Magnetic position detector device for measuring displacement along a first axis

Abstract

Magnetic position detector device for measuring a displacement along a first axis (A), having a first structural element (1) and a second structural element (2) which are movable relative to each other along the first axis (A) and are positioned at a mutual distance (h) perpendicular to the first axis (A). At least two magnetic induction elements (Hj) are positioned on the first structural element (1) along the first axis (A) at a mutual induction distance (d). At least two magnets (Mi) are positioned on the second structural element (2) along the first axis (A) at a mutual magnet distance (a). A processing unit (5) is connected to the at least two magnetic induction elements (Hj) and is arranged to determine a displacement along the first axis (A) with sensor signals (Sj) from the at least two magnetic induction elements (Hj).

Description

TECHNICAL FIELD

[0001] The present invention relates to a long-stroke linear position detector device, more in particular to a magnetic position detector device for measuring displacement along a first axis, comprising a first structural element and a second structural element which are mutually movable along the first axis and are positioned at a mutual distance. I.e. the first structural element and the second structural element are positioned in a plane-parallel manner. Embodiments of the present invention can be applied in applications requiring high accuracy in long-stroke movements, such as position sensing in (smartphone) camera modules. BACKGROUND

[0002] US patent publication US 2010 / 0270469 discloses a lens position sensor for a camera that is particularly useful in lens assemblies with a relatively limited axial travel between near and far field lens focus positions. The camera includes a magnet or other exciter coupled to a rotatable lens that extends within a plane of the magnet, wherein the plane of the magnet is not perpendicular to the optical axis of the lens. A magnetic or other sensor senses the position of the magnet, which is indicative of the lens position. SUMMARY

[0003] The present invention seeks to provide an improved magnetic position detector device for measuring displacement along a first axis (i.e. linear position) with a high accuracy of about 0.1% over a long stroke.

[0004] According to the present invention, there is provided a magnetic position detector device as defined above, further comprising at least two magnetic induction elements positioned on the first structural element at a mutual induction distance along the first axis, at least two magnets positioned on the second structural element at a mutual magnet distance along the first axis, and a processing unit connected to the at least two magnetic induction elements and configured to determine the displacement along the first axis from sensor signals from the at least two magnetic induction elements.

[0005] Embodiments of the present invention allow to determine the displacement (linear position) along the first axis from the at least two sensor signals with a very high accuracy. Moreover, the device can be easily integrated in a camera module, such as a smartphone camera module. BRIEF DESCRIPTION OF DRAWINGS

[0006] The present invention will be described in more detail in the following, with reference to the attached drawings, in which

[0007] Figure 1A a graph of magnetic induction versus displacement is shown for a typical sliding Hall sensor configuration;

[0008] Figure 1B a graph of magnetic induction versus displacement is shown for a typical "front side" Hall sensor configuration;

[0009] Figure 2shows a schematic cross-sectional view of a magnetic position detector device according to a first embodiment of the present invention;

[0010] Figure 3 Shown from Figure 2 A graph of the sensor signal of the magnetic sensing element as a function of displacement is shown;

[0011] Figure 4 a graph showing a sensor signal from a second magnetic sensing element compared to a sensor signal from a first magnetic sensing element;

[0012] Figure 5 shows a schematic cross-sectional view of a magnetic position detector device according to a second embodiment of the present invention;

[0013] Figure 6 Shown from Figure 5 The sensor signal of the magnetic sensing element is shown as a function of displacement;

[0014] Figure 7 a graph showing a sensor signal from the second magnetic sensing element compared to the sensor signal from the first magnetic sensing element, and a graph showing a sensor signal from the third magnetic sensing element compared to the sensor signal from the first magnetic sensing element;

[0015] Figure 8 Shown Figure 5 a graph showing the number of blur points as a function of the distance between the first magnetic sensing element and the third magnetic sensing element for the configuration shown;

[0016] Figure 9 a schematic cross-sectional view showing a magnetic encoder device according to a third embodiment of the present invention; and

[0017] Figure 10 A flow chart illustrating a position calculation algorithm applied in an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0018] Due to continuous innovations and improvements in optics, miniaturization and image processing, the quality of smartphone cameras is now catching up with large standalone cameras such as Digital Single-Lens-Reflect (DSLR) or Full-Frame Mirrorless cameras. Today’s smartphones usually have 2 to 3 rear cameras, sometimes up to 4 to 5 cameras. Today, smartphone users simply focus and shoot, without having to change heavier lenses for the DSLR as photographers did a decade ago. The phone automatically combines the photos taken by the multiple camera modules integrated in the phone and post-processes them to obtain the final photo with the highest quality in just a few seconds. A recent analysis showed that, except for zoom quality, smartphones outperform or are comparable to standalone cameras in most aspects.

