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MIDDLE EAST TECHNICAL UNIVERSITY Mechanical Engineering Department. ME 445 Integrated Manufacturing Systems. ROBOTICS. Robotics Terminology. Robot: An electromechanical device with multiple degrees-of-freedom (DO F) that is programmable to accomplish a variety of tasks.

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middle east technical university mechanical engineering department
MIDDLE EAST TECHNICAL UNIVERSITYMechanical Engineering Department

ME 445

Integrated Manufacturing Systems

slide3

Robotics Terminology

Robot: An electromechanical device with multiple degrees-of-freedom(DOF) that is programmable to accomplish a variety of tasks.

Industrial robot:The Robotics Industries Association (RIA) 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 theperformance of a variety of tasks”

slide4

Robotics Terminology

Robotics: The science of robots. Humans working in this area are called roboticists.

slide5

Robotics Terminology

DOF degrees-of-freedom: the number of independent motions a device can make. (Also called mobility)

five degrees of freedom

slide6

Robotics Terminology

Manipulator:Electromechanical device capable ofinteractingwith its environment.

Anthropomorphic:Like human beings.

ROBONAUT (ROBOtic astroNAUT), an anthropomorphic robot with two arms,

two hands, a head, a torso, and a stabilizing leg.

slide7

Robotics Terminology

End-effector:The tool, gripper, or other device mounted at the end ofa manipulator, for accomplishing useful tasks.

slide8

Robotics Terminology

Workspace:The volume in space that a robot’s end-effectorcan reach,both in position and orientation.

A cylindrical robots’ half workspace

slide9

Robotics Terminology

Position:The translational (straight-line) location of something.

Orientation:The rotational (angle) location of something. A robot’s orientation is measured by roll, pitch, and yawangles.

Link:A rigid piece of material connecting joints in a robot.

Joint:The device which allows relative motion betweentwo links in a robot.

A robot joint

slide10

Robotics Terminology

Kinematics:The study of motion without regard to forces.

Dynamics:The study of motion with regard to forces.

Actuator:Provides force for robot motion.

Sensor:Reads variables in robot motion for use in control.

slide11

Robotics Terminology

  • Speed
    • The amount of distance per unit time at which the robot can move,usually specified in inches per second or meters per second.
    • The speed is usually specified at a specific loadorassuming that the robot is carrying a fixed weight.
    • Actual speed may vary dependingupon the weight carried by the robot.
  • Load Bearing Capacity
    • The maximum weight-carrying capacity of the robot.
    • Robots that carry large weights, but must still be preciseare expensive.
slide12

Robotics Terminology

  • Accuracy
    • The ability of a robot to go to the specified position without makinga mistake.
    • It is impossible to position a machine exactly.
    • Accuracy is therefore defined as the ability of the robot to positionitself to the desired location with the minimal error (usually 25 mm).
  • Repeatability
    • The ability of a robot to repeatedly position itself when asked toperform a task multiple times.
    • Accuracy is an absolute concept, repeatability is relative.
    • A robot that is repeatable may not be very accurate, visaversa.
robotics history

350 B.C

The Greek mathematician, Archytas builds a mechanical bird named "the Pigeon" that is propelled by steam.

322 B.C.

TheGreekphilosopher Aristotle writes;

“If every tool, when ordered, or even of its own accord, could do the work that befits it... then there would be no need either of apprentices for the master workers or of slaves for the lords.”...

hinting how nice it would be to have a few robots around.

200 B.C.

The Greek inventor and physicist Ctesibus of Alexandria designs water clocks that have movable figures on them.

Robotics History

slide15

Robotics History

1495

Leonardo DaVinci designs a mechanical device that looks like an armored knight. The mechanisms inside "Leonardo\'s robot" are designed to make the knight move as if there was a real person inside.

slide16

Robotics History

Leonardo’s Robot

slide17

Robotics History

1738

Jacques de Vaucanson begins building automata. The first one was the flute player that could play twelve songs.

1770

Swiss clock maker and inventor of the modern wristwatch Pierre Jaquet-Droz start making automata for European royalty. He create three doll, one can write, another plays music, and the third draws pictures.

