Computer-Controlled Machines and Processes

CHAPTER 13A. Computer Fundamentals
Useful devices for machine and process control

  As manufacturing systems are becoming increasingly computer-based, understanding of computer fundamentals is essential.

  All computers consist of two basic components: hardware and software.

Hardware
The physical component which makes up the computer system

  • Power supply
  • Floppy disk
  • Hard drive
  • Motherboard
  • Microprocessor chip
  • ROM chips
  • RAM chips
  • Peripheral cards
  • Expansion slots

Software
A computer program, a list of instructions telling the computer what to do

The program are usually stored on some form of mass storage system, such as a floppy disk, and loaded into the computer’s random access memory (RAM) as required.

  Disk drive act as both input and output devices, used for getting information into the computer as well as storing information from the computer.

  Floppy disk (diskette) is a magnetic storage device on which information is stores for later retrivel. The information is stored on tracks in sectors of the disk; the location of the information is configured to allow the computer access to a sector to read the information.

  Hard disk drives store and retrieve data more quickly and can hold much more information than floppy disk. The hard disk mass storage system is permanently located within the computer and can store a large number of programs simultaneuosly.

a. System Software
Provides the programs that allow to interact with computer—to operate the disk drives, the printer, and other devices used by the computer

The most popular operating system for personal computers is MS-DOS, MS refers to the manufacturer, Microsoft, and DOS to its Disk Operating System. DOS creates a common platform for all the software use and allows to:

  • Read, write, and edit files  – View error messages
  • Back up files  – Display the contents of a disk
  • Organize a disk  – Manage file

  File is a collection of data stored under a single name. Some important types of files include:

  • Executable file. A list of instruction to the CPU
  • Data file. A list of information
  • Text file. A series of characters like a letter
  • Graphic file. A picture converted to digital code

  The BIOS (Basic Input/Output System) serves as a link between the computer hardware and the software programs.

Application Software
Programs writen to give the computer a specific application, such as a word processor

Directories are simply a way of organizing all the programs and files of the hard drive in computer. The directory structure performs the same basic function as a filling cabinet. The first and main directory of the computer is called the root directory. The second level of hte directory structure ideally contains of the disk.

  Tree is a DOS command that will show the directory structure of computer.

  The DOS prompt (A>) is an indicator that DOS is loaded and that the computer is ready for you to enter a command.

  DOS is simply a very large list of commands that the computer can use and understand to control, manage, and run other programs. Commands DOS:

  • DIR command  – CLS command
  • COPY command  – REN command
  • DEL command  – TYPE command
  • FORMAT command  – DISKCOPY command
  • CD command  – CHKDSK command
  •   Microsoft’s Windows is a graphics-based interface for MS-DOS. It use graphical images to replace the verbal commands to run DOS.

      Program in Windows share the CPU resources, passing control back and forth at times when the computer is not being controlled by the user. Windows multitasking operation is one of the principal factors drawing people away from DOS application development.

      Ports are the connecting devices that stick out the back end of the computer case.

      Ports are usually a preset number of pins to allow the proper cable connection and are reffered to as male or female (with pins or holes to fit the pins).

      Ports are usually referred to as serial (for a mouse connection) or parallel (for a printer connection).

      The serial port is often referred to as an RS-232 port (Electronics Industries Associations designation). The parallel port is often called a Centronics port.

    Key specifications in selecting a computer:

    1. Access time  f. Baud
    2. Bus  g. Cache
    3. Clock speed  h. Central processing unit (CPU)
    4. Hard disk drive  i. Monitors
    5. RAM

B. Computers in Process and Machine Control

  Computer –integrated manufacturing systems prvide individual machines used in manufacturing with data communication functions and compatibility, allowing the individual devices to be integrated inti a single system.

  Data communication system were provide between programmable controllers, but it was apparent that the advantages of integrated manufacture required computer-controlled and numerically controlled machines and robot controllers to be connected to the programmable controller, which in turn would interconnect with a host computer and oyher equipment via the factory local area network.

