A piezoresistive flexible sensor to detect soft actuator deformation

Abstract

A textile-based strain sensor for measuring the length of a McKibben pneumatic actuator has been developed. McKibben actuators are flexible, lightweight, and widely used in all those applications where compliance and safety are required, e.g. soft robotics and power assisting device. The actuator length needs to be measured to control the device accurately. However, properties such as flexibility and lightness might be lost if rigid sensors such as potentiometers or linear encoders are directly attached to the actuators. For this reason, flexible and stretchable sensors are necessary. In this study, a flexible sensor using conductive textile is proposed to actively measure the length of manufactured McKibben actuators. Firstly, the electro-mechanical characteristics of the proposed sensor were obtained and a model to compensate its nonlinearities was evaluated. Secondly, an estimation of the accuracy was performed during dynamic actuator contractions. The results showed that, using this sensor, a direct measurement of the actuator axial displacement can be obtained within 20% error, without affecting its performances in terms of contraction.

A Self-sensing Inverse Pneumatic Artificial Muscle

“…This error is not negligible for applications that need high precision, but still, the proposed solution is very advantageous for monitoring actuator functioning through self-sensing properties, without the need of additional sensing elements. The precision that we obtain in the prediction of the actuator strain is in line with previous works on sensorized positive pneumatic actuators [16], [20]. Relatively to the inverse pneumatic actuators, the sensing presented in [23] and [24] is more accurate, but it is based on the inductance variation principle of a rigid constituting element of the actuator.…”

“…This material can be encapsulated into soft channels disposed longitudinally, circumferentially [14] or helically [15] around the actuator body. Other sensorization strategies based on piezoresistive [16], dielectric [17], [18] and optical [19] principles were investigated, but still relying on the attachment of the sensor to the soft actuator, thus with limited integration features. The goal of creating a selfsensing McKibben actuator was pursued by replacing some of the fibers constituting the braided mesh with electrically conductive insulated wires [20], [21].…”