END EFFECTORS

➢In robotics, an “end effector” is a device or tool connected to the end of a robot arm to
enable the robot to accomplish a specific task.
➢Basically, it is a tool to grip, hold, and transport object and position them in a desired
location. End effectors are the devices through which a robot interacts with the world
around it, grasping and manipulating parts, inspecting surfaces, and working on them. As
such, end effectors are among the most important elements of a robotic system.

➢ Robot end effectors are also known as robot’s

hand, robotic peripherals, robotic accessories,
robot tools or robotic tools, end-of-arm
tooling (EOA), or end-of-arm devices.
➢ An end effector attached to the robot arm is
shown in the figure.
➢ The two categories of end effectors are
grippers and tools.
GRIPPERS
➢Grippers are end effectors used to grasp and manipulate objects during the work
cycle. The objects are usually work parts that are moved from one location to
another in the cell.
➢Grippers take advantage of point-to-point control and are used in applications for
machine loading and unloading, material handling, and assembling.
▪ Grippers can be categorized as follows:
➢Mechanical grippers
✓Single grippers
✓Double grippers
➢Other types of grippers
✓Vacuum grippers
✓Magnetic grippers
✓Adhesive grippers
✓Hooks, scoops, and other miscellaneous
devices
MECHANICAL GRIPPERS
➢A mechanical gripper is an end effector which consists of two or more mechanical
fingers that can be actuated by the robot controller to grasp the workpart.
➢A robot’s hand can have a maximum of three fingers and these fingers, sometimes, are
also called as jaws.
➢Mechanical grippers can further be classified as follows:
▪ Single grippers
▪ Double grippers
➢ Single grippers: These grippers have only one gripping
device attached to the robot’s wrist and are used mainly
for pick and place applications.
➢ Double grippers: These grippers have two gripping
devices attached to the robot’s wrist and are used to
handle two separate objects. These grippers are mainly
used in machine loading & unloading applications as both
of the grippers can be actuated independently.
MECHANICAL GRIPPERS
VACUUM GRIPPERS
➢ Vacuum grippers are used in the robots for grasping the non-ferrous objects.
➢ It uses vacuum cups as the gripping device, which is also commonly known as suction
cups. This type of grippers will provide good handling if the objects are smooth, flat, and
clean. It has only one surface for gripping the objects. Most importantly, it is not best
suitable for handling the objects with holes.
➢ Generally, the vacuum cups (suction cups) are in the round shape. These cups are developed
by means of rubber or other elastic materials. Sometimes, they are also made up of soft
plastics. Moreover, the vacuum cups are prepared of hard materials for handling the soft
material objects.
➢ These devices are mainly used for holding objects like
glass, ceramic tiles, etc. to avoid the marks on the
object’s surface as the use of mechanical grippers may
produce scratches which ruin the aesthetic look of the
object.
VACUUM GRIPPERS
 VACUUM GRIPPERS
➢Advantages
▪ The gripper is light weight.
▪ No danger of scratches or crushing of fragile objects.
▪ Distribution of uniform pressure on the objects during operation.
▪ It works and does not let the workpiece fall down during the power failure.
▪ It requires only one surface of the object to grasp.
▪ Many different materials can be used in grasping operation.
➢Disadvantages
▪ It works only on flat, clean and smooth surfaces.
▪ The maximum force is limited by size of suction cups.
▪ Time may be needed form vacuum creation.
▪ It is not suitable for the curved surfaces or the surfaces with holes & cavities.
▪ Sometimes, positioning may be inaccurate.
MAGNETIC GRIPPERS
➢Magnetic grippers are most commonly used in a robot as an end effector for grasping the
ferrous materials.
➢ It is another type of handling the work parts other than the mechanical grippers and vacuum
grippers.
➢The magnetic grippers can be categorized as follows:
▪ Magnetic grippers with electromagnets, and
▪ Magnetic grippers with permanent magnets.
➢Electromagnetic gripper:
▪ It includes a controller unit and a DC power for handling the materials.
▪ This type of grippers is easy to control, and very effective in releasing the part at the end
of the operation than the permanent magnets.
▪ If the work part gripped is to be released, the polarity level is minimized by the
controller unit before the electromagnet is turned off.
▪ This process will certainly help in removing the magnetism on the work parts. As a
result, a best way of releasing the materials is possible in this gripper.
MAGNETIC GRIPPERS
➢Permanent magnets gripper: It does not require any sort of external power as like the
electromagnets for handling the materials.
➢After this gripper grasps a work part, an additional device called as stripper push-off pin will
be required to separate the work part from the magnet. This device is incorporated at the sides
of the gripper.
➢The advantage of this permanent magnet gripper is that it can be used in hazardous
applications like explosion-proof apparatus because of no electrical circuit. Moreover, there is
no possibility of spark production as well.
MAGNETIC GRIPPERS
 MAGNETIC GRIPPERS

