Abstract:
Method arid apparatus for accelerating a multi-phase motor having a rotatable rotor are disclosed. The method incorporates use of a motor control circuit to predict a subsequent loss of frequency lock between the motor control circuit and a motor while the motor control circuit and the motor remain frequency locked, and based on the prediction, steps to avert a loss of frequency lock during acceleration. The apparatus includes at least a motor control circuit detecting frequency lock wit a motor when a motor signal falls within a timing window, and while frequency locked, predicting a subsequent loss of frequency lock based on a relative position of the motor signal within the timing window

Description:
FIELD OF THE INVENTION 
     This invention relates generally to the field of control systems and more particularly, but without limitation, to a method and apparatus for controlling a portion of an acceleration process for a motor. 
     BACKGROUND 
     Accelerating a motor can take many steps before achieving a nominal run speed, and depending on the environment, heightened care must be taken during an acceleration of the motor. Control of spindle motors used for spinning discs in a data storage device pose particularly distinct control issues. 
     Because spindle motors of data storage devices can be operated at velocities of 10K RPM or greater, motor control circuits optimized for operating the spindle motor at the nominal run speed of the spindle motor do not always have the bandwidth to effectively respond to changes in speed of the spindle motor at low speeds. Operating characteristics are very different between 1000 RPM and 10K (or higher) RPM. Such things as the commutation duration, response timing, device-to-device variations in electronics, operating environment including power and temperature differences, and basic physics differences between devices such as inertia and mass play a significant role in how a particular spindle motor accelerates. 
     While various approaches for compensating variations in motor acceleration during spin up have been proposed, there nevertheless remains a continued need for improvements in the art, and it is to such improvements that the present invention is generally directed. 
     SUMMARY OF THE INVENTION 
     In accordance with preferred embodiments, an apparatus and method are provided for averting a loss of frequency lock between a spindle motor and a motor control chip of a motor control circuit during a portion of an acceleration of the motor to a predetermined velocity. The method generally comprises a use of a motor control circuit to predict a subsequent loss of frequency lock between the motor control circuit and a motor while the motor control circuit and the motor remain frequency locked, and based on the prediction, steps to avert a loss of frequency lock during acceleration of the motor. 
     The apparatus generally comprises a motor control circuit detecting frequency lock with a motor when a motor signal falls within a timing window, and while frequency locked, predicting a subsequent loss of frequency lock based on a relative position of the motor signal within the timing window. 
     These and various other features and advantages which characterize the claimed invention will be apparent from reading the following detailed description and a review of the associated drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view of a data storage device constructed and operated in accordance with preferred embodiments of the present invention. 
         FIG. 2  provides a functional block representation of control circuits of the device of  FIG. 1 . 
         FIG. 3  is a diagram depicting an active acceleration of the spindle motor of  FIG. 1 . 
         FIG. 4  is a flowchart showing a method for maintaining frequency lock between the spindle motor and its motor control chip during acceleration of the motor. 
         FIG. 5  is a flowchart showing a current controlled locking (CCL) mode for use within the method of  FIG. 4 . 
         FIG. 6  is graphical representation of a response of the spindle motor of  FIG. 1  operating under the current controlled locking mode of  FIG. 5 . 
         FIG. 7  is a flowchart showing a mode controlled locking (MCL) mode for use within the method of  FIG. 4 . 
         FIG. 8  is a graphical representation of a response of the spindle motor of  FIG. 1  operating under the mode controlled locking mode of  FIG. 7 . 
         FIG. 9  is a graphical representation of a comparison of the acceleration of the spindle motor of  FIG. 1  when operated under the CCL mode of  FIG. 5 , the MCL mode of  FIG. 7 , and no locking control mode. 
