JPH01155778A - Auto focusing device for video camera - Google Patents

Abstract

PURPOSE:To reduce power consumption and cost and to simplify the title device by fixing the front lens group of a lens system constituting a zooming lens, focussing a master lens group by vibrating and moving it in the direction of optical axis by a pulse motor and stopping a current during the holding in the vibration mode. CONSTITUTION:When the exciting mode rotates for a half step as from 8H to 9H, the vibration pattern area is entered. After the lapse of the minimum time t10 to operate half step within a time t1, all four phases are made zero and no current flows in a motor 19. At this time, the rotor of a pulse motor 11 does not rotate as does in an excited state at 9H. Therefore, when given exciting mode 1H in order to vibrate next, the pulse motor 11 rotates in a half-step CW direction, and a current is made flow through a coil during a time t2. After the lapse of the time t2, in order to return the rotor to its pre-vibration state, the exciting mode 9H is given and the motor rotates for a half step in the CCW direction. The 9H exciting time is made t10, and after the lapse of the time t10, all four phases are made zero in order not to let any current flow. As a result, no special vibrating mechanism needs to be set on the optical axis, and the saving of power consumption can be achieved with a simple constitution.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an autofocus device for a video camera, an electronic still camera, etc., and in particular extracts high frequency components of a photographic signal and maximizes the level thereof. The present invention relates to an autofocus device suitable for controlling a busy lens position.

[Conventional technology]

Conventional autofocus device VC changes the state of the subject image on the imaging plane by slightly vibrating the lenses that make up the mask group of the zoom lens in the optical axis direction using a reference frequency signal. Some devices change the position of the subject image formed on the light-receiving surface. In such an autofocus device, the focus state of the subject also changes in response 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 a 1-size foot circuit determines in which direction the front lens group, which is a focusing lens group, should be moved relative to the subject in the optical axis direction. Based on this result, the front lens group is moved to focus on the subject.

That is, the feedback circuit is configured so that the high frequency component signal is maximized. As an example of such a conventional example, 1, for example, as described in Japanese Patent Application Laid-Open No. 60-40723, a perturbation lens is arranged in a piezo master lens group, the lens is held by a piezoelectric element, and a predetermined amount is applied to the piezoelectric element. By inputting frequency electrical signals.

The lens is vibrated to determine the focus state, and the front lens group is moved in the direction of the original axis to focus on the subject.

Mata Nasinal Technical Review), Volume 31, No. 6.

As described in December 1985, pages 65-6, a method has been proposed in which a part of the master lens group is held and vibrated by a piezoelectric element as described above.

Also, as shown in Figure 1, the zoom lens system used in video cameras is generally a focusing lens (front lens).
The basic configuration includes a variator lens group, a compensator lens group, an aperture device, and a master lens (imaging lens) group.

As is well known, in this basic configuration, the focusing lens group has the function of focusing on a photographic subject at an arbitrary distance, the variator lens group has the function of changing magnification for zooming, and the compensator lens group has the function of focusing. A correction function that moves with zooming and prevents the subject from shifting its focus while zooming.

The imaging lens has the function of forming an optical image on the imaging device.

Examples shown in the above-mentioned documents include lens systems with such a basic configuration, in which a prism or master lens separately placed in front of the image sensor is vibrated with a small optical path length by a piezoelectric element, in addition to the focusing lens group. This is achieved by providing a vibration mechanism.

[Problem that the invention seeks to solve]

The above conventional technology has the advantage that since the lens focusing device is included in the feedback loop, an autofocus device with good focusing accuracy can be realized even if the mechanical precision such as the assembly accuracy of the focusing device is rough. However, as described above, the conventional technology requires an optical path length micro-vibration mechanism using a piezoelectric element, and therefore, its installation requires structural innovation in consideration of long-term stability, such as a supporting method.

Further, k for driving the piezoelectric element requires a driving voltage of several tens of square meters or more, and power consumption is also large. In the case of devices such as video cameras that operate on low-voltage batteries, it is necessary to provide an extra means for generating such a relatively high voltage.

