Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01G—WEIGHING
  • G01G11/00—Apparatus for weighing a continuous stream of material during flow; Conveyor belt weighers
  • G01G11/08—Apparatus for weighing a continuous stream of material during flow; Conveyor belt weighers having means for controlling the rate of feed or discharge

Definitions

• the present invention relates to a method and apparatus for filling target vessels with a predetermined target mass of a flowable substance from a reservoir.
• Such filling devices find particular use when dosing small quantities, as they are necessary for example in the pharmaceutical sector their use. Frequently, such target vessels are placed on a balance in order to weigh the amount of substance discharged from the metering device, so that it can subsequently be further processed as intended.
• the substance to be dosed is located, for example, in a removal vessel or reservoir, which has a dosing head. It is desirable to discharge the substance to be metered through an opening of the metering device, so that at the end of the filling process, a predetermined target mass is in the target vessel. It is important that the actual mass in the target vessel corresponds as closely as possible to the predetermined target mass. Furthermore, it is important that the filling process can be carried out as quickly as possible.
• the discharge speed u is subject to many influencing factors, such as the free area A of the valve, the resulting from the level height h of the substance in the reservoir substance and the hydrostatic pressure rheological properties of the substance, such as the particle size d of the powder.
• the rheological properties are often very complex and subject factors that are not known. For example, it is difficult to take into account the flow delay occurring in Bingham's media or powders at the beginning of the flow process.
• factors such as particle size, moisture content and surface quality of the individual grains play a major role.
• US 4893262 discloses a control system for filling containers. Through different filling cycles, the system is optimized, in which the mass flow is optimized from cycle to cycle and the filling time is adjusted until the filled mass corresponds as closely as possible to the predetermined target mass.
• This system is mainly used for filling large quantities, which make much lower demands in terms of accuracy than the inventive system.
• Another problem is the optimization over different cycles, since the predetermined target mass is actually achieved in the necessary accuracy after a few test cycles. The substance discharged during these trial cycles can not continue to be used since it could become contaminated by the process of removal and removal from the target vessel. Especially when bottling expensive substances, this represents a decisive disadvantage.
• US 6987228 B1 discloses a method and an apparatus for accurately and reproducibly filling a small mass of particles.
• the device has a control unit for controlling the energy application on a sieve in which the particles to be discharged are located.
• the energetic application causes a small mass of the particles in the sieve to fall onto a scale placed under the sieve. Due to the weight measured by the balance, the control unit controls the energy application to the sieve.
• the amount of energy applied can be controlled depending on the mass still to be discharged, whereby the discharge rate of the particles can be varied.
• the problem here is that due to the sieve used only powdery substances can be filled. For other flowable
• this method is not suitable. Also at the filling of powdery substances, this process has disadvantages, since depending on the particle size of the substance another sieve must be used. The main disadvantage is the control of the energy order on the sieve in dependence of the weighing signal. Due to the delayed reaction time of the balance, the filling process would have to be carried out so slowly that the balance has enough time to react. However, this would take a long time to fill.
• US 4762252 discloses control system for filling containers. To determine the mass flow during the filling process, the changing weight of the reservoir is used. The particular mass flow is compared to a desired mass flow. If the specific mass flow differs too much from the desired mass flow, the mass flow is corrected accordingly.
• the system described is suitable for filling of about 25 -50 kilograms per hour. When filling small quantities, as they are necessary in the pharmaceutical industry, high accuracy requirements are made and small measurement inaccuracies can exert a significant influence on the filled mass. At the same time, the filling process should take as little time as possible.
• the inventive method and the inventive device fills a target vessel with a predetermined target mass m z of a flowable substance from a reservoir by means of a metering device for metered filling of the substance in the target vessel.
• the metering device has a valve which allows a variable adjustment of the mass flow m from the reservoir into the target vessel.
• the metering device has a time recording for the determination since Beginning of the filling process elapsed time t, a scale for determining the mass m of the substance located in the target vessel and a control unit with a valve control module for controlling the valve on.
• the control unit has a correction module, wherein in the correction module a desired mass flow m, is stored and if for the time t, the mass flow m (t) is smaller than the desired mass flow m, the mass flow is
• the dead time ⁇ corresponds to the time between the application of the mass on the balance and the display of the mass on the balance.
• the dead time ⁇ is determined by means of measurements. It has been shown that the dead time ⁇ depends mainly on the nature of the scale.
• environmental parameters have an influence on the dead time ⁇ . For example, low-frequency vibrations and / or vibrations result in an increase in the dead time ⁇ . This means that in the dead time ⁇ is mainly the scale-specific measurement delay to environmental parameters. Physical properties of the substance to be dosed play a minor role.
• the dead time ⁇ can be included in the determination of the desired mass flow i.
