HK1027156B - Overload protector for a force-measuring device, particularly for a balance - Google Patents

Description

Overload protection device for a force-measuring device, in particular a balance

The invention relates to an overload protector for a force-measuring device, in particular a balance, comprising a load receiver which has two parts, the first part of which is intended to introduce a force to be measured into the force-measuring device. The second part of which, for transmitting the force to be measured to a load cell, is connected to the first part in a parallelogram-like arrangement by means of two parallel guides, the longitudinal directions of which extend transversely to the force-measuring direction, which parallel guides are rigid in relation to their longitudinal direction and elastically flexible in their transverse direction. The overload protector has a first and a second joining point, which are formed on the first and the second part, respectively, by means of which the first and the second part are joined to each other, preventing their displacement relative to each other in the force introduction direction. The overload protector also includes a preloaded resilient element that urges the first and second portions into spring-loaded contact with one another and opposes a force to be measured that is introduced on the first portion.

The purpose of such overload protectors, particularly on sensitive balances, is to protect the load cell and the part for transmitting the force being measured to the load cell against overloads resulting from forces that greatly exceed the normal load specified for the balance. Such detrimental effects of force may occur, for example, when a load to be weighed is placed on the weighing pan in an improperly sudden manner due to improper operation of the balance. In this case, the instantaneous force acting on the load receiver will exceed the rated tolerance force. Even if a stationary stop is provided to limit the amount of travel of the load receiver in the force introduction direction, the load receiver is excessively accelerated until its movement stops at the stationary stop. This causes an inertial force of corresponding magnitude on the load cell and for transmitting the force to be measured; and/or it will cause momentary peaks of tensile and compressive stress at the pivot and coupling, which the balance is not prepared to withstand since it is designed for a certain allowable load.

In the known overload protector (DE2830345C3) described at the beginning and arranged on a balance, the two guide pieces of the overload protector are formed in a triangular or trapezoidal shape from a flat material and are connected to the second part at the long base of the triangular or trapezoidal guide piece and to the first part at the diagonal or shorter sides of the triangular or trapezoidal guide piece, respectively, by means of clamping screws. For connecting the guides, the second part is equipped, on the side facing away from the first part, with a bracket which is located at a distance from the second part and extends in a transverse direction with respect to the two guides. The main part of the support bracket in the second part passes through the material-free inner region of the triangle or trapezoid defined by the sheet portions forming the guide, which extends along the sides of the triangle or trapezoid extending between the two parts. This geometrical arrangement of the overload protector requires a relatively large amount of space. In addition, the cost of assembling the first part with the clamping bolt, the second part and the guide is also high.

On the other hand, a particularly space-saving arrangement of the overall design of the components for introducing and transmitting the measured force to the load cell (DE4119734a1) is known, which, however, does not comprise an overload protector for the load receiver.

The object of the invention is to provide an overload protection device of the type mentioned at the outset which combines a particularly space-saving design with low assembly outlay.

According to the invention, the solution to this problem is to design the two parts and the two guides as integrally connected material parts of one integral piece of material, wherein the guides are separated from each other by a material-free space through the piece of material.

Since the two parts of the load receiver are integrated into one integral part by the guide, the assembly effort of the overload protector of the invention is reduced, as long as the pretensioned elastic element urging the two parts into spring-loaded contact with each other is inserted. In addition, the volume occupied inside the block of material by the material-free space separating the two parts and the two guides from each other can be kept small, and therefore the space required by the overload protector will also be small. Various economical machining methods for forming material free spaces may be provided including, for example, milling, drilling or spark erosion and combinations of these methods. In particular, the last-mentioned spark erosion proves to be particularly suitable.

As long as the pre-tensioning spring urges the two parts into spring-loaded contact with each other, the first part and the second part will be rigidly coupled to each other and the force introduced into the first part will be transmitted and guided by the second part to the load cell. On the other hand, if the force introduced into the first part exceeds the contact force corresponding to the pre-load force of the spring, the first part will be displaced and moved relative to the second part until the first part comes to a stop against a stationary stop. However, the part of the inertial force exceeding the preload force is not transmitted to the second part. Thus, harmful inertial forces are prevented from reaching the load cell and those other parts of the load cell which are used for transmitting forces. Here, the amount of pretension of the elastic element is chosen to be of a suitable magnitude to keep the two parts in spring-loaded contact until the nominal allowable load of the balance is reached.

In a further development of the invention, a practical solution is provided in which the first joining point is formed by a first shoulder in the material part constituting the first part, and the second joining point is formed by a second shoulder in the material part constituting the second part. Each shoulder projects towards a respective opposite material portion. The first shoulder has a free surface facing the first guide, i.e. facing the direction of the force to be measured, and the second shoulder has a free surface facing the second guide, i.e. facing the same direction as the force to be measured. The material portions forming the first and second portions are pressed against each other at the free surface by the pretensioned elastic element. Assuming, on the one hand, that the free surface of the shoulder of the second part faces in the direction of the introduction of the force, i.e. that the surface vector of this free surface has the same direction as the introduction of the force, and, on the other hand, that the free surface of the shoulder of the first part faces in the direction of the introduction of the force, i.e. that the surface vector of this free surface has the opposite direction to the introduction of the force, the force acting on the first part will have a tendency to separate the free surface of the shoulder of the first part from the free surface of the shoulder of the second part, and therefore the first part will be displaced in the direction of the introduction of the force with respect to the second part. However, this displacement only occurs when the applied force exceeds the pre-load force of the spring urging the two free surfaces into compressive engagement against the applied force.