Taking these points into consideration, if the focusing lens group described in the above-mentioned literature could be moved while being slightly vibrated by a motor, the configuration would be simplified since there would be no need to separately install the above-mentioned optical path length micro-vibration mechanism. Conceivable. However, generally a DC motor is used for driving for focusing.

It is difficult to put such a motor into practical use by slightly vibrating the focusing lens group, also from the viewpoint of the life of the motor.

The present invention realizes a device that can perform both optical path length micro vibration and focusing without installing an optical path length micro vibration device using a piezoelectric element (focusing is performed by moving the lens slightly). The present invention provides an effective, low-cost, and simple autofocus device.

[Means for solving problems]

The above purpose is to have a focusing mechanism after the variator lens group, move part or all of the master lens to maximize the high frequency component of the imaging signal, and perform focusing at a predetermined frequency. This is achieved by driving a pulse motor to move while making slight vibrations, and power saving can be achieved by the pulse motor driving method.

[Effect]

In general zoom lens systems, it is possible in principle to adjust the focus on any subject from close range to infinity by fixing the front lens group, which is the focusing lens, and moving part or all of the master lens group. It is. In this case, a focusing function is provided after the variator lens group, so if zooming is performed and the zoom position changes, a focus shift will occur even for objects at the same distance, and therefore, the optimal master lens position will change with zooming. However, in the autofocus device configured as described above, the feedback circuit is configured so that the high frequency component of the video signal is maximized, in other words, the blur of the captured image is detected and the blur is minimized. Since this is an autofocus device, the autofocus operation can be performed even when a zooming operation is performed, so that an appropriate photographed image can be obtained. In addition, the master lens group is sufficiently smaller (and lighter) than the front lens group, so it can be driven by a small, low-torque pulse motor.
Since the step angle is highly accurate, the lens can be controlled with high precision, and the lens position can be detected by counting the number of pulses, which has the advantage of not requiring a potentiometer or the like.

Furthermore, when using a pulse motor to generate minute vibrations, significant power savings can be achieved by cutting the hold current.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure 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 composed of three lenses, 3 is a variator lens group that performs a variable power function, 4 is a supercompensator lens group that corrects aberrations caused by variable power, and 5 6 is a master lens group, 6 is an aperture device, and 7 is an image sensor. 8
is the inner cylinder holding the master lens group, fixing the outer cylinder 20, and the inner cylinder 81! A ball 9 is provided between the inner tube 8 and the outer tube 20 so that the inner tube 8 and the outer tube 20 can be moved back and forth in the optical axis direction. 10 is a retainer that prevents the ball 9 from coming off.

The method of moving the inner cylinder 8 is to provide a frame 22 on a lead screw type shaft 21 provided on the pulse motor 11,
The frame 22 and the inner cylinder 8 are connected by a support rod, and the pulse motor 1
The frame 22 performs linear motion by 10 rotations.

The inner cylinder 8 is interlocked.

The output signal of the image sensor 7 is amplified by a preamplifier 12, and a camera signal is generated by a camera circuit 13.

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 contains the change component because the focus is slightly changed. 15 is a detection circuit that detects the change component, that is, the slightly fluctuating reference frequency component, and the detection signal is sent to the synchronous detection circuit. 16 and performs synchronous detection using the signal from the reference signal generating circuit 17. In this way, 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 11 is activated so that the level of the high frequency component of the image sensor 7 is maximized, that is, to perform focusing. It is operated via a drive circuit 19.

