Abstract:
Apparatus for clearing of an obstacle if the smooth transfer of a head is interfered with in an apparatus for reproducing data recorded in a recording medium having address information. If an obstacle is detected, the head, which is frictionally engaged in a movable manner with a drive shaft secured to an oscillation actuator that expands and contracts in response to the application of a drive signal, is transferred by driving the oscillation actuator such that it expands and contracts at different speeds.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a driver for moving a movable member by driving a drive shaft with which the movable member is frictionally engaged by using a piezo element or the like controlled to expand and contract at different speeds, and a control method for the driver. More particularly, the present invention relates to a reproducing apparatus for reproducing information by drivably moving a head by driving a drive shaft with which the head is frictionally engaged by using a piezo element or the like controlled to expand and contract at different speeds, a head transfer apparatus, and a head transfer method. 
   2. Description of the Related Art 
   Hitherto, there has been known a method using the combination of a rotating motor, a rack and a pinion gear to move a read-write head in a radial direction. The read-write head is adapted to record data in a recording medium, such as a disk, and reproduce the data from the recording medium. The head fixed to the rack moves as the pinion gear fixed to the rotating shaft of a motor rotates as the motor revolves, and the rack meshed with the pinion gear moves as the pinion gear rotates. 
   The head driving method based on the combination of the rack, the pinion gear and the rotating motor has been disadvantageous in that it is difficult to reduce the size of the motor for obtaining an adequate motor torque for driving the pinion gear. 
   To solve the problem, a head transfer mechanism using an impact drive actuator has been proposed. The head transfer mechanism has an oscillating element, such as a piezo element, a drive shaft secured to one end of the piezo element, and a head frictionally engaged with the drive shaft or a frictional engagement member to which a head is secured. 
   This type of driver using the aforesaid conventional impact drive actuator will be described in conjunction with  FIG. 1  showing the construction of the driver. 
   Reference numeral  1  denotes a piezo element serving as an oscillating element formed of a piezoelectric ceramic constituent, which is the impact drive actuator. A rod  2  is firmly secured by an adhesive agent or the like to one end, namely, the right end, the piezo element  1  oscillating in the right direction. A counterbalance  3  is firmly secured by an adhesive agent or the like to the other end of the piezo element  1 . The counterbalance  3  is retained by a support member  4  supported by a chassis, which is not shown. The other end of the rod  2  is held by the support member  4  such that no play occurs in the shaft diameter direction, while an allowance for oscillation is provided in the axial direction. 
   Reference numeral  5  denotes a driven member, e.g., an optical pickup. The optical pickup  5  receives the lower surface of the rod  2  by a frictional connection surface  6  on the upper side in the drawing. The upper surface of the rod  2  is in frictional contact with a leaf spring  7 , as shown in  FIG. 3 . This means that the optical pickup  5  frictionally holds the rod  2  between the frictional connection surface  6  and the leaf spring  7 . 
   The optical pickup  5  has a guide shaft  8  parallel to the rod  2  and supported mainly by the chassis  9 . Guide bearings  10 ,  10  of the optical pickup  5  are held by the guide shaft  8 . Thus, the optical pickup  5  is movable in the radial direction of a disk, not shown, that is held by chucking of a spindle motor  11 . 
   The impact drive actuator is driven by applying a square-wave voltage ( FIG. 2 ) to the piezo element  1  to cause oscillation or the expansion and contraction to take place, thereby moving the optical pickup  5 . More specifically, when the piezo element  1  slowly expands, as indicated by a waveform S 1 , the optical pickup  5  in frictional contact with the rod  2  moves. When the piezo element  1  instantaneously contracts, as indicated by a waveform S 0 , the optical pickup  5  slides and stops. This expansion and contraction is repeated to drive the optical pickup  5 . 
   In the impact drive actuator, however, the force of friction between the rod  2  and the optical pickup  5  may change if, for example, wastes or dust stick to the rod  2  or the inertial force of the optical pickup  5  causes a frictional contact surface  6  to excessively press the rod  2 . To prevent such a change, increasing the drive voltage applied to the piezo element  1  is being considered. However, in the case of a battery-driven apparatus, the voltage cannot be increased due to a restricted battery voltage. Therefore, applying a higher voltage may not be ideal corrective measures to prevent the changes in the frictional force described above. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a head transfer apparatus for controllably transferring a head for reading data from a recording medium, in which address information indicating a recording position has been recorded, to the vicinity of an input target address, including: 
   a drive shaft with which the head is frictionally engaged in a movable manner; 
   an oscillation actuator having one axial end thereof that expands and contracts under the application of a voltage and is secured to a fixing portion, and the other end thereof secured to the drive shaft; 
   a driver for transferring the head in a predetermined direction by supplying a signal for setting the expansion and contraction of the oscillation actuator at different speeds to the oscillation actuator; and 
   a controller for carrying out control such that the oscillation actuator is driven by the driver to cause the head to be transferred alternately in one direction and the other direction, respectively, for a predetermined time if it is determined that the transfer of the head is being interfered with. 
