Non-Slip Gripper Options

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  • If 1 of 10 parts is slipping, then that is a 10% failure rate.

    If 1 of 20 parts is slipping, then that is a 5% failure rate.

    Both cases are utterly unacceptable because of damaged work pieces, equipment, and disrupted operations.

    The design issue is to provide enough grip force and enough coefficient of friction to hold the work piece. It appears there is an opportunity for improvement that will provide a robust solution.

    Any of the soft stuff applied to gripper fingernails will become a maintenance issue, disrupting continuous production and uptime. As you have discovered.

    The toothed inserts will certainly provide more friction if your work pieces. But it will involve surface disruption.

    You might consider going back to the beginning with (1) properly designed fingernails (not trivial) and (2) properly sized gripper mechanisms (again, not trivial).

    Every gripper manufacturer I have ever encountered provides rigorous engineering guide for proper application of their gripper. Defining the fingernail geometry to grip multiple parts is usually a fun challenge. An expensive alternative for multiple incompatible work piece geometries is multiple grippers and tool changers. But that requires extra programming to be effective.

  • Looks like you have a UR of some type. (Not especially relevant, I suppose.) Robotiq gripper, second one mounted also? What I might lean towards is leaving some extra space in the fingers to bolt in maybe Urethane blocks which can have a texture of some sort, maybe simple as milled grooves lengthwise. Quick and easy replacement for when they wear out. Also, accommodate for shims to adjust tighter or looser as required.

  • I mentioned urethane because it should be pretty durable and have a little give to it. I am not sure of its properties in your environment. These are the kind of shims I am used to seeing in most machine tool applications.

    They allow for adjustment by inserting or removing from between the piece being bolted on and that to which it is bolted. You could add to compensate for wear, rather than just replace.

  • The Robotiq gripper closes to a commanded force level, correct (with internal closed-loop control, IIRC)? So theoretically, it should compensate for wear on the fingers over time, unless/until the wear becomes really excessive.

    So the real issue is making a finger surface that can grip a wet bar of soap, metaphorically speaking.

    The closest I ever saw to a sandpaper-like surface was metal that had been subjected to "plasma blasting" or "plasma coating" -- I don't recall exactly, but it wasn't hard to find a local machine shop that could handle it. It basically resurfaced the contact area of the finger to something similar to sandpapaer (the shop doing the coating could produce a requested "grit" level). It gripped quite well even when coated with some very slick lubricants, and I never saw it wear over the course of 2-3 years.

  • Those look like the material is Aluminum, important to know what the base metal is. What are the dimensions? When you get back to me with that I could see if sales could give a ball park number. There are places out your way. Look for metallizing, plasma spray, flame spray and ITSA (International Thermal Spray Association).

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