JPH01248145A - Lens driving method for optical device - Google Patents

Abstract

PURPOSE:To remove the influence of the play of a lens driving system and to accurately control a lens to a target position by moving the lens in a predetermined constant direction without fall right before the lens stops at the target position. CONSTITUTION:A CPU 46 detects the current position (x) of the lens 20 from a motor 58 and drives the motor 58 while regarding a position (x-a) which is a distance (a) below the position (x) as the target position. Then the CPU 46 sets the target position (a) above next and elevates the lens 20. Thus, the target position is lowered by (a) and raised by (a) to place the lens 20 at the lower-limit position of the movable range of the play of the driving system, and this position is stored as the operation start position x2 of the lens 20. Consequently, there is no error wherever in the movable range of the play of the driving system the lens is right before automatic focusing operation is started.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a lens driving device that uses a motor to move a projection lens of an optical device such as a microfilm reader.

(Technical Background of the Invention) There are optical devices such as microfill readers in which a projection lens is moved by a motor. For example, an autofocus device that calculates the contrast of an image from an image read by an image sensor such as a line sensor, detects the lens position where this contrast is maximum, and moves the lens to this position (focus position) using a motor. is publicly known.

In this case, since there is play in the lens drive system, even if the motor position exactly matches the target position, the lens position does not necessarily match the target position. As a result, the reproducibility of the position deteriorates, resulting in the problem that the lens position cannot be controlled with high precision.

The play in the drive system can be roughly divided into errors in the optical axis direction of the lens and errors in non-optical axis directions (tilt direction). It is clear that the former error directly affects autofocus accuracy. Furthermore, the latter error causes image movement during autofocus operation. In other words, autofocus operation first confirms that an image suitable for autofocus is projected onto the image sensor, and then moves the lens to obtain a contrast signal. However, if the lens is tilted, the lens The image will move while the lens is moving, and contrast signals may be obtained for different images while the lens is moving, or the image may disappear. Therefore, the tilt error of the lens significantly reduces autofocus accuracy or makes autofocus operation impossible.

On the other hand, it is also possible to control the motor without detecting the lens position with high precision using a position detector such as a linear encoder and feeding it back to the motor, but in this case an expensive position detector is required. Therefore, there is also the problem that the number of parts increases.

(Object of the Invention) The present invention has been made in view of the above circumstances, and it is possible to match the lens position with the target position with high precision without using an expensive position detector to detect the lens position. An object of the present invention is to provide a lens driving device for an optical device.

(Structure of the Invention) According to the present invention, the object is to provide a projection lens driving device for an optical device in which a projection lens is moved to a target position by a motor, in which the lens moving direction immediately before stopping at the target position is determined in advance. This is achieved by a lens driving device for an optical device, which is characterized in that the lens driving device is configured to drive the lens in a fixed direction.

(Example) Fig. 1 is an overall diagram of a microfilm league using an embodiment of the present invention, Fig. 2 is an output waveform diagram of each part thereof, and Fig. 3 is a diagram showing the change in contrast signal with respect to the lens position and the movement process of the lens. FIG. 4 is a flowchart showing the operation.

In FIG. 1, reference numeral 10 is a light source, and the light from this light source 10 is transmitted to a condenser lens 12, a heat-insulating glass 14, a cold mirror 16, a microfilm 18, a projection lens 20,
Transmissive screen 28 via mirrors 22, 24, 26
The microfilm 18 is placed on this screen 28.
Forms an enlarged image of

A part of the projected image passing through the projection lens 20 is a half mirror.
30, and is guided to a line sensor 34 via a lens 32. This lens 32 is the screen 28
The focal length is determined so that the image is formed on the line sensor 34 when the image is focused. The image signal a, which is the output of the line sensor 34, undergoes signal processing such as correction for variations in each pixel, and then is input to a bandpass filter 36, and is further input to a rectifier circuit 38. The signal is input to the CPU 46 via the integrating circuit 40, the A/D converter 42, and the input interface 44. Projection lens 2
The type of 0 is detected by the sensor 48, and the signal is CP
Input to U46. 50 is ROM, here is C
A program for the PU 46 and data for each type of lens 20, such as depth of focus, are stored in advance. 5
2 is a RAM, and 54 is an output interface.

