Abstract:
A twin-shaft concentric motor includes first and second stators arranged concentrically to each other; and first and second rotors formed between the first and second stators, the rotors being rotatable independently of each other. The twin-shaft concentric motor may also include first and second stator partition walls and first and second rotor partition walls for maintaining a vacuum side and an atmospheric side separated, respectively, so that the stators are located under atmospheric pressure while the rotors are located under vacuum pressure.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a twin-shaft concentric motor, and specifically to a novel improvement for miniaturization and space saving by coaxially aligning a pair of motors to reduce the shaft length. 
     2. Description of the Related Art 
     As the type of a conventional twin-shaft motor, a motor structure shown in FIG. 1 is disclosed in WO94/23911 according to PCT Application, for example. 
     That is, as shown in FIG. 1, in a case  1 , first and second motors  2  and  3  are arranged to be laid up in the axial direction. A first rotor  4  of the first motor  2  and a second rotor  5  of the second motor  3  are respectively connected to first and second members  6  and  7  disposed in the upper part. 
     Therefore, the members  6  and  7  can be independently operated by independent rotation of each of the motors  2  and  3 . 
     Since the conventional twin-shaft motor is structured as above, the following problem has been involved. 
     That is, since the motors are arranged in series to be laid up in the axial direction, the longitudinal length increases so that miniaturizing cannot be achieved by reducing the shaft length. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to solve the above-mentioned problem, and in particular to provide a twin-shaft concentric motor for achieving miniaturization and space saving by coaxially aligning a pair of motors to reduce the shaft length. 
     A twin-shaft concentric motor according to the present invention comprises first and second stators arranged concentrically to each other; and first and second rotors formed between the first and second stators and being rotatable independently of each other. The twin-shaft concentric motor may further comprise first and second stator partition walls and first and second rotor partition walls for maintaining a vacuum side and an atmospheric side separated, respectively, so that the stators are located under atmospheric pressure while the rotors are located under vacuum pressure. Also, in the twin-shaft concentric motor, a permanent magnet may be provided on each surface of the rotors. Furthermore, the twin-shaft concentric motor may further comprise first and second detecting means for independently detecting the rotational angle of each of the rotors, wherein the first and second detecting means may be formed of code plates disposed in each of the rotors and sensors respectively opposing each of the code plates, and wherein the code plates and the sensors may form magnetic encoders. Preferably, the code plates are made of a ferromagnetic material and have anticorrosive coating formed on the surfaces thereof, and a hollow portion is formed in the axial center of a case supporting the stators. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view showing a structure of a conventional twin-shaft concentric motor; 
     FIG. 2 is a sectional view of a twin-shaft concentric motor according to the present invention; and 
     FIG. 3 is an enlarged sectional view of essential parts of the twin-shaft concentric motor shown in FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of a twin-shaft concentric motor according to the present invention will be described below with reference to the drawings. In addition, the description will be made while like reference characters designate like portions common to those of the conventional example. 
     As shown in FIGS. 2 and 3, a case  1  has a hollow portion  10  in the axial center, and outside the hollow portion  10 , an outer-rotor-type second motor  3  and an inner-rotor-type first motor  2  are concentrically arranged. 
     The second motor  3  disposed inside inner than the first motor  2  is formed of a ring-shaped second stator  12  disposed toward the case  1  and having a stator coil  11  wound therearound and a ring-shaped second rotor  13  rotatably arranged in the case  1  via second bearings  23 A. 
     While a second permanent magnet  14  is disposed on the internal surface of the second rotor  13 , a ring-shaped second rotor partition wall  15   a  and a second stator partition wall  15  are respectively arranged inside the second rotor  13  and outside the second stator  12 . Both ends of the second rotor partition wall  15   a  are sealed to be airtight by both ends of the second rotor  13  via sealing members  100  while both ends of the second stator partition wall  15  are brought into intimate contact with fitting members  16  and  17  on both ends of the second stator  12 , so that the second rotor  13  and the second stator  12  are separated with each other so as to be positioned in a vacuum region “A” and an atmospheric region “B”, respectively. 
     Inside a ring-shaped external wall  20  disposed in the extreme exterior and extended from the case  1 , a first stator  22  having a stator coil  21  is arranged. On first bearings  23  disposed inside the external wall  20 , a first rotor  24  disposed close to the exterior of the second rotor  13  and having a first permanent magnet  24   a  is rotatably mounted. 
     On the internal surface of the first stator  22 , a ring-shaped first stator partition wall  25  is disposed. Both ends of the first stator partition wall  25  are brought into intimate contact with fitting members  26  and  27  disposed at both ends of the external wall  20  while a ring-shaped first rotor partition wall  25   a  is brought into intimate contact with the exterior of the first rotor  24  via sealing members  28  and  29 , so that the first rotor  24  and the first stator  22  are separated with each other so as to be positioned in the vacuum region “A” and the atmospheric region “B”, respectively. 
     The rotors  24  and  13  are concentrically arranged close to each other. At one end of each of the rotors  24  and  13 , ring-shaped first and second code plates  30  and  31  having anticorrosive coating formed thereon and extending in the radial direction perpendicular to the axis of the rotors  24  and  13  are respectively fixed with screws  32  and  33 . 
     The code plates  30  and  31  oppose first and second sensors  34  and  35  disposed in the external wall  20  of the case  1 , respectively. Each of the code plates  30  and  31  and each of the sensors  34  and  35  form first and second detecting means  40  and  41  for detecting rotation and the rotational angle of each of the rotors  24  and  13 , respectively. 
     When each of the code plates  30  and  31  is a gear, a magnetic encoder can be thereby formed while when a rotating disc, a known optical encoder can be thereby formed although the sensors  34  and  35  are slightly changed in shape. 
     Both ends of each of the partition walls  25  and  15  are welded to each of the fitting members  26 ,  27 ,  16 , and  17  by welded portions  50 , respectively while each of the partition walls  25   a  and  15   a  are brought into intimate contact with each of the sealing members  28 ,  29 , and  100 , respectively, so that the motor can be divided into the vacuum region “A” and the atmospheric region “B” at the upper end of the case  1  shown in FIG.  2 . When the case  1  is used in a vacuum atmosphere (vacuum chamber, etc.), for example, positions around the rotors  24  and  13 , and the code plates  30  and  31  are the vacuum region “A” while other portions are the atmospheric region “B”. 
     Then operations will be described. When the case  1  is attached to a vacuum chamber, for example, and arms or the like (not shown) are fitted to the first and second rotors  24  and  13 , the arms or the like disposed in the rotors  24  and  13  can be freely operated under the vacuum pressure by respectively exiting the stators  22  and  12 . 
     The hollow portion  10  provided in the case  1  may be used for a retracting space of a ball screw and the like. 
     Since the twin-shaft concentric motor according to the present invention is formed as described above, the following effects can be obtained. That is: since the twin shaft is coaxially aligned rather than the conventional structure arranged in series in the axial direction, the longitudinal length is substantially reduced; since the hollow portion is formed in the axial center, miniaturization can be achieved while a ball screw and the like can be accommodated therein, thereby achieving space saving.