Experimental Estimation of Slipping in the Supporting Point of a Biped Robot

When developing a gait cycle on a low-friction surface, a biped robot eventually tends to slip. In general, it is commonto overcome this problem by means of either slow movements or physical adaptations of the robot at the contact pointwith the walking surface in order to increase the frictional characteristics. In the case of slipping, several types ofsensors have been used to identify the relative displacement at the contact point of the supporting leg with the walkingsurface for control purposes. This work is focused on the experimental implementation of a low-cost force sensor as ameasurement system of the slipping phenomenon. It is shown how, supported on a suitable change of coordinates,the force measurement at the contact point is used to obtain the total displacement at the supporting point due to thelow-friction conditions. This is an important issue when an accurate Cartesian task is required

Reflex based walking pattern adaptation for biped robots

Employing robots to replace humans in heavy and dangerous tasks is an important research area. Biped robots have advantages in obstacle avoidance and are therefore suitable to work in the human environment in such tasks. However, their control is a very difficult problem because of their nonlinear and unstable nature. Even very small disturbances can lead to instability. Disturbances can vary from slippery ground surfaces to collisions and unexpected contact with the environment to variations in the payload. For dynamically stable robots (walking on two or less feet), constraints on timing and foot placement increase the difficulty of designing controllers that can anticipate changes in the payload or react to errors. This thesis demonstrates the effectiveness of preprogrammed high-level responses to locomotion in a complex dynamic environment. A suite of responses allows a simulated, three dimensional, bipedal robot to recover from falling down due to a sudden change in the payload. Many environment contact errors would be avoided if the control system can respond fast to the errors that have already taken place and adapt the biped locomotion. In the case of the biped robot considered in this work, the controller might have less than a few tenths of a second in which to choose or plan an appropriate recovery. In this thesis reflexes are defined as responses with no explicit modeling and limited sensing. That is the robot can detect the payload change and makes no attempt to estimate the properties of the load to calculate a corresponding recovery plan. These reflexes are defined at high level because they involve changes of the biped body configuration and trajectory. Sensing elements are used just to detect the error and trigger the reflex. Explicit dynamic modeling of the biped robot is complicated and the controller cannot use it to compute precise and appropriate reactions. In addition, accurate and precise information on load addition is not available to the controller. The method presented changes the walk trajectory and shifts the center of gravity to keep the balance of the walk. Thereafter, the original trajectory is brought back by a smooth trajectory interpolation function. The reflex-adaptation technique considered is tested for a variety of payloads at different loading times. The method shows a good functionality by recovering the biped and allowing stable and balanced original walking pattern. The approach is successful and is a candidate for real applications

Active Ankle Response for a 2-D Biped Robot with Terrain Contact Sensing

This investigation explored the possibility of controlling a biped robot in the lateral direction as well as sensing terrain properties. A literature review was conducted to learn from and build off of previous research. Little research existed that deals directly with this topic, since most research dealing with biped robots deals with ambulation in the forward direction or control systems. The literature review supported the idea of controlling a biped in the lateral direction in theoretical terms, but has not ever been addressed by designing and fabricating a test bed and control system. Terrain sensing has been addressed in various aspects, but this research was aimed to acquire quantifiable values to determine how rigid the terrain is

Fast biped walking with a neuronal controller and physical computation

Biped walking remains a difficult problem and robot models can greatly {facilitate} our understanding of the underlying biomechanical principles as well as their neuronal control. The goal of this study is to specifically demonstrate that stable biped walking can be achieved by combining the physical properties of the walking robot with a small, reflex-based neuronal network, which is governed mainly by local sensor signals. This study shows that human-like gaits emerge without {specific} position or trajectory control and that the walker is able to compensate small disturbances through its own dynamical properties. The reflexive controller used here has the following characteristics, which are different from earlier approaches: (1) Control is mainly local. Hence, it uses only two signals (AEA=Anterior Extreme Angle and GC=Ground Contact) which operate at the inter-joint level. All other signals operate only at single joints. (2) Neither position control nor trajectory tracking control is used. Instead, the approximate nature of the local reflexes on each joint allows the robot mechanics itself (e.g., its passive dynamics) to contribute substantially to the overall gait trajectory computation. (3) The motor control scheme used in the local reflexes of our robot is more straightforward and has more biological plausibility than that of other robots, because the outputs of the motorneurons in our reflexive controller are directly driving the motors of the joints, rather than working as references for position or velocity control. As a consequence, the neural controller and the robot mechanics are closely coupled as a neuro-mechanical system and this study emphasises that dynamically stable biped walking gaits emerge from the coupling between neural computation and physical computation. This is demonstrated by different walking experiments using two real robot as well as by a Poincar\'{e} map analysis applied on a model of the robot in order to assess its stability. In addition, this neuronal control structure allows the use of a policy gradient reinforcement learning algorithm to tune the parameters of the neurons in real-time, during walking. This way the robot can reach a record-breaking walking speed of 3.5 leg-lengths per second after only a few minutes of online learning, which is even comparable to the fastest relative speed of human walking

