Robot Sensors 2.12 Introduction to Robotics

Lecture HandoutSeptember 20, 2004

H. Harry AsadaMassachusetts Institute of Technology

Touch Sensor

CCD Camera Vision System

Ultrasonic Sensor

Torque Sensor

Touch Sensors

Photo removed for copyright reasons:

Sony Aibo™ dog robot. http://www.sony.net/

Products/aibo/.

Ultrasonic Sensor

Photo removed for copyright reasons.

Transition Technology meal delivery robot.

Wrist Force Sensor

Tension Sensor

Tactile Sensor

copyright reasons.

finger and thumb.

Photo removed for

Robot hand with

Infrared

Bumper Sensor

Distance Sensor

Slip Sensors

Internal and External Sensors

Actuators

Internal Sensors

Environment

External Sensors

Reference Command

Robot sensor taxonomy

• Internal sensors – Position sensor – Velocity sensors – Torque and acceleration sensors

• External sensors – Tactile sensors – Force and torques sensors – Proximity sensors – Range sensors – Vision sensors– Others

Actuator &Load

PositionSensors

ReferenceCommand

FeedbackLaw

• Potentiometer• Optical shaft encoder

DC Motor

Arm Links

Gearing

Joint Axis

Internal Position Sensors

Optical Shaft Encoder

Disk with grid patternLight source: LED

Opaque

Translucent

Shaft

Photodetector

As the shaft rotates, a pulse train is generated. Counting the number pulses gives the angle of rotation.

Distinguishing clockwise and counter-clockwise rotations

Track A

Track B

Photodetectors

Clockwise rotation Counter-clockwise rotation

A

-90o

B

+90o

A

B

Track A is 90 degrees ahead of track B. Track A is 90 degrees behind.

Using an up-down counter, CW and CCW rotations are correctly counted.

A Phase Up-Down Counter

Most sensitive bit

B Phase

n-bit parallel

Least sensitive bit

Clear/Initialization

Initialization of the Up-Down Counter

When the joint is brought to a home position, the z-phase pulse is generated for initializing the up-down counter.

Home Position

Z B A

Absolute Encoder

Parallel Data

No initialization needed

Velocity Measurement Using an Encoder

Internal Velocity Sensors

~Velocity = Pulse Frequency

Counter clear

TSampling period

= Pulse counting interval

The drawback of pulse frequency measurement

As the angular velocity gets slower, only a few pulses are observed in the fixed time interval:

discretization error increases.

T

t int

A better alternative is to measure the interval between adjacent pulses tint, and take the reciprocal for estimating the velocity.

1ω ∝tint

Hybrid velocity counterMeasuring the time interval between adjacent pulses:

More accurate in slower speed

Low speed counter

High speed counter

t int

T

Counting the number of pulses in a fixed time interval: More accurate in higher speed

Sensor as a “System”

Multi-stageSignal transduction

and modulationKey Transducer

Signal Source

Low-level Filtering

High-level Filtering

Active Modulation

A sensor is often a system consisting of multiple stages of signal transduction and modulation, low-level and high-level filters, and a modulation unit. It comprises a communication and a power unit as well.

The shaft encoder for measuring both position and velocity

Shaft rotation

Disc rotation

LED-PD

Threshold : binary signals

A-B phase detection and counting

Hybrid velocity estimation

Key Transducer

Signal Source

Low-level Filtering

High-l

Light intensity modulation

evel Filtering

Active Modulation

Torque Measurement

iKtm ⋅=τ

Via armature current measurement:

The current is measured by inserting a small resister (2~3 Ω) in series and measuring the voltage drop across the resister.

i

Rt

iRV tt ⋅=

Internal Torque Sensors

Torque Measurement

θτ ∆⋅= am k

Via measurement of the torsion/strain of the shaft:

Strain Gauges

Strain Gauge Force/Torque Sensors

Strain Gauges

outV

Temperature-Compensated Wheatstone Bridge

6-Axis Wrist Force/Torque Sensor

Strain Gauges

Outputs:y1, y2, …, ym

Fy

NyFz

Nz

Fx Nx

Strain Gauges

Wrist Force/Torque Sensors

Strain Gauges

Outputs:y1, y2, …, ym

6-Axis Wrist Force/Torque Sensor

⎟⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜⎜

⎝

⎛

=⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛=∆

⎟⎟⎟⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜⎜⎜⎜

⎝

⎛

∂∂

∂∂

∂∂

∂∂

∂∂

∂∂

=

∆⋅=

z

z

y

x

m

z

m

x

m

x

zyx

sensor

sensor

N

FFF

y

y

Ny

Fy

Fy

Ny

Fy

Fy

M

M

LL

MO

MO

L

Fy

J

yJF

,1

2

111

#

Fy

NyFz

Nz

Fx Nx

Hybrid Position/Force Control

Wrist Force/Torque Sensor

Position Feedback

control

control

Robot Task

Environment

Position Reference

Inputs

Force Reference

Inputs

+

+

+

+

_

_

Position/velocity

compensator

Force/torque

compensator

Force Feedback

Tactile SensorsPrinciple

Tactile Pad

Resistance R

P

Electrodes

Conductive Rubber:

Force/Pressure

Media impregnated with conductive dopants Force/Pressure P

Other Methods:CapacitiveOpticalPiezoelectricMagneto-resistiveMagneto-strictive

Sensor Pad:2-D sensor array

Pressure distribution

Technical Issues: How to process the 2-D data of pressure distribution How to reduce wires

A tactile sensor = Measuring 2-D pressure distribution

A Matrix Wiring Structure for Reducing Cables

Sensor Element

N Switches

N Switches

B.E. Robertson and A.J. Walkden, 1985

16 x 16, 256 elements

Photo and diagrams removed for copyright reasons.

