Sadettin Kapucu

Residual swing/vibration reduction using a hybrid input shaping method

This paper addresses a hybrid input shaping method to reduce the residual swing of a simply suspended object transported by a robot manipulator or the residual vibration of equivalent dynamic systems. The method is based on the successive use of two input shaping methods. A cycloid is chosen as the trajectory to be preshaped. First of all, a ramp function is superimposed onto the cycloid and then the resulting trajectory is convolved with a sequence of two impulses. The resulting trajectory is preshaped twice. A hydraulically actuated robot manipulator carrying a simply suspended object is employed as the experimental system. Simulation and experimental results for each method constituting the hybrid method are presented and compared to what we call hybrid input shaping method. The results indicate that a swing-free stop is obtainable at the end of a move with a high degree of robustness to uncertainties in the natural frequency of the swinging or vibrating system by employing the hybrid method. The method is simple and easy to implement, and most importantly robust to uncertainties (15% of xn) in the natural frequency of the system. ” 2001 Elsevier Science Ltd. All rights reserved.

Hybrid input shaping to suppress residual vibration of flexible systems

This paper presents a hybrid input shaping method to eliminate residual vibration of multi-mode flexible systems. This method, initially designed for one degree of systems, is modified to apply on linear and nonlinear multi-mode systems. In this method, firstly the flexible system is uncoupled using modal analysis method, and then the parameters of the decoupled system are used to shape the command template signal. A ramp plus ramped cycloid plus ramped versine is proposed as the command template signal to be preshaped. The template function is preshaped to yield zero residual vibration for point to point motion and then the resulting trajectory is convolved with a sequence of two impulses to obtain a twice shaped input. The proposed method is applied to eliminate residual vibration of a linear multimass and flexible joint manipulator types of systems. Simulation results show that the oscillations are considerably decreased with a high degree of robustness in the presence of system parameters uncertainty.

On preshaped reference inputs to reduce swing of suspended objects transported with robot manipulators

One of the application areas of robot manipulators is pick-and-place operations where some objects may not be grasped by robot manipulators due to the task constraints. Such objects, for example those simply suspended, need to be carried by a hook or a similar device attached to the manipulator endpoint. This paper presents the results and implications of a study into preshaped reference inputs to reduce the swing of suspended objects at the end of a desired trajectory. Two reference input preshaping methods are considered; (i) superimposing a ramp function onto another function, and (ii) convolving a sequence of impulses with a desired reference input to generate a shaped input. A hydraulically actuated robot manipulator carrying a compound pendulum was employed as an experimental system to test the methods. Simulation and experimental results are presented to demonstrate the feasibility of both methods. It is concluded that while superimposing a ramp function onto another function such as a cycloid does not increase the transportation time while reducing the swing, whereas the latter, convolving a sequence of impulses with a cycloid, increases the transportation time. In addition to this, the robustness of the first method to the uncertainties in the natural frequency of the suspended object is better than that of the second method. The simulation and experimental results prove that by properly preshaping the reference input of a robot manipulator, a swing-free stop is obtainable. The proposed approaches are simple and easy to implement.

Swing-free transportation of suspended objects with robot manipulators

This paper addresses the swing-free transport of simply suspended objects which cannot be grasped by robot manipulators, and therefore, must be carried by a hook or a similar device attached to the manipulator endpoint. Two methods are presented to stop the suspended object in a swing-free state at the end of a move/gross motion; (1) limiting transportation time, thus stopping the manipulator at the instant when the object completes one or more full cycle(s), and (2) adjusting traveling time of each section of a three-piece continuous trajectory provided that a given transportation time is unchanged. A hydraulically actuated robot manipulator carrying a compound pendulum was employed as an experimental system to test the methods. Simulation and experimental results are presented to demonstrate the feasibility of both methods. It is concluded that while limiting transportation time is not a preferred way to eliminate swing at the end of the move as it depends on the period of oscillation of the suspended object, the latter is a more practical and applicable method and is valid for moves of any length. The results reveal that by properly planning the acceleration of the transporting device, a robot manipulator or a similar device such as a crane, a swing-free stop is obtainable. The proposed approaches are simple and easy to implement.