         FIG. 10  is a partial cut-away elevational view of the spindle motor of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     For purposes of promoting an enhanced understanding of the present invention, and not by way of imparting any limitations on the present invention, a three phase motor model has been selected as a framework for discussion of the present invention throughout the instant disclosure. During each commutation step of a three phase motor, current is applied to one phase, sunk from another phase, and a third phase is held at a high impedance in an unenergized state. A key to successful and efficient acceleration of a motor is the application of current in the right phase and at the right time. A misapplication of current across the winding, i.e., an out of phase application of current across the windings, either premature or extended, generates negative/reverse torque which retards acceleration and in effect serves as a brake. 
     Such a model is utilized in a data storage device  100  shown in  FIG. 1 . The device  100  includes a base deck  102  which cooperates with a top cover  104  (shown in partial cut-away) to form an environmentally controlled housing for the device  100 . 
     A spindle motor  106  (also referred to herein as motor  106 ) supported within the housing rotates a number of rigid magnetic recording discs (discs)  108  in a rotational direction  109 . An actuator  110  supports a corresponding number of heads  112  adjacent tracks (not shown) defined on the disc surfaces. A voice coil motor (VCM)  114  is used to rotate the actuator  110  and hence, move the heads  112  radially across the discs  108 . 
     The VCM  114  includes a moveable actuator coil  116  and a stationary magnetic circuit. The magnetic circuit includes a permanent magnet  118  supported on a magnetically permeable pole piece  120 . A second pole piece and a second permanent magnet are normally disposed over the coil to complete the magnetic circuit, but these components have been omitted in  FIG. 1  to provide a better view of the actuator coil  116 . 
     Communication and control electronics for the device  100  are supported on a printed circuit board assembly (PCBA)  122  mounted to the underside of the base deck  102 . 
       FIG. 2  provides a functional block diagram showing control circuitry provided by the PCBA  122  of the device  100  (of  FIG. 1 ). Data and host commands are provided from a host device to the device  100  using interface (I/F) circuitry  126  in conjunction with a top level control processor  128 . Data are transferred between the discs  108  and the host device using the read/write head  112 , a (preamp)  130 , a read/write (R/W) channel  132  and I/F circuitry  126 . 
     Head positional control is provided by a closed-loop servo circuit  134  comprising demodulation (demod) circuitry  136 , a servo processor (controller)  138  (preferably comprising an Advanced RISC Machine, or ARM  140 ) and motor control chip (MCC)  142  communicating with the actuator coil  116  and controls application of activation currents across the actuator coil  116  to rotate the actuator  110 . 
     Spindle motor control is provided by motor control circuitry  144 . In addition to the MCC  142 , the motor control circuitry  144  comprises the controller  138  with the ARM  140  and a Synchronicity Monitoring and Adjustment Circuit (SMAC)  146  (which may be implemented in either software or hardware form). The MCC  142  includes a digital timer  148  and a resynchronization circuit  150 . 
     The SMAC  146  monitors and adjusts the synchronicity between the MCC  142  and the spindle motor  106  to facilitate an efficient acceleration of the spindle motor  106 , by assuring acceleration current is applied in the right phase and at the right time across motor windings of the spindle motor  106 . 
     In a preferred embodiment, while the MCC  142  is in a coast mode, and the spindle motor  106  is coasting (i.e., no current being applied across the motor windings), the MCC  142  automatically synchronizes a selected phase of the MCC  142  with a corresponding selected winding of the motor  106  (i.e., the corresponding phase of the motor  106 ), to attain frequency locking between the motor  106  and the MCC  142 . 
     To confirm frequency locking between the spindle motor  106  and the MCC  142 , the MCC  142  opens a timing window when the MCC  142  expects to detect a zero crossing (ZC) in a back electro motive force (BEMF) signal from windings of the spindle motor  106 . If the ZC is detected during the time period that the timing window is open, frequency lock is confirmed. The timing window opening is triggered off a timeout of the digital timer  148 , which is set based on previous velocity measurements detected from the BEMF signal. In an alternate embodiment, a phase-locked-loop circuit, or other timing technique may be used in place of the digital timer  148 . 
