Air jet screening machine and method for operating an air jet screening machine

Abstract

Shown and described is an air jet sieve machine (24), in particular for laboratory use, with a sieve passage housing (29) into which a sieve (5) that can be covered with a sieve lid (6) can be inserted, wherein the sieve (5) has a sieve bottom (8) and the sieve passage housing (29) delimits a sieve passage space (9) below the sieve bottom (8) when the sieve (5) is inserted, with a slotted nozzle (20) that is rotatable about a vertical central axis, wherein the slotted nozzle (20) is arranged in the sieve passage space (9) below the sieve bottom (8) when the sieve (5) is inserted, with a rotary drive (37) for the slotted nozzle (20) and with an air supply to the slotted nozzle (20) and an air discharge through the sieve passage housing (29) from the sieve passage space (9).According to the invention, a weighing unit (30) comprising the sieve passage housing (29) and a force measuring device with at least one force transducer (26) are provided, wherein the weight force of the weighing unit (30) can be transferred to the force transducer (26) and the weight force and / or the weight of the weighing unit (30) can be determined with the force measuring device.

Description

[0001] The invention relates to an air jet sieve machine, in particular for laboratory use, with a sieve passage housing into which a sieve that can be covered with a sieve lid can be inserted, wherein the sieve has a sieve bottom and the sieve passage housing, when the sieve is inserted, delimits a sieve passage space below the sieve bottom, with a slot nozzle rotatable about a vertical central axis, wherein the slot nozzle, when the sieve is inserted, is arranged in the sieve passage space below the sieve bottom, with a rotary drive for the slot nozzle and with an air supply to the slot nozzle and an air discharge through the sieve passage housing from the sieve passage space.

[0002] Furthermore, the present invention relates to a method for operating an air jet screening machine, in particular for grain size analysis, wherein the air jet screening machine has a screen passage housing into which at least one screen which can be covered with a screen cover can be inserted and which, when a screen is inserted, delimits a screen passage space below a screen bottom of the screen, and wherein the air jet screening machine has a slot nozzle which is rotatable about a vertical central axis and a rotary drive for the slot nozzle, an air supply to the slot nozzle and an air discharge through the housing from the screen passage space, a control and evaluation device and a force measuring device with at least one force transducer, in particular a load cell.

[0003] Finally, the present invention relates to a further method for operating an air jet screening machine, wherein an air supply to a slot nozzle of the air jet screening machine and / or an air discharge from a screening passage space through a screening passage housing of the air jet screening machine takes place via at least one fixed air inlet part, in particular connected to a machine frame, and / or at least one fixed air outlet part, in particular connected to a machine frame, and at least one seal is provided in the air flow path between the screening passage housing and the air inlet part and / or the air outlet part.

[0004] Sieving machines of this type and methods for operating such machines are used primarily in analytical sieving. They are primarily used to determine the fineness and grain size distribution of dry, powdery materials. Automation of analytical sieving is used to prevent operating errors and achieve high measurement accuracy and reproducibility.

[0005] Air jet screening machines have a housing onto which a sieve can be placed. The sieve usually consists of a frame with a flat sieve base made of sieve mesh. The sieve space above the sieve base is closed with a lid during sieving. Below the sieve, the housing has an open space. In this sieve passage space, a slotted nozzle is arranged, which rotates around the vertical center axis of the sieve. During sieving, air is blown against the sieve from below through the evenly rotating slotted nozzle, or the sieve space below the sieve is vacuumed using a powerful suction unit. The air stream rinses the mesh of the sieve clear and swirls up the sieved material lying on the sieve. Fine particles in the sieve are carried along by the air jet and transported as sieve passage through the sieve mesh from top to bottom into the space below the sieve. The sieve passage can then be vacuumed orseparated via a cyclone and collected in a sample tube. Coarse particles larger than the mesh size of the respective sieve cannot pass through the sieve bottom and remain on the sieve bottom as sieve residue after sieving.

[0006] To determine a particle size distribution curve, several sieves must be sieved using sieves with different mesh sizes. For this purpose, the coarse fraction remaining on the sieve after the first sieve, the sieve residue, is subjected to further sieving. The first sieve used with a first mesh size is removed from the screening machine, and a second sieve with a larger mesh size is inserted. The sieve residue from the first sieve is fed to the second sieve and a second sieving is carried out. The sieve residue remaining from the second sieve is then fed to a third sieve. If required, several sieves can be carried out in the desired particle size increments using sieves with different mesh sizes. After each sieving, the sieve residue must be weighed in order to determine the particle size distribution curve.However, material can also be re-weighed and subjected to a sieving process for each sieving.

[0007] The manual weighing of the sieve sample, the collection and manual weighing of the sieve residue and the calculation of the particle size distribution curve in sieve analyses require a considerable amount of time and personnel.

[0008] In order to make the operation of air jet screening machines easier and therefore more economical, it is already known from the prior art to determine the mass or weight of the screening residue via its weight with the help of load cells. For example, DE 44 19 153 A1 discloses a generic air jet screening machine, wherein a load cell with a force introduction point on the center axis of the screen is arranged below the housing. The known air jet screening machine has a three-armed holder which is attached to the load cell with a connecting element at the force introduction point and which carries a lifting ring via rods for receiving a test sieve, which is inserted into the lifting ring via an elastic support ring. The load cell is attached to a receiving part which carries an adjustment device with which the load cell together with the lifting ring can be moved or adjusted in the direction of the center axis of the screen relative to the housing.The adjustment device can be designed as a motor with a threaded spindle engaging in the housing. During sieving, the receiving part with load cell and holder and thus also the lifting ring are in a lowered position, i.e. a rest position, with the lifting ring disengaged from the support ring on the test sieve. The test sieve therefore rests with its support ring in a form-fitting manner on a seat of the housing. After sieving is finished, the receiving part and the parts fastened therein are raised by the adjustment device so that the lifting ring engages with the support ring and with it the test sieve is lifted from its seat on the housing. The load cell can then determine the total weight of the test sieve and sieve residue as well as the lifting ring with holder and can determine the amount of sieve residue using the empty weight of the test sieve determined before sieving.

[0009] The lifting of the test sieve from the housing of the air-jet screening machine, which defines the sieve passage space, as known from DE 44 19 153 A1, is structurally complex and prone to failure due to the precise engagement of the lifting ring and support ring required to lift the test sieve. In particular, the intended insertion of the test sieve into the lifting ring via the support ring requires considerable time and complicates the operation of the known air-jet screening machine. The automatic lifting of the test sieve required for determining the mass of the sieve residue is also time-consuming, which is disadvantageous, particularly in connection with the determination of a particle size distribution curve based on multiple sievings in the desired particle size increments using sieves of different mesh sizes.The prior art method also requires determining the net weight of the test sieve prior to sieving, which increases the time and manual effort required to determine the mass of the sieve residue. Another significant disadvantage of the known design is that sample particles fall through the sieve mesh when the sieve rests on the lifting rod. Thus, the known air jet sieve machine can only determine the weight of the sieve residue; the mass of sample particles that have fallen through the sieve mesh cannot be determined using the load cell.

[0010] The object of the present invention is to provide an air-jet screening machine and a method for operating an air-jet screening machine of the type mentioned above, which are characterized by a high degree of automation and high measurement accuracy, as well as minimal time and manual effort in determining the mass of the screening residue. Furthermore, the air-jet screening machine should have a simple design and allow the weight of the screening residue to be determined with high operating comfort. Finally, a simple method for determining the screening duration of a screening process and for screening identification should be provided.

[0011] The aforementioned objects are achieved by an air jet screening machine having the features of claim 1, by a method for operating an air jet screening machine having the features of claim 13, and by a method for operating an air jet screening machine having the features of claim 14. Advantageous embodiments of the invention are the subject of the dependent claims.

[0012] To achieve the above-mentioned objects, according to the invention, in an air jet screening machine of the type mentioned at the outset, a weighing unit comprising the screening passage housing and a force measuring device or weighing device with at least one force transducer are provided, wherein the weight of the weighing unit, in particular of the screening passage housing, can be transferred to the force transducer and the weight and / or the weight of the weighing unit can be determined with the force measuring device.

[0013] According to the invention, the sieve passage housing is a mass component of the mass of a weighing unit, which is determined using the force measuring device provided according to the invention. Unlike the air jet screening machine known from DE 44 19 153 A1, the invention provides for the measurement or determination of the weight force and / or the weight of the sieve passage housing.

