As a common mechanical connection in the manufacturing industry, the quality inspection of threads is of paramount importance. The quality of threads is directly related to the performance, safety and service life of products. However, traditional thread inspection methods face many challenges and are difficult to meet the demands of modern high-precision and high-efficiency production. With the development of science and technology, in-line image measuring instruments have emerged to provide innovative solutions to the difficulties in thread inspection.

Anatomy of a Thread Inspection Difficulty

1、High measurement accuracy requirements 

The parameters of a thread, such as pitch, tooth angle, center diameter, etc., play a decisive role in its fit accuracy. In aerospace, automotive and other high-end fields, for example, the requirements for thread accuracy in these industries can reach the micron level. Any slight deviation may lead to loosening of the threaded connection, leakage or even cause serious safety accidents. Traditional inspection tools, such as thread plug gauges, micrometers, etc., are greatly affected by human factors, and it is difficult to ensure the accuracy and repeatability of the measurements under the micron-level precision.

2、Low detection efficiency 

In the process of mass production, there are many threaded parts. If manual testing one by one, not only consumes a lot of time and labor costs, and the detection speed is far from keeping up with the production rhythm. For example, in the manufacture of electronic equipment, a small screw may have dozens of threads, artificial detection efficiency is extremely low. Even with some semi-automatic testing equipment, frequent manual clamping in the detection process, adjustment will also seriously affect the overall detection efficiency.

3、Complex thread detection difficulties 

With the continuous innovation of industrial design, the types of threads are becoming more and more diversified, such as the emergence of complex structures such as multi-head threads, variable pitch threads, shaped threads and so on. The parameter measurement of these complex threads is very difficult, and the traditional inspection methods are often unable to accurately obtain the complete parameter information. For example, due to the existence of multiple helixes, it is difficult for conventional measurement methods to take into account the parameters of each head at the same time, resulting in inaccurate detection results.

Working Principle and Advantages of Online Image Measuring Instruments

A：Working Principle

Based on machine vision technology, the in-line image measuring instrument collects images of threaded parts with a high-resolution camera, and then analyzes and processes the images using advanced image processing algorithms. The system first preprocesses the captured image with graying and filtering to enhance the clarity and contrast of the image. Then, the contour information of the thread is extracted by the edge detection algorithm, and then the parameters, such as pitch, tooth angle, center diameter, etc., are calculated according to the geometric characteristics of the thread and the measurement algorithm. The whole measurement process is fast and accurate without touching the threaded parts, avoiding damage to the surface of the parts.

B: Advantages

1, high-precision measurement: online image measuring instrument using high-resolution cameras and advanced image processing algorithms, can achieve sub-micron level measurement accuracy. Compared with traditional inspection tools, its measurement repeatability and accuracy is greatly improved, and it can meet the stringent requirements of high-end manufacturing industry on thread accuracy. For example, in the manufacture of precision molds, the measurement accuracy of the thread diameter can reach ± 0.001mm, effectively ensuring the assembly accuracy and service life of the mold.

2, efficient detection: the measuring instrument can realize automated online detection, detection speed is very fast. In the production line, the threaded parts can be real-time, continuous detection, without manual intervention, greatly improving the detection efficiency. Taking the production of automobile parts as an example, dozens of threaded parts can be detected per minute, which greatly shortens the production cycle and improves the production efficiency and market competitiveness of enterprises.

3, to adapt to the complex thread detection: for the complex structure of the thread, online image measuring instrument with its powerful image processing capabilities and flexible measurement algorithms, can accurately identify and measure the parameters of a variety of complex threads. Through the accurate analysis of thread profile, it can simultaneously obtain the parameters of each head of multi-head threads, as well as the special parameters of variable pitch threads and shaped threads, providing a reliable solution for the quality inspection of complex threads.

In-line image measuring instrument to solve the specific application of thread inspection difficulties

(A) High-precision Measurement Realization

In practical applications, the online image measuring instrument is able to accurately measure key parameters such as pitch, tooth angle, and center diameter by precisely analyzing the image of the thread. Taking pitch measurement as an example, the system utilizes image processing algorithm to identify and locate the adjacent tooth types of threads, and then calculates the distance between the corresponding points of adjacent tooth types, which is then converted by a precise algorithm to arrive at the accurate value of pitch. For tooth angle measurement, the gauge calculates the size of the tooth angle by extracting the contour line of the threaded tooth pattern and utilizing a geometric algorithm. In terms of center diameter measurement, the image-based non-contact measurement method avoids the measurement errors caused by the traditional contact measurement due to force measurement and other factors, and is able to accurately measure the center diameter of the thread to ensure the accuracy of the thread fit.

In-Line Image Gauge can be seamlessly integrated into automated production lines for in-line inspection of threaded parts. When the threaded part is transferred to the measuring area via the conveyor belt, the gauge automatically triggers the camera to capture the image and analyze the measurement. The entire inspection process takes only a few seconds and the results are fed back to the production line control system in real time. If unqualified products are detected, the system can immediately issue an alarm and marking, and at the same time, adjust the production parameters, realizing real-time monitoring and quality control of the production process, which greatly improves the production efficiency and product quality stability.

(B) Complex thread detection program

For multi-head threads, the online image measuring instrument utilizes its multi-view image acquisition and analysis technology to simultaneously acquire the thread images of each head and perform parameter measurement and analysis respectively. The parameters of multiple heads are comprehensively evaluated through unique algorithms to ensure the overall quality of multi-head threads. For variable pitch threads and shaped threads, the gauge uses customized measurement algorithms and image processing processes based on their special geometry. Through point-by-point analysis and fitting of the thread profile, it accurately obtains the pitch change rule of variable pitch threads and the special parameters of alien threads, providing comprehensive data support for the design, manufacture and quality inspection of complex threads.

With its high precision, high efficiency and strong detection ability for complex threads, online image measuring instrument has become a powerful tool to solve the difficulties of thread inspection. In the manufacturing industry's continuous pursuit of high precision and high efficiency, the application of in-line image measuring instrument will bring revolutionary changes to thread inspection, help enterprises to improve product quality, reduce production costs, and promote the manufacturing industry to intelligent, high-end development. POMEAS, as a professional supplier of measuring instruments, is committed to providing customers with advanced and reliable in-line image measuring instrument solutions to meet the stringent requirements of thread inspection in different industries.