METHOD OF AND APPARATUS FOR ASSEMBLING AN ELECTRIC MOTOR CAPABLE OF USING A MOTOR HOUSING HAVING LOW DIMENSIONAL PRECISION

Abstract: In assembling an electric motor used in the motor unit for a scroll compressor for an air conditioner, the gap between the stator (2) and the rotor (3) can be uniformly formed even when the dimensional precision of the motor housing (1) is low. The outside diameters of the bearings (5) and (6) are smaller than the inside diameter of the motor housing (1). In a first bearing assembling machine A, the center of the inner circumference of the stator (2) which is fixed in the motor housing (1), and the center of the bearing (5) are aligned. The bearing (5) is welded to the motor housing (1). The rotary shaft (5) to which the rotor (3) is fitted externally and fixed is inserted into the central part of the motor housing (1). In a second assembling machine C, the center of the bearing (5) is aligned with that of the bearing (6). The bearing (6) is welded to the motor housing (1), thus obtaining an electric motor having the stator (2), and bearings (5) and (6) whose centers are aligned with each other.

Description: TECHNICAL FIELD The present invention relates to a method and apparatus for assembling an electric motor for use in assembling a variety of electric motors including an electric motor section of a scroll compressor to be employed in an air conditioner. BACKGROUND ART A scroll compressor for use in an air conditioner has a construction as shown in Fig. 8 where a compressor section 8 is integrated with an electric motor section 7 composed of a casing body 1, a stator 2, a rotor 3, a rotary shaft 4, an upper bearing 5, and a lower bearing 6. In the electric motor section 7, the stator 2 is fixed inside the cylindrical casing body 1 by shrink fitting or the like method. The rotor 3 is inserted in the stator 2 with a specified gap provided and fixed around the rotary shaft 4 which serves as a crank shaft by the press fitting or the like method. The upper bearing 5 and the lower bearing 6 are mounted in both end portions of the casing body 1 while rotatably supporting the rotary shaft 4. The electric motor section 7 of such a scroll compressor is assembled normally according to a procedure as shown in Fig. 9. The casing body 1 in which the stator 2 has been inserted is vertically inverted, and the upper bearing 5 is fixed into a lower end portion of the casing body 1 by welding. The rotary shaft 4 around which the rotor 3 has been mounted is inserted into a center portion of the casing body 1 with a lower end portion of the rotary shaft 4 inserted into the upper bearing 5. The lower bearing 6 is inserted into an upper end portion of the casing body 1 with an upper end portion of the rotary shaft 4 inserted into the lower bearing 6, and the lower bearing 6 is fixed by welding. The upper bearing 5 and the lower bearing 6 are both mounted to the casing body 1 with the inner peripheral surface of the casing body 1 used as a reference surface for positioning. According to the assembling procedure described as above, when the casing body is formed in a complete cylinder shape, the centers of the bearings 5 and 6 coincide with the center of the casing body 1 to achieve an even gap between the stator 2 and the rotor 3. However, the method of producing the casing body 1 has been simplified for cost reduction in a recent scroll compressor. It may be considered that the casing body 1 be produced by rolling a flat plate. The casing body 1 thus produced has a degraded dimensional accuracy. When the bearings 5 and 6 are directly mounted to the casing body 1, the centers of the bearings 5 and 6 are displaced from the center of the stator 2, which results in an uneven gap between the stator 2 and the rotor 3 to significantly reduce the performance of the electric motor. Therefore, it is impossible to use a casing body 1 having a low dimensional accuracy, which has been a cause of hampering the cost reduction of the scroll compressor. A known method of assembling an electric motor is disclosed in US-A-5 127 148. DISCLOSURE OF THE INVENTION Accordingly, the object of the present invention is to provide a method and apparatus for assembling an electric motor capable of keeping the evenness of a gap between a stator and a rotor even when a casing body has a low dimensional accuracy. In order to achieve the above-mentioned object, the present invention provides a method for assembling an electric motor wherein bearings each having an outer diameter smaller than an inner diameter of a casing body are each mounted to each of both ends of the casing body in which a stator is inserted, and a rotary shaft around which a rotor is mounted is supported by the bearings at a center portion of the casing body, the method comprising: a first bearing assembling step of inserting the one bearing into an one end of the casing body in which the stator is inserted and fixed, holding the one bearing in an assembling position with the center of the one bearing placed in a specified position, and welding the casing body to the one bearing in a plurality of positions on an outer peripheral surface of the casing body while holding the casing body in an assembling position so that the center of an inner peripheral surface of the stator is aligned with the center of the one bearing to thereby mount the one bearing in one end of the casing body; a rotary shaft assembling step of inserting the rotary shaft around which the rotor is mounted from the other end of the casing body toward the center portion of the casing body and