[0014] A first method according to the invention for operating an air jet screening machine, in particular for grain size analysis, accordingly provides the following method steps: - Determination of the weight force and / or the weight of a weighing unit comprising the sieve passage housing with the force measuring device and, preferably, - Determination of the weight of a sieve residue taking into account the determined weight force and / or the determined weight of the weighing unit.

[0015] The air jet screening machine according to the invention and the method according to the invention for operating an air jet screening machine, in particular for grain size analysis, are particularly associated with process, cost and handling advantages.

[0016] A particular advantage is that, according to the invention, the mass of the weighing unit can be derived together with the mass of the complete sample via the force transducer. The integration of a weighing function into the air jet sieve machine eliminates the need for weighing using an external scale, resulting in less space and lower equipment costs compared to weighing with an external scale. Furthermore, the integration of a weighing function into the air jet sieve machine avoids interface problems when using external scales and reduces maintenance effort. Finally, an external scale often represents a non-validated process component, which is also a disadvantage when weighing with an external scale.

[0017] The measurement of the weight of the weighing unit or the determination of the weight of the weighing unit provided by the invention enables automated weight determination of the sieve residue in a structurally simple manner with low susceptibility to failure and high ease of use. By determining the weight of the weighing unit and / or the weight of the weighing unit with the force sensor, a very precise weight determination of the sieve residue is possible with significant time savings, especially compared to manual weighing of the sieve residue.

[0018] The weighing unit of the air jet screening machine according to the invention comprises in particular a screen passage housing of the air jet screening machine, which delimits the screen passage space, and optionally further components connected to the screen passage housing, the masses of which are recorded together with the mass of the screen passage housing when weighing the weighing unit.

[0019] In particular, when determining the weight of the weighing unit, the mass of a sieve inserted into the sieve passage housing, if applicable the mass of a sieve cover and / or the mass of a sieve sample placed on the sieve as well as parts of the sieve passage can be taken into account and / or measured or determined.

[0020] According to the invention, the sieve and sample can be handled together with the weighing unit, in particular together with the sieve passage housing, which simplifies handling and reduces the risk of sample fragments being carried over, spilled, and lost during transfer into transfer vessels. The use of transfer vessels is provided for in the prior art when external precision balances with a typically small weighing platform and / or draft shield are used.

[0021] In contrast to the procedure known from DE 44 19 153 A1, whereby the sieve must be lifted from the housing using a lifting device to determine the weight of the sieve residue, the invention provides a weighing unit which comprises or has the sieve passage housing and optionally further components and component groups, wherein the weight of the weighing unit is transmitted to the force transducer and the weight and / or the weight of the weighing unit is determined using the force measuring device. By weighing the sieve passage housing as part of the weighing unit, optionally together with a sieve inserted into the housing and further optionally with a sieve sample inserted into the sieve and / or with the sieve residue, the method according to the invention eliminates the need to mechanically lift the sieve using an adjusting device, which also leads to a shorter time for determining the weight of the sieve residue.

[0022] According to the invention, the determination of the weight force and / or the weight of the weighing unit using the force transducer of the weighing device can be carried out discontinuously before inserting a sieve into the sieve passage housing of the weighing unit or after the sieve, optionally with the sieve cover, has been inserted into the sieve passage housing. The method according to the invention thus also enables a simple determination of the weight of the sieve and, optionally, the sieve cover.

[0023] The method according to the invention can in particular comprise the following method steps: First, the empty weight of the weighing unit enclosing the sieve passage housing is determined in a first process step before a sieve is inserted into the sieve passage housing. For this purpose, the weight of the weighing unit is transferred to the force transducer. The determined weight or the determined weight of the weighing unit can be stored in a memory of the force measuring device.

[0024] Subsequently, in a second process step, a sieve without a sieve cover can be inserted into the sieve passage housing of the weighing unit, and the total weight of the weighing unit with the sieve inserted into the sieve passage housing can be determined. For this purpose, the weight of the weighing unit together with the weight of the sieve inserted into the sieve passage housing is transmitted to the force transducer. The total weight of the weighing unit with the sieve inserted into the sieve passage housing can be stored in a memory of the force measuring device. The empty weight of the sieve can be determined by subtracting the mass of the empty weight of the weighing unit determined in the first process step before inserting a sieve into the sieve passage housing. The empty weight of the sieve can be determined by taring the resulting weighing system or by weight compensation.

[0025] In a third process step, a sieved material or a sieve sample can then be placed onto the sieve inserted into the sieve passage housing of the weighing unit. The total weight of the weighing unit, including the sieve and the sieve material placed onto the sieve, as well as any sieve material components that have fallen through the sieve onto the sieve passage housing, can then be determined again. The weight of the sieved material is determined from the total weight thus determined, after subtracting the empty weight of the weighing unit determined in the first process step and the weight of the sieve determined in the second process step. The previous masses can be deducted by taring the resulting weighing system or weight compensation. The weight of the sieved material can be stored in the memory of the force measuring device.

[0026] In a fourth process step, the sieve lid can then be placed on the sieve and the total weight of the weighing unit can be determined, including the sieve inserted into the sieve passage housing of the weighing unit, the material to be sieved placed on the sieve, the material to be sieved that has already passed through the sieve, and the sieve lid placed on the sieve. The force is transferred from the weight of the weighing unit, together with the weight of the sieve, the weight of the material to be sieved, and the weight of the sieve lid, to the force transducer. Here, too, the total weight can be stored in the weighing device's memory. Before placing one of the masses of sieve, sample, and lid on the sieve, all other masses of the travel unit can be deducted by prior taring, so that only the weight of interest in the respective process step can be displayed or stored in isolation.

[0027] The fifth process step involves sieving. The space beneath the sieve bottom can be vacuumed using a powerful suction unit. The air drawn in flows through the slotted nozzle, which rotates just below the sieve bottom. The incoming air swirls the material being sieved and distributes it evenly across the entire sieve surface. The air flow reorients the particles on the sieve surface, and particles smaller than the sieve mesh size are vacuumed away or can be separated by a cyclone and collected in a sample tube.

[0028] At the end of the sieving process with a rotating slotted nozzle, a tapping sieve can be used to transmit vertical tapping pulses, in particular, to the sieve and / or sieve lid to complete the sieve passage of the sample. Tapping is usually used to remove sample deposits from the sieve or lid that have stuck to the sieve due to residual moisture or have remained above the sieve mesh due to electrostatic adhesion.

[0029] A further aspect of the present invention, which may also be subordinate to the above-described features, i.e. which can be implemented independently of the features described above, relates to a sieve lid for a sieving machine, in particular for an air jet sieving machine, having the preamble features of claim 1, wherein the sieve lid consists of a conductive antistatic plastic (ESD plastic) or comprises such a plastic. This makes it possible to reduce or completely prevent adhesion of sample particles to the sieve lid due to electrostatic effects. A statically charged sieve lid, on the other hand, can act like a magnet for light, powdery sample components. Sample adhesion to the sieve lid can falsify the result of the weight force determination. By tapping, it is possible to at least partially knock off sample particles adhering to a statically charged sieve lid.However, tapping is less convenient to use.

[0030] An embodiment in which an air flow is conveyed by a turbo machine via the air supply to the slot nozzle is not excluded.

[0031] During the screening process, a large portion of the screening material is removed from the screening chamber along with the air discharged from the screening housing. Parts of the screening material can settle on the housing base, parts of the slotted nozzle, and, if applicable, a discharge duct provided and / or formed on the screening housing through which the air is discharged from the screening housing along with the screening material. These particles are then present in the weighing unit at the end of the screening process.

[0032] In order to easily determine the sieve residue on the sieve bottom after the sieving process without manual sieve weighing, a sixth process step is provided for determining the weight of the weighing unit including any sieve residue deposited in and / or on the sieve passage housing or on machine parts connected to the sieve passage housing, the sieve with sieve cover inserted into the sieve passage housing, and the sieve residue remaining on the sieve bottom. The total weight can then be stored in the weighing device's memory. Taring can then be provided so that the weight value is zero before the sieve, sieve cover, and sieve residue are lifted from the sieve passage housing. When the masses of the sieve, sieve cover, and sieve residue are subsequently lifted, a negative backweighing value results.

