Ultrasonic linear motor

p0001The invention relates to an ultrasonic linear motor and can be used in inexpensive optical precision systems or similar devices.

p0002Ultrasonic linear motors with ultrasonic oscillators designed as platelets on which the friction element is fastened are known (see, for example, FIG <patcit id="pcit0001" dnum="EP1267425A"><text>EP 1 267 425 A</text></patcit>). A pressing device is designed in such a way that the force applied to the friction element is transferred completely to the linear ball bearing of the movable element. This increases friction losses and it is not possible to use inexpensive plain bearings in such motors.

p0003Ultrasonic linear motors are also known in which the movable element includes the ultrasonic oscillator (see, for example, FIG <patcit id="pcit0002" dnum="EP0601671A1"><text>EP 0 601 671 A1</text></patcit>). In these motors, the ultrasonic motor forms a guide rail for the movable element. No linear ball bearings are required for these motors.

p0004The disadvantage of these motors is that the oscillator is complicated in its conical design and is therefore expensive to manufacture. The motors can be used in inexpensive optical systems. However, they are inaccurate in the positioning of the movable member, and it is not possible to reduce them arbitrarily.

p0005It is an object of the present invention to provide an improved ultrasonic linear motor with a simplified construction which also allows an increase in the accuracy of the positioning of the movable element, a simpler manufacturing and mounting technology of the motor, a reduction in cost and smaller dimensions. This object is achieved by an ultrasonic linear motor having the features of claim 1. Expedient further developments of the inventive idea are the subject matter of the dependent claims.

p0006The invention includes the essential idea of ​​placing a plate-shaped ultrasonic oscillator known as such in an arrangement with a movable element which has two friction parts and is in engagement with a guide rail into a suitable force constellation with respect to these guide means. In this case, by selecting the plate shape and the design of the movable element, it is also possible to use a part of the contact pressure force of the friction elements on the surfaces of the oscillator which is executed for pressing the movable element of the motor against its guide.

p0007The invention also includes the idea of ​​providing a resilient connection between said friction parts which provides a suitable pressing force of the movable element against the side surfaces of the ultrasonic oscillator. Furthermore, a suitable pressing force is thereby provided between the movable element and the mentioned guide rail. Finally, the invention involves the idea of ​​bringing the abovementioned pressing forces into a predetermined relationship by means of an inclined embodiment of the lateral surfaces of the ultrasonic oscillator.

p0008The invention makes it possible to substantially simplify the design of the miniature ultrasonic linear motor and to dispense with the use of precision rolling bearings. As a result, the adjustment accuracy of the movable element is increased since its movement relative to the surface of the precisely ground guide rail. The frictional losses in the plain bearing are reduced, the assembly technology is simplified, the production costs are reduced, the dimensions are reduced. This makes it possible to use the motor in inexpensive optical precision systems.

p0009In one embodiment of the invention it is provided that connection electrodes of the ultrasonic oscillator have elastic thin conductive rods, one end of which is fixedly connected to the corresponding electrodes and the other end of which is firmly fixed relative to the guide rail. This expands the design possibilities of the miniature motor according to the invention.

p0010In a further embodiment, it is provided that the guide rail is constructed in the manner of a bracket and is fixedly connected to a common electrode of the ultrasonic oscillator. This simplifies the design of the miniature motor.

p0011The main surfaces of the ultrasonic oscillator are rectangular in a suitable embodiment, and in a further embodiment this also applies to the side surfaces.

p0012The resilient or elastic connection of the friction parts of the movable element with one another is realized in a suitable embodiment by a compression spring which elastically prestresses the friction parts against each other. In an embodiment of this embodiment, this pressure spring is also formed in the manner of a clip, the friction parts being placed on the free ends of the limbs of the clip.

