Synchronous control method of high-rotating-speed filter wheel and camera and multispectral imaging system

Abstract

The present application relates to a kind of high speed filter wheel and the synchronous control method of camera and multispectral imaging system, belong to multispectral imaging technical field, including high speed filter wheel, brushless motor, motor controller, camera, time synchronization device and main control unit, high speed filter wheel includes rotating wheel structure and multiple filters being evenly distributed on rotating wheel structure, the diameter of each filter in the circumferential direction of rotating wheel structure is greater than in the diameter of radius direction of rotating wheel structure, high speed filter wheel and brushless motor are connected using direct drive mode.The present application uses the driving mode of brushless motor, more compact in structure, more easily realize integrated design;In filter mode, filter wheel rotates continuously, using position and speed double closed loop control mode, ensure that in camera exposure time period, in filter structure can be imaged, do not need to trigger camera after reaching position, solve the problem that imaging quality is poor and camera cannot realize high frequency image acquisition caused by position jitter.

Description

Technical Field

[0001] This invention belongs to the field of multispectral imaging technology, and particularly relates to a method for synchronous control of a high-speed filter wheel and a camera, as well as a multispectral imaging system. Background Technology

[0002] Multispectral imaging of the same target can integrate spatial, radiometric, and spectral information, greatly enhancing the information dimension of target observation. Multispectral imaging using a filter wheel involves adding filters to the imaging optical path for spectral dispersion. By rotating the filter wheel, light is forced through narrowband filters with different wavelength transmittances, ultimately forming an image on the sensor. This method has the advantages of a simple optical path structure and flexible filter replacement, and has been applied in multiple fields. Currently, most filters are circular, driven by stepper motors or brushed motors. After reaching a designated position, an exposure command is sent to the camera via a driver or additional position detection device. After the camera exposure is complete, the filter wheel rotates to the next position. However, this method has the following problems:

[0003] (1) The working mode of the filter wheel is positioning, rotation, and repositioning. During positioning, jitter is inevitable. The jitter after the filter is rotated to the correct position has a significant impact on the image quality.

[0004] (2) When the filter wheel rotates from one filter to the next, the camera cannot form an image, so high-frequency image acquisition cannot be achieved;

[0005] (3) Using stepper motors or brushed motors as the driving method makes it difficult to achieve integrated design and results in poor control accuracy. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned problems existing in current filter wheel devices and their control methods, and to propose a synchronous control method for a high-speed filter wheel and a camera, as well as a multispectral imaging system.

[0007] To solve the above problems, the present invention adopts the following technical solution:

[0008] A method for synchronous control of a high-speed filter wheel and a camera, wherein the high-speed filter wheel includes a rotating wheel structure and a plurality of filters evenly distributed on the rotating wheel structure, wherein the diameter of each filter in the circumferential direction of the rotating wheel structure is larger than the diameter in the radial direction of the rotating wheel structure, the high-speed filter wheel is directly driven to a brushless motor, and the tail end of the brushless motor is equipped with a high-precision absolute encoder.

[0009] The method includes the following steps:

[0010] In filter mode, the time synchronization device receives instructions from the main control unit, determines the current camera trigger frequency, generates three rising edge synchronization signals, namely the camera trigger signal, the position synchronization trigger signal, and the 1kHz synchronization pulse signal, and sends the camera trigger signal to the camera, and sends the position synchronization trigger signal and the 1kHz synchronization pulse signal to the motor controller.

[0011] The camera receives instructions from the main control unit and selects a trigger exposure mode, which is either internal trigger exposure or external trigger exposure based on the camera trigger signal;

[0012] The motor controller receives feedback signals from a high-precision absolute encoder to obtain the current position information of the filter wheel. When the camera trigger exposure mode received by the motor controller from the main control unit is external trigger exposure, the main control unit calculates the rotational speed of the filter wheel based on the camera synchronization trigger frequency and sends the rotational speed to the motor controller. The motor controller determines the theoretical position where the filter will not be blocked each time a position synchronization trigger signal is received, based on the rotational speed of the filter wheel and the number of filters. At the same time, the motor controller obtains the position guidance value through the position synchronization trigger signal and the 1kHz synchronization pulse signal. Under the dual closed-loop of filter wheel speed command and position guidance value, the motor controller drives the filter wheel to rotate. When the position synchronization trigger signal is received, the motor controller determines whether the position error is less than a predetermined value. If so, it feeds back a position synchronization flag to the main control unit, and the main control unit sets the camera to acquire image information.