inserting one end of the rotary shaft into the one bearing; and a second bearing assembling step of inserting the other bearing into the other end of the casing body to insert the other end of the rotary shaft into the other bearing, holding the casing body in an assembling position so that the center of the one bearing which is already mounted is placed in a specified position, and welding the casing body to the other bearing in a plurality of positions on the outer peripheral surface of the casing body while holding the other bearing in an assembling position so that the center of the other bearing is aligned with the center of the one bearing to thereby mount the other bearing in the other end of the casing body. According to the method for assembling an electric motor of the present invention, in the first bearing assembling step, the one bearing is held in the assembling position so that the center of the one bearing is placed in a specified position. Then the casing body in which the stator is inserted and fixed is held in the assembling position with the center of the inner peripheral surface of the stator aligned with the center of the one bearing. In the above-mentioned condition, the one bearing is welded to the casing body. Therefore, the one bearing and the stator are concentrically aligned with each other. In the second bearing assembling step, the casing body is held in the assembling position so that the center of the one bearing is placed in a specified position. With the other bearing held in the assembling position and with the center of the other bearing aligned with the center of the one bearing, the other bearing is welded to the casing body. Therefore, the other bearing is concentrically aligned with the one bearing and the stator. Thus the centers of both the bearings are aligned with the center of the stator without being influenced by the dimensional accuracy of the casing body. In other words, the stator and the bearings are concentrically aligned with each other regardless of the dimensional accuracy of the inner peripheral surface of the casing body to make even the gap between the stator and the rotor supported by the bearings. In welding the end portions of the casing body to the bearings in the plural number of positions on the outer peripheral surface of the casing body, when the weldings are started simultaneously in the plural number of positions and the heat input quantity and the welding wire supply quantity in each welding position are made same, the same welding metal solidifying process can be achieved in each welding position to prevent the possible eccentricity of the bearings at the end portions of the casing body due to such uneven solidifying process. Therefore, the concentricity of the stator and the bearings can be maintained. The present invention also provides an apparatus for assembling an electric motor wherein bearings each having an outer diameter smaller than an inner diameter of a casing body are each mounted to each of both ends of the casing body in which a stator is inserted, and a rotary shaft around which a rotor is mounted is supported by the bearings at a center portion of the casing body, the apparatus comprising: a first bearing assembling machine for mounting the one bearing into an one end of the casing body in which the stator is inserted and fixed; and a second bearing assembling machine for mounting the other bearing into the other end of the casing body in which the one bearing is already mounted and in a center portion of which the rotary shaft is inserted with the rotor mounted around the rotary shaft, said first bearing assembling machine comprising a bearing positioning mechanism for holding the one bearing in an assembling position with the center of the one bearing placed in a specified position, a casing body positioning mechanism for holding in an assembling position the casing body in which the stator is inserted and fixed so that the center of an inner peripheral surface of the stator is aligned with the center of the one bearing, and a welding mechanism for welding the casing body to the one bearing in a plurality of positions on an outer peripheral surface of the casing body held in the assembling position, and said second bearing assembling machine comprising a casing body positioning mechanism for holding in an assembling position the casing body in which the one bearing is already mounted and the rotary shaft is already inserted so that the center of the one bearing is placed in a specified position, a bearing positioning mechanism for holding the other bearing in an assembling position so that the center of the other bearing is aligned with the center of the one bearing, and a welding mechanism for welding the casing body to the other bearing at a plurality portions on the outer peripheral surface of the casing body held in the assembling position. According to the apparatus for assembling an electric motor of the present invention, in the first bearing assembling machine, the one bearing is held in the assembling position with the center of the one bearing placed in the specified position. The casing body in which the stator has been inserted is held in the assembling position so that the center of the inner peripheral surface of the stator is aligned with the center of the one bearing. In the above-mentioned condition, the one bearing is welded to the casing body. Therefore, the one bearing and the stator are concentrically aligned with each other. According to the second bearing assembling machine, the other bearing is welded