Lecture 7 - Switches & Proximity Sensors (2) PDF

MCT 317: Design of Mechatronics Systems (1) Lecture-07: Sensors Overview Mohamed Nabil, PhD Assistant Professor Mechatronics Engineering department, Faculty of Engineering, 1 Faculty of Engineering – Egyptia...

MCT 317: Design of Mechatronics Systems (1) Lecture-07: Sensors Overview Mohamed Nabil, PhD Assistant Professor Mechatronics Engineering department, Faculty of Engineering, 1 Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Outlines Wrapping up current Progress Sensors Problem … Dead Reckoning Time of Flight Sensors Inertial Sensors Beacon Based Positioning Sensors Vision Based Sensors Next time..  2  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department -Wrapping up What is done in research so far? current Progress Over the world, researchers and industrial players are developing systems that are more and more reliant on themselves. “Autonomous Systems” These systems are responsible for themselves with minimum intervention from any human operator. These systems are capable of achieving different tasks in their unstructured environments. During their motion they need to know their state and the surrounding environment behavior. 3  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department -Wrapping up Autonomous Systems Examples: current Progress Based on the previous definitions, several autonomous Systems can be seen such as: 4  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department -Wrapping up Autonomous Systems Examples: current Progress Based on the previous definitions, several autonomous Systems can be seen such as: 5  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department See-Think-Act Cycle: Mobile Robot Control Scheme can -Sensors Problem.. be visualized as: The focus of this lecture is on the sensing and perception part. 6  Faculty of Engineering – Egyptian Chinese University (ECU) Mechatronics Department Perception Levels: Perception could be classified into the following levels: -Sensors Problem.. Places/Situations Objects Perception Maturity Increase Features Raw Data 7  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Easy is Hard (and vice versa): In Autonomous Robot Systems applications, “the easy problems are hard and the hard problems are easy.” as mentioned by S. Pinker in -Sensors Problem.. the Language instinct. New York in 1994. Beating this is EASY Detecting this Kid is HARD 8  Faculty of Engineering – Egyptian Chinese University (ECU) Mechatronics Department Proprioceptive Vs. Exteroceptive Sensors: Sensors could be classified as Proprioceptive or Exteroceptive. -Sensors Problem.. Proprioceptive Sensors: – The type of sensors used to measure internal states to the system (robot), such as its speed, heading, battery charging level, etc. Exteroceptive Sensors: – The type of sensors used to measure information from the surrounding environment, such as distance of obstacles, type of obstacles, etc. 9  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Active Vs. Passive Sensors: On another level of classification, sensors could be classified as active or passive sensors. -Sensors Problem.. Active Sensors: – These sensors emit their proper energy and measure the reaction from the environment. (Ex: Ultrasonic sensor) Passive Sensors: – These sensors measure energy coming from the environment. It is highly affected by the surrounding environment. (Ex: Potentiometer) 10  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department History: Since 2000 B.C. dead reckoning has been widely used for localization of ships and their motion in oceans. -Dead Reckoning Based upon the info of: – Speed – Direction 11  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Usage: Based upon the same concept of dead reckoning, localization of autonomous mobile robots is possible. -Dead Reckoning For Wheeled Mobile Robots (WMR), we can use: – Encoder: to determine the velocity of motion – Compass: to determine the heading of the robot 12  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Encoder: Electro-mechanical device that converts linear or angular position of a shaft to an analog or a digital signal. -Dead Reckoning Measure position or speed of the wheels or steering angles. Integrate wheel movements to get an estimate of the position [Odometry] Optical encoders are proprioceptive sensors Typical resolutions: 64 - 2048 pulses per revolution and for higher resolution we can use interpolation. 13  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Encoder: Regular encoder counts the number of pulses, however it cannot tell the direction of rotation. -Dead Reckoning Quadrature encoders can count the number of pulses and they can tell the direction of rotation. Optical Vs. Magnetic Encoders. 14  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Magnetometer (Digital Compass): Magnetometer is used to determine the robot’s orientation and inclination with respect to a given reference. -Dead Reckoning Digital Compasses measure the angle between the sensor current heading and the magnetic field of the earth. Several drawbacks such as: – Weakness of the earth magnetic field (30 micro-Tesla) – Easily distributed by magnetic objects or other sources. – Not suitable for indoor environments for absolute orientation 15  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Time of Flight Concept: Several sensors rely upon the concept of the time of flight and its measurement, knowing the medium that the wave is traveling in. -Time of Flight The following sensors use this concepts: Sensors – Ultrasonic sensors – Laser Range Finders – Light Detection and Ranging (LiDAR) Sensor – Time of Flight Camera 16  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Ultra-Sonic Sensors: The ultra-sonic range sensor is used to measure the distance of a certain obstacle in front of a robot. It is based upon the concept of reflection of the emitted wave and measuring the time between emitting and sensing. -Time of Flight Sensors Problems: – Cross-Talk – Perpendicularity 17  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department LiDAR Sensor: It operates on the concept of the Ultrasonic sensor, however instead of the ultrasonic beam, it transmit pulsed laser, and it measures the elapsed time directly. This is resolved in picoseconds. -Time of Flight Sensors 18  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Inertial Sensors: Inertial Measurement Unit (IMU) Sensor is a device that uses measurements systems such as gyroscopes and accelerometers to estimate the relative position and orientation with respect to an inertial fixed frame. The IMU Sensor is composed mainly of 3 main sensors: -Inertial Sensors – Accelerometer – Gyroscope – Magnetometer (previously described) 19  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Accelerometer: Accelerometers measure all external forces acting upon the sensor or its attached body, including gravity. Accelerometers act like a mass-spring-damper system: 𝑭𝒂𝒑𝒑𝒍𝒊𝒆𝒅 = 𝑭𝒊𝒏𝒆𝒓𝒕𝒊𝒂𝒍 + 𝑭𝒅𝒂𝒎𝒑𝒊𝒏𝒈 + 𝑭𝒔𝒑𝒓𝒊𝒏𝒈 -Inertial Sensors Where, (m) is the proof mass, (c) is the damping coefficient, (k) is the spring stiffness constant. 