20MTT62 – MECHANICS OF SERIAL MANIPULATOR

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History of Robot

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“Robota” - Forced Labour

History of Robot

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History of Robot

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History of Robot

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History of Robot

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Evaluation of Industrial Manipulator

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“A robot is a programmable, multifunction manipulator designed to move material, parts, tools, or special devices through variable programmed motions for the performance of a variety of tasks”

Robot Institute of America

Industrial Robots Definition

A robot is a programmable arm simulator

1. A robot may not injure a human being or, through inaction, allow a human being to come to harm.

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• A robot must obey orders given it by human beings except where such orders would conflict with the First Law.

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• A robot must protect its own existence as long as such protection does not conflict with the First or Second Law.

Laws of Robotics

Isaac Asimov @ 1939

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Basic Components of Robot

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Manipulator

The manipulator consists of segments that may be jointed and that move about, allowing the robot to do work. It moves materials, parts, tools, or special devices through various motions to provide useful work.

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End Effector

The end effector is the robot’s hand, or the end-of-arm tooling on the robot.

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It is a device attached to the wrist of the manipulator for the purpose of grasping, lifting, transporting, maneuvering, or performing operations on a workpiece.

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Robot’s performance is a direct result of how well the end effector meets the task requirements.

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Area within reach of the robot’s end effector is called its work envelope.

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Controller

The controller is the part of a robot that coordinates all movements of the mechanical system.

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It also receives input from the immediate environment through various sensors.

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The heart of the robot’s controller is generally a microprocessor linked to input/output and monitoring devices.

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The commands issued by the controller activate the motion control mechanism, consisting of various controllers, amplifiers, and actuators.

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This movement is initiated by a series of instructions, called a program, stored in the controller’s memory.

The means for programming is used to record movements into the robot’s memory.

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A robot may be programmed using any of several different methods. The teach pendant, also called a teach box or handheld programmer teaches a robot the movements required to perform a useful task.

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The operator uses a teach pendant to move the robot through the series of points that describe its desired path. The points are recorded by the controller for later use.

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Means for Programming:

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Provides the energy to drive the controller and actuators.

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It may convert ac voltage to the dc voltage required by the robot’s internal circuits, or it may be a pump or compressor providing hydraulic or pneumatic power.

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The three basic types of power supplies are electrical, pneumatic and hydraulic.

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Power supply

The individual joint motions associated with the performance of task or Number of independent parameter required to define the motion

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Describe a robot’s freedom of motion in three dimensional space. The ability to move

• to the left and to the right - rotational traverse (x- axis)
• forward and backward - radial traverse (y-axis)
• up and down - vertical traverse (z-axis)

Degrees of Freedom

Additional degree of freedom can be obtained from wrist

• up and down - pitch (x-axis)
• side to side - yaw (y- axis)
• swivel - roll (z- axis)

Degrees of Freedom

A robot requires a total of six degrees of freedom to locate and orient its hand at any point in its work envelope

Manipulator Joints

• Translational motion (Prismatic Joint (P))
• Linear joint (type L)
• Orthogonal joint (type O)

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• Rotary motion

(Revolute Joint (R))

• Rotational joint (type R)
• Twisting joint (type T)
• Revolving joint (type V)

Wrist Configurations

• Wrist assembly is attached to end-of-arm
• End effector is attached to wrist assembly
• Function of wrist assembly is to orient end effector
• Body-and-arm determines global position of end effector
• Two or three degrees of freedom:
• Roll
• Pitch
• Yaw
• Notation :RRT

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Joint Notation Scheme

• Uses the joint symbols (L, O, R, T, V) to designate joint types used to construct robot manipulator
• Separates body-and-arm assembly from wrist assembly using a colon (:)

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• Example: TLR : TR

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• Common body-and-arm configurations …

Example

• Sketch following manipulator configurations

(a) TRT:R, (b) TVR:TR, (c) RR:T.

