A DTOF camera calibration system and method based on controllable delay optical fiber

Abstract

The present invention relates to a DTOF camera calibration system and method based on controllable time-delay optical fiber, the system comprising: a time-delay optical fiber switching module, comprising an optical fiber switch, a transmitting optical fiber and a receiving optical fiber, the transmitting optical fiber being connected to the transmitting end of the DTOF camera, the receiving optical fiber comprising a plurality of optical fiber branches of different lengths and all connected to the receiving end of the DTOF camera, the optical fiber switch being used to switchably form an optical path between the transmitting optical fiber and any of the optical fiber branches in the receiving optical fiber; a laser intensity calibration module being provided on the transmitting optical fiber for dynamically modulating the laser intensity of the DTOF camera; a temperature calibration module being provided at the transmitting end and the receiving end for performing temperature calibration on the DTOF camera; a control module being respectively connected to the optical fiber switch, the laser intensity calibration module and the temperature calibration module for controlling each calibration module to form a multimodal calibration environment. The present invention simplifies the calibration process of the DTOF camera and improves the calibration accuracy and flexibility.

Description

Technical Field

[0001] The present invention relates to the field of optical measurement technology, and in particular to a DTOF camera calibration system and method based on controllable time-delay optical fiber. Background Art

[0002] DTOF (Distributed Time-of-Flight) is a measurement technology based on the time-of-flight principle that can be used to measure the three-dimensional shape or distance information of objects in space. DTOF technology offers the advantages of non-contact measurement, high speed, and high accuracy, and is widely used in industrial automation, robotic navigation, medical imaging, and other fields. The basic principle of a DTOF camera is that a laser pulse is emitted from a transmitter (TX). The laser pulse propagates through space and is reflected back upon encountering an object. The receiver (RX) receives the reflected laser pulse and calculates the distance between the object and the measurement system by measuring the time-of-flight (TOF) of the laser pulse. By scanning the entire measurement area, a DTOF camera can obtain the object's three-dimensional shape or distance information.

[0003] However, the performance of DTOF cameras is affected by a variety of factors, including the performance of the transmitter and receiver, the stability of the optical path, and environmental noise. To ensure the accuracy and reliability of DTOF cameras, they must be calibrated. Calibration involves determining the parameters and performance of the measurement system through a series of experiments under known conditions, allowing for correction and calibration during actual measurements.

[0004] Currently, the calibration method of DTOF cameras has the following main shortcomings:

[0005] (1) Complex calibration process: Traditional DTOF calibration methods require multiple calibration devices and steps, which are cumbersome and time-consuming, and are not conducive to rapid deployment and field application.

[0006] (2) Limited calibration accuracy: Due to the limitations of calibration equipment and methods, traditional DTOF camera calibration methods often find it difficult to achieve high calibration accuracy, which affects the performance of the measurement system.

[0007] (3) Lack of flexibility: Traditional DTOF camera calibration methods are usually targeted at specific measurement scenarios and equipment configurations, lack versatility and flexibility, and are difficult to adapt to different measurement requirements and environmental changes. Summary of the Invention

[0008] (1) Technical issues to be resolved

[0009] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a DTOF camera calibration system and method based on controllable delay optical fiber, aiming to simplify the calibration process of DTOF cameras and improve calibration accuracy and flexibility.

[0010] (2) Technical solution

[0011] In order to achieve the above objectives, the main technical solutions adopted by the present invention include:

[0012] In a first aspect, an embodiment of the present invention provides a DTOF camera calibration system based on a controllable time-delay optical fiber, comprising:

[0013] A time-delay fiber switching module includes a fiber switch and a transmitting fiber and a receiving fiber disposed on either side of the fiber switch. The transmitting fiber is connected to the transmitting end of the DTOF camera. The receiving fiber includes at least two fiber branches of different lengths, both connected to the receiving end of the DTOF camera. The fiber switch is configured to switchably form an optical path between the transmitting fiber and any of the receiving fiber branches.

[0014] The laser intensity calibration module is provided on the transmitting optical fiber and is used to apply a modulation voltage to change the transmission characteristics of the laser transmitted in the transmitting optical fiber to dynamically modulate the laser intensity of the DTOF camera;

[0015] The temperature calibration module is set at the transmitter and receiver to change the ambient temperature of the transmitter and receiver to perform temperature calibration on the DTOF camera;

[0016] The control module is connected to the optical fiber switcher, the laser intensity calibration module and the temperature calibration module respectively, and is used to control the optical fiber switcher, the laser intensity calibration module and the temperature calibration module to form a multi-modal calibration environment.

