Method for sensorless detection of load torque of stepping motor based on current chopping mode

Abstract

The present invention relates to the technical field of motor load torque detection, and discloses a method for sensorless detection of the load torque of a stepping motor based on the current chopping mode. In the present invention, during the rotation of the motor controlled by current chopping, the charging and discharging times of the inductance on the motor winding are counted, and the change of the load torque is judged according to the energy change in the two stages of inductance charging and discharging. The open-loop control method is adopted, and no sensor is used to measure the load torque. By calculating the time integral difference between tON and tFD within the current chopping period, the change of the load torque is estimated, rather than estimating the load torque by detecting the winding terminal voltage at the current zero crossing point and measuring the back electromotive force (BEMF). The open-loop control does not use sensors, the circuit is simple and the cost is low, solving the problem of high cost in detecting the load torque in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of motor load torque detection, and particularly to a method for sensorless detection of the load torque of a stepping motor based on a current chopping mode. Background Art

[0002] The output torque of a stepping motor is related to the current. In a traditional open-loop drive system of a stepping motor, in order to generate sufficient torque, the current is maintained at the maximum value. However, in most cases, the torque actually required by the load is not that large (for example, most ATMs are in a stationary or low-speed state), that is, the torque output by the motor is overly redundant, which will cause a large amount of energy loss and the temperature rise will affect the service life of the motor.

[0003] Therefore, increasing the detection of the load torque and adjusting the current size accordingly is an important function of the stepping motor drive system. To detect the load torque, there are two existing technologies. One is called closed-loop control, which relies on a position sensor and can accurately detect the change of the load torque, but the cost will increase. The other is open-loop control. Under the micro-stepping chopping control technology, when the current waveform on the winding of the stepping motor passes through the zero point, the voltage across the winding is detected. This voltage can show the magnitude of the back electromotive force BEMF at the current speed, and the magnitude of the load torque can be indirectly deduced.

[0004] In the prior art, the closed-loop control relies on sensors, which increases the complexity and cost of the system; for open-loop control, detecting the voltage across the winding, i.e., the back electromotive force BEMF, when the current passes through the zero point, has the following disadvantages: 1) It is difficult to accurately control the current zero point. If the winding current is not 0, the collected voltage includes the voltage of the resistance and inductance on the winding; 2) The acquisition window will limit the motor from running at high speed, and there may be a period of voltage oscillation on the winding when switching to the zero point, and it is necessary to wait for it to stabilize, which will further lengthen the time of the acquisition window; 3) It must be detected under micro-stepping operation. In full-step application, there is no zero crossing point and it cannot be detected; 4) The back electromotive force BEMF is too small at low speed to be detected. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for sensorless detection of the load torque of a stepping motor based on a current chopping mode, aiming to solve the problem of high cost in detecting the load torque in the prior art.

[0006] The present invention is implemented as follows. In the first aspect, the present invention provides a method for sensorless detection of the load torque of a stepping motor based on a current chopping mode, including:

[0007] Controlling the stepping motor to rotate through a current chopping mode, and the current chopping mode includes a charging stage, a fast decay stage, and a slow decay stage;

[0008] Perform a periodic analysis of the current waveform of the motor winding of a stepper motor in current chopping mode to divide the current sine waveform period of the motor winding into four quadrants: Q1, Q2, Q3, and Q4;

[0009] Mark the motor winding in the stepper motor that needs to estimate the load torque as the target estimation winding, and select the corresponding quadrants of the four quadrants Q1, Q2, Q3, and Q4 according to the target estimation winding to obtain the target analysis quadrant;

[0010] Perform time accumulation processing on the charging stage and the rapid decay stage of the target analysis quadrant to obtain the total charging time and the total rapid decay time in the target analysis quadrant;

[0011] Perform difference analysis on the total charging time and the total rapid decay time to obtain the torque change feedback characteristic;

[0012] Obtain the out-of-step deviation value of the stepper motor, and perform deviation correction processing on the torque change feedback characteristic according to the out-of-step deviation value to obtain the load torque estimation value of the target estimation winding of the stepper motor.