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Solution:

Links

Joints & DoF

a) Revolute (1 DOF, 1 rotational)

b) Screw/Spiral (1 DOF, 1 rotational)

c) Prismatic (1 DOF, 1 translational)

d) Cylindrical (2 DOF, 1 translational &

1 rotational)

e) Planar (3 DOF, 2 translational &

1 rotational)

f) Spherical (3 DOF, 3 rotational)

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DoF Calculation -  Kutzbach  Equation�(Planer Mechanism)

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where:

F = Number of degrees of freedom

n = Total number of links in the mechanism

J1 = No. of joints with 1 DOF

J2 = No. of joints with 2 DOF

F = 3 (n-1) – 2J1 – J2

Planer Mechanism – Slider Crank

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F = 3 (n-1) – 2J1 – J2

F = 3 (4-1) – 2 (4) - 0 = 1

n = 4

J1 = 4

J2 = 0

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Planer Mechanism

F = 3 (6-1) – 2 (7) - 0 = 1

n = 6

J1 = 7

J2 = 0

F = 3 (n-1) – 2J1 – J2

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Planer Mechanism – 5 Bar

F = 3 (5-1) – 2 (5) - 0 = 2

n = 5

J1 = 5

J2 = 0

F = 3 (n-1) – 2J1 – J2

DoF Calculation -  Kutzbach  Equation�(Spatial Mechanism)

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where:

F = Number of degrees of freedom

n = Total number of links in the mechanism

J1 = No. of joints with 1 DOF

J2 = No. of joints with 2 DOF

J3 = No. of joints with 3 DOF

J4 = No. of joints with 4 DOF

J5 = No. of joints with 5 DOF

F = 6 (n-1) - 5J1 - 4J2 - 3J3 - 2J4 – J5

Spatial Mechanism – Tripod

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F = 6 (n-1) - 5J1 - 4J2 - 3J3 - 2J4 – J5

F = 6 (8-1) – 5(6) – 4(1) – 3(1) – 2(0) – (0) = 5

n = 8

J1 =6

J2 =1

J3 =1

J4 =0

J5 =0

Stewart Platform – 6 DoF Parallel Manipulator

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n=14, J1=6, J2=6, J3=6

J4 =0, J5 =0

F = 6 (14-1) – 5(6) – 4(6) – 3(6) – 2(0) – (0)

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F = 6

F = 6 (n-1) - 5J1 - 4J2 - 3J3 - 2J4 – J5

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• Planer Manipulator – 3 DoF
• Spatial Manipulator – 6 DoF
• Redundant Manipulator
• Planer Manipulator more than 3 DoF
• Spatial Manipulator more than 6 DoF
• Under Actuated Manipulator
• Planer Manipulator less than 3 DoF
• Spatial Manipulator less than 6 DoF

Polar Coordinate �Body-and-Arm Assembly

• Notation TRL/RRP/2RP:

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• Consists of a sliding arm (L joint) actuated relative to the body, which can rotate about both a vertical axis (T joint) and horizontal axis (R joint)

Cylindrical Body-and-Arm Assembly

• Notation TLO/RPP/R2P:

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• Consists of a vertical column, relative to which an arm assembly is moved up or down
• The arm can be moved in or out relative to the column

Cartesian Coordinate �Body-and-Arm Assembly

• Notation LOO/PPP/3P:
• Consists of three sliding joints, two of which are orthogonal
• Other names include rectilinear robot and x-y-z robot

Jointed-Arm Robot (PUMA)

• Notation TRR/RRR/3R:

Programmable Universal Machine for Assembly

SCARA Robot

• Notation VRO/RRP/2RP
• SCARA stands for Selectively Compliant Assembly Robot Arm
• Similar to jointed-arm robot except that vertical axes are used for shoulder and elbow joints to be compliant in horizontal direction for vertical insertion tasks

Determined by�– Physical configurations�– Size�– Number of axes�– The robot mounted position (overhead gantry, wall-mounted, floor mounted, on tracks)�– Limits of arm and joint configurations�– The addition of an end-effector can move or offset the entire work volume

Reach (Work Volume / Work envelop)

