Robot Foot Research Articles

Synergy-Based Gaussian Process Estimation of Ankle Angle and Torque: Conceptualization for High Level Controlling of Active Robotic Foot Prostheses/Orthoses.

Human gait is the result of a complex and fascinating cooperation between different joints and segments in the lower extremity. This study aims at investigating the existence of this cooperation or the so-called synergy between the shank motion and the ankle motion. One potential use of this synergy is to develop the high level controllers for active foot prostheses/orthoses. The central point in this paper is to develop a high level controller that is able to continuously map shank kinematics (inputs) to ankle angles and torques (outputs). At the same time, it does not require speed determination, gait percent identification, switching rules, and look-up tables. Furthermore, having those targets in mind, an important part of this study is to determine which input type is required to achieve such targets. This should be fulfilled through using minimum number of inputs. To do this, the Gaussian process (GP) regression has been used to estimate the ankle angles and torques for 11 subjects at three walking speeds (0.5, 1, and 1.5 m/s) based on the shank angular velocity and angle. The results show that it is possible to estimate ankle motion based on the shank motion. It was found that the estimation achieved less quality with only shank angular velocity or angle, whereas the aggregated angular velocity and angle resulted in much higher output estimation quality. In addition, the estimation quality was acceptable for the speeds that there was a training procedure before and when it was tested for the untrained speeds, the estimation quality was not as acceptable as before. The pros and cons of the proposed method are investigated at different scenarios.

Effect of toe joint stiffness and toe shape on walking biomechanics

During typical human walking, the metatarsophalangeal joints undergo extension/flexion, which we term toe joint articulation. This toe joint articulation impacts locomotor performance, as evidenced by prior studies on prostheses, footwear, sports and humanoid robots. However, a knowledge gap exists in our understanding of how individual toe properties (e.g. shape, joint stiffness) affect bipedal locomotion. To address this gap, we designed and built a pair of adjustable foot prostheses that enabled us to independently vary different toe properties, across a broad range of physiological and non-physiological values. We then characterized the effects of varying toe joint stiffness across a range of different ankle joint stiffness conditions, and the effects of varying toe shape on walking biomechanics. Ten able-bodied individuals walked on a treadmill with prostheses mounted bilaterally underneath simulator boots (which immobilized their biological ankles). We collected motion capture and ground reaction force data, then computed joint kinematics and kinetics, and center-of-mass (COM) power and work. To our surprise, we found that varying toe joint stiffness affected COM Push-off dynamics during walking as much as, or in some cases even more than, varying ankle joint stiffness. Increasing toe joint stiffness increased COM Push-off work by up to 48% (6 J), and prosthetic anklefoot Push-off work by up to 181% (12 J). In contrast, large changes in toe shape had little effect on gait. This study brings attention to the toes, an aspect of prosthetic and robotic foot design that is often overlooked or overshadowed by design of the ankle. Optimizing toe joint stiffness in assistive and robotic devices (e.g. prostheses, exoskeletons, robot feet) may provide a complementary means of enhancing Push-off or other aspects of locomotor performance, in conjunction with the more conventional approach of augmenting ankle dynamics. Future studies are needed to isolate the effects of additional toe properties (e.g. toe length).

Force Balance Control and Optimization of the Quadruped Hydraulic Robot Based on Materials Structure Design

In this paper, in order to meet the requirements of stable foot support and balanced walking of quadruped hydraulic robot, a new control method is proposed. The "hard" contact between the feet of the quadruped hydraulic robot and the ground are changed into "semi flexible" contact to reduce the impact force produced by the contact and collision of the two and reduce the unbalance of the force. The designed "semi flexible" scheme was to coat the "semi flexible" modified polytetrafluoroethylene (PTFE) material on the surface of the bottom material of the robot's foot. The modification of PTFE was optimized by SRIM, and the optimization scheme was selected for experimental study to obtain the Al2O3/PTFE material for which the abrasive resistance met the requirement of robot motion. It was also used in robot force imbalance control experiment research optimization. The study clearly revealed that it can effectively reduce the power of the impact force caused by the contact and collision of the feet of the quadruped robot and the ground, reduce the swing and the unbalance of the motion force of the quadruped robot, and meet the requirements of the precise positioning and the force balance walking of the motion of quadruped hydraulic robot to a certain extent.

