Abstract:
This invention describes a method and apparatus to determine a safe rotational speed for a CD/DVD drive by detecting the amount of vibration of the disk by measuring the operating conditions of the spindle motor. A disk drive includes a motor for rotating the disk and an apparatus for monitoring the current or back emf in the windings of the motor. When the current or the back emf varies from a normal level, the disk is vibrating and a signal indicating a vibration condition is sent to the spindle motor driver. The maximum speed that the disk rotated is slowed until a vibrating condition is no longer detected and the rotational speed associated with a particular disk is based dynamically on the amount of vibration detected. Disks may also be identified that cannot spin a minimum rate of speed.

Description:
FIELD OF THE INVENTION 
   The present invention relates to the field of mass storage devices. More particularly, this invention relates to disk drives that use a plastic medium such as CD, CD-ROM and DVD drives. 
   BACKGROUND OF THE INVENTION 
   One of the key components of any computer system is a place to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disk drive, such as a CD-ROM or DVD. The most basic parts of a disk drive are a plastic disk that is rotated, an actuator that moves a transducer to various locations over the disk, and electrical circuitry that is used to write and read data to and from the disk. Some of these drives have read only memory. Others can read the read only memory media and are capable of writing as well. The disk drives also include circuitry for decoding information read from the disk into data so that it can be successfully retrieved from the disk. For writable media, the disk drives also include encoders for encoding the data to a form that can be written to the disk surface so that the data can be retrieved at a later date. A microprocessor controls most of the operations of the disk drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disk. 
   In each type of disk drive, the media, which is in the shape of a disk, spins during reading information representing data from the media. The disk also spins when information representing data is written to the drive. There is a constant push to spin the media faster and faster during either the read or write operation so that time required to access data from the disk is shorter or so that the time to write data to the disk is shorter. Some CD-ROM drives and DVD drives spin the media at constant angular velocity. Others vary the spin speeds as a function of the radial position of the data so that the media passes by the transducer at a constant linear velocity. These drives are referred to as constant linear velocity drives and achieve the highest rates of spin when the information representing data is at the outer perimeter of the recording surface. The first CD-ROM drive had a maximum speed of 1×. Current CD-ROM and DVD drives spin at maximum speeds which are multiples of the maximum speed of the 1× CD-ROM drive. Current CD-ROM and DVD drives are 16×, 32×, 40× and 52× which represent the multiple of the original CD-ROM maximum spin speed. 
   Spinning the disks at higher spin speeds have resulted in problems associated with CD-ROM and DVD drives. An increasing number of broken disks are being found in the high speed CD/DVD drives. Some believe that the disks have disintegrated due to structural defects such as cracks and the like. Another possibility is that the problem is caused when a disk is spinning at a high rate and begins to vibrate on the disk drive spindle. 
   Analysis of the construction of CD/DVD drives shows that this is a possibility. These disk drives include a disk tray. As the disk tray travels into the drive housing, the motor drive spindle and laser pickup assembly are pivoted up so the motor drive spindle goes through the newly inserted disk. At the same time, an upper spindle body fits over the lower spindle and is held by a magnet in the lower spindle. The result is that the only force holding the disk to the spindle is from the magnet. 
   If a disk begins to vibrate, at some point the magnet can no longer hold the upper spindle to the lower spindle to retain the disk. When the magnet can no longer hold the vibrating disk, the disk will be released and will spin off of the spindle at a high rate of speed in an uncontrolled direction. It is obvious what happens at this point. The disk slams against the housing and is destroyed. The resulting particles may also lodge within critical mechanisms within the drive and result in ruining the disk drive as well. For example, a plastic portion lodged near a mirror may block the light needed to read from the drive or prevent the mirror movement needed to focus the beam. 
   Therefore, there is a need for a method and apparatus that can detect vibration in a drive that holds a disk using a magnet having a relatively small force. There is also a need for a method and apparatus that can slow the disk drive in response to a detected vibration condition so as to prevent destruction of the disk in the disk drive. 
