A General Approach to Achieving Stability and Safe Behavior in Distributed Robotic Architectures

This paper proposes a unified energy-based modeling and energy-aware control paradigm for robotic systems. The paradigm is inspired by the layered and distributed control system of organisms, and uses the fundamental notion of energy in a system and the energy exchange between systems during interaction. A universal framework that models actuated and interacting robotic systems is proposed, which is used as the basis for energy-based and energy-limited control. The proposed controllers act on certain energy budgets to accomplish a desired task, and decrease performance if a budget has been depleted. These budgets ensure that a maximum amount of energy can be used, to ensure passivity and stability of the system. Experiments show the validity of the approach

Safety and Guaranteed Stability Through Embedded Energy-Aware Actuators

Safety is essential for robots in unknown environments, especially when there is physical Human-Robot Interaction (pHRI). Control over energy, or passivity, is an effective safety mechanism. However, when the control algorithm is implemented in a discrete-time computer, computation and communication delays readily lead to loss of passivity and to instability. In this paper, a way to make the actuators aware of the energy that they inject into the system is presented. Passivity and stability are then always guaranteed, even in situations of total communication loss. These Embedded Energy-Aware Actuators are a model-free passivity and safety layer that make complex robotic systems dependable, well-behaved and safe. The proposed method is validated in simulation and experiments

Dynamic walking with Dribbel

This paper describes the design and construction of Dribbel, a passivity-based walking robot. Dribbel has been designed and built at the Control Engineering group of the University of Twente. This paper focuses on the practical side: the design approach, construction, electronics, and software design. After a short introduction of dynamic walking, the design process, starting with simulation, is discussed

Passivity based control of hydraulic robot arms using natural Casimir functions: Theory and experiments

This paper gives a new passivity based control of hydraulic arms based on a new model using “natural��? Casimir functions. Not only passivity but also Casimir functions are used in the modeling and control as a new structural property. First, we refer port-Hamiltonian systems and their properties. Second, we propose two stabilization methods, a new dynamic asymptotic stabilization method and a new partial stabilization method. Third, we give a new model of hydraulic arms using Casimir functions. Furthermore, the proposed two stabilization methods are applied to this model and finally, the validity of our methods are confirmed by not only numerical simulations but also experiments even thought the bulk modulus is not identified at all

A novel energy-efficient rotational variable stiffness actuator

This paper presents the working principle, the design and realization of a novel rotational variable stiffness actuator, whose stiffness can be varied independently of its output angular position. This actuator is energy-efficient, meaning that the stiffness of the actuator can be varied by keeping constant the internal stored energy of the actuator. The principle of the actuator is an extension of the principle of translational energy-efficient actuator vsaUT. A prototype based on the principle has been designed, in which ball-bearings and linear slide guides have been used in order to reduce losses due to friction

Lending a helping hand: toward novel assistive robotic arms

Assistive robotics is an increasingly popular research field, which has led to a large number of commercial and noncommercial systems aimed at assisting physically impaired or elderly users in the activities of daily living. In this article, we propose five criteria based on robotic arm usage scenarios and surveys with which assistive robotic arms can be classified. Different possibilities and implementations to obtain each criterion are treated, and examples of current assistive robotic arms are given. Implementations and systems are discussed and rated qualitatively, which leads to the observation that variable stiffness actuation offers great benefits for assistive robotic systems despite an increase in the overall complexity

Energy-based Safety in Series Elastic Actuation

This work presents the concept of energy-based safety for series-elastic actuation. Generic actuation passivity and safety is treated, defining several energy storage and power flow properties related to passivity. Safe behaviour is not guaranteed by passivity, but can be guaranteed by energy and power limits that adapt the nominal behaviour of an impedance controller. A discussion on power flows in series-elastic actuation is presented and an appropriate controller is developed. Experimental results validate the effectiveness of the energy-based safety in elastic actuation

A General Approach to Achieving Stability and Safe Behavior in Distributed Robotic Architectures

This paper proposes a unified energy-based modeling and energy-aware control paradigm for robotic systems. The paradigm is inspired by the layered and distributed control system of organisms, and uses the fundamental notion of energy in a system and the energy exchange between systems during interaction. A universal framework that models actuated and interacting robotic systems is proposed, which is used as the basis for energy-based and energy-limited control. The proposed controllers act on certain energy budgets to accomplish a desired task, and decrease performance if a budget has been depleted. These budgets ensure that a maximum amount of energy can be used, to ensure passivity and stability of the system. Experiments show the validity of the approach

The Variable Stiffness Actuator vsaUT-II: Mechanical Design, Modeling, and Identification

In this paper, the rotational variable stiffness actuator vsaUT-II is presented. This actuation system is characterized by the property that the apparent stiffness at the actuator output can be varied independently from its position. This behavior is realized by implementing a variable transmission ratio between the internal elastic elements and the actuator output, i.e., a lever arm with variable pivot point position. The pivot point is moved by a planetary gears mechanism, which acquires a straight motion from only rotations, thereby providing a low-friction transmission. The working principle details of the vsaUT-II are elaborated and the design is presented. The actuator dynamics are described by means of a lumped parameter model. The relevant parameters of the actuator are estimated and identified in the physical setup and measurements are used to validate both the design and the derived model

Wireless motion control of paramagnetic microparticles using a magnetic-based robotic system with an open-configuration

In this work, motion control of paramagnetic microparticles is achieved using a magnetic system with an open-configuration. This control is done using a permanent magnet and an electromagnetic coil under microscopic guidance. The permanent magnet and the electromagnetic coils are fixed to the end-effector of a robotic arm with 4 degrees-of-freedom to control the motion of the microparticles in three-dimensional (3D) space. A closed-loop control of the robotic arm is done at the joint-space to orient the magnetic field gradients of the permanent magnet and the electromagnetic coil towards a reference point in 3D space. Point-to-point motion control is achieved at an average speed of 117 ϵm/s using the permanent magnet and the robotic arm, whereas the electromagnetic coil and the robotic arm achieve average speed of 46 ϵm/s. In addition, the permanent magnet and the robotic arm achieves maximum position error of 600 ϵm, in the steady-state, as opposed to 100 ϵm for the electromagnetic coil and the robotic arm. We also demonstrate experimentally that our control system moves the microparticles towards a reference position in the presence of a constrain on the motion of the end-effector. The precise motion control of paramagnetic microparticles using a magnetic system with open-configuration provides broad possibilities in targeted therapy and biomedical applications that cannot be achieved using magnetic systems with closed-configurations