JP2997895B2 - Camera auto focus device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device for a camera that performs a focusing operation using an ultrasonic motor, and in particular, applies longitudinal vibration and bending vibration to a flat vibration elastic body. The standing waves are generated, and the lens is moved by the driving force of both vibrations to perform a focusing operation.

[Prior Art] A camera utilizing an ultrasonic motor for an automatic focusing device is already known.

As this type of ultrasonic motor, a motor having a traveling waveform has been put to practical use. On the other hand, in a traveling wave vibrator, it is necessary to prevent a reflected wave from occurring at the end of the vibrator in order to maintain a stable traveling wave. In this regard, if the vibrating body is formed in a ring shape, it is not necessary to consider such an end condition, and thus a ring-shaped ultrasonic motor is used in an automatic focusing device of the camera.

[Problems to be Solved by the Invention] However, when such a conventional traveling waveform ultrasonic motor is used for an automatic focusing device of a camera, the appearance of the lens barrel is restricted by the shape of the ultrasonic motor, and Due to the nature of the traveling wave, there is a problem in how to support the vibrating body, and it is difficult to increase the efficiency as a motor.

[Purpose of the Invention] The present invention has been made in view of such problems in the related art, and a piezoelectric body is bonded to an opposing surface of a flat elastic body, and the two piezoelectric bodies are focused on a focusing signal. By alternately switching and applying an AC voltage to cause vibration, a longitudinal vibration and a bending vibration are generated in the elastic body, and the focus generated by driving the lens using the vibration generated in the elastic body can be adjusted. It is an object of the present invention to provide an automatic focusing device driven by an ultrasonic motor.

Means for Solving the Problems The gist of the present invention to achieve the above object is to provide an automatic focus of a camera having a focus signal means for detecting a distance to a subject and transmitting a focus signal. In the apparatus, a power supply unit for generating a high-frequency AC voltage, a flat elastic body and an opposing surface of the elastic body are respectively joined and selectively connected to the power supply unit, thereby providing longitudinal vibration and bending vibration. A vibrating body portion comprising a first piezoelectric body and a second piezoelectric body for generating the respective standing waves in the elastic body; and a starting force generated on the surface of the elastic body due to the coupling of the vibrations, in contact with the elastic body. An ultrasonic motor comprising: a motion extracting unit for selectively extracting the power source unit and each of the piezoelectric bodies; and a switching unit for switching a motion direction of the driving force. Sound wave Either the vibrating body part or the motion extracting means of the motor is coupled to the stationary part of the camera, and the other is coupled to the lens driving side, and the switching means is switched in the forward and reverse directions by the in-focus signal of the camera. The present invention is directed to an automatic focusing device for a camera.

[Operation] In the above configuration, regarding the ultrasonic motor, first, when power is applied to the first piezoelectric body, longitudinal vibration parallel to the plane is excited in the elastic body. When the longitudinal vibration is excited, the bending vibration having a vibration component perpendicular to the plane is also excited. In this case, since the first piezoelectric body in an electrically short state and the second piezoelectric body in an open state have different mechanical hardness, the first piezoelectric body is asymmetric with respect to the neutral surface of the bending vibration, and therefore, the longitudinal vibration And a bending vibration, thus producing an elliptical vibration which can be converted into a driving force.

Next, when the first piezoelectric body is opened and power is turned on to the second piezoelectric body, a counterclockwise elliptical motion is generated. At this time, the moving body portion pressed against the surface of the elastic body rotates in the opposite direction.

On the other hand, either the vibrating body of the ultrasonic motor or the motion extracting means is connected to the stationary part of the camera, and the other of the vibrating body or the motion extracting means is connected to the driving side of the lens. Have been.

The connection between each piezoelectric body of the vibrating body section and the power supply section is selected by the switching means, and the two are not connected at the same time.

Now, assuming that the power supply unit is connected to the first piezoelectric body,
Each standing wave of longitudinal vibration and bending vibration induced by the longitudinal vibration occurs in the elastic body of the vibrating body. In the elastic body, an elliptical motion that rotates in a direction opposing each other across the support point supporting the elastic body occurs, and this elliptical motion acts on the surface of the elastic body in a direction opposing each other across the support point. Appears as driving force.

