ARRANGEMENT COMPRISING AN INDUCTIVE PROXIMITY SENSOR, AND METHOD IMPLEMENTING SUCH A SENSOR

• US 20120303305A1
• Filed: 06/13/2012
• Published: 11/29/2012
• Est. Priority Date: 12/15/2009
• Status: Active Grant

• Current Assignee: Posic SA
• Original Assignee: Posic SA
• Inventors: Bergqvist, Johan, Wouters, Sietse
• Granted Patent: US 9,255,818 B2
• Time in Patent Office: Days
• US Class Current: 702/65
• CPC Class Codes: G01D 5/2208 by influencing the self-induction of the coils
• CPC Class Codes: G01D 5/225 by influencing the mutual induction between the two coils

Abstract

An electronic circuit detecting proximity includes an excitation coil emitting an inductive excitation field toward a target. A first pair of detection coils obtains a first differential inductive signal that is modified by a transition of the target within the inductive field. An out-of phase second pair of detection coils obtains a second differential inductive signal that is modified by a transition of the target within the inductive field. A comparator generates a transition signal when the difference between the first and second differential signals reaches a threshold value. A stationary target, in a ferromagnetic or conductive material, creates an offset to the signals at the outlet of the coil pairs. The offset is decreased during the presence of a movable target within the same type of material or increased during the presence of a movable target within another type of material. A comparator detects the offset level.

Claims

1. Method implementing an inductive type proximity sensor for detecting a transition in a target in front of said sensor, including the following steps:

generating by means of an excitation coil a magnetic signal directed towards said target;

obtaining a first differential inductive signal with a first pair of detection coils and of a second differential inductive signal with a second pair of detection coils that are phase-shifted relative to said first pair, wherein said differential inductive signals depend on the voltages induced in said detection coils, wherein said induced voltages depend on the position of said target;

detecting one said transition at the instant when the difference between said first differential inductive signal and said second differential inductive signal reaches a predetermined threshold value.

2. The method of claim 1, wherein the sign of at least one of said differential inductive signals is used to distinguish between the arrival of a target in front of said detection coils and the departure of a target moving away from these detection coils.

3. The method of claim 1, wherein a transition is detected when and only when said first and second differential inductive signals (s0, s1) are different from zero and equal to one another.

4. The method of claim 1, wherein a transition is detected only when said first differential inductive signal and/or said second differential inductive signal are greater than a threshold.

5. The method of claim 1, wherein said excitation coil and said detection coils are made on a same semiconductor substrate.

6. The method of claim 5, wherein the difference between said first differential inductive signal and said second inductive signal is obtained by means of a comparator on said semiconductor substrate.

7. The method of claim 5, wherein the difference between said first differential inductive signal and said second inductive signal is obtained by means of a computer software executed by a microcontroller on said semiconductor substrate.

8. The method of claim 1, wherein a stationary target is placed in a permanent manner in front of at least one of said detection coils so as to create an offset on said first differential inductive signal and on said second differential signal, said offset being increased or decreased by the presence of a movable target.

9. The method of claim 8, wherein at least one of said differential inductive signals is compared to a threshold value in order to distinguish between the presence and the absence of a movable target.

10. Arrangement, including:

an excitation coil for emitting an inductive excitation field directed towards a target;

a first pair of detection coils mounted in a differential fashion and arranged for generating a first differential inductive signal depending on said target;

a second pair of detection coils mounted in a differential fashion and arranged for generating a second differential inductive signal depending on said target;

a comparator for obtaining the difference between said first differential inductive signal and said second differential inductive signal and for generating a transition signal at the instant (i) when said difference reaches a threshold value.

11. The arrangement of claim 10, further comprising a stationary target for modifying the coupling between the excitation and at last one detection coil so as to introduce in a permanent manner in at least one of said differential inductive signals an offset that enables a distinction between the presence and the absence of target to be made.

12. The arrangement of claim 11, wherein said stationary target is made of a ferromagnetic material so as to increase the coupling between said excitation coil and the detection coil or coils in front of which said stationary target is placed.

13. The arrangement of claim 11, wherein said stationary target is made of a non ferromagnetic conductive material so as to decrease the coupling between said excitation coil and the detection coil or coils in front of which said stationary target is placed.

14. The arrangement of claim 10, including a printed circuit onto which an integrated circuit including said coils is mounted,

said stationary target being constituted of a metallic layer on a track or layer of said printed circuit that is not the same as the track or layer onto which the integrated circuit is mounted.

15. The arrangement of claim 10, wherein said movable target is constituted by a machine part of a ferromagnetic material.

16. The arrangement of claim 10, wherein said movable target is constituted by a conductor track on a printed circuit.

17. The arrangement of claim 10, wherein said excitation coil and said detection coils are made on a same semiconductor substrate.

18. The arrangement of claim 10, wherein said stationary target covers partly one of the detection coils, wherein the coupling between said partly covered detection coil or coils and the excitation coil is modified by the presence of a movable target.