An intermittent control model of flexible human gait using a stable manifold of saddle-type unstable limit cycle dynamics

Stability of human gait is the ability to maintain upright posture during walking against external perturbations. It is a complex process determined by a number of cross-related factors, including gait trajectory, joint impedance and neural control strategies. Here, we consider a control strategy that can achieve stable steady-state periodic gait while maintaining joint flexibility with the lowest possible joint impedance. To this end, we carried out a simulation study of a heel-toe footed biped model with hip, knee and ankle joints and a heavy head-arms-trunk element, working in the sagittal plane. For simplicity, the model assumes a periodic desired joint angle trajectory and joint torques generated by a set of feed-forward and proportional-derivative feedback controllers, whereby the joint impedance is parametrized by the feedback gains. We could show that a desired steady-state gait accompanied by the desired joint angle trajectory can be established as a stable limit cycle (LC) for the feedback controller with an appropriate set of large feedback gains. Moreover, as the feedback gains are decreased for lowering the joint stiffness, stability of the LC is lost only in a few dimensions, while leaving the remaining large number of dimensions quite stable: this means that the LC becomes saddle-type, with a low-dimensional unstable manifold and a high-dimensional stable manifold. Remarkably, the unstable manifold remains of low dimensionality even when the feedback gains are decreased far below the instability point. We then developed an intermittent neural feedback controller that is activated only for short periods of time at an optimal phase of each gait stride. We characterized the robustness of this design by showing that it can better stabilize the unstable LC with small feedback gains, leading to a flexible gait, and in particular we demonstrated that such an intermittent controller performs better if it drives the state point to the stable manifold, rather than directly to the LC. The proposed intermittent control strategy might have a high affinity for the inverted pendulum analogy of biped gait, providing a dynamic view of how the step-to-step transition from one pendular stance to the next can be achieved stably in a robust manner by a well-timed neural intervention that exploits the stable modes embedded in the unstable dynamics.     

Metabolic and cardiopulmonary responses of older wheelchair-dependent and ambulatory patients during locomotion∗

To determine preferred velocities and magnitudes of metabolic and cardiopulmonary responses of older wheelchair-dependent (WD) patients and ambulatory (AMB) psychiatric patients during locomotion, eight WD (mean age 62 years) and ten AMB (mean age 58 years) patients travelled over a level tiled circular course. During wheelchair locomotion and walking, respectively, mean results were: velocity, 2·0, 3·1 km hour^?1; oxygen uptake, 0·532, 0·8061min^?1; net locomotive energy cost, 0·574, 0·558netkcal kg^?1 km^?1; pulmonary ventilation, 19·6, 25·71 min^?1; heart rate, 94·6, 92·7 beats min^?1. Although walking at 3·1 km hour^?1 required greater absolute energy expenditure than for wheelchair locomotion at 2·0 km hour^?1, locomotive efficiency was approximately the same. When considering differences in exercise capability between arms and legs, relative stresses experienced by the WD and AMB subjects appeared to be similar. Locomotive efficiency was reduced when the AMB subjects reduced their walking speed to 20km hour^?1. This study suggests that self-selected velocities for wheelchair locomotion and walking are related to both maximal physical capability for each activity and locomotive efficiency.     

Biped 4R2C six-bar mechanism with inner and outer feet

Most current biped robots are equipped with two feet arranged in the right and left which inspired by the human body system. Different from the existing configurations, a novel biped robot with inner and outer feet based on a spatial six-bar 4R2C(R and C denote revolute and cylindric joints, respectively) mechanism is proposed. It can move along a line or a curve by three walking modes that are dwell adjustment mode, limit position adjustment mode and any position adjustment mode. Kinematic, gait planning and stability analyses are performed respectively, and a prototype is developed. Lastly, a potential application is considered and two manipulating modes(sphere and cylinder manipulating modes) are carried out. This interesting mechanism feathering its single closed-chain structure and unique work performance is expected to motivate the configuration creation of biped robots.     

Manipulating the Level of Sensorimotor Stimulation during LI-rTMS Can Improve Visual Circuit Reorganisation in Adult Ephrin-A2A5-/- Mice

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive brain stimulation technique that has the potential to treat a variety of neurologic and psychiatric disorders. The extent of rTMS-induced neuroplasticity may be dependent on a subject’s brain state at the time of stimulation. Chronic low intensity rTMS (LI-rTMS) has previously been shown to induce beneficial structural and functional reorganisation within the abnormal visual circuits of ephrin-A2A5^-/- mice in ambient lighting. Here, we administered chronic LI-rTMS in adult ephrin-A2A5^-/- mice either in a dark environment or concurrently with voluntary locomotion. One day after the last stimulation session, optokinetic responses were assessed and fluorescent tracers were injected to map corticotectal and geniculocortical projections. We found that LI-rTMS in either treatment condition refined the geniculocortical map. Corticotectal projections were improved in locomotion+LI-rTMS subjects, but not in dark + LI-rTMS and sham groups. Visuomotor behaviour was not improved in any condition. Our results suggest that the beneficial reorganisation of abnormal visual circuits by rTMS can be significantly influenced by simultaneous, ambient visual input and is enhanced by concomitant physical exercise. Furthermore, the observed pathway-specific effects suggest that regional molecular changes and/or the relative proximity of terminals to the induced electric fields influence the outcomes of LI-rTMS on abnormal circuitry.     

