System Components - Drexel Force Feedback Team :: Home

Submitted To:

Dr. B.C. Chang

Dr. Wei Sun

Dr. Moshe Kam

Dr. Leonid Hrebien

Pramod Abichandani

Chirag Jagadish

Problem Background


Surgical Techniques


Open


Minimally Invasive (MIS)


Laparoscopic


Minimally Invasive Robotic Surgery (MIRS)


Traditional Laparoscopic


Instruments manipulated by hand through small incision


Endoscope used to view operating space


Laparoscopic limitations


“chopstick effect”


2D representation on monitor

Minimally Invasive Robotic Surgery
(MIRS)


Robotic systems were developed to overcome the
awkward hand
-
eye coordination involved in laparoscopic
procedures [1]


Intuitive Surgical’s
daVinci®

system is most popular for
minimally invasive robotic surgery (MIRS)


Approved by the FDA in July of 2000 [2]


860 units sold and more than 70,000 surgeries performed
each year [3, 4]

The
da Vinci

Surgical System

[5]

[6]

Strengths and Drawbacks

of MIRS


MIRS strengths


Geometric accuracy


Free from tremors and fatigue


Sterile


Resistant to infection


MIRS drawbacks


Current systems lack realistic, continuous force feedback [7]


Training is expensive and time consuming


Inexperienced surgeons take longer using MIRS than
conventional methods


MIRS Statistics


Taken from “Clinical Efficacy
-

Comparison of Open
Prostatectomy, Laparoscopic and da Vinci Prostatectomy” [8]

Open

Laparoscopic

da Vinci
MIRS

Patients

100

50

100

Operative Time (Min.)

164

248

140

Blood Loss (mL)

900

380

<100

Cancer Remaining

24%

24%

5%

Complications

15%

10%

5%

Catheter, Days

15

8

7

Hospitalization (Days)

3.5

1.3

1.2

Problem Statement


Current minimally invasive robotic surgical systems lack realistic
force feedback


Tactile sense is one of the most important tools for surgeons


Surgeons rely on tactile sense in order to characterize tissue and
make intra
-
operative decisions [9].


Surgeons must rely on visual cues only, which requires
significant experience [1].


Lack of realistic force feedback can lead to tissue damage or
other mistakes


Without force feedback in blunt dissection, the number of errors
resulting in tissue damage increased by over a factor of 3 [10]


Increased operating time and cost

Force Feedback


Preliminary research shows that force feedback improves
on the gains made by MIRS over conventional techniques


Possible to tie tighter, more consistent sutures [7]


Improves arterial dissection by reducing unintentional
transections [12]


Reduces learning curve for surgeons with little or no
experience using MIRS [13]

Design Objective


Prototypic slave
-
master surgical robotic system


Sense force at the slave (surgical manipulator)


Generate force at the master (user controls)


Microprocessor communication between master
controller and slave gripper allows us to:


Control gripper angle


Reproduce gripper forces at the surgeon user control


Translate the
EndoWrist
in two axes

Method of Solution

System Components


Two electromechanical systems in a slave
-
master
configuration


Master includes custom user controls, force feedback
actuator, and microprocessor


Slave includes
EndoWrist®
, x
-
y stage, and microprocessor


Host computer to display important information and set
system parameters

The
EndoWrist


Precision surgical manipulator
developed by Intuitive Surgical for the
da Vinci

Surgical System


Offers 7 degrees
-
of
-
freedom


Complex movements made possible
using four control knobs


EndoWrist
Control Knobs

Slave Interface to
EndoWrist


Three components:


Base includes four holes into which DC motors can be
mounted


Cylindrical adapter can be used to attach a motor shaft to an
EndoWrist
control knob or to hold control knob in place


Clamp used to attach the base to the
EndoWrist


Modular
–

Additional motors can be added if needed

Base of Slave Interface

Top View

Bottom View

Adapter for Slave Interface

Top View

Bottom View

Force Sensing


Motors will be controlled using PWM controlled H
-
bridge
circuits


To sense force, a current sensor will be placed in series
with the
EndoWrist
’s drive motor


Does not require any physical modifications to the
EndoWrist


x
-
y Stage


The
EndoWrist
and the mechanical interface assembly will
be mounted on an x
-
y stage


