JP3090779B2 - Lens position detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens position detecting device for detecting a position of a lens fed by a feed screw mechanism, and more particularly to a device for detecting a home position of a movable lens such as a still camera and a video camera.

[0002]

2. Description of the Related Art Conventionally, a mechanism using a feed screw mechanism driven by a stepping motor has been known as a mechanism for automatically extending a lens of a still camera or a video camera.

As shown in FIG. 7, as the feed screw mechanism, a movable portion 13 screwed with the lead screw 12 is provided on a lead screw 12 which is driven to rotate by a stepping motor 11, and is attached to the movable portion 13. lens
There is known a device in which a stepping motor 14 is moved to a predetermined position by a stepping motor 11.

By the way, when such a feed screw mechanism is driven by the stepping motor 11, the movable portion 13
Can be obtained from the number of pulses input to the stepping motor 11 during the feed period. However, the absolute position of the movable portion 13, that is, the lens 14 cannot be known by itself, and the lens 14 is automatically moved to a predetermined position. Is difficult to set.

Therefore, conventionally, a light-shielding plate 15
And a light projecting unit 16 and a light receiving unit 17 are arranged at predetermined intervals at a reference position of the lens (a photo interrupter is formed by the light projecting unit 16, the light receiving unit 17, and the light shielding plate 15). There is known a lens position detecting device which detects whether or not the lens 14 is set at a reference position. That is, when the movable section 13 moves to the reference position, the light from the light emitting section 16 is blocked by the light shielding plate 15 and the light receiving section 17
The amount of received light at is reduced. When the amount of received light decreases below a predetermined threshold level, it is determined that the movable unit 13, that is, the lens 14, is set at the reference position.

In this way, when the camera is started, the lens 14 is set at the reference position, and after that, a number of pulses corresponding to the desired lens position are input to the stepping motor 11 to move the lens 14 to the desired position. Can be set automatically.

[0007]

However, according to the above-described reference position detection technique, the output of the photointerrupter fluctuates due to a change in the ambient temperature, so that the lens position at the time of reaching the threshold level changes. Become.

That is, as shown in FIG. 8, when the ambient temperature is -10.degree.
It has the characteristics shown by the solid line at 50 ° C. and the long dashed line at 50 ° C. Therefore, when the ambient temperature reaches -10 ° C and 50 ° C, the lens position when reaching the threshold level is 30μ.
It will be shifted by about m. Further, the lens is moved from the rear side to the front side, and the position corresponding to the first excitation phase 1 (arbitrarily selected from the four excitation phases of the stepping motor) which is lower than the threshold level is set as a reference. If the position is detected as a position (home position: HP), a position corresponding to the adjacent excitation phase 1 may be detected as a reference position due to a change in environmental temperature. In this case, one pulse of the stepping motor,
That is, if the interval corresponding to one of the excitation phases is 12.5 μm, the detection error of the lens position becomes 12.5 μm × 4, and eventually
The result is a detection error of μm.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and it is an object of the present invention to accurately detect a reference position of a lens fed by a feed screw mechanism using a stepping motor without being affected by a change in environmental temperature. It is an object of the present invention to provide a lens position detecting device capable of performing the above.

[0010]

SUMMARY OF THE INVENTION A lens position detecting device according to the present invention detects whether a lens held by a movable portion of a feed screw mechanism driven by a stepping motor is set at a predetermined reference position. In the detection device, when the rotating plate is set to rotate in synchronization with the rotation of the lead screw portion of the feed screw mechanism, which is screwed with the movable portion, and when the rotating plate is disposed at a predetermined rotation position. And a magnet provided on one of the opposing portions of the rotating plate and the movable portion and a magnet provided on the other, which magnetically affects the Hall element, and Position detection for comparing the detection signal output from the Hall element with a predetermined threshold value and determining whether or not the lens is set to the reference position based on the comparison result. And it is characterized in that consists of stages.

[0011]

According to the above arrangement, the Hall element is provided at one of the positions where the movable portion of the feed screw mechanism and the rotating plate oppose each other, and the magnet is provided at the other position. The output of the Hall element has a peak.

Since this peak value increases as the Hall element approaches the magnet, it is necessary to set a threshold level so as to be a value between the peak value appearing near the reference position and the immediately preceding peak value. By detecting whether or not the threshold level has been crossed, it can be determined that the lens position is near the reference position.

Thereafter, when a predetermined excitation phase (an excitation phase corresponding to the lens reference position is determined in advance) within this peak can be detected first, the lens can be detected at the lens reference position. Can be recognized.

As shown in FIGS. 3 and 6, the peak of the Hall element output has a steep rise as compared with the prior art shown in FIG. Since the difference in peak value between adjacent peaks becomes extremely large, it is easy to set this threshold level so that only the peak value of a desired peak exceeds the threshold level even if the environmental temperature changes.