p0013Advantages and expediencies of the invention will become apparent from the following description of a preferred embodiment as well as modifications thereof and preferred aspects of the invention with reference to the figures. Of these show:

p0014<ul><li><figref idrefs="f0001">FIG</figref> The construction of the proposed engine in one embodiment,</li><li><figref idrefs="f0002">FIG</figref> The ultrasonic oscillator of the motor <figref idrefs="f0001">FIG</figref>,</li><li><figref idrefs="f0003">FIG</figref> A schematic representation in the motor of occurring forces, </li><li><figref idrefs="f0004">FIG</figref> A motor with rod-shaped connection electrodes,</li><li><figref idrefs="f0005">FIG</figref> A motor with a bracket - shaped guide rail and</li><li><figref idrefs="f0006">FIG</figref> A focusing block.</li></ul>

p0015A proposed ultrasonic motor 1 according to FIG <figref idrefs="f0001">FIG</figref> Consists of an ultrasonic oscillator 2, which is arranged in a holder 3. The oscillator 2 is designed as a plate 4 having parallel rectangular side faces (main faces) 5, end faces 6 and side faces 7 and 8.

p0016The motor 1 comprises a movable element 9, which is coincident with at least one guide rail 10. The movable element 9 consists of two friction parts 11 and 12, which are connected to one another via a compression spring 13, each of the friction parts being pressed against the corresponding side face 7 and 8 of the plate 4.

p0017The pressure spring 13 has special fixing points 14 and 15 for the support of the friction parts 11 and 12. Furthermore, it can have a running groove 16, on which the movable element 9 of the guide rail 10 slides.

p0018In the proposed motor, the side surfaces 7 and 8 of the plate 4 are defined as being at the angle λ to a longitudinal symmetry surface 19 of the plate 4 as in FIG <figref idrefs="f0002">FIG</figref> Inclined surfaces 17 and 18. A cut line 20 of the surfaces 17 and 18 of the plate 4 with the symmetry surface 19 extends parallel to the main edges 5. L is the length of the plate 4 and d is the length of the center line of the end face. The ratio of L / d is selected to be about 2.34.

p0019The longitudinal symmetry plane 19 is understood to be the plane which runs perpendicular to the main surfaces 5 and through a longitudinal symmetry line 21 of the surface 5. The line 21 represents the symmetry line of the surface 5 parallel to the length of the plate 4 (<figref idrefs="f0002">FIG</figref>.).

p0020The ultrasonic oscillator 2 of the proposed motor has two generators 22 and 23 for asymmetrical acoustic standing waves.

p0021The plate 4 of the oscillator 2 can be made entirely from piezoelectric ceramics. In this case, it may have two excitation electrodes 24 and 25 and a common electrode 26. In this case, each of the generators 22 and 23 is formed with the corresponding electrode 24 or 25, a part of the electrode 26 and the piezoceramic between the electrodes 24 and 25 and a part of the electrode 26. In order that an electrical excitation voltage can be applied, each of the electrodes 24, 25 and 26 must have an elastic connection, via which the electrode is connected to the electrical excitation source of the oscillator (not shown in the figures).

p0022In another embodiment of the oscillator 2, the plate 4 can be embodied as a multilayer part with two multilayer generators for acoustic waves.

p0023The plate 4 can also be a composite part consisting of a passive resonator and a piezoelectric exciter element connected thereto (the latter not shown in the figures).

p0024Thin abrasion-resistant layers of abrasion-resistant material can be applied to the side faces 7 and 8.

p0025<figref idrefs="f0003">FIG</figref> 12 is a schematic motor view from above. It illustrates the forces applied to the compression spring 13 in the motor 1. The force F_p Represents the spring force of the spring 13, which act on the friction parts 11 and 12 from the direction of the fixing points 14, 15 and the spring 13. These forces are transmitted to the side faces 7, 8 of the plate 4. Each of the forces F_p Can be converted into the force component F_n, Which acts perpendicular to the surface 7 or 8, ie, perpendicular to the surface 17 or 18, and into the force component F_t, Which acts along the surface 7 or 8, ie, along the surfaces 17 or 18.

p0026Since the force F acts along the guide rail 10, it is transmitted by means of the spring 13 to the contact point 27 of the running groove 16 of the spring 13 (movable element 9) with the guide rail 10 where they are added at one point. The force F_a Represents the resulting force resulting from the superposition of the two forces F_t To the symmetry plane 19. This force acts on the spring 13, namely from the side of the movable element 9 in the direction of the guide rail 10. The counterforce F is produced in the rail 10_s.