Inhibition of Bruton Tyrosine Kinase Reduces Neuroimmune Cascade and Promotes Recovery after Spinal Cord Injury

Microglia/astrocyte and B cell neuroimmune responses are major contributors to the neurological deficits after traumatic spinal cord injury (SCI). Bruton tyrosine kinase (BTK) activation mechanistically links these neuroimmune mechanisms. Our objective is to use Ibrutinib, an FDA-approved BTK inhibitor, to inhibit the neuroimmune cascade thereby improving locomotor recovery after SCI. Rat models of contusive SCI, Western blot, immunofluorescence staining imaging, flow cytometry analysis, histological staining, and behavioral assessment were used to evaluate BTK activity, neuroimmune cascades, and functional outcomes. Both BTK expression and phosphorylation were increased at the lesion site at 2, 7, 14, and 28 days after SCI. Ibrutinib treatment (6 mg/kg/day, IP, starting 3 h post-injury for 7 or 14 days) reduced BTK activation and total BTK levels, attenuated the injury-induced elevations in Iba1, GFAP, CD138, and IgG at 7 or 14 days post-injury without reduction in CD45RA B cells, improved locomotor function (BBB scores), and resulted in a significant reduction in lesion volume and significant improvement in tissue-sparing 11 weeks post-injury. These results indicate that Ibrutinib exhibits neuroprotective effects by blocking excessive neuroimmune responses through BTK-mediated microglia/astroglial activation and B cell/antibody response in rat models of SCI. These data identify BTK as a potential therapeutic target for SCI.     

仿蚯蚓蠕动微机器人牵引与运动控制

为进入人体腔道开展作业,开发了一种直径6mm的仿蚯蚓多关节蠕动微机器人样机．机器人使用十字万向节连接直线驱动器,在弯曲腔道中能自适应改变自身姿态．基于Preisach模型和偏转模型,提出了形状记忆合金偏转机构的前馈控制方案,头舱控制最大偏转误差为2.6°．基于新型蠕动原理,建立了牵引模型,给出了有效驱动的条件．对机器人的牵引力、运动速度、在不同摩擦系数介质表面上的运动能力、头舱姿态进行了试验．结果表明,机器人的爬坡能力依赖于机器人和运动表面间的摩擦系数,新型蠕动原理能提供较大的牵引力,合适的驱动频率下可以得到最大的运动速度．     

基于目标导向行为和空间拓扑记忆的视觉导航方法

针对在具有动态因素且视觉丰富环境中的导航问题,受路标机制空间记忆方式启发,提出一种可同步学习目标导向行为和记忆空间结构的视觉导航方法.首先,为直接从原始输入中学习控制策略,以深度强化学习为基本导航框架,同时添加碰撞预测作为模型辅助任务;然后,在智能体学习导航过程中,利用时间相关性网络祛除冗余观测及寻找导航节点,实现通过...     

一种可重构蛇形机器人的研究

提出了一种新型的可重构蛇形机器人机构。该机构主要特点是单关节结构模块化，具有可适应地面形状变化的柔性连接环节和类似于蛇腹鳞摩擦特性的机构底部，手动可重构，当单自由度关节轴线互相平行连接时，该机构可实现多种平面运动形式，当单自由度关节轴线垂直依次连接时，形成的蛇形机器人具有两自由度的关节，可进行多种空间运动。试验结果证实，该蛇形机构重量轻，控制简单，运动灵活，能够很好地仿生蛇的多种运动形式。     

一种求两足机器人运动学逆解的解析方法

在两足机器人的上身建立基坐标系,给出了一种解析方法,并用这种方法进行步态规划,通过仿真实验验证了该方法的正确性。同时没有把运动分解到横向面和纵向面以简化计算,而是一种完全3维的运动学分析方法,可以处理机器人任意复杂的下肢运动。该方法适用于目前常见的两足机器人自由度布置方式,因此具有一定的通用性。     

基于RoboCup3D仿真平台的双足机器人大脚球进攻策略设计

RoboCup3D仿真系统融合了人工智能、传感器、通信、智能控制等多门学科的相关技术.针对RoboCup3D仿真中双足机器人的踢球动作设计问题(如:踢球力度弱、摔倒等)提出了一种基于大脚球的进攻策略.采用大脚球的进攻策略可以有效的促使足球快速的踢进对方半场后方,在仿真比赛中极具攻击性.仿真结果验证了它的有效性和实用性.