Background Image: The 532 nm green laser of DORISS illuminates a cube filled with natural
gas hydrate from a deep-sea gas vent at Guaymas Basin during the 2003 MBARI Gulf of
California Expedition.
Compiled by Karen A. Salamy and Sheri N. White for MBARI, December 2003
MBARI has developed and deployed a Precision Underwater Positioner (PUP)
for use with its laser Raman spectrometer DORISS (Deep Ocean Raman In Situ
Spectrometer), which is capable of obtaining chemical and structural information
in situ from gaseous, liquid or solid targets in the deep ocean (See preceding
poster OS32A-0235). However, when analyzing solid, opaque objects, the
instrument probe head must be positioned with a precision of ~0.1 mm.
Additionally, the probe head must be free of vibration and stable for tens of
minutes for data acquisition. While the PUP was designed to meet the needs of
the DORISS instrument, it is a stand-alone system that can also be used with
other sensors that require similar positioning requirements (such as in situ
microscopic instrumentation, and microscopic photography).
The PUP was designed to have a 5 degrees-of-freedom positioner on a tripod
platform - Z, R, q, and pan & tilt at the sensor head. It is carried and powered by a
remotely operated vehicle (ROV) and off-loaded onto the sea floor. Adjustable
legs will allow it to accommodate to uneven terrain. The prototype PUP consists
of 2 degrees-of-freedom (horizontal and vertical axes), and rigid legs. It has
been built, tank tested, and deployed on the sea floor (~1020 m depth) for at-sea
tests. This testing has verified that the PUP is capable of providing the stability
and positioning necessary to collect quality Raman spectra of solid and opaque
targets on the sea floor (to depths as great as 4000 m).
Abstract PUP Technical Specifications
Precision positioning is necessary to obtain quality Raman spectra from solid,
opaque targets on the sea floor. We have built and deployed a 2 DOF precision
underwater positioner (PUP). The full 5 degrees-of-freedom system decided
upon in the concept phase will be completed next year and will greatly enhance
the ability of DORISS to collect quality data from a variety of targets and deepsea
environments. We plan to deploy DORISS/PUP at Hydrate Ridge and at
hydrothermal vents on the Cleft Segment of the Juan de Fuca Ridge during a
2004 expedition.
PUP Deployments
Acknowledgements
PUP Software
Linear actuators (image at left) from Exlar
Corporation were modified to include an
oil compensation system for deep water
(4000 meter) use. They are rated to exert
a force of 400 lbs. and have a travel
distance of 20 cm. Dovetail ways (image
at right) are used to provide precision
travel. The dovetails are mounted directly
to the actuator housing that provides
stiffness without adding weight.
PUP TESTING
The PUP project leveraged off-the-shelf components to
hasten development. Two purchases in particular, the
motion controller board from Galil and the video server
from Axis, lowered the software development time and
cost for the project. The Galil unit implements all the lowlevel
motor control loops necessary to move the PUP
actuators to a desired position. The Axis video server
provides a standard internet video feed that can be
displayed directly on the PUP computer screen in any
web browser (see image at left).
GENERAL REQUIREMENTS
The PUP system:
Shall be capable of operating in stand-alone mode (in air or water) for in-lab
use and testing
Shall be deployed on the seafloor by an ROV
Shall maintain stability over full range of motion
Shall accommodate uneven ocean floor (e.g. slopes up to 30 degrees), a
variety of seafloor surfaces (e.g., rocks, sediment, mud)
Shall accomodate a sensor head in either the horizontal or vertical orientation
Shall have an external camera, lighting, and crossing lasers mounted to the
sensor mount for positioning
Shall be controlled by a shipboard scientist via a GUI with position feedback
May accommodate other (non-DORISS) sensors
PERFORMANCE REQUIREMENTS
Minimum position travel of the beam spot (each dimension) 15 cm
Maximum travel increment of the beam spot (each dimension) 0.1 m
Maximum time to travel full range (each dimension) 1 minute
Relative precision (each dimension) 0.1 mm
Relative accuracy (each dimension) 1 mm
Pan and tilt range (for either horizontal or vertical orientation) +/- 45 degrees
Maximum sensor weight allowed on mounting surface (in air) 30 kg
Maximum sensor size allowed on mounting surface 60 x 20 x 20 cm
Maximum weight of complete system (in air) 100 kg
Maximum stowed size 122 cm W x 61 cm H x 61 cm D
Power
Input power (Tiburon) 240 VDC, 5 kW
Input power (Ventana) 110 VAC, 2 kW
Environmental
Operating depth 4000 m
o Operating temperature (ambient) 0 to 50 C
Operating current (water velocity) 0 to 0.5 knots
Functional Requirements
Encoder Driver
MotorAdapter
-servo:Driver*
-_pEncoder:Encoder*
<<adaptee>>
+Initialize(channel:MotionChannel)
+jogAbsolute()
+jogRelative()
Motor
-PositionError:Exception
…
+createAdapter()
+initialize(channel:MotionChannel)
+jogAbsolute()
+jogRelative()
+run()
+waitForStop()
CDMCWin
+Command()
Axis
+NotHomed:Exception
+Timeout:Exception
+initialize(pupcfg:PupCfg*)
+runFindHome()
AtoDAdapter DigIOAdapter
AtoD
-_pAdapter:AtoDAdapter*
+AtoD(driver:Driver*)
DigIO
-_pAdapter:DigIOAdapter*
+DigIO(driver:Driver*)
GALIL API
<<adaptee>>
<<adaptee>>
1..2
MotionController MotionChannel
<<factory>>
-_atod:AtoD
-_digIO:DigIO
-_motionchan:MotionChannel**
-_servos:Driver**
...
