trying to design a pressure sensitive hand
Ulrich
Posts: 11
I'm a student at San Jose State University in San Jose, CA studying electrical engineering. I'm interested in a senior project that involves an artificial hand that can sense pressure and respond with an equal amount of pressure, ie sense a handshake and return a handshake with equal amount of squeezing. Would you have any ideas as to what might be the best sensor for something like this? Thank you for anything you might be able to help me with. Ulrich
Comments
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lets see what this does... KA BOOM (note to self do not cross red and black)
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lets see what this does... KA BOOM (note to self do not cross red and black)
An "artificial" hand which can sense pressure begs the question, "Where does it sense the pressure?" (one small spot on the artificial hand, or severl/many), and "How little/much pressure must it sense?", for example.
An "artificial" hand which can exert pressure (same little to much pressure) begs the question, "Exerts pressure on what?"
An "artificial" hand that can engage in a "handshake" is yet another to-be-defined capability --shake hands like a human, or just "hold hands", while sensing / exerting pressure?
The question about "which sensor" can probably be answered better after the question "What does your "artificial" (model) hand look like (i.e., what are its design parameters that will let it sense, exert force, "shake"; who is it going to "shake" with; and no doubt other parameters)?"
So, what simplifications will you·make in your model, in order to pare it down to a tractable problem --one that can be completed by December? (E.g., calling it a "hand" conceptually paints you into a pretty dark corner already; maybe you would prefer to design a "finger" first? Or even something less complex than that?
PAR
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Coming from a background of robotics in the prosthetic community for over 10 years, I think PAR has hit the nail on the head.· You need to define a set of parameters that you
have at hand (no pun) and work from there.· A prosthetic hand can be a very complex device.· In my prosthetic research and development endeavor I have seen
numerous approaches to accomplish or attempt to accomplish what you are out to seek.·
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Here are just a few off of the top of my head that might give you an idea.
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1)·Individual pressure sensors located within each finger tip, capable of relaying information back to the user.
2) liquid filled tubes running along inside each finger which "transmit" pressure anywhere along the tube to a sensing element.
3) Current monitoring of the motor that powers·the hand... normal open and close operation creates a "signature" if you will of the current requirements throughout the
··· cycle of the hand from open to close; An obstruction from grasping an object alters the signature which is used to determine the amount·of·force exerted.
4) Hand position feedback, (also used with #3 above) can be used to determine if an external force is acting upon the prosthetic hand.
5) strain-gauge sensors located on each finger can be used in a method similar to #3 and #4 with a more dynamic·precession.
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Just as a side note from personal experience: Prosthetics can be tough on sensors; there are a lot of sheer stresses involved that aren't necessarily part of your initial equation that can tear apart sensors in a matter of·minutes.· In other words, it is a must to design functionality and durability at all times.
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You mentioned a "Pressure for Pressure" system of relaying information, but there are other·methods for relaying information back to the patient that can be of equal or
greater complexity and there are several approaches that can be taken there as well...
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1) audio feedback
2) proportional "pressure to vibration"
3) electrical stimulus proportional to pressure (similar to a T.E.N.S. unit)
4) proportional servo·with a restricting cuff around·user's residual limb.
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Another note from personal experience: You must consider that a prosthetic arm or leg is·worn for very long time intervals.· Any type of·external stimulus·must conform in a way
as not to interfere with close proximity skin contact of the·wearer.· It must be able withstand and operate under high moisture content (sweat) and not interfere with the comfort
level of the wearer.
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Above all, the·final product must be as lightweight as possible including the·power supply to avoid a "pendulum effect" toward the extremity of the prosthesis.
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If what I have said or suggested has made you sit and re-think if your project is "too ambitious" or not, it was meant to do exactly that, but at the same time I don't want to
discourage you.· This is an excellent idea, and who knows you may have the answer that nobody else has even considered.
Best of luck!
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Once that concept was complete or nearly so, it would be much clearer at that point what options·make sense·to sense force applied, and sense the amount of force returned, and control it.
So, now you have a method of sensing force applied, in the case of a handshake probably force applied across the width of the palm... Then you need your electromechanical method of closing the hand, or applying force in return. Also, your going to need to be able to monitor the amount of force being returned to the person shaking your robotic hand. Current shunt on an electrical actuator, pressure sensor such as the Parallax sensor, etc.
Also, and probably most importantly, you'll need safety mechanisms if this thing is going to interact with people shaking their hands, to prevent excesive force from being applied to a person. Personally I would design in an absolute limit to its capability of applying force, that way if all else failed it simply couldnt apply enough force to cause serious injury.
Good luck
Chris
One possibility of a scaled down version might be a game where the uses presses one human finger to a prosthetic finger, the finger could press back with similar force. When this works, go to two fingers, and build from there. The end result could be a game where·the user places their fingers on the prosthetic fingers. When a finger is pressed, the hand responds with equal force. Each finger could work independently so that the user could choose how many fingers to press and how hard to press each finger.
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Five servos and five force sensors along with a “brain” could theoretically get you going.
your idea sounds great, don't slowdown and don't stop asking questions once you choose what to do.
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Magic Smoke Theory of Electronics –
Inside every electronic part there is magic smoke.
The magic smoke is what makes everything work.
If you release the magic smoke, the part stops working!
9 months with the help of your colleagues, teachers from college and the great minds that exist inside this box; can help you have your project completed.
Fear of not being able to accomplish something is the greatest enemy of progress and imagination.
I would love to be in your shoes, you have a great future ahead if these are the kind of projects you have decided to undertake.
I am just a Sign Maker, and wanted so much to become a robot engineer, but life has other plans for us, we must accept the challenges that are thrown at us.
I decided a few months ago to try what here has been described as a great undertaking myself, even for an engineer, inventors and companies.
I work few a hours here and there, and so far 9 months later this is what I have.
http://forums.parallax.com/forums/default.aspx?f=5&m=176953
I should be done with the arm in few months, then a few more months for the touch, temperature and sensing part of it. The fun will then start for the programing.
Again, I am just a Sign Maker and a High School graduate, I urge you, dont stop.... keep going. The future is of whom wants it bad enough.
Fernando Gomez
Dunedin, Florida