Optical Surface Scanning Head with Parabola Normal Approximation

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Solution Overview

Problem

Current surface scanning methods using motorized scanning heads on coordinate positioning machines face limitations due to friction, unequal spring stiffness, and surface changes beyond the scanning head's bandwidth, which restrict scanning flexibility and accuracy.

Innovation Solution

The method involves approximating the surface profile to a parameterized parabola, determining the surface normal from this parabola, and adjusting the scanning device's distance or force in the normal direction, using a controller to manage the scanning head's movement and deflection, allowing for more precise and flexible scanning of complex surfaces.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a motorised scanning head is used to increase scanning flexibility, then the ability to position the stylus in many different orientations is improved, but friction and unequal spring stiffness cause measurement errors and reduce accuracy

Engineering Contradiction:

Improvescanning flexibilityVSAvoidmeasurement accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent replaces the mechanical contact probe system with an optical scanning system. The optical probe uses light reflection and triangulation to measure surface geometry without physical contact, eliminating friction and spring stiffness issues entirely. The system captures surface points by projecting light patterns and detecting their reflection, substituting mechanical measurement forces with optical field interactions.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces light as an intermediary between the scanning head and the workpiece surface. Instead of direct mechanical contact, the optical system uses light patterns and their reflection off the surface as a mediator to transfer geometric information from the workpiece to the sensor, avoiding the harmful effects of mechanical friction and unequal spring constants.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If the scanning head moves quickly to improve productivity, then scanning speed is improved, but the scanning head cannot adequately respond to surface changes beyond its bandwidth

Engineering Contradiction:

Improvescanning speedVSAvoidsurface profile accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The optical scanning system eliminates mechanical inertia and bandwidth limitations by using light-based measurement. The system can capture surface geometry at very high speeds because light travel time is negligible compared to mechanical response times. The optical sensor can detect surface variations instantaneously as the workpiece or scanner moves, removing the mechanical bandwidth constraint that limits conventional contact scanning systems.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If contact probes are used to measure surface profiles, then direct surface contact enables measurement, but friction and spring stiffness variations introduce measurement errors

Engineering Contradiction:

Improvesurface profile measurement capabilityVSAvoidfriction and spring stiffness errors

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent completely replaces the mechanical contact probe with an optical measurement system. Instead of using a physical stylus that contacts the surface and relies on spring forces and friction, the system projects optical patterns onto the surface and detects their reflection. This substitution eliminates the harmful effects of friction and unequal spring stiffness that plague contact-based measurement systems.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

Light serves as an intermediary that transfers measurement information without the harmful mechanical interactions. The optical system uses light reflection and triangulation to obtain surface profile data without the stylus needing to physically contact the surface, thereby eliminating friction and spring stiffness as sources of measurement error.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentEP1877729B1Method for scanning the surface of a workpiece

Publication Date: 2011.10.12 RENISHAW PLC

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AI summary

A method for measuring a surface profile using a surface sensing device mounted on an articulating probe head in which the probe head is moved along a nominal path relative to the surface profile, an at least approximation of the surface normal of the surface profile, the surface profile is sensed with the surface sensing device and the distance or force of the surface sensing device relative to the surface profile substantially in the direction of the surface normal. The surface normal may be determined by approximating at least one section to a curved profile which can be mathematically parameterised.