Accurate and robust localization for walking robots fusing kinematics, inertial, vision and LIDAR.

In this article, we review methods for localization and situational awareness of biped and quadruped robotics. This type of robot is modelled as a free-floating mechanical system subject to external forces and constrained by whole-body distributed rigid contacts. Measurements of the state of the robot can be made using a variety of sensor information-such as kinematics (the sensing of the joint angles of the robot), contact force (pressure sensors in the robot's feet), accelerometers and gyroscopes as well as external sensors such as vision and LIDAR. This high-frequency state estimate is then passed to the control system of the robot to allow it to traverse terrain or manipulate its environment. In this article, we describe the development of an estimator for the Boston Dynamics Atlas humanoid robot. It was later adapted to the HyQ2 quadruped, developed by the Istituto Italiano di Tecnologia. Some discussion is given as to future trends while also considering briefly the relationship with biological systems.

Position tracking control in torque mode for a robotic running foot for footwear testing

Available automatic footwear testing systems still lack flexibility and bio-fidelity to represent the human foot and reproduce the wear conditions accurately. The first part of this article introduces a new design of the robotic running foot for footwear testing using cable conduit mechanisms. This robotic running foot is integrated with an upper leg mechanism to form a complete integrated footwear testing system. The cable conduit mechanisms help remove the bulky actuators and transmissions out of the fast-moving robotic foot. Thus, this robotic running foot design not only allows high-power actuators to be installed, but also avoids a significant dynamic mass and inertia effects on the upper leg mechanism. This means that the integrated footwear testing system can have multiple powered degrees of freedom in the robotic running foot and simulate much higher human running speeds than other available systems. However, cable conduit mechanisms cause significant challenges in control approaches, especially in high-speed systems, due to their nonlinear transmission characteristics. Furthermore, the robotic running foot actuators must operate in a torque/force control mode to reproduce the foot–shoe interaction during gaits while it is critical to control the foot joints’ position in the swing phase of gaits. The latter part of this article presents a study on position tracking control in torque mode for the robotic running foot joints using adaptive and proportional–integral–derivative control designs to evaluate the system’s ability to mimic the human foot kinematics in running. Both controllers proved their effectiveness, implying that the proposed control approach can be implemented on the integrated footwear testing system to control the foot joints’ position in the swing phase of running gaits.

Direct torque control for cable conduit mechanisms for the robotic foot for footwear testing

As the shoe durability is affected directly by the dynamic force/pressure between the shoe and its working environments (i.e., the contact ground and the human foot), a footwear testing system should replicate correctly this interaction force profile during gait cycles. Thus, in developing a robotic foot for footwear testing, it is important to power multiple foot joints and to control their output torque to produce correct dynamic effects on footwear. The cable conduit mechanism (CCM) offers great advantages for designing this robotic foot. It not only eliminates the cumbersome actuators and significant inertial effects from the fast-moving robotic foot but also allows a large amount of energy/force to be transmitted/propagated to the compact robotic foot. However, CCMs cause nonlinearities and hysteresis effects to the system performance. Recent studies on CCMs and hysteresis systems mostly addressed the position control. This paper introduces a new approach for modelling the torque transmission and controlling the output torque of a pair of CCMs, which are used to actuate the robotic foot for footwear testing. The proximal torque is used as the input signal for the Bouc–Wen hysteresis model to portray the torque transmission profile while a new robust adaptive control scheme is developed to online estimate and compensate for the nonlinearities and hysteresis effects. Both theoretical proof of stability and experimental validation of the new torque controller have been carried out and reported in this paper. Control experiments of other closed-loop control algorithms have been also conducted to compare their performance with the new controller effectiveness. Qualitative and quantitative results show that the new control approach significantly enhances the torque tracking performance for the system preceded by CCMs.

