Issue 35

B. Lian et alii, Frattura ed Integrità Strutturale, 35 (2016) 389-395; DOI: 10.3221/IGF-ESIS.35.44 391 Control and Configuration Equipment of the Introduced System Outline of the system dedicated to the control of the LED stroboscope’s flash timing is schematically depicted in Fig. 3. This system is composed of (1) the motor and the spindle that is controlling the rotation of the fatigue specimen, (2) the timing gear at opposite side of the specimen is also rotated in the same way, (3) the magnetic sensor placed in the vicinity of the gear, (4) the servo-motor, which is introduced here to set the position of the magnetic sensor at any angular position around the gear, (5) the control system that gives the flash directive signal (pulse frequency) to the LED stroboscope, (6) the high-definition digital video camera, which records at a predetermined interval of time, (7) the long working distance microscope, and (8) the personal computer to record and analyze the data obtained. Figure 3 : Schematic of system components. Figure 4 : Relationship between magnetic sensor position and output voltage signal. Depending on the relative position of the timing gear’s tooth, the magnetic field of the magnetic sensor will change. Thus, it is possible to determine the position of the gear according to the output voltage signal from the sensor, as one can see in Fig. 4. Indeed, the magneto resistance elements inside the sensor will induce a different resistance value depending on the magnetic field. Since the resistance value change conducts to a variation of the voltage, the output voltage from the magnetic sensor will show a sinusoidal shape function against time. After treatment by the control system, one can obtain the pulse signal (or the digital signal), which is given to the LED stroboscope to flash at the appropriate timing. In addition, it is possible to adjust the flash period by changing the threshold value when converting the pulse signal. Therefore, one can adjust with an error as slight as possible the microscope observation field flashed by LED stroboscope, in accordance with the rotation speed of the rotating bending fatigue machine. Timing of the LED flashing is determined by the position of the tooth of the gear and the magnetic sensor around the gear at an angle controlled by a servo motor, as shown in Fig. 5. The LED stroboscope flashes in a short time lapse at the time of the sensor detects that the tooth A is approaching. In the Fig. 5(a), since the sensor angular position is 1, when the