Machine Tool Transmission Error Estimation via Dual Encoder Feedback
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Solution Overview
Problem
Machine tools experience significant downtime and quality degradation due to 'lost motion' caused by backlash and friction in transmission mechanisms, leading to inaccurate position control and increased vibration during machining, which conventional techniques struggle to accurately estimate and address.
Innovation Solution
A machine tool system incorporating a drive mechanism, motor, first and second encoders, servo control unit, and numerical control unit to detect and estimate transmission errors by calculating differences in position errors before and after direction inversion, allowing for real-time monitoring and maintenance timing notifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional techniques are used to detect lost motion, then the machine tool can operate, but the lost motion amount cannot be accurately estimated leading to delayed maintenance
Solution Approach 1:
The system uses feedback from two encoders (one on the motor shaft, one on the control target) to continuously monitor the actual position of the control target and compare it with the commanded position. This feedback mechanism enables real-time detection of lost motion by calculating the difference between expected and actual positions, allowing accurate estimation without requiring external measuring instruments or machine shutdown.
Solution Approach 2:
The patent introduces an intermediary calculation method that uses the difference in position errors before and after direction inversion to estimate lost motion. Instead of directly measuring lost motion with external equipment, the system uses the encoder position data as an intermediary to infer the lost motion amount through computational analysis, achieving accurate detection without additional hardware or downtime.
2Productivity
If the machine tool operates with a transmission mechanism containing backlash and friction, then productivity is maintained, but position control accuracy deteriorates
Solution Approach 1:
The patent replaces mechanical measurement methods (such as DBB measuring instruments requiring disassembly and external measurement) with an electronic/digital detection system using encoders and computational analysis. This substitution allows the system to detect lost motion and position errors electronically while the machine tool remains operational, maintaining productivity while improving position control accuracy through real-time data acquisition and analysis.
3Manufacturing precision
If the machine tool is shut down for repair and adjustment, then position control accuracy can be improved, but productivity decreases due to prolonged downtime
Solution Approach 1:
The system performs preliminary detection and estimation of lost motion while the machine tool is still operating normally. By continuously monitoring position errors and calculating lost motion amounts using encoder data, the system can identify transmission mechanism issues before they severely impact machining quality. This preliminary action allows for planned maintenance scheduling rather than reactive shutdowns, improving both precision and productivity.
Solution Approach 2:
The machine tool performs self-diagnosis by using its own encoder system to detect and estimate lost motion without requiring external measuring instruments or expert intervention. The numerical control unit automatically calculates position errors and estimates lost motion amounts, enabling the system to monitor its own health status and alert operators when maintenance is needed, reducing downtime by eliminating the need for external inspection and measurement procedures.
Data Source
AI summary
A machine tool according to an embodiment includes a drive mechanism configured to move a control target; a motor configured to operate the drive mechanism; a first encoder configured to detect a position of the control target; a second encoder configured to detect a position of the motor; a servo control unit configured to control the motor; and a numerical control unit configured to receive or calculate an error between the position of the control target obtained from a detection result of the first encoder and a position of the control target obtained from a detection result of the second encoder from the servo control unit, and to estimate a transmission error of the drive mechanism based on a change amount of the error between before and after inversion of a moving direction of the control target.