Dosing system, dosing method and production method

Abstract

The invention describes a dosing system (3) for a shear-thinning or thixotropic liquid to viscous dosing material. It comprises a nozzle (1) with a closure channel (55), within which a closure element (21) is controlled during operation by means of an automatic control unit (63) in an ejection direction (E) and/or retraction direction (R). To this end, the closure channel (55) is realized in at least one cross-section perpendicular to the ejection direction (E) and/or retraction direction (R) relative to the cross-section of the closure element (21) in the same plane to give an aperture gap (57) between the outer surface (S.sub.1) of the closure element (21) and the inner surface (S.sub.2) of the closure channel (55), which aperture gap (57) is shaped and/or dimensioned to form an outlet channel, at least in places, for the dosing material. The control unit (63) is realized to generate control signals (SS.sub.1, SS.sub.2) for different movements of the closure element (21) in at least two movement modes (M.sub.1, M.sub.2, M.sub.4, M.sub.5, M.sub.6), whereby it deliberately moves the closure element (21) during operation in order to reduce the viscosity of the dosing material in at least a region of the aperture gap (57). The invention further describes a method of manufacturing such a dosing system (3), and a dosing method that can be carried out with the dosing system (3).

Claims

1. A dosing system for a shear-thinning or thixotropic liquid to viscous dosing material, comprising a nozzle with a closure channel, within which a closure element is controlled during operation by means of a control unit alternately in an ejection direction or a retraction direction, wherein the closure channel is configured in at least one cross-section perpendicular to the ejection direction or the retraction direction relative to the cross-section of the closure element in the same plane to give an aperture gap between the outer surface of the closure element and the inner surface of the closure channel, which aperture gap is shaped or dimensioned to form an outlet channel, at least in places, for the dosing material, wherein the control unit is programmed to generate control signals for different movements of the closure element in at least two movement modes, wherein the control unit is programmed to deliberately oscillate the closure element in the ejection direction and the retraction direction during operation in at least one of the movement modes in order to reduce a viscosity of the dosing material in at least a region of the aperture gap, wherein, in a first movement mode, the closure element is controlled during operation by means of the control unit in the ejection direction and the retraction direction, wherein the first movement mode comprises a first motion pattern with up-and-down movements of the closure element, whose stroke or frequency or sequence is configured to overcome forces inside the dosing material in order to reduce the viscosity of the dosing material, wherein, in a second movement mode, the closure element is controlled during operation by means of the control unit in the ejection direction, wherein the second movement mode comprises a second motion pattern with ejection movements of the closure element, whose stroke or frequency or sequence is configured for ejecting the dosing material drop-wise or as a jet through an outlet opening of the nozzle, and wherein movements of the first motion pattern are shorter in stroke and higher in frequency than the ejection movements of the second motion pattern.

2. The dosing system according to claim 1, wherein the first movement mode comprises the first motion pattern with up-and-down movements between two extreme positions, wherein the closure element is held in at least one extreme position for a certain duration.

3. The dosing system according to claim 1, wherein the control unit is programmed to combine the different motion patterns or movement modes.

4. The dosing system according to claim 3, wherein the first movement mode or the second movement mode comprises a combination of different motion patterns.

5. The dosing system according to claim 3, wherein the control unit is programmed to carry out different movement modes sequentially.

6. The dosing system according to claim 3, wherein the control unit is programmed to carry out different movement modes alternately.

7. The dosing system according to claim 1, wherein the aperture gap comprises at least one clearance between the outer surface of the closure element and the inner surface of the closure channel with a height corresponding to the length of at least one particle of the dosing material.

8. The dosing system according to claim 7, wherein, on account of the clearance, a flow resistance acts on the dosing material that is at least as great as a flow resistance in the region of an outlet opening of the nozzle.

9. The dosing system according to claim 1, wherein the closure element is exchangeable with another closure element and the closure channel is exchangeable with another closure channel.

10. The dosing system according to claim 1, comprising a dosing material collection cavity, arranged between the closure channel and an outlet opening for the dosing material, and which has a shape or a position such that the closure element does not completely fill the dosing material collection cavity on account of the shape or the position of the dosing material collection cavity.

11. The dosing system according to claim 1, comprising an actuator system for the automatic controlled movement of the closure element, comprising at least one piezoelectric actuator.

