Quadruped robot trotting over irregular terrain assisted by stereo-vision

Legged robots have the potential to navigate in challenging terrain, and thus to exceed the mobility of wheeled vehicles. However, their control is more difficult as legged robots need to deal with foothold computation, leg trajectories and posture control in order to achieve successful navigation. In this paper, we present a new framework for the hydraulic quadruped robot HyQ, which performs goal-oriented navigation on unknown rough terrain using inertial measurement data and stereo-vision. This work uses our previously presented reactive controller framework with balancing control and extends it with visual feedback to enable closed-loop gait adjustment. On one hand, the camera images are used to keep the robot walking towards a visual target by correcting its heading angle if the robot deviates from it. On the other hand, the stereo camera is used to estimate the size of the obstacles on the ground plane and thus the terrain roughness. The locomotion controller then adjusts the step height and the velocity according to the size of the obstacles. This results in a robust and autonomous goal-oriented navigation over difficult terrain while subject to disturbances from the ground irregularities or external forces. Indoor and outdoor experiments with our quadruped robot show the effectiveness of this framework.     

轮式移动机器人航向跟踪预估控制算法

本文提出了一种轮式移动机器人航向跟踪预估控制算法,航向预估量根据机器人前 轮偏角和纵向速度实时得出,预估量与机器人实际航向之和作为控制反馈航向.仿真和实验 时用PID控制器和航向预估算法结合进行航向跟踪,结果表明该算法与常规PID算法相比,对 机器人纵向速度适应范围较宽,能有效地改善控制器的动态特性,表现出了较好的自适应能 力.     

Gait transition and modulation in a quadruped robot: A brainstem-like modulation approach

In this article, we propose a bio-inspired architecture for a quadruped robot that is able to initiate/stop locomotion; generate different gaits, and to easily select and switch between the different gaits according to the speed and/or the behavioral context. This improves the robot stability and smoothness while locomoting.We apply nonlinear oscillators to model Central Pattern Generators (CPGs). These generate the rhythmic locomotor movements for a quadruped robot. The generated trajectories are modulated by a tonic signal, that encodes the required activity and/or modulation. This drive signal strength is mapped onto sets of CPG parameters. By increasing the drive signal, locomotion can be elicited and velocity increased while switching to the appropriate gaits. This drive signal can be specified according to sensory information or set a priori.The system is implemented in a simulated and real AIBO robot. Results demonstrate the adequacy of the architecture to generate and modulate the required coordinated trajectories according to a velocity increase; and to smoothly and easily switch among the different motor behaviors.     

Three-dimensional locomotion control of single-legged robot: Resonance hopping and running direction

This study proposes a locomotion controller for a single-legged robot. The locomotion controller comprises five parts: virtual spring, height control, forward velocity control, body attitude control, and angular momentum control. First, we propose an effective method called a virtual spring to generate a springy force using a linear actuator. Two virtual springs are adopted to compute the energy exchange and to compensate the energy loss during hopping. A simple and intuitive method is proposed to implement resonance oscillation in terms of energy loss. A height controller is proposed based on the resonance oscillation using a virtual spring. In addition, a running direction controller, which has never been resolved in previous studies, is proposed. This novel controller can remove the unexpected angular momentum about the yaw direction during running. All of the proposed algorithms and methods are validated through dynamic simulations.     

Asymptotically stable path following for lateral motion of an unmanned ground vehicle

This study proposes an asymptotically stable path following controller for autonomous navigation of an unmanned ground vehicle (UGV) using vector field and robust-integral-signum error (RISE) feedback. The path following controller is divided into two parts: one part generating a heading command and another part designing a robust control. To determine the reference heading command under various uncertainties, the vector field method is employed, and then the RISE feedback controller is designed to follow the heading command. Finally, experiments are conducted on paved and unpaved roads to validate the effectiveness of the proposed method.     

An unsupervised neural network for low-level control of a wheeledmobile robot: noise resistance, stability, and hardware implementation

We have recently introduced a neural network mobile robot controller (NETMORC). This controller, based on previously developed neural network models of biological sensory-motor control, autonomously learns the forward and inverse odometry of a differential drive robot through an unsupervised learning-by-doing cycle. After an initial learning phase, the controller can move the robot to an arbitrary stationary or moving target while compensating for noise and other forms of disturbance, such as wheel slippage or changes in the robot's plant. In addition, the forward odometric map allows the robot to reach targets in the absence of sensory feedback. The controller is also able to adapt in response to long-term changes in the robot's plant, such as a change in the radius of the wheels. In this article we review the NETMORC architecture and describe its simplified algorithmic implementation, we present new, quantitative results on NETMORC's performance and adaptability under noise-free and noisy conditions, we compare NETMORC's performance on a trajectory-following task with the performance of an alternative controller, and we describe preliminary results on the hardware implementation of NETMORC with the mobile robot ROBUTER.     

