JPH0821944A - Lens driving device - Google Patents

Abstract

PURPOSE:To realize braking control proportional to moving speed by using only information on a lens position in a lens driving device using a voice coil motor. CONSTITUTION:A last detection value Vs<-1> is compared with a present detection value Vs by means of a position sensor (S25), and whether the lens position is changed by minimum changing amount or not is discriminated (S26). The value of a counter is increased for every controlling period in the case where the lens position is not changed (S27). On the other hand, when the lens position is discriminated to be changed (S27), the reciprocal of the count number so far is regarded as a value corresponding to the lens moving speed, a value obtained by multiplying the reciprocal by a constant A is subtracted from the value of the controlling signal Vo of the voice coil motor, and the braking proportional to the moving speed is applied (S28).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens driving device,
More specifically, the present invention relates to a technique for correcting drive control in accordance with the moving speed of a lens in the control of moving the lens to a target position.

[0002]

2. Description of the Related Art DC motors and stepping motors have been conventionally known as actuators for driving lenses for focusing and zooming in video cameras, still cameras and the like, but in recent years, voice coil motors have been used. Those have been developed (see Japanese Patent Laid-Open No. 4-25811, etc.).

In the voice coil motor, a ring-shaped coil and a ring-shaped magnet magnetized in the radial direction of the center are concentrically provided. When an electric current is applied to the coil, the voice coil motor operates according to Fleming's left hand rule. The linear motor is an actuator that uses a coil to move by receiving a force in the axial direction, and is a linear motor that moves a lens supporting member that fixes the coil in the optical axis direction by controlling energization of the coil.

In the lens driving device using the above voice coil motor, since the torque generated by the motor can be directly used for driving the lens, there is an advantage that the power consumption is low and the driving speed is high, and the lens supporting member is used. Since it can be integrated with a motor, there is an advantage that the lens barrel can be made smaller and lighter. However, in the lens driving device using the above voice coil motor, there is no stable position of the lens when not energized and the lens cannot be mechanically held at a certain position. It is necessary to control the drive coil so that it stays at that position after the stop, and in the related art, the above-described control has been performed by the following configuration.

FIG. 6 shows a system block diagram of a conventional lens driving device in which a voice coil motor is applied to drive a focusing lens in a video camera, and FIG. 7 shows a control block diagram thereof (Technical Report of the Television Society).
Vol.17 no.5 pp. 21-26 "Development of linear motors for video cameras"). In FIG. 6, the image formed on the CCD 7 through the photographing lens group 1 including the zoom lens 2 and the focusing lens 3 is the image pickup circuit 8,
The signal is output to the microcomputer 11 via the AF (autofocus) signal detection circuit 9 as a signal corresponding to defocus.

The microcomputer 11 shows the focus shift signal (autofocus signal), the zoom lens position information, the focusing lens position information, and the relationship between the object distance and the focusing lens with respect to the zoom lens position stored in advance. Based on the information in the data table to represent
A target position to move the focusing lens for focusing is calculated, and further, a coil energization control signal is calculated. Then, the drive coil 4 is energized via the focus drive amplifier 12 to drive the focusing lens 3 to the target position.

The position information of the focusing lens is read from the focusing lens position sensor 6 into the microcomputer 11 via the amplifier 15. When the user of the video camera operates the zoom switch 16, the microcomputer 11 controls the step motor 18 via the zoom motor driver 17 to drive the zoom lens 2. Also, the zoom lens 2
In order to correct the focal position which changes according to the position change of the target lens, the target position to move the focusing lens 3 is calculated from the information of the data table, and the focusing lens 3 is driven to the target position. .

In FIG. 6, 5 is a yoke and 13 is a magnet, and the drive coil 4, the yoke 5 and the magnet 13 constitute a voice coil motor as a lens driving actuator. In addition, in FIG.
Is a zoom lens starting point sensor that detects whether or not the zoom lens 2 is at the starting point position. FIG. 7 shows the microcomputer 11
6 is a block diagram of a control algorithm after the target focusing lens position Vx is determined by.