1801

Joseph Jacquard builds an automated loom that is controlled with punched cards.

slide18

Robotics History

Joseph Jacquard’s Automated Loom

slide19

Robotics History

1898

Nikola Tesla builds and demonstrates a remote controlled robot boat.

slide20

Robotics History

1921

Czech writer Karel Capek introduced the word "Robot" in his play "R.U.R" (Rossuum\'s Universal Robots). "Robot" in Czech comes from the word "robota", meaning "compulsory labor“.

1940

Issac Asimov produces a series of short stories about robots starting with "A Strange Playfellow" (later renamed "Robbie") for Super Science Stories magazine. The story is about a robot and its affection for a child that it is bound to protect. Over the next 10 years he produces more stories about robots that are eventually recompiled into the volume "I, Robot" in 1950.Issac Asimov\'s most important contribution to the history of the robot is the creation of his “Three Laws of Robotics”.

slide21

Robotics History

  • Three Laws of Robotics:
    • A robot may not injure a human being, or, through inaction, allow a human being to come to harm.
    • A robot must obey the orders given it by human beings except where such orders would conflict with the First Law.
    • A robot must protect its own existence as long as such protection does not conflict with the First or Second Law.
  • Asimov later adds a "zeroth law" to the list:
  • Zeroth law: A robot may not injure humanity, or, through inaction, allow humanity to come to harm.
slide22

Robotics History

1946

George Devol patents a playback device for controlling machines.

1961

Heinrich Ernst develops the MH-1, a computer operated mechanical hand at MIT.

1961

Unimate, the company of Joseph Engleberger and George Devoe, built the first industrial robot, the PUMA (Programmable Universal Manipulator Arm).

1966

The Stanford Research Institute creates Shakey the first mobile robot to know and react to its own actions.

slide23

Robotics History

Unimate PUMA

SRI Shakey

slide24

Robotics History

1969

Victor Scheinman creates the Stanford Arm. The arm\'s design becomes a standard and is still influencing the design of robot arms today.

slide25

Robotics History

1976

Shigeo Hirose designs the Soft Gripper at the Tokyo Institute of Technology. It is designed to wrap around an object in snake like fashion.

1981

Takeo Kanade builds the direct drive arm. It is the first to have motors installed directly into the joints of the arm. This change makes it faster and much more accurate than previous robotic arms.

1989

A walking robot named Genghis is unveiled by the Mobile Robots Group at MIT.

slide26

Robotics History

1993

Dante an 8-legged walking robot developed at Carnegie Mellon University descends into Mt. Erebrus, Antarctica. Its mission is to collect data from a harsh environment similar to what we might find on another planet.

1994

Dante II, a more robust version of Dante I, descends into the crater of Alaskan volcano Mt. Spurr. The mission is considered a success.

slide27

Robotics History

1996

Honda debuts the P3.

slide28

Robotics History

1997

The Pathfinder Mission lands on Mars

1999

SONY releases the AIBO robotic pet.

slide29

Robotics History

2000

Honda debuts new humanoid robot ASIMO.

power sources for robots
Power Sources for Robots
  • An important element of a robot is the drive system. The drive system supplies the power, which enable the robot to move.
  • The dynamic performance of a robot mainly depends on the type of power source.
there are basically three types of power sources for robots
There are basically three types of power sources for robots:

1. Hydraulic drive

  • Provide fast movements
  • Preferred for moving heavy parts
  • Preferred to be used in explosive environments
  • Occupy large space area
  • There is a danger of oil leak to the shop floor
slide33
2. Electric drive
  • Slower movement compare to the hydraulic robots
  • Good for small and medium size robots
  • Better positioning accuracy and repeatability
  • stepper motor drive: open loop control
  • DC motor drive: closed loop control
  • Cleaner environment
  • The most used type of drive in industry
slide34
3. Pneumatic drive
  • Preferred for smaller robots
  • Less expensive than electric or hydraulic robots
  • Suitable for relatively less degrees of freedom design
  • Suitable for simple pick and place application
  • Relatively cheaper
robotic sensors
Robotic Sensors
  • 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 as follows:
slide36
Position sensors:

Position sensors are used to monitor the position of joints. Information about the position is fed back to the control systems that are used to determine the accuracy of positioning.

slide37
2.Range sensors:

Range sensors measure distances from a reference point to other points of importance. Range sensing is accomplished by means of television cameras or sonar transmitters and receivers.

slide38
3. Velocity Sensors:

They are used to estimate the speed with which a manipulator is moved. The velocity is an important part of the dynamic performance of the manipulator. The DC tachometer is one of the most commonly used devices for feedback of velocity information. The tachometer, which is essentially a DC generator, provides an output voltage proportional to the angular velocity of the armature. This information is fed back to the controls for proper regulation of the motion.

slide39
4. Proximity Sensors:

They are used to sense and indicate the presence of an object within a specified distance without any physical contact. This helps prevent accidents and damage to the robot.

