IE458CAM Computer Aided Manufacturing Part5 Robotic Systems

1
IE458 CAMComputer Aided ManufacturingPart-5Robo
tic Systems

• Industrial Engineering Department
• King Saud University

2
Contents

• What is an industrial robot?
• The basic components of a robot
• Power sources for robots
• Hydraulic drive
• Electric drive
• Pneumatic drive
• Robot sensors
• The hand of a robot (end-effector)
• Robot Movement and Precision

• The robot joints
• Robot classification
• Physical classification
• Control classification
• Robot reach
• Robot motion analysis and control
• Robot Programming and Languages
• Robot Selection
• Robot applications
• Robot Economic

3
What is an industrial robot?
The word "robot" is derived from a satirical
fantasy play, "Rossum's Universal Robots,"
written by Karel Capek in 1921. In his play,
Capek used the word to mean, "forced labor." The
Robotics Industries Association (RIA), formerly
known as the Robotics Institute of America,
defines robot in the following way   An
industrial robot is a programmable
multi-functional manipulator designed to move
materials, parts, tools, or special devices
through variable programmed motions for the
performance of a variety of tasks.
4
An industrial robot consists of a number of rigid
links connected by joints of different types,
controlled and monitored by a computer. To a
large extent, the physical construction of a
robot resembles a human arm. The link assembly
mentioned above is connected to the body, which
is usually mounted on a base. This link assembly
is generally referred to as a robot arm. A wrist
is attached to the arm. To facilitate gripping or
handling, a hand is attached at the end of the
wrist. In robotics terminology, this hand is
called an end-effector. The complete motion of
the end-effector is accomplished through a series
of motions and positions of the links, joints,
and wrist. A typical industrial robot with
six-degrees of freedom is shown in.
Figure 1
5
The widespread use of CNC in manufacturing is
ideal for the use of industrial robots to perform
repetitive tasks. Such tasks may involve handling
heavy and sometimes hazardous materials.
Sophisticated CNC machining centers can contain
palette changers and special interfaces that can
easily accommodate industrial robots.
6
Specialized robots can assist in both assembly
and inspection processes.
7
Material handling robots are used in many
industries. It may be surprising to find such
robots used even in the fast food industry.
8
This material handling robot is used in preparing
palettes for shipping.  Repetitive tasks are
ideal to be performed by such machines.
9
Shown is a Fanuc M-16i Robotic Arm used in a
precision grinding process on automotive parts.
10
Shown is a Fanuc Robot arm lifting three heavy
boxes at once.  In using robotics, human safety
factors in such a task are completely eliminated.
This also greatly reduces the risks of repetitive
stress injuries to factory workers.
11
Handling of dangerous materials is an important
task for Robots to perform.  The size and weight
of some automotive parts may be too cumbersome
and hazardous for humans to manipulate in certain
processes.
12
Shown is a robotic arm used in conjunction with a
small punch press. Together these two machines
could comprise a small manufacturing cell. The
use of Robotics in such a setup can greatly
reduce the chance of human error and injury.
13
It is now commonplace to find automotive
manufacturers using robotics in many phases of
the automotive assembly line.   Here an
automotive spray booth utilizes a Fanuc Robot arm
is used to precisely deposit paint on this car
body.  The use of robotics can improve the
quality of certain manufactured goods.
14
Here a Fanuc S-420W material handling robot is
used in the electronic appliances industry.  You
will note several others in the background used
in other steps of the manufacturing process.
15
Another Fanuc A-510 robot arm used in the food
industry. Improved productivity is an important
factor in using robotic equipment is repetitive
production line operations. It can greatly reduce
the human factors which can lead to errors and
risk of injury.
16
Shown are two Fanuch Robot arms employed to
perform precision welding tasks. This type of
process would be extremely difficult to achieve
by humans.
17
THE BASIC COMPONENTS OF A ROBOT The basic
components of a robot include the manipulator,
the controller, and the power supply sources. The
types and attributes of these components are
discussed next.

• Power Sources for Robots
• An important element of a robot is the drive
  system. The drive system supplies the power,
  which enables the robot to move. The dynamic
  performance of the robot is determined by the
  drive system adopted, which depends mainly on the
  type of application and the power requirements.
•  
• The three types of drive systems are generally
  used for industrial robots
• Hydraulic drive
• Electric drive
• Pneumatic drive

18

• Hydraulic Drive
• A hydraulic drive system gives a robot great
  speed and strength.
• These systems can be designed to actuate linear
  or rotational joints.
• The main disadvantage of a hydraulic system is
  that it occupies floor space in addition to that
  required by the robot.
• Problems of leaks, making the floor messy.
• Because they provide high speed and strength,
  hydraulic systems are adopted for large
  industrial robots.
• Hydraulic robots are preferred in environments in
  which the use of electric-drive robots may cause
  fire hazards, for example, in spray painting.