12. The dosing system according to claim 1, wherein the up-and-down movements of the closure element have a frequency greater than 10 kHz.

13. The dosing system according to claim 1, wherein the viscosity of the dosing material is reduced by at least 50%.

14. The dosing system according to claim 1, wherein the viscosity of the dosing material is reduced by at least 99%.

15. The dosing system according to claim 1, wherein the aperture gap comprises at least one clearance between the outer surface of the closure element and the inner surface of the closure channel with a height corresponding to the length of three adjacent particles of the dosing material.

16. The dosing system according to claim 1, wherein the aperture gap comprises at least one clearance between the outer surface of the closure element and the inner surface of the closure channel with a height corresponding to 50 micrometers.

17. A dosing method for a shear-thinning or thixotropic liquid to viscous dosing material, wherein the dosing material is dispensed through a nozzle, and wherein the nozzle comprises a closure channel, within which a closure element is moved during operation alternately in an ejection direction or a retraction direction, wherein the closure channel is configured in at least one cross-section perpendicular to the ejection direction or the retraction direction relative to the cross-section of the closure element in the same plane to give an aperture gap between the outer surface of the closure element and the inner surface of the closure channel, which aperture gap is shaped or dimensioned to form an outlet channel, at least in places, for the dosing material, and wherein the closure element is moved at different times in one of at least two different movement modes, wherein the closure element is deliberately oscillated in the ejection direction and the retraction direction during at least one of the movement modes to reduce a viscosity of the dosing material in at least a region of the aperture gap, wherein, in a first movement mode, the closure element is controlled during operation by means of the control unit in the ejection direction and the retraction direction, wherein the first movement mode comprises a first motion pattern with up-and-down movements of the closure element, whose stroke or frequency or sequence is configured to overcome forces inside the dosing material in order to reduce the viscosity of the dosing material, wherein, in a second movement mode, the closure element is controlled during operation by means of the control unit in the ejection direction, wherein the second movement mode comprises a second motion pattern with ejection movements of the closure element, whose stroke or frequency or sequence is configured for ejecting the dosing material drop-wise or as a jet through an outlet opening of the nozzle, and wherein movements of the first motion pattern are shorter in stroke and higher in frequency than the ejection movements of the second motion pattern.

18. A method of manufacturing a dosing system for a shear-thinning or thixotropic liquid to viscous dosing material, comprising at least the following steps: providing a closure channel, arranging a closure element within the closure channel in such a way that the closure element can be moved alternately in an ejection direction or a retraction direction during operation of the nozzle, providing an aperture gap between the closure element and the closure channel by forming the closure channel, in at least one cross-section perpendicular to the ejection direction or the retraction direction relative to the cross-section of the closure element in the same cross-sectional plane, such that the aperture gap ensues between the outer surface of the closure element and inner surface of the closure channel, wherein the aperture gap is formed or dimensioned to provide an outlet channel for the dosing material at least in places, and connecting the closure element or an actuator system for moving the closure element to a control unit that is programmed to generate, during operation, control signals for different movements of the closure element in at least two movement modes, wherein the control unit is programmed to deliberately oscillate the closure element in the ejection direction and the retraction direction during operation in at least one of the movement modes such that a viscosity of the dosing material is reduced in a region of the aperture gap, wherein, in a first movement mode, the closure element is controlled during operation by means of the control unit in the ejection direction and the retraction direction, wherein the first movement mode comprises a first motion pattern with up-and-down movements of the closure element, whose stroke or frequency or sequence is configured to overcome forces inside the dosing material in order to reduce the viscosity of the dosing material, wherein, in a second movement mode, the closure element is controlled during operation by means of the control unit in the ejection direction, wherein the second movement mode comprises a second motion pattern with ejection movements of the closure element, whose stroke or frequency or sequence is configured for ejecting the dosing material drop-wise or as a jet through an outlet opening of the nozzle, and wherein movements of the first motion pattern are shorter in stroke and higher in frequency than the ejection movements of the second motion pattern.

Description

(1) Other objects and features of the present invention will become apparent from the following detailed descriptions considered in conjunction with the accompanying drawings. In the diagrams, like numbers refer to like objects throughout.

