During the French CASSIOPEE mission that will fly onboard MIR space station in 1996, ergonomic evaluations of a force reflecting handcontroller will be performed on a simulated robotic task. This handcontroller is a part of the COGNILAB payload that will be used also for experiments in neurophysiology. The purpose of the robotic experiment is the validation of a new control and design concept that would enhance the task performances for telemanipulating space robots. Besides the handcontroller and its control unit, the experimental system includes a simulator of the slave robot dynamics for both free and constrained motions, a flat display screen and a seat with special fixtures for holding the astronaut

Delpech, M.

Matzakis, Y.

English

NASA Technical Reports Server

ROBOTIC EXPERIMENT
WITH A FORCE REFLECTING HANDCONTROLLER
ONBOARD MIR SPACE STATION N95- 23707
M. DELPECH, Y. MATZAKIS,
CNES
18 Avenue Edouard Belin
31055, TOULOUSE Cedex, France
E. ROUCHOUSE
Matra Marconi Space
31, rue des Cosmonautes
31077 TOULOUSE Cedex, France
ABSTRACT
During the French CASSIOPEE mission
that will fly onboard MIR space station in
1996, ergonomic evaluations of a force
reflecting handcontroller will be performed on
a simulated robotic task. This handcontroller is
a part of the COGNILAB payload that will be
used also for experiments in neurophysiology.
The purpose of the robotic experiment is the
validation of a new control and design concept
that would enable to enhance the task
performances for telemanipulating space
robots. Besides the handcontroller and its
control unit, the experimental system includes
a simulator of the slave robot dynamics for
both free and constraints motions, a fiat
display screen and a seat with special fixtures
for holding the astronaut.
INTRODUCTION
When robot manipulators are being used in
unstructured environments, telemanipulation
represents either the nominal or at least the
contingency mode of operation. Kinesthetic
force feedback constitutes then a classical fea-
ture to enhance task performances when time
delay is not a problem.
Several constraints, however, limit the introduc-
lion of force reflecting devices for teleoperating
robots in space:
- the device working area must remain small
enough for accommodation reasons and this
prevents the use of classical 6D anthro-
pomorphic structures,
- the dynamics of large external manipulators
such as the Shuttle RMS is much slower than the
operator hand, this reduces the reflected force
bandwidth and so the benefit of the device,
- the computing power necessary for achieving
satisfactory performances has to be very high,
- the microgravity obliges to introduce special
astronaut holding equipment.
Passive devices remain then the baseline
specially after tile success of the ROTEX
control ball [1] which has brightly proven its
efficiency when coupled to a shared control
robot. Such facts force to reconsider the
kinesthetic force reflecting technique from a
different point of view. This paper introduces
a new control and design approach that
addresses some of these problems. It presents
then the device developped according to this
approach and the experiments that will be
performed in space to evaluate the ergonomy
of its utilization for robotics.
HAND CONTROLLER DESIGN
APPROACH
The vast majority of robotic tasks can be
represented by a sequence of elementary actions,
each involving motions along at most 2 or 3 axes
simultaneously.
It has been taken advantage of this property in
advanced telemanipulation systems where the
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operatorisofferedavarietyof controlmodes
that allow mobility within only a subset of the
cartesian space. To perform a drilling task for
instance, after adjusting the orientation and
position of the driller, the operator needs to keep
control along the drilling axis only, the other
axes are being blocked during the operation. In
such a way, computer aided teleoperation
enhances task performances since the operator
can concentrate his perception and actuation
abilities on the most rewarding part of the job.
Those remarks can trigger a discussion about the
necessity to provide operators with 6 d.o.f, hand
controllers when half of them are supposed to be
blocked most of the time.
Tile alternative we are proposing consists in
using 3 d.o.f force reflecting joysticks.
The advantages of such simpler mechanisms are
numerous:
- the compacity of the structure makes its
accomodation more realistic for space vehicles,
- the smaller envelope prevents the operator
t?om reaching uncomfortable positions,
- the stiffness and the dynamics can be
