A milking system comprising a controlled air inlet valve

Abstract

The present invention relates to a milking system comprising a milkline (1), a plurality of milking units (2) connected to the milkline, and a receiver (3) configured to receive milk from the milking units (2) via the milkline (1). A vacuum system (4) provides a vacuum in the milkline (1) via the receiver (3), and an air inlet valve (6) is configured to introduce an amount of air into the milkline (1). A control unit (7) communicates with a milk level sensor (8, 8') and controls the air inlet valve (6) to provide a steady airflow rate into the milkline (1) in response to the milk level reaching a threshold level (9), wherein the steady airflow rate is configured to maintain a stratified milk flow in the milkline (1).

Description

[0001] A milking system comprising a controlled air inlet valve

[0002] TECHNICAL FIELD

[0003] The present invention relates to a milking system comprising a milkline, a plurality of milking units connected to the milkline, a receiver connected to the milkline and configured to receive milk transported from the milking units to the receiver via the milkline, and a vacuum system configured to supply a vacuum in the milkline via the receiver.

[0004] Each milking unit comprises a plurality of teatcups, which are attached to the teats of a dairy animal, and a long milk tube, which is connected to the milkline, wherein the milk is extracted from dairy animals by means of the vacuum provided in the milking units via the milkline.

[0005] Moreover, for the purpose of cleaning the milkline, after a completed milking session, the milking system comprises a controllable air injector configured to introduce an amount of air into the milkline, wherein a control unit is configured to control the air injector so that a liquid slug is created for a mechanical cleaning action of the milkline.

[0006] BACKGROUND

[0007] WO2021 / 230798 discloses an example of a cleaning arrangement for the milkline. The milkline is connected to a cleaning liquid source, and a controllable air injector is configured to introduce anamount of air into the milkline to produce a slug of cleaning liquid in the milkline. The control unit is configured to control the slug characteristics (velocity and / or length) during a cleaning sequence by controlling the vacuum level supplied by the vacuum system and / or the amount of air introduced by the controllable air injector. A periodic (transient) air admission is provided by the controllable air injector to generate different slug characteristics during different cleaning sequences of the milkline.

[0008] The initially described milking system defines a known set-up of a conventional milking system, wherein each milking unit comprises teat cups, which are (manually) attached to the teats of the dairy animals being milked in the milking system (milking parlour). This set-up may also be utilized in an automatic milking system (AMS) to provide a cost-efficient milk transport in for instance an AMS-batch milking parlour comprising several milking robots, which automatically attaches the teat cups of the milking units.

[0009] The extracted milk enters the milkline and is transported to the receiver by means of gravity, which is achieved by a milkline having a certain slope towards the receiver. The milk transporting capacity of the milkline increases with increased slope on the milkline, which may be in a range of 0.5% to 2%. Current performance standards recommend a milkline slope of at least 1% to ensure efficient milk transport to the receiver and stable vacuum in the milkline during milking.

[0010] It is thereby recommended that the milkline is designed to provide a stratified (slug-free) milk flow towards the receiver in order to provide a stable vacuum level in the milkline and the milking unitsduring milking. The milkline is thereby dimensioned to provide a sufficient upper free space along the milkline to ensure a stable vacuum communication between the receiver and the milking units. Typical design considerations for the milkline include the choice of a sufficiently large diameter and slope based on an intended number of milking units and an average peak milk flow rate of the dairy animals being milked in the milking system.

[0011] However, since the peak milk flow rates of dairy animals tend to increase by more efficient milking techniques and continuous breeding on dairy animals giving higher milk yield and flow, it would be desirable to achieve an increased milk transporting capacity on the milkline without having to increase its diameter and / or slope towards the receiver.

[0012] SUMMARY

[0013] It is an object of the present invention to provide a milking system comprising a milkline exhibiting an improved milk transporting capacity without requiring an increased diameter and / or slope on the milkline towards a receiver.

[0014] The object of the invention is achieved by means of a milking system comprising:

[0015] - a milkline,

[0016] - a plurality of milking units connected to the milkline,

[0017] - a receiver connected to the milkline and configured to receive milk transported from the milking units to the receiver via the milkline,- a vacuum system configured to supply a vacuum in the milkline via the receiver,

[0018] - an air inlet valve configured to introduce an amount of air into the milkline, and

[0019] - a control unit configured to control the operation of the air inlet valve,

[0020] characterized in that the control unit is configured to communicate with at least one sensor for measuring a milk level in the milkline, and that, during milking, the control unit is configured to control the air inlet valve to provide a steady airflow rate into the milkline in response to the measured milk level reaching a threshold level, wherein the steady airflow rate is configured to maintain a stratified milk flow in the milkline.

