Simplified approach for dynamics estimation of a minor mobility parallel robot

This paper presents the identification of an approximated polynomial model for the dynamics of a parallel kinematics machine. The case study of a specific translational Cartesian manipulator is faced. Firstly, an analysis of robot dynamics is performed to verify the presence of poorly relevant terms. A polynomial simplified model is then built by fitting the actual behaviour of the robot prototype. The seek of the coefficients of the interpolating polynomials has been constrained taking advantage of robot peculiarities, such as symmetry and intrinsic properties of multibody systems dynamics. The effectiveness of the proposed simplification is then verified by comparison with robot behaviour.     

Industrial robot accurate trajectory generation by nested loop iterative learning control

Common error sources of industrial robot manipulators include joint servoing error, imprecise kinematics, mechanical compliance, and transmission error. In this work we present a nested loop iterative learning control (ILC) feedforward structure: an inner loop that compensates for motor dynamics, and an outer loop that corrects the deviation along the path tracked, that features practically efficient implementation. Taking advantage of industrial robot’s speed reduction transmission, single-input-single-output method is demonstrated effective for the nonlinear coupled robot dynamics. Data-based inversion technique that incorporates motion constraint is used for fast inner loop convergence. The outer loop utilizes inverse Jacobian matrix for joint reference modification. For nonlinear static friction that is difficult to be compensated for with only joint command, notch filtering is utilized in the learning process to avoid exciting vibration inherently exists in the robot. The proposed nested loop ILC requires only the nominal kinematic parameters from the robot manufacturer, and can be readily implemented without modifying the existing robot controllers. The effectiveness of the proposed method is experimentally verified on a six degree-of-freedom robot manipulator.     

自攀爬幕墙清洗机器人控制系统设计

本文以国家大剧院椭球状幕墙的清洗作业为应用背景,设计了一台复杂曲面幕墙自攀爬机器人样机.简单介绍了机器人系统的机械本体结构;详细讨论基于CAN总线网络结构的控制系统和以P80C592单片机为核心构成的分布节点控制器;软件采用模块化设计以实现了机器人运动功能.实验表明样机控制系统合理可靠.     

Distributed control for unit-compressible robots: goal-recognition, locomotion, and splitting

We present a distributed self-reconfiguring robot system with unit-compressible modules called the Crystal robot. A new design for the Crystal is presented that decouples the x axis and y axis actuation, has on-board sensing and has neighbor-to-neighbor communication. We also describe a suite of distributed control algorithms for this type of robot and associated experiments for each algorithm. Several of the algorithms presented are instantiations of generic distributed algorithms for self-reconfiguring robots. Specifically, we present an algorithm for distributed goal recognition, two new distributed locomotion algorithms designed for unit-compressible actuation and a new generic-division algorithm. We also present the integration of a locomotion algorithm with distributed goal recognition, allowing the robot to reconfigure and recognize the achievement of its goal, all without the use of a central controller. For all of these algorithms, we describe the implementation, sketch correctness analysis and present experimental data. Our experiments empirically verify the usefulness of our distributed algorithms on a self-reconfiguring system.     

Reconfiguration of a parallel kinematic manipulator with 2T2R motions for avoiding singularities through minimizing actuator forces

This paper aims to develop an approach for the reconfiguration of a parallel kinematic manipulator (PKM) with four degrees of freedom (DoF) designed to tackle tasks of diagnosis and rehabilitation in an injured knee. The original layout of the 4-DoF manipulator presents Type-II singular configurations within its workspace. Thus, we proposed to reconfigure the manipulator for avoiding such singularities (owing to the Forward Jacobian of the PKM) during typical rehabilitation trajectories. We achieve the reconfiguration of the PKM through a minimization problem where the design variables correspond to the anchoring points of the robot limbs on fixed and mobile platforms. The objective function relies on the minimization of the forces exert by the actuators for a specific trajectory. The minimization problem considers constraints equations to avoid Type-II singularities, which guarantee the feasibility of the active generalized coordinates for a particular path. To evaluate the proposed conceptual strategy, we build a prototype where reconfiguration occurs by moving the position of the anchoring points to holes bored in the fixed and mobile platforms. Simulations and experiments of several study cases enable testing the strategy performance. The results show that the reconfiguration strategy allows obtaining trajectories having minimum actuation forces without Type-II singularities.     

