Conveyor-belt system for measuring conditions that vary the resonant frequency of a resonant circuit

• US 10,191,001 B2
• Filed: 12/18/2015
• Issued: 01/29/2019
• Est. Priority Date: 04/15/2014
• Status: Active Grant

• Current Assignee: Laitram LLC
• Original Assignee: Laitram LLC
• Inventors: Kleczewski, Lazlo
• Primary Examiner(s): Gibson, Randy
• Application Number:
  US14/974,890
• Publication Number:
  US 20160103084A1
• Time in Patent Office: 1,138 Days
• CPC Class Codes: B65G 17/08 the surface being formed by the traction element
• CPC Class Codes: B65G 17/30 Details; Auxiliary devices belts B65G15/30; framework B65G21/00
• CPC Class Codes: B65G 43/02 detecting dangerous physical condition of load carriers, e.g. for interrupting the drive in the event of overheating
• CPC Class Codes: G01D 5/243 influencing the phase or frequency of ac
• CPC Class Codes: G01G 19/035 using electrical weight-sensitive devices
• CPC Class Codes: G01G 7/02 by electromagnetic action
• CPC Class Codes: G01G 7/06 by electrostatic action
• CPC Class Codes: G01L 1/14 by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators
• CPC Class Codes: G01L 1/144 with associated circuitry G01L1/146 and G01L1/148 take precedence
• CPC Class Codes: G01L 5/101 using sensors inserted into the flexible member
• CPC Class Codes: G01N 27/023 where the material is placed in the field of a coil
• CPC Class Codes: G01N 27/028 Circuits therefor measuring impedance per se G01R27/02
• CPC Class Codes: G01N 27/228 Circuits therefor measuring capacitance per se G01R27/26

Abstract

A conveyor belt and a sensing system for sensing various conditions on a conveyor belt. The belt includes an array of sensing elements embedded in the belt to measure belt conditions. The sensing elements form parts of passive resonant circuits that each include a capacitor and an inductive coil. The capacitor or the inductive coil can be a sensing element. Measuring circuits external to the belt are inductively or capacitively coupled to the resonant circuits in the belt as they pass closely by. The sensing elements change the resonant frequency of their resonant circuits as a function of the sensed conditions. Frequency detectors in the measuring circuits measure that frequency change and convert it into a functionally related value used to determine a belt condition. Exemplary conditions include temperature, pressure, humidity, spillage, and product weight.

Claims

1. A conveyor belt comprising:

an endless belt body;

a plurality of resonant circuits disposed at sensor positions in the endless belt body, each of the resonant circuits including;

an inductor; and

a capacitor connected to the inductor to form the resonant circuit with a resonant frequency determined by the inductance of the inductor and the capacitance of the capacitor;

a plurality of capacitor plates, wherein each of the resonant circuits is connected to one or more capacitor plates to capacitively couple the resonant circuit through one or more stationary capacitor plates external to the conveyor belt;

wherein at least one of the inductance of the inductor and the capacitance of the capacitor is varied by a varying condition affecting the conveyor belt.

2. A conveyor belt as in claim 1 wherein the inductor has a fixed inductance and is arranged to inductively couple the resonant circuit to a stationary activation circuit external to the conveyor belt.

3. A conveyor belt as in claim 1 wherein the capacitor has a fixed capacitance and is arranged to capacitively couple the resonant circuit to a stationary activation circuit external to the conveyor belt.

4. A conveyor belt as in claim 1 further comprising a plurality of coupling coils each connected to one of the resonant circuits to inductively couple the resonant circuit to a stationary activation circuit external to the conveyor belt.

5. A conveyor belt as in claim 1 wherein the inductance of the inductor or the capacitance of the capacitor in each of the resonant circuits is varied by changes in the dimensions of the inductor or the capacitor caused by the varying condition affecting the conveyor belt.

6. A conveyor belt as in claim 1 wherein the inductor in each of the resonant circuits has coil windings and a core inside the coil windings and wherein the varying condition affecting the conveyor belt causes changes in the length of the core inside the windings, which changes the inductance of the inductor.

7. A conveyor belt as in claim 1 wherein the capacitor in each of the resonant circuits has a first plate and a second plate separated from the first plate by a gap and a dielectric slab in a portion of the gap and wherein the varying condition affecting the conveyor belt causes changes in the dimensions of the dielectric slab and the portion of the gap occupied by the dielectric slab, which changes the capacitance of the capacitor.

8. A conveyor belt as in claim 7 wherein the first plate and the second plate diverge from first ends of the plates to opposite second ends so that the gap is wider at the second end than at the first end and wherein the dielectric slab is disposed in a portion of the gap between the first ends of the plates and wherein the remaining portion of the gap from the dielectric slab to the second ends of the plates is an air gap into which spilled liquids can collect and change the effective permittivity and the capacitance of the capacitor.

9. A conveyor belt as in claim 1 wherein the varying condition affecting the conveyor belt is selected from the group consisting of:

weight of articles conveyed on the conveyor belt, temperature of the conveyor belt, ambient pressure on the conveyor belt, ambient humidity, and liquid spillage onto the conveyor belt.

