Chatter stability of robotic rotary ultrasonic countersinking

In recent years,industrial robots have received extensive attention in manufacturing field due to their high flexibility and great workspace.However,the weak stiffness of industrial robots makes it extremely easy to arouse chatter,which affects machining quality inevitably and generates noise pollution in severe cases.Compared with drilling,the chatter mechanism of robotic countersinking is more complex.The external excitation changes with cutting width and depth in countersinking.This characteristic results in time-varying and nonlinearity of robotic countersinking dynamics.Thus,it is urgent to propose a new method of chatter suppression and provide an accurate stability analysis model.As a new special machining technology,rotary ultrasonic machining has been proved to improve robotic drilling and milling stability effectively.Based on this,robotic rotary ultrasonic countersinking(RRUC)is proposed to improve the robotic countersinking stability in this paper.A three-dimensional stability domain method of RRUC is established.First,the countersinking process was divided intoρparts.The dynamic model of every unit was constructed based on ultrasonic function angle(γ)and dynamic chip area.Then,the stability region of RRUC is obtained based on the semi-discrete method(SDM).Compared with the robotic conventional countersinking(RCC),RRUC improves the stability by 27%.Finally,the correctness and effectiveness of the stability region model are proved by robotic ultrasonic countersinking experiments.

Machine Vision for Non-Contact Automated Countersink Measurement

The slug rivet is widely used in wing assembly due to its longer fatigue life and better sealing performance compared with other connection technologies.As a countersink with dual-angle is widely adopted for this type of connection,the countersink diameter and depth are key factors that affect assembly quality.Therefore,it is of great importance to efficiently inspect the countersink quality to ensure high accuracy.However,contact measurements are susceptible to the loss of accuracy due to cutting debris and lube build-up,while the hole-scanning method using laser profilometry is time consuming and complex.In this paper,a non-contact method for countersink diameter and depth measurement based on a machine vision system is proposed.The countersink diameter can be directly measured by the machine vision system,while the countersink depth is determined through the countersink diameter indirectly.First,by means of image processing technology together with an improved edge detection algorithm,the countersink diameter can be obtained.Then,a 3D microscope is employed to measure the countersink depth,which helps to model the countersink.As a result,once the countersink diameter is measured,so is the depth.The experimentation demonstrated that this method has strong feasibility and enables time saving,which is conducive to improve the riveting efficiency.