【Original】Ensuring the electrical safety of powered exoskeletons

From improving mobility for people with spinal cord injuries to helping factory and construction workers lift heavy objects and enhancing soldiers’ capabilities on the battlefield, the benefits of combining robotics and kinesiology are becoming too great to ignore. However, like almost any wearable technology or powered device, exoskeleton structures present inherent risks that designers and engineers must address to ensure the health and safety of the user.

The inherent safety risks of many electronic products become more important when they are used in direct contact with the human body for a long time. For wearable devices, such as headphones or watches, there are concerns about problems such as overheating or electrostatic discharge. However, users can usually remove the device in a very short time (a few seconds), so there is almost no possibility of causing any serious harm.

This is not always the case with exoskeleton architectures, as they are often securely attached to or fully enclosed within a body part, such as an arm, leg, etc. In these cases when a malfunction causes overheating or a short circuit, for example, the user may not be able to quickly disengage from the system, increasing the chance of injury.

In addition, since many exoskeleton structures use high-torque servo motors to provide sufficient force for movement, sufficient power source is crucial. Lithium-ion batteries (Li-ion) are the choice of some miniaturized exoskeleton structures, which do not require a large driving force. However, in many cases (especially in industrial applications), the exoskeleton structure must be connected to an external outlet and fixed. This connection inevitably exposes the user to high current, which undoubtedly brings the risk of electric shock.

The temperature of electronic devices in contact with the skin should not exceed 37°C, which is the core temperature of the human body. Exceeding this temperature will cause discomfort to the user and may even cause burns in severe cases. Therefore, many exoskeleton structures must comply with medical electronic standards, including design requirements to prevent overheating, and hazards such as electrostatic discharge and radiation must also be avoided.

For many exoskeletons used in medical applications, the U.S. Food and Drug Administration (FDA) Code of Federal Regulations (CFR) 21 addresses risks and concerns regarding electrical shock, thermal burns, and biocompatibility. Page 890 of the CFR 21 document defines a powered exoskeleton as “a prescription device that is an externally powered orthotic device that can be used on a paralyzed or debilitated limb to achieve a medical purpose.” Specific testing and safety instructions are as follows:

For exoskeletons, they have their own power source, and batteries are a concern, which is one of the biggest safety risks for users. Thermal runaway is a concern for devices using rechargeable lithium-ion batteries, which occurs when the temperature rises and causes an exothermic reaction, which releases too much heat. This heat causes the rate of the exothermic reaction to increase, and the exothermic reaction releases more heat. Thermal runaway in exoskeletons is a very serious risk.

In recent years, wearable system manufacturers have taken various measures to address battery-related safety risks, such as some systems using large-capacity disposable batteries instead of rechargeable lithium-ion batteries. Other companies are exploring more advanced battery management solutions, such as monitoring the health of the battery and maximizing the battery life. A recent development is the use of smart textiles in low-power wearable devices, which can absorb sunlight to generate electricity internally, while also ensuring softness and flexibility for movement.

Terminal blocks are critical to the reliability and performance of wearable electronics, yet their low cost and simplicity often make them overlooked during development and implementation. This is especially true in the field of exoskeleton structural design, where a large number of expensive integrated circuits and servo motors are used, which is also a precedent.

When inspecting wearable electronic devices for malfunction, one of the most common causes found by inspectors is the loss of connection between two interfaces, which is often the result of a terminal block failure. Exoskeleton structures often use hundreds of connectors to connect components such as sensors, batteries, circuit boards, etc. Since these are all potential failure points, choosing the right connector is critical.

The market for powered exoskeletons in the medical and industrial fields has grown rapidly in recent years. Although the benefits of these and other wearable electronic products are becoming increasingly difficult to ignore, designers and manufacturers must be vigilant about the potential safety risks they may pose to users. Although many innovative measures are being used to solve problems related to electronic interfaces and human contact, the use of high-quality and high-reliability components (such as connectors and wired connections) has proven time and again to be the most effective way to ensure the overall success of the product in terms of performance and reliability.

Original link:

https://www.mouser.cn/blog/ensuring-the-electrical-safety-of-powered-exoskeletons