Compliance of a Robot Arm using Torque-Based Cartesian Impedance Control
(2021)Department of Automatic Control
- Abstract
- Robots have become important for the development of today’s society. They are known to obtain good accuracy and repeatability of tasks that either complement or replace human labour. Furthermore, as machine-learning is emerging in many technologies, it is important to consider the uncertainties that are introduced when this method is used in robotics. This work aims at developing and evaluating a torque-based control framework that allows a state-of-the-art robot arm to be seen as an impedance, and its environment as an admittance. Using said control strategy allows the robot to behave as a mass-spring-damper system, which allows it to act more compliantly. Moreover, the type of strategy is referred to as Cartesian impedance control.
The... (More) - Robots have become important for the development of today’s society. They are known to obtain good accuracy and repeatability of tasks that either complement or replace human labour. Furthermore, as machine-learning is emerging in many technologies, it is important to consider the uncertainties that are introduced when this method is used in robotics. This work aims at developing and evaluating a torque-based control framework that allows a state-of-the-art robot arm to be seen as an impedance, and its environment as an admittance. Using said control strategy allows the robot to behave as a mass-spring-damper system, which allows it to act more compliantly. Moreover, the type of strategy is referred to as Cartesian impedance control.
The framework was developed both in a simulation environment called Dynamic Animation and Robotics Toolkit (DART), but also in the common robotics environment called Robot Operating System (ROS). The latter framework was in turn used to run the control strategy on a real robot arm.
The results showed compliant behaviour of the robot in Cartesian space, both in simulation and on the real system. Translational, rotational and nullspace compliances were tested and evaluated. For reasonably high stiffness values, these experiments showed the expected behaviour when the robot was subjected to external forces. Moreover, the behaviour of the robot in selected singularities was also studied, and the robot was stable in all the tested singular configurations with no apparent oscillations. The experiments also revealed some limitations of the real system, allowing the robot to behave sufficiently well only under certain bounds. That is, the inheritance of friction on the real system limited the tracking ability when lower stiffness values were used. A peg-in-hole assembly experiment was also done both on the real system and in simulation, in order to get a sense of how the robot performs in the intended contact-rich tasks. The results of these experiments showed that the robot could insert the attached peg into a box with a hole, after sliding along the surface of the box for some time. The peg insertion in simulation was about twice as fast compared to the real robot. Moreover, the specific path of the end-effector in
simulation compared to the real system did not match precisely due to uncertainties and limitations such as calibration errors and friction. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9069366
- author
- Chouman, Oussama
- supervisor
- organization
- year
- 2021
- type
- H3 - Professional qualifications (4 Years - )
- subject
- report number
- TFRT-6147
- other publication id
- 0280-5316
- language
- English
- id
- 9069366
- date added to LUP
- 2021-12-23 14:03:21
- date last changed
- 2021-12-23 14:03:21
@misc{9069366,
abstract = {{Robots have become important for the development of today’s society. They are known to obtain good accuracy and repeatability of tasks that either complement or replace human labour. Furthermore, as machine-learning is emerging in many technologies, it is important to consider the uncertainties that are introduced when this method is used in robotics. This work aims at developing and evaluating a torque-based control framework that allows a state-of-the-art robot arm to be seen as an impedance, and its environment as an admittance. Using said control strategy allows the robot to behave as a mass-spring-damper system, which allows it to act more compliantly. Moreover, the type of strategy is referred to as Cartesian impedance control.
The framework was developed both in a simulation environment called Dynamic Animation and Robotics Toolkit (DART), but also in the common robotics environment called Robot Operating System (ROS). The latter framework was in turn used to run the control strategy on a real robot arm.
The results showed compliant behaviour of the robot in Cartesian space, both in simulation and on the real system. Translational, rotational and nullspace compliances were tested and evaluated. For reasonably high stiffness values, these experiments showed the expected behaviour when the robot was subjected to external forces. Moreover, the behaviour of the robot in selected singularities was also studied, and the robot was stable in all the tested singular configurations with no apparent oscillations. The experiments also revealed some limitations of the real system, allowing the robot to behave sufficiently well only under certain bounds. That is, the inheritance of friction on the real system limited the tracking ability when lower stiffness values were used. A peg-in-hole assembly experiment was also done both on the real system and in simulation, in order to get a sense of how the robot performs in the intended contact-rich tasks. The results of these experiments showed that the robot could insert the attached peg into a box with a hole, after sliding along the surface of the box for some time. The peg insertion in simulation was about twice as fast compared to the real robot. Moreover, the specific path of the end-effector in
simulation compared to the real system did not match precisely due to uncertainties and limitations such as calibration errors and friction.}},
author = {{Chouman, Oussama}},
language = {{eng}},
note = {{Student Paper}},
title = {{Compliance of a Robot Arm using Torque-Based Cartesian Impedance Control}},
year = {{2021}},
}