[0021] Accordingly, the air inlet valve is opened by the control unit to provide the steady airflow rate when the milk level reaches or exceeds the threshold level in the milkline. Conversely, the air inlet valve is closed when the milk level drops and / or remains below the threshold level. The milk transporting capacity is in this way enhanced by increasing the frictional forces that act on the milk surface by the steady airflow rate, which is introduced and flowing over the milk surface in the milkline towards the receiver. The milk transporting capacity of the milkline is thereby increased without requiring an increased diameter and / or slope on the milkline. The characterizing features may also beneficially be used to modify an existing milkline to improve its milk transporting capacity without requiring an investment in a new milkline having a larger diameter and / or slope.The steady airflow rate is configured to maintain a stratified milk flow towards the receiver. Accordingly, the steady airflow rate is configured to avoid a milk slug flow in the milkline during milking. For example, the steady airflow rate is constant over a time period of at least 10 seconds. More preferably, it is constant over a time period longer than 10 seconds, such as at least 20 seconds or at least 30 seconds. Thus, in contrast, it is not a periodic (transient) air admission, which is required for producing liquid slugs for cleaning the milkline. A periodic air admission typically involve an opening time of an air injector in a range of 2 to 5 seconds depending on a diameter and length of the milkline. The air injector for slug cleaning also provides relatively higher air admissions into the milkline in order to create the liquid slug compared to the steady airflow rate from the air inlet valve, which is configured to maintain a stratified milk flow. Thus, the opening time of the air inlet valve is more extended in time and the steady airflow rate is lower in magnitude compared to the periodic air admissions of the air injector for the slug cleaning of the milkline.

[0022] According to an embodiment, the threshold level is in a range of 0.5 to 0.8 of an inner diameter of the milkline. Thus, the threshold level is in the range of 50% to 80% of the inner diameter of the milkline. The initial increase in milk level in itself will improve the milk transporting capacity of the milkline, which is typically more than doubled at a milk level of 0.5 compared to 0.3. Thus, it is neither energy efficient nor necessary to provide the steady airflow rate at milk levels below 0.5 in the milkline. More preferably, the threshold level is in a range of 0.6 to 0.8 of the inner diameter of the milkling. Thus, the threshold level is more preferably in the range of 60% to 80% of the inner diameter of the milkline. Asuitable threshold level for opening the air inlet valve generally depends on the diameter and / or slope of the milkline. Thus, a smaller diameter and / or slope generally requires an earlier opening of the air inlet valve to improve the milk transporting capacity, while ensuring the stratified milk flow and the stable vacuum level in the milkline.

[0023] According to an embodiment, each milking unit comprises a milk flow meter, wherein the at least one sensor for measuring the milk level includes the milk flow meters of the milking units, and the measured milk level is based on the measured milk flow from the milk flow meters of the milking units.

[0024] According to a further embodiment, the at least one sensor for measuring the milk level inside the milkine comprises a milk level sensor, such as a temperature sensor, a float switch sensor, an ultrasonic sensor, an optical sensor, a pressure sensor, a conductivity sensor, or a capacitive sensor, arranged on the milkline.

[0025] A temperature sensor is configured to detect a temperature increase when the milk level reaches the threshold level. A float switch sensor is configured to detect when the milk level reaches the threshold level. Alternatively, an ultrasonic sensor, which emits ultrasonic sound waves to determine a distance between the sensor and the milk surface, may be arranged on the milkline. The emitted ultrasonic sound waves bounce off the milk surface and return to the sensor, whereby the milk level is measured by determining the time taken for the emitted ultrasonic waves to travel back to the sensor. An optical sensor typically uses aninfrared or laser beam to measure the milk level. The optical sensor emits the beam and detects changes in light transmission or reflection caused by the milk level inside the milkline. A pressure sensor measures a pressure excerted by the milk column or level above it. The pressure sensor produces an electrical signal proportional to the pressure, which is converted into a milk level in the milkline. A conductivity sensor is configured to detect a change in conductivity when the milk level reaches the threshold level. A capacitive sensor comprises electrodes that detect changes in capacitance as the milk level rises or falls by one electrode emitting an electrical signal and the other electrode receiving it. When the milk level increases inside the milkline, the capacitance between the electrodes changes, which is detected to measure the milk level in the milkline.

[0026] According to an embodiment, the milk level sensor is arranged on a section of the milkline that exhibits a highest milk level during milking. This is usually a section of the milkline that is proximal to the receiver. Accordingly, the milk level in the milkline tends to be higher at a lower section of the sloping milkline compared to a higher section that is distal to the receiver.

