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introduction to mechatronics


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introduction to mechatronics

  1. 1. Introduction to Mechatronics Before mid Prepared by Imran khan 13me12 introduction to mechatronics (by Imran khan 13me12) 1
  2. 2. Mechatronics • Mechatronics is a multidisciplinary field of science that includes a combination of mechanical engineering, electronics, computer engineering, engineering, systems and control engineering. As technology advances, the subfields of engineering multiply and adapt. Mechatronics' aim is a design process that unifies these subfields. Originally, mechatronics just included the combination of mechanics and electronics, hence the word is a combination of mechanics and electronics; however, as technical systems have become more and more complex the definition has been broadened to include more technical areas. • Many people treat "mechatronics" as a modern buzzword synonymous with "electromechanical engineering" • A mechatronics engineer unites the principles of mechanics, electronics, and computing to generate a simpler, more economical and reliable system. The term "mechatronics" was coined by Tetsuro Mori, the senior engineer of the Japanese company Yaskawa in 1969. An industrial robot is a prime example of a mechatronics system; it includes aspects of electronics, mechanics, and computing to do its day-to-day jobs. introduction to mechatronics (by Imran khan 13me12) 2
  3. 3. Mechatronics refers to a flexible, multi-technological approach for integration of mechanical engineering, computer engineering, electronics and information sciences. Mechatronics is essential in the design of intelligent products. It allows engineers to transform their virtual concepts into real life applications. It is a relatively new concept relating to the design of systems, devices and products aimed at achieving an optimal balance between basic mechanical structure and its overall control introduction to mechatronics (by Imran khan 13me12) 3
  4. 4. • Course structure • Mechatronic students take courses in various fields • Mechanical engineering and materials science • Electrical engineering • Computer engineering (software & hardware engineering) • Computer science • Systems and control engineering • Optical engineering introduction to mechatronics (by Imran khan 13me12) 4
  5. 5. • Application • Machine vision, Automation and robotics, Servo-mechanics, Sensing and control systems, Automotive engineering, automotive equipment in the design of subsystems such as anti-lock braking systems, Computer-machine controls, such as computer driven machines like IE CNC milling machines, Expert systems, Industrial goods, Consumer products, Mechatronics systems, Medical mechatronics, medical imaging systems, Structural dynamic systems, Transportation and vehicular systems, Mechatronics as the new language of the automobile, Computer aided and integrated manufacturing systems, Computer-aided design, Engineering and manufacturing systems, Packaging, Microcontrollers / PLCs, Mobile apps, and M&E Engineering etc. introduction to mechatronics (by Imran khan 13me12) 5
  6. 6. Transducer • Transducer • A transducer is a device that converts one form of energy to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and control systems, where electrical signals are converted to and from other physical quantities (energy, force, torque, light, motion, position, etc.). The process of converting one form of energy to another is known as transduction. • For example, the common mercury thermometer converts variations in temperature into variations in the length of a column of mercury. Since the variation in the length of the mercury column is rather simple to measure, the mercury thermometer becomes a convenient device for measuring temperature. • On the other hand, the actual temperature variation is not as easy to display directly. Another example is manometer, which detects pressure and indicates it directly on a scale calibrated in actual units of pressure. • Thus the transducer is a device, which provides a usable output in response to specific input measured, which may be physical or mechanical quantity, property or condition. The transducer may be mechanical, electrical, magnetic, optical, chemical, audio, thermal nuclear, or a combination of any two or more of these. introduction to mechatronics (by Imran khan 13me12) 6
  7. 7. • A transducer will have basically two main components 1. Sensing element The physical quantity or its rate of change is sensed and responded to by this part of the transistor. 2. Transduction element The output of the sensing element is passed on to the transduction element. This element is responsible for converting the non-electrical signal into its proportional electrical signal. There may be cases when the transduction element perform the action of both transduction and sensing. The best example of such a transducer is a thermocouple. A thermocouple is used to generate a voltage corresponding to the heat that is generated at the junction of two dissimilar metals. introduction to mechatronics (by Imran khan 13me12) 7
