Optical system for position determination device

Abstract

The invention relates to an optical system (30) for a position determination device (20), in particular an optical stylus, for determining the position of the device (20) relative to a position coding surface (50) having a different position coding pattern (52). The optical system (30) comprises: an image sensor (31) for capturing at least one image of any position encoding pattern (52) of the position encoding surface (50); one or more light sources (42) for irradiating any one of the position encoding patterns; a diaphragm aperture (48); an objective lens (32), one side of the objective lens (32) being positioned at a first distance (d1) from the diaphragm aperture; and an image lens (34), one side of which is positioned at a second distance (d2) from the diaphragm aperture (48). The optical system (30) further comprises a dynamic optical element (36) configured to be electrically actuated to form a focused image of any position encoding pattern (52) of the position encoding surface (50) onto the image sensor (31) within a working distance (WD) of the position determining device (20) comprising the optical system (30). The invention also relates to a method for determining a working distance of an optical stylus as a function of a 3D pose of the optical stylus relative to a position encoding surface, and to a method for controlling a voltage to be applied to a dynamic optical element of an optical stylus.

Description

Technical Field

[0001] The invention relates to an optical system for a position determining device, such as an optical stylus, for determining the position of the device relative to a position encoding surface. The invention also relates to a method for determining a working distance of the position determining device relative to the position encoding surface. The invention also relates to a method for controlling a voltage to be applied to a dynamic optical element of the position determining device as a function of the working distance of the position determining device relative to the position encoding surface. Background Art

[0002] Among user input devices, touch-sensitive displays provide the most natural way for human-computer interaction through simple gestures, symbols or even handwritten text. Usually, using fingers as input devices leads to inaccurate results. Styluses as position determination devices are widely used for more accurate data input.

[0003] However, regardless of the technology used, most existing styluses have various limitations and require physical contact or a very small interval between the pen and the screen. Therefore, their application range is still limited to coarse graphic input within a two-dimensional plane.

[0004] WO2022064412 discloses a multifunctional optical stylus for 2D and 3D applications, which uses an alternative method to determine the distance of an object. The optical stylus described in this document is designed for a position determination device, which includes a position coding surface with different position coding patterns. The optical stylus includes: an image sensor for capturing an image of any position coding pattern of the position coding surface; and an optical device, which includes a dynamic optical element configured to be electrically actuated to adjust the focus of the optical stylus according to the spacing distance between a reference point of the optical stylus and the position of any position coding pattern to have a substantially focused position coding pattern corresponding to the position of the optical stylus.

[0005] In machine vision applications where parallax errors should be limited, it is known to use telecentric systems comprising an objective lens and an image lens arranged on both sides and at a focal length from the stop aperture. Telecentric systems advantageously provide a constant magnification of the object, regardless of the distance between the object and the objective lens. However, these systems have a limited depth of field, within which the object forms a sharp, focused image.

[0006] This problem can be solved by reducing the diameter of the diaphragm aperture, increasing the depth of field at the expense of light collecting power, thereby retrieving images at low illumination levels, resulting in reduced contrast and higher noise levels. In addition, reducing the diameter of the diaphragm aperture produces diffraction effects, which limit the maximum achievable resolution of the optical system.

[0007] Optical systems composed of dynamic optical elements have the advantage of increased depth of field compared to traditional telecentric systems. However, unlike traditional telecentric systems, dynamic optical elements do not perform well in controlling magnification changes at different focal lengths.

[0008] Therefore, the object of the present invention is to propose an optical system with dynamic optical elements for a position determining device, in particular an optical stylus, which can focus on near objects and far objects when the position determining device operates within a predefined working distance range, while the magnification remains within a controlled magnification range for near objects and far objects.

[0009] Another object of the present invention is to propose a method for determining the working distance of a position determining device, in particular an optical stylus, relative to a position-coding surface.

[0010] Another object of the invention is to propose a method for controlling a voltage to be applied to a dynamic optical element of a position determining device, in particular an optical stylus, as a function of the working distance of the position determining device, in particular of a position encoding surface. Summary of the invention

[0011] These objects are achieved in particular by an optical system for a position determination device, in particular an optical stylus, for determining the position of the device relative to a position coding surface having different position coding patterns. The optical system comprises an image sensor for capturing at least one image of any position coding pattern of the position coding surface; one or more light sources for illuminating any position coding pattern of the position coding pattern; a diaphragm aperture; an objective lens, one side of which is positioned at a first distance from the diaphragm aperture; and an image lens, one side of which is positioned at a second distance from the diaphragm aperture. The optical system further comprises a dynamic optical element, which is positioned in contact with the diaphragm aperture or which is positioned within a distance of 5 mm from the diaphragm aperture along the optical axis of the optical system. The dynamic optical element is configured to be electrically actuated to form a focused image of any position coding pattern of the position coding surface onto the image sensor within a working distance of the position determination device comprising the optical system.

[0012] In an embodiment, the range of working distances has a minimum value of 10 mm and a maximum value of 100 mm.