[0019] To obtain “optical” zoom pictures, smartphones use pictures taken by cameras with different focal lengths, e.g. the main camera (1x zoom) and the tele camera (e.g. 2x zoom), and then digitally blend them to generate the final picture with any zoom factor between 1x and 2x. In smartphone modules, the focal length of the tele camera lens is usually 5-7mm (focal ratio ~2x), which is limited by the thickness of the phone. Periscope-type tele camera modules have started to appear, where the light from the scene is folded by 90 degrees by a prism and travels along the length of the phone to reach the image sensor. This way, the focal length can be greatly extended to 20-30mm or more, equivalent to a zoom factor of 5-7x or even more.

[0020] So far, all periscope (tele) cameras in smartphones have been fixed focal length. The effect of a variable zoom factor is still done by digital blending of pictures. To further improve the quality, it is necessary to optically adjust the zoom factor by moving some lens elements over a long stroke, e.g. from 4mm to 15mm or more, while maintaining the positioning accuracy at a few microns or higher. The accuracy requirement is absolute accuracy, which means that at any time, the lens position relative to the image sensor must be accurately determined.

[0021] The moving lens elements can be driven by motors, e.g. Voice Coil Motor (VCM), Piezo motor or Shape Memory Alloy (SMA) motor. The motors are driven by a drive IC that employs closed-loop control techniques, which requires absolute positioning of the lens elements.

[0022] The strict accuracy of long-stroke movements is a real challenge for any known positioning sensor technology used in the camera module industry. For example, if an accuracy of 3pm is required over a stroke of 15mm, this corresponds to a required accuracy of 0.02%.

[0023] In the camera module industry, a well-known technology is to use a magnetic sensor (such as a Hall effect sensor, or any magnetoresistive effect sensor) to sense the magnetic field generated by a tiny magnet. For example, the magnet is attached to a moving lens, and the sensor is mounted on a fixed substrate. The magnetic field around the magnet varies with distance, so when the lens moves, the magnetic field measured by the Hall sensor changes accordingly. Due to the highly nonlinear magnetic field gradient, this technology is generally suitable for short distances (such as those used for autofocus or image stabilization). As a rule of thumb, the operating range of Hall-effect sensing technology is related to the size of the magnet. For example, the magnets used in camera modules are typically 0.5 mm in size, so the maximum operating range is 0.5 mm.

[0024] There are two Hall sensing configurations commonly used in the camera module industry. The most common configuration is the “sliding” configuration, where the magnetization axis of the magnet is parallel to the direction of movement, see Figure 1A . Figure 1A A plot of magnetic induction versus displacement for a typical sliding Hall sensor configuration is shown. In this example, the magnet dimensions are assumed to be 0.5x0.2x0.2mm. 3 . The magnetization direction is in the X direction, along the longest dimension of the magnet (0.5 mm). Assume that the magnet is translated in the X direction relative to the Hall sensor by a distance of 0.3 mm. The magnetic induction Bz in the Z direction (the sensitive direction of the sensor) is plotted against the position X of the magnet. The operating range of this configuration is a fairly linear section between the minimum and maximum values, which is approximately the length of the magnet (expressed as about 0.48 mm). Beyond that, even if the magnetic field is still large, the signal cannot be used because its characteristics are multi-valued.

[0025] The second, less popular, configuration is the "head-on" configuration, where the magnetization axis coincides with the direction of movement, see Figure 1B . Figure 1B A plot of magnetic induction versus displacement for a typical "front-facing" Hall sensor configuration is shown. The magnetic field gradient across the sensor is single-valued, but highly nonlinear and decreases rapidly as the magnet moves away from the sensor. Therefore, the operating range is approximately no greater than 1-2 times the magnet size, and in the example shown, the same Figure 1A The magnets in the example are similar in size and measure approximately 0.5 mm.

[0026] It is known to use sensing technology with more sensitive sensors, such as Anisotropic Magneto Resisance (AMR) sensors, Giant Magneto Resistance (GMR) sensors or Tunnel Magneto Resistance (TMR) sensors. These sensors are 1-2-3 orders of magnitude more sensitive than Hall sensors, respectively, and can therefore sense weaker magnetic fields and thus extend the working range. However, because the sensors are more sensitive, they can also pick up unwanted magnetic interference, such as from voice coil motor magnets in the vicinity of the same module, or from any magnetic field outside the phone, such as permanent magnets, or even the earth's magnetic field. Furthermore, GMR, TMR sensors are typically more expensive than Hall sensors and cannot be directly integrated on Si.