     During acceleration of the motor  106 , if the ZC is detected to be within the detection window, the MCC  142  and the spindle motor  106  are synchronized, and the MCC  142  continues to correctly direct the application of current across the windings for the right phase and at the right time to accelerate the motor. However, if the ZC is not detected to be within the detection window, the spindle motor  106  and the MCC  142  are out of synchronicity and loss of frequency lock has occurred. 
     The MCC  142  is unable to detect and respond to a condition when frequency lock between the spindle motor  106  and the MCC  142  is lost. The MCC  142  in this situation continues to operate in normal run mode as best as possible. However a loss of frequency lock means that the applied current has been misapplied across the windings thereby retarding acceleration of the spindle motor. The MCC  142  is in effect acting as a brake, and the power consumed for any misapplied periods has been wasted. 
     To mitigate the loss of frequency lock, the SMAC  146  predicts an oncoming loss of frequency lock (i.e., an out-of-phase condition) between the spindle motor  106  and the MCC  142 , and the controller  138  intervenes by altering the current being applied to the motor windings. Direct alteration of the current being applied, and a reduction in applied current through a forced entry of the MCC  142  into a coast mode are two of many forms of current alteration available to the controller  138 . A forced entry of the MCC  142  into a coast mode halts current applied to the motor windings and resynchronizes the MCC  142  to the spindle motor  106 . 
     One correction method embodiment involves altering the acceleration of the spindle motor  106  by controlling the amplitude of the current driving the spindle motor  106 . In the event that the ZC occurs after the MCC  142 &#39;s expectation, directly increasing the current will result in more torque and faster acceleration thereby lessening the effects of a loss of frequency lock between the spindle motor  106  and MCC  142 . Similarly, in the event the ZC occurs before the MCC  142 &#39;s expectation, decreasing the current will result in less torque and slower acceleration also lessening the effects of a loss of frequency lock between the spindle motor  106  and MCC  142 . 
     Another correction method embodiment consists of forcing the MCC  142  into the coast mode for resynchronization, based on a predicted loss of frequency lock. Forcing the MCC  142  onto the coast mode eliminates misapplied current, because resynchronization of the spindle motor  106  to the MCC  142  occurs prior to a loss in frequency lock between the spindle motor  106  to the MCC  142 . 
       FIG. 3  shows a plurality of ZCs, such as  152 , of a BEMF voltage signal  154  of an accelerating spindle motor  106  (of  FIG. 2 ), as can be seen by the successive reductions in time between occurrences of a ZC  152 . During operation of the spindle motor  106  (of  FIG. 2 ), each ZC  152  is used to confirm frequency lock between the spindle motor  106  and the MCC  142  (of  FIG. 2 ), while the MCC  142  is in a coast mode. Frequency lock is confirmed by recognition of the ZC  152  with any timing window such as  156 . 
     Opening of each timing window  156  is timed to correspond with the expected arrival of its corresponding ZC  152 . The arrival of each ZC  152  is expected to arrive in substantial alignment with a central position  158  of the timing window  156 . The rotational velocity of the spindle motor  106  at any given ZC  152  is used as the basis for predicting the opening of the next timing window  156 . When the spindle motor  106  is operating at its operational velocity, the accuracy of the predicted opening time for each timing window  156  is quite high. During acceleration at lower speeds, the large changes and variability in ZC frequency makes predicting the opening time more difficult to calculate. 
     Because during periods of closure of the timing windows  156  current is being applied to the windings of the spindle motor  106 , and due to the dependence on velocity readings of the spindle motor  106  for opening of the timing windows  156 , the successive earlier arrivals of the ZCs  152 , as shown by the sign numbers  160  and  162 , is not an unexpected result. It is also not unexpected that a continual succession of earlier occurrence of ZCs  152  will lead to a loss of frequency lock, such as shown by sign number  164 . The MCC  142  operates as a “go no-go” test for frequency lock, that is, either the ZC  152  occurred within the timing window  156 , or it did not. The MCC  142  lacks the capability of identifying where within the timing window  156  that a ZC  152  occurred. 
