Vibration type actuator and manufacturing method of vibration type actuator

A vibration type actuator including vibrating elements and a contact element that is brought into contact with each other in a first direction. The vibration of the vibrating elements includes vibration in a first vibration mode in the first direction and vibration in a second vibration mode in a second direction intersecting the first direction. In the vibrating elements, a minimum value of a resonance frequency in the second vibration mode is greater than or equal to a maximum value of a resonance frequency in the first vibration mode, and a ratio of a difference between the maximum value and the minimum value of the resonance frequency in the second vibration mode to the minimum value of the resonance frequency in the second mode is less than or equal to a predetermined value.

BACKGROUND

Field of the Disclosure

The present disclosure relates to a vibration type actuator.

Description of the Related Art

Conventionally, a vibration type actuator has been proposed. The vibration type actuator is configured so that a contact element that is brought into contact with a vibrating element (elastic element, piezoelectric element) is driven by vibration excited by the vibrating element (the vibrating element and the contact element are relatively moved).

For example, Japanese Patent Application Laid-Open No. 2011-259559 discusses an actuator includes two vibrating elements or a plurality of vibrating elements. The two vibrating elements are linearly driven or the plurality of vibrating elements is rotationally driven.

However, in a vibrating element, a resonance frequency varies due to variations in dimensions of an elastic element and a piezoelectric element. Thus, in a case where one contact element is driven by a plurality of vibrating elements using one booster circuit, namely, a common alternating signal, a performance of an actuator might be degraded in some cases depending on a combination of vibrating elements.

SUMMARY

The present disclosure is directed to a technique that reduces a deterioration of a performance caused by variations of a resonance frequency of a plurality of vibrating elements disposed in a vibration type actuator.

According to an aspect of the present disclosure, a vibration type actuator includes a plurality of vibrating elements, and a contact element that is brought into contact with contact sections of the plurality of vibrating elements and vibration excited in each of the plurality of vibrating elements causes relative movement of the plurality of vibrating elements and the contact element. The vibration includes vibration in a first vibration mode where the contact sections are displaced in a first direction in which one of the plurality of vibrating elements and the contact element are made to pressure contact with each other and vibration in a second vibration mode where the contact sections are displaced in a second direction intersecting the first direction. In the plurality of vibrating elements, a minimum value of a resonance frequency in the second vibration mode is greater than or equal to a maximum value of a resonance frequency in the first vibration mode, and a ratio of a difference between the maximum value and the minimum value of the resonance frequency in the second vibration mode to the minimum value of the resonance frequency in the second mode is less than or equal to a predetermined value.

DESCRIPTION OF THE EMBODIMENTS

First, a conventional technique is described with reference toFIGS. 8A to 9C.

FIG. 8Ais a plan view of the vibrating element, andFIG. 8Bis a side view of the vibrating element. InFIGS. 8A and 8B, a vibrating element1includes an electrical energy-to-mechanical energy conversion element (piezoelectric element)3having a shape of a rectangular (quadrangular) thin plate, and an elastic element2that is integrally bonded to (one plane of) the piezoelectric element3.

The elastic element2includes a main section2-3and support sections2-4.

The main section2-3includes a base section2-1and two protrusions2-2. The base section2-1, which has a shape of a rectangular thin plate, vibrates together with the piezoelectric element3. The protrusions2-2protrude from one plane of the base section2-1(the plane of the elastic element2opposite to the plane to which the piezoelectric element3is bonded). The protrusions2-2each include a side wall section2-2-1and a contact section2-2-2, for example, as discussed in Japanese Patent Application Laid-Open No. 2011-234608. The side wall section2-2-1protrudes from the one plane of the base section2-1to a direction of making pressure contact with the contact element (first direction) and has a hollow (continuous) structure. The contact section2-2-2is at a leading edge of each of the protrusions2-2and is brought into contact with the contact element.

The support sections2-4each have flexibility and are structurally integral with the main section2-3. The support sections2-4each have a thin section2-5, which is configured by partially thinning each support section2-4so that vibration of the main section2-3is not transmitted outside as much as possible. Further, the support sections2-4have a circular hole2-6and a slotted hole207, respectively, to be used for positioning when the piezoelectric element3is bonded and the vibrating element is assembled. Hereinafter, a Z direction is defined as a direction of making pressure contact with the vibrating element and the contact element, an X direction is defined as a direction of relative movement of the vibrating element and the contact element, and a Y direction is defined as a direction perpendicular to the X direction and the Z direction, respectively.