➢Advantages
▪ It can handle objects with holes.
▪ It requires only one surface to grasp the object.
▪ Pickup times are very fast.
▪ It can tolerate the variations in object size.
▪ It does not require separate designs for handling different size of materials.
➢Disadvantages
▪ Residual magnetism remaining in the object may cause problems.
▪ Possible side slippage if moved quickly.
▪ While picking up the sheet from the stack, it is possible that more than a single sheet is
lifted (if the magnetic attraction tends to penetrate beyond the top sheet in the stack).
▪ Sometimes, oil on the surface can reduce the strength of the gripper.
▪ The machining chips may stick to the gripper during operation.
 ADHESIVE GRIPPERS
➢In this gripper, the adhesive body is used to grasp the fabric objects. It is also very much
suitable for carrying the light-weight materials. As like magnetic and vacuum grippers, it
uses only one surface for gripping the objects.
➢One disadvantage in this gripper design is that it will lose its strong adhesive substances
when it is used continuously. As a result, the consistency of the gripper is reduced and leads
to the improper grasping of objects.
➢This disadvantage can be solved by constantly applying the adhesive substances on the
gripper. It can be done by using a continuous ribbon connected to a feeding system, which is
placed in the robot wrist. This process looks very much related to the operation of a
typewriter ribbon system.
ADHESIVE GRIPPERS
 HOOKS, SCOOPS, & INFLATABLE DEVICES
➢Hooks: A hook gripper is incorporated in an operation for picking up the containers of
parts. A hook that grips an object will require a handle for permitting the gripper to grasp
it. Moreover, this type of grippers can be used in the part loading and unloading process in
which the work parts hang from the overhead conveyors.
➢Scoops: Scoop is used as an end effector for grasping the material in the form of powder
or liquid. It handles some objects like molten metal, food, chemicals, and granular. There
are two problems in this gripper such as:
▪ The control of the material is very difficult.
▪ It may also spill out the materials, while performing the process.
➢ Inflatable bladder type grippers: The inflatable bladder type gripper is made of rubber
or some sort of elastic materials. It can be used to pick up the fragile objects by
expanding the inflatable bladder. The mechanical gripper applies concentrated power for
grasping a material, while this type of gripper applies a constant handling pressure in
opposition to the object surface.
GRIPPERS
 TOOLS AS END EFFECTORS
➢A tool is mounted on the robot's wrist for carrying out several operations on the work
parts instead of grasping it. A tool itself acts as an end effector when it is attached
directly to the robot’s wrist.
➢In some applications, there will be a need for multi-tool task, and changing the tool all
the time from the robot wrist will be highly difficult. As a result, a gripper is used in
this process to grasp and manipulate the tool. It certainly helps the robot to handle
several tools in an operation, and thus makes the multi-tooling function possible.
Moreover, the time taken to change the tool is very low.
 TOOLS AS END EFFECTORS
➢Some examples of tools used as end effectors in robot applications include:
▪ Spot welding tools
▪ Spray painting nozzle
▪ Arc welding torch
➢Rotating spindle for operations such as:
✓Drilling
✓Routing
✓Wire brushing
✓Grinding
➢Liquid cement applicators
➢Water jet cutting tool
➢Heating torches
ACTUATORS
➢Actuators are the devices which provide the actual motive force for the
robot joints.
➢Actuators are the muscles of robots. If you imagine that the links and the
joints are the skeleton of the robot, the actuators act as muscles, which
moves or rotate the links to change the configuration of robots.
➢The actuators must have enough power to accelerate and decelerate the links
and to carry the loads, yet be light, economical, accurate, responsive,
reliable and easy to maintain.
➢Actuators in robotic system basically consists of :
▪ A power supply.
▪ A power amplifier.
▪ A servomotor.
▪ A transmission system.
 𝑷𝒑 : Primary source of power (Electric, Press. fluid,
Actuator system compress. Air)
𝑷𝒄 : Input control power usually electric .
𝑷𝒂 : Input power to motor Electric, Hydraulic, or
POWER
Pneumatic.
SUPPLIES
𝑷𝒎 : Power output from motor.
𝑷𝒖 : mechanical power required
𝑷𝒑
MOTOR
𝑷𝒄
POWER 𝑷𝒂 OR
𝑷𝒎 TRANSMISSION 𝑷𝒖
AMPLIFIER SERVO MOTOR

