Lens apparatus

Abstract: The present invention relates to a lens apparatus employed in a video camera. The present invention provides a lens apparatus, suited to manipulation of an operator, using a vibratory wave motor as a driving source for driving a photographing lens of the lens apparatus, wherein on the occasion of change of a driving direction, application of cyclic signals to a piezoelectric device of the motor is suspended and thereafter application of cyclic signals to the piezoelectric device is restarted.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to control of vibration type driving apparatus for applying a cyclic signal to an electro-mechanical energy conversion element such as an electrostrictive device or a piezoelectric device to induce vibration of a vibrator and drive a driven body by use of this vibration, and to an apparatus such as a video camera or a lens for video camera using the vibration type driving apparatus as a driving source. Related Background Art There are known systems using a DC motor as a driving motor for focus, zoom, iris diaphragm, extender, macro, and so on in the video camera or in the lens for video camera. Fig. 5 illustrates a control system of a video camera lens using a known DC motor. In this control system a position detector 206 detects information of a real position of lens 205 and the information of real position is input into a position comparator 202. The position comparator 202 compares the real position of lens 205 detected, with a target position supplied from a command signal generator 201 and supplies a control signal to zero the difference between them to a motor driving circuit 203. When this control system is used for focusing, the command signal generator 201 is a potentiometer for detecting a focus control amount given by a cameraman, which supplies the target position (focus demand) ranging from nearest to infinity, to the position comparator 202. Then the motor driving circuit 203 applies a driving signal according to the control signal to the DC motor 204 to drive the lens 205 toward the target position. In the above control system using the DC motor, however, when the target position is altered during driving of the lens toward the target position, particularly when a new target position is a position which the lens has already passed, the driving direction of the lens has to be reversed At this time the motor is reversed by inverting the polarity of the driving signal applied to the DC motor. Some time is necessary for actual reversal of rotating direction of the motor after the inversion of the polarity of driving signal, because of the inertia of the motor. This poses a problem that the system fails to follow quick inversion manipulation of focus demand conducted by the cameraman. US-A-4896179 discloses apparatus for driving a lens of a camera, and reversing the direction of drive, using a DC motor or an ultrasonic motor which rotates in response to a travelling oscillating wave. EP-A-0700103 and US-A-4984000 also disclose the use of an ultrasonic motor to drive a camera lens. SUMMARY OF THE INVENTION The present invention provides a control circuit as set out in claim 1, apparatus for driving a photographic lens as set out in claim 7, a method as set out in claim 10, and a camera as set out in claim 8 or claim 9. Optional features are set out in the remaining claims. In an embodiment, a photographic lens is driven by use of a vibration type motor as a driving source for applying cyclic signals to an electro-mechanical energy conversion element to induce vibration of a vibrator and achieve driving force thereby, wherein for reversing the driving direction, application of the cyclic signals to the electro-mechanical energy conversion element is stopped and thereafter the application is restarted. Embodiments are described below by reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a control system in a lens apparatus for a TV camera, which is the first embodiment of the present invention; Fig. 2 is an overall operation flowchart of the above control system; Fig. 3 is an operation flowchart of a stop process of the above control system; Fig. 4 is an operation flowchart of another stop process of the above control system; and Fig. 5 is a block diagram of a known control system. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 illustrates a control system of a lens for a TV camera, which is the first embodiment of the present invention. In this figure reference numeral 104 designates a microcomputer (hereinafter referred to as "micro") for controlling the operation of the lens apparatus, and 105 a D/A converter for converting a number-of-rotation control signal (digital signal) outputted from the micro 104 to an analog signal. Numeral 106 denotes a V/F (Voltage/Frequency) converter, which outputs or stops a cyclic voltage according to an output voltage from the D/A converter 105 in response to an actuation control signal (start/stop) from the micro 104. Numeral 107 represents a frequency divider/phase shifter, which divides the cyclic voltage from the V/F converter 106 to output two rectangular signals (cyclic signals) having a phase difference of π/2. A direction of the phase difference between the two rectangular signals corresponds to a rotating direction of the vibration type motor 109 and the phase difference direction is determined according to a direction control signal (cw/ccw) from the micro 104. Numeral 108 stands for a power amplifier, which amplifies the outputs of rectangular signals from the frequency divider/phase shifter 107 to voltage and current that can drive the vibration type motor 109. Numeral 109 designates the vibration type motor (vibration type driving device), which is composed of a piezoelectric device (electro-mechanical energy conversion element) for causing vibration with application of the rectangular signals from the power amplifier 108 thereto, a vibrator induced to vibrate by the piezoelectric device, and a moving body kept in press contact with this vibrator and driven to rotate by vibration of the vibrator. Numeral 110 denotes a lens, this lens 110 being mechanically connected to the moving body of the vibration type motor 109, so that the lens 110 moves in the optic-axis direction and rotates about the optic axis with rotation of the moving body. Numeral 111 indicates an encoder for detecting movement of the lens 110, and 112 a counter for counting detected signals by the encoder 111. These elements detect a