Magnetic odometer with direction indicator systems and method

Systems and methods for determining a directional movement of an object such as a wheeled vehicle. The system includes a magnet having a north pole and a south pole mounted to the object, a single magnetic sensor positioned such that the sensor can individually detect each magnetic pole as the object moves, the sensor configured to produce a first characteristic signal when a north pole is detected and a second characteristic signal when a south pole is detected, and a processing device in signal communication with the sensor, the processing device configured to determine a directional movement of the object based on a configuration of a signal doublet that includes the first and second characteristic signals. The methods include sensing the north and south poles as they pass the magnetic sensor and determining a direction based on an order in which the north and south poles are sensed.

BACKGROUND OF THE INVENTION

In a dead reckoning system for wheeled applications, it is sometimes important to know the direction of travel as well as the displacement. The displacement is typically derived from the counting of odometer pulses by some means such as magnetic, optical, or direct connections to a vehicle's odometer sensors. For a wheeled application, the direction of travel is also typically very important. Generally, some other means is used to distinguish the direction of travel such as connections to a backup light signal, if one exists. In many applications, the installation of such an elaborate odometer sensor, including connections to a separate direction indicator is prohibitively expensive or not practical at all. Although systems that detect direction using magnetic sensors exist, they typically require two or more magnetic sensors to operate, such as a device described in U.S. Pat. No. 6,446,005 that uses two hall-effect magnetic sensors in a sensing component to detect direction.

SUMMARY OF THE INVENTION

The present invention includes systems and methods for determining a directional movement of an object. In an example embodiment, the system includes at least one magnet having a north pole and a south pole mounted to the object, a single magnetic sensor positioned such that the sensor can individually detect each pole of at least one magnet when at least one magnet passes by the magnetic sensor as the object moves, the sensor configured to produce a predetermined first characteristic signal when a north pole is detected and a predetermined second characteristic signal when a south pole is detected, and a processing device in signal communication with the sensor, the processing device configured to determine a directional movement of the object based on a configuration of a signal doublet that includes the first and second characteristic signals. In an example embodiment, the methods include sensing a north pole of a magnet mounted on an object as the north pole passes a single magnetic sensor, sensing a south pole of the magnet as the south pole passes the single magnetic sensor, and determining a direction selected from a first direction and a second direction opposite the first direction based on an order in which the north and south poles are sensed.

In accordance with further aspects of the invention, the invention includes a system for determining a direction of a wheeled vehicle. In an example embodiment, the system includes a chassis, a first wheel rotationally coupled to the chassis, a magnet having a north pole and a south pole mounted to the first wheel of the wheeled vehicle, a single magnetic sensor configured to produce a predetermined first characteristic signal when a north pole is detected and a predetermined second characteristic signal when a south pole is detected, and a processing device in signal communication with the magnetic sensor, the processing device configured to determine rotational direction of the first wheel and a corresponding direction of the wheeled vehicle selected from forward or reverse based on a configuration of a signal doublet that includes the first and second characteristic signals from the magnetic sensor.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a diagram of a system10formed in accordance with an embodiment of the invention for determining a direction of motion of an object12. The system10includes a magnet11mounted to the object12. The object12is movable in at least a first direction13and a second direction14opposite the first direction13. The system10includes a single magnetic sensor15that is positioned to individually detect a north pole16and a south pole17of the magnet11as they pass by the magnetic sensor15. The magnetic sensor15is configured to produce a predetermined first characteristic signal when a north pole of a magnet such as the north pole16is detected and a predetermined second characteristic signal when a south pole of a magnet such as the south pole17is detected. The magnetic sensor15is in signal communication with a processing device18. The processing device18is configured to determine a directional movement of the object12based on a configuration of a signal doublet that includes the first and second characteristic signals (SeeFIG. 4).

FIG. 2is a diagram of a system20for determining a rotational direction of a wheel in accordance with an embodiment of the invention. The system20includes at least one magnet22mounted to a wheel24having a rotational center26and an axis of rotation28. Each of the magnets22include a north pole30and a south pole32. The magnets22are preferably spaced at approximately equal angular intervals around the wheel24. Each of the magnets22are also typically arranged such that the north pole30and the south pole32of each magnet face the same direction as the wheel24rotates. In some example embodiments, each of the magnets22may be positioned such that the north pole30and the south pole32are approximately equidistant from the rotational axis28.

