Wheel capable of detecting direction of rotation
A wheel or wheel assembly for a non-motorized vehicle, such as a shopping cart, is disclosed that detects its direction of rotation. In one embodiment, the wheel assembly includes a plurality of magnets mounted to a rotating portion of the wheel, and includes a magnetic sensor, such as a tunneling magnetoresistance sensor, mounted to a non-rotating portion. As the wheel rotates the magnets produce a varying magnetic field that is sensed by the sensor, which outputs a signal corresponding to the sensed magnetic field. The magnets are arranged—preferably asymmetrically—such that the sensor's output signal differs depending upon whether the wheel is rotating in the clockwise versus counterclockwise direction. A controller analyzes the sensor's output signal to determine the direction of rotation. In another embodiment, the magnets are replaced by conductive targets, and an eddy current sensor is used for the magnetic sensor.
1. A wheel assembly comprising:
a wheel having mounted thereon a plurality of magnets;
a magnetic sensor mounted to a non-rotating portion of the wheel assembly such that the magnets pass by the magnetic sensor as the wheel rotates, the magnetic sensor configured to generate an output signal corresponding to a sensed magnet field; and
a controller configured to determine, based on the output signal, a direction of rotation of the wheel;
wherein the magnets are mounted on the wheel in an angularly asymmetrical arrangement such that no two successive angles of separation between angularly adjacent magnets are the same, said angularly asymmetrical arrangement enabling the controller to determine the direction of rotation of the wheel based solely on the output signal of the magnetic sensor.
2. The wheel assembly of claim 1 , wherein the number of said magnets is three, and the magnets are asymmetrically arranged on the wheel to form three different angles of separation between adjacent magnets.
3. The wheel assembly of claim 2 , wherein the plurality of magnets includes a first magnet having a north pole pointed radially outward and a second magnet having a north pole pointed radially inward.
4. The wheel assembly of claim 1 , wherein the magnetic sensor is a tunneling magnetoresistance (TMR) sensor.
5. The wheel assembly of claim 1 , wherein the magnetic sensor operates as a binary switch that switches between two output levels, and the controller is configured to determine the direction of rotation based on timings of transitions between the two output levels.
6. The wheel assembly of claim 5 , wherein the controller is a microcontroller configured to generate an interrupt in response to transitions between the two output levels.
7. The wheel assembly of claim 1 , wherein the magnetic sensor outputs an analog signal representing a sensed magnetic field, and the controller is configured to analyze a digitized representation of the analog signal to determine the direction of rotation.
8. The wheel assembly of claim 7 , wherein the magnetic sensor has an analog output buffer capable of being turned off by the controller.
9. The wheel assembly of claim 1 , wherein the number of said magnets is three.
10. A method of sensing a direction of rotation of a wheel of a human-propelled vehicle, wherein the wheel comprises a rotating portion having a plurality of magnets mounted thereon in an angularly asymmetrical arrangement, the method comprising:
generating, with a magnetic sensor mounted to a non-rotating portion of the wheel, a signal representing a varying magnetic field produced by movement of the magnets relative to the magnetic sensor as the wheel rotates, wherein the signal has a first pattern when the wheel rotates in a first direction, and a has second pattern that is different from the first pattern when the wheel rotates in a second direction, said different first and second patterns resulting from the angularly asymmetrical arrangement of the magnets; and
by a controller coupled to the magnetic sensor, sensing said direction of rotation of the wheel by analyzing the pattern of said signal;
wherein the magnets are asymmetrically arranged on the rotating portion of the wheel such that no two successive angles of separation between angularly adjacent magnets are the same.
11. The method of claim 10 , wherein the plurality of magnets include a first magnet having a north pole pointed radially outward and a second magnet having a north pole pointed radially inward.
12. The method of claim 10 , wherein the magnetic sensor is a tunneling magnetoresistance (TMR) sensor.
13. The method of claim 10 , wherein the magnetic sensor operates as a binary switch that switches between two output levels, and the method comprises sensing the direction of rotation based on timings of transitions between the two output levels.
14. The method of claim 13 , wherein the controller is a microcontroller configured to generate an interrupt in response to transitions between the two output levels.