58 is a motor that moves the projection lens 20 on the optical axis; 6
0 is a motor that moves the line sensor 34 in a direction perpendicular to the optical axis, and these motors are composed of a stepping motor, a servo motor, or the like.

Next, the operation of this embodiment will be explained based on FIG. 4.

The CPU 46 detects the current position χ of the lens 20 from the motor 58, and drives the motor 58 with a position (χ-a) located a distance 1ila below this position χ as the target position (FIG. 4, Step Zoo). In this embodiment, the lens 20 is moved upward and then stopped, but if this is done, the weight of the lens 20 causes the lens 20 to descend due to play in the lens drive system, and its position changes. This can be prevented. Further, the distance a is set to be sufficiently larger than the movement distance of the lens 20 due to play in the drive system. This downward movement of the lens 20 corresponds to part A in FIG. The CPU 46 then sets the target position upward by a and raises the lens 20 (step 102). This operation corresponds to part B in FIG.

By performing the operation of step 1OO1102 after lowering the target position by a and then returning it upward by a, the lens 20 can be placed at the lower limit position of the movable range due to play in the drive system, and this position can be The operation start position of the lens 20 is memorized as ←. As a result, no error occurs even if the lens position is anywhere within the movable range due to play in the drive system immediately before starting the autofocus operation. Furthermore, since the above-mentioned lens tilt error can be absorbed by this series of operations, there is no movement of the image during autofocus operation. As a result, even if the lens is manually moved in the opposite direction and then stopped, image movement due to play in the drive system can be corrected.

In this way, by steps 100 and 102, the lens 20
After initializing the position, the CPU 46 moves the line sensor 34 (step 104) and positions it within a predetermined focus zone (step 106). is moved until it enters a focus zone with an image suitable for autofocus operation (step 108).
). The presence or absence of an image can be determined by, for example, whether the number of black and white inversions of the image is greater than a certain value. Note that before starting this focus zone determination operation, it is determined whether the amount of light received by the line sensor 34 is appropriate, and the amount of light from the light source 10 is changed.
Of course, the amount of light received can be adjusted by changing the driving pulse period of the line sensor 34 and changing its accumulation time. If there is a suitable image, the CPU 46 lowers the target position of the lens 20 by l+a) (step 110). The text here shows the lens 2 necessary to obtain the contrast signal C5.
As shown in FIG. 3, the lens position χ0 (focus position) at which the contrast signal C3 is at its maximum is always set within the range of 2fL. This distance varies depending on the focal length and type of lens 20,
R in advance according to the type of lens 20 detected by the sensor 48.
It is determined by reading the corresponding data from the data stored in the OM50. This lens lowering operation corresponds to section C in FIG.

Next, the CPU 46 sets the target position of the lens 20 to 2(fL+a
) and increase it (step 112). CP during this time
U46 continues to obtain the contrast signal C5 one after another, and obtains a curve representing the contrast signal C5 with respect to the lens position χ, as shown in the upper part of FIG. This operating range corresponds to section D in FIG.

The image signal a of the line sensor 34 is filtered through the bandpass filter 3
6, a predetermined spatial frequency component is extracted and output (see Fig. 2), and this output is further connected to a rectifier circuit 38.
The signal is full-wave rectified to form waveform C. This output waveform C
is integrated, and this integrated value becomes the contrast signal C3.

This contrast signal C5 is stored in the RAM 52, and this operation is repeated while moving the lens 20 (step 1
12).

When the above operations are performed for the entire range of 2(jl+a), the CPU 46 determines the lens position χ0 at which the contrast signal C8 stored in the RAM is maximized (step 114).

