A product development group in a large company planned to develop
a device to automate the book checkout process in libraries. The
books have a security device, a magnetic strip, that is detected at
the door if someone tries to leave without checking it out properly.
This is the same technology we all have seen in retail stores.
The client hired me to perform a preliminary design study for a
device that would automatically scan a magnet across an area large
enough for the library book. The magnet would demagnetize the
security strip before the library patron left the building. The
client specified the size, shape, and weight of the magnet; the
overall weight of the device; the travel distance of the magnet; the
amount of time to complete a scan; and the accuracy of the
end-stops. The customer also specified a target cost for
manufacturing the device.
This job required mechanical design and motor circuit analysis. I
hired a mechanical engineer to develop the mechanical concept, and I
researched the dynamics of moving the magnet using stepping motors.
I found a inexpensive and small stepping motor would do the job.
The mechanical designer created an excellent aluminum structure that
met both the weight and strength requirements. I priced out the unit
cost, excluding development costs, and found that we came close to
the customer's very aggressive cost target.