As a preferred feature, the shoulder of at least one of the two parts is designed to allow displacement of the shoulder relative to that part in a direction transverse to the direction of introduction of the force.

It is known that the measured force acting on the load receiver also generates a torque, causing a little twisting of the load receiver. For example, the more eccentrically the weight is placed on the weighing pan supported by the load receiver, the more strongly the problem called longitudinal eccentric loading will be. The distortion caused by the longitudinal eccentric load may cause the interengaging shoulders of the first and second parts to slide slightly relative to each other. This can lead to balance errors. In case the shoulder on at least one of the two parts of the load receiver is designed to be displaceable in a direction transverse to the direction of introduction of the force, the corresponding shoulder will follow the twisting caused by the eccentric load, whereby slipping at the junction of the shoulders and associated balancing errors will be avoided. For this purpose it is sufficient if one of the two shoulders of the first part or the second part is designed to be movable in the transverse direction. However, it is also possible to design both shoulders such that they can be displaced in a direction transverse to the direction of introduction of the force.

In a further advantageous development of the invention, the displaceable shoulder is formed in a material portion which is delimited by the material-free space and which is connected to the portion comprising the displaceable shoulder by a narrow portion which is designed to be elastically bendable in a direction transverse to the force to be measured. This construction allows the displaceable shoulder to be formed on the respective part in a space-saving manner and without increasing the assembly outlay.

In addition, it has proven to be feasible if the pretensioned elastic element is a pretensioned compression spring. The required pre-load of the compression spring is achieved by compression deformation, so that the space occupied by the spring can be reduced.

In an advantageous embodiment of the invention, the compression spring is designed as a helical spring, one end of which is pushed against a bearing surface which is located on the material portion forming the second part and faces the direction of force introduction. The other end of the helical spring is pushed against a surface facing the bearing step of a bolt in the same direction as the force introduction, which bolt axially penetrates the material portion of the second part and the helical spring with lateral play in the direction of the force introduction. The bolt is anchored on the first part and can be axially displaced relative to the second part against the pretension of the compression spring. According to this design, the bolt, which is firmly connected to the first part and is movable relative to the material part forming the second part, extends with lateral play in the helical spring in a direction parallel to the direction of force introduction. The purpose of the lateral play is to ensure that the bolt does not hinder the mobility of the first part relative to the second part. The material portion forming the second portion contains a bearing surface facing the direction of introduction of the force for holding one end of the helical spring and thereby pushing that end of the compression spring against the applied force. Starting from this bearing surface, the compression spring surrounds the shank of the bolt with lateral play and extends towards the force-introduction-facing direction of the bolt, i.e. the bearing shoulder opposite to the bearing surface of the material part forming the second part. When a force exceeding the rated load capacity (set by the degree of pretension of the compression spring) is introduced into the first part, the compression spring is further compressed, causing the bearing shoulder of the bolt to move towards the bearing surface of the second part, in other words, causing a displacement of the first part relative to the second part in the direction of force introduction.

In the same case, a further development of the invention provides a cavity in the second part around the circumference of the helical spring. The cavity may in a simple manner be formed by a bore hole having the same axial direction as the direction of force introduction and partly through the material part forming the second part and the guide part adjoining the second part on the side of force introduction. In this case, the bottom of the bore hole forming the cavity simultaneously serves as a fixing surface for the helical spring.

In a further development, a stop is provided in the cavity in the material part forming the second part, which stop limits the axial displacement of the bolt. The stop can be provided, for example, by the bottom end of the blind hole forming the cavity, with a gap between the bottom of the blind hole and the end of the bolt pointing in the direction of introduction of the force, so as to provide a displacement-stop position for the end of the bolt. The stop limits the range of travel of the bolt without other limiters such as by displacement-stop contact of a balance pan bracket attached to the load receiver to a stationary stop on the housing.

In a further alternative practical design, the end of the bolt pointing in the direction of force introduction projects from the surface of the piece of material. The projecting end portion may act in conjunction with a housing-based rest stop to limit travel after assembly.

In the same case, it is possible to have a connector part for receiving the force to be measured at the end of the bolt facing the force introduction direction. In this case, the bolt guides the coil spring while serving to receive the force introduced into the first portion. For use in a balance, the connector part of the bolt is preferably in the form of a conical support column for seating a balance pan thereon.

In an advantageous spatial arrangement of the aforementioned embodiment, the bolt is arranged at a portion of the load receiver extending between the two guides. This has the advantage that the amount of space required can be minimized given the size of the space determined by the guide while accommodating the bolts.

In addition. A design is preferred in which the material free space is at least partly formed by only one narrow linear cut through the piece of material. The width of the narrow linear cutting slit may be reduced to the minimum amount required to still allow sufficient displacement of the first part relative to the second part in an overload situation. Such narrow linear cuts can be produced primarily by spark erosion processes and are virtually unlimited in terms of their shape. The achievable cutting seam width can therefore be as small as, for example, a few tenths of a millimeter. A suitable raw material for the block of material may be, for example, an aluminium alloy, but many other raw materials are also contemplated, including, for example, steel alloys or composite materials.