Therefore, a driving force in one direction on one side of the support point of the elastic body is transmitted to the motion extracting means in contact with the vicinity of one end of the elastic body, and this driving force is ultimately transmitted to the lens of the camera. Directional movement, for example, to the payout side.

When the power supply unit is connected to the second piezoelectric body, a driving force in the opposite direction is generated in the elastic body of the vibrating body unit, and therefore, the motion extracting means moves the camera lens in the opposite direction. ,
For example, it acts in the degenerating direction of the lens.

Therefore, a focusing signal is now generated from the focusing signal means of the camera. For example, in the case of a so-called front pin, the switching means is switched to connect the power supply unit to the first piezoelectric body side, and the lens is extended. It is localized at the in-focus position.

When the signal is, for example, a so-called rear focus, the switching unit connects the power supply unit to the second piezoelectric body side, and the lens of the camera is retracted and positioned at the in-focus position.

[Basic Principle of the Invention] Hereinafter, the operation principle of the present invention will be described.

According to the present invention, the surface of a piezoelectric body (piezoelectric ceramics) generates polarization charges due to mechanical deformation. At this time, the piezoelectric body is in an electrically open state (open state) or a short-circuit state (short-circuit state). ) Is used to make use of the fact that the mechanical hardness of the piezoelectric body is different depending on whether or not the above-mentioned condition is satisfied.

The difference in mechanical hardness between the two appears as a difference in sound speed (velocity of longitudinal waves). Therefore, when the difference in mechanical hardness between the two is indicated by the speed of sound, in the case of an electrical short-circuit, the polarization charge disappears, and the speed of sound is expressed by the first formula.

On the other hand, in the case of the electrical open state, since the polarization charge does not discharge, the speed of sound is represented by the second equation.

here. C ₁₁ is the elastic modulus of the piezoelectric body, e ₃₁ is the piezoelectric constant,
ε ₃₃ is the dielectric constant of the piezoelectric body.

FIG. 1 is a diagram showing a basic configuration of an ultrasonic vibration device of the present invention in which asymmetry is electrically obtained by utilizing the above-mentioned electromechanical properties of a piezoelectric body. In this figure, reference numeral 4 denotes a plate-like elastic body made of metal. Reference numerals 5a and 5b denote plate-shaped piezoelectric bodies (piezoelectric ceramics) polarized in the thickness direction. One (5a) is bonded to the upper surface of the elastic body 4 and the other (5b) is bonded to the lower surface, facing each other. I have. 6a is an electrode formed on the upper surface of the piezoelectric body 5a. Reference numeral 7 denotes an excitation power supply for outputting a high-frequency voltage of the longitudinal vibration resonance frequency of the elastic body 4. One terminal of the power supply 7 is electrically connected to the elastic body 4, and the other terminal is electrically connected to the electrode 6 a. I have.

The elastic body 4 has a sectional shape symmetrical with respect to the neutral plane N of the bending vibration, and is formed so that the longitudinal vibration resonance frequency and the bending vibration resonance frequency coincide with or approach each other.

here. C ₁₁ is the elastic modulus of the piezoelectric body, e ₃₁ is the piezoelectric constant,
ε ₃₃ is the dielectric constant of the piezoelectric body.

FIG. 1 is a diagram showing a basic configuration of an ultrasonic vibration device of the present invention in which asymmetry is electrically obtained by utilizing the above-mentioned electromechanical properties of a piezoelectric body. In this figure, reference numeral 4 denotes a plate-like elastic body made of metal. Reference numerals 5a and 5b denote plate-shaped piezoelectric bodies (piezoelectric ceramics) polarized in the thickness direction. One (5a) is bonded to the upper surface of the elastic body 4 and the other (5b) is bonded to the lower surface, facing each other. I have. 6a is an electrode formed on the upper surface of the piezoelectric body 5a. Reference numeral 7 denotes an excitation power supply for outputting a high-frequency voltage of the longitudinal vibration resonance frequency of the elastic body 4. One terminal of the power supply 7 is electrically connected to the elastic body 4, and the other terminal is electrically connected to the electrode 6 a. I have.

The elastic body 4 has a sectional shape symmetrical with respect to the neutral plane N of the bending vibration, and is formed so that the longitudinal vibration resonance frequency and the bending vibration resonance frequency coincide with or approach each other.

