CA2700614C

CA2700614C - Ultrasonic drive

Info

Publication number: CA2700614C
Application number: CA2700614A
Authority: CA
Inventors: Dmytro Vyshnevsky
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-04-16
Filing date: 2010-04-16
Publication date: 2015-12-08
Anticipated expiration: 2030-04-16
Also published as: CA2700614A1

Abstract

The proposed ultrasonic drive is intended for use as a driver of moving parts working in fields of strong direct and secondary (e.g.
scatter) radiation. Typically, these drives use electromagnetic motors however irradiating field destroys their electrical insulation and some motor parts become radioactive in strong radiation fields. There are existing drives in which an ultrasonic actuator is used as a driven element. Such drives are made using a piezoelectric resonant element to which the friction element is attached using an organic adhesive layer. This layer can also decompose under radiation influence. In the proposed drive, the piezoelectric resonant elements, the friction elements and friction layer are located, in such way that the junction of these elements with the piezoelectric resonant element is screened from irradiating field by the body of the piezoelectric resonant element or by the body of the driven element.

Description

ULTRASONIC DRIVE
BACKGROUND OF THE INVENTION
The proposed ultrasonic drive is intended for use as a driver of moving parts working in fields of strong direct and secondary alpha, beta, gamma or neutron radiation, such as that found in particle accelerators, medical irradiating apparatus, in open space or other similar locations where there is a strong radiation field present.
In medical X-ray applications, for example, the radiation consists of direct X-ray and secondary X-ray radiation. Direct X-ray radiation is emitted directly from the radiation source and secondary X-ray radiation is also known as scattered radiation.
A specific example where such an ultrasonic drive may be applicable is as the drive system of the leaves of a multi-leaf collimator which provides conformal shaping of medical radiotherapy treatment beams to tumours.
THE PURPOSE OF THE INVENTION
To achieve an increase in force, speed, reliability and durability of drives working in strong radiation fields and to increase the drive lifetime and sphere of application.
DISCLOSURE OF THE INVENTION
In the framework of the invention, the goal was to create an ultrasonic drive with the new features to achieve the purpose of the invention in the simplest possible way, in both design and implementation.
DESCRIPTION OF THE PRIOR ART
Drives are known to exist that move devices or parts of devices within fields of alpha, beta, gamma,

2 or neutron radiation. They employ electromagnetic motors and are described in various US patents [1, 2,

3, 4].
A drawback of such drives is that the radiating field destroys the electrical insulation within the electrical motor windings. This leads to the possibility of a short circuit within the motor system. Therefore, such drives can be unreliable and can fail frequently.
Another drawback of such designs is that the employed conventional, electrical motors can have cobalt-iron material as a component in their armatures and stators which can become radioactive in strong radiation fields. Radioactive elements such as Co-57 and Co-60 can be produced. With such isotopes having half-lives of over five years, there can be long-term storage or disposal costs for failed motors. There are also regulatory risks involved should these radioactive motors inadvertently get into the normal waste stream.
Also, there are known drives in which an ultrasonic actuator is used as a driven element. Such drives are made using a piezoelectric resonant element to which the friction element is attached using an organic, adhesive layer, as described in US patent [5]. These piezoelectric elements do not have electrical windings and can therefore not short circuit, and radiation fields do not influence the piezoelectric effect they employ.
The disadvantage of these drives is that irradiating the piezoelectric actuator with alpha, beta, gamma, or neutron radiation can affect the organic adhesive layer between the piezoelectric resonant element and the friction element. Radiation breaks long organic chemical bonds, prevent bond recombination and cause permanent damage in organic material. This could lead to the degradation of the organic adhesive, and a reduction in the strength of the joint between friction element with a piezoelectric resonant element. This could limit the pulling force developed by the drive, reduce the maximum speed of the driven element and reduce the stability, reliability and lifespan of the drive.
Thus, the drive's field of application could be limited.
Furthermore, the influence of a strong radiation field jointly with a strong ultrasonic field leads to the destruction of the contact surfaces of the friction element and a driven element's friction layer. As, well, radiation fields ionize the air in the area of frictional contact of the friction element with the driven element. Both of these effects decrease the stability of the frictional contact and the reliability of the drive.
SUMMARY OF THE INVENTION
The proposed ultrasonic drive is made having one or more ultrasonic actuators consisting of resonant piezoelectric elements which are attached to them.
Friction elements that are pressed to the driven element making frictional contact and located in a radiating field of a direct and (or) secondary radiation beam and the piezoelectric resonant elements are made of piezoelectric ceramic containing lead, and the driven element is made wholly or partly of a material which absorbs alpha, beta, gamma or neutron radiation, such as tungsten or its alloys, lead or its alloys, oxide ceramics or metal ceramic alloys that contain these materials, and the friction elements and the friction layer are located in relation to the radiation field, in such way that the junction of these elements with the piezoelectric resonant element is screened from an irradiating field by the body of the piezoelectric resonant element or by the body of the driven element.
Furthermore, the drive can be made in the form of packets of ultrasonic actuators, each of which, or each pair of which has the driven element, and the

