JP2007252103A - Drive unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin drive unit using a piezoelectric device. <P>SOLUTION: An AF drive unit 10 has the piezoelectric device 12 bent due to voltage application, a retaining member 14 for retaining one edge of the piezoelectric device 12, a driven member 16 brought into frictional contact with a free edge of the piezoelectric device 12, a lens frame 18 jointed with the driven member 16, a pressurized mechanism for pressing the piezoelectric device 12 and the driven member 16 with constant force, a guide 20 for retaining the driven member 16 so as to slide freely in a Z direction, and a unit case 22 for accommodating these devices. The thickness of the AF unit 10 is constituted so as to be thin in the same way as a braking region of the lens frame 18, by disposing the piezoelectric device 12 so that the thinnest dimension edge may be disposed in the Z direction. The piezoelectric device 12 is bent to slide the driven member 16 in the Z direction by the frictional force between the piezoelectric device 12 and the driven member 16. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a drive device including a piezoelectric actuator, and more particularly to a drive device suitable as an autofocus unit for a small optical lens.

  Recently, as a development trend in digital cameras, miniaturization and weight reduction have been promoted, and development of a compact and lightweight autofocus mechanism for such a camera has been carried out. Further, in camera-equipped mobile phones, cameras having an autofocus function are being mounted instead of conventional cameras using single focus lenses.

  Various devices using piezoelectric elements have been proposed as such small autofocus devices (see, for example, Patent Documents 1 and 2). For example, the driving device disclosed in Patent Document 1 has a structure in which a rod member is fixed to an end of a piezoelectric element that causes expansion / contraction displacement, and an engagement member holding a lens is engaged with the rod member. ing. In this drive device, the piezoelectric element is slowly displaced, and the engaging member and the lens are moved by the displacement amount of the piezoelectric element by utilizing the frictional force between the rod member and the engaging member. And then, an autofocus device is disclosed in which the piezoelectric element is instantaneously displaced to slide the rod member relative to the engaging member, and restore the state of the piezoelectric element without changing the position of the engaging member and the lens. Yes.

  In addition, the actuator disclosed in Patent Document 2 is basically piezoelectric, although there is a difference in the arrangement of the piezoelectric element and the lens frame that is the driven body, compared to the driving device disclosed in Patent Document 1. The element driving method is the same.

However, in these driving devices and the like, the moving direction of the lens as the driven body and the expansion / contraction direction of the piezoelectric element are the same. For this reason, the thickness of the driving device becomes thick under the influence of both the braking distance of the lens and the element length of the piezoelectric element, and is not suitable for mounting on a thin device such as a mobile phone.
Japanese Patent No. 3711935 (FIGS. 1, 17, paragraph [0008], etc.) Japanese Patent Laying-Open No. 2005-354829 (FIG. 2, paragraphs [0023], [0025] to [0027], etc.)

  The present invention has been made in view of such circumstances, and an object thereof is to provide a thin drive device.

  According to the present invention, a piezoelectric element that generates a bending displacement by applying a predetermined voltage, a holding member that holds one end of the piezoelectric element, a driven body that frictionally contacts the free end of the piezoelectric element, A pressurizing mechanism for pressing the piezoelectric element and the driven body with a constant force; and a guide for slidably holding the driven body in a predetermined direction, and applying a predetermined voltage to the piezoelectric element. Then, by bending the piezoelectric element, a driving device is provided in which the driven body is slid in a guide direction by the guide by a frictional force between the piezoelectric element and the driven body. .

  In this drive device, when the piezoelectric element is bent and the driven body is slid in a predetermined direction and then the piezoelectric element is displaced in a direction opposite to the direction in which the driven body is moved, Preferably, the piezoelectric element is driven by adjusting the displacement speed so that the piezoelectric element slides relative to the driven body so that the return of the piezoelectric element is reduced. The piezoelectric element is preferably driven at a frequency different from the natural frequency, that is, non-resonant driving.

  It is preferable to provide a sliding portion made of a wear-resistant material at the free end of the piezoelectric element. The sliding part and the sliding part in contact with the sliding part in the driven body are either cylindrical, semi-cylindrical, elliptical column, or semi-elliptical column. It is preferable to have a configuration in which the longitudinal axis of the sliding portion is orthogonal.