Self-organized adaptive legged locomotion in a compliant quadruped robot

In this contribution we present experiments of an adaptive locomotion controller on a compliant quadruped robot. The adaptive controller consists of adaptive frequency oscillators in different configurations and produces dynamic gaits such as bounding and jumping. We show two main results: (1) The adaptive controller is able to track the resonant frequency of the robot which is a function of different body parameters (2) controllers based on dynamical systems as we present are able to “recognize” mechanically intrinsic modes of locomotion, adapt to them and enforce them. More specifically the main results are supported by several experiments, showing first that the adaptive controller is constantly tracking body properties and readjusting to them. Second, that important gait parameters are dependent on the geometry and movement of the robot and the controller can account for that. Third, that local control is sufficient and the adaptive controller can adapt to the different mechanical modes. And finally, that key properties of the gaits are not only depending on properties of the body but also the actual mode of movement that the body is operating in. We show that even if we specify the gait pattern on the level of the CPG the chosen gait pattern does not necessarily correspond to the CPG’s pattern. Furthermore, we present the analytical treatment of adaptive frequency oscillators in closed feedback loops, and compare the results to the data from the robot experiments.

Gait pattern changing of quadruped robot using pulse-type hardware neural networks

This paper studied about gait pattern changing of the constructed quadruped robot system using pulse-type hardware neural networks (P-HNN). We constructed the 20 cm in size prototype quadruped robot system. Quadruped robot system consisted of mechanical components and electrical components. The mechanical components consisted of four legs, body frames and four servo motors. Quadruped animal-like locomotion could realize by only four servo motors using link mechanisms to each leg. The electrical components consisted of P-HNN, power supply circuit, control board and battery. P-HNN was constructed by analog discrete circuits which could mount on top of the quadruped robot. As a result, constructed P-HNN could output the locomotion rhythms which were necessary to generate the gait pattern of the quadruped robot. P-HNN could output the locomotion rhythms without using software programs or analog digital converter. In addition, P-HNN could change the locomotion rhythms by inputting the trigger pulse to the P-HNN. Our constructed quadruped robot system could perform the locomotion without using external devices.     

Target point‐based path‐following controller for a car‐type vehicle using bounded controls

In this paper, we have studied the control problem of target point‐based path following for car‐type vehicles. This special path‐following task arises from the needs of vision‐based guidance systems, where a given target point located ahead of the vehicle, in the visual range of the camera, must follow a specified path. A solution to this problem is developed through a nonlinear transformation of the path‐following problem into a reference trajectory tracking problem, by modeling the target point as a virtual vehicle. The use of target point complicates the control problem, as the development produces a first‐order nonlinear nonglobally Lipschitz differential equation with finite escape time. This problem is solved by using small control signals. Bounded feedback laws are designed to control the real vehicle's angular acceleration and the virtual vehicle's velocity, to achieve stability. The resulting controller is globally asymptotically stable with respect to the origin, the proof of which is derived from Lyapunov‐based arguments and a bootstrap argument. It is also shown that the use of exponentially convergent observers/differentiators does not affect the stability of the closed‐loop system. The effectiveness of this controller has been illustrated through simulations. Copyright © 2014 John Wiley & Sons, Ltd.     

Central pattern generator based reflexive control of quadruped walking robots using a recurrent neural network

This paper presents a novel Central Pattern Generator (CPG) model for controlling quadruped walking robots. The improvement of this model focuses on generating any desired waveforms along with accurate online modulation. In detail, a well-analyzed Recurrent Neural Network is used as the oscillators to generate simple harmonic periodic signals that exhibit limit cycle effects. Then, an approximate Fourier series is employed to transform those mentioned simple signals into arbitrary desired outputs under the phase constraints of several primary quadruped gaits. With comprehensive closed-form equations, the model also allows the user to modulate the waveform, the frequency and the phase constraint of the outputs online by directly setting the inner parameters without the need for any manual tuning. In addition, an associated controller is designed using leg coordination Cartesian position as the control state space based on which stiffness control is performed at sub-controller level. In addition, several reflex modules are embedded to transform the feedback of all sensors into the CPG space. This helps the CPG recognize external disturbances and utilize inner limit cycle effect to stabilize the robot motion. Finally, experiments with a real quadruped robot named AiDIN III performing several dynamic trotting tasks on several unknown natural terrains are presented to validate the effectiveness of the proposed CPG model and controller.     

