JPH0822027B2 - Camera with autofocus device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera, an electronic still camera or the like equipped with an autofocus device,
In particular, the present invention relates to a camera equipped with an autofocus device suitable for extracting a high frequency component of an image pickup signal and controlling the lens position so that the level thereof becomes maximum. 2. Description of the Related Art In a conventional autofocus device such as a video camera, a lens forming a master group of a zoom lens is slightly vibrated in the optical axis direction by a signal of a reference frequency, so that an object on an image plane is formed. There is one that changes the state of an image, that is, changes the position of a subject image formed on a light receiving surface of an image pickup element by a zoom lens. In such an autofocus device, the focus state of the subject also changes according to this change. Therefore, the level of the high frequency component signal obtained from the video signal from the image sensor changes. This high-frequency component signal is extracted, and the determination circuit determines to which direction in the optical axis direction the position of the front lens group, which is the focusing lens group, should be moved with respect to the subject. Based on this result, the front lens group is moved so as to focus on the subject. That is, the feedback circuit is configured so that the high frequency component signal is maximized. As such a conventional example, for example, a vibrating lens is arranged in a master lens group as described in JP-A-60-40723,
The lens is held by a piezoelectric element and the lens is vibrated by inputting an electric signal of a predetermined frequency to the piezoelectric element,
Thereby, the focus state is determined and the front lens group is moved in the optical axis direction to focus on the subject. National Technical Report, 31
Vol. 6, No. 6, December 1985, pp. 65-67, a method has been proposed in which a part of the master lens group is held by a piezoelectric element as described above and vibrated. Further, as shown in FIG. 1, a zoom lens system in a video camera or the like generally includes a focusing lens (front lens) group, a variator lens group, a compensator lens group, a diaphragm device, and a master lens (imaging lens) group. It has a basic structure. As is well known, among these basic configurations, the focusing lens group has a function of focusing on a subject to be photographed at an arbitrary distance, the variator lens group has a zooming function for zooming, and the compensator lens group has The master lens has a function of moving together with zooming, a function of correcting defocus during zooming of an object, and a function of forming an optical image on the image sensor. In the examples described in the above-mentioned documents, in a lens system having such a basic structure, a prism or a master lens separately arranged in front of the image pickup element is vibrated by a piezoelectric element in addition to the focusing lens group. This is achieved by providing an optical path length microvibration mechanism. In the above-mentioned prior art, since the focus adjusting device of the lens is in the feedback loop, the focusing accuracy is low even if the mechanical accuracy such as the assembly accuracy of the focus adjusting device is rough. There is an advantage that a good autofocus device can be realized. However, as described above, the conventional technique requires an optical path length micro-vibration mechanism using a piezoelectric element, and therefore a structural devise in consideration of long-term stability is required in its attachment support method and the like. In addition, a driving voltage of several tens of volts or more is required to drive the piezoelectric element, and power consumption is large. In the case of a device operated by a low voltage battery such as a video camera, it is necessary to additionally provide means for generating such a relatively high voltage. In consideration of such a point, if the focusing lens group in the above-mentioned document can be moved while being slightly vibrated by a motor, it is not necessary to separately install the above-mentioned optical path length minute vibrating mechanism, so that the structure is simple. It is believed that However, DC is generally used for driving for focusing.
