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 objects, said objects mounted in an angularly asymmetrical arrangement, wherein the number of said objects is at least three and the objects are arranged in an angularly asymmetric arrangement on the wheel to form at least three different angles of separation between adjacent objects;
a single magnetic sensor mounted to a non-rotating portion of the wheel assembly such that the objects pass by the single 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 time varying output signal of the single magnetic sensor;
wherein the objects and the magnetic sensor are positioned substantially equidistant from a center of the wheel.
2 . The wheel assembly of claim 1 , wherein the objects are magnets, and the magnetic sensor is a tunneling magnetoresistance (TMR) sensor.
3 . The wheel assembly of claim 1 , wherein the objects are conductive targets, and the magnetic sensor is an eddy current sensor.
4 . The wheel assembly of claim 1 , wherein no two angles of separation between angularly adjacent objects are the same.
5 . The wheel assembly of claim 1 , wherein the objects are arranged to form at least three different angles of separation between angularly adjacent objects.
6 . The wheel assembly of claim 1 , wherein the wheel assembly is a non-castered shopping cart wheel assembly.
7 . 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.
8 . The wheel assembly of claim 7 , wherein the controller is a microcontroller configured to generate an interrupt in response to transitions between the two output levels.
9 . The wheel assembly of claim 1 , wherein the magnetic sensor is not located in a plane in which the objects rotate.
10 . A method of sensing a direction of rotation of a wheel of a wheel assembly, the wheel having a plurality of objects mounted thereon in an angularly asymmetrical arrangement, wherein the number of said objects is at least three, and the objects are arranged in an angularly asymmetric arrangement on the wheel to form at least three different angles of separation between adjacent objects, the method comprising:
generating, with a single magnetic sensor mounted to a non-rotating portion of the wheel assembly, a signal representing movement of the objects 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 has a 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 objects, wherein the magnetic sensor and the objects are positioned approximately equidistant from a center of the wheel; and
by a controller coupled to the magnetic sensor, sensing said direction of rotation of the wheel by analyzing the pattern of said signal, whereby the controller senses the direction of rotation based solely on an output of the single magnetic sensor.
11 . The method of claim 10 , wherein the objects are magnets, and the magnetic sensor is a tunneling magnetoresistance (TMR) sensor.
12 . The method of claim 10 , wherein the objects are conductive targets, and the magnetic sensor is an eddy current sensor.
13 . The method of claim 10 , wherein no two angles of separation between angularly adjacent objects are the same.
14 . The method of claim 10 , wherein the wheel assembly is a non-castered shopping cart wheel assembly.
15 . 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.
16 . A wheel assembly comprising:
a wheel having mounted thereon a plurality of objects, said objects mounted in an angularly asymmetrical arrangement, wherein no two angles of separation between angularly adjacent objects are the same;
a single magnetic sensor mounted to a non-rotating portion of the wheel assembly such that the objects pass by the single 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 time varying output signal of the single magnetic sensor;
wherein the objects and the magnetic sensor are positioned substantially equidistant from a center of the wheel.
17 . A wheel assembly comprising:
a wheel having mounted thereon a plurality of objects, said objects mounted in an angularly asymmetrical arrangement such that the objects form at least three different angles of separation between angularly adjacent objects;
a single magnetic sensor mounted to a non-rotating portion of the wheel assembly such that the objects pass by the single 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 time varying output signal of the single magnetic sensor;
wherein the objects and the magnetic sensor are positioned substantially equidistant from a center of the wheel.
18 . A method of sensing a direction of rotation of a wheel of a wheel assembly, the wheel having a plurality of objects mounted thereon in an angularly asymmetrical arrangement, wherein no two angles of separation between angularly adjacent objects are the same, the method comprising:
generating, with a single magnetic sensor mounted to a non-rotating portion of the wheel assembly, a signal representing movement of the objects 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 has a 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 objects, wherein the magnetic sensor and the objects are positioned approximately equidistant from a center of the wheel; and
by a controller coupled to the magnetic sensor, sensing said direction of rotation of the wheel by analyzing the pattern of said signal, whereby the controller senses the direction of rotation based solely on an output of the single magnetic sensor.