The vibrating element1causes a first bending motion in a short direction (Y) as illustrated inFIG. 9A. The first bending motion mainly causes leading edges of the protrusions2-2to be displaced in a Z direction (first direction). Further, the vibrating element1causes a second bending motion in a longitudinal direction (X). The second bending motion mainly causes the leading edges of the protrusions2-2to be displaced in a direction including an X direction component (direction which intersects the first direction: hereinafter, “second direction”). At this time, the first bending motion and the second bending motion are generated to have a temporal phase difference. Thus, the leading edges of the protrusions2-2each make an ellipsoidal motion, and a contact element, not illustrated, is driven in the X direction as illustrated inFIG. 9A. Herein, “the direction which intersects the first direction” (second direction) includes also “a direction orthogonal to the first direction”.FIG. 9Balso illustrates the first bending motion (first vibration mode or mode 1). Further,FIG. 9Calso illustrates the second bending motion (second vibration mode or mode 2). Herein, an order of the first vibration mode (first order) illustrated inFIGS. 9A and 9Bis 1, and an order of the second vibration mode (second order) illustrated inFIGS. 9A and 9Cis 2. The order means a number of antinodes of vibration.

An exemplary embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings. In the present exemplary embodiment, a vibration type actuator includes a vibrating element where vibration is excited and a contact element that is brought into pressure contact with the vibrating element. The vibrating element and the contact element perform relative movement by the vibration. That is, the vibration type actuator is configured so that a drive output from the vibrating element can be taken out by the relative movement of the vibrating element and the contact element.

FIGS. 1A and 1Billustrate a first exemplary embodiment of the present disclosure.

FIG. 1Ais a perspective view illustrating disassembled parts of a rotary actuator having three (a plurality of) vibrating elements (of vibration type actuator), illustrated inFIGS. 8A and 8B, disposed on a circumference.FIG. 1Bis an enlarged and developed perspective view illustrating a periphery of a vibrating element1.

As illustrated inFIG. 1A, the three (plurality of) vibrating elements1are disposed on a circular base (support member)7to rotationally drive a rotor (contact element)8that is brought into contact with the vibrating elements1.

Each of the vibrating elements1is held onto a small base (holding member4) by fitting pins4aof a holding member4into a circular hole2-6and a slotted hole2-7of a support section, respectively, and bonding them. Further, the holding member4is positioned to be freely moved in a pressurizing direction by fitting pins7aof a support member7into holes4b, respectively.

A rectangular through hole4cis provided to the holding member4, and a pressing member6that presses each of the vibrating elements1fits into the through hole4c. When the pressing member6touches the support member7, a pressurizing member (such as a spring), not illustrated, causes the pressing member6to press the vibrating element1via a vibration isolating member5(such as felt). Further, the pressing member6is relatively movable in the pressurizing direction with respect to the holding member4.

Such a configuration makes it difficult for the support sections2to4to receive a reaction force generated upon pressurizing, and thus prevents the bonding of a piezoelectric element from being peeled. A flexible printed board (power feeding substrate)33that feeds power is bonded to an electric energy-to-mechanical energy conversion element (piezoelectric element)3. An alternating-current signal is applied to the piezoelectric element3via the power feeding substrate33to drive the vibrating element1.

Positioning pins6aand6bare disposed on the pressing member6. The pressing member6is positioned by fitting the positioning pins6aand6binto holes7band7c, respectively, disposed on the support member7. Further, the pressing member6is brought into contact with a semicircular column-shaped surface (protruded section)7dof the support member7to be rotatable in a pitching direction (direction of a relative motion with respect to the contact element8).

FIG. 2is a block diagram illustrating a configuration of a drive control apparatus of a rotary actuator illustrated inFIGS. 1A and 1B. The drive control apparatus includes a position command generation unit11that generates a target value of a driven element9that is driven integrally with the contact element8. An output side of the position command generation unit11is connected to an operation amount determination unit16via a comparison unit12. The comparison unit12compares the target value output from the position command generation unit11with a current position of the driven element9output from a position detection unit10. The operation amount determination unit16calculates an operation amount of the vibration type actuator based on the comparison result of the comparison unit12. The operation amount determination unit16is a proportional-integral (PI) controller or a proportional-integral-derivative (PID) controller.

The position detection unit10, which is, for example, an encoder, detects a position of the driven element9. Vibrating elements a, b, and c, which are the above-described three vibrating elements1illustrated inFIG. 1A, integrally drive the contact element8and the driven element9. An output side of the operation amount determination unit16is connected to an ellipse ratio determination unit13and a drive frequency determination unit14. The ellipse ratio determination unit13sets an ellipse ratio of an ellipsoidal motion. The drive frequency determination unit14sets a frequency of an alternating-current signal.