19

• Electric Drives
• Compared with a hydraulic system,
• An electric system provides a robot with less
  speed and strength.
• Electric drive systems are adopted for smaller
  robots.
• Robots supported by electric drive systems are
  more accurate, exhibit better repeatability
• Cleaner to use.

20

• Pneumatic Drive
• Pneumatic drive systems are generally used for
  smaller robots.
• These robots, with fewer degrees of freedom,
  carry out simple pick-and-place material-handling
  operations, such as picking up an object at one
  location and placing it at another location.
  These operations are generally simple and have
  short cycle times.
• Pneumatic robots are less expensive than electric
  or hydraulic robots.
• Most pneumatic robots operate at mechanically
  fixed end points for each axis.
• A big advantage of such robots is their simple
  modular construction, using standard commercially
  available components. This makes it possible for
  a firm to build its own robots at substantial
  cost savings for simple tasks such as pick and
  place, machine loading and unloading, and so
  forth.

21

• Robotic Sensors
• The motion of a robot is obtained by precise
  movements at its joints and wrist. While the
  movements are obtained, it is important to ensure
  that the motion is precise and smooth. The drive
  systems should be controlled by proper means to
  regulate the motion of the robot. Along with
  controls, robots are required to sense some
  characteristics of their environment. These
  characteristics provide the feedback to enable
  the control systems to regulate the manipulator
  movements efficiently. Sensors provide feedback
  to the control systems and give the robots more
  flexibility.
•  
• Sensors such as visual sensors are useful in the
  building of more accurate and intelligent robots.
  The sensors can be classified in many different
  ways based on their utility. In this section we
  discuss a few typical sensors that are normally
  used in robots
• Position sensors. They are used to monitor the
  position of joints.
• Range sensors. Range sensors measure distances
  from a reference point to other points of
  importance.
• Velocity sensors. Velocity sensors are used to
  estimate the speed with which a manipulator is
  moved
• Proximity sensors. Proximity sensors are used to
  sense and indicate the presence of an object
  within a specified distance or space without any
  physical contact

22
The Hand of a Robot End-Effectors The
end-effectors (commonly known as robot hand)
mounted on the wrist enables the robot to perform
specified tasks. Various types of end-effectors
are designed for the same robot to make it more
flexible and versatile.
End-effectors are categorized into two major
types 1.      Grippers 2.      Tools.
23

• Grippers are generally used to grasp and hold an
  object and place it at a desired location.
  Grippers can be classified as
• Mechanical grippers,
• Vacuum or suction cups,
• Magnetic grippers,
• Adhesive grippers,
• Hooks,
• Scoops,
• Others.

Figure 2
Grippers usually operate in jaw type fashion by
having fingers which either attach to the
gripper, or are part of the construction, open
and close. The attached fingers can be replaced
with new or different fingers, allowing for
flexibility, see Figure 2. Grippers can operate
with two fingers or more.
24
End-effectors - Tools
At times, a robot is required to manipulate a
tool to perform an operation on a work part.
Spot-welding tools, arc-welding tools,
spray-painting nozzles, and rotating spindles for
drilling and grinding are typical examples of
tools used as end-effectors.
25
Gripper designs  There are many approaches to
gripper designs. These Figures shows the various
linkages which result in pivoting action for
gripping.
26

• Robot Movement and Precision
• Speed of response and stability are two important
  characteristics of robot movement.
• Speed defines how quickly the robot arm moves
  from one point to another.
•  
• Stability refers to robot motion with the least
  amount of oscillation. A good robot is one that
  is fast enough but at the same time has good
  stability.
•  
• The precision of robot movement is defined by
  three basic features
• high resolution
• Accuracy
• Repeatability

27

• 1. Spatial Resolution
• The spatial resolution of a robot is the smallest
  increment of movement into which the robot can
  divide its work volume. It depends on
• the system's control resolution and
• the robot's mechanical inaccuracies.
• The control resolution is determined by the
  robot's position control system and its feedback
  measurement system. The controller divides the
  total range of movements for any particular joint
  into individual increments that can be addressed
  in the controller. The bit storage capacity of
  the control memory defines this ability to divide
  the total range into increments. For a particular
  axis, the number of separate increments is given
  by

