1. Robotics: Unit-II
End Effectors

2. Consider typical robots…
What could a robot do without “end effectors”?

3. End Effectors
The special tooling for a robot that enables it to perform a specific task
An end effector is the device that is at the end of a robotic arm.
We can think of an end effector like a human hand. Even though a human hand is very versatile, an end effector has one great advantage that humans do not have and that is the interchangablility of end effectors. If the end effector is not suitable than it can be changed unlike the human hand.

4. Types of an end effector?
There are two main types of end effectors: tools and Grippers.
Tools – to perform a process, e.g., spot welding, spray painting
Grippers – to grasp and manipulate objects (e.g., parts) during work cycle

5. Common end effectors 1. Tools Spot welding Arc welding
Drilling, grinding, de-burring, etc.
Cutting device (laser, water jet,
torch, etc.)
Spray painting

6. Common end effectors (cont)
2. Grippers
Mechanical
Vacuum
Magnetized
Adhesive
Simple (hooks, scoops)

7. Grippers and Tools

9. Types of Grippers

10. Robot Mechanical Gripper
A two-finger mechanical gripper for grasping rotational parts

11. Grippers
Grippers are devices which can be used for holding or gripping an object.
They include what you might call mechanical hands and also anything like hooks, magnets and suction devices which can be used for holding or gripping.
Grippers take advantage of point-to-point control (exact path that the robot takes between what it is picking up and where it is placing it.
Grippers should be designed so that it requires the minimum amount of manoeuvring in order to grip the work piece

12. Main Types of Mechanical Grippers
2 or more “fingers”
Parallel
Angular

13. Main Types of Mechanical Grippers
Parallel
Angular
2 or more “fingers”

14. Mechanical Grippers: Limitations
Watch out for dynamic forces and moments when sizing a gripper.
Gripper could drop part with loss in air pressure (can order spring clamps to solve this problem)
Angular grippers are less expensive, but the arcing motion of the jaws may require additional tooling clearance and will grip at varying points as part width varies. A parallel gripper is simpler to tool to compensate for part size variance.

15. Mechanical Gripper Specifications
Grip force: ranges tiny forces .1 lbs to over 1600 lbs (don’t forget dynamic forces, moments)
Part sizes: typically .01 to 36 inches
Number of jaws: typically 2 to 4 jaws or fingers
Repeatability: typically +/ to .005 inches
Cycles to failure: up to 10 million cycles
Supporting technologies: air valves, air compressors, sensors, I/O interfaces

16. Mechanical Grippers
We can think of a mechanical gripper as a robot hand. A basic robot hand will have only two or three fingers
A mechanical hand that wraps around an object will rely on friction in order to secure the object it is holding.
Friction between the gripper and the object will depend on two things, First is the type of surface whether it be metal on metal, rubber on metal, smooth surfaces or rough surfaces and the second is the force which is pressing the surfaces together.
Mechanical grippers are often fitted with some type of pad usually made from polyurethane as this provides greater friction. Pads are less likely to damage the workpiece. Pads are also used so to have a better grip as the polyurethane will make contact with all parts of the surface when the gripper is closed
Mechanical grippers can be designed and made for specific purposes and adjusted according to the size of the object. They can also have dual grippers. We are all familiar with the saying ‘two hands are better than one” and robots benefit from having dual grippers as they can increase productivity, be used with machines that have two work stations where one robot can load two parts in a single operation, operations in which the size of objects or part change due to the machining processes and where the cycle time of the robot is too slow to keep up with the production of other machines.

17. Vacuum Grippers (suction cups)

18. Types of Vacuum Grippers
Uneven objects
“A suitable suction cup is available for virtually any situation – with very few exceptions. Suction cups are very well suited for a wide variety of needs and circumstances. They can handle plate, eggs, paper, wood – practically any material. Be it smooth, irregular, bent, porous, airtight, lightweight, heavy, angled, hot or cold, the material can be handled by suction cups safely, gently and quickly.”
Small to medium objects
Large, heavy objects

19. Types of Vacuum Grippers
Level compensator A level compensator compensates for differences in level and absorbs shocks. The mounting also reduces the need for accurate positioning in height.
Ball joint A ball joint adjusts itself automatically to different contact angles and reduces the bending moments on the suction cup. The ball-joint is recommended in the following typical cases:
for lifting heavy objects or plates
for handling workpieces that are in motion
for handling workpieces that are curved or have irregular surfaces

