A Hardware Design For Electro-hydraulic Servo Testing Machines' Measuring And Control Technology

In this article some information about fatigue testing machines and the principle about electro-hydraulic testing machines were described firstly. Fatigue testing on emphasis components is very important procedure for the fatigue designing. In the fatigue testing on emphasis components, many components were used up. It is very discommodious to facture different sample for dissimilar designs. So standard samples were made to do fatigue testing mostly, which has simple structure and was made cheaply. Electro-hydraulic testing machines are universal equipment for fatigue testing. The principle about electro-hydraulic were described that high hydraulic oil passed the pipes from hydraulic pump station which provided the invariable pressure source, was controlled into the servo actuators by electro-hydraulic servo valve which had electro-hydraulic servo exciter and vibrator on its coil already. The electro-hydraulic servo exciter from the control circuit drove the electro-hydraulic servo valve. In the control circuit, the difference between the import and the feedback from control setting can adjust to be the electro-hydraulic servo exciter. At the same time all the sensors was measured.Afterwards a hardware design for electro-hydraulic testing machines' measuring and control technology was described in the article. Measuring all the sensors and controlling the servo actuators were realized, based on PCI bus by use of FPGA and MCU. FPGA execute measuring all the sensors, and MCU execute controlling the servo actuators. Both parts can do their own work unattached. So the time of computer would use a little, it can make room for further analysis and displaying. The electro-hydraulic testing machines' measuring and control unit is in a printed circuit board, which was installed in one PCI slot. So it is easily to update, and it is possible to realize multi-channel controlling. In addition the part for controlling the servo actuators by MCU can unlade from the board. Then the left part can work as a signal acquisition card.The part of sensors amplifier, or the output part of controlling, or each the other part of output or input had his own special signal modulation in a plug, connected to the board by an electric cable. They can distinguish from each other by communicating with FPGA, or control and setup by it. In the special signal modulation there was another MCU, and it can communicate with FPGA by IIC bus, at the same time it can control D/A , DPC, and MUX. So the measuring and control unit can have more sensors, and the unit and each special signal modulation can adjust, or test. If it is needful to replace the sensors, or to add the sensors, the alter happened on the board, or on the special signal modulation, would be little.All kinds of ports, signal acquisition, and the setting of the special signal modulation were all realized in FPGA by programming. We can also obtain the function of FIFO by programming in FPGA. It can reduce the times what computer visiting the port on signal acquisition cost. Then it can economize the time for computer to analysis and displaying. By programming FPGA can realize the port between FLASH and FPGA. So all kinds of waveforms can load to the FLASH. Then the electro-hydraulic testing machine can obtain more waveforms, and the users can more kinds of tests.Waveform generator, PID control algorithms, control output, and feedback signal acquisition were realized by MCU. Waveform generator realized waveforms and controlled their frequency by DDS. The precision of the frequency decided by the clock source and the digits of the summator. The summator has more digits, and then the frequency of the waveform is more exact. The precision of the clock source can adjust by taking count of it for long time. The changing speed of the frequency is decided by the time of the summator and DAC. The mean ,the amplitude, and the initial angle of the waveform can control by MCU. MCU can process PID control algorithms, and then make output control the electro-hydraulic servo valve. By this servo actuators can be moved. All the processes were digital, and analog accessories are easy infection by temperature and long-time, so the digital was more stabile.