As discussed earlier in the report the system will utilize eight different sensors. We have already discussed the orientation of where each sensor will be placed on the shoe, as seen in figure 9. Now we have to decide where the sensors will be placed in relation to the other parts of the shoe. They could be placed on top of the insole, below the insole, embedded in the bottom of the shoe, or stuck to a sock in the shoe. We needed to put them in a place where they will carry the load of the foot and not be damaged in the process. Luckily the sensors that we decided to buy are flexible which allowed us to place the sensors freely. Embedding them in the bottom of the shoe did not make much sense, it would make the process a lot of work and because the sensors were flexible they did not need to remain perfectly flat. A similar option is to place a hard surface in the bottom of the shoe which the sensors could be placed in. This idea was used by the previous group to do this project. They placed a piece of wood in the bottom of the shoe and carved a path for the sensors to go in. This option did not make sense for us because our FSR's are virtually flat, where their load cells were about a quarter of an inch high. We are also making the shoe for athletics and one of the major criteria is to make the system comfortable so that the user doesn't even know that the sensors are there.
Below are pictured the three different size sensors.
Attaching the sensor to a sock would also be difficult. The sock expands when a person puts their foot in it, this means that the sensors will move when a person takes the sock off or puts it on. It would be hard to place the sensors in an accurate spot, the user would also have to make sure that he puts the sock on the exact same way every time he uses it. If the sensors are in a slightly different position every time the sock is put on it could cause the sensors to give inconsistent readings. For these reasons the sock idea was also scratched.
The two best ideas seemed to be attaching the sensors to either the bottom or the top of the insole. We had already been told by the manufactures that we could attach the sensors to a surface using scotch brand adhesive, which would make it easy to attach them to a flexible surface such as the insole. The advantage to placing them on top of the insole is that they would be in direct contact with the foot. It would also be easy to line the sensors up with the crucial load areas of the foot because you could see them on top of the insole. The wiring would also be easier because we can see where the wires are going along the insole and where the best place would be to run the wires out of the shoe. The disadvantage of placing the sensors on the top is that they are not sitting on a hard surface. When the sensors are stepped on the insole will compress and absorb some of the weight before the reading is taken. Sense the sensors are flexible they will also slightly bend inwards when they are stepped on because of the soft surface underneath them. The user will also be able to feel the wires underneath their foot if the sensors are place in the top of the shoe, this could cause discomfort for the user.
The final option was to attach the sensors to the bottom of the insole. The advantages and disadvantages of this are the opposite of placing the sensors on the top of the insole. The advantage is that the sensors are sitting on the bottom of the shoe which is a hard surface. This will make sure that the sensors remain flat when they are stepped on. The user will not be able to feel the wires if they are underneath the insole because of the padding provided by the insole. The disadvantages are that the sensors cannot be seen once the insole is in the shoe so we have to guess where the maximum load sections of the foot will land on the insole. Since we can't see the sensors while the foot is in the shoe the group cannot be certain that the sensors are in exactly the best spots. The other disadvantage is that the wires and connections cannot be seen once the insole is in the shoe so if a wire is on top of one of the other sensors, getting bent the wrong way, or gets un-attached from a sensor we cannot see it. It is also hard to see where the best place for the wires to exit the shoe will be if the wires are hidden underneath the insole. In this scenario the insole will absorb some of the load before the sensor is actuated by the foot. This will cause the loads to be more distributed then they actually would be and could cause the results to be inaccurate.
After analyzing the advantages and disadvantages of all of the attachment strategies the group decided to place the sensors on the bottom of the insole. The most important factor was that the sensors remain flat while being loaded; the hard bottom of the shoe will provide us with the support needed. The other major impact was the load distribution taken by the insole. The group felt that the load will be less distorted underneath the insole then if the sensors were on top and physically sand into the insole before reading the load. The best possibility would be to eliminate the insole all together and avoid this problem, but this would eliminate the comfort for the user and would make the product unmarketable.
The picture above was taken to show the actual sensor layout.
This is a picture of a foot with each bones marked from 1-17. The highest pressure areas correspond to the areas where we placed sensors on the insole.