A rotor angle monitoring and correction method for a servo motor

Abstract

The present invention provides a method for monitoring and correcting the rotor angle of a servo motor, comprising the following steps: A. taking a set portion on a spoke located at the same rotation radius as the center of a receiver as a research object, and obtaining the displacement of the set portion when the spoke is bent; B. obtaining the time required for the displacement of the set portion obtained by step A; C. based on the acceleration or deceleration of the rotor, subtracting or adding the time obtained by step B on the basis of the moment when the receiver actually outputs a voltage fluctuation signal, thereby obtaining the moment when the receiver outputs a voltage fluctuation signal in an ideal state without spoke bending. The method for monitoring and correcting the rotor angle of a servo motor provided by the present invention uses an algorithm to correct the abnormal voltage fluctuation signal output by the receiver caused by the bending of the spokes caused by the acceleration and deceleration of the motor, thereby improving the monitoring accuracy of the photoelectric encoder on the rotor angle.

Description

Technical Field

[0001] The invention relates to a correction method, and in particular to a rotor angle monitoring and correction method for a servo motor. Background Art

[0002] The servo motor relies on its own encoder to monitor the rotation angle and speed of its rotor, so that the controller of the servo motor can accurately control the angle change of the rotor. As a commonly used encoder, the laser emitted by the photoelectric encoder passes through the grating that rotates synchronously with the rotor and reaches the receiver. When the grating rotates, the laser passing through the grating will be intermittent, and the laser signal received by the receiver will also be intermittent. The receiver converts the intermittent laser signal into a voltage fluctuation signal and sends it to the controller, so that the controller can accurately monitor the angle and speed of the rotor rotation. There are multiple spokes between the inner hub and the outer hub on the grating. Each spoke is evenly distributed along the circumference of the inner and outer hubs at the same interval angle, and there are light-transmitting through holes between adjacent spokes. When the grating rotates with the rotor of the motor, when the through hole passes between the light emitter and the receiver, the laser can pass through the grating smoothly, and a voltage square wave will be generated on the receiver. When the spoke passes between the light emitter and the receiver, the laser is blocked, and no voltage square wave is generated on the receiver. Therefore, the relative position relationship between the spoke and the through hole determines the accuracy of the voltage signal output by the receiver. When the motor rotor rotates at a constant speed, the spokes are naturally stretched. When the motor rotor accelerates or decelerates, the spokes are bent because the rotation of the outer hub lags behind the inner hub. However, since the installation positions of the emitter and the receiver remain unchanged, generally between the two ends of the spokes along the radial direction of the motor rotor, when the motor accelerates or decelerates, the spokes suddenly bend, and the set spokes that should arrive between the emitter and the receiver on time will be delayed or arrive in advance between the emitter and the receiver, thereby interfering with the voltage fluctuation signal output on the receiver. Summary of the invention

[0003] The purpose of the present invention is to overcome the existing defects and provide a rotor angle monitoring and correction method for a servo motor to solve the problem of decreased accuracy of rotor angle monitoring by current photoelectric encoders.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] A method for monitoring and correcting the rotor angle of a servo motor, the servo motor comprising a housing and a rotor, the portion of the rotor extending out of the housing being sleeved with a grating, the housing being fixedly provided with a bracket, the bracket being provided with cantilevers respectively located on both sides of the grating, one of the cantilevers being provided with a light emitter, the other cantilever being provided with a receiver, the light emitter and the receiver being aligned in a direction parallel to the axial direction of the rotor, the grating comprising an inner hub, the inner hub being annular and having an interference fit with the rotor and being capable of rotating synchronously with the rotor, the outer side wall of the inner hub being evenly distributed with a plurality of spokes, each of the spokes being arranged along the radial direction of the rotor, an annular outer hub being arranged on the outer side of each of the spokes, the outer side of the outer hub and the inner hub both being cosymmetrically centered with the rotor, the inner end of each of the spokes being connected to the outer side wall of the inner hub, and the outer end being connected to the inner side wall of the outer hub, characterized in that it comprises the following steps:

[0006] A. Take a set part on the spoke that is located at the same rotation radius as the center of the receiver as the research object, and obtain the displacement of the set part when the spoke is bent;

[0007] B. The time required to obtain the displacement of the set part obtained in step A;

[0008] C. Based on the acceleration or deceleration of the rotor, subtract or add the time obtained in step B to the time when the receiver actually outputs the voltage fluctuation signal, so as to obtain the time when the receiver outputs the voltage fluctuation signal under the ideal state without spoke bending.

[0009] Furthermore, the content of step A is specifically as follows:

[0010] Analyze a spoke. The inner end of the spoke is connected to the inner hub, which is connected to the rotor. The inner hub is the driving component. The outer end of the spoke is connected to the outer hub, which is the driven component. When the rotor accelerates, the inner end of the spoke follows the inner hub to rotate around the center of the rotor. Its tangential acceleration is a. This acceleration is both the acceleration of the inner end relative to the center of the rotor and the acceleration of the inner end relative to the outer end. The acceleration of the outer end relative to the inner end is -a. The negative sign represents that the direction of the acceleration is opposite to the acceleration a of the inner end. When the rotor decelerates, analyze the same spoke. At this time, the acceleration of the inner end relative to the outer end is still a, which is opposite to that when the rotor accelerates. Similarly, the acceleration of the outer end relative to the inner end is still -a, and its direction is also opposite to that when the rotor accelerates.

