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Internal sensors. Josep Amat and Alícia Casals Automatic Control and Computer Engineering Department . Program. Chapter 1. Introduction Chapter 2. Robot Morphology Chapter 3. Control Chapter 4. Robot programming Chapter 5. Perception

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Internal sensors
Internal sensors

Josep Amat and Alícia Casals

Automatic Control and Computer Engineering Department


Program
Program

Chapter 1. Introduction

Chapter 2. Robot Morphology

Chapter 3. Control

Chapter 4. Robot programming

Chapter 5. Perception

Chapter 6. Mobile robots. Architecture, components and characteristics

Chapter 7. Robotics applications.

Robotization


Chapter 2. Robot Morphology

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.


Components of a Robot

External

Sensors

Environment

Programming

Net

Internal

Sensors

Control Unit

Actuators

Mechanical Structure

User


Detectors

Position sensors

Mechanical:

Internal

sensors

Actuators

Mechanical structure


Electromagnetic:

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

Detectors

Internal

sensors

Position sensors

Actuators

Mechanical structure


Detectors

Position sensors

Optical:

From the interruption of a light beam, or reflection.

Internal

sensors

Actuators

Mechanical structure


Types of sensors

Angular

Linear


Digital

Vcc

R1

V = Vcc

R

R

R2

a R

a

R1

V = Vcc

= Vcc

a

a0

a0R

0 V

Types of sensors

Resistive (Potentiometers)

Angular

Analog


Ve = A sin (wt)

Ve = A sin(wt ) cos a

Ve = A sin(wt ) sin a

Types of sensors

Resistive (Potenciometers)

Angular Inductive ( Resolver )

Analog

Digital

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


Low resolution conversions

S1 = V cos a

a

aX

A/D

A/D

D/A

a

S2 = V sin a

High resolution conversions

mcontroler

aX

e

A

S1

S2

Ve = V sin (wt)

S1 = V sin(wt ) cos a

S2 = V sin(wt ) sin a

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


Resistive (Potentiometers)

Angular Inductive ( Resolver )

Absolute

Incremental

Analog

Digital

Types of sensors


Optical Encoder Absolute

Fotoelectric sensor

n paths

2n divisions

n optical barriers

2 paths

4 divisions


Ambiguity when reading the natural binary code

Commercially

10 bits 1024 div.  Resol. 0.35º

12 bits 4096 div.  Resol. 0.088º

14 bits 16384 div.  Resol. 0.022º

Encoder diameters: de 50 a 175 mm

Elimination of the reading ambiguity using the Gray code



Types of Sensors of an angular encoder

Resistive (Potentiometers)

Angular Inductive ( Resolver )

Absolute

Incremental

Analog

Digital


Commercially of an angular encoder

10 bits 1024 div.  Resol. 0.35º

12 bits 4096 div.  Resol. 0.088º

14 bits 16384 div.  Resol. 0.022º

Signal obtained after displacing the sensor over a coded disc

1 2 3 4 5 6 7 8 9 10 11 12

Gray code


Commercially of an angular encoder

10 bits 1024 div.  Resol. 0.35º

12 bits 4096 div.  Resol. 0.088º

14 bits 16384 div.  Resol. 0.022º

Gray code

Possibility of detecting the counting sense using two sensors


Incremental Optical Encoder of an angular encoder

A

B

R

1 mark = 4divisions


0 of an angular encoder 1

200 x 4 = 800

P

Q

Q

P


r of an angular encoder

120 cm.

60

60

j = 60º

360

360

q = 210

l = 2 p 1200

l = 1256 mm.

1256 mm.

r =

170,6

Computing resolution

=

=

q = 170,6

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

= 7,3 mm.

js


Measuring strategies of an angular encoder

1 : 1

0 j

Arm

0 360º

0 j

Encoder

Absolute

Code j

dn-1 . . . . do

dn-1 . . . . do

Incremental

Counter


Arm of an angular encoder

360º

j

n =

Absolute

Code j

dn-1 . . . . do

dn-1 . . . . do

Incremental

Counter

Measuring strategies

1 : n

0 j

0 360º

Encoder


Arm of an angular encoder

360º

n = m

j

m · · · m = 2 m = 1

Code j

Absolute + Inc.

dn+p-1 . . dn-1 · · · · do

dn+p-1 . . dn-1 · · · ·do

Counter

Incremental

Measuring strategies

1 : n

0 j

Encoder

0 360º

0 360º

Encoder coupledto the arm with atransmissionratio: m x n


r of an angular encoder

120 cm.

j = 60º

l = 1256 mm.

1256 mm.

r =

x 6 x 8

8192

Computing resolution

q = 8 · 210

=

q = 8192

= 0,15 mm.

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


l of an angular encoder = 1256 mm.

1256 mm.

r =

204.800

0 1 2 3 · · · 199 200

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

200 x 1024 = 204.800

= 0,006 mm.

Sinusoidal light obtained from Moore interference

r < 0,01 mm.


Types of sensors of an angular encoder

Resistive (Potentiometers)

Angular Inductive ( Resolver )

Incremental

Absolute

Analog

Digital

Resistive

Inductive ( Inductosyn )

Linear LVDT

Optical rule

Analog

Digital


R of an angular encoder

Sensing with a linear potentiometer


Types of sensors of an angular encoder

Resistive (Potentiometers)

Angular Inductive ( Resolver )

Incremental

Absolute

Analog

Digital

R

Resistive

Inductive ( Inductosyn )

Linear LVDT

Optical rule

Analog

Digital


Inductosyn sensor

0,2 mm of an angular encoder

Inductosyn sensor

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

* With an analog interpolation using a 8 bits ADC


Resistive (Potentiometers) of an angular encoder

Angular Inductive ( Resolver )

Incremental

Absolute

Analog

Digital

Resistive

Inductive ( Inductosyn )

Linear LVDT

Optical rule

Analog

Digital

Types of sensors


LVDT of an angular encoder

LVDT = Linear Voltage Differential Transformed)

Linear sensing displacements


LVDT of an angular encoder

V1

v

V2

V1

V2

V1- V2

Linear sensing displacements


Analog of an angular encoder

Digital

Analog

Digital

Types of sensors

Resistive (Potentiometers)

Angular Inductive ( Resolver )

Incremental

Absolute

Resistive

Inductive ( Inductosyn )

Linear LVDT

Optical rule


Incremental optical rule of an angular encoder

Head reader

Absolute optical rule


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