METHOD AND DEVICE FOR MONITORING THE WETTING HEIGHT OF A MIXING CUP

Description

[0001] The present invention relates to a method for monitoring the wetting height of a mixing bowl in a centrifugal mixer.

[0002] To mix different media, centrifugal mixers, also called rotary mixers or planetary mixers, are used in the state of the art. In these mixers, a mixing bowl filled with media is rotated around two diagonally running axes of rotation according to the principle of the dual asymmetric centrifuge. The double rotation of the mixing bowl (usually in opposite directions) enables particularly efficient production of bubble-free, homogeneous mixtures of media, for example, adhesives, sealants, powders, etc. This process can also be carried out under vacuum in order to degas the media or the mixed medium simultaneously during mixing. The two counter-rotating rotations, i.e.A rotation of the mixing bowl about its own axis and an additional rotation of the mixing bowl about another axis of rotation, which in particular runs obliquely to the first axis of rotation, typically occurs in the prior art with a predetermined fixed ratio of the rotational speeds, for example, 3:1. In this case, a common drive can be used that effects both rotational movements via a gear.

[0003] With such known centrifugal mixers, one problem is that excessively high rotation speeds can cause medium to escape from the interior of the mixing bowl. On the other hand, it is desirable to provide the highest possible rotation speeds for thorough mixing, but this, in turn, entails the risk of medium escaping from the mixing bowl.

[0004] Document US 2021 / 086153 A1 discloses a method for monitoring a mixing bowl in a centrifugal mixer, and a device according to the preamble of claim 6.

[0005] It is therefore the object of the present invention to provide a method for monitoring the wetting height of a mixing cup in a centrifugal mixer, with which the mixing of media can be optimized and leakage of medium from the mixing cup can be reliably prevented.

[0006] This object is achieved by a method having the features of claim 1. In this method, the wetting height of a mixing bowl in a centrifugal mixer is monitored. In this method, the wetting height is understood to be the maximum height to which a medium located in the mixing bowl extends during operation due to the existing centrifugal forces. If, for example, the wetting height is greater than the height of the inner wall of the mixing bowl, medium escapes from the interior of the mixing bowl during operation. In the method according to the invention, the mixing bowl filled with media is set in rotation about two axes of rotation running obliquely to one another (in particular in opposite directions), namely with the aid of a first drive and a second drive, wherein the two drives are or can be controlled independently of one another. Furthermore, the wetting height within the mixing bowl is optically recorded using an image capture device.A controller then controls the two drives in such a way that a specified wetting height is reached and / or not exceeded. This can be achieved by adjusting the speed of the first and / or the second drive. By optically detecting the wetting height and the resulting control of the centrifugal mixer drives, any medium escaping from the mixing bowl during operation can be reliably prevented. At the same time, the drives can be controlled in such a way that the media in the mixing bowl are mixed as thoroughly as possible by driving them at a maximum permissible speed. The amount of medium to be mixed in the mixing bowl can also be optimized, for example by reducing the inclination of the mixing bowl while maximizing the wetting height during operation.

[0007] Advantageous embodiments of the invention are described in the description, the drawings and the subclaims.

[0008] According to a first advantageous embodiment, it is possible to enter a maximum wetting height into the control system. This allows the control system to ensure that a predetermined wetting height is reached and / or that the maximum wetting height is not exceeded by adjusting the speed of the first and / or second drive accordingly.

[0009] According to a further advantageous embodiment, the controller can regulate the wetting height to a predetermined target value. Therefore, should the density or volume of the medium within the mixing cup change, for example, due to degassing, the predetermined wetting height can be maintained by regulating the speed of the first and / or second drive.

[0010] According to a further advantageous embodiment, the image capture device can have a stationary image sensor, for example a camera, with which an image of the interior of the mixing bowl is captured. For this purpose, the mixing bowl can be illuminated with a pulsed light source that is synchronized with at least one of the drives. This allows a still image to be generated that is synchronized with the rotation of the mixing bowl, which in turn can be evaluated by the image capture device to determine the actual wetting height within the mixing bowl. Furthermore, it can be advantageous if the light source emits radiation that has at least two, in particular at least three, different color temperature maxima.Since different media are usually mixed in the mixing cup, which are not always equally easy to detect with just one wavelength, illumination with different colors, for example RGB, enables a more reliable determination of the wetting height.