[0013] In an embodiment, the magnification ratio of the optical system between the focused image formed or projected onto the image sensor is below 3 when the position determining device is at a minimum and a maximum of the working distance range.

[0014] In an embodiment, the first distance is in the range of 0.5 to 1.2 times the focal length of the objective lens.

[0015] In an embodiment, the optical system is a bi-telecentric system, wherein the first distance is equal to the focal length of the objective lens and the second distance is equal to the focal length of the image lens.

[0016] In an embodiment, the optical system is of the object space telecentric system type, wherein the first distance is equal to the focal length of the objective lens.

[0017] In an embodiment, the first distance is shorter than the focal length of the objective lens and the second distance is shorter than the focal length of the image lens.

[0018] In an embodiment, the first distance is at most two thirds of the focal length of the objective lens and the second distance is at most one half of the focal length of the image lens.

[0019] In an embodiment, the optical system further comprises a circuit board. The dynamic optical element is an electrically tunable lens mounted on one side of the circuit board, for example, the electrically tunable lens is a liquid lens or a polymer lens. The circuit board comprises an aperture.

[0020] In an embodiment, the optical system further comprises a distance measuring sensor mounted between the dynamic optical element and the objective lens, for example, the distance measuring sensor is an optical time-of-flight sensor.

[0021] In an embodiment, the optical system further comprises an optical filter arranged to allow light emitted by the light source to pass to reach the image sensor and to prevent light emitted by the distance measuring sensor from reaching the image sensor or at least attenuate light emitted by the distance measuring sensor before reaching the image sensor.

[0022] In an embodiment, the optical filter is in the form of a coating applied to the image lens.

[0023] In an embodiment, the one or more light sources are arranged such that the central axis of the cone of light emitted by the or each light source intersects the optical axis of the objective to achieve optimum illumination intensity.

[0024] Another aspect of the present invention relates to an optical stylus including an optical system.

[0025] In an embodiment, one or more light sources are mounted between the dynamic optical element and the distal end of the optical stylus, preferably one or more light sources are mounted between the dynamic optical element and the objective lens.

[0026] In an embodiment, the optical stylus further includes an ink chamber.

[0027] Another aspect of the invention relates to a method for determining a working distance of an optical stylus based on a 3D pose of the optical stylus relative to a position-coding surface comprising a position-coding pattern. The optical stylus comprises: an image sensor for capturing at least one image of any position-coding pattern of the position-coding surface; an objective lens and an image lens, the objective lens and the image lens being arranged on both sides of an aperture of an aperture; a dynamic optical element, the dynamic optical element being mounted between the objective lens and the image lens and being configured to be electrically actuated to form a focused image of any position-coding pattern of the position-coding surface onto the image sensor within a working distance along an optical axis of the stylus; a distance measuring sensor for measuring the working distance, for example, the distance measuring sensor is an optical time-of-flight sensor; and a processing unit for controlling the dynamic optical element based on the working distance.

[0028] The processing unit corrects the signal acquired by the distance measurement sensor in real time according to the tilt angle and the roll angle of the 3D posture of the optical stylus relative to the position encoding surface to calculate the working distance.

[0029] In an embodiment, the pitch angle and roll angle of the 3D pose of the optical stylus relative to the position-coding surface are obtained from an inertial measurement unit IMU, or from an algorithm based on stereo distortion of an image of a position-coding pattern as captured by an image sensor, or by using data obtained from both the IMU and the algorithm.

[0030] In an embodiment, the working distance of the optical stylus is obtained by executing the following formula by the processing unit:

[0031]

[0032] in,

[0033] D M is the distance measured by the distance measuring sensor,

[0034] L o is the distance along the optical axis of the stylus between the distance measuring sensor and the outer surface of the objective lens, r is the orthogonal distance between the optical axis of the stylus and the position of the distance measuring sensor,

[0035] and ψ are the tilt angle and roll angle of the optical stylus, respectively.

[0036] In an embodiment, the distance between the position-encoding surface and the distal end of the optical stylus along an axis parallel to the optical axis is obtained by the processing unit executing the following formula:

[0037]

[0038] in,

[0039] D M is the distance measured by the distance measuring sensor,

[0040] L o is the distance between the distance measurement sensor and the objective lens along the optical axis of the stylus,

[0041] r is the orthogonal distance between the optical axis of the stylus and the position of the distance measurement sensor,

[0042] and ψ are the tilt angle and roll angle of the optical stylus,

[0043] L tip is the distance along the optical axis of the stylus between the outer surface of the objective lens and the distal end of the optical stylus, and

[0044] R is the orthogonal distance between the optical axis O and the axis of the stem of the stylus.

