CN118129806A - Single-circle absolute photoelectric axial angle encoder based on m-sequence code and design method thereof - Google Patents
Single-circle absolute photoelectric axial angle encoder based on m-sequence code and design method thereof Download PDFInfo
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- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/347—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells using displacement encoding scales
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- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/347—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells using displacement encoding scales
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- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
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Abstract
The invention discloses a single-circle absolute photoelectric shaft angle encoder based on m-sequence codes and a design method thereof, which belong to the technical field of angle measuring devices and solve the problems of low resolution and poor stability of the existing single-circle absolute photoelectric shaft angle encoder in angle measurement. The invention is used for measuring angle position information, angular displacement, angular speed and the like, has high miniaturization degree and simple structure, and can be flexibly applied to various angle measuring environments.
Description
Technical Field
The invention belongs to the technical field of angle measuring devices, and particularly relates to a single-circle absolute photoelectric shaft angle encoder based on m-sequence codes and a design method thereof.
Background
At present, a known photoelectric shaft angle encoder is a sensor for measuring angles by utilizing a photoelectric conversion technology, and has wide application in the fields of high-precision angle measurement, motor control, speed measurement and the like. The photoelectric shaft angle encoder can be divided into two types of absolute encoders and incremental encoders, wherein the absolute encoders can be divided into single-circle absolute encoders and multi-circle absolute encoders according to the number of code channels.
The incremental encoder has a uniform coded disc line spacing, outputs an incremental pulse corresponding to each resolution interval, and a counter performs accumulated count on the output pulse relative to a reference position. The incremental encoder has the advantages of easy realization of miniaturization, quick response and simple structure, and has the defects of needing to independently set a fixed zero point, easily causing the loss of current position data after power failure recovery and having error accumulation phenomenon.
The absolute photoelectric shaft encoder generally uses a binary code disc, code tracks on the code disc are arranged according to a certain rule, and unique binary codes are arranged corresponding to each resolution interval, so that the codes which can be output at different positions are different. The absolute encoder has the advantages that the output code is a single-value function of the shaft angle, the anti-interference capability is strong, the restarting is not needed to return to zero and calibrate after power failure, the accumulated error is avoided, and the like.
The coding and decoding principle and the scribing process of the single-turn absolute type photoelectric shaft encoder code wheel in the market are mature, the single-turn absolute type code wheel can be purchased in batches in the market, the key technology and the main innovation point are the research of the decoding technology and the subdivision algorithm, but the related prior art of the decoding and the subdivision technology of the single-turn absolute type encoder is less, and independent research is needed.
The following problems exist with today's photoelectric shaft encoder:
(1) In the photoelectric axial angle encoder market, absolute encoders occupy a small amount, and most of the absolute encoders are incremental encoders. Mainly because the absolute encoder has lower resolution (most of the resolution is lower than 20 bits), the cost is high, and the stability and the reliability of the absolute encoder are to be improved, and the absolute encoder is not suitable for the working scene with high precision.
(2) In absolute encoder designs, single-turn absolute encoders that utilize photoelectric image conversion have little prior art involvement. Most of the encoders adopt multi-turn absolute photoelectric axial angle encoders encoded by Gray codes, so that the volume of the encoder is large, and the use field is limited.
(3) In the field of miniaturized single-turn absolute photoelectric axial angle encoders, few products apply the coding principle of m-sequence codes and a mode of combining coarse codes and fine codes, and the precision is rarely up to 24 bits or more.
Disclosure of Invention
The invention aims at:
In order to solve the problems of low resolution and poor stability of the existing single-turn absolute photoelectric axial angle encoder in angle measurement, the single-turn absolute photoelectric axial angle encoder based on m-sequence codes and a design method thereof are provided.
The technical scheme adopted by the invention is as follows:
The single-turn absolute photoelectric axial angle encoder based on m-sequence codes comprises a turntable, wherein a code disc is arranged on the top surface of the turntable, an outer ring channel and an inner ring channel are respectively arranged on a plane, close to the outer edge of the code disc, a coding region is arranged between the outer ring channel and the inner ring channel, m-sequence code stripes are uniformly arranged in the coding region, transmission stripes are arranged between the m-sequence code stripes, a light source is further arranged on one side of the code disc, a CMOS image sensor matched with the light source is arranged on the other side of the code disc, and the CMOS image sensor is electrically connected with an FPGA processing plate.