[0017] Optionally, the receiving optical fiber includes at least two optical fibers with a length difference of The optical fiber branch, It is positively correlated with the set target delay amount;

[0018] The end of the optical fiber branch is provided with an optical fiber interface, which is used for pluggable connection with the receiving end.

[0019] Optionally, the transmitting end includes: a laser light source and a first collimating mirror;

[0020] The laser light source is used to generate the emitted laser;

[0021] The first collimating mirror is connected to the transmitting optical fiber and is used to collimate the transmitting laser into the transmitting optical fiber.

[0022] Optionally, the receiving end includes: a second collimating lens, frosted glass, and a receiving lens;

[0023] The second collimator is connected to the receiving optical fiber and is used to collimate the laser transmitted in the receiving optical fiber into parallel laser light;

[0024] The frosted glass is used to scatter the parallel laser light into a uniformly distributed spot signal;

[0025] The receiving lens is used to receive the light spot signal sent by the frosted glass and transmit the light spot signal to the measurement module of the DTOF camera.

[0026] Optionally, the laser intensity calibration module includes: a polarizer, an analyzer, and an electro-optical modulator;

[0027] The polarizer is arranged at the receiving end of the electro-optical modulator and connected to the transmitting end of the DTOF camera through the transmitting optical fiber. When the initial laser is received, it is used to convert the initial laser into linearly polarized laser and send it to the electro-optical modulator.

[0028] The electro-optic modulator is used to apply a modulation voltage to change the polarization state of the linearly polarized laser to generate a modulated laser;

[0029] The polarization analyzer is arranged at the transmitting end of the electro-optical modulator and is connected to the optical fiber switcher through the transmitting optical fiber. It is used to detect the polarization state of the modulated laser and transmit the modulated laser back to the transmitting optical fiber after detection.

[0030] The polarization transmission axes of the polarizer and the analyzer are perpendicular to each other, and the electro-optical modulator is arranged on the polarization transmission axis.

[0031] Optionally, the laser intensity calibration module further includes: a first lens and a second lens;

[0032] The first lens is arranged at the connection between the polarizer and the transmitting optical fiber, and is used to collimate the initial laser onto the polarizer;

[0033] The second lens is arranged at the connection between the polarizer and the transmitting optical fiber, and is used to converge the modulated laser light after detection into the transmitting optical fiber.

[0034] In a second aspect, an embodiment of the present invention provides a DTOF camera calibration method, which is applied to the above-mentioned DTOF camera calibration system based on controllable delay optical fiber, and the method includes:

[0035] Collaboratively control the delayed optical fiber switching module, laser intensity calibration module and temperature calibration module to perform temperature calibration, depth calibration and intensity calibration in a preset order;

[0036] In temperature calibration, by adjusting the ambient temperature and collecting depth images at multiple temperature points, the relationship between temperature and ranging deviation is fitted to obtain the temperature compensation coefficient;

[0037] In depth calibration, the fiber optic switcher is controlled to switch between fiber optic branches of different lengths and collect corresponding depth images. The mapping relationship between the measured value and the theoretical length is established through linear regression to obtain the depth calibration coefficient.

[0038] In intensity calibration, the laser intensity is dynamically adjusted and the depth image associated with the intensity is collected. The relationship between intensity and ranging error is fitted to obtain the intensity calibration coefficient.

[0039] Write the temperature compensation coefficient, depth calibration coefficient, and intensity calibration coefficient into the DTOF camera.

[0040] Optionally, by adjusting the ambient temperature and collecting depth images at multiple temperature points, fitting the relationship between temperature and ranging deviation, and obtaining the temperature compensation coefficient, the following formula is included:

[0041] After controlling the fiber switcher to select a fiber branch whose optical path is within the ranging range of the DTOF camera and controlling the laser intensity calibration module to apply the optimal modulation voltage for the DTOF camera's ranging, the temperature calibration module is driven to change the ambient temperature of the transmitter and receiver at a preset gradient;

[0042] During the temperature change process, the depth image collected by the DTOF camera is acquired at the set temperature interval, and the ranging mean of all pixels in the depth image at each temperature is calculated;

[0043] Based on the ranging mean, calculate the deviation between the actual ranging value of all pixels in the depth image at each temperature and the ranging mean;

[0044] All temperatures and corresponding deviations are traversed to perform polynomial curve fitting, and the polynomial coefficients of the obtained fitting curve are determined as temperature compensation coefficients.

