Artificial limbs that offer an individual enhanced capabilities for grasping, holding and overall
maneuverability has been the ultimate goal for many years. Recently, The Johns Hopkins University
Applied Physics Laboratory (APL) in Laurel, Md., was awarded a contract to manage the development and
testing of the Modular Prosthetic Limb (MPL) system on human subjects, using a brain-controlled interface.
The final design offers 22 degrees of motion, including independent movement of each finger, in a package
that weighs about nine pounds (the weight of a natural limb). Providing nearly as much dexterity as a
natural limb, the MPL is capable of unprecedented mechanical agility and is designed to respond to a
user's thoughts.
A number of components for this MPL are being designed and produced by HDT Engineering Systems with the help
of micro manufacturing afforded with the microwaterjet® manufacturing system.
We sat down with Ezra Johnson, Manager of Systems Engineering, HDT Engineering Services, Inc., to discuss the
program and how the microwaterjet® manufacturing system helped them achieve their goals.
MWJ: What made you choose Micro Waterjet technology instead of other available processes?
Ezra: For metallic parts, the cost of producing parts using the Micro Waterjet cutting system is less than wire
EDM and we were able to hold to tight tolerances. In the past we were using punching for thinner parts and we
had to make a tool for each part. As an engineering firm, our parts are often manufactured, tested, slightly
modified and then manufactured again. So, each time a design changed for parts which will ultimately be made
by punching, new tools had to be made. This was time consuming and costly, but with Micro Waterjet cutting
process we can have modified parts manufactured simply by sending them a new design file. Changes are now
fast and cost-effective and the Micro Waterjet cut parts are more precise than punching.
We have also used lasers in the past for smaller, critical parts but some materials have compatibility issues
since the laser tends to burn thinner materials. But, with the Micro Waterjet process we have no issues with
burning or heat effected zones.
MWJ: What advantages do you feel the Micro Waterjet process has over conventional processes?
Ezra: The biggest advantage we have found with micro waterjet cutting is material compatibility as compared
to laser or Wire EDM. The micro waterjet system can cut a wider range of materials with a very high degree
of precision. Also, the cost of producing prototype parts is less with the micro waterjet process when compared
to punching or wire EDM.
MWJ: How has it been working with Micro Waterjet?
Ezra: HDT has listed Micro Waterjet into our preferred database and they have a 4 star rating in every category.
Additionally, Micro Waterjet's pricing is fair and consistent. Unlike other suppliers who have raised their
prices when they are busy and then lowered them again when they are slow, we have never had an issue with Micro
Waterjet in this regard. Micro Waterjet's consistency and accuracy are dependable. So far, their parts have
never been out of spec and we are happy to report that we have never had to send a part back for any reason.
Micro Waterjet has been very responsive. They respond quickly to our pricing requests, purchase orders and
overall correspondence and I am pleased to say that they deliver on time.
If you would like to learn more about the Modular Prosthetic Limb (MPL) system, you can check out these
articles on the internet. Click on the links below to read the full articles.
DARPA-funded prosthetic arm reaches phase three, would-be cyborgs celebrate
Hopkins Applied Physics Lab Awarded DARPA Funding
to Test Thought-Controlled Prosthetic Limb System
DARPA-funded prosthetic arm reaches proviso 3, would-be cyborgs applaud