DOSING SYSTEM WITH PIEZOCERAMIC ACTUATOR

Description

[0001] The invention relates to a metering system for a metering substance comprising a nozzle, a feed channel for the metering substance, an ejection element, and a piezoelectric actuator coupled to the ejection element and / or the nozzle. The invention further relates to the use of a piezoelectric actuator in a metering system for metering the metering substance, as well as a method for operating or manufacturing such a metering system.

[0002] In general, dispensing systems are used in a wide variety of applications to precisely dispense a medium, typically a liquid to viscous substance. In so-called "micro-dispensing technology," it is often necessary to apply very small quantities of the medium to the target surface with pinpoint accuracy and without contact, i.e., without direct contact between the dispensing system and the target surface. Such a contactless method is frequently referred to as a "jet dispensing method." A typical example is the dispensing of adhesive dots, solder pastes, etc., during the assembly of printed circuit boards or other electronic components, or the application of converter materials for LEDs.

[0003] A key requirement is the highly precise delivery of the dosing agents to the target surface – that is, at the right time, in the right place, and in a precisely measured quantity. This can be achieved, for example, by dispensing the dosing agent drop by drop through a nozzle of the dosing system. In this process, the medium only comes into contact with the interior of the nozzle and a section, usually the front, of the ejection element of the dosing system. A preferred method is the ejection of individual droplets using an "ink-jet" process, similar to that used in inkjet printers. The droplet size, or the amount of medium per droplet, can be precisely predetermined by the design, control, and resulting effect of the nozzle. Alternatively, the dosing agent can also be sprayed onto the target surface in a jet or mist.

[0004] To dispense the medium from the dosing system, a movable ejector element can be arranged in the nozzle of the dosing system. The ejector element can be pushed forward at a relatively high speed inside the nozzle towards a nozzle opening or outlet, thereby ejecting a droplet of the medium, which is then retracted.

[0005] Alternatively, the nozzle of the metering system itself can be moved in an ejection or retraction direction. To dispense the metering material, the nozzle and an ejection element located inside the nozzle are moved relative to each other. This relative movement can be achieved either solely by moving the outlet or nozzle, or at least partially by moving the ejection element.

[0006] The ejector element can typically be moved into a closed position by firmly engaging a sealing seat in the nozzle opening and remaining there temporarily. With more viscous metering media, it may also be sufficient for the ejector element to simply remain in the retracted position, i.e., away from the sealing seat, without any drop of the medium escaping.

[0007] Since the basic structure of the different types of dosing systems with piezo actuators and the underlying operating principles are generally known, they will not be discussed in more detail here.

[0008] Regardless of the specific dispensing or operating principle of the dosing system, the dispensing of the metering substance always involves a relative change in the position of the dispensing element and the nozzle or outlet opening relative to each other. The necessary movement of the dispensing element and / or the outlet opening is usually achieved using an actuator system within the dosing system. Such an actuator system can be implemented in various ways, with piezoelectric actuators being particularly preferred in applications requiring very fine dispensing resolution. Piezoelectric actuators, also known as piezoelectric actuators, offer the advantage over other types or actuators operating on different principles of very precise and, above all, faster controllability. Advantageously, piezoelectric actuators are characterized by extremely short reaction or response times.The typical response time of a piezo actuator, less than 0.1 ms, is significantly lower than that of other actuator types. Another advantage is that piezo actuators require comparatively little installation space within a dispensing system compared to other actuator types. Therefore, piezo actuators represent an efficient solution for operating dispensing systems, especially for highly precise dispensing requirements.

[0009] Despite these advantages, the reliability of piezoelectric actuators in dispensing systems has often proven insufficient in the past. Due to the high electric field strength applied to a surface of the piezoelectric actuator during operation, polar molecules, such as water molecules, are attracted from the ambient air of the actuator or dispensing system, leading to increased conductivity at the actuator surface, particularly in the case of ceramic piezoelectric actuators. As a result of the increasing leakage current, the piezoelectric actuator may need to be replaced after only a short period of use, causing the entire dispensing system to be out of service for a certain period. This unnecessarily reduces the efficiency of the dispensing system.

[0010] DE 10 2008 007202 shows a dosing system according to the state of the art.

[0011] It is therefore an object of the present invention to provide a dosing system with a piezo actuator, a use of a piezo actuator in a dosing system and a respective method for operating or manufacturing a dosing system with a piezo actuator, with which the disadvantages described above can be avoided.

[0012] This problem is solved by a dosing system according to claim 1, a use of a piezo actuator in a dosing system according to claim 12, a method for operating a dosing system according to claim 13 and a method for manufacturing a dosing system according to claim 14.

[0013] A metering system according to the invention for a liquid to viscous metering agent comprises at least one nozzle, a feed channel for the metering agent, an ejection element, and at least one piezoelectric actuator coupled to the ejection element and / or the nozzle to move the ejection element and / or the nozzle relative to each other. The metering agent to be dispensed enters a region of the metering system encompassing the nozzle via a feed channel.

[0014] The dispensing of the metering substance from the metering system according to the invention can be carried out according to any of the methods described above; that is, the metering system is not limited to a specific ejection or operating principle. Accordingly, as is usually the case, a ejection element movable at a relatively high speed can be arranged in the nozzle of the metering system (especially in the area of ​​the nozzle, e.g., shortly before the outlet opening) for ejecting the metering substance from the nozzle. Alternatively or additionally, as mentioned, an outlet opening of the metering system according to the invention can be designed to be movable. The outlet opening is an opening belonging to the nozzle of the metering system, leading from the interior of the metering system to the outside (which can also be a channel – usually very short) for dispensing the metering substance from the metering system. At least some areas or...A component of the nozzle, which includes the outlet opening, must be designed to be movable relative to other stationary parts of the metering system in an ejection and / or retraction direction.

[0015] In the metering system according to the invention, the metering agent is ejected from the nozzle by the ejection element itself. To eject the agent from the nozzle, the ejection element comes into contact with the metering agent to be dispensed and, due to a movement of the ejection element and / or the nozzle, "pushes" or "pushes" the metering agent out of the nozzle of the metering system. The metering agent is thus "actively" ejected from the nozzle by means of the ejection element. This distinguishes the metering system according to the invention from other dispenser systems in which a movement of a closure element merely leads to the opening of the nozzle, whereby the pressurized metering agent then escapes from the nozzle on its own. This is the case, for example, with fuel injectors of internal combustion engines.

[0016] Depending on the specific (previously explained) design of the dosing system according to the invention, the movement of the ejection element and / or the outlet opening is effected by a respective coupling of the ejection element and / or the outlet opening (i.e. the component with the outlet opening) with at least one piezo actuator of the dosing system.

[0017] In principle, the coupling is independent of the specific ejection principle of the metering system according to the invention, such that the forces and movements exerted by the piezo actuator are transmitted in such a way that the desired movement of the respective movable elements of the metering system, i.e., the ejection element and / or the outlet opening, results in the dispensing of the metering material from the nozzle. The at least one piezo actuator is designed and arranged such that it can move the respective movable elements of the metering system directly and / or indirectly, for example by means of a movement mechanism.

[0018] Preferably, the movement mechanism can include a coupling element to transmit the movements of the piezoelectric actuator to a movable element of the dispensing system. Particularly preferably, the coupling element can include a translation element to increase the displacement of the piezoelectric actuator by a specific value or factor. Specifically, the translation element can be configured to generate a specific translation ratio between a displacement or stroke of the piezoelectric actuator and a resulting movement or stroke of a movable element of the dispensing system. By means of the translation element, a displacement of the piezoelectric actuator can be translated into a specific, desired displacement of the movable element of the dispensing system.

[0019] Particularly due to such a translation element, the metering system is also particularly suitable for metering substances with a medium and high viscosity of e.g. up to 0.5 Pa*s, preferably up to 1 Pa*s, particularly preferably up to 1000 Pa*s.

[0020] The translation element can, for example, comprise a tiltable lever that is in operative contact with the piezo actuator and a movable ejection element of the dosing system, such as a plunger. This means that one lever arm is designed to generate a specific translation / stroke ratio.

[0021] According to the invention, the at least one piezo actuator of the dosing system is hermetically encapsulated in a housing. Preferably, a monolithic piezoceramic actuator, in particular a multilayer piezoceramic actuator, or a monolithic piezoelectrically operated multilayer actuator can be arranged in a hermetically sealed enclosure. The housing with the piezo actuator arranged therein, as well as any other elements associated with the housing, is hereinafter referred to as the actuator unit.

[0022] Within the scope of the invention, "hermetically sealed encapsulation" means that the housing surrounding the piezoceramic actuator is sealed so tightly that no substances can penetrate the housing from the outside. Conversely, this also means that no substances can escape from the interior of the housing to the outside. In particular, the housing is designed to be impermeable to water and moisture in general.