[0045] Optionally, the fiber optic switcher is controlled to switch fiber optic branches of different lengths and corresponding depth images are collected. A mapping relationship between the measured value and the theoretical length is established through linear regression to obtain the depth calibration coefficient, including:

[0046] After controlling the laser intensity calibration module to apply the optimal modulation voltage for the DTOF camera's ranging and driving the temperature calibration module to set the temperature of the DTOF camera to the optimal temperature state, the fiber optic switch is controlled to sequentially switch fiber optic branches with increasing lengths until a preset ranging threshold is reached;

[0047] The DTOF camera collects multiple depth images under each fiber branch, and calculates the mean distance measurement of the pixels at the same position in all depth images under each fiber branch to obtain the mean depth image.

[0048] The distance measurement mean of each pixel in the mean depth image belonging to all optical fiber branches is linearly fitted with the theoretical distance measurement value belonging to the actual length of the optical fiber branch, and the fitting coefficient of the obtained fitting curve is determined as the depth calibration coefficient.

[0049] Optionally, dynamically adjusting the laser intensity and collecting an intensity-related depth image, fitting the relationship between intensity and ranging error, and obtaining an intensity calibration coefficient include:

[0050] After controlling the fiber switcher to select the fiber branch whose optical path is within the ranging range of the DTOF camera and driving the temperature calibration module to set the temperature of the DTOF camera to the optimal temperature state, the modulation voltage output by the laser intensity calibration module is dynamically adjusted;

[0051] The DTOF camera collects multiple depth images at each intensity level, and calculates the distance measurement mean and intensity mean of the pixels at the same position in all depth images at each intensity level to obtain the mean depth image and mean intensity image.

[0052] Taking the mean depth image at the lowest intensity level as a reference, obtaining an error depth image between the mean depth image at each intensity level and the mean depth image at the lowest intensity level;

[0053] A polynomial curve is fitted on the distance measurement values ​​and intensity values ​​of the pixels at the same position in the error depth image and the mean intensity image under all intensity levels, and the polynomial coefficients of the obtained fitting curve are determined as intensity calibration coefficients.

[0054] (3) Beneficial effects

[0055] The beneficial effects of the present invention are:

[0056] First, the present invention adopts an integrated calibration system, which integrates the functions of depth calibration, intensity calibration and temperature calibration through a delayed optical fiber switching module, a laser intensity calibration module and a temperature calibration module, thereby simplifying the calibration process, reducing the calibration equipment and steps, and improving the calibration efficiency.

[0057] Secondly, the delayed fiber optic switching module in the present invention uses a fiber optic switch to switch fiber optic branches of different lengths, which can accurately control the optical path, improve the calibration accuracy, and ensure the accuracy and reliability of the DTOF camera.

[0058] Furthermore, the present invention realizes automatic calibration and calibration through the control module, and can adjust and optimize calibration parameters according to different measurement requirements and environmental changes, thereby enhancing the flexibility and adaptability of the calibration system. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1A schematic diagram of the composition of a DTOF camera calibration system based on a controllable time-delay optical fiber proposed in one embodiment of the present invention;

[0060] Figure 2 A schematic flow chart of a DTOF camera calibration method based on a controllable time-delay optical fiber proposed in one embodiment of the present invention;

[0061] [Description of Reference Numerals]

[0062] 1: Laser light source; 2: First collimator; 3: First transmitting optical fiber; 4: First lens; 5: Polarizer; 6: Electro-optic modulator; 7: Analyzer; 8: Second lens; 9: Second transmitting optical fiber; 10: Fiber optic switcher; 11: Receiving optical fiber; 12: Second collimator; 13: Frosted glass; 14: Receiving lens; 15: Measurement module; 16: Temperature calibration module; 17: Control module. DETAILED DESCRIPTION

[0063] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation methods in conjunction with the accompanying drawings.

