Control method for automatically switching reading direction of absolute encoder

Abstract

The invention relates to a method for changing the reading direction of an absolute encoder, which is particularly suitable for a motion control system needing a specific motion direction. The feedback signal direction of the encoder can be dynamically adjusted based on the actual motion direction so as to ensure that accurate motion control and angle feedback can still be realized when the equipment installation direction is wrong. According to the method, hardware does not need to be added, the reading direction is automatically recognized and feedback correction is completed through a built-in encoder conversion table and a direction judgment algorithm in the controller, and the method is suitable for high-precision equipment such as a large-aperture telescope.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of absolute encoder reading direction automatic switching method for precision equipment control system, it is especially applicable to the motion control system of large aperture astronomical telescope.The method is realized by digital signal processing technology, and the absolute encoder reading direction is automatically switched, ensure that direction error that appears in the equipment assembly process can be automatically corrected, so as to ensure the high-precision pointing and stable tracking capability of large aperture telescope, with significant practical application value. BACKGROUND

[0002] Large aperture telescope as indispensable tool in astronomical research, its high-resolution imaging capability enables it to capture the light signal of remote celestial body.In the assembly and debugging process of telescope, the accurate control of shaft system is particularly important, especially the reliability and accuracy of position feedback system directly determines the pointing and tracking accuracy of telescope.Commonly used encoder mainly includes incremental encoder and absolute encoder.Incremental encoder usually needs to initialize position by scanning reference point signal, and absolute encoder can provide real-time absolute position of equipment, without reference point zero reset, so it is widely used in astronomical telescope, celestial tracking platform and the motion control of other precision equipment.

[0003] However, the reading direction of absolute encoder is usually determined by internal mechanism or design, and cannot be changed by modifying wiring or adjusting parameters like incremental encoder.Especially in the assembly process of large aperture telescope shaft system, due to the large volume and complex structure of equipment, if the installation direction of encoder is wrong, the feedback signal direction will be inconsistent with the actual motion direction, which will cause the control system to be unable to correctly calculate the position and angle of equipment, and ultimately affect the pointing accuracy and tracking capability of telescope.Therefore, a method for realizing automatic identification and adjustment of absolute encoder reading direction through digital control is needed to ensure that the telescope can still be accurately controlled in the case of installation direction error. SUMMARY

[0004] The present application aims to provide a control method for realizing absolute encoder reading direction automatic switching without additional hardware equipment, especially suitable for position feedback problems caused by installation direction error in the assembly process of large aperture astronomical telescope.Through the use of digital signal processing technology, the present application can detect the direction of encoder feedback signal in real time, and correct its direction through algorithm, to ensure that the feedback signal is always consistent with the actual motion direction during equipment operation.

[0005] The control method for automatically switching the reading direction of absolute encoder of the present application specifically includes the following steps: First, the feedback signals of multiple absolute encoder readheads are sequentially stored in an encoder conversion table. These signals are then added and subtracted to obtain the forward and reverse signal position values ​​corresponding to each readhead. The forward signal position value is the average of the feedback values ​​of multiple encoder readheads, and the reverse signal position value is the inverse of the forward signal value. For this step, the addition and subtraction processing is implemented in the control system in digital form to form a standardized forward and reverse position signal template for subsequent automatic judgment and compensation correction. The encoder conversion table stores and processes the feedback signals of multiple reading heads to ensure that the system can calculate and identify feedback signals in different directions. When the feedback signal direction error is detected, the system can automatically apply Reverse algorithm Correction.

[0006] Specifically, the use of A (i.e. multiple) absolute encoder reading heads measure the position of a target rotating axis, where is an integer greater than or equal to 2. The encoder reading head is installed at different positions of the rotating shaft or at different coaxial angular positions, and is used to collect the angle feedback signal of the rotating shaft in real time.

