|Volume 25 Issue 10 - Publication Date: 1 October 2006
|The PVT, an Elastic Conservative
|Johan Ingvast, Jan
Wikander and Christian Ridderström The Royal Institute
of Technology (KTH), Department of Machine Design, Mechatronics Lab, S-100
44 Stockholm, Sweden
|This paper presents an innovative
transmission called the passively variable transmission (PVT) that has a
high torque ratio for large loads and a low velocity ratio for small loads.
The change in these ratios depends passively on the load, in contrast to
the continuous variable transmission (CVT), where the transmission ratio
is controlled explicitly. Another difference from the CVT is that the PVT
is elastic and the term transmission ratio is therefore not applicable.
A theory section formulates alternative ways of describing the torque and
velocity relations for elastic conservative transmisions as well as other
|This theory is used to analyze
and illustrate the characteristics of a PVT. The theory is also used to
compare the PVT with another novel elastic conservative transmission, called
load sensitive CVT. The nonlinearities and elasticity of the PVT make it
difficult to control using linear control theory. Feedback linearization
was therefore used to design a torque controller, and experimental results
show low impedance at small loads. Further, the controller tracks a reference
torque well as long as the reference rate does not cause motor saturation.
|The abilities of the PVT are
also illustrated by comparing it with an actuator having a traditional transmission.
The load case is recorded joint torques and angles from the carpus joint
of a walking horse. Simulation show that the required peak power is reduced
by more than 20% and the product of the maximum torque and the maximum angular
velocity is reduced by approximately 30%.