An integrated system, composed of an arm, a wrist, and a mechanical multifingered hand is treated. The hand is on development for possible application in telemanipulation, and is realized in separate parts. The redundancy of the degrees of freedom of the system, the sensors, the application of logical rules, and the supervision of teleoperators may be applied in order to have an optimum of reliability of the system in space telemanipulations

Cavestro, Paolo

Rovetta, Alberto

English

NASA Technical Reports Server

N90-29792
REDUNDANT SENSORIZED ARM+HAND SYSTEM
FOR SPACE TELEROBOTIZED MANIPULATION
prof.Alberto Rovetta, en_. Paolo Cavestro
Department of Mechanics
Politecnico di Milano,Italv
Abstract
This paper deals with an inteerated system, composed of an
arm, a wrist, a mechanical multifin_ered hand, which has been
realized in separate parts, and which is on development for
possible application in telemanipulation.
The redundancy of the degrees of freedom of the system and
of the sensors, the application of logical rules and the
supervision of teleoperators may be applied in order to have an
optimum of reliability of the system in space telemanipulations.
1.INTRODUCTION
This paper deals with the reallzation of a mechanical
system, (indicated FCR8) for telemanipuiation in the space
(Fig.l).
Objects of generic shape, of relatively small and big sizes,
of different masses and deformabilities, may be manipulated and
grasped by a robotized system, which is constituted by an arm
{fig.2), a wrist and a multifingered hand {fig.3).
By means of a strict integration among the sensors data ,
the mechanical and electronic software for the control of hand
and arm motion, is possible to perform a multipurpose task in the
space.
The redundancy of the system may be utilized to different
goals, with specific reference to the telemanipulation.
The recognition in the space application is performed by the
hand itself, which touches the object and determines parameters
for the optimization of the prehension configuration.
After the recognition phase, the hand is moved to the final
manipulation, also with the support of the teleoperator.
A parallel process of simulation and modelization, also with
the aid of expert systems, may be performed.
The feasibility project is reported, for the first
laboratory prototype.
2.USE OF BASIC PRINCIPLES OF TELEOPERATIONS IN THE DESIGN OF THE
MANIPULATION SYSTEM
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The basic DrinciDles of teleoperations in space, adopted in
the development of the feasibility project of the mechanical
svstem FCR8, are reported.
They are:
- internal functionality of the hand, with its own
capabilities in the prehension of objects° according to physical
principles:
- redundancy of informations and data from the sensors and
communications channels from the hand, from the arm and from the
environment towards the operator, with the evaluation in every
moment of the reliability of every signal and data;
- teleoperations in macrooperations and in microoperations,
with different ranges of tolerances and precision, with the
supervision of the whole process by a second operator, able to
assist the general process, instead of the single phases, and in
every case to assist the main operator.
The concept of a double teleoperation is devoted to the
redundancy of control, in order to obtain a local intelligent
control by one operator, and a whole supervision, during the
process, and in the same time with the aims of serving an
emergency recovery, in front of unforeseen events.
Reliability in teleoperations and telemanipulations in the
space is the main fact in front of the evaluation of the quality
of the work in the space.
3.MANIPULATION SYSTEM DESCRIPTION
The manipulation system is composed of a mechanical hand,
with three fingers and a palm, (see References /I/), connected to
a supporting system, with 6 degrees of freedom.
The hand performs the manipulation process, grasping the
elements and moving the single fingers in order to perform the
task.
The mechanical system, which supports the hand, presents six
degree of freedom in the motion.
It is similar to a robot, where the arm presents 4 degrees
of freedom, and the extremity part, analogue to a wrist, presents
two degrees of freedom.
The total system presents six degrees of freedom in the
support structure and 13 degrees of freedom in the hand.
The strategy of the control system is that the redundancy of
the degrees of freedom is fundamental to obtain a manipulation
process which offers reliability.
4.DESIGN OF THE SUBSYSTEMS
The design of the hand is obtained with reference to some
130
basic principles, connected with mechanical and systems laws.
Some of these principles are:
use of three fin_ers and one palm, to obtain a multiple
points contact, to ensure a reliable prehension; use of friction
surfaces for the fingers and of smooth surfaces for the palm, to
increase prehension stability; use of a settlement phase, able to
obtain a sequence of micromotions of the object in the hand,
which perform the process of seifadjustment of the ob.ject inside
the hand; integration of sensors data, by using the redundancy of
the sensors output signals for improving the reliability and
capability of the control system; development of different
parallel sensors, for the control of the prehension process
itself.