Next, the output voltage of the high frequency component of the image sensor 7 and the control method of the motor drive circuit will be explained using FIG. 2. If the master lens group 5 is moved from the close focusing distance to the infinity focusing distance and there is a subject at a distance P, for example, the level of the high-frequency component signal will be the highest at the position po as shown in Figure 2. Shows the shape of. Reference numeral 24 indicates minute vibrations of the master lens group, and when the subject is located close to the subject, a signal with the polarity 25 is sent to the detection circuit 15, and when the subject is located far away, the signal with the polarity 26 is sent to the detection circuit 15. detected in the output. The signal obtained by synchronously detecting the signal 25 drives the motor toward infinity, and the signal obtained by synchronously detecting the signal 26 drives the motor toward the nearest direction. stabilizes at the top of the mountain.

Next, the case where the pulse motor 11 is used will be explained with reference to FIG.

When using a pulse motor, minute vibrations can be obtained by driving one step in the CW (clockwise) direction and one step in the CCW direction (counterclockwise). If the amplitude of the vibration is small, it can be easily increased by increasing the number of steps.If the vibration of the pulse motor and the in-phase pattern are set as the front pin state, the rear pin state will be detected as the opposite phase, and it will be possible to determine whether the vibration is in phase or not. You can determine whether it is front focus or rear focus, and know the moving direction of the master lens group.Also, rotate the master lens group, that is, the pulse motor, until the level v27 of the high frequency component obtained by vibration becomes near O.

When the level 1127 of the high frequency component becomes close to O, it is determined that the camera is in focus, and minute vibrations are performed more intermittently, that is, at longer cycles.

Next, FIG. 4 shows how the master lens group is moved while being slightly vibrated. This is a case of moving from a close range to an infinite flash in fn steps, that is, l/n in l pulses. Here, a pattern is shown in which one step of minute vibration is followed by eight steps of movement in the infinite direction, and in FIG. 3, the front pin is in the state. In the rear pin state, the rising state of the moving region becomes a falling state. This minute vibration and movement pattern are repeated at a predetermined period Tf, as shown in FIG. Although the figure shows eight steps of movement, depending on one condition, for example, it is possible to easily move closer to the in-focus point (or move in fewer steps).

Next, a method for realizing the pattern shown in FIG. 4 using a stepping motor will be described.

FIG. 5 is a lead connection 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-phase and 2-phase excitation are: (1) 1-phase excitation has a full step angle and requires a small power supply, but the coil usage efficiency is poor. .

(2) Two-phase excitation has a full step angle as in (1), and all of the coils are excited, so the damping characteristics are good and the coil utilization efficiency is also good.

The l-2 phase excitation has the above (11, (2
), and the step angle is a half step. In other words, the amount of movement of one step with the same pulse motor? The point is that the amount of movement can be controlled with 1/2, that is, twice the resolution.

Next, a pulse waveform for driving the minute vibration soil movement pattern shown in FIG. 4 using 1-2 phase excitation will be described.

Figure 8 shows a general micro-vibration + movement pattern.

It is a time chart of each phase of the pulse motor 11 when driven by 1-2 phase excitation. The vibrating section is driven by a half step in the CW direction and a half step in the CCW direction, and moves by 4 (8 steps X+) steps in the CW direction. When this time chart is programmed and outputted from the microcomputer to the driver circuit shown in Figure 6, the movement of the vibration + movement pattern is performed, but the diagonally shaded part in Figure 8 (hold state)
It was found that a current flows (hereinafter referred to as the hold current) and the power consumption is large.

Therefore, the present invention eliminates the hold current shown in FIG. 8 and uses a time chart as shown in FIG. 9 in order to reduce power consumption. In Fig. 9, the excitation mode is 88 (16
Half step rotation (movement) from 9H (base number display),
Enter the vibration pattern area. After the minimum time t1G for half-step operation within time tl has elapsed, all four phases are set to 0, and no current flows 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 coil vibrates next time, when the excitation mode IH is applied, it rotates in the direction of the half-step C field and current flows through the coil for one hour t2. After time t22 has elapsed, in order to return the trochanter to its pre-vibration state, excitation mode 9HY is applied and the trochanter is rotated half-step in the CCW direction. The excitation time of 9H is &tlo and 1
After time tto, all four phases are set to O, and no current is applied.