  • infra red sensors
  • acoustic sensors
  • touch sensors
  • force sensors
  • tactile sensors for more accurate data on the position
the hand of a robot end effector
The Hand of a Robot: End-Effector

The end-effector (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: grippers and tools.

the hand of a robot end effector2
The Hand of a Robot: End-Effector

Grippers are generally used to grasp and hold an object and place it at a desired location.

  • mechanical grippers
  • vacuum or suction cups
  • magnetic grippers
  • adhesive grippers
  • hooks, scoops, and so forth
the hand of a robot end effector3
The Hand of a Robot: End-Effector

At times, a robot is required to manipulate a tool to perform an operation on a workpiece. In such applications the end-effector is a tool itself

  • spot-welding tools
  • arc-welding tools
  • spray-painting nozzles
  • rotating spindles for drilling
  • rotating spindles for grinding
robot movement and precision
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.
robot movement and precision1
Robot Movement and Precision

Speed and stability are often conflicting goals. However, a good controlling system can be designed for the robot to facilitate a good trade-off between the two parameters.

the precision of robot movement is defined by three basic features
The precision of robot movement is defined by three basic features:
  • 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.

slide47
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. This definition of accuracy applies in the worst case when the target point is between two control points.The reason is that displacements smaller than one basic control resolution unit (BCRU) can be neither programmed nor measured and, on average, they account for one-half BCRU.
slide48
The accuracy of a robot is affected by many factors. For example, when the arm is fully stretched out, the mechanical inaccuracies tend to be larger because the loads tend to cause deflection.
slide49
3. Repeatability: It is the ability of the robot to position the end effector to the previously positioned location.
the robotic joints
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-effector along a path from one position to another as desired.

the robotic joints1
The Robotic Joints

The basic movements required for a desired motion of most industrial robots are:

  • 1. rotational movement: This enables the robot to place its arm in any direction on a horizontal plane.
  • 2. Radialmovement: This enables the robot to move its end-effector radially to reach distant points.
  • 3. Vertical movement: This enables the robot to take its end-effector to different heights.
the robotic joints2
The Robotic Joints

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 arm. 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 prismaticorrevolute.

the robotic joints3
The Robotic Joints
  • Prismaticjoints(L)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.
the robotic joints4
The Robotic Joints

Revolute joints permit only angular motion between links. Their variations include:

  • Rotational joint (R)
  • Twisting joint (T)
  • Revolving joint (V)
the robotic joints5
The Robotic Joints

In a prismatic joint, also known as a sliding or linear joint (L), the links are generally parallel to one

the robotic joints6
The Robotic Joints

A rotational joint (R) is identified by its motion, rotation about an axis perpendicular to the adjoining links. Here, the lengths of adjoining links do not change but the relative position of the links with respect to one another changes as the rotation takes place.

the robotic joints8
The Robotic Joints

A twisting joint (T) is also a rotational joint, where the rotation takes place about an axis that is parallel to both adjoining links.

the robotic joints9
The Robotic Joints

A revolving joint (V) is another rotational joint, where the rotation takes place about an axis that is parallel to one of the adjoining links. Usually, the links are aligned perpendicular to one another at this kind of joint. The rotation involves revolution of one link about another.

robot classification
ROBOT CLASSIFICATION

Robots may be classified, based on:

  • physical configuration
  • control systems
robot classification1
ROBOT CLASSIFICATION

Classification Based on Physical Configuration:

  • 1. Cartesian configuration
  • 2. Cylindrical configuration
  • 3. Polar configuration
  • 4. Joint-arm configuration
robot classification2
ROBOT CLASSIFICATION

Cartesian Configuration:

  • Robots with Cartesian configurations consists of links connected by linear joints (L). Gantry robots are Cartesian robots (LLL).
slide65

Cartesian Robots

  • A robot with 3 prismatic joints – the axes consistent with a Cartesian coordinate system.
  • Commonly used for:
  • pick and place work
  • assembly operations
  • handling machine tools
  • arc welding
cartesian robots
Cartesian Robots

Advantages:

  • ability to do straight line insertions into furnaces.
  • easy computation and programming.
  • most rigid structure for given length.

