Using Miniature Wearable Sensors to Monitor the Physical Condition of Construction WorkersAn IoT solution to improve safety at construction sites encountered a unique problem

Background

In Japan, construction workers are more likely to be involved in a workplace accident than workers in other sectors. This is attributable to a decline in the number of young construction workers, and an increase in the number of older and unskilled workers. This means that it is very important to create a good work environment and exercise good management. However, supervisors cannot be everywhere, so there is a great interest in the use of IoT (Internet of Things) technology to monitor the workers’ physical condition and working environment, and use that information to foresee and predict dangers. Monitoring is performed while the employee is on the job, thus wearable monitor device is required not to burden the worker in any means, do not impair productivity, will not cause discomfort, and should be easy to use. The client, a manufacturer of industrial wearable devices, was developing wearable sensors to meet this need.

Problems

The Problem with Button Type Batteries

The development division faced a tricky problem. In order to make their wearable sensor unit smaller and lighter, they powered it with non-rechargeable (primary) button type batteries, but found that in some environments, these batteries would become depleted in no time at all. A dead battery meant no data and therefore no monitoring. At the same time, the client found that if they used a larger battery to avoid the risk of battery failure, the weight would be a burden on the worker, and disrupt his or her work. There were other issues too: these cells needed to be replaced and disposed of as necessary.

Energy Harvesting Reveals Other Issues

After some consideration, it was suggested that the problem could be solved by using combination of energy harvesting (using dye sensitized solar cells) and rechargeable batteries. The team set about building a prototype. However, they realized that because energy harvesting is only able to supply minuscule power of a few microwatts, they would require a rechargeable battery that could output the large power needed for the sensors and wirelessly transmit the collected data. As the client had now reached the limits of knowledge for rechargeable battery, the development process came to a halt.

Main Issues

Non-rechargeable (primary) batteries would become depleted quickly in some environments.
While there was little risk of high-capacity rechargeable batteries going flat, their weight would be a burden on workers, and interfere with the task.
Conventional non-rechargeable (primary) batteries needed to be replaced, and disposed of eventually.
Energy harvesting on its own would be unable to provide power for sensor or wirelessly transmit the information collected, since it can only generate minuscule power in the order of a few microwatts.

The Solution Enabled by EnerCera battery