Number of increments 2n where n is the number
of bits in the control memory.
28
EXAMPLE A robot's control memory has 8-bit
storage capacity. It has two rotational joints
and one linear joint Determine the control
resolution for each joint, if the linear link can
vary its length from as short as 0.2 m to as long
as 1.2 m.   Solution Control memory 8 bit
From the equation above, number of increments
28 256 (a) Total range for rotational joints
360 Control resolution for each rotational joint
360/256 1.40625 (b) Total range for linear
joint 1.2 - 0.2 1.0 m Control resolution for
linear joint 1/256 0.003906 m 3.906 mm
29
2. Accuracy Accuracy can be defined as the
ability of a robot to position its wrist end at a
desired target point within its reach. In terms
of control resolution, the accuracy can be
defined as one-half of the control resolution.
3. Repeatability Repeatability refers to the
robot's ability to position its end-effectors at
a point that had previously been taught to the
robot. The repeatability error differs from
accuracy as described below
30
Let point A be the target point as shown in
Figure a. Because of the limitations of spatial
resolution and therefore accuracy, the programmed
point becomes point B. The distance between
points A and B is a result of the robot's limited
accuracy due to the spatial resolution. When the
robot is instructed to return to the programmed
point B, it returns to point C instead. The
distance between points B and C is the result of
limitations on the robot's repeatability.
However, the robot does not always go to point C
every time it is asked to return to the
programmed point B. Instead, it forms a cluster
of points. This gives rise to a random phenomenon
of repeatability errors. The repeatability errors
are generally assumed to be normally distributed.
If the mean error is large, we say that the
accuracy is poor. However, if the standard
deviation of the error is low, we say that the
repeatability is high.   We pictorially
represent the concept of low and high
repeatability as well as accuracy in Figure b, c,
d, and e. Consider the center of the two
concentric circles as the desired target point.
The diameter of the inner circle represents the
limits up to which the robot end-effector can be
positioned and considered to be of high accuracy.
Any point outside the inner circle is considered
to be of poor or low accuracy. A group of closely
clustered points implies high repeatability,
whereas a sparsely distributed cluster of points
indicates low repeatability.
31
Figure a.
32
Figure (a) Accuracy and repeatability (b), high
accuracy and high repeatability (c) high
accuracy and low repeatability (d) low accuracy
and high repeatability (e) low accuracy and low
repeatability.
33

• THE ROBOTIC JOINTS
•  A robot joint is a mechanism that permits
  relative movement between parts of a robot arm.
•  
• The joints of a robot are designed to enable the
  robot to move its end-effectors along a path from
  one position to another as desired.
•  
• The basic movements required for the desired
  motion of most industrial robots are
• Rotational movement.- This enables the robot to
  place its arm in any direction on a horizontal
  plane.
• Radial movement. This enables the robot to move
  its end-effectors radially to reach distant
  points.
• Vertical movement. This enables the robot to take
  its end-effector to different heights.

34
These degrees of freedom, independently or in
combination with others, define the complete
motion of the end-effector. These motions are
accomplished by movements of individual joints of
the robot aim. The joint movements are basically
the same as relative motion of adjoining links.
Depending on the nature of this relative motion,
the joints are classified as prismatic or
revolute.   Prismatic joints are also known as
sliding as well as linear joints. They are called
prismatic because the cross section of the joint
is considered as a generalized prism. They permit
links to move in a linear relationship.
  Revolute joints permit only angular motion
between links.
35

• The five joint types are
• Linear joint (L). The relative movement between
  the input link and the output link is a linear
  sliding motion, with the axes of the two links
  being parallel.
• Orthogonal joint (O). This is also a linear
  sliding motion, but the input and output links
  are perpendicular to each other during the move.
• Rotational joint (R). This type provides a
  rotational relative motion of the joints, with
  the axis of rotation perpendicular to the axes of
  the input and output links.
• Twisting joint (T). This joint also involves a
  rotary motion, but the axis of rotation is
  parallel to the axes of the two links.
• Revolving joint (V). IN this joint type, the axis
  of the input link is parallel to the axis of
  rotation of the joint, and the axis of the output
  link is perpendicular to the axis of rotation.

36

• two forms of linear joint-type L
• two forms of orthogonal joint-type O
• rotational joint-type R
• twisting joint-type T
• revolving joint-type V.

37
Example
38

• A typical robot manipulator can be divided into
  two sections
• A body-and-arm assembly, and
• A wrist assembly.
• There are usually 3 degrees of freedom associated
  with the body-and-arm, and either 2 or 3 degrees
  of freedom usually associated with the wrist.

