Patent Application
20100062895
This invention relates to a reduction mechanism.
Reduction mechanisms are generally known and are used to convert the speed of a motor, for instance an electric motor, to a lower speed.
A known reduction mechanism is a planetary gear transmission. A planetary gear transmission usually comprises an input gear wheel provided with an outer toothing, which cooperates with at least one planetary gear wheel. The rotation axis of a planetary gear wheel moves around the input gear wheel and is not fixedly arranged. The planetary gear wheels cooperate with a ring-shaped output gear wheel.
When in particular applications a high transmission ratio is desirable, use is made, for instance, of a reduction mechanism of the ‘harmonic drive’ principle.
A harmonic drive reduction mechanism comprises an outer toothed ring, provided with an inner toothing, in which outer toothed ring an inner toothed ring provided with an outer toothing is operative, this inner ring being flexible but connected with the fixed world so as to be restrained from rotation. The inner toothed ring has two teeth less than the outer toothed ring, and is pressed against the outer toothed ring by two press-on bodies. The two press-on bodies are rotatably arranged symmetrically with respect to an input situated on an input shaft. The input is situated eccentrically with respect to the outer toothed ring. As a consequence, at two respective points, the inner toothed ring has a number of teeth cooperating with teeth of the outer toothed ring. When the two press-on bodies are going to rotate about the common shaft of inner and outer ring, then, owing to the inner toothed ring being connected with the fixed world so as to be restrained from rotation, the outer toothed ring will start to rotate. This rotation amounts, per revolution of the press-on bodies, to an angle corresponding to the angle of rotation of two teeth.
Accordingly, a harmonic drive reduction mechanism has a high transmission ratio.
A disadvantage of a harmonic drive reduction mechanism is that the mechanism is relatively complex because it includes many parts. Also, the mechanism has a relatively high overall height and a relatively low efficiency.
An object of the invention is to provide an alternative reduction mechanism, whereby the disadvantages mentioned can be obviated whilst maintaining the advantages.
To this end, the invention provides a reduction mechanism comprising
an input gear wheel provided with an outer toothing, for coupling with a driving motor, which input gear wheel is provided with an evoloid toothing with only 1 or 2 teeth;
an output gear wheel provided with an inner toothing;
at least one intermediate gear wheel which is operative between the input gear wheel and the output gear wheel and whose rotation axis is fixedly arranged.
An evoloid toothing of the input gear wheel is understood in this context to mean a pinion having a toothing according to DIN 3960, whereby
the number of teeth Z is equal to 1 or 2;
the tooth angle β is greater than 15°;
the profile correction x1 of the pinion is greater than 0.5;
the profile correction x2 of the intermediate gear wheel is less than or equal to 0;
the tooth root height factor hFfP2 of the intermediate gear wheel is greater than or equal to the tooth head height factor haP1 of the pinion; and
the tooth head height factor haP2 of the intermediate wheel is substantially equal to the tooth root height factor hFfp1 of the pinion. The intermediate gear wheel and the output gear wheel have a corresponding toothing.
Such an evoloid toothing is a special variant of the involute toothing and is discussed in more detail by K. Roth in Zahnrad Technik—Evolventen Sonderverzahnungen, Springer Verlag ISBN 3-540-64236-6.
By virtue of the use of an input gear wheel with an evoloid toothing cooperating via an intermediate gear wheel with the output gear wheel, in a simple manner an input gear wheel with a small tooth number can be used in the reduction mechanism. This results in a simple and compact construction.
By using two or more intermediate gear wheels, operational reliability can be enhanced, and the construction can remain simple. By virtue of the use of two or more intermediate gear wheels, in particular, the force transmitted by the reduction mechanism can be large, since an input force is divided between the two intermediate gear wheels.
By making use of an output gear wheel provided with an inner toothing, the intermediate gear wheels and input gear wheel can be enclosed by the output gear wheel in a compact and elegant manner. This renders the reduction mechanism robust and less vulnerable.
In an advantageous embodiment, the gear wheels are situated substantially in one plane. As a result, a low overall height is obtained, which renders the construction of the reduction mechanism more compact.
In another advantageous embodiment, the input shaft of the reduction mechanism is situated directly on an output shaft of a driving motor. As a consequence, fewer parts can be used, so that the overall construction of the reduction mechanism can be rendered still more compact.
The invention will be further elucidated on the basis of an exemplary embodiment which is represented in a drawing. In the drawing:
It is noted that the figures are only schematic representations of a preferred embodiment of the invention, which is described by way of non-limiting exemplary embodiment. In the figures, the same or corresponding parts are designated with the same reference numerals.
A reduction mechanism according to the invention is shown in
Further, the reduction mechanism 1 comprises an output gear wheel 3 provided with an evoloid inner toothing c. During use, the speed of the output gear wheel 3 is lower than the speed of the input gear wheel 2. The speed is reduced in accordance with the transmission ratio of the reduction mechanism.
Furthermore, the reduction mechanism 1 in the exemplary embodiment of
The input gear wheel 2 is situated in the centre of the output gear wheel 3 designed as a toothed ring, arranged concentrically around the input gear wheel 2. In particular, the centerline of the input gear wheel 2 is coaxial with the centerline of the output gear wheel 3.
The intermediate gear wheels 4 have rotation axes which are fixedly arranged with respect to the fixed world, as schematically represented in
In the embodiment of
In an advantageous embodiment, the input gear wheel 2 is carried directly on an output shaft 5 of a driving motor not shown here. In this way too, the overall construction of the reduction mechanism remains compact, and little space is needed for the reduction mechanism.
The output gear wheel 3 may be coupled with an output shaft 6 of the reduction mechanism, as shown schematically in
It will be clear that the invention is not limited to the exemplary embodiments represented here. Many variants will be clear to those skilled in the art and are understood to be within the scope of the invention as set forth in the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1033127 | Dec 2006 | NL | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NL2007/050697 | 12/21/2007 | WO | 00 | 11/10/2009 |