to the casing body in the condition where the casing body is held in the assembling position so that the center of the one bearing is placed in the specified position and the other bearing is held in the assembling position so that the center of the other bearing is concentrically aligned with the center of the one bearing. With the above-mentioned arrangement, the other bearing is concentrically aligned with the one bearing and the stator. Thus the centers of the bearings are aligned with the center of the stator without being influenced by the dimensional accuracy of the casing body. In other words, the stator and the bearings are concentrically aligned with each other regardless of the dimensional accuracy of the casing body to make even the gap between the stator and the rotor supported by the bearings via the rotary shaft. The electric motor includes not only a general-use electric motor but also an electric motor section of an electric motor of which casing body contains a compressor section. It is preferred that the positioning mechanism for holding in the assembling position the casing body or each bearing inserted in the end portion of the casing body is provided with the misalignment detecting mechanism for detecting the misalignment of the positioning mechanism and the correction drive mechanism for moving the positioning mechanism so that the detected misalignment is corrected. With the above-mentioned arrangement, even when the positioning mechanism is deformed by heat in the welding step, the misalignment due to the deformation is automatically canceled by the movement of the positioning mechanism. It is also preferred that the misalignment detecting mechanism is comprised of a master bar which is mounted to the positioning mechanism as arranged in parallel with the center line of the positioning mechanism and two displacement sensors for measuring the quantity of eccentricity of the master bar in two directions which are perpendicular to each other as provided on a base of the assembling machine. With the above-mentioned arrangement, when the positioning mechanism is misaligned by heat in the welding step, the master bar becomes eccentric according to the misalignment. By measuring the quantity of eccentricity of the master bar in two directions which are perpendicular to each other by the two displacement sensors, the direction and the magnitude of the above-mentioned misalignment are obtained. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 (a), 1 (b), and 1 (c) are schematic views for explaining an exemplified method for assembling an electric motor of the present invention; Fig. 2 is a longitudinal sectional view showing the construction of a first bearing assembling machine; Fig. 3 is a front view showing the entire construction of a second bearing assembling machine; Fig. 4 is a side view showing the entire construction of the second bearing assembling machine; Fig. 5 is a longitudinal sectional view showing in detail the construction of a principal portion of the second bearing assembling machine; Fig. 6 is a perspective view showing the construction of a misalignment detecting mechanism; Fig. 7 is a plan view showing the construction of the misalignment detecting mechanism; Fig. 8 is a sectional view schematically showing the construction of a scroll compressor; and Fig. 9 is a sectional view schematically showing a conventional assembling method. BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the invention will now be described with reference to the accompanying drawings. The present method for assembling an electric motor is for use in assembling an electric motor section of a scroll compressor. The method is composed of a first bearing assembling step for mounting an upper bearing 5 in a lower end portion of a casing body 1 (placed upside down) in which a stator 2 is inserted and fixed as shown in Fig. 1 (a), a rotary shaft assembling step for inserting a rotary shaft 4 around which a rotor 3 is mounted and fixed into a center portion of the casing body 1 to which the upper bearing 5 has been mounted as shown in Fig. 1 (b), and a second bearing assembling step for mounting a lower bearing 6 in an upper portion of the casing body 1 in which the rotary shaft 4 has been inserted as shown in Fig. 1 (c). The upper bearing 5 is transferred to a first bearing assembling machine A as shown in Fig. 2 by a pallet 10 to be mounted to the casing body 1. The casing body 1 to which the upper bearing 5 has been mounted is further mounted with the rotary shaft 4 and then transferred to a second bearing assembling machine C as shown in Figs. 3, 4, and 5 by the pallet 10, the lower bearing 6 being mounted in the upper end portion of the casing body 1. The inner diameter of the casing body 1 is made greater than the outer diameters of the upper bearing 5 and the lower bearing 6 to provide a gap between the inner peripheral surface of the casing body 1 and the outer peripheral surfaces of the upper bearing 5 and the lower bearing 6. The pallet 10 has a bearing support base 12 provided projectingly from a center portion of a surface of a base plate 11 as shown in Fig. 2. The bearing support base 12 supports thereon the upper bearing 5 horizontally. The upper bearing 5 supported on the bearing support base 12 is held in a center position of the pallet 10 by chucks 13 provided around the bearing support base 12. Around the chucks 13 is provided a body support base 14 for supporting thereon the casing body 1 vertically. On the periphery of the base plate 11 outwardly of the body support base 