[0045] In an embodiment, the closest distance between the position-encoding surface and the distal end of the optical stylus is obtained by executing the following formula by the processing unit:

[0046]

[0047] Another aspect of the invention relates to a method for controlling a voltage to be applied to a dynamic optical element of an optical stylus according to a 3D pose of the optical stylus relative to a position-coding surface comprising different position-coding patterns. The optical stylus comprises: an image sensor for capturing at least one image of any position-coding pattern of the position-coding surface; a dynamic optical element configured to be electrically actuated to form a focused image of any position-coding pattern of the position-coding surface onto the image sensor within a working distance of the optical stylus; a distance measurement sensor for measuring the working distance; and a processing unit for controlling the dynamic optical element according to the working distance.

[0048] The method comprises the following steps: a. measuring the working distance using a distance measuring sensor, and b. determining a voltage to be applied to a dynamic optical element using a distance-to-voltage conversion model, the distance-to-voltage conversion model using an analytical model or a lookup table, the analytical model describing the relationship between the voltage to be applied and the measured distance of the working distance, the lookup table storing the value of the voltage to be applied for any measurement of the working distance.

[0049] In an embodiment, step a. of the method is followed by the following additional steps: c. obtaining at least one measurement performed by a further sensor included in the optical stylus, for example, the further sensor is an image sensor or an IMU sensor, and d. running a sensor fusion algorithm on a processing unit to obtain a more accurate measurement of the working distance based on the data obtained by the distance measurement sensor and the further sensor, for example, the sensor fusion algorithm is a Kalman filter.

[0050] In an embodiment, the method comprises the following additional steps:

[0051] - determining by an image analysis algorithm whether the quality of one or more images acquired by the image sensor is above a given threshold to ensure that the image of the position-coding pattern is good enough for use with the optical stylus, and

[0052] - In the event that the quality is below a given threshold, adjusting the distance-to-voltage conversion model to modify the focus of the dynamic optical element to restore the quality of one or more images to above the given threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The invention will be better understood with the help of the description of several embodiments given by way of example and illustrated by the accompanying drawings, in which:

[0054] - Figure 1a is a perspective view of an optical module of an optical system according to an embodiment;

[0055] - Figure 1b shows a cross-sectional perspective view of a portion of an optical stylus including an optical system according to an embodiment;

[0056] - Figure 1c Shows Figure 1b Side view of

[0057] - Figure 2a shows a cross-sectional perspective view of a portion of an optical stylus including an optical system according to another embodiment,

[0058] - Figure 2b Shows Figure 2a Side view of

[0059] - Figure 3a and Figure 3b is a schematic explanatory diagram of an optical system according to an embodiment, in which opposite sides of an image lens include coatings respectively having an optical filter and an anti-reflection filter, and a variable focal length lens and an objective lens each include an anti-reflection coating.

[0060] - Figure 4 A schematic diagram showing an optical system of the type of a double telecentric system according to an embodiment, comprising a lens with a variable focal length;

[0061] - Figure 5 A schematic diagram showing an optical system of the object space telecentric system type according to another embodiment, which includes a lens with a variable focal length;

[0062] - Figure 6 shows a schematic diagram of a compact optical system according to another embodiment, the compact optical system including a lens with a variable focal length and designed to focus on both near and far objects while the magnification remains within a controlled magnification ratio;

[0063] - Figure 7 shows a schematic diagram of an optical system according to another embodiment, the optical axis of the optical system being perpendicular to the surface of the position encoding surface and the optical system comprising a distance measuring sensor and a light source arranged between a lens with a variable focal length and an objective lens;

[0064] - Figure 7a A side view of an optical position determining device is shown, the optical position determining device comprising a position coding surface and an integrated Figure 7 an optical stylus of the optical system, the optical axis of the optical stylus being perpendicular to the surface of the position encoding surface;

[0065] - Figure 8 A schematic diagram of an optical system according to another embodiment is shown, the optical system comprising a distance measuring sensor and a light source, the distance measuring sensor and the light source being arranged such that the central axes of the light cones emitted by both the distance measuring sensor and the light source intersect the optical axis of the system, and

[0066] - Figures 9a to 9c Shows Figure 1b and Figure 1c Different views of parts of an optical stylus and different geometrical parameters for correcting a signal acquired by a distance measuring sensor as a function of a working distance of the optical stylus relative to a position-coding surface. DETAILED DESCRIPTION

[0067] In a preferred embodiment, the position determination device is an optical stylus 20, such as Figure 1b and Figure 1c The optical stylus is configured to Figure 7a The 3D pose of the position-encoding surface 50 is determined as shown and described in detail in WO2022 / 064412, the contents of which are hereby incorporated by reference. In the context of the present invention, the term "3D pose" of the optical stylus 20 is understood to be a combination of the following (1) to (3): (1) the two-dimensional coordinates of a reference point of the optical stylus (e.g., the distal end or tip 26 of the optical stylus) relative to the position-encoding surface, (2) the distance between the reference point of the optical stylus and the position-encoding surface, and (3) the orientation of the optical stylus relative to the position-encoding surface, wherein the orientation can be represented by Euler angles, yaw angles, pitch angles, roll angles, quaternions, or rotation matrices.