(2) FIG. 1 shows a front view of an embodiment of a dosing system according to the invention;

(3) FIG. 2 shows a side view of the same dosing system of FIG. 1 along a section A-A;

(4) FIG. 3 shows a detailed view of the section of FIG. 2;

(5) FIG. 4 shows a sectional view of the same dosing system of FIG. 1 along a section B-B;

(6) FIG. 5 shows a detailed view of the section of FIG. 4;

(7) FIG. 6 shows a schematic representation of a path of motion of a closure element in a first embodiment of the method according to the invention;

(8) FIG. 7 shows a schematic representation of a path of motion of a closure element in a second embodiment of the method according to the invention;

(9) FIG. 8 shows a schematic representation of a path of motion of a closure element in a third embodiment of the method according to the invention

(10) FIG. 9 shows a schematic representation of a path of motion of a closure element in a fourth embodiment of the method according to the invention.

(11) FIGS. 1 and 2 show a dosing system according to an embodiment of the invention, while FIG. 3 shows a detail of FIG. 2. The dosing system 3 comprises a nozzle 1, a dosing material container 5 with a dosing material reservoir 7 and a housing 35, in which an actuator chamber 25 is arranged in addition to the nozzle 1.

(12) The housing 35 comprises a first, lower housing part 37 and a second, upper housing part 39. The two housing parts 37, 39 are connected to each other in a spring-loaded manner by means of holding screws 41 and by means of vertically mounted springs 43 connected to the holding screws 41. A gap, i.e. a certain play, ensues on both sides along the edge between the two housing parts 37, 39.

(13) The actuator chamber 25 is arranged centrally in an actuator region 59 in the housing. A first piezoelectric actuator 23a and a second piezoelectric actuator 23b are oriented in a direction along a (central) axis X and positioned along the direction of the axis X. Together, the piezoelectric actuators 23a, 23b give an actuator system 61. The actuator chamber 25 is closed at the upper side by a spacer 27, whose position can be adjusted from the outside of the housing 35 by means of a spacer adjusting screw 29. Two contact terminals 31, 33 serve to connect an electronic control unit 63 to the two piezoelectric actuators 32a, 23b, at a maximum voltage of 240 V.

(14) The two piezoelectric actuators 23a, 23b are realized as tubular, cylindrical piezoelectric actuators 23a, 23b and are arranged to travel essentially in an axial direction along the axis X during operation. Preferably, the piezoelectric actuators 23a, 23b are piezo-stacks of annular piezo-elements. Within the cavity of the first piezoelectric actuator 23a, a longitudinal connector element 51 is arranged that fills the entire cavity and projects outwards in the manner of a collar from above the end of the first piezoelectric actuator 23a that faces the second piezoelectric actuator 23b. In this way, the connector element 51 connects the two piezoelectric actuators 23a, 23b in the region of its collar in a form-fit and force-fit way, and ensures a mechanical coupling of forces between them. To stabilize its position, it extends a little into a cavity 52 of the second piezoelectric actuator 23b. Alternatively, a tubular piezoelectric actuator 23a, 23b can be replaced, for example, by several, preferably at least two, most preferably at least three piezo-rods (for example also in the form of piezo-stacks) arranged in parallel and operating in parallel. These piezo-rods can for example be evenly distributed on a circumference, and can be controlled as a group (i.e. as an actuator), in order to achieve the same effect as a tubular piezoelectric actuator 23a, 23b. In other words, the direction of motion of the connection element 51 is coaxial to the effective direction axis of the parallel-connected piezo-rods behaving as a single actuator.

(15) The two piezoelectric actuators 23a, 23b are driven in an offset or counterbalanced manner. This means that the first piezoelectric actuator 23a reduces its overall length in a longitudinal direction, i.e. in a vertical direction, while the second piezoelectric actuator 23b increases its length in the same direction by the same amount, at the same time. Equally, the first piezoelectric actuator 23a increases its overall length in the longitudinal direction, while the second piezoelectric actuator 23b decreases its length in the same direction by the same amount, at the same time. This means that, during operation of the actuator system, the overall length of the two piezoelectric actuators 23a, 23b along the axis X remains essentially unchanged at all times. By coupling the connecting element 51 to the actuators 23a, 23b at the joint (or contact position) between the actuators 23a, 23b, the connecting element 51 will always be pushed away from the currently lengthening actuator 23a, 23b, while the other actuator 23a, 23b makes place but remains in contact with the connecting element 51 and thereby even exerts a slight counter-pressure. In this way, the connecting element 51 is securely held in a compact actuator assembly during an up-and-down motion, and the lengthening piezoelectric actuator 23a, 23b remains preloaded.

