robotics (vii semester, b.tech. mechatronics) prepared by: nehul j. thakkar asst. professor...

ROBOTICSROBOTICS(VII Semester, B.Tech. Mechatronics)(VII Semester, B.Tech. Mechatronics)

Prepared By:Nehul J. ThakkarAsst. ProfessorU.V.Patel College of EngineeringGanpat University

Chapter 2: Fundamentals of Chapter 2: Fundamentals of Robot TechnologyRobot Technology

Robot Anatomy Robot Motions Work Volume Degree of Freedom (DOF) Robot Drive Systems Speed of Motions Load-carrying Capacity Control Systems Dynamic Performance Compliance End Effectors Sensors

April 21, 2023 Cont.2

Robot AnatomyRobot Anatomy

The physical construction of the body, arm and wrist of the machine

The wrist is oriented in a variety of positions Relative movements between various components of body, arm

and wrist are provided by a series of joints Joints provide either sliding or rotating motions The assembly of body, arm and wrist is called “Manipulator”


Robot Anatomy..Robot Anatomy..

Attached to the robot’s wrist is a hand which is called “end effector”

The body and arm joints position the end effector and wrist joints orient the end effector


Robot Anatomy..Robot Anatomy..Robot Configurations Variety of sizes, shapes and physical configuration

1. Cartesian Coordinates Configuration2. Cylindrical Configuration3. Polar or Spherical Configuration4. Articulated or Jointed-arm Configuration5. Selective Compliance Assembly Robot Arm (SCARA) Configuration


Robot Anatomy..Robot Anatomy..1. Cartesian Coordinate Configuration Uses three perpendicular slides to construct x , y and z axes X-axis represents right and left motions, Y-axis represents forward-backward

motions and Z-axis represents up-down motions Kinematic designation is PPP/LLL Other names are xyz robot or Rectilinear robot or Gantry robot Operate within a rectangular work volume


Robot Anatomy..Robot Anatomy..1. Cartesian Coordinate Configuration..


Robot Anatomy..Robot Anatomy..1. Cartesian Coordinate Configuration.. Advantages

Linear motion in three dimension Simple kinematic model Rigid structure Higher repeatability and accuracy High lift-carrying capacity as it doesn’t vary at different locations in work volume Easily visualize Can increase work volume easily Inexpensive pneumatic drive can be used for P&P operation


Robot Anatomy..Robot Anatomy..1. Cartesian Coordinate Configuration.. Disadvantages

requires a large volume to operate in work space is smaller than robot volume unable to reach areas under objects must be covered from dust

Applications Assembly Palletizing and loading-unloading machine

tools, Handling Welding


Robot Anatomy..Robot Anatomy..2. Cylindrical Configuration Use vertical column which rotates and a slide that can be moved up or down

along the column Arm is attached to slide which can be moved in and out Kinematic designation is RPP Operate within a cylinder work volume Work volume may be restricted at the back side


Robot Anatomy..Robot Anatomy..2. Cylindrical Configuration..


Robot Anatomy..Robot Anatomy..2. Cylindrical Configuration.. Advantages

Simple kinematic model Rigid structure & high lift-carrying capacity Easily visualize Very powerful when hydraulic drives used

Disadvantages Restricted work space Lower repeatability and accuracy Require more sophisticated control

Applications Palletizing, Loading and unloading Material transfer, foundry and forging


Robot Anatomy..Robot Anatomy..3. Polar or Spherical Configuration Earliest machine configuration Has one linear motion and two rotary

motions First motion is a base rotation, Second

motion correspond to an elbow rotation and Third motion is radial or in-out motion

Kinematic designation is RRP Capability to move its arm within a

spherical space, hence known as ‘Spherical’ robot

Elbow rotation and arm reach limit the design of full spherical motion


Robot Anatomy..Robot Anatomy..3. Polar or Spherical Configuration..


Robot Anatomy..Robot Anatomy..3. Polar or Spherical Configuration.. Advantages

Covers a large volume Can bend down to pick objects up off the

floor Higher reach ability

Disadvantages Complex kinematic model Difficult to visualize

Applications Palletizing Handling of heavy loads e.g. casting,

forging


Robot Anatomy..Robot Anatomy..4. Jointed Arm Configuration Similar to human arm Consists of two straight components like human forearm and upper arm,

mounted o a vertical pedestal Components are connected by two rotary joints corresponding to the shoulder

and elbow Kinematic designation is RRR Work volume is spherical


Robot Anatomy..Robot Anatomy..4. Jointed Arm Configuration..


