Narrow weighing system arranged in narrowly spaced rows in the lateral direction

A weighing system that works on the principle of electromagnetic force compensation. The weighing system has two guide members (4′), which connect a load support (5′) to a base region fixed to the housing. The weighing system also has at least one transmission lever (6′), which is mounted on the base region. The base region is divided into two separate subregions (2′, 3′), the transmission lever (6′) extends between these two subregions. Two weighing systems are arranged laterally side by side and their base regions are interconnected in such a way that the two subregions (2, 3) of the base region of the one weighing system are connected to the two subregions (2′, 3′) of the base region of the other weighing system such that their positions are fixed relative to each other.

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a weighing system that works on the principle of electromagnetic force compensation. The weighing system has two guide members that act as a parallel guide unit and connect a load support to a base region that is fixed to a housing. The weighing system also has at least one transmission lever, which has lever arms of different lengths, supported on the base region. The weight force of a load to be weighed is transmitted by a load support, and the force is applied to the shorter lever arm of the transmission lever via a coupling element. The longer lever arm is secured to a coil that protrudes into an air gap of a permanent magnet system.

A weighing system as described above is disclosed in the German patent specification DE 32 43 350 C2. In the weighing system described in DE 32 43 350 C2, the transmission lever, the permanent magnet system and the coil are located in an area that is within the parallel guide unit (i.e., within the base region, the load support and the two guide members). However, if this system is made narrower, the length of the transmission lever and the space available for the permanent magnet system would be very limiting.

A similar system is disclosed in the European publication EP 0 291 258 A2. In EP 0 291 258 A2, the base region of the weighing system is configured as two subregions that are interconnected by spacers. However, this configuration would also limit the length of the lever and the space available for the permanent magnet system.

To avoid this drawback, EP 518 202 A1 discloses a design in which the transmission lever is guided laterally along both sides adjacent to the base region by extending the lever using two braces. EP 518 202 A1 also discloses a design that disposes the coil and the permanent magnet system on the other side of the base region—i.e., outside the parallel guide unit.

A similar system is disclosed in DE 100 15 311 A1. In DE 100 15 311 A1, however, the transmission lever is guided along only one side of the base region. Thus, the design is not symmetrical with respect to the base region.

However, in the above systems, the lateral braces of the transmission lever extension will interfere if a plurality of weighing systems is arranged side by side. Therefore, the weighing systems cannot be arranged laterally in a row as tightly spaced as possible, and the lateral distance between two weighing system cannot be minimized to a desired extent. For example, if the body of the system formed by the base region, the guide members, the load support and the transmission lever is 10 mm wide, the braces to extend the transmission lever are 2 mm wide and a lateral play of 0.5 mm each is required, the distance between two weighing systems cannot be made smaller than 15.5 mm.

SUMMARY OF THE INVENTION

An object of the invention is to provide a weighing system whose width is narrow such that a plurality of weighing systems can be tightly arranged side by side without significantly limiting the length and the width of the transmission lever and/or the space available for the permanent magnet system.

An apparatus consistent with the present invention works on the principle of electromagnetic force compensation. The apparatus includes at least two weighing systems, each weighing system including: a housing; a load support; a base region fixed to the housing; two guide members that connect the load support to the base region; at least one transmission lever supported on the base region, the at least one transmission lever having a short lever arm and a long lever arm; and a permanent magnet system having at least one coil.

The short lever arm may be configured to apply a weight force transmitted by the load support to the long lever arm, which may be fixed to the at least one coil. The at least one coil may be configured to protrude into an air gap of the permanent magnet system.

The base region may comprise two subregions that are not interconnected in the individual weighing system. However, the at least two weighing systems may be interconnected such that the two subregions of one weighing system are connected to the two subregions of another weighing system. Accordingly, the positions of the respective subregions are fixed relative to each other.

