ROTOR FOR INDUCTIVE POSITION SENSOR

An inductive position sensor subsystem is disclosed. The inductive position sensor includes a fine rotor located on a first printed circuit board, and a metallic coarse rotor including a metal support to which the first printed circuit board is coupled. The inductive position sensor also includes a fine sensor receiver and a coarse sensor receiver that generate respective pluralities of sensor signals based on the rotation of the fine rotor and the metallic coarse rotor. The fine sensor receiver and the coarse sensor receiver are located on a second printed circuit board separate from the first printed circuit board.

TECHNICAL FIELD

This disclosure is related to sensors and, more particularly, to inductive angular position sensors.

BACKGROUND

In many computer and mechanical systems, a variety of sensors may be employed to detect different environmental and operational conditions, and to generate analog or digital signals corresponding to the detected conditions. In some systems, temperature sensors may be employed to detect the temperature of a system in order to determine if the system is operating in a specified temperature range. Other systems may employ accelerometer sensors to aid in the determination of movement of the system or part of the system. In robotic systems, rotational sensors may be used to determine how far a portion of a system, e.g., a robotic arm, has rotated.

SUMMARY

Various embodiments of an inductive position sensor are disclosed. Broadly speaking, an inductive position sensor includes a fine rotor located on a first printed circuit board, and a metallic coarse rotor including a metal support to which the first printed circuit board is coupled. The inductive position sensor also includes a fine sensor receiver configured to generate a plurality of fine sensor signals based on a first rotation of the fine rotor, and a coarse sensor receiver configured to generate a plurality of coarse sensor signals based on a second rotation of the metallic coarse rotor. The fine sensor receiver and the coarse sensor receiver are located on a second printed circuit board separate from the first printed circuit board.

Many of the electrical connections in the drawings are shown as direct couplings having no intervening devices, but are not expressly stated as such in the following description. Nevertheless, this paragraph shall serve as antecedent basis in the claims for referencing any electrical connection as “directly coupled” for electrical connections shown in the drawings with no intervening device(s).

Definitions

“A,” “an,” and “the,” as used herein, refers to both singular and plural referents unless the context clearly dictates otherwise. By way of example, “a processor” programmed to perform various functions refers to one processor programmed to perform each and every function, or more than one processor collectively programmed to perform each of the various functions.

In relation to electrical devices (whether stand alone or as part of an integrated circuit), the terms “input” and “output” refer to electrical connections to the electrical devices, and shall not be read as verbs requiring action. For example, a differential amplifier (such as an operational amplifier) may have a first differential input and a second differential input, and these “inputs” define electrical connections to the operational amplifier, and shall not be read to require inputting signals to the operational amplifier.

“Controller” or “controller circuit” shall mean, alone or in combination, individual circuit components, an application specific integrated circuit (ASIC), a microcontroller with controlling software, a reduced-instruction-set computing (RISC) circuit with controlling software, a digital signal processor (DSP), a processor with controlling software, a programmable logic device (PLD), a field programmable gate array (FPGA), or a programmable system-on-a-chip (PSOC), configured to read inputs and drive outputs responsive to the inputs.

DETAILED DESCRIPTION

Various sensor circuits may be used in a variety of computer, mechanical, and electro-mechanical systems. Such sensor circuits determine and relay environmental and/or operational information that can be used as part of a control mechanism. For example, to control servo motors, robotic arms, and collaborative robots (referred to as “cobots”), multiple rotation sensors may be employed.

One type of rotation sensor that can be employed in systems is an inductive angular position sensor. In such a sensor, an excitation coil may be fabricated on a printed circuit board (“PCB”), while a rotor that is made from conductive material is connected to an object whose rotation is to be measured and rotates above the PCB and excitation coil.

When a current is driven through the excitation coil, a resultant magnetic field induces a current in the rotor. As the induced current flows in the rotor, another magnetic field is generated around the rotor which, in turn, induces respective currents or voltages in one or more receiver coils (referred to as “stators”) that are also fabricated on the PCB.

The coupling of the magnetic field of the rotor into the one or more stators is a function of the angular position of the rotor to the stators. By measuring the voltage polarity and the voltage amplitude induced in the stators, the angle of the rotor relative to the stators can be determined.

