Numerical Controller Integral Term Back Calculation
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Solution Overview
Problem
Existing numerical controllers face issues with unintended changes in the integral term during feedback control, leading to potential damage to tools and workpieces due to uncontrolled spindle load deviations and overheating, when output values are restricted or controlled.
Innovation Solution
The numerical controller performs back calculation of the integral term and updates it to ensure desirable output values by using a speed computation unit that adjusts the feeding speed based on program instructions to maintain a constant spindle load, incorporating a substitute value when the output value exceeds a predefined limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the feeding speed is increased to increase cutting volume when spindle load is low, then productivity is improved, but the spindle load becomes unstable and may cause damage to tool and workpiece
Solution Approach 1:
The system implements feedback control by continuously monitoring the spindle load and adjusting the feeding speed accordingly. The control unit receives feedback signals about the actual spindle load and modifies the feeding speed in real-time to maintain the load within a predetermined range, preventing both underutilization and overload conditions.
Solution Approach 2:
The feeding speed is made dynamic rather than fixed, allowing it to change continuously based on the current spindle load conditions. The system automatically increases feeding speed when load is low and decreases it when load approaches the upper limit, creating a dynamic adaptation to processing conditions.
2Reliability
If the feeding speed is restricted to prevent damage, then reliability is improved, but productivity decreases due to limited cutting volume
Solution Approach 1:
Instead of applying a static restriction to feeding speed, the system uses dynamic adjustment based on real-time spindle load monitoring. The feeding speed is only restricted when necessary (when load approaches upper limit) and can be increased when conditions permit, optimizing both protection and productivity.
Solution Approach 2:
The system changes the feeding speed parameter dynamically based on spindle load conditions. By monitoring the load and adjusting the speed parameter in real-time, the system maintains reliability while maximizing cutting volume within safe operational limits.
3Reliability
If PID control is used to maintain constant spindle load, then reliability is improved, but the integral term shows unintended change when output value is restricted, causing delay in feedback control
Solution Approach 1:
The system performs preliminary calculation of the feeding speed based on the PID control output before applying restrictions. By calculating the ideal speed first and then adjusting for restrictions, the system prevents unintended changes in the integral term and avoids control delays.
Solution Approach 2:
The control unit acts as an intermediary between the PID control algorithm and the actual feeding speed execution. It receives the PID output, applies necessary restrictions, and adjusts the integral term accordingly before executing the speed command, preventing unintended integral term changes and maintaining responsive control.
Data Source
AI summary
A numerical controller, which is capable of controlling an output value without causing delay or the like in feedback control, includes an instruction program analysis unit configured to analyze a program instruction and generate instruction data instructing movement of the axis, and a speed computation unit configured to start speed computation processing to compute a feeding speed of the axis by the instruction data or an override for the feeding speed by feedback control such that the spindle load value becomes constant. The speed computation unit is configured to update a feature amount intended for elimination of deviation between a desired value and a feedback value in the feedback control when another override that is different than the override that has been computed is output. The feature amount is updated to a value obtained by back calculation from the other override that is to be output.