is a planar under-actuated robot with two rotational joints. The
two links are connected by a passive rotational joint and the first
link is directly connected with the motor axis. Next figure shows
two perspective images of the Pendubot.
figure shows a photographic image of the Pendubot together with
the power state, the UPM module (universal power module).
the two links have a mobility of 360 degree. This is possible thanks
to 6 slipring contacts set at the base of the first link, as shown
in the figure above. The slipring contacts allows the signals transmssion
without requiring a fixed link. Nevertheless, the slipring contacts
cause a non negligible fricition.
The first link has a flattened shape, to offer a higher stiffness,
needed for a faster transmission of the motion to the non actuated
Every joint has an icremental encoder. The motor encoder has a resolution
of 1/8192 of total angle, while the encoder on the passive joint
has an half resolution (1/4096 of total angle). The angular velocities
of the links are obtained from the position informations.
actuator is a direct current motor with permanent magnet (Pittman
14205), drived in current by the UPM module. The power module modulates
the power flow using a control signal, and send it to the power
source of the motor. The signal applied to the motor is a PWM signal
(pulse width modulation). The PWM control is useful to improve the
throughput of the power states (greather than 0.9) and to obtain
the motor with a current signal instead of a voltage signal we obtain
a system characterized by a lower dependence from the motor parameters
(like the torque constant, the motor resistence, etc.), which often
depend from the operating conditions.
front of the Pendubot we have installed a fixed webcam, that allows
to record the experimental activities. To have better light contrast
and cleaner images we put white panels behind the system. This solution
also improves the MPEG compression for the digital video.
presence of a non actuated link, give more interest to the postion
control experiments with the second link in the up position.