[0007] The controller receives The raw position signal of the encoder reading head , , ..., , and store them in the encoder conversion table in sequence In which the index Indicates the encoder reading heads (i = 1, 2, ..., n). To achieve unified position processing and direction compensation, the controller The raw readings of the encoders are Addition and subtraction operations , calculate the average position value under the standard direction , its mathematical expression is as follows: (1) above Indicates the average position measured by multiple encoder reading heads, which is used to represent the standard (positive) angular position of the axis. In order to achieve the reverse correction of the encoder installation direction, the position compensation value is obtained by the following transformation: and direction reversal value : (2) (3) in: represents twice the original mean position value; is the position reverse signal, that is When an encoder has an opposite position reading due to different installation directions, replace its reading with , thereby achieving consistency in the reading direction of all encoders in the system.

[0008] Secondly, the controller determines the directional difference between the current feedback value of a single encoder reading head and the above average position value. If the feedback trend of a reading head is opposite to the average direction, it is identified as a reading direction error. When it is determined that there is a direction error, the system replaces the encoder's reading signal with the reverse position value calculated in real time based on the current multiple reading head feedback signals. , in order to achieve consistent correction of reading direction.

[0009] This step first uses addition operation to calculate the average position value of all reading heads , and based on the formula Generate a position signal with the opposite direction. Subsequently, the system compares the signs of the motor drive angle change direction and the encoder feedback position change direction in real time. The motor drive angle change direction can be determined by the control instruction sign sent by the controller to the motor driver, and the encoder feedback position change direction is determined based on the change trend of the signal collected by each reading head before and after. If the two signs are opposite, it means that the reading direction of the reading head is inconsistent with the actual movement direction. At this time, the system automatically switches the signal of the reading head to the reverse value. , thereby correcting the feedback direction of the reading head to keep it consistent with the actual movement direction.

[0010] Finally, the controller recalculates the overall shaft angle based on the corrected encoder feedback signal, ensuring that the system can still obtain the correct axial position even if some encoders are installed in the reverse direction.

[0011] The encoder feedback signal after direction correction will be used as the input signal of the controller. This signal is used as the feedback signal of the speed loop and position loop to implement the operation control of the telescope altitude axis to ensure that the direction of the telescope pointing and tracking is not affected by the installation position of the encoder.

[0012] The present invention has the following advantages: Digital control: This method relies on the built-in digital signal processing unit (DSP) of the Power UMAC controller to build a feedback signal direction adjustment mechanism that does not require additional hardware intervention. Its core technical logic is as follows: When the position feedback signal output by the Heidenhain grating readhead reverses direction due to mechanical installation errors, the digital signal processing unit in the controller can capture the signal phase characteristics in real time, calculate the phase difference and determine the direction. If the direction is reversed, the controller will execute The method adjusts the direction of the feedback signal through a digital signal processing unit inside the controller, and the signal correction can be realized without adding additional hardware devices, thereby greatly reducing the complexity and cost of the system.

[0013] Precise motion control: the control system uses the corrected signal for subsequent position and speed control, ensuring that the feedback direction always coincides with the actual motion direction, ensuring that the telescope can achieve high-precision motion control and stable tracking under different assembly conditions. BRIEF DESCRIPTION OF DRAWINGS

[0014] Fig. 1 : Schematic diagram of the high-altitude axis structure of a large-aperture telescope. It shows the motion principle, angle range and running direction of the telescope; Fig. 2 : Schematic diagram of the reading head arrangement of the HEIDENHAIN grating encoder. It shows the installation position of the encoder and the signal acquisition method; Fig. 3 : Logic diagram of the data processing of the encoder conversion table. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solution and advantages of the present application clearer, the present application will be further described in combination with the drawings and actual examples of the high-altitude axis.

[0016] In combination with Figs. 1-3 , the present application will be described in detail.

[0017] First, the feedback signals of a plurality of absolute encoder reading heads are sequentially stored in the encoder conversion table, and these signals are subjected to addition and subtraction processing to obtain the positive signal position value and the negative signal position value corresponding to each reading head, respectively. The positive signal position value is the average value of the feedback values of the plurality of encoder reading heads, and the negative signal position value is the opposite of the positive signal value.