Bipedal humanoid robot control by fuzzy adjustment of the reference walking plane

The two-legged humanoid structure has advantages for an assistive robot in the human living and working environment. A bipedal humanoid robot can avoid typical obstacles at homes and offices, reach consoles and appliances designed for human use and can be carried in human transport vehicles. Also, it is speculated that the absorption of robots in the human shape into the human society can be easier than that of other artificial forms. However, the control of bipedal walk is a challenge. Walking performance on solely even floor is not satisfactory. The complications of obtaining a balanced walk are dramatically more pronounced on uneven surfaces like inclined planes, which are quite commonly encountered in human surroundings. The difficulties lie in a variety of tasks ranging from sensor and data fusion to the design of adaptation systems which respond to changing surface conditions. This thesis presents a study on bipedal walk on inclined planes with changing slopes. A Zero Moment Point (ZMP) based gait synthesis technique is employed. The pitch angle reference for the foot sole plane −as expressed in a coordinate frame attached at the robot body − is adjusted online by a fuzzy logic system to adapt to different walking surface slopes. Average ankle pitch torques and the average value of the body pitch angle, computed over a history of a predetermined number of sampling instants, are used as the inputs to this system. The proposed control method is tested via walking experiments with the 29 degreesof- freedom (DOF) human-sized full-body humanoid robot SURALP (Sabanci University Robotics Research Laboratory Platform). Experiments are performed on even floor and inclined planes with different slopes. The results indicate that the approach presented is successful in enabling the robot to stably enter, ascend and leave inclined planes with 15 percent (8.5 degrees) grade. The thesis starts with a terminology section on bipedal walking and introduces a number of successful humanoid robot projects. A survey of control techniques for the walk on uneven surfaces is presented. The design and construction of the experimental robotic platform SURALP is discussed with the mechanical, electronic, walking reference generation and control aspects. The fuzzy reference adjustment system proposed for the walk on inclined planes is detailed and experimental results are presented

Slipping and Tripping Reflexes for Bipedal Robots

Many robot applications require legged robots to traverse rough or unmodeled terrain. This paper explores strategies that would enable legged robots to respond to two common types of surface contact error: slipping and tripping. Because of the rapid response required and the difficulty of sensing uneven terrain, we propose a set of reexes that would permit the robot to react without modeling or analyzing the error condition in detail. These re exive responses allow robust recovery from a variety of contact errors. We present simulation trials for single-slip tasks with varying coe cients of friction and single-trip tasks with varying obstacle heights

Slipping and Tripping Reflexes for Bipedal Robots

Many robot applications require legged robots to traverse rough or unmodeled terrain. This paper explores strategies that would enable legged robots to respond to two common types of surface contact error: slipping and tripping. Because of the rapid response required and the difficulty of sensing uneven terrain, we propose a set of reflexes that would permit the robot to react without modeling or analyzing the error condition in detail. These reflexive responses allow robust recovery from a variety of contact errors. We present simulation trials for single-slip tasks with varying coefficients of friction and single-trip tasks with varying obstacle heights. Keywords--- reactive control, reflexes, rough terrain, slipping, tripping, biped locomotion I. Introduction R OUGH terrain occurs not only in natural environments but also in environments that have been constructed or modified for human use. Currently, most legged robots lack the control techniques that would allow them to behave ..

Estudio del deslizamiento del robot Pasibot

Este proyecto tiene dos objetivos claros. Basándose en los modelos del Robot PASIBOT proporcionado por el grupo MAQLAB de la Universidad Carlos III de Madrid, el principal objetivo es obtener dos coeficientes de rozamiento que limiten distintas zonas de deslizamiento del pie de apoyo del Robot cuando camina. El primer coeficiente limita la zona de deslizamiento continuo de la zona de deslizamiento discontinuo y el segundo coeficiente limita la zona de deslizamiento discontinuo de la zona de deslizamiento nulo. El segundo objetivo, mediante el estudio del objetivo principal en Working Model 2D y en MSC.Adams, es realizar una comparativa entre los dos programas en lo que respecta al deslizamiento del bípedo PASIBOT, que ayudaría a determinar cuál de los dos programas obtiene unos resultados más veraces. _____________________________________________________________________________________________________________This project has two clear objectives. Based on models of the Robot PASIBOT that group MAQLAB have given me by Carlos III University of Madrid, the main objective is to obtain two coefficients of friction that limit different sliding areas suffering the Robot´s feet when it is walking. The first coefficient of friction limits the continuous sliding zone of the discontinuous sliding zone and the second coefficient of friction is limiting the discontinuous sliding area of the zone of zero slip. The second objective, by studying the main objective in two programs: Working Model 2D and MSC.Adams, is to make a comparison between the two programs in terms of bipedal PASIBOT slip, which would help to determine which of the two programs get more accurate results.Ingeniería Industria