End effectors, as we described in our previous article, are one of the components of a robot that are known to be devices that are mounted to the wrist or at the end of the robotic arm whose first and foremost purpose is to pick or grab or handle the workpieces produced by the manufacturing machine. The movement and interaction of any industrial robot with its environment including end effectors are possible by an appropriate robot programming language.
End effectors are also used in holding the machining tools used in the machining (metal removal) processes. They are a critical part of any industrial robot whose widespread applications are no longer an open secret today. They (the end effectors) must be selected under the object to be handled in terms of its weight, geometry, aesthetic value, and like.
They are custom-made in most cases due to specific handling requirements that vary from one operational need to another. For example, one class of end effectors used to handle and transfer workpieces (for instance, grippers, permanent magnet, electro-mechanical or vacuum-cup end effectors) is not suitable in applications where part inspection or quality control is required (in that case, the end effector may be of a stylus shape and connected with the measuring instrument.
It does not end here. End effectors may also take the form of a power tool, such as for deburring and tightening small screws with grinders and screwdrivers, respectively. They are also used as an attachment in welding and painting operations.
The function of end effectors depends upon the sensorial data collected by the robot sensors which are located at various locations both inside and outside the robot’s body.
The present article would chiefly focus on the end effectors used for handling materials/work parts and so forth.
Types of End Effectors
Some of the end effectors used with industrial robots include the following:
- Permanent Magnetic End Effectors
- Electromagnetic End Effectors
- Vacuum-cup End Effectors
- Purpose-specific end effectors
- End effectors based on a power source
The most common type of end effector is a gripper. They are simpler in design and lighter in weight in many cases and are primarily used to hold parts made in distinct geometrical shapes. They are further of several types (or forms) as follows.
Two Finger Grippers
As its name implies, it is equipped with two fingers that perform the gripping function. They are chiefly used to hold parts with constant cross-sectional areas known as prismatic objects.
They may be further of external or internal type. The two-finger external gripper typically resembles the human thumb and the index finger. It is fundamentally used to grip a tiny part or an object arranged in a closely packed setting (Figure below).
Its modified variation includes two parallel fingers used in internal gripping with replaceable inserts that are machinable to take different geometrical shapes as required (Figure below).
Three Finger Grippers
As its name implies, it is equipped with three fingers as jaws that perform the gripping function. They are suited to pick objects of revolution since they simulate the motions of the thumb, index, and middle fingers. The figure below illustrates a non-servo-controlled robot equipped with a three-finger gripper.
- Soft Blank-Finger Grippers: These are the unique forms of a gripper that can be easily modified for taking special shapes.
- Parallel and Angular Grippers: The grippers are also known based on the configuration in which the gripping elements are uniquely styled. In this category, they may be of parallel and angular type. In the parallel type, the jaws move parallel to the body of the gripper. They are used in certain linkage mechanisms.
- The angular grippers are the ones that open up or close in an angular fashion. They are more economical than their parallel counterpart and are used in specific applications dispensing on part geometry.
Permanent Magnetic End Effectors
As shown in the figure below, it consists of a permanent magnet that is made to travel in and out. It is guided by a cylinder made of aluminum.
When the actuator energizes the cylinder, the permanent magnet gets pushed to pick up a ferrous object due to the establishment of a magnetic field.
When the actuator stops energizing, the magnet is withdrawn into the cylinder, and the magnetic field is broken, thereby releasing the ferrous object.
Since these effectors are effective only with the ferrous work parts, they give shorter cycle times per production shot. They can handle several objects at a time when they are mounted on a special adapter.
Electromagnetic End Effectors
As their name suggests, they operate by creating a magnetic field using electromagnetic coils by energizing and de-energizing these coils, the end effectors hold and release the part, respectively.
They are used where mechanical grippers are not of much importance due to issues specific to non-conducive working environments (high temperatures, exposure to chemicals, and the like).
Vacuum-cup End Effectors
They consist of a polymeric cup. When it comes into contact with a flat surface, it seizes it due to the vacuum applied to the suction cup. When the vacuum is released, the object falls under gravity.
In using these grippers, special heed should be paid to monitor the pick and release time as operationally desired. Solenoid valves are used to serve this purpose: they operate to control the airflow through the vacuum cups precisely. They are, therefore, equipped with a vacuum tank as well.
They find their applications where the objects to be moved are fragile in construction, such as CRTs, dishes, LED bulbs, lightweight sheet metal panels as well and flat stocks.
Purpose-Specific End Grippers
As stated above in the beginning, the end grippers may serve purposes other than part handling. They take the form of power tools such as grinding, drilling, or deburring tools, welding torches, paint guns, and so on.
- The jointed arm robot, as shown in the figure below, is equipped with a welding torch that works as an end effector. It is effective in many applications where welding with conventional manual manners is not possible.
- In the figure illustrated below, the robot is provided with the spray painting tool as an end effector.
- In the figure shown below, the end effector is the spot welding gun. Diagram A is for C-type arrangement, while diagram B is for X-type.
- The figure cited below shows the rotating spindle provided with the drilling or grinding tool as an end effector.
- The end effectors in the figure illustrated below show deburring brush (A) and deburring tool (B).
End Effectors Based on Power Source
Based on the power source that drives the end effectors, they may be classified as pneumatic type, hydraulic type, or electric type.
- The figure shown below illustrates an end effector driven by compressed air introduced in the cylinder-rod arrangement.
- The figure shared below illustrates an end effector driven by a hydraulic fluid instead of compressed air in the piston-rod setting.
Frequently Asked Questions
What is the end effector of a robot?
It is called the hand of a robot. A manipulator or robot’s end effector is provided at the end or precisely to the wrist of the robotic arm.
What is the difference between a gripper and an end effector?
The end effector is a general of which gripper is one type. A gripper is specific in its operation for picking, grabbing, or holding the part. Whereas, the end effector may be used in gripping a part as well as in performing industrial operations automatically machining, painting, welding, and alike.
What is the example of an end effector?
The end effector may be a gripper, permanent magnet end effector, electromagnet end effector, suction-cup end effector, and the alike. It may also take the form of a welding torch, spray gun, grinding/welding/deburring tool, and so on.
I am the author of Mechanical Mentor. Graduated in mechanical engineering from University of Engineering and Technology (UET), I currently hold a senior position in one of the largest manufacturers of home appliances in the country: Pak Elektron Limited (PEL).