An analog CMOS central pattern generator for interlimb coordination in quadruped locomotion.

This paper proposes a neuromorphic analog CMOS controller for interlimb coordination in quadruped locomotion. Animal locomotion, such as walking, running, swimming, and flying, is based on periodic rhythmic movements. These rhythmic movements are driven by the biological neural network, called the central pattern generator (CPG). In recent years, many researchers have applied CPG to locomotion controllers in robotics. However, most of these have been developed with digital processors and, thus, have several problems, such as high power consumption. In order to overcome such problems, a CPG controller with analog CMOS circuit is proposed. Since the CMOS transistors in the circuit operate in their subthreshold region and under low supply voltage, the controller can reduce power consumption. Moreover, low-cost production and miniaturization of controllers are expected. We have shown through computer simulation, such circuit has the capability to generate several periodic rhythmic patterns and transitions between their patterns promptly.     

四足机器人对角小跑步态非线性控制方法仿真

针对现有的四足机器人对角小跑步态控制方法存在的机器人运动速度较慢、灵活性较差等问题,提出了一种基于虚拟模型的四足机器人对角小跑步态非线性控制方法。方法需要构建一个四足机器人模型,并在该模型的工作范围内建立一个平面直角坐标系,在不考虑机器人足端车轮滑动的情况下,将驱动四足机器人的运动方程转换成矩阵的形式,寻找有界输入平动线速度和转动角速度,使矩阵在其控制下产生的误差可以在大范围内保持稳定。求解该四足机器人在工作平面坐标系中姿态误差的微分方程,构造该微分方程的Lyapunov函数并对其求导,根据求导结果设计一个四足机器人驱动控制器,通过该驱动控制器实现对四足机器人的对角小跑步态非线性控制。仿真结果表明,所提方法能够在快速、灵活的情况下实现对四足机器人对角小跑步态的非线性控制,且鲁棒性较高,能够满足用户需求。     

Roll of the rhythmic component in the proactive control of a human hand

In terms of evolution, the strategy of catching prey would have been an important part of survival in a constantly changing environment. A prediction mechanism would have developed to compensate for any delay in the sensory-motor system. In a previous study, “proactive control” was found, in which the motion of the hands preceded the virtual moving target. These results implied that the positive phase shift of the hand motion represents the proactive nature of the visual-motor control system, which attempts to minimize the brief error in the hand motion when the target changes position unexpectedly. In our study, a visual target moves in circle (13 cm diameter) on a computer screen, and each subject is asked to keep track of the target’s motion by the motion of a cursor. As the frequency of the target increases, a rhythmic component was found in the velocity of the cursor in spite of the fact that the velocity of the target was constant. The generation of a rhythmic component cannot be explained simply as a feedback mechanism for the phase shifts of the target and cursor in a sensory-motor system. Therefore, it implies that the rhythmic component was generated to predict the velocity of the target, which is a feed-forward mechanism in the sensory-motor system. Here, we discuss the generation of the rhythmic component and its roll in the feed-forward mechanism.     

Vision-based hybrid control scheme for autonomous parking of a mobile robot

This paper presents a novel vision-based hybrid controller for parking of mobile robots. Parking or docking is an essential behavioral unit for autonomous robots. The proposed hybrid controller comprises a discrete event controller to change the direction of travel and a pixel error-driven proportional controller to generate motion commands to achieve the continuous motion. At the velocity control level, the robot is driven using a built-in PID control system. The feedback system uses image plane measurements in pixel units to perform image-based visual servoing (IBVS). The constraints imposed due to the non-holonomic nature of the robot and the limited field of view of the camera are taken into account in designing the IBVS-based controller. The controller continuously compares the current view of the parking station against the reference view until the desired parking condition is achieved. A comprehensive analysis is provided to prove the convergence of the proposed method. Once the parking behavior is invoked, the robot has the ability to start from any arbitrary position to achieve successful parking given that initially the parking station is in the robot's field of view. As the method is purely based on vision the hybrid controller does not require any position information (or localization) of the robot. Using the Pioneer 3AT robot, several experiments are carried out to authenticate the method. The experimental system has the ability to achieve the parking state and align laterally within ±0.5 cm of the target pose.     

