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Mechatronics sensors3.1
- 1. Mechatronics References : 1. RoboticEngineering – An Integrated Approach Richard D. Klafter, Thomas A. Chmielewski, Michael Negin 2. NPTEL, Mechanical Engineering, Robotics - Prof. P. Sheshu, Prof. Kurien Issac, Prof. C. Amarnath, Prof. Bhartendu Seth, Asst. Prof. P.S.Gandhi, IIT, Bombay 3. Introduction to Robotics – S. K. Saha, Tata McGraw Hill 19 dec 2017 1
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- 3. VELOCITY SENSOR -Tachometer In case of tachometer it is necessary that: 1. Voltage vs. Speed should be linear 2. Output voltage must be free of ripple 3. Should be light in weight
- 4. VELOCITY SENSOR –Hall Effect sensor
- 5. Hall Effect Sensor Thiscomponent can be used in a circuit to open and close a contact when exposed to alternating N and S poles of a magnet. Will also work if exposed to the same pole on alternative sides of the sensor. Many uses including: Counting revolutions, oscillations, or sequences Turning LEDs, alarms, or other devices on/off Detecting presence of magnetized materials Intruder/theft alarms Monitor start/stop of a moving process Robotic effects and magic tricks! Source: http://www.lessemf.com
- 6. Accelerometers LVDT Mass M spring Direction of motion Rigid mounting structure Force =Ma = Ky Therefore a = K y / M http://zone.ni.com/cms/images/devzone/ph/fa647a871560.gif Using LVDT
- 7. Accelerometers The piezoelectric accelerometeris based on a property exhibited by certain crystals where a voltage is generated across the crystal when stressed. For accelerometers, the principle is shown in figure. Here, a piezoelectric crystal is spring- loaded with a test mass in contact with the crystal. When exposed to an acceleration, the test mass stresses the crystal by a force (F = ma), resulting in a voltage generated across the crystal. A measure of this voltage is then a measure of the acceleration. http://zone.ni.com/devzone/cda/ph/p/id/284
- 8. Accelerometer Digital Accelerometer Example: LIS302is a 3-axis digital accelerometer ■ 2.16V to 3.6V supply voltage Application ■ Free-Fall detection ■ Motion activated functions ■ Gaming and virtual reality input devices ■ Vibration monitoring and compensation Description The LIS302DL is an ultra compact low-power three axes linear accelerometer. It includes a sensing element and an IC interface able to provide the measured acceleration to the external World http://www.st.com/
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- 10. External State Sensors ProximitySensors – Contact sensors – rod + switch - strain gauges - piezoelectric
- 11. External Sensors Proximity Sensors- Non-contact type - reflected light sensors *two different object positions produce same voltage – giving incorrect value * ambient light * sensitivity depends on reflectivity of object * errors due to variations in light-source output, drift in detector characteristics, environmentally aused changes in reflectivity of object
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- 14. Optical proximity sensors DavisInstruments Ecdcontrols.com
- 15. Fibre – OpticScanning sensors • Opposed or beam break configuration • Retroreflective • Reflective
- 17. Digital Sensors forMotion Measurement Ref: Introduction to Mechatronics and Measurement Systems, Histand & Alciatore, 1999 McGraw Hill
- 20. Digital Encoder • Adigital optical encoder converts motion into a sequence of digital pulses. • By decoding a set of bits, the pulses can be converted to relative or absolute position measurements. • Encoders have both linear and rotary configurations.
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- 22. Absolute encoder • Theoptical disk of the absolute encoder is designed to produce a digital word that distinguishes N distinct positions of the shaft.
- 23. Incremental encoder The incrementalencoder, sometimes called a relative encoder, consists of two tracks and two sensors whose outputs are called channels A and B. As the shaft rotates, pulse trains occur on these channels at a frequency proportional to the shaft speed, and the phase relationship between the signals yields the direction of rotation.
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Editor's Notes
- #3 An LVDT transformer is exited with a fixed frequency sine wave. The distance of displacement of the movable core will change the amplitude of the transformer output which is is converted to a dc voltage by the LT1967 True RMS converter. The direction of the core movement is indicated by the phase shift of the sine wave and is detected by a simple phase comparator circuit.