Design Of Household Non-invasive CPAP Ventilator System

Obstructive sleep apnea hypopnea syndrome was one of the most common chronic respiratory diseases,which caused patients to suffer from recurrent pathophysiological changes such as apnea or hypopnea due to upper respiratory tract muscle collapse in sleep.At present,continuous positive pressure ventilation provided by household ventilator was the mainstream treatment for OSAHS.In this paper,a household non-invasive CPAP ventilator was designed to provide continuous positive pressure ventilation for OSAHS patients after the investigation and analysis of mainstream products in the market.Specific works included functional hardware circuit and peripheral driver,motor control hardware circuit and algorithm,water box temperature control system,data transmission and storage management,Free RTOS embedded multi task system transplantation and modification,etc.Firstly,the drive circuit and algorithm of brushless DC motor were implemented based on magnetic field directional control.Phase current sample noise was significant restrained due to the improved hardware scheme and optimized FOC algorithm parameters were more suitable to the hardware platform.The transient response speed of the motor in the constant torque mode was also improved by setting the parameters of the torque PI controller.Meanwhile,it shortened torque stabilization time and lowered the airflow fluctuation generated by the motor rotation.Secondly,integrated mute design of algorithm,motor,machinery and structure was particularly important since household ventilator was mainly used at night.According to the optimization of the driver algorithm parameters and the silicone coating design of the motor shell,the engine noise was significantly cut down.The ventilation pipe with honeycomb structure can bring down the noise caused by the air flow driven by the motor fan and the vibration of the pipe.At the same time,a sponge was added at the air inlet of the pipeline and a cushion was added at the fixed position of the shell to absorb the shell vibration noise caused by the rotation of motor.Thirdly,the software transplantation and modification of Free RTOS embedded system was completed based on STM32 microcontroller.On the basis of Free RTOS,five core tasks were completed including multi task execution mechanism,task communication and synchronization mechanism,hardware interface peripheral driver design,data transmission and storage protocol frame format design,and the corresponding driver modules.Simultaneously,the UI design and software driver of human-computer interactive touch interface were also finished and the copyright of computer software was also authorized by Copyright Protection Center of China.Finally,the ventilator function tests were accomplished which verified the integrity and reliability of the system function,including the power system function test,motor drive phase current scheme comparison test,FOC drive algorithm performance test,data transmission and storage function test,and water box temperature control system test.Through the comparative test,it can be found that the noise of the whole machine was significantly decreased after the parameter optimization and the shell structure improvement.By comparing the output pressure steady-state error and steady-state time with the mainstream products,it was verified that the whole system met the steady-state accuracy requirements,while curtailed the time required for stability.