Therefore, according to the lens position detecting device of the present invention, the reference position of the lens fed by the feed screw mechanism using the stepping motor can be detected with high accuracy without being affected by changes in the environmental temperature. Becomes

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show a lens moving device equipped with a lens position detecting device according to an embodiment of the present invention. That is, the lens moving device includes a stepping motor 1, a lead screw 2 rotated by the stepping motor 1, a screw screwed with the lead screw 2, and an axial direction of the lead screw 2 according to the rotation of the lead screw 2. A movable part 3 that moves to the movable part 3, a shaft of the lead screw 2 attached to the movable part 3, and a lens 4
Lens frame for holding the lens 4 so that the optical axes of the lenses become parallel
4a. The movable section 3 is guided by a guide section (not shown) so that the movable section 3 does not rotate even when the lead screw 2 rotates, and travels straight with high accuracy.

On the other hand, a lens position detecting device mounted on the lens moving device is mounted at the end of the lead screw 2 above the rotary plate 5 coaxially with the lead screw 2 and above the movable portion 3. In addition, a Hall element plate 6 on which the Hall element 6a is mounted, a small magnet (permanent magnet) 7 mounted on the rotating plate 5 at a position facing the Hall element 6a, In response, a detection unit is provided that compares the detection signal output from the Hall element 6a with a predetermined threshold level and determines whether or not the lens 4 is set at the reference position based on the comparison result.

The discriminating unit is a stepping motor 1
The control unit 9 outputs a drive signal to the stepping motor driver based on the discrimination signal from the discrimination unit so as to move the lens 4 by a desired distance. Send to 10.

As shown in FIG. 2, the lens position detecting device includes a Hall output amplifying circuit 8 for amplifying a signal from the Hall element 6a.

As described above, when the lead screw 2 is rotated by the stepping motor 1, the rotating plate 5 is rotated, and the movable part 3 is moved along the lead screw 2.

A detection signal is output from the Hall element 6a at the timing when the small magnet 7 is brought into a state of facing the Hall element 6a with the rotation of the rotary plate 5. That is,
One detection pulse is output each time the rotating plate 5 makes one rotation. This detection signal is a pulse signal that rises as shown in FIG. 3, and the shorter the distance between the small magnet 7 and the Hall element 6a, the larger the peak value of the signal.

Next, the procedure of the operation of determining the reference position in the control section 9 will be described.

First, the lens 4 is moved from the stepping motor 1 side (rear side) toward the rotary plate 5 side (front side) by a drive signal from the control unit 9. As described above, when the lens 4 is moved from the rear side to the front side, a pulse as shown in FIG.
Output from The peak value of the pulse output from the Hall element 6a increases as approaching the reference position.
In the present embodiment, the movable portion stops when it has moved 7 pulses after passing through the reference position, and does not move forward any more.

The output of the Hall element is input to the discriminating section,
It is compared with a predetermined threshold level. As a result of this comparison, a "L" level discrimination signal is output when the Hall element output does not exceed the threshold level, and "H" when the Hall element output exceeds the threshold level.
A level determination signal is output.

By the way, in this embodiment, an initial setting process is performed before the above-mentioned lens is fed forward. This initialization process will be described with reference to the flowchart shown in FIG. That is, it is determined whether or not the determination signal is at "L" level [S1]. If the determination signal is at "L" level, the stepping motor 1 is driven so that the lens 4 moves backward by one pulse [S2]. ], The process of step 2 [S2] is performed [S4] until the movement for 40 pulses is performed (until the lead screw 2 makes one rotation). On the other hand, if the level is "H", the stepping motor 1 is driven so that the lens 4 moves backward by 10 pulses [S3].

In this embodiment, movement for one pulse corresponds to movement for a distance of 12.5 μm.

The reason why the lens 4 is moved rearward by 40 pulses when the signal is at the "L" level is to prevent the lens 4 from being located in front of the reference position in the initial stage.

That is, as described above, since the lens 4 moves forward from the reference position by less than one rotation of the lead screw 2, this processing operation [S
2, S4], the lens 4 is always located behind the reference position in the initial stage.

The reason why the lens 4 is moved rearward by 10 pulses when the level is at the "H" level is to eliminate backlash between the lead screw 2 and the movable part 3.

After such initial setting processing, the main processing of the reference position determination operation is performed. In this processing, as shown in the flowchart of FIG.
The stepping motor 1 is driven so as to move every pulse [S5].

Each time the lens 4 moves by one pulse, the output of the Hall element is compared with the threshold level, and it is determined whether or not the above-mentioned determination signal is at the "H" level [S6].

If the signal is at the "L" level, the movement process [S5] for one pulse is performed again.

