Abstract:
A load receiver ( 10 ) for a balance with arms ( 11 ) is designed to support weights of various shapes and sizes ( 13, 14, 15, 16 ) by cradling the weights in a depression sloped at a variable slope angle towards the middle of the load receiver. A loading stage ( 1 ) arranged to cooperate with the load receiver ( 10 ) has one or more weight-placement devices ( 5 ) designed so that the load receiver ( 10 ) can reach through the weight-placement device ( 5 ) without touching the latter. The loading stage ( 1 ) and the load receiver ( 10 ) are moveable up and down in relation to each other. The weight-placement device ( 5 ) is suitably configured to support the different weights ( 13, 14, 15, 16 ). The load receiver ( 10 ) and loading stage ( 1 ) are used in a mass comparator for testing weight standards with a high degree of precision.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates to a load receiver and a loading stage, and it also relates to a balance, particularly a mass comparator, that is equipped with the inventive load receiver and/or loading stage. The load receiver has an arrangement of narrow ridges and a horizontal receiving surface for a weight, with a depression or concavity so that the center of the load receiver is lower than the peripheral portions. The loading stage supports at least one weight-loading device, which can be connected to the loading stage and is shaped so that the load receiver reaches from below through the weight-loading device without touching the latter. The loading stage and the load receiver are movable up and down in relation to each other.  
           [0002]    A load receiver with a funnel-shaped depression at the center as disclosed in U.S. Pat. No. 5,332,870 is designed for the specific purpose of weighing flat filters. The conical surface of the load receiver consists of a net or a metal foil with perforations.  
           [0003]    Loading stages are found in comparator balances for masses and volumes and serve to automatically interchange weights that are being compared to each other. This type of balance is used for the exact determination of masses and volumes of weight standards, primarily in governmental institutes of metrology. The comparison weighings often involve weights of different sizes.  
           [0004]    A mass comparator balance with a load receiver designed for weights of unequal size is described in the German utility model DE U 295 17 368. It has a freely suspended load receiver with an arrangement of narrow ridges to support the weight standards that are to be tested. A weight-exchanging mechanism has a weight-loading and -unloading plate perforated by slots. When the weight-exchanging mechanism lowers the loading/unloading plate to set a weight on the load receiver, the ridges of the load receiver pass through the slots and take up the weight. The arrangement of narrow ridges of the load receiver consists of at least four branches that are joined by a connecting ridge. This design also allows a plurality of weights of different sizes to be weighed together with the highest degree of accuracy.  
           [0005]    It is possible that a weight comparison involves test masses of different shapes, such as spherical weights, cylindrical weights with knobs, or disc-shaped weights. This makes it necessary to place individual weights of different shape and size in an exactly centered position on the load receiver, e.g., to limit the magnitude of eccentric loading errors as much as possible and, as an ultimate purpose, to perform a precise comparison that is independent of the shapes of the masses being compared. The mass comparator according to the last-mentioned reference does not meet this requirement, based on the design of its load receiver and/or weight-changing mechanism.  
         OBJECT OF THE INVENTION  
         [0006]    In view of the state of the art as described above, the present invention has the objective of proposing a load receiver for a balance, particularly a mass comparator, which, preferably in combination with a loading stage, has the capability to receive test masses of different shapes and sizes without a loss of precision due to a less than perfectly centered placement of the test weights. As a further objective, the invention aims to provide a design for a loading stage which, in cooperation with a load receiver, will put the test weights in a precisely centered position on the load receiver. In addition, the present invention has the objective of providing a mass comparator balance that allows test weights of different shapes and sizes to be measured with high precision.  
         SUMMARY OF THE INVENTION  
         [0007]    As a solution to the foregoing problem, the present invention proposes a load receiver for a balance with an arrangement of arms for supporting the masses to be weighed. The load-supporting surface of the load-receiver forms a depression, sloping downward towards the center of the load receiver at an angle that varies along the load-receiver arms.  
