What is the application of the lead screw in syringe pumps?

When we think of syringes,we usually think of the disposable types used by doctors and nurses to administer vaccines or individual doses of drugs.But some conditions require frequent or constant doses of critical drugs,making administration through a single-use syringe undesirable or even infeasible.In other cases,patients are unable to take normally administered medications orally for physiological reasons,such as dysphagia or adverse side effects that render oral medications ineffective.When oral administration is not an option,medical personnel often opt for subcutaneous administration via a syringe pump.

 

According to the Food and Drug Administration,an infusion pump is"a medical device used to deliver fluid into a patient's body in a controlled manner."One way the FDA classifies infusion pumps is through their method of operation,which includes syringe pumps,elastic pumps,and peristaltic pumps.

Syringe pumps can be designed for stationary use in hospitals,clinics,and research laboratories,or for outpatient(portable)use,allowing patients to walk around and carry the pump with them,usually in a shoulder bag or bag.

The basic premise of the syringe pump is to keep the fluid(medicine)in the syringe,whose plunger is driven by an electromechanical device to control the delivery of the fluid to the patient.This electromechanical drive is usually realized by a lead screw driven by a stepper motor.The lead screw nut is connected to a mechanism(usually a block)that pushes the syringe plunger in a specified amount at a controlled rate.The push rod block is supported and guided by two parallel shafts with sliding bearings to ensure smooth sliding and no tilting.The entire assembly is essentially a miniature linear actuator - consisting of two linear guides,a lead screw and a stepper motor.

A small linear actuator consisting of a lead screw,a sliding bearing guide and a stepper motor drives the syringe pump in this bench top model for research and testing.

 

Like any medical device,a lead screw syringe pump is mission critical,or as some have called it,"life critical" equipment,and its failure can compromise patient safety,so performance and reliability are important.Anti-backlash lead screw nuts ensure accurate fluid delivery,and PTFE coated screws with bronze or plastic nuts help reduce adhesion or stick-slip in syringe pumps.PTFE coated screws eliminate the lubrication requirement for syringe pump assemblies,where lubrication free operation is typically required.

 

Precision control is key to providing the exact volume needed to administer a drug or perform critical laboratory studies and tests,which typically involve dispensing fluids in microliters.Since the stability of the syringe flow rate is directly related to the number of steps the motor can complete,syringe pumps typically use stepper motors with microstep control.

Size and weight are key criteria in syringe pump design - especially for those intended for ambulatory use - and the ability to customize the lead screw nuts helps syringe pump manufacturers make their devices as compact as possible.Because the lead screws have no recirculation parts,they produce less noise than other actuation mechanisms and help the syringe pump assembly meet low noise requirements.

A dynamic syringe pump like this one needs to be particularly compact and quiet.

https://www.autolinearmotion.com/lead-screws.html