movement amount of the lens 110. Numeral 101 represents a command signal generator 101 for outputting the target position information according to the target position of the lens 110 set by manipulation of demand by the cameraman. Numeral 102 is a selection switch, and the cameraman can arbitrarily select a waiting time between stop and restart of rotation upon reversal of rotating direction of the vibration type motor 109, described hereinafter, by manipulating the selection switch. In the control system constructed as described above, the micro 104 first calculates the difference between the target position information and the real position information of the lens 110 from the counter 112 to determine the motor rotating direction and the number of rotations of the motor necessary for zeroing the difference, i.e., for agreement of the real position with the target position, and then outputs a direction control signal corresponding to the motor rotating direction thus determined to the frequency divider/phase shifter 107 and a number-of-rotation control signal corresponding to the number of rotations of the motor to the D/A converter 105. The D/A converter 105 converts the number-of-rotation control signal to an analog signal and the V/F converter 106 converts this analog signal to a cyclic voltage. Further, the frequency divider/phase shifter 107 receives the direction control signal from the micro 104 and converts the cyclic voltage to two rectangular signals having a phase difference corresponding to the direction control signal. These two rectangular signals are amplified to the voltage and current values of predetermined level by the power amplifier 108 to be applied to the piezoelectric device of the vibration type motor 109. This rotates the vibration type motor 109, whereby the lens 110 is driven toward the target position. Supposing here that during movement of the lens 110 toward the target position a new target position is set by manipulation of demand by the cameraman and that the lens 110 has already passed this new target position, the rotating direction of the vibration type motor 109 needs to be reversed. In this case, the present embodiment is arranged so that the micro 104 interrupts output of the V/F converter 106, so as to suspend the application of rectangular signals to the vibration type motor 109. This immediately stops rotation of the vibration type motor 109 and movement of the lens 110. After stop of the vibration type motor 109 and lens 110, the micro 104 waits until the waiting time selected through the selection switch 102 has elapsed. Then the micro 104 outputs the direction control signal to the frequency divider/phase shifter 107 and outputs the number-of-rotation control signal to the D/A converter 105, for moving the lens 110 to the new target position. This restarts the application of rectangular signals to the vibration type motor 109, so that the lens 110 is driven toward the new target position. The operation of the control system as described above is carried out based on a program installed in the micro 104. This program will be described referring to the flowcharts shown in Fig. 2 and Fig. 3. The overall flow of a position control process of the lens 110 will be described first referring to the flowchart of Fig. 2. After the position control process routine of the lens 110 is started in step 301, the micro reads the command signal according to the target position set by demand (focusing) manipulation of the cameraman in step 302. The micro 104 stores this as target position information in a memory inside the micro 104. In step 303 the micro then reads the position signal corresponding to the real position of the lens 110 from the counter 112 to store it as real position information in the memory. In step 304 the micro then calculates the difference between the target position information and the real position information stored in the memory of the micro 104. In subsequent step 305 the micro reads the number-of-rotation control signal output to the D/A converter 105 and the actuation control signal output to the V/F converter 106, for checking the number of rotations of the vibration type motor 109. When the number-of-rotation control signal is zero or when the actuation control signal is stop, the micro makes a decision that the vibration type motor 109 stands still, and then the micro goes to step 308. When the number-of-rotation control signal is not zero and when the actuation control signal is start, the micro determines that the vibration type motor 109 is rotating, and goes to step 306. In step 306 the micro reads the direction control signal output to the frequency divider/phase shifter 107 and compares the motor rotating direction indicated by this direction control signal with a motor rotating direction for zeroing the positional difference calculated in step 304. When these motor rotating directions agree with each other, the micro goes to step 309; when they disagree, the micro goes to step 307. In step 307 the micro performs a process for stopping the vibration type motor 109. In this process the micro executes the program indicated by the flowchart shown in Fig. 3. First entering a driving stop process routine of the motor in step 501, the micro reads the output from the selection switch 102 in step 502 and converts it to a waiting time, corresponding thereto, for the application of rectangular signals to the vibration type motor 109. Then the micro stores it in the memory in the micro 104. In next step 503 the micro outputs the actuation control signal (stop) to the V/F converter 106 to stop generation of the cyclic voltage and to start the clock counter in the micro 104. Then the micro proceeds to step 504 to determine whether the count time by the clock counter after the stop of the motor reaches the application waiting time stored in the memory. When the time does not have elapsed yet, this step is repeated; when the time has elapsed, the micro proceeds to step 505 to go to step 308 of the main flow shown in Fig. 2. In step 308 the micro outputs the direction control signal corresponding to the rotating direction of the vibration type motor 109 determined for decreasing the positional difference, based on the arithmetic result of step 304, to the frequency divider/phase shifter 107. In step 309 the micro outputs the number-of-rotation control signal corresponding to the number of rotations of the motor 109 determined for zeroing the positional difference, based on the arithmetic