significantly increased, thus allowing better
performances,
- the computational cost of forward/inverse
kinematics is redticed and alleviates the
implementation requirements.
For controlling 6 d.o.f, robots, the
operator is provided with a set of two
complementary 3 d.o.f joysticks: one for the
translations, the other for the rotations. This
system being operated with both hands enables
then to control a robot in free space like any
classical 6 d.o.f serial mechanism. The
performances may be even better since
translation and rotation motions are
decoupled When doing constrained motions,
the coupling between the two joysticks
appears however in a rather remarkable way.
Let us consider an operator inserting a peg in
a hole by moving only the translation joystick:
if there is some orientation error a resistive
force will be applied by the joystick to his
controlling hand and at the same time he will
feel some force in its idle hand generated by
the rotation joystick. He may resist to this
tbrce and then block the peg or comply and
allow the orientation correction. In this latter
case, one hand is the "controller" and the other
one is the "follower". Our opinion that needs
to be confirmed by experimentation is that the
operator, after some training, will better
interpret multi component forces. For that
purpose, a complete telemanipulation system
involving such joysticks is under deveioFment
and should be ready within months.
Besides this utilization, this kind of device
is specially relevant for shared control modes
already described by Hirzinger [2] or Hayati
[3] since it will provide force feedback in the
operator controlled subspace.
HANDCONTROLLER
PRESENTATION
The 3 d.o.f active joystick presented
here-below has been developped to serve two
purposes:
- analysis of human neuromuscular models,
- robot telemanipulation.
since the requirements were convergent in
terms of kinematics and performances. Table 1
shows the joystick present characteristics.
Axes
Features
Working envelope
X,Y
+/- 120 mm
Z (Rotation)
10000 N/m
+/- 120 °
Maximum force 25 N 0.6 Nm
Residual Friction < 1N <0.03 Nm
Maximum speed 0.5 m/s 200 °/s
Maximum stiffness 200 Nm/rad
Table 1
The selected kinematics with 3 rotations
(Figure 1) enables no dynamic coupling between
the axes. The actuation is provided by servo-
motors through Harmonic Drive gears. To
cancel the residual gear friction, active
compliance is implemented on the joystick
controller and relies on a 3 d.o.f, force/torque
sensor located beneath the handle. Joystick
control is based on a 68040 CPU board and runs
at a high rate.
For doing force feedback evaluation
experiments, the joystick system is linked via
VME bus to a simulator running on a second
68040 board (Figure 2). The typical control
178
scheme being used for implementing force
reflection is presented on Figure 3 (pure force
feedback) and is achieved at a medium sampling
rate for realistic simulations.
However, as long as simulation is concerned, it
is possible to implement higher sampling rate
systems and so increase the force signal
bandwidth by running at high in the joystick
controller a simple interaction model whose
parameters are computed by the simulator and
updated with the force at medium rate. This
enables to emulate systems running at higher
frequencies.
The stiffness characteristics from Table 1 have
been obtained according to this method for an
infinitely stiff and light robot interacting with a
pure spring.
EXPERIMENT DESCRIPTION
Objective
The purpose of this space experiment
involving a single 3 d.o.f, joystick is twofold:
- to evaluate the ergonomy of synthetic force
reflection with and without shared control
- to assess its potential benefit w.r.t, other
techniques (use of passive devices such as
ROTEX control ball).
tlarware description
The experimental system includes the
following components accommodated inside
one of the M1R modules (Figure 4):
- the astronaut seat that constitutes the
structural part of the system and that is fixed
in the present design to the module floor.
- the motorized joystick,
- the experiment calculator including the
joystick controller, the simulator computer
and a graphic board,
- a flat display screen and a optical tunnel to
eliminate the visual distractions.
- a handle with switches to control the
CXl)eriment.
The spaceflight model of the joystick is
based on ground technology: except for
specially developped power electronic boards,
the other elements are only hardened to satisfy
the mechanical, thermal and safety
requirements.
The calculator is VME based and includes
standard CPU boards (MVME 162 with
