Patent ID: 12228398

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG.3is a diagram illustrating a sensing mechanism300using a curved target320to improve range and accuracy, according to an embodiment of the present invention. In this embodiment, a mirror310rotates about pivot axis305and curved target315is offset from, and is placed behind, pivot axis305. By placing target315behind pivot axis305, curved target315may move side to side rather than forward and backwards. In some embodiments, the maximum and minimum rotation of mirror310is +/−12 Degrees.

In this embodiment, proximity sensors320Aand320Bface curved target315rather than mirror310. Further, rather than placing proximity sensors320Aand320Bon opposites sides of pivot axis305, proximity sensors320Aand320Bare placed on opposites sides of curved target315, for example. This way, the movement of curved target315may be controlled in relation to proximity sensors320Aand320B, producing a small displacement giving the linearity.

For purposes of explanation with respect to the embodiments of the subject application, the term “proximity” may be defined as there being no direct contact in order for sensors320Aand320B(e.g., hall effect sensors) to perform the measurements. In other words, by changing the airgap between sensors320Aand320Band target315, there is a change in the magnetic field, causing a change in voltage allowing sensors320Aand320Bto perform measurement.

It should also be appreciated that sensors320Aand320Bare calibrated based on a calibration sheet. So, as the airgap changes and the magnetic field is altered, there is a change in voltage in the Wheatstone bridge. This change in voltage (otherwise known as ΔV) is compared with a calibration sheet to determine the distance between sensors320Aand320Band target315.

Also, in this embodiment, curved target315may have a curved surface of any shape. Although a spherical surface is shown inFIG.3, the embodiments are not limited to a spherical surface. Instead, any curved surface, such as conic sections (ellipsoids, parabolas, and hyperbolas), polynomials, trigonometric curvatures, etc., may be used. SeeFIGS.7A and7B, which are discussed in more detailed below.

In certain embodiments, the target surface of the curve is offset from a pivot line by a dimension that matches a curved surface movement to the full calibrated range of sensor320Aand320B. For instance, in the case of a spherical target315, the position of the sphere center is the index to be offset from pivot axis305. In this embodiment, the offset is used to move the target surfaces towards or away from the head of sensors320Aand320B. The change in distance form target315to the head of sensors320Aand320Balters the magnetic field. This alteration in the magnetic field changes the current into the Wheatstone bridge altering the differential potential (voltage) between opposite point in the Wheatstone Bridge.

In some embodiments, the radius of a curvature is maximized based on an available design space for the purpose of minimizing the effective “tilt” of the curved surface as mechanism300moves over its angular range. For example, the neutral position for a proximity sensor320Aor320Busing a curved target315will align centerline axis of proximity sensor320Aor320Bto point through the center of curved target315. This configuration allows the field lines from proximity sensor320Aor320Bto be equally distributed within curved target315. As mechanism300rotates, the center of curved target315shifts slightly off the centerline of proximity sensor320Aor320Bwith the result that one zone of curved target315will be somewhat closer to proximity sensor320Aor320Bthan the opposite zone.

FIG.4is a diagram illustrating a movement of a curved target315, according to an embodiment of the present invention. Because of the curvature of curved target315, the shift in curved target315toward and away from proximity sensor320is nominal, and the detrimental effect on the performance of proximity sensor320is small compared to measurement of a flat target. For example, inFIG.4, the field lines, which emanate from proximity sensor320, remain nearly symmetric when curved target315moves (i.e., when mechanism300shown inFIG.3moves about the pivot axis). In practice, the portion of curved target315that captures the field is the same as in a flat surface, so the range-to-resolution ratio will be close. Further, the performance of proximity sensor320remains linear while preserving the operating range.

In certain embodiments, the surface of curved target315interacts with the field lines over a smaller volume than a flat surface. This may cause the range to be slightly reduced. Further, the interaction between the field lines and curved target315, as shown inFIG.4, exaggerate this effect. During operation, the portion of curved target315that captures the field lines are nearly the same as that of the flat surface. This may cause the range-to-resolution ratio to be close.

It should also be noted that the surface of curved target315interacting with the emitted field has tight accuracy requirements and should be electrically conductive. As a practical matter, the surface of curved target315may be produced by precision single point diamond machining of an electrically conductive, machinable metal such as aluminum. For example, high quality diamond machining may achieve surface profile accuracies on the order of 0.1 microns or less. For a curved surface, there are three ranges of spatial frequency geometry variations of interest.

First are the small tooling grooves generated by the diamond tool. In this case, the emitted fields generally envelope a large number of these grooves and are individually very small. For example, the emitted fields are small enough and occur at a high spatial frequency to be averaged out by sensor320without materially affecting the accuracy.

At the other extreme, large scale deviations from a spherical profile (or any surface of revolution profile) that develop over the scale of the emitted field may be features that can be accommodated by calibration. In some cases, large scale variations may have a slightly ellipsoidal surface rather than a perfect sphere. These features, for example, may not be difficult to calibrate than manufacturing errors such as slightly non-planar mechanism pivot axes or small offset of the sphere center from the line of action normal to the pivot axes.

Finally, the third range of spatial frequency profile errors may be between the ranges where the profile may vary erratically as a result of machining errors and tooling limitations. The magnitude and distribution of these errors are difficult to fully calibrate out, and if so, may limit accuracy to less than theoretically possible. In general, depending on the application and design parameters, mid-range random and quasi-random spatial profile errors may start to become significant above or about 0.1 micrometers occurring over surface profile dimensions of about micro to several millimeters for typical optical applications.