• the dead time ⁇ should behave antiproportionally to the desired mass flow m, m » oc - ⁇
• the tolerance m T defines what deviation the mass m at the end of the metering process in the target vessel may have from the target mass m z . In other words, at the end of the dosing process, the mass m in the target vessel must be in the interval
• the tolerance m ⁇ is large, it can be ensured even with a large desired mass flow m "that the target mass m z is within the specified tolerance m ⁇ . If, on the other hand, the tolerance m ⁇ is small, the desired mass flow m »must be chosen small enough to ensure that the target mass m z is within the specified tolerance m ⁇ . It follows that the desired mass flow should be proportional to the tolerance m ⁇ :
• Overshoot is understood to mean a substance introduced at least by the tolerance m ⁇ above the target mass m z into the target vessel:
• this changed dead time ⁇ can be used for an adaptation of the desired mass flow i.
• the correction module compares the desired mass flow m »with the currently present mass flow m (t) uu ⁇ if there is a deviation between these two variables, it adjusts the present mass flow with) to the desired m" mass flow. To ensure that the desired mass flow is present during the entire filling process, the correction module is applied repeatedly. Particularly advantageous is a repeated application of the correction module for the same size of time steps. In order to avoid instabilities, the mass flow m should not be changed too fast. It is therefore advantageous to let the previously present mass flow m alt be incorporated into the new mass flow m again :
• the factor a is a weighting factor that can take any value between zero and one, i. a e (0,1). In this way, the mass flow m changes more slowly.
• One way of avoiding exceeding the target mass m z is to determine the actual mass in the target vessel with the aid of the present mass flow m (t), the weight signal m (t) measured by the balance, and the dead time ⁇ . This can be done with the help of
• the risk of exceeding the target mass m z is additionally reduced by the desired mass flow m, and thus also the current mass flow with) is reduced towards the end of the filling process.
• the valve has an outlet opening provided with a circular cross-section and a closure element, wherein the outlet opening and the closure element are arranged on a common axis and the closure element rotates relative to the housing about the common axis and translationally displaceable along the common axis the or in the outlet opening and is retractable and the closure element has a cylindrical closure portion and a Austragungs Suite, whereby the valve can be opened or closed by translation about a length L of the closure element.
• the discharge area of the closure element is designed in such a way that the substance can flow through the discharge area if the translation is greater than the minimum translation L min and less than the maximum tranlation L max. If the translation is smaller than the minimum translation L mm or greater than the maximum translation L n ⁇ x , the outlet opening is closed by the cylindrical closure area and the substance can not escape through the discharge area.
• the mass flow m is directly correlated with the translation L of the closure element.
• the balance signal can also be used.
• the first derivative is determined by the time of the scale signal:
• ⁇ ⁇ > 0 can be chosen arbitrarily.
• the determination of the mass flow with) according to equidistant discrete Time steps At is preferred. For this purpose, starting from the opening of the valve at time t ⁇ , in each case after each time step At at the time
• n is a natural number between 2 and 10. If a larger n is used, then the mass flow is determined with,) over a larger time interval, whereby on the one hand statistical fluctuations of the balance signal are compensated. On the other hand reacts with, when using a large time interval only relatively slowly, whereby a modified mass flow is detected relatively late.
• valve is opened or closed by means of equal stepwise translation movements AL of the closure element.
• the minimum translation Z mn at which the substance can flow and / or the maximum translation L max is determined. Furthermore, it makes sense to determine the actual mass at the end of the filling process.
• These parameters can be stored and used by the control unit during subsequent filling operations. As a result, these parameters must be determined only once and subsequent filling operations can be faster be performed.
• These parameters from previous fill operations can be stored in a memory module, in particular a RFID (Radio Frequency Identification) tag, and used in later fill operations. It is particularly advantageous to attach the RFID tags to the respective reservoir, since this ensures a direct relationship between the substance in the reservoir and the data stored in the RFID tag. However, it is also the use of other storage media possible.
• the valve is opened with equally large stepwise translation movements AL of the closure element until the substance begins to flow, whereby the minimum translation Z mn is defined.
• the closure element is opened by a distance L mm + AL.
• the valve is displaced with equal stepwise translation movements AL of the closure element until the substance ceases to flow, whereby the maximum translation L max is defined.
• the closure element can be opened and closed in any manner.
• the discharge region of the closure element has a variable opening cross-section A.
• the size of the mass flow m flowing through the valve is directly correlated with the position of the closure element of the valve.
• A A (L)
• the valve has a striking mechanism, whereby a variable beat frequency F is struck against the already opened valve.
• the beat frequency F correlates directly with the mass flow m flowing through the valve, and an increase in the beat frequency F leads to a larger mass flow m. It can be beaten both in the direction of the axis and perpendicular to the direction of the axis of the closure element.
• the control unit can be implemented partially or in its entirety as a computer-based system.
• Figure 1 is a schematic representation of the inventive device for filling target vessels
• FIG. 2 shows a valve with a valve housing and a closure element
• FIG. 3 shows graphs with an idealized profile of the opening cross-section and the resulting mass profile