   SUMMARY OF THE INVENTION 
   This invention describes a method and apparatus to determine a safe rotational speed for a CD/DVD drive by detecting the amount of vibration of the disk by measuring the operating conditions of the spindle motor. A disk drive system includes a base, a spindle for holding a DVD or CD-ROM disk, and a motor for rotating the disk. The disk drive also includes an apparatus for monitoring the current or back emf in the windings of the motor. When the current or the back emf varies from a normal level, the disk is vibrating and a signal indicating a vibration condition is sent to the spindle motor driver. The maximum speed that the disk rotated is slowed until a vibrating condition is no longer detected and the rotational speed associated with a particular disk is based dynamically on the amount of vibration detected. Disks may also be identified that cannot spin a minimum rate of speed. 
   Advantageously, the method and apparatus detects a vibrating condition in a CD-ROM or DVD drive that holds a plastic disk. When vibration is detected a signal is sent to the controller that slows the speed of the spindle. This also prevents loss of data that may be on the disk. This not only prevents destruction of the disk but also prevents destruction of the disk drive or one of its subsystems. The invention also provides for safer operation of a CD-ROM or DVD disk drive. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded isometric view of a disk drive. 
       FIG. 2  is a schematic diagram of a three-phase spindle motor used in a disk drive. 
       FIG. 3  is a schematic view of the invention showing a voltage driven motor  300 . 
       FIG. 4  is a schematic view of the invention showing a current driven motor. 
       FIG. 5  is a flow chart showing various steps associated with a first embodiment of the invention. 
       FIG. 6  is a flow chart showing various steps associated with a second embodiment of the invention. 
       FIG. 7  is a schematic view of a computer system. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
   Referring to  FIG. 1 , the principal electrical and mechanical components of a disk drive  100  constructed in accordance with a preferred embodiment of the present invention are illustrated. The disk drive includes a base  122  and a cover. Attached to the base  122  is a spindle  126 . A disk  134  is placed on the spindle  126 . A spindle motor  200  (shown schematically in  FIG. 2 ) rotates the spindle  126  and the disk  134 . A spindle motor driver  240  controls either the current, the voltage, or both the current and the voltage within the coils of the spindle motor  200  to produce a torque and controllably rotate the spindle  126  and disk  134  attached to the spindle. 
   A laser diode  140  emits a low-energy infrared beam toward a reflecting mirror  142 . A servo motor, on command from a microprocessor (not shown), positions the beam to the correct track on the CD-ROM or DVD by moving the reflecting mirror  142 . When the beam hits the disk  134 , the light is refracted. The refracted light is gathered and focused through a lens  150  beneath the disk and bounced off the reflecting mirror  142  and sent toward a beam splitter  160 . The beam splitter  160  directs the returning laser light toward a second focusing lens  162 . The focusing lens  162  directs the light to a photo detector  170  where the light is converted to electrical impulses. The electrical impulses are decoded and subjected to error correction by a channel chip  180  so that information stored on the disk  134  is converted to the data originally stored on the disk  134 . 
     FIG. 2  is a schematic diagram of a three-phase spindle motor  200  used in a disk drive  100 . The spindle motor  200  includes a first phase  210 , a second phase  220 , and a third phase  230 . Each of the phases are represented by a coil  212 ,  222 ,  232 . Of course, it should be understood that each of the phases is actually made up of several coils. The motor  200  includes a motor driver  240 . The motor  200  can be driven by voltage or by current or by a combination of both current and voltage. The motor driver  240  keeps the current in a current driven motor constant or keeps the voltage in a voltage driven motor constant. Each phase is offset from the other phases so as to keep the rotating portion of the electrical motor spinning smoothly. 
