Development and evaluation of motor-driven, pusher-plate-type artificial heart system

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A pulse width modulation (PWM) algorithm with fixed duty ratio and variable voltage has been developed to drive and control the implantable electro-mechanical actuator for blood pumps. The actuator incorporated with a dc brushless motor was attached to a pusher-plate-type blood pump. Rotation of the motor is converted into a linear motion by a ball screw. The position of the pusher-pate was monitored with a Hall-effect sensor mounted on the back plate and a magnet attached to the plate. Any other monitors are not necessary for the open-loop operation of the pump. The size of the actuator is 50 mm OD and 30 mm length, and the weight is 480 g. Eight-bit and sixteen-bit microprocessor-based systems were used to drive the motor and to control the whole system, respectively.The torque performance of the motor assembled in the actuator was studied in detail for the development of the software which controls the speed and the input voltage of the motor without any feed back informations. The results indicated that the pump fulfills the specified performance.Software was developed based on the results obtained from the torque test. The sixteen-bit microprocessor controls the operation of the pump, monitoring the position of the pusher-plate in the systolic phase and using a timer in the diastole. The eight-bit microprocessor controls the phase of rotating magnetic field and input voltage of the motor according to the data table derived from the torque test.The system performance studied with a mock circulator satisfied the design specifications. The pump outflow of 6 1/min was obtained at the rate of around 100 bpm against the afterload of 100 mmHg. The temperature rise and the pump efficiency were around 6 % and 18 C, respectively.