Disadvantages:

  • requires large operating volume.
  • exposed guiding surfaces require covering in corrosive or dusty environments.
  • can only reach front of itself
  • axes hard to seal
robot classification3
ROBOT CLASSIFICATION

Cylindrical Configuration:

  • Robots with cylindrical configuration have one rotary ( R) joint at the base and linear (L) joints succeeded to connect the links.
cylindrical robots
Cylindrical Robots
  • A robot with 2 prismatic joints and a rotary joint – the axes consistent with a cylindrical coordinate system.
  • Commonly used for:
  • handling at die-casting machines
  • assembly operations
  • handling machine tools
  • spot welding
cylindrical robots1
Cylindrical Robots

Advantages:

  • can reach all around itself
  • rotational axis easy to seal
  • relatively easy programming
  • rigid enough to handle heavy loads through large working space
  • good access into cavities and machine openings

Disadvantages:

  • can\'t reach above itself
  • linear axes is hard to seal
  • won’t reach around obstacles
  • exposed drives are difficult to cover from dust and liquids
robot classification4
ROBOT CLASSIFICATION

Polar Configuration:

  • Polar robots have a work space of spherical shape. Generally, the arm is connected to the base with a twisting (T) joint and rotatory (R) and linear (L) joints follow.
robot classification5
ROBOT CLASSIFICATION
  • 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. An articulated robot more closely resembles the human arm.
robot classification6
ROBOT CLASSIFICATION

Joint-arm Configuration:

  • The jointed-arm 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. Many commercially available robots have this configuration.
slide74

Articulated Robots

  • A robot with at least 3 rotary joints.
  • Commonly used for:
  • assembly operations
  • welding
  • weld sealing
  • spray painting
  • handling at die casting or fettling machines
slide75

Articulated Robots

Advantages:

  • all rotary joints allows for maximum flexibility
  • any point in total volume can be reached.
  • all joints can be sealed from the environment.

Disadvantages:

  • extremely difficult to visualize, control, and program.
  • restricted volume coverage.
  • low accuracy
slide76

SCARA (Selective ComplianceArticulated Robot Arm)Robots

  • A robot with at least 2 parallel rotary joints.
  • Commonly used for:
  • pick and place work
  • assembly operations
slide77

SCARA (Selective ComplianceArticulated Robot Arm)Robots

Advantages:

  • high speed.
  • height axis is rigid
  • large work area for floor space
  • moderately easy to program.

Disadvantages:

  • limited applications.
  • 2 ways to reach point
  • difficult to program off-line
  • highly complex arm
spherical polar robots
Spherical/Polar Robots
  • A robot with 1 prismatic joint and 2 rotary joints – the axes consistent with a polar coordinate system.
  • Commonly used for:
  • handling at die casting or fettling machines
  • handling machine tools
  • arc/spot welding
spherical polar robots1
Spherical/Polar Robots

Advantages:

  • large working envelope.
  • two rotary drives are easily sealed against liquids/dust.

Disadvantages:

  • complex coordinates more difficult to visualize, control, and program.
  • exposed linear drive.
  • low accuracy.
robot classification8
ROBOT CLASSIFICATION

Classification Based on Control Systems:

  • 1. Point-to-point (PTP) control robot
  • 2. Continuous-path (CP) control robot
  • 3. Controlled-path robot
point to point control robot ptp
Point to Point Control Robot (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.
  • Common applications include:
    • component insertion
    • spot welding
    • hole drilling
    • machine loading and unloading
    • assembly operations
continuous path control robot cp
Continuous-Path Control Robot (CP):
  • The CP robot is capable of performing movements along the controlled path. With CP from one 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. Applications 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 (teach-in).
continuous path control robot cp1
Continuous-Path Control Robot (CP):

Typical applications include:

  • spray painting
  • finishing
  • gluing
  • arc welding operations
controlled path robot
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.
robot reach
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.

