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Title:
SOLID STATE GYROSCOPE ELECTRODES FOR ADJUSTABILITY
Document Type and Number:
WIPO Patent Application WO/2007/120158
Kind Code:
A1
Abstract:
A cup or bell shaped angular rate sensor electrode has drive or sense electrodes repositioned from their typical location at the nodes. One pair of electrodes, residing on opposite sides of the cup, is uniformly displaced in one direction while a second pair of electrodes is uniformly displaced in the opposing direction. By adjusting the gain ratio of these two pairs, the effective sensing vector or node can be directed without adding conductor connections.

Inventors:
WATSON WILLIAM S (US)
Application Number:
PCT/US2006/020768
Publication Date:
October 25, 2007
Filing Date:
May 25, 2006
Export Citation:
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Assignee:
WATSON IND INC (US)
WATSON WILLIAM S (US)
International Classes:
G01P9/04; G01C19/00
Foreign References:
US5471875A1995-12-05
US6272925B12001-08-14
US5445007A1995-08-29
US6805007B22004-10-19
US5587529A1996-12-24
US4759220A1988-07-26
US5540094A1996-07-30
Attorney, Agent or Firm:
PEDERSEN, Brad (Thuente & Skaar P.A.,4800 IDS Center,80 South 8th Stree, Minneapolis Minnesota, US)
Download PDF:
Claims:

What is" claimed ' is: '

1. An inertial sensor apparatus for use in producing an angular rotation signal indicative of a rate of angular rotation of the inertial sensor apparatus, the inertial sensor apparatus of the type comprising a vibratory resonator cup (100) having an outer surface and having a first node axis (115) associated with a desired mode of oscillation, characterised by: a first pair of sense electrodes (112a) located substantially on the outer surface of the vibratory resonator cup (100), the sense electrodes (112a) located substantially opposite one another to define a first sense axis displaced from the first node axis (115), the sense electrodes (112a) configured and arranged to generate a first signal in response to rotation of the inertial sensor apparatus.

2. The inertial sensor apparatus of claim 1 , further characterised by a first pair of drive electrodes (102) located substantially opposite one another and offset from the sense electrodes (112a) and substantially on the outer surface of the vibratory resonator cup (100), the drive electrodes (102) configured and arranged to control excitation of the vibratory resonator cup (100).

3. The inertial sensor apparatus of claim 2, wherein the vibratory resonator cup (100) further defines a second node axis (116) associated with the desired mode of oscillation, the second node axis (116) offset from the first node axis (115), and wherein the vibratory resonator cup (100) further comprises a second pair of sense electrodes (112b) located substantially on the outer surface of the vibratory resonator cup (100) and substantially opposite one another to define a second sense axis displaced from the second node axis (116), the sense electrodes (112b) configured and arranged to generate a second signal in response to rotation of the inertial sensor apparatus.

4. The inertial sensor apparatus of claim 3, further characterised by a second pair of drive electrodes (102) located substantially opposite one another and offset from the second sense axis and substantially on the outer surface of the vibratory resonator cup (100), the drive electrodes (102) configured and arranged to control excitation of the vibratory resonator cup (100).

5. 1 he inertial sensor apparatus of claim 1 , further characterised by a stem (110) for supporting the vibratory resonator cup (100).

6. The inertial sensor apparatus of claim 1 , wherein the vibratory resonator cup (100) is formed at least in part from a piezoceramic material rated for a low quality factor Q.

7. A gyroscope of the type comprising an inertial sensor apparatus of the type comprising a vibratory resonator cup (100) having an outer surface and having a first node axis (115) associated with a desired mode of oscillation, the vibratory resonator cup (100) configured and arranged to vibrate in response to an excitation voltage, and a standoff for supporting the vibratory resonator cup (100) and for allowing the vibratory resonator cup (100) to vibrate in response to the excitation voltage, the inertial sensor apparatus characterised by: an inertial sensor apparatus for use in producing an angular rotation signal indicative of a rate of angular rotation of the inertial sensor apparatus, the inertial sensor apparatus comprising a first pair of sense electrodes (112a) located substantially on the outer surface of the vibratory resonator cup (100), the sense electrodes (112a) located substantially opposite one another to define a first sense axis displaced from the first node axis (115), the sense electrodes (112a) configured and arranged to generate a first signal in response to rotation of the inertial sensor apparatus.