The system20also includes a single magnetic sensor34having a sensitive axis35. The magnetic sensor34is positioned to individually detect each of the north pole30and south pole32of the magnets22when the magnets22pass by the magnetic sensor34as the wheel24rotates. The magnetic sensor34is configured to produce a predetermined first characteristic signal when the north pole30is detected and a predetermined second characteristic signal when the south pole32is detected (SeeFIG. 4).

The system20also includes a processing device36in signal communication with the magnetic sensor34. In an example, the processing device36includes an amplifier38for amplifying a raw signal from the magnetic sensor34. The amplifier38is in signal communication with an analog to digital converter (ADC)40that digitizes the amplified signal from the amplifier38. The ADC40is in signal communication with a processor42that processes the digitized signal from the ADC40. A memory44is in data communication with the processor42. The processor42is configured to determine a direction of the wheel24and a distance traveled by the wheel24. The processor42is configured to determine the direction of the wheel24based on a configuration of a signal doublet that includes the first and second characteristic signals in similar fashion to that described with respect toFIG. 1. The processor42is configured to determine a displacement or distance traveled by the wheel24based on an odometer pulse count. The odometer pulse count can be taken as the leading pulse in the signal doublet, the following pulse in the signal doublet, or the center of the signal doublet. The processor42determines the number of revolutions of the wheel24based on the odometer pulse count and the number of magnets22located on the wheel24. The processor42determines the displacement based on the size (circumference) of the wheel24, the number of doublets detected, and the number of magnets22mounted on the wheel. The processing device36is in signal communication with other systems46in some embodiments. The signal communication may be wired or wireless, and the other systems46may be systems such as navigation systems or tracking systems, for example.

FIG. 3is a diagram of a system80for determining a direction of a wheeled vehicle81formed in accordance with an example embodiment of the invention. The wheeled vehicle81may be controlled by a user or may be a robotic vehicle. The wheeled vehicle81may be a shopping cart, an automobile, a golf cart, a robotic lawnmower, or a robotic vacuum cleaner, for example. The wheeled vehicle81includes a chassis82, a first wheel84rotationally coupled to the chassis82, and a second wheel86rotationally coupled to the chassis82. The first wheel84may be coupled to the chassis82with a first axle88and the second wheel86may be coupled to the chassis82with a second axle90, for example. At least one first magnet92having a north and a south pole is mounted to the first wheel84and at least one second magnet94having a north and a south pole is mounted to the second wheel86in similar fashion to that described with respect to the magnet22and the wheel24shown inFIG. 2. A first single magnetic sensor96is positioned such that the magnetic sensor96can individually detect each pole of the first magnet92as it passes by the magnetic sensor96as the first wheel84rotates. In an example embodiment, the magnetic sensor96is positioned in similar fashion to that described for the magnetic sensor35in relation to the wheel24with respect toFIG. 2. In an example, the magnetic sensor96is coupled to the chassis82. In similar fashion to the positioning of the magnetic sensor96, a second single magnetic sensor98is positioned such that the magnetic sensor98can individually detect each pole of the second magnet94as it passes by the magnetic sensor98as the second wheel86rotates. The first and second magnetic sensors96,98are each configured to produce a predetermined first characteristic signal when a north pole is detected and a predetermined second characteristic signal when a south pole is detected.

A processing device100is in signal communication with the first single magnetic sensor96and the second single magnetic sensor98. The processing device100determines a rotational direction of the first wheel84and a corresponding direction of travel of the wheeled vehicle81. In an example, the rotational direction of the first wheel84is selected from forward or reverse based on a configuration of a first signal doublet that includes the first and second characteristic signals from the first single magnetic sensor96. The processing device100determines the rotational direction of the first wheel84based on whether the first or second characteristic signal from the first single magnetic sensor96appears first in the first signal doublet, for example.