  Local area network is to provide communication between PLCs or between PLCs and computers.

  LANs come in three basic topologies (that is, the physical layout or configuration of the communications network): star, ring, and bus. The points where the device connect to the transmission medium are known as nodes or stations.

Star Network

  The central control device is connected to a number of nodes. This allows for bidirectional communication between the central control device and each node. All transmission must be between the central control device and the nodes, since the central control device controls all communication.

Bus Network

  Each node is connected to a central bus. When a node sends a message on the network, the message is aimed at a particular station or node number. As the message moves along the total bus, each node is listening for its own node identification number and accepts only information sent to that number. Control can be either centralized or distributed among the nodes.

Ring Network

  Each node is connected to another node. There is no end or beginning to the network. Messages are aimed at a particular node or station number, with each node listening for its own identification number. Signals are passed around the ring, and are regenerated at each node. Control can be centralized or distributed.

  Protocol refers to a predetermined set of conventions which specify the format and timing of message transmission between two or more communicating devices.

The two basic network communication formats are master-slave and peer-to-peer.

  A master-slave system uses a host computer to manage all network communications between network devices.

  A peer-to-peer system makes network device has the ability to request use of, and then take control of, the network for the purpose of transmitting information from other network devices. This type of network

Computer Numerical Control

  • Numerical control is a flexible method of automatically controlling machines through the use of numerical values.
  • Numerical control enables an operator to communicate with machine tolls through a series of numbers and symbols.
  • Many languages exist for writing an NC program, but the one most used is called automatically programmed tools (APTs).
  • Data that is input manually can be used to program the control system by setting the dials, switches, pushbuttons, etc.
  • Numerical control is ideally suited for operations which involve the production of parts made from similat feedstock (raw material) with variations in size and shape.

Microprocessor-based control equipment brought features to NC machines, such as :

  • Improved program mass storage, disk instead of punched tape
  • Ease of editing programs
  • Possibility of more complex contouring because of the computer’s capability for mathematical manipulation
  • Reusable machine pattern, which could be stored and retrieved as required
  • Possibility of plant wide communication with many peripheral devices.

Using a computer to assist in program writing allows the program to be :

  • Stored on a convenient mass storage system
  • Retrieved and edited as required
  • Tested off-line prior to using the program to control a machine
  • Plotted using a plotter connected to the computer to assist in program de-bugging.

ROBOTICS

  • Robots are computer-controlled devices which perform tasks usually done by humans.
  • The basic industrial robot in wide use today is an arm or manipulator which moves to perform industrial operations.
  • Tasks are specialized and vary tremendously which include :
  • Handling
  • Processing
  • Assembling
  • Dismantling
  • Welding
  • Transporting
  • Painting
  • Hazardous tasks
  • A robot is simply a series of mechanical links driven by servomotors. The area at each junction between the links is called a joint or axis.
  • The reach of the robot is defined as the work envelope. All programmed points within the reach of the robot are part of the work envelope.
  • End-of-arm tooling, commonly called the end effector, varies depending on the type of work the robot does.
  • In the open-loop system, there are no sensors or feedback signals that measure how the manipulator actually moved in response to the command signals.
  • The closed-loop system uses feedback signals from joint position sensors.
  • The term servo robot is often used to refer to a closed-loop (feedback) system, and the term nonservo robot to refer to an open-loop (no feedback) system.

The controller includes the following devices that are used to operate the system :

  • Operator Panel, performing tasks such as powering up and powering down the system; calibrating the robot and etc
  • Teach Pendant, performing tasks such as jogging the robot; teaching positional data; testing program execution and etc
  • CRT Screen and Keyboard, performing tasks such as displaying status and diagnostic information; and entering, translating and debugging programs

Source: McGraw Hill International Edition. Electrical & Electronic Technology Series

 

 

 

 

 

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