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Design and Control of Field and Service Robots

Prof. T. AsokanIndian Institute of Technology Madras

asok@iitm.ac.in

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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-

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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