Development of a Self-tuning PID Controller on Hydraulically Actuated Stewart Platform Stabilizer with Base Excitation

International Journal of Control, Automation and Systems - Stewart platform is a six degrees of freedom (DOF) parallel robot manipulator with rather high powerto- weight ratio and more accurate...     

位－力驱动的线驱连续型机器人的动力学建模及实验验证

提出了一种位－力混合驱动的线驱连续型机器人的动力学模型。首先,基于集中质量矩阵法进行机器人动力学建模,将机器人动能的连续积分等效离散为三点求和形式,可简化建模过程并提升仿真的计算效率。其次,分析了驱动力与驱动线几何约束的力学关系,将线驱动作用等效建模为电机的驱动参数与牵引线张力的线性方程组,不仅可以精确地满足牵引线对系统的约束条件,还可以在不使用拉力传感器的条件下得到线的驱动力,降低了机器人成本及控制难度,这种方法适用于任意数量牵引线的连续型机器人。最后,将线驱连续型机器人的仿真和实验结果进行对比,机器人末端点的轨迹最大误差为3.85%,验证了所提模型的有效性。     

Inverse Kinematics and Workspace Analysis of a 3 DOF Flexible Parallel Humanoid Neck Robot

To mimic the human neck’s three degree-of-freedom (DOF) rotation motion, we present a novel bio-inspired cable driven parallel robot with a flexible spine. Although there exists many parallel robotic platform that can mimic the human neck motion, most of them have only two DOF, with the yaw motion being actuated separately. The presented flexible parallel humanoid neck robot employs a column compression spring as the main body of cervical vertebra and four cables as neck muscles to connect the base and moving platform. The pitch and roll movements of moving platform are realized by the two dimensional lateral bending motion of the flexible spring, and a bearing located at the top of the compression spring and embedded in the moving platform is used to achieve the yaw motion of the moving platform. By combing the force and torque balance equations with the lateral bending statics of the spring, inverse kinematics and optimizing the cable placements to minimize the actuating cable force are investigated. Moreover, the translational workspace corresponding to pitch and roll movements and rotational workspace corresponding to yaw movement are analyzed with positive cable tension constraint. Extensive simulations were performed and demonstrated the feasibility and effectiveness of the proposed inverse kinematics and workspace analysis of the novel 3 DOF flexible parallel humanoid neck robot.     

Control of minimally constrained cobots

Cobots are devices which use computer‐oriented passive constraints to guide an end‐effector driven by a human. This synergistic union of human skill and robotic precision is desired in fields such as surgical robotics (our application area of interest) where the surgeon would prefer not to hand over control of a procedure to an autonomous robot. Typical cobot designs intrinsically allow at most one degree of freedom of motion, but there are some tasks (such as using a bone saw to cut a plane in knee replacement surgery) where allowing two or more degrees of freedom is desireable. While it is possible to use selective constraint alignment to increase the apparent degrees of freedom of a cobot, this requires more actuators than are strictly necessary for the task, as well as a force sensor to detect the user's intent. We, therefore, introduce here the concept of minimally constrained cobots for multiple degree of freedom (DOF) tasks such as planar cutting, and outline a general framework for controlling such devices. We illustrate our control algorithms by using a planar cart example and discuss how they might be applied to potential designs for three‐dimensional parallel cobots intended for surgical applications. © 2002 Wiley Periodicals, Inc.     

Planar Translational Cable‐Direct‐Driven Robots

We present the simulated dynamics and control of a planar, translational cable‐directdriven robot (CDDR). The motivation behind this work is to improve the serious cable interference problem with existing CDDRs and to avoid configurations where negative cable tensions are required to exert general forces and moments on the environment and during dynamic motions. Generally for CDDRs the commanded rotations are more demanding than commanded translations in terms of slack cable conditions. Therefore we propose a translational CDDR whose end‐effector may be fitted with a traditional serial wrist mechanism to provide rotational freedom (assuming proper design to resist the moments). Only the translational CDDR is considered in this article, including kinematics and statics modeling, statics workspace (wherein all possible Cartesian forces and moments may be exerted with only positive cable tensions), plus a dynamics model and simulated control for planar CDDRs. Here we focus only on planar CDDRs, to clearly demonstrate our dynamics and control work; we will extend this work to spatial CDDRs in the future. Examples are presented to demonstrate simulated control including feedback linearization of the four‐cable CDDR (with one degree of actuation redundancy) performing a Cartesian task. An on‐line dynamic minimum torque estimation algorithm is introduced to ensure all cable tensions remain positive for all motion; otherwise slack cables can result from CDDR dynamics and control is lost. © 2003 Wiley Periodicals, Inc.     

