Abstract:
A system for hardware intelligent speed monitoring and auto-retract is disclosed. The system contains a monitoring device that monitors the TACH (Tachometer) output of motor driver. The device provides a trigger to the signal processor and a retract mechanism to retract the actuator when the spindle motor speed is unexpectedly much higher or lower than normal speed. The system DSP (Digital Signal Processor) is unaware of such occurrence.

Description:
This patent application claims priority from U.S. Provisional application No. 60/130,304, filed Apr. 21, 1999. 
    
    
     FIELD OF INVENTION 
     The present invention relates generally to regulation of the speed of a spindle motor in a disc drive, and more particularly to a hardware based dedicated circuit to ensure that the heads on the actuator arm retract to the landing zone on the occurrence of an unexpected over speed or under speed of the spindle motor. 
     BACKGROUND OF THE INVENTION 
     In a typical disc drive, there is one or more discs mounted on a spindle. The disc surface is divided into concentric tracks where data can be stored. Both sided of a disc provide for data storage. When data is to be retrieved or stored, a read/write head is used. The read/write head is mounted on a finger, which is in turn mounted on to the end of an actuator arm. The number of read/write heads is double of the total number of discs in a disc drive. The spindle is driven by the spindle motor to rotate the discs. The actuator arm is driven by VCM (Voice Coil Motor) to pivotally position the head over the disc surface such that it flies over the disc surface above a thin layer of air during operation. The read/write head and the disc surface are kept apart by the air bearing between them. When the spindle speed slows down such that the air bearing can not be sustained, the read/write head will tend to crash into and drag along the surface. This will cause permanent damage to the disc surface. Such situations usually occur during spindle start-up and spindle turn-off. 
     All modern disc drives have some means of preventing a read/write head of an actuator from crashing into the disc surface when there is either an intentional or emergency power shut-down. Actuators are typically moved to a non-data storage area on the disc surface during a power shutdown. Such an area on the disc surface is known as the landing zone where the actuator is parked when there is no read/write operation. 
     U.S. Pat. No. 4,371,903 issued on Feb. 1, 1983 to DMA Systems Corporation entitled “EMERGENCY HEAD RETRACT SYSTEM FOR MAGNETIC DISC DRIVES”, U.S. Pat. No. 4,786,995 issued on Nov. 22, 1988 and U.S. Pat. No. 4,866,554 issued on Sep. 12, 1989 to Peripheral Technologies, Inc. both entitled “AUTOMATIC HEAD RETRACT SYSTEM” teach how the problem of damage to the disc drive surface can be minimized. 
     U.S. Pat. No. 4,371,903 provides an electrical circuit with a switch means which is operatively positioned between the stator winding of a magnetic DC motor and a linear motor positioner coil (also known as Voice Coil). The magnetic DC motor is used as the spindle motor during normal operation. When an emergency situation arise, the switch means will couple the coil to the stator windings and relay means responsive to the emergency situation where the kinetic energy from the spindle mass is used to unload the read/write head. 
     U.S. Pat. No. 4,786,995 and U.S. Pat. No. 4,866,554 provide a latching system to retract the read/write head to the landing zone in response to electric power turn off (whether intentional or attributable to an emergency condition involving electric power loss). The read/write head is automatically retracted by operating the positioner motor (also known as the Voice Coil Motor) under the control of logic within the disc drive unit so as to control the speed of the carriage to avoid high speed crashing against its travel limit. 
     The means of managing retract of the read/write head are taught in the prior art mentioned above. In these prior art, the retract of the read/write head is in response to a power loss or an emergency situation. However, there is another aspect that would lead to the read/write head crashing into the disc surface. This involves the risk of abnormalities in the speed of the spindle motor. Such abnormalities are caused by the unexpected over or under speed of the spindle motor. 
     In the latest generation of disc drives, the spindle speed is regulated by the servo processor, which also controls the actuator. There are situations where the servo processor unexpectedly stops monitoring and controlling the spindle speed. These abnormalities may occur when the processor gets stuck in a loop or when the processor unexpectedly moves to a state where it expects not to have to monitor the spindle speed. The occurrence of such abnormalities increase as the code driving these processors becomes more complex. When spindle speed regulation is lost, the spindle speed invariably increases or decreases beyond a reasonable range. Early detection of abnormalities in the spindle speed has been used such that action may be taken to prevent the head from crashing into the disc surface by moving the actuator to the landing zone. U.S. Pat. No. 4,807,062 issued Feb. 21, 1989 to Kabushiki Kaisha Toshiba, entitled “MULTIPLE FORCE RETRACT CIRCUIT FOR A MAGNETIC DISC DRIVE” describes a magnetic disc drive which provides for the magnetic head to move to the landing zone under abnormal conditions of the spindle motor. The magnetic disc drive has an abnormality detection means for detecting whether the drive is in an abnormal condition, a position detection circuit for detecting whether the magnetic head is at the landing zone, a control means and drive means to move the magnetic head, if it is not already at the landing zone. A microprocessor and many other elements in the whole circuit are used to ensure that the actuator is parked at the landing zone when abnormality arises. 