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 reach1
Robot Reach:
  • 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 the reach is part of a hollow spherical shape.
  • Robot reach for a jointed-arm configuration does not have a specific shape.
robot motion analysis
ROBOT MOTION ANALYSIS

In robot motion analysis we study the geometry of the robot arm with respect to a reference coordinate system, while the end-effector moves along the prescribed path .

robot motion analysis1
ROBOT MOTION ANALYSIS

The kinematic analysis involves two different kinds of problems:

  • 1. Determining the coordinates of the end-effector or end of arm for a given set of joints coordinates.
  • 2. Determining the joints coordinates for a given location of the end-effector or end of arm.
robot motion analysis2
ROBOT MOTION ANALYSIS

The position, V, of the end-effector can be defined in the Cartesian coordinate system, as:

V = (x, y)

robot motion analysis3
ROBOT MOTION ANALYSIS

Generally, for robots the location of the end-effector can be defined in two systems:

a. joint space and

b. world space (also known as global space)

robot motion analysis4
ROBOT MOTION ANALYSIS

In joint space, the joint parameters such as rotating or twisting joint angles and variable link lengths are used to represent the position of the end-effector.

  • Vj = (q, a) for RR robot
  • Vj = (L1, , L2) for LL robot
  • Vj = (a, L2) for TL robot

where Vj refers to the position of the end-effector in joint space.

robot motion analysis5
ROBOT MOTION ANALYSIS

In world space, rectilinear coordinates with reference to the basic Cartesian system are used to define the position of the end-effector.

Usually the origin of the Cartesian axes is located in the robot\'s base.

  • VW = (x, y)

where VW refers to the position of the end-effector in world space.

robot motion analysis6
ROBOT MOTION ANALYSIS
  • The transformation of coordinates of the end-effector point from the joint space to the world space is known as forward kinematic transformation.
  • Similarly, the transformation of coordinates from world space to joint space is known as backward or reverse kinematic transformation.
forward kinematictransformation
Forward KinematicTransformation

LL Robot:

Let us consider a Cartesian LL robot

Joints J1 and J2 are linear joints with links of variable lengths L1 and L2. Let joint J1 be denoted by (x1 y1) and joint J2 by (x2, y2).

From geometry, we can easily get the following:

x2=x1+L2y2 = y1

forward k inematictransformation
Forward KinematicTransformation

These relations can be represented in homogeneous matrix form:

or

X2=T1 X1

forward kinematictransformation1
Forward KinematicTransformation

where

If the end-effector point is denoted by (x, y), then:

x = x2

y = y2 - L3

forward kinematictransformation2
Forward KinematicTransformation

therefore:

X = T2 X2

or

TLL = T2 T1

and

forward kinematictransformation3
Forward KinematicTransformation

RR Robot:

Let q and a be the rotations at joints J1 and J2 respectively. Let J1 and J2 have the coordinates of (x1, y1) and (x2, y2), respectively.

One can write the following from the geometry:

x2 = x1+L2 cos(q)

y2 = y1 +L2 sin(q)

forward kinematictransformation4
Forward KinematicTransformation

In matrix form:

or

X2 = T1 X1

On the other end:

x = x2 +L3 cos(a-q)

y = y2 - L3 sin(a-q)

forward kinematictransformation5
Forward KinematicTransformation

In matrix form:

or

X = T2 X2

Combining the two equation gives:

X = T2 (T1 X1) = TRR X1

forward kinematictransformation7
Forward KinematicTransformation

TL Robot:

Let a be the rotation at twisting joint J1 and L2 be the variable link length at linear joint J2.

One can write that:

x = x2 + L2 cos(a)

y = y2 + L2 sin(a)

forward kinematictransformation8
Forward KinematicTransformation

In matrix form:

or

X = TTL X2

backward kinematic transformation
Backward Kinematic Transformation

LL Robot:

In backward kinematic transformation, the objective is to drive the variable link lengths from the known position of the end effector in world space.

x = x1 + L2

y = y1 - L3

y1 = y2

By combining above equations, one can get:

L2 = x - x1

L3 = -y +y2

backward kinematic transformation1
Backward Kinematic Transformation

RR Robot:

x = x1 + L2 cos(q) + L3 cos(a-q)

y = y1 + L2 sin(q) - L3 sin(a-q)

backward kinematic transformation2
Backward Kinematic Transformation

One can easily get the angles:

and

backward kinematic transformation3
Backward Kinematic Transformation

TL Robot:

x = x2 + L cos(a)

y = y2 +L sin(a)

One can easily get the equations for length and angle:

example
EXAMPLE

An LL robot has two links of variable length.

