BALANCED MASS-MOMENT BALANCE BEAM WITH ELECTRICALLY CONDUCTIVE PIVOTS

• US 3,685,604 A
• Filed: 09/28/1970
• Issued: 08/22/1972
• Est. Priority Date: 09/28/1970
• Status: Expired due to Term

• Current Assignee: James E. Smith, Victor F. Borgogno
• Original Assignee: James E. Smith, Victor F. Borgogno
• Inventors: Smith, James E., Borgogno, Victor F.
• Primary Examiner(s): Tomsky, Stephen J.
• Assistant Examiner(s): Miller, Jr., George H.
• Application Number:
  US05/075,987
• Time in Patent Office: 694 Days
• Field of Search: 177/184,190,194,210,246,DIG.9
• US Class Current: 177/184
• CPC Class Codes: G01G 1/246 of the parallelogram type
• CPC Class Codes: G01G 21/00 Details of weighing apparatus
• CPC Class Codes: G01G 21/02 Arrangements of bearings bearings per se F16C
• CPC Class Codes: G01G 7/04 with means for regulating the current to solenoids
• CPC Class Codes: Y10S 177/09 Scale bearings

Abstract

A pivotally mounted balance beam is constructed and arranged to nullify its pendular characteristics by appropriately distributing and balancing the moments of the mass both parallel and perpendicular to the beam plane so that whenever the beam reference plane is tilted out of the horizontal any weighing errors resulting from tilt and vibration of the frame of the weigh balance apparatus are minimized. In forming a part of the weigh balance apparatus, a circuit generates an output proportional to load as a function of beam deflection sensed by capacitive sensors and operates through an electromagnetic restoring device including a beam mounted forcer coil to restore the beam to its null position. The coil is connected through electrically conductive knife edges and bearing flats to receive the circuit output and has its position relative to the magnet of the restoring device set so that the restoring device has a linear response to the circuit output. A display receives the circuit output and is compensated for errors caused by changes in the response of the restoring device as a function of its operating temperature to provide a readout representing load.

Claims

1. In an electronic balance, a beam type weighing apparatus comprising a frame, a horizontally extending beam pivotally mounted on said frame by electrically conductive pivot means and having a beam plane extending horizontally through its pivot axis whereby loads weighed by said weighing apparatus are measured as a function of the displacement vertically of said beam from its reference plane, and said balance beam having the mass associated therewith selectively distributed to balance the moments of mass parallel and perpendicular to said beam plane whereby to substantially eliminate the pendular characteristics of said balance beam so as to be relatively insensitive to tilt and vibration of said frame, sensor means including frame-mounted sensor elements and beam mounted sensor elements to indicate the displacement of said beam relative to said beam reference plane and to generate an electrical signal representative of beam displacement whereby variations in the load weighed by said weighing apparatus are measured, circuit means associated with said frame mounted sensor elements and said beam mounted sensor elements to receive the electrical signal generated to develop an electrical output proportional to the load being weighed by said weighing apparatus, and electromagnetic null restoring means associated with said balance beam and electrically connected to said circuit means through said electrically conductive pivot means, said null restoring means being operative to restore said beam to its original disposition with respect to its reference plane in response to the electrical output generated by said circuit means.

2. The invention recited in claim 1, wherein said null restoring means includes a forcer coil and a magnet mounted in said weighing apparatus to be movable relative to each other by pivotal movement of said balance beam, said forcer coil being connected to said circuit means and including means for selectively setting the relative positions of said forcer coil and said magnet with respect to each other about which said forcer coil and said magnet are moved relative to each other by pivotal movement of said balance beam so that said null restoring means has a substantially linear response to said electrical output.

3. The invention recited in claim 1, wherein said null restoring means includes a forcer coil and a magnet, said forcer coil mounted on said balance beam and said magnet mounted on said frame to interact with said forcer coil, said forcer coil positioned relative to said magnet by pivotal movement of said balance beam, and wherein said balance beam is pivotally connected on said frame by electrically conductive pivot means, said forcer coil being electrically connected to said circuit means through said electrical conductive pivot means.

4. The invention recited in claim 3, wherein said electrically conductive pivot means are comprised of carbide knife-edged pivots and carbide bearing flats.

5. The invention recited in claim 3, including means for selectively setting the position of said beam mounted forcer coil with respect to said magnet about which said forcer coil is pivotally moved by said balance beam so that said null restoring means has a substantially linear response to said electrical output.

6. The invention recited in claim 1 wherein said null restoring means includes a forcer coil and a magnet mounted in said weighing apparatus to be movable relative to each other by pivotal movement of said balance beam, said forcer coil being connected to said circuit means and including a temperature sensing means mounted on said null restoring means to sense its operating temperature, said temperature sensing means connected to said circuit means and being operable to compensate for error in said electrical output due to changes in response of said null restoring means to said electrical output as a result of changes in the operating temperature of said null restoring means.

