Link Manipulator Research Articles

Collision avoidance analysis of human-robot physical interaction based on null-space impedance control of a dynamic reference arm plane.

When the terminal upper limb rehabilitation robot is used for motion-assisted training, collisions between the manipulator links and the human upper limb may occur due to the null-space self-motion of the redundant manipulator. A null-space impedance control method based on a dynamic reference arm plane is proposed to realize collision avoidance during human-robot physical interaction motion for the collision problem between the manipulator links and the human upper limb. Firstly, a dynamic model and a Cartesian impedance controller of the manipulator are established. Then, the null-space impedance controller of the redundant manipulator is established based on the dynamic reference plane, which manages the null-space self-motion of the redundant manipulator to prevent collision between the manipulator links and the human upper limb. Finally, it is experimentally verified that the method proposed in this paper can effectively manage the null-space self-motion of the redundant manipulator, and thus achieve collision avoidance during the human-robot physical interaction motion. This research has significant potential in improving the safety and feasibility of motion-assisted training with rehabilitation robots.

Elements of the theory of designing manipulators from composite materials for ground robotic complexes for special purposes

Elements of the theory of designing manipulators from composite materials intended for use in ground-based robotic complexes for special purposes have been developed. Circuit solutions of manipulators and constructive execution of their main components and elements are proposed. Special hinges and remote drives for moving links of manipulators have been developed. To ensure the required static and dynamic characteristics, special mechatronic modules are implemented in the form of geared motors that are outside the manipulators. Control systems of geared motors are implemented on the basis of artificial neural networks using the results of mathematical modeling of statics and dynamics of manipulators by helical calculus methods. The developed manipulators significantly increase the functionality of ground robotic complexes when they work with dangerous objects.

The system of coordinated operation of two underwater vehicles in a complex environment

The paper discusses methods that ensure the coordinated operation of two autonomous underwater vehicles, one of which is equipped with a multi–link manipulator and a vision system, and the second - auxiliary – only a vision system. These methods ensure the joint operation of two autonomous underwater vehicles both in the mode of semi-automatic positional remote control of the manipulator, and in the mode of automatic execution of operations with various objects by them. At the same time, in both modes, work is considered in situations when the vision system of the main underwater vehicle does not allow observing the object of work, which is nevertheless located in the working area of the manipulator. In this case, the auxiliary inspection underwater vehicle with its own vision system is used to monitor the object. In the semi-automatic remote control mode, the manipulator automatically takes into account the current spatial orientation of the optical axis of the vision system of the inspection underwa-ter vehicle, as well as the spatial orientations of both underwater vehicles at yaw angles in the absolute coordinate system. And in automatic mode, an accurate transfer of the spatial location and orientation of the object, which are determined using the vision system of the inspection underwater vehicle, is additionally provided to the associated coordinate system of the main underwater vehicle. At the same time, it is possible to identify and eliminate errors that occur during the operation of the vision system and navigation systems of both underwater vehicles. The re-sults of experimental studies have confirmed the operability of the proposed methods, the technical implementa-tion of which does not cause fundamental difficulties.

Modeling and fuzzy control of flexible manipulator link with moving end effector

In this paper, a flexible robotic arm system was designed and constructed based on the aspect ratio of flexible arms. The mathematical modeling was derived using finite element method. In addition, necessary information about the dynamic behavior of the suggested system was collected and used to design controllers based on knowledge of fuzzy logic theory. The purpose of building the flexible robotic arm was to perform different movements while ensure the accuracy of the derived mathematical dynamic model. This was achieved by comparing the experimental responses with theoretical ones where both systems were controlled through control strategies designed on the basis of fuzzy logics. The resulted control system is a 2-input, 1-output system. Different fuzzy controllers were suggested in addition to the non-conventional fuzzy control method (Fuzzy Control). This includes traditional-fuzzy control method with PID as well as PD controllers.The results showed that the error ratio between theoretical and practical responses does not exceed 16% in Fuzzy Control method and 11% in the PD-Fuzzy Control and 9% in the PID-Fuzzy Control method. This mismatch is due to the nonlinearities and friction effects between the different mechanical parts that have not be considered. In addition, the overshoot percentage also does not exceed 7% in the first and second methods and 8% in the third method. All outcomes are scientifically discussed and analyzed to obtain the best approach to design a high performance flexible robotic arm system.

