Session: MSNDC-05-01 Motion Planning, Dynamics, and Control of Robots

Paper Number: 90937

90937 - Stability Analysis of a One Degree-of-Freedom Robot Model With Sampled Digital Acceleration Feedback Controller in Turning 

Machining with robots is a growing area in the manufacturing industry. In the present state, robots are not well suited for tasks related to metal material removal, as geometrical accuracy is the main goal during these processes. The built-in controller provided by the manufacturer is designed to handle relatively simple operations like pick and place. These tasks do not expose the slender and not stiff robot to large forces, which are typical in machining. Usually, a proportional-derivative feedback controller is utilized to manage the positioning of the robot. However, this solution often lacks the ability to provide the necessary precision and surface quality required in metal cutting. In order to prepare robots for the demanding task of machining metal parts and mitigate the vibrations arising from the machining process, the dynamic performance of the system must be improved. Because the manufacturer is concerned about responsibility and safety issues, the parameters of the built-in controller cannot be altered. A possible solution could be to add an additional signal to the position feedback loop of the built-in controller of the robot. Acceleration feedback can prove to be a viable option thanks to its simplicity and reasonable application price. Therefore, we are investigating the stability of the robot, when an additional acceleration signal is applied together with the built-in controller.

Feedback controllers introduce time delays in the system, which can considerably influence the stable parameter regions, even if the delays are relatively small. These delays can originate from various sources, for example, measurement, computational and actuator delays. In machining, regenerative machine tool chatter also introduces time delay, which is related to the relative vibration between the tool and the workpiece. Furthermore, modern digital control systems work with sampled quantized signals leading to time-periodic time delays instead of constant continuous delays. The digital sampling effect can also influence stability, for example, advanced delay differential equations with constant continuous delays are always unstable; however, with sampled signals, they can be stabilized. Moreover, systems with several digital delays require special care, because of the underlying complexity in handling multiple periods in time-periodic systems. In this study, we investigate a simple one degree-of-freedom model representing the structure of the robot.

In our study, we considered a proportional-derivative built-in digital controller.An additional digital acceleration feedback controller is connected to the conventional built-in controller of the robot. First, we show stable parameter domains without any machining present. This is a crucial step to ensure the stability of the robot. Then we introduce a simple turning model and analyse its stability thoroughly.

Presenting Author: Andras Bartfai Budapest University of Technology and Economics

Presenting Author Biography: I am a PhD student at Budapest University of Technology and Economics. I am also part of the MTA-BME Lendület Machine Tool Vibration Research Group. I am working on the topic of machining with robots. The correct representation of these systems require to deal with time-delay systems, which is an essential part of my research.

Authors:

Andras Bartfai Budapest University of Technology and Economics
Asier Barrios IDEKO
Zoltan Dombovari Budapest University of Technology and Economics