p0027<figref idrefs="f0004">FIG</figref> Shows the construction of the proposed motor in which the connecting electrodes 24, 25, 26 are designed as elastic rods 28, 29, 30. One ends of the terminals are fixedly connected to the surface of the corresponding electrodes. The other ends are fixed relative to the guide rails 10. For this purpose, they can be fastened on the plate 31, which fixes them, on which the guide rail 10 is also located. The plate 31 can at the same time serve as a connecting plate or as a printed circuit board.

p0028In the proposed motor, the guide rail 10 can be embodied as a clamp 32 with a guide part 33. The clamp 32 is fixedly connected to the common electrode 26 and may also be part of the fixed terminal 30 of the common electrode 6 (<figref idrefs="f0005">FIG</figref>) be. The fixed connections 28, 29, 30 can be made of thin steel wire or beryllium bronze with a rectangular or round cross-section. They are soldered or attached to the surface of the corresponding electrodes of the oscillator 2 with conductive adhesive.

p0029In each of the proposed motor variants, the moving part 9 of the optical system, for example the optical lens, the objective or the optical filter (these elements are described in the <figref idrefs="f0001">FIG</figref>, <figref idrefs="f0002">2</figref>, <figref idrefs="f0003">3</figref>, <figref idrefs="f0004">4</figref> Not shown). For this purpose, the spring 13 can have openings 34 (<figref idrefs="f0001">FIG</figref>, <figref idrefs="f0004">4</figref>, <figref idrefs="f0005">5</figref>). The moving part can also be fixed in any other way.

p0030<figref idrefs="f0006">FIG</figref> Shows a focusing block 35 of the miniature camera. The block 35 consists of the housing 3 with a base plate 36, a holder 37 for a lens group 38 with the optical axis 39, a support 40 for the oscillator 2, a cover 41 and a fixing spring 42.

p0031By means of the forces F_p The compression spring 13 presses with its fixing points 14 and 15 the friction parts 11 and 12 against the side faces 7 and 8 of the plate 4 of the oscillator 2 (<figref idrefs="f0001">FIG</figref>). The forces F_p Are determined by the elasticity of the spring 13 and by the required tensile stress F_m Of the miniature motor.

p0032Since the planes 17 and 18 of the side surfaces 7 and 8 are arranged at the angle λ (<figref idrefs="f0002">FIG</figref>) Are inclined to the longitudinal symmetry plane, the forces F are shared_p On the surfaces 7 and 8 (<figref idrefs="f0003">FIG</figref>) Into a force F_n, Which press the friction parts against the surfaces 7 and 8 and into a force F_t , Which acts along the surfaces 7 and 8 (along the planes 17 and 18).

p0033F_n = F_{p *} cosλ F_t = F_{p *} sinλ

p0034The ratio of the forces is:

p0035F_t/ F_n= T_G*λ

p0036The force F_n Is determined by the required pressing force of the friction parts 11 and 12 against the surfaces 7 and 8 and is extended by the maximum tensile force F_m Max of the motor and the coefficient of friction of the friction pair K_f As follows:

p0037F_n = F_mMax / K_f

p0038The force F_p Is determined according to the following formula:

p0039F_p = F_mMax / K_{f *}cos

p0040The force F_t Is transmitted to the guide rail 10 by the spring 13 and engages at point 17 (<figref idrefs="f0003">FIG</figref>) at. Each time, the force acts at the angle λ to the plane of symmetry 19. The resulting force F_a - Result of the two attacking forces F_t ; Which presses the movable element 9 against the guide rails 10, is:

p0041F_a = 2 F_t Cos λ = 2 F_{p *} sin λ_*cos λ

p0042By applying a excitation voltage to the electrodes 24 or 25, relative to the common electrode 26, the generator is activated for acoustic oscillations 22 or 23. As a result, an asymmetrical acoustic standing wave is formed in the oscillator 2 of the motor, resulting in a movement of the movable element 9 in the direction of the excited generator, as shown in FIGS<figref idrefs="f0001">FIG</figref>, <figref idrefs="f0004">4</figref>, <figref idrefs="f0005">5</figref>, <figref idrefs="f0006">6</figref> With arrows. Switching the excitation voltage from one (eg No. 22) to the other generator (eg No. 23) causes the direction of movement of the element 9 to be reversed.

