Motor Controller that Reliably Starts and Quickly Ramps Miniature Turbo Molecular Pumps to Maximum Speed
There are currently no controllers for miniature turbo pumps that are able to reliably start and quickly ramp up to maximum-speed turbo pumps of this size.
The invention, which has been reduced to practice is a complete motor controller system to control miniature turbo molecular vacuum pumps. As described below, the controller system reliably starts the vacuum pump motor from rest and quickly ramps its speed to 200,000 rpm.
The system of the invention consists of an electronics board, a field-programmable gate array (FPGA) running custom firmware, and custom software. The system interfaces with the motor with three wires connected to the three motor windings. The electronics board consists of the power field-effect transistors (FETs) that drive the windings and other circuitry for interfaces, control of the FETs, and generating the amount of current called for by the FPGA. The firmware on the FPGA consists of the algorithm controlling the sequencing of the commutation signals based on the back-EMF (electromotive force) signal of the motor speed calculation, and the pathway for translation of desired motor current from the software to the electronics board. The software consists of the algorithm that controls the higher-level starting and ramping sequence, the setting of parameters within the FPGA firmware, and the setting of the desired motor current.
In operation, the software algorithm first jogs the motor to a known starting point with a large voltage applied to a single winding. The software then begins to step the motor, rotating it at a constant low speed without the use of the back-EMF position location signal, and ramps the speed by continuously reducing the delay between successive commutation signals. The rate at which the speed is ramped depends on the current calculated speed. Finally, the control of commutation timing is switched to using the back-EMF signal and the desired motor speed is ramped up until the motor reaches a maximum speed of 200,000 rpm, thereby achieving a significant vacuum at the pump inlet.
The advantages of the motor controller system of the invention are as follows. The system:
* Does not require the use of hall sensors or other position sensors to provide position location at time of start,
* Achieves a speed of 200,000 rpm by using an acceleration algorithm to achieve the maximum speed quickly,
* Is low power,
* Is robust in that it starts the miniature turbo pumps reliably every time, and
* Does not require pulsewidth modulation (PWM) micro-stepping, so it is therefore less complex to implement.
Mr. M. T. Hickman