GB2440443A

GB2440443A - A device for dosing powder

Info

Publication number: GB2440443A
Application number: GB0714291A
Authority: GB
Inventors: Thomas Brinz; Juergen Goetz
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2006-07-24
Filing date: 2007-07-20
Publication date: 2008-01-30
Anticipated expiration: 2027-07-20
Also published as: DE102006034115B4; GB0714291D0; DE102006034115A1; GB2440443B

Abstract

A device for dosing powder 5 has a storage container 3, wherein the storage container 3 comprises an outlet channel 7 through which the powder 5 may be fed to a collecting device 9. The storage container 3 is connected to a vibration exciter 11, wherein at least part of the storage container 3 is acted upon by vibrations that are generated by the vibration exciter 11. The vibration exciter 11 may be connected to the outlet channel 7 and may generate a square-wave or triangular oscillation with an amplitude lower than 150m and the frequency is higher than 300 Hz.

Description

Device for dosing powder

Background art

The invention relates to a device for dosing powder according to the preamble of claim 1.

Flexible laboratory analysis (high-throughput experimentation) entails the dosing of powders within a large quantitative range. The powder quantity to be dosed may in this case range from less than 1 mg up to more than g.

The powder dosing is effected in this case for example with the aid of vibrating channels. With these, however, there is the problem that continuous feeding from a storage tank of the feed system may be realized only with difficulty.

Furthermore, the quantity discharged from the vibrating channel is l.a. dependent on the discharge quantity of the feed system. The entire vibrating channel is moreover contaminated with powder, so that this vibrating channel may be used only for a single powder. For this reason, as soon as a plurality of different powders are to be added in a metered manner, a plurality of vibrating channels are also required. A further drawback of the vibrating channel is that, on completion of the metered addition, the powder lies exposed to the ambient air. It is also a drawback of the vibrating channel that a reliable dosing of powder quantities smaller than 1 mg is not possible. Furthermore, the discharge quantity is dependent upon an external feed system. A relatively large set-up is moreover required for the dosing of a powder. Two actuators are needed: one as a drive of the feed system and a second for driving the vibrating channel.

Further dosing systems known from the background art are for example metering screws, proportioning belts, star wheel feeders, compartment dosing devices and reciprocating dosing devices. A further drawback of each of these different dosing systems is that with them dosing quantities smaller than 1 mg may not be realized.

Disclosure of the invention

Advantages of the invention A device for dosing powder that is designed according to the invention comprises a storage container, which comprises an outlet channel, through which the powder may be fed to a collecting container. The storage container is connected to a vibration exciter, wherein at least part of the storage container is acted upon by vibrations generated by the vibration exciter. By virtue of at least part of the storage container being acted upon by vibrations a uniform flow of powder out of the storage container is achieved. The vibrations moreover prevent the formation in the storage container of solids bridges that would obstruct the outlet channel and therefore prevent further dosing of the powder.

In a preferred form of construction, the vibration generated by the vibration exciter is a square-wave oscillation. Surprisingly, it has emerged that with a square-wave oscillation rather than with other forms of oscillation a uniform flow of powder is achieved. Also, with square-wave oscillations fewer solids bridges are formed and so obstructions are avoided. Alternatively, it is possible for the vibration exciter to generate a triangular oscillation. In contrast to square-wave oscillation, with triangular oscillation lower feed quantities may be realized.

Besides the type of vibration that is applied to at least part of the storage container, the cross section of the outlet channel is also a ruling quantity for the powder stream. For example, with a smaller cross section of the outlet channel a smaller powder quantity flows out of the storage container than with a larger cross section. Thus, with a smaller diameter a finer dosing of the powder quantity is possible.

The elimination of obstructions in the storage container and/or in the outlet channel and a continuous flow of powder out of the opening of the outlet channel is achieved according to the invention in that the vibration exciter is preferably designed in such a way that the amplitude is lower than 150 pm and the frequency is higher than 300 Hz, preferably in the region of 400 to 1000 Hz.

In order to be able to achieve a square-wave oscillation with the vibration exciter, the vibration exciter preferably comprises a piezoelectric element. By means of the piezoelectric element a rapid expansion and/or contraction is achieved, thereby almost producing a square-wave oscillation. By square wave oscillation in the context of the present invention is meant any oscillation, in which an amplitude change is at most 3/10 of a period.

In a preferred form of construction, the vibration exciter is connected to the outlet channel of the storage container, so that the outlet channel is acted upon by the vibration generated by the vibration exciter. The outlet channel is therefore set in vibration, thereby preventing powder bridges from forming in the outlet channel and hence preventing clogging of the outlet channel.