     There remain a need for an improved method to detect abnormalities of the spindle speed such that the servo processor recover from such situations even if it were in a loop or in an unexpected state. 
     There is also a need for a simple retract circuit for moving the actuator arm to the “landing zone” during abnormalities in the spindle speed where the servo processor is interrupted by a hardware mechanism to reset the servo processor to a known state. From such a known state, to servo processor should then be able to sense the spindle speed and lock to he spindle speed for speed regulation, or failing which, it should be able to brake the spindle and restart the power up procedure to restore spindle control. This will be a graceful way of recovering from an unexpected situation where spindle speed regulation is lost, and the servo processor is not aware of the loss of spindle speed regulation. It will be evident from the following description that the present invention offers this and other advantages. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to minimize the above-mentioned problems with an improved retract system for an actuator in a disc drive. The actuator is retracted when spindle motor is under speed or over speed. According to the present invention, there is provided a disc drive with 
     The present invention provides a check of the spindle speed to minimize abnormalities in addition to the sudden slowing down or speeding up of the spindle speed either in an intentional and emergency power turn-off. Abnormalities are detected by setting a fixed range for comparing to the spindle motor speed of an operating disc drive such that a spindle motor will function without causing the read/write head to crash into the disc drive surface within that range. 
     The present invention can also be implemented in a disc drive a disc on a spindle, such that the spindle is rotatably driven by a motor at a spindle speed monitored by a frequency sensor. The disc drive also has a head for reading and writing data on a surface of the disc. The head being suspended from an actuator arm over the disc which is driven by a voice coil motor. The disc drive includes a retract device that has a comparator circuit to compare input signal from the frequency sensor with a predefined threshold range and outputs a comparison signal when the input signal falls outside of the predefined threshold range. The retract device also includes a delay filter which determine a duration of the comparator signal. A trigger initiates a retract mechanism when the comparison signal falls outside of the predefined threshold range for a predetermined duration of time. The retract mechanism being configured to move the head away from the surface of the disc. 
     The retract device has a comparator system to compare input signal from the frequency device with a predefined threshold range. There is also a delay filter to determine signal duration from the comparator system. A trigger is also included to initiate a retract mechanism when there is a resultant signal from the delay filter. 
     In another aspect of the present invention, the retract device having a circuit with a frequency-voltage converter, a comparator system, a delay filter and a trigger. The frequency-voltage converter in the circuit converts input frequency to voltage output to the comparator system where the voltage is compared with a predefined higher and lower threshold voltage range. The delay filter determines if the duration of the voltage supply from the comparator system is significant to be considered as an abnormality. This is achieved by comparing the duration of the voltage supply with a predefined threshold value set in the delay filter. If the duration of the voltage supply exceed the predefined threshold value, the voltage from the delay filter will simultaneously interrupt a processor and initiate a retract mechanism through the trigger. 
     In another embodiment of the present invention, the comparator system in the circuit has two comparators to determine if the voltage is within the threshold range; where one comparator is set at a higher threshold value and the other is set at a lower threshold value. To facilitate such a comparison, the voltage output from the frequency-voltage converter split into the two comparators. In order to obtain a single resultant output, an OR gate is incorporated into the comparator system to link the two comparators. 
     In another embodiment of the present invention, a low pass filter is used to provide a time delay as part of the delay filter. The low pass is made up of a resistor and a capacitor. There is also a fast discharge path linked to the OR gate of the comparator system during a low output. A third comparator, set at a predefined threshold value, is used to provide an adjustable delay value in the delay filter. It is preferred that the delay filter includes an AND logic gate to provide a single resultant output from the third comparator and the OR gate. 
     In yet another embodiment of the present invention, the signal processor is reset to a known state following the interruption such that it is enabled to restart the power-up procedure to restore spindle control. 
     In the present invention, the retract mechanism is initiated to enable the actuator to return to the landing zone. 
