The present invention relates to a milking machine comprising at least one teat cup containing a liner for receiving a teat, which liner has an interior milk conducting part and forms with the surrounding wall of the teat cup a pulsation chamber between the teat cup and the liner, and means for subjecting the milk conducting part of the interior of each liner to a pressure being lower than atmospheric pressure, and for subjecting each pulsation chamber to a pulsating pressure varying between a low and a high pressure, which high pressure is higher than the pressure in the interior of each liner. Further, the milking machine comprises means for controlling the respective pressures in the interior of each liner and each pulsation chamber, and a means for indicating the size of the milk flow. During milking the milk flows from the teats in a flow which during an initial first phase of the milking increases to a main flow, during a second phase of the milking amounts to said main flow, and during a terminating third phase of the milking decreases from the main flow. The invention also relates to a method of milking by means of such a milking machine.

Milking machines of this kind are disclosed in US 3 754 532 and GB 1 506 636.

The known milking machine according to US 3 754 532 is arranged to keep the low pressure in each pulsation chamber and the pres¬ sure in the interior of each liner, i.e. in the milk conduc¬ ting part of each liner, substantially higher when the milk flow is less than a predetermined relatively small value than when the milk flow exceeds this flow value. When milking with this machine the teats are subjected to weaker suction forces more careful to the teats during the first milking phase before the milk has started flowing through the teats and during the third milking phase when the milk flow has ceased, than when the milk flows through the teats in a flow exceeding said small value. This is to advantage, since a teat is considerably more

sensitive to external influences when it is empty than -when milk is flowing through it. Hereby the risk of injuring the teats is decreased.

The known milking machine according to GB 1 506 636 operates in a similar way as the machine according to US 3 754 532 but is arranged to keep only the low pressure in each pulsation chamber substantially higher when the milk flow during milking is below a predetermined relatively small value, than when the milk flow exceeds this value. Hereby, each liner does not open completely during the pulsating pressure in each pulsation cham¬ ber when the milk flow is below said small value, which results in that only the tip of each teat is subjected to suction forces while the rest portion of each teat is protected against these.

Thus, the above described known milking machines aim at more careful treatment of the teats during so called dry milking of the latter i.e. when there is no milk flowing through the teats. However, these known machines do not solve the problem of preventing crawling of the teat cups on the teats during the third milking phase when the milk, flow ceases.

During the second milking phase each teat is distended and is in a firm friction engagement with the liner, so that the teat cup is in an intended position on the teat. Howeverj when the milk flow decreases during the third milking phase each teat will be slacker and slacker and its friction engagement with the liner weaker and weaker, whereby the teat tends to be sucked deeper into the teat cup. Thus, each teat cup crawls on the teat towards the udder and thereby causes throttling of the milk conducting interior of the teat close to the udder, so that the milking is made more difficult and the milk flow finally completely ceases in spite of the fact that some milk still remains in the udder.

The object of the present invention is to provide a new milking machine of the present kind, by means of which crawling of each teat cup is counteracted when the milk flow decreases during milking. A further object of the invention is to provide a method of milking by means of such a milking machine so that crawling of each teat cup is counteracted.

These objects are obtained by means of a milking machine of the kind initially stated, which mainly is characterized in that the pressure control means are adapted to control the various pressures in response to the indication means, when this during said third milking phase has indicated that the milk flow has decreased to a predetermined part of the main flow, such that the low pressure in each pulsation chamber is higher than the pressure in each liner, at least during a part of the third milking phase. Hereby, each liner will open only partly during said part of the third milking phase when the low pressure prevails in each pulsation chamber, which means the advantage that the pressure of each liner against its teat will be stronger than that of a completely opened liner, so that the friction engagement of each liner with its teat will be stronger, whereby crawling of each teat cup is counteracted. Because of said stronger pressure of each liner against its teat it is true that the teat canal at the tip of the teat will be somewhat throttled, but this will only result in that the milk flow decreases somewhat so that the milking time is prolonged insignificantly. The main thing is that crawling of each teat cup is counteracted so that the udder is completely emptied.