A feature of advantageous embodiments of the invention is that the two guides on two sides facing each other are profiled by a narrow linear cut section, while at each end of each guide a narrow flexible portion is defined between the narrow linear cut section and the respective opposite, outward side in the guide. Thus forming a parallelogram mechanism which guides the first part of the load receiver, while the four corners of the parallelogram are defined by the narrow flexible portion.

In yet another practical refinement of the above embodiment, the narrow linear cutting slit has a segment that begins at an end of the first shoulder proximate the first portion and terminates at an end segment that defines a segment of the first guide proximate the end of the first portion. The narrow linear cutting slit also has a segment that begins at an end of the first shoulder proximate the second portion and terminates at an end of the segment defining the second guide proximate the end of the first portion. The narrow linear cutting slot segment extending from the shoulder towards the guide element thus defines, together with the shoulder extending transversely to the force introduction direction, the contour shape of the first and second portions facing each other in a complementary manner, so that in particular the material portion forming the second portion extends between the two guide elements towards the material portion forming the first portion. In this arrangement the shoulder extending transversely to the force introduction direction is located at the location of the force sensor, which location extends substantially between the narrow flexible portions of the guide near the first portion. The resilient member urging the two shoulders into contact with each other is arranged, for example, in the vicinity of the shoulder, the side of the load receiver facing away from the first part.

In one particular arrangement of this arrangement, the narrow linear cut slit segments defining the guides are at least partially wider than the segments joining the segments defining the two guides. The wider portions are arranged such that they allow an increased amount of displacement travel of the first portion relative to the second portion.

It is also within the scope of the invention that the material portion forming the second section is guided in a parallel movement relative to the stationary part of the force-measuring device by two parallelogram guides which extend in a longitudinal direction transverse to the force introduction direction and are rigid in their longitudinal direction and elastically flexible in their transverse direction, each parallelogram guide being connected at one end to the material portion forming the second section and at the opposite end to the stationary part of the force-measuring device, and wherein the material portion forming the second section is connected to a mechanism for transmitting the force to the force-measuring transducer. As long as the nominal maximum allowable load is not exceeded, the first and second portions of the load receiver will remain rigidly coupled to each other, and the load receiver is therefore guided by the parallelogram guide in a translational movement in the direction of the force. The small or virtual displacement translational movement, which is caused by the measured force or load and is not quantifiable, can be transferred to the force transfer mechanism and can cause the force to be transferred to the load cell. The force transfer mechanism and the load cell are protected from excessive inertial forces when the rated maximum load is exceeded and the first and second portions are disengaged from each other.

A particularly advantageous embodiment which is further improved in this respect is characterized in that the parallelogram guide and the stationary part are formed as material portions of one piece of material which are integrally connected to the second part and which are separated from each other by a material-free space through the piece of material. It will thus be appreciated that the advantages of the unitary construction are required for the measurement method not only in terms of the overload protector but also in terms of the guidance limits of the load receiver.

Preferably, this embodiment is arranged such that the parallelogram guides have flexible portions at their longitudinal ends defined by material-free spaces. An arrangement is particularly feasible in which at least one of the material-free spaces defining the pliable portion is formed by a narrow linear cut slit opening out to the outer boundary of the block of material, and from that open end a curved portion is formed which approximates tangentially to the longitudinal direction of the parallelogram guide.

In a further development of this embodiment, the force transmission means have at least one lever, one arm of which is connected to the material part forming the second part by a coupling piece which extends in the direction of force introduction and is rigid in the longitudinal direction and elastically flexible in the transverse direction. After the measured force is introduced onto the load receiver, the force will be reduced or increased by the at least one lever to a magnitude that is appropriate for the load cell.

In this case, the advantage of a monolithic structure can again be recognized, in which the coupling piece and the lever are formed as integrally connected material parts bounded by a material-free space in a material region of the stationary part, which material region penetrates into the space between the two parallelogram guides. In addition, in view of minimizing the size of the space required and increasing the strength of the portion of the force-measuring device subject to the force to be measured, it would be advantageous if the material-free space defining the coupling member and the lever were at least partially formed only by narrow linear cut slits dividing a block of material.

Finally, particularly applicable to all layouts of embodiments of the invention, the block of material has substantially the shape of a rectangular block, wherein a maximum pair of surfaces extends parallel to the longitudinal direction of the parallelogram guide. Here, the material-free space runs through the material block from one of the two largest sides of the material block to the other side in a direction parallel to one of the smaller boundary surfaces of the material block, thus resulting in a bulge-free, compact, block-shaped overall design layout.

Other features, details and advantages of the invention will become more apparent from the following description and the accompanying drawings, to which reference is also made for a disclosure of details which are not explicitly mentioned in the above description and which are important for the invention. In the drawings:

FIG. 1 is a side view of a force measuring device assembly with an overload protector;

fig. 2 is a side view of an embodiment that is simplified compared to the embodiment of fig. 1.

Fig. 1 shows a plan view of a block of material 1 of substantially rectangular block shape, seen from the direction of the largest face 2 of the block. The load receiver, the overload protector and other components of the force measuring device are formed in the block of material 1. In particular, the force measuring device represents a balance for measuring the weight of a load to be weighed.