[0023] Preferably, the housing is designed to maintain a substantially constant "atmosphere" inside the housing, surrounding the piezoceramic actuator, for a specific period of time. In particular, the hermetically sealed housing allows a predetermined "atmosphere" to be maintained largely unchanged inside the housing even during operation of the encapsulated piezoceramic actuator in the dispensing system, i.e., during operation of the dispensing system according to the invention. A detailed description of the "atmosphere" and the housing surrounding the piezoceramic actuator is given elsewhere.

[0024] The invention further relates to the use of at least one hermetically sealed piezoelectric actuator in a housing in a dosing system for dispensing liquid to viscous dosing material. Preferably, the encapsulated piezoelectric actuator is used in a dosing system according to the invention as previously described.

[0025] Advantageously, in the dosing system according to the invention, with at least one hermetically encapsulated piezoelectric actuator, or by using such a hermetically encapsulated piezoelectric actuator in a housing within a dosing system, the piezoelectric actuator is largely or completely shielded from harmful or adverse external (environmental) influences, even during operation of the dosing system. This increases the service life or "longevity" of the piezoelectric actuator in the dosing system according to the invention, thus significantly reducing the frequency of replacing defective piezoelectric actuators compared to conventional dosing systems, i.e., without encapsulation of the piezoelectric actuator. Advantageously, this also significantly increases the (uninterrupted) operating time of the dosing system according to the invention.

[0026] By reducing undesirable or unscheduled downtime of the dosing system according to the invention, which inevitably results from an actuator change, the efficiency of the dosing system according to the invention can be significantly increased compared to conventional dosing systems. Furthermore, it is advantageous that the dosing system according to the invention can be used in new application areas, particularly those unsuitable for comparable dosing systems of conventional design, e.g., in environments with very high humidity or even underwater.

[0027] In an inventive method for operating a dosing system for dispensing a dosing substance with a piezoelectric actuator hermetically encapsulated in a housing, wherein the dosing system preferably corresponds to a previously described inventive dosing system, the operation of the dosing system is particularly preferably controlled as a function of at least one operating parameter of the encapsulated piezoelectric actuator. Preferably, the operating parameter is determined during the operation of the dosing system by means of at least one sensor arranged inside the housing. A (measured) value underlying the operating parameter can be transmitted to a control unit of the dosing system, whereby the control unit can regulate the operation of the dosing system as a function of the measured value (actual value) such that a predefinable setpoint value of the operating parameter is maintained or reached.Therefore, within the scope of the invention, a control unit also includes features of a control unit.

[0028] In a method according to the invention for manufacturing a dosing system for dispensing a dosing substance with a piezoelectric actuator, preferably for manufacturing a dosing system according to the invention, at least one piezoelectric actuator is hermetically encapsulated in its own housing (actuator housing). The housing of the piezoelectric actuator (actuator housing) is then inserted into a housing (housing block) of the dosing system. The piezoelectric actuator, together with its actuator housing, can be arranged in the housing block of the dosing system such that it is completely enclosed by the housing block, or it can be (at least partially) accessible from the outside, e.g., mounted in an open recess of the housing block.

[0029] Further, particularly advantageous embodiments and developments of the invention will result from the dependent claims and the following description.

[0030] In the context of the invention, a piezo actuator or piezoelectrically operated actuator, in particular a piezoceramic actuator, is defined as a component which may be made up of several elements, e.g. several stacked piezo crystals or layers of a piezoelectrically active material, in particular ceramic, but forms a composite which is controlled as a whole by a control unit, i.e., has, e.g., a common electrical connection for controlling its individual elements.

[0031] The encapsulated piezo actuator of the dosing system underlying this invention, apart from the housing, is preferably a monolithic piezoceramic multilayer actuator with a number of stacked layers of a piezoelectrically active material (e.g., lead zirconate titanate) and conductive inner electrodes arranged between the individual layers. Preferably, the inner electrodes are alternately applied to a surface of the actuator, electrically connected in parallel, and grouped into two clusters, which form the two terminal poles of the piezoceramic actuator. The basic structure of unencapsulated piezoceramic actuators is known, for example, from EP 0 844 678 A1.

[0032] In principle, it would be possible within the scope of the invention to hermetically encapsulate a plurality, i.e., two or more of the previously described piezo actuators, for use in the dosing system according to the invention in a common housing. However, unless explicitly stated otherwise, for the sake of simplicity, the following description assumes that a single piezo actuator, preferably a piezoceramic actuator, is hermetically enclosed in a housing, without limiting the invention thereto.

[0033] Depending on the specific design of the dosing system according to the invention, it may be preferred that a plurality of individually encapsulated piezoceramic actuators are arranged in a single dosing system according to the invention. For this purpose, a first encapsulated piezo actuator and a second encapsulated piezo actuator could be arranged one behind the other in such a way that the respective lengths of the two piezo actuators can be almost added together. If the two encapsulated piezo actuators are arranged parallel to each other, the forces exerted by the two piezo actuators at a single moment can be substantially added together.

[0034] Alternatively or additionally, in the dosing system according to the invention, a plurality of encapsulated piezo actuators could also be connected and / or aligned in opposite directions, e.g., in the manner of a "push-push arrangement". A dosing system operating according to this basic principle, albeit without encapsulated piezo actuators, is known from EP 2 969 248 B1.

[0035] Accordingly, in one embodiment of the dosing system according to the invention, one of two encapsulated piezo actuators of the dosing system can directly or indirectly push the outlet opening or a component of the nozzle that includes the outlet opening in a predetermined direction. This means that while the first of the two encapsulated piezo actuators expands and pushes the outlet opening in one direction, the second encapsulated piezo actuator contracts, thus creating the necessary space for the outlet opening to move in the desired direction. To move the outlet opening in the other (opposite) direction, the respective functions of the encapsulated piezo actuators are reversed; that is, the second piezo actuator expands again and now pushes the outlet opening, while the first piezo actuator contracts.

[0036] Advantageously, the invention can be used with all common types of dispensing systems with piezo actuators, as described in the introduction, regardless of the specific ejection principle. Therefore, in the dispensing system according to the invention, the movable ejection element and / or the movable outlet opening can each be coupled to a number of encapsulated piezoceramic actuators of the dispensing system according to the invention, where the term "number" is to be understood as meaning that the feature in question can be present singly or multiple times.

[0037] Nevertheless, for the sake of clarity, the invention—without limitation thereto—will be described below using a metering system in which the dispensing agent is released solely by means of a movable ejector element, the movement of which is effected by a single encapsulated piezoelectric actuator. As explained above, the ejector element is preferably configured to substantially completely close a nozzle opening or to firmly connect it to a sealing seat mounted inside the nozzle opening, thus sealing the metering system.

[0038] As already explained, the movement of the ejection element is effected by means of at least one hermetically encapsulated piezoelectric actuator of the dosing system. Preferably, the housing hermetically enclosing the piezoelectric actuator, i.e., the actuator housing, is designed to be resistant to fatigue.

[0039] Within the scope of the invention, "fatigue-resistant" or "fatigue-resistant" means that, within the typical service life of the piezoelectric actuator itself, i.e., after a number of oscillations (displacements) that the piezoelectric actuator can typically undergo during operation of the dosing system (due to its design), regardless of the encapsulation, no signs of fatigue appear on the housing itself. Preferably, the housing is designed such that no failure behavior occurs in the piezoelectric actuator. In particular, the occurrence of leakage currents at the actuator surface or the increase of such leakage currents beyond a predefinable (tolerable) limit value should be prevented sufficiently "permanently." "Sufficiently durable" within the scope of the invention means that the aforementioned advantageous features of the housing are maintained within the scope of typical operation.The service life of the encapsulated piezo actuator in a dispensing system should be essentially maintained under the conditions typically encountered. This assumes, for example, that the deflection of the encapsulated piezo actuator remains within the range typical for piezo actuators used in dispensing systems. Typically, the deflection of the (expanded) piezo actuator can be, for example, 1.4‰ to 1.7‰ of the piezo actuator at rest.

[0040] Preferably, the housing is designed such that it remains sufficiently intact during the use of the actuator unit in the dosing system, i.e., during operation of the dosing system. In other words, fatigue phenomena such as the appearance of cracks, slits, fissures, fractures, or other types of leaks in the housing area should be prevented under the conditions typically encountered during operation of the dosing system (e.g., with regard to the frequency and magnitude of the deflection, the temperature in the dosing system, etc.). Preferably, the housing is designed to form a sufficiently durable and continuously effective hermetic diffusion barrier for substances between the interior of the housing and the exterior surrounding the housing, particularly for moisture, e.g., for the duration of a typical (routine) maintenance interval of the dosing system. Preferably, the housing is diffusion-tight.Preferably, the housing is designed in such a way that it remains completely intact even after a number of at least 1*10^9, particularly preferably at least 1*10^10, cycles or deflections of the encapsulated piezo actuator.

