WO2010028912A2

WO2010028912A2 - Gripper device, robot arm, milking robot and method

Info

Publication number: WO2010028912A2
Application number: PCT/EP2009/059950
Authority: WO
Inventors: Sten Mellberg
Original assignee: Delaval Holding Ab
Priority date: 2008-09-10
Filing date: 2009-07-31
Publication date: 2010-03-18
Also published as: WO2010028912A3

Abstract

The invention relates to a gripper device (1) mountable on a robot arm (10) of a milking robot (13) provided for automatically attaching teat cups (11) to the teats of a milking animal. The gripper device (1) comprises an electromagnet (2) for gripping teat cups (11) comprising a magnetic material. The gripper device 1 is characterised by means (7, S1, S2, S3, S4); (14) for demagnetizing the electromagnet (2) thereof. The invention also relates to a method for releasing a teat cup held by the gripper device (1) and to a milking robot and a robot arm comprising the gripper device.

Description

Gripper device, robot arm, milking robot and method

Field of the invention

The present invention relates generally to the field of animal arrangements, and in particular to means for automatically attaching teat cups to the teats of the animal.

Background of the invention

International patent publication W02005/122753 (DELAVAL) discloses a gripper device mountable on a robot arm of a milking robot used e.g. for automatically attaching teat cups to the teats of a milking animal. The gripper device comprises an electromagnet for gripping teat cups made of a magnetic material. The electromagnet comprises a coil fed with a current and a core of a magnetic material arranged within the coil. The core of the electromagnet comprises two end portions constituting different poles of the electromagnet and having a shape that enables a close fit between the two end portions and a teat cup .

The gripper device of the above-described publication attaches firmly to the teat cups and the teat cups are held in a very steady grip. In fact, the electromagnet of the gripper device is arranged in such a close fit with the teat cup and holds it so firmly that it may occasionally be difficult to release the teat cup from the gripper device.

In an effort to facilitate the release of the teat cup, the gripper device can be arranged in a less close fit. In particular, the gripper device can be designed so that there is provided some space between the electromagnet of the gripper device and the teat cup. The teat cup is thereby released more easily. However, the lessened fit between the gripper device and the teat cup, although facilitating the release thereof entails the risk of the teat cups being unintentionally released.

The lessened gripping strength can then be increased by providing the electromagnet with a higher voltage, however at the cost of an increased power consumption and increased generation of heat.

Summary of the invention

The close fit of the earlier mentioned WO-publication is thus desirable in order to provide a reliable grip of the teat cup. It has been noted by the inventor of the present application that the close fit causes a remanence in the gripper device, which in turn provides a remaining gripping strength even after the current has been turned off. This remanence thus leads to the above-mentioned difficulties of releasing the teat cups. If the fit between the gripper device and the teat cup is less close, as described above, the remanence does not become as pronounced and does not affect the release of the teat cup.

In view of the above, it would be desirable to provide a gripper device, wherein the close fit and resulting firm grip is maintained, while the release of the teat cup is improved.

It is an object of the invention to provide such gripper device. In particular, it is an object of the invention to provide a gripper device enabling a close fit to the teat cup, thereby providing a firm grip, and still having quick and reliable release of the teat cups.

These objects, among others, are achieved by a gripper device and by a method as claimed in the appended independent claims. In accordance with the invention, a gripper device mountable on a robot arm of a milking robot is provided. The milking robot is provided for automatically attaching teat cups to the teats of a milking animal . The gripper device comprises an electromagnet for gripping teat cups comprising a magnetic material. The gripper device is characterised by means for demagnetizing the electromagnet thereof. Ey means of the invention, a close fit between the gripper device and a teat cup is enabled while still providing a reliable and quick release of the teat cup. The automatic milking of an animal is thus rendered more reliable in that the teat cups are held in a firm grip by the gripper device during milking and they are released swiftly and reliably upon termination of the milking.

In accordance with an embodiment of the invention, the means for demagnetizing comprises an electrical circuit for reversing the current provided to the electromagnet. The electrical circuit may for example comprise an H-bridge and components readily available on the market may thus be utilized for implementing the invention, providing an easily implemented improvement of the release of teat cups.

In another embodiment of the invention, the electrical circuit is arranged to reverse the current several times when the release of the gripper device is to be performed. A most reliable demagnetization is thereby accomplished rapidly.

In accordance with still another embodiment of the invention, the means for demagnetizing comprises a mechanical device arranged for enabling mechanical demagnetizing of the gripper device. Preferably, the mechanical device is arranged to hammer the electromagnet of the gripper device, thereby accomplishing the demagnetization.

In accordance with yet another embodiment of the invention, the electromagnet comprises a coil and a core. The core in turn comprises two end portions constituting different poles of the electromagnet. The two end portions are preferably- shaped to be engagable with the teat cups in a close fit . A very firm grip is thereby enabled.