[0068] exist Figure 1a to Figure 1c In the illustrated embodiment, the optical stylus 20 includes a rod-shaped member 24 and a housing 21 that accommodates the rod-shaped member 24. In an embodiment, the rod-shaped member 24 may include an ink chamber for writing or drawing on a piece of paper in a conventional manner. The optical stylus 20 includes an optical system 30, which is mounted in the stylus housing 21 and adjacent to the stylus rod-shaped member 24. The optical system 30 includes an image sensor 31, an objective lens 32 arranged on a first side of an aperture 48, and an image lens 34 arranged on a second side of the aperture 48, the second side being opposite to the first side. The image sensor 31 and the image lens 34 are arranged on a sensor chamber 23 of the stylus housing 21. The image lens 34 is mounted on the front side of the chamber 23, while the image sensor 31 is mounted on the rear side of the chamber 23, and the image sensor 31 is used to capture an image of any position-coding pattern 52 of the position-coding surface 50, such as Figure 7a shown.

[0069] The image lens 34 is arranged against the shoulder 23b on the front side of the sensor chamber 23. The optical system 30 also includes an optical filter 35, which is mounted against the image lens 34 as a separate component. The optical filter may alternatively be a lens coating as described below. The shoulder 23b surrounds the chamber opening 23a through which light can pass, thereby traveling through the image lens 34, the optical filter 35 and onto the image sensor 31. The function of the optical filter 35 will be described in detail later.

[0070] Figure 1a to Figure 1cThe optical system 30 of an embodiment of the present invention further comprises an optical module 40, which is mounted between the objective lens 32 and the image lens 34. The optical module 40 comprises a circuit board 46 having a first side facing the image lens 34 and a second side facing the objective lens 32. The dynamic optical element 36 is mounted against the first side of the circuit board 46, while one or more light sources 42 (e.g. LEDs) are mounted on the second side of the circuit board 46. The circuit board 36 further comprises an aperture 48, which is aligned with the optical axis O of the optical system 30. However, according to a variant, the aperture can be separated from the circuit board.

[0071] Preferably, the dynamic optical element 36 is an electrically tunable lens, for example, the electrically tunable lens is a liquid lens or a polymer lens, and the dynamic optical element 36 is in direct contact with the aperture 48 or the dynamic optical element 36 is within a distance of 5 mm from the aperture.

[0072] The electrically tunable lens 36 is electrically connected to the circuit board 46 so that a voltage can be applied to the electrically tunable lens 36 depending on the working distance of the optical stylus 20 relative to the position-coding surface 50, as described later. In the context of the present invention, the "working distance WD" of the optical stylus is understood to be the distance along the optical axis O of the optical system 30 between any position-coding pattern 52 of the position-coding surface 50 and the outer surface of the objective lens 32 of the optical system.

[0073] The constant control of the voltage applied to the electrically tunable lens 36 ensures that any position-coding pattern 52 is sufficiently clear within the working distance WD of the optical stylus 20. The working distance WD can vary between 10 mm (when the distal end 26 of the stylus is in contact with the position-coding surface) and 100 mm, preferably, the working distance WD can vary between 15 mm and 65 mm.

[0074] exist Figure 1a to Figure 1c In the illustrated embodiment, the optical module 40 includes a plurality of LEDs 42 connected to a second side of a circuit board 46, for example three LEDs angularly offset by approximately 120° from each other around an aperture 48. The optical module 40 also includes a distance measurement sensor connected to the second side of the circuit board 46, preferably an optical time-of-flight sensor 44.

[0075] refer to Figure 1c , one side of the objective lens 32 of the optical system 30 is positioned at a first distance d1 from the aperture 38, and one side of the image lens 34 is positioned at a second distance d2 from the aperture. The ratio between the first distance d1 and the second distance d2 can be determined according to the following reference Figures 4 to 6 The optical system described varies.

[0076] In an embodiment, the optical stylus 20 further includes a tilt angle for adjusting the optical stylus. and the roll angle ψ( Figures 9a to 9c )Inertial Measurement Unit (IMU) 35 for taking measurements.

[0077] In another embodiment, the tilt angle of the optical stylus The angles φ and φ of roll are calculated by a positioning algorithm based on image analysis of the captured position-coding pattern 52. In another embodiment, the tilt angle of the optical stylus is The and roll angles ψ are obtained by fusing the data measured by the IMU 35 with the data acquired by the positioning algorithm to obtain more robust values ​​of these angles.

[0078] The optical module 30 and the IMU both communicate with a processing unit (not shown) of the optical stylus 20 to control the voltage to be applied to the electrically tunable lens 36 (as described below) based on the output of the distance measurement sensor 44, thereby controlling the focal length of the electrically tunable lens 36 to ensure that the image of any position-coding pattern 52 acquired by the image sensor 31 is clear enough to be decoded by the image recognition algorithm. The image recognition algorithm may also be adapted to control the quality of the images acquired by the image sensor 31 in real time, so as to control the voltage applied to the electrically tunable lens 36 when the quality of these images is too poor to be decoded.

