CNC Position Control with Posture-Dependent Deflection Compensation
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Solution Overview
Problem
Conventional position control systems for numerically controlled machines fail to accurately compensate for deflections caused by structural members with low rigidity, leading to deviations in the tool's position relative to the workpiece, especially during high-acceleration operations.
Innovation Solution
A position control apparatus that includes a machine deflection amount estimation unit to calculate the deflection caused by structural members, a compensation unit to generate compensation values for positional, speed, and torque commands, and a command value calculation unit to adjust these values based on the machine's posture, ensuring continuous compensation for deflections and maintaining the tool's desired locus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If feed-forward control is used to compensate for ball screw deflection, then response speed is improved, but deflection caused by structural members with low rigidity cannot be compensated
Solution Approach 1:
The system performs preliminary calculation of deflection compensation amounts based on pre-stored rigidity data and machine posture information before executing the motion command. This allows the control system to proactively compensate for both ball screw and structural member deflections in advance, rather than merely reacting to position errors after they occur.
Solution Approach 2:
The system changes the parameter of rigidity from a fixed value to a variable that depends on machine posture. By storing multiple rigidity values corresponding to different machine postures and selecting the appropriate value based on current posture, the system accurately reflects the actual rigidity conditions during motion, enabling precise compensation for structural member deflections.
2Stability of the object's composition
If conventional feedback control is used, then system stability is maintained, but deflection compensation is insufficient during high-acceleration operations
Solution Approach 1:
The control system calculates deflection compensation amounts in advance based on the motion command and current machine posture before the actual motion occurs. This preliminary compensation is added to the motion command, allowing the system to maintain stability through feedback control while proactively correcting for anticipated deflections during high-acceleration operations.
Solution Approach 2:
The system introduces an intermediary deflection compensation calculation mechanism that bridges feedback control and feed-forward compensation. By calculating compensation amounts based on the relationship between motion commands, machine posture, and stored rigidity data, the system creates an intermediate layer that enhances positional accuracy without compromising the stability provided by feedback control.
3Device complexity
If machine posture is not considered in deflection compensation, then control complexity is reduced, but compensation accuracy varies with machine posture
Solution Approach 1:
The system performs preliminary organization of rigidity data according to different machine postures during the setup phase. This pre-arranged data structure allows the control system to quickly retrieve the appropriate rigidity value based on current posture without performing complex real-time calculations, thus maintaining simple control logic while achieving posture-dependent compensation accuracy.
Solution Approach 2:
The system changes the rigidity parameter from a single fixed value to multiple values corresponding to different machine postures. By storing rigidity data segmented by posture and selecting the appropriate value based on current position, the system achieves variable compensation accuracy across different postures without significantly increasing control complexity.
Data Source
AI summary
In a position control apparatus that drives a feed-axis with a servomotor of a machine tool, the machine tool may be quickly accelerated or decelerated in a state where a machine structural member that supports and fixes a structural member including a driving system has a lower rigidity, or in a state where an element having a lower rigidity is present beyond a load position where the detection by a linear scale is performed. In such cases, a generated deflection may induce a displacement in a mechanical system. A relative locus error may be generated between a workpiece to be processed and a front end portion of the tool. Further, a mechanism rigidity generally changes according to a machine posture. The generated deflection amount changes in magnitude. The present embodiment estimates and compensates a displacement amount of the front end portion of the tool that may be caused by the deflection of the mechanical system. Moreover, in calculating an estimation amount, the present embodiment can change a parameter corresponding to the mechanism rigidity based on the machine posture. Thus, the front end of the tool can move accurately along a desired locus relative to the workpiece to be processed.