Transcript Skyworker - Mobile Manipulator Critical Design Review William “Red” Whittaker Peter Staritz Chris Urmson Field Robotics Center November 18, 1999 SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-1 The Next Step.

Skyworker - Mobile Manipulator
Critical Design Review
William “Red” Whittaker
Peter Staritz
Chris Urmson
Field Robotics Center
November 18, 1999
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-1
The
Next
Step
Space Solar Power (SSP) Facilities
• Constellation of SSP
satellites in GEO
• 1GW of energy to the
ground
4000 m
• Microwave transmission
antenna 1 km in diameter
• Mass of 4800 MT (10X as
massive as ISS)
• Assembled over 1 year,
maintained for 30 years
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-2
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Assembly, Inspection, Maintenance
• Extremely large scale structures
• Poor accessibility
• Long life cycle
• Dangerous environment
• Necessitates a robotic workforce
– Assembly, Inspection, Maintenance (AIM)
Radiator
Parabolic Reflector
Radi
ator
Parabolic Reflector
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Skyworker CDR 11/18/99-3
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Objectives
• Demonstrate the viability of using robots for orbital
construction
• Prove the validity of using structure walkers for orbital
AIM
• Demonstrate SSP AIM relevant tasks using robotics
• Simulate prospective SSP AIM robots and tasks
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-4
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Representative Tasks
• Walk, turn, and transition across planes on a truss
structure
• Pick up and place a payload at arbitrary locations and
orientations in space
• Carry a payload while walking, turning, and
transitioning
• Conduct calibration and inspection tasks
• Connect power and communications cables
• Cooperatively carry massive or large payloads
• Perform tasks that require multiple robot collaboration
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-5
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Demonstration
• Prototype Robot
– Pick up and carry a model transmitting element the length of the
truss, turn while carrying, couple the element to the structure
– Connect Power Management and Distribution (PMAD) to the
element
– Perform a mock calibration
• Simulation
– Large scale construction utilizing multiple robots
– Coordinated installation of full scale transmitting elements
– Demonstrate extended lifetime operations
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-6
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Configuration - Key Metrics
• Continuous Gait
• Forces exerted / Forces experienced
• Workspace
• Control Complexity
• DOF
• Mass
• Cost
• Energy Consumption
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-7
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Skyworker
• Continuous Gait
– Reduced forces on
structure
– Low energy
consumption
– Constant contact with
structure
– Requires 4 joint
synchrony
• 11 Degrees of freedom
• Extensive Workspace
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-8
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Skyworker - Specifications
• Tetherless Mobile Manipulator
• Processor: Pentium166
• Walking Speed: 10cm/s
• Mass: <37kg
• Dimensions:
3m x 0.5m x 0.1m
• Degrees of Freedom: 11
• Material: Aluminum
• Power: 200W peak
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-9
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Force Analysis
• Mass Estimates
• Forces Due to imperfect
GC system
• Maximum torque 16 N-m
• Maximum force 12 N
Original Mass Estimates
Mass Quantity Group Mass
Joints
2 kg
11
22 kg
Links
4.5 kg
3
13.5 kg
Grippers 3.0 kg
3
9 kg
Total
44.5 kg
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-10
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Joint Development
• Determined maximum
torque, speed, and
travel needed for gait
• Modularity
considerations
• Motor / Reduction
Combination
– 16 Nm torque +
– 44 degrees/second +
Joint Required Max Torque Required Max Speed
1
16 Nm
32.1 deg/s
2
Variable
Variable
3
Variable
Variable
4
Variable
Variable
5
10 Nm
43.2 deg/s
6
Variable
Variable
7
1 Nm
32.7 deg/s
8
9 Nm
35.1 deg/s
9
Variable
Variable
10
Variable
Variable
11
Variable
35.1 deg/s
Max Theta
+/- 180 deg
+/- 90 deg
+/- 90 deg
+/- 90 deg
+/- 180 deg
+/- 90 deg
+/- 180 deg
+/- 180 deg
+/- 90 deg
+/- 90 deg
+/- 180 deg
• Skyworker actuators
– 57.5 degrees/second at
32 Nm torque
– 62.5 degrees/second at
16 Nm torque
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-11
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Reduction
• Two Stage Transmission
• Stage 1 - Planetary Gearhead
