Why should the encoder phase of the permanent magnet AC servo motor be aligned with the rotor magnetic pole phase?
Its sole purpose is to achieve the goal of vector control, decoupling the d-axis excitation component and the q-axis output component, so that the electromagnetic field generated by the stator winding of the permanent magnet AC servo motor is always orthogonal to the permanent magnetic field of the rotor, so as to obtain the best output effect , That is, "DC-like characteristics", this control method is also called field-oriented control (FOC). The external performance of achieving the FOC control goal is that the "phase current" waveform of the permanent magnet AC servo motor is always the same as the "opposite potential" waveform Be consistent, as shown in the figure below:
![[PLC Servo and Motion Control] Servo motor encoder and rotor magnetic pole phase alignment](/UploadFiles/2020-07/2020071710020151949.jpg)
Therefore, it can be known from the reverse calculation that as long as the "phase current" waveform of the permanent magnet AC servo motor is always consistent with the "opposite potential" waveform, the FOC control goal can be achieved, and the primary electromagnetic field and magnetic pole permanent magnetic field of the permanent magnet AC servo motor can be achieved. Orthogonal, that is, the difference between the waveforms is 90 degrees, as shown in the following figure:
![[PLC Servo and Motion Control] Servo motor encoder and rotor magnetic pole phase alignment](/UploadFiles/2020-07/2020071710033239500.jpg)
How to find a way to make the "phase current" waveform of the permanent magnet AC servo motor always consistent with the "opposite potential" waveform? It can be seen from Figure 1 that as long as the electrical angle phase of the sinusoidal back EMF waveform can be detected at any time, then it is relatively easy to generate a sinusoidal phase current waveform consistent with the back EMF waveform based on the electrical angle phase.
What needs to be clearly stated here is that the so-called electrical angle of the permanent magnet AC servo motor is the sinusoidal (Sin) phase of the a-phase (U-phase) opposite electric potential waveform, so the phase alignment can be converted into the alignment of the encoder phase and the back-EMF waveform phase. On the other hand, the electrical angle is also the angle between the d-axis (direct axis) of the rotor coordinate system and the a-axis (U-axis) or α-axis of the stator coordinate system, which is helpful for graphic analysis.
In actual operation, European and American manufacturers are accustomed to aligning the phases of the encoder and rotor poles by applying a direct current smaller than the rated current to the motor windings to orient the motor rotor. When the windings of the motor are supplied with a DC current smaller than the rated current, under the condition of no external force, the primary electromagnetic field interacts with the permanent magnetic field of the magnetic poles, and they will attract each other and be positioned to a balanced position with a phase difference of 0 degrees, as shown in the following figure:
![[PLC Servo and Motion Control] Servo motor encoder and rotor magnetic pole phase alignment](/UploadFiles/2020-07/2020071710034778518.jpg)
Comparing Figure 3 and Figure 2 above, it can be seen that although the position of the a-phase (U-phase) winding (red) is the same at the peak center (specific angle) of the electromagnetic field waveform, under the control of FOC, the center of the a-phase (U-phase) and the permanent magnet The q-axis is aligned; while in no-load orientation, the center of a-phase (U-phase) is aligned with the d-axis. That is to say, relative to the primary (stator) winding, the d-axis of the secondary (rotor) magnet coordinate system will shift to the left by 90 electrical degrees in no-load orientation, which coincides with the original position of the q-axis under FOC control. In this way, the alignment relationship between the a-axis (U-axis) or the α-axis and the d-axis when the rotor is oriented without load is realized.
At this time, the phase is aligned to the electrical angle of 0 degrees, the direction of the rotor directional current applied to the motor windings is bc phase (VW phase) in, a phase (U phase) out, because b phase (V phase) and c phase (W phase) ) Is a parallel connection. The current flowing through phase b (V phase) and c phase (W phase) may be unbalanced, which will affect the accuracy of rotor orientation.