Further, the FPGA processing board comprises an FPGA internal module and a peripheral circuit module, and the FPGA internal module comprises a data processing module and a serial port communication configuration module for communication.
Further, the data processing module comprises a binarization processing module, a pixel counting module, a read-only memory core writing module, a coarse code identification module, a fine code centroid algorithm module, an angle subdivision module and a coarse code and fine code combination module.
Further, the FPGA internal module further comprises an image sensor drive configuration module, an AD drive configuration module and a code value data module communicated with the data processing module.
Further, the peripheral circuit module comprises an AD drive configuration module, an AD analog-to-digital conversion module, a CMOS illumination image acquisition module and a data display window module, wherein the AD analog-to-digital conversion module is in communication connection with the data processing module, the CMOS illumination image acquisition module is connected with the image sensor drive configuration module, and the data display window module is connected with the serial port communication configuration module.
Further, the peripheral circuit module further comprises a power circuit module, a level conversion circuit module, a clock circuit module, a reset circuit module and a chip configuration JTAG circuit module.
The design method of the single-turn absolute photoelectric axial angle encoder based on the m-sequence code comprises the following steps:
Step A, designing m sequence codes:
Setting an encoder to read n-bit code numbers each time to perform angle judgment, setting m-sequence codes as cyclic sequence codes, wherein one group of codes are single-value functions of angles, scribing 2 n-1 code values on code channels in a coding area (11) on a code disc (2), moving the read sequence codes by one bit when the encoder rotates by one resolution, simultaneously moving out one-bit codes and moving in one-bit codes in a sequence code reading range, and forming a new group of sequence codes by the unchanged n-1-bit codes and the newly moved one-bit codes, namely realizing the judgment of the angles of corresponding positions by reading the new group of sequence codes;
step B, designing the scribing of the code wheel (2):
Setting m-sequence code stripes as coarse codes with the width being larger than that of transmission stripes, wherein the transmission stripes are fine codes with the width being smaller than that of the m-sequence code stripes, designing the mechanical structure of the code disc (2) in a scribing way, setting part of the m-sequence code stripes as bright lines and performing chromium plating treatment, setting the rest part of the m-sequence code stripes as transmission areas, inserting the fine codes into the transmission areas between adjacent coarse codes for subdivision treatment, and designing code channels on the code disc (2) by adopting 12-bit codes;
step C, designing a decoding principle:
Decoding comprises two parts of coarse code identification and fine code identification; and (3) identifying the rough codes: a ROM table of a coarse code is preset in the FPGA, and m-sequence codes are identified in a table look-up mode to obtain angle position information of the coarse code; identification of fine codes: identifying the center of the fine code by adopting a centroid algorithm with a threshold value, and cracking a corresponding angle value by calculating the movement of the center of the fine code; final angular position = coarse code angle value + fine code angle value;
Step D, designing a hardware circuit:
The circuit structure is designed according to the decoding principle: a photoelectric coupling device linear array CMOS is selected as photoelectric receiving conversion equipment, a circuit board is divided into an FPGA internal circuit and a peripheral circuit, light emitted by a light source (3) is irradiated on a code disc (2) after being collimated and expanded by a lens, a CMOS image sensor (4) of the peripheral circuit receives an image transmitted through the code disc (2), the acquired image is converted by an AD analog-digital conversion module in the peripheral circuit, an optical signal is converted into an electric signal, and the electric signal is transmitted into a data processing module in the FPGA internal circuit at the rear end to decode image information.
Further, in the step B, the width of the coarse code is set to 0.04mm, the interval is set to 0.04mm, the width of the fine code is set to 0.02mm and set to be bright line, the line length of the code track is 1mm, the grating period is 0.087912 °, wherein the middle diameter wide angle of the coarse code is 0.044502 °, the middle diameter wide angle of the fine code is 0.022251 °, the interval wide angle of the coarse code and the fine code is 0.010580 °, and the width corresponding to a group of 12-bit code values is 0.92mm.
