Abstract:
A shake correcting device is capable of preventing a correcting optical device from hitting against a component part in the vicinity thereof to generate noise upon outputs from an H bridge driver for driving the correcting optical device being enabled. The device includes an angular velocity sensor that detects shaking of an image pickup apparatus, a position sensor that detects the current position of a shift lens movably disposed for optically correcting the shaking of the apparatus, an H bridge driver that drives the lens according to a drive target value, and an integrator that generates a target correction value based on the output from the angular velocity sensor. The drive target value is calculated based on the target correction value and output data from the position sensor.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims priority from Japanese Patent Application No. 2003-206574 filed Aug. 7, 2003, which is hereby incorporated by reference herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a shake correcting device incorporated in cameras or video cameras, a shake correcting method for apparatuses, such as cameras or video cameras, and a control program for implementing the shake correcting method. 
   2. Description of the Related Art 
   Conventionally, an optical shake correcting device has been proposed as a shake correcting device incorporated in image pickup apparatuses, such as cameras or video cameras. The optical shake correcting device performs shake correction by moving at least one of taking lenses in a direction perpendicular to the optical axis thereof and thereby changing the optical axis.  FIG. 9  shows an example of the arrangement of the optical shake correcting device (disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2000-66260). 
   In  FIG. 9 , reference numeral  101  designates an angular velocity sensor that is comprised of a vibration gyro, and detects a shake of an image pickup apparatus,  102  a bypass filter that eliminates a drift and other undesired components of the output from the angular velocity sensor  101 ,  103  an amplifier that amplifies an angular velocity signal indicative of the detected angular velocity, and  120  a microcomputer that controls the overall operation of the image pickup apparatus, including autofocus (AF) control, zoom control, automatic exposure (AE) control, mechanical part control, and power supply control. 
   Reference numeral  104  designates an A/D converter incorporated in the microcomputer  120 . The angular velocity signal is converted to a digital signal by the A/D converter  104  to provide angular velocity data. The angular velocity data is subjected to predetermined signal processing through a high-pass filter (HPF)  105  and a phase compensation filter  106 , and an integrator  108  at the next stage generates a shake correction signal. The output from the integrator  108  is used as a target drive value for a shift lens  119 , and converted into a PWM signal by a pulse width modulator (PWM)  117 , followed by being outputted as a PWM output from the microcomputer  120 . 
   Reference numeral  901  designates a low-pass filter (LPF) that converts the PWM output into a direct current corresponding to a correction amount, i.e. the target drive value. Reference numeral  114  designates a position sensor that detects the current position of the shift lens  119 , and  905  an amplifier that amplifies the output from the position sensor  114 . An adder  902  calculates the difference between the target drive value, i.e. the output from the LPF  901  and a value corresponding to the current position of the shift lens  119 , i.e. the amplified output from the position sensor  114 . The output from the adder  902  is supplied to a driver  904  that is implemented by an operational amplifier, and the driver  904  passes an electric current through a coil (not shown) that drives the shift lens  119 , to thereby move the shift lens  119  such that a desired optical axis correction angle can be obtained. Shake correction is achieved through these operations. 
   Further, in  FIG. 9 , symbol Vp designates a power supply for driving the shift lens  119 . The electric power of the power supply Vp is supplied to the driver  904 . On the other hand, symbol Vc designates a control power supply, and the electric power of the control power supply Vc is used for driving component parts other than the driver  904 . Reference numerals  804  and  805  designate switches operated for supplying power from the respective power supplies Vp and Vc to their associated component parts. For example, in a reproduction mode in which the video camera as the image pickup apparatus does not need an anti-shake function, the switches  804  and  805  are kept off by a power supply controller  803  that operates according to commands from the microcomputer  120 , whereby the drive current is interrupted for saving energy. 
   Now, there are problems in turning on and off the power of the shake correcting device. More specifically, if the drive current suddenly starts flowing upon turning-on of the power, a lens retainer frame that retains the shift lens  119  hits against an inner end of a lens barrel, thereby causing large impact noise. On the other hand, when the power is turned off, the retaining force is cancelled and the shift lens  119  drops due to its own weight so that the lens retainer frame hits against an opposite inner end of the lens barrel, thereby also generating impact noise. The impact noise thus generated degrades the quality of the image pickup apparatus. 
   To overcome the problem that occurs when the power is turned on, the proposed shake correcting device is configured such that a DC potential to be obtained by smoothing the PWM output from the microcomputer  120  becomes equal to the reference voltage of each of the sections or component parts of the device, and the switches  804  and  805  are controlled to be turned on in the same timing, to thereby suppress generation of impact noise due to hitting of the lens retainer frame against the inner end of the lens barrel. On the other hand, to overcome the problem that occurs when the power is turned off, just before the switches  804  and  805  are turned off, the shift lens  119  is caused to slowly move to a point close to the inner end of the lens barrel, and then the switches  804  and  805  are turned off to thereby suppress generation of impact noise to the minimum, as disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2000-66260. 
   In the conventional correcting device constructed as above, however, since the shift lens  119  is driven by a drive coil which is driven by the operational amplifier, the circuit has a large internal loss, leading to increased power consumption. 