A soft robot capable of 2D mobility and self-sensing for obstacle detection and avoidance

Soft robots have shown great potential for surveillance applications due to their interesting attributes including inherent flexibility, extreme adaptability, and excellent ability to move in confined spaces. High mobility combined with the sensing systems that can detect obstacles plays a significant role in performing surveillance tasks. Extensive studies have been conducted on movement mechanisms of traditional hard-bodied robots to increase their mobility. However, there are limited efforts in the literature to explore the mobility of soft robots. In addition, little attempt has been made to study the obstacle-detection capability of a soft mobile robot. In this paper, we develop a soft mobile robot capable of high mobility and self-sensing for obstacle detection and avoidance. This robot, consisting of a dielectric elastomer actuator as the robot body and four electroadhesion actuators as the robot feet, can generate 2D mobility, i.e. translations and turning in a 2D plane, by programming the actuation sequence of the robot body and feet. Furthermore, we develop a self-sensing method which models the robot body as a deformable capacitor. By measuring the real-time capacitance of the robot body, the robot can detect an obstacle when the peak capacitance drops suddenly. This sensing method utilizes the robot body itself instead of external sensors to achieve detection of obstacles, which greatly reduces the weight and complexity of the robot system. The 2D mobility and self-sensing capability ensure the success of obstacle detection and avoidance, which paves the way for the development of lightweight and intelligent soft mobile robots.

Design and Analysis of a Six-Dimensional Force Sensor

In order to obtain the force of the foot of a multi-foot robot, a new type of structure based on the sliding axis is proposed. [1] This structure is improved based on the traditional cross beam six-dimensional force sensor. The structural characteristics of the sensor and the principle of force measurement are analyzed. Static and dynamic simulation of the elastic body is carried out by using the finite element method. The deformed cloud, strain cloud, mode shape and natural frequency of the elastic element are obtained. According to the result of finite element analysis, the position of the patch is simulated in the three-dimensional model, and the elastic element of the sensor is decoupled and linearity analyzed. Finally, the calibration matrix of the sensor is obtained.

A Bio-Inspired Control Strategy for Locomotion of a Quadruped Robot

In order to effectively plan the robot gaits and foot workspace trajectory (WT) synchronously, a novel biologically inspired control strategy for the locomotion of a quadruped robot based on central pattern generator—neural network—workspace trajectory (CPG-NN-WT) is presented in this paper. Firstly, a foot WT is planned via the Denavit-Hartenberg (D-H) notation and the inverse kinematics, which has the advantages of low mechanical shock, smooth movement, and sleek trajectory. Then, an improved central pattern generator (CPG) based on Hopf oscillators is proposed in this paper for smooth gait planning. Finally, a neural network is designed and trained to convert the CPG output to the preplanned WT, which can make full use of the advantages of the CPG-based method in gait planning and the WT-based method in foot trajectory planning simultaneously. Furthermore, virtual prototype simulations and experiments with a real quadruped robot are presented to validate the effectiveness of the proposed control strategy. The results show that the gait of the quadruped robot can be controlled easily and effectively by the CPG with its internal parameters; meanwhile, the foot trajectory meets the preplanned WT well.

Research on the model of Human-Robot football professional skills competition

In this paper, the robot (humanoid robot) soccer activity is decomposed according to the process of Human-Robot football professional skill competition. This paper analyzes the shooting problem of robot in the forward range and outside the range of the door frame, applies it to the rotation angle of robot foot, and gives the mathematical model of linear motion through the force of the center of the ball. Then, the further research direction are discussed.

Design and Development of an IOT Based Multi Terrain Humanoid Robot Foot

Design and Development of an IOT Based Multi Terrain Humanoid Robot Foot

Nonanthropomorphic exoskeleton with legs based on eight-bar linkages

This article presents the principles upon which a new nonanthropomorphic biped exoskeleton was designed, whose legs are based on an eight-bar mechanism. The main function of the exoskeleton is to assist people who have difficulty walking. Every leg is based on the planar Peaucellier–Lipkin mechanism, which is a one degree of freedom linkage. To be used as a robotic leg, the Peaucellier–Lipkin mechanism was modified by including two more degrees of freedom, as well as by the addition of a mechanical system based on toothed pulleys and timing belts that provides balance and stability to the user. The use of the Peaucellier–Lipkin mechanism, its transformation from one to three degrees of freedom, and the incorporation of the stability system are the main innovations and contributions of this novel nonanthropomorphic exoskeleton. Its mobility and performance are also presented herein, through forward and inverse kinematics, together with its application in carrying out the translation movement of the robotic foot along paths with the imposition of motion laws based on polynomial functions of time.

