Method for cleaning of a milk filter, and milking system for the method

Abstract

A method for cleaning a milk-filtering device (5) in a milking system (1), and a milking system (1) for the method are provided. The milking system comprises a milking device (2), a milk tank (3) for the milk, a milk line (4) for transporting the milked milk from the at least one milking device to the milk tank, and a milk-filtering device (5). The latter is configured to filter the milked milk and has a filter housing (51) containing a filter body (55) with filter ducts (56). The milking system also has a milk filter-cleaning device with a sensor device (60) which measures a sensor value which is indicative of the flow resistance for milk passing through the milk-filtering device, a control unit (54) which controls the milk filter-cleaning device based on the measured sensor value, a cleaning fluid inlet (52), a fluid outlet (53), a valve device (61, 63) controllable by the control unit for flow-connecting the milk-filtering device with either the milk line (4), or the cleaning fluid inlet and the fluid outlet. The method comprises transporting the milk through the milk-filtering device in a first direction, with the sensor device measuring said sensor value, passing cleaning fluid according to one of at least two various counterflow cleaning programs through at least said filter body in a second, opposite direction, depending on the measured sensor value. By making the counterflow cleaning operation dependent on the flow resistance, it is possible to choose a different type of cleaning operation at a certain measured resistance. This results in a savings on resources and may sometimes yield improved cleaning results.

Description

[0001] Method for cleaning of a milk filter, and milking system for the method

[0002] The present invention generally relates to the cleaning of a milk filter.

[0003] More particularly, the invention, in a first aspect, relates to a method for cleaning a milk-filtering device in a milking system. The milking system comprises at least one milking device for milking milk from a dairy animal, a milk tank for storing milk of the milked milk suitable for human consumption, a milk line for transporting the milked milk from the at least one milking robot to the milk tank, and a milk-filtering device. The milkfiltering device is configured to filter the milked milk and comprises a filter housing which is flow-connected with the milk line and contains a filter body with a multitude of filter ducts. In addition, there is a milk filter-cleaning device with a sensor device which repeatedly measures a sensor value which is indicative of the flow resistance for milk passing through the milk-filtering device, in particular a pressure drop across the filtering device, with a control unit which controls the milk filter-cleaning device based on the measured pressure drop, with a cleaning fluid inlet, with a fluid outlet, and with a valve device controllable by the control unit for flow-connecting the milk-filtering device with at least one of the milk line, the cleaning fluid inlet and the fluid outlet. The method comprises transporting the milk through the milk line and the milk-filtering device to the milk tank in a first direction, measuring said sensor value with the sensor device, passing cleaning fluid through at least said filter body in a second, opposite direction.

[0004] Such a method is known from NL2026404A1 , in which a milk filter of a milking device is cleaned in counterflow if a pressure drop measured across the filter exceeds a value.

[0005] In theory, cleaning of said milk filter works well, but it has been found, in practice, to not always be the most suitable cleaning method.

[0006] It is an object of the present invention to provide a method of the kind indicated which makes a more efficient cleaning operation possible.

[0007] The invention achieves this object by means of a cleaning method according to Claim 1 . In this case, the inventors started from the idea that the single threshold value for cleaning does not take into account the various possible causes for exceeding of this threshold value, and that having at least two different counterflow cleaning programs could result in various situations being treated differently and more efficiently. In particular, contamination of the filter may slowly increase due to the fact that, with each milking operation, some dirt or particles in the milk itself are intercepted via the milk passing through the filter. After all, this is the purpose of the filter. Although it is usually customary to start a counterflow cleaning operation of the filter once a threshold has been exceeded, this provides little information, if any, about the cause of the contamination, let alone about the dairy animal involved. By contrast, it is also possible for a dairy animal with mastitis milk or otherwise heavily contaminated milk to be milked. In this case, due to the sometimes significant presence of flakes in the milk or other dirt, the filter will clog up very quickly, and the filter might also clog up quickly to a greater degree than would be the case due to slow contamination by milk of healthy dairy animals, such as when transferring the milk of a single milking operation by pumping. Under such circumstances, it is often the case that an even higher pressure drop, or increase in the latter, is measured than is the case during or after a “normal" milking operation. With such a filter which has become contaminated more quickly and to a greater degree, it has been found to be advantageous to perform a different cleaning program, which can take into account a (possible) cause for the relatively significant pressure drop. For example, it has been found that, for instance, particles of mastitis milk which are associated with a suddenly and / or greatly increasing filter resistance adhere more strongly to the filter body than normal dirt particles, such as bedding material. A standard counterflow cleaning operation would either not clean sufficiently well or cost too much water and the like. Partly for this reason, it is advantageous, according to the invention, to perform at least two different counterflow cleaning programs, depending on the measured sensor value. All this will be explained in more detail below.

