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High-Performance Mechanical Transmissions

J. Angeles, L. Slutski, M. A. González-Palacios, R. Spiteri, P. Montagnier, C. Teng, O. Navarro, C. J. Wu, D. Wang, S. Asamoah

We are currently developing a new generation of mechanical transmissions, intended to replace gears in applications where backlash, friction, and flexibility cannot be tolerated. We have thus produced two prototypes of Speed-o-Cam, a speed-reduction mechanism based on cams and pure-rolling contact, that is capable of producing, in one single stage, a reduction of N:1, where N is an integer that depends on the type of mechanism. We have produced one prototype that is intended for the coupling of parallel shafts; a second prototype, in its final stages of production, is aimed at coupling shafts with intersecting axes. Although the prototype of the latter was designed for shafts intersecting at right angles, virtually any angle can be accommodated, from tex2html_wrap_inline1838 to tex2html_wrap_inline1840 . In the extreme cases, an angle of tex2html_wrap_inline1838 produces an external plate cam; an angle of tex2html_wrap_inline1840 an internal plate cam. Planar Speed-o-Cam is intended to replace spur and helical gears, while its spherical counterpart is targeted at bevel gears.
 


Assembled planar Speed-o-Cam prototype


 


The limiting factor in N is the pressure angle: for the planar mechanism, intended to couple parallel shafts, a value of N up to 8 is possible within a maximum pressure angle of tex2html_wrap_inline1850 ; for spherical mechanisms, the corresponding value of N is 12. In each case, the low-speed shaft carries two cams located in different planes or, correspondingly, different concentric spheres, with the purpose of guaranteeing positive action for every mechanism configuration, without the need to add springs to maintain contact. The high-speed shaft is rigidly attached to a roller-carrying plate, with uniformly-distributed rollers on each side of the plate. The cams are close to cardioid, with the spherical ones of convex shape; the planar ones bear a small region where the profile becomes concave, but this element is essentially convex as well. For this reason, the load-carrying capacity of Speed-o-Cam is substantially higher than that of its gear-train counterpart for the same size and same speed-reduction ratio. Additionally, design provisions have been taken to allow for a preloading of the mechanism so that backlash will be eliminated.
 


A rendering of the spherical Speed-o-Cam


 


Other mechanical transmissions are also envisaged for the near future, in applications that require to replace rack-and-pinion transmissions or to rectify a nonuniform speed ratio or of a nonuniform torque-transmission ratio.


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Annual Report

Fri Nov 26 23:00:32 GMT 1999