The ellipse ratio determination unit13sets a ratio between an X-axis amplitude and a Z-axis amplitude of the ellipsoidal motion generated on the protrusion (contact section) of each of the vibrating elements1based on an output from the operation amount determination unit16. As a result, the ellipse ratio determination unit13can set a temporal phase difference of two amplitude modes that achieve this ratio. The drive frequency determination unit14can set a drive frequency of an alternating-current voltage to be applied to each of the vibrating elements1based on the output from the operation amount determination unit16. Further, output sides of the ellipse ratio determination unit13and the drive frequency determination unit14are connected to a drive signal generation unit15.

The drive signal generation unit15generates a two-phase alternating-current signal having a frequency determined by the drive frequency determination unit14and a phase difference determined by the ellipse ratio determination unit13. An output side of the drive signal generation unit15is connected to a booster circuit17. The booster circuit17boosts the two-phase alternating-current signal generated by the drive signal generation unit15. The boosted two-phase alternating-current signal is applied to the three vibrating elements1(vibrating elements a, b, and c) in parallel. The booster circuit17can be a power amplifier, a switching element, a direct current (DC)-direct current (DC) circuit, or a transform circuit.

FIG. 3Aillustrates an example of impedance characteristics of the respective three vibrating elements1(three kinds of lines indicate impedance characteristics of different vibrating elements, respectively). An axis of abscissa represents the drive frequency, and an axis of ordinate represents admittance (reciprocal of the impedance). A peak frequency of the admittance is a resonance frequency. One vibrating element1has two peaks that are the resonance frequency of the first bending motion (first vibration mode) and the resonance frequency of the second bending motion (second vibration mode) described above. In the first bending motion, displacement is caused based on a first order. In the second bending motion, displacement is caused based on a second order. In a pressurized motor state, the two peaks tend to be close to each other. Note that the first order “1” and the second order “2” are desirable orders in (vibration type actuator having) the vibrating element1illustrated inFIGS. 8A and 8B. Accordingly, the first order and the second order are variable depending on the types of (the vibration type actuator having) the vibrating element1, and thus orders for carrying out the present disclosure are not limited to the orders described here.

In this example, in the plurality (three) of the vibrating elements1, a difference between a maximum value f2max (94.0 kHz) and a minimum value f2min (93.3 kHz) of the resonance frequency in the second vibration mode where displacement is caused based on the second order is 0.7 kHz. That is, in the three vibrating elements1, a ratio (0.7/93.3) of the difference (0.7 kHz) between the maximum value f2max and the minimum value f2min of the resonance frequency in the second vibration mode, where displacement is caused based on the second order to the minimum value f2min (93.3 kHz), is 0.0075 (0.75%).

FIG. 3Billustrates an example of a measured result representing a relationship between the difference in the resonance frequency in the second vibration mode obtained inFIG. 3A(f2max−f2min) and a motor performance. A horizontal axis represents a difference between a maximum value and a minimum value in a resonance frequency in the second vibration mode. An axis of ordinate represents power consumption at a maximum number of revolutions and a predetermined number of revolutions.FIG. 3Cis a diagram where representation of a horizontal axis ofFIG. 3Bis replaced by a ratio of the difference between the maximum value and the minimum value of the resonance frequency in the second vibration mode to the minimum value of the resonance frequency in the second vibration mode.

The maximum number of revolutions is 90 rpm in order to prevent breakage of the vibrating elements1. As illustrated inFIG. 3B, in the plurality of vibrating elements1where the minimum value f2min of the resonance frequency in the second vibration mode is 90 kHz, in a case where the difference between the maximum value f2max and the minimum value f2min of the resonance frequency in the second vibration mode exceeds 0.9 kHz, the power consumption tends to increase and thus a motor efficiency decreases. That is, in the plurality of vibrating elements1, in a case where the ratio of the difference between the maximum value f2max and the minimum value f2min of the resonance frequency in the second vibration mode to the minimum value f2min exceeds 0.01 (1%), the power consumption tends to increase and thus the motor efficiency (performance) decreases. (SeeFIG. 3C)

Therefore, the plurality of vibrating elements1is selected from the plurality of stratified (classified) vibrating elements1to be combined so that the ratio of the difference between the maximum value f2max and the minimum value f2min of the resonance frequency in the second vibration mode to the minimum value f2min is less than or equal to 0.01 (1%). As a result, performance degradation due to variations in the resonance frequency can be reduced, and thus an actuator having satisfactory performance can be provided. Details of stratification will be described below.

