Sensors and Sensing Force, Torque, Tactile and Olfaction Todor Stoyanov Mobile Robotics and Olfaction Lab Center for Applied Autonomous Sensor Systems Örebro University, Sweden todor.stoyanov@oru.se 03.12.2015 T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 1 / 18
Outline 1 Force and Torque Sensors 2 Pressure and Tactile Sensing 3 Gas Sensors 4 Practice: Exam Questions T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 2 / 18
Force and Torque Sensors Outline 1 Force and Torque Sensors 2 Pressure and Tactile Sensing 3 Gas Sensors 4 Practice: Exam Questions T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 2 / 18
Force and Torque Sensors Force Sensitive Resistors 1 A force sensitive resistor can measure the magnitude of a force applied to a surface. The sensor is usually implemented based on a mix of conductive and non-conductive particles, suspended in a volume. Deforming the surface increases conductivity / decreases resistance. Can also be printed in silicon. An array of resistors can cover a larger area and provide a position of applied force. 1 Image source: https://www.sparkfun.com T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 2 / 18
Optical Force Sensors Force and Torque Sensors 2 Force sensitive resistors are only useful for force magnitude, but not direction. More complex sensing modalities are needed for measuring a 3D force vector. Optical means are useful for determining deformation of a known surface. The amount of deformation and position can be used for determining a force vector. 2 Image source: http://optoforce.com T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 3 / 18
Force and Torque Sensors Strain Gauges Strain gauges are a building component for several more complicated sensors. A strain on an object is induced by a set of non-balanced torques. Strain induces deformation, which can be measured using a strain gauge. Hard limits on maximum strain before breaking occurs. 3 3 Image source: Wikipedia T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 4 / 18
Force and Torque Sensors Torque Sensors 4 Torque sensors are often used on output shafts of motors in robotics. Useful for determining the amount of force a kinematic chain is exerting / experiencing. Implemented using a set of strain gauges and slip rings which transfer the rotational momentum to the output shaft. Often bulky. Miniaturization is very much still an open problem. 4 Image source: http://futek.com T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 5 / 18
Force and Torque Sensors Torque Sensors Torque sensors are often used on output shafts of motors in robotics. Useful for determining the amount of force a kinematic chain is exerting / experiencing. Implemented using a set of strain gauges and slip rings which transfer the rotational momentum to the output shaft. Often bulky. Miniaturization is very much still an open problem. 4 4 Image source: http://dlr.de T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 5 / 18
Pressure and Tactile Sensing Outline 1 Force and Torque Sensors 2 Pressure and Tactile Sensing 3 Gas Sensors 4 Practice: Exam Questions T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 6 / 18
Pressure Sensors Pressure and Tactile Sensing Pressure is defined as amount of force acting per surface area. Pressure sensors thus often are based on a force sensor. Different applications: air pressure, liquid pressure in hydraulic systems. 5 5 Image source: https://www.sparkfun.com T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 6 / 18
Pressure and Tactile Sensing Contact Sensors Contact sensors (bumpers) are probably the most basic sensor in robotics. Useful for a hardware emergency stop implementation. A buffer suspended on a spring coupled with a hard contact sensor. When enough force is applied, the sensor is conductive. Can easily break if impact force is too high. T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 7 / 18
Pressure and Tactile Sensing Tactile Sensing Tactile sensing refers to a mimicing of the human sense of touch. Tactile sensors measure contact forces over an area. Force vector and magnitude, as well as contact position. A tactile array usually has to cover a large area and be very sensitive. 6 6 Image source: http://www.syntouchllc.com T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 8 / 18
Pressure and Tactile Sensing Tactile Sensing 6 Tactile sensing refers to a mimicing of the human sense of touch. Tactile sensors measure contact forces over an area. Force vector and magnitude, as well as contact position. A tactile array usually has to cover a large area and be very sensitive. 6 Image source: http://www.syntouchllc.com T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 8 / 18
Pressure and Tactile Sensing Artificial Skin 7 A hot research topic that covers tactile sensing. Artificial skin has to have tactile, as well as moisture/pressure/temperature modalities. Should also be stretchable and cover a large area. 7 Image source: http://www.technologyreview.com T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 9 / 18
Gas Sensors Outline 1 Force and Torque Sensors 2 Pressure and Tactile Sensing 3 Gas Sensors 4 Practice: Exam Questions T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 10 / 18
Gas Sensors Gaseous Substances and Electronic Noses Sense of smell is one of the most complex. In practice, a smell sensor needs to recognize a mixture of different complex mollecules. An electronic nose is An instrument that comprises an array of heterogeneous electrochemical gas sensors with partial specificity and a pattern recognition system capable of recognizing simple or complex odors Individual gas sensors are usually sensitive to particular chemical compounds in a gas (or vapour) form. T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 10 / 18
Gas Sensors Gas Dispersion The problem of sensing gases in an uncontrolled environment is complicated by turbulence. 8 8 Image source: Smyth and Moum 2001 T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 11 / 18
Metal-Oxide Gas Sensors Gas Sensors Metal-Oxide (MOX) gas sensors provide in-situ measurements of gas concentration. Printed on a silicon subtrate. Include a heated gas-sensitive surface. Gas molecules are trapped by the metal oxide in the surface, which results in a change of resistance. 9 9 Image source: http://www.figarosensor.com T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 12 / 18