[0027] According to a further embodiment, each milking unit comprises a vacuum adjustment valve, which is configured to reduce the vacuum level in the milking unit during an attachment phase and / or a detachment phase of each milking unit.

[0028] Lowering the vacuum level of each milking unit during the attachment / detachment phase(s) will not only save energy and improve animal welfare, but also reduce an amount of uncontrolledtransient air adminssions into the milkline that risk creating the slug flow condition in the milkline during the milking session and the attachment / detachment of each milking unit.

[0029] An uncontrolled and high air admission through the teatcups of the milking unit may arise during the attachment phase depending on the attachment skills of an operator / milker or an attachment rate of the milking units (time period it takes to attach the teatcups). The amount of uncontrolled transient air adminssions is in this way reduced by lowering the vacuum level locally in each milking unit.

[0030] An efficient milking technique - marketed as DeLaval Flow-Responsive™ Milking - which is developed by the applicant may hereby be utilized in combination with the invention. It adjusts key milking parameters - vacuum and pulsation - during the milking session to reduce the milking time of the dairy animal. The vacuum level in the milking unit is hereby adjusted by the vacuum adjustment valve in response to the milk flow rate of the dairy animal, wherein a higher vacuum level is provided in the milking unit during a high milk flow rate of the dairy animal. The vacuum adjustment valve provides the reduced / low vacuum level during the attachment phase including an initial stimulation phase of the dairy animal, and also reduces the vacuum level once the high milk flow subsides at the end of the milking. Accordingly, the vacuum adjustment valve also provides the reduced / low vacuum level during the detachment phase including a milk sweep phase of the long milk tube, whereafter the vacuum to the milking unit is shut off by the vacuum adjustment valve.According to an embodiment, the control unit is configured to open and / or close the air inlet valve after a predetermined time delay from a point in time when the measured milk level passes the threshold level. The predetermined time delay introduces an inertia into the control of the air inlet valve, which helps reduce a risk of periodic or intermittent air admissions from the air inlet valve if the milk level fluctuates around the threshold level.

[0031] According to a further embodiment, the predetermined time delay is at least 5 seconds, such as in a range of 5 to 10 seconds.

[0032] According to an embodiment, the control unit is further configured to adjust an opening of the air inlet valve and / or adjust the threshold level to a different threshold level in response to a rate of change on the measured milk level during a time period before it reaches the threshold level.

[0033] For instance, if the measured milk level is rising rapidly (exhibits a relative high rate of change) during the time period before it reaches the threshold level, the air inlet valve can be opened immediately (without any time delay) when the measured milk level reaches the threshold level. Additionally, the control unit has the capability to adjust the threshold level to a lower value within the range of 0.5 to 0.8 if the measured milk level rises rapidly.

[0034] According to an embodiment, the milking system comprises means for identifying dairy animals that enter the milking system, wherein the control unit is configured to retrieve historic milking data on the identified dairy animals, and the control unit is further configured to adjust an opening of the air inlet valve and / or adjustthe threshold level to a different threshold level in response to the historic milking data of the identified dairy animals.

[0035] A more predictive control is achieved by using historic milking data from the identified dairy animals (milk flow rates, milk yields and milking times), which may be retrieved from a herd management system. Thus, when several dairy animals with similar or known milk flow rates enter the milking system at any point in time, the control unit may adjust the opening of the air inlet valve and / or the threshold level to for instance a lower / higher threshold level within the range of 0.5 to 0.8 if many of the identified dairy animals exhibit relatively high / low milk flow rates.

[0036] According to an embodiment, the control unit is communicating with a vacuum pressure sensor for measuring a vacuum level in the milkline, wherein the control unit is configured to reduce the steady airflow rate to a lower steady airflow rate or shut off the steady airflow rate by controlling the air inlet valve in response to a fluctuating vacuum level in the milkline.

[0037] A reliable indicator of stratified milk flow is that the vacuum level remains stable in the milkline during milking. A milk slug in the milkline causes a rapid drop in the vacuum level below the stable vacuum level, followed by a quick recovery when the milk slug enters the receiver.

[0038] According to a further embodiment, the fluctuating vacuum level includes a transient vacuum level drop of 2 kPa or more in the milkline.A stable vacuum level is hereby defined as one that does not show transient vacuum fluctuations (drops) of 2 kPa or more in the milkline. The slug flow condition is in this way detected by the vacuum pressure sensor, whereby the air inlet valve is controlled to re-establish the stratified milk flow by reducing or shutting off the steady air flow rate in the milkline.