[0008] The way in which the counterflow cleaning programs differ from each other is not limited in any particular way. For example, the second counterflow cleaning program, also referred to below as “the second program”, is started immediately once a criterion has been met, such as the measured sensor value exceeding a threshold value or the like, whereas the first counterflow cleaning program, also referred to below as “the first program”, is only started after the milked milk has been transferred by pumping. It is also possible for the second program to be executed using a different cleaning fluid, using different settings, such as pressure and / or temperature for cleaning fluid, using different steps, etc. However, what is important is the fact that the choice of executing the first program or the second program depends on the measured sensor value.

[0009] It is important to note here that, in the context of the present invention, the expression "exceeding a threshold value" is understood to mean that the threshold value, coming from a range of desired values which is associated with correct functioning of the milk filter, passes a threshold value to a range of values which is associated with contamination which is too excessive for the filter to be able to still function correctly. Depending on the type of parameter, it is possible to pass this threshold value both in an upward and in a downward direction. In the case of conventional parameter values, this is equivalent with a rise of the parameter value beyond a limit. However, it is possible to choose a parameter which then rather drops below a threshold value. For the sake of brevity, this "dropping below a threshold value " is also deemed to be covered by the phrasing "exceeding a threshold value", with a "higher threshold value" obviously just meaning a "lower threshold value". All this will immediately be clear to the person skilled in the art from the kind of parameter which is being used.

[0010] Specific embodiments are described in the dependent claims, as well as in the part of the description which follows below.

[0011] In embodiments, a first counterflow cleaning program comprises stopping the flow connection of the milk line and the filter body using the valve device, flowconnecting the cleaning fluid inlet, the filter body and the fluid outlet, and passing cleaning fluid, not being milk, in particular cleaning water, through the filter body, if the measured sensor value lies between a predetermined first threshold value and a predetermined second, higher threshold value. When the first threshold value is exceeded without the second threshold value being exceeded as well, it is assumed that the contamination of the filter has increased in the conventional, slow way, and it is assumed that the cleaning method known per se from the prior art will suffice. With this cleaning method, first the inflow of milk is stopped and then cleaning liquid intended for the purpose is passed through the filter body in counterflow, which cleaning liquid is then discharged, together with the loosened and entrained contamination, via the fluid outlet. This method may per se be realized in a large variety of ways, such as for example the methods which are described in the abovementioned NL2026404A1 , and also in NL2026405A1 and NL2026406A1 .

[0012] The concrete values for the first and second threshold value, respectively, obviously depend on the parameter used, such as pressure drop across the milk filter or filter body, milk flow, time for a litre of filtered milk, etc. In addition, the threshold values in practice depend on the type of milk filter and all kinds of other properties of the milking system. The wishes of the user are also quite important in this matter, since one user may start the cleaning procedure sooner than another, for example because the requirements made on the milk differ, for example for cheese milk. Something similar also applies to the difference between the first and second threshold value. For example, it is possible to choose the second threshold value to be x% "more stringent", such as 25% higher in the case of a pressure drop. Thus, the first threshold value may be 1 .0 bar, and the second threshold value may be 1.25 bars. Alternatively, it is possible to choose a value which is more stringent in an absolute sense, for example a milk flow (through the milk filter) which is 20 litres / minute for the first threshold value and 12 litres / minute for the second threshold value. However, for each of these parameters the person skilled in the art or the user will readily be able to choose values which work well for him / her.

