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- Offer Profile
- Our research focuses on the
role of sensing and mechanical design in motor control, in both robots and
humans. This work draws upon diverse disciplines, including biomechanics,
systems analysis, and neurophysiology. The main approach is experimental,
although analysis and simulation play important parts. In conjunction with
industrial partners, we are developing applications of this research in
biomedical instrumentation, teleoperated robots, and intelligent sensors.
Product Portfolio
Surgical Robotics
3D Ultrasound-Guided Robotic Motion Compensation for Beating Heart Intracardiac
Surgery
- Traditionally, surgeons have coped with heart motion during cardiac
surgery by stopping the heart and using the heart-lung machine to
pump and oxygenate the blood. There is great interest in avoiding
the use of the heart-lung machine because it has serious side
effects. Furthermore, the outcome of a surgery on a stationary heart
is challenging to predict. Beating-heart surgery prevents the
morbidities associated with the heart-lung machine and potentially
improves surgical outcomes by allowing the surgeon to evaluate the
repair during the operation. However, this type of procedure is
difficult for surgeons to perform because of heart motion. We have
developed a 3D ultrasound-guided motion compensation system that
tracks heart motion and allows the surgeon to operate on the fast
moving structures of the beating heart without risk of damaging
them.
Guiding Intracardiac Beating Heart Procedures
With Real-Time Three-Dimensional Ultrasound
- To perform
procedures inside a patient's heart (intracardiac surgery),
cardiopulmonary bypass is necessary so the surgeon can work on a
relaxed open heart. Although this technique is the current standard,
new studies have identified numerous adverse effects of a
cardiopulmonary bypass. Minimally invasive procedures could
eliminate the need for a cardiopulmonary bypass, thereby allowing
the surgeon to work directly inside the beating heart.
Unfortunately, there currently is no suitable imaging modality to
facilitate intracardiac beating heart surgery as traditional
endoscopes are ineffective due to the opacity of blood. However,
recent developments by Philips Medical Systems have yielded a new
real-time three-dimensional ultrasound system which may enable
beating heart intracardiac surgery.
Force Feedback in Surgery: An Analysis of Blunt Dissection
- Force
feedback is widely assumed to enhance performance in robotic
surgery, but its benefits have not yet been systematically assessed.
In this study we examine the effects of force feedback on a blunt
dissection task. Subjects used a telerobotic system to expose an
artery in a synthetic model while viewing the operative site with a
video laparoscope. Performance was compared between force feedback
gains of 75% and 150% and no force feedback. The absence of force
feedback increased the average force magnitude applied to the tissue
by at least 50%, and increased the peak force magnitude by at least
a factor of 2. The number of errors that damage tissue increased by
over a factor 3. The rate and precision of dissection were not
significantly enhanced with force feedback. We hypothesize that
force feedback is helpful in this blunt dissection task because the
artery is stiffer than the surrounding tissue. This mechanical
contrast serves to constrain the subjects’ hand from commanding
inappropriate motions that generate large forces.
Surgical Modeling and Planning
Mitral Valve Modeling:
- Surgical
repair of the heart's mitral valve is hard. Repair is typically
performed with the heart on bypass (i.e., emptied of blood and no
longer beating.) With the heart in this state, it is difficult for
the surgeon to predict how to modify the structures of the valve so
that the valve will function properly when the heart is sewn up,
refilled with blood and allowed to resume beating. A surgical
planning system based on patient-specific medical images that allows
surgeons to simulate and compare potential repair strategies could
greatly improve surgical outcomes. In such a surgical simulator, the
mathematical model of mechanics used to close the valve must be able
to compute the closed state quickly and to handle the complex
boundary conditions imposed by the chords that tether the valve
leaflets. We have developed a system for generating a triangulated
mesh of the valve surface from volumetric image data of the opened
valve. We then rapidly compute the closed position of the mesh using
a mass-spring model of dynamics.
Teleoperated Robotics
Effect of link and joint flexibility in a teleoperated
robot
- A
teleoperation system makes it possible for a user to interact with
environments that are inaccessible to direct human contact, e.g.,
because of their constrained space or remoteness. Minimally invasive
surgery and space exploration are two examples where telerobotic
operation is advantageous. Haptic feedback can improve task
performance during both space and surgical teleoperation. Current
research on haptic teleoperation assumes ideal dynamics for the
slave robot, i.e., a single mass (or a mass and a damper) model for
it. Such an assumption is grossly violated in current space and
surgical robots due to the presence of flexibility in the links and
joints of the robots. Indeed, space robots are designed to be
lightweight and compact for minimum liftoff cost and energy
consumption during robot control, and therefore involve flexibility.
