Production Automation Technologies

1
Production Automation Technologies

• Henry C. Co
• Technology and Operations Management,
• California Polytechnic and State University

2
Evolution of Production Technology
3
(No Transcript)
4
(No Transcript)
5
(No Transcript)
6

• Computer managed numerical control (NC) is a
  generic term that encompasses.
• Computer numerical control (CNC),
• Direct numerical control (DNC), and.
• Industrial robots.
• Computer managed numerical control, integrated
  with an automated material handling and storage
  system, form the building blocks of the flexible
  manufacturing system (FMS).

7
Numerical Control (NC)
8

• Numerical control (NC) is a form of flexible
  (programmable) automation in which the process is
  controlled by numbers, letters, and symbols.
• The electronic industries association (EIA)
  defined NC as
• A system in which actions are controlled by the
  direct insertion of numerical data at some point.
  The system must automatically interpret at least
  some portion of this data.

9
Basic Components

• An NC system consists of the machine tools, the
  part-program, and the machine control unit (MCU).

10
Machine Tools

• The machine tools perform the useful work.
• A machine tool consists of.
• A worktable,
• One or more spindles, motors and controls,
• Cutting tools,
• Work fixtures, and.
• Other auxiliary equipment needed in the machining
  operation.

11

• The drive units are either powered by stepping
  motors (for open-loop control), servomotors (for
  close-loop control), pneumatic drives, or
  hydraulic drives.

12
The Part-program

• The part-program is a collection of all data
  required to produce the part. It is arranged in
  the form of blocks of information.
• Each block contains the numerical data required
  for processing a segment of the work piece.

13
The Machine Control Unit

• The machine control unit consists of the data
  processing unit (DPU) and the control loop unit
  (CLU).
• The DPU decodes the information contained in the
  part-program, process it, and provides
  instructions to the CLU.
• The CLU operates the drives attached to the
  machine leadscrews and feedback signals on the
  actual position and velocity of each one of the
  axes. The drive units are actuated by voltage
  pulses.

14
The Machine Control Unit

• The number of pulses transmitted to each axis is
  equal to the required incremental motion, and the
  frequency of these pulses represent the axial
  velocity.
• Each incremental motion is called a basic length
  unit (BLU).
• One pulse is equivalent to 1 BLU.
• The BLU represents the resolution of the NC
  machine tool.

15
Types of NC Systems
16
Point-to-point (PTP) NC

• The cutting tool is moved relative to the work
  piece (i.E., Either the cutting tool moves, or
  the work piece moves) until the cutting tool is
  at a numerically defined position and then the
  motion is paused.
• The cutting tool then performs an operation.
• When the operation is completed, the cutting tool
  moves relative to the work piece until the next
  point is reached, and the cycle is repeated.
• The simplest example of a PTP NC machine tool is
  the NC drilling machine.

17
Straight-cut NC

• Straight-cut system are capable of moving the
  cutting tool parallel to one of the major axes
  (X-Y-Z) at a controlled rate suitable for
  machining.
• It is appropriate for performing milling
  operations to fabricate work pieces of
  rectangular configurations.
• Straight-cut NC systems can also perform PTP
  operations.

18
Contouring NC

• In contouring (continuous path) operations, the
  tool is cutting while the axes of motion are
  moving.
• The axes can be moved simultaneously, at
  different velocity.
• The path of the cutter is continuously controlled
  to generate the desired geometry of the work
  piece.

19
Computer-assisted NC Programming
20

• The computer interprets the instructions in the
  program into computer-usable form.
• The computer performs the necessary geometry and
  trigonometry calculations required to generate
  the part surface.
• The part-programmer specifies the part outline as
  the tool path. Since the tool path is at the
  periphery of the cutter that machining actually
  takes place, it must be offset by the radius of
  the cutter.

21

• The cutter offset computations in contour
  part-programming are performed by the computer.
• Part-programming languages are general-purpose
  languages. Since NC machine tool systems have
  different features and capabilities, the computer
  must take the general instructions and make them
  specific to a particular machine tool system.
  This function is called post processing.

22

• After converting all instructions into a detailed
  set of machine tool motion commands, the computer
  controls a tape punch device to prepare the tape
  for the specific NC machine.
• Graphic proofing techniques provide a visual
  representation of the cutting tool path.

23

• This representation may be a simple
  two-dimensional plot of the cutter path or a
  dynamic display of tool motion using computer
  generated animation.
• If necessary, part-programs are also verified on
  the NC station using substitute materials such as
  light metals, plastics, foams, wood, laminates,
  and other castable low cost materials used for NC
  proofing.

24
Computer Numerical Control (CNC)
25

• The EIA definition of computer numerical control
  (CNC).
• A numerical control system wherein a dedicated,
  stored program computer is used to perform some
  or all of the basic numerical control functions
  in accordance with control programs stored in the
  read-write memory of the computer.

