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Design and Control of Field and Service Robots
Prof. T. AsokanIndian Institute of Technology Madras
Contents• Introduction
• Evolution of Robotics Research
• Design of Surgical robot– System Design
– Slave arm
– Surgical tool
– Master arm
– Controller
• Design of a novel Quadrotor- VOOPS– Concept
– Mathematical modelling
– Thrust loss due to overlap and offset
– Controller design
– Experimental studies
• Conclusions
Evolution of Robotics Research
Source: IEEE
Medical Robotics:
Design of Tele-operated Surgical Robot
A Robot ? What for?
Progress in the field of surgery
Open surgery
↓
Laparoscopic surgery - 1990
↓
Robotic surgery - 2003
Minimally Invasive Surgery
• The Minimally Invasive Surgery (MIS)
• Open access Surgery vs MIS
• Advantages of MIS
A surgical robot: what for?
• Tasks with a complex geometry
• Third hand
• Carry or hold heavy tools
• Remote action
• Motion and force augmentation or scaling
• Force controlled actions
• Intra-body tasks
• Tasks on moving targets
Surgical Robot: System Design
IIT Madras Surgical Robot
System Design
2 slave arms of 7 dof1 camera arm of 2 dof2D vision2 master arms of 7 dofVision systemHaptic feedback capabilityClutch, brake and safety features
System at a glance
Surgical Robot
Surgeons Master Control
Patient side Robotic Slave Arm(s)
Robotic Master Control input Device
Surgeons Vision System
Dual arm surgical manipulator
Camera arm
Haptic force feedback sensor
Camera
3D Endoscope
The master Console
Haptic feedback actuator
Surgical Robot Design: Basic Block Diagram
16
• Laparoscopic tool and Degrees of Freedom
Design of Slave Arm
Design Requirements
• Long endoscope instruments
• Motion scaling
–Coarse hand movement translated to fine robotic movement
• 7 degrees of freedom
• Fulcrum at trocar point-Remote Centre of Motion
Da Vinci Arm
The laparoscopic manipulator
7 degrees of freedom (dof)• 2/3 arm movements
•Up-down (4)•In-out (5)•Side-side (6)
• 3 wrist movements•Yaw (left-right) (1)•Pitch (up-down) (2)
•Roll (circular) (3)• Grip
•Action of the instrument•90 degrees of articulation
AB
RCM Mechanism
Trocar point
RCM Mechanism Design
Double Parallelogram System
RCM with Linear Motion Guide
Linear drive motor
Linear Slide
RCM Mechanism
Roll
3 DOF SurgicalTool
Pitch
Translation
Tool rotation
Features• Reduced inertia due to rope drive
• Preloaded to negate backlash
4 DOF Surgical Tool
Decoupled degrees of freedomInnovative design to reduce wire rope friction (patent filed)All the drives near the tool base to reduce rope transmissionCAN based communication
Drive box of Surgical tool
Wire rope transmission
Wire rope
Diverter pulley
Surgical tool prototype
End effector tool tip
Final prototype
Surgical end effector tip movement
Master Arm design
Design Requirements
6DOF +grasping action
Static and Dynamic Balancing
Haptic feedback
Ergonomic design
Decoupled positioning and orientation
Master Arm Design
Encoder
Counter massGraspers
Gimbal
Master Arm Design
Gimbal assembly
Counter weight
Positioning assembly
Motor for inertia & gravity compensation
Decoupled degrees of freedomStatic Balancing for surgeons’ comfort and easiness of useAdditional dynamic compensationProvision for haptic feedback7 dof (including gripper)Innovative grasper design (PATENT filed)
6dof Master arm prototype
Gripper Design
Camera Arm• Passive control of camera arm
• 2D camera used in the prototype (3D camera will enhance visual feedback; approx. cost Rs 50 lakhs)
Haptic feedback to surgeon
• Need of haptics in Master-Slave based surgical robots
• Advantage of force feedback
• Effective force control
Force feedback (Radius Surgical System )
Force controlled gripper
Robot Control
Design, Analysis, and Control of a Micro Aerial Robot with a Vertically Offset Overlapped
Propulsion system (VOOPS)
21/08/2015
General Quadrotor System
43
• VTOL
• 6DoF – 2 Coupled DoF
• Mechanical Simplicity No SwashPlates => Less Maintainence and reliable
• No tail rotor to Balance torque
Design of Quadrotor for Improved Performance
Performance Parameters
• Endurance• Payload• Stability• Maneuverability• Footprint
