Laser beam welding apparatus using an ultrasonic motor

Abstract: Herein disclosed is a small-sized ultrasonic motor which can produce a high torque and a stable turning force. The ultrasonic motor comprises: a cylindrical casing; a hollow output shaft extending coaxially through the cylindrical casing and supported rotatably by the same; a ring-like stator fixedly mounted on the inner surface of the cylindrical casing and having piezoelectric elements fixed on the back surface of the same; a ring-like rotor mounted on the hollow output shaft and facing the front surface of the stator; and bias means for pushing the rotor toward the stator. Also disclosed is a laser beam welding apparatus for welding the inner circumferential surface of a tube by using the ultrasonic motor.

Description: BACKGROUND OF THE INVENTION: The present invention relates to an ultrasonic motor and a laser beam welding apparatus and, more particularly, to a hollow type ultrasonic motor which is suitably used in a laser beam welding apparatus for carrying out a laser beam welding in the thin heat transfer tubes of a heat exchanger. For example, a steam generator used in a nuclear power plant is a shell-and-tube type heat exchanger, in which some of thin heat transfer tubes may experience damage for various causes. As a convenient and reliable method for repairing those damaged tubes, it is well known to insert and fix a thin cylindrical member called a sleeve in the damaged portion, of the heat transfer tube. The method of fixing the sleeve in the heat transfer tube has been exemplified by the soldering or expanding method, but it has been found that the laser beam welding is very effectual for it. We have developed a sleeve welding apparatus, as disclosed in the specification U.S.P. No. 4,839,495 (corresponding to Japanese Patent Laid-Open No. 27788/1989). This apparatus has, as described therein, an optical system including a reflecting mirror for directing a welding laser beam to the inner surface of the heat transfer tube or sleeve. In order to bond the sleeve and the heat transfer tube firmly by the circumferential seal welding, it is necessary to turn the optical system around its axis, and as a rotation mechanism therefore an electromagnetic motor or a piston-cylinder mechanism is used. For a high-quality circumferential seal welding by using a laser beam, the rotational drive mechanism is required to produce a stable turning force with high torque and to rotate at a speed suited for the welding operation. In order to meet these requirements, generally speaking, the electromagnetic motor has to be equipped with a reduction, gear mechanism, as disclosed in the specification of the U.S.P., so that it requires a relatively large mounting space. In the laser beam welding of this kind, on the other hand, the apparatus has to be equipped with an optical fiber for transmitting the laser beam and hoses for feeding cooling gas or shielding gas. Moreover, the diameter of the heat transfer tube of the steam generator, into which the laser beam welding apparatus of this kind is to be inserted, is as small as 20 mm or the like, and the rotary drive mechanism is required to be smaller in size. Incidentally, the heat transfer tube having a diameter exceeding 20 mm could be anyhow welded by a welding apparatus using an electromagnetic motor as a rotary drive mechanism. However, a laser beam welding apparatus for the heat transfer tube having a diameter less than 20 mm cannot be practicable as long as the electromagnetic motor is used. In a rotary drive mechanism using a piston-cylinder mechanism, on the other hand, the linear movements of the piston in an axial direction can be converted into the turning motions of the cylinder having helical grooves. The control of the rotation is very difficult although the aforementioned hose mounting space could be retained in the piston. The disadvantages of the prior art discussed above are overcome by a laser beam welding apparatus according to the single patent claim. Ultrasonic motors are known per se from D1 Patent Abstracts of Japan, vol. 014, no. 268, 11 June 1990 and vol. 014, no. 346, July 26, 1990. The laser beam welding apparatus according to the present invention can be so small-sized by using the above-specified ultrasonic motor as rotary drive means that the optical fiber for transmitting the welding laser beam and the gas hose are allowed to extend through the hollow output shaft of the