Abstract:
A disk drive emergency retract architecture for providing power to a voice coil motor (VCM) to retract a transducing head from a surface of a recordable medium during loss of power from an external power supply. The disk drive emergency retract architecture comprises a spindle motor, having an internal inductance and an internal resistance, for spinning the recordable medium. The spinning recordable medium creates a back electromotive force (BEMF) in the spindle motor. A boost circuit transfers the back electromotive force located in the spindle motor to a capacitor which stores and supplies power to the VCM. The capacitor is connected to a power switch circuit, which supplies power from the capacitor to the VCM when the power switch circuit is in a conducting state and prevents power from being supplied to by the capacitor to the VCM when the power switch circuit is in a non-conducting state. A retract circuit supplies a signal to the power switch circuit, dictating whether the power switch circuit is in the conducting state or the non-conducting state. The retract circuit operates to alternate the power switch circuit between the conducting state and the non-conducting state at a set frequency, resulting in power being provided from the capacitor to the VCM at this frequency.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S)  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/590,207 filed Jul. 22, 2004 for “Low Cost Emergency Disk Drive Head Retract Architecture” by J. Brenden and J. Dahlberg.  
       INCORPORATION BY REFERENCE  
       [0002]     The aforementioned U.S. Provisional Application No. 60/590,207 is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     The present invention relates to disk drives and storage devices. In particular, the present invention relates to utilizing back electromotive force (BEMF) energy from the spinning spindle motor to retract the head to a safe landing zone during emergency loss of power.  
         [0004]     Generally, a magnetic hard disk drive (HDD) includes a magnetic read/write head and several magnetic disks, each disk having concentric data tracks for storing data. The disks are mounted on a spindle motor, which causes the disks to spin. The read/write head is typically mounted on a slider, which is carried by a suspension or load beam. The load beam is attached to an actuator arm of an actuator, which moves the read/write head over the spinning disk during operation. As the disks spin, the slider suspended from the actuator arm flies a small distance above the disk surface. The slider carries a transducing head for reading from or writing to a data track on the disk.  
         [0005]     In addition to the actuator arm, the slider suspension comprises a bearing about which the actuator arm pivots. A large scale actuator motor, such as a voice coil motor (VCM), is used to move the actuator arm (and the slider) over the surface of the disk. When actuated by the VCM, the actuator arm can be moved from an inner diameter to an outer diameter of the disk along an arc until the slider is positioned above a desired data track on the disk.  
         [0006]     A control circuit is coupled to a coil in the VCM in order to controllably supply current to the coil. When a current is passed through the coil, a motive force is exerted on the actuator arm.  
         [0007]     Parking zones in an HDD allow the read/write head to be safely landed after the hard drive has ceased operation. When an HDD is powered down, it usually performs certain operations before actually disconnecting from the external power source. One of these power down operations is to operate the actuator arm to move the head to the parking zone. If the head is not moved to the parking zone prior to power down, the head will land on the disk after the disk stops spinning, potentially damaging the disk and the read/write head.  
         [0008]     During emergency loss of power, the read/write head must still be moved to the landing zone to avoid damage to the disk and the read/write head. This situation is referred to as an emergency retract. The problem is where does the power come from necessary to move the read/write head to the landing zone. One solution is to store the necessary energy within the circuit, usually through use of a large capacitor, sufficient to power the VCM during emergency retract. Another solution is to use energy inherent to the operation of the disk drive system to supply power to the VCM and move read/write head to the safe landing zone. The smaller the disk however, the less inherent energy is present to help move the read/write head to the safe landing zone.  
         [0009]     Thus, there is a need for a design that can efficiently harness and use the inherent power available in the disk drive system to safely move the read/write head to the parking zone during emergency loss of power.  