[0013] The present invention provides a method for sensorless detection of the load torque of a stepper motor based on the current chopping mode, and has the following beneficial effects:

[0014] In the present invention, during the process of controlling the rotation of the motor by current chopping, the charging and discharging times of the inductance on the motor winding are statistically calculated, and the change of the load torque is judged according to the change of the energy in the two stages of inductance charging and discharging. An open-loop control method is adopted, and no sensor is used to measure the load torque. By calculating the time integral difference between tON and tFD within the current chopping period, the change of the load torque is estimated, rather than by detecting the winding terminal voltage when the current passes through zero, and estimating the load torque by measuring the back electromotive force (BEMF). With open-loop control and no use of sensors, the circuit is simple and the cost is low, solving the problem of high cost in detecting the load torque in the prior art. Description of the Drawings

[0015] Figure 1 is a schematic diagram of the steps of a method for sensorless detection of the load torque of a stepper motor based on the current chopping mode provided by an embodiment of the present invention;

[0016] Figure 2 is a schematic diagram of the structure of a stepper motor provided by an embodiment of the present invention;

[0017] Figure 3 is another schematic diagram of the structure of a stepper motor provided by an embodiment of the present invention;

[0018] Figure 4It is a schematic diagram of the period of the stepper motor provided by the embodiment of the present invention in the current chopping mode;

[0019] Figure 5 It is a waveform diagram of the winding of the stepper motor provided by the embodiment of the present invention in the current rising stage;

[0020] Figure 6 It is a waveform diagram of the winding of the stepper motor provided by the embodiment of the present invention in the current falling stage;

[0021] Figure 7 It is a schematic diagram of the correlation between the current chopping period and the current falling stage of the stepper motor provided by the embodiment of the present invention. Detailed implementation manners

[0022] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

[0023] The implementation of the present invention will be described in detail below with reference to specific embodiments.

[0024] Refer to Figures 1-7 As shown, it is a preferred embodiment provided by the present invention.

[0025] In the first aspect, the present invention provides a method for sensorless detection of the load torque of a stepper motor based on the current chopping mode, including:

[0026] S1: Controlling the rotation of the stepper motor through the current chopping mode, where the current chopping mode includes a charging stage, a fast decay stage, and a slow decay stage;

[0027] S2: Performing a periodic analysis of the current waveform of the motor winding of the stepper motor in the current chopping mode to divide the current sine waveform period of the motor winding into four quadrants Q1, Q2, Q3, and Q4;

[0028] S3: Marking the motor winding that needs to estimate the load torque in the stepper motor as the target estimation winding, and selecting the corresponding quadrants of Q1, Q2, Q3, and Q4 according to the target estimation winding to obtain the target analysis quadrant;

[0029] S4: Performing a time accumulation process on the charging stage and the fast decay stage of the target analysis quadrant to obtain the total charging time and the total fast decay time in the target analysis quadrant;

[0030] S5: Performing a difference analysis on the total charging time and the total fast decay time to obtain a torque change feedback feature;

[0031] S6: Obtain the out-of-step deviation value of the stepping motor, and perform deviation correction processing on the torque change feedback feature according to the out-of-step deviation value to obtain the load torque estimation value of the target estimated winding of the stepping motor.

[0032] Specifically, in step S1 of the embodiment provided by the present invention, the current chopping mode is a method for controlling the current of a motor (especially a stepping motor and a DC motor). Its core idea is to adjust the current by quickly switching the on-off state of the power supply, so as to achieve precise control of the motor. The current chopping mode usually uses PWM (Pulse Width Modulation) technology. PWM control adjusts the current of the motor by changing the duty cycle of the pulse signal (that is, the switching time ratio of the pulse signal). The current chopping mode needs to monitor the current in the motor winding in real time. When the current reaches the set upper limit value, the control circuit will quickly cut off the power supply (enter the fast or slow decay stage). When the current drops to the set lower limit value, the power supply will be turned on again (enter the charging stage).

[0033] More specifically, the current chopping mode includes three main stages: Charging stage: The power switch is turned on, the current starts to increase, and the current in the motor winding rises; Fast decay stage: The power switch is turned off, and the current drops rapidly. This stage is usually achieved through the freewheeling diode in the winding; Slow decay stage: The power switch is turned off, but the current slowly drops through the inductance of the motor winding. This stage is usually achieved through the free-running diode.

[0034] More specifically, with the development of technology, in order to make the motor rotate more smoothly, the micro-stepping technology is usually adopted to control the current shapes loaded on the two-phase windings (phase A and phase B) of the stepping motor to be sine waveforms, so that the current change is smoother. The phase difference between the two phases is 90° (reference Figure 4 ), since micro-stepping is a commonly used technology, it will not be elaborated here.

[0035] Specifically, in step S2 of the embodiment provided by the present invention, perform a period analysis on the current waveform of the motor winding of the stepping motor in the current chopping mode to divide the sine waveform period of the current of the motor winding into four quadrants Q1, Q2, Q3, and Q4.

[0036] More specifically, since the current on the control winding by the current chopping is a sine waveform, a sine period can be divided into four quadrants Q1 / Q2 / Q3 / Q4. Taking the phase A winding as an example, the current on the Q1 and Q2 windings flows from AOUT1 to AOUT2, and the current on the Q3 and Q4 flows from AOUT2 to AOUT1.