[0018] In order to achieve high-precision tracking control of the astronomical telescope, a high-precision position sensor is selected. The present application uses a HEIDENHAIN absolute grating encoder as the position feedback element of the telescope high-altitude axis. The grating circumference is uniformly distributed with 25993 lines, and the inner diameter is 270mm; an absolute position code disc (28bit) HEIDENHAIN TTR ECA 4402 drum is equipped with 4 equally spaced reading heads AK ECA 4410, which meets the resolution requirements of the angle encoder.

[0019]

[0020] In order to improve the measurement accuracy of the system on the shaft angle position, and have the fault tolerance ability to the reading direction error, the even distribution method is adopted for installation. Four reading heads are connected with four channel data acquisition card ACC-84E of UMAC multi-axis motion controller through four shielded twisted pairs, and the connection mode can effectively reduce electromagnetic interference, and guarantee the stability and accuracy of signal transmission. Each reading head is responsible for collecting telescope position information, outputting digital signal and transmitting to Power UMAC motion controller. Meanwhile, in order to further improve the angle measurement accuracy and resolution of the turntable, the position information of the telescope height axis is accurately obtained through the digital quantity addition mode of four evenly distributed reading heads. The average position value after the digital quantity addition of the reading heads is .

[0021] The feedback signal of the reading head is stored and processed through the encoder conversion table, so that the system can calculate and identify the feedback signal in different directions. When the direction error of the feedback signal is detected, the system can automatically apply the reverse algorithm correction condition.

[0022] Detecting running direction In order to realize the consistency detection and correction of the direction, the control system judges the current position change direction through the motion trend in the process of motor running, and compares with the change direction of the feedback position information of the encoder. When it is judged that there is direction error, the system replaces the reading signal of the encoder with the reverse position value calculated in real time according to the feedback signal of the current four reading heads , so as to realize the consistency correction of the reading direction.

[0023] The reading head of the grating position sensor is connected with the four channel data acquisition card through the interface module. The data acquisition card can convert the signal into digital signal and then transmit to Power UMAC controller. The position information collected by the four reading heads is respectively stored in the register corresponding address, and is identified by a unique global variable. The four channel data state observer is built in the controller, which can monitor the variable value corresponding to the storage address of each reading head in real time.

[0024] ​​​The conventional motion range of the height axis is 0° to 90°, wherein 0° usually indicates that the telescope is in the lowest or horizontal state (pointing to the horizon), and 90° indicates that the telescope is in the highest or vertical state (pointing to the zenith). During actual installation, if the absolute encoder is installed on the two sides of the height axis journal in inconsistent directions, the encoder reading direction may be opposite to the actual motion direction, and thus the phenomenon of reverse reading may occur, i.e., the encoder reading is 0° when the telescope points to the zenith and 90° when the telescope points to the horizon.

[0025] To realize the detection and correction of the inconsistent directions, the height axis control system judges the current position change direction through the motion trend during the motor operation, and compares the direction with the feedback position information change direction of the encoder. Specifically, the system calculates the current position change (i.e., the positive or negative direction of the angle change) caused by the motor motion in real time, and reads the change trend of the encoder feedback signal, and when the direction signs of the two are inconsistent, the system determines that the current encoder reading direction is opposite to the actual motion direction.

[0026] Once the above inconsistent direction is detected, the system will automatically trigger the direction reversal mechanism, call the reverse position signal of the encoder conversion table to replace the original feedback value , so as to realize the automatic correction of the encoder feedback direction, ensure that the encoder feedback direction is consistent with the actual running direction of the height axis, and avoid the pointing error caused by the installation direction error.

[0027] Feedback correction Corrected encoder feedback signal The controller participates in the calculation of the overall shaft angle again according to the above-mentioned feedback value , so as to ensure that the system can still obtain the correct shaft position in the case of incorrect installation direction of the encoder.

[0028] In the actual operation process, when the feedback direction of the encoder reading head is consistent with the actual motion direction of the height axis, the system controller takes the position data in the encoder conversion table as the current effective feedback value, i.e., adopts the average value calculated in real time by the multiple reading heads .

[0029] If the system detects that the reading direction of the encoder is opposite to the actual motion direction of the height axis, the controller replaces the feedback value of the encoder with the reverse signal position in the encoder conversion table , i.e., the position information calculated by the reverse calculation .