In a form of construction, the storage container comprises a closing device, by means of which the outlet channel may be closed. The closing device prevents powder from flowing out of the storage container after the dosing operation has ended. The closing device preferably comprises a conical plug. When a closing device is provided, the closing device instead of the outlet channel may alternatively be set in vibration by means of the vibration exciter. In a first form of construction, the plug is connected in such a way to the vibration exciter that the plug is set in vibration such that it vibrates in axial direction, in relation to the outlet channel. It is also possible for the plug to be set in vibration such that it vibrates in radial direction, in relation to the outlet channel. In order to prevent the formation of powder bridges in the outlet channel by vibrations of the plug, the plug is preferably connected to a rod that is accommodated in the outlet channel. As soon as the plug is set in vibration, the rod is likewise acted upon by vibrations, so that situated in the region of the outlet channel is a vibrating element, by means of which the formation of powder bridges is prevented. It is also possible for the rod to be acted upon by the vibration, with the result that the closing device, comprising the plug and the rod, is likewise set in vibration.

To enable precise dosing, the collecting container for the powder is preferably connected to a balance. A closed-loop control circuit, which connects the balance to the vibration exciter, allows the metered addition of a precise powder quantity. As soon as the balance measures the powder quantity that is to be dosed, a signal is sent to the vibration exciter and optionally to the plug, so that the vibration exciter stops setting part of the storage container in vibration and at the same time the plug, where provided, closes the outlet opening of the outlet channel.

This allows powder to be dosed in a quantity of less than 1 mg to an accuracy of 0.1 mg.

Short description of the drawings

Embodiments of the invention are represented in the drawings and explained in detail in the following

description.

The drawings show Figure 1 a device according to the invention for dosing powder in a first form of construction, Figure 2 a detail of the device of Figure 1, Figure 3 a device designed according to the invention in a second form of construction, Figure 4 a closing device with conical plug, Figure 5 a storage container with the closing device according to Figure 4, Figure 6 an enlarged view of the outlet channel with closing device according to Figure 5, Figure 7 a device designed according to the invention in a third form of construction, Figure 8 an enlarged view of the connection of the vibration exciter to the plug, Figure 9 a holding device of the storage container of Figure 7 and Figure 10 a device designed according to the invention in a fourth form of construction.

In the following figures identical reference characters signify in each case identical elements.

Figure 1 shows a device designed according to the invention for dosing powder in a first form of construction.

A dosing device 1 comprises a storage container 3, which contains powder 5 that is to be dosed. The storage container 3 is equipped with an outlet channel 7, through which the powder 5 flows from the storage container 3 into a collecting container 9, which here takes the form of a tray. According to the invention, the storage container 3 with the outlet channel 7 connected to it is aligned in such a way that the powder is conveyed solely by the force of gravity. Because of the adhesive forces between the individual grains of powder, powder bridges may form and obstruct the outlet channel 7. In order to destroy these powder bridges, the outlet channel 7 in the form of construction illustrated in Figure 1 is connected to a vibration exciter 11. The vibration exciter 11 comprises a piezoelectric element 13, by means of which a square-wave frequency may be generated. However, besides the piezoelectric element 13, any other vibration exciter 11 known to the person skilled in the art and capable of generating a square-wave frequency may also be used.

The oscillation generated by the vibration exciter 11 preferably has an amplitude of at most 150 pm. The frequency of the oscillation is preferably higher than 300 Hz. With a vibration exciter 11 that comprises a piezoelectric element 13 it is possible to generate an oscillation having a frequency of up to 3000 Hz. A further advantage of a piezoelectric element 13 is that, when the vibration stops, the vibratory motion is immediately halted. Post-pulse oscillation does not occur. The expansion of piezoelectric elements 13 is moreover in the region of up to approximately 100 pm. Thus, with a piezoelectric element 13 an adequate amplitude may be realized without additional transformation.

In order to determine the precise quantity of powder 5 to be dosed, the collecting container 9 is connected to a balance 15. The measuring accuracy, to which the powder may be dosed into the collecting container 9, is in this case dependent upon the measuring accuracy of the balance 15. The greater the accuracy of the balance 15, the more precise the dosed addition of the powder quantity may be.

In the form of construction illustrated here, the storage container 3 is held by means of a holding device 16.

Besides the illustrated form of construction, in which the outlet channel 7 is oriented vertically downwards, it is also possible for the storage container 3 with the outlet channel 7 to be disposed in an inclined manner. The inclination is in said case preferably so selected that the powder is fed by the force of gravity in the storage container 3 and the outlet channel 7.