  8. 8. • Classification of Transducer • The transducers may be classified in various ways such as on the basis of electrical principles involved, methods of application, methods of energy conversion used, nature of output signal etc. • Active and Passive Transducers • Primary and Secondary Transducers • Analog and Digital Transducers • Transducer and Inverse Transducer • Bidirectional introduction to mechatronics (by Imran khan 13me12) 8
  9. 9. • Active and Passive Transducers Transducers, on the basis of methods of energy conversion used, may be classified into active and passive transducers. 1. Active Self-generating type transducers i.e. the transducers, which develop their output in the form of electrical voltage or current without any auxiliary source, are called the active transducers. Such transducers draw energy from the system under measurement. Normally such transducers give very small output and, therefore, use of amplifier becomes essential. 2. Passive Transducers, in which electrical parameters i.e. resistance, inductance or capacitance changes with the change in input signal, are called the passive transducers. These transducers require external power source for energy conversion. In such transducer electrical parameters i.e. resistance, inductance or capacitance causes a change in voltages current or frequency of the external power source. These transducers may draw sour energy from the system under measurement. Resistive, inductive and capacitive transducer falls in this category. introduction to mechatronics (by Imran khan 13me12) 9
  10. 10. • Primary and Secondary Transducers • Some transducers contain the mechanical as well as electrical device. The mechanical device converts the physical quantity to be measured into a mechanical signal. Such mechanical device are called as the primary transducers, because they deal with the physical quantity to be measured. • The electrical device then convert this mechanical signal into a corresponding electrical signal. Such electrical device are known as secondary transducers introduction to mechatronics (by Imran khan 13me12) 10
  11. 11. introduction to mechatronics (by Imran khan 13me12) 11
  12. 12. • Analog and Digital Transducers 1, Analog transducer • These transducers convert the input quantity into an analog output which is a continuous function of time. • Thus a strain gauge, an L.V.D.T., a thermocouple or a thermistor may be called as Analog Transducers as they give an output which is a continuous function of time. 2, Digital Transducer • These transducers convert the input quantity into an electrical output which is in the form of pulses and its output is represented by 0 and 1. introduction to mechatronics (by Imran khan 13me12) 12
  13. 13. Transducer and Inverse Transducer Transducer • Transducers convert non electrical quantity to electrical quantity. Inverse Transducer • Inverse transducers convert electrical quantity to a non-electrical quantity. A piezoelectric crystal acts as an inverse transducer because when a voltage is applied across its surfaces, it changes its dimensions causing a mechanical displacement. introduction to mechatronics (by Imran khan 13me12) 13
  14. 14. • Bidirectional • Bidirectional transducers convert physical phenomena to electrical signals and also convert electrical signals into physical phenomena. Examples of inherently bidirectional transducers are antennae, which can convert conducted electrical signals to or from propagating electromagnetic waves, and voice coils, which convert electrical signals into sound (when used in a loudspeaker) or sound into electrical signals (when used in a microphone). Likewise, DC electric motors may be used to generate electrical power if the motor shaft is turned by an external torque. introduction to mechatronics (by Imran khan 13me12) 14
  15. 15. • Basic requirements of a transducer • The main function of a transducer is to respond only for the measurement under specified limits for which it is designed. It is, therefore, necessary to know the relationship between the input and output quantities and it should be fixed. Transducers should meet the following basic requirements. introduction to mechatronics (by Imran khan 13me12) 15
  16. 16. • Ruggedness. • It should be capable of withstanding overload and some safety arrangement should be provided for overload protection. • Linearity. • Its input-output characteristics should be linear and it should produce these characteristics in symmetrical way. • Repeatability. • It should reproduce same output signal when the same input signal is applied again and again under fixed environmental conditions e.g. temperature, pressure, humidity etc. • High Output Signal Quality. • The quality of output signal should be good i.e. the ratio of the signal to the noise should be high and the amplitude of the output signal should be enough. • High Reliability and Stability. • It should give minimum error in measurement for temperature variations, vibrations and other various changes in surroundings. • Good Dynamic Response. • Its output should be faithful to input when taken as a function of time. The effect is analyzed as the frequency response. • No Hysteretic. • It should not give any hysteretic during measurement while input signal is varied from its low value to high value and vice-versa. • Residual Deformation. • There should be no deformation on removal of local after long period of application. introduction to mechatronics (by Imran khan 13me12) 16
