WO2024157163A1

WO2024157163A1 - Non-contact calibration of an eyeglass display system with filament kinematics

Info

Publication number: WO2024157163A1
Application number: PCT/IB2024/050615
Authority: WO
Inventors: Miro Taphanel
Original assignee: VIAHOLO GmbH
Priority date: 2023-01-25
Filing date: 2024-01-23
Publication date: 2024-08-02
Also published as: DE102023101777A1

Abstract

The invention relates to a device and method for calibrating an eyeglass display system (1) which is designed to display a virtual image in a field of vision of a user and which has a scanning deflection unit having at least two beam splitter elements (11, 11', 11'') that are each mechanically coupled to one another via at least one filament element (16, 16', 16'', 16'''); wherein the beam splitter elements (11, 11', 11'') are movably mounted so as to be tiltable about a tilting axis (15) and, when used as intended, move between two reversal positions (116) at which the tilting speed of the beam splitter elements (11, 11', 11'') is zero. The method comprises: detecting a deviation of the beam splitter elements (11, 11', 11''), which are coupled to one another via the at least one filament element (16, 16', 16'', 16'''), from a parallel position; using a heating device (115) to heat the at least one filament element (16, 16', 16'', 16''') without contacting it, causing the at least one filament element (16, 16', 16'', 16''') to change in length; and controlling the heating device (115) in such a way that the detected deviation is reduced in order to carry out a calibration process in which the length of each filament element (16, 16', 16'', 16''') can be adjusted with high accuracy, for example in the three-digit nanometre range.

Description

Non-contact calibration of a glasses display system with thread kinematics

The disclosure relates to a device and method for calibrating a glasses display system, wherein the glasses display system is designed to display a virtual image in a field of vision of a user and has a scanning deflection unit with at least two beam splitter elements that are mechanically coupled to one another via at least one thread element. The beam splitter elements are mounted so that they can be tilted about a tilt axis and, when used as intended, move between two

Reversal positions at which the tilting speed of the beam splitter elements is zero.

With a glasses display system, or augmented reality (AR) glasses, which is based on a scanning principle, i.e. in which light from a display unit is directed as computer-generated image information into spatial areas in a user's eye, each assigned to a specific image content, by means of a series of mirrors, the respective mirrors, i.e. beam splitter elements, must ideally be moved parallel to one another. One way to achieve this is to drive each beam splitter element and thus each mirror separately and to use sensors to detect the respective angle, the tilt angle, by which the beam splitter element is tilted. In this case, synchronization takes place by means of control via a microcontroller. An alternative approach is a mechanical coupling of the beam splitter elements, as described, for example, in DE 10 2022 212 256.9. The parallelism of the mirrors is achieved by means of a mechanical coupling via a thread kinematics, i.e. a positive and thus play-free connection of the respective beam splitter elements by means of at least one, i.e. one or more thread elements. The content of DE 10 2022 212256.9 is hereby incorporated by reference for the subject matter described in more detail below.

In such a system, the requirements for parallelism are extremely high. They are derived from the resolution of the human eye, which is approximately 1/60° and, due to the law "angle of incidence = angle of reflection", in a scanning process such as the one described here, results in a doubled requirement of 1/120° for the accuracy of positioning the scanning mirrors, i.e. the beam splitter elements. As a result, for a lever arm of, for example, 3.5 mm, to which such a thread element is attached, there is a sensitivity with regard to the thread length of tan(l/120°) x 3.5 mm = 509 nm. A change in length of just 500 nm therefore leads to a tilting of neighboring mirror elements of 1/120° and can therefore be perceived with the naked eye. With regard to production, a manufacturing tolerance of the thread length of less than 500 nm must therefore be technically achieved. Tolerances of this size can only be achieved with mechanical production processes and, in particular, when assembling different elements, with great effort. Accordingly, a calibration process is advantageous in which the length of the respective thread element can be adjusted with great accuracy, for example in the three-digit nanometer range.

This object is achieved by the subject matter of the independent patent claims. Advantageous embodiments emerge from the dependent patent claims, the description and the figures.

One aspect relates to a method for calibrating a glasses display system for displaying a virtual image in a user's field of vision, i.e. AR glasses (augmented reality glasses). These can, for example, have a line screen unit for emitting light as computer-generated image information in a radiation direction. The radiation direction is then a vertical direction when used as intended by the user. The radiation direction can be understood as the middle direction of an emitted non-parallel light beam as emitted light. To parallelize the emitted light, one or more lens elements, in particular one or more free-form lens elements, can be arranged in a beam path of the light between the screen unit and the scanning deflection unit described below. The line screen unit can also be referred to as a line-shaped screen unit, since at a given time it can only display one or a few lines of a two-dimensional (2D) image to be displayed. The second dimension of the image to be displayed is then made available by displaying further lines of the image to be displayed at other times. A length as the main direction of extension of the cellular screen unit can be at least one order of magnitude, i.e. a factor of 10, in particular at least 1.5 orders of magnitude, i.e. a factor of 50, greater than a width of the cellular screen unit running transversely to the length. In particular, the width and length of the screen unit run transversely, i.e. essentially perpendicular (perpendicular or perpendicular up to a predetermined deviation) to the direction of radiation.