In some embodiments, a curved target provides angular sensing around two axes when the pivot axis is nominally in or close to the same plane. As in the one-axis embodiment shown above, the center of the curved surface is located on an axis normal to the pivots, and in this case, aligned with the nominal intersection of the pivot axis centerlines. The sensor may provide angle measurements in a two-axis mechanism when (1) the mechanism pivot axis are in the same plane to within suitably close manufacturing tolerances, (2) the line between target center and pivot axis intersection is normal to the plane of the pivot axes to within suitable manufacturing tolerances, and (3) the line between target center and pivot axis intersection passes through the pivot axis intersection to within suitable manufacturing tolerances.

FIG.5is a diagram illustrating displacement of a target310around a “drive axis, according to an embodiment of the present invention. In certain embodiments, when cross-axis position is zero, the difference in cross-axis target eddy current capture is zero, because both proximity sensors320Aand320Bobserve the same change in target position, resulting in no change in sensor output. However, when there is also motion around the cross-axis, the sensor gain versus angle changes slightly. Thus, proper calibration requires each of the two-axis angles to be identified with both sensor outputs in order to compensate for this effect. Systems with flat targets are subject to the same phenomenon, so this is not a characteristic only of the two-axis curved target sensor, merely one that requires calibration against both axes.

Similarly, manufacturing errors will result in small differences in cross-axis sensor readings that have to be included with calibration. In both the one-axis and two-axis embodiments, proximity sensors320Aand320Bare fixed to base, and therefore, the proximity sensor cables do not move. This may improve reliability, and reduce cable friction and stiffness effects, on the mechanism.

FIG.6is a diagram illustrating a spherical target315being offset with respect to the rotation axis “X”, according to an embodiment of the present invention. In this diagram, an encoder330measures a rotational axis X. Data from this encoder is taken and compared with the data received from the sensors to show320Aand320Bthat the embodiments are functional. See, for example, the data illustrated inFIG.8. InFIG.8, graph800shows results from a command for the system to perform a sinusoidal motion with an amplitude of +/−7 degrees, according to an embodiment of the present invention. In should be appreciated that the linearity error (in the Hall effect Sensors is proportional to the distance from sensor to target) is reduced to a minimum, permitting the correct geometry of the target to achieve high accurate measure of angular displacement for larger angles.

In graph800, the error805from the optical encoder, and the error810from the Hall effect Sensors, are extracted. As expected, the error805from the optical encoder is irrelevant in its angular position. The error810of the Hall Effect sensors is less than 0.4 micro radian. A calibration factor due to “not-up-to date” thermal compensation Sensor Circuit is suspected, so if properly corrected, the error810may be reduced similar or closer to the error805from the encoder. This data essentially proves that the curved shape of the target minimizes the nonlinear effect encountered with a flat target.

Further investigation indicated that the 0.4 microradian discrepancy can be attributed to error due to not enough thermal compensation of the Hall Effect sensors' head electronic circuit. Current production Hall Effect sensors' head circuit have better thermal compensator that the one used for the experiment. The Hall effect Sensor used in the experiment.

The test results shown in the highlighted section proves that the Hall Effect sensors' heads tracks the encoder reading with an accuracy of 0.5 micro radian. This small discrepancy is an absolute demonstration that for 7 degrees of rotation, the nonlinearity is non existing. For common flat targets, the nonlinearity stars at approximately 5 to 7 milliradians of rotation and progresses quadratically from there and on.

Returning toFIG.6, this embodiment was set up to verify that a specially shaped target can reduce or eliminate the nonlinearity normally experienced with flat targets. The angular reading of encoder330, that does not experience nonlinearity, is used as a witness to compare the reading of the Hall effect sensors' heads for the rotation of the test set up.

FIG.7Ais a diagram illustrating a center of target705being offset with respect to the rotation axis “Z”, according to an embodiment of the present invention. In this embodiment, center on target705is offset with respect to the axis of rotation “Z”. As target705rotations around “Z” axis, target oscillates, widening and closing the gap of the opposite sensors, which are oriented in the direction of the “X” axis. Put simply, this embodiment infers that one is not limited to a spherical target only, but may apply to any target body (e.g., rectangular) that is offset with the rotation center of the axis.

FIG.7Bis a diagram illustrating a target705rotating around axis “Z”, according to an embodiment of the present invention. In this embodiment, as target705rotates around the “Z” axis, target oscillates, widening and closing the gap of the opposite sensors oriented in the direction of the “X” axis. Simply put, this embodiment shows that, as the geometric center of the cylinder rotates, gap730Ais widened on the left side (sensor) and gap730Bon the right side (sensor) decreases. It creates an imbalance of voltage, allowing for a displacement to be read.

Currently, sensors are capable of reading with acceptable accuracy rotation around one axis “Z”. See, for example,FIG.1. If a second axis of rotation is added orthogonal to the axis “X”, as depicted inFIG.1, then a second set of sensors would be required to measure rotation around the axis “X”. If a compound angle is commanded, the target will be oriented (or tilted) with respect to the sensors as shown inFIG.2. This will result in unacceptable errors. Some embodiments overcome these issues as shown inFIGS.3-7Band as described above.

It will be readily understood that the components of various embodiments of the present invention, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the detailed description of the embodiments, as represented in the attached figures, is not intended to limit the scope of the invention as claimed but is merely representative of selected embodiments of the invention.

The features, structures, or characteristics of the invention described throughout this specification may be combined in any suitable manner in one or more embodiments. For example, reference throughout this specification to “certain embodiments,” “some embodiments,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in certain embodiments,” “in some embodiment,” “in other embodiments,” or similar language throughout this specification do not necessarily all refer to the same group of embodiments and the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

It should be noted that reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussion of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment.

Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention.

One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention. In order to determine the metes and bounds of the invention, therefore, reference should be made to the appended claims.