In cases where two stators are employed, each with a different rotational symmetry over the measurement range, the signals from the two stators resolve to a unique angular position of the rotor provided that the only common factor between the rotational symmetries is 1 (referred to as being “co-prime” or “relatively prime”). While such an arrangement of a rotor and stators is relatively immune to rotor eccentricity (i.e., the center of rotation is not above the center of the stator) and rotor tilt (i.e., the axis of rotation is not perpendicular to the plane of the stator), error can result from a lateral movement and tilt of the rotor.

Rotors can be fabricated on a single-layer printed circuit board or made from a machined piece of metal that matches the receiver coil's geometry. Such rotors may be rigid and firmly attached to a shaft that is attached to an object being rotated, where the shaft is perpendicular to the stator.

Machined rotors that meet the mounting requirements cannot be machined to match the fine geometries used in Vernier sensor coils. Rotors fabricated on printed circuit boards can be made with the fine geometries for Vernier sensor coils, but mounting such rotors can prove difficult, as any piece of overlapping metal can result in a short circuit, which can decrease the sensor signals.

The embodiments described herein may provide techniques for implementing a sensor that uses a hybrid rotor solution that employs a combination of a metallic coarse rotor and a printed circuit board based fine rotor. Such a combination enables the metallic coarse rotor to support the fine rotor, thereby enabling the fine rotor to be positioned close to the stator in order to increase signal amplitudes while decreasing harmonic distortion.

A block diagram of a sensor subsystem is depicted inFIG.1. As illustrated, sensor subsystem100includes sensor101and interface circuit102. In various embodiments, sensor101includes stator assembly103and rotor assembly104. As described below, stator assembly103includes fine sensor receiver111and coarse sensor receiver112, while rotor assembly104includes fine rotor109and metallic coarse rotor110.

In various embodiments, fine rotor109is located on a particular printed circuit board. Metallic coarse rotor110is coupled to the particular printed circuit board. For example, the metallic coarse rotor110may be a machined-metal rotor that supports the printed circuit board of the fine rotor109. In some embodiments, the thickness of fine rotor109may be on the order of 1 mm, while the thickness of metallic coarse rotor110may be in excess of 5 mm. Accordingly, metallic coarse rotor110may be at least five times as thick as fine rotor109. As described below, metallic coarse rotor110may be coupled to the particular printed circuit board using any suitable combination of screws, rivets, bolts, and adhesives.

Fine sensor receiver111is configured to generate fine sensor signals105based on a rotation of fine rotor109. In a similar fashion, coarse sensor receiver112is configured to generate coarse sensor signals106based on a rotation of metallic coarse rotor110. In various embodiments, fine sensor receiver111and coarse sensor receiver112are located on a different printed circuit board separate from the particular printed circuit board. It is noted that, in various embodiments, fine sensor signals105and coarse sensor signals106can each include at least two sensor signals. The use of multiple fine and coarse sensor signals can, in some embodiments, allow for a more accurate determination of a rotation angle.

In various embodiments, interface circuit102is configured to generate output angle value107using fine sensor signals105and coarse sensor signals106. In some cases, to generate output angle value107, interface circuit102is further configured to perform one or more analog-to-digital conversion operations on fine sensor signals105and coarse sensor signals106. In some embodiments, interface circuit102is also configured to generate excitation current108, which may be applied to an excitation coil in stator assembly103.

Turning toFIG.2, an exploded perspective view of rotor assembly104is depicted. As illustrated, rotor assembly104includes fine rotor109and metallic coarse rotor110. In various embodiments, fine rotor109is fabricated on printed circuit board203(denoted as “PCB203”).

Fine rotor109may, in various embodiments, be fabricated on PCB203using copper or any other suitable material. PCB203may include multiple instances of mounting hole206that can be used to couple PCB203to metallic coarse rotor110. By fabricating fine rotor109on PCB203, a fine structure can be achieved to enable high resolution in measuring rotation. As described below, with the support provided by metallic coarse rotor110, PCB203may be located close enough to stator assembly103to improve signal amplitude of fine sensor signals105while reducing harmonic distortion.

