A method and device for measuring the absolute rotational position of a planar CCD

Abstract

The present invention relates to the field of rotational position measurement technology, and discloses a planar CCD absolute rotational position measurement method and device. By shooting a simple image of a rotating disk rotating, using a cross ratio algorithm and a spiral curve polar coordinate position, the absolute rotational position can be obtained, and by repeatedly shooting images and calculating, the real-time rotational position measurement can be realized; and in this device, the rotating shaft is installed at the center of the rotating disk, the shooting module is installed on one side of the rotating disk for acquiring image data, the light source is installed next to the shooting module or on the opposite side of the shooting module to provide a light source, and a spiral curve layer is also provided on the rotating disk. The present invention simplifies the production of the rotating disk, the assembly of the equipment and the equipment technology system, and the measurement of the rotational position can be completed by using a simple shooting module and a spiral curve layer, and the real-time measurement of the rotational position can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of rotational position measurement, and in particular to a method and device for measuring the absolute rotational position of a planar CCD. Background Art

[0002] Currently, the main method for precise measurement of the rotational angle is to use a circular grating. A circular grating is a circular dividing element with a large number of uniformly distributed transparent and opaque intervals engraved on a circular ring area on the surface of a glass disc. According to the type of measurement data, it is divided into two types: incremental and absolute measurement.

[0003] For incremental measurement, each obtained measurement data is the relative angular displacement relative to the position before measurement. Therefore, in order to obtain the current rotational position, the system needs to accumulate the rotational data each time. If the system loses this data midway, it needs to move to the initial position before it can start recording the rotational position again.

[0004] For absolute measurement, each obtained measurement data is the current rotational position. The system does not need to record the rotational history. However, this type of sensor is more complex in structure than the incremental type. Currently, when using a circular grating, the transmissive type is mostly adopted. Therefore, the grating disc is mostly made of glass material, which will reduce the shock resistance of the device to a certain extent. In the scenario of precise measurement, this type of device also has the following problems:

[0005] (1) It is difficult to fabricate a high-resolution precision grating; the commonly used fabrication methods currently are mechanical scribing, photoelectric scribing, and holographic scribing. However, all of them require expensive equipment, and each fabrication takes a long time. During the fabrication time, it is necessary to ensure that the equipment can operate precisely for a long time and there is no environmental vibration interference.

[0006] (2) The assembly accuracy requirements for precision gratings and optoelectronic signal detection components are high, and the assembly time is long. This process relies on senior technicians and often requires manual fine repair of the installation surface, which has high requirements for the skills and experience of personnel and is difficult to achieve mass production.

[0007] (3) The involved technologies are diverse and complex. It involves precision machinery manufacturing, optoelectronic signal acquisition, signal processing hardware and software development, etc. It is difficult and costly to gather and coordinate multiple technicians for product research and development and production. Summary of the Invention

[0008] The technical problem to be solved by the present invention is: in view of the above problems, a method and device for measuring the absolute rotational position of a planar CCD are provided, which simplifies the fabrication of the rotating disc, as well as the assembly and technical system of the device, and can achieve precise measurement.

[0009] The technical solution adopted by the present invention is as follows: A method for measuring the absolute rotational position of a planar CCD, comprising the following steps:

[0010] S1: Take an image of the rotating disk during rotation through the shooting module;

[0011] S2: Select two points on the image, and use the cross-ratio algorithm to calculate the actual distance between the two points on the rotating disk;

[0012] S3: Substitute the distance value of the two points into the polar coordinate equation of the spiral curve, calculate the angle of the rotational position, and complete the measurement of the rotational position;

[0013] S3: Repeat S1, S2, and S3 to achieve real-time measurement of the rotational position of the rotating disk.

