Abstract:
A method for controlling the rotation speed of an optical storage device. In the first mode, a first signal is produced, and in the second mode, a second signal is produced. In one mode, a first pulse of a first voltage and a second pulse of a second voltage are sent to the motor, which causes the motor to produce a first armature current and a second armature current. In another mode, a DC signal of a third voltage is produced, which causes the motor to produce a third armature current. The armature currents are detected, and test voltages are outputted. The first and second voltages, and the first and second test voltages are used to find a motor coefficient. The third voltage, the motor coefficient, and the third test voltage are used to calculate a motor rotation speed. The calculated speed is used to control the real motor speed.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method and apparatus to control an optical storage device, and more particularly to a method and apparatus to control the spindle motor rotation speed of the optical storage device by detecting the armature currents of the spindle motor.  
           [0003]    2. Description of the Prior Art  
           [0004]    In the realm of optical storage devices there exists two major types of spindle motors. The first type is a three-phase motor, typically installed with a Hall sensor. Such motor can provide FG signal to indicate the rotation speed of the motor. Therefore the optical storage device can use the FG signal to know the current angular velocity of the motor and perform constant angular velocity (CAV) control to the motor. In addition, three-phase motors can rotate at very high speeds, so they are very popular in high-speed CD-ROM, CD-RW, and DVD-ROM applications. However, a major weakness of three-phase motors is that the motor itself, and its corresponding driving circuits, are rather expensive. Therefore, in most low-speed optical storage devices, such as DVD players and CD players, a DC motor is used as a spindle motor, so as to reduce the cost.  
           [0005]    For optical storage devices using DC motors, there&#39;s no FG signal provided. The optical storage devices can only perform low speed constant linear velocity (CLV) control. Furthermore, because there is no easy way to sense the current angular velocity of the DC motor, it is difficult to control the deceleration rate and time before ejecting the optical medium from the optical storage device. Traditional control methods include using the optical pick-up of the optical storage device to read the timing information recorded on the optical medium, and calculating the DC motor rotation speed before performing the braking operation on the DC motor. Then, according to the calculated angular velocity of the DC motor, the system implements a constant deceleration for the corresponding period of time, causing the motor to stop spinning. Finally, the deceleration is stopped, and the ejection of the optical medium is performed. Under normal operation, this type of control method is capable of braking the medium-loaded optical storage device in a stable fashion. However, in some cases, the method will start ejection of the optical medium prior to complete deceleration of the DC motor, and cause damages to the surface of the medium. Such cases include:  
           [0006]    1.)Erroneous calculation of the angular velocity of the DC motor. If the optical medium contains pre-existing and heavy damaged surface, the timing information recorded on the medium can not be properly read. The deceleration begins while the angular velocity of the DC motor is still unstable.  
           [0007]    2.)Inconsistent loading of the spindle motor. For example, an 8 cm or a 12 cm optical disc, or optical discs of different thicknesses.  
           [0008]    3.)Inherent inconsistent characteristics of the spindle motors. Same control currents applied to different spindle motors may lead to different deceleration operations.  
         SUMMARY OF INVENTION  
         [0009]    It is therefore an objective of the present invention to provide an apparatus and method that senses the armature current of the spindle motor to estimate the current angular velocity of the motor. The present invention calculates the angular velocity of the motor from the armature current, and then accurately controls the DC motor to a halt through a simple motor control circuit.  
           [0010]    Briefly, the present invention provides an optical storage device control method that is used to control a real angular velocity of a motor, which spins an optical medium and uses optical pick-up to read information on the medium. In a first control mode, producing a first control signal, and in a second control mode, producing a second control signal. In the first control mode, according to the first control signal, a first pulse of a first control voltage, and a second pulse of a second control voltage are produced to cause the motor, on receiving the pulses, to produce, respectively, a first armature current and a second armature current. In the second control mode, according to the second control signal, a DC signal of a third control voltage is produced to cause the motor, upon receiving the DC signal, to produce a third armature current. The first, second, and third armature currents are measured, and first, second and third corresponding test voltages are outputted. The first and second control voltages, and the first and second test voltages are used to find a motor coefficient. The third control voltage, the motor coefficient, and the third test voltage are then used to find a relative angular velocity of the motor. The real angular velocity of the motor is controlled according to the relative angular velocity found above.  
           [0011]    The present invention further provides an optical storage device control apparatus, which is used to control a real angular velocity of a motor, which spins an optical medium, and uses optical pick-up to read information stored on the medium. The apparatus includes an angular velocity control circuit, which produces a first control signal while in a first control mode, and produces a second control signal while in a second control mode. The apparatus also includes a motor driving circuit, which while in the first control mode, according to the first control signal, produces a first pulse of a first control voltage, and a second pulse of a second control voltage, to cause the motor, on receiving the pulses, to produce, respectively, a first armature current and a second armature current, and in the second control mode, according to the second control signal, produces a DC signal of a third control voltage, to cause the motor, upon receiving the DC signal, to produce a third armature current. Finally, the apparatus has a sensor circuit, which measures the first, second, and third armature currents, and outputs first, second and third corresponding test voltages. The angular velocity control circuit uses the first and second control voltages, and the first and second test voltages to find a motor coefficient. The angular velocity control circuit also uses the third control voltage, the motor coefficient, and the third test voltage to find a relative angular velocity of the motor. In the second control mode, the angular velocity control circuit, according to the relative angular velocity, changes the third control signal to modify the third control voltage, causing the real angular velocity of the motor to change.  
