US Patent 7635349 Syringe pumps

A syringe pump has a motor rotating a leadscrew, which drives a plunger head retainer to push a plunger along the barrel of a syringe so as to dispense medication to a patient. A force sensor in the head retainer measures the force on the plunger to detect when there is an occlusion restricting flow of medication. When an excess force is detected an alarm is generated and the motor is reversed to reduce the force to about 10% of that at which the occlusion is detected. The occlusion can be removed with a reduced risk of a bolus of medication being dispensed after which the user restarts the pump so that the plunger is driven normally.