Ten times more sensitive than conventional technologies, these light-weight strain sensors can be incorporated into rehabilitation gloves to improve their sensitivity and performance. (Image courtesy of the researchers)

A research team from National University of Singapore (NUS) has taken a first step towards improving the safety and precision of industrial robotic arms by developing a new range of nanomaterial strain sensors that are 10 times more sensitive when measuring minute movements, compared to existing technology.

Fabricated using flexible, stretchable, and electrically conductive nanomaterials called MXenes, these novel strain sensors are ultra-thin, battery-free, and can transmit data wirelessly. With these desirable properties, the novel strain sensors can potentially be used for a wide range of applications.

Asst Professor Chen Po-Yen explained, “Performance of conventional strain sensors has always been limited by the nature of the sensing materials, so users have had limited options for customizing the sensors for specific applications. In this work, we have developed a facile strategy to control the surface textures of MXenes, which has enabled us to control the sensing performance of strain sensors for various soft exoskeletons. The sensor design principles developed in this work will significantly enhance the performance of electronic skins and soft robots.”

One area where the novel strain sensors could be put to good use is in precision manufacturing, where robotic arms are used to carry out intricate tasks, such as fabricating fragile products like microchips. The sensors can be coated on a robotic arm like an electronic skin to measure subtle movements as they are stretched. When placed along the joints of the arms, the strain sensors allow the system to understand precisely how much the robotic arms are moving and their current position relative to their resting state. Current off-the-shelf strain sensors do not have the required accuracy and sensitivity to carry out this function.

Conventional automated robotic arms used in precision manufacturing require external cameras aimed at them from different angles to help track their positioning and movement. These ultra-sensitive strain sensors will help improve the overall safety of robotic arms by providing automated feedback on precise movements with an error margin below one degree. That will remove the need for external cameras, as they can track positioning and movement without any visual input.

The technological breakthrough is the development of a production process that has enabled the researchers to create highly customizable ultra-sensitive sensors over a wide working window with high signal-to-noise ratios.

A sensor’s working window determines how much it can stretch while still maintaining its sensing qualities. Also, having a high signal-to-noise ratio means greater accuracy, which enables the sensor to differentiate between subtle vibrations and minute movements of the robotic arm.

This production process allows the team to customize their sensors to any working window between 0 and 900 percent, while maintaining high sensitivity and high signal-to-noise ratio. Standard sensors can typically achieve a range of only up to 100 percent. By combining multiple sensors with different working windows, the researchers can create a single ultra-sensitive sensor that would otherwise be impossible to achieve.

The research team developed a working prototype of the application of sensors for the soft exoskeletons in a soft robotic rehabilitation glove. The sensors impart the ability to sense a patient’s motor performance, particularly in terms of their range of motion. This will ultimately enable the soft robot to better understand the patient’s ability and provide the necessary assistance to their hand movements.

The team is currently working with the Singapore General Hospital to explore their application in soft exoskeleton robots for rehabilitation and in surgical robots for transoral robotic surgery. “As a surgeon, we rely on not just our sight, but also our sense of touch, to feel the area inside the body that we are operating on. Cancerous tissues, for instance, feel different from normal, healthy tissue. By adding ultra-thin wireless sensing modules to long robotic tools, we can reach and operate in areas where our hands can’t reach and potentially “feel” the tissue stiffness without the need for open surgery,” said Dr Lim Chwee Ming of Singapore General Hospital.