CHAPTER 13 : COMPUTER NUMERICAL CONTROL (CNC)

CNC (Computer Numerical Control) is a machine that controlled by a computer using a numerical language in process. In other explanation CNC is a flexible method automatically controlling machine through the use of numerical values. So, in CNC machine we didn't use manually operation for example in turning, drilling, and milling using manual or conventional machine. In CNC we can use a computer as an automatically controller for user.
For example below, the CNC machine type milling machine from HAAS :

CNC machine can be analogous as a printer machine. We must design in computer and the execute or print into CNC machine.

Actually, some industry using CNC machines to producing some product, there are two type of CNC machine in manufacturing industry :

1. CNC Machine Two Axis : This machine using two axis, X axis for perpendicular movement and Z Axis for parallel to rotary axis. For examples : Lathe Machine.
2. CNC Machine Three Axis : The machine using three axis, X Axis for horizontal direction movements, Y Axis for transverse direction movements, and Z axis for vertical direction movements. For Example : Milling Machine.

References :

Petruzella, D. Frank (1996). Industrial Electronics. New York : McGraw-Hill 

Nugraha, R. Andias (2014). Manufacturing Process Labwork Module.Bandung : Prosman Laboratory Telkom Universty

CHAPTER 12 : PROGRAMMABLE LOGIC CONTROL (PLC)

Programmable Logic Control (PLC) is a digitally operating electronic which uses a programming memory for internal storage of instructions for implementing specific functions such as logic, sequencing, timing, counting and arithmetic to control through digital or analog modules, various types of machines or process.

There are some components in PLC :

Power Supply : provides the voltage needed to run the primary PLC components.

I/O Modules : Provide signal conversion and isolation between the internal logic and also level signals inside the PLC and fields high level signal.

Processor : provide intelligence to command and govern the activities of the entire PLC systems.

Programming Device : used to enter the desired program that will determine the sequence of operation and control of process equipment or driven machine.

Memory : used to save the programming in PLC device. There are several memory like flash memory, EPROM, PROM, EEPROM.

There are 2 kind of PLC : fixed/compact PLC and modular PLC.

Advantages of PLC :

• Flexible
• A lot of contact.
• Low Cost
• Safe
• Sort time

Disadvantages of PLC :

• Training for users.
• Required a relay system for safety.

Reference :

Petruzella, D. Frank (1996). Industrial Electronics. New York : McGraw-Hill

CHAPTER 11 : TYPE OF PROCESSES

There are 3 type of processes in modern manufacturing industries :

• Continuous Process
• Batch Process
• Individual Products Production

1. Continuous Process 

Process which raw materials enter one end of the system and the finished product comes out the other end of the system and the process itself runs continuously. Continuous process using long period of time such as minutes, days or month. It's depending on process in manufacturing industry.

2. Batch Process

There is no flow of product material from one section of the process to another. Each batch of product may be different, many chemically company  based products are manufactured by using batch processes. Because as we known a lot of chemical company using a lot of material.

3. Individual Products Process

Process which is the most common of all processing systems, with this manufacturing process, a series of operation produces a useful output product. The item being produces may be required to be bent, drilled, welded, and so on. At different steps in process, the workpiece is normally a discrete part that must be handled on individual basis.

There are 3 type of processes and in modern automated industrial plant, the control of machines of processes can be divided into the following categories :

• Electromechanical Control
• Hardwired electronic control
• Programmable hardwired electronic control
• PLC (Programmable Logic Control)
• Computer Control (NC)

Reference :

Petruzella, D. Frank (1996). Industrial Electronics Page 304-305 . New York : McGraw-Hill

 

CHAPTER 10 :PRESSURE CONTROL

Pressure control is one type of control using pressure to control some equipment. Pressure controls can be control or maintenance the pressure of a gas and liquid or solid at some value. Another limit is sense that pressure has reached some preset limit or is moving out of some safe range.

Pressure is defined as a force per unit. Unit can be pounds per square inch (psi) or most popular is pascal/kilopascal (kPa). Pressure is one important industrial process variables.

