Gustavo A. Medrano-Cerda

Shape function-based kinematics and dynamics for variable length continuum robotic arms

This paper presents a new three dimensional kinematic and dynamic model for variable length continuum arm robotic structures using a novel shape function-based approach. The model incorporates geometrically constrained structure of the arm to derive its deformation shape function. It is able to simulate spatial bending, pure elongation, and incorporates a new stiffness control feature. The model is validated through numerical simulations, based on a prototype continuum arm, that yields physically accurate results.

Pneumatic muscle actuator technology: a light weight power system for a humanoid robot

This work reports on the construction of components for a humanoid robot powered by a new low mass, high power weight and volume actuation system, called the pneumatic muscle actuator (PMA). In addition to their power and force capabilities the PMA, being pneumatic, produces a more natural human muscle like contact and as such can be considered a soft actuation system with the inherent safety implication when working in close proximity to humans. The integration and testing of the performance of the component sections is also considered to show how these structures and actuators can be combined to produce the various systems needed for a low mass humanoid and the potential for future application in humanoid and other robotic fields.

Development of a dynamic simulator for a compliant humanoid robot based on a symbolic multibody approach

This paper reports on development of an open source dynamic simulator for the Compliant huMANoid robot, COMAN. The key advantages of this simulator are: it generates efficient symbolic dynamical equations of the robot with high degrees of freedom, it includes a user-defined model of the actuator dynamics (the passive elasticity and the DC motor equations), user defined ground models and fall detection. Users have the freedom to choose the proposed features or include their own models. The models are generated in Matlab and C languages, where the user can leverage the power of Matlab and Simulink to carry out analysis to parameter variations or optimization and also have the flexibility of C language for realtime experiments on a DSP or FPGA chip. The simulation and experimental results of the robot as well as an optimization example to tune the ground model coefficients are presented. This simulator can be downloaded from the IIT website [1].

Novel modal approach for kinematics of multisection continuum arms

This paper presents a new three dimensional (3D) kinematic model based on mode shape functions (MSF) for multisection continuum arms. It solves the singularity problems associated with previous models and introduces a novel approach for intuitively deriving exact, singularity-free MSFs, thus avoiding mode switching schemes and simplifying error models. The model is able to simulate spatial bending, pure elongation/contraction, and introduces inverse orientation kinematics for the first time to multisection continuum arms. Also, it carefully accounts for physical constraints in the joint space to provide enhanced insight into practical mechanics, and produces correct results for both forward and inverse kinematics. The model is validated through simulations, based on a prototype continuum robotic arm. Proposed approach is applicable to a broad spectrum of continuum robotic arm designs.

Stability and performance of the compliance controller of the quadruped robot HyQ

A legged robot has to deal with environmental contacts every time it takes a step. To properly handle these interactions, it is desirable to be able to set the foot compliance. For an actively-compliant legged robot, in order to ensure a stable contact with the environment the robot leg has to be passive at the contact point. In this work, we asses some passivity and stability issues of the actively-compliant leg of the quadruped robot HyQ, which employs a highperformance cascade compliance controller. We demonstrate that both the nested torque loop performance as well as the actuator bandwidth have a strong influence in the range of virtual impedances that can be passively rendered by the robot leg. Based on the stability analyses and experimental results, we propose a procedure for designing cascade compliance controllers. Furthermore, we experimentally demonstrate that the HyQs actively-compliant leg is able to reproduce the compliant behavior presented by an identical but passively-compliant version of the same leg.

On the role of load motion compensation in high-performance force control

Robots are frequently modeled as rigid body systems, having torques as input to their dynamics. A high-performance low-level torque source allows us to control the robot/environment interaction and to straightforwardly take advantage of many model-based control techniques. In this paper, we define a general 1-DOF framework, using basic physical principles, to show that there exists an intrinsic velocity feedback in the generalized force dynamics, independently of the actuation technology. We illustrate this phenomena using three different systems: a generic spring-mass system, a hydraulic actuator, and an electric motor. This analogy helps to clarify important common aspects regarding torque/force control that can be useful when designing and controlling a robot. We demonstrate, using simulations and experimental data, that it is possible to compensate for the load motion influence and to increase the torque tracking capabilities.

Modelling human balance using switched systems with linear feedback control

We are interested in understanding the mechanisms behind and the character of the sway motion of healthy human subjects during quiet standing. We assume that a human body can be modelled as a single-link inverted pendulum, and the balance is achieved using linear feedback control. Using these assumptions, we derive a switched model which we then investigate. Stable periodic motions (limit cycles) about an upright position are found. The existence of these limit cycles is studied as a function of system parameters. The exploration of the parameter space leads to the detection of multi-stability and homoclinic bifurcations.

Gain Scheduling Control for a Class of Variable Stiffness Actuators Based on Lever Mechanisms

This paper is concerned with the design of a control strategy for variable stiffness actuators in series configuration, exploiting the lever concept to adjust the stiffness at the transmission. A control strategy based on gain scheduling is proposed, which is able to regulate both stiffness and position at output link. The gain scheduling is designed based on a set of linear quadratic regulators (LQRs), because LQRs inherent robustness properties can accommodate significant variation in the actuation plant parameters. The link positioning relies on continuous adjustment of the control effort based on the current transmission stiffness; the stiffness perceived at the output link is regulated through combined action of the transmission stiffness and the positioning gains of the scheduling strategy. The effectiveness of the controller is verified in simulation and experiments on the actuator with adjustable stiffness. The overall strategy has been proven to be locally stable.

Comparison of various active impedance control approaches, modeling, implementation, passivity, stability and trade-offs

Impedance control, as method to improve the interaction ability of robotic systems, has gained great attention by the robotic community and a large number of different implementations have been reported in the literature. Most implementations are based on an outer impedance loop and a number of nested inner loops. In this paper, various active Impedance Control (IC) schemes are designed, analyzed and tested based on different inner control loops, namely velocity, position and torque. IC on link and motor side are considered. Stability, passivity, safety and performance of the different IC schemes are presented. All the IC schemes are evaluated and tested on a 1-dof series elastic actuator. The system dynamics are modeled including gearbox meshing friction and harmonic drive torque ripple. Simulation and experimental results are compared.

Dynamic continuum arm model for use with underwater robotic manipulators inspired by octopus vulgaris

Continuum structures with a very high or infinite number of degrees of freedom (DOF) are very interesting structures in nature. Mimicking this kind of structures artificially is challenging due to the high number of required DOF. This paper presents a kinematic and dynamic model for an underwater robotic manipulator inspired by Octopus vulgaris. Then, a prototype arm inspired by live octopus is presented and the model validated experimentally. Initial comparisons of simulated and experimental results show good agreement.