Kinematic design of a redundant parallel mechanism for maskless lithography optical instrument manipulations

A new precision parallel mechanism having actuation redundancy will be introduced in this paper. Physical contribution of the actuation redundancy for the precision parallel mechanism is reviewed. In addition, several kinematic configurations have been analyzed for degrees of freedom verification and actuation redundancy. A new kinematic configuration which is 4-[P P]PS is suggested. The suggested 4-[P P]PS mechanism which has actuation redundancy provides six degrees of freedom to the mobile platform. For position control and path planning of the mobile platform, the inverse and the forward kinematics are solved for closed-form solutions. In order to verify the inverse and the forward kinematics, a numerical simulation result is presented. In addition to the inverse and forward accuracy proof, the numerical analysis provides other information such as independent translation motion, calibrated rotation arm at tilting motion, and symmetric motion at rotating motion.     

一类新的PPA型三连杆欠驱动机器人的控制策略

PPA型机器人是一类新型的三连杆欠驱动机械系统,具有3个自由度,但只有1个驱动装置.针对这类欠驱动机器人的运动控制,提出一种分区的控制策略,使之从垂直向下的位置摇起到垂直向上的位置,并实现稳定控制.首先,将系统的运动空间划分为摇起区和吸引区;其次,应用一种基于Lyapunov函数的控制方法来增加系统能量和控制驱动杆姿态,实现摇起操作;再次,采用最优控制方法设计平衡控制,实现稳定的平衡控制;最后,通过仿真实验验证了所提出控制方法的有效性.     

Robotic welding system with parallel degrees of freedom

This paper considers some problems concerning robotic welding of large structures. If spot welding is applied, then the task consists of fast motions between welding points, and at each point the end effector stops and maintains position for a short time. Similar examples can be found in arc welding applications. Since large structures and, accordingly, large robots are considered, a significant problem appears when extremely nonuniform motion is required. One way to solve this problem is to introduce parallel degrees of freedom. Two methods for this distribution of motion to parallel degrees of freedom are discussed. The theory resulted in the design of a large portal robot with high dynamic capabilities.     

智能材料DE 驱动的两态串并联机器人系统的运动特性

本文利用电活性绝缘弹胶体DE 的机电驱动特点,结合两态驱动的概念,设计了一种包含3 个两态驱 动器件的并联机构,将其作为串—并联离散驱动机器人系统的基本单元,并据此构建多个单元串联组成的多级离散 驱动系统．文中首先利用智能DE 材料制作满足这一驱动特性的圆柱形两态驱动器件,先测试其直线驱动特性,即 变形值．其次,将该变形值作为并联机构数学模型的驱动值,分析单级及多级并联机构的运动状态、特性及工作空 间的特点．最后,利用数学工具Mathematica 描绘出上述两态驱动并联机构系统所能达到的工作空间分布点云图, 分析了结构参数与驱动量对系统工作空间的范围、精度的影响．     

Intuitive Bilateral Teleoperation of a Cable-driven Parallel Robot Controlled by a Cable-driven Parallel Robot

International Journal of Control, Automation and Systems - Intuitive remote multiple degrees of freedom (DOF) robot control has distinct advantages in field robotics applications, especially for a...     