   To overcome this inconvenience of increased power consumption, a control method has been proposed e.g. in Japanese Laid-Open Patent Publications (Kokai) No. H08-136962 and No. H11-308521, in which an H bridge circuit is used to drive the drive coil directly by the PWM output. 
     FIG. 10  is a block diagram showing the arrangement of a conventional optical shake correcting device based on the PWM drive control method using a H bridge circuit. In  FIG. 10 , component parts and elements corresponding to those shown in  FIG. 9  are designated by identical reference numerals, and detailed description thereof is omitted. 
   In  FIG. 10 , reference numeral  116  designates an A/D converter incorporated in the microcomputer  120 . The A/D converter  116  converts the amplified output from the position sensor  114  into a digital signal. Reference numeral  111  designates an adder that calculates the difference between a value corresponding to the current position of the shift lens  119  and the target drive value for the shift lens  119 . The output from the adder  111  provides an actual correction amount. Reference numeral  112  designates a low-pass filter (LPF) for reducing drive noise generated by an H bridge driver  113 . The output from the LFP  112  is subjected to pulse width modulation (PWM) by the PWM section  117 , followed by being delivered as the PWM output from the microcomputer  120 . The shift lens  119  is driven by this PWM output via the H bridge driver  113 . 
   The use of the PWM drive control method makes it possible to avoid internal loss, thereby improving energy conversion efficiency and hence reducing power consumption in contrast with the shake correcting device shown in  FIG. 9 . 
   Further, the use of the PWM drive control method makes it possible to turn off the drive current without using the power switches  804  and  805  appearing in  FIG. 9 , so that the peripheral arrangement associated with the power supply can be simplified. This point will be further described with reference to  FIGS. 11A and 11B .  FIG. 11A  shows the arrangement of the input and output terminals of the H bridge driver  113  and elements associated therewith, and  FIG. 11B  shows the logic of the input and output terminals. 
   When the PWM drive control method is employed, outputs  1  and  2  from the H bridge driver  113  exhibit output values shown in  FIG. 11B , according to the PWM waveform inputted to an input terminal  113   a , and depending on the outputs  1  and  2 , an electric current flows through a drive coil  113   c  to drive the shift lens  119 . 
   An enable terminal  113   b  appearing in  FIG. 11A , when its logic level is set to an L level, as shown in  FIG. 11B , in the reproduction mode which does not need shake correction, brings the outputs  1  and  2  into a disabled (Hi-Z: high impedance) state to thereby make the state of power consumption equivalent to a power-off state. Therefore, through the execution of PWM drive, it is possible to turn off the drive current without using the power switches  804  and  805  in  FIG. 9 . 
   The above-described conventional shake correcting device based on the PWM drive control method using the H bridge circuit provides the advantageous effects of reduced power consumption and simplified construction as described above. However, it still suffers from the problem of impact noise generated by hitting of the shift lens  119  against the inner end of the lens barrel. 
   More specifically, when the PWM drive control method is employed, the controller is disposed in the microcomputer  120  as shown in  FIG. 10 , of such that the microcomputer  120  controls whether to enable the outputs from the H bridge driver  113 . The power supply system is controlled such that power-system electric power (voltage of not lower than 5V) is supplied to the H bridge driver  113  alone, and control-system electric power (voltage e.g. of 3V) is supplied to the other component parts. When the shake correction is started immediately after the turning-on of the power of the image pickup apparatus or from a state e.g. in the reproduction mode, which does not need shake correction, the outputs from the H bridge driver  113  are switched from the disabled state to the enabled state, as described above, whereby the drive current is supplied to the drive coil  113   c.    
   However, the outputs from the H bridge driver  113  are enabled when the shift lens  119  is in the vicinity of the inner end of the lens barrel, so that while the output from the position sensor  114  assumes a value corresponding to a point close to the inner end of the lens barrel, the target drive value corresponds to a point close to the center position of the shift lens  119 . For this reason, the PWM output to be applied to the H bridge driver  113  as the correction amount, which corresponds to the difference between the two values is such as will cause a sudden motion of the shift lens  119 . Consequently, when the outputs from the H bridge driver  113  are enabled, a large electric current suddenly flows through the drive coil  113   c  of the shift lens  119 . As a result, the shift lens  119  is caused to hit against the inner end of the lens barrel, which generates large impact noise. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a shake correcting device and a shake correcting method which are capable of preventing a correcting optical device from hitting against a component part in the vicinity thereof to generate noise upon outputs from an H bridge driver for driving the correcting optical device being enabled, and a control program for implementing the method. 
   To attain the above object, in a first aspect of the present invention, there is provided a shake correcting device that corrects a shake of an object image picked up by an apparatus, comprising a shake detecting device that detects a shake of the apparatus, a correcting optical device that is movably disposed for optically correcting the shake of the apparatus, a position detecting device that detects a current position of the correcting optical device, a driving device that drives the correcting optical device according to a drive signal, an output control device that controls enabling and disabling of an output from the driving device, a target data-generating device that generates target correction data based on an output from the shake detecting device, and a drive signal-calculating device that calculates the drive signal based on the target correction data generated by the target data-generating device and output data from the position detecting device, wherein the target data-generating device sets the output data from the position detecting device to the target correction data for use in calculation of the drive signal by the drive signal-calculating device, while the output from the driving device is held in a disabled state by the output control device, and the target data-generating device sets the target correction data generated by the target data-generating device to the target correction data for use in calculation of the drive signal by the drive signal-calculating device, after the output from the driving device is enabled by the output control device. 
