In order to prevent the humanoid robot TUlip from falling a start has been made with a Zero
Moment Point (ZMP) based controller. The chosen controller, which is called the Linear Inverted
Pendulum Tracker (LIPT) controller, is based upon a lag between the real and reference ZMP
and is used in simulations for initial testing.
TUlip's walking gait is based on the Cart-Table (CT) model based ZMP to keep it stable during
walking. However, during simulations and experiments it turned out that TUlip did not remain
balanced at all times. Because the gait is based on the ZMP, a ZMP based controller is chosen
to obtain a stable gait.
Since the LIPT controller is based on a lag between the real ZMP and the reference ZMP, a
lag needed to be found. In this report a lag of 0.02 seconds is found between the real ZMP,
based on the Center of Pressure (CoP), and the reference ZMP, based on the CT model. A state
space representation is derived and implemented in the simulation model. Initial simulations
showed a working controller which, given enough time, brought the ZMP back to it's reference
position. However, simulations for testing the controller on the robot showed no improvement
in the stability of the walking gait.
During simulations it was found that the existing ground contact model, developed to prevent
large peak forces when a foot is lifted or put to the ground, was not sti enough. This resulted
in larger oscillations in the CoP than for the CT model based ZMP, where similar results where
expected. Is is recommended to x the ground contact model before continuing the development
of the ZMP based controller.
Open space project. - DC 2014.008