(16) A closure element 21 in the form of a longitudinal ceramic plunger 21 extends into the connecting element 51 in the first piezoelectric actuator 23a. Ceramic closure elements are particularly suitable due to their extreme lightness. The housing and nozzle parts surrounding the closure element 21 are preferably made of a high-strength material such as titanium. The plunger 21 is connected to the first piezoelectric actuator 23a by means of a guide element 47 screwed into the connecting element 51 (above the collar of the connecting element 51). The plunger 21 is also arranged along the axis X and is held in this orientation by the guide element 47. To this end, the guide element 47 is arranged about the plunger 21 in the manner of a sleeve, and engages in a form-fit manner with an upper wider region of the plunger 21.

(17) The end of the plunger 21 facing away from the first piezoelectric actuator 23a extends into the region of the nozzle 1. It is passed though a seal 45, namely a ring seal 45, and extends into a closure channel 55. This closure channel 55 is formed by a cylindrical sheath-like element 55, which encloses a cylindrical cavity in its interior. At the lower end of the plunger 21, the closure channel 55 is adjoined by a dosing material collection cavity 17, below which lies the outlet opening 19 of the nozzle 1. This dosing material collection cavity 17 is formed such that the plunger 21, on account of its shape and position, cannot entirely fill the cavity in any of its operating positions.

(18) A feed inlet 15 of a supply line 13 is arranged above the closure channel 55, namely between the ring seal 45 and the closure channel 55, to feed dosing material in the direction of the nozzle 1 from the dosing material reservoir 7 through a connecting stopper 11.

(19) The dosing material reservoir 7 is pressure-charged, so that the dosing material is pressed through the supply line 13 in the direction of the nozzle 1. A fastener 9 serves to connect the dosing material reservoir 7 to the other parts of the dosing system 3.

(20) During operation of the dosing system 3, the electronic control unit 63 generates first control signals SS.sub.1 and second control signals SS.sub.2, which are forwarded to the two piezoelectric actuators 23a, 23b via the contact terminals 31, 33 and which control their movement, i.e. their displacement. These control signals SS.sub.1, SS.sub.2 are such that the two piezoelectric actuators 23a, 23b are driven to counteract each other. This achieves the mutually opposite motion pattern described above for the two piezoelectric actuators 23a, 23b. The movement of the first piezoelectric actuator 23a, which is effectively connected to the plunger 21, results in an up-and-down movement of the plunger 21. When the second piezoelectric actuator 23b contracts while the first piezoelectric actuator 23a is simultaneously extending, the plunger 21 will be pushed by the first piezoelectric actuator 23a up into the retraction direction R. In the case of the opposite movement, the plunger 21 will be pushed downwards by the second piezoelectric actuator 23b in the ejection direction. The effective direction axis WR, shared in this case by the two piezoelectric actuators 23a, 23b, is oriented along the axis X as are the ejection and retraction directions E, R, whereby the coupling of the plunger 21 with the actuator system formed by the first piezoelectric actuator 23a and second piezoelectric actuator 23b at the junction between the two piezoelectric actuators 23a, 23b ensures that the plunger 21 is always pushed in the desired direction by the currently extending piezoelectric actuator 23a, 23b.

(21) In this context, it should be mentioned than an opening and a closing of the nozzle in the context of the invention is to be understood differently from non-open systems of the prior art. This is because the opening effect in this exemplary embodiment of the dosing system 3 according to the invention is better described as an ejection effect instead of a mere opening effect. This ejection effect ensues in that the plunger 21 penetrates into an upper region of the dosing material collection cavity 17 and generates an overpressure such that the dosing material collected therein is forced out of the outlet opening 19. Accordingly, the ejection direction can also be referred to as an opening direction. In the known dosing systems, in contrast, a plunger would have an opening effect in the exact opposite direction: it would uncover an outlet opening of a nozzle and thereby allow passage through the outlet opening. On the other hand, the nozzle is closed after the ejection when the plunger is moved back in the opposite retraction direction, e.g. in a completely retracted position or a resting state (for example with both actuators in an intermediate position). In the present case, no further dosing material escapes from the nozzle owing to the small opening of the nozzle and the high viscosity of the dosing material under the applicable pressure conditions of the dosing material in the dosing system. In this respect, the retraction direction can also be regarded as a closing direction.