[0014] Further, in the cross-ratio algorithm, four points A, B, C, and D are set on the image. A is the reference point, B is the point at a unit length from point A, C is the point at an actual distance c from the reference point A, and D is the infinite point. The two points selected in S2 are point A and point C respectively; the cross-ratio formula is as follows:

[0015]

[0016] Let the distance from point A to point B on the image be x 1 , the distance from point A to point C be x c , and the distance from point A to point D be x 2 ; then the above formula is as follows:

[0017]

[0018] Further, before S1, it also includes calibrating the measuring device. The specific steps of the calibration are as follows:

[0019] Step a: Rotate the rotating disk, take a photo every time it rotates by an angle a, and after rotating 360 degrees, obtain an image sequence PS, and record the rotation angle corresponding to each image;

[0020] Step b: According to the cross-ratio algorithm, find the image Pmax with the largest AC image distance in the image sequence PS, and find the rotation angle corresponding to Pmax;

[0021] Step c: Rotate the rotating disk to the rotation angle value of Pmax, and rotate it at an interval angle b, where b is less than or equal to a;

[0022] Step d: Repeat step a and step b, and use the obtained maximum image Pmax as the origin of the measuring device;

[0023] Step e: Starting from the position corresponding to the origin of the measuring device, rotate by a known angle n times in sequence and take images. Using the cross-ratio algorithm, calculate the coordinate values of points B and D in the cross-ratio algorithm, and store the calculation results in the device system to complete the device calibration work; n is a natural number greater than or equal to 2.

[0024] Further, the image includes a basic circle identification image and a spiral curve image.

[0025] Further, in S2, take a horizontal midline passing through the center of the rotating disk on the image. The intersection points of the horizontal midline with the basic circle identification image and the spiral curve image are A and C. Take the intersection points A and C, and use the cross-ratio algorithm to calculate the actual distance between points A and C on the rotating disk.

[0026] Further, the polar coordinate equation formula of the spiral curve is as follows:

[0027] r = r0 + θ·a;

[0028] Where r0 is the radius of the basic circle identification set fixedly, a is a fixed constant, r is the actual distance between two points selected on the image on the rotating disk, and θ is the rotation position angle and θ ∈ [0, 2π].

[0029] A planar CCD absolute rotation position measuring device includes: a rotating disk, a rotating shaft, a light source, and a shooting module. The rotating shaft passes through the center of the rotating disk and is fixedly connected to the rotating disk; the shooting module is arranged on one side of the rotating disk to shoot the rotating disk; the light source is arranged on one side of the rotating disk to provide the light source required during shooting; a spiral curve layer is provided on the surface of the rotating disk.

[0030] Further, when the light source and the shooting module are arranged on the same side of the rotating disk, the measuring device is a reflective structure; when the light source is arranged on the opposite side of the shooting module, the measuring device is a projection structure.

[0031] Further, the light source uses an LED that emits white light or monochromatic light.

[0032] Further, the shooting module uses a camera module or a camera module.

[0033] Compared with the prior art, the beneficial effects of adopting the above technical solutions are: The present invention uses a mature camera module, and by taking an image of a simple pattern, the absolute rotation position can be obtained; this technical solution has no excessive requirements for the manufacturing and installation accuracy of each component, and the measurement accuracy can be ensured through the measurement algorithm and calibration; and the calibration process is easy to achieve automation and unattended, which is convenient for batch production of the device. Description of the Drawings

[0034] Figure 1 is the image captured by the present invention;

[0035] Figure 2 is the image of the present invention with a horizontal center line;

[0036] Figure 3 is a schematic diagram of the cross - ratio algorithm;

[0037] Figure 4 is a top view of the rotating disk;

[0038] Figure 5 is a schematic diagram of the reflective structure;

[0039] Figure 6 is a schematic diagram of the projection structure.

[0040] Reference numerals: 1 - local edge image of the spiral curve, 2 - local edge image of the base circle, 3 - horizontal center line, 4 - base circle, 5 - rotating disk, 6 - center of the rotating shaft, 7 - spiral curve layer, 8 - shooting module, 9 - light source. Detailed implementation manners

[0041] The present invention will be further described below with reference to the accompanying drawings.

[0042] Embodiment 1

[0043] The present invention provides a method for measuring the absolute rotational position of a planar CCD to achieve precise measurement, including the following steps:

[0044] 1. Take a picture of the rotating disk during rotation through the shooting module. When the rotating disk rotates at a high speed, the stroboscopic shooting method can be used to obtain an instantaneous rotating image; when rotating at a medium - low speed, the general shooting method can be used to obtain a clear image of the rotating disk. The obtained rotating image is as Figure 1 shown, and the figure shows the local edge image of the spiral line and the local edge image of the base circle.