At the end of the manipulator's wrist is an
object that is related to the task that must be
accomplished by the robot. For example, the
object might be a workpart that is to be loaded
into a machine, or a tool that is manipulated to
perform some process. The body- and-arm of the
robot is used to position the object and the
robot's wrist is used to orient the object.

• To establish the position of the object, the
  body-and-arm must be capable of moving the object
  in any of the following three directions
• Vertical motion (z-axis motion)
• Radial motion (in-and-out or y-axis motion)
• Right-to-left motion (x-axis motion or swivel
  about a vertical axis on the base)

39

• To establish the orientation of the object, we
  can define 3 degrees of freedom for the robot's
  wrist. The following is one possible
  configuration for a 3 d.o.f. wrist assembly
• Roll. This d.o.f. can be accomplished by a T-type
  joint to rotate the object about the arm axis.
• Pitch. This involves the up-and-down rotation of
  the object, typically done by means of a type R
  joint.
• Yaw. This involves right-to-left rotation of the
  object, also accomplished typically using an
  R-type joint.
• These definitions are illustrated in the following

Typical configuration of a 3-degree-of-freedom
wrist assembly showing roll, pitch, and yaw.
Yaw
40

• ROBOT CLASSIEFICATION AND ROBOT REACH
•  Normally robots are classified on the basis of
  their physical configurations. Robots are also
  classified on the basis of the control systems
  adopted.
•  
• Classification Based on Physical Configurations
• Four basic configurations are identified
• Cartesian configuration
• Cylindrical configuration
• Polar configuration
• Jointed-arm configuration.

41
Cartesian Configuration Robots with Cartesian
configurations, consist of links connected by
linear and orthogonal joints (L and O). The
configuration of the robot's arm can be
designated as LOO. Because the configuration has
three perpendicular slides, they are also called
rectilinear robots.
42
Cartesian coordinate body-and-arm assembly (LOO).
43
Cylindrical Configuration In the cylindrical
configuration, as shown in Figure 7, robots have
one twisting (T) joint at the base and linear (L)
joints succeed to connect the links. The robot
arm in this configuration can be designated as
TLO. The space in which this robot operates is
cylindrical in shape, hence the name cylindrical
configuration.
44
Cylindrical body-and-arm assembly (TLO)
45
Polar Configuration Polar robots, as shown in
Figure 8, have a work space of spherical shape.
Generally, the arm is connected to the base with
a twisting (T) joint and rotatory (R) and/or
linear (L) joints follow. The designation of the
arm for this configuration can be TRL or TRR.
Robots with the designation TRL are also called
spherical robots. Those with the designation TRR
are also called articulated robots.
46
Polar coordinate body-and arm assembly (TRL).
47
Jointed-Arm Configuration The jointed-arm
configuration, is a combination of cylindrical
and articulated configurations. The arm of the
robot is connected to the base with a twisting
joint. The links in the arm are connected by
rotatory joints.
48
Jointed-arm body-and-arm assembly (TRR).
49

• Classification Based on Control Systems
• Based on the control systems adopted, robots are
  classified into the following categories
• Point-to-point (PTP) control robot
• Continuous-path (CP) control robot
• Controlled-path robot