The CNC uses a dedicated microprocessor to
perform the MCU functions.
26

• CNC supports programming features not available
  in conventional NC systems
• Subroutine macros which can be stored in memory
  and called by the part-program to execute
  frequently-used cutting sequence.
• Inch-metric conversions, sophisticated
  interpolation functions (such as cubic
  interpolation) can be easily accomplished in CNC.
  
• Absolute or incremental positioning (the
  coordinate systems used in locating the tool
  relative to the work piece) as well as PTP or
  contouring mode can be selected.

27

• The part-program can be edited (correction or
  optimization of tool path, speeds, and feeds) at
  the machine site during tape tryout.
• Tool and fixture offsets can be computed and
  stored.
• Tool path can be verified using graphic display.
• Diagnostics are available to assist maintenance
  and repair.

28
Direct Numerical Control (DNC)
29

• The EIA definition of DNC.
• A system connecting a set of numerically
  controlled machines to a common memory for part
  program or machine program storage with provision
  for on-demand distribution of data to machines.
• In DNC, several NC machines are directly
  controlled by a computer, eliminating substantial
  hardware from the individual controller of each
  machine tool. The part-program is downloaded to
  the machines directly (thus omitting the tape
  reader) from the computer memory.

30
Industrial Robots
31

• A programmable device equipped with a tool that
  can move along several directions.

Stand-Alone Operation once a program is entered,
the robot can function with or without further
human intervention.
32
The Manipulator

• The manipulator is the equivalent of the machine
  tool in CNC. It consists of a series of
  segments, jointed or sliding relative to one
  another, that performs the work such as grasping
  and/or moving objects.
• The manipulator is composed of the main frame
  (the arm of the robot), and the wrist.
• The tools, called the end-effectors, are attached
  to the wrist. The end-effectors perform a
  prescribed task ordinarily done by the human
  worker.

33
The Main Frame

• Structurally, the robot can be classified
  according to the coordinate system of the main
  frame. The types of coordinate systems are
• Cartesian coordinate manipulator, which consists
  of three linear axes,
• Cylindrical coordinate manipulator, which
  consists of two linear axes and one rotary axis,
• Spherical coordinate manipulator which consists
  of one linear and two rotary axes,
• Articulated or jointed robots which consists of
  three rotary axes, and
• Gantry robot
• SCARA robot.

34
Cartesian Robot
35
Cylindrical Robot
36
Spherical Robot
37
Articulated (Jointed) Robot
38
Gantry Robot
39
SCARA Robot
40
The Wrist

• The end-effectors is connected to the main frame
  of the robot through the wrist.
• The wrist has three rotary axes -- roll, bend
  (pitch), and swivel (yaw).
• The end-effectors. Attached to the wrist is the
  end-effectors. The end-effectors is the robot's
  hand. The most common end-effectors is the
  gripper, which is a device by which a robot may
  grasp and hold external objects.
• Other standard end-effectors include welding
  torch, magnetic vacuum, gun mounts for spray
  painting or coating operations, hydraulic toggle,
  and custom made tools.

41
Resolution,Accuracy,Repeatability

• Resolution is the smallest increment of distance
  that can be read and acted upon by an automatic
  control system of a robot.
• The unit of measure is the basic resolution unit
  (BRU).
• The accuracy of an industrial robot is the
  ability of the robot to make a motion with an end
  point as specified by a program.
• The closeness of agreement of repeated position
  movement under the same conditions to the same
  location is called the repeatability of the robot.

42
Programming

• An industrial robot can be programmed using the
• Manual teaching method,
• Lead-through method, or a
• Programming language.

43
Applications

• Perhaps the most extensive applications of
  industrial robots are in jobs involving
  repetitive tasks. Industrial robots installed
  to-date are in
• Material handling (about 40),
• Painting and arc welding (45),
• Inspection, assembly and
• Other operations (15).

44

• Operations that require precise positioning
  control.
• For example, in spray painting where severe
  articulation is required.
• Use of industrial robots in sand blasting is on
  the rise not only because of the abrasive
  environment, but the severe articulation
  requirements of the process.

45

• In areas where hazardous working conditions exist
  and/or where heavy parts are involved.
• For example, in unloading of die casting
  machines, the workplace is dirty and hot (molten
  metal) in spot welding operations, the welding
  guns are heavy and the work cycles rigorous and
  in investment casting, the environment is
  abrasive and of the loads heavy.
• Industrial robots are also replacing the human
  operator in corrosive environment, such as
  handling of dangerous chemicals.

46

• Hazards, operator tasks, inspection, quality,
  part presentation, part weight, product
  variation, product runs, frequency of changeover,
  process variables, process equipment, floor
  space, and cycle time, are some of the variable
  that must be examined in justifying the use of
  industrial robots.
• However, industrial robots should not be treated
  simply as an emulation of human work. More
  importantly, the justification process should
  reflect an accurate implementation of corporate
  manufacturing plans for competitive advantage and
  productivity improvement.