TCP Acceleration Limiting in Joint-Interpolated Robot Motion
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Solution Overview
Problem
Industrial robots using joint interpolated motion often exceed the vacuum gripper's capability, leading to package detachment due to unpredictable tool center point accelerations, which is detrimental to productivity.
Innovation Solution
A method to compute robot motion that limits tool center point acceleration in Cartesian space by defining a user-defined acceleration limit, using an S-curve technique to recalibrate joint motions if the calculated acceleration exceeds the limit, ensuring the gripper maintains its grasp on the package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If joint interpolated motion is used to maximize robot speed, then productivity is improved, but tool center point acceleration becomes unpredictable and may exceed vacuum gripper capability
Solution Approach 1:
The system performs preliminary calculation of tool center point acceleration at significant points on the S-curve before executing the motion. By predicting acceleration values in advance and comparing them against the maximum allowable acceleration, the system can pre-adjust the motion profile to prevent package detachment, thus maintaining both high speed and reliability.
Solution Approach 2:
The system implements a feedback mechanism where calculated tool center point accelerations are continuously compared against the maximum allowable acceleration. When the acceleration exceeds the limit, the system automatically reduces the scale factor to bring acceleration back within acceptable ranges, ensuring package grasp stability while maintaining optimal robot speed.
2Productivity
If robot acceleration is increased to improve productivity, then package detachment risk increases due to excessive force on vacuum gripper
Solution Approach 1:
The system dynamically adjusts the scale factor parameter based on calculated tool center point accelerations. When acceleration approaches or exceeds the maximum allowable value, the scale factor is reduced to decrease the actual acceleration. This parameter adjustment ensures that the force applied to the package remains within the vacuum gripper's capability while allowing the robot to operate at high speeds during safe acceleration phases.
3Reliability
If robot motion is slowed down to prevent package detachment, then productivity decreases
Solution Approach 1:
The system employs dynamic motion control where the scale factor is adjusted in real-time based on the robot's position on the S-curve and the calculated tool center point acceleration. During phases where acceleration is naturally low, the robot operates at full speed. When acceleration approaches critical thresholds, the scale factor is dynamically reduced to maintain package grasp stability. This dynamic approach optimizes the balance between reliability and productivity.
Data Source
AI summary
A method for computing robot motion where the tool center point translational acceleration does not exceed a defined limit. Robot motion for an upcoming segment of a trajectory is computed using a known “S-curve” technique, where joint motions are calculated which move the robot from a start pose to an end pose in the shortest time given maximum joint velocity, acceleration and jerk values. Significant points on the S-curve are identified which correspond with maximum translational acceleration of the tool center point. Tool center point Cartesian motion is then calculated from the joint motions using forward kinematics. The maximum translational acceleration of the tool center point is determined and compared to the defined acceleration limit. If the maximum acceleration of the tool center point exceeds the acceleration limit, the joint motions for the trajectory segment are re-calculated using a scale factor which reduces the joint and tool center point accelerations.