On the other hand, if it is "H" level, it is determined whether or not the excitation phase of the stepping motor 1 at that time is 1 [S7]. That is, if it is “H level”, it can be confirmed that the lens 4 is located near the reference position,
It is not known whether it is set to the reference position (see FIG. 6). Therefore, the reference position is determined in advance so as to coincide with the excitation phase 1 of the stepping motor 1, and the reference position is detected by determining the excitation phase 1 that appears for the first time after the above-mentioned determination signal becomes “H” level. I have to.

The excitation phase number corresponding to the reference position can be set to an arbitrary value.

FIG. 5 is a circuit diagram showing the Hall element 6a and the Hall output amplifier circuit 8.

That is, the sensor 24 composed of the Hall element 6a
Receives a constant current from a constant current circuit including a constant voltage circuit 21, an operational amplifier 22, and a resistor 23, and generates a potential difference between two output terminals according to the magnitude of a magnetic field. This potential difference is amplified by the differential amplifier circuit 25 and
Is output to

Incidentally, each peak of the Hall element output shown in FIG. 3 changes its peak value due to a change in environmental temperature. The situation of this change is shown in FIG.
As shown in the figure, the temperature decreases as the temperature rises to -10 ° C, 20 ° C, and 50 ° C.

However, the fluctuation range of the peak value due to the change in the environmental temperature does not actually overlap the fluctuation range of the peak value of the adjacent peak, so that an appropriate value (1.7 V in this embodiment) is used. By setting the threshold level in (1), the peak near the reference position of the lens 4 can be reliably detected without being affected by the environmental temperature.

That is, as shown in FIG. 3, the difference between the peak value and the adjacent peak located so as to include the reference position is much larger than the level difference due to the change in the environmental temperature. It can be set easily.

As described above, when the reference position of the lens 4 is detected, the lens 4 is moved by a distance from the reference position to a required lens setting position.
A predetermined number of pulses are input to the stepping motor 1, whereby the lens 4 can be moved to a required lens setting position.

It should be noted that the lens position detecting device of the present invention is not limited to the above-mentioned embodiment, and various other modes can be changed.

For example, the number of input pulses to the stepping motor 1 for rotating the lead screw 2 once can be selected from an arbitrary number of pulses other than 40 pulses.

In the above embodiment, the movable element 3 is provided with the Hall element plate 6 and the rotary plate 5 is provided with the small magnet 7. However, the movable element 3 is provided with a small magnet and the rotary element 5 is provided with the Hall element plate 6 Can be provided, and an electromagnet can be used as the small magnet 7.

In the above embodiment, the rotary plate 5 is attached to the lead screw 2. However, the rotary plate 5 does not necessarily need to be attached to the lead screw 2, and rotates in synchronization with the rotation of the lead screw 2. What is necessary is just to be formed so that it may perform.

Further, the threshold level (threshold) to be compared with the Hall element output in the discrimination processing is not limited to the value of the above-described embodiment, and the level difference between the peak including the reference position and the peak adjacent thereto and the environmental temperature May be set to an appropriate value in consideration of the fluctuation range of the peak value due to the change in.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a lens moving device equipped with a lens position detecting device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the apparatus shown in FIG.

FIG. 3 is a graph showing a Hall element output that changes according to a lens position in the apparatus shown in FIG. 1;

4 is a flowchart showing a processing procedure of the apparatus shown in FIG.

FIG. 5 is a circuit diagram showing a Hall element and an amplifier circuit of the device shown in FIG. 1;

FIG. 6 is a graph showing an enlarged part of the graph shown in FIG. 3;

FIG. 7 is a perspective view showing a conventional technique.

8 is a graph showing a photointerrupter output that changes according to a lens position in the apparatus shown in FIG. 7;

[Explanation of symbols]

 1,11 Stepping motor 2,12 Lead screw 3,13 Moving part 4,14 Lens 4a Lens frame 5 Rotating plate 6 Hall element plate 6a Hall element 7 Small magnet 8 Hall output amplifier circuit 9 Control part (discriminating part) 10 Stepping motor driver

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B ⁷ /02-7/105 G01B 7/00

Claims (1)

(57) [Claims] A detecting device for detecting whether or not a lens held by a movable portion of a feed screw mechanism driven by a stepping motor is set at a predetermined reference position; A rotary plate set to rotate in synchronization with the rotation of the lead screw portion of the feed screw mechanism, and when the rotary plate is disposed at a predetermined rotation position,
A Hall element provided on one of the opposing parts of the rotating plate and the movable part and a magnet provided on the other, which magnetically affects the Hall element, A lens position detecting unit that compares a detection signal output from the Hall element with a predetermined threshold value and determines whether or not the lens is set at the reference position based on a result of the comparison. Detection device.