4 packets arranged so that the frictional contact and place of connection of each friction element with a piezoelectric resonance element is screened from direct or secondary alpha, beta, gamma, or neutron radiation by the driven elements of the packets of actuators themselves. In addition, the friction element of each actuator can be made wholly or partially from a material that absorbs or attenuates alpha, beta, gamma or neutron radiation, such as aluminium oxide, zirconium oxide with the addition of tungsten or tungsten carbide or tungsten or its alloys, lead or its alloys or cermets containing these materials. Both these design features create an additional shield layer for the adhesive and the frictional contact, which will stabilize the ultrasonic drive performance.
An ultrasonic actuator mounting is used for crimping and fixing the ultrasonic actuator. The proposed drive uses a non-organic mounting material for the ultrasonic actuator that will retain the actuator in its minimum oscillating velocity, for example, material that absorbs or attenuates alpha, beta, gamma or neutron radiation, such as aluminium oxide, zirconium oxide.
Furthermore, the proposed drive uses a non-organic mounting material (for example, material that absorbs or attenuates alpha, beta, gamma or neutron radiation, such as aluminium oxide, zirconium oxide) for the ultrasonic actuator that can be part of the actuator resonant system. This increases the reliability of the mounting of the ultrasonic actuator.
BRIEF DESCRIPTION OF THE DRAWINGS
Figures: 1 - 4: Design variants of the proposed ultrasonic drive.
Fig. 5. The ultrasonic drive that includes packets of actuators 1 and packets of driven elements 5.

1. Ultrasonic actuator.
2. Piezoelectric resonant element.
3. Friction element.
4. Frictional layer

5. Driven element.

6,7. Springs.
8. Bearing.
9. Acoustic wave generator.
10. Electrical excitation source.
11. Adhesive layer.
12. Arrow indicating the direction of the strong radiation field.
13. Strong radiation field beam.
14. Radial direction of propagation of the field of secondary radiation.
15. Secondary radiation field.
16. Radial plane.
17. Strip.
18. Reflected radiation field.
19. Packet of actuators 1.
20. Packet of driven elements 5.
21. Beam shape.
22. Frictional contact DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENTS
The proposed ultrasonic drive (see Fig.1, Fig.2) contains one or more ultrasonic actuators 1 having an operating frequency fo. Each actuator 1 consists of a piezoelectric resonant element plate 2, made of a piezoelectric ceramic containing lead, lead niobium-stibium, zirconate-titanate or lead zirconate titanate (PZT). Such piezoelectric ceramics has shielding properties from alpha, beta, gamma or neutron radiation.
In such design the friction element 3 is rigidly attached to resonant element 2. The friction element 3 is made from a hard, wear resistant oxide ceramic, for example aluminum oxide, zirconium oxide with the addition of tungsten or tungsten carbide, or a cermet based on tungsten carbide. These materials also absorb or attenuate alpha, beta, gamma, or neutron radiation.
The friction element 3 of actuator 1 is pressed against the frictional layer 4 of the driven element 5, forming a frictional contact 22 between the friction element 3 and the frictional layer 4 of the driven element 5.
The frictional layer 4 and the driven element 5 may be made of aluminium oxide, zirconium oxide with the addition of tungsten or tungsten carbide, or a cermet based on tungsten carbide.
Ultrasonic actuator mounting can be made in a form of springs or other elastic elements, thus actuator 1 is prevented from having longitudinal displacement by metal bracing springs 6, metal flat springs 7, cylindrical springs (not shown).
Springs 6 or 7 may also be the resonant elements, which are a part of the resonant system of the actuator 1. For this purpose, one of the resonance frequencies of the springs 6 or 7 should coincide with the resonance frequency fo of actuator 1.
The driven element 5 can be mounted in bearings 8 (Fig. 1) or it may be held in place by two actuators 1 located directly opposite of one another (Fig. 2).
The piezoelectric resonant element 2 can have two, four or more acoustic wave generators 9. Each generator 9 is comprised of an energizing electrode, a common electrode and the piezoelectric ceramic between them (not shown). Each acoustic wave generator 9 is connected to an electric exitation source10.
The friction element 3 can be attached to the piezoelectric resonant element 2 by means of a high temperature, organic adhesive layer 11. This adhesive can be, for example, epoxy-resin-based bonding agent for example polyimide adhesive or some other high temperature organic adhesive.

