Hottinger Baldwin Measurements Inc.

Eric Laimins

Harry E Lockery

The present patient weighing scale provides an automatic display of the patient's weight in digital form. For this purpose, a stretcher is secured to a cantilever boom through supporting means including two beam type transducers, for example double bending beam transducers, responsive to vertical forces and located in the respective ends of a tubular crossbar. The tubular crossbar is one element in a chain of supporting elements between trhe stretcher and the cantilever boom. The supporting elements include preferably pivots or bearings arranged so that the forces resulting from the weight of the patient extend in parallel to the direction of gravity whereby the transducer measuring axis always coincides with the direction of the gravity vector independently of the boom angle.

Patient weighing scale with hoist

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

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.

A strain gage force measuring transducer is described in which distortion of measurements of a given strain on a given surface due to the interaction between the given strain and a second strain is eliminated by making a combined measurement of both strains on that same surface, equating the measured value of the second strain with the value of the distortion, and entering the so measured and equated value of the second strain into the combined measurement with a sign opposite to the sign of the distortion so as to cancel same. In a typical use, a shear beam shear-type transducer having a high degree of point-of-load insensitivity is provided thereby.

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Belmont, MA, United States of America

Eric Laimins