The glasses display system comprises a scanning deflection unit for scanning the screen unit and for deflecting the data from the scanned screen unit. unit radiated computer-generated image information into one of the user's eyes in a second direction which is different from the radiation direction. The second direction can also be understood as a directional range which covers various possible positions of the eye when used as intended, i.e. positions of the eye in a so-called eyebox, as well as a target position for the line of the 2D image displayed by the line screen unit at a given time in the user's field of vision. The second direction can then be understood as an essentially horizontal direction or an essentially horizontal directional range. The second direction or the second directional range is then accordingly oriented horizontally up to a predetermined deviation of, for example, a maximum of 45 or a maximum of 30° when used as intended, i.e. the second directional range then only includes directions which deviate from the horizontal by less than the predetermined deviation. The predetermined deviation can also be less, for example 25 or 15°, and can be specified individually for a deviation from the horizontal in the positive and negative vertical direction.

The scanning-deflection unit has at least two, preferably more than two, for example 4 or 5 or 6 or 7 or 8 or 9 or 10, beam splitter elements arranged one behind the other in the direction of emission of the light, each with a mirror layer that is partially transparent to the light emitted by the screen unit. The beam splitter elements can also be arranged one behind the other in the direction of emission, offset in the horizontal direction. The beam splitter elements are mounted so as to be movable, i.e. tiltable, around a respective central position and thus tiltable between two reversal positions along a tilt axis running perpendicular to the direction of emission and the second direction. At the reversal positions, the tilting speed of the beam splitter elements is zero when used as intended, in which the screen unit is scanned or the computer-generated image information is redirected to different positions in the user's eye by tilting back and forth between the two reversal positions. The tilt axis runs along a main extension direction, a length of the beam splitter elements. Since the beam splitter elements only have one dimension actively scan, namely the dimension perpendicular to the tilt axis and thus perpendicular to the (main extension direction of the) line screen unit, the scanning deflection unit can in this case also be referred to as a one-dimensional (ID) scanning deflection unit.

The screen unit and scanning deflection unit can be arranged on a common frame unit, a glasses frame unit, by means of which the glasses display system can be worn by the user on his head. The glasses display system can have a control unit for controlling the scanning deflection unit and the screen unit, which synchronizes the angular position of the beam splitter elements based on sensor data from a sensor unit for detecting the respective angular position of the beam splitter elements with the image contents of the screen unit, i.e. synchronizes the light emitted as computer-generated image information at a given point in time.

The scanning deflection unit has at least one thread element which mechanically couples two or more beam splitter elements, in particular the beam splitter elements closest to each other, and is designed to hold the beam splitter elements coupled by the thread element in a predetermined parallel position (in a calibration process as described below) when the beam splitter elements coupled by the thread element are moved around the tilt axis. The thread element thereby creates a positive, tension-positive mechanical connection between the beam splitter elements coupled to each other. The thread element can be understood as a thread in the broader sense.

Accordingly, the thread element can consist in particular of glass fiber, polyethylene, polyamide, nylon, steel, stainless steel, carbon fiber, aramid, natural fibers (such as silk or spider threads or wool) or other fibers, or comprise one or more of the components mentioned. Both metallic thread elements and non-metallic thread elements are therefore possible. The thread element can also be selected as a monofilament or as a filament bundle, and can be braided or twisted in some other way. It does not have to be a round Cross-section can be selected for the thread element(s); the thread element can also be designed in the form of a flat strip, for example. Also referred to as thread elements here are form-fitting mechanical connections which are made using thin and therefore thread-like etched parts, for example using structures etched from silicon, glass or metal. This means that the mechanical coupling of the thread element in the form of a thin thread-like structure to the associated beam splitter elements can be integrated as a common etched part. As an alternative to this integration, the thread element can be connected to the beam splitter element in a form-fitting manner by means of gluing, whereby alternatively or additionally other joining methods can be used, such as welding and/or knotting or others.

The thread element is therefore a thin structure compared to the beam splitter element, which creates a mechanical connection between two moving, adjacent beam splitter elements, is positively connected to the respective beam splitter elements and enables relative movement through beam splitter elements, preferably exclusively by means of elastic deformation. Spring energy can also be absorbed by the thread element, which stores kinematic energy as a participating spring element during an oscillating movement of the beam splitter elements and thus influences the natural frequency of the coupled beam splitter elements.