Autonomous feature following for visual surveillance using a small unmanned aerial vehicle with gimbaled camera system

This paper represents the development of feature following control and distributed navigation algorithms for visual surveillance using a small unmanned aerial vehicle equipped with a low-cost imaging sensor unit. An efficient map-based feature generation and following control algorithm is developed to make an onboard imaging sensor to track a target. An efficient navigation system is also designed for real-time position and velocity estimates of the unmanned aircraft, which is used as inputs for the path following controller. The performance of the proposed autonomous path following capability with a stabilized gimbaled camera onboard a small unmanned aerial robot is demonstrated through flight tests with application to target tracking for real-time visual surveillance.     

Dynamic turning control of a quadruped locomotion robot using oscillators

We propose a dynamic turning control system for a quadruped robot that uses non-linear oscillators. It is composed of a spontaneous locomotion controller and voluntary motion controller. We verified the mechanical capabilities of the dynamic turning motion of the proposed control system through numerical simulations and hardware experiments. Various turning speeds and orientations made the motion of the robot asymmetrical in terms of the duty ratio, stride and center of pressure. The proposed controller actively and adaptively controlled redundant degrees of freedom to cancel out dynamic asymmetry, and established stable turning motion at various locomotion speeds and turning orientations.     

A Smooth Path Tracking Algorithm for Wheeled Mobile Robots with Dynamic Constraints

In order to avoid wheel slippage or mechanical damage during the mobile robot navigation, it is necessary tosmoothly change driving velocity or direction of the mobile robot. This means that dynamic constraints of the mobile robotshould be considered in the design of path tracking algorithm. In the study, a path tracking problem is formulated asfollowing a virtual target vehicle which is assumed to move exactly along the path with specified velocity. The drivingvelocity control law is designed basing on bang-bang control considering the acceleration bounds of driving wheels. Thesteering control law is designed by combining the bang-bang control with an intermediate path called the landing curve whichguides the robot to smoothly land on the virtual target's tangential line. The curvature and convergence analyses providesufficient stability conditions for the proposed path tracking controller. A series of path tracking simulations and experimentsconducted for a two-wheel driven mobile robot show the validity of the proposed algorithm.     

Observer-Based Path Tracking Controller Design for Autonomous Ground Vehicles With Input Saturation

This paper investigates the problem of path tracking control for autonomous ground vehicles (AGVs), where the input saturation, system nonlinearities and uncertainties are considered. Firstly, the nonlinear path tracking system is formulated as a linear parameter varying (LPV) model where the variation of vehicle velocity is taken into account. Secondly, considering the noise effects on the measurement of lateral offset and heading angle, an observer-based control strategy is proposed, and by analyzing the frequency domain characteristics of the derivative of desired heading angle, a finite frequency H_∞ index is proposed to attenuate the effects of the derivative of desired heading angle on path tracking error. Thirdly, sufficient conditions are derived to guarantee robust H_∞ performance of the path tracking system, and the calculation of observer and controller gains is converted into solving a convex optimization problem. Finally, simulation examples verify the advantages of the control method proposed in this paper.      

Combining series elastic actuation and magneto-rheological damping for the control of agile locomotion

All-terrain robot locomotion is an active topic of research. Search and rescue maneuvers and exploratory missions could benefit from robots with the abilities of real animals. However, technological barriers exist to ultimately achieving the actuation system, which is able to meet the exigent requirements of these robots. This paper describes the locomotion control of a leg prototype, designed and developed to make a quadruped walk dynamically while exhibiting compliant interaction with the environment. The actuation system of the leg is based on the hybrid use of series elasticity and magneto-rheological dampers, which provide variable compliance for natural-looking motion and improved interaction with the ground. The locomotion control architecture has been proposed to exploit natural leg dynamics in order to improve energy efficiency. Results show that the controller achieves a significant reduction in energy consumption during the leg swing phase thanks to the exploitation of inherent leg dynamics. Added to this, experiments with the real leg prototype show that the combined use of series elasticity and magneto-rheological damping at the knee provide a 20 % reduction in the energy wasted in braking the knee during its extension in the leg stance phase.     

Markerless visual servo control of a servosphere for behavior observation of a variety of wandering animals

ABSTRACT

Servospheres are robotized observation equipments that produce endless fields for behavior observation of wandering animals. This paper first proposes a markerless visual tracking technique for estimation of the position and the heading direction of wandering animals, since existing techniques for servospheres require special markers or do not estimate the heading direction. The proposed markerless visual tracking technique is then integrated with a visual servo controller for a servosphere. The integrated markerless visual servo controller is available for wandering animals whose shapes in the image plane are represented by long bodies and thinner parts than their bodies. This paper demonstrates that the proposed controller is available for ants, crickets, mantises and spiders, while the shapes of their bodies and legs are different from each other.