Another advantage with the milking machine according to the invention is that the risk of having a so called impact is decreased. Impact means that small milk droplets are sucked backwards in a high velocity into the liner when this opens. Such small milk droplets of a high velocity can penetrate the teat canal and give rise to infections. Since according to the

invention each liner is opened only partly during the pulsation . the resulted momentary pressure reduction in the liner below the tip of its teat is decreased, so that milk droplets flowing backwards cannot obtain the same high velocity as in a com- pletely opening liner. Thus, the risk of small milk droplets penetrating the teat canal of each teat is reduced.

Yet an advantage with the milking machine according to the invention is that the teat cups can be designed lighter than conventional teat cups, which facilitates the manual handling of the teat cups when applying and removing them, without increasing the risk of crawling of the teat cups during milking. A conventional teat cup is usually designed exaggeratedly heavy to prevent crawling, but instead the risk of the conventional heavy teat cup falling off the teat during milking is decreased.

A further advantage with the milking machine according to the invention is that when using it for milking of e.g. a cow the teats of the cow are treated more careful than when milking by means of the previously described known milking machines. At least one of the teats of a cow usually terminates earlier to yield milk than the other teats. The first mentioned teat will therefore be dry-milked in an injurious way at least until the other teats terminate to yield milk. By means of the new milking machine such an injuriously dry milking of a teat can be avoided by controlling the liners to open only partly when the milk flow has decreased to a predetermined part of the main flow, e.g. corresponding to about full flow from three of the four teats of the cow. Thus, at presence of dry-milking of at least one of the teats the liners will only open partly, whereby all of the teats are treated carefully.

By the expression "main flow" is intended a flow, the average

value of which during a plurality of pulsation cycles does not substantially deviate from a maximum flow value indicated by the indication means. The size of the main flow usually differs from one animal to another and from one milking occasion to another. However, the above described advantages with the milking machine according to the invention are obtained independently of how big the main flow is at a certain milking occasion, since during the third milking phase the pressure control means are only adapted to control the pressure relation between the interior of each liner and each pulsation chamber in response to the indicating means indicating the size of the milk flow relative to the size of the main flow.

The pressure control means may be adapted to control either only the low pressure in each pulsation chamber, or only the pressure in each liner, or both of these pressures. However, the pressure control means are suitably adapted to increase the low pressure in each pulsation chamber in response to the indication means indicating during the third milking phase that the milk flow has decreased to said predetermined part of the main flow, such that said low pressure exceeds the pressure in each liner.

Preferably, in response to the indication means the pressure control means are in a way known per se adapted to adjust the low pressure in each pulsation chamber during the first milking phase to a first value, when the milk flow from the teats is below a predetermined relatively small flow, and to a second value, when the milk flow at least amounts to said small flow, and during the second milking phase to maintain the low pressure in each pulsation chamber on said second value. In addition, the pressure control means are adapted to maintain the pressure in each liner on a predetermined value at least during the second milking phase and during said part of the third milking phase, which predetermined value of the pressure in each liner is smaller than said first value and bigger than or equal to said

second value. According to the invention the pressure control means are adapted to adjust the low pressure in each pulsation chamber to said first value in response to the indication means indicating during the third milking phase that the milk flow has decreased to said predetermined part of the main flow.

According to an embodiment of the milking machine according to the invention the pressure control means comprise a first ad¬ justing device for adjusting the pressure in each liner, a second adjusting device for adjusting the low pressure in each pulsation chamber, and a control unit connected to the adjusting devices and the indicating means for controlling the adjusting devices in response to indications from the indication means.

The indication means is suitably constituted by a flow sensing member.

The invention also relates to a method of milking by means of the new milking machine, which method mainly is characterized in that during said third milking phase, ^' when the milk flow has decreased to a predetermined part of the main flow, the low pressure in each pulsation chamber is kept higher than the pressure in each liner, during at least a part of the third milking phase.

The invention will be described more closely in the following with reference to the accompanying drawing, in which figure 1 shows an embodiment of the milking machine according to the invention, and figure 2 shows a constitutial diagram for the milk flow Q per time unit t (kg/min) and the pressures P (kPa) in the liners and the pulsation chambers, respectively, per time unit t (minute) during milking by means of the milking machine according to figure 1. In the diagram the low pressure in the pulsation chamber is represented by the graph pu and the pressure in the liner by the graph k.

