overview of the 3 dof parallel- architecture wrist mechanism stephen canfield, professor department...
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Overview of the 3 DOF Parallel-Architecture Wrist Mechanism
Stephen Canfield, ProfessorDepartment of Mechanical EngineeringTennessee Technological UniversityNovember 10, 2008
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Overview
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About Parallel Mechanisms
Multiple load-bearing chains b/n output and base
Kinematics Advantages
Stronger, lighter Disadvantages
Reduced range of motion, kinematics
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About the PAW
3-5R Spatial Parallel-architecture mechanism
3dof Pitch, yaw, plunge
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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
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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
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Gimbal Kinematics, Options
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Past applications
Robotic end-effector, compliant design for pointing mirrors, sub 10nm precision manipulator
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Point Design Applications: Thruster
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Part Layout
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Thruster as built
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Application for pointing thruster
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Design Point: Solar-Array Mount
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Solary Array Mount
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Solar Array Mount
Table I: Summary of 3D solar-array tracking mechanism
ComponentDescription 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 cylinderHeight is selectable
5.5 inch cylinder
Stowed Volume* 3 high x 7 radius cylinder (inches)
7x3 inch cylinder
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Miniature Gimbal:
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Compliant mechanism applications
Conventional 3 dof manipulator (pointing task)
Compliant 3 dof manipulator
High precision compact design
From known topology
Compact, 6 dof compliant manipulator
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Kinematics
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Force Analysis
Closed-form kinetostatic analysis
0 50 100 150 200 250 300 350 4000
20
40
60
80
100
120
140
160
180motor torque profile of rotary move
rotation (deg)
mot
or t
orqu
es
Beta=60 degrees
0 50 100 150 200 250 300 350 400-100
-50
0
50
100
150
200
250motor torque profile of rotary move
rotation (deg)
mot
or t
orqu
es
Beta=30 degrees
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Path planning and trajectory control
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Embedded electronics
Currently Motorola S-12 family MCU IK ~ 12k in HCS-12 CPU assembly
(unoptimized) 8 channel PWM, Quadrature encoders,
drivers
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Summary