Gait control for redundant legged biped robot at constant velocity and constant height of the waist

In this paper, we propose a gait control method for redundant legged biped robot based on leg center of mass (COM) position control at constant velocity and constant height of the waist. The developed biped robot has redundant legs, which have four degrees of freedoms (DOFs) on each in the sagittal plane. The redundant DOF enables movement of its leg tip position and its leg COM position independently. Therefore, the proposed robot has structural capability to control the leg COM position for maintaining the projection of the total COM inside the support polygon without upper body motion. Such capability enables the stable static walk in the arbitrarily desired velocity and height of the waist motion. The validity of the proposed method for the static walk at constant velocity and constant height of the waist in the leg COM position control for redundant legged biped robot is confirmed by several results of simulation and experiment. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(4): 51–59, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20357     

复合扰动下双足机器人位姿修正解耦控制研究

双足机器人在驱动步行中受到活动部件的复合扰动作用容易产生耦合误差,导致解耦控制的稳定性不好,为了提高双足机器人驱动步行中的解耦控制的稳定性,提出一种基于变步长动态平衡反馈调节的双足机器人驱动步行位姿修正解耦控制方法。采用分布式传感器阻力力学采集方法进行双足机器人的姿态参量测量和动态融合处理,构建双足机器人驱动步行位姿修正解耦控制的约束参量模型和控制目标函数,采用Kalman滤波方法进行双足机器人驱动步行的地面环境适应校正和误差修正,采用变步长动态平衡反馈调节方法确定精准的驱动步行姿态参量,实现双足机器人准确的姿态定位和参量解算。仿真结果表明,采用该方法进行双足机器人驱动步行姿态定位控制的准确度较高,环境适应性较好,实现零误差驱动步行,提高了双足机器人的控制品质。     

A motion control for two-wheel inverted pendulum type of mobile manipulator

Two-wheel inverted pendulum type of mobile manipulator has no casters and it is expected that quick and robust motion may be realized according to road surface. However the dynamical behavior is so complicated from a viewpoint of motion stability. To address this issue, this paper describes a motion control strategy to realize a stable pushing operation of the two-wheel inverted pendulum type of mobile manipulator. Here the manipulator platform is considered as a passive joint and a stabilization control of the passive joint is achieved by using null space motion of the mobile manipulator. Then workspace observer is also employed to obtain the robust null space motion.The proposed approach is verified by several numerical and experimental results. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

应用于直线电机的平滑切换模糊PID控制方法

为了适应直线电机的快速动态特性,抑制由于直接驱动使参数摄动和负载扰动等不确定因素对伺服特性的影响,提出了一种新的平滑函数模型,设计了平滑切换式模糊PID复合控制器,并应用于直线电机位置伺服控制。通过模糊控制提高伺服系统的动态性能,用PID控制保证系统的稳态性能,利用平滑函数改善控制切换过程。在PRS-XY型混联机床上的应用表明,该控制算法明显提高了伺服系统的动态性能,减小了位置跟随误差,对非线性扰动因素具有良好的适应性。     

基于运动学方法研究人体运动的计算机实现

详细论述了逆运动学方法实现的人体走、跑运动。运动模型是基于人体步态实验多次观察的实验数据构建的。运动控制主要分 3个层级 :首先根据输入参数 (速度、步态 )确定控制运动所需参数 (步长、周期等 ) ;第二层 ,用曲线拟合脚踝及质心在笛卡尔空间中的运动轨迹 ;第三层 ,用逆运动学方法求出人体模型在关节空间中的状态。控制中高层参数的调节可以生成同一种运动的不同运动姿态 ;同时 ,逆运动学方法的使用保证了运动的实时性。最后 ,文章给出了实验数据并指明下一步研究方向     

Quantitative analysis of the ankle strategy under translational platform disturbance.

