Capacitive linear encoder

Patent metadata

Field	Value
Publication number	US-10132653-B2
Application number	US-201514958802-A
Country	US
Kind code	B2
Filing date	Dec 3, 2015
Priority date	Dec 4, 2014
Publication date	Nov 20, 2018
Grant date	Nov 20, 2018

Abstract

Some embodiments of the invention include a capacitive linear encoder for determining positions comprising a scale and a read head for capacitively scanning the scale, wherein scale and read head are movable relative to one another. The scale has at least one, preferably capacitive, position reference marker. On the basis of the position references provided by the capacitive position reference marker, the positions are locatable in absolute terms and verifiable.

First claim

The invention claimed is:

1. A capacitive linear encoder for determining positions along a feed direction comprising:
a read head having a multiplicity of first coupling electrodes arranged along the feed direction,
a scale having a multiplicity of second coupling electrodes arranged along the feed direction, and
a control and evaluation unit, wherein:
read head and scale are displaceable relative to one another in the feed direction,
the width of the first coupling electrodes and the width of the second coupling electrodes are coordinated with one another,
the first coupling electrodes have at least three coupling signal phases offset with respect to one another, wherein the sequence of the coupling signal phases is defined by a phase permutation, such that in each case a series of adjacent first coupling electrodes form a P-interval,
upon control by the control and evaluation unit temporally changing coupling signals are exchanged by capacitive coupling between the first and second coupling electrodes,
the positions are determinable by the control and evaluation unit by a signal evaluation of the coupling signals exchanged between the first and second coupling electrodes, wherein the second coupling electrodes are divided into at least two mutually reciprocal types for a differential evaluation of the coupling signals, and
the scale
is passive, for which purpose the linear encoder comprises capacitive, signal transfer means for transferring the coupling signals between scale and read head, and
has at least one position reference marker which is formed by means of the signal transfer means, for which purpose signal transfer means are modified at a location of the scale that defines a position reference,
for position reference marker identification the position reference marker is identifiable by means of identification signals controlled by the control and evaluation unit.

2. The linear encoder according to claim 1 , wherein:
the signal transfer means comprises a capacitive signal transfer means.

3. The linear encoder according to claim 1 , wherein:
the position reference marker comprises a capacitive position reference marker.

4. The linear encoder according to claim 1 , wherein:
the second coupling electrodes comprise receiver electrodes.

5. The linear encoder according to claim 4 , wherein:
the read head has at least two third coupling electrodes, wherein at least one third coupling electrode is fitted in a manner disposed upstream and/or downstream of each first transfer electrode in the feed direction, and the third coupling electrodes are usable as shielding electrodes for electrically shielding the respective first transfer electrode, wherein the read head has, between the respective first transfer electrode and the respective third coupling electrodes,
further shielding electrodes serving for electrically shielding the first transfer electrodes.

6. The linear encoder according to claim 1 , wherein:
the first coupling electrodes comprise emitter electrodes.

7. The linear encoder according to claim 1 , wherein:
the first coupling electrodes have four coupling signal phases offset with respect to one another by in each case one quarter.

8. The linear encoder according to claim 1 , wherein:
the positions are locatable in absolute terms on the basis of a reference position marker defining an absolute reference point, and/or
the scale has a plurality of position reference markers in the feed direction, wherein positions located in absolute terms on the basis of the reference position markers are verifiable.

9. The linear encoder according to claim 1 , wherein:
the signal feedback means are embodied as transfer electrodes, wherein the scale has a plurality of second transfer electrodes per type of the second coupling electrodes, and the read head has at least one first transfer electrode per type of the second coupling electrodes, wherein:
each second transfer electrode is electrically conductively connected to one or a plurality of second coupling electrodes of one type, second transfer electrodes couple capacitively to the at least one first transfer electrode of the same type.

10. The linear encoder according to claim 9 , wherein:
a respective position reference marker is formed by means of adjacent modified second transfer electrodes, wherein in each case at least two adjacent second transfer electrodes are short-circuited for the modification, wherein:
the read head has at least one third coupling electrode which
is suitable for transmitting identification signals which change temporally, and
by means of capacitive coupling the identification signals are transmittable between the third coupling electrode and second transfer electrodes,
a respective position reference marker is identifiable on the basis of the identification signals.

11. The linear encoder according to claim 10 , wherein:
the at least one third coupling electrode is fitted to the read head in the feed direction upstream and/or downstream of a first transfer electrode and in a manner electrically insulated therefrom, and the third coupling electrode and the second transfer electrodes are coordinated with one another in such a way that the modified second transfer electrodes serve for transmitting the identification signals between the third coupling electrode and the first transfer electrode.

12. The linear encoder according to claim 11 , wherein:
the third coupling electrode and the second transfer electrodes are coordinated with one another by virtue of the fact that two or more short-circuited second transfer electrodes have an extent in the feed direction such that with a constant relative position of read head with respect to scale the short-circuited second transfer electrodes are capacitively couplable both to the respective first transfer electrode and to the third coupling electrode, such that a transfer of identification signals transmitted by the third coupling electrode to the control and evaluation unit takes place only in the presence of a capacitive position reference marker in the form of the short-circuited second transfer electrodes.

13. The linear encoder according to claim 12 , wherein:
the second transfer electrodes are adjacent in the feed direction.

14. The linear encoder according to claim 12 , wherein:
the read head has shielding electrodes for electrically shielding the first transfer electrodes, whereby disturbances of the coupling signals caused by external or internal sources are at least reduced.

15. The linear encoder according to claim 1 , wherein:
for robustness relative to deviations from an ideal alignment of the read head with respect to the scale transversely with respect to the feed direction the extent transversely with respect to the feed direction of transfer electrodes coupling to one another of the scale and of the read head differ from one another, and/or
each second transfer electrode is connected to a sequence of second coupling electrodes that are adjacent in the feed direction, wherein the length of each such sequence corresponds to the length over which exactly one of the P-intervals extends on the read head.

16. The linear encoder according to claim 1 , wherein:
the first and/or second coupling electrodes are surrounded by an electrically shielding protective electrode, and/or
the first and/or second coupling electrodes are coordinated with one another in such a way that a sinusoidal profile of the capacitive coupling is generated by a displacement of the scale relative to the read head, wherein
for as dense an arrange

Assignees

• Hexagon Technology Ct Gmbh

Inventors

• Rohner Marcel
• Bednarek Ingo
• Wohlgenannt Rainer
• Baumann Lukas

Classifications

• G01D5/2415 Primary

  adapted for encoders · CPC title