[0041] Advantageously, a housing designed to withstand continuous vibration allows the dosing system to operate largely without interruption (at least as far as the piezo actuator is concerned) for a predefined period, e.g., a maintenance cycle. This reduces undesirable downtime of the dosing system and increases its efficiency.

[0042] To achieve fatigue strength in the housing, it can be predominantly made of a metallic material. Alternatively, individual areas of the housing could be made of a different, i.e., non-metallic, material. For example, a housing base and / or lid could be made of a ceramic material or a flexible membrane. Other materials are also conceivable, as long as they allow for a sufficiently durable hermetic seal of the housing, as defined above, even during operation of the dosing system.

[0043] Preferably, the housing can be designed, at least in sections, in the form of a folded metal bellows. For this purpose, the housing can comprise a base, preferably parallel to the surface, and an adjoining and firmly connected elongated body or housing shell, e.g., a metal tube. A bellows can be incorporated into the housing shell, at least in some areas. The upper end of the housing is formed by a housing cover, preferably parallel to the surface, which is firmly connected to the housing shell.

[0044] Preferably, the interior space formed within the sealed housing is dimensioned such that a piezoelectric actuator of the type described above can be arranged, preferably along its entire length, between the housing base and the housing cover. Preferably, the piezoelectric actuator can be arranged within the interior of the sealed housing such that its respective ends or end regions rest directly on the housing base or cover, particularly when the piezoelectric actuator is in a resting, i.e., unexpanded, state. Preferably, at least one end region of the piezoelectric actuator, e.g., an actuator base, can be rigidly connected to the housing base.

[0045] Preferably, the housing can be designed such that a surface of the piezo actuator arranged in the housing and an inner wall of the housing do not touch each other, at least in the area of ​​the housing shell. In other words, an inner cross-section of the housing shell or the housing, which runs essentially transversely to the longitudinal extent of the housing, can preferably be larger than a corresponding cross-section of the piezo actuator arranged in the housing.

[0046] Advantageously, by designing at least part of the housing in the manner of a metallic bellows, it can be achieved that the housing is at least partially flexible, thereby reducing its stiffness. This allows the piezoelectric actuator to expand as freely and unimpeded as possible within the housing when a voltage is applied. Advantageously, this ensures that essentially all the force generated by the piezoelectric actuator can be used to move the ejector element or nozzle of the dispensing system. Thus, the dispensing system combines the advantages of an encapsulated piezoelectric actuator (e.g., higher dispensing system efficiency) with those of an unencapsulated piezoelectric actuator (e.g., minimal additional resistance from the housing).

[0047] Piezoelectric actuators can exhibit temperature-dependent behavior. This applies equally to the deflection of the piezoelectric actuator under voltage and to its dimensions in the resting state. The temperature of the piezoelectric actuator can therefore have a direct impact on the functionality of the dispensing system and can, for example, undesirably influence the movement and / or position of the ejector element.

[0048] To monitor the temperature, preferably at least one temperature sensor can be arranged inside the housing. Alternatively or additionally, at least one temperature sensor can be arranged on an outer surface of the housing facing away from the encapsulated piezoelectric actuator or the housing's interior. For the sake of clarity, it is assumed below that at least one temperature sensor is arranged inside the housing, without limiting the invention to this.

[0049] Preferably, a temperature sensor can be arranged inside the housing in an area between the actuator and an inner wall of the housing. The inner wall of the housing comprises the respective inner surfaces of the housing base, casing, and lid—that is, all areas or surfaces of the housing that face the piezoelectric actuator for encapsulation or to form the interior of the housing. For example, a temperature sensor could be arranged in a central area between the piezoelectric actuator and the inner wall, or between the housing base and lid, thus "floating" freely within the housing. The temperature inside the housing can be used to control the operation of the dosing system (depending on this operating parameter), as explained below.

[0050] Preferably, at least one temperature sensor can be arranged on or attached to an outer surface of the piezoelectric actuator. Preferably, the temperature sensor can be arranged on the actuator's outer surface such that it is in sensing contact with the actuator's outer surface. The actuator's outer surface is also referred to as the actuator surface.

[0051] The temperature sensor can be positioned on the actuator surface in such a way that the temperature is measured in the immediate vicinity of the actuator surface. Alternatively or additionally, the temperature of the actuator surface itself could also be measured, e.g., as a measure or gauge of a temperature in the actuator core.

[0052] Preferably, a plurality of temperature sensors can be arranged in measuring contact with the outer surface of the actuator. For example, to detect a temperature gradient along the longitudinal extent of the piezo actuator, several temperature sensors can particularly preferably be arranged in different areas of the actuator surface. The longitudinal extent is understood to be the greatest or longest extent of the piezo actuator in one direction.

[0053] Preferably, a number of temperature sensors can be arranged in the peripheral (end) regions of the piezoelectric actuator, which form the respective outer terminations of the piezoelectric actuator along its longitudinal extent and are referred to as the foot and head regions of the piezoelectric actuator. Particularly preferably, one or more temperature sensors can also be arranged in a central region of the piezoelectric actuator located midway between the two opposing peripheral end regions. In particular, the central region can be characterized by a comparatively high temperature. This applies to both the actuator surface and the actuator core.

[0054] Furthermore, at least one temperature sensor can be arranged on or attached to the inner wall of the housing. Preferably, a number of temperature sensors can be arranged in measuring contact with the inside of the housing shell. For example, temperature sensors could be implemented on one or more protrusions or indentations of the bellows-like housing shell.

[0055] Additionally or alternatively, a number of temperature sensors could be arranged in the area of ​​the housing base and / or lid, particularly in the immediate vicinity of a foot or head area of ​​the piezo actuator or a passage through the housing which will be explained later.

[0056] Particularly preferably, the temperature sensors can be arranged in the housing such that the temperature sensors located on the inner wall, especially on the housing shell, and those located on the actuator surface are essentially opposite each other or face directly towards each other. Advantageously, this allows a temperature gradient between the respective area of ​​the actuator surface and the opposite area of ​​the housing or housing shell to be determined, in order to draw conclusions, for example, about the effectiveness of a cooling device in the dosing system.

[0057] Preferably, a temperature sensor can also be arranged inside the piezoceramic actuator or in a core (actuator core) of the piezoceramic actuator. In other words, the temperature sensor can be in measuring contact with the interior of the actuator. In a top view of a cross-section of a piezo actuator, the actuator core is understood to be the central, middle region of the cross-section of the piezo actuator. The actuator core therefore runs continuously along the longitudinal extent of the piezo actuator between the two peripheral ends that define the piezo actuator.

[0058] The temperature sensor can be located directly in the actuator core, i.e., in a central point of the cross-sectioned piezo actuator, or in a radially spaced (edge) area.

[0059] As explained above, a number of temperature sensors can also be arranged inside the piezo actuator in different areas (along the longitudinal extent) of the piezo actuator, e.g. in a foot area of ​​the piezo actuator, in the central area of ​​the piezo actuator and in a head area of ​​the piezo actuator.

[0060] Particularly preferably, a number of temperature sensors can be arranged in the housing such that the respective temperature sensors, which are located in several areas of the inner wall, the actuator surface, and the actuator core, are each situated on a common imaginary line. Preferably, these common lines are evident in both a top view of a cross-sectional and a longitudinal section of the piezoelectric actuator. A longitudinal section is understood to be a section along the longitudinal extent of the piezoelectric actuator.

[0061] In principle, the temperature sensors are designed to transmit the measured values, preferably via a temperature sensor connection cable, automatically and without prompting to a control unit of the dosing system, essentially in real time. The control unit can then evaluate, display, and / or store the measured values. However, it is particularly preferred that the control unit also regulates the operation of the dosing system based on the supplied temperature measurements, as explained below.

[0062] In principle, the hermetic encapsulation of the piezo actuator in the dosing system offers a number of advantages for the operation of the dosing system. While the basic design of encapsulated piezo actuators is already known, e.g., from EP 1 419 539 B1, it is not yet known for use in dosing systems of the type mentioned above.

[0063] Due to the high-precision dosing resolution typically required by a dosing system, the interior of the housing can heat up considerably in extreme cases—for example, at particularly high operating or dosing frequencies (frequency of the dispensing material or droplets)—as a result of the high-frequency expansion of the piezoelectric actuator and the associated heat generation. In such cases, the heat generated may not be dissipated quickly enough by the encapsulated piezoelectric actuator. To fully utilize the advantages of an encapsulated piezoelectric actuator in the dosing system, even under extreme conditions, it is beneficial to protect the piezoelectric actuator from overheating through additional measures.It has therefore proven particularly advantageous to continuously monitor the temperature in the critical areas of the actuator, especially in the actuator core, during operation of the dosing system in order to counteract any potential overheating of the piezo actuator at an early stage.

