1. Super Dupers for Robotics (7ME6.2A)course in RTU
by:
Mrs. Nisha Payal
Associate Professor
Vivekanada Institute of Technology, Jaipur

2. Question:
What is an actuator and it’s types used in robotic applications? Also explain various types of end effectors or grippers?
Max marks: 16

3. Guidelines to answer this question:
Define an actuator. (Draw a simplified figure of a robot)
Give the requirements of an actuator for robotic applications.
Explain different types of actuators with specific advantages, disadvantages and uses.
Explain how end effectors or grippers can be classified.
Explain various types of grippers with advantages, disadvantages, uses and figures.

4. Define an actuator
Actuators are devices which drive a robot including its grippers. Draw following figs.
Actuator = drive + gripper
Drive muscles of human arm
Gripper human hand

5. Requirements of an actuator for robotic applications
Low inertia
High power – to –weight ratio
Possibility of overload and delivery of impulse torques
Capacity to develop high accelerations
Wide velocity ranges
High positioning accuracy
Good trajectory tracking and positioning accuracy

6. Different types of actuators
Basically actuators are of following three types:
Electric actuators
Hydraulic actuators
Pneumatic actuators

7. Electric actuators
Electric actuator = electric motor + mechanical transmission, e.g., gears etc.
Advantages:
Widespread availability of power supply
Basic drive is lighter as compared to others
High power conversion efficiency
No pollution of working environment
Easily maintained and repaired
Drive system is well suited to electronic control

8. Electric actuators Disadvantages:
They need incorporation of some sort of mechanical transmission system
Unwanted movements in transmission system
Due to transmission system, additional cost, weight and maintenance is required.
They are not safe in explosive environments such as in spray painting, etc.

9. Electric actuators Advancements and applications:
Introduction of direct drive in electric actuators eliminate requirement of mechanical transmission system
Newer brushless motors can be used in fire risk applications such as spray painting
Stepper motors do not require feedback system and digital to analog conversion
DC motors are easily controllable with simple electronics
DC motors allow high power output at high speeds and give high power to weight ratio
Servomotors are motors with motion feedback control

10. Hydraulic actuators
Hydraulic actuators utilize high – pressure fluid such as oil to transmit forces to the point of application desired. Basic components are a reservoir to hold fluid, pumps to move it, valves to control the flow and an actuator to carry out the dictates of the fluid on some load.

11. Hydraulic actuators Advantages:
High efficiency and high power to size ratio
Accurate control over speed, position and direction of actuators
Large forces cab be applied
No mechanical linkage is required
Self lubricating
Due to presence of reservoir, sudden demand for power can be met.
More capable of withstanding shock loads.

12. Hydraulic actuators Disadvantages: Leakages can occur
The power pack is noisy
Changes in temperature alter the viscosity
For smaller robots hydraulic power is not economical. Such systems do not follow scale of size

13. Pneumatic actuators
Pneumatic actuators utilize compressed air for the actuation of cylinders. Basic components are filter, compressor, cooler, dryer, control valve and air actuator.

14. Pneumatic actuators Advantages: It is cheapest of all
Compressed air can be stored and conveyed easily over long distances.
Compressed air is clean, explosion proof and temperature insensitive.
It has few moving parts.
Since compressed air is easily available in the industry, so people are familiar with the technology.

15. Pneumatic actuators Disadvantages:
Precise control of speed and position is not simple
Pneumatics is not suitable for moving heavy loads under precise control
If moisture penetrates the units and ferrous metals have been used then damage to individual components can result

16. What are end effectors and how are they classified ?
End effectors or grippers are used to grasp an object or tool and hold it like hands of the robot
Classification of grippers:
On the basis of grasping mechanisms:
Mechanical gripper
Pneumatic gripper
Magnetic gripper
b. On the basis of how it holds the object:
External gripper (external grasping)
Internal gripper (grasping interior surface)

17. Various gripper types Magnetic gripper:
They are based on property of a magnet so is used for ferrous materials only
Variation in object sizes can be tolerated
Operations are fast
Require only one surface to hold the object
No electric spark in handling hazardous material
Cannot pick thin sheets one at a time
Require external stripping mechanism to release the object

18. Various gripper types Vacuum gripper:
Suitable to handle large flat objects
Material is no concern but it should not have holes
Figure below shows vacuum gripper using suction pumps made up of elastic material

19. Various gripper types Adhesive gripper:
Adhesive substance is used for grasping objects
Used for handling light weight objects such as fabrics
Loses its effectiveness with repeated uses so is to be continuously fed like ribbon of typewriter

20. Various gripper types Hook and scoop grippers:
Hook is used when part is to be lifted.
Precise control cannot be done with a hook.
Part to be hooked must have some sort of eyebolt, handle or ring.
Scoop or ladle is commonly used to
scoop up molten metal and pour it.
While using scoop, it is difficult to control the amount of material.
Spilling of material while scooping is another problem.

21. Various gripper types Roller mechanism
Allows for misalignment of object during gripping
slow action
Suitable for irregular shape

22. Various gripper types
Figure below shows how motor can be used to drive a gripper.

23. Self exploration resources
Introduction to Robotics by S.K. Saha
Robotics and Control by R. K. Mittal and I. J. Nagrath
Thank You