Transcript NUMERICAL CONTROL AND INDUSTRIAL ROBOTICS

Lecture # 11
AUTOMATION TECHNOLOGIES
FOR MANUFACTURING SYSTEMS
1.
2.
3.
4.
Automation Fundamentals
Hardware Components for Automation
Numerical Control
Industrial Robotics
Manufacturing Systems
A manufacturing system can be defined as a collection of
integrated equipment and human resources that
performs one or more processing and/or assembly
operations on a starting work material, part, or set of
parts
 The integrated equipment consists of production
machines, material handling and positioning devices,
and computer systems
 The manufacturing systems accomplish the valueadded work on the part or product
Automation Fundamentals
Automation can be defined as the technology by which
a process or procedure is performed without human
assistance
 Humans may be present, but the process itself
operates under is own self-direction
 Three components of an automated system:
1. Power
2. A program of instructions
3. A control system to carry out the instructions
Two Types of Control System
 (a) Closed loop and (b) open loop
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Three Basic Types of Automation
 Fixed automation - the processing or assembly steps
and their sequence are fixed by the equipment
configuration
 Programmable automation - equipment is designed
with the capability to change the program of
instructions to allow production of different parts or
products
 Flexible automation - an extension of programmable
automation in which there is virtually no lost
production time for setup changes or reprogramming
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Features of
Fixed Automation
 High initial investment for specialized equipment
 High production rates
 The program of instructions cannot be easily changed
because it is fixed by the equipment configuration
 Thus, little or no flexibility to accommodate product
variety
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Features of
Programmable Automation
 High investment in general purpose equipment that
can be reprogrammed
 Ability to cope with product variety by reprogramming
the equipment
 Suited to batch production of different product and
part styles
 Lost production time to reprogram and change the
physical setup
 Lower production rates than fixed automation
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Features of
Flexible Automation
 High investment cost for custom-engineered
equipment
 Capable of producing a mixture of different parts or
products without lost production time for changeovers
and reprogramming
 Thus, continuous production of different part or
product styles
 Medium production rates
 Between fixed and programmable automation types
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Hardware Components for
Automation
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Sensors
Actuators
Interface devices
Process controllers - usually computer-based devices
such as a programmable logic controller
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Sensors
A sensor is a device that converts a physical stimulus or
variable of interest (e.g., force, temperature) into a
more convenient physical form (e.g., electrical voltage)
for purpose of measuring the variable
 Two types
 An analog sensor measures a continuous analog
variable and converts it into a continuous signal
 A discrete sensor produces a signal that can have
only a limited number of values
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Actuators
An actuator is a device that converts a control signal
into a physical action, usually a change in a process
input parameter
 The action is typically mechanical, such as a change
in position of a worktable or speed of a motor
 The control signal is usually low level, and an
amplifier may be required to increase the power of
the signal to drive the actuator
 Amplifiers are electrical, hydraulic, or pneumatic
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Interface Devices
 Interface devices allow the process to be connected
to the controller and vice versa
 Sensor signals form the process are fed into the
controller
 Command signals from the controller are sent to
the process
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Process Controllers
 Most process control systems use some type of
digital computer as the controller
 Requirements for real-time computer control:
 Respond to incoming signals from process
 Transmit commands to the process
 Execute certain actions at specific points in time
 Communicate with other computers that may be
connected to the process
 Accept inputs from operating personnel
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Programmable Logic Controllers
(PLCs)
A PLC is a microcomputer-based controller that uses
stored instructions in programmable memory to
implement logic, sequencing, timing, counting, and
arithmetic control functions, through digital or analog
input/output modules, for controlling machines and
processes
 PLCs are widely used process controllers that satisfy
the preceding real-time controller requirements
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Major Components of a
Programmable Logic Controller
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Numerical Control
A form of programmable automation in which the
mechanical actions of a piece of equipment are
controlled by a program containing coded
alphanumeric data
 The data represent relative positions between a
workhead (e.g., a cutting tool) and a workpart
 NC operating principle is to control the motion of the
workhead relative to the workpart and to control the
sequence of motions
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Components of a NC System
1. Part program - detailed set of commands to be
followed by the processing equipment
2. Machine control unit (MCU) - microcomputer that
stores and executes the program by converting each
command into actions by the processing equipment,
