Linear inductive position sensor
A position of a target is determined using a linear inductive position sensor that includes a target coil, an excitation coil, two sensors and a Vernier processor. The sensors each include two or more receive coils. The receive coils include multiple twisted loops. In the first sensor, the coils have a first period, with loops offset by first distance. In the second sensor, the coils have a second period, with loops offset by a second distance. The target coil width is a function of the first distance and the second distance. During operation, the coils output voltages in which third, fifth and/or seventh harmonics are cancelled. Based on the voltages, the sensors output respective first and second position signals, from which the Vernier processor calculates the target's position along an axis of the position sensor.
1. A linear inductive position sensor, comprising:
an excitation coil extending along an axis of a substrate, the excitation coil generating a first electromagnetic field in response to an alternating current (AC) signal received from a power source;
a target coil configured to move above the excitation coil and along the axis, the target coil inductively coupled to the excitation coil and generating a second electromagnetic field;
a first sensor extending along the axis, the first sensor including a first receiver coil and a second receiver coil inductively coupled to the target coil so as to generate a first voltage in the first receiver coil and a second voltage in the second receiver coil depending on a position of the target coil relative to the axis, the first receiver coil being separated from the second receiver coil by a distance based on a period λ of the first receiver coil; and
a first processor coupled to the first sensor, the first processor configured to generate a position signal based on the first voltage and the second voltage, the position signal representing the position of the target coil.
2. The linear inductive position sensor of claim 1 , wherein the excitation coil extends in a multi-loop configuration around a perimeter of the substrate.
3. The linear inductive position sensor of claim 1 , wherein the excitation coil encloses the first receiver coil and the second receiver coil.
4. The linear inductive position sensor of claim 1 , wherein the first receiver coil includes a first plurality of loops, and the second receiver coil includes a second plurality of loops.
5. The linear inductive position sensor of claim 4 , wherein first and second loops of the first plurality of loops are offset from one another by a distance D1.
6. The linear inductive position sensor of claim 5 , wherein D1=λ/14.
7. The linear inductive position sensor of claim 6 , wherein even numbered harmonics generated in the first voltage and the second voltage are nullified.
8. The linear inductive position sensor of claim 4 , wherein;
the first sensor further includes a third receiver coil inductively coupled to the target coil so as to generate a third voltage in the third receiver coil, depending on a position of the target coil relative to the axis,
the third receiver coil includes a third plurality of loops of which each loop is offset from a corresponding loop of the first plurality of loops and a corresponding loop of the second plurality of loops by a distance λ/3, and
the position signal is additionally based on the third voltage.
9. The linear inductive position sensor of claim 1 , further comprising:
a second sensor extending along the axis, the second sensor including first and second receiver coils inductively coupled to the target coil so as to generate a voltage Vr1′ in the first receiver coil of the second sensor and voltage Vr2′ in the second receiver coil of the second sensor, depending on a position of the target coil relative to the axis, the first and second receiver coils of the second sensor being separated by a distance based on a period λ2 of the second receiver coil of the second sensor; and
a second processor coupled to the second sensor, the second processor configured to generate a position signal X2 based on the voltage Vr1′ and the voltage Vr2′, the position signal X2 representing the position of the target coil.
10. The linear inductive position sensor of claim 9 , wherein:
the first receiver coil of the second sensor includes a first plurality of loops in a twisted loop configuration, and
the second receiver coil of the second sensor includes a second plurality of loops in a twisted loop configuration.
11. The linear inductive position sensor of claim 10 , wherein;
the second sensor further includes a third receiver coil inductively coupled to the target coil so as to generate a voltage Vr3′ in the third receiver coil of the second sensor, depending on a position of the target coil relative to the axis,
the third receiver coil includes a third plurality of loops of which each loop is offset from a corresponding loop of another at least one of the first receiver coil or the first receiver coil by a distance λ/3, and
the position signal X2 is additionally based on the voltage Vr3′.
12. The linear inductive position sensor of claim 11 , wherein first and second loops of the first plurality of loops are offset from one another by a distance D2.
13. The linear inductive position sensor of claim 12 , wherein first and second loops of the second plurality of loops are offset from one another by the distance D2.
14. The linear inductive position sensor of claim 12 , wherein D2=λ2/10 and the target coil has a width D3=3/5 λ=4/7 λ2.
15. The linear inductive position sensor of claim 14 , wherein odd numbered harmonics generated in the voltage Vr1′, the voltage Vr2′, and the voltage Vr3′ are nullified.
16. A linear inductive position sensor, comprising:
an excitation coil extending along an axis of a substrate;
a target coil configured to move above the excitation coil and along the axis, the target coil inductively coupled to the excitation coil when the excitation coil is provided with an alternating current, the target coil having a width;
a first sensor having a first plurality of receiver coils offset from one another by a distance λ, each receiver coil of the first plurality of receiver coils being inductively coupled to the target coil and including a first plurality of twisted loops, wherein a first twisted loop of the first plurality of twisted loops is offset from a second twisted loop of the first plurality of twisted loops by a first distance;
a second sensor having a second plurality of receiver coils offset from one another by a distance λ2, each receiver coil of the second plurality of receiver coils being inductively coupled to the target coil and including a second plurality of twisted loops, wherein a first twisted loop of the second plurality of twisted loops is offset from a second twisted loop of the second plurality of twisted loops by a second distance;
a first processor configured to generate a first position signal representing a position of the target coil, from a first set of voltages induced in the first plurality of receiver coils;
a second processor configured to generate a second position signal representing a position of the target coil, from a second set of voltages induced in the second plurality of receiver coils; and
a processor coupled to the first processor and the second processor, the processor configured to generate a final position signal using a Vernier principle, the final position signal representing a position of the target coil that is based on the first position signal X1 and the second position signal.
17. The linear inductive position sensor of claim 16 , wherein width depends on the distance λ and the distance λ2.
18. The linear inductive position sensor of claim 16 , wherein the first processor cancels 3 rd and 5 th harmonics in the first set of voltages.
19. The linear inductive position sensor of claim 16 , wherein the second processor cancels 3 rd , 5 th , and 7 th harmonics in the second set of voltages.
20. A method, comprising:
receiving a first position signal from a first processor, the first position signal representing a position of a target coil, based on a first set of voltage signals generated by a first sensor;
receiving a second position signal from a second processor, the second position signal representing a position of the target coil, based on a second set of voltage signals generated by a second sensor; and
determining the position of the target coil from the first position signal and the second position signal using a Vernier principle, wherein
third harmonics are cancelled from the first set of voltage signals,
fifth harmonics are cancelled from the second set of voltage signals, and
the target coil is sized to nullify seventh harmonics from at least one of the first set of voltage signals and the second set of voltage signals.