Gap compensation for magnetostrictive torque sensors
A gap compensated torque sensing system and methods for using the same are provided. The system can include a sensor head in communication with a controller. The sensor head can contain a torque sensor and a proximity sensor coupled to the sensor head. The torque and proximity sensors can each sense magnetic fluxes passing through the target and a gap between the sensor head and the target. The controller can estimate torque applied to the target from magnetic fluxes sensed by the torque sensor. The controller can determine an improved gap measurement that is independent of electromagnetic properties of the target from magnetic fluxes sensed by the torque and proximity sensors. The estimated torque can be modified by the improved gap measurement to compensate for changes in magnetic properties of the target due to variations in the gap. In this manner, the accuracy of the torque measurements can be increased.
1. A magnetostrictive sensor, comprising:
a sensor head including,
a driving pole having a driving coil coupled thereto that is configured to generate magnetic fluxes in response to a driving current
two magnetic sensors coupled to respective sensing poles and each configured to output a first signal based at least upon first magnetic fluxes and second magnetic fluxes sensed by the two magnetic sensors, the first sensed magnetic fluxes resulting from interaction of the generated magnetic fluxes with a target, a gap between the sensor head and the target and the second sensed magnetic fluxes resulting from interaction of the generated magnetic fluxes with the gap; and
a proximity coil coupled to the driving pole that is configured to output a second signal based at least upon the first magnetic fluxes, the second magnetic fluxes, and third magnetic fluxes sensed by the proximity coil, the third magnetic fluxes resulting from interaction of the generated magnetic fluxes with the gap.
2. The sensor of claim 1 , including a controller in electrical communication with the sensor head and configured to,
receive the first signals and the second signal;
determine a force applied to the target based upon the first signals;
determine the gap based upon the first signals and the second signal; and
adjust the force determined from the first signals based upon the gap determined from the first signals and the second signal.
3. The sensor of claim 2 , wherein the force is a torque.
4. The sensor of claim 1 , wherein the two magnetic sensors are arranged approximately symmetrically with respect to the driving pole.
5. The sensor of claim 1 , wherein the third sensed magnetic flux is approximately independent of electromagnetic properties of the target.
6. The sensor of claim 1 , wherein the second and third magnetic fluxes avoid impinging the target.
7. A proximity sensing method, comprising:
generating magnetic fluxes that extend through a first region, a second region, and a third region, the first region including a target, a pair of first sensors, and a second sensor, the second region including the pair of first sensors and the second sensor, and the third region including the second sensor;
measuring, by the pair of first sensors, a combination of the first magnetic fluxes resulting from interaction of the generated magnetic fluxes and the target and second magnetic fluxes resulting from interaction of the generated magnetic fluxes and a gap between the second sensor and the target; and
measuring, by the second sensor, a combination of the first magnetic fluxes, the second magnetic fluxes, and third magnetic fluxes, the third magnetic fluxes resulting from interaction of the generated magnetic fluxes and the gap.
8. The method of claim 7 , further including,
determining the third magnetic fluxes based upon combination of the first and second magnetic fluxes measured by the pair of first sensors and the first, second, and third magnetic fluxes measured by the second sensor; and
determining the gap based upon the third magnetic fluxes.
9. The method of claim 8 , wherein the third magnetic flux is approximately independent of electromagnetic properties of the target.
10. The method of claim 7 , wherein the second and third magnetic fluxes avoid impinging the target.
11. The method of claim 7 , wherein each of the first and second sensors are inductive sensors configured to output a signal based upon magnetic fields respectively extending therethrough.
12. The method of claim 7 , wherein the pair of first sensors are positioned approximately symmetrically with respect to a source of the generated magnetic flux.
13. A sensing method, comprising:
generating magnetic fluxes with a driving coil coupled to a driving pole of a magnetostrictive torque sensor;
outputting, by two magnetic sensors coupled to respective sensing poles of the magnetostrictive sensor, first signals based at least upon first magnetic fluxes and second magnetic fluxes sensed by the two magnetic sensors, the first sensed magnetic fluxes resulting from interaction of the generated magnetic fluxes with a target, a gap between the magnetostrictive torque sensor and the target, and the two sensing poles and the second sensed magnetic fluxes resulting from interaction of the generated magnetic fluxes with the gap and the two sensing poles; and
outputting, by a proximity coil coupled to the driving pole, a second signal based at least upon a combination of the first magnetic fluxes, the second sensed magnetic fluxes, and third magnetic fluxes sensed by the proximity coil, the third magnetic fluxes resulting from interaction of the generated magnetic fluxes with the gap.
14. The method of claim 13 , further including,
determining a torque applied to the target based upon the first signals;
determining the gap based upon the first signals and the second signal; and
adjusting the torque determined from the first signals based upon the gap determined from the first signals and the second signal.
15. The method of claim 14 , wherein the force is a torque.
16. The sensor of claim 13 , wherein the two magnetic sensors are arranged approximately symmetrically with respect to the driving pole.
17. The sensor of claim 13 , wherein the third sensed magnetic flux results from interaction of the generated magnetic flux with the gap only.
18. The sensor of claim 13 , wherein the second and third magnetic fluxes avoid impinging the target.