[0039] The steady airflow rate may be provided by an air inlet valve comprising a fixed orifice that allows air to enter the milkline at a non-variable steady airflow rate. In this case, the control unit shuts off the steady airflow rate by simply closing the air inlet valve. The steady airflow rate may also be provided by an air inlet valve comprising a variable orifice that allows air to enter the milkline at variable steady airflow rates. Thus, this enables the control unit to provide different steady airflow rates depending on the circumstances. In this case, the control unit may re-establish the stratified milk flow by reducing the steady airflow rate to a lower steady airflow rate in the milkline.

[0040] According to a further embodiment, the control unit is configured to reduce or shut off the steady airflow rate by controlling the air inlet valve if a number of transient vacuum level drops reaches a threshold value during milking.

[0041] Occasional milk slugs or transient milkline vacuum level fluctuations of 2 kPa are unlikely to affect the milking performance significantly. However, it is important for the milk flow to remain stratified in the milkline for a majority of the milking time, ideally between at least 90% to 95% of the milking time. Thus, the steady airflow rate should be configured with a duration and a (limited)magnitude so that the milk flow remains stratified in the milkline during milking or during at least 90% to 95% of the milking time. The slug flow condition may however arise - during for instance high milk flows and high milk levels in the milkline, in combination with some uncontrolled air admissions from the milking units - if the steady airflow rate is set too high at such circumstances. The control unit hereby reduces the steady airflow rate to re-establish the stratified milk flow if the number of milk slugs reaches the threshold value during milking.

[0042] A suitable magnitude on the steady airflow rate varies depending on the design, diameter and slope on the milkline, as well as the (peak) milk flow rates of the dairy animals, and / or the number of milking units connected to the milkline. It may also vary depending on more or less uncontrolled amounts of transient air adminssions from the milking units during milking. Such transient air admissions may, as previously mentioned, arise as a result of a milker’s handling of the milking units during attachment, but also due to liner slips and / or milking unit fall-offs during milking. The steady airflow rate (L / min) may be several times higher than a milk flow rate (L / min) in the milkline without giving rise to a milk slug flow. However, it is recommendable to provide a safety margin on the magnitude of the steady airflow rate, such that an estimated / average amount of uncontrolled transient air admissions are allowed without giving rise to the undesired milk slug flow condition.

[0043] A suitable magnitude on the steady airflow rate may be found using design recommendations, flow equations for milklines, and / or routine experiments on a specific milkline design, while providingthe safety margin aimed at avoiding a milk slug flow in the milkline during milking.

[0044] According to an embodiment, the receiver is connected to a first end of the milkline, and the air inlet valve is connected at an opposite second end of the milkline, wherein the plurality of milking units are connected to an intermediate milkline section, which is extening between the receiver and the air inlet valve.

[0045] Thus, during milking, the frictional forces that act on the milk surface by the steady airflow rate will act over the entire milk surface in the milkline.

[0046] According to a further embodiment, the control unit is configured to control a second air inlet valve, which is connected to the intermediate milkline section, to provide a second steady airflow rate into the milkline in response to the milk level reaching the threshold level.

[0047] Accordingly, the milkline is hereby provided with a plurality of air inlet valves. This is beneficial for enhancing the milk transporting capacity of relatively longer milklines. The air inlet valves are hereby (evenly) distributed along a length of the milkline. Thus, the second air inlet valve is preferably situated halfway between the first inlet valve at the second end and the receiver at the first end of the milkline. In this way, the control unit may for instance be configured to open the second air inlet valve when only some of the milking units (closer to the receiver) are milking.According to a further embodiment, the control unit is configured to control the vacuum level supplied by the vacuum system by controlling a vacuum pump to compensate for an opening of the air inlet valve providing the steady airflow rate into milkline.

[0048] BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Fig. 1 is showing an embodiment of a milking system according to the present invention,

[0050] Fig. 2 is showing a vacuum adjustment valve of a milking unit, Fig. 3 is showing a fluctuating vacuum level in a milkline, and Fig. 4 is showing a process running on a control unit of the invention.

[0051] DETAILED DESCRIPTION OF AN EMBODIMENT

[0052] Fig. 1 is showing a milking system according to an embodiment of the invention. The milking system comprises a milkline 1 and a plurality of milking units 2 connected to the milkline 1. Each milking unit 2 comprises teatcups for the milking of a dairy animal.

[0053] The milking system further comprises a receiver 3 connected to the milkline 1 and configured to receive milk transported from the milk units 2 to the receiver 3 via the milkline 1.

[0054] A vacuum system 4 is configured to supply a vacuum level in the milkline 1 via the receiver 3. The vacuum system 4 comprises a vacuum pump 5 and a vacuum line that connects the receiver 3 with the vacuum pump 5. A vacuum level supplied by the vacuumsystem is controlled by controlling the rotation of the vacuum pump 5. The vacuum system 4 is hereby configured to provide a stable vacuum level to the receiver 3 during milking.