[0037] More specifically, reference Figure 5, I_REF is the target current for each microstep. During the charging phase (i.e., the tON phase), the current on the winding inductance rises. When it reaches I_REF, the charging phase ends, and then it enters the decay phase (the decay period tOFF is configurable). Q1 and Q3 are the current rising quadrants. Only in the slow decay phase (i.e., the tSD phase) (refer to Figure 6 , tOFF = tSD), Q2 and Q4 are the current falling quadrants, which consist of the fast decay phase (i.e., the tFD phase) and the slow decay phase (i.e., the tSD phase) (the tFD period can also be configured, but it should satisfy tOFF = tFD + tSD). Refer to Figure 6 , where tBLANK is the blanking time of the current comparator, which is the minimum delay from the start of tON to the comparator stably detecting the current, and is also simply referred to as tBL.

[0038] Specifically, in step S3 of the embodiment provided by the present invention, determine the motor windings in the stepper motor that need to estimate the load torque. Generally, a stepper motor has multiple windings (such as the A-phase and B-phase windings), and one or more windings need to be selected as the target estimation windings.

[0039] More specifically, divide the current sine waveform period of the stepper motor into four quadrants: Q1, Q2, Q3, Q4. Each quadrant represents a specific stage of the current waveform. For example: Q1: the current rising stage, Q2: the current reaches the peak and starts to fall, Q3: the current falling stage, Q4: the current reaches the valley and starts to rise.

[0040] More specifically, according to the target estimation windings, select the corresponding quadrants of the windings for the four quadrants of the current waveform period. The goal of this step is to determine the current behavior in each quadrant for load torque estimation. Based on the current characteristics of the target estimation windings, select one or more quadrants as the target analysis quadrants. The target analysis quadrants are important time periods for load torque estimation.

[0041] Specifically, in step S4 of the embodiment provided by the present invention, perform time accumulation processing on the charging phase and the fast decay phase in the target analysis quadrants to obtain the total charging time and the total fast decay time in the target analysis quadrants.

[0042] Specifically, in step S5 of the embodiment provided by the present invention, perform difference analysis on the total charging time and the total fast decay time to obtain the torque change feedback characteristics.

[0043] It should be noted that, from the perspective of energy, in the current drop quadrant (sinusoidal waveform Q2 / Q4), the change in load torque is deduced based on the changes in tON and tFD within the chopping period. Taking the sinusoidal current of phase A winding in the Q2 quadrant as an example, it should be clear that at the beginning of the current Q2 quadrant, the winding inductance has stored the full energy EL, which was filled during the tON period in the Q1 quadrant. And throughout the Q2 quadrant, it is a process of the inductance energy release. During this process, the energy to overcome the torque mainly comes from EL and the very short power supply (at the tON moment).

[0044] More specifically, after the start of the Q2 stage, the energy changes during the tON and tFD stages within each chopping period are analyzed separately.

[0045] More specifically, during the tON stage, the energy output by the power supply VM, EON = ELstore + ETon, where ELstore is the energy stored in the winding inductance and ETon is the energy to overcome the load torque.

[0046] More specifically, during the tFD stage, the energy released by the winding inductance, ELrelease = EFD + ETfd, where EFD is the energy fed back to the power supply (which can be called useless work or reactive power), and ETfd is the energy to overcome the load torque.

[0047] More specifically, when the load carried by the motor is small or no-load, both ETon and ETfd are very small, and the EON energy is all converted into ELstore. To maintain the sinusoidal current drop (Q2 / Q4), ELrelease ≈ EFD should be greater than ELstore, so that the energy EL stored in Q1 can be released completely, that is, EL + ELstore - ELrelease = 0, which means that the TtFD discharge time should be much greater than the TtON charge time (here TtFD and TtON refer to the total time of tON and tFD within all chopping periods of the entire quadrant). Otherwise, the current cannot be controlled according to the sinusoidal waveform, which is determined by the characteristics of the current chopping mode.

[0048] More specifically, when the load increases, both ETon and ETfd increase. At this time, EON is almost all provided to ETon, and ELstore is almost 0. Note that if ELrelease releases too fast, some energy still needs to be supplemented to ELstore, and the tON time will increase, that is, TtON will increase relatively. And ELrelease is almost all provided to ETfd, then EFD will decrease (EFD will not be 0 because the minimum tFD in each chopping period is the same as the minimum tBL time of tON), that is, TtFD will decrease relatively.

[0049] In summary, the difference between TtFD and TtON (the total time integral difference of tFD and tON, with the unit being microseconds, us) can indirectly reflect the change in load torque.

[0050] Specifically, in step S6 of the embodiment provided by the present invention, the out-of-step deviation value of the stepper motor is obtained, and the torque change feedback characteristic is corrected according to the out-of-step deviation value to obtain the load torque estimation value of the target estimated winding of the stepper motor.