   With the arrangement of the first aspect of the present invention, it is possible to prevent the correcting optical device from largely moving to hit against a component part in the vicinity thereof to thereby generate impact noise upon the outputs from the drive device being enabled. 
   To attain the above object, in a second aspect of the present invention, there is provided a shake correcting device that corrects a shake of an object image picked up by an apparatus, comprising a shake detecting device that detects a shake of the apparatus, a correcting optical device that is movably disposed for optically correcting the shake of the apparatus, a position detecting device that detects a current position of the correcting optical device, a driving device that drives the correcting optical device according to a drive signal, an output control device that controls enabling and disabling of an output from the driving device, a target data-generating device that has a time constant, and generates target correction data based on an output from the shake detecting device, and a drive signal-calculating device that calculates the drive signal based on output data from the target data-generating device and output data from the position detecting device, wherein the target data-generating device includes a switching device that stops generation of the target correction data and sets the output data from the position detecting device as the output data from the target data-generating device, while the output from the driving device is held in a disabled state by the output control device, and resumes generation of the target correction data and switches the output data from the target data-generating device from the output data from the position detecting device to the target correction data generated by the target data-generating device according to the time constant, after the output from the driving device is switched from the disabled state to an enabled state. 
   To attain the above object, in a third aspect of the present invention, there is provided a shake correcting device that corrects a shake of an object image picked up by an apparatus, comprising a shake detecting device that detects a shake of the apparatus, a correcting optical device that is movably disposed for optically correcting the shake of the apparatus, a position detecting device that detects a current position of the correcting optical device, a driving device that drives the correcting optical device according to a PWM drive signal, an output control device that controls enabling and disabling of an output from the driving device, a target data-generating device that has a time constant, and generates target correction data based on an output from the shake detecting device, and a drive signal-calculating device that calculates the PWM drive signal based on output data from the target data-generating device and output data from the position detecting device, wherein the target data-generating device includes a storage device that stores data related to the output data from the target data-generating device, and a switching device that carries out a process for changing a content of the storage device to the output data from the position detecting device to thereby set the output data from the position detecting device to the output data from the target data-generating device, while the output from the driving device is held in a disabled state by the output control device, and stops the changing process and switches the output data from the target data-generating device from the output data from the position detecting device to the target correction data generated by the target data-generating device according to the time constant, after the output from the driving device is switched from the disabled state to an enabled state. 
   To attain the above object, in a fourth aspect of the present invention, there is provided a shake correcting method for a shake correcting device including a shake detecting device that detects a shake of an apparatus that picks up an object image, a correcting optical device that is movably disposed for optically correcting the shake of the apparatus, a driving device that drives the correcting optical device according to a drive signal, and a position detecting device that detects a current position of the correcting optical device, comprising a target data-generating step of generating target correction data based on an output from the shake detecting device, a setting step of setting enabling and disabling of an output from the driving device, a selecting step of selecting output data from the position detecting device, while the output from the driving device is held in a disabled state, and selecting the target correction data generated in the target data-generating step after the output from the driving device is enabled, and a drive signal-calculating step of calculating the drive signal based on the data selected in the selecting step and the output data from the position detecting device, and outputting the calculated drive signal. 
   To attain the above object, in a fifth aspect of the present invention, there is provided a shake correcting method for a shake correcting device including a shake detecting device that detects a shake of an apparatus that picks up an object image, a correcting optical device that is movably disposed for optically correcting the shake of the apparatus, a driving device that drives the correcting optical device according to a drive signal, and a position detecting device that detects a current position of the correcting optical device, comprising a target data-generating step of generating target correction data based on an output from the shake detecting device, a setting step of setting enabling and disabling of an output from the driving device, a switching step of stopping generation of the target correction data in the target data-generating step and sets output data from the position detecting device to output data generated in the target data-generating step, while the output from the driving device is held in a disabled state, and resuming the generation of the target correction data and switching the output data generated in the target data-generating step from the output data from the position detecting device to the target correction data generated in the target data-generating step according to a time constant, after the output from the driving device is switched from the disabled state to an enabled state, and a drive signal-calculating step of calculating the drive signal based on the output data generated in the target data-generating step and the output data from the position detecting device. 
   To attain the above object, in a sixth aspect of the present invention, there is provided a shake correcting method for a shake correcting device including a shake detecting device that detects a shake of an apparatus that picks up an object image, a correcting optical device that is movably disposed for optically correcting the shake of the apparatus, a driving device that drives the correcting optical device according to a PWM drive signal, and a position detecting device that detects a current position of the correcting optical device, comprising a target data-generating step of generating target correction data based on an output from the shake detecting device, a setting step of setting enabling and disabling of an output from the driving device, a switching step of carrying out a process for changing a content of a storage device that stores data related to output data generated in the target data-generating step to output data from the position detecting device to thereby set the output data from the position detecting device to the output data generated in the target data-generating step, while the output from the driving device is held in a disabled state, and stopping the changing process and switching the output data generated in the target data-generating step from the output data from the position detecting device to the target correction data generated in the target data-generating step according to a time constant, after the output from the driving device is switched from the disabled state to an enabled state, and a drive signal-calculating step of calculating the PWM drive signal based on the output data generated in the target data-generating step and the output data from the position detecting device. 