   It is another object of the present invention to provide a head transfer method for controlling the transfer of a head for reading data from a recording medium in which address information indicating a recording position has been recorded to the vicinity of an input target address, the head being frictionally engaged in a movable manner with a drive shaft secured to one end of an oscillation actuator with the other end thereof fixed and expanding and contracting under the application of a drive signal, a signal for setting the expansion and contraction of the oscillation actuator at different speeds being supplied to the oscillation actuator, the method including: 
   a step for the oscillation actuator to drive the drive shaft for a predetermined period of time; 
   a step for detecting an obstacle to the transfer of the head; and 
   a step for applying, for a predetermined number of times, a drive signal for causing the oscillation actuator to transfer the head in one direction and the other direction, respectively, for a predetermined time if an obstacle to the transfer of the head is detected. 
   It is yet another object of the present invention to provide a reproducing apparatus for reading data recorded at a predetermined address from a recording medium in which address information indicating recording positions has been recorded, including: 
   a reproducing device for reading the address information from the recording medium; 
   a drive shaft with which the reproducing device is frictionally engaged in a movable manner; 
   an oscillation actuator having one axial end thereof that expands and contracts under the application of a voltage and is secured to a fixing portion of the reproducing apparatus, and the other end thereof secured to the drive shaft; 
   a driver for transferring the reproducing device in a predetermined direction by supplying a signal for setting the expansion and contraction of the oscillation actuator at different speeds to the oscillation actuator; 
   an obstacle detector for detecting an obstacle to the transfer of the reproducing device; and 
   a controller for controlling the driver to transfer the reproducing device by the driver alternately in one direction and the other direction, respectively, for a predetermined time if the obstacle detector detects an obstacle to the transfer of the reproducing device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view of an optical pickup using an impact drive actuator; 
       FIG. 2  is a diagram showing a square-wave pulse of the impact drive actuator; 
       FIG. 3  is a side view of the optical pickup shown in  FIG. 1 ; 
       FIG. 4  is a block circuit diagram; 
       FIG. 5  is a diagram showing a square-wave pulse illustrating repeated microjogging; 
       FIG. 6  is a flowchart of a control procedure; and 
       FIG. 7  is a flowchart of a microjogging procedure. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of a driver and a driving method in accordance with the present invention will be described with reference to the accompanying drawings, taking a driver of an optical pickup for reading data from a magneto-optical disc, as an example. The driver uses an impact drive actuator. 
     FIG. 1  is a plan view of an optical pickup using an impact drive actuator, and  FIG. 3  is a side view thereof. 
   Reference numeral  1  denotes a piezo element serving as an oscillating element formed of a piezoelectric ceramic constituent, which is the impact drive actuator. A rod  2  is firmly secured by an adhesive agent or the like to one end, namely, the right end in  FIG. 1 , the piezo element  1  oscillating in the right direction. A counterbalance  3  is firmly secured by an adhesive agent or the like to the other end of the piezo element  1 . The counterbalance  3  is retained by a support member  4  supported by a chassis, which is not shown. The other end of the rod  2  is held by the support member  4  such that no play occurs in the shaft diameter direction, while an allowance for oscillation is provided in the axial direction. 
   Reference numeral  5  denotes a driven member, e.g., an optical pickup. The optical pickup  5  receives the lower surface of the rod  2  by a frictional connection surface  6  on the upper side in the drawing. The upper surface of the rod  2  is in frictional contact with a leaf spring  7 , as shown in  FIG. 3 . This means that the optical pickup  5  frictionally holds the rod  2  between the frictional connecting surface  6  and the leaf spring  7 . 
   The optical pickup  5  has a guide shaft  8  parallel to the rod  2  and supported mainly by the chassis  9 . Guide bearings  10 ,  10  of the optical pickup  5  are held by the guide shaft  8 . Thus, the optical pickup  5  is movable in the radial direction of a disk, not shown, that is held by chucking of a spindle motor  11 . 
