Encoder-Based Machining Defect Detection via Lost Motion and Spindle Lag
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Solution Overview
Problem
Current machining quality monitoring methods are inefficient due to signal-to-noise problems, especially in detecting light cuts or small errors, and lack linear sensitivity, particularly in vertical axes, leading to difficulties in identifying machining defects like non-cleanup conditions in aluminum drilling.
Innovation Solution
The method involves measuring lost motion and spindle lag deviations by comparing linear and rotary encoder positions to identify machining defects, using a controller to analyze these deviations and determine if they exceed predetermined thresholds, thereby identifying defects without requiring additional external sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external sensors (accelerometers, force sensors, current sensors) are used for process monitoring, then process characteristics can be measured, but signal-to-noise ratio deteriorates for light cuts or small process errors
Solution Approach 1:
The patent replaces external mechanical sensors (accelerometers, force sensors) with encoder-based measurement systems that utilize the machine's existing feedback infrastructure. Linear encoders measure actual position while rotary encoders measure commanded position, eliminating the need for separate vibration and force sensors that suffer from signal-to-noise problems in light cutting operations.
Solution Approach 2:
The patent introduces encoders as intermediary measurement devices that indirectly detect machining quality through position feedback rather than directly measuring vibration or force. The linear encoder serves as an intermediary that translates mechanical position into electrical signals, providing a cleaner measurement pathway that avoids the noise issues of direct vibration sensing.
2Measurement precision
If external sensors are added for process monitoring, then monitoring capability is improved, but device complexity increases
Solution Approach 1:
The patent makes the existing encoder systems serve dual purposes: their primary function for position control and an additional function for quality monitoring. The same linear and rotary encoders used for motion control are repurposed to detect machining defects, eliminating the need for separate dedicated sensors and reducing overall system complexity.
Solution Approach 2:
The machine tool's existing feedback system serves itself by using its own encoder infrastructure for quality monitoring. Rather than requiring external sensors to monitor the process, the system uses its inherent position measurement capabilities to detect anomalies, making the monitoring system self-sufficient and reducing hardware requirements.
3Measurement precision
If traditional process monitoring is used, then general process characteristics can be measured, but linear sensitivity is lost for vertical axes due to gravity effects
Solution Approach 1:
The patent replaces gravity-sensitive vibration sensors with encoder-based position measurement that is immune to gravitational effects. Linear encoders measure position through electromagnetic or optical means rather than mechanical vibration, eliminating the non-linear sensitivity problems caused by gravity acting on accelerometers during vertical axis movements.
Data Source
AI summary
A method of measuring quality in a machining operation of a device includes measuring lost motion for at least one axis of the device during the machining operation, calculating a spindle lag of a spindle of the device during the machining operation, determining a lost motion deviation, determining a spindle lag deviation, and identifying a machining defect based on the lost motion deviation coinciding with the spindle lag deviation.