   To attain the above object, in a seventh aspect of the present invention, there is provided a control program for executing a shake correcting method for a shake correcting device including a shake detecting device that detects a shake of an apparatus that picks up an object image, a correcting optical device that is movably disposed for optically correcting the shake of the apparatus, a driving device that drives the correcting optical device according to a drive signal, and a position detecting device that detects a current position of the correcting optical device, comprising a target data-generating module for generating target correction data based on an output from the shake detecting device, a setting module for setting enabling and disabling of an output from the driving device, a selecting module for selecting output data from the position detecting device, while the output from the driving device is held in a disabled state, and selecting the target correction data generated by the target data-generating module, after the output from the driving device is enabled, and a drive signal-calculating module for calculating the drive signal based on the data selected by the selecting module and the output data from the position detecting device, and outputting the calculated drive signal. 
   To attain the above object, in an eight aspect of the present invention, there is provided a control program for executing a shake correcting method for a shake correcting device including a shake detecting device that detects a shake of an apparatus that picks up an object image, a correcting optical device that is movably disposed for optically correcting the shake of the apparatus, a driving device that drives the correcting optical device according to a drive signal, and a position detecting device that detects a current position of the correcting optical device, comprising a target data-generating module for generating target correction data based on an output from the shake detecting device, a setting module for setting enabling and disabling of an output from the driving device, a switching module for stopping generation of the target correction data by the target data-generating module and sets output data from the position detecting device to output data generated by the target data-generating module, while the output from the driving device is held in a disabled state, and the generation of the target correction data and switching the output data generated by the target data-generating module from the output data from the position detecting device to the target correction data generated by the target data-generating module according to a time constant, after the output from the driving device is switched from the disabled state to an enabled state, and a drive signal-calculating module for calculating the drive signal based on the output data generated by the target data-generating module and the output data from the position detecting device. 
   To attain the above object, in a ninth aspect of the present invention, there is provided a control program for executing a shake correcting method for a shake correcting device including a shake detecting device that detects a shake of an apparatus that picks up an object image, a correcting optical device that is movably disposed for optically correcting the shake of the apparatus, a driving device that drives the correcting optical device according to a PWM drive signal, and a position detecting device that detects a current position of the correcting optical device, comprising a target data-generating module for generating target correction data based on an output from the shake detecting device, a storing module for storing data related to output data generated by the target data-generating module, a setting module for setting enabling and disabling of an output from the driving device, a switching module for carrying out a process for changing the data stored by the storing module to output data from the position detecting device to thereby set the output data from the position detecting device to the output data generated by the target data-generating module, while the output from the driving device is held in a disabled state, and stopping the changing process and switching the output data generated by the target data-generating module from the output data from the position detecting device to the target correction data generated by the target data-generating module according to the time constant, after the output from the driving device is switched from the disabled state to an enabled state, and a drive signal-calculating module for calculating the PWM drive signal based on the output data generated by the target data-generating module and the output data from the position detecting device. 
   The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram schematically showing the arrangement of a shake correcting device according to a first embodiment of the present invention; 
       FIGS. 2A and 2B  are flowcharts showing an optical shake correction control process executed by a microcomputer appearing in  FIG. 1 , in which: 
       FIG. 2A  shows a main process; and 
       FIG. 2B  shows an interrupt process; 
       FIG. 3  is a flowchart showing details of an initial operation process executed in the main process in  FIG. 2A ; 
       FIG. 4  is a block diagram schematically showing the arrangement of a shake correcting device according to a second embodiment of the present invention; 
       FIG. 5  is a block diagram showing the arrangement of an integrator appearing in  FIG. 4 ; 
       FIG. 6  is a flowchart showing a main process of an optical shake correction control process executed by a microcomputer appearing in  FIG. 4 ; 
       FIG. 7  is a continued part of the flowchart in  FIG. 6 ; 
       FIG. 8  is a flowchart showing an interrupt process of the optical shake correction control process executed by the microcomputer; 
       FIG. 9  is a block diagram showing the arrangement of a conventional optical shake correcting device; 
       FIG. 10  is a block diagram showing the arrangement of a conventional optical shake correcting device based on a PWM drive control method using an H bridge circuit; and 
       FIGS. 11A and 11B  are diagrams useful in explaining an H bridge driver appearing in  FIG. 10 , in which: 
       FIG. 11A  shows the arrangement of input and output terminals of the H bridge driver and elements associated therewith; and 
       FIG. 11B  shows the logical states of the input and output terminals and the outputs from the H bridge driver. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will now be described in detail with reference to the drawings showing preferred embodiments thereof. Shake correcting devices according to the embodiments of the present invention described below are applied to a video camera. 