8. The gyroscope of claim 7, further characterised by a first pair of drive electrodes (102) located substantially opposite one another and offset from the sense electrodes (112a) and substantially on the outer surface of the vibratory resonator cup (100), the drive electrodes (102) configured and arranged to control excitation of the vibratory resonator cup.

9. The gyroscope of claim 8, wherein the inertial sensor apparatus further comprises a gain ratio adjustment subsystem (510) for adjusting a gain ratio between the drive and sense electrodes.

10. The gyroscope of claim 8, wherein the vibratory resonator cup (100) further defines a second node axis (116) associated with the desired mode of oscillation, the second node axis (116) offset from the first node axis (115), and wherein

the Vibratory resonator cup mrtner comprises a second pair of sense electrodes (112b) located substantially on the outer surface of the vibratory resonator cup (100) and substantially opposite one another to define a second sense axis displaced from the second node axis (116), the sense electrodes (112b) configured and arranged to generate a second signal in response to rotation of the inertial sensor apparatus.

11. The gyroscope of claim 10, wherein the inertial sensor apparatus further comprises a second pair of drive electrodes (102) located substantially opposite one another and offset from the second sense axis and substantially on the outer surface of the vibratory resonator cup (100), the drive electrodes (102) configured and arranged to control excitation of the vibratory resonator cup (100).

12. The gyroscope of claim 8, wherein the vibratory resonator cup (100) is formed at least in part from a piezoceramic material rated for a low quality factor Q.

Description:

SOLID STATE GYROSCOPE ELECTRODES FOR ADJUSTABILITY

TECHNICAL FIELD

[0001] The present disclosure relates generally to angular rate sensors, and more particularly to vibrating element angular rate sensors used as rate gyroscopes.

BACKGROUND OF THE DISCLOSURE

[0002] Instrumentation sensors operating on a principle of vibration of constrained actuator masses are known in the art. Angular rate gyroscopes make use of the principle of inertia to measure the rate of rotation through an angle with respect to a sensing axis. One type of angular rate gyroscope is the solid state gyroscope. Such systems utilize standing waves that are excited in a resonating element to produce a desired mode of oscillation having a predetermined number of nodes. The oscillations have an inherent oscillatory inertia that is independent of the linear and rotational motion of the gyroscope itself. When the resonating element is rotated about its sensing axis, the oscillations will essentially maintain their inertial orientation. The nodes that define the desired mode of oscillation will rotate with respect to the physical structure of the resonating element. The amount of rotation of the nodes is proportional to the rate of inertial rotation applied to the resonating element. Accordingly, it is possible to determine the rate of rotation, in addition to the magnitude and direction of rotation by measuring the rotation of the nodes.

[0003] Solid-state gyroscopes based on the principle described above are capable of sensing rotation only and then usually about a single axis. To obtain information sufficient to determine the relative attitude of a body, it is necessary to group three such gyroscopes in an orthogonal relationship covering the x, y, and z Cartesian axes.

[0004] One well known type of angular rate sensor comprises the use of piezoelectric ceramic bender elements in a paired tuning fork arrangement. In this type of arrangement, a pair of drive elements is energized to induce a controlled vibration within a single plane. The application of rotational forces upon the vibrating elements parallel to the plane of vibration and on the axis of symmetry induces a measurable signal characteristic of the angular relationship between the sensing object and the vibrating elements. Inherent to tuning fork designs are the bending forces that result from the oscillating drive elements. Although there have been some designs that attempt to reduce such undesirable forces through isolation between drive and sense

elerriefi't ' s 'the error " reMairϊS, fcaϋs'ing reduced signal to noise and false indication of rotation.

[0005] One well known type of angular rate sensor utilizes a cup or bell shaped sensor that is supported upon a stem and secured to the chassis of the sensor. The surface of the cup comprises drive electrodes and sense electrodes that are alternately oriented symmetrically around the perimeter surface. Exciting the drive electrodes induces a controlled oscillation upon the cup. The sense electrodes produce a signal that is demodulated in control circuitry to determine the angular rate at which the sensor is rotated. As part of the control circuitry, the drive elements can have the drive adjusted to correct any errors in the desired mode of oscillation.