[0079] The position-coding pattern 52 may be in the form of a tag encoding an XY two-dimensional coordinate grid, for example, or in the form of a different pattern that can be decoded back to the coordinates of a specific position on the position-coding surface 50. Alternatively, the position-coding pattern 52 may be in the form of a unique tag or symbol that can be uniquely assigned to a specific position on the position-coding surface 50. A lookup table including data of a series of corresponding unique tags or symbols and the position of each unique pattern or symbol relative to the coding surface may be stored in a memory that may be integrated into the stylus housing 21 of the optical stylus, or in a host device that communicates with the optical stylus, to receive unprocessed optical signals from the optical stylus corresponding to the unique tags or symbols.

[0080] exist Figure 2a , Figure 2b In the embodiment shown, the optical stylus 20 and Figure 1b to Figure 1c The optical stylus 21 is similar to that of , the only difference being that the light source is integrated at the level of the objective 32. More specifically, several LEDs 42 are integrated in the stylus housing 21 in a manner surrounding the objective 32, for example three LEDs offset from each other by approximately 120°.

[0081] refer to Figure 3a and Figure 3b, preferably, an LED 42 is selected that emits light that is invisible to the human eye, such as a NIR LED with a wavelength in the range of 800nm ​​to 900nm, preferably about 850nm. The emitter of the optical time-of-flight sensor 44 typically sends photons with a longer wavelength of more than 900nm, preferably about 940nm. Figure 3a , the light source emits light, which passes through the objective lens 32 and enters the position coding pattern 52 of the position coding surface 50. Then, the light is reflected / scattered on the surface 50, and is sent back through the objective lens 32, and passes through the electrically tunable lens 36 and the image lens 34 to reach the image sensor 31, which is used to acquire an image of the position coding pattern 52.

[0082] In an embodiment, the objective lens 32 and the electrically tunable lens 26 each include at least one anti-reflection coating AR to minimize reflections and improve the transmission of light through these optical components to achieve optimal contrast of the captured image.

[0083] Reference now Figure 3b , the photons sent by the time-of-flight sensor 44 pass through the objective lens 32 to the position coding pattern 52 on the position coding surface 50. Then, the photons are reflected / scattered on the surface 50 and sent back through the objective lens 32, and a portion of the photons are received by the time-of-flight sensor 44 to measure the working distance WD, as shown in Figures 10a to 10c. Another portion of the photons passes through the electrically tunable lens 36. However, these photons should not reach the image sensor because they will reduce the quality of the acquired image, thereby possibly preventing the decoding of the position coding pattern.

[0084] Therefore, the image lens 34 comprises a coating integrated with an optical filter 35, which is suitable for preventing photons emitted by the time-of-flight sensor 44 from reaching the image sensor 31, while allowing the light emitted by the LED 42 to pass, so that the image sensor can capture an image of the position-coding pattern 52. The optical filter 35 can be a bandpass filter, a short-pass filter, or a combination of different filters.

[0085] Figures 4 to 6 Different arrangements of the optical system 30 according to different embodiments are schematically shown.

[0086] exist Figure 4In the embodiment of the present invention, the optical system 30 is a double telecentric system type, which includes a dynamic optical element 36 located at the level of the aperture (not shown). Therefore, the first distance d1 between the objective lens 32 and the aperture is equal to the focal length of the objective lens, and the second distance d2 between the image lens 22 and the aperture is equal to the focal length of the image lens. The optical system 30 according to the present embodiment ensures that the image sensor 31 acquires a focused image of the coding pattern 52 at any position within the offset δD of the working distance WD in the following way: the voltage applied to the electrically tunable lens 36 is controlled in real time according to the offset δD, so that the electrically tunable lens 36 has different optical powers.

[0087] Therefore, the magnification of any position-coding pattern 52 captured by the image sensor 31 remains constant within a shift δD of the working distance WD.

[0088] exist Figure 5 In an embodiment, the optical system 30 is of the object space telecentric system type, and the optical system 30 includes a dynamic optical element 36 located at the level of the aperture (not shown). Therefore, a first distance d1 between the objective lens 32 and the aperture is equal to the focal length of the objective lens, while a second distance d2 between the image lens 34 and the aperture is less than the focal length of the image lens 34, for example, the second distance d2 between the image lens 34 and the aperture is half the focal length of the image lens 34.

[0089] exist Figure 6 In an embodiment of the invention, the optical system 30 is a non-telecentric system, which comprises a dynamic optical element 36 located at the level of an aperture (not shown). A first distance d1 between the objective lens 32 and the aperture is at most two thirds of the focal length of the objective lens 32, while a second distance d2 between the image lens 34 and the aperture is at most one half of the focal length of the image lens. The optical system 30 according to this embodiment allows a limited relative variation of the optical magnification of any position coding pattern within a shift δD of the working distance. This relative variation is still controlled, for example, this relative variation is less than 50%, and preferably less than 30%. Small variations in the optical magnification can be advantageously used to extract information about the working distance WD of the optical stylus without affecting the readability of the position coding pattern.

