Wonkyun Lee

Distributed Component Friction Model for Precision Control of a Feed Drive System

Nonlinear friction is a dominant factor of the complexity growth of feed drive dynamic behavior. In particular, a feed drive system equipped with rolling contact components such as ball screws and linear motion (LM) guides undergoes impalpable friction behavior. Therefore, proper modeling and compensation of friction in feed drive components play a crucial role in improving the precision of a feed drive system. In this study, to overcome the accuracy limitation of the simplified feed drive model, a distributed component friction model (DCFM) of a feed drive system is developed. Friction has been modeled as a single element of entire feed drive system in the conventional model. However, the proposed DCFM is composed of models of individual feed drive components such as ball screw and LM guide including their friction behaviors. To take advantage of the DCFM by considering both presliding and sliding friction behaviors of each component, LuGre model is applied. For experimental verification of the accuracy of the proposed DCFM, a specially designed feed drive testbed is constructed. Using the testbed, the friction forces of ball screws and LM guides are measured independently. Using the DCFM, a friction observer is built for real-time monitoring and compensation of the friction force. A proportional-derivative feed drive position controller with an observer-based friction compensator is implemented and the experimental results are presented.

Tactile Display to Render Surface Roughness for Virtual Manufacturing Environment

In smart factories, the entire manufacturing process from design to the final product is simulated in a virtual manufacturing environment and optimized before starting production. Suppliers and customers make decisions based on the simulation results. Therefore, effective rendering of the information of the virtual products to suppliers and customers is essential for this manufacturing paradigm. In this study, a method of rendering the surface roughness of the virtual products using a tactile display is presented. A tactile display device comprising a 3 x 3 array of individually controlled piezoelectric stack actuators is constructed. The surface topology of the virtual products is rendered directly by controlling the piezoelectric stack actuators. A series of experiments is performed to evaluate the performance of the tactile display device. An electrical discharge machined surface is rendered using the proposed method.

Hardware-in-the-loop Simulation of CNC-controlled Feed Drives

Design and application of hardware-in-the-loop simulation (HILS) for design of CNC-controlled machine tool feed drives is discussed. The CNC machine tool is a complex mechatronics system where the complexity results from the software-based controller composed of a variety of functionalities and advanced control algorithms. Therefore, using a real CNC controller in the control simulation has merits considering the efforts and accuracy of the simulation modeling. In this paper challenges in HILS for a CNC controlled feed drive, such as minimization of time delay and transmission error that are caused by discretization of the feed drive model, is elaborated. Using an experimental HILS setup of a machine tool feed drive applications in controller gain selection and CNC diagnostics are presented.