A method for searching the starting zero position of a servo motor for a sewing machine

Abstract

The present invention provides a method for searching for the starting zero position of a servo motor for a sewing machine, belonging to the technical field of motor control. It solves the problem that the existing method of searching for the zero position by low-speed rotation results in a long searching time and thus low working efficiency. The method for searching for the starting zero position of a servo motor for a sewing machine, on which an incremental encoder is installed, includes the following steps: S1, detecting the initial point position; S2, detecting the actual rotation angle of the servo motor at the zero position point; S3, detecting the actual rotation angle of the servo motor during reverse rotation; S4, performing position control to find the zero position. The method for searching for the starting zero position of a servo motor for a sewing machine has the advantages of short time, high-speed and high-precision zero position searching.

Description

Technical Field

[0001] The present invention belongs to the technical field of motor control and relates to a method for searching the zero position at startup for a servo motor of a sewing machine. Background Art

[0002] A servo system is an automatic control system that enables the output controlled variables such as the position, orientation, and state of an object to follow any change in the input target (or given value). Servo mainly relies on pulses for positioning. Basically, it can be understood that when the servo motor receives 1 pulse, it will rotate by an angle corresponding to 1 pulse, thereby achieving displacement. Because the servo motor itself has the function of emitting pulses, every time the servo motor rotates by an angle, it will emit a corresponding number of pulses. In this way, it forms a correspondence, or a closed loop, with the pulses received by the servo motor. In this way, the system will know how many pulses have been sent to the servo motor and how many pulses have been received back. In this way, the rotation of the motor can be accurately controlled, thereby achieving accurate positioning, which can reach 0.001 mm.

[0003] For the servo motor of the sewing machine servo system, it is necessary to automatically find the zero position of the motor every time it starts up and runs. The working speed of the servo motor used for the sewing machine is relatively high. If it searches for the zero position at high speed after starting up and running, due to the inertia existing after the servo motor detects the zero position and stops, the inertia brought by high speed is relatively large, so the motor cannot immediately stop at the zero position. After stopping, the deviation from the actual zero position is relatively large, resulting in poor accuracy of zero position search and positioning. Currently, generally, it runs at a low speed of 200 - 300 rpm to search for the zero position. When the system detects the zero position signal, the servo motor immediately stops, and the zero position search ends. This method has relatively high accuracy of zero position search and positioning. However, there are still mainly the following problems: Since it uses low-speed rotation to search for the zero position, the time is relatively long, and the sewing worker has to wait for the zero position search to be completed before normal operation, reducing work efficiency. Summary of the Invention

[0004] The purpose of the present invention is to solve the above technical problems and propose a method for searching the zero position at startup for a servo motor of a sewing machine with high speed and high precision positioning.

[0005] The purpose of the present invention can be achieved by the following technical solutions: A method for searching the zero position at startup for a servo motor of a sewing machine, an incremental encoder is installed on the servo motor, and it includes the following steps:

[0006] S1. Initial point position detection: When the sewing machine system starts running, the position of the initial point of the servo motor is determined by detecting the Z-signal level output by the Z-signal optocoupler, whether it is on the left or right side of the zero position. Accordingly, the position controller outputs a corresponding rotational position command to determine the rotational direction towards the zero position, and at the same time, by outputting the AB quadrature signals, the actually detected rotational angle value θ of the servo motor is fed back.

[0007] S2. Detection of the actual rotational angle of the servo motor at the zero point: The servo motor rotates in the rotational direction determined in step S1. When the Z-signal level jump is detected, that is, the zero position is detected, the actually detected rotational angle value θ of the servo motor fed back by the position controller at this time is recorded. 0 ; At the same time, the position controller outputs a rotational direction command opposite to the rotational direction determined in step S1 to control the servo motor to rotate in the reverse direction.

[0008] S3. Detection of the actual rotational angle of the servo motor during reverse rotation: After the servo motor in step S2 detects the zero position, it will continue to rotate in the rotational direction of step S1 under the action of inertia until the speed drops to zero. The actually detected rotational angle value θ of the servo motor fed back by the position controller at this time is recorded. 1 ;

[0009] S4. Position control to find the zero position: The position controller in step S2 uses θ 1 -θ 0 to re-correct the position command to control the servo motor to rotate in the rotational direction opposite to the rotational direction determined in step S1 by an angle of θ 1 -θ 0 to the accurate zero position, and thus the zero position search ends.

