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UAProsthetics - A Powered Hand

UAProstheticHand is a dexterous under-actuated robotic hand designed to grasps everyday objects with low mental loading and at low cost

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Project Video: https://www.youtube.com/watch?v=hetpdrneoNI
The ability to control the many muscles within our body is a gift - one that people do not completely have. UAProstheticHand, short for “ Under-Actuated Prosthetic Hand, is a prosthetic hand that aims to provide full hand actuation capability at low cost and low mental loading. A Linear servo motor is is used to actively retract the index finger as this control is necessary for nearly all grasping. The middle finger, ring finger, and pinky serve a less crucial purpose for the majority of day to day tasks, thus UAProstheticHand implements a double differential to actuate these three fingers. The double differential allows the three fingers to be actuated together and allows the three fingers to conform around any objects it grasps using an active close passive (elastic) open mechanism.

One of the most important aspects of consideration in the realm of prosthetic design is mental loading. The ability to control the many muscles within our body is a gift - one that people with amputees do not completely have. There are are range of prosthetic arms on the market today, each of which have downfalls whether that might be functionality, ergonomics, usability or what might not necessarily come to mind at first  - cost! Often times high quality prosthetic limbs can be quite expensive too.

UAProstheticHand, short for “ Under-Actuated Prosthetic Hand, is a prosthetic hand that aims to provide full hand actuation capability at low cost and low mental loading. There are five digits in the human hand each of which are extremely important in creating a hand that is extremely dexterous and capable of maneuvering a range of different objects. It is important to note that most of the functionality of the human hand comes through cooperative use of each of the five digits. The index finger and the thumb are arguably the most important fingers in the human hand as they are necessary for most methods of precision gripping in addition to nearly all other five digit methods of grasping. The middle finger, ring finger, and pinky serve a less crucial purpose for the majority of day to day task and tend to move in in sync largely conforming around objects that are grasped. In order to reduce the mental loading associated with these muscles UAProstheticHand implements a double differential to control these three fingers. This reduces the degrees of freedom(DOF from 3 to 1 thereby simplifying the control of UAProstheticHand, reducing the weight, and the cost. The double differential allows the three fingers to be actuated together and allows the three fingers to conform around any objects it grasps using an active close passive (elastic) open mechanism.

The thumb is the most complex digit on the human hand as it can move in many directions. For this reason the thumb on UAProstheticHand is designed with 2 DOF, where one degree allows for Abduction/Adduction (rotation of the thumb joint) and Flexion/Extension of the thumb joint. A 2 DOF thumb encompasses the movement required for nearly all methods of grasping giving UAProstheticHand the ability to hold nearly any object that it is presented with.

UAProstheticHand will also have a much lower cost than other high functionality prosthesis on the market due to the fact that most parts can be 3d printed, and the fact that there are a total of only 4 motors

Four primary goals were established at the beginning of UAProstheticHand’s conception, which have heavily influenced its design. First of all the prosthesis should serve the user; the user should not be the servant of the prosthesis. This is extremely important in the design of a good prosthetic as the user should always feel completely in control of the prosthetic otherwise the user will likely not feel comfortable using it. Second of all the prosthesis must be user friendly or simple to learn to use. Any device should be intuitive and natural. Third of all the prosthesis should not sacrifice any human functional ability. The prosthesis should be used to supplement, not subtract, from available function. This is necessary for the prosthesis to be deemed truly useful. Last of all the prosthesis must look natural. Movements that appear mechanical in nature attract unwanted attention in social situations and may not be pleasing to the eye.

Thank you for taking the time to check this project out we look forward to showing our progress and making this game changing device!

- Taran Ravindran

ALL STLs.zip

Can Be 3D Printed using SLS, SLA, or FDM manufacturing methods!

x-zip-compressed - 4.09 MB - 10/17/2017 at 03:21

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sheet - 56.94 kB - 10/17/2017 at 03:20

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Prosthetic Hand Assmebly.STEP

Feel free to make edits to the current design!

step - 33.86 MB - 10/17/2017 at 03:16

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Prosthetic Hand Assmebly.EASM

Solidworks eAssembly - eViewer can be download for free and is a great resource to play around with the assembly and see where parts fit

easm - 4.59 MB - 10/17/2017 at 02:39

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  • 5 × 2 Part Joint - Tip Finger Tip - 3D Printed
  • 9 × 2 Part Joint Single FInger Digit - 3D Printed
  • 1 × Inner Surface of Hand 4
  • 1 × Motor Mount (Optional)
  • 4 × Motor String Adapter

View all 23 components

  • Ready for Testing

    Taran Ravindran10/18/2017 at 16:11 0 comments

    UAProstheticHand is now fully assembled! Within the next few days I will be releasing a full release Video showing the capabilities of the hand and how it was built.

