Force-sensitive resonator load cell

• US 4,751,849 A
• Filed: 06/17/1986
• Issued: 06/21/1988
• Est. Priority Date: 06/17/1986
• Status: Expired due to Term

• Current Assignee: Weigh-Tronix, Inc. (Illinois Tool Works Inc.)
• Original Assignee: Paroscientific Incorporated
• Inventors: Wearn, Richard B. Jr., Busse, Donald W., Chinn, Martin D., Kistler, Walter P., Paros, Jerome M.
• Primary Examiner(s): Ruehl, Charles A.
• Application Number:
  US06/875,327
• Time in Patent Office: 735 Days
• Field of Search: 73/862.59, 73/862.63, 73/517 AV, 73/702, 73/704, 73/855, 73/778, 73/DIG. 1, 73/DIG. 4, 310/346, 310/338
• US Class Current: 73/862.59
• CPC Class Codes: G01G 3/16 measuring variations of frequency of oscillations of the body
• CPC Class Codes: G01L 1/162 using piezoelectric resonators
• CPC Class Codes: G01P 15/097 by vibratory elements
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends

Abstract

A load cell having single or multiple resonators arranged to receive a strain that is proportional to the strain in a beam to which the resonator(s) is attached. Arrangement of the multiple resonators with respect to a force-bearing beam of the cell determines whether the cell is a bending mode load cell or a shear mode load cell. Absolute and differential pressure sensors, accelerometers and weighing devices are disclosed which employ the multiple-resonators of the invention.

Claims

1. A resonator load cell comprising:

a beam supported at one or more locations, said beam being adapted to receive a force at a location spaced from the location(s) where the beam is supported, thereby causing said beam to bend in proportion to the magnitude of said force; and

a force-sensitive resonator mounted on said beam, one end of said resonator being mounted to said beam at a first point of attachment thereto and the other end of said resonator being mounted on a relatively rigid coupling member extending in parallel with the axis of sensitivity of said resonator to a second point of attachment to said beam, said first and second points of attachment to said beam being spaced apart along the longitudinal axis of said beam, said coupling member having a coefficient of thermal expansion that is matched to the coefficient of thermal expansion of said resonator so that the thermally induced strain of said resonator is matched by the thermally induced strain of said coupling member, whereby said coupling member transmits the strain of said beam to said resonator while making said load cell relatively insensitive to temperature variations.

2. The resonator load cell of claim 1 wherein said resonator and said coupling member extend in equal distances along the axis of sensitivity of said resonator and have substantially identical coefficients of thermal expansion.

3. A resonator load cell, comprising:

a resilient beam adapted to receive a force applied between two spaced-apart locations, thereby causing said beam to bend in proportion to the magnitude of said force;

a force-sensitive resonator having an axis of sensitivity extending between first and second mounting pads, said first mounting pad being secured to said beam at a first location; and

a compensating leg having a first end secured to the second mounting pad of said resonator and a second end coupled to said beam at a second location spaced apart from said first location, said compensating leg having a coefficient of thermal expansion that is matched to the coefficient of thermal expansion of said resonator, so that the thermally induced strain of said resonator is compensated for by the thermally induced strain of said compensating leg.

4. The resonator load cell of claim 3, further including a relatively rigid actuating member extending between the second end of said compensating leg and said beam at said second location, thereby coupling the second end of said compensating leg to said beam.

5. The resonator load cell of claim 4, wherein said actuating member extends in parallel with said resonator and said compensating leg.

6. The resonator load cell of claim 3, wherein said resonator and compensating leg extend in equal distances along the axis of sensitivity of said resonator and have substantially identical coefficients of thermal expansion.