| This project is supported by the State Natural Sciences Fund (Project Number:60702004), and it aims to make a research into the method of liquid fine discrimination and liquid identification based on the liquid drop fingerprint (LDF). The liquid drop analyzer is the hardware foundation of obtaining LDF, so the accuracy, reliability and stability of the instrument has a great influence on the liquid fine discrimination and liquid identification based on LDF.Theoretically, liquid drop analysis should be carried out when the drop is under the condition of static equilibrium state. It actually means the growth rate of the drop must be very slow and stable, and almost achieves the quasi-equilibrium state. Since the drop growth rate is essentially controlled by the capillary flow of the feed liquid pump, all sorts of liquid drop analysis systems require a microflow-feeding device. To solve the problem mentioned above, this paper introduces a steady and controllable microflow-feeding device with reliable performance and high precision. The development of this system mainly includes the mechanical structure design and the hardware and software design of the control system.In terms of the mechanical design, the mechanical structure of the feeding system is designed based on the research of the development and technical characteristics of the domestic and abroad metering pump. In addition, the three-dimensional simulation of the transmission device is worked out to make sure that the agency is feasible. The transmission device of this system adopts the basic principle of the piston metering pump. A pair of reduction gears is driven by the stepping motor, and then the screw begins to move in vertical direction result from the interaction of the transmission shaft and the sliding key. The movement of the screw can changes the piston stroke, and directly caused the flowrate variation of the metering pump. Besides, the key parts of the transmission organ have been made a comprehensive checked to ensure the feasibility and reliability.In terms of the hardware design of the control circuit, AT89C52 single-chip microcomputer (SCM) is adopted as the main control chip, and it can realize to drive and control the microflow-feeding device through the function expansion and interface technology. Besides, the constant current cut-wave divided driving system is used to drive the stepping motor, and it remarkably enhance the control precision of the stepping motor. In addition, this SCM control system can communicate with a PC through the standard asynchronous communication protocol, and thus realize the auxiliary control of the pump flow as well as the processing and display of the relevant state information on a PC. In terms of the software development, the main program and the subprograms (such as the stepping motor control program and the interrupt program) are developed on the Keil C51 software platform. With the hardware supporting, it realize the real-time control of micro-flow feeding system. On this basis, this paper analyzes the sources and the influence of various interferences on the SCM system, and proposes the corresponding anti-interference technology from the hardware and software.The research proves that the device based on the Single-Chip Microcomputer (SCM) technology introduced in this paper can accurately control the flow rate and the flow velocity. It has important practical value. Therefore, this system is a kind of low cost and high flexible solution. It can be used in liquid process control, environment monitoring and other fields where micro-flow feeding device is needed.
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