The monolithic material block 1 is divided into several material portions, which are separated from each other by material free spaces within the material block 1. These material free spaces penetrate the block of material perpendicularly to the plane of the drawing from a maximum plane 2 coinciding with the plane of the drawing to an opposite maximum plane at a distance behind the plane of the drawing. The two pairs of smaller surfaces 3, 3 'and 4, 4' of the material block extend perpendicular to the plane of the drawing between the two largest faces and form the outer boundary of the material block 1. The majority of the material-free space is formed by narrow linear cutting slits whose width, if measured in a direction parallel to the maximum surface 2, may be as small as a few tenths of a millimeter to a few millimeters, for example. For example, they are formed by spark erosion machining using an erosion wire.

Two material portions indicated by reference numerals 5, 5 ' extend along the respective minor parallel sides 4, 4 ', and these sides 4, 4 ' are longer (measured in the plane of the drawing) than a further pair of minor parallel sides 3, 3 ' extending perpendicularly to the sides 4, 4 '. At its inner boundary facing away from the smaller side 4, 4 ', the material section 5, 5 ' is bounded by a material-free space 6, 6 ', while the material spaces 6, 6 ', except for their ends, extend parallel to the smaller side 4, 4 '.

Starting from the bore 7 for inserting the spark-erosion wire, the material-free space has an end section 8 with a curvature that is convex toward the minor lateral surface 4, followed by a main section 9 that extends parallel to the minor lateral surface 4. After the main section 9, an end section 10 is bent with a convex side facing the minor side 4 and finally extends into a section 11 extending substantially parallel to the minor side 3, while the minor side 3 is perpendicular to the minor side 4.

A segment 12 is connected to the material-free space 6, which extends parallel to the smaller side 3 and the segment 11, while the segment 11 is suspended together with the material-free space 6. At their ends, the segments 11 and 12, which are parallel to each other and to the minor lateral surface 3, have curved segments and their convex lateral surfaces face each other, thus defining two narrow flexible portions 13 and 14, while the two flexible portions 13 and 14 are connected to the portion of material delimited by the two parallel segments 11, 12.

Segment 11 terminates outside the narrow portion 14 and is connected outside the narrow portion 13 to the curved end segment 10 of the material free space 6, while segment 12 terminates outside the narrow portion 13 and is connected outside the narrow portion 14 to the curved end segment 16 of the material free space 6'. Starting from the bore 17 diagonally opposite the bore 7, the curved end section 16 approaches the side face 4 ' in a convex curve, then enters the main section 9 ' of the material-free space 6 ' parallel to the smaller side face 4 ' and ends at the end section 18 opposite the end section 16 and also has a curvature which is convex to the smaller side face 4 '. The two material free spaces 19, 20 opposite the convexly curved ends 16, 18 of the material free space 6 ' approximately form a mirror image of the convexly curved end sections 16, 18 with respect to the longitudinal axis of the material portion 5 ' extending parallel to the main section 9 '. The end sections 19, 20 are formed by narrow linear cuts which start from the minor side 4 'and define, at each end of the material portion 5', a narrow flexible portion 21, 22 between themselves and the end sections 16 and 18. Likewise, the ends of the material portion 5 are shaped as narrow flexible portions 23, 24, which flexible portions 23, 24 are defined on the one hand by the convexly curved extremities 8, 10 of the material free space 6 and on the other hand by arcuate recesses 25, 26 formed in the material block 1. These arcuate recesses 25, 26 start from the smaller side 4 and are in approximately mirror image relationship with the convexly curved end portions 8, 10 of the material-free space 6 relative to the longitudinal central axis of the material portion 5.

The material portions 5, 5 ' form a parallelogram guide of a parallel-guiding mechanism, by means of which a material portion 27 of the material block 1, which is adjacent to the material portion 15 and is connected to the parallelogram guide 5, 5 ' by means of two narrow portions 21, 23, is guided upon displacement thereof relative to the material portion 28, while the material portion 28 is connected to the parallelogram guide 5, 5 ' by means of narrow portions 22, 24, the narrow portions 22, 24 being located at opposite ends of the narrow portions 21, 23, respectively. The narrow portions 21, 22, 23, 24 thus form the four corners of a parallelogram, where the parallelogram guide 5, 5' is flexible in bending in the transverse direction and rigid in the longitudinal direction. The material portion 28 serves to fix the material block 1 on, for example, a stationary base plate of a balance and thus corresponds to a stationary portion. In contrast to this stationary material section 28, the material section 27 is displaceable in parallel due to the flexibility of the parallelogram guide and serves as a load receiver for the balance. As will be described below, it is through the material portion 27 that the measured measuring force, i.e. in the case of a balance the gravity force, is introduced.

The material portion 28 forming the stationary part has an area which projects into the space between the parallelogram guides 5, 5' and supports a lever system of two levers working in series, which lever system is formed by the material portions 29, 30 of the material block 1 and which are separated from each other by a material-free space. On the side facing the parallelogram guide 5, the material section 29 is delimited by the material-free space 6, while the material-free space 6 also delimits the parallelogram guide 5. On the side facing away from the parallelogram guide 5, the material-free space 31 delimiting the material portion 29 is likewise composed mainly of a series of narrow linear cut slit segments. The first segment 32, starting from where the segment 12 enters the convexly curved segment thereof defining the narrow flexible portion 13, said segment 12 delimiting the material portion 15 on the side closest to the material portion 28, the first segment 32 approximately forming a mirror image of the convexly curved segment. Opposite the first segment 32 and extending curved like a mirror image of the segment 32 is an end segment 33 of one segment 34, whereas the segment 34 extends substantially along the longitudinal direction of the parallelogram guide 5, 5'. Defined by the first segment 32 and the end segment 33 is a narrow flexible portion 35, which flexible portion 35 is substantially aligned with the narrow flexible portion 13 with respect to the longitudinal direction of the parallelogram-shaped guides 5, 5'.