[0051] It should be noted that let the load torque estimation value TorqueLoad = TtFD - TtON. According to the foregoing, when the load is very small or no-load, TorqueLoad is much greater than 0, which may be several hundred microseconds. When the load increases, TorqueLoad will gradually decrease. When it drops to near 0, the load torque will exceed the maximum torque output by the motor, resulting in out-of-step or stalling. Specifically, at what value of TorqueLoad the out-of-step occurs is related to the type of stepper motor (different resistances and inductances), the power supply voltage, and the working current, because these parameters will affect the charging and discharging current of the winding, and further cause tON and tOFF to change, resulting in the out-of-step threshold may be between -100 and 100; therefore, an out-of-step deviation value Soffset needs to be added, and the formula becomes TorqueLoad = TtFD - TtON + Soffset. For the same model of stepper motor, Soffset is basically fixed.

[0052] Note that in the Q4 quadrant, the load torque estimation value can also be calculated. It's just that the current direction is from AOUT2 to AOUT1. When AOUT2 = H and AOUT1 = L, it is tON; when AOUT2 = L and AOUT1 = H, it is tFD; when AOUT2 = L and AOUT1 = L, it is tSD.

[0053] Therefore, the load torque estimation value of winding A can be calculated in the Q2 / Q4 quadrant. Similarly, the load torque estimation value of winding B can be calculated in the Q1 / Q3 quadrant. In this way, a TorqueLoad can be obtained in each quadrant.

[0054] The present invention provides a method for sensorless detection of the load torque of a stepper motor based on the current chopping mode, which has the following beneficial effects:

[0055] During the rotation of the motor controlled by current chopping in the present invention, the charging and discharging times of the inductance on the motor winding are counted, and the change of the load torque is judged according to the energy change in the two stages of inductance charging and discharging. An open-loop control method is adopted without using a sensor to measure the load torque. The change of the load torque is estimated by calculating the time integral difference between tON and tFD within the current chopping period, rather than estimating the load torque by detecting the winding terminal voltage at the zero-crossing point of the current and measuring the back electromotive force (BEMF). The open-loop control does not use a sensor, the circuit is simple and the cost is low, which solves the problem of high cost of detecting the load torque in the prior art.

[0056] Preferably, the stepper motor has a phase-A winding and a phase-B winding, and the stepper motor has output terminals AOUT1 and AOUT2;

[0057] In the Q1 and Q2 quadrants, the current of the phase-A winding flows from AOUT1 to AOUT2, and the current of the phase-B winding flows from AOUT2 to AOUT1;

[0058] In the Q3 and Q4 quadrants, the current of the phase-A winding flows from AOUT2 to AOUT1, and the current of the phase-B winding flows from AOUT1 to AOUT2.

[0059] Specifically, the stepper motor has two windings: a phase-A winding and a phase-B winding, and the output terminals of the motor are AOUT1 and AOUT2. In the Q1 and Q2 quadrants: the current of the phase-A winding flows from AOUT1 to AOUT2, and the current of the phase-B winding flows from AOUT2 to AOUT1; in the Q3 and Q4 quadrants: the current of the phase-A winding flows from AOUT2 to AOUT1, and the current of the phase-B winding flows from AOUT1 to AOUT2.

[0060] More specifically, the current flow directions in each quadrant are recorded and analyzed in detail: In the Q1 quadrant: the current of the phase-A winding rises, and the current of the phase-B winding falls; in the Q2 quadrant: the current of the phase-A winding reaches the peak and starts to fall, and the current of the phase-B winding reaches the valley and starts to rise; in the Q3 quadrant: the current of the phase-A winding falls, and the current of the phase-B winding rises; in the Q4 quadrant: the current of the phase-A winding reaches the valley and starts to rise, and the current of the phase-B winding reaches the peak and starts to fall.

[0061] Preferably, the motor winding in the stepper motor that needs to estimate the load torque is marked as the target estimation winding, and the steps of selecting the corresponding quadrants of the winding for the Q1, Q2, Q3, and Q4 quadrants according to the target estimation winding to obtain the target analysis quadrant include:

[0062] S31: When the motor winding in the stepper motor that needs to estimate the load torque is the A-phase winding, mark the A-phase winding as the target estimation winding, and select Q2 or Q4 as the target analysis quadrant of the target estimation winding. The Q2 and Q4 quadrants are the current decline stages of the A-phase winding. In the current decline stage, the current chopping period of the A-phase winding includes a charging stage, a rapid decay stage, and a slow decay stage.