  In the driving device of the present invention, the length direction and the width direction of the piezoelectric element can be orthogonal to the moving direction of the driven body, and even if the thickness of the piezoelectric element matches the moving direction of the driven body, Since the length can be kept within the range of the braking distance of the driven body, the structure can be made extremely thin.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, a case where the driving device of the present invention is applied to an automatic focus mechanism (AF unit) that moves a focus lens of a camera will be described. I will do it.

  FIG. 1 is a perspective view showing a schematic structure of the AF unit 10, and FIG. 2 is a cross-sectional view taken along line AA in FIG. The AF unit 10 is in frictional contact with a piezoelectric element 12 that generates a bending displacement by applying a predetermined voltage, a holding member 14 that holds one end of the piezoelectric element 12 in the length direction, and a free end of the piezoelectric element 12. A driven member 16, a lens frame 18 connected to the driven member 16, a pressurizing mechanism (not shown) for pressing the piezoelectric element 12 and the driven member 16 with a constant force, and the driven member 16 in the Z direction. And a guide case 20 that is slidably held, and a unit case 22 that accommodates these guides. The AF unit 10 is connected to a drive control device 10A for driving the piezoelectric element 12.

  As the piezoelectric element 12, as shown in FIG. 2, a bimorph element having a structure in which a piezoelectric plate 32 is bonded to both main surfaces of a metal reinforcing plate 31 is preferably used. The piezoelectric element 12 may be a unimorph element in which a piezoelectric plate 32 is attached to one main surface of the reinforcing plate 31, and the piezoelectric plate 32 may have a laminated structure.

  The piezoelectric elements 12 are arranged such that the length direction is the X direction, the width direction is the Y direction, and the thickness direction is the Z direction. As shown in FIG. 2, by applying a predetermined voltage to the piezoelectric plate 32 of the piezoelectric element 12, a bending displacement whose main component is a displacement in the Z direction is generated at the tip of the piezoelectric element 12.

  A sliding member 26 made of a material having excellent wear resistance, for example, a ceramic material such as silicon nitride, silicon carbide, or alumina, or a metal material such as stainless steel or cast iron is attached to the free end of the piezoelectric element 12. The sliding member 26 has a semi-cylindrical shape extending in the width direction of the piezoelectric element 12.

  The tip of the reinforcing plate 31 may be directly brought into frictional contact with the driven member 16 without providing the sliding member 26. However, it is preferable to use a material having a high spring property for the reinforcing plate 31. Sufficient durability may not be obtained. Therefore, it is preferable to provide the sliding member 26 that is more excellent in wear resistance than the reinforcing plate 31 from the viewpoint of enhancing durability. In addition, when the material which has sufficient abrasion resistance is used for the reinforcement board 31 by the relative relationship with the material which comprises the to-be-driven member 16, it is not necessary to provide the sliding member 26. FIG.

  The holding member 14 holding one end of the piezoelectric element 12 is fixed to the unit case 22, whereby one end of the piezoelectric element 12 is fixed immovably. The holding member 14 may be integrated with the unit case 22.

  A portion of the driven member 16 that contacts the sliding member 26 is formed with a semi-cylindrical sliding portion 28 such that its length direction is the Z direction. Further, as described above, the sliding member 26 attached to the piezoelectric element 12 has a semi-cylindrical shape and the length direction thereof is the Y direction. Therefore, since the sliding member 26 and the slidable portion 28 are orthogonally contacted, these contact points have a certain area but are point contacts.

  For example, in the case where the piezoelectric element 12 and the driven member 16 are in a structure where the surfaces are brought into contact with each other, high accuracy is required for the arrangement of the piezoelectric element 12 and the driven member 16, and driving is performed when this is not satisfied. This causes a problem that the characteristics are extremely deteriorated. However, as described above, by making the sliding member 26 and the sliding portion 28 anti-cylindrical, the width direction of the piezoelectric element 12 slightly deviates from the Y axis, and the length direction of the sliding portion 28 Even if they slightly deviate from the Z direction, it is easy to ensure these contacts, and the drive characteristics can be prevented from greatly deteriorating.

  The shapes of the sliding member 26 and the slid portion 28 are not limited to a semi-cylindrical shape, and the same effect as described above can be obtained even if the shape is a cylindrical shape, an elliptical column shape, or a semi-elliptical column shape. When the sliding member 26 is not provided on the element 12, it is preferable that the side surface on the free end side of the reinforcing plate 31 be a semi-cylindrical shape or the like.

