What is meant by Microsensors?

                 Since microsensors do not transmit power, the scaling of force is not typically significant. As with conventional-scale sensing, the qualities of interest are high resolution, absence of drift and hysteresis, achieving a sufficient bandwidth, and immunity to extraneous effects not being measured. Microsensors are typically based on either measurement of mechanical strain, measurement of mechanical displacement, or on frequency measurement of a structural resonance. 

                   The former two types are in essence analog measurements, while the latter is in essence a binary-type measurement, since the sensed quantity is typically the frequency of vibration. Since the resonant-type sensors measure frequency instead of amplitude, they are generally less susceptible to noise and thus typically provide a higher resolution measurement. According to Guckel et al., resonant sensors provide as much as one hundred times the resolution of analog sensors. 

               They are also, however, more complex and are typically more difficult to fabricate. The primary form of strain-based measurement is piezoresistive, while the primary means of displacement measurement is capacitive. The resonant sensors require both a means of structural excitation as well as a means of resonant frequency detection. Many combinations of transduction are utilized for these purposes, including electrostatic excitation, capacitive detection, magnetic excitation and detection, thermal excitation, and optical detection.

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What is meant by Electromagnetic Actuation?

                   Electromagnetic actuation is not as omnipresent at the micro-scale as at the conventional-scale. This probably is due in part to early skepticism regarding the scaling of magnetic forces, and in part to the fabrication difficulty in replicating conventional-scale designs. Most electromagnetic transduction is based upon a current carrying conductor in a magnetic field, which is described by the Lorentz equation: where F is the force on the conductor, I is the current in the conductor, l is the length of the conductor, and B is the magnetic flux density. 

               In this relation, the magnetic flux density is an intensive variable and thus (for a given material) does not change with scale. Scaling of current, however, is not as simple. The resistance of wire is given by where ρ is the resistivity of the wire (an intensive variable), l is the length, and A the cross-sectional area. If a wire is geometrically decreased in size by a factor of N, its resistance will increase by a factor of N. Since the power dissipated in the wire is I 2 R, assuming the current remains constant implies that the power dissipated in the geometrically smaller wire will increase by a factor of N. Assuming the maximum power dissipation for a given wire is determined by the surface area of the wire, a wire that is smaller by a factor of N will be able to dissipate a factor of N 2 less power. Constant current is therefore a poor assumption. 

            A better assumption is that maximum current is limited by maximum power dissipation, which is assumed to depend upon surface area of the wire. Since a wire smaller by a factor of N can dissipate a factor of N2 less power, the current in the smaller conductor would have to be reduced by a factor of N 3/2. Incorporating this into the scaling of the Lorentz equation, an electromagnetic actuator that is geometrically smaller by a factor of N would exert a force that is smaller by a factor of N 5/2. Trimmer and Jebens have conducted a similar analysis, and demonstrated that electromagnetic forces scale as N2 when assuming constant temperature rise in the wire, N 5/2 when assuming constant heat (power) flow (as previously described), and N 3 when assuming constant current density [23,24]. In any of these cases, the scaling of electromagnetic forces is not nearly as favorable as the scaling of electrostatic forces. 

             Despite this, electromagnetic actuation still offers utility in microactuation, and most likely scales more favorably than does inertial or gravitational forces. Lorentz-type approaches to microactuation utilize surface.

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What is meant by Electrostatic Actuation?

              The most widely utilized multicomponent microactuators are those based upon electrostatic transduction. These actuators can also be regarded as a variable capacitance type, since they operate in an analogous mode to variable reluctance type electromagnetic actuators (e.g., variable reluctance stepper motors). Electrostatic actuators have been developed in both linear and rotary forms. The two most common configurations of the linear type of electrostatic actuators are the normal-drive and tangential or comb-drive types, which are illustrated in Figs. respectively. Note that both actuators are suspended by flexures, and thus the output force is equal to the electrostatic actuation force minus the elastic force required to deflect the flexure suspension. The normal-drive type of electrostatic microactuator operates in a similar fashion to a condenser microphone. 

