Timbermill Controller - Seminar Report

Introduction

Today world is looking for efficient and accurate mechanism to control industrial operations. Timber mill is such an industry. There heavy woods are placed on a platform on a rail to move it through the running saw. A worker will drive a steering to move the platform along the rail. The forward and reverse direction of the platform is depending on the direction of the steering. It is totally a mechanical and manpower consuming process.  

Here an electronic system is introduced to manage the platform on the rail. This will eliminate the use of manpower and provides more accuracy. An electric motor is used to drive the platform. By controlling the power to the motor the operator can control the speed and movements of the platform. The direction of the motor controls the direction of the platform.  Operator can manage it with a single switch.

Working

Digitizing the interface, power electronic control for electrical control and motorizing the drive are the main ideas used for building a timber mill controller. In advanced technology equipments feather touch switches using for human machine interaction. In this project three switches used are in this type. To increase to decrease and to reset the speed of the motor this type of switch is used. A monostable multivibrator is used to prevent the false trigger of switch.

An up-down counter will manage the increment and decrement of the motor speed. A pulse on the up counter input the counter increments its four bit binary output. The down counter decrements the same output when it receives a pulse. That means the four bit binary value decides the speed of the motor.

An AC motor is used to control the rail platform. To control the speed of the motor a solid state circuit is used. By varying the firing point of AC cycles, the power in a circuit can be controlled. Four firing circuit are used to achieve four different firing points. Each has a RC circuit which determines the time to trigger.

A selector circuit will enable one out of four firing circuit according to the data from the up-down counter.

A relay circuit is also there to control the direction of the motor. The direction change is achieved by changing the polarity of the winding of the motor.  

Switch and FTP

Micro-button switches are used to give the inputs (Up and Down). While pressing a switch, some noise may be generated. This noise signal may retrigger the input. This trigger is actually a false trigger. A circuit arrangement should be there to prevent this. A monostable multivibrator circuit is used to prevent the false triggers.

Up-Down Counter

This section is used to determine the speed of the motor. A mode counters with two inputs and single output buffer is used for this purpose. Input UP increments and input DOWN decrements the counter value. A four bit binary represents the output.

Switching Circuit

In output section, only one firing circuit is working at a time. Since the output of Up-Down counter is a four bit binary, a circuit should be there to select the firing circuit according to the value of Up-Down counter.  A de-multiplexer IC is used for this purpose.

Firing Circuit

The motor used is an AC motor. So regulating the AC supply is the best way to control the speed of the motor. A solid state regulator is used to control the AC. It starts conducting only after when it get fired. So by selecting different the firing points in the cycles it is possible to control the speed of the motor. A RC circuit determines the time to trigger.  

TRIAC

The TRIAC is the solid state switch.

Direction

A toggle switch is used to select the direction. It determines the position of relay.

Relay

The relays are used to change the polarity of current flow through the motor winding.

CIRCUIT DESCRIPTION

A timber mill controller has the following circuits section.

1. Switch and FTP

2. UP-DOWN Counter

3. Selector

4. Opto-couplers

5. Firing circuit

6. Output

Switch and FTP

        This circuit is used to take speed control inputs from the operator. It has two push button micro-switches. The output of this switch is connected to the input of a monostable multivibrator (IC 555). The multivibrator is the False Trigger Preventer. When the switch is pressed the input of monostable multivibrator goes low and gets triggered. Now the output of the MV goes to a quasi stable state and returns after a certain time. This output clocks the counter in the next stage. The monostable multivibrator will not accept any change in its input during the quasi stable state.

UP-DOWN Counter

          IC 74LS193 is used as the Up-Down counter. The output of monostable multivibrator is connected to the input of this IC. It has a reset pin and it is connected to the reset switch. The operator can reset the count to the initial value by resetting the IC. Depend on the input IC increments or decrements the count. The counter value is available on its four output pins.

Selector

           IC CD4067, a multiplexer/de-multiplexer, is used to achieve selection function. The four bit output of counter section is connected to this IC. This circuit selects the firing circuit according to the counter value. The output of this circuit is routed to firing circuits through opto-couplers.

Opto-couplers

              Opto-couplers are used to maintain an electrical isolation between digital circuit and AC circuit. Combination of LED and Diac are used in this opto-coupler.  A HIGH on input illuminates the led and the light of LED makes the Diac conducting. The Diac handles AC required for the firing circuit.