The specific chinese meaning of the related english abbreviations mentioned in the present invention is as follows:
FPGA (Field Programmable GATE ARRAY): a programmable gate array;
CMOS (Complementary Metal Oxide Semiconductor): the complementary metal oxide semiconductor is a readable and writable RAM chip (Random Access Memory ) on the main board and is used for storing the hardware configuration information of the current system and certain parameters set by a user;
AD (Analog-to-digital): an analog-to-digital converter for converting a continuous signal in analog form into a discrete signal in digital form;
ROM (Read-Only Memory): a read-only memory;
JTAG (Joint Test Action Group): and (5) combining the test working groups.
In summary, due to the adoption of the technical scheme, the beneficial effects of the invention are as follows:
The device has high miniaturization degree and simple structure, and can directly read the angle by only one code disc, reading head and processing plate after improvement; meanwhile, the invention occupies small space, the code disc adopts m-sequence codes and adds fine codes, the space utilization rate is high, the scribing is compact, the volume is small, the outer diameter of the code disc is only 110mm, and the invention can be flexibly applied to various narrow environments requiring angle measurement.
The device adopts a coding mode of combining coarse codes and fine codes, develops a corresponding decoding algorithm, can realize accurate measurement of angles, has resolution of 24 bits, has angle stability within 1 angular second, can identify the rotating speed of 420 degrees per second, and is superior to most of the encoders of the same type on the market.
The device adopts the absolute angle measurement principle, so that the zero point can be marked randomly during angle measurement, the device can read normally after power failure and restarting, and the zero point does not need to be marked again.
Drawings
FIG. 1 is a block diagram of a single-turn absolute encoder of the present invention;
FIG. 2 is a partial view of m-code scribing on a code wheel according to the present invention;
FIG. 3 is a schematic diagram of a scribing effect of a code wheel according to the present invention;
FIG. 4 is a schematic diagram of the internal structure of the FPGA of the present invention;
Fig. 5 is a waveform diagram of a CMOS illumination image acquisition image according to the present invention.
The marks in the figure: the device comprises a 1-turntable, a 2-code disc, a 3-light source, a 4-CMOS image sensor, a 5-FPGA processing board, a 6-bright stripe coarse code, a 7-dark stripe coarse code, an 8-transmission stripe fine code, a 9-outer loop, a 10-inner loop and an 11-coding region.
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The invention provides a single-circle absolute photoelectric axial angle encoder based on m codes, which can reach 24-bit high resolution, maintain the reading stability at +/-0.5 angular seconds, can recognize the angular speed of 420 DEG/second, has simple structure and small volume, and can be applied to various industries requiring angle measurement, such as military industry, aerospace, elevators, textiles and the like.
As shown in fig. 1, m-sequence codes (thick codes) are uniformly inscribed on a plane on a code wheel 2 on a turntable 1, and black stripes (thin codes) are inserted in each thick code, forming a sequence code distribution as shown in fig. 2. After the light emitted by the light source 3 is collimated and expanded by a lens, the light is irradiated on the code disc 2, a high-precision linear array photoelectric coupling device linear array CMOS is placed on the same side or different sides of the code disc 2, the acquired image is converted into an electric signal through AD conversion, the electric signal is transmitted into a miniaturized FPGA data processing board at the rear end to decode the image information, and finally the decoded waveform is shown in figure 5. The position information of the angle can be successfully obtained after the image is decoded. The same side of the code wheel 2 adopts a reflective light path structure, and the different side of the code wheel 2 adopts a transmissive light path structure.
The invention takes the design of the marking of the code wheel 2, the design of the decoding principle algorithm and the design of a hardware circuit as the key points, selects the linear array CMOS of the photoelectric coupling device as photoelectric receiving and converting equipment, realizes the accurate positioning of stripes by the encoder subdivision technology, and realizes the scheme of the 24-bit single-circle absolute photoelectric axial angle encoder based on the m code sequence. The following is a detailed description of each step:
(1) Scribing design of the code wheel 2:
m-sequence code principle: the m-sequence code is a cyclic set of sequence codes and during a cyclic period, the set of codes is a single value function of angle, so only 2 n-1（2n states excluding all 0 need to be scored on the code track). When the resolution is rotated, one bit is moved, the n-1 bit code which is unchanged and the one bit code which is newly moved in form a new group of codes, and so on, the angle of the corresponding position can be judged by reading the group of sequence codes at the moment.