After the end section 33, the sections 34 continue partly in a straight line and converge slightly towards the main section 6 of the material-free space 9, through a bore 36 and then to a bore 37. These two bores can be used for inserting spark-erosive wires. After the bore 37, the segment 34 is bent around two bores 38, 39 in the material portion 30, which bores are arranged in the longitudinal direction of the parallelogram guide 5, 5'. Before reaching an imaginary first straight line extending perpendicular to the parallelogram guide 5, 5' in the vicinity of the narrow portions 22, 24, the segment 34 forms a curved portion 41, the convex side of which curved portion 41 approaches the imaginary first straight line. After the curved portion 41, the segment 34 extends a short distance along the imaginary first straight line and then forms a curved end segment 42, the convex side of which also approaches the imaginary first straight line. Opposite the portion of segment 34 extending from the curved portion 41 to the curved end portion 42 and forming a mirror image with respect to the imaginary first straight line is a narrow linear cut slit segment 43, which segment 43 together with the mirror image portion of segment 43 in segment 34 defines two narrow flexible portions 44, 45 lying on the imaginary first straight line.

The material portion 29 delimited by the material free spaces 6 and 31 forms a lever which is supported on the material portion 28 by a narrow flexible portion 35 forming the fulcrum of the lever. The material portion 15, one end of which is connected to the end of the lever 29 closest to the load receiver 27 by the narrow flexible portion 13, and the other opposite end of which is connected to the load receiver 27 by the narrow flexible portion 14, serves as a connection between the load receiver 27 and the lever 29.

At the end furthest from the load receiver 27, the lever 29 is connected to the material portion 30 forming the second lever of the lever system by a narrow portion 44, a material portion extending between the narrow portions 44, 45, and by a narrow portion 45.

The second lever formed by material portion 30 is separated from lever 29 by the portion of section 34 extending from bore 37 to end section 42. Similarly, material free spaces 46, 47 formed by narrow linear cut seams define the material portion 30 forming the second lever proximate the material portion 28. Starting from the bore 37, the material-free space 46 extends locally perpendicularly to the longitudinal direction of the parallelogram guide 5, 5 ' to a bore 48, from which bore 48 it extends continuously in the longitudinal direction of the parallelogram guide 5, 5 ' to a curved end section 49, the outer convex side of which end section 49 is close to an imaginary second straight line extending perpendicularly to the parallelogram guide 5, 5 '. Which extends in the area of the material block 1 adjoining the imaginary first straight line (defined by the narrow portions 44, 45) and extending to the nearest smaller side 3'. The material free space 47 has the form of a narrow linear cut slit which, starting from the bore 7, extends in a direction towards a convexly curved end section 49 of the material free space 46, at which end section 49 the material free space 47 ends with an end section 51, which end section 51 is in a mirror image relationship with the end section 49 with respect to an imaginary second straight line. The end sections 49, 51 define between themselves a narrow flexible portion 52, at which portion 52 the second lever 30 has its fulcrum on the material portion 28.

With this device, the force to be measured, which is introduced in a direction perpendicular to the parallelogram guides 5, 5' onto the conical support column 53 for the weighing pan (not shown), is coupled with the lever 29 by means of the coupling piece 15 extending parallel to the direction of introduction of the force. The lever 29 is in turn joined to the second lever 30 by a portion of material extending between the narrow portions 44, 45. A load cell (not shown) is coupled to the second lever 30, for example by means of a force transmitting member (not shown) attached to the bores 38, 39 of the second lever 30, which load cell receives the load which has been reduced by the levers 29, 30. The load cell, which delivers a measuring signal corresponding to the measured force magnitude, can be supported, for example, by a stationary support (not shown), which is anchored to the stationary part 28 by means of the bore 17 and the further bore 54.

The load receiver is divided by a material free space 55 through the piece of material 1 into a first part 56 and a second part 57, wherein the material part forming the second part 57 is connected by the narrow parts 21, 23 to the material parts 5, 5' forming the parallelogram guide and by the narrow part 14 to the material part forming the link 15. The material-free space 55, which is largely formed by a narrow linear cutting seam, in turn defines two mutually parallel guide elements 58, 59, by means of which guide elements 58, 59 the first part 56 and the second part 57 are connected to one another in a parallelogram linkage. On the side facing away from the guide 59, the guide 58 is defined by a material-free region 60 belonging to the material-free space 55, while the material-free region 60 widens gradually over the distance from the first portion 56 to the second portion 57 and then extends closest to the guide 58 to the smaller side 4, where the material-free region 60 opens out into the outer periphery of the material block 1. The material free region 60 thus truncates a surface portion 61 from the minor side 4, thereby defining between itself and the surface portion 61 a load receiving portion 62 overhanging the second portion 57 from which the support post 53 projects upwardly. On the side facing away from the guide 58, the guide 59 is delimited by a shallow recess 63, which shallow recess 63 is formed in the smaller side 4 ' of the material block 1 facing away from the support column 53 and, close to the end of the guide 59, projects into a narrow linear cutting slit 64, 64 ' extending along the smaller side 4 '.

