RADIAL INDUCTIVE POSITION SENSOR FOR DETECTING A ROTATIONAL MOVEMENT, HIGH-RESOLUTION POSITION SENSOR SYSTEM AND TORQUE SENSOR SYSTEM

Abstract

A radial inductive position sensor, high-resolution position sensor system and a torque sensor system for detecting a rotational movement are disclosed. The radial inductive position sensor includes at least one transmitter coil, at least one receiver coil pair with a first receiver coil and a second receiver coil, and a moving conductive target, which is connected or connectable to a rotating shaft, wherein the at least one transmitter coil and the at least one receiver coil pair are arranged on a substrate, wherein the substrate has a radial configuration for at least partially surrounding the moving conductive target and/or the rotating shaft.

Claims

1. A radial inductive position sensor for detecting a rotational movement, the radial inductive position sensor comprising: at least one transmitter coil; at least one receiver coil pair comprising a first receiver coil and a second receiver coil; and a moving conductive target connected or connectable to a rotating shaft, wherein the at least one transmitter coil and the at least one receiver coil pair are arranged on a substrate, and wherein the substrate has a radial configuration for at least partially surrounding the moving conductive target and/or the rotating shaft.

2. The radial inductive position sensor according to claim 1, wherein the substrate is a printed circuit board and the at least one transmitter coil and the at least one receiver coil pair are formed by copper traces on the printed circuit board.

3. The radial inductive position sensor according to claim 1, wherein the substrate is flexible or has a thickness that allows the radial configuration of the substrate, or wherein the substrate comprises multiple parts that can be arranged radially around the moving conductive target and/or the rotating shaft.

4. The radial inductive position sensor according to claim 1, wherein the first receiver coil is a sine receiver coil and the second receiver coil is a cosine receiver coil.

5. The radial inductive position sensor according to claim 1, wherein the at least one receiver coil pair has one period for detecting the absolute position of the moving conductive target.

6. The radial inductive position sensor according to claim 1, wherein the at least one receiver coil pair has multiple periods for detecting a high-resolution position of the moving conductive target.

7. The radial inductive position sensor according to claim 1, wherein the at least one receiver coil pair comprises a first receiver coil pair having one period for detecting the absolute position of the moving conductive target and a second receiver coil pair having multiple periods for detecting a high-resolution position of the moving conductive target.

8. The radial inductive position sensor according to claim 1, wherein the moving conductive target comprises one active portion or multiple active portions.

9. The radial inductive position sensor according to claim 1, wherein the substrate completely surrounds the moving conductive target and/or the rotating shaft.

10. The radial inductive position sensor according to claim 1, wherein the moving conductive target is arranged inside or outside the substrate having the radial configuration.

11. The radial inductive position sensor according to claim 1, wherein the at least one transmitter coil and/or the at least one receiver coil pair are implemented twice on the substrate, on separate layers or with an interleaved or distributed coil design.

12. A high-resolution position sensor system comprising: a first inductive position sensor; and a second inductive position sensor, wherein at least one of the first inductive position sensor and the second inductive position sensor is the radial inductive position sensor according to claim 1, and wherein periods of the at least one receiver coil pair of the first inductive position sensor and the at least one receiver coil pair of the second inductive position sensor are different.

13. The high-resolution position sensor system according to claim 12, wherein the at least one receiver coil pair of the first inductive position sensor has one period for detecting the absolute position of the moving conductive target and the at least one receiver coil pair of the second inductive position sensor has multiple periods for detecting a high-resolution position of the moving conductive target, or wherein the periods of the at least one receiver coil pair of the first inductive position sensor and the at least one receiver coil pair of the second inductive position sensor are different to provide a Nonius scale.

14. A torque sensor system comprising: a first inductive position sensor; and a second inductive position sensor, wherein at least one of the first inductive position sensor and the second inductive position sensor is the radial inductive position sensor according to claim 1, and wherein the first inductive position sensor and the second inductive position sensor are mounted on different ends of the rotating shaft subject to torque.