+initialize(numaxis:Int16)
+masterReset()
+stopAllMotors()
-filter:PIDFilter
-fls:ioport
-id:MotorID
-rls:ioport
-trajectory:Trajectory
...
We would like to thank the David and Lucile Packard Foundation for their generosity
in funding this project, Jill Pasteris (Washington University, St. Louis, MO) for her
scientific contributions to PUP; Martin Lee of US Stepper for his consultation during
the concept design process; Duane Thompson, Tom Marion, Jose Rosal, and Pete
Braccio for technical support; the Captain and crew of the R/V Point Lobos; and the
pilots of the ROV Ventana for an incredible amount of support.
PUP Deflection Plot
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Distance Extended (cm)
Deflection (mm)
11.3 kg load
15.9 kg load
20.4 kg load
Precision requirement = 0.10 mm
Development of a precision underwater positioner for in situ spectrographic applications
William J. Kirkwood, Sheri N. White (sheri@mbari.org), Mark O. Brown, Scott Jensen, Rich Henthorn, Alana Sherman, Karen A. Salamy, Peter G. Brewer, Edward T. Peltzer
(Monterey Bay Aquarium Research Institute (MBARI), 7700 Sandholdt Rd., Moss Landing, CA 95039, United States)
M B A R I
The graphical user interface (GUI) (shown below) was designed to present all the motion control and critical data to
the user in a single window. The controls available include moving to arbitrary and previously visited coordinates
and moving in variable increments and motor speeds. Buttons are presented to control power to onboard lights,
camera, crossing laser guides, and the DORISS subsystem.
The prototype PUP consists of a 2 DOF (R
and Z axes) system with non-adjustable
legs, drive electronics (capable of
supporting 5 DOF), a color camera and
crossing lasers. Subsequent phases will
include the addition of the remaining
degrees-of-freedom, adjustable legs, and
a cable management system for stand-off
distances greater than 2 meters.
A single cable from the ROV provides
power and communications (Ethernet) to
PUP and DORISS via a vehicle interface
can (VIC) (see diagram at left). PUP is
capable of running off either 120 VAC or
240 VDC.
Our selected concept is a 5 DOF system on a tripod base (image above). Three
axes (R, Z and q) provide movement within the working envelope . A pan and tilt
device allows the laser beam to be positioned at an optimal angle to the surface
to provide maximum signal. A tripod base provides stability, and adjustable legs
allow the PUP to accommodate uneven sea floor.
Design Concept
OS32A
0236
Conclusions
Sub-Assembly Testing (Load and Deflection)
The linear actuator was modified from the “as-built” mechanism received from the vendor to provide a stiff assembly capable
of carrying the weight of the probe head. Early prototype testing of the slide sub-assembly under various load conditions was
performed to verify that the system could meet the load requirements. The load testing was conducted for 1 cm incremental
extensions of the slide mechanism (see image below left) up to 15 cm (~5.9 inches). Loads were increased in 20 lb (9.1 kg)
increments from 25 to 85 lbs (11.3 kg and 38.5 kg, respectively). The data revealed that the system behaves repeatably. For a
25 lb (11.3 kg) load (twice the weight of the DORISS probe head in water), the deflection is just within our precision
requirement of 0.10 mm (see figure below right).