     FIG. 1  is a block diagram schematically showing the arrangement of a shake correcting device according to a first embodiment of the present invention. The shake correcting device shown in  FIG. 1  basically has the same arrangement as that of the shake correcting device shown in  FIG. 9 . Therefore, component parts and elements corresponding to those shown in  FIG. 9  are designated by identical reference numerals, and detailed description thereof is omitted. Shake correction is typically carried out biaxially in lateral and longitudinal directions, but in the present embodiment, a description will be given of only shake correction carried out along a single axis, for simplicity. Further, in a microcomputer appearing in  FIG. 1 , there are illustrated only sections related to the control of shake correction. 
   The arrangement of the shake correcting device of the present embodiment is distinguished from the conventional shake correcting device shown in  FIG. 9  in that the microcomputer  120  additionally includes an output selection switch  110  that switches between signals to be supplied to one of the input terminals of an adder  111 , and a driver controller  118  that controls enabling and disabling of the outputs from an H bridge driver  113  and switches the output selection switch  110  in accordance with this control operation. More specifically, the output selection switch  110  determines, based on a control signal from the driver controller  118 , whether to calculate the correction amount of a shift lens  119  using a target drive value as the output from an integrator  108  or using the output from a position sensor  114 . 
   In the following, a detailed description will be given of a shake correction control process executed when the power of the video camera, for example, is turned on, with reference to flowcharts shown in  FIGS. 2A ,  2 B, and  3 . 
     FIGS. 2A and 2B  are flowcharts showing the optical shake correction control process executed by the microcomputer  120 .  FIG. 2A  shows a main process, while  FIG. 2B  shows an interrupt process. The main process in  FIG. 2A  only shows a part related to the present invention, which is executed once per vertical synchronization period of a television signal.  FIG. 3  is a flowchart showing details of an initial operation process executed in a step S 502  in  FIG. 2A . The processes of  FIGS. 2A ,  2 B, and  3  are executed in accordance with programs stored in a storage device, not shown, provided in the microcomputer  120 . 
   Referring to  FIG. 2A , first, when the power of the video camera is turned on, initialization is executed in a step S 500 . More specifically, initial values of registers and the like within the microcomputer  120 , an interruption period, and so forth are set. In the next step S 501 , it is determined whether or not the count of an initial counter for determining timing of an initial operation of the shake correcting device has reached its maximum count. The initial counter is initialized to 0 in the step S 500 . If the count of the initial counter has not reached its maximum count in the step S 501 , the process proceeds to the step S 502 , wherein the initial operation process is executed according to the flowchart shown in  FIG. 3 . 
   In the initial operation process in  FIG. 3 , first, it is determined in a step S 201  whether or not the count of the initial counter is equal to 0. Initially, the count of the initial counter is equal to 0, and therefore the process proceeds to a step S 202 , wherein the output selection switch  110  is switched to select the output from the position sensor  114 , and in the next step S 203 , initialization of data is executed. In this step, a filter constant in the microcomputer  120  is set, and then the interrupt process shown in  FIG. 2B  is started. 
   In the next step S 208 , the count of the initial counter is incremented, and then steps S 209  and S 210  are executed to prevent the count of the initial counter from exceeding its maximum count. 
   Referring again to  FIG. 2A , after completion of the initial operation process in the step S 502 , the process proceeds to a step S 503 , wherein it is determined whether or not the count of an interrupt counter has reached a preset count. In this step, the execution of the process is awaited until the interrupt process shown in  FIG. 2B  is executed a predetermined number of times. The interrupt process is carried out using a timer operating at a frequency of e.g. 1200 Hz or 900 Hz, depending on the capacity of the microcomputer  120 . The frequency is set such that it is synchronized to the main process executed once per vertical synchronization period. 
   In a step S 521  in  FIG. 2B , an output signal from an angular velocity sensor  101  is received by an A/D converter  104 , and then in a step S 522 , an HPF operation is carried out using an HPF  105 . Further, in a step S 522 , a phase compensation operation is carried out by a phase compensation filter  106 , and in a step S 524 , an integrating operation is carried out by an integrator  108 . 
   In the next step S 525 , an output signal from the position sensor  114  is received by an A/D converter  116 , and then in a step S 526 , one of the output (indicative of the current position of the shift lens  119 ) from the position sensor  114  and an output (indicative of a target correction value) from the integrator  108  is selected by the output selection switch  110 . Thereafter, in a step S 527 , an adding operation is carried out by the adder  111 , and then in a step S 528 , an LPF operation for reducing drive noise generated by the driver  113  is carried out using an LPF filter  112 . 
   In the next step S 529 , a PWM output is delivered to the H bridge driver  113  by a PWM section  117 . It is assumed here that in the step S 202 , the output selection switch  110  has selected the output from the position sensor  114 , so that the output signal from the position sensor  114  is outputted as a target drive value from the adder  111 . This causes the PWM output outputted from the microcomputer  120  as a result of the adding operation in the step S 527  to serve to maintain the current position of the shift lens  119 . 
