What is an End Effector and how do you use one?
End effectors are the “business end” of every robot.
In this guide, we cover the essential basics of what they are and how to use them.
Robotic systems can seem quite complex when you first use them. Most robots require a whole set of accessories and add-ons before you can use them for any task in your business. End effectors or end-of-arm-tools (EOAT) can be particularly tricky to get your head around. There are literally hundreds of different end effectors on the market from many different manufacturers. What’s even more confusing is that many end effectors look almost exactly the same but have hugely different specifications.
In this short guide, we’ll clarify some end effector basics and advice.
What is an End Effector?
An end effector is a peripheral device that attaches to a robot’s wrist, allowing the robot to interact with its task. Most end effectors are mechanical or electromechanical and serve as grippers, process tools, or sensors. They range from simple two-fingered grippers for pick-and-place tasks to complex sensor systems for robotic inspection.
The term “End Of Arm Tool” (EOAT) may also be used. Basically, an end effector is the “business end of the robot.” Without an end effector, most robots are practically useless. An articulated robotic arm can be programmed to a particular location within its workspace, but without some sort of end effector, it has no way to perform any operation.
The 3 basic types of End Effector
There are so many different types of end effector that it would be almost impossible (or at least unhelpful) to list all of them here. Specially when it comes to surface finishing tasks you have to decide if you use a passive system (force/torque) or an active compliant technology system (sensitive force compliance). However, there are 3 basic types that you are likely to come across in most situations.
These types are:
1. Process Tools
A simplistic way to think of process tools is like a worker operating a power tool.
While a gripper can only grasp the workpiece, a process tool actually changes the workpiece.
There are as many different process tools as there are different operations in manufacturing. Examples include, robot welding tools, robot machining tools, robot painting tools, 3D printing tools, material removal tools, surface finishing tools, sanding tools, grinding tools, and the list goes on and on.
If you can do it with a power tool, you can probably do it with a robot. If you can do it with another automated machine, you might be able to do it with a robot.
The most common robot end effector is the humble gripper. It allows you to pick up and manipulate objects, which makes it best suited to tasks like pick-and-place, assembly, and machine tending. There are possibly more different types of gripper than there are any other type of end effector. By far the most popular are fingered grippers, which come with 2, 3, 4, or 5 fingers — it is possible to use 6 fingers or more but it is rarely necessary. Then, there are vacuum grippers, magnetic grippers, needle grippers, and there are amazing new gripper technologies being developed all the time.
You can also attach a sensor to use the robot as a programmable sensor-orientation device. This is particularly useful for applications like robotic inspection which reduce the amount of hands-on time that inspection engineers need to spend collecting data. Many sensors can serve as an end effector, including ultrasonic sensors, laser scanners, 2D and 3D cameras, and infrared sensors (such as those used at NASA).
Extra: Tool Changers
Though not technically classed as end effectors themselves, tool changers also attach to the end of the robot — between the wrist and the end effector. They allow the robot to autonomously change between different tools.
A system with a taper toolholder works differently:
Here, the end effector's connection shaft is configured to accept taper toolholders and features a fail-safe pneumatic toolholder release. If more tools are needed for a workpiece, they can be quickly picked up from the tool magazine. The changeover time is only a few seconds and is fully automatic. Afterwards, the next step of the machining process is started immediately. Brushing, cutting, grinding, eccentrics, polishing, satin finishing and much more. A large selection of tools provides sufficient possibilities for every conceivable type of surface treatment.
Which End Effector is right for you?
There are so many different end effectors available it can be quite confusing to know which is the best for your particular application. To be on the safe side and prepared for future tasks you should choose a system with active compliance. Learn more below.
Robotic Force Compliance End Effectors
Robotic Force Compliance devices allow you to automate processes and give an industrial robot a "human" touch. Their moving element (stroke) allows the process equipment to maintain contact with a part's surface with a specific force. This technology is a closed-loop system that works independently of the robot arm. Unlike, force torque sensors, this device does not have to move the mass of the robot arm. Instead, it only deals with the weight on the end of the moving element. That makes this robotic force compliance devices faster, more accurate, precise, and easier to use than other equipment on the market. Make sure that each tool has absolute calibration (artificial conditioning) which guarantees a constant process for multiple cells (roll-out) or spare devices all over the world. This is critical when dealing with surface finishing applications (grinding, sanding, deburring, weld shaving) where consistency (repeatability) is key to achieving a beautiful surface finish.