The practical rotor directional current application method is b-phase (V phase) in, a-phase (U-phase) out, that is, a-phase (U-phase) and b-phase (V-phase) are connected in series to obtain a-phase with the same amplitude. (U-phase) and b-phase (V-phase) currents are conducive to the accuracy of orientation. At this time, the position of the a-phase (U-phase) winding (red) differs from the d-axis by 30 degrees, that is, the a-axis (U-axis) Or the α axis is aligned to the electrical angle position which is 30 degrees different from the d axis (minus), as shown in the figure:
![[PLC Servo and Motion Control] Servo motor encoder and rotor magnetic pole phase alignment](/UploadFiles/2020-07/2020071710040810986.jpg)
The relationship between the winding reverse potential waveform and the line back EMF corresponding to the above two rotor orientation methods, as well as the electrical angle is shown in the following figure. The brown line is the a-axis (U-axis) or the a-axis is aligned with the d-axis, that is, it is directly aligned to the electrical angle 0 point; the purple line is the a-axis (U-axis) or α-axis aligned to the electrical angle position that is 30 degrees different from the d-axis (negative), that is, the electrical angle point is aligned to -30 degrees:
![[PLC Servo and Motion Control] Servo motor encoder and rotor magnetic pole phase alignment](/UploadFiles/2020-07/2020071710042354268.jpg)
The vector relationship between the above two rotor orientation methods in the dq rotor coordinate system and abc (UVW) or αβ stator coordinate system is shown in Figure 6:
![[PLC Servo and Motion Control] Servo motor encoder and rotor magnetic pole phase alignment](/UploadFiles/2020-07/2020071710043622365.gif)
The d-axis shown by the solid brown line in the figure is aligned with the a-axis (U-axis) or α-axis, that is, aligned to the electrical angle 0 point. The alignment method is to apply a current vector whose electrical angle phase is fixed at -90 degrees to the motor windings, as shown by the brown dashed line in the figure. Under no load, the d-axis of the motor rotor will move to the current with an electrical angle phase of -90 degrees under FOC control. The position where the q-axis component of the vector is located, that is, the position that coincides with the a-axis or the a-axis in the figure, and is finally oriented at this position, that is, the electrical angle is 0 degrees.
The d-axis shown by the purple solid line differs from the a-axis (U-axis) or α-axis by 30 degrees, which is aligned to the electrical angle point of -30 degrees. The alignment method is to apply a current vector whose electrical angle phase is fixed to -120 degrees to the motor windings. Under no load, the d-axis of the motor rotor will move to the position where the q-axis component of the current vector whose electrical angle phase is -120 degrees under FOC. , That is, the position that is 30 degrees clockwise from the a-axis or the a-axis in the figure, and is finally oriented at this position, that is, the electrical angle is -30 degrees.
Explain one point: The description of U, V, W phase and a, b, c phase, U, V, W axis and a, b, c axis in the text has a one-to-one correspondence.
Mainstream servo motor position feedback components include incremental encoders, absolute encoders, sin-cos encoders, resolvers and so on.
Phase alignment of incremental encoder
In this discussion, the output signal of the incremental encoder is a square wave signal, which can be divided into an incremental encoder with a commutation signal and an ordinary incremental encoder. The ordinary incremental encoder has two Phase quadrature square wave pulse output signals A and B, and zero signal Z; Incremental encoder with commutation signal in addition to ABZ output signal, also has 120 degrees of mutual electronic commutation signal UVW, UVW respectively The number of cycles per revolution is consistent with the number of pole pairs of the motor rotor. The alignment method between the phase of the UVW electronic commutation signal of the incremental encoder with commutation signal and the phase of the rotor magnetic pole, or the electrical angle phase, is as follows:
1. Use a DC power supply to pass a DC current less than the rated current to the UV winding of the motor, V in, U out, and orient the motor shaft to a balanced position;
2. Observe the U-phase signal and Z signal of the encoder with an oscilloscope;
3. Adjust the relative position of the encoder shaft and the motor shaft;
4. While adjusting, observe the encoder's U-phase signal transition edge and Z signal until the Z signal is stable at a high level (here by default the normal state of the Z signal is low), lock the encoder and the motor relative Positional relationship;
5. Twist the motor shaft back and forth, after letting go, if the Z signal can be stabilized at a high level every time the motor shaft freely returns to the equilibrium position, the alignment is valid.
After removing the DC power supply, verify as follows:
1. Use an oscilloscope to observe the U-phase signal of the encoder and the UV back-EMF waveform of the motor;
2. Rotate the motor shaft counterclockwise, the rising edge of the U-phase signal of the encoder coincides with the zero-crossing point of the motor's UV line back-EMF waveform from low to high, and the Z signal of the encoder also appears at this zero-crossing point.
The above verification method can also be used as an alignment method.
It should be noted that at this time, the phase zero of the U-phase signal of the incremental encoder is aligned with the phase zero of the UV line back EMF of the motor. Because the U reverse potential of the motor is 30 degrees different from the UV line back EMF, so After alignment, the phase zero of the U-phase signal of the incremental encoder is aligned with the -30 degree phase point of the reverse potential of the motor U, and the electrical angle phase of the motor is consistent with the phase of the U reverse potential waveform, so at this time the incremental encoder The phase zero point of the U-phase signal is aligned with the -30 degree point of the electrical angle phase of the motor.
