Design and Development of Friction Compensator Algorithm for One Link Robot

Abstract

Many robots excel at their positioning and trajectory tracking using software control and most successful robotic application utilize this ability – examples include CNC machining, robotic welding, painting and pick-and-place board assembly. The mechanical design of these robots focuses on rigid transmissions and minimizing compliance in the structure, so the software controller can accurately track a desired position with respect to time, regardless of any disturbance forces. However, there is class of tasks, for which rigid actuation is not ideal.

For dynamic behaviors such as running, the performance limitations of robot are often due to limitations of friction. A robot is an integrated system of electronics, software, and mechanical, and each part of the system limits or enables the behavior of the whole. Friction effects are particularly critical for industrial robots. Friction deteriorates the performance of industrial robots causes disturbances such as positioning errors, tracking errors and stick-slip errors in robotics. Friction effects in robotics depend on many factors, such as displacement and relative velocity of the robot, properties of surface materials, presence of lubrication. Robotic systems are equipped with position sensors and friction is generally velocity dependent, so friction requires velocity estimation techniques

The effects of friction in robotics are greatly compensated by friction models. The friction compensation model are of two types i.e. kinetic friction model and dynamic friction model.

To achieve high accuracy the negative effect of friction must be taken into account. The objective of this thesis is to derive a friction compensation strategy for a one link robot, which reduces steady-state errors. Because friction generally has a velocity dependency and in this case no velocity sensors are available an estimate of the velocities must be made; this is done by means of a reduced-order observer. Finally simulation and experimental results of the observer based friction compensation strategy are presented. This thesis is organized as follows:

Chapter 1 is the introduction chapter. The introduction regarding robotics, components, characteristics and literature survey is discussed. Applications of robot, and need for stabilization are also given. Chapter 2 gives an introduction to Fiction. Brief description of friction phenomenon and various friction models. Chapter 3 gives an introduction to various friction compensation strategies used in the field of robotics. Chapter 4 includes the problem formulation and provides the mathematical model for the friction compensator for one link robot system.