In one embodiment, hardened carbon beam is proposed as the material for the thread element, i.e. as the (thread) material from which the thread element can consist or which can comprise the thread element. This can, for example, have a thickness of at most 50 qm, preferably at most 20pm, particularly preferably at most 10pm, for example 10pm+/-lprn, so that the thread element can still be wound around comparatively small radii without plastic deformation occurring. The load-bearing capacity with regard to tensile forces in a wire shape, i.e. with a round or square cross-section, can under certain circumstances already be too low, so that, for example, a metal strip of the mentioned thickness and less than 3 mm wide, preferably less than 500 qm wide, particularly preferably less than 55pm wide, for example 50 qm wide and 10 pm thickness. The use of hardened carbon steel has the advantage that no plastic deformation can occur during assembly, since hardened steel either breaks as a brittle fracture or does not plastically deform. In addition, the yield strength of hardened steel is very high, which means that a very small thread element can be realized, which is beneficial to the overall system due to the resulting low mass. The advantage here is low damping due to movement through the air with a small surface and low masses compared to the total mass of the mass-spring system and thus a low influence on it. In addition, the yield strength is related to the minimum radius that the thread material can be bent without the maximum permissible tension of the yield strength being exceeded. Accordingly, the minimum bending radius that can be structurally required in the glasses display system can be smaller, the higher the yield strength. Hardened carbon steels offer one of the highest yield strengths here and are therefore particularly advantageous. It should be noted that the thickness of the thread element, for example the metal strip or wire, also influences the minimum radius. Accordingly, the use of a thread material with high yield strength allows the use of a thicker wire or strip. This is advantageous because semi-finished products in the thickness range of 10 pm, i.e. foils or microwires, can only be produced with great effort.

The method for calibration described here comprises, as a method step, detecting a deviation of the beam splitter elements coupled to one another via the at least one thread element from a parallel position. In the parallel position, the respective partially reflecting surfaces, the mirrors, and thus the beam splitter elements are aligned parallel. Accordingly, the relative angle of two adjacent beam splitter elements can be monitored by measurement, for example by means of an auto-collimator. A further method step is contactless heating of the at least one thread element by means of a heating device, with an automatic change in the length of the at least one thread element between the two beam splitter elements as an (automatic) consequence of the heating, which accordingly changes the relative angle of the two adjacent beam splitter elements. Elements are also controlled, in particular the heating device is regulated, in such a way that the detected deviation is permanently reduced, ie over the period of heating and thus also when the thread element has cooled back to its original temperature.

This has the advantage that a structural change in the thread material, the material of the thread element, i.e. for example a change in the crystal structure, but also a change in another structure, can be used to specifically adjust the length of the heated thread element via a volume change in the thread element associated with the structural change. This means that the parallel position of the beam splitter elements can be calibrated with the desired accuracy of, for example, at least three-digit nanometers, without coming into mechanical contact with the thread element.

This is explained here using the hardened carbon steel mentioned above as an example of the materials that can be used for this calibration process. The process can be used for any thread material that reacts to heating with a permanent change in structure. Carbon steel exists in different crystal structures, including martensite, austenite, bainite or pearlite. The steel takes up a different amount of space in each of these different material structures. Hardened carbon steel is predominantly present as martensite.

During heat treatment, i.e. heating of the hardened carbon steel, the material structure is at least partially changed, which also changes the dimensional stability of a component made from the steel, for example. In the case of hardened carbon steel as a thread material, the structure can be influenced by heating and thus the length of the respective thread element can be changed. For example, for a hardened 100 CR6 steel with a structure of 80% martensite, 15% austenite and 5% carbide residues, the following volume changes occur when heated:

The length of a thread element made of hardened carbon steel can therefore be permanently changed by heating it. For example, if a thread element with a length of 50 pm is heated to a temperature that results in a volume change of 0.15% shrinkage, the thread shortens by 75 nm.

It should be noted that the method described does not require steel to be used as the material for the thread element. Rather, any material with a structure that can be manipulated by heating is basically suitable. Another example of an alloy with a complex structure, i.e. a material that changes its volume and/or anisotropically its length over the long term when heated, is titanium grade 5. In general, other titanium alloys or aluminum alloys can also be considered, and pure metals with temperature-dependent structural changes can also be used. Depending on the thread material used for the thread element, heating can cause the thread element to shrink or grow in length, so that different manufacturing tolerances can be responded to. Overall, this creates an effective and efficient method for calibrating beam splitter elements that are mechanically coupled to one another using thread elements in a scanning glasses display system.