ultrasonic motor so that the apparatus can be inserted into the thin tube. BRIEF DESCRIPTION OF THE DRAWINGS: Other objects, features and advantages of the present invention will become apparent from the following description to be made with reference to the accompanying drawings, in which: Fig. 1 is a section showing the structure of an ultrasonic motor. Fig. 2 is a section showing the structure of an embodiment of the present invention, in which the aforementioned ultrasonic motor is applied to the laser welding apparatus; and Fig. 3 is a section showing the structure of the case, in which the aforementioned ultrasonic motor is applied to a visual inspection apparatus. DESCRIPTION OF THE PREFERRED EMBODIMENTS: An ultrasonic motor will be described in the following with reference to Fig. 1. As shown in the drawing Fig. 1 two motors A and B of similar structures are arranged in tandem. Thanks to this tandem arrangement, it is possible to establish a high turning force. It is quite natural, however, that only one motor may be sufficient depending upon the turning force required. It is to be noted that this invention is not limited to the tandem arrangement. A hollow shaft 1 is connected so as to transmit the turning force to a rotary optical system, as will be specified hereinafter, and can be understood as an output shaft. A cylindrical casing 2 encloses the hollow shaft 1 to support it rotatably by means of ball bearings 3. The casing 2 is fixed like that of an ordinary motor on the frame of an apparatus to be used. Since the motors A and B are constructed to have an identical structure, the following description will be directed to the motor A. An annular rotor retainer 5 is fixedly fitted on the hollow shaft 1 and is formed at its two ends with shoulders, on which ring-like rotors 4 are individually placed. Ring-like stators are fixedly mounted in the casing 2 by means of supports 9. Each of stators 7 is disposed to face its corresponding the rotor 4, which is covered by a lining 8 at their faced surfaces. Conical disc springs 6 are sandwiched between the back surfaces of the rotors 4 and the large-diameter central portion of the rotor sleeve 5 to push the lining 8 of the rotors 4 onto the end surfaces of the stators 7. Piezoelectric elements 10 are adhered to the back surfaces of the stators 7 which do not face the stators 4. For each of the stators 7, there are circumferentially arranged at least two arcuate piezoelectric elements 10. These piezoelectric elements 10 are connected with a high frequency generator circuit. The progressive wave type ultrasonic motors thus constructed have their operating principle disclosed in Japanese Patent Publication 17353/1989 (or Japanese Patent Laid-Open No. 148682/1983) filed by one of us. The two piezoelectric elements 10 are caused to generate flexual vibrations with progressive wave propagating in the circumferential direction by applying high-frequency voltages with different phases such as sine waves and cosine waves. In a surface of each stator 7 thus vibrated, which is in contact with the lining 8, there are generated small elliptical motions so that the surfaces of the stators 7 are moved in the direction opposed to the traveling direction of the waves. Since the linings 8 of the rotors 4 are pushed to be in contact with the surfaces of the stators 7 by the actions of the conical disc springs 6, they are driven in the direction opposed to that of the progressive wave by the frictional forces generated by the aforementioned elliptical motions. The rotational motions due to the frictional forces between the stators 4 and the linings 8 are transmitted from the rotors 4 to the rotor retainer 5 and further to the hollow shaft 1 thereby rotating a rotating member to be driven. Fig. 2 is a section showing an embodiment of the present invention, in which the ultrasonic motor shown in Fig. 1 is applied to a laser beam welding apparatus to be used for repairing a thin heat transfer tube of a steam generator with a mending sleeve. In Fig. 2, an ultrasonic motor 11 is provided with an encoder 12 on the hollow shaft 1 shown in Fig. 1, although its detailed structure is not shown. The ultrasonic motor 11 is fixed in a tool casing 13. This tool casing 13 is connected to a flexible tube not shown and may be inserted into a steam generator tube 14 and a sleeve 15. As illustrated in Fig. 2, a lens casing 16 is connected to the leading end of the hollow shaft 1. In and