[0013] In particular, said first counterflow cleaning program is started either after transporting the milk which has been milked during said milking of said dairy animal, or after a predetermined threshold time after said transporting of the milk which has been milked during said milking of said dairy animal has started. The variant in which the first counterflow cleaning program is executed after the milked milk has been transferred by pumping will require little explanation. Obviously, the valves in the valve device have to be switched correctly, but otherwise the procedure is straightforward. The variant in which the first counterflow cleaning program is executed after a threshold time has passed, is based on the idea that there may be cases where, due to the state of the filter, pumping off the milk will effectively take too long, or the amount of milk to (still) be pumped off is too large. It is then deemed to be better to interrupt the pumping operation and first try to clean the milk filter using the first counterflow cleaning program.

[0014] In attractive embodiments, a second counterflow cleaning program comprises a milk flushing step of passing milk which has passed through the filter body through the filter body in the second direction and discharging it to the fluid outlet, if the measured sensor value is above said second threshold value, and / or if the measured sensor value changes at least by a predetermined threshold degree within a predetermined period of time. With this second program, it is assumed that the milk filter has become blocked due to specific contamination by the milk of a single dairy animal, such as a mastitis animal, although there may also be other causes, such as an inadequate cleaning operation of very contaminated teats, sucked up dirt due to a milking cup having been kicked off, etc. After all, either the contamination is now so significant that it would actually never occur in case of a normally increasing contamination when transferring the milk of one milking operation by pumping, because a standard cleaning operation would already have been executed during an earlier milking operation, or the contamination has occurred so quickly that it is likewise not the result of a normally increasing contamination. In both cases, the idea is that it is good to immediately initiate a cleaning operation, even if only a part of the milked milk has been transferred by pumping. However, in this case, it is not cleaning liquid which is used, at least not exclusively, but the milk that has passed through the filter body but has not yet reached the filter housing. After all, this milk cannot easily be pumped further, but could be used to try to clean the filter. To this end, this milk, which is sufficiently pure as it has been filtered by the filter, is passed through the filter body in counterflow. This may be achieved, for example, by means of compressed air or, optionally, water or another fluid, in order to carry the milk with the loosened contamination away to the fluid outlet. Thus, the milk that cannot be transported further and processed anyway, can still be put to good use, while at the same time leading to a savings in cleaning fluid. Incidentally, it is not ruled out to use an additional fluid, such as water, besides the filtered milk in order to try to remove the dirt from the filter body. However, it is important that this filtered milk is not first drained off via an outlet, but is actively used during the flushing procedure.

[0015] As has already been indicated for the first counterflow cleaning program, the threshold values are not particularly limited and they may, in practice, readily be chosen by the user / person skilled in the art. This applies to the first and second threshold values mentioned earlier, but also to said threshold degree. For example, the latter is chosen to be an increase in the pressure drop of 0.1 bar in 1 minute, or a flow reduction of 1 l / minute in 5 seconds, but it will be clear that other values are equally possible.

[0016] In particular, as has already been indicated above as an option, the milk flushing step is followed by a subsequent rinsing step passing cleaning fluid, not being milk, in particular compressed air and / or cleaning water, through the filter body in the second direction. This step helps to remove milk residues from the milk-filtering device.

[0017] In particular forms, said second counterflow cleaning program comprises measuring said sensor value again during or after the milk flushing step, and repeating the milk flushing step until the re-measured sensor value meets a stop criterion or until the milk flushing step has been executed a predetermined first number of times, followed by said rinsing step. In this case, it is assessed for each milk flushing step whether the milk filter has been cleaned sufficiently to be able to continue the transfer of the milked milk by pumping. If the measured sensor value does not meet the stop criterion, cleaning of the filter has to be continued. This may be achieved by again passing another portion of the milk to be transferred by pumping through the filter, and by again passing this filtered milk through the filter body in counterflow. In other words, this cleaning step is repeated. It may be repeated until the measured sensor value does meet the stop criterion, or until this milk flushing step has been performed a predetermined maximum number of times. After all, it may be sensible to execute such a milk flushing step when only a small part of the milk to be transferred by pumping contained a significant amount of contaminants, so that the remaining milk is sufficiently pure not to cause the milk filter to clog up again during a milk flushing step, while it makes little sense, if for example the entire batch of milk to be transferred by pumping is highly contaminated, to try to pass the entire amount through the filter in stages, i.e. per milk flushing step. In such a case, a different cleaning method may be opted for. This will be explained in more detail below. Finally, a rinsing step is performed using fluid, for example water. During such a rinsing step, more fluid may be used, so that the cleaning effect of the filtered milk can be amplified in counterflow, while additionally removing contaminated milk residues from the milking system.