[0011] The outer hub is supported on the inner hub by multiple spokes. If the mass of the outer hub is M and the number of spokes is J, the mass m supported by each spoke is set, and its calculation method is shown in formula (1):

[0012]

[0013] That is, the mass connected to the outer end of each spoke is m;

[0014] When the rotor accelerates or decelerates, the spokes bend and deform because the outer end of each spoke has an acceleration of -a relative to the inner end, and each spoke has a connected mass m. When the grating rotates, the mass connected to the outer end of each spoke, combined with the acceleration, will generate a force F at the outer end. The calculation method is shown in formula (2):

[0015] F=-ma (2)

[0016] Substituting formula (1) into formula (2), we get

[0017]

[0018] This force F is the reason why the spokes are bent and deformed during the acceleration and deceleration of the rotor;

[0019] The above spoke bending deformation conforms to the beam bending deformation principle in material mechanics, that is, the left end of the beam is connected to a fixed object, the left end is the fixed end, and the right end of the beam is the free end. A force F is applied to the right end, and the deflection curve equation of the beam is used to calculate the displacement of the set position on the beam after the bending deformation. The deflection curve equation of the beam in material mechanics is:

[0020]

[0021] In formula (4), x is the distance between the set position and the fixed end of the beam, y is the displacement of the set position after the beam is bent and deformed, L is the total length of the beam, F is the force applied to the free end of the beam, and EI is the bending stiffness of the beam using the set material;

[0022] Replace the beam in the above process with a spoke, and take the set position on the spoke with the same rotation radius as the center of the receiver as the research object. L is the total length of the spoke. When the spoke is bent and deformed, the displacement of the set position is y. The radius of the outer wall of the inner hub relative to the center of the rotor is R1, and the radius of the center of the receiver relative to the center of the rotor is R2. The calculation formula for the distance x between the set position and the inner end of the spoke is:

[0023] x=R2-R1 (5)

[0024] The inner end of the spoke is connected to the outer wall of the inner hub and moves in a synchronous circular motion with the outer wall. The acceleration a of the inner end of the spoke is:

[0025]

[0026] In formula (6), v is the tangential velocity of the outer wall of the inner hub, ω is the angular velocity of the inner hub, and t is the time variable. Since ω = 2πn, n is the rotation speed of the inner hub, formula (6) is transformed into formula (7):

[0027]

[0028] Substituting formula (3), formula (5) and formula (7) into formula (4) yields formula (8):

[0029]

[0030] In formula (8), is the speed change rate k of the inner hub, that is

[0031] Formula (8) is applicable to both the motor rotor acceleration state and the motor rotor deceleration state. If the rotor accelerates and the speed of the inner hub is faster than that of the outer hub, the y obtained is a positive value. If the rotor decelerates and the speed of the inner hub is slower than that of the outer hub, the y obtained is a negative value.

[0032] Furthermore, the content of step B is specifically as follows:

[0033] Due to the existence of the displacement y, when the deformed spoke rotates to the front of the receiver, the setting position needs to move a distance |y| more than when the spoke is not deformed. Since the distance |y| caused by the spoke deformation is extremely small, it is equivalent to the arc length, and the time required for the arc length movement process is T;

[0034] The speed of the inner hub and spokes is n, and the time required for each revolution is Q. The arc length of the above-mentioned setting part rotating one circle is 2πR2, and the time T required for the setting part to rotate through the arc length |y| is:

[0035]

[0036] Substituting formula (8) into (9) yields formula (10):

[0037]

[0038] In formula (10), the speed n of the inner hub is equal to the speed of the rotor. Substituting the rotor speed collected by the encoder most recently before the motor speed regulation into formula (10), the calculation formula for the speed change rate k of the inner hub is:

[0039]

[0040] Among them, n2 is the rotor set speed after the motor speed regulation, n1 is the rotor speed collected by the encoder most recently before the motor speed regulation, and T0 is the average time required for the front and rear speed switching process when the motor speed is regulated. Substituting formula (11) and related parameters into formula (10), formula (12) is obtained as follows:

[0041]

[0042] When the rotor accelerates, the inner hub is faster than the outer hub, and the above time T is the delay time for the set position to arrive directly in front of the receiver 7. When the rotor decelerates, the inner hub is slower than the outer hub, and the above time T is the advance time for the set position to arrive directly in front of the receiver.