Open Sampling Systems Gas Sensors A MOX sensor exposed to a gas experiences a three-phase process: Rise phase: the sensor is reacting to the substance being introduced. Depending on substance and sensor different rise times. Saturation phase: the sensor has reached saturation at a particular resistance. Fall phase: the remaining gas molecules are eliminated by clean air. T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 13 / 18
Open Sampling Systems Gas Sensors When the gas flow is not uniform, the sensor response is more chaotic. 10 10 Image source: MRO course, A. J. Lilienthal T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 13 / 18
Laser-Based Gas Sensors Gas Sensors Laser-based systems are also used for measuring of gas concentration. A laser beam of a particular wavelength is used. The absorption rate of the target compound is known. The intensity of the reflected laser beam can be used to deduce the total absorption along the traveled path. An integral measurement no knowledge of where along the ray the gas was detected. 11 11 Image source: MRO course, A. J. Lilienthal T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 14 / 18
Gas Sensors Sensing environmental conditions Several other environmental paramteres play a big role in gas dispersion. In order to model gas dispersion, it may be useful to measure temperatrure, humidity, wind direction and strength. Wind sensors are known as anamometers In the past mechanical designs In robotics usually based on ultrasonic transceivers/receivers: time of flight of sonar pulses is offset by the projection of the wind vector along the travel path. 3D wind direction + magnitude T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 15 / 18
Gas Sensors Sensing environmental conditions Several other environmental paramteres play a big role in gas dispersion. In order to model gas dispersion, it may be useful to measure temperatrure, humidity, wind direction and strength. Wind sensors are known as anamometers In the past mechanical designs In robotics usually based on ultrasonic transceivers/receivers: time of flight of sonar pulses is offset by the projection of the wind vector along the travel path. 3D wind direction + magnitude T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 15 / 18
Gas Sensors Sensing environmental conditions Several other environmental paramteres play a big role in gas dispersion. In order to model gas dispersion, it may be useful to measure temperatrure, humidity, wind direction and strength. Wind sensors are known as anamometers In the past mechanical designs In robotics usually based on ultrasonic transceivers/receivers: time of flight of sonar pulses is offset by the projection of the wind vector along the travel path. 3D wind direction + magnitude T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 15 / 18
Practice: Exam Questions Outline 1 Force and Torque Sensors 2 Pressure and Tactile Sensing 3 Gas Sensors 4 Practice: Exam Questions T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 16 / 18
Practice: Exam Questions Sample questions a: MOX gas sensors measure the concentration of a target gas in the environment by measuring the change of resistance of a heated silicon substrate. b: Signals from metal oxide gas sensors have two distinct phases: rise and fall. c: Tactile sensor arrays can pinpoint the point of contact between the sensor surface and an object. Some reminders/remarks: You may bring any form of printed material to the exam Computers, cell phones, e-book readers etc. are not allowed Three types of questions at the exam: True/False, Design, Derive T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 16 / 18
Feedback from Labs Practice: Exam Questions Labs are being graded, you will get results ASAP. High-level comments that will help you for next lab report: T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 17 / 18
Feedback from Labs Practice: Exam Questions Overall, reports look professional. Please follow the lab tasks in the report. It helps to pinpoint that you actually did the work required for every task. Read instructions carefully and make sure you demonstrate in the report that you have completed every task. For example, no one provided current sensor readings when the motor is turning. Scale your graphs accordingly. It is very difficult to see if the tracking performance is good if you also show the PWM in the same graph (axis scales). Evaluation of tuned controllers: from a first look, some do not report the final tuned values / performance experiments. More details on what you evaluate, how you tested it and what the results were. Language. I will give you more detailed feedback individually. T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 17 / 18
Feedback from Labs Practice: Exam Questions Some feedback regarding coding styles. It is good practice to remove the TODO comments once you are done with them. It helps both you while you work, and me when I read. Comment your code. You will be thanking yourself if you have to read it again. Create new members to hold additional data, don t overwrite things you used for the previous tasks. T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 17 / 18
Practice: Exam Questions Closing Remarks Thanks for attending the course! Don t forget to fill in the course evaluations at the end. If you have direct feedback, let me know. Good luck with the exam and the labs. Happy Holidays! T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 18 / 18
Practice: Exam Questions Closing Remarks Thanks for attending the course! Don t forget to fill in the course evaluations at the end. If you have direct feedback, let me know. Good luck with the exam and the labs. Happy Holidays! T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 18 / 18
Practice: Exam Questions Sensors and Sensing Force, Torque, Tactile and Olfaction Todor Stoyanov Mobile Robotics and Olfaction Lab Center for Applied Autonomous Sensor Systems Örebro University, Sweden todor.stoyanov@oru.se 03.12.2015 T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 18 / 18
Practice: Exam Questions References T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 03.12.2015 18 / 18