[0033] Finally, in a seventh process step, the sieve, including the sieve residue and sieve lid, is lifted from the weighing unit to determine the weight of the sieve residue. The weight of the sieve residue is then calculated from the total weight of the weighing unit determined in the sixth process step, including any deposited sieve residue, sieve with sieve lid, and sieve residue, minus the weight of the sieve and sieve lid previously determined or determined by manual sieving. Manual weighing of the sieve with the sieve residue and, if applicable, the sieve lid is not necessary. If taring is planned at the end of the sixth process step as described above, the mass of the sieve residue can then be determined from the negative residual weight using the known weight of the sieve and sieve lid.

[0034] The method according to the invention thus enables the weight of the sieve residue to be determined in a convenient manner with high accuracy of the weight determination and with high operating comfort.

[0035] Preferably, the determination of the weight force and / or the weight of the weighing unit is carried out with the force transducer before and after the end of a screening process, i.e. before and after the end of the rotational movement of the slot nozzle. In principle, however, it is also possible to continuously determine the weight force and / or the weight of the weighing unit during the screening process, whereby with increasing duration of the screening process, the weight force and / or the weight of the weighing unit decreases due to the discharge of the screening passage from the screening passage housing of the weighing unit. In this context, a control and / or evaluation device of the air jet screening machine can be designed such that a screening process is automatically terminated when a predetermined weight or force value of the weighing unit and thus a predetermined screening duration is reached.If the weighing signal does not change or changes only insignificantly over a certain period of time, the control and / or evaluation device can also automatically terminate a sieving process.

[0036] Furthermore, the operator of the air jet screening machine can easily determine whether a screen is inserted into the screen passage housing or not from the weight or force value output by the force measuring device. This simplifies the process for the operator and allows for a simple plausibility check.

[0037] A precise weight or force value can correlate with a specific sieve weight, so that the weight or force value can also be used to determine whether a specific sieve is inserted into the sieve passage housing. In this context, an automatic control of the air jet screening machine can be provided depending on the weight force determined by the force measuring device and / or the specific weight of the weighing unit, in particular such that screening is only performed when a weight or force value is reached that corresponds to or exceeds the weight or force value of the weighing unit with the sieve inserted.

[0038] To enable sieve recognition based on the determined weight force and / or the determined weight of the weighing unit, it is also preferable to use sieves with different mesh sizes and different sieve weights. Thus, each sieve can be assigned a specific sieve weight that uniquely identifies the respective sieve.

[0039] Particularly preferably, the weight force and / or the weight of the weighing unit can be determined in a mass-decoupled manner from the weight force of a machine frame and components of the air jet screening machine connected to the machine frame. The term "mass-decoupled" in the sense of the invention means that only the weight force of the weighing unit is measured, and the mass of the machine frame and other components connected to the machine frame, in particular a machine housing and / or a base plate of the screening machine and / or a rotary drive for the slot nozzle, are not taken into account when determining the weight (force) of the weighing unit. The machine frame serves to secure the geometric position of machine elements and machine devices, to absorb loads, forces, and moments occurring during the machine process, and to accommodate functional assemblies.In the following, components that are connected to the machine frame are referred to as “fixed”.

[0040] A “fixed” machine part is in particular a machine part that is directly or indirectly connected, in particular rigidly, to a machine frame, a machine housing and / or a base plate of the air jet screening machine.

[0041] The force transducer can have at least one deformable, in particular bendable and / or deflectable, measuring body. The measuring body is connected to a machine frame of the air jet screening machine, and the weight of the weighing unit is transmitted to the measuring body, and the measuring body is deformed and / or deflected due to the transmission of the weight. The force measuring device comprises a force transducer with a measuring body and control and / or evaluation electronics, in particular signal processing electronics, for converting a measurement signal from the force transducer into a weight or force value. The measuring body can be rigidly connected to or attached to a machine part of the machine frame, for example, a frame component, a base plate, or a machine housing.By introducing the weight force of the weighing unit into the measuring body, the measuring body is then deformed and / or deflected from a rest position, whereby a measured variable dependent on the deformation / deflection state of the measuring body is recorded in order to determine the weight force or weight transferred from the weighing unit to the measuring body.

[0042] Particularly preferably, weight is determined using a load cell. The load cell contains a spring body as the measuring body, which is rigidly connected at one end to the machine frame or to a component of the screening machine rigidly connected to the machine frame. A force introduction point for the weight of the weighing unit can then be provided at the other, free end of the measuring body in order to introduce the weight of the weighing unit into the load cell. Due to this force introduction, a slight elastic deformation or geometric change, in particular a deflection, of the measuring body occurs. As a result, the electrical resistance of the strain gauges changes proportionally to the deformation caused by the applied weight load of the weighing unit. Using signal conditioning electronics, the electrical resistance of the strain gauges can be measured, and the resulting signal can be output as a weight or force value.

[0043] The measuring body can, in principle, be formed by any component of the screening machine according to the invention that is rigidly connected to a stationary machine part or directly or indirectly to the machine frame and whose geometry changes under the influence of the weight or weight force of the weighing unit, or that is slightly elastically deformed under the influence of the weight or weight force of the weighing unit. Elastic deformation of the component is then detected by strain gauges and converted into an electrical signal.

[0044] In particular, the component can be a substantially rigid pipeline which is connected to the weighing unit, in particular the screen passage housing, and the machine frame or a component of the screening machine which is rigidly connected to the machine frame. The supply of air to the slotted nozzle and / or the discharge of air from the screen passage housing together with the screen passage can take place via the pipeline, which forms a spring body or measuring body of a load cell. The pipeline can be rigidly connected at one end to the weighing unit, in particular the screen passage housing, and at the other end to the machine frame or a component of the screening machine connected to the machine frame, in particular a fixed air inlet part and / or a fixed air outlet part, and can have a sufficiently high elasticity such that the geometry of the pipeline adapts to the effect of the weight orthe weight of the weighing unit. An elastic deformation of the pipe is then detected by strain gauges and converted into an electrical signal. At least one pipe connection between the weighing device and a stationary screening machine part allows the air supply to the slotted nozzle and / or the air discharge from the screen passage housing to be carried out together with the screen passage without the need for sealing elements in the area of ​​the air supply and / or air discharge, which further simplifies the design of the machine.

[0045] The force measurement can be based on the principle of a beam balance and include a position-measuring system that determines the deflection of a beam arm when subjected to the weight of the weighing unit. This enables high precision in weight determination, repeatability, speed, and temperature compensation.

[0046] Electromechanical force compensation is also possible and advantageous. Scales or load cells with electromagnetic force compensation are basically beam scales. However, with electromagnetic force compensation, the counterforce to the load on the reference side is generated using a coil that acts as an electromagnet and a permanent magnet into which the coil is immersed. A lever system reduces the load to such an extent that it can be compensated by the electromagnet. A position sensor, often optical, on the lifting beam influences the current in the coil used for force compensation via a control amplifier. The current, which is strictly proportional to the compensating force, is converted into a voltage via a shunt with high long-term stability and a low temperature coefficient of electrical resistance. This voltage is usually fed to an analog-to-digital converter.This allows for subsequent digital processing of the measurement results. Such a load cell enables high resolution and good reproducibility while simultaneously achieving extremely short measurement times.

[0047] In addition, the force measurement can be based on the well-known vibrating wire measuring principle, whereby electromagnetic vibrations are measured on a resonance body.

[0048] Instead of strain gauge-based force sensors, piezoelectric sensors can also be used. These consist of crystal discs with an electrode foil mounted between them. When a force is applied, a charge is generated, which can be detected using a charge amplifier. The charge is proportional to the applied weight.

[0049] A design in which the force measuring device forms a functionally and / or structurally independent unit within the screening machine is not excluded. The force measuring device can then be used within the screening machine as a turnkey component. The integration of a force measuring device into the screening machine as an accessory and / or retrofit component is also not excluded.

[0050] The air jet screening machine preferably has a machine housing into which the weighing unit is integrated or which encloses the weighing unit. The weighing unit forms a mass unit integrated into the air jet screening machine, which can be weighed with the force measuring device provided according to the invention independently of a machine frame or other stationary components of the air jet screening machine, in particular those connected to the machine frame.

[0051] When determining the weight force and / or the weight of the weighing unit with the force transducer, the weight force of the screen passage housing together with the weight force of the slotted nozzle, and, preferably, the weight force of a drive shaft of the slotted nozzle, and, more preferably, the weight force of a shaft bearing of the drive shaft and / or if appropriate the weight force of coupling parts of a shaft coupling, and if appropriate the weight force of other components or machine parts that are connected to the screen passage housing and are a mass component of the total mass of the weighing unit, can be transferred to the force transducer.