[0064] For this purpose, at least one temperature measurement (operating parameter) from inside the housing and / or an area of ​​the outer surface (exterior) of the housing, preferably a plurality of temperature measurements from different areas of the housing, can be supplied to the control unit as an actual temperature value. Depending on the supplied temperature measurement (actual value), the operation of the dosing system can be regulated by the control unit so that a predefinable setpoint temperature in this specific area, particularly inside the encapsulated piezo actuator, is reached or not exceeded. To achieve active temperature regulation (temperature management) in the housing or the encapsulated piezo actuator, the control unit can regulate the cooling capacity of a cooling device of the dosing system, as will be explained later.

[0065] Depending on the application of the dosing system, the control unit could also regulate the operation of the dosing system in such a way that the dosing frequency is temporarily reduced, thereby reducing the heat production by the piezo actuator by a certain degree.

[0066] Alternatively or additionally, the control unit can regulate the circuitry or control of the encapsulated piezo actuator depending on the temperature measurement. This compensates for temperature-related changes in the length of the (heated) piezo actuator and thus ensures the most precise possible dispensing of the metering agent at all times. By comparing the temperature measurement, which preferably corresponds to the temperature in the actuator core, with a predefined correction value (e.g., an actuator-specific, temperature-dependent expansion coefficient), the control unit can take the temperature-related change in length of the (heated) piezo actuator into account during the circuitry adjustment. This allows, for example, the voltage at contact to be reduced or increased accordingly.

[0067] To achieve the most efficient temperature management of the encapsulated piezo actuator, a thermally conductive medium can be arranged in the housing, i.e., in a space between the inner wall of the housing and an outer surface of the encapsulated actuator (actuator surface). Preferably, the thermally conductive medium is designed to dissipate heat from the actuator surface.

[0068] Preferably, the thermally conductive medium can be configured to transfer heat from the actuator surface to a region of the housing by conduction. Alternatively, the thermally conductive medium can be configured to transport heat from the actuator surface to a region or section of the housing by convection. A predominantly liquid thermally conductive medium can be used for this purpose, particularly preferably.

[0069] Preferably, the thermally conductive medium can have a temperature or heat resistance that is above the temperatures typically occurring on the surface of the piezoelectric actuator during operation of the dosing system. Preferably, the thermally conductive medium should be heat-stable at least up to a temperature of 140°C, particularly preferably up to at least 150°C, and especially up to at least 160°C.

[0070] In principle, it would also be possible to implement heat dissipation from the actuator surface using a heat pipe design. Accordingly, a (heat-conducting) medium could be arranged within the hermetically sealed housing (the heat pipe), with the medium existing in a liquid state to a lesser extent and a vapor state to a greater extent within the housing. The actuator surface could then represent a corresponding heat transfer surface for the heat source, with a predefined area of ​​the housing serving as the heat transfer surface for the heat sink. The design of a preferred "heat sink" within a specific area of ​​the housing will be discussed in more detail later.

[0071] Regardless of the specific design, the heat-conducting medium is preferably implemented as part of an "atmosphere" arranged inside the housing. Preferably, the "atmosphere" is configured such that particularly advantageous conditions for the operation and functionality of the encapsulated piezo actuator are created within the housing. Within the scope of the invention, the term "atmosphere" is broadly defined as a medium that substantially completely fills the interior of the housing, wherein the interior space is formed between an outer surface of the piezo actuator facing the interior (i.e., the actuator surface) and the inner wall of the housing. The atmosphere thus surrounds or envelops the actuator surface almost completely and could therefore also be referred to as the ambient medium. Preferably, the atmosphere can comprise a mixture of various gaseous, liquid, and / or solid media.

[0072] To achieve the most efficient possible heat dissipation from the actuator surface, the housing includes a defined heat dissipation area. This heat dissipation area is thermally coupled to a cooling unit of the dosing system.

[0073] A heat dissipation area, as used here, is understood to be an area that forms a heat sink towards the surroundings. In other words, the heat dissipation area represents a heat transfer surface for the heat sink. Besides an area of ​​the outer surface of the housing, the heat dissipation area can also include the corresponding area of ​​the inner wall of the housing, as well as intermediate areas of the housing, e.g., the metal body.

[0074] Preferably, the heat dissipation area is designed to transfer the process heat generated by the piezo actuator outwards via the housing, i.e., into an area of ​​the dosing system surrounding the housing. Particularly in conjunction with the cooling system's cooling unit, the heat dissipation area can be used to regulate the temperature within the housing, especially within the actuator core. For example, increased cooling by the cooling unit can increase the amount of heat dissipated in the heat dissipation area, thereby also dissipating more heat from the actuator surface.

[0075] Preferably, the heat dissipation area is designed and arranged in or on the housing, or as part of the housing, in such a way that the most effective possible heat dissipation from the heat dissipation area is achieved by means of the cooling device. For example, the heat dissipation area could be implemented by means of a number of cooling fins or other elements for increasing the surface area in a region or section of the housing shell. The heat dissipation area can therefore only be partial, i.e., it can only comprise a limited sub-area of ​​the housing.

[0076] The cooling device interacting with the heat dissipation area preferably uses a coolant flowing around the housing from the outside, which may comprise a gaseous and / or liquid medium. Preferably, at least the heat dissipation area, and optionally the entire actuator unit, may be surrounded by the coolant, which may comprise a mixture of different cooling substances.

[0077] In principle, the coolant is designed to carry heat away from the heat dissipation area to a location of lower temperature. For this purpose, a coolant, particularly a gaseous coolant such as ambient air, can be continuously supplied from the outside to a chamber (actuator chamber) of the dosing system surrounding the housing of the piezo actuator, allowing the coolant to flow through essentially the entire actuator chamber. Compressed air, i.e., conventionally compressed room air, is preferably used as the coolant, since compressed air is readily available in most systems anyway. The heat dissipation area or the housing then acts as a kind of heat exchanger: The heat generated by the piezo actuator and transferred to the housing, preferably the heat dissipation area, is transferred to the coolant or carried away from the housing by means of the coolant.

[0078] Preferably, the metering system can include at least one inlet and one outlet opening for the coolant. Preferably, a coolant-conducting channel, also referred to as an inlet channel, extends predominantly parallel to the actuator unit within the metering system housing, starting from the inlet opening of the metering system. This channel comprises a number of substantially right-angled, channel-like, coolant-conducting branches. Each of these branches extends from the inlet channel through the metering system housing in such a way that each branch forms an inlet opening into the actuator chamber for the coolant; that is, a single inlet opening of the metering system can interact with a plurality of inlet openings in the actuator chamber.

[0079] Preferably, to regulate the cooling capacity of the cooling device (and thus also to regulate the temperature in the housing), the volume of coolant supplied to the actuator chamber over time (actively) can be regulated by the control unit, e.g., depending on the temperature in the housing. Preferably, at least at the feed opening of the metering system, a "coolant supply device," e.g., a pump, which can be controlled by the control unit (preferably with a control unit), can be arranged to regulate the coolant flow into the actuator chamber (actively) so that a predefinable setpoint temperature is reached in a specific area of ​​the housing. Alternatively, a quantity of compressed air supplied from a compressor or compressed air reservoir can be regulated by the control unit using a proportional valve.

[0080] Preferably, the coolant in the actuator chamber can be directed specifically to the heat dissipation area of ​​the housing. Particularly preferably, each inlet opening of the actuator chamber can be associated with a corresponding outlet opening, wherein the respective inlet and outlet openings are positioned relative to each other and to the heat dissipation area such that the incoming coolant, on its way from a respective inlet opening to its corresponding outlet opening, is forced to flow around at least a portion of the heat dissipation area. Preferably, the individual outlet openings of the actuator chamber can combine to form a common outlet channel, which can be designed analogously to the inlet channel.

[0081] Alternatively, the actuator chamber could also comprise only a single inlet and outlet opening for the coolant, i.e., the inlet and outlet opening of the actuator chamber would simultaneously correspond to the inlet and outlet opening of the metering system. Preferably, flow-directing elements, such as guide vanes or fans, can be arranged in the actuator chamber to guide the incoming coolant as directly as possible from an inlet opening of the actuator chamber to the heat dissipation area and subsequently to an outlet opening of the actuator chamber. Alternatively or additionally, the coolant could also be circulated within the actuator chamber for a specific period of time, i.e., without an inflow of new coolant into the actuator chamber, provided that sufficient cooling capacity is achieved.

[0082] Depending on the nature of the coolant and the conditions prevailing in the coolant or in the housing, especially with regard to temperature and pressure exerted on the coolant, the coolant may also be predominantly liquid or partly liquid and partly gaseous.

[0083] Preferably, the cooling device can be designed such that mechanical abrasion, which results e.g. from the expansion movement of the housing or other moving parts in the actuator chamber, is carried away by the coolant from the actuator chamber to an area outside the actuator chamber, preferably outside the metering system.