[0013] Meanwhile, the present invention also proposes a multispectral imaging system, including a high-speed filter wheel, a brushless motor with a high-precision absolute encoder, a motor controller, a camera, a time synchronization device, and a main control unit. The multispectral imaging system uses the aforementioned synchronous control method of the high-speed filter wheel and the camera to control the rotation of the high-speed filter wheel and the exposure and image acquisition of the camera.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) In terms of driving method, the high-speed filter wheel in this invention adopts the driving method of brushless motor. The brushless motor has a large driving torque and can drive the filter wheel in a direct drive manner. The structure is more compact and easier to achieve integrated design. In addition, a high-precision absolute encoder is used as the feedback data source, which can effectively improve the position accuracy.

[0016] (2) In terms of structure, the shape of the filter has been optimized from the traditional circle to a shape in which the diameter in the circumferential direction of the rotating structure is larger than the diameter in the radial direction of the rotating structure, such as waist or ellipse. The camera can obtain the image of the frequency band when exposed in this waist or ellipse, and the imaging frequency is higher.

[0017] (3) In terms of control method, when in filter mode, the filter wheel rotates continuously and adopts a dual closed-loop control method of position and speed to ensure that the light is in the filter structure during the camera exposure time period and can be imaged within the filter structure. It does not need to trigger the camera after it is in position, which solves the problems of poor image quality caused by position jitter and the inability of multispectral imaging systems to achieve high-frequency image acquisition. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the multispectral imaging system in this invention;

[0019] Figure 2 This is a flowchart of the synchronization control method between the high-speed filter wheel and the camera in this invention;

[0020] Figure 3 A diagram illustrating the acquisition of positional guidance values;

[0021] Figure 4 This is a schematic diagram of the theoretical position of the filter when it does not cause obstruction. Detailed Implementation

[0022] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and preferred embodiments.

[0023] like Figure 1 As shown, the present invention provides a multispectral imaging system, including a high-speed filter wheel, a brushless motor and a high-precision absolute encoder, a motor controller, a camera, a time synchronization device and a main control unit.

[0024] The high-speed filter wheel comprises a rotating structure and multiple filters. These filters are evenly distributed on the rotating structure, and their structures can be identical or different. Each filter's diameter along the circumference of the rotating structure is larger than its diameter along the radius; for example, it can be oblong, elliptical, or other similar shapes. The number of filters on the high-speed filter wheel can be selected according to imaging needs, such as 5 or 6 filters, without limitation. The high-speed filter wheel is directly driven to the brushless motor. The brushless motor has a high-precision absolute encoder at its tail end, which feeds back position signals to the motor controller, improving control accuracy.

[0025] The multispectral imaging system of this invention employs a synchronous control method between a high-speed filter wheel and a camera to control the rotation of the high-speed filter wheel and the camera's exposure and image acquisition. The synchronous control method between the high-speed filter wheel and the camera specifically includes the following steps:

[0026] The multispectral imaging system of this invention has two operating modes: position mode and filter mode. In position mode, the main control unit sends a command to the camera, controlling the camera to select an internal trigger mode for exposure. Simultaneously, the motor controller receives the position command from the main control unit, drives the brushless motor to rotate, and feeds back position information through a high-precision absolute encoder. When the position error is less than a predetermined value, a position completion flag is fed back to the main control unit. At this time, the main control unit can operate the camera and acquire images.

[0027] In filter mode, such as Figure 2 As shown, the motor controller receives the filter wheel speed information from the main control unit, and simultaneously receives the position synchronization trigger signal and the 1kHz synchronization pulse signal from the time synchronization device, thereby generating a position guidance value. Under dual closed-loop control of the position guidance value and the filter wheel speed command, when the motor controller receives the position synchronization trigger signal, it determines whether the position error is less than a predetermined value. If so, it feeds back the position synchronization flag to the main control unit; otherwise, it continues to execute the dual closed-loop control. A shutdown operation is required when switching operating modes.

[0028] Specifically, in filter mode, the time synchronization device receives instructions from the main control unit, determines the current camera trigger frequency, and generates three rising edge synchronization signals: one is a camera trigger signal, which is sent to the camera for external trigger control; the other two are a position synchronization trigger signal and a 1kHz synchronization pulse signal, both of which are sent to the motor controller to generate the theoretical position and guide position of the filter wheel.