Hardware design and distributed embedded control architecture of a mobile soccer robot

Designing robust, modular and fast mobile robots, operating in high dynamic environments is a challenging task. This includes design of the mechanics and the control system of the robot. This paper presents the modular hardware design of a mobile soccer robot platform, including the mechanics, electronic system and the low-level distributed control architecture of the robot. The basic idea behind this paper is not to introduce a new distributed control architecture, both at low and high levels of control, but to focus on a novel approach to manage the distributed control system of a single robot, consisting of a number of microcontroller based modules connected together through a data bus.     

Calculation of a robot manipulator model in the form of arecurrent neural net

A neural model for robot manipulator is proposed similar to the mathematical model of a robot manipulator in the form of a Lagrange-Euler equation. A learning algorithm based on the backpropagation method is given for a neural model. A numerical example of calculation of a neural model for Puma 560 robot is presented.     

Application of Photoelectric Devices to Robot Soft Grasp

A robot slide tactile sensor based on photoelectric devices is introduced.The sensor is mounted on the hydraulic manipulator and used in a soft grasp control system.The experimental results are also presented.     

Intelligent switching control of a pneumatic muscle robot arm using learning vector quantization neural network

Pneumatic cylinders are one of the low-cost actuation sources used in industrial and prosthetic application, since they have a high power/weight ratio, high-tension force and long durability. However, problems with the control, oscillatory motion and compliance of pneumatic systems have prevented their widespread use in advanced robotics. To overcome these shortcomings, a number of newer pneumatic actuators have been developed, such as the McKibben Muscle, Rubber Actuator and Pneumatic Artificial Muscle (PAM) Manipulators. In this paper, the solution for position control of a robot arm with slow motion driven by two pneumatic artificial muscles is presented. However, some limitations still exist, such as a deterioration of the performance of transient response due to the changes in the external load. To overcome this problem, a switching algorithm of the control parameter using a learning vector quantization neural network (LVQNN) is proposed in this paper. The LVQNN estimates the external load of the pneumatic artificial muscle manipulator. The effectiveness of the proposed control algorithm is demonstrated through experiments with different external working loads.     

Global minimum-jerk trajectory planning of robot manipulators

A new approach based on interval analysis is developed to find the global minimum-jerk (MJ) trajectory of a robot manipulator within a joint space scheme using cubic splines. MJ trajectories are desirable for their similarity to human joint movements and for their amenability to path tracking and to limit robot vibrations. This makes them attractive choices for robotic applications, in spite of the fact that the manipulator dynamics are not taken into account. Cubic splines are used in a framework that assures overall continuity of velocities and accelerations in the robot movement. The resulting MJ trajectory planning is shown to be a global constrained minimax optimization problem. This is solved by a newly devised algorithm based on interval analysis and proof of convergence with certainty to an arbitrarily good global solution is provided. The proposed planning method is applied to an example regarding a six-joint manipulator and comparisons with an alternative MJ planner are exposed     

3DCLIMBER: Climbing and manipulation over 3D structures

This paper describes the development of a novel pole climbing robot with the ability of climbing and manipulating across 3D structures, like petrochemical pipelines. The robot consists of a 4-DOF serial climbing mechanism and two grippers. Unlike many other developed pole climbing robots, 3DCLIMBER can overcome bends, T-junctions, flanges, and sharp changes on the pole’s diameter. With the current gripper, the robot can operate on circular profiles with diameters ranging from 200 mm to 350 mm and is able to scan the exterior surface of the pole. Existence of separate gripping and climbing modules allows application of various grippers for different profile shapes and sizes without any change on the climbing mechanism. In case of power failure the robot maintains its status without slipping on the structure. Furthermore, some nondestructive test operations require fine manipulation over the structure. Fine manipulation with an industrial arm encounters many well known difficulties. Such difficulties become even more problematic when the base of the robot’s arm is mobile. This problem was addressed by a robotic proprioception solution embedded into the robot by integration of inclinometers and range finder sensors as well as error compensation and self calibration algorithms. The proposed algorithms and sensors significantly improved the manipulation accuracy of the robot.     