In general, the resonance frequency fL of a plate-like elastic body is expressed by the following equation (3).

Here, E is the rung modulus of the elastic body, ρ is its density, and l is its length.

On the other hand, the resonance frequency fB of the bending vibration on the surface of the plate-like elastic body is expressed by the following equation (4).

Here, w is the width of the elastic body, and t is its thickness.

Α is the root of the fifth formula, and corresponds to the order of the resonance mode of the symmetric bending vibration from the smaller one.

From the above, when fL = fB, that is, If the length l, width w, and thickness t of the elastic body satisfy the relationship of the sixth formula, the vibration mode of the longitudinal vibration and the vibration mode of the bending vibration coexist, and as described above, the elliptical vibration is generated on the surface of the elastic body. Is raised. In this case, any two of the three variables of length 1, width w, and thickness t can be freely selected.

In the above configuration, if the power supply 7 is turned on to the thick electric body 5a,
A longitudinal vibration parallel to the plane is excited in the elastic body 4. When the longitudinal vibration is excited, the bending vibration having a vibration component perpendicular to the plane is also excited. In this case, since the piezoelectric body 5a in the electrically open state and the piezoelectric body 5b in the short state have different mechanical hardness, the elastic body 4 is asymmetric with respect to the neutral plane of the bending vibration. Therefore, longitudinal vibration and bending vibration are combined,
Thus, an elliptical vibration that can be converted into a driving force is generated.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

 First, an ultrasonic motor as a driving source will be described.

FIG. 2 is a sectional view for explaining the driving principle of the ultrasonic motor according to the present invention, and FIG. 3 is a perspective view of the same. In this drawing, reference numeral 10 denotes a plate-like elastic body made of a metal material such as stainless steel or aluminum. Piezoelectric bodies (piezoelectric vibrators) 12a and 12b are arranged on both surfaces of the elastic body 10 so as to be opposed to each other and bonded. Have been. The elastic body 10 and the piezoelectric bodies 12a and 12b substantially constitute a vibrating body of the ultrasonic driving device.
A conductive layer (not shown) is formed on at least the surface of the piezoelectric members 12a and 12b on both sides that are not in contact with the elastic member 10. The elastic body 1 of the two planes of the piezoelectric bodies 12a and 12b
One end of each of the electric lines 14a, 14b is connected to the surface not in contact with 0, and the other end of each of the electric lines 14a, 14b is connected to the terminals 16a, 16b of the switch mechanism 16, respectively. I have. One end of an electric line 14c is connected to the elastic body 10, and the other end is connected to a single-phase power supply 18 for excitation. On the side of the elastic body 10 on which the piezoelectric body 12a is provided, a motion extractor 20 is disposed so as to directly contact the elastic body 10. The elastic body 10 has a convex portion 11 extending from the longitudinal center portion of the elastic body 10.
Is fixedly supported by a frame member (not shown) by passing a fixing screw 15 through a hole 13 provided in the hole. The convex portion 11 is set at a position of a node generated from resonance of longitudinal vibration determined by the length of the elastic body 10. Further, in this example,
The elastic body 10 has a shape (length, length, etc.) in which the resonance frequency of longitudinal vibration generated in the length direction of the elastic body 10 in the state of being fixed to the frame member substantially matches the resonance frequency of bending vibration generated in the width direction. (Width and thickness). The piezoelectric bodies 12a and 12b are arranged on the elastic body 10 such that a node of the longitudinal vibration generated at the midpoint in the longitudinal direction of the elastic body 10 is located substantially at the center in the longitudinal direction of each of the voltage bodies 12a and 12b. Has been established.

The single-phase power supply 18 is a power supply for supplying a high-frequency voltage having the same frequency as the longitudinal vibration resonance frequency of the elastic body 10 to the piezoelectric bodies 12a and 12b, and the switch mechanism 16 includes a switch 16
This is electrical switching means for selectively applying the high-frequency voltage output from the single-phase power supply 18 to the voltage bodies 12a and 12b by the switching operation of c. In addition, the exercise extractor
Reference numeral 20 denotes a rotatable roller-shaped member which is positioned on the elastic body 10 by any means and is pressed against the elastic body 10 by any pressing means.