[0018] The stop criterion is not particularly limited. In particular, however, said stop criterion comprises that the re-measured sensor value drops to below said first threshold value, more particularly below a third, lower threshold value. If the measured sensor value has dropped below the first threshold value, a situation has again been achieved in which the filter still works without having been excessively clogged up. It may be advantageous to continue flushing until the measured sensor value has improved further, such as dropped below a lower third threshold value, in order thus to have some margin. After all, it does not make a lot of sense to only flush for a sufficiently long time to achieve a value just below the first threshold value, and then to have to flush again after a relatively short period of time. Obviously, other criteria are also possible, for example flushing until the measured sensor value remains below the third threshold value at least for a predetermined time period or for a predetermined amount of litres.

[0019] In a further particular form, said second counterflow-cleaning program comprises repeating said one or more milk flushing steps and said rinsing step until the re-measured sensor value meets said stop criterion or until the milk flushing step has been executed a predetermined total second number of times. In this case, the abovedescribed cycle is repeated one or more times. The reasoning behind this is that the first cycle of milk flushing steps and the rinsing step sometimes may not be able to remove the dirt in the filter body, but may be able to soak it to a sufficient degree to be able to remove it during a subsequent cycle.

[0020] In particular, the second counterflow cleaning program is executed if said sensor value lies above said second threshold value for at least a predetermined first time period or if the measured sensor value increases at least by said threshold degree during a predetermined second time period. In order to prevent that a short, inherently meaningless peak in the sensor value or an increase of the latter immediately results in a cleaning operation, the intention here is to assess the sensor value for a predetermined time period, such as 10 seconds or 3 seconds, respectively, for the first or second time, respectively, even if other values are obviously also possible.

[0021] In embodiments, i.e. in the case where the second counterflow cleaning program is performed, a mastitis alert is generated for the dairy animal from which the milked milk originated. The execution of this second program is caused in a relatively large number of cases by mastitis milk, so that the alert is a relatively efficient measure, even if it is not decisive. If the milking system is provided with a plurality of milking devices and milk of a plurality of dairy animals successively passes through the milk line and thus the milk-filtering device, it is more difficult to indicate exactly which milk of a dairy animal has triggered the mastitis alert. In this case, it is thus alternatively possible to assign a provisional mastitis alert to a group of one or more dairy animals which have been milked during a predetermined time interval before execution of the second counterflow cleaning program and either to pass on this provisional mastitis indication directly based on the measured sensor value, or to only convert the provisional mastitis indication for one or more of the dairy animals of said group into a full mastitis indication for the relevant animal if the second counterflow cleaning program is again performed at the next milking operation within said time interval after milking the dairy animal.

[0022] In embodiments, each of the at least two counterflow cleaning programs comprises a completion step of blowing one or more pulses of compressed air through the milk-filtering device to the fluid outlet. In many variants of both the first program and the second program, water is passed through the milk filter. In order to prevent some of this water which remains behind in the milk filter from ending up in the milk, compressed air is blown through the milk filter and, if desired, other milk-carrying parts.

[0023] It should be noted here that it is effectively true for all methods according to the invention that, if a counterflow cleaning program is executed, be that the first or the second, a choice can be made as to what is to be done with the milked milk which is yet to be transferred by pumping. It is possible not to transfer this milk by pumping, either by temporarily switching off the milk pump to this end, or to keep the milk pump switched on, but to close the flow connection of the milk line from the milk glass with the milked milk to the milk filter, in which case the milk pump will continue to pump, despite the flow connection being closed. The remaining milked milk would then, upon successful cleaning of the milk filter, be able to proceed to the milk tank, to a residual milk collection point, such as a calf milk collection point, or may even, if the cleaning operation has to be continued, be used in the second counterflow cleaning program for the cleaning operation itself. Alternatively, it is also possible to decide to allow the remaining milk to flow away to the fluid outlet, almost always the sewer or a residual milk collection point. This may be favourable, in particular in case the second threshold value was exceeded, because the milk is probably not wanted in the consumption milk tank or even at the residual milk collection point, and this also makes the milking device available more quickly for a next milking operation. On the other hand, this may thus lead to milk being lost which might nevertheless be usable, for example in raising calves. In particular if there was no next dairy animal in line waiting to be milked, this would on balance be a drawback. However, with the present invention, both possibilities are an option.