Because the base region of a weighing system in the present invention is divided into, for example, two separate subregions, which are not interconnected in each individual weighing system, the transmission lever may be guided between the two subregions in such a way that the full width of the body of the system is available for the two subregions and the transmission lever. The system body is formed by the base region, the guide members, the load support and the transmission lever. Therefore, when the two weighing systems are laterally arranged side by side with the subregions of each base region connected only to the subregions of the base region of the other weighing system, the two subregions of each base region of a weighing system are fixed in their positions relative to each other only by the connections to the two subregions of the base region of the other weighing system.

By separating the base region into two subregions, the transmission lever can be made to practically any length since it is possible to guide the transmission lever between the two subregions. Of course, because the subregions within each weighing system are not interconnected, each individual weighing system is not functional. However, by connecting two weighing systems, the divided base regions of each weighing system may be fixed. By using such a design, a connection is formed without increasing the width of the individual weighing systems. In the illustrative example described above, the lateral minimum distance between two weighing systems drops from 15.5 mm to 10.5 mm.

Preferably, but not necessarily, the two weighing systems are substantially identical and are paired in such a way that the one weighing system is rotated about its horizontal central longitudinal axis relative to the other weighing system, and the two weighing systems are then connected to each other, e.g., with screws or adhesive.

An optical position sensor, comprising a transmitter and a receiver, for controlling the current flowing through the coil may be included in the weighing system pair. One part of the position sensor, e.g., the transmitter, may be disposed on the base region of one weighing system, and the other part, e.g., the receiver, may be disposed on the base region of the other weighing system. Therefore, each weighing system may include a position transmitter and a position receiver.

A permanent magnet system may also be included in the weighing system pair. The width of the permanent magnet system of each weighing system may be approximately as wide as the combined width of the two system bodies with each weighing system having a clearance into which the permanent magnet system of the other weighing system can protrude. As a result, the permanent magnet system of each weighing system can be significantly larger in diameter, which allows for a greater load carrying capacity. In the illustrative, numerical example provided above, the permanent magnet system may have a diameter up to 20.5 mm. The use of a common permanent magnet system with two air gaps is also possible.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows two system bodies1and1′ respectively part of two weighing systems. The system body1has a base region that is divided into two subregions2and3. The system body1also has two guide members4, a load support5, and a transmission lever6. A weighing tray (not depicted) is fastened onto the load support at hole10. The two guide members4act as a parallel guide unit and connect the load support5to the base region. The transmission lever6is pivotably supported on the base region by the thin point8. The weight force of a load to be measured is transmitted by the load support5to the shorter lever arm of the transmission lever6via a thin point9. The end7of the longer lever arm has fastening holes11for a coil15(FIG. 3). The coil15is located in an air gap of a permanent magnet system17(FIG. 3) and generates a counterforce that is proportional to the weight force. As illustrated inFIGS. 1 and 3, a system body, a coil, a permanent magnet system and the associated electronics form a weighing system. In the description below, the functions of the weighing system not pertinent to the understanding of the present invention will not be described in detail.

The system body depicted inFIG. 1is configured such that the two subregions2and3of the base region are not interconnected. Thus, there is no fixed connection between the two subregions2and3, which are hidden behind the transmission lever6inFIG. 1. As a result, the transmission lever6can pass between the two subregions2and3and can have any length. The transmission lever6can nevertheless be configured to practically have the full width of the body of the system. The transmission lever6is therefore highly stable and does not tend to be subject to interfering natural oscillations. A weighing system with the system body1ofFIG. 1is, of course, not operational on its own because the subregions2and3are not connected. However, the weighing system can become operational when two weighing systems are interconnected. That is, the two subregions of the base region of one weighing system may be connected to the two subregions of the base region of the other weighing system such that their positions are fixed relative to each other. As shown inFIG. 2, the system bodies1and1′ of the two weighing systems are arranged side by side such that the base regions may be interconnected after assembly.

InFIGS. 1 and 2, the individual components of the two system bodies1and1′ are provided with the same reference numbers; the components of the system body1′ are simply provided with a prime mark to distinguish them from the components of the system body1.

