JPH05196854A - Lens driving controller - Google Patents

Abstract

PURPOSE:To provide a lens driving controller stably locating a lens system in the vicinity of a focusing position, but not having the out of focus by the disturbance such as panning and camera shake. CONSTITUTION:The lens driving controller is provided with a guiding means guiding a lens group in an arbitrary one-way, a lens driving means 84 driving the lens group along the guiding means, a lens position detecting means 85 detecting the position of the lens group, and a lens position control means 80 controlling the position of the lens group, based on the output of the lens position detecting means 85, a loop gain till the lens group reaches the vicinity of a set value from the position away from the set value, is set different from the loop gain after the lens group reaches the vicinity of the set value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens drive control device for driving a photographing lens of a camera / video camera and a photographing lens of a video projector.

[0002]

2. Description of the Related Art Motors such as DC motors and stepping motors are often used as lens driving actuators in conventional lens drive control devices of this type.

FIG. 4 is a vertical sectional view showing a lens barrel of a conventional zoom lens for a video camera, and FIG. 5 is a vertical sectional view taken along the line AA of FIG. In FIGS. 4 and 5, 25a-2
Reference numeral 5d denotes a lens group. A DC motor 26 drives a variator lens group 25b for changing a field angle, and a stepping motor 28 drives a lens group 25d having a focus position change and a focusing function in accordance with a view angle change. It is driving. 27 is a motor for driving the shutter unit.

On the other hand, in recent cameras and video cameras, miniaturization has been advanced, and it has become necessary to reduce the volume and weight while maintaining the functions equal to or higher than conventional ones.
As a means for this, a magnet is arranged on the outer periphery of a moving frame for holding the lens group, a coil and a yoke are arranged on the outer periphery of the magnet to form a voice coil motor, and the lens group is arranged on the optical axis. A directional driving system is described in, for example, Japanese Patent Application No. 2-206593. In the system described in this publication, a compact lens drive actuator is realized by making the optical axis of the voice coil substantially coincide with the optical axis.

FIG. 6 shows an application example of the voice coil motor, and FIG. 7 is a vertical section taken along the line BB of FIG.
6 and 7, 31a to 31c are lens groups, 32 is a lens holding frame for holding the lens groups 31a to 31c, 33
Is a coil wound around the bobbin 34, 35 and 36 are yokes adhered to the magnet 37, and 38 is a lens barrel that holds the yokes 35 and 36 and the magnet 37.

The lens holding frame 32 is held movably in the optical axis direction by two guide rods 39a and 39b arranged in parallel inside the lens barrel 38.

Since the magnet 37 is magnetized as shown in the figure, a magnetic field is formed between the yokes 35 and 36 in the radial direction.

Since the coil 33 is wound in the circumferential direction between the yokes 35 and 36, when an electric current is passed through the coil 33, a driving force in the optical axis direction is generated and is integrated with the bobbin 34. Lens holding frame 32 and lens group 31a
.About.31c are driven in the optical axis direction.

In FIG. 6, the magnet is fixed and the coil moves, whereas in FIG. 8, the coil is fixed and the magnet moves. In the magnet moving type of FIG. 8, the magnet 4 magnetized in the radial direction is provided on the outer peripheral portion of the lens holding frame 42 holding the lens 41.
3 is adhered, and a coil 43 wound around in the circumferential direction is provided by adhering to the inner periphery of the yoke 45 with a magnet 43 and an appropriate gap provided on the outer periphery thereof.

The lens holding frame 42 is held by two guide rods 46a and 46b so as to be movable in the optical axis direction. Move in the axial direction.

FIG. 9 shows an example in which a video lens system of a type in which a magnet moves is constructed by using the above-mentioned voice coil actuator. In the figure, a variator lens group 61b for zooming and a focus lens group 61d are shown. Is driven by using a voice coil actuator, and encoders 51 and 5 for detecting the absolute positions of the variator lens group 61b and the focus lens group 61d.
2 is attached.

As the encoders 51 and 52, linear type volumes, those of a type in which an electrode on which a gray code pattern is formed are traced with a brush, and light-emitting elements such as iRED and photoelectric cells such as PSD that move together with a lens holding frame are used. A type in which position detection is performed using a conversion element and the like can be considered.

The outputs from the encoders 51 and 52 are read by the respective reading circuits 54 and 55, and the CPU 5
Sent to 6. Also, the video signal from the CCD 66 is
It is processed in the signal processing circuit 53 (peak detection circuit), the peak value of the luminance signal is extracted, and is sent to the CPU 56 as information regarding the current focus state.

Since the video lens system shown in FIG. 9 is a so-called rear focus lens in which focusing is performed by the lens group on the image plane side of the variator lens group, the variator lens group and the focus lens group are selected depending on the object distance. The positional relationship that should be taken changes. This is shown in FIG.