The ankle strategy is one of the postural adjustment maneuvers humans utilize when the support platform is disturbed. This paper presents a quantitative analysis of the ankle strategy. A three-link sagittal biped model is considered. The first link represents the two legs locked together. The second link represents the two thighs locked together. The third link represents the hip, the torso, the upper limbs, the neck, and the head. The dynamics, control, and stability of the three-link biped, under platform translation, are considered. The disturbance of the platform is represented as an input and the effect of the muscular system is reduced to a set of torques applied to the joints and across the joints. Two digital computer simulations are presented to demonstrate the behavior of the biped under backward or forward platform disturbance. The simulations are compared with experimental measurements of humans subjected to postural disturbances. It is shown that the effect of a horizontal disturbance at the ankle appears to be about 40 times that of the effect of the disturbance at the knees and at least a few hundred times larger than the effect of a disturbance at the hip. This means that, under translational platform disturbance, the ankle angle is subjected to the largest excursion. The knee and the hip angle excursions are relatively minor. Consequently, the biped, as a whole, appears to move as a single inverted pendulum. Major postural corrections are initiated by the ankle excursion. Further, when the available ankle torque is limited or nonexistent, the stability requires resorting to the knee or hip strategies.     

倒立摆的模型和控制问题

小车-倒摆系统常用四阶的运动方程来描述。但如果小车是交流伺服电机来驱动的，交流伺服电机需要和它的控制系统构成一个闭环系统才能工作，使小车的运动受到约束，系统的动态方程退化成为二阶。文中对该系统的特性作了详尽的分析，并指出这样的实验装置适合于研究二阶不稳定对象的镇定问题。     

A Three-Dimensional Biomechanical Evaluation of Quadriceps and Hamstrings Function Using Electrical Stimulation

Neurological disorders such as stroke impair locomotor control and result in abnormal 3-D gait kinematics. Establishment of effective rehabilitation strategies requires an understanding of how individual muscles contribute to pathological movement. Forward dynamic simulations account for complexities of interjoint coupling and can be used to predict dynamic muscle function. However to date, limited experimental validations of dynamic models have been performed. Our objective was to measure 3-D movement induced by the biceps femoris (BF), rectus femoris (RF), and vastus lateralis (VL) in limb configurations corresponding to the swing phase of gait, and to assess the biomechanical factors that affect dynamic function. Subjects were positioned in a robotic gait orthosis that included a compliant interface. Electrical stimulation was introduced into individual muscles while induced hip and knee joint movements were recorded. Measured hip to knee sagittal plane acceleration ratios were consistent with dynamic musculoskeletal model simulations. However RF and VL induced substantially larger frontal plane hip movements than model-based predictions. Sensitivity analyses on musculoskeletal model parameters revealed that muscle function depends primarily on moment arm assumptions. Though generic musculoskeletal models are suitable for predicting sagittal plane muscle function, improvements in moment arm accuracy are essential for investigation of 3-D pathological gait.     

A study on higher‐order disturbance observer and robust stability

In earlier papers, it has been reported that a fast and precise servo system, which has low sensitivity to parameter variation and disturbance, can be realized with simple structure by using a high‐order disturbance observer. However, no clear and simple design method satisfying specifications for robust stability, the influence of measurement noise, and relative stability (damping characteristics) for large parameter variation has been proposed. In this paper, we clarify the class of robust servo systems realized by adjusting the order of the disturbance observer and the control parameters. We apply this strategy to the design of a second delay system, such as a position servo system, and realize a high‐performance robust servo system using a high‐order disturbance observer. © 1999 Scripta Technica, Electr Eng Jpn, 128(1): 37–44, 1999     

相贯曲线插接焊缝冗余扫查机器人运动学分析

针对插接管道相贯焊缝缺陷超声扫查机器人的运动学问题,采用D-H方法建立了连杆坐标系下的机器人运动学模型,并通过实际扫查作业轨迹约束下的仿真实验,验证了该方法求解冗余机器人运动学问题的正确性,保证了机器人关节空间与笛卡儿空间映射的唯一性与轨迹封闭性,为实现插接管道相贯焊缝的连续超声波扫查检测提供可靠的方法。     

Variable Dynamic Threshold of Jerk Signal for Contact Detection in Industrial Robots without Force Sensor

