Mingguo Zhao

Analysis of a biped powered walking model based on potential energy compensation

The most important factor in powered walking based on Passive Dynamic Walking is to counter-balance the energy which is lost at heel-strike. In this paper, we discuss a model with only one mass at the hip, which compensates the lost energy with the potential energy through extending and shortening the stance leg instantaneously over one walking cycle. The results show that there exists periodical gait when the model has appropriate length shorten ratio ß, inter-leg angle φ0, extension angle θΈ, and shortening angle θw, and it has asymptotic stability within a wide range. The energy efficiency can be modulated by adjusting these parameters, and the highest energy efficiency can be 0.0569. Besides, it can realize varying-speed walking under the parameters tunning.

Constant-velocity steering control design for unmanned bicycles

Compared to unmanned cars, unmanned bicycles have the inherent problem of keeping balance. This paper proposes the design of a steering controller to achieve the balance control of bicycles when the forward velocity remains constant, bringing us closer to the autonomous driving of unmanned bicycles. Firstly, we introduce the modeling of the bicycle dynamics. Then, we design the constant-velocity steering controller, combining feedback with feedforward control, and verify the effectiveness of the controller using Matlab simulations. Finally, we proceed to test the steering controller on our prototype bicycle, finding that the bicycle can achieve stable motion and turning with flexibility, thus proving the effectiveness of our steering controller design.

Rimless wheel with asymmetric flat feet

The purpose of this paper is to have a better understanding of the function of human flat foot. To analyze its dynamics, we propose a passive rimless wheel with asymmetric flat feet. The model has a point mass in center and massless spokes. The rigid asymmetric flat feet were equipped at the end of spokes. The walking process of this model which has “heel-strike” and “toe-strike” is similar to human walking which has two peaks of vertical contact force in one stride. The stability was analyzed through eigenvalues of the linearized return map. The energy efficiency was analyzed in two ways, one from CoM trajectory and collision angle, another one from speed and step length. The proposed model has faster walking speed, higher energy efficiency, but lower local stability, compared with regular rimless wheel.

Human behavior inspired obstacle avoidance & road surface quality detection for autonomous bicycles

Most of the modern, advanced obstacle avoidance systems for ground vehicles are rather complicated and expensive, and cannot be directly applied to the complex autonomous bicycle problem. With this paper we introduce a novel and minimal design and implementation approach for a single laser range sensor (LRS)-based obstacle avoidance and road surface quality detection system, specifically created for use on-board an autonomous bicycle and mainly inspired from the human riding behavior. The system utilizes the measurements from the mounted LRS to detect dynamic obstacles that lie inside the bicycles immediate environment and avoid the ones with paths intersecting its own. The LRSs mechanical base and rotating mechanism were specially designed to fit the lightweight structure of the bicycle and a specific rotation pattern on the sagittal plane of the bicycle was created to maximize sensing efficiency, resembling the way humans combine information from one glance. The RANSAC Line Detection algorithm is used to identify the ground surface line, evaluate the road surface quality and detect bumps or holes on the bicycle path in order to avoid them. Our experimental results show promising bicycle behavior and reliable obstacle avoidance in both indoor and outdoor environments at different speeds.

Analysis of the disturbance rejection ability of a passive dynamic walker with hip spring

In numerous passive dynamic walking experiments, we found a spring added between walkers two legs increase its walking success rate dramatically. To explore the inherent nature of this phenomenon, we make a simulation comparison between the method to add hip springs and the method to change leg mass center position and foot radius, on the extent how much walking disturbance rejection ability can be improved. We find that the hip springs placed between legs center of mass have an enlarged basin of attraction of the walking cycle as well as a strengthened walking ability on irregular slope. Further, parameters study is performed by simulating the influence of hip spring, mass distribution and foot radius on the walkers disturbance rejection ability. The results show that hip springs can increase the walkers disturbance rejection ability while keeping the existence of stable equilibrium state unchanged, and arc foot can only obtain the same performance when the radius ia large, and the mass center position has little contribution to the disturbance rejection ability.

