JPH0197910A - Focus position control method for focusing lens - Google Patents

Abstract

PURPOSE:To control the focus position with a high precision by driving a motor with a reverse supply voltage to fix the energy before switching from driving with the supply voltage to driving with a constant voltage. CONSTITUTION:A driver 5 is provided with a changeover switch which switches the voltage output of a battery 8 to both of positive and negative polarities to give it to a motor 4, and this changeover switch is controlled by the switching command of a microcomputer 6. The motor 4 is driven with the supply voltage up to an extent of motor rotation corresponding to a target rotation controlled variable determined by a distance measured value, and the supply voltage is applied to the motor 4 with the opposite polarity only for time corresponding to the extent of motor rotation, and the motor 4 is driven with the constant voltage only in the remaining section of the rotation controlled variable. Thus, the focus position is controlled with a high precision independently of the rotation controlled variable.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an autofocus camera, and more particularly to a focus position control method for moving a focus lens to a focus position.

-Background of the Invention- In an autofocus camera, when photographing, a distance measuring system automatically measures the focal length to a subject, and the focus lens position is moved in the optical axis direction according to this measured value.

The focus lens is controlled by a motor between the shortest focus position and the infinite focus position.

FIG. 3 shows a focus lens position control device. The focus lens 1 is supported slidably in the optical axis direction P, and its position in the optical axis direction P is adjusted by a feed rod 2 fixed to the connecting portion IA. That is, the feed rod 2 has a threaded portion 2a that engages with the internal thread of the reduction gear 3, and therefore the feed rod 2 is moved in a direction parallel to the optical axis direction P by the rotational movement of the reduction gear 3 rotated by the DC motor 4. sent to. In other words, the amount of rotation of this motor 4 is the amount of rotation of the focus lens 1.
is proportional to the amount of drive. The motor 4 is turned on and off by a driver 5, and an on/off command is given from a microcomputer 6. The rotational speed of the motor 4 is detected by the photointerrupter 7 as a pulse number. The microcomputer 6 controls the unidirectional (forward) rotation amount of the motor 4 by comparing the rotation amount of the motor 4 determined from the distance measurement value with the number of output pulses of the photointerrupter 7 . In other words, since feedback control based on position detection of the focus lens 1 and forward/reverse control of the motor complicate the position detection means and control circuit, the focus lens 1 can only be detected based on the amount of rotation of the motor 4 in one direction.
The position of the robot is controlled.

In such unidirectional open loop control, cutting off the power to the motor 4 when the amount of rotation of the motor 4 reaches a value (rotation control amount) corresponding to the measured distance value will cause fluctuations in battery voltage and The position error due to the difference in inertia of the mechanisms increases. Therefore, conventionally, a control method has been adopted in which the rotation amount of the motor 4 is decelerated when it approaches the rotation control amount.

FIG. 4 shows a time chart of motor applied voltage according to the conventional control method. The microcomputer 6 changes the output voltage of the driver 5 to the voltage vII of the battery 8 at the time of starting control.
At the time t1 when the detected value from the photointerrupter 7 approaches the target rotation control amount, the output voltage of the driver 5 is selected as the stabilizing constant voltage VCC of the constant voltage circuit 9, and the constant rotation period is set at a predetermined rotation amount ( Constant voltage driving is performed until time tz).

With this control method, most of the target rotational control amount is fed at high speed using the high voltage of the battery 8, and when the target position is approached, a stop position corresponding to the rotational control amount is obtained by constant voltage and low speed feeding.

Problems to be Solved by the Invention - In conventional control methods, when controlling the position of the focus lens 1 over a wide range or when allowing a wide range of voltage fluctuations in the battery 8, the constant voltage drive period must be made relatively long. to ensure position control accuracy. In this case, there is a problem in that the battery voltage drive period for high-speed feeding becomes shorter as the constant voltage period becomes longer, and the focusing time from the start to the end of position control becomes longer.

An object of the present invention is to provide a focus position control method that can increase the accuracy of focus position control without increasing focusing time.

Means and operation for solving one problem - In order to achieve the above object, the present invention detects the amount of rotation of a motor that drives a focus lens, and operates the motor in a unidirectional open loop according to the distance measurement value. In an autofocus camera that controls
The motor is driven with the power supply voltage until the motor rotation amount corresponds to the target rotation control amount determined from the measured distance value, and after this, the power supply voltage is applied with the opposite polarity to the motor for a time corresponding to the motor rotation amount. , it is proposed to drive the motor at a constant voltage only during the remaining period of the rotation control amount. .

With this control method, focusing time is shortened by driving with a high voltage power supply voltage, and the motor is braked by applying reverse polarity power supply voltage. Through this braking, the inertia force of the mechanical system such as the motor is almost constant, and the focusing time is kept constant. A certain amount of drive is performed to obtain the target rotation control amount.