[0064] refer to Figure 1 As shown, an embodiment of the present invention proposes a DTOF camera calibration system based on a controllable delay optical fiber, which includes: a delay optical fiber switching module, including an optical fiber switch 10 and a transmitting optical fiber and a receiving optical fiber 11 arranged on both sides of the optical fiber switch 10, the transmitting optical fiber is connected to the transmitting end of the DTOF camera, the receiving optical fiber 11 includes at least two optical fiber branches of different lengths and are both connected to the receiving end of the DTOF camera, and the optical fiber switch 10 is configured to switchably form an optical path between the transmitting optical fiber and any optical fiber branch of the receiving optical fiber 11; a laser intensity calibration module, arranged on the transmitting optical fiber, for applying a modulation voltage to change the transmission characteristics of the transmitted laser in the transmitting optical fiber to dynamically modulate the laser intensity of the DTOF camera; a temperature calibration module 16, arranged at the transmitting end and the receiving end, for changing the ambient temperature of the transmitting end and the receiving end to perform temperature calibration on the DTOF camera; a control module 17, respectively connected to the optical fiber switch 10, the laser intensity calibration module and the temperature calibration module 16, for controlling the optical fiber switch 10, the laser intensity calibration module and the temperature calibration module 16 to form a multimodal calibration environment.

[0065] This embodiment uses an integrated calibration system that integrates depth calibration, intensity calibration, and temperature calibration functions through a delayed fiber switching module, a laser intensity calibration module, and a temperature calibration module 16. This simplifies the calibration process, reduces calibration equipment and steps, and improves calibration efficiency. Furthermore, the delayed fiber switching module in this embodiment uses a fiber switcher 10 to switch between fiber branches of different lengths, enabling precise control of the optical path, improving calibration accuracy, and ensuring the accuracy and reliability of the DTOF camera. Furthermore, this embodiment implements automated calibration and calibration through a control module 17, allowing for adjustment and optimization of calibration parameters based on different measurement requirements and environmental changes, thereby enhancing the flexibility and adaptability of the calibration system.

[0066] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. Rather, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0067] Specifically, refer to Figure 1 As shown, this embodiment proposes a DTOF camera calibration system based on controllable delay optical fiber, which includes: a delay optical fiber switching module, a laser intensity calibration module, a temperature calibration module 16 and a control module 17.

[0068] First, the delayed fiber switching module includes a fiber switch 10 and two optical fibers, a transmitting fiber and a receiving fiber 11, disposed on either side of the fiber switch 10. The transmitting fiber is connected to the transmitting end of the DTOF camera. The receiving fiber 11 includes at least two fiber branches of different lengths, both connected to the receiving end of the DTOF camera. The fiber switch 10 is configured to switchably form an optical path between the transmitting fiber and any of the fiber branches in the receiving fiber 11.

[0069] In this embodiment, the receiving optical fiber 11 includes at least two optical fibers with a length difference of Fiber branch (L 1… L n ), It is positively correlated with the set target delay; the end of the optical fiber branch is provided with an optical fiber interface, which is used for pluggable connection with the receiving end. The optical fiber switch 10 has multiple input ends and output ends, the input end is connected to the transmitting optical fiber, and one output end is connected to an optical fiber branch. The optical fiber switch 10 selects different optical fiber paths by switching the connection relationship between the input end and the output end. By selecting different optical fiber branches, the optical path of the laser can be changed, thereby realizing the calibration of different optical paths of the DTOF camera. Specifically, the measurement module 15 of the DTOF camera in the receiving end calculates the flight time of the laser in different optical fiber paths (the time difference from the laser emission to the reception), and then obtains the optical path of the laser and the distance information of the object. Among them, all input ends of the optical fiber switch 10 can be connected to the transmitting ends of the corresponding number of DTOF cameras through the transmitting optical fiber, realizing the synchronous calibration of multiple DTOF cameras.

[0070] In this embodiment, the transmitting end of the DTOF camera includes: a laser light source 1 and a first collimator 2. The laser light source 1 is used to generate a transmitting laser; the first collimator 2 is connected to the transmitting optical fiber and is used to collimate the transmitting laser into the transmitting optical fiber.

[0071] In this embodiment, the receiving end of the DTOF camera includes a second collimator 12, a frosted glass 13, and a receiving lens 14. The second collimator 12 is connected to the receiving optical fiber 11 and is used to collimate the laser light transmitted by the receiving optical fiber 11 into parallel laser light. The frosted glass 13 is used to scatter the parallel laser light into a uniformly distributed spot signal. The receiving lens 14 is used to transmit the spot signal sent by the frosted glass 13 to the measurement module 15 of the DTOF camera after receiving the spot signal.

