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This paper presents a piecewise-linear control strategy applied to a two degree-of-freedom (DOF) manipulator performing under variablaload and variablepath conditions. Each axis of the robot arm is modelled as a separate SISO system with a single nonlinear parameter, inertia, which varies according to the load carried and position of the manipulator. The trajectory of the robot arm is divided into zones. Within each zone, an estimate of the inertial load for each axis is obtained. The inertial value for each axis is then assumed to be constant throughout the zone. A PID controller is designed within each zone for each axis which minimizes an ITAE performance index for the estimated value of inertia The result of this algorithm is a robust controller which tunes its parameters at specific times and can withstand a wide range of variations of the payload and path. The controller was implemented on a two DOF manipulator and was found to perform as theoretically predicted. It was also able to reduce manipulator vibration due to mechanical resonance.