The invention also relates to a robot arm comprising the gripper device, and to a milking robot comprising the robot arm. Further, the invention relates to a method for releasing a teat cup, whereby advantages corresponding to the above are achieved.

Further features and advantages thereof will become clear upon reading the following detailed description.

Brief description of the drawings

Figure 1 illustrates a gripper device in accordance with the invention.

Figure 2 illustrates an electromagnet of the gripper device of figure 1.

Figure 3 illustrates an example of an electrical circuit for accomplishing demagnetization in accordance with the invention.

Figure 4 illustrates the gripper device in accordance with the invention arranged on a robot arm of a milking robot.

Figure 5 illustrates steps of a method in accordance with the invention.

Detailed description of embodiments of the invention

Figure 1 illustrates a gripper device in accordance with the invention. The gripper device 1 comprises an electromagnet 2 arranged in a support structure 3. The support structure 3 in turn comprises attachment means 4a, 4b for connection to a robot arm (illustrated in figure 4) . Alternatively, the support structure is an integral part of the robot arm.

With reference to figure 2, the electromagnet 2 is illustrated in a schematic top view. The electromagnet 2 comprises a coil 5 consisting of a number of turns. The ends of the coil 5 are connected, respectively, to a positive and a negative pole of a power supply 6 , the power supply 6 thereby providing current to the coil 5. Although shown as a DC power source, the power supply 6 could alternatively be an AC power source. A controllable switching device 7 is also provided for switching the current on and off, which will be described more in detail later.

The electromagnet 2 further comprises a core 8 of a magnetic material, e.g. iron or steel, arranged at least partly within the coil 5.

The core 8 has a substantially E-shaped cross section with three parallel legs 8a, 8b, 8c, wherein the coil 5 is arranged around the middle leg 8b. The end portion of the middle leg 8b constitutes a pole of the electromagnet 2, and the two outer legs 8a, 8c constitute the other pole of the electromagnet 2.

The dashed line schematically illustrates a surface part of the teat cup to be held by the gripper device 1. Surface parts of the three parallel legs 8a, 8b, 8c that face the same direction are shaped so as to be engagable with the teat cup in a close fit. As the teat cups are essentially circular, having a circular outer surface, the surface parts of the parallel legs 8a, 8b, 8c that are to grip the teat cup, each have a shape conforming to the circular shape. The surfaces are thus arched and concave .

It is realised that the electromagnet 2 and its core 5 may have alternative designs, the core for example having U-shaped or C-shaped cross sections. In this regard, reference is made to the earlier mentioned international patent publication WO2005/122753, assigned to the same applicant as the present application.

As mentioned, it has been found that there may occasionally be difficulties in the release of the teat cup. The reason for the difficulties is remaining magnetism, known as remanence, in the electromagnet 2. The atomic dipoles of the core 8 material align themselves with the external magnetic field generated when a current is led through the coil 5 of the electromagnet 2. Ceasing of the current flow to the coil 5 will normally eliminate the magnetic field. However, even when the external field is removed, part of the alignment will be retained and thus causes the remaining or residual magnetization. This residual magnetization may then cause difficulties at the release of the teat cups.

In accordance with the invention, possible residual magnetism of the electromagnet 2 is cancelled.

In a first embodiment, an electrical circuit for reversing the current is provided. The above-described magnetic dipoles of the core 8 are aligned along the direction of the magnetic field applied for enabling the gripping of the teat cups. When the direction of the magnetic field is changed, the magnetic dipoles will try to switch direction. When the magnetic field is sufficiently high, most of the magnetic dipoles align themselves along this field. However, when the magnetic field is reduced and reversed, there will be magnetic dipoles that do not change direction. Therefore, by reversing the magnetic field repeatedly and by reducing the magnetic field strength, the remaining magnetism can be eliminated.

Figure 3 illustrates an embodiment of the invention, for accomplishing the above-described demagnetization. In particular, an alterable magnetic field is created by- reversing the current from the power source 6. The switching device 7 of figure 2 is therefore an electrical circuit able to perform a polarity reversal . In particular, a conventional H-bridge circuit may be utilised, comprising four switches Sl, S2, S3, S4. When the switches Sl and S4 are closed and switches S2 and S3 open, a positive voltage is applied across the coil 5. By opening switches Sl and S4 and closing switches S2 and S3, the voltage and hence the current will be reversed. The electromagnetic field will then also be reversed and the magnetic dipoles of the core 8 will try to switch direction.

When the teat cup is to be released from the gripper device 1, the switches Sl, S2, S3, S4 are closed and opened so as to reverse the current a number of times in the above-described scheme. A single reversal could be enough for some applications, but depending on e.g. the strength and duration of the magnetic field that is applied, the amount of remanence of the electromagnet 2 may be higher or lower. Therefore, a control device, schematically indicated at reference numeral 9, controlling the attachment and release of the teat cup is preferably set to reverse the current repeatedly, for example 5 times with reduced time intervals between the reversals.