–
–
–
–
Integral Unit
4.8 to 1 reduction
1.3 deg no-load backlash
80% efficiency
• Stage 2 - Harmonic Drive
– High reduction ratio with zero
backlash
– Low mass - high torque ratio
– Efficiencies ranging from 70% to
80%
CSF 2A-GR-14
Harmonic Drive
Ratio
Rated torque at 2000 rpm
Rated average torque
Limited repeated peak
Limit momentary peak
Maximum Input Speed
Average Input Speed
Mass
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-12
100 to 1
7.8 Nm
11 Nm
28 Nm
54 Nm
5000 rpm
3500 rpm
.09 kg
The
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Motor Selection
• Motors Selection Criteria
– Power Minimization
– Mass
– Available with integral encoder
and planetary gearhead
– Space relevance
• Maxon Motors
– DC Graphite Brushed
– Rated for 42 volts, operating at
30 volts
– .340 kg
– 4800 rpm & 24 Nm output
torque requires 48 watts
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-13
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Joint Overview
2 Offset (Cantilever) revolute
3 Inline revolute (Size A)
3 Inline revolute (Size B)
3 Axial revolute
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-14
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Axial Revolute Joint
• Most
Complicated
• Interface
between F/T
sensor and
Gripper
• Mass 1.48 kg
• Shear key
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-15
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Anatomy of a Joint
Harmonic Housing
Force Torque Interface Cap
Harmonic Drive
Output Shaft
Force Torque Closing Plate
Bearing Secure
Potentiometer Belt
Bearings
Bearing Baseplate
Force Torque Interface
Motor/Planetary/
Encoder Package
Potentiometer
Feedback Drum
Potentiometer Pulley
Gripper Interface
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-16
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Structure Overview
• High bending and
torsional stiffness
• Weight minimization
– Truss reduction
• Access via removable
bottom plates
– Also serve as internal
attachment points
• Each link is unique
– Little opportunity for
modularity
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-17
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Gripper
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-18
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• Clamping force
needed to counteract
effects of stride
Force (N)
Gripper’s Force Analysis
Singularity in stride
• Maximum force
required: 500N
Force (N)
Time (s)
y
Time (s)
x
z
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Skyworker CDR 11/18/99-19
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Concept
•
Dynamic gait requires a robust and
fast gripping mechanism
•
Robustness
• Simple Design - Single jaw actuated
• Low Power - Limited motor torque
required
• Error Correction - Designed with
mechanical allowance for imperfect
approach
•
Speed
• Fast Approach - Direct approach allowed
by configuration
• Fast Mechanism - High speed
advantage provided by linkage
• Fast Motor - High RPM attained with low
torque requirement
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-20
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Mechanism
•
Gripping Mechanism: “Vise Grip”
Four bar linkage
– Speed Advantage: Moving jaw
adequately slowed at final closing
– Force Advantage: Motor force
multiplied at locking
– Power Advantage: Zero power
required when locked
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-21
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Coating
• Potential for wear of
aluminum gripping face
mandated protective
coating
• Stainless Steel Coating
• Reduced wear
• Increased coefficient of
friction
• Thermally sprayed coating
courtesy of the State
University of New York at
Stony Brook’s Center for
Thermal Spray Research
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-22
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Gravity Compensation
• Skyworker requires gravity
compensation to operate properly
• Marionette style cable support
counteracts the force of gravity
• Combination Active/Passive
system
– Vertical axis is passive
– Horizontal axis are active
• Modify a heritage gravity
compensation system
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-23
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Robot Interface Modifications
• Four attachment
points
• Sliding interface to
allow transition
between walking
and manipulating
postures
• Arc center located
at CG
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-24
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Feedback Controller
Optical Angle Sensor
Picture of shuttle with
angle sensor board
(to be taken w/ digital camera)
Output voltages linear function of angles.