44
• Improve Power Plant• Fuel cells• Super Capacitors
• Efficient Blade Design• Aerodynamically efficient Airfoil
• Use of light materials • Composites
• Re-Configure Propulsion system• Alternative prop configurations
VOOPS Quadrotor Design
• Overlap • Offset
"A MULTIROTOR WITH A VERTICALLY OFFSET OVERLAPPING CONFIGURATION AND USES THEROF"
Patent Application Number: 5621/CHE/201445
Thrust Generated by a PropellerBlade Element Momentum Theory BEMT
46
Inflow Ratio
BEMT
Thrust generated by the propeller,
Ref. Lieshman Gordon ,Helicopter Dynamics, Year
VOOPS - Introduction
Vertically Offset Overlapping Propulsion System is a designconcept where the propellers are vertically offset to enableoverlap
• Bi-layered frame, each layer accommodates two rotors• The crucial factors are the overlap and offset.• Accommodate larger propeller without affecting footprint 47
Highlights of Seminar -1
Dynamic Model
48
Basic dynamic model adopted from Paul Pounds [2002]
Loss Due to Overlap and Offset
• Thrust loss in the overlapped region of a lower propeller, for various speeds of the upper and lower propellers can be computed
• Maximum losses due to overlap occur at higher rotor speeds
• Considerable reduction in the overall size of the quadrotor is possible in VOOPS configuration
49
Thrust loss 15 inches propeller
Size of VOOPS vs Conventional quadrotor
U2
U1
L1
L2
Offset 3cm, Overlap 20%
Thrust, Drag and Power Measurement - Experimental Setup and Results
Experimental setupVariation in thrust
Variation in drag torque Variation in power 50
Offset :3cmOverlap : 0-100%Rotors at hover RPMs
Payload and Flight time for VOOPS
Flight time,
Optimal battery capacity * ,
Battery mass
Battery const.
Propeller efficiency
Maximum Overlap loss for chosen configuration.
Capacity of the battery
51
Design Constraints - Overlap
52
Vertical Offset
Wayne Johnson,Helicopter Theory,199553
Thrust Loss due to Offset
54
2R2R/5
Test Platform and results
55
VOOPS vs. Conventional Quadrotor
Factor (units)VOOPS
QuadRegular Quad (5in) Gain%
Endurance (mins) 21 19.6 7.14
Specific Thrust (g/Watt) 5.36 5.08 5.51
Hover Power (Watts) 94.5 99.7 5.50
Additional Payload (g) 354 218 62.38
Factor (units)VOOPS
Quad
Regular Quad
(5.5in)
Loss
%
Endurance (mins) 21 21.8 3.67
Specific Thrust (g/Watt) 5.36 5.41 0.92
Hover Power (Watts) 94.5 93.58 0.97
Additional Payload (g) 354 367 3.54
Performance Comparison of VOOPS Quadrotor with a regular quad (5.5 inch propeller)
Performance Comparison of VOOPS Quadrotor with a regular quad (5 inch propeller)
56
Controller Design: System Architecture
• Mission planner pre-computes the waypoints for the entire mission based on the flying height and camera parameters
• The waypoints are given one at a time to the path generation and course correction block
• Path generation and course correction block feeds the set points to the position controller
• Position controller provides set points to the attitude controller
57
Mission Waypoints
Path generation & Course
correction
WPn
WPn-1
Mission Planner
Position Controller
Attitude Controller
VOOPSQuadrotor
WaypointsTrigger
Controller Design PI-PID
• The gains were tuned for the inner loop first, followed by the outer loops. Ziegler-Nichols method was used to tune the gains.
58
• The position/attitude controller is a cascaded PI-PID controller The inner PID loop isa velocity loop which resists the change in linear/angular velocities.
• The outer PI loop controls the linear/angular position of the quadrotor which helps inposition-hold/stabilize and compensates the drift in the inner loop due to the sensornoise and other disturbances.
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Standard PI-PID controller as used in PX4, APM and Pixhawk autopilots Lorenz Meier, ETH Zurich
Simulation studies PI-PID: Position hold
Deviation in position due to windOrientation of the quadrotor while fighting wind
Steady state error is due to the reason that the gains were tuned for no wind condition.
15m/s Wind
(0,0)
60
Simulation studies PI-PID: Attitude
Input• A sinusoidal variation of
pitch with peak to peak of 45 degrees.