Dynamics and control of redundantly actuated parallel manipulators

It has been shown that redundant actuation provides an effective means for eliminating singularities of a parallel manipulator, thereby improving its performance such as Cartesian stiffness and homogeneous output forces. Based on this concept, several high-performance parallel manipulator prototypes have been designed. A major difficulty that prevents application of the vast control literature developed for the serial counterparts to redundantly actuated parallel manipulators is the lack of an efficient dynamical model for real-time control. In this paper, using the Lagrange-D'Alembert formulation, we propose a simple scheme for computing the inverse dynamics of a redundantly actuated parallel manipulator. Based on this approach, four basic control algorithms, a joint-space proportional derivative (PD) control, a PD control in generalized coordinates, an augmented PD control, and a computed-torque control, are formulated. A two-degrees-of-freedom redundantly acutated parallel manipulator designed for a high-speed assembly task is used to verify the simplicity of the proposed approach and to evaulate the performance of the four control algorithms.     

Tool-Center-Point control of the KAI manipulator using constrained QP optimization

The KAI manipulator is a four joint mobile manipulator, which will be used within the German road clearance package to investigate improvised explosive devices and ordnance from within an armored vehicle. To improve handling of the manipulator, a Tool-Center-Point (TCP) control is implemented. By using constrained quadratic optimization (cQP) it is possible to allow for the control of the manipulator within three different operating spaces. The QP is formulated to account for constraints in the joint angular rates and TCP velocities, as well as additional velocity constraints, e.g. on the movement of the center of mass of the manipulator. The proposed algorithm is able to handle redundant as well as non redundant manipulator kinematics. By using an efficient QP solver the algorithm can be used within a real-time trajectory generation scheme. The performance of the algorithm is demonstrated using simulation results and validated by measurements of the TCP control.     

Application of rubber artificial muscle manipulator as arehabilitation robot

The application of a robot to rehabilitation has become a matter of great concern. This paper deals with functional recovery therapy, one important aspect of physical rehabilitation. Single-joint therapy machines have already been achieved. However, for more efficient therapy, multjoint robots are necessary to achieve more realistic motion patterns. This kind of robot must have a high level of safety for humans. A pneumatic actuator may be available for such a robot, because of the compliance of compressed air. A pneumatic rubber artificial muscle manipulator has been applied to construct a therapy robot with two degrees of freedom (DOF). Also, an impedance control strategy is employed to realize various motion modes for the physical therapy modes. Further, for efficient rehabilitation, it is desirable to comprehend the physical condition of the patient. Thus, the mechanical impedance of the human arm is used as an objective evaluation of recovery, and an estimation method is proposed. Experiments show the suitability of the proposed rehabilitation robot system     

Minimum delay PID control of interpolated joint trajectories ofrobot manipulators

The digital implementation of an optimal PID (proportional integral derivative) controller of linearly interpolated joint trajectories is presented. The controller obtains optimal performance by reformulating the PID control law to minimize the time delay between the position transducer reading and the application of the corrective torque. Compared with the PID controller that is computed in a straightforward fashion, this formulation reduces the time delay by a factor of three. The superior performance of the proposed minimum-delay PID (MD PID) is demonstrated by experiments on a robot manipulator. Other practical issues associated with a digital PID control of joint trajectories of a robot manipulator, such as integer overflow and compensation for dynamics and joint-friction, are discussed     

Self-localisation of indoor mobile robots using multi-hypotheses and a matching algorithm