Simultaneous localization and mapping for autonomous bicycles

Bicycles and similar two-wheeled vehicles are a scientifically interesting category of means of transportation, whose simultaneous localization and mapping problem, in contrast to other ground vehicles, has yet to be examined in depth and fully resolved. In this article, we introduce for the first time a comprehensive theoretical framework for the application of simultaneous localization and mapping specifically for autonomous bicycles and akin vehicles, based on the kinematics and dynamics models of the bicycle and the specific effects they have on the motion/odometry and measurement models that are essential for the solution of the simultaneous localization and mapping problem. In addition, we present our laboratory’s first autonomous bicycle platform and its functional sensor system and sensor rotation pattern, specifically adjusted to the special characteristics of bicycles. Moreover, we investigate the effect of the bicycle frame roll, the main uncertainty factor of the bicycle simultaneous localization and mapping problem, on the overall simultaneous localization and mapping performance. The experimental results performed on our bicycle platform verify the potency of our proposed modeling and simultaneous localization and mapping application framework and provide further insight on future improvements for the two-wheeled vehicle simultaneous localization and mapping problem.

Laser-Based Obstacle Avoidance and Road Quality Detection for Autonomous Bicycles

This paper presents a novel design and implementation approach for a laser range sensor (LRS)-based obstacle avoidance and road quality detection system specifically created to be used onboard an autonomous bicycle. The system uses the measurements from a single LSR to detect dynamic obstacles inside the bicycle’s environment and avoid the ones whose paths intersect with its own. The LSR’s mechanical base and rotating mechanism were specially designed to fit the lightweight structure of the bicycle and a specific rotation pattern on the bicycle’s sagittal plane was created to maximize sensing efficiency. The RANSAC Line Detection algorithm is applied to detect the ground line, assess the road surface quality, and avoid bumps or holes on the bicycle path. Our experimental results show promising bicycle behavior and reliable obstacle avoidance at different speeds.

Follow my step: A framework for biped robots to imitate human walking

This paper presents a motion planning framework to generate continuous walking gait on a biped robot using kinesthetic teaching. While imitating human leg movement, the generated gait could also track a given swing foot trajectory and a given ZMP trajectory simultaneously, so as to form a stable stride with an expected foot displacement. An algorithm based on local linearization and nonlinear optimization is proposed to achieve single foot stance motion planning. An ad-hoc double loop is designed to handle the change of supporting foot so as to form a continuous walking gait with multiple steps. The algorithm is firstly verified via simulation results, then shows its robustness in experiments on the THU-Striker, a 1.34m humanoid robot in robocup2014, Brazil.

A dynamic bipedal walking method using coupled elastic actuation

The aim of this research is to find an actuated level ground walking method, which is analogous to the dynamics of a passive dynamic walker on a slope. We propose to take advantage of the coupled elastic to actuate legs. As a result, maintaining the character of passive dynamic and a simple control algorithm are achieved simultaneously. In our walking model, actuated bars are installed on each leg and connected with a linear spring at their ends. By properly swinging the bars forward and backward periodically, the spring is stretched to store potential energy at the walkers each stride. And after the heel strike the stored energy is transported to the whole system to compensate for the energy lost at the heel strike. By tuning three control parameters, namely the spring coefficient, the length and amplitude of the actuated bar, the walker exhibits stable periodical walking gait. While continuously changing these parameters, the gait of the walker also demonstrates period-doubling bifurcation and chaos. In some certain parameters, the gait can also evolves from chaos back to bifurcation. This gait evolution phenomenon has never been reported in the actuated walking robot before, it shows that the walkers dynamics is somewhat analogical to the passive dynamic walker. We also show this walker can walk over a wide range of speed, that have a reference value to build the actual robot.

Analysis of Time Zero Reset method for Virtual Slope Walking

In our previous work, we proposed a novel method Virtual Slope Walking(VSW) for biped locomotion. Mechanical energy is restored by actively extending stance leg in this method. VSW has two kinds of implementations, termed self-excited mode and parametric excited mode, respectively. In self-excited mode, stance leg extension is controlled according to its angle, but the measure of legs angle is difficult in practical implementation; while in parametric excited mode stance leg extension is controlled according to time. In this paper, we investigate a method for VSW using parametric excited mode named Time Zero Reset method, which controlling stance leg extension with relative time, time zero is reset at each heelstrike. The method generates stable period-1 and multi-period walking cycles which not seen in VSW before. The results of stability analysis show the method has strong tolerance to disturbances. Compared to previous parametric excited mode with open-loop control, it has wider speed range and is more robust to disturbances with low cost as only touchdown sensors are needed.