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-25
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Feedback Controller
Control Issues
• Gantry pendulum is a fourth order system
• Model as a second order system
– Second order model sufficiently accurate over a small range of
inputs.
– Skyworker will only move over a small range of velocities.
– Tune PID controller for good responses over these inputs.
– Hack: Zero integral term with change of direction (faster
response)
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-26
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Skyworker: Power Electronics
• Power Budget:
– Motors: 140W peak power required
– Motor controllers, communications, sensors, digital
electronics, CPU, and miscellaneous: +5, +10, -10 volt
supplies, 60W maximum
– Worst case: 200W
– Mass Constraint:  4kg (batteries+converters)
• Skyworker must be capable of performing operations
for a minimum of 20 minutes prior to recharging
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-27
The
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Battery Technologies
• Batteries we considered:
Energy/kg
Energy/cm3
Charge Rate
Ease of Charging
Max. Discharge Rate
(Power)
Cost/W
Mass/W
Volume/W
NiCd
Fair
Fair
High
Easy
High
NiMH
Good
Good
Moderate
Easy
Moderate
New NiMH
Good
Good
High
Easy
High
Li-Ion
Excellent
Excellent
Low
Difficult
Low
Low
Low
Moderate
Low
Moderate
Moderate
Low
Low
Moderate
High
High
High
• New high-rate discharge NiMH batteries will be used, because
they provide a high power/weight ratio along with other desirable
properties
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-28
The
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Panasonic High Rate Discharge NiMH
Cell size
Mass per cell
Cell voltage
Current
Charge rate
Max discharge rate
Other nice features
Comparison to NiCd
Sub C
55g
1.25V down to 1V during discharge
3000mA-hours
8 to 9 amps continuously for 20 minute demo
3.4 usable watt-hours per cell
1 hour quick charge with delta-V charger
(Standard NiCd battery charger)
10 Amps (10 Watts/cell minimum)
No memory effect
500 charge/discharge cycles
Equal or better in every way to NiCd, with twice the energy
density of NiCd and (amazingly) no more expensive
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-29
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Power System
• Two separate battery packs
– Motor pack
• 30 cells
• 102 watt-hours
– Electronics pack
•
•
•
•
20 cells
68 watt-hours
Further optimization possible (to equalize run time)
Powers three switching power supplies that produce +5V, +10V
and –10V
• Safety System
– E-stop switches located on robot and at control station
– Power switching circuitry prevents simultaneous connection
of multiple power sources
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-30
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Testing Batteries
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-31
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Battery and Tethered Operation
• Charging
– Using external delta-V chargers to charge batteries without
removing them from Skyworker
• Battery Monitoring System
– Battery voltage monitoring circuitry will let Skyworker know
that it’s batteries are nearly drained
• When Skyworker’s batteries are recharging, it can
run off of a tether that supplies 36V and 24V to
Skyworker’s motors and voltage regulators.
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-32
The
Next
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Electrical Wiring Diagram
MC
MC
MC
DC/DC
10V
DC/DC
-10V
DC/DC
5V
SC
SC
µP
A/D
FT
SC
SC
MC MC
MC
MC
MC
30V BATT
24V BATT
MC
MC
FT
A/D
A/D
FT
MC MC
MC MC
Legend:
+24V Power
-10V Power
+10V Power
+36V Power
RS232 Bus
Sensor Bus
Data Bus A/D
Data Bus 1
Data Bus 2
Data Bus 3
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-33
The
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Joint Labeling Scheme
11
10
8
9
5
3
6
7
2
4
1
SPACE ROBOTICS INITIATIVE
Skyworker CDR 11/18/99-34
The
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