       BRIEF SUMMARY OF THE INVENTION  
       [0010]     The present invention is a disk drive emergency retract architecture for providing power to a voice coil motor (VCM) to retract a transducing head from a surface of a recordable medium during loss of power from an external power supply. The emergency retract architecture includes a spindle motor which operates to spin the recordable medium of the disk drive system. The spindle motor includes an internal inductance and an internal resistance. The spinning recordable medium induces a back electromotive force (BEMF) in the spindle motor. The emergency retract architecture includes a boost circuit which transfers the BEMF energy induced in the spindle motor to a capacitor. The capacitor provides energy received from the BEMF to the VCM. Energy stored in the capacitor is provided to the VCM through a power switch circuit, which operates to supply power to the VCM when the power switch circuit is in a conducting state, and operates to prevent power from being supplied to the VCM from the capacitor when the power switch circuit is in a non-conducting state. A retract circuit supplies a signal to the power switch circuit, dictating whether it is in the conducting state or non-conducting state. The retract circuit provides a signal, such that the power switch circuit is alternated between the conducting state and the non-conducting state at a set frequency, resulting in power being provided from the capacitor to the VCM. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is an illustration of a disk drive system with a safe parking zone.  
         [0012]      FIG. 2  is a schematic diagram of a typical VCM control circuit with emergency retract capabilities.  
         [0013]      FIG. 3  is a schematic diagram of a VCM control circuit of the present invention with emergency retract capabilities. 
     
    
     DETAILED DESCRIPTION  
       [0014]      FIG. 1  is an illustration of typical disk drive system  10 . Disk drive system  10  includes disk  12 , spindle motor  14 , slider  15  carrying read/write head  16 , actuator arm  18 , voice coil motor (“VCM”)  20 , safe landing zone  22  and VCM control  24 .  
         [0015]     In normal operation, a drive current is provided to VCM  20  to actuate actuator arm  18 . When actuated by VCM  20 , actuator arm  18  can be moved from an inner diameter to an outer diameter of disk  12  along arc  28  until the read/write head  16  is positioned above a desired data track on the disk. Disk  12  includes a plurality of concentric tracks on which data and position information is recorded. Disk  12  is mounted on spindle motor  14 , which causes disk  12  to spin. Read/write head  16  suspended from actuator arm  18  flies above the surface of disk  12  as it spins. Read/write head  16  is operable to read the data and position information from tracks of disk  12  and generate an input signal representative of the data and position information.  
         [0016]     When a disk drive is powered down, it usually performs certain operations before actually disconnecting from the external power source. One of these power down operations is to operate actuator arm  18  to move read/write head  16  to safe landing zone  22 . Safe landing zone  22  allows read/write head  16  to be safely landed after the disk drive  10  has ceased operation. Safe landing zone  22  is located at the outermost (as shown in  FIG. 1 ) or innermost edge of disk  12  and typically includes a ramp to raise read/write head  16  and park it off of disk  12  in an elevated position. If the head is not moved to safe landing zone  22  prior to power down, the read/write head  16  will land on disk  12  after disk  12  stops spinning, potentially damaging disk  12  and read/write head  16 .  
         [0017]     In the event of a catastrophic shut down (i.e., external power is suddenly removed) there is no external power to perform power down procedures, including moving read/write head  16  to safe landing zone  22 . Typically, a large capacitor is used to store the energy required to drive VCM such that actuator arm  18  actuates to place read/write head  16  in the safe landing zone.  
         [0018]      FIG. 2  is a schematic diagram of typical emergency retract circuit  30 . Emergency retract circuit  30  operates to supply sufficient power to VCM  32  such that read/write head is moved to safe landing zone during emergency loss of power. Emergency retract circuit  30  includes external power supply  34 , supply monitor  36 , charge pump circuit  38 , logic for retract circuit  40 , voltage regulator  42 , and large capacitor  44 . The load components of VCM  32  are shown as resistor RVCM and inductor LVCM.  
         [0019]     During normal operation, while external power supply  34  is still available, external power supply  34  supplies power to charge pump circuit  38 . Charge pump circuit  38  operates to boost external power supply  34  in order to charge large capacitor  44  to a large voltage. Supply monitor  36  operates to detect when input voltage from external power supply  34  drops below a given threshold, indicating that emergency retract operation should begin. Supply monitor  36  sends a signal to logic for retract circuit  40 , which uses the energy stored in large capacitor  44  to supply the power necessary to VCM  32  such that the read/write head is retracted to the safe landing zone. Voltage regulator  42  operates to maintain a consistent output voltage. Some of the energy stored in large capacitor  44  is lost through internal resistance of voltage regulator  42 . Therefore, large capacitor  44  must be capable of storing sufficient energy to power logic for retract circuit  40  and voltage regulator  42 , and to provide sufficient energy to VCM  32  such that the read/write head is moved to the safe landing zone during emergency retract.  
