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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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Integrated Manufacturing Systems
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”
Robotics: The science of robots. Humans working in this area are called roboticists.
DOF degrees-of-freedom: the number of independent motions a device can make. (Also called mobility)
five degrees of freedom
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.
End-effector:The tool, gripper, or other device mounted at the end ofa manipulator, for accomplishing useful tasks.
Workspace:The volume in space that a robot’s end-effectorcan reach,both in position and orientation.
A cylindrical robots’ half workspace
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
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.
The Greek mathematician, Archytas builds a mechanical bird named "the Pigeon" that is propelled by steam.
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.
The Greek inventor and physicist Ctesibus of Alexandria designs water clocks that have movable figures on them.
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.
Jacques de Vaucanson begins building automata. The first one was the flute player that could play twelve songs.
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.
Joseph Jacquard builds an automated loom that is controlled with punched cards.
Joseph Jacquard’s Automated Loom
Nikola Tesla builds and demonstrates a remote controlled robot boat.
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“.
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”.
George Devol patents a playback device for controlling machines.
Heinrich Ernst develops the MH-1, a computer operated mechanical hand at MIT.
Unimate, the company of Joseph Engleberger and George Devoe, built the first industrial robot, the PUMA (Programmable Universal Manipulator Arm).
The Stanford Research Institute creates Shakey the first mobile robot to know and react to its own actions.
Victor Scheinman creates the Stanford Arm. The arm's design becomes a standard and is still influencing the design of robot arms today.
Shigeo Hirose designs the Soft Gripper at the Tokyo Institute of Technology. It is designed to wrap around an object in snake like fashion.
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.
A walking robot named Genghis is unveiled by the Mobile Robots Group at MIT.
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.
Dante II, a more robust version of Dante I, descends into the crater of Alaskan volcano Mt. Spurr. The mission is considered a success.
Honda debuts the P3.
The Pathfinder Mission lands on Mars
SONY releases the AIBO robotic pet.
Honda debuts new humanoid robot ASIMO.
1. Hydraulic drive
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.
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.
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.
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.
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.
Grippers are generally used to grasp and hold an object and place it at a desired location.
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
Speed of response and stability are two important characteristics of robot movement.
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 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.
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 basic movements required for a desired motion of most industrial robots are:
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.
Revolute joints permit only angular motion between links. Their variations include:
In a prismatic joint, also known as a sliding or linear joint (L), the links are generally parallel to one
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.
A twisting joint (T) is also a rotational joint, where the rotation takes place about an axis that is parallel to both adjoining links.
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.
Robots may be classified, based on:
Classification Based on Physical Configuration:
Classification Based on Control Systems:
Typical applications include:
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.
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 .
The kinematic analysis involves two different kinds of problems:
The position, V, of the end-effector can be defined in the Cartesian coordinate system, as:
V = (x, y)
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)
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.
where Vj refers to the position of the end-effector in joint space.
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.
where VW refers to the position of the end-effector in world space.
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
These relations can be represented in homogeneous matrix form:
If the end-effector point is denoted by (x, y), then:
x = x2
y = y2 - L3
X = T2 X2
TLL = T2 T1
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)
In matrix form:
X2 = T1 X1
On the other end:
x = x2 +L3 cos(a-q)
y = y2 - L3 sin(a-q)
In matrix form:
X = T2 X2
Combining the two equation gives:
X = T2 (T1 X1) = TRR X1
TRR = T2 T1
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)
In matrix form:
X = TTL X2
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
x = x1 + L2 cos(q) + L3 cos(a-q)
y = y1 + L2 sin(q) - L3 sin(a-q)
One can easily get the angles:
x = x2 + L cos(a)
y = y2 +L sin(a)
One can easily get the equations for length and angle:
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).
(x1, y1) = (0, 0)
Therefore the end-effector point is given by (3, -5).
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.
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)
It is given that (x1, y1) = (0, 0)
Therefore the end-effector point is given by (1.8667, 0.5)
It is given that (x, y) = (1, 0), therefore,
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)
a) It is given that (x2, y2) = (0, 0); L = 1m and a = 30o
(x, y) = (0.866, 0.5)
b)It is given that (x, y) = (0.7071, 0.7071)
sin(a) = (y-y2)/L = (0.7071-0)/1 = 0.7071
a = 45o
Loading/unloading parts to/from the machines
Provides a consistency in paint quality. Widely used in automobile industry.
Electronic component assemblies and machine assemblies are two areas of application.
Payback period method:
n = number of years that the investment is paid back
net investment cost = total investment cost of robot - investment tax credit
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
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 $20 including fringe benefits. There is no increase in production rate. Determine the payback period for one-shift and two-shift operations.
Net investment cost = capital cost – tax credits
Net investment cost = 160,000 [$]- 20,000 [$]
= 140,000 [$]
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 [$/yr] (for a double shift)
Annual saving = annual labor cost – annual maintenance and operating cost
Annual saving = 80,000 [$/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)
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]
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.
The characteristics of robots generally considered in a selection process include:
Size of class
Degrees of freedom
Weight of the robot
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.
3. Velocity: Velocity consideration is effected by the robot’s arm structure.
4. Drive type:
5. Control mode:
Continuous path control(CP)
Controlled path control
20-40 kg and so forth