Next, the operation of the ultrasonic driving device having the above configuration will be described with reference to FIG.

FIG. 4 shows that the elastic body 10 is formed to have a dimension and shape in which the longitudinal vibration in the vibration mode L ₁₀ (one node) and the bending vibration in the vibration mode B ₂₀ (two nodes) are caused to be the same due to resonance. Vibration body part is shown, not shown, vibration mode
Protrusions are provided on both sides so as to correspond to the positions of the nodes of L _10, these projections are fixed to and supported by the frame members (not shown).

In the vibrating body portion shown in FIG.
When exciting the piezoelectric element 12a (at a predetermined longitudinal vibration resonance frequency) on power against, with the vibration mode L ₁₀ of longitudinal vibration in the longitudinal direction of the elastic body 10 occurs, above in the width direction vibration mode B ₂₀ of the bending vibration in resonance with the longitudinal vibration is induced. Then, an elliptical vibration is generated on the surface of the elastic body 10 by the combination of these two vibrations. In this example, the vibration mode of the bending vibration is the B _20, the direction of rotation in the elliptical vibration in the elliptical vibration and both end portions 10s in the central portion 10c to boundary nodes of the bending vibration in the width direction of the elastic body 10 Opposite to each other. At this time, for example, if the motion extractor 20 is configured to contact only the central portion 10c of the elastic body,
A driving force in a certain direction can be extracted. Next, when the switch 16c is switched to turn on the power to the piezoelectric body 12b, the piezoelectric body 12b is excited.
With the longitudinal vibration mode L ₁₀ of vibration in the longitudinal direction of the occurs, vibration modes B ₂₀ of the bending vibration in resonance with the longitudinal vibration is induced in the width direction. In this example, the piezoelectric body 1
The same-phase longitudinal vibration (the same-phase longitudinal vibration with respect to the deformation in the same direction) is generated by the excitation of either 2a or 12b, but the phase of the bending vibration depends on which of the piezoelectric bodies 12a and 12b is excited. They are 180 degrees different from each other. For this reason, when the piezoelectric body 12a is excited, the elliptical vibration generated on the surface of the elastic body 10 rotates, for example, in the direction shown by the solid line arrow in FIGS. The direction of the extracted movement (driving force) is also the direction indicated by the solid arrow in FIG. Next, when switching to excitation of the piezoelectric body 12b,
The elliptical vibration generated on the surface of the elastic body 10 is reversed, for example, in the direction indicated by the dashed arrow in FIG.
The movement (driving force) taken out by 20 is also reversed in the direction indicated by the dashed arrow in FIG.

If the driving force of the elliptical vibration is decomposed into components,
The motion extractor 20 is provided with a levitation force by bending vibration and a driving force by longitudinal vibration.

According to the above configuration, a card-shaped member on the linked extractor 20,
If an object to be conveyed such as a paper sheet is brought into contact, the object to be conveyed can be transferred in an arbitrary direction by switching the switch 16c.

In addition, since the convex portion 11 fixed and supported by the frame member is provided at the position of the node of the longitudinal vibration, attenuation of the longitudinal vibration due to the fixed support of the elastic body 10 can be prevented.

Furthermore, since the vibration mode of the bending vibration is generated in the width direction of the elastic body 10, even if the position of the node of the longitudinal vibration is fixed by the frame member, both ends in the length direction of the elastic body 10 In, the generation of the vibration mode of the bending vibration is not suppressed.

Therefore, a highly efficient driving force excellent in responsiveness can be obtained.