p0043In the excited oscillator 2, the maximum tensile force F is produced_mMax which is pressed by the force F pressing the friction elements 11 and 12 against the side faces 7 and 8 of the plate 4_n Is determined. These forces are influenced by the force F acting by the spring 13 at the angle λ_p certainly.

p0044An essential feature of this motor construction is that, for pressing the movable element 9 against the guide rail 10, only a part of the force F generated by the pressure spring 13 is produced_p (Component F_t) is used. This part of the force can be changed by changing the angle λ to such an extent that only the force F required for pressing the element 9 to the guide rail 10 is required_a . This makes it possible to reduce frictional losses between the movable member 9 and the guide rail 10 to a minimum.

p0045The force F_t Causes the motor to move between the guide rail 10 and the holder 3 (<figref idrefs="f0001">FIG</figref>) Is compressed. As a result, the gap between the element 9 and the guide rail 10 disappears, whereby a robust construction which is stable against external influences is formed.

p0046The movable member 9 moves relative to the profile of the surface of the guide bar 10 made as a precision ground bar, on which the raceway 16 (<figref idrefs="f0001">FIG</figref>).

p0047In the <figref idrefs="f0004">FIG</figref> , The fixed connections 28, 29, 30 and the guide rail 10 are fastened on the plate 31. This expands the design possibilities of the proposed miniature motor. As a result, such a motor can be mounted as an electronic component on a printed circuit board.

p0048In the <figref idrefs="f0005">FIG</figref> , The running groove of the movable element 9 slides in the guide part 33 of the clamp 32, which is fixed on the surface of the oscillator 2. This substantially simplifies the motor and reduces the friction losses in the friction contact.

p0049<figref idrefs="f0006">FIG</figref> Shows an example of the application of the proposed motor in a focussing block 35 of a miniature photographic apparatus.

p0050In this application, the oscillator 2 is pressed against the support 40 by the force components of the compression spring 13 and is fixed in the vertical direction by the spring 42. The block consists of two guide rails 10 against which the running grooves 16 arranged on the holder 37 of the lens group 38 are pressed. The construction of the focusing block 35 allows a displacement of the lens group 38 parallel to its optical axis 39 with an accuracy determined by the alignment accuracy of the guide rails 10.

p0051reference signs

p0052<ul><li>motor</li><li>2 Ultrasonic oscillator</li><li>3 holders</li><li>4 Oscillator plate 2</li><li>5 Main surfaces of the plate 4</li><li>6 End faces of the plate 4</li><li>7, 8 faces of the plate 4</li><li>9 Moving element</li><li>10 Guide rail</li><li>11,12 Friction parts of the movable element 9</li><li>13 Pressure spring</li><li>14, 15 fixation points for holding the friction parts 11, 12</li><li>16 Running groove</li><li>17, 18 surface of the side surfaces 7, 8</li><li>19 longitudinal plane of the plate 4</li><li>20 is a sectional view of the planes 17, 18, 19</li><li>21 The longitudinal symmetry plane of the surface 5</li><li>22, 23 Asymmetrical standing wave generators</li><li>24, 25 excitation electrodes</li><li>26 Common electrode</li><li>27 contact point between the movable element 9 and the guide rail 10</li><li>28, 29, 30 fixed connections</li><li>31 plate</li><li>32 part of the connection 30 as a clamp</li><li>33 guide part of the clamp 32</li><li>34 Mounting holes</li><li>35 Focusing block of the photo apparatus</li><li>36 Base plate of the block 35</li><li>37 Holder for the lens group 38</li><li>38 Lens group 38</li><li>39 Optical axis of the lens group 38</li><li>40 Support for the oscillator 2</li><li>41 Cover</li><li>42 Fixing spring</li></ul>