           [0012]    It is an advantage of the present invention that it measures the armature current of a spindle motor to find an angular velocity of the spindle motor. By calculating a counter-electromotive force, and thus the angular velocity of the motor, according to the size of the armature current, and then using a simple motor control circuit, the present invention allows a deceleration control process to proceed in a closed-loop circuit, allowing for precise control of the DC motor to a complete stop.  
           [0013]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0014]    [0014]FIG. 1 shows a simplified model of a DC motor.  
         [0015]    [0015]FIG. 2 shows a circuit block diagram of an optical storage device angular velocity control apparatus according to the present invention.  
         [0016]    [0016]FIG. 3 shows an armature current sensor circuit according to the present invention.  
         [0017]    [0017]FIG. 4 shows a flow chart of an optical storage device angular velocity control method according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]    [0018]FIG. 1 shows a simplified model of a DC motor. From the simplified model, the following equalities can be obtained:  
                 (   t   )     f     =         1     L   a              e   a          (   t   )         -         R   a       L   a              i   a          (   t   )         -       1     L   a              e   b          (   t   )                   (   1   )                 t   )     =       K   1            i   a          (   t   )                 (   2   )                         )     =       K   b            w   m          (   t   )                 (   3   )                               
 
         [0019]    where i a (t) is the armature current, R a  is the armature resistance, e a (t) is the armature voltage, L a  is the armature inductance, e b (t) is the counter-electromotive force (CEMF), K i  is the torque coefficient, T m (t) is the motor torque, K b  is the CEMF constant, w m (t) is the armature angular velocity, and T L (t) is the load torque.  
         [0020]    From equation (3), it can be seen that the armature angular velocity w m  (t) is directly proportional to the CEMF e b (t). According to equation (1), if the armature voltage e a (t) is known, the relative value of the current motor armature angular velocity w m (t) can be obtained via the armature current i a (t)  
         [0021]    [0021]FIG. 3 shows an armature current sensor circuit according to one preferred embodiment of the present invention. The sensor circuit comprises five resistors (R 1 , R 2 , R 3 , R 4 , R 5 ), and an operational amplifier (OPAMP)  32 . The circuit is used to measure the armature current i a  produced by the spindle motor  31 . Resistor R 1  and the spindle motor  31  are connected in series. Resistors R 2  and R 3  are connected at one end to either end of resistor R 1 , and at another end to the non-inverting input and inverting input of the OPAMP  32 , respectively. Resistor R 4  is connected from the non-inverting input of the OPAMP  32  to a reference voltage V ref . Resistor R 5  acts as a negative feedback and is connected from the output of the OPAMP  32  to the inverting input of the OPAMP  32 . The output of the OPAMP  32  is a test voltage V ia .  
         [0022]    In this embodiment, the resistance of resistors R 2  and R 3 is much larger than the resistance of resistor R 1 . Therefore, the current through resistor R 1  is approximately equal to the current through the spindle motor  31 , and is thus treated as i a (t). Due to the armature current sensor circuit described above, we can derive the following relation:  
       =         V   ref            R   2         R   2     +     R   1                  R   3     +     R   5         R   3         +       V   +            R   4         R   4     +     R   2                  R   3     +     R   5         R   3         -       (       V   +     -       i   a          R   1         )            R   5       R   3                                 
 
         [0023]    where V +  is the voltage at the node connecting R 1  and R 2 . With R 2 =R 3 =K 1  and R 4 =R 5 =K 2 , the relationship between V ia  and i a  can be simplified as:  
                 (   t   )     f     =         1     L   a              e   a          (   t   )         -         R   a       L   a              i   a          (   t   )         -       1     L   a              e   b          (   t   )                   (   1   )                 t   )     =       K   1            i   a          (   t   )                 (   2   )                         )     =       K   b            w   m          (   t   )                 (   3   )                               
 
         [0024]    Therefore, we can find the armature current from the magnitude of V ia .  
         [0025]    Here, the value of V ref  can be modified such that the output voltage V ia  falls within the input voltage range of the analog-to-digital converter in the angular velocity control circuit (explained below) that receives the output voltage V ia .  