[0027] For long motion strokes, a popular and classic linear position sensing technology is the use of magnetic encoders. This solution can provide a micrometer's precision over a very long stroke. A typical setup includes a magnetic sensor chip containing an array of Hall elements (e.g. four or more elements) and a magnetic scale or balance. For example, the magnetic scale has two tracks of multi-pole magnets for incremental and absolute position signals. This concept is therefore not preferred for small form factor and low cost of a smartphone camera module.

[0028] The subject matter of embodiments of the invention described herein is a technology for accurate sensing of the linear absolute position of at least one movable component within a long stroke. A magnetic position detector device according to embodiments of the invention comprises a sensor IC 6 connected to a fixed position (e.g. a first structural element 1) and at least two small magnets Mi connected to a movable component (e.g. a second structural element 2). In another exemplary configuration, the sensor IC 6 is connected to the movable component 2 and a plurality of magnets Mi are connected to the fixed component 1. Figure 2 An exemplary cross-sectional schematic view in FIG. 1 illustrates an exemplary embodiment of a magnetic position detector device. Embodiments of the invention generally relate to a magnetic position detector device for measuring displacement along a first axis A, comprising a first structural element 1 and a second structural element 2 movable relative to each other along the first axis A and positioned at a mutual distance h perpendicular to the first axis A, at least two magnetic induction elements Hj positioned on the first structural element 1 along the first axis A at a mutual induction distance d, at least two magnets Mi positioned on the second structural element 2 along the first axis A at a mutual magnet distance a. A processing unit 5 is connected to the at least two magnetic induction elements Hj and arranged to determine displacement along the first axis A with sensor signals Sj from the at least two magnetic induction elements Hj.

[0029] Embodiments of the invention can be applied in long stroke scenarios, e.g. the lens elements on the first and second structural elements 1, 2 can be moved more than 1 mm, 4 mm, up to 15 mm or more. Correspondingly, the relative movement of the first and second structural elements 1, 2 can be more than 1 mm, e.g. 5 mm, 6 mm or 10 mm.

[0030] The sensor IC 6 comprises a processing unit 5 and at least two magnetic induction elements Hj. The number of magnets Mi is chosen in proportion to the required movement stroke. With reference to the attached figures, a number of exemplary embodiments will be described with specific effects and advantages. It is noted that the size, distance, direction of the magnetic moment and magnetic induction of the magnets Mi can be similar, different or random. If it is necessary to overcome ambiguities in long strokes, the number of magnetic induction elements Hj can exceed two. The distance between the magnetic induction elements Hj and between the magnets Mi can be chosen by an optimization process such that there are no ambiguity points and the distinction of the sensor signal at any position is maximized. The combination of the sensor signals at each position is unique, whereby the position can be determined. In this way, by e.g. using a look-up table, possibly in combination with a search algorithm, the absolute mutual position of the movable parts (first and second structural elements 1, 2) can always be determined, directly after power-up. Embodiments of the invention can be implemented as part of a smartphone camera module, e.g. a periscope camera module. The solution can also be used in any application where the precise position of a linearly movable part or parts needs to be determined.

[0031] Figure 2 A first exemplary embodiment of the inventive magnetic sensor device is shown in a schematic cross-sectional view. The device comprises two (permanent) magnets M1 and M2, of identical size, both 0.2 x 0.2 mm, length L i = 0.5 mm, and placed at a distance a12= 2 mm from each other. The magnetic problem is considered to be planar, so the depth dimension is not important. The magnets M1, M2 are mounted on a moving part of e.g. a camera module, as shown by the second structural element 2. The magnetic moments of the magnets M1, M2 are pointing in opposite directions, as shown, parallel to the length and direction of motion (first axis A) of the magnets M1, M2. Figure 2

[0032] On a fixed frame (first structural element), there is an integrated circuit 6 with two integrated magnetic induction elements H1 and H2. The sensitive direction of the magnetic induction elements H1, H2 is perpendicular to the main plane of the integrated circuit 6. The magnetic induction elements H1, H2 are located at a distance d12= 0.25 mm from each other. In this exemplary embodiment, the distance between the sensor plane and the bottom face of the magnets M1, M2 is 0.2 mm.