15. The torque sensor system according to claim 14, further comprising at least one further radial inductive position sensor for providing a high-resolution position sensor system in combination with the first inductive position sensor and/or the second inductive position sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 shows a schematic view of an embodiment of an axial inductive position sensor according to the prior art.

[0035] FIG. 2 shows a schematic view of a first embodiment of a radial inductive position sensor.

[0036] FIG. 3 shows a detailed view of the printed circuit board with the set of coils of the radial inductive position sensor of FIG. 2.

[0037] FIGS. 4A-4C show different configurations of the set of coils and the moving conductive target of a radial inductive position sensor.

[0038] FIG. 5 shows a detailed view of another embodiment of a substrate with a set of coils for a radial inductive position sensor.

[0039] FIG. 6 shows a schematic view of a high-resolution position sensor system comprising a radial inductive position sensor.

[0040] FIG. 7 shows a schematic view of a torque sensor system comprising an axial inductive position sensor.

[0041] FIG. 8 shows a schematic view of a torque and high-resolution position sensor system comprising a radial inductive position sensor.

DETAILED DESCRIPTION

[0042] FIG. 1 shows a schematic view of an embodiment of an axial inductive position sensor 1 for detecting a rotational movement according to the prior art. The inductive position sensor 1 detects the movement of a conductive target 2 relative to a receiver coil pair 3, 4, comprising a sine receiver coil 3 and a cosine receiver coil 4, which generate a corresponding analog sine output signal and a corresponding analog cosine output signal.

[0043] The position sensor 1 of FIG. 1 is an inductive position sensor 1 implementing a magnet-free technology, utilizing the physical principles of eddy currents or inductive coupling to detect the position of the conductive target 2 that is moving above a set of coils 3, 4, 5, including for example one transmitter coil 5 and the receiver coil pair 3, 4, such as the sine receiver coil 3 and the cosine receiver coil 4.

[0044] In a practical implementation of the three coils 3, 4, 5, one transmitter coil 5 and two receiver coils 3, 4, are typically provided as copper traces on a printed circuit board (PCB) 7. They are arranged such that the transmitter coil 5 induces a secondary voltage in the two receiver coils 3, 4, which depends on the position of the conductive, e.g., metallic, target 2 above the receiver coils 3, 4. Therefore, the inductive position sensor 1 comprises or is connected to an oscillator that generates a radio-frequency signal, which is applied to the transmitter coil 5 to create a high frequency magnetic field. This high frequency magnetic field is picked up by the receiver coils 3, 4, for example the sine receiver coil 3 and the cosine receiver coil 4. Depending on the position of the conductive target 2 above the coils 3, 4, 5, the secondary voltage picked up by the receiver coils 3, 4 is changing in amplitude, allowing the determination of the target's position by analysing this effect. For example, the target position is calculated by the arctangent of the sine signal divided by the cosine signal. The calculation is performed by a processing unit 6, which is arranged on the PCB 7 or is a separate component connected to the receiver coil pair 3, 4.

[0045] According to the prior art, the inductive position sensor 1 for detecting a rotational movement, the transmitter coil 5 and the receiver coil pair 3, 4 are arranged on the substrate 7 extending in a plane perpendicular to the longitudinal axis of the rotating shaft 8, as shown in FIG. 1. The conductive target 2 is attached to the rotating shaft 8 and extends in a radial direction, so that the conductive target 2 is moving above the set of coils 3, 4, 5. This configuration is referred to as an axial inductive position sensor 1 as the set of coils 3, 4, 5 is arranged in an axial plane.

[0046] A signal representation of the target's position over the coils 3, 4, 5 is obtained by demodulating and processing the secondary voltages from the receiver coils 3, 4 in the processing unit 6. Usually, after filtering the receiver signals are demodulated and amplified, then converted to a digital signal by an analog-to-digital converter and further processed in a digital signal processor, like being converted from sine and cosine signals into an angle representation by means of a CORDIC algorithm, transforming rectangular coordinates to polar coordinates. Following this digital signal processing, a signal representative of the target's position over the coils 3, 4, 5 is available in digital format and fed to an output interface of the inductive position sensor 1.