Synthesis and analysis of a flexible elephant trunk robot

This paper presents a novel synthesis and analysis of a flexible elephant trunk robot (biological continuum–style manipulator). The robot includes eight flexible segments, although it can be extended to more segments as necessary. In this study the gravity of the springs is neglected due to the fact that the manipulation force is much larger than these gravity forces. This mechanism exhibits a wide range of maneuverability and has a large number of degrees of freedom. Each segment is designed using a novel flexible mechanism based on the loading of a compression spring in both transverse and axial directions, and using cable–conduit systems. The rotational motion is transformed to tendon-like behavior, which enables the location of the actuators away from the trunk (e.g. at the end of the trunk). The forward kinematics of the mechanism is also presented and lends itself well to computer control. It is shown that the solution of the transverse deflection of each segment is obtained in a general form, while the stiffness coefficients are obtained in closed form from a two-dimensional model (small and large deflection angles) and from a three-dimensional model used in a finite element method to verify results. The friction in the analysis between the cable and the conduit is neglected in the analysis. A prototype trunk segment is experimentally tested, the results are verified and the elephant trunk robot is built. A bench-top actuation system has been developed and a control scheme used in prosthetic hand control has been implemented to control the mechanism.     

Trajectory planning of a suspended cable driven parallel robot with reconfigurable end effector

In this paper, a new suspended cable driven parallel robot (CDPR) with reconfigurable end effector is presented. This robot has been conceived for pick and place operations in industrial environments. For such applications, the possibility to change the configuration of the cables at the end-effector level is a promising way to avoid collisions with obstacles in the approaching phases, while reducing at the same time the duration of motion in the remaining part of the trajectory. An optimized trajectory planning algorithm is proposed, which implements a pick and place operation in the operational space with dynamic on-line reconfiguration of the end effector. The results on a simplified scenario demonstrate the ability of the system to obtain reduced movement times together with obstacle avoidance.     

Design and prototype of parallel,wire-actuated robots with a constraining linkage

Currently, wire-actuated robots are not used extensively in industry, but they are gaining more attention due to advantages they possess. Low weight, cost, and power consumption are features that make wire-controlled robots worth researching. This article investigates the designs of two different, 4 degrees of freedom parallel, wire-actuated robots so that a prototype of one of these can be built. A design methodology is developed and presented. The process will be beneficial to those working on designing and prototyping a new robot or modifying an existing robot. Stability of both designs is considered first to ensure that the robots are able to exert and withstand end effector forces in different positions throughout their respective workspaces. The stiffness and strength of the materials used in the designs is also investigated using finite element analysis. © 2004 Wiley Periodicals, Inc.     

具有7自由度和双球型髋关节的仿人机器人下肢运动分析与规划

提出了具有7自由度和双球型髋关节的仿人机器人下肢机构．它和传统的6自由度双足步行机构相比,具有下述两大优点．首先双球型髋关节使机器人在不增加腰部关节的情况下实现腰部的基本运动功能,使机器人能够直立行走;其次在给定腰和足部位置时,它也能和人类一样实现转动双腿的动作．本文还对该复杂机构进行了运动特性分析、运动学求解、运动规划和实验验证．     

Dynamic Load Carrying Capacity of Flexible Cable Suspended Robot: Robust Feedback Linearization Control Approach

In this paper dynamic load carrying capacity (DLCC) of a cable robot equipped with a closed loop control system based on feedback linearization, is calculated for both rigid and flexible joint systems. This parameter is the most important character of a cable robot since the main application of this kind of robots is their high load carrying capacity. First of all the dynamic equations required for control approach are represented and then the formulation of control approach is driven based on feedback linearization method which is the most suitable control algorithm for nonlinear dynamic systems like robots. This method provides a perfect accuracy and also satisfies the Lyapunov stability since any desired pole placement can be achieved by using suitable gain for controller. Flexible joint cable robot is also analyzed in this paper and its stability is ensured by implementing robust control for the designed control system. DLCC of the robot is calculated considering motor torque constrain and accuracy constrain. Finally a simulation study is done for two samples of rigid cable robot, a planar complete constrained sample with three cables and 2 degrees of freedom and a spatial unconstrained case with six cables and 6 degrees of freedom. Simulation studies continue with the same spatial robot but flexible joint characteristics. Not only the DLCC of the mentioned robots are calculated but also required motors torque and desired angular velocity of the motors are calculated in the closed loop condition for a predefined trajectory. The effectiveness of the designed controller is shown by the aid of simulation results as well as comparison between rigid and flexible systems.     