[0006] In order to accomplish the correction of undesirable oscillation alignment, early designs split one of the drive electrodes into two electrically isolated electrodes. One side provides the desired oscillation mode drive signal, similar to the other drive elements, and the other side, with the split element, provides a corrective drive signal. In order to maintain uniformity of the oscillation, the mass and size of all of the elements are matched as closely as possible. The result of the one differing split drive plate has a negative impact on the overall uniformity and ability to maintain the desired oscillation mode. Additionally, this requires two conductor connections instead of the single conductor utilized on the other elements, the mass of which must also be compensated for. Compensation techniques tend to add complexity and cost to the design. Further, these techniques also tend not to be very effective. Therefore, a need exists for a cup electrode design that can provide both the desired oscillation mode drive signal and the corrective drive signal that maintains the physical symmetry and mass uniformity of the cup electrode. In addition, such a design should have relatively low complexity and low cost.

SUMMARY OF THE DISCLOSURE

[0007] According to various embodiments, a cup or bell shaped angular rate sensor electrode has drive or sense electrodes repositioned from their typical location at the nodes. One pair of electrodes, residing on opposite sides of the cup, is uniformly displaced in one rotational direction while a second pair of electrodes is uniformly displaced in the opposing rotational direction. By adjusting the gain ratio of the signals from these two pairs, the effective sensing vector or node can be directed without adding conductor connections.

[uuubj in one emDoαimeπx, an inertial sensor apparatus for use in producing an angular rotation signal indicative of a rate of angular rotation of the inertial sensor apparatus comprises a vibratory resonator cup having an outer surface and having a first node axis associated with a desired mode of oscillation. A first pair of sense electrodes is located substantially on the outer surface of the vibratory resonator cup. The sense electrodes are located substantially opposite one another to define a first sense axis displaced from the first node axis and are configured and arranged to generate a first signal in response to rotation of the inertial sensor apparatus. [0009] In the application of the foregoing embodiment to a gyroscope, the vibratory resonator cup is configured and arranged to vibrate in response to an excitation voltage. A standoff supports the vibratory resonator cup and allows the vibratory resonator cup to vibrate in response to the excitation voltage. [0010] In a preferred embodiment, a pair of drive electrodes may be located substantially opposite one another and offset from the sense electrodes on the outer surface of the vibratory resonator cup. The drive electrodes serve to control excitation of the vibratory resonator cup.

[0011] As a further beneficial feature, the resonator cup defines a second node axis associated with the desired mode of oscillation, which is offset from the first node axis. A second pair of sense electrodes located on the outer surface of the resonator cup substantially opposite one another defines a second sense axis displaced from the second node axis. The second pair of sense electrodes generates a second signal in response to rotation of the inertial sensor apparatus.

[0012] Additional advantages and features will be set forth in part in the description which follows, and in part, will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] - FIG. 1 is a perspective view of a cup electrode illustrating displaced sense electrodes according to one example embodiment. [0014] FIG. 2 is a top view of the cup electrode of FIG. 1.

[0015] FIG. 3 is a schematic diagram of one embodiment of the control circuitry used to control the angular relationship between the drive and sense electrodes by adjusting the gain ratio.

[uuiϋj γHJ. όf\ is a' scnematrc diagram of one embodiment of the control circuitry used to control the angular relationship between the sense electrodes by adjusting the gain ratio to get the oscillation drive signal.

[0017] FIG. 4 is a generalized diagram of a vibrating structure gyroscope utilizing a cup electrode according to another embodiment.

[0018] FIG. 5 is a block diagram of components of an example gyroscope model that may be used within a gyroscope system.

[0019] FIG. 6 illustrates one preferred embodiment showing the gain ratio adjust circuitry that could be incorporated into a gyroscope system.

[0020] FIG. 7 illustrates a perspective view of a cup having displaced drive electrodes.

[0021] FIG. 8 illustrates a top view of a cup having displaced drive electrodes as shown in FIG. 7.

[0022] FIG. 9 illustrates adjustment of the alignment of sense axes, according to one embodiment.

[0023] FIG. 10 illustrates adjustment of the alignment of drive axes, according to another embodiment.

