STRUCTURE AND METHOD FOR FIXING RADIAL TYPE ROTOR TO OUTPUT SHAFT OF SYNCHRONOUS MOTOR

Abstract: The structure has rotor cores (16) and magnets (14) arranged alternately in the circumferential direction, of a synchronous motor to an output shaft (10). A moulding resin (24) is packed in a clearance between the inner circumferential surface of the rotor (12) and the outer circumferential surface of the output shaft (10) and hardened.

Description: The present invention relates to a joint structure of a radial type rotor and an output shaft of the type defined in the pre-characterizing part of claim 1. The invention also relates to a method of making such joint structure. A joint structure of the above type in which a radial type rotor is mounted fixedly on an output shaft by attaching end plates to the opposite ends of the rotor, and fixing the end plates to the output shaft is known from EP-A1-0107317. A shrinkage fit is another method of fixedly mounting a rotor on an output shaft. Another method is the use of pins for fastening a rotor to an output shaft. Most rotors are impregnated with an impregnant to prevent the play of the component rotor cores and magnets thereof relative to each other. When the rotor is assembled by either the method employing a shrinkage fit or the method using pins, a gap is formed between the rotor and the output shaft, except for end portions of the rotor, and therefore, the output shaft within the rotor is bent when an external force acts on the rotor assembly. The method employing a shrinkage fit is unable to fasten a long, high-torque rotor to an output shaft with a high reliability, because torque is transmitted from the rotor to the output shaft through only the two front and rear portions where the rotor and the output shaft are joined together by a shrinkage fit, regardless of the length of the rotor, while the output torque of a longer rotor is greater than that of a shorter rotor. GB-A-1008927 disclosed a joint structure of a one-piece rotor body and an output shaft in a dynamo electric machine, wherein a resin is filled into the gap between the inner circumference of the rotor and the circumference of the output shaft. However, said document does not disclose how the resin is put into said gap between the output shaft and the rotor. The problem underlying the present invention is to provide a joint structure of a rotor and an output shaft, capable of preventing the bending of the output shaft and fastening the rotor to the output shaft with a high reliability. The above problem is solved according to the present invention by the characterizing features of claim 1. A method of making a joint structure of a radial type rotor and an output shaft is defined in claim 6. Since the molding resin is filled and hardened in the gap between the inner circumference of the rotor and the circumference of the output shaft, a bending action on the output shaft is unable in practice to bend the output shaft. Since the torque generated by the rotor is transmitted through the molding resin filling the gap over the entire length of the rotor to the output shaft, the local concentration of torque, namely, the concentration of torque on portions corresponding to the opposite ends of the rotor, is obviated. Thus, the joint structure of a rotor and the output shaft has a high reliability structure and a high torque transmitting reliability. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a front view of a rotor assembly constructed by joining a rotor and an output shaft according to the present invention; Figure 2 is an enlarged fragmentary cross-sectional view taken along the line II-II in Fig. 1; Figure 3 is a fragmentary cross-sectional view showing a joint structure according to the present invention in one stage of fabrication; and Figure 4 is a fragmentary cross-sectional view of a rotor assembly constructed by another method of fabrication different from the method shown in Fig. 3. BEST MODE OF CARRYING OUT THE INVENTION The present invention will be described in detail hereinafter with reference to the accompanying drawings. A method of fixedly joining a radial type rotor 12 comprising an alternate circumferential arrangement of magnets 14 and rotor cores 16 to an output shaft 10, and a joint structure constructed by the above method will be explained. In this embodiment, the rotor 12 comprises four unit rotors 12a, 12b, 12c and 12d having a predetermined axial length and arranged in an axially contiguous arrangement, and rods 18 for positioning rotor cores 16 at a predetermined radial position in cooperation with end plates 26 are inserted through the cores 16 to hold magnets 14. When the relatively long rotor 12 consisting of the four unit rotors 12a, 12b, 12c and 12d, which are penetrated by the rods 18, is fastened to the output shaft with the end plates 26, a gap is formed between the inner circumference of the rotor 12 and the output shaft 10. The central holes of the end plates 26 provided on the opposite ends of the rotor 12 have a diameter suitable for mounting the end plates 26 on the output shaft 10 by a light press-fitting. The output shaft 10 is pressed into the rotor 12 provided with the end plates 26 at opposite ends thereof by press fitting, by applying a small force to the output shaft 10 to be stopped at a predetermined axial position relative to the rotor 12. The output shaft 10 is provided at a predetermined position with a groove 32 having an inlet 28 opening outside of one of the end plates 26. A molding resin, such as an epoxy resin, is injected into the gap between the rotor 12 and the output shaft 10 through the groove 32 to fill the gap with the molding resin. As the molding resin 24 is injected continuously through the inlet 28 into the gap between the rotor 12 and the output shaft 10 after the gap has been filled with the molding resin, the resin 24 overflows through gaps between the magnets 14 and the rotor cores 16 and flows over the surface of the rotor 12. If the resin 24 is simply injected into the gap, the overflown resin 22' protudes as shown in Fig. 4. As is generally known, a minute clearance is provided between the circumference of the rotor and that of the stator, and hence the resin bulges 22' must not protude beyond a circle corresponding to the maximum diameter of the rotor. To prevent such an excessive protuberance of the overflown resin, the rotor 12 is covered with a cylindrical jig case 30, as shown by way of example in Fig. 3, when injecting the resin 24 into the gap. Then, the overflow resin 22 is confined within a circle corresponding to the maximum outside diameter of the rotor 12 as shown in Fig. 2. Although the resin filling the gap between the inner circumference of the rotor 12 and the output shaft 10 cannot be observed, the perfect packing of the gap with the resin can be confirmed by the leakage of the resin onto the surface of the rotor 12. When the resin is thus filled and hardened in the gap between the inner circumference of the rotor 12 and the output shaft 10, a portion of the output shaft 10 between a pair of bearings 20 supporting the output shaft 10 is not subject to bending. As is obvious from Fig. 2, an output torque generated in the rotor 12 is transmitted to the resin 24 filled and hardened in the gap with a required high reliability, because the inner circumference of the rotor 12 has a polygonal shape. The reliability in torque transmission of the circular boundary between the output shaft 10 and the resin 24 is lower than that of a polygonal boundary, and therefore, it is preferable to finish the surface of the output shaft to be coated with the resin 24 by knurling or the like. When determining the shape of the resin 24 filled and hardened in the gap, the concentration of mechanical stresses, and thermal stresses which may be induced by temperature variation, must be taken into account, and the rotor must be designed so that the resin 24 filled and hardened in the gap is formed in a uniform thickness within an allowance and within a range which will not adversely affect the torque transmission reliability of the resin 24 filled and hardened in the gap. As apparent from the foregoing description, the present invention provides a joint structure of a rotor and an output shaft having a high reliability structure and excellent torque transmission characteristics and capable of a high resistance to a bending of the output shaft. LIST OF REFERENCE NUMBERS 10 Output Shaft 12 Rotor 14 Magnet 16 Rotor Core 22, 22', 24 Molded Resin 28 Inlet 30 Cylindrical Jig Case 32 Groove

