Patent Application
20210270593
The field of the present invention is angular position sensors and encoders (also known as rotary encoders or shaft encoders or angle transducers) and in particular—such sensors and encoders that utilize capacitive (or electrostatic) coupling and are therefore termed capacitive angular position sensors and encoders.
Capacitive angular position sensors (CAPS for short) serve to continuously measure the absolute angular position of a rotary body in a variety of electro-mechanical devices and systems. They utilize capacitive- or electrostatic coupling between electrodes on mutually adjacent discs that varies with the position to be sensed. Various structures and arrangements of such sensors are known. For example, U.S. Pat. No. 6,492,911 to the present applicant, incorporated herein by reference, discloses a capacitive angular position sensor (also termed motion encoder) that comprises at least one stationary disc (also referred to as stator), connected to a stationary part of a device and a rotary disc (also referred to as rotor), connected to the rotary body in the device; all the discs are disposed parallel and in close proximity to each other. One face of a first stationary disc includes electrodes plated thereon in a certain pattern, to serve as excitation (or transmitting) electrodes; the same face or a face of a second stationary disc also includes one or more electrodes plated thereon, to serve as receiving (or collection) electrodes. One or both faces of the rotary disc include one or more electrodes, termed transfer- or reflecting electrodes, formed thereon in another pattern. Alternating voltage signals (excitation signals) applied to the excitation electrodes induce corresponding charges in electrodes on the rotary disc, which, in turn, induce corresponding charges in the receiving electrodes; the latter charges are converted into corresponding received voltage signals by electronic circuitry coupled to the receiving electrodes. The electronic circuitry is designed so that the received signals are proportional to the effective capacitance between excitation electrodes and receiving electrodes (which results from the series combination of the capacitance between the rotary electrodes and, on the one hand, the corresponding excitation electrodes and, on the other hand, the corresponding receiving electrodes). The patterns of the various electrodes are designed so that the effective capacitance presented to each transmitted signal (and thus also the amplitude of the corresponding received signal) is related to the angular position of the rotary disc.
The structure and design of the various instances of CAPS offered commercially or proposed in the literature differ from one another, inter alia, in the number and nature of the excitation signals and in the patterns of the excitation electrodes and of the transfer electrodes. These relate mainly to the degree of resolution of the angular position, as well as to efficient use of space within the sensor.
It is noted that the output of the electronic circuitry is usually one or more voltages whose values are analogous to the angular position of the body. Therefore the name of apparatus that is the subject of the present invention includes the term “sensor”. Since, however, such apparatus may include additional circuitry that converts these voltages into digital signals, its name may include the term “encoder”. In what follows, the term “angular position sensor” will be used comprehensively, regardless of whether the output values are in analog or digital format.
It is further noted that, while the above example and the description to follow relate to angular position, the present invention is equally applicable, with obvious minor modifications, also to capacitive linear sensors and encoders, utilized to measure the linear position of a body along a given axis.
A problem frequently arising in the deployment of a capacitive position sensor is that ambient electric fields, such as emanate from the equipment to which it is coupled or from an adjacent motor or other apparatus, induce interfering signals in the electrodes of the sensor and, in particular, in the receiving electrodes. A major conduit for interfering fields may be the shaft through which the rotor is coupled to the rotary body. Such interfering signals combine in the electronic circuitry with the position-related signals and thus act to reduce the sensitivity, resolution and/or accuracy of the sensing process and to introduce errors into the output position values.
There is provided, according to various embodiments of the invention, a capacitive angular position sensor for sensing an angular position between a rotary body and a stationary body, including a stationary disk, connected to the stationary body, and a rotary disk, connected to the rotary body,
the disks disposed parallel to each other and each having, on one of its faces, a patterned conductive layer,
wherein the conductive layer on the stationary disk includes—a plurality of first electrodes, each capacitively coupled to at least a portion of the conductive layer on the rotary disk, the capacitive coupling being variable with the angular position,
a second electrode, formed as a ring and capacitively coupled with at least a portion of the conductive layer on the rotary disk and
a third electrode, formed as a ring and disposed so as to have capacitive coupling with the conductive layer on the rotary disk, the capacitive coupling being significantly lower than the capacitive coupling between the second electrode and the conductive layer on the rotary disk.
In some embodiments the angular position sensor further includes electronic circuitry, connected to the second electrode and to the third electrode and is operative to receive signals electrically induced in the second electrode and in the third electrode, to amplify the signals and to subtract the amplified signal received from the third electrode from the amplified signal received from the second electrode.
In some of the embodiments the electronic circuitry is configured to enable adjusting the amplification factor of at least one of the signals so that any noise component in the results of the subtraction is reduced to an attainable minimum value and operative to process the results of the subtraction to yield corresponding angular position values.
