Display system and method of operation - Patents.com

Abstract

8507054 v1 32 Abstract Display module and system and method of operation A display system comprises a plurality of display modules, each display module comprising at least one light source movable along a predetermined closed path, an image controller adapted to modulate an intensity of light emitted by said at least one light source as said at least one light source 5 moves along said predetermined closed path to make a desired image visible with persistence of vision, a drive mechanically coupled to said at least one light source for moving said at least one light source along said predetermined closed path, and a sensor generating a synchronization signal including a synchronization feature indicative of the at least one light source passing a reference point on the predetermined closure 10 path, and a drive controller for controlling a speed of the driver, the drive controller adapted to receive the synchronization signal from the sensor and a reference signal including a periodic timing feature having a period based on a desired rotational speed of the at least one light source along the predetermined closure path, the drive controller further adapted to generate a drive signal for controlling a speed of the driver 15 such that a phase shift between the synchronization feature or a phase-shifted version thereof and the timing feature or a phase-shifted version thereof is maintained at a predetermined value. The plurality of display modules are arranged in at least two groups, each of the at least two groups including one or more of the plurality of display modules, the predetermined closure path of the or each display module in each group lies within a plane 20 associated with the group, and the plane associated with each group is unique to that group. The display modules are arranged such that each is located within an area around an intersection of a row and a column in a grid, each module being adjacent in its row and column only to modules of different ones of the at least two groups, the light sources of each adjacent pair of display modules moving along their predetermined closed paths in opposite orientations, 25 the predetermined closed paths of each adjacent pair overlapping. The predetermined value of the phase shift between the synchronization feature or a phase shifted version thereof and the timing feature or a phase shifted version thereof for each of the plurality of display modules is selected such that the at least one light source or the member to which it is attached does not occupy a position where the at least one light source or the member to which it is attached 30 8507054 v1 33 obscures the at least one light source of another display module of the plurality of display modules.

Description

[Technical field]

[0001] The present invention relates to a display system comprising multiple display modules and a method for displaying a desired image using multiple display modules. [Background technology]

[0002] A variety of different kinds of devices are used to display images. One type involves a light source moving along a path, typically circular, and the intensity of light emitted by the light source as it moves along the path is altered to produce an image that is visible by persistence of vision. A particular advantage of this type of display is that it can produce an image using relatively few light sources. DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0003] This type of display is particularly attractive for use in a variety of applications such as retail displays, advertising, and public events. However, each situation within these applications tends to be different, requiring a large number of display sizes to be available. This is costly in terms of designing and manufacturing a bespoke display for each situation. Furthermore, when rotating a linear array of light sources to generate an image, there are engineering difficulties when larger displays are required, as the speed of light source movement can be extremely fast at the point furthest from the center of rotation to ensure an adequate refresh rate. Apart from the potential dangers associated with such high speed operation, there will inevitably be some vibrations that can result in image distortion unless measures are taken to balance the array.

[0004] One approach to overcoming these challenges is to construct a larger display using display modules, which are mechanically coupled to ensure that their respective arrays of light sources all rotate in sync and without colliding with one another. However, this arrangement is expensive to implement due to the mechanical linkages, and is rather cumbersome and noisy. This makes such types of displays unsuitable for many situations in which they could be used as an alternative.

[0005] Some of these challenges can be overcome using a synchronous electronic system. However, systems proposed to date are impractical for a variety of reasons. First, there is a large inertia when the modules begin to rotate, which cannot be easily controlled by a simple electronic system. Also, there are slight variations in the acceleration profiles of different motors in adjacent modules, and each module may experience a different degree of air resistance when the light sources begin to rotate, with one module being more susceptible to airflow turbulence than an adjacent module. This results in modules rotating without the synchronization required at start-up of the system. Thus, there is a significant risk that they will collide during start-up and result in damage. The inventors have found that these challenges exist for approximately 1-3 minutes after start-up. Furthermore, the arrays of light sources need to be held in the correct relative position (e.g., a 45 degree rotational offset between the light source arrays of adjacent modules). Thus, such a system necessarily requires some form of mechanical interlock to hold the arrays of light sources on each of the modules in the correct position for successful start-up.

[0006] One way to avoid these issues is to stagger adjacent modules so that their light source arrays lie in different planes. In this way, they can be out of sync and not collide. However, this creates undesirable image artifacts when one module's array passes in front of an adjacent module's array.

[0007] One of these artifacts is shown in Figures 1a-c and 2. Figure 1a shows two cross-shaped arrays of light-emitting diodes (LEDs). One of the arms of the left-hand array passes in front of one of the arms of the right-hand array. A closer view of this is also shown, where it can be seen that the arm of the left-hand array obscures some of the LEDs of the right-hand array. The two arrays are counter-rotated. Figure 1a shows the situation where the left-hand array is 10° from horizontal and the right-hand array is 15° from horizontal.

[0008] Figure 1b shows the situation after the arrays have been rotated a further 5°, so that the array on the left is now 15° from horizontal and the array on the right is now 20° from horizontal. In the detailed view it can be seen that the array on the left obscures a different set of LEDs on the array on the right than the set obscured in Figure 1a. The quadrilateral shapes labeled 1 in the detailed view indicate pixels that have already been obscured.

[0009] Figure 1c shows the situation after the arrays have been rotated a further 5°, so that the array on the left is now 20° from horizontal and the array on the right is now 25° from horizontal. In the detailed view it can be seen that the array on the left obscures a different set of LEDs on the array on the right than the set it obscures in Figures 1a and 1b. The quadrilateral shapes labelled 1 and 2 in the detailed view indicate pixels that have already been obscured.

[0010] Thus, as the arrays rotate, a roughly arcuate portion of the right-hand array becomes obscured. The overall effect is shown in Figure 2. The circular outlines described by the left and right arrays are shown at 3 and 4, respectively. The roughly arcuate portion that is obscured is shown at 5. This appears as a dark area in the image produced by the two arrays. This phenomenon is known as a "missing dot" artifact.