Firing Circuits

                  A resistor capacitor combination and a Diac are the components used in the firing circuit. In each half cycles of AC, the capacitor charges through the resistor. When the voltage reaches the firing point of Diac, it fires the Triac. The charging of capacitor is initialized on each AC half cycle’s null point. The time to charge is depending on the resistor value. The opto-coupler is connected in series with resistor and capacitor. So it will work only when the opto-coupler is on.

Output

               The output section has two units to control the motor. One is a Triac and other is a relay. Triac controls the power of the motor and relay controls the direction of the motor.  

Power Supply

A 12V step down transformer is used to step down the 230V to 12V. The bridge rectifier is constructed with 1N4007 diodes. A 1000MFD capacitor is used to filter the DC.

PCB Fabrication

Laser printers and photocopiers use plastic toner, not ink, to draw images. Toner is the black powder that ends up on your clothes and desk when replacing the printer cartridge. Being plastics, toner is resistant to etching solutions used for making PCBs - if only we could get it on copper! Modifying a printer for working with copper is out of question, but we can work around it with the toner-transfer principle. Like most plastics, toner melts with heat, turning in a sticky, glue-like paste. So why not print on paper as usual, place the sheet face-down on PCB copper, and melt toner on copper applying heat and pressure.

The perfect paper should be: glossy, thin, and cheap. Cut the paper to a size suitable for your printer. Try to get straight, clean cuts, as jagged borders and paper dust are more prone to clog printer mechanism. An office cutter is ideal, but also a blade-cutter and a steady hand work well.

Laser printers are not designed for handling thin, cheap paper, so we must help them feeding the sheets manually instead of using the paper tray. Selecting a straight paper path minimizes the chances of clogging. This is usually achieved setting the printer as if it were printing on envelopes.

We want to put as much toner on paper as possible, so disable “toner economy modes” and set printer properties to the maximum contrast and blackness possible. We want to print your PCB to exact size, so disable any form of scaling/resizing (e.g. “fit to page”). If your printer driver allows, set it to “center to page” as it helps to get the right position using a non-standard size sheet.

Print the PCB layout as usual, except we must setup the printer as described above and you must print a mirrored layout.

PCB material is fibreglass like, and a trick to cut it effortlessly is to score a groove with a blade cutter or a glass cutter. The groove weakens the board to the point that bending it manually breaks it along the groove line. This method is applicable only when cutting the whole board along a line that goes from side to side, that is we can’t cut a U or L shaped board with it.

For small boards, lock the PCB material in a vice, aligning vice edge and cut line. Use an all-aluminium vice which is soft and doesn’t scratch copper, if we use a steel vice protect copper surface with soft material.

Using the vice as a guide, score BOTH board sides with a blade cutter (be careful) or another sharp, hardened tool (e.g. a small screwdriver tip). Ensure to scratch edge-to-edge. Repeat this step 5-6 times on each side.

Bend the board. If groove is deep enough, the board will break before reaching a 30 degrees bend. It will break quite abruptly so be prepared and protect our hands with gloves.

To make paper alignment easier, cut a piece of PCB material that is larger (at least 10mm/0,39 inch for each side) than the final PCB.

It is essential that the copper surface is spotlessly clean and free from grease that could adverse etching. To remove oxide from copper surface, use the abrasive spongy scrubs sold for kitchen cleaning. It’s cheaper than ultra-fine sandpaper and reusable many times. Metallic wool sold for kitchen cleaning purposes also works. Thoroughly scrub copper surface until really shiny. Rinse and dry with a clean cloth or kitchen paper.

To make paper alignment easy, cut excess paper around one corner (leave a small margin though). Leave plenty of paper on the other sides to fix the paper to the desk. As the board is larger than the final PCB, there is large margin for easy placement of paper on copper.

Turn the iron to its maximum heat (COTTON position) and turn off steam, if present. While the iron warms up, position the materials on the table. Don’t work on an ironing board as its soft surface makes it difficult to apply pressure and keep the PCB in place. Protect table surface with flat, heat-resistant material (e.g. old magazines) and place the board on top, copper face up. Lock the board in place with double-adhesive tape. Position the PCB printout over the copper surface, toner down, and align paper and board corners. Lock the paper with scotch tape along one side only. This way, we can flip the paper in and out instantly.

