Solution to the position accuracy of stepping motor
Improvement of the drive circuit
First, the rated voltage (current) drive: from the rated voltage to reduce the voltage to drive the stepper motor, found that the positional positioning accuracy is worse.
For example, in the case of no-load, the encoder is used as the load, and the accuracy at the rated voltage (current) is lower than the rated voltage (current). As shown in the figure above, the cogging torque makes the degree of characteristic distortion varies depending on the applied voltage. The lower the voltage, the more obvious the effect of cogging torque. The author's experience is that it is very cumbersome to have poor angle accuracy, which will cause measurement voltage (current) inaccurate. You will notice that the torque has a certain relationship with the voltage, and if the relationship is different, the angular accuracy at no-load will become poor or become a blind spot.
Second, 2-phase excitation drive: 1-phase excitation drives the stator teeth and rotor teeth for positional positioning. Relative to the 2-phase excitation, the two phase windings of the stator are excited, and the rotor tooth magnetic field is balanced with the stator magnetic field for position. When the 1-phase excitation is driven, the error accuracy is the mechanical accuracy of each stator phase, and the 2-phase excitation error is determined by the multi-pole position, the error is alleviated, and the accuracy is improved. Especially vertical two-phase PM type stepping motor of the column type, the 1-phase excitation is compared with the 2-phase excitation, and the 1-phase excitation accuracy is worse.
Third, multi-step position positioning: two-phase stepping motor with 2 or 4 step position positioning drive; three-phase stepper motor 3 or 6 step position positioning drive. "Measurement of step angle accuracy of stepping motor"
The article mentioned an example of a two-phase HB type stepping motor, such as positioning every 4 step positions, the accuracy is greatly improved.
For example, when positioning at 1.8° position, 1.8° is not using full stepping, but using a stepping motor of 0.9°, driving 1.8° position positioning in 2 steps, and selecting a stepping motor of 0.6° in full stepping,3 step drive has a drive mode of 0.6 ° × 3 = 1.8 °. This way can greatly improve the accuracy.
Improvement of fine-tuning the stator structure: It is known that the fine-tuning structure of the stator can improve the positional positioning accuracy. Taking a two-phase motor as an example, the fine-tuning structure can reduce the cogging torque, and the angular characteristic becomes a sine wave.
Three-phase HB type 1.2° stepping motor, the six main poles are not fine-tuned, and the positional accuracy is compared with the 12-pole main-stepped full-step drive.
The positional positioning accuracy of the 1/8 subdivision drive is compared as shown below:
When the stepping motor of the three-phase 12 main pole fine adjustment structure is fully stepped, the position positioning accuracy can be improved within ±2%. In subdivision, the fine-tuning structure accuracy is improved by nearly 50%. Subdivision step angle accuracy is more than full step angle accuracy. When the step size is 8 divisions, the step angle is 1.2°/8=0.15°, which is used as the control calculation reference, and the accuracy value is of course higher than the full step angle.
Improvement of three-phase HB high-resolution motor: Three-phase HB type stepping motor has two-phase 1.8° 1/3, that is, 0.6° high resolution motor. Since the driver chip can be purchased in the market, it can be easily achieved high-precision positioning.
Improvements in RM-type subdivision: When the angle is subdivided by the HB type stepping motor, the accuracy is problematic when used for positional positioning. When the RM type 10 subdivision position is positioned, the calculated position is linearly changed, and the angular precision of the micro stepping subdivision is compared.