Sensors and Robotics Sensors and Robotics MOBI LE ROBOTI CS DAUIN - PDF document

Sensors and Robotics Sensors and Robotics MOBI LE ROBOTI CS DAUIN – Politecnico di Torino Basilio Bona CY 02CFI C CFI DV CA – 01 OBOTI C RO

The Mobile Robotics Challenge � Objective: perceive, analyze and understand the environment state around the robot CY 02CFI C � Measurements change due to the dynamical nature of the environment or of some parts; moreover they CFI DV are affected by a high level of noise/ disturbances ff t d b hi h l l f i / di t b � Examples: CA – 01 – Variability of light condition (scene illumination) – Reflexions OBOTI C – Surfaces with high variability of sound/ light absorption/ reflection properties RO – Sensitivity of measurements with respect to robot pose Basilio Bona – DAUI N – Politecnico di Torino 001/ 2

Encoders � They measure the angular position and speed of They measure the angular position and speed of onboard motors � Odometry: measurements are integrated to give an CY y g g 02CFI C estimate of the position or pose � Forniscono misure (imprecise) rispetto al riferimento CFI DV locale (propriocettori) CA – 01 OBOTI C RO Basilio Bona – DAUI N – Politecnico di Torino 001/ 3

receiver Transparent slids Encoders Rotating Rotating Disk Light rays source Light CY 02CFI C CFI DV CA – 01 OBOTI C RO

Absolute Encoders notch Zero Incremental CY 02CFI C CFI DV CA – 01 OBOTI C RO

Receiver Source Electronics Shaft Shaft Disk Encoders Receiver Source Electronics Shaft Shaft Disk CY 02CFI C CFI DV CA – 01 OBOTI C RO

Encoders CY 02CFI C CFI DV CA – 01 OBOTI C RO

Encoders CY 02CFI C CFI DV CA – 01 OBOTI C RO

001/ 9 Basilio Bona – DAUI N – Politecnico di Torino Encoders CY 02CFI C CFI DV CA – 01 OBOTI C RO

Heading Sensors � Gyroscopes, inclinometers, compasses, gyrocompasses CY 02CFI C � They measure the horizontal or vertical angle referred to a given direction CFI DV � Together with speed measurements they provide an estimate of the position CA – 01 � This procedure is also called dead reckoning and is a characteristic of maritime navigation characteristic of maritime navigation OBOTI C RO Basilio Bona – DAUI N – Politecnico di Torino 001/ 10

Com passes � Known since the ancient times � Is based on the Earth magnetic field (absolute g CY 02CFI C measurement) � Physical methods: mechanical (magnetic needle), y ( g ), CFI DV Hall effect, magnetostrictive effect Piezoelectric resonators have been used as standard clocks in. recent electronics technologies because of their sharp resonance profiles. We propose a magnetic field sensor consisting of a piezoelectric resonator and magnetostrictive magnetic layers. It is verified that its resonance Frequency changes in a t d t t i ti ti l It i ifi d th t it F h i CA – 01 magnetic field with sensitivity high enough to detect terrestrial magnetic field. So, it is useful as an electronic com pass that is in great dem and from the mobile telecommunication technology [ I] . The advantage of this sensor is that it can readily be downsized maintaining a high S/ N because it detects an external field through change of the resonance frequency rather than the analogue output as in the OBOTI C MI or the flux gate sensors. (Yoshizawa, N. Shimada, Y. ) � Limitations RO – The Earth magnetic field is rather weak – Easily disturbed by near metallic objects – Less used for indoor navigation Basilio Bona – DAUI N – Politecnico di Torino 001/ 11

Gyroscopes � They provide an absolute measurement, since they maintain the initial orientation with respect to a CY 02CFI C fixed reference frame fixed reference frame � Mechanical or Optical CFI DV � Mechanical – Standard (absolute) CA – 01 – Rated (differential) � Optical Optical OBOTI C – Rated (differential) RO Basilio Bona – DAUI N – Politecnico di Torino 001/ 12

Mechanical Gyroscopes � Concept: inertial properties of a rotor that spins fast: � Concept: inertial properties of a rotor that spins fast: precession phenomenon CY � Angular moment is conserved and keep the wheel Angular moment is conserved and keep the wheel 02CFI C axis with a constant orientation � Negligible torque is transmitted to the external CFI DV mounting of the wheel axis i f h h l i τ � Reaction torque is proportional to the rotation speed the inertia and the precession velocity Ω ω ω Γ Γ Ω speed , the inertia and the precession velocity CA – 01 τ = Γω Ω OBOTI C � If the rotation axis is aligned along the N-S meridian, the Earth rotation does not influence the RO measurements t � If the rotation axis is aligned along the E-O meridian the horizontal axis measures the Earth meridian, the horizontal axis measures the Earth rotation Basilio Bona – DAUI N – Politecnico di Torino 001/ 13