Flip out the paper, and preheat copper surface placing the iron on top of it for 30 seconds. Remove the iron, flip back paper into its previous position over the copper. It is essential that paper does not slip from its position. We can also cover with a second sheet of blank paper to distribute pressure more evenly. Keep moving the iron, while pressing down as evenly as we can, for about one minute.

Remove the iron and let the board to cool down.

This is the fun part. When the board is cool enough to touch, trim excess paper and immerge in water. Let it soak for 1 minute, or until paper softens.

Cheap paper softens almost immediately, turning into a pulp that is easy to remove rubbing with your thumb. Keep rubbing until all paper dissolves (usually less than 1 minute). Don’t be afraid to scratch toner, if it has transferred correctly it forms a very strong bond with copper.

The board with all paper removed. It is OK if some microscopic paper fibres remain on the toner (but remove any fibre from copper), giving it a silky feeling. It is normal that these fibres turn a little white when dry.

There are many alternatives for etching liquids, and we can use the one that suits your taste. Using ferric chloride (the brown stuff): it’s cheap, can be reused many times, and doesn’t require heating. Actually, moderate heating can speed up etching, but  find it reasonably fast also at room temperature (10…15 minutes).

The down side of this stuff is that it’s incredibly messy. It permanently stains everything it gets in contact with: not only clothes or skin (never wear your best clothes when working with it!), but also furniture, floor tiles, tools, everything. It is concentrated enough to corrode any metal – including your chrome-plated sink accessories. Even vapours are highly corrosive: don’t forget the container open or it will turn any tool or metallic shelf nearby into rust.

For etching, place the container on the floor (some scrap cardboard or newspaper to protect the floor from drops). Fit the board on the hanger, and submerge the PCB. Stir occasionally by waving the hanger.

First impression may be that nothing happens, but in less than 10 minutes some copper is removed, making first tracks to appear. From now on, stir continuously and check often, as the process completes rather quickly. We don’t want to overdo it, otherwise thinner tracks start being eroded sideways. As a rule of thumb, stop 30 seconds after we don’t see any copper leftovers over large areas.

Rinse the board with plenty, plenty, plenty of water.

PCB layout

The PCB design process typically involves placing and connecting parts; specifying how they're to be packaged; uniquely identifying them; adding information for simulation, synthesis, board layout, purchasing, or other external functions; and incorporating information from external functions.

Once you finish a first pass at placing and connecting parts, use the commands on the Tools menu in the project manager to complete the process. Click on the command names in the figure for information about the tool commands.

As shown in the figure, you use Annotate, Design Rules Check, and Cross Reference to package the parts in your design and make sure there are no unconnected parts, unwanted connections, or other invalid design conditions. In practice, you might run these tools several times before moving on to the next phase.

Generally, you should run Design Rules Check to verify your design before you generate a netlist. This allows for more efficient netlist creation, and you can concentrate on netlist-specific problems if they should occur during the Create Netlist process. Design Rules Check warns you if certain conditions exist in your design. The severity of the specific problem may prevent completion of the design. Other conditions are subject to your judgment, and may be of no consequence. Once you are satisfied with the results of design tests like Design Rules Check, and then proceed with the creation of a netlist.

You can add properties or change their values at any point, and there are several ways to do this. If you want to change the value of one or two properties, just edit them on the schematic page. To edit properties on many parts at the same time, use Update Properties or Capture's built-in spreadsheet editor (from the Edit menu, choose Browse and then Parts). If you're more comfortable editing in a full-featured spreadsheet or database program, use Export Properties to write design data out and Import Properties to read the changes back in.

Once you're satisfied with your design use Create Netlist to create a netlist in any of the formats supported by Capture. This is often the point at which you use Bill of Materials to create a list of parts used in the design.

Use Back Annotate to incorporate any packaging changes necessary because of routing or manufacturing constraints. You may need to add or modify properties again or make other changes in the design, as shown in the figure.

Preparing a Capture design for Layout is a two-part process. First, you must create a valid design and then create a netlist in an .MNL format for Layout. After you have prepared your Capture design, you can create a new Layout design using the .MNL netlist.

