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| Robot hands: Robust underactuated robotic hand (MARS) |
One of the first
robotic hands developed in the laboratory is the MARS hand (Main Articulé
Robuste Sous-actionnée, i.e. robust underactuated robotic hand). Built in 1996,
it is the result of a collaboration with l'Institut de Recherche en Santé et en
Sécurité du Travail (IRSST), the Institute of health and safe work environments
research. The objective was to design a hand which is both robust and has a
large dexterity so that it can carry out a wide variety of tasks, including
tasks in hostile environments (involving radioactivity, extreme temperatures,
polluted air, etc.).
A prototype of the underactuated 12-DOF robotic hand with 6 actuators was thus
built in 1996. The design process involved the use of a CAD software, various
simulation programs, and the construction of a cardboard model. The hand is
nearly twice the size of the human hand ans weighs 9 kg (20 lbs), yet, its
maximum payload is 70 kg (155 lbs.). The hand is actuated by three brushless DC
motors for the closing/opening of the fingers and three DC motors for orienting
the fingers. The hand is capable of performing cylindrical, spherical and planar
grasps with both power and precision grips. The prototype is capable of large
enough forces to perform common industrial tasks. It is also equipped with
tactile sensors.
The design of the robotic hand is protected by US patents (US 5,762,390) and a
Canadian patent (CA 2 209 863 AA). |
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| Robot hands: Underactuated robotic
hand for the Canadarm (SARAH) |
| Highly
Underactuated 10-DOF Robotic Hand (for the Canadarm) The robotic hands
developed in the laboratory up to this point, had an underactuation only in the
fingers. Each finger was thus actuated by its own motor. In 1998 the company MDA
Space Missions (previously SPAR Aerospace) contacted the laboratory in order to
request the development of a hand for the well-known Canadarm. One of the
specifications requested for this new hand was that it should be actuated by
only two motors.
This led to the principle of a hand featuring under actuation among the fingers;
the opening and closing of the fingers is controlled by only one motor. In fact,
one motor is sufficient since it is not necessary for all three fingers to close
independently, because all fingers will close to grasp an object as firmly as
possible. If one finger is firmly wrapped around an object, the other fingers
will continue to close until all fingers are firmly closed. The underactuation
among the fingers is achieved through an innovative gear differential mechanism.
A second motor allows the orientation of the fingers to be changed to achieve
cylindrical, spherical and planar grasps.
A prototype of the highly underactuated self-adaptive 10-DOF robotic hand with 2
actuators was built in 1999. The new hand, SARAH (Self Adaptive Robotic Auxilary
Hand), is slightly smaller and weighs only half as much as its 12-DOF
predecessor (MARS Hand). It has the same mobility, but is actuated by only two
motors.
The SARAH hand was built in collaboration with the Canadian Space Agency. Its
design is covered by a US patent (No. 6,505,870) as well as by a pending WIPO
patent. The current version is adapted as an end-effector to the SPDM of the
Canadian Space Arm for the International Space Station. |
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| Robot hands: Robotic hand for the
cleaning of nuclear sites |
| In 2005-2006, the
Robotics Laboratory has been working on the development of a robotic hand for
the United Kingdom Atomic Energy Authority (UKAEA). The main business of UKAEA
is the clean-up of nuclear sites. One of their tasks is to retreive radio-active
waste from old storing sites in order to package and store it in safer
conditions. The retrieval of the waste is a timely and complex task. The waste
is composed of cans and a variety of debris. Presently, several grippers are
used, each one being adapted to a specific type of object. Unfortunately, the
changeout of the grippers is time consuming. The use of a more flexible gripper
that will replace several specialized grippers will facilitate and accelerate
the retrieval process.
This flexible gripper is adapted from the SARAH hand, which was developed by
the Robotics Laboratory and originally designed for use in space. The SARAH hand
includes three underactuated and orientable fingers, driven by only two motors.
In order to satisfy the requirements of the waste retieval tasks, several
components were redesigned. Among others, the new gripper has a significantly
larger payload and is adapted to a nuclear environment. Also, the tip of the
fingers is designed to grasp cans located in confined spaces, and are yet still
capable of handling a variety objects. A plastic prototype of the new gripper
(shown above) was built and tested successfully. |
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| Parallel Mechanisms:
The Agile Eye |
The Agile Eye is a
3-DOF 3-RRR spherical parallel manipulator developed for the rapid orientation
of a camera. Its mechanical architecture leads to high velocities and
accelerations. First, the kinematic model of this manipulator was developed.
Then, a geometric optimization was carried out in order to determine the
dimensional parameters which would produce the best accuracy for the mechanism.
A complete dynamic model was then established. Finally, a prototype was designed
and built, and a high-performance controller based on a DSP was developed. The
prototype was built in 1993 and has been gaining in popularity ever since.
The workspace of the Agile Eye is superior to that of the human eye. The
miniature camera attached to the end-effector can be pointed in a cone of vision
of 140° with ±30° in torsion. Moreover, due to its low inertia and its inherent
stiffness, the mechanism can achieve angular velocities above 1000 °/sec and
angular accelerations greater than 20000 °/sec2 which is beyond the capabilities
of the human eye.
One of the most interesting topics of research related to the Agile Eye is the
analysis of its singularities. Surprisingly, the singularity loci of the Agile
Eye are independent from the chosen branch (there are a total of 8 branches).