[0047] The accuracy of the inductive position sensor 1 shown in FIG. 1 depends on the airgap between the set of coils 3, 4, 5 and the conductive target 2. By increasing the airgap, the distance between the set of coils 3, 4, 5 and the conductive target 2 increases, which results in reduced amplitudes, increased signal noise and affected system linearity. A further source of error is an axial tolerance or axial play of the rotating shaft 8, to which the conductive target 2 is connected. Due to the axial tolerance or axial play the distances between the set of coils 3, 4, 5 and the moving conductive target 2 may continuously change over time and/or position.

[0048] FIG. 2 shows a schematic view of a first embodiment of a radial inductive position sensor 1 for detecting a rotational movement. The radial inductive position sensor 1 shown in FIG. 2 comprises a transmitter coil 5 and a receiver coil pair 3, 4 with a first receiver coil 3 and a second receiver coil 4. The first receiver coil 3 is a sine receiver coil and the second receiver coil 4 is a cosine receiver coil. The transmitter coil 5 and the receiver coil pair 3, 4 are arranged on a substrate 7. The substrate 7 is for example a printed circuit board (PCB) and the transmitter coil 5 and the receiver coil pair 3, 4 are formed by copper traces on the PCB.

[0049] The radial inductive position sensor 1 shown in FIG. 2 further comprises a moving conductive target 2, which is connectable to a rotating shaft 8, for example of a motor. The rotating shaft 8 is not shown in FIG. 2. Alternatively, the moving conductive target 2 can be connected to the rotating shaft 8.

[0050] The substrate 7 has a radial configuration and at least partially surrounds the moving conductive target 2. According to the first embodiment shown in FIG. 2, the substrate 7 partially surrounds the moving conductive target 2.

[0051] In the radial configuration, the set of coils 3, 4, 5, i.e., the transmitter coil 5 and the receiver coil pair 3, 4, are arranged in a plane that is radially surrounding the moving conductive target 2 and the rotating shaft 8, once the moving conductive target 2 has been connected to the rotating shaft 8. Thus, the substrate 7 on which the coils 3, 4, 5 are arranged has a circular shape and at least partially surrounds the moving conductive target 2 and/or the rotating shaft 8. The substrate 7 can have the form of a hollow cylinder, a C-shape, a U-shape or similar.

[0052] The radial configuration of the inductive position sensor 1 has the advantage that an axial tolerance or axial play of the rotating shaft 8 has no respectively only an insignificant impact on the accuracy of the position sensor 1, for example on the signal amplitudes of the receiver coil pair 3, 4. Thus, the radial inductive position sensor 1 is robust against errors resulting from axial tolerances or axial play of the rotating shaft 8.

[0053] A further advantage of the radial configuration is a cost reduction because the size of the substrate 7 can be optimized, whereas the axial configuration known from the prior art as shown in FIG. 1 usually requires a cut-off in the substrate 7 for the rotating shaft 8. Another advantage is a weight reduction due to target design optimization because the size of the moving conductive target 2 can be smaller for the radial configuration compared to an axial configuration of the inductive position sensor 1, for example if the moving conductive target 2 is arranged inside the circular substrate 7.

[0054] Further electronic components, like the processing unit 6 for processing the signals of the receiver coil pair 3, 4 or controlling an oscillator connected to the transmitter coil 5, can be arranged on the same substrate 7 as the set of coils 3, 4, 5 or be a separate part.

[0055] The substrate 7 respectively PCB is flexible or has a thickness that allows the radial configuration of the substrate 7 respectively PCB. The flexible substrate 7 respectively PCB is held in the radial configuration by a housing or guide 9, to which the flexible substrate 7 respectively PCB is connected, e.g., by fixtures or mountings.

