Miniature Six-Axis Force/Torque Sensor Based on a Stewart Platform and FBG Sensing for Endoscopic Surgery

The lack of force sensing and force feedback remains unresolved in endoscopic surgery (ES). In order to restore the sense of force, DESIGN of a miniature six-axis force/torque sensor (FTS) is urgently needed. This sensor employs a Stewart platform with flexural joint as the flexible structure. A nondominated sorting genetic algorithm (NSGA-II) considering isotropy of generalized force and sensitivity is introduced to optimize the geometric parameters in order to best suit the given loads. Stress and strain distribution of the Stewart platform under given loads are discussed, and the rationality of design of the flexible structure is verified. The measurement system of this sensor is implemented by using an optical sensing interrogator and the fiber Bragg grating (FBG) method. A dedicated static calibration platform is designed to provide precise external loads for this sensor prototype, and the linear relationship between the external loads and wavelength changes of the sensing FBGs are recorded. The static calibration matrix is obtained using the least-squares method. Technical indicators, such as the measurement ranges and resolutions of this sensor, are evaluated. According to the static calibration, measurement ranges of
${F}_{x}$
,
${F}_{y}$
, and
${F}_{z}$
, and
${M}_{x}$
,
${M}_{y}$
, and
${M}_{z}$
are 10 N, 150
$\text{N}\cdot $
mm, and 100
$\text{N}\cdot $
mm, and resolutions are 0.15 N, 0.3 N, and 6
$\text{N}\cdot $
mm. The experimental results reflect that this sensor prototype has good compatibility with the surgical instrument, and it is feasible for force sensing and force feedback in ES.