Abstract: Roots-type blowers with helical cycloidal rotors exhibit variation in leakback flow with angular position intrinsic to these rotor geometries. Calibration of individual blowers using a combination of high-resolution alignment and enhanced detection of residual noise phenomena permits noise in as-produced blowers to be significantly attenuated. Intrinsic lower limits of noise induced by leakback variation are associated with manufacturing tolerances, necessary clearances, and particular geometric considerations. Gross alignment errors (excluding contact between rotors) produce a characteristic noise pulse rate that is three times the shaft rate. Proper alignment suppresses this and reveals a pulse sequence at double this rate and at about half of the amplitude of faulty alignment. The novel process explains the error mechanisms and defines repeatable calibration methods for a mass-production environment, introducing appropriate gauges and methods for the task.

Abstract: A bi-directional flow sensor is adapted for reducing pneumatic noise during pressure sensing with a flow passing through the flow sensor. The flow sensor comprises a hollow, tubular member having a throat section disposed between a ventilator end and a patient end. A flow restrictor is disposed in the throat section and is adapted to measure differential pressure in the flow. A baffle is mounted at the ventilator end and is adapted to minimize non-axial flow at pressure taps located on opposing ends of the flow restrictor. The patient end includes a flow obstruction configured to promote uniform velocity across the flow at the pressure taps during exhalation flow from the patient end to the ventilator end. The flow sensor minimizes pneumatic noise to less than 0.1 LPM to allow accurate patient flow measurement and triggering of inhalation and exhalation phases at flow rates of 0.2 LPM.

Abstract: A Roots-type blower with helical cycloidal rotors features relief recesses in the chamber walls, isolated from the input and output ports. The relief recesses counter variation in leakback flow with angular position intrinsic to helical cycloidal rotors, attenuating a noise source.

Abstract: A method and apparatus for controlling a brushless DC (BLDC) motor over a wide range of angular speeds is presented. Analog magnetic sensors provide continuous signal measurements related to the rotor angular position at a sample rate independent of rotor angular speed. In one embodiment, analog signal measurements are subsequently processed using an arctangent function to obtain the rotor angular position. The arctangent may be computed using arithmetic computation, a small angle approximation, a polynomial evaluation approach, a table lookup approach, or a combination of various methods. In one embodiment, the BLDC rotor is used to drive a Roots blower used as a compressor in a portable mechanical ventilator system.

Abstract: A method and apparatus for controlling a brushless DC (BLDC) motor over a wide range of angular speeds is presented. Analog magnetic sensors provide continuous signal measurements related to the rotor angular position at a sample rate independent of rotor angular speed. In one embodiment, analog signal measurements are subsequently processed using an arctangent function to obtain the rotor angular position. The arctangent may be computed using arithmetic computation, a small angle approximation, a polynomial evaluation approach, a table lookup approach, or a combination of various methods. In one embodiment, the BLDC rotor is used to drive a Roots blower used as a compressor in a portable mechanical ventilator system.

Abstract: A portable ventilator uses a ROOTS-type blower as a compressor to reduce both the size and power consumption of the ventilator. Various functional aspects of the ventilator are delegated to multiple subassemblies having dedicated controllers and software that interact with a ventilator processor to provide user interface functions, exhalation control and flow control servos, and monitoring of patient status. The ventilator overcomes noise problems through the use of noise reducing pressure compensating orifices on the ROOTS-type blower housing and multiple baffling chambers. The ventilator is configured with a highly portable form factor, and may be used as a stand-alone device or as a docked device having a docking cradle with enhanced interface and monitoring capabilities.

Abstract: The invention comprises a method and apparatus for reducing the noise generated by compressors, including Roots-type blowers. The invention has particular use for reducing noise generated by compressors used in mechanical ventilators, though the advantages thereof may be realized in many different applications. One embodiment of the invention comprises a noise-attenuating gas flow path for a compressor contained in a portable ventilator housing. In one embodiment, the gas flow path comprises a plurality of chambers interconnected by flow tubes. The flow path is folded so as to fit into the limited space of a portable ventilator housing. The dimensions of the chambers and the flow tubes are selected so that an impedance mismatch is created between the chambers and the flow tubes. In one embodiment of the invention, the flow path comprises one or more perforated tubes located in one or more of the chambers.

Abstract: A portable mechanical ventilator uses a constant-speed compressor compressor and a recirculating bypass circuit. Bypass flow is governed by a spring-biased bypass valve so connected to both the inlet and the outlet of the main flow control valve as to maintain a differential pressure across the flow valve sufficient to operate the ventilator with minimal energy consumption. The flow valve is operated by a microprocessor in accordance with empirically derived lookup tables to both produce the desired air flow and provide a measure of that air flow.

Abstract: An exhalation valve assembly for use in the mechanical ventilation of respiratory patients in which the PEEP valve and the exhalation valve are combined into a single valve mechanism, and which includes a wye in which the patient tube splits at equal angles into the ventilator tube and a tube closed off by the PEEP valve, so as to maintain the exhalation drive hose and the ventilator hose generally parallel, and avoid sharp angles in the air flow.