14 is fixed a member 15 having a pin hole 15a for positioning the pallet 10. The first bearing assembling machine A is provided, as shown in Fig. 2, with a bearing positioning mechanism 20 for holding the upper bearing 5 in an assembling position, a body positioning mechanism 30 for holding the casing body 1 in an assembling position, and a welding mechanism 40 for welding the positioned upper bearing 5 to the casing body 1. The bearing positioning mechanism 20 has a lift unit 21 for pushing up the pallet 10 transferred to the first bearing assembling machine A. The lift unit 21 is moved up and down by, for example, an air cylinder (not shown). When the pallet 10 is pushed up by the lift unit 21, positioning pins 23 fixed to a main body base 22 are inserted into the pin hole 15. With the above-mentioned operation, the pallet 10 is held in the assembling position of the first bearing assembling machine A, and consequently the upper bearing 5 on the pallet 10 is held in the assembling position of the first bearing assembling machine A where the center of the upper bearing 5 is placed in a predetermined position. The body positioning mechanism 30 is entirely moved in the vertical direction and in the horizontal direction by an air cylinder (not shown), and has a pressure rod 31 vertically provided at a center portion of a main body 30a. The pressure rod 31 has at its lower end an engagement portion 31a to be closely engaged with a center hole 5a of the upper bearing 5 and a flange portion 31b which has a diameter greater than that of the engagement portion 31a and presses down the upper end of the upper bearing 5. The pressure rod 31 moves down to hold the upper bearing 5 on the pallet 10 with its engagement portion 31a and flange portion 31b. In the above time, the upper bearing 5 and the pressure rod 31 are concentrically aligned with each other. Around the pressure rod 31 is provided a plurality of chucks 32. The chucks 32 move synchronously in radial directions of the pressure rod 31 by a drive section located above (not shown) to thereby hold the stator 2 from inside. Then the stator 2 is transferred to the stator assembling position of the first bearing assembling machine A to place the casing body 1 mounted around the stator 2 on the body support base 14. The welding mechanism 40 has four welding torches 41 (only two of them are shown) arranged at intervals of 90° in angle in the circumferential direction. The welding torches 41 are disposed outside the lower end portion of the casing body 1 placed on the body support base 14, where plug welding is performed with a wire 42 by a tungsten-inert-gas arc (TIG) welding method. Then, as shown in Fig. 5, the rotary shaft 4 around which the rotor 3 has been mounted and fixed is inserted into the hole 5a of the upper bearing 5 fixed to the casing body 1. The second bearing assembling machine C is provided, as shown in Fig. 5, with a body positioning mechanism 50 for holding the casing body 1 in an assembling position, a bearing positioning mechanism 60 for holding the lower bearing 6 in an assembling position, a welding mechanism 70 for welding the positioned casing body 1 to lower bearing 6, and a correction drive mechanism 80 and a misalignment detecting mechanism 90 for correcting the possible misalignment of the bearing positioning mechanism 60. The body positioning mechanism 50 has the same construction as that of the bearing positioning mechanism 20 of the first bearing assembling machine A as shown in Fig. 5, and operates to hold the upper bearing 5 in an assembling position of the second bearing assembling machine C by positioning the aforementioned pallet 10 pushed up by a lift unit 51 by means of positioning pins 53 mounted to a main body base 52 and a pin hole 15a. In other words, the casing body 1 is held in the assembling position of the second bearing assembling machine C so that the center of the upper bearing 5 is placed in a specified position. The bearing positioning mechanism 60 has an aligning rod 61 at its center portion. The aligning rod 61 is moved up and down in the bearing positioning mechanism 60 by a cylinder 62, with which a small-diameter portion 61a at the lower end of the aligning rod 61 is inserted into a hole 4a provided in an end surface of the rotary shaft 4 inside the casing body 1. With the above-mentioned operation, the aligning rod 61 and the rotary shaft 4 are concentrically aligned with each other. Around the aligning rod 61 is provided a chuck 63. The chuck 63 clamps the lower bearing 6 to hold the lower bearing 6 concentrically with the aligning rod 61, i.e., in a center position of the bearing positioning mechanism 60. Around the chuck 63 are provided a plurality of lifting pawls 64 (only one of them is shown in Fig. 5) and a stop block 65. The lifting pawls 64 are moved up and down by a cylinder 66 to penetrate through a hole 6a formed in the lower bearing 6 and lift the lower bearing 6 by engaging its pawl portion with the lower surface of the lower bearing 6 to press the lower bearing 6 against the lower surface of the stop block 65. The bearing positioning mechanism 60 is entirely moved in the vertical and horizontal directions by the correction drive mechanism 80 described hereinafter. The welding mechanism 70 has three welding torches 71 arranged at intervals of 120° in angle in the circumferential direction. The welding torches 71 are disposed outside the upper portion of the casing body 1 held in an assembling position of the second bearing assembling machine C and performs plug welding with a wire 72 by the TIG