     By establishing an intervention criteria  166  within a simulated timing interval  168 , which corresponds to a timing window  156 , and by defining an effective center  170  of the intervention criteria  166  aligned in time with the central position  158  of the timing window  156 , the amount of separation in time between the occurrence of the ZC  152  relative to the effective center  170  can be monitored by the SMAC  146 . The intervention criteria  166  can also be characterized as a second timing window within each first timing window  156  as depicted in  FIG. 3 . 
     Upon an occurrence of the ZC  152  falling outside of the intervention criteria  166 , while remaining within the timing window  156 , the SMAC  146  responds by adjusting the current applied to the windings of the motor  106 . The SMAC  146  adjusts the current to the windings by either a direct adjustment of the current being supplied, or by placing the MCC  142  into its coast mode. It is noted that each of the boundaries,  165  and  167 , of the intervention criteria  166  are empirically determined for each type of data storage device. 
       FIG. 4  shows a flowchart  200  of an acceleration process for accelerating a device to a predetermined velocity. The process commences at process step  202  with the activation of a Synchronicity Monitoring and Adjustment Circuit (such as SMAC  146 ), and continues at process step  204  with an application of current for acceleration of a device (such as spindle motor  106 ). At process step  206 , a controller (such as  138 ) derives and opens a simulated timing interval (such as  168 ) for use as a basis in determining a deviation in time between a ZC event (such as  152 ) and a central position (such as  158 ), of a timing window (such as  156 ), of a device control chip (such as MCC  142 ). At process step  208 , the timing window of the device control chip is opened for use in detecting a frequency lock between the device control chip and the device. With the timing window opened, the device control chip monitors for an occurrence of a device signal (such as ZC  152 ) at process step  210 . 
     At process step  212 , a detection of the device signal within the timing window permits continuance of the acceleration of the device. At process step  214 , a level of timing compliance between the central position of the timing window and an occurrence of the device signal is determined. At process step  216 , adjustments to the current driving the acceleration of the device are made based on the level of timing compliance determined by process step  214 . At process step  218 , a determination of whether or not a predetermined velocity for the device has been met. If the predetermined velocity for the device has been met, the process concludes at end process step  220 . However, if the predetermined velocity for the device has not been met, the process reverts to process step  204  and continues until the predetermined velocity has been met. 
       FIG. 5  shows a flowchart  216 A, which is an embodiment of a method for adjusting the current driving the acceleration of the device (such as spindle motor  106 ) called for by process step  216  of the acceleration process flowchart  200  (of  FIG. 4 ). The embodiment for adjusting the current driving acceleration of the device shown by flowchart  216 A is referred to as a current controlled locking mode (CCL mode). When operating under the CCL mode, a synchronicity monitoring and adjustment circuit (SMAC) (such as SMAC  146  of  FIG. 4 ) is activated by a controller (such as  138 ) at process step  222  with the commencement of the CCL mode. The process continues at process step  224  with a correlation of and effective center (such as  170 ) of an intervention criteria (such as  166 ) and a central position (such as  158 ) of a timing window (such as  156 ). At process step  226 , the controller operating the SMAC analyzes the relative position of a device signal (such as ZC  152 ) to the effective center of the intervention criteria. 
     At process step  228 , a determination of whether or not the device falls within the intervention criteria is made. If the timing of the device signal falls within the intervention criteria, the process proceeds to process step  218  with the verification of whether or not the device has attained a predetermined velocity. If the device has attained the predetermined velocity, the process concludes at end step  220 . If the device has not attained the predetermined velocity, the process reverts to process step  204  (of  FIG. 4 ), and continues until attainment of the predetermined velocity. 
