by Skip Meetze & Jon Schull
at Rochester Enable Lab
Draft updated: June 12, 2018
The Adjustowrap Gripper Arm System is an experimental modular system of upper limb prosthesis components. These components are intended to be compatible with a range of traditional medical devices provided by prosthetists as well as the experimental volunteer-designed devices being developed by the e-NABLE Community. Many components in the system include fabrication using the 3D printers available to our volunteers.
This is an update of the Skip Meetze Gripper Thumb Terminal Device and the Adjustowrap Arm recently developed by Skip Meetze and Jon Schull. Some background for these developments can be seen in the The Gripper Matures, a blog post sketching the early evolution the system.
Herein, we will describe 4 sizes of components that are intended to be useful to trans-radial amputees ranging in size from 3-year olds to adult males including the following:
- links to the current Designs in 4 sizes that should span most cases
- description and rough instructions for the Adustowrap sleeve system.
The Jedi Gripper
The Jedi Gripper is an experimental Passive Prehensor Terminal Device that is a remix of the Gripper Thumb Hand. It can be attached to a conventional socket that has been fitted by a Certified Prosthetist with a 1/2 – 20 hex bolt or nut. It is also compatible with the Jedi Adjustowrap Arm.
STL files for Left Jedi Gripper Hand:
- 8087L A Thumb.stl for preschoolers with left side trans-radial amputation
- 8087L A Palm.stl for preschoolers with left side trans-radial amputation
- 8087L B Thumb.stl for elementary kids with left side trans-radial amputation
- 8087L B Palm.stl for elementary kids with left side trans-radial amputation
- 8087L C Thumb.stl for teens and adult females with left side trans-radial amputation
- 8087L C Palm.stl for teens and adult females with left side trans-radial amputation
- 8087L D Thumb.stl for adult males with left side trans-radial amputation
- 8087L D Palm.stl for adult males with left side trans-radial amputation
STL files for Right Jedi Gripper Hand:
- 8087R A Thumb.stl for preschoolers with right side trans-radial amputation
- 8087R A Palm.stl for preschoolers with right side trans-radial amputation
- 8087R B Thumb.stl for elementary kids with right side trans-radial amputation
- 8087R B Palm.stl for elementary kids with right side trans-radial amputation
- 8087R C Thumb.stl for teens and adult females with right side trans-radial
- 8087R C Palm.stl for teens and adult females with right side trans-radial amputation
- 8087R D Thumb.stl for adult males with right side trans-radial amputation
- 8087R D Palm.stl for adult males with right side trans-radial amputation
The orientation shown is optimized for FDM printing with support touching the build plate. It can also be printed with the SLS (such as provided by Shapeways). Wall thickness is typically 1.6mm to be similar to injection molded parts.
In the STL files provided, numbers in the identification are date codes that give us a basic version control management. The larger the number, the newer the design version. 8087 refers to the 87th day of the year 2018. The letter A designates the size for a typical preschool child, B for a typical grade school child, C for teens and adult females, D for adult males.
Tinkercad, an easy-to-use design tool was used rather than parametric CAD tools. We share the designs by making the Tinkercad projects “Public” when we feel comfortable that the design is printable and can be successfully fabricated. You can also export the STL files from Tinkercad here: 8087 Right Jedi Gripper Hand
Feel free to remix this device for your own prosthetics research, but be sure that a qualified clinician (such as a physician or Certified Prosthetist) is involved in fitting the device, especially to a young child.
As a “passive prehensor”, the 8087 device can be used on an amputee with a long residual forearm without a hinge and triceps cuff (with proper suspension on the forearm). This allows a natural pronation/supination movement that is valuable in tasks such as eating with a spoon or fork as we learned from our friends Rajab Hamis and Gilbert Cameron in Tanzania using a differently designed passive prehensor. Used with or without the elbow hinge and triceps cuff, the Jedi Gripper can be used without a Bowden cable or harness by placing objects into its grasp with the unaffected hand.
Like the earlier gripper designs, the 8087 Grippers are assembled with zip-ties attaching the thumb to the palm using a latex ring for the gripping force. The basic functions of the Jedi Gripper can be seen in this video which uses a paper binder clip (as proposed by Yoav Medan) rather than the zip-ties and latex ring for gripping force. Since available binder clips will deform when flexed by all but the smallest Gripper designs, the design is not made public at present. Other experimental variations of the Gripper’s gripping force are being developed by Dean Rock using a rack and pinion with a flexible printed spring, and by Grit 3D using a coiled torsion spring and by Ed Choy with open fingers for wearing gloves.
The Adjustowrap Arm System.
The Adustowrap system is designed for transradial (below elbow) amputees.
It is comprised of a few 3D-printed parts and laminated plastic that is produced using a consumer-laminator available from retailers such as Staples or Walmart. The resulting “fairing” (cosmetic sleeve) is remarkably slick, easily customized, and can accommodate either a prosthetist-crafted custom socket, or, when that is unavailable, be worn as-is and padded as necessary. (See below)
These modular arm components can be scaled in the slicer to fit the residual arm/socket, and the laminated cone can be adjusted to fit the printed rings. Rivets can be fabricated from filament using a soldering iron to flatten the ends.
STL files for Jedi Adjustowrap Arm:
60mm inside diameter can be scaled in slicer for trans-radial (left or right) amputation.
- 8067 Adjustowrap Elbow for use with Hinges and attached to laminate with pegs made from filament.
- 8067 Adjustowrap Hinges for use with Elbow to form an ornamental triceps cuff from laminated artwork
- 8067 Adjustowrap Endcap for use as alternative to extruded edge trim.
- 8067 Adjustowrap Joint for use with two sections of laminated forearm when arm is too long for a single section.
The Forearm Joint can be used to provide devices for longer forearms. The Forearm Endcap can be fitted over a conventional socket. The Elbow and Hinges (for a triceps cuff) can be used for amputees with a short residual forarm to help with suspension of the device. Three different configurations are illustrated below.
Filament for Rivets can be fabricated from filament by using a soldering iron to melt a flat head on a short bit of filament. Use either 1.75mm filament (using a 1/16 in drill for holes) or 2.85mm filament (using a 1/8th inch drill). Translucent nylon filament makes a good tough rivet, but we typically use the same filament that was used to print the Gripper.
Clear Packing Tape for Holding the Assembly Together
Thumb Tip Alternatives include silicone nipples from pacifiers or a bit of 1/4 inch ID latex tubing (which also makes a good elastic ring to provide gripping force).
Zip Ties and Tubing for Spring-Loaded Gripper Thumb
Assembly of the Adjustowrap.
Please see the draft Assembly of the Adjustowrap playlist for sequential playing of assembly instructions.
Or you can look at any of the 9 individual instructional videos: