Measurement Of The Spindle’s Stress Of Machine Tool Based On Fiber Bragg Grating Sensor

At present, machine tool which is the most fundamental production equipment must is developed along the direction of high speed and high precision, with the quick development of science and technology. Spindle is one of most important part in the machine tool, the performance of spindle has a great influence on the machine tool’s machining precision and stability. The spindle spinning at high speed often happens the phenomenon of fatigue damage, and the reliability of spindle depends on the stress imposed on it. Therefore, it is very important to design, condition monitoring and damage assessment for the spindle.Spinning at high speed is the most important and obvious characteristics for spindle. At the same time, the machine tool has a compact structure, a small space and very harsh environment, and so on. All the factors should be considered at the time of measuring the stress of spindle. At past, we measured the stress by the electric resistance type strain gauge, the traditional method is very complex when solving the issue like this, which is easily affected by the outside conditions, what’s more, it may not solve this problem. However, measuring the spindle’s stress with fiber Bragg grating sensor could work out the problems like this perfectly, it has high measuring precision, and it is also fit for all kind compact and harsh environment. But above all, it provides data and technical support for the condition monitoring and damage assessment of spindle in the future.The process of measuring spindle’s stress based on fiber Bragg grating sensor mainly includes the following sections. The optical signal from the broad-band source goes through the isolators and the couplers, and passes into the fiber optic rotary joint, which is made of optic fiber collimator. At last, it arrives at the fiber Bragg grating sensor, which is installed on the internal surface of the spindle, the optical signal contents with resonant condition will be reflected at this area. The central wavelength of reflected light signal would drift with the stress imposed on the spindle’s surface. And then, the reflected light signal contained with strain information goes through the fiber optic rotary joint again, then it gets to the unbalanced Mach-Zehnder interferometer demodulation, which translates the fiber Bragg grating wavelength signals in which the strain information is contained into the phase signals. After the three light signal goes through the modules of receiving the signal, they were translated into this signal which is fit for data-collections. Finally, the three signal were collected by the modules of high-speed data acquisition system, and the work of the fiber grating sensor system signal demodulation would be conducted on the Lab VIEW. At last, the value of measured strain can be obtained.Among them, in order to measure the spindle’s strain by fiber Bragg grating sensor, there are some difficult points. For example, how to transmit optical signal into the spinning spindle, the receiving optical signals, and the collection and demodulation of sensor signals. To overcome these problems, we designed a fiber optic rotary joint which meets certain precision. The issues of transmitting light signal have been solved satisfactorily. At the same time, we also designed circuit to receive optical signals and Lab VIEW programs to collect and demodulate sensor signals.The work we have done provides a new way to measure the spindle’s strain, the accuracy and precision of measurement has been risen greatly. They are very important to detect conditions for the spindle.