• FIG. 4 shows graphs illustrating the idealized influence of the opening cross section A, the impact frequency F and the rotational speed ⁇ on the mass flow m.
• FIG. 1 shows a target vessel 100 which can be filled with a substance located in the reservoir 200 up to the filling level height h via a metering device 300.
• the metering device 300 is associated with a time recording 400, with the help of which the time elapsed since the beginning of the filling process? can be detected and transmit the determined time signal to a control unit 600.
• the target vessel 100 is arranged on a scale 500, so that the weight of the substance located in the target vessel 100 can be determined.
• the determined weighing or mass signal m can likewise be transmitted to the control unit 600.
• the time and the mass signal are linked and results in the present at a certain time since the beginning of the dosing mass with).
• the dead time ⁇ is a scale-specific parameter which is independent of the physical properties of the substance to be filled.
• the dead time ⁇ may be determined before the first filling operation and stored in the control unit 600.
• the dead time ⁇ depends on the technical characteristics of the balance 500 and environmental parameters.
• the environmental parameters may change during a filling process, which may also change the dead time ⁇ . This change in the dead time ⁇ can be determined continuously and the desired mass flow i can be adjusted as a function of the changed dead time ⁇ .
• the determined mass flow with) is passed on to a correction module 620, which compares the mass flow with) with the desired mass flow m. If the mass flow with) is less than the desired mass flow m, the mass flow is increased by dm and if the mass flow with) is greater than the desired mass flow m, the mass flow is reduced by dm. After correction, the present mass flow should correspond to the desired mass flow m i. From the correction module 620, the signal for changing the mass flow is given to valve 310. The determination of the present mass flow is applied repeatedly during the filling process and, if necessary, the mass flow is corrected. The determination of the present mass flow and / or the correction of the mass flow can be carried out after equidistant time steps.
• FIG. 2 shows a valve 310 with a housing 311 and an outlet opening 312 provided with a circular cross section.
• a closure element 313 is arranged in the valve 310.
• the closure element 313 has a cylindrical closure region 314 and a discharge region 315.
• the outlet opening 312 and the closure element 313 are arranged on a common axis, and the closure element 313 can be rotated relative to the housing 311 both about the common axis 350 and translationally displaced along the common axis 340. This allows the closure element 313 out of or into the outlet opening 312 and retracted.
• This rotation 350 or translation 340 of the closure element 313 takes place with the aid of a drive which is coupled to the closure element 313 via a coupling element 316.
• a return element 318 is arranged, which enables a return of the closure element 313.
• this return element 318 is a closing spring. The provision of the closing spring is limited by a stop 317.
• a cavity is present, which serves as a reservoir 200 for the substance to be discharged.
• the substance to be discharged from the reservoir 200 via the discharge region 315 of the closure element 313 through the outlet opening 312 from the valve 310 reach the target vessel 100.
• the valve 310 has a memory module 320.
• This memory module 320 allows, for example, the storage of material properties of the substance to be metered, flow parameters from previous filling operations and / or scale-specific parameters, such as e.g. the dead time ⁇ .
• the memory module 320 is mounted on or in the valve housing 311.
• FIG. 3 shows a graph 1 with a profile of the desired mass flow i, another graph 2 with a profile of the mass flow with) the filling process according to the invention and a further graph 3 with the mass signal resulting from the course of the mass flow with FIG. Due to the delay between application of the mass with) in the target vessel 100 and the display of the mass on the scale 500 of Figure 1 and 2, there is a dead time ⁇ . As soon as a mass is displayed by the scale 500, the mass flow can be determined with. At the beginning of the filling process, the valve 310 is opened relatively quickly, which after the dead time ⁇ has a large mass flow with) and a steep increase in the mass with) the result.
• a too large opening cross-section A has a large mass flow with) result, which harbors a rapid filling of the target container 100 and the risk of overshooting the target mass m z in itself. For this reason, it may be useful to slow down the filling process by reducing the desired mass flow m * and consequently the opening cross-section A towards the end of the filling process.
• the opening cross section A of the valve and thus the mass flow with is reduced.
• the mass located in the target vessel 100 can slowly approach the target mass m z , thus avoiding exceeding the target mass m z .
• FIG. 4 shows an idealized profile of the opening cross-section A, an abruptly increasing impact frequency F and an abruptly increasing rotational speed ⁇ during a filling process.
• the superimposition of these parameters ideally leads to the course of the mass flow m shown. It becomes clear that both the opening cross-section A, the impact frequency F and the rotational speed ⁇ exert an influence on the course of the mass flow m.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Basic Packing Technique (AREA)
• Control Of Non-Electrical Variables (AREA)
• Measuring Volume Flow (AREA)
• Weight Measurement For Supplying Or Discharging Of Specified Amounts Of Material (AREA)

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• 2008
  • 2008-08-25 EP EP08162902A patent/EP2159555B1/de not_active Not-in-force
• 2009
  • 2009-08-13 CN CN2009801379173A patent/CN102165290B/zh not_active Expired - Fee Related
  • 2009-08-13 JP JP2011524315A patent/JP5452599B2/ja not_active Expired - Fee Related
  • 2009-08-13 WO PCT/EP2009/060524 patent/WO2010023111A1/de not_active Ceased
• 2011
  • 2011-02-23 US US13/032,953 patent/US8768632B2/en active Active

Patent Citations (3)

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