EJ501 PLC AND AUTOMATION SYSTEM

The automatic operation or control of equipment, a process, or a system.The techniques and equipment used to achieve automatic operation or control.The condition of being automatically controlled or operated.

Productivity gains and cost reductionReliability and precisionHealth and environmentConvertibility and turnaround time

Replacing human operators in tasks that involve hard physical or monotonous work. Replacing humans in tasks done in dangerous environments (i.e. fire, space, volcanoes, nuclear facilities, underwater, etc.)Performing tasks that are beyond human capabilities of size, weight, speed, endurance, etc.Economy improvement: Automation may improve in economy of enterprises, society or most of humanity. For example, when an enterprise invests in automation, technology recovers its investment; or when a state or country increases its income due to automation like Germany or Japan in the 20th Century.

Unemployment rate increases due to machines replacing humans and putting those humans out of their jobs.Technical Limitation: Current technology is unable to automate all the desired tasks.Security Threats/Vulnerability: An automated system may have limited level of intelligence; hence it is most likely susceptible to commit error.Unpredictable development costs: The research and development cost of automating a process may exceed the cost saved by the automation itself.High initial cost: The automation of a new product or plant requires a huge initial investment in comparison with the unit cost of the product, although the cost of automation is spread in many product batches.

Fixed/Hardwired automationA process using mechanized machinery to perform fixed and repetitive operations in order to produce a high volume of similar parts. A good example of this would be an automated production line where a series of workstations are connected by a transfer system to move parts between the stations. What starts as a piece of sheet metal in the beginning of the process, becomes a car at the end.

Characteristics:Justified/used where production rates/volumes are highHigh initial investment for custom engineered equipmentNormally cannot accommodate product changesDepend largely on skill to organize the operationsProduces large numbers of nearly identical partsProduct design must be stable over its life

Examples:Mechanized assembly linesMechanical lines

Programmable automation

Programmable automation is a form of automation for producing products in batches. The products are made in batch quantities ranging from several dozen to several thousand units at a time. For each new batch, the production equipment must be reprogrammed and changed over to accommodate the new product style.

Characteristics:Sequence controlled by a programHigh investment in general purpose equipmentLower production ratesFlexibility to deal with variationSuitable for batch production

Smaller volumes (than fixed) of many different partsMore flexible than fixed automationMajor disadvantage: setup prior to each new partLarge batch size (due to setups)Speed sacrificed for flexibility

Examples:Numerically controlled (NC) machinesIndustrial robots

Flexible automationFlexible Automation is an extension of programmable automation. It is a system capable of producing a variety ofproducts with virtually no time lost due to the change over from one product to next or one part style to the next. There is no lost production time while reprogramming the system and altering the physical combination and schedules of parts or products instead of requiring that they be made in batches. It is designed to manufacture a variety of product or parts with low production rates, varying product design and demand.

Characteristics:It is extension of programmable automationNo time lost for change overHigh investment in custom-engineered systemsProduction of product mix

Flexibility to deal with design variationsLow to medium quantitiesCompromise between fixed and programmable automation in speed and flexibilityAdvantage: programming and setup performed off-lineMore expensive - size and tool change capabilitiesSmall batch sizes are justified - reduced WIP and lead timeTypical parts are expensive, large and require some complex machining

Examples:Use of pallet fixtures for holding partsFMS (Flexible manufacturing systems)Automated Guided Vehicles (AGV) for material handling

Increase production rate eliminate portions of process that directly increase production time: machine processing time, handling time, setup times (SMED)Remove humans from hazardous environments exposure to chemicals, fumes, temperature or radiation robotic applications: L/UL furnaces, spray painting, weldingRemove humans from processes that require extremely clean environments: e.g., semiconductors, drugsReduce number of defective productsReduce direct labor one worker monitors a larger number of machineIncrease production rateStrengths of (computer-based) machinesPerform repetitive tasks consistentlyStore large amounts of dataRetrieve data from memory reliablyPerform multiple tasks simultaneouslyApply high forces and powerPerform computations quickly

Labor resistanceCost of upgraded labor ; Chrysler Detroit plant spend 1 million hours of retrainingInitial investmentManagement of process improvementIntellectual assets versus technological assetsAppropriate use of technologyA system approach to automation is importantEquipment incompatibilities

Relays are electromagnetically actuated switches. They consist of housing with electromagnet and movable contacts. An electromagnetic field is created when a voltage is applied to the coil of the electromagnet. This results in attraction of the movable armature to the coil core. The armature actuates the contact assembly. The contact assembly can open or close a specific number of contacts by mechanical means. If the flow of current through the coil is interrupted, a spring returns the armature to its original position.

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Relays are either Normally Open or Normally Closed. Normally open relays have a switch that remains open until energized (ON) while normally closed relays are closed until energized.

All relays operate using the same basic principle. Our example will use a commonly used 4 - pin relay. Relays have two circuits: A control circuit (shown in GREEN) and a load circuit (shown in RED). The control circuit has a small control coil while the load circuit has a switch. The coil controls the operation of the switch.

