For Phase 2, I decided to change some of the details for the device. In particular, I didn’t like the flexibility of the Acrylic pieces, and needed something more solid – solid means faster motion, which means speed in updating.

My solution was to create the head out of plates of acrylic, which are then bolted together. The result is much stiffer, much stronger, and therefore faster moving:

Another change is the use of linear bearings for the motion (orange tubes in diagram). The layers of acrylic hold the tubes in place, with the end pieces slightly smaller to prevent them from slipping out. This lets them ride on two solid steel rails for smooth and easy speeding. The result so far is ‘finger-tip’ movement, which means the motor doesn’t have to work as hard to move the head.

Another feature of the head is the incorporation of sensors – the yellow ones (gear positioning), and green (switches for end motion). Not shown are the opto sensors at the bottom, for detecting end of travel. I put space for two in the design, but only one is currently needed (end of motion for both left and right can be detected with a single sensor). However, I may use the second one later if I can’t detect Braille rod positioning well enough – in that case, I could use it on a cut slotted rail that would show when we are on a rod (hole) and in between (blocked).

So far the head is performing well – while there is a bit of play in the bearings, I’m hoping it won’t cause any problems. The bearings are 8mm, while the rod is 5/16″ – the difference is only a few hundredths of an inch (5/16″=7.9375mm), but that plus the natural spacing in the bearing leads to some give. Nonetheless, as I am moving it from the center (the hole at the top is for attaching the sideways movement racks) the play is negligible – it only appears if I try an off-center pressure.

Already I am tweaking the design – the holes are a bit small, the sensor area needs a bit more room, etc – but I’m happy with it overall. Now I’m on to the other drive, and the gearing…