Metallic coarse rotor110includes multiple instances of mounting hole207, which are used to couple metallic coarse rotor110to corresponding instances of mounting hole206on PCB203using one or more of screw204. Alternatively, or additionally, metallic coarse rotor110may be attached to PCB203using adhesive210. In various embodiments, adhesive210may be thermally and/or electrically conductive. Although adhesive210is depicted as surrounding shaft opening209, in other embodiments, adhesive210may be used in any suitable location on metallic coarse rotor110that can be attached to PCB203.

Metallic coarse rotor110further includes shaft opening209. In various embodiments, a diameter of shaft opening209may be based, at least in part, on a diameter of a shaft (not pictured) connected to an object whose rotation is to be sensed. In various embodiments, metallic coarse rotor110is attached to the shaft by inserting screw205into mounting hole208until it makes contact with the shaft. Although the embodiment ofFIG.2depicts the use of screw204and screw205, in other embodiments, screws204and205may be replaced with any suitable combination of rivets, bolts, adhesives, or other suitable coupling hardware.

Turning toFIG.3, a top view of an embodiment of stator assembly103is depicted. As illustrated, stator assembly103includes excitation coil301, and receiver coils302-305. In various embodiments, receiver coils302and303form a fine sensor receiver that is configured to generate fine sensor signals105, while receiver coils304and305form a coarse sensor receiver that is configured to generate coarse sensor signals106.

Excitation coil301is fabricated (or “printed”) on a printed circuit board or “PCB” (not shown). In various embodiments, excitation coil301is fabricated using copper or any other suitable material that can be printed on a PCB. Although excitation coil301is depicted as a single trace, in other embodiments, excitation coil301may include multiple concentric traces.

Receiver coils302-305are also fabricated from a conductive material on the PCB. In various embodiments, receiver coils302and303have different geometries than receiver coils304and305. In some cases, receiver coils302and303may have more loops away from the center to increase resolution relative to receiver coils304and305. Although only two receiver coils are depicted for each of the fine and coarse sensor receivers in the embodiment ofFIG.3, in other embodiments, any suitable number of receiver coils may be employed for the fine and coarse sensor receivers.

To measure the rotation, interface circuit102is configured to apply an alternating current signal to excitation coil301. As the alternating current flows in excitation coil301, a magnetic field is generated around excitation coil301. In various embodiments, the coupling from excitation coil301to fine rotor109and coarse rotor110is independent of the angular position of fine rotor109and110, but is a function of a distance between excitation coil301and fine rotor109and coarse rotor110.

The magnetic field generated by excitation coil301induces currents in fine rotor109and coarse rotor110, which, in turn, generates a magnetic field around fine rotor109and coarse rotor110. The respective magnetic fields generated by the induced current in fine rotor109and coarse rotor110superimpose to form a composite magnetic field which couples into receiver coils302-305. The coupling from a given rotor to a given receiver coil is a function of both the distance between the given rotor and the given receiver coil, as well as the angular position of the given rotor and the given receiver coil. It is noted, however, that since fine rotor109has a different rotational symmetry than receiver coils304and305, there is minimal coupling between fine rotor109and receiver coils304and305. In a similar fashion, since coarse rotor110has a different rotational symmetry than receiver coils302and303, there is minimal coupling between coarse rotor110and receiver coils302and303.

The magnetic field generated by fine rotor109induces respective currents or voltages in both receiver coils302and303, while coarse rotor110induces respective currents or voltages in both receiver coils304and305. As described below, interface circuit102is configured to measure the polarity and amplitude of the respective voltages of receiver coils302-305. Using the polarity and amplitude measurements, interface circuit102is further configured to determine output angle value107. As described above, a number of periods in the signals of receiver coils302and303can depend on the geometry of receiver coils302and303, while a number of periods in the signals of receiver coils304and305can depend on the geometry of receiver coils304and305. In various embodiments, receiver coils302and303may generate fine sensor signals105, while receiver coils304and305may generate coarse sensor signals106.

Turning toFIG.4, a cross-section diagram of an embodiment of a sensor is depicted. As illustrated, sensor400includes rotor PCB401, stator PCB402, and coarse rotor403. In various embodiments, sensor400may correspond to sensor101as depicted inFIG.1.