Some servo companies are accustomed to directly align the zero point of the U-phase signal of the encoder with the zero point of the electrical angle of the motor. To achieve this, you can:
1. Use a DC power supply to pass a DC current less than the rated current to the UVW winding of the motor, VW in, U out, and orient the motor shaft to a balanced position;
2. Observe the U-phase signal and Z signal of the encoder with an oscilloscope;
3. Adjust the relative position of the encoder shaft and the motor shaft;
4. While adjusting, observe the encoder's U-phase signal transition edge and Z signal until the Z signal is stable at a high level (here by default the normal state of the Z signal is low), lock the encoder and the motor relative Positional relationship;
5. Twist the motor shaft back and forth, after letting go, if the Z signal can be stabilized at a high level every time the motor shaft freely returns to the equilibrium position, the alignment is valid.
The verification method is as follows:
1. Connect 3 resistors of equal resistance value into a star shape, and then connect the 3 resistors connected in the star shape to the UVW three-phase winding leads of the motor respectively;
2. Observe the midpoint of the motor's U-phase input and star resistance with an oscilloscope, you can approximate the motor's U reverse potential waveform;
3. Rotate the motor shaft counterclockwise, and it can be seen that the rising edge of the U-phase signal of the encoder coincides with the zero-crossing point of the opposite potential waveform of the motor U from low to high.
The above verification method can also be used as an alignment method.
Since ordinary incremental encoders do not have UVW phase information, and the Z signal can only reflect one point within a circle, it does not have the potential for direct phase alignment, so it is not the topic of this discussion.
Phase alignment of absolute encoder
The phase alignment of the absolute encoder is not much different for single-turn and multi-turn. In fact, the phase alignment of the encoder's detection phase and the electrical angle of the motor is within one turn. Early absolute encoders will give the highest level of the single-turn phase with a separate pin. Using this level of 0 and 1 inversion, the phase alignment of the encoder and the motor can also be achieved. The method is as follows:
1. Use a DC power supply to pass a DC current less than the rated current to the UV winding of the motor, V in, U out, and orient the motor shaft to a balanced position;
2. Use an oscilloscope to observe the highest count level signal of the absolute encoder;
3. Adjust the relative position of the encoder shaft and the motor shaft;
4. While adjusting, observe the transition edge of the highest count signal until the transition edge accurately appears at the directional balance position of the motor shaft, and lock the relative position relationship between the encoder and the motor;
5. Twist the motor shaft back and forth, after letting go, if the jumping edge can be accurately reproduced every time the motor shaft freely returns to the equilibrium position, the alignment is effective.
This type of absolute encoder has been widely replaced by new type absolute encoders that adopt EnDAT, BiSS, Hyperface and other serial protocols, as well as Japanese special serial protocols, so the highest signal does not exist. At this time, the alignment encoder and The method of motor phase has also changed. One of the very practical methods is to use the EEPROM inside the encoder to store the measured phase after the encoder is randomly installed on the motor shaft. The specific method is as follows:
1. Install the encoder on the motor randomly, that is, consolidate the encoder shaft and motor shaft, as well as the encoder housing and motor housing;
2. Use a DC power supply to pass a DC current less than the rated current to the UV winding of the motor, V in, U out, and orient the motor shaft to a balanced position;
3. Use the servo drive to read the single-turn position value of the absolute encoder and store it in the EEPROM that records the initial phase of the electrical angle of the motor inside the encoder;
4. The alignment process ends.
Since the motor shaft has been oriented in the -30 degree direction of the electrical angle phase at this time, the position detection value stored in the internal EEPROM of the encoder corresponds to the -30 degree phase of the motor electrical angle. After that, the drive will make the difference between the single-turn position detection data at any time and this stored value, and perform the necessary conversion according to the number of motor pole pairs, and add -30 degrees to obtain the electrical angle phase of the motor at that time.
This alignment requires the support and cooperation of the encoder and the servo driver. The fundamental reason why the encoder phase of the Japanese servo is not convenient for the end user to directly adjust is that it refuses to provide users with the functional interface and Method of operation. The big advantage of this alignment method is that it only needs to provide the motor windings with the rotor orientation current that determines the phase sequence and direction, without adjusting the angle relationship between the encoder and the motor shaft, so the encoder can be directly installed at any initial angle. On the motor, there is no need for fine or even simple adjustment process, simple operation and good manufacturability.
