USPOREDBA EFIKASNOSTI SLIJEĐENJA TRAJEKTORIJE ROBOTA PRI UPOTREBI RAZLIČITIH METODA NELINEARNOG UPRAVLJANJA

The Denavit-Hartenberg algorithm and the Lagrange-Euler method are used to derive realistic kinematics and dynamic models of a three-axis electric driven articulated planar robot with viscous, dynamic and static frictions. These robot models are further used for testing the following presented nonlinear robot control methods: fuzzy control, variable-structure control and model-reference variable-structure control. In the fuzzy-logic control method seven fuzzy sets are defined for two input variables. Triangular input membership functions and the 7x7 fuzzy rule table are chosen. The fuzzy controller output value is calculated according to the centre of gravity principle. The same fuzzy control algorithm is used in all robot servo control loops with a proper scaling of the linguistic variables. To eliminate the chattering of the variable-structure control signal and to reduce energy consumption, sign function in the original variable-structure control law is replaced with the following functions: a continuous, saturation and exponential function, all of them with a very thin boundary layer. The same modifications are also made in the original model-reference variable-structure control method. In all presented control methods controller parameters are chosen according to the principle of maximal allowed tracking error and a minimum of energy consumption. These control methods are tested by computer simulations in C programming language in the case of moving the tool of the chosen robot arm. The simulation results proved similar efficiencies of all mentioned modified nonlinear robot control methods, although modified variable structure control algorithms are the most suitable because of their simplicity and lower number of controller parameters.Denavit-Hartenbergov algoritam i Lagrange-Eulerova metoda upotrijebljeni su za izradu realnog kinematičkog i dinamičkog modela troosnog rotacijskog ravninskog robota s električnim motorima i viskoznim, dinamičkim i statičkim trenjem. Ti su modeli robota kasnije korišteni za provjeru sljedećih predstavljenih nelinearnih postupaka upravljanja robotom: neizrazitog upravljanja, upravljanja s promjenjivom strukturom te upravljanja s referentnim modelom i promjenjivom strukturom. U metodi upravljanja s neizrazitom logikom definirano je sedam neizrazitih skupova za dvije ulazne varijable. Izabrane su trokutaste ulazne funkcije pripadnosti i tablica neizrazitih pravila veličine 7 x 7. Vrijednost izlaza neizrazitog regulatora izračunata je po principu težišta neizrazitog skupa. Isti neizraziti upravljački algoritam upotrijebljen je u svim petljama slijednog upravljanja robotom, uz odgovarajuće skaliranje jezičnih varijabli. Za uklanjanje trešnje iz upravljačkog signala s promjenjivom strukturom i zbog smanjenja potrošnje energije, funkcija predznaka je u prvobitnom zakonu upravljanja s promjenjivom strukturom zamijenjena sljedećim funkcijama: neprekidnom, funkcijom zasićenja i eksponencijalnom funkcijom, s vrlo tankim graničnim slojem u svima. Iste su promjene također napravljene i u originalnoj metodi upravljanja s referentnim modelom i promjenjivom strukturom. U svim su predstavljenim postupcima upravljanja parametri regulatora izabrani po principu najveće dozvoljene pogreške slijeđenja i najmanje potrošnje energije. Ove su metode upravljanja provjerene računalnim simulacijama u programskom jeziku C na primjeru kretanja alata izabrane robotske ruke. Rezultati simulacija dokazali su sličnu efikasnost svih spomenutih promijenjenih nelinearnih postupaka upravljanja robotom, iako su modificirani upravljački algoritmi s promjenjivom strukturom najprimjenjiviji zbog svoje jednostavnosti i manjeg broja parametara regulatora

Control Improvement of Low-Cost Cast Aluminium Robotic Arm Using Arduino Based Computed Torque Control

Gravity causes non-linearity in position control of an articulated industrial robotic arm. Especially for a joint position control of a robot’s shoulder and elbow that works parallel with the gravity direction. To overcome the problem, Computed Torque Control algorithm was implemented. This algorithm linearized the feedback, so a regular linear Proportional Derivative controller can be implemented. The contribution of this research is to find an effective controller to control a heavy weight low-cost robotic arm link/body using low-cost controller such as Arduino. A Computed Torque Control was implemented to control the shoulder joint of an articulated robotic arm. This joint is the most affected joint by the gravity. It works along the vertical plane, and loaded by the rest of the arm and the robot’s load. The proposed controller was compared to a Proportional Integral Derivative (PID) Controller and a Cascade PID Controller. The experiment showed that the Computed Torque Controller can control the position of the arm properly both in the direction along or against the gravity. A linear PID controller could not bring the arm to the set point when it moves against the gravity, but it works well when the arm moves in the opposite direction. A Cascade PID controller has an overshot when the arm moves along the gravity. But it works properly when it moves up against the gravity. A Computed Torque Control works well in both directions even in the presence of gravity force because it includes the gravity on its algorithm

The Efficiency of an Optimized PID Controller Based on Ant Colony Algorithm (ACO-PID) for the Position Control of a Multi-articulated System