The mechanical structure design of the code wheel 2 is: as shown in fig. 2, the "black stripe" is encoded as a bright line, i.e., a bright stripe rough code 6, which is subjected to a chrome plating treatment; the dark stripe rough code 7 is a transmission area and is not processed. The code channel adopts 4095 coarse codes with the width of 0.04mm and the interval of 0.04mm, fine codes are inserted between the two coarse codes for subdivision treatment, the fine codes with the width of 0.02mm are bright lines, and the chromium plating treatment is also carried out. As shown in FIG. 3, the scored code wheel 2 has an outer diameter of 110mm, and uniformly distributed coarse codes with a width of 0.04mm, and the number of the coarse codes is 4095. The line length of the code channel is 1mm, the grating period is 0.087912 degrees, the diameter-width angle in the coarse code is 0.044502 degrees, the diameter-width angle in the fine code is 0.022251 degrees, the interval-width angle between the coarse code and the fine code is 0.010580 degrees, and the corresponding width of a group of 12-bit code values is 0.92mm, namely the width of a group interval of 12-bit coarse code plus 11.
(2) And (3) designing a decoding principle:
The decoding comprises a coarse code identification part and a fine code identification part. And (3) identifying the rough codes: and a ROM table of the coarse code is preset in the FPGA, and the m-sequence code (the coarse code) is identified in a direct table look-up mode, so that the angle position information of the coarse code can be obtained. Identification of fine codes: and identifying the center of the fine code by adopting a centroid algorithm with a threshold value, and cracking a corresponding angle value by calculating the position movement of the center of the fine code. Final angular position = coarse + fine.
(3) Hardware circuit design:
According to the decoding principle, the designed circuit structure is as shown in fig. 4: the whole circuit board is divided into an FPGA internal functional block and a peripheral circuit. In order to realize decoding of the acquired images, a binarization processing module, a coarse code identification module, a fine code centroid algorithm module, a coarse code and fine code combination module and a serial port communication configuration module for communication are required to be designed in the FPGA.
The types of key electronic components can be selected as follows:
AD converter: AD9826;
An image sensor: pinus maritima s15611;
FPGA processing chip: altera-ep4ce6e22c8.
Alternatively, the invention may be implemented as follows:
The layout of the code wheel 2, the light source 3, the CMOS image sensor 4 and the FPGA processing board 5 can be changed at will, but the positions of the parts meet the following characteristics: the image of the code wheel 2 irradiated by the light source 3 is collected by the CMOS image sensor 4 and finally is transmitted to the FPGA data processing board for processing.
The light source 3 can be replaced by a light source 3 with arbitrary power, different colors and different collimation degrees.
The material of the code wheel 2 can be replaced by glass, such as metal, alloy and other objects with better reflectivity. The size of the code wheel 2 can be replaced by any size from an outer diameter of 110 mm.
The CMOS image sensor 4 may be replaced with another CCD (Charge-coupled Device) on the market, or a CMOS image sensor of a different model.
The chip of the FPGA processing board 5 may be replaced with other chips of different models.
The FPGA implementation algorithm may be other edge detection algorithms or sub-pixel detection algorithms including, but not limited to, gaussian fitting, sobel (sobel operator, an edge detection algorithm), canny (Canny's edge detection algorithm, a multi-level edge detection algorithm proposed by John f Canny in 1986), matrix edge algorithms, and the like.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.
Claims (8)
1. The single-turn absolute photoelectric shaft angle encoder based on m-sequence codes is characterized by comprising a turntable (1), wherein a code disc (2) is arranged on the top surface of the turntable (1), an outer loop (9) and an inner loop (10) are respectively arranged on a plane, which is close to the outer edge of the code disc (2), a coding region (11) is arranged between the outer loop (9) and the inner loop (10), m-sequence code stripes are uniformly arranged in the coding region (11), transmission stripes are arranged between the m-sequence code stripes, a light source (3) is further arranged on one side of the code disc (2), a CMOS image sensor (4) matched with the light source (3) is arranged on the other side of the code disc (2), and the CMOS image sensor (4) is electrically connected with an FPGA processing board (5).
2. The m-sequence code based single-turn absolute optoelectronic shaft encoder of claim 1, wherein the FPGA processing board (5) comprises an FPGA internal module and a peripheral circuit module, the FPGA internal module comprising a data processing module and a serial communication configuration module for communication.