[0090] In this embodiment, the distance d3 between the image lens 34 and the image sensor 31 is in the range of 0.8 times to 1.2 times the focal length of the objective lens 32 .

[0091] Figure 73 shows an optical system 30 according to an embodiment, wherein a distance measuring sensor 44 and one or more light sources 42 are mounted between an electrically tunable lens 36 and an objective lens 32. The optical system 30 is suitable for integration into an optical stylus 20 to be used with an optical stylus such as Figure 7a The position-coding surface 50 shown is used together with the position-coding surface 50. The position-coding surface 50 includes a plurality of position-coding patterns 52 to detect the 3D pose of the stylus 20 relative to the surface 50.

[0092] refer to Figure 8 In an embodiment of the present invention, one or more light sources 42 are arranged so that the central axis of the light cone emitted by each light source intersects the optical axis of the objective lens 32 to achieve optimal illumination intensity. The distance measurement sensor 44 can also be arranged so that the central axis of the light cone emitted by the sensor 44 intersects the optical axis of the objective lens 32. This allows the sensor to receive more photons to increase the robustness of the measurement.

[0093] The voltage to be applied to the electrically tunable lens 36 of the optical stylus 20 is determined according to the 3D pose of the optical stylus 20 relative to the position-coding surface 50 comprising the position-coding pattern 52. The output of the distance measurement sensor 44 can be used directly for applications where a rough measurement of the working distance WD is sufficient.

[0094] On the other hand, for applications requiring accurate measurement of the working distance WD, the output of the distance measurement sensor 44 must be corrected to take into account the following: Figures 9a to 9c Geometric constraints shown.

[0095] The processing unit of the optical stylus pen is used according to the tilt angle of the 3D posture of the optical stylus pen 20 relative to the position encoding surface 50. The signal acquired by the distance measurement sensor 44 is corrected in real time by the roll angle ψ to calculate the working distance WD. The roll angle ψ is either measured in real time by the IMU 35 of the optical stylus or calculated by a localization algorithm based on the captured image of the position-coding pattern or by fusing data from the IMU and data calculated by the localization algorithm.

[0096] More specifically, the working distance WD is obtained by the processing unit executing the following formula:

[0097]

[0098] in,

[0099] D M is the distance measured by the distance measuring sensor 44,

[0100] Lo is the distance between the distance measuring sensor and the outer surface of the objective lens 32 along the optical axis O of the stylus,

[0101] r is the orthogonal distance between the optical axis O of the stylus and the position of the distance measurement sensor 44, and

[0102] and ψ are the tilt angle and roll angle of the optical stylus, respectively.

[0103] To determine the working distance WD of optical stylus 20, the distance value acquired by measurement sensor 44 is corrected by applying the geometric constraints as described above. The voltage to be applied to electrically tunable lens 36 is determined using the corrected distance with the aid of a distance-to-voltage conversion model.

[0104] In an embodiment, the conversion model uses an analytical model that describes the relationship between the voltage to be applied to the electrically tunable lens 36 and the working distance WD calculated by the processing unit of the optical stylus based on the output of the distance measurement sensor.

[0105] In another embodiment, the conversion model uses a lookup table that stores the voltage values ​​to be applied to the electrically tunable lens 36 for any value of the working distance WD calculated by the processing unit of the stylus.

[0106] In an embodiment, determining the working distance WD in an accurate manner is a multi-step process comprising the following steps:

[0107] The working distance WD is roughly measured by using the distance measurement sensor 44;

[0108] obtaining at least one measurement performed by one or more sensors (e.g., image sensor 31 of optical stylus 20 and / or IMU 45), and

[0109] A sensor fusion algorithm is run on the processing unit to obtain a more accurate measurement of the working distance WD based on the data obtained by the distance measurement sensor 44 of the optical stylus, the image sensor 31 and / or the IMU 45, for example, the sensor fusion algorithm is a Kalman filter.

[0110] The processing unit of the optical stylus can run an image analysis algorithm to determine whether the quality of one or more images acquired by the image sensor is above a given quality threshold to ensure that the image of the position-coding pattern is good enough for use by the optical stylus. The "quality" of the acquired image can be associated with the following indicators: contrast, sharpness, entropy, and signal-to-noise ratio.

[0111] The quality of the image acquired by the image sensor may indeed vary over time, since electrically tunable lenses tend to degrade in the long term, which can negatively affect the flexibility of the lens. Therefore, the voltage applied to the electrically tunable lens to obtain a given focal length may vary over time.

[0112] Therefore, when the quality of the image acquired by the image sensor is below the quality threshold, the distance-to-voltage conversion model must be adjusted to modify the focal length of the electrically tunable lens 36 so as to restore the quality of the image to above the quality threshold to overcome possible degradation of the electrically tunable lens.