[0011] According to a further advantageous embodiment, the temperature of a medium in the mixing bowl can be measured using an optical temperature detection device, for example, an infrared measuring device. The control system regulates the speed of at least one drive so that a predetermined maximum temperature is not reached or exceeded. In this case, the rotational speed of the mixing bowl is controlled or regulated based on the temperature measurement in order to achieve a temperature specific to the medium or to avoid exceeding a temperature critical for the medium.

[0012] According to a further aspect, the present invention relates to a device comprising a centrifugal mixer with at least one mixing bowl, which can be set in rotation by a first and a second drive about two rotational axes extending obliquely to one another. Furthermore, an image capture device is provided with which a wetting height within the mixing bowl can be detected. A controller of the device is designed and configured such that it adjusts, in particular regulates, the rotational speed of the first and / or second drive such that a predetermined wetting height is reached and, in particular, not exceeded.

[0013] The present invention is described below purely by way of example using an advantageous embodiment. It should be understood that not all features of the described advantageous embodiment are to be considered essential to the invention.

[0014] The figure shows a highly simplified representation of a centrifugal mixer 10 that can rotate a mixing bowl 12 about two axes of rotation D1 and D2 that extend obliquely to one another. For this purpose, the mixing bowl 12 is inserted into a holder 14 that is fastened to a rotating arm 16, which in turn can be rotated about the axis of rotation D1 by a first drive 18. The axis of rotation D1 can be oriented vertically. However, the rotating arm 16 is angled so that the central axis of the mixing bowl 12, which can be identical to the axis of rotation D2, runs at an acute angle α to the first axis of rotation D1. In the exemplary embodiment, the mixing bowl 12 is therefore oriented obliquely to the vertical.

[0015] A second drive 20 is provided on the rotating arm 16, with which the holder 14 and thus also the mixing cup 12 can be set in rotation about the second axis of rotation D2.

[0016] The two drives 18 and 20 are controlled via a controller 22, wherein the controller 22 is connected, for example, via slip rings to the drive 20 rotating about the axis D1.

[0017] During operation, the rotating arm 16 rotates about the rotation axis D1, exerting a centrifugal force on the media M located within the mixing bowl 12. The rotational speed or rotational velocity, indicated by arrow 24, can be regulated over a wide range for the rotation about the axis D1. Depending on this rotational velocity, the surface of the media M within the mixing bowl 12 takes on the shape of a paraboloid of revolution. The shape of the surface of the media within the mixing bowl 12 is proportional to the rotational speed and independent of the viscosity of the media, as long as the mixing bowl 12 is simultaneously rotated about the axis D2. The rotational velocity about the axis D2 is indicated by reference numeral 26. This rotational velocity or the rotational velocity of the second drive 20 also influences the maximum height that the media M can reach within the mixing bowl 12.This is designated in the figure by the reference symbol B and is referred to in the present application as the wetting height.

[0018] In the illustrated embodiment, the angle of inclination α of the mixing cup 12 determines how full the mixing cup 12 can be in the idle state and the maximum rotational speed around the rotational axis D1 that is possible to prevent any medium from escaping from the mixing cup 12. Without regulating the speed of the drives 18 and 20, an angle α in the order of 45° may be suitable. For larger filling quantities, however, it may be advantageous to individually adjust and regulate the rotational speeds of the two drives 18 and 20, whereby the angle α can be selected to be smaller, which in turn enables larger filling quantities.

[0019] As the figure illustrates, a minimum distance A should be present between the upper edge of the mixing cup 12 and the medium M located in the mixing cup 12 in order to prevent medium from escaping from the mixing cup. It is clear that the wetting height B can be maximized by reducing the minimum distance A. In order to ensure during operation that, on the one hand, a desired wetting height B is achieved and, on the other hand, a minimum distance A is maintained, an image capture device 30 is provided in the illustrated embodiment, with which the wetting height B within the mixing cup 12 can be captured. For this purpose, the image capture device has a stationary image sensor 32, for example a digital camera, which captures an image of the interior of the mixing cup 12 and, with the aid of image analysis software, determines the actual maximum height of the medium M within the mixing cup 12, i.e. the wetting height B.To enable good image analysis despite the mixing bowl 12 rotating about two axes, a pulsed light source 34 is also provided, which illuminates at least part of the interior of the mixing bowl 12. The light source 34 is synchronized with at least one of the drives 18, 20 to generate a still image that can be analyzed. For this purpose, the light source 34 is operated in a pulsed manner like a stroboscope, and the synchronization pulse for controlling the light source 34 and the camera 32 can be generated, for example, by a switching contact or a rotary encoder of the drives 18 and / or 20.