In the vicinity of the guide 58 defined by the gradually widening material-free field 60, on the side facing the guide 59 and close to the end of the guide 58 closest to the first portion 56, for insertion of the spark-erosive wire, a bore 65 is provided, which bore 65 passes through the portions of the first portion 56 and the second portion 57 which are adjacent to each other. Starting from the bore 65, a narrow linear cut 66 approaches and extends close to the narrow end of the gradually widening material-free region 60, while another narrow linear cut 66' starts along the length of the guide 58 towards the end close to the second portion 57 and approaches and extends close to the gradually widening material-free region 60 in the vicinity of that end. Thus, the linear cutting slit segments 66, 66' define narrow flexible portions 67, 68 at either end of the guide 58 between themselves and the side of the guide 58 facing away from the guide 59.

Starting from the bore 65, a further narrow linear cutting seam segment 69 of the material-free space 55 extends essentially in the direction of force introduction until a short linear cutting seam segment 70 extending transversely to the direction of force introduction is reached. At the end furthest from the linear cutting seam section 69, the linear cutting seam section 70 opens into a narrow linear cutting seam section 71 of the material-free space 55, which extends essentially in the force introduction direction. On the side joining the narrow linear cutting slit segment 70, the narrow linear cutting slit segment 71 has a limb which extends in the direction towards the guide 58 and which between its end portion and the linear cutting slit segment 69 defines a narrow portion 72, which portion 72 is flexible transversely to the direction of force introduction.

On the other side, which merges with the narrow linear cutting slit segment 70, the narrow linear cutting slit segment 71 has a limb which extends in a direction away from the support column 53 toward the guide 59, first a portion parallel to the direction of force introduction and then at an angle toward the second portion 57 to merge into a narrow linear cutting slit segment 73, which segment 73 delimits the guide 59 on the side facing the guide 58, wherein the narrow linear cutting slit segment 71 opens into the segment 73 at the end of the guide 59 which is close to the first portion 56. Near the end of the guide 59, the linear cutting slit segment 73 extending in the lengthwise direction of the guide 59 approaches and extends close to the narrow linear cutting slit segments 64, 64 'of the shallow groove 63, so that, at these locations, two narrow flexible portions 74, 75 are formed at the end of the guide 59 between the narrow linear cutting slit segments 64, 64' and the terminal segment of the linear cutting slit segment 73.

On the portion closer to first portion 56, both linear cut seam segments 66' and 73 are wider than the width of the narrow linear cut seam 55 at the remaining material free space 55. The linear cut seam segments 66', 73 may be either parallel or have a widening taper in the direction towards the minor side 3.

On the side closer to the support column 53, the linear cutting slit segment 70, which extends between the linear cutting slit segments 69 and 71 perpendicularly to the direction of introduction of the force, defines a second shoulder 76 on the material portion 57 forming the second section, which second shoulder 76 projects towards the material portion forming the first section 56 and the free surface of which faces in the same direction of introduction of the force. At the same time, on the side closer to the guide 59, the linear cutting slit segment 70 defines, on the material portion 56 forming the first part, a first shoulder 77, which shoulder 77 projects towards the material portion forming the second part 57 and the free surface of which faces in the opposite direction to the introduction of force.

The first and second shoulders 77, 76 serve as engagement areas, the free surfaces of which are urged into compressive contact by a pre-tensioned resilient member in the form of a pre-tensioned compression spring 78 (shown in the drawings as a helical spring). The end of the helical spring 78 facing the direction of introduction of the force, i.e. the end close to the support column 53, is held by the facing support shoulder 79 of a bolt 80 in a blind hole which extends in the same direction as the direction of introduction of the force in the region of the guide elements 58, 59 of the material block 1. The blind hole passes through the load receiving portion 62 of the material portion forming the first portion, through the guide 58 abutting the load receiving portion 62, and extends into the adjacent portion of the material portion forming the second portion 57, thereby forming a radially enclosed cavity 81 of sufficient diameter to accommodate and leave radial clearance for the compression spring 78 and the portion containing the bearing shoulder 79 on the head 82 of the bolt 80. At an axial distance from the guide 59, at the bottom of the cavity 81 of the second part, a bearing surface 83 is formed facing the force introduction direction to hold the end of the helical spring 78 in the direction pointing towards the force introduction direction. The diameter of the blind bore has a step larger than the cavity 81 in the portion passing through the guide member 58 and the load receiving portion 62 to receive the head of the bolt 80. At the load-receiving portion 62, the blind hole is in the form of a threaded bore 84 to mate with the same threaded head of the bolt 80, so that the bolt 80 can be rigidly anchored to the first portion 56.

The end 85 of the bolt 80 pointing in the force introduction direction faces the bottom surface serving as the bearing surface 83 over a small axial distance. This limits the axial travel of the bolt 80 and thus the amount of displacement of the first portion 56 relative to the second portion 57 in the force introduction direction.

At the opposite end of the bolt 80, the bolt head 82 projects from the material block 1 and supports the conical support column 53 of the weighing pan carrying the balance. In this manner, the measured force is transmitted through the bolt 80 into the first portion 56 of the load receiver 27. Since the preloaded compression spring 78 holds the first portion 56 in compressive engagement with the second portion 57, the force to be measured is transmitted to the second portion. However, if the applied force exceeds the pre-load force of the compression spring 78, the excess force cannot be transmitted to the second portion 57. Instead, the first part 56 will move relative to the second part 57 until the weighing pan rests on a fixed, stationary stop on the balance housing (not shown).