In one embodiment, the contactless heating is a local heating, wherein in particular the at least one thread element is warmed or heated by at least one order of magnitude more, preferably at least two or at least three orders of magnitude more, than one of the beam splitter elements or the beam splitter elements. This has the advantage that other elements of the glasses display system, in particular the beam splitter elements, are not changed by the heating and the calibration can accordingly be carried out particularly precisely. In a further embodiment, the contactless heating is carried out on a central section of the at least one thread element, which extends between two fastening areas of the at least one thread element, in particular between two fastening areas of the at least one thread element designed with unwinding areas. The central section is preferably spaced from the fastening areas by a distance greater than zero. An unwinding area of the respective thread element can in particular be defined as an area which, when used as intended, comes into mechanical contact with the beam splitter element at least temporarily. This has the advantage that the structural change caused by the heating does not affect the fastening areas of the respective thread elements and accordingly does not impair the reliability of the mechanical coupling of the beam splitter elements, so that the accuracy of the system is reliably maintained. In addition, local heat treatment influences the structure and thus the mechanical yield point, which in turn changes the requirements for a minimum bending radius. It is therefore advantageous not to change the structure in the unwinding area.

In a further embodiment, it is provided that during the control, a duration of the contactless heating and/or a size of a section, in particular a size of a subsection of the central section, of the at least one thread element on which the heating device acts, is set depending on a size of the detected deviation. This has the advantage that, with great dynamics, the smallest changes in the length of the thread element can be set very sensitively. For example, with a size of the central section, i.e. the largest possible heat-affected zone between two adjacent beam splitters, of 4 mm, assuming a change in volume or length of 0.15%, a change in length of up to 6 pm can be achieved. If the above-mentioned heating in a section of 50 pm size is assumed as the lower limit, this results in a change in length that can be set between 75 nm and 6 pm, to an accuracy of around 75 nm.

In another embodiment, a check is provided as to whether the length of the at least one thread element must be increased or decreased in order to reduce the detected deviation, and depending on a Result of the checking during control, setting a first heating power which corresponds to a local first temperature of the at least one thread element if the length has to be reduced, and setting a second heating power which is different from the first heating power and corresponds to a local second temperature of the at least one thread element if the length has to be increased. The heating powers can be determined, for example, by heating power ranges for the temperatures to be achieved. They can, for example, be calculated depending on the heating device used and the respective geometry of the thread elements and stored in a table in order to control the heating device. Alternatively or additionally, the heating power can also be regulated depending on the detected deviation and in accordance with a result of the checking. This has the advantage that particularly large manufacturing tolerances can be compensated for by calibration.

Accordingly, it can be provided here that the deviation is quantified during the check, and the first and/or second heating power is selected from predetermined first and second heating power ranges depending on the result of the quantification. In particular, several different first and/or second heating power ranges are specified. Depending on the temperature-dependent structural changes of the thread material used for the respective thread elements, the different heating power ranges can also be interlocking heating power ranges with increasing temperature: a first heating power range is then followed by a second heating power range with increasing temperature, and this in turn is followed by another first heating power range, etc., as is the case, for example, in the table shown above. The heating power ranges can be assigned to respective temperature ranges which are achieved with a heating power in the corresponding heating power range on the thread element with the respective heating device. This has the advantage that the accuracy of the calibration procedure is even better adapted to the respective material properties and accordingly a more precise calibration with greater dynamics can be achieved. In another embodiment, it is provided that the beam splitter elements are coupled to one another via at least one first thread element and at least one second thread element, with the tilt axis running between the first thread element and the second thread element. Accordingly, the first thread element can be attached to the beam splitter elements in a respective first end region and the second thread element can be attached to the beam splitter elements in a respective second end region. The two end regions of a beam splitter element are each separated by a central region through which the tilt axis runs. Thus, when the beam splitter elements are tilted in a first tilt direction, corresponding mechanical forces are transmitted essentially completely by the first thread element and when the beam splitter elements are tilted in a second tilt direction opposite to the first tilt direction, the mechanical forces are transmitted essentially completely by the second thread element. In particular, the thread elements can also be pre-tensioned, i.e. braced against each other, taking advantage of the respective elasticity of the thread elements, and thus be under tension even when the beam splitter elements are not moving, which enables particularly precise calibration of the parallel position.

