Link Manipulator Research Articles

Minimizing constraint forces and moments of manipulators using teaching–learning-based optimization and octahedron point mass model

The octahedron seven point mass model of equimomental point masses and optimization technique “teaching–learning-based optimization” is presented to minimize constraint forces and moments at joints of an industrial manipulator. The octahedron point mass model configuration presented offers positive values for equimomental point masses to facilitate link shape formation. Equations are derived to compute point masses and their locations for the rigid links of an industrial manipulator. The flow chart of the teaching–learning-based optimization applicable in solving the manipulators problem is presented and used. The constraint moments at heavily loaded joints are reduced significantly. Moreover, the maximum values of driving torques are also reduced at joints. It is observed that teaching–learning-based optimization gives better results with less computational effort vis-à-vis genetic algorithm for the manipulator optimization problem formulated. The teaching–learning-based optimization algorithm introduced first time for manipulator balancing as optimization solver.

Collision Detection and Safe Reaction Algorithm for Non-backdrivable Manipulator with Single Force/Torque Sensor

In this paper, we propose collision detection and safe reaction for a non-backdrivable manipulator with a base force/torque sensor. Measurement of the base force/torque sensor is compensated for using quasi-static dynamic information of the manipulator. Collision point, magnitude of force, and direction of force are detected by assuming an external collision to be pure force. While the manipulator is not convex, a collision point may not be unique when only using this assumption, so we assumed that a collision is applied outside the convex hull of the manipulator. For a simple calculation of collision point candidates, a cylinder model is applied to each manipulator link. Three different safe collision reaction strategies are proposed for reactions to a variety of force positions and directions One other strategy is proposed to remove the remaining contact force and to create a margin to avoid additional collisions. We ran several experiments to verify the effectiveness and performance of the strategies.

Intelligent tuning of vibration mitigation process for single link manipulator using fuzzy logic

In this work, active vibration mitigation for smart single link manipulator is presented. Two piezoelectric transducers were utilized to act asactuator and sensor respectively. Classical Proportional (P) controller was tested numerically and experimentally. The comparison between measured results showed good agreement. The proposed work includes the introducing of fuzzy logic for tuning controller's gain within finite element method. Classical Proportional-Integral (PI), Fuzzy-P and Fuzzy-PI controllers were totally integrated as a series of [IF-Then] states and solved numerically by using Finite Element (FE) solver (ANSYS). Proposed method will pave the way on solving the tuning process totally within single FE solver with high efficiency. Proposed method satisfied mitigation in the overall free response with about 52% and 74% of the manipulator settling time when Fuzzy-P and Fuzzy-PI controllers were activated respectively. This contribution can be utilized for many other applications related to fuzzy topics.

Analysis of Joint and Hand Impedance During Teleoperation and Free-Hand Task Execution

Teleoperated robotic surgery allows filtering and scaling the hand motion to achieve high precision during the surgical interventions. Teleoperation represents a very complex sensory-motor task, mainly due to the kinematic and kinetic redundancies that characterize the human motor control. It requires an intensive training phase to acquire sufficient familiarity with the master–slave architecture. We estimated the hand stiffness modulation during the execution of a simulated suturing task in teleoperation, with two different master devices, and in free hand. Kinematic data of eight right-handed users were acquired, using electromagnetic and optical tracking systems, and analyzed using a musculoskeletal model. Through inverse dynamics, muscular activation was computed and used to obtain the joint torque and stiffness, leading to end-point stiffness estimation. The maximal stiffness value and its angular displacement with respect to the trajectory tangent were computed. The results show that there is a difference in how the main stiffness axis was modulated by using the two master devices with respect to free hand, with higher values and variability for the serial link manipulator. Moreover, a directional modulation of the hand stiffness through the trajectory was found, showing that the users were aligning the direction of the main stiffness axis perpendicularly to the trajectory.

