Numerical Control Apparatus Tool Posture Limiting
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Solution Overview
Problem
In five-axis machine tools, tool posture fluctuations caused by quantization errors lead to increased rotational movement and machining inaccuracies, especially when the tool posture approaches a peculiar posture, resulting in significant backlash, lost motion, and friction.
Innovation Solution
A numerical control apparatus that includes a program reading unit, a determining unit, a tool-posture control unit, and an interpolation/acceleration and deceleration processing unit, which analyzes machining programs to determine if the tool posture is within a predetermined range and limits the change in tool posture near the peculiar posture, thereby controlling the rotation axes to reduce movement amounts and improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If tool posture is controlled according to machining program with quantization errors, then tool position accuracy is improved, but rotation axis movement amount increases significantly when near peculiar posture
Solution Approach 1:
The control device performs preliminary detection of tool posture near peculiar posture before execution, and preemptively switches to alternative control processing that limits rotation axis movement, preventing the problem from occurring
Solution Approach 2:
The control system dynamically switches between different control modes: normal control for general postures and limited-movement control when near peculiar posture, making the system adaptable to different operational conditions
2Measurement precision
If rotation axis movement amount increases to correct tool posture, then tool posture accuracy is improved, but machining time increases
Solution Approach 1:
The control device changes the control parameters by switching between normal control processing and limited control processing, adjusting the relationship between tool posture correction and rotation axis movement to optimize both accuracy and efficiency
3Manufacturing precision
If linear axis interpolation is corrected based on rotation axis interpolation, then tool tip position accuracy is improved, but backlash and lost motion effects increase
Solution Approach 1:
The control device takes preliminary action to prevent backlash and lost motion by detecting near-peculiar postures in advance and using alternative control processing that avoids large rotation axis movements, counteracting the harmful effects before they occur
Data Source
AI summary
A numerical control apparatus that controls a machine tool including a plurality of linear axes and rotation axes, and controls a relative tool posture with respect to work on a table includes a program reading unit that sequentially reads a tool posture with respect to the work from a machining program, a determining unit that determines whether the read tool posture is within a predetermined tool posture range, a tool-posture control unit that determines control content of the tool posture according to the determination by the determining unit, and an interpolation/acceleration and deceleration processing unit that controls the linear and rotation axes according to the control content of the tool posture. When the read tool posture is within the predetermined range, the tool-posture control unit determines rotation axis angles of the rotation axes such that a change of tool posture from the last tool posture is limited.