[0033] ​The sensor signals S1, S2 are proportional to the magnetic fields from the magnets M1, M2 of the magnetic induction elements H1, H2 and to x (the horizontal position of the second structural element 2 relative to the first structural element 1 along the first axis A), as Figure 3 The signals S1, S2 are quantized to 10 bits (1024 levels) for example. The magnetic fields from the two magnets M1, M2 extend over 4 mm or more, allowing to measure the mutual position of this long stroke. It is clear that the combination of the signals S1, S2 from the two magnetic induction elements H1, H2 will determine the position x of the moving part (second structural element 2) along the 4 mm stroke (i.e. along the first axis A).

[0034] Note that there can be several ambiguous positions of the signal combination S1, S as Figure 3 indicated in the graph of but over a large range of the displacement x, an unambiguous determination can be made.

[0035] To visualize the possible ambiguity problem, a graph of the sensor signal S2 compared to the sensor signal S1 is plotted in Figure 4 . The different points on this curve represent the signal combination S1, S2 at different positions x. It is noted that this curve has no less than six crossing points, each crossing point representing two different positions x, corresponding to one same combination of the sensor signals S1 and S2 (ambiguous point). For example, the first ambiguous point encountered when starting from the triangle starting point Figure 3 x = -2 mm in Figure 3 corresponds to the positions x = xi and x = x2in At positions xi = -1.81 mm and x2= 1.33 mm, the combination of the sensor signals S1 and S2 is the same. In other words, when the sensor IC 6 detects this combination, it is not possible to judge whether the second structural element 2 is at position xi or at x2.

[0036] Figure 5 To solve the ambiguity problem, a third magnetic induction element H3 is added to the IC 6, for example at a distance d13= 0.5 mm from the first magnetic induction element H1, as indicated in the schematic cross-sectional view of another embodiment in . This exemplary embodiment can be described as a magnetic position detector device, wherein the at least two magnetic induction elements Hj comprise three magnetic induction elements H1, H2, H3, which allow to solve the ambiguity problem, as described below.

[0037] Furthermore, in this exemplary embodiment, the three magnetic induction elements H1, H2, H3 are positioned at unequal distances along the first axis A (i.e. d13> d12).

[0038] Figure 6The graph shown plots the sensor signals S1, S2, S3 of the magnetic induction elements H1, H2, H3 compared to the position x. It can be clearly seen that now at positions x1 and x2, although the values of S1 and S2 are identical, the value of S3 is clearly different, so the ambiguity is solvable. In Figure 6 , it can be seen that for Figure 4 the previous ambiguity points, this is true. Figure 7 A similar graph is shown in Figure 4 , the second curve representing S3 compared to S1. To avoid ambiguity, the intersection of the S2 with S1 curve must not occur at the same S1 value as the intersection of the S3 with S1 curve. This means that to avoid ambiguity, the (self-) intersection of the two curves is not allowed to lie on the vertical line, which is the case in this particular embodiment.

[0039] The device configuration, such as the distances d13 and d12 between the magnetic induction elements H1, H2, H3, the distance h between the sensor plane and the magnet plane, and the distance a12 between the magnets M1, M2, can be optimized by an optimization design process to ensure that there are no ambiguity points and to maximize the signal value separation at different positions. For example, if the distance d12 is fixed to 0.25 mm, and assuming the distance d13 varies between 0.2 mm and 0.6 mm, the number of ambiguity points decreases and stabilizes to zero when d13 > 0.5 mm, as shown in Figure 8 . Figure 8 A graph showing the number of ambiguity points as a function of the distance d13 between the first and third magnetic induction elements H1, H3 is shown in Figure 5 . As shown in the above example, with only two magnets M1, M2 of length 0.5 mm, the magnetic position detector device can cover a stroke of 4 mm, which is much larger than the total length of both magnets M1, M2.

[0040] To further extend the stroke, more magnets Mi can be added in further embodiments of the invention. For example, to cover a stroke of 6 mm, at least three magnets Mi of similar size are used, etc. From experience, each magnet Mi can cover a span of approximately four times its length L i . When the span is larger than four times its length L i , the magnetic field of the magnet Mi can be too small to be detected by typical magnetic induction elements Hj, such as Hall sensors.

[0041] When using more than two magnets Mi, the magnetic moment vectors of the magnets Mi are alternating (e.g. left-right-left-...), so that the largest magnetic field gradient along the whole stroke exists on the sensor plane of the associated magnetic induction element Hj. In a general description, in another embodiment, a magnetic position detector device is provided, wherein the magnetic moment vector directions of two adjacent magnets of the at least two magnets Mi are opposite.