Full System Testing (Spectral Acquisition)
Testing was performed in the lab (in air) to verify that the PUP system could position the probe head precisely enough
to obtain quality spectra. This testing was performed with the DORISS stand-off optic which has a focal depth of ~1
mm in air (see figure below left). We used PUP to focus DORISS on a polished silicon wafer (a strong Raman scatter
with stringent positioning requirements). After obtaining a spectrum, the PUP was moved to the home position and
commanded back to the position at which the first spectrum was taken. A second spectrum was then taken which
matches the first exactly (see figure below right), thus verifying the ability to return to a previous position with a high
degree of accuracy.
PUP has been deployed
three times in Monterey
Bay to a depth of 1020 m
using the ROV Ventana
(see image at left). The offloadable
component of
PUP with the DORISS
probe head has an in-water
weight of ~25 lbs. The
Ventana manipulator was
able to easily lift and
position PUP on the
seafloor.
PUP indicated that despite sitting
on soft sea floor, PUP was stable
through the entire range of motion.
We were able to use the PUP
camera to visualize targets and the
crossing-lasers used to identify
distance to the target (see pictures
below and right).
As is typical during the development of a new instrument, we have encountered a
variety of problems with the PUP system. These include faulty limit switches in the
actuators, sticking of the actuator mechanism possibly caused by temperature or
pressure effects, defective cables, and networking problems. Additionally, the
DORISS system has had a number of problems that have prevented us from
obtaining spectra on the sea floor with the PUP/DORISS system. These problems
have been addressed and we plan to collect the first in situ spectra using
PUP/DORISS during a December 16-18, 2003 cruise on the R/V Western Flyer
using the ROV Tiburon.
0
1000
2000
3000
4000
5000
6000
7000
8000
-3 -2 -1 0 1 2 3
Distance from Center of Focus (mm)
-1 Raman Intensity at 520 Dcm
Immersion Optic
Stand-off Optic
500
1000
1500
2000
2500
3000
3500
Counts
490 500 510 520 530 540 550
-1 Raman Shift (Dcm )
Spectra of polished silicon wafer in air
initial spectrum
spectrum after movement
Figure at left is a spectrum of
marble obtained in the lab (in
air) using PUP to position the
DORISS probe head.
31
1
0.1
752.84
1098.1
1313.8
14.8
41
4024.6
0
2000
4000
6000
8000
10000
Counts
500 1000 1500 2000 2500 3000 3500 4000
-1 Raman Shift (Dcm )
Marble
PUP consists of a three-legged platform,
within which rests a pressurized glass
sphere (image at right). Two linear
actuators (R and Z) are mounted to the
frame of the platform. The DORISS probe
head is held in a collar mounted on the end
of the R-axis actuator. The collar can be
mounted to the motor in two
configurations, such that the probe head
is oriented either parallel or perpendicular
to the sea floor.
DORISS Electronics
and Spectrometer
Housings
VIC
Probe Head
PUP
Actuators
(Z, R)
Servo
Power Supply
Ethernet Hub
Video Server
Motion Controller
Servo Amplifiers
Low
Voltage
Power
Camera
Lasers
To ROV
Fiber Optic
Cabling
Comms
Power
Toolsled components
Off-loaded components
System Block Diagram
The glass sphere houses all the electronics needed to power and control the motors, lasers, camera, and light
(image above left). The R and Z-axis actuators require a stand-alone motion controller (Galil Motion Control, Inc.)
and digital servo drives (Advanced Motion Controls). The video signal from the camera feeds into a video server
(Axis Communications). Both the video server and the motion controller are TCP/IP compatible, so all
communications to the PUP system are through the Ethernet protocol. The sphere houses two sensor boards
(Applied Geomechanics Inc.) which measure pressure, water, humidity temperature, and tilt.
The motor control program was built re-using a
successful design from MBARI’s Environmental
Sample Processor (ESP) project. With a solid
foundation of motor control code available, a
more aggressive schedule for the PUP has been
pursued. Some of the GUI design style for the
PUP interface has also been borrowed from
ESP. In particular, the event loop used to poll for
information was lifted directly from ESP. The
"look-and-feel" of the PUP interface, however, is
new and reflects the high level of interaction
necessary during deployment (see image
above).
A series of tests were performed on the sea floor to test all of PUP's functions. Both
actuators were able to move through their full range of motion at a variety ofspeeds
and were able to move in increments as small as 0.1 mm. The tilt sensors on
(Taken from Brewer
et al., in press.)
The data section displays
critical data during a PUP
mission. Current motor
position is displayed along
with environmental data
such as temperature,
relative humidity, and X-Y
tilt angles.