001/ 14 Mechanical Gyroscopes Basilio Bona – DAUI N – Politecnico di Torino Rotation axis Rotation axis CY 02CFI C CFI DV CA – 01 OBOTI C RO

Differential Gyroscopes � Same construction concept but the cardanic � Same construction concept, but the cardanic joints= gimbals are constrained by a torsion spring CY – An angular velocity is measured instead of an angle g y g 02CFI C � Other gyroscopes use the Coriolis effect to measure the orientation variation (e.g., Analog Device ADXRS150 and ADXRS300) ADXRS300) CFI DV CA – 01 OBOTI C RO Basilio Bona – DAUI N – Politecnico di Torino 001/ 15

Optical gyroscopes � Two monochromatic laser rays are produced and injected into an optical fiber coiled around a CY 02CFI C cylinder � One ray turns in one sense, the other in the opposite sense it CFI DV � That ray that turns in the same sense of the rotation, covers a shorter path and shows a rotation covers a shorter path and shows a CA – 01 higher frequency; the frequency difference between the two rays is proportional to the between the two rays is proportional to the OBOTI C cylinder angular speed � Solid state sensors; directly integrable on ; y g RO silicon together with the electronic circuits Basilio Bona – DAUI N – Politecnico di Torino 001/ 16

Beacons � Guide systems with known G ide s stems ith kno n absolute position. Also CY known as landmarks known as landmarks 02CFI C artificial or natural – Known and used since ancient Known and used since ancient CFI DV times: sun, mountains, capes, bell towers, marine lighthouses � Necessary for indoor CA – 01 motion, where GPS is OBOTI C impossible impossible � Expensive, they require an RO i f infrastructure t t � Not easy to adapt to varying environment conditions i t diti Basilio Bona – DAUI N – Politecnico di Torino 001/ 17

001/ 18 Basilio Bona – DAUI N – Politecnico di Torino GPS CY 02CFI C CFI DV CA – 01 OBOTI C RO

Distance Sensors � Also known as range sensors, they measure CY “large” distances large distances 02CFI C � They use the time-of-flight principle CFI DV � Ultrasonic (sonar) or laser sensor, since the sound or light speed is known CA – 01 = d cT OBOTI C Distance (two ways) RO Time measured Wave speed p (sound/electromagnetic) Basilio Bona – DAUI N – Politecnico di Torino 001/ 19

Distance Sensors � Speed of sound approx 0.3 CY 02CFI C m/ ms / � Speed of light (in vacuum) 0 3 m/ ns 0.3 m/ ns CFI DV � Rate 10 6 � 3 m 3 CA – 01 – 10 ms using sound waves – only 10 ns with a laser sensor only 10 ns with a laser sensor OBOTI C – difficult to measure – laser sensor expensive RO Basilio Bona – DAUI N – Politecnico di Torino 001/ 20

Distance Sensors � The measurements quality depends on CY 02CFI C – Uncertain arrival time of the reflected wave (laser and sonar) – Uncertain time-of-flight (laser) U t i ti f fli ht (l ) CFI DV – Aperture angle (sonar) CA – 01 – Interaction with surfaces (sonar and laser) – Variability of the speed (sonar) OBOTI C – Possible speed of the source (sonar) RO Basilio Bona – DAUI N – Politecnico di Torino 001/ 21

Ultrasonic Sensors � � A package of sound (pressure) waves is generate and emitted A package of sound (pressure) waves is generate and emitted the so called chirp CY � Relation is simply: Relation is simply: 02CFI C cT d = 2 CFI DV � The sound speed in air is give as The sound speed in air is give as CA – 01 = γ γ c RK OBOTI C γ = specific heat constant = RO R R gas constant = K temperature in Kelvin p Basilio Bona – DAUI N – Politecnico di Torino 001/ 22

Ultrasonic Sensors CY 02CFI C CFI DV CA – 01 OBOTI C RO Basilio Bona – DAUI N – Politecnico di Torino 001/ 23

Ultrasonic Sensors � Used frequencies 40-200 kHz � Used frequencies 40 200 kHz � Generated from a piezoelectric source CY 02CFI C � Transmitter and receiver may be separated or not Transmitter and receiver may be separated or not � Sound is emitted in a conic shape � Aperture angle 20-40 degrees A t l 20 40 d CFI DV CA – 01 Density spatial distribution OBOTI C RO Basilio Bona – DAUI N – Politecnico di Torino 001/ 24