50
Point-to-Point (PTP) The PTP robot is capable of
moving from one point to another point. The
locations are recorded in the control memory. PTP
robots do not control the path to get from one
point to the next point. The programmer exercises
some control over the desired path to be followed
by programming a series of points along the path.
Common applications include component insertion,
spot welding, hole drilling, machine loading and
unloading, and crude assembly operations.
Continuous-Path (CP) The CP robot is capable of
performing movements along the controlled path.
With CP control, the robot can stop at any
specified point along the controlled path. All
the points along the path must be stored
explicitly in the robot's control memory.
Straight-line motion is the simplest example for
this type of robot. Some continuous- path
controlled robots also have the capability to
follow a smooth curve path that has been defined
by the programmer. In such cases the programmer
manually moves the robot arm through the desired
path and the controller unit stores a large
number of individual point locations along the
path in memory. Typical applications include
spray painting, finishing gluing, and arc welding
operations.
51
Controlled-Path Robot In controlled path robots,
the control equipment can generate paths of
different geometry such as straight lines,
circles, and interpolated curves with a high
degree of accuracy. Good accuracy can be obtained
at any point along the specified path. Only the
start and finish points and the path definition
function must be stored in the robot's control
memory. It is important to mention that all
controlled-path robots have a servo capability to
correct their path.
52
Robot Reach Robot reach, also known as the work
envelope or work volume, is the space of all
points in the surrounding space that can be
reached by the robot arm or the mounting point
for the end-effectors or tool. The area reachable
by the end-effectors itself is not considered
part of the work envelope. Reach is one of the
most important characteristics to be considered
in selecting a suitable robot because the
application space should not fall out of the
selected robot's reach.   Robot reach for
various robot configurations is shown in the
following Figure   For a Cartesian configuration
the reach is a rectangular-type space. For a
cylindrical configuration the reach is a hollow
cylindrical space. For a polar configuration it
is part of a hollow spherical shape. For a
jointed-arm configuration does not have a
specific geometric shape.
53
Robot reach (work envelope) (a) polar (b)
cylindrical robot (c) Cartesian.
54
Robot reach (work envelope) Joint arm (revolute)
robot.
55
Robot Motion Analysis and Control
56
(No Transcript)
57
(No Transcript)
58
(No Transcript)
59
(No Transcript)
60
(No Transcript)
61
(No Transcript)
62
(No Transcript)
63
(No Transcript)
64
(No Transcript)
65
A Four-Jointed Robot in Three Dimensions Most
robots possess a work volume with three
dimensions. Consider the four degree-of-freedom
robot in Figure 7.18. Its configuration is TRL
R. Joint 1 (type T) provides rotation about the z
axis. Joint 2 (type R) provides rotation about a
horizontal axis whose direction is determined by
joint 1. Joint 3 (type L) is a piston that allows
linear motion in a direction determined by joints
1 and 2. And joint 4 (type R) provides rotation
about an axis that is parallel to the axis of
joint 2. The values of the four joints are,
respectively, ?1, ?2, ?3 and ?4. Given these
values, the forward transformation is given by
Figure 7.18 A four degree robot with
configuration TRLR.
66
(No Transcript)
67
(No Transcript)
68
(No Transcript)
69
ROBOT PROGRAMMING AND LANGUAGES

• The primary objective of robot programming is to
  make the robot understand its work cycle. The
  program teaches the robot the following
• The path it should take
• The points it should reach precisely How to
  interpret the sensor data
• How and when to actuate the end-effector
• How to move parts from one location to another,
  and so forth

70

• Programming of conventional robots normally takes
  one of two forms
• Teach-by-showing, which can be divided into
• Powered lead through or discrete point
  programming
• Manual lead through or walk-through or continuous
  path programming
• (2) Textual language programming

• In teach-by-showing programming the programmer is
  required to move the robot arm through the
  desired motion path and the path is defined in
  the robot memory by the controller.
• Control systems for this method operate in
  either
• teach mode is used to program the robot
• run mode is used to run or execute the program.

71

• Powered lead through programming uses a teach
  pendant to instruct a robot to move in the
  working space.
• A teach pendant is a small handled control box
  equipped with toggle switches, dials, and buttons
  used to control the robot's movements to and from
  the desired points in the space.
• These points are recorded in memory for
  subsequent playback. For playback robots, this is
  the most common programming method used. However,
  it has its limitations
• It is largely limited to point-to-point motions
  rather than continuous movement, because of the
  difficulty in using a teach pendant to regulate
  complex geometric paths in space. In cases such
  as machine loading and unloading, transfer tasks,
  and spot welding, the movements of the
  manipulator are basically of a point-to-point
  nature and hence this programming method is
  suitable.

72
Manual lead through programming is for
continuous-path playback robots. In walk-through
programming, the programmer simply moves the
robot physically through the required motion
cycle. The robot controller records the position
and speed as the programmer leads the robot
through the operation. If the robot is too big
to handle physically, a replica of the robot that
has basically the same geometry is substituted
for the actual robot. It is easier to manipulate
the replica during programming. A teach button
connected to the wrist of the robot or replica
acts as a special programming apparatus. When the
button is pressed, the movements of the
manipulator become part of the program. This
permits the programmer to make moves of the arm
that will not be part of the program. The
programmer is able to define movements that are
not included in the final program with the help
of a special programming apparatus.
73

• Teach-by-showing methods have their limitations
• Teach-by-showing methods take time for
  programming.
• These methods are not suitable for certain
  complex functions, whereas with textual methods
  it is easy to accomplish the complex functions.
• Teach-by-showing methods are not suitable for
  ongoing developments such as computer-integrated
  manufacturing (CIM) systems.
• Thus, textual robot languages have found their
  way into robot technology.

