Machine Tool Artefact Offsets for Thermal Drift Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Machining centers face inaccuracies due to thermal growth, which existing error compensation techniques struggle to accurately and efficiently address, often requiring complex sensor systems and costly cooling methods.
Innovation Solution
A method that involves performing initial and subsequent machining operations with varying tolerances, measuring the position of an artefact to calculate and apply offsets, thereby compensating for thermal drift without relying on extensive sensor networks or sophisticated cooling systems, ensuring precise alignment between the machining head and workpiece holder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If thermal growth is controlled through lubrication and cooling systems, then machining accuracy is improved, but device complexity and operating cost increase
Solution Approach 1:
The patent extracts the thermal management function from complex cooling systems and relocates it to a simple artefact mounted on the workpiece holder. By measuring thermal drift through artefact position changes rather than actively cooling the spindle, the system achieves thermal compensation without requiring chillers, coolant pumps, or temperature-controlled oil showers, thereby dramatically reducing device complexity while maintaining machining accuracy
Solution Approach 2:
The artefact serves as an intermediary element that mediates between the thermal drift problem and the measurement system. Instead of directly measuring spindle temperature or position with complex sensors, the artefact translates thermal drift into measurable position changes of its features, enabling indirect but accurate thermal compensation through simple probing operations
2Manufacturing precision
If multiple sensitive thermal and position sensors are installed for real-time error correction, then machining accuracy is improved, but maintenance difficulty and time consumption increase
Solution Approach 1:
The patent replaces expensive, sensitive, and maintenance-intensive thermal and position sensors with a simple, robust artefact that has no moving parts or electronic components. The artefact can be easily replaced or repositioned if damaged, and its measurement features are inherently maintenance-free, eliminating the maintenance burden associated with sensitive sensors while maintaining measurement capability for error compensation
Solution Approach 2:
The artefact is designed to be self-servicing in that it automatically provides reference features for measurement without requiring calibration, zeroing, or maintenance. The machining centre's existing probing system automatically measures the artefact features to calculate offset values, eliminating the need for separate sensor calibration procedures and reducing maintenance intervention requirements
3Manufacturing precision
If a comprehensive thermal model is built from sensitive measurements for error compensation, then machining accuracy is improved, but measurement time and model building time increase
Solution Approach 1:
The artefact is pre-positioned on the workpiece holder with known feature geometry before machining operations begin. This preliminary setup eliminates the need for time-consuming model building during operation, as the artefact's fixed features provide immediate reference points for calculating thermal drift offsets, enabling rapid error compensation without extensive measurement campaigns or iterative model development
Solution Approach 2:
The patent changes the measurement parameter from complex thermal and positional data requiring comprehensive modeling to simple artefact feature coordinates. By measuring known artefact features at different temperatures and comparing positions, the system directly calculates thermal drift offsets without building complex thermal models, dramatically reducing measurement and model building time while maintaining accuracy
4Manufacturing precision
If error compensation is applied continuously, then machining accuracy is improved, but cycle time increases
Solution Approach 1:
The patent implements periodic error compensation by measuring artefact features at strategic intervals during machining operations, particularly before critical high-precision operations. This periodic approach maintains machining accuracy when needed while minimizing interruption to the machining cycle, contrasting with continuous compensation that would constantly measure and adjust, thereby reducing cycle time while preserving productivity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces machine tool drift and improves machining accuracy by applying calculated offsets before critical operations, minimizing cycle time and maintenance costs, achieving significant reductions in machining errors and defective parts.
Implementation Method 1
Thermally induced error ('thermal growth') is a major source of inaccuracy arising within machining centres. Such errors can arise due to heat generation in and around the machine structure, which may result in growth and tilt of the machine tool spindle and various other structural components of the machine tool relative to one another.
Data Source
AI summary
The present disclosure concerns machine tools and more specifically compensation of variations which may occur within a multi-axis machine tool during a cutting process. An example embodiment includes a method of machining a workpiece using a machine tool comprising a machining head and a workpiece holder moveable relative to each another the method comprising: performing a first machining operation on a workpiece mounted to the workpiece holder according to a first programmed series of movements of the machining head relative to the workpiece holder, the first machining operation having a first maximum machining tolerance; performing a second machining operation on the workpiece according to a second programmed series of movements of the machining head relative to the workpiece holder, the second machining operation having a second maximum machining tolerance; performing a measurement operation to determine a position of an artefact on the machine tool; calculating an offset relative to a corresponding previously stored position of the artefact; and applying the offset to the second programmed series of movements prior to performing the second machining operation, wherein the second maximum machining tolerance is smaller than the first maximum machining tolerance.