In some embodiments the stationary disk is formed with a central hole and the rotary disc is mechanically coupled to a rotary shaft, which passes through the hole. In some of the embodiments the third electrode is nearer the center of the stationary disk than the first and second electrodes. The second electrode may be formed as a ring, interposed between the first electrode and the third electrode. The third electrode may be formed, at least in part, as plating on a rim of the hole.
There is also provided, according to other embodiments of the invention, a capacitive angular position sensor for sensing or encoding an angular position between a rotary body and a stationary body, including a first and second stationary disk, disposed parallel to each other and connected to the stationary body, and a rotary disk, disposed between the stationary disks and connected to the rotary body, each of the stationary disks having a patterned conductive layer on one of its faces, the conductive layers on the first and second stationary disks facing each other, wherein the conductive layer on the second stationary disk includes—one or more first electrodes, capacitively coupled with the conductive layer on the first stationary disk through the rotary disk, the coupling capacitance being variable with the angular position, and
a second electrode, formed as a ring and disposed so as to have capacitive coupling with the conductive layer on the first stationary disk that is significantly lower than any capacitive coupling between the first electrodes and the conductive layer on the first stationary disk.
In some embodiments the angular position sensor further includes electronic circuitry, connected to the first and second electrodes on the second stationary disk and operative to receive signals electrically induced in the first electrode and the second electrode, to amplify the signals and to subtract the amplified signal received from the second electrode from the amplified signal received from any of the receiving electrodes.
In some of the embodiments the electronic circuitry is configured to enable adjusting the amplification factor of at least one of the signals so that any noise component in the results of the subtraction is reduced to an attainable minimum value and operative to process the results of the subtraction to yield corresponding angular position values.
In some embodiments the second stationary disk is formed with a central hole and the rotary disc is mechanically coupled to a rotary shaft, which passes through the hole. In some of the embodiments one of the second electrodes is nearer the center of the second stationary disk than all of the first electrodes. The one second electrode may be formed, at least in part, as plating on a rim of the hole.
In some embodiments the rotor includes dielectric material, formed and configured to affect the variability of coupling capacitance.
There is also provided, according to the invention,
a method for sensing an angular position between a rotary body and a stationary body, including
The method may further include
Unless otherwise defined herein, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein may be used in the practice or testing of embodiments of the invention, exemplary methods and/or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.
The discs are made of a rigid non-conductive material, such as, for example, a material used for printed circuit boards. The inner faces of the discs, i.e. the faces nearest each other, are plated with a conductive layer, having a thickness of typically 0.1 mm, which is formed into variously shaped parts or segments, electrically isolated from each other, serving as electrodes, as discussed below. Some such segments, e.g. 24, 34 and 36, are seen in cross section in
Preferably (as in the illustrated example embodiment) the design of the sensing electrodes (i.e. the receiving electrode 26 and the compensation electrode 27) is such that they are subject as equally as possible to the interfering fields and thus will have commensurately similar noise signals induced in them —enabling optimal noise cancellation in the processed received signal (as described below). It is noted that the interfering fields may vary in space not only in overall amplitude (which may easily be compensated for by differential amplification of the signals), but also in the relative amplitudes of various frequency components. Hence it is desirable that these two sensing electrodes be as close to each other. Also preferably (again as in the illustrated example embodiment) the compensation electrode 27 is placed as close to the shaft 13 as possible, since the latter is generally the main conduit through which electric noise is transmitted to the sensor (as any electric noise transmitted through the air is usually blocked by appropriate screening).
In the example embodiment the two electrodes are shaped as complete rings. Receiving electrode 26 is facing, and has good capacitive coupling with, the inner transfer electrode 35 (
In the illustrated example embodiment, the two outer bands on the face of the stator 20 are divided each into sectors. These sectors are designed to function as excitation electrodes and will be also referred to as such below. The excitation electrodes are connected to a driving circuit (not shown), as described below. The outermost band consists of sixteen sectors 24, designed to serve for fine angular position sensing, while the adjacent band consists of four sectors 25, designed to serve for coarse angular position sensing. In some other embodiments, the number of bands of excitation electrodes, as well as the number of sectors in each band, are different from those in the illustrated embodiments. Preferably, however, the entire pattern of excitation electrodes is such that they are confined to an annular band exclusive of the receiving- and compensation electrodes.
