CMM Probe Timing Subsystem Synchronization
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Solution Overview
Problem
Existing coordinate measuring machines (CMMs) face timing discrepancies between measurement synchronization trigger signals and scanning probe data acquisition, leading to inaccurate measurements due to signal acquisition, processing, and transmission delays, and these issues are exacerbated by limited electrical connections and compatibility problems with smart probes.
Innovation Solution
A probe measurement timing subsystem that determines predictable times for measurement synchronization trigger signals and calculates a pre-trigger lead time based on the probe's sample period and system latency, allowing for precise synchronization of measurement data with CMM position coordinate values, even in older host systems without dedicated signal lines or advanced data transmission protocols.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If measurement synchronization trigger signals are used to trigger measurements from CMM scales and scanning probes, then measurement coordination is achieved, but timing discrepancies arise due to signal acquisition, processing, and transmission delays
Solution Approach 1:
The system pre-calculates and stores timing deviation values for different trigger frequencies before actual measurement. The lookup table is populated with pre-measured delay values, allowing the system to compensate for timing discrepancies without real-time calculation delays.
Solution Approach 2:
A timing deviation compensation mechanism acts as an intermediary between the trigger signal generation and the actual measurement acquisition. The system introduces adjustable delay elements that can be configured to match the specific timing characteristics of different scanning probe systems.
2Measurement precision
If dedicated signal lines are provided for each timing signal in CMM subsystems, then synchronization precision is improved, but device complexity and cost increase
Solution Approach 1:
The system uses a universal trigger signal line that can operate at multiple frequencies (e.g., 1 kHz, 2 kHz, 4 kHz, 8 kHz) to accommodate different scanning probe requirements. A single physical connection serves multiple timing functions through software-configurable parameters rather than requiring separate dedicated lines for each frequency.
Solution Approach 2:
The system compensates for timing deviations by changing software parameters (lookup table values, trigger frequencies, sample periods) rather than changing the physical signal transmission infrastructure. This allows timing precision to be adjusted through parameter modification without adding physical complexity.
3Adaptability or versatility
If smart probes with local digital electronics are used, then measurement functionality is enhanced, but timing synchronization becomes more difficult due to limited electrical connections
Solution Approach 1:
The scanning probe interface is designed to handle multiple functions through a single connection protocol. The same electrical connection carries trigger signals, measurement data, and timing synchronization information, eliminating the need for separate dedicated lines for each function.
Solution Approach 2:
The system introduces a software-based timing compensation layer that mediates between the limited physical connections and the multiple timing requirements of smart probes. The lookup table mechanism translates various trigger frequencies into appropriately compensated measurement timing without requiring additional physical signal lines.
4Productivity
If trigger frequencies are increased to improve measurement rate, then productivity increases, but timing deviations and synchronization errors increase
Solution Approach 1:
The system pre-characterizes timing deviations at multiple trigger frequencies and stores compensation values in lookup tables. When operating at higher trigger frequencies for improved productivity, the system automatically retrieves and applies the appropriate pre-calculated compensation values to maintain synchronization accuracy.
Solution Approach 2:
The system incorporates feedback mechanisms where the actual timing behavior at different frequencies is measured and used to update compensation parameters. This allows the system to optimize timing synchronization for each operating frequency, enabling high-speed operation without sacrificing accuracy.
Data Source
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AI summary
A method is disclosed for operating a coordinate measuring machine (CMM) including a CMM control system, a surface scanning probe that measures a workpiece surface by outputting probe workpiece measurements, and a probe measurement timing subsystem. The method comprises: operating the CMM control system to output a measurement synchronization trigger signal at predictable times; operating the probe measurement timing subsystem to determine a pre-trigger lead time that is a fraction of a current duration of a probe workpiece measurement sample period, to initiate a current instance of the probe measurement sample period at the pre-trigger lead time before a next predictable time of the measurement synchronization trigger signal; operating the CMM control system to latch a current set of CMM position coordinate values; and operating the surface scanning probe to output the current instance of the probe workpiece measurement in association with the current set of CMM position coordinate values.