The design of the arm which supports the hand is developed
in order to offer to the hand a support of 8 degrees of freedom,
which may be controlled in a parallel way.
5.CHARACTERSOF THE TELEROBOTIZATION
The manipulation process may be
phases, both in time and in space.
subdivided in different
The first phase is the approach phase, where the
manipulation system is moved in order to approach the objects to
be manipulated, inside a certain operative radius in the working
area.
The mechanical arm and the wrist must be moved in order to
get a position, with a large capability of motion and operation.
The control of the motion is obtained according to the rules
of the expert systems, in order to have a collision avoidance and
a optimal trajectory choice, also considering the reliability of
the system.
{The methodology of the expert system application for
collision avoidance and optimal trajectory choice has been
presented and developed in Ref. /2/. )
After the approach phase, the manipulation phase may be_in.
It is subdivided in two parts: the first part is the
operation of grasping of the object or of the tool, the second
part is the motion of the object or of the tool.
The presence of a double arm may simplifie the procedure, in
front of a better dexterity of the system.
In conclusion, the operations are a sequence of
macrooperations and of microoperations, which are performed by
the system.
The teleoperation is obtained by means of the choice of the
strategies of approaches and of the tasks.
The tasks are subdivided in elementary tasks, and the
elementary tasks, developed by the elements of the system, are
supervised by the teleoperator.
131
Teleoperation in the system here presented conslsts in tl,e
subdivision of tasks in sub-task.
Teleoperator decides the subdivision of tasks, and the
system operates freely inside the subtasks, according to simple
boundary conditions or more complex expert systems rules.
The here described task has been under development, in
different subsystems, in the Laboratory of Robotics, Department
of Mechanics, Politecnico di Milano.
The process of interaction must be developed in the future
according to the design rules, represented synthetically in
Fig.4.
6.REQUIREMENTS FOR MANIPULATION IN THE SPACE
The FCR8 system presents some features for telemanipulation
in the space.
They are mainly:
I) capability to approach the operating position, by the use of
inverse kinematics, applied to the mechanical arm, with the
choice of optimal trajectories, according to prerequired
functions;
2) possibility of developing dynamic control with reliability
evaluation of different functions, by the consideration of the
reliability functions of the mechanical components ( see
Ref./3/};
3) adaptabilit_ of the hand to different functions, with the
selfadjustable prehension and grasping phase, both for the single
object or for a working tool;
4) sensitivity of the mechanical hand in front of dynamical
perturbations, by means of the motion of the fingers, in order to
obtain a stable prehension in grasping and a reliable gripper for
the use of the tools;
5) reliability of the system . in front of a mechanical and
electric design, which need no lubricant or liquid material, and
which may be applied to loads of Nw up to hundred of Nw. with a
selfadaptability of the prehension system.
The teleoperation may be performed by means of two levels:
- macrooperations
- microoperations.
The macrooperations may be performed with the support of the
sensors which are in the system.
The operating sensors are : force sensors and tactile system
in the hand for a first recognition of the unknown object to be
grasped; vision and recognition system on the arm, able to
determine the characters of the environment.
The integration of the sensors with the "experience" of the
robotized system and of the teleoperator is a main character of
the system on development.
132
Multiprocessor system and transputer system
application for adapting the computers capabilities
telerobotized system requirements.
7.CONCLUSIONS
are on
to the
An integrated system, composed with an arm, a wrist and a
hand with redundancies in the mechanical design and in the
sensors, may be used for telerobotics in space, where reliability
of the system is a basic element.
The application in the space is indicated in front of
different subtasks which may be performed by the robot.
Supervision in the steps of the tasks is obtained by the
operator, where a second operator may evaluate the reliability of
the single subtasks in front of the results.
This paper has been developed with the
Italian Education Ministry.
support of the
References
/I/ Nato Workshop on "Robots with Redundancy : Design, Sensing
and Control", Salo' , Italy, June 1988
/2/ A.Rovetta, R.Sala, Optimization of trajectories in assembly
with logical support, Tecniche dell'Automazione, june 1988
/3/ A.Rovetta, M. Battaini, Reliability on robots: an applicative
study, Meccanica, in print
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FIG.1 ARM+WRIST+HAND (6+13 DOF)
133
Fig. 2 Mechanical arm with 6
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Fig. 4 Conceptual scheme for
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134
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Redundant sensorized arm+hand system for space telerobotized manipulation

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