Hottinger Baldwin Measurements Inc.

Flintec, Inc.

Ncr Corporation

Armour and Company

Flintab Ab

The Flintec Group, Ltd.

Flintab

Hottinger Baldwin Measurement, Inc.

Harry E Lockery

Eric Laimins

Robert L Gray

Paul Oliver Detwiler

David Lee Gregerson

Rolf P Haggstrom

Edward Freymiller

Leo J Hansen

Harold O Ballou

Systems and techniques for scanner scale implementation and operation using a plurality of load cells mounted in a planar arrangement. A plurality of load cells is mounted to a scanner base. The load cells are secured within a mounting chassis in such a way that the load bearing elements of the load cells extend through the protective cover. The mounting chassis and load cells may be mounted to the scanner base. A scanner top plate may be secured to the load cells such that the weight of the scanner top plate and any object placed on the scanner top plate is borne by the load bearing elements of the load cells, part of the weight being borne by the load bearing element of each load cell. Upon presentation of an object for weighing, weight signals generated by the load cells are processed to produce a weight reading for the object.

Methods and apparatus for multiple support and weight measurement points in a scanner scale combination

A bending beam load cell can be compensated for side-to-side off center load sensitivity by simple electrical adjustments if a pair of shear sensing strain gages are bonded to each bending beam midway between axial strain gages used to measure bending strains. The shear sensing strain gages measure torque on the load cell, and are incorporated in bridge circuits that make it possible to vary the amount of torque sensitivity correction by changing the value of a trimming resistor. The bridge circuits also include circuit components for compensation of front-to-back off center load error and for zero adjustment. Four strain gages on each bending beam can be part of a single composite strain gage element, so the shear sensing strain gages do not add any cost to the load cell. Such a load cell can also be hermetically sealed before any compensation of offset load errors is done.

Bending beam load cell with torque sensitivity compensation

A low cost strain gage load cell made without compromising accuracy and stability by a composite structure using a sensing element formed of a load cell quality material, such as metal or a metal alloy, and adjoining non-sensing elements formed of a molded plastic material. Stable and secure joints between the load cell sensing element and the plastic non-sensing element of such a load cell are provided using various structures and related structural manufacturing methods. For example, non-sensing elements, such as a mounting block to mount the load cell to a base support and a load application block to receive a load platform, are formed of an injection molded plastic and sensing elements, such as first and second parallel beams of a load cell quality metal alloy, have ends embedded in the injected molded plastic non-sensing elements. The composite load cell structure is applicable to many different types of load cell designs.

Composite load cell

A precision double bending beam load cell made at low cost by using load cell quality material in the bending beams only, while less costly material is used for end blocks to maintain the beams in a predetermined parallel relationship and to mount the load cell, provided that the joints between the beams and the end blocks are slip free. Slip free joints can be obtained by making the end blocks in the form of rods with necks press fitted into matching holes at the ends of the beams, or by laser welding or hard soldering metal end blocks to metal bending beams. Plastic end blocks can also be injected molded onto the ends of bending beams with holes and scalloped edges for the injection molded plastic to grip onto. Shrinkage or expansion of the plastic material during the curing process will then make the joints prestressed and slip free.

Double bending beam load cell

The cost of machining a shear beam load cell can be greatly reduced by cutting pockets for the central web with a side cutting tool, such as a Woodruff Cutter or a Key Cutter tool, in a vertical spindle milling machine, so all machining can be done with one single setup. The thickness of a web formed by side cutting tools will increase slowly and gradually with distance from the center of the web, which means that there will be no abrupt shear stress changes near the strain gages. The disclosed shear beam load cell is accordingly not only less expensive to make, but also inherently more accurate than prior art shear beam load cells.

Shear beam load cell and method for making it

A strain gage bridge circuit and method for sensitivity equalization, particularly suitable for load cell devices for precision measurement. The sensitivity of opposing half-bridges in a strain gage bridge circuit is equalized by a pair of equal, fixed resistors connected across a bridge diagonal formed by the two half-bridges, and a third resistor connecting the junction of the two equal, fixed resistors to the center of the half-bridge with the highest sensitivity. The effective shunting of the most sensitive half bridge can be changed by changing the value of the third resistor, while the ratio of the two equivalent shunting resistance values remain exactly constant. The total load on the bridge diagonal also remains constant when the value of the third resistor is changed. Both sets of orthogonally arranged opposed half-bridges in a strain gage bridge circuit can be equalized independently when two sets of equalizing resistors are used.

Strain gage bridge circuit with sensitivity equalization and method for

A strain gage transducer system, such as a load cell based weighing system, is protected against moisture related errors by an electrically conducting guard circuit for terminals and other parts subject to wet or humid conditions. The guard circuit is connected to an electrical potential close to a potential of signal terminals in a strain gage bridge, for instance to a center tap in a power supply for the strain gage bridge.

