Development Of A Device For Medical Dilution

Objective: Dilutors have been widely applied in fine chemical engineering andbiomedical laboratories. In general, medicine liquid is prepared artificially in thelaboratory. Due to individual differences, artificial liquid medicine preparation haslarge errors and instabilities, as the liquid medicine preparation is unrecoverable, sothe wrong ratio of liquid medicine preparation will result in liquid waste. Comparedwith the artificial liquid medicine preparation, the dilutor has unmatched advantages.By using mechanical device to drive the syringe, the dilutor can transfer fluidprecisely, smoothly and pulse-freely; the use of mechanical device can also provide awide range of operating speed, accurate flow rate, and high control precision. Forlarge amount of toxic or corrosive liquid existing in laboratories, the use of dilutorcan lower the potential hazards of such liquid to operating persons. Based on these,the dilutor is especially suitable for the fine chemical, medical liquid preparation, aswell as the area of industry, and agriculture and biomedical and other applicationswhich require precise liquid preparation. At present, biomedical Laboratories in Chinamainly use imported medical dilutors with high automation, easy use, but high costand difficult to spread. The number of domestic dilutor manufacturers is small, mostof these manufacturers only purchase accessories from foreign countries and dosimply secondary processing, with no independent intellectual property rights. As aresult, the accuracy of their product can hardly equal to the imported ones. The needof precise instrument for medicine liquid preparation in China is large, so it isnecessary to develop a medical dilutor with high precision and, high adaptability.Methods: After analyzing the technical characteristics of the dilutors in the world, weput forward a development plan of the medical dilutor considering with thedevelopment of the dilutor in China: to develop a kind of dilutor with embeddedmicrocontroller technology, sensor technology and intelligent control theory. The dilutor’s mechanical structures, such as assemble parts, transmission structure of themodule, and assemble methods were designed by3D modeling software. Using theschematic design software, the circuit of the dilutor was designed, and finally thecircuit design of the dilutor hardware modules was completed. The printed circuitboard of the dilutor was designed by printed circuit board design software. Thedilutor functions, such as liquid transfer, dilution, liquid preparation and otherautomated processes, were designed by microcontroller programming language. Thecontrol module features were made by intelligent software system. Thecommunication interface sent initialization, reset and operation command to thedilutor through RS232serial data transceiver interface. After receiving the computerinstructions, the programmable microcontroller controlled the chip of steppingmotor then driven it, achieving the initialization, reset and corresponding operatingfunctions. The stepping motor could push the dispensing valve directly orpush-and-pull the syringe through the synchronous screw structure, finallycompleting the precise liquid quantitative distribution. The position of reversingvalve spool and syringe piston were monitored by photoelectric sensor, finallycompleting the initialization, reset, and reversing operation of reversing valve as wellas the pull-and-push operation of syringe.Contents: The works in this paper consist with the mechanical structural design,hardware design, software design and prototype testing of the medical dilutor. Themain contents are as follows:(1) The mechanical structural design of the dilutorincludes prototype exterior design, modeling, processing, prototype mechanicaldesign, prototype mechanical structure processing, printed circuit board processing,and the prototype of the overall installation. Its3D shape was modeled with CATIA.(2) The hardware design of the dilutor includes programmable micro control unitmodule, stepping motor driver module, the photoelectric sensor positioning module,the RS232serial data transceiver module, power module and the external interfacecircuit. Its schematic was drafted with ORCAD and the printed circuit board wasdrafted with PADS.(3) The software design of the dilutor is complied with embedded systems development tools IAR, it programmed the micro control unit, finallyachieving the Initialization, reset, dilution, liquid separation and distributionfunctions.(4) The test of dilutor prototype mainly tests the performance, stability,accuracy, practicality and other performance indexes of the prototype by a largenumber of experiments.Results: Designed and completed the dilutor prototype, with a separate set of keycomponents of the overall, hardware, software, and mechanical structure design.The main contents are as follows:(1) Designed and completed the overall operationframework of the dilutor prototype, established unified and coordinated contactrelationships between the mechanical structure, hardware and software, drawn andcompleted the overall design diagram of the prototype.(2) Designed and completedthe mechanical structure of the prototype dilutor, drawn and completed the3Dmodel diagram of the prototype. Designed and successfully conducted the locationdetermination method of valve and syringe by using photoelectric sensors andpositioning grid plate, combined with the stepping motor shaft custom processing.The transition between the rotation of the stepping motor and the linear motion ofthe syringe piston was achieved by screw synchronization structure, finally achievedthe pull-and-push operation of the syringe.(3) Programmed and debugged thesoftware system of the dilutor, successfully determined the positions of thedistribution valve and syringe position, complete dilution the initialization, reset,dilution, liquid separation and distribution functions of the dilutor.(4) Assembled theprototype body, printed circuit board, stepping motor, syringe, valve and screwsynchronous drive devices to complete the prototype dilutor, debugged themechanical structure, hardware, software, testing the performance of each module,and modified the design of each module.(5) Combined the actual conditions testedthe prototype dilutor, the experimental results shows: the prototype has preferablestability and reliability, applies to the three distribution valve, dilute and distributetime frame for1min-60min, the accuracy is <1%.Conclusion：On account of the prototype testing, the dilutor achieved a precision liquid dilution with features of automation, high accuracy and convenience, itsoverall design is compact, easy to use, reliable performance, so it can provides apractical and advanced technical means for biological experiments and clinical liquidmedicine preparation. However, the dilutor of this paper is only designed forlaboratory use, under the actual conditions of use, taking into account the impact ofdifferent working environment, in order to further improve the adaptability andstability of the dilutor, on the basis of the research work of this paper, In order toenable the machine to meet the application under different conditions, the circuitand the mechanical structure design can be further optimized, Moreover, in order tomake the dilution able to adapt a variety of valve, the software algorithms also canbe further improved. Therefore, these areas are the subsequent focus of this paper.