You can bring Capture netlist information into Layout in two ways. You can choose one of the AutoECO options to merge the netlist with the board file, or you can select the Run ECO to Layout option in Capture (in the Create Netlist dialog box) to automatically communicate modifications to Layout. If the board file is open when you update the netlist file, Layout automatically displays a dialog box asking if you want to load the new netlist file. If the board file is not open when the netlist changes, Layout prompts you to load the modified netlist when you re-open the board file. Then after auto placing or manual placing auto-routing will complete all routing works. If not completed then we can route manually

COMPONENT STUDY

RELAYS

    Basically, a relay is an electrically operated switch, and actually the predecessor of the transistor. Solenoids are relays also but the very large types which carry huge amounts of current. Relays are the smaller types. Relays come in three types: electro mechanical, solid-state, and so-called hybrids which are a combination of the first two. There are also some specialized types that fall into neither category but I will deal with them later in this tutorial. Lets take electro-mechanical types first, they are available in three main models; armature, plunger, and reed. The Armature Relays are the elegant. Plenty turns of very fine magnet-wire are wound around an iron core to form an electro-magnet. The movable metal armature has an electrical contact that is positioned over a fixed  

contact attached to the relay frame. A spring holds the armature up so that the movable and fixed contacts are normally separated (open). When the coil is energized, it attracts the pivoting armature and pulls it down, closing (make) the SPST contacts and completes the power circuit. Vice-versa, this relay can be made to open the contacts instead of closing them, or can do both either way. The armature relay is pretty old and no longer used in new applications, they do still exist however and are being used still at the time of writing this document.

Relays are components which allow a low-power circuit to switch a relatively high current on and off, or to control signals that must be electrically isolated from the controlling circuit itself. Newcomers to electronics sometimes want to use a relay for this type of application, but are unsure about the details of doing so. Here.s a quick rundown to make a relay operate, you have to pass a suitable .pull-in. and holding current (DC) through its energising coil. And generally relay coils are designed to operate from a particular supply voltage often 12V or 5V, in the case of many of the small relays used for electronics work. In each case the coil has a resistance which will draw the right pull-in and holding currents when its connected to that supply voltage. So the basic idea is to choose a relay with a coil designed to operate from the supply voltage you are using for your control circuit and then provide a suitable .relay driver circuit so that

your low-power circuitry can control the current through the relays coil. Typically this will be somewhere between 25mA and 70mA Often your relay driver can be very simple, using little more than an NPN or PNP transistor to control the coil current. All your low-power circuitry has to do is provide enough base current to turn the transistor on and off, as you can see from diagrams A and B.

regulated power supply

   Most digital logic circuits and processors need a 5 volt power supply. To use these parts we need to build a regulated 5 volt source. To make a 5 volt power supply, we use a LM7805 voltage regulator IC (Integrated Circuit). The IC is shown below.

The LM7805 is simple to use. You simply connect the positive lead of your unregulated DC power supply (anything from 9VDC to 24VDC) to the Input pin, connect the negative lead to the Common pin and then when you turn on the power, you get a 5 volt supply from the Output pin. Sometimes the input supply line may be noisy. To help smooth out this noise and get a better 5 volt output, a capacitor is usually added to the circuit, going between the 5 volt output and ground (GND). We use a 220 uF capacitor. 12V supply is also made in a same manner

AC motors

Main article: AC motor

In 1882, Nikola Tesla discovered the rotating magnetic field, and pioneered the use of a rotary field of force to operate machines. He exploited the principle to design a unique two-phase induction motor in 1883. In 1885, Galileo Ferraris independently researched the concept. In 1888, Ferraris published his research in a paper to the Royal Academy of Sciences in Turin.

Tesla had suggested that the commutators from a machine could be removed and the device could operate on a rotary field of force. Professor Poeschel, his teacher, stated that would be akin to building a perpetual motion machine.[17] Tesla would later attain U.S. Patent 0,416,194, Electric Motor (December 1889), which resembles the motor seen in many of Tesla's photos. This classic alternating current electro-magnetic motor was an induction motor.

Michail Osipovich Dolivo-Dobrovolsky later invented a three-phase "cage-rotor" in 1890. This type of motor is now used for the vast majority of commercial applications.

