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I would like to build a gripper that can pick and place irregularly shaped objects, for example, vegetables. I'd like to grasp the object with enough force so that it does not slip form the jaws, but not too much, so that I don't damage the object or the gripper.

I'd like my gripper to be electrically driven, but I cannot find a single off the shelf actuator that would allow me to control the jaw position and the gripping force.

Question

Does it make sense to want to control the gripper by exerted force, and if so, what is a popular approach to do this that I could find an off the shelf component for?

My research

One approach I found is to exert the force via an extension spring. As illustrated in this video. I believe that this approach belongs to "tendon" family, and maybe something like this is used in this high end dexterous hand. But I can't any generic components that I could buy and use in my gripper.

Another approach is to exert the force via a rotary spring, and potentially localize the mechanism very closely to the motor. I'm not sure if that's exactly what is done here, but something to this end: (Force servo, f-servo). Both links point to very experimental solutions, and again, I can't find anything I could buy.

I skimmed the book "Robot Grippers" by Monkman et. all., did not find anything there. All the DYI projects I find on google use simple servo motors, which I don't understand how they won't break the first time you miscalculate something.

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  • $\begingroup$ maybe something like three balloons arranged in a triangle ... inflate balloons to grip the object $\endgroup$
    – jsotola
    Nov 24, 2022 at 16:50

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Gripper or end effector design is still very much an open field of research. There are many different approaches, tendon driven, gear/linkage driven, over actuated, under actuated, spring loaded etc.

They are typically very customized for the individual tasks to which they are to be applied. You're unlikely to find a full design that works for your specific application. And staying away from the shopping question aspect of this.

In general there are not standalone actuators or other components for grippers as the space constraints are too tight to allow for standardized interfaces. And manufacturing volumes are too small to support a marketplace

All the DYI projects I find on google use simple servo motors, which I don't understand how they won't break the first time you miscalculate something.

The solution to this is to have various forms of compliance in your system which protect the actuator from over torque conditions. As your research has found this is often through the use of springs either extensional or rotary.

There are extreme examples such as the iRobot Hand with fingers that a baseball can be hit out of the gripper (video) and it doesn't break and use inherently compliant construction materials.

Does it make sense to want to control the gripper by exerted force, and if so, what is a popular approach to do this that I could find an off the shelf component for?

It does make sense to sense and control per the force applied. Again the volume is low enough that this is mostly a research topic for pressure sensitive surface treatments. There are many different approaches which support pressure sensitivity, proximity sensing, and shear sensing. All of which are potentially very valuable to the ability to control the gripper.

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  • $\begingroup$ Thanks @Tully, very helpful! I now feel more confident that I need to build something rather than go shopping. $\endgroup$
    – psarka
    Nov 30, 2022 at 10:41

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