10. A conveyor-belt measuring system comprising:

a conveyor belt including;

a plurality of resonant circuits disposed at sensor positions in the conveyor belt, each of the resonant circuits having a resonant frequency and including;

an inductor; and

a capacitor connected to the inductor to form the resonant circuit with a resonant frequency determined by the inductance of the inductor and the capacitance of the capacitor;

wherein either the inductor is a sensing element whose inductance is varied by a varying condition affecting the conveyor belt or the capacitor is the sensing element whose capacitance is varied by the varying condition affecting the conveyor belt;

wherein the variation of the inductance or the capacitance of the sensing element changes the resonant frequency as a function of the condition affecting the conveyor belt;

a coupling element connected to the sensing element;

at least one stationary measurement circuit external to the conveyor belt and including;

a frequency detector; and

a stationary coupling element coacting with the coupling elements in the conveyor belt as they pass close to the stationary coupling element to couple the resonant circuits to the frequency detector;

wherein the frequency detector measures changes in the resonant frequency of the resonant circuits caused by the condition affecting the conveyor belt.

11. A conveyor-belt measuring system as in claim 10 wherein the coupling element in the conveyor belt and the stationary coupling element provide one or the other of inductive coupling and capacitive coupling.

12. A conveyor-belt measuring system as in claim 10 wherein the coupling element in the conveyor belt includes a first plate of a capacitor and the stationary coupling element includes a second plate of the capacitor formed as the first plate in the conveyor belt passes closely by the second plate.

13. A conveyor-belt measuring system as in claim 10 wherein the coupling element in the conveyor belt is a spring-loaded plate and the stationary coupling element includes a pair of spaced apart plates forming separate capacitors with the spring-loaded plate in the conveyor belt.

14. A conveyor-belt measuring system as in claim 10 wherein the at least one stationary measurement circuit includes a differentiating amplifier connected between the stationary coupling element and the frequency detector.

15. A conveyor-belt measuring system as in claim 10 wherein the at least one stationary measurement circuit includes an oscillator oscillating at a nominal resonant frequency and connected between the stationary coupling element and the frequency detector, wherein changes in the resonant frequency of the resonant circuits change the frequency of the oscillator from the nominal resonant frequency as the resonant circuits pass the at least one stationary measurement circuit.

16. A conveyor-belt measuring system as in claim 10 wherein the condition affecting the conveyor belt is selected from the group consisting of:

weight of articles conveyed on the conveyor belt, temperature of the conveyor belt, ambient pressure on the conveyor belt, ambient humidity, and liquid spillage onto the conveyor belt.

17. A conveyor-belt measuring system as in claim 10 comprising a controller and wherein the frequency detector determines the frequencies of the resonant circuits and sends the frequencies to the controller.

18. A conveyor-belt measuring system as in claim 17 further comprising an array of stationary measurement circuits under the conveyor belt across its width and wherein the sensing elements sense the weight of articles conveyed on the conveyor belt and change the resonant frequencies of the resonant circuits accordingly and wherein the controller computes the position, the skew, or the center of gravity of each of the conveyed articles from the weights determined from the array of stationary measurement circuits.

19. A conveyor-belt measuring system comprising:

a conveyor belt including;

a plurality of sensing elements disposed at sensor positions in the conveyor belt, wherein an electrical property of each of the sensing elements is changed by a condition affecting the conveyor belt;

at least one stationary measurement circuit external to the conveyor belt and including;

a frequency detector; and

a stationary coupling element coupling the at least one stationary measurement circuit to the plurality of sensing elements in the conveyor belt as they pass close to the stationary coupling element;

wherein each of the sensing elements forms part of a resonant circuit having a resonant frequency that depends on the electrical property of sensing element;

wherein the frequency detector measures changes in the resonant frequency of the resonant circuit due to changes in the electrical property of the sensing element caused by the condition affecting the conveyor belt;

wherein the sensing element is an inductor or a capacitor and the electrical property is the inductance of the inductor or the capacitance of the capacitor.

20. A conveyor-belt measuring system as in claim 19 further comprising a plurality of coupling elements in the conveyor belt, each connected to a respective one of the sensing elements for coupling the sensing element to the at least one stationary measurement circuit through the stationary coupling element.

21. A conveyor-belt measuring system as in claim 19 wherein each of the sensing elements is also a coupling element coupling to the at least one stationary measurement circuit through the stationary coupling element.

22. A conveyor-belt measuring system as in claim 19 wherein the resonant circuit is disposed in the conveyor belt.

23. A conveyor-belt measuring system as in claim 19 wherein the resonant circuit is distributed between the conveyor belt and the at least one stationary measurement circuit.

24. A conveyor-belt measuring system as in claim 19 wherein the condition affecting the conveyor belt is selected from the group consisting of:

weight of articles conveyed on the conveyor belt, temperature of the conveyor belt, ambient pressure on the conveyor belt, ambient humidity, and liquid spillage onto the conveyor belt.