           [0008]    A load receiver designed according to this concept can support weights of different shapes and sizes. A weight can be centered accurately on the load receiver regardless of the shape and size of the weight, which is a significant factor in high-precision weighing.  
           [0009]    In an advantageous embodiment of the invention, the load receiver has at least one step in its downward-sloping profile and/or at least one horizontal portion.  
           [0010]    The top surface of the load-receiver arms is preferably also slanted perpendicular to the main direction of the aforementioned slope. In addition, the load-receiver arms may have sideways breaks or bends.  
           [0011]    In a preferred embodiment of the invention, the arms of the load receiver are shaped like wings extending from a common root portion at the center of the load receiver. In particular, the load receiver has four wing-shaped arms arranged mirror-symmetrically in relation to a vertical plane through the center of the load-receiver. The four arms are arranged to form two wing pairs, where the arms of a pair enclose an angle of less than 90°.  
           [0012]    A preferred means for putting a weight on a load receiver with an arrangement of arms to support the weight consists of a loading stage with at least one weight-placement device, where the load receiver reaches through the weight-placement device without contacting the latter as the weight-placement device and the load receiver move up and down in relation to each other. Each of the weight-placement devices is shaped with a depression sloping downward towards the center of the weight-placement device and has a free space in the area of its centerpoint.  
           [0013]    The inventive loading stage in combination with a specially configured load receiver has the advantage that the weight-placement device can accommodate weights of different shapes and sizes and that the weights can be centered more easily with a load receiver and weight-placement device that do not have a planar seating surface of the kind that is known in the prior art. In particular, this saves time in the weighing process while at the same time improving the precision of the weighing, independent of the shape and size of the weight. In addition, the exact positioning of the weight when the latter is put on the weight-placement device is easier and less time-consuming in comparison to prior-art devices.  
           [0014]    A preferred embodiment of the loading stage according to the invention has one weight-placement device, which has a free cutout space between the resting points where a weight rests on the weight-placement device. The resting points on the weight-placement device are in close proximity to corresponding load-receiver seating points where the weight is seated on the load receiver as the latter reaches from below through the cutout space in the weight-placement device. It is advantageous if the load receiver likewise has a top surface shaped with a depression at the center, and if the depressions of the load receiver and the weight-placement device have the same slope angles varying in the same manner along the profile of the depressions.  
           [0015]    In an advantageous embodiment of the loading stage, the weight-placement device has arcuate, loop-shaped weight-placement members holding the weights. The substantially upward-facing top surface of each weight-placement member is slanted towards the inside of the loop at a slant angle that can vary from the periphery toward the center of the weight-placement device. The weight-placement members can also have sideways bends or breaks, and the material width of the weight-placement members can likewise vary from the periphery toward the center of the weight-placement device.  
           [0016]    In a particularly preferred embodiment of the invention, the loading stage is configured substantially as a circular plate that is rotatably supported at its mid-portion and has at least two loading locations where weight-placement devices are installed. To automate the process of comparative weighing, the loading stage is turned by a motor, and the raising and lowering is also automated. The mounting attachment of the weight-placement devices on the disc of the loading stage is height- and level-adjustable.  
           [0017]    The inventive concept is embodied in particular in a combination of a load receiver and a loading stage. The load receiver with an arrangement of arms to support the weight, and the loading stage with at least one weight-placement device, are configured so that the load-receiver and the weight-placement device do not touch each other as the load-receiver arms pass through the weight-placement device when the loading stage and the load receiver move up and down in relation to each other. The load receiver is shaped with a depression that is sloped to the midpoint of the load receiver, and each weight-placement device has a depression that is centered in relation to the load receiver, when the weight-placement device is positioned to place the weight on the load receiver. Also, each weight-placement device has a free break-through space in the area where the midpoint of the load receiver is located.  
