Towards Shape Estimation of Meso-Scale Continuum Robots Using Direct Laser Written Piezoresistive Strain Sensors

Minimally invasive surgery is a promising application for continuum robots. The flexibility of continuum robotic surgical tools has the potential to minimize patient trauma. However, the flexibility makes shape estimation for continuum robots challenging. Several methods for shape estimation of continuum robots have been proposed, including imaging, optical sensing, magnetic sensing, and resistive sensing. The resistive sensing method involves incorporating a piezoresistive material into the robot which changes its resistance in response to strain. From the strain in the sensor, the shape of the robot can be estimated. In this paper, we utilize the direct laser writing (DLW) method to create piezoresistive carbonized traces on a polyimide (PI) substrate. DLW has been used in the past to create low-cost, flexible strain sensors in a single-step process, using the same machinery that is often used to fabricate continuum robots for surgical applications. We integrated DLW strain sensors onto three separate meso-scale continuum robotic joints. The sensors detected the strain on the robot with gauge factors ranging from 0.437 to 2.78. In another experiment, the resistances in the strain sensors were used to estimate the deflection angles of the joints, achieving 2.77° to 5.21° RMSE.