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Sensor and Actuator Transduction Characteristics?

             Characteristics of concern for both microactuator and microsensor technology are repeatability, the ability to fabricate at a small scale, immunity to extraneous influences, sufficient bandwidth, and if possible, linearity. Characteristics typically of concern specifically for microactuators are achievable force, displacement, power, bandwidth (or speed of response), and efficiency. Characteristics typically of concern specifically for microsensors are high resolution and the absence of drift and hysteresis. 

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What is meant by Programmable Logic Controllers?

                  A programmable logic controller (PLC) is a microprocessor-based control unit designed for an industrial installation (housing, terminals, ambient resistance, fault tolerance) in a power switchboard to control machinery or an industrial process. It consists of a CPU with memories and an I/O interface housed either in a compact box or in modules plugged in a frame and connected with proprietary buses. The compact box starts with about 16 I/O interfaces, while the module design can have thousands of I/O interfaces. Isolated inputs usually recognize industrial logic, 24 V DC or main AC voltage, while outputs are provided either with isolated solid state switches (24 V for solenoid valves and contactors) or with relays. Screw terminal boards represent connection facilities, which are preferred in PLCs to wire them to the controlled systems. I/O logical levels can be indicated with LEDs near to terminals. Since PLCs are typically utilized to replace relays, they execute Boolean (bit, logical) operations and timer/counter functions (a finite state automaton). Analog I/O, integer or even floating point arithmetic, PWM outputs, and RTC are implemented in up-to-date PLCs. A PLC works by continually scanning a program, such as machine code, that is interpreted by an embedded microprocessor (CPU). The scan time is the time it takes to check the input status, to execute all branches (all individual rungs of a ladder

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What is the differents by Microprocessors and Microcontrollers?

               

               There is no strict border between microprocessors and microcontrollers because certain chips can access external code and/or data memory (microprocessor mode) and are equipped with particular peripheral components. Some microcontrollers have an internal RC oscillator and do not need an external component. However, an external quartz or ceramic resonator or RC network is frequently connected to the built-in, active element of the clock generator. 

                  Clock frequency varies from 32 kHz (extra low power) up to 75 MHz. Another auxiliary circuit generates the reset signal for an appropriate period after a supply is turned on. Watchdog circuits generate chip reset when a periodic retriggering signal does not come in time due to a program problem. There are several modes of consumption reduction activated by program instructions. Complexity and structure of the interrupt system (total number of sources and their priority level selection), settings of level/edge sensitivity of external sources and events in internal (i.e., peripheral) sources, and handling of simultaneous interrupt events appear as some of the most important criteria of microcontroller taxonomy. 

                    Although 16- and 32-bit microcontrollers are engaged in special, demanding applications (servo-unit control), most applications employ 8-bit chips. Some microcontrollers can internally operate with a 16-bit or even 32-bit data only in fixed-point range—microcontrollers are not provided with floating point unit (FPU). New microcontroller families are built on RISC (Reduced Instruction Set) core executing due to pipelining one instruction per few clock cycles or even per each cycle

One can find further differences in addressing modes, number of direct accessible registers, and type of code memory (ranging from 1 to 128 KB) that are important from the view of firmware development. Flash memory enables quick and even in-system programming (ISP) using 3–5 wires, whereas classical EPROM makes chips more expensive due to windowed ceramic packaging.

                 Some microcontrollers have built-in boot and debug capability to load code from a PC into the flash memory using UART (Universal Asynchronous Receiver/Transmitter) and RS-232C serial line. OTP (One Time Programmable) EPROMor ROM appear effective for large production series. Data EEPROM (from 64 B to 4 KB) for calibration constants, parameter tables, status storage, and passwords that can be written by firmware stand beside the standard SRAM (from 32 B to 4 KB). The range of peripheral components is very wide.

