Operating an infusion pump system

An infusion pump device comprising:

• a pump housing having a first end and a second end opposite to the first end, the pump housing defining a space open at the first end for receiving a medicine cartridge through the first end;
• a piston rod contained within the pump housing, the piston rod being movable toward an output end of a medicine cartridge received within the pump housing;
• a plunger engagement device connected to a forward end of the piston rod, the plunger engagement device including a plurality of substantially rigid pins or an adhesive layer;
• a cap device configured to engage the pump housing at the first end such that the cap device covers an exterior opening of the pump housing at the first end and retains the medicine cartridge in the space defined by the pump housing;
• wherein, the plunger engagement device is configured to attach the piston rod to a plunger of the medicine cartridge, at the second end of the pump housing, via the plurality of substantially rigid pins penetrating longitudinally into the plunger or the adhesive layer engaging a rear face of the plunger.