[0024] In a second aspect, the invention relates to a milking system according to Claim 11 . This milking system comprises at least one milking device for milking milk of a dairy animal, a milk tank for storing milk of the milked milk suitable for human consumption, a milk line for transporting the milked milk from the at least one milking device to the milk tank, and said milk-filtering device which is configured to filter the milked milk and which comprises a filter housing which is flow-connected with the milk line and contains a filter body with a multitude of filter ducts arranged therein. The milking system furthermore comprises a milk filter-cleaning device with a sensor device which repeatedly measures a sensor value which is indicative of the flow resistance for milk through the milk-filtering device, a control unit which controls the milk filter-cleaning device based on the measured sensor value, a cleaning fluid inlet, a fluid outlet, a valve device controllable by the control unit for flow-connecting the milk-filtering device with either the milk line, or the cleaning fluid inlet and the fluid outlet. The milk filter-cleaning device is configured to carry out a method according to the first aspect of the invention. The advantages of such a milking system largely correspond with the advantages as described for the method according to the present invention, so that they do not have to be unnecessarily repeated here.

[0025] In embodiments, said sensor device comprises a pressure drop sensor which measures a pressure drop across the filtering device as said sensor value. Here, the sensor value is a pressure drop, but, as has also been described for the method, other parameters are certainly possible, such as a milk flow meter, etc.

[0026] In embodiments, the milking system comprises a plurality of milking devices, in particular a plurality of milking robots. It should be noted here that the advantages of the present invention can be noted particularly with a milking system having at least one milking robot. After all, in non-robotic systems the milker already checks whether the milk, at least the foremilk, is highly contaminated or not. A visual check for cleanliness of the udder and teats is also already being carried out, so that the risk of a significant amount of contamination is much smaller in these cases. With a robotic milking device, this visual check by a milker is not performed, and quality control often takes place indirectly, such as by means of the sensor device.

[0027] Another relevant aspect is the fact that, if the milking system comprises a plurality of milking devices, it is possible that, while milked milk is being pumped off by a first milking device, a second milking device also starts to pump. In this case, there is a greater risk that the pumping off of the milked milk will take longer than expected, since the milked milk of two or more dairy animals has to be transferred by pumping, which leads to greater resistance in the milk line. If all of this milk is pumped off via one (main) milk line, no differentiation is made between the milk of individual dairy animals. The clogging up of the milk filter may nevertheless play a part in this case. However, the advantages of the present invention also become evident here.

[0028] The type of filter body as such is not particularly limited, except for the fact that it has to be suitable for counterflow cleaning. Thus, milk filter socks, in which the particles to be filtered out are caught in a woven cloth or otherwise spatial structure, are less suitable or unsuitable for counterflow cleaning operation. By contrast, a filter body which comprises a metal plate, in particular a metal pipe, with a multitude of holes as the filter ducts is suitable. Here, the contaminants largely remain behind on the surface of the filter, in particular, but not exclusively, if the filter ducts also widen in the first direction in which milk to be filtered flows through the filter body. Contaminants lying on the surface are relatively easily carried along again by a counterflow cleaning operation. However, alternatives are possible, such as wire filters which comprise a relatively simple woven pattern of metal wires. Details about suitable filters can be found, inter alia, in patent publications NL1044124A1 , NL2026404A1 , NL2026405A1 , NL2028863A1 ,

[0029] NL2028864A1 and NL2028865A1.

[0030] The invention will be explained in more detail below by means of a few exemplary embodiments as well as the drawing, in which:

[0031] - Figure 1 diagrammatically shows a milking system 1 according to the invention; and

[0032] - Figure 2 shows a diagrammatical cross-sectional view of at least a part of the milk-filtering device 5 in greater detail.

[0033] Figure 1 diagrammatically shows a milking system 1 according to the invention. The milking system 1 comprises a milking device 2, a milk tank 3, a milk line 4 and a milk-filtering device 5.

