in the figures , components which correspond to one another have been given the same reference numerals . in fig1 there is shown a milking plant according to the invention comprising a first milking unit a and a second milking unit b , which are adapted to milk independently of each other . the first milking unit a comprises four teatcups a1 , and a milk conduit a2 , which is connected to the teatcups a1 . the milking unit a further comprises a flow meter a3 , a receiver a4 , a pump a5 and a milk filter a6 , which are connected to the milk conduit a2 in said order , as seen in the milk flow direction . the milk filter a6 is automatically exchangeable for a new milk filter as indicated in fig1 . the second milking unit b comprises four teatcups b1 , a milk conduit b2 , a flow meter b3 , a receiver b4 , a pump b5 and a milk filter b6 , which are connected to one another in the corresponding manner described above in connection with the first milking unit a . downstream of the milk filters a6 and b6 the two milk conduits a2 and b2 are connected to a milk tank 8 via two valves a7 and b7 and connected to two drain conduits a10 and b10 via two drain valves a9 and b9 . a displacement means 12 is adapted to displace the teatcups a1 and the teatcups b1 , respectively , between a milking position i and a stand - by position ii . in fig . i the teatcups a1 are in the milking position i , while the teatcups b1 are in the stand - by position ii . a cleaning device comprises four cleaning cups 13 , which are connectable to teatcups in the stand - by position ii , and a cleaning apparatus 14 , which is connected to the cleaning cups 13 via a cleaning conduit 15 . the cleaning apparatus 14 is connectable to the milk conduit a2 between the milk filter a6 and the valve a7 via a valve 16 , and to the milk conduit b2 between the milk filter b6 and the valve b7 via a valve 17 . the displacement means 12 comprises a holding means 18 , which carries the teatcups a1 , b1 and which is rotatable about a vertical shaft 19 , see fig3 . the teatcups a1 and b1 are arranged in respective rows on opposite sides of the shaft 19 . a control unit 20 is adapted to control a device 21 for connection of the cleaning cups 13 and removal of these from teatcups which are in the stand - by position ii , and to control the displacement means 12 to turn the holding means 18 180 ° about the shaft 19 to switch the teatcups a1 , b1 between the milking position i and the stand - by position ii . in fig3 there is shown the teatcups a1 in their milking position i and the teatcups b1 in their stand - by position ii . the holding means 18 carries the teatcups a1 close to a stall 22 , which is adapted to house one animal 23 at a time for milking of the latter . an automatic milking device 24 has an attachment means in the form of a robot arm 25 , which is adapted to bring teatcups , in this case the teatcups a1 , from the milking position i and attach them to the teats of the animal . for example , the robot arm 25 may be of the type disclosed in ep - b1 - 452 381 . the milking plant according to fig1 and 3 operates in the following manner . when the teatcups a1 are used for milking , the valves 16 and a9 are closed while the valve a7 is open , whereby extracted milk can flow through the conduit a2 via the flow meter a3 , the receiver a4 , the pump a5 and the milk filter a6 to the milk tank 8 . if desired , the milking unit b may be cleaned simultaneously by activating the control unit 20 to control the device 21 such that the latter connects the cleaning cups 13 to the teatcups b1 . then the milk filter b6 is removed from the milk conduit b2 and the valve 17 is opened while the valve b7 is closed . the cleaning apparatus 14 supplies cleaning liquid through the cleaning conduit 15 to the cleaning cups 13 . from the cleaning cups 13 the cleaning liquid is conducted via the teatcups b1 , the flow meter b3 , the receiver b4 , the pump b5 and the valve 17 back to the cleaning apparatus 14 . when the cleaning operation is finished the milking unit b is first drained off by removing the cleaning cups 13 and opening the drain valve b9 . then a new milk filter b6 is fitted in the conduit b2 and the valves 17 and b9 are closed while the valve b7 is opened , whereby the cleaned milking unit b is ready for use . when the milking unit a is to be cleaned the control unit 20 is activated to control the displacement means 12 to turn the holding means 18 180 °, whereby the teatcups a1 are displaced to the stand - by position ii while the teatcups b1 are displaced to the milking position i . now an animal can be milked by means of the milking unit b . after the cleaning cups 13 have been connected to the teatcups a1 and the cleaning apparatus 14 has been connected to the milk conduit a2 by closing the valve a7 and opening the valve 16 , and the milk filter a6 has been removed , the milking unit a can be cleaned in the corresponding manner described above for the milking unit b . fig2 shows a milking plant which is identical to the milking plant according to fig1 except that the displacement means is designed differently and that there is an additional cleaning device . thus , the milking plant according to fig2 has a displacement means 26 , which comprises a holding device 27 carrying the teatcups a1 and b1 in two aligned rows , and a drive means 28 , which is displaceable back and forth between two end positions along a guide rail 29 and which is rigidly connected to the holding means 27 , see fig4 . when the drive means 28 is in one of its two end positions the teatcups a1 are in the milking position i while the teatcups b1 are in a stand - by position iia , and when the drive means 28 is in its other end position the teat cups b1 are in the milking position i while the teatcups a1 are in a stand - by position iib . by means of the device 21 the cleaning cups 13 are connectable to the teatcups b1 , when the teatcups b1 are in their stand - by position iia . said additional cleaning device comprises four cleaning cups 30 , which are connectable to the teatcups a1 , when these are in their stand - by position iib , and a cleaning apparatus 31 , which is connected to the cleaning cups 30 via a cleaning conduit 32 . the cleaning apparatus 31 is connectable to the milk conduit a2 between the milk filter a6 and the valve a7 via a valve 32 . in this case the cleaning apparatus 14 is only connectable to the milk conduit b1 via the valve 17 . a device 33 of the same kind as the device 21 is adapted to connect the cleaning cups 30 to and to remove these from the teatcups a1 , when the teatcups a1 are in their stand - by position iib . a control unit 34 is adapted to control the devices 21 and 33 , and to control the drive means 28 for its displacement along the guide rail 29 between said end positions ( indicated by an arrow in fig4 ). when the teatcups b1 are in their stand - by position iia , as illustrated in fig2 and 4 , the milking unit b can be cleaned by activating the control unit 34 to control the device 21 such that the cleaning cups 13 are connected to the teatcups b1 . the milk filter b6 is removed from the milk conduit b2 and the valve b7 is closed while the valve 17 is opened . when the cleaning operation is finished the milking unit b is drained off and is prepared for milking in the corresponding manner described above for the milking plant according to fig1 and 3 . in case the teatcups a1 are in their stand - by position iib and the milking unit b is utilized for milking , the milking unit a can be cleaned by activating the control unit 34 to control the device 33 such that the cleaning cups 30 are connected to the teatcups a1 . the milk filter a6 is removed and the valve a7 is closed while the valve 32 is opened . when the cleaning operation is finished the milking unit b is first drained off by removing the cleaning cups 30 and opening the drain valve a9 . then a new milk filter a6 is fitted in the conduit a2 and the valves a9 and 32 are closed while the valve a7 is opened , whereby the cleaned milking unit a is ready for use .
a milking plant comprises a stall adapted to house one animal at a time for milking of the animal and a device for automatic milking of the animal in the stall . according to the invention the automatic milking device comprises a first milking unit with teatcups and a second milking unit with teatcups and an attachment means adapted to attach the teatcups of either the first or the second milking unit onto the animal &# 39 ; s teats . during milking , the milking unit which is not used for milking may be cleaned or serviced , in order to be prepared for the next animal to be milked .