FIGS. 5 (a), 5 (b) and 5 (c) are views showing a main part configuration as an ultrasonic motor. FIG. 5 (a) is a plan view, and FIGS. It is a partial sectional view. In these figures, parts corresponding to the respective parts shown in FIGS. 2 and 3 are denoted by the same reference numerals, and description thereof will be omitted. In this example, as the elastic body 10, for example, a SUS420 (stainless steel) plate having a size of 27.3 [mm] × 1 [mm] × 8 [mm] is used. As in the first embodiment, the piezoelectric bodies 12a and 12b are attached, respectively. For example, a PZT (zirconate titanate) plate having a size of 15 [mm] × 0.5 [mm] × 8 [mm] is used as the piezoelectric bodies 12a and 12b. The elastic body 10 has a frame member formed by convex portions 11, 11 extending from substantially the center thereof.
30 fixedly supported. A pair of arms 36a and 36b are provided along both side surfaces of the frame member 30, and these arms 36a and 36b are rotatably supported at one end by a shaft 34 provided at one end of the frame member 30. Have been. The other ends of the arms 36a and 36b are connected via a spring support member 38, so that the pair of arms 36a and 36b can be integrally turned. Also, at each intermediate portion of the arms 36a and 36b,
A motion extractor support shaft 40 that rotatably supports the roller-shaped motion extractor 20 is penetrated. As shown in FIG. 5 (a), the motion extractor 20 is disposed substantially at the center in the width direction of the elastic body 10 and near the end in the length direction.
The pressure spring 42 is stretched by one end locked to the end surface of the frame member 30 and the other end locked to the spring support member 38 in order to constantly press the motion extractor 20 against the elastic body 10. ing.

In the second embodiment, a single-phase power supply, a switch mechanism and the like having the same configuration as in the first embodiment are appropriately used, but are omitted in FIG. 5 for simplicity.

In the above configuration, the frequency of 98
A high frequency voltage of KHz is applied to the piezoelectric body 12a or 12b via the switch mechanism. Thereby, the piezoelectric body 12a or
12b is excited, on the elastic member 10, to generate a vibration mode B ₂₀ of the bending vibration and the vibration mode L ₁₀ of the longitudinal vibration. These two generated vibrations are connected to each other, and this connection causes an elliptical motion. The motion extractor 20 extracts a driving force from the generated elliptical motion, and the extracted driving force is transmitted to the pulley 44.

FIG. 5D is a graph showing measured values of the torque T-revolution speed N characteristic transmitted to the pulley 44 by the ultrasonic drive device of this example. As shown in this figure, when a voltage of 11 V was applied, a maximum torque of 15 [gcm] and a no-load rotation speed of 600 [rpm] were obtained for the torque [T] and the rotation speed [N].

FIG. 6 shows an ultrasonic motor A that drives the focus ring C in response to a subject distance signal from the focusing signal means E and extends or retracts the lens unit B to automatically perform a focusing operation. FIG. 7 and FIG. 8 are views showing the assembled state as viewed from the front and back.

The ultrasonic motor A has a frame 30a and a frame 30b, and both frames are connected by connecting rods 41a and 41b.

Each of the frames 30a and 30b has an elastic body mounting plate 31 respectively.
a, 31b are provided, and the flat elastic body 10
Are fixed to the mounting plates 31a and 31b.

First and second piezoelectric bodies 12a and 12b having the same width and a short length are attached to both surfaces of the elastic body 10, respectively.

As shown in FIGS. 6 and 8, a pickup roller 20, which is a motion extractor, is rotatably in contact with the elastic body 10 via a shaft 40. The first transmission gear 31 is fixed to the shaft 40. Further, as shown in FIG. 6, the shaft 40 is pivotally supported by a pressing member 36 for pressing the pickup roller 20 against the elastic body 10. This press contact member 36 is a frame
A pressing force adjusting bolt 44 screwed into the bent portion 32 of 31a,
The contact between the pickup roller 20 and the elastic body 10 can be adjusted by being pulled by a pressure contact spring 42 that is stretched between the bent portion 32 of the pressure contact member 44.

The first transmission gear 31 has a second transmission gear 32 supported by a shaft 37.
Are engaged. The shaft 37 is supported by a shaft hole 36a of the press contact member 36, and penetrates through the shaft hole 36a.
The pressing member 36 presses the pickup roller 20 against the elastic body 10 with the shaft 37 as a fulcrum.

Further, the third transmission gear 34 is press-fitted into the shaft 39 supported by the frames 30a and 30b, meshes with the second transmission gear 32, and the output gear 33 is fixed coaxially. Numeral 33 meshes with the internal gear C1 of the focus ring C of the camera as shown in FIG.

FIG. 9 shows a block diagram of the entire automatic focusing device of the camera.

FIG. 10 is a front perspective view of a camera G equipped with the automatic focusing device of the present invention.

