Flexible Bio-tensegrity Manipulator with Multi-degree of Freedom and Variable Structure

Abstract

Conventional manipulators with rigid structures and stiffness actuators have poor flexibility, limited obstacle avoidance capability, and constrained workspace. Some developed flexible or soft manipulators in recent years have the characteristics of infinite degrees of freedom, high flexibility, environmental adaptability, and extended manipulation capability. However, these existing manipulators still cannot achieve the shrinking motion and independent control of specified segments like the animals, which hinders their applications. In this paper, a flexible bio-tensegrity manipulator, inspired by the longitudinal and transversal muscles of octopus tentacles, was proposed to mimic the shrinking behavior and achieve the variable motion patterns of each segment. Such proposed manipulator uses the elastic spring as the backbone, which is driven by four cables and has one variable structure mechanism in each segment to achieve the independent control of each segment. The variable structure mechanism innovatively contains seven lock-release states to independently control the bending and shrinking motion of each segment. After the kinematic modeling and analysis, one prototype of such bionic flexible manipulator was built and the open-loop control method was proposed. Some proof-of-concept experiments, including the shrinking motion, bending motion, and variable structure motion, were carried out by controlling the length of four cables and changing the lock-release states of the variable structure mechanism, which validate the feasibility and validity of our proposed prototype. Meanwhile, the experimental results show the flexible manipulator can accomplish the bending and shrinking motion with the relative error less than 6.8% through the simple independent control of each segment using the variable structure mechanism. This proposed manipulator has the features of controllable degree-of-freedom in each segment, which extend their environmental adaptability, and manipulation capability.

Dynamic Obstacle Avoidance and Trajectory Planning of a Five Axis Redundant Industrial Manipulator

“…Figure . 5, Figure 6 and Figure 7 are compared, and it can be found that there is little difference between the changes of joints 5 and 6. This is because 6  is determined by 2  and 5  together in the calculation, while in the process of moving, the change of 5  is much greater than that of 2  , and the effect on 2  is much less than that of 5…”

“…For example, the large amount of computation leads to more response time than the general manipulator, and the complexity shows that even if the algorithm can be optimized to reduce the amount of computation, it is difficult to apply to the actual obstacle avoidance. The second method is local control, which is different from global planning obstacle avoidance in that it is based on the control level and solves the obstacle avoidance problem through the bottom control, which involves a small amount of calculation and more flexible calculation [5]. The local control method is proposed for the redundant manipulator to perform obstacle avoidance, and the critical point in the obstacle avoidance is kept away from the obstacles.…”

A Novel Trajectory Tracking Control with Modified Supertwisting Sliding Mode for Human-Robot Cooperation Manipulator in Assembly Line

“…Although many advanced control methods, such as adaptive control [7], neural network control [8], and variable structure control [9], can be applied to human-robot cooperation manipulator control system, they all have some limitations. Deng [10] developed a novel finite-time command filter backstepping method, which allows the traditional command filter backstepping control and ensures the finite-time convergence.…”

Multi-Directional Shape Change Analysis of Biotensegrity Model Mimicking Human Spine Curvature

“…Using the force density method to solve the inverse kinematics, a modular tensegrity robot inspired by the vertebrae morphologies to grasp objects was developed [15]. An investigation on the motion patterns of a flexible biotensegrity manipulator mimicking the shrinking behavior of octopus tentacles was also conducted [16]. Although many studies of biotensegrity robots have been conducted through numerical and experimental works, the static and kinematic problems are hardly solved due to highly constrained coupling systems, particularly when subjected to an external load [17].…”