Scale configuration for inductive position encoder
An inductive type position encoder includes a scale, a detector portion and a signal processor. The scale includes a periodic pattern of signal modulating elements (SME) arranged along a measuring axis, with a spatial wavelength W 1 . One type of SME in the pattern comprises similar conductive plates or loops. The detector portion comprises sensing elements and a field generating coil that generates a changing magnetic flux. The sensing elements may comprise conductive loop portions arranged along the measuring axis and configured to provide detector signals which respond to a local effect on the changing magnetic flux provided by adjacent SME's. In various implementations, the first type of SMEs have an average dimension DSME along the measuring axis direction that is greater than DSEN and at least 0.55*W 1 and at most 0.8*W 1 , which provides advantageous detector signal characteristics.
1 . An electronic position encoder usable to measure a relative position between two elements along a measuring axis direction, the electronic position encoder comprising:
a scale extending along the measuring axis direction which includes a periodic scale pattern comprising at least a first type of signal modulating elements, wherein the periodic scale pattern has a spatial wavelength W 1 and signal modulating elements of the first type comprising conductive plates that are located along the measuring axis direction corresponding to the spatial wavelength W 1 , and wherein the signal modulating elements of the first type each have a same shape and each have a same average dimension DSME along the measuring axis direction, for which the average dimension DSME is an edge to edge value that includes the entire width of a respective conductive plate of the conductive plates, wherein the entire width is a dimension in the measuring axis direction, and wherein non-signal modulating spaces between the signal modulating elements of the first type each have a same shape and a same average dimension DSPC along the measuring axis direction which is equal to W 1 minus DSME;
a detector portion configured to be mounted proximate to the periodic scale pattern and to move along the measuring axis direction relative to the periodic scale pattern, the detector portion comprising:
a field generating coil fixed on a substrate, the field generating coil surrounding an interior area configured to be aligned with the periodic scale pattern of the signal modulating elements during operation, the field generating coil configured to generate a changing magnetic flux in the interior area in response to a coil drive signal; and
a set of sensing elements arranged along the measuring axis direction and fixed on the substrate, members of the set of sensing elements comprising conductive loops having a nominal sensing element width dimension DSEN along the measuring axis direction for that portion of the sensing element that is aligned with or overlaps the interior area, for which the nominal sensing element width dimension DSEN is an edge to edge value that includes the entire maximum width of a respective conductive loop of the conductive loops, wherein the entire maximum width is a dimension in the measuring axis direction, and wherein the set of sensing elements are configured to provide detector signals which respond to a local effect on the changing magnetic flux provided by adjacent signal modulating elements of the signal modulating elements of the scale pattern; and
a signal processing configuration that is operably connected to the detector portion to provide the coil drive signal and is configured to determine a relative position between the detector portion and the scale pattern based on the detector signals input from the detector portion,
wherein DSME is greater than DSEN, and DSME is at least 0.7*W 1 and at most 0.8*W 1 .
2 . The electronic position encoder of claim 1 wherein the average dimension DSME is at most 1.6*DSEN.
3 . The electronic position encoder of claim 1 wherein 0.45*W 1 <DSEN<0.55*W 1 .
4 . The electronic position encoder of claim 1 wherein DSEN is approximately 0.5*W 1 .
5 . The electronic position encoder of claim 1 wherein the scale includes an approximately planar scale substrates and the detector portion is configured to be mounted approximately parallel to the periodic scale pattern with a nominal operating gap between the detector portion and the scale pattern which is at least 0.075*W 1 .
6 . The electronic position encoder of claim 5 wherein the nominal operating gap is at least 0.15*W 1 .
7 . The electronic position encoder of claim 1 , wherein the conductive loops of the sensing elements comprise parallel conductor segments that are perpendicular to the measuring axis direction, and that are configured to align with or overlap the interior area, and the parallel conductor segments are spaced at the nominal sensing element width dimension DSEN along the measuring axis direction.
8 . The electronic position encoder of claim 1 , wherein the conductive plates of the signal modulating elements of the first type that each have the same shape and each have the same average dimension DSME along the measuring axis direction comprise approximately parallel plate edges that are perpendicular to the measuring axis direction and that bound their effective region, and those parallel plate edges are spaced at the average dimension DSME along the measuring axis direction.
9 . The electronic position encoder of claim 1 wherein the average dimension DSME is more than 0.7*W 1 .
10 . The electronic position encoder of claim 9 wherein the average dimension DSME is less than 0.8*W 1 .
11 . The electronic position encoder of claim 1 wherein the signal modulating elements are each configured to have an effective width Weff that is sensed by the sensing elements, for which the effective width Weff results from the average dimension DSME and the effective width Weff is less than the average dimension DSME.
12 . The electronic position encoder of claim 11 wherein the effective width Weff is closer to 0.66*W 1 than the average dimension DSME is to 0.66*W 1 .
13 . The electronic position encoder of claim 12 wherein the effective width Weff is configured to provide a spatial filtering of a third harmonic from the detector signals.
14 . The electronic position encoder of claim 13 wherein the effective width Weff is approximately 0.66*W 1 .
15 . The electronic position encoder of claim 13 wherein the average dimension DSME is less than 0.8*W 1 .
16 . The electronic position encoder of claim 15 wherein the average dimension DSME is more than 0.7*W 1 .