Kinematic Couplings In Robotics

1
Kinematic Couplings In Robotics

• ME 250 Precision Machine Design
• San Jose State University
• Spring 2003
• Kevin Zhang
• K.C. Jones

2
Overview

• Motivation of Research
• Applications in Robotics
• Types of Couplings
• High-load Tool Mountings
• Case Studies
• Results

3
Motivation of Research

• Apply kinematic design principles to high-load
  robotic application in order to
• Improve repeatability and accuracy in mounting
  different tools on the robotic arm.
• Improve repeatability and accuracy in positioning
  robots on the manufacturing floor.
• Eliminate need for on-floor calibration of
  precision robotic tools with each tool change or
  floor layout change.

4
Applications in Robotics

• Tool Mounting
• Robot Positioning

5
Types of Couplings
Surface
Surface/Line
Line
Point
Stiffness
Repeatability
6
High-load Tool Mountings
Assume 2000 N total force 304 stainless
mounts Yield Stress 276 MPa
6 Point Contacts ?25.4 mm balls Contact
Pressure 1.63 GPa
6 Line Contacts ?25.4 mm cylinders 25.4 mm
long Contact Pressure 46.4 MPa
7
Option 1 Ball/Canoe Groove

• Exact constraint design create contacts at single
  points or lines, resulting in high contact
  stress.
• Canoe/ball design place a section of a sphere of
  diameter 1 meter on a small block.

• Stiffness and load capability are 100 times
  better than a 1 ball.

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Option 1 Ball/Canoe Groove
15mm Diameter

• Canoe ball surface after eleven base mountings.

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Option 1 Ball/Canoe Groove
Robot Wrist
Robot Base

• Expensive canoe features on permanent structure
  and cheaper groves on the disposable wrist.

• Predicted laboratory repeatability in the microns

10
Option 2 Three Pins
11
Option 2 Three Pin

• In-plane preload Fp and contact reaction force
  (F1, F2, F3) against three pin interface.

12
Option 2 Three Pin
Interface plates fitted with three pin couplings
13
Results

• Based on the measurement results, the overall
  accuracy benefits of precision machine canoe ball
  setup is negligible over the simple three-pin
  interface.
• Canoe ball (1000-3000) 10-100X more expensive
  than the simple pin

14
Summary

• When interfaces are standardized across
  manufacturer, the kinematic interface becomes a
  simple handshake.
• Quick-change factory interface improve
  flexibility during production
• Reducing uncertainty involved in the
  repair/replace decision
• Replacement and maintenance process are faster
  and more efficient.

15
References

• 1 Hart, J. Design and Analysis of Kinematic
  Couplings for Modular Machine and Instrumentation
  Structures, S.M. Thesis, MIT, 2001.
• 2 Willoughby, P. Kinematic Alignment of
  Precision Robotic Elements in Factory
  Environments, S.M. Thesis, MIT, 2002.
• 3 Line Hertzian Contact Calculator. (n.d.)
  Retrieved March 14, 2003, from http//grove.ufl.ed
  u/wgsawyer/Laboratory/Software/Line/LineContacts.
  HTML

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Hertzian Stress
http//grove.ufl.edu/wgsawyer/Laboratory/Software
/Line/LineContacts.HTML