If the absolute encoder neither has EEPROM available for use, nor has the highest count bit pin available for detection, the alignment method will be relatively complicated. If the drive supports the readout and display of single-turn absolute position information, you can consider:
1. Use a DC power supply to pass a DC current less than the rated current to the UV winding of the motor, V in, U out, and orient the motor shaft to a balanced position;
2. Use the servo drive to read and display the single-turn position value of the absolute encoder;
3. Adjust the relative position of the encoder shaft and the motor shaft;
4. After the above adjustment, make the displayed single-turn absolute position value sufficiently close to the corresponding single-turn absolute position point of the motor -30 degree electrical angle calculated according to the number of pole pairs of the motor, and lock the relative position relationship between the encoder and the motor ；
5. Twist the motor shaft back and forth, after letting go, if the motor shaft freely returns to the equilibrium position each time, the above-mentioned converted position points can be accurately reproduced, the alignment is effective.
If the user cannot even obtain the absolute value information, he can only use the original factory special tooling to detect the absolute position detection value while detecting the electrical angle phase of the motor. Use the tooling to adjust the relative angular position relationship between the encoder and the motor. The encoder phase and the electrical angle phase of the motor are aligned with each other, and then locked. In this way, the user has no way to solve the phase alignment problem of the encoder by himself.
Personally recommend the method of storing the initial installation position in EEPROM, which is simple, practical, and easy to open to users so that users can install the encoder by themselves and complete the phase adjustment of the electrical angle of the motor.
Phase alignment of sin-cos encoder
The ordinary sine-cosine encoder has a pair of quadrature sin, cos 1Vp-p signals, which is equivalent to the AB quadrature signal of the incremental encoder of the square wave signal, and many signal cycles are repeated in each circle, such as 2048 And a narrow symmetrical triangle wave Index signal, which is equivalent to the Z signal of an incremental encoder, usually one per revolution; this sine-cosine encoder is essentially an incremental encoder. In addition to the above-mentioned orthogonal sin and cos signals, another sine-cosine encoder is equipped with mutually orthogonal 1Vp-p sinusoidal C and D signals in which only one signal period appears in one turn. If the C signal is used If it is sin, the D signal is cos, and the encoder shaft is rotated counterclockwise. The Index signal equivalent to the Z signal will generally be aligned with the zero crossing point of the C signal from low to high. Through the high-rate subdivision technology of sin and cos signals, not only can the sine-cosine encoder obtain a finer nominal detection resolution than the original signal period, such as 2048-line sine-cosine encoder after 2048 subdivision, it can achieve With a nominal detection resolution of more than 4 million lines per revolution, many European and American servo manufacturers currently provide such high-resolution servo systems, but domestic manufacturers are still rare; in addition, the C, D signal of the sine-cosine encoder After the D signal is subdivided, it can also provide higher absolute position information per revolution, such as 2048 absolute positions per revolution. Therefore, the sine cosine encoder with C and D signals can be regarded as an analog single-turn absolute encoder Device.
The initial electrical angle phase alignment of the servo motor using this encoder is as follows:
1. Use a DC power supply to pass a DC current less than the rated current to the UV winding of the motor, V in, U out, and orient the motor shaft to a balanced position;
2. Use an oscilloscope to observe the C signal and Index signal waveforms of the sine-cosine encoder;
3. Adjust the relative position of the encoder shaft and the motor shaft;
4. While adjusting, observe the waveforms of C signal and Index signal until the zero-crossing point of C signal or the effective level of Index signal accurately appear at the directional balance position of the motor shaft, and lock the relative position relationship between the encoder and the motor;
5. Twist the motor shaft back and forth and let it go. If the zero-crossing point of the C signal or the effective level of the Index signal can be accurately reproduced every time the motor shaft returns to the equilibrium position freely, the alignment is effective.
After removing the DC power supply, verify as follows:
1. Use an oscilloscope to observe the C-phase signal of the encoder and the UV back-EMF waveform of the motor;
2. Rotate the motor shaft counterclockwise, the zero-crossing point of the C phase signal of the encoder from low to high or the jump edge of the Index signal coincides with the zero-crossing point of the motor's UV line back-EMF waveform from low to high.
This verification method can also be used as an alignment method.
At this time, the zero-crossing point of the C signal is aligned with the -30 degree point of the electrical angle phase of the motor.