                 Every chip has bidirectional I/O (input/output) pins associated in 8-bit ports, but they often have an alternate function. Certain chips can set an input decision level (TTL, MOS, or Schmitt trigger) and pull-up or pull-down current sources. Output drivers vary in open collector or tri-state circuitry and maximal currents. At least one 8-bit timer/counter (usually provided with a prescaler) counts either external events (optional pulses from an incremental position sensor) or internal clocks, to measure time intervals, and periodically generates an interrupt or variable baud rate for serial communication. General purpose 16-bit counters and appropriate registers form either capture units to store the time of input transients or compare units that generate output transients as a stepper motor drive status or PWM (pulse widthmodulation) signal. 

                A real-time counter (RTC) represents a special kind of counter that runs even in sleep mode. One or two asynchronous and optionally synchronous serial interfaces (UART/USART) communicate with a master computer while other serial interfaces like SPI, CAN, and I2 C control other specific chips employed in the device or system. 

Almost every microcontroller family has members that are provided with an A/D converter and a multiplexer of single-ended inputs. Input range is usually unipolar and equal to supply voltage or rarely to the on-chip voltage reference. The conversion time is given by the successive approximation principle of ADC, and the effective number of bits (ENOB) usually does not reach the nominal resolution 8, 10, or 12 bits. 

                    There are other special interface circuits, such as field programmable gate array (FPGA), that can be configured as an arbitrary digital circuit. Microcontroller firmware is usually programmed in an assembly language or in C language. Many software tools, including chip simulators, are available on websites of chip manufacturers or third-party companies free of charge. 

                    A professional integrated development environment and debugging hardware (in-circuit emulator) is more expensive (thousands of dollars). However, smart use of an inexpensive ROM simulator in a microprocessor system or a step-by-step development cycle using an ISP programmer of flash microcontroller can develop fairly complex applications.

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windings in ACTUATORS?

The windings has two functions: 

          a. Generation of a magnetic field. 

          b. Generation of a force or torque in a magnetic field. 

        Windings are placed on both the stator and the rotor. Mostly the windings are made of copper; in some exceptional cases the are made of aluminum or silver. The field windings are thin and have a relatively low current value. The force generating windings are thick and have a high current value. The magnet field windings can be replaced by permanent magnets. Permanent magnets have a strong magnetic field in relation with its volume, that is why small motors have most of the time a permanent magnet. The current in the windings caused conducting losses. These losses heats the actuator, with is very disadvantageous. The windings are positioned in such a way that they get rid of their heat very easy. 

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The rotor or armature in ACTUATOR?

The rotor or armature is the movable part on the shaft, which is placed in the bearing of the stator. The rotor has also copper windings that can generate a force when the windings carry a current in a magnetic field. For a continue force the current direction in the windings must react on the value of the magnetic field. For direct current motors this phenomenon is called commutation. Consist the rotor of permanent magnetic material then the stator windings must have carry current depending of the rotor position. Induction motors working according to the induction principle. The rotor consists of short-circuited bars or windings. There is no commutation. At last the rotor can consist only of magnet iron. The generation of force is according the reluctance principle. The rotor iron follows a moving magnetic field. Because the rotor has to guide the magnetic field from one side to the other side of the stator it is nearly totally made of magnet iron. Exception of this construction are the so called air gap rotors and permanent magnets rotors. The form of the rotors can be like a cylinder, a disk or like a cup. The cup and disk forms are the air gap rotors, they have a low inertia. That is why those motors are very capable for situations with high accelerations and decelerations (servo applications). In case the armature moves from left to right it is called a linear actuator (lineator). The working principle is the same as for rotational actuators, but the choice for linear movable actuators is much greater. The reason is that there are so many different type of lineators and mostly custom made.

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The stator in actuator?

                      The stator has a physical and a constructional function. First it is the closing way for the magnetic fields and made of magnet iron. Magnet iron is a general name for all kinds of iron that has favorably properties for magnetic fields. Second the stator gives protection and solidity to the actuator. Next it has often some possibilities for assembling as screwing holes, assembling shields and sockets. The bearings of the shaft are also mounted on the stator. The stator has copper windings for generating a magnetic field in the air gap or generating an magnetic force. The windings can be replaced by permanent magnets with the same function as the stator windings. For decreasing the magnetical losses the stator is mostly made as a laminated core structure. In small mechatronic products the stator is highly integrated with the whole construction. 

