Page 56 - Handbook of Biomechatronics

50 Reva E. Johnson and Jonathon W. Sensinger

Fig. 10 Linear transmissions: (A) lead screw, (B) ball screw, (C) roller screw, and (D) rack
and pinion. ((B) Photograph by Glenn McKechnie; (C) Reproduced with permission from
Sandu, S., Biboulet, N., Nelias, D., Abevi, F., 2018. An efficient method for analyzing the roller
screw thread geometry. Mech. Mach. Theory 126, 243–264.)

are conceptually similar to lead screws, but the threaded rod has grooves, and
the nut has balls in it that rotate in the channels of the screw (Fig. 10B).
Thus, ball screws roll rather than slide, and accordingly have substantially
better efficiency than lead screws. This efficiency, however, comes with a
more complicated design; greater cost; and often with greater noise and
backlash. In addition, the contact between the balls and the grooved rod
are point-contacts vs the line contacts of lead screws, which substantially
decreases the forces that can be handled.
Differential roller screws combine the best attributes of lead screws and
ball screws in that they can withstand high loads and yet have high efficiency
(Fig. 10C). However, their manufacture requires high precision and is
accordingly expensive. They are used in some prosthetic devices (e.g.,
Lenzi et al., 2016).
Designs are occasionally seen with a rack and pinion design (Fig. 10D),
although other transmissions typically have a broader range of desirable
attributes.