Note that for general 3-RRR spherical parallel manipulators, the singularity
loci are strictly dependent on the chosen branch. In addition, in the Agile Eye,
there exist four poses for the mobile platform in which arbitrary finite motions
of the actuators do not produce any output at the mobile platform. Finally, the
direct kinematic problem of the Agile Eye allows 8 assembly modes. |
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| Parallel
Mechanisms: Flight simulator |
The area of motion
simulation, especially that of flight simulators (Figure 1), is currently the
main commercial application of parallel mechanisms. These simulators, albeit
very popular and providing very realistic cues, have several notable
disadvantages including a restricted workspace (mainly with respect to
rotation), prohibitive cost, limited operation and they require high
maintenance. Moreover, the oils contained in the actuators can be an
environmental problem for some people.
To eliminate these disadvantages, the laboratory has designed a low-cost flight
simulator having a limited number of degrees of freedom and a simple
architecture, which is able to create motion cues realistic enough to allow it
to be used for the training of pilots (during the first phases of their
training).
Several research studies were carried out during this project, including a
comparison of cues which can be created by various 3-DOF architectures so as to
choose the most suitable architecture. Then, a design of a mechanism was
achieved incorporating several innovative ideas, such as static balancing and
the use of rotoid electric actuators.
The model has 2 legs, of types RRU and RUS, and one passive Hooke joint on
which the seat, controls and screen are mounted. The legs allow rotations to be
carried out around a cone, while a motor added to the platform allows the
platform to pivot in a plane normal to it. Thus a range of motion of ±60 degrees
is possible. |
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| Parallel
Mechanisms: SHaDe (a spherical 3-DOF haptic device) |
A 3-DOF haptic
device, called SHaDe, an acronym standing for Spherical Haptic Device, was
developed in our laboratory to allow a human operator to control motions while
being subjected to force feedback. The mechanism presents the particularity of
having only three degrees of freedom, leading to a simpler design and a more
ergonomic utilization. Moreover, the use of a spherical geometry in this haptic
device offers several advantages, namely, a pure rotation around a point located
inside the user's hand (no translations at this point), a large workspace, a
comfortable use, and precise manipulation while the arm is resting.
The prototype makes use of a particular design in which only revolute joints are
used, based on a spherical geometry. Indeed, it is a spherical parallel
mechanism with two spherical linkage chains of type RRR and one chain of type
RRRR. Kinematically, however, the parallel mechanism is equivalent to a
spherical 3-RRR one. The RRR(RR) chain was used in order to minimize the link
interferences. In SHaDe, all joint axes, passive and active, intersect at a
common point which is the center of rotation of the end effector. Such a
spherical geometry has also been used in the design of the high-performance
camera orienting device, referred to as the Agile Eye.
Numerical analysis was used to optimize the prototype's characteristics with
respect to given performance criteria. To this end, a weighted combination of
indices was used, including the size of the workspace, the minimal dexterity,
the average dexterity, etc. The prototype was built using a Fused Deposition
Modeling (FDM) rapid prototyping machine using a commercially available CAD
package.
The force control involves an intelligent multi-axis force sensor communicating
at a high speed through a serial link with the sensor control sub-program. This
sub-program is in turn communicating with the motor torque control and running
under QNX, a real-time micro-kernel operating system. Different control laws
were created to simulate a robot arm's behaviour or distant hazardous
environments. The force control itself is based upon a classical PID scheme
enhanced with static compensation plus a feedforward term in order to improve
the performance. |
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| Tripteron and
Quadrupteron robots |
Tripteron
Theoretical research often leads to fascinating discoveries: in this case the
tripteron, a 3-DOF translational parallel mechanism. The prototype was first
developed through mathematical derivations (systematic type synthesis) based on
screw theory. This unique and patented robot enables linear displacements in all
directions. It is in fact equivalent to serial Cartesian robots. But since it is
a parallel robot, it offers numerous other advantages, including the positioning
of its actuators on the base, which reduces the moving inertia and thus allows
rapid movements.
Moreover, the tripteron has very simple kinematics, which are actually the same
as those of serial Cartesian robots. Also, this robot is isotropic and fully
decoupled, i.e. each of the actuators is controlling one Cartesian degree of
freedom, independently from the others. This robot thus has no singularities
within its workspace and its dexterity is always optimal.
The figures below also indicate that it is possible to orient the linear
actuators in different directions, for example in a parallel or co-planar manner
rather than orthogonally. The prototype developed in our laboratory is of the
type 3-PRRR.
Quadrupteron
Akin to the tripteron, the quadrupteron was also developed through systematic
type synthesis. Ressembling the tripteron on many ways, the unique feature of
the quadrupteron is mainly its 4 DOFs. In addition to the three translations,
one rotation along the vertical axis is possible. The prototype thus has three
legs of the type PRRU and one leg of type PRRR.
The quadupteron reproduces the same movements, although with an increased
dexterity, as the well-known SCARA robot (Selective Compliant Assembly Robot
Arm), i.e., the Schönflies motions. The quadrupteron is isotropic in
translation. The singularities are only present in two orientations, ±90
degrees, which cannot be reached since the workspace is ±60 degrees (which is
already very attractive).
The design of the prototype was achieved through a variety of studies in order
to reduce the presence and size of the singularities and to optimize the
deterity and workspace.
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| Navigation |
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| Activities |
| The research activities of the laboratory are
mainly focused on the study of parallel mechanisms and articulated robot hands,
two areas in which the laboratory has acquired an international reputation. Our
research also includes projects on walking robots, deployable mechanisms, the
use of rapid prototyping in robotics and other areas. |
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