Spatial region within which the end of the robot’s wrist can be manipulated

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(c) Cartesian

(b) Cylindrical

(a) Polar

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Coordinate Systems

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World coordinate system Tool coordinate system

• Size of the working envelope

• Precision of movement� – Resolution� – Accuracy� – Repeatability

• Lifting capability

• Number of robot axes

• Speed of movement� – maximum speed� – acceleration/deceleration time

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• Motion control� – path control� – velocity control

• Types of drive motors� – hydraulic� – electric� – pneumatic

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Technical Specifications

The lifting capability provided by manufacturer doesn’t include the weight of the end effector

• Usual Range 2.5lb-2000lb (1.13 kg to 907.18 kg)

• Condition to be satisfied:

Load Capability > Total Wt. of workpiece

+ Wt. of end effector

+ Safety range

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Weight Carrying Capacity

(Pay load)

•Acceleration/deceleration times are crucial for cycle time.

•Determined by

– Weight of the object� – Distance moved� – Precision with which object must be positioned

Speed of Movement

Speed with which the robot can manipulate the end effector

• Path control - how accurately a robot traces a given path (critical for gluing, painting, welding applications);

• Velocity control - how well the velocity is controlled (critical for gluing, painting applications)

• Types of control path:

• point to point control (used in assembly, palletizing, machine loading); - - continuous path control/walkthrough (paint spraying, welding).�- controlled path (paint spraying, welding).

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Motion Control

• Hydraulic�– High strength and high speed�– Large robots, Takes floor space�– Mechanical Simplicity�– Used usually for heavy payloads

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• Electric Motor (Servo/Stepper)�– High accuracy and repeatability

– Low cost �– Less floor space

– Easy maintenance

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• Pneumatic �– Smaller units, quick assembly�– High cycle rate

– Easy maintenance

Type of Drive System

Example

(Motoman MA1400 DX100: Welding robot)

Example

(Unimation – PUMA 500)

Model: 550

Axes : 6 DoF

Speed : 1000 m/s

Actuator : Electrical

Payload : 3kg

Repeatability : ±0.10

Applications:

M/c tool loading, Part transfer, Assembly, Welding, Inspection etc.

Depends on the position control system, feedback measurement, and mechanical accuracy

Precision of Movements: (i) Resolution

Smallest increment of motion at the wrist end that can be controlled by the robot

• One half of the distance between two adjacent resolution points

• Affected by mechanical Inaccuracies

• Manufacturers don’t provide the accuracy (hard to control)

(ii) Accuracy

Capability to position the wrist at a target point in the work volume

• Repeatability errors form a random variable

• Mechanical inaccuracies in arm, wrist components

• Larger robots have less precise repeatability values

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(iii) Repeatability

Ability to position back to a point that was previously taught

(iii) Dexterity

Skill in performing tasks, especially with the hands

Robot's ability to cope with a variety of objects and actions

(iii) Singularity

Loss of Degrees of Freedom

Formula

Spatial Resolution = Control Resolution + 6σ

Accuracy = Spatial Resolution / 2

Repeatability = ± 3σ

A cylindrical robot has a prismatic joint with a range of travel of 800mm. The control memory for this joint has 10 bit. It has been recorded that the associated mechanical inaccuracies with above said arm show a random distribution of random variable of the robot position gives a standard deviation of 0.1mm. The standard deviation is equal in all direction. Determine,

Spatial Resolution = CR+6σ = 0.78+6(0.1) = 1.38 mm

Accuracy = SR / 2 = 1.38 / 2 = 0.69 mm

Repeatability = ± 3σ = ± 3(0.1) = ± 0.3 mm

Robot Programming

• Leadthrough programming
• Work cycle is taught to robot by moving the manipulator through the required motion cycle and simultaneously entering the program into controller memory for later playback
• Robot programming
• Textual programming language to enter commands into robot controller
• Simulation and off-line programming
• Program is prepared at a remote computer terminal and downloaded to robot controller for execution without need for leadthrough methods

Leadthrough Programming

1. Powered leadthrough
• Common for point-to-point robots
• Uses teach pendant
2. Manual leadthrough
• Convenient for continuous path control robots
• Human programmer physical moves manipulator