           [0018]    In the foregoing combination, the weight-placement device has two arcuate, loop-shaped weight-placement members, and the load receiver has four wing-shaped arms arranged in two pairs. When the weight-placement device is positioned to cooperate with the load receiver so that the latter passes through the weight-placement device, a wing of one pair and an adjacent wing of the other pair embrace each of the two loop-shaped members of the weight-placement device.  
           [0019]    According to the invention, it is preferred to make the loading stage, the weight-placement device and/or the load receiver either of a plastic material and/or of a metal with a plastic coating.  
           [0020]    To perform highly precise weight comparisons on test weights of different shapes and sizes, the present invention proposes a mass comparator that includes a balance with a load receiver having an arrangement of load-receiver arms to support the test weights. The mass comparator is further equipped with a loading stage with at least one weight-placement device, where the load receiver reaches through the weight-placement device without contacting the latter as the loading stage and the load receiver move up and down in relation to each other. Each of the weight-placement devices is shaped with a depression sloping to the center of the weight-placement device and has a free space in the area of its center point.  
           [0021]    The inventive mass comparator has the advantage that its load receiver as well as the loading stage can accommodate weights of different shapes and sizes and that the weights can be centered more easily with a load receiver and weight-placement device that do not have a planar seating surface of the kind that is known in the prior art. In particular, this saves time in the weighing process while at the same time improving the precision of the weighing, independent of the shape and size of the weight. In addition, the exact positioning of the weight when the latter is put on the weight-placement device is easier and less time-consuming in comparison to prior-art devices.  
           [0022]    In a further preferred embodiment of the mass comparator according to the invention, the weight-placement device also has a free cutout space between the resting points where a weight rests on the weight-placement device. The resting points on the weight-placement device are in close proximity to corresponding load-receiver seating points where the weight is placed on the load receiver as the latter reaches from below through the cutout space in the weight-placement device.  
           [0023]    Other advantageous further developments of the mass comparator have a load receiver and/or weight-placement device shaped with a depression of varying slope angle from the periphery towards the center, with the slope angles of the load receiver and the weight-placement device varying in the same manner along the profile of the respective depressions.  
           [0024]    In a particularly advantageous further development of the mass comparator, the weight-placement device has arcuate, loop-shaped weight-placement members, and/or the load receiver has wing-shaped arms, with the respective shapes of the loop-shaped members and the wing-shaped arms conforming to each other. Preferably, there are four wing-shaped arms in a mirror-symmetric arrangement relative to a vertical plane through the center of the load receiver. The wings reach through the weight-placement device, with two of the wings embracing each loop-shaped weight-placement member.  
           [0025]    In a preferred embodiment of a mass comparator according to the invention, the substantially upward-facing top surface of each weight-placement member and/or of each load-receiver arm is slanted perpendicular to the slope direction of the depression. The weight-placement members can also have sideways bends or breaks, and the material width of the weight-placement members can likewise vary from the periphery toward the center of the weight-placement device. In addition the weight-placement device and/or the load receiver can have steps and horizontal seating surfaces along their slopes.  