InFIG. 1the subregions2and3and2′ and3′, which are as wide as the body of the system, are hatched. The other regions are 0.2 mm narrower, so that they do not contact each other after assembly and can move independent of each other. Thus, once the two system bodies are assembled, only the hatched parts of the subregions of the base region can touch each other. Because of the geometry of these subregions, however, only the cross-hatched surfaces of the subregions actually touch each other. That is, the contact surface31touches the contact surface31′, the contact surface21touches the contact surface21′, the contact surface20touches the contact surface30′, and the contact surface30touches the contact surface20′. The areas of the subregions contacting each other are firmly connected with screws. The corresponding holes or threaded holes29and29′ are visible inFIG. 1. Thus, the subregion3′, via the contact surfaces30′-20and31′-31, interconnects the two subregions2and3of the base region of the system body1. The subregion2′, via the contact surfaces21′-21and20′-30, also interconnects the two subregions2and3of the base region of the system body1. Because of this double connection, the two subregions2and3form a stable base region for the system body1. Likewise, the subregion3, via the contact surfaces30-20′ and31-31′, interconnects the two subregions2′ and3′ of the base region of the system body1′. In addition, the subregion2, via the contact surfaces21-21′ and20-30′, also interconnects the two subregions2′ and3′ of the base region of the system body1′. These connections thus create a weighing system pair in which the two base regions2and3and2′ and3′ of weighing systems1and1′, respectively, form a stable unit. As a result, both the separate subregions2and3of the base region of the system body1and the separate subregions2′ and3′ of the base region of the system body1′ are fixed with respect to each other and behave like a non-separate base region.

According to another exemplary embodiment, the system bodies1and1′ depicted inFIG. 1have identical components. The system body1′ is rotated 180° about a horizontal central longitudinal axis40(shown inFIG. 3) in relation to the system body1. With this arrangement, each load support5,5′ has a fixation hole10,10′ on the topside and/or underside of the weighing system for a weighing pan. In addition, the system bodies1and1′ shown inFIG. 1are each formed integrally from a single metal block (e.g., by milling or wire Electrical Discharge Machining (EDM)). This method of construction makes it possible to manufacture highly reproducible weighing systems because the method does not require any clamping, screwing, etc. with respect to the flexible or movable parts. To produce an individual system body, thin connecting webs28or28′ may be provided. These connecting webs connect, in particular, the two subregions2and3or2′ and3′ of the base region across the transmission lever6or6′, respectively, and thereby prevent the subregions2and3or2′ and3′ from falling apart. After the two individual system bodies1and1′ have been assembled into a pair, stability is provided by the mutual connection, and the connecting webs may be cut. (All the figures show the connecting webs already cut.)

As shown inFIG. 1, end7of the transmission lever6extends laterally and slightly beyond the base region2/3. At the corresponding point, the subregion2′ of the base region of the (secondy system body1′ has a clearance22′, which is configured to receive the protruding part of the end7of the transmission lever6. Likewise, the protruding end7′ of the transmission lever6′ of the second system body1′ can project into the clearance22in the subregion2of the base region of the first system body1. As a result, the ends7and7′ of the transmission levers6and6′ of the respective system bodies1and1′ forming the weighing system pair are aligned with each other on the vertical center plane of the weighing system pair. Thus, a common dual magnet, which will be described in greater detail below with reference toFIGS. 3 and 4, may be used for both weighing systems of the pair.

As shown inFIGS. 1 and 2, an optical position sensor for controlling the electromagnetic force compensation can also be included in the weighing system pair. The optical position sensor comprises a transmitter and a receiver. The transmitter for the first weighing system19is located in the hole14in the subregion2of the base region and illuminates the slot12on the tab27at the rear end7of the transmission lever6. The receiver, which responds to the light passing through the slot, is located in the hole13′ in the subregion2′ of the system body1′ of the second weighing system. Likewise, the transmitter for the second weighing system19′ is arranged in a hole14′ (FIG. 2) formed in the subregion2′ of the base region. The light from the transmitter pass through the slot12′ and is detected by a receiver located in the hole13.