[0045] 2. As Figure 2 shown, take a horizontal center line of the image on the image. The horizontal center line must pass through the center point of the rotating disk. When installing the shooting module, finely adjust the shooting module to ensure that a horizontal center line passing through the center of the image can be obtained in the captured image. The intersection points of the horizontal center line with the local edge image of the base circle and the spiral curve image are A and C. Take the intersection points A and C, and use the cross - ratio algorithm to calculate the actual distance between points A and C on the rotating disk.

[0046] Cross - ratio algorithm formula:

[0047] R(AB,CD) = AC * BD / (BC * AD); (1)

[0048] Points A, B, C, and D are collinear, where A is the reference point, B is the point at a unit length from point A, C is the point at a distance c from the reference point, and D is the point at infinity. Then the cross-ratio is as follows:

[0049]

[0050] As Figure 3 shown, the intersection points of the horizontal center line of the image with the basic circle and the edge of the spiral curve are points A and C respectively. At the same time, on the horizontal center line, the point B, which is at a unit length from point A and outside the basic circle, and the image point of the point at infinity on the horizontal center line is D. That is, points A and C are actual existing points in the image, and points B and D are non-existing points on the image.

[0051] Let the lengths of line segments AB, AC, and AD on the image be x 1 、x c 、x 2 respectively; the actual distance from point C to point A on the rotating disk is c, where x c (x c can be calculated from the image) and c are known quantities. Then there are the following relationships:

[0052]

[0053] For the above equation, knowing at least 2 different coordinates of point C can solve for x 1 、x 2 ; when there are more than 2 coordinates of point C, the least squares method can be used to solve for x 1 、x 2 , which helps to improve the solution accuracy.

[0054] When measuring the rotation angle, x 1 、x 2 、x c in Equation 3 are known quantities. The image coordinates of point C are obtained on the image, and the distance of x c on the image is calculated from the image coordinates of point A. The value of c is the quantity to be solved. Then it can be directly solved using Equation 3.

[0055] III. After obtaining the value of c, substitute it into the polar coordinate equation of the spiral curve for calculation. The equation is as follows:

[0056] r = r0 + θ·a; (4)

[0057] Among them, r0 is the radius of the basic circle identifier set fixedly, a is a fixed constant, r is the actual distance between points A and C, that is, the value of c. So after obtaining the value of c, only by substituting it into the equation can the value of the rotation angle θ be obtained, and

[0058] θ ∈ [0 2π], Figure 4 which is the top view image of the rotating disk.

[0059] IV. Repeat the above steps I, II, and III to measure the rotation angle of the rotating disk in real time, realizing the real-time measurement of the rotation angle of the rotating disk. At the same time, measurements such as acceleration can also be completed.

[0060] Before using this method for testing, it is also necessary to calibrate the test equipment. The calibration steps are as follows:

[0061] (1) Rotate the rotating disk 360 degrees. Take a photo every time the rotation angle is a, where a is less than 360 degrees. Finally, obtain an image sequence PS, and at the same time record the corresponding rotation angle a_real of each image (this angle is output by the auxiliary rotation measurement device); when the rotating disk rotates, its normal does not change, that is, there is no relative position change with the shooting module.

[0062] (2) According to the above algorithm, find the image Pmax with the largest distance between AC images in PS, and at the same time obtain its corresponding a_real value.

[0063] (3) Rotate to near this a_real value and make micro-rotations at an interval angle b (b <= a), and record the images and actual rotation angles according to step (1). Repeat the operation in step (2) for the obtained images. The obtained image Pmax_real is the origin of this device.

[0064] (4) Starting from the position corresponding to the image Pmax_real, rotate n times by known angles in sequence and take pictures. When n >= 2 and there are coordinates of multiple different C points, use the above cross-ratio algorithm to solve for x 1 、x 2 , that is, calculate the values of points B and D on the horizontal center line, and permanently store the calculation results in the device system to complete the device calibration work.

[0065] When the device is calibrated, by fixing the coordinate values of points A and C, the coordinate values of points B and D can be calculated. After the device is calibrated and tested, in using the above test method, because the coordinate values of B and D on the horizontal center line have been fixed, and there is no relative position change between the rotating disk and the shooting module, so through formula 3, the actual distance c between points A and C can be easily obtained. Substitute the c value into formula 4 to find the rotation angle, which is simple, convenient, and accurate.