A fractional-order controller for single-link flexible robots robust to sensor disturbances

This work presents a new methodology for the design of the positioning control of single-link flexible manipulators which present only one vibration mode in their dynamics. In this work, the standard phase-lead compensator will be extended to a fractional-order compensator which will be used to minimize the vibrations of the flexible-link. The control objective is the precise positioning of the link tip by combining a precise motor positioning as well as reducing large part of the flexible-link vibration. The control strategy is based on combining a feedforward term and a feedback fractional-order controller. The methodology proposed in this work deals with two perturbations which are usually present in strain gauges, which are sensor habitually used to close feedback control loops of flexible link manipulators. These perturbations are: 1) the high frequency noise and 2) the offset of the signal. Experimental results illustrate the performance of the proposed controller and the advantages that this new design methodology provides.

Inverse dynamic analyzing of flexible link manipulators with translational and rotational joints

Inverse dynamic problem analyzing of flexible link robot with translational and rotational joints is presented in this work. The new model is developed from single flexible link manipulator with only rotational joint. The dynamic equations are built by using finite element method and Lagrange approach. The approximate force of translational joint and torque of rotational joint are found based on rigid model. The simulation results show the values of driving forces at joints of flexible robot with desire path and errors of joint variables between flexible and rigid models. Elastic displacements of end-effector are shown, respectively. There are remaining issues which need be studied further in future work because the error joints variables in algorithm to solve inverse dynamic problem of flexible with translational joint has not been mentioned yet.

Modeling of Two Link Flexible Manipulator using Bond Graph Technique

A mechanism involves a number of interconnected rigid bodies. To design and control a system, modeling of mechanism plays an important role .There are many methods used for modeling like Newton –Euler, Lagrange’s Euler and Hamiltonian method. These methods become very laborious and cumbersome for complex multibody systems. The above mention techniques however, do not expose the cause and effect relationship. In this paper, bond graph approach is used for modeling two link manipulator by considering the flexibility at the joints. Bond graph technique shows the pictorial representation of the dynamics of the system. Moreover it may also be used for modeling multi energy domain systems

Decreasing infinite-mode vibrations in single-link flexible manipulators by a continuous function

Unwanted vibrations caused by the commanded motions degrade positioning accuracy and safety in flexible link manipulators. There are an infinite number of vibration modes in a single-link flexible manipulator. The contribution of the first mode is fundamental, but the high modes might also have some impacts on the overall system dynamics. A continuous function is designed to control the vibrations of the total modes by smoothing the driving commands. Comparison between the new continuous function and input shaper, which is a series of impulses, is also explored and evaluated. Numerous simulations and experiments for a wide range of working conditions and modeling errors are performed to validate the effectiveness of the new continuous function.

Compact Arrangements of Cable-Pulley Type Zero-Free-Length Springs

A methodology to develop springs with zero-free-length (ZFL) characteristics is presented, and the configurations for placing the springs precisely on the manipulators are introduced. A spring–string arrangement installed between two separate links of a serial-type manipulator is employed and is divided into three regions for mounting, tensioning, and placing the string. The springs can develop ZFL characteristics if adequate length is ensured for mounting the springs. To shorten the length for placing strings, a reference length acquired from the link configurations is utilized. The minimization of the placing length can therefore be described clearly. Because the overextended springs and links occupied the workspace of the other links as a result of the long mounting length, the springs are reorganized using pulleys and wire winding configurations to shorten the mounting length. The springs can then be arranged in alignment on the links. As achieved with this additional arrangement, comprehensive spring configurations on the manipulators can be shown. Two examples are presented after deriving the spring configurations for ZFL characteristics and the configurations with wire winding, respectively.

On the unstable operating modes of manipulator electric drives

The mathematical model of dynamics of the electric-power DC drive for actuating links of tripod manipulator with self-breaking transmission has been considered. Analytical conditions of lack of dynamic jamming the drive have been obtained.

Building dynamic equations of manipulator with flexible links


 
 
 This paper presents the research of general model and building dynamic equations of two flexible links manipulator motion in the horizontal plane. Dynamic modeling is considered with adding factors which are payload, elastic friction, mass and initial moment of rotors. So it is closed to reality. Dynamic equations are derived through finite element method based on Lagrange approach. Dynamic behaviors of the system with payload were simulated like a specific example. The results can be used to building the control system which increases accuracy position of manipulators under influence of elastic displacements of links. 
 