Coarse rotor403may, in various embodiments, correspond to coarse rotor110as depicted in the embodiment ofFIG.2. As described above, coarse rotor403may be coupled to side413of rotor PCB401using one or more screws, rivets, bolts, or any suitable adhesive. In some embodiments, coarse rotor403includes ring base409(also referred to as a “support”). In such cases, ring base409may be coupled, via one or more screws, rivets, or bolts, to a shaft that is attached to an object subject to rotation. Coarse rotor403and ring base409may be fabricated using any suitable metallic material.

Rotor PCB401includes fine rotor404. In various embodiments, fine rotor404is located on side412of rotor PCB401. Side412may, in some embodiments, be opposite side413of rotor PCB401. In various embodiments, fine rotor404may be fabricated using copper or any other suitable material that can be printed on rotor PCB401.

Coarse sensor405and fine sensor406are located on side411of stator PCB402. In various embodiments, coarse sensor405and fine sensor406may have different rotational symmetries. In some embodiments, coarse sensor405and fine sensor406may be fabricated using copper or any other suitable material that can be printed on stator PCB402.

In various embodiments, rotor PCB401and stator PCB402are positioned relative to each other such that fine rotor404is separated from fine sensor406by fine air gap407. Such a position also results in coarse rotor403being separated from coarse sensor405by coarse air gap408. It is noted that, in this arrangement, fine air gap407is less than coarse air gap408. In some cases, optional washer410can be included between coarse rotor403and rotor PCB401to increase the size of coarse air gap408. In various embodiments, optional washer410can be fabricated from any suitable non-conductive material.

In some cases, the coarse rotor403can also be included on the same printed circuit board as the fine rotor404. By including the fine and coarse rotors on the same printed circuit, the spacing between the rotors and their corresponding receiver coils can be adjusted by changing which sides of the printed circuit boards the different rotors and receiver coils are located.

A cross-section diagram of an embodiment of a sensor that includes two printed circuit boards is depicted inFIG.5. As illustrated, sensor500includes rotor PCB501and stator PCB502. Rotor PCB501includes coarse rotor503and fine rotor504, while stator PCB502includes coarse sensor505and fine sensor506. In various embodiments, sensor500may correspond to sensor101as depicted inFIG.1.

Coarse rotor503is located on side509of rotor PCB501, while fine rotor504is located on side510of rotor PCB501. As depicted, side510of rotor PCB501is opposite side509of rotor PCB501. In various embodiments, coarse rotor503and fine rotor504are fabricated using copper or any other suitable material that can be printed on rotor PCB501. In some embodiments, coarse rotor503and fine rotor504may have different rotational symmetries.

Coarse sensor505and fine sensor506are located on side511of stator PCB502. In various embodiments, coarse sensor505and fine sensor506may have different rotational symmetries. In some embodiments, coarse sensor505and fine sensor506may be fabricated using copper or any other suitable material that can be printed on stator PCB502.

In various embodiments, rotor PCB501and stator PCB502are positioned relative to each other such that fine rotor504is separated from fine sensor506by fine air gap507. Such a position also results in coarse rotor503being separated from coarse sensor505by coarse air gap508. It is noted that, in this arrangement, fine air gap507is less than coarse air gap508, which increases the coupling between fine rotor504and fine sensor506.

Turning toFIG.6, a cross-section of a different embodiment of a sensor is depicted. As illustrated, sensor600includes rotor PCB601and stator PCB602. Rotor PCB601includes coarse rotor603and fine rotor604, while stator PCB602includes coarse sensor605and fine sensor606. In various embodiments, sensor600may correspond to sensor101as depicted inFIG.1.

Coarse rotor603is located on side609of rotor PCB601, while fine rotor604is located on side610of rotor PCB601. As depicted, side610is on an opposite side of rotor PCB601than side609. In various embodiments, coarse rotor603and fine rotor604are fabricated using copper or any other suitable material that can be printed on rotor PCB601. In some embodiments, coarse rotor603and fine rotor604may have different rotational symmetries.

Fine sensor606is located on side611of stator PCB602, while coarse sensor605is located on side612of stator PCB602. As depicted, side611is on an opposite side of stator PCB602than side612. In various embodiments, coarse sensor605and fine sensor606may have different rotational symmetries. In some embodiments, coarse sensor605and fine sensor606may be fabricated using copper or any other suitable material that can be printed on stator PCB602.

