Numerical Controller Cycle Motion Start Point for Screw Thread Cutting
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Solution Overview
Problem
Conventional screw thread cutting techniques face issues with incomplete threads due to insufficient acceleration distance, leading to increased cycle time and suboptimal approach motions, as the machining starts before the feed axis stabilizes, and existing solutions do not adequately address the optimization of the screw thread cutting start point and acceleration distance.
Innovation Solution
A numerical controller with an optimal approach function that calculates a cycle motion start point based on the screw thread cutting start point, cutting feed speed, rapid traverse speed, and time constants for X and Z axes, allowing for overlapping axis motions to achieve a specified cutting feed speed and zero speed of the orthogonal axis at the screw thread cutting start point, thereby optimizing the approach motion and reducing cycle time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the screw thread cutting start point is set close to the end face to reduce cycle time, then productivity is improved, but the feed axis speed is not stabilized and incomplete threads are produced, worsening manufacturing precision
Solution Approach 1:
The system performs preliminary acceleration of the feed axis before reaching the screw thread cutting start point. The numerical controller calculates an acceleration distance and starts acceleration at a predetermined point before the cutting start point, ensuring the feed axis reaches the specified feed speed before cutting begins, thus preventing incomplete threads while maintaining short cycle time.
Solution Approach 2:
The system dynamically adjusts the acceleration distance and timing based on the distance between the screw thread cutting start point and the end face. When this distance is small, the controller modifies the acceleration profile to ensure proper speed stabilization, making the acceleration distance variable rather than fixed, thereby adapting to different machining conditions.
2Device complexity
If a fixed acceleration distance (e.g., three or five pitches) is used, then the control is simplified, but the cycle time increases and the approach motion becomes suboptimal, worsening productivity
Solution Approach 1:
The numerical controller dynamically calculates the acceleration distance based on the actual distance between the screw thread cutting start point and the end face, rather than using a fixed value. This dynamic adjustment optimizes the approach motion for each specific machining condition, reducing cycle time while ensuring proper speed stabilization before cutting.
Solution Approach 2:
The system changes the acceleration distance parameter dynamically based on machining conditions. The controller calculates the optimal acceleration distance using the formula that considers the distance to the end face, cutting feed speed, and rapid traverse speed, thereby adapting the motion parameters to minimize cycle time while ensuring quality.
3Ease of manufacture
If the tool change position is set at the screw thread cutting instruction start point, then the setup is simplified, but the approach motion is not optimized and cycle time increases, worsening productivity
Solution Approach 1:
The system performs preliminary calculations to determine the optimal tool change position that allows for optimized approach motion. Instead of always using the instruction start point, the controller calculates a position that enables better acceleration profiles and shorter cycle times while still maintaining ease of setup through automated calculation.
Data Source
AI summary
A numerical controller includes a motion start point determination unit that calculates a cycle motion start point where the screw thread cutting cycle is to be started, an acceleration/deceleration control unit that moves the tool from the cycle motion start point to a screw thread cutting start point with motions of a plurality of axes overlapped, and a control unit that controls motions of a machining device based on control instructions received from an instruction analysis unit and the acceleration/deceleration control unit. The cycle motion start point is a point from which acceleration or deceleration of a first axis and a second axis orthogonal to the first axis is started so as to make a speed of the first axis reach a specified cutting feed speed and to make a speed of the second axis substantially become zero at time of arrival at the screw thread cutting start point.