Sliding mode control of robotic finger and control of SMA
This thesis is focused on the control and modeling of a robots finger.
The control target of this project is position tracking during the
finger motion. A new sliding mode control algorithm is developed in this
project. It originates from the author’s 3-stages approach. i.e. the
reaching phase, the sliding mode and the steady state. This approach is
mainly based on two key idea, as follows: (i) During the reaching phase,
the speed of reaching can be related to the distance between the state
trajectory and the switching manifold, (ii) During the sliding motion,
the state velocity is directly related to the state variable for
2nd-order non linear systems.
This new control algorithm is a
functional relationship for the speed of reaching during the reaching
phase. The simulation result demonstrates that this algorithm performs
better than Gao and Hung’s “power rate” reaching law both in chattering
reduction and reaching time. The above robot finger is developed via the
transition from a biological model for the human thumb to a mechanical
prototype. A main concern of the biological model is the relationships
on the excursion of finger tendons. The newly developed relationships in
this project involves the shape and size of the associated phalanx, as
well as the pulley mechanism besides the angle of rotation. The
treatment of these relationships in this thesis are more complete and
applicable than the approach by Landsmeer. Landsmeer’s model involves
only the angle of rotation.
Moreover, the mechanical prototype
developed in this project retains anthropomorphic features of the human
thumb. Such features include the quad-circles at the ends of each piece,
and the very low friction in motion via artificial tendons. These
properties are unique in the above robot finger compared to the work on
robot hands by other research groups. In addition, SMA-wires are used as
actuator for the above robot finger. A major problem of the SMA
material is the “residue” stress. This is a defect since it prevents the
wire from returning to the same position before re-activation in the
next cycle. Hence a new approach: the “interval insertion” method has
been developed in this project. Implementations show that this method
really solves the above stated problem.
Author: Loh, Albert Ming
Source: City University of Hong Kong
Author: Loh, Albert Ming
Source: City University of Hong Kong
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