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The PVT, an elastic conservative transmission
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).ORCID iD: 0000-0002-7550-3134
2006 (English)In: The international journal of robotics research, ISSN 0278-3649, E-ISSN 1741-3176, International journal of robotics research, Vol. 25, no 10, 1013-1032 p.Article in journal (Refereed) Published
Abstract [en]

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 important properties. 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%

Place, publisher, year, edition, pages
2006. Vol. 25, no 10, 1013-1032 p.
Keyword [en]
Elastic conservative transmission, Passively variable transmission, PVT, Torque ratio, Velocity ratio
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-9032DOI: 10.1177/0278364906069188ISI: 000241829700004Scopus ID: 2-s2.0-33749064910OAI: oai:DiVA.org:kth-9032DiVA: diva2:14571
Note
QC 20100831Available from: 2006-01-26 Created: 2006-01-26 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Quadruped robot control and variable leg transmissions
Open this publication in new window or tab >>Quadruped robot control and variable leg transmissions
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The research presented in this thesis regards walking of quadruped robots, and particularly the walking of the Warp1 robot. The motivation for the robot is to provide a platform for autonomous walking in rough terrain.

The thesis contains six papers ranging from development tools to actuation of robot legs. The first paper describes the methods and tools made for control development. These tools feature: programming of the robot without low level coding (C-code); that the controller has to be built only once for simulation and experiments; and that names of variables and constants are unchanged through the chain of software Maple -- Matlab -- Simulink -- Real~Time~Workshop -- xPC--Target.

Three controllers, each making the robot walk are presented. The first controller makes the robot walk using the crawl gait. The method uses static stability as method for keeping balance and the instantaneous trunk motions are given by a concept using the so called weight ratios. A method for planning new footholds based on the positions of the existing footholds is also proposed and the controller experimentally verified.

The second walking controller shows that the robot also can walk dynamically using the trot gait. The method proposed uses information from ground contact sensors on the feet as input to control balance, instead of, which is common, inertial sensors. It is experimentally verified that Warp1 can trot from level ground onto a slope and turn around while staying balanced.

The main ideas of these two walking controllers are fused in the third which enables smooth transitions between crawl and trot. The idea of using the ground contact sensors from the first controller is here used to estimate the position of the center of mass. This controller uses weight ratios in the gait crawl as well as in the dynamic gait trot. Hence, the method of using weight ratios is not only useful for static stability for which it was originally intended. The controller is experimentally verified on Warp1.

The Warp1 robot weighs about 60 kg, has 0.6 m long legs with three actuated joints on each. The speed and strength is sufficient only for slow walking, even though the installed power indicates that it should be enough for faster walking. The reason is that a walking robot often needs to be strong but slow when the feet are on the ground and the opposite when in the air. This can not be achieved with the motors and transmissions currently used.

A transmission called the passively variable transmission (PVT) is proposed which enhance motor capabilities of robot joints. It is elastic, nonlinear and conservative. Some general properties for elastic transmissions are derived such that they can be compared with conventional transmissions. The PVT gives strong actuation at large loads and fast actuation at small loads. The proposed transmission is compared to a conventional transmission for a specific task, and the result is that a smaller motor can be used.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. xii, 50 p.
Series
Trita-MMK, ISSN 1400-1179 ; 2006-02
Keyword
walking robot, quadruped, walking, crawl, trot, passively variable transmission, PVT, variable transmission, continuously variable transmission, velocity ratio, torque ratio
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-600 (URN)91 7178 257 5 (ISBN)
Public defence
2006-02-10, M2, Brinellv. 64, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100831Available from: 2006-01-26 Created: 2006-01-26 Last updated: 2010-08-31Bibliographically approved

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