welding method. The correction drive mechanism 80 has an upper table 81 movable in the direction of the y-axis in parallel with the horizontal plane, a lower table 82 movable in the direction of the x-axis which is in parallel with the horizontal plane and perpendicular to the y-axis, and a back plate 83 movable in the vertical direction of the z-axis. The upper table 81 concurrently serves as a base plate of the bearing positioning mechanism 60 and moves reciprocatingly on the lower table 82 in the direction of the y-axis while using a first servomotor 84 as a power source. The lower table 82 is supported in a cantilever-like style in front of the back plate 83 and moves reciprocatingly in the direction of the x-axis while using the second servomotor 85 mounted to the back plate 83 as a power source. The back plate 83 uses a third servomotor 86 as shown in Figs. 3 and 4 as a power source and is moved up and down via a feed screw 87. By virtue of the upward and downward movement, the bearing positioning mechanism 60 reciprocates between an upper retreating position and a lower operating position. The misalignment detecting mechanism 90 is composed of a vertical master bar 91 extending vertically under from a base plate of the bearing positioning mechanism 60 and two displacement sensors 92 provided on a base of the second bearing assembling machine C as shown in Figs. 3 and 4. The master bar 91 is positioned above the two displacement sensors 92 when the bearing positioning mechanism 60 is positioned in the upper retreating position. When the bearing positioning mechanism 60 moves to the lower operating position, a lower end portion of the master bar 91 traverses the optical axes of the displacement sensors 92. The following describes the condition where the bearing positioning mechanism 60 is in the operating position unless a special notice is provided. The two displacement sensors 92 are arranged on an upper surface of a frame 93 provided upright on the base of the second bearing assembling machine C. The two displacement sensors 92 are each composed of a laser projector 92a and a laser detector 92b provided at a specified interval as shown in Figs. 6 and 7. The optical axis of one displacement sensor 92 directed in the direction of the x-axis and the other displacement sensor 92 directed in the direction of the y-axis cross each other above a center portion of the frame 93. When no deformation takes place in the second bearing assembling machine C, the center of the master bar 91 coincides with the position at which the optical axes of the two displacement sensors 92 cross each other. As a result, laser beams from the respective laser projectors 92a are completely shaded by the master bar 91, with which the quantity of light received in the laser detector 92b is made to be zero. When the center of the master bar 91 is displaced from the position at which the optical axes of the two displacement sensors 92 cross each other, the quantity of light received in each of the laser detectors 92b increases according to the quantity of the displacement. With the above-mentioned arrangement, the quantities of eccentricity of the master bar 91 in both the direction of the x-axis and the direction of the y-axis can be obtained according to the variance in quantity of light received in the two laser detectors 92b. The detected quantities of eccentricity of the master bar 91 in the directions of the x-axis and the direction of the y-axis are input to a control unit (not shown). The control unit controls the servomotors 84 and 85 of the aforementioned correction drive mechanism 80 so that the quantities of eccentricity become zero. The present apparatus for assembling an electric motor assembles the electric motor section of the aforementioned scroll compressor in a sequence as follows thereby implementing the method for assembling an electric motor of the present invention. The upper bearing 5 is held in the center position of the pallet 10. The pallet 10 is transferred to the first bearing assembling machine A in a manner as shown in Fig. 2 and then positioned by the bearing positioning mechanism 20. With the above-mentioned operation, the upper bearing 5 is held in the assembling position of the first bearing assembling machine A so that the center of the upper bearing 5 is placed in a specified position. When the positioning of the upper bearing 5 is completed, the casing body 1 is held in the assembling position of the first bearing assembling machine A by the body positioning mechanism 30. The casing body 1, which has been fitted with the stator 1, is held in the assembling position with the inner peripheral surface the stator 2 clamped so that the inner peripheral surface is placed in a specified position. The upper bearing 5 is in the lower end of the casing body 1, where the center of the upper bearing 5 is made to be aligned with the center of the stator 2. In other words, the casing body 1 and the upper bearing 5 are combined with each other with the center of the casing body 1 ignored. When the upper bearing 5 is combined with the casing body 1, the casing body 1 is plug-welded by the TIG welding method to the upper bearing 5 simultaneously in four positions on the outer peripheral surface of the casing body 1 by the welding mechanism 40. With the above-mentioned operation, the upper bearing 5 is mounted to the casing body 1 as concentrically aligned with the stator 2. Since there is a gap between the casing body 1 and the upper bearing 5 in the simultaneous welding in plural number of positions, unless the