There are some term in pressure switch specification :

1. Adjustable operating range is range of pressures within which the pressure sensing element of the switch can be set to actuate the contact on the switch.
2. Adjustable differential range / deadband is range of pressure between higher pressure limit which change electrical contact and the lower pressure limit which returns electrical contacts to their normal conditions.
3. Set point repeatability is ability of the switch to operate repeatitively at its set point.
4. Enclosure type is rating of enclosure based on NEMA.
5. Electrical rating is current and voltage rating of electrical contacts.
6. Switch arrangement is type of switch supplied.

CHAPTER 9 : MOTOR STOPPING

Motor stopping used to stop or remove the supply voltage and motor will stop. Some application, motor must stop more quickly or held in position by some sort of braking device. Electric braking uses the windings of the motor to produce a retarding torque. There are two different means of electrical braking:

1. plugging stops a polyphase motor quickly, by momentarily connecting the motor for reverse rotation while the motor is still running in the forward direction.
2. A zero speed switch is coupled to a moving shaft on the machinery whose motor is to plugged.

Dynamic braking is a method of braking that uses the motor as a generator during the braking period immediately after the motor is turned OFF.

Electric braking can be achieved with three phase induction motor by removing the ac power supply from the motor and applying direct current to one of the stator phases,

Electromechanical friction brake refers to a device external to the motor that provides retarding torque.

Electric load brake / eddy current brake is simple, rugged device that consists of an iron rotor mounted inside  a stationery field assembly.

CHAPTER 8 : ARC SUPPRESSION

Arc suppression is the reduction of sparks formed when current carrying contacts are separated. The sparks is a luminous discharge of highly energized electrons and ions, and is an electrical arc. In other explanation arc suppression is required to keep contacts in the device from burning up.

In industrial, arc suppression used to devices such as electromechanical power switches, relays and contactors. 

There are two effectiveness using arc suppression :

1. Visual inspection of the arc.
2. Graphical representation of measurement obtained by an oscilloscope.

There are 5 benefits from arc suppression :

1. Minimizes contact damage from arcing and therefore reduced maintenance, repair, and replacement frequency.
2. Increased contact reliability
3. reduced heat generation resulting in less heat management measures such as venting and fans.
4. Reduce ozone and pollutant emissions.
5. Reduced Electromagnetic Interference (EMI) from arcs a common sources of radiated EMI.

From the figure above, we can analyze , contact A and contact B with and without arc suppression. 

References :

Petruzella, D. Frank (1996). Industrial Electronics. New York : McGraw-Hill

CHAPTER 7 : TIMING RELAYS

One kind of industrial control system is timing relays. Timing relays used to start of event must be delayed until another event has occurred.

Timing relays are conventional relays that equipped with an additional hardware mechanism or circuity to delay the opening or or closing of loads contacts.

There are two kind of timing relays :

1. Pneumatic (air) timing relay uses mechanical linkage and air bellows system to achieve its timing cycle. In pneumatic relay consists of two timed and two instantaneous contacts. when the coil is energized the timed contacts are prevented from opening or closing. When the coil is deenergized the contacts return immediately to their normal state.
   
2. Solid State Timing relay uses electronic circuitry to achieving its time cycle. Some of these timers use a resistor/capacitor (RC) time constant to obtain the time base, and others are quartz clocks as the time base. An RC oscillator networks generates  a highly stable and accurate pulse that it used to provide the different time delay increments and switch a contact output.
   

Time-delay relays can be classified into two basic :

• ON delay relay is often referred to as DOE (Delay On Energized) when power is connected to the coil of ON delay timer , the contacts delay changing position for some period of time.
• OFF delay relay is often referred to as DODE (Delay On Deenergize), the operation is opposite of the operation of the ON delay timer, when voltage is applied to the coil of the OFF delay timer, the contacts will change position immediately. when the coil is deenergized there is a time delay before the contacts change to their normal position.

Reference :

Petruzella, D. Frank (1996). Industrial Electronics. New York : McGraw-Hill