  The pressurizing mechanism may be one that presses the piezoelectric element 12 against the driven member 16, or may be one that presses the driven member 16 against the piezoelectric element 12. Although this pressurizing mechanism is not shown, for example, a leaf spring, a coil spring, or the like can be used. When adopting a structure in which the driven member 16 is pressed against the piezoelectric element 12, for example, in the X direction, the driven member 16, a bearing, a plate member, The structure which is contacting in order of a leaf | plate spring and the wall part of the unit case 22 is mentioned.

  Moreover, as a pressurization mechanism, the thing of the structure which fits and fixes the one side plate 22a which comprises the unit case 22 in the side plate 22b orthogonal to this side plate 22a is mentioned. That is, the side plate 22a is provided with a claw portion having a barb, and the side plate 22b is provided with a hole portion for fitting the claw portion so that the barb does not come off, and the piezoelectric element 12 is in contact with the driven member 16 Then, by applying a certain force, the claw portion is fitted into the hole portion and fixed. According to this, when the side plate 22a is attached to the side plate 22b, the piezoelectric element 12 is in a state of applying pressure to the driven member 16 with a constant force.

  The guide 20 is fixed to the unit case 22, has a substantially T-shaped cross section, and its length direction is the Z direction. The driven member 16 includes a groove for fitting the guide 20 so as to be movable in the Z direction along the guide 20.

  Since the lens frame 18 is connected to the driven member 16, the lens frame 18 moves according to the movement of the driven member 16. The drive control device 10 </ b> A generates a drive voltage for the piezoelectric element 12.

  Next, the driving mode of the AF unit 10 will be described. FIG. 3 shows an example of a voltage waveform for driving the piezoelectric element 12. FIG. 4 schematically shows how the piezoelectric element 12 is displaced and how the driven member 16 is moved. Here, the piezoelectric element 12 is displaced in the + Z direction (upward) when a positive voltage is applied to the piezoelectric plate 32, and is displaced in the −Z direction (downward) when a negative voltage is applied to the piezoelectric plate 32. To do.

First, the driven member 16 is in a stationary state at time t ₀ and voltage V ₀ . The drive control unit 10A, increasing the voltage at a constant gradient from the voltage V ₀ to the voltage V _1, and bent so as to move the free end of the piezoelectric element 12 to the + Z side, the sliding portion and the sliding member 26 at this time The driven member 16 is moved to the + Z side by the frictional force 28. The amount of movement of the driven member 16 at this time is indicated by δ in FIG.

At this time, paying attention to the position of the sliding member 26, if the moving amount of the sliding member 26 to the + Z side increases, the moving amount to the −X side also increases. The frictional force between the moving parts 28 is reduced. Therefore, when the piezoelectric element 12 is displaced by a certain amount or more, the driven member 16 cannot move. The voltage V ₁ may be a voltage at which the driven member 16 cannot move or a voltage at which the driven member 16 can move.

Further, the voltage gradient from the value of the voltage V ₀ which voltages V ₁ to the voltages V _1, the difference in the movement mode of the driven member 16 occurs. For example, when the voltage gradient is gentle and there is a sufficient frictional force between the sliding member 26 and the sliding portion 28 at the voltage V ₁ , the driven member 16 moves to the movement of the sliding member 26. Move together. On the other hand, in this voltage gradient is steep, and, if there is not enough friction to move the driven member 16 between the voltages V ₁ in the sliding member 26 and the sliding portion 28, the driven member 16 is moved by being kicked by the sliding member 26.

  Since a pressurized pressure is applied between the piezoelectric element 12 and the driven member 16, even if the piezoelectric element 12 is displaced, the sliding member 26 is displaced by this pressure as long as the displacement is within a certain range. The state in contact with the sliding portion 28 is maintained. The sliding member 26 may be driven so as to always come into contact with the sliding portion 28 or may be driven so as to be separated from the sliding portion 28.

Then lowered steeply voltage from voltages _{V 1} to the voltage _{V 2.} For example, the voltage V ₂ = −V ₁ . As a result, the displacement of the piezoelectric element 12 is reversed. At this time, since the displacement speed of the piezoelectric element 12 is high, the sliding member 26 slides with respect to the sliding portion 28, thereby moving the position of the sliding member 26 to the −Z side and the driven member 16. The position can be held on the + Z side. In actuality, when the voltage is changed from V ₁ to V ₂ , a certain frictional force acts between the sliding member 26 and the sliding portion 28, and the driven member 16 has a certain amount of −Z side. However, this return is ignored in FIG.