[0063] S32: When the motor winding in the stepper motor that needs to estimate the load torque is the B-phase winding, mark the B-phase winding as the target estimation winding, and select Q1 or Q3 as the target analysis quadrant of the target estimation winding. The Q1 and Q3 quadrants are the current rise stages of the A-phase winding. In the current rise stage, the current chopping period of the A-phase winding includes a charging stage and a slow decay stage.

[0064] Specifically, determine the motor winding that needs to estimate the load torque according to actual requirements. If the target estimation winding is the A-phase winding, mark it as the target estimation winding; if the target estimation winding is the B-phase winding, mark it as the B-phase winding accordingly.

[0065] More specifically, if the target estimation winding is the A-phase winding: Select Q2 or Q4 as the target analysis quadrant. The Q2 and Q4 quadrants are the current decline stages of the A-phase winding. In these quadrants, the current chopping period of the A-phase winding includes a charging stage, a rapid decay stage, and a slow decay stage.

[0066] More specifically, if the target estimation winding is the B-phase winding, select Q1 or Q3 as the target analysis quadrant. The Q1 and Q3 quadrants are the current rise stages of the A-phase winding. In these quadrants, the current chopping period of the A-phase winding includes a charging stage and a slow decay stage.

[0067] More specifically, in the target analysis quadrant, carefully analyze the current chopping period of the target estimation winding, specifically including: Charging stage: The current passes through the winding and increases. Rapid decay stage (only in the Q2 and Q4 quadrants): The current rapidly decreases, usually by releasing energy through a reverse diode. Slow decay stage: The current slowly decreases, and the current is gradually reduced by controlling a switch (such as PWM).

[0068] Preferably, the steps of performing time accumulation processing on the charging stage and the rapid decay stage of the target analysis quadrant to obtain the total charging time and the total rapid decay time in the target analysis quadrant include:

[0069] S41: collecting the stage time of the charging stage in the target analysis quadrant to obtain the stage time of each charging stage in the target analysis quadrant, and accumulating the stage time of each charging stage in the target analysis quadrant to obtain the total charging time in the target analysis quadrant; wherein the total charging time is positively correlated with the load of the stepper motor, and the greater the load of the stepper motor, the longer the total charging time;

[0070] S42: collecting the stage time of the fast decay stage in the target analysis quadrant to obtain the stage time of each fast decay stage in the target analysis quadrant, and accumulating the stage time of each fast decay stage in the target analysis quadrant to obtain the total fast decay time in the target analysis quadrant; wherein the total fast decay time is negatively correlated with the load of the stepper motor, and the smaller the load of the stepper motor, the longer the total fast decay time.

[0071] Specifically, if the target estimated winding is the A-phase winding, select the Q2 or Q4 quadrant, and if the target estimated winding is the B-phase winding, select the Q1 or Q3 quadrant.

[0072] More specifically, within the target analysis quadrant, each charging stage is identified, the time of each charging stage is collected using a timing analysis tool (such as an oscilloscope or a dedicated data acquisition system), and the time of all charging stages within the target analysis quadrant is accumulated to obtain the total charging time.

[0073] More specifically, in the target analysis quadrant, each fast decay stage is identified, the time of each fast decay stage is collected using the same timing analysis tool as the charging stage, and the time of all fast decay stages in the target analysis quadrant is accumulated to obtain the total fast decay time.

[0074] More specifically, the collected charging stage time and fast decay stage time are processed and analyzed. The total charging time is the accumulation of the time of all charging stages, and the total fast decay time is the accumulation of the time of all fast decay stages.

[0075] More specifically, the load torque is calculated based on the total charging time and the total rapid decay time. The total charging time is positively correlated with the load: the larger the load, the longer the total charging time. The total rapid decay time is negatively correlated with the load: the smaller the load, the longer the total rapid decay time. Therefore, the total charging time and the total rapid decay time can provide feedback on the load torque.

[0076] More specifically, based on the estimated load torque, the drive control parameters (such as current limit, PWM duty cycle, etc.) are adjusted to optimize the motor operation.

[0077] It can be understood that by precise time acquisition and cumulative processing, the load of the stepper motor can be estimated more accurately, avoiding the errors that may be brought by simply relying on the current amplitude. The total charging time and the total rapid decay time directly reflect the load condition of the motor. Through real-time monitoring and adjustment, the operating state of the motor can be optimized and the performance can be improved.

[0078] Preferably, stepper motors of the same model have consistent out-of-step deviation values. The steps for obtaining the out-of-step deviation value of a stepper motor include:

[0079] S61: Pre-test the out-of-step deviation values of various models of stepper motors to obtain the out-of-step deviation values of various models of stepper motors, and record the out-of-step deviation values of various models of stepper motors in a preset database;

[0080] S62: Obtain the model of the stepper motor to be estimated, and retrieve the corresponding out-of-step deviation value from the preset database, so as to obtain the out-of-step deviation value of the stepper motor.