The milking machine shown in figure 1 comprises a milking means 1 with four teat cups 2, in which liners 3 are mounted (only two teat cups are shown) . Each liner 3 has an interior milk conducting part 4 and forms with the surrounding wall of the teat cup 2 a pulsation chamber 5 between the teat cup 2 and the liner 3. A teat cup claw 6 is connected to the liners via short milk tubes 7, the interior of which communicates with the interior of the liners, and to the teat cups 2 via short pulsation tubes 8, the interior of which communicate with the pulsation chambers 5. Via the teat cup claw 6 the short pulsation tubes 8 are connected in pairs with a long pulsation tube each, 9 and 10, respectively, extending upwards from the teat cup claw 6 to the pulsator 11, which is adapted to reduce the pressure alterna-tely in the pulsation chambers of two pairs of teat cups. Via an adjusting device 12 for adjusting the pressure in the pulsator the pulsator is connected to a conduit 13, the interior of which being subjected to a subpressure produced by a vacuum source not shown.

Via the teat cup claw 6 all of the short milk tubes 7 are connected to a long milk tube 14 extending upwards from the teat cup claw 6 to a milk conduit 15, the interior of which communicates with the vacuum source not shown. In the long milk conduit 14 there is an adjusting device 16 for adjusting the pressure in the conduit 14 and a flow sensing member 17 for sensing the milk flow.

A control unit 18 is connected to the adjusting devices 12, 16 and the flow sensing member 17 through respective control conduits 19, 21 for controlling the adjusting devices 12, 16 in response to sensings from the flow sensing member 17.

The milking machine is operated in the following way:

The teat cups 2 are applied on e.g. a cow to be milked. In the

beginning of the milking during a first phase I the control unit 18 controls the adjusting device 12 so that the pulsator subjects the pulsation chambers 5 with a pulsating pressure varying between a low pressure pi of 58 kPa and a high pressure of 100 kPa, i.e. the atmospheric pressure (fig. 2). The pressure in the pulsation chambers pulsates in a frequency of about 1 pulse/second. At the same time the control unit 18 controls the adjusting device 16 so that the pressure in the milk conducting parts 4 of the liners are kept on a value p2 of 66 kPa, i.e. higher than the low pressure pi in the pulsation chambers 5. Hereby, it is secured that the liners 3 are opened completely during the pulsations, whereby the start up of the milk flow through the teats is facilitated.

When the milk flow has increased to a relatively small value ql of about 0.2 kg/min., which is indicated by the flow sensing member 17, the control unit 18 controls the adjusting devices 12 and 16, so that the low pressure in the pulsation chambers 5 is decreased to a value p3 of 42kPa, while the pressure in the liners 3 is decreased to a value p4 of 50 kPa, i.e. to a value which is higher than the value of the low pressure in the pulsation chambers 5, which secures a complete opening of the liners during the pulsations. In addition to this, the liners are opened relatively fast when each liner is subjected to a pressure difference of 8 kPa between the interior of the liner and the pulsation chamber during each pulsation , which results in that a milk flow of a relatively long duration arises during each pulsation when the liners are open. Now the milk flow increases rapidly to a main flow, the size q2 of which here is supposed to be about 4.5 kg/min. in average. The size of the main flow differs usually from one animal to another . Then, a second phase II of the milking ensues, during which said main flow prevails and the main part of the milk in the udder of the cow is extracted. During phase II the control unit 18 registers the size q2 of the main flow.

After phase II of the milking a third phase III ensues, during which the milk flow decreases from the main flow. When the main flow during phase III has decreased to a predetermined part (here 90 ) of the size of the main flow, the control unit 18 controls the adjusting device 12 so that the low pressure in the pulsation chambers 5 is increased from 42 kPa (p3) to 58 kPa (pi), i.e. to a value which is higher than the value of the pressure in the liners. Hereby the liners are not completely opened during the pulsations, whereby the friction engagement of the liners with the teats will be stronger.

When the milk flow during phase III has decreased to said relatively small value ql of about 0.2 kg/min. the control unit 18 controls the adjusting device 16 so that the pressure in the liners is increased from 50 kPa (p4) to 66 kPa (p2). By this the liners are completely opened during the pulsations, so that the rest of the milk easily can be milked out of the udder and the liners thereafter easily can be removed from the teats manually or by means of an automatic removing device.