[0020] In the illustrated embodiment, it may be advantageous if the light source 32 emits radiation having a plurality of different colors, for example at least two, in particular at least three different color temperature maxima, in order to be able to clearly recognize different media within the mixing cup 12.

[0021] Furthermore, an optical temperature detection device can be provided which detects the temperature of the medium M in the mixing cup 12, wherein the optical temperature detection device can be coupled to the controller 22 so that it regulates the speed of at least one drive 18, 20 such that a predetermined maximum temperature of the medium M is not reached or exceeded.

[0022] In a method according to the invention for monitoring the wetting height B of a mixing bowl 12 in a centrifugal mixer, the mixing bowl 12 filled with various media M is rotated about the first axis of rotation D1 by means of the first drive 18 and about the second axis of rotation D2 by means of the second drive 20, wherein the two axes of rotation are inclined to one another by the angle α and the rotations are in particular oriented in opposite directions. With the aid of the image capture device 30, the wetting height B within the mixing bowl 12 can then be recorded during operation. This makes it possible to control the drives 18 and / or 20 with the aid of the controller 22 in such a way that a predetermined wetting height B is achieved by setting a suitable speed of the first and / or second drive 18, 20.The control system 22 can also control the drives 18, 20 in such a way that the wetting height B is not exceeded, so that a minimum distance A is always present so that no medium M escapes from the mixing cup 12.

Claims

1. A method for monitoring the wetting height (B) of a mixing cup (12) in a centrifugal mixer, in which method the mixing cup (12) filled with media (M) is set into rotation about two axes of rotation (D1, D2) extending obliquely to one another by a first drive and by a second drive, said method comprising the following steps: optically detecting the wetting height (B) within the mixing cup (12) by means of an image acquisition device (30), controlling the drives (18, 20) by a control (22) such that a predefined wetting height (B) is reached or is not exceeded by setting the rotational speed of the first and / or the second drive (18, 20).

2. A method according to claim 1, characterized in that a maximum wetting height is entered into the control.

3. A method according to claim 1 or claim 2, characterized in that the control regulates the wetting height to a predefined desired value.

4. A method according to any one of the preceding claims, characterized in that the image acquisition device (30) acquires an image of the mixing cup (12) using a stationary image sensor (32), in that the mixing cup (12) is illuminated by a pulsed light source (34) which is synchronized with at least one of the drives (18, 20), and in that radiation which has at least two different color temperature maxima, in particular at least three different color temperature maxima, is emitted by the light source (34).

5. A method according to any one of the preceding claims, characterized in that the temperature of a medium (M) in the mixing cup (12) is detected by means of an optical temperature detection device, and in that the rotational speed of at least one drive (18, 20) is regulated by the control (22) such that a predefined maximum temperature is not reached or not exceeded.

6. An apparatus, in particular for carrying out a method according to any one of the preceding claims, comprising: a centrifugal mixer (10) comprising at least one mixing cup which can be set into rotation about two axes of rotation (D1, D2) extending obliquely to one another by a first and a second drive, characterized by an image acquisition device (30) by which a wetting height (B) within the mixing cup (12) can be detected, and a control (22) by which the rotational speed of the first and / or the second drive (18, 20) is set, in particular regulated, such that a predefined wetting height (B) is reached and is in particular not exceeded.

7. An apparatus according to claim 6, characterized in that the image acquisition device (30) has a stationary image sensor (32) which acquires an image of the mixing cup (12), in that a pulsed light source is provided that illuminates the mixing cup (12) and that is synchronized with at least one of the drives (18, 20), and in that the light source (32) emits radiation which has at least two different color temperature maxima, in particular at least three different color temperature maxima.

8. A apparatus according to one of the preceding claims 6 or 7, characterized in that an optical temperature detection device is provided that detects the temperature of a medium in the mixing cup (12), and in that the control (22) is configured to regulate the rotational speed of at least one drive (18, 20) such that a predefined maximum temperature is not reached or not exceeded.