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[DPRG] Animatronic Hand Robot 3D printer

Subject: [DPRG] Animatronic Hand Robot 3D printer
From: Quinones, Jose jquinones at ti.com
Date: Wed Apr 18 16:55:40 CDT 2012

Hmmm! Torque control? I have always wondered on an application where you could use current regulation to control torque and finger grip strength would be the one!

Most people think that current regulation controls speed because that is how most speed control loops are implemented. In essence, current and voltage are the same once you take the resistance into consideration. So when you regulate current, what you are doing is changing the PWM duty cycle which in turns results in a proportional voltage, ergo a proportional speed.

OK, enough blahbing. What is the point with current regulation and John's idea to control hand grip strength? If you have a simple H Bridge with current control (OK, not that simple...) which happens to be directly proportional to an analog input (e.g. VREF), you can then control the torque each motor will exert by applying an analog output. The H Bridge then takes care of regulating the current (AKA torque). The missing link is a pressure sensor or gauge which tells the hand whether the pressure exerted is enough or not. Here is where I am at a loss. But assuming there is such a sensor that can tell where the hand load is slipping or not (in humans this measly sensor is called brain made of about a terillion (and yes I patented this word) neural synapses determining whether the hammer is slipping or not, or whether we are about to break the egg), you could then vary VREF according to the sensor output. For example, if you increase VREF, the hand grip increases, and vice versa.

You could also let the motor ask for as much current as it requires, but then there would be no control and you could in essence break mechanisms (or the egg) if you just tell the motor to go and use the maximum available current. At the same time, every time you tell the hand to close, the motors would reach its end and for a brief period of time you would experience a stall, or maximum current. With current control the hand would only exert the needed force and save on battery power. Kind of important if you consider that the cybernetic hand will most likely not run on Chef Boyardee or Banana Splits.

Clearly, one of these days we will all be able to enjoy from cybernetic hands and I am positive these hands will be able to do much more than our current ones. I will surely want one trained to play guitar ;-)

Best regards,

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From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org] On Behalf Of John Dolecek
Sent: Wednesday, April 18, 2012 7:26 AM
To: dprglist at dprg.org
Subject: Re: [DPRG] Animatronic Hand Robot 3D printer

Wow! That had to take some serious time. I suppose you could monitor the current from the servos and get some idea of the gripping force. Thoughts?

On Tue, Apr 17, 2012 at 8:07 PM, Brad garton <bgart at iadfw.net<mailto:bgart at iadfw.net>> wrote:
That's cool. I want one!

-----Original Message-----
From: dprglist-bounces at dprg.org<mailto:dprglist-bounces at dprg.org> [mailto:dprglist-bounces at dprg.org<mailto:dprglist-bounces at dprg.org>] On Behalf
Of David Anderson
Sent: Tuesday, April 17, 2012 6:56 PM
To: dprglist at dprg.org<mailto:dprglist at dprg.org>
Subject: [DPRG] Animatronic Hand Robot 3D printer



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