Robot Arm Metrology Using 2D Scales for End Tool Accuracy
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Solution Overview
Problem
Existing robotic systems face limitations in accuracy for determining end tool position due to assumptions of straight arm portions and perfect rotary joint motion, leading to inaccuracies from bending, twisting, and joint wobble, which are not accounted for by traditional rotary encoders.
Innovation Solution
The supplementary metrology position determination system uses 2D scales and cameras attached to the robot arms to detect and measure undesirable motions such as bending, twisting, and joint wobble, providing more accurate position data by integrating this information into the kinematic model.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional rotary encoders are used for position sensing, then the system is simple and cost-effective, but the measurement precision is limited to approximately 100 microns due to mechanical stability limitations and encoder performance
Solution Approach 1:
The patent introduces 2D scales and cameras as intermediary components between the robot arms and the position determination system. The 2D scales are attached to the robot arms as reference markers, and cameras capture images of these scales to determine arm positions and end tool location with higher precision than traditional rotary encoders alone
Solution Approach 2:
The patent replaces purely mechanical position sensing (rotary encoders) with an optical measurement system consisting of 2D scales and cameras. This substitution allows for more accurate position determination by using optical image analysis to detect arm positions and calculate end tool location, overcoming the mechanical stability limitations of encoder-based systems
2Reliability
If the robot system assumes straight arm portions and perfect rotary joint motion, then the control system is simple, but the reliability of position determination deteriorates due to unaccounted bending, twisting, and joint wobble
Solution Approach 1:
The patent implements a feedback mechanism where the 2D scales and cameras continuously monitor the actual positions of robot arms, and this information is used to update and refine the kinematic model. The system compares measured positions with model predictions and adjusts for deviations caused by bending, twisting, and joint wobble, improving reliability through continuous correction
Solution Approach 2:
The patent transitions from a static kinematic model assuming rigid arms and perfect joints to a dynamic model that accounts for real-world deviations. The system adapts the kinematic model to reflect actual arm behavior under load, including bending and twisting, by using real-time position data from the optical measurement system to compensate for these dynamic effects
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves higher accuracy in end tool position determination, potentially improving it from 100 microns to 10 microns or better, enhancing precision in applications like workpiece measurements and precision drilling.
Implementation Method 1
The first camera is for acquiring an image of the first 2D scale at an image acquisition time. The second camera is for acquiring an image of the second 2D scale at the image acquisition time.
Data Source
AI summary
A supplementary metrology position determination system is provided for use with a robot. The robot includes a movable arm configuration and a motion control system configured to control an end tool position with a robot accuracy (i.e., based on sensors included in the robot). The supplementary system includes cameras and 2D scales, each of which is attached to the movable arm configuration (e.g., as attached on arm portions and/or rotary joints). The cameras are operated to acquire images for determining relative positions of the scales. The scales may be coupled to rotary joints (e.g., as may be utilized to determine rotary motion as well as any motion transverse to a rotary axis), and/or to arm portions (e.g., as may be utilized to determine any bending or twisting of the arm portions). Such information may be utilized to achieve higher accuracy (e.g., for measurement operations and/or control of the robot, etc.).