Three Degrees of Freedom Stewart-Like Platform for Testing Humanoids Postural Capabilities

Abstract

In this paper, a novel design of a Stewart-like platform is introduced with the purpose of testing humanoids postural capabilities. It performs three motions including surge (forward-backward), heave (up-down), and pitch (tilting). The suggested novel design is inspired from Stewart platform, a kind of parallel manipulator, distinguished for its high stability, and rigidity, but a narrower workspace compared to serial manipulators. Stewart platform provides six degrees of freedom, which are more kinds of motions than needed for testing humanoids balance. For this, Stewart platform is optimized to perform required motions to test humanoids balance of surge, heave, and pitch, by reducing the numbers of actuators from six to four, and re-configuring joints and links connecting the platform to its fixed base. While four actuators are sufficient for three degrees of freedom, 4th actuator was added for wider stability range, which adds the possibility for 4th motion of rolling. Mathematical analyses are conducted for the suggested novel design including kinematics, Jacobians, and dynamic modeling using both Lagrange formulation and Newton Euler methods, those analysesare based on the side view projection of the platform. Different control techniques were considered including model based controller, and independent joint controller. MATLAB Simulink was the software environment simulation has been conducted in, where S-function tool is used to replace the plant through its derived dynamic equations for the purpose of testing model based controller. CATIA software was used to 3D model the new design, and to manipulate its parts observing its motion. CATIA was also used to conduct structural analysis of the platform.A prototype has been built and controlled to demonstrate the new design performing surge, heave, and pitch motions.Prototype has shown high rigidity, and high stability. The new design can be considered for various types of applications other than testing humanoids balance, including simulators,and machining technologies.