  17. 17. • Mechanical transducers • Mechanical transducer are simple and strong in construction, cheaper in cost, accurate and operate without external power supplies but are not advantageous for many of the modern scientific experiments and process control instrumentation due to their poor frequency response, requirement of large forces to overcome mechanical friction, in compatibility when remote control or indication is required, and a lot of other limitations. introduction to mechatronics (by Imran khan 13me12) 17
  18. 18. • Electrical transducers • Mostly quantities to be measured are non-electrical such as temperature, pressure, displacement, humidity, fluid flow, speed etc., but these quantities cannot be measured directly. Hence such quantities are required to be sensed and changed into some other form for easy measurement. • Electrical quantities such as current, voltage, resistance. Inductance and capacitance etc. can be conveniently measured, transferred and stored, and therefore, for measurement of non-electrical quantities these are to be converted into electrical quantities first and then measured. • The function of converting non-electrical quantity into electrical one is skillful by a device called the electrical transducer. Basically an electrical transducer is a sensing device by which a physical, mechanical or optical quantity to be measured is transformed directly, with a suitable mechanism, into an electrical signal (current, voltage or frequency). The production of these signals is based upon electrical effects which may be resistive, inductive, capacitive etc. in nature. • The input versus output energy relationship takes a definite reproducible function. The output to input and the output to time behavior is knowable to a known degree of accuracy, sensitivity and response, within the specified environmental conditions. introduction to mechatronics (by Imran khan 13me12) 18
  19. 19. • Strain Gauge Transducers • The strain gauge is an example of a passive transducer the; uses electrical resistance variation in wires to sense the strain produced by a force on the wires. It is a very versatile detector and transducer for measuring weight pressure mechanical force, or displacement. • Stress is defined as the internal force per unit area. The stress equation is • 𝑆 = 𝐹 𝐴 • Where • S= the stress in kilograms per Square meter • F= the force in kilograms • A= the area in square meters • As a consequence of strain two physical qualities are of particular interest: (1) the change in gauge resistance and (2) the change in length. The relationship between these two variables expressed as a ratio is called the gauge factor. • G.F. Expressed mathematically as • 𝐺. 𝐹 = ∆𝑅/𝑅 ∆𝐿/𝐿 • Where • K = the gauge factor • R = the initial resistance in ohms (without strain) • ΔR= the change in initial resistance in ohms • L = the initial length in meters (without strain) • ΔL= the change in initial length in meters • As 𝜖 = ∆𝐿/𝐿 • So 𝐺. 𝐹 = ∆𝑅/𝑅 𝜖 • Robert Hooke pointed out in the seventeenth century that for many common materials there is a constant, ratio between stress and strain. introduction to mechatronics (by Imran khan 13me12) 19
  20. 20. • EXAMPLE.2.1. • A resistant strain gauge with a gauge factor of 2 is fastened to a steel member, which is subjected to a strain of 1 X 10-6. If the original resistance value of the gauge is 130. Calculate the change in resistance. • Data: ∈= 1 × 10−6, 𝐺. 𝐹 = 2 , R = 130𝛺 • Solution • As 𝐺. 𝐹 = ∆𝑅/𝑅 ∈ • So ∆𝑅 = 𝐺. 𝐹 × 𝑅 ×∈ • Hence ∆𝑅 = (2)(130)(1 × 10−6 ) • ∆𝑅 = 260𝜇𝛺 introduction to mechatronics (by Imran khan 13me12) 20
  21. 21. EXAMPLE.2.2. • A round steel bar, 0.02 m in diameter and 0.40 m in length, is subjected to a tensile force of 33.000 kg, where E=2x1010 kg/m2. Calculate the elongation, L, in meters. • Data: d = 0.02m, L = 0.40m, F = 33.0kg, 𝐸 = 2 × 1010 𝑘𝑔/𝑚2 • solution mx mkgxmx mxkg AE FL L LL AF G S E mx mD A 3 21024 24 22 101.2 0 )/102()1014.3( 40.0000.33 / / 1014.3 2 02.0 2 (                     introduction to mechatronics (by Imran khan 13me12) 21
  22. 22. • Eddy Current Transducer • This type of transducer is comparatively low in the measurement field and depends mostly on the quality of a high alternating source which is fed to • a set of coils. • Eddy-Current sensors operate with magnetic fields. The driver creates an alternating current in the sensing coil in the end of the probe. This creates an alternating magnetic field with induces small currents in the target material; these currents are called eddy currents. The eddy currents create an opposing magnetic field which resists the field being generated by the probe coil. The interaction of the magnetic fields is dependent on the distance between the probe and the target. As the distance changes, the electronics sense the change in the field interaction and produce a voltage output which is proportional to the change in distance between the probe and target. The target surface must be at least three times larger than the probe diameter for normal, calibrated operation; otherwise, special calibration may be required. introduction to mechatronics (by Imran khan 13me12) 22