[0081] Specifically, prepare out-of-step test equipment, including a high-precision encoder, a controller, and measurement software. Select the model of the stepper motor to be tested to ensure that the sample is representative. Set standard test conditions (such as voltage, current, load, and frequency, etc.). Install the encoder on the output shaft of the stepper motor to accurately measure the actual displacement of the motor. Run the stepper motor, apply a certain load and a stepping command, and repeat the test multiple times to ensure the reliability and consistency of the data.

[0082] More specifically, conduct statistical analysis on the test data, calculate the average value and standard deviation of the out-of-step deviation value, record the out-of-step deviation value of each model of stepper motor, including the average value and standard deviation. Design a preset database for storing the out-of-step deviation values of various models of stepper motors, enter the out-of-step deviation value data into the database, and associate it with the corresponding motor model.

[0083] More specifically, in actual applications, identify the model of the stepper motor to be estimated, retrieve the out-of-step deviation value of the corresponding model from the preset database, and use the obtained out-of-step deviation value to calibrate and adjust the stepper motor control system. During operation, conduct real-time monitoring and adjustment based on the out-of-step deviation value to improve the accuracy and stability of the system.

[0084] Preferably, the steps for pre-testing the out-of-step deviation values of various models of stepper motors to obtain the out-of-step deviation values of various models of stepper motors include:

[0085] S611: Prepare several stepper motors of the same model, conduct running tests on each stepper motor of the same model, and collect the torque change feedback characteristics of the running-tested stepper motors to obtain the torque change feedback characteristics of each stepper motor;

[0086] S612: Collect the load torque of the stepper motors under running tests through sensors or voltage measurement methods to obtain the load torque values of each stepper motor.

[0087] S613: Perform difference calculations and mean analysis based on the load torque values of each stepper motor and the torque change feedback characteristics to obtain the out-of-step deviation value of the stepper motors of this model.

[0088] S614: Repeat the above steps for stepper motors of various models to obtain the out-of-step deviation values of stepper motors of various models.

[0089] Specifically, select several stepper motors of the same model to ensure the representativeness and reliability of the test results, and prepare necessary test equipment, including high-precision torque sensors, voltage measurement instruments, controllers, and data acquisition systems.

[0090] More specifically, install the torque sensor on the output shaft of the stepper motor to monitor the torque change in real time. Run the stepper motor according to the set control parameters to simulate the actual working conditions. During the operation, collect the torque change feedback characteristics of the stepper motor in real time. According to the specific situation, select the sensor method or voltage measurement method to measure the load torque, and record the load torque values of each stepper motor under different operating states.

[0091] More specifically, calculate the difference between the load torque value of each stepper motor and its corresponding torque change feedback characteristic, perform statistical analysis on the difference data, calculate the mean and standard deviation to obtain the out-of-step deviation value of the stepper motors of this model, and ensure that the sample size is large enough to improve the reliability and representativeness of the statistical results.

[0092] More specifically, repeat the above steps for stepper motors of other models to obtain the out-of-step deviation values of various models, and record the test results in a preset database for subsequent query and application.

[0093] Preferably, after obtaining the estimated load torque value of the stepper motor, perform out-of-step analysis on the estimated load torque value according to a preset threshold. When the estimated load torque value drops below the threshold, generate an out-of-step report.

[0094] Specifically, detect out-of-step and stall. Set a threshold value, such as 50 us. When the load torque increases and TorqueLoad drops below 50, report out-of-step. In the application of the stepper motor in the stage control, the out-of-step report can let the system know that the stage has moved to the edge of the guide rail, which is beneficial for its positioning without the need to additionally increase a position limiter. At the same time, once out-of-step is detected, the motor rotation can be controlled to stop to prevent stall, because stall will increase the current of the motor and may burn out the motor.

[0095] Preferably, after obtaining the load torque estimation value of the stepping motor, perform current adjustment analysis on the stepping motor according to the load torque estimation value to obtain the current adjustment scheme of the stepping motor, and perform current adjustment processing on the stepping motor according to the current adjustment scheme;

[0096] The steps of performing current adjustment analysis on the stepping motor according to the load torque estimation value to obtain the current adjustment scheme of the stepping motor include:

[0097] Analyze and process the load torque estimation value according to a preset adjustment execution threshold. When the load torque estimation value first reaches the adjustment execution threshold, retrieve the preliminarily set adjustment amplitude corresponding in advance as the current adjustment scheme;

[0098] Collect the load torque estimation value of the stepping motor after executing the current adjustment scheme, and analyze and process the load torque estimation value according to the preset adjustment execution threshold. If the load torque estimation value still reaches the adjustment execution threshold, retrieve the re-adjustment amplitude preset and corresponding as the current adjustment scheme.

