Many medical devices need precise embedded motion control at low speed, and in the era of Covid-19, medical ventilators are one of the pieces of healthcare equipment very much in demand for treating patients.
To address this, Trinamic Motion Control (part of Maxim Integrated), has released an open-source reference board to accelerate medical ventilator design, as part of its Trinamic Open-Source Ventilator (TOSV) project. The resulting TMC4671+TMC6100-TOSV-REF reference design board featuring both hardware and software as open-source, combines its TMC4671 and TMC6100 devices in a compact module. The BLDC servo driver is capable of 12 to 36V with up to 6A RMS to accommodate medical ventilators or respiratory systems. To speed up design cycles even further, the open-source module features an SBC connector in Raspberry Pi style and space for a pressure sensor add-on board.
Since automatic ventilators must be equipped with appropriate sensor technology for monitoring changes and reacting to these such as pressure flow, volume, and respiration rate, the module comes with a Hall sensor interface and connectors for an optional pressure sensor add-on board. This data can be directly visualized on a Raspberry Pi with touch screen using the free, open-source firmware developed for the reference design module by Trinamic.
The company said its goal with this reference design is to show engineers how medical ventilators can be built using readily available components, bypassing increased lead-times of traditional components during the Covid-19 crisis. Trinamic emphasizes that its goal is not to produce medical ventilators, but to offer something that offers high quality ventilation can be mass-produced by medical equipment companies in the short term.
The founder of Trinamic, Michael Randt, explained, “Right from the start, we decided to use a high-RPM turbine motor based on a BLDC motor. Together with pressure and volume flow sensors, the dynamically controlled motor enables both pressure-controlled and flow-controlled ventilation modes.”
Drawing on previous experience with the control of CPAP (continuous positive airway pressure) device turbines, Trinamic said one thing was clear: providing fast and dynamic control of low-induction BLDC motors can be exceptionally challenging. It requires careful consideration of the trade-off between high switching frequency and current ripples and their consequent switching and stator losses, respectively. With its embedded TMC4671 servo controller IC, the module generates a PWM frequency and current controller clock of 100 kHz independent of the microcontroller. With this, the current consumption of the system is reduced, with no performance penalty, by up to 15 percent when compared to a frequency of 25 kHz.
An add-on board for I2C and analog sensors allows support for pressure sensors from various manufacturers. The TMC4671+TMC6100-TOSV-REF can be plugged into a single-board computer to access the user interface and high-level control functions. In case of the TOSV project, a Raspberry Pi with touch screen display was used.
The completely open-source reference board TMC4671+TMC6100-TOSV-REF is available from mid-July. All hardware, firmware, and software is open-source under the MIT license.