Robot Anatomy..Robot Anatomy..4. Jointed Arm Configuration.. Advantages

Maximum flexibility Cover large space relative to work volume

objects up off the floor Suits electric motors Higher reach ability

Disadvantages Complex kinematic model Difficult to visualize Structure not rigid at full reach

Applications Spot welding, Arc welding


Robot Anatomy..Robot Anatomy..5. SCARA Configuration Most common in assembly robot Arm consists of two horizontal revolute joints at the waist and elbow and a final

prismatic joint Can reach at any point within horizontal planar defined by two concentric circles Kinematic designation is RRP Work volume is cylindrical in nature Most assembly operations involve building up assembly by placing parts on top of a

partially complete assembly


Robot Anatomy..Robot Anatomy..5. SCARA Configuration..


Robot Anatomy..Robot Anatomy..5. SCARA Configuration.. Advantages

Floor area is small compare to work area

Compliance Disadvantages

Rectilinear motion requires complex control of the revolute joints

Applications Assembly operations Inspection and measurements Transfer or components


Robot MotionsRobot Motions Industrial robots perform productive work To move body, arm and wrist through a series of motions and positions End effector is used to perform a specific task Robot’s movements divided into two categories:

1. Arm and body motions2. Wrist motions

Individual joint motions referred as ‘ DOF ’ Motions are accomplished by powered joints


Robot Motions..Robot Motions.. Three joints are associated with the action of arm

and body Two or three used to actuate the wrist Rigid members are used to connect manipulator

joints are called links Input link is closest to the base Output link moves with respect to the input link


Robot Motions..Robot Motions.. Joints involve relative motions of the adjoining links that may be linear

or rotational Linear joints involve a sliding or translational motion which can be

achieved by piston, telescopic mechanism May be called ‘Prismatic’ joint Represented as L or P joint Three types of rotating motion:

1. Rotational (R)2. Twisting (T)3. Revolving (V)


Robot Motions..Robot Motions..


Robot Motions..Robot Motions.. Physical configuration of the robot can be

described by a joint notation scheme Considering the arm and body first Starting with the joint closest to the base till

the joint connected to the wrist Examples are LLL, TLL, TRL, TRR, VVR Wrist joints can be included for notation From joint closest to the arm to the

mounting plate for the end effector have either T or R type

Examples are TRL : TRT, TRR : RT The scheme also provide that robot move

on a track or fixed to a platform Example TRL : TRT, L-TRL : TRT


Robot Work VolumeRobot Work Volume The space within which the robot can

manipulate its wrist end different end effector might be

attached to wrist but not counted as part of the robot’s work space

Long end effector add to the extension of the robot compared to smaller end effector

End effector may not be capable of reaching certain points within the robot’s normal work volume

Larger volume costs more but can increase capabilities of robot


Robot Work Volume..Robot Work Volume.. It depends upon following physical

characteristics: Robot’s configuration Size of the body, arm and wrist components Limits of the robot’s joint movements


Robot Work Volume..Robot Work Volume..


Degree of Freedom (DOF)Degree of Freedom (DOF)

Rotate Base of ArmPivot Base of ArmBend ElbowWrist Up and DownWrist Left and RightRotate Wrist


Degree of Freedom..Degree of Freedom.. It is a joint , a place where it can

bend or rotate or translate Can identify by the number of

actuators on the arm Few DOF allowed for an application

because each degree requires motor, complicated algorithm and cost

Each configurations discussed before utilizes three DOF in the arm and the body

Three DOF located in the wrist give the end effector all the flexibility


Degree of Freedom..Degree of Freedom.. A total 6 DOF is needed to locate a

robot’s hand at any point in its work space

The arm and body joints move end effector to a desired position within the limits of robot’s size and joint movements

Polar, cylindrical and jointed arm configuration consist 3 DOF with the arm and body motions are:

1. Rotational traverse: Rotation of the arm about vertical axis such as left-and-right swivel of the robot arm about a base


Degree of Freedom..Degree of Freedom..

2. Radial traverse: Involve the extension and retraction (in or out movement) of the arm relative to the base

3. Vertical traverse: Provide up-and-down motion of the arm

For a Cartesian coordinate robot, 3 DOF are vertical movement (z-axis motion), in-and-out movement (y-axis motion), and right-and-left movement (x-axis motion) which are achieved by slides of the robot arm


Degree of Freedom..Degree of Freedom.. Wrist movement enable the robot to

orient the end effector properly to perform a task

Provided with up to 3 DOF which are:

1. Wrist Pitch/Bend: Provide up-and-down rotation to the wrist

2. Wrist Yaw: Involve right-and-left rotation of the wrist

3. Wrist Roll/Swivel: Is the rotation of the wrist about the arm axis


Drive SystemsDrive Systems Capacity to move robot’s body, arm

and wrist Determine speed of the arm

movements, strength of the robot & dynamic performance

Type of applications that the robot can accomplish

Powered by three types of drive systems:1. Hydraulic2. Pneumatic 3. Electric


Drive Systems..Drive Systems..


Drive Systems..Drive Systems..1. Hydraulic Drive

Associated with large robot Provide greater speed & strength Add floor space Leakage of oil Provide either rotational or linear

motions Applications such as:

• Spray coating robot• Heavy part loading robot• Material handling robot• Translatory motions in cartesian robot• Gripper mechanism


Drive Systems..Drive Systems..1. Hydraulic Drive..