         [0026]    Additionally, in the armature current sensor circuit described above, generally speaking, because the inductance of the spindle motor is not large, the armature current can settle very quickly, so in practical use, equation (1) can be simplified as:  
         = e         (   t )− R             i         (   t )   (4)  
         [0027]    Knowing that the motor armature angular velocity w m (t) is directly proportional to the CEMF e b , in practical use, we need not measure the actual armature voltage and current. Instead, we can use the control voltage (DMOLVL) of the motor driving circuit (explained below) in substitute for the armature voltage, and use the test voltage V ia  outputted by the armature current sensor circuit in substitute for the armature current, and enter a motor coefficient K ia  to get the following relationship:  
         ∝e         (t)∝(DMOLVL−K ia V ia (t))   (5)  
         [0028]    The motor coefficient K ia  used here is related to the internal resistance of the motor and special characteristics involved in producing the armature current. So, we must measure the motor coefficient either before velocity measurement begins, or directly after turning on the power supply. The method of finding the motor coefficient K ia  is to send two pulses of voltages V 1  and V 2  to the motor in a very short period of time. Because the duration of the pulses is very short, we can assume that in this time, the angular velocity of the motor does not change, and can therefore derive the following relationship:  
           ia   V         =−V   2   −K             V   ia2    (6)  
         [0029]    where V ia1  and V ia2  represent the voltages outputted by the armature current sensor circuit when producing pulses V 1  and V 2 , respectively.  
         [0030]    From equation (6), we can find the following equation for the motor coefficient:  
               V1   +   V2           V   ia        1     -       V   ia        2               (   7   )                               
 
         [0031]    Therefore, substituting the motor coefficient found from equation (7) and the known control voltage DMOLVL into equation (5), we can find the relative value of the motor armature angular velocity w m (t).  
         [0032]    [0032]FIG. 2 shows a circuit block diagram of an optical medium angular velocity control apparatus according to the preferred embodiment. This apparatus uses the principles and the armature current sensor circuit described above. This apparatus is used to control the actual angular velocity of the spindle motor  22 . The spindle motor  22  spins an optical medium  21 , and uses optical pick-up to read information stored in the medium  21 . The apparatus comprises an armature current sensor circuit  23 , an angular velocity control circuit  24 , and a motor driving circuit  25 .  
         [0033]    The angular velocity control circuit  24  produces a first control signal while in a first control mode, and a second control signal while in a second control mode. The first control mode can find the motor coefficient, according to the principle described above in equation (7), when the power is turned on or right before deceleration begins. The second control mode is used to perform deceleration.  
         [0034]    In the first control mode, the motor driving circuit  25  receives a first control signal and sends the first pulse of the first control voltage V 1  and the second pulse of the second control voltage V 2  to the spindle motor  22 , causing the spindle motor  22  to produce the first armature current and the second armature current upon receiving the first pulse and the second pulse, respectively. In the second control mode, the motor control circuit  25  receives a second control signal and produces a DC signal of the voltage DMOLVL, causing the spindle motor  22  to produce the third armature current upon reception of the DC signal.  
         [0035]    The armature current sensor circuit  23  measures the first, second, and third armature currents, mentioned above, and outputs the proportional first test voltage V ia1 , the second test voltage V ia2 , and the third test voltage V ia3 , respectively.  
         [0036]    In this manner, the angular velocity control circuit  24 , according to equation (7), uses the ratio of the sum of the control voltages V 1  and V 2  to the difference of the test voltages V ia1  and V ia2  to find the motor coefficient K ia  of the spindle motor. The control circuit  24  then, according to equation (5), takes the difference of the control voltage DMOLVL and the product of the motor coefficient K ia  and the third test voltage V 3  to find the relative armature angular velocity w m (t) of the spindle motor  22 . In the second control mode, the angular voltage control circuit  24  uses the relative value of the spindle motor armature angular velocity w m (t) to change the third control signal and adjust the control voltage DMOLVL, changing the actual speed of the spindle motor  22 .  
         [0037]    [0037]FIG. 4 shows a flow chart of a method of controlling an angular velocity of an optical medium, according to the preferred embodiment. First, in step  41 , in a first control mode, produce a first control signal, and in a second control mode, produce a second control signal.  
         [0038]    Then in step  42 , in the first control mode, according to the first control signal, send a first pulse of a first control voltage, and a second pulse of a second control voltage to the spindle motor, to cause the spindle motor to produce a first armature current and a second armature current when receiving the first pulse and the second pulse, respectively. In the second control mode, according to the second control signal, produce a DC signal of a third control voltage to cause the spindle motor, upon reception of the DC signal, to produce a third armature current.  
         [0039]    Then, in step  43 , use an armature current sensor circuit, such as the one shown in FIG. 3, to sense the first, second and third armature currents, and output respective the first, second and third test voltages relative to the armature currents.  
         [0040]    In step  44 , take the ratio of sum of the first and second control votages to the difference of the first and second test voltages to find the motor coefficient of the spindle motor.  
         [0041]    In step  45 , proceed to take the difference of the third control voltage and the product of the motor coefficient and the third test voltage to find the relative armature angular velocity of the spindle motor.  
         [0042]    In conclusion, the present invention provides a control apparatus and method that uses an armature current of a spindle motor to find the angular velocity of the spindle motor. According to the magnitude of the armature current, calculation of the CEMF, approximation of the motor angular velocity, and through use of a simple motor control circuit, the present invention can perform motor deceleration control in a closed loop, efficiently bringing the DC motor to a complete stop.  
         [0043]    Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.