Robotics
Robotics is a young field of modern technology that crosses traditional engineering limits. Understanding the complexity of robots and their applications requires knowledge of electrical engineering, mechanical engineering, systems and industrial engineering, computer science, economics, and mathematics. New disciplines of engineering, such as knowledge engineering, applications engineering, and manufacturing engineering have emerged to work with the complexity of the field of robotics and factory automation [5].
Concepts of Kinematics a Dynamics
Kinematics belongs to the motion of bodies in a robotic mechanism without the regarding of the forces/torques that cause the motion. Since robotic mechanisms are by their very essence designed for motion, kinematics is the most fundamental aspect of robot design, analysis, control, and simulation.
In the other hand, the robot dynamics provides the relationships between actuation and contact forces, and the acceleration and motion trajectories that result. The dynamic equations of motion provide the basis for a number of computational algorithms that are useful in mechanical design, control and simulation.
Robot components
The main body of a robot consisting of the links, joints, and other elements. This body is called the manipulator. A manipulator becomes a robot when the wrist and gripper are attached and the control system is implemented.
Robotic manipulators are kinematically composed of links connected by joints to form a kinematic chain. However, a robot as a system, consists of a manipulator, a wrist, an end-effector, actuators, sensors, controllers, processors and software.
The individual rigid bodies that make up a robot are called links. In robotics is used sometimes the word “arm” to mean link. A robot arm or a robot link is a rigid member that have relative motion with respect to other links.
Two links are connected by contact at a joint where their relative motion can be expressed by a single coordinate. Joints are typically revolute (rotary) or prismatic (translatory) (figure 1).
Figure 1 Symbolic representation of robot joints [1]
Redundant Manipulators
Prismatic and revolute joints provide one degree of freedom. Therefore, the number of joints of a manipulator is the degrees of freedom (DoF) of the manipulator. Usually the manipulator should possess at least six DoF: three for positioning and three for orientation. A manipulator having more than six DoF is referred to as a kinematically
redundant manipulator. (figure 2)
Because of the ability of avoiding some constraints or obstacles, the redundant robot is now used more and more for research purpose. [3]
Philips experimental robot arm
Philips Applied Technologies announced a new robot technology [4]. This robot manipulator emulates one human arm. The manipulator makes easy the human-interaction applications, it means, that is of the form people-friendly robot arm (figure 3). The biological archetype of kinematically redundant manipulator like the human arm inspires the terminology used to characterize the structure of serial-chain manipulators. In fact, the human arm has three DoF at the shoulder, two DoF at the elbow and two DoF at the wrist. [5]
Figure 3 Philips experimental robot arm
Research purpose
Energy is one of the fundamental concepts in science and engineering practice, where it is common to view dynamical systems as energy-transformation devices.This perspective is particularly useful in studying complex nonlinear systems by decomposing them into simpler subsystems that, upon interconnection, add up their energies to determine the full system’s behavior (6). The state-of-the-art nonlinear control techniques are based in the analysis of the energy or “energy-shaping” in the system, in this case, the system is the robot arm. The problem consist in desing one optimun control for the arm.
The above problem will be solved through the design and implemention of the kinematic model which will be used to design and implement the dynamic model. The last step of the research is to implement one controller for the arm throughout the nonlinear control techniques.
This “energy-shaping” approach is the essence of passivity-based control (PBC), a controller design technique that is very well known in mechanical systems.
The Discrete Technology & Production Automation (DTPA) from the Faculty of Mathematics and Natural Sciences (FWN) is speciallized in the automation control techniques such PBC, port-hamiltonian control among other.
References
[1]. Spong M. et al. 2006. Robot Modeling and Control. John Wiley & Sons
[2]. Hollerbach, J. 1985. Optimun kinematic design for a seven degree of freedom manipulator, in: Robotics Research, The Second International Symposium. Kyoto , Japan
[3]. Liu, Lacheng. 2009. Visual Feedback Control of Philips experimental robot arm. Internship report. Philips Applied Technologies.
[4]. http://www.apptech.philips.com
[5]. Siciliano, B. et al. 2008. Springer Handbook of Robotics. Springer.
[6]. Ortega, R. et al. 2001. Putting Energy Back in Control. IEEE Control Systems Magazine.
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