7 The connection made by the adhesive glue layer 11 must be rigid, but at the same be capable of compensating for the difference in the coefficients of thermal expansion of materials of which piezoelectric resonant element 2 and friction element 3 are to compensate difference in stiffness (E-modulus) of these materials, the adhesive layer 11 should be sufficiently thick. Such an adhesive glue layer 11 may contain particles of solid material that absorbs radiation, for example, particles of tungsten, tungsten carbide, lead oxide or boron.
The proposed drive is designed to operate in fields of strong alpha, beta, gamma, or neutron radiation. In most practical cases, for example in linear accelerators, such radiation fields extend from the radiation source in the form of a beam. The direction of propagation of such beam is shown in the figures by the arrow 12.
In Fig. 3 and subsequent figures, the strong radiation field beam is depicted in the form of the cylinder 13 or cone (not shown). The source emitting the beam 13 on the figures is not shown. The fields of scattered radiation extends in radial directions as part of the beam 13, is shown by the dotted lines 14 whose intensity could gradually decrease, depending on the type of radiation. The field of secondary radiation shown in Fig. 3 and in other figures is shown by dotted lines 15, located in one of the radial plane 16.
Devices for which the proposed drive is suited may contain metal parts from which the beam 13 or the secondary radiation field 15 is reflected. Such a part is shown in Fig. 3 in the form of a strip 17.
Such reflected field in this figure is shown by the lines 18.
Fig. 4 shows the proposed ultrasonic drive in which two actuators 1 which are located directly opposite each other are holding the driven element 5.

8 Fig. 5 shows the proposed ultrasonic drive, which consists of a packet 19 of ultrasonic actuators 1. In the packet 19 each pair of ultrasonic actuators 1 holds and sets in motion the driven element 5. This forms the package of the driven elements 20.
Such a package of driven elements 20, driven by the proposed ultrasonic actuators packet 19 can be used to conformally shape the radiation beam 13 to the shape of a tumour. Shape 21 in Fig. 5 shows a possible shape of the beam 13 after passing it through the package of the driven elements 20.
The proposed ultrasonic drive works as follows using Fig. 1: The electrical excitation source 10 supplies the electrical exciting voltage having frequency fo to one or two generators of ultrasonic acoustic waves 9 of the actuator 1, which corresponds to the resonant frequency of the piezoelectric resonant element 2. This voltage, as a result of the inverse piezoelectric effect, excites a standing acoustic wave in the actuator 1.
With the spread of the wave in the actuator 1 its friction element 3 begins to waver on an inclined or elliptical trajectory.
Since the friction element 3 is rigidly connected to the resonant element 2 of the actuator 1, the force developed by the resonant element 2 is passed to the driven element 5 by the friction element 3 though the frictional contact 22 between the friction element 3 and the friction layer 4. This force causes movement of the driven element 5 and is shown in Fig. 1 and 2 as a double arrow. The direction of the movement of the driven element 5 is determined by the position of the excited generator 9 relatively to the friction element 3 (Fig. 2, 3, 4) or by a phase shift between the exciting voltages supplied to generators 9 (Fig.1).
The proposed embodiment of the invention places the friction element 3, friction layer 4 and