[0052] The slotted nozzle can be mounted on the screen passage housing or on a component connected to the screen passage housing. When measuring the weight of the weighing unit, the mass of the screen passage housing is recorded together with the masses of the slotted nozzle, and preferably, a drive shaft of the slotted nozzle and, if applicable, coupling parts of a drive coupling connected to the drive shaft, and the weight forces of the aforementioned components are transferred to the force transducer of the force measuring device. The weight of the weighing unit then comprises the weight of the screen passage housing and the weight of the slotted nozzle mounted on the housing, as well as, preferably, the weight of a drive shaft of the slotted nozzle and, if applicable, the weight of coupling parts for coupling the drive shaft to a rotary drive for the slotted nozzle.

[0053] Force shunts can adversely affect the accuracy of the force and / or weight determination of the weighing unit. Therefore, it is preferably provided that the weight of the weighing unit is transmitted to the force transducer at least substantially free of force shunts, which partially divert the weight of the weighing unit past the force transducer and into the machine frame. Force shunts can occur at the connection points between the weighing unit and stationary machine parts.

[0054] In particular, when determining the weight force and / or the weight of the weighing unit, a force shunt decoupling of the weighing unit from the rotary drive is provided.

[0055] In this context, it can be provided that the slotted nozzle is connected to the rotary drive via a drive shaft with a shaft coupling, and that the determination of the weight force and / or the weight of the weighing unit takes place when the shaft coupling is uncoupled. A force shunt of the rotary drive is thus removed from the mass balance. For example, a claw coupling can be provided which can be converted from a coupled state during screening to a uncoupled state when determining the weight force and / or the weight of the weighing unit. In the uncoupled state, a mechanical connection between the drive shaft and the rotary drive via the shaft coupling is then interrupted. In the uncoupled state, the claws of a claw coupling can be released so that no friction and no force transmission occurs between the coupling parts.

[0056] The air supply to the slot nozzle and / or the air discharge from the sieve passage space through the housing can be effected via at least one fixed machine part, wherein, preferably, when determining the weight force and / or the weight of the weighing unit with the force transducer, a force shunt decoupling of the weighing unit from the fixed machine part is provided.

[0057] Particularly preferably, the air supply to the slot nozzle takes place via at least one fixed air inlet part connected to a machine frame and / or the air discharge from the screen passage space through the screen passage housing via at least one fixed air outlet part connected to a machine frame, wherein when determining the weight force and / or the weight of the weighing unit with the force transducer, a force shunt decoupling of the weighing unit from the air inlet part and / or air outlet part can be provided.

[0058] The air can be supplied to the weighing unit via an inlet duct and / or the air can be discharged from the weighing unit via an outlet duct, wherein the inlet duct can be formed in a fixed air inlet part and / or the outlet duct can be formed in a fixed air outlet part of the screening machine, and wherein, during the transmission of the weight force of the weighing unit to the force transducer, a force shunt decoupling of the weighing unit from the air inlet part and / or the air outlet part can be provided. According to the invention, force shunts are preferably prevented by connecting the weighing unit to fixed machine parts, i.e. to a machine frame or machine frame, in particular a base plate and / or an outer machine housing, via which the air is supplied or discharged. This contributes to a high degree of accuracy in the force and / or weight determination.

[0059] The air can be supplied to the slotted nozzle via a supply duct and / or the air can be removed from the screen passage space and the screen passage housing via a removal duct, wherein the supply duct can be formed in an air supply part connected to the weighing unit, in particular the screen passage housing, and the removal duct can be formed in an air removal part connected to the weighing unit, in particular the screen passage housing. The mass of the air supply part and / or the mass of the air removal part can be introduced into the force transducer or transferred to the force transducer together with the masses of the screen passage housing and other machine parts connected to the screen passage housing, in particular the slotted nozzle and optionally a drive shaft of the slotted nozzle as well as coupling parts of a shaft coupling, when determining the force and / or weight of the weighing unit.

[0060] The feed channel to the slot nozzle and the discharge shaft can also be formed by a housing wall of the screen passage housing.

[0061] The transfer of the closing force of a sealant to the weighing unit can lead to a change in the value for the weight force and / or the weight of the weighing unit determined by the force transducer.

[0062] When determining the weight force and / or the weight of the weighing unit with the force transducer, a force shunt decoupling of the weighing unit from a fixed air inlet part and / or from a fixed air outlet part is preferably provided.

[0063] In particular, air is supplied to the weighing unit via at least one fixed air inlet part connected to a machine frame and / or air is discharged from the weighing unit via at least one fixed air outlet part connected to a machine frame, wherein a force shunt decoupling of the weighing unit from the air inlet part and / or air outlet part is provided when determining the weight force and / or the weight of the weighing unit with the force transducer.

[0064] In particular, a force shunt decoupling is provided between a fixed air inlet part and a supply line connected to and / or formed on the screen passage housing for supplying air to the slot nozzle and / or between a fixed air outlet part and a discharge line connected to and / or formed on the screen passage housing for discharging air from the screen passage space via the screen passage housing.

[0065] At least one activatable seal can be provided between the weighing unit, in particular the supply line, and the fixed air inlet part and / or between the weighing unit, in particular the discharge line, and the fixed air outlet part, wherein the weighing unit is sealingly connected to the air inlet part and / or the air outlet part in an activated state of the seal and wherein the weighing unit is force-bypass decoupled, in particular spatially separated, from the air inlet part and / or the air outlet part when determining the weight force and / or the weight of the weighing unit with the force transducer in a non-activated state of the seal.

[0066] An "activatable" seal within the meaning of the invention is, in particular, a seal that can be inflated radially, laterally, or axially with a fluid, such as air or a liquid, such as a pneumatic seal, a stretch seal, a roll-out seal, an expansion seal, a pneumatically or hydraulically activated profile, or an inflatable seal. In these seals, the closing force for the seal is applied by the fluid pressure. A peristaltic pump can preferably be provided to convey the fluid to the seal and to generate sufficient fluid pressure. This peristaltic pump is, in particular, connected to or held on a machine frame of the screening machine. The peristaltic pump is preferably not a mass component of the weighing unit.Channels can be formed in a supply line leading to the slotted nozzle and / or in a discharge line of the weighing unit leading from the screen passage chamber and the screen passage housing in order to conduct an activation fluid to the seal or to discharge it from the seal.

[0067] Instead of inflatable seals, actuator-operated sealing elements can also be provided, whereby the closing force can be generated by a motor or magnet.

[0068] Furthermore, seals can be provided which have an elastically deformable sealing element which, under negative pressure, in particular during screening, rests against a sealing surface and releases a sealing gap after the negative pressure has ceased to be generated.

[0069] A closing force support of the seal is preferably provided on a fixed machine part of the air jet screening machine according to the invention.

[0070] If, in particular, activatable seals are provided on opposite sides of the weighing unit, the closing forces can cancel each other out when the seals are in the closed state, so that a “force shunt decoupling” within the meaning of the invention can also occur in the sealed state.

[0071] In addition, it is possible to determine the sealing and / or contact forces of the seal that act on the weighing unit in the sealed state and to take them into account when determining the force and / or weight of the weighing unit in order to determine the actual weight of the weighing unit as accurately as possible.

[0072] In particular, the activatable seal can have at least one sealing element which, by axial sliding, radial or lateral constriction, axial or radial or lateral inflation, squeezing or sliding, or by axial and / or radial coupling due to the elastic deformation of a sealing means in the presence of negative pressure of the air supply or air discharge, leads to a sealing effect between a movable machine part of the weighing unit and a stationary machine part of the air jet screening machine.

[0073] An embodiment is not excluded in which the air supply to the slot nozzle and / or the air discharge from the screen passage space through the housing takes place via highly elastic hose connections, so that the air supply to the slot nozzle and / or the air discharge from the screen passage space through the housing is in turn force shunt decoupled.

[0074] A further aspect of the present invention relates to a method for operating an air jet screening machine, wherein an air supply to a slot nozzle of the air jet screening machine takes place via at least one fixed air inlet part and / or an air discharge from a screen passage space through a screen passage housing of the air jet screening machine via at least one fixed air outlet part and at least one seal is provided in the air flow path between the screen passage housing and the air inlet part and / or the air outlet part, wherein the seal, in an activated state, sealingly connects the screen passage housing and the air inlet part and / or the air outlet part to one another and the screen passage housing and the air inlet part and / or the air outlet part are force-bypass decoupled in a non-activated state of the seal.