In this article, a robot manipulator is controlled by the PID controller in a closed loop system with unit feedback. The difficulty of using the controller is parameter tuning, because the tuning parameters still use the trial and error method to find the PID parameter constants, namely Proportional Gain (Kp), Integral Gain (Ki) and Derivative Gain (Kd). In this case the Ant colony Optimization algorithm (ACO) is used to find the best gain parameters of the PID. The Ant algorithm is a method of combinatorial optimization, which utilizes the pattern of ants search for the shortest path from the nest to the place where the food is located, this concept is applied to tuning PID parameters by minimizing the objective function such that the robot manipulator has improved performance characteristics. This work uses the Matlab Simulink environment, First, after obtaining the system model, the ant colony algorithm is used to determine the proper coefficients p, i, and Kd in order to minimize the trajectory errors of the two joints of the robot manipulator. Then, the parameters will implement in the robot system. According to the results of the computer simulations, the proposed method (ACO-PID) gives a system that has a good performance compared with the classical PID

PARAMETER IDENTIFICATION OF A ROBOT ARM USING GENETIC ALGORITHMS

An identification method for inverse dynamics of a robot arm based on genetic algorithms (GA) is considered. It is shown that GAs are able to find robot parameters effectively even if the robot has low resolution position encoders. It is possible because the method only requires position feedback and there is no need to find out the speed and acceleration of the links that usually can only be done through finite differences calculations that cause dramatic errors during identification. The effectiveness of the algorithm is demonstrated on the example of parameter identification of the real robot PUMA 560 (for second and third links)

Studies on Trajectory Tracking of Two Link Planar Manipulator

In robotic manipulator control situations, high accuracy trajectory tracking is one of the challenging aspects. This is due to nonlinearities in dynamics and input coupling present in the robotic arm. In the present work, a two link planar manipulator revolving in a horizontal plane is considered. Its kinematics, Jacobian analysis, dynamic equations are obtained from modelling. It is proposed to use this manipulator for following a desired trajectory by using an effective control method. Initially, computed torque control scheme is used to obtain the end effector motions. The dynamic equations are solved by numerical method and the joint space results are used to obtain the error and its derivative. This linearized error dynamic control uses constant gains and an attempt is made to obtain a correct set of gains in each error cycle to refine the control performance. A scaled prototype is made with aluminium links and joint servos. A mechatronic system with an arduino microcontroller board is employed to drive the servos in incremental fashion as per the tracking point and its inverse kinematics. The computer results are shown for two trajectories namely a straight line and spline. The errors are reported as a function of time and the corresponding joint torques computed in each time step are plotted. Finally to illustrate the mechatronic control system on the prototype, a path containing three points is considered and corresponding errors and repeatability are presented

Modeling and computed torque control of a 6 degree of freedom robotic arm

This paper presents modelling and control design of ED 7220C - a vertical articulated serial arm having 5 revolute joints with 6 Degree Of Freedom. Both the direct and inverse kinematic models have been developed. For analysis of forces and to facilitate the controller design, svstem dvnamics have been formulated. A non-linear control technique, Computed Torque Control (CTC) has been presented. The algorithm, implemented in MATLAB/Simulink, utilizes the derived dynamics as well as linear control techniques. Simulation results dearly demonstrate the efficacy of the presented approach in terms of traiectory tracking Various responses of the arm joints have been recorded to characterize the performance of the control algorithm. The research finds its applications in simulation of advance nonlinear and robust control techniques as well as their implementation on the physical platform. © 2014 IEEE

Design and Control of an Articulated Robotic Arm Using Visual Inspection for Replacement Activities

Design of robotic systems and their control for inspection and maintenance tasks is highly complex activity involving coordination of various sub-systems. In application like inspections in fusion reactor vessels and deep-mining works, a regular off-line maintenance is necessary in certain locations. Due to the hostile environments inside, robotic systems are to be deployed for such internal observations. In this regard, current work focuses on the methodology for maintenance of the first wall blanket modules in a fusion reactor vessel using a manipulator system. A design is proposed for wall tile inspections in an ideal environment in which vacuum and temperature conditions are not accounted and wall surface curvature is not accounted initially. The entire design has four important modules: (i) mathematical modelling (ii) control system design (iii) machine vision and image processing, (iv) hardware development and testing. A five- axis articulated manipulator equipped with a vision camera in eye-to-hand configuration is designed for performing the pick and place operations of the defected tiles in a systematic manner. Kinematic and dynamics analysis of the system are first carried-out and a scaled prototype is fabricated for testing various operating issues. Forward kinematics of manipulator allows in estimation of robot workspace and in knowing the singular regions during operation, while the inverse kinematics of the manipulator would be needed for real time manipulator control task. Dynamics of manipulator is required for design of model-based controllers. Interactive programs are developed in Matlab for kinematics and dynamics and three-dimensional manipulator assembly configuration is modelled in SolidWorks software. Motion analysis is conducted in ADAMS software in order to compare the results obtained from the classical kinematics. Two types of model-based control schemes (namely Computed Torque Control and Proportional Derivative-Sliding Mode Control approach) with and without external disturbances are implemented to study trajectory tracking performance of the arm with different input trajectories. A disturbance observer model is employed in minimizing the tracking errors during the action of external disturbances such as joint friction and payload. In order to experimentally understand the inspection and replacement activities, a test set-up is developed using vision camera and microcontroller platform to guide the robot joint servos so as to perform defected object replacement activity. Presence of crack and the coordinate of the region are indicated with the use of image-processing operations. Using a high resolution Basler camera mounted at fixed distance from the tile surface, the surface images are acquired and image processing module identifies the crack details using edge detection algorithms. Necessary motion of the end-effector will be provided based on the pose calculations using coordinate transformations. Both visual inspection and joint guidance are combined in a single application and the results are presented with a test case of tile replacement activity. The results are presented sequentially using a test surface with uniform rectangular tiles