[0010] In the above method for searching the starting zero position of a sewing machine servo motor, the determination of whether the initial point position of the servo motor is on the left or right side of the zero position by detecting the Z-signal level output by the Z-signal optocoupler in step S1, and accordingly, the position controller outputs a corresponding rotational position command to determine the rotational direction towards the zero position is specifically as follows:

[0011] When the detected output Z-signal is at a low level, that is, when ZFlag = 0, the initial point position of the servo motor is on the left side of the zero position. At this time, the position controller outputs a counterclockwise rotational position command to control the servo motor to rotate counterclockwise towards the zero position; when the detected output Z-signal is at a high level, that is, when ZFlag = 1, the initial point position of the servo motor is on the right side of the zero position. At this time, the position controller outputs a clockwise rotational position command to control the servo motor to rotate clockwise towards the zero position.

[0012] In the above-mentioned method for searching the starting zero position of a sewing machine servo motor, the servo motor in step S2 rotates in the rotation direction determined in step S1. When the Z signal level jumps, that is, the zero position is detected, record the actual rotation angle value θ of the servo motor detected by the position controller feedback at this time. 0 Specifically:

[0013] Signals A and B in the incremental encoder are approximate sine waves with a 90-degree phase difference. These two-phase signals are amplified and shaped into square waves. If phase A leads phase B, it corresponds to the servo motor rotating clockwise; if phase B leads phase A, it corresponds to the servo motor rotating counterclockwise. If counting pulses are generated at the rising or falling edge of this square wave, a pulse sequence representing clockwise and counterclockwise angular displacements can be formed. The actual rotation angle value θ of the above servo motor is calculated by calculating the number of the above pulses from the start of the servo motor to the detection of the Z signal level jump. 0 。

[0014] In the above-mentioned method for searching the starting zero position of a sewing machine servo motor, the position controller in step S2 outputs a rotation direction command opposite to the rotation direction determined in step S1 to control the servo motor to rotate in the reverse direction. Specifically:

[0015] When the zero position is detected, the position controller outputs a reverse rotation command to control the servo motor to rotate in the reverse direction. However, at this time, since the servo motor is rotating at a high speed, it cannot immediately rotate in the reverse direction. Instead, it first decelerates until the speed becomes zero and then executes the reverse rotation command.

[0016] In the above-mentioned method for searching the starting zero position of a sewing machine servo motor, record the actual rotation angle value θ of the servo motor detected by the position controller feedback in step S3. 1 Specifically:

[0017] The actual rotation angle value θ of the servo motor 1 is obtained by calculating the number of AB-phase square wave pulses between the initial point position of the servo motor and the position where the speed drops to zero in step S3.

[0018] Compared with the prior art, the method for searching the starting zero position of this sewing machine servo motor has the following advantages:

[0019] 1. The zero position orientation of the servo motor is initially determined at the initial point position, ensuring the correct zero position search direction at the start, avoiding the motor rotating back and forth to determine the zero position direction, so as to reduce the search time and improve the search speed;

[0020] 2. The motor rotates at high speed for searching, achieving high-speed and efficient zero-position searching. At the same time, the position control mode is adopted to find the zero position, and the position command is corrected by the error between the zero position and the actual stop position (i.e., the motor position when the speed drops to zero), so as to achieve high-precision zero-position searching. In summary, high-speed and high-precision zero-position searching are achieved simultaneously. Description of the Drawings

[0021] Figure 1 is the flowchart of the working process of this starting zero-position searching method. Detailed Embodiments

[0022] The following are specific embodiments of the present invention and in combination with the drawings, the technical solutions of the present invention are further described, but the present invention is not limited to these embodiments.

[0023] This starting zero-position searching method for a sewing machine servo motor is equipped with an incremental encoder on the servo motor. There are three types of pulse encoders: photoelectric, contact, and electromagnetic induction. The photoelectric pulse encoder can convert mechanical displacement, rotation angle, or speed change into electrical pulses output, and it is a commonly used detection sensor for precision digital control. The biggest feature of the photoelectric encoder is non-contact, with high precision, fast response, and high reliability. The photoelectric encoder is a sensor that converts the rotation angle and displacement into digital pulses in various code forms by photoelectric methods. In the photoelectric pulse encoder, between the light-emitting element and the photoelectric receiving element, there is a code disk directly installed on the rotating shaft with a considerable number of light-transmitting fan-shaped areas. When the light source forms a parallel light beam through the optical system and projects it on the code disk, rotating the code disk, the light passes through the light-transmitting and non-light-transmitting areas of the code disk, and light pulses are formed on the other side of the code disk. The pulsed light irradiates on the photoelectric element to generate corresponding electrical pulse signals. The pattern and light pulse signals of the incremental encoder are uniform, and any position can be used as a reference point. Starting from this point, the displacement or rotation angle is detected in a certain quantization unit, and the displacement or rotation angle can be converted by measuring the number of pulses. In this embodiment, the code disk in the incremental encoder is fixedly installed on the rotor of the servo motor. The phase difference between phase A and phase B in the incremental encoder is 90 degrees, and signals A and B are approximate sine waves with a 90-degree phase difference. These two-phase signals are amplified and shaped into square waves. If phase A leads phase B, it corresponds to the forward rotation of the working axis; if phase B leads phase A, it corresponds to the reverse rotation of the working axis. If counting pulses are generated at the leading edge or trailing edge of this square wave, a pulse sequence representing positive and negative angular displacements can be formed. Whenever the working axis rotates one week, the photoelectric element generates a Z-phase one-turn reference pulse signal. The zero position of the servo motor is generally consistent with the position where the Z-phase pulse is emitted by the pulse encoder.