Drive Systems..Drive Systems..2. Pneumatic Drive

Reserved for smaller robot Limited to “pick-and-place” operations

with fast cycles Drift under load as air is compressible Provide either rotational or linear

motions Simple and low cost components Used to open and close gripper


Drive Systems..Drive Systems..


Drive Systems..Drive Systems..3. Electric Drive

Rotor, stator, brush and commutator assembly

Rotor has got windings of armature and stator has got magnets

The brush and the commutator assembly switch the current in armature windings

The most commonly used are DC servomotors, AC servomotors and stepper motors


Drive Systems..Drive Systems..3. Electric Drive..

ServomotorApril 21, 2023 Cont.52

Speed of MotionSpeed of Motion Speed determines how quickly the

robot can accomplish a given work cycle

Desirable in production to minimize cycle time

Industrial robot speed range up to a maximum of 1.7 m/s

Speed would be measured at wrist Highest speed can be obtained by

large robot with fully extended arm


Speed of Motion..Speed of Motion.. Most desirable speed depends on factors:

Accuracy Weight of the object Distance

Inverse relation between the accuracy and the speed

Heavier objects must be handled more slowly

Capable of traveling one long distance in less time than a sequence short distances whose sum is equal to the long distance


Speed of Motion..Speed of Motion.. Short distance may not permit for

programmed operating speed


Load-Carrying CapacityLoad-Carrying Capacity It depends upon size, configuration,

construction and drive system Robot arm must be in its weakest

position to calculate load-carrying capacity

In polar, cylindrical and jointed-arm, the robot arm is at maximum extension

Ranges from less than a pond to several thousand pounds

Gross weight include the weight of the end effector


Control SystemsControl Systems Controlling drive system to properly

regulate its motions Four categories according to control

systems1. Limited-sequence robot2. Playback robots with PTP control3. Playback robots with continuous path control4. Intelligent robot


Speed of Response & Speed of Response & StabilityStability The speed of response refers to the

capability of the robot to move to the next position in a short amount of time

Stability is defined as a measure of the oscillations which occur in the arm during movement from one position to the next

Good stability exhibit little or no oscillation and poor stability indicated by a large amount of stability

Damping control stability but reduces the speed of response


Speed of Response & Speed of Response & Stability..Stability..


Spatial ResolutionSpatial Resolution


Spatial Resolution..Spatial Resolution.. Defined as smallest increment of

movement into which the robot can divide its work volume

Depends on two factors: system’s control resolution and the robot’s mechanical inaccuracies

Control resolution is determined by robot’s position control system and its feedback measurement system

Ability to divide total range of movement for the particular joint into individual increments that can be addressed in the controllerApril 21, 2023 Cont.63

Spatial Resolution..Spatial Resolution.. Joint range depends on the bit storage

capacity in the control memory Number of increments for a axis is given by Number of Increments = 2n

Have a control resolution for each joint in case of several DOF

Resolution for each joint to be summed vectorially

Total control resolution depend on the wrist motions as well as the body and arm motions


Spatial Resolution..Spatial Resolution.. Mechanical inaccuracies come from

elastic deflection in the structure elements, gear backlash, stretching of pulley cords, leakage of hydraulic fluids and other imperfections in the mechanical system

Also affected by load being handled, the speed of arm moving, condition of maintenance of robot


AccuracyAccuracy Ability to position its wrist end at a

desired target point within the work volume


Accuracy..Accuracy.. Depends on spatial resolution means

how closely the robot can define the control increments

Lie in the middle between two adjacent control increments

One half of the control resolution


Accuracy..Accuracy.. Depends on spatial resolution means how closely

the robot can define the control increments Lie in the middle between two adjacent control

increments One half of the control resolution Same anywhere in work volume It may be changed in work volume due to

mechanical inaccuracies


Accuracy..Accuracy.. Affected by many factors

Mechanical inaccuracies Work range Weight


RepeatabilityRepeatability Ability to position its wrist at a point in space that

had been taught Accuracy relates to its capacity to be programmed

to achieve a given target point Programmed point and target point may be different

due to limitations of resolution Repeatability refers to ability to return to the

programmed point when commanded to do so


Repeatability..Repeatability..


ComplianceCompliance Displacement of the wrist end in response to a force or a torque

exerted against it High compliance means that wrist is displaced a large amount

by small force known as ‘Springy’ Reduce the robot precision of movement under load Directional feature Reaction force of the part may cause deflection to the

manipulator


Thank YouThank You

April 21, 2023 73

robotics (vii semester, b.tech. mechatronics) prepared by: nehul j. thakkar asst. professor...

Documents

xyz robot

rectilinear robot

robot volumeunable

rectangular work volume

arm joints

wrist joints

machinethe wrist

robots wrist