In an example embodiment, the processing device100is further configured to determine a rotational displacement of the first and second wheels84,86based on signals received from the first and second magnetic sensors96,98, respectively. The processing device100also determines a rotational direction of the second wheel86based on a configuration of a second signal doublet that includes the first and second characteristic signals from the second magnetic sensor98. The processing device100may also determine a direction of the wheeled vehicle81based on the determined rotational directions and determined rotational displacements of the first and second wheels84,86.

In one embodiment, the processing device100is also further configured to determine a displacement of the wheeled vehicle81based on the determined direction of the wheeled vehicle81and the determined rotational displacements of the first and second wheels84,86during a predetermined time period in some examples. The processing device100determines a position of the wheeled vehicle81based on an initial position, an initial heading, the determined displacement of the wheeled vehicle81, and the determined direction of the wheeled vehicle81.

In the example shown, the first wheel84and the second wheel86are rear wheels of the wheeled vehicle81and only rotate axially in relation to the chassis82. The wheeled vehicle81also includes a first front wheel140and a second front wheel142. The first front wheel140and the second front wheel142are coupled to the chassis82with a first front axle146and a second front axle148respectively. The first and second front wheels140,142rotate axially with respect to the chassis82and also may be turned with respect to the chassis82.

FIG. 4is a diagram of example signals used in determining a direction of an object such as the object12shown inFIG. 1, the wheel24shown inFIG. 2, or the wheeled vehicle81shown inFIG. 3in accordance with an embodiment of the invention.FIG. 4shows an example signal trace158, such as might be produced by a magnetic sensor such as the magnetic sensor15ofFIG. 1, the magnetic sensor34ofFIG. 2, or the magnetic sensors96,98ofFIG. 3. In the example shown, the signal trace158is a representation of a digital signal after amplification and analog to digital conversion of a raw signal produced by a magnetic sensor. However, the general shape and features of the signal trace158also reflect the characteristics of the raw analog signals produced by the magnetic sensors. The signal trace158includes a first signal doublet160that includes a first characteristic signal peak162and a second characteristic signal peak164. A signal doublet represents detection of both a magnetic north pole and a magnetic south pole in a single magnet by a magnetic sensor. The signal trace158includes some bias with a baseline that is lower than zero. The first characteristic signal peak162is a positive peak that occurs at a magnitude of approximately 4. The second characteristic signal peak164is a negative peak that occurs at a magnitude of approximately −3.9. In an example, a magnetic sensor may be oriented such that the first characteristic signal peak162corresponds to detection of a magnetic north pole at its closest distance to the magnetic sensor and the second characteristic signal peak164corresponds to detection of a magnetic south pole at its closest distance to the magnetic sensor.

In the example shown, the horizontal axis represents time, with the first characteristic signal peak162appearing before the second characteristic peak164in the first signal doublet160. This configuration of characteristic signals in a signal doublet corresponds to a first movement direction of an object where the north pole is detected by the magnetic sensor before the south pole. This may correspond to movement in the direction48shown inFIG. 2, for example. A second doublet166includes a characteristic signal peak168having a negative magnitude followed by a characteristic signal peak170having a positive magnitude. In this example, characteristic signal peaks having negative magnitudes represent detection of a south pole and characteristic signal peaks having positive magnitudes represent detection of a north pole. Although the characteristic signal peaks168,170have magnitudes below that of the second characteristic signal peak164and the first characteristic signal peak162, respectively, they are still in the form of a signal doublet with magnitudes great enough to represent detection of a south and a north pole. A predetermined signal strength threshold may be used in some examples before a characteristic signal peak is considered to represent detection of a magnetic pole. The configuration of the second signal doublet166corresponds to a second movement direction of an object where the south pole is detected by the magnetic sensor before the north pole. This may correspond to a reversal of direction from the direction48to the direction50shown inFIG. 2, for example.

The signal trace158also includes three additional signal doublets, with the first having a positive characteristic signal peak172followed by a negative characteristic signal peak174. The second additional signal doublet includes a negative characteristic signal peak176followed by a positive characteristic signal peak178and the third additional signal doublet includes a positive characteristic signal peak180followed by a negative characteristic signal peak182.