[0072] Secondly, a laser intensity calibration module is installed on the transmitting fiber. It applies a modulation voltage to change the transmission characteristics of the laser light transmitted through the transmitting fiber, thereby dynamically modulating the laser intensity of the DTOF camera. The laser intensity calibration module includes a polarizer 5, an analyzer 7, an electro-optical modulator 6, a first lens 4, and a second lens 8.

[0073] In this embodiment, the polarizer 5 is disposed at the receiving end of the electro-optical modulator 6 and is connected to the transmitting end of the DTOF camera via a transmitting optical fiber (a first transmitting optical fiber 3). Upon receiving the initial laser light emitted by the transmitting end, the polarizer 5 converts the initial laser light into a linearly polarized laser light and transmits the converted light to the electro-optical modulator 6. The electro-optical modulator 6 is configured to apply a modulation voltage to change the polarization state of the linearly polarized laser light, thereby generating a modulated laser light. The analyzer 7 is disposed at the transmitting end of the electro-optical modulator 6 and is connected to the optical fiber switch 10 via a transmitting optical fiber (a second transmitting optical fiber 9). The analyzer 7 is configured to detect the polarization state of the modulated laser light and transmit the detected modulated laser light back to the transmitting optical fiber (the second transmitting optical fiber 9). The first lens 4 is disposed at the junction of the polarizer 5 and the transmitting optical fiber to collimate the initial laser light onto the polarizer 5. The second lens 8 is disposed at the junction of the analyzer 7 and the transmitting optical fiber to converge the detected modulated laser light into the transmitting optical fiber. The polarization transmission axes of the analyzer 7 and the polarizer 5 are perpendicular to each other, and the electro-optical modulator 6 is disposed on the polarization transmission axis.

[0074] Next, the temperature calibration module 16 is set at the transmitting end and the receiving end of the DTOF camera, and is used to change the ambient temperature of the transmitting end and the receiving end to perform temperature calibration on the DTOF camera.

[0075] In this embodiment, temperature calibration module 16 utilizes a semiconductor refrigeration chip. This chip heats or cools the transmitting end (i.e., laser source 1 and its associated components) and the receiving end (i.e., receiving lens 14 and its associated components) according to instructions from control module 17, thereby precisely controlling their ambient temperature. This temperature control further reduces measurement errors caused by temperature fluctuations, improving the stability and accuracy of the DTOF camera.

[0076] Finally, the control module 17 is connected to the fiber optic switch 10, the laser intensity calibration module and the temperature calibration module 16 respectively, and is used to control the fiber optic switch 10, the laser intensity calibration module and the temperature calibration module 16 to form a multi-modal calibration environment.

[0077] In this embodiment, the control module 17 can coordinately control the delayed optical fiber switching module, the laser intensity calibration module and the temperature calibration module 16, perform temperature calibration, depth calibration and intensity calibration in a preset order, and write the multi-dimensional calibration parameters such as the temperature compensation coefficient, depth calibration coefficient, and intensity calibration coefficient obtained during the calibration process into the DTOF camera to complete the calibration of the DTOF camera.

[0078] In addition, reference Figure 2 As shown, an embodiment of the present invention further proposes a DTOF camera calibration method, which is applied to the above-mentioned DTOF camera calibration system based on controllable delay optical fiber. The execution body is the control module 17, and the method includes:

[0079] S100 , collaboratively controlling the delayed optical fiber switching module, the laser intensity calibration module and the temperature calibration module 16 to perform temperature calibration, depth calibration and intensity calibration in a preset order.

[0080] S200a: In temperature calibration, by adjusting the ambient temperature and collecting depth images at multiple temperature points, the relationship between temperature and ranging deviation is fitted to obtain a temperature compensation coefficient.

[0081] S200b, in depth calibration, control the optical fiber switch 10 to switch optical fiber branches of different lengths and collect corresponding depth images, establish a mapping relationship between the measured value and the theoretical length through linear regression, and obtain a depth calibration coefficient.

[0082] S200c, in intensity calibration, dynamically adjust the laser intensity and collect the intensity-related depth image, fit the relationship between intensity and ranging error, and obtain the intensity calibration coefficient.

[0083] S300: Write the temperature compensation coefficient, the depth calibration coefficient, and the intensity calibration coefficient into the DTOF camera.

