JPH04324408A - Lens position detection device - Google Patents

Abstract

PURPOSE:To obtain the device which can measure constituent elements in a short response time with high accuracy and can be incorporated in a very narrow space by providing strain gauges to a flexible and elastic deformation member coupled with a lens which is held movably. CONSTITUTION:Element lenses 1a-1c constitute a movable positive lens group. The strain gauges 11 and 12 are adhered to the top and reverse surfaces of part of a coil spring 10. Then detection amplifiers 20 and 21 of a signal processing system are connected to the strain gauges 11 and 12 in order and a differential amplifier 22 is connected to the detection amplifiers 20 and 21. The coil spring 10 expands and contracts as the lens group moves and is strained and the strain gauges 11 and 12 contacting the spring 10 detects its straining quantity. A normal strain gauge utilizes variation in resistance value when a semiconductor is strained, and the detection amplifiers 20 and 21 convert the resistance value into electric signals. Then the signals are inputted to a circuit which converts the strain value into a lens position signal and converted into the signal indicating the lens position.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring the position on the optical axis of a component lens moving within a lens barrel of an optical instrument such as a still camera, a video camera, or an observation device.

0002

[Prior Art] Conventionally, in the lens barrel of still cameras and video cameras, the lens is moved using a DC motor, a feed screw, and a cam, and the actual lens position and movement speed are controlled by a potentiometer or a light source. Detection was done using an encoder or variable capacitor.

[0003] In particular, small rear focus zoom lenses require high lens positioning accuracy; for example, an 8x zoom for a 1/3' CCD image sensor may require a detection resolution of several microns. . Furthermore, autofocus, which determines the focus state from image signals, requires a mechanism (wop ring) that vibrates part of the lens in the optical axis direction at high speed, so high detection response is also desired.

In particular, with the miniaturization of image pickup devices such as CCDs, the influence of dust generated within the lens on images has increased, so a mechanism that does not generate dust is desired.

On the other hand, there is also known a lens position adjustment device that does not have a closed-loop configuration but uses an open-loop control using a stepping motor.

[0006] In the closed-loop control device described above, it is necessary to measure the position of the optical axis of the lens in advance, but for example, with respect to a potentiometer, the frictional resistance due to sliding is large;
It easily generates dust and the life of the element is short. Encoders that use light have many components and are therefore expensive.
The equipment tends to become larger. In devices using variable capacitance, the electrodes must be wide, so the device often becomes larger. Furthermore, in the open-loop system using a stepping motor, it is necessary to minimize play and backlash in the gears and threaded parts for transmitting driving force, so the cost of such mechanical parts is high and the shape is large. Additionally, if the motor goes out of step or if the photographer manually operates the lens, the position of the lens cannot be detected.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus capable of measuring the position of a component with high precision and quick response time.

[0008]

Means for Solving the Problems A strain gauge is provided on a flexible and elastic deformable member connected to a movably held lens.

It is assumed that the deformable member partially or entirely expands, contracts, and bends as the lens moves, causing distortion in the tissue.

[0010] Also, the strain gauge measures the amount of strain in the deformable member, and corresponds to the position of the lens from the circuit or table according to the relational expression between the amount of strain and the lens position determined in advance in the conversion electronic circuit. form a signal.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention, and FIG. 2 shows an example of a zoom lens suitable for applying this device.

In FIG. 2, A is a fixed positive lens group on the object side, and B is a fixed positive lens group on the object side.
is a negative lens group movable in the optical axis direction for conversion, C is a fixed positive lens group, and D is a movable positive lens group for ensuring image plane movement during zooming, focusing, and wobbling. Note that the lens group includes a single lens.

In FIG. 1, component lenses 1a, 1b, and 1c constitute a movable positive lens group D, and 2 is a lens holding cylinder which indicates the positive lens group D. 3 is a sleeve, and lens holding tube 2
is connected to. A guide bar 4 passes through the sleeve 3. Reference numeral 5 denotes an outer tube of the lens barrel, and the guide bar 4 is fixed thereto.