[0099] Specifically, after obtaining the load torque prediction value, change the magnitude of the working current according to the magnitude of this value to achieve the functions of energy saving and temperature reduction. When the TorqueLoad value is very large, it indicates that the torque output by the current motor is much greater than the load demand. At this time, the working current can be reduced. For example, it can be set that when TorqueLoad is greater than 400 us, the working current is reduced (the reduction amplitude can be set). If it is still greater than 400 us, continue to reduce it until it reaches 50% of the original current at the lowest. In this way, the ohmic loss (I / 2)2R can be reduced by 75% compared with I2R before the reduction, and the energy saving effect is remarkable. At the same time, the motor temperature will also be greatly reduced, extending the service life of the motor. When the load torque suddenly increases, TorqueLoad will decrease. A threshold can be set. For example, when it is less than 100 us, increase the working current (the increase amplitude can be set) to ensure that the torque output by the motor is sufficient to meet the load demand. This function can be called the torque adaptive function.

[0100] Preferably, the method for sensorless detection of the load torque of a stepping motor based on the current chopping mode has an effective motor speed range. When the speed of the stepping motor is within the effective motor speed range, the load torque estimation value obtained by the method for sensorless detection of the load torque of a stepping motor based on the current chopping mode is a valid value.

[0101] Specifically, there are certain limitations in the use of the load torque estimation method of the present invention. Firstly, at low speeds, the value of TorqueLoad may be negative because the stepping speed of the motor is slow, the duration of the sine current in each quadrant is long, and in the current decreasing quadrant, in order to keep the waveform a sine curve, there must be a long enough tON to charge the winding inductance, which will cause TtON to be greater than TtFD and make TorqueLoad negative. Therefore, it is necessary to set a certain speed or above for TorqueLoad to be effective. Secondly, at high speeds, the micro-stepping control method can no longer control the current to maintain a sine waveform, and the waveform will be distorted and may become a triangular wave. At this time, TorqueLoad is no longer accurate. Therefore, when using, it is necessary to set a minimum speed and a maximum speed. For example, when the rotational speed is above 60 RPM and below 240 RPM, the load torque estimation value is valid.

[0102] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for detecting stepper motor load torque without sensor based on current chopping mode, characterized in that: include: The stepper motor is controlled to rotate by a current chopping mode, wherein the current chopping mode includes a charging stage, a fast decay stage, and a slow decay stage; Performing a period analysis of a current waveform on a motor winding of a stepper motor in a current chopping mode to divide the current sinusoidal waveform period of the motor winding into four quadrants, namely, Q1, Q2, Q3 and Q4; Mark the motor winding in the stepper motor that needs to perform load torque estimation as the target estimation winding, and select the quadrant corresponding to the winding for four quadrants Q1, Q2, Q3 and Q4 according to the target estimation winding to obtain the target analysis quadrant; Performing time accumulation processing on the target analysis quadrant during the charging phase and the rapid decay phase to obtain the total charging time and the total rapid decay time in the target analysis quadrant; Performing a difference analysis on the total charging time and the total fast decay time to obtain a torque change feedback characteristic; The step-out deviation value of the stepping motor is obtained, and the torque change feedback characteristic is subjected to deviation correction processing according to the step-out deviation value to obtain a load torque estimation value of a target estimation winding of the stepping motor.

2. The method for detecting the load torque of a stepper motor based on a current chopping mode sensorless as claimed in claim 1, characterized in that: The stepper motor has an A-phase winding and a B-phase winding, and the stepper motor has output terminals AOUT1, AOUT2, BOUT1, and BOUT2; In the Q1 and Q2 quadrants, the current of the A-phase winding flows from the AOUT1 to the AOUT2, and the current of the B-phase winding flows from the BOUT2 to the BOUT1; In the Q3 and Q4 quadrants, the current of the A-phase winding flows from the AOUT2 to the AOUT1 , and the current of the B-phase winding flows from the BOUT1 to the BOUT2 .

3. The method for detecting the load torque of a stepper motor based on a current chopping mode sensorless as claimed in claim 2, characterized in that: The steps of marking the motor windings in the stepper motor for which load torque estimation is required as target estimation windings, and selecting the winding corresponding quadrants for four quadrants Q1, Q2, Q3 and Q4 according to the target estimation windings to obtain the target analysis quadrants include: When the motor winding for which load torque estimation is required in the stepping motor is the A-phase winding, the A-phase winding is marked as a target estimation winding, and Q2 or Q4 is selected as a target analysis quadrant of the target estimation winding, the Q2 and Q4 quadrants are the current drop phase of the A-phase winding, and in the current drop phase, the current chopping cycle of the A-phase winding includes a charging phase, a fast decay phase, and a slow decay phase; When the motor winding in the stepper motor that needs to perform load torque estimation is the B-phase winding, the B-phase winding is marked as the target estimation winding, and Q1 or Q3 is selected as the target analysis quadrant of the target estimation winding. The Q1 and Q3 quadrants are the current rising stage of the A-phase winding. In the current rising stage, the current chopping cycle of the A-phase winding includes a charging stage and a slow decay stage.