The stage will be positioned vertically to allow to allow the
user to grip, lift, and pull a sample placed beneath the
EndoWrist

Slave Processor


The slave processor will:


Execute control algorithms for the
EndoWrist

and the x
-
y
stage


Collect and transmit force measurements to the master
processor


A second, less powerful processor (the “stage controller”)
will drive the motors for the x
-
y stage


Master Grip Controller


Two gripper levers onto
which plastic finger
splints will be placed


Levers will rotate the
shaft of a DC motor


Optical encoder will
measure shaft position


Drive motor to provide
force feedback

Translation Controller


Used to control the movement of the x
-
y stage


Will be integrated with the grip controller


Possible options:


Joystick controller


Translation sensor (e.g. optical mouse sensor)


Master Processor


The master processor will:


Receive force measurements from the slave processor


Transmit position data to the slave processor


Execute a position
-
force control algorithm to create a
realistic sense of touch


Transmit data to the host computer via USB


Host Computer


Connected to the master processor via USB


A graphical user interface (GUI) will display information
about system operation to the user


May include real time graphs of force and position


GUI will also be used to set system parameters (e.g.
scaling ratios)

Deliverables


The design should meet the following criteria:


The user will command grip and 2D translational motion of
the
EndoWrist


The user will be able to sense an object in the grasp of the
EndoWrist

Alternative Solutions

Alternative Solutions


Two key components to any force feedback solution


Instrumentation Design
-

Placement of sensors


Sensing Method
-

Measure force


The key components are interdependent
–

certain methods of
sensing force require specific placements for sensors


Based on the selection of the key components, it’s possible to
choose a control algorithm


Two common force feedback control algorithms are:


Force
-
Position


Position
-
Error

Alternative Solutions (Cont’d)



For force feedback, the force sensing elements placed at
the slave, on the laparoscopic instrument


Laparoscopic instrument is inserted into the body through
an insertion which is 3
-
12mm in diameter


Particular sensors may have limitations on feasible
locations



Placement of Sensors

1.
At the joint actuation unit

2.
Shaft portion outside abdominal wall

3.
Shaft portion inside abdominal wall

4.
End effector's articulated joints

[14]

Methods of Sensing Force

1.
Displacement

2.
Current

3.
Pressure

4.
Resistive

5.
Capacitive

6.
Piezoelectric

7.
Vibration

8.
Optical

Sensor and Placement Selections


Current
-
based sensing


Exploits the relationship between shaft torque and armature
current, which is linear in the region of interest


Placed at the joint actuation unit


Four motor driver knobs to control gripper orientation and
actuation

Advantages of Selections


Minimizes redesign of
da Vinci


Allows the
EndoWrist
to be used without redesign


Known to be comparatively simple approach


Calibration and experimentation can be used in lieu of
system modeling to determine erroneous forces


No need for sterilizability and biocompatibility


Lower recurring cost to end user than internally placed
sensor
-

no need to be cleaned or replaced after each
operation

Disadvantages of Selections


Measurements may be inaccurate due to approximations
which are based on torque
-
current curve


Force signal may have magnitude and phase distortions


Mechanical linkages introduce error due to:


Friction


Backlash


Inertia


Mechanical moments



Final Analysis of Key

Component Selections


Inexpensive


Low complexity


Adaptable to existing robotic surgery systems


Alternative methods may require redesign of the
laparoscopic instrument


Feasible using available senior design resources

Design Constraints


Cost and time


Limited funding


Must be completed within next two terms


Complexity limited by funding and duration


FDA regulations specify that the slave surgical
manipulator must be biocompatible and sterilizable [15]


Constraint is met by placing sensors outside the body

Design Constraints (Cont’d)


Geometry


Ability of instrument to be
inserted through trocar


Induced Master Motion


Stability is compromised by
allowing force feedback
signal to influence position


Gains are limited to values
that ensure system stability


Trocar

Skin

[1]

Project Management

Gantt Chart

Task Tree

Industry Budget

a.
Includes cost of H
-
bridge, current sensor, and quadrature decoder

b.
Includes cost of Pro
-
E and SolidWorks

c.
Cost of Labor:4 junior engineers, $55K salary, 15 hrs/week, 36 weeks

d
. Overhead: 50% of total Cost of Labor

Economic Analysis


Dr. B.C. Chang provided
EndoWrist
and 2 DC motors with
encoders for free


Manufacturing provided at Olympic Tool’s expense


Freescale Semiconductor provided 2 microcontroller
development boards for free by sponsorship agreement