During calibration, a check is carried out to determine whether the length of the first thread element or the length of the second thread element must be reduced in order to reduce the detected deviation, and, depending on the result of the check, the first thread element is heated, in particular only the first thread element, or the second thread element is heated, in particular only the second thread element. Preferably, thread materials are used here which only shrink permanently when heated. This has the advantage that when producing the glasses display system, materials for the thread element which only shrink permanently when heated can also be considered, so that greater freedom is achieved with regard to the design of the thread elements and the calibration process can still be achieved with the desired accuracy. In addition, thread elements with different thread materials can also be used, for example a first thread element with a first thread material and a second thread element with a second thread material which is different from the first Thread material is different. For example, a first, coarser calibration can be achieved by changing the length of the first thread element and a second, finer calibration can be achieved by changing the length of the second thread element.

In a further embodiment, the contactless heating is carried out using a laser device as a heating device. This has the advantage that at least one thread element can be heated with particular precision, i.e. the size of the section on which the heating device acts can be set particularly precisely, thereby achieving particularly precise adjustment of the length change of the respective thread element. Alternatively or additionally, the respective thread element can also be heated using electricity or induction or other heat radiation. Particularly when using a laser, subsequent calibration is also advantageously possible, i.e. calibration after the glasses display system has been fully assembled and, accordingly, recalibration after a predetermined number of operating hours, for example after 100 operating hours. Accordingly, the contactless heating can take place at a time when the beam splitter elements are already protected from mechanical and other influences from the environment of the glasses display system by a - preferably transparent - protective device such as a spectacle lens. This also contributes to the success of the calibration, as it reduces the probability of subsequent interference with the calibrated glasses display system.

In another embodiment, a temperature reached in the thread element is measured, in particular as a function of an elongation of the thread element during heating, and the heating device is controlled (in particular regulated) as a function of the temperature measured for the thread element, in particular using a material-specific table stored for the respective thread material of the respective thread element, which describes a relationship between length and temperature change. The measurement can alternatively be carried out via a radiation spectrum of the heated thread element. During the measurement, a change in a relative angle of the beam splitter elements to one another can preferably be measured during during heating, which, according to the laws of physics, consists of a temporary thermal elongation and a permanent structural change, the amounts of which can be determined individually for each thread element based on the thread element geometry and thread material. This means that the temperature reached and thus the permanent change in length in the thread element can be determined from an angle change determined via the thermal elongation of the thread element when the beam splitter element is heated. This has the advantage that the accuracy of the control or regulation is improved and thus the accuracy of the calibration process is increased overall.

In a further embodiment, it is provided that during the contactless heating, a material of the at least one thread element, a thread material, is heated with a volume that changes permanently during the heating. Accordingly, during the manufacture of the spectacle display system, the thread material is selected depending on the respective structural changes during heating. The thread materials that can be used are, in particular, the thread materials mentioned above, in particular a carbon steel, such as a hardened carbon steel. As is in principle also the case with hardening, a structure can also be set in advance during the manufacture of the thread element, which is then changed again by the contactless heating after it has been attached to the respective beam splitter elements. This possibility is not limited to metallic thread materials.

Accordingly, a further aspect is a manufacturing and calibration method with the method according to one of the described embodiments with setting a material structure, for example a crystal structure, in particular with hardening, of a thread material of the thread element before carrying out the above-mentioned method steps of detecting the deviation, contactless heating and controlling, so that the previously set material structure can be dissolved by the contactless heating, ie the setting of the material structure can be reversed. This means that even more different materials can be selected for the thread elements, so that a better functioning of the glasses display system is possible. A further aspect relates to a calibration and/or manufacturing device for carrying out a method according to one of the described embodiments.

Another aspect relates to a glasses display system for displaying a virtual image in a user's field of vision, with a scanning deflection unit with at least two beam splitter elements that are each mechanically coupled to one another via at least one thread element, wherein the beam splitter elements are mounted so that they can be tilted about a tilt axis and are designed to move between two reversal positions when used as intended, at which a tilting speed of the beam splitter elements is zero. The beam splitter elements coupled to one another via the at least one thread element are calibrated in a parallel position using the method described above according to one of the embodiments described. The method can be demonstrated, for example, by a grinding profile and analysis of the locally adjusted structure and/or a tensile test with the respective thread element, whereby it is examined whether there are other yield points in the unrolling area relative to the connection area of the thread between two beam splitters.

Advantages and advantageous embodiments of calibration and/or manufacturing devices as well as glasses display systems correspond to advantages and advantageous embodiments as described for the methods.

The features and combinations of features mentioned above in the description, including in the introductory part, as well as the features and combinations of features mentioned below in the description of the figures and/or shown in the figures alone can be used not only in the combination specified in each case, but also in other combinations without departing from the scope of the invention. Thus, embodiments are also to be regarded as encompassed and disclosed by the invention that are not explicitly shown and explained in the figures, but which emerge and can be produced by separate combinations of features from the explained embodiments. Embodiments and combinations of features are also to be regarded as disclosed, which therefore do not have all the features of an originally formulated independent claim. Furthermore, embodiments and combinations of features, in particular through the embodiments set out above, are to be considered as disclosed, which go beyond or deviate from the combinations of features set out in the references to the claims.