     FIG. 3  is a schematic view of the invention showing a current driven motor  300 . A current driven motor has a driver current source  310 , and includes a voltage meter  320  placed across one of the motor windings, such as motor winding  212 . Thus, the voltage of the motor winding  212  is monitored during operation of the spindle motor  300 . The phase of the signal out from the volt meter may be fed into a phase detector  330 . The phase of the driver current source may also be fed into the phase detector  330 . At the phase detector  330 , the phase of the motor winding is compared to the phase of the driver current source. The detector  330  detects a change in a condition of the motor in response to a force on the spindle. The phase of the current from the voltage source is compared to the phase of the current from the current detector to determine a change in force. Generally, the phase of the driver current source and the phase of one of the motor windings will be out of phase, since the motor winding  212  is a coil. However, if the difference between the two phases is beyond a normal range, then generally vibration is detected. In other words, the phase of the voltage across a winding is compared to the phase of the driver current source  310 , plus some additive amount of different. The driver current source phase, plus the selected amount of phase difference can be also thought of as a reference phase for detecting vibration or a disk that is vibrating within the disk drive  100 . The voltage across one of the motor windings  212  may also be placed into an amplitude detector  340 . A reference amplitude  342  is also fed into the amplitude detector  340 . When the amplitude of the voltage from the voltmeter  320  is outside a specific or desired range from the reference amplitude  342 , a signal is output from the amplitude detector  340  which indicates a vibration of the disk drive or a vibration of the disk  134  on the spindle of the disk drive  100 . It should be noted that either both the phase detector  330  and the amplitude detector  340  may be used together, or may be used separately. In other words, one embodiment of the invention shown in  FIG. 3  may be only the phase detector, and yet another embodiment of the invention shown in  FIG. 3  may include only the amplitude detector and not the phase detector. The reference amplitude  342  may be from any number of sources, including the voltage associated with other windings,  222 ,  232  of the electrical motor. Using the volt meter  320 , measured across at least one of the windings  212 , is a measure of the back electromotive force, or back EMF of the motor  300  which includes a driver current source  310 . 
     FIG. 4  is a schematic view of the inventions showing a voltage driven motor  400 . The voltage driven motor includes a driver voltage source  410  and a current detector or ammeter  420 , which measures the amount of current within one of the motor windings  212 . The current within the winding  212  is detected by the current detector  420 , and output to a phase detector  430 . The phase of the driver voltage source is also input to the phase detector  430 . When the phases of the output of the current detector or ammeter  420  varies from the phase of the driver voltage source  410  within a selected range, the phase detector  430  outputs a signal indicating that vibration has been detected. Furthermore, the output from the ammeter  420  can be fed to an amplitude detector  440 . A reference amplitude  442  is also fed into the amplitude detector. When the differences between the amplitude of the current within one of the motor windings  212  is different from the reference amplitude  442  by a selected amount, the amplitude detector outputs a signal indicating that vibration has been detected. In essence, the amplitude detector detects when a drag change occurs within the electrical motor  400 . It should be noted that the reference amplitude  442  could be a selected reference amplitude, or the average amplitude of all the phases or all the motor windings  212 ,  222 ,  232 . It should be noted that in  FIG. 4 , both a phase detector  430  and an amplitude detector  440  are shown. It should be noted that both are not actually needed, and one embodiment might include not having a phase detector  430 , and only an amplitude detector comparing the amplitude of the measured current from ammeter  420  with a reference amplitude  442 . Another embodiment would be to have the phase detector  430  and not have the amplitude detector  440 . Thus there are actually three embodiments shown, one in which both phase detector  430  and the amplitude detector  440  are used, and another where only the phase detector  430  is used, and another where only the amplitude detector  440  is used. 