[0084] Advantageously, efficient temperature management of the encapsulated piezo actuator can significantly increase the uninterrupted operating time of the dispensing system. The individual components involved in temperature management, especially when working together, form an effective temperature management system, enabling early detection and, advantageously, prevention of impending overheating of the piezo actuator. Through this temperature management system and the associated operating method for the dispensing system, the temperature of the piezo actuator can be kept nearly constant during operation, within a range that is beneficial for the actuator's longevity.

[0085] A further advantage is that the temperature management system also improves the precision of the dosing system. Under certain circumstances, the temperature-dependent expansion behavior of the encapsulated piezoelectric actuator can negatively affect the accuracy of the dosing system's dispensing accuracy, for example, if the ejector element can no longer reliably seal the nozzle due to a change in the piezoelectric actuator's length (longitudinal expansion). Advantageously, the temperature management system allows the piezoelectric actuator's temperature to be maintained at a specific setpoint, ensuring that the actuator maintains a substantially constant length during operation of the dosing system, thereby significantly increasing the system's precision.

[0086] For the sake of completeness, it should be noted that heat dissipation from the heat-dissipating area, i.e., the cooling of the encapsulated piezo actuator, can also occur, at least partially, through "natural" convection via the air surrounding the actuator unit. With this type of "passive" cooling, targeted temperature management of the piezo actuator is therefore not possible, making the previously described active temperature control preferable.

[0087] To enable the operation of the dosing system based on the temperature inside the housing as part of the temperature management system, at least one temperature measurement should be transmitted to the control unit. Therefore, the housing preferably includes at least one feedthrough for a number of electrical conductors or conductor tracks. More preferably, the housing includes at least two separate feedthroughs, more preferably at least three separate feedthroughs, and most preferably at least four separate feedthroughs, each for at least one electrical conductor.

[0088] Particularly preferably, the feedthroughs are designed and arranged in such a way that the respective electrical conductor runs hermetically sealed and electrically insulated between the interior or inner area of ​​the housing and an outer or outer area surrounding the housing.

[0089] Preferably, at least two of the electrical conductors are configured for communication with the control unit; that is, control signals for controlling the encapsulated piezoelectric actuator are transmitted from the control unit to the piezoelectric actuator. The piezoelectric actuator can, for example, have two contact points or terminals, each terminal being coupled to a group of the parallel-connected internal electrodes of the piezoelectric actuator. Preferably, each terminal of the piezoelectric actuator is permanently connected to one of the two electrical conductors, e.g., by soldering. Two further electrical conductors are preferably configured to contact a number of temperature sensors in the housing or to transmit corresponding temperature readings to the control unit. For example, a single PT100 temperature sensor could be contacted via the two electrical conductors.Alternatively, multiple (bus-enabled) temperature measurement ICs or IC temperature sensors could be contacted via the two electrical conductors. If multiple PT100 temperature sensors are arranged in the housing, each of these temperature sensors could be contacted via two separate electrical conductors, each dedicated to a specific temperature sensor.

[0090] Preferably, the electrical conductors can be implemented using electrical connectors or connecting pins. Preferably, each connector passes through the housing via a glass insert permanently integrated into the housing. Preferably, the respective glass inserts or glass feedthroughs can be incorporated into the housing base and / or housing cover. Particularly preferably, the electrical connectors or conductors are hermetically sealed and electrically insulated from the inside of the housing to the outside by means of a glass insert.

[0091] It should be noted that the connection of the encapsulated piezo actuator or the temperature sensors within the housing via the feedthroughs can also be achieved in a manner other than that described above. For example, at least one temperature sensor could be connected to a contact (terminal) of the piezo actuator, thus requiring only three feedthroughs. Additionally, a further feedthrough (e.g., for transmitting a measurement signal from the temperature sensor) could be eliminated by connecting the potential of the associated electrical conductor to the metallic housing, making it accessible from the outside. Alternatively, the temperature readings (sensor signals) of at least one temperature sensor could be applied to the terminals of the encapsulated piezo actuator and modulated accordingly, as is done, for example, when setting up a Powerline or DirectLAN connection.The (up-)modulation of the sensor signals could also be achieved by transmitting the temperature readings from multiple temperature sensors (e.g., bus-compatible temperature measurement ICs) to the control unit, or by transmitting the collected temperature readings from multiple temperature sensors as a single data stream. If the metallic housing were used as a contact element, as mentioned previously, the piezoelectric actuator and a number of temperature sensors could then be connected via a single feedthrough. However, the following discussion assumes a housing with four separate feedthroughs, without limiting the invention to this configuration.

[0092] Preferably, a through-hole electrical conductor can also include a multi-core cable for transmitting electrical signals. This also makes it possible to transmit the individual measured values ​​(measurement signals) of a plurality of temperature sensors to the control unit in parallel. For this purpose, a plurality of fine wires could be guided together through a single through-hole, with the individual wires arranged at a suitable distance from each other and potted together with glass solder. Such a through-hole could also be referred to as a multi-core through-hole.

[0093] Advantageously, the feedthroughs through the housing of the encapsulated piezo actuator allow it to be controlled in the same way as a conventional dosing system with an unencapsulated piezo actuator; that is, control units from conventional dosing systems can also be used to control the encapsulated piezo actuator. Furthermore, the temperature measurements taken allow the operation of the dosing system to be controlled based on the temperature inside the housing.

[0094] To further increase the longevity of the encapsulated piezo actuator, a moisture-suppressing medium can be arranged inside the housing, i.e., in an area between the inner wall of the housing and the surface of the actuator. Preferably, the moisture suppression is such that any moisture (e.g., water or water vapor) occurring inside the housing is immediately and substantially completely bound and / or converted. Preferably, the moisture-suppressing medium is designed to reliably shield or insulate the actuator surface from contact with moisture.In particular, the moisture-suppressing medium can be used to keep the amount of "available" water that could theoretically accumulate on the actuator surface sufficiently and permanently below a critical threshold for the operation of the piezo actuator, at least for the duration of typical use of the piezo actuator in the dosing system.

[0095] For moisture suppression within the housing, the moisture-suppressing medium can comprise various liquid and / or solid media that chemically convert or reactively consume moisture. Preferably, the moisture-suppressing medium can comprise at least one water-absorbing or hygroscopic medium, which can be implemented, for example, as a dry gel or in the form of a molecular sieve. Alternatively or additionally, the moisture-suppressing medium can comprise a water-transporting, electrically insulating medium. Preferably, a liquid, anhydrous, and water-conducting insulating medium can be used for this purpose.

[0096] Preferably, in addition to the heat-conducting or moisture-reducing medium, the atmosphere may also include other components that promote the uninterrupted operation of the dosing system.

[0097] Preferably, the atmosphere of the housing can include a pressure equalization zone. This pressure equalization zone, which could also be referred to as an expansion zone, provides a specific volume within the housing to compensate for the thermal expansion of the piezoelectric actuator. Preferably, the expansion zone is implemented using a gas or gas mixture that exhibits high compressibility. In principle, the medium forming the expansion zone can be freely dispersed within the atmosphere. For example, the atmosphere could include a liquid and / or solid moisture-reducing and / or thermally conductive medium, as well as a gaseous expansion zone, e.g., a gas bubble. Alternatively, the expansion zone could be located in a closed or enclosed space.The enclosed area must be separated from the rest of the interior of the housing by an at least partially flexible shell or partition, thus being materially separated from the rest of the atmosphere.

[0098] Advantageously, the pressure equalization zone is designed to compensate for temperature-related volume changes in the piezo actuator that occur during typical operation of the dosing system. This ensures that a predefined pressure inside the housing (internal pressure) remains essentially constant even during operation. By creating a defined atmosphere within the housing, both the uninterrupted operating time and the precision of the dosing system can be improved.

[0099] To continuously monitor the internal pressure during operation of the dosing system, at least one pressure sensor can be arranged in the housing to measure the internal pressure. Preferably, at least one pressure measurement can be supplied to the control unit as the actual pressure value, as already described analogously for temperature measurements. Preferably, the operation of the dosing system can also be regulated by the control unit based on the supplied pressure measurement value so that a predefined setpoint pressure value in the housing is not exceeded. For this purpose, the actual pressure value could be taken into account within the framework of the previously described temperature management; that is, the temperature and / or pressure in the housing can be regulated by means of the temperature management.

[0100] In addition to or as an alternative to the detection methods already mentioned, at least one strain gauge can be installed inside the housing (e.g., in the area of ​​the inner housing wall) and / or on an outer surface of the housing to monitor the absolute length and the dynamic length change of the encapsulated piezo actuator or the entire actuator unit. If a strain gauge is located inside the housing, the corresponding measurement signals can be routed through the housing to the control unit via a previously described feedthrough. The signal obtained in this way can provide information about the current operating state of the piezo actuator or the actuator unit and can therefore also be used for appropriate compensation measures, such as adjusting the coolant flow or changing the control voltage.

