Overview of the 3 DOF Parallel-Architecture Wrist Mechanism Stephen Canfield, Professor Department of Mechanical Engineering Tennessee Technological University November 10, 2008

Overview

About Parallel Mechanisms Multiple load-bearing chains b/n output and base Kinematics Advantages Stronger, lighter Disadvantages Reduced range of motion, kinematics

About the PAW 3-5R Spatial Parallel-architecture mechanism 3dof Pitch, yaw, plunge

Characteristics of the PAW High payload-to-weight, good dynamic performance Ground-relative actuation All-revolute design Closed-form forward/inverse kinematics exist Large range of motion in orientation Singularity free workspace (interior),greater than hemisphere Removes constraint on control algorithms Improved dexterity

Advantages of proposed design Parallel-architecture: High payload, accuracy, good dynamic performance in light-weight system Large, singularity-free range of motion Eliminate need for slip-rings Provide accuracy needed for solar concentrators Inherently redundant system - Application for pointing solar arrays – Video

Gimbal Kinematics, Options

Past applications Robotic end-effector, compliant design for pointing mirrors, sub 10nm precision manipulator

Point Design Applications: Thruster

Part Layout

Thruster as built

Application for pointing thruster

Design Point: Solar-Array Mount

Solary Array Mount

Table I: Summary of 3D solar-array tracking mechanism Solar Array Mount Component Description Mass/ Workspace Motor Drive: Maxon EC90 Flat Motor 1.5 lb Drive reduction Harmonic Drive HDC 1M 2.6 lb Bearings Bronze bushings, ¾, 3/8 ID Shaft 440c SS Link components 7075 Al Mechanism weight * (without actuation) 14.75 lb 3D Mechanism weight (with actuation, includes a 20% factor) 32.5 lb Working Volume* 5.5 inch radius cylinder Height is selectable 5.5 inch cylinder Stowed Volume* 3 high x 7 radius cylinder (inches) 7x3 inch cylinder Table I: Summary of 3D solar-array tracking mechanism

Miniature Gimbal:

Compliant mechanism applications High precision compact design From known topology Conventional 3 dof manipulator (pointing task) Compliant 3 dof manipulator Compact, 6 dof compliant manipulator

Kinematics

Force Analysis Closed-form kinetostatic analysis Beta=30 degrees

Path planning and trajectory control

Embedded electronics Currently Motorola S-12 family MCU IK ~ 12k in HCS-12 CPU assembly (unoptimized) 8 channel PWM, Quadrature encoders, drivers

Summary