FIG. 3illustrates a central longitudinal section of a weighing system pair without the permanent magnet system. In addition to the components discussed above,FIG. 3shows the two coils15and15′ of the weighing system pair19/19′, which are connected to the ends7or7′ of the respective transmission levers6and6′with fastening screws16or16′. The permanent magnet system (not shown) for the (rear) weighing system19is located in the clearance23below the horizontal central longitudinal axis40. The permanent magnet system for the (front) weighing system19′ is located in the clearance23′ above the horizontal central longitudinal axis40. The permanent magnet systems may, for instance, be fastened to the adjoining subregions2and2′ of the base region.

As shown inFIG. 3, the two subregions2and3of the base region have no fixed connection to each other at all. They are interconnected by the connecting webs28(shown cut inFIG. 3) only during manufacture. The connecting web between the load support5and the subregion3of the base region protects the thin points of the guide members4from excessive deflection during manufacture and assembly.

FIG. 3also shows the end7of the transmission lever6Also visible is the tab27′ with the slot12′ on the (front) weighing system19′ as it protrudes into the clearance22in the subregion2of the (rear) weighing system19.

FIG. 4is a perspective view of a weighing system pair19/19′ including the permanent magnet system17/17′. The permanent magnet system may be a system having two individual permanent magnets, which in the example shown, have one common external soft iron return path, or a system with a single longer permanent magnet having an upper air gap for the coil15′ and a lower air gap for the coil15. To reduce magnetic leakage into the environment, the permanent magnet system17/17′ has an upper shielding cover18′ and a lower shielding cover18. The permanent magnet system17/17′ may be as wide as the complete weighing system pair, i.e., about twice as wide as an individual system body1or1′. This configuration makes it possible to obtain a relatively wide permanent magnet system despite the narrow system body and, thus, a relatively high load carrying capacity. Similarly, a round permanent magnet system may have a diameter that is as large as two individual system bodies.

The weighing system pair inFIG. 4is depicted in greater detail so that some details not shown inFIGS. 1 to 3for the sake of clarity are visible inFIG. 4. For example, the connecting screws41that connect the two system bodies are illustrated inFIG. 4. The connecting screws are screwed in from the front side through the holes29′ (FIG. 1) in the subregions2′ and3′ of the base region, and the holes29′ are countersunk such that the heads of the screws do not protrude. In contrast, the threaded hole29″ (visible at the bottom inFIG. 4) is not countersunk because, here, the connecting screws are screwed in from the rear and the object is to maintain the full width of the system body to impart stability to the threaded connection. For the head (not visible) of this connecting screw, the corresponding hole in subregion3of the base region is, of course, countersunk on the rear side. InFIG. 4it may also be seen that a substantial portion of the transmission lever6′ is milled thinner than the width if the system body and only a circumferential web26′ has the full width of the system body. This makes the transmission lever lighter without significantly affecting its stability.

As shown inFIG. 5, the pair of weighing systems19/19′ each have a weighing tray25and25′ with a prismatic support surface, e.g., for tablets. However, the weighing tray is not limited to just this design. Each weighing system19/19′ may also be provided with a protective plate24and24′. The protective plate24′ is firmly screwed to the subregions2′ and3′ of the base region of the front weighing system19′ with screws32′. The protective plate24is likewise firmly screwed to the subregions2and3of the base region of the rear weighing system19. The protective plates protect the weighing system pair19/19′ from environmental influences.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. For example, one (or more) additional transmission lever(s) may be provided between the load support5or5′ and the transmission lever6or6′. The two base regions of the two weighing systems may be joined to form a weighing system pair using bonding, riveting or other joining methods instead of screws. It is also possible to make the entire system body1or1′ in a uniform thickness and to ensure a slight distance between the two system bodies when the weighing system pair is assembled by using washers around the holes29so that the load supports, the guide members and the transmission levers of the two weighing systems can move independent of each other. It is also possible to make both system bodies of a weighing system pair from a single metal block. To accomplish this, the contours of the two system bodies are milled out from each side and the separations in the region of the load supports, the guide members and the transmission levers are created by thin vertical cuts using, for example, wire EDM.

Details of the weighing system pair that are not essential to the invention, e.g., overload protections, overload limit stops, off-center load adjustment mechanisms, etc., and the complete electronics have not been discussed because they are conventional in the art.