Manual de funciones

Make sure the moulds are clean and silicone residue from previous castings is removed. Continue by tying the electrode to the centre piece of the mould with the yarn. It is important that this is done tightly because if not the edges of the electrode might reach through the silicone which results in tears. Cut of the remaining yarn close to the nod and push the centring pin so that it sticks out at the opposite site of the cable. Put aside until it needs to be put into the silicone.

Now put the exterior part of the casting area on top of the base plate to prepare it for the casting. Combine the silicone components with the help of the spatula in the mixing containment according to the instructions provided by the silicone and mix them well. About 4g of silicone have been enough for casting one ring. Try to avoid adding to many big air bubbles into the silicone when mixing and pop them if possible with a pointy object, like a needle or the thin end of the spatula used here.

Pour the silicone mixture into the prepared casting area, it should be about half full. Take the centre piece and align it so that the wire is in the location where the silicone is a bit thicker. This provides additional support to the ring. Try to pop any bigger air bubbles again after it is poured in the mould.

Figure 6.4

Now push the centre piece into the silicone filled moulding area. The centring pin should allow you to keep it in the middle, if it has some play to it make sure to approximately centred by pushing it slightly.

Now it is time to cure the silicone. This can be sped up by using a a hot air gun. Make sure to move it plenty in the beginning to prevent the silicone from being blown out of ring itself. When the top stops to move, the movement of the hot air gun can also be reduced. The overall time for the supported curing is about 25min. Be careful not to take it out too early, the top might be set already but also the middle part of the silicone needs to be done to do so. A good indicator are the small air bubbles in the middle of the silicone; If they are not moving any more when pressure is applied to the top of the mould, give it a few more minutes to make sure it is set completely.

Now take the sensor out of the mould. Remove the base plate first, then push the centre piece out which will take the ring with it. Now carefully push the centre piece out, use knife to score overflown silicone to ease the process if necessary. Then you can clean the ring up with the knife by cutting back all unwanted silicone parts. One last essential step is the removal of the yarn used to attach the electrode to the centre piece. Use the knife to carefully cut into the silicone, where you see the yarn, and then pull it out. Then it can be cut off. Make sure all the yarn is removed where only the silicone is left since it prohibits it from stretching. After that the electrode is done.

Chapter 7

Evaluation

In this chapter, the outcome of this project is evaluated. The results are divided into two main parts: the manuals for the sensor production as well as the resulting sensors from them. Both are tested with the list of requirements provided in section 4.4. First, the functional requirements for the resulting sensors are tested. These can be evaluated by looking at the sensor’s output in special tests. To evaluate the non-functional requirements, three user tests have been done, two of which focused on sensor production and one on the sensor’s application. All of the test participants have been interviewed afterwards with questions aimed evaluating the non-functional requirements. Transcriptions of the interviews can be found in appendix C while a discussion of the results for each non-functional requirement can be found in this chapter in section 7.2. To show that the sensors can be applied in the context of wearable technology, three application prototypes were done. These can ba found in section 7.3. Lastly, a summarizing conclusion about how well the developments fit the requirements is done.

7.1

Testing of functional requirements

In order to test the functional requirements, tests have been performed with the sensors. The electrode ring is not strictly a sensor, it picks up either the skin resistance or the heart beat from the body. Therefore, it was only evaluated in respect to its interference. Both the stretch and the pressure sensor have additionally been tested for the linearity of their transfer function as well as the repeatability of measurements.