J. Estremera

Generating continuous free crab gaits for quadruped robots on irregular terrain

This paper presents a method for generating free gaits for quadruped robots capable of performing statically stable, omnidirectional locomotion on irregular terrain containing forbidden areas. The rule-based deliberative algorithm can generate flexible sequences of leg transferences while maintaining constant vehicle speed. The foothold planning method is compatible with the use of these flexible leg sequences, and is designed to maintain a minimum absolute stability margin despite the terrain height uncertainty. The integration of exteroceptive terrain profile data has been considered to improve adaptability. Experimental results are presented to show the gaits efficiency in adapting to an irregular terrain containing forbidden areas.

Thrust Control, Stabilization and Energetics of a Quadruped Running Robot

In order to achieve powered autonomous running robots it is essential to develop efficient actuator systems, especially for generating the radial thrust in the legs. In addition, the control of the radial thrust of the legs can be a simple, effective method for stabilizing the body pitch in a running gait. This paper presents the mechanical systems, models and control strategies employed to generate and control leg thrust in the KOLT quadruped running robot. An analytical model of the electro-pneumatic leg thrusting system is presented and analyzed to evaluate its performance and to facilitate the design of control strategies. Several experiments have been conducted to estimate the energy losses and determine their origins as well as to compute the energetic efficiency of the actuation system. Two thrust control methods are also proposed and tested experimentally. The closed loop method regulates thrust through the control of the hip liftoff speed, a conceptually simple control strategy that stabilizes the body pitch in pronk and trot gaits without the need for central feedback, even on irregular terrain. The open-loop control method regulates the energy added in each hop based on the model of the actuator system. The efficacy of these models and techniques is tested in several planar trot and pronk experiments, and the results are analyzed focusing on the body stabilization, the power consumption and the energetic efficiency.

SIL04: a true walking robot for the comparative study of walking machine techniques

This article presents the SIL04 walking robot, a medium-sized quadruped mechanism built for basic research and development as well as for educational purposes. The SIL04 is a compact, modular, robust machine capable of negotiating irregular terrain, surmounting obstacles up to 250 mm tall and carrying about 15 kg in payload at a maximum velocity of about 1.5 m/min, depending on the gait it is using. A brief description of SIL04s leg and body structures, foot mechanisms and robot configuration is provided, and some insights into the hardware, software and simulation tools developed for SIL04 are presented.

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.

Continuous free-crab gaits for hexapod robots on a natural terrain with forbidden zones: An application to humanitarian demining

Autonomous robots are leaving the laboratories to master new outdoor applications, and walking robots in particular have already shown their potential advantages in these environments, especially on a natural terrain. Gait generation is the key to success in the negotiation of natural terrain with legged robots; however, most of the algorithms devised for hexapods have been tested under laboratory conditions. This paper presents the development of crab and turning gaits for hexapod robots on a natural terrain characterized by containing uneven ground and forbidden zones. The gaits we have developed rely on two empirical rules that derive three control modules that have been tested both under simulation and by experiment. The geometrical model of the SILO-6 walking robot has been used for simulation purposes, while the real SILO-6 walking robot has been used in the experiments. This robot was built as a mobile platform for a sensory system to detect and locate antipersonnel landmines in humanitarian demining missions.

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.

Location of legged robots in outdoor environments

Knowledge of a robots position with an accuracy of within a few centimeters is required for potential applications for legged robots, such as humanitarian de-mining tasks. Individual sensors are unable to provide such accuracy. Thus information from various sources must be used to accomplish the tasks. Following this trend, this paper describes the method developed for estimating the position of legged robots in outdoor environments. The proposed method factors in the specific features of legged robots and combines dead-reckoning estimation with data provided by a Differential Global Positioning System through an extended Kalman filter algorithm. This localization system permits accurate trajectory tracking of legged robots during critical activities such as humanitarian de-mining tasks. Preliminary experiments carried out with the SILO4 system have shown adequate performance using this localization system.

DYLEMA: Using walking robots for landmine detection and location

Detection and removal of antipersonnel landmines is an important worldwide concern. A huge number of landmines has been deployed over the last twenty years, and demining will take several more decades, even if no more mines were deployed in future. An adequate mine-clearance rate can only be achieved by using new technologies such as improved sensors, efficient manipulators and mobile robots. This paper presents some basic ideas on the configuration of a mobile system for detecting and locating antipersonnel landmines efficiently and effectively. The paper describes the main features of the overall system, which consists of a sensor head that can detect certain landmine types, a manipulator to move the sensor head over large areas, a locating system based on a global-positioning system, a remote supervisor computer and a legged robot used as the subsystems’ carrier. The whole system has been configured to work in a semi-autonomous mode with a view also to robot mobility and energy efficiency.

Optimizing Leg Distribution Around the Body in Walking Robots

Walking-robot technology has reached an advanced stage of development, as has already been demonstrated by a number of real applications. However, further improvement is still needed if walking robots are to compete with traditional vehicles. Some potential improvements could be gained through optimization. Thus, this paper presents a method for distributing the legs around the robot’s body such as to reduce the forces the legs must exert to support and propel the robot. The method finds through non-linear optimization techniques the middle leg displacement that nulls the difference between foot forces in a middle leg and a corner leg. A walking robot has been built to assess the theoretical results.

Analyzing Bounding and Galloping Using Simple Models

This paper focuses on modeling the gait characteristics of a quadrupedal gallop. There have been a number of studies of the mechanics of the stance phase in which a foot is in contact with the ground. We seek to put these studies in the context of the stride, or overall motion cycle. The model used is theoretical, and is kept simple in the interest of transparency. It is compared to empirical data from observations of animals, and to data from experiments with robots such as our KOLT machine, and results from sophisticated simulation studies. Modeling of the energy loss inherent in the interaction between the system and the environment plays a key role in the study. Results include the discovery of a hidden symmetry in the gait pattern, usually regarded as being completely asymmetrical. Another result demonstrates that the velocities with which the two front feet impact and leave the ground are different, and similarly for the rear feet. The velocities of the foot pairs mirror each other. This is consistent with empirical observation, but is at variance with the assumption used almost universally when modeling stance. A further result elicits the importance of the pitch moment of inertia and other effects that make the mammalian architecture, in which the center of mass is closer to the shoulders than to the hips, beneficial.