Strain gage transducer system with guard circuit

A force or weight measuring load cell arrangement of the planar gaged plate load cell type with bending beam members is made insensitive to the point of load application by bonding strain gages alternately on the top surfaces and on the bottom surfaces of bending beam members and shunting half-bridges by pairs of substantially equal resistors to reduce the errors caused by corner loading.

Force measuring device with sensitivity equalization

The load measuring sensitivities of transducers, such as beam type transducers, or the like, are desensitized by connecting a desensitizing resistance in series with the strain gages attached to a transducer so that these desensitizing resistances become part of the respective bridge arm in which the corresponding strain gage is located. In a group of four transducers, each carrying, for example two strain gages, the transducer which has the lowest sensitivity is ascertained. Thereafter, the sensitivities of the other three transducers are reduced by the desensitizing resistors connected directly in series with the strain gages in the other three transducers so that all have substantially the same sensitivity as the mentioned lowest initial sensitivity in the group of transducers. Any influences of these desensitizing resistors from one bridge arm to another bridge arm are considered in the derivation of the correct desensitizing resistances. Thereafter, a further sensitivity equalization may be achieved by mechanically increasing the sensitivity of those transducers in the group still having a lower sensitivity than the lowest sensitivity transducer in the group. Such mechanical sensitivity increase involves removing material from the sensing portion of a transducer for example by filing or grinding until all transducers of a group have the same sensitivity within an acceptable tolerance range, for example, 0.02%.

Method and means for equalizing the measuring sensitivity of a plurality

A platform for a scale is formed by elongate elements rigidly interconnected to provide a platform frame structure having, for example, an H-configuration. The strain gage transducer beams are formed integrally at each end of the elongate elements. Vertical load components are introduced into the transducer beams by suitably locating support feet under the platform frame structure so that the beams may properly flex. Load transfer from an upper platform to the transducer beams is preferably accomplished by ball and socket loading devices provided at each end of the elongate elements forming the frame structure.

Gaged plate transducer weighing apparatus

In a platform scale in which the strain gage transducer beams are preferably formed as an integral part of a platform it is important that any distortions such as horizontal or angular force components that could falsify the reading of the weight, are prevented from affecting the transducers. For this purpose, the vertical load or weight representing force components are transmitted to each strain gage transducer beam through at least two cooperating curved, preferably spherical, surfaces. One curved surface has a larger curvature than the other so that a sufficient motion in any horizontal direction is permitted. The horizontal yielding prevents the transmission of a horizontal or angular force component to the sensing strain gages of the respective transducer beam but does not adversely affect the vertical force transmission to the transducer beams.

Apparatus for applying a load to a strain gage transducer beam

The moment sensitivity of shear beam transducers is mechanically compensated to make such transducers relatively insensitive to load applications which are off-center relative to an optimal point of load application. Such shear beam transducers have a free end forming a load application section, a mounting section, and a fillet located substantially where the sections merge. The compensation is made by providing the fillet initially with a larger radius than the final compensating radius. The compensation is made by gradually changing the fillet radius until the transducer output shows substantially no difference between the measurement resulting from applying a defined load in the optimal loading point and the measurement resulting from applying the same load off-center the optimal loading point whereby the transducer becomes substantially insensitive to such off-center load applications.

Mechanical moment sensitivity compensation in shear beam transducers

A transducer bridge circuit arrangement which may include a plurality of individual bridge circuits is improved by standardizing the source resistance and open circuit sensitivity of each bridge circuit in a group of such circuits. For this purpose a small resistor is connected in series with one or both output terminals of each individual bridge circuit, or resistors may be inserted in series with the bridge excitation terminals. Thus, the output signal sensitivity and source resistance are adjusted to a standard ratio value and the prior art adjustment for so-called corner sensitivity in electronic scales has been eliminated or at least substantially reduced where strain gauge load cells are employed in multiple transducer installations.

Transducer bridge circuit arrangement and method

A platform and transducer elements are combined so that the transducer elements form integral components of the platform proper. For this purpose slots are milled, machined or cut into the platform so that two parallel slots define a beam structure, the sensitivity of which is established by drilling holes into the platform, at the end of each slot and intermediate the ends of each slot. Strain gage elements are then secured to the so formed beam structures, the free end of which are operatively connected to support elements. Overload limiting means are so arranged that the flexing of each beam structure is limited to a predetermined value.

Unitized weighing apparatus and method for making such an apparatus

The moment sensitivity of shear beam transducers is mechanically compensated to make such transducers relatively insensitive to load applications which are off-center relative to an optimal point of load application. The compensation is made by gradually increasing the depth of a load application hole in the transducer. The load application hole extends in the direction of a load application axis and its depth is increased until said moment sensitivity becomes substantially zero. In other words, the load sensitivity becomes substantially independent of the location of the point of load application. A further linearization of the moment sensitivity is accomplished by placing inserts into the load application hole.

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Sudbury, MA, United States of America

Harry E Lockery