This paper proposes a new, fast and computationally light weight methodology to pinpoint a robot in a structured scenario.The localisation algorithm performs a tracking routine to pinpoint the robot’s pose as it moves in a known map, without the need for preparing the environment, with artificial landmarks or beacons. To perform such tracking routine, it is necessary to know the initial position of the vehicle. This paper describes the tracking routine and presents a solution to pinpoint that initial position in an autonomous way, using a multi-hypotheses strategy.This paper presents experimental results on the performance of the proposed method applied in two different scenarios: (1) in the Middle Size Soccer Robotic League (MSL), using artificial vision data from an omnidirectional robot and (2) in indoor environments using 3D data from a tilting Laser Range Finder of a differential drive robot (called RobVigil).This paper presents results comparing the proposed methodology and an Industrial Positioning System (the Sick NAV350), commonly used to locate Autonomous Guided Vehicles (AGVs) with a high degree of accuracy in industrial environments.     

Optimization of a spherical mechanism for a minimally invasive surgical robot: theoretical and experimental approaches

With a focus on design methodology for developing a compact and lightweight minimally invasive surgery (MIS) robot manipulator, the goal of this study is progress toward a next-generation surgical robot system that will help surgeons deliver healthcare more effectively. Based on an extensive database of in-vivo surgical measurements, the workspace requirements were clearly defined. The pivot point constraint in MIS makes the spherical manipulator a natural candidate. An experimental evaluation process helped to more clearly understand the application and limitations of the spherical mechanism as an MIS robot manipulator. The best configuration consists of two serial manipulators in order to avoid collision problems. A complete kinematic analysis and optimization incorporating the requirements for MIS was performed to find the optimal link lengths of the manipulator. The results show that for the serial spherical 2-link manipulator used to guide the surgical tool, the optimal link lengths (angles) are (60 degrees, 50 degrees). A prototype 6-DOF surgical robot has been developed and will be the subject of further study.     

Identification of dynamic and friction parameters of a parallel manipulator with actuation redundancy

The dynamic model is formulated in the joint space for a parallel manipulator with actuation redundancy. The established model is expressed in its linear matrix form with respect to the dynamic and friction parameters, and then the Weighted Least Square (WLS) method is applied to estimate the parameters. In order to get satisfying estimated results, the filters of joint angle and actuated torque are designed for the parallel manipulator. A simple and effective method is presented to design the excitation trajectory by analyzing the mechanism structure characteristics of the actual parallel manipulator. Another type of trajectory which is different from the excitation trajectory is adopted to verify the estimated parameters. The dynamic control experiments based on the identified model with the estimated parameters are implemented on an actual 2-DOF parallel manipulator with actuation redundancy, and the tracking accuracy of the identified model is compared with the result of the so-called nominal model.     

System design and control of an apple harvesting robot

There is a growing need for robotic apple harvesting due to decreasing availability and rising cost in labor. Towards the goal of developing a viable robotic system for apple harvesting, this paper presents synergistic mechatronic design and motion control of a robotic apple harvesting prototype, which lays a critical foundation for future advancements. Specifically, we develop a deep learning-based fruit detection and localization system using a RGB-D camera. A three degree-of-freedom manipulator is designed with a hybrid pneumatic/motor actuation mechanism to achieve dexterous movements. A vacuum-based end-effector is used for apple detaching. These three components are integrated into a robotic apple harvesting prototype with simplicity, compactness, and robustness. Moreover, a nonlinear control scheme is developed for the manipulator to achieve accurate and agile motion control. Field experiments are conducted to demonstrate the performance of the developed apple harvesting robot.     

基于分布式的移动机器人控制系统设计与实现

移动机器人是近年来研究的热点,针对机器人系统自由度多,可靠性和实时性要求高的特点,提出了一种基于分布式的移动机器人控制系统。利用多借点连接方式的网络拓扑机构,将其他设备和多个机器人连接组成机器人控制系统,以控制芯片ARM Cortex-A9和STM32F407为基础,将开源操作系统植入到开源嵌入式系统中,设计分布式上位机控制软件和下拉机程序,设计了基于分布式的移动机器人控制系统的搭建,实现对分布式移动机器人的控制。该分布式移动机器人软硬件开源、性能高、成本低、具有很好的可扩展性、实时性和稳定性。