The performance of the actuator mostly depends on an amount of displacement in the X direction in the second vibration mode. The displacement in the Z direction in the first vibration mode can be achieved with a certain amount, and thus the amount of the displacement needs not to exceed that certain amount. Therefore, attention is paid only to the resonance frequency in the second vibration mode in a case of a drive using the plurality of vibrating elements1.

The actuator is driven with a high frequency, and the frequency is lowered to be close to the resonance frequency in the second vibration mode. Thus, the speed of the actuator is increased. For this reason, if the resonance frequency in the second vibration mode is not higher than the resonance frequency in the first vibration mode, vibration amplitude in the first vibration mode abruptly decreases beyond the resonance frequency before vibration amplitude in the second vibration mode becomes large. Thus, satisfactory performance cannot be obtained.

Therefore, in the case of the drive using the plurality of vibrating elements1, as illustrated inFIG. 3A, the minimum value f2min of the resonance frequency in the second vibration mode is set to be more than or equal to a maximum value fimax of the resonance frequency in the first vibration mode.

As to Δf regarding a single vibrating element1, which is a difference (f2−f1) between the value f2 of the resonance frequency in the second vibration mode and the value f1 of the resonance frequency in the first vibration mode, Δf is desired to be more than or equal to 0.5 kHz and less than or equal to 5 kHz. If Δf is less than 0.5 kHz, when the vibrating element1is driven with around the resonance frequency in the second vibration mode, the possibility that the drive frequency is beyond the resonance frequency in the first vibration mode and the vibration amplitude abruptly decreases might increase. On the other hand, if Δf is more than 5 kHz, when the vibrating element1is driven with around the resonance frequency in the second vibration mode, the drive frequency is far from the resonance frequency in the first vibration mode and the vibration amplitude in the first vibration mode is hard to become large.

FIG. 4is a flowchart illustrating steps of manufacturing the vibration type actuator according to the exemplary embodiment of the present disclosure.

As illustrated inFIG. 4, in step S18, the piezoelectric element3is bonded to an elastic element, and in step S19, the flexible printed board (power feeding substrate)33is bonded to the piezoelectric element3. After steps S18and S19, the resonance frequencies in the two vibration modes are measured by impedance measurement using a single vibrating element1in step S20. Stratification is performed within a stratification range of 1% based on the measured resonance frequency in the second vibration mode.

The stratification is to classify the plurality of vibrating elements1into groups. For example, in the plurality of vibrating elements1, in a case where the minimum value f2min of the resonance frequency in the second vibration mode is 100 kHz, the ratio 0.01 (1%) is 1 kHz. Therefore, for example, the vibrating elements1in a range from 100 kHz or more to less than 101 kHz are classified into a first group, and the vibrating elements1in a range from 101 kHz or more to less than 102 kHz are classified into a second group. Further, the vibrating elements in a range from 102 kHz or more to less than 103 kHz are classified into a third group.

In this stratification in step S21, in the vibrating elements1within the group, the ratio of the difference between the maximum value f2max and the minimum value f2min of the resonance frequency in the second vibration mode to the minimum value f2min can be set to a value less than or equal to 0.01 (1%). Therefore, in step S22, the vibrating elements1are selected at random within a group. In step S23, bonding of the vibrating element holding member is performed. In step S24, motor assembly is performed. In such a manner, a motor having satisfactory performance can be obtained.

FIG. 5is a flowchart illustrating a variation example of the steps of manufacturing the vibration type actuator according to the exemplary embodiment of the present disclosure. This variation example can be used in a certain situation of a production site. That is, when the time from bonding of the power feeding substrate33in step S19to measurement of the resonance frequency in step S120is desired to be shortened, the measurement of the resonance frequency in step S120is performed one hour after the bonding of the power feeding substrate33in step S19(temperatures of the vibrating elements1are securely room temperature).

As illustrated inFIG. 6, however, the resonance frequency changes during the 24 hours after the power feeding substrate33has been bonded. Thus, variations in a changing quantity of the resonance frequency until the resonance frequency becomes constant should be taken into consideration. Therefore, in the measurement of the resonance frequency in step S120, the range of the stratification in step S121is narrowed and the ratio is less than or equal to 0.007 (0.7%).

The exemplary embodiments of the present disclosure have been described in detail above. However, the present disclosure is not limited to such specific exemplary embodiments, and variations are included in the present disclosure without deviating from the scope of the present disclosure. For example, the vibrating element1according to the exemplary embodiment of the present disclosure is applied not only to the rotary actuator illustrated inFIGS. 1A and 1B. For example, the vibrating element1can be applied also to a linear actuator where two vibrating elements1are disposed in a drive direction or are disposed on upper and lower surfaces of a contact element, respectively.