[0101] Preferably, the housing surrounding the piezoceramic actuator can exert a predefinable mechanical preload on the piezoceramic actuator. As explained above, the (stationary) piezo actuator is arranged in the housing such that the two peripheral end regions have direct contact with the housing base or cover. Preferably, the housing can be dimensioned and designed such that it exerts a specific pressure on the (stationary) piezo actuator or causes it to compress.

[0102] Advantageously, this allows the piezo actuator to be mechanically pre-tensioned in its resting state. This provides increased protection against tensile stresses in the piezoelectric material under dynamic loading, further reducing the failure probability of the dispensing system. Consequently, the design of the dispensing system can be simplified, as components (e.g., actuator springs) used in conventional dispensing systems to return the unencapsulated piezo actuator to its resting state can be eliminated or at least made weaker.

[0103] The invention is explained in more detail below with reference to the accompanying figures and exemplary embodiments. The same components are designated with identical reference numerals in the various figures. The figures are generally not to scale. They show: Figure 1 a cross-sectional view of an embodiment of a dosing system according to the invention, Figures 2 and 3 Parts of another embodiment of a dosing system according to the invention, shown in cross-section, Figures 4 and 5 Sectional views of different possible embodiments of actuator units for a dosing system according to the invention, Figure 6 a perspective view of another possible embodiment of an actuator unit for a dosing system according to the invention.

[0104] Based on the Figure 1A specific preferred embodiment of a dosing system 1 according to the invention will now be described. The dosing system 1 is shown here in its usual intended position, e.g., during operation. In this configuration, a nozzle 40 is located in the lower region of the dosing system 1, so that the droplets of the medium are ejected downwards through the nozzle 40 in an ejection direction R. Therefore, wherever the terms "bottom" and "top" are used below, these descriptions always refer to such a generally common position of the dosing system 1. However, this does not preclude the possibility that the dosing system 1 can also be used in a different position in specific applications, with the droplets, for example, being ejected laterally. Depending on the medium, pressure, and the precise design and control of the entire ejection system, this is also fundamentally possible.

[0105] The dosing system 1 comprises, as essential components, an actuator assembly 10 and a fluidic assembly 30. In the embodiment of the dosing system 1 shown here, the actuator assembly 10 and the fluidic assembly 30 are permanently connected to one another, e.g., by means of a fixing screw 23. However, it should be noted that the respective assemblies 10 and 30 can also be implemented as interlocking plug-in couplings to form a quick-release coupling. Accordingly, the actuator assembly 10 and the fluidic assembly 30 could be coupled to one another without tools to form the dosing system 1.

[0106] The actuator assembly 10 essentially comprises all components that provide for the drive or movement of an ejection element 31 in the nozzle 40, e.g. the actuator unit 60, a motion mechanism to actuate the ejection element 31 of the fluidics assembly 30, a control unit 50 to control a piezo actuator 61 and similar components, as will be explained below.

[0107] The fluidic assembly 30 comprises, in addition to the nozzle 40 and the supply line 44 of the medium to the nozzle 40, all other parts that are in direct contact with the medium, as well as the elements required to assemble the relevant parts in contact with the medium or to hold them in their position on the fluidic assembly 30.

[0108] In the embodiment of the dosing system 1 shown here, the actuator assembly 10 comprises a housing block 11 with two internal chambers: firstly, an actuator chamber 12 containing an actuator unit 60 with at least one piezoceramic actuator encapsulated in a housing 62 (not visible here); and secondly, an action chamber 13 into which a movable ejection element 31, here a plunger 31, of the fluidic assembly 30 projects. Via a movement mechanism 14, which projects from the actuator chamber 12 into the action chamber 13, the plunger 31 is actuated by the actuator unit 60 such that the fluidic assembly 30 ejects the medium to be metered in the desired quantity at the desired time. As will be explained later, the plunger 31 closes a nozzle opening 41 and thus also serves as a closing element 31.However, since most of the medium is only ejected from the nozzle opening 41 when the plunger 31 moves in the closing direction, it is referred to here as the ejection element 31.

[0109] To control the actuator unit 60, the actuator unit 60 or the piezo actuator arranged in the housing 62 (see Figure 4 ) electrically or via signal technology connected to a control unit 50 of the dosing system 1. The connection to this control unit 50 is made via control cables 51, which are connected at their ends to suitable actuator unit control connections 64, e.g. suitable plugs. Unlike in Figure 1As shown, the control connections 64 can be sealed and routed through the housing 10 in such a way that essentially no outside air can penetrate into the actuator chamber 12 in the area of ​​the respective control connections 64, e.g., as part of the compressed air cooling of the actuator unit 60 described below. The actuator unit 60, in particular the actuator unit control connections 64, can be equipped, for example, with a suitable storage unit (e.g., an EEPROM or the like) in which information such as an article name, etc., or control parameters for the actuator unit 60 are stored. This information can then be read by the control unit 50 to identify the actuator unit 60 and control it appropriately. The control cables 51 can comprise several control lines and data lines. However, since the basic control of piezo actuators is known, it will not be discussed further here.

[0110] For the hermetically sealed and electrically insulated passage of an electrical conductor through the housing 62, the actuator unit 60 comprises four contact pins 65 in a housing cover 67. The contact pins 65 are here (as also in the Figures 3 and 4 ) for the sake of clarity, they are arranged in parallel or in a row, whereby the contact pins 65 can also be implemented in another suitable arrangement (see Figure 6 The two outer contact pins 65 are used to control the piezo actuator and / or for communication between the piezo actuator and the control unit 50. Outside the housing 62, the contact pins 65 are coupled to the control unit 50 via the respective actuator control connections 64. Inside the housing 62, each contact pin 65 is connected to one of the two terminals of the piezo actuator (see figure). Figure 5The two contact pins 65 shown here in the middle are used to transmit the measured values ​​from temperature sensors 78 (see Figure 4 ) from the housing 62 to the control unit 50. For this purpose, the contact pins 65 are each connected on one side to the control unit 50 by means of temperature sensor connection cables 86 and on the other side (inside the housing) to the individual temperature sensors 78, preferably by means of respective temperature sensor connection cables (not shown here). A detailed description of the contacting of the temperature sensors in the housing will be given later.

[0111] The piezo actuator arranged in housing 62 (see Figure 4The housing 62 can expand and contract longitudinally within the actuator chamber 12 according to a control signal from the control unit 50. The actuator unit 60 can be inserted into the actuator chamber 12 from above. A spherical cap adjustable in height by a screw movement (not shown here) can then serve as the upper support, allowing precise adjustment of the actuator unit 60 to a movement mechanism 14, in this case a lever 16. Accordingly, the actuator unit 60 is supported downwards by a pressure piece 20 tapering at an acute angle on the lever 16, which in turn rests on a lever bearing 18 at the lower end of the actuator chamber 12. The lever 16 can be tilted about a tilting axis K via this lever bearing 18, so that a lever arm of the lever 16 projects through an opening 15 into the action chamber 13.At the end of the lever arm, it has a contact surface 17 pointing towards the plunger 31 of the fluidic assembly 30 coupled to the actuator assembly 10, which presses against the contact surface 34 of the plunger head 33. The piezo actuator or pressure piece 20 on the one hand and the plunger head 33 or a plunger 31 on the other act on the same side of the lever 16 with respect to the tilting axis K. However, the respective distances between the piezo actuator and the tilting axis K and between the plunger 31 and the tilting axis K are different.

[0112] The lever 16 or the movement mechanism 14 here represents a transmission element to increase the deflection (stroke) of the plunger 31 relative to the stroke of the piezoelectric actuator in a specific ratio. Such a transmission element is particularly advantageous for metering substances with a medium or high viscosity, wherein the viscosity can be up to 0.5 Pa*s, preferably up to 1 Pa*s, and most preferably up to 1000 Pa*s.

[0113] It should be mentioned here that in the illustrated embodiment, the contact surface 17 of the lever 16 is permanently in contact with the contact surface 34 of the plunger head 33, by means of a plunger spring 35 pressing the plunger head 33 downwards against the lever 16. However, it would also be possible, in principle, for a gap to exist between the plunger 31 and the lever 16 in an initial or rest position of the plunger spring 35, so that the lever 16 initially travels freely through a certain section of its path as it pivots downwards, thereby gaining speed, and then strikes the plunger 31 or its contact surface 34 with a high impulse to increase the ejection impulse that the plunger 31 then delivers to the medium. In order to enable an almost constant preload of the drive system (lever-actuator unit-motion system), the lever 16 is pushed upwards at the end where it comes into contact with the plunger 31 by an actuator spring 19.

[0114] In its lower section, the action chamber 13 includes a discharge opening 22 for a coolant, e.g., compressed ambient air. The discharge opening 22 runs through a chamber wall of the action chamber 13 or through the housing block 11 directly, i.e., without branching, from an interior of the action chamber 13 to an exterior of the metering system 1. In this case, the discharge opening 22 corresponds equally to the discharge opening 22 of the action chamber 13 and to the discharge opening 22 of the metering system 1.

