CMM Probe Timing Subsystem Synchronization
Solution Overview
Problem
Coordinate measuring machines (CMMs) face challenges in accurately combining measurement data from scanning probes due to timing discrepancies between measurement synchronization trigger signals and signal processing delays, which can lead to distortion errors and reduced measurement throughput, especially when retrofitting smart probes onto older systems lacking necessary signal lines and data transmission protocols.
Innovation Solution
A probe measurement timing subsystem is introduced that operates within the CMM to output synchronization trigger signals at predictable times, initiating measurement sample periods with pre-trigger lead times to synchronize probe measurements with CMM position coordinate values, allowing for adjustable sampling durations to achieve both fast and accurate measurement data acquisition, thereby compensating for timing deviations and improving data compatibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If measurement synchronization trigger signals are used to trigger measurements from CMM scales and scanning probe, then measurement data can be acquired, but timing discrepancies arise due to signal processing delays causing measurement errors
Solution Approach 1:
The patent applies preliminary action by calculating and applying a timing offset compensation value before measurements are taken. The system determines the timing discrepancy between CMM scale measurements and scanning probe measurements in advance, then uses this compensation value to adjust subsequent measurements, ensuring accurate correlation without real-time delays
Solution Approach 2:
The system implements feedback by using measured timing discrepancy information to adjust future measurements. The timing offset compensation value is determined based on actual signal processing delays observed in the system, and this feedback loop ensures that measurements from different sources are properly synchronized
2Measurement precision
If slower feed rate is used to reduce CMM distortion errors and position uncertainty, then measurement accuracy improves, but measurement throughput decreases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the feed rate based on the measured stand-off distance. When the probe is far from the workpiece, higher feed rates are used to maintain productivity. When approaching the workpiece surface, the feed rate is reduced to ensure measurement accuracy, optimizing both throughput and precision
3Adaptability or versatility
If smart probes with local digital electronics are added to CMM systems, then measurement capabilities improve, but system complexity and wiring requirements increase
Solution Approach 1:
The patent applies universality by designing a timing offset compensation mechanism that works with both traditional CMM systems and modern smart probes with local digital electronics. The solution provides a common approach for synchronizing measurements regardless of the probe type, reducing the need for separate systems for different probe configurations
Data Source
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AI summary
A method is disclosed for operating a coordinate measuring machine (CMM) including a workpiece scanning probe. The method provides two different measurement sampling period durations in the scanning probe: a first shorter sampling duration provides a faster measurement having a first accuracy, a second longer sampling duration provides a slower measurement having a second (better) accuracy. The shorter sampling duration may be repeatedly interleaved or alternated with the longer sampling duration to provide sufficient accuracy and response time for motion control purposes during ongoing operation of the CMM. The longer sampling duration may provide high accuracy probe measurements to combine with position coordinate values from encoders located on motion axes of the CMM (outside the scanning probe) to provide high accuracy workpiece measurements at a desired frequency, or upon demand. A probe measurement timing subsystem may determine initiation times of the first and second sampling durations.