Calibration system, method for calibrating light intensity indication, and system for determining line-of-sight direction

Abstract

To provide a calibration system for calibrating a light intensity indication (IM).SOLUTION: A calibration system 100 includes: a first light emitter (102) for emitting light; a first light receiver (112) for receiving the emitted light and generating an output signal; and a controller (116). The controller is configured to: provide a first control signal (118) to the first light emitter to cause it to emit a first light pulse (106) during a first time period (t0 to t1); measure a first output signal; provide a second control signal to the first light emitter to cause it to emit a second light pulse during a second time period (t2 to t3); measure a second output signal; calculate a second difference (I1 - I2) between the first output signal and the second output signal; and calibrate a light intensity indication using the calculated second difference.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates generally to eye tracking, and more particularly to a calibration system for calibrating light intensity indications. The present disclosure also relates to a method for calibrating light intensity indications. The present disclosure also relates to a system for determining gaze direction.

[0002] Eye tracking is a key function performed as part of many modern applications, such as the display of virtual objects in Virtual Reality, Augmented Reality and Mixed Reality applications, interactive games, etc. Eye tracking is important because it can detect which direction a user is looking by determining the gaze direction of the wearer of such a device. Gaze information can be used to control devices such as head mounted displays (HMDs) and can also be used to track the gaze, for example to control the focus of active glasses.

[0003] Among the many technologies that have been developed for gaze tracking, light-emitting diodes (LEDs) have been widely used due to their energy efficiency, lifetime, and accuracy. However, gaze tracking with LEDs is problematic for various reasons. For example, the temperature of the LEDs and / or photodiodes (PDs) employed in the HMD increases with prolonged use of the HMD. The increase in temperature of the LEDs and / or PDs leads to several undesirable effects, such as a decrease in light output, a shift in the wavelength of the emitted light, and latency issues. As a result, the effectiveness of gaze tracking decreases.

[0004] From the above discussion, it can be readily appreciated that a need exists for calibrating light intensity readings to compensate for variations due to temperature and to enable accurate eye tracking.

[0005] It is an object of the present disclosure to provide a calibration system for calibrating light intensity indications and a method for calibrating light intensity indications, as defined in the referenced attached independent claims. These calibration systems and methods allow for accurate calibration of light intensity indications associated with light emitters (such as light emitting elements used in eye tracking systems). Such accurate calibration of light intensity indications allows for accurate determination of the gaze direction of a user, e.g. a wearer of autofocus glasses. As a result, accurate eye tracking allows for fast focusing of the glasses, for example. Advantageous features are set out in the attached dependent claims.

[0006] Another object of the present disclosure is to provide a system for determining gaze direction, which allows for accurate determination of a user's gaze direction, which can be used to control a device or gather information related to the user, such as where the user is looking.

[0007] Throughout the description and claims of this specification, the words "comprise", "have", and "include" do not limit the presence of only those elements, but do not exclude the presence of other elements, values, or steps. Furthermore, even if the number of elements is not explicitly stated as being plural, the number of the elements may be plural, unless otherwise limited.

[0008] The foregoing summary, as well as the following detailed description of exemplary embodiments, will be better understood when read in conjunction with the accompanying drawings. For the purpose of illustrating the disclosure, example configurations of the disclosure are shown in the drawings. However, the disclosure is not limited to the specific methods and apparatus disclosed therein. Also, the drawings are not drawn to scale. Similar elements are designated by the same numerals wherever possible. [Brief description of the drawings]

[0009] Embodiments of the present disclosure will now be described, by way of example only, with reference to the following drawings, in which: [Figure 1]1 is an illustration of a calibration system according to an embodiment of the present disclosure. [Diagram 2] 4 is a timing graph illustrating timing relationships for emitting pulsed light from a light source according to an embodiment of the present disclosure. [Diagram 3] 1 illustrates a system for determining gaze direction according to an embodiment of the present disclosure. [Figure 4] FIG. 2 is a right side view of eyewear including a calibration system worn by a wearer according to an embodiment of the present disclosure. [Diagram 5] 1 is a graph showing a standard curve illustrating the relationship between the temperature of a light emitter and the intensity difference between two light emission pulses, according to an embodiment of the present disclosure. [Figure 6] 1 is a flow chart illustrating steps of a method for calibrating a light intensity reading according to an embodiment of the present disclosure. In the accompanying drawings, underlined numbers are used to represent the item at which the number is located or adjacent to the number. Numbers without underlines are associated with the item identified by the line extending from the number. When a number is not underlined and is written with an arrow, the number is used to identify the general item to which the arrow points. Detailed Description of the Embodiments

[0010] The following detailed description illustrates embodiments of the present disclosure and how they may be practiced. Although several forms for carrying out the present disclosure have been disclosed, those skilled in the art will recognize that other forms for carrying out the present disclosure are possible.

[0011] According to a first aspect, the present disclosure provides a calibration system for calibrating a light intensity reading, the calibration system comprising: a first light emitter configured to emit light; a first optical receiver configured to receive at least a portion of the emitted light and generate an output signal that is a function of the intensity of the received light; With the controller; wherein the controller: providing a first control signal to the first light emitter to cause it to emit a first light pulse during a first time period (t0-t1); measuring a first output signal generated by the first optical receiver during the first time period (t0-t1); providing a second control signal to the first light emitter, the second control signal differing from the first control signal by a first difference (P1-P2), to cause the first light emitter to emit a second light pulse during a second time period (t2-t3) after the first time period; measuring a second output signal generated by the first optical receiver during the second time period (t2-t3); calculating a second difference (I1-I2) between the first output signal and the second output signal; calibrating a light intensity reading (IM) using said calculated second difference (I1-I2); It is configured as follows.

[0012] The term "calibration system" as used throughout this disclosure refers to a system of interconnected electrical and / or electronic components to enable calibration of a light intensity reading. The term "light intensity reading" as used throughout this disclosure refers to a numerical value related to the amount of light received following transmission of light.