[0043] Furthermore, the content of step C is specifically as follows:

[0044] According to the delay or advance time, the actual voltage fluctuation signal obtained by the receiver according to the intermittent laser signal received by the spoke is corrected as follows:

[0045] Under ideal conditions where the spokes do not bend or deform when accelerating or decelerating, the control voltage fluctuation signal sent by the controller has a voltage valley value of U1 and a peak value of U2. When time t reaches T1, the frequency of the square wave increases, the purpose of which is to increase the speed of the motor. The voltage fluctuation signal converted by the receiver based on the received laser signal has a voltage valley value of U3 and a peak value of U4. The characteristics of the servo motor are: every time the controller sends out a voltage square wave, the motor rotor rotates a fixed angle. If the receiver outputs a voltage square wave every time the rotor rotates the fixed angle, the square wave sent by the controller corresponds to the square wave output by the receiver. Since there is a time delay between the controller sending the control signal and the receiver outputting the corresponding signal, when time t reaches T2, the receiver outputs the corresponding square wave and its frequency also increases synchronously, where T2>T1. The time delay T2-T1 is affected by factors such as motor temperature, humidity, wiring harness resistance, and magnetic field, and is not a constant value;

[0046] When the motor accelerates, the voltage fluctuation signal sent by the controller, when time t reaches T1, the frequency of the square wave increases, which is used to increase the speed of the motor. At this time, the rotor accelerates, and the inner hub is faster than the outer hub. The voltage fluctuation signal output by the receiver should appear at time T2, but the square wave is delayed to time T3, where T3>T2, and there is a time difference T3-T2 in the middle. As mentioned above, the time difference T calculated according to formula (12) is used to obtain T2 through the formula T2=T3-T, that is, the time when the receiver outputs the voltage fluctuation signal under the ideal state without spoke bending;

[0047] Similarly, when the motor decelerates, for the voltage fluctuation signal sent by the controller, when the time t reaches T1, the frequency of the square wave decreases to reduce the rotational speed of the motor. At this time, the rotor decelerates, the inner hub is slower than the outer hub, and the voltage fluctuation signal output by the receiver that should have appeared at time T2 appears in advance at time T4, where T1 < T4 < T2, and there is a time difference T2 - T4 in the middle. As described above, this time difference is the variable T. Therefore, the time difference T calculated according to formula (12), through the formula T2 = T4 + T, T2 is obtained, that is, the time when the receiver outputs the voltage fluctuation signal in the ideal state without spoke bending is obtained.

[0048] A method for monitoring and correcting the rotor angle of a servo motor according to the present invention corrects the abnormality of the voltage fluctuation signal output by the receiver caused by the spoke bending due to the acceleration and deceleration of the motor through an algorithm, thereby improving the monitoring accuracy of the photoelectric encoder for the rotor rotation angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. In the drawings:

[0050] Figure 1 is a schematic structural diagram of the servo motor in the present invention;

[0051] Figure 2 is a schematic diagram of the grating when the rotor rotates at a constant speed in the present invention;

[0052] Figure 3 is a schematic diagram of the grating when the rotor rotates at an accelerated speed in the present invention;

[0053] Figure 4 is a schematic diagram of the force analysis of a single spoke when the rotor rotates at an accelerated speed in the present invention;

[0054] Figure 5 is a schematic diagram of the grating when the rotor rotates at a decelerated speed in the present invention;

[0055] Figure 6 is a schematic diagram of the force analysis of a single spoke when the rotor rotates at a decelerated speed in the present invention;

[0056] Figure 7 is a schematic diagram of the principle of beam flexural deformation;

[0057] Figure 8 is a schematic diagram of the positional relationship between the spoke before and after bending and the receiver in the present invention;

[0058] Fig. 9 is a schematic diagram of the comparison of voltage fluctuation signals when the spoke does not undergo bending deformation in the present invention;

[0059] Fig.10It is a schematic diagram for comparing voltage fluctuation signals when the rotor accelerates and the spokes bend in the present invention;

[0060] Fig.11 It is a schematic diagram for comparing voltage fluctuation signals when the rotor decelerates and rotates and the spokes bend in the present invention;

[0061] Fig.12 It is a schematic diagram for explaining the frequency unstable square wave in the present invention. DETAILED DESCRIPTION

