ROBOTICS
(VII Semester, B.Tech. Mechatronics)
Prepared By:
Nehul J. Thakkar
Asst. Professor
U.V.Patel College of Engineering
Ganpat University
Chapter 2: Fundamentals of Robot
Technology
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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
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Robot Anatomy
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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”
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Robot Anatomy..
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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
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Robot Anatomy..
Robot Configurations
 Variety of sizes, shapes and physical
configuration
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Cartesian Coordinates Configuration
Cylindrical Configuration
Polar or Spherical Configuration
Articulated or Jointed-arm Configuration
Selective Compliance Assembly Robot Arm
(SCARA) Configuration
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Robot Anatomy..
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Cartesian Coordinate Configuration
Uses three perpendicular slides to construct
x , y and z axes
X-axis represents right and left motions,Yaxis 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
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Robot Anatomy..
1.
Cartesian Coordinate Configuration..
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Robot Anatomy..
1.
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Cartesian Coordinate Configuration..
Advantages
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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
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Robot Anatomy..
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Cartesian Coordinate Configuration..
Disadvantages
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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
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Assembly
Palletizing and loading-unloading machine tools,
Handling
Welding
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Robot Anatomy..
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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
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Robot Anatomy..
2.
Cylindrical Configuration..
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Robot Anatomy..
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Cylindrical Configuration..
Advantages
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Disadvantages
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Simple kinematic model
Rigid structure & high lift-carrying capacity
Easily visualize
Very powerful when hydraulic drives used
Restricted work space
Lower repeatability and accuracy
Require more sophisticated control
Applications
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Palletizing, Loading and unloading
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Material transfer, foundry
and forging
Cont.
Robot Anatomy..
3.
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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
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Robot Anatomy..
3. Polar or Spherical Configuration..
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Robot Anatomy..
3.
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Polar or Spherical Configuration..
Advantages
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Disadvantages
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Covers a large volume
Can bend down to pick objects up off the floor
Higher reach ability
Complex kinematic model
Difficult to visualize
Applications
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Palletizing
Handling of heavy loads e.g. casting, forging
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Robot Anatomy..
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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
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Cont.
Robot Anatomy..
4. Jointed Arm Configuration..
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Robot Anatomy..
4. Jointed Arm Configuration..
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Robot Anatomy..
4.
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Jointed Arm Configuration..
Advantages
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Disadvantages
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Maximum flexibility
Cover large space relative to work volume
objects up off the floor
Suits electric motors
Higher reach ability
Complex kinematic model
Difficult to visualize
Structure not rigid at full reach
Applications
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Spot welding, Arc welding
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Robot Anatomy..
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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
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Cont.
Robot Anatomy..
5. SCARA Configuration..
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Robot Anatomy..
5. SCARA Configuration..
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Cont.
Robot Anatomy..
5.
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SCARA Configuration..
Advantages
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Disadvantages
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Floor area is small compare to work area
Compliance
Rectilinear motion requires complex control of
the revolute joints
Applications
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Assembly operations
Inspection and measurements
Transfer or components
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Robot Motions
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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:
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Arm and body motions
Wrist motions
Individual joint motions referred as ‘ DOF ’
Motions are accomplished by powered joints
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Robot Motions..
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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
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Robot Motions..
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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:
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Rotational (R)
Twisting (T)
Revolving (V)
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Robot Motions..
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Robot Motions..
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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
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Robot Motions..
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Robot Motions..
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Robot Motions..
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Robot Work Volume
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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
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Robot Work Volume..
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It depends upon following physical
characteristics:
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Robot’s configuration
Size of the body, arm and wrist components
Limits of the robot’s joint movements
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Robot Work Volume..
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Robot Work Volume..
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Degree of Freedom (DOF)
Rotate Base of Arm
Pivot Base of Arm
Bend Elbow
Wrist Up and Down
Wrist Left and Right
Rotate Wrist
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Degree of Freedom..
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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
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Degree of Freedom..
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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
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Degree of Freedom..
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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 (yaxis motion), and right-and-left movement (x-axis
motion) which are achieved by slides of the robot
arm
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Degree of Freedom..
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Degree of Freedom..
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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
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Degree of Freedom..
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Degree of Freedom..
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Drive Systems
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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:
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3.
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Hydraulic
Pneumatic
Electric
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Drive Systems..
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Drive Systems..
Hydraulic Drive
1.
Associated with large robot
Provide greater speed & strength
Add floor space
Leakage of oil
Provide either rotational or linear motions
Applications such as:
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Spray coating robot
Heavy part loading robot
Material handling robot
Translatory motions in cartesian robot
Gripper mechanism
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Drive Systems..
1.
Hydraulic Drive..
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Drive Systems..
1.
Hydraulic Drive..
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Drive Systems..
Pneumatic Drive
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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
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Drive Systems..
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Drive Systems..
Electric Drive
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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
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Drive Systems..
3.
Electric Drive..
Servomotor
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Drive Systems..
3.
Electric Drive..
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Drive Systems..
3.
Electric Drive..
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Speed of Motion
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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
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Speed of Motion..
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Most desirable speed depends on factors:
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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
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Speed of Motion..
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Short distance may not permit for
programmed operating speed
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Load-Carrying Capacity
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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
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Control Systems
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Controlling drive system to properly regulate
its motions
Four categories according to control systems
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Limited-sequence robot
Playback robots with PTP control
Playback robots with continuous path control
Intelligent robot
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Speed of Response & Stability
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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
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Speed of Response & Stability..
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Spatial Resolution
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Spatial Resolution..
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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 controller
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Spatial Resolution..
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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
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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
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Spatial Resolution..
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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
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Accuracy
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Ability to position its wrist end at a desired
target point within the work volume
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Accuracy..
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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
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Accuracy..
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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
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Accuracy..
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Affected by many factors
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Mechanical inaccuracies
Work range
Weight
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Repeatability
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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
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Repeatability..
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Compliance
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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
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Thank You
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