On the other hand, 6 is a transmission motor, and 7 is a feed screw, which are connected to the rotating shaft of the motor 6. A nut 8 is screwed onto the feed screw 7 and coupled to the lens holding cylinder 2.

Reference numeral 9 denotes a solid-state image sensor, which includes component lenses 1a, 1
The beams emitted from the beams b and 1c are received. 10 is a coil spring having a rectangular cross section as shown in FIG. 3, and is press-fitted between the lens holding tube 2 and the rear convex portion of the lens barrel 5.

Both strain gauges 11 and 12 are bonded to the front and back surfaces of a portion of the coil spring 10, respectively, as shown in FIG.

Next, in the signal processing system, 20 and 21 are detection amplifiers which are connected to strain gauges 11 and 12 in order, respectively. 22 and 24 are differential amplifier circuits, and 22 is connected to the detection amplifiers 20 and 21. 23 is a linearity correction circuit, 25 is a control circuit, and 26 is a power amplifier circuit.

With the above configuration, when the motor 6 rotates, the feed screw 7 rotates, and the nut 8 screwed into the feed screw 7 moves in the axial direction. At that time, the coil spring 10 is connected to the sleeve 3 and the bar 4.
It serves as a bias spring to eliminate backlash and bumpiness between the feed screw 7 and the nut 8.

Furthermore, the coil spring 10 expands and contracts as the lens group moves, and at this time the structure of the spring becomes distorted. Strain gauges 11 and 12 in close contact with the spring detect this amount of strain. A typical strain gauge utilizes the property that the resistance value changes when strain is applied to a semiconductor, and the detection amplifiers 20 and 21 convert the resistance value into an electrical signal.

[0020] Basically, only one strain gauge is required. However, as a method for eliminating the influence of temperature changes on the resistance value, a method of canceling by using two strain gauges is adopted, but the method is not limited to this. In addition, the coil spring may be deformed due to vibrations received by the entire lens barrel, which may change the resistance value of the strain gauge. Therefore, such measures may be necessary depending on the required performance.

Therefore, in this embodiment, strain gauges are arranged with a spring in between, and the difference in output is detected by the operating amplifier circuit 22, taking advantage of the fact that the effects of the two are symmetrical, thereby controlling temperature changes and the entire lens barrel. The effects of vibration are removed.

Subsequently, the linearity correction circuit 23 converts the output of the operational amplifier circuit 22 into a signal indicating the lens position and outputs the signal. Through the above operations, the position of the lens group on the optical axis is determined as an electrical signal.

In general, strain gauges have high resolution and high reproducibility in principle because the elements themselves do not generate noise. Therefore, the position detection resolution of this device is 10-4 to 10-
A diameter of the order of 5 mm was obtained, which is sufficient for positioning the lens of a camera.

Furthermore, since there are no factors that cause sliding or rattling in the element itself, the detection response is fast and the driving state is not affected.

By using the circuits 24, 25, and 26 shown in FIG. 1, the lens drive system is constructed in a closed loop.
It is also possible to construct a system that can perform high-speed positioning for a desired command value. Therefore, for example, high-speed wobbling for autofocus using the output of a solid-state imaging device is also possible.

Although a semiconductor type strain gauge has been exemplified above, a strain gauge using a piezoelectric element may also be used. Further, it is preferable to provide two or more sets of strain gauges so as to cancel vibrations in multiple directions. It is also possible to manufacture the strain gauge itself integrally with the elastic spring 10 by etching or the like.

As explained above, the device according to the first embodiment serves both as a bias spring and a position detection mechanism, and can be manufactured in a small size and at low cost. Furthermore, since the position detection resolution is high and the response is fast, this lens position detection device is suitable for electro-optical equipment.

Next, a second embodiment will be explained using FIGS. 5 and 6. FIG. 5 corresponds to the diametrical cross section of FIG.

In FIG. 5, the lens groups 1a, 1b, 1c, holding tube 2, and lens barrel 5 are the same as in FIG.