     One advantage of the present invention is that it is able to initiate two actions at the same time with a single resultant from a two-step process. 
     Another advantage of the present invention is that it provides a filter of non-genuine abnormalities like noise disturbances. 
    
    
     These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings. 
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is disc drive in which the present invention is applied. 
     FIG. 2 is a flow diagram of the process provided by the present invention. 
     FIG. 3 is a flow diagram of one of the pre-defined process illustrated in FIG.  2 . 
     FIG. 4 is a flow diagram of one of the predefined process illustrated in FIG.  2 . 
     FIG. 5 is a circuit layout of one of the embodiments of the present invention. 
     FIG. 6 is a graphical illustration of how the present invention works. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows an exemplary disc drive such as one in which the present invention may be implemented. A base  100  and a cover  102  form an enclosure for the various components in the disc drive. The components include one or more disc  103  that are rotatably mounted on a spindle  104  which is driven by a spindle motor  106 . Data is stored on the disc surfaces  107  which are arranged in concentric tracks. A read/write head  8  mounted on an actuator  109  flies over the disc surface  107  with a very thin layer of air in between. The actuator  109  is controlled by a VCM (voice coil motor)  110  about a pivot  111 . The actuator  109  includes one or more actuator arm  112 . Each actuator arm  112  is connected to at least one suspension  113 . The read/write head  108  is supported at the end of the suspension  113 . The actuator  109  can be rotated to position the read/write head  108  over the desired track on the disc surface  107  for read/write operations. The speed of the spindle motor  106  controls the rate at which the disc  103  rotates. 
     FIG. 2 to FIG. 4 illustrates the process of the most preferred embodiment of the present invention. 
     FIG. 2 shows the process in which the present invention provides. The present invention provides for an input frequency of the spindle motor speed to a frequency-to-voltage converter  114 . The output voltage from  114  is then compared to a fixed range of voltage threshold to determine if the spindle motor is over speed or under speed in the pre-defined process  116 . Abnormalities would arise, if there is an over speed or under speed. The output from  116  will be fed to another predefined process  118  where the duration of the voltage output from  114  will be monitored. If the duration of the voltage output from  114  is less than a certain pre-defined time, the abnormality will not be considered and the trigger  120  will not be activated. The trigger  120  is triggered when the spindle over speed or under speed for a significant duration. Once the trigger  120  is activated, the actuator will be retracted  122  to the landing zone and the servo will be reset to a known state  124 . 
     FIG. 3 further illustrates the pre-defined process  116 . The voltage from  114  is split to two  126 . The split voltage is then fed to two comparators  128  and compared to a higher and a lower threshold voltage  130 . At each comparator, the resultant digital output state is determined and the outputs are fed through an OR gate to provide a single resultant output at  132 . The digital output at  132  may be a high state or a low state depending on the speed of the spindle motor. 
     FIG. 4 further illustrates the pre-defined process  118 . The resultant output from  132  is split into two at  134  and fed to a delay filter  136 . The resultant from the delay filter at  136  is then fed to an AND gate at  138  to determine the resultant digital output. The delay filter monitors the duration of the spindle speed by comparing to a predefined threshold duration. The resultant output is than combined through the AND gate  138 . The resultant from the AND gate  138  is then fed to  120 . 
     The most preferred embodiment of the present invention is a circuit illustrated in FIG. 5 where an output generated based on the back EMF (Electromotive Force) of the three phase spindle motor is used to monitor the speed of the spindle motor. The frequency of the TACH (Tachometer) output  140  is proportional to the speed of the spindle motor. The higher the speed of the motor, the higher the frequency at the TACH output  140 . This output  140  is provided as frequency input  142  to a frequency-to-voltage converter  141 . This frequency input  142  is then converted to voltage output  144  in the frequency-voltage converter  41  and is used to monitor the spindle TACH feedback output. The voltage output  144  is fed to a comparator system  176  which consist of a pair of comparators  146  and  150  to trigger a retract whenever a lower or higher speed threshold is breached. In order to minimize the risk of the read/write head crashing into the disc drive surface, the speed of the spindle motor is allowed to vary over a small range between S 1  and S 2 . This sets the normal speed conditions which the disc drive will operate without glitches. S 1  is the lower threshold frequency and S 2  is the higher threshold frequency. These frequency threshold values are directly proportional to the speed of the spindle motor. When there is a variation in speed below S 1  rpm (revolutions per minute) or above S 2  rpm, and the duration is longer than x seconds, the circuit provides a trigger  179  to interrupt the DSP (Digital Signal Processor)  174  as well as to the retract pin at  172  of the motor driver. The retract trigger consist of an AND gate  170  and is qualified by a bit written to the spindle driver register by an output port  174  to enable or disable the retraction. This is for times when the circuit should not be enabled, such as spin-up, and when the drive is actually commanded to slow down. Thus, the circuit will only be activated when the DSP  174  does not expect the spindle to spin down, and will only be triggered when there is an unexpected over speed or under speed occurrence. The triggered retract pin will force a hardware retract of the actuator to the landing zone. The interruption of the DSP  174  informs the DSP  174  of an unexpected retract occurrence, and thus allow the DSP  174  to recover gracefully. At normal speed conditions, if there is a sudden change of motor speed less than x seconds, the circuit will not trigger. This is to ensure that the VCM (Voice Coil Motor) will not retract due to false trigger. 