A motor is used, and it is difficult to practically vibrate the focusing lens group with such a motor from the viewpoint of the life of the motor. An object of the present invention is to realize a device for moving a lens while performing a fine movement for focusing without installing a device for vibrating the optical path length by a piezoelectric element, that is, a device which can perform both the optical path length minute vibration and focusing. The present invention provides a video camera equipped with a low-cost, simple autofocus device, which has the effect of saving power. In order to achieve the above object, a front lens group, a master lens group, and a front lens group and a master lens group in which a subject image is formed on an image pickup element and fixed A zoom lens configured by a variator lens group provided between the pulse motor and the pulse motor, the pulse motor being step-driven, a shaft of the pulse motor being a lead screw, and a part or all of the master lens group and the pulse motor. Drive mechanism that is connected to the lead screw screw, an extraction circuit that extracts a high frequency component signal from a video signal obtained from the image pickup device, the pulse motor is step-driven, and the master is driven via the drive mechanism. A part or all of the lens group is displaced in the optical axis direction so that the high frequency component signal extracted by the extraction circuit becomes maximum. A control circuit for moving a part or all of the star lens group is provided, and a drive current is supplied to the pulse motor for a predetermined time during one step drive period, and the drive current is stopped until the next step drive. The feature is that power consumption can be reduced by the driving method of the pulse motor. In a general zoom lens system, the front lens group, which is a focusing lens, is fixed, and a part or all of the master lens group is moved to adjust the focus on an arbitrary subject from a close range to infinity. It is possible in principle. In this case, since a focusing function is provided after the variator lens group, zooming is performed, and if the zoom position changes, a focus shift occurs even for a subject at the same distance, and therefore the optimum master lens position changes with zooming. However, the autofocus device configured as described above is provided with a feedback circuit so that the high frequency component of the video signal is maximized, in other words, the blur of the photographed image is detected, and the blur is minimized. Since the autofocus device is configured, the autofocus operation can be performed even when the zooming operation is performed, so that an appropriate captured image can be obtained. Since the master lens group is sufficiently smaller and lighter than the front lens group, it can be driven by a small, low-torque pulse motor. Since the pulse motor has high step angle accuracy, the lens can be controlled with high accuracy.
Since the lens position can be detected by counting the number of pulses, there is an advantage that a potentiometer or the like is not required. Further, there is provided a control circuit configured so that the pulse motor is step-driven to step-drive part or all of the master lens group in the direction of the optical axis for focusing, and a current is not passed immediately after step driving the pulse motor. As a result, it is possible to significantly reduce the power consumption. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of an autofocus device according to the present invention. In the figure, 1 is a zoom lens system, 2 is a front lens group consisting of three lenses, 3 is a variator lens group for performing a zooming action, 4 is a compensator lens group for correcting aberrations caused by the zooming action, Reference numeral 5 is a master lens group, 6 is a diaphragm device, and 7 is an image sensor. Reference numeral 8 denotes an inner cylinder holding the master lens group, which fixes the outer cylinder 20 and mounts a ball 9 between the inner cylinder 8 and the outer cylinder 20 so that the inner cylinder 8 can be moved back and forth in the optical axis direction. Set up. Reference numeral 10 is a retainer which prevents the balls 9 from coming off. The method of moving the inner cylinder 8 is the pulse motor 1
The lead screw type shaft 21 provided in 1 is provided with a frame 22, the frame 22 and the inner cylinder 8 are connected by a support rod, and the frame 22 makes a linear motion by the rotation of the pulse motor 11,
The inner cylinder 8 is interlocked. The output signal of the image pickup device 7 is the preamplifier 12
And the camera circuit 13 generates a camera signal. Reference numeral 14 is a high frequency component extraction circuit 14 that extracts high frequency components from the video signal. The output signal of the high frequency component extraction circuit 14 includes the change component because the focus is slightly changed. Reference numeral 15 is a detection circuit for detecting the change component, that is, the fine fluctuation reference frequency component, which inputs the detection signal to the synchronous detection circuit 16 and performs synchronous detection using the signal of the reference signal generation circuit 17. Thus, the polarity and vibration of the detected reference frequency component signal are detected, and in addition to the control signal generation circuit 18, the pulse motor 1 is controlled so that the level of the high frequency component of the image sensor 7 is maximized, that is, focusing is performed.
1 is moved via the drive circuit 19. Next, the output voltage of the high frequency component of the image pickup device 7 and the control method of the motor drive circuit will be described with reference to FIG. When the master lens group 5 is moved from the closest focusing distance to the infinity focusing distance, and there is a subject at a distance P ₀ , for example, the level of the high frequency component signal becomes the maximum at the position P _{0 as} shown in FIG. Shows the shape of. Reference numeral 24 indicates a minute vibration of the master lens group. When the signal is located on the short distance side with respect to the subject, the signal having the polarity of 25 is 2 when it is located on the far distance side.
A signal of 6 polarity is detected at the output of the detection circuit 15. Two
The signal of 5 is synchronously detected and the motor is moved toward infinity.
