This paper presents a fiber Bragg grating (FBG)-based six-dimensional (6-D) force/torque (F/T) sensor that can be mounted on robot joints for the detection of comprehensive force/torque information. The sensor is designed based on a new concept of multilayer measurement in which the elastic structure is divided into four layers. A single optical fiber inscribed with 12 FBGs is symmetrically attached to the elastic structure to sense force/torque-induced strains by means of differential measurements. Because of the mechanical decoupling function of the structure and the reasonable arrangement of the FBG sensing elements, the designed sensor possesses a great advantage of low cross coupling compared with existing 6-D force/torque sensors, which simplifies the calibration and maintenance of the sensor. Calibration experiments demonstrate high resolutions of 7.8 N mm, 7.2 N mm, 15.8 N mm, 0.0067 N, 0.0066 N and 0.0825 N within the range of ±1.56 Nm, ±1.56 Nm, ±1.56 Nm, ±10 N, ±10 N and ±25 N for the detection of Mx, My, Mz, Fx, Fy and Fz, respectively. Dynamic performances of the designed sensor have been evaluated in comparison with a commercial force/torque sensor.

This work presents a fiber Bragg grating (FBG) wide-range tilt sensor based on a cam structure. Two FBGs are fixed on a specially-designed sensor shell. When one FBG is stretched by the rotating cam driven by tilt, the other FBG moves along a standard semicircle with a constant radius, and compensates for temperature variations of the stretched FBG. By detecting the difference of the central wavelength shifts of two FBGs, variations of the tilt angle can be measured. The detailed mechanical structure design and measurement theory of the sensor is presented, and the sensor prototype is discussed. Testing results of comprehensive performance show that there is a good linear relationship between the tilt angle and the central wavelength of the FBG over three intervals from -90° to 90°. The repeatability and creep resistance of the FBG tilt sensor are good, the measuring accuracy is 1.516°, and the measuring resolution is 0.003°. The measurement range is much larger than comparable existing sensors, and it avoids cross-sensitivity between temperature and strain for FBG. The sensitivity of the sensor can be easily adjusted by changing the outline of the cam, or the length of the optical fiber between two fixed points.