74
Textual language programming methods use an
English-like language to establish the logical
sequence of a work cycle. A cathode ray tube
(CRT) computer terminal is used to input the
program instructions, and to augment this
procedure a teach pendant might be used to define
on line the location of various points in the
workplace. Off-line programming is used when a
textual language program is entered without a
teach pendant defining locations in the program.
75
Programming Languages Different languages can be
used for robot programming, and their purpose is
to instruct the robot in how to perform these
actions. Most robot languages implemented today
are a combination of textual and teach-pendant
programming. Some of the languages that have been
developed are WAVE VAL AML RAIL MCL TL-
10 IRL PLAW SINGLA VAL II
76

• VAL II
• It is one of the most commonly used and easily
  learned languages.
• It is a computer-based control system and
  language designed for the industrial robots at
  Unimation, Inc.
• The VAL II instructions are clear, concise, and
  generally self explanatory.
• The language is easily learned.
• VAL II computes a continuous trajectory that
  permits complex motions to be executed quickly,
  with efficient use of system memory and reduction
  in overall system complexity.
• The VAL if system continuously generates robot
  commands and can simultaneously interact with a
  human operator, permitting on-line program
  generation and modification.
• A convenient feature of VAL If is the ability to
  use libraries of manipulation routines. Thus,
  complex operations can be easily and quickly
  programmed by combining predefined subtasks.

77

• Programming With VAL II
• The first step in any robot programming exercise
  is the physical identification of location points
  using the teach pendant. We do not have to teach
  all the points that the robot is programmed to
  visit only a few key points have to be shown
  (e.g., the comer of a pallet). Other points to
  which it can be directed can be referenced from
  these key points. The procedure is simple. First
  use the keys or button of the teach pendant to
  drive the robot physically to the desired
  location and then type the command HERE with the
  symbolic name for that location. For example,
• HERE P1
• This command will identify the present location
  as P1.

78

• Rules for the location name are as follows
• It is any string of letters, numbers, and
  periods.
• he first character must be alphabetic.
• There must be no intervening blank.
• Every location name must be unique.
• There may be a limit on the maximum number of
  characters that can be used.
• The following example illustrates the general
  command format for VAL II
• 100 APPRO P1 15
• In this example, 100 is the label that refers to
  this instruction, APPRO is the instruction to the
  robot to approach the location named P1 by a
  distance of 15 mm.

79
In the following, we describe the most commonly
used VAL II commands.
80
(No Transcript)
81

82
logarithmic, exponential, and similar functions.
The following relational and logical operators
are also available. EQ Equal to NE Not equal
to GT Greater than GE Greater than or equal to
LT Less than LE Less than or equal to
AND Logical AND operator OR Logical OR
NOT Logical complement
83
TYPE "text This statement displays the message
given in the quotation marks. The statement is
also used to display output information on the
terminal. PROMPT "text", INDEX This statement
displays the message given in the quotation marks
on the tenninal. Then the system waits for the
input value, which is to be assigned to the
variable INDEX. In most real-life problems,
program sequence control is required. The
following statements are used to control logic
flow in the program. GOTO 10 This command causes
an unconditional branch to statement 10.
84
(No Transcript)
85
SUBROUTINES can also be written and called in VAL
II programs. Monitor mode commands are used for
functions such as entering locations and systems
supervision, data processing, and communications.
Some of the commonly used monitor mode commands
are as follows EDIT (Program name) This makes
it possible to edit the existing program or to
create a new program by the specified program
name.
86
EXIT This command stores the program in
controller memory and quits the edit mode. STORE
(Program name) This allows the program to be
stored on a specified device. READ (Program
name) Reads a file from storage memory to robot
controller. LIST (Program name) Displays
program on monitor. PRINT (Program name)
Provides hard copy. DIRECTORY Provides a
listing of the program names that are stored
either in the controller memory or on the disk.
ERASE (Program name) Deletes the specified
program from memory or storage. EXECUTE (Program
name) Makes the robot execute the specified
program. It may be abbreviated as EX or EXEC.
ABORT Stops the robot motion during
execution. STOP The same as abort.
87
EXAMPLE 1 Develop a program in VAL II to
command a PUMA robot to unload a cylindrical part
of 10 mm diameter from machine 1 positioned at
point P1 and load the part on machine 2
positioned at P2. The speed of robot motion is 40
in./s. However, because of safety precautions,
the speed is reduced to 10 in./s while moving to
a machine for an unloading or loading operation.
88

• Solution
• SIGNAL 5
• SPEED 40 IPS
• OPEN 100
• APPRO PI, 50
• SPEED 10 IPS
• MOVE PI
• GRASP 10, 100
• DEPART P1, 50
• SPEED 40 IPS
• APPRO P2, 50
• SPEED 10 IPS
• MOVEP2
• BELOW
• OPENI 100
• ABOVE
• DEPART P2, 50
• STOP