  • Video Log Update as of October 15th

    Taran Ravindran10/16/2017 at 02:53 0 comments

  • Dyeing SLS Parts Blue

    Taran Ravindran10/16/2017 at 00:52 0 comments

    As discussed in my previous log, I wasn't the biggest fan of the white colour of parts, so I have decided to dye the parts grey. I followed the instructable for dyeing Nylon parts that can be found here. 

    http://www.instructables.com/id/How-to-Dye-Your-Nylon-3D-Prints/

    The process was extremely easy and straight-forward, and although my parts didn't exactly turn out grey I was pleasantly surprised to find out that my parts had turned a dark blue colour! Photos below show the colour of the parts before and after dyeing.  I was impressed at how consistently coloured the parts were, as I had expected the parts to be super blotchy. One thing I would suggest for anyone trying to evenly dye their partts is to make sure that your parts are completely submerged in your dying solution (I used RIT fabric dye) and to make sure to continually  stir the parts in the dying solution! 

  • First Look at 3D printed Parts

    Taran Ravindran10/16/2017 at 00:41 0 comments

    Parts have finally arrived! All packaged up nicely. I had them printed out of SLS Nylon and they turned out amazingly. the only criticism I have is the colour. I am not too much of a fan of the white colour they came in so in my next log I will be documenting my method of changing part colour via dyeing them!

  • SLS Manufacturing of parts

    Taran Ravindran09/21/2017 at 03:09 0 comments

    Today allot of progress was made in the departments of part manufacturing for USProstheticHand! For awhile I was planning on having parts made on Formlabs' new Fuse 1 3D Printer, but due to unforseen circumstances I was unable to print them on this device. After this is started looking around for cheap SLS 3D print shops and stumbled on a website called 3DHubs.com which is a great resource that helps connect people who want to have parts 3D printed to 3D Print shops all across the world. And at reasonable prices too! Today I selected a print shop in Boston that will be printing my parts out in the next week. There were some issues that Chris saw in my parts as seen in the images below (red spots) as a result of features that were too small in the CAD to be actually printed. Luckily Chris allowed me to modify the parts and make them more suitable for SLS Manufacturing.


    The parts should be shipped out of the shop on September 27th and I have to say I am eagerly awaiting them! I am excited to see what my new friend Chris has in store for us!

  • Hackaday Release Photos and Video

    Taran Ravindran09/04/2017 at 03:55 0 comments

    Project Video: https://youtu.be/5F6oQ7GGX9E

    CAD Renders

  • Manufactured and Purchased Parts

    Taran Ravindran09/04/2017 at 03:53 0 comments

  • Actuation and Motor Mounting Design

    Taran Ravindran09/04/2017 at 03:51 0 comments

    The next thing that was to be considered was the design of the motor Mount for UAProstheticHand. A decision was made to use bowden guide cable to transfer power as they allow for easy and efficient  linear power transfer. The following photo illustrates the design selected. 

  • Overall Hand Design

    Taran Ravindran09/04/2017 at 03:48 0 comments

    There are five digits in the human hand each of which are extremely important in creating a hand that is extremely dexterous and capable of maneuvering a range of different objects. The index finger and the thumb are independently driven with teh thumb being given 2 DOF, where one degree allows for Abduction/Adduction (rotation of the thumb joint) and) and Flexion/Extension of the thumb joint. A 2 DOF thumb encompasses the movement required for nearly all methods of grasping giving UAProstheticHand the ability to hold nearly any object that it is presented with.

    The middle finger, ring finger, and pinky serve a less crucial purpose for the majority of day to day task and tend to move in in sync largely conforming around objects that are grasped. In order to reduce the mental loading associated with these muscles UAProstheticHand implements a double differential to control these three fingers. This reduces the degrees of freedom (DOF)from 3 to 1 thereby simplifying the control of UAProstheticHand, reducing the weight, and the cost. The double differential allows the three fingers to be actuated together and allows the three fingers to conform around any objects it grasps using an active close passive (elastic) open mechanism. a more simplified diagram for the double differential is shown in the second photo

  • Finger Actuation Design

    Taran Ravindran09/04/2017 at 03:43 0 comments

    Below is a concept drawing for an under-actuated finger mechanism driven by a cable or string active close and passive open system. The term "under-actuated" in this case refers to the fact that despite there being 3 joints per finger each finger is only driven by one motor. This allows the fingers to conform around any object that it is presented with as opposed to being rigid  and fully controlled. the benefit of this is that the finger can put equally distributed force on an object no matter what the size or shape of the object. This is important in the manipulation of delicate object like for example an egg. 

View all 13 project logs

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Discussions

Taran Ravindran wrote 10/15/2017 at 23:27 point

Hey Shrad, not sure if I'm understanding your idea correctly. Are you suggesting a method to allow individual actuation of each digit of a finger? That is a very intriguing idea, but it was actually by design that each finger is only actuated as a whole, as opposed to individual digit actuation. Fewer degrees of freedom means fewer motors are necessary, and also allows the fingers to conform around objects naturally! I really like the idea though, and I'll definitely look into something like this for a future iteration! :) 

  Are you sure? yes | no

Shrad wrote 10/10/2017 at 19:25 point

simple idea here... why not use some laminated foil as tensors to move the fingers? (like those front panel selectors in amplifiers which use a metal sliding foil reaching a soldered switch)

one could stack three or four laminated foils per finger to achieve the same degree of move as a natural hand, and it would enable a decent amount of force to be applied to handle heavier objects

  Are you sure? yes | no

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