Assuming that the origin of the globalcoordinate system is defined at joint J1, determine the following:

a)The coordinate of the end-effector point if the variable link lengths are 3m and 5 m.

b) Variable link lengths if the end-effector is located at (3, 5).

example2
EXAMPLE

Solution:

  • It is given that:

(x1, y1) = (0, 0)

Therefore the end-effector point is given by (3, -5).

example3
EXAMPLE

b) The end effector point is given by (3, 5)

Then: L2 = x - x1 = 3 - 0 = 3 m

L3 = -y + y1 = -5 + 0 = -5 m

The variable lengths are 3 m and 5 m. The minus sign is due to the coordinate system used.

example4
EXAMPLE

An RR robot has two links of length 1 m. Assume that the origin of the global coordinate system is at J1.

a) Determine the coordinate of the end-effector point if the joint rotations are 30o at both joints.

b) Determine joint rotations if the end-effector is located at (1, 0)

example5
EXAMPLE

It is given that (x1, y1) = (0, 0)

Therefore the end-effector point is given by (1.8667, 0.5)

example7
EXAMPLE

It is given that (x, y) = (1, 0), therefore,

example9
EXAMPLE

In a TL robot, assume that the coordinate system is defined at joints J2.

a) Determine the coordinates of the end-effector point if joint J1 twist by an angle of 30o and the variable link has a length of 1 m.

b) Determine variable link length and angle of twist at J1 if the end-effector is located at (0.7071, 0.7071)

example11
EXAMPLE

a) It is given that (x2, y2) = (0, 0); L = 1m and a = 30o

example12
EXAMPLE

(x, y) = (0.866, 0.5)

example13
EXAMPLE

b)It is given that (x, y) = (0.7071, 0.7071)

sin(a) = (y-y2)/L = (0.7071-0)/1 = 0.7071

a = 45o

robot applications
ROBOT APPLICATIONS

Loading/unloading parts to/from the machines

  • 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
  • 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
robot applications1
ROBOT APPLICATIONS

Welding

  • Spot welding: Widest use is in the automotive industry
  • Arc welding: Ship building, aerospace, construction industries are among the many areas of application.

Spray painting:

Provides a consistency in paint quality. Widely used in automobile industry.

Assembly:

Electronic component assemblies and machine assemblies are two areas of application.

Inspection

economic justification of robots
ECONOMIC JUSTIFICATION OF ROBOTS

Payback period method:

n = number of years that the investment is paid back

economic justification of robots1
ECONOMIC JUSTIFICATION OF ROBOTS

net investment cost = total investment cost of robot - investment tax credit

economic justification of robots2
ECONOMIC JUSTIFICATION OF ROBOTS

net annual cash flow = annual anticipated revenues

from robot installation including

direct labor and material cost

savings – annual operating costs including labor, material and maintenance costs of the robot system

economic justification of robots3
ECONOMIC JUSTIFICATION OF ROBOTS

EXAMPLE: A company is planning to replace a manual painting system by a robotic system. The system is priced at $160,000 which includes sensors, grippers and other required accessories. The annual maintenance and operation cost of robot system on a single-shift basis is $10,000. The company is eligible for a $20,000 tax credit from the government under its technology investment program. The robot will replece two operators. The hourly rate of an operator is $20 including fringe benefits. There is no increase in production rate. Determine the payback period for one-shift and two-shift operations.

economic justification of robots4
ECONOMIC JUSTIFICATION OF ROBOTS

Net investment cost = capital cost – tax credits

Net investment cost = 160,000 [$]- 20,000 [$]

= 140,000 [$]

economic justification of robots5
ECONOMIC JUSTIFICATION OF ROBOTS

Annual labor cost = operator rate x number of operators x days per x hours per day

Annual labor cost = 20 [$/hr] x 2 x 250 [d/yr] x 8 [hr/d]

Annual labor cost = 80,000 [$/yr] (for a single shift)

