May 06, 2004
Kinkajou Gamma Prototype Construction Begins
The Gamma prototype design is now complete, and machining begun. A number of detail changes have improved producibility. The major ones are the elimination of the pressed contour in the covers and a redesigned aluminum cage that can be water-jet cut flat, and bent to shape. Two acceptable quotes have been received for the extruded heat sink. 90% of the purchased parts and material for the prototype has been received. The optics have been redesigned to incorporate 3 condenser lens elements and the projector lens housing has been redesigned to fit a tethered lens cap used on propane bottles.
A sectioned view through the optics path shows the close spacing between the LED and the first condenser element made possible by inclusion of a third condenser lens (a duplicate of the second element) to reduce the focal length. The condenser lenses are plastic aspherics taken from the Fisher-Price "Show-and-Tell" toy projector. The projector lenses are taken from the eyepiece of the Fisher-Price "Viewmaster" toy telescope. The projector lens is larger (19mm v 8mm) than that in the Beta prototype, and will permit more light to be delivered to the screen. The exact spacing of the elements is still to be determined by experiment.
The section through the microfilm reel shows the larger bearing permitted by elimination of the recess in the cover, the one-way clutch to allow the film only to be tensioned by the hand knob, and the leaf spring mounted on the bottom plate that creates some friction on the reel, while pushing it up into place. Film is changed by working with the projector in an inverted position, removing 7 screws holding the bottom plate.
This view of the exterior shows the impact cage (which will deform plastically, absorbing energy if the unit falls to the ground, and can be bent back into shape by hand). The screws formerly attaching the front plate to the extrusions have been eliminated by including a slot in the extrusions and use of multiple screws top and bottom for the covers. All of these changes were enabled by the decision to eliminate the hinged covers, and accept that entering the unit to change film will entail somewhat more effort. The original reasons for adding the pressed contour to the covers were to protect the knobs by depressing them into the surface, and to stiffen the cover so that hinges and two screws would put adequate pressure on the sealing gasket. The addition of the cage and additional screws have achieved these objectives in other ways. The covers can now be cut on a water jet machine, or punched out without needing the presswork tooling. This view also shows a power switch, although it is to be replaced with a sealed switch, which will have a slightly different appearance.
The view from underneath shows the relationship of the optics assembly to the printed circuit board that mounts the LED. A thermistor on the board will monitor the LED temperature and reduce power if it gets too high.
For the prototype, the heat sinks will be cut from solid aluminum by a CNC mill, but the 75 pilot projectors will use extrusions, which will cost about $7 apiece in the pilot quantity, to go down to $3.55 each in quantity production. The covers, cage and film gate will be cut out by water jet for the prototype, and possibly also for the pilots. The optics barrells and spacers are screw machine parts.
Exploded view of the gamma prototype. See the pdf version [PDF]
We expect the prototype to be complete by 24 May.
Posted by Allen Armstrong at May 6, 2004 07:09 PM
