PROXIMITY DETECTION SYSTEM

• US 20080122458A1
• Filed: 11/21/2007
• Published: 05/29/2008
• Est. Priority Date: 11/28/2006
• Status: Active Grant

• Current Assignee: Penta Gear Metrology LLC
• Original Assignee: Process Equipment Co. (Nexplore Corporation)
• Inventors: Lenz, Robert G.
• Granted Patent: US 8,164,354 B2
• Time in Patent Office: Days
• US Class Current: 324/687
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 2217/94026 Automatic threshold calibration; e.g. threshold automatically adapts to ambient conditions or follows variation of input
• CPC Class Codes: H03K 2217/94094 Wired transmission, e.g. via bus connection or similar

Abstract

Proximity sensing arrangements utilize one or more sensing devices to detect and/or to discern objects that are or become proximate, or are expected to be proximate to a position of interest. For example, one or more capacitive sensors may be distributed to locations about a machine, e.g., attached to, incorporated with, or otherwise associated with a moving or otherwise operating component of the machine. Corresponding control electronics drive each capacitive sensor, using a corresponding excitation signal, as well as process information read from each capacitive sensor to make intelligent proximity related decisions.

Claims

1. A proximity detection system comprising:

a capacitive sensor having a sense electrode that is arranged to secure to a surface of a system component;

an excitation source that generates an excitation signal for driving the capacitive sensor;

a circuit that couples the excitation source to the capacitive sensor such that when the excitation signal from the excitation source drives the capacitive sensor, a capacitive field is generated relative to the sense electrode that corresponds to the capacitance of the capacitive sensor, wherein the presence of objects that are or become proximate to the capacitive sensor alter the capacitive field thus changing the overall capacitance of the capacitive sensor;

a monitor that performs measurements of the circuit where the measurements are influenced by the capacitive field associated with the capacitive sensor; and

a controller operatively configured to evaluate one or more measurements taken by the monitor and to trigger a predetermined action if the evaluation corresponds to a triggering event;

wherein the controller is configured to dynamically update at least one parameter that alters the evaluation with regard to the triggering event to accommodate changes in at least one system condition.

2. The system according to claim 1, further comprising:

at least one threshold table that stores data values that are used by the controller to dynamically adjust a threshold value corresponding to the dynamically updated parameter, wherein the controller is further configured to utilize a select one of the data values from the threshold table based upon a detected change in at least one system condition to evaluate the measurement.

3. The system according to claim 2, wherein the at least one system condition comprises a known position of the capacitive sensor within a defined space, wherein the controller is further configured to dynamically update a requirement to satisfy the triggering event based upon a value of the known position of the capacitive sensor.

4. The system according to claim 2, wherein the at least one system condition comprises a relative time, wherein the controller is further configured to dynamically update a requirement to satisfy the triggering event based upon a value of the relative time.

5. The system according to claim 2, wherein the at least one system condition comprises a known position of an object relative to the capacitive sensor that is not desired to trigger the predetermined action, wherein the controller is further configured to dynamically update a requirement to satisfy the triggering event based upon a value of the known position of the object.

6. The system according to claim 1, further comprising at least one shield that is placed between the capacitive sensor and a system component that is not intended to trigger the predetermined action, wherein each such shield is driven by excitation signal from the excitation source.

7. The system according to claim 1, further comprising:

at least one additional capacitive sensor coupled to the proximity detection system, wherein;

the excitation source is further configured to drive each the capacitive sensor with a unique excitation signal;

the monitor independently collects measurements from each capacitive sensor; and

the controller is operatively configured to evaluate one or more measurements taken by the monitor for each sensor and to trigger a predetermined action if the evaluation corresponds to a triggering event.

8. The system according to claim 1, further comprising a cable that connects the capacitive sensor to the circuit, wherein:

the capacitive sensor further comprises a shield electrode; and

the monitor comprises a signal amplifier to buffer a signal read from the sensor electrode of the capacitive sensor and a shield driver to drive the shield electrode of the capacitive sensor with a copy of the signal so as to reduce effects of cable capacitance in the cable.

9. The system according to claim 1, wherein the capacitive sensor further comprises:

an inner insulator over the surface of the system component;

a first conductive layer over the inner insulator to form a shield electrode;

an intermediate insulator over the inner insulator and first conductive layer; and

a second conductive layer formed over the intermediate insulator to form the sense electrode.

10. The method according to claim 9, wherein:

the first and second conductive layers comprise electrically conductive paint;

further comprising;

an outer protective layer provided over the second conductive layer.