[0042] To avoid a repeating magnetic pattern along the stroke, in further embodiments, the distance a between the magnets Mi, the magnet size, even the magnetic induction strength and direction can be different.

[0043] For longer strokes with more than two magnets, more magnetic induction elements Hj can be added, if needed, to avoid ambiguities. Figure 9 A schematic cross-sectional view showing yet another exemplary embodiment of the present application is shown, wherein five magnets M1-M5 and four magnetic induction elements H1-H4 are used. The size of the magnets M1-M5 and the distance a between them are different. Also the distance d between the magnetic induction elements H1-H4 is different. The magnetic moment directions are alternating, and at least one magnet M3 has a magnetic moment vector perpendicular to the movement along the first axis A. This is to avoid a repeating pattern and thus ambiguities in the signal combination. Thus, in another embodiment, a magnetic position detector device is provided, wherein the at least two magnets Mi comprise five magnets M1-M5, and the at least two magnetic induction elements Hj comprise four magnetic induction elements H1-H4. Further, or alternatively, the magnetic moment vector of one or more of the five magnets M1-M5 can be perpendicular to the first axis A.

[0044] In a further alternative embodiment, the direction of the magnetic moment to the first axis A is in the range of 0 to 90 degrees. This will lead to a similar configuration as the embodiments shown in Figure 2 , 5 or 9, wherein the magnetic moments of M1 / M2 or M1-M5 are also perpendicular to the axis A and opposite to each other, instead of parallel to the axis A. For example, Figure 9 the embodiment of

[0045] As a general guideline for the magnet Mi size (length L i ) and mutual magnet distance a, the magnet length L i is taken as a starting point, wherein i is the index of the magnet Mi within the total number of N magnets Mi. The distance between magnet i and i+1 is chosen as a i，i+1 = k * (L i / 2 + Li+1 / 2), wherein k is an integer value between 1 and 7, for example between 3 and 5, for example equal to 4. The total stroke that the magnetic position detector device can cover afterwards is:

[0046]

[0047] In Figure 5 the exemplary embodiment shown, k = 4, N = 2, L i = L i+1 = 0.5 mm, so S = 4 mm.

[0048] In other words, in another embodiment, a magnetic position detector device is provided, wherein the at least two magnets Mi each have an associated magnet length L i along the first axis A, and the distance a i，i+1 between two adjacent magnets of the at least two magnets Mi is defined as: a i，i+1 = k*(L i / 2 + L i+1 / 2), wherein k is an integer value between 1 and 7, for example the value of k is between 3 and 5, for example k = 4.

[0049] When the value k = 4 is chosen, the distance a12 between the two magnets M1, M2 is thus 2 mm, which is used as an example in the above description of the Figure 2 and Figure 5 embodiments. The dimensions of the magnets Mi chosen for this example are 0.2 x 0.2 x 0.5 mm, so the distance a12 is a typical size for a camera module, but can be different in further application embodiments.

[0050] The size of the magnetic induction elements Hj is as small as possible to obtain a high resolution (point size induction). For example, silicon-based Hall sensor chips are usually composed of several Hall plates close to each other. This set of Hall plates is currently used for the so-called current spin technology to overcome the Hall voltage offset drift due to temperature and stress variations. The size of this set of Hall plates is typically 40 to 150 pm, depending on the silicon processing technology and the sensor design.

[0051] The minimum distance from sensor to sensor is defined by the sensor size. The distance is defined as the distance from the center of one sensor to the center of the next sensor. The minimum distance is at least equal to the sensor size, but more advantageously 1.5 times the sensor size. For example, if the size of a Hall sensor (comprising 4 Hall plates in a set) is 60 pm, then the minimum distance between two sensors is 60 pm, or more advantageously 80 pm. Thus, in another embodiment of the invention, the at least two magnetic induction elements Hj each have an associated sensor length along the first axis A, and the minimum distance between two adjacent ones of the at least two magnetic induction elements Hj is at least equal to 1.5 times the associated sensor length.