[0013] The calibration system comprises a first light emitter configured to emit light. The term "light emitter" as used throughout this disclosure relates to an electrical or electronic component capable of receiving an electric current as an input and generating light as an output, where the generated light corresponds to the magnitude of the electric current supplied to the light emitter. For example, the "light emitter" is an infrared light emitting diode (IR LED) capable of emitting infrared light. The term "infrared light" as used throughout this disclosure relates to radiation having a wavelength between 780 nm and 1 mm.

[0014] The calibration system further comprises a first receiver configured to receive at least a portion of the emitted light and generate an output signal. The term "receiver" as used throughout this disclosure refers to an electrical or electronic element capable of receiving light emitted by one or more light emitters. The "receiver" also allows for the determination of the amount of light received. The received light may be directly emitted by one or more light emitters, or may be emitted by the light emitters and then reflected from a reflective surface (such as the human eye, human skin, etc.). For example, the "receiver" is an infrared photodiode (infrared PD) capable of detecting infrared light emitted from an infrared LED. The first receiver receives at least a portion of the light emitted by the first light emitter. The term "at least a portion of the emitted light" refers to a portion of the light originally emitted by the first light emitter and then reflected from a surface (such as the user's eye) that is captured or received by the first receiver. It will be appreciated that the light emitted from the light emitter will be reflected by the user's eye and the skin around the eye. As a result, the amount of light received by the receiver will depend on various factors, such as the position of the receiver relative to the light emitter, the distance of the receiver from the user's eye and / or skin, the skin color of the user, the color of the user's eye, the presence of reflective or blocking surfaces in the path of travel of the emitted light, the presence of reflective or blocking surfaces in the path of travel of the reflected light. For example, light emitted by a light emitter located below the user's eye may not substantially reach a receiver located above the user's eye due to the presence of eyelids and / or eyelashes. However, such light may be received by another receiver located adjacent to the light emitter. The first receiver generates an output signal. It will be appreciated that when the reflected light hits the first receiver, an electrical signal in the form of a voltage, current or digital value is generated depending on the type of the first receiver and its configuration. For example, if the first receiver is an infrared PD, the generated output signal is a photodiode current corresponding to the light received by the receiver. The generated output signal is a function of the intensity of the received light. It will be appreciated that when the intensity of the received light is high, the generated output signal will be larger than when the intensity of the received light is low.The term "light intensity" as used throughout this disclosure relates to the amount of energy carried by light. For example, it relates to the amount of energy that emitted light retains after reflection. Light intensity varies with various factors, such as the inherent power associated with the light emitter, the wavelength of the emitted light, interferences or obstacles in the path of travel of the light, the distance traveled by the light, and the medium through which the light travels. The output signal generated is a "function of intensity" and the value of the output signal generated depends on the intensity of the received light. As a result, a change in the intensity of the reflected light corresponds to a change in the output signal generated. For example, if the first receiver is an infrared PD that generates an output signal (such as a photodiode current) when reflected light strikes the surface of a photodiode, then when a greater amount of light or light having a relatively high intensity strikes the first receiver, an output signal having a relatively high value is generated. Similarly, when a smaller amount of light or light having a relatively low intensity strikes the first receiver, an output signal having a relatively low value is generated. In this way, the output signal generated (such as a photodiode current) is a direct function of "light intensity".

[0015] The calibration system includes a controller. The term "controller" as used throughout this disclosure refers to an electrical or electronic element capable of receiving one or more inputs, processing the received inputs to generate one or more outputs, and then using or transmitting the generated output or outputs to control the function of other components of the calibration system. The calibration system also includes a battery connected to the controller, which provides current to the controller (and in some embodiments the first light emitter and the first light receiver) to enable the controller to operate. The controller is connected to the first light emitter and the first light receiver using a wired or wireless connection. The controller is coupled to a current measurement circuit that measures the current of the photodiode that receives the light. The current measurement circuit converts the measured photodiode current to a corresponding digital value for calculation.

[0016] The controller is configured to provide a first control signal to the first light emitter to emit a first light pulse during a first period of time. The term "light pulse" as used throughout this disclosure refers to each event of emission of light by a light emitter (such as the first light emitter). The emitted light is associated with a particular intensity of light. The controller provides the first control signal to the first light emitter, for example, to provide a first amount of current to the first light emitter to enable the first light emitter to emit a first light pulse having a first intensity. The calibration system includes an adjustable current driver connected to the controller and the first light emitter (and in some embodiments the second, third, fourth, fifth and sixth light emitters). The term "adjustable current driver" refers to a device or circuit that adjusts and controls the amount of current provided from a power source to a load. The controller controls the adjustable current driver to provide a first amount of current to the first light emitter to enable the emission of the first light pulse. The adjustable current driver varies the electrical energy provided to the first light emitter based on instructions from the controller to modulate the intensity of the emitted light. For example, the first light pulse is coupled to providing a current of 10 milliamps (mA) to the first light emitter, and the first light pulse is emitted for a first period of time, such as, for example, 2 microseconds. The controller is further configured to measure a first output signal generated by the first light receiver during the first period of time. The controller activates the first light receiver simultaneously with the emission of the first light pulse by the first light emitter such that the first light pulse reflected by the user's eye and / or skin is received by the first light receiver. In the above example, the controller activates the first light receiver for 2-5 microseconds to measure the first output signal associated with the first light pulse. The controller receives the photodiode current as the first output signal. The photodiode current is associated with the first light pulse. It will be appreciated that in low power applications such as eye tracking, the received output signal is generally of low intensity. For example, if the first light pulse is associated with providing a current of 10 milliamps to the first light emitter, the first output signal may be as low as 0.5 microamps.The photodiode current of the first output signal is measured using a current measurement circuit. The measured photodiode current is then converted to a corresponding digital value and the digital value is stored. In some embodiments, the calibration system includes a memory coupled to the controller. The controller stores the digital value associated with the first output signal in the memory.