The CPU 46 only needs to align the lens 20 with the obtained focus position χG, but at this time the CPU 46 moves the lens 20 in the upward direction just before the lens 20 stops at the focus position χ0. Control. That is, CPU46
is the distance 1 from the lens position to the focus position χO at this time!
l1m is determined, and the position lowered by (m+a) is set as the target position (step 116). The operation at this time corresponds to part E in FIG. Then, the CPU 46 again sets the target position above a and moves it (step 118, section F in FIG. 3). As a result, the lens 20 can reach the target position χO while moving from the bottom to the top. In other words, the lens position χl at the start of operation and the lens position during the determination of the contrast signal C5 are both positions determined when the lens 20 is at the lower limit position due to play in the drive system, and therefore the determined target position χ0 is also This is when the lens 20 is at the lower limit position of this play. Therefore, if the lens 20 is raised to reach the target position χ0 while keeping the lens 20 at the lower limit of play, highly accurate position control can be achieved. This operation mainly absorbs the error in the optical axis direction among the two types of errors in the lens drive system described above.

When this operation is completed, the CPU 46 returns the line sensor 34 to the reference position and all operations are completed (step 12).
0).

In this way, in the overall control sequence, the lens moves an extra amount a, and the time required for the operation increases by that amount, but compared to the overall operation time, this time increase is very small, and the machining process Significant cost reductions can be expected compared to other methods, such as increasing precision and reducing play in the drive system. Note that step 100.10
2 may proceed at the same time as starting to move the sensor, step 120 is step 114.116.11
If it is executed in parallel with 8, the time required for the operation can be further shortened.

Although the above embodiment is applied to an autofocus device that sets the target position to the focus position χ0, it goes without saying that the present invention can also be applied to systems in which the target position is set manually or by other means. , including things like this.

Furthermore, in this embodiment, the focus position χ0, which is the target position, is determined as the position with the maximum contrast in one scan of the line sensor 34, but it goes without saying that the focus position χ0 may be determined using other methods. For example, - the scanning section may be divided into a plurality of sections, the contrast signal for each section may be obtained separately, and the focusing position χ0 may be determined as the average value of these, for example, based on the lens position where each contrast signal is maximum. .

In this embodiment, the lens is moved from bottom to top and then stopped, but it goes without saying that in the present invention, the lens may be moved from top to bottom and then stopped. However, in general, it is more convenient to use the direction that opposes the weight of the lens as a reference, as this often improves accuracy and prevents the lens from moving when the power is turned on and off.

Although the optical axis direction was vertical in this embodiment, the optical axis may be set horizontally or in other directions. Of course, the same effect can be obtained by absorbing the play and applying the present invention.

Furthermore, the present invention is applicable not only to microflume readers but also to various optical devices such as copying machines and cameras, and includes these.

(Effects of the Invention) As described above, the present invention always moves the lens in a predetermined direction immediately before stopping at the target position, so the influence of play (backlash) in the lens drive system can be reduced. The structure is simple because the lens can be controlled to the target position without any interference, and the lens can be controlled by detecting only the motor rotational position without using a position detector to detect the lens position.

[Brief explanation of the drawing]

FIG. 1 is an overall diagram of a microfilm reader using an embodiment of the present invention, FIG. 2 is a diagram of output waveforms of each part thereof, and FIG. 3 is a diagram showing changes in contrast signal with respect to lens position and lens movement process. FIG. 4 is a flowchart showing the operation. 20... Projection lens, 34... Line sensor, 46... CPU, χ0...
・Focus position as target position. Patent applicant Fuji Photo Film Co., Ltd. Agent Patent attorney Yama 1) Yu Fumi (1 other person) Figure 1 Figure 2 Figure 3 Figure 4

Claims (2)

[Claims] (1) A projection lens driving device for an optical device in which a projection lens is moved to a target position by a motor, characterized in that the lens movement direction immediately before stopping at the target position is a predetermined constant direction. A lens driving device for an optical device. (2) The lens drive device for an optical device according to claim (1), wherein the projection lens is moved in the vertical direction, and the lens movement direction immediately before the lens stops is set upward.