solidification of the melted metal in each welding position is completed at the same time, there may be produced the eccentricity of the upper bearing 5 which moves to the side where the solidification is completed first. Therefore, in the present embodiment, the welding is started simultaneously in each welding position, and the heat input quantity and the welding wire supply quantity in each welding position are made same. With the above-mentioned arrangement, the quantity of melted metal is made same and the solidification of the melted metal in each welding position is completed at the same time to prevent the possible occurrence of the eccentricity of the upper bearing 5 and thereby maintain the concentricity of the upper bearing 5 and the stator 2 in the casing body 1. In order to achieve the same heat input quantity, for example, the supply voltage, supply current, and weld time are made same in each welding position. When the mounting of the upper bearing 5 is completed, the casing body 1 is transferred by the pallet 10 to a place to assemble a rotary shaft with the upper bearing 5 held on the pallet 10. Then the rotary shaft 4 to which the rotor 3 has been mounted is inserted into the center portion of the casing body 1 with its lower end inserted into the upper bearing 5. When the insertion of the rotary shaft 4 is completed, the casing body 1 is transferred to the second bearing assembling machine C by the pallet 10. The pallet 10 transferred to the second bearing assembling machine C is positioned by the body positioning mechanism 50. With the above-mentioned operation, the casing body 1 on the pallet 10 is held in the assembling position of the second bearing assembling machine C so that the center of the upper bearing 5 and the center of the inner peripheral surface of the stator 2 are aligned with each other. When the positioning of the casing body 1 is completed, the lower bearing 6 is held in an assembling position of the second bearing assembling machine C by the bearing positioning mechanism 60. The lower bearing 6 is inserted into the upper end portion of the casing body 1, and the upper end portion of the rotary shaft 4 is inserted into the lower bearing 6. The center of the lower bearing 6 is aligned with the center of the upper bearing 5 mounted in the lower end portion of the casing body 1. The center of the upper bearing 5 is already aligned with the center of the stator 2. Therefore, the stator 2, the upper bearing 5, and the lower bearing 6 are concentrically aligned with each other. When the mounting of the lower bearing 6 is completed, the casing body 1 is plug-welded by the TIG welding method to the lower bearing 6 simultaneously in three positions of the outer peripheral surface of the casing body 1 by the welding mechanism 70. In the present simultaneous welding, the welding is started simultaneously in each welding position so that the solidification process of melted metal in each welding position is made same, and the heat input quantity and the welding wire supply quantity in each welding position are made same to prevent the possible eccentricity of the lower bearing 6 with respect to the stator 2 and the upper bearing 5. Furthermore, the welding is performed in positions close to the bearing positioning mechanism 60 in the simultaneous welding described as above. Therefore, when the welding operation is repeated, the bearing positioning mechanism 60 may be deformed due to accumulation of welding heat. The deformation of the bearing positioning mechanism 60 results in the misalignment of the mechanism to consequently make the lower bearing 6 eccentric. However, when the bearing positioning mechanism 60 is deformed by heat, the master bar 91 of the misalignment detecting mechanism 90 becomes eccentric according to the misalignment in the present embodiment. When the master bar 91 becomes eccentric, the direction and the quantity of the eccentricity are detected by the two displacement sensors 92, and the bearing positioning mechanism 60 entirely moves in the horizontal direction so that the eccentricity is corrected. By virtue of the mechanism, there is produced no misalignment even when the bearing positioning mechanism 60 is deformed by heat. Therefore, the possible eccentricity of the lower bearing 6 due to the deformation by heat is prevented. Thus an electric motor in which the stator 2, the upper bearing 5, and the lower bearing 6 are concentrically aligned with each other can be obtained regardless of the dimensional accuracy of the casing body 1. Although the mechanism for preventing the eccentricity due to the deformation by heat is provided at the bearing positioning mechanism 60 in the above-mentioned embodiment, the mechanism can be provided at the body positioning mechanism 30 of the first bearing assembling machine A. The mechanism can be also provided at the bearing positioning mechanism 20 of the first bearing assembling machine A or the body positioning mechanism 50 of the second bearing assembling machine C. When the mechanism is provided at any of them, the misalignment due to the deformation by heat can be prevented. As is apparent from the description as above, according to the method for assembling an electric motor of the present invention, an one bearing is concentrically aligned with an inner peripheral surface of a stator when the one bearing is mounted in a first bearing assembling step. When a rotary shaft has been inserted and the other bearing is being mounted in a second bearing assembling step, the center of the other bearing and the center of the