Precision weighing and dispensing device for fine-grained products, with rotation of the dispensing tray decoupled from the weighing

Abstract

Dosing scale with weighing containers that can be tipped out by means of a rotary cylinder or electric drive, characterized in that there is no mechanical contact between the load cell and the tipping mechanism until the tipping movement begins and then the connection is made with integrated magnets, so that the weighing is decoupled from external influences

Description

BACKGROUND OF THE INVENTIONThe precise metering of bulk materials which are to be dispensed in a predetermined quantity requires an exact portioning. In particular in applications requiring dosing with an accuracy of grams or milligrams, dosing balances play a decisive role. These scales generally function according to the principle that the bulk material is transported via a vibrating chute and accurately weighed in a weighing container. In industry, such systems are frequently supplied under designations such as "linear Bowger", "filling scale" or "dosing scale" and are used especially in the processing of dry, flowable bulk materials. In these cases, the combination of conveying accuracy and weighing technology is of decisive importance in order to meet the requirements for weighing accuracy and efficiency.Prior ArtIn the current state of the art, highly precise measurement techniques are used in modern systems for fine weighing in continuous batch processing in order to exactly record and dose the weight of bulk materials, liquids or powders. These systems consist of several components that allow precise control of material supply and are essential in the pharmaceuticals, chemical and food industries. A central element is the differential dosing scale (loss-in-weight, LIW), which continuously records the weight of a container via a weighing cell. As the material is metered, the load cell measures weight loss, thereby ensuring precise control of material flow. Alternatively, flow balances can be used which are integrated in conveyor belts or conveying systems and measure the weight of materials during transport. For the exact metering, vibration metering balances are used which use a combination of a vibration trough and a precision weighing unit. Controlled oscillations supply the material in constant quantities, while an automatic control unit continuously adjusts the material flow based on the weight measurement.In addition, there are platform balances with automation, which are equipped with an electronic weighing module. These modules can be integrated into conveying systems or packaging lines and allow highly accurate weight control. Alternatively, suspended or container balances are used which are mounted on a rack or silo and monitor the mass of a material during emptying. The smooth operation of such systems is provided by a control unit which evaluates signals from the weighing cells and sensors and adjusts the dosing mechanisms such as conveyor screws, pumps or flaps accordingly. By integration into a higher-order PLC or SCADA control system, the material supply can be automated and optimized in order to ensure a constant product qualityThe publication SU 249 675 A1 describes an automatic dosing balance with magnetic balance, which is distinguished by a simplified construction. The weighing system consists of a rotor arm with levers and cups, to the ends of which ferromagnetic cores or magnets are attached. These magnets interact with a fixedly mounted magnet on the housing and allow precise weight measurement. In the initial state, the magnetic attractive force maintains the rotor arm in a fixed position while placing a cup under a delivery system that fills the material to be weighed. Once the weight in the cup exceeds a certain threshold, the equilibrium is disturbed, the rotor arm rotates and the weighed quantity is discharged into a collecting container. At the same time, the next weighing element is brought into position, whereby the process is automatically repeated.Problem situationA significant problem relates to the construction of the weighing container, in particular with respect to the shape, volume, geometry and the integration of a flap which is opened and closed (in the worst case) via a pneumatic cylinder attached to the weighing container. As a result of the pneumatic hoses attached to the pneumatic cylinder, transverse forces are produced which can have a negative influence on the weighing result. A lack of mechanical decoupling prevents a stable zero position of the scale and results in the scale drifting out of the zero point. In extreme cases, this can lead to a start of dosing being prevented, since the scale either remains in a non-resting position or is outside the tolerance around the zero point. A solution to this problem can be achieved by a mechanical correction, a renewed calibration of the balance or a zero point shift. However, the latter is very difficult to use in calibration mode of the scale and can result in additional production and cost delays.The present construction results from the avoidance of a plurality of specific problems which are set out below: 1. the geometry of the weighing container is not optimally adapted to the properties of the bulk material to be metered. This concerns both the shape and volume and the mechanism for opening the flap. This is relevant in particular in the case of sensitive bulk materials such as, for example, live food (larvae), tablets, cereals or all bulk materials, which generally have to be weighed very precisely and exactly and must not be subjected to damage by mechanical influences: the flap of the weighing container can lead to destruction thereof by squeezing and pressure when these sensitive materials are metered in.Moreover, a 90 degree angle of the container side walls complicates unloading and leads to material adhesion to the container walls and to the flap itself. This may result in deviations from the weighed amount due to loss of adhesion and the aforementioned problems. In addition, the non-mechanical construction in combination with the firmly connected pneumatic lines of the cylinder can lead to faults in the weighing process, since the zero point of the balance is displaced. In the worst case, this may prevent the start of the weighing process.In summary, it can be stated that the described problems considerably limit the possible uses