[0011] A second image artifact is shown in Figure 3. Again, there are two arrays: a left array 6 and a right array 7. One way to show a single image on the two arrays is to use the entire area of ​​the left array to generate an image, but only the part of the right array that does not pass behind the left array is used. This is shown by the shaded area in front of the two arrays 6, 7 in Figure 3. This approach works well when viewed vertically. However, when the observer moves off-axis, as shown in Figure 3 by the arrow looking into the gap between arrays 6 and 7, the image is not visible in the part of the right array 7 behind the left array 6.

[0012] Thus, while the approach described in the immediately preceding paragraph solves the dead dot problem, it creates its own problems. Various attempts have been made to overcome this, including controlling the brightness of the overlapping parts of the images produced by the LEDs of each array 6, 7. However, these reintroduce the dead dot problem, and there is a trade-off between the dead dot problem and the presence of gaps in the image that become visible when viewed off-axis. [Means for solving the problem]

[0013] According to a first aspect of the present invention, there is provided a display system comprising a plurality of display modules, each display module having: at least one light source movable along a predetermined closing path; an image controller adapted to modulate an intensity of light emitted by the at least one light source as the at least one light source moves along the predetermined closed path to make a desired image visible with persistence of vision; a drive mechanically coupled to the at least one light source to move the at least one light source along the predetermined closure path; a sensor generating a synchronization signal including a synchronization feature indicative of the at least one light source passing a reference point on the predetermined closed path; a drive controller for controlling a speed of the drive, the drive controller being adapted to receive the synchronization signal from the sensor and a reference signal including a periodic timing feature having a period based on a desired rotation speed of the at least one light source along the predetermined closed path, the drive controller being further adapted to generate a drive signal for controlling the speed of the drive such that a phase shift between the synchronization feature, or a phase-shifted version thereof, and the timing feature, or a phase-shifted version thereof, is maintained at a predetermined value; the plurality of display modules are arranged into at least two groups, each of the at least two groups including one or more of the plurality of display modules, the predetermined closure path of the or each display module in each group lies within a plane associated with the group, the plane associated with each group being unique to that group; the display modules are arranged such that each is within an area about an intersection of a row and a column in a grid, each module being adjacent in its row and column to only modules in different ones of the at least two groups, the light sources of each adjacent pair of display modules moving along their predetermined closed paths in opposite orientations, and the predetermined closed paths of each adjacent pair overlap; A display system is provided in which the predetermined value of the phase shift between the synchronization feature or a phase-shifted version thereof and the timing feature or a phase-shifted version thereof for each of the plurality of display modules is selected such that the at least one light source or a member to which it is attached does not occupy a position which obscures the at least one light source of another display module of the plurality of display modules.

[0014] By controlling the speed of the drivers in each display module to maintain the phase shift between the synchronization feature (or a phase-shifted version thereof) and the timing feature (or a phase-shifted version thereof) at a predetermined value, it can be ensured that the at least one light source (or the arm or member to which it is attached) of a first display module is not directly in front of the at least one light source of another display module disposed adjacent to the first display module, and the phase shift between the synchronization feature (or a phase-shifted version thereof) and the timing feature (or a phase-shifted version thereof) of the remaining display modules is also controlled to an appropriate predetermined value, thereby eliminating the missing dot problem mentioned above.

[0015] The at least one light source of each display module is typically an array of light sources. The array of light sources may be arranged in several shapes, but a typical one is a cross-shaped array, as shown in FIG. 1 for example. LEDs are an excellent choice for the light source, as they are economical to purchase and very power-efficient in operation. The at least one light source may be capable of emitting light of different color spectrums, corresponding to a predefined color gamut, such as sRGB or Adobe® RGB for example. For this purpose, RGB LEDs are particularly suitable. To accommodate the use of light sources capable of emitting light of different color spectrums to reproduce a desired image in color, the image controller may be adapted to modulate the intensity and color of the light emitted by the at least one light source as it moves along a predefined closed path.

[0016] Each area around a row and column intersection in the grid may extend from said intersection by an amount of 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 centimeters. Each display module may be located directly on its respective intersection or elsewhere within its surrounding area.

[0017] Typically, the at least one light source is attached to one or more arms, which can be made of transparent or opaque materials, such as plastic or metal. For example, if the at least one light source is an array of light sources arranged in a cross shape, there may be two arms joined at the center of the cross. The arms may be made of aluminum, steel, or a suitable engineering plastic, such as nylon.

[0018] The light source of each display module or the predetermined closed path along which each light source moves is usually circular. If the at least one light source is an array of light sources, each light source may be movable along its own unique predetermined closed path. Thus, if the predetermined closed path is circular, each light source moves around a central axis along its own unique circular path. If the array of light sources is cross-shaped, the light sources on one of the two arms may be interlaced with the light sources on the other arm.

[0019] The driver of each display module may be a motor, such as a brushless DC (BLDC) motor. The at least one light source may be coupled to a drive shaft of the motor. The at least one light source may thus rotate around a central axis defined by the drive shaft of the motor. For example, if the at least one light source is a cross-shaped array, the cross may be attached at its center to the drive shaft of the motor.

[0020] The sensor of each display module may detect the passage of a respective index feature having a fixed spatial relationship to the at least one light source of the display module as the at least one light source moves along its predetermined closed path, and the sensor generates a pulse in the synchronization signal in response to the passage of the index feature past the sensor.

[0021] The sensor may be an optical sensor, for example a sensor that functions by detecting the reflection of light emitted by the sensor. In this case, the index feature may be a reflectivity or a gap in a reflective strip that passes through the sensor as the at least one light source moves along the predetermined closed path. Another suitable type of optical sensor is a transmissive type that detects light emitted by a light source in the sensor that can reach a detector in the sensor. In this case, the index feature may be an opaque feature that blocks light from reaching the detector, or a gap in an opaque strip that allows light to reach the detector.

[0022] Alternatively, the sensor may be a magnetic sensor, in which case the index features may be made of a magnetic material that the sensor can detect when passing by the sensor.

[0023] Each display module may further comprise sub-index features spaced apart from each other and from their respective index features such that as the at least one light source moves along the predetermined closed path, the index feature and each of the one or more sub-index features pass the sensor in sequence, the sensor generating a pulse in the synchronization signal in response to the or each sub-index feature passing through the sensor.