     According to FIG. 5, when the spindle motor speed is below S 1  rpm, it will manifest as a lower VCO (Voltage Controlled Oscillator) frequency (above F 1  Hz (Hertz)) at the TACH output  140 . This frequency change is converted to voltage by the frequency to voltage converter  141 . The voltage  144  is compared with the threshold voltages of the pair of comparators,  146  and  150 . The threshold voltages in each comparator can be set via resistor ratio. The threshold of comparator  146  is set at T 1  V (volts), which is equivalent to S 1  rpm. Any voltage below this shall trigger the comparator  146 . The triggered comparator  146  will output a high state to the OR gate  153 , which in-turn present a high state to the delay filter circuit  178 . 
     When the spindle motor speed is above S 2  rpm, it will manifest as higher VCO frequency (F 2  Hz) at the TACH output  140 . This frequency change is converted to voltage  144  by the frequency-to-voltage converter  141 . The threshold of comparator  150  is set at T 2  V, which is equivalent to S 2  rpm. Any voltage above this shall trigger the comparator  150 . The voltage  144  is then compared with the thresholds of comparator  150 . This time, comparator  150  is activated and outputs a high state to the OR gate  153 , which in-turn presents a high state to the delay filter circuit  178 . 
     During normal conditions, the speed of the spindle motor will fall within the range of S 1  and S 2 . This means that the voltage output T V at  144  from the frequency-to voltage converter  141 , will be higher than T 1  V and lower than T 2  V. Therefore the output from the  2  comparators,  146  and  150 , will be at low states to the OR gate  153 , which in-turn presents a low state to the delay filter circuit  178 . 
     All other conditions will result in a high state output to the delay filter through the OR gate  153 . 
     The delay filter circuit  178  consists of a low pass filter, a fast discharge path made up of a diode  162  and a resistor  158  and a comparator  166 . The low pass filter provides a time delay with a resistor  160  and a capacitor  156 . The voltage on the capacitor  156  will discharge rapidly through the diode  162  during the time when the OR gate  153  output is held low. This is to prevent accumulation of charges on the capacitor  156 . The threshold setting, T 3  V for the comparator  166  is to provide an adjustable delay value setting. The delay filter circuit  178  will monitor the output of the OR gate  153  for x seconds during which the output of OR gate  153  will have to stay high before the delay filter will send out a trigger to be qualified by the AND gate  168 . If the output of the OR gate  153  drops low during the x seconds delay period, the delay period will be reset through the diode  162  until the next occurrence of the output of OR gate  153  going high. This is to ensure that the variation is genuine and sustained, and not due to spurious noise disturbances or during spin down occurrences. Hence, at normal speed condition, if there is a speed glitch of less than x seconds, there will be no trigger as the diode  162  will set the capacitor  156  to discharge mode through a ground  154  and hence will not be qualified by the threshold T 3 . 
     When the output from the OR gate  153  is a high state, the output at the AND gate  168  may be a high state or a low state. The high or low state of AND gate  168  depends on whether the change of speed of the spindle motor is longer that the duration set by the threshold T 3  at comparator  166 . 
     When the output from the OR gate  153  is a low state, the output at the AND gate  168  will always be at a low state. 
     The output of the delay at AND gate  168  is qualified with the output port enabled bit, at the AND gate  170  when fed to the trigger  179 . The qualified output of the AND gate  170  will interrupt the DSP  174  and activate the retract pin of the motor driver. When the output from the AND gate  168  is a low state while the output port is enabled, the output at AND gate  170  will be a low state and vice versa. 