Leadthrough Programming

• Advantages:
• Easily learned by shop personnel
• Logical way to teach a robot
• No computer programming

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• Disadvantages:
• Downtime during programming
• Limited programming logic capability
• Not compatible with supervisory control

Robot Programming

• Textural programming languages
• Enhanced sensor capabilities
• Improved output capabilities to control external equipment
• Program logic
• Computations and data processing
• Communications with supervisory computers
• Programming Languages:
• WAVE, AL, VAL, AML, RAIL, HELP, JARS, RPL, PAL, ADA etc. (200+)

Classification of Robot Languages

First generation language:

• Off-line programming in combination with the programming through teach pendant
• Limited handling of sensory data (Except On/OFF binary data) and communication with other computers
• Branching, I/O interfacing and commands leading to sequence of movements of arm and body, and opening and closing of end effecter are possible
• E.g. VAL

Example Program (VAL)

1. APPRO PART, 50 : - Move to location, 50 mm above location PART (location to be defined)
2. MOVES PART :- Move along a straight line to PART
3. CLOSEI: - Close the gripper jaws to grip the object immediately
4. DEPARTS 150:- Withdraw 150 mm from PART along straight line path
5. APPROS BOX, 200 : - Approach along straight line to location 200 mm above the location, BOX ( to be defined later)
6. MOVE BOX :- Move to BOX
7. OPENI :- Open the hand ( and drop the object)
8. DEPART 75 : - Withdraw 75 mm from BOX

END

Line 1,6,7 : Joint interpolated motion

Line 2,4,5 : Straight line motion

Line 3,7 : hand control instructions

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Classification of Robot Languages

Second generation language:

• Structured programming languages performing complex task
• Handle both analog and digital signals
• Force, torque, slip and other sensors can be incorporated on the joints
• Wrist or gripper fingers and the robot controller is capable of communicating with sensory device
• If error or faults occurs, the first generation robot will probably stop functioning and it can not cope with situation. But it can recover in the event of malfunction probably by activating some other programs
• Better interacting facility with other computers
• Data processing, file management and keeping all records of event happening in the work cell can be done more efficiently
• E.g.: AML, RAIL, MCL, VAL II etc.

Classification of Robot Languages

World modelling and task-oriented object level language

• Advanced future language
• Task is defined through command
• Capable of performing step by step functions to accomplish the objective
• Possible only if the robot is capable of sensing the world around it
• Intelligent required and robot should be capable of making decisions

Computer control and Robot software

Monitor Mode:

• Programmer can define location
• Load a particular piece of information in a particular register
• Store information in the memory
• Save, transfer program from storage into computer control system memory
• Enable or disable, move back and forth into edit or run mode

Editor mode:

• Programmer can edit or change a set of instructions of existing programs or introduce new set of program
• Erase some instructions and replace them by new lines
• Error can be corrected

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Computer control and Robot software

Run mode or Execute mode:

• Program to carry out the predefined task can be executed in the run mode
• Sequential steps as written by the programmer are followed during run mode
• Sometimes dry run can be tested by making the switch disable (e.g. Arc welding: Trajectory can be tested by dry run)
• Error can be rectified by debugging
• Interpreter or complier used to translate the source program to machine language

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Robot Applications

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• Spot welding, Arc welding , Spray painting, Grinding
• Drilling holes, Routing, Polishing, Nut running, Driving of screws
• Parts handling/Transfer, Assembly operation, parts sorting, part inspection
• Teleoperators, Gauging, Space, Under water, Harvesting, Prosthetics, Medical, Surgery, Millitary

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Smart Robotics Application

• Carry 340 lb
• Run 4 mph
• Climb, run, and walk
• Move over rough terrain
• Robot with rough-terrain mobility that could carry equipment to remote location

BigDog

Cleans Gutter

Vacuum Floors

Smart Robotics Application

Medical Applications

Prosthetics

• Arms, Legs, and other body parts

can be replaced with

electromechanical ones