A work-in-progress prosthetic for my partner’s mother who lost 2 fingers and the use of their remaining 2 fingers and thumb. The prosthetic uses wrist movement to actuate the fingers.

 

In its final form the prosthetic will hold a pen with a separate attachment and actuate the ring and little fingers. 

 

The plastic (gray and black) and rubber (pink) components in the design are 3D printed.

The prototype was delivered and her mother was extremely happy! I added a universal connector to enable her to attach pen holders/hairbrushes etc. Still lots to improve and the next version will use motors instead of wrist movement.

The image below shows a render of the final prosthetic design.

The video below shows the prosthetic being used to life household objects and test the motion before and after lifting to check for discontinuities or stretch in the components. As you can see the prosthetic is as intuitive and responsive before and after.

In the final version though the infill and wall thickness for the parts will be enhanced for added strength and multiple loops of cord will be used to add stiffness and durability.

I have a ring and little finger so to fit and test the prosthetic I needed to subtract a section of the prosthetic.

The sketch below shows the initial concept for the prosthetic including the hinge design. The main design concept remained the same but the hinge was removed.

The rubber printed springs are shown in red in the render below.

A timelapse of a late prototype is shown below.

The image below shows how a hand-scan skeleton model approach was used to define ergonomic and to-scale fingers and palm cover designs.

The motion study below shows how the fingers move when the wrist is actuated.

The image below shows an initial concept which had a wrist hinge. The hinge experienced large forces during actuation due to the multidirectional forces from the wrist, particularly susceptible to misalignment.

In the following designs the hinge was removed from the design, sacrificing comfort, but enhancing durability since the material options for the design are limited.

The hinge design concept sketch is shown below.

A sketch of the hand section and strap is shown below.