[0115] The discharge opening 22, in conjunction with a corresponding supply opening 21 of the metering system 1 for the coolant in the upper region of the actuator chamber 12, can be used to ensure that the actuator chamber 12 and the action chamber 13 are continuously supplied with coolant. Preferably, mechanical abrasion from the actuator chamber 12 or action chamber 13 can be removed from the metering system 1 via the discharge opening 22 by means of the coolant flow. The supply opening 21 of the action chamber 12 corresponds here to the supply opening 21 of the metering system 1. Figure 1 The feed opening 21 includes an external plug nipple for contacting a hose for supplying compressed air to the actuator chamber 12.

[0116] Another essential aspect of the coolant mentioned is the cooling of the piezo actuator or actuator unit 60 encapsulated in the housing 62. This will be explained in detail elsewhere.

[0117] As mentioned, the fluidic assembly 30 is connected to the actuator assembly 10 by means of a fixing screw 23. The plunger 31 is supported on a plunger bearing 37 by means of the plunger spring 35, to which a plunger seal 36 is attached below. The plunger spring 35 pushes the plunger head 33 away from the plunger bearing 37 in an axial direction upwards. This also pushes a plunger tip 32 away from a sealing seat 43 of the nozzle 40. That is, without external pressure from above on the contact surface 34 of the plunger head 31, the plunger tip 32 is located at a distance from the sealing seat 43 of the nozzle 40 when the plunger spring 35 is in its rest position. Thus, in the rest state (unexpanded state) of the piezo actuator, a nozzle opening 41 is also free or unblocked.

[0118] The metering medium is supplied to the nozzle 40 via a nozzle chamber 42 and an adjoining feed channel 44. The feed channel 44 is connected to a medium reservoir 46 by means of a reservoir interface 45. Furthermore, the fluidic assembly can include a number of additional components commonly used in metering systems of this type, such as a frame part 47, a heating device 48 with heating connection cables 49, etc., to name just a few. Since the basic structure of metering systems is known, for the sake of clarity, primarily those components that at least indirectly relate to the invention are shown here.

[0119] Figure 2Figure 1 shows a cross-section of a portion of a metering system according to a further embodiment of the invention. The housing block 11 comprises the actuator chamber 12, in the interior of which the actuator unit 60 is arranged (shown here only by way of example). A narrow gap remains between the housing 62 and an inner surface 80 of the chamber wall 79, which forms the interior of the actuator chamber 12. This gap encircles the housing 62 and serves as the coolant flow channel. To supply the coolant to the flow area, the actuator chamber 12 is connected to an inlet channel 26 by means of an inlet opening 24, here in the form of an opening 24 through the chamber wall 79. The inlet channel 26 runs substantially parallel to the actuator chamber 12 through the housing block 11 and has a number of predominantly right-angled branching channels, whereby, due to the way the illustration is presented, only one inlet opening 24 and one outlet opening 25 are visible.Starting from the inlet opening 24, the coolant flow is, by design (and necessarily), directed to an associated outlet opening 25 such that the housing 62 is surrounded by coolant on both sides. The outlet opening 25 is connected to an outlet channel 27 for the discharge of coolant from the actuator chamber 12 or from the metering system 1.

[0120] Due to the bellows-like design of the housing, at least in the area of ​​the housing shell (see Figure 6 ), it can be achieved that the coolant flows in a targeted manner from a respective supply opening 24 to a corresponding discharge opening 25. The coolant can flow along a respective (horizontal) recess of the bellows-like or wave-shaped housing 62, with the coolant flow being limited upwards and downwards by the respective adjacent bulges. This is particularly advantageous in Figure 3 clearly.

[0121] In Figure 3The main purpose is to illustrate the operation of the cooling device of the dosing system, while other components of the dosing system are not shown for the sake of clarity.

[0122] The inlet channel 26 originates in a single feed opening 21 of the metering system and then branches out along the actuator chamber 12 into a number of feed openings 24 of the actuator chamber 12. To regulate the coolant flow into the inlet channel 26 or into the actuator chamber 12, a coolant supply device 28, here a pump 28, is interposed between a coolant supply 84 and the feed opening 21. The pump 28 can be controlled by the control unit 50 via a control connection 29. As an alternative to the embodiment shown here, the coolant supply device 28 or the pump 28 could also be arranged outside the housing 11 of the metering system. As part of the temperature management of the piezo actuator, temperature measurements from the housing 62 are supplied to the control unit 50 via a temperature sensor connection cable 86.Depending on one (or more) determined temperature values ​​(actual value), the control unit 50 can control the pump 28 so that a setpoint temperature in a specific area of ​​the housing 62, e.g., in the actuator core, is not exceeded. For this purpose, the amount of coolant supplied to the actuator chamber 12 by the pump 28 can be adjusted as needed.

[0123] As an alternative to using a separate pump for the coolant, e.g., to blow room air into the actuator chamber 12, compressed air from a reservoir of an existing compressed air system, already used for other purposes, can also be used to cool the actuator unit 60. In this compressed air system, room air is typically compressed and stored in an existing reservoir or storage tank (not shown) until it is supplied to the actuator chamber 12. The flow rate of the compressed air into the actuator chamber 12 can be regulated, e.g., by means of a proportional valve (not shown), whereby the proportional valve, as previously explained for the pump, can be controlled by the control unit 50 depending on at least one temperature value.

[0124] The inflow channel 26 runs directly along an outer surface 81 of the chamber wall 79, facing away from the inner surface 80 of the chamber wall 79. In other words, the inflow channel 26 is at least partially, i.e., in the direction of the actuator chamber 12, bounded or formed by the outer surface 81 of the chamber wall 79.

[0125] The actuator chamber 12 itself is formed inside the housing block 11 by the inner surface 80 of the chamber wall 79. Due to the bellows-like, wave-shaped design of the housing 62 of the piezo actuator, the housing 62 abuts directly against the inner surface 80 of the chamber wall 79 in the area of ​​each respective bulge 82. Periodically arranged between the respective bulges 82 are essentially horizontal indentations 83 or grooves 83. The at least partially bellows-like design of the housing 62 in the area of ​​the housing shell 74 (see Figure 6) corresponds to a preferred embodiment of the actuator unit 60, as explained below.

[0126] The actuator unit 60 is arranged in the actuator chamber 12 such that a supply opening 24 and a cooperating discharge opening 25 of the actuator chamber 12 are arranged in a horizontal plane with a single channel 83 of the housing 62. Thus, the gaseous or liquid coolant flowing in through a respective supply opening 24 is guided along a respective channel 83, which is vertically bounded by the adjacent projections 82, essentially horizontally from the supply opening 24 to the associated discharge opening 25, whereby the housing 62 is surrounded by flow for heat dissipation.

[0127] From the respective discharge opening 25, the coolant enters the outflow channel 27, which, analogous to the inflow channel 26, comprises or combines a number of discharge openings 25 of the actuator chamber 12 and finally opens into a single discharge opening 22 of the metering system, which in turn is coupled to a coolant discharge 85.

[0128] In Figure 4 Figure 1 shows a longitudinal section through an embodiment of an actuator unit of the dosing system according to the invention. The piezo actuator 61 is hermetically enclosed in a housing 62. The housing 62 comprises a base 66, a housing shell 74 firmly connected to it, and a housing cover 67 forming the upper end. The piezo actuator 61 rests directly on the base 66 with an inactive (foot) area 73, the opposite end area 73 of the piezo actuator 61 having direct contact with the housing cover 67. The piezo actuator 61 is firmly connected to the housing cover 67, e.g., by adhesive bonding.

[0129] The housing cover 67 includes four glass feedthroughs 69, through which the contact pins 65 are hermetically sealed and electrically insulated from the interior of the housing 62 to the outside of the housing 62. Each contact pin 65 is connected on one side of the piezo actuator 61 to an outer electrode 70 of the piezo actuator 61, e.g., by soldering. The two outer electrodes 70 run along the longitudinal extent of the piezo actuator 61 between the two inactive head and foot regions 73 on the outer surface 77 of the piezo actuator 61. This is particularly advantageous in Figure 5 clearly.

[0130] The two outer electrodes 70 connect the inner electrodes 71 arranged in the piezo actuator 61 and alternately guided to the surface, thus connecting them to form two electrically parallel groups (see Figure 4 ). The two connecting pins 65 thus form the two connection poles of the piezoceramic actuator 61.