           [0026]    A particularly preferred embodiment of the inventive mass comparator has a loading stage configured substantially as a circular plate that is rotatably supported at its mid-portion and has at least two loading locations where weight-placement devices are installed. To automate the process of comparative weighing, the loading stage is turned by a motor, and the raising and lowering is also automated. The mounting attachment of the weight-placement devices on the disc of the loading stage is height- and level-adjustable. The loading stage, weight-placement device and/or load receiver are made preferably of a plastic material and/or of metal with a plastic coating. Preferably, the load-receiver frame is freely suspended. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    Details of a load receiver and loading stage for a balance, particularly for a mass comparator, will be discussed in the following description of an embodiment that is illustrated in the drawings, wherein  
         [0028]    [0028]FIG. 1 represents a perspective view from above showing how a frame-shaped carrier for the load receiver of a balance cooperates with a loading stage carrying four different weights to be tested;  
         [0029]    [0029]FIG. 2 represents a perspective view from above of a weight-placement device according to the invention; and  
         [0030]    [0030]FIG. 3 represents a perspective view of a load receiver according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]    [0031]FIG. 1 illustrates a loading stage  1  with four loading locations  9  serving to automatically place test weights on a load receiver. The number of loading locations  9  could, of course, be more or less than four, but the preferred arrangement of the loading locations is in a circle at equal intervals as illustrated. The loading stage  1  consists of a substantially circular disc  2  with an opening  3  through its mid-portion  39 . The disc  2  is rotatably supported on a vertical shaft (not shown) passing through the opening  3 . At each of the four loading locations  9 , the loading stage has a cutout  4  in the shape of a circular segment to receive a weight-placement device  5 . Each weight-placement device  5  has three fastening lugs  6  that fit into recesses  7 ,  7 ′ of the loading stage  1  and serve to fasten the weight-placement devices  5  to the loading stage  1 . The fastenings lugs  6  pointing towards the mid-portion  39  are fastened in recesses  7 ′ which have a defined vertical depth that defines a reference level for the weight-placement devices  5 . The other two fastening lugs  6  of each weight-placement device  5  are underlayed with an elastically compressible spring element that cooperates with a fastener such as a screw  8 , so that by turning the latter, the height of the respective lug can be adjusted to level the weight-placement device  5 .  
         [0032]    [0032]FIG. 1 shows a load receiver  10  cooperating with the weight-placement device  5  facing the viewer. The load receiver  10  has two pairs of wings  11  reaching up through the open space to the front and rear of the loop-shaped members  12  of the weight-placement device  5 . A small knob-handle weight  16  is shown resting on the weight-placement device  5  that faces the viewer. A detailed description of the weight-placement device  5  and the load receiver  10  is given below in the context of the FIGS. 2 and 3. The term load receiver as used in the field of weighing technology represents that part of a balance which receives the load to be weighed, normally a weighing pan, but also includes any other kind of load-receiving device such as the specialized load receiver of the present invention.  
         [0033]    The loading stage  1  is rotatable about its center for transporting the weights successively into position for weighing. In addition, the loading stage can be lowered and raised to put the test weights on the load receiver  10  and to subsequently take them off again. Setting down and lifting off the same weight several times in a row is also a method of centering a weight on the load receiver, as will be explained below in more detail. The load platform may be turned as well as lowered and raised automatically by a motor.  
         [0034]    As shown in FIG. 1, the weights at the four loading locations  9  are of different shape and size: a spherical weight  13 , a-large knob-handle weight  14 , a disc-shaped weight  15 , and a small knob-handle weight  16 . The knob-handle weights  14  and  16  are shown lying on their sides. It has been found that the latter position is more conducive for the weight to center itself. For volume determinations, which usually involve weighing the same object in air and in water (dry and wet weighing), the sideways position of cylindrical weights is preferable because it avoids the formation of air bubbles or air pockets that can occur at the underside of a cylindrical weight if it is lowered into the water in an upright position, especially if the weight has a recessed portion in its bottom surface. In this context it has to be mentioned, that by using the term mass comparator, a volume comparator is regarded to be included.  
         [0035]    The load receiver  10 , shown cooperating with the weight-placement device  5  carrying the small knob-handle weight  16 , is supported by a rectangular load-receiver frame  17  which connects to the force transducer of the balance (not shown in the drawing). The opening width of the load-receiver frame  17  accommodates the segment of the disc  2  that is surrounded by the load-receiver frame  17 . The upper horizontal member of the load-receiver frame  17  has a notch  36  at the center, where the load-receiver frame  17  is coupled to the force transducer, e.g., by means of a hook. At the midpoint of the lower horizontal member of the load-receiver frame  17 , a load-receiver seat  20  is provided for the load-receiver  10 . The design of the load-receiver frame  17  with slots  18  as shown in FIG. 1 minimizes weight while preserving an adequate degree of structural rigidity. The resulting structure of the load receiver frame  17  thus consists of two rectangular frames  38  connected by transverse webs  19 .  