[0034] The milking device 2 here is a robotic milking device with a milking robot 21 with a robot arm 22, a milking cup 23, a milk glass 24, a vacuum pump 25, a milk pump 26 and a milking hose 27. Such robotic milking devices, which are illustrated highly diagrammatically here, are known per se and many details have not been shown here. For example, robotic milking devices for cows comprise four milking cups 23, but for the sake of clarity only one has been drawn.

[0035] In use, the robot arm 22 of the milking robot 21 attaches the milking cup 23 to the teats 101 of the dairy animal 100, such as a cow. The vacuum pump 25 provides a negative pressure by means of which the milk is milked and temporarily stored in the milk glass 24. From there, the milk, if it is suitable for human consumption, is pumped to the milk tank 3 via the milking hose 27, the milk-filtering device 5 and the milk line 4 by the milk pump 26. Moreover, a second milking hose 27' is shown which is connected to a second milking device (not shown here). Both this second milking device and the illustrated milking device 2 do not necessarily have to be robotic milking devices. Also, the number of milking devices may be different, such as a total of one, or, by contrast, more, such as three, four or even more.

[0036] When passing through the milk-filtering device 5, the milk will be filtered, with contaminants being removed from the milk. The milk-filtering device 5 comprises a filter housing 51 , a fluid inlet 52, a fluid outlet 53 and a control unit 54. The milk-filtering device 5 will have to be cleaned regularly to remove contaminants, in order to be able to filter new milk correctly, and in order not to allow the flow resistance to become excessive. The cleaning operation is activated by the control unit 54.

[0037] The cleaning of the milk-filtering device 5 may be effected in many different ways, such as a main cleaning operation, in which the entire milking system 1 is cleaned, wherein hot water and / or cleaning agents are passed through the system 1 , including the milk-filtering device 5. In particular, however, the milk-filtering device 5 may be cleaned by means of a counterflow cleaning operation. In this case, cleaning fluid, such as water, is passed through the filter housing 51 via the fluid inlet 52 in counterflow, and discharged via the fluid outlet 53, often via a sewer. Details relating to the counterflow cleaning operation will be explained by means of the remaining figures.

[0038] Figure 2 shows a diagrammatical cross-sectional view of at least a part of the milk-filtering device 5 in more detail. Similar components have the same reference numerals, if desired provided with one or more accents.

[0039] The milk-filtering device 5 has a filter housing 51 containing a filter body 55 with filter ducts 56 which run from a dirty filter side 57 to a clean filter side 58. Reference numeral 59 denotes a filter core and reference numeral 60 a pressure drop meter.

[0040] The milking hose 27 comprises a first three-way valve 61 with the fluid outlet 53 going towards a sewer 62. The milk line 4 comprises a second three-way valve 63, comprising the fluid inlet 52, to which a water container 64 is connected via a water valve 65 and a water connection, and to which a compressed air container 67 is connected via a compressed air valve 68 and a compressed air connection 69.

[0041] With the normal filtering position, milk will flow through milking hose 27 to the filter housing 51 by means of the illustrated position of the first three-way valve 61 , according to the single arrows. In the filter housing 51 , the milk arrives via the dirty filter side 57 at the filter body 55. This comprises a circular metal pipe that is closed off at the top and the bottom, with filter ducts 56, being holes in the pipe. The holes allow the milk through and block the contaminants, except for the very smallest, depending on the diameter of the holes. The milk then arrives at the clean filter side 58 which is limited in volume by the filter core 59. From there, the filtered milk flows to the milk line 4 via the second three-way valve in the illustrated position, and continues to the milk tank (not shown).

[0042] The milk-filtering device 5 can be cleaned with, for example, a first counterflow cleaning program which is started if the pressure drop meter 60 measures a pressure drop value which is beyond a first threshold value, such as 1 .0 bar, but still below a second threshold value, such as 1.25 bars, during filtering of the milk. Incidentally, the sensors of the pressure drop meter shown here are very close to each other. It is definitely also possible to place the two part-sensors for the pressure upstream of and the pressure downstream of the filter body near or in the entrance or the exit of the filter housing, respectively.