     FIG. 6 illustrates a simulation on the circuit of the above-mentioned embodiment. In this simulation, the range in which the disc drive will operate without risk of the read/write head crashing into the disc surface is set between S 1 =6800 rpm (TACH=5670 Hz), higher threshold limit and S 2 =7800 rpm (TACH=1980 Hz), lower threshold limit. The delay duration is set at 0.6 seconds and the threshold value at T 3  is 0.6 V while R 1 =600 K, R 2 =80 K, C 1 =2 u. Various stages of the simulation result are shown in FIG.  6 . The values  180 ′,  182 ′,  184 ′ and  186 ′ of the TACH inputs VCO (Voltage Controlled Oscillator) frequencies are shown in I. The voltages  180 ′,  182 ′,  184 ′ and  186 ′ from the frequency-to-voltage  41  are shown in  11 . The resultant trigger outputs  180 ″,  182 ″,  184 ″ and  186 ″ from AND gate  170  shown in III. These are the corresponding values in four cases: normal speed  180 ,  180 ′ and  180 ″; over speed  182 ,  182 ′ and  182 ″; under speed  184 ,  184 ′ and  184 ″; and sudden change of speed but less than 0.6 seconds  186 ,  186 ′ and  186 ″. From III, two triggers (i.e. high state  1 ) are observed. The first trigger is due to over speed of the spindle motor while the second trigger is due to under speed of the spindle motor. These will in turn trigger the retract pin and the DSP (Digital Signal Processor) to force retract of the VCM. The other two trigger values are at a low state 0 as expected. At normal speed of the spindle motor no trigger will occur and the disc drive will operate as per normal. While the other low state is due to a glitch which held at a duration that is below the set threshold of 0.6 seconds. 
     The above embodiment can be implemented as an ASIC (part in motor driver IC (INTEGRATED CIRCUIT). The IC shall have extra two pins, one input pin for external output port enable and the other for the trigger output. In addition, three registers shall be added for two threshold voltage settings and the time delay settings. 
     In summary, a disc drive having a disc  103  on a spindle  104 , such that the spindle  104  is rotatably driven by a motor at a spindle speed monitored by a frequency sensor. The disc drive also has a head  108  for reading and writing data on a surface  107  of the disc  103 , the head  108  being suspended from an actuator arm over the disc  103  which is driven by a voice coil motor  110 . The disc drive includes a retract device that has a comparator circuit  176  to compare input signal from the frequency sensor with a predefined threshold range and outputs a comparison signal when the input signal falls outside of the predefined threshold range. The retract device also includes a delay filter  178  which determine a duration of the comparator signal. A trigger  179  initiates a retract mechanism when the comparison signal falls outside of the predefined threshold range for a predetermined duration of time, the retract mechanism being configured to move the head away from the surface of the disc. 
     In a disc drive, a circuit with a frequency-voltage converter  141 ; a pair of comparators,  146  and  150 , to compare an input voltage  144  with a higher and lower threshold range; a delay filter  178  to determine the length of time the input voltage last; and a AND gate  170  to interrupt a processor as well as to initiate a retract mechanism such that the actuator is brought to the landing zone. The frequency-voltage converter  141  is connected to the pair of comparators,  146  and  150  such that the input voltage  144  is provided to the comparators,  146  and  150 . The 2 comparators,  146  and  150 , provides an output voltage to the delay filter  178 . The delay filter  178  is connected to the AND gate  170  where the output from the AND gate  170  is split into two. 
     The first comparator  146  is to determine and compare the output voltage  144  from the frequency-voltage converter  141  with the higher threshold voltage. The second comparator  150  is to determine and compare the output voitage  144  from the frequency-voltage converter  141  with the lower threshold voltage. The OR logic gate  153  to provide a single resultant voltage output from the first comparator  146  and second comparator  150 . 
     The delay filter  178  has a low pass filter to provide a time delay; a fast discharge path during a low output from the OR gate  153 ; the third comparator  166  to provide an adjustable delay value; and a AND logic gate  168  to provide a single voltage output from the third comparator  166  and the OR logic gate  153 . The low pass filter is made up of a resistor  160  and a capacitor  156 . The third comparator  166  is set at a predefined threshold voltage. 
     A disc drive having at least one disc on a spindle motor, an actuator and means to return the actuator to the landing zone when the speed of there is an over speed or under speed of the spindle motor. 
     The foregoing description is only illustrative of various embodiments of the invention, and a person skilled in the art will understand that changes can be made to the details of structure, function and processes without going beyond the scope of the present invention.