Referring again to
The rotor 60 affects the capacitance, and therefore also the capacitive coupling, between each of the excitation electrodes on the first stator 50 and the receiving electrodes on the second stator 70 by its dielectric effect. The capacitance varies with the angular position of the rotor (and thus—of the rotational body), between some highest value and some lowest value; this angular variation is a function of the outline of the rotor disc 60 (i.e. of the outer region 64) for fine position sensing and of the inner region 65 for coarse position sensing. Thus the capacitive coupling between each outer-band excitation electrode 54 and the receiving electrode 74 varies with the position angle as a direct function of the relative area of the thick outer region 64 of rotor 60 that lies between them. Similarly the capacitive coupling between each inner-band excitation electrode 55 and the receiving electrode 75 varies with the position angle as an inverse function of the relative area of the thin inner region 65 of rotor 60 that lies between them. It is noted that the compensation electrode 77, though positioned near the innermost region 67 of the rotor (which is of dielectric material as well), does not face an excitation electrode; thus its capacitive coupling with the excitation electrodes 54 and 55 is significantly lower than the capacitive coupling between the receiving electrodes 74 and 75 and the corresponding excitation electrodes, i.e. any capacitance between compensation electrode 77 and an excitation electrode 54 or 55 is less than half (preferably less than a quarter) the lowest value of capacitance between that excitation electrode and a corresponding receiving electrode 74 or 75. This, again, insures that the amplitude of the eventual sensed signal after subtracting the compensation signal (as described below) is not reduced enough to adversely affect the accuracy of the results.
In some other embodiments (not illustrated) the rotor is made of material similar to that of the stators 50 and 70, has uniform thickness and is plated with two pairs of transfer electrodes, each pair deployed identically on both faces of the rotor and electrically interconnected. One member of each pair faces a corresponding band of excitation electrodes 54 or 55 while the other member faces a corresponding receiving electrode 74 or 75. Thus each pair of transfer electrodes provides capacitive coupling (as two capacitors in series, with commensurate effective capacitance) between corresponding electrodes on the two stators. The member of each pair that faces an excitation electrode is shaped and positioned similarly to a corresponding region 64 or 65 on the illustrated embodiment of rotor 60, so as to capacitively couple each band of excitation electrodes on the first stator with a corresponding receiving electrode on the second stator, wherein the capacitance varies with the angular position of the rotor, thus serving for fine and coarse position sensing, respectively. The other member of each pair of transfer electrodes on the rotor (i.e. the one facing a receiving electrode) is, in some embodiments, shaped similarly to the first member, while in other embodiments it is shaped as an annular ring, similar to the corresponding receiving electrode 74 or 75. It is noted that compensation electrode 77 has, again, minimal capacitive coupling with all the other electrodes, i.e. its effective capacitance with the excitation electrodes 54 or 55 is substantially smaller than that of the receiving electrodes 74 and 75.
With regard to the embodiments described above, as well as any alternative embodiments, all excitation electrodes are electrically connected to corresponding output terminals of a provided electrical driving unit (not shown), which is designed and operative to apply to the excitation electrodes appropriate excitation signal voltages, adapted for the particular pattern of excitation electrodes deployed. The nature of the signal and the manner of its generation are similar to those used in CAPS of prior art, disclosed, for example, in U.S. Pat. No. 6,492,911. Also in common with prior art and as disclosed, for example, in U.S. Pat. No. 6,492,911, there is provided an electrical processing unit (not shown), with input terminals connected to corresponding receiving electrodes, which is operative to amplify signals electrically (e.g. capacitively) induced in the receiving electrodes and to process them so as to obtain an electrical analog of the angular position of the rotor. Optionally and again as known from prior art, an analog-to digital converter is provided, operative to convert this electrical analog into a corresponding digital representation of the angular position, thus rendering the whole apparatus to be an angular position encoder.
The processing unit according to example embodiments of the present invention includes also a compensation circuit, interjected at one or more stages of amplification in each channel of processing (if more than one), and is operative to receive also a signal electrically induced in the compensation electrode (mainly by interfering, or noise, fields), to amplify the signals received from the receiving electrodes and from the compensation electrode, with generally different amplification factors, and to subtract one from the other.
When more than one compensation electrode is deployed (as may be the case in some embodiments), the compensation circuit may have corresponding additional input terminals, connected to them. In some embodiments the processing unit may include a plurality of compensation circuits, such as described above, and is generally operative to amplify voltages capacitively induced in the various sensing electrodes and to subtract the amplified voltage originating in the compensating electrode from amplified voltages originating in any of the receiving electrodes or a combination of such voltages—all with appropriately adjusted amplification—or attenuation—factors.
It will be appreciated that, similarly to signals obtained in conventional angular position sensors and encoders, the results of the compensation and the further signal processing—whether in terms of voltages or in digital form—are analogous to the angular position of the rotary body and may be readily translated into actual angle values. However, unlike conventional sensors and encoders, the resultant angular position values have minimal or practically no error.
It will also be appreciated that the above descriptions are intended only to serve as examples and that many other embodiments are possible within the scope of the present invention as defined in the appended claims.
To the extent that the appended claims have been drafted without multiple dependencies, this has been done only to accommodate formal requirements in jurisdictions which do not allow such multiple dependencies. It should be noted that all possible combinations of features which would be implied by rendering the claims multiply dependent are explicitly envisaged and should be considered part of the invention.