11. A method of detecting proximity comprising:

providing a capacitive sensor having a sense electrode that is arranged to secure to a surface of a system component;

utilizing an excitation source to generate an excitation signal that drives the capacitive sensor such that a capacitive field is generated relative to the sense electrode that corresponds to the capacitance of the capacitive sensor, wherein the presence of objects that are or become proximate to the capacitive sensor alter the capacitive field thus changing the overall capacitance of the capacitive sensor;

collecting measurements that are related to the capacitive field associated with the capacitive sensor; and

evaluating one or more measurements taken to trigger a predetermined action if the evaluation corresponds to a triggering event, comprising;

filling a circular buffer with said collected measurements;

filtering the collected measurements by computing at least one discrete Fourier transform component from the collected measurements in the circular buffer;

evaluating at least one computed Fourier transform component;

triggering a predetermined action if the evaluation corresponds to a triggering event; and

dynamically updating at least one parameter that alters the evaluation with regard to the triggering event to accommodate changes in at least one system condition.

12. The method according to claim 11, wherein dynamically updating at least one parameter that alters the evaluation comprises at least one of:

updating a current value in a threshold table, evaluating a function, evaluating a rule, evaluating an expression or performing a computation.

13. The method according to claim 11, wherein dynamically updating at least one parameter that alters the evaluation comprises computing a rate of change of capacitance.

14. The method according to claim 11, wherein the circular buffer is filled with collected measurements by:

accumulating measurements to a select one of two sample buffers; and

transferring the currently selected sample buffer contents to the circular buffer when the currently selected sample buffer becomes filled with measurements and accumulating samples in the remaining sample buffer.

15. The method according to claim 11, wherein computing at least one discrete Fourier transform component further comprises:

calculating a real component of the discrete time Fourier transform;

calculating an imaginary component of the discrete time Fourier transform; and

combining the real and imaginary components, wherein;

the evaluation for triggering a predetermined action if the evaluation corresponds to a triggering event is based upon the combination of real and imaginary components.

16. The method according to claim 11, wherein

dynamically updating at least one parameter that alters the evaluation with regard to the triggering event to accommodate changes in at least one system condition comprises:

defining at least one table of threshold values, wherein the at least one system condition is evaluated to determine an index into the table to recover a corresponding threshold value.

17. The method according to claim 16, wherein defining at least one table of threshold values comprises defining data in multiple dimensions mapped into a bound space and designating a resolution of data values that can vary across the bound space.

18. The method according to claim 11, wherein evaluating at least one computed Fourier transform component comprises implementing a narrow band filter to reject harmonics of the measured excitation signal by computing the at least one discrete Fourier transform component at the excitation frequency used to drive the capacitive sensor.

19. The method according to claim 11, wherein the discrete Fourier transform is computed only for the coefficients at a known frequency of the first excitation signal.

20. The method according to claim 11, further comprising:

providing at least one additional capacitive sensor that couples to a surface of a system component;

providing an additional capacitive circuit corresponding to each additional capacitive sensor;

generating each excitation signal at a unique frequency; and

processing samples associated with each capacitive sensor based upon a set of reconfigurable parameters that define for each capacitive sensor, at least the excitation frequency, filter sample rate and DFT coefficient length.

21. A proximity detection system comprising:

a capacitive sensor that couples to a surface of a first system component to sense the presence of objects of interest that are or become proximate to the capacitive sensor;

a capacitive circuit comprising the capacitive sensor;

a drive shield positioned between the capacitive sensor and a second system component that is not associated with the capacitive sensor;

an excitation source that generates an excitation signal for driving both the drive shield and the capacitive circuit including the capacitive sensor;

a monitoring circuit that performs a measurement of the capacitive circuit that corresponds to capacitance of the capacitive circuit, wherein the capacitance of the capacitive circuit is influenced by a capacitive field associated with the capacitive sensor; and

a controller operatively configured to perform a comparison of the measurement with a function or threshold value and to trigger a predetermined action if the comparison corresponds to a triggering event, wherein the drive shield prevents the controller from triggering predetermined action, even if proximate to the capacitive sensor.

22. The proximity detection system according to claim 21, wherein the second system component comprises a housing and the capacitive sensor is configured to reciprocate into and out of the housing.

23. The proximity detection system according to claim 21, wherein the second system component comprises another moving component of a system that cannot contact a structure that the capacitive sensor is mounted to.