20  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Accelerometer: The model described in the previous slide is for the mechanical accelerometer. However there exist different types of accelerometers. Modern accelerometers rely upon the technology of Micro-Electro- Mechanical Systems (MEMS) consisting of a spring like structure with a proof mass. While damping results from the residual gas sealed in -Inertial Sensors the device fabrication itself. Piezoelectric accelerometers are based on the property exhibited by specific crystals to generate voltage when they are subjected to a mechanical stress. 21  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Gyroscope: Gyroscopes are defined as heading sensors that preserve their orientation in relation to a fixed reference frame. They provide an absolute measure for the heading of a mobile robot system, and they come into two versions: -Inertial Sensors – Standard Gyro (measures the angle) – Rate Gyro (measures the speed). Optical Gyroscopes !!! 22  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Gyroscope: Mechanical Gyroscopes rely upon the concepts of inertial properties of a fast-spinning rotor. Angular momentum associated with a pinning wheel keeps the axis of the gyroscope inertially stable. -Inertial Sensors Spinning axis will be stable in its motion. However, friction in the axes bearings will introduce torque and so drift  precision will decrease. High quality mechanical gyro costs up to 100,000 $ (Too expensive !!) 23  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department What is a Beacon? Another important positioning system is based upon the usage of different beacons. But what is a beacon?? Through the utilization of the different existing infrastructure it is possible to localize different -Beacon Based moving entities. Positioning Sensors 24  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Global Positioning System (GPS): The ability to accurately localize the position of the robot in an environment could be achieved using the Global Positioning System (GPS) Sensor. Several satellites orbit the planet in fixed orbits. On each satellite there is an atomic clock which continuously -Beacon Based transmit the exact time and precise Positioning Sensors location of the satellite. Location of any GPS receiver is calculated based on trilateration and time correlation. 25  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Global Positioning System (GPS): GPS Sensors are almost used in all applications nowadays for localization. With commercial sensors accuracy up to 3m. Problems affecting GPS accuracy exist such as: -Beacon Based Positioning Sensors 26  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Differential Global Positioning System: DGPS requires that a GPS receiver (base station) is set up on a precisely known location. This receiver captures the received data from satellites and calculates the difference between measured and actual positions. This difference is applied to any nearby moving mobile platform -Beacon Based to correct its readings. Positioning Sensors The accuracy of this is DGPS is sub-meter to cm range. 27  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Can it see? The eyes remain on top of the sensors used by humans in their daily lives. And over the years the question of could the computer/machine see or not is becoming more appealing. Giving the (system) the ability to see and deduce information from images is the core of any vision-based sensor. Several vision-based solutions exist in the development and -Vision Based implementation of the autonomous systems. Some of them are Sensors explored in the upcoming slides. 28  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Monocular Vision: The utilization of a single camera is considered as the basic approach towards the introduction of computer vision approaches to autonomous robot systems. Through the single camera, different approaches are possible to be implemented such as: – Pedestrian detection – Vehicle detection -Vision Based – Semantic Segmentation. Sensors Disadvantage ??? 29  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department April Tags: April tags are becoming more used nowadays as a way for localization and recalibration of the location of robots in their environments. They are a set of specific shaped marks such as (barcodes and QR- codes) that could be classified through computer vision approaches. -Vision Based They could be used in both Sensors indoor and outdoor working environments. 30  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Stereo Vision: To counter the disadvantage of the monocular camera about losing the depth, stereo vision systems are used. Two cameras are fixed at specific distance where each one of them is tilted a small angle inwards. The concepts of epipolar geometry are -Vision Based used to measured the depth of any Sensors point in an image. 31  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Kinect: Kinect is one of the sensors that are commonly used nowadays for autonomous mobile robots applications. It handles the limitation of the monocular camera in terms of losing the information of the depth. It provides as an output RGB-D image that holds the info of the depth of each pixel in the image. It is widely used for indoor -Vision Based applications using structured Sensors light. However it is highly affected by infrared lights (outdoor applications). 32  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department 3D Reconstruction Results -Vision Based Sensors 33  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Visual Odometry: On another level of applications, the usage of a single camera could be used for Odometry localization. Instead of having the camera looking forward, it is fixed to face the ground. Using this, and tracking the main features of the texture of the ground, the robot can estimate its traveled distance as well as change in heading. -Vision Based One of the most recent trends in research. Sensors 34  Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department Upcoming next: In the next Lecture we will cover: – Sensors Fundamentals and Basic Analysis In the next Tutorial/Lab we will cover: – Sensors Overview -Next time  35 Faculty of Engineering – Egyptian Chinese University( ECU) Mechatronics Department See you Next time …  36