Saturday, April 15, 2017

The Limits of Rapid Prototyping

Rapid prototyping is the process of virtually testing parts, pieces, assemblies, and entire units using Computer Assisted Design (CAD).  At one time, the only method of testing was through building partial or full scale models.  In many ways, rapid prototyping has replaced modeling, and it shortens up the process from idea to assembly line significantly.  Rapid prototyping, however have its limits.

Case in point.  I use a wheelchair.  My current wheelchair is a new and innovatively designed unit with seating that offers full tilt, recline, leg articulation and seat lift.  The seat lift is engineered to allow the user to operate the wheelchair while the seat is elevated.  This way, the wheelchair user can be at eye level with a person walking next to them (hence the name iLevel). 

I drive an accessible van from my wheelchair.  While I was driving, the seat back reclining mechanism failed, causing the seat-back to recline.  This became a major problem given my lack of core strength and trunk control.  I was driving the vehicle when the failure happened.

With the help of my son, I was able to get the wheelchair home.  The technician temporarily propped the plunger unit with a piece of metal and industrial tie wraps so that the seat back would stay upright.  It will get a permanent fix after the Easter holiday.  The reason for the failure?  A nylon gear/spindle assembly that failed.

The problem is this.  A part failure on a major assembly of a wheelchair while it is being operated by the end-user can have significant consequences.  To a person with a disability, a wheelchair allows them to perform activities of daily living.  For this reason, an electric wheelchair needs to be nearly bullet-proof.  Going from idea to prototyping to manufacturing to end user earmarks the end user as part of the testing process.  This presents a unique problem for a person with a disability.  And it highlights the limits of rapid prototyping.

It is impossible to simulate the end-user experience by using a virtual experience.  And in the case of a wheelchair, the parts used in sub-assemblies must consist of high-level materials.  Rapid prototyping is limited with relation to the materials aspect of manufacturing. 

Moreover, it is very tempting for manufacturers to utilize assembly parts that marginally meet minimum requirements for normal use.   Electric wheelchairs are being designed and manufactured for people with a wide variety of disabilities.  For this reason, wheelchair manufacturers must exceed minimum requirements.


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