3. The m-sequence code based single-turn absolute photoelectric axial angle encoder of claim 2, wherein the data processing module comprises a binarization processing module, a pixel counting module, a read-only memory core writing module, a coarse code identification module, a fine code centroid algorithm module, an angle subdivision module and a coarse code and fine code combination module.
4. The m-sequence code based single-turn absolute photo-axial encoder of claim 2, wherein the FPGA internal module further comprises an image sensor drive configuration module, an AD drive configuration module, and a code value data module in communication with the data processing module.
5. The m-sequence code based single-turn absolute photoelectric axial angle encoder of claim 4, wherein the peripheral circuit module comprises an AD analog-to-digital conversion module communicatively connected with the AD drive configuration module and the data processing module, a CMOS illumination image acquisition module connected with the image sensor drive configuration module, and a data display window module connected with the serial communication configuration module.
6. The m-sequence code based single-turn absolute optoelectronic shaft encoder of claim 2, wherein the peripheral circuit module further comprises a power circuit module, a level shift circuit module, a clock circuit module, a reset circuit module, and a chip configuration JTAG circuit module.
7. A method for designing a single-turn absolute photoelectric axial angle encoder based on m-sequence codes, which is used for designing the single-turn absolute photoelectric axial angle encoder based on m-sequence codes as claimed in any one of claims 1 to 6, and is characterized by comprising the following steps:
Step A, designing m sequence codes:
Setting an encoder to read n-bit code numbers each time to perform angle judgment, setting m-sequence codes as cyclic sequence codes, wherein one group of codes are single-value functions of angles, scribing 2 n-1 code values on code channels in a coding area (11) on a code disc (2), moving the read sequence codes by one bit when the encoder rotates by one resolution, simultaneously moving out one-bit codes and moving in one-bit codes in a sequence code reading range, and forming a new group of sequence codes by the unchanged n-1-bit codes and the newly moved one-bit codes, namely realizing the judgment of the angles of corresponding positions by reading the new group of sequence codes;
step B, designing the scribing of the code wheel (2):
Setting m-sequence code stripes as coarse codes with the width being larger than that of transmission stripes, wherein the transmission stripes are fine codes with the width being smaller than that of the m-sequence code stripes, designing the mechanical structure of the code disc (2) in a scribing way, setting part of the m-sequence code stripes as bright lines and performing chromium plating treatment, setting the rest part of the m-sequence code stripes as transmission areas, inserting the fine codes into the transmission areas between adjacent coarse codes for subdivision treatment, and designing code channels on the code disc (2) by adopting 12-bit codes;
step C, designing a decoding principle:
Decoding comprises two parts of coarse code identification and fine code identification; and (3) identifying the rough codes: a ROM table of a coarse code is preset in the FPGA, and m-sequence codes are identified in a table look-up mode to obtain angle position information of the coarse code; identification of fine codes: identifying the center of the fine code by adopting a centroid algorithm with a threshold value, and cracking a corresponding angle value by calculating the movement of the center of the fine code; final angular position = coarse code angle value + fine code angle value;
Step D, designing a hardware circuit:
The circuit structure is designed according to the decoding principle: a photoelectric coupling device linear array CMOS is selected as photoelectric receiving conversion equipment, a circuit board is divided into an FPGA internal circuit and a peripheral circuit, light emitted by a light source (3) is irradiated on a code disc (2) after being collimated and expanded by a lens, a CMOS image sensor (4) of the peripheral circuit receives an image transmitted through the code disc (2), the acquired image is converted by an AD analog-digital conversion module in the peripheral circuit, an optical signal is converted into an electric signal, and the electric signal is transmitted into a data processing module in the FPGA internal circuit at the rear end to decode image information.
8. The method for designing an m-sequence code based single-turn absolute photoelectric axial encoder according to claim 7, wherein in the step B, the width of the coarse code is set to 0.04mm, the interval is set to 0.04mm, the width of the fine code is set to 0.02mm and set to be bright line, the line length of the code track is 1mm, the grating period is 0.087912 °, wherein the pitch diameter width angle of the coarse code is 0.044502 °, the pitch diameter width angle of the fine code is 0.022251 °, the pitch width angle of the coarse code and the fine code is 0.010580 °, and the width corresponding to a set of 12-bit code values is 0.92mm.
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