Next, when the voltage is increased from the voltage V ₂ to the voltage V ₁ with a constant gradient, the free end of the piezoelectric element 12 bends so as to move to the + Z side, and the friction between the sliding member 26 and the sliding portion 28 occurs. The force gradually increases, and the driven member 16 moves to the + Z side by this frictional force. The amount of movement of the driven member 16 at this time is indicated by η in FIG. Naturally, η> δ. After the voltage V ₁ is thus set, the driving of the voltages V _{1 to} V ₂ is repeated, and when the driven member 16 is moved to a predetermined position, the voltage is suddenly set to 0 V or held at that voltage. When the driven member 16 is moved to the −Z side, the driving voltage shown in FIG. 3 may be reversed.

  The driving of the piezoelectric element 12 described above is driving at a frequency different from the natural frequency of the piezoelectric element 12, that is, non-resonant driving. When resonance driving is used, another vibration mode appears, and the movement of the piezoelectric element 12 described above may be hindered. In addition, since the resonance frequency depends on the shape, if a drive power supply with a constant drive frequency is used, there is a risk that the performance difference between AF units may increase. By using the non-resonant driving method, occurrence of these problems can be suppressed.

  As described above, in the AF unit 10, by applying a predetermined voltage to the piezoelectric element 12 and bending the piezoelectric element 12, the frictional force between the piezoelectric element 12 and the driven member 16, that is, the sliding member 26 and the driven member 16. The driven member 16 can be slid in the guide direction by the guide 20 by the frictional force with the sliding portion 28.

  In the AF unit 10, the sliding direction of the driven member 16 and the lens frame 18 connected to the driven member 16 is the Z direction, and the piezoelectric element 12 is arranged so that the thickness direction with the shortest dimension is the Z direction. In addition, since the thickness of the piezoelectric element 12 can be made thinner than the braking distance of the lens frame 18, the thickness of the AF unit 10 does not depend on the shape of the piezoelectric element 12. The thickness can be made as thin as the braking range of the lens frame 18.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to such a form. For example, when the AF unit 10 is actually mounted on a camera, a sensing unit for detecting the lens position held by the lens frame 18 or for determining whether or not the focus is appropriate based on the degree of blurring of a visible digital image. And the piezoelectric element 12 needs to be feedback-controlled based on the signal from the sensing unit. Needless to say, the drive control apparatus 10A may have such a feedback function.

1 is a perspective view showing a schematic structure of an AF unit according to an embodiment of the present invention. AA sectional view of an AF unit. The figure which shows an example of the voltage waveform for driving a piezoelectric element. The figure which shows typically the aspect of the displacement of a piezoelectric element, and the movement of a to-be-driven member.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... AF unit, 10A ... Drive control apparatus, 12 ... Piezoelectric element, 14 ... Holding member, 16 ... Driven member, 18 ... Lens frame, 20 ... Guide, 22 ... Unit case, 22a, 22b ... Side plate, 26 ... Sliding A moving member, 28 ... a sliding part, 31 ... a reinforcing plate, 32 ... a piezoelectric plate.

Claims (5)

A piezoelectric element that generates a bending displacement by applying a predetermined voltage;
A holding member for holding one end of the piezoelectric element;
A driven body in frictional contact with the free end of the piezoelectric element;
A pressurizing mechanism for pressing the piezoelectric element and the driven body with a constant force;
A guide that slidably holds the driven body in a predetermined direction;
By applying a predetermined voltage to the piezoelectric element and bending the piezoelectric element, the driven body is slid in a guide direction by the guide by a frictional force between the piezoelectric element and the driven body. The drive device characterized.   When the piezoelectric element is bent to slide the driven body in a predetermined direction and then the piezoelectric element is displaced in a direction opposite to the direction in which the driven body is moved, The drive device according to claim 1, further comprising a drive control device that adjusts a displacement speed of the piezoelectric element so that the piezoelectric element slides relative to the driven body so as to reduce a return.   The drive device according to claim 1, further comprising a drive control device that drives the piezoelectric element at a frequency different from a natural frequency of the piezoelectric element.   The driving device according to any one of claims 1 to 3, further comprising a sliding portion made of an abrasion-resistant material at a free end of the piezoelectric element. Both the sliding part and the sliding part in contact with the sliding part in the driven body are either a cylindrical shape, a semi-cylindrical shape, an elliptical cylindrical shape, or a semi-elliptical cylindrical shape,
The drive device according to claim 4, wherein a length direction axis of the sliding portion and a length direction axis of the slid portion are orthogonal to each other.

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