[0062] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0063] like Figure 1 As shown, the servo motor 1 includes a housing 2 and a protruding rotor 3, a grating 4 is sleeved on the rotor 3, a bracket 5 is fixedly provided on the housing 2, and two cantilevers are provided on the bracket 5, which are respectively located on both sides of the grating 4. The light emitter 6 is located on one cantilever, and the receiver 7 is located on the other cantilever. The light emitter 6 and the receiver 7 are aligned in a direction parallel to the axial direction of the rotor 3. Figure 2 As shown, the grating 4 includes an inner hub 41 sleeved on the outer side of the rotor 3 with a co-symmetrical center line. The inner hub 41 is annular and has an interference fit with the rotor 3 and rotates synchronously with the rotor 3. The outer wall of the inner hub 41 is evenly distributed with a plurality of spokes 42. Each spoke 42 is arranged along the radial direction of the rotor 3 and each spoke 42 has a common symmetric plane along the radial direction of the rotor 3. An annular outer hub 43 is arranged outside each spoke 42. The outer hub 43 and the rotor 3 have a co-symmetrical center line. The inner end of each spoke 42 is connected to the outer side wall of the inner hub 41, and the outer end is connected to the inner side wall of the outer hub 43. Figure 2 As shown, the receiver 7 is arranged along the radial direction of the rotor 3 and is located between the two ends of the spokes 42. When the rotor 3 rotates, the rotor drives the inner hub 41 to rotate synchronously, and the inner hub 41 drives the outer hub 43 to rotate through the spokes 42. Figure 2 As shown in FIG. 1 , when the rotor 3 rotates at a constant speed, the spokes 42 do not deform because the angular velocities of the inner and outer hubs are equal. When the rotor 3 accelerates, the rotation speed of the inner hub 41 is faster than that of the outer hub 43, and the spokes 42 present as shown in FIG. Figure 3 When the rotor 3 decelerates, the rotation speed of the inner hub 41 is slower than that of the outer hub 43, and the spokes 42 present the bending deformation shown in FIG. Figure 5 Bending deformation shown.

[0064] When the rotor 3 accelerates, Figure 4As shown, one of the spokes 42 is analyzed. The inner end of the spoke 42 is connected to the inner hub 41, and the inner hub 41 is connected to the rotor 3. The inner hub 41 is a driving component. The outer end of the spoke 42 is connected to the outer hub 43, and the outer hub 43 is a driven component. When the rotor 3 accelerates, the inner end of the spoke 42 rotates around the center of the rotor following the inner hub 41, and its tangential acceleration is a. This acceleration is both the acceleration of the inner end relative to the rotor center and the acceleration of the inner end relative to the outer end. Then, the acceleration of the outer end relative to the inner end is -a, and the negative sign represents that the direction of the acceleration is opposite to the acceleration a of the inner end. When the rotor 3 decelerates, the same spoke 42 is analyzed. At this time, the acceleration of the inner end relative to the outer end is still a, and its direction is as shown in FIG. Figure 6 As shown, it is opposite to that when the rotor 3 is accelerated. Similarly, the acceleration of the outer end relative to the inner end is still -a, and its direction is also opposite to that when the rotor 3 is accelerated.

[0065] The outer hub 43 is supported on the inner hub 41 by a plurality of spokes 42. If the mass of the outer hub 43 is M and the number of spokes is J, the mass m supported by each spoke is set, and the calculation method is shown in formula (1):

[0066]

[0067] That is, the mass connected to the outer end of each spoke 42 is m.

[0068] According to the above analysis, when the rotor 3 accelerates or decelerates, the following occurs: Figure 3 and Figure 5 The spokes 42 in the figure are bent and deformed because the outer end of each spoke has an acceleration -a relative to the inner end, and each spoke outer end has a connected mass m. When the grating 4 rotates, regardless of the mass of the spoke itself, the air resistance and the gravity, the mass connected to the outer end of each spoke cooperates with the acceleration and generates a force F at the outer end, which is calculated as shown in formula (2):

[0069] F=-ma (2)

[0070] Substituting formula (1) into formula (2), we get

[0071]

[0072] The force F is the reason why the spokes 42 are bent and deformed during the acceleration and deceleration of the rotor 3 .

[0073] right Figure 4 The spoke 42 in the figure is analyzed separately. The inner end of the spoke is fixedly connected to the inner hub 41, and the outer end is subjected to a force F. Under the action of F, the outer end of the spoke is bent downward relative to the inner end. This situation conforms to the beam flexural deformation principle in material mechanics, such as Figure 7As shown, the left end of the beam 11 is connected to a fixed object, the left end is a fixed end, and the right end of the beam 11 is a free end. A force F is applied to the right end, and the deflection curve equation of the beam is used to calculate the displacement of a set portion on the beam after bending deformation.

[0074] The deflection curve equation of a beam in material mechanics is:

[0075]

[0076] like Figure 7 As shown, the solid line represents the state of the beam before bending deformation, and the dotted line represents the state of the beam after bending deformation. In formula (4), x is the distance between the set position and the fixed end of the beam (meter), y is the displacement of the set position after the bending deformation of the beam (meter), L is the total length of the beam (meter), F is the force applied to the free end of the beam (N), and EI is the bending stiffness of the beam using the set material.

[0077] like Figure 3 As shown, the radius of the outer wall of the inner hub 41 relative to the center of the rotor 3 is R1 (meter), and the radius of the center position of the receiver 7 relative to the center of the rotor 3 is R2 (meter).

[0078] Figure 8 FIG. 4 shows the relative position relationship between the spokes 42 and the receiver 7 when the rotor 3 is accelerated. Figure 8 The spoke position 1 421 represented by the dotted line is the state before the spoke 42 is bent and deformed, and the spoke position 2 422 represented by the solid line is the state after the spoke 42 is bent and deformed. It can be seen that if the spoke 42 is not bent and deformed, the spoke 42 will just reach the front of the receiver 7. However, after the spoke 42 is bent and deformed, the spoke 42 is still displaced y from the front of the receiver 7. The set part on the spoke 42 located at the same rotation radius as the center of the receiver 7 is taken as the research object. When the spoke 42 is bent and deformed, the displacement of the set part is y.