   As described above, the impact drive actuator is driven by applying a square-wave voltage generated by a driver  12 , as shown in  FIG. 2 , to the piezo element  1  to cause oscillation or the expansion and contraction to take place, thereby moving the optical pickup  5 . More specifically, when the piezo element  1  slowly expands in the direction of an arrow “a” as indicated by a waveform S 1 , the optical pickup  5  in frictional contact with the rod  2  moves in the direction of the arrow “a”. When the piezo element  1  instantaneously contracts in the direction of an arrow “b”, as indicated by a waveform S 0 , the optical pickup  5  slides and stops at a position reached after moving for the period of time S 1  due to its inertia. This expansion and contraction is repeated to drive the optical pickup  5  in the direction indicated by the arrow “a”. It is needless to say that the optical pickup  5  can be driven to move in the direction of the arrow “b” by repeating the contraction and expansion as follows. The piezo element  1  is first contracted in the direction of the arrow “b” at a speed at which the optical pickup  5  in frictional contact with the rod  2  can be moved by the frictional force in the direction of the arrow “b”, then the piezo element  1  is suddenly expanded in the direction of the arrow “a.” 
   Referring now to  FIG. 4 , which is a block circuit diagram, the driver will be further described. 
   A target jump destination address At is supplied to a transfer amount calculator  301  and a movement amount determiner  302  of an emergency detector  304 . An address demodulator  308  receives an address modulation signal recorded on a magneto-optical disk  314  read by an optical head  313  to demodulate an address signal Ar. This makes it possible to know the current reading position of the optical head  313  on the magneto-optical disk  314 . 
   The address signal Ar output from the address demodulator  308  is supplied to the transfer amount calculator  301  in which the distance from the current point to a specified jump destination is calculated. A number of pulses Np for an actuator  311  required to move the optical head  313  to the target jump destination is output from the transfer amount calculator  301 . 
   In a normal transfer operation of the optical head  313 , a normal transfer signal is supplied from a normal transfer controller  307  to a driver  310  through the intermediary of a selector  309  on the basis of a received number of pulses Np. A drive signal for the actuator  311  is output from the driver  310  to transfer the optical head  313  on a rod  312  to a target jump destination address. In this case, the reach at the target address can be checked by the address signal Ar output from the address demodulator  308 . 
   The following will explain a case where an obstacle prevents smooth transfer of the optical head  313 . 
   It is assumed that address information indicating recording position on a disk for each predetermined volume of data has been allotted on the recording tracks provided in an optical disk  314 , and that the position on the recording tracks being scanned by the optical head  313  can be read as address information Ar. 
   The same procedure as that of the normal transfer operation applies, up to the point where a drive pulse for transferring the optical head  313  to the vicinity of a target address is supplied to the actuator  311 . The pulse quantity comparator  303  of the emergency detector  304  compares the number of pulses Np required to transfer the optical head  313  to the target address calculated by the transfer amount calculator  301  with a number of pulses Npp actually output from the normal transfer controller  307 . Based on the result of the comparison, it is determined whether the number of pulses required for transferring the optical head  313  to the target address At has been sent to the actuator  311 . 
   Based on the result of the comparison by the pulse quantity comparator  303 , it is determined whether the difference between the address Ar of the current position of the optical head  313  determined by the movement amount determiner  302  and the target jump destination address At should be transmitted to a microjogging controller  306 . More specifically, if it is determined that a predetermined number of drive pulses has been sent to the actuator  311 , then a switch  305  is closed so as to cause the microjogging controller  306  to determine whether the difference between the address Ar read from the magneto-optical disk  314  and the target jump destination address At is not more than a predetermined range. 
   The microjogging controller  306  determines whether the received address difference lies within a predetermined range. If the difference is larger than a predetermined value, meaning that it has been determined that the optical head  313  is at a position Aerr considerably deviating from the target value At due to some obstacle, then the microjogging controller  306  supplies a predetermined number of drive pulses to the actuator  311  to carry out microjogging to clear the obstacle. 
   If, for example, wastes or dust is on the rod  312 , or clinging or the like takes place between the rod  312  and the optical head  313 , then a square-wave pulse signal p is repeatedly applied for a short time to the piezo element in the forward and reverse directions to perform microjogging in a period P, as shown in  FIG. 5 . This will clear the wastes or dust, or the clinging or the like between the rod  312  and the optical head  313 , allowing the optical head  313  to smoothly move to the target jump destination. In other words, the signal shown in  FIG. 5  is applied to the piezo element  1  shown in  FIG. 1  so as to repeatedly drive the optical head  5  in the direction indicated by arrow A and the direction indicated by arrow B, respectively, for a short time. 
   The selector  309  is controlled by the microjogging controller  306  such that it switches to connect the microjogging controller  306  with the driver  310  only when the microjogging controller  306  is ready to output a pulse. Alternatively, the control may be carried out by a CPU or the like in place of the selector  309 . 