Robotic date fruit harvesting using machine vision and a 5‐DOF manipulator

AbstractDate fruits can be found at the highest point of the palm tree, so harvesting can be a dangerous task for humans. In this study, a robotic arm is presented to harvest date fruits. A manipulator, traveling on a U‐shaped rail with four prismatic joints and one revolute joint, was designed and constructed to approach the fruits efficiently. The end‐effector of the manipulator was an electric chainsaw capable of cutting the date bunch. Two cameras were located on the manipulator in perpendicular directions to capture images, which were then transmitted to a decision‐making unit to control the speed of the manipulator links. The decision‐making unit included three fuzzy inference systems that used the location data of the fruit bunch stems and the area of tree leaves in the images to determine the speed of electromotors of the trolley, horizontal link, and vertical link. An artificial palm tree with dimensions similar to a real palm tree was constructed to evaluate the performance of the robot. The performance of the robot was evaluated in various lighting conditions. The results showed that the introduced image processing algorithm could adequately detect the stems of the date bunches with accuracy, precision, and recall of 0.88, 0.92, and 0.96, respectively, in suitable lighting, that is, when there was sufficient natural lighting. Moreover, the experimental results revealed that the accuracy of the control system in cutting the stems was 87%, with a production loss of 5%. The proposed robot makes it possible to improve the capacity of using mechanized harvesting in date palm fields.

On the issue of ensuring the equilibrium stability of the manipulator links

On the issue of ensuring the equilibrium stability of the manipulator links

Mathematical modeling and kinematic analysis of 5 degrees of freedom serial link manipulator for online real-time pick and place applications

<span lang="EN-US">Modeling and kinematic analysis are crucial jobs in robotics that entail identifying the position of the robot’s joints in order to accomplish particular tasks. This article uses an algebraic approach to model the kinematics of a serial link, 5 degrees of freedom (DOF) manipulator. The analytical method is compared to an optimization strategy known as sequential least squares programming (SLSQP). Using an Intel RealSense 3D camera, the colored object is picked up and placed using vision-based technology, and the pixel location of the object is translated into robot coordinates. The LOBOT LX15D serial bus servo controller was used to transmit these coordinates to the robotic arm. Python3 programming language was used throughout the entire analysis. The findings demonstrated that both analytical and optimized inverse kinematic solutions correctly identified colored objects and positioned them in their appropriate goal points.</span>

Trajectory Tracking and Adaptive Fuzzy Vibration Control of Multilink Space Manipulators with Experimental Validation

This paper investigates the problem of modeling and controlling a space manipulator system with flexible joints and links. The dynamic model of the flexible manipulator system is derived by using the Lagrange equation and the floating frame of reference formulation, where the assumed mode method is adopted to discretize flexible links, while the flexible joints are regarded as linear torsion springs. The natural characteristics of a single flexible link manipulator, under three different boundary conditions, are compared to reveal the effect of the flexibility of joints on the manipulator system and to choose suitable assumed modes. Furthermore, singular perturbation theory is introduced to decompose the system into a slow subsystem that describes the rigid-body motion, and a fast subsystem that describes the elastic vibration. Since the system is underactuated, a compound control strategy, which consists of the underactuated computed torque controller and the adaptive fuzzy controller, is presented to improve the accuracy of the trajectory tracking of the flexible joints and to suppress the elastic vibration of the flexible links, in the meantime. Both numerical simulation and experimentation are performed to verify the effectiveness of the proposed compound controller, and a comparison with the proportional-derivative (PD) controller is provided to highlight its superiority in suppressing the residual vibration of the tip.

