Pulse width control refers to the use of a control law to determine the duration of fixed-height force pulses for point-to-point position control of a plant that is subject to mechanical friction, including stiction. The use of constant-gain pulse width control laws for precise positioning of structurally flexible plants subject to stiction and Coulomb friction is analyzed. It is shown that when the plant is a simple two-mass system subject to stiction and Coulomb friction, a position error limit cycle can result. Sufficient conditions for stability and self-sustained oscillation of this closed-loop system are derived. The sufficient conditions for stability are used to determine conditions on the plant parameters and the control gain that guarantee closed-loop stability and thus limit-cycle-free operation and zero steady-state position error. The analysis methods that are introduced are demonstrated in applications to the control of the position of the end-effector of an industrial robot.

Issue Section:
Technical Papers
Keywords:
end effectors, industrial manipulators, position control, flexible manipulators, stiction, closed loop systems, stability
Topics:
Coulombs, End effectors, Errors, Friction, Oscillations, Robots, Stability, Steady state, Stiction, Dynamics (Mechanics), Limit cycles, Closed loop systems, Position control
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 by ASME
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