Coordinate Positioning Arm Metrology Frame Segmentation
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Solution Overview
Problem
Articulated robots face challenges in achieving high accuracy and repeatability due to cumulative positional errors from their serial mechanical linkage structure, making them less suitable for demanding applications that require precision, despite their flexibility and reach.
Innovation Solution
A coordinate positioning arm design with a metrology frame that is substantially separate and independent from the drive frame, featuring a specific arrangement of metrology axes to avoid overconstraint and ensure accurate measurement of the head end's position and orientation relative to the base end, allowing for improved accuracy and repeatability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a serial mechanical linkage with multiple rotary joints is used to achieve flexibility and reach, then the robot can manipulate tools into various poses and reach wide working volumes, but cumulative positional errors from each joint reduce accuracy and repeatability
Solution Approach 1:
The patent divides the measurement function from the drive function by implementing separate metrology axes (for measurement) and drive axes (for positioning). The metrology frame is substantially separate from the drive frame, with each frame having its own axes. This segmentation allows the drive frame to achieve full flexibility while the metrology frame independently measures position, eliminating the cumulative errors that occur when measurement and drive functions are combined in a serial linkage.
Solution Approach 2:
The patent introduces an intermediary metrology frame that acts as a mediator between the drive frame and the measurement function. This separate metrology frame with its own axes provides a reference framework that is not affected by the mechanical errors of the drive linkage. The metrology frame measures the actual position of the tool flange relative to the base, providing accurate measurements despite the flexible, error-prone drive mechanism.
2Manufacturing precision
If calibration is performed to map positional errors, then accuracy can be improved, but the calibration process becomes significantly more complex and challenging for articulated robots with multiple rotary joints
Solution Approach 1:
The patent extracts the measurement function from the drive function by providing separate metrology axes that are independent of the drive axes. This extraction eliminates the need for complex calibration procedures because the metrology frame provides direct, error-free measurement of the tool flange position. The metrology axes are arranged to measure position in all three dimensions and rotation about all three axes independently, providing accurate measurements without requiring calibration of the flexible drive linkage.
3Manufacturing precision
If a Cartesian machine with three fixed orthogonal axes is used, then calibration is straightforward and accuracy is high, but the machine loses the flexibility and reach capabilities of articulated robots
Solution Approach 1:
The patent merges the advantages of both Cartesian and articulated machines by combining a flexible articulated drive frame with a separate metrology frame that has fixed, orthogonal measurement axes. The drive frame provides the flexibility and reach of an articulated robot, while the metrology frame provides the measurement accuracy and simplicity of a Cartesian machine. The metrology axes are arranged in an orthogonal configuration that is fixed relative to the metrology frame, providing straightforward measurement without the calibration complexity of articulated robots.
Data Source
AI summary
A coordinate positioning arm includes: a base end and a head end; a drive frame for moving the head end relative to the base end; and a metrology frame for measuring a position and orientation of the head end relative to the base end. The drive frame includes a plurality of drive axes arranged in series between the base end and the head end. The metrology frame includes a plurality of metrology axes arranged in series between the base end and the head end. The metrology frame is adapted and arranged to be substantially separate and/or independent from the drive frame, for example by supporting the metrology frame substantially only at the base end and head end and by providing the metrology frame with sufficient degrees of freedom (via the metrology axes) to avoid creating an additional constraint between the metrology frame and the drive frame.