         [0020]      FIG. 3  is a diagram illustrating an exemplary embodiment of the emergency retract architecture of the present invention. Emergency retract architecture  50  includes emergency retract circuitry  52 , spindle motor  54 , VCM  56  and external power supply  58 . Spindle motor  54 , as shown in  FIG. 1 , operates to spin the disk during operation.  
         [0021]     In this exemplary embodiment, spindle motor  54  is a three-phase motor. The spinning of the disk by spindle motor  54  creates back electromotive forces (BEMF), inherent in every electric motor. During emergency loss of power, although no power is being supplied to spindle motor  54 , inherent energy remains in spindle motor  54  due to the inertia present in the spinning disk. The use of a three phase motor in this embodiment results in the creation of three phase oscillating BEMF voltages labeled as BEMF( 1 ), BEMF( 2 ), and BEMF( 3 ). Rm( 1 ), Rm( 2 ), and Rm( 3 ) represents the internal resistances of the phases of spindle motor  54 . Likewise, Lm( 1 ), Lm( 2 ), and Lm( 3 ) represent the internal inductances of the phases of spindle motor  54 .  
         [0022]     Emergency retract circuitry  52  includes supply monitor  60 , boost monitor  62 , boost and retract logic  64 , transistors M 1 , M 2  and M 3 , VM capacitor  66 , and power inverter  68 . A number of diodes (D 1 , D 2 , D 3 , D 4 , D 5  and D 6 ) are shown to represent the body diode effect present in transistors that have been switched off. Therefore, when transistor M 1  is turned off by boost and retract logic  64 , the body diode present in transistor M 1  will operate electrically as diode D 1 . Diodes D 4 , D 5  and D 6  are shown as diodes because during boost and retract operations, the transistors represented by D 4 , D 5  and D 6  will always be off and will therefore operate electrically as diodes. In this exemplary embodiment, MOSFET transistors M 1 , M 2  and M 3  are used, however one of ordinary skill in the art would recognize that any number of switching circuits may be used in place of transistors M 1 , M 2  and M 3 .  
         [0023]     Supply monitor  60  operates to detect when input voltage from external power supply  58  drops below a given threshold, indicating that emergency retract operation should begin. When emergency retract is necessary, supply monitor  60  sends a signal to boost and retract logic  64  to begin boosting and driving VCM  56 . Boost and retract logic  64  operates to direct energy located in spindle motor  54  into VM capacitor  66 .  
         [0024]     Boost and retract logic  64  is connected to the gates of transistors M 1 , M 2  and M 3 , allowing boost and retract logic  64  to selectively turn the transistors on and off. The drains of transistors M 1 , M 2  and M 3  are connected to both spindle motor  54  and VM capacitor  66  through the respective diodes D 4 , D 5  and D 6 . The nodes located at the drains of transistors M 1 , M 2  and M 3  are labeled as PU, PV and PW respectively. The drains of transistors M 1 , M 2  and M 3  are each connected to a phase of three phase spindle motor  54 . The drain of transistor M 1  is connected through Rm( 1 ) and Lm( 1 ) to BEMF( 1 ), the drain of transistor M 2  is connected through Rm( 2 ) and Lm( 2 ) to BEMF( 2 ), and the drain of transistor M 3  is connected through Rm( 3 ) and Lm( 3 ) to BEMF( 3 ). Because spindle motor  54  is a three phase motor, each BEMF voltage will be out of phase with the other two BEMF voltages. Therefore, at different points in time, nodes PU, PV and PW will have varying voltage levels corresponding to the oscillating three phases of BEMF( 1 ), BEMF( 2 ) and BEMF( 3 ). The sources of transistors M 1 , M 2  and M 3  are connected to ground. Boost and retract logic  64  is also connected to power inverter  68 , operating to provided a pulse width modulated (PWM) signal to power inverter  68  to alternately turn power inverter  68  on and off. When power inverter  68  is turned on, VM capacitor  66  operates to drive VCM  56 .  
