Tool Magazine Slot Assignment for Faster CNC Tool Changes
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Solution Overview
Problem
Existing methods for assigning tools to spaces in a machine tool's tool magazine are inefficient, particularly when dealing with large problem sizes, as they struggle to process sequences in an acceptable time using mixed-integer programming.
Innovation Solution
A method using a greedy algorithm to iteratively assign tools to spaces in the tool magazine, ensuring the machine tool does not wait for the feeder or waits for the shortest possible time, by considering the processing times and movement times of tools.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mixed-integer programming is used to optimize tool assignment, then the solution quality is improved, but the processing time becomes unacceptable for large problem sizes
Solution Approach 1:
The patent segments the tool assignment problem into smaller sub-problems by dividing the sequence of working steps into groups. Each group is optimized independently using mixed-integer programming, while groups are ordered using a greedy algorithm. This segmentation allows the computationally intensive optimization to be applied to manageable subsets rather than the entire large-scale problem, thereby reducing total processing time while maintaining solution quality within each segment.
Solution Approach 2:
The patent changes the parameter of problem size by transforming the original large-scale assignment problem into multiple smaller sub-problems. By modifying how the problem is structured (from one large optimization to multiple small optimizations), the computational complexity is reduced, making it feasible to process large tool magazines and long working sequences within acceptable time frames.
2Speed
If tools are assigned to spaces closer to the transfer point, then the feeder movement time is reduced, but the tool magazine space utilization decreases
Solution Approach 1:
The patent applies local quality by assigning different spatial positions to tools based on their specific requirements. Tools that are frequently used or have tight timing constraints are placed closer to the transfer point for faster access, while tools with more flexible timing are placed in spaces farther away. This creates a non-uniform spatial distribution optimized for local performance needs rather than uniform spacing.
Solution Approach 2:
The patent introduces dynamics by considering the temporal characteristics of tool usage. The assignment is not static but is determined based on the processing times and sequences of working steps. Tools are dynamically positioned in spaces that optimize the feeder's movement pattern according to the actual operational sequence, allowing the system to adapt to varying production requirements.
3Loss of time
If the feeder moves tools quickly between spaces, then the machine tool waiting time is reduced, but the complexity of coordinating feeder movements increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and pre-assigning tools to specific spaces before the actual machining process begins. The greedy algorithm determines an optimal assignment sequence in advance, considering all working steps and their timing requirements. This preliminary planning eliminates the need for complex real-time coordination during operation, as the feeder simply follows the pre-determined assignment pattern.
Solution Approach 2:
The system achieves self-service by using the working sequence and processing time data (which already exist for production planning) to automatically generate the tool assignment. The algorithm serves itself by utilizing existing production data to create the optimization solution without requiring additional complex coordination mechanisms or external control systems.
Data Source
AI summary
A machine tool which is designed to carry out a specified sequence of work steps is provided. A tool and a processing time is assigned to each work step. A tool magazine is designed to keep a number of tools ready for the machine tool and includes a feeder for conveying tools from and to a transfer point for the machine tool. In a method for assigning tools to spaces of the tool magazine, a number of work steps are determined from the sequence, the respective processing time of each work step being shorter than a specified cycle time of the tool magazine. A work step is iteratively selected from the number of work steps; a previously used tool and a subsequently used tool are assigned spaces of the tool magazine; and the work step is removed from the number of work steps.