The Study Of Key Technology Of Ventilator

Sleep Apnea Syndrome (Sleep Apnea Syndrome, SAS) is a chronic disease that seriously affects people’s health. Sleep apnea syndrome in clinic are divided into Obstructive (Obstructive SAS, OSAS), Central (Central SAS, CSAS) and Mixed (Mixed SAS, MS AS) three types, and OSAS is most common.Obstructive sleep apnea syndrome clinical characteristics were repeated apnea and snoring, sleep at night awakening, and daytime sleepiness, accompanied by memory decline, with serious mental and psychological behavior anomaly. Serious apnea can cause hypoxemia, possible coronary heart disease, high blood pressure, stroke, and type 2 diabetes complications, or even lead to sudden death at night. Obstructive sleep apnea syndrome is one of the important cause of heart, cerebrovascular diseases.Direct pathogenesis of OSAS is respiratory tract obstruction and narrow, but it’s not just a simple airway stenosis and occlusion. Actual is caused by upper respiratory failure, accompanied by respiratory central nervous dysregulation. There are many e reasons caused upper respiratory tract obstruction and narrow, including the temporomandbulbar joint stiffness, above Ⅱ° tonsil hypertrophy, mandibular arch, and nasal septum after bending, the chin deformity, the soft palate is too long, a few cases of hyoid backwards, giant tongue, on both sides of the joint stiffness of the secondary small micromaxillary deformity, etc. In addition, the oropharynx or hypopharynx cancer, obesity and airway tissue mucous edema and so on is also the cause of OSAS. Detailed causes for OSAS, there is no clear conclusion in medical field, still needs further research.At present the main means of treatment of OSAS have noninvasive continuous positive airway pressure therapy, behavior therapy, surgical treatment and medication, and the treatment using noninvasive ventilator has become a recognized OSAS treatment the most effective and safe method, its curative effect is as high as 90～ 95%. The principle of noninvasive ventilation treatment is to use a noninvasive ventilator with Continuous Positive Airway Pressure (Continuous Positive Airway Pressure, CPAP), double the level of Positive Pressure ventilation (Bi-level Positive Airway Pressure, Bi-PAP) and Automatic Positive Airway Pressure (Automatic Positive Airway Pressure, APAP) treatment. Noninvasive positive airway pressure (CPAP) treatment has become more and more popular is because do not need surgery and medication, guarantee the effect of a noninvasive ventilation treatment.CPAP is most commonly used in noninvasive ventilation treatment, its basic principle is through adjusting the rotational speed of the fans, to keep the patients in the course of the inhalation and exhalation, continue to the upper respiratory tract through the mask is a constant pressure, maintain upper respiratory muscle tension and increase the width of the pharyngeal cavity wall, by influencing the caliber of the upper respiratory tract and lung capacity, avoiding the due to airway collapse of apnea and hypopnea syndrome.The United States is one of the earliest countries treatments using breathing machine in OSAS, in 2005 the country’s therapeutic breathing machine has reached 1 million units in total demand, and in the past ten years demand growth rate at about 20% every year. The total demand number of breathing machine of Western Europe in 2005 was about 700000, the total demand growth rate of about 20% a year. Since2003Japan brought OSAS diagnosis and treatment into the scope of insurance, the demand for breathing machine raised sharped, annual demand has reached more than two million in 2005. But in our country, the people lacked the awareness of the dangers of OSAS, the popularity of treatment is very slow. In recent years, with the popularity of sleep medicine knowledge and the improvement of people’s living standards, more and more people began to pay more attention to their health, noninvasive sleep ventilator has the huge market potential; On the other hand, with the development of science and technology, noninvasive sleep ventilator’s performance will be improved, using breathing machine for treatment of obstructive sleep apnea syndrome more evident advantages. At the same time, the types of breathing machine on the market are multitudinous, but people are not limited to reach to the requirement of sleep-related breathing machine treatment effect, but at the same time of treatment effect, the use of comfort have higher pursuit.In the design of sleep-related breathing machine, motor core control algorithm, the system hardware design and software algorithm are the key technology to determine the system noise level and comfort. This article gathered and analyzed the requirements of sleep breathing machine requirements, and combined the domestic and foreign demand, studied the key technologies of the above. We designed a sleep apnea machine core components with moderate cost, high efficiency of motor control, low noise level and the use of comfort.In the treatment of sleep apnea machine process, in order to ensure that users the best comfort and minimum interference of sleep, sleep apnea machine need to adjust output pressure, according to patients breathing fast so the motor selection and control put forward higher requirements. On the motor type selection, this paper integrated the consideration of cost and performance, choose the brushless dc motor that is widely used in the sleep-related breathing machine. The traditional control method of brushless dc motor is driven by the stator six-step square