[0017] The controller is further configured to provide a second control signal to the first light emitter to cause it to emit a second light pulse during a second period of time. The second control signal differs from the first control signal by a first difference, and the second period of time is after the first period of time. Similar to the controller providing the first control signal to the first light emitter, the controller provides a second control signal to the first light emitter to provide a second amount of current to the first light emitter to enable the first light emitter to emit a second light pulse having a second intensity, for example. The second control signal differs from the first control signal by a first difference, and the second control signal is stronger than the first control signal by a certain amount. For example, if the first difference is 20 milliamps and the first light pulse is associated with providing a 10 milliamp current to the first light emitter, the second light pulse is associated with providing a 30 milliamp current to the first light emitter. In some embodiments, the second control signal is weaker than the first control signal. For example, if the first difference is 10 milliamps and the first light pulse is associated with providing a current of 40 milliamps to the first light emitter, the second light pulse is associated with providing a current of 30 milliamps to the first light emitter. The second period is after the first period, and the second control signal is provided either instantaneously after providing the first control signal to the first light emitter or after a specific period has elapsed after providing the first control signal to the first light emitter. For example, the second control signal is provided during the second period (e.g., 2 microseconds) 5 microseconds to 20 microseconds after providing the first control signal to the first light emitter. Furthermore, the interruption associated with the specific period between the first and second light pulses ensures that the second light pulse does not interfere with the reflected light of the first light pulse, thereby improving the accuracy associated with the calibration of the first light emitter. However, providing the second control signal instantaneously after providing the first control signal makes it possible to avoid changes in ambient factors between providing the two control signals.

[0018] The controller is further configured to measure a second output signal generated by the first receiver during the second time period. The controller activates the first receiver simultaneously with the emission of the second light pulse by the first light emitter such that the second light pulse reflected by the user's eye and / or skin is received by the first receiver. In the above example, the controller activates the first receiver for 2 microseconds to measure a second output signal associated with the second light pulse. The controller receives the photodiode current as the second output signal. The photodiode current is associated with the second light pulse. The current measurement circuit measures the second output signal, the photodiode current, converts the measured photodiode current to a corresponding digital value, and stores the digital value in the memory. In the above example, the second light pulse is coupled to providing a current of 30 milliamps to the first light emitter, and the second output signal is 0.9 microamps.

[0019] It will be understood that the values ​​of the first and second current magnitudes corresponding to the first and second control signals, respectively, are merely exemplary and other values ​​and / or sets of values ​​could occur without departing from the scope of the present disclosure. In one example, the first control signal is coupled to provide 20 milliamps of current and the second control signal is coupled to provide 30 milliamps. In another example, the first control signal is coupled to provide 10 milliamps of current and the second control signal is coupled to provide 20 milliamps of current. In yet another example, the first control signal is coupled to provide 40 milliamps of current and the second control signal is coupled to provide 10 milliamps of current.

[0020] The controller is configured to calculate a second difference between the first output signal and the second output signal. The term "second difference" as used throughout this disclosure relates to the difference in intensity associated with the first and second light pulses received by the first receiver during the first and second time periods, respectively. The controller receives or accesses, for example, from a memory, stored digital values ​​of the first and second output signals and calculates the second difference between the first and second output signals.

[0021] The controller is further configured to calibrate the light intensity reading using the calculated second difference. The light emitted by the first light emitter, i.e. the light intensity reading, may deviate from the requested light intensity reading associated with the first light emitter. Such "deviation" may be caused, for example, by changes in the operating temperature of the first light emitter. The controller calibrates the light intensity reading associated with the first light emitter. Such calibration of the light intensity reading associated with the first light emitter allows the wearer's gaze direction to be accurately detected after the calibration is performed. Calibration of the light intensity reading allows the effect of temperature changes of the first light emitter to be eliminated. Furthermore, continuous or periodic calibration of the light intensity reading associated with the first light emitter improves the consistency, accuracy, and reliability of the application of the first light emitter in various fields such as gaze detection. Overall, the first aspect provides a fast and reliable method for finding the relative (difference) value between the reception of the emitted light from the first light emitter to the first receiver. Experiments have shown that this difference corresponds to the error in the reading due to temperature. Knowing this difference allows the measured intensity reading to be calibrated to the correct value, which is necessary for applications such as gaze direction detection.

[0022] The first and second periods may range from 5 nanoseconds to 500 microseconds. For example, the first and second periods may be from 5, 10, 15, 25, 50, 100, 200, 250, 350, 500, 700, 850, 900, 990 nanoseconds to 1, 7, 9, 25, 57, 68, 99, 125, 145, 197, 278, 289, 326, 339, 362, 421, 450, 470, 489, 499, or 500 microseconds. The time difference between the first and second light pulses may be from 20 nanoseconds to 100 microseconds. For example, the time difference can be from 21, 30, 45, 55, 50, 120, 211, 262, 315, 502, 721, 868, 910, 999 nanoseconds to 2, 8, 11, 24, 37, 44, 58, 69, 76, 82, 99 or 100 microseconds.

