Greasing Robot Hands: Variable Friction Makes Robo-Mitts More Like Our Own

Unless you are in the fields of robotics or prosthetics, you likely take for granted the fine motor skills our hands have. Picking up and using a pen is no small feat for a robot which doesn’t have a dedicated pen-grabbing apparatus. Holding a mobile phone with the same gripper is equally daunting, not to mention moving that phone around once it has been grasped. Part of the wonder of our hands is the shape and texture which allows pens and phones to slide around at one moment, and hold fast the next moment. Yale’s Grab Lab has built a gripper which starts to solve that problem by changing the friction of the manipulators.

A spring-loaded set of slats with a low-friction surface allow a held object to move freely, but when more pressure is exerted by the robot, the slats retract and a high-friction surface contacts the object. This is similar to our fingers with their round surfaces. When we brush our hands over something lightly, they graze the surface but when we hold tight, our soft flesh meets the surface of the object and we can hold tightly. The Grab Lab is doing a great job demonstrating the solution and taking steps to more capable robots. All hail Skynet.

We have no shortage of gripper designs to choose from, including pneumatic silicone and one that conforms to an object’s surface, similar to our hands.

7 thoughts on “Greasing Robot Hands: Variable Friction Makes Robo-Mitts More Like Our Own

  1. I was my unsderstanding that the ridges and valleys of fingerprints (which are all over your hands, not just your finger tips) do a very similar job.
    Well done! Now we just need a macro-scopic version…

  2. Thing is…you don’t change the friction of the material your hand is made of, you change your grip strength. The thing the human hand has to make this possible is that you have very precise senses that let you know when the phone is sliding vs stationary in your hand. It is cool that they are adjusting the grip but the real secret sauce here is knowing when the grip is too light or too heavy. Would need super sophisticated sensors for that, lots of them and very fast response to them.

    1. Hey Steven, You are very right the friction of the material of the hand stays the same, but adjusting grip strength modifies contact area and changes the effective friction. I’m one of the people behind this device and we actually used a torque controller to set the friction. If you are interested there are more details on human finger friction modulation and the controller in the paper:
      https://www.researchgate.net/publication/326428926_Variable-Friction_Finger_Surfaces_to_Enable_Within-Hand_Manipulation_via_Gripping_and_Sliding

      Cheers,

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