Engineering software available


Not considering labor and overhead costs


Out
-
of
-
Pocket Costs

Description

Cost

Quantity

Total Cost

Translation (x
-
y) Stage

$1,274.00

1

$1,274.00

Digital Motor Controller
Board

$400.00

2

$800.00

Total

$2,074.00

Societal and Environmental Impact


Implementation of force feedback will allow more delicate surgeries


For example, Mitral Valve Repair (MVR) is significantly less dangerous
when MIRS is used [16]


2001 STS Nat’l Database

Sternotomy MVR

da Vinci
Trial

Patients

893

112

Mortality

2.2%

0%

Major Complications

12.1%

9.8%

Neurological Complications

2.4%

0%

Hospitalization (Days)

8.5

4.7

Societal and Environmental Impact
(Cont’d)


Improvements to MIRS should further reduce:


Complications


Supplemental surgeries to correct complications


Hospital stay times


Operation time


Cost of surgery may be decreased


Implementation of force feedback in surgical robotics
should have a minimal impact on the environment


Reduction in number of operations and operation time will
minimize the amount of electricity used in the operating
room





Conclusion


Statistics indicate that use of MIRS will continue to grow


Prototype of slave
-
master surgical robotic system with
grip force feedback


Current
-
based force sensing


Custom designed user controls,
EndoWrist

interface


Surgeon controls grip and 2D translation of
EndoWrist


Beneficial impact on the evolution of medical robotics

Questions?

References


[1] K. Seibold, U.and Bernhard and G. Hirzinger. Prototypic force feedback instrument for
minimally invasive robotic surgery. In V. Bozovic, editor, Medical Robotics, page 526. I
-
Tech
Education and Publishing, Vienna, Austria, 2008.


[2] M. Meadows. Robots lend a helping hand to surgeons. FDA Consum, 36(3):10
–
5, 2002.


[3]
www.intuitivesurgical.com/corporate/newsroom/mediakit/da_Vinci_Surgical_System_FAQ.p
df


[4] www.pacrimrobotics.com/forms/orangecounty_reg.pdf


[5] http://www.childrenshospital.org/clinicalservices/Site1860/Images/robotics(E).jpg


[6] http://www.healthaffairs.uci.edu/urology/prostate/daVinci.html


[7] http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1283126


[8] Menon M. Robotic radical retropubic prostatectomy. BJU Int. 2003 Feb;91(3):175
-
180.


[9] G. Tholey. A teleoperativehaptic feedback framework for computer
-
aided minimally
invasive surgery. PhD thesis, Drexel University, 2007.

References (Cont’d)


[10] C.R. Wagner, N. Stylopoulos, and R.D. Howe. The role of force feedback in surgery:
analysis of blunt dissection. In Haptic Interfaces for Virtual Environment and Teleoperator
Systems, 2002. HAPTICS 2002. Proceedings. 10th Symposium on, pages 68
-
74, 2002.


[11] http://www.ingentaconnect.com/content/klu/11548/2008/00000003/F0020003/00000228


[12] Deml, B. “Minimally Invasive Surgery: Empirical Comparison of Manual and Robot
Assisted Force Feedback Surgery” Proceedings of EuroHaptics 2004, Munich Germany, June
5
-
7, 2004.


[13] Reiley, C. “Effects of visual force feedback on robot
-
assisted surgical task performance”
The Journal of Thoracic and Cardiovascular Surgery, January 2008.


[14] P. Puangmali, K. Althoefer, L.D. Seneviratne, D. Murphy, and P. Dasgupta. State
-
of
-
the
-
Art in Force and Tactile Sensing for Minimally Invasive Surgery. Sensors Journal, IEEE,
8(4):371
–
381, 2008.


[15] Allison M. Okamura. Haptic feedback in robot
-
assisted minimally invasive surgery.
Submitted to Current Opinion in Urology, August 2008.


[16] http://www.sts.org/2003webcast/shows/tatooles/tatooles.html