[0023] In some embodiments, the calculated second difference indicates the temperature of the first light emitter. During use of the calibration system, the temperature of various components of the calibration system may increase due to heat conduction from the user's skin, heat convection from the environment surrounding the calibration system, ambient light, etc. For example, the first light emitter may be located closer to the wearer's skin, while the second light emitter may be located relatively farther from the wearer's skin. In such an example, the temperature of the first light emitter will be closer to the wearer's skin temperature, while the temperature of the second light emitter will be closer to the environmental temperature surrounding the calibration system. As a result, the difference in temperature between the first and second light emitters will cause the light intensity reading associated with the first light emitter to differ from the light intensity reading associated with the second light emitter. In particular, infrared LEDs may have a strong temperature dependency on the light intensity reading. For example, an infrared LED emitting infrared light at a wavelength of 940 nm will have a light intensity reading that changes by more than 1% for every 1° C. change in temperature. Furthermore, the light intensity reading also varies depending on the temperature of the receiver that receives the emitted light. However, infrared PDs are less susceptible to temperature changes compared to infrared LEDs. The calibration system may have multiple light emitters physically located at different spatial locations. For example, the calibration system may have a first, second, third, fourth, fifth, and sixth light emitters located at different locations. Each light emitter may experience a different magnitude of temperature change based on, for example, the temperature of the wearer's skin and the ambient temperature. In such cases, the difficulty associated with determining the temperature of each light emitter increases. The calculated second difference, i.e., the difference between the second output signal and the first output signal, is indicative of the temperature of the first light emitter. For example, the second difference is indicative of the amount of temperature change experienced by the first light emitter since the calibration system began operating. It should be noted that, at the beginning of the calibration system, the initial temperature of the first light emitter may be considered to be approximately equal to the ambient temperature. The temperature of the first light emitter as indicated by the second difference may cause the controller to adjust the amount of current provided to the first light emitter. The controller may thereby adjust the amount of current supplied based on temperature to maintain a constant light intensity reading associated with the first light emitter.Determining the temperature of the first light emitter based on the calculation of the second difference provides various advantages over, for example, employing a temperature sensor to determine the temperature. Determining the temperature using the second difference eliminates the need for a dedicated temperature sensor, thereby reducing the cost and size associated with the calibration system. It is noted that temperature sensors may experience delays due to thermal inertia during operation. This may make them unsuitable for time-dependent applications such as eye tracking. Also, the temperature changes experienced by the first light emitter may be within a narrow range, for example due to ambient temperatures associated with cold climates. Determining the temperature within such a narrow range may require the employment of advanced pulse control and detection techniques to achieve high accuracy associated with the temperature determination. However, such techniques may be susceptible to degradation due to external factors such as humidity, pressure, and / or the presence of corrosive elements. However, the determination of the temperature of the first light emitter through the emission of light pulses and the determination of the second difference is non-mechanical and therefore resistant to such degradation due to external factors. This allows for convenient, low-cost, and accurate determination of the temperature of the first light emitter in a wide variety of applications and external factors.

[0024] The temperature of the first light emitter can be determined, for example, by using a look-up table. In this case, the look-up table pre-stores a relationship between the second difference and the temperature of the first light emitter (and in some embodiments, the first light receiver) for various sets of the first and second control signals. Such a look-up table can be obtained, for example, on a factory line by determining the second difference and the temperature for various sets of the first and second control signals. The obtained look-up table can be stored in a memory. The controller can then access the temperature of the first light emitter using the look-up table and automatically calibrate the light intensity reading of the first light emitter, thereby enabling accurate tracking of the user's gaze direction. In some embodiments, the relationship between the second difference and the temperature of the first light emitter is obtained as a function based on various sets of the twelfth control signal and the second control signal. For example, if the first control signal is 10 milliamps, the second control signal is 40 milliamps, and the second difference is 0.5 microamps, the temperature of the first light emitter is determined to be 30° C. based on the data in the look-up table. In another example, if the first control signal is 10 milliamps, the second control signal is 50 milliamps, and the second difference is 0.7 microamps, the temperature of the first light emitter is determined to be 10° C. Such determination of the temperature of the first light emitter using the second difference allows the light intensity indication of the first light emitter to be calibrated without requiring additional components, such as a temperature sensor, which is bulky, has high power consumption, and increases the manufacturing and operational complexity associated with the eye tracking system. As a result, the eye tracking system improves the convenience associated with determining the temperature of the first light emitter, thereby enabling an accurate calibration of the light intensity indication associated with the first light emitter to be ensured.

[0025] In some embodiments, the temperature of the first light emitter is used to determine a bias signal to be applied to the measurement control signal of the first light emitter to emit a measurement light pulse. The term "bias signal" as used throughout this disclosure relates to a correction to a control signal provided by the controller to enable emission of a calibrated light pulse by the first light emitter. The term "measurement control signal" as used throughout this disclosure relates to a control signal provided by the controller to the first light emitter during operation of the first light emitter to emit a light pulse (e.g., to determine the gaze direction of the wearer). The controller uses the temperature of the first light emitter to determine a bias signal to apply to the measurement control signal to obtain an accurate light intensity indication associated with the first light emitter. The bias signal can be applied by the controller, for example, by changing the amount of current supplied by the controller to the first light emitter or by changing a voltage associated with the current supplied to cause emission of a calibrated light pulse by the first light emitter. Application of such a bias signal to the measurement control signal allows for quickly and conveniently overcoming temperature changes experienced by the first light emitter, thereby ensuring accurate determination of the gaze direction of the wearer.

[0026] The aforementioned temperature-based calibration of the light intensity readings of the first light emitter plays an important role in ensuring accuracy and consistency under various environmental and situational factors. Such calibration not only counteracts the inherent temperature effects of the first light emitter, but also accounts for external influences. For example, the user's skin temperature can cause inconsistencies in the measurements, especially in proximity applications such as Head-Mounted Displays (HMDs) and autofocus lenses / goggles / glasses. Similarly, changes in ambient temperature, whether due to direct sunlight, the stark contrast between a hot summer day and a cold winter day, or proximity to a heat source such as a radiator, can all substantially alter the performance of the first light emitter. The calibration system disclosed above neutralizes such temperature-induced variations associated with the first light emitter, enabling accurate and reliable use of the first light emitter for various applications such as eye tracking. In some embodiments, the calibration system can have a second, third, fourth, fifth, and sixth light emitter in addition to the first light emitter. The controller applies different bias signals simultaneously or sequentially to the measurement control signals supplied to each of the first, second, third, fourth, fifth and sixth light emitters. For example, the controller supplies 10 milliamps to the first light emitter, 12 milliamps to the second light emitter and 9 milliamps to the third light emitter based on the respective temperatures of the first, second and third light emitters. As a result, the measured values ​​of the light intensities associated with the first, second and third light emitters are calibrated to be equal, so that the wearer's line of sight can be accurately determined.