Show

Fig. 1 shows the schematic structure of an exemplary embodiment of a glasses display system with thread kinematics;

Fig. 2a is a schematic view of the coupling of several beam splitter elements with one or more threads with at least one thread element; and

Fig. 2b the coupling of Fig. 2a with further details.

Identical or functionally equivalent elements are provided with the same reference symbols in the different figures.

Fig. 1 shows an exemplary embodiment of a glasses display system 1. A screen unit 110 emits light which is parallelized by a lens unit 111, i.e., imaged to infinity. Parallel light rays in the emission direction corresponding to the light beam 112 thus leave the lens unit 110 in the negative z-direction as the emission direction. The parallelized light strikes partially transparent beam splitter elements 11 which are mounted around a tilt axis 15 which runs parallel to the screen unit 110, perpendicular to the plane of the drawing and thus in a y-direction. The beam splitter elements 11 scan in a tilt range 0 with respective reversal positions 116 and a respective center position 116'. At the reversal positions 116, the beam splitter elements 11 have a speed of 0.

According to the law "angle of incidence = angle of reflection", the field of view is twice as large as the tilt range 0 (in this case composed of the angle ranges 114, 114' with center position 113), in the light, represented here by light beam 112, is deflected. A human observer, a user, with eye 10 and pupil 101 can thus see computer-generated image information in the field of vision. For this purpose, the screen unit 110 is sensor-coupled to the angular position of the beam splitter elements 11, which is not shown here.

For the glasses display system to function, it is important that the individual beam splitter elements 11 are aligned parallel to one another. To this end, a positive mechanical connection is created using a thread element 16. In the exemplary embodiment shown here, two thread elements 16 are shown arranged symmetrically about the tilt axis 15. A first thread element 16 is thus arranged in an area of the beam splitter elements 11 facing the eye, and a further thread element 16 is arranged in an area of the beam splitter elements 11 facing away from the eye 10, with the tilt axes 15 running between the two areas. For the purpose of better recognition in the figure, the thread element 16 is shown here as a non-tightened thread element 16 for optical reasons alone. When used as intended, the thread serves the purpose of a mechanical coupling between adjacent beam splitter elements 11, whereby forces must also be transmitted via the respective thread element 16. A tensioned thread element 16 is a prerequisite for this.

The parallelism of the beam splitter elements 11 to one another is crucial for the function. There is an optical overlap area between adjacent beam splitter elements 11, as will be explained using the example of the visual beam 14. The visual beam 14 corresponds to beam paths in which the light 112 can be directed to the same place in the eye by two different beam splitter elements 11. Accordingly, the visual beam 14 touches both a lower edge 13' of an upper beam splitter element 11' and an upper edge 13" of a next-neighboring lower beam splitter element 11". Since the pupil 101 typically has an opening diameter of approximately 2.5 mm, the overlap region formed in the eye 10, in which light directed into the eye by the upper beam splitter element 11' and the lower beam splitter element 11" simultaneously overlaps, larger than in Fig. 1, visualized abstractly geometrically constructed with the viewing beam 14. In the overlap area, image information is thus perceived simultaneously by means of the two different beam splitter elements 11', 11". The tilt angle range that corresponds to this overlap area 2 (Fig. 2b) is referred to as the overlap tilt angle range.

In general, the resolving power of the human eye is typically given as 1/60 degree. Due to the law "angle of incidence = angle of reflection" when reflecting light on a beam splitter element 11, the requirement for the accuracy of the parallelism of the beam splitter elements 11 is twice as high. If there were a deviation from parallelism of 1/120 degrees, two pixels would be perceived as overlapping by the user when the screen unit 110 was viewed simultaneously via two adjacent beam splitter elements 11 if the vertical resolution of the computer-generated image information was 1/60 degrees. As soon as two pixels optically overlap, this is perceived by the user as a disadvantageous message as a lower resolution. In order to prevent such image deterioration accordingly, the beam splitter elements 11 must have a smaller maximum deviation from parallelism so that the image deterioration can be neglected. This can be achieved, for example, by a specified maximum deviation of less than 1/120 degrees or ideally less than 1/1200 degrees.

