Patent Application
20080048595
A disc drive is a data storage device used to store digital data. A typical disc drive includes a number of rotatable recording discs that are axially aligned and mounted to a spindle motor for rotation at a high rotational velocity. A corresponding array of read/write heads access tracks defined on the respective disc surfaces to write data to and read data from the discs.
Disc drive spindle motors are typically provided with a three-phase, direct current (DC) brushless motor configuration. The phase windings are arranged about a stationary stator on a number of radially distributed poles. A rotatable spindle motor is provided with a number of circumferentially extending permanent magnets in close proximity to the poles. Application of current to the windings induces electromagnetic fields that interact with the magnetic fields of the magnets to apply torque to the spindle motor hub and induce rotation of the discs. It should be understood, however, that, while this Detailed Description uses disc drives and spindle motors as example implementations, other phased motors are also contemplated using the described technology.
Present spindle motor designs use electronic commutation and back electromagnetic force (BEMF) detection circuitry to provide closed-loop spindle motor control. Such approach generally entails applying a predetermined sequence of commutation states to the phase windings of the spindle motor over each electrical revolution (period) of the motor. A commutation state involves supplying the motor with current to one phase winding, sinking current from another phase winding, and holding the third phase winding at a high impedance.
Detection circuitry measures the BEMF voltage generated on the unenergized phase, compares this BEMF voltage to the voltage at a center tap of the motor's windings, and outputs a signal at a zero crossing of the BEMF voltages of the phase windings during rotation; that is, when the BEMF voltage changes polarity with respect to the voltage at the center tap. This zero crossing point is then used as a timing reference or synchronization signal for the next commutation state, as well as a reference to indicate the position and relative rotational velocity of the motor.
It should be understood that each cycle through a full sequence of commutation states comprise one electrical revolution of the phased motor 102. The number of electrical revolutions in a physical, mechanical revolution of the phased motor hub is determined by the number of poles. With 3 phases, a 12-pole motor will have six electrical revolutions for each mechanical revolution of the phased motor.
The communication logic circuit 110 includes three stages, each stage pertaining to one of the phase windings. For the purposes of this descriptions, the phase windings have been designated as A, B, and C. As such, the commutation logic circuit 110 has a stage A, a stage B, and a stage C, each stage responsible for driving current through a corresponding winding in the phased motor. The resulting current flow through two of the windings in each commutation state induces electromagnetic fields that interact with a corresponding array of permanent magnets (not shown) mounted to the rotor of the phased motor (e.g., the spindle motor hub), thus inducing torque upon the spindle motor hub in a desired rotational direction.
A component of a base excitation signal is input to each stage from a state machine 118. The base excitation signals are generated to control rotation of the phased motor 102, as described with regard to
In a three phase motor, if one phase is low and another phase is high, the third phase is held at high impedance (i.e., tri-stated) using the tri-state buffers 116. In one implementation, the tri-state buffers 116 are also controlled by the state machine 118. When tri-stated, a driver effectively operates as an “open” circuit, such that it neither sources nor sinks current relative to the phased motor.
The commutation logic circuit 110 is powered by a voltage VM, which is coupled to a voltage VCC via an ISOFET switch 122. During normal operation, the active braking signal 120 is disabled (e.g., low voltage), and the base excitation signals from the state machine 118 are input to the corresponding stages to apply a sequence of base excitation signals to the phases of the phased motor 102. In one implementation, for example, the base excitation signals issued from the commutation logic circuit 110 to the phased motor 102 in each commutation state follow a sequence to rotate the phased motor (the phase signal not shown in each pair below is tri-stated):
A
Active braking can be obtained by complementing each base excitation signal in each commutation state of the sequence. Using the circuit illustrated in
BĀ, CĀ, C
The excitations signals listed in sequence (2) are complementary to those listed in sequence (1). In one implementation, a base excitation signal is complemented by inputting it, in combination with an active high active braking signal, to an XOR logic circuit (e.g., XOR gate 124), the output of which is coupled to a driver. It should be understood however that other configurations for complementing a base excitation signal are also contemplated. Accordingly, a complementary excitation signal to the base excitation signal of normal operation is applied to the phased motor 102 in each commutation state, thereby actively decelerating the rotation of or “brake” the phased motor 102.