[0055] An air inlet valve 6, 6’ is configured to introduce an amount of air into the milkline 1, and a control unit 7 is configured to control the operation of the air inlet valve 6, 6’.

[0056] The control unit 7 is configured to communicate with at least one sensor 8, 8’ for measuring a milk level inside the milkline 1. More precisely, during milking, the control unit 7 is hereby configured to control the air inlet valve 6, 6’ to provide a steady airflow rate into the milkline 1 in response to the measured milk level reaching a threshold level 9. The steady airflow rate from the air inlet valve 6, 6’ is configured to maintain a stratified milk flow in the milkline 1. Thus, the steady airflow rate is configured to avoid a milk slug flow in the milkline 1 during milking.

[0057] The threshold level 9 is in a range of 0.5 to 0.8 of an inner diameter d of the milkline 1 (see also Fig. 2). In the shown embodiment, the threshold level is set to 0.5, but it may also beneficially be set at a higher threshold level, such as in a range of 0.6 to 0.8 of the inner diameter d of the milkline 1. Higher threshold levels 9 may beneficially be used on relatively larger diameters and / or slopes on the milkline 1.

[0058] Each milking unit 2 comprises a milk flow meter 8, wherein the at least one sensor 8, 8’ for measuring the milk level comprises the milk flow meters 8, and the measured milk level in the milkline 1 isbased on the measured milk flows from the milk flow meters 8 of the milking units 2.

[0059] The at least one sensor for measuring the milk level inside the milkine can also comprise a milk level sensor 8’, which is arranged on a section 10 of the milkline 1 that exhibits a highest milk level during milking. This section 10 of the milkline 1 is typically proximal to the receiver 3. It is hereby emphasized that a single milk level sensor 8’ alone can be used to detect when the milk level reaches the threshold level 9.

[0060] The milk level sensor 8’ can for instance be a temperature sensor configured to detect a temperature increase when the milk level reaches the threshold level 9. Alternatively, the milk level sensor 8’ may be a float switch sensor configured to detect when the milk level reaches the threshold level 9. The milk level sensor 8’ may be various types of milk or liquid level sensors, such as an ultrasonic sensor, an optical sensor, a pressure sensor, and / or a capacitive sensor, which is suitably arranged on the milkline section 10 proximal to (near) the receiver 3 that typically exhibits the highest milk level during milking. Thus, as mentioned previously, the milk level in the milkline tends to be higher at a lower section 10 that is proximal to the receiver 3 compared to a higher section of the sloping milkline that is distal to the receiver.

[0061] The receiver 3 is connected to a first end 1’ of the milkline 1 , and the air inlet valve 6 is connected at an opposite second end 1” of the milkline 1, wherein the milking units 2 are connected to an intermediate milkline section extending between the receiver 3 and the air inlet valve 6. Thus, during milking, all of the milking units 2typically supply milk to the milkline 1, whereby the additional frictional forces provided by the steady airflow rate from the air inlet valve 6 will act over the entire milk surface in the milkline 1 to improve its milk transporting capacity.

[0062] Furthermore, the control unit 7 in the shown embodiment is configured to control a second air inlet valve 6’, which is connected to the intermediate milkline section, to provide a second steady airflow rate into the milkline 1 in response to the milk level reaching the threshold level 9. A plurality of air inlet valves is beneficial for enhancing the milk transporting capacity of relatively longer milklines. The air inlet valves 6, 6’ are hereby evenly distributed along a length of the milkline. Thus, the second air inlet valve 6’ in the embodiment is situated halfway between the first inlet valve 6 and the receiver 3. Several air inlet valves 6, 6’ are beneficially provided on longer milklines, and opened sequentially or simultaneously when the milk level reaches the threshold level in the longer milklines.

[0063] The second steady airflow rate from the second air inlet valve 6’ may be equal to the first steady airflow rate from the first air inlet valve 6 or larger / smaller than the first airflow rate from the first air inlet valve 6.

[0064] Furthermore, the control unit 7 in the embodiment can be configured to open the second air inlet valve 6’ alone when only some of the milking units 2 (closer to the receiver) are milking. Thus, it can be beneficial to only open one or the other air inlet valve 6 or 6’ depending on the circumstances. For instance, as mentioned above, the highest milk level is typically in the milklinesection proximal to the receiver 3, wherein the milk tansporting capacity can be raised in this section by only opening the air inlet valve 6’ situated closer to the receiver 3.

[0065] Moreover, the control unit 7 is communicating with a vacuum pressure sensor 12 for measuring a vacuum level in the milkline 1. The control unit 7 is hereby configured to reduce or shut off the steady airflow rate by controlling the air inlet valve 6, 6’ in response to a fluctuating vacuum level in the milkline 1.