[0052] The maximum distance from sensor to sensor is defined by two factors, depending on which factor is more limiting. The first factor is the decay length of the vertical component of the magnetic induction B along the line connecting the sensors Hj in the sensor plane. The vertical component of the magnetic induction is maximum when the edge of the magnet Mi is aligned with the magnetic induction element Hj, and then decays towards zero when the magnet is moved further away (see also Figure 1A and 1B , as described above). The decay length herein is defined as the distance between the edge alignment position and the position where the magnetic signal is equal to or smaller than the detection threshold of the magnetic induction element Hj. Typically, the decay length is about 1.5 times the magnet length L i . The maximum distance between the magnetic induction elements Hj is chosen to be not larger than the decay length of the shortest magnet Mi. For example, if the magnet length is L i = 0.5 mm (assuming all magnets Mi have the same length), then the decay length is 1.5 * L i = 0.75 mm, and thus the maximum distance between the magnetic induction elements Hj is also 0.75 mm. Thus, in another embodiment, the maximum distance between two of the at least two magnetic induction elements Hj is at least equal to the associated magnet length L i along the first axis A. For example, the maximum distance can be chosen between 1 and 5 to obtain proper sensing operation of the magnetic induction elements Hj. The choice can depend on the sensitivity of the magnetic induction elements Hj, for example: if Hall sensors are used, then the maximum distance is 1.5 times the associated magnet length L i , and if GMR or TMR sensors are used (which have orders of magnitude higher sensitivity), then the maximum distance can be larger.

[0053] A second factor defining the maximum sensor-to-sensor distance is the allowed size of the integrated circuit 6. Since all magnetic induction elements Hj shall be integrated on a single substrate (the silicon die of the IC), the maximum size of the silicon die defines the maximum distance. Therefore, in another embodiment, at least two magnetic induction elements Hj are provided in the integrated circuit 6, allowing for efficient integration in many applications by connecting the single integrated circuit 6 to the first or second structural element 1, 2. Alternatively, if the integrated circuit 6 comprises multiple dies, the maximum distance is defined by the maximum distance between two points on two different dies in the same sensor package.

[0054] The relevant vertical distance h between a magnetic induction element Hj and a magnet Mi is defined as the distance between the surface of the magnet Mi closest to the sensor Hj and the sensor plane. This distance h is chosen as small as possible to obtain a high magnetic gradient and a high absolute value of the magnetic induction sensed by the magnetic induction element Hj. The minimum distance also depends on the magnetic position detector device structure, which defines the distance between the sensor plane and the upper surface of the sensor die / sensor package. Furthermore, specific application program design dimensions play a role, such as camera module assembly capabilities and / or tolerances. The sensor IC 6 as shown in the embodiments described herein is placed at a distance that allows for mass production processes, without touching the magnets Mi during operation. Typically, the distance between the magnet surface and the sensor die surface (in case of a bare die and flip-chip process) found in camera modules is 0.2 to 0.6 mm. In other words, in another embodiment, a magnetic position detector device is provided, wherein the shortest distance between the first plane spanning at least two magnets Mi and the second plane spanning at least two magnetic induction elements Hj in a direction perpendicular to the first axis A is between 25% and 200% of the magnet length L i In a practical implementation, this can correspond to a shortest distance between 0.2 mm and 0.6 mm.

[0055] The relevant horizontal position of the magnetic induction elements Hj relative to the magnets Mi is related to the stroke range S of the magnetic position detector device. The magnetic induction elements Hj operate (move) in a range defined by the total length of the magnet assembly consisting of at least two magnets Mi plus the decay length of the outermost magnet Mi. This is to ensure that a detectable magnetic field is always present on any magnetic induction element Hj at any position in the working range. The movement of any magnetic induction element Hj does not exceed the edge of the outermost magnet Mi plus the decay length of that magnet Mi. For example, with reference to the embodiment shown in Fig. 1, assuming a magnet length L Figure 5 i ​The distance a12 between the magnets M1, M2 is 2 mm, the total length of the magnet assembly is 0.5 + 2 + 0.5 = 3 mm. The decay length of the two magnets M1, M2 is 1.5 * 0.5 = 0.75 mm. Thus, the maximum operating range in this exemplary embodiment is 3 + 0.75 + 0.75 = 4.5 mm. During operation, the sensor IC 6 moves relative to the magnet assembly such that the sensor on the left side (H3) does not move more than the edge of the left magnet M1 plus its decay length, i.e. the edge of M1 plus 0.75 mm. Similarly, the sensor on the right side (H2) does not move more than the edge of M2 plus the decay length, i.e. the edge of M2 plus 0.75 mm.

[0056] Generally, a Hall sensor can be used as the magnetic sensing element Hj in the present magnetic position detector device embodiments, because a Hall sensor can be easily integrated in a silicon integrated circuit. Notably, or any suitable magnetic sensing element can be used. In another embodiment, at least two magnetic sensing elements Hj are one of a Hall sensor, an anisotropic magnetoresistive (AMR) sensor, a giant magnetoresistive (GMR) sensor, or a tunneling magnetoresistive (TMR) sensor.