[0075] By transferring the seal to the activated state, a compressive force is transferred to the weighing unit, resulting in a change in the weight force determined by the force measuring device and / or the weight of the weighing unit. From the change in the weight force and / or the weight of the weighing unit, it is possible to draw conclusions about the closed state of the seal and the presence of any leakage in the pressure system formed by the weighing unit.

[0076] The weight force and / or the weight of the weighing unit can be determined with a force measuring device having at least one force transducer, in particular a load cell, wherein the activation state and / or the closing force of the seal is preferably determined automatically from the determined weight force and / or the determined weight of the weighing unit.

[0077] In principle, the pressure force or closing force of the seal on the weighing unit can also be determined in terms of its magnitude and is then taken into account accordingly in the weight force and / or the determined weight of the weighing unit determined with the force measuring device in order to determine the actual weight force and / or the actual weight of the weighing unit.

[0078] For force shunt decoupling of the weighing unit from at least one stationary machine part of the screening machine, via which the air is supplied to the slotted nozzle and / or the air is discharged from the screening passage through the housing, in particular for force shunt decoupling of the weighing unit from a stationary air inlet part and / or stationary air outlet part, a seal can also be provided which has a very low deformation resistance such that the weighing unit is preferably at least substantially force shunt decoupled from the stationary machine part when the seal is in the sealed state. For example, the seal can be made of a low-hardness elastomer material. The sealant then permanently seals the transition between the weighing unit and the stationary machine part.The formulation “at least substantially force shunt decoupled” in the sense of the invention comprises a force shunt influence due to the connection of the weighing unit to the stationary machine part via the sealing means on the weight force determined by the weighing device and / or the determined weight of the weighing unit of less than 10%, preferably of less than 5%, of the actual value of the weight force and / or the weight of the weighing unit with complete force shunt decoupling or separation of the weighing unit from the stationary machine part.

[0079] The reading or display accuracy of the weight and / or force value output by the force measuring device can be between 0.001 g and 0.01 g. "At least substantially force shunt decoupled" within the meaning of the invention can be present if the deviation of the actual value of the weight force and / or the weight of the weighing unit from the weight and / or force value determined by the weighing device is less than 5, preferably less than 3, weighing units.

[0080] Carryover of the sample, sample transfer, moisture, buildup, electrostatic effects, interference with false readings caused by electromagnetic radiation, wind, vibration, temperature, and hysteresis can all influence the weighing result, which can significantly exceed the weighing accuracy. The reading or display accuracy of the weight and / or force value output by the force measuring device can therefore be between 0.01 g and 0.1 g.

[0081] In an alternative embodiment, a non-contact seal can be provided for force shunt decoupling of the weighing unit from at least one stationary machine part of the screening machine, via which the air is supplied to the slotted nozzle and / or the air is discharged from the screening passage through the housing, in particular for force shunt decoupling of the weighing unit from a stationary air inlet part and / or stationary air outlet part. The non-contact seal is arranged in the flow path of the supplied or discharged air between the weighing unit, in particular a supply line and / or a discharge line connected to the screening passage housing, and the stationary machine part of the screening machine, in particular a stationary air inlet part and / or a stationary air outlet part.A labyrinth or gap seal can be provided as a non-contact seal, for example, whereby the sealing effect is achieved by extending the flow path through the gap to be sealed.

[0082] Alternatively, the flow guide between the weighing unit, in particular a supply line and / or a discharge line connected to the screening passage housing, and a fixed machine part of the screening machine, in particular a fixed air inlet part and / or fixed air outlet part, can also be designed unsealed or seal-free.

[0083] Further details, features, and advantages of the subject matter of the invention emerge from the dependent claims and from the following description of the accompanying drawings, which illustrate preferred embodiments of the invention by way of example. Structural and / or functionally identical components of the illustrated embodiments are designated by the same reference numerals. In the drawings: Fig. 1 a schematic representation of an air jet screening system with an air jet screening machine known from the prior art; Fig. 2 a schematic representation of an air jet screening system with an air jet screening machine according to the invention; Fig. 3 a schematic representation of a method according to the invention for operating an air jet screening machine according to the invention; Fig. 4 a schematic plan view of an arrangement with a sieve passage housing of an air jet screening machine according to the invention and with an air supply to the sieve passage housing and an air discharge from the sieve passage housing; Fig. 5 a schematic representation of the force shunt decoupling of a weighing unit of an air jet screening machine according to the invention from fixed machine parts using activatable seals in the open or non-activated state of the seals; Fig. 6 a schematic representation of the force shunt decoupling of a weighing unit of an air jet screening machine according to the invention from a stationary machine part, wherein a contactless seal is provided between the weighing unit and the stationary machine part; Fig. 7 a schematic representation of the air supply to a screen passage housing of an air jet screening machine according to the invention, wherein a substantially rigid supply line forms an uninterrupted supply channel for supplying an air stream to a slot nozzle of the air jet screening machine; Fig. 8 a schematic representation of the transmission of a pressure force from an activatable seal to a weighing unit of an air jet screening machine according to the invention in the closed state of the seal.

[0084] Fig. 1 shows an air jet screening system 1 with an air jet screening machine 2 known from the prior art. The air jet screening machine 2 has a housing unit 3 with a screening passage housing 4, onto which a screen 5 with a screen cover 6 can be placed for a screening process. The screening chamber 7 above a screen bottom 8 is closed with the screen cover 6 during a screening process. Below the screen bottom 8, the screening passage housing 4 has a screening passage chamber 9. Arranged in the screening passage chamber 9 is a slot nozzle 10 that can rotate about a vertical center axis of the screen 5.

[0085] During screening, an air stream 11 is directed from below against the screen bottom 8 through the rotating slotted nozzle 10. To generate the air stream 11, a suction device 12 with a suction unit 13 and an upstream filter 14 is provided. The screen passage space 9 is suctioned with the suction unit 13. The extracted air stream 11 flows through the slotted nozzle 10, causing a screening material 15 to be swirled up by the incoming air and distributed evenly across the screen surface.The air stream 11 reorients particles on the sieve surface, and particles with a particle size smaller than the mesh size of the sieve 5 are sucked away by the suction unit 13 together with the air stream 11. They pass as the sieve passage 20 from the sieve passage chamber 9 through the sieve passage housing 4 via an outlet channel 17 formed on a fixed machine part 16 into a cyclone 18, where the particles are separated from the air stream 11 and collected in a sample glass 19. The outlet channel 17 forms a suction connection (not shown). The air stream 11 is sucked in by the suction unit 13 via the suction connection.

[0086] The air flow 11 is supplied to the slot nozzle 10 via a supply channel 21 formed in the machine part 16. The air flow 11 reaches the slot nozzle 10 via the supply channel 21, exits via the slot nozzle 10 into the sieve passage space 9 and flows upwards through the sieve bottom 8 of the sieve 5.

[0087] The slot nozzle 10 is driven by a rotary drive 22, which is connected to the slot nozzle 10 via a drive shaft 23 and a shaft coupling (not shown).

[0088] Components with the same function and / or construction as those listed below Fig. The embodiments described in Figures 2 to 8 are identified by the same reference numerals.

[0089] In Fig. 2 schematically shows an air jet screening system 23 with an air jet screening machine 24, wherein a force sensor 26 of a force measuring device is integrated into the air jet screening machine 24 and directly or indirectly attached to a machine frame 25 of the air jet screening machine 24. The force sensor 26 is a load cell. The machine frame 25 is in Fig. 2 is shown only schematically. The machine frame 25 can, in particular, comprise frame components that are rigidly connected to one another and, preferably, to a base plate (not shown) of the air jet screening machine 24 and / or a machine housing (not shown).

[0090] The force introduction point 27 of the force transducer 26 is arranged, for example, below a housing edge 28 of a sieve passage housing 29 in the embodiment shown. The force transducer 26 is formed by a measuring body with strain gauges, wherein one end of the measuring body is attached to the machine frame 25 and the force introduction point 27 for the weight of a weighing unit 30 comprising the sieve passage housing 29 is provided at the other, free end of the measuring body. Fig. Figure 2 schematically shows the comprehensive system boundary of the weighing unit 30 as a dashed line. Due to the force applied by the weighing unit 30 to the force transducer 26, a slight deflection or deformation of the measuring body and the connected strain gauges occurs. This deformation causes the electrical resistance of the strain gauges to change proportionally. Using signal conditioning electronics 51, the electrical resistance of the strain gauges can be measured, and the resulting signal can be output as a weight or force value.