9 frictional contact 22 (which is between the friction element 3 and the friction layer 4) and the adhesive layer 11 in a location between the body of the actuator 1 and the driven element 5. Thus the body of the actuator 1 shields the friction element 3, the friction layer 4 and the frictional contact 22 from the radiation beam 13, the secondary radiation 15 and the reflected radiation 18. Furthermore, since the actuator 1 is placed on the radiation downstream side (13, 15, 18) of the driven element 5, further radiation shielding is provided by the driven element (Fig 1, 3). (The radiation shielding from the driven element 5 is only provided to half of the actuators in the embodiment of the invention shown in Fig 2, 4 and 5.) Thus, the adhesive layer 11 is subject to reduced radiation degradation due to the protection afforded by this shielding. As well, since the piezoelectric resonance element 2 and the friction element 3 are made of a material which attenuates radiation, the proposed actuator frictional contact 22 and the adhesive layer 11 between the friction element 3 and the piezoelectric plate 2 is subject to a further reduction in radiation (13, 15, 18) exposure.
In addition, the proposed drive can contain packets 19 of ultrasonic actuators 1 and packages of driven elements 20, as shown in Fig. 5. In this case, additional shielding from the radiation field 13, the secondary radiation 15 and the reflected field 18 is provided by adjacent neighbour actuators to frictional contacts 22 and adhesive layers 11. Reducing the degradation of the adhesive layer 11 between the friction element 3 and the piezoelectric resonant element 2 allows an increase in the developed driving force and an increase in the operational speed of the driven element 5. With a reduction of the radiation reaching frictional contact 22, the destruction of the friction surface of friction contact 22 from the double exposure to strong radiation field and intensive ultrasonic field is reduced. Also, a reduction of the radiation reaching the frictional contact 22 reduces the ionization of the air layer in the friction contact area. Both of these effects stabilize the properties of the frictional contact 22 and increase the drive lifetime.
Thus, with the above features, it is possible to achieve an increase of the reliability of an ultrasonic drive operating in the field of strong radiation. Increased reliability and increased service life makes the proposed drive suitable for service in medical devices that produce intense alpha, beta, gamma, and/or neutron radiation but also extends the field of application of ultrasonic drives to other similar environments.
REFERENCES
[1] K. J. Brown, US Patent #4,882,741, 378/152, G21K
1/021 November 21, 1989.
[2] C. S. Nunan, US Patent # 4,868,844, 378/152, A61N
5/10 1 September 19, 1989.
[3] J. Y. Yao, US Patent # 5,591,983, 250/505.1 A61N
5/10 1 January 7, 1997.
[4] C. W. Perkins, US Patent # 7,596,209, 378/152, G21K 1/04 1 September 29, 2009.
[5] W. Wischnewskiy, US Patent # 6,765,335, 310/323.02, HOlL 41/09 1 July 20, 2004.

Claims

WHAT IS CLAIMED IS

1. An ultrasonic drive having one or more ultrasonic actuators consisting of resonant piezoelectric elements and attached to them friction elements that are pressed to a driven element making frictional contact and located in a radiating field of a direct and (or) secondary radiation beam, wherein the piezoelectric resonant elements are made of piezoelectric ceramic containing lead, and the driven element is made wholly or partly of a material which absorbs alpha, beta, gamma or neutron radiation, such as tungsten or its alloys, lead or its alloys, oxide ceramics or metal ceramic alloys that contain these materials, and the friction elements and a friction layer are located in relation to the radiation field, in such way that the junction of these elements with the piezoelectric resonant element is screened from an irradiating field by the body of the piezoelectric resonant element or by the body of the driven element.

2. The ultrasonic drive according to claim I wherein it is developed as packets of ultrasonic actuators, each of which, or each pair of which has its own driven element, and the packets of these actuators are arranged in such way that each packet of ultrasonic piezoelectric actuators screens a frictional contact and the junction of each friction element and piezoelectric resonant element from direct or secondary alpha, beta, gamma, or neutron radiation.

3. The ultrasonic drive according to claim 1 and 2 wherein an ultrasonic drive has the friction element of each actuator made wholly or partly of a material that absorbs alpha, beta, gamma or neutron radiation, such as aluminium oxide, zirconium oxide with the addition of tungsten or its alloys, lead or its alloys or metals or ceramics containing these materials.

4. The ultrasonic drive of claims 1, 2 and 3 wherein an ultrasonic actuator mounting is made from non-organic materials that hold the ultrasonic actuator in its minimum oscillation velocity.

5. The ultrasonic drive of claims 1, 2, 3 and 4 wherein the ultrasonic actuator mounting is made from non-organic materials and is a part of a resonant actuator system.