Abstract: An approach for achieving reliable, built-in, high-accuracy force sensing for legged robots is presented, based on direct exploitation of the properties of a robot�s mechanical structure. The proposed methodology relies on taking account of force-sensing requirements at the robot design stage, with a view to embedding force-sensing capability within the mechanical structure of the robot itself. The test case is ROBOCLIMBER, a bulky, quadruped climbing and walking machine whose weighty legs enable it to carry out heavy-duty drilling operations. The paper shows that, with finite-element analysis of ROBOCLIMBER�s mechanical configuration during the design stage, candidate positions can be selected for the placement of force transducers to measure indirectly the contact forces between the feet and the ground. Force sensors are then installed at the theoretically best positions on the mechanical structure, and several experiments are carried out to calibrate all sensors within their operational range of interest. After calibration, the built-in sensors are subjected to experimental performance evaluation, and the final best sensor option is found. The built-in force-sensing capability thus implemented is subjected to its first test of usability when it is employed to compute the actual centre of gravity of ROBOCLIMBER. The method is shown to be useful for determining variation during a gait (due to the non-negligible weight of the legs). Afterwards the force sensors are shown to be useful for controlling foot�ground interaction, and several illustrative experiments confirm the high sensitivity, reliability and accuracy of the selected approach. Lastly, the built-in sensors are used to measure ground-reaction forces and to compute the zero-moment point for ROBOCLIMBER in real time, both while standing and while executing a dynamically balanced gait.

Abstract: The Dual Smart Drive is a specially designed nonlinear actuator intended for use in climbing andwalking legged robots. It features a continuously changing transmission ratio and dual properties and is very suitable for situations where the same drive is required to perform two different types of start-stop motions of a mobile link. Then, the associated control problem to this nonlinear actuator is established and a backstepping design strategy adopted to develop Lyapunov-based nonlinear controllers that ensure asymptotic tracking of the desired laws of motion, which have been properly selected using time-optimal control. The approach is extended for bounded control inputs. Both simulation and experimental results are presented to show the effectiveness and feasibility of the proposed nonlinear control methods for the Dual Smart Drive.

Abstract: In this paper we consider the postural stability problem for nonlinearly actuated quasi-static biped robots, both with respect to the joint angular positions and also with reference to the gripping effect between the foot/feet against the ground during robot locomotion. Zero moment point based mathematical models are developed to establish a relationship between the robot state variables and the stability margin of the foot (feet) contact surface and the supporting ground. Then, in correspondence with the developed dynamical model and its associated uncertainty, and in the presence of non-modeled robot mechanical structure vibration modes, we propose a robust control architecture that uses two cascade regulators. The overall robust control system consists of a nonlinear robust variable structure controller in an inner feedback loop for joint trajectory tracking, and anH� linear robust regulator in an outer, direct zero moment point feedback loop to ensure the foot�ground contact stability. The effectiveness of this cascade controller is evaluated using a simplified prototype of a nonlinearly actuated biped robot in double support placed on top of a one-degree-of-freedom mobile platform and subjected to external disturbances. The achieved experimental results have revealed that the simplified prototype is successfully stabilized.

Abstract: The perspective of using humanoid robots in practical applications is attracting an important research effort and the late steps forward in robot technology shows many remarkable achievements where design aspects, control systems and software evolution regarding humanoid machines have been realised. However, and although most of humanoid robots are intended to offer by some means a good degree of autonomy so that they could deploy all their intrinsic capabilities to perform �useful� tasks, the current state of this technology is being still far from allowing to attain such a goal. Among all the concerned features, and aiming to improve humanoid robot overall performance, it is required that they could work for a long time spending minimum energy without losing their kinematical skills. In this direction, a new kind of non-linear actuator, SMART, based on quasi-resonance principle, have been developed by the Industrial Automation Institute to improve the overall performance of biped locomotion. One of the major advantages provided by SMART is their inherent low energy consumption in comparison to classical transmission ratio actuators. However, due to their intrinsically non- linear characteristic, the practical use of these actuators poses some complications, in particular when it is necessary to realise advanced control schemes. To overcome this problem it is demonstrated how force sensing, implemented in one of the four-bar linkages of the mechanism, along with angular position measurement and motor current sensing, provides, throughout a sensor fusion strategy, an extra sensitivity to the non-linear actuator, resulting in an enhanced responsiveness. By using this approach the foreseen theoretical SMART actuator properties are fully demonstrated and experimental results are used to verify the practical advantages of the proposed method.

Abstract: In the last two decades in particular, climbing and walking robots have been the subject of important research activity worldwide. However, the practical use of these robots is still limited and only a few are in actual use in live situations. In the general framework of the CLAWAR Thematic Network, several working groups have been established to formulate requirements, to define specifications and to investigate those aspects of climbing and walking robot technology that are more relevant with respect to selected application domains. The aim of this paper is to present an overview of the investigations carried out by the CLAWAR network, and to show various realizations that could offer a good picture of how to rise above the barriers to exploit this innovative class of robotic systems.

Abstract: Improving walking robots overall performance requires that they could work for a long time spending minimum energy without losing their kinematic skills. In this paper the efficiency of locomotion mechanisms when designing humanoid robots is considered, and it is shown that proficient application of non-linear drives in selected joints allows extending humanoid robot functioning. A novel humanoid robot, SILO2, is employed for the experimental confirmation of the proposed approach .

Abstract: In this paper it is presented the undertaken research effort oriented to provide with self-tuning control capabilities to two walking robots : 1) a self propelling robot that is able to reach a desired remote location by means of special adhering devices attached to both ends of its kinematic chain; and, 2) a four legged locomotion robot. The digital control tasks are performed by specific hardware which is based on specialized microcontrollers what frees the host processor for implementing other tasks, like the plant transfer function identification and the digital filter tuning. On first place the hardware set-up is briefly introduced. It follows the identification sections showing how the several elements of the electromechanical chain (ZOH, amplifier, dc motor and load, encoder) are identified as a whole, in a very practical way, and considerations about stability of the algorithm, selection of the sampling rate, nonlinearities influence, ..., are made. In the third section it is shown how a pseudo deadbeat control is designed so that it suits to the digital filter hardwared implemented and then it is employed succesfully to the self-tuning of the different walking robots joints. Some experimental results are then reported.

Abstract: This paper describes the design and control concepts of a wall-climbing robot. It has an hexapod configuration and it is able to manoeuvre on vertical surfaces carrying high payloads. Configuration and leg design criteria specific for climbing tasks are discussed. The controller architecture showing decentralised parallel control and hard real-time performance is outlined. New stability criteria for wall locomotion are introduced and a climbing gait using force distribution shows the working of our control scheme for wall gait generation. We call this four phase discontinuous sawing gait. This prototype is an example of a climber specifically tailored for industrial applications.

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