[0091] The drive shaft 32 can be mounted directly or indirectly on a housing base 38 of the screen passage housing 29. The total mass of the weighing unit 30 is then composed of the mass of the screen passage housing 29, the mass of a slotted nozzle 31, the mass of a drive shaft 32 with shaft bearing 33, the mass of one or more coupling parts 35 of a detachable shaft coupling 34 with coupling parts 35, 36, via which the drive shaft 32 can be coupled to a stationary rotary drive 37 connected to the machine frame 25, and, if applicable, the masses of other components or machine parts that are connected to the screen passage housing 29 and whose weight force is introduced into the force transducer 26 when the weight or force value of the weighing unit 30 is determined.

[0092] The mass of the rotary drive 37 is not part of the mass of the weighing unit 30.

[0093] Connected to the sieve passage housing 29 is a supply line 39 for supplying air to the slotted nozzle 31 via a supply channel 40 and a discharge line 41 for discharging air from the sieve passage chamber 9 and the sieve passage housing 29 via a discharge shaft 42. The supply line 39 and the discharge line 41 are also mass components of the weighing unit 30.

[0094] A fixed air inlet part 43 connected to the machine frame 25 forms an inlet channel 44 for the air supply to the supply line 39 and thus to the slot nozzle 31. A fixed air outlet part 45 also connected to the machine frame 25 forms an outlet channel 46 for the air discharge from the screen passage space 9 and the screen passage housing 29 via the discharge shaft 42. A suction line 47 is connected to the air outlet part 45, via which the air flow 11 is connected to a suction device 12 (not shown) as shown in FIG. Fig. 1 is extracted as described above. The air inlet part 43 and the air outlet part 45 are not mass components of the weighing unit 30.

[0095] The air flow 11 is supplied via a silencer 48 which is connected to the air inlet part 43.

[0096] A sieve 5 with a sieve cover 6, which has a sieve bottom 8, is placed on the sieve passage housing 29. A sieve seal 50 is provided to seal the sieve 5 from the sieve passage housing 29.

[0097] When determining the weight force and / or the weight of the weighing unit 30, the weight force of the weighing unit 30 is transmitted to the force transducer 26. The weight force of the screen passage housing 29 can be transmitted to the force transducer 26 together with the weight forces of the slotted nozzle 31, the drive shaft 32, the shaft bearing 33, the coupling part 35 of the shaft coupling 34 as well as the feed line 39 forming the feed channel 40 and the discharge line 41 forming the discharge shaft 42.

[0098] For force shunt decoupling of the weighing unit 30 from the rotary drive 33, the determination of the weight force and / or the weight of the weighing unit 30 is carried out in the uncoupled state of the shaft coupling 34. For example, the shaft coupling 34 can be a claw coupling whose claws are brought out of contact for force shunt decoupling.

[0099] Furthermore, when determining the weight force and / or the weight of the weighing unit 30, a force shunt decoupling of the weighing unit 30 from the stationary air inlet part 43 and the stationary air outlet part 46 is provided. For this purpose, the air inlet part 43 can be connected to the supply line 39 connected to the sieve passage housing 29 and / or the air outlet part 46 can be connected to the discharge line 41 connected to the sieve passage housing 29 via activatable seals 49.

[0100] The activatable seals 49 can preferably be inflatable seals or actuator-adjustable seals, wherein the supply line 39 is sealingly connected to the stationary air inlet part 43 and / or the discharge line 41 is sealingly connected to the stationary air outlet part 45 in an activated, inflated or actuator-adjusted state of the seal 49. In a non-activated state of the seals 49, the weighing unit 30 is force-bypass decoupled from the stationary air inlet part 43 and / or the stationary air outlet part 45. In the non-activated state of the seals 49, the supply line 39 is not sealed from the stationary air inlet part 43 and the discharge line 41 is not sealed from the air outlet part 45, and weighing takes place. During a screening process with the slot nozzle 31 rotating, the seals 49 are in the activated state.

[0101] The force transducer 28 is connected to signal conditioning electronics 51 to measure the electrical resistance of strain gauges of the force transducer 26 and to output the signal resulting from the transmission of the weight force of the weighing unit 30 to the force transducer 26 as a force value or weight value.

[0102] Fig. 3 shows schematically the process sequence when operating the air jet screening machine 24 from Fig. 2, in particular for grain size analysis, the method comprising the following steps: First, the empty weight of the weighing unit 30 is determined before inserting a sieve 5 into the sieve passage housing 29 of the weighing unit 30 ( Fig. 3A). Furthermore, the weight of the weighing unit 30 is transmitted to the force transducer 26. The determined weight or the determined weight of the weighing unit 30 can be stored in a memory of the force measuring device.

[0103] Subsequently, in a second process step ( Fig. 3B) a sieve 5 without a sieve cover 6 is inserted into the sieve passage housing 29 of the weighing unit 30, and the total weight of the weighing unit 30 with the sieve 5 inserted into the sieve passage housing 29 can be determined. For this purpose, a force transmission of the weight of the weighing unit 30 together with the weight of the sieve 5 inserted into the sieve passage housing 29 to the force transducer 26 is provided. The total weight can be stored. The sieve weight is determined from the determined total weight, after deducting the empty weight of the weighing unit 30 before inserting a sieve 5.

[0104] In a third procedural step ( Fig. 3C), a screening material 15 is placed onto the inserted screen 5. The total weight of the weighing unit 30 with the screen 5 and the screening material 15 placed onto the screen 5 can then be determined again. The weight of the screening material 15 is determined from the total weight thus determined, after deducting the stored weight of the weighing unit 30 and the stored weight of the screen 5. The weight of the screening material 15 can be stored.

[0105] In a fourth step ( Fig. 3D), the sieve cover 6 can then be placed on the sieve 5, and the total weight of the weighing unit 30 with the inserted sieve 55, the material to be sieved 15 placed on the sieve 5, the sieve passage 20 already completed, and the sieve cover 6 placed on the sieve 5 can be determined. Here, too, the total weight can be stored in the memory of the force measuring device.

[0106] It now follows a fifth process step ( Fig. 3E) a screening process as described above is carried out. At the end of the screening process with rotating slotted nozzle 31, a preferably manually performed tap screening process can be provided to transmit vertical tap pulses to screen 5 and / or screen cover 6 in order to complete the screening passage 20.

[0107] During the screening process, a large portion of the screening passage 20 is removed from the screening passage chamber 9 with the air discharged from the screening passage housing 29. Parts of the screening passage 20 may be deposited on the housing base 38, parts of the slotted nozzle 31, and possibly in the discharge duct 42, through which the air is discharged from the screening passage housing 29, and are not discharged from the weighing unit 30 with the air flow 11.

[0108] In order to determine the sieve residue 50a on the sieve bottom 8 of the sieve 5 in a simple manner without manual sieve weighing after the sieving process has been completed, a sixth process step ( Fig. 3F) a determination of the total weight of the weighing unit 30 including any sieve passage residues 20 deposited in and / or on the sieve passage housing 29 or on machine parts connected to the sieve passage housing 29, the sieve 5 inserted into the sieve passage housing 29 with the sieve cover 6, and the sieve residue 50a remaining on the sieve bottom 8 is provided. The total weight can also be stored.

[0109] Finally, the sieve 5 with the sieve residue 50a and sieve cover 6 is removed in a seventh process step ( Fig. 3g) is lifted from the weighing unit 30 to determine the weight of the sieve residue 50a. The weight of the sieve residue 50a is then determined from the total weight of the weighing unit 30 determined in the sixth method step, including any deposited sieve residue 20, sieve 5 with sieve cover 6, and sieve residue 50a, minus the weight of the sieve 5 and the sieve cover 6 determined previously or by manual sieving. Manual weighing of the sieve residue 50a is not provided.

[0110] Fig. 4 shows an embodiment in which the air supply to the slotted nozzle 31 and the air discharge from the screen passage housing 29, together with the screen passage 20, are provided on the same side of the housing. Accordingly, the supply line 39 to the slotted nozzle 31, which forms the supply channel 40, and the discharge line 41, which forms the discharge shaft 42, are provided on the same side of the housing. The supply channel 40 can connect to an inlet channel 44 via an activatable seal 49, and the discharge shaft 42 can connect to an outlet channel 46 via an activatable seal 49. The inlet channel 44 and the outlet channel 46 can be formed in a stationary machine part 52 connected to the machine frame 25. The inlet channel 44 and the outlet channel 46 are then located on the same side of the housing. It is also possible for the inlet channel 44 and the outlet channel 46 to be formed in separate, fixed machine parts.The air supply to the slot nozzle 31 and the air discharge from the screen passage housing 29 together with the screen passage 20 on the same side of the housing and the symmetrical arrangement of the air supply and air discharge enable a compact structural design.