In FIG. 10, the vertical axis is the focus lens position, the horizontal axis is the variator lens position, and the object distance is used as a parameter, and the cam locus to be followed by each lens group is shown. Therefore, it is necessary for each voice coil motor to maintain the in-focus state by deciding the speed / direction in which the lens group should move based on various information provided in the system.

FIG. 11 is a diagram showing each signal of an autofocus system using a video signal. FIG. 11A shows the luminance signal S ₀ output from the peak detection circuit 53 on the vertical axis and the focus on the horizontal axis. It is a waveform diagram which took the lens position. As shown in the figure, according to the peak value of the luminance signal S ₀ ,
An approximate defocus amount will be detected. Based on these information and the information from the ROM 59 having the information about the cam locus shown in FIG. 10 as data, the CPU 5
The current value or its waveform to be passed through the coils 62 and 63 is determined in the coil 6, and the current flows through the coils 62 and 63 via the respective drivers 57 and 58.

With the above system, the variator lens group 61b and the focus lens group 61d can maintain a positional relationship such that they are always in focus.

Next, a system from the state where the variator lens group 61b is fixed and the subject is out of focus to the in-focus state, that is, an autofocus (AF) system will be described.

In FIG. 9, a drive signal of a constant cycle is given to the focus motor driver 57 by the oscillator 69, and the focus lens group 61d is driven by the output of the focus motor driver 57 so as to slightly vibrate in the optical axis direction. Then, the output from the peak detection circuit 53 also vibrates in synchronization with it. In FIG. 11, if the focus lens is located closer to the focus position than the focus position, the vibration of the lens and the phase of the video signal match, and if the focus lens is located far away, the phase shifts by 180 °.

Therefore, in FIG. 9, the peak detection circuit 53
Output from the phase detector 68 via the frequency detector 67
Then, by comparing with the phase in the oscillator 69, it is possible to judge whether it is the front pin or the rear pin.

Further, the amplitudes of the outputs when the focus lens is located on the front focus side and the rear focus side are respectively shown in FIG.
A _N and A _F shown in Fig. 3 are obtained, and A _M = 0 when focusing.

When these signals are synchronously detected with the output of the oscillator 69 as a reference timing, a synchronous detection signal (hereinafter referred to as signal) S ₁ shown in FIG. 11B is obtained. That is,
Since the signal at the short distance has the same phase as the reference timing, the positive signal S ₁ is output, and the signal at the long distance has the opposite phase to the reference timing, the negative signal S ₁ is output.

As described above, the amplitude of the signal S ₁ becomes 0 at the time of focusing, and the amplitude also increases as the defocus amount increases, so that the absolute value of the signal S ₁ also changes with it. Therefore, when a current proportional to this signal S ₁ is passed through the voice coil, the lens can be brought into focus.

However, since the signal S ₁ becomes small when the blur becomes large, the current applied to the voice coil also becomes small. Therefore, when S ₀ is less than V _H is currently the 1V previous S ₀ that shown in FIG. 11 (c) without using the signal S ₁ S ₀
The signal S ₂ obtained by comparing Since this signal S ₂ is the output of the comparator, it is a signal having a constant value and only a code for driving the lens.

That is, at the time of large blur, the lens is driven at a high speed in the focusing direction by passing a current through the voice coil according to the signal S ₂ , and when the focus is approached, the signal S ₁ is output at the speed. By performing the operation of converging to the in-focus point where the signal S ₁ becomes zero, the automatic focus adjustment operation is performed.

Further, if the motor speed based on the signal S ₁ is too high, the amount of overshooting of the in-focus position becomes large, causing hunting, and if it is too small, it takes time to reach in-focus. Therefore, it is necessary to have a proper gain.

[0027]

However, in the above-mentioned conventional example, when the lens system is in focus, the focus lens cannot maintain the focus position due to disturbance such as panning and camera shake, and an unnatural focus shift occurs. There was a problem that caused it.

An object of the present invention is to obtain a lens drive control device which solves the above problems.

[0029]

SUMMARY OF THE INVENTION The present invention is a lens driving device having the following structure. (1) Guide means for guiding the lens group in one arbitrary direction, lens driving means for driving the lens group along the guide means, lens position detecting means for detecting the lens group position, and the lens group A lens position control means for controlling the position of the lens group based on the output of the lens position detection means, and a loop gain until the lens group reaches a target value vicinity from a position away from the target value By changing the loop gain after reaching, it is possible to smoothly focus without causing a focus shift easily due to a disturbance even after reaching the focus. (2) A voice coil motor is used as the lens driving means.

[0030]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a diagram best representing the features of the present invention. FIG. 1 is a diagram similar to FIG. 9 and shows a signal S ₀ of the peak detection circuit 53 and a signal S ₁ obtained by synchronously detecting the signal S ₀ .

The dotted line K _{1 in} FIG. 1B has a value larger than the inclination of the signal S ₁ near the in-focus point. After the focus is out of focus, the automatic focusing device is made to function, and the current is passed through the voice coil to reach the focus on the solid line K ₂ in FIG. 1B, and then the mode is changed, such as panning or camera shake. When the lens is displaced due to the disturbance, a current is passed through the voice coil along the dotted line K ₁ in the figure.

