The FBG Sensing Medium Structure, Transmission Characteristics And Contact Force Measuring

FBG (fiber Bragg grating) is a kind of stress-strain sensor with high precision, which recently has been widely used in lots of buildings, dams, bridges, etc, together with simple machines for structural health monitoring. However, the utilization of FBG sensors is only in the simple stress-strain measuring stage, while the one in more complex mechanical systems remains nearly an empty field. So a research has been done on the principle, characteristics and the current application of the FBG sensor. And the main problem is the solution to the Dimension Matching Problem appears in the FBG sensing process and the Non-uniform Strain Problem appears the detecting area.To solve the Dimension Matching Problem that exists in most of the measuring processing between the FBG measuring characteristics and the deformation of objects to be measured a combination about the technologies of the FBG sensing and Compliant Mechanisms has been made, according to which a compliant mechanism that sensitive to the plane strain was made, and then some analysis on the characteristics of the system were done. After establishing the mathematical model, through the comparison and the calculation between the displacement input to the compliant mechanism and the detection output from the FBG sensor, the solution was proved to be a feasible one.To solve the problem on the contact force between two objects, a kind of sensing-medium has been brought in, then the FEM software was used to do some analysis on the sensing-medium structure and the sensing characteristic of it, and the problem on the non-uniform strain on the FBG caused by the same scale of the FBG sensor and the contact interface was discussed. The elastic half-space theory included in contact mechanics has been referred to establish a mathematical model between the normal contact force on the contact interface and the FBG wavelength shift.Finally, by solving the problem on the FBG frangibility, the security of the large number of the FBG sensors, the high noise in the signal and so on, the FBG sensing technology was managed to be used in the contact force measuring experiment on the gripper of the forging manipulating made in Qingdao Huadong Machine Factory. The accordant between the result of the experiment and the theoretical calculation shows that the model proposed previously on the non-uniform strain measuring and identifying is of great valid.