  23. 23. • Selection of Transducers • The points to be considered in determining a transducer suitable for a specific measurement are as follows: • Range. The range of the transducer should be large enough to encompass all the expected magnitudes of the measured. • Sensitivity. The transducer should give a sufficient output signal per unit of measured input in order to yield meaningful data. • Electrical Output Characteristics. The electrical characteristics-the output impedance, the frequency response, and the response time of the transducer output signal should be compatible with the recording device and the rest of the measuring system equipment. • Physical Environment. The transducer selected should be able to withstand the environmental conditions to which it is likely to be subjected while carrying out measurements and tests. • Such parameters are temperature, acceleration, shock and vibration, moisture, and corrosive chemicals might damage some transducers but not others. • Errors. The errors inherent in the operation of the transducer itself, or those errors caused by environmental conditions of the measurement, should be small enough or controllable enough that they allow meaningful data to be taken. • However the total measurement error in a transducer-activated system may be reduced to fall within the required accuracy range by adopting the following techniques. • Calibrating the transducer output against some known standards while in use under actual test conditions. This calibration should be performed regularly as the measurement proceeds. • Continuous monitoring of variations in the environmental conditions of the transducer and correcting the data accordingly. • Controlling the measurement environment artificially in order to reduce possible transducer errors. Artificial environmental control includes the enclosing of the transducer in a temperature-controlled housing and isolating the device from external shocks and vibrations.introduction to mechatronics (by Imran khan 13me12) 23
  24. 24. • Ideal characteristic • High dynamic range • High Repeatability • Low noise • Low hysteresis introduction to mechatronics (by Imran khan 13me12) 24
  25. 25. Application Accelerometers, Air flow sensors, Electroactive polymers, Rotary motors, linear motors, Galvanometers, pH probes, Electro-galvanic fuel cells, Hydrogen sensors, Antennae – converts propagating electromagnetic waves to and from conducted electrical signals, magnetic cartridges – converts relative physical motion to and from electrical signals, Tape head, disk read-and-write heads – converts magnetic fields on a magnetic medium to and from electrical signals, Hall effect sensors – converts a magnetic field level into an electrical signal, Linear variable differential transformers or rotary variably differential transformers, Load cells – converts force to mV/V electrical signal using strain gauges, Microelectromechanical systems, Potentiometers (when used for measuring position), Pressure sensors, String potentiometers, Tactile sensors, Vibration powered generators, Resistance temperature detectors (RTD) – converts temperature into an electrical resistance signal, Thermocouples – converts relative temperatures of metallic junctions to electrical voltage,Thermistors (includes PTC resistor and NTC resistor) introduction to mechatronics (by Imran khan 13me12) 25
  26. 26. Sensors • In the broadest definition, a sensor is an object whose purpose is to detect events or changes in its environment, and then provide a corresponding output. A sensor is a type of transducer; sensors may provide various types of output, but typically use electrical or optical signals. For example, a thermocouple generates a known voltage (the output) in response to its temperature (the environment). A mercury-in-glass thermometer, similarly, converts measured temperature into expansion and contraction of a liquid, which can be read on a calibrated glass tube. • Sensors are used in everyday objects such as touch-sensitive elevator buttons (tactile sensor) and lamps which dim or brighten by touching the base, besides innumerable applications of which most people are never aware. With advances in micromachinery and easy-to-use micro controller platforms, the uses of sensors have expanded beyond the most traditional fields of temperature, pressure or flow measurement,[1] for example into MARG sensors. Moreover, analog sensors such as potentiometers and force-sensing resistors are still widely used. Applications include manufacturing and machinery, airplanes and aerospace, cars, medicine, and is also included in our day-to-day life. • A sensor's sensitivity indicates how much the sensor's output changes when the input quantity being measured changes. For instance, if the mercury in a thermometer moves 1 cm when the temperature changes by 1 °C, the sensitivity is 1 cm/°C (it is basically the slope 𝑑𝑦 𝑑𝑥 assuming a linear characteristic). Some sensors can also affect what they measure; for instance, a room temperature thermometer inserted into a hot cup of liquid cools the liquid while the liquid heats the thermometer. introduction to mechatronics (by Imran khan 13me12) 26