The signal of 26 is synchronously detected to drive the motor toward the closest direction, so that it is stable at the maximum value of the level of the high frequency component signal, that is, at the peak of FIG. Next, the case where the pulse motor 11 is used will be described with reference to FIG. When a pulse motor is used, the minute vibration is C
It is obtained by driving one step in the W (clockwise direction) and one step in the CCW direction (counterclockwise direction). When the vibration amplitude is small, it can be easily increased by increasing the number of steps. When the vibration of the pulse motor and the in-phase pattern are set to the front pin state, the rear pin state is detected as a reverse phase, and it can be determined whether it is the front pin or the rear pin depending on whether it is in phase
The moving direction of the master lens group can be known. Further, the master lens group, that is, the pulse motor is rotated until the level v27 of the high frequency component obtained by the vibration is close to zero. When the level v27 of the high frequency component becomes close to 0, it is determined that the object is in focus, and the minute vibration is more intermittently performed, that is, in a long cycle. Next, FIG. 4 shows how the master lens group is moved while being slightly vibrated. This is a case where the amount of movement from the closest distance to infinity ∞ is moved in n steps, that is, 1 pulse is moved in 1 pulse. Here, after one step of small vibration, 8
It shows the pattern of moving toward step infinity,
This is the state of the front pin in FIG. In the rear pin state, the rising state of the moving area is the falling state. The minute vibration and the movement pattern are repeated at a predetermined cycle Tf as shown in FIG. Although the figure shows the case of 8-step movement, depending on the conditions, for example, when the focus is approached, the number of steps can be reduced, that is, the movement can be made slowly. Next, a method of realizing the pattern of FIG. 4 by using a stepping motor will be described. FIG. 5 is a lead wiring diagram for a bipolar drive of a stepping motor, and FIG. 6 is a general bipolar driver circuit diagram. FIG. 7 shows a 1-2 phase excitation pattern during CW rotation. The reason why bipolar 1-2 phase excitation is mentioned here is that (1) 1 phase excitation and 2 phase excitation are full-step step angles and small power source, but use of coil The rate is bad. (2) In the two-phase excitation, the step angle is a full step as in the case of (1) and all the coils are excited, so that the damping characteristics are good and the utilization efficiency of the coils is also good. The 1-2 phase excitation is characterized by an intermediate feature between the above (1) and (2) and a step angle of half step. That is, with the same pulse motor, 1
This is that the movement amount of the step can be controlled with a resolution of 1/2, that is, twice the resolution. Next, pulse waveforms for driving the microvibration + movement pattern shown in FIG. 4 by 1-2 phase excitation will be described. FIG. 8 is a time chart of each phase of the pulse motor 11 when the micro vibration + movement pattern is generally driven by the 1-2 phase excitation. The vibrating section is driven by half step in the CW direction and half step in the CCW direction,
Move 4 (8 steps x 1/2) steps in the direction. When this time chart is programmed and output from the microcomputer to the driver circuit of FIG. 6, the movement of the vibration + movement pattern is performed, but a current flows in the shaded portion (hold state) of FIG. 8 (hereinafter, this is the hold current. It was found that the power consumption is large. Therefore, the present invention uses the time chart as shown in FIG. 9 in order to remove the hold current of FIG. 8 and reduce the power consumption. In FIG. 9, the excitation mode is 8H
Half step rotation (movement) from (hexadecimal number display) to 9H enters the vibration pattern area. After the minimum time t ₁₀ of half-step operation within the time t ₁ , the four phases are set to 0,
No current is passed through the motor coil. At this time, the rotor of the pulse motor does not move in the same state as the excited state of 9H. Therefore, when the next vibration occurs, when the excitation mode 1H is applied, the coil rotates in the half step CW direction, and the current is passed through the coil for the time t ₂ . In order to return the rotor to the state before vibration after the lapse of time t ₂ , the excitation mode 9H is applied and the rotor is rotated in the CCW direction by half step. The excitation time of 9H is t _10, and after the time t ₁₀ , all four phases are set to 0, and no current flows. Next, the excitation mode 8H is applied to vibrate in the opposite direction. Time t ₄ after gives the excitation mode 9H, enters the movement pattern back to the state before the vibration. The movement pattern is a conventional method, and FIG.