[0111] Fig. Figure 5 shows schematically and in partial representation the structure of an air jet screening machine 53 with a force transducer 26 of a force measuring device, wherein the weight of a weighing unit 30 can be transferred to the force transducer 26 and the weight and / or the weight of the weighing unit 30 can be determined with the force measuring device. For the functional structure of the air jet screening machine 53, reference is made to the Fig. 2 and Fig. 3A-G described embodiment of the air jet screening machine 24.

[0112] The force sensor 26 is arranged below a schematically shown weighing unit 30. The force sensor 26 is a load cell.

[0113] The force introduction point 27 of the force transducer 26 is provided below a supply line 39 connected to a screen passage housing 29 leading to the slotted nozzle 31. The supply line 39 is formed and / or attached to the screen passage housing 29 and is a mass component of the mass of the weighing unit 30. The force transducer 26 is arranged below the weighing unit 30, so that when determining the weight force and / or the weight of the weighing unit 30 with the force measuring device, the weight force of the weighing unit 30 is introduced into the force transducer 26 from above.

[0114] The force sensor 26 is formed by a measuring body with strain gauges. One end of the measuring body is attached to a fixed air inlet part 43 connected to a machine frame 25. The other, free end of the measuring body contains the force introduction point 27 for the weight of the weighing unit 30. Due to this force introduction, a slight deflection or deformation of the measuring body and the associated strain gauges occurs. Due to this deformation, the electrical resistance of the strain gauges changes proportionally. Using signal conditioning electronics (not shown), the electrical resistance of the strain gauges can be measured, and the resulting signal can be output as a weight or force value.

[0115] As will be further Fig. 5, during the determination of the weight force and / or the weight of the weighing unit 30 with the force transducer 26, a force shunt decoupling of the weighing unit 30 from a rotary drive 37 for a drive shaft 32 of the slotted nozzle 31 is provided. The rotary drive 37 can be connected to the drive shaft 32 for a screening process via a detachable coupling (not shown) in order to enable the rotation of the slotted nozzle 31 during a screening process. When determining the weight force and / or the weight of the weighing unit 30 with the force transducer 26, however, the coupling connection between the drive shaft 32 and the rotary drive 37 is interrupted, so that a force shunt decoupling is achieved.

[0116] A shaft bearing can be provided on the screen passage housing 29, but is also in Fig. 5 not shown.

[0117] As will be further Fig. 5, a discharge line 41 is formed and / or fastened to the sieve passage housing 29, which forms a discharge shaft 42 and is a mass component of the mass of the weighing unit 30.

[0118] During screening, an air stream is discharged from the screening passage chamber 9 through the screening passage housing 29, along with the screening passage, via the discharge duct 42. An air outlet duct 46, formed in a fixed air outlet part 45, is connected to the discharge duct 42. The air outlet part 45 is connected to the machine frame 25.

[0119] The air inlet part 43 and the air outlet part 45 can also be formed in one piece and, preferably, be provided next to each other on the same side of the screen passage housing 29, as shown schematically in Fig. 4 is shown.

[0120] For force shunt decoupling of the supply line 39 from the stationary air inlet part 43 and / or for force shunt decoupling of the discharge line 41 from the stationary air outlet part 45, activatable seals 49 can be provided, which can be pneumatically or hydraulically inflated and thus converted into a sealed or activated state. An air flow 54 can be supplied to the seals 49 for activating the seals 49 via air channels 55, which can be formed in the air inlet part 43 and the air outlet part 45. Preferably, a peristaltic pump 55a is provided, which draws in ambient air and supplies both seals 49 with air.

[0121] Fig. Figure 5 shows the seals 49 in a non-activated state, in which the weighing unit 30 is spatially separated from the air inlet part 43 and the air outlet part 45 and thus decoupled from the force shunt. In the activated state of the seals 49, or in the sealed state, however, the supply line 39 is sealed to the stationary air inlet part 43, and the discharge line 41 is sealed to the stationary air outlet part 45, thus preventing the ingress of false air during the screening process.

[0122] Alternatively, the seals 49 can also be adjustable seals that can be moved or adjusted by actuators from a non-sealing state to a sealed state. In the non-sealing state, the supply line 39 is spatially separated from the stationary air inlet part 43, and the discharge line 41 is spatially separated from the stationary air outlet part 45, so that no weight force can be transmitted and a force shunt decoupling is achieved during the weight (force) determination of the weighing unit 30. In the sealed state during the sieving process, however, the supply line 39 is sealingly connected to the stationary air inlet part 43, and the discharge line 41 is physically connected to the stationary air outlet part 45.

[0123] Fig. 6 shows, by way of example only for the air inlet side and schematically with reference to Fig. 5 the use of non-contact seals in an air jet screening machine 56 in order to achieve a force shunt decoupling of the weighing unit 30 from stationary machine parts, in particular a supply line 39 from a stationary air inlet part 43, during the determination of the weight force and / or the weight of a weighing unit 30. A non-contact seal can be designed as a gap or labyrinth seal. A corresponding non-contact seal can be arranged between a seal described above with reference to Fig. 5 described discharge line 41 and a fixed air outlet part 45 may be provided.

[0124] An embodiment is not excluded in which no seal is provided between the weighing unit 30 and fixed machine parts, in particular between a supply line 39 of the weighing unit 30 and a fixed air inlet part 43 and / or a discharge line 41 of the weighing unit 30 and a fixed air outlet part 45, so that there is a free space and the flow transition is always unsealed.

[0125] As a further alternative, activatable seals can be provided which have an elastically deformable sealing element in order to achieve a force shunt decoupling of the weighing unit 30 from stationary machine parts, in particular a supply line 39 leading to the slotted nozzle 31 from a stationary air inlet part 43 and / or a discharge line 41 leading from the screen passage space 9 from a stationary air outlet part 45, during the determination of the weight force and / or the weight of a weighing unit 30. Due to the air flow during the air supply to the slotted nozzle 31 and / or the air discharge from the screen passage space 9 via the screen passage housing 29, elastic deformation of the sealing element can occur, so that the sealing element is transferred from a non-activated open state into an activated sealed state, in which the sealing element presses against the supply line 39 and / or the air inlet part 43 orseals against the discharge line 41 and / or the air outlet part 45 and prevents the passage of false air.

[0126] Fig. 7 shows an example of the air inlet side and schematically with reference to Fig. 6 shows an embodiment of an air jet screening machine 57 in which a substantially rigid supply line 59 forms a continuous supply channel 58 for supplying an air stream to a slotted nozzle 31, wherein the supply line 59 is rigidly connected at one end to a screen passage housing 29 and at the other end to a machine frame 25. Strain gauges 60, preferably arranged opposite one another, are arranged on the supply line 59. The supply line 59, together with the strain gauges 60, forms a load cell. When the weight of a weighing unit 30 comprising the screen passage housing 29 is introduced into the supply line 59 as described above, a slight deflection or deformation of the supply line 59 and the connected strain gauges 60 occurs. Due to the deformation, the electrical resistance of the strain gauges 60 changes proportionally.Using signal conditioning electronics (not shown), the electrical resistance of the strain gauges 60 can be measured, whereby the resulting signal can be output as a weight or force value.

[0127] Fig. 8 shows a highly schematic and exemplary view of the air inlet side of the Fig. 5 shows the activated state of the seal 49 between the fixed air inlet part 43 and the supply line 39 to the slot nozzle 31. The seal 49 can be an inflatable seal or an actuator-movable seal.

[0128] Fig. 8 shows schematically and only in a partial representation with reference to Fig. 5 the transmission of a compressive force 61 or closing force in the activated sealing state of an activatable seal 49 to the supply line 39 and thus to the weighing unit 30, wherein the transmission of the compressive force 61 leads to a change in the weight or force value determined by the force transducer 26. The force transducer 26 is deformed due to a force transmission from the weighing unit 30, wherein the deformation can be measured by strain gauges via a change in the electrical resistance of the strain gauges proportional to the deformation with the aid of signal conditioning electronics. The transmission of the compressive force 61 to the weighing unit 30 leads to a change in the electrical resistance of the strain gauges on the force transducer 26, so that a conclusion about the sealing state of the seal 49 can be drawn based on the determined weight or force value.