  27. 27. • A good sensor obeys the following rules. • It is sensitive to the measured property, • It is insensitive to any other property likely to be encountered in its application, and, • It does not influence the measured property, • The sensitivity is then defined as the ratio between the output signal and measured property. For example, if a sensor measures temperature and has a voltage output, the sensitivity is a constant with the unit [V/K]; this sensor is linear because the ratio is constant at all points of measurement, • For an analog sensor signal to be processed, or used in digital equipment, it needs to be converted to a digital signal, using an analog-to-digital converter. introduction to mechatronics (by Imran khan 13me12) 27
  28. 28. • Sensor deviation • If the sensor is not ideal, several types of deviations can be observed: • The sensitivity may in practice differ from the value specified. This is called a sensitivity error. • Since the range of the output signal is always limited, the output signal will eventually reach a minimum or maximum when the measured property exceeds the limits. The full scale range defines the maximum and minimum values of the measured property. • If the output signal is not zero when the measured property is zero, the sensor has an offset or bias. This is defined as the output of the sensor at zero input. • If the sensitivity is not constant over the range of the sensor, this is called nonlinearity. Usually, this is defined by the amount the output differs from ideal behavior over the full range of the sensor, often noted as a percentage of the full range. • If the deviation is caused by a rapid change of the measured property over time, there is a dynamic error. Often, this behavior is described with bode plot showing sensitivity error and phase shift as a function of the frequency of a periodic input signal. • If the output signal slowly changes independent of the measured property, this is defined as drift (telecommunication). Long term drift usually indicates a slow degradation of sensor properties over a long period of time. • Noise is a random deviation of the signal that varies in time. • Hysteresis is an error caused by when the measured property reverses direction, but there is some finite lag in time for the sensor to respond, creating a different offset error in one direction than in the other. • If the sensor has a digital output, the output is essentially an approximation of the measured property. The approximation error is also called digitization error. • If the signal is monitored digitally, limitation of the sampling frequency also can cause a dynamic error, or if the variable or added noise changes periodically at a frequency near a multiple of the sampling rate may induce aliasing errors. • The sensor may to some extent be sensitive to properties other than the property being measured. For example, most sensors are influenced by the temperature of their environment. • All these deviations can be classified as systematic errors or random errors. Systematic errors can sometimes be compensated for by means of some kind of calibration strategy. Noise is a random error that can be reduced by signal processing, such as filtering, usually at the expense of the dynamic behavior of the sensor. introduction to mechatronics (by Imran khan 13me12) 28
  29. 29. • Resolution • The resolution of a sensor is the smallest change it can detect in the quantity that it is measuring. Often in a digital display, the least significant digit will fluctuate, indicating that changes of that magnitude are only just resolved. The resolution is related to the precision with which the measurement is made. For example, a scanning tunneling probe (a fine tip near a surface collects an electron tunneling current) can resolve atoms and molecules. introduction to mechatronics (by Imran khan 13me12) 29
  30. 30. • Criteria of selecting sensor • Sensitivity • Resolution • Repeatability • Accuracy • Precession • Response time • Calibration • Size • Linearity • Stability • Frequency response • Range • Error • Cost • Availability • Life time • Environment effect introduction to mechatronics (by Imran khan 13me12) 30
