIGS. 1 and 2 in accordance with a first embodiment of the present invention.

The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which an embodiment of the invention is shown.

Referring to FIG. 1, there is shown a block diagram of a data storage and/or computer system 1 including a disk drive 2 in accordance with the present invention. Disk drive 2 includes a storage medium in the form of one of more disks 3 , each of which may contain data on both sides of the disk. Data is written to disks 3 and/or read therefrom by one or more read/write heads 4 . The read/write head 4 is connected to an arm 5 , with both read/write head 4 and arm 5 being positionally controlled by a voice-coil motor (“VCM”) 6 and a position system 7 . The position system 7 , through VCM 6 , positionally maintains and/or moves head 4 radially over the desired data on disks 3 . A read channel 8 converts an analog read signal from head 4 into digital form. A write channel 9 provides data in analog form to read/write head 4 for storing on a disk 3 . A pre-amplifier 10 suitably conditions data read from and data to be-written to disk 4 . Channel controller 11 recognizes and organizes the digital data from the read channel 8 and digital data to be sent to write channel 9 into bytes of data. An interface adapter 12 provides an interface between channel controller 11 and a system bus 13 that may be particular to the host (data storage and/or computer-based) system. The host system will also typically have other devices that communicate on system bus 13 , including a central processing unit (“CPU”) 14 and memory 15 . A spindle motor (“SPM”) 16 and SPM control circuit 17 rotate disk 3 and maintain disk 3 at the proper speed for performing a memory access operation (read or write operation). The SPM control circuit 17 may communicate with interface adapter 12 , as shown in FIG. 1 . Alternatively, SPM control circuit 17 may be controlled by or otherwise communicate with channel controller 11 , as shown in dashed lines in FIG. 1 . It is understood that disk drive 2 may be divided into and/or include other function blocks from those shown in FIG. 1, and that the particular function block implementations illustrated in FIGS. 2 and 3 are presented as an exemplary embodiment of the present invention.

Referring to FIG. 2, there is shown SPM control circuit 17 for controlling spindle motor 16 of disk drive system 1 in accordance with an embodiment of the present invention. The SPM control circuit 17 (hereafter referred to as the “controller 17 ”) may directly communicate with interface adapter 12 , as shown in FIG. 1 .

Controller 17 preferably controls the sequence of drive signals applied to the input/output (I/O) terminals of phase windings or lines P 1 -P 3 of motor 16 in order to, among other things, suitably spin motor 16 so that data stored on the associated media disk (not shown) may be accessed. It is understood, however, that controller 17 may be utilized in controlling the operation of a polyphase motor for other systems as well.

Controller 17 is preferably programmable to execute a number of operations. For example, controller 17 may be programmed to measure electrical characteristics of the phase windings of motor 16 which can then be used to determine rotor position. In addition, controller 17 may be programmed to execute a resynchronization operation in which drive signals to be applied to phase windings P 1 -P 3 are synchronized with the position of a presently spinning rotor. Controller 17 may be further programmed to execute a spin-up procedure in which drive signals are applied to phase windings P 1 -P 3 to bring motor 16 from a stationary position.

In particular, controller 17 may include or otherwise be associated with a processing block 18 and lookup table 19 (FIG. 2 ). The lookup table 19 may be utilized to, among other things, store program instructions to be carried out by processing block 18 in controlling the operation of motor 16 . Alternatively, controller 17 may include state machine circuitry (not shown) to sequentially step through a series of operations to control the operation of motor 16 .

Further, processing block 18 may include sense circuitry 18 A to measure current levels in phase windings P 1 -P 3 , and timing circuitry 18 B to measure the amount of time that elapses for a phase winding current to reach a predetermined threshold level I th . Processing block 18 may further include arithmetic circuitry 18 C to compare various measured time values with each other, identify the smallest measured time value and determine whether spindle motor 16 is moving based upon the comparisons and identifications. The specific operation of controller 17 is described below. Processing block 18 may further include registers 18 D, for storing time values generated by timing circuitry 18 A. One such register 18 D, minreg, may store a minimum time value generated by timing circuitry 18 A. Another register 18 D, maxreg, may store a maximum time value generated by timing circuitry 18 A.

Controller 17 may further include a predriver circuit 20 which, in general terms, receives control signals 21 from processing block 18 and derives drive signals 22 to be applied to phase windings P 1 -P 3 of motor 16 . Predriver circuit 20 may include memory and other circuitry (not shown) for utilizing any of a number of drive techniques for driving and/or controlling motor 16 , such as pulse width modulation.