Components

A typical AC motor consists of two parts:

· An outside stationary stator having coils supplied with AC current to produce a rotating magnetic field, and;

· An inside rotor attached to the output shaft that is given a torque by the rotating field.

 Torque motors

A torque motor (also known as a limited torque motor) is a specialized form of induction motor which is capable of operating indefinitely while stalled, that is, with the rotor blocked from turning, without incurring damage. In this mode of operation, the motor will apply a steady torque to the load (hence the name).

A common application of a torque motor would be the supply- and take-up reel motors in a tape drive. In this application, driven from a low voltage, the characteristics of these motors allow a relatively-constant light tension to be applied to the tape whether or not the capstan is feeding tape past the tape heads. Driven from a higher voltage, (and so delivering a higher torque), the torque motors can also achieve fast-forward and rewind operation without requiring any additional mechanics such as gears or clutches. In the computer gaming world, torque motors are used in force feedback steering wheels.

Another common application is the control of the throttle of an internal combustion engine in conjunction with an electronic governor. In this usage, the motor works against a return spring to move the throttle in accordance with the output of the governor. The latter monitors engine speed by counting electrical pulses from the ignition system or from a magnetic pickup [18] and, depending on the speed, makes small adjustments to the amount of current applied to the motor. If the engine starts to slow down relative to the desired speed, the current will be increased, the motor will develop more torque, pulling against the return spring and opening the throttle. Should the engine run too fast, the governor will reduce the current being applied to the motor, causing the return spring to pull back and close the throttle.

Slip ring

The slip ring is a component of the wound rotor motor as an induction machine (best evidenced by the construction of the common automotive alternator), where the rotor comprises a set of coils that are electrically terminated in slip rings. These are metal rings rigidly mounted on the rotor, and combined with brushes (as used with commutators), provide continuous unswitched connection to the rotor windings.

In the case of the wound-rotor induction motor, external impedances can be connected to the brushes. The stator is excited similarly to the standard squirrel cage motor. By changing the impedance connected to the rotor circuit, the speed/current and speed/torque curves can be altered.

(Slip rings are most-commonly used in automotive alternators as well as in synchro angular data-transmission devices, among other applications.)

The slip ring motor is used primarily to start a high inertia load or a load that requires a very high starting torque across the full speed range. By correctly selecting the resistors used in the secondary resistance or slip ring starter, the motor is able to produce maximum torque at a relatively low supply current from zero speed to full speed. This type of motor also offers controllable speed.

Motor speed can be changed because the torque curve of the motor is effectively modified by the amount of resistance connected to the rotor circuit. Increasing the value of resistance will move the speed of maximum torque down. If the resistance connected to the rotor is increased beyond the point where the maximum torque occurs at zero speed, the torque will be further reduced.

When used with a load that has a torque curve that increases with speed, the motor will operate at the speed where the torque developed by the motor is equal to the load torque. Reducing the load will cause the motor to speed up, and increasing the load will cause the motor to slow down until the load and motor torque are equal. Operated in this manner, the slip losses are dissipated in the secondary resistors and can be very significant. The speed regulation and net efficiency is also very poor.

Stepper motors

Closely related in design to three-phase AC synchronous motors are stepper motors, where an internal rotor containing permanent magnets or a magnetically-soft rotor with salient poles is controlled by a set of external magnets that are switched electronically. A stepper motor may also be thought of as a cross between a DC electric motor and a rotary solenoid. As each coil is energized in turn, the rotor aligns itself with the magnetic field produced by the energized field winding. Unlike a synchronous motor, in its application, the stepper motor may not rotate continuously; instead, it "steps" — starts and then quickly stops again — from one position to the next as field windings are energized and de-energized in sequence. Depending on the sequence, the rotor may turn forwards or backwards, and it may change direction, stop, speed up or slow down arbitrarily at any time.

Simple stepper motor drivers entirely energize or entirely de-energize the field windings, leading the rotor to "cog" to a limited number of positions; more sophisticated drivers can proportionally control the power to the field windings, allowing the rotors to position between the cog points and thereby rotate extremely smoothly. This mode of operation is often called microstepping. Computer controlled stepper motors are one of the most versatile forms of positioning systems, particularly when part of a digital servo-controlled system.

