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

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

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.

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

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

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

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

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.

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

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.

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.

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

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

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.

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

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)

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

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

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

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.

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

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

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