through this hollow shaft 1, there extends an optical fiber cable 17. Thus, the lens casing 16 is rotated by the ultrasonic motor 11. In the lens casing 16, there are accommodated a condenser lens group 18 and a mirror 19. By this structure, the laser beam transmitted from the optical fiber cable 17 is focused at the welding point 20 on the sleeve 15 so that it may weld the inner surface of the sleeve 15 circumferentially while the lens casing 16 being rotated by the ultrasonic motor 11. Fig. 3 is a section showing the structure of the case, in which the ultrasonic motor in Fig. 1 is applied to a visual inspection apparatus for inspecting the welded point 20 illustrated in Fig. 2. In Fig. 3, the ultrasonic motor 11 is mounted in a tool casing 21, and a mirror casing 22 is connected to the leading end of the hollow shaft 1. In and through this hollow shaft 1, there extend both a fiber scope 23 and an illumination cable not shown. Here, the mirror casing 22 is equipped therein with illumination mirrors 24, 25 and a visual inspection mirror 26. With this structure, the welded point 20 is observed with the fiber scope 23 by illuminating the welded point 20 and its vicinity with the illumination mirrors 24, 25 and by reflecting the state of the welded point 20 by the visual inspection mirror 26. Since, in this case, the mirror casing 22 is rotated by the ultrasonic motor 11, it is possible to observe the welded points 20 distributed along a circumference of the sleeve. As has been described hereinbefore, it is possible to provide an ultrasonic motor which is small-sized but can establish a stable turning force with a high torque. According to the present invention, moreover, it is possible to provide a laser beam welding apparatus which is so small-sized that it can be inserted into a thin tube such as the heat transfer tube of the steam generator to subject them to the laser beam welding.

Claims: A laser beam welding apparatus for the inner circumferential surface of a tube, comprising: an elongated flexible tube having an optical fiber extending therein and longitudinally thereof for transmitting a laser beam therethrough; position determining means disposed in the vicinity of the tip end of said flexible tube for determining the position of the same with respect to a work tube in which said flexible tube is inserted; holding means having an expander and disposed adjacent to said position determining means for holding the tip end of said flexible tube in said work tube; rotary drive means disposed closer to the tip end of said flexible tube than to said holding means; a rotary cylinder connected to said rotary drive means to be rotated with respect to said flexible tube; guide means mounted on said rotary cylinder in a manner to rotate with respect to said rotary cylinder and held in contact with the inner face of said work tube for supporting said rotary cylinder concentrically of said work tube; and an optical train arranged within said rotary cylinder for receiving the laser beam emitted from said optical fiber and for focusing a reflected laser beam onto the inner surface of said tube, characterized in that said rotary drive means is an ultrasonic motor comprising : a cylindrical casing; a hollow output shaft extending coaxially through said cylindrical casing and supported rotatably by the same; a ring-like stator fixedly mounted on the inner surface of said cylindrical casing and having piezoelectric elements fixed thereto; and a ring-like rotor mounted on said hollow output shaft and biased toward said stator; wherein said optical fiber extends through said hollow output shaft.

Inventors: AKABA TAKASHI C O KOBE SHIPYAR, NAGASHIMA TADASHI C O KOBE SHI, SASHIDA TOSHIIKU, SHIRASU ISAO C O KOBE SHIPYARD, TSUKAMOTO YOSHIMASA C O KOBE S, YOSHIOKA KYOICHI C O KOBE SHIP, AKABA, TAKASHI C/O KOBE SHIPYARD & ENGINE WORKS, NAGASHIMA,TADASHI C/O KOBE SHIPYARD & ENGINE WORKS, SHIRASU, ISAO C/O KOBE SHIPYARD & ENGINE WORKS OF, TSUKAMOTO,YOSHIMASA C/O KOBE SHIPYARD & ENG. WORKS, YOSHIOKA,KYOICHI C/O KOBE SHIPYARD & ENGINE WORKS, Akaba, Takashi c/o Kobe Shipyard &amp; Engine Works, Nagashima,Tadashi c/o Kobe Shipyard &amp; Engine Works, Shirasu, Isao c/o Kobe Shipyard &amp; Engine Works of, Tsukamoto,Yoshimasa c/o Kobe Shipyard &amp; Eng. Works, Yoshioka,Kyoichi c/o Kobe Shipyard &amp; Engine Works
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1991
Main classification: H01L41
IPC codes: B23K26, H02N2, H01L41