[0066] A reliable indicator of a stratified milk flow is that the vacuum level remains stable in the milkline 1 during milking. A milk slug in the milkline causes a rapid drop in the vacuum level below the stable vacuum level, followed by a quick recovery when the milk slug enters the receiver 3. This is detected by the vacuum pressure sensor 12 measuring a fluctuating vacuum level or transient vacuum level drop AP of 2 kPa or more in the milkline (see Fig. 3). The slug flow condition is in this way detected by the vacuum pressure sensor 12, whereby the air inlet valve 6, 6’ is controlled to re-establish the stratified milk flow by reducing or shutting off the steady air flow rate in the milkline 1.

[0067] Fig. 3 is showing a vacuum level P (e.g. in a range of 45 - 49 kPa) in the milkline 1 measured by the vacuum pressure sensor 12. A stable vacuum level is hereby defined as one that does not show vacuum fluctuations or transient vacuum level drops AP of 2 kPa or more in the milkline 1. Stable vacuum level indicates a stratified milk flow in the milkline with proper vacuum communication between the receiver 3 and the milking units 2. In Fig. 3 however, it can be seen that, a first milk slug S1 at time t1 is detected by afirst transient vacuum level drop AP1, which exceeds the 2 kPa limit. As previously mentioned, one or more occasional milk slugs or transient vacuum level drops do not affect the milking performance significantly. But the milk flow should remain stratified in the milkline 1 for a majority of the milking time, ideally between 90% to 95% of the milking time. Thus, in Fig. 3, it can be seen that another second milk slug S2 is detected at time t2 by a second transient vacuum level drop AP2, which exceeds the 2 kPa limit. Furthermore, a third milk slug S3 is detected at time t3 by a third transient vacuum level drop AP3, which exceeds the 2 kPa limit, and a fourth milk slug S4 is detected at time t4 by a fourth transient vacuum level drop AP4, which exceeds the 2 kPa limit.

[0068] The control unit 7 is hereby configured to reduce or shut off the steady airflow rate by controlling the air inlet valve 6, 6’ if a number of transient vacuum level drops AP reaches a threshold value N during the milking session. In the situation shown in Fig. 3, the control unit 7 would attempt to restore the stratified milk flow in the milkline 1 by reducing the steady airflow rate and / or closing at least one of the air inlet valves 6, 6’.

[0069] The vacuum level in the receiver 3 and milkline 1 may drop slightly when any one of the air inlet valves 6, 6’ are opened. The vacuum system 4 itself typically comprises a vacuum regulator that compensates for any vacuum fluctuations or deviations, so that the vacuum level remains stable at a desired vacuum level in the receiver 3. However, the control unit 7 in this embodiment is configured to control the vacuum level supplied by the vacuum system 4 by controlling a speed of the vacuum pump 5 to compensate for the opening and closing of the air inlet valve 6, 6’.In this way the vacuum regulation is more proactive than reactive, because the control unit 7 controls both the air inlet valve(s) 6, 6’ and the vacuum pump 5 of the vacuum system 4. Thus, the control unit 7 will hereby send a control signal to the vacuum pump 5 at the same time as it controls (open / close / adjust) one or both of the air inlet valves 6, 6’ to compensate for the varying conditions.

[0070] Fig. 2 is showing an enlarged portion of a vacuum adjustment valve 11, which is configured to reduce the vacuum level in the milking unit 2 during an attachment phase and / or a detachment phase of its teatcups. The vacuum adjustment valve 11 is connected between the milkline 1 and the long milk tube of the milking unit 2. The vacuum adjustment valve 11 comprises a flexible membrane 11a configured to open / close an adjustable passage 11b arranged between the milkline 1 and the milking unit 2. A control vacuum level Pc is hereby provided to a chamber on a dry section of the flexible membrane 11a to achieve a desired vacuum level in the milking unit 2.

[0071] Atmospheric pressure is provided to the dry section of the flexible membrane 11a to close the passage 11b completely and shut off the vacuum to the milking unit 2. A vacuum level equal to the vacuum level in the receiver 3 (e.g. in a range of 40 - 50 kPa) is provided to the dry section of the flexible membrane 11a to open the passage 11b completely and supply a corresponding vacuum level via the milkline 1 to the milking unit 2. The vacuum adjustment valve 11 is also configured to reduce the vacuum level in the milking unit 2 by providing a control vacuum level Pc (e.g. in a range of 30 - 35 kPa), which is lower than the vacuum level (e.g. 40 - 50 kPa) in the receiver 3. The vacuum adjustment valve11 is in this way controlled to reduce the opening of the adjustable passage 11b, so that the vacuum level is reduced during the attachment / detachment phase.

