Internal sensors Josep Amat and Alícia Casals Automatic Control and Computer Engineering Department.

Internal sensors

Josep Amat and Alícia Casals Automatic Control and Computer Engineering Department

Program

Chapter 1. IntroductionChapter 2. Robot MorphologyChapter 3. ControlChapter 4. Robot programming Chapter 5. PerceptionChapter 6. Mobile robots. Architecture, components

and characteristicsChapter 7. Robotics applications.

Robotization

2.1 – Mechanical Structures. Classical Architectures.

2.2 – Characteristics of a Manipulator. Definitions.

2.3 - Actuators. Pneumatic, Hydraulic and Electrical.

2.4 – Movement transmission systems: Gearboxes, movement transmission and conversion.

2.5 – Robot internal sensors. Position sensors, speed and acceleration.

2.6 – End Effectors.

Chapter 2. Robot Morphology

UserComponents of a Robot

Control Unit

Programming

ExternalSensorsEnvironment

InternalSensors

ActuatorsMechanical Structure

Net

Internal sensors

Actuators

Mechanical structure

Detectors

Position sensors

Mechanical:

Internal sensors

Actuators

Mechanical structure

Detectors

Position sensors

Electromagnetic:

Detection from the variations of the oscillation conditions of an L – C sensor circuit

Internal sensors

Actuators

Mechanical structure

Detectors

Position sensors

Optical:From the interruption of a light beam, or reflection.

Types of sensors

Angular

Linear

Resistive (Potentiometers)

Angular

Analog

Digital

R1

R2

Vcc

0 V

R

V = Vcc R1

RRV = Vcc R

= Vcc

Types of sensors

Resistive (Potenciometers)

Angular Inductive ( Resolver )

Analog

Digital

Ve = A sin (t)

Ve = A sin(t ) cos

Ve = A sin(t ) sin

A is obtained through the lecture in a look up table of arcsin and arccos

Types of sensors

Ve = V sin (t)

S1 = V sin(t ) cos

S2 = V sin(t ) sin

A

S1

S2

S1 = V cos

S2 = V sin

e

Possibility of obtaining the value of by means of “tracking”

A/D

A/D

D/A

controler

Low resolution conversions

High resolution conversions

X

X

Resistive (Potentiometers)

Angular Inductive ( Resolver )

Absolute

Incremental

Analog

Digital

Types of sensors

Optical Encoder Absolute

2 paths4 divisions

Fotoelectric sensor

n paths2n divisions

n optical barriers

Commercially

10 bits 1024 div. Resol. 0.35º12 bits 4096 div. Resol. 0.088º14 bits 16384 div. Resol. 0.022º

Encoder diameters: de 50 a 175 mm

Elimination of the reading ambiguity using the Gray code

Ambiguity when reading the natural binary code

Example of a disc with the Gray code Example of an angular encoder

Resistive (Potentiometers)

Angular Inductive ( Resolver )

Absolute

Incremental

Types of Sensors

Analog

Digital

Gray code

Commercially

10 bits 1024 div. Resol. 0.35º12 bits 4096 div. Resol. 0.088º14 bits 16384 div. Resol. 0.022º

1 2 3 4 5 6 7 8 9 10 11 12Signal obtained after displacing the sensor over a coded disc

Gray code

Commercially

10 bits 1024 div. Resol. 0.35º12 bits 4096 div. Resol. 0.088º14 bits 16384 div. Resol. 0.022º

Possibility of detecting the counting sense using two sensors

Incremental Optical Encoder

ABR

1 mark = 4 divisions

0 1

200 x 4 = 800

P Q

P

Q

s

120 cm.

Computing resolution

= 60º l = 2 1200

60360

q = 210 60360

l = 1256 mm.

=q = 170,6

=

r

r =1256 mm.

170,6= 7,3 mm.

Using a a 10 bits encoder directly coupled to the motor axis

1 : 1 Measuring strategies

Arm

0 360º

0

0 Encoder

Absolute

Incremental dn-1 . . . . doCounter

dn-1 . . . . doCode

1 : n Measuring strategies

Arm

0 360º

0

Encoder

Absolute

Incremental dn-1 . . . . doCounter

dn-1 . . . . doCode

n =360º

1 : n Measuring strategies

Arm

0 360º

0

Encoder

n = m360º

0 360º

m · · · m = 2 m = 1

Absolute + Inc.

Incremental

dn+p-1 . . dn-1 · · · · doCode

Counterdn+p-1 . . dn-1 · · · ·do

Encoder coupled to the arm with a transmission ratio: m x n

120 cm.

Computing resolution

= 60º

l = 1256 mm.q = 8192

=

r

r =1256 mm.

8192= 0,15 mm.

q = 8 · 210

x 6 x 8Using a 10 bits encoder coupled with a 1:64 transmission ratio

l = 1256 mm.200 x 1024 = 204.800

r =1256 mm.

204.800= 0,006 mm.

r < 0,01 mm.

Sinusoidal light obtained from Moore interference

With a 10 bits A/D converter r’ = r/1024

0 1 2 3 · · · 199 200

Types of sensors Resistive (Potentiometers)

Angular Inductive ( Resolver )

Incremental

Absolute

Resistive Inductive ( Inductosyn )

Linear LVDT

Optical rule

Analog

Digital

Analog

Digital

R

Sensing with a linear potentiometer

Types of sensors

Resistive (Potentiometers)

Angular Inductive ( Resolver )

Incremental

Absolute

Resistive Inductive ( Inductosyn )

Linear LVDT

Optical rule

Analog

Digital

Analog

Digital

R

Inductosyn sensor

With two secondary sensors shifted 90º, the resolution is: 0,2 / 28 < 0.001 mm *

0,2 mm

* With an analog interpolation using a 8 bits ADC

Types of sensors Resistive (Potentiometers)

Angular Inductive ( Resolver )

Incremental

Absolute

Resistive Inductive ( Inductosyn )

Linear LVDT

Optical rule

Analog

Digital

Analog

Digital

LVDT = Linear Voltage Differential Transformed)

LVDT

Linear sensing

displacements

V1 V2

V1 - V2

V1

V2

vLVDT

Linear sensing displacements

Types of sensors Resistive (Potentiometers)

Angular Inductive ( Resolver )

Incremental

Absolute

Resistive Inductive ( Inductosyn )

Linear LVDT

Optical rule

Analog

Digital

Analog

Digital

Head reader

Incremental optical rule

Absolute optical rule