[0056] FIG. 3 shows a detailed view of the PCB 7 with the set of coils 3, 4, 5 of the radial inductive position sensor 1 of FIG. 2. The first receiver coil 3 is a sine receiver coil 3 with one period along the movement path of the moving conductive target 2 and the second receiver coil 4 is a cosine receiver coil 4 with one period along the movement path of the moving conductive target 2. Although the substrate 7 is shown in FIG. 3 in plane it is actually radially surrounding the moving conductive target 2 of the radial inductive position sensor 1. FIG. 3 shows the configuration of the set of coils 3, 4, 5 on the substrate 7 and not the positioning of the substrate 7 relative to the moving conductive target 2 and/or rotating shaft 8.

[0057] As shown in FIG. 2, the moving conductive target 2 has one active portion, i.e., conductive part above the set of coils 3, 4, 5 to adapt the signals received by the receiver coils 3, 4 in response to the signal emitted from the transmitter coil 5, which is adapted by the position of the moving conductive target 2, such as the position of the active portion of the moving conductive target 2.

[0058] The receiver coil pair 3, 4 with one period along the movement path of the moving conductive target 2 can detect the absolute position of the moving conductive target 2.

[0059] FIGS. 4A-4C show different configurations of the set of coils 3, 4, 5 and the moving conductive target 2 of a radial inductive position sensor 1. The left-hand side of FIGS. 4A-4C show a top or bottom view of radial inductive position sensor 1 along the axis of the rotating shaft 8 and the right-hand side shows a plane view of the substrate 7 according to FIG. 3.

[0060] In all three embodiments shown in FIGS. 4A-4C, the substrate 7 completely surrounds the moving conductive target 2 and rotating shaft 8, which are arranged centrally inside the circular substrate 7. The portion of the substrate 7 comprising the processing unit 6, a connector and/or other components extends radially outside, as shown on the left-hand side of FIGS. 4A-4C.

[0061] Furthermore, in all three embodiments shown in FIGS. 4A-4C the pair of receiver coils 3, 4 comprise one period along the portion of the substrate covered by the set of coils 3, 4, 5.

[0062] According to FIG. 4A, the set of coils 3, 4, 5 extends along the complete circumference of the A moving conductive target 2 and rotating shaft 8, i.e., over 360°. Over this 360° the first receiver coil 3 and the second receiver coil 4 each have one period, as for example shown in FIG. 3. In this embodiment, the moving conductive target 2 has one active portion, which for example extends over 180°. This embodiment is used to determine the absolute position of the moving conductive target 2.

[0063] According to FIG. 4B, the set of coils 3, 4, 5 extends along 90° of the circumference of the moving conductive target 2 and rotating shaft 8. In this embodiment the moving target 2 has four active portions spaced by 90°, so that always one active portion is arranged above the set of coils. In this embodiment, the radial inductive position sensor 1 provides a high-resolution signal for determining the position of the moving conductive target 2. However, the radial inductive position sensor 1 according to FIG. 4B is unable to determine the absolute position of the moving conductive target 2.

[0064] According to FIG. 4C, the radial inductive position sensor comprises a second set of coils 3, 4, 5, wherein each set of coils 3, 4, 5 extends along 90° of the circumference of the moving conductive target 2 with 4 portions and the rotating shaft 8. The first set of coils 3, 4, 5 and the second set of coils 3, 4, 5 are located on opposite sides of the rotating shaft, i.e., they are spaced about 180° from each other. The two sets of coils 3, 4, 5 are separate in a redundant configuration or are connected in series (3 with 3, 4 with 4, 5 with 5). The transmitter coils 5 of the two set of coils 3, 4, 5 can be connected in series to an oscillator, so that they are operated simultaneously. Like in FIG. 4B, the moving conductive target 2 has four active portions spaced by 90°.

[0065] The substrate of the embodiments shown in FIGS. 4B and 4C must not completely surround the moving conductive target 2 and rotating shaft 8. For example, the portions of the substrate without any coil portions or other components could be removed, as indicated by the dashed lines in FIGS. 4B and 4C. This simplifies the mounting of the radial inductive position sensor 1 because it could be mounted sideways and thus independent of the spacing next to the end of the rotating shaft 8.