[0024] The presence of sub-index features improves the accuracy of synchronization. The or each sub-index feature is typically smaller than the index feature. The sub-index features can have a structure similar to that of the index features described above for use with optical or magnetic sensors. A typical arrangement is to have castellations arranged in the plane of a castellated disk or perpendicular to the disk. Each castellation represents one of the index or sub-index features. If the sensor is a transmissive optical sensor, the castellations are made of an opaque material that blocks light emitted by the light source in the sensor. If the sensor is a reflective optical sensor, the castellations are made of a reflective material that reflects light emitted by the sensor back to the sensor. If the sensor is magnetic, the castellations are made of or include a magnetic material.

[0025] The display module may further comprise a second sensor configured to generate an image synchronization signal indicating that the at least one light source has passed an image starting point on the predetermined closed path, or the image synchronization signal may be generated from the synchronization signal, the image starting point having a fixed spatial relationship to the reference point.

[0026] The image starting point may be offset along the predetermined closure path relative to the reference point or may be at the reference point. The second sensor may be optical or magnetic, similar to the sensors described above. The image synchronization signal may be used by the image controller to determine when the at least one light source has reached a starting point for the reproduction of the desired image. The image controller may then output illumination control signals to the at least one light source to define the desired image and reproduce the desired image by modulating the intensity of light and / or color emitted according to image data stored by the image controller.

[0027] The desired image may be changed over time to enable playback of a video image. To enable this, the image controller may be adapted to receive video data, for example via an HDMI connection.

[0028] The image controller of each display module may be further adapted to modulate the intensity of light emitted by the at least one light source according to a respective luminance mask to adjust the intensity of light emitted by the at least one light source based on a predetermined profile.

[0029] For example, the predetermined profile may adjust an intensity of light emitted by the at least one light source when the at least one light source is at a position on the predetermined closed path that is within a predetermined overlap zone, which may be a zone where the predetermined closed path of one display module passes directly in front of a predetermined closed path of another display module disposed adjacent to the first display module.

[0030] Thus, for example, if the at least one light source is a cross-shaped array of light sources and the predetermined closed path is circular, the predetermined profile may cause the intensity of light emitted by the light sources in the array to decrease in the overlap zone with increasing distance from the center. This gradient profile allows reproduction of the entire image across several adjacent display modules without any gaps appearing when the image is viewed off-axis. This allows the entire image to be displayed without the second image artifact mentioned above. Furthermore, the above trade-off no longer exists and both image artifacts mentioned above no longer occur.

[0031] The reference signal may be generated by the display module itself. However, it may also be generated by an external control unit. This has the advantage that the reference signal can be distributed to several identical display modules. Thus, the phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version for each module can be maintained at the respective phase shift with reference to the same reference signal. Thus, synchronization of the at least one light source of each module can be ensured as it rotates around its respective predefined closed path.

[0032] The synchronization feature is typically a pulse (such as a pulse generated by the sensor upon passing an index feature as described above). Similarly, the periodic timing feature is typically a pulse that occurs once per revolution around the predetermined closed path. For example, if the at least one light source is to move around the predetermined closed path at a speed of 750 revolutions per minute, the pulse may be generated at a rate of 750 times per minute or 12.5 Hz.

[0033] The drive controller can measure a time difference between the periodic timing feature, or a phase-shifted version thereof, and the synchronization feature, or a phase-shifted version thereof. This time difference can be used to calculate an actual phase shift between the synchronization feature, or a phase-shifted version thereof, and the timing feature, or a phase-shifted version thereof. If this phase shift is the predetermined value, then the time difference is a required value. If the measured time difference is greater or less than the required value, the drive controller can adjust the speed of the drive to bring the measured time difference to the required value.

[0034] The predetermined value of the phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version may be set to 0°, 45°, or any other value depending on the situation. This predetermined value of the phase shift is specific (but not necessarily unique) to each display module. In one scenario where multiple display modules are placed adjacent to each other and the predetermined closing paths of adjacent displays overlap, the predetermined value of the phase shift between the synchronization feature and the phase-shifted version of the timing feature is maintained at 180°. The reference signal is received by each display module and phase-shifted by a respective amount to introduce a specific phase shift for that display module. The specific phase shift may be different for different display modules or groups of display modules, thereby enabling the relative positions of the at least one light source on adjacent display modules to be controlled as they move along their predetermined closing paths such that at least one light source or member attached to a first one of the adjacent displays does not occupy a position where it obscures the at least one light source of the other one of the adjacent display modules.

[0035] The predetermined value of the phase shift between the synchronization feature, or a phase-shifted version thereof, and the timing feature, or a phase-shifted version thereof, may be programmed into a memory device at the time of manufacture of the display module, or may be programmed by a user using appropriate software running on a desktop computer or a mobile phone. The software may communicate with an external control unit coupled to an interface on the display module using a fiber optic cable. Image data representing the desired image (or a series of images in the form of video data) may also be communicated to a memory device on the display module for access by the image controller.

[0036] As is evident from the above description, the drive controller of each display module maintains the phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version at a predefined value. This means that one of the following four can be maintained at a predefined value by the drive controller: i) the phase shift between the synchronization feature and the timing feature; ii) the phase shift between the phase-shifted version of the synchronization feature and the timing feature; iii) the phase shift between the synchronization feature and the phase-shifted version of the timing feature; and iv) the phase shift between the phase-shifted version of the synchronization feature and the phase-shifted version of the timing feature. The phase shift is measured relative to the reference signal, one period of which represents a phase of 360°.

[0037] For each of the plurality of display modules, the predetermined value of the phase shift between the synchronization feature, or a phase-shifted version thereof, and the timing feature, or a phase-shifted version thereof, may be dynamically adjustable, e.g., within a successive rotation or number of rotations around the predetermined closing path, the predetermined value may be adjusted or changed by a few degrees, e.g., 1-5°.

[0038] The rows and columns in the grid may lie on horizontal and vertical axes, respectively. Alternatively, the rows and columns may be at an angle to the horizontal and vertical. Each of the plurality of display modules may be arranged in a respective one of a first and a second group, such that each module in the first group is adjacent to only modules in the second group in its row and column, and each module in the second group is adjacent to only modules in the first group in its row and column.

[0039] The first orientation may be clockwise and the second orientation may be counterclockwise, or vice versa.

