1. Field of the Invention
The present invention relates in general to a hand-held vibratory massager, and more particularly to such a vibratory massager with an applicator head in which a vibration-generating member is mounted together with a drive motor therefor.
2. Description of the Prior Art
As disclosed in Japanese Utility Model publication (KOKOKU) No. 44-12708, there has been already proposed a hand-held vibratory massager with an applicator head mounting therein a drive motor and an eccentric flyweight driven thereby to produce vibration. The applicator head is resiliently supported by means of a coil spring to a hand grip for limited movement in all directions in relation to the hand grip. Such prior massager is found advantageous in eliminating any driving connection between the hand grip and the applicator head, utilizing the weight of the motor itself to increase vibratory energy produced at the applicator head, and in turn reducing the weight of the hand grip for easy manipulation of the massager. However, it poses another problem that the hand grip is likely to suffer from an excessive counter shaking which is a reaction movement transmitted back from the vibrating applicator head through the resiliency of the coil spring, producing fatigue of the user's hand holding the hand grip. This occurs when the center of mass of the flyweight is displaced from that of the entire applicator head in the axial direction thereof. In fact, such displacement is inevitable in the prior art massager because of that the mass center of the entire applicator head is approximately in coincidence with that of the incorporated motor which itself is of heavy construction and accounts for almost all of the weight of the applicator head, and that the flyweight connected to the end of the motor output shaft has its mass center correspondingly offset in the axial direction of the output shaft from the mass center of the motor, or the applicator head. The above problem will be easily understood from FIGS. 5A and 5B, 6A and 6B of the attached drawings in which the applicator head 2 is schematically shown to be coupled to the hand grip 1 by means of the coil spring 3. As shown in these figures, when the mass center Mf of the flyweight is offset by a distance L in the axial direction from the mass center Mc of the entire applicator head 2, a vibratory force F produced at the flyweight being in motion will cause a torque (F.times.L) about the mass center Mc of the applicator head 2, which torque in turn causes a reaction force to be transmitted back to the hand grip 1 through the resiliency of the coil spring 3, eventually shaking it about the mass center C of the hand grip 1. This occurs equally either the mass center Mf is offset on the opposite side of the mass center Mc from the hand grip 1 (FIGS. 5A and 5B) or it is offset to the hand grip 1 from the mass center Mc (FIGS. 6A and 6B). The above shaking or jerky movement of the hand grip compels the user holding the hand grip to keep it in position against the continuing shaking movement during the massaging process, greatly accumulating fatigue of the user's hand and therefore adversely affecting the performance of the massager.
Other prior massagers which are found to be relevant to the present invention are listed in following.
1. U.S. Pat. No. 4,224,932 issued to Farb; PA0 2. U.S. Pat. No. 4,604,993 issued to Moriwaki et al.
U.S. Pat. No. 4, 224, 932 (Farb) discloses a massager with an applicator head which is rotatably supported on a rigid drive shaft extending from a hand grip. The applicator head includes an eccentric flyweight bearing which is connected to the drive shaft for rotation in a circular pattern about the drive shaft. The patent neither provides the resilient connection between the applicator head and the hand grip nor discloses the provision of incorporating a drive motor within the applicator head.
U.S. Pat. No. 4,604,993 (Moriwaki et al) discloses a massager in which an applicator head is resiliently supported to a hand grip. But, the applicator head of this patent is designed to be driven by a drive motor mounted within the hand grip through an elongated drive linkage extending from the hand grip into the applicator head. Thus, this patent is not intended to incorporate the drive motor in the applicator head itself.