DETAILED DESCRIPTION

[0024] Numerous vibration based cup angular rate sense systems exist; however, the current systems available fail to provide a simple and economical design with the ability to (i) adjust the angular relationship between the drive and sense electrodes and (ii) maintain uniform mass structures in order to maintain desired oscillatory modes.

[0025] In the following description, numerous specific details are set forth in order to provide a thorough understanding of various embodiments of the present invention. It will be apparent to one skilled in the art that various embodiments may be practiced without some or all of these specific details. In other instances, well known components have not been described in detail in order to avoid unnecessarily obscuring the invention.

[0026] FIGS. 1 and 2 show one example embodiment in which an angular rate sensor is in the form of an electrode cup 100. The cup 100 comprises a rim 105 that includes drive electrodes 102 and sense electrodes 112. It will be known by those skilled in the art that the term electrode is used to describe the conductor used to transmit signals to and from an angular rate sensor. A stem 110 resides at the base of

the πrrπut). Node rererence lines 115 and 116 connect the oscillation nodes, locations at which the vibration amplitude is substantially zero. In some conventional designs, the sense electrodes would be centered on the node reference lines 115 and 116. In the embodiment shown in FIGS. 1 and 2, by contrast, the sense electrodes 112 are displaced with respect to the node reference lines 115 and 116. For example, as shown in FIG. 2, the sense electrode pair 112a is displaced counterclockwise from the node reference line 115, and the sense electrode pair 112b is displaced clockwise with respect to the node reference line 116.

[0027] FIG. 3 illustrates the cup electrode system 200 which includes a cup 100 and control circuitry used to control the orthogonality between the two pair of sense electrodes. The cup 100 comprises a rim 105 having sense electrode pairs 112a and 112b. Signal lines 202 and 204 transmit signals from the sense electrode pair 112a through a buffer 210. The buffer 210 produces a buffered sense output 212 as a function of the position of the node reference line 115 as a plane along which the vibration of the surface of the rim 105 will be minimal. Similarly, signal lines 206 and 208 transmit signals from the sense electrode pair 112b through a buffer 215 to produce a buffered sense signal 217. The buffered sense signal 217 represents the position of the node reference line 116 as a plane along which the vibration of rim 105 will be minimal. In one preferred embodiment, an inverter 220 produces an inverted sense signal 222 that is opposite in polarity to the sense signal 217. A rheostat 225 receives the buffered sense signal 217 and the inverted sense signal 222. The rheostat 225 adjusts the ratio between the buffered sense signal 217 and the inverted sense signal 222 to produce a ratio signal 230, changing the electrical position of the electrodes with respect to the node reference lines 115 and 116. In this way, the setting for minimal drive signal at 230 can be determined. Alternatively, in one embodiment, the inverter 220 may be omitted, as shown in FIG. 3A, thereby effectively summing the buffered sense signal 212 and the buffered sense signal 217. In this implementation, the rate sense signal is canceled. If the inverter 220 is omitted, the predominant signal is from the drive oscillation, and the rheostat 225 adjusts out the rate signal and leaves only the drive sensing signal at 327 which is used to provide correction in a drive amplitude feedback loop, as described more fully below in connection with FIG. 6. Both functions can be implemented at the same time using signals 217 and 212 as the root of both operations.

[0028] In some embodiments, the sense electrode pairs 112a and 112b shown in

FIG. 3 may be substituted with drive electrode pairs and utilized in a similar manner with

oscillation drive circuitry in order to electrically change the position of the node reference lines 115 and 116. One such implementation is further illustrated in a cup electrode system 600 of FIGS. 7 and 8. A rim 605 includes drive electrodes 602 and sense electrodes 612. A stem 610 resides at the base of the rim 605. Node reference lines 115 and 116 connect the oscillation nodes, locations at which the vibration amplitude is substantially zero. In some conventional designs, the sense electrodes would be centered on the node reference lines 115 and 116. As can be seen in FIG. 8 in the top view of the cup 600, however, a drive electrode pair 602a is displaced counterclockwise from the reference line 115 and a drive electrode pair 602b is displaced clockwise from the reference line 116.