FEATURES OF KINEMATICS AND CONTROL OF MULTI-LINK MANIPULATOR ROBOTS

The subject of research is multi-link manipulators, their kinematics and methods of controlling multi-link manipulator robots. To improve the accuracy of movement of each link and their synergy of work with each other during operation. In addition, the subject of the research is the analysis of the requirements for multi-link robot manipulators and the improvement of the kinematics of the robot-manipulator movements based on the comparison of mathematical methods in operating conditions. In different operating conditions manipulators and the automation of the production line is a big step for industry. Instead of a traditional industrial robot, a multi -link manipulator robot can be a good intermediate solution. It is more maneuverable, flexible, and has more complex movements for working on serial production. Multi-link robots provide a quick replacement of skilled labor in case of a shortage of employees or when production needs to be accelerated. As with any revolutionary technology, it is necessary to be critical of its implementation. The most decisive advantage of a robot over a single-link industrial robot is flexibility. Especially since the production environment needs to be able to adapt to handle the work with small volumes and a large number of different tasks. Such robots are more mobile and take up less space than traditional industrial robots. They are easier to reprogram to perform different jobs or product variants. However, it is worth noting that programming a traditional robot, which in its specialized environment requires deep knowledge and endless settings. When using a robot, the entry barrier for operators is significantly reduced, while deployment and ROI are accelerated. The aim of the work is to determine how the project context affects the choice of motion techniques and to determine the dependencies between requirements discovery methods. The article solves the following tasks: to study the trajectory of robots and compare mathematical control methods. Requirements in industry, create and draw a parallel regarding the practice of using demonstration robots and requirements in real conditions of using multi-link structures, determine the preferences of practitioners regarding detection methods and determine how the project context affects the choice of requirements detection techniques, determine dependencies between requirements detection methods. The task using such a method as a parametric form of the task is to prove that: the mathematical model of motion trajectories is the most reliable. Development and improvement of kinematic movements of manipulators with synergy of movements between manipulators. The following results were obtained: The best detection methods were identified and compared with other comprehensive studies. Conclusion: It was concluded that the choice of the shape of the wave-like trajectory of the movement; a traveling wave in a coordinate system moving along this sine wave form should be used as a control program for an automatic drive system. The assignment of a form in the form of a sine wave appears unsuitable for this task, because the obvious disadvantage of the sine wave is a continuous change in curvature and greater curvature at the peaks at large amplitudes.

Vibration suppression method for flexible link underwater manipulator considering torsional flexibility based on adaptive PI controller with nonlinear disturbance observer

Achieving stable and high-precision control of underwater manipulators in complex ocean environments is one of the biggest challenges faced by the research of marine robotics at present. Flexible link manipulators can be installed on unmanned underwater vehicles to realize underwater operations such as underwater cable inspection, deep sea rescue, and marine organizational collections. The flexible link underwater manipulator will vibrate due to the influence of torsional flexibility and water flow disturbance during rotation, which will seriously affect the motion accuracy of the end actuator. In this paper, a control strategy combining the adaptive proportional-integral (PI) controller and the nonlinear disturbance observer is proposed, which indirectly suppresses vibration by improving the speed control accuracy. Firstly, according to the assumed mode method, a dynamic model of the flexible link underwater manipulator considering torsional flexibility and external disturbance is established. Next, the overload compensation control law is proposed to meet the closed-loop stability of the flexible link underwater manipulator. In addition, the PI controller's adaptive law is designed according to the Lyapunov theorem. Finally, the effectiveness of the adaptive PI controller with a nonlinear disturbance observer is proved by the simulation and control experiments of different control strategies. The results show that the proposed controller can achieve stable speed tracking and has a better vibration suppression effect.

