Patent Publication Number: US-RE38347-E

Title: Flat coreless vibrator motor having no output shaft

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a flat coreless vibrator motor having no output shaft, which motor is suitable used as a silent information source for a small-sized radio calling device (or a pager) or as a vibration source for a massager and, more particularly, to an improved fixed shaft type structure of the coreless vibrator motor provided with a thin fixed shaft. 
     2. Description of the Related Art 
     Conventionally, a flat vibrator motor without an output shaft has been known, especially as a flat coreless motor disclosed in the U.S. Pat. No. 5,036,239. As shown in FIG. 6, this motor has the structure wherein a rotor R is eccentrically disposed within a housing H comprised of a casing  28  and a bracket  29  and rotatably supported by a lubricant-containing bearing  32  and  33  disposed in the casing  28  and the bracket  29 , respectively, through a rotor holder  30  and a shaft  31 . It should be noted that since the eccentric rotor R is fixed to the shaft  31 , the position of the rotor R is determined by the shaft  31  which is flush with the housing H. 
     However, where the motor is of the above-described twin bearing type, the concentricity between the upper and the lower bearings becomes important. In the case of a coin type flat motor whose thickness is about 3 mm, in order to prevent the tilting and blocking of the rotor, it becomes necessary to make the concentricity between the bracket fitting portion and each of the bearings as small as 10 μm or less, so that each of the parts of the motor is required to have a high degree of dimensional accuracy. 
     Such a problem ought to be solved by using only one of the bearings as a cantilever type bearing, however, as will be understood from the thickness of the motor, the soft lubricant-containing bearing is not practical in use because of the weakness of its fixing strength. When the bearing fitting portion is elongated, the thickness of the motor can not be reduced. When the thickness is forced to be reduced, in turn, the fitting allowance of the rotor holder fitted about the shaft becomes short, resulting in another problem in the actual use thereof. 
     Further, there is also disclosed in JP-B-59-14966 (refer to FIG. 1) a shaft-fixed type vibrator motor in which the shaft is prevented from projecting outside its housing. 
     As maybe understood from its drawings, however, since both ends of the shaft are fixed to a bracket, it is difficult to assemble the rotor. That is, to explain the structure by using the reference numerals given in the drawings, it is generally difficult to mount the rotor  12  to the bearings  5  and  6  respectively fitted in the brackets  2  and  3  through the shaft supporting brackets  10  and  11 , because of the existence of the stator  7  as an obstacle. Further, the bearings  5  and  6  are not to be mounted to the shaft  4  but unavoidably mounted to the brackets  2  and  3  for the purpose of facilitating the lead wire connection process. Thus, the outer diameter of the bracket is obliged to be made large, so that the sliding loss with respect to the shaft-supporting brackets  10  and  11  becomes too large for the motor to be put in practical use. Unlike the shaft, the degree of roughness of the brackets  10  and  11  cannot be made small. 
     In this connection, in order to overcome the above-described various problems, the present inventors formerly proposed an invention disclosed in JP-B-6-81443 by taking notice of the fact that a vibrator motor having no output shaft which makes use of the vibration of its rotor itself is not required to rotate its shaft and that the shaft has only to be fixed at one end thereof. Thus, this motor has now been produced as a shaft-fixed type flat vibrator motor having no output shaft. Such a motor is now popular in the market due to the ease of assembly of the rotor and the excellence of its cost performance. 
     With the recent trend of miniaturization of portable equipment, the motor to be mounted in the equipment is required to be more and more miniaturized with minimum power consumption. If a motor with a shaft having a diameter of about 0.6 mm (a shaft having a diameter of 1.2 mm might be accepted) must be used, such a small-diameter shaft of cantilever supporting type may require careful consideration to its impact resistance making the fixing portion of the shaft large, in turn, may affect adversely the reduction of the overall thickness of the motor. 
     The present invention has been made to overcome the above-described problems and an object of the invention is to provide a flat vibrator motor having no output shaft with a sufficient degree of impact resistant, using a small-diameter shaft, which can be assembled in a simple manner and which is thereby advantageous in view of manufacturing cost. 
