End of Arm Tooling: Power Sources and Sensors

An End of Arm Tool (EOAT) can be classified as any type of tooling used to interact with different components on a production line, typically located at the end of an industrial or collaborative robot arm. EOATs are entirely customizable with nearly unlimited possibilities. They can be any sort of gripper used in automated plant processes, such as an electronic or vacuum tooling used to palletize boxed products or a stationary welding torch holder.

The complexity of an EOAT is determined by the complexity of the task to be completed. Some tooling has nothing connected to it and the shape of the tool is enough to complete the task at hand. In other cases, the tooling must be made more complex and use sensors, pneumatics, and other electronics to complete the job. Additionally, special consideration must be taken when routing cables and hoses to the end of the arm to ensure that wires and cables are not pinched or cut in the rotation of an industrial robot’s many axes.  

Figure 1. EOATs are customizable and have near infinite design and power possibilities. Image used courtesy of Universal Robots

 

Types of End of Arm Tooling

There are nearly an unlimited type of EOATs, but this article will classify them into the five main methods based on how they are powered: 

• Pneumatic

• Electric

• Vacuum

• Hydraulic

• Stationary / Shape Based

Each type of tooling has its own set of advantages and disadvantages that need to be taken into consideration when designing a robotic cell. Regardless of their power source, most of them need some sort of sensor to be able to operate properly.   

 

Figure 2. Schunk’s 2-finger parallel gripper. Image used courtesy of Schunk

 

Pneumatic

Pneumatic EOATs are very common in the industrial workplace and offer a number of advantages depending on the type of application. A pneumatic gripping system usually consists of any type of tooling that is powered by a pneumatic cylinder. Pneumatics are often quite powerful and can be used to grab heavy objects or control certain mechanisms in order to open or close the gripping system. 

Pneumatics are reliable and usually have a long working lifespan, however, they require dedicated hoses and piping systems that have to be carefully run to prevent leaks or pinch points. They are also less energy efficient than their electrically equivalent counterparts.

 

Figure 3. Tolomatic’s IMA linear servo actuators. Image used courtesy of Tolomatic 

 

Electric 

Many different aspects of gripping systems can be electrically powered, including magnets, motors, and servos used to complete different tasks. Electromagnets are often useful when moving parts that are ferrous. Servos can be used to move certain parts of the gripper in reliable repeatable ways, and solenoids can be used to push or pull different components of the gripper. Electric motors are useful for a myriad of different gripper components and have been used to control a number of different robot tool applications. They are often more complex and expensive than pneumatics, however.

 

Figure 4. Universal Robots EPick vacuum gripper. Image used courtesy of Universal Robots

 

Vacuum

Vacuum based gripping systems have countless applications but are most often used in palletizing processes. Vacuum can be used to pick up different items and are advantageous because they offer speed and simplicity over some other gripping systems. They are often limited to uniform surfaces such as boxes or slip sheets. While they can be quite powerful, they usually perform better on lighter weight products. The use of vacuum can be loud in some applications and should be taken into account when designing the cell.

 

Figure 5. Emerson’s Bettis BHH Series Hydraulic Valve Actuator. Image used courtesy of Emerson

 

Hydraulic      

Hydraulic EOATs are among the strongest of any type of tooling. Hydraulic systems have an extreme amount of power and can be used on large robotic systems to pick up heavy objects. They have the pitfall of being slower than other types of systems and require a dedicated hydraulic system complete with automatic valves and pump. Because of this, they can become expensive to design and build. In most applications, hydraulic tooling is unnecessary in all but the most heavy duty applications.

 

Figure 6. KUKA’s arc welding robot holding a torch stationary at the end of its arm. Image used courtesy of KUKA

 

Stationary / Shape-Based Tooling 

For some applications, there is no need to add moving parts to the tooling. For example, welding torch holders are EOATs with the goal of holding a torch stationary on the end of the robotic arm. In another example, some tooling can be made a certain shape so that when the arm rotates, it friction locks the product in place, such as large water bottle grippers that slide a collar over the neck of the bottle. Once around the neck, a rotation of the gripper causes the neck of the bottle to become locked into the EOAT where it can then be moved and released. 

This type of tooling is by far the cheapest but there are a limited number of applications that can take advantage of this simplicity. When designing a cell, however, it may be useful to not overlook the idea that mechanical complexity may not be necessary in certain applications.

 

Figure 7. Panasonic’s position, distance, and proximity sensors. Image used courtesy of Panasonic

 

Distance and Proximity Sensors on EOATs

There are very few EOATs that can function correctly without the use of some type of sensor to send feedback to the control unit. While the placement and use of sensors is as varied as the types of EOATs they are placed on, there are some common sensors that find their way into familiar places on tooling. For instance, pneumatic cylinders often have position reed sensors which are capable of relaying the status of the cylinder to the control unit, generally whether it is open or closed. This can be useful for pick confirmation, or to send error codes in the case of a malfunction.  

Proximity sensors located near the product grip location are another common type of sensor used. They can either be on or off sensors or distance sensors. Distance sensors are useful in determining how close the EOAT is to the product of its intended location. 

Lastly, vacuum or pressure sensors can be used to detect the change in vacuum for the system to determine whether the product has been properly picked up and held during transit. Pressure sensors can also detect when a gripper firmly closes around the workpiece, even if the cylinder does not always reach a specific position. This is very useful for picking and placing objects of varying sizes.

 

Figure 8. EOATs are necessary to connect a robot to its ‘outside world.’ Image used courtesy of KUKA

 

EOAT Possibilities

EoATs are an important choice when considering the addition of an industrial or collaborative robotic arm to any plant process. They give life to the arm and connect it to the job it is supposed to be completing, whether it is powered by pneumatics, hydraulics, or another power source.