of conventional dosing balances. They are not suitable for applications requiring automated repeatable precision in the low weight range and exhibit weaknesses in the range of fast and precise dosages. There is thus an urgent need for an improved design which overcomes these deficiencies and ensures both precision and efficiency. In addition, a shift of the zero point of the scale is to be prevented permanently in order to promote a rapid transient response of the scale, which in turn leads to a rapid restart of the weighing process or only allows the latter.Furthermore, there are frequently also other disturbing influences, such as hoses or cables, which are required for carrying out the rotation, but which constitute a source of disturbing influences.Object of the InventionThe present object and objective is to realize the most precise, quick and automated possible weighing of any desired quantity X of a dry bulk material (among other things powder, granulate, teas). Taking into account the aspects set out in the problem, the aim is to also capture very small amounts of the bulk material and also particularly sensitive substances, such as, for example, live feed, in extremely precise weight units, such as, for example, 1 gram, and to meter these into a product-preserving weighing container (tray) instead of into a container with a mechanical flap, instead of into a container with a flap.SolutionIn order to avoid the above-mentioned problems, a dosing scale according to the invention uses a connection between the weighing object and the measuring cell which is of limited flexibility. The rotation is triggered by pneumatic actuation of an intermediate disc which has a slotted link in which two cams on the pneumatic drive disc engage. These have some play, the rotary movement ending in magnetic holders for fine positioning.The half shell into which the weighing object is introduced is connected to the load cell (DMS) via the aforementioned bearing mechanism. They are emptied by a 180° rotation about the longitudinal axis by means of a pneumatic device. In this case, the weighing container (half shell) into which the weighing object is introduced is connected to the load cell (DMS) via a bearing mechanism, while emptying takes place by rotating the shell through 180 degrees by means of a pneumatic device.In order that the driver disk and the weighing pan do not influence each other or even touch each other, permanent magnets are used which hold the weighing pan in its filling position until the weighing process is completed.This contactless fixing of the weighing pan by magnets integrated into the plastic of the housing is decisive. Since the dosing scale is predominantly used in the food industry, these are usually FDA-certified materials.With this mechanical decoupling, it is possible to realize very fine dosages of bulk materials in the range from about 50 mg) to about 1000 g at high cycle numbers. Since no transverse forces (cables, pneumatic hoses, etc.) influence the weighing) and only the weighing pan is mounted with its holder on the load cell, a very rapid settling of the load cell can take place. This means that the zero position of the balance can be ensured very accurately and also permanently.DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE DRAWINGSFIG. 1 shows a weighing device, consisting of a weighing container (1) which serves to hold the material to be weighed and is fastened to a holding element (2) which acts as a connection between the container and the remaining mechanism. The weighing container is rotatably mounted and coupled via a pin (3) to a cylinder (4) which controls the movement of the container. For the transmission of force, a shaft (5) is provided, which is guided by at least one ball bearing (6) in order to ensure a precise and low-friction movement. The mechanism also comprises magnets (7) which serve to fix or control the movement. The entire device is accommodated in a stable housing (8), which protects the functional units and enables a structured arrangement of the components. The weight is measured by a weighing cell (9) which ensures exact detection of the material introduced into the weighing container. FIG. 2 shows the pin with oval cut-outs (10), which enable a defined movement or guidance of the weighing container.In FIG. 3, a chute ( 12) is caused to vibrate via the vibration motor ( 11) and the product ( 13) is conveyed into the weighing container ( 1). In this case, the desired weight is detected via the load cell ( 9) and a control sensor. The weighing containers (1) are inverted by a pneumatic cylinder (4) and the product is discharged.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedSU 249 675 A1

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Claims

Dosing scale with weighing containers which can be tilted out by a rotary cylinder or an electric drive, characterised in that no mechanical contact exists between the weighing cell and the tilting mechanism until the start of the tilting-out movement and the connection to integrated magnets then takes place, so that the weighing is decoupled from external influencesDosing scale according to claim 1, characterised in that the rotating shaft is guided by two bearings within a plastic housing with high internal damping, wherein in the rest or filling position the magnets lying opposite the housing connection hold the shaft in its rotational position, while the rotational movement for emptying and returning into the initial position takes place via a coupling of the rotary drive acting only temporarily mechanically.Dosing scale according to claim 1 or 2, characterised in that said temporary coupling takes place by two projecting cams engaging in the keyway of a transfer disc and the pin mounted on the rotary drive shaft being connected in a rotationally locked manner to two small cams which project into the openings of the disc, when the cams enter the end position of the keyways when the rotary movement is carried out and bring about the rotation.Dosing scale according to one or more of the preceding claims, characterized in that the weighing container is a half-segmented spherical hollow body which together with the shaft and magnet is pushed onto a shaft with countermagnet, wherein the connection is stable but can be released by pulling in order to facilitate cleaning and replacement.

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