Surgical robots have thin instruments for entering the patient's
body through ports for minimal invasiveness. As the surgical
instruments become thinner (e.g., < 3 mm in pediatric surgery), the
effect of tool flexibility becomes more crippling. Moreover, due to
space limitations, actuation of a distal dexterous wrist is
performed from outside the patient and propagated to the wrist
through flexible cables, which introduce joint flexibility. In this
work, we systematically analyze transparency and stability
limitations under robot link or joint flexibility and examine the
added benefits offered by tip sensors during teleoperation with a
flexible slave, and the cost-benefit tradeoffs of reducing or
eliminating the effect of flexibility in haptic teleoperation.
World Modeling by Tele-Manipulation
- At
present, teleoperation is the only way that robots can perform
sophisticated manipulation tasks in unstructured environments. In
this control mode, the human operator performs all required sensing
and planning, and generates all motion commands based on feedback
from the remote environment. In practical teleoperation systems
(e.g. undersea operations, tele-surgery, etc ), the sensory feedback
is often limited to video images without force feedback, which
greatly restricts dexterity and productivity. We have been working
to alleviate this situation by using information from the remote
robot arm's sensors to assist in teleoperated manipulation tasks .
We have derived algorithms that identify essential local geometric
properties of objects in the remote environment including geometry,
dimensions, and orientations.
Tissue Mechanics
Characterizing the Nonlinear Mechanical Response of Liver to Surgical Manipulation
- Computer-aided medical technologies such as simulators for surgical
training and planning require accurate representation of soft tissue
behavior under large deformations. Limited datasets, and unrealistic
models for soft tissues currently hinder the advancement of surgical
simulation. This work presents data and modeling efforts to realize
a constitutive model for liver whose parameters have a physical
basis. The model can predict the behavior of liver independent of
loading modality. Implementing such physically-based constitutive
models into simulation systems provide realistic behavior, and
ensure that errors made are not from the virtual environment.
Image-Based Mechanical Characterization of Soft Tissue
- Conventional material testing methods, such as indentation testing,
only provide a limited local insight into material response. This
project aims to develop parameter identification techniques suitable
for material parameter estimation, combining three-dimensional
ultrasound imaging with conventional indentation testing methods.
Estimates of complete deformation fields obtained through imaging
are incorporated into an iterative finite-element modeling (FEM)
scheme to identify tissue-specific parameters of a physically-based
nonlinear poro-viscoelastic constitutive law.
Robotic Grasping and Shape Deposition Manufacturing
Robust Robotic Mechanisms and Sensors via Shape Deposition Manufacturing
- One of the
greatest successes of biologically-inspired design has been the
development of mechanically robust robots. One promising biomimetic
facbrication technique is Shape Deposition Manufacturing (SDM),
which alternates material deposition and machining to produce robot
structures with compliant joints and embedded sensing and actuation
elements. We explore the benefits of using Shape Deposition
Manufacturing for constructing a simple two-fingered gripper and add
to the tools available to robot designers by developing a range of
sensing modalities compatible with the process. These include
Hall-effect sensors for joint angle sensing, embedded strain gauges
for 3 axis force measurements, optical reflectance sensors for
tactile sensing, and piezoelectric polymers for contact detection.
In addition to a simple construction process, the resulting parts
are extremely robust, fully functional after high impact loads and
other forces due to unintended contact.
Compliant Grasping for Unstructured Environments
- Compliance
conveys several advantages for robotic grasping. In unstructured
environments, sensing uncertainties are large and target object size
and location may be poorly known. Finger compliance allows the
gripper to conform to a wide range of objects while minimizing
contact forces. Robot joint compliance or stiffness has often been
considered in the context of active control, where active control
uses sensors and actuators to achieve a desired force-deflection
relationship. In contrast, passive compliance, implemented through
springs in robot joints, offers additional benefits, particularly in
impacts, where control loop delays may lead to poor control of
contact forces. The reduced need for the sensing required to create
active compliance can also lead to lower implementation costs.