[0131] Two further contact pins 65 serve to connect a number of temperature sensors 78 in the housing. Each of the temperature sensors 78 is connected to the two contact pins 65 via a respective temperature sensor connection cable (not shown). For contact, a (constant) measuring current is supplied to each temperature sensor 78 via one of the two contact pins 65 and the respective temperature sensor connection cable connected thereto. A measurement signal (e.g., a voltage change) from each temperature sensor 78 is transmitted via a respective temperature sensor connection cable (not shown) to a further (fourth) connection pin 65.For the transmission of the measurement signals (temperature measured values) of a plurality of temperature sensors 78 to the control unit, the individual sensor signals can, as already explained, be placed on only one contact pin 65 and modulated in a suitable manner, provided that the temperature sensors 78 are bus-capable IC temperature sensors.

[0132] Alternatively, it would also be possible to contact each temperature sensor 78 in the housing using two separate contact pins 65, each assigned only to the respective temperature sensor 78 (not shown here). Preferably, a decision can be made between the two alternatives depending on the situation, since while the separate contacting of each individual temperature sensor 78 using its own contact pins 65 reduces the electrical complexity of the modulation, it also places higher demands on the manufacturing of the actuator unit 60.

[0133] In Figure 4Three temperature sensors 78 are arranged in measuring contact with the inner wall of the housing 62 or with the housing shell 74 (shown here on the left). Furthermore, three additional temperature sensors 78 are arranged on the surface 77 of the piezo actuator 61 such that one temperature sensor 78 of the inner wall and one of the actuator surface 77 are located on a common, imaginary, predominantly horizontal line, as can be seen in the longitudinal section.

[0134] The actuator unit 60 comprises, in addition to the housing 62, the piezo actuator 61, and the connecting pins 65, the atmosphere arranged within the housing 62. In the embodiment shown here, the atmosphere consists of a liquid and a solid filling medium 75, as well as an expansion region 76. The expansion region 76 is represented here as a gas bubble 76 or gas-filled region 76.

[0135] In Figure 5A longitudinal section through another embodiment of an actuator unit 60 of the dosing system is shown. In contrast to Figure 4 Temperature sensors 78 are also arranged here at the inactive foot region 73 and in the inactive head region 73 of the piezo actuator 61, there in the immediate vicinity of the feedthrough 69. The expansion region 76 is enclosed here in a "balloon-like" manner, i.e., materially separated from the filling medium 75, and is arranged in the housing 62. For the sake of clarity, in Figure 5 Only one contact pin 65 is shown.

[0136] A strain gauge 87 is arranged on the outside of the piezo actuator 61 within the housing 62. The strain gauge 87 extends essentially along the entire longitudinal extent of the encapsulated piezo actuator 61, i.e., between a base region 73 and a head region 73. The corresponding measured values ​​(sensor signals) of the strain gauge 87 can be transmitted to the control unit of the dosing system via contact pins 65, as has already been explained analogously for the temperature sensors 78. Another strain gauge 87 is arranged on the outside of the housing 62, extending between the housing base 66 and the housing cover 67, and thus capable of detecting the total deflection (including any temperature-induced change in length) of the actuator unit 60 or the encapsulated piezo actuator 61.

[0137] The Figure 6Figure 1 shows a side perspective exterior view of a further embodiment of an actuator unit 60 for a dosing system according to the invention. The actuator unit 60 essentially corresponds to the one shown in Figure 2. Figure 1 , wherein the contact pins 65 and the feedthroughs 69 are arranged differently in the respective actuator units 60. In Figure 6The bellows-like housing shell 74 is clearly visible, comprising a periodic sequence of protrusions 82 and depressions 83 or grooves 83. In the embodiment shown here, the preferred heat dissipation area 68 of the actuator unit 60 corresponds essentially to, or is formed by, the entire bellows-like area of ​​the housing shell 74. The heat dissipation area 74 is designed such that, within the framework of the temperature management of the piezo actuator, the most efficient possible heat removal from the heat dissipation area 74 is achieved by means of the cooling device. The housing 62 has a predominantly circular diameter D, which is preferably larger than a corresponding diameter of the encapsulated piezo actuator 61.

[0138] Finally, it should be noted once again that the dosing systems described in detail above are merely exemplary embodiments which can be modified in various ways by those skilled in the art without departing from the scope of the invention. For example, the piezo actuator could be arranged in the housing without a defined "protective" atmosphere. Furthermore, the dosing system can include additional or alternative features or assemblies to the components described above, which are commonly used in dosing systems of the type described. Moreover, the use of the indefinite articles "a" or "an" does not preclude the possibility that the features in question may be present multiple times. Reference symbol list

[0139] 1 Dosing system 10 Actuator assembly 11 Housing block 12 Actuator chamber 13 Action chamber 14 Movement mechanism 15 Opening 16 Lever 17 Lever contact surface 18 Lever bearing 19 Actuator spring 20 Push piece 21 Dosing system feed opening 22 Dosing system discharge opening 23 Fixing screw 24 Actuator chamber feed opening 25 Actuator chamber discharge opening 26 Inlet channel 27 Outlet channel 28 Pump 29 Pump control connection 30 Fluidic assembly 31 Plunger 32 Plunger tip 33 Plunger head 34 Plunger contact surface 35 Plunger spring 36 Plunger seal 37 Plunger bearing 40 Nozzle 41 Nozzle opening 42 Nozzle chamber 43 Sealing seat 44 Feed channel 45 Reservoir interface 46 Medium reservoir 47 Frame part 48 Heating device 49 Heating connection cable 50 Control unit 51 Control cable 60 Actuator unit 61 Piezoelectric ceramic actuator 62 Housing 64 Actuator unit control connections 65 Contact pin 66 Housing base 67 Housing cover 68 Heat dissipation area 69 Glass feedthrough 70 Outer electrode 71 Inner electrode 72 Piezoactive material 73 Inactive area74 Housing shell 75 Filling medium 76 Expansion area 77 Actuator surface 78 Temperature sensor 79 Chamber wall 80 Inside of chamber wall 81 Outside of chamber wall 82 Housing bellows bulge 83 Housing bellows indentation 84 Coolant supply 85 Coolant outlet 86 Temperature sensor connection cable 87 Strain gauge D Diameter K Tilting axis R Ejection direction

Claims

1. A metering system (1) for a metering substance, comprising a nozzle (40), a feed channel (44) for a metering substance, a discharge element (31) and a piezo actuator (61) coupled to the discharge element (31) and / or the nozzle (40), wherein the piezo actuator (61) is hermetically encapsulated in a housing (62), characterized in that the housing (62) comprises a defined heat dissipation zone (68), wherein the heat dissipation zone (68) forms a heat sink to the environment, and wherein the heat dissipation zone (68) is thermally coupled to a cooling device (21, 22, 24, 25, 26, 27, 28, 84, 85) of the metering system (1).

2. The metering system according to Claim 1, wherein the housing module (62) is designed to be vibration fatigue-resistant.

3. The metering system according to any one of the preceding claims, wherein at least one temperature sensor (78) is arranged inside the housing (62) and / or on an outer side of the housing (62).

4. The metering system according to Claim 3, wherein at least one temperature sensor (78) is arranged on an outer side (77) of the piezo actuator (61) and / or inside the piezo actuator (61).

5. The metering system according to Claim 3 or 4, wherein at least one temperature sensor (78) is located on an inner wall of the housing (62).

6. The metering system according to any one of the preceding claims, wherein at least one strain gauge (87) is arranged inside the housing (62) and / or on an outer side of the housing (62).

7. The metering system according to any one of the preceding claims, wherein the housing (62) comprises at least one feed-through (69) for a number of electrical conductors (65).

8. The metering system according to any one of the preceding claims, wherein a thermally conducting medium (75) and / or a medium (75) for moisture suppression are located in the housing (62).

9. The metering system according to any one of the preceding claims, wherein a pressure compensation zone (76) is located in the housing (62).

10. The metering system according to any one of the preceding claims, wherein the cooling device (21, 22, 24, 25, 26, 27, 28, 84, 85) uses a coolant which comprises a gaseous and / or liquid medium.

11. The metering system according to any one of the preceding claims, wherein the cooling device (21, 22, 24, 25, 26, 27, 28, 84, 85) is designed in such a way that mechanical abrasion debris is removed from an actuator chamber (12) of the metering system (1) by the coolant.

12. Use of a piezoceramic actuator (61) hermetically encapsulated in a housing (62) in a metering system (1) according to any one of the preceding claims.

13. A method for operating a metering system (1) according to any one of the preceding Claims 1 to 11, wherein the operation of the metering system (1) is preferably regulated as a function of at least one operating parameter of the encapsulated piezo actuator (61).

14. A method for producing a metering system (1) for metering a metering substance, having a piezo actuator (61), wherein the piezo actuator (61) is hermetically encapsulated in a housing (62) and wherein the housing (62) of the piezo actuator (61) is arranged in a housing (11) of the metering system (1), wherein the housing (62) comprises a defined heat dissipation zone (68) wherein the heat dissipation zone (68) forms a heat sink to the environment, and wherein the heat dissipation zone (68) is thermally coupled to a cooling device (21, 22, 24, 25, 26, 27, 28, 84, 85) of the metering system (1).