[0057] In another embodiment of the present application, the magnetic sensing elements Hj can be integrated in a motor driver IC as an example of the above-mentioned integrated circuit 6. The motor driver IC can comprise a digital / microcontroller block, a power supply driver block, a sensing block (with the magnetic sensing elements Hj), and other blocks, such as a communication block, a power supply block. The motor driver IC and the connected motor are used to move one of the first and second structural elements 1, 2, e.g. along the first axis A.

[0058] In the above-described exemplary embodiments, the magnets M1 are attached to the first structural (e.g. moving) element 1, and the sensor IC 6 with the magnetic sensing elements Hj is mounted on the second structural element (e.g. stationary frame), such as the housing of a camera module. Alternatively, the sensor IC 6 with the magnetic sensing elements Hj is mounted on the first structural (moving) element 1, and the magnets M1 are mounted on the second structural element 2 (stationary frame).

[0059] If multiple moving parts are located closely within the device (e.g. the focus lens group and the afocal zoom lens group of a zoom camera module), the magnets M1 are advantageously mounted on the second structural element 2 (stationary frame), and the sensor ICs 6 (one per moving part) are mounted on the first structural element 1 (moving parts). In this way, cross-talk between the sensing signals of the two moving parts can be eliminated. If for some reason the sensor ICs 6 have to be mounted on the stationary frame, the magnets M1 of the two moving parts are sufficiently separated to minimize cross-talk.

[0060] Note that in the above example it is assumed that a 10 bit resolution is applied. If a higher resolution / accuracy is required, then only the number of ambiguous points can be reduced. This means that once it is guaranteed that there are no ambiguous points for the low bit resolution, there will also be no ambiguous points if the resolution is increased.

[0061] The sensitive direction of the magnetic induction elements can alternatively be parallel to the plane of the integrated circuit 6, for example using another type of sensor, for example a vertical Hall plate. In this case, the magnetization direction of the magnets Mi is chosen to be perpendicular to the IC 6 plane.

[0062] In another embodiment, the processing unit 5 is arranged to determine the displacement along the first axis A using a look-up table. The determination can be done using a search algorithm, for example a look-up table, a look-up table in combination with interpolation or a non-linear least square solver, a fitting function. Using any suitable search algorithm, for example a look-up table, a look-up table in combination with interpolation and a non-linear least square solver, or a fitting function, the position of the moving part (or the mutual position of the first and second structural elements 1, 2) is calculated from the sensor signals Sj. The look-up table or the fitting function can be predefined by a characterization or calibration step during manufacturing of the device.

[0063] In Figure 10 an example of a flow chart of the algorithm to calculate the position is given. In the memory of the IC 6, a look-up table 7 can be stored. The look-up table 7 can also be stored in an external memory and loaded into the IC 6 upon power-up. The look-up table 7 can store data for all magnetic induction elements Hj, but can also store data for one of the magnetic induction elements Hj. Since the magnetic induction elements Hj are spatially offset from each other, the data for the other magnetic induction elements Hj can be derived from the data for the first magnetic induction element Hj. The look-up table can comprise position interval data at a higher resolution than required.

[0064] During operation, the signals Sj from all magnetic induction elements Hj are collected and searched in the look-up table 7 to find the closest matching combination from which the coarse position is determined (block 8 in Figure 10 In a next step, a few data points in the look-up table 7 around this coarse position are used to define a more accurate position 10 using interpolation and a non-linear least square solver (block 9).

[0065] The calibration data of the magnetic induction elements Hj can also be fitted into a function and the corresponding parameters can be stored in the memory. During operation, the function can be reconstructed using the stored parameters.

[0066] The sensor data can also be compressed and stored, instead of storing the raw data of the sensor signal Sj compared to the position x. During power-up, the compressed data is loaded to the sensor IC 6 and decompressed. As an example of a compression method, the raw data is converted to the spatial frequency domain using a Fourier transform. The Fourier transform is optimized to be as short as possible while still maintaining accuracy. In this way, the number of data points stored (when stored in Fourier transform format) can be reduced compared to the raw data, without loss of accuracy. During operation, an inverse Fourier transform is performed to reconstruct the data of the sensor signal Sj compared to the position x, and interpolation (up-sampling) can be performed to obtain accurate positions without loss of information.

[0067] As mentioned above, embodiments of the present application relate to a magnetic position detector arrangement or sensor configuration for linear long-stroke position sensing, with at least two magnets Mi and a sensor integrated circuit 6 with at least two magnetic induction elements Hj. The number of magnets Mi is proportional to the required movement stroke. The size, distance, direction of magnetic moment and magnetic induction strength of the magnets Mi can be the same, different or random. Thus, in one set of embodiments, the at least two magnets Mi are identical, and in another set of embodiments, the at least two magnets Mi have e.g. different magnetic induction field distributions, e.g. by choosing different sizes and / or different magnetic properties.