one command at a time
3. Processing equipment - accomplishes the sequence
of processing steps to transform the starting
workpart into completed part
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
NC Coordinate System
 Consists of three linear axes (x, y, z) of Cartesian
coordinate system, plus three rotational axes (a, b, c)
 Rotational axes are used to orient workpart or
workhead to access different surfaces for
machining
 Most NC systems do not require all six axes
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
NC Coordinate Systems
 Coordinate systems used in numerical control: (a) for
flat and prismatic work and (b) for rotational work
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NC Motion Control Systems
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Two types:
1. Point-to-point
2. Continuous path
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Point-to-Point (PTP) System
Workhead (or workpiece) is moved to a programmed
location with no regard for the path taken to get to
that location
 When the move is completed, some processing
action is performed by the workhead
 Examples: drilling a hole
 Thus, the part program consists of a series of point
locations at which operations are performed
 Also called positioning systems
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Continuous Path (CP) System
Continuous simultaneous control of more than one axis,
thus controlling path followed by tool relative to part
 Permits tool to perform a process while axes are
moving, enabling system to generate angular
surfaces, two-dimensional curves, or 3-D contours in
a workpart
 Examples: many milling and turning operations,
flame cutting
 Also called contouring in machining operations
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Two Types of Positioning
 Absolute positioning
 Locations are always
defined with respect
to origin of axis
system
 Incremental positioning
 Next location is
defined relative to
present location
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
NC Positioning System
 Motor and leadscrew arrangement in a numerical
control positioning system
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
NC Positioning System
Converts the coordinates specified in the NC part program
into relative positions and velocities between tool and
workpart
 Leadscrew pitch p - table is moved a distance equal
to the pitch for each revolution
 Table velocity (e.g., feed rate in machining) is set by
the RPM of leadscrew
 To provide x-y capability, a single-axis system is
piggybacked on top of a second perpendicular axis
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Two Basic Types of Control in
Numerical Control
 Open loop system
 Operates without verifying that the actual position
is equal to the specified position
 Closed loop control system
 Uses feedback measurement to verify that the
actual position is equal to the specified location
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Two Basic Types of Control in
Numerical Control
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Operation of an Optical Encoder
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Precision in Positioning
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Three critical measures of precision in positioning:
1. Control resolution
2. Accuracy
3. Repeatability
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Control Resolution (CR)
Defined as the distance between two adjacent control
points in the axis movement
 Control points are locations along the axis to which
the worktable can be directed to go
 CR depends on:
 Electromechanical components of positioning
system
 Number of bits used by controller to define axis
coordinate location
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Control Points along Linear Axis
 A portion of a linear positioning system axis, indicating
control resolution, accuracy, and repeatability
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Statistical Distribution of
Mechanical Errors
 When a positioning system is directed to move to a
given control point, the movement to that point is
limited by mechanical errors
 Errors are due to various inaccuracies and
imperfections, such as gear backlash, play between
leadscrew and worktable, and machine deflection
 Errors are assumed to form a normal distribution
with mean = 0 and constant standard deviation
over axis range
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Accuracy in a Positioning
System
Maximum possible error that can occur between desired
target point and actual position taken by system
 For one axis:
Accuracy = 0.5 CR + 3
where CR = control resolution; and  = standard
deviation of the error distribution
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Repeatability
Capability of a positioning system to return to a given
control point that has been previously programmed
 Repeatability of any given axis of a positioning
system can be defined as the range of mechanical
errors associated with the axis
Repeatability = 3
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
NC Part Programming
Techniques
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Manual part programming
Computer-assisted part programming
CAD/CAM-assisted part programming
Manual data input
Common features:
 Points, lines, and surfaces of workpart must be
defined relative to NC axis system
 Movement of cutting tool must be defined
relative to these part features
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Applications of Numerical
Control
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Operating principle of NC applies to many processes
 Many industrial operations require the position of
a workhead to be controlled relative to the part or
product being processed
Two categories of NC applications:
1. Machine tool applications
2. Non-machine tool applications
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Machine Tool Applications
