Variable Impedance Control and Learning—A Review

Abstract

Robots that physically interact with their surroundings, in order to accomplish some tasks or assist humans in their activities, require to exploit contact forces in a safe and proficient manner. Impedance control is considered as a prominent approach in robotics to avoid large impact forces while operating in unstructured environments. In such environments, the conditions under which the interaction occurs may significantly vary during the task execution. This demands robots to be endowed with online adaptation capabilities to cope with sudden and unexpected changes in the environment. In this context, variable impedance control arises as a powerful tool to modulate the robot's behavior in response to variations in its surroundings. In this survey, we present the state-of-the-art of approaches devoted to variable impedance control from control and learning perspectives (separately and jointly). Moreover, we propose a new taxonomy for mechanical impedance based on variability, learning, and control. The objective of this survey is to put together the concepts and efforts that have been done so far in this field, and to describe advantages and disadvantages of each approach. The survey concludes with open issues in the field and an envisioned framework that may potentially solve them.

A variable admittance controller for human-robot manipulation of large inertia objects

“…In the past decades, several studies have proposed different methods to determine the parameters of the impedance model in order to improve the physical human-robot interaction and make the cooperation transparent. A survey of the methods that involve adaptation of the impedance parameters can be found in [7]. R. Ikeura together with his team proposed methods for designing the robot's admittance model based on the human impedance characteristics, which were identified through a collaborative task between two humans [8].…”

“…In all the aforementioned works, the problem of handling an object with high inertia is not explicitly addressed; a case which is commonly found in industrial applications. In [3], [16], which are not covered by [7], an admittance controller is utilized for the cooperative manipulation of a heavy object, which adjusts the target inertia and damping matrices depending on the acceleration. However, the paper tackles only one of the objectives of the current paper, as only the problem of enhancing the user's feeling of control over the task is addressed, i.e.…”

“…The order of execution for these six methods was randomly generated for each participant based on a uniform distribution. The employed evaluation metrics are: a) the energy transferred by the human to the robot, calculated by the integral of the power from (7), i.e. E + T 0 P + dt, with T denoting the interaction duration, which reflects the effort of the human; b) the energy transferred from the robot to the human, calculated by the integral of the negative power accordingly, i.e.…”

Variable Admittance Control of a Hand Exoskeleton for Virtual Reality-Based Rehabilitation Tasks

“…Variable admittance strategies (see Figure 7 ) are the ones that aim at imitating human's approach to motion: specifically, humans change their bodies, dynamic properties while performing complex movements like walking or interacting with different objects (Hogan, 1984 ). This same idea has been explored in the human-robot interaction field resulting in many different strategies (Ikeura et al, 1994 ; Tsumugiwa et al, 2002 ; Duchaine and Gosselin, 2007 ; Abu-Dakka and Saveriano, 2020 ). The user's intention is detected during a preliminary phase through sensors and inference algorithms, then input into the admittance model and proper parameters values ( K , B , and M ) are computed with some heuristics technique (Lee and Buss, 2008 ; Song et al, 2019 ).…”

Damping in Compliant Actuation: A Review

“…This article acknowledges the maturity of the field by presenting a survey of damping technologies and their applications in robotic actuation. In particular, to narrow the breadth of our analysis and walk in the shoes of an actuator designer, we focus on solutions that include physical damping elements, referring the interested reader to [28] and [29] as access points to explore the vast literature on active control approaches to dampen compliant robots. Information from the database (see the "Database Identification" section) has been cross-checked to count the papers according to their control (b) A compact Arm from [26] (license 5210131303438).…”