Next, excitation mode 8H is applied to vibrate in the opposite direction again. After time t4 has passed, excitation mode 9H1f! : Give, return to the state before vibration and enter the movement pattern. The movement pattern is a conventional method, and FIG. 9 shows the case of rotating in the CW direction, and the excitation mode is used when rotating in the CCW direction.

9→8→C→4→6→2→3→1→9 It's fine.

Also, in the time chart of Fig. 9, if the vibration part, that is, times t2 and t4, does not need to be held because of the relationship t2 * '4 >'1G, then from the rise of t2 to after tto and the fall of t4 in the region of t2 and t4. After tto, if all four phases are set to 0, the current in the coil W in the vibration pattern region becomes even smaller (and the power consumption can be reduced).

The method for removing the hold current described above can be applied both when the vibrating section is rotated by one step (half step x 2) as shown in FIG. 10, and when a vibration pattern of several pulses is used.

In addition, although the case of 1-2 phase excitation has been described in FIG. 9, it can also be applied to 1- and 2-phase excitation.

The method described above removes the hold current by software,
A method for reducing power consumption by flowing less current during primary hold than during drive will be described.

FIG. 11 shows a circuit for controlling the current of the drive circuit of FIG. That is, the transistor Tr and the resistor RY 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 set to the power supply voltage Vcc, and when the pulse motor is rotating, the transistor Tr1f! :
ONL, in hold state, Tr is 0FFL,
A current is supplied to the drive circuit via the resistor R.

FIG. 12 shows a time chart for controlling the l-2 phase excitation and the transistor Tr in the drive pattern shown in FIG. 8. In FIG. 12, the time during which the hold current shown by diagonal lines flows is equal to the signal φ that controls the transistor Tr. .

20, and the blade that rotates the motor is φCC''l.

The pulse waveform φCC for controlling the Tr can be created using software in the same way as when driving a motor.

〔Effect of the invention〕

According to the present invention, there is no need to install a special optical axis pressure micro-vibration mechanism separately from the autofocus focusing mechanism.
This can be achieved with a simple configuration in which the master lens group of a zoom lens system is moved and focused while being vibrated minutely by a pulse motor, and the hold current during vibration can be reduced, resulting in power savings.

[Brief explanation of the drawing]

Fig. 1 is a system configuration diagram showing one embodiment of the present invention;
The figure is a level characteristic diagram of high frequency components obtained from the image sensor with respect to the focus lens position. FIG. 3 is also a filter characteristic diagram of high frequency components with respect to lens position. Figure 4 shows master lens photography Figure 7 shows CW
A time chart of a 1-2 phase excitation pattern during rotation is shown. FIG. 8 is a time chart when the pattern shown in FIG. 4 is driven by 1-2 phase excitation. FIG. 9 is a seta time chart with the hold current in FIG. 8 removed. FIG. 10 is a time chart when the step angle during vibration is increased. 1...Zoom lens system, 2...Front lens group. 3... Variator lens group. 4...Compensator lens group, 5...Master lens group, 7...Image sensor, 8...
- Inner cylinder, 20...outer cylinder. 9...Pole, 11...Pulse motor. 21...Lead screw. 14...High frequency component extraction circuit.

Claims (1)

[Claims] 1. A zoom lens that forms a subject image on an image sensor, a circuit that extracts a high frequency component signal from a video signal obtained from the image sensor, and a high frequency component signal of the circuit. The front lens of the lens system constituting the zoom lens is comprised of a circuit that controls a mechanism that moves a part of the lens system of the zoom lens in the optical axis direction so that the An automatic video camera characterized in that the lens group is fixed, a part or all of the master lens group is vibrated and moved in the optical axis direction using a pulse motor for focusing, and no current is passed when the vibration mode is held. focus device. 2. The autofocus device for a video camera according to claim 1, wherein the power supply of the pulse motor is controlled so that the current is smaller when holding the vibration mode than when rotating.