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 16.12.2014 T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 16.12.2014 1 / 16
Lab Reports The Lab reports were not as good as we expected. In most cases you did the work but you did not do the report properly. When writing a report you should assume you are writitng a scientific paper. Describe the steps you take. Describe why you take these steps, what are the objectives. Give precise, motivated and accurate answers. (e.g. "about 200" is not what we are looking for) Always analyze your results. Is this what you expect to see? Why are your results good or bad? What could you do to improve? T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 16.12.2014 2 / 16
Outline 1 Force and Torque Sensors 2 Pressure and Tactile Sensing 3 Gas Sensors T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 16.12.2014 3 / 16
Force and Torque Sensors Outline 1 Force and Torque Sensors 2 Pressure and Tactile Sensing 3 Gas Sensors T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 16.12.2014 3 / 16
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 16.12.2014 3 / 16
Force and Torque Sensors Optical Force 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 16.12.2014 4 / 16
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 16.12.2014 5 / 16
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 16.12.2014 6 / 16
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 16.12.2014 6 / 16
Pressure and Tactile Sensing Outline 1 Force and Torque Sensors 2 Pressure and Tactile Sensing 3 Gas Sensors T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 16.12.2014 7 / 16
Pressure and Tactile Sensing Pressure Sensors 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 16.12.2014 7 / 16
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 16.12.2014 8 / 16
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 16.12.2014 9 / 16
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 16.12.2014 9 / 16
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 16.12.2014 10 / 16
Gas Sensors Outline 1 Force and Torque Sensors 2 Pressure and Tactile Sensing 3 Gas Sensors T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 16.12.2014 11 / 16
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 16.12.2014 11 / 16
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 16.12.2014 12 / 16
Gas Sensors Metal-Oxide 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 16.12.2014 13 / 16
Gas Sensors Open Sampling Systems 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 16.12.2014 14 / 16
Gas Sensors Open Sampling Systems 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 16.12.2014 14 / 16
Gas Sensors Laser-Based 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 16.12.2014 15 / 16
Gas Sensors 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 last lab. Happy Holidays! T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 16.12.2014 16 / 16
Gas Sensors 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 last lab. Happy Holidays! T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 16.12.2014 16 / 16
Gas Sensors 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 16.12.2014 T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 16.12.2014 16 / 16
Gas Sensors References T. Stoyanov (MRO Lab, AASS) Sensors & Sensing 16.12.2014 16 / 16