The camera G has a lens unit B at the front of the camera body D.
The focus ring C is attached so as to be adjustable in focus by a focus ring C. The focus ring C can be automatically adjusted in focus by the operation of the automatic focusing device having the structure shown in FIG. 9 and can also be manually adjusted from the outside. ing.

Note that the focusing signal means E is composed of a first light receiving element E1 and a second light receiving element E composed of CCDs and the like arranged at intervals of the base line length.
2, the first lens E3 and the second lens E4 for condensing the reflected light from the object on the light receiving elements E1 and E2, and comparing the data captured by each light receiving element E1 and E2 to determine whether the front focus is on. And a signal processing circuit E5 for judging whether or not it is the back focus.

The in-focus signal means E has a difference of 0 between the output data of the first light receiving element E1 and the second light receiving element E2 when the object is in focus, and the difference of the output data is + The signal processing circuit E5 is adjusted in advance so that the difference between the output data changes to-in the rear focus state.

That is, the state of the front focus or the rear focus is determined by the in-focus signal means E.
Outputs an inverted output to the ultrasonic motor driving circuit shown in FIG.

FIG. 11 shows the ultrasonic motor drive circuit, in which CW / CCW
One of the step-up transformers T1 and T2 is stepped up by inverting the terminal to the H level or the L level according to the output from the focus signal means E, and one of the piezoelectric bodies 12a or 12b corresponding thereto. When a voltage is applied to the elastic member 10, the elastic body 10 is excited. Then, the motion extractor 20 rotates according to the excitation state of the elastic body 10 and drives the lens unit B to adjust the focus.

[Effect of the Invention] As described above, according to the present invention, a piezoelectric body is bonded to an opposing surface of a flat elastic body, and the two piezoelectric bodies are alternately switched by a focus signal to apply an AC voltage and vibrate. Therefore, since the longitudinal vibration and the bending vibration are generated in the elastic body, the automatic focusing device driven by the ultrasonic motor capable of driving the lens using the two vibrations generated in the elastic body to perform focusing adjustment. Can be provided.

[Brief description of the drawings]

FIG. 1 is a view showing a basic configuration of an ultrasonic motor according to the present invention, FIG. 2 is a sectional view for explaining a driving principle of the ultrasonic motor, FIG. 3 is a perspective view of the same, and FIG. FIG. 5A is a diagram for explaining the operation of the ultrasonic motor according to the present invention.
FIG. 5 is a diagram showing a configuration of a main part of the ultrasonic motor in FIG. 2, FIGS. 5 (b) and 5 (c) are cross-sectional views, and FIG. 5 (d) shows experimental values of torque-rotation speed characteristics of the device. FIG. 6 is an overall exploded perspective view of the ultrasonic motor shown in FIGS. 2 to 5, FIGS. 7 and 8 are assembled perspective views of the ultrasonic motor of FIG. FIG. 10 is a block diagram of an automatic focusing device of a camera, FIG. 10 is a perspective view of a camera provided with the automatic focusing device of the present invention, and FIG. 11 is a drive circuit diagram of an ultrasonic motor according to the present invention. A: Ultrasonic motor, 10: Vibrating body, 12a, 12b: Piezoelectric body, 16: Switching means, 20: Motion extracting means, E
...... In-focus signal means

Continuation of the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B ^7/ 28-7/40 G03B 3/00-3/12 H02N 2/00-2/18

Claims (1)

(57) [Claims] An auto-focusing device for a camera having a focusing signal means for detecting a distance to a subject and transmitting a focusing signal, comprising: a power supply unit for generating a high-frequency AC voltage; a flat elastic body; A first piezoelectric body and a second piezoelectric body that generate standing waves of longitudinal vibration and bending vibration in the elastic body by being respectively connected to opposing surfaces of the elastic body and selectively connected to the power supply unit. A vibrating body section made of a piezoelectric body, a motion extracting means for extracting a starting force generated on the elastic body surface by coupling of the vibration by contacting the elastic body, and the power supply section and each of the piezoelectric bodies. And a switching means for switching the direction of movement of the driving force, and one of the vibrating part of the ultrasonic motor and the movement extracting means is fixed to a camera. To the other is bound to the lens drive side, the automatic focusing device of a camera, characterized in that as switch the switching means to the normal and reverse two directions by the focus signal of a camera.