Translational Planar Cable-Direct-Driven Robots

A planar cable-direct-driven robot (CDDR) architecture is introduced with only translational freedoms. The motivation behind this work is to improve the serious cable interference problem with existing CDDRs and to avoid configurations where negative cable tensions are required to exert general forces on the environment and during dynamic motions. These problems generally arise for rotational CDDR motions. Thus, we propose a class of purely translational CDDRs; of course, these are not general but may only perform tasks where no rotational motion or resistance of moments is required at the end-effector. This article includes kinematics and statics modeling, determination of the statics workspace (the space wherein all possible Cartesian forces may be exerted with only positive cable tensions), plus a dynamics model and simulated control for planar translational CDDRs. Examples are presented to demonstrate simulated control including feedback linearization of the 4-cable CDDR (with two degrees of actuation redundancy) performing a Cartesian task. We introduce an on-line dynamic minimum torque estimation algorithm to ensure all cable tensions remain positive for all motion; otherwise slack cables result from the CDDR dynamics and control is lost.     

A new TSMC prototype robust nonlinear task space control of a 6 DOF parallel robotic manipulator

In this study, a new terminal sliding mode control (TSMC) prototype robust nonlinear task space control approach is developed for 6 degree of freedom (DOF) parallel robotic manipulators in light of TSMC principle integrated with Lyapunov redesign method. Corresponding stability analysis is presented to lay a foundation for analytical understanding in generic theoretical aspects and safe operation for real systems. An illustrative example of a 6 DOF parallel robot is bench tested to validate the effectiveness of the proposed approach.     

A Highly-Maneuverable Demining Autonomous Robot: an Over-Actuated Design

Based on the well-known advantages of using an over-actuated mechanism for robots, this research proposes a holonomic highly-maneuverable autonomous robot design for demining service applications. The proposed approach provides an interesting compromise between the design requirements of the demining robot applications and the over-actuated autonomous robots. The robot body is mainly divided into two parts: the first part provides the robot with its required locomotion and it consists of a driving/steering subsystem with four driving wheels (4WD), four steering mechanisms (4SW), and a passive suspension subsystem. The second part is a manipulator with three degrees of freedom that is designed based on two parallelogram mechanisms. The proposed design insures many advantages over existing designs, including stability, maneuverability, autonomous navigation, and simplicity of the control effort constraints. The robot model and its corresponding stability analysis were conducted and simulated in order to evaluate the motion of the robot over different environments rough terrains and slanted surfaces. Moreover, a prototype of the proposed robot was developed and built and different types of sensors were used in order to help it take precise actuation decisions for navigation and control. The prototype was experimentally tested for different scenarios and environments in order to validate the proposed design. The testing results demonstrated decent performance of the robot in autonomous navigation and in localizing the detected objects.     

A flexible controller for robots

The structure of a flexible microprocessor-based controller for a low-cost robot for component handling is described. The robot demonstrates three degrees of freedom within cylindrical coordinate motion. One axis uses end-stop pneumatic actuation with the remaining two axes being actuated by specially designed hydropneumatic drives. By using hydropneumatic actuation and incremental encoder feedback, point-to-point positioning is provided through a real-time closed-loop control algorithm designed and implemented within the controller structure. Interactive programming aids have also been implemented within the control structure to allow operatives to describe robot handling tasks by using a shop floor oriented language. Both hardware and software for the controller have been developed in a modular form to increase its flexibility allowing the modules produced to be used for the control of other work-handling systems.     

Design and evaluation of an actuated exoskeleton for examining motor control in stroke thumb

Chronic hand impairment is common following stroke. This paper presents an actuated thumb exoskeleton (ATX) to facilitate research in examining motor control and hand rehabilitation. The ATX presented in this work aims to provide independent bi-directional actuation in each of the 5 degrees of freedom (DOF) of the thumb using a novel flexible shaft-based mechanism that has 5 active DOF and 3 passive DOF. A prototype has been built and experiments have been conducted to measure the allowable workspace at the thumb and evaluate the kinematic and kinetic performance of the ATX. The experimental results show that the ATX is able to provide individual actuation at all five thumb joints with high joint velocity and torque capacities. Further improvement and future work are discussed.