Active Compliant Technology
Automated Active Compliant Tools utilize internal closed-loop, feedback control along with internal force, acceleration and position sensors to accurately apply the desired force to your part. Accurate force is maintained over complex contours, in any orientation. Just tell it what force you want and an Active tool will apply it up, down, or any orientation in between. Active compliance must be set by the user and will vary for each application process. It is commonly set up via software programming of the servo joints and uses sensors (vision sensors, force sensors, torque sensors, etc.). This family of compliance methods is aiming for better flexibility in the manufacturing process.
Automated Passive Tools are simple, cheap, open-loop devices. Mostly they rely on external, customer-supplied air pressure regulators to set the applied force. While they may lack the ultra-high precision and flexibility of Active compliance, they work extremely well for less demanding flat or prismatic parts or more specialized processes like weld shaving where high-accuracy force control is unnecessary. Passive compliance is applied during the setup of the robotic cell and will always stay active in the background to fulfill its safety role. It may be inherent to the structure of the robot, like a torque limitation device on the end effector or a torque limitation on the joints. It can also be a form of collision detector that prevents collisions from occurring or prevents them from being harmful. These devices are for safety purposes and are important when human-robot collaboration is intended.
When do i need force compliance?
In industrial robotics, the term compliance refers to flexibility and suppleness. To define what compliance is, the definition of non-compliance is useful. A non-compliant (stiff) robot end effector is a device which is designed to have predetermined positions or trajectories. No matter what kind of external force is exerted the robotic end effector will follow the exact same path each and every time. On the other hand, a compliant end effector can reach several positions and exert different forces on a given object. To make things clearer: an active compliant robotic sander exactly keeps the force needed for perfect material removal or surface finishing tasks, even on complex shaped geometries without proper settings because it evens out the surface irregularities itself. A non-compliant sanding tool will hit the surface to hard or lifts off because the robot detects an error (this means it loses contact to the ground). Further it goes into idle or continues its given operation. That might cause the damage of the material.
Why use active compliance?
Many robotic industrial processes need flexibility, if not freedom of movement, in certain directions. For example, loading or unloading a machine will require freedom in two axes (to prevent crushing the pieces if they are misaligned) and no freedom in the loading/unloading direction.
You may also want to use Active Compliant Technology for applications such as grinding, polishing, deburring, finishing, etc. Such processes need to have active compliance, because of the differences from one part to another. You don't want to use a non-compliant robotic tool for a certain part and have a completely different result for the next part.
Compensation of gravity
To be prepared for future tasks you should check if the end effector you are working with does a self-controlled compensation of gravity. An Active Compliant Tool balances the payload in any orientation in realtime. So you have always the defined force without complex programming. That's a major benefit. It is the real force control technology for sensitive robotic material removal like grinding, sanding, deburring and for other tasks in your world of smart robotics and industrial automation.
Should you use a robotic sander or grinder?
If so, which type is the best and what specifications does it need? Active or passive process tool? Which one?
Unfortunately, the answer is really… it depends.
To determine which end effector is best suited to your application, you need to take a step back and ask yourself: What are we trying to achieve with this task?
Picking the right End Effector
When you have refocused on the purpose of the task, follow these steps:
- Determine which actions the robot has to perform to achieve the task.
- Make a shortlist of the different types of end effector that could deliver these actions.
- Assess each type for cost, programming complexity, and any other relevant factors.
- Finally, pick the end effector that best suits the needs of this particular task.
There may be several ways to achieve the same task using different robot end effectors.
For example, think about a surface finishing task. On one hand, you could mount a grinding end effector as a process tool onto the robot’s wrist, which would be simple to do. On the other hand, you could use a gripper to bring the part to a mounted grinding machine (part-to-tool), which would allow the robot to quickly move to another task and would not require a custom end effector.
Neither option is wrong, it just depends on what you need. Could be pieces to be produced in a certain time or the final quality needed.
How to use an End Effector with your robot
Every end effector is operated in a slightly different manner. They use different communication protocols, different programming interfaces, and require different levels of skill to get them up and running.
The basic steps for using any end effector with a robot are:
- Physically mount the end effector onto the robot’s or cobot’s wrist.
- Attach any power connections, e.g. electric, pneumatic, hydraulic.
- Attach any communication interfaces between the end effector and robot controller or computer.
Incorporate the end effector programming into the robot’s program.
This last stage (programming) has often been the most challenging of these steps. But, not any more! Programming an end effector doesn’t need to be difficult. With the right robot programming software, you could have a version of any end effector working in only 5 minutes.
With RoboDK you can simply create a robot tool by loading the 3D model and drag and drop it to your robot within the tree. You can also self calibrate the tip of the tool by touching the same point with different orientations.
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