[0040] The phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version of each display module may be a multiple of 45° and may be different from the phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version of each adjacent display module in that row and column.

[0041] The display system may further comprise an external control unit that generates the reference signal. The external control unit may communicate with the set of the plurality of display modules using one or more fiber optic cables. The fiber optic cables may transmit signals such as the reference signal. It may also communicate image data representing the desired image (or a series of images in the form of video data) for use by the image controller in the display modules. The set of the plurality of display modules may include all display modules. However, in some cases, there may be multiple external control units, each assigned to a respective set of the display modules. The multiple external control units may be coupled to each other to share the reference signal and image data, for example using an HDMI connection.

[0042] Each display module may be assigned to a respective row and column in the grid, and the external control unit may comprise a memory in which the assigned rows and columns for each display module are stored. Each display module may be assigned to a respective row and column in the grid by a user using a software application capable of communicating with the external control unit.

[0043] The external control unit may be coupled to each of the display modules by a communications link (e.g., the fiber optic cable mentioned above) capable of transmitting image data to each display module, the image data representing a portion of an overall image displayed by all the display modules together.

[0044] The external control unit may include an image processor that, for each display module, offsets the portion of the overall image represented by the image data by a calibration amount to account for misalignment of the display module. The calibration amount may be set by a user during a set-up process using a software application capable of communicating with the external control unit. By displaying calibration images on each display module and accepting user input indicating how these images should be adjusted to account for inconsistencies caused by imperfect installation of the display modules, the external control unit may determine the appropriate translational offset to apply to the image data.

[0045] The predetermined values ​​of phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version for each of the plurality of display modules may be selected such that the difference between each adjacent pair of predetermined values ​​has a desired value or is between an upper threshold and a lower threshold, thereby setting an initial phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version for each of the plurality of display modules.

[0046] Typically, the desired value is 45° if the phase shift between the synchronization feature and the timing feature is maintained at the predetermined value. However, this is a convenient value and is not critical. In some circumstances, a lower or higher value can be set, for example 42° or 48°. Therefore, instead of having a desired value, it is often appropriate to ensure that the difference is between an upper threshold and a lower threshold. In other cases where the phase shift between the synchronization feature and the phase-shifted version of the timing feature is maintained at a predetermined value, the desired value may be 180° or 0°.

[0047] The initial phase shift of each display module may be adjusted by adding or subtracting an amount equal to the angle subtended by a sensor on the display module and a second sensor when drawn in a straight line to the center of the predetermined closed path, the second sensor generating an image synchronization signal indicative of the passage of the at least one light source past an image starting point on the predetermined closed path.

[0048] The initial phase shift of a display module may be adjusted by a calibration amount input by a user to account for misalignment between said display module and one or more adjacent display modules.

[0049] Selection of the predetermined value for setting the initial phase shift and adjustments to the initial phase shift may be made by external control unit 11. This may occur at initialization of the system. For example, the predetermined value may be set when external control unit 11 is informed where each display module is located (i.e. the row and column in the grid). Such adjustments may be made based on information that external control unit 11 stores regarding the angles subtended by two sensors and on user input it receives indicating misalignment between adjacent display modules.

[0050] According to a second aspect of the present invention, there is provided a method of displaying a desired image using a plurality of display modules, each display module having at least one light source movable along a respective predetermined closed path, said method comprising: arranging the plurality of display modules into at least two groups, each of the at least two groups comprising one or more of the plurality of display modules, in each group the predetermined closure path of the or each display module being located in a plane associated with the group, the plane associated with each group being unique to the group; arranging the display modules such that each is located within an area around an intersection of a row and a column in a grid, each module being adjacent in its row and column only to modules from different ones of the at least two groups, the light sources of each adjacent pair of display modules moving along their predetermined closed paths in opposite orientations, and the predetermined closed paths of each adjacent pair overlap; 2. In each of the plurality of display modules, moving said at least one light source along its respective predetermined closed path; modulating an intensity of light emitted by the at least one light source of each of the plurality of display modules as the at least one light source moves along its respective predetermined closed path to make a respective portion of the desired image visible with a persistence of vision, wherein the respective portion of the desired image is visible on each of the plurality of display modules that together form the desired image; generating a respective synchronization signal including a synchronization feature indicative of the at least one light source passing a reference point on the respective predetermined closed path; receiving a reference signal including a periodic timing feature having a period based on the desired rotational speed of the at least one light source along each of the predetermined closed paths; and controlling the speed at which the at least one light source moves along the respective predetermined closed path such that a phase shift between the synchronization feature, or a phase-shifted version thereof, and the timing feature, or a phase-shifted version thereof, is maintained at a predetermined value; A method is provided, wherein the predetermined value of phase shift between the synchronization feature or a phase-shifted version thereof and the timing feature or a phase-shifted version thereof for each of the plurality of display modules is selected such that the at least one light source does not occupy a position that obscures the at least one light source of another display module of the plurality of display modules.

[0051] The method may further include detecting, with a respective sensor, the passage of an index feature in each display module having a fixed spatial relationship to the at least one light source as the at least one light source moves along its predetermined closed path, the sensor generating a pulse in the synchronization signal in response to the passage of the index feature past the sensor.

[0052] In each display module, the sensor may generate a pulse in a synchronization signal in response to the passage of the sub-index features spaced apart from each other and from the index feature such that the index feature and one or more sub-index features each pass the sensor in sequence as the at least one light source moves along the predetermined closed path.

[0053] The method may further include generating, at each display module, an image synchronization signal indicating when the at least one light source has passed an image starting point on the predetermined closed path.

[0054] The method may further include modulating an intensity of light emitted by the at least one light source according to a luminance mask to adjust an intensity of light emitted by the at least one light source based on a predetermined profile.

[0055] The method may further include dynamically adjusting, for each of the plurality of display modules, the predetermined value of a phase shift between the synchronization feature, or a phase-shifted version thereof, and the timing feature, or a phase-shifted version thereof.

[0056] The method may further include arranging the plurality of display modules into first and second groups, wherein each module in the first group is adjacent to only modules in the second group in its row and column, and each module in the second group is adjacent to only modules in the first group in its row and column.

[0057] The phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version of each display module may be a multiple of 45° and may be different from the phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version of each adjacent display module in that row and column.