     SUMMARY OF THE INVENTION 
     In a vibrator motor having no output shaft and constructed such that an eccentric rotor comprising a plurality of armature coils is disposed within a housing comprised of a casing and brackets, a commutator is disposed on the rotor, brushes are brought into sliding contact with the commutator, a magnet is caused to confront the rotor leaving a space from the latter and a shaft supporting the rotor is prevented from projecting outside the housing, an improvement is made in such a manner that one end of the shaft is fixed to a portion of the housing, the rotor is rotatably mounted on the shaft by assembling the rotor in the housing from the other end of the shaft, the rotor is brought into sliding contact with the housing by urging the rotor forward or rearward in the axial direction and the other end of the shaft is fitted into a concave portion formed in the other portion of the housing thereby preventing the shaft from moving in the radial direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of an essential portion of a flat vibrator motor having no output shaft according to a first embodiment of the present invention especially when the motor has a coreless type eccentric rotor; 
     FIG. 2 is a plan view of the eccentric rotor of the motor shown in FIG. 1; 
     FIG. 3 is a sectional view of an essential portion of a first modification of the flat coreless vibrator motor shown in FIG. 1; 
     FIG. 4 is a sectional view of an essential portion of a second modification of the flat coreless vibrator motor shown in FIG. 1; 
     FIG. 5 is a sectional view of an essential portion of a flat vibrator motor according to a second embodiment of the present invention especially when the motor has a cored type eccentric rotor; and 
     FIG. 6 is a sectional view of an essential portion of a conventional flat vibrator motor having no output shaft. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The first embodiment of the present invention is an application of the invention to a flat coreless vibrator motor shown in FIG.  1  the   1 . The motor includes a thin stainless steel shaft  2 is  fixed to the center of a bracket  1  forming part of a housing H by pressure-fitting one end of the shaft into a holder  1 a projecting inward as an integral part of the bracket  1  an  1 . An eccentric rotor  3  is rotatably mounted on the shaft  2  from the open end of the shaft. 
     More concretely, the eccentric rotor  3  is constructed such that as shown in FIG. 2, three air-core armature coils  3 a,  3 b and  3 c are arranged eccentrically toward one side on the rear surface of a flat plate commutator  5  at an arrangement pitch of about 60°, and are made integral with the commutator  5 , which is provided with spark quenching elements  4 a, by a resin material  4  of a low friction factor. That is, the low friction factor resin itself serves as a bearing at the same time. Further, in the bracket  1  there is placed a ring-shaped magnet  6  contains neodymium and which confronts the rotor  3  leaving a certain space from the latter and inside a central opening of ring-shaped magnet  6  there are embedded a pair of brushes  7  and  7  at a sliding open angle of 90° so that the brushes  7  and  7  are brought into sliding contact with the flat plate commutator  5  with a suitable pressure contacting force. 
     On the other hand, a casing  8  which forms the other part of the housing includes at its center a tapering through hole  8 a into which the other end of the above-described thin stainless steel shaft  2  is mounted. The eccentric rotor  3  is brought into sliding contact with the casing  8  by the pressure contacting force of the pair of brushes  7  and  7  by means of a ridge  3 d and a polyester film washer P disposed around the through hole  8 a. Consequently, the rotor  3  is constantly urged toward the casing  8  and rotatably pressed against the polyester film washer P so that there is no fear of the rotor  3  moving toward the casing  8  to rub against it. The rotor  3  can be rotatably supported in a stabilized manner while always keeping a predetermined gap from the casing  8  without varying the rotational position thereof. 
     Further, the ridge  3 d is provided with a U-shaped or V-shaped groove which is concentric with the shaft  2  and which serves as a lubricant retaining means so that a lubricant such as grease can be maintained and a longer working life can be expected of the rotor. 
     The above-described assembling structure can be realized in a simple manner in which the rotor  3  prepared in advance is fitted in the bracket  1 , also prepared in advance, from the open end of the shaft  2 , the casing  8  is placed over the bracket  1  and assembled with the bracket  1  by caulking or welding the outer periphery of the bracket  1  to the open edge  8 b of the casing  8 . 
     Further, as a modification of the instant embodiment there is shown in FIG. 3 a coin battery type vibrator motor having a casing and a bracket serving as current feeding electrodes. 
     In this modification, a concave portion  88 a of a casing  88  for receiving the other end of the shaft  2  may be a resin material  88 b having a good sliding property and an insulating means  11 a, such as polyethylene terephthalate resin, may be outsert molded along the outer periphery of a bracket  11  so that the concave portion  88 a is insulated from the casing  88  at the time of assembling the rotor. Further, in FIG. 3, reference symbol VV designates a V-shaped or U-shaped groove which is concentric with the shaft  2  and which serves as a lubricant retaining means disposed on the side of the resin  88 b of good sliding property, facing a portion of the low frictional factor resin  4  of the rotor  3 . 
     In the instant embodiment, in order to make the casing and the bracket serve as current feeding electrodes, one of the brushes  77  is directly soldered to the bracket  11  while the other brush  77  extends under the magnet  6  through a flexible plate F so as to be connected to the inside of the casing  88 . 
