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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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The ability to control the many muscles within our body is a gift - one that people with amputees 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. The thumb on UAProstheticHand is designed with 2 DOF, where one degree allows for Abduction/ Adduction and the other allows for Flexion/Extension of the thumb joint.

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

7-Zip - 5.87 MB - 09/03/2017 at 12:21

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x-zip-compressed - 46.46 MB - 09/03/2017 at 12:08

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  • SLS Manufacturing of parts

    Taran Ravindran7 hours ago 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. 

  • To Do log as of July 23rd, 2017

    Taran Ravindran09/04/2017 at 03:33 0 comments

    In order to help organize the work that we still have to do before we can bring UAProstheticHand to life, we created a table tasking different team members with things to do.

    DATE

    ITEM

    MEMBERS

    Sunday July 23, 5 PM, Gear Lab

    CAD or draw out detailed design

    Joyce, Sanjeevani, Farhan, whoever else can come

    Thursday July 20, 5 PM

    Machining parts

    • Joyce is getting materials)
    • Laurel, bring scrap metal

    Joyce, Sanjeevani, Laurel, Farhan, whoever else

    Meeting next Wednesday TBD

    Contact Jaipur Foot

    • Joyce, please talk to Stacey

    Mechanical team or everyone?

    ongoing

    Check up on printed products

    • When are they arriving?
    • Anything else to be printed?

    Taran

    After we finish design

    Talk to Chandrashekar

    • Ask about UX
    • mentorship

    Anyone 

  • Early Design Brainstorming

    Taran Ravindran09/04/2017 at 03:27 0 comments

    Once we came up with a set of goals and requirements for our prosthetic hand the next logical step was to determine what we wanted the the hand to be capable of actually doing. Ideally the hand should be extremely easy to use and should be capable of gripping a range of different objects without being too difficult or confusing to the user. The following picture illustrates the brainstorming that went into the design  throughout the process of determining where the degrees of freedom would be in comparison to an actual human hand. The image also shows the general systems that we will likely have to take into consideration in the design of our prosthetic. 

  • Project Requirements and Goals

    Taran Ravindran09/04/2017 at 02:56 0 comments

      Before going straight into the design process with whatever ideas came to mind a decision was made to come up with a set or requirements and goals for our prosthetic hand. We came up with  a total of 5 primary goals which we will continue to look at throughout the design process such that we stay aligned with our true objectives. 

      Prosthetic design Goals

      1. The prosthesis should serve the user; the user should not be the servant of the prosthesis.
      2. User friendly or simple to learn to use. Any device should be intuitive and natural. An amputee should be able to learn to use the prosthesis quickly and easily.
      3. Independence in multifunctional control. Control of any function or degree of freedom, should be able to be executed without interfering with the other control functions of a multifunctional prosthesis.
      4. No sacrifice of human functional ability. The prosthesis should be used to supplement, not subtract, from available function. The control system should not encumber any natural movement that an amputee can apply to useful proposes.
      5. Natural appearance. Movements that appear mechanical in nature attract unwanted attention in social situations and may not be pleasing to the eye.

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