How to set subdivision of stepper motor driver

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The subdivision principle of the stepper motor driver is introduced. The stepper motor is equipped with a rotor with permanent magnets, and the stator has at least two windings. When the rotor magnetism is consistent with the stator winding, the second winding will be driven. The two windings are alternately turned on and off, which will cause the motor to lock in the desired step position. The direction of the current through the winding can also be reversed.

　　In a stepper motor with two stator windings, there are four steps spaced 90° apart. The stepper motor drive is subdivided into steps that can be precisely controlled based on the pulses supplied to the stator windings. Speed control of a stepper motor can be achieved by supplying a pulse frequency to the windings, while the direction of rotation can be changed by reversing the pulse sequence. The pole pieces inside the motor have a number of teeth that help locate the rotor position relative to the stator. Some stepper motors also have teeth on the stator stages. Depending on the control technique used, stepper motors can be controlled in full-stepping, half-stepping, or micro-stepping. Simple square pulses can control the motor in full steps, while advanced control techniques such as pulse width modulation (PWM) can be used for micro-stepping.

The subdivision principle of stepper motor driver is introduced. In China, the majority of users do not have a special understanding of "subdivision". Some of them just think that subdivision is to improve accuracy. In fact, subdivision is mainly to improve the running performance of the motor. The following is explained: The subdivision control of the stepper servo motor is achieved by the driver accurately controlling the phase current of the stepper motor. Taking a two-phase motor as an example, if the rated phase current of the motor is 3A, if a conventional driver (such as the commonly used constant current chopping method) is used to drive the motor, the current in its winding will suddenly change from 0 to 3A or from 3A to 0 for each step of the motor. The huge change of phase current will inevitably cause vibration and noise in the operation of the motor. If a subdivision driver is used to drive the motor in the state of 10 subdivisions, the current in its winding will only change by 0.3A instead of 3A for each microstep of the motor, and the current changes in the law of a sine curve, which greatly improves the vibration and noise of the motor. Therefore, the advantage in performance is the real advantage of subdivision. Since the subdivision driver needs to accurately control the phase current of the motor, the driver must have quite high technical and process requirements, and the cost will also be higher.

　　It should be noted that some domestic drivers use "smoothing" to replace subdivision, and some are also called subdivision, but this is not true subdivision. I hope that the majority of users must distinguish the essential differences between the two:

　　Subdivision of stepper motor driver 1. "Smoothing" does not precisely control the phase current of the motor, but only slows down the rate of change of the current, so "smoothing" does not produce microsteps, while subdivided microsteps can be used for precise positioning.

　　Subdivision of stepper motor driver 2. After the phase current of the motor is smoothed, it will cause the motor torque to decrease, but subdivision control will not cause the motor torque to decrease, on the contrary, the torque will increase.

　　The subdivision principle of the stepper motor driver is introduced. The stepper motor is equipped with a rotor with permanent magnets, and the stator has at least two windings. When the rotor magnetism is consistent with the stator winding, the second winding will be driven. The two windings are alternately turned on and off, which will cause the motor to lock in the desired step position. The direction of the current through the winding can also be reversed.

How to set subdivision of stepper motor driver

　　1. Set the subdivision number of the stepper driver. Generally, the higher the subdivision number, the higher the control resolution. However, too high a subdivision number will affect the feed speed. Generally speaking, for mold machine users, the pulse equivalent can be considered to be 0.001mm/P (at this time, the feed speed is 9600mm/min) or 0.0005mm/P (at this time, the feed speed is 4800mm/min); for users with low precision requirements, the pulse equivalent can be set larger, such as 0.002mm/P (at this time, the feed speed is 19200mm/min) or 0.005mm/P (at this time, the feed speed is 48000mm/min). For two-phase stepper motors, the pulse equivalent calculation method is as follows: Pulse equivalent = lead screw pitch ÷ subdivision number ÷ 200.