  31. 31. Strain Gauge:- • A strain gage is a resistor in which the resistance changes with strain. A strain gage is a thin piece of conducting material that may look like the drawing above. (Although, there are also semiconductor strain gages - not covered here.) It is literally glued on to the device where you want to measure strain. • A strain gage (sometimes referred to as a Strain gage) is a sensor whose resistance varies with applied force; it converts force, pressure, tension, weight, etc., into a change in electrical resistance which can then be measured. When external forces are applied to a stationary object, stress and strain are the result. Stress is defined as the object's internal resisting forces, and strain is defined as the displacement and deformation that occur. introduction to mechatronics (by Imran khan 13me12) 31
  32. 32. • Sensor for Force:- • A force-sensing resistor is a material whose resistance changes when a force or pressure is applied. They are also known as "force-sensitive resistor" and are sometimes referred to by the initialism "FSR" • Force Sensing Resistors (FSR) are a polymer thick film (PTF) device which exhibits a decrease in resistance with an increase in the force applied to the active surface. Its force sensitivity is optimized for use in human touch control of electronic devices. FSRs are not a load cell or strain gauge, though they have similar properties. FSRs are not suitable for precision measurements. • Force-sensing resistors are commonly used to create pressure-sensing "buttons" and have applications in many fields, including musical instruments, car occupancy sensors, artificial limbs, Foot pronation systems and portable electronics. introduction to mechatronics (by Imran khan 13me12) 32
  33. 33. • Sensor for Pressure:- • A pressure measurement can be described as either static or dynamic. The pressure in cases where no motion is occurring is referred to as static pressure. Examples of static pressure include the pressure of the air inside a balloon or water inside a basin. Often times, the motion of a fluid changes the force applied to its surroundings. Such a pressure measurement is known as dynamic pressure measurement. For example, the pressure inside a balloon or at the bottom of a water basin would change as air is let out of the balloon or as water is poured out of the basin. Head pressure (or pressure head) measures the static pressure of a liquid in a tank or a pipe. Head pressure, P, is a function solely on the height of the liquid, h, and weight density, w, of the liquid being measured as shown in Figure 1 below. introduction to mechatronics (by Imran khan 13me12) 33
  34. 34. • Sensor for Temperature:- • The most commonly used type of all the sensors are those which detect Temperature or heat. These types of temperature sensor vary from simple ON/OFF thermostatic devices which control a domestic hot water heating system to highly sensitive semiconductor types that can control complex process control furnace plants. • We remember from our school science classes that the movement of molecules and atoms produces heat (kinetic energy) and the greater the movement, the more heat that is generated. Temperature Sensors measure the amount of heat energy or even coldness that is generated by an object or system, allowing us to “sense” or detect any physical change to that temperature producing either an analogue or digital output. • There are many different types of Temperature Sensor available and all have different characteristics depending upon their actual application. A Temperature Sensor consists of two basic physical types: introduction to mechatronics (by Imran khan 13me12) 34
  35. 35. • Types of Temperature sensors • • Contact Temperature Sensor Types – • These types of temperature sensor are required to be in physical contact with the object being sensed and use conduction to monitor changes in temperature. They can be used to detect solids, liquids or gases over a wide range of temperatures. • • Non-contact Temperature Sensor Types – • These types of temperature sensor use convection and radiation to monitor changes in temperature. They can be used to detect liquids and gases that emit radiant energy as heat rises and cold settles to the bottom in convection currents or detect the radiant energy being transmitted from an object in the form of infra-red radiation (the sun). • The two basic types of contact or even non-contact temperature sensors can also be sub- divided into the following three groups of sensors, Electro-mechanical, Resistive and Electronic and all three types are discussed below. introduction to mechatronics (by Imran khan 13me12) 35
  36. 36. • Example No. 1 A thermistor has a resistance value of 10KΩ at 25oC. Calculate the voltage drop across the thermistor and hence its output voltage (V out) for both temperatures when connected in series with a 1kΩ resistor across a 12v power supply. At 25oC introduction to mechatronics (by Imran khan 13me12) 36
  37. 37. • Example No. 2 A thermistor has a resistance value of 100Ω at 100oC. Calculate the voltage drop across the thermistor and hence its output voltage (V out) for both temperatures when connected in series with a 1kΩ resistor across a 12v power supply. At 100oC introduction to mechatronics (by Imran khan 13me12) 37
