Machine element or mechanism – Gearing
Patent
1990-01-09
1991-05-21
Diehl, Dwight
Machine element or mechanism
Gearing
475177, F16H 3706
Patent
active
050164910
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a gear assembly comprising two strain wave gears. The double strain wave gear arrangement, which is referred herein as dual strain wave gearing enables the connect of a motor to a gear assembly according to the invention to produce a compact gear motor organization. One advantageous application of such a motor is in mechanism characterized by a high torsional moment, a low speed of rotation, a small availability of space and low weight and where good parking accuracy may be required from the power device. An example of such device is the driving means of the movement joints in industrial robots.
In several known motor types, the greatest power is obtained from the motor at a speed of rotation higher than what is required for moving the load. Therefore, a reduction gear must be provided between the motor and the load so that the greater power obtained from the motor can be utilized as a high torsional moment at a low speed of rotation. As is known, a strain wave or harmonic gear provides a high reduction ratio while the gear takes up little space and its performance is good.
The principle of a strain wave gear is disclosed in U.S. Pat. No. 2,906,143, Sept. 29, 1959, Musser, and that of a dual strain wave gear in U.S. Pat. No. 2,943,513, Jun. 5,1960, Musser.
SUMMARY OF THE INVENTION
According to the invention two dual strain wave gears can be connected in parallel in such a way that the primary moment can be supplied to the gear assembly; for example, via an external annular primary shaft positioned between the gears, whereby the secondary shaft of the gear assembly may be sleevelike. The rotor in a motor, which can be made annular, can be directly used as a primary shaft. The invention can be employed with various types of electric motors, such as brushless direct-current motors or stepper motors, or it can be used with motors of other types, such as pneumatic motors. Because the moment transmission ability of the gear assembly of the invention is very high, its compact form and its range of transmission ratio (about 25 to 100:1) make it well suited for use as a reduction gear in an annular motor without considerably increasing the need of space thereof. The gear assembly can also be constructed substantially without clearances, and its diameter and, as a consequence, the moment transmission ability can be varied within wide limits while retaining the compact structure. Alternatively, where desired, the primary moment can be supplied to the gear assembly in other ways; for instance, via a separate drive shaft to an external ring or via a bearing positioned internally in the flexspline.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following the invention and the preferred embodiments thereof will be described in more detail with reference to the examples of the attached drawings, wherein
FIG. 1 illustrates the overall structure of a gear assembly according to the invention in a partial longitudinal cross-sectional view;
FIG. 2 illustrates an end projection of the previous figure;
FIG. 3 is a partial longitudinal cross-sectional view of a gear assembly whereto a brushless direct-current motor is attached as motor;
FIG. 4 is a cross-sectional view of the motor of FIG. 3 in the direction of the line A--A;
FIG. 5 illustrates the magnetic circuits for making the flexspline elliptical in the gear assembly of FIG. 3;
FIG. 6 is a reduced view of the operation of the gear assembly according to the invention as an end projection when the assembly is in motion;
FIG. 7 illustrates the distribution of tangential stresses in the flexspline of the gear assembly within the dual strain wave gears as an end projection when the gear assembly is under load.
FIGS. 1 and 2 illustrate the overall structure of a gear assembly. As showing the gear assembly can be comprises dual strain wave gears 1a and 1b having a common flexspline 2. The flexspline 2, at one end is provided with external teeth 3a operative as part of the gear 1a and interengageable with peripheral teeth 4a on
REFERENCES:
patent: 4425822 (1984-01-01), Marschner et al.
patent: 4479403 (1984-10-01), Marschner et al.
patent: 4616529 (1986-10-01), Heinemann
Diehl Dwight
Innoke Oy
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