[0029] FIG. 4 represents a generalized diagram of a Vibrating Structure

Gyroscope (VSG) 300, utilizing a cup shaped transducer with electrodes. A drive circuit 305 applies a controlled vibration 307 to a transducer 310, such as a cup electrode or other type of transducer. The transducer 310 transfers a portion of the vibration 307 to a sensing circuit 315 as a sensed vibration signal 312 when an angular motion 322 is applied, for example, when the gyroscope 300 is rotated from a nominal steady-state position. The sense circuit 315 transforms the sensed vibration signal 312 to produce an output signal 325 that is representative of the angular position change caused by rotation of the VSG 300. The sense circuit 315 additionally provides a control signal 317 as feedback to the transducer 310 to modify the response of the output signal 325. The control signal 327 is used by the drive circuit 305 to control the level of oscillation to control the sensitivity of the gyroscope 300. The purpose of the feedback signal 317 is to counteract the vibrations from angular motions in the transducer so that the quality factor Q of the transducer is forced to be lower. Reducing the quality factor Q of the transducer will increase the bandwidth of the system.

[0030] FIG. 5 depicts one embodiment that may be used within a gyroscope system. A gyroscope system 400 incorporates drive and sense circuits. A drive signal 407 passes to a transducer 410, which includes a phase shift function, an adder 411 , and a multiplier 413. The multiplier 413 processes the drive signal 407. In particular, the multiplier 413 modulates an angular rate signal 422 from an angular rate input 420 as a function of the drive signal 407. The driven oscillations are monitored through a drive sense signal 427. The drive sense signal 427 is transmitted to an amplifier 430, which produces an amplified drive correction signal 432 that is in turn transmitted to an automatic gain control (AGC) circuit 435. The AGC circuit 435 produces an adjusted drive signal 440 that has been adjusted to overcome inaccuracies and to provide

sufficient arnplltϋde to maintain consistent drive to the transducer in the transducer 410. The adjusted drive signal 440 is further processed by a phase shifter 445 to correct any phase shift that resulted within the transducer and during the signal processing and produces the drive signal 407.

[0031] The multiplier 413 generates a force signal 450 based upon the angular rate signal 422. The force signal 450 is transmitted to the adder 411 to be added to a control signal 417, producing a vibration signal 412. The vibration signal 412 is then transmitted to a sensing demodulator 416, which produces a rectified sine wave signal 455. An integrator 415 further processes the rectified sine wave signal 455 to produce an output signal 425 that is representative of the angular position change caused by gyroscope rotation. The integrator 415 also transmits an adjusted output signal 460 to a modulator 465, which converts the adjusted output signal 460 to the control signal 417. In this way, the system realizes a closed loop or torque loop 408 that forces down vibrations at the sensing electrodes. The torque loop 408 provides improved bandwidth and linearization of the gyroscope system 400. The effect of the torque loop 408 is to resist transducer vibration in the sense direction, to assist the dissipation of sense deflections, and to serve as an effective method to produce high bandwidth rate signals in conditions of systems having a high quality factor Q.

[0032] FIG. 6 illustrates another embodiment in which a gain ratio adjustment subsystem 510 is incorporated into a gyroscope system 500. The gain ratio adjustment subsystem 510 may comprise both the angular rate sensing and drive vibration sensing or either set individually, as described above. That is, the control signal 327 is adjusted to be all drive vibration sensing signal and the sensed vibration signal 312 is adjusted to be all rate sensing signal. The gain ratio adjustment subsystem 510 receives as input a gain input signal 502, for example, via the sense signal lines 202, 204, 206 and 208 of FIG. 3.

[0033] The gain ratio adjustment subsystem 510 can be used to adjust the alignment of the sense axes. FIG. 9 conceptually illustrates the use of the gain ratio adjustment subsystem 510 to adjust the alignment of the sense axes. FIG. 9 assumes a four-node vibration pattern of a stem-mounted cup, giving rise to two node axes and two drive axes. The node axes are located between the drive axes and are defined by the nature of the vibration pattern. With a four-node vibration pattern, the node axes are orthogonal to one another, and the drive axes are also orthogonal to one another. It should be noted that other modes of vibration would involve a different number of

nodes, ana tnus a αirrereπrnumDerOf node axes and drive axes with different angular relationships.