20. Vacuum Grippers Application
PACKAGING:
Canning Tray Making Bottling Box Making Capping Labeling Bagging & Sealing
MATERIAL HANDLING:
Auto Manufacturing Steel Fabricators Conveyors Manufacture & Packaging of Compact Disc Electronics Heavy Industry

21. Vacuum Gripper Specifications
Gripping force: generally up to 300 lbs. Multiple cups can pick up to 6,000 lbs.
Pressures: requires –3 to –15 psi gauge
Sizes: suction cups typically range between .05 and 18 inch diameters
Supporting Technologies: Compressors, valves, air filters, controllers

22. Suction Grippers There are two types of suction grippers:
Devices operated by a vacuum – the vacuum may be provided by a vacuum pump or by compressed air
Devices with a flexible suction cup – this cup presses on the workpiece. Compressed air is blown into the suction cup to release the workpiece. The advantage of the suction cup is that if there is a power failure it will still work as the workpiece will not fall down. The disadvantage of the suction cup is that they only work on clean, smooth surfaces.
There are many more advantages for using a suction cup rather than a mechanical grip including: there is no danger of crushing fragile objects, the exact shape and size does not matter and the suction cup does not have to be precisely positioned on the object
The downfalls of suction cups as an end effector include: the robot system must include a form of pump for air and the level of noise can cause annoyance in some circumstances

23. Magnetic Grippers
Magnetic grippers obviously only work on magnetic objects and therefore are limited in working with certain metals.
For maximum effect the magnet needs to have complete contact with the surface of the metal to be gripped. Any air gaps will reduce the strength of the magnetic force, therefore flat sheets of metal are best suited to magnetic grippers.
If the magnet is strong enough, a magnetic gripper can pick up an irregular shaped object. In some cases the shape of the magnet matches the shape of the object
A disadvantage of using magnetic grippers is the temperature. Permanent magnets tend to become demagnetized when heated and so there is the danger that prolonged contact with a hot workpiece will weaken them to the point where they can no longer be used. The effect of heat will depend on the time the magnet spends in contact with the hot part. Most magnetic materials are relatively unaffected by temperatures up to around 100 degrees.
Electromagnets can be used instead and are operated by a DC electric current and lose nearly all of their magnetism when the power is turned off.
Permanent magnets are also used in situations where there is an explosive atmosphere and sparks from electrical equipment would cause a hazard

24. Hooks and Scoops
Hooks and scoops are the simplest type of end effectors that can be classes as grippers.
A scoop or ladle is commonly used to scoop up molten metal and transfer it to the mould
A hook may be all that is needed to lift a part especially if precise positioning in not required and if it is only to be dipped into a liquid.

25. Types of Grippers
There are four main categories which makes use of a gripper
No gripping – in this situation the workpiece is held in a jig (a specially designed purpose built holder) and the robot performs an activity on it. Jobs which use no gripping can include spot welding, flame cutting and drilling.
Coarse gripping – in this case the robot holds the workpiece but the gripping does not have to be precise. Jobs which use coarse gripping include handling and dipping castings, unloading furnaces, stacking boxes or sacks.
Precise gripping – A robot holds the workpiece which requires accurate positioning for example unloading and loading machine tools.
Assembly – the robot is required to assemble parts which requires accurate positioning and some form of sensory feedback to enable the robot to monitor and correct its movements.

26. Advances in Mechanical Grippers
Dual grippers
Interchangeable fingers
Sensory feedback
To sense presence of object
To apply a specified force on the object
Multiple fingered gripper (similar to human hand)
Standard gripper products to reduce the amount of custom design required

27. Tools
Tools are devices which robots use to perform operations on an object, for example, drills, paint sprays, grinders, welding torches and any other tool which get a specific job done.
Tools take advantage of continuous path control (the path the end effector takes needs to careful, steady and continuously controlled at every moment)
If we think of a spray gun and if it moves to quickly then the paint will be too thin on the other hand if it moves to slowly the paint will be too thick or in blobs.
Any tool required can be fitted to the end of the robotic arm and can be programmed to select and change tools without human intervention

28. Types of Tools
A common tool used as an end effector is the welding tool. Welding is the process of joining two pieces of metal by melting them at the join and there are 3 main welding tools: a welding torch, spot welding gun and a stud welding tool
Other common tools are paints praying, deburring tools, pneumatic tools such as a nut runner to tighten nuts.