EP-4741773-A1 - AN INDUCTIVE ENCODER

EP4741773A1EP 4741773 A1EP4741773 A1EP 4741773A1EP-4741773-A1

Abstract

An inductive encoder comprising first and second members relatively moveable along a measurement direction, configured such that: the first member has, arranged at or toward a front side thereof which faces the second member, at least a first scale track; and such that the second member has, arranged at or toward a front side thereof which faces the first member: an excitation coil through which an alternating current is passed at a predetermined operating frequency so as to generate an alternating magnetic field which is manipulated by the first scale track; and at least a first receiver coil for sensing the alternating magnetic field as manipulated by the first scale track, via which the relative position of the first and second members along the measurement direction can be measured. The inductive encoder is further configured such that: i) the first member comprises magnetically permeable material having a relative magnetic permeability µ r of at least 2 at said operating frequency so as to increase, at least at the first scale track, the magnetic flux density of the magnetic field generated by the excitation coil; and/or ii) the second member comprises magnetically permeable material having a relative magnetic permeability µ r of at least 2 at said operating frequency so as to increase, at least at the first scale track, the magnetic flux density of the magnetic field generated by the excitation coil.

Inventors

The designation of the inventor has not yet been filed

Assignees

Renishaw plc

Dates

Publication Date: 20260513
Application Date: 20241106

Claims (16)

An inductive encoder comprising first and second members relatively moveable along a measurement direction, configured such that: • the first member has, arranged at or toward a front side thereof which faces the second member, at least a first scale track, • the second member has, arranged at or toward a front side thereof which faces the first member: ∘ an excitation coil through which an alternating current is passed at a predetermined operating frequency so as to generate an alternating magnetic field which is manipulated by the first scale track; and ∘ at least a first receiver coil for sensing the alternating magnetic field as manipulated by the first scale track, via which the relative position of the first and second members along the measurement direction can be measured, characterised in that : i) the first member comprises magnetically permeable material having a relative magnetic permeability µ r of at least 2 at said operating frequency so as to increase, at least at the first scale track, the magnetic flux density of the magnetic field generated by the excitation coil; and/or ii) the second member comprises magnetically permeable material having a relative magnetic permeability µ r of at least 2 at said operating frequency so as to increase, at least at the first scale track, the magnetic flux density of the magnetic field generated by the excitation coil.
An inductive encoder as claimed in claim 1, in which: • the magnetically permeable material of the first member is arranged behind the scale track; and/or • the magnetically permeable material of the second member is arranged behind the excitation coil and/or at least first receiver coil.
An inductive encoder as claimed in claim 1 or 2, in which: • the first member comprises a layered construction, and wherein the magnetically permeable material of the first member is sandwiched between a first layer thereof which comprises the first scale track, and a second layer thereof; and/or • the second member comprises a layered construction, and wherein the magnetically permeable material of the second member is sandwiched between a first layer thereof which comprises the excitation and receiver coils, and a second layer thereof.
An inductive encoder as claimed in claim 3, in which the second layer of the first member is a mounting member, comprising features via which the first member can be mounted to a machine part.
An inductive encoder as claimed in claim 3 or 4, in which the second layer of the first member comprises a metallic layer.
An inductive encoder as claimed in any of claims 3 to 5, in which the second layer of the second member comprises one or more electronic components mounted thereon.
An inductive encoder as claimed in any preceding claim, in which the magnetically permeable material of the first member and/or of the second member comprises a substrate having magnetic particles dispersed therethrough.
An inductive encoder as claimed in any preceding claim, in which the magnetically permeable material of the first member and/or of the second member has a relative magnetic permeability µ r at the operating frequency of at least 10, optionally of at least 20, for example of at least 30.
An inductive encoder as claimed in any preceding claim, in which: • the position and width of the magnetically permeable material of the first member, is such that it sits directly behind and extends over at least 75% of the entire width of the at least first scale track; and/or • the position and width of the magnetically permeable material of the second member, is such that it sits directly behind and extends over at least 75% of the entire width of the excitation and receiver coils.
An inductive encoder as claimed in any preceding claim, in which: • the magnetically permeable material of the first member extends along at least 75% of the length of the at least first scale track as measured along the measurement direction; and/or • the magnetically permeable material of the second member extends along at least 75% of the length of the excitation and receiver coils as measured along the measurement direction.
An inductive encoder as claimed in any preceding claim, in which the magnetically permeable material of the first member and/or of the second member increases, at least at the first scale track, the magnetic flux density of the magnetic field generated by the excitation coil, by at least 5%, optionally by at least 10%, for example by at least 20%.
An inductive encoder as claimed in any preceding claim, in which the inductive encoder is rotary inductive encoder, wherein: • the first and second members are relatively rotatable about an axis of rotation and wherein the measurement direction is a rotational measurement direction; • the at least first scale track extends annularly around a scale track axis; • the excitation and receiver coils extend annularly around a coil axis at different radii to each other; and wherein: - the magnetically permeable material of the first member extends around the scale track axis along the measurement direction; and/or - the magnetically permeable material of the second member extends around the coil axis along the measurement direction.
An inductive encoder as claimed in claim 12, in which the excitation coil is a single direction excitation coil such that in use current flowing through the excitation coil does so in one direction only around the coil axis at any given instant in time.
An inductive rotary encoder as claimed in claims 12 or 13, in which: • the first member has second and third scale tracks extending annularly around the scale track axis at different radii to each other and to the first scale track; • the second member comprises a second receiver coil for sensing the alternating magnetic field as manipulated by the second scale track, and a third second receiver coil for sensing the alternating magnetic field as manipulated by the third scale track, via which the relative rotational position of the first and second members about the axis of rotation can be measured, the second and third receiver coils have different radii to each other and to the excitation coil and the first receiver coil; • the first and second receiver coils are located on the same radial side of the excitation coil as each other, wherein the first receiver coil is radially separated from the excitation coil by the second receiver coil; • the third receiver coil is provided on the opposite radial side of the excitation coil to the first and second receiver coils.
An inductive rotary encoder as claimed in any preceding claim characterised in that at least one of the first and second members comprises a magnetic flux increaser within which a current flow is generated by the excitation coil's alternating magnetic field, and which in turn itself generates a magnetic field which acts to increase the magnetic flux density of the alternating magnetic field.
An apparatus as claimed in any preceding claim, in which the scale track(s) is(are) configured to manipulate the amplitude of the magnetic field dependent on the relative position of the first and second members along the measurement direction.