In various embodiments, rotor PCB601and stator PCB602are positioned relative to each other such that fine rotor604is separated from fine sensor606by fine air gap607. Such a position also results in coarse rotor603being separated from coarse sensor605by coarse air gap608. It is noted that, in this arrangement, fine air gap607is less than coarse air gap608.

Turning toFIG.7, a cross-section of a different embodiment of a sensor is depicted. As illustrated, sensor700includes rotor PCB701and stator PCB702. Rotor PCB701includes coarse rotor703and fine rotor704, while stator PCB702includes coarse sensor705and fine sensor706. In various embodiments, sensor700may correspond to sensor101as depicted inFIG.1.

Coarse rotor703and fine rotor704are located on side709of rotor PCB701. In various embodiments, coarse rotor703and fine rotor704are fabricated using copper or any other suitable material that can be printed on rotor PCB701. In some embodiments, coarse rotor703and fine rotor704may have different rotational symmetries.

Fine sensor706is located on side710of stator PCB702, while coarse sensor705is located on side711of stator PCB702. As depicted, side710is on an opposite side of stator PCB702than side711. In various embodiments, coarse sensor705and fine sensor706may have different rotational symmetries. In some embodiments, coarse sensor705and fine sensor706may be fabricated using copper or any other suitable material that can be printed on stator PCB702.

In various embodiments, rotor PCB701and stator PCB702are positioned relative to each other such that fine rotor704is separated from fine sensor706by fine air gap707. Such a position also results in coarse rotor703being separated from coarse sensor705by coarse air gap708. It is noted that, in this arrangement, fine air gap707is less than coarse air gap708.

Turning toFIG.8, a top-view of an embodiment of a printed circuit board rotor assembly is depicted. As illustrated, rotor printed circuit board800(denoted “Rotor PCB800”) includes fine coil801to form a fine rotor, and coarse coil802to form a coarse rotor. In various embodiments, rotor PCB800may correspond to any of rotor PCB501, rotor PCB601, or rotor PCB701as depicted inFIGS.5,6, and7, respectively.

In various embodiments, fine coil801and coarse coil802may be fabricated on a common side of rotor PCB800. Alternatively, fine coil801and coarse coil802may be fabricated on opposite sides of rotor PCB800. In some embodiments, fine coil801and coarse coil802may be implemented using copper or any other suitable metal available in a printed circuit board manufacturing process.

As illustrated fine coil801has a higher count per revolution than coarse coil802. In various embodiments, the respective counts per revolution of fine coil801and coarse coil802may be based on a physical size of a rotational sensor, a desired level of accuracy for the rotational sensor, or any other suitable characteristic of the rotational sensor. In some cases, the count per revolution of fine coil801may typically be higher than 10, with values such as 16, 32, or higher, being common. In contrast, the count per revolution of coarse coil802may typically be less than 10, with values such as 3 or 5 being common.

Turning toFIG.9, a flow diagram depicting an embodiment of a method for operating a sensor subsystem is illustrated. The method, which may be applied to various sensor subsystems, e.g., sensor subsystem100, begins in block901.

The method includes generating, by a fine sensor receiver, a plurality of fine sensor signals based on rotating a fine rotor included on a first printed circuit board (block902). In various embodiments, the fine sensor receiver may include a plurality of first coils fabricated from a conductive material on the first printed circuit board.

The method also includes generating, by a coarse sensor receiver, a plurality of coarse sensor signals based on rotating a metallic coarse rotor coupled to the first printed circuit board (block903). In various embodiments, the coarse sensor receiver may include a plurality of second coils fabricated from the conductive material on the first printed circuit board. The rotational symmetry of the fine sensor receiver is different than the rotational symmetry of the coarse sensor receiver, such that the fine sensor receiver can measure the rotation of the fine rotor with a higher resolution than the coarse sensor receiver can measure the rotation of the metallic coarse rotor.

In various embodiments, the metallic coarse rotor is coupled to the first printed circuit board using at least one screw. In other embodiments, the metallic coarse rotor is coupled to the first printed circuit board using glue or any other suitable adhesive. In some embodiments, the metallic coarse rotor is coupled to the first printed circuit board via an insulating washer.

In various embodiments, the fine sensor receiver and the coarse sensor receiver are located on a second printed circuit board separate from the first printed circuit board. In some cases, the fine sensor receiver and the coarse sensor receiver are located on a common side of the second printed circuit board. In some embodiments, a first distance between the first printed circuit board and the second printed circuit board is less than a second distance between the metallic coarse rotor and the second printed circuit board.