[0084] In this embodiment, step S200a may include the following sub-steps S210a to S240a:

[0085] S210a, after controlling the optical fiber switch 10 to select an optical fiber branch whose optical path is within the ranging range of the DTOF camera and controlling the laser intensity calibration module to apply the optimal modulation voltage for ranging of the DTOF camera, drive the temperature calibration module 16 to change the ambient temperature of the transmitting end and the receiving end with a preset gradient.

[0086] The optical fiber switch 10 is controlled to select an optical fiber branch whose optical path is within the DTOF ranging range, ensuring that the optical path is always within the ranging range of the DTOF camera during the temperature change process.

[0087] S220a. During the temperature change process, obtain the depth image collected by the DTOF camera at the set temperature interval, and calculate the ranging mean of all pixels in the depth image at each temperature.

[0088] For example, within the set temperature range (-20℃~60℃), a depth image is recorded every 0.5℃, and the mean ranging value of all pixels in the depth image at each temperature is calculated as the reference value of the current temperature change, which is used to calculate the deviation of the ranging value of each pixel at each temperature from the reference value.

[0089] S230a: Based on the distance measurement mean, calculate the deviation between the actual distance measurement value and the distance measurement mean of all pixels in the depth image at each temperature.

[0090] S240a, performing polynomial curve fitting on all temperatures and corresponding deviations, and determining the obtained polynomial coefficients of the fitting curve as temperature compensation coefficients.

[0091] In this embodiment, step S200b may include the following sub-steps S210b to S230b:

[0092] S210b, after controlling the laser intensity calibration module to apply the optimal modulation voltage for ranging of the DTOF camera and driving the temperature calibration module 16 to set the temperature of the DTOF camera to the optimal temperature state, control the optical fiber switch 10 to switch optical fiber branches with increasing lengths in sequence until the preset ranging threshold is reached.

[0093] For example, the optical fiber switch 10 sequentially switches optical fiber branches with increasing lengths until a preset ranging threshold is reached, which may be in the range of 0.1 m to 15 m.

[0094] S220b, collect multiple frames of depth images under each optical fiber branch through the DTOF camera, and calculate the distance measurement mean of the pixels at the same position in all depth images under each optical fiber branch to obtain the mean depth image

[0095] S230b, performing linear fitting between the distance measurement mean of each pixel in the mean depth image belonging to all optical fiber branches and the theoretical distance measurement value belonging to the actual length of the optical fiber branch, and determining the fitting coefficient of the obtained fitting curve as the depth calibration coefficient.

[0096] For each pixel in the depth image, the corresponding pixel measurement is x in the depth image collected by each optical path, and the theoretical distance is D. We can get several sets of {x, D} and use linear fitting to calculate the correspondence between x and D. The fitting coefficient is the depth calibration coefficient.

[0097] In this embodiment, step S200c may include the following sub-steps S210c to S240c:

[0098] S210c, after controlling the optical fiber switch 10 to select the optical fiber branch whose optical path is within the ranging range of the DTOF camera and driving the temperature calibration module 16 to set the temperature of the DTOF camera to the optimal temperature state, dynamically adjust the modulation voltage output by the laser intensity calibration module.

[0099] S220c. Collect multiple depth images at each intensity level using a DTOF camera, and calculate the distance measurement mean and intensity mean of pixels at the same position in all depth images at each intensity level to obtain a mean depth image and a mean intensity image.

[0100] The intensity variation range is determined by the modulation voltage, and its intensity value is proportional to the modulation voltage. For example, when the modulation voltage is 0V, the corresponding intensity value is 1; when the modulation voltage is 12V, the corresponding intensity value is 0.5; when the modulation voltage is 24V, the corresponding intensity value is 0.

[0101] S230c: Taking the mean depth image at the lowest intensity level as a reference, obtain an error depth image between the mean depth image at each intensity level and the mean depth image at the lowest intensity level.

[0102] S240c, performing polynomial curve fitting on the distance measurement values ​​and intensity values ​​of the pixels at the same position in the error depth image and the mean intensity image at all intensity levels, and determining the obtained polynomial coefficients of the fitting curve as intensity calibration coefficients.