[0043] Counterflow cleaning is in principle not started until the milked milk has passed the milk-filtering device 5. Subsequently, the control unit 54 (not shown) puts the first and second three-way valves in the other position, with fluid being able to flow through the filter housing 51 in counterflow according to the double arrows, via the fluid inlet 52, through the filter body 55 and to the fluid outlet 53, towards the sewer 62. For example, water from the water container 64 is passed through the filter housing 55 by opening the water valve 65. Alternatively, additionally or subsequently, compressed air from the compressed air container 67 may be passed through the filter housing 55 by opening the compressed air valve 68. This may be done in pulses or in an uninterrupted stream. By means of all these measures, as many contaminants in the filter body 55 as possible are carried along and discharged, and water is removed from the milk-filtering device plus the required parts of the milking hose 27 and the milk line 4.

[0044] It is possible for the pressure drop meter 60 to indeed measure a pressure which is between the first and second threshold value, such as 1.1 bar, but that the pumping off of the milked milk takes too long, that is to say longer than a predetermined time which, incidentally, may depend on the amount of milk still to be pumped off. In this case, the control unit infers that the filter body 55 is clogged up to an excessive degree, and will either start said first counterflow cleaning program, even if not all of the milked milk has been pumped off yet, or, alternatively, start the second counterflow cleaning program. This second program is explained below.

[0045] In the above-described case, but in particular if the measured sensor value is higher than the second threshold value, therefore in the example when the pressure drop across the milk filter is greater than 1 .25 bars, and / or if the measured pressure value rises faster than in a threshold degree, the control unit infers a mastitis-like contamination which requires the second counterflow cleaning program to be started. After all, in the latter case, it is clear that (almost) the entire contamination of the filter originates from one dairy animal, with the risk of it coming from mastitis milk being considerable. For example, the pressure drop increases by 0.5 bars within 10 seconds, although other limits are certainly possible.

[0046] In this second counterflow cleaning program, the control unit closes off the milk-filtering device 5 from the milking hose 27 and the milk line 4 by closing the two three- way valves 61 and 63. However, instead of passing water from the water container 64 through the filter body 55 to loosen up the contamination, the filtered milk which is present in the clean filter side 58 is used. It is blown, optionally in a pulsed manner, by means of compressed air from the compressed air container, back through the filter body 55 and discharged via the sewer 62, thus carrying along contaminants. After such a milk-flushing operation, the three-way valves 61 and 63 are switched in such a way that new milked milk can flow through the milk-filtering device 5. At least, the sensor value is measured again. If it is still too high, that is to say at least greater than the second threshold value, but also, for example, not yet dropped sufficiently, such as to below a third threshold value, such as 0.5 bars or the like, the milk-flushing operation of the second counterflow cleaning program is repeated. After all, filtered milk has again remained behind in the clean filter side 58 which can be flushed through the filter body 55 again. If the contamination was indeed caused by mastitis milk, which contamination adheres more strongly to the filter body 55, the risk of the operation having to be repeated one or more times is significant. Incidentally, the control unit may in this case generate a mastitis alert for the dairy animal whose milked milk caused the contamination. It is true that mastitis is not yet a certainty, but the probability is relatively large. Should the milk-flushing operation not lead to the desired result in terms of sensor value once it has been executed a predetermined number of times, such as five times, then a counterflow cleaning operation with water, or optionally another cleaning fluid, such as hot water or water with cleaning agent, is then performed nevertheless, as described for the first counterflow cleaning program. Finally, any cleaning fluid which may have remained behind is blown away with compressed air from the compressed air container 67.

[0047] If desired, a milk-flushing operation may then be performed again one or more times, followed by a blowing operation, until the pressure drop comes down to below the desired value, or until the total number of milk-flushing operations has reached a predetermined maximum number. In the latter case, automatic cleaning is evidently not sufficiently successful, and the control unit will emit an alarm signal.

[0048] Flushing with milk in the second counterflow cleaning program saves cleaning fluid and actually uses milk which could not be pumped to the milk tank anyway. The invention is not limited to the illustrated embodiments. Rather, the scope of protection is defined by the attached claims.

