Multi-Axis Machine Tool Offset Compensation for Thermal Drift
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Solution Overview
Problem
Multi-axis machine tools face inaccuracies due to thermal growth, which existing error compensation techniques struggle to address effectively, often requiring complex sensor installations and maintenance, and are costly, especially when using temperature-controlled cooling systems.
Innovation Solution
A method that involves measuring the position of an artefact before and after a machining operation to calculate and apply offsets to the machine tool's axes, compensating for thermal drift without relying on extensive sensor networks or cooling systems, ensuring accurate alignment and minimizing downtime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If temperature-controlled cooling systems are used to control thermal growth, then thermal-induced errors are reduced, but device complexity and operating cost increase significantly
Solution Approach 1:
The patent replaces the mechanical cooling system with a computational approach. Instead of physically controlling thermal growth through cooling mechanisms, the invention uses measurement systems to detect thermal drift and applies computational offsets to compensate for the drift, thereby substituting a mechanical thermal control system with a measurement-and-compensation system.
Solution Approach 2:
The patent creates a virtual model of the thermal drift behavior through measurements taken at different temperatures. By copying the thermal drift characteristics into a lookup table or model, the system can retrieve pre-determined offset values without needing to physically control the thermal conditions during machining.
2Manufacturing precision
If multiple sensitive thermal and position sensors are installed for real-time error correction, then thermal drift compensation is achieved, but maintenance complexity and time consumption increase
Solution Approach 1:
The patent extracts the thermal drift compensation function from complex sensor networks and isolates it into a single artefact-based measurement system. By removing the need for multiple sensitive sensors and concentrating the measurement function into a simple artefact with known geometry, the system eliminates maintenance complexity while preserving compensation capability.
Solution Approach 2:
The patent uses a simple, robust artefact that can be easily replaced if needed, rather than expensive, sensitive sensors that require complex calibration and maintenance. The artefact serves as a durable reference object that withstands the machining environment without requiring delicate handling or frequent servicing.
3Measurement precision
If machine characterisation is performed with sensitive measurements to build thermal models, then compensation accuracy is improved, but time consumption increases significantly
Solution Approach 1:
The patent performs the characterisation measurements in advance, before production machining begins. By conducting the time-consuming measurements during machine setup or idle periods, the thermal drift characteristics are captured and stored in lookup tables, allowing rapid offset retrieval during actual machining operations without time loss.
Solution Approach 2:
The patent copies the thermal drift data into lookup tables during preliminary characterisation. This creates a pre-computed reference that can be quickly accessed during machining without requiring real-time complex calculations or repeated sensitive measurements, thereby reducing time consumption during production.
4Manufacturing precision
If error compensation is applied continuously, then machining accuracy is maintained, but productivity decreases due to frequent measurement interruptions
Solution Approach 1:
The patent implements periodic measurement of the artefact at predetermined intervals during machining operations, rather than continuous measurement. This periodic approach maintains accuracy by correcting thermal drift at appropriate intervals while minimizing interruptions to the machining process, thereby preserving productivity.
Solution Approach 2:
The patent uses pre-computed offset values from lookup tables that were generated during preliminary characterisation. By copying the compensation data into easily accessible tables, the system can apply corrections rapidly without requiring complex real-time calculations or prolonged measurement interruptions, thus maintaining both accuracy and 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 significantly reduces machine variation and part deviation, improving machining accuracy by correcting thermal-induced misalignments before critical operations, thereby enhancing the fidelity of machined workpieces and reducing the number of 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
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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 (100) comprising a machining head (101) and a workpiece holder (108) moveable relative to each another the method comprising: performing a first machining operation on a workpiece (106) mounted to the workpiece holder (108) according to a first programmed series of movements of the machining head (101) relative to the workpiece holder (108), the first machining operation having a first maximum machining tolerance; performing a second machining operation on the workpiece (106) according to a second programmed series of movements of the machining head (101) relative to the workpiece holder (108), the second machining operation having a second maximum machining tolerance; performing a measurement operation to determine a position of an artefact (202) on the machine tool (100); calculating an offset relative to a corresponding previously stored position of the artefact (202); 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.