Real-Time Tip Position Control of a Flexible Link Robot

Lightweight flexible robots are widely used in space applications due to their fast response and operation at high speed compared to conventional industrial rigid link robots. But the modeling and control of a flexible robot is more complex and difficult due to distributed structural flexibility. Further, a number of control complexities are encountered in case of flexible link robots such as non-minimum phase and under actuated behavior, non linear time varying and distributed parameter systems. Many control strategies have been proposed in the past, but most of the works have not considered the actuator dynamics and experimental validation of the modeling. In this thesis, we consider the actuator dynamics is considered in modeling and also we have undertaken the experimental validation of the modeling. Tip positioning is the prime control objective of interest in many robotics applications. A tip feedback joint PD control has been proposed for tip positioning of the single link flexible robot. Gains of the controller have been obtained by using genetic algorithm and bacteria foraging optimization methods. By exploiting the above two evolutionary computing techniques for obtaining optimal gains good tip position control has been achieved together with good tracking control. The performances of the above two evolutionary computing tuned controller have been verified by both simulation and experiments

Design and modeling of a compliant mechanism

Compliant mechanisms are widely used in high precision systems, because they provide high resolution, frictionless, smooth and continuous motion. These kinds of mechanisms are also cheaper than the other types of high precision mechanisms. The main idea of this kind of mechanism is that no additional joints are used for creating the motion, the deflection of the flexible elements are used to create the desired motion. In this thesis, a planar parallel compliant mechanism is designed. The mechanism is actuated from three ends by using piezo mike micromotors to create motion in XY plane. The mathematical model of the mechanism is derived by using Euler Bernoulli dynamic equation for the three beams on the mechanism. The separation of variables technique is used to solve the dynamic equations. Necessary transformations are calculated for defining the center position of the stage in terms of the deflections of the beam. The mathematical model is represented in state space form and it is simulated in MATLAB Simulink. The position results are compared with another simulation called COMET. The mathematical model is reduced to two input and two output system in order to make the XY position control of the mechanism by using PID control. Finally, the mechanism is manufactured by using laser cutting and water jet cutting techniques, open loop experiments of the mechanism are verified by actuating the piezo motors manually and by giving voltage signal

Modeling of Flexible-Link Manipulators with Prismatic Joints

The axially translating flexible link in flexible manipulators with a prismatic joint can be modeled using the Euler-Bernoulli beam equation together with the convective terms. In general, the method of separation of variables cannot be applied to solve this partial differential equation. In this paper, we present a nondimensional form of the Euler-Bernoulli beam equation using the concept of group velocity and present conditions under which separation of variables and assumed modes method can be used. The use of clamped-mass boundary conditions lead to a time-dependent frequency equation for the translating flexible beam. We present a novel method to solve this time-dependent frequency equation by using a differential form of the frequency equation. We then present a systematic modeling procedure for spatial multi-link flexible manipulators having both revolute and prismatic joints. The assumed mode/Lagrangian formulation of dynamics is employed to derive closed form equations of motion. We show, using a model-based control law, that the closed-loop dynamic response of modal variables become unstable during retraction of a flexible link, compared to the stable dynamic response during extension of the link. Numerical simulation results are presented for a flexible spatial RRP configuration robot arm. We show that the numerical results compare favorably with those obtained by using a finite element-based model