89
EXAMPLE 2 Suppose we want to drill 16 holes
according to the pattern shown in the Figure. The
pendant procedure can be used to teach the 16
locations, but this would be quite time-consuming
and using the same program in different robot
installations would require all points to be
taught at each location. VAL II allows location
adjustment under computer control. The program
allows all holes to be drilled given just one
location, called STA at the bottom right-hand
corner of the diagram. Actually, two programs are
required, since one will be a subroutine.
90
(No Transcript)
91
EXAMPLE 3
92

• ROBOT SELECTION
  
• This phenomenal growth in the variety of robots
  has made the robot selection process difficult
  for applications engineers. Once the application
  is selected, which is the primary objective, a
  suitable robot should be chosen from the many
  commercial robots available in the market.
• The technical features are the prime
  considerations in the selection of a robot. These
  include features such as
• degrees of freedom,
• control system to be adopted,
• work volume,
• load-carrying capacity, and
• accuracy and repeatability.

93

• The characteristics of robots generally
  considered in a selection process include
• Size of class
• Degrees of freedom
• Velocity
• Actuator type
• Control mode
• Repeatability
• Lift capacity
• Right-Left-Traverse
• Up-down-traverse
• In-Out-Traverse
• Yaw
• Pitch
• Roll
• Weight of the robot

94

• We elaborate on some of these characteristics.
• Size of class. The size of the robot is given by
  the maximum dimension (x) of the robot work
  envelope. Four different classes are identified
• Micro (x lt1M)
• Small (1ltx lt2 m)
• Medium (2 ltxlt5m)
• Large (x gt5m)
• 2. Degrees of freedom. The degrees of freedom can
  be one, two, three, and so on. The cost of the
  robot increases with increasing number of degrees
  of freedom.

95

• Velocity. Velocity considerations are affected by
  the robot's arm structure. There are various
  types of arm structures. For example, the arm
  structure can be classified into the following
  categories
• Rectangular
• Cylindrical
• Spherical
• Articulated horizontal
• Articulated vertical
• 4. Actuator types. Actuator types have been
  discussed in the earlier sections. They are
• Hydraulic
• Electric
• Pneumatic
• Sometimes, a combined electrical and hydraulic
  control system may be preferred.

96

• 5. Control modes. Possible control modes
  -include
• Nonservo
• Servo point-to-point (PTP)
• Servo continuous path (CP)
• Combined PTP and CP
• Characteristics such as lift capacity, weight,
  velocity, and repeatability are divided into
  ranges. Based on the ranges, the characteristics
  are categorized in subclasses. For example, lift
  capacity can be categorized as 0-5 kg, 5-20 kg,
  20-40 kg, and so forth.
• A simple approach to selecting a robot is to
  identify all the required features and the
  features that may be desirable.

97
The desirable features may play an important role
in the selection of robots. These desirable
features in an individual robot may be ranked on
a scale of, say, 1 to 10 and the desirability of
these features itself may be assigned weights.
Finally, rank the available robots that have
these features based on cost and quality
considerations.
98
EXAMPLE A manufacturing company is planning to
buy a robot. For the type of application, the
robot should have at least six required features.
It will be helpful to have more features that
would add some flexibility in its usage
capabilities. The company is looking at six more
desirable features. Five robots are selected from
the initial elimination process based on
required features. The rating score matrix R is
given as The entry in position (i, j )
represents the score given to the ith robot model
based on how well it satisfies the j th desirable
feature. The score is given on a scale of 0 to
10. These scores are assigned by the applications
engineers based on their experience and practical
requirements. Furthermore, if the importance of
desirable features is given by the following
weight vector, determine the priority ranking of
robots for the given application. W (0.9
0.3 0.6 0.5 0.8 0.4 )
99
(No Transcript)
100
(No Transcript)
101
Robot Applications

• The common industrial applications of robots in
  manufacturing involve loading and unloading of
  parts. They include
• The robot unloading parts from die-casting
  machines
• The robot loading a raw hot billet into a die,
  holding it during forging, and unloading it from
  the forging die
• The robot loading sheet blanks into automatic
  presses, with the parts falling out of the back
  of the machine automatically after the press
  operation is performed
• The robot unloading molded parts formed in
  injection molding machines
• The robot loading raw blanks into NC machine
  tools and unloading the finished parts from the
  machines
• Safety and relief from handling heavy loads are
  the key advantages of using robots for loading
  and unloading operations.