[0129] The air jet screening machine 53 can have a control and / or evaluation device that, upon reaching a specific weight or force value, detects, preferably automatically, an activated sealing state of the seal 49 and / or a specific pressure force 61 or sealing force and outputs this via a corresponding signal. Depending on this, the operation of the air jet screening machine 53 can be controlled, in particular such that a screening process can only be initiated upon reaching a predetermined pressure force 61 or sealing force.

[0130] The Fig. 5 and Fig. Figure 8 shows the sealing with activatable sealing elements 49 for a vertical parting line. Sealing with a horizontal or axial parting line or with an inclined parting line is also possible. List of reference symbols: 1 air jet screening system 2 air jet screening machines 3 Housing unit 4 sieve passage housing 5 Sieve 6 sieve lids 7 Screening chamber 8 Sieve bottom 9 Screen passage space 10 slot nozzle 11 Airflow 12 Extraction device 13 vacuum cleaners 14 filters 15 screenings 16 Machine part 17 Exhaust channel 18 Cyclone 19 sample tube 20 sieve passes 21 Feed channel 22 Rotary drive 23 Air jet screening system 24 air jet screening machine 25 machine part 26 force transducers 27 Force application point 28 Housing edge 29 Screen passage housing 30 weighing units 31 Slot nozzle 32 drive shaft 33 Shaft bearing 34 Shaft coupling 35 Coupling part 36 Coupling part 37 Rotary drive 38 Case back 39 Supply line 40 feed channel 41 Discharge line 42 discharge shaft 43 Air intake part 44 Inlet channel 45 Air outlet part 46 exhaust channel 47 Suction line 48 silencers 49 Seal 50 sieve seal 50a sieve residue 51 Signal processing electronics 52 machine part 53 Air jet screening machine 54 Airflow 55 Air duct 55a pump 56 Air jet screening machine 57 Air jet screening machine 58 feed channel 59 Supply line 60 strain gauges 61 compressive force

Claims

[1] Air jet sieving machine (24), in particular for laboratory use, with a sieve passage housing (29) into which a sieve (5) that can be covered with a sieve lid (6) can be inserted, wherein the sieve (5) has a sieve bottom (8) and the sieve passage housing (29) delimits a sieve passage space (9) below the sieve bottom (8) when the sieve (5) is inserted, with a slotted nozzle (20) rotatable about a vertical central axis, wherein the slotted nozzle (20) is arranged in the sieve passage space (9) below the sieve bottom (8) when the sieve (5) is inserted, with a rotary drive (37) for the slotted nozzle (20) and with an air supply to the slotted nozzle (20) and an air discharge through the sieve passage housing (29) from the sieve passage space (9), characterized bythat a weighing unit (30) comprising the sieve passage housing (29) and a force measuring device with at least one force transducer (26) are provided, wherein the weight of the weighing unit (30) can be transferred to the force transducer (26) and the weight and / or the weight of the weighing unit (30) can be determined with the force measuring device. [2] Air jet screening machine (24) according to claim 1, characterized by that the weight force and / or the weight of the weighing unit (30) can be determined in a mass-decoupled manner from the weight force of a machine frame (25) of the air jet screening machine (24). [3] Air jet screening machine (24) according to claim 1 or 2, characterized bythat the force transducer (26) has at least one deformable, in particular bendable, and / or deflectable measuring body, wherein the measuring body is connected to a machine frame (25) of the air jet screening machine (24) for force dissipation and wherein the weight force of the weighing unit (30) is transmitted to the measuring body and the measuring body is deformed and / or deflected due to the transmission of the weight force. [4] Air jet screening machine (24) according to one of the preceding claims, characterized by that a machine housing is provided and that the weighing unit (30) is integrated into the machine housing. [5] Air jet screening machine (24) according to one of the preceding claims, characterized by that the mass of the weighing unit (30) comprises the mass of the slot nozzle (20) and, preferably, the mass of a drive shaft (32) of the slot nozzle (20), and, further preferably, the mass of a shaft bearing (33) of the drive shaft (32). [6] Air jet screening machine (24) according to one of the preceding claims, characterized by that the weight force of the weighing unit (30) can preferably be transferred to the force transducer (26) at least substantially free of force shunts. [7] Air jet screening machine (24) according to one of the preceding claims, characterized by that when determining the weight force and / or the weight of the weighing unit (30) with the force transducer (26), a force shunt decoupling of the weighing unit (30) from the rotary drive (37) is provided. [8] Air jet screening machine (24) according to one of the preceding claims, characterized by that the slotted nozzle (20) is connected to the rotary drive (37) via a drive shaft (32) with a shaft coupling (34) and that the determination of the weight force and / or the weight of the weighing unit (30) is carried out with the force transducer (26) in the uncoupled state of the shaft coupling (34). [9] Air jet screening machine (24) according to one of the preceding claims, characterized by that the air supply to the weighing unit (30) takes place via at least one fixed air inlet part (43) connected to a machine frame (25) and / or the air discharge from the weighing unit (30) takes place via at least one fixed air outlet part (45) connected to a machine frame (25), wherein when determining the weight force and / or the weight of the weighing unit (30) with the force transducer (26), a force shunt decoupling of the weighing unit (30) from the air inlet part (43) and / or air outlet part (45) is provided. [10] Air jet screening machine (24) according to claim 9, characterized bythat at least one activatable seal (49) is provided between the weighing unit (30) and the air inlet part (43) and / or the air outlet part (45), wherein the weighing unit (30) is sealingly connected to the air inlet part (43) and / or the air outlet part (45) in an activated state of the seal (49), and wherein the weighing unit (30) is force-bypass decoupled from the air inlet part (43) and / or the air outlet part (45) when determining the weight force and / or the weight of the weighing unit (30) with the force transducer (26) in a non-activated state of the seal (49). [11] Air jet screening machine (24) according to claim 9, characterized bythat at least one seal (49) is provided between the weighing unit (30) and the air inlet part (43) and / or the air outlet part (45), which seal has a low deformation resistance such that the weighing unit (30) is preferably at least substantially force-bypass decoupled from the air inlet part (43) and / or the air outlet part (45) when the seal (49) is in a sealed state. [12] Air jet screening machine (24) according to claim 9, characterized by that at least one contactless seal is provided between the weighing unit (30) and the air inlet part (43) and / or the air outlet part (45) or that the air transition between the weighing unit (30) and the air inlet part (43) and / or the air outlet part (45) is unsealed. [13] A method for operating an air jet screening machine (24), in particular for grain size analysis, wherein the air jet screening machine (24) has a screening passage housing (29) into which at least one screen (5) that can be covered with a screen cover (6) can be inserted and which, in the inserted state of a screen (5), delimits a screening passage space (9) below a screen bottom (8) of the screen (5), and wherein the air jet screening machine (24) has a slotted nozzle (20) rotatable about a vertical central axis and a rotary drive (37) for the slotted nozzle (20), an air supply to the slotted nozzle (20) and an air discharge through the screen passage housing (29) from the screening passage space (9), a control and evaluation device and a force measuring device with at least one force transducer (26), in particular a load cell, in particular for operating an air jet screening machine (24) according to one of the preceding claims, wherein the procedure includes: - Determination of the weight force and / or the weight of a weighing unit (30) comprising the sieve passage housing (29) with the force measuring device and, preferably, - Determining the weight of a sieve residue (50a) taking into account the determined weight force and / or the determined weight of the weighing unit (30). [14] Method for operating an air jet screening machine, in particular an air jet screening machine (24) according to one of the preceding claims, in particular method according to claim 13, wherein an air supply to a slot nozzle (20) of the air jet screening machine (24) and / or an air discharge from a screening passage space (9) through a screening passage housing (29) of the air jet screening machine (24) takes place via at least one fixed air inlet part (43) and / or at least one fixed air outlet part (45) and at least one seal (49) is provided in the air flow path between the screening passage housing (29) and the air inlet part (43) and / or the air outlet part (45),wherein the seal (49) in an activated state sealably connects the screen passage housing (29) and the air inlet part (43) and / or the air outlet part (45) to one another, and the screen passage housing (29) and the air inlet part (43) and / or the air outlet part (45) are force-bypass decoupled in a non-activated state of the seal (49). [15] Method according to claim 14, characterized by that the weight force and / or the weight of the weighing unit (30) is determined by means of a force measuring device having at least one force transducer (26), in particular a load cell, wherein the activation state and / or the closing force of the seal (49) is preferably determined automatically from the determined weight force and / or the determined weight of the weighing unit (30).

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