As shown in FIG. 7, a control signal corresponding to the deviation between the target focusing lens position Vx and the actual focusing lens position Vs is corrected by friction compensation or the like and output from the microcomputer 11 to the drive amplifier 12. To be done. Further, in order to prevent the influence of the oscillation phenomenon in the high frequency region while taking advantage of the high speed of the linear motor, braking feedback proportional to the lens moving speed is applied, and the braking feedback uses the speed detection coil 14. Then, the generated electromotive force is output to the lens drive amplifier 12.

With respect to the speed detecting coil 14, a bar magnet fixed to the lens holding member moves in the coil relative to the movement of the lens, and the bar magnet moves. The change rate of the magnetic flux generated by the coil, that is, the induced electromotive force according to the moving speed of the lens
It is supposed to occur in 14. In FIG. 7, Kp
Is proportional gain, Ki is integral gain, Kc is circuit gain,
Kv is a velocity feedback gain, T is a circuit time constant, and S is a Laplace variable.

[0011]

By the way, according to the above-mentioned conventional system, the speed detecting coil 14 is used to apply the braking feedback proportional to the moving speed of the lens.
As a result, in order to control the drive of the lens, the speed detection coil is required in addition to the position sensor, which causes a problem of cost increase.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a low-cost lens driving device without impairing the high speed of the linear motor.

[0013]

Therefore, the lens drive device according to the invention of claim 1 controls the lens drive means to move the lens to the target position based on the position of the lens detected by the lens position detection means. A moving speed detecting means for detecting the moving speed of the lens based on the information of the lens position detected by the lens position detecting means, and a moving speed detected by the moving speed detecting means. Correction control means based on a moving speed for correcting the control of the lens driving means by the control means,
Is provided and configured.

In the lens driving device according to the second aspect of the present invention, the lens driving means drives the lens by the voice coil motor. In the lens driving device according to the invention of claim 3, the time until the moving speed detecting means detects that the lens position has changed by a predetermined unit change amount is set as the moving speed of the lens. It is configured to measure as a corresponding value.

In the lens driving device according to the fourth aspect of the present invention, the predetermined unit change amount is set to the minimum change amount detected by the lens position detecting means. In the lens driving device according to the fifth aspect of the present invention, the time until it is detected that the lens position has changed by a predetermined unit change amount is set as the count value of the counter that is counted up every control cycle of the control means. It is configured to measure.

[0016]

According to the lens driving device of the first aspect of the present invention, there is provided means for detecting the lens position, but not means for directly detecting the moving speed of the lens.
The moving speed of the lens is detected based on the information on the lens position. Then, the lens drive control is corrected according to the moving speed of the lens, and the braking control and the like according to the moving speed of the lens are enabled.

In the lens driving device according to the second aspect of the present invention, the lens is driven by the voice coil motor, so that the lens can be driven at high speed and the lens barrel can be made small and lightweight. On the other hand, the lens position can be held and braked by the control correction according to the moving speed. In the lens driving device according to the invention of claim 3, the moving speed of the lens is detected by measuring the time required for the lens position to change by a predetermined unit change amount, and the speed is calculated as the reciprocal of the time. In addition to the above, the lens position detecting means does not require high resolution.

In the lens driving device according to the fourth aspect of the present invention, the predetermined unit change amount for measuring the time is set to the minimum change amount that can be detected by the lens position detecting means, and the detection performance of the lens position detecting means is maximized. It is possible to detect the moving speed by demonstrating the above. In the lens drive device according to the invention of claim 5, by counting up the counter for each lens drive control cycle, the time is simply measured by the count value of the counter. I did it.

[0019]

Embodiments of the present invention will be described below. Figure 1
FIG. 6 shows a system block diagram of one embodiment, and FIG.
The same components as the components shown in FIG. In the lens driving device shown in FIG. 1, a microcomputer 11 (control means) uses a focusing lens position sensor to move a focusing lens 3 to a focus position by a voice coil motor (lens driving means) including a driving coil 4 and a magnet 13. 6 (lens position detecting means) controls the energization of the drive coil 4 in accordance with the deviation between the actual position of the focusing lens 3 and the target position.

