Automatic pressure compensation in a fluid syringe for blood glucose enzyme dispensing system

In manufacturing blood glucose test strips, enzyme weight per dot plays a critical role effecting the reading of blood sugar level. Normally, the weight error per dot is kept within 1.5% of nominal value for reliable blood sugar reading. In addition, enzyme level in a fluid syringe of a dispensing system gradually decreases as manufacturing process goes on, hence making the dispensing amount of enzyme per dot smaller and smaller. Therefore the dispensing machine has to be stopped constantly whenever after several thousands of dispensing operation for manually adjusting (i.e. increasing) the syringe air pressure so that enzyme weight per dot can be kept within the target range. This consumes a large portion of the manufacturing time. In this paper an automatic air pressure compensation system in the fluid syringe is developed for assuring manufacturing quality of dispensing enzyme weight per dot. The adopted automatic compensation system consists of a pressure sensor, a pressure regulator, a MyRio embedded microcontroller, and a fuzzy sliding mode controller (FSMC). Experiment results show that the average error of enzyme weight per dot is about 1.04% without air pressure compensation in the fluid syringe (however, the latter part of enzyme weight per dot exceeds 1.5% when the enzyme fluid level is low), whereas the average error is only 0.133% with syringe air pressure compensation, which is 7.82 times better. In addition, the standard deviation without air pressure control is about 0.0024; the standard deviation with FSMC air pressure control is only 0.000476, which is 5.04 times better. Therefore the developed automatic syringe air pressure compensation system shows effectiveness in maintaining the enzyme weight per drop within the target range for a blood glucose dispensing system, without having to stop the machine constantly.