[0058] The method may further comprise generating the reference signal using an external control unit.

[0059] The method may further include assigning each display module to a respective row and column in the grid, and storing the assigned row and column of each display module in the external control unit.

[0060] The method may further include transmitting image data to each display module, the image data representing a portion of an overall image to be displayed by all of the display modules together. For each display module, the portion of the overall image represented by the image data may be offset by a calibration amount to account for misalignment of the display modules.

[0061] The predetermined value of the phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version for each of the plurality of display modules is selected such that the difference between the predetermined values ​​of each adjacent pair has a desired value or is between an upper threshold and a lower threshold, thereby setting an initial phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version for each of the plurality of display modules.

[0062] The initial phase shift of each display module may be adjusted by adding or subtracting an amount equal to the angle subtended by a first sensor and a second sensor on the display module when drawn in a straight line to the center of the predetermined closure path, the first sensor may detect the passage of an index feature having a fixed spatial relationship to the at least one light source as it moves along the predetermined closure path, and the second sensor may generate an image synchronization signal indicative of the passage of the at least one light source past an image starting point on the predetermined closure path.

[0063] The initial phase shift of a display module is adjusted by a calibration amount input by a user to account for misalignment between the display module and one or more adjacent display modules.

[0064] This method corresponds to the display system of the first aspect, and the description of that system applies to this method, and therefore any of the features described above with respect to said display system can be combined with any of the features of this method. [Brief description of the drawings]

[0065] [Figure 1] Figure 1 (1a)-(1c) show two display modules in various positions and in an overlapping arrangement where the missing dot issue may occur. [Diagram 2] Figure 2 shows the appearance of a missing dot. [Diagram 3] FIG. 3 illustrates another image artifact occurring in the gap between adjacent displays located in two different planes. [Figure 4] FIG. 4 shows a schematic diagram of a display system according to the invention. [Diagram 5] Figure 5a shows an example of a mounting arrangement suitable for use with a display module of the present invention to manufacture a display system, and Figure 5b shows an example of a mounting arrangement suitable for use with a display module of the present invention to manufacture a display system. [Figure 6] FIG. 6 shows a block diagram of the electrical and electronic components of the display module. [Figure 7] FIG. 7 shows a castellated disk for use with a sensor in the display module. [Figure 8] FIG. 8 shows the signal generated by the sensor. [Figure 9] FIG. 9 shows the reference signal. [Figure 10] FIG. 10 shows how a gradient mask can be used in conjunction with adjacent display modules. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0066] 4 shows an array 10 of display modules. In this case, there are six display modules in the array 10. However, this number is arbitrary and there may be more or fewer display modules in the array.

[0067] An external control unit 11 is connected to each display module in the array 10 via fiber optic cables 12. These fiber optic cables 12 (one for each display module) are used to transmit reference signals to synchronize the movement of the display modules in the array. They are also used to transmit image or video data to the display modules.

[0068] Image or video data may be provided to the external control unit 11 from a suitable source 13 (e.g., a desktop or laptop computer, a television, a DVD or Blu-ray player) via an HDMI connection 14. The external control unit 11 may store the image or video data received from the source 13. This may then be transmitted on demand to the display module 10 as required. The image or video data may be transferred to the external control unit 11 via any suitable interface, such as HDMI, Ethernet or Wi-Fi. The external control unit 11 may also pass image or video data received via HDMI directly to the display module 10. The external control unit 11 may also be connected to speakers 15 for playing audio content accompanying the image or video data.

[0069] The external control unit may also be connected through router 16 (using Wi-Fi, or to the Internet, or to a software application running on a computer 17 or mobile device 18). Computer 17 or mobile device 18 may be used to program the array as described below.

[0070] As mentioned above, the external control unit 11 provides multiple fiber optic outputs, each connected to a respective display module. If more display modules are required than there are fiber optic outputs, additional external control units can be connected using HDMI® cables. The HDMI® cables are used to transmit the reference signal as well as transmit image or video data between the external control units.

[0071] Figures 5a and 5b show one way of mounting the display module to create a display system. The display module has an array of LEDs arranged on two arms in a cross shape. The LEDs are RGB LEDs so that a wide spectral range of colors can be reproduced. The LEDs extend along the entire length of the arms in a cross shape. They may be arranged such that the LEDs on one arm are interlaced with the LEDs on the other arm.

[0072] In Figure 5a a clip 20 for holding a display module is shown mounted directly to a substrate such as a wall. An adjacent clip 21 is mounted to standoffs 22 which are attached to said substrate. The effect of this is that the arms of the display module mounted to clip 21 lie in a plane which is forward (with respect to said substrate) relative to the plane in which the arms of the display module mounted to clip 20 lie. A display module 23 is shown mounted to a clip which has a standoff behind it, whilst an adjacent display module 24 is mounted to a clip which does not have a standoff.

[0073] This pattern of alternating standoffs 22 is repeated in both vertical and horizontal directions to form a grid of display modules as shown in Figure 5b, where 12 display modules are arranged in 3 rows and 4 columns. Thus, the display modules in Figure 5b shown with cross-shaped arms oriented vertically and horizontally are attached directly to the wall using clips 20, 21, while the display modules shown with cross-shaped arms oriented at 45° to the horizontal and vertical are attached to the wall using said clips and standoffs 22. The arms on displays attached with standoffs 22 all lie in the same plane (relative to the substrate) in front of the plane in which the arms are located on displays attached using only clips 20, 21.

[0074] In the arrangement of Fig. 5b, each display module is at the intersection of a row and a column in the grid. The display modules attached directly with the clips represent a first group of display modules, and the display modules attached using the standoffs in addition to the clips represent a second group of display modules. Each module of the first group is adjacent to only modules of the second group in its row and column, and each module of the second group is adjacent to only modules of the first group in its row and column. In other words, when moving along any row or column, the display modules are arranged such that the cross-shaped arms alternate between a rear or a front plane. This ensures that the arms cannot collide. As mentioned above, this is particularly important since the system starts when electronic synchronization of the modules is used.

[0075] Each module in the first group is rotated in a first sense, for example clockwise, and each module in the second group is rotated in a second opposite sense, for example counterclockwise.