• A pulse of 22.5 degrees and 45 degrees for 4 seconds each.
• An impulse at time t=25 seconds.
PI-PID Attitude controller response
62
Pitch (
degre
es)
Contd..
PI-PID Attitude controller response PI-PID Attitude controller response
Step input of 10 degrees on Roll and Yaw axis at 5th second
• There is a undesirable Pitch due to the input on both the axis• PI-PID starts correction after the error has happened• Need for a model based controller which can apply corrective action
even before the error happens 19
The Back-stepping* control scheme is a nonlinear control methodbased on the Lyapunov stability theorem.
• Systematic and recursive design methodology• Design flexibility, due to its recursive use of Lyapunov
functions• Ability to deal with nonlinearities• Satisfying performance over the whole flight envelope• Guaranteed convergence of the tracking error and the
global asymptotic stability of the closed loop system.
Controller Design: Back-stepping Controller
* Controller adopted from the works of Samir Bouabdallah and Roland Siegwart64
Advantages over PI-PID• Guarantees convergence of error• Unlike PI-PID, Back-stepping controller takes model
into consideration• PI-PID does not consider influences from other axes• Lesser number of gains to be tuned (12 against 30 )
0 5 10 15 20 25-8
-6
-4
-2
0
2
Time (seconds)
Pit
ch
(deg
rees)
0 5 10 15 20 25-2
0
2
4
6
8
Time (seconds)
Ro
ll (
deg
rees)
VOOPS BS
VOOPS PI-PID
Simulation studies BS vs PI-PID: Position hold
Deviation in position due to windOrientation of the quadrotor while fighting wind
65
0 5 10 15 20 25
0
0.2
0.4
Time (seconds)
X (
mete
rs)
0 5 10 15 20 25
0
0.2
0.4
Time (seconds)
Y (
mete
rs)
VOOPS BS
VOOPS PI-PID
15m/s Wind
(0,0)
Steady state error due the reason that the gains were tuned for no wind condition.
Parameters VOOPS
Overall size (tip to tip diameter, (cm)) 81.5
Battery Capacity (Ah | Wh) 26 |577.2
0.0121
0.0013
0.1104
0.1875
1.3
0.3
3.185
4.41
0.1225
83.3
VOOPS – Side view
VOOPS – Top view
Experimental Studies: VOOPS Vehicle Design
• Overlap 20% (7.62 cm)
• Offset of 3 cm 66
Experimental Validation - Test Bench
67Block Diagram of the setup
Serial 2
IMU PC
Micro ControllerESC (4)Motor(4)
VOOPS QuadrotorLoop rate : 200Hz
RC-PWM (4)
Serial 1
Experimental Test Bench
Experimental validation – Field testing
71
PI-PID Attitude controller
PI-PID Waypoint tracking
• Take off • Attitude stablization• Position Hold
• Position hold• Trajectory tracking
Experimental validation – Payload and Flight time
72
• Experiments were conducted using the same vehicle with a little modification• 5Ah Lithium Polymer battery was used (20% of the battery at reserve)• Due to the wind, and payload oscillations, the quadrotor was not able to maintain aperfect hovering condition. This led to the reduction in the overall flight time.
0 1000 2000 3000 4000 5000 60000
2
4
6
8
10
12
14
16
18
Payload (grams)
Flig
ht
tim
e (
min
s)
Theoretical (Conventional)
Theoretical (VOOPS)
Experimental (Conventional)
Experimental (VOOPS)
flight time vs payload
flight time vs payload experiment
Summary
• A theoretical framework was proposed and experimentally validated for thrust, dragand power losses due to overlap
• A Back-stepping based controller was proposed for VOOPS and it showed betterperformance than a PI-PID controller in simulation and bench experiments
• VOOPS quadrotor was compared with conventional quadrotor for payload andendurance
• Path tracking simulation and experiment were conducted with the VOOPS vehicle.
73
Conclusions
• VOOPS configuration is a promising design for MAV• It was found that the losses due overlap were minimal for overlap up to 20%
and the losses due to offset were almost negligible at rotor operating velocities.• Satisfactory performance of a PI-PID controller for the control of the VOOPS is
observed in simulation studies and field test.• Back-stepping controller shows superior performance when compared PI-PID on
the simulation and test bench• VOOPS has shown superior performance and best suitable for aerial survey
applications due to its dynamic response, disturbance handling capabilities,increased payload capacity (~94% more) and increased endurance (~24% at nopayload).
Thank you