It should be understood that other logic configurations may be employed to generate the complementary excitation signal, and such alternatives are contemplated within the described technology. For example, the state machine may generate complementary excitation signals directly, the state machine or commutation logic may be capable of advancing the phase of the base excitation signals by a predetermined number of phases (e.g., three phases for a three phase motor) to generate complementary excitation signals, etc.
For normal operation, an example sequence of base excitation signals is listed below diagram 200, matching sequence (1). It should be understood that other sequences are contemplated. In braking operation, the complementary excitation signal of each base excitation signal is listed in corresponding commutation states. Application of these complementary excitation signals to the phased motor in sequence while the phased motor is rotating results in deceleration of the phased motor.
An initiation operation 304 detects an event that triggers the active braking of the phased motor. For example, a free-fall detector might determine that system is falling and therefore initiate various protective steps, including asserting the active braking signal. Alternatively, a shock sensor or another catastrophic event sensor may detect a need to stop the spindle motor and therefore signal the control circuitry to brake the spindle motor.
A synchronization operation 306 determines whether the motor has reached the end of a commutation state, whether by detecting a zero-crossing or by some other synchronization detection action. If not, the synchronization operation 306 continues to loop until the end of the commutation state is detected.
At the end of the commutation state, an advancement operation 308 advances the state machine one commutation state forward in the commutation sequence. A reverse torque operation 310 applies a complementary excitation signal, relative to the normal excitation signal for the current commutation state, to the phased motor, thereby reducing the rotational velocity of the motor. For example, if the normal excitation signal for the current commutation state is A
A decision operation 312 determined whether the rotational velocity of the phased motor has reduced to a predetermined threshold. If not, processing returns to the synchronization operation 306 to await the end of the current commutation state. However, if the rotational velocity has reduced to a predetermined threshold, a termination operation 314 disables the active braking signal, and a dynamic braking operation 316 enables all of the low-side drivers and disables all of the high-side drivers to complete the braking of the motor. In this manner, the phased motor will not begin to spin in the opposite direction after its rotational velocity reaches zero. It should be understood that dynamic braking can be performed in other configurations, such as by disabling all of the low-side drivers and enabling all of the high-side drivers.
Embodiments of the present invention will be discussed with reference to a magnetic disc drive. One skilled in the art will recognize that the present invention may also be applied to any data storage device, such as an optical disc drive, a magneto-optical disc drive, or a compact disc drive, that is capable of operating in two or more power levels. Further, one skilled in the art will understand that embodiments of the present invention are equally applicable to any type of electrical or electronic device capable of operating at more than one power level. For example, devices that may implement embodiments of the present invention include but are not limited to notebook computers, handheld devices such as Personal Digital Assistants (PDAs), cell phones, office equipment such as copiers and fax machines, etc.
During a seek operation, the track position of the heads 418 is controlled through the use of a voice coil motor (VCM) 424, which typically includes a coil 426 attached to the actuator assembly 410, as well as one or more permanent magnets 428 which establish a magnetic field in which the coil 426 is immersed. The controlled application of current to the coil 426 causes magnetic interaction between the permanent magnets 428 and the coil 426 so that the coil 426 moves in accordance with the well-known Lorentz relationship. As the coil 426 moves, the actuator assembly 410 pivots about the bearing shaft assembly 412, and the heads 418 are caused to move across the surfaces of the discs 408.
The spindle motor 406 is typically de-energized when the disc drive 400 is not in use for extended periods of time. The heads 418 are moved away from portions of the disk 408 containing data when the drive motor is de-energized. The heads 418 are secured over portions of the disk not containing data through the use of an actuator latch arrangement and/or ramp, which prevents inadvertent rotation of the actuator assembly 410 when the drive discs 408 are not spinning.