[0029] The camera selects the exposure trigger mode by receiving instructions from the main control unit. In filter mode, it uses the camera trigger signal sent by the time synchronization device for external trigger synchronization control. In position mode, it selects the internal trigger mode for camera exposure control.

[0030] The main control unit sends the operating mode to the motor controller. Simultaneously, it sets the camera to acquire image information.

[0031] The motor controller receives feedback signals from a high-precision absolute encoder to obtain the current position information of the filter wheel. Simultaneously, the motor controller receives instructions from the main control unit to determine the current operating mode. When the camera trigger exposure mode received by the motor controller from the main control unit is external trigger exposure (i.e., in filter mode), the main control unit can calculate the rotational speed of the filter wheel based on the camera's synchronization trigger frequency. For example, if the camera synchronization trigger frequency f is 50Hz and the number of filters p is 6, then the theoretical rotational speed of the filter wheel s = 60 × f / p = 500 (RPM). The main control unit sends the calculated filter wheel rotational speed information to the motor controller. The motor controller receives two trigger signals from the time synchronization device: one is a position synchronization trigger signal, and the other is a 1kHz synchronization pulse signal. It obtains the position guidance value through the position synchronization trigger signal and the 1kHz synchronization pulse signal.

[0032] Furthermore, once the filter structure is determined, the minimum position value s1 when the filter does not cause obstruction can be determined first. Since the filters are uniformly distributed on the filter wheel, the theoretical position value s2 when the filter does not cause obstruction during the next camera exposure can be calculated. Subsequent theoretical position calculations follow the same logic. Assume that the theoretical position s2 when the position synchronization trigger signal is received for the (i+1)th time is s2. i+1 Then its calculation formula is: s i+1 =s i +360 / p, i = 1, 2, ..., where s i Let i be the theoretical position where the filter will not be blocked when the position synchronization trigger signal is received for the i-th time, such as... Figure 4 As shown. For example, if s1 = 20°, then the theoretical position when receiving the next position synchronization trigger signal should be s2 = s1 + 360 / p = 80°, and the theoretical position when receiving the next position synchronization trigger signal after that should be s3 = s2 + 360 / p = 140°, and so on. To achieve the ideal position where the filter does not cause obstruction, a dual closed-loop control method of position and speed is required. However, an ideal position alone is not enough; a position guide value is needed to prevent large jumps in position commands during motor rotation, thereby achieving precise control. The position guide value is obtained through the position synchronization trigger signal and a 1kHz synchronization pulse signal, such as... Figure 3 As shown. When the position synchronization trigger signal and the 1kHz synchronization pulse signal are triggered simultaneously, the corresponding theoretical position s is updated. i And assign this number to the position guide value t = s iThe purpose of the position guidance value is as follows: Since the position loop frequency of the motor controller is 1kHz, while the frequency of the camera's position synchronization trigger signal, i.e., the camera's exposure frequency, is below 1kHz (generally not exceeding 100Hz), the theoretical position obtained solely from the filter without obstruction is insufficient. It is also necessary to know the position from the theoretical position s. i to theoretical position s i+1 The position the filter wheel should move to every 1 ms (position loop frequency is 1 kHz) is the position guide value t. If only a 1 kHz synchronization pulse signal is received, the position increment value of the 1 kHz synchronization pulse signal is added to the position guide value. The position guide value at this time is t = t + k, where the formula for calculating the position increment value k of the 1 kHz synchronization pulse signal is: k = 360 × f / (1000 × p), where f is the camera synchronization trigger frequency and p is the total number of filters.

[0033] After obtaining the position guidance value t, the motor controller drives the filter wheel to rotate under the dual closed loop of the filter wheel speed command and the position guidance value. When it receives the position synchronization trigger signal, it determines whether the position error is less than the predetermined value. If so, it feeds back the position synchronization flag to the main control unit, and the main control unit sets the camera to acquire image information.

[0034] This invention achieves synchronous control of the filter wheel position and camera triggering in filter mode, and its beneficial effects are as follows:

[0035] In the filter mode, the filter wheel rotates continuously without needing to be in position to trigger the camera, thus solving the problems of poor image quality caused by position jitter and the inability of multispectral imaging systems to achieve high-frequency image acquisition.

