Mechanical Force Feedback

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Mechanical Force Feedback

Postby LesHall » Mon Aug 24, 2015 10:29 am

I've been cultivating an idea for a while now, and it's time to share. There have been a lot of efforts to accomplish sensory perception of touch, for example in the fingers of a hand using electronics. These designs all have their merits and flaws as any design has, and I'm not knocking them here at all, it's just that I figured out a way to do this mechanically. In fact, the idea generalizes to any flesh/plastic interface that bends so it's not just for fingers. First though, we will look at fingers.

For one thing we already have a bit of Mechanical Force Feedback in our hand designs because when the wrist is bent to make a fist, the flesh palm must press against the device or it's strap with a force proportional to the force exerted on the fingers altogether. So a sum of forces already exists. Great.

What is wanted is to be able to sense the forces applied to individual fingers, or so I imagine (recipients please chime in here). If that is the case, then I've got one way to do it. Taking a look at our fingers, they have this "stop" or raised "tab" that butts up against the palm so that the palm can push on the fingers. Without this the fingers would just bend back and never squeeze on anything.

The idea here is to design this stop and the palm so that this force (or part of it) is conveyed through a slot in the plastic palm to a pad or paddle where it then presses onto the backside of the flesh palm located inside the device. So when a recipient bends their wrist to make a fist, they feel an aggregate of forces against the device and also they feel individual forces against the back of the knuckle area on a per-finger basis. In other words the index finger presses onto the area behind the index finger knuckle with a force proportional to the force that the index finger is experiencing. same for all other fingers and thumb too I guess.

OK so now hopefully you've got the idea for fingers. Now let's generalize it. Let's say we have a limb with a flexor such as a wrist, elbow, or shoulder, ankle, knee, or hip - really anything that bends. It's got a physical difference in that it's the last part extending out from the body that bends. What does it bend? a straight bone segment of some length. Well, what's good for a finger is good for an elbow I figure, so we ought to be able to generalize this notion to provide mechanical feedback to any segment of the body that needs it. Now that I think of it, this may only be required for fingers and toes because the mroe macroscopic mechanism exists already. Or perhaps we use cable to transmit the force feedback up an arm to the elbow that is flexing the hand for someone without a wrist.

Well, there are lots of possibilities to use Mechanical Force Feedback in various assistive devices it seems. Let's focus primarily on the fingers of a hand and keep the other possibilities in mind as well.

I hope my description has been clear and I open this topic up for discussion! Happy imagineering...


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Re: Mechanical Force Feedback

Postby Les » Thu Sep 03, 2015 7:05 am

e-NABLE FFF 1st test - 1.jpg
first test of ffff
e-NABLE FFF 1st test - 1.jpg (1.23 MiB) Viewed 832 times

Above we see the curved shape of my first test of this FFFF (Force Feedback Flexi Finger) concept.

I found that the concept does work in that force applied to the "finger" part is, as you would expect, felt by the palm. To do this test I simply placed the shape between my index and middle fingers on my left hand and pressed on the finger with my hand or the table.

It's a bit oversimplified because the shape does not have any system for opening and closing the fingers, which would also exert force on the palm. I figure that would be even better, as the palm then senses any forces involved.

More to follow as I fit more tests into my creativity schedule / routine / chaos!


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