　　2. Start-up speed: This parameter corresponds to the start-up frequency of the stepper motor. The so-called start-up frequency is the frequency at which the stepper motor can start working directly without acceleration. Reasonable selection of this parameter can improve processing efficiency and avoid the low-speed section where the stepper motor has poor motion characteristics; but if this parameter is selected too large, it will cause stalling, so a margin must be left. The factory parameters of the motor generally include the start-up frequency parameter. However, after the machine tool is assembled, this value may change, and generally decreases, especially when doing load movement. Therefore, this setting parameter is determined by actual measurement after referring to the factory parameters of the motor.

　　3. Single-axis acceleration: used to describe the acceleration and deceleration capability of a single feed axis, in millimeters per second squared. This indicator is determined by the physical characteristics of the machine tool, such as the mass of the moving part, the torque of the feed motor, the resistance, the cutting load, etc. The larger this value is, the less time is spent on acceleration and deceleration during the movement, and the higher the efficiency is. Usually, for stepper motors, this value is between 100 and 500, and for servo motor systems, it can be set between 400 and 1200. During the setting process, start with a smaller setting, run for a while, repeat various typical movements, pay attention to observation, and if there is no abnormality, then gradually increase it. If an abnormality is found, reduce the value and leave a 50% to 100% insurance margin.

　　4. Curve acceleration: used to describe the acceleration and deceleration capabilities of multiple feed axes when linked, and the unit is mm/s2. It determines the speed of the machine tool when making circular motion. The larger this value is, the greater the allowable speed of the machine tool when making circular motion. Usually, for machine tools composed of stepper motor systems, this value is between 400 and 1000, and for servo motor systems, it can be set between 1000 and 5000. If it is a heavy machine tool, the value should be smaller. During the setting process, start with a smaller setting, run for a period of time, repeat various typical linkage movements, pay attention to observation, and if there is no abnormality, then gradually increase it. If an abnormality is found, reduce the value and leave a 50%~100% insurance margin.

　　Usually, considering the driving ability of the stepper motor, the friction of the mechanical assembly, and the bearing capacity of the mechanical parts, the speed of each axis can be modified in the manufacturer's parameters to limit the speed of the three axes when the machine tool user actually uses it.

　　5. According to the installation position of the zero point sensors of the three axes, set the parameters for returning to the machine origin in the manufacturer parameters. When the settings are correct, you can run the "Return to the machine origin" in the "Operation" menu. Return the single axis first. If the movement direction is correct, continue to return. Otherwise, stop and reset the direction of returning to the machine origin in the manufacturer parameters until all axes can return to the machine origin.

　　6. Set the automatic refueling parameters (set them to a smaller value, such as refueling every 5 seconds) and observe whether the automatic refueling is correct. If it is correct, set the automatic refueling parameters to the actual required parameters.

　　Whether the setting values of the electronic gear and pulse equivalent match. You can make a mark on any axis of the machine tool, set the coordinates of that point as the working zero point in the software, use direct input commands, jog or handwheel to make the axis move a fixed distance, and use a vernier caliper to measure whether the actual distance is consistent with the distance displayed by the coordinates in the software.

　　8. Determine whether there is pulse loss. You can use an intuitive method: use a sharp tool to point a point on the workpiece blank, set the point as the work origin, raise the Z axis, and then set the Z axis coordinate to 0; repeatedly move the machine tool, such as running a typical machining program with an empty tool.

The difference between subdivision and non-subdivision of stepper motor driver

　　The difference between subdivided and non-subdivided stepper motor drivers: Subdivided drive has high precision.

　　Subdivision means that the stepper motor driver divides each pulse sent by the upper device into a coefficient of pulses according to the subdivision coefficient set by the stepper motor driver and outputs it.

　　For example, a stepper motor has 200 pulses per rotation. If the stepper motor driver is subdivided into 32, then the stepper motor driver needs to output 6400 pulses for the stepper motor to rotate one circle.

　　Usually the stepper motor subdivisions are 2, 4, 8, 16, 32, 62, 128, 256, 512...

　　In foreign countries, two-phase hybrