Novel Advanced Powered Air Purifying Respirator (PAPR) Concepts

电动空气净化呼吸器(PAPR)是用于保护受污染空气的装置。它们通常包含一个过滤器、离心式鼓风机和一个由电池供电的电机。标准防毒面具的工作原理是负压，使用者必须通过过滤器吸入才能净化空气。在某些情况下，所需过滤器的厚度可能非常大，从而产生非常大的呼吸阻力。这会给使用者带来不适，并可能损害身体性能。PAPRS中的离心式鼓风机用于向用户提供正压，并通过吸入空气使过滤器产生的阻力最小化。直到最近，PAPR才被开发出来，为用户提供持续的空气流动。固定空气流量基于平均呼吸频率，并且当用户的呼吸需求由于体力消耗增加而增加时，其所能提供的保护是有限的。持续的气流供应也对设备中的一些部件的效率造成不利影响。过滤器有一个定义的寿命，这取决于它们正在过滤的气体的浓度和通过它的空气流量。为了最大限度地延长过滤器的使用寿命，首先应该认识到，只有在使用者吸入时才需要使用它。当使用者呼气时，来自他们肺部的所有额外空气和仍在运行的离心式鼓风机通过口罩中的排气阀被分散。如果离心式鼓风机只在用户吸入时向其提供空气，则过滤器的使用寿命可以延长。这些PAPR的控制被归类为呼吸响应型控制，为开发这些控制而发表的文献很少。在这个项目中认识到，PAPR中单个组件的微小变化可能会导致性能的巨大变化，从而使控制器的开发变得困难。人们还认识到，为单个案例创建控制器将是有限的，因为优化组件的开发将使其低于平均水平。该项目旨在创建一种形式的控制器，可以考虑PAPR组件中的个别开发，使系统的设计模块化。通过这样做，控制器还应该能够根据系统的变化进行更改。例如，通过改变过滤器的厚度；口罩的形状；离心式鼓风机；电机。为了实现自适应控制器，本项目采用系统辨识。这一过程包括对系统性能的彻底调查，以便定义一个动态模型来描述电机的输入电压和鼓风机的输出压力之间的关系。已经在频域中对该系统进行了分析，以评估感兴趣的带宽中任何非线性效应的严重程度，并且已经在时间域中开发出了能够很好地适合描述这种动态行为的模型。这方面的挑战是用不同的过滤器厚度和离心式鼓风机来测试模型。如果一个单一的模型能够表现出一致的稳定收敛，并且它的性能良好，那么它对于一个以模块化设计为目标的控制器来说可能是足够通用的。然后，它可以被开发用于自适应控制器，目的是使控制器能够在线识别。然而，在实现这一点之前，可以离线使用导出的模型来开发简单的PI控制器，并测试辨识过程的有效性。

Powered air purifying respirators (PAPRs) are devices used for protection against contaminated air. They typically contain a filter, centrifugal blower and a motor powered by a battery. Standard gas masks work on the principal of negative pressure, where the user must inhale through the filter in order to clean the air. For some cases the thickness of the required filter can be very large, creating a very large resistance to breathing. This causes discomfort for the user and can impair physical performance. The centrifugal blower in PAPRs is used to provide a positive pressure to the user and minimise the resistance caused by the filter by drawing air through it.Until recently, PAPRs have been developed to provide a constant flow of air to the user. The fixed airflow is based on average breathing rates and has limitations to the protection it can provide when the breathing demand from the user increases due to increased physical exertion. The constant airflow supply also has consequential detriments to the efficiency of some of the components in the device. Filters have a defined lifespan that is dependent on the concentration of the gas they are filtering and the volume of airflow through it. To maximise the lifespan of the filter it should first be recognised that it is only required for use on the user's inhalation. When the user exhales, all the additional air from their lungs and the, still running, centrifugal blower is dispersed through an exhaust valve in the mask. If the centrifugal blower were to only provide air to the user upon their inhalation, the lifespan of the filter could be increased. The control of these PAPRs have been categorised as breath-responsive and the literature published for the development of these is minimal.It is recognised in this project that small changes to individual components in a PAPR can create large changes in performance, making the development of a controller difficult. It is also recognised that creating a controller for an individual case would be limited, as developments to optimise components would make it subpar. This project aims to create a form of controller that could account for individual developments in the PAPR components, making the design of the system modular. By doing this, the controller should also be able to alter depending on changes to the system. For example, by changing the: thickness of the filter; shape of the mask; centrifugal blower; motor.To achieve an adaptive controller, this project uses system identification. This process includes a thorough investigation into the performance of the system in order to define a dynamic model to describe the relationship between an input voltage to the motor and the output pressure of the blower. The system has been analysed in the frequency domain to assess the severity of any nonlinear effects in the bandwidth of interest and models in the time domain have been developed that provide a good fit to describe this dynamic behaviour. The challenge with this is to test the model with a variety of filter thicknesses and centrifugal blowers. If a single model can show consistently stable convergence and its performance is good, then it may be generic enough for a controller aimed towards modular design. It can then be developed for use in an adaptive controller, with the intention of making the controller capable of being identified online. Before this is achieved, though, the derived model can be used offline to develop simple PI controllers and test the effectiveness of the identification procedure.