• Retaking this Project

    Rodrigo Loza10/13/2016 at 02:03 0 comments

    It's been a few tough weeks. But, it is time to retake this. I am not into building stuff in 3D printing or anything like this. So, it is going to be kind of hard for me to build the hand.

    What i am already thinking is on applying machine learning to the hand. I can teach it to move or react to external stimulus. But, for this i will need sensors. Pressure sensors should do the trick.

    For now, my journey on building this starts. I have to train the NN in my head to use solidworks good enough to replicate what i've seen on the antecedents and to copy the hand's anatomy.

  • Anatomy of the Human Hand

    Rodrigo Loza09/05/2016 at 20:20 0 comments

    1. Introduction

    I am not going to describe all the anatomy of the hand because it has a lot of names that describe each of the bones and muscles. I think that the key elements to understand are the muscles, ligaments and joints because understanding them allow the analogy with a mechanical system. Just what i was looking to comprehend.

    So, i am linking the following videos that depict with detail the anatomy of the hand, the kinematics of the hand and the finger movement anatomy.

    Video 1. Hand Anatomy

    Video 2. Flexor Tendon Anatomy

    Video 3. Wrist Joint Movements

    Video 4. In case you still wonder

    how the fingers move

  • Research of Previous Models

    Rodrigo Loza09/05/2016 at 19:54 0 comments

    1. Introduction

    The Hackaday page has lots of projects that describe how to make prosthesis. Actually, there is a wide set of projects. Some that replicate a human hand, others that replicate a human leg and even some exoskeletons to enhance human movement. So, in order to design my own prosthesis i am going to make a summary of the "Open Source" devices i consider to be the best.

    2. Antecedents

    2.1 OpenBionics

    I think this the best project in the "Open Source" bionic hand field. The novel design they have modeled allows adaptive grips, great movility and very low cost. They have a great tutorial on how to build his device.

    They basically use linear actuators to pull tendons (made of string) and, thus, move the fingers. Here's a video that shows their device:

    2.2 Biohand

    Biohand seems to be a very accurate design. As his video show:

    The thesis demonstrates that hacking commercial RC servomotors can be achieved and with his design it is possible to create linear actuators. Therefore, with those tools he was able to simulate tendons that move fingers in a human way. His design also included a robotic thumb. It was built using a servomotor to simulate abduction/adduction and the same linear actuar to simulate the flexion/extension of the finger.

    The cost of the device is 400$, very cheap for such a functional prototype. As i read in the thesis and can be demonstrated by his videos, the user has enough functionality to perform some graspings and movements. This would allow the user the ability to perform some daily tasks such as getting dressed, eating, drinking and opening doors.

    2.3 Dextra

    Dextra is an amazing device also hosted here on Hackaday. This is a very representative video:

    The design uses linear actuators to pull a tendon made of string. As he claims, this design would allow the user to perform adaptive grips. What i like about this design is that it is more compact and seems to require less power. The problem with Biohand was the use of rigid phalanges which limits the biomechanics of the device. Apart from that, the mechanical design is almost the same as the other prototypes.

    3. Devices' Summary

    After reading about the previous models, i decided to make a comparative table to summarize the following features: material, technique of construction, grasping functionality, movement functionality, DOFs and cost. The grasping and movement features will be scored using three parameters (low, medium, high).

    DeviceMaterialWeightTechnique of ConstructionGrasping FunctionalityMovement FunctionalityDegrees of FreedomCost
    OpenBionicsPLA, ABS335gFDMMedium Medium6132.5$
    DextraPLA, ABSunknownFDMHighMedium15unknown
    BiohandPLA, ABSunknownFDMHighMedium6100$

    4. Discussion

    Okay, so i checked all the devices that i found to be the most useful. I think they all present a trade-off between cost and functionality. Therefore, this feature gives me a good intuition about what i should do.

    For what i've seen, there is missing information about the human hand anatomy. I think that making a log about this is necessary to summarize useful information that can be used for the design. It's just like biomimetics.

    Other important feature i consider important is weight, i really liked Biohand 's discussion about the weight and size of current prosthesis. I agree with him in the fact that actual prosthesis might be heavy for users as a friend that has one claims. I think that user comfort is important, but it is better to sacrifice comfort for functionality. Eventually materials will become lighter, therefore, it's better to trade this feature. About the size, i think that personalized designs according to human proportions are adequate. That means 0.6% of the total mass of the body for men and 0.5% of the total mass of the body for women.

    Now, i want to talk about the mechanical designs that i've seen in all the devices. Unfortunately, i am not a mechatronics or a mechanical engineer. In this sense, i have almost no experience with mechanisms or actuators. Nonetheless,...

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