  Redundant cascade manipulators actuated by pneumatic bellows actuators are
passively compliant, rugged and dexterous which are qualities making them
exceptionally well suited for applications in agriculture. Unfortunately
bellows actuators are notoriously difficult to precisely position. This paper
presents a novel control algorithm for the control of a parallel platform
actuated by pneumatic bellows actuators, which is serving as one module of a
cascade manipulator. The algorithm combines a feed-forward controller and a
variable gain I-controller. The feed-forward controller was designed using
experimental data and two regression steps to create a mathematical
representation of the data. The gain of the I-controller depends linearly on
the total reference error, which allows the I-controller to work in concert
with the feed-forward part of the controller. The presented algorithm was
experimentally verified and its performance was compared with two controllers,
an ANFIS controller and a constant gain PID controller, to satisfactory
results. The controller was also tested under dynamic loading conditions
showing promising results.