If you want to align directly with the 0 degree point of the electrical angle of the motor, you can consider:
1. Use a DC power supply to pass a DC current smaller than the rated current to the UVW winding of the motor, VW in, U out, and orient the motor shaft to a balanced position
2. Use an oscilloscope to observe the C signal and Index signal waveform of the encoder;
3. Adjust the relative position of the encoder shaft and the motor shaft;
4. While adjusting, observe the waveforms of C signal and Index signal until the zero-crossing point of C signal or the effective level of Index signal accurately appear at the directional balance position of the motor shaft, and lock the relative position relationship between the encoder and the motor;
5. Twist the motor shaft back and forth and let it go. If the zero-crossing point of the C signal or the effective level of the Index signal can be stabilized at a high level every time the motor shaft freely returns to the equilibrium position, the alignment is effective.
The verification method is as follows:
1. Connect 3 resistors of equal resistance value into a star shape, and then connect the 3 resistors connected in the star shape to the UVW three-phase winding leads of the motor respectively;
2. Observe the midpoint of the motor's U-phase input and star resistance with an oscilloscope, you can approximate the motor's U reverse potential waveform;
3. Rotate the encoder shaft counterclockwise and observe that the zero-crossing point of the encoder's phase C signal from low to high or the jump edge of the Index signal should coincide with the zero-crossing point of the motor U opposite potential waveform from low to high.
The above verification method can also be used as an alignment method.
Since ordinary sine-cosine encoders do not have phase information within a circle, and the Index signal can only reflect one point within a circle, it does not have the potential for direct phase alignment, so it is not a topic of discussion here.
If the servo drive that can be connected to the sine-cosine encoder can provide users with the absolute position information of a single circle obtained from C and D, you can consider:
1. Use a DC power supply to pass a DC current less than the rated current to the UV winding of the motor, V in, U out, and orient the motor shaft to a balanced position;
2. Use the servo drive to read and display the absolute position information of the single circle obtained from the C and D signals;
3. Adjust the relative position of the resolver shaft and the motor shaft;
4. After the above adjustments, make the displayed absolute position value sufficiently close to the absolute position point corresponding to the -30 degree electrical angle of the motor converted according to the number of pole pairs of the motor, and lock the relative position relationship between the encoder and the motor;
5. Twist the motor shaft back and forth, after letting go, if the motor shaft freely returns to the equilibrium position every time, the above converted absolute position points can be accurately reproduced, and the alignment is effective.
After that, after removing the DC power supply, the alignment verification effect is basically the same as before:
1. Use an oscilloscope to observe the C-phase signal of the sine-cosine encoder and the UV line back EMF waveform of the motor;
2. Rotate the motor shaft to verify that the zero-crossing point of the encoder's phase C signal from low to high coincides with the zero-crossing point of the motor's UV line back-EMF waveform from low to high.
If you use non-volatile memory such as EEPROM inside the drive, you can also store the phase measured after the sine-cosine encoder is randomly installed on the motor shaft. The specific method is as follows:
1. Install the sine and cosine on the motor randomly, that is, consolidate the encoder shaft and motor shaft, as well as the encoder shell and the motor shell;
2. Use a DC power supply to pass a DC current less than the rated current to the UV winding of the motor, V in, U out, and orient the motor shaft to a balanced position;
3. Use the servo drive to read the single-turn absolute position value analyzed by the C and D signals, and store it in the drive's internal non-volatile memory such as EEPROM that records the initial installation phase of the motor's electrical angle;
4. The alignment process ends.
Since the motor shaft has been oriented in the -30 degree direction of the electrical angle phase at this time, the position detection value stored in the drive's internal EEPROM and other non-volatile memory corresponds to the -30 degree phase of the motor electrical angle. After that, the drive will make the difference between the single-turn absolute position value related to the electrical angle parsed by the encoder at any time and the stored value, and perform the necessary conversion according to the number of motor pole pairs, plus -30 degrees, you can get The electrical angle phase of the motor at this moment.
This kind of alignment requires the domestic and operational support and cooperation of the servo drive. Moreover, since the non-volatile memory such as EEPROM that records the initial phase of the electrical angle of the motor is located in the servo drive, once aligned, the motor is aligned with The drive is actually bound. If you need to replace the motor, sine-cosine encoder, or drive, you need to re-align the initial installation phase and re-bind the matching relationship between the motor and the drive.
Phase alignment of resolver
The resolver is abbreviated as resolver. It is composed of high-performance silicon steel laminates and enameled wires with a special electromagnetic design. Compared with the encoder using photoelectric technology, it has heat resistance and vibration resistance. The ability to adapt to harsh working environments such as impact resistance, oil resistance, and even corrosion resistance, so it is widely used in applications with harsh working conditions such as weapon systems. A pair of pole (single speed) resolvers can be regarded as a single-turn absolute feedback The system is also the most widely used. Therefore, only single-speed rotary transformers will be discussed here. Multi-speed rotary transformers are matched with servo motors. I personally think that the number of pole pairs is best to use the submultiple of the motor pole pairs. Correspondence and pole logarithmic decomposition.
