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From: "Victor B. Naumov" <nau@iias.spb.su>
Subject: Russian Robotics 7/8: Weightless Robotics
Message-ID: <MBOYER.95Jul5164927@pellan.ireq-robot.hydro.qc.ca>
Lines: 81
Sender: news@ireq.hydro.qc.ca (Netnews Admin)
Organization: St.-Petersburg Institute for Informatics and Automation, RAN
Date: Wed, 5 Jul 1995 20:49:27 GMT
Approved: mboyer@ireq-robot.hydro.qc.ca, crr@ireq-robot.hydro.qc.ca

                 ACADEMY OF SCIENCES OF RUSSIA
   ST.-PETERSBURG INSTITUTE FOR INFORMATICS AND AUTOMATION
                         ROBOTICS LAB.
                     of Prof.F.M.Kulakov


                        ROBOT-LIKE DEVICE
                        -----------------
                  FOR THE PHYSICAL SIMULATION
                  ---------------------------
                      OF THE BODY'S MOTION
                      --------------------
                    IN WEIGHTLESS CONDITIONS
                    ------------------------


Fields of Application
----------------------
Physical simulation of a body's motion in weightless conditions are
used in space technics.  This is part of a ground-based testbed to
model different manipulations with weightless objects.

Description of Idea
-------------------

The popular method of weightlessness simulation, based on the use of
an air cushion, has some deficiencies.  The main drawback is the
difficulty of simulating 3D body motion.  An alternative technique 
simulates weightlessness with the help of a water bath.  In this case,
the body is submerged, and problems begin to arise from the resistance
of the water which varies depending on the body's velocity.

The robot-like device, which is described below, is free from these
deficiencies.  In addition, it allows researchers to extend the
functional possibilities of similar devices.

For the simulation of a body's motion in weightless conditions
a special device has been developed.  It is similar to a robot with 
six DOF equipped with a special gripper.  The "weightless" body is
placed into this gripper.  The robot uses a six dimensional wrist
force/torque sensor to define the forces and torques applied to the
body.  

The robot control system includes a special program module.  Inputs to
this module are forces and torques applied to the body.  This module
calculates the trajectory of the body under the conditions of
weightlessness.  In addition, it also models forces applied to it by
means of numerical integration of the body's dynamic equations (mass
and inertia of body must be known).  The standard program module of
the robot control system uses this data for the solution of the 
robot's inverse kinematics and forms time laws of joint coordinates. 
This provides motion of the body according to the calculated
trajectory. 

Another sister project being developed in Russia by the Institute for
Informatics and Automation is measuring, by robot, mass, Inertia
matrix, and the position of the center of mass for a body in
weightlessness conditions.

Theoretical analyses shows that a system of ten algebraic equations,
can be used to calculate 10 unknown parameters:  m - mass, J11 , J12,
J13, J22, J23, J33 - elements of Inertia matrix, X1, X2, X3 -
projections of the mass center, if vectors of force and torque,
applied to the body as well as the body's velocity and position are
known during some time, t.

A solution to these equations can be found using the 6-D robot with
wrist force/torque sensor, which must grasp the body very strongly and
move it.  It is then possible to measure the vector of the
force/torque which are applied to body during time, t, as well as 
the body's velocity and position during the same time, t. This data
can then be used to solve for the unknown parameters.

This device is used by Scientific Industrial Union "ENERGIA", Central
Institute of Robotics.


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