 NC widely used for machining operations such as
turning, drilling, and milling
 NC has motivated development of machining centers,
which change their own cutting tools to perform a
variety of machining operations
 Other NC machine tools:
 Grinding machines
 Sheet metal pressworking machines
 Thermal cutting processes
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Non-Machine Tool Applications
 Tape laying machines and filament winding machines
for composites
 Welding machines, both arc welding and resistance
welding
 Component insertion machines in electronics
assembly
 Drafting machines (x-y plotters)
 Coordinate measuring machines for inspection
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Benefits of NC
 Reduced non-productive time
 Results in shorter cycle times
 Lower manufacturing lead times
 Simpler fixtures
 Greater manufacturing flexibility
 Improved accuracy
 Reduced human error
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Industrial Robotics
An industrial robot is a general purpose programmable
machine that possesses certain anthropomorphic
features
 The most apparent anthropomorphic feature is the
robot’s mechanical arm, or manipulator
 Robots can perform a variety of tasks such as loading
and unloading machine tools, spot welding
automobile bodies, and spray painting
 Robots are typically used as substitutes for human
workers in these tasks
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Robot Anatomy
An industrial robot consists of
 Mechanical manipulator
 A set of joints and links to position and orient the
end of the manipulator relative to its base
 Controller
 Operates the joints in a coordinated fashion to
execute a programmed work cycle
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
 Manipulator of
an industrial
robot (photo
courtesy of
Adept)
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Manipulator Joints and Links
 A robot joint is similar to a human body joint
 It provides relative movement between two parts
of the body
 Typical industrial robots have five or six joints
 Manipulator joints - classified as linear or rotating
 Each joint moves its output link relative to its input
link
 Coordinated movement of joints enables robot to
move, position, and orient objects
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Manipulator Design
Robot manipulators can usually be divided into two
sections:
 Arm-and-body assembly - function is to position an
object or tool
 Three joints are typical for arm-and-body
 Wrist assembly - function is to properly orient the
object or tool
 Two or three joints are associated with wrist
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Five Basic Arm-and-Body
Configurations
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2.
3.
4.
5.
Polar
Cylindrical
Cartesian coordinate
Jointed-arm
SCARA (Selectively Compliant Assembly Robot
Arm)
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Basic Arm-and-Body
Configurations
 (a) Polar, (b) cylindrical, and (c) Cartesian coordinate
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Basic Arm-and-Body
Configurations
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(d) Jointed-arm and (e) SCARA (Selectively Compliant
Assembly Robot Arm)
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Manipulator Wrist
 The wrist is assembled to the last link of the
arm-and-body
 The SCARA is sometimes an exception because it is
almost always used for simple handling and
assembly tasks involving vertical motions
 A wrist is not usually present at the end of its
manipulator
 Substituting for the wrist on the SCARA is
usually a gripper to grasp components for
movement and/or assembly
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
End Effectors
Special tooling that connects to the robot's wrist to
perform the specific task
1. Tools - used for a processing operation
 Applications: spot welding guns, spray painting
nozzles, rotating spindles, heating torches,
assembly tools
2. Grippers - designed to grasp and move objects
(usually parts)
 Applications: part placement, machine loading
and unloading, and palletizing
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Gripper End Effector
 A robot gripper: (a) open and (b) closed to grasp a
workpart
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Robot Programming
 Robots execute a stored program of instructions that
define the sequence of motions and positions in the
work cycle
 Much like a part program in NC
 In addition to motion instructions, the program may
include commands for other functions:
 Interacting with external equipment
 Responding to sensors
 Processing data
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Two Basic Robot Programming
Methods
1. Leadthrough programming
 Teaching-by-showing - manipulator is moved
through sequence of positions in the work cycle
and the controller records each position in
memory for subsequent playback
2. Computer programming languages
 Robot program is prepared at least partially offline for subsequent downloading to robot
controller
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Where Should Robots be Used?
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Work environment is hazardous for humans
Work cycle is repetitive
The work is performed at a stationary location
Part or tool handling is difficult for humans
Multi-shift operation
Long production runs and infrequent changeovers
Part positioning and orientation are established at the
beginning of work cycle, since most robots cannot
see
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Applications of Industrial Robots
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Three basic categories:
1. Material handling
 Moving materials or parts (e.g., machine
loading and unloading)
2. Processing operations
 Manipulating a tool (e.g., spot welding, spray
painting)
3. Assembly and inspection
 May involve moving parts or tools
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e