The method further includes generating, by an interface circuit, an output angle value using the plurality of fine sensor signals and the plurality of coarse sensor signals (block904). In various embodiments, generating the output angle value includes performing a plurality of analog-to-digital conversion operations on the plurality of fine sensor signals and the plurality of coarse sensor signals. The method concludes in block905.

Turning toFIG.10, a flow diagram depicting an embodiment of a method for operating a sensor subsystem with fine and coarse rotors on a common printed circuit board is illustrated. The method, which may be applied to various sensor subsystem, e.g., sensor subsystem100, begins in block1001.

The method includes generating, by a fine sensor receiver, a plurality of fine sensor signals based on rotating a fine rotor included on a first printed circuit board (block1002). In various embodiments, the fine sensor receiver is included on a second printed circuit board separate from the first printed circuit board.

The method also includes generating, by a coarse sensor receiver, a plurality of coarse sensor signals based on rotating a coarse rotor included on the first printed circuit board (block1003). In various embodiments, the coarse sensor receiver is included on the second printed circuit board.

As described above, the fine rotor includes a fine coil, and the coarse rotor includes a coarse coil. In some embodiments, a first count per revolution of the fine coil may, in some embodiments, be greater than a second count per revolution of the coarse coil.

In some embodiments, the fine rotor is located on a first side of the first printed circuit board, and the coarse rotor is located on a second side of the first printed circuit board opposite the first side. In various embodiments, the fine sensor receiver and the coarse sensor receiver are located on a common side of the second printed circuit board. In other embodiments, the fine sensor receiver is located on a first side of the second printed circuit board, and the coarse sensor receiver is located on a second side of the second printed circuit board opposite the first side. In some cases, a first distance between the first side of the second printed circuit board and the first printed circuit board is less than a second distance between the second side of the second printed circuit board and the first printed circuit board.

The method further includes generating, by an interface circuit, an output angle value using the plurality of fine sensor signals and the plurality of coarse sensor signals (block1004). In various embodiments, generating the output angle value includes performing a plurality of analog-to-digital conversion operations on the plurality of fine sensor signals and the plurality of coarse sensor signals. The method concludes in block1005.

Turning toFIG.11, a block diagram of a system configured to control rotation of a portion of a mechanical device is depicted. As illustrated, system1100includes control circuit1101and mechanical device1102, which includes sensor subsystem100. In various embodiments, system1100may be used as part of a servo motor control mechanism, a robotic limb control mechanism, a cobot control mechanism, or any other suitable control mechanism.

Control circuit1101is configured to receive input signal1103. In various embodiments, input signal1103may be either a digital or analog circuit whose value indicates an amount to rotate all or a portion of mechanical device1102. In various embodiments, control circuit1101may be configured to generate control signal1104using input signal1103.

In response to receiving control signal1104, mechanical device1102may be configured to rotate at least a portion of itself, e.g., a robotic limb. For example, mechanical device1102may be configured to activate a motor in response to an activation of control signal1104. The motor may then cause a portion of mechanical device1102to rotate while control signal1104is active.

As described above, sensor subsystem100is configured to generate rotation angle1105based on the rotation of the portion of mechanical device1102. In various embodiments, rotation angle1105may be a word of digital data including any suitable number of bits to achieve a desired resolution of rotation angle1105.

Control circuit1101may be further configured to deactivate control signal1104based on rotation angle1105. In various embodiments, control circuit1101may be configured to compare rotation angle1105to a desired rotation angle. In response to a determination that rotation angle1105is within a threshold value of the desired rotation angle, control circuit1101may deactivate control signal1104. Control circuit1101may be implemented using a controller.

The present disclosure includes references to “an embodiment” or groups of “embodiments.” As used herein, embodiments are different implementations of instances of the disclosed concepts. References to “an embodiment,” “some embodiments,” and the like do not necessarily refer to the same embodiment. Many embodiments are possible and contemplated, including those specifically disclosed as well as modifications or alternatives that fall within the spirit or scope of the disclosure.

The above disclosure is meant to illustrate some of the principles and various embodiments of the disclosed concepts. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.