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Journal ArticleDOI

Development and validation of an end-effector for mitigation of collisions

01 Apr 2022-Journal of Mechanical Design (American Society of Mechanical Engineers Digital Collection)-Vol. 144, Iss: 4, pp 1-33
TL;DR: This paper focuses on the development of a special end-effector that can withstand impacts and is able to protect the robot from impulsive forces caused by collisions of the end- effector, but it has no effect on possible collisions between the links and obstacles.
Abstract: In robotics the risk of collisions is present both in industrial applications and in remote handling. If a collision occurs, the impact may damage both the robot and external equipment, which may result in successive imprecise robot tasks or line stops, reducing robot efficiency. As a result, appropriate collision avoidance algorithms should be used or, if it is not possible, the robot must be able to react to impacts reducing the contact forces. For this purpose, this paper focuses on the development of a special end-effector that can withstand impacts. It is able to protect the robot from impulsive forces caused by collisions of the end-effector, but it has no effect on possible collisions between the links and obstacles. The novel end-effector is based on a bi-stable mechanism that decouples the dynamics of the end-effector from the dynamics of the robot. The intrinsically non-linear behavior of the endeffector is investigated with the aid of numerical simulations. The effect of design parameters and operating conditions are analyzed and the interaction between the functioning of the bi-stable mechanism and the control system is studied. In particular, the effect of the mechanism in different scenarios characterized by different robot velocities is shown. Results of numerical simulations assess the validity of the proposed end-effector, which can lead to large reductions in impact forces. Numerical results are validated by means of specific laboratory tests.
Citations
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Journal ArticleDOI
TL;DR: In this paper , the authors propose an online method to adapt the trajectory of the robot to the human movements using a single depth camera, which eliminates the robot from the scene using a simple calibration process.
Abstract: In the last years, collaborative human-robot applications have become more and more appealing thanks to the robot’s easiness of programming and the promise of increasing precision and safety. However, by combining two resources (the cobot and the human operator) there is a problem of safety since cobot and human operator have to work in the same workspace. To ensure human safety, the distance between robot and operator must be assessed and the robot must adapt accordingly either by reducing its velocity or by modifying its trajectory. In this paper, we propose a new online method to adapt the trajectory of the robot to the human movements using a single depth camera. This algorithm eliminates the robot from the scene using a simple calibration process. Then, it interpolates the shared workspace, captured by the depth camera, using Radial Basis Functions (RBFs). The result is a continuous function that is representative of the risk of collision with obstacles on the plane. Its gradient is used as a repulsive potential in the Artificial Potential Field (APF) method to generate the path. This method eliminates the need to calculate the distance between operator and robot since it is intrinsically considered in the potentials. Results shows the validity of the method.

1 citations

Book ChapterDOI
01 Jan 2022
TL;DR: In this paper , a hydraulic module is presented to interpose between the end-effector and the robot flange to mitigate the effects of accidental collisions occurring in such a direction.
Abstract: Abstract The increasing number of artificial intelligence (AI) applications, and the adoption of collaborative robots in the industry are rising the necessity for the development of systems and algorithms able to detect and mitigate collisions. These are due to the probabilistic nature of AI applications and the environment. Indeed, an AI can perform poorly in unpredictable scenarios, and a cobot may face a distracted operator. These scenarios result in an unsafe situation where the robot impacts with its external environment. Solutions must be developed to mitigate these impacts with obstacles and manipulated objects. This paper presents a hydraulic module to be interposed between the end-effector and the robot flange. This module decouples the end-effector from the robot along the approach axis of the end-effector, thus mitigating the effects of accidental collisions occurring in such direction. Numerical results show the pros and cons of the new system.
References
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Journal ArticleDOI
01 Oct 1993
TL;DR: It is shown that a proper use of an four channels is of critical importance in achieving high performance telepresence in the sense of accurate transmission of task impedances to the operator.
Abstract: Tools for quantifying teleoperation system performance and stability when communication delays are present are provided A general multivariable system architecture is utilized which includes all four-types of data transmission between master and slave: force and velocity in both directions It is shown that a proper use of an four channels is of critical importance in achieving high performance telepresence in the sense of accurate transmission of task impedances to the operator It is also shown that transparency and robust stability (passivity) are conflicting design goals in teleoperation systems The analysis is illustrated by comparing transparency and stability in two common architectures, as well as a recent passivated approach and a new transparency-optimized architecture, using simplified one-degree-of-freedom examples >

2,083 citations

Journal ArticleDOI
TL;DR: This survey addresses the subject of bilateral teleoperation, a research stream with more than 50 years of history and one that continues to be a fertile ground for theoretical exploration and many applications.

1,584 citations

Journal ArticleDOI
TL;DR: In this paper, the Kelvin-Voigt model is shown to be logically untenable, for it indicates that the bodies must exert tension on one another just before separating, and it denotes that the damping energy loss is proportional to the square of the impacting velocity, instead of to its cube.
Abstract: During impact the relative motion of two bodies is often taken to be simply represented as half of a damped sine wave, according to the Kelvin-Voigt model. This is shown to be logically untenable, for it indicates that the bodies must exert tension on one another just before separating. Furthermore, it denotes that the damping energy loss is proportional to the square of the impacting velocity, instead of to its cube, as can be deduced from Goldsmith's work. A damping term $\lambda x^n \dot{x} $ is here introduced; for a sphere impacting a plate Hertz gives $n = 3/2$. The Kelvin-Voigt model is shown to be approximated as a special case deducible from this law, and applicable when impacts are absent. Physical experiments have confirmed this postulate.

1,390 citations

Journal ArticleDOI
TL;DR: The state of the art in the design of actuators with adaptable passive compliance is described, which is not preferred for classical position-controlled applications such as pick and place operations but is preferred in novel robots where safe human- robot interaction is required or in applications where energy efficiency must be increased by adapting the actuator's resonance frequency.
Abstract: In the growing fields of wearable robotics, rehabilitation robotics, prosthetics, and walking k robots, variable stiffness actuators (VSAs) or adjustable compliant actuators are being designed and implemented because of their ability to minimize large forces due to shocks, to safely interact with the user, and their ability to store and release energy in passive elastic elements. This review article describes the state of the art in the design of actuators with adaptable passive compliance. This new type of actuator is not preferred for classical position-controlled applications such as pick and place operations but is preferred in novel robots where safe human- robot interaction is required or in applications where energy efficiency must be increased by adapting the actuator's resonance frequency. The working principles of the different existing designs are explained and compared. The designs are divided into four groups: equilibrium-controlled stiffness, antagonistic-controlled stiffness, structure-controlled stiffness (SCS), and mechanically controlled stiffness.

772 citations

Journal ArticleDOI
TL;DR: In this paper, the authors considered the problem of designing joint-actuation mechanisms that can allow fast and accurate operation of a robot arm, while guaranteeing a suitably limited level of injury risk.
Abstract: This article considered the problem of designing joint-actuation mechanisms that can allow fast and accurate operation of a robot arm, while guaranteeing a suitably limited level of injury risk. Different approaches to the problem were presented, and a method of performance evaluation was proposed based on minimum-time optimal control with safety constraints. The variable stiffness transmission (VST) scheme was found to be one of a few different possible schemes that allows the most flexibility and potential performance. Some aspects related to the implementation of the mechanics and control of VST actuation were also reported.

620 citations