When rotating in the W direction and rotating in the CCW direction, the excitation mode may be set to 9⇒8⇒C⇒4⇒6⇒2⇒3⇒1⇒9. Further vibration portion or time in the time chart t ₂ and t ₄ in FIG. 9, t _4> If you do not need to hold the relationship of t ₁₀ time t ₂ and t ₄ of the area t from the rise of t ₂ After ₁₀ and t ₁₀ from the fall of t4, all four phases are 0
Then, the coil current in the vibration pattern region is further reduced, and power saving can be reduced. The method of removing the hold current described above is as follows.
It can be applied to the case where the vibrating section is rotated by one step (half step × 2) as shown in FIG. Although the case of 1-2 phase excitation has been described with reference to FIG. 9, it is also applicable to 1 and 2 phase excitation. The above-mentioned method was to softly remove the hold current and reduce the power consumption. Next, a method for supplying a smaller current than the driving time to hold the power to save power will be described. FIG. 11 shows a circuit for controlling the current of the drive circuit shown in FIG. That is, the transistor Tr and the resistor R are connected in parallel and connected to the power supply line of the drive circuit. The other of the transistor Tr and the resistor R is the power supply voltage Vcc,
Transistor Tr when rotating the pulse motor
Is turned on, and Tr is turned off in the hold state,
A current is supplied to the drive circuit via the resistor R. In the drive pattern shown in FIG. 8, 1-
FIG. 12 shows a time chart for controlling the two-phase excitation and the transistor Tr. In FIG. 12, the time during which the shaded hold current flows is the signal φcc = 0 for controlling the transistor Tr, and φcc = 1 when the motor is rotated.
And The pulse waveform φcc for controlling Tr can be created by software as in the case of driving the motor. According to the present invention, the pulse motor is step-driven to step-drive part or all of the master lens group in the optical axis direction through the lead screw to focus the pulse. Since the control circuit configured so that the current does not flow immediately after the step driving of the motor is provided, the power consumption of the autofocus device can be reduced, and a portable camera using a battery or the like as a power source can bring advantages such as long-time recording.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system configuration diagram showing an embodiment of the present invention. FIG. 2 is a level characteristic diagram of a high frequency component obtained from an image sensor with respect to a focus lens position. FIG. 3 is a level characteristic diagram with respect to a lens position of a high frequency component. FIG. 4 is a vibration and movement pattern diagram of a master lens. FIG. 5 is a lead wiring diagram of a pulse motor. FIG. 6 is a bipolar drive circuit diagram. FIG. 7 shows a time chart of a 1-2 phase excitation pattern during CW rotation. FIG. 8 is a time chart when the pattern of FIG. 4 is driven by 1-2 phase excitation. 9 is a time chart of the motor from which the hold current in FIG. 8 is removed. FIG. 10 is a time chart when the step angle during vibration is increased. FIG. 11 is a circuit diagram for controlling the power supply of a motor driver. 12 is a time chart of the power supply control of FIG. [Explanation of Codes] 1 ... Zoom lens system, 2 ... Front lens system, 3 ... Variator lens group, 4 ... Compensator lens group, 5 ... Master lens group, 7 ... Image sensor, 8 ... Inner cylinder, 9 ... Ball, 11 ... Pulse motor, 14 ... High frequency component extraction circuit,
20 ... Outer cylinder, 21 ... Lead screw,

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenji Sano             Stock, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa             Company Home Appliance Research Laboratory, Hitachi, Ltd. (72) Inventor Takesuke Maruyama             Stock, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa             Company Home Appliance Research Laboratory, Hitachi, Ltd.              (56) Reference JP-A-57-186872 (JP, A)               JP-A-56-147131 (JP, A)

Claims (1)

[Claims] 1. A zoom lens composed of a fixed front lens group, a master lens group, and a variator lens group provided between the front lens group and the master lens group, and a step drive Pulse motor, and the shaft of the pulse motor is a lead screw screw,
A part or all of the master lens group and the pulse mode
Drive mechanism that is connected to the lead screw of the input device, an extraction circuit that extracts a high frequency component signal from the video signal obtained from the image sensor, step drive the pulse motor, and the drive mechanism through the drive mechanism. A control circuit for displacing part or all of the master lens group in the optical axis direction and moving part or all of the master lens group so that the high frequency component signal extracted by the extraction circuit becomes maximum. The pulse motor has a predetermined time during one step driving period.
Supply the drive current, and drive current until the next step drive
A camera equipped with an autofocus device, which is characterized by stopping supply .