VALIDATION OF THE MODEL OF A MILKING MACHINE VACUUM SYSTEM BY THE MEANS OF TEATCUP FALL-OFF TESTS

R. Roşca, P. Cârlescu, I. Ţenu, C-tin Chirilă

Abstract
   A previous paper presented some preliminary researches regarding the use of a variable frequency driver (VFD) in order to maintain a constant vacuum in a milking system, by adjusting the speed of the vacuum pump; the PID controller used by the vacuum regulating system was tuned by the method of trial and error, rather than as a result of a theoretical study. In order to proceed to a more systematic approach to this solution for vacuum regulation a mathematical model of the vacuum system should be developed. In the present paper a mathematical model is presented; the model is used to study the dynamic behavior of the milking system and it assumes that the system consists of a single air tank, provided with a vacuum pump port and an air-using port.
   In order to validate the model and study the system's response to vacuum variation due to a pulse air leak the detachment (fall-off) of one teatcup was simulated; the teatcup was detached for 10, 20 and 30 seconds respectively. During the fall-off tests the rate of air flow into the system was measured by the means of a rotameter and the vacuum level was recorded. The experimental results were compared with the ones predicted by the model and it was concluded that the model accurately describes the response of the system.

Key words: variable frequency drive, vacuum system model, teatcup fall-off