𝑷𝒅𝒂 𝑷𝒅𝒔 𝑷𝒅𝒕

Pds, Pdt , Pda : Powers lost in dissipation for the conversion performed by the Amplifier,
Motor, Transmission
▪ An actuator system converts an input control signal into a desired physical motion (such as
rotation or linear displacement) by processing energy through several stages: power supply,
amplification, motor actuation, and mechanical transmission.
CHARACTERISTICS OF AN ACTUATOR
➢Load (e.g. torque to overcome own inertia)
➢Speed (fast enough but not too fast)
➢Accuracy (will it move to where you want?)
➢Resolution (can you specify exactly where?)
➢Repeatability (will it do this every time?)
➢Reliability (mean time between failures)
➢Power consumption (how to feed it)
➢Energy supply & its weight.
 TYPES OF ACTUATORS
• Based on the source of Input Power actuators are
classified in to three groups :
1. Pneumatic Actuators.
▪ These utilize pneumatic energy provided by the
compressor and transforms it into mechanical
energy by means of pistons or turbines.
2. Hydraulic Actuators.
▪ These Transform the energy stored in reservoir
into mechanical energy by means of suitable
pumps.
3. Electric Actuators.
▪ Electric actuators are simply electro-mechanical
devices which allow movement through the use
of an electrically controlled systems of gears
Pneumatic and Hydraulic Actuators
▪ Both these actuators are powered by moving fluids.
▪ In the first case, the fluid is compressed air and
▪ In the second case, the fluid is pressurized oil.
▪ Pneumatic systems typically operate at about 100lb/in2
▪ Hydraulic systems at 1000 to 3000 lb/in2.
▪ Both Hydraulic and Pneumatic actuators are classified as
▪ linear Actuators (Cylinders).
▪ Rotary Actuators (Motors).
Pneumatic and Hydraulic Actuators
linear Actuators
Pneumatic and Hydraulic Actuators
linear Actuators

• The simplest power device could be used to actuate a linear

joint by means of a moving piston.
• There are two relationships of particular interest when
discussing actuators:
1. The velocity of the actuator with respect to input power
and
2. Force of the actuator with respect to the input power.
Pneumatic and Hydraulic Actuators
linear Actuators
Pneumatic and Hydraulic Actuators
Rotary Actuators
 Pneumatic and Hydraulic Actuators
Rotary Actuators
• There is a relationship of particular interest when
discussing Rotary actuator:
• The angular velocity, ω, and Torque, T.

• R, outer radius of the vane., r, inner radius., h, thickness

of the vane., ω, angular velocity., T, torque.
Advantages and limitations of Pneumatic actuators
ADVANTAGES LIMITATIONS
▪ It is cheapest form of all actuators. Components are ▪ Since air is compressible, precise
readily available and compressed air normally is an
readily available facility in factories. control of speed and position is not
easily obtainable unless much more
▪ Compressed air can be stored and conveyed easily
over long distances. complex electro mechanical devices
are incorporated in to system.
▪ They have few moving parts making them inherently
reliable and reducing maintenance costs. ▪ If mechanical stops are used
▪ They have quick action and response time thus resetting the system can be slow.
allowing for fast work cycles.
▪ If moisture penetrates the units and
▪ No mechanical transmission is usually required. ferrous metals have been used then
▪ These systems are usually compact thus the control damage to individual components
is simple e.g: mechanical stops are often used. may happen.
Advantages and limitations of Hydraulic actuators
ADVANTAGES LIMITATIONS
▪ Leakages can occur causing a loss in
▪ High efficiency and high power to size ratio.
performance and general
▪ Complete and accurate control over speed position contamination of the work area. There
and direction of actuators are possible. is also a higher fire risk.
▪ No mechanical linkage is required i.e., a direct drive ▪ The power pack can be noisy typically
is obtained with mechanical simplicity. about 70 decibel or louder if not
▪ They generally have a greater load carrying capacity protected by an acoustic muffler.
than electric and pneumatic actuators. ▪ Changes in temp alter the viscosity of
▪ Self lubricating and non corrosive. hydraulic fluid. Thus at low
▪ Hydraulic robots are more capable of with standing temperatures fluid viscosity will
shock loads than electric robots. increase possibly causing sluggish
movement of the robot.
Electric and Stepper Motors
➢There are a variety of types of motors used in robots. The most common types are
Servomotors and Stepper motors.
➢ Electric actuators are simply electro-mechanical devices which allow movement through
the use of an electrically controlled systems of gear.
➢ Electric motors usually have a small rating, ranging up to a few horsepower.
➢ They are used in small appliances, battery operated vehicles, for medical purposes and in
other medical equipment like x-ray machines.
➢ Electric motors are also used in toys, and in automobiles as auxiliary motors for the
purposes of seat adjustment, power windows, sunroof, mirror adjustment, blower motors,
engine cooling fans.
 STATOR