     A further modification of the motor of FIG. 2 is shown in FIG. 4 in which the other end of the shaft  2  engages an adhesive polyester film P 1  in a through hole T in the casing  8 . 
     Further, in order to form the concave portion for receiving the other end of the shaft  2  for the insulating and sliding functions, the through hole T is drilled through the casing  8  to receive the shaft  2  the  2 . The through hole T has a diameter a little larger than that of the shaft  2  so that the other end of the shaft  2  enters the through hole T by one half of the depth thereof and contacts the adhesive polyester film P 1  covering around  the through hole T. 
     In the above case, it is desirable that the portion of the casing  8  which surrounds the through hole T be recessed in such a manner that the thickness of the motor itself or the space provided in the casing is not sacrificed by the thickness of the adhesive polyester film P 1  and then the film P 1  be applied to the recessed portion. 
     By so doing, it is possible to obtain a structure capable of securing the insulating and sliding properties of the rotor without sacrificing the advantage of the motor being of small thickness. Accordingly, it goes without saying that the structure can be applied also to the above-described coin battery type motor. 
     FIG. 5 is a sectional view of an essential portion of a shallow cored type flat vibrator motor having no output shaft according to a second embodiment of the present invention wherein reference numeral  12  designates a metallic dish-type casing with a bracket B fitted to an open edge thereof. As in the case of the first embodiment, to the bracket B there is pressure-fixed a small-diameter shaft  2 . Further, to the shaft  2  a cored rotor  13 , formed of two eccentric silicon steel plates K respectively bent outward at the outer peripheries thereof in opposite directions and an armature coil  13 a wound around the plates, is rotatably mounted through a lubricant containing bearing J fitted inside. In addition, to the cored rotor  13 , there is attached a cylindrical commutator C having a sliding surface C with which a pair of brushes  77  and  78  are brought into sliding contact. The base portion of each of the brushes is embedded in the bracket B through a synthetic resin brush base  79 . At the top of the dish-type casing  12  there is provided a concave portion  12 a which is formed by outsert-molding a resin material having a good sliding property so that when the rotor is assembled, the other end of the shaft  2  is supported by this concave portion  12 a. 
     Reference numeral  14  in FIG. 5 designates a cylindrical field magnet disposed in the casing  12  leaving a space from the cored rotor  13  with the magnetic center MC of the magnet being displaced from the center RC of the cored rotor  13  whereby the cored rotor  13  is always urged in the direction of the displacement. Accordingly, since the cored rotor  13  is constantly urged toward a slider  15 , there is no fear of the rotor slipping off downward and the position of the rotor is stabilized. 
     Further, a core cover Ka made of a resin material may be extended inward so that it may serve as a resin bearing in lieu of the above-described lubricant containing bearing J. 
     By so doing, it becomes possible to bring the rotor into direct sliding contact with the ceiling portion of the casing  12  through such a resin bearing. 
     As a modification of the above-described second embodiment of the invention, it is, of course, possible to provide a battery type motor by eliminating the lead wires and terminals and causing the casing and the bracket to serve as electrodes, respectively. Further, one end of the shaft  2  may be fixed to the casing instead of the bracket. 
     Thus, even in the case of such embodiment, since the rotor lies at a position to which the center of gravity of the rotor has moved, a large centrifugal force generated at the time of rotation of the rotor so that the rotor acts as a vibrating motor. 
     As described above, according to the present invention, the rotor is rotatably mounted on the shaft from one end of the shaft whose other end is fixed to the housing, so that the rotor can be assembled from one side of the shaft in a simple manner thereby facilitating automation, and since the radial movement of the shaft can be prevented without enlarging the fixing portion of the end of the shaft, even if the diameter of the shaft is small, the shaft can withstand an impact at the time when the motor falls down, and the like. Further, since the rotor can be urged forward or rearward in the axial direction, the variation of rotational position of the rotor can be prevented so that the rotor can be rotatably supported in a stabilized manner without running against any other structural member. 
     Further, if the rotor is brought into sliding contact with the housing by the pressure force of the brushes as a means of urging the rotor, the rotor can be urged by only the spring pressure of the brushes so that the axial movement of the rotor can be controlled by a simple structure by making the effective use of the spring pressure of the brushes without increasing the number of parts. 
     Still further, in the case of the rotor, which is brought into sliding contact with the housing by the magnetic force of the magnet, it is possible to make the effective use of the attractive force between the rotor and the magnet. 
     It should be noted that the present invention can be carried out in a variety of modes without departing from the technical idea or characteristics thereof. Accordingly, any of the above-described embodiments is nothing but a mere illustration and should therefore be not interpreted limitatively. Further, the technical scope of the present invention is represented by the appended claims and is not bound by the text of the specification.