So that at least part of the storage container 3 is acted upon by the vibrations generated by the vibration exciter 11, the vibration exciter 11 in the form of construction illustrated here is connected by a rod 17 to the outlet channel 7. As Figure 2 reveals, the rod 17 is coupled to the outlet channel 7 by an annular eye 19. The annular eye 19 is fastened for this purpose to the rod 17 and at the other end surrounds the outlet channel 7, which in the form of construction illustrated here has a circular cross section. As soon as the vibration exciter starts to vibrate, these vibrations are transmitted to the rod 17 and then by means of the annular eye 19 also to the outlet channel 7. The outlet channel 7 starts to vibrate at the same frequency and with the same amplitude as the rod 17.

For this purpose, the annular eye 19 is preferably connected in a close-fitting manner to the outlet channel 7. As soon as a play develops between the annular eye 19 and the outlet channel 7, the amplitude, with which the outlet channel 7 vibrates, is reduced by the play.

Figure 3 shows a device designed according to the invention in a second form of construction.

In the form of construction illustrated in Figure 3, in contrast to the form of construction illustrated in Figure 2 the collecting container 9 is designed with a higher edge 21. The higher edge 21 of the collecting container 9 allows the outlet channel 7 to project into the collecting container 9. This prevents powder escaping in the form of dust from the collecting container 9. In the form of construction illustrated here, the vibration exciter acts preferably inside the edge 21 of the collecting container 9 upon the outlet channel 7. For this purpose, there is accommodated on the vibration exciter 11 a bent rod 23 that transmits the vibrations generated by the vibration exciter 11 to the outlet channel 7. The connection of the bent rod 23 to the outlet channel 7 in the form of construction illustrated here is effected preferably by means of the annular eye 19, in an identical manner to that illustrated in Figure 2. The curvature of the bent rod 23 is designed such that the annular eye is situated inside the collecting container 9, while the bent rod 23 projects above the edge 21 of the collecting container 9 and is connected to the vibration exciter 11.

Figure 4 shows a closing device, by means of which the outlet channel 7 may be closed. The closing device 25 illustrated in Figure 4 comprises a conically designed plug, which is connected to a rod 29 that is accommodated in axial direction in the outlet channel 7, so that the plug 27 may be drawn into the outlet opening of the outlet channel 7 and hence closes the outlet channel 7. For this purpose, the diameter D1 is larger than the inside diameter of the outlet channel 7. The diameter D2 of the rod 29 is so selected that the flow of powder is not impeded by the rod 29.

Figure 5 shows a storage container 3 with a closing device 25. The movement of the rod 29 is represented by a double arrow 31. The direction of movement in this case is axial relative to the outlet channel 7. When the plug 27 is moved out of the outlet channel 7, the outlet channel 7 is opened and powder may flow out of the storage container 3.

As soon as the powder dosing operation is complete, the plug 27 is moved into the outlet channel 7 and hence closes the outlet opening of the outlet channel 7.

Figure 6 shows to an enlarged scale the outlet channel 7 with plug 27 in a position, in which powder may flow out of the outlet channel 7. Because of the rod 29, to which the conically designed plug 27 is fastened, there is formed at the outlet channel 7 an annular net orifice, through which the powder may flow out. This net orifice is closed by a movement of the plug 27 in the direction of the outlet channel 7. A further advantage of the conically designed plug 27 is that it allows an adjustment of the net orifice.

The further the conically designed plug 27 projects from the outlet channel 7, the larger the net orifice. In a corresponding manner, the size of the net orifice decreases, the further the conically designed plug 27 is drawn into the outlet channel 7.

Figure 7 shows a device designed according to the invention in a third form of construction.

In the form of construction illustrated in Figure 7, the vibration exciter 11 is connected to the rod 29 of the closing device 27. Consequently, the vibration generated by the vibration exciter 11 is transmitted to the rod 29.

The direction of the vibration is represented by the double arrow 33. The direction of vibration is therefore at right angles to the axial direction of the rod 29. The rod 29 therefore moves radially relative to the outlet channel 7.

The vibration is transmitted via the rod 29 as far as the plug 27. In order that the rod 29 and the plug 27 move relative to the outlet channel 7 and the powder bridges, which may form in the outlet channel 7, are therefore destroyed, the outlet channel is fixed by means of a holding device 35. The connection of the rod 29 to the vibration exciter 11 is effected by means of the rod 17 and the annular eye 19. This connection is shown to an enlarged scale in Figure 8. In order that the rod 29 is connected free of play to the annular eye 19, the annular eye is preferably press-fitted onto the rod 29. This guarantees that the amplitude, with which the rod 29 vibrates, is identical to that transmitted via the rod 17 from the vibration exciter 11 to the rod 29.

The holding device of the outlet channel 7 is illustrated to an enlarged scale in Figure 9. The outlet channel 7 for this purpose is held in an annular eye 37. However, any other fastening of the outlet channel 7 that is known to the person skilled in the art is also possible. The fastening is to be designed in each case such that a movement of the outlet channel 7 is suppressed, so that the rod 29 and the plug 27 move relative to the outlet channel 7.