ROTATING
(COMMUTATOR)
ARMATURE

Brushes
COMPONENTS OF DC ELECTRIC MOTOR
➢The principle components of an electric motor are: North and south magnetic poles to
provide a strong magnetic field. Being made of bulky ferrous material they traditionally form
the outer casing of the motor and collectively form the stator.
➢An armature, which is a cylindrical ferrous core rotating within the stator and carries a large
number of windings made from one or more conductors.
➢A commutator, which rotates with the armature and consists of copper contacts attached to
the end of the windings.
➢Brushes in fixed positions and in contact with the rotating commutator contacts. They carry
direct current to the coils, resulting in the required motion.
➢DC motors :In DC motors, the stator is a set of fixed permanent magnets, creating a fixed
magnetic field, while the rotor carries a current. Through brushes and commutators, the
direction of current is changed continuously, causing the rotor to rotate continuously.
➢AC motors : These are similar to DC motors except that the rotor is permanent magnet, the
stator houses the windings, and all commutators and brushes are eliminated.
➢A Servomotor is a DC,AC, brushless, or even stepper motor with feedback that can be
controlled to move at a desired speed (and consequently, torque), for a desired angle of
rotation. To do this, a feedback device sends signals to the controller circuit of the
servomotor reporting its angular position and velocity.
COMPONENTS OF DC ELECTRIC MOTOR
➢ A simple DC electric motor: when the coil is powered, a magnetic field is generated
around the armature. The left side of the armature is pushed away from the left magnet
and drawn toward the right, causing rotation.
➢ The armature continues to rotate, When the armature becomes horizontally aligned, the
commutator reverses the direction of current through the coil, reversing the magnetic
field. The process then repeats.
STEPPER MOTOR
➢When incremental rotary motion is required in a robot, it is possible to use stepper
motors.
➢ A stepper motor possesses the ability to move a specified number of revolutions or
fraction of a revolution in order to achieve a fixed and consistent angular movement.
➢This is achieved by increasing the numbers of poles on both rotor and stator
➢Additionally, soft magnetic material with many teeth on the rotor and stator cheaply
multiplies the number of poles(reluctance motor)
STEPPER MOTOR
ADVANTAGES & LIMITATIONS OF ELECTRIC ACTUATORS
ADVANTAGES LIMITATIONS
▪ Wide spread availability of power supply.
▪ Electric actuators often require some
▪ The basic dive element in an electric motor is
sort of mechanical transmission
usually lighter than that for fluid power.
system this increases the unwanted
▪ High power conversion efficiency. movement, additional power and may
▪ No pollution of working environment complicate control.
▪ The accuracy and repeatability of electric ▪ Due to increased complexity of the
power driven robots are normally better than transmission system additional cost is
fluid power robots in relation to cost. incurred for their procurement and
▪ Easily maintained and repaired. maintenance.
▪ The drive system is well suited to electronic ▪ Electric motors are not intrinsically
control. safe. They cannot therefore be used in
for example explosive atmospheres.
APPLICATIONS

▪ Stepper motors can be a good choice whenever controlled movement is

required.
▪ They can be used to advantage in applications where you need to control
rotation angle, speed, position and synchronism.
▪ These include :
▪ printers
▪ plotters
▪ medical equipment
▪ fax machines
▪ automotive and scientific equipment etc.
Comparison of actuating systems
Comparison of actuating systems