One example- Examples of the present invention will be described in detail below.

In the device configuration shown in FIG. 3, the driver 5 is provided with a changeover switch that switches the voltage output of the battery 8 to the motor 4 in both forward and reverse polarities, and this changeover switch is activated by a changeover command from the microcomputer 6. be configured to be controlled.

The microcomputer 6 has a control flow for focusing control as shown in the time chart shown in FIG. The voltage VB of the battery 8 is applied from the control start time t0 to tl. This interval T is determined as the motor rotation amount commensurate with the target rotation control amount obtained from the measured distance value, and the interval T1 is determined by comparison with the rotation amount detection value of the photointerrupter 7. Next, the microcomputer 6 controls the changeover switch of the driver 5 at time 1, and applies the voltage of the battery 8 to the motor 4 with the reverse polarity. This interval T is set in advance as the transmission voltage application time or the rotation amount of the motor 4 according to the motor rotation amount. This reverse voltage section T2 absorbs the inertial force applied to the motor 4, etc., and brakes the motor 4 to a substantially constant energy level. In other words, section T2 is the previous section T1.
The energy is made constant regardless of the target focal position by absorbing energy during the braking period according to the inertial force accumulated in the section T1 corresponding to the magnitude of the amount of movement to the focal position. As a result, in sections T and T2, the voltages are only of opposite polarity, but the voltage level is the same, and it is possible to prevent them from being influenced by voltage fluctuations of the battery 8.

Next, the microcomputer 6 performs constant voltage drive control for the remaining section T of the target rotational control amount described above. Through this section T, the energy made constant in the section T2 is driven to a certain amount of driving distance, and the lens is stopped at the focal position with a target rotational control amount.

In this way, before transitioning from battery voltage drive to constant voltage drive, battery reverse voltage drive is controlled over an interval T approximately corresponding to the rotation control amount.
By performing only 2, accurate position control can be performed regardless of the magnitude of the rotational control amount, that is, the magnitude of the distance to the focusing position, and regardless of fluctuations in battery voltage.

FIG. 2 is a time chart showing another control method of the present invention, in which a constant voltage drive section T3 is followed by a battery reverse voltage drive section T4, and further a braking section T using a low voltage V. be. In this control method, the constant voltage driving section Ts is shortened, the energy required for this shortening is absorbed in the battery reverse voltage section T4, and the constant voltage Va
The brake is applied in +S interval T5 to stop the vehicle at the target position.

In this embodiment, by shortening the constant voltage drive period T3, power loss in the constant voltage circuit 9 can be reduced, and the accuracy of the stop position can be further improved.

Effects of the Invention As described above, according to the present invention, energy is made constant by reverse voltage driving of the power supply before shifting from power supply voltage driving to constant voltage driving, so that the rotation control amount is not affected by the magnitude of the rotation control amount. In other words, it is possible to achieve accurate focusing control while widening the focal position control range, and has the effect of widening the battery (power supply) voltage fluctuation, that is, the voltage tolerance range.

[Brief explanation of the drawing]

Fig. 1 is a time chart showing one embodiment of the control method of the present invention, Fig. 2 is a time chart showing another embodiment, Fig. 3 is a configuration diagram of a focus lens position control device, and Fig. 4 is a conventional control method. 3 is a time chart showing a control method. 1...Focus lens, 4...DC motor, 5.
...Driver, 6...Microcomputer, 7...
- Photo interrupter, 8... battery, 9... constant voltage circuit. Figure 1 Figure 2 Figure 3 Figure-5 (

Claims (1)

[Claims] 1) In an autofocus camera that detects the amount of rotation of a motor that drives a focus lens and performs unidirectional open loop control of the motor according to the measured distance value, target rotation control determined from the measured distance value. The motor is driven with the power supply voltage until the motor rotation amount corresponds to the motor rotation amount, and then the power supply voltage is applied with the opposite polarity to the motor for a time corresponding to the motor rotation amount, and after this, the remaining rotation control amount is A method for controlling a focus position of a focus lens, characterized in that the motor is driven with a constant voltage only in a section. 2) In an autofocus camera that detects the rotation amount of the motor that drives the focus lens and performs unidirectional open loop control of the motor according to the measured distance value, the motor rotation corresponds to the target rotation control amount determined from the measured distance value. The motor is driven with the power supply voltage until the amount of rotation is reached, and then the power supply voltage is applied to the motor with the opposite polarity by a rotation amount corresponding to the rotation amount of the motor, and after this, the motor is driven for the remaining section of the rotation control amount. A method for controlling the focal position of a focus lens, characterized by driving it with a constant voltage.