[0076] 6 shows a block diagram of the electrical and electronic components of a display module. The components are conceptually divided by a horizontal line into a rotor and a stator, as indicated by corresponding labels. The rotor is the moving part of the display module and the stator is the fixed part.

[0077] In the stator, data is received by an FPGA 30 from an external control unit 11. This data includes reference signals and image data to be displayed by the display modules. External control unit 11 divides the overall image displayed by the array of display modules such that only data for the portion of the image displayed by each display module is sent to that display module.

[0078] The reference signal is shown in Figure 9. It consists of periodically occurring pulses. The period between pulses in the signal is equal to the time for one rotation of the rotor. Thus, if the rotor needs to rotate at 750 revolutions per minute, the period between pulses will be 80 milliseconds. In other words, the pulses will be generated at a rate of 12.5 Hz.

[0079] FPGA 30 includes a phase shift calculation module and a phase correction module that cooperate to maintain the rotational speed of the rotor at a desired speed, which also maintains the desired position of the cross arm (and therefore the array of LEDs) when each pulse in the reference signal is generated, a function of which is described below.

[0080] The FPGA 30 provides signals (derived from the phase correction module, as described below) to control a motor driver 31 that drives a BLDC motor 32 that rotates the rotor. The signals provided to the motor driver 31 cause the motor driver 31 to control the rotational speed of the BLDC motor 32.

[0081] To provide power from the stator to the rotor, FPGA 30 is connected to a wireless power driver 33 which operates a transformer winding 34a. A corresponding transformer winding 34b in the rotor is coupled to a wireless power driver 35. Thus, power is available to the rotor for electronics and LEDs.

[0082] The shaft of BLDC motor 32 is hollow, which allows for optical transmission of image data representing an image to be displayed by the display module from FPGA 30 to the rotor. To accomplish this, FPGA 30 can control laser driver 36 to drive a laser 37 in optical communication with a photodiode 38 through the hollow shaft of BLDC motor 32. Photodiode 38 is then coupled to an FPGA 39 on the rotor. Laser driver 36 can thus be used to transmit the image data from the stator to the rotor by modulating the light transmitted by laser 37 to photodiode 38.

[0083] The FPGA 39 is coupled to four arrays of LEDs 40a-40d, each of which is on a respective one of the portions of the arms that extend from the center where the cross-shaped arms meet outwards. They extend in a straight line. It is therefore possible to generate images by persistence of vision, by illuminating the LEDs as the arm in which they are located rotates. How this is controlled by the FPGA 39 will be described later.

[0084] Two light sensors 41 and 42 are also provided, said sensors being connected to FPGAs 30 and 39 respectively, the function of which will now be described.

[0085] Sensor 41 on the rotor is responsible for image synchronization, while sensor 42 (under the control of BLDC motor 32) is responsible for maintaining the rotational speed of the rotor and its relative position as it rotates.

[0086] 7 shows a castellated disk 50 coupled to and rotating with the rotor. The castellations on the disk extend perpendicularly from the disk 50. The sensor 42 detects the passage of each castellation and generates a corresponding pulse. The index castellation 51 is larger than the 19 sub-index castellations 52. Thus, the passage of the index castellation 51 generates a longer pulse than the pulse generated by the passage of the sub-index castellations 52.

[0087] The resulting synchronization signal is shown in Figure 8. Essentially, the longer pulses generated by the index castellations passing the sensor 42 occur once per revolution, and each longer pulse is followed by a shorter pulse generated by each sub-index castellation 52 passing the sensor.

[0088] The FPGA 30 receives this synchronization signal from the sensor 42 and passes it to a phase shift calculation unit. The phase shift calculation unit also receives a reference signal generated by the external control unit 11. The reference signal shown in FIG. 9 is phase shifted by an amount equal to the required phase shift of the display module (calculated as described below). The leading edge of each adjacent pair of pulses in the reference signal represents a phase shift of 360°. For example, if the period of the reference signal is 80 ms and an index pulse generated by an index castellation passing the sensor 42 arrives 10 ms after the pulse of the reference signal, the phase shift between them is 45°. The phase shift calculation unit measures the time difference between the pulse in the phase-shifted reference signal and the longer index pulse generated by the index castellation passing the sensor 42. This time difference becomes zero when the required phase shift is achieved.

[0089] Thus, if the time difference is not zero, a correction is required. This correction is accomplished by adjusting the speed of the BLDC motor 32. The phase correction module does this. In response to receiving an indication from the phase shift calculation module that the time difference is not zero, the phase correction module generates appropriate signals that are provided to the motor driver 31 to appropriately accelerate or decelerate the BLDC motor 32 to bring the time difference to zero, and thus the phase shift to the required value. Once the required value is achieved, the feedback mechanism can maintain it at that value.

[0090] The sub-index pulses can be used by the phase shift calculation unit to detect variations from a desired phase shift before the next index pulse is received. This is possible by interpolating between pulses of the reference signal to predict when the next sub-index pulse should be received. Although not required, the sub-index pulses improve the accuracy of the system.

[0091] Sensor 41 detects the passage of image synchronization features on the rotor and generates a pulse with the passage of each such feature. An image controller in FPGA 39 processes the pulses received from sensor 41. Because there is a fixed spatial relationship between the image synchronization features and LEDs, the position of an LED can be inferred from the pulse generated by the image synchronization feature passing by sensor 41.

[0092] The display area and image is divided into sectors (e.g., 2000 sectors). When the image controller receives a pulse, it begins displaying the content associated with that sector (which will be a different part of the image for each of the four LED arrays 40a-40d) between the pulse and the neighbors. It can stay synchronized by calculating the time available within the sector to display the associated content.

[0093] It is not necessary to use two sensors as in this embodiment, instead it is possible to use only sensor 42 and pass information about the rotor position from the phase shift calculation module to the image controller.

[0094] During the setup of the display system, a user may use a mobile device or computer running software that interfaces with an external control unit 11. This software is used to assign each display module in the system to a specific position in the array of display modules. The external control module 11 then determines the rotation direction and the initial phase shift. For example, the rear module in the system of FIG. 5b may be assigned a clockwise rotation direction and the front module may be assigned a counterclockwise rotation direction. The initial phase shift is selected such that each display is at 45° relative to its neighboring displays. For example, the front module may be set to an initial phase shift of 0° and the rear module to an initial phase shift of 45°. Although angles of 0° and 45° are typically used, other pairs of angles with suitable differences may be used instead. It is necessary that the difference between the angles selected for the neighboring modules (i.e., between the front and rear modules in this example) is such that the arm with the LED attached to the front module does not occupy a position that would obscure the LED of the rear module when the arm rotates.