   In the next step S 530 , the number of interrupts is counted, i.e. the count of the interrupt counter is incremented, followed by terminating the interrupt process. When the interrupt process is executed a predetermined number of times, it is judged in the step S 503  that the count of the interrupt counter has reached the preset count, and the main process shown in  FIG. 2A  proceeds from the step S 503  to a step S 504 . 
   In the step S 504  in  FIG. 2A , the count of the interrupt counter is cleared. Thereafter, the optical shake correction control process returns to the step S 501 , wherein the main process is started again. 
   This time, when the process proceeds to the initial operation process (step S 502 ) shown in  FIG. 3 , it is determined in the step S 201  that the count, of the initial counter is not equal to 0, and therefore the process proceeds to a step S 204 , wherein it is determined whether or not the count of the initial counter is equal to a predetermined count A. If the count of the initial counter is not equal to the predetermined count A, it is determined in a step S 206  whether or not the count of the initial counter is equal to A+1. If the count of the initial counter is not equal to A+1, the count of the initial counter is incremented in a step S 208 , followed by the process proceeding to the step S 503  in  FIG. 2A . This sequential processing is repeatedly carried out until the count of the initial counter becomes equal to the predetermined count A. The predetermined count A is set to a value corresponding to a time period required for a filtered output obtained (through the steps S 521  to S 524 ) from the output (gyro signal) from the angular velocity sensor  101  to become stable. 
   When the count of the initial counter becomes equal to the predetermined count A, the outputs from the H bridge driver are enabled in a step S 205 . At this time, the target correction value (target drive value) for the shift lens  119  is set to a value corresponding to the current position, and therefore the shift lens  119  does not move. Then, during the next vertical synchronization period, the count of the initial counter becomes equal to A+1 (YES to step S 206 ), so that the process proceeds from the step S 206  to a step S 207  in  FIG. 3 , wherein the output selection switch  110  is switched to select an actual target correction value as the output from the integrator  108 . As a result, the target correction value is selected in the interrupt processing step S 526  shown in  FIG. 2B , and a shake correcting operation by the shift lens  119  is started. 
   When the target correction value is selected in the step S 526 , the PWM output in the step S 529  should largely change, but the LPF operation as a countermeasure against noise generated by the H bridge driver  113  has been executed in the preceding step S 528 , so that a sharp change in the PWM output is suppressed. 
   As described above, according to the present embodiment, in the optical shake correcting device using an H bridge driver, the target correction value for the shift lens  119  is set to a value corresponding to the current position before the outputs from the H bridge driver  113  are enabled, so that at a time point the outputs from the H bridge driver  113  are enabled (i.e. when the driving of the shift lens  119  is started), the shift lens  119  can be held in the current position, and thereafter, when the drive signal is switched to the actual correction target signal, the action of the filter for eliminating high-frequency components of the signal suppresses a sharp change in the target value that otherwise occurs at the time of the signal switching. This makes it possible to prevent the shift lens  119  from largely moving and hitting against a inner end of the lens barrel to generate impact noise. 
     FIG. 4  is a block diagram schematically showing the arrangement of a shake correcting device according to a second embodiment of the present invention. The shake correcting device shown in  FIG. 4  basically has the same arrangement as that of the shake correcting device shown in  FIG. 1 . Therefore, component parts and elements corresponding to those shown in  FIG. 1  are designated by identical reference numerals, and detailed description thereof is omitted. 
   The arrangement of the shake correcting device according to the present embodiment is distinguished from that of the shake correcting device shown in  FIG. 1  in that in the microcomputer  120 , the integrator  108  is replaced by an integrator  401  as a characterizing feature of the present embodiment; the output selection switch  110  is omitted; and a switching signal from the driver controller  118  and an output signal from the A/D converter  116  as data indicative of the output from the position sensor  114 , are additionally supplied to the integrator  401 . Reference numeral  410  in  FIG. 4  designates a switch that switches the video camera between a recording mode and a reproduction mode. 
     FIG. 5  is a block diagram showing the construction of the integrator  401  appearing in  FIG. 4 . 
   As shown in  FIG. 5 , the integrator  401  is comprised of an intermediate variable (Z- 1 )  701 , an integral constant (K)  702 , an adder  703 , and a changeover switch  704 . Further, although not shown, there are provided a RAM for storing the intermediate variable (Z- 1 )  701 , and a RAM for storing output data from the integrator  401 . 
   When a common terminal of the changeover switch  704  is connected to a switching terminal T 2 , the integrator in its entirety serves as an integrator, whereas when the common terminal is connected to a switching terminal T 1 , data indicative of the output from the position sensor  114  is set to the intermediate variable (Z- 1 )  701 , and at the same time delivered as the output from the integrator  401 . In other words, when the common terminal is connected to the switching terminal T 1 , the data acquired from the position sensor is written into both the RAM for storing the intermediate variable (Z- 1 )  701  and the RAM for storing output data from the integrator  401 . 
   With this construction, when the common terminal of the changeover switch  704  is switched from the switching terminal T 1  to the switching terminal T 2 , the output from the integrator  401  is switched from the data from the position sensor  114  to normal target correction value data from the angular velocity sensor, according to the time constant of the integrator  401 . 