[0072] The amounts of uncontrolled transient air adminssions is in this way reduced by lowering the vacuum level locally in each milking unit 2. Thus, it reduces the amounts of uncontrolled transient air adminssions into the milkline that risk creating the slug flow condition during the milking session and the attachment / detachment of each milking unit 2.

[0073] Fig. 4 is showing a schematic process running on the control unit 7 in the embodiment of Fig. 1. The control unit 7 is hereby configured to open and / or close the air inlet valve(s) 6, 6’ after a predetermined time delay AT from a point in time when the measured milk level passes the threshold level 9. A start of a milking session initiates the process on the control unit 7, wherein the milk level sensor(s) 8, 8’ provide(s) input on the current milk level in the milkline 1 to the control unit 7. At some point in time, the milk level reaches / passes the threshold level 9, whereby the predetermined time delay AT (e.g. 7 seconds) is triggered before the control unit 7 is authorized to open the air inlet valve(s) 6 and / or 6’. If the milk level thereafter (after 7 seconds) remains at / above the threshold level 9, the control unit 7 will open the air inlet valve(s) 6 and / or 6’ to improve the transporting capacity of the milkline 1. However, if the milk level thereafter (after 7 seconds) has dropped below the threshold level 9, the control unit 7 keeps the air inlet valve(s) 6 and / or 6’ shut.The process is running in a corresponding way on the control unit 7 when the milk level is dropping from a level above the threshold level 9 and the air inlet valve(s) 6 and / or 6’ is / are open. Accordingly, at some point in time, the milk level in the milkline 1 drops / passes the threshold level 9, whereby the predetermined time delay AT (e.g. 7 seconds) is triggered before the control unit 7 is authorized to close the air inlet valve(s) 6 and / or 6’. If the milk level thereafter (after 7 seconds) has risen to a level at / above the threshold level 9, the control unit 7 will keep the air inlet valve(s) 6 and / or 6’ open. However, if the milk level thereafter (after 7 seconds) remains below the threshold level 9, the control unit 7 is authorize to close the air inlet valve(s) 6 and / or 6’ shut.

[0074] Thus, the predetermined time delay AT introduces an inertia into the opening / closing of the air inlet valve(s), which helps reduce the risk of periodic opening / closing or intermittent air admissions from the air inlet valve(s) 6, 6’ if the milk level fluctuates around the threshold level 9. The predetermined time delay AT is hereby preferably at least 5 seconds, such as in a range of 5 to 10 seconds. The process running on the control unit 7 is stopped when the milking session is finished.

[0075] However, the control unit 7 is also configured to adjust an opening of the air inlet valve 6, 6’ and / or adjust the threshold level to a different threshold level 9 in response to a rate of change on the measured milk level during a time period before it reaches the threshold level 9. Thus, as previously mentioned, if the measured milk level is rising rapidly (exhibits a relative high rate of change) during the time period before it reaches the threshold level 9, the air inlet valve may be opened immediately (without any time delay)as soon as the measured milk level reaches the threshold level 9. Moreover, the control unit can also adjust the threshold level to a lower value within the range of 0.5 to 0.8 if the measured milk level rises rapidly. In this way the control unit provides an adaptive control to the milk flow rates in the milking units 2 and milkline 1.

[0076] Moreover, the milking system of Fig. 1 comprises means 13 for identifying dairy animals that enter the milking system, wherein the control unit 7 is configured to retrieve historical milking data 14 on the identified dairy animals, and the control unit 7 is further configured to adjust an opening of the air inlet valve 6, 6’ and / or adjust the threshold level 9 to a different threshold level 9 in response to the historical milking data of the identified dairy animals. A more predictive control is in this way achieved by using the historical milking data from the identified dairy animals (milk flow rates, milk yields and milking times), which is typically retrieved from a herd management system. When several dairy animals with similar or known milk flow rates enter the milking system simultaneously, the control unit 7 may adjust the opening of the air inlet valve 6, 6’ and / or the threshold level 9 to a lower / higher threshold level within the range of 0.5 to 0.8 if many of the identified dairy animals exhibit relatively high / low milk flow rates. The means 13 for identifying the dairy animals typically comprises one or more RFID-readers arranged at the entrance and / or each milking position in the milking system (milking parlour), with the dairy animals being equipped with RFID-tags.