     FIG. 6  is a flowchart illustrating a control procedure. 
   In S 501 , a target jump destination address At is received. In S 502 , an address Apo on a magneto-optical disk at which an optical head can current read data is acquired. Then, in S 503 , a distance L is calculated on the basis of the addresses At and Apo obtained in S 501  and S 502 , respectively. 
   In S 504 , based on the distance L calculated in S 503 , the number of times the actuator is driven, i.e., the number of pulses Np is calculated. Next, in S 505 , based on the number of pulses Np calculated in S 504 , the actuator is driven the number of pulses Np times to transfer the optical head to the target address. After the actuator is driven for the number of pulses Np, an address Ap 1  read from the magneto-optical disk is acquired in S 506  in order to check the current position of the optical head. 
   Subsequently, in S 507 , it is determined whether the difference between the target address At and the address Ap 1  actually read from a disk is a predetermined value g or less. If it is determined that the difference between the target address and the actually read address is the predetermined value or less, then it means that the optical head has normally reached the vicinity of a target jump destination. Hence, a fine adjustment is made to transfer the optical head to the target position in S 509 . This terminates the procedure. 
   If, however, it is determined in S 507  that the difference between the target address At and the address Ap 1  actually read from the disk exceeds the predetermined value g, then a microjogging operation p explained in conjunction with  FIG. 5  is performed in S 508 , then the processing is repeated from S 502 . Since the immediately preceding address Ap 1  has been acquired in S 506 , this address may be used to calculate the moving distance L to resume the processing from S 504 , rather than repeating the processing from S 502 . 
     FIG. 7  is a flowchart of the microjogging operation carried out in S 508 . 
   To repeatedly apply a square-wave pulse signal in forward and reverse directions in a short time to the piezo element  1  to apply a drive wave p thereto, as previously described, the number of repetitions n is first set in S 601 . Using the timer that has been set in S 602 , the optical pickup is driven in the moving direction “a” shown in  FIG. 1  in S 603 . In the microjogging operation of the optical pickup, it is determined in S 604  whether the count on the timer has been finished, and if it is determined that the timer count has been finished, then the optical pickup is driven in the moving direction b shown in  FIG. 1  in S 606  on the basis of the setting on the timer made in S 605 . In the operation for driving the optical pickup, it is determined in S 607  whether the timer count has been finished, and if it is determined that the timer count has been finished, then it is further determined in S 608  whether the drive in the two directions has been repeated n times. If it is determined that the drive has been repeated n times, then the procedure is terminated. 
   The present invention is not limited to the embodiment described above in conjunction with the accompanying drawings. It is to be understood that the invention is capable of changes or modifications within the scope of the inventive concept as expressed herein. 
   For instance, in the present invention, the target positions are the vicinities of the positions where recorded data is read. Alternatively, the target positions may be set to the vicinities of the current position of a head in order to detect the presence of an obstacle, rather than the vicinities of the positions where recorded data is read. In this case, quick transfer is carried out, and it is determined whether the head has been transferred to the vicinity of a target address. This is advantageous when the transfer of a head requires a longer time, as in the case of transferring the head from the innermost periphery to the outermost periphery of a magneto-optical disk. More specifically, it is quicker than detecting an obstacle after completing such a prolonged transfer to first detect the presence of any obstacle by carrying out a shorter transfer operation to check for failure. Thus, the time required for the head to be transferred to a final target point where recorded data is read can be shortened. 
   In the embodiment discussed above, the descriptions have been given of the case where an obstacle interferes with smooth transfer of the optical pickup or the optical head. It is alternatively possible to microjog the optical pickup as necessary when the power is turned ON thereby to perform smooth transfer thereof. 
   In the foregoing embodiment, the descriptions have been given of the driving apparatus and method for the optical pickup adapted to read data from a magneto-optical disk by using the impact drive actuator. The present invention, however, can be extensively applied also to other types of optical heads and magnetic heads that use impact drive actuators. Obviously, the recording media from which data is read are not limited to magneto-optical disks, but may be magnetic disks or optical disks. 
   Thus, according to the inventive driving apparatus and method, if smooth drive of a driven member with respect to a rod is prevented by undue friction, the rod is repeatedly microjogged for a short time in forward and reverse directions by an oscillating element under the control of a microjogging controller so as to remove wastes or dust from the rod or to clear the clinging or the like between the rod and the optical pickup, permitting smooth start of the optical pickup. The features of the present invention make it possible to achieve highly reliable head transfer apparatus and method, and a highly reliable reproducing apparatus.