P. Gonzalez de Santos

A six-legged climbing robot for high payloads

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.

Mobile-robot navigation with complete coverage of unstructured environments

Abstract There are some mobile-robot applications that require the complete coverage of an unstructured environment. Examples are humanitarian de-mining and floor-cleaning tasks. A complete-coverage algorithm is then used, a path-planning technique that allows the robot to pass over all points in the environment, avoiding unknown obstacles. Different coverage algorithms exist, but they fail working in unstructured environments. This paper details a complete-coverage algorithm for unstructured environments based on sensor information. Simulation results using a mobile robot validate the proposed approach.

Minimizing Energy Consumption in Hexapod Robots

Minimization of energy expenditure in autonomous mobile robots for industrial and service applications is a topic of huge importance, as it is the best way of lengthening mission time without modifying the power supply. This paper presents a method to minimize the energy consumption of a hexapod robot on irregular terrain. An energy-consumption model is derived for statically stable gaits before applying minimization criteria. Then, some parameters that define the foot trajectories of the legged robot are computed to minimize energy expenditure during every half a locomotion cycle. The method is evaluated using an accurate geometric model of the SILO-6 walking robot.

Ship building with ROWER

A four-legged mobile platform increases productivity and improves quality and working conditions for industrial naval applications. It is an automatic welding system for ship construction processes. It increases productivity by increasing total arc time, improving weld quality, and creating better working conditions for operators. The overall system consists of a commercial welding system handled by a commercial manipulator. These subsystems are carried on a mobile platform that provides mobility in the working area. A stereo vision system finds the starting and ending points of the welding seam. All four subsystems are remote-controlled by a computer supervised by an operator located off the work site. The supervisor computer also contains a database of the geometric description of each working cell.

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.

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.

Terrain-adaptive gait for walking machines

One of the primary advantages of walking machines is their inherent capacity for moving over different terrains. However, it is important to provide algorithms that modify the gait ac cording to the terrain. Existing articles about terrain-adaptive locomotion are based on intelligent foothold selection, and use periodic and/or aperiodic gaits. This article proposes a strategy to adapt walking robot locomotion to an irregular terrain in real time that is based on the variations of parameters of a periodic gait affecting leg coordination. Its main feature is that it does not require knowledge of footholds. In addition, this adaptive gait control can be incorporated into a system with external stereoceptive sensors to select footholds. As a working example, a particular class of periodic gaits, called wave-crab gaits, are used in a quadruped robot. However, the proposed adaptive-gait method can be used for any other periodic gait and for robots with a greater number of legs. Adaptive-gait control has been implemented in a quadruped robot named RIMHO, demonstrating its ability to move over different ter rains. Static stability results from computer simulations and experimentally obtained velocity results are also presented.

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.

On the Improvement of Walking Performance in Natural Environments by a Compliant Adaptive Gait

It is a widespread idea that animal-legged locomotion is better than wheeled locomotion on natural rough terrain. However, the use of legs as a locomotion system for vehicles and robots still has a long way to go before it can compete with wheels and trucks, even on natural ground. This paper aims to solve two main disadvantages plaguing walking robots: their inability to react to external disturbances (which is also a drawback of wheeled robots); and their extreme slowness. Both problems are reduced here by combining: 1) a gait-parameter-adaptation method that maximizes a dynamic energy stability margin and 2) an active-compliance controller with a new term that compensates for stability variations, thus helping the robot react stably in the face of disturbances. As a result, the combined gait-adaptation approach helps the robot achieve faster, more stable compliant motions than conventional controllers. Experiments performed with the SILO4 quadruped robot show a relevant improvement in the walking gait

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.