Now the lever arm from the tilt axis 15 to the outer edge of the beam splitter element 11, to which the thread element 16 is fixed, is typically around 2.5 mm. This results in a permissible manufacturing tolerance when manufacturing the parallel oriented beam splitter elements 11 of Tan(l/120 degrees) x 2.5 mm = 363 nm. This means that a deviation from parallelism, a tilt error, of 1/120 degrees would result if one of the two thread elements 16 were to lengthen or shorten by 363 nm. Tolerances in the nanometer range are, however, very difficult to set mechanically. Particularly in view of the fact that a mechanical bearing must be implemented around the tilt axis 15 and that such a mechanical bearing is subject to further tolerances of a non-negligible size, it is clear that the problem cannot be easily solved. For this reason, a positive synchronization of the beam splitter elements 11 by means of a thread element 16 is advantageous, for example because the synchronization with the thread element can be carried out without bearing play with a permanent preload. In addition, the thread element 16 can be used to take advantage of the fact that, due to the relative position of the overlapping areas of the beam splitter elements 11 to the pupil 101 of the eye 10, the overlapping area is only visible in a very small angular range of the entire field of view. A tilting error of adjacent beam splitter elements 11, ie the parallelism of adjacent beam splitter elements 11, only has to be realized in a relatively small angular range, for example less than 15 degrees, or better still less than 10 degrees, ideally less than 3 degrees. It is therefore sufficient to ensure the parallelism of the beam splitter elements 11 with the greatest precision only in a sub-angle range, the overlap tilt angle range, which makes production significantly easier and makes it easier to achieve a high effective accuracy with regard to parallelism. The thread kinematics described is particularly suitable for this.

In Fig. 2a, three beam splitter elements 11, 11', 11" are shown, which are held in a parallel position by at least one, in this case several thread elements 16, 16', 16", 16'" during swinging, i.e. tilting about the tilt axis 15. The thread elements 16, 16', 16", 16'" each connect two beam splitter elements 11, 11', 11" to one another in a form-fitting manner and here also with pre-tension. They touch the corresponding beam splitter elements 11, 11', 11" in respective rolling areas 113, 113', 113".

In Fig. 2b, the thread elements 16', 16" are shown with a gap 117 to the respective unwinding area 118 for a clearer illustration. On the right-hand side, in the positive x-direction, two thread elements 16' and 16" are shown, which are arranged offset in the y-direction. The thread element 16' connects the uppermost beam splitter element 11 in the z-direction with the middle beam splitter element 11' and the thread element 16" connects the uppermost beam splitter element 11 with the lowermost beam splitter element 11".

The beam splitter elements 11, 11', 11" swing in the z-direction around a first position in which the respective thread elements 16', 16" start from the respective starting points 119 and 119' or 119" up to the position 181 and 181' or 181" rest on the respective beam splitter element 11, 11'. As a result, depending on the tilt angle of the respective beam splitter elements 11, 11', the corresponding thread elements 16', 16" each rest on the beam splitter element 11 or 11' up to the position 182 and 182' or up to the position 182* and 182*'. Accordingly, the respective thread element, here for example the thread element 16', can be divided into the following sections: a rolling area between the positions 182, 182* or 182' and 182*', a transition area 183, 183' and a central section 184. The respective rolling area plus the area between the positions 182 or 182*' and the attachment points 119 or 119' can be regarded as the fastening area. The central area is subjected to a purely tensile load homogeneously across the entire cross-section. The transition area 183, 183' between the respective rolling areas and the central section 184 corresponds accordingly to a spacing of the central section 184 from the rolling areas and thus the fastening areas. In the central area 184 as a calibration area, corresponding length changes can be generated by means of heating. For this purpose, a laser device with a focal point 151 is provided as a heating device 115. The heating thus takes place essentially exclusively in the area of the focal point 151.

During an oscillating movement, the highest stresses in the thread material occur when bending around the unwinding area between positions 182, 182* and 182', 182*'. For this reason, in the case of a metallic thread material, the thread element must be selected with a small thickness of, for example, 10 pm (the thickness is measured in the central section 184 in the x direction). In order to ensure fatigue strength, the thread material must not deform plastically in the unwinding area, i.e. the maximum stress must not reach the yield point. In contrast, the stresses in the calibration area are significantly lower because the force is distributed over the entire cross-section. As a result, heating, in which the structure of the thread material is locally changed, for example by the laser, does result in changes to the mechanical properties of the thread material, but these are not relevant due to the significantly lower requirements for tensile strength in the central section 184. The size of the influence zone, for example the focus point 151, the set temperature and The duration of the temperature can be used to adjust the change in the structure of the thread material and thus the lengthening or shortening of the thread element 16, 16', 16", 16'". The limits of the adjustment options are essentially determined by the thread material.