This study proposes a variable dynamic threshold for a jerk signal for achieving contact detection in industrial robots. Sensorless force control is useful in applications in advanced industrial robots. The external torque of each joint is estimated accurately by using a disturbance observer and by inverse dynamics calculations. However, the phase lag of the disturbance observer and the dynamic parameter error create force estimation errors. These errors hamper quick and reliable contact detection in industrial robots. Therefore, this study proposes a useful approach to contact detection that uses a variable dynamic threshold for a jerk signal. The proposed variable dynamic threshold reduces contact detection failures caused by force estimation errors during the free motion of a robot. The proposed threshold is suitable for robot motion and improves the speed of contact detection. Numerical simulation results show that the proposed method is valid for the parameter variations in an actual industrial robot. In addition, experimental results show that the dynamic threshold is a useful technique for application to general robot systems as well. The dynamic threshold is useful in applications for any industrial sensorless force control system.     

Control of biped walking robot for human living environment

This paper introduces biped robot adaptation to human living environment from viewpoints of battery operation time extension and environmental recognition. These issues are important when robots actually work at home. First, in order to extend battery operation time, we propose energy-saving bipedal locomotion gait. The problem is formulated as an optimal control problem, which is conventionally hard to solve when a target system is complicated. In this paper, partial derivatives appeared in optimal control problem are implicitly represented by using automatic differentiation technique. This approach enables complicated optimal control problem solvable. In combination with receding horizon control, its computation cost is also reduced. Second, we introduce the biped walk tracking based on the camera image mounted on the walking robot, and the visual servoing by the posture change for the purpose of the target image tracking in the camera frame. We propose a new control law to track the rotated target object using the characteristic of the walking, which considered the interference between translational motion and rotational motion. The decoupling is realized by simulations and experiments. As a result, the walking robot tracked the translated and rotated target object without a practical issue. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Biped robot control strategy and open-closed-loop iterative learning control

Master-slaver dual-leg coordination control was proposed for the biped robot with heterogeneous legs (BRHL), in order to reduce gait planning and to get a good tracking performance. The key to coordination is gait trajectory tracking control. Bionic knee joint with closed-chain 4links makes robot walking more humanlike, but the model is complex and tracking of the bionic leg to the artificial leg is more difficult. P-type open-closed-loop iterative learning control (ILC) is not based on model parameters and has advantages in both open-loop and closed-loop ILC; so this paper proposes a complex robot gait trajectory tracking. The convergence is proved by using functional analysis and the stability condition is given. A tracking simulation based on the virtual prototype pe was done. The results show that this control strategy and algorithm are effective and robust, and the convergence speed is better than separate open-loop or closed-loop ILC. Translated from Journal of Northeastern University (Natural Science), 2005, 26(8): 722–725 [译自: 东北大学学报(自然科学版)]     

Development of Sensor and Control Systems of a Wearable Robot to Walk on a Step

The goal of our study is to develop a system for walking on a step using a wearable robot. Our system consists of (1) sensing of a step from the movement of the walker, (2) detection of the foot placement state related to the step, and (3) generation of gait patterns of climbing and stepping down for the step. In the generation of gait patterns for the step, toe trajectories are generated according to the height of the step to avoid collision of the swinging leg with the step. The hip trajectory is generated by an optimization technique that minimizes the sum of the joint angular jerk of the robot subject to constraints on the hip position and the velocity at toe liftoff. Each joint angle trajectory is calculated from the generated trajectories by means of inverse kinematic equations. We investigated the feasibility of the proposed sensor and control systems for two steps with different heights.     