  38. 38. • Sensor for motion • A motion detector is a device that detects moving objects, particularly people. A motion detector is often integrated as a component of a system that automatically performs a task or alerts a user of motion in an area. Motion detectors form a vital component of security, automated lighting control, home control, energy efficiency, and other useful systems. • There are several motion detection technologies in wide use: introduction to mechatronics (by Imran khan 13me12) 38
  39. 39. • Passive infrared (PIR):-Passive infrared sensors are sensitive to a person's skin temperature through emitted black body radiation at mid-infrared wavelengths, in contrast to background objects at room temperature. No energy is emitted from the sensor, thus the name "passive infrared" (PIR). This distinguishes it from the electric eye for instance (not usually considered a "motion detector"), in which the crossing of a person or vehicle interrupts a visible or infrared beam. • Microwave:-These detect motion through the principle of Doppler radar, and are similar to a radar speed gun. A continuous wave of microwave radiation is emitted, and phase shifts in the reflected microwaves due to motion of an object toward (or away from) the receiver result in a heterodyne signal at low audio frequencies. • Ultrasonic:-An ultrasonic wave (sound at a frequency higher than a human can hear) is emitted and reflections from nearby objects are received.[1] Exactly as in Doppler radar, heterodyne detection of the received field indicates motion. The detected Doppler shift is also at low audio frequencies (for walking speeds) since the ultrasonic wavelength of around a centimeter is similar to the wavelengths used in microwave motion detectors. One potential drawback of ultrasonic sensors is that the sensor can be sensitive to motion in areas where coverage isn't desired, for instance, due to reflections of sound waves around corners.[2] Such extended coverage may be desirable for lighting control, where the point is detection of any occupancy in an area. But for opening an automatic door, for example, one would prefer a sensor selective to traffic in the path toward the door. • Tomographic motion detector:-Tomographic motion detection systems sense disturbances to radio waves as they pass from node to node of a mesh network. They have the ability to detect over complete areas because they can sense through walls and obstructions.introduction to mechatronics (by Imran khan 13me12) 39
  40. 40. • Video camera software:-With the proliferation of inexpensive digital cameras capable of shooting video, it is possible to use the output of such a camera to detect motion in its field of view using software. This solution is particularly attractive when the intention was to record video triggered by motion detection, as no hardware beyond the camera and computer is required. Since the observed field may be normally illuminated, this may be considered another passive technology. However it can also be used in conjunction with near-infrared illumination to detect motion in the "dark" (that is, with the illumination at a wavelength not detected by the human eye). • Dual-technology motion detectors:-Many modern motion detectors use combinations of different technologies. While combining multiple sensing technologies into one detector can help reduce false triggering, it does so at the expense of reduced detection probabilities and increased vulnerability. For example, many dual-tech sensors combine both a PIR sensor and a microwave sensor into one unit. In order for motion to be detected, both sensors must trip together. This lowers the probability of a false alarm since heat and light changes may trip the PIR but not the microwave, or trees may trigger the microwave but not the PIR. If an intruder is able to fool the PIR or microwave, however, the sensor will not detect. Dual-tech sensors are only as strong as their weakest link. • Often, PIR technology will be paired with another model to maximize accuracy and reduce energy usage. PIR draws less energy than microwave detection [dubious - discuss], and so many sensors are calibrated so that when the PIR sensor is tripped, it activates a microwave sensor. If the latter also picks up an intruder, then the alarm is sounded. introduction to mechatronics (by Imran khan 13me12) 40
  41. 41. Common Sensors and Transducers Quantity being Measured Input Device (Sensor) Output Device (Actuator) Light Level Light Dependant Resistor (LDR) Photodiode Photo-transistor Solar Cell Lights & Lamps LED’s & Displays Fibre Optics Temperature Thermocouple Thermistor Thermostat Resistive Temperature Detectors Heater Fan Force/Pressure Strain Gauge Pressure Switch Load Cells Lifts & Jacks Electromagnet Vibration Position Potentiometer Encoders Reflective/Slotted Opto-switch LVDT Motor Solenoid Panel Meters Speed Tacho-generator Reflective/Slotted Opto-coupler Doppler Effect Sensors AC and DC Motors Stepper Motor Brake Sound Carbon Microphone Piezo-electric Crystal Bell Buzzer Loudspeaker introduction to mechatronics (by Imran khan 13me12) 41
  42. 42. introduction to mechatronics (by Imran khan 13me12) 42