Annual labor cost = 160,000 [$/yr] (for a double shift)

economic justification of robots6
ECONOMIC JUSTIFICATION OF ROBOTS

Annual saving = annual labor cost – annual maintenance and operating cost

Annual saving = 80,000 [$/yr] - 10,000 [$/yr]

= $70,000 [$/yr] (for a single shift)

Annual saving = 160,000 [$/yr] - 20,000 [$/yr]

= $140,000 [$/yr] (for a double shift)

economic justification of robots7
ECONOMIC JUSTIFICATION OF ROBOTS

for a single shift:

Payback period = 140,000 [$] / 70,000 [$/yr] = 2 [yr]

for a double shift:

Payback period = 140,000 [$] / 140,000 [$/yr] = 1 [yr]

economic justification of robots8
ECONOMIC JUSTIFICATION OF ROBOTS

EXAMPLE:

  • Compute the cycle time and production rate for a single machine robotic cell for an 8 hour shift if the system availability is 90%. Also determine the percent utilization of machine and robot.
  • Machine processing time 30 s
  • Robot picks up the part from the conveyor 3.0 s
  • Robot moves the part to the machine 1.3 s
  • Robot loads the part on to the machine 1.0 s
  • Robot unloads the part from the machine 0.7 s
  • Robot moves the part to the conveyor 1.5 s
  • Robot puts the part on to the outgoing
  • conveyor 0.5 s
  • Robot moves from the output conveyor
  • to the input conveyor 4.0 s
  • Total 12 s
economic justification of robots9
ECONOMIC JUSTIFICATION OF ROBOTS

Solution:

  • The total cycle time: 30 + 12 = 42 s

Production rate:

  • (1/42) part/s 3600 s/hr 8 hr/shift 0.90 (uptime)
  • = 617 parts/shift

Machine utilization:

  • Machine cycle time/total cycle time = 30/42
  • = 71.4%

Robot utilization:

  • robot cycle time/total cycle time : 12/42
  • = 28.6%
slide136

Advantages

  • Greater flexibility, re-programmability
  • Greater response time to inputs than humans
  • Improved product quality
  • Maximize capital intensive equipment in multiple workshifts
  • Accident reduction
  • Reduction of hazardous exposure for human workers
  • Automation less susceptible to work stoppages
slide137

Disadvantages

  • Replacement of human labor
  • Greater unemployment
  • Significant retraining costs for both unemployed and users of new technology
  • Advertised technology does not always disclose some ofthe hidden disadvantages
  • Hidden costs because of the associated technologythatmust be purchased and integrated into a functioningcell.Typically, a functioning cell will cost 3-10 timesthe cost of the robot.
slide138

Limitations

  • Assembly dexterity does not match that of humanbeings,particularly where eye-hand coordination required.
  • Payload to robot weight ratio is poor, often less than 5%.
  • Robot structural configuration may limit joint movement.
  • Work volumes can be constrained by parts ortooling/sensorsadded to the robot.
  • Robot repeatability/accuracy can constrain the range ofpotential applications.
slide139

ROBOT SELECTION

In a survey published in 1986, it is stated that there are 676 robot models available in the market. Once the application is selected, which is the prime objective, a suitable robot should be chosen from the many commercial robots available in the market.

slide140

ROBOT SELECTION

The characteristics of robots generally considered in a selection process include:

Size of class

Degrees of freedom

Velocity

Drive type

Control mode

Repeatability

Lift capacity

Right-left traverse

Up-down traverse

In-out traverse

Yaw

Pitch

Roll

Weight of the robot

slide141

ROBOT SELECTION

1. Size of class: The size of the robot is given by the maximum dimension (x) of the robot work envelope.

Micro (x < 1 m)

Small (1 m < x < 2 m)

Medium (2 < x < 5 m)

Large (x > 5 m)

2. Degrees of freedom. The cost of the robot increases with the number of degrees of freedom. Six degrees of freedom is suitable for most works.

slide142

ROBOT SELECTION

3. Velocity: Velocity consideration is effected by the robot’s arm structure.

Rectangular

Cylindrical

Spherical

Articulated

4. Drive type:

Hydraulic

Electric

Pneumatic

slide143

ROBOT SELECTION

5. Control mode:

Point-to-point control(PTP)

Continuous path control(CP)

Controlled path control

6.Lift capacity:

0-5 kg

5-20 kg

20-40 kg and so forth

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