Claims

CLAIMS1. A milking system comprising:- a milkline (1),- a plurality of milking units (2) connected to the milkline (1), - a receiver (3) connected to the milkline (1) and configured to receive milk transported from the milking units (2) to the receiver (3) via the milkline (1 ),- a vacuum system (4) configured to supply a vacuum level in the milkline (1) via the receiver (3),- an air inlet valve (6, 6’) configured to introduce an amount of air into the milkline (1), and- a control unit (7) configured to control the operation of the air inlet valve (6, 6’),characterized in that the control unit (7) is configured to communicate with at least one sensor (8, 8’) for measuring a milk level inside the milkline (1), and that, during milking, the control unit (7) is configured to control the air inlet valve (6) to provide a steady airflow rate into the milkline (1) in response to the milk level reaching a threshold level (9), wherein the steady airflow rate is configured to maintain a stratified milk flow in the milkline (1).

2. The milking system according to claim 1, wherein the threshold level (9) is in a range of 0.5 to 0.8 of an inner diameter (d) of the milkline (1), and more preferably in a range of 0.6 to 0.8 of the inner diameter (d) of the milkline (1).

3. The milking system according to claim 1 or 2, wherein each milking unit (2) comprises a milk flow meter (8), and the at least one sensor (8, 8’) for measuring the milk level comprises the milkflow meters (8), wherein the measured milk level in the milkline is based on the measured milk flows from the milk flow meters (8) of the milking units (2).

4. The milking system according to any one of the preceding claims, wherein the at least one sensor for measuring the milk level inside the milkine (1) comprises a milk level sensor (8’), such as a temperature sensor, a float switch sensor, an ultrasonic sensor, an optical sensor, a pressure sensor, a conductivity sensor, or a capacitive sensor, arranged on the milkline (1).

5. The milking system according to claim 4, wherein the milk level sensor (8’) is arranged on a section (10) of the milkline (1) that exhibits a highest milk level during milking.

6. The milking system according to claim 5, wherein the section (10) of the milkline that exhibits the highest milk level during milking is proximal to the receiver (3).

7. The milking system according to any one of the preceding claims, wherein each milking unit (2) comprises a vacuum adjustment valve (11), which is configured to reduce the vacuum level in the milking unit (2) during an attachment phase and / or a detachment phase of each milking unit (2).

8. The milking system according any one of the preceding claims, wherein the control unit (7) is configured to open and / or close the air inlet valve (6, 6’) after a predetermined time delay (AT) from a point in time when the measured milk level passes the threshold level (9).

9. The milking system according to claim 8, wherein the predetermined time delay (AT) is at least 5 seconds, such as in a range of 5 to 10 seconds.

10. The milking system according to any one of the preceding claims, wherein the control unit (7) is further configured to adjust an opening of the air inlet valve (6, 6’) and / or adjust the threshold level to a different threshold level (9) in response to a rate of change on the measured milk level during a time period before it reaches the threshold level (9).

11. The milking system according to any one of the preceding claims, wherein the milking system comprises means for identifying dairy animals (13) that enter the milking system, wherein the control unit (7) is configured to retrieve historical milking data (14) on the identified dairy animals, and the control unit (7) is further configured to adjust an opening of the air inlet valve (6, 6’) and / or adjust the threshold level (9) to a different threshold level in response to the historical milking data (14) of the identified dairy animals.

12. The milking system according to any one of the preceding claims, wherein the control unit (7) is configured to communicate with a vacuum pressure sensor (12) for measuring a vacuum level in the milkline (1), wherein the control unit (7) is configured to reduce the steady airflow rate to a lower steady airflow rate or shut off the steady airflow rate by controlling the air inlet valve (6, 6’) in response to a fluctuating vacuum level in the milkline (1).

13. The milking system according to claim 12, wherein the fluctuating vacuum level includes a transient vacuum level drop (AP) of 2 kPa or more in the milkline (1).

14. The milking system according to claim 12 or 13, wherein the control unit (7) is configured to reduce or shut off the steady airflow rate by controlling the air inlet valve (6, 6’) if a number of transient vacuum level drops (AP) reaches a threshold value (N) during milking.

15. The milking system according to any one of the preceding claims, wherein the receiver (3) is connected to a first end (1’) of the milkline (1), and the air inlet valve (6) is connected at an opposite second end (1”) of the milkline, wherein the plurality of milking units (2) are connected to an intermediate milkline section extending between the receiver (3) and the air inlet valve (6).

16. The milking system according to claim 15, wherein the control unit (7) is configured to control a second air inlet valve (6’), which is connected to the intermediate milkline section, to provide a second steady airflow rate into the milkline (1) in response to the milk level reaching the threshold level (9).

17. The milking system according to any one of the preceding claims, wherein the control unit (7) is configured to control the vacuum level supplied by the vacuum system (4) by controlling a vacuum pump speed to compensate for the opening and closing of the air inlet valve (6, 6’).

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