Claims

Expectations

1. Method for calibrating a glasses display system (1) which is designed to display a virtual image in a field of vision of a user and which has a scanning deflection unit with at least two beam splitter elements (11, 11', 11") which are each mechanically coupled to one another via at least one thread element (16, 16', 16", 16"'); wherein the beam splitter elements (11, 11', 11") are mounted so as to be movable about a tilt axis (15) and, when used as intended, move between two reversal positions (116) at which a tilt speed of the beam splitter elements (11, 11', 11") is zero; with the method steps:

- detecting a deviation of the beam splitter elements (11, 11', 11") coupled to one another via the at least one thread element (16, 16', 16", 16'") from a parallel position;

- contactless heating of the at least one thread element (16, 16', 16", 16'") by means of a heating device (115), with a change in a length of the at least one thread element (16, 16', 16", 16'");

- Controlling the heating device (115) such that the detected deviation is reduced.

2. Method according to the preceding claim, characterized in that the contactless heating is a local heating, wherein in particular the at least one thread element (16, 16', 16", 16'") is heated by at least one order of magnitude more, preferably at least two or at least three orders of magnitude more, than one of the beam splitter elements (11, 11', 11") or the beam splitter elements (11, 11', 11").

3. Method according to one of the preceding claims, characterized in that the contactless heating is carried out on a central section (184) of the at least one thread element (16, 16', 16", 16'"), which extends between two fastening areas of the at least one thread element (16, 16', 16", 16'"), in particular between two fastening areas of the at least one thread element (16, 16', 16", 16'") designed with unwinding areas, and preferably is spaced from the mounting areas.

4. Method according to one of the preceding claims, characterized in that during the control, a duration of the contactless heating and/or a size of a section of the at least one thread element (16, 16', 16", 16"') on which the heating device (115) acts is set depending on a size of the detected deviation.

5. Method according to one of the preceding claims, characterized by

- checking whether the length of the at least one thread element (16, 16', 16", 16'") needs to be increased or decreased in order to reduce the detected deviation; and, depending on a result of the checking, controlling:

- setting an initial heating power if the length needs to be reduced, and

- setting a second heating power different from the first heating power if the length needs to be increased.

6. Method according to the preceding claim, characterized in that the deviation is quantified during the checking, and the first and/or second heating power is selected from respectively predetermined first and second heating power ranges depending on a result of the quantification, wherein in particular a plurality of different first and/or second heating power ranges are predetermined.

7. Method according to one of the preceding claims, wherein the beam splitter elements (11, 11', 11") are coupled to one another via at least one first thread element (16, 16'") and at least one second thread element (16', 16"), wherein the tilt axis (15) runs between the first thread element (16, 16'") and the second thread element (16', 16"), characterized by

- checking whether the length of the first thread element (16, 16'") or the length of the second thread element (16', 16") needs to be reduced in order to reduce the detected deviation; and, depending on a result of the checking, during the heating: - heating the first thread element (16, 16"'), in particular only the first thread element (16, 16"'), or

- Heating the second thread element (16', 16"), in particular only the second thread element (16', 16").

8. Method according to one of the preceding claims, characterized in that the contactless heating is carried out by means of a laser device as a heating device (115).

9. Method according to one of the preceding claims, characterized by

- measuring a temperature reached in the thread element (16, 16', 16", 16'"), in particular as a function of an elongation of the thread element (16, 16', 16", 16'") during heating; and

- Controlling the heating device (115) as a function of the temperature measured for the thread element (16, 16', 16", 16'"), in particular as a function of a material-specific table stored for the thread element (16, 16', 16", 16'").

10. Method according to one of the preceding claims, characterized in that during the contactless heating a material of the at least one thread element (16, 16', 16", 16'") is heated with a volume that changes permanently during the heating.

11. Method according to one of the preceding claims, characterized in that during the contactless heating a carbon steel of the at least one thread element (16, 16', 16", 16'"), in particular a hardened carbon steel, is heated.

12. Manufacturing and calibration method with the method according to one of the preceding claims, characterized by adjusting a material structure, in particular by hardening, a material of the thread element (16, 16', 16", 16'") before carrying out the method of preceding claims, so that the adjusted material structure can be dissolved by heating.

13. Calibration and/or manufacturing device for carrying out a method according to one of the preceding claims.

14. Glasses display system (1) for displaying a virtual image in a field of vision of a user, with a scanning deflection unit with at least two beam splitter elements (11, 11', 11"), each mechanically coupled to one another via at least one thread element (16, 16', 16", 16"'), wherein the beam splitter elements (11, 11', 11") are mounted so as to be movable about a tilt axis (15) and are designed to move between two reversal positions (116) when used as intended, at which a tilting speed of the beam splitter elements (11, 11', 11") is zero; characterized in that the beam splitter elements (11, 11', 11") coupled to one another via the at least one thread element (16, 16', 16", 16'") are coupled to one another via the at least one thread element (16, 16', 16", 16'") using the method according to a of claims 1 to 11 are calibrated in a parallel position.