However, in the structure of the present embodiment shown in FIG. 1, the speed detecting coil 14 shown in FIG. 6 is not provided, but only the focusing lens position sensor 6 is provided, and the drive amplifier 12 is provided. The braking feedback control for is not performed. The position sensor 6 is composed of a tilted magnet whose tip portion is tilted, and a Hall element which is arranged so as to face the tilted portion of the tilted magnet.
The magnetic flux density from the inclined magnet with respect to the Hall element changes in accordance with the movement of the, the output voltage from the Hall element changes, and this voltage corresponds to the position of the focusing lens 3.

Since the change in the output voltage of the Hall element is in a linear relationship with the change in the position of the tilting magnet installed in the focusing lens frame, that is, the change in the position of the focusing lens, if the output voltage of the Hall element is A / D converted. ,
The minimum unit of position control is, for example, an A / D converter with an 8-bit A / D converter for a total moving amount of the focusing lens of 5 mm.
When converted, it becomes 5 mm / 256 = 19.5 μm. The position sensor is not limited to this, and may be a method of detecting electrically or optically, and the sensor output change need not be an analog amount of the moving amount of the focusing lens, and the sensor output May be directly output as a digital quantity. It goes without saying that, when the sensor output is a digital value, the minimum unit of position control is the minimum unit of the digital output of the sensor.

Here, the lens drive control in the lens drive device shown in the system block diagram of FIG. 1 is performed as shown in the flow chart of FIG. First, after performing various types of initialization processing (S1), it is determined whether or not the zoom switch 16 has been operated (S2),
When the zoom switch 16 is not operated, the change of the autofocus signal (focus position) is detected based on the signal from the AF signal detection circuit 9 (S3).

Then, a data table showing the autofocus signal, the zoom lens position information, the focusing lens position information, and the relationship between the object distance and the focusing lens position with respect to the zoom lens position stored in advance (see FIG. 4). ), The target position Vx of the focusing lens to be moved for focusing is calculated (S4), and the drive coil 4 is energized via the focus drive amplifier 12 according to the target position Vx,
The focusing lens 3 is driven to the target position (S
5).

On the other hand, when the zoom switch 16 is operated, the zoom direction is detected (S6), and further, as shown in FIG.
By referring to the data table as shown in (S7), the correction target position of the focusing lens 3 by the zoom operation is calculated (S8). Then, the zoom lens 2 is driven according to the operation of the zoom switch 16 (S9), while the focusing lens 3 according to the corrected target position Vx.
Is driven (S10).

That is, in any case, the target position Vx of the focusing lens 3 calculated by the microcomputer 11 is calculated, and a voltage proportional to the difference voltage between this target position Vx and the actual focusing lens position Vs is applied to the drive coil. The focusing lens 3 is moved by applying the voltage to No. 4 (see FIG. 3). However, the mechanism for moving the lens has frictional resistance, and external forces such as gravity, acceleration of the entire lens, and vibration are applied depending on the attitude of the lens. Integral compensation and friction compensation are applied to (see FIG. 3).

By the way, unless the microcomputer processing is performed at a speed higher than the moving speed of the lens, the lens drive cannot be stably controlled. Therefore, in this embodiment, the lens moves at the maximum speed. Also, the motor driving routine (control means) shown in the flowchart of FIG. 5 is executed a plurality of times per unit time while the position of the focusing lens 3 moves by the minimum unit (minimum change amount) in detection. is there. That is, even if the lens moves at the maximum speed, the motor drive routine must be set to be executed a plurality of times before the detected value of the lens position shows the minimum step change (minimum change amount). is there.

Therefore, the number of times the motor drive routine is executed while the movement of the minimum unit is detected is
This corresponds to the time required for the lens to move by the minimum change amount, and the reciprocal of this time corresponds to the moving speed of the focusing lens. Therefore, in the present embodiment, according to the motor driving routine shown in the flowchart of FIG. 5, the braking feedback proportional to the lens moving speed is performed in the lens drive control without directly detecting the moving speed by the speed detecting coil. 3)).