[0103] In summary, this embodiment proposes a DTOF camera calibration system and method based on controllable time-delay optical fiber. First, through an integrated calibration system, the functions of intensity calibration, optical path calibration and temperature calibration are integrated together to realize multi-dimensional parameter calibration of the DTOF camera, and also simplify the calibration process, reduce the calibration equipment and steps, and improve the calibration efficiency. Secondly, by using components such as a high-precision laser light source 1, a collimating mirror, an electro-optical modulator 6, an optical fiber switcher 10, a temperature calibration module 16 and a measurement module 15, multi-dimensional parameter calibration is performed by precisely controlling the laser intensity, optical path and ambient temperature, thereby improving the calibration accuracy and ensuring the accuracy and reliability of the DTOF camera. In addition, automated calibration and calibration are achieved through the control module 17, which can be adjusted and optimized according to different measurement requirements and environmental changes, thereby enhancing the flexibility and adaptability of the system.

[0104] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROMs, optical storage, etc.) containing computer-usable program code.

[0105] The present invention is described with reference to flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions.

[0106] It should be noted that, in the description of the present invention, the word "a" or "an" preceding a component does not exclude the presence of a plurality of such components. The present invention can be implemented by means of hardware comprising several distinct components and by means of a suitably programmed computer. The use of the words first, second, third, etc., is merely for convenience and does not imply any order. These words should be understood as part of the component name.

[0107] In addition, it should be noted that, in the description of this specification, the description of the terms "one embodiment", "some embodiments", "embodiment", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory.

[0108] Although preferred embodiments of the present invention have been described, those skilled in the art will be able to make additional changes and modifications to these embodiments after obtaining the basic inventive concepts.

[0109] Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the invention.

Claims

1. A DTOF camera calibration method, characterized in that: include: Collaboratively control the preset delay optical fiber switching module, laser intensity calibration module and temperature calibration module to perform temperature calibration, depth calibration and intensity calibration in a preset order; In temperature calibration, by adjusting the ambient temperature and collecting depth images at multiple temperature points, the relationship between temperature and ranging deviation is fitted to obtain the temperature compensation coefficient; In depth calibration, the fiber optic switch in the delayed fiber optic switching module is controlled to switch fiber optic branches of different lengths and collect corresponding depth images. The mapping relationship between the measured value and the theoretical length is established through linear regression to obtain the depth calibration coefficient; In the intensity calibration, the laser intensity is dynamically adjusted and the depth image associated with the intensity is collected, and the relationship between the intensity and the ranging error is fitted to obtain the intensity calibration coefficient, including: after controlling the optical fiber switcher to select the optical fiber branch whose optical path is within the ranging range of the DTOF camera and driving the temperature calibration module to set the temperature of the DTOF camera to the optimal temperature state, the modulation voltage output by the laser intensity calibration module is dynamically adjusted; multiple frames of depth images at various intensity levels are collected by the DTOF camera, and the ranging mean and the intensity mean of the pixels at the same position in all depth images at each intensity level are calculated respectively to obtain the mean depth image and the mean intensity image; with the mean depth image at the lowest intensity level as the benchmark, the error depth image of the mean depth image at each intensity level and the mean depth image at the lowest intensity level is obtained; the ranging values ​​and intensity values ​​of the pixels at the same position in the error depth images and the mean intensity images at all intensity levels are traversed to perform polynomial curve fitting, and the polynomial coefficient of the obtained fitting curve is determined as the intensity calibration coefficient; Write the temperature compensation coefficient, depth calibration coefficient, and intensity calibration coefficient into the DTOF camera.

2. The DTOF camera calibration method according to claim 1, wherein: By adjusting the ambient temperature and collecting depth images at multiple temperature points, the relationship between temperature and ranging deviation is fitted to obtain the temperature compensation coefficients including: After controlling the fiber switcher to select a fiber branch whose optical path is within the ranging range of the DTOF camera and controlling the laser intensity calibration module to apply the optimal modulation voltage for the DTOF camera's ranging, the temperature calibration module is driven to change the ambient temperature of the transmitter and receiver at a preset gradient; During the temperature change process, the depth image collected by the DTOF camera is acquired at the set temperature interval, and the ranging mean of all pixels in the depth image at each temperature is calculated; Based on the ranging mean, calculate the deviation between the actual ranging value of all pixels in the depth image at each temperature and the ranging mean; All temperatures and corresponding deviations are traversed to perform polynomial curve fitting, and the polynomial coefficients of the obtained fitting curve are determined as temperature compensation coefficients.