[0027] In some embodiments, the temperature of the first light emitter is used to correct the measurement output signal generated by the first receiver. The term "measurement output signal" as used throughout this disclosure refers to an output signal received by the first receiver due to the emission of a calibrated light pulse by the first light emitter. The emission of a calibrated light pulse by the first light emitter may be performed, for example, to determine the gaze direction of the wearer. The term "correcting the measurement output signal" refers to an adjustment or correction of the measurement output to counteract or eliminate errors introduced into the calibration system due to factors such as temperature changes. The controller can utilize the temperature of the first light emitter to adjust the output signal received by the first receiver. For example, if it is determined that a temperature of 10 degrees Celsius generates a measurement output signal that is 0.2 microamps higher for the first light emitter, the controller receives the measurement output signal generated by the first receiver and subsequently corrects the received measurement output signal by subtracting 0.2 microamps from the measurement output signal to generate a calibrated measurement output signal. In such an example, if the received measurement output signal is 0.7 microamps, the controller corrects the measurement output signal to generate a calibrated measurement output signal of 0.5 microamps. In some embodiments, the controller adaptively corrects the measurement output signal generated by the first receiver based on a temperature change of the first receiver. For example, if it is determined that a temperature of 10 degrees Celsius generates a measurement output signal that is 0.2 microamps higher for the first receiver, the controller corrects the measurement output signal by subtracting 0.2 microamps from the measurement output signal to generate a calibrated measurement output signal. After further use of the calibration system, if it is determined that a temperature of 20 degrees Celsius generates a measurement output signal that is 0.3 microamps higher for the first light emitter, the controller adaptively corrects the measurement output signal by subtracting 0.3 microamps from the measurement output signal to generate a calibrated measurement output signal.

[0028] In some embodiments, the calculated second difference indicates a correction value used to correct the measurement output signal generated by the first receiver. The term "correction value" as used throughout this disclosure refers to a quantity or coefficient that can be added, multiplied, divided, or subtracted from the measurement output signal to adjust for discrepancies, inaccuracies, or systematic errors observed in the initial light intensity readings. As previously described, the second difference is related to the difference between the intensity of the first light pulse and the intensity of the second light pulse. As a result, the second difference indicates the difference between the intensity of the generated light pulse and the intensity of the light pulse that was intended to be generated. For example, the controller supplies the same amount of current to the multiple light emitters as a control signal to emit light pulses from each of these light emitters. For example, a current of 10 milliamps is supplied to each of the first light emitter, the second light emitter, and the third light emitter. And for example, the second difference may indicate an increase of 0.2 microamps between the first and second output signals for the first light emitter, a decrease of 0.3 microamps between the first and second output signals for the second light emitter, and an increase of 0.4 microamps between the first and second output signals for the third light emitter. In such an example, the controller calibrates the first, second, and third light emitters by correcting the measured output signal associated with the first light emitter by subtracting 0.2 microamps, correcting the measured output signal associated with the second light emitter by adding 0.3 microamps, and correcting the measured output signal associated with the third light emitter by subtracting 0.4 microamps. Such corrections may be made by varying the magnitude of the current provided by the controller to each of the first, second, and third light emitters.

[0029] In some embodiments, the light intensity reading indicates the amount of light emitted from the first light emitter and received by the first light receiver, either directly or through reflection, during a measurement cycle, and the calibrated light intensity reading indicates an adjusted light intensity reading that adjusts said light intensity reading to account for differences caused by temperature. The term "measurement cycle" as used throughout this disclosure refers to the process of propagation of a light pulse from the light emitter towards the wearer's eye, propagation of the emitted light pulse or a reflection of the emitted light pulse towards the receiver, reception of the reflected light by the receiver, and then processing of the reflected light by the controller to calibrate the light intensity reading associated with the light emitter. Such a measurement cycle also encompasses the period between the emission of a light pulse and the calibration of the light intensity reading of the light emitter by the controller. The term "calibrated light intensity reading" as used throughout this disclosure refers to the adjusted light intensity reading associated with the light emitter. Such adjustments may be performed by the controller, for example, by processing temperature induced differences in the light intensity readings and applying a bias signal to the measurement control signal; correcting the measurement output signal; or a combination thereof, thereby enabling the emission of accurate light pulses for determining the wearer's gaze direction.

[0030] According to a second aspect, the present disclosure provides a method of calibrating a light intensity reading. The method includes emitting a first light pulse during a first time period and emitting a second light pulse during a second time period. The controller enables a current supply to the first light emitter during the first time period and the second time period to cause emission of the first light pulse and the second light pulse, respectively. The method further includes measuring a light intensity associated with each of the first light pulse and the second light pulse. A first light receiver is used to measure a light intensity associated with each of the first light pulse and the second light pulse. The first light receiver generates a signal based on the light intensity of each light pulse. The method further includes determining a difference between the measured light intensities. As previously mentioned, the determined difference corresponds to a second difference between the first output signal and the second output signal. The controller analyzes the generated signal for each pulse and determines the second difference. The method further includes emitting a measurement light pulse during a third time period. The term "measurement light pulse" as used throughout this disclosure refers to a light pulse emitted by a light emitter after calibration of a light intensity reading associated with the light emitter. The method further includes measuring a light intensity reading associated with the measurement light pulse. Such measurement light intensity reading associated with the measurement light pulse corresponds to the calibrated light intensity reading. The method further includes calibrating the measurement light intensity reading using the determined difference.