Stepper motors can be rotated to a specific angle in discrete steps with ease, and hence stepper motors are used for read/write head positioning in computer floppy diskette drives. They were used for the same purpose in pre-gigabyte era computer disk drives, where the precision and speed they offered was adequate for the correct positioning of the read/write head of a hard disk drive. As drive density increased, the precision and speed limitations of stepper motors made them obsolete for hard drives—the precision limitation made them unusable, and the speed limitation made them uncompetitive—thus newer hard disk drives use voice coil-based head actuator systems. (The term "voice coil" in this connection is historic; it refers to the structure in a typical (cone type) loudspeaker. This structure was used for a while to position the heads. Modern drives have a pivoted coil mount; the coil swings back and forth, something like a blade of a rotating fan. Nevertheless, like a voice coil, modern actuator coil conductors (the magnet wire) move perpendicular to the magnetic lines of force.)

Stepper motors were and still are often used in computer printers, optical scanners, and digital photocopiers to move the optical scanning element, the print head carriage (of dot matrix and inkjet printers), and the platen. Likewise, many computer plotters (which since the early 1990s have been replaced with large-format inkjet and laser printers) used rotary stepper motors for pen and platen movement; the typical alternatives here were either linear stepper motors or servomotors with complex closed-loop control systems.

So-called quartz analog wristwatches contain the smallest commonplace stepping motors; they have one coil, draw very little power, and have a permanent-magnet rotor. The same kind of motor drives battery-powered quartz clocks. Some of these watches, such as chronographs, contain more than one stepping motor.

Stepper motors were upscaled to be used in electric vehicles under the term SRM (Switched Reluctance Motor).

[edit] Linear motors

Main article: Linear motor

A linear motor is essentially an electric motor that has been "unrolled" so that, instead of producing a torque (rotation), it produces a straight-line force along its length by setting up a traveling electromagnetic field.

Linear motors are most commonly induction motors or stepper motors. You can find a linear motor in a maglev (Transrapid) train, where the train "flies" over the ground, and in many roller-coasters where the rapid motion of the motorless railcar is controlled by the rail. On a smaller scale, at least one letter-size (8.5" x 11") computer graphics X-Y pen plotter made by Hewlett-Packard (in the late 1970s to mid 1980's) used two linear stepper motors to move the pen along the two orthogonal axes.

 Feeding and windings

 Doubly-fed electric motor

Main article: Doubly-fed electric machine

Doubly-fed electric motors have two independent multiphase windings that actively participate in the energy conversion process with at least one of the winding sets electronically controlled for variable speed operation. Two is the most active multiphase winding sets possible without duplicating singly-fed or doubly-fed categories in the same package. As a result, doubly-fed electric motors are machines with an effective constant torque speed range that is twice synchronous speed for a given frequency of excitation. This is twice the constant torque speed range as singly-fed electric machines, which have only one active winding set.

A doubly-fed motor allows for a smaller electronic converter but the cost of the rotor winding and slip rings may offset the saving in the power electronics components. Difficulties with controlling speed near synchronous speed limit applications.

Singly-fed electric motor

Singly-fed electric motors incorporate a single multiphase winding set that is connected to a power supply. Singly-fed electric machines may be either induction or synchronous. The active winding set can be electronically controlled. Induction machines develop starting torque at zero speed and can operate as standalone machines. Synchronous machines must have auxiliary means for startup, such as a starting induction squirrel-cage winding or an electronic controller. Singly-fed electric machines have an effective constant torque speed range up to synchronous speed for a given excitation frequency.

The induction (asynchronous) motors (i.e., squirrel cage rotor or wound rotor), synchronous motors (i.e., field-excited, permanent magnet or brushless DC motors, reluctance motors, etc.), which are discussed on this page, are examples of singly-fed motors. By far, singly-fed motors are the predominantly installed type of motors.

Nanotube nanomotor

Researchers at University of California, Berkeley, recently developed rotational bearings based upon multiwall carbon nanotubes. By attaching a gold plate (with dimensions of the order of 100 nm) to the outer shell of a suspended multiwall carbon nanotube (like nested carbon cylinders), they are able to electrostatically rotate the outer shell relative to the inner core. These bearings are very robust; devices have been oscillated thousands of times with no indication of wear. These nanoelectromechanical systems (NEMS) are the next step in miniaturization and may find their way into commercial applications in the future.