The resolver's signal leads are generally six, divided into three groups, corresponding to one excitation coil and two orthogonal induction coils. The excitation coil receives the input sinusoidal excitation signal, and the induction coils are based on the mutual angle of the resolver stator The positional relationship induces detection signals with SIN and COS envelopes. The resolver SIN and COS output signals are the result of modulating the excitation sinusoidal signal according to the angle between the rotor and the stator. If the excitation signal is sinωt and the electrical angle between the rotor and stator is θ, then the SIN signal is sinωt×sinθ, then the COS signal It is sinωt×cosθ. According to the SIN, COS signals and the original excitation signal, through the necessary detection circuit, a higher resolution position detection result can be obtained. The detection resolution of the current commercial resolver system can reach 12 per revolution. The power is 4096, and scientific research and aerospace systems can even reach 2 to the 20th power, but the volume and cost are also very considerable.
Here, it is assumed that when the resolver rotor CCW rotates, the electrical angle phase of the resolver increases, and the resolver rotor CW rotates, and the resolver electrical angle phase decreases.
The method of aligning the electrical angle phase of commercial resolver and servo motor is as follows:
1. Use a DC power supply to pass a DC current less than the rated current to the UV winding of the motor, V in, U out;
2. Then use an oscilloscope to observe the signal lead output of the resolver's SIN coil;
3. According to the convenience of operation, adjust the relative position of the resolver rotor on the motor shaft and the motor shaft, or the relative position of the resolver stator and the motor housing;
4. While adjusting, observe the envelope of the resolver SIN signal, adjust until the amplitude of the signal envelope is completely zeroed, and lock the resolver;
(4'). While adjusting, observe the Lissajous figure with the resolver Sin signal as the horizontal axis and the excitation signal as the vertical axis until the Lissajous figure becomes a vertical line that coincides with the ordinate, and faces the CCW direction Twist the perpendicular to the 1st and 3rd quadrants, and twist the perpendicular to the 2nd and 4th quadrants in the CW direction to lock the resolver;
5. Twist the motor shaft back and forth, and after letting go, if the motor shaft freely returns to the equilibrium position each time, the zero-crossing point of the signal envelope amplitude can be accurately reproduced, or the Lissajous figure can coincide with the ordinate as a vertical axis. Line, the alignment is valid.
Remove the DC power supply and perform alignment verification:
1. Use an oscilloscope to observe the resolver's SIN signal and the motor's UV line back EMF waveform;
2. Rotate the motor shaft to verify that the zero-crossing point of the resolver's SIN signal envelope coincides with the zero-crossing point of the motor's UV line back-EMF waveform from low to high.
This verification method can also be used as an alignment method.
At this time, the zero-crossing point of the SIN signal envelope is aligned with the -30 degree point of the electrical angle phase of the motor.
If you want to align directly with the 0 degree point of the electrical angle of the motor, you can consider:
1. Use a DC power supply to pass a DC current less than the rated current to the UVW winding of the motor, VW in, U out, and orient the motor shaft to a balanced position;
2. Observe the resolver's SIN signal with an oscilloscope;
3. Adjust the relative position of the resolver shaft and the motor shaft;
4. While adjusting, observe the envelope waveform of the SIN signal, adjust until the amplitude of the signal envelope is completely zeroed, and lock the resolver;
(4'). While adjusting, observe the Lissajous figure with the resolver Sin signal as the horizontal axis and the excitation signal as the vertical axis until the Lissajous figure becomes a vertical line that coincides with the ordinate, and faces the CCW direction Twist the perpendicular to the 1st and 3rd quadrants, and twist the perpendicular to the 2nd and 4th quadrants in the CW direction to lock the resolver;
5. Twist the motor shaft back and forth, and after letting go, if the motor shaft freely returns to the equilibrium position each time, the zero-crossing point of the signal envelope amplitude can be accurately reproduced, or the Lissajous figure can coincide with the ordinate as a vertical axis. Line, the alignment is valid.
The verification method is as follows:
1. Connect 3 resistors of equal resistance value into a star shape, and then connect the 3 resistors connected in the star shape to the UVW three-phase winding leads of the motor respectively;
2. Observe the midpoint of the motor's U-phase input and star resistance with an oscilloscope, you can approximate the motor's U reverse potential waveform;
3. Use an oscilloscope to observe the zero-crossing point of the resolver's SIN signal envelope and the zero-crossing point of the reverse potential waveform of the motor U from low to high. These two zero-crossing points should coincide.