     However, if at process step  228  the intervention criteria has not been met and the timing of the occurrence of the device signal falls outside of the intervention criteria, the process proceeds to process step  230 . At process step  230 , the current driving the device is adjusted by a control function, responding to the deviation of the timing of the device signal relative to the effective center of the intervention criteria, and then continues to process step  218  for the conclusion of the process. 
       FIG. 6  shows a graphical print out  232  of the active response of the spindle motor  106  (of  FIG. 2 ) to the application of the process steps described by the flowchart of  FIG. 5 . 
       FIG. 7  shows a flowchart  216 B, which is an preferred embodiment of a method for adjusting the current driving the acceleration of the device (such as spindle motor  106 ) called for by process step  216  of the acceleration process flowchart  200  (of  FIG. 4 ). The preferred embodiment method for adjusting the current driving acceleration of the device shown by flowchart  216 B is referred to as a mode controlled locking mode (MCL mode). When operating under the MCL mode, a synchronicity monitoring and adjustment circuit (SMAC) (such as SMAC  146  of  FIG. 4 ) is activated by a controller (such as  138 ) at process step  234  with the commencement of the MCL mode. The process continues at process step  236  with a correlation of and effective center (such as  170 ) of an intervention criteria (such as  166 ) and a central position (such as  158 ) of a timing window (such as  156 ). At process step  238 , the controller operating the SMAC analyzes the relative position of a device signal (such as ZC  152 ) to the effective center of the intervention criteria. 
     At process step  240 , a determination of whether or not the device falls within the intervention criteria is made. If the timing of the device signal falls within the intervention criteria, the process proceeds to process step  218  with the verification of whether or not the device has attained a predetermined velocity. If the device has attained the predetermined velocity, the process concludes at end process step  220 . If the device has not attained the predetermined velocity, the process reverts to process step  204  (of  FIG. 4 ), and continues until attainment of the predetermined velocity. 
     However, if at process step  240  the intervention criteria has not been met and the timing of the occurrence of the device signal falls outside of the intervention criteria, the process proceeds to process step  242 . At process step  242 , the controller places a device control chip (such as MCC  142 ) into a coast mode, and activates a resynchronization circuit (such as  150 ), which resynchronizes the device with the control chip, thereby reestablishing a more precise frequency lock between the device and the control chip, prior to a loss of frequency locking between the control chip and the device. Following the reestablishment of a more precise frequency lock between the device and the control chip, the controller returns the control chip to a run mode, and then proceeds to process step  218  for the conclusion of the process. 
       FIG. 8  shows a graphical print out  244  of the active response of the spindle motor  106  (of  FIG. 2 ) to the application of the process steps described by the flowchart of  FIG. 7 . 
       FIG. 9  shows a comparison graph  246 , comparing differences between; an original acceleration curve  248 , for a spindle motor (such as  106  of  FIG. 2 ) operating under an application of a maximum allowable current specified for the spindle motor; a CCL acceleration curve  250  for the same spindle motor, but incorporating the use of the current controlled locking (CCL) mode, and operating in accordance with the flowcharts shown by  FIGS. 4 and 5 ; and a MCL acceleration curve  252  for the same spindle motor operating under the use of the mode controlled locking (MCL) mode, and in accordance with the flowcharts shown by  FIGS. 4 and 7 . Although significant performance improvements are realized through the adaptation of the CCL mode (as shown by acceleration curve  250 ), even greater performance improvements are realized through the adaptation of the MCL mode (as shown by MCL acceleration curve  252 ). The spindle motor  106  shown by  FIG. 10  is a preferred embodiment that includes a rotor hub  260  (also referred to as rotor  260 ) supporting a plurality of permanent magnets (one shown at  262 ). The permanent magnets  262  are adjacent three motor windings  264  supported by a stator shaft  266 . The stator shaft  266 , confines motor contacts A, B, and C  268 , for locating the rotor  260  and operating the spindle motor  106 . 
     It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this detailed description is illustrative only, and changes may be made in detail, especially in matters of structure and arrangements of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.