(22) The specific ejection/opening effect and closing effect of the dosing system 3 or the nozzle 1 will be explained in more detail in the following with reference to FIG. 5, which shows a detailed view of a region Y of FIG. 4, which in turn shows a section of the nozzle 1 of the dosing system 3 along a section line B-B of FIG. 1. It can be seen that the closure channel 55 is centrally arranged inside an annularly formed holding arrangement 58 of the nozzle 1. Its midpoint lies exactly on the axis X (cf. FIG. 2). The plunger 21 is arranged in the closure channel 55. In this cross-section and (as is preferred according to the invention) in all cross-sections along the longitudinal direction of the closure channel 55, there is a circumferential annular aperture gap 57 (which also preferably has the same area in each cross-section) between the plunger 21 and the closure channel 55. The aperture gap 57 comprises a clearance of 0.1 mm between the outer surface S.sub.1 of the plunger 21 and the inner surface S.sub.2 of the closure channel 55. Theoretically, the dosing material can flow through this aperture gap 57 under appropriate pressure conditions from the dosing material reservoir 7 in the direction of the outlet opening 19 of the nozzle 1, as long as its viscosity is sufficiently low.

(23) However, since the dosing material is a shear-thinning or thixotropic mixture with a high viscosity, the distance between the two surfaces S.sub.1, S.sub.2 is chosen to be 0.1 mm such that its viscosity is sufficiently great in the resting state and the dosing material is retained in the aperture gap 57. This applies therefore to a resting state of the plunger 21, during which flow through the aperture gap 57 is not permitted. When the plunger 21 is caused to move according to a suitable movement pattern, the viscosity of the dosing material can be reduced to an extent that permits a relative easy passage through the aperture gap 57. This has the effect that the dosing material can flow practically freely from the feed inlet 15 in the direction of the dosing material collection cavity 17. Here, it collects and can be ejected by a deliberate ejection movement of the plunger 21.

(24) Each of the piezoelectric actuators 23a, 23b has a stroke of 0.069 mm. A stroke that is smaller than this 0.069 mm is enough in order to overcome the viscosity of the dosing material. Ultimately, in the case of many dosing materials, a slight oscillation of the plunger 21 is enough to overcome the shear forces within the dosing material, so that its passage through the aperture gap 57 is made possible.

(25) In this context, FIG. 6 schematically shows one possible motion pattern of the plunger 21. The path s (not to any scale) of the plunger 21 is shown against time t (also not to any scale). It can be seen that the plunger 21 carries out three different movement modes M.sub.1, M.sub.2, M.sub.3.

(26) A first movement mode M.sub.1 is performed between a zero time instant t.sub.0 and a first time instant t.sub.1, between a second time instant t.sub.2 and a third time instant t.sub.3 and between a fourth time instant t.sub.4 and a fifth time instant t.sub.5. This movement mode M.sub.1 comprises small, relative rapid oscillations between two positions s.sub.1, s.sub.2. Here, the movement of the plunger 21 has only small amplitude A.sub.1 or a short stroke A.sub.1, with a uniform rate and a relatively high frequency. This movement serves exclusively to maintain the liquidity of the dosing material, whereby it is not liquefied to the extent that dosing material would continually seep from the nozzle. The first movement mode M.sub.1 may therefore be characterized as a liquidity maintenance mode.

