Transcript www.DLR.de • Chart 1 COMPONENT VERIFICATION ON ISS ROKVISS - FIVE YEARS IN SPACE Wieland Bertleff – 15.

www.DLR.de • Chart 1
COMPONENT VERIFICATION ON ISS
ROKVISS - FIVE YEARS IN SPACE
Wieland Bertleff – 15. May 2013
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COMPONENT VERIFICATION ON ISS (ROKVISS)
FIVE YEARS IN SPACE
EXPERIMENTAL RESULTS ON FRICTION PARAMETER IDENTIFICATION
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Index
• DLR – Robotics and Mechatronics Center
• The ROKVISS Mission
• ROKVISS Hardware
• Friction Model / Friction Identification
• Follow-up Inspections
• Results
• Outlook
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DLR - Robotics and Mechatronics Center
• Long-term goal:
Relieving people from dangerous tasks.
• Designing multisensory light-weight robots
for space applications
• Developing control algorithms for closing
smart sensor feedback loops
• Working on telerobotic concepts and manmachine interfaces
• Transfer technologies for applications in
societal areas such as medical robotics,
factory of the future, and personal robot
assistance
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The ROKVISS Mission – 5 Years In Space
• In-flight qualification of DLR‘s Light
Weight Robot III modules – behaviour
under space conditions
• Prove concept of using components of
the shelf, COTS
• Tests of future robot applications
• Dealing with signal round trip delays;
haptic feedback for telerobot control
strategies (telemanipulation with a force
joystick)
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ROKVISS Hardware
• Two lbr III torque-controlled joints,
with partly space qualified
components, mounted on UWP
• Stereo camera
• Illumination system
• Earth observation camera
• Power supply
• Mechanical contour
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> Lecture > Author • Document > Date
The Friction Identification
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Friction Model
• 𝐼𝑠 = 𝑘𝑚 𝜏𝑚
(nominal current value)
• 𝐼𝑠 = 𝑘𝑚 (𝜏𝐹 + τ)
(estimated current value)
• τF = τF + μ τ + d1 q1 sign(q1 )
(friction model)
• 𝑒 𝑝 =
1
𝑁
𝑁
𝑖=1(𝐼𝑠𝑖
𝑝 − 𝐼𝑠𝑖 )²
(optimization problem)
• 54 friction identifications
• Several stiffness idents
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A Few Words About The Friction Plots ..
• Friction parameters (torque losses) are illustrated by three different bars
• Joint velocity is indicated by the small, coloured bars on top
• Joint temperature is diagrammed through ten colour steps
different speed
viscose friction
load-dependent friction
coulomb friction
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Friction Plot – Joint 1
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Follow-up Inspections – Thermal Vacuum
Chamber Tests
• Atmospheric conditions like on the outside
of the ISS (e.g. vacuum)
• Simulation of solar radiation by additional
heater foils
• Different temperature profiles/steps
•  Identify joint friction at different
parameters, to reproduce the mission
conditions
• Read-out the internal- and external
temperature sensors
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Results Of Some Follow-Up Inspections
Test 1:
Internal Heaters Turned Off
• Ten temperature steps:
-17°C to +34°C
• After reaching a defined
temperature step – thermal
equilibrium, measurement (friction
identification) was performed
 Same behaviour like in space
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Results Of Some Follow-Up Inspections
Test 2:
Drop Of Temperature
• Measurement without thermal
equilibrium
• Pass through the temperature
range; perform the identification on
different steps and compare them
with the results of test 1
 One can see just a small
difference
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Results Of Some Follow-Up Inspections
Test 3:
Solar Irradiation
• Influence of solar irradiation
(heating foils)
• Comparing the results again with
test 1
 The idea: heating up one side of
the robot housing could create a
clamping somewhere.
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Summary
• Temperature has a big effect for space-robots
• Friction in space is increasing directly (at a short time)
• The grease (Braycote 601) should be analysed in detail in a vacuum
chamber
• Enhanced friction model with a temperature term
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Thank you !