Technical Article

Industrial Robot End-of-Arm Tooling Comparison and Selection

June 07, 2023 by Simon Mugo

Most grippers are powered by either air or electricity. Learn about the questions and factors an engineer should consider to make the best decisions while selecting a gripper to use for unique applications.

Industrial robots are becoming increasingly common features in modern manufacturing firms because of their efficiency and speed while undertaking specific operations. Robots have been deployed to operate in all sectors of manufacturing, including working in extreme or dangerous temperature conditions where humans cannot survive.

Engineers have been improving how robots interact with the workpieces, from simple mechanical linkages to complex humanoid hands. In this article, our main focus is to filter the selection criteria when deciding how a robot should grip objects in manufacturing production lines, hospitality, and automobile industries. This is made possible through the use of well-designed grippers that leverage the powering mechanism to best achieve the tasks.

 

Robot vacuum gripper

Figure 1. Vacuum robot gripper in action. Courtesy of Adobe Stock

 

Quick Review; What are Robot Grippers?

Grippers, also known as manipulators, end effectors, or end-of-arm tools (EoAT), are special mechanical devices designed to help a robot handle or grasp an object perfectly in industrial setups. Such grippers intend to handle repetitive tasks and replace the human hand, which is prone to inconsistency.

Grippers come in different shapes. Some are similar to human hands, others adopt the hand but with two or three fingers, but most appear like simple clamping jaws. Some grippers are fitted with vacuum suction cups, some have soft round picking balls, and some magnetized tips.

Different powering methods, such as electrical, pneumatic (air), and sometimes even hydraulic (hydraulic), are utilized in activating the grippers. These can include vacuum, pneumatic jaws, electric servo jaws, hydraulic motor and actuator jaws, jamming devices (for randomly shaped objects), soft, and magnetic coils.

All these grippers find specialized use in the area of robotics, but in the end, the user must select the best gripper for industrial and robotic use by considering several factors and specifications.

 

OnRobot servo gripper

Figure 2. Electrically powered gripper example from OnRobot.

 

How Do You Choose the Right Gripper?

Choosing the right gripper for your robot is one of the most crucial considerations during the initial design stage. Several factors act as your guide during this process. Naturally, the most critical factor is the application in mind for your robot gripper, so this makes the best starting point to consider the design.

  • Is the gripper intended to handle single item types (one type of product, such as boxes of similar sizes) or mixed items (various sizes, orientations, or even types of products)?

    If the gripper is intended to handle mixed items, then you should choose a gripper that you can vary its speed and the item gripping force. This can be achieved by selecting a gripper like an electric gripper, driven by a servo, to enable you to adjust the closed jaw width and speed. In addition, electric grippers are fitted with a force sensor which helps them handle mixed parts. However, they can be much more expensive compared to pneumatic styles.

  • Do you expect to have data feedback delivered by the gripper? Some grippers deliver information to the user through an interface like a display screen, more advanced than simply on/off signals.

    If feedback is required, then you will have to consider a gripper that is fitted with sensors according to the feedback that you expect. For example, a force sensor will give feedback on the gripping force, and a proximity sensor will help you approximate the distance between the gripper and the item to be gripped. Again, electric grippers often contain all such information built-in.

  • What is the payload (maximum weight capacity) of the gripper you want?

    Some grippers, such as the electric and hydraulic grippers, are preferred for heavy or bigger payloads, while pneumatic jaws and vacuums are better suited for lighter payloads. Purely mechanical grippers, like pallet forks, can lift the maximum weight rated by the robot itself!

  • What is the size of the area where the gripper is to be used?

    Some grippers might be suitable for smaller or bigger areas of use. Pneumatic grippers, with relatively short throws, are used in tight-spaced areas because they can work in limited spaces, while electric grippers require a larger area to operate.

  • Is the design priority based on cycle speed or accuracy?

    For some designs, cycle speed is not quite as important as the accuracy of placement (like loading a CNC machine, speed is determined by the CNC machine, not the robot). But if speed is critical, pneumatic jaws are able to open and close much more quickly than hydraulic and many electric grippers.

  • What power source is available?

    Hydraulic grippers are the most restrictive, requiring tubing and an existing external hydraulic system. Pneumatic systems (especially vacuum generators) can be electrically powered and fully contained near the robot gripper if an existing shop air supply isn’t readily accessible. Electric power does not need the bulk of an external fluid pressure source, but usually will require power wires routed on the outside of the robot arm.

When such questions are answered the right way, the engineer will make the best selection of the robot gripper.

 

Schunk magnetic gripper

Figure 3. Electromagnet gripper example from Schunk.

 

Work Environment

The cleanliness of the product you are dealing with is another special consideration. Can the items be contaminated, or must they retain food/medical-grade cleanliness? This is very significant because every kind of item has a specialized gripper that suits its handling.

 

Gripping Force Magnitude

Even though it is often difficult to determine the exact gripping force magnitude, the below factors are considered in the process.

  • Weight/hardness of the object to be handled
  • Center of the mass of the object to be grasped
  • The robot arm speed and the direction of connection between the gripper and the movement
  • Ability to determine friction and physical constriction during the picking of the object
 
Soft Robotics food grade gripper
Figure 4. Food-grade gripper example from Soft Robotics.

 

Grippers in Manufacturing

Grippers are the primary point of contact for picking, holding, and moving products from one location to the other. They introduce a speed that supersedes the human hand and offers a higher output accurately. This is the main reason why robots are increasingly being considered in industrial manufacturing.

Getting a powerful gripper will not only be beneficial in performing repetitive tasks but will play a role in tackling heavy-duty objects. Certain industrial tasks cannot be fulfilled by humans, and in this case, robots can help to ensure that the whole work has been achieved.