Drive device for a membrane fluid pump and operating method

A cardiac support system comprising:

• a membrane blood pump;
• an inlet cannula connected to the membrane blood pump, the inlet cannula configured to supply blood to the membrane blood pump;
• an outlet cannula connected to the membrane blood pump, the outlet cannula configured to conduct the blood out of the membrane blood pump into a blood vessel;
• a working pump, the working pump connected to the membrane blood pump via a pressure line and configured to drive the membrane blood pump, the working pump comprising a hollow cylinder and a working piston, the working piston configured to oscillate axially in the hollow cylinder between two reversal points for contraction and expansion of a working chamber in the working pump, the working chamber being in a pressure exchanging connection with the pressure line;
• and
• a control unit configured to control a movement of the working piston between the two reversal points, the controlled movement of the working piston comprising three temporally successive phases including a first phase, a second phase, and a third phase,
• wherein the control unit is configured to cause, in the first phase, acceleration of the working piston to a speed that is greater than a speed of the working piston at the end of the first phase,
• wherein the control unit is configured to cause the working piston to move, in the second phase, such that a specified speed of the working piston, a specified relative pressure in the working chamber, or a specified force of the working piston is kept on a reference trajectory, and
• wherein the control unit is configured to cause the working piston to move at a negative acceleration in the third phase.