     FIGS. 6 ,  7 , and  8  are flowcharts showing an optical shake correction control process executed by the microcomputer  120  in  FIG. 4 .  FIGS. 6 and 7  are a flowchart showing a main process, while  FIG. 8  is a flowchart showing an interrupt process. In the present embodiment, a description will be given of the case where the outputs from an H bridge driver  113  are enabled when the video camera is switched from the reproduction mode which does not need shake correcting operation, to the recording mode which needs shake correcting operation. The processes of  FIGS. 6 ,  7 , and  8  are executed in accordance with programs stored in a storage device, not shown, provided in the microcomputer  120 . 
   When the power is turned on in the reproduction mode, first in a step S 601  in  FIG. 6 , the microcomputer  120  is initialized. Then, in a step S 602 , it is determined, based on the setting state of the mode changeover switch  410 , whether the video camera is in the recording mode or in the reproduction mode. Since the video camera is now in the reproduction mode as described above, the process proceeds to a step S 615 , wherein a vertical synchronizing signal is awaited. This is because the video camera is controlled in synchronism with the vertical synchronizing signal. When the vertical synchronizing signal is received, the process proceeds to a step S 616 , wherein processing in the reproduction mode is executed. Then, in a step S 617 , the count of an initial counter is cleared. 
   The next steps S 618  to S 621  are executed to disable the outputs from the H bridge driver  113  when the video camera is switched from the recording mode to the reproduction mode. First, it is determined in the step S 618  whether or not the outputs from the H bridge driver  113  are in a disabled state. If the outputs from the H bridge driver  113  are in an enabled state, the process proceeds to a step S 619 , wherein it is determined whether or not processing for disabling the outputs from the H bridge driver  113 , i.e. the processing for shifting the shift lens  119  to a point close to the inner end of the lens barrel, as described before with reference to  FIG. 9 , is completed. If the processing for shifting the shift lens  119  to the point close to the inner end of the lens barrel is not completed, the shifting processing is continued in a step S 620 , whereas if the shifting processing is completed, the outputs from the H bridge driver  113  are disabled in the step S 621 . 
   As described above, when the power is turned on in the reproduction mode, the outputs from the H bridge driver  113  are in the disabled state, and when the video camera is switched from the recording mode to the reproduction mode, the outputs from the H bridge driver  113  are also disabled by execution of the steps S 618  to S 621 , so that energy can be saved. 
   On the other hand, when the video camera is switched from the reproduction mode to the recording mode, the process proceeds from the step S 602  to a step S 603 . Processing from the step S 603  to a step S 613  is substantially identical to the initial operation process described above with respect to the first embodiment with reference to  FIG. 3 . 
   More specifically, it is determined in the step S 603  whether or not the count of the initial counter has reached its maximum count. If the count of the initial counter has not reached its maximum count, it is determined in the step S 604  whether or not the count of the initial counter is equal to 0. The count of the initial counter is equal to 0 immediately after the video camera is switched to the recording mode, and therefore the changeover switch  704  of the integrator  401  is set to select the output (switching terminal T 1 ) from the position sensor in the step S 605 . Then, in the step S 606 , initialization related to shake correction is carried out and the interrupt process in  FIG. 8  are started. 
   In the next step S 611 , the count of the initial counter is incremented, and the process proceeds to a step S 612 , wherein the execution of the process is awaited until the interrupt process shown in  FIG. 8  is executed a predetermined number of times. In short, it is determined whether or not the count of an interrupt counter has reached a preset count. Similarly to the first embodiment, the interrupt process is carried out using a timer operating at a frequency of e.g. 1200 Hz or 900 Hz, such that it is synchronized with the vertical synchronizing signal. The preset count in the step S 612  is set to 20 when the interrupt frequency is 1200 Hz, and to 15 when the interrupt frequency is 900 Hz, so as to match with the vertical synchronizing signal of 60 Hz. 
   As shown in  FIG. 8 , in this interrupt process, first in a step S 651 , an output signal from the angular velocity sensor  101  is received by the A/D converter  104 , and in a step S 652 , an output signal from the position sensor  114  is received by the A/D converter  116 . Thereafter, in a step S 653 , an HPF operation is carried out by an HPF  105 , and in a step S 654 , a phase compensation operation is carried out by a phase compensation filter  106 . 
   In the next step S 655 , it is determined whether or not the changeover switch  704  of the integrator  401  is connected to the position sensor side (switching terminal T 1 ). If the changeover switch  704  is connected to the position sensor side, the process proceeds to a step S 656 . 
   In the step S 656 , the data from the position sensor  114  is delivered as the output from the integrator  401  and set to the intermediate variable (Z- 1 ), whereby the target correction value is set to a value corresponding to the current position of the shift lens  119 . In the actual program, data indicative of the output from the position sensor  114  and received in the step S 652  is written into both the RAM for storing the intermediate variable (Z- 1 )  701  and the RAM for storing the output data of the integrator  401 . Then, in a step S 657 , an adding operation is carried out by an adder  111  whereby a correction amount is calculated. 
   Further, in a step S 658 , an LPF  112  having received the calculated correction amount carries out an LPF operation for reducing drive noise generated by the driver  113 , and in the next step S 660 , a PWM output is delivered to the H bridge driver  113  by a PWM section  117 . Then, in a step S 660 , the count of the interrupt counter is incremented, followed by terminating the interrupt process. 
