Advantages And Disadvantages Of Different Industrial Sensor

Published Date: 02 Nov 2017

The term mechatronics is a combination of mechanical and electronic components. Before mechatronics was introduced mechanical components where purely mechanical while electrical and electronics where just electrical and electronics. But then an introduction of mixing mechanical parts with electronic ones was taking place. Mechatronics was always being improved trough years until the day. In the early 1980’s an introduction to microprocessors and the ever increasing desired performance to cost ratio revolutionized the engineering design. The number of new products being developed which intersect with the traditional disciplines of engineering, computer science, and the natural sciences is ever intersecting. Such microprocessors nowadays are found in computer hardware, production lines and so on. The ongoing information technology revolution, advances in wireless communication, smart sensors design which were enabled by MEMS Technology and embedded systems, wireless communication technology, in which these will be continue to evolve. MEMS stand for Micro-Electro Mechanical System.

The replacement of some mechanical functions with electronic and software one distinguish mechatronics system or products from earlier electromechanical systems. This result is much greater flexibility of both design and operation. Another is increased speed and precision of performance. Another benefit is the ability to conduct automated data collection and reporting. Nowadays advanced mechatronics systems have the ability to implement distributed control in complex systems. Microprocessors and other devices, helps increasing considerably the performance of products.

The key elements of mechatronics are:

Physical Systems Modelling

Sensors and Actuators

Signals and Systems

Computers and Logic System

Software and Data Acquisition

Engineering design approach has improved and provided a lot of help in such systems. Modern engineering products are characterised by the complexity. In order to satisfy needs, manufacturers are designing increasingly complex customer products and using increasingly more complex manufacturing. Digital processors have contributed to this increase in complexity, with the benefits of having more sophisticated and multi-task products. Mechatronic design methods today emphasise mechanical modelling before any hardware is built. Model based design simplifies the development of mechatronic systems because it provides a common environment for design and communication across different engineering disciplines such as dynamic and performance requirements. It also uses a system level which is used to define executable specifications by describing the natural and controlled behaviour of the equipment in a mathematical form. Such software includes CAD, CATIA, and Inventor. With the benefit of such design programs an engineer can simulate the design and establish different behaviour and properties of such design.

Outline why many engineering designs today can be classified as mechatronic systems.

Nowadays many engineering designs can be classified as mechatronic systems. This is because the primary disciplines in a design include mechanics, electronics, controls, and computer engineering. Reeves and Shipman states that a discussion about the design must embedded in the overall design process.

A mechatronic system is designed by a group of engineers that work with each so as to design a mechatronic system. Such group of engineers consists of mechanical, electrical and control engineers. Such engineers are required because a mechatronic system does not contain only mechanical or electrical parts but contain a mixture of both technologies along with other technologies such as controls and electronics. A mechatronic system allows a system to be more reliable and efficient, meaning that such systems can offer the user a product that contains all the necessary features at the best possible comfort ability. Such systems are able to gain better profit then mechanical or electrical system with the benefit of reducing errors, while they must be more expensive to purchase compared to mechanical and electrical systems.

The combination of electronic parts with those mechanical offered an accurate system that is being integrated in several components and machinery. Such devices tha make up a mechatronic system are sensors, actuators, motor, displays, amplifiers and many more. Obviously, even on the conceptual design level, mechanical and electrical design aspects of mechatronic systems are highly intertwined through a substantial number of constraints existing between their components.

Define and explain input and output signals of a mechatronic system.

Usually a mechatronic system is represented as a block diagram. The input of such system is translated to a specified output by means of several components. An input of system generally handles several peripherals that are used so as to translate the gathered information to the required output. Input data is usually gathered by means of sensory equipment which can either provide an analogue or digital signal. The simplest type of input analogue signal is a voltage level with a direct correlation to the input condition. Another type of analogue signal is called the pulse width modulate signal, while the last type is called a waveform. This is an input that produces any form of waves as an input.

Meanwhile an output signal of a system is a compilation of different components that are used to translate an input to a designed output. Such components can include converters, amplifiers, motors, etc...The output of a system is used to display or provide information to the user. Output devices can be monitors, LCD displays, and other sensory equipment and so on. A system can be either an open loop system of a closed loop system. In a closed loop system a feedback is required by the output device. A typical application for such discussion is the measurement of pressure. The input pressure sensor is used to detect the pressure in a system, where this data is converted from an analogue signal to a digital signal by means of ADC, so that the pressure measurement can be displayed onto a screen.

Outline the advantages and disadvantages of different industrial sensor types.

The use of sensors has increased of the past years. There are various types of industrial sensors that are used nowadays. Digital encoders, pressure sensors, temperature sensors, capacitive sensors and infrared sensors are five sensors commonly used in different industries.

Digital encoders are used to convert motion input into a sequence of digital pulses. Such encoders are known for their simple construction and low cost. They also are eligible to offer high sensitivity and resolution for the application being used for. Encoders suffer from brush bounce due to vibration, thus making them limited to be used in such environments. They are also exposed to friction; hence their lifetime is relatively much lower due to wear and tear of mechanical components.