result of step 304, to the D/A converter 105. The vibration type motor 109 is reversed in this way, so that the lens 110 is driven toward the new target position. According to the control described above, when during movement of the lens 110 toward a target position a new target position is set by the cameraman and when the lens 110 has already passed this new target position, the application of cyclic signals to the vibration type motor 109 is suspended and application of cyclic signals is then restarted for reversing the motor 109. Since upon the suspension of application of cyclic signals the vibration type motor 109 immediately stops rotating by frictional force between the vibrator and the moving body, without continuing to rotate because of the inertia as was the case with the DC motor, the driving direction of the lens 110 can be reversed with a faster response to the reversal of the demand input by the cameraman, as compared with the known control system using the DC motor. In addition, because the waiting time from stop of the motor 109 to start of reverse drive can be arbitrarily set by manipulation of the selection switch 102, the response speed can be set by preference of the cameraman, thereby realizing an easy-to-use lens system. The present embodiment was described as an example in which setting of the speed of response to reversal of the input demand was effected by the manipulation signal of the selection switch 102, but a read signal from the memory may be used in place of the manipulation signal of the selection switch 102, for example. The present embodiment was described as an example having the function to permit the speed of response to the reversal of the input demand to be arbitrarily set, but this function may be excluded. In this case, the stop process of the motor 109 in step 307 can be carried out according to the program shown in Fig. 4 instead of the program of Fig. 3. Specifically, after the drive stop process routine of motor is started in step 401, step 402 is carried out to output the actuation control signal (stop) to the V/F converter 106 to stop generation of cyclic voltage. Then the micro proceeds immediately from step 403 to step 308 to start the reverse driving of the motor 109 without a waiting time. The above embodiment was described as to the case wherein the focus demand (a dial or the like) manipulated by the cameraman was used for setting the target position of the lens, but the present invention can also be applied to lens apparatus for setting the target position according to a control signal from an autofocus device. In this case, the present invention can increase the speed of the reversal operation after passing through the in-focus point in the so-called hill climbing process of autofocus. As detailed above, embodiments of the present invention provide a structure in which, on the occasion of reversal of the driving direction of the driven body, the application of cyclic signals to the electro-mechanical energy conversion element of the vibration type driving device is suspended and thereafter the cyclic signals for reversing the vibration type driving device are applied, to provide stable lens driving control with fast response speed to quick reversal of the focus demand input by the cameraman, for example. When the apparatus is provided with the means for selecting the time after the suspension of the application of cyclic signals to the electro-mechanical energy conversion element and before the restart of application, the response time can be adjusted by preference of the cameraman, to provide an easy-to-use lens apparatus or camera apparatus.

Claims: A control circuit for a lens (110) having a moving element driven in a first direction by applying cyclic signals in a first phase relation to a vibration-type motor (109) and driven in a second direction by applying cyclic signals in a second phase relation to the motor (109), the control circuit comprising means (104,107) to select the first or second phase relation for the cyclic signals, characterised in that the control circuit comprises delay means (104) to provide an interval between the application to the motor of cyclic signals in one of the said phase relations and the application to the motor of cyclic signals in the other said phase relation. A control circuit according to claim 1 in which the delay means is arranged to provide a predetermined interval. A control circuit according to claim 1 or claim 2, comprising setting means (102) for variably setting the interval provided by the delay means. A control circuit according to claim 3 in which the setting means (102) is arranged to be actuated by an operator. A control circuit according to any one of the preceding claims in which the means to select the first or second phase relation comprises: a direction setting circuit (107) for setting the phase relation of said cyclic signals according to a direction signal indicating a driving direction of said lens; and means (104) for generating the direction signal. A control circuit according to any one of the preceding claims which is arranged to stop formation of said cyclic signals during the interval between application of the signals in one phase relation and application of the signals in the other phase relation. Apparatus for driving a photographic lens (110), comprising a vibration type motor (109) and a control circuit according to any one of the preceding claims. A camera incorporating apparatus according to claim 7 for driving a lens of the camera. A camera according to claim 8 which is a video or TV camera. A method of operating a motorised lens having a movable lens element driven in a first direction by applying cyclic signals in a first phase relation to a vibration-type motor and in a second direction by applying cyclic signals in a second phase relation to the motor, and selector means to select either the first or the second phase relation for the cyclic signals, characterised in that when the phase relation of the cyclic signals applied to the motor is changed from one of the said phase relations to the other said phase relation, the application of the cyclic signals to the motor is suspended for an interval under control of delay means provided in a control circuit. A method according to claim 10 in which the said interval is predetermined.

Inventors: AKIIKE MICHIHIRO, AKIIKE, MICHIHIRO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1998
Main classification: G02B7
IPC codes: H01L41, H02N2, G02B7