The above verification method can also be used as an alignment method.
It should be pointed out that in the above operation, it is necessary to effectively distinguish the positive half cycle and the negative half cycle in the resolver's SIN envelope signal. Since the SIN signal is the modulation result of the excitation signal with the sinθ value of the angle between the stator and the stator, in the SIN signal envelope corresponding to the positive half cycle of sinθ, the modulated excitation signal is in phase with the original excitation signal, and In the SIN signal envelope corresponding to the negative half cycle of sinθ, the modulated excitation signal is inverted from the original excitation signal. Based on this, the positive and negative half cycles of the SIN envelope signal waveform output by the resolver can be distinguished. Take the zero-crossing point of the SIN envelope signal corresponding to the transition point of sinθ from the negative half-circle to the positive half-circle. If it is inverted or not accurately judged, the aligned electrical angle may be misaligned by 180 degrees, which may cause the outer speed loop Enter positive feedback.
If the resolver-enabled servo drive can provide users with absolute position information related to the electrical angle of the motor obtained from the resolver signal, you can consider:
1. Use a DC power supply to pass a DC current less than the rated current to the UV winding of the motor, V in, U out, and orient the motor shaft to a balanced position;
2. Use the servo drive to read and display the absolute position information related to the electrical angle of the motor obtained from the resolver signal;
3. According to the convenience of operation, adjust the relative position of the resolver shaft and the motor shaft, or the relative position of the resolver housing and the motor housing;
4. After the above adjustment, make the displayed absolute position value sufficiently close to the absolute position point corresponding to the -30 degree electrical angle of the motor, which is converted according to the number of pole pairs of the motor, and lock the relative position relationship between the rotary actuator and the motor shaft;
5. Twist the motor shaft back and forth, after letting go, if the motor shaft freely returns to the equilibrium position every time, the above converted absolute position points can be accurately reproduced, and the alignment is effective.
After that, after removing the DC power supply, the alignment verification effect is basically the same as before:
1. Use an oscilloscope to observe the resolver's SIN signal and the motor's UV line back EMF waveform;
2. Rotate the motor shaft to verify that the zero-crossing point of the resolver's SIN signal envelope coincides with the zero-crossing point of the motor's UV line back-EMF waveform from low to high.
If you use non-volatile memory such as EEPROM inside the drive, you can also store the measured phase after the resolver is randomly installed on the motor shaft. The specific method is as follows:
1. Install the resolver on the motor randomly, that is, consolidate the resolver shaft and the motor shaft, as well as the resolver housing and the motor housing;
2. Use a DC power supply to pass a DC current less than the rated current to the UV winding of the motor, V in, U out, and orient the motor shaft to a balanced position;
3. Use the servo drive to read the absolute position value related to the electrical angle resolved by the resolver, and store it in the drive's internal non-volatile memory such as EEPROM that records the initial installation phase of the motor electrical angle;
4. The alignment process ends.
Since the motor shaft has been oriented in the -30 degree direction of the electrical angle phase at this time, the position detection value stored in the drive's internal EEPROM and other non-volatile memory corresponds to the -30 degree phase of the motor electrical angle. After that, the drive will make the difference between the absolute position value related to the electrical angle resolved by the resolver at any time and the stored value, and perform the necessary conversion according to the number of motor pole pairs, and add -30 degrees to get the time The electrical angle phase of the motor.
This kind of alignment requires the domestic and operational support and cooperation of the servo drive. Moreover, since the non-volatile memory such as EEPROM that records the initial phase of the electrical angle of the motor is located in the servo drive, once aligned, the motor is aligned with The drive is actually bound. If you need to replace the motor, resolver, or drive, you need to re-align the initial installation phase and re-bind the matching relationship between the motor and the drive.
note
1. In the above discussion, the so-called -30-degree phase alignment to the electrical angle of the motor is based on the premise that the UV back-EMF waveform lags the U-phase 30 degrees.
2. In the above discussion, the VU phase is energized and the UV line back-EMF waveform is referred to as an example. Some servo system alignment methods may use UW phase energization and refer to the UW line back-EMF waveform.