3. The DTOF camera calibration method according to claim 1, wherein: The fiber optic switch in the time-delay fiber optic switching module is controlled to switch fiber optic branches of different lengths and collect corresponding depth images. The mapping relationship between the measured value and the theoretical length is established through linear regression, and the depth calibration coefficient is obtained, including: After controlling the laser intensity calibration module to apply the optimal modulation voltage for the DTOF camera's ranging and driving the temperature calibration module to set the temperature of the DTOF camera to the optimal temperature state, the fiber optic switch is controlled to sequentially switch fiber optic branches with increasing lengths until a preset ranging threshold is reached; The DTOF camera collects multiple depth images under each fiber branch, and calculates the mean distance measurement of the pixels at the same position in all depth images under each fiber branch to obtain the mean depth image. The distance measurement mean of each pixel in the mean depth image belonging to all optical fiber branches is linearly fitted with the theoretical distance measurement value belonging to the actual length of the optical fiber branch, and the fitting coefficient of the obtained fitting curve is determined as the depth calibration coefficient.

4. A DTOF camera calibration system based on controllable delay optical fiber, characterized in that: The DTOF camera calibration system is used to execute the DTOF camera calibration method according to any one of claims 1 to 3, and the system includes: A delayed fiber optic switching module includes a fiber optic switch and a transmitting fiber and a receiving fiber disposed on either side of the fiber optic switch. The transmitting fiber is connected to the transmitting end of the DTOF camera. The receiving fiber includes at least two fiber branches of different lengths, both of which are connected to the receiving end of the DTOF camera. The fiber optic switch is configured to switchably form an optical path between the transmitting fiber and any of the fiber branches of the receiving fiber. The transmitting end includes a laser light source and a first collimator, the first collimator being connected to the transmitting fiber and configured to collimate the transmitting laser light generated by the laser light source into the transmitting fiber. The receiving end includes a second collimator connected to the receiving fiber and configured to collimate the laser light transmitted in the receiving fiber into a parallel laser light. The laser intensity calibration module is provided on the transmitting optical fiber and is used to apply a modulation voltage to change the transmission characteristics of the laser transmitted in the transmitting optical fiber to dynamically modulate the laser intensity of the DTOF camera; The temperature calibration module is set at the transmitter and receiver to change the ambient temperature of the transmitter and receiver to calibrate the DTOF camera and reduce the measurement error caused by temperature change through temperature control; The control module is connected to the optical fiber switcher, the laser intensity calibration module and the temperature calibration module respectively, and is used to control the optical fiber switcher, the laser intensity calibration module and the temperature calibration module to form a multimodal calibration environment under a single variable in a preset order.

5. The DTOF camera calibration system according to claim 4, wherein: The receiving optical fiber contains at least two optical fibers with a length difference of The optical fiber branch, It is positively correlated with the set target delay amount; The end of the optical fiber branch is provided with an optical fiber interface, which is used for pluggable connection with the receiving end.

6. The DTOF camera calibration system according to claim 4, wherein: The receiving end includes: Ground glass and receiving lens; The frosted glass is used to scatter the parallel laser light into a uniformly distributed spot signal; The receiving lens is used to receive the light spot signal sent by the frosted glass and transmit the light spot signal to the measurement module of the DTOF camera.

7. The DTOF camera calibration system according to claim 4, wherein: The laser intensity calibration module includes: a polarizer, an analyzer and an electro-optical modulator; The polarizer is arranged at the receiving end of the electro-optical modulator and connected to the transmitting end of the DTOF camera through the transmitting optical fiber. When the initial laser is received, it is used to convert the initial laser into linearly polarized laser and send it to the electro-optical modulator. The electro-optic modulator is used to apply a modulation voltage to change the polarization state of the linearly polarized laser to generate a modulated laser; The polarization analyzer is arranged at the transmitting end of the electro-optical modulator and is connected to the optical fiber switcher through the transmitting optical fiber. It is used to detect the polarization state of the modulated laser and transmit the modulated laser back to the transmitting optical fiber after detection. The polarization transmission axes of the polarizer and the analyzer are perpendicular to each other, and the electro-optical modulator is arranged on the polarization transmission axis.

8. The DTOF camera calibration system according to claim 7, wherein: The laser intensity calibration module further includes: a first lens and a second lens; The first lens is arranged at the connection between the polarizer and the transmitting optical fiber, and is used to collimate the initial laser onto the polarizer; The second lens is arranged at the connection between the polarizer and the transmitting optical fiber, and is used to converge the modulated laser light after detection into the transmitting optical fiber.

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