4. The method for detecting stepper motor load torque based on current chopping mode sensorless according to claim 1, characterized in that: The step of performing time accumulation processing on the target analysis quadrant in the charging phase and the rapid decay phase to obtain the total charging time and the total rapid decay time in the target analysis quadrant comprises: The stage time of the charging stage is collected for the target analysis quadrant to obtain the stage time of each charging stage in the target analysis quadrant, and the stage time of each charging stage in the target analysis quadrant is accumulated to obtain the total charging time in the target analysis quadrant; wherein the total charging time is positively correlated with the load of the stepper motor, and the greater the load of the stepper motor, the longer the total charging time; The stage time of the fast decay stage of the target analysis quadrant is collected to obtain the stage time of each fast decay stage in the target analysis quadrant, and the stage time of each fast decay stage in the target analysis quadrant is accumulated to obtain the total fast decay time in the target analysis quadrant; wherein the total fast decay time is negatively correlated with the load of the stepper motor, and the smaller the load of the stepper motor, the longer the total fast decay time.

5. The method for detecting stepper motor load torque based on current chopping mode sensorless according to claim 1, characterized in that: The same model of stepper motors have consistent step-out deviation values. The steps for obtaining the step-out deviation value of the stepper motor include: Performing out-of-step deviation value tests on various types of stepper motors in advance to obtain out-of-step deviation values ​​of various types of stepper motors, and recording the out-of-step deviation values ​​of various types of stepper motors in a preset database; The model of the stepper motor to be estimated is obtained, and the corresponding out-of-step deviation value is retrieved from the preset database, so as to obtain the out-of-step deviation value of the stepper motor.

6. The method for detecting stepper motor load torque based on current chopping mode sensorless as claimed in claim 5, characterized in that: The steps of testing the step-out deviation values ​​of various types of stepper motors in advance to obtain the step-out deviation values ​​of various types of stepper motors include: Prepare a plurality of stepper motors of the same model, perform operation tests on each stepper motor of the same model, and collect torque change feedback characteristics of the stepper motors in the operation tests to obtain torque change feedback characteristics of each stepper motor; The load torque of the stepper motor under test is collected by a sensor or voltage measurement method to obtain the load torque value of each stepper motor; According to the load torque value and torque change feedback characteristics of each stepper motor, difference calculation and mean analysis are performed to obtain the step-out deviation value of the stepper motor of this model; Repeat the above steps for various types of stepper motors to obtain the step-out deviation values ​​of the various types of stepper motors.

7. The method for detecting stepper motor load torque based on current chopping mode sensorless according to claim 1, characterized in that: After the load torque estimation value of the stepper motor is obtained, a step-out analysis is performed on the load torque estimation value according to a preset threshold value, and when the load torque estimation value decreases below the threshold value, a step-out report is generated.

8. The method for detecting stepper motor load torque based on current chopping mode sensorless according to claim 1, characterized in that: After the load torque estimation value of the stepper motor is obtained, a current adjustment analysis is performed on the stepper motor according to the load torque estimation value to obtain a current adjustment scheme for the stepper motor, and a current adjustment process is performed on the stepper motor according to the current adjustment scheme; The step of performing current adjustment analysis on the stepper motor according to the load torque estimation value to obtain the current adjustment scheme of the stepper motor comprises: Analyzing and processing the load torque estimation value according to a preset adjustment execution threshold value, and when the load torque estimation value reaches the adjustment execution threshold value for the first time, retrieving a corresponding preliminary adjustment amplitude preset in advance as a current adjustment scheme; The load torque estimation value of the stepper motor after executing the current adjustment scheme is collected, and the load torque estimation value is analyzed and processed according to the preset adjustment execution threshold. If the load torque estimation value still reaches the adjustment execution threshold, the preset corresponding setting re-adjustment amplitude is called as the current adjustment scheme.

9. The method for detecting stepper motor load torque based on current chopping mode sensorless according to claim 1, characterized in that: The method for detecting the load torque of a stepper motor by sensorless based on the current chopping mode has an effective range of motor speed. When the speed of the stepper motor is within the effective range of motor speed, the load torque estimation value obtained by the method for detecting the load torque of a stepper motor by sensorless based on the current chopping mode is a valid value.

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