Vijay
I have been working with braille for about 3 years now. My first attempt at a prototype used a dot-matrix printer head: http://www.angadmakes.com/my-portfolio/virtual-brailler
At Makerfaire Bangalore, I met Paul D'souza and was amazed by his innovative designs for refreshable braille displays. One of his designs used these vibrator motors.
Im looking to build on that brillant idea and build a system that is more robust and can be understood and reproduced and improved by people all over the world for the visually impared , similar to how the open source prosthetics movement have helped so many amputees.
The method of working is as follows:
Motor+Cam :
The heart of the mechanism is a series of pico-motors that are commonly used as vibration motors with a weight on the end.
We modify the weight to have a profile similar to the above so that is may act like a cam, when shaft axis is verticle.
Motor holder + Stoppers:
The motor holder holds all the motors in the appropriate positions to actuate the pins. There are stoppers that prevent the cam from rotating continuously that are integrated into the design.
At the particular position where the cam followers are placed, depending on the rotation of the motor, the cam follower will he higher, when motor rotates one direction, and is lower in the other. The stopper make the motors behave in a "binary" fashion. The functioning will become clearer once the cam follower is explained.
Cam follower + Lever + Spring + Pins:
The cam followers, that will be riding on the motor's cam is shown in the first image( the three projections). The cam follower is attached to the lever bar, that is fixed on one end ( the large rectangular part). The level bar has the braille pins on the other end.
The material used for this part would be ABS, or Nylon, that would be slightly flexible without causing fatigue.
Thus the movement of the cam, wold cause the cam follower to move up, that flexes the lever pushing the braille pin upwards and the lever is displaced from its natural position. when the cam causes the cam follower to fall, the level bar falls back to its natural position and thus acts like a spring.
Everything is assembled in the above fashion. Two lever arrangements and six motors make up a single braille cell.
Faceplate+ Pin Guide:
The faceplate forms the surface on which the pins pop out.
One module contains two refreshable braille cells( like above).Modules will be linked together to make a full braille display. i.e, for a 20 character refreshable braille display, 10 modules would be used.
The below image illustrates the working better. the white arrows indicate direction of motion.
W. Jason Altice
Kristjan Berce
Harry Svensson
With all those motors, driving them is a real issue, especially if the whole thing needs to be compact.
How much voltage and current do these motors need?
They may be small enough to directly controll the windings to the outputs of a uC or HC595 shift register.
That would be 2 motors on the 8 outputs of a 74HC595 Maybe these motors are available in different current / voltage combinations.
Maybe put 2 outputs in parallel to lower output resistance.
If the motors do not have to be driven you can put the outputs in Tri-state.
Another way to drive bipolar motors is to directly connect one side of each motor winding directly to GND, and the other to either a positive or negative voltage.
The two techniques can also be combined. Then you will need 2 switchable voltaga rails that can be either switched to GND or Vcc, and you connect these to one side of all the A and B coils of all the motors. Then switch the other side of those motor windings individually with the outputs of your shift registers. There are SOIC ic's with mosfet's in Half H-bridge configuration. They can be used to increase the current handling of the shift register outputs if needed. But just 2 transistors per output also work.