Toward real-time clamping load measurement using DSPI

Finding a reliable technique to determine clamping load in bolted joint has been a challenging problem for several years. A new technique that was recently introduced, addresses this problem by deploying the Digital Speckle Pattern Interferometry (DSPI) technique to measure the deformation of the surface being clamped and correlate it to the clamping load. The optical part of the system has been developed using the Spatial Phase Shifting technique to determine the deformation caused by the applied torque. The images produced by this technique are of low signal-to-noise ratio and require filtering in order to achieve accurate deformation calculation. However, image filtering requires significant processing time, particularly in video streams, which can cause delays in the system and therefore undesirable results. In this paper we propose a method to automate the process of calculating the deformation in a suitable time frame. This method uses a new filtering technique to reduce the computation overhead of the controlling software and therefore increase the overall speed of the system by up to seven times. Achieving a practical processing time in the software will result in more robust and reliable control over the fastener and therefore higher accuracy of clamping load. The methods used to design this system ultimately can automate the entire process of clamping and provide a reliable closed-loop clamping load controller for bolted joint.