[0031] In some embodiments, the calibrated light intensity reading is used to calibrate the light intensity reading for an eye tracking system. The term "eye tracking system" refers to a system of interconnected electrical and / or electronic components for detecting the gaze direction of a user. Such a system is used, for example, to detect where a wearer of an HMD having an eye tracking system is looking at at a given time. Such an eye tracking system comprises one or more light emitters, one or more light receivers, and a controller connected to each light emitter and each light receiver. The controller is configured to control the operation of each light emitter and each light receiver to determine the gaze direction of the wearer. In an eye tracking device, there is typically a set of light emitters and a set of light receivers spatially arranged around the eye tracking device. In such a device, it is highly likely that some of the components are at different temperatures from each other. If the eye tracker is constructed with uncalibrated parts, large errors in tracking can occur. Therefore, a calibrated light intensity reading is important.

[0032] According to a third aspect, the present disclosure provides a system for determining gaze direction. The term "system for determining gaze direction" refers to a system with interconnected electrical and / or electronic components for detecting a user's gaze direction. Such a system is used, for example, to detect where a wearer of autofocus glasses with an eye tracking system is looking at a given time. Such an eye tracking system comprises one or more light emitters, one or more light receivers, and a controller connected to each light emitter and each light receiver. The controller is configured to control the operation of each light emitter and each light receiver to determine the wearer's gaze direction. The system comprises a set of light emitters configured to emit measurement light pulses towards the eye. The system also comprises a set of light receivers configured to receive at least a portion of the measurement light reflected from the eye and generate a light intensity indication. The system further comprises a calibration system for calibrating the light intensity indication. The system further comprises a controller configured to determine the gaze direction using the calibrated light intensity indication.

[0033] In one example, a system for determining a gaze direction comprises one or more light emitters and one or more light receivers. Such an eye tracking system allows for detecting a user's gaze direction, for example, detecting where the user is looking at any given time. The system may comprise multiple light emitters. For example, the system comprises a first light emitter set for detecting the gaze direction of the wearer's right eye and a second light emitter set for detecting the gaze direction of the wearer's left eye. Each of the first light emitter set and the second light emitter set comprises multiple light emitters. For example, the first light emitter set comprises a first light emitter arranged above the wearer's right eye, a second light emitter arranged below the right eye toward the lower left side, and a third light emitter arranged below the right eye toward the lower right side. Similarly, the second light emitter set comprises a fourth light emitter arranged above the wearer's left eye, a fifth light emitter arranged below the left eye toward the lower left side, and a sixth light emitter arranged below the left eye toward the lower right side. Furthermore, the first light emitter, the second light emitter and the third light emitter are arranged equidistantly from each other, for example, at 120° intervals from each other. Similarly, the fourth light emitter, the fifth light emitter and the sixth light emitter are arranged equidistantly from each other, for example, at 120° intervals from each other. The first light emitter (or the second light emitter or the third light emitter) emits light toward the right eye of the wearer according to a specific amount of current supplied to the first light emitter. For example, the specific amount of current is 10 milliamps. In some embodiments, the fourth light emitter simultaneously emits light toward the left eye of the wearer.

[0034] The system also includes a plurality of receivers. For example, the system includes a first receiver set corresponding to the first light emitter set to enable detection of the gaze direction of the wearer's right eye, and a second receiver set corresponding to the second light emitter set to enable detection of the gaze direction of the wearer's left eye. Each of the first and second sets of receivers includes a plurality of receivers. For example, the first receiver set includes a first receiver disposed adjacent to the first light emitter, a second receiver disposed adjacent to the second light emitter, and a third receiver disposed adjacent to the third light emitter. Similarly, the second receiver set includes a fourth receiver disposed adjacent to the fourth light emitter, a fifth receiver disposed adjacent to the fifth light emitter, and a sixth receiver disposed adjacent to the sixth light emitter.

[0035] The system further comprises a controller connected to each of the first, second, third, fourth, fifth and sixth light emitters and the light receiver. The controller calibrates the light intensity readings of each of the first, second, third, fourth, fifth and sixth light emitters, for example, in the manner described with respect to the first light emitter above. Calibrating the light intensity readings associated with each of the first, second, third, fourth, fifth and sixth light emitters allows for accurate detection of the wearer's gaze direction. Such accurate detection of the wearer's gaze direction allows for accurate detection of where the user is looking, thereby improving the user experience and functionality of the system. In some embodiments, the light intensity readings are calibrated by adjusting the control signal of each light emitter in the light emitter set with a respective bias signal. The control signal can be adjusted by controlling the operation of an adjustable current driver to respectively change the amount of current supplied to each light emitter in the light emitter set. The bias signal relates to a signal that increases or decreases the amount of current supplied to each of the light emitters in the light emitter set. The amount of current is increased or decreased based on, for example, the temperature of each light emitter included in the light emitter set.

[0036] The first and second output signals generated by the first receiver can be indicative of the interaction of light with a surface (such as a user's eye), and these signals can be related to the direct emission or reception of light, or any combination of reflection, absorption, or diffraction of light prior to reception.

[0037] In some embodiments, the first receiver can be disposed in the travel path of the emitted light. The system can include a first light emitter and a first receiver. The first receiver can be disposed linearly with respect to the first light emitter such that the light emitted by the first light emitter is directly received by the first receiver without substantial reflection, refraction, diffraction, etc. The controller causes the first light emitter to emit a first light pulse and a second light pulse such that the first receiver obtains a first output signal and a second output signal. The controller then calculates a second difference based on the obtained first output signal and second output signal, such that the temperature of the first light emitter is related to the second difference.

[0038] In some embodiments, the light intensity reading is adjusted by correcting the generated light intensity reading with a correction value.

[0039] In some embodiments, the light intensity reading is calibrated using the calibration system described above.

[0040] In some embodiments, the controller is configured to calibrate the light intensity reading, as described above.

[0041] In brief, a system (which may be, for example, autofocus glasses) having the described calibration mechanism can operate in a variety of ambient temperature environments to account for the possibility that parts of the system may be hotter than other parts.