[0030] Through the above-mentioned manner, the system can automatically correct the inconsistent direction of the encoder feedback according to the real-time motion direction .The feedback correction switching is performed between the two directions, so that the encoder feedback direction is consistent with the actual operation direction of the height axis even if the encoder installation direction is wrong, and the reliability and precision of system control are improved.

[0031] Performing movement: The encoder feedback signal after direction correction is used as the input signal of the controller, and the signal is used as the feedback signal of the speed loop and the position loop to implement the operation control of the height axis of the telescope, so that the direction of the telescope pointing and tracking is not affected by the installation position of the encoder.

[0032] The application provides a control method for automatically switching the reading direction of an absolute encoder without adding additional hardware devices, and is particularly suitable for large-aperture telescopes, astronomical observation equipment and other precision control systems. The method can effectively avoid the direction deviation problem of the control system caused by the wrong installation position of the encoder, greatly reduces the assembly cost and workload, and can significantly improve the pointing accuracy and tracking stability of the equipment.

Claims

1. A control method for automatically switching the reading direction of an absolute encoder, characterized in that: The specific steps include: Will The feedback signals of the absolute encoder reading heads are stored in the encoder conversion table in turn, and these signals are added and subtracted to obtain the positive signal position value and the reverse signal position value corresponding to each reading head. The positive signal position value is The average value of the feedback value of the encoder reading head, the reverse signal position value is the opposite of the forward signal value; The control system determines the direction of current position change based on the motion trend of the motor during operation and compares it with the direction of change of the encoder's feedback position information; When it is determined that there is a direction error, the system replaces the encoder reading signal with the current The reverse position value is calculated in real time from the feedback signal of the reading head , to achieve consistency correction of reading direction; The controller recalculates the overall shaft angle based on the corrected encoder feedback signal. The encoder feedback signal after direction correction will be used as the input signal of the controller. This signal is used as the feedback signal of the speed loop and position loop to implement the operation control of the telescope altitude axis to ensure that the direction of the telescope pointing and tracking is not affected by the installation position of the encoder.

2. The control method for automatically switching the reading direction of an absolute encoder according to claim 1, characterized in that: The addition and subtraction processing is implemented in a digital form in the control system to form a standardized forward and reverse position signal template for subsequent automatic judgment and compensation correction.

3. The control method for automatically switching the reading direction of an absolute encoder according to claim 1, characterized in that: When the feedback signal is detected to be in the wrong direction, the system can automatically apply the reverse algorithm to correct it; Specifically, the use of An absolute encoder reading head measures the position of a target rotating axis, where Is an integer greater than or equal to 2, the encoder reading head is installed at different positions of the rotating shaft or coaxial different angular positions for real-time acquisition of the angle feedback signal of the rotating shaft; The controller receives The raw position signal of an encoder reading head , , ..., , and store them in the encoder conversion table in sequence In which the index Indicates the encoder reading heads (i = 1, 2, ..., n). To achieve unified position processing and direction compensation, the controller The raw readings of the encoders are Addition and subtraction operations , calculate the average position value under the standard direction , its mathematical expression is as follows: (1) above Indicates the average position measured by multiple encoder reading heads, which is used to represent the standard (positive) angular position of the axis. In order to achieve the reverse correction of the encoder installation direction, the position compensation value is obtained by the following transformation: and direction reversal value : (2) (3) in: represents twice the original mean position value; is the position reverse signal, that is When an encoder has an opposite position reading due to different installation directions, replace its reading with , thereby achieving consistency in the reading direction of all encoders in the system.

4. The control method for automatically switching the reading direction of an absolute encoder according to claim 1, characterized in that: The system compares the signs of the motor drive angle change direction and the encoder feedback position change direction in real time; the motor drive angle change direction is determined by the control instruction sign sent by the controller to the motor driver, and the encoder feedback position change direction is determined based on the change trend of the signal collected by each reading head before and after; if the two signs are opposite, it means that the reading direction of the reading head is inconsistent with the actual movement direction. At this time, the system automatically switches the signal of the reading head to the reverse value , thereby correcting the feedback direction of the reading head to keep it consistent with the actual movement direction.

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