Position and altitude tracking control for toe support phase of biped walking robot

No paper has been published on the active use of the foot toe of biped walking robots. In other words, the sole of the supporting leg is usually assumed to completely contact the ground. To maintain this condition, the robot walking has a restriction such as the maximum walking speed limitation. If the point contact of the toe to the ground through walking is available, a variety of walking can be realized. In this paper, a new control method for biped robots, in which the contact of the sole to the ground becomes a point contact, is proposed. The COM (Center of Mass) and swing leg can track the desired path and each heel joint angle can be controlled by the proposed controller while a biped walking robot is following a forward falling. Therefore, the motion of the body does not need to be limited to quiet motion. The proposed method is verified by simulation and experimental results with “Ken,” a six‐joint DOF biped robot. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(1): 72–79, 2006; Published online in Wiley InterScience ( http://www.interscience.wiley.com ). DOI 10.1002/eej.20094     

预测函数控制及其在伺服系统中的仿真研究

根据预测函数控制（PFC）的基本原理和特点，在分析其一般算法的基础上，设计了典型伺服控制系统的预测函数控制器。采用同步齿型带传动的单级倒立摆系统，对该广义被控对象进行线性拟合简化后得到单级倒立摆系统的预测模型，通过PFC与PID串级控制仿真研究，结果表明PFC串级控制能在快速系统中改善系统的跟踪性能，适应快速、高精度受控对象对控制算法的要求；PFC控制系统的动静态品质及在参数时变等情况下的鲁棒性均优于常规PID串级控制，抗干扰能力强，具有较高的工程应用价值。     

基于终端滑模控制的移动机器人轨迹跟踪

针对移动机器人受到外部不规则扰动时易出现速度和位姿误差跳变的问题,提出了一种基于扰动观测器的动态终端滑模控制方法。结合运动学模型,利用李雅普诺夫法设计虚拟控制器,进一步设计非奇异动态终端滑模轨迹跟踪控制器。为减小外部扰动对系统的影响,设计非线性扰动观测器对控制器进行扰动补偿。最后,将本文所提方法与自适应滑模控制方法进行仿真比较。结果显示,在第15 s扰动发生阶跃变化时,自适应滑模控制方法的线速度和角速度分别发生1.4 m/s和1.24 rad/s的跳变,而本文所提方法速度跳变幅度小于自适应滑模控制方法的1/10。仿真结果表明,本文所提方法可有效地抑制扰动对系统的影响,减小移动机器人速度和位姿误差的跳变幅度。     

永磁直线伺服电机L2鲁棒控制的研究

对永磁直线电机伺服系统提出非线性L2鲁棒控制.给出电机的非线性数学模型,在此基础上,为实现对速度和电流的准确跟踪,建立了误差系统的动态模型;将跟踪和干扰抑制归结为L2设计问题,通过构造适当的存储函数得到描述系统L2控制器的两个定理;证明定理给出的控制器能满足干扰抑制和系统的渐进稳定.仿真结果表明,用该方法设计的系统能很好的抑制扰动和跟踪给定,满足对高性能永磁直线伺服系统控制的要求.     

永磁直线伺服系统非线性自适应鲁棒控制器设计

对永磁直线伺服系统提出非线性自适应鲁棒控制器的设计方法。在永磁直线伺服系统非线性数学模型的基础上,为实现对速度和电流的准确跟踪,建立了误差系统的动态模型。将跟踪和干扰抑制归结为非线性自适应鲁棒控制器设计问题,通过构造存储函数得到包含电阻辨识算法的自适应鲁棒控制器的定理,证明定理给出的控制器能满足干扰抑制和系统的渐进稳定。仿真结果表明,用该方法设计的系统能很好的抑制扰动和跟踪给定,满足对高性能永磁直线伺服系统控制的要求。     

Assisted Control of Step Passage Motion and Its Comfort Evaluation in Two‐Wheel Wheelchair Systems

Two‐wheel wheelchair systems have been attracting attention because their mobility is better than that of conventional four‐wheel wheelchair systems. However, two‐wheel wheelchair systems must achieve stabilization control in the presence of disturbances caused by modeling error or the road situation, since these systems are underactuated systems similar to the inverted pendulum. In this investigation, step passage motion in two‐wheel wheelchair systems is considered. A reaction torque observer was employed to estimate the pitch angular interaction torque and the pure external wheel disturbance. Repulsive compliance control was employed to determine the optimal pitch angle command to compensate for the center of gravity of the user and to assist the whole step passage motion. Experimental results are evaluated in terms of user comfort by utilizing the ISO 2631‐1 generalized index.