[0042] [Detailed description of the drawings] 1, a calibration system 100 according to an embodiment of the present disclosure is shown. The calibration system 100 includes a first light emitter 102 (such as an infrared LED). The first light emitter 102 is connected to an adjustable current driver 104 that varies the amount of current provided to the first light emitter 102.

[0043] In a first phase, the first light emitter 102 emits a first light pulse 106 (for a first time period) towards a reflective surface 108 (e.g., an eye of a user of the calibration system 100). The emitted light pulse 106 reflects off the reflective surface 108, and the reflected light 110 is received by a first light receiver 112 (e.g., an infrared PD). The first light receiver 112 is connected to a current measurement circuit 114. The current measurement circuit 114 generates a first output signal (e.g., a photodiode current) related to the reflected light 110.

[0044] In a second phase, the first light emitter 102 emits a second light pulse (similar to the first light pulse 106) for a second period of time, except that the second light pulse is different from the first light pulse 106. The emitted second light pulse reflects off the reflective surface 108. The first light receiver 112 receives the reflected light from the reflective surface 108 in response to the second light pulse. The current measurement circuit 114 generates a second output signal. The controller 116 calculates a second difference between the generated first and second output signals and calibrates a light intensity reading (IM) of the first light emitter 102. The controller 116 provides a control signal 118 based on the calibrated light intensity reading to emit a calibrated light pulse from the first light emitter 102.

[0045] Referring to FIG. 2, a timing graph 200 is shown illustrating the timing relationship of the emission of pulsed light from a light source according to an embodiment of the present disclosure. Graph 202 relates to the intensity of the light pulse emitted by the light emitter, and graph 204 relates to the intensity of the reflected light received by the light receiver. The light emitter emits a first light pulse 206 with an intensity P1 during a first time period t0-t1, and in response, the light receiver receives a reflected light 208 with an intensity I1. The light emitter then emits a second light pulse 210 with an intensity P2 during a second time period t2-t3, and in response, the light receiver receives a reflected light 212 with an intensity I2. The controller calculates a first difference P1-P2 and a second difference I1-I2, where the second difference I1-I2 is related to the temperature of the light emitter. The second difference I1-I2 can be used as a correction coefficient to calibrate the light intensity reading (IM) of the light emitter. Because the difference between the two signals is taken into account to calculate a correction factor, the present disclosure can reduce or eliminate systematic errors or offsets in the measurement of emitted light. The controller adjusts operating parameters (e.g., adjusts the magnitude of the current supplied to the light emitter) to enable emission of a calibrated light pulse 214 having an intensity PM, and the light receiver provides a calibrated light intensity reading 216 related to the intensity IM. Such calibrated light pulse 214 and calibrated light intensity reading 216 are employed to determine the wearer's gaze direction.

[0046] 3, a system 300 for determining gaze direction is shown, according to an embodiment of the present disclosure. The system 300 includes a right frame 304 for receiving a right lens 306 for a wearer's right eye. The system 300 also includes a left frame 308 for receiving a left lens 310 for a wearer's left eye. The left and right frames 304, 308 are connected by a bridge 312 that rests on the wearer's nose during use. The right frame 304 has a right temple 314 that supports the wearer's right ear and a left temple 316 that supports the wearer's left ear.

[0047] The calibration system 302 comprises a first light emitter 318 that emits light towards the right eye of the wearer, and a first light receiver 320 configured to receive at least a portion of the light emitted by the first light emitter 318. The calibration system 302 also comprises a second light emitter 322 and a second light receiver 324, and a third light emitter 326 and a third light receiver 328. Each of these light emitters and receivers is configured to emit light or receive emitted light to enable determination of the gaze direction of the left eye.

[0048] The calibration system 302 similarly comprises a fourth light emitter 330, a fourth light receiver 332, a fifth light emitter 334, a fifth light receiver 336, a sixth light emitter 338 and a sixth light receiver 340. These light emitters and receivers are each configured to emit light or receive emitted light to enable determination of the gaze direction of the right eye. The eye tracking system may comprise a set of light emitters selected from a first light emitter 318, a second light emitter 322, a third light emitter 326, a fourth light emitter 330, a fifth light emitter 334 and a sixth light emitter 338. Similarly, the eye tracking system may include a set of receivers selected from a first light receiver 320, a second light receiver 324, a third light receiver 328, a fourth light receiver 332, a fifth light receiver 336, and a sixth light receiver 338. Those skilled in the art will appreciate that any number of light emitter and receiver sets may be arranged in the eye tracking system.

[0049] The calibration system 302 further comprises a controller 342 connected to each of the first light emitter 318, the first light receiver 320, the second light emitter 322, the second light receiver 324, the third light emitter 326, the third light receiver 328, the fourth light emitter 330, the fourth light receiver 332, the fifth light emitter 334, the fifth light receiver 336, the sixth light emitter 338 and the sixth light receiver 340, and controlling the operation of the aforementioned components. The calibration system 302 also includes a battery 344 connected to each of the first light emitter 318, the first light receiver 320, the second light emitter 322, the second light receiver 324, the third light emitter 326, the third light receiver 328, the fourth light emitter 330, the fourth light receiver 332, the fifth light emitter 334, the fifth light receiver 336, the sixth light emitter 338, the sixth light receiver 340, and the controller 342 to provide electrical current for operation of the aforementioned components. The controller 342 sequentially activates the first light emitter 318, the second light emitter 322, and the third light emitter 326 for a first period of time, causing each of these elements to emit a first light pulse. The first light receiver 320, the second light receiver 324, and the third light receiver 328 each receive at least a portion of the emitted first light pulse (e.g., reflected light) and generate a first output signal based on the received light. Then, after a certain time (e.g., 50 nanoseconds) has elapsed after the first period, the controller 342 sequentially activates the first light emitter 318, the second light emitter 322, and the third light emitter 326 for a second period to emit a second light pulse. The first light receiver 320, the second light receiver 324, and the third light receiver 328 each receive at least a portion of the emitted second light pulse (e.g., reflected light) and generate a second output signal based on the received light. The controller 342 analyzes the generated first and second output signals to determine a correction value for each of the first light emitter 318, the second light emitter 322, and the third light emitter 326. The determined correction values ​​are used to calibrate the light intensity readings of the first light emitter 318, the second light emitter 322 and the third light emitter 326. Furthermore, the controller 342 analyzes the output signals indicative of the reflected light pattern (e.g., photon distribution across the light receiving surface), intensity and angle to determine the user's gaze direction.

