Configuring Robot Kinematics Using a Velocity Preset Controller

Owned by Saheed Quadri
Oct 12, 2024
3 min read

This document covers the process taken to derive a desired path for simulating the dynamics of the team’s 6 axis robot arm using a velocity preset model controller in SimulationX.

The preset model controller for the arm, designed by Josiah Lodewyk of Xcellerated Protrotyping Inc (XPI) takes in tables of angular positions X in (deg or rad) of each axis at times t in second. The synchronization of these positions can be used to configure the movement of the arm along a desired path at calculated velocities.
The controller was used to validate that the model can provide meaningful results for simulating the dynamic torque output required from actuators on each axis.

 

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Tasks to be Performed

  • Move from home position to pick up a 5kg payload symmetrically positioned in front of and below the drivetrain chassis

    • Roughly define arm module placement on the drivetrain relative to base coordinate

    • Define payload placement in front of the drivetrain based on competition examples

    • Given symmetry in y axis, the kinematics will involve Axis 1, Axis 2 linkages and Axis 5.

    • End effector will be aligned with the vertical

  • Actuate Axis 4 (elbow roll) and Axis 6 (wrist roll) within motions to examine their torque requirements

  • Vertically raise 5kg payload towards a certain height

    • Define the vertical distance

  • Bring arm to max horizontal extension to examine distal moment in worst case scenario

  • Actuate Axis 1 (base) within it’s end limits to examine driving torque

  • Return to home position

 

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Robot Arm Kinematics

A robot arm is a system with multiple degrees of freedom and a manipulator at the output axis. Here, we examine a 6 axis robot arm designed by the UW Robotics team. When considering the Kinematics of the arm, we define a base coordinate axis that w.r.t the first axis, which is fixed. We can then consider the relative displacement and rotation of all other axes that determines the output orientation and position of the manipulator.

Two approaches were taken to derive a simple motion for the arm.

 

Inverse Kinematics

Coordinate frames for each axis are examined with the arm in a base confiuguration1

Denavit Haitenberg Rules

  • Z axis must be the axis of rotation

  • Follow the right hand rule

  • The X axis of the current coordinate frame must be perpendicular to the Z axis in the previous frame

  • The X axis must intersect the Z axis from the previous joint

 

 

 

Trigonometry