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How to choose a machine tending collaborative robot

by John Saunders
19th Feb 20 5:31 pm

Currently, the most extensive use of Cobots (collaborative robots) in the market is machine tending. If you are a machine shop that uses the latest machines, you probably use Computer Numerical Control (CNC) machines such as milling, lathe, etc. These machines have to be fed raw parts by workers, which have to be removed after the program ends. With the scarcity of qualified laborers, a robot is the best solution to carry out the repetitive tasks, and the human worker is left to carry out more cognitive tasks.

Machine tending with a Cobot

Robot Specs

Cobot are a term that describes robots that have limited force and power, and can be used without any safety guards. This means the robot can work alongside humans without having to be fenced off to prevent injury. Introducing cobot to a CNC machine is a little more complicated than it seems. You have to choose a robot that can do the job, and that can reach performance levels comparable to human workers. Here is a list of things to consider before selecting robotic machine-tending robots.

Payload

The payload translates to the total weight the cobot can carry. You need to weigh the most substantial raw parts and the tool weight. This will tell you what your robot payload is. Calculate the part weight by multiplying its volume by its density, or add an extra 20% payload weight to allow you to reach the highest accelerations, and ensure you do not create errors when running this program.

Repeatability

Your machines may be repeatable, and you need the precision of your part, but do not necessarily need cobot that are as precise as your machine. Mostly, cobots are used for the initial setups where the finished part is usually smaller than the unfinished part, therefore allowing minor positioning variations.

The robot needs to have a repeatability ratio of 0.1mm. To ensure repeatability, you can use make use of force-torque sensors or mechanical stoppers. Ensure you leave one free axis when you insert a part into a lathe or vice, which prevents wear and tear on the cobot’s actuators.

Reach

The cobot’s task will be to take a part and place it into the machine. Measure how significant the distance is between the two pints and divide it by 2. This will give you the cobot’s maximum use. For a broader reach, the cobot’s payload increases automatically. The scope includes how many degrees or axes of freedom the cobot arm has.

Gripper Specs

Strokes

The gripper is termed as the cobot’s ‘hand,’ although the gripper is not as flexible as a human hand. Grippers work well when the part its picking has two parallel surfaces at the least. The gripper’s stroke limits the size of the part you can handle. Ensure you measure the most significant part, and then purchase a gripper that is suitable to pick this part. Try and buy an adaptive gripper that can select different sizes and shape of parts without having to modify the cobot’s program or its fingers. When analyzing the manufactured parts, ensure the gripper can handle at least 85 to 95% of the manufactured parts, while the remaining percentage can be manually loaded.

Payload

The gripper payload is the weight the gripper can handle. Ensure you respect the gripper’s payload so that the gripper lasts longer. If the gripper’s fingertips always grasp parts using the fingers, the gripper wears out quickly.

Interface

The interface between the CNC machine and the cobot is a crucial integration part. However, this is not always the case for devices from different manufacturers. Ensure you get two machines that can communicate with each other by ensuring the cobot and the CNC machine can easily share one interface. Some CNC machines may not speak the same language as your cobot, and vice versa.

Conclusion

Machine tending with cobots is made more comfortable when you know what to look for when buying cobot. You have to consider the payload, repeatability and the reach. For the gripper, you have to consider the gripper strokes, the payload and the interface compatibility.

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