   Once vibration has been detected, a signal from either a phase detector or an amplitude detector which indicates a vibration is sent to a motor controller. The motor controller will slow the motor down, or at least change the speed of the motor until vibration is no longer detected.  FIG. 5  is a flow chart showing the various steps associated with embodiments of the invention shown in  FIGS. 3 and 4 .  FIG. 5  begins by an initial spin-up of the disk drive  100  at a low speed. The inner identification track on the disk  134  is read, as depicted by reference numeral  510 . A parameter of the motor is then measured, as depicted by reference numeral  512 , and the measured parameter is compared to a measured reference value of the parameter, as depicted by reference numeral  514 . Then it is determined whether the measured parameter is within a selected range of the reference parameter, as depicted by decision box  516 . If the measured parameter is not within the selected range of the reference parameter, this generally indicates that a vibration condition has been detected, so therefore the motor is slowed, as depicted by reference numeral  518 . And then the parameter of the motor is then measured, as depicted by reference numeral  512 . If the measured parameter is within the selected range of the reference parameter, then it is determined whether of not the speed of the spindle motor is less than the maximum speed of the spindle motor. If the speed of the spindle motor is less than the maximum speed of the spindle motor, the motor controller increases the motor speed, as depicted by reference numeral  520 , and then the parameter of the motor is measured, as depicted by reference numeral  512 , and steps  512 ,  514 , and  516  are repeated. If the speed of the spindle motor is not less than the maximum speed of the spindle motor, then the process is over, and the process is ended, as depicted by reference numeral  522 . 
     FIG. 6  is a flowchart showing the various steps associated with another embodiment of the invention. This is a specific process  600 , and begins by initial start of the disk at a low speed, and reading of the inner identification track, as depicted by reference numeral  612 . The monitor then the currents of the motor, and specifically the currents of the various phases of the motor, are monitored as depicted by reference numeral  614 . The speed of the spindle motor is increased, as depicted by reference numeral  616 , while continuing to measure the currents in the various phases of the motor, as depicted by reference numeral  618 . The variance among the currents in the various motor phases are then compared, as depicted by reference numeral  620 . The next step is a decision box, which determines whether the current of the phases within the motor are all within range of one another, and if the motor is less than the maximum speed, as shown by reference numeral  622 . If the current of the phases of the motor are within the range and the motor is operating at less than the maximum speed, then the process returns to step  616 , where the speed of the spindle motor is increased, and steps through the process steps leading up to decision box  622 . If the current of the motor is not within the range, or is less than the maximum speed, then the disk is vibrating and the motor controller is commanded to reduce the speed of the spindle until the variance is within range, as depicted by reference  624 . Once the process is completed such that the vibration is gone, or such that the phases of the currents in the spindle motor are within a range of variance, the achieved disk speed is compared to an acceptable disk speed, as depicted by reference numeral  626 . If the disk cannot spin at a reasonable rate, then an alert is sent to the users, as well as to the computer system, of a possible problem with the disk, as depicted by reference numeral  628 . 
   Advantageously, the method and apparatus detects a vibrating condition in a CD-ROM or DVD drive that holds a plastic disk. When vibration is detected a signal is sent to the controller which slows the speed of the spindle. This also prevents loss of data that may be on the disk. This not only prevents destruction of the disk but also prevents destruction of the disk drive or one of its subsystems. The invention also provides for safer operation of a CD-ROM or DVD disk drive. 
     FIG. 7  is a schematic view of a computer system. Advantageously, the invention is well-suited for use in a computer system  2000 . The computer system  2000  may also be called an electronic system or an information handling system and includes a central processing unit, a memory and a system bus. The information handling system includes a central processing unit  2004 , a random access memory  2032 , and a system bus  2030  for communicatively coupling the central processing unit  2004  and the random access memory  2032 . The information handling system  2000  includes a magneto-optical device which includes the cooling mechanism or heat removal mechanism described above. The information handling system  2000  may also include an input/output bus  2010  and several devices peripheral devices, such as  2012 ,  2014 ,  2016 ,  2018 ,  2020 , and  2022  may be attached to the input output bus  2010 . Peripheral devices may include hard disk drives, magneto-optical drives, floppy disk drives, monitors, keyboards and other such peripherals. 
   It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.