Assuming that the material portion containing the second shoulder 76 is delimited within the material portion forming the second portion 57 by branches of the narrow linear cut slit segments 71 leading to the narrow portion 72 and is suspended with the second portion 57 only by this narrow portion 72, the joint formed by the second shoulder 76 can be displaced in a transverse direction with respect to the introduction of force. Thus, the joint can flexibly follow the lateral movement of the two parts 56, 57 caused by the eccentric load.

Figure 2 shows a simplified embodiment without transverse elastic flexibility of the joint between the first and second parts of the load receiver as provided in the embodiment of figure 1. Otherwise, the embodiment of fig. 2 is largely identical to the embodiment of fig. 1. Since the parts in fig. 2 are identical to the parts of fig. 1, they are identified by the same reference numerals and will not be described again. In this respect, the description of fig. 1 also applies to the same parts of fig. 2.

In contrast to fig. 1, the bore 165 for inserting the spark erosion wire in fig. 2 is arranged in the vicinity of the guide 59 on the side opposite the support column 53. Starting from the bore 165, a narrow linear cutting slit segment 173 of the material-free space 55 is first in close proximity to the outer boundary at the smaller side 4 'of the material block 1 and then parallel thereto for a short distance in the direction towards the second portion 57, so that the linear cutting slit segment 173 together with the outer boundary of the smaller side 4' of the material block 1 delimits a narrow flexible portion 174 at the end of the guide 59. The next segment of the linear cut seam segment 173 is turned away from the minor side 4 'and then extends again along the length of the guide 59 defined between the linear cut seam segment 173 and the minor side 4'. At the end opposite the bore 165, the narrow linear cutting slit again turns to the minor flank 4 'and then runs parallel to the minor flank 4', so that at this end of the guide 59 a narrow section 175 is formed which corresponds to the narrow section 174. A narrow linear cut slit segment 166 of the material free space 55 defines between itself and the minor side 4 carrying the support column 53 the upper guide 58 with narrow portions 167, 168, (while the narrow portions 167, 168 correspond to the narrow portions 174, 175 respectively), while forming a mirror image of the linear cut slit segment 173 with respect to a plane parallel to and extending equidistant from the minor sides 4, 4'.

The material free space 55 also contains a linear cut seam segment 169 that connects linear cut seam segments 166 and 173. Starting from position 170 (where the linear cutting slit segment 166 bounding the guide 58 is turned away from its path parallel to the lengthwise direction of the guide 58 and continues to extend towards the narrow portion 167 adjoining the first portion 56), the narrow linear cutting slit segment 169 extends a distance along the direction of force introduction, but before reaching the linear cutting slit segment 173 bounding the guide 59, the linear cutting slit segment 169 changes direction and extends over a segment 171 transverse to the direction of force introduction, while the segment 171 has the same length as the guides 58, 59, if measured lengthwise between the flexible portions 167, 168 and 174, 175, respectively. After segment 171, linear cutting slit segment 169 again extends in the direction of force introduction, finally at position 172, linear cutting slit segment 173 is connected, and at position 172, linear cutting slit segment 173 is turned away from its path parallel to the length direction of guide 59, continuing to extend toward narrow portion 175 adjacent second portion 57. Thus, on the side facing guide 58, segment 171 defines a second shoulder 176 serving as a junction for second portion 57, while on the side facing guide 59, segment 171 defines a first shoulder 177 serving as a junction for first portion 56.

At the location of the blind hole of the embodiment of fig. 1, the embodiment of fig. 2 has a hole which passes all the way through the block 1 and which exhibits a step change in diameter as it passes through the guide 58 and the adjacent portion of the material portion containing the second portion 57, while at the second portion 57 a cavity 81 is formed to receive the compression spring 78. At the end of the cavity 81 near the guide 59, the diameter of the bore is reduced enough to form a bearing surface 83 to retain the compression spring 78 while allowing the bolt 80 to pass through the bore with radial play. Subsequently, a further reduced bore from shoulder 177 passes through the material portion forming first portion 56 to narrow linear cut seam segment 173 separating guide 59 from first portion 56. The bore of the segment has the form of a threaded hole 178, where a bolt 80 provided with a matching thread is firmly anchored in the first part.

The continuation of the multi-step bore passes through the guide 59 adjoining the narrow linear cutting slit segment 173. At this point, the end 182 of the bolt 80 pointing in the same direction as the force introduction passes with play through the guide 59 and protrudes beyond the surface of the material block 1. At the end opposite the end 182 and with a small gap in the axial direction, the balance is provided with a stationary stop (not shown) which limits the displacement travel of the load receiver 27 in the force introduction direction.

The figures show further boreholes, which have not been explained so far, some extending parallel to the drawing plane and some extending transversely to the drawing plane. A portion of these boreholes is used only for holding the piece of material 1 during spark erosion; others may be used to secure the stationary part 28 to the stationary base plate of the balance; still further parts may be used for connecting other components of the force measuring device. A detailed description of these boreholes appears to be omitted as it is not necessary for an understanding of the present invention.