(27) In contrast, the second movement mode M.sub.2, performed between the first time instant t.sub.1 and the second time instant t.sub.2, between the third time instant t.sub.3 and the fourth time instant t.sub.4, and between the fifth time instant t.sub.5 and a sixth time instant t.sub.6 comprises a different pattern of motion. It serves to eject dosing material from the dosing material collection cavity 17 and may therefore be described as an ejection mode. For this reason it has a greater amplitude A.sub.2 or longer stroke A.sub.2. Its frequency, which can be clearly seen in the double ejection movement between the fifth time instant t.sub.5 and the sixth time instant t.sub.6, is significantly lower than that of the motion in the first movement mode M.sub.1. The rate of this movement can also be described as uniform. The third movement mode M.sub.3, performed after the sixth time instant t.sub.6, comprises a simple stand-still of the plunger 21 and has the effect that the dosing material is initially slowed in the aperture gap 53 due to its inner friction, and then held, since its viscosity is no longer reduced by any motion of the plunger 21.

(28) The motion pattern of FIG. 7 differs from the motion graph of FIG. 6 only in the ejection mode M.sub.4. Instead of a simple saw-tooth up-and-down movement as in the second movement mode M.sub.2 of FIG. 6, the plunger 21 maintains its uppermost position s.sub.4 for a certain duration. During this time, dosing material can flow in front of the plunger 21. This is followed by a very rapid movement of the plunger 21 in the ejection direction E. The plunger 21 once again maintains its lowermost position s.sub.3 in the ejection direction for a certain duration. During this time, the movement of the dosing material is somewhat checked, in order to avoid a delayed release of dosing material with the subsequent movement of the plunger 21 in the retraction direction.

(29) The motion pattern of FIG. 8 again differs from the motion graph of FIG. 7 only in the ejection mode M.sub.5. Here, the motion pattern in the first movement mode M.sub.1i.e. the jittering motion of the plunger 21is superposed during the ejection movement on the motion pattern of the movement mode shown in FIG. 7. This is expedient when the viscosity of the dosing material increases relatively quickly when the extremely fine jitter motion ceases. Superposing the motion patterns ensures that the viscosity of the dosing material is continually lowered.

(30) FIG. 9 shows a motion pattern that can for instance be suitable for applying a rope, i.e. an uninterrupted band of uniform thickness, by closely depositing individual dots of dosing material side by side. Depending on the dosing material, the first and last drops might be larger than the intermediate drops, even if the stroke length of the plunger 21 was the same for each drop. In this case, it can be expedient to apply different ejection modes M.sub.2, M.sub.6, that only differ in their stroke lengths. For example, for the first and last drops, a movement mode M.sub.2 can be selected that has a shorter stroke than for the intermediate drops.

(31) The examples clearly show that it is ideally possible with the invention to precisely adjust the specific parameters of the different movement modes and the sequence of the movement modes to each of the dosage materials to be processed as well as to the dosing assignment. It shall once again be pointed out that the components of the dosing system or the nozzle and the actuator system described in detail above are simply exemplary embodiments that may be modified in various ways by the skilled person and whose features may be combined in new ways without leaving the scope of the invention. For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality. Furthermore, a unit may comprise one or more components that may also be spatially separate.

LIST OF REFERENCE SIGNS

(32) 1 nozzle 2 dosing system 5 dosing material container 7 dosing material reservoir 9 connecting screw 11 connecting stopper 13 supply line 15 feed inlet 17 dosing material collection cavity 19 outlet opening 21 closure element-plunger 23a first piezoelectric actuator 23b second piezoelectric actuator 25 actuator chamber 27 spacer 29 spacer adjusting screw 31 contact terminal 33 contact terminal 35 housing 37 first housing part 39 second housing part 41 retaining screws 43 springs 45 seal-ring seal 47 guiding element 49 connecting element 51 connecting element 52 cavity 53 gap 55 closure channel 58 holding means 59 actuator region 61 actuator system 63 electronic control unit A.sub.1, A.sub.2 amplitude-travel E ejection direction M.sub.1 movement mode-liquid retention mode M.sub.2 movement mode-ejection mode M.sub.3 movement mode-still-stand M.sub.4 movement mode-ejection mode M.sub.5 movement mode-ejection mode M.sub.6 movement mode-ejection mode R retraction direction s path S.sub.1 outside surface s.sub.1, s.sub.2, s.sub.3, s.sub.4 positions S.sub.2 inside surface SS.sub.1 first control signal SS.sub.2 second control signal t time t.sub.0, t.sub.1, t.sub.2, t.sub.3, t.sub.4, t.sub.5, t.sub.6 time instances WR effective direction axis X (central) axis Y region