Relay energized (ON)Current flowing through the control circuit coil (pins 1 and 3) creates a small magnetic field which causes the switch to close, pins 2 and 4. The switch, which is part of the load circuit, is used to control an electrical circuit that may connect to it. Current now flows through pins 2 and 4 shown in RED, when the relay in energized.

Relay de-energized (OFF)When current stops flowing through the control circuit, pins 1 and 3, the relay becomes de-energized. Without the magnetic field, the switch opens and current is prevented from flowing through pins 2 and 4. The relay is now OFF.

When no voltage is applied to pin 1, there is no current flow through the coil. No current means no magnetic field is developed, and the switch is open. When voltage is supplied to pin 1, current flow though the coil creates the magnetic field needed to close the switch allowing continuity between pins 2 and 4.

SPST Single Pole Single ThrowThese have two terminals which can be connected or disconnected. Including two for the coil, such a relay has four terminals in total. It is ambiguous whether the pole is normally open or normally closed. The terminology "SPNO" and "SPNC" is sometimes used to resolve the ambiguity.

SPDT - Single Pole Double Throw A common terminal connects to either of two others. Including two for the coil, such a relay has five terminals in total.

DPST - Double Pole Single ThrowThese have two pairs of terminals. Equivalent to two SPST switches or relays actuated by a single coil. Including two for the coil, such a relay has six terminals in total.

DPDT - Double Pole Double ThrowThese have two rows of change-over terminals. Equivalent to two SPDT switches or relays actuated by a single coil. Such a relay has eight terminals, including the coil.

The "S" or "D" may be replaced with a number, indicating multiple switches connected to a single actuator. For example 4PDT indicates a four pole double throw relay (with 14 terminals).

Relays are remote control electrical switches that are controlled by another switch, such as a horn switch or a computer as in a power train control module. Relays allow a small current flow circuit to control a higher current circuit.

Contactor is a control device that uses a small control current to energize or de-energize the load connected to it. A contactor possesses several contact elements, normally between 4 and 10. There are also different types of contactors with various combinations of normally closed contacts, normally open contacts, changeover contacts, delayed normally closed contacts etc. The contacts are divided into coil, main contact elements and auxiliary contacts (control contacts).

Coil to control the switching of the contacts.Main contact main contact elements for power switching are also called power contactors (main contactors).Additional contact/Auxiliary contact used to simultaneously switch further control functions or logic operations.

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Contactors work on the same basic principle as relays. The typical features of contactor are:double- break ( 2 break points per contact),positive-action contacts and closed arcing chambers (spark arresting chambers).

A magnetic motor starter is an electrically-operated switch (contactor) that includes motor overload protection. Magnetic motor starters are identical to contactors except that they have overloads attached to them. The overloads have heaters or electronic overloads (located in the power circuit) which sense excessive current flow to the motor. The heaters open the NC overload contacts (located in the control circuit) when the overload becomes dangerous to the motor.

A category of timers that operate through a combination of electricity and mechanical motion. Electromechanical timers are gradually being replaced by solid state technology.

On-delay action - TR energized, contacts change state after set time intervalOff-delay action - TR de-energized, contacts change state after set time interval

An electromechanical timer uses a small synchronous AC motor turning a cam against a comb of switch contacts. The AC motor is turned at an accurate rate by the alternating current, which power is carefully regulate. The shaft has a clutch that engages or disengages it to the motor. Gears drive a shaft at the desired rate, and turn the cam. When the shaft is engaged (energized), the motor turns the shaft and the cams actuate several sets of contacts. When the time-delay period has elapsed, the time-delay contacts will change from open to closed or from closed to open and the timer motor will reset for the next cycle.

The most common application of this timer now is in washers, driers and dishwashers. This type of timer often has a friction clutch between the gear train and the cam, so that the cam can be turned to reset the time.

A category of counters that operate through a combination of electricity and mechanical motion. Electromechanical counters receive an electrical input signal and convert it to mechanical action to output a count, stop a count, or reset the counter to zero.

Contacts CTR change state after the preset numbers of counts are accumulated by CTR coil symbol. CTR device may also take a reset input that clears counter.

Mechanical counter wheels showing both sides. The bump on the wheel shown at the top engages the ratchet on the wheel below every turn.

Electromechanical counter is an impulse motor driven unit with standard or reverse clutch operation.When power is applied to the clutch terminals on standard units, the clutch engages and instantaneous contacts transfer enabling the counter to receive and register counts. A 40 ms pulse to the count motor will register a count by moving the count progress pointer toward the zero point on the dial. When the progress pointer reaches zero, the unit is counted out and a set of delayed switches transfer. Additional counts will not be registered until the unit is reset. Removal of power from the clutch terminals resets the counter.On reverse action clutch operation, removal of power from the clutch terminals enables the counter to receive counts.

The most common application of this counter now is in printing process, paper copier and vending machine. For example to count the numbers of paper copies.