Active Target Gimbal Alignment for Laser Tracker Volumetric Error Compensation
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Solution Overview
Problem
Conventional retroreflectors in precision measuring systems have limited acceptance angles, restricting their ability to track the position of machine tools with multiple axes and wide rotational ranges, leading to inaccuracies and increased machine downtime due to the need for manual adjustments and limited angular working ranges.
Innovation Solution
An active target with a retroreflector mounted on motorized gimbals and a position-sensitive detector to maintain alignment with the tracker laser beam, allowing for a full 360-degree rotation and overcoming the limitations of traditional spherical mounted retroreflector systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional retroreflector is used, then the structure is simple, but the acceptance angle is limited restricting tracking capability
Solution Approach 1:
The retroreflector is mounted on motorized gimbals that dynamically adjust its orientation to maintain alignment with the laser tracker beam across a full 360-degree rotational range. This dynamic positioning capability transforms the system from a static limited-angle retroreflector to an active tracking target with unlimited angular working range
Solution Approach 2:
A position-sensitive detector provides real-time feedback on the retroreflector's alignment with the laser beam. This feedback signal controls the gimbal motors to automatically maintain optimal alignment, enabling the system to achieve full 360-degree tracking capability through closed-loop control
2Productivity
If manual adjustments are made to maintain alignment, then the system remains simple, but machine downtime increases
Solution Approach 1:
The active target system performs self-alignment through the gimbal motors that automatically adjust the retroreflector's orientation based on feedback from the position-sensitive detector. This eliminates the need for manual intervention and alignment adjustments, enabling continuous measurement operation without machine downtime
Solution Approach 2:
Manual mechanical adjustment operations are replaced by an automated electro-mechanical system comprising gimbal motors and a position-sensitive detector. This substitution enables continuous automated tracking and measurement, eliminating the time loss associated with manual realignment
3Measurement precision
If the retroreflector rotates manually, then alignment can be maintained, but measurement accuracy decreases due to thermal drift
Solution Approach 1:
The laser tracker and active target system operates continuously without interruption for manual realignment. The automated gimbal system maintains constant alignment throughout the measurement process, eliminating the thermal drift that occurs during pauses and manual adjustments, thereby maintaining high measurement precision throughout the entire working volume
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
Enables fast and highly accurate volumetric error compensation of machine tools, reducing machine downtime and increasing precision by four to tenfold, while minimizing thermal drift from temperature fluctuations, allowing for continuous, precise measurements across the machine's working volume.
Implementation Method 1
an optical retroreflector mounted at the center of two motorized gimbals
Implementation Method 2
A position sensitive detector is placed behind the retroreflector to detect the relative orientation between the tracker laser beam and the retroreflector by means of measuring a small portion of the laser beam transmitted through the aperture
Data Source
AI summary
A volumetric error compensation measurement system and method are disclosed wherein a laser tracker tracks an active target as the reference point. The active target has an optical retroreflector mounted at the center of two motorized gimbals to provide full 360 degree azimuth rotation of the retroreflector. A position sensitive detector is placed behind an aperture provided at the apex of the retroreflector to detect the relative orientation between the tracker laser beam and the retroreflector by measuring a small portion of the laser beam transmitted through the aperture. The detector's output is used as the feedback for the servo motors to drive the gimbals to maintain the retroreflector facing the tracker laser beam at all times. The gimbals are designed and the position of the retroreflector controlled such that the laser tracker always tracks to a pre-defined single point in the active target, which does not move in space when the gimbals and/or the retroreflector makes pure rotations. Special mechanism and alignment algorithm are used in the gimbal design and retroreflector centering alignment to achieve accurate rotational axis alignment and repeatability.