Leg placement algorithm for foot impact force minimization

Walking is considered to be a rather complicated task for autonomous robots. Sustaining dynamic stability, adopting different gaits, and calculating correct foot placement are a necessity to overcome irregular terrain, various environments and completing a range of assignments. Besides that, certain assignments require that robots have to walk on fragile surfaces without damaging it. Furthermore, under some other circumstances, if walking is careless, robots could suffer damage caused by the impact of the terrain. Foot placement, leg motion speed must be controlled to avoid braking surface or even sensors on robot’s feet. In this article, a simple leg placement algorithm is proposed that controls hexapod robot’s leg speed. Thus, force dependence on leg motion speed and step height has been measured by using a piezoelectric sensor. Then, by using leg placement algorithm, we show that the reduction of the impact force between robot’s foot and surface is possible. Using this algorithm, robot feet’s impact force with the surface can be minimized to almost 0 N.

Momentum Control of an Underactuated Flying Humanoid Robot

The letter takes the first step toward the development of a control framework for underactuated flying humanoid robots. These robots may thus have the capacities of flight , contact locomotion , and manipulation , and benefit from technologies and methods developed for Whole-Body Control and Aerial Manipulation . As in the case of quadrotors, we assume that the humanoid robot is powered by four thrust forces. For convenience, these forces are placed at the robot hands and feet. The control objective is defined as the asymptotic stabilization of the robot centroidal momentum. This objective allows us to track a desired trajectory for the robot center of mass and keep small errors between a reference orientation and the robot base frame. Stability and convergence of the robot momentum are shown to be in the sense of Lyapunov. Simulations carried out on a model of the humanoid robot iCub verify the soundness of the proposed approach.

Design and Experimental Development of a Pneumatic Stiffness Adjustable Foot System for Biped Robots Adaptable to Bumps on the Ground

Walking on rough terrains still remains a challenge that needs to be addressed for biped robots because the unevenness on the ground can easily disrupt the walking stability. This paper proposes a novel foot system with passively adjustable stiffness for biped robots which is adaptable to small-sized bumps on the ground. The robotic foot is developed by attaching eight pneumatic variable stiffness units to the sole separately and symmetrically. Each variable stiffness unit mainly consists of a pneumatic bladder and a mechanical reversing valve. When walking on rough ground, the pneumatic bladders in contact with bumps are compressed, and the corresponding reversing valves are triggered to expel out the air, enabling the pneumatic bladders to adapt to the bumps with low stiffness; while the other pneumatic bladders remain rigid and maintain stable contact with the ground, providing support to the biped robot. The performances of the proposed foot system, including the variable stiffness mechanism, the adaptability on the bumps of different heights, and the application on a biped robot prototype are demonstrated by various experiments.

Research on the Integration of Bionic Geometry Modeling and Simulation of Robot Foot Based on Characteristic Curve

The bionic research of shape is an important aspect of the research on bionic robot, and its implementation cannot be separated from the shape modeling and numerical simulation of the bionic object, which is tedious and time-consuming. In order to improve the efficiency of shape bionic design, the feet of animals living in soft soil and swamp environment are taken as bionic objects, and characteristic skeleton curve, section curve, joint rotation variable, position and other parameters are used to describe the shape and position information of bionic object’s sole, toes and flipper. The geometry modeling of the bionic object is established by using the parameterization of characteristic curves and variables. Based on this, the integration framework of parametric modeling and finite element modeling, dynamic analysis and post-processing of sinking process in soil is proposed in this paper. The examples of bionic ostrich foot and bionic duck foot are also given. The parametric modeling and integration technique can achieve rapid improved design based on bionic object, and it can also greatly improve the efficiency and quality of robot foot bionic design, and has important practical significance to improve the level of bionic design of robot foot’s shape and structure.

