Numerical Controller Spindle Load Correction for Adaptive Control Overshoot
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Solution Overview
Problem
Overshoot occurs in adaptive control when PID control is performed based on low spindle load at the start of cutting, leading to excessive spindle load and reduced machining speed, as the integral term dominates the control signal, causing the spindle load to exceed the target load.
Innovation Solution
A numerical controller with a spindle load correction unit that adjusts the spindle load based on the ratio of the cutting volume to the tool diameter, using the corrected spindle load for PID control to prevent overshoot by providing accurate feedback and maintaining the spindle load close to the target load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If PID control is performed based on low spindle load at the start of cutting, then the feeding speed can be increased, but the spindle load overshoots the target load
Solution Approach 1:
The system performs preliminary detection of the cutting state at the start of cutting and proactively adjusts the target spindle load before overshoot occurs. By detecting that the cutting amount is smaller than a predetermined threshold, the system sets an initially lower target load and gradually increases it, preventing the integral term from causing excessive speed increase and subsequent load overshoot.
Solution Approach 2:
The target spindle load is made dynamic rather than fixed. The system automatically adjusts the target load based on the detected cutting state, setting it to a lower initial value when cutting just begins and gradually increasing it to the normal target value. This dynamic adjustment allows the PID control to respond appropriately to changing conditions without causing overshoot.
2Stability of the object's composition
If the gain (Kp) of the proportional term is increased to suppress overshoot, then the spindle load overshoot is reduced, but the machining speed is delayed
Solution Approach 1:
Instead of changing the proportional gain Kp, the system changes the target spindle load parameter dynamically. By adjusting the target load based on cutting state detection, the system maintains appropriate control response without needing to modify controller gains, thus avoiding the trade-off between overshoot suppression and speed maintenance.
Data Source
AI summary
A numerical controller can suppress overshoot in adaptive control and includes a speed calculation unit and a spindle load correction unit. The speed calculation unit performs PID control to adjust a feeding speed based on a spindle load measured by a measurement unit. The spindle load correction unit corrects the spindle load so as to have a value close to a target load until the spindle load reaches the target load. The speed calculation unit performs PID control using the corrected spindle load.