[0066] FIG. 5 shows a detailed view of another embodiment of a substrate 7 with a set of coils 3, 4, 5 for a radial inductive position sensor 1. According to the embodiment shown in FIG. 5, the radial inductive position sensor 1 comprises one transmitter coil 5, a first receiver coil pair 3, 4 and a second receiver coil pair 10, 11, which are arranged on substrate 7. The transmitter coil 5, the first receiver coil pair 3, 4 and the second receiver coil pair 10, 11 are connected to an external processing unit 6. The first receiver coil pair 3, 4 comprises a first receiver coil 3 and a second receiver coil 4 and the second receiver coil pair 10, 11 comprises a third receiver coil 10 and a fourth receiver coil 11.

[0067] The substrate 7 has a radial configuration for at least partially surrounding the moving conductive target 2 and/or the rotating shaft 8. The moving conductive target 2 has one active portion, which moves above the set of coils 3, 4, 5, 10, 11 along a 360° movement. The first receiver coil pair 3, 4 has one period along the substrate 7 and can be used to determine the absolute position of the moving conductive target 2. The second receiver coil pair 10, 11 has multiple periods along the substrate 7 and can be used to determine a high-resolution position of the moving conductive target 2. Combining the results of the first receiver coil pair 3, 4 and the second receiver coil pair 10, 11 results in a high-resolution absolute position detection of the moving conductive target 2.

[0068] FIG. 6 shows a schematic view of a high-resolution position sensor system 13 comprising at least two inductive position sensors 1. According to the embodiment shown in FIG. 6, both inductive position sensors 1 are radial inductive position sensors 1. However, it is sufficient if only one position sensor 1 is a radial inductive position sensor 1, while the other inductive position sensor 1 is an axial inductive position sensor 1 according to the prior art. The periods of the receiver coil pairs 3, 4 of the first radial inductive position sensor 1 and the second radial inductive position sensor 1 are different. For example, the receiver coil pair 3, 4 of one radial inductive position sensor 1 has one period for detecting the absolute position of the moving conductive target 2 and the receiver coil pair 3, 4 of the other inductive position sensor 1 has multiple periods for detecting a high-resolution position of the moving conductive target 2. Alternatively, the periods of the receiver coil pairs 3, 4 of the first radial inductive position sensor 1 and the second inductive position sensor 1 are different to provide a Nonius scale.

[0069] The high-resolution position sensor system 13 shown in FIG. 6 uses two different radial inductive position sensors 1 to determine the absolute position of the conductive moving target with a high-resolution. Both radial inductive position sensors 1 are mounted next to each other around the rotating shaft 8, to which a moving conductive target 2 is mounted.

[0070] FIG. 7 shows a schematic view of a torque sensor system 14 comprising two radial inductive position sensors 1. The first radial inductive position sensor 1 and the second radial inductive position sensor 1 are mounted on different ends of a rotating shaft 8 subject to torque. By measuring the position of the different ends of the rotating shaft 8 using the first and second radial inductive position sensors 1 a torque of the rotating between the two radial inductive position sensors 1 can be determined by simply comparing the results of the first and second radial inductive position sensors 1.

[0071] FIG. 8 shows a schematic view of a torque and high-resolution position sensor system 15 comprising two radial inductive position sensors 1 and an axial inductive position sensor 1 according to the prior art. The configuration of the two radial inductive position sensors 1 corresponds to the torque sensor system shown in FIG. 7. The additional axial inductive position sensor 1 is used for providing an absolute high-resolution position of the moving conductive target 2 mounted to the rotating shaft 8 in combination with one of the radial inductive position sensors 1. Alternatively, a third radial inductive position sensor 1 could be used instead of the axial inductive position sensor 1. The axial inductive position sensor 1 can be mounted to an end of the rotating shaft 8 having less axial tolerance or axial play.