PMD Announces Availability of Portescap BLDC Developer Kit
The hallmark of ventilator control is the need to deliver air to the patient that follows a specified pressure or airflow profile. The exact form of these profiles can be complex and depends on the characteristics and condition of the patient's lungs, and the ability of the patient to perform some of the breathing function on their own.
There are several different pump types commonly used in ventilators including piston pumps, diaphragm pumps, bladder pumps, compressors, and vacuum pumps. In this motion application we will focus on piston and diaphragm pumps which are position-proportional pumps meaning a programmed change in the pump position results in a proportional volume of air being delivered. Both piston and diaphragm pumps frequently use Brushless (BLDC) motors. Piston pumps use a linear actuator configuration to control the piston position (generally a lead screw or ball screw mechanism) while diaphragm pumps are more often of the rotary type.
Whatever type of pump is used, a key concept in ventilator control is an outer loop controller which drives a downstream position or velocity control loop. The outer loop takes as input a desired pressure or airflow value, combines with an actual measurement of those quantities, and generates an output command to the position or velocity loop motor controller.
Outer loop controllers used in ventilators do not follow familiar motion control profiles such as a point-to-point trapezoidal profile. An example profile is shown in the figure below. It has two major phases as air is first provided to the lungs (inspiration) and then drawn out (expiration). So another important capability of motor controllers used for ventilation is the ability to execute arbitrary profile shapes that can be changed on the fly.
The diagram below shows a control flow diagram for a typical high performance motion controller with a cascaded outer loop/velocity loop control function. This diagram shows separate analog signal inputs for pressure and airflow transducers. The current loop and amplifier are of the digital switching type which results in very efficient and cool operation.