"Soft" Grippers and Bugbots
- Collaborators from Stanford and UC Berkley have designed and
produced a robot modeled after the cockroach, utilizing knowledge of
the insect's locomotion characteristics and new manufacturing
techniques. The interesting feature of the robot is a passive rubber
spring joint connecting the legs to the body. This joint, mimicking
the springy, resilin lined joints of the insect, aids in disturbance
rejection, accomplished without sensory feedback. Our contribution
to the project will be a mechanical gripper designed using similar,
passive spring joints with variable stiffness, which will aid in the
task of grasping an object in a unfamiliar environment, without the
use of complex sensory technology.
Tactile Sensing and Display
Remote Palpation Instruments for Minimally
Invasive Surgery
- We are
developing remote palpation systems to convey tactile information
from inside a patient's body to the surgeon's fingertips during
minimally invasive procedures. These new instruments will contain
tactile sensors that measure pressure distribution on the
instruments as tissue is manipulated. The signals from these sensors
will be sampled by a dedicated computer system, which will apply
appropriate signal processing algorithms. Finally, the tactile
information will be conveyed to the surgeon through tactile
"display" devices that recreate the remote pressure distribution on
the surgeon's fingertips. Creation of remote palpation technology
will increase safety and reliability in present minimally invasive
procedures, and bring the advantages of minimally invasive
techniques to other, more complex procedures, which are not possible
today.
A Tactile Shape Display Using RC Servomotors
- Tactile
displays are used to convey small-scale force and shape information
to the tip of the finger. In this paper, we present a 6x6 tactile
shape display that uses commercial RC servomotors to actuate an
array of mechanical pins. The display has a maximum pin deflection
of 2 mm along with a resolution of 4 bits. Pin spacing is 2 mm with
a pin diameter of 1 mm. The display can accurately represent
frequencies up to 25 Hz for small amplitudes and is slew rate
limited at 38 mm/sec for larger amplitudes.
Tactile Shape Displays
- The
tactile display in our prototype system consists of a line of 10
individually actuated pins that are raised against the fingerpad.
Shown below is a drawing of our design. A line configuration was
chosen since the palpation instrument will be scanned across the
tissue allowing motion to provide the other dimension. This also
simplifies the design. SMA wires are used to drive the pins. As
electric current heats the wire, it goes through a phase
transformation and shortens, thus pushing the pin up. With this
design, each pin can move 3 mm and produce over 1 N of force. A
primary problem with SMA is the slow response times. We overcame
this by using water cooling and position feedback for each pin from
optical sensors. Figure 5 shows the response of the pin as a
function of desired position frequency. The output displacement
drops by 30% (-3 db point) at 40 Hz. This satisfies the design
specification set by the finger speed experiments.
Vibrotactile Sensing and Display
- We have
developed tactile sensors and display for measuring and conveying
task-related vibrations in robotic manipulation, teleoperation and
virtual environments. Vibration displays can be implemented with
inexpensive, open loop devices that can be added to many existing
manipulation systems to improve performance. Aside from developing
vibration sensing and display devices, we have worked to delineate
the kinds of tasks where high frequency vibratory feedback is
important. In inspection and exploration tasks the detection of
vibrations can be the fundamental goal of the task, while in some
manipulation tasks vibrations can enhance performance by reducing
reaction times or permitting minimization of forces. We have also
developed a vibration sensing and display system for a high-capacity
undersea teleoperated robot, and field tested it on an offshore oil
platform.
Biological Motor Control
A Quantitative Investigation of the Effects of Hypnosis on Stroke Recovery
- Physical
rehabilitation after stroke requires complex interactions between
the mind, brain and body. My research focuses on characterizing
these interactions through biomechanical analysis of movement during
physical therapy, medical imaging of neurological changes in the
motor control system and hypnosis as a means of altering the mental
state of stroke patients. By combining quantitative methods with a
holistic approach to rehabilitation I hope to gain insight into how
mind-body interactions affect motor recovery after stroke.
Mechanical Impedance of the Human Hand
- We have
worked to determine how humans modulate the mechanical impedance of
their hands in response to task requirements. The results help
explain sensing and motor control strategies in dextrous
manipulation. Our approach involves experimental measurement of
force-motion relationships of the hand and fingers during task
execution. These studies have measured the impedance of the index
finger in extension and abduction, and the impedance of the
precision pinch grasp during lifting. We have also examined learning
of impedance strategies and applications of these results to fast
tasks like drumming.