Classification of ultrasonic signals using machine learning to identify optimal frequency for elongation control : Threaded fastening tools

Sammanfattning: Studying the preload in a screw joint has been the focus of today’s industry. The manufacturer reflects that demand by investigating different opportunities and techniques to develop this area. There are four different ways of controlling the tightening of bolts and joints to achieve the required clamp force that can hold for a specific preload. Torque control, angle control, gradient control, and ultrasonic clamp-force or elongation control. Many studies do exist about the first three mentioned techniques. However, there are a small number of studies for the ultrasonic clamp-force technique, and there is no study focusing on the usage of machine learning in that technique. This study investigates the use of machine learning to find the optimal frequency used to transmit the ultrasonic signals into the bolt for calculating the bolt elongation. Two machine learning models have been constructed, presenting two approaches: one for one-dimensional data (1D-CNN) and one for two-dimensional data (2D-CNN). The models classify the received signals (echos) with different frequencies into either accepted or non-accepted signals to get the optimal frequencies to be used later on, in the bolt elongation process. Both the 1D-CNN and 2D-CNN show an accepted performance of around 85% accuracy. The results indicate that there does exist a pattern in these ultrasonic signals that are useful for classifying them into accepted and non-accepted frequencies, so the usage of machine learning for the problem is feasible.