Integrating sensor elements with signal processing circuitry on a VLSI chip

Integrating sensor elements with signal processing circuitry on a VLSI chip

Pressure patterns (a) Intensity(b) Contour

VLSI tactile array sensor with 20 x 20 grids of 75 um separation

by M.H. Raibert and J.E. Tanner, 1982

Two photos removed for copyright reasons.

Ultrasonic SensorsDistance Sensors

Object

Transmitted Sonic Pulse

Reflected Echo

tpulse

Echo pulse

Transmitted

Measuring the distance d to an object by the time interval between the transmitted and reflected sonic pulses.

2 d = v t v = speed of sound, t= time interval

_ _ _ _ _ _ _ _ _ _

PiezoelectricTransducer for Transmitting and Receiving Acoustic Signals

Actuator Sensor

Pressure Wave

F + + + + + + + + + + ∆x

F = d33 ⋅ q Piezoelectric Material V = d33 ⋅∆x

(Force) = proportional to (Charge) (Voltage) = proportional to (Displacement)

V

Dielectric Capacitance Transducer for Transmitting and Receiving Acoustic Signals

Figure by MIT OCW.

Swept frequency method

Auditory Link (Earphones)

Variable Frequency Generator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

Filter Process

Hearing Process

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Auditory Link(Earphones)

Variable FrequencyGenerator

CWFM Sonar for Blind Persons and Machines

Human Processor

Machine

FilterProcess

HearingProcess

Drive Amplifier

Receive Amplifier

Tx Transducer

Rx Transducer

Figure by MIT OCW.

Proximity Sensors

Basic Principle

Transmitter +

Receiver

Transmitter +

Receiver

The approach of an object changes: Back pressure: pneumatic sensor Inductance: inductive/magnetic sensors Capacitance: capacitive sensor

Pneumatic Proximity SensorSupply Pressure

Object

Distance

Back Pressure

Output Pressure

Threshold

Distance

Magnetic Lead SwitchesFilled with

Glass Tube Inert Gas

S N

S N N S

Leads Permanent OFF ON Magnet

For extending the detectable range Magnetic Lead Switch

Permanent Magnet

Magnetic Material

Magnetic Material:

A Fake Mine

Optical Proximity Sensors

LED Photo Detector

R2

Vout

R1

3V

Photodiode

LED

Photo Detector

Imaging Sensors CCD CameraPhoto-electric effect

Photon Photo Current oc Illumination Intensity

Absorbs photon energy to move electrons to a higher energy level

Energy = (Plank’s Constant) x (Speed of Light)/(Wavelength)

CCD (Charge Coupled Device)

+ + + ---

Light beam

Photo Sensitive ArrayScanned pixel by pixel

Image ProcessingA. Two-dimensional Images

Structured Lighting

Figure by MIT OCW.

CameraCameraCameraCameraCameraCamera Slit LightSlit LightSlit LightSlit LightSlit LightSlit LightSlit LightSlit LightSlit LightSlit Light

Figure by MIT OCW.

Structured LightingSlight light scanned over 3D objects

Photos removed for copyright reasons.

3D range Finders

X

T

B

M

N

L

O

M

B

S O

LN

T

S

D

D

2

2

Rotational Mirror

Detector

Laser Light Source

Laser Range Finder

Known distance between the mirror and the detector

3D Range Finders

Figure by MIT OCW.

Simultaneous Location And Mapping (SLAM)

Sensor Data Map Building

Location EstimationRobot Control

Image courtesy of JPL.

Planet Exploration Robotics

Human Sensors

Human Operator Joystick

Figure by MIT OCW.

Measuring human motion for controlling Remote manipulators

Hazardous environment

Manipulator

Surgical Robot System

Robot ControlVirtual

Reality

Photo removed for copyright reasons. Surgical robot with virtual reality

workstation (left) and robot (right)

Data Glove Fingernail Sensors:Measurement of hand Measurement of Fingertip Touch Force

posture and touch force and Posture through Nail Color Change

Free-Fingered Glove

Photos removed for copyright reasons.

Instrumented Fingernails

Figure by MIT OCW. After Spence, Basic Human Anatomy.

Nail Matrix

Nail

Nail B ed

Micro LED & Photo Detectors

Pressure:vein occlusion

No sensor pad is needed

Measurement Principle

T ransm itted L ight R e f

L ight

3V

R 1 P h o todio d e

660 nm R ed LE D

lec ted Vout

R 2

V ou t 0 Contact

Pressure

Applications

Virtual Switches Task and Skill Monitoring

Photos removed for copyright reasons.