Claims: A joint structure of a radial type rotor (12) and an output shaft (10) in a synchronous motor, the rotor (12) comprising an alternate circumferential arrangement of rotor cores (16) and magnets (14); wherein a resin (24) is provided in a gap between the inner circumference of the radial rotor (12) and the circumference of the output shaft (10), characterized in that the output shaft has means (28, 30) for injecting said resin into said gap after the output shaft (10) has been inserted into the rotor (12) A joint structure according to claim 1, wherein the outer surfaces of the magnets are coated with the overflowing molding resin (22). A joint structure according to claim 1 or 2, wherein the rotor (12) is an elongated rotor (12) comprising a plurality of unit rotors (12a ... 12d) contiguously and axially arranged in succession. A joint structure according to any of claims 1 to 3, wherein the output shaft (10) is provided with a groove (32) having an inlet (28) opening outside of one of end plates (26) between said rotor cores (16) and magnets (14) are mounted. A joint structure according to claim 1, wherein said inner circumference of said radial rotor (12) is a polygonal inner circumference to define the gap between the inner circumference of the rotor (12) and the circumference of the output shaft (10) as a non-cylindrical annular gap to thereby enhance a tightness of the joining of said rotor and said output shaft via said hardened molding resin. A method of making a joint structure of a radial type rotor (12) and an output shaft (10) in a synchronous motor, the rotor comprising an alternate circumferential arrangement of rotor cores (16) and magnets (14), the method comprising the steps of: a) providing a groove (32) in the surface of the output shaft (10) having an inlet (28) at a predetermined location; b) inserting the output shaft (10) into the rotor (12), which has end plates (26) at opposite ends thereof; c) stopping the insertion at a predetermined axial position relative to the rotor such as the said inlet (28) opens outside of one of said end plates (26) and d) injecting resin into a gap between the output shaft (10) and the rotor (12) through said inlet (28) and said groove (32).

Inventors: TAGAMI KIYOSHI, UCHIDA HIROYUKI FANUC MANSION, TAGAMI, KIYOSHI, UCHIDA, HIROYUKI FANUC MANSION HARIMOMI 7-107
Applicants: FANUC LTD, FANUC LTD.
Application year: 1989
Main classification: H02K1
IPC codes: H02K1, H02K17