A Novel Absolute Rotary Encoder Based on Soft Pneumatic Sensing Chambers

The aim of this study is to design and fabricate a novel rotary encoder called soft pneumatic rotary encoder (SPRE) using soft pneumatic sensing chambers (SPSCs). In an SPRE, the volumetric changes developed inside the chambers due to the rotation of an eccentric structure are read by the air pressure sensors and converted into rotary displacements. In this research, for the first time, a soft rotary encoder is developed. Implementing soft measurement methods will bring advantages that are not easily achievable in conventional sensors. The soft nature of SPRE and its electrical isolation from measurement objects have converted it into a proper alternative used in body-interacting mechanisms, such as rehabilitation tools. Besides, its nonmetallic structure paves the way for its utilization as an electromagnetic compatible sensor. With respect to its flexible design properties and availability of its components, this sensor can be designed and manufactured according to the considered need. Here, the SPSC-governing mechanical model was developed by experimental tests and Abaqus finite-element software. Then, the geometrical parameters were evaluated and optimized in Abaqus by exploiting this model, and an SPRE was built based on these conditions. To compensate for the effect of temperature and convert pressure data into angular output, a temperature compensation tube and trigonometric converter were used. The maximum absolute measurement error, resolution, and repeatability of this encoder were 3.34°, 0.062°, and 1.09°, respectively.