The flow chart of FIG. 5 is as described above.
Even when the lens moves at the maximum speed, it is designed to be executed at every minute time such as a plurality of times while the position of the focusing lens 3 moves by the minimum detectable change amount. First, the current position Vs of the focusing lens 3 detected by the focusing lens position sensor 6 is read (S21).

Then, the deviation between the target position Vx and the current position Vs is calculated (S22), and the integral gain (S23) and friction compensation (S24) are added to this to set the output Vo to the drive coil 4. (See FIG. 3). On the other hand, by comparing the current position Vs detected this time with the position Vs _-1 detected and stored in the previous execution of this routine (S25), it is determined whether or not the position of the focusing lens 3 has changed. Is determined (S26).

In the present embodiment, even if the lens moves at the maximum speed, the routine is set to be executed a plurality of times during the period in which the position information read by the microcomputer 11 shows a step change. During the execution cycle of this routine,
Since the lens position does not change beyond the minimum unit for detection, if the change in the lens position is determined in S26, it means that the lens has moved by the minimum unit.

When the movement of the focusing lens 3 is not discriminated, the counter is incremented by 1 (S27) and the output Vo is output to the drive coil 4 via the drive amplifier 12 (S31). On the other hand, when the movement of the focusing lens 3 is discriminated (S26), the number counted by the counter until then is the focusing lens 3
Corresponds to the time required to move by the minimum unit, that is, the moving speed of the focusing lens 3,
A value obtained by multiplying the reciprocal of the number counted by the counter by the speed feedback gain A is subtracted from the output Vo to correct and set the output Vo in the braking direction (S).
28: moving speed detection means, correction control means by moving speed).

The speed feedback gain A is an absolute value | Vx-Vs | of the difference between the current position Vs and the position command Vx.
It can be considered as the degree of braking, and is large when | Vx−Vs | is small and conversely is small when it is large. In other words, when issuing a position command, if the current position is close to the target position, control is performed while braking so that the speed does not exceed the necessary speed so as not to pass the target position. When the current position is far from the position, little or no braking is applied, the command proceeds from the current position at which the command is issued to the target position at the highest speed, and the amount of braking gradually increases as the target position is approached. Try to reach the target command position while reducing the speed. If the braking amount of this speed (speed feedback gain A) is too small, it will have to pass once again and return again, and it will repeat again for a while, so the lens vibrates before and after the target position and it will be difficult to reach the target position. This speed feedback gain A is a very important value in the sense of performing appropriate control, because it cannot be reached, or if it is too large, it does not reach the target position and it takes more time than necessary. This A is
S28 in the motor drive routine of FIG.
It is used in the above, but not shown here,
When x-Vs | is very large and A = 0, another branch may be provided before this S28 so that S28 can be skipped, which requires less time for this motor drive routine.

Then, by resetting the counter to zero (S29), the time required until it is detected that the focusing lens 3 has moved by the minimum unit for detection is executed. Be counted as a number of times. Further, the position Vs of the focusing lens 3 detected this time is set to the previous value Vs _-1 (S3
0), so that the next change in position is determined based on the current position.

Thus, in this embodiment, the position sensor 6
The number of times the coil driving routine is executed until the position of the focusing lens 3 detected by (3) is changed is counted, and the moving speed of the lens 3 is detected by the counted value. Then, the output Vo is corrected and set so that braking is applied according to the detected moving speed, and the drive amplifier is set.
It is configured to be output to 12, and the output has been subjected to braking feedback at the stage of being input to the drive amplifier 12.

Therefore, it is not necessary to provide a speed detecting coil in order to apply braking feedback in the control of the voice coil motor, and the lens moving speed is counted up by the counter counted every cycle of the control routine. Position sensor 6 because it is detected by the measurement result
As a result, a high resolution is not required, and the braking feedback can be realized at low cost.

That is, in the case of a configuration in which the amount of change in position per constant time is calculated and the moving speed is obtained based on the amount of change, the resolution of the position detecting means including the position sensor 6 and the A / D converter. If the value is not high, accurate speed detection cannot be performed, but in the present embodiment, the time required to move by the unit change amount is measured with reference to the unit change amount of the preset position. By sufficiently shortening the execution cycle of the drive routine, the moving speed can be detected with high accuracy.

