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General Discussion

Can the current AR4 handle a 2.7 kg workpiece for slow machine tending?

Hi everyone,

We are evaluating the current AR4 for a broaching machine tending application and would appreciate advice from Chris and anyone with experience using the robot with heavier payloads.

Our workpiece specifications are:

  • Outer diameter: 82 mm
  • Inner diameter: 72 mm
  • Length: 285 mm
  • Weight: 2.7 kg
  • Approximate working area: 500 mm

We will also need a gripper, so the total payload at the robot flange will of course be higher than 2.7 kg. We intend to keep the gripper as light as reasonably possible.

Speed is not important for this application. The robot can move slowly and we can use low acceleration. Repeatability, reliability and long-term operation are much more important to us than cycle time.

Before we start modifying the design, we would like to understand what you would recommend for the current AR4 design.

In particular:

  • Is this application realistic for the current AR4?
  • What total payload would you consider reasonable for this type of slow operation?
  • Which joints or components would become the limiting factors with a 2.7 kg workpiece plus gripper?
  • Would you recommend any changes to the motors, gearboxes, belts, bearings, shafts or wrist assembly?
  • Has anyone tested a similar payload repeatedly over a large number of cycles?
  • Is there anything about the robot position or working envelope that we should consider when designing the cell?

We are seriously considering building the robot for this application, and we are also planning to purchase the STEP/SolidWorks CAD files so that we can review and, if necessary, modify the mechanical parts for our use case.

We are able to manufacture or modify mechanical parts if necessary, so we are also interested in any modifications that would make this application more reliable.

Thank you for any guidance or real-world experience.

  • 1 comment

Chris Annin

Hi,

This application is pushing the limits of the AR4 a little bit, but depending on the required reach and wrist orientation, I think it could be feasible.

I currently rate the AR4 for a 2 kg payload, but I have done quite a bit of testing with approximately 5 lb (2.27 kg). You can see an example of that testing here at about 2:45:

AR4 5 lb payload testing on YouTube

With a 2.7 kg part plus the weight of the gripper, you would be above what I officially rate the robot for, so I wouldn't want to guarantee performance without testing the actual motion required.

The two areas I would be most concerned with are J3 and J5. J5 is particularly sensitive when the wrist needs to rotate a heavy load from a downward orientation to an upward orientation. J3 also becomes increasingly loaded as the arm extends outward. The AR4 was designed primarily for applications such as pick-and-place and machine tending so this is a great application for the robot.

If the arm doesn't need to operate fully outstretched, and the wrist can remain primarily in a downward-facing orientation rather than repeatedly rotating from down to up, I think your application becomes considerably more feasible. Since speed isn't important, keeping the speeds and accelerations low will also help.

If you can give me a little more information on the maximum reach from the center of the robot and the articulation/orientation required of the part and gripper, I can try to duplicate something similar here with a comparable payload and do some testing for you.

Thanks,
Chris