[0079] like Figure 3 As shown, the inner end of the spoke 42 is connected to the outer wall of the inner hub 41, so the calculation formula of the distance x between the above-mentioned set position and the inner end of the spoke is:

[0080] x=R2-R1 (5)

[0081] like Figure 4 As shown, the inner end of the spoke 42 is connected to the outer wall of the inner hub 41 and moves in a synchronous circular motion with the outer wall. Then, the acceleration a of the inner end of the spoke 42 is:

[0082]

[0083] In formula (6), v is the tangential velocity of the outer wall of the inner hub 41 (m / s), ω is the angular velocity of the inner hub (radians / s), and t is the time variable (seconds). Since ω=2πn, n is the rotation speed of the inner hub (rev / s), formula (6) is transformed into formula (7):

[0084]

[0085] Substituting formula (3), formula (5) and formula (7) into formula (4) yields formula (8):

[0086]

[0087] In formula (8), is the speed change rate k of the inner hub, that is

[0088] When the rotor 3 decelerates, the derivation process is the same and will not be repeated. The displacement calculation formula of the set position is also formula (8), that is, formula (8) is applicable to both the motor rotor acceleration state and the motor rotor deceleration state. The calculated y can be a positive value or a negative value. If the rotor accelerates, such as Figure 3 As shown in the figure, when the speed of the inner hub is faster than that of the outer hub, the y is positive. Then, when the rotor slows down, Figure 5 As shown, when the rotation speed of the inner hub is slower than that of the outer hub, the resulting y is a negative value.

[0089] like Figure 8 As shown, when the rotor 3 accelerates, due to the existence of the displacement y, when the spoke 42 rotates from the spoke position 2 422 to the front of the receiver 7, the setting part needs to move a distance |y| more than when the spoke is not deformed. Similarly, when the rotor 3 decelerates, the setting part needs to move a distance |y| less than when the spoke is not deformed. Since the distance |y| caused by the deformation of the spoke is extremely small, it is equivalent to the arc length, and the time required for the movement of the arc length is T.

[0090] The speed of the inner hub and spokes is n (r / s), and the time required for each circle is Q (seconds), then the arc length of the above-mentioned set part during one rotation is 2πR2, and the time T (seconds) required for the set part to rotate through the arc length |y| is:

[0091]

[0092] Substituting formula (8) into (9) yields formula (10):

[0093]

[0094] In formula (10), the speed n of the inner hub is equal to the speed of the rotor. The most recent rotor speed collected by the encoder before the motor speed regulation is substituted into formula (10) for calculation. In addition, the calculation formula for the speed change rate k of the inner hub is:

[0095]

[0096] Among them, n2 is the rotor set speed (r / s) after the motor speed regulation, n1 is the rotor speed (r / s) collected by the encoder most recently before the motor speed regulation, and T0 is the average time required for the front and rear speed switching process obtained by the experiment when the motor speed is regulated. Substituting formula (11) and related parameters into formula (10) yields formula (12) as follows:

[0097]

[0098] like Figure 3-4 As shown in FIG. 1 , when the rotor 3 accelerates, the inner hub 41 is faster than the outer hub 43, and the above time T is the delay time for the set position to arrive in front of the receiver 7. Figure 5-6 As shown, when the rotor 3 decelerates, the inner hub 41 is slower than the outer hub 43, and the above time T is the advance time for the set position to arrive directly in front of the receiver 7. According to the delay or advance time, the original voltage fluctuation signal obtained by the receiver according to the intermittent laser signal received by the spoke needs to be corrected, and the method is as follows:

[0099] In the ideal case where the spokes do not bend or deform when accelerating or decelerating, Fig. 9 As shown, Fig. 9 (a) shows the control voltage fluctuation signal sent by the controller, whose voltage valley is U1 and peak is U2. When time t reaches T1, the frequency of the square wave increases, the purpose of which is to increase the speed of the motor. Fig. 9 (b) shows the voltage fluctuation signal converted by the receiver 7 according to the received laser signal, and its voltage valley is U3 and its peak is U4. The characteristics of the servo motor are: every time the controller sends a voltage square wave, the motor rotor rotates a fixed angle. If the rotor rotates the fixed angle and the receiver 7 outputs a voltage square wave, then Fig. 9 Each square wave in (b) is Fig. 9 (a) The square waves correspond one to one. Since there is a time delay between the controller sending the control signal and the receiver outputting the corresponding signal, Fig. 9 As shown in (b), when the time reaches T2, the receiver 7 outputs the corresponding square wave and its frequency also increases synchronously, where T2>T1. The time delay T2-T1 is affected by factors such as motor temperature, humidity, wiring harness resistance, magnetic field, etc., and is not a constant value.