7. The invention recited in claim 6, wherein said circuit means and said temperature sensing means are connected in series To receive said electrical output of said circuit means and the resistance of said temperature sensing means is proportional to its temperature.

8. The invention recited in claim 1, including:

downwardly facing first knife-edged pivot means mounted on said balance beam, said balance beam being pivotally mounted on said frame by said first knife-edged pivot means, upwardly facing second knife-edged pivot means mounted on said balance beam, the knife edges of said first and second pivot means being aligned to define said beam reference plane, a weigh pan for supporting a load to be weighed including structure pivotally mounting said weigh pan on the knife edges of said second pivot means, said structure including first and second arms which are perpendicular to each other, said first arm positioned to rest on the knife edges of said second pivot means, and means for vertically supporting said second arm, said support means being selectively adjustable to bias said second arm in a substantially vertical plane whereby said first arm is maintained in a substantially horizontal plane and a load placed at any location on said weigh pan is transmitted without error to said balance beam at the knife edges of said second pivot means through said first arm portion.

9. The invention recited in claim 8 wherein said support means includes:

an upright member mounted on said frame, a stabilizer member positioned between said second arm portion and said upright member to vertically stabilize said second arm portion, and first and second mount means mounted, respectively, on said second arm portion and said upright member for receiving said stabilizer member, at least one of said mount means being adjustable so that the effective length of said stabilizer member between said upright and second arm portion may be adjusted to bias said second arm portion in a substantially vertical plane.

10. The invention recited in claim 1, including:

first counterweight means mounted on said balance beam for selective positioning perpendicular to said beam plane whereby the moments of mass parallel to said beam plane are balanced by selectively positioning said first counterweight means, and second counterweight means mounted on said balance beam for selective positioning parallel to said beam plane whereby the moments of mass perpendicular to said beam plane are balanced by selectively positioning said second counterweight means.

11. In an electronic balance, a beam type weighing apparatus wherein a balance beam pivotally mounted on a frame has a beam reference plane which extends through its pivot axis to indicate beam position, and a load weighed by said weighing apparatus is measured as a function of the displacement of said beam plane as indicated by beam mounted sensors from a reference plane defined by frame mounted sensors, and an electrical output is generated proportionately to the load being weighed, the improvement comprising:

a null-restoring device including a beam mounted forcer coil being excited by said electrical output to restore said balance beam to its null position with respect to the beam reference plane, and electrically conductive pivot means mounting said balance beam on said frame, said forcer coil being electrically connected to said electrically conductive pivot means to receive the electrical output generated in response to displacement of said balance beam.

12. The invention recited in claim 11, wherein said electrically conductive pivot means are comprised of carbide knife-edged pivots and carbide bearing flats.

13. The invention recited in claim 11 wherein said balance beam has the mass associated therewith selectively distributed to balance the moments of mass parallel and perpendicular to said beam plane whereby to substantially eliminate the pendular characteristics of said balance beam so that said weighing apparatus is relatively insensitive to tilt and vibration.

14. In a beam type weighiNg apparatus wherein a balance beam pivotally mounted on a frame has a beam plane defined which extends through its pivot axis to indicate beam position and loads weighed by said weighing apparatus are measured as a function of the displacement of said balance beam from the reference plane, the improvement comprising:

capacitive sensor means including frame mounted capacitor plates and beam mounted capacitor plates which indicate the position of said beam plane relative to said reference plane, said capacitive sensor means being operable to measure the displacement of said beam plane from said reference plane and generate an electrical signal representative of beam displacement whereby variations in the load weighed by said weighing apparatus are measured, circuit means associated with said frame mounted capacitor plates to receive the electrical signal for generating an electrical output proportional to the load being weighed by said weighing apparatus, first electrically conductive pivot means mounting said balance beam on said frame, null restoring means including a forcer coil and a magnet for positioning and setting said balance beam to restore said beam plane in line with said reference plane in response to said electrical output generated by said circuit means, said forcer coil being mounted on said balance beam and connected through said electrically conductive pivot means to said circuit means, said magnet being mounted on said frame to interact with said forcer coil, said forcer coil being positioned relative to said magnet by pivotal movement of said balance beam, and said balance beam having the mass associated therewith selectively distributed to balance the moments of mass parallel and perpendicular to said beam plane whereby to substantially eliminate pendular characteristics of said balance beam so that said weighing apparatus is relatively insensitive to tilt and vibration.

15. The invention recited in claim 14, including means for selectively setting the position of said beam mounted forcer coil with respect to said magnet about which said forcer coil is pivotally moved by said balance beam so that said null restoring means has a substantially linear response to said electrical output.