 

A new quadrotor manipulation system: Modeling and point-to-point task space control

This article introduces a novel quadrotor manipulation system that consists of 2-link manipulator with unique topology attached to the bottom of a quadrotor. This new system presents a solution for the limitations found in the current quadrotor manipulation system. Unlike the current system, the proposed system enables the end effector to achieve an arbitrary position and orientation with minimum possible number of actuators/links. System kinematics and dynamics are derived. A new closed form inverse kinematics algorithm is presented such that a task space motion controller can be implemented. To study the feasibility of the proposed system, a quadrotor with high enough payload, to add the 2-link manipulator, is designed and constructed. The system controller is designed based on three control techniques: Feedback Linearization based PID (FL-PID), Direct Fuzzy Logic Control (DFLC), and Fuzzy Model Reference Learning Control (FMRLC). Simulation framework is implemented in MATLAB/SIMULINK based on real system parameters to emulate a realistic setup. These controllers are tested under the effect of picking/placing a payload and changing the operating region. Results enlighten the system feasibility, the superior performance of the FMRLC, and the efficiency of the proposed inverse kinematics algorithm.

Minimum time control of a two DOF robotic arm with noised measurements

This paper presents a new approach for minimum time control dynamics of a two links manipulator robot in the case of noised outputs. Briefly, this technique consists of linearizing a nonlinear dynamic model of the robot by using a feedback linearization control. Once, the linear model has been obtained, a minimum time control with constraints, using the Pontryagin Minimum Principle will be developed. Here, the objective is to control the arm robot from an initial configuration to the final configuration in minimum time. The state variables are estimated by a Kalman-Luenberger observer. In order to show the efficiency of the proposed method, some simulation results are given.

A Virtual Torque-Based Approach to Kinematic Control of Redundant Manipulators

This paper presents an inverse kinematics algorithm for a redundant manipulator. The proposed approach combines analytical and numerical methods to solve generalized inverse kinematics problems simultaneously in both free and constrained working spaces. The method introduces a virtual repulsive torque imposed by the topological configuration of robot links, joint limits, and obstacles with motion trajectories. The method calculates the shortest distances between joint limit, links, and obstacles. Links of manipulator and obstacles are modeled in ellipsoids so as to evaluate the minimum distances between obstacles and links of a redundant robot. Virtual repulsive torques imposed on links are estimated based on the shortest distances between these ellipsoidal objects. A numerical method obtains the tendency of major joints’ movements and calculates their potential velocities by composing these acting torques. In trajectory tracking, collision avoidance occurring on links can finally be achieved by utilizing the characteristics of joint redundancy. The validity and efficiency of the proposed method are measured in simulations of movement along trajectories in terms of a defined index of motion availability, by which it verifies that the method is not only feasible to constrained motions but also has better performances in free motions than inverse Jacobian techniques.

囲い込み制御による揺動型空気圧マニピュレータの従来法との比較

The passive dynamic control (PDC) is a mechanical system control method based on an inherently safe design means using a brake mechanism effectively. Since the follow-up control by the PDC can be envisaged as gradually narrowing down the wide area around a control object to enclose it toward the target trajectory, the authors designate this control as “enclosing control.” Here, the proposed method is evaluated by comparing with PI control and sliding mode control for rotary pneumatic 2 link manipulator. By experiments, in the enclosing control, the stick-slip is suppressed by the brake mechanism, and good follow-up accuracy can be obtained compared with the other control methods.

パラレルリンク型 2 自由度関節機構とその制御手法の開発

In a decade, the use of robots is expected not only for industrial usage but also for human support fields. The robots for human support in many cases are provided with redundant robot arm. This study proposes a shoulder joint that realizes the motion of two degree of freedom by using of the parallel mechanisms that consist of three serial links manipulators. This paper deals with the proposed shoulder joint mechanism and the shoulder joint kinematics composed of the kinematics of three serial links manipulator. Numerical simulations are conducted to confirm the feasibilities of the proposed shoulder mechanism into practice.