[0100] like Fig.10 As shown, when the motor accelerates, Fig.10 (a) still shows the voltage fluctuation signal sent by the controller. When time t reaches T1, the frequency of the square wave increases to increase the rotational speed of the motor. At this time, the rotor 3 accelerates, the inner hub 41 is faster than the outer hub 43, and the voltage fluctuation signal output by the receiver 7 is as Fig.10 (b) shows that the square wave that should have appeared at time T2 is delayed until time T3, where T3 > T2, and there is a time difference T3 - T2 in the middle. This time difference is the variable T as described above. Therefore, the time difference T calculated according to formula (12), through the formula T2 = T3 - T, T2 is obtained, and then for the Fig.10 (b) shown voltage fluctuation signal is corrected. The delayed square wave is translated T units to the left along the time axis, and the other square waves remain unchanged. The translated square wave and the unchanged square waves are connected by the original valley voltage line to obtain the Fig.10 (c) voltage fluctuation signal, making this voltage fluctuation signal consistent with the Fig. 9 (b) voltage fluctuation signal and returning to the voltage fluctuation signal in the ideal case where the spokes do not deform. The delayed square wave refers to all the square waves with unstable frequencies from the square wave whose frequency starts to change until the square wave whose frequency stabilizes after the time point T1 when the controller sends the speed regulation signal. For example, the Fig.10 (b) and Fig.10 (c) two square waves within the circle P1, that is, the duration of each square wave or the interval duration between adjacent square waves is inconsistent. The square waves with unstable frequencies represent that the rotational speed of the motor rotor has not reached the stable set rotational speed after speed regulation. When the rotational speed is stable, the grating rotates uniformly, and the spokes no longer bend and deform, and the corresponding square waves do not need to be corrected.

[0101] Similarly, as Fig.11 shown, when the motor decelerates, Fig.11 (a) still shows the voltage fluctuation signal sent by the controller. When time t reaches T1, the frequency of the square wave decreases to reduce the rotational speed of the motor. At this time, the rotor 3 decelerates, the inner hub 41 is slower than the outer hub 43, and the voltage fluctuation signal output by the receiver 7 is as Fig.11 (b) shows that the square wave that should have appeared at time T2 appears in advance at time T4, where T1 < T4 < T2, and there is a time difference T2 - T4 in the middle. This time difference is the variable T as described above. Therefore, the time difference T calculated according to formula (12), through the formula T2 = T4 + T, T2 is obtained, and then for the Fig.11 (b) shown voltage fluctuation signal is corrected. The advanced square wave is translated T units to the right along the time axis, and the other square waves remain unchanged. The translated square wave and the unchanged square waves are connected by the original valley voltage line to obtain the Fig.11The voltage fluctuation signal in (c) returns to the voltage fluctuation signal in the ideal case where the spokes are not deformed. The advanced square wave refers to the square wave whose frequency starts to change after the controller sends the speed control signal at time T1 until the square wave with a stable frequency. All the square waves with unstable frequencies in between, such as Fig.11 (b) and Fig.11 The two square waves in circle P2 in (c), that is, the duration of each square wave and the interval between adjacent square waves are inconsistent. The unstable frequency square wave means that the motor rotor speed has not reached the stable set speed after speed regulation. When the speed is stable, the grating rotates at a constant speed, and the spokes no longer bend and deform. The corresponding square wave does not need to be corrected.

[0102] As a preferred embodiment, the time T0 is selected from the time point T1 when the controller sends the speed regulation signal until the above-mentioned square wave with a stable frequency appears, and the time required between the time T t , T t The controller determines and calculates the voltage fluctuation signal output by the receiver 7. t More accurate, thus obtaining a more accurate variable T, but this process requires more controller computing resources and increases the time delay of the controller using this method to correct the voltage fluctuation signal.

[0103] The above-mentioned correction of the receiver output voltage fluctuation signal change caused by the acceleration and deceleration of the motor through the time difference T can enable the controller to collect more accurate rotor angle signals, thereby improving the motor's control accuracy over the rotor rotation angle, that is, improving the control accuracy of the motor's external output displacement.

[0104] As a preferred embodiment, the rotor angle monitoring and correction method of the present invention is also applicable to the acceleration and deceleration of the motor rotor caused by the change of the motor load during the motor speed change. At this time, the time difference T ′ Calculated by formula (13):

[0105]

[0106] Among them, n ′ 1 is the rotor speed (r / s) collected by the motor encoder for the first time; n ′ 2 is the rotor speed (r / s) collected by the motor encoder for the second time; T0 ′ It is the time required for the square wave in the voltage fluctuation signal output by the receiver to change from frequency stability to instability and then to stability during the two acquisition periods, that is, the time required from the first unstable square wave to the next stable square wave. Fig.12 As shown, the controller determines and calculates based on the voltage fluctuation signal output by the receiver, and the two square waves in circle P3 are frequency unstable square waves.

