Pablo González de Santos

Free Gaits for Quadruped Robots over Irregular Terrain

Although walking machines exhibit many advantages over wheeled or tracked vehicles, legged vehicles have yet to be introduced in real applications because of the primitive development of specific techniques such as gait generation. This article addresses the design, implementation and experimentation of gaits to negotiate uneven terrain with a real machine. The gaits presented are a mixture of free and discontinuous gaits. Discontinuous gaits were selected because of their ground adaptability features and ease of implementation, while free gaits were chosen because they facilitate path tracking. The fusion of these two main gaits plus the addition of extra constraints to avoid leg-transfer deadlocking produced a new free-crab gait, a free-spinning gait and a free-turning gait. Some experiments have been conducted to illustrate the features of these gaits on a real machine.

An improved energy stability margin for walking machines subject to dynamic effects

Several static and dynamic stability criteria have been defined in the course of walking-robot history. Nevertheless, previous work on the classification of stability criteria for statically stable walking machines (having at least four legs) reveals that there is no stability margin that accurately predicts robot stability when inertial and manipulation effects are significant. In such cases, every momentum-based stability margin fails. The use of an unsuitable stability criterion yields unavoidable errors in the control of walking robots. Moreover, inertial and manipulation effects usually appear in the motion of these robots when they are used for services or industrial applications. A new stability margin that accurately measures robot stability considering dynamic effects arising during motion is proposed in this paper. The new stability margin is proven to be the only exact stability margin when robot dynamics and manipulation forces exist. Numerical comparison has been conducted to support the margins suitability. Stability-level curves are also presented on the basis of a suitable stability margin to control the trajectory of the center of gravity during the support phase.

Application of CLAWAR Machines

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.

Generation of discontinuous gaits for quadruped walking vehicles

Discontinuous gaits for walking machines have not yet been properly studied. Research has focused on the investigation, comprehension, and mathematical formulation of natural gaits. These gaits feature the fact that the body is in constant motion. The results have been significant, but they seem more adequate for animals than machines. On the other hand, discontinuous gaits, executed by animals under extreme conditions, exhibit excellent attributes for implementation in walking machines. This article presents a comparative study of continuous and discontinuous gaits with regard to their maximum achievable velocity and stability. Other aspects such as implementation in real machines, power requirements, and control under terrain difficulties are mentioned briefly. An elemental discontinuous gait is stated, and some variations on deriving crab and turning gaits are performed. Different methods for enlarging the achievable crab angle and improving stability are discussed for discontinuous crab gaits. A similar study is also done for turning gaits. (c) 1995 John Wiley & Sons, Inc.

A new legged-robot configuration for research in force distribution

Force-controlled legged vehicles are the subject of worldwide research due to their intrinsic advantages in locomotion over different types of unstructured terrains. This paper presents a design for feet and ankles with an integrated sensor system to detect both force and contact surface orientation, thus enabling the implementation in a real legged robot of force optimization schemes that take into account these two interaction parameters. With such schemes, the robot can minimize the risk of foot slippage by computing a favorable set of foot forces to command to a force feedback control system. A walking robot was built based on this configuration, and its mechanics and control are also presented in this paper.

The Rotation Period of C/1995 O1 (Hale-Bopp)

C/1995 O1 (Hale-Bopp) was observed in daylight on 16 days between 1997 April 1 and 1997 April 28, five of which had long time sequences (up to 10 hr of data), using the near infrared CAIN camera on the 1.5 m Carlos Sanchez Telescope at Teide Observatory (Tenerife, Canary Islands, Spain). Three spiral dust jet structures were observed for several almost complete rotations. A nucleus rotation period of 11.34±0.02 hr was determined from two different methods. No variations of the rotation period with time due to precessional effects were found in our data. However, the time sampling of the observations, similar to the suggested spin precession period, prevents us from ascertaining whether such variations exist. We note, though, that the good agreement of our results with the rotation periods at different epochs reported by other groups suggests that if they exist, these variations must be small, hence the rotation cannot be very complex.

Velocity Dependence in the Cyclic Friction Arising with Gears

Recent research on friction in robot joints and transmission systems has considered meshing friction a position-dependent friction component. However, in this paper we show experimental evidence that meshing friction depends highly on joint speed. We identify the meshing friction in the gearboxes of a robotic leg, and we propose a new mathematical model that considers the rate dependency of meshing friction. The resulting model is validated through experimentation. Results show that meshing friction is responsible for friction torque oscillations with an amplitude up to 25 percent of the average friction torque at low speeds. Therefore, this friction component should be taken into account if an accurate friction model is desired.

Detailed Study of Amplitude Nonlinearity in Piezoresistive Force Sensors

This article upgrades the RC linear model presented for piezoresistive force sensors. Amplitude nonlinearity is found in sensor conductance, and a characteristic equation is formulated for modeling its response under DC-driving voltages below 1 V. The feasibility of such equation is tested on four FlexiForce model A201-100 piezoresistive sensors by varying the sourcing voltage and the applied forces. Since the characteristic equation proves to be valid, a method is presented for obtaining a specific sensitivity in sensor response by calculating the appropriate sourcing voltage and feedback resistor in the driving circuit; this provides plug-and-play capabilities to the device and reduces the start-up time of new applications where piezoresistive devices are to be used. Finally, a method for bypassing the amplitude nonlinearity is presented with the aim of reading sensor capacitance.

Analysing and solving body misplacement problems in walking robots with round rigid feet

Abstract Round rigid feet for multi-legged robots offer a number of advantages over flat feet, and even over flat feet with articulated ankles. The main benefits are low cost, low complexity and robustness. A round rigid foot of small radius works well on hard terrain; however, it is prone to sink into soft terrain. Sinking can be avoided by increasing the radius of the foot, but in that case a round foot will roll during the leg-support phase, causing the hip to become misplaced and the robot to assume an incorrect attitude. This paper analyses this problem and provides a hip-control algorithm for restoring leg coordination. The algorithm is implemented in a real leg with a large-radius ball foot in order to evaluate how the algorithm would perform if applied to a real robot.

Climbing, walking and intervention robots

Explains how the Automatic Control Department of the Instituto de Automatica Industrial (CSIC) in Madrid, Spain has been developing robots for over 15 years. This activity began in the 1980s with the realization of industrial robots and then the department focused its attention on the area of robots for hostile/hazardous environments. Describes several achievements in this field including a complex tele‐operated system for steam generator inspection and maintenance in nuclear power plants; a tele‐manipulator for servicing a new concept of urban infrastructures; a self‐propelling climbing robot with magnetic feet; and a four‐legged walking robot for hazardous environments.