[0066] Embodiment 2

[0067] The present invention also provides a planar CCD absolute rotation position measurement device, including: a rotating disk, a rotating shaft, a white light source, and a camera module. The rotating shaft passes through the center of the rotating disk and is fixedly connected to the rotating disk, and the rotating disk rotates together with the rotating shaft.

[0068] AsFigure 5 As shown, a white light source and a camera module are arranged on the upper side of a rotating disk, providing a light source and taking images; at this time, the measuring device is of a reflective structure.

[0069] The surface of the rotating disk is also covered with a spiral curve layer, which is processed by commercial printing technology.

[0070] Embodiment 3

[0071] On the basis of Embodiment 2, preferably, the white light is replaced by monochromatic light.

[0072] Embodiment 4

[0073] On the basis of Embodiment 2 / 3, preferably, the camera module is replaced by a camera module.

[0074] Embodiment 5

[0075] On the basis of Embodiment 2 / 3 / 4, preferably, as Figure 6 shown, the camera module is arranged on the upper side of the rotating disk, and the light source is arranged on the opposite side of the camera module, that is, the lower side of the rotating disk. At this time, the measuring device is of a projection structure.

[0076] The present invention is not limited to the foregoing specific embodiments. The present invention extends to any new feature or any new combination disclosed in this specification, as well as any new method or process step or any new combination disclosed. If those skilled in the art make non-substantive changes or improvements without departing from the spirit of the present invention, they should fall within the scope of protection of the claims of the present invention.

Claims

1. A method for measuring the absolute rotational position of a planar CCD, characterized in that, it includes: S1: Taking an image of the rotating disk when it rotates through a shooting module; S2: Selecting two points on the image and calculating the actual distance between the two points on the rotating disk using the cross - ratio algorithm; S3: Substituting the distance value between the two points into the polar coordinate equation of the spiral curve to calculate the angle of the rotational position and completing the measurement of the rotational position; S4: Repeating S1, S2, and S3 to achieve real - time measurement of the rotational position of the rotating disk; In the cross - ratio algorithm, four points A, B, C, and D are set on the image. A is the reference point, B is the point at a unit length from point A, C is the point at an actual distance c from the reference point A, and D is the point at infinity. The two points selected in S2 are point A and point C respectively. The cross - ratio formula is as follows: Let the distance from point A to point B on the image be x 1 , the distance from point A to point C be x c , and the distance from point A to point D be x 2 ; then the above formula is as follows: Before S1, it also includes calibrating the measuring device. The specific steps of the calibration are: Step a: Rotate the rotating disk. Take a photo every time it rotates by an angle a. After rotating 360 degrees, obtain an image sequence PS and record the rotation angle corresponding to each image; Step b: According to the cross - ratio algorithm, find the image Pmax with the maximum AC image distance in the image sequence PS and find the rotation angle corresponding to Pmax; Step c: Rotate the rotating disk to the rotation angle value of Pmax and rotate at an interval angle b, where b is less than or equal to a; Step d: Repeat step a and step b, and take the obtained maximum image Pmax as the origin of the measuring device; Step e: Starting from the position corresponding to the origin of the measuring device, rotate n times by known angles in sequence and take images. Using the cross - ratio algorithm, calculate the coordinate values of points B and D in the cross - ratio algorithm and store the calculation results in the device system to complete the device calibration work; n is a natural number greater than or equal to 2.

2. A method for measuring the absolute rotational position of a planar CCD according to claim 1, characterized in that, the image includes a basic circle identification image and a spiral curve image.

3. A method for measuring the absolute rotational position of a planar CCD according to claim 1, characterized in that, in S2, take a horizontal median line passing through the center of the rotating disk on the image. The intersection points of the horizontal median line with the basic circle identification image and the spiral curve image are A and C. Take the intersection points A and C and use the cross - ratio algorithm to calculate the actual distance between points A and C on the rotating disk.

4. A method for measuring the absolute rotational position of a planar CCD according to claim 1, characterized in that, the polar coordinate equation formula of the spiral curve is as follows: r = r0 + θ·a; where r0 is the radius of the fixed basic circle identification, a is a fixed constant, r is the actual distance between the two points selected on the image on the rotating disk, and θ is the rotational position angle and θ ∈ [0, 2π].

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