[0034] In FIG. 9, the centroids of the drive electrodes are coincident with the drive axes, but the centroids of the sense electrodes are displaced by an angle θ with respect to the respective node axes, which connect the nodes of oscillation. The signal produced on each sense electrode is proportional to the vibration amplitude at its location. At the node, for example, there is no vibratory movement, and the signal is zero. If the sense electrode is located along a drive axis, the signal is that of the full drive vibration. Between these extremes, the signal is proportional to the sine of a geometric constant times the angle θ from the node. In a system having a four-node vibration pattern, the geometric constant is 2. More generally, the geometric constant is N/2, where N is the number of nodes in the vibration pattern. Accordingly, in a system having a four-node vibration pattern, the signals from the electrode axes are:

5 1 = D sin 2θ + DK

5 2 = D sin 2θ - DK where Si is the signal from the first sense electrode axis, S 2 is the signal from the second sense electrode axis, D is the signal for the electrode at the drive axis, θ is the skew angle by which the sense axes are skewed with respect to the node axes, and DK is the signal from an angular rate input. By adding and subtracting the signals S 1 and S 2 , the rate sensing signal and the drive sensing signal can be determined. In particular, the rate sensing signal can be obtained as a function of the difference between the signals from the sense electrode axes:

S 1 - S 2 = 2DK

The drive sensing signal can be obtained as a function of the sum of the signals from the sense electrode axes:

S 1 + S 2 = 2D sin 2θ

While the two sense electrode axes are perfectly aligned in an ideal product, in a real world product, the two sense electrode axes will not be perfectly aligned. By making slight adjustments in the gain balance between the two sense outputs via the gain ratio adjustment subsystem 510, alignment errors can be compensated. [0035] Applying the same principles above to the drive system facilitates adjusting the angle of the drive and node axes by changing the gain ratio for the two drive electrode sets, as shown conceptually in FIG. 10. FIG. 10 assumes a four-node vibration pattern of a stem-mounted cup, giving rise to two node axes and two drive axes. In FIG. 10, the drive electrodes are displaced from their respective drive axes by

an aYigϊe B.' If all or the drive voltage amplitude is applied only to the pair of drive electrodes on electrode axis 1 , then the drive and node axes would be rotated counterclockwise by an angle θ. On the other hand, if all of the drive voltage amplitude is applied only to the pair of electrodes on electrode axis 2, then the drive and node axes would be rotated clockwise by an angle θ. It should be noted that electrode axis 2 has an opposite oscillation phase relative to electrode axis 1. Accordingly, if the drive voltage amplitude is applied equally to electrode axes 1 and 2, the drive and node axes would not be rotated. The offset angle of the drive oscillation θ can be set to any value between +θ and -θ by adjusting the ratio of the voltages applied to the two pairs of drive electrodes on electrode axes 1 and 2 using the gain ratio adjustment subsystem 510. [0036] By adjusting the alignment of the drive axes using the gain ratio adjustment subsystem 510, the base signal of Si - S 2 can be substantially eliminated when the sensor is at rest. Making this adjustment dynamically may facilitate damping of displaced driven vibrations, which can be used as a torque mechanism to extend the bandwidth of the gyroscope output or to control quadrature oscillations. As a result, fewer electrode connections may be used, thereby enhancing simplicity and greater symmetry for better resonance performance.

[0037] It is to be understood that even though numerous characteristics and advantages of various embodiments have been set forth in the foregoing description, together with details of the structure and function of various embodiments, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles described herein to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the material used in the cup may be of a non- homogeneous type instead of the homogeneous piezoceramic as described herein. It will be known by those skilled in the art that the methods of manufacture of the components that comprise the cup are numerous and are typically chosen based upon the type of materials or orientation that is required for each application. In addition, although the embodiments described herein are directed to cup electrodes for use on vibrating actuator mass sensor systems, it will be appreciated by those skilled in the art that the teachings disclosed herein can be applied to other systems, such as various drive control systems, ultrasonics, and power converters, without departing from the scope and spirit of the present invention, which is defined solely by the claims that follow. As a further example, the principles described herein can be applied to other gyroscope configurations, such as gyroscopes employing ring and plate type vibrating

structures, ratner man a cup: "in-sαch implementations, like the cup implementation described herein, the sensing and driving electrodes, which use capacitive or magnetic sensing and driving, are skewed from the typical orientation by a small angle. The same functions and advantages as shown above may be produced as a result.