Pressure sensors are used to measure and control the pressure used by a system. Pressure sensors offer the ability to display the amount of pressure being utilized. They are not shock or vibration sensitive compared to mechanical gauges. Also they do not suffer from signal losses or interference. Their main disadvantage is that they can easily fail. This is because when corroded such sensor can no longer offer accurate readings.

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Temperature sensors are used to measure different temperatures. These types of sensors offer a stable output for long period of time, while they can be easily calibrated. Temperature sensors offer accurate reading while they have an easily conditioned output. On the other hand they are expensive to purchase while they get less rugged in high vibration environments.

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Moreover capacitive sensors are used for detection of metallic and non-metallic parts without having any contact. These type of sensors offer good stability and resolution, while are known for their high speed efficiency, power usage and low cost. On the contrary the major drawback of such sensors is that they are affected by both temperature and environment. Therefore this makes their application limited. Capacitive sensors are also sensitive to noise while they do not offer a good linearity. Accuracy for these sensors is not superior to that of inductive sensors.

Infrared sensors are suitable for applications where thermal energy detection is required. They are used to sense some aspect of its surroundings since they emit or detect infrared radiation, which are capable to sense both living and non-living object. Also infrared sensors can detect light from far distance, while they operate in real-time and detect movement. Due to these factors such sensors offer great reliability. On the opposition to this, infrared sensors are incapable to understand the difference between objects that irradiate similar thermal energy levels, while proper aligning is required. Also these type of sensors are relatively expensive.

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Explain and describe the characteristics of sensors and actuators.

Actuators are used in mechatronic systems since they involve some sort of motion or action. Motion is created by a force or torque that results in acceleration and displacement such a linear motion or angular displacement. There are different types of actuators including solenoids, electric motors, hydraulic and pneumatic cylinders and so on. It is important that the appropriate actuation system is properly chosen based on the application at hand. Similar to sensors actuators also have characteristics such as range, resolution, repeatability, impedance, system response and so on. It is important that all characteristics are well identified and categorised so that the proper sensory and actuation components are chosen for the application at hand.

Sensors and actuators are two components that make up a closed loop system. Sensors translate an input quantity to an output quantity. A sensor can consist of a simple physical measurement system or can consist of additional components requiring sophisticated data acquisition systems. No matter the type of sensor, input type, or output type, every sensor has inherent characteristics that allow the user to select the appropriate sensor for a particular application.

Characteristics that should be considered for both sensors and actuators are:

Range- generally specified by the manufacturer. Range is the difference between the minimum and maximum input that will give a valid output.

Resolution- is the smallest increment that can be reliably detected

Sensitivity- is closely related to resolution, where the change in output per change in input is measured

Error- is the difference between a measured value and the true input value

Repeatability- is the ability of a sensor to give similar outputs for the same inputs

Linearity and Accuracy- linearity is the percentage of full scale, while the accuracy is inversely proportional to error, where high accuracy result in low errors and vice versa

Impedance- is known as the ratio of voltage and current that floe through a sensor.

System response- is the behaviour of inputs that change with time. It is also known as stability of a system, where it is related to the equilibrium of a system.

Frequency response- is the quantitative measure of the output spectrum of a system or device in response to stimulus, which is used t characterise the dynamics of a system.

Power requirement- is the identification of the type of power required to energise the sensor devices or actuators. This can be direct current, alternating current, pneumatic or hydraulic actuation, etc...

Speed characteristics- the force/torque required versus the speed relationship of the actuator

Heat dissipation- is the maximum wattage of heat dissipation in continuous operation

Explain the fundamentals of simple electromechanical sensors, including proximity sensors and switches.

Electromechanical sensors are type of sensors that are considered as safety devices. These sensors are used to stop a machine or workcell in case of breakdowns and failures. Such types of devices are so called proximity sensors and switches. Proximity sensor complies of an element that changes either it state or analogue signal when and object is close to such element. There are different types of proximity sensors in which these are:

Magnetic proximity sensors and switches- such devices are actuated by the presence of a permanent magnet. The operation of such sensor consists of reed contacts. When reciprocal attraction of both reeds is present in the magnetic field, electrical contact is established. The attraction of both reeds in the presence of of magnetic field is caused by the magnetic induction of the sensor.

Proximity Switch brochure

Capacitive proximity sensors and switches- such sensors and switches are used to detect both metallic and non-metallic objects. The variation of capacitance between the device and the object indicates the preset distance of an object. When such object is at the preset distance from the sensitive side of the sensor, oscillations of an electronic circuit inside the sensor will start to occur. The rise or fall of such oscillation is identified by a threshold circuit that drives an amplifier for the operation of an external load.

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Inductive proximity sensors and switches- these type of sensors are used to detect metallic objects. The principle of operation for such sensors consists of a coil and oscillator that are used to change the oscillation amplitude when a metal object is detected. This detection is recognised by a threshold circuit which is used to change the output of the sensor.

