Active Vibration Control of a Flexible Robotic Manipulator

Abstract

A five-degree-of-freedom (5-DOF) robot manipulator for agricultural applications was developed by previous members of the robotic lab at University of Saskatchewan. The manipulator was designed to be installed on a mobile base vehicle for monitoring targeted crops in a farm field using sensors installed on its tip. The crop monitoring is called phenotyping. When the manipulator mobile base moves along the field, vibration is induced from the farm terrain to the base of manipulator. Thus, the sensors mounted at the end-effector (EE) of the manipulator may not record data accurately. To address this issue, vibration suppression of the manipulator is necessary. The objectives of this research were: 1. Evaluation of vibration experienced by the 5-DOF manipulator’s tip; and 2. Study active vibration control to remedy vibration experienced by the manipulator; also, some efforts were done for possible implementation of active vibration control on the manipulator in a laboratory setting. Free and forced vibration simulation studies were conducted to evaluate the amplitude of vibration transmitted to the EE from the base of the manipulator. To eliminate excitation coming from the manipulator’s base, an active vibration suppression method using a model-based controller was used. To obtain a mathematical model for the manipulator, finite element analysis was utilized using commercial software and was verified manually. This method was applied to three different cases: 1- a cantilever beam, 2- a two-link, two-joint manipulator (2L2JM), and 3- the 5-DOF manipulator. For active vibration control, model reduction was applied to a state-space model of systems via a matched-DC algorithm. The LQR (linear-quadratic regulator) was used for the cantilever beam vibration control. For the 2L2JM and the 5-DOF manipulator, a H∞ controller was used. This was an optimal and robust controller based on the H∞ norm. Based on vibration evaluation, it was found that an active vibration suppression was necessary for the 5-DOF manipulator. Mathematical models of several systems were developed and verified using finite element analysis. The controllers suppressed random vibration that were applied to the base of the 5-DOF manipulator. For the closed-loop control system of the manipulator, a look-up table was created for the actuators. Through this study, the vibration of the 5-DOF manipulator was analyzed. Then, mathematical models of different geometries as well as the 5-DOF manipulator were obtained. Then these models were compared with the software models. The model reduction approach made the large finite element models reduce to systems with a small order. Using models and control strategies, simulation studies were conducted for the vibration suppression of the manipulator.