         [0025]     During emergency retract operations, boost and retract logic  64  performs two functions. First, boost and retract logic  64  operates to extract energy inherent in spindle motor  54 . Second, boost and retract logic  64  operates to send retract PWM signal  70  to drive inverter  68  such that power is supplied in an economic way to VCM  56 . These operations are not performed in exclusionary fashion. Boost and retract logic  64  may operate to extract energy from spindle motor  54  while supplying retract PWM signal  70  to power inverter  68 .  
         [0026]     During boost operations, in which VM capacitor  66  is charged to a desired voltage level, boost and retract logic  64  operates to control a two stage cycle by alternately turning transistors M 1 , M 2  and M 3  on and off. During the first stage when transistors M 1 , M 2  and M 3  are on, current is ramped up in inductors Lm( 1 ), LM( 2 ) and Lm( 3 ). During the second stage, boost and retract logic  64  turns transistors M 1 , M 2  and M 3  off such that energy stored in inductors Lm( 1 ), Lm( 2 ) and Lm( 3 ) is transferred to VM capacitor  66 . To understand how this works in operation, an example cycle is described. For purposes of the example, during the first stage of the cycle the BEMF voltages are assumed to be phased such that BEMF( 1 ) represents the highest voltage, BEMF( 2 ) represents a middle voltage, and BEMF( 3 ) represents the lowest voltage. Therefore, node PU will be at the highest voltage level at this point in time, node PW will be at the lowest voltage level at this point in time, and node PV will be at a voltage in between nodes PU and PW, most likely around 0 V. Because node PU is at a higher voltage than node PW, a current path is created from node PW to node PU. Specifically, current will travel from the ground contact of the source of transistor M 3 , through transistor M 3  which has been turned on by boost and retract logic  64 , then through Rm( 3 ) and Lm( 3 ), then through Lm( 1 ) and Rm( 1 ) to node PU, and finally through transistor M 1  which has been turned on by boost and retract logic  64  to the ground contact connected to the source of transistor M 1 . The effect of this current path from node PW to node PU is the build up of current in inductors Lm( 1 ) and Lm( 3 ).  
         [0027]     During the second stage of the boost operation, boost and retract logic  64  extracts the current built up in spindle motor inductors Lm( 1 ), Lm( 2 ) and Lm( 3 ) for use in charging VM capacitor  66 . The second stage is marked by boost and retract logic  64  operating to turn transistors M 1 , M 2  and M 3  off. When transistors M 1 , M 2  and M 3  are off, the current path discussed with respect to the first stage of the boost operation is broken. However, the current built up during the first stage of the boost operation is maintained by the spindle motor inductors Lm( 1 ), Lm( 2 ) and Lm( 3 ) which store magnetic energy and resist rapid changes in current. Continuing the example discussed above, recall that current was flowing from node PW, through the spindle motor inductors Lm( 3 ) and Lm( 1 ), to node PU. Spindle motor inductors Lm( 3 ) and Lm( 1 ) operate to maintain this current even after transistors M 1 , M 2  and M 3  are turned off. Current continues to flow through inductors Lm( 3 ) and Lm( 1 ) due to the nature of inductors in resisting changes in current. By turning transistors M 1 , M 2  and M 3  off the current path is altered, such that current now flows from ground, through diode D 3  representing the body diode effect of transistor M 3 , through Rm( 3 ) and Lm( 3 ), then through Lm( 1 ) and Rm( 1 ) to node PU. Because transistor M 1  is off, current will flow through diode D 4  and into VM capacitor  66 , resulting in the charging of VM capacitor  66 .  