A flex assembly 430 provides the requisite electrical connection paths for the actuator assembly 410 while allowing pivotal movement of the actuator assembly 410 during operation. The flex assembly 430 includes a printed circuit board 434 to which a flex cable 432 connected with the actuator assembly 400 and leading to the head 418 is connected. The flex cable 432 may be routed along the actuator arms 414 and the flexures 416 to the heads 418. The printed circuit board 434 typically includes circuitry for controlling the write currents applied to the heads 418 during a write operation and a preamplifier for amplifying read signals generated by the heads 418 during a read operation. The flex assembly 434 terminates at a flex bracket 436 for communication through the base deck 402 to a disc drive printed circuit board (not shown) mounted to the bottom side of the disc drive 400.
In an exemplary implementation, spindle motor control circuitry in the disc drive 400 includes an active braking trigger, a state machine, and a commutation logic circuit that applies active braking to the spindle motor until the rotational velocity of the spindle motor reduces to a threshold. At that point, the commutation logic circuit applies dynamic braking until the spindle motor stops rotating.
The discs are rotated at a constant high speed by a spindle motor control circuit 548, which typically electrically commutates the spindle motor through the use, typically, of back electromotive force (BEMF) sensing. During a seek operation, wherein an actuator 510 moves heads 518 between tracks, the position of the heads 518 is controlled through the application of current to the coil 526 of a voice coil motor. A servo control circuit 550 provides such control. During a seek operation the microprocessor 542 receives information regarding the velocity of the head 518, and uses that information in conjunction with a velocity profile stored in memory 543 to communicate with the servo control circuit 550, which will apply a controlled amount of current to the voice coil motor coil 526, thereby causing the actuator assembly 510 to be pivoted.
Data is transferred between the host computer 540 or other device and the disc drive by way of an interface 544, which typically includes a buffer to facilitate high speed data transfer between the host computer 540 or other device and the disc drive. Data to be written to the disc drive is thus passed from the host computer 540 to the interface 544 and then to a read/write channel 546, which encodes and serializes the data and provides the requisite write current signals to the heads 518. To retrieve data that has been previously stored in the data storage device, read signals are generated by the heads 518 and provided to the read/write channel 546, which performs decoding and error detection and correction operations and outputs the retrieved data to the interface 544 for subsequent transfer to the host computer 540 or other device.
In an exemplary implementation, spindle control 548 in the disc drive includes a state machine and a commutation logic circuit that applies active braking to the spindle motor until the rotational velocity of the spindle motor reduces to a threshold. At that point, the commutation logic circuit applies dynamic braking until the spindle motor stops rotating.
The technology described herein is implemented as logical operations and/or modules in one or more systems. The logical operations may be implemented as a sequence of processor-implemented steps executing in one or more computer systems and as interconnected machine or circuit modules within one or more computer systems. Likewise, the descriptions of various component modules may be provided in terms of operations executed or effected by the modules. The resulting implementation is a matter of choice, dependent on the performance requirements of the underlying system implementing the described technology. Accordingly, the logical operations making up the embodiments of the technology described herein are referred to variously as operations, steps, objects, or modules. Furthermore, it should be understood that logical operations may be performed in any order, unless explicitly claimed otherwise or a specific order is inherently necessitated by the claim language.
The above specification, examples and data provide a complete description of the structure and use of example embodiments of the invention. Although various embodiments of the invention have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention. In particular, it should be understood that the described technology may be employed independent of a personal computer. Other embodiments are therefore contemplated. It is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative only of particular embodiments and not limiting. Changes in detail or structure may be made without departing from the basic elements of the invention as defined in the following claims.
Although the subject matter has been described in language specific to structural features and/or methodological arts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts descried above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claimed subject matter.
