(This project was created for the course TfCD at the TU Delft)
The idea was to create a bookmark that can also function as a small reading light. We wanted to use the ‘smart material’ SMA (shape memory alloy) to automatically shape the wire (from folded flat between pages to up high to distribute light) when it’s turned on. The electronics are clipped on the back cover of the book and the wire runs over the back of the book and forms like a reading lamp on the top of the book (like in the figure, on the right bottom drawing).
Step 1: Step 1: the Smart Memory Alloy
We got our Shape Memory Alloy (SMA) from this website.
You can probably find a supplier near you on the internet. The wires cost about €5 per meter. We used NiTinol wire from 0.37 mm that will start to deform at 70 ºC.
The wires can be programmed to a shape, in which it will return whenever the wire is heated afterwards. This programming can be done by heating it to it’s annealing temperature while restraining it in the shape you want your wire to be programmed in. The best result can be acquired by heating it in an oven for 20 minutes at 54 0ºC. It can also be done by heating it very short to extreme temperatures. We went for this quick and dirty method, by using a blowtorch.
When using a blowtorch keep a few things in mind:
- You can’t heat the wire for too long: it will become white and brittle and break in use.
- The material needs to be heated a number of times for the best result.
- Give it time to cool down after each round of heating.
- The material needs to be restrained in the position you want it to be programmed in.
- Do not pull the wire when it is heated: It will break.
We programmed the wire in different steps. First we straightened it. Then we made a big rounding at the end of the straight wire to make it curl up. To make this rounding we restrained it around a cake tin and heated it. To make the light shine down on the page we made another smaller rounding at the end of the big curve by constraining it around a small coil and heating it again.
We programmed the wire while it was two-folded and cut it afterwards, so we had two wires with the exact same shape.
Step 2: Step 2: Insulating the Wires
In use the SMA wires will get hot and there will be the risk of shocking the user when the wires are not wrapped up in something. To insulate the wires we cut electrical wires open and wrapped the SMA wires in their plastic insulation.
Step 3: Step 3: Batteries
The coin cell batteries originate from old broken bike lights (3V, 7.5mA), as did the LED light. To increase the current the 4 cells are connected in parallel circuit (the voltage stays 3V, current goes up to 30mA), this is enough to light the lamp and heat the SMA to the temperature needed for contraction.
How we did this is shown in the picture. We used electric wire to connect all plus- and minus-poles of the batteries. The wires are kept in place by the isolation tape.
Step 4: Step 4: Electronics
The picture shows the circuitry of the product. The contacts were soldered to keep all in place.
Step 5: Step 5: Casing
To keep the components in place, a casing is made with a clip that can be attached to the back cover of the book. The casing is made of polystyrene (EPS) it is bended after contact with an electrical heat-wire into the shape that’s also on the template.
The clip is attached to the casing with double-sided tape and the on/off-switch is clamped between the casing (also on the template). Next the battery pack is folded in the casing and then you’ve got a working product.
Step 6: Possible Additions
To keep the lamp more stable a solid beam can be added in between the SMA wires. This should be done at the back of the book cover. This will ensure a triangular structure like on the picture.