wave process. In the process of six-step square wave control, give a pair of winding electricity until the rotor to the next position, then the motor phase to the next, and the hall sensor is used to determine the position of the rotor, by using electronic means to motor commutation. Six-step square wave algorithm method of the method is simple, easy to implement, but easy to produce noise, and to need according to the changes of the patients breathing fast changes motor speed sleep-related breathing machine, its response ability is obviously insufficient. In view of this, this article will Field Oriented Control (Field-Oriented Control and FOC) algorithm is used for sleep apnea machine motor Control. Field oriented control, also known as the decoupling control and vector control, in the 1970 s, American P.C.C ustman and A.A.C lark to apply for patent "coordinate transformation control of induction motor stator voltage" and Germany’s Siemens F.B laschke etc. Put forward the "field oriented control of induction motor principle," laid the foundation of vector control, the structure of its main idea is through asynchronous motor can’t separate excitation current and torque current through the separation of coordinate transform into phase difference of 90° to control excitation current and torque current, so as to achieve rapid accurate speed control.This article firstly introduced the related theory knowledge of sleep-related breathing machine, for the treatment of sleep apnea machine applied in OSAS advantage makes a brief comparative analysis. Then, the paper introduced the machine’s working principle and system composition of breathing during sleep, explains the sleep-related breathing machine in the working process of the requirements for the motor response speed and noise. Given six step square-wave brushless dc motor of the traditional control method, its corresponding to the problem of shortage of capacity, and based on the mathematical model of brushless dc motor and control theory for the research and analysis, determined adopting FOC for the motor control. This article uses the FOC motor control algorithm, the first through the coordinate transformation, the three-phase static coordinate system is transformed into two phase rotating coordinate system, so that the three phase coupling of stator current into orthogonal to each other, independent decoupling of torque and excitation component, so as to achieve similar to other excited dc motor by controlling the torque current the purpose of the direct torque control.In the aspect of hardware, this paper chosen TM4C129 and TMS320F2806 dual processor architecture.TM4C129 is based on the Cortex-M4 architecture, the chip has rich internal resource, that can drastically reduce the use of peripheral modules, especially in the internal integrated LCD controller and efficient signal processing ability, could meet the design of the LCD driver, and breath signal acquisition and processing needs.TMS320F2806 processor is fixed-point DSP based on C28X kernel, is a high level of integration, performance, strong motion control chip series, can meet the needs of complex operation in FOC motor control algorithm. In this design, TM4C129 receive data from differential pressure/pressure sensors, and judge patients breathe in and out process, sleep apnea event detection by relevant identification process.TMS320F2806 is used to implement the FOC motor control algorithm, outputting three PWM to drive three-phase stator, and control the running of the brushless DC motor, the chip high-speed computing power ensure the real-time motor control, at the same time, the internal integration of large capacity storage space without external RAM can meet the demand of storage, to ensure the high reliability of control system. The human-machine interactive parts in the system include the key, the LCD screen and a buzzer. Buttons are mainly used for system control and parameter setting of input. LCD screen in setting mode, the system used for each menu configuration interaction, and can display the current breathing waveform in the process of treatment. In the process of system operation, power supply or mask off, buzzer will send out alarm.In the aspect of software, this paper implemented system driver and critical algorithm. Drivers include the system configuration, A/D conversion program, modulus conversion, LCD driver, SD card read and write the driver, etc. In algorithm, we have realized intelligent start, breathing/pressure following, breathing events identify and leak detection and compensation algorithms. If patients appear apnea, low ventilation or blocked events in sleep, system rises up the output pressure, to achieve therapeutic effect; In normal state, the system reduce the pressure, until again detected apnea, low ventilation or blocking events, system to increase pressure, so repeatedly, can adapt to adjust pressure is suitable for the optimal treatment of patients in the titration.Test prototype test results show that the design of the key units of breathing during sleep with the advantage of fast response speed, stable output pressure, low level noise, can be adjusted according to patients with respiratory accurately and rapidly the output pressure and flow, accurately identify the occurrence of respiratory events, and leak detection and compensation. In performance is comparable with international sleep breathing machine leading brand ResMed S9. The key unit of breathing we designed is of great value in clinical application, and lay the foundation technology of CPAP, APAP and Bi-PAP machine.