[0068] The number of magnetic induction elements Hj can be three or more, to allow overcoming the ambiguity problem in long-stroke. The distance d between the magnetic induction elements Hj can be designed by an optimization process, to maximize the distinction of the sensor signal Sj for any position, and without ambiguous points. The combination of the sensor signals Sj is unique for each position, whereby the position can be determined.

[0069] Embodiments of the present application are advantageously applied as part of a camera module, e.g. a periscope camera module, of e.g. a smartphone, and are also advantageously usable in any other application requiring determination of the precise position of a linear movable component or some components.

[0070] The present application has been described above with reference to a number of exemplary embodiments shown in the drawings. Modifications and alternative implementations are possible, and are included in the scope of the protection defined by the appended claims.

Claims

1. A magnetic position detector device for measuring displacement along a first axis (A), comprising a first structural element (1) and a second structural element (2) movable relative to each other along said first axis (A) and positioned at a mutual distance (h) perpendicular to said first axis (A), at least two magnetic induction elements (Hj) positioned on said first structural element (1) along said first axis (A) at a mutual induction distance (d), at least two magnets (Mi) positioned on said second structural element (2) along said first axis (A) at a mutual magnet distance (a), the magnetic moment vector direction of two adjacent magnets of said at least two magnets (Mi) being opposite and parallel to said first axis (A), and a processing unit (5) connected to said at least two magnetic induction elements (Hj) and arranged to determine displacement along said first axis (A) using sensor signals (Sj) from said at least two magnetic induction elements (Hj).

2. The magnetic position detector device of claim 1, wherein, said at least two magnets (Mi) each have an associated magnet length (L i ) along said first axis (A), a distance (a i，i+1 ) between two adjacent magnets of said at least two magnets (Mi) is defined as: a i，i+1 = k * (L i / 2 + L i+1 / 2), wherein k is an integer value between 1 and 7.

3. The magnetic position detector device of claim 2, wherein, said at least two magnetic induction elements (Hj) each have an associated sensor length along said first axis (A), and the minimum distance between two adjacent magnetic induction elements of said at least two magnetic induction elements (Hj) is at least equal to 1.5 times said associated sensor length.

4. The magnetic position detector device of claim 3, wherein, a maximum distance between two adjacent ones of the at least two magnetic induction elements (Hj) is at least equal to the associated magnet length (L i ) along the first axis (A), the minimum distance being smaller than the maximum distance.

5. The magnetic position detector device according to any one of claims 1 to 4, wherein, said at least two magnetic induction elements (Hj) comprise three magnetic induction elements (H1, H2, H3).

6. The magnetic position detector device of claim 5, wherein, said three magnetic induction elements (H1, H2, H3) are positioned at unequal distances along said first axis (A).

7. The magnetic position detector device according to any one of claims 1 to 4, wherein said at least two magnets (Mi) comprise five magnets (M1-M5) and said at least two magnetic induction elements (Hj) comprise four magnetic induction elements (H1-H4).

8. The magnetic position detector device of any one of claims 1-4, further comprising at least one magnet, wherein, the magnetic moment vector of said at least one magnet is perpendicular to said first axis (A).

9. The magnetic position detector device according to any one of claims 2-4, wherein, In a direction perpendicular to said first axis (A), the shortest distance between a first plane spanning said at least two magnets (Mi) and a second plane spanning said at least two magnetic induction elements (Hj) is between 25% and 200% of said magnet length (L i ).

10. The magnetic position detector device according to any one of claims 1-4, wherein, said at least two magnetic induction elements (Hj) are provided in one integrated circuit (6).

11. The magnetic position detector device according to any one of claims 1 to 4, wherein, said at least two magnets (Mi) are identical.

12. The magnetic position detector device according to any one of claims 1 to 4, wherein, said at least two magnets (Mi) have different magnetic induction field distributions.

13. The magnetic position detector device according to any one of claims 1-4, wherein, said at least two magnetic induction elements (Hj) are one of: a Hall sensor, an anisotropic magnetoresistive sensor, a giant magnetoresistive sensor or a tunneling magnetoresistive sensor.

14. The magnetic position detector device according to any one of claims 1-4, wherein, said processing unit (5) is arranged to determine displacement along said first axis (A) using a look-up table.

Images