Cap Lamp Flash Signals for Communications

Cap Lamp Flash Signals for Two-Way Signalling, V2P Collision Warning System, Alerts and Hazard Area Warnings

The mining industry is transitioning into the digital age. Miners are the most critical assets of any mine. They are initially being integrated into mines’ digital systems via their Cap Lamp since it is the only electronic device to be carried by every miner at all times. Today’s Cap Lamps have transformed from simple illumination devices to IoT (Internet-of-Things) Cap Lamps with tracking and communication capabilities. However, by design, a Cap Lamp has limited user inputs. The only way for the control room to communicate to miners is via flashing lights, which we call “signals”. These flash signals could represent warnings, general alerts or confirmations and acknowledgements.

Currently, there are two systems of signalling Cap Lamps. The first is two-way signalling on a networked Cap Lamp. The control room can send emergency evacuation calls to miners via rapid fast flashes on Cap Lamps. The control room can also page miners by sending slow flashes. Miners can acknowledge that they have received these alerts by pressing the button on their lamps. The second system is the V2P Collision Warning System (CWS) Cap Lamps. When a vehicle enters the CWS zone of a miner, the Cap Lamp slow flashes. As the vehicle gets closer, the flashes become faster. However, signalling complications begin to arise when you combine both systems. How do you differentiate between a page and far CWS signal or an emergency evacuation call and a near CWS signal? So far, Cap Lamp manufacturers have struggled to incorporate both signalling systems into a single Cap Lamp. To make matters more complicated, a single Cap Lamp can have multiple communication technologies built in. For example, some of Roobuck’s IoT Cap Lamps have both Wi-Fi and LTE for networking and sending emergency alerts and pages. It also has uses DSRC (Dedicated Short-Range Communications) or UWB (Ultra-Wideband) as part of its CWS. Furthermore, it can use BLE (Bluetooth Low Energy), RFID (Radio Frequency ID) or Wi-Fi for access control area management and equipment identification. All these functions could be sending signals to miners at the same time. When binary flash signals become too complicated, miners might as well be learning morse code. This is when flashing signal management becomes critical.

Effective management must consider the following six signals:

Fast flash: High frequency, rapid flashes.
Burst flicker: High frequency, low duty cycle rapid blink burst followed by a short pause.
Slow flash
Flicker: A low duty cycle and low frequency light blink. We explain this in detail in our comprehensive study.
Oscillating brightness: Light intensity fluctuates between low and high brightness in a series of smooth transitions.
Oscillating frequency: Flashes fluctuate between low and high frequency in a series of smooth transitions.

Here is a series of guidelines to make flash signal systems simple, practical and effective:

Real-World Use: Flash signals should be as simple and as intuitive as possible, based on real-world everyday occurrences.
Flash frequency must remain below 10hz, as most seizures occur between 10-20hz. Above 20hz, flashes become too fast for the human eye to detect and are perceived as a constant stream of light.
Signals must be assigned in a way that misinterpretation of signals will not result in harm to the miner.
Urgent alerts that require quick response speed from miners should be assigned with fast signals that can be immediately recognised, so miners can react swiftly.
There should be a hierarchy of signals. More urgent signals should override less urgent signals.
For regulatory and safety reasons, LEDs can never be turned off during normal operations. As such, Cap
Lamp LEDs cannot flash between OFF and ON for signalling; they must flash between low- and high-brightness level.
Low contrast between low- and high-brightness flashes is difficult to see in well-lit areas. Conversely, high contrast flashes in dark areas can be blinding to miners. An appropriate balance must be struck between the two polarising lighting environments.

The following is a signal assignment example based on the above guidelines.

Message	Alert Level	Response Speed	Flash Signal
Collision Avoidance (Near)	Highest	Fastest	Continuous fast flashes
Collision Avoidance (Far)	Highest	Fastest	Continuous burst flickers
Emergency Alert (Evacuation)	High	Fast	Continuous oscillating brightness
Paging	Medium	Medium	Continuous low frequency flickers
Hazard Area Warning	Medium	Slow	3 slow flashes
Confirmations & Acknowledgements	Low	Not required	3 slow flashes

This signal assignment was developed through comprehensive research and in-depth experiments which indicated multiple challenging situations that needed to be accounted for in the design. For example, what happens when multiple Cap Lamps flash simultaneously, but out of sync? What signals are used in similar real-world situations? How do we make sure CWS signals override all other signals? How does environmental lighting affect signal visibility? What are the possible dangers when signals are misinterpreted?

Readers can view the full article on this topic via the link below.