Injector control

Abstract

A control system for an angiographic injector which precisely regulates the speed of a motor used to expel contrast media from a syringe. The control system is centered around a microprocessor which receives commands from the operator via a keyboard, and then regulates the speed of the motor by supplying drive command pulses to a circuit which integrates the difference in frequency between the command pulses and another pulse train whose frequency is proportional to actual motor speed. The control system also includes a velocity loop which uses the motor back EMF to supply an analog voltage also proportional to motor speed to a difference amplifier in a conventional velocity loop. The system is a dual loop controller where the second loop provides approximate speed control, while the first loop provides a 'velocity correction' voltage required to bring the system to zero steady state speed error. Motor speed pulses are provided by an incremental encoder, the pulses from which are counted by the microprocessor to limit the volume of fluid injected. Various safety systems guard the injectors performance and help prevent over volume injections. These systems are part of the velocity control and are also disclosed.