         [0036]    [0036]FIG. 2 gives a perspective view of an embodiment of the weight-placement device  5  as seen from above at an oblique viewing angle. A rim  21  in the shape of a circular segment constitutes a supporting frame with three outward-pointing attachment lugs  6  positioned at about 120° from each other. Two weight-placement members  12 , designed to hold the test weights, extend horizontally from the rim  21  towards the center  23  of the weight-placement device  5 , forming narrow arches  22  near the center  23  to enhance the rigidity of the weight-placement members  12 . A gap is left open between the narrow arches  22  as a passage for a part of the load receiver  10  (not shown in FIG. 2). The two arcuate weight-placement members  12  are not aligned with the horizontal plane of the loading stage  1  but are inclined at a downward angle, forming a depression with the lowest point at the narrow arches  22  near the center  23  of the weight-placement device  5 . This design is enormously helpful in centering the weights. With spherical weights  15 , the seating position is positively defined; with knob-handle weights  14 ,  16 , the seating position is defined transverse to the cylinder axis and requires centering in the axial direction. The seating position for disc weights  15  is not defined, so that the latter need to be centered relative to more than one direction.  
         [0037]    The weights are centered by the known process of seating and raising the weight on the load receiver  10  several times in succession by moving the loading stage  1  up and down. If the weight is not perfectly centered, the load receiver frame  17  with the load receiver  10  and the weight will swing to a slightly oblique position after the loading stage  1  has been lowered, because the combined center of gravity of the load receiver frame  17  with the load receiver  10  and the test weight has slightly moved in relation to the center of gravity with an empty load receiver  10 . When the test weight is re-seated on the weight-placement device  5  by raising the loading stage  1 , the center of gravity of the weight will be closer to the center of the weight-placement device  5  and consequently, the weight will be centered better on the load receiver  10  when the loading stage  1  is lowered again.  
         [0038]    The weight-placement device  5  according to the invention is designed for a secure positioning of disc weights  15 , so that the latter will not sit in a tilted position. Steps  24  at the topside of the arcuate weight-placement members  12 , distanced from the center  23  in accordance with the diameter of the disc weights  15 , provide horizontal resting surfaces  37  for stable positioning and preliminary centering of a disc weight  15 .  
         [0039]    The continuing vertical profile of the arcuate weight-placement members  12  towards the center  23  has a varying slope angle, as the upward-facing ridge surface  25  descends at an increasingly steeper downward slope towards the center  23 . The ridge surface  25  may have sections of different constant slope angle, or the slope may increase continuously in a smoothly curved shape. Of course, the inclined ridges  25  may also be interrupted by additional steps  24 , e.g., for the positioning of smaller-diameter disc weights  15 .  
         [0040]    As the ridge surfaces  25  are also slanted towards the free spaces  26  enclosed by the arcuate weight-placement members  12 , a sphere  13  or a knob-handle weight  14 ,  16  will rest on four points of the mirror-symmetric weight-placement members  12 , instead of the normal three-point support required for stable positioning of a body.  
         [0041]    Furthermore, the horizontal direction of the weight-placement members  12  has several slight inward- or outward breaks or bends in relation to the enclosed free space  26 . This design ensures greater versatility for accommodating knob-handle weights or other cylindrical weights of different height and diameter as well as spheres of different sizes.  
         [0042]    The weight-placement device  5  is installed interchangeably at its loading location  9  (see FIG. 1). The weight-placement device  5  is precisely positioned by means of the fastening lug  6 , which points to the mid-portion  39  of the loading stage  1  and is attached in a recess  7 ′ of the mid-portion  39 . The segment-shaped rim  21  of the weight-placement device  5  is reinforced with a cylindrical wall segment  30  which also serves as a guide in installing the weight-placement device  5  on the circular disc  2 .  
