Robot Alignment Sensor and XY Scale for Precise End Tool Metrology
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Solution Overview
Problem
Existing robotic systems face limitations in achieving high accuracy and reliability for end tool position determination, particularly in SCARA robots, due to factors like mechanical stability and encoder performance, which can result in insufficient precision for all orientations during operations.
Innovation Solution
A supplementary metrology position coordinates determination system that includes a first imaging configuration, an XY scale, an operational alignment subsystem, and a metrology position coordinate processing portion, which uses a camera and alignment sensors to improve the accuracy of end tool position determination by aligning the XY scale and imaging configuration parallel to the optical axis, allowing for better than robot accuracy positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If robot position sensors (e.g., rotary encoders) are used to determine end tool position, then the system is simple and easy to operate, but the measurement precision is limited to approximately 100 microns due to encoder performance and mechanical stability
Solution Approach 1:
An alignment sensor is introduced as an intermediary device between the robot system and the XY scale. The alignment sensor detects the direction normal to the XY scale and provides feedback signals that enable active alignment, thereby mediating the interaction between the robot positioning system and the external measurement scale to achieve higher precision without directly modifying the robot's internal sensors
Solution Approach 2:
The patent replaces reliance on mechanical position sensors (rotary encoders) with an optical measurement system consisting of a camera and alignment sensor. This substitution transitions from mechanical measurement to optical field-based measurement, achieving sub-micron precision by capturing images of the XY scale and calculating positions through image processing rather than mechanical encoder readings
2Measurement precision
If a camera and XY scale system is added to improve positioning accuracy, then measurement precision improves beyond robot accuracy, but device complexity increases
Solution Approach 1:
The alignment sensor provides continuous feedback signals regarding the alignment between the camera's optical axis and the XY scale. This feedback enables the operational alignment subsystem to actively adjust and maintain optimal alignment, ensuring that the external measurement system remains synchronized with the robot's coordinate system throughout operation, thereby maintaining high measurement precision
Solution Approach 2:
The camera system serves multiple functions: it captures images of the XY scale for position determination, works in conjunction with the alignment sensor for alignment verification, and integrates with the robot's existing coordinate system. This multi-functionality justifies the added complexity by providing both measurement and alignment capabilities within a single integrated system
3Reliability
If the robot system operates without active alignment control, then the system is easier to operate, but the reliability of position determination deteriorates due to misalignment between camera optical axis and XY scale
Solution Approach 1:
The operational alignment subsystem performs self-alignment by using the alignment sensor to detect misalignment conditions and automatically adjusting the camera or XY scale positioning. This self-service capability ensures that the system maintains reliable alignment without requiring constant manual intervention, thereby improving reliability while minimizing operational complexity
Solution Approach 2:
The system performs preliminary alignment using the alignment sensor before actual measurement operations begin. By establishing proper alignment between the camera optical axis and XY scale in advance, the system ensures reliable position determination throughout subsequent operations without requiring continuous adjustment during measurement tasks
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
The system enhances the accuracy of end tool position determination to better than robot accuracy, particularly for vector components transverse or perpendicular to the scale imaging axis, improving reliability and precision in workpiece measurements and other processes.
Implementation Method 1
an alignment sensor mounted in a rigid configuration relative to the first camera and configured to provide an alignment signal indicative of the scale imaging axis direction
Implementation Method 2
the first imaging configuration is configured to capture an image of the XY scale... the metrology position coordinate processing portion is configured to input the captured image and identify at least one respective imagable feature included in the captured image of the XY scale
Data Source
AI summary
A supplementary metrology position coordinates determination (SMPD) system is used with a robot. “Robot accuracy” (e.g., for controlling and sensing an end tool position of an end tool that is mounted proximate to a distal end of its movable arm configuration) is based on robot position sensors included in the robot. The SMPD system includes an imaging configuration and an XY scale and an alignment sensor for sensing alignment/misalignment therebetween, and an image triggering portion and processing portion. One of the XY scale or imaging configuration is coupled to the movable arm configuration and the other is coupled to a stationary element (e.g., a frame above the robot). The imaging configuration acquires an image of the XY scale with known alignment/misalignment, which is utilized to determine metrology position coordinates that are indicative of the end tool position, with an accuracy level that is better than the robot accuracy.