Shadow-Hand Calibration Tool
Master-Thesis at group TAMS
Motivation
The Shadow Dexterous Robot Hand is an advanced robotic hand
that closely matches the size of a male human hand.
With four joints per finger and five joints for the thumb,
and an actuated wrist, it can mimic a large subset of
human grasps and manipulation motions.
However, performance of the hand is often limited by the lack
of automatic calibration, as actual finger positions often
differ from the commanded positions.
This is especially critical if fingers collide, as this results
in high forces on the tendons (which can break) and the motors
(which overheat quickly).
Also, the tactile sensors on the fingertips are very sensitive
and can be overloaded and damaged if finger positions are wrong.
The current calibration approach uses a complicated manual process,
where the fingers are aligned with mechanical jigs one by one,
and the corresponding sensor readings are then entered into
configuration files.
Despite their complex and nonlinear behaviour, there is no
calibration procedure for the BioTAC tactile sensors at all.
Automatic Calibration Tool: Hardware
The core idea of the proposed thesis is to develop a single
(or a set of a two or three) sensing object to be grasped
by the Shadow Hand during an automated calibration sequence.
The tool will be shaped so that the fingers reach and touch
sensors (switches, light interrupters, force sensors) during
the calibration process, allowing the software to record
precise finger motions and also finger forces.
The whole process must be designed to be safe for the hand,
even when starting from uncalibrated initial finger positions
which might have collisions with other fingers (or the tool).
One possible approach is to start the hand in a limited
low-power mode for initial rough calibration, and to repeat
the process with higher power and precision once the initial
state of the hand is known.
After basic calibration of the hand geometry, the next step
in the automatic calibration sequence targets to record
the tactile sensor outputs, pressing against the force
sensors in the calibration tool to determine zero-bias
and gains.
For the BioTAC sensors it would also be interesting
to calibrate their reaction to contacts at different parts
of the sensor, and the reaction to shearing-forces
applied on the center of the sensor.
Software
The precise scope of the software implementation is to be discussed,
but the software must be integrated into the ROS framework
and the EtherCAT-based real-time driver for the Shadow Hand.
Thesis Goals:
- design and construction of a force-sensing object,
- for automatic calibration of the Shadow hand,
- using the ROS open-source framework and environment,
- integration into existing safety mechanics
- collect ideas and experiment data leading to a publication
Requirements
- as always, interest in the topic area, here graphical user-interfaces and robot manipulation
- programming skills in Python or C/C++ and Qt
- basic knowledge of the ROS framework
Contact