Claims

CLAIMS1 . Method for cleaning a milk-filtering device in a milking system, which milking system comprises at least one milking device for milking milk from a dairy animal, a milk tank for storing milk of the milked milk suitable for human consumption, a milk line for transporting the milked milk from the at least one milking device to the milk tank, and said milk-filtering device which is configured to filter the milked milk and which comprises a filter housing which is flow-connected with the milk line and contains a filter body with a multitude of filter ducts, furthermore comprising a milk filter-cleaning device with:- a sensor device which repeatedly measures a sensor value which is indicative of the flow resistance for milk passing through the milk-filtering device, in particular a pressure drop across the filtering device,- a control unit which controls the milk filter-cleaning device based on the measured sensor value,- a cleaning fluid inlet,- a fluid outlet,- a valve device controllable by the control unit for flow-connecting the milk-filtering device with either the milk line, or the cleaning fluid inlet and the fluid outlet, wherein the method comprises:- transporting the milk through the milk line and the milk-filtering device to the milk tank in a first direction,- measuring said sensor value with the sensor device,- passing cleaning fluid through at least said filter body in a second, opposite direction, according to one of at least two different counterflow cleaning programs, depending on the measured sensor value.

2. Method according to Claim 1 , wherein a first counterflow cleaning program comprises stopping the flow connection of the milk line and the filter body using the valve device, flow-connecting the cleaning fluid inlet, the filter body and the fluid outlet, and passing cleaning fluid, not being milk, in particular cleaning water, through the filter body, if the measured sensor value lies between a predetermined first threshold value and a predetermined second, higher threshold value.

3. Method according to Claim 2, wherein said first counterflow cleaning program is started either after transporting the milk which has been milked during said milking of said dairy animal, or after a predetermined threshold time after said transportingof the milk which has been milked during said milking of said dairy animal has started.

4. Method according to one of the preceding claims, wherein a second counterflow cleaning program comprises:- a milk flushing step of passing milk which has passed through the filter body through the filter body in the second direction and discharging it to the fluid outlet, followed by- a rinsing step of passing cleaning fluid, not being milk, in particular cleaning water, through the filter body in the second direction; if the measured sensor value is above said second threshold value, and / or if the measured sensor value changes at least by a predetermined threshold degree within a predetermined period of time.

5. Method according to Claim 4, wherein said second counterflow cleaning program comprises measuring said sensor value again during or after the milk flushing step, and repeating the milk flushing step until the re-measured sensor value meets a stop criterion or until the milk flushing step has been executed a predetermined first number of times, followed by said rinsing step.

6. Method according to Claim 5, wherein said stop criterion comprises that the re-measured sensor value has dropped below said first threshold value.

7. Method according to Claim 6, wherein said second counterflow cleaning program comprises repeating said one or more milk flushing steps and said rinsing step until the re-measured sensor value meets said stop criterion or until the milk flushing step has been executed a predetermined total second number of times.

8. Method according to one of Claims 4-7, wherein the second counterflow cleaning program is executed if said sensor value lies above said second threshold value for at least a predetermined first time period or if the measured sensor value increases at least by said threshold degree for a predetermined second time period.

9. Method according to one of Claims 4-8, wherein a mastitis alert is generated for the dairy animal from which the milked milk originated.

10. Method according to one of the preceding claims, wherein each of the at least two counterflow cleaning programs comprises a completion step consisting of blowing one or more pulses of compressed air through the milk-filtering device to the fluid outlet.11 . Milking system comprising at least one milking device for milking milk from a dairy animal, a milk tank for storing milk of the milked milk suitable for humanconsumption, a milk line for transporting the milked milk from the at least one milking device to the milk tank, and said milk-filtering device which is configured to filter the milked milk and which comprises a filter housing which is flow-connected with the milk line and contains a filter body with a multitude of filter ducts, furthermore comprising a milk filter-cleaning device with:- a sensor device which repeatedly measures a sensor value which is indicative of the flow resistance for milk passing through the milk-filtering device,- a control unit which controls the milk filter-cleaning device based on the measured sensor value,- a cleaning fluid inlet,- a fluid outlet,- a valve device controllable by the control unit for flow-connecting the milk-filtering device with either the milk line, or the cleaning fluid inlet and the fluid outlet, wherein the milk filter-cleaning device is configured to carry out a method according to one of the preceding claims.

12. Milking system according to Claim 11 wherein said sensor device comprises a pressure drop sensor which measures a pressure drop across the filtering device as said sensor value.

13. Milking system according to Claim 11 or 12, comprising a plurality of milking devices, in particular a plurality of milking robots.

14. Milking system according to one of Claims 11 -13, wherein the filter body comprises a metal plate, in particular a metal pipe, with a multitude of holes as said filter ducts.

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