A robust motion design technique for flexible-jointed manipulation systems

This paper presents a robust input shaping technique that significantly reduces (almost eliminates) the residual vibration of manipulation systems typified by a flexible-jointed robot manipulator. The technique consists of two stages. In the first stage, a ramp function is superimposed onto the main trajectory to be preshaped. In the second stage, the outcome of the first stage is convolved with a sequence of two impulses. The robustness of the technique to the uncertainties in the system natural frequency and damping ratio are quantified through simulation and experimental evaluation. Simulation and experimental results demonstrate that the technique is not only effective in reducing the residual vibrations, but also it is robust to the uncertainties of as m35% from the ideal value of the system natural frequency. Further, it has been found that the proposed input shaping technique is insensitive to the uncertainties in the damping ratio. The results allow us to suggest that the proposed technique is versatile and robust enough to apply it to the motion design of any flexible-jointed manipulation system making a point-to-point motion.

Robotic arm dynamic and simulation with Virtual Reality Model (VRM)

This paper presents a study on control and simulation of the robotic arm system. A dynamic model is designed, and a Virtual Reality Model (VRM) is built for the robot. A kinematic model is represented for the robot links and joints. A simulation module is built by using SIMULINK/SimMechanics and by estimation of motor-gear transfer function. A PID control system (Proportional-Integral-Derivative) is then applied. The virtual model is created by Simulink 3D Animation. OWI-535 robotic arm is an articulated manipulator robot, it was chosen as testing system. The robot was developed with an interface control system. The interface control system is built to perform closed-loop control. Different trajectories were implemented on the robot. The results were shown for the simulated system and real robot in designing accuracy and system control response. Robot followed the desired trajectories efficiently.

A New Artificial Neural Network Approach in Solving Inverse Kinematics of Robotic Arm (Denso VP6242).

This paper presents a novel inverse kinematics solution for robotic arm based on artificial neural network (ANN) architecture. The motion of robotic arm is controlled by the kinematics of ANN. A new artificial neural network approach for inverse kinematics is proposed. The novelty of the proposed ANN is the inclusion of the feedback of current joint angles configuration of robotic arm as well as the desired position and orientation in the input pattern of neural network, while the traditional ANN has only the desired position and orientation of the end effector in the input pattern of neural network. In this paper, a six DOF Denso robotic arm with a gripper is controlled by ANN. The comprehensive experimental results proved the applicability and the efficiency of the proposed approach in robotic motion control. The inclusion of current configuration of joint angles in ANN significantly increased the accuracy of ANN estimation of the joint angles output. The new controller design has advantages over the existing techniques for minimizing the position error in unconventional tasks and increasing the accuracy of ANN in estimation of robots joint angles.

Vibration Reduction of a Lightly Damped System Using a Hybrid Input Shaping Method

Abstract This paper describes three different methods for generating a command profile for a lightly damped second-order system to manoeuvre it from one position to another, eliminating the residual vibrations likely to occur after the completion of the manoeuvre. The first method is a preshaped command input obtained by superimposing a cycloid onto a ramped versine + ramp function, and the second method is a reshaping of the input of any profile by convolving it with a sequence of two impulses. The third method, the ‘hybrid input method’, combines the first two methods to obtain a better robustness. The methods are tested on simulations, and the robustness of each is examined. The results show that the hybrid input shaping method is more robust to uncertainties in system parameters, namely the natural frequencies and damping ratio. The applicability of the methods is shown by experimental results.

On the identification of linear mechanical systems

Abstract General purpose controllers or controllers commanding systems which operate at varying conditions need a system identification routine to obtain a model for the response of the system so that it can adapt itself accordingly. Most such mechanical systems are composed of masses moving under the action of position and velocity dependent forces and hence can be modeled by second order linear differential equations. This paper describes how to obtain a simpler mathematical response model in the form of a linear difference equation for a second order linear system. Coefficients of the equation are calculated by using the least squares technique to minimize the error between the discrete position data from the system resulting when actuated by a pseudo-random binary command signal and what the model generates. An analytical solution obtained by the z -transformation of the system transfer function is also presented, to clarify the physical meaning of the coefficients. Experimental and analytical solutions for a variety of systems are presented as application examples.

Electronic System and Software Architecture of Modular Reconfigurable Robot Module OMNIMO

A robot is an electromechanical system, which is guided by software via electronic circuitry. In the absence of electronic systems, there is no way to make a connection between software and mechanical components. This means that all robotic systems require mechanical systems, electronic systems and software. OMNIMO, as a modular reconfigurable robot, has sophisticated electronic systems and software. Electronic system of OMNIMO includes controllers, actuators, transducers, communication units, regulators, batteries, user interface units and complementary components. In addition, OMNIMO is controlled by four different layers of software. In this paper, electronic hardware details, system integration and control software architecture of modular reconfigurable robot module OMNIMO are presented. In addition, adaptation of components and communication protocol details of hardware are given.