3. If you want to directly align to the 0 degree phase point of the electrical angle of the motor, you can also connect the U phase to the negative end of the low voltage DC source, connect the V phase and W phase in parallel to the positive end of the DC source. The orientation angle will be offset by 30 degrees relative to the way the UV phase is energized in series. After aligning with the corresponding alignment method given in the article, it will in principle be aligned to the 0-degree phase of the electrical angle of the motor, instead of -30 degrees. the amount. This seems to be beneficial, but considering the inconsistency of the motor winding parameters, after the V-phase and W-phase are connected in parallel, the currents flowing through the V-phase and W-phase windings are likely to be inconsistent, which will affect the accuracy of the motor shaft orientation angle. . When the VU phase is energized, the U-phase and V-phase windings are simply connected in series, so the current flowing through the U-phase and V-phase windings must be the same, and the accuracy of the motor shaft orientation angle will not be affected by the winding orientation current .
4. It is not ruled out that the servo manufacturer intentionally misaligned the initial phase, especially in the feedback system that can provide absolute position data, the misalignment of the initial phase will be easily compensated by the offset of the data, in this way Maybe it can play a role in protecting one's own product line. Only in this way, the user has no way of knowing where the initial phase of the servo motor feedback element should be aligned. Naturally, users are not willing to meet such a supplier.
Summary of basic methods of electrical angle phase alignment
1. Waveform observation method
Suitable for incremental encoders, sine and cosine encoders, resolvers with commutation signals.
1) Use an oscilloscope to directly observe the phase alignment relationship between the zero-crossing point of the UV line back-EMF waveform and the rising edge/Z signal of the sensor's U-phase signal, or the zero-crossing point of the Sin signal, or the zero-crossing point of the Sin envelope signal. The above signal edges or zero crossing points are aligned to -30 degrees electrical angle phase;
2) A star shape is formed by three equivalent resistors with an appropriate resistance range, connected to the UVW power line of the permanent magnet servo motor, and the virtual U between the center point of the U-phase power line and the star equivalent resistance is observed with an oscilloscope. The potential waveform and the phase alignment relationship with the sensor's U-phase signal rising edge/Z signal, or Sin signal zero-crossing point, or Sin envelope signal zero-crossing point, this method can align the above-mentioned signal edge or zero-crossing point of the sensor to an electrical angle Phase 0 point;
2. Rotor orientation method
It is suitable for the waveform alignment of incremental encoders with commutation signals, sine and cosine codes, resolvers, or absolute encoders, sine and cosine codes, resolvers, etc. that can provide single-turn absolute position value information alignment.
1) Connect the V phase to the positive terminal of the low-voltage DC source and the U phase to the negative terminal of the DC source to orient the motor shaft
After that, while adjusting the relative position relationship between the sensor and the motor, observe the sensor signal with an oscilloscope until the rising edge of the U-phase signal or the Z signal, or the zero-crossing point of the Sin signal, or the zero-crossing point of the Sin envelope signal is accurately reproduced. The above-mentioned signal edge or zero-crossing point of the sensor is aligned to -30 degrees electrical angle phase;
You can also adjust the relative position relationship between the sensor and the motor while trying to observe the numerical information of the single-turn absolute position until the data zero is accurately reproduced. This method can also align the single-turn absolute position zero of the sensor to -30 degrees. Angular phase
If the value of the absolute position of the single-turn corresponding to the electrical angle of -30 degrees is estimated in advance, the relative position relationship between the sensor and the motor can be adjusted until the value is accurately reproduced, and the zero point of the single-turn absolute position can be directly aligned to the electrical angle phase. 0 points (this method may be more accurate than the latter method that will be summarized in the next section 2);
Of course, it is not necessary to adjust the relative position relationship between the sensor and the motor, but simply install the encoder randomly, use the read absolute position information of the single circle as the initial installation offset value, and realize the absolute position of the single circle through subsequent calculations. The logical alignment of the information and the electrical angle phase zero point requires the lowest manual operation.
2) Connect the U phase to the negative pole of the low voltage DC source, connect the V phase and W phase in parallel to the positive pole of the DC source, and orient the motor shaft
After that, while adjusting the relative position relationship between the sensor and the motor, observe the sensor signal with an oscilloscope until the rising edge of the U-phase signal or the Z signal, or the zero-crossing point of the Sin signal, or the zero-crossing point of the Sin envelope signal is accurately reproduced. The above-mentioned signal edge or zero-crossing point of the sensor is aligned to the electrical angle phase 0 point;
You can also adjust the relative position relationship between the sensor and the motor while trying to observe the numerical information of the single-turn absolute position until the data zero is accurately reproduced. This method can also align the above-mentioned signal edge or zero-crossing point of the sensor to the electrical angle phase 0 points.