Walk-through programming for robotic manipulators based on admittance control

Abstract

The present paper addresses the issues that should be covered in order to develop walk-through programming techniques (i.e. a manual guidance of the robot) in an industrial scenario. First, an exact formulation of the dynamics of the tool the human should feel when interacting with the robot is presented. Then, the paper discusses a way to implement such dynamics on an industrial robot equipped with an open robot control system and a wrist force/torque sensor, as well as the safety issues related to the walk-through programming. In particular, two strategies that make use of admittance control to constrain the robot motion are presented. One slows down the robot when the velocity of the tool centre point exceeds a specified safety limit, the other one limits the robot workspace by way of virtual safety surfaces. Experimental results on a COMAU Smart Six robot are presented, showing the performance of the walk-through programming system endowed with the two proposed safety strategies

Impedance Control

“…The most classical application of impedance control is the peg-in-hole task (e.g., Caccavale et al 2001), while a more recent application is here presented, where the robot end effector is interacting with a human operator that has to guide it to teach a specific task trajectory to the robot (Ficuciello et al 2015). Such kind of application is very useful for industrial robot programming, and it is also known as walkthrough programming that, however, is usually carried out by resorting to an admittance control approach for the motivations discussed in the admittance control entry (Bascetta et al 2013). Ficuciello et al (2015) proposed to adopt an impedance control to facilitate the human task making it more intuitive by modulating the robot impedance according to the human behavior.…”

Admittance Control

“…One of the first and most common applications of admittance control is the so-called walk-through Admittance Control, Fig. 4 Example of lead-through programming (Courtesy of ABB in Deutschland) or lead-through programming (Bascetta et al 2013) that is a robot programming technique to teach poses of the end effector by manually guiding the robot in each of them. Manual guidance is enabled by admittance control setting null stiffness matrices so that the robot moves along directions of the force applied to the end effector equipped with a force sensor.…”

Smart Sensors Applications for a New Paradigm of a Production Line

“…In [25], the authors proposed an approach based on the adoption of force/torque sensors to implement a control scheme that imposes a specific velocity profile according to the sensor measures. Many classical control schemes can also be found, like force control [26], impedance control [27], and admittance control [28,29], as well as more advanced methodologies like adaptive admittance control schemes [30] and variable impedance control schemes [31]. A further interesting approach based on the adoption of vision systems was presented in [32]; in this case, the robot motion is obtained using the images provided by a camera.…”