Capacitively coupled sensor system for conveyor belts

Patent metadata

Field	Value
Publication number	US-10801902-B2
Application number	US-201816609364-A
Country	US
Kind code	B2
Filing date	Mar 28, 2018
Priority date	May 2, 2017
Publication date	Oct 13, 2020
Grant date	Oct 13, 2020

Abstract

A sensor system for a conveyor belt comprising a sensor stage on the conveyor belt and a stationary drive and detection stage external to the conveyor belt in the belt carryway. In an exemplary version, the sensor stage includes a capacitor sensor whose capacitance varies with the weight of a load atop a pressure platform at the belt's conveying surface. An oscillator in the drive and detection stage drives the capacitor sensor through capacitors formed when plates in the sensor stage in the advancing conveyor belt overlap stationary plates in the drive and detection stage during the belt's passage along the carryway. The corresponding plates in the belt and the carryway have different longitudinal dimensions to ensure constant plate overlap area of longer duration and despite lateral belt-tracking offset. The drive and detection stage detects the capacitance of the sensor and converts it into a weight value.

First claim

What is claimed is:

1. A conveyor-belt measuring system comprising:
a conveyor belt having a top side and a bottom side;
a drive and detection stage external to the conveyor belt and including:
an oscillator producing a drive signal;
a first external capacitor plate positioned near the bottom side of the conveyor belt and connected in series with the oscillator;
a second external capacitor plate positioned near the bottom side of the conveyor belt;
a detector connected to the second external capacitor plate;

a first belt capacitor plate mounted in the conveyor belt near the bottom side of the conveyor belt;
a second belt capacitor plate mounted in the conveyor belt near the bottom side of the conveyor belt;
wherein the first belt capacitor plate and the first external capacitor plate are aligned to form a drive capacitor when the second belt capacitor plate and the second external capacitor plate are aligned to form a communication capacitor;
a sensor mounted in the conveyor belt and connected in series between the drive capacitor and the communication capacitor;
wherein the drive capacitor couples the drive signal to the sensor to produce a sensor signal indicative of a physical property measured by the sensor; and
wherein the detector receives the sensor signal from the communication capacitor.

2. A conveyor-belt measuring system as in claim 1 wherein the sensor is a capacitor whose capacitance changes with the physical property.

3. A conveyor-belt measuring system as in claim 1 wherein the drive and detection stage further includes:
a first external reference capacitor plate positioned near the bottom side of the conveyor belt and connected in series with the oscillator;
a second external reference capacitor plate positioned near the bottom side of the conveyor belt;
a reference detector connected to the second external capacitor plate; and
wherein the conveyor-belt measuring system further comprises:
a first belt reference capacitor plate mounted in the conveyor belt near the bottom side of the conveyor belt;
a second belt reference capacitor plate mounted in the conveyor belt near the bottom side of the conveyor belt;
wherein the first belt reference capacitor plate and the first external reference capacitor plate are aligned to form a reference drive capacitor and the second belt reference capacitor plate and the second external reference capacitor plate are aligned to form a reference communication capacitor when the first and second belt capacitor plates are aligned with the first and second external capacitor plates;
a reference capacitor having a fixed capacitance mounted in the conveyor belt and connected in series between the reference drive capacitor and the reference communication capacitor;

wherein the reference drive capacitor couples the drive signal to the reference capacitor to produce a reference signal insensitive to the physical property measured by the sensor, but sensitive to ambient conditions affecting the sensor;
wherein the reference detector receives the reference signal from the reference communication capacitor.

4. A conveyor-belt measuring system as in claim 3 wherein the first external capacitor plate and the first external reference capacitor plate are the same capacitor plate.

5. A conveyor-belt measuring system as in claim 3 wherein the overlapping plate areas of the drive capacitor and the reference drive capacitor are equal and the overlapping plate areas of the communication capacitor and the reference communication capacitor are equal.

6. A conveyor-belt measuring system as in claim 1 wherein the drive and detection stage further includes:
a front external height capacitor plate positioned near the bottom side of the conveyor belt;
a rear external height capacitor plate positioned near the bottom side of the conveyor belt and spaced apart from the front external height capacitor plate in a conveying direction; and
wherein the conveyor-belt measuring system further comprises:
a front belt height capacitor plate mounted in the conveyor belt near the bottom side of the conveyor belt;
a rear belt height capacitor plate mounted in the conveyor belt near the bottom side of the conveyor belt and spaced apart from the front belt height capacitor plate in the conveying direction;

wherein the first external capacitor plate overlaps first portions of the front and rear belt height capacitor plates to form front and rear height drive capacitors and a second portion of the front belt height capacitor plate overlaps the front external height capacitor plate to form a front height capacitor when a second portion of the rear belt height capacitor plate overlaps the rear external height capacitor plate to form a rear height capacitor;
wherein the front height drive capacitor is in series with the front height capacitor with a front series capacitance and the rear height drive capacitor is in series with the rear height capacitor with a rear series capacitance;
wherein the first external capacitor plate couples the drive signal to the front and rear height capacitors to produce front and rear height signals indicative of the front and rear series capacitances;
wherein deviation of the ratio of the front series capacitance to the rear series capacitance from unity is a measure of the pitch of the belt.

7. A conveyor-belt measuring system as in claim 6 wherein:
the front external height capacitor plate comprises a right front external height capacitor plate and a left front external height capacitor plate spaced apart from the right front external height capacitor plate in a direction perpendicular to the conveying direction;
the rear external height capacitor plate comprises a right rear external height capacitor plate and a left rear external height capacitor plate spaced apart from the right rear external height capacitor plate in a direction perpendicular to the conveying direction;
the front height capacitor forms a right front height capacitor in series with the front height drive capacitor with a right front series capacitance and a left front height capacitor in series with the front height drive capacitor with a left front series capacitance;
the rear height capacitor forms a right rear height capacitor in series with the rear height drive capacitor with a right rear series capacitance and a left rear height capacitor in series with the rear height drive capacitor with a left rear series capacitance;
wherein the first external capacitor plate couples the drive signal to the right front, left front, right rear, and left rear height capacitors to produce right front, left front, right rear, and left rear height signals indicative of right front, left front, right rear, and left rear series capacitances;
wherein a deviation of the ratio of the right front series capacitance to the left front series capacitance from unity and a deviation of the ratio of the right rear series capacitance to the left rear series capacitance from unity are measures of the roll of the belt.

8. A conveyor-belt measuring system as in claim 1 wherein the drive and measurement circuit further includes:
a right external tracking capacitor plate positioned near the bottom side of the conveyor belt;
a left external tracking capacitor plate positioned near the bottom side of the conveyor belt and spaced apart from the right external tracking capacitor plate in a direction perpendicular to a conveying direction; and
wherein the conveyor-belt measuring system further comprises a belt tracking capacitor plate mounted in the conveyor belt near the bottom side of the conveyor belt;
wherein the first external capacitor plate overlaps a first portion of the belt tracking capacitor plate to form a tracking dr

Assignees

• Laitram Llc

Inventors

• Kleczewski Lazlo

Classifications

• B65G2203/042

  Sensors · CPC title

• B65G2203/0258

  Weight of the article · CPC title

• B65G43/08 Primary

  Control devices operated by article or material being fed, conveyed or discharged {(and controlling the discharging devices B65G47/42)} · CPC title

• G01G7/00

  Weighing apparatus wherein the balancing is effected by magnetic, electromagnetic, or electrostatic action, or by means not provided for in the preceding groups · CPC title

• G01L1/146 Primary

  for measuring force distributions, e.g. using force arrays (G01L1/148 takes precedence) · CPC title