[0036] This invention employs a brushless motor and a high-precision absolute encoder, which not only provides higher control accuracy but also allows the filter wheel structure to be directly driven by the motor, making the structure more compact and easier to achieve integrated design.

[0037] This invention employs a filter structure in which the diameter in the circumferential direction of the rotating structure is larger than the diameter in the radial direction of the rotating structure, such as a waist-shaped or elliptical shape. When the camera is exposed within this waist-shaped or elliptical section, it can obtain an image in that frequency band, resulting in a higher imaging frequency.

[0038] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0039] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for synchronously controlling a high-speed filter wheel and a camera, characterized in that, The high-speed filter wheel includes a rotating wheel structure and multiple filters evenly distributed on the rotating wheel structure. The diameter of each filter in the circumferential direction of the rotating wheel structure is larger than its diameter in the radial direction of the rotating wheel structure. The high-speed filter wheel is directly driven to a brushless motor, and the tail end of the brushless motor is equipped with a high-precision absolute encoder. The method includes the following steps: In filter mode, the time synchronization device receives instructions from the main control unit, determines the current camera trigger frequency, generates three rising edge synchronization signals, namely the camera trigger signal, the position synchronization trigger signal, and the 1kHz synchronization pulse signal, and sends the camera trigger signal to the camera, and sends the position synchronization trigger signal and the 1kHz synchronization pulse signal to the motor controller. The camera receives instructions from the main control unit and selects a trigger exposure mode, which is either internal trigger exposure or external trigger exposure based on the camera trigger signal; The motor controller receives feedback signals from a high-precision absolute encoder to obtain the current position information of the filter wheel. When the camera trigger exposure mode received by the motor controller from the main control unit is external trigger exposure, the main control unit calculates the rotational speed of the filter wheel based on the camera synchronization trigger frequency and sends the rotational speed to the motor controller. The motor controller determines the theoretical position where the filter will not be blocked each time a position synchronization trigger signal is received, based on the rotational speed of the filter wheel and the number of filters. At the same time, the motor controller obtains the position guidance value through the position synchronization trigger signal and the 1kHz synchronization pulse signal. Under the dual closed-loop of filter wheel speed command and position guidance value, the motor controller drives the filter wheel to rotate. When the position synchronization trigger signal is received, the motor controller determines whether the position error is less than a predetermined value. If so, it feeds back a position synchronization flag to the main control unit, and the main control unit sets the camera to acquire image information.

2. The method for synchronous control of a high-speed filter wheel and a camera according to claim 1, characterized in that, The process by which the motor controller obtains the position guidance value through the position synchronization trigger signal and the 1kHz synchronization pulse signal includes: when the position synchronization trigger signal and the 1kHz synchronization pulse signal are triggered simultaneously, the corresponding theoretical position si is updated, and this theoretical position is assigned to the position guidance value t = s. i When only a 1kHz synchronization pulse signal is received, the position increment value of the 1kHz synchronization pulse signal is added to the position guidance value. At this time, the position guidance value is t = t + k. The formula for calculating the position increment value k of the 1kHz synchronization pulse signal is: k = 360 × f / (1000 × p), where f is the camera synchronization trigger frequency and p is the total number of filters.

3. The method for synchronous control of a high-speed filter wheel and a camera according to claim 1, characterized in that, The formula for calculating the rotational speed s of the filter wheel is as follows: s = 60 × f / p Where f is the camera synchronization trigger frequency and p is the total number of filters.

4. The method for synchronous control of a high-speed filter wheel and a camera according to claim 1, characterized in that, The theoretical position s at which the filter will not be blocked when the position synchronization trigger signal is received for the (i+1)th time is calculated using the following formula. i+1 : s i+1 =s i +360 / p,i=1,2,… Among them, s i This is the theoretical position where the filter will not be blocked when the position synchronization trigger signal is received for the i-th time.

5. The method for synchronous control of a high-speed filter wheel and a camera according to claim 1, characterized in that, The filter is either waist-shaped or elliptical.

6. The method for synchronous control of a high-speed filter wheel and a camera according to claim 1, characterized in that, The total number of filters is 5 or 6.

7. A multispectral imaging system, characterized in that, The system includes a high-speed filter wheel, a brushless motor with a high-precision absolute encoder, a motor controller, a camera, a time synchronization device, and a main control unit. The multispectral imaging system uses the synchronization control method described in any one of claims 1 to 6 to control the rotation of the high-speed filter wheel and the exposure and image acquisition of the camera.

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