| Milking machine is one of the key points in control of mastitis in dairy farms.Its quality and usage status are related to the sustainable and healthy development of dairy farming.Based on lack of good design theory of milking machine and lack of scientific settings of system vacuum or milk flow threshold of automatic cluster remover,this paper analyzed the characteristics of vacuum and temperature distribution of the whole system of milking machine.Mathematical model of milking machine was constructed by using the bonding graph technique.The dynamic characteristics of milking machine were analyzed.Based on mathematical model analysis method and frequency response analysis technique,the dynamics of milking machine was studied.Vacuum pump production capacity,internal volume of the system and cross-sectional area of pipeline on the dynamic changes of milking machine system were analyzed.24 dairy cows were used to study the effect of system vacuum of milking machine.Machine milk yield,average milk flow rate,somatic cell counts(SCC)and the change rate of teat end wall thickness were used as milking effect evaluation index.In the system vacuum setting in the range of 44 to 48 kPa,effects of system vacuum on both short milk tube vacuum and mouth piece chamber vacuum of milking process were studied.The effect of system vacuum on the evaluation index of milking effect was quantified.The effect of milk flow threshold of automatic cluster remover on milking effect was studied.The first batch of milk cows with two milk time per day was taken as the object of study,and the experiment was carried out by using cross-experiment design.(0.2 kg/min and 0.3 kg/min)combined with maximal cup time(7.2 min)on status of teat,clinical mastitis,machine milk yield and milking duration.The results show that mathematic model of milking machine system constructed by the bonding graph technique is a good way to describe the dynamic characteristics of milking machine system.Milk machine system dynamics studies have shown that increasing internal volume of the system can reduce the cyclical changes in the system due to functional factors such as pulsation.In addition,increasing the capacity of vacuum pump capacity could reduce the pressure fluctuation intensity caused by non-functional factors.It was considered that the dynamic change of the whole system can be weakened by reducing cross-sectional area of milking machine when the frequency of the periodic disturbance is close to the natural frequency of the system.The experimental results show that when system vacuum was increased from 44 kPa to 48 kPa,increasing rate of short milk tube vacuum during peak milk flow period and over milking period was 4.9%(P<0.001)and 10.8%(P<0.001),respectively.Meanwhile,increasing rate of mouthpiece vacuum during peak milk flow period and over milking period were 373.8%(P<0.001)and 53.7%(P<0.001),respectively.There were no significant differences for machine milk yield,average milk flow rate and milking time except logioSCC(P<0.05)between 44 and 48 kPa.The change rate of teat end wall thickness was lower at the lower system vacuum level(44 kPa)after milking,and increased(P<0.05)as the system vacuum level was raised to 48 kPa.The findings of this study indicate that with a lower vacuum level of 44 kPa,the cows are milked better than those with 46 or 48 kPa.The experimental results show that when milk flow threshold of automatic cluster remover was increased from 0.2kg/min to 0.3kg/min,the amount of milk residue increased from 0.12kg to 0.23kg(P<0.001),and milking duration decreased from 6.82min to 6.13min(P<0.001).There was no significant difference in machine milk yield,somatic cell counts and the incidence of clinical mastitis between the two groups.The results show that milking effect was better when milk flow threshold of automatic cluster remover was set to 0.3kg/min,meanwhile,the teat end condtion of dairy herds were better and the number of subhealth dairy cows were less. |
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