[0113] In some digital applications, for example when a user brings a stylus into contact with a position-encoding surface, it is necessary to know the distance D between the position-encoding surface 50 and the distal end or tip 26 of the optical stylus 20 along an axis parallel to the optical axis O. tip The distance can be obtained by executing the following formula in the processing unit:

[0114]

[0115] in,

[0116] D M is the distance measured by the distance measuring sensor 44,

[0117] Lo is the distance between the distance measuring sensor and the outer surface of the objective lens 32 along the optical axis O of the stylus,

[0118] r is the orthogonal distance between the optical axis O of the stylus and the position of the distance measuring sensor 44,

[0119] and ψ are the tilt angle and roll angle of the optical stylus,

[0120] L tip is the distance between the outer surface of the objective lens 32 and the tip of the stylus along the optical axis O of the stylus, and R is the orthogonal distance between the optical axis O and the axis of the shaft 24 of the stylus.

[0121] In other digital applications, a minimum distance from the distal end 26 of the optical stylus 20 may be required. For example, the closest distance between the tip 26 and The corresponding Z coordinate is necessary for 3D design applications. It can also be used to display a shadow that follows the movement of the optical stylus directly under the tip. This distance is obtained by the processing unit executing the following formula:

[0122]

[0123] The above invention is not limited to optical styluses. The optical system can be integrated into virtually any device for position determination.

[0124] Reference numerals list

[0125] Position determination device (eg optical stylus) 20

[0126] Housing 21

[0127] Sensor room 23

[0128] Chamber opening 23a

[0129] Shoulder 23b

[0130] Rod-shaped member 24

[0131] Ink room 25

[0132] Distal end 26

[0133] Optical system 30

[0134] Image sensor 31

[0135] Objective 32

[0136] Anti-reflective coating AR

[0137] Image lens 34

[0138] Anti-reflective coating AR

[0139] Optical filter 35

[0140] Dynamic Optics 36

[0141] Electrically tunable lens

[0142] Anti-reflective coating AR

[0143] Optical module 40

[0144] Light Source 42

[0145] For example, LED

[0146] Distance measurement sensor 44 (eg, time-of-flight sensor)

[0147] IMU 45

[0148] Circuit board 46

[0149] Aperture: 48

[0150] Position coding surface 50

[0151] Position coding pattern 52 The first distance d1 The second distance d2 Optical axis O

[0152] Working distance WD Working distance offset δD Tip distance D Tip

[0153] Closest distance

Claims

1. An optical system (30) for a position determination device (20), in particular, the position determination device (20) is an optical stylus, the position determination device (20) being used to determine the position of the device (20) relative to a position coding surface (50) having different position coding patterns (52), the optical system (30) comprising: an image sensor (31) for capturing at least one image of any position-coding pattern (52) of the position-coding surface (50); one or more light sources (42) for illuminating any of the position-coding patterns; a stop aperture (48); An objective lens (32), one side of which is positioned at a first distance (d1) from the aperture; and an image lens (34), one side of which is positioned at a second distance (d2) from the aperture (48), the optical system (30) further comprising a dynamic optical element (36), the dynamic optical element (36) being positioned in contact with the aperture (28) or the dynamic optical element (36) being positioned within a distance of 5 mm from the aperture along the optical axis (O) of the optical system (30), the dynamic optical element (36) being configured to be electrically actuated to form a focused image of any position coding pattern (52) of the position coding surface (50) onto the image sensor (31) within a working distance (WD) of the position determining device (20) including the optical system (30).

2. The optical system (30) according to claim 1, wherein: The range of working distance (WD) has a minimum value of 10 mm and a maximum value of 100 mm.

3. The optical system (30) according to claim 2, wherein: When the position determination device (20) is at the minimum and maximum of the range, the magnification ratio of the optical system between the focused image formed on the image sensor (31) is below 3.

4. The optical system (30) according to any preceding claim, wherein: The first distance (d1) is in the range of 0.5 to 1.2 times the focal length of the objective lens (32).

5. The optical system (30) according to any of the preceding claims, being of the double telecentric system type, wherein: The first distance (d1) is equal to the focal length of the objective lens (32), and the second distance (d2) is equal to the focal length of the image lens (34).

6. An optical system (30) according to any one of claims 1 to 4, being of the object space telecentric system type, wherein: The first distance (d1) is equal to the focal length of the objective lens (32).

7. The optical system (30) according to any one of claims 1 to 4, wherein: The first distance (d1) is shorter than the focal length of the objective lens (32), and wherein the second distance (d2) is shorter than the focal length of the image lens (34).

8. The optical system (30) according to claim 7, wherein: The first distance (d1) is at most two thirds of the focal length of the objective lens (32), and wherein the second distance (d2) is at most one half of the focal length of the image lens (34).

9. The optical system (30) according to any preceding claim, further comprising a circuit board (36), wherein: The dynamic optical element (36) is an electrically tunable lens (ETL), which is mounted on one side of the circuit board (46), the circuit board including the aperture (48), for example, the electrically tunable lens is a liquid lens or a polymer lens.