[0024] As Figure 1 shown, this starting zero-position searching method includes the following steps:

[0025] S1. Initial point position detection: When the sewing machine system starts running, the position of the initial point of the servo motor is determined by detecting the Z-signal level output by the Z-signal optocoupler, that is, whether the initial point position of the servo motor is on the left or right side of the zero position. Accordingly, the position controller outputs a corresponding rotational position command to determine the rotational direction towards the zero position, and at the same time, the actual rotational angle value θ of the detected servo motor is fed back by outputting the AB quadrature signal.

[0026] Specifically, the servo motor in this embodiment rotates at a high speed to search for the zero position. When the detected output Z-signal is at a low level, that is, when ZFlag = 0, the initial point position of the servo motor is on the left side of the zero position. At this time, the position controller outputs a counterclockwise rotational position command to control the servo motor to rotate counterclockwise towards the zero position. When the detected output Z-signal is at a high level, that is, when ZFlag = 1, the initial point position of the servo motor is on the right side of the zero position. At this time, the position controller outputs a clockwise rotational position command to control the servo motor to rotate clockwise towards the zero position. The zero position orientation of the servo motor is initially determined at the initial point position, ensuring that the zero position search direction is correct at startup, avoiding the motor rotating back and forth to determine the zero position direction, thereby reducing the search time and increasing the search speed.

[0027] S2. Detection of the actual rotational angle of the servo motor at the zero point: The servo motor rotates in the rotational direction determined in step S1. When the Z-signal level jumps, that is, when the zero position is detected, the actual rotational angle value θ of the servo motor detected and fed back by the position controller at this time is recorded. 0 At the same time, the position controller outputs a rotational direction command opposite to the rotational direction determined in step S1 to control the servo motor to rotate in the reverse direction.

[0028] In this embodiment, taking the rotational direction determined in step S1 as the counterclockwise rotational direction as an example, the servo motor rotates counterclockwise. When the Z-signal level jumps, that is, when the zero position is detected, the actual rotational angle value θ of the servo motor detected and fed back by the position controller at this time is recorded. 0 where the actual rotational angle value θ of the servo motor 0 is obtained by calculating the number of the above-mentioned pulses from the start of the servo motor to the jump of the Z-signal level.

[0029] At the same time, when the zero position is detected, the position controller outputs a clockwise rotational command to control the servo motor to rotate in the reverse direction clockwise. However, since the servo motor is rotating at a high speed at this time, it cannot immediately rotate in the reverse direction. Instead, it first decelerates until the speed becomes zero and then executes the reverse clockwise rotational command.

[0030] S3, detect the actual rotation angle of the servo motor during reverse rotation. After the servo motor in step S2 detects the zero position, it will continue to rotate in the direction of rotation of step S1 under the action of inertia until the speed drops to zero. Record the actual rotation angle value θ of the servo motor detected by the position controller feedback at this time 1 ;

[0031] This embodiment takes the counterclockwise rotation direction as an example after the rotation direction determined in step S1. After the servo motor in step S2 detects the zero position, it will continue to rotate counterclockwise under the action of inertia until the speed drops to zero. The actual rotation angle value θ of the servo motor detected by the position controller feedback is recorded at this time. 1 , the actual rotation angle value of the servo motor θ 1 It is obtained by calculating the number of AB phase square wave pulses between the servo motor's initial position and the position where the speed drops to zero in step S3.

[0032] S4, position control to find the zero position, the position controller in step S2 uses θ 1 -θ 0 Re-correct the position command to control the servo motor to rotate in the opposite direction of the rotation direction determined in step S1 by θ 1 -θ 0 Angle to the exact zero position, and the zero position search is completed.

[0033] This embodiment is described by taking the rotation direction determined in step S1 as the counterclockwise rotation direction. The position controller in step S2 uses θ 1 -θ 0 Re-correct the position command to control the servo motor to rotate in the clockwise direction θ 1 -θ 0 Angle to the accurate zero position, at which point the servo motor stays accurately at the zero position and finds the zero position with high precision.

