Patent Application
20160290833
The invention relates generally to a position sensor, and more particularly to a contactless sensor for determining a presence and/or relative position of a target structure in a proximity to the sensor.
Position sensors, such as brushes, slip rings, or wire conductors, often employ contacts to indicate the position of a movable member. The elimination of contacts is desirable and can reduce electrical noise and disturbances caused by sliding electric contact. The contactless sensors maintain a gap between the sensor and a target structure. It can be challenging to maintain the sensing range in the presence of such a physical gap.
Examples of contactless sensors include capacitance-based position sensors, laser-based position sensors, eddy-current sensing position sensors, and linear displacement transducer-based position sensors. While each type of position sensor has its advantages, each type of the sensor may be best suited for a particular application. For example, the size of capacitors can make the sensor impractical when the position sensor must be small in size. The optical sensor can fail in the presence of dirt or grease. Magnetic sensors require precision housings and mechanical assembly to avoid errors caused by magnet or sensor misalignment, which can be difficult in some applications. In addition, in some applications, the size of the gap between the sensor and the target structure can change with time, and the location of the target structure can cause problems to the accuracy of some linear position sensors.
Accordingly, there is a need for a contactless sensor for determining a presence and/or relative position of a target structure arranged at a different distances from the sensor.
Some embodiments of the invention are based on recognition that the magnetic flux of an electromagnetic near field used during inductive coupling is sensitive to any variations in the electromagnetic near-field. The variations in the electromagnetic near-field caused by the changes of the magnetic flux that can be detected by, e.g., by measuring the voltage of across the coil caused by the current induced by the magnetic flux via inductive coupling.
Some embodiments of the invention are based on realization that a presence of an external electromagnetic structure moving within the electromagnetic near-field disturbs the magnetic field and thus can be detected based on the changes in the measurements of the voltage. For example, the resonant coupling of the target structure that changes the shape of the magnetic near-field, which in turn changes the current in the connected coils generated by that near-filed. Moreover, the effect of such a presence is affects the entire near-filed making such detection less sensitive to the distance between the source generating the near-field and the target structure. In such a manner, the presence of the target structure within the near field, even at a relatively great distance from the source, can be detected.
Moreover, if the magnetic flux induces current over multiple connected coils, then the magnitude and/or differences between the voltages of different coils are indicative of the relative position of the target structure within the near field. For example, a trajectory of potential movement of the target structure can be sampled to determine a combination of voltages of the connected coils corresponding to specific position of the target structure on the trajectory.
Accordingly, one embodiment discloses a sensor including a source including an electromagnetic structure generating an electromagnetic near-filed upon receiving energy; a detecting unit including at least one coil arranged in proximity to the source such that the electromagnetic near-filed induces, via an inductive coupling, a current passing through the coil; a measuring unit for measuring a voltage across the coil; and a processor for detecting a presence of a target structure in proximity to the source upon detecting a change in a value of the voltage, wherein the target structure is an electromagnetic structure moving at a distance from the source.
Another embodiment discloses a sensor including a source including an electromagnetic structure; a power source for supplying a power signal with the resonance frequency to the electromagnetic structure to generate a magnetic near-filed around the electromagnetic structure; a detecting unit including connected coils arranged in proximity to the source such that the magnetic near-filed induces a current passing through the connected coils via an inductive coupling, wherein connected coils includes a first coil and a second coil; a measurement unit for measuring voltages across each connected coils including a first voltage measured across the first coils and a second voltage measured across the second coil; and a processor for comparing the first voltage and the second voltage and for determining a relative position of a target structure with respect to the source or with respect to the pair of connected coils based on a difference between the first and the second voltages.
Some embodiments of the invention are based on realization that a presence of external electromagnetic structure, such as a target structure 160 moving within the electromagnetic near-field disturbs the magnetic field and thus can be detected based on the changes in the measurements of the voltage. For example, the resonant coupling of the target structure that changes the shape of the magnetic near-field, which in turn changes the current in the connected coils generated by that near-filed. Moreover, the effect of such a presence is felt within the entire near-filed making such detection less sensitive to the distance between the source generating the near-field and the target structure. In such a manner, the presence of the target structure within the near field even at a relatively great distance from the source can be detected.
Accordingly, the presence 140 or absence 150 of the target structure 160 in proximity to the source 110 can be determined, using a processor 170, based on detecting 145 or not detecting 155 a change 135 in a value of the voltage.
The sensor includes source including a source structure 230 and a detecting unit including a detecting structure 240. The source structure is an electromagnetic structure generating an electromagnetic near-filed upon receiving energy. For example, the source structure is an electric current carrying coil. The detecting structure is at least one coil arranged. In some embodiments, the detecting structure includes a pair or more of connected coils.
The source structure 230 is inductively coupled 235 with the detecting structure 240 and can be integrated onto one dielectric substrate, such that the relative position of the source and detecting structures is fixed. The source structure can be fed by a radio frequency power source 270. For example, in one embodiment, the power source 270 can supply the energy to the source via a power signal having the same resonance frequency as the target structure. In this embodiment, the target structure can be resonantly coupled 223 to the source structure.
Upon receiving the energy, the magnetic flux passes through each coil of the detecting structure and generates an induced voltage across each coil. The induced voltages of the coil pair are recorded by a measurement unit 250. The voltage information is submitted to a processing unit 260 and the magnitudes of the voltages and/or the difference of the voltages is used to determine the position 280 of the target structure.