In another embodiment of the invention, the electromagnet is demagnetized by mechanical means. The electromagnet may for example be hammered on or vibrated so as to demagnetize it. Such hammering can be accomplished by any suitable mechanical means arranged close to the electromagnet 2, schematically illustrated at reference numeral 14 in figure 4. The mechanical means 14 may for example be arranged on the attachment means 4a, 4b or on the support structure 3 of the electromagnet 2. It is to be noted that the switching device 7 may comprise other known demagnetization circuits or means to be utilized for accomplishing the desired demagnetization.

Figure 4 illustrates the gripper device 1 arranged on a robot arm 10 of a milking robot 13. The milking robot 13 is arranged in or close to a milking station 15, into which a milking animal enters in order to be milked. The control device 9 controls the milking robot 13, for example the attachment and release of the teat cups 11, and also the operation of the milking machine and opening and closing of gates, etc. It is noted that the gripper device 1 may as well be used for gripping other milking related equipment, comprising a magnetic material, for example teat cleaning cups 12.

In another aspect of the invention, a method 20 is provided for releasing a teat cup 11 held by the gripper device 1 as described above. The method 20 comprises the first step 21 of demagnetizing the electromagnet 2 of the gripper device 1.

Thereby the magnet coupling between the teat cup 11 and the gripper device 1 is reliably removed. In a second step 22 of the method, the teat cup 11 is released. The release is made reliably and quickly as soon as the demagnetizing step is completed.

The step 21 of demagnetizing can be performed in different ways. In a first embodiment, the electromagnet 2 is supplied with a current from the power source 6. When the teat cup 11 is to be released, the polarity of the current is reversed and the new current direction is used during a predetermined period of time. The step of reversing the current can be repeated a number of times. The current reversal can be performed with shorter and shorter time intervals.

As an example of the above, the current can be reversed five times with the time interval between two consecutive current reversals being shortened by e.g. 10 ms each time. However, it is noted that this is just one example, the number of polarity- reversals and time intervals between the reversals can be chosen in dependence on the duration and strength of the magnetic field applied on the electromagnet 2, on the type of core 8 of the electromagnet 2, on the material being magnetized etc.

In a second embodiment, the step of demagnetizing the electromagnet 2 is accomplished by hammering on the electromagnet 2 by a mechanical hammering device 14.

Claims

1. A gripper device (1) mountable on a robot arm (10) of a milking robot (13) provided for automatically attaching teat cups (11) to the teats of a milking animal, said gripper device (1) comprising an electromagnet (2) for gripping a teat cup (11) comprising a magnetic material, characterised by means (7, Sl, S2, S3, S4 ; 14) for demagnetizing said electromagnet (2) .

2. The gripper device (1) as claimed in claim 1, wherein said means (7, Sl, S2, S3, S4) for demagnetizing comprises an electrical circuit (Sl, S2 , S3, S4) arranged to reverse the current provided to said electromagnet (2) .

3. The gripper device (1) as claimed in claim 2, wherein said electrical circuit (Sl, S2, S3, S4) is arranged to reverse the current several times when release of said gripper device (1) is to be performed.

4. The gripper device (1) as claimed in claim 2 or 3 , wherein said electrical circuit (Sl, S2 , S3, S4) comprises an H- bridge .

5. The gripper device (1) as claimed in claim 1, wherein said means for demagnetizing comprises a mechanical device (14) arranged for enabling mechanical demagnetizing of said gripper device (1) .

6. The gripper device (1) as claimed in any of the preceding claims, wherein said electromagnet (2) comprises a coil (5) and a core (8) , and wherein said core (8) comprises end portions (8b; 8a, 8c) constituting different poles of said electromagnet (2) .

7. The gripper device (1) as claimed in claim 6, wherein said end portions (8b; 8a, 8c) are shaped to be engagable with said teat cup (11) in a close fit.

8. A robot arm (10) comprising a gripper device (1) as claimed in any of claims 1-7.

9. A milking robot (13) comprising a robot arm (10) as claimed in claim 8.

10. A method (20) for releasing a teat cup (11) held by a gripper device (1) as claimed in any of claims 1-7, characterized by a step (21) of demagnetizing said electromagnet (2) of said gripper device (1) , after which said teat cup (11) is released (22) .

11. The method as claimed in claim 10, wherein said step (21) of demagnetizing said electromagnet (2) comprises reversing a current provided to a coil (5) of said electromagnet (2) .

12. The method as claimed in claim 11, wherein said step (21) of reversing the current is repeated a number of times.

13. The method as claimed in claim 10, wherein said step (21) of demagnetizing said electromagnet (2) comprises hammering said electromagnet (2) by means of a mechanical device (14) .