Planetary gear transmission systems or components – Planet periphery surrounds axis of interacting gear
Patent
1989-07-21
1991-02-19
Braun, Leslie A.
Planetary gear transmission systems or components
Planet periphery surrounds axis of interacting gear
475178, F16H 128
Patent
active
049940058
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a new movement translation element, a so-called transmitter or driving dog, the primary task of which is to translate the rotation of the excentrically mounted excentric gear wheel in an excentric gear to the output shaft thereof. Another application is as a coupling between shafts, particularly within the art of servo systems, and where the coupling does not transmit a bending movement.
A gear of the kind mentioned has an excentric gear wheel, also known as a satellite wheel or planet wheel, which is freely mounted on an excentric stub shaft which rotates together with the input shaft of the gear. The excentric gear wheel is in mesh with an outer, stationary, fixed gear wheel and rolls over the internal teeth thereof. The circumference of the excentric gear wheel is somewhat less than that of the fixed gear wheel. As it runs over the internal teeth of the fixed gear wheel, the excentric wheel executes slow rotation about its mounting on the excentric shaft simultaneously as its centre of gravity rotates at a high rotational rate about the input shaft. The Harmonic Drive .RTM. gear is not counted as an excentric gear. Neither are planet gears or differential gears where the translation of rotation takes place with gear wheels to the output shaft. With regard to the properties of these gear types I refer to the description in my international patent application with the title "Excentric Gear" with the number 87 00291-1.
It is known to use a lever system or two slides, which are mutually displaced 90.degree. (see Swedish patent 342 875) to translate the slow rotation of the excentric wheel to the output shaft.
These known transmission mechanisms are complicated and voluminous. They also have large backlash when the direction of rotation of the input shaft is reversed. Transmission means of this kind are used in such as ships, where such backlash can be tolerated and where there are no restrictions on space. In connection with ships, it is thus known to utilize pins as translation means, where the pins engage in holes in the excentric gear wheel. Two excentric wheels are used with the excentricity displaced by 180.degree., so that the gear will not have backlash due to the necessary diameter difference between the pins or rollers and the holes.
This well-known and often used principle has several serious disadvantages:
(a) Each roller is activated as force transmitter under a given angle of each completed revolution of the input shaft. The radial distance to the centre of the excentric wheel from the force transmitting roller varies as this angle is passed through. (The excentricity direction sweeps with the rotational rate of the input shaft past each roller). This radial variation in distance causes a sinus-shaped pulsation to be superposed on the rotational rate of the output shaft. In other words, the gear does not transmit a true angle. This pulsation can be reduced, but not eliminated, by using a large number of pins and rollers.
(b) Very tight tolerances on the ingoing components are required to get the gear to be free from backlash.
(c) Each roller must momentarily transmit the major part of the output shaft torque. A large reaction force then loads the output shaft bearing.
(d) The structure is complicated. The principle is difficult to use for small servo gears.
(e) The gear is noisy.
Another principle for translating the rotation of the excentric gear wheel to the output shaft is to use two universal joints. The disadvantage is that the structure is voluminous axially. Using one universal joint allowing axial movements in each direction is theoretically conceivable.
It is also known to utilize an elastic ruber connection between driving dog pins, which are arranged on the output shaft, and holes which are situted in the excentric wheel.
The present invention relates to a translation element of the kind described in the introduction, which does not have the disadvantages of the previously mentioned structures with regard to complexity, large volume, play, high noise
REFERENCES:
patent: 3037400 (1962-06-01), Sundt
patent: 3546972 (1970-12-01), Morozumi
patent: 3913408 (1975-10-01), Moore
patent: 4228698 (1980-10-01), Winiasz
patent: 4429595 (1984-02-01), Butterfield
patent: 4512213 (1985-04-01), Newton
Braun Leslie A.
Ta Khoi Q.
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