Comments on “Design of two-layered fractional order fuzzy logic controllers applied to robotic manipulator with variable payload”

Sharma et al. have investigated the performance of two-layered fractional order fuzzy logic controller (TL-FOFLC) for a 2-link rigid planer robotic manipulator with payload. In this work, the performance of TL-FOFLC has been compared with two-layered FLC (TL-FLC), single-layered FLC (SL-FLC) and the conventional proportional-integral-derivative (PID) controllers, for trajectory tracking, model uncertainties and disturbance rejection. In this comment, it is pointed out that this work has several missing essential parameters, and therefore, it is not possible for the reader to validate all the claimed results of Sharma et al. (2016). Six numerical values, three gains for each of the used two PID controllers are found to be unreported in addition to the six gains for each of the used two SL-FLCs. Since the performances of the PIDs and the SL-FLCs are highly dependent on their tuned gains it is concluded that the reported performances of these controllers cannot be validated.

Nonlinear adaptive fractional order fuzzy PID control of a 2-link planar rigid manipulator with payload

The main objective of this paper is to demonstrate that fractional order operators (differentiator/integrator) can increased the robustness of an intelligent controller. In this paper, a nonlinear adaptive fractional order fuzzy proportional integral derivative (NLA – FOFPID) controller is presented to control a nonlinear, coupled, multi-input and multi-output and uncertain system i.e. a 2-link planar rigid robotic manipulator with payload. The NLA – FOFPID controller is realized using non-integer order differentiator and integrator operators in nonlinear adaptive fuzzy proportional integral derivative (NLA – FPID) controller. The control objective is to track a reference trajectory in virtual industrial environment and under model uncertainties by minimizing the combination of integral of time weighted absolute error and integral of time weighted absolute change in controller output. The industrial environment was simulated by incorporating measurement noise, sinusoidal disturbance and model uncertainties. The gains of NLA – FPID and NLA – FOFPID controllers are optimized using recently reported Backtracking Search Algorithm. Intensive simulations were performed to assess the performances of NLA – FPID and NLA – FOFPID controllers for servo and regulatory mode. It has been observed that NLA – FOFPID controller outperforms NLA – FPID controller by offering much better performance. Particularly in uncertain environment it offered very robust behavior as compared to NLA – FPID controller. The sufficient stability conditions are also established for bounded-input and bounded-output stability of overall closed loop system by using small gain theorem.

Dynamics and Control of a Robotic Arm Having Four Links

The manipulator control is an important problem in robotics. To work out this problem, a correct dynamic model for the robot manipulator must be in hand. Hence, this work first presents the dynamic model of an existing 4-DOF robot manipulator based on the Euler–Lagrange principle, utilizing the body Jacobian of each link and the generalized inertia matrix. Furthermore, essential properties of the dynamic model are analyzed for the purpose of control. Then, a PID controller is designed to control the position of the robot by decoupling the dynamic model. To achieve a good performance, the differential evolution algorithm is used for the selection of parameters of the PID controller. Feedback linearization scheme is also utilized for the position and trajectory tracking control of the manipulator. The obtained results reveal that the PID control coupled with the differential evolution algorithm and the feedback linearization control enhance the performance of the robotic manipulator. It is also found out that increasing masses of manipulator links do not affect the performance of the PID position control, but higher control torques are required in these cases.

Joint configuration for physically safe human–robot interaction of serial-chain manipulators

Manipulators with a series of revolute joints usually have more than 6-DoFs from the shoulder to the wrist to conduct miscellaneous tasks for humans. To add physical interaction or safety to manipulators, functions of compliance or safety components are implemented to joints or links of manipulators. However, a physical interaction by a collision may occur anywhere from the base to the end-effector of the manipulators. If a collision occurs at upper link, which has relatively fewer-DoFs joints, an external force may not be transmitted to the respective joints and links properly. Therefore, a study of the overall joint configurations for manipulators is necessary. This paper suggests a simplified methodology for joint configurations of manipulators using two types of revolute joints, rotational (type R) or twist (type T) joints. When an external force is applied to the link attached to these joints, the characteristics of torque transmission are described. Then, optimal joint configurations at the shoulder joint of 2- or 3-DoFs are described for physical interaction to manipulators. Experimental results followed by the scenario from pre-collision to collision show that joint configurations affect the safety performance of the manipulator.