10. An optical system (30) according to any preceding claim, further comprising a distance measuring sensor (44), which is mounted between the dynamic optical element (36) and the objective lens (32), for example, the distance measuring sensor (44) is an optical time-of-flight sensor.

11. An optical system (30) according to the preceding claim, further comprising an optical filter (35), the optical filter (35) being arranged to allow light emitted by the light source to pass through to reach the image sensor (31) and to prevent light emitted by the distance measuring sensor (44) from reaching the image sensor (31) or at least to attenuate the light emitted by the distance measuring sensor (44) before reaching the image sensor.

12. The optical system (30) according to any preceding claim, wherein: The one or more light sources (42) are arranged so that the central axis of the light cone emitted by the or each light source intersects the optical axis (O) of the objective lens (32) to achieve optimum illumination intensity.

13. An optical stylus (20) comprising an optical system (30) according to any preceding claim.

14. The optical stylus (20) according to the preceding claim, wherein One or more light sources (42) are mounted between the dynamic optical element (36) and the distal end (26) of the optical stylus (20), preferably, one or more light sources (42) are mounted between the dynamic optical element (36) and the objective lens (32).

15. A method for determining a working distance (WD) of an optical stylus based on a 3D pose of the optical stylus (20) relative to a position-coding surface (50) comprising a position-coding pattern (52), the optical stylus (20) comprising: an image sensor (31) for capturing at least one image of any position-coding pattern (52) of the position-coding surface (50), an objective lens (32) and an image lens (34), said objective lens (32) and said image lens (34) being arranged on both sides of the diaphragm aperture (48), a dynamic optical element (36) mounted between the objective lens (32) and the image lens (34) and configured to be electrically actuated to form a focused image of any position-coding pattern (52) of the position-coding surface (50) onto the image sensor (31) within a working distance (WD) along the optical axis (O) of the stylus; a distance measuring sensor (44) for measuring the working distance (WD), for example, the distance measuring sensor (44) is an optical time-of-flight sensor, - a processing unit for controlling the dynamic optical element (36) according to the working distance (WD), The processing unit determines the position of the optical stylus (20) according to the tilt angle of the 3D posture of the optical stylus (20) relative to the position coding surface (50). and roll angle (ψ) to perform real-time correction on the signal acquired by the distance measurement sensor (44) to calculate the working distance (WD).

16. The method according to the preceding claim, wherein: The tilt angle and a roll angle (ψ) are obtained by an inertial measurement unit IMU (45) according to an algorithm based on stereo distortion of an image of the position coding pattern (52) captured by the image sensor (31), or by using data obtained by both the IMU (45) and the algorithm.

17. The method according to claim 15 or 16, wherein: The working distance (WD) is obtained by the processing unit executing the following formula: in, D M is the distance measured by the distance measuring sensor (44), L o is the distance between the distance measuring sensor and the outer surface of the objective lens (32) along the optical axis (O) of the stylus, r is the orthogonal distance between the optical axis (O) of the stylus and the position of the distance measuring sensor (44), and ψ are the tilt angle and roll angle of the optical stylus, respectively.

18. A method for controlling a voltage to be applied to a dynamic optical element (36) of an optical stylus (20) depending on a 3D pose of the optical stylus (20) relative to a position-coding surface (50) comprising different position-coding patterns (52), the optical stylus comprising: an image sensor (31) for capturing at least one image of any position-coding pattern (52) of the position-coding surface (50), a dynamic optical element (36) configured to be electrically actuated to form a focused image of any position-coding pattern (52) of the position-coding surface (50) onto the image sensor (31) within a working distance (WD) of the optical stylus; - a distance measurement sensor (44) for measuring the working distance (WD); and - a processing unit for controlling the dynamic optical element (36) according to the working distance (WD), Wherein, the method comprises the following steps: a. measuring the working distance (WD) using the distance measurement sensor (44); b. Determining the voltage to be applied to the dynamic optical element (36) by means of a distance-to-voltage conversion model using either: - an analytical model describing the relationship between the voltage to be applied and the measuring distance of the working distance (WD), or - a look-up table storing the voltage value to be applied for any measured value of the working distance (WD).

19. The method according to the preceding claim, wherein: Step a. is followed by the following additional steps: c. obtaining at least one measurement performed by a further sensor included in the optical stylus, for example, the further sensor being an image sensor (31) or an IMU sensor (45), and d. Running a sensor fusion algorithm on the processing unit to obtain a more accurate measurement of the working distance (WD) based on the data obtained by the distance measurement sensor (34) and the further sensor, for example, the sensor fusion algorithm is a Kalman filter.

20. The method according to claim 18 or 19, comprising the following additional steps: - determining by an image analysis algorithm whether the quality of one or more images acquired by the image sensor is above a given threshold to ensure that the image of the position-coding pattern is good enough for use by the optical stylus, and - in case the quality is below the given threshold, adapting the distance-to-voltage conversion model to modify the focal length of the dynamic optical element so as to restore the quality of the one or more images to above the given threshold.

Images