         [0043]    As illustrated in FIG. 3, the load receiver  10  according to the invention has a cylindrical stem  27  with a conical point at the bottom and a support cradle  28  resembling two pairs of wings on top. Immediately below the support cradle  28 , the stem  27  has a wider portion that serves as a load-receiver seat  29  for installing the load receiver  10  on the load-receiver frame  17 .  
         [0044]    The two pairs of wing-shaped load-receiver arms  11  meet at the center point  32 , which also represents the center of gravity of the load receiver. Each pair of arms  11  is joined in a root portion  31 . The arms of a pair enclose an angle of less than 90°, and the root portions are narrowed down towards the center point  32  of the load receiver  10 .  
         [0045]    Conforming to the arcuate shape of the weight-placement members  12  of the weight-placement device  5 , the center point  32  of the load receiver  10  is at a lower level than the outer ends of the wing-shaped arms  11 . The downward slope angle of the upward-facing ridge surfaces  33  becomes progressively steeper from the outer end of the arms  11  towards the center point  32 . At their outer ends, the ridges  33  have an exactly horizontal portion  34  for the stable positioning of disc weights  15 . In comparison to the horizontal ridge sections  37  of the weight-placement device  5 , the horizontal ridge portions  34  of the arms  11  can extend farther towards the center point  32  of the load receiver  10 . For the positioning of large disc weights there is no need for a step on the load receiver. However, if the load receiver  10  is to be used also for even smaller sizes of disc weights, the arms  11  will have to be designed with a step closer to the center point  32 . Like the weight-placement members  12 , the remaining portions of the ridges  33  of the load receiver  10  are also slanted perpendicular to the slope direction.  
         [0046]    Also, like the arcuate weight-placement members  12  of the weight-placement device  5 , the wing-shaped arms  11  of the load receiver  10  have at least two bends or breaks in a horizontal plane, so that they are slightly S-shaped. In the installed state, the load receiver  10  is oriented in relation to the weight-placement device  5  so that the arcuate weight-placement members  12  extend within the obtuse angles between the load-receiver arms  11 . The horizontal profile of the root portions  31  of the load-receiver arms  11  conforms essentially to the shape of the members  12  of the weight-placement device  5 , but leaving a small gap of about 1 to 2 millimeters. The vertical profiles, i.e., the slopes of the load-receiver arms  11  and the weight-placement members  12  run about parallel to each other. Furthermore, the top surfaces of the load-receiver arms  11  as well as the weigh-placement members  12  are slanted towards the free spaces  26  inside the arcuate members  12 , with an increasingly steeper slant angle towards the center.  
         [0047]    The loading stage  1 , weight-placement device  5  and load receiver  10  are made preferably of a polymer material or of a metal with a polymer coating. This serves to prevent oxidation of these components if they are used for wet-weighing in a volume determination.  
         [0048]    Preferably, the load-receiver frame  17  is freely suspended, but arrangements are possible where the load receiver  10  itself is suspended or in some other way connected to the balance, e.g., free-standing. Of course, one could also design a system where the load receiver  10  is raised and lowered instead of raising and lowering the loading stage.  
                                       1   loading stage       2   circular disc       3   opening       4   segment-shaped cutout       5   weight-placement device       6   mounting lug       7, 7′   recesses       8   screw       9   loading location       10   load receiver       11   wing-shaped arms of the load receiver       12   arcuate, loop-shaped members of the weight-           placement device       13   spherical weight       14   large knob-handle weight       15   disc-shaped weight       16   small knob-handle weight       17   load-receiver frame       18   slot       19   transverse web       20   load-receiver seat       21   segment-shaped rim       22   narrow arch       23   center of the weight-placement device       24   step       25   upward-facing ridge surface       26   free space       27   stem of the load receiver       28   support cradle       29   load-receiver seat       30   cylinder wall segment       31   root portion       32   center point of the load receiver       33   upward facing surface of the load receiver       34   horizontally leveled portion       36   notch       37   horizontal surface portion       38   rectangular frame       39   mid-portion