Manipulability analysis of a snake robot without lateral constraint for head position control

Two dynamic manipulability criteria of a snake robot with sideways slipping are proposed with the application to head trajectory tracking control in mind. The singular posture, which is crucial in head tracking control, is characterized by the manipulability and examined for families of typical robot shapes. Differences in the singular postures from those of the robot with lateral constraints, which have not been clear in previous studies, are clarified in the analysis. In addition to the examination of local properties using the concept of manipulability, we discuss the effect of isotropic friction as a global property. It is well known that, at least empirically, a snake robot needs anisotropy in friction to move by serpentine locomotion if there are no objects for it to push around. From the point of view of integrability, we show one of the necessary conditions for uncontrollability is satisfied if the friction is isotropic

Head-Trajectory-Tracking Control of a Snake Robot and Its Robustness Under Actuator Failure

This brief considers the problem of trajectory tracking of a planar snake robot without a lateral constraint. The reference trajectory of the head position and the orientation of link 1 are given, and torque control is determined to reduce tracking errors. The performance of the controller was tested in a number of simulations. The robustness during actuator failure was also studied. We assumed that one of the actuators was broken and the corresponding joint became passive. Furthermore, as a more realistic situation, we considered an instance when some of the states were not readily accessible from the sensor readings and needed to be estimated by an observer. The extended Kalman filter was employed for this purpose, and the performance of the closed-loop system with the observer was also tested in simulations

Three-dimensional steering for an articulated mobile robot with prismatic joints with consideration of hardware limitations

The paper presents a three-dimensional steering method for an articulated mobile robot that contains links, rotational joints, prismatic joints, and active wheels. The robot can change the angles of its links using the rotational joints and vary the lengths of its links using the prismatic joints. The target motion of this robot is represented by a continuous curve and the motions of the joints and the wheels are calculated by fitting the entire robot to this target curve. The forward velocity of the robot\u27s head is adjusted to satisfy the hardware limitations of the robot; e.g. joint angle, joint velocity, and wheel velocity limitations. In addition, a terrain-following method is presented that considers the changes in the lengths of the links. An experimental articulated mobile robot was developed and experiments were carried out to demonstrate the effectiveness of the proposed method

Redundant Control of a Planar Snake Robot with Prismatic Joints

This paper presents a control method of a planar snake robot with prismatic joints. The kinematic model is derived considering velocity constraints caused by passive wheels. The proposed control method based on the model allows the robot to track a target trajectory by appropriately changing its link length using prismatic joints. The degrees of freedom of prismatic joints are represented as kinematic redundancy in the model and are used in realizing subtasks such as singularity avoidance and obstacle avoidance. In addition, the link length is below its limit when introducing a sigmoid function into the kinematic model. Simulations are carried out to demonstrate the effectiveness of the proposed method and show a novel motion that avoids singular configurations through changes in link lengths

Passive joint control of a snake robot by rolling motion

Snake robots are capable of adapting to difficult situations, such as cluttered environments, using its many degrees of freedom. However, if one of the joints gets passive, it is generally very difficult to achieve ordinary performance. In this paper, control of a passive joint using rolling motion is considered, with the use of crawler gait in mind. Crawler gait is a state-of-the-art motion pattern for snake robots that is capable of moving on uneven terrain, but if there is a passive joint, the motion can be interrupted by freely moving part of the robot itself. As a key to solving this difficulty, this paper proposes to use the rolling motion, which has not been used in controlling a passive joint. A simplified model is proposed to consider the control, and based on this, one simple controller is adopted. The validity of the idea of using rolling motion is tested by numerical simulations

ヘビ型ロボットのパラメトリックな運動の解析およびノンパラメトリックな運動の制御

京都大学0048新制・課程博士博士(工学)甲第18942号工博第3984号新制||工||1614(附属図書館)31893京都大学大学院工学研究科機械理工学専攻(主査)教授 松野 文俊, 教授 椹木 哲夫, 教授 藤本 健治学位規則第4条第1項該当Doctor of Philosophy (Engineering)Kyoto UniversityDGA

Resolving Undesired Bias in Optimization of Environmentally Adaptive Control Policies

Significant research on experiment-based black-box optimization using Bayesian optimization techniques is being performed because of its usefulness in a wide range of fields. Several algorithms using Bayesian optimization for optimizing environmentally adaptive control policies have been developed. This adaptivity is expected to be crucial for applications such as mobile robots. In this work, the unbiased expected improvement metric was the key to efficiently obtain the approximated optimal policy. The purpose of the metric was to remove the bias in sample points that is inevitable if ordinary metrics, such as the expected improvement, are used. This paper clarified the mechanism that causes the bias and showed that the bias should be attenuated to achieve efficient experiments. Based on the understanding of the mechanism, a simple solution was proposed to attenuate this bias. Using numerical tests, it was shown that our method effectively attenuated the bias and that this led to better optimization performance in that it often required less samples than the existing method

Step Climbing Control of Snake Robot with Prismatic Joints

The ultimate goal of this research study is to perform continuous rather than sequential movements of prismatic joints for effective motion of a snake robot with prismatic joints in a complex terrain. We present herein a control method for robotic step climbing. This method is composed of two parts: the first involves the shift reference generator that generates the joint motion for climbing a step, and the other is use of the trajectory tracking controller, which generates the joint motion for the head to track the target trajectory. In this method, prismatic joints are divided into those that are directly controlled for climbing a step and those that are represented as redundancies. By directly controlling the link length, it is possible to prevent the trailing part from back motion when climbing a step, and to avoid a singular configuration in the parts represented as redundancies. A snake robot that has rotational and prismatic joints and can move in three-dimensions was developed, and the effectiveness of the proposed method was demonstrated by experiments using this robot. In the experiment, it was confirmed that the proposed method realizes the step climbing, and the link length limitation using the sigmoid function works effectively