15. The method of claim 10 , wherein the magnetic sensor outputs an analog signal representing a sensed magnetic field, and the controller is configured to analyze a digitized representation of the analog signal to sense the direction of rotation.
16. The method of claim 15 , wherein the magnetic sensor has an analog output buffer capable of being turned off by the controller, and the method comprises the controller turning off the analog buffer.
17. The method of claim 10 , wherein the number of said magnets is three.
18. A wheel assembly comprising:
a wheel having mounted thereon a plurality of conductive targets;
a magnetic sensor mounted to a non-rotating portion of the wheel assembly such that the conductive targets pass by the magnetic sensor as the wheel rotates, the magnetic sensor configured to generate an output signal that varies in response to movement of the conductive targets past the magnetic sensor; and
a controller configured to determine, based on the output signal, a direction of rotation of the wheel;
wherein the conductive targets are mounted on the wheel in an angularly asymmetrical arrangement such that no two successive angles of separation between angularly adjacent conductive targets are the same, said angularly asymmetrical arrangement enabling the controller to determine the direction of rotation of the wheel based solely on the output signal of the magnetic sensor.
19. The wheel assembly of claim 18 , wherein the number of said conductive targets is three, and the conductive targets are asymmetrically arranged on the wheel to form three different angles of separation between adjacent magnetic targets.
20. The wheel assembly of claim 18 , wherein the magnetic sensor is an eddy current sensor.
21. The wheel assembly of claim 20 , wherein the eddy current sensor operates as a binary switch that switches between two output levels, and the controller is configured to determine the direction of rotation based on timings of transitions between the two output levels.
22. The wheel assembly of claim 21 , wherein the controller is a microcontroller configured to generate an interrupt in response to transitions between the two output levels.
23. The wheel assembly of claim 18 , wherein the number of said conductive targets is three.
24. A method of sensing a direction of rotation of a wheel of a human-propelled vehicle, wherein the wheel comprises a rotating portion having a plurality of conductive targets mounted thereon in an angularly asymmetrical arrangement, the method comprising:
generating, with a magnetic sensor mounted to a non-rotating portion, a signal representing movement of the conductive targets relative to the magnetic sensor as the wheel rotates, wherein the signal has a first pattern when the wheel rotates in a first direction, and a has second pattern that is different from the first pattern when the wheel rotates in a second direction, said different first and second patterns resulting from the angularly asymmetrical arrangement of the conductive targets, wherein the conductive targets are asymmetrically arranged on the rotating portion of the wheel such that no two successive angles of separation between angularly adjacent conductive targets are the same; and
by a controller coupled to the magnetic sensor, sensing said direction of rotation of the wheel by analyzing the pattern of said signal.
25. The method of claim 24 , wherein the magnetic sensor is an eddy current sensor.
26. A wheel assembly comprising:
a wheel having mounted thereon a plurality of objects, said objects mounted in an angularly asymmetrical arrangement such that no two successive angles of separation between angularly adjacent objects are the same;
a magnetic sensor mounted to a non-rotating portion of the wheel assembly such that the objects pass by the magnetic sensor as the wheel rotates, wherein the objects induce a response in the magnetic sensor as the wheel rotates, causing the magnetic sensor to generate a time varying output signal that differs, as a result of the angularly asymmetrical arrangement, depending upon whether the wheel is rotating in a clockwise versus counterclockwise direction; and
a controller configured to determine the direction of rotation of the wheel based solely on the output signal of the magnetic sensor.
27. The wheel assembly of claim 26 , wherein the objects are magnets, and the magnetic sensor is a tunneling magnetoresistance (TMR) sensor.
28. The wheel assembly of claim 26 , wherein the objects are conductive targets, and the magnetic sensor is an eddy current sensor.
29. The wheel assembly of claim 26 , wherein the number of said objects is three, and the objects are arranged in an angularly asymmetric arrangement on the wheel to form three different angles of separation between adjacent objects.
30. The wheel assembly of claim 26 , wherein the wheel assembly further comprises a battery that powers the controller and the magnetic sensor.
31. The wheel assembly of claim 30 , wherein the battery, the controller and the magnetic sensor are housed within the wheel.
32. The wheel assembly of claim 26 , wherein the wheel assembly is a non-castered shopping cart wheel assembly.