[0095] This initial phase shift can be adjusted by the angle that the two sensors 41 and 42 make with respect to each other, in other words the angle that they subtend when drawn in a straight line to the central axis of rotation. For one of a group of displays rotating in one of the two directions (clockwise and counterclockwise), the adjustment is made by adding the full phase angle, and for the other direction by subtracting said angle.

[0096] Calibration is then performed to determine the offset angle and translation of each display module to ensure that its images are in the correct orientation and position. This is done by displaying calibration images on each display module and accepting user input indicating how these images need to be adjusted to account for small discrepancies caused by imperfect mounting of the display module and situations where a display module needs to be mounted at an angle, on its side or upside down. The translation input of each display module is used to adjust the portion of the image or video data sent to that display module by the external control module 11. The offset angle of each display module is either added to the adjusted initial phase shift when the display module rotates in one of the clockwise or counterclockwise directions, or subtracted from the adjusted initial phase shift when the display module rotates in the other of the clockwise or counterclockwise directions. The offset angle of each display module in the array is also sent by the external control module 11 to that display module so that the FPGA 39 can apply an offset to the image data when the image data is displayed.

[0097] The above process results in a set of phase shifts that move all of the display modules to positions where the images displayed on each of the display modules are aligned with each other and where the arms to which the LEDs are attached do not obscure the LEDs on adjacent displays.

[0098] The set of phase shifts calculated above can then be sent to the respective display modules and used as the phase shift to which the reference signal must be adjusted. As described above, the speed of the BLDC motor can then be adjusted to maintain a 0° phase shift between the index pulse and the pulse in the phase-shifted reference signal.

[0099] In this way, the display modules operate such that the arms of one display module never occupy a position that obscures the LEDs of another display module, thus overcoming the problem of dead dots.

[0100] FIG. 10 illustrates how the overlapping area of ​​two adjacent display modules can have a luminance gradient mask applied to the image generated by each of said display modules. In this example, the overlapping area extends from A to B (in the cross-section shown in the figure). The image luminance mask applied to the front display module 60 causes the luminance of the image generated by the front display module 60 to decrease linearly from 100% to 0% from point A to point B. Similarly, the image luminance mask applied to the rear display module 61 causes the luminance of the image generated by the front display module 61 to decrease linearly from 100% to 0% from point B to point A. This reduces the effect of the above-mentioned second image artifact that appears in the gap between adjacent displays when viewed off-axis. This is because each of the two display modules 60 and 61 is generating a portion of the overall image. When viewed on-axis, the image appears complete. When viewed off-axis, the tendency for the second image artifact to be present is radically reduced.

Claims

1. A display system comprising a plurality of display modules, each display module comprising: at least one light source movable along a predetermined closing path; an image controller adapted to modulate an intensity of light emitted by the at least one light source as the at least one light source moves along the predetermined closed path to make a desired image visible with persistence of vision; a drive mechanically coupled to the at least one light source to move the at least one light source along the predetermined closure path; a sensor generating a synchronization signal including a synchronization feature indicative of the at least one light source passing a reference point on the predetermined closed path; a drive controller for controlling a speed of the drive, the drive controller being adapted to receive the synchronization signal from the sensor and a reference signal including a periodic timing feature having a period based on a desired rotation speed of the at least one light source along the predetermined closed path, the drive controller being further adapted to generate a drive signal for controlling the speed of the drive such that a phase shift between the synchronization feature, or a phase-shifted version thereof, and the timing feature, or a phase-shifted version thereof, is maintained at a predetermined value; the plurality of display modules are arranged into at least two groups, each of the at least two groups including one or more of the plurality of display modules, the predetermined closure path of the or each display module in each group lies within a plane associated with the group, the plane associated with each group being unique to that group; the display modules are arranged such that each is within an area about an intersection of a row and a column in a grid, each module being adjacent in its row and column to only modules in different ones of the at least two groups, the light sources of each adjacent pair of display modules moving along their predetermined closed paths in opposite orientations, the predetermined closed paths of each adjacent pair overlapping; A display system, wherein the predetermined value of the phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version for each of the plurality of display modules is selected such that the at least one light source or the member to which it is attached does not occupy a position that obscures the at least one light source of another display module of the plurality of display modules.

2. 2. The display system of claim 1, wherein the sensor of each display module detects the passage of a respective index feature having a fixed spatial relationship to the at least one light source of the display module as the at least one light source moves along its predetermined closing path, and the sensor generates a pulse in the synchronization signal in response to the passage of the index feature past the sensor.

3. 3. The display system of claim 2, wherein each display module further comprises sub-index features spaced apart from each other and from their respective index features such that as the at least one light source moves along the predetermined closed path, the index feature and each of the one or more sub-index features pass the sensor in sequence, and the sensor generates a pulse in the synchronization signal in response to the or each sub-index feature passing the sensor.

4. A display system according to any one of claims 1 to 3, wherein each display module further comprises a second sensor for generating an image synchronization signal indicating that the at least one light source has passed an image starting point on the predetermined closed path.

5. 5. A display system according to claim 1, wherein the image controller of each display module is further adapted to modulate the intensity of light emitted by the at least one light source according to a respective luminance mask to adjust the intensity of light emitted by the at least one light source based on a predetermined profile.

6. A display system according to any one of claims 1 to 5, wherein for each of the plurality of display modules, the predetermined value of the phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version is dynamically adjustable.

7. 7. A display system as claimed in any one of claims 1 to 6, wherein each of the plurality of display modules is arranged in a respective one of a first and a second group, each module of the first group being adjacent in its row and column only to modules of the second group, and each module of the second group being adjacent in its row and column only to modules of the first group.

8. 8. A display system according to claim 1, wherein the phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version of each display module is a multiple of 45° and is different from the phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version of each adjacent display module in that row and column.

