Yesterday, I got an email from element14 which inform that my proposed project is accepted for Safe & Sound design challenge. The aim is "designing a wearable that protects a person from personal and environmental risks, or monitors personal health or protects personal property from theft" and the only requirement is using Texas Instruments’ latest microcontroller.
My project is building a safe working place for the miners. I decided to build this project because, in the 21st century, we still get news miners are missing and the result is usually catastrophic (Gas explosion kills 33 Chinese miners-2016, 9 miners dead and 23 missing after an explosion in Ukrainian coal mine).
The main reason for the coal mine explosions is the methane gas explosions. The gas concentration, temperature, and pressure effect the explosion(Why Do Coal Mines Explode?). In order to prevent explosions, these parameters should be observed carefully. Firstly, the design will measure these parameters.
Even all the measures are taken, the explosion may occur and some miners can be stuck inside the mining area and it may take long times to reach them. In Chilean mine explosion, it took 17 days to find the sign of the miners were alive with the help of dozens of holes drilled by rescue teams (Chilean miners: Where are they now?). The time run against miners' lives. Therefore, if we know where they are exactly, we can reach them faster and increase the possibility of the saving lives. Secondly, the design will track the workers.
Another important feature is preventing human ignorance like not wearing the required safety-uniform, helmet, or mask. By nature, some people don't follow the rules. There should be always a control mechanism to push them to follow rules. It is possible to add RFID or similar technology to inside the helmet so that workers must wear the safety equipment to pass the gates. Thirdly, the design will prevent the unsafe access.
In order to solve these problems, I will design a trackable safety-helmet. This can be also implemented on a safety suit where it is required. Let's see the required tasks to create this design.
1 - As I mentioned above, the main problem is high methane gas concentration. If the air includes 5% to 15% methane it can explode. Because of this, methane concentration must be observed. This should be placed in many areas of the mining area but if we implement the sensor on the helmet, we can see how the concentration change around the workers. How concentration change in a time and place will give important information about the estimating explosions. Methane gas sensors, like Methane CNG Gas Sensor - MQ-4, usually have analogue output and MSP432P401R has 14-bit 1MSPS differential SAR ADC. The first task is connecting an analogue gas sensor to MSP432P401R and process it.
2 - Methane concentration is the obvious indicator of the explosion. However, there are other important parameters like pressure and temperature so they should be measured. BOOSTXL-SENSORS booster pack has an environmental sensor which can measure ambient temperature, pressure, and humidity. This information can be analysed and gas concentration limitation can be changed dynamically.
3 - In order to achieve a reliable system, it is required to have a communication link. The main reason is the collected data can be analysed by the central point and if something is wrong warning signal can be activated. It also brings other benefits like if something happens to the worker, he can send an emergency message. The kit includes Bluetooth and Wi-Fi network processors. Bluetooth is not suitable hence it is not supporting meshing (Bluetooth 5 bring this support) and distance is short. Wi-Fi is the better option because it has mesh support and longer range. However, it is still not enough distance, if we imagine the mine area and any explosion can disrupt communication if a link is destroyed. Long-range communication link will be feasible for this application like narrow band communication. The required data rate is not high so Lo-Ra, SigFox, or sub 1GHz long range RF can be preferred. Hence, the mine are under the ground and there may be lots of distractions during the path, this is the hardest part of the project. I will implement the project by Wi-Fi but it should be changed considering the outline of the mine. Implementation will be similar only the RF part and protocol is changing.
4 - Another problem is after an explosion it takes long times to reach the miners sometimes it takes months. If we can build a tracking system it will help us to reach them swiftly. Actually, the previous task also cover this topic. If we implement a reliable mesh network, we can use both time of flight (ToF) and received signal strength indicator(RSSI) to track the miners. However, inside the mine, both of these may not give the accurate results. This should be supported by the dead-reckoning. Dead-reckoning can be implemented by using inertia measurement unit (IMU) which includes accelerometer and gyroscope. BOOSTXL-SENSORS booster pack also includes IMU sensor. Dead-reckoning can be synchronised at the mesh points so accuracy can be increased.
5 - Hence, we have IMU sensor for tracking, we can add additional functionality. We can detect the falling of the workers and help them immediately. This looks unnecessary because of the emergency message but if the miner loses the conscious, the automated fall detection can help to find worker immediately.
6 - Some people are ignorant and unless you do not push them to wear safety uniform, they don't wear it. In order to be sure helmet is worn, workers should be controlled at the mine access area and helmetless entry shouldn't be allowed. To achieve this RFID-enabled ticket can be placed inside the helmet and gates are opened by the helmet. Bluetooth can also be preferred if the power consumption problem is solved for wearable. With the implementation of the Bluetooth, the helmet can act as a Bluetooth smart key fob and access is denied without the helmet.
The hardest part of the project is designing a reliable communication network. It is one of the key parts of the project. If a reliable network connection is provided, it will be so easy to implement emergency messaging and make the tracking easier. There are lots of computationally intensive task for the processor to do, I am not sure one processor can handle all of these so multiple processors may be required but this will increase price and size. It is also possible to send the data to the centre and make calculation there and the send back to the result like the idea in the IoT systems. Dead-reckoning can be also challenging if the proper synchronisation and filtering are not done. Processing data (correlation between different variables) will require a comprehensive research for implementing this system into real mine. I may implement an estimated or dummy correlation hence the real data correlation includes different disciplines and measurements inside the real mine.
The idea of designing Trackable Safety Helmet for Miners is simple but it requires many challenging tasks. The tasks focused on the safety but additional functionality can be added at a time. If you have any suggestion, I look forward to hearing from you.
The key benefits of the project can be summarised as
- Foreseen the possible explosion and warn the workers
- Provide personal safety while not allowing access to work area without helmet
- Detecting fall and warning the others to help
- Tracking worker and in case of the explosion reach them faster
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