one bearing are aligned with each other via the center of the rotary shaft. By virtue of the above-mentioned arrangement, the center of the stator is aligned with the centers of the two bearings regardless of the dimensional accuracy of the casing body, with which the rotary shaft supported by the two bearings is concentrically aligned with the stator. As a result, the gap between the rotor mounted around the rotary shaft and the stator is made even to prevent the possible degradation in performance of the electric motor due to the unevenness of the gap. The above-mentioned arrangement allows a casing body having a low dimensional accuracy to be used to achieve cost reduction of the electric motor. In welding the end portions of the casing body to the bearings in plural number of positions on an outer peripheral surface of the casing body, when the welding operation is started simultaneously in the plural number of positions and the heat input quantity and the welding wire supply quantity in each welding position are made same, the possible eccentricity of the bearings due to the uneven solidification of the metal in the simultaneous welding is avoided. Therefore, the evenness of the gap between the rotor and the stator is still more improved to further improve the performance of the electric motor. According to the apparatus for assembling an electric motor of the present invention, when the one bearing is mounted by the first bearing assembling machine, the center of the bearing and the center of the inner peripheral surface of the stator are aligned with each other. Furthermore, when the other bearing is being mounted by the second bearing assembling machine after insertion of the rotary shaft, the center of the other bearing and the center of the one bearing are aligned with each other via the center of the rotary shaft. By virtue of the above-mentioned arrangement, the center of the stator is aligned with the centers of the two bearings regardless of the dimensional accuracy of the casing body, with which the rotary shaft supported by the two bearings is concentrically aligned with the stator. As a result, the gap between the rotor mounted around the rotary shaft and the stator is made even to prevent the possible degradation in performance of the electric motor due to the unevenness of the gap. The above-mentioned arrangement allows a casing body having a low dimensional accuracy to be used to achieve cost reduction of the electric motor. When the positioning mechanism for holding in each assembling position the casing body or the bearing inserted in the end portion of the casing body is provided with the misalignment detecting mechanism for detecting the misalignment of the positioning mechanism and the correction drive mechanism for moving the positioning mechanism so that the detected misalignment is corrected, the possible misalignment of the positioning mechanism due to the deformation thereof by heat is prevented. Therefore, the evenness of the gap between the rotor and the stator is still more improved to further improve the performance of the electric motor. INDUSTRIAL APPLICABILITY The present invention is for use in assembling an electric motor to be employed in, for example, an air conditioner.

Claims: A method for assembling an electric motor wherein bearings (5 and 6) each having an outer diameter smaller than an inner diameter of a casing body (1) are each mounted to each of both ends of the casing body (1) in which a stator (2) is inserted, and a rotary shaft (4) around which a rotor (3) is mounted is supported by the bearings (5 and 6) at a center portion of the casing body (1), the method comprising: a first bearing assembling step of inserting the one bearing (5) into an one end of the casing body (1) in which the stator (2) is inserted and fixed, holding the one bearing (5) in an assembling position with the center of the one bearing (5) placed in a specified position, and welding the casing body (1) to the one bearing (5) in a plurality of positions on an outer peripheral surface of the casing body (1) while holding the casing body (1) in an assembling position so that the center of an inner peripheral surface of the stator (2) is aligned with the center of the one bearing (5) to thereby mount the one bearing (5) in one end of the casing body (1); a rotary shaft assembling step of inserting the rotary shaft (4) around which the rotor (3) is mounted from the other end of the casing body (1) toward the center portion of the casing body (1) and inserting one end of the rotary shaft (4) into the one bearing (5); and a second bearing assembling step of inserting the other bearing (6) into the other end of the casing body (1) to insert the other end of the rotary shaft (4) into the other bearing (6), holding the casing body (1) in an assembling position so that the center of the one bearing (5) which is already mounted is placed in a specified position, and welding the casing body (1) to the other bearing (6) in a plurality of positions on the outer peripheral surface of the casing body (1) while holding the other bearing (6) in an assembling position so that the center of the other bearing (6) is aligned with the center of the one bearing (5) to thereby mount the other bearing (6) in the other end of the casing body (1). A method for assembling an electric motor as claimed in Claim 1, wherein the electric motor is an electric motor section (7) of a compressor of which casing body (1) contains a compressor section (8). A method for assembling an electric motor as claimed in Claim 1, wherein, when