For example, when the source structure receives an alternating current, a magnetic near field is generated in the vicinity of the source structure. When the detecting structure is in the vicinity of the source structure, the magnetic flux passes through the coils of the detecting structure and the induced voltage is generated at each coil. When the detecting structure is arranged such that the same amount of the magnetic flux passes through each coil, the induced voltages across each coils are the same. For example, if the connected coils include a first coil and a second coil, a difference between a first voltage across the first coils and a second voltage across the second coil is zero.
When a target structure is placed in the near field of the source structure, the resonance of target structure can be excited, and the magnetic field is coupled to the target structure. Current is induced in the target structure, which generates an induced magnetic field. Due to the resonance in target structure, the induced magnetic field can cause disruption in the overall magnetic flux going through each of the detecting coil. Depending on the relative position of the target structure to the sensing structure, the change in the magnetic flux distribution caused by the target structure is different and the induced voltage at each detecting coil is different. The difference in induced voltage can then be used as an indication of the position of target structure.
For example, if a center of the target structure is aligned with the center of the detecting structure, then the effect of the magnetic flux generated by the target structure to each coil is the same, thus the induced voltages are still the same and the differential voltage is zero. When there is an offset between the center of target structure and that of the detecting structure, the effect of magnetic flux generated by the target structure is asymmetric on the two detecting coils resulting in a non-zero differential voltage. In general, the larger is the offset, the larger the differential voltage. The relationship between a differential voltage value and corresponding relative position can be determined, e.g., by experiment data, which can be stored in a memory 290 operatively connected to a processor of the processing unit. A measured differential voltage value is sent to the processing unit, which then maps this value to the corresponding position information.
The sensor continuously measures 340 new values of V1, V2, and ΔV, which are sent to the processing unit for comparison with stored reference values. If there is no change detected, then there is no target structure in range 390. If there is change in measured values 350, then these values are analyzed by the processing unit. If both V1 and V2 are changed, but the new differential voltage ΔV′ is still the same ΔV 360, then the target structure is aligned with the sensing structure, and is at zero position. If the new differential voltage value ΔV′ is different than ΔV, then the target structure is in range of the sensor, and is not aligned with zero position 370. The position information is then determined by the processing unit using pre-stored relationship between differential voltage and position.
Some embodiments of the invention are based on realization that when the magnetic flux induces current through multiple connected coils, the magnitude and/or differences between the voltages of different coils are indicative of the relative position of the target structure within the near field. For example, a trajectory of potential movement of the target structure can be sampled to determine a combination of voltages of the connected coils corresponding to specific position of the target structure on the trajectory. Accordingly, some embodiments of the invention determine a mapping between information indicative of different combination of the values of the voltages across the coils of the detecting unit a relative position of the target structure.
For example, in one embodiment, the detecting unit includes a pair of connected coils including a first coil and a second coil. The measurement unit measures a difference between a first voltage across the first coils and a second voltage across the second coil, and wherein the processor determines a relative position of the target structure with respect to the source based on the value of the voltage. In some implementations, the resonant structure moves according to a trajectory in a plane parallel to the electromagnetic structure of the source, and the memory 290 stores a mapping between a set of positions of the target structure on the trajectory and a set of values of the measured voltages.
In another embodiment, the measurement unit measures the voltage across each connected coils including a first voltage measured across the first coils and a second voltage measured across the second coil. In one implementation of this embodiment, the memory stores a mapping between a set of positions of the target structure on the trajectory and a set of corresponding differences between the first and the second voltages. In alternative implementation, the memory a mapping 410 between a set of different relative positions 440 of the target structure and a set of corresponding pairs of values of the first 410 and the second 420 voltages.
An advantage of using differential measurements is the tolerance to the change in gap between target structure and sensing structure. As the effect of the magnetic flux on the induced voltage of the two detecting coils is the same even with different gap sizes. The induced voltages V1 and V2 changes simultaneously, and the differential voltage V1−V2 is maintained the same. Such sensors can be used as a position switch, in which case just the zero point is detected by the sensor based on zero differential voltage, or a linear position sensor, in which case the linear position around the zero point is detected by the change in differential voltage. An advantage of using resonant structures coupled to the sensing structure is that the range can be much larger than conventional inductive coupling, such that greater gap size between target structure and sensing structure is allowed.
In some embodiments of the invention, the target structure is resonant at operating frequency. Various embodiments design the target structure with high quality factor to extend the sensing range. The resonant target structure can also take many different forms to be implemented at printed circuit boards or as stranded or Litz wires.
The sensors can also be used as part of a larger sensor. For example, multiple resonant structures can form target structure, which can serve as a marker of positions or a linear scale. The sensing structure formed by the source and detecting structures can also include multiple pairs of differential coils. In this case, multiple output channels can extend linear sensing range or form a linear encoder.
In those embodiments, the resonant structures can be of the same or different designs, and can have the same or different resonant frequencies. The induced magnetic field on the target structure is different at different positions, and impacts the induced voltages differently. Thus the target structure serves as a scale corresponding to different positions, and can be utilized by the sensor to determine the position information. The three measurement channels can determine the position of the target structure independently. Thus the additional channels can serve as redundancy as the first channel. In case there is an object in the vicinity of one channel and impacting the measurement, the redundant channels help obtain the correct position information. Because the relative positions between the three measurement channels are known, the multiple channels can also work together and serve as part of a linear encoder.
The above-described embodiments of the present invention can be implemented in any of numerous ways. For example, the embodiments may be implemented using hardware, software or a combination thereof. Use of ordinal terms such as “first,” “second,” in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.
Although the invention has been described with reference to certain preferred embodiments, it is to be understood that various other adaptations and modifications can be made within the spirit and scope of the invention. Therefore, it is the object of the append claims to cover all such variations and modifications as come within the true spirit and scope of the invention.
