Proximity detection system
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.
1. A proximity detection system comprising:
an excitation source that generates an excitation signal;
a capacitive sensor having a sense electrode that secures to a surface of a system component, wherein the capacitive sensor forms a circuit with the excitation source to generate a capacitive field about the sense electrode at least in a direction of interest, wherein the capacitive field changes due to the presence of objects present within the capacitive field, thus changing the overall capacitance of the capacitive sensor;
a monitor coupled to the circuit formed of the excitation source and capacitive sensor that obtains measurements that are influenced by the capacitive field associated with the capacitive sensor;
a mapping of threshold values at a plurality of positions of the capacitive sensor within a space; and
a controller that, for a given position of the capacitive sensor within the mapped space:
determines a measured value from at least one measurement from the monitor for the given position;
retrieves, based at least in part upon the given position, a threshold value from the mapping to derive an anticipated value;
performs an evaluation based upon the determined value and the anticipated value; and
performs a predetermined action if the determined value is outside a predetermined range of the anticipated value.
2. The proximity detection system according to claim 1 , wherein the mapping of threshold values is stored in a threshold table.
3. The proximity detection system according to claim 2 , further comprising a motion controller that monitors the position of the capacitive sensor to determine an index into the threshold table based upon the mapping.
4. The proximity detection system according to claim 2 , further comprising:
an axis interface that provides coordinates of the position of the capacitive sensor to the controller to define an index into the mapping of the threshold table.
5. The proximity detection system according to claim 2 , wherein:
the threshold table comprises a plurality of threshold values, each threshold value at a designated position within a defined space, where each threshold value accounts for interference with the capacitive field that is anticipated within normal conditions.
6. The proximity detection system according to claim 2 , wherein the controller derives the anticipated value by using the retrieved threshold value from the table as an offset parameter.
7. The proximity detection system according to claim 2 , wherein the threshold mappings are stored in a multi-dimensional format such that the threshold value at a given position within a defined space changes as a function of time.
8. The proximity detection system according to claim 2 , wherein the threshold table defines a spatial mapping defining at least a three dimensional array of sensor readings taken at predetermined intervals;
the threshold table comprises three separate tables;
the intervals are specified in one table per axis, each table containing a list of normalized axis positions; and
any combination of three dimensional coordinate values taken from the tables thus defines the position of a mapped point and the location of a value within a table determines an index into the three dimensional array of sensor readings.
9. The proximity detection system according to claim 1 , wherein the mapping of threshold values is implemented from a function.
10. The proximity detection 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 a copy of the excitation signal, wherein the capacitive sensor and the system component move relative to each other.
11. The proximity detection system according to claim 1 , wherein:
the controller is configured to control, based upon at least one user-assignable parameter, at least one of the excitation source, the mapping of threshold values and the performance of the evaluation based upon the determined value and the anticipated value.
12. A proximity detection system comprising:
an excitation source that generates an excitation signal;
a capacitive sensor having a sense electrode that secures to a surface of a system component, wherein the capacitive sensor forms a circuit with the excitation source to generate a capacitive field about the sense electrode at least in a direction of interest, wherein the capacitive field changes due to the presence of objects present within the capacitive field, thus changing the overall capacitance of the capacitive sensor;
a monitor coupled to the circuit formed of the excitation source and capacitive sensor that obtains measurements that are influenced by the capacitive field associated with the capacitive sensor;
a mapping of threshold values at a plurality of points in time relative to a start time of a programmed operation of the system component to which the capacitive sensor is attached, each threshold value uniquely associated with the corresponding point in time of the corresponding programmed operation; and
a controller that evaluates the capacitive field of the capacitive sensor during execution of the programmed operation of the system component at points in time corresponding to the mapping of threshold values, wherein the controller, for a given point in time of the mapping:
determines a measured value from at least one measurement from the monitor;
retrieves a threshold value from the mapping corresponding to the given point in time of the mapping, to derive an anticipated value;
performs an evaluation based upon the determined value and the anticipated value; and
performs a predetermined action if the determined value is outside a predetermined range of the anticipated value.
13. The proximity detection system according to claim 12 , wherein the mapping of threshold values is stored in a threshold table.
14. The proximity detection system according to claim 13 , further comprising a motion controller that monitors the position of the capacitive sensor over time to determine an index into the threshold table based upon the mapping.
15. The proximity detection system according to claim 13 , wherein:
the mapping of threshold values further comprises a plurality of threshold values, each threshold value at a designated position within a defined space, where each threshold value accounts for interference with the capacitive field that is anticipated within normal conditions.
16. The proximity detection system according to claim 13 , wherein the controller derives the anticipated value by using the retrieved threshold value from the table as an offset parameter.
17. The proximity detection system according to claim 12 , wherein the mapping of threshold values is implemented from a function.
18. The proximity detection system according to claim 12 , wherein the threshold mappings are stored in a multi-dimensional format such that the threshold value at a given point in time also corresponds to a position within a defined space.
19. The proximity detection system according to claim 12 , 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 a copy of the excitation signal, wherein the capacitive sensor and the system component move relative to each other.
20. The proximity detection system according to claim 12 , wherein:
the controller is configured to control, based upon at least one user-assignable parameter, at least one of the excitation source, the mapping of threshold values and the evaluation of the capacitive field of the capacitive sensor during execution of the programmed operation.