Further, since the time required for the lens to move by the unit change amount is measured by the counter which counts up every control cycle, it is not necessary to add a new component for time measurement. In addition, the unit change amount that measures the time required for the lens to move is set to the minimum change amount that can be detected in position detection, so that the position detection performance is maximized to detect the moving speed. Can be made.

In the control shown in the flowchart of FIG. 5, braking feedback (speed feedback) is applied only when a change in lens position is detected. It is also possible to adopt a configuration in which braking feedback is applied with an appropriate attenuation characteristic until the detection of. Further, in the present embodiment, the rear focus type zoom lens is used, but it goes without saying that a front focus type zoom lens may be used, or another optical system may be used. Further, in the above, the lens moving speed is calculated by measuring the time with the number of executions of the motor drive routine of FIG. 5, but the measured time is of course an integer multiple of one clock time of the CPU. Therefore, the time during execution of the motor drive routine shown in FIG. 5, that is, the CPU clock is directly counted, which is exactly the same.

[0039]

As described above, according to the lens driving device of the first aspect of the present invention, it is possible to realize the braking feedback according to the moving speed while eliminating the need for a dedicated sensor for detecting the moving speed of the lens. The cost can be reduced by omitting the sensor.

According to the lens driving device of the second aspect of the present invention, since the lens is driven by the voice coil motor, high-speed driving can be performed, and the lens barrel can be made compact and lightweight. Also, braking feedback can be applied to the drive control of the voice coil motor without providing a sensor for detecting the moving speed. According to the lens driving device of the third aspect of the present invention, the moving speed is detected by measuring the time until it is detected that the lens position has moved by the unit change amount.
High resolution is not required for detection of the lens position, and there is an effect that cost increase can be avoided.

According to the lens driving device of the fourth aspect of the present invention, the unit change amount is set to the minimum change amount that can be detected by the position detecting means, so that the detection performance of the position detecting means is maximized. There is an effect that the moving speed can be detected. According to the lens driving device of the fifth aspect of the present invention, since the time measurement is performed by the counter that counts up every control cycle, the time required for the unit movement of the lens movement speed to change the position of the lens does not need to be added. There is an effect that it can be detected as.

[Brief description of drawings]

FIG. 1 is a system block diagram according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an outline of lens drive control in the embodiment.

FIG. 3 is a control block diagram in the embodiment.

FIG. 4 is a diagram showing a zoom correction data table in the embodiment.

FIG. 5 is a flowchart showing speed detection and braking feedback in the embodiment.

FIG. 6 is a system block diagram of a conventional lens driving device.

FIG. 7 is a control block diagram of a conventional lens driving device.

[Explanation of symbols]

 1 Photographic lens group 2 Zoom lens 3 Focusing lens 4 Drive coil 5 Yoke 6 Focusing lens position sensor 7 CCD 8 Imaging circuit 9 AF signal detection circuit 10 Zoom lens origin sensor 11 Microcomputer 12 Drive amplifier 13 Magnet

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location G03B 3/10 13/34 G03B 3/10

Claims (5)

[Claims] 1. A lens driving means for driving a lens, a lens position detecting means for detecting a position of the lens, and a lens for moving the lens to a target position based on the position of the lens detected by the lens position detecting means. In a lens driving device comprising: a control unit that controls the lens driving unit, a moving speed detecting unit that detects a moving speed of the lens based on information on a lens position detected by the lens position detecting unit, A lens driving device, comprising: a moving speed correction control unit that corrects the control of the lens driving unit by the control unit based on the moving speed detected by the moving speed detecting unit. 2. The lens driving device according to claim 1, wherein the lens driving means is a voice coil motor. 3. The moving speed detecting means measures the time until the lens position detecting means detects that the lens position has changed by a predetermined unit change amount, as a value corresponding to the moving speed of the lens. The lens driving device according to claim 1, wherein the lens driving device is a lens driving device. 4. The lens driving device according to claim 3, wherein the predetermined unit change amount is a minimum change amount detected by the lens position detecting means. 5. The lens driving device according to claim 3, wherein the time is measured as a count value of a counter which is counted up every control cycle of the control means.