[0050] 4, a right side view of eyewear 400 including a calibration system 402 according to an embodiment of the present disclosure is shown worn on a wearer 404. The calibration system 402 comprises a first light emitter 406 disposed at a distance D1 from the skin of the wearer 404 and a second light emitter 408 disposed at a distance D2 from the skin of the wearer 404. As shown, D2 is less than D1. The first light emitter 406 emits a light pulse 410 toward the right eye 412 of the wearer 404, and the second light emitter 408 emits a light pulse 414 toward the right eye 412 of the wearer 404. The calibration system 402 further comprises a first light receiver 416 disposed longitudinally between the first light emitter 406 and the second light emitter 408. A first receiver 416 receives light 418 reflected from the right eye of the wearer 404 to enable determination of a gaze direction associated with the right eye 420 of the wearer 404 .

[0051] 5, a graph 500 is shown illustrating standard curves representing the relationship between the temperature of a light emitter and the difference in intensity of two emission pulses, according to an embodiment of the present disclosure. These standard curves are generated based on determining the difference in intensity of the first and second controlled emission pulses as a function of temperature in a controlled environment. The standard curves are employed to determine the temperature of the light emitter for various sets of light pulses emitted from the light emitter.

[0052] Referring to FIG. 6, a flow chart 600 is shown illustrating steps of a method for calibrating a light intensity reading according to an embodiment of the present disclosure. In step 602, a first light pulse is emitted during a first time period. In step 604, a second light pulse is emitted during a second time period. In step 606, a light intensity associated with each of the first and second light pulses is measured. In step 608, a difference between the measured light intensities is determined. In step 610, a measurement light pulse is emitted during a third time period. In step 612, a light intensity reading associated with the measurement light pulse is measured. In step 614, the determined difference is used to calibrate the measured light intensity reading.

[0053] The embodiments of the present disclosure described above can be modified without departing from the scope defined by the appended claims. The terms "including," "comprising," "incorporating," "having," "being," and the like used to describe and claim the present disclosure are intended to be interpreted in a non-exclusive manner, i.e., to allow for the presence of items, parts, or components not expressly described. The absence of a plurality of elements does not preclude the presence of a plurality of the elements.

Claims

1. 1. A calibration system for calibrating a light intensity reading, the calibration system comprising: A first light emitter configured to emit light; a first optical receiver configured to receive at least a portion of the emitted light and generate an output signal that is a function of the intensity of the received light; A controller; The controller comprises: providing a first control signal to the first light emitter to cause it to emit a first pulse of light for a first time period; measuring a first output signal generated by the first optical receiver during the first time period; providing a second control signal to the first light emitter, the second control signal differing from the first control signal by a first difference to cause the first light emitter to emit a second light pulse during a second time period after the first time period; measuring a second output signal generated by the first optical receiver during the second time period; calculating a second difference between the first output signal and the second output signal; calibrating the light intensity reading using said calculated second difference; It is configured as follows: Calibration system.

2. The calibration system of claim 1 , wherein the second difference is indicative of a temperature of the first light emitter.

3. The calibration system of claim 2 , wherein the temperature of the first light emitter is used to determine a bias signal applied to a measurement control signal of the first light emitter to emit a measurement light pulse.

4. 4. A calibration system according to claim 2 or 3, wherein the temperature of the first light emitter is used to correct a measurement output signal generated by the first light receiver.

5. The calibration system of claim 4 , wherein the second difference indicates a correction value used to correct the measured output signal.

6. 6. A calibration system as described in any one of claims 1 to 5, wherein the light intensity reading indicates the amount of light emitted from the first light emitter during a measurement cycle and received by the first light receiver either directly or via reflection, and the post-calibration light intensity reading indicates an adjusted light intensity reading in which the light intensity reading is adjusted to account for differences caused by temperature.

7. 1. A method of calibrating a light intensity reading, comprising: emitting a first pulse of light for a first period of time; emitting a second pulse of light during a second time period; measuring a light intensity associated with the first light pulse and a light intensity associated with the second light pulse; determining a difference between the measured light intensities; emitting a measurement light pulse during a third time period; measuring a light intensity associated with said measurement light pulse; calibrating the measured light intensity reading using the determined difference; A method comprising:

8. The method of claim 7 , wherein the calibrated light intensity readings are used to calibrate light intensity readings for an eye-tracking system.

9. 1. A system for determining gaze direction, comprising: a set of light emitters configured to emit measurement light pulses toward the eye; a set of receivers configured to receive at least a portion of the emitted measurement light reflected from the eye and generate an indication of light intensity; a calibration mechanism for calibrating the light intensity reading; A controller configured to determine a line of sight direction using the calibrated light intensity readings; A system comprising:

10. 10. The system of claim 9, wherein the light intensity reading is calibrated by adjusting a control signal for each light emitter in a light emitter set with a respective bias signal.

11. 11. The method of claim 9 or 10, wherein the light intensity reading is adjusted by correcting the generated light intensity reading with a correction value.

12. 12. A system according to any of claims 9 to 11, wherein the light intensity reading is calibrated using a calibration system according to any of claims 1 to 6.

13. 13. A system as claimed in any of claims 9 to 12, wherein the controller is configured to calibrate the light intensity readings in accordance with a method as claimed in claim 7 or 8.

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