Creation of a 3D kinematic model of the Delta manipulator using computer-aided design in NX

The article discusses the design of the Delta robot, which is part of a multirobotic system for aliquoting biological fluid. The purpose of the article is to obtain a dynamic model of the Delta manipulator using 3D modeling, which will allow studying the kinematic and dynamic characteristics of the manipulator for the specified parameters. A computer-aided design (CAD) system is used for modeling. The article presents an analytical calculation of the kinematic and dynamic parameters of the Delta manipulator in the RS structure, a solution to the inverse problem is presented. The process of creating a digital calculation model in the NX Nasrtan system is described. The preliminary calculation of kinematic and dynamic parameters made it possible to set parameters in the NX Nastran system to ensure the rotation of the drive shafts of the engines in accordance with the specified trajectory of the output link. For all parts of the manipulator, the center of mass is determined and the material is assigned. Motion simulation was carried out and dependences of changes in speeds, accelerations and movements of the manipulator links were obtained to implement the required trajectory of the mobile platform. This calculation allows you to build the trajectory of the output link with a given speed, setting the rotation of the drive links of the calculated model taking into account the forces of inertia.

A practical method for the deformation of long‐stroke hydraulic manipulators in grasping‐handling tasks

AbstractLong‐stroke hydraulic manipulators are utilized in various grasping‐handling tasks, and the flexible deformation of these manipulators is the primary obstacle that affects precise position control of the end‐effectors in Cartesian space. This deformation is manifested in the following three aspects: joint deformation, structural deformation and clearance variation. Due to deformation uncertainty, methods that model the hydraulic manipulator as a combination of flexible multibody systems and hydraulic actuators are unsuitable. In this article, we propose an incremental inverse kinematics model (IIKM) as a new approach to solving the above deformation difficulties. The projection method is used to obtain the inverse kinematic analytical solution of long‐stroke hydraulic manipulators, which is based on the manipulator deformation in the current configuration (current configuration refers to the arrangement of the manipulator links when the manipulator starts to move to the target position). The proposed method avoids complex flexible multibody modeling and parameter identification, allowing long‐stroke hydraulic manipulators to be accurately controlled within a certain neighborhood. An evaluation coefficient is proposed to analyze the calculation accuracy of the IIKM in combination with the success rate obtained from 190 grasping experiments. Through these experiments, we determine the optimal calculation height range of the IIKM in the vertical direction and the optimal calculation position area in the horizontal direction and prove that the IIKM result can guarantee the success of grasping‐handling tasks when the end‐effector is within the optimal calculation height range.

Two-link Manipulator Driven by a Pair of Antagonistic Rubber Artificial Muscle

Pneumatic rubber artificial muscles have been extensively researched as a driving device capable of soft movements that are compatible with humans, and are expected to be applied to human friendly robots. However, it is difficult in principle to achieve high-precision positioning and high-rigidity position retention due to low stiffness and delayed response as a result of air compressibility. Normally, a 2-link manipulator requires 4 (2 pairs) artificial muscles, but here, by attaching two MR brakes to each axis and switching the drive shaft, a manipulator that controls a 2-link manipulator with 2 (1 pair) artificial muscles, is proposed.

Research on Constraint Following Control of Flexible Joint Manipulators Based on Singular Perturbation

For the control of 2-link flexible joint manipulators, a control method based on the singular perturbation theory and the Udwadia-Kalaba (U-K) method was proposed. The control design was implemented by 2 steps. First, the system order was reduced based on the singular perturbation method and the system was divided into fast and slow sub-systems, to simplify the solution process and overcome the system flexibility. Second, the state feedback constraint following control law for the fast and slow sub-systems was designed with the U-K method, to make the constraint following errors of the fast and slow sub-systems converge to zero, even if the system can't initially satisfy the constraints. The proposed method can deal with holonomic and nonholonomic servo constraints at the same time without the auxiliary variables of the Lagrange multiplier and the pseudo generalized velocity. The method was applied to 2-link flexible joint manipulator systems to solve the flexible oscillation and constraint following problems. Through simulations on MATLAB, and was compared with the traditional PID control, to verify the effectiveness and superiority.