[0107] According to the above analysis, if the speed collected for the second time is greater than the speed collected for the first time, it means that the motor speed has increased. The delayed square wave is shifted to the left along the time axis by T. ′ , the rest of the square waves remain unchanged, and the shifted square wave is connected to the unchanged square wave through the original valley voltage line; similarly, the delayed square wave refers to all the unstable square waves from the square wave whose frequency starts to change after the first speed acquisition to the square wave whose frequency is stable. The unstable square wave means that the motor rotor speed has not reached a stable speed after the speed changes due to the load change.

[0108] If the speed collected for the second time is less than the speed collected for the first time, it indicates that the motor speed is decreasing. The advanced square wave is shifted to the right along the time axis by T. ′ , the rest of the square waves remain unchanged, and the shifted square waves are connected to the unchanged square waves through the original valley voltage line; the advanced square wave refers to all the unstable frequency square waves from the square wave whose frequency starts to change after the first speed acquisition to the square wave whose frequency is stable. The unstable frequency square wave means that the motor rotor speed has not reached a stable speed after the speed changes due to the load change.

[0109] The above two rotor speed acquisition time points are selected as needed. If the square wave frequency output by the receiver fails to return to a stable frequency after being changed within the interval between the two acquisition time points, this method cannot be used for correction.

[0110] The present invention discloses a servo motor rotor angle monitoring and correction method, which uses an algorithm to correct the abnormal voltage fluctuation signal output by a receiver caused by spoke bending caused by motor acceleration and deceleration, thereby improving the monitoring accuracy of the rotor angle by a photoelectric encoder.

[0111] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for monitoring and correcting the rotor angle of a servo motor, the servo motor comprising a housing and a rotor, the portion of the rotor extending out of the housing being sleeved with a grating, the housing being fixedly provided with a bracket, the bracket being provided with cantilevers respectively located on both sides of the grating, one of the cantilevers being provided with a light emitter, the other cantilever being provided with a receiver, the light emitter and the receiver being aligned in a direction parallel to the axial direction of the rotor, the grating comprising an inner hub, the inner hub being annular and having an interference fit with the rotor and being capable of rotating synchronously with the rotor, the outer side wall of the inner hub being evenly distributed with a plurality of spokes, each of the spokes being arranged along the radial direction of the rotor, an annular outer hub being arranged on the outer side of each of the spokes, the outer side of the outer hub and the inner hub both being cosymmetrically centered with the rotor, the inner end of each of the spokes being connected to the outer side wall of the inner hub, and the outer end being connected to the inner side wall of the outer hub, characterized in that The following steps are involved: A. Take a set part on the spoke that is located at the same rotation radius as the center of the receiver as the research object, and obtain the displacement of the set part when the spoke is bent; B. The time required to obtain the displacement of the set part obtained in step A; C. Based on the acceleration or deceleration of the rotor, the time obtained in step B is subtracted or added to the time when the receiver actually outputs the voltage fluctuation signal, so as to obtain the time when the receiver outputs the voltage fluctuation signal in an ideal state without spoke bending; The content of step A is specifically as follows: Analyze a spoke. The inner end of the spoke is connected to the inner hub, which is connected to the rotor. The inner hub is the driving component. The outer end of the spoke is connected to the outer hub, which is the driven component. When the rotor accelerates, the inner end of the spoke follows the inner hub to rotate around the center of the rotor. Its tangential acceleration is a. This acceleration is both the acceleration of the inner end relative to the center of the rotor and the acceleration of the inner end relative to the outer end. The acceleration of the outer end relative to the inner end is -a. The negative sign represents that the direction of the acceleration is opposite to the acceleration a of the inner end. When the rotor decelerates, analyze the same spoke. At this time, the acceleration of the inner end relative to the outer end is still a, which is opposite to that when the rotor accelerates. Similarly, the acceleration of the outer end relative to the inner end is still -a, and its direction is also opposite to that when the rotor accelerates. The outer hub is supported on the inner hub by multiple spokes. If the mass of the outer hub is M and the number of spokes is J, the mass m supported by each spoke is set, and its calculation method is shown in formula (1): （1） That is, the mass connected to the outer end of each spoke is m; When the rotor accelerates or decelerates, the spokes bend and deform because the outer end of each spoke has an acceleration of -a relative to the inner end, and each spoke has a connected mass m. When the grating rotates, the mass connected to the outer end of each spoke, combined with the acceleration, will generate a force F at the outer end, which is calculated as shown in formula (2): （2） Substituting formula (1) into formula (2) we get （3） This force F is the reason why the spokes are bent and deformed during the acceleration and deceleration of the rotor; The above spoke bending deformation conforms to the beam bending deformation principle in material mechanics, that is, the left end of the beam is connected to a fixed object, the left end is the fixed end, and the right end of the beam is the free end. A force F is applied to the right end, and the deflection curve equation of the beam is used to calculate the displacement of the set position on the beam after the bending deformation. The deflection curve equation of the beam in material mechanics is: （4） In formula (4), x is the distance between the set position and the fixed end of the beam, y is the displacement of the set position after the beam is bent and deformed, L is the total length of the beam, F is the force applied to the free end of the beam, and EI is the bending stiffness of the beam using the set material; The beam in the above process is replaced by a spoke, and the set position on the spoke with the same rotation radius as the center of the receiver is taken as the research object. L is the total length of the spoke. When the spoke is bent and deformed, the displacement of the set position is y. The radius of the outer wall of the inner hub relative to the center of the rotor is , the radius of the receiver center relative to the rotor center is , then the calculation formula for the distance x between the setting position and the inner end of the spoke is: （5） The inner end of the spoke is connected to the outer wall of the inner hub and moves in a synchronous circular motion with the outer wall. The acceleration a of the inner end of the spoke is: （6） In formula (6), v is the tangential velocity of the outer wall of the inner hub, ω is the angular velocity of the inner hub, and t is the time variable. , n is the speed of the inner hub, then formula (6) is transformed into formula (7): （7） Substituting formula (3), formula (5) and formula (7) into formula (4) yields formula (8): （8） In formula (8), is the speed change rate k of the inner hub, that is ; Formula (8) is applicable to both the motor rotor acceleration state and the motor rotor deceleration state. If the rotor accelerates and the speed of the inner hub is faster than that of the outer hub, the y obtained is a positive value. If the rotor decelerates and the speed of the inner hub is slower than that of the outer hub, the y obtained is a negative value.