         [0028]     As stated above, boost and retract logic  64  operates transistors M 1 , M 2  and M 3  to create a two stage cycle, meaning that boost and retract logic  64  will turn transistors M 1 , M 2  and M 3  on and off a number of times during a single retract operation. Thus, boost and retract logic  64  operates the transistors in order to alternate between ramping up current in spindle motor inductors Lm( 1 ), Lm( 2 ) and Lm( 3 ) and providing this current to VM capacitor  66 . In this manner, VM capacitor  66  can be regulated to any arbitrary voltage level desired. This differs from other methods, which provide the BEMF voltage from a spindle motor directly to a capacitor. This method only allows the capacitor to be charged to a voltage less than or equal to that of the BEMF voltage provided by the spindle motor. In the exemplary embodiment of the invention described above, because a current is provided by spindle motor inductors Lm( 1 ), Lm( 2 ) and Lm( 3 ), the voltage of VM capacitor  66  may be charged to any arbitrary voltage, and may in fact be higher than the voltage level provided by BEMF( 1 ), BEMF( 2 ) and BEMF( 3 ). In an exemplary embodiment, the duty cycle of the two stages just described is selectable over a range of 50% to 90% by a programmable register.  
         [0029]     The other function of boost and retract logic  64  is to provide retract PWM signal  70  to power inverter  68 , such that VCM  56  is operated to retract the read/write head. A power inverter is described in this exemplary embodiment, although one of ordinary skill in the art would recognize that any number of circuits may be utilized to perform the function of power inverter  68 . The exemplary embodiment of the present invention shown in  FIG. 3  utilizes pulse width modulation (PWM) through power inverter  68  to provide VCM  56  with a number of discrete power bursts. When power inverter  68  is on, power is drawn from VM capacitor  66 , through power inverter  68 , to VCM  56 . Retract PWM signal  70  operates to provide a number of short power burst at regular intervals to provide an overall average amount of power to VCM  56 . Retract PWM signal  70  is described in terms of duty cycles, defined as the amount of time the signal is in an active state compared with the total cycle of the PWM. For example, in one exemplary embodiment of the present invention, retract PWM signal  70  has a duty cycle of 15%, meaning that power inverter  68  is turned on 15% of the time and turned off 85% of the time. The duty cycle is selected by a programmable register which is capable of producing duty cycles ranging from 0% to 100%. In this method, the mechanical nature of VCM  56  can be taken advantage of, allowing the inertia of VCM to continue moving the read/write head during periods when power inverter  68  is turned off and no power is supplied to VCM  56 . Use of retract PWM signal  70  results in an economic use of the energy stored in VM capacitor  66 . For example, if boost and retract logic  64  sends retract PWM signal  70  with a duty cycle of 15%, then power inverter  68  draws power from VM capacitor  66  only 15% of the time.  
         [0030]     The use of power inverter  68 , in contrast with the voltage regulator used in the prior art and shown in  FIG. 2 , also allows for more economic use of the stored energy in VM capacitor  66 . VCM  56  only draws power when retract PWM signal  70  turns power inverter  66  on. When power inverter  66  is off, negligible current is drawn from VM capacitor  66 . In one exemplary embodiment, power inverter  66  makes use of complimentary metal oxide semiconductors (CMOS).  
         [0031]     In one exemplary embodiment of the present invention, retract PWM signal  70  is the inverse of the cycle in which transistor M 1 , M 2  and M 3  are turned on and off. In this embodiment, when PWM signal is such that power inverter  68  is on, then transistors M 1 , M 2  and M 3  are off. For example, if PWM signal has a duty cycle of 15%, then power inverter  68  will be on 15% of the time. This means that transistors M 1 , M 2  and M 3  will be on 85% of the time, and off 15% of the time. The benefit of this arrangement, is that during the 15% of the duty cycle in which power inverter  68  draws power from VM capacitor  66 , it may also draw power from the inductor current provided by inductors Lm( 1 ), Lm( 2 ) and Lm( 3 ) being used to charge VM capacitor  66 . This allows for the capacitance of VM capacitor  66  to be even smaller.  
         [0032]     The present invention therefore describes an architecture for utilizing back electromotive forces from the disk drive spindle motor to retract the read/write head from the surface of the disk to a safe landing zone during emergency loss of power situations. The architecture includes a boost circuit which transfers energy from the spindle motor to a capacitor. The energy is then provided to the voice coil motor such that the read/write head is moved away from the disk and placed on the safe landing zone.  
         [0033]     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.