Thread Shape Measurement Using Dual-Axis Illumination
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Solution Overview
Problem
Conventional methods for measuring thread shapes, such as silhouette methods, contact probes, and laser rangefinders, face challenges in accurately measuring hook-like flank faces and thread bottom end portions due to issues like shadowing, particle adherence, and specular reflection, leading to reduced measurement accuracy and increased time consumption.
Innovation Solution
A thread shape measuring apparatus utilizing a dual optical system with a first illuminating unit emitting parallel lights orthogonal to the thread axis and a second unit tilting the optical axis beyond the thread's lead angle, combined with an image-capturing unit and arithmetic operation unit, captures and processes images to calculate the thread shape, including flank faces and thread bottom end portions, using shading patterns and focusing measures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a silhouette method is used to measure thread shape, then the measurement process is simple, but hook-like flank faces and thread bottom end portions cannot be accurately measured due to shadowing
Solution Approach 1:
The measurement process is divided into two distinct stages: first capturing the silhouette image to obtain the basic thread profile, then capturing the reflected light image to obtain the flank face and thread bottom end portion details. This segmentation allows each stage to focus on specific measurement objectives, resolving the contradiction between simplicity and precision.
Solution Approach 2:
The patent introduces a polarizing filter as an intermediary element between the light source and the thread portion. This filter converts specularly reflected light into detectable signals by controlling polarization states, enabling the measurement of previously inaccessible surfaces like hook-like flank faces without complicating the overall measurement system.
2Measurement precision
If a contact probe is used to measure thread shape, then measurement accuracy can be maintained, but measurement time increases and particles may adhere to the probe
Solution Approach 1:
The patent replaces the mechanical contact probe system with an optical measurement system using reflected light imaging. This substitution eliminates physical contact, thereby removing the time-consuming aspects of probe movement and particle adherence issues, while maintaining measurement accuracy through optical detection of thread geometry.
3Productivity
If a laser rangefinder in a triangulation system is used, then measurement speed is improved, but hook-like flank faces cannot be measured due to specular reflection
Solution Approach 1:
The polarizing filter serves as an intermediary that modifies the interaction between light and the thread surface. By controlling polarization states, it converts specularly reflected light from hook-like flank faces into detectable signals, enabling the laser rangefinder to measure these previously inaccessible surfaces at high speed without sacrificing accuracy.
4Device complexity
If conventional silhouette method is used, then device complexity is low, but measurement accuracy of difficult thread shapes is insufficient
Solution Approach 1:
The measurement system is segmented into two functional components: a silhouette imaging path for basic profile capture and a reflected light imaging path for detailed surface measurement. This segmentation allows the system to maintain low overall complexity while achieving high measurement accuracy for difficult thread shapes through the complementary information from both paths.
Solution Approach 2:
The imaging device is designed to perform multiple functions: capturing both silhouette images and reflected light images using the same hardware platform. This multi-functionality reduces device complexity compared to having separate systems, while enabling accurate measurement of various thread shapes including difficult-to-measure features.
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 enables accurate measurement of thread shapes that are difficult for conventional methods, reducing measurement time and improving accuracy by capturing shading patterns and focusing measures, allowing for precise calculation of thread dimensions and angles.
Implementation Method 1
an image-capturing unit that has a visual axis parallel to the optical axis of the first illuminating unit, includes a telecentric lens, has a focusing position matching the cross section, and detects, out of the parallel lights emitted from the first illuminating unit, the light that has not been blocked by the thread portion to capture an image of the detected light
Implementation Method 2
a first illuminating unit that has an optical axis in a direction orthogonal to a cross section including a thread axis of a thread portion and emits parallel lights to illuminate the thread portion
Implementation Method 3
a second illuminating unit that has an optical axis in a direction forming an angle larger than a lead angle of the thread portion with respect to the direction orthogonal to the cross section and emits parallel lights to illuminate the thread portion
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
A thread shape measuring apparatus (100) includes: a first illuminating unit (1) that has an optical axis in a direction orthogonal to a cross section M including a thread axis A and emits parallel lights to illuminate the thread portion; a second illuminating unit (2) that has an optical axis in a direction forming an angle θ larger than a lead angle γ of the thread portion with respect to the direction orthogonal to the cross section and emits parallel lights to illuminate the thread portion; an image-capturing unit (3) that has a visual axis parallel to the optical axis of the first illuminating unit (1), includes a telecentric lens (32), has a focusing position matching the cross section, and detects, out of the parallel lights emitted from the first illuminating unit (1) or the second illuminating unit (2), the light that has not been blocked by the thread portion to capture an image of the detected light; and an arithmetic operation unit (4) that arithmetically operates a shape of the thread portion based on a captured image captured by the image-capturing unit (3).