Sliding Mode Control of a 2 DOF Of Freedom Robot Arm Using Permanent Magnet Synchronous Motor
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2018-03
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Abstract
This thesis study aims at the problem of modeling and control of a two DOF robot arm using
Permanent magnet synchronous actuators. Permanent magnet synchronous actuator have been
used in various industrial and domestic applications because of its advantages like simple
structure, large torque, long use. Trajectory tracking is a very difficult topic in robot arm control.
This is due the nonlinearities and input couplings present in the dynamics of the arm caused by
dynamics changes rapidly as the manipulator moves within its working range. Moreover, for a
robot with gear transmissions, the gears have nonlinearities such as hysteresis, backlash, friction,
and nonlinear elasticity. In industrial applications such complex systems are controlled using the
traditional PID controllers. However, a major drawback of the linear PID control is failed to track
the desired trajectory of the robot arm when the nonlinear system dynamics is dominant. In this
thesis sliding mode controller is modeled to overcome the shortcomings of PID controller. The
SMC is designed to control the joint trajectory of the robot. SMC adopts a switching function, and
these results in high-frequency oscillations (the so-called chattering) in the control signal. To
reduce chattering, saturation function is used.
The simulation is carried out using Level-2 MAT-LAB s-function and Simulink. PID controller
is designed for the comparison purpose with SMC without disturbance and parameter variation
and the result shows Steady State error of SMC is 0.029% for joints one and 0.0098% for joint two
and increased to 15% and 24% respectively overshoot remain the same, rise time is decreased by
0.16sec, and settling time is decreased by 0.4sec for both joints when PID controller is used. The
SMC and PID with disturbance and parameter variation also tested and results show that the
performances with disturbance and parameter variation are almost the same for SMC. The control
input voltage is increased by 0.03v and 0.02v for joint one and two respectively for SMC. However
the amplitude of the control effort of PID controller with disturbance and parameter variation is
much larger when compared to the control effort without disturbance and it is increased by 18v
and 6.5v. Generally from the result it is possible to conclude that SMC has better performance,
more stable and robust than PID controller.
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Keywords
SMC, PID, Level-2 MAT-LAB s-function, Simulink, DOF