welding the end portions of the casing body (1) respectively to the bearings (5 and 6) in the plural number of positions on the outer peripheral surface of the casing body (1), the welding operation in the plural number of positions is started simultaneously and a heat input quantity and a welding wire supply quantity in each welding position are made same. A method for assembling an electric motor as claimed in Claim 2, wherein, when welding the end portions of the casing body (1) respectively to the bearings (5 and 6) in the plural number of positions on the outer peripheral surface of the casing body (1), the welding operation in the plural number of positions is started simultaneously and a heat input quantity and a welding wire supply quantity in each welding position are made same. An apparatus for assembling an electric motor wherein bearings (5 and 6) each having an outer diameter smaller than an inner diameter of a casing body (1) are each mounted to each of both ends of the casing body (1) in which a stator (2) is inserted, and a rotary shaft (4) around which a rotor (3) is mounted is supported by the bearings (5 and 6) at a center portion of the casing body (1), the apparatus comprising: a first bearing assembling machine (A) for mounting the one bearing (5) into an one end of the casing body (1) in which the stator (2) is inserted and fixed; and a second bearing assembling machine (C) for mounting the other bearing (6) into the other end of the casing body (1) in which the one bearing (5) is already mounted and in a center portion of which the rotary shaft (4) is inserted with the rotor (3) mounted around the rotary shaft (4), said first bearing assembling machine (A) comprising a bearing positioning mechanism (20) for holding the one bearing (5) in an assembling position with the center of the one bearing (5) placed in a specified position, a casing body positioning mechanism (30) for holding in an assembling position the casing body (1) in which the stator (2) is inserted and fixed so that the center of an inner peripheral surface of the stator (2) is aligned with the center of the one bearing (5), and a welding mechanism (40) for welding the casing body (1) to the one bearing (5) in a plurality of positions on an outer peripheral surface of the casing body (1) held in the assembling position, and said second bearing assembling machine (C) comprising a casing body positioning mechanism (50) for holding in an assembling position the casing body (1) in which the one bearing (5) is already mounted and the rotary shaft (4) is already inserted so that the center of the one bearing (5) is placed in a specified position, a bearing positioning mechanism (60) for holding the other bearing (6) in an assembling position so that the center of the other bearing (6) is aligned with the center of the one bearing (5), and a welding mechanism (70) for welding the casing body (1) to the other bearing (6) at a plurality portions on the outer peripheral surface of the casing body (1) held in the assembling position. An apparatus for assembling an electric motor as claimed in Claim 5, wherein the electric motor is an electric motor section (7) of a compressor of which casing body (1) contains a compressor section (8). An apparatus for assembling an electric motor as claimed in Claim 5, wherein the positioning mechanism for holding the casing body (1) or the bearings inserted in the casing body (1) in the corresponding assembling position is provided with a misalignment detecting mechanism (90) for detecting misalignment of the positioning mechanism and a correction drive mechanism (80) for moving the positioning mechanism so that the detected misalignment is corrected. An apparatus for assembling an electric motor as claimed in Claim 6, wherein the positioning mechanism for holding the casing body (1) or the bearings inserted in the casing body (1) in the corresponding assembling position is provided with a misalignment detecting mechanism (90) for detecting misalignment of the positioning mechanism and a correction drive mechanism (80) for moving the positioning mechanism so that the detected misalignment is corrected. An apparatus for assembling an electric motor as claimed in Claim 7, wherein the misalignment detecting mechanism (90) is comprised of a master bar (91) which is mounted to the positioning mechanism as arranged in parallel with a center line of the positioning mechanism and two displacement sensors (92) for measuring quantity of eccentricity of the master bar (91) in two directions which are perpendicular to each other, the displacement sensors (92) being provided on a base of the assembling machine. An apparatus for assembling an electric motor as claimed in Claim 8, wherein the misalignment detecting mechanism (90) is comprised of a master bar (91) which is mounted to the positioning mechanism as arranged in parallel with a center line of the positioning mechanism and two displacement sensors (92) for measuring quantity of eccentricity of the master bar (91) in two directions which are perpendicular to each other, the displacement sensors (92) being provided on a base of the assembling machine.

Inventors: INOUE TAKAYOSHI, KAWASAKI KENJI, MAKI YASUO, INOUE, TAKAYOSHI, KAWASAKI, KENJI, MAKI, YASUO, KANAOKA-KOJO, INOUE, TAKAYOSHI, KANAOKA-KOJO, SAKAI-SEISAKUSHO, KAWASAKI, KENJI, KANAOKA-KOJO, SAKAI-SEISAKUSHO, MAKI, YASUO, KANAOKA-KOJO, SAKAI-SEISAKUSHO OF
Applicants: DAIKIN IND LTD, DAIKIN INDUSTRIES, LIMITED
Application year: 1993
Main classification: H02K15
IPC codes: F04C18, H02K15, F04C29