102
A Single-Machine Robotic Cell Application

• Consider a machining center with inputoutput
  conveyors and a robot to load the parts onto the
  machine and unload the parts from the machine as
  shown in the Figure. A typical operation sequence
  consists of the following steps
• The incoming conveyor delivers the parts to a
  fixed position.
• The robot picks up a part from the conveyor and
  moves to the machine.
• The robot loads the part onto the machine.
• The part is processed on the machine.
• The robot unloads the part from the machine.
• The robot puts the part on the outgoing conveyor.
• The robot moves from the output conveyor to the
  input conveyor.
• This operation sequence of the robotic cell is
  accomplished by a cell controller. Production
  rate is one of the important performance measures
  of such cells. We provide an example of
  determining the cycle time and production rate of
  a robotic cell.

103
(No Transcript)
104
EXAMPLE Compute the cycle time and production
rate for a single-machine robotic cell for an 8-h
shift if the system availability is 90. Also
determine the percent utilization of machine and
robot. On average, the machine takes 30 s to
process a part. The other robot operation times
are as follows Robot picks up a part from the
conveyor 3.0s Robot moves the part to the
machine 1.3s Robot loads the part onto the
machine l.0s Robot unloads the part from the
machine 0.7s Robot moves to the
conveyor 1.5s Robot puts the part on the
outgoing conveyor 0.5s Robot moves from the
output conveyor to the input conveyor 4.0s
105
(No Transcript)
106
(No Transcript)
107
A Single-Machine Cell with a Double-Gripper Robot

• A double-gripper robot has two gripping devices
  attached to the wrist. The two grip ping devices
  can be actuated independently. The double gripper
  can be used to handle a finished and an
  unfinished work piece at the same time. This
  helps increase productivity, particularly in
  loading and unloading operations on machines. For
  example, with the use of a double-handed gripper,
  the following robot operations could be performed
  during the machine operation cycle time
• 1. Move to conveyor
• 2. Deposit a part and pick up a new part
• 3. Move to the machine
• However, it must be mentioned that this is
  possible only if the machine operation cycle time
  is more than the combined time for activities
  1,2, and 3. Furthermore, there is no need to move
  the robot arm from the output conveyor to the
  input conveyor.

108
(No Transcript)
109
ECONOMIC JUSTIFICATION OF ROBOTS

• We have seen in the previous section on robot
  applications that robots are being used in a
  variety of industrial and domestic environments.
  Some of these applications are justified on the
  basis that the type of work, such as welding or
  painting, is dangerous and unhealthy for humans.
  It is, however, equally important to study
  whether the robotization is also economically
  justified. A large number of models for economic
  evaluation exist (for details, refer to White et
  al, 1989). In this section we provide a simple
  treatment by considering the payback period as a
  measure of economic justification of robots.

110
Payback Period Method
The primary idea behind the payback period method
is to determine how long it takes to get back the
money invested in a project. The payback period i
can be determined from the following
relation Net investment cost total
investment cost of robot and accessories
-investment tax credits available from the
government, if any Net annual cash flows annual
anticipated revenues from robot
installation including direct labor and
material cost savings - annual operating
costs including labor, material, and maintenance
cost of the robot system
111
Example

• Detroit Plastics is planning to replace a manual
  painting system by a robotic system. The system
  is priced at 160,000.00, which includes sensors,
  grippers, and other required accessories. The
  annual maintenance and operation cost of the
  robot system on a single-shift basis is
  10,000.00. The company is eligible for a
  20,000.00 tax credit from the federal government
  under its technology investment program. The
  robot will replace two operators. The hourly rate
  of an operator is 2000 including fringe
  benefits. There is no increase in production
  rate. Determine the payback period for one- and
  two-shift operations.

112

• Solution
• Net investment cost capital cost - tax credits
  160,000 - 20000.00 140000.00
• Annual labor cost operator rate (20/hr) X number
  of operators (2) X days per year
• (250 d/yr) X single shift (8 h/d) 80,000 (for
  a single shift)
• For double-shift operation, the annual labor cost
  is 160,000.00.
• For a single-shift operation
• Annual savings annual labor cost - annual robot
  maintenance and operating cost
• 80,000.00 - 10,000.00 70,000.00
• The payback period for single-shift operation is
  Sl40,000,00/70,000.00 2 years
• For double-shift operation,
• Annual savings 160,000.00 - 20,000.00
  140,000.00.
• Therefore, the payback period for double-shift
  operation is 140,000.00/ 140,000.00 1.00
  years.
• A payback period of 2 years or less is a very
  attractive investment. In this example we have
  not considered any production rate increase with
  the robot system installation. Typically, such a
  system results in 30 to 75 increase in
  productivity. Based on these figures. this is an
  attractive proposal.