Figure 10 shows a device according to the invention in a fourth form of construction. In contrast to the form of construction illustrated in Figure 7, in the form of construction illustrated in Figure 10 the vibration exciter 11 is attached in such a way that the rod 29 of the closing device 25 vibrates in axial direction. For this purpose, the vibration exciter 11 is oriented in such a way that the vibrations generated by the vibration exciter 11 are generated parallel to the rod 29. The rod 17, by which the vibrations are transmitted from the vibration exciter 11 to the rod 29, is disposed likewise parallel to the rod 29.

The connection of the rod 17 to the rod 29 is effected, as in the other forms of construction, preferably likewise by means of the annular eye 19.

Besides the connection of the rod 17 to the rod 29 by means of the annular eye 19 that is illustrated in the drawings, it is equally possible to connect the rod 17 to the rod 29 by means of any other desired non-positive or positive connection that is known to the person skilled in the art.

Thus, the rod 17 and the rod 29 may be fastened to one another for example also by means of a weld joint or a glued joint. It is moreover also possible to form on the rod 17 or on the rod 29 a thread, onto which the respective other rod 17, 29 is screwed.

Instead of by means of the annular eye 19, the connection of the rod 17 and/or of the bent rod 23 to the outlet channel 7 may alternatively be effected by means of any other connection known to the person skilled in the art.

Here too, almost all non-positive or positive connections are suitable. Thus, the fastening of the rod 17 and/or the bent rod 23 to the outlet channel 7 may be effected for example also by welding, gluing, soldering or screwing them to one another.

When connecting the rod 17 to the rod 29 or the bent rod 23 to the outlet channel 7, it merely has to be ensured that the connection is free of play so that the vibration generated by the vibration exciter 11 is transmitted with its full amplitude to the rod 29 and/or the outlet channel 7.

The material, from which the storage container 3 is manufactured, may be selected freely in dependence upon the powder. It merely has to be ensured that the storage container 7 is not damaged by the powder. Preferred material for the storage container 3 is rigid plastic material. The storage container 3 may however also be manufactured from any desired metal, glass or ceramic material. As a material for the outlet channel 3, preferably a material is selected, which may be acted upon by vibrations and which transmits the vibrations. Such a material is preferably an elastically deformable material.

If a brittle material is used for the outlet channel 7, there is a risk that the outlet channel 7 may fracture when acted upon by the vibrations.

Besides the forms of construction illustrated here, in which either the outlet channel 7 or the rod 29 of the closing device 25 is connected to the vibration exciter 11, it is also possible to connect the rod 29 and the outlet channel 7 to a vibration exciter. In this form of construction, it is preferred when the amplitudes and/or frequencies, at which the outlet channel 7 and/or the rod 29 are set in vibration, differ from one another.

Claims

Claims 1. Device for dosing powder (5) having a storage container (3),

wherein the storage container (3) comprises an outlet channel (7), through which the powder (5) may be fed to a collecting device (9), characterized in that the storage container (3) is connected to a vibration exciter (11), wherein at least part of the storage container (3) is acted upon by vibrations that are generated by the vibration exciter (11)
2. Device according to claim 1, characterized in that the vibration exciter (11) generates a square-wave oscillation.

3. Device according to claim 1, characterized in that the vibration exciter (11) generates a triangular oscillation.

4. Device according to one of claims 1 to 3, characterized in that the vibration exciter (11) is so designed that the amplitude generated by the vibration exciter (11) is lower than 150pm and the frequency is higher than 300 Hz.

5. Device according to one of claims 1 to 3, characterized in that the vibration exciter (11) comprises a piezoelectric element (13) 6. Device according to one of claims 1 to 5, characterized in that the vibration exciter (11) is connected to the outlet channel (7), so that the outlet channel (7) is acted upon by the vibration generated by the vibration exciter (11) 7. Device according to one of claims 1 to 6, characterized in that the storage container (3) comprises a closing device (25), by means of which the outlet channel (7) may be closed.

8. Device according to claim 7, characterized in that the closing device (25) is connected in such a way to the vibration exciter (11) that the closing device (25) is set in vibration by the vibration exciter (11) 9. Device according to claim 8, characterized in that the closing device (25) comprises a conical plug (27), which is set in vibration by the vibration exciter (11) 10. Device according to claim 9, characterized in that the plug (27) is set in vibration such that it vibrates in axial direction, in relation to the outlet channel (7) 11. Device according to claim 9, characterized in that the plug (27) is set in vibration such that it vibrates in radial direction, in relation to the outlet channel (7).

12. Device according to one of claims 1 to 11, characterized in that the collecting device (9) is connected to a balance (15) 13. A device for closing powder substantially as herein described.