Hello everyone! Welcome to my (late) introduction blog. I'm very excited to be a part of this challenge and wish good luck to all participants!
Why safety glasses?
According to Prevent Blindness America, more than 700,000 Americans injure their eyes at the work place, making eye-related injuries one of the most common. In 70 percent of the accidents, the eye injury was caused by an object or equipment. What is perhaps more alarming, is that according to the Occupational Health and safety administration (OSHA), 90 percent of the cases can be prevented by wearing protective eyewear.
Despite those discouraging statistics, and despite the safety rules that probably exist in the work place, many workers still prefer to not use eye protection (perhaps due to discomfort, decrease in visibility, etc.) and employers are having trouble imposing those rules.
Smart Safety Glasses to the rescue
The idea is relatively straight forward: Sensor equipped safety glasses that can detect whether they are being worn by a worker/operator. The glasses are wirelessly linked to a power tool or some other equipment that require the use of safety glasses. Unless the power tool receives a signal, indicating the operator is indeed wearing the safety glasses, it will not switch on, thus forcing the worker to put the eye protection glasses on.
The project will consist of two units: the safety glasses unit and the power tool unit.
The safety glasses will be equipped with the MSP processor , Bluetooth transceiver, and a combination of sensors. The sensor’s function is to identify that a worker is indeed wearing the safety glasses.
Meanwhile, the power tool to be operated is not working since the mains switch is open and the tool is not receiving any power. Only when the above mentioned signal from the glasses is received, does the switch closes and allows normal use.
Safety Glasses unit
The main challenge will probably be to implement a reliable human-skin detection which will be hard to fool, but no too cumbersome.
Currently I see three possible ways to go about it:
1. Resistive touch sensor
The principal here is very simple: use the skin as a conductor to complete a circuit and switch on a transistor. Two conductive patches (fabric or tape) can be placed in spots where the glasses make contact with the skin and function as a simple switch contacts.
In some cases the skin surface resistance can be quite high (in the order of a few MegaOhms), so a mosfet transistor, which has a very low gate current (fast switching times aren't really a concern), will be appropriate in this case.
A disadvantage of this approach is that it's easily fooled: simply short the two patches using a piece of wire and some tape and off you go. Of course more sophisticated methods can be used to actually measure the skin resistance, but the added complexity and the high variability of skin resistance as a function of the person and environmental conditions makes this approach less attractive.
2. Capacitive touch sensor
Capacitive touch sensors can sense a change in capacitance caused by the contact or proximity of a human (or other conductive objects). Obviously the safety glasses will make skin contact and thus there should be an effect on the measured capacitance.
Fortunately, the kit comes with the 430Boost-Sense1 capacitive touch sensor and the MSP432 is equipped with an oscillator-based capacitive measurement (which I will definitely investigate in future blogs), so initial testing should go smoothly.
However, the form factor of the 430Boost-Sense1 may not be suitable for the finished product, which will require us to use a customized sensing pad. This will probably require extensive trial and error in order to match the target capacitance of the 430Boost-Sense1 (again, future blogs will definitely cover this topic).
The bit potential benefit of this approach, I believe, is that with the right algorithm behind the hardware, it can be made quite robust to any "fooling" attempts.
3. Stretchable conductive fabric
A neat feature of this fabric is that its resistivity depends on how much it is being stretched. By attaching this fabric to the head support band of the safety glasses it is possible to detect when the glasses are being used (i.e. band is stretched over the head).
Again, this approach can also be fooled quite easily, but as a supplement to the capacitive touch sensor it can prove to be useful.
As you can see, each of the above approaches has its own pros and cons. I'll probably start working on the capacitive touch method first, but perhaps some kind of combination of the above methods is the way to go.
Power tool unit
This unit's implementation should be relatively straight forward. It will be based around an Arduino UNO and a HC-05 bluetooth model.
Once the appropriate word is received through the BT module, the arduino will switch on a relay that will enable the mains voltage to reach the power tool.
The aim of this project is to help reduce the amount of eye injuries in the work place by implementing Smart Safety Glasses. The Smart Slasses will not allow the worker to turn on his equipment unless they are being worn.
Obviously, the biggest challenge of the project will be to reliably detect when an operator is wearing the safety glasses. The second one will probably be the sensors and electronics mounting, such that the glasses could be comfortably used.
Hopefully , the other parts of the project should go relatively smoothly.
While the kit is arriving, its a good time to start researching various capacitance measurement methods and determine the most suitable one.