Soil arching effect analysis and structure optimization of a robot foot sinking in soft soil

In this study, to analyze the influence of the cross-sectional shape of a rigid foot on its sinking performance in soft soil, a numerical model of the subsidence of a single leg was built using the arbitrary Lagrangian–Eulerian method in ABAQUS to describe the interaction between the foot and soil. After performing a simulation of circular, annular, X-shaped, and improved X-shaped feet, all with the same cross-sectional area, the end resistance, side resistance, and distribution of contact pressure along the radial direction were analyzed. The simulation results showed that the soil arching area caused by the hole at the bottom of a rigid foot can effectively increase the end resistance and that the side resistance increases with an increase in the side perimeter. The end resistance and side resistance of the improved X-shaped robot foot were higher than those of the X-shaped robot foot during the sinking process. The effects of the improved geometric parameters of the X-shaped robot foot on its sinkage w...

Terrain edge detection for biped walking robots using active sensing with vCoP-position hybrid control

Perception of terrain is one of the most important technical impediments for biped robots to locomote in human environments. Perception error exists due to imperfect exteroceptive devices causing issues such as limited viewing angles or occlusion of visual sensors. This error can cause unexpected contact between the robot and the environment. The reaction wrenches from unexpected contact negatively affect the control and balance of the biped robot. In this study, active sensing method is proposed to estimate the edges of the contact terrain using robot link geometry information. By generating proper active motion that maintains the contact, the geometric information of the contact link is collected to estimate the edge of the contact terrain. To recognize contact and calculate its geometry, a multi-modal sensory strategy with 6 degrees of freedom (DOF) force/torque sensors at robot ankles and joint encoders is proposed. The concept of virtual Center-of-Pressure (vCoP) is utilized to generate active motion of the foot while maintaining the contact. To prevent loss of balance during active motion, the normal force condition of the vCoP is taken into account and the contact moment of the supporting foot is controlled. The operational space control scheme for a floating-base robot is adopted to apply compliant motion and vCoP-position hybrid control framework. The proposed method is verified by experiments using a 12-DOF biped robot to estimate the edge line of a block that has contact with the robot foot.

Generating Feasible Solutions for Dynamically Crossing a Wide Ditch by a Biped Robot

The aim of this research work is to generate feasible motion for a biped robot to dynamically cross a wide ditch which is defined as a ditch with width more than or equal to the leg length. We propose an approach to obtain feasible solutions for dynamically crossing the wide ditch considering the dynamic balance of the biped robot, friction between the robot foot and ground, impact on the foot, limitations on the joint actuator torques and angular velocities. The biped robot is modeled as a seven link planar robot with the ditch crossing task consisting of two single support phases and a double support phase. An algorithm is developed to find the joint trajectories and the joint torques in each phase of ditch crossing by formulating the ditch crossing task as a constrained nonlinear optimization problem. In order to make the algorithm converge fast and to give feasible solutions, additional constraints called Adopted Constraints (ACs) are incorporated into the system of constraints. With time being one of the parameters, the developed algorithm adaptively adjusts the time for crossing a wide ditch. The significance of ground reaction force constraints in obtaining feasible solutions for crossing the wide ditch is shown through simulations. Feasible solutions obtained from simulation results provide not only the feasible joint angle trajectories, but also the joint torques required for the selection of actuators for a biped robot crossing the wide ditch.

Hexapod Adaptive Gait Inspired by Human Behavior for Six-Legged Robot Without Force Sensor

Legged robots are usually installed with force sensors in order to negotiate with the uneven ground. To eliminate the risk of force sensor failure, adaptive gaits integrating indirect force-estimation are of great importance. Robot Octopus III is a robot designed for carrying a payload in the harsh environment. There is no electric device installed on the lower limb of the robot. The indirect force-estimation method, which is based on its spatial parallel mechanism leg, can estimate the external force exerted on the foot tip. In this paper, an adaptive gait is designed after observing human actions. Experiments are carried out to observe how a human walks through the uneven ground when his/her eyes are covered. A static tripod gait mimics the human behavior during the blind walking. When the foot collides with the obstacle, the robot will adjust the foot’s height and try to overcome the obstacle. Just like human blind walking, the robot foot tries different locations before it steps on somewhere. The gait also detects if the robot is facing a ditch too deep to step or an obstacle is too high to step on. The gait is implemented in the real-time control system. Experiments are carried out to validate the proposed gait. The robot walked through the uneven ground with maximum obstacle height of 0.2m successfully. The proposed gait enables the robot without foot tip force sensors to walk through the field with obstacles.