Position sensing system with an electromagnet
A position sensing system for measuring a position of a moving object includes an electromagnet configured to generate an alternating magnetic field, and a magnetic sensor configured to measure an intensity of a first magnetic field that is based on the alternating magnetic field. A controller is configured to estimate a position of the moving object based on the measured intensity of the first magnetic field.
1. A position sensing system for measuring a position of a moving object, comprising:
an electromagnet configured to generate an alternating magnetic field;
a magnetic sensor configured to measure an intensity of a first magnetic field that is based on the alternating magnetic field; and
a controller configured to estimate a position of the moving object based on the measured intensity of the first magnetic field, wherein the controller is configured to estimate the position of the moving object based further on a nonlinear model of a magnetic field produced by the electromagnet as a function of position around the electromagnet.
2. The position sensing system of claim 1 , wherein the moving object is a piston positioned within a cylinder.
3. The position sensing system of claim 2 , wherein the electromagnet is positioned on the piston, and the magnetic sensor is positioned on the cylinder.
4. The position sensing system of claim 2 , wherein the electromagnet is positioned on the cylinder, and the magnetic sensor is positioned on the piston.
5. The position sensing system of claim 4 , wherein the magnetic sensor on the piston is powered by a battery, and wherein no wires are connected to the piston.
6. The position sensing system of claim 2 , wherein the electromagnet and the magnetic sensor are positioned on the cylinder.
7. The position sensing system of claim 6 , and further comprising:
a permanent magnet positioned on the piston.
8. The position sensing system of claim 7 , wherein the first magnetic field is based on both the alternating magnetic field and a magnetic field produced by the permanent magnet.
9. The position sensing system of claim 6 , and further comprising:
an inductive coil positioned on the piston.
10. The position sensing system of claim 9 , wherein the electromagnet is configured to induce an alternating current in the inductive coil during on portions of an on-off duty cycle of the electromagnet.
11. The position sensing system of claim 10 , wherein the magnetic sensor is configured to measure the intensity of the first magnetic field only during off portions of the on-off duty cycle of the electromagnet.
12. The position sensing system of claim 2 , wherein the electromagnet is positioned on the cylinder and the magnetic sensor is positioned on a piston rod of the piston, wherein the electromagnet and the magnetic sensor are external to the cylinder, and wherein no components of the position sensing system are located inside of the cylinder.
13. The position sensing system of claim 12 , wherein the magnetic sensor on the piston rod is battery-powered with a rechargeable battery, and wherein the battery is recharged inductively each time the piston rod is fully retracted and stationary.
14. The position sensing system of claim 1 , wherein a frequency of the alternating magnetic field is much higher than a frequency of motion of the moving object and is also much higher than a frequency of motion of any unexpected disturbances from other nearby moving magnetic or ferromagnetic objects.
15. The position sensing system of claim 1 , wherein the controller includes a high-pass or band-pass filter that extracts only an intensity of the first magnetic field at a specific known alternating frequency of the alternating magnetic field.
16. The position sensing system of claim 1 , wherein the moving object has rotational motion and wherein relative rotational motion between the electromagnet and the magnetic sensor is used to compute a relative rotational angle of the moving object.
17. A method of measuring a position of a moving object, comprising:
generating an alternating magnetic field with an electromagnet;
measuring an intensity of a first magnetic field that is based on the alternating magnetic field; and
estimating a position of the moving object based on the measured intensity of the first magnetic field and based further on a nonlinear model of a magnetic field produced by the electromagnet as a function of position around the electromagnet.
18. The method of claim 17 , wherein the moving object is a piston positioned within a cylinder.
19. A position sensing system for measuring a position of a moving object, comprising:
an electromagnet configured to generate an alternating magnetic field;
a magnetic sensor configured to measure an intensity of a first magnetic field that is based on the alternating magnetic field;
a controller configured to estimate a position of the moving object based on the measured intensity of the first magnetic field, wherein the moving object is a piston positioned within a cylinder, and wherein the electromagnet and the magnetic sensor are positioned on the cylinder; and
an inductive coil positioned on the piston, wherein the electromagnet is configured to induce an alternating current in the inductive coil during on portions of an on-off duty cycle of the electromagnet, and wherein the magnetic sensor is configured to measure the intensity of the first magnetic field only during off portions of the on-off duty cycle of the electromagnet.