Controller 17 may further include a power driver circuit 23 which is adapted to receive an electrical signal from any terminal of the phase winding P 1 -P 3 that is not currently being driven, and send the received signal to processing block 18 . Power driver circuit 23 also receives drive signals 22 from predriver circuit 20 and applies drive signals 22 to phase windings P 1 -P 3 of motor 16 .

The operation of embodiments of the present invention will be described with reference to FIG. 3 . As discussed above, a disk drive 2 may undergo a relatively prolonged period of inactivity without having to respond to a request for memory access. During this period of inactivity in which the disk drive is in a “standby” state, the motor is undriven by controller 17 . Consequently, motor 16 may considerably spin down to a relatively slow speed and in some instances stop spinning altogether. In order to relatively rapidly ramp up motor 16 from a standby state in response to a request for memory access, controller 17 initially causes a predetermined phase to be energized. Controller 17 senses or measures an electrical characteristic of a single, selected phase winding or line of motor 16 to determine whether or not the motor's rotor is spinning.

In accordance with an embodiment of the present invention, minreg 18 D is preset at step 30 (FIG. 3) so that each register bit slice therein stores a logic high value, and maxreg 18 D is reset so that each register bit slice therein stores a logic low value. Next, the appropriate windings P 1 -P 3 of motor 16 are energized for a predetermined phase, such as phase 0 , at step 31 . Timing circuitry 18 B is then initialized and activated to begin counting at step 32 and sense circuitry 18 A senses current on a single phase winding (P 1 , P 2 or P 3 ) at step 33 at that time, until the sensed current approximately reaches and/or surpasses a predetermined threshold current level I th . At that point, timing circuitry 18 B is deactivated at step 34 and the measured time value Tval shown in timing circuitry 18 B is compared with the values stored in minreg 18 D and maxreg 18 D by arithmetic circuitry 18 C.

In particular, if the measured time value Tval stored in timing circuitry 18 B is less than the value presently stored in minreg 18 D, then the measured time value Tval is stored in minreg 18 D at step 35 . Moreover, if the measured time value Tval is greater than the value stored in maxreg 18 D, then the measured time value Tval stored in timing circuitry 18 B is stored in maxreg 18 D at step 36 .

In the event the sensed current does not reach and/or surpass the predetermined threshold current level I th , an error flag is set within controller 17 . At this point, the threshold current level I th may be reset to another level.

Next, the appropriate windings P 1 -P 3 of motor 16 are energized at step 37 corresponding to a second predetermined phase, such as phase 3 . The windings P 1 -P 3 are energized for a first predetermined period of time. The windings P 1 -P 3 are then tristated for a second predetermined period of time at step 38 . Windings P 1 -P 3 are energized during step 37 to compensate for and/or offset the windings being energized during step 31 .

Steps 31 - 38 are repeated a predetermined number of times, such as six times. Once a predetermined number of measured time values.Tval have been taken, the value stored in minreg 18 D and the value stored in maxreg 18 D are compared to each other at step 39 by arithmetic circuitry 18 C. If the value stored in minreg 18 D, representing the minimum measured time value Tval min , is within a predetermined percentage of the value stored in maxreg 18 ,D, the maximum measured time value Tval max , then processing block 18 determines that the rotor of motor 16 is not spinning at step 40 . In the alternative, processing block 18 determines at step 39 that the rotor of motor 16 is spinning if the minimum measured time value Tval min is not within a predetermined percentage of maximum measured time value Tval max . Having determined whether or not the rotor of motor 16 is spinning, controller 17 performs the appropriate drive operation or set of drive operations to bring motor 16 to an operable speed for disk drive 2 to perform a memory access operation.

For examples, if controller 17 determines that the rotor of motor 16 is not spinning, the position of the rotor of motor 16 is then determined at step 44 . Having information relating to the position of stationary motor 16 , a spin-up operation is performed at step 45 so as to spin the rotor and bring the spin speed thereof to an operable level at which the requested memory access operation may occur. By eliminating an initial resynchronization operation and instead initially performing a sensing operation immediately followed by a spin-up operation, controller 17 is capable of bringing the disk drive 2 from a standby state to an operable state much more rapidly than experienced in prior disk drive systems.

If controller 17 determines that the rotor of motor 16 is spinning, controller 17 executes a resynchronization operation at step 47 to synchronize and/or resynchronize the application of drive signals to the spinning motor 16 . In this way, the spin of the rotor will be smoothly increased upon application of the drive signals.

Controller 17 has been described within the context of a disk drive 2 for exemplary purposes only. It is understood that the embodiment of the present invention may be utilized in devices that include a polyphase motor other than disk drive systems. For instance, controller 17 may form part of a compact disc (CD) player for controlling the spin of the spindle motor thereof.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.