Description

The present invention relates to an inductive encoder, in particular an inductive rotary encoder. Inductive encoders are known and typically comprise: i) a first member (e.g. what is commonly referred to as a "rotor", in the case of a rotary encoder) for mounting to a first part of a machine (e.g. such as a shaft that is rotatable relative to a static part of the machine about an axis); and ii) a second member (e.g. what is commonly referred to as a "stator", in the case of a rotary encoder) for mounting to a second (e.g. static) part of a machine. Typically, one of the members (e.g. the second member/"stator") is an active/powered component and comprises transmit (or "excitation") and receiver coils (and associated electronics) for creating and sensing an alternating magnetic/electromagnetic field. The terms "magnetic field" and "electromagnetic field" are used interchangeably herein because the magnetic fields referred to herein are created by an electric current and therefore can also be referred to as an electromagnetic field. Also, as will be understood, references herein to a magnetic field created by an excitation or transmit coil are references to an "alternating" magnetic field created thereby, and is often referred to herein simply as a "magnetic field" for brevity. Typically, the other member (e.g. the first member/"rotor") is a passive/unpowered component comprising scale features which manipulate the electromagnetic field sensed by the second member's (e.g. the stator's) sensor coils such that the output(s) of the second member's (e.g. the stator's) receiver coil(s) are dependent on the relative position (e.g. relative rotational orientation about an axis, in the case of a rotary encoder) of the first and second members about the axis. Accordingly, the relative (e.g. rotational) position (and/or derivatives thereof) of the second member/stator and first member/rotor (and hence of the different parts of the machine) can be measured from the output(s) of the second member's/stator's receiver coil(s). The present invention relates to improvements in connection with inductive encoders. In particular the present document describes an inductive rotary encoder apparatus having first and second members relatively moveable along a measurement direction. The first member can have arranged at or toward a front side thereof which faces the second member, at least a first scale track. The second member can have arranged at or toward a front side thereof which faces the first member: an excitation coil through which an alternating current is passed at a predetermined operating frequency so as to generate an alternating magnetic field which is manipulated by the first scale track; and at least a first receiver coil for sensing the alternating magnetic field as manipulated by the first scale track, via which the relative position of the first and second members can be measured. According to a first aspect of the invention there is provided an inductive encoder comprising first and second members relatively moveable along a measurement direction, configured such that: the first member has arranged at or toward a front side thereof which faces the second member, at least a first scale track; the second member has arranged at or toward a front side thereof which faces the first member: an excitation coil through which an alternating current is passed at a predetermined operating frequency so as to generate an alternating magnetic field which is manipulated by the first scale track; and at least a first receiver coil for sensing the alternating magnetic field as manipulated by the first scale track, via which the relative position of the first and second members can be measured, characterised in that: i) the first member comprises magnetically permeable material having a relative magnetic permeability µr of at least 2 at said operating frequency so as to increase, at least at the first scale track, the magnetic flux density of the magnetic field generated by the excitation coil; and/or ii) the second member comprises magnetically permeable material having a relative magnetic permeability µr of at least 2 at said operating frequency so as to increase, at least at the first scale track, the magnetic flux density of the magnetic field generated by the excitation coil. As mentioned above, the first member has a "front" side which is configured to face the second member, and at or toward which, the at least first scale track is arranged. Accordingly, references herein to relative directional terms with respect to the first member, e.g. terms such as "front", "back", "rear", "in front of" and "behind", are made in connection therewith. In preferred embodiments, the magnetically permeable material of the first member is arranged behind the scale track. Preferably, the magnetically permeable material of the first member is arranged directly behind the scale track. As mentioned above, the second member has a "front" side w