2. The method for monitoring and correcting the rotor angle of a servo motor according to claim 1, characterized in that: The specific contents in step B are: Due to the displacement y, when the deformed spoke rotates to the front of the receiver, the setting position needs to move a distance more than when the spoke is not deformed. , the distance due to spoke deformation It is extremely small, so it is equivalent to the arc length, and the time required for the movement of this arc length is T; The speed of the inner hub and spokes is n, and the time required for each revolution is Q. , then the arc length of the above set part rotating one circle is , then the set position rotates through the arc length The time T required is: （9） Substituting formula (8) into (9) yields formula (10): （10） In formula (10), the speed n of the inner hub is equal to the speed of the rotor. Substituting the rotor speed collected by the encoder most recently before the motor speed regulation into formula (10), the calculation formula for the speed change rate k of the inner hub is: （11） in, It is the rotor set speed after the motor speed is adjusted. It is the rotor speed that the encoder collected most recently before the motor speed regulation. is the average time required for the front and rear speed switching process when the motor is speed-regulated. Substituting formula (11) and related parameters into formula (10), formula (12) is obtained as follows: （12） When the rotor accelerates, the inner hub is faster than the outer hub, and the above time T is the delay time for the set position to arrive directly in front of the receiver 7. When the rotor decelerates, the inner hub is slower than the outer hub, and the above time T is the advance time for the set position to arrive directly in front of the receiver.

3. The method for monitoring and correcting the rotor angle of a servo motor according to claim 2, characterized in that: The content of step C is specifically as follows: According to the delay or advance time, the actual voltage fluctuation signal obtained by the receiver according to the intermittent laser signal received by the spoke is corrected as follows: In the ideal case where the spokes do not bend or deform when accelerating or decelerating, the control voltage fluctuation signal sent by the controller has a voltage valley value of , the peak value is , when time t arrives When the frequency of the square wave increases, the purpose is to increase the speed of the motor. The receiver converts the received laser signal into a voltage fluctuation signal, and its voltage valley value is , the peak value is The characteristics of the servo motor are: every time the controller sends out a voltage square wave, the motor rotor rotates a fixed angle. If the receiver outputs a voltage square wave every time the rotor rotates through the fixed angle, the square wave sent by the controller and the square wave output by the receiver correspond one to one. Since there is a time delay between the controller sending the control signal and the receiver outputting the corresponding signal, when time t reaches When the receiver outputs the corresponding square wave and its frequency increases synchronously, ; Time delay Affected by factors such as motor temperature, humidity, wiring harness resistance, magnetic field, etc., it is not a constant value; When the motor accelerates, the controller sends a voltage fluctuation signal. When time t reaches When the frequency of the square wave increases, it is used to increase the speed of the motor. At this time, the rotor accelerates, the inner hub is faster than the outer hub, and the voltage fluctuation signal output by the receiver should be The square wave that appears at the moment is delayed to The moment appears, , there was a time difference in the middle As mentioned above, the time difference is the variable T. Therefore, the time difference T calculated according to formula (12) is obtained by formula get , that is, the moment when the receiver outputs the voltage fluctuation signal in the ideal state without spoke bending; Similarly, when the motor decelerates, the voltage fluctuation signal sent by the controller will When the frequency of the square wave decreases, it is used to reduce the speed of the motor. At this time, the rotor slows down, and the inner hub is slower than the outer hub. The voltage fluctuation signal output by the receiver should be The square wave appears in advance at The moment has appeared, in which , there was a time difference in the middle As mentioned above, the time difference is the variable T. Therefore, the time difference T calculated according to formula (12) is obtained by formula get , that is, the moment when the receiver outputs a voltage fluctuation signal in an ideal state without spoke bending.

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