Investigating the Potential of Flexible Links for Increased Payload to Mass Ratios for Collaborative Robotics

One of the main restrictions of commercial cobots can be found in their limited payload to mass ratios. Flexible link manipulators seem to offer interesting advantages over traditional rigid robotics, in terms of lower self-weight, lower energy consumption and safer operation. However, the design and loading specifications in the general literature on flexible link manipulators differ from those expected in a collaborative industrial setting. In this paper, we want to investigate whether the use of flexible links can be truly beneficial for collaborative robotics. Firstly, the theoretical potential of flexible links to increase the payload to mass ratio is investigated. The feasibility to design a cylindrical flexible link for specific, realistic loading conditions is investigated, and the effect of link flexibility on the demanded motor torque and maximum reachable payload is visualised, while considering cylindrical links. Subsequently, to get insights in the accuracy and usability of such a manipulator, we experimentally quantify to what extent the undesired side effects of the flexible design can be counteracted using an appropriate controller. To comply with the envisioned application of collaborative robotics, a control strategy based on strain measurements along the link and robust to payload changes is proposed. The obtained accuracy was measured by tracking the end effector position using a Vicon motion capture system, considering two types of single link designs; firstly, a very flexible link setup with rectangular cross section, and secondly, a cylindrical flexible link, loaded to reach a payload to mass ratio of 1.

Precise Automation of Rotary Flexible Link Manipulator Using Hybrid Input Shaping With Single State Feedback Fuzzy Logic and Sliding Mode Controllers

Precise Automation of Rotary Flexible Link Manipulator Using Hybrid Input Shaping With Single State Feedback Fuzzy Logic and Sliding Mode Controllers

Investigation and analysis of the linear dimensions of the flexible manipulator section in the process of tilting

A feature of the functioning of such a device is a change in the position of each of the sections. The study of the peculiarities of changing the position of the link is an important task. The article investigates the features of the functioning of the flexible manipulator link in the process of tilting. Three rods are responsible for the process of changing the position of the link. Depending on the nature of the movement rods increase or decrease in length. The principle of position changing when the link is tilted evenly on two rods is considered. With the help of analytical geometry the analysis of changes in the linear dimensions of moving elements is carried out. The results of the calculations are presented in the form of graphs and allow us to show the process of changing the position of the rods in the process of tilting.

The literature review in modeling and fuzzy control of flexible manipulator link with moving end effector

This investigation provides a review of the literature on the control of robot arms using the fuzzy logic control and the traditional control with a focus on the first one. With the flexible link classification of single link and multi-link manipulators. In addition to showing common methods for deriving the mathematical modeling of the flexible link manipulator and its comparison based on criteria in the flexible link used. Therefore the main distinguishing feature of the review literature here is that it takes a holistic view of the control process in the various systems, rather than focusing on one side in it, which leads to an insufficient understanding of the control systems used.

Partial Lagrangian for Efficient Extension and Reconstruction of Multi-DoF Systems and Efficient Analysis Using Automatic Differentiation

In the fields of control engineering and robotics, either the Lagrange or Newton–Euler method is generally used to analyze and design systems using equations of motion. Although the Lagrange method can obtain analytical solutions, it is difficult to handle in multi-degree-of-freedom systems because the computational complexity increases explosively as the number of degrees of freedom increases. Conversely, the Newton–Euler method requires less computation even for multi-degree-of-freedom systems, but it cannot obtain an analytical solution. Therefore, we propose a partial Lagrange method that can handle the Lagrange equation efficiently even for multi-degree-of-freedom systems by using a divide-and-conquer approach. The proposed method can easily handle system extensions and system reconstructions, such as changes to intermediate links, for multi-degree-of-freedom serial link manipulators. In addition, the proposed method facilitates the derivation of the equations of motion-by-hand calculations, and when combined with an analysis algorithm using automatic differentiation, it can easily realize motion analysis and control the simulation of multi-degree-of-freedom models. Using multiple pendulums as examples, we confirm the effectiveness of system expansion and system reconstruction with the partial Lagrangians. The derivation of their equations of motion and the results of motion analysis by simulation and motion control experiments are presented. The system extensions and reconstructions proposed herein can be used simultaneously with conventional analytical methods, allowing manual derivations of equations of motion and numerical computer simulations to be performed more efficiently.

Dynamics analysis and vibration suppression of a spatial rigid-flexible link manipulator based on transfer matrix method of multibody system

Dynamics analysis and vibration suppression of a spatial rigid-flexible link manipulator based on transfer matrix method of multibody system