9. A display system according to any one of the preceding claims, further comprising an external control unit for generating said reference signal.

10. 10. The display system of claim 9, wherein each display module is assigned to a respective row and column in the grid, and the external control unit comprises a memory in which the assigned rows and columns of each display module are stored.

11. A display system as described in claim 9 or 10, wherein the external control unit is coupled to each of the display modules by a communication link capable of transmitting image data to each display module, the image data representing a portion of an overall image displayed by all the display modules together.

12. 12. The display system of claim 11, wherein the external control unit comprises an image processor for each display module that offsets the portion of the overall image represented by the image data by a calibration amount to account for misalignment of the display module.

13. 13. A display system according to claim 1, wherein the predetermined values ​​of the phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version for each of the plurality of display modules are selected such that a difference between the predetermined values ​​of each adjacent pair has a desired value or is between an upper threshold and a lower threshold, thereby setting an initial phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version for each of the plurality of display modules.

14. 14. The display system of claim 13, wherein the initial phase shift of each display module is adjusted by adding or subtracting an amount equal to the angle subtended by the sensor on the display module and a second sensor when drawn in a straight line to the center of the predetermined closed path, and the second sensor generates an image synchronization signal indicating the passage of the at least one light source past an image starting point on the predetermined closed path.

15. 15. A display system as claimed in claim 13 or 14, wherein the initial phase shift of a display module is adjusted by a calibration amount inputted by a user to account for misalignment between the display module and one or more adjacent display modules.

16. 1. A method for displaying a desired image using a plurality of display modules, each display module having at least one light source movable along a respective predetermined closed path, the method comprising: arranging the plurality of display modules into at least two groups, each of the at least two groups comprising one or more of the plurality of display modules, in each group the predetermined closure path of the or each display module being located in a plane associated with the group, the plane associated with each group being unique to the group; arranging the display modules such that each is located within an area around an intersection of a row and a column in a grid, each module being adjacent in its row and column only to modules of different ones of the at least two groups, the light sources of each adjacent pair of display modules moving along their predetermined closed paths in opposite orientations, and the predetermined closed paths of each adjacent pair overlap; In each of the plurality of display modules, the following steps are performed: moving said at least one light source along its respective predetermined closed path; modulating an intensity of light emitted by the at least one light source of each of the plurality of display modules as the at least one light source moves along its respective predetermined closed path to make a respective portion of the desired image visible with a persistence of vision, wherein the respective portion of the desired image is visible on each of the plurality of display modules that together form the desired image; generating a respective synchronization signal including a synchronization feature indicative of the at least one light source passing a reference point on the respective predetermined closed path; receiving a reference signal including a periodic timing feature having a period based on the desired rotational speed of the at least one light source along each of the predetermined closed paths; and controlling the speed at which the at least one light source moves along the respective predetermined closed path such that a phase shift between the synchronization feature, or a phase-shifted version thereof, and the timing feature, or a phase-shifted version thereof, is maintained at a predetermined value; The method, wherein the predetermined value of the phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version for each of the plurality of display modules is selected such that the at least one light source does not occupy a position that obscures the at least one light source of another display module of the plurality of display modules.

17. 17. The method of claim 16, further comprising: detecting, with a respective sensor, in each display module the passage of an index feature having a fixed spatial relationship to the at least one light source as the at least one light source moves along its predetermined closed path, the sensor generating a pulse in the synchronization signal in response to the passage of the index feature past the sensor.

18. 18. The method of claim 17, wherein in each display module, the sensor generates a pulse in the synchronization signal in response to passage of the sub-index features spaced apart from each other and from the index feature such that the index feature and one or more sub-index features each pass the sensor in sequence as the at least one light source moves along the predetermined closed path.

19. 19. The method of any one of claims 16 to 18, further comprising generating, at each display module, an image synchronization signal indicating when the at least one light source has passed an image starting point on the predetermined closed path.

20. 20. The method according to any one of claims 16 to 19, further comprising, in each display module, modulating the intensity of light emitted by the at least one light source according to a luminance mask to adjust the intensity of light emitted by the at least one light source according to a predetermined profile.

21. 21. The method of claim 16, further comprising dynamically adjusting, for each of the plurality of display modules, the predetermined value of the phase shift between the synchronization feature or a phase-shifted version thereof and the timing feature or a phase-shifted version thereof.

22. 22. The method of claim 16, further comprising arranging the plurality of display modules into first and second groups, wherein each module of the first group is adjacent in its row and column to only modules of the second group, and each module of the second group is adjacent in its row and column to only modules of the first group.

23. 23. A method according to any one of claims 16 to 22, wherein the phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version of each display module is a multiple of 45° and is different from the phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version of each adjacent display module in that row and column.

24. The method of any one of claims 16 to 23, further comprising generating the reference signal using an external control unit.

25. 25. The method of claim 24, further comprising: assigning each display module to a respective row and column in the grid; and storing the assigned row and column of each display module in the external control unit.

26. 26. The method of claim 24 or 25, further comprising transmitting image data to each display module, said image data representing a portion of an overall image to be displayed by all of said display modules together.

27. 27. The method of claim 26, wherein for each display module, the portion of the overall image represented by the image data is offset by a calibration amount to account for misalignment of the display module.

28. 28. The method of claim 16, wherein the predetermined values ​​of the phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version for each of the plurality of display modules are selected such that a difference between the predetermined values ​​of each adjacent pair has a desired value or is between an upper threshold and a lower threshold, thereby setting an initial phase shift between the synchronization feature or its phase-shifted version and the timing feature or its phase-shifted version for each of the plurality of display modules.

29. 29. The method of claim 28, wherein the initial phase shift of each display module is adjusted by adding or subtracting an amount equal to the angle subtended by a first sensor and a second sensor on the display module when drawn in a straight line to the center of the predetermined closure path, the first sensor detects the passage of an index feature having a fixed spatial relationship to the at least one light source as it moves along the predetermined closure path, and the second sensor generates an image synchronization signal indicative of the passage of the at least one light source past an image starting point on the predetermined closure path.

30. 30. The method of claim 28 or 29, wherein the initial phase shift of a display module is adjusted by a calibration amount inputted by a user to account for misalignment between the display module and one or more adjacent display modules.

Images