FIG. 5is a diagram showing a flowchart of a method200of determining a direction of an object in accordance with an embodiment of the invention. The object may be the object12shown inFIG. 1, the wheel24shown inFIG. 2, or the wheeled object81shown inFIG. 3, for example. First, at a block202, a first pole of a magnet mounted on an object is sensed with a single magnetic sensor. The magnet may be the magnet11shown inFIG. 1or the magnet22shown inFIG. 2, for example. The single magnetic sensor may be the magnetic sensor15or the magnetic sensor34, for example. Next, at a block204, a second pole of the magnet is sensed with the single magnetic sensor. The first pole and the second pole may be a north pole and a south pole respectively or alternatively a south pole and a north pole respectively, for example. Then, at a block206, a direction of the object is determined based on when the first and second poles were sensed. Then, at a block208, a displacement of the object is determined based on a doublet that includes the sensed first and second poles, and a previously determined known distance (linear or angular) between magnets or magnet if alone on a wheel. Next, at a block210, a position of the object is determined based on an initial object position and the determined displacement of the object.

FIG. 6is a diagram showing a flowchart of a method230of determining a direction of a wheeled vehicle in accordance with an embodiment of the invention. First, at a block232, a first pole of a first magnet mounted on a first wheel of a wheeled vehicle is sensed with a first single magnetic sensor. The first magnet may be the magnet92, the first wheel may be the first wheel84, the first single magnetic sensor may be the first single magnetic sensor96, and the wheeled vehicle may be the wheeled vehicle81shown inFIG. 3, for example. Next, at a block234, a second pole of the first magnet is sensed with the first single magnetic sensor. The first pole and the second pole of the first magnet may be a north pole and a south pole respectively or alternatively a south pole and a north pole respectively, for example. Then, at a block236, a rotational direction of the first wheel is determined based on when the first and second poles of the first magnet were sensed. Next, at a block238, a rotational displacement of the first wheel is determined based on at least one of the sensed first and second poles of the first magnet and the known distance between magnets or magnet if alone on the wheel. Determination of the rotational direction and rotational displacement of the first wheel may be performed by the processing device100, for example.

In an example embodiment, the method230also includes a series of steps that may be performed at the same time as those performed in the blocks232,234,236, and238. First, at a block240, a first pole of a second magnet mounted on a second wheel of the wheeled vehicle is sensed with a second single magnetic sensor. The second magnet may be the magnet94, the second wheel may be the second wheel86, the second single magnetic sensor may be the second single magnetic sensor98, and the wheeled vehicle may be the wheeled vehicle81shown inFIG. 3, for example. Next, at a block242, a second pole of the second magnet is sensed with the second single magnetic sensor. The first pole and the second pole of the second magnet may be a north pole and a south pole respectively or alternatively a south pole and a north pole respectively, for example. Then, at a block244, a rotational direction of the second wheel is determined based on the sensed first and second poles of the second magnet. Next, a rotational displacement of the second wheel is determined based on at least one of the sensed first and second poles of the second magnet.

In an example embodiment, the method230also includes a series of steps that use results of the steps performed in the blocks232,234,236,238and the blocks240,242,244,246. At a block248, a direction of the wheeled vehicle is determined based on the determined rotational directions of the first and second wheels and the determined rotational displacements of the first and second wheels. Then, at a block250, a displacement of the wheeled vehicle is determined based on the determined rotational directions of the first and second wheels and the determined rotational displacements of the first and second wheels. Next, at a block252, a position of the wheeled vehicle is determined based on an initial position of the wheeled vehicle and the determined displacement of the wheeled vehicle.

While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. For example, magnets may be attached to an object in a different manner than the mounting of individual magnets. A strip having multiple magnetic poles may be used, for example. Magnets may be integral to an object rather than mounted to an object, or the tracked object may be a magnet itself. Additionally, various components of the processing devices such as amplifiers and analog to digital converters may be separate components or may be integrated in the magnetic sensors rather than in the processing devices. The processing devices may be implemented using any combination of hardware and software configured to perform the processing functions. Example hardware may include microcontrollers, signal processors, field programmable gate arrays, or application specific integrated circuits. Additionally, the systems and methods may also determine the rate at which an object moves in addition to the object's displacement based on sensed magnetic poles. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.