   When the above-described interrupt process is executed the predetermined number of times, it is judged in the step S 612  that the count of the interrupt counter has reached the preset count, and the main process in  FIG. 6  proceeds to a step S 613 , wherein the count of the interrupt counter is cleared. Thereafter, in a step S 614 , actual operations in the recording mode are carried out, followed by the program returning to the step S 602 . 
   On the other hand, if the count of the initial counter is equal to a value other than 0 in the step S 604 , the process proceeds to a step S 607 , wherein it is determined whether or not the count of the initial counter is equal to a predetermined count A. The predetermined count A used here is set to a count value corresponding to a time period required for the result of the phase compensation operation (step S 654 ) carried out in the interrupt process to become stable. 
   If the count of the initial counter is equal to the predetermined count A, the process proceeds to a step S 608 , wherein the outputs from the H bridge driver are enabled. At this time, the target drive value for the shift lens  119  has been set to the value corresponding to the current position of the shift lens  119 , so that the shift lens  119  is held in the current position. Then, during the next vertical synchronization period, the count of the initial counter becomes equal to A+1, and therefore the process proceeds from a step S 609  to a step S 610 , wherein the switch  704  in the integrator  401  is switched to the switching terminal T 2 . 
   When the interrupt process is carried out after execution of the step S 610 , the process proceeds from the step S 655  to a step S 661  in the interrupt process, whereby the normal filtering operation of the output signal from the angular velocity sensor  101  starts to be carried out. This operation shifts the target drive value (the output from the integrator  401 ) from the value corresponding to the current position of the shift lens  119  to an actual target correction value, according to the time constant of the integrator  401 . Thus, hitting of the shift lens  119  against the inner end of the lens barrel and resulting generation of impact noise can be prevented. 
   In the main process, the count of the initial counter is continually incremented from then on, and it is determined in the step S 603  whether or not the count of the initial counter has reached its maximum value. When the maximum value is reached, the process proceeds from the step S 603  to the step S 612 . Thus, the initial operation process at the time of switching the mode switching is completed. 
   As described above, in the present embodiment, at a time point the outputs from the H bridge driver  113  are enabled, data indicative of the output from the position sensor  114  is outputted from the integrator  401 , whereas immediately after the enabling of the outputs, the output from the integrator  401  is switched to data of the target correction value based on the output from the angular velocity sensor  101 , according to the time constant of the integrator  401 . This makes it possible to prevent the shift lens  119  from hitting against the inner end of the lens barrel to generate impact noise at the time point the outputs from the H bridge driver  113 , are enabled to carry out a shake correcting operation by the PWM drive. 
   Although in the present embodiment, the time constant set for normal operation of the integrator  401  is fixed, it may be made variable. For example, when the common terminal of the changeover switch  704  in  FIG. 5  is connected to the switching terminal T 1 , the time constant may be set short by changing the integral constant (K), so as to shorten the time period required for the output from the integrator  401  to become stable after switching of the changeover switch  704  from the switching terminal T 1  to the switching terminal T 2 . In this case, the integral constant (K) is returned to its normal value after the output from the integrator  401  has been stabilized. 
   Further, although the first and second embodiments relate to optical shake correction using the shift lens  119  of the video camera, the present invention can be applied to optical shake correction using a mechanism, such as a VAP (Vari-Angle Prism), and further, the present invention can be applied to optical apparatuses, such as cameras or digital cameras incorporating an optical shake correcting device based on the PWM drive method using an H bridge driver. 
   The present invention may either be applied to a system composed of a plurality of apparatuses or to a single apparatus. 
   It is to be understood that the object of the present invention may also be accomplished by supplying a system or an apparatus (e.g., a personal computer) with a storage medium in which a program code of software which realizes the functions of either of the above described embodiments is stored, and causing a computer (or CPU or MPU) of the system or apparatus to read out and execute the program code stored in the storage medium. 
   In this case, the program code itself read from the storage medium realizes the functions of any of the embodiments described above, and hence the program code and the storage medium in which the program code is stored constitute the present invention. 
   Examples of the storage medium for supplying the program code include a floppy (registered trademark) disk, a hard disk, an optical disk, a magnetic-optical disk, a CD-ROM, a CD-R, a CD-RW, DVD-ROM, a DVD-RAM, a DVD-RW, a DVD+RW, a magnetic tape, a nonvolatile memory card, and a ROM. Alternatively, the program may be downloaded via a network from another computer, a database or the like, not shown, connected to the Internet, a commercial network, a local area network, or the like. 
   Further, it is to be understood that the functions of either of the above described embodiments may be accomplished not only by executing a program code read out by a computer, but also by causing an OS (operating system) or the like which operates on the computer to perform a part or all of the actual operations based on instructions of the program code. 
   Further, it is to be understood that the functions of either of the above described embodiments may be accomplished by writing a program code read out from the storage medium into a memory provided on an expansion board inserted into a computer or in an expansion unit connected to the computer and then causing a CPU or the like provided in the expansion board or the expansion unit to perform a part or all of the actual operations based on instructions of the program code.