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Eddy-currents proximity sensors and switches- are non contact devices that operate with magnetic fileds. The driver creates an alternating current that creates an alternating magnetic field. These alternating fields induce small currents in the material being measured called as eddy currents. Eddy currents create an opposing magnetic field that resists the field being generated by the coil. Thus when the distance between the sensing device and object increases a change in the field is sensed, producing a voltage output that is proportional to the change in distance between the device and the object.

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Explain the fundamentals of nanomachines.

Nanomachines are relatively small machinery that makes use of MEMS devices, microsensors and microactuators, built from individual atoms. Their size is measured in nanometres since nanomachines deal with molecules between one and one hundred nanometers in diameter. These individual atoms often called molecular components are capable to perform mechanical functions that are used to operate something.

Nanomachines can be intrinsically self-contained. This means that each machine can contain a set of instructions or codes that are used to realize the projected tasks. These codes or sequences are embedded in the molecular structure of the nanomachines or can be read from another molecular structure used to store instructions. This programming enables such machines to replicate themselves or can even work with larger machines. Nanomachines are becoming widely used in medical equipment, space technology, and military technology. Although nanomachines are very small in size, they offer better and faster response, and offer improved quality. Also such technology offers the user to create functional material, device and systems. Durability is another benefit of such machines. Nanomachines are also very cost-effective despite their advantages and capabilities. Such machines specifically for precision application, because they are environment friendly and are very accurate and precise regardless of their shape.

What types of smart materials are used for mechatronics applications? Outline smart material uses.

Smart materials are a new era of materials that can be defined as material whose properties or shape can change in response to some stimulus from the environment by means of design. Smart materials differ from conventional materials since they are used to solve engineering problems with unattainable efficiency and provide an opportunity for creation of new products that generate revenue. Smart materials are required to undergo persistent and reversible changes playing an active part in the way the structure or device works. Response of such materials implies a large amplitude change while their agility implies a fast response. Smart materials used for mechatronics applications such as sensory devices, actuators, structures, machines and mechanical systems, biomedical machines, robotics and so on. Different type of materials used is:

Shape memory alloys (SAM): these materials have the ability to withstand large strains, with the ability of recovering their actual shape at the end of the deformation process. According to Richard Lin SMAs are useful for actuators that are subjected to change shape, stiffness, position, natural frequency, and other mechanical characteristics in response to temperature or electromagnetic fields

Piezo-electric materials: these types of materials produce a voltage in response to an applied force. Such materials are mainly used for manufacturing of pressure sensors and strain gauges. The main key properties of such material are to produce a voltage output to the applied stress and to produce a strain output in response to an applied voltage.

Electrostrictive materials: these type of materials do not posses spontaneous polarisation unlike piezo-electric materials. Electrostrictive materials strain proportionally to the square of the applied voltage of the applied electric field. This results in little or no hysteresis loss even at very high frequencies of operation.

Magnetostrictive materials: consist of ferro-magnets that act as permanent magnets. When magnetic fields are applied strain is induced which is proportional to the square of the applied magnetic field, where the induced strain is independent of the direction of the applied magnetic fields.

Electrorheological materials: ER materials whose rheological properties, deformation and flow behaviour in response to a stress, are strong functions of the electric field strength imposed upon them. These types of material are generally in form of fluids and are mainly used for actuator systems.

Optic fibre materials: these materials consist of molten silica glass which is used to transmit data. This glass make such materials to be used for sensing applications including high elastic strain limits, high fracture toughness, high flexibility in bending, high sensitivity to strain and high resolution temperatures.

Ion exchange polymers: such smart materials exploit the electro-osmosis phenomenon where actuation of a cylinder is done by natural ionic polymers. These materials are used to develop artificial muscles and limbs. When voltage is applied across the cross-linked polyelectrolytic network a net charge is attained to the ionizable groups resulting in a mechanical deformation.

Define microactuators and microsensors.

Micro technology is always advancing as a technology; therefore it is becoming widely used due to its principles. Micro technology is a type of technology that is able to offer similar equipment that already existing on a far smaller scale. This feature allows such devices to be used in production lines or other applications where bulky machines are not feasible. Microactuators and microprocessors are two components that make up such technology.

Microactuators are based on three dimensional mechanical structures but on very small dimensions. This down scaling of such component characteristics minimizes the characteristics of the microactuators such as the actuator force. This does not mean that the concept of the actuator is lost. Microactuators are used to convert electrical, energy to mechanical energy. These devices allow completely new mechanical designs that make them suitable for specified applications. Micro actuators work in response to a command or control signal given by either a PLC or microcontroller. There are different types of actuation systems such as electrical, electrostatic, electromagnetic, piezoelectric, thermal and optical.

Meanwhile microsensors are smaller versions of the actual size sensors with improved performance at lower costs. Microsensors were developed by the help of micromachining technology. These devices are capable of sensing and relaying environmental information such as biological, thermal, chemical and other forms of data. This data is then sent to a processor, where such data is translated to an output that can be accessed for a variety of uses. These type of sensors do not transmit power therefore the scaling of force is not typically significant. Microsensors are typically based on either measurement of mechanical strain, measurement of mechanical displacement, or on frequency measurement of a structural resonance. There are various types of microsensors that are used to measure strain, force, acceleration, pressure and so on.