As a result, the focus lens is fixed at the in-focus position, and it is possible to make a system in which the focus is not easily blurred even by some disturbance.

FIG. 2 shows a block diagram of a control circuit 80 as a lens position control means for driving the voice coil motor and stabilizing the lens group at the target position.

When the lens group is driven and the target value to be positioned is input, the input voltage is the phase compensation filter 81.
The voltage / current conversion circuit 82 converts the current i into a current i by the resistance R determined by the voice coil, and the current / thrust conversion circuit 83 further converts the current i into a thrust f determined by the magnetic flux density of the magnet and the coil effective length.

The voice coil motor 84 operates in response to the output of the current / thrust conversion circuit 83, and drives the lens in the optical axis direction according to the output x. The driven lens position is measured by an encoder (sensor) 85 according to a certain sampling cycle, and a voltage V corresponding to the measurement result is output.

This voltage output is multiplied by the loop gain K in the multiplier 86, then compared with the target value in the adder / subtractor 87, and the voltage of the difference is added to the phase compensation filter 81. FIG. 3 shows how the lens position is settled to the target value within a certain fixed time.

In the above, when the lens is driven by the voltage value, the voltage is kept constant and the means for driving the lens by the periodic rectangular wave is shown. That is, in the figure, when the target value is farther than the current position, T3 in FIG. 3, the duty (L ₁ / L ₂ ) of the rectangular wave becomes large, and in the case of T1 in FIG. The duty (L ₁ / L ₂ ) becomes smaller. That is, in FIG. 2, it is possible to drive the lens by the voice coil motor while changing the duty ratio by the difference between the target value and the current value.

In this case, since the motor speed increases or decreases depending on the difference between the target value and the current value, the lens position shift with respect to the lens position at that time is read by the position encoder after reaching the in-focus position, and the motor is moved to the in-focus position. The return speed can be easily determined.

Since the ratio of the return speed can be arbitrarily set in advance, focusing is achieved by setting the gain to be larger than the gain when the automatic focusing device is used. It is possible to easily obtain a stable image without any focus shift even after the exposure.

In the above two embodiments, the present invention is implemented with respect to the defocusing of the focus lens group in the lens group. However, as a position fixing system for the variator lens group 61b in FIG. 9, an encoder is used. When the lens group is positioned in the vicinity of the target value in accordance with the output of 51, the objective can be achieved by having a loop gain higher than that in the case where the lens group is controlled to be positioned from the position farther than the target value. ..

Further, the present invention is not limited to the positioning of the lens group in the direction of the optical axis, but is similarly applicable to the case of controlling the lens group and the lens system main body at positions decentered or inclined with respect to the optical axis of the lens system main body for image stabilization. By controlling by changing the loop gain, the lens can be stably fixed to the target value.

[0042]

As described above, according to the present invention,
Since the motor gain for returning the lens to the in-focus position after reaching the in-focus position is larger than the motor gain until the lens group reaches the in-focus position, the focus lens is stabilized near the in-focus position. It is possible to obtain the effect that the focus is not displaced due to a disturbance such as panning or camera shake.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a signal that determines a voice coil motor drive speed in a lens drive control device of the present invention.

FIG. 2 is a block diagram showing a drive circuit of a voice coil motor in the lens drive control device of the present invention.

3 is an explanatory diagram of a transient response in the device of FIG.

FIG. 4 is a vertical sectional view showing a lens barrel of a conventional zoom lens for a video camera.

5 is a vertical cross-sectional view taken along the line AA of FIG.

FIG. 6 is a transverse sectional view of a conventional lens barrel to which a voice coil motor is applied.

7 is a vertical sectional view taken along the line BB of FIG.

FIG. 8 is an exploded perspective view showing another example of a conventional lens barrel to which a voice coil motor is applied.

FIG. 9 is a configuration diagram of a video lens system to which a voice coil motor is applied.

FIG. 10 is a diagram showing a cam locus of a rear focus zoom.

FIG. 11 is a diagram showing each signal of an autofocus system using a video signal.

[Explanation of symbols]

 61a-61d Lens group 69a, 69b Guide rod (guide means) 80 Lens position control means (control circuit) 84 Voice coil motor (lens drive means) 85 Sensor (lens position detection means)

Claims (2)

[Claims] 1. A guide means for guiding the lens group in one arbitrary direction, a lens driving means for driving the lens group along the guide means, a lens position detecting means for detecting the lens group position, and A lens position control means for controlling the position of the lens group based on the output of the lens position detection means, and a loop gain until the lens group reaches the vicinity of the target value from a position farther from the target value and the target value. A lens drive control device characterized in that a loop gain after reaching a vicinity is different. 2. The lens drive control device according to claim 1, wherein a voice coil motor is used as the lens drive means.