Jörg Bauer

Model-based off-line compensation of path deviation for industrial robots in milling applications

The scope of applications for industrial robots is limited in cases with strong forces at the end effector and high positioning and path accuracies required. Thus, their use in machining applications as a cost-saving, flexible alternative for machining tools is restricted due to mechanical compliance. A model-based off-line concept is presented to analyze, predict, and compensate the resulting path deviation of the robot under process force in milling applications. For this purpose a rigid multi-body dynamics model of the robot extended with additional joint elasticities and tilting effects is coupled with a material removal simulation providing the process forces. After systematically adjusting model parameters, an efficient simulation-based path correction strategy shows significant improvements of path accuracy. The general framework is applicable to any tree structured robots and allows for sensitivity analysis with respect to arbitrary model parameters.

Tool path adaption based on optical measurement data for milling with industrial robots

Industrial robots are used in a great variety of applications for handling, welding and milling operations. They represent a cost-saving and flexible alternative for machining applications. A reduced pose and path accuracy, especially under process force load due to the high mechanical compliance, restrict the use of industrial robots for further machining applications. Test results showed that these deviations range up to 0.6xa0mm. In this paper, a method is presented to determine the resulting path deviation of the robot under process force by using a structured light scanner. The obtained data is compared with the CAD (Computer Aided Design) data of the machined part within a developed software module. Additionally, the developed module provides functions for manipulation, registration of STL (Surface Tessellation Language) surface point clouds and a postprocessor for program translation. The comparison is performed using a dexel discretization of each data set. Based on this comparison the robot path is adapted to improve the machining quality. This method can be applied to 3- and 5-axis machining operations. The results show that the deviation can be reduced to 0.1xa0mm.

Analysis of Industrial Robot Structure and Milling Process Interaction for Path Manipulation

Industrial robots are used in a great variety of applications for handling, welding, assembling and milling operations. Especially for machining operations, industrial robots represent a cost-saving and flexible alternative compared to standard machine tools. Reduced pose and path accuracy, especially under process force load due to the high mechanical compliance, restrict the use of industrial robots for machining applications with high accuracy requirements. In this chapter, a method is presented to predict and compensate path deviation of robots resulting from process forces. A process force simulation based on a material removal calculation is presented. Furthermore, a rigid multi-body dynamic system’s model of the robot is extended by joint elasticities and tilting effects, which are modeled by spring-damper-models at actuated and additional virtual axes. By coupling the removal simulation with the robot model the interaction of the milling process with the robot structure can be analyzed by evaluating the path deviation and surface structure. With the knowledge of interaction along the milling path a general model-based path correction strategy is introduced to significantly improve accuracy in milling operations.

Low-frequency dynamics of an electrorheological fluid in squeeze and shear mode. Part I: experiments

Electrorheological fluids (ERFs) offer a rapid control of damping using very low power requirements. Different models have been proposed to simulate the hysteresis phenomenon observed experimentally in ERF. This paper describes the steps to be taken to extract measurements of an ERF in squeeze and shear mode. A novel modular test facility was designed to perform measurements of a specific ERF in squeeze and shear mode. This device allows the measurement of the dynamic response of the fluid under various excitation conditions. Dense measurement grids of fluid force and electrode displacement at harmonic excitation are collected in dependency of the excitation frequency, the displacement amplitude and the applied electric field. The main problems to be solved during the setup and execution of the measurements are discussed. The steps to be taken during signal processing to achieve high-quality measurements as inputs for material model fitting are described in detail. Example measurements for both squeeze and shear mode are presented. The fitting of the obtained results to a material model for ERF and discussion of the resulting extended Bouc–Wen model will be the topic of an accompanying paper.