Grinding Error Compensation via Metrology Surface Height Feedback
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Solution Overview
Problem
Existing crankshaft grinding machines face challenges in maintaining roundness accuracy due to height variations caused by temperature changes and friction-related heat, leading to increased roundness errors, especially in orbital grinding processes where the height difference between the workpiece and grinding wheel axes can vary significantly.
Innovation Solution
A machine tool system that includes a metrology surface inclined relative to the infeed direction, allowing for real-time measurement of height variations between the workpiece and tool supports using a position probe, which adjusts the infeed arrangement to improve the accuracy of the grinding process by incorporating actual height measurements into the infeed equation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the height difference between workpiece axis and grinding wheel axis is assumed fixed at manufacture, then the infeed equation can be simplified for control, but temperature variations during operation cause height changes leading to roundness errors
Solution Approach 1:
The patent implements a feedback mechanism where the actual height difference H is continuously measured during operation (rather than assumed fixed), and this measured value is fed back to update the infeed equation calculations. This allows the system to compensate for thermal expansion and height changes in real-time, maintaining roundness accuracy despite temperature variations during unattended operation.
Solution Approach 2:
The patent changes the parameter H from a fixed manufacture-time value to a dynamic operation-time value. By measuring the actual height difference during operation and using this updated parameter in the infeed equation, the system adapts to thermal conditions and maintains manufacturing precision despite environmental temperature changes.
2Manufacturing precision
If post process roundness measurement and process repeatability are used for compensation, then some roundness errors can be corrected, but the variability in roundness errors of orbiting crankpin diameters remains significant
Solution Approach 1:
The patent performs the height measurement and compensation calculation during the grinding operation itself (in-process), rather than waiting for post-process measurement. This preliminary action during manufacturing allows real-time adjustment of the infeed equation, preventing roundness errors from occurring in the first place rather than attempting to correct them after the fact.
3Productivity
If the machine operates unattended in varying ambient temperatures, then productivity is improved, but thermal expansion causes height variations between axes leading to increased roundness errors
Solution Approach 1:
The patent implements real-time feedback measurement of the height difference H during unattended operation. This allows the system to detect and compensate for thermal expansion effects automatically, maintaining manufacturing precision even when operating unattended through temperature cycles from daytime to nighttime conditions.
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 solution enables precise control of the grinding wheel's position relative to the workpiece, reducing roundness variability and improving the accuracy of crankpin diameters by compensating for height changes caused by temperature fluctuations, even in machines lacking a vertical machine axis.
Implementation Method 1
The local temperature rise of the wheelspindle structure causes normal thermal expansion that moves the centre of rotation of the wheelspindle with respect to the surrounding elements of the machine.
Data Source
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AI summary
A machine tool, such as an orbital grinding machine, and method of operation thereof are disclosed whereby a metrology surface (60) formed on a component (50) of the machine tool is rigidly fixed relative to one of a workpiece support (10,12) and a tool support(22,32), such that the metrology surface (60) can be probed using a position probe (34) rigidly fixed relative to the other of the workpiece support and the tool support. The positions of the workpiece and tool supports at which the position probe contacts the metrology surface may be used to calculate a measure relating to the height between reference points or axes of the workpiece support and tool support (such as a tool infeed arrangement). This height measure may be used by a controller of the machine to improve the accuracy of its control of the location of the tool relative to the workpiece.