Virtual Surface Control for CMM Stylus Scanning
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Solution Overview
Problem
Coordinate measuring machines with tactile systems face challenges in scanning surfaces with indentations or depressions, as the stylus can get caught or damaged when moving over these features, especially when the positions of depressions are unknown, requiring methods to prevent immersion and ensure accurate scanning without prior knowledge of surface geometry.
Innovation Solution
The introduction of virtual surfaces defined by the user, which can be arranged in any shape and position in the measuring space, supplements the actual workpiece surface, allowing the stylus to 'jump' over indentations by guiding it along a virtual trajectory, preventing immersion and maintaining contact force equilibrium, thus preventing the stylus from getting caught in depressions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If scanning methods are used to quickly record a large number of measuring points, then productivity is improved, but the stylus may get caught in indentations causing damage or measurement errors
Solution Approach 1:
The virtual surface is defined in advance based on target geometry information before the actual scanning measurement begins. This preliminary definition creates a protective guide that prevents the stylus from entering indentations during the high-speed scanning process.
Solution Approach 2:
A virtual surface is introduced as an intermediary between the stylus and the actual workpiece surface. This virtual interface acts as a mediator that guides the stylus movement, allowing the stylus to follow the virtual surface contour rather than directly contacting the physical surface with indentations.
2Productivity
If the stylus is moved quickly along the workpiece surface to detect many measuring points, then productivity is improved, but the probing force becomes difficult to control
Solution Approach 1:
The virtual surface is pre-defined based on target geometry, establishing a predetermined measurement path and contact points. This allows the control device to maintain consistent probing force settings throughout the scanning process without needing to dynamically adjust for surface variations.
Solution Approach 2:
The invention changes the measurement parameter from direct physical contact with the actual surface to contact with a virtual surface defined by target geometry. This parameter change allows probing force to be controlled based on the virtual surface model rather than reacting to actual surface irregularities.
3Measurement precision
If individual points are touched to measure completely unknown geometries, then measurement precision is improved, but the measurement time increases significantly
Solution Approach 1:
Target geometry information is utilized in advance to define the virtual surface and measurement path. This preliminary use of geometric knowledge guides the scanning process, allowing the stylus to efficiently trace the workpiece surface along predetermined paths rather than randomly sampling points.
Solution Approach 2:
The scanning method enables continuous movement of the stylus along the workpiece surface, continuously detecting measuring points along the path. This continuous scanning action is more efficient than stopping at each individual point, maintaining measurement precision while reducing total measurement time.
4Measurement precision
If the stylus is pressed against the workpiece surface with constant force, then measurement precision is improved, but the stylus may get caught in indentations
Solution Approach 1:
The virtual surface serves as an intermediary that redirects the stylus movement. Instead of the stylus directly contacting the physical surface with indentations, it contacts the virtual surface defined by target geometry, which acts as a protective guide preventing immersion into actual surface features.
Solution Approach 2:
The virtual surface is defined in advance based on target geometry, creating a predetermined safe path for the stylus. This preliminary preparation ensures that the stylus follows a controlled trajectory that avoids indentations while maintaining appropriate contact force for accurate measurement.
Data Source
Figure 1
Figure 2~3b
Figure 4a~4c
AI summary
The present invention relates to a method (10) for controlling a measurement process of a coordinate measuring machine (46) for measuring a measurement object (12), wherein the coordinate measuring machine (46) comprises a control device (64) and a probe head (60) with a stylus (18), and wherein a relative movement between the stylus (18) and a surface (14) of the measurement object (12) is controlled by the control device (64). Furthermore, the surface (14) comprises at least one actual section (24) corresponding to a measurement object surface (13) and at least one virtual section (26). The present invention also relates to a corresponding coordinate measuring machine and computer program.