[0034] The servo motor rotates at high speed to search for zero position at high speed and high efficiency. At the same time, the position control mode is used to find the zero position, and the position command is corrected by the error between the zero position and the actual stop position (that is, the motor position when the speed drops to zero) to achieve high-precision search for zero position; because the position control method is used to find the zero position, there will be no position deviation, thus achieving high-precision zero position search. In summary, high-speed and high-precision zero position search can be achieved at the same time.

[0035] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A method for searching the starting zero position of a servo motor for a sewing machine, an incremental encoder is installed on the servo motor, characterized in that, it includes the following steps: S1. Initial point position detection: When the sewing machine system starts to run, the Z signal level output by the Z signal optocoupler is detected to determine whether the initial point position of the servo motor is on the left or right side of the zero position. Thereby, the position controller outputs a corresponding rotation position command to determine the rotation direction to rotate towards the zero position. At the same time, the actually detected rotation angle value θ of the servo motor is fed back by outputting the AB quadrature signal; S2. Detect the actual rotation angle of the zero-position servo motor. The servo motor rotates in the rotation direction determined in step S1. When the Z-signal level jumps, that is, the zero position is detected, record the actual rotation angle value θ of the servo motor detected by the feedback of the position controller at this time. 0 At the same time, the position controller outputs a rotation direction command opposite to the rotation direction determined in step S1 to control the servo motor to rotate in the reverse direction. S3. Detection of the actual rotation angle of the servo motor during reverse rotation. After the servo motor in step S2 detects the zero position, it will continue to rotate in the rotation direction of step S1 under inertia until the speed drops to zero, and record the actual rotation angle value θ of the servo motor detected by the feedback of the position controller at this time 1 ; S4, position control to find the zero position, the position controller in step S2 uses θ 1 -θ 0 Re-correct the position command to control the servo motor to rotate in the opposite direction of the rotation direction determined in step S1 by θ 1 -θ 0 Angle to the exact zero position, and the zero position search is completed.

2. A method for searching the starting zero position of a servo motor for a sewing machine according to claim 1, characterized in that, the step of determining whether the initial point position of the servo motor is on the left or right side of the zero position by detecting the Z signal level output by the Z signal optocoupler in step S1, and thereby the position controller outputs a corresponding rotation position command to determine the rotation direction to rotate towards the zero position is specifically: When the detected Z signal is at a low level, that is, when ZFlag = 0, the initial point position of the servo motor is on the left side of the zero position. At this time, the position controller outputs a counterclockwise rotation position command to control the servo motor to rotate counterclockwise towards the zero position; when the detected Z signal is at a high level, that is, when ZFlag = 1, the initial point position of the servo motor is on the right side of the zero position. At this time, the position controller outputs a clockwise rotation position command to control the servo motor to rotate clockwise towards the zero position.

3. A method for searching the starting zero position of a servo motor for a sewing machine according to claim 1 or 2, characterized in that, The servo motor in step S2 rotates in the rotation direction determined in step S1. When the Z signal level jumps, that is, the zero position is detected, record the actual rotation angle value θ of the servo motor detected by the feedback of the position controller at this time 0 Specifically: The signals A and B in the incremental encoder are approximate sine waves with a 90-degree phase difference. After these two-phase signals are amplified and shaped, they form square waves. If phase A leads phase B, it corresponds to the clockwise rotation of the servo motor; if phase B leads phase A, it corresponds to the counterclockwise rotation of the servo motor. If counting pulses are generated at the rising edge or falling edge of this square wave, a pulse sequence representing clockwise and counterclockwise angular displacements can be formed. The actual rotation angle value θ of the above servo motor is calculated by calculating the number of the above pulses from the start of the servo motor to the detection of the Z-signal level jump. 0 .

4. A method for searching the starting zero position of a servo motor for a sewing machine according to claim 3, characterized in that, the step that the position controller in step S2 outputs a rotation direction command opposite to the rotation direction determined in step S1 to control the servo motor to rotate in the reverse direction is specifically: When the zero position is detected, the position controller outputs a reverse rotation command to control the servo motor to rotate in the reverse direction. However, at this time, since the servo motor is rotating at a high speed, it cannot immediately rotate in the reverse direction, but first decelerates until the speed becomes zero and then executes the reverse rotation command.

5. A method for searching the starting zero position of a servo motor for a sewing machine according to claim 3, characterized in that, Record the actual rotation angle value θ of the servo motor detected by the position controller feedback at this time in step S3 1 Specifically: The actual rotation angle value θ of the servo motor 1 is obtained by calculating the number of AB-phase square wave pulses between the initial point position of the servo motor and the position where the speed drops to zero in step S3.

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