For many years now, the progress made in the field of mechanization and automation have enabled breeders specialized in milk production to improve their working conditions and their animals' production.
In addition to the automatic milking devices which have been in use for a long time now, there are also devices for the automatic identification of the animals, milk meters for measuring the production of each animal, which meters can also control the automatic release of the milking cups of the milking machine, automatic milk sampling devices which are combined with the milk meters, and concentrated fodder automatic supplying devices for dispensing to the animals the balanced milk-producing rations that they need.
However, there is at least one operation which still has to be perfomed by hand: that is the positioning of the milking cups of the milking machine on the animal' teats. A device which automatically performs this operation would eliminate the compelling need for a person to be present in the milking parlor twice a day, every day of the year.
It has also been found that the animals' production increases if they are milked every time they come up to a fodder dispensing station. A complete automatization of the milking would make it possible to conduct four to five milkings a day on each animal, which is of course impossible, from a practical and economical point of view, when some of the operations have to be performed by hand.
Devices for the automatic positioning of the milking cups have been proposed. Reference can be made in particular to the following patents or patent applications: US-4,010,714, GB-2 007 486, EP-0 091 892, WO-85/02973, EP-0 188 303 and EP-0 202 202.
These known devices are generally combined with stalls in which the animals are kept throughout the milking operation and where they are automatically fed with fodder.
In the devices described in documents US-4 010 714 and WO-85/02973, the positions of the milking cups are adjusted as a function of pre-recorded information relative to the animals' teats. Yet it is impossible to guarantee a good positioning of the teats every time, because the immobilization of the animal in the stall even with restraining means such as inflatable cushions being used (US-4 010 714), is not sufficient to ensure exact reproduction of the teats coordinates from one milking operation to another, and this, not only for different animals, but also for the same animal, due to morphology variations during lactation, from one day to another and also between two milkings.
This drawback may be overcome by measuring the position of the tests of each animal entering the stall, as proposed in documents EP-0 091 892, EP-0 188 303 and EP-0 202 202. To this effect, a position sensor, using for example, an ultra-sound transmitter-receiver system, is mounted on a support fixed on the end of movable arm and equipped with four milking cups of which the positions on the support are adjustable. There are various drawbacks in this arrangement, due to the overall dimension of the support and to the risk that the sensor can be damaged by the animal.
The same drawbacks due to overall dimensions are also found with other known devices which, likewise, use a single support for all the milking cups, such as for example the devices described in the above cited documents US-4 010 714 and WO-85/02972. The bulkiness is due not only to the fact that the movable support carries the four milking cups, but also to the fact that said support must also carry the means necessary for individually moving each milking cup with respect to the support in at least two directions. Because of such overall dimensions, the aforementioned known devices provide means for holding the animal in a position in which the support can be brought near the tests without any hindrance, said means consisting in raising the middle part of the stall floor. However, as a result, the animal is held in a strained and uncomfortable position.
Other devices have been proposed in which a single control arm is used for positioning the milking cups on the teats, one by one and successively, as described in documents GB-2 007 486 and EP-0 091 892. In such devices, the control of the arm raises problems which are difficult to solve in order to reach the teats of the animals, from one spot where the milking cups are stored, without interfering with the milking cups already in position and with the tubes to which said cups are connected. Also, time may be lost, and this is liable to affect hormonal secretion which is short-lasting, when milking cups have to be replaced on the teats after being accidentally knocked off, for example by a kick; indeed, in order to fit back a milking cup which has dropped off, it may be necessary to remove all the cups still in position, hence provoking an interruption in the milking process.
The production of devices which makes it possible to know exactly the positions of the animals' teats, and to readily position the milking cups on the teats without excessive discomfort for the animal, is not only technically difficult, it must also provide an acceptable compromise between, on the one hand, the reliability and strength of such devices, and on the other hand, their cost. On this point, it has been proposed in document EP-0 091 892 to serve a plurality of stalls with a single robot, but the difficult access to the teats may make it necessary for the robot to come so close to the animal that a kick from the latter could damage it.