Reference numerals 31 and 32 are both gimbal springs, which are formed by punching out a spring plate leaving the hatched part as shown in the front view in FIG. There is. The holding tube 2 is directed to the lens barrel at the front and rear by gimbal springs 31 and 32.

[0031] 33a and 33b are permanent magnets each having an annular shape cut out by about four semicircles and having their N and S poles brought into close contact with each other;
a, 34b and 35a, 35b are inner and outer yokes. 37 is an annular bobbin, and 36 is an electromagnetic coil.

On the other hand, 41 to 44 and 45 to 48 are strain gauges, respectively.

This example has a structure in which the lens group is directly moved by electromagnetic induction instead of the DC motor and feed screw mechanism of all examples, and the yokes 34a, 34b, 35a, 35b,
The permanent magnets 33a, 33b and the coil 36 constitute a closed magnetic voice coil type linear actuator.

It is assumed that the electromagnetic coil 36 is wound on a bobbin 37, and the bobbin is connected to the lens holding cylinder 2. As mentioned above, some of the inner bands of the gimbal springs 31 and 32 are joined to the lens holding tube 2, and the outer edges are joined to the lens barrel 5. Therefore, the combination of the gimbal springs 31 and 32 and the holding cylinder allows the lens group to be linearly guided only in the optical axis direction.

Furthermore, when a current is passed through the coil 36, the lens group receives a propulsive force in the optical axis direction.

FIGS. 7 and 8 are drawn so that the neutral state and the deformed state of the gimbal springs 31 and 32, which direct the lens groups, can be compared. FIG. 8 shows a case where a force is applied to the lens holding cylinder 2 in the direction of the arrow.

With the structure shown in the figure, there is no place for sliding, and the negative effects of friction can be avoided, making it possible to drive with high efficiency and high speed.

On the other hand, in this example, the strain gauges 41 to 48 are bonded at four locations on orthogonal lines, one pair each on the front and back sides with the gimbal spring in between, to measure the amount of deformation of the spring. The reason why they are placed at four of these locations is to take into consideration the case where the deformation of the gimbal spring is not rotationally symmetrical; basically, they may be placed at one location or at each location on the orthogonal line. However, in order to perform precise position detection, it is desirable to take the average of four sets.The reason for providing strain gauges on the front and back surfaces is the same as that described above.

As described above, in this device, neither the driving section nor the position detecting section has any parts that cause friction due to sliding, and high-speed and accurate positioning is possible, and there is no generation of dust due to friction. Further, the lens position detection device is particularly effective in a drive system using a voice coil actuator or the like, in the sense that there are no sliding parts at all.

[0040]

The present invention described above can meet the most recent demand for miniaturization, and is particularly inexpensive. Furthermore, despite the limitations of being small and inexpensive, it has the advantage of being able to perform highly accurate detection with a high response speed.

Further, according to the present invention, it is possible to construct a device that is not easily affected by external disturbances such as temperature changes and vibrations, and furthermore, a device that does not generate sliding or friction and does not generate dust.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a conceptual diagram of a zoom lens suitable for applying the present invention.

FIG. 3 is a diagram showing a part of an example.

FIG. 4 is a diagram showing a part of an example.

FIG. 5 is a sectional view showing another embodiment.

FIG. 6 is a front view of the configuration shown in FIG. 5, viewed from the axial direction.

FIG. 7 is a perspective view showing the components of the embodiment in a neutral state.

FIG. 8 is a perspective view showing a deformed state of the constituent elements of the embodiment.

[Explanation of symbols]

1a, 1b, 1c component lens 2 Lens holding tube 10 Coil spring 11, 12 Strain gauge 20, 21 Detection amplifier circuit 22 Differential amplifier circuit 23 Linearity correction circuit

Claims (2)

[Claims] 1. A lens position detection device comprising: a deformable member connected to a movable lens; and a measuring means for measuring distortion of the deformable member. 2. The lens position detecting device according to claim 1, wherein there are two measuring means, and the two measuring means are provided at positions where the signs of distortion of the deformable member are opposite.