Inversion Compensation for Machine Tool Position Control
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Solution Overview
Problem
In large-size machine tools, the low rigidity of the feeding mechanism leads to phase delays and instability in position feedback loops, causing vibrations and increased sliding resistance, which results in position errors and inefficiencies in machining due to insufficient lubrication and increased friction, especially during small-section reciprocation with low velocities.
Innovation Solution
A position control apparatus that includes an inversion detector and an inversion compensation calculator, which uses a deflection characteristic stored in a storage unit to calculate an inversion compensation amount based on the torque command value before and after inversion, and applies this compensation to the position command value to quickly correct deflection and reduce delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the table is reciprocated with low velocity over a small operation range, then machining precision can be maintained, but lubrication becomes insufficient and sliding resistance increases causing position errors
Solution Approach 1:
The control system performs preliminary detection of inversion timing and pre-calculates the compensation amount based on stored deflection characteristics before the actual inversion occurs. This allows the system to proactively compensate for the upcoming increase in sliding resistance rather than reacting after the position error has occurred, thereby maintaining both position accuracy and reliable operation during low-velocity reciprocation.
2Manufacturing precision
If the position feedback loop uses scale position feedback, then position control is implemented, but phase delay occurs and control stability deteriorates due to low rigidity of the feeding mechanism
Solution Approach 1:
The system uses feedback from the rotary encoder to detect the motor position and calculates the difference between the motor position and scale position. This feedback mechanism allows the system to identify phase delays and compensate for them by calculating appropriate inversion compensation amounts based on the detected position discrepancy and stored deflection characteristics.
3Device complexity
If inversion compensation is not applied, then the control system operates simply, but deflection during inversion increases causing position errors and machining streaks
Solution Approach 1:
The control system stores deflection characteristics in advance and uses them to pre-calculate compensation amounts before inversion occurs. This preliminary preparation allows the system to apply accurate compensation without requiring complex real-time calculations during inversion, thus maintaining control system simplicity while improving position accuracy.
4Manufacturing precision
If the motor inverts quickly to cancel deflection, then position control accuracy improves, but the table responds slowly due to high sliding resistance causing delay
Solution Approach 1:
The control system applies preliminary anti-action by detecting the inversion timing in advance and pre-calculating the compensation amount based on stored deflection characteristics. This allows the system to counteract the upcoming increase in sliding resistance before it fully manifests, enabling faster and more accurate motor inversion without excessive delay in table response.
Data Source
AI summary
A position control apparatus includes an inversion detector which detects an inversion of a position command and generates an inversion detection signal, a deflection characteristic storage unit which stores a deflection characteristic representing an amount of deflection with respect to a torque command, and an inversion correction calculator which calculates an inversion correction amount. The inversion correction calculator stores a torque command immediately before the inversion, and calculates the inversion correction amount from a difference between an amount of deflection immediately before inversion in which the stored torque command is checked with the deflection characteristic, and an amount of deflection after the inversion in which a value obtained by inverting a sign of the stored torque command is checked with the deflection characteristic. A value obtained by adding the inversion correction amount to the position command value is used for position error calculation.