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The general running principle of actuators?

The actuator has an electrical side and a mechanical side. The most important principle is that current in an electrical conductor move inside of a magnetical field. Such actuators has the ability to convert electrical energy to mechanical energy and vice versa. The energy conversion takes place in and around the rotor. It is easy to explain the conversion with the Lorentz-force law. The actuator is working in motor mode when electrical power is transformed to mechanical power. It is in generator mode as mechanical power is transformed to electrical power. When an actuator gets both electrical and mechanical energy input it is a dissipator (plugging mode). This mode can be used as a brake. Figure shows schematically the electrical mechanical converter with the possible energy flows. A magnetic field is necessarily for the conversion, which gives always losses of electrical, mechanical and magnetical nature. The mechanical losses are ventilation, the static and viscous friction; electrical losses are conduction (copper) losses. The magnetical losses can be iron losses (eddy current) or indirect from leakage fields. In chapter 2 the magnetical losses will be described. All the losses caused an irritating heat, which reduces the functions of the actuator.

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PRINCIPLE AND CONSTRUCTION OF AN ELECTRICAL ACTUATOR?

         The actuator consists of a not movable part called the stator and a movable part the rotor or armature. Both parts are separated by an air gap, whose thickness can variate between about 0,1 mm to 2 mm. Magnetic an air gap is a disadvantageously property and should be as small as possible. Both the stator and rotor can contain windings or permanent magnets. As described above the important parts are:
The stator
The rotor
The windings

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ELECTRICAL ACTUATOR IN MECHATRONIC DESIGNS?

- The power. 

               There is an electrical source needed for the power for actuator and electronic controllers. Examples are the AC- main voltage supply 230/400 V 50 Hz, a battery or a generator. It will be clear that the used power influenced the choice of the actuator.

- The convertor.

             This part is responsible for current and voltage for the actuator needed for realizing the desired movements of the mechanical load.. The controller gives input signal for the convertor. Sometimes the convertor and controller are combined to one unit. The feedback of the load (position, speed) and the current of the actuator controls the convertor. Examples are frequency controllers for induction motors, controlled current sources for direct current (DC)-motors, servo-amplifiers and rectifier circuits.

- The actuator.

             The conversion of electrical energy to mechanical energy is done by the actuator and vice versa. Examples are step-motors, induction motors, relay, magnetical valve.

- The transmission. 

         Through the transmission the actuator is connected to the load. The transmission is an adjustment between the mechanical behaviour of the actuator and the load. The transmission is frequently a source of error (friction, margin, backlash), that is why the transmission is avoided and sometimes the actuator is direct coupled to the load (direct drive). Examples are a magnetic transmission, cogwheels and slip transmission.

- The load. 

           The load is the whole of desired movements of an object or a tool. The movements can be linear or rotational. Examples are rotation with a constant speed, go to a position with a defined accuracy and a movement of a mass accordently with a speed profile.

- The controller. 

         This part is the heart of the drive system. Dependent on reference input signals and the sensor signals, the controller will react so that the whole system is working alright. Sometimes the protection of the drive system is integrated with the controller. The controller exists for a great part of electronic devices (micro-controllers). In some cases the converter and controller build as one unit. The data processing is more and more done in a digital way. Also the modern sensors generate digital signals. This is one of the reasons that software plays an important role for controllers. The Digital Signal Processor is a complete computer system with parallel data processing and often used as controllers. They are very fast.

- The sensors. 

         Several quantity of the drive system has to be measured as data input for the controller. Those devices are called sensors or transducers, they transform a physical quantity into an electrical signal. In figure some incoming lines for the controller connected with a sensor. The sensor signals define the mechanical behavior of the load and the electrical behavior of the actuator. Some sensors generate signals for protection (end-switches). Examples are optical transducers for position, speed, resolvers, tachogenerators and Hall-transducers, current and voltage transducers. 

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