Development and Laboratory Testing of a Bucket Milking Machine with Flow-Controlled Vacuum, Based on an NI Data Acquisition System

In the present paper, the idea of regulating the vacuum level by means of a variable frequency drive (VFD) in order to control the speed of the vacuum pump of a milking system was considered. Wet tests (using water instead of milk) were performed in order to tune the PID controller, which drives the VFD; then, the virtual instrument built using the LabVIEW environment was adapted in order to regulate the vacuum level as a function of the flow rate. The system was tested in order to verify vacuum stability and system response time. Wet tests have proven that the vacuum level in the system was affected by presence of the liquid column in the milk line; as a result, the standard deviation of the vacuum level was comprised between 0.067 kPa and 1.43 kPa (depending on the flow rate and vacuum level), while in the previous dry tests the standard error was comprised between 0.186 kPa and 0.194 kPa. Nevertheless, vacuum fluctuations did not exceed the imposed limit of ±2 kPa relative to the nominal vacuum in the flow-controlled vacuum system. In order to reduce the vacuum fluctuations, the original claw of the installation was replaced with a larger one, with a volume of 330 cm3; under these conditions, the standard deviation of the vacuum level decreased to 0.134–0.288 kPa.