Claims (23)

1. An overload protector for a force-measuring device with a load receiver, in particular a balance, having:

a first part for introducing the force to be measured into the force-measuring device,

a second part for transmitting the force to be measured to a load cell and which is connected to the first part in a manner similar to a parallelogram arrangement by means of first and second guides extending parallel to each other in a direction transverse to the direction of the force measurement, which guides are rigid in their longitudinal direction and elastically flexible in their transverse direction,

-a first shoulder formed in the material portion constituting the first part and a second shoulder formed in the material portion constituting the second part, each of said shoulders projecting towards the respectively opposite material portion, the first shoulder having a free surface facing in the direction opposite to the direction of introduction of the force and the second shoulder having a free surface facing in the same direction as the direction of introduction of the force, the free surfaces facing each other and abutting together to mutually couple the first and second parts, whereby the two parts are prevented from being displaced from each other in the direction of introduction of the force, and

a pretensioned elastic element which urges the first part and the second part into spring-loaded mutual contact while opposing the force to be measured which is introduced on the first part,

the method is characterized in that: the first and second portions and the first and second guides are formed as integrally connected material portions of a single block of material, wherein the first and second guides are separated from each other by a material free space through the block of material.

2. An overload protector according to claim 1, in which the material parts forming the first and second parts are pressed against each other at the free surfaces by pre-tensioned resilient elements.

3. An overload protector according to claim 1, in which the shoulder of at least one of the two sections is designed to allow the shoulder to be displaced relative to the respective section in a transverse direction relative to the force being measured.

4. An overload protector according to claim 3, in which the displaceable shoulder is formed in a material section defined by a material-free space and connected to the section including the displaceable shoulder by a narrow section designed to flex resiliently in a direction transverse to the force being measured.

5. An overload protector according to claim 1, in which the pre-tensioned resilient element is a pre-tensioned compression spring.

6. An overload protector according to claim 5 in which the pre-tensioned compression spring is a helical spring, one end of which is urged against a bearing surface on the second part and facing the direction of the force being measured, the other end of which is urged against a bearing step facing the same direction as the force being measured, the bearing step being on a bolt which passes axially with lateral play through the second part and the helical spring in the direction of the force being measured, the bolt being anchored to the first part and being axially movable relative to the second part against the pre-tension of the compression spring.

7. An overload protector according to claim 6, in which a cavity in the material part forming the second part surrounds the circumference of the helical spring.

8. An overload protector according to claim 7 in which the cavity in the section of material forming the second part has a stop to limit the axial displacement of the bolt.

9. An overload protector according to claim 7, in which the end of the bolt which points in the same direction as the force being measured projects from the surface of the block of material.

10. An overload protector according to claim 6 in which the end of the bolt which points opposite the force being measured has a support post for receiving the force being measured.

11. The overload protector according to claim 6, wherein the bolt is disposed at a portion of the load receiver extending between the first guide member and the second guide member.

12. An overload protector according to claim 1, in which the material free spaces are formed at least in part only by narrow linear cuts through the block of material.

13. An overload protector according to claim 12, in which the first and second guides on opposite sides facing each other are profiled by narrow linear cut slit segments defining a narrow flexible portion at each end of each guide between themselves and the respective outward, opposed sides of the first and second guides.

14. An overload protector according to claim 12, wherein the narrow linear cut seam has a segment which begins at the end of the first shoulder adjacent the first portion and terminates at a terminal segment which defines a segment of the first guide member adjacent the end of the first portion, and wherein the narrow linear cut seam also has a segment which begins at the end of the first shoulder adjacent the second portion and terminates at a terminal segment which defines a segment of the second guide member adjacent the end of the first portion.

15. The overload protector according to claim 12, wherein the narrow linear cut seam segments defining the first and second guide members are at least partially wider than a width of the segment beginning at an end of the shoulder of the first portion and terminating at a terminal segment of the segments defining the first and second guide members.

16. An overload protector according to claim 1, in which the material section forming the second section is guided in parallel movement relative to the stationary section of the force-measuring device by two parallelogram guides which extend in a longitudinal direction transversely to the direction of the force to be measured and are rigid in their longitudinal direction and elastically flexible in their transverse direction, each parallelogram guide being connected at one end to the material section forming the second section and at its other, opposite end to the stationary section of the force-measuring device; and wherein the material part forming the second part is connected to a mechanism supported by the stationary part and serving to transmit the measured force to the sensor.

17. The overload protector according to claim 16, wherein the parallelogram guide and the stationary portion are formed as material sections of a block of material that are integrally connected to the second portion and are separated from each other by a material free space through the block of material.

18. An overload protector according to claim 16, in which the parallelogram guides have flexible portions at their longitudinal ends defined by material-free spaces.

19. An overload protector according to claim 18, in which at least one of the material-free spaces defining the flexible portion is formed by a narrow linear cut open to the outer periphery of the block of material, and from that open end a curved portion which approximates tangentially to the longitudinal direction of the parallelogram guide.

20. An overload protector according to claim 16, in which the force transmission means comprises at least one lever, one arm of which is connected to the section of material forming the second part by a link which extends in the direction of the force to be measured and is stiff in the longitudinal direction and resiliently flexible in the transverse direction.

21. The overload protector according to claim 20, wherein the link and the lever are formed as integrally connected material sections bounded by a material-free space in a material region of the stationary part, the material region extending into a space between the two parallelogram guides.

22. The overload protector according to claim 21, wherein the material free space defining the link and the lever is formed at least in part only by narrow linear cut seams dividing a piece of material.

23. An overload protector according to any one of claims 1 to 22, wherein the block of material has substantially the shape of a rectangular block with a maximum pair of side surfaces extending parallel to the longitudinal direction of the parallelogram guide.