See also:

· Molecular motors

· Electrostatic motor

 Efficiency

To calculate a motor's efficiency, the mechanical output power is divided by the electrical input power:

 ,

where η is energy conversion efficiency, Pe is electrical input power, and Pm is mechanical output power.

In simplest case Pe = VI, and Pm = Tω, where V is input voltage, I is input current, T is output torque, and ω is output angular velocity. It is possible to derive analytically the point of maximum efficiency. It is typically at less than 1/2 the stall torque.

Implications

Because a DC motor operates most efficiently at less than 1/2 its stall torque, an "oversized" motor runs with the highest efficiency. IE: using a bigger motor than is necessary enables the motor to operate closest to no load, or peak operating conditions.

Torque capability of motor types

When optimally designed for a given active current (i.e., torque current), voltage, pole-pair number, excitation frequency (i.e., synchronous speed), and core flux density, all categories of electric motors or generators will exhibit virtually the same maximum continuous shaft torque (i.e., operating torque) within a given physical size of electromagnetic core. Some applications require bursts of torque beyond the maximum operating torque, such as short bursts of torque to accelerate an electric vehicle from standstill. Always limited by magnetic core saturation or safe operating temperature rise and voltage, the capacity for torque bursts beyond the maximum operating torque differs significantly between categories of electric motors or generators.

Note: Capacity for bursts of torque should not be confused with Field Weakening capability inherent in fully electromagnetic electric machines (Permanent Magnet (PM) electric machine are excluded). Field Weakening, which is not readily available with PM electric machines, allows an electric machine to operate beyond the designed frequency of excitation without electrical damage.

Electric machines without a transformer circuit topology, such as Field-Wound (i.e., electromagnet) or Permanent Magnet (PM) Synchronous electric machines cannot realize bursts of torque higher than the maximum designed torque without saturating the magnetic core and rendering any increase in current as useless. Furthermore, the permanent magnet assembly of PM synchronous electric machines can be irreparably damaged, if bursts of torque exceeding the maximum operating torque rating are attempted.

Electric machines with a transformer circuit topology, such as Induction (i.e., asynchronous) electric machines, Induction Doubly-Fed electric machines, and Induction or Synchronous Wound-Rotor Doubly-Fed (WRDF) electric machines, exhibit very high bursts of torque because the active current (i.e., Magneto-Motive-Force or the product of current and winding-turns) induced on either side of the transformer oppose each other and as a result, the active current contributes nothing to the transformer coupled magnetic core flux density, which would otherwise lead to core saturation.

Electric machines that rely on Induction or Asynchronous principles short-circuit one port of the transformer circuit and as a result, the reactive impedance of the transformer circuit becomes dominant as slip increases, which limits the magnitude of active (i.e., real) current. Still, bursts of torque that are two to three times higher than the maximum design torque are realizable.

The Synchronous WRDF electric machine is the only electric machine with a truly dual ported transformer circuit topology (i.e., both ports independently excited with no short-circuited port). The dual ported transformer circuit topology is known to be unstable and requires a multiphase slip-ring-brush assembly to propagate limited power to the rotor winding set. If a precision means were available to instantaneously control torque angle and slip for synchronous operation during motoring or generating while simultaneously providing brushless power to the rotor winding set (see Brushless wound-rotor doubly-fed electric machine), the active current of the Synchronous WRDF electric machine would be independent of the reactive impedance of the transformer circuit and bursts of torque significantly higher than the maximum operating torque and far beyond the practical capability of any other type of electric machine would be realizable. Torque bursts greater than eight times operating torque have been calculated.

ADVANTAGES

1. It user friendly

2. Lowers the manual efforts

3. Saves time.

4. It avoids accidents due to overloading the Saw.

APPLICATIONS

1. Complicated work can be simply implemented by digital ICs.

2. Human efforts can be reduced.

3. Industrial application

4. Same principle is used lift and crane

CONCLUSION

Timber mill automation offers a lot of advantages to the owners, operators and customers. Speeding up the work, accuracy eliminates amount of waste and automation lowers manpower.

This timber mill controller is only a part of the total timber mill automation solution. But it offers a lot of advantages. The rail platform management is a risky work. The speed may cause overloading in the saw. This will break the saw and cause accidents. This project offers a solution for the speed controlling of the rail platform.