Further, the vibration type actuator according to the exemplary embodiment of the present disclosure is applicable to various usages such as lens drive of an image pickup apparatus (optical device), rotary drive of a photoconductive drum in a copying machine, or drive of a stage. Herein, as an example, an image pickup apparatus (optical device) where a vibration type actuator, which has a plurality of vibrating elements circularly disposed that rotationally drive the contact element, is used for driving lenses disposed in a lens barrel.

FIG. 7Ais a top view illustrating a schematic configuration of an image pickup apparatus700as an electronic device.

The image pickup apparatus700includes a camera body730having an image pickup element710and a power button720. The image pickup apparatus700further includes a lens barrel740having a first lens group (not illustrated), a second lens group320, a third lens group (not illustrated), a fourth lens group340, and vibration type actuators620and640. The lens barrel740is detachable as an interchangeable lens from the camera body730.

In the image pickup apparatus700, the vibration type actuator620drives the second lens group320as a driven member. The vibration type actuator640drives the fourth lens group340as a driven member. The vibrating elements1described with reference toFIGS. 1A to 7Aare used in the vibration type actuators620and640. For example, rotation of a contact element configuring the vibration type actuator620is converted into linear motion in an optical axis direction by a gear, and a position of the second lens group320in the optical axis direction is adjusted. Much the same is true for the vibration type actuator640.

FIG. 7Bis a block diagram illustrating a schematic configuration of the image pickup apparatus700. The first lens group310, the second lens group320, the third lens group330, the fourth lens group340, and a light quantity adjustment unit350are disposed on predetermined positions on the optical axis inside the lens barrel740. Light, which has passed through the first lens group310to the fourth lens group340and the light quantity adjustment unit350, is imaged on the image pickup element710. The image pickup element710converts an optical image into an electric signal to be output. The output is transmitted to a camera processing circuit750.

The camera processing circuit750amplifies the output signal from the image pickup element710or performs gamma correction on the output signal. The camera processing circuit750is connected to a central processing unit (CPU)790via an auto exposure (AE) gate755, and is connected to the CPU790via an autofocus (AF) gate760and an AF signal processing circuit765as well. A video signal, which has been subject to predetermined processing in the camera processing circuit750, is transmitted to the CPU790via the AE gate755, and the AF gate760and the AF signal processing circuit765. The AF signal processing circuit765extracts a high-frequency component of the video signal, generates an evaluation value signal for autofocus (AF), and supplies the generated evaluation value to the CPU790.

The CPU790, which is a control circuit that controls an overall operation of the image pickup apparatus700, generates a control signal for determining exposure or focusing based on the obtained video signal. The CPU790controls drive of the vibration type actuators620and640and a meter630so that the determined exposure and a suitable focused state can be obtained. Thus, the positions of the second lens group320, the fourth lens group340, and the light quantity adjustment unit350in the optical axis direction are adjusted.

Under the control using the CPU790, the vibration type actuator620moves the second lens group320in the optical axis direction, and the vibration type actuator640moves the fourth lens group340in the optical axis direction. Further, the meter630controls drive of the light quantity adjustment unit350.

The position of the second lens group320, which is driven by the vibration type actuator620, in the optical axis direction is detected by a first encoder770. The CPU790is notified of the detected result, and then feeds back the detected result to the drive of the vibration type actuator620. In a similar manner, the position of the fourth lens group340, which is driven by the vibration type actuator640, in the optical axis direction is detected by a second encoder775. The CPU790is notified of the detected result, and then feeds back the detected result to the drive of the vibration type actuator640.

The position of the light quantity adjustment unit350in the optical axis direction is detected by a diaphragm encoder780. The CPU790is notified of the detected result, and then feeds back the detected result to the drive of the meter630.

The vibration type actuators620and640are not limited to the application for driving the lens groups in the image pickup apparatus in the optical axis direction. The vibration type actuators620and640can also be used for an application for driving an image blur correction lens or an image pickup element in a direction orthogonal to the optical axis to correct image blurring.

According to the present disclosure, in a vibration type actuator having a plurality of vibrating elements, performance degradation caused by variations in the resonance frequency in the plurality of vibrating elements can be reduced.

This application claims the benefit of priority from Japanese Patent Application No. 2019-006395, filed Jan. 17, 2019, which is hereby incorporated by reference herein in its entirety.