mezzanine IO boards) for both joystick
control and simulation/experiment
management.)
Experiment protocol
Robotic task
The robotic task to be performed is a
"peg in a hole insertion".that involves a
simulated robot interacting with a virtual
environment. The robot is a 3 d.o.f.
mechanical system that enables to move its
end effector within a plane (2 translations
along the X, Y axes and a rotation for its
orientation). Figure 5 presents the model of
this task. Using the joystick, the operator has
to displace the peg in front of the hole, adjust
its orientation and insert it smoothly until it
touches the bottom. He monitors the robot
displacement by watching a 3D graphic display
of the scene that is representative of an image
coming from a global view camera (figure 6).
The simulation includes the following
features:
- the robot dynamics is finite (represented by a
second order transfer function on all axes),
- the tool (peg) is attached to the robot by
some compliant interface (compliance along 3
axes),
- contact interactions such as jamming effects
can be represented: the obstacle stiffness is
considered infinite and the only structural
deformations take place at the compliant
interface.
The simulation process runs in 12 ms: the
force reflecting loop is closed at 75 Hz but the
joystick model based joystick control runs up
to 750 Hz..
The operator is asked to insert the peg in
the minimum time while keeping the contact
forces as low as possible: the performance
criterion is a combination of those two
informations.
179
Modes of operation
Three modes of operation are considered:
- Velocity control with visual force reflection
(Mode 1)
- Position control with kinesthetic force
reflection along all axes (Mode 2)
- Position control with kinesthetic force
reflection along translation axes only (Mode
3).
- Mode 1 simulates the way ROTEX
manipulator was operated by the astronaut
within the Spacelab module [1]. The joystick
is blocked in a central position to emulate a 3
d.of "control ball" and force information is
,displayed on tile screen using 3 bars (Figure
5). The slave robot moves under shared
control: active compliance is provided along
the orientation axis when contact is achieved.
- Mode 2 represents classical kinesthetic force
feedback where all axes are controlled by the
operator.
-.Mode 3 is an example of kinesthetic force
reflection applied in a shared control scheme.
The slave robot is controlled like in Mode 1
but now the operator feels the forces along 2
degrees of freedom (X, Y).
These 3 modes will be used for
performing the insertion task with two types
of simulated robots:
- a high dynamics structure corresponding to
some small servicing manipulator
- a low dynamics structure representative of
long external manipulators.
This will make a total of six different control
configurations for the experiment.
Three astronauts will participate in the
experiment during the 11 days flight mission.
Each astronaut will perform a specified
number of repetitions of the task in the
different control configurations (a minimum of
10 repetitions is required to allow a valid
statistical analysis). In order to compare the
obtained results with a fair reference so that
the influence of gravity can be identified, the
astronauts will perform exactly the same tests
on ground before the mission.
CONCLUSION
The experiment presented in this paper
constitutes a first shot in the evaluation of
kinesthetic force reflecting techniques for
teleoperation in space. We expect to
demonstrate that the technique is not only
feasible but enables to improve task
performances when implemented with small 3
d.o.f joysticks. However, the main purpose is
the collection of experimental data for
performing ergonomic analysis. It will permit
then to improve the design of a complete 6
d.o.f, system (two joysticks) and to get ready
for a full scale demonstration with a real space
robot.
[1] G.Hirzinger and als.
The sensory telerobotic aspects of the space
technology experiment ROTEX. iSAIRAS,
Toulouse, September 1992.
[2] G. Hirzinger 1989.
Multisensory shared autonomy - a key issue in
the space robot technology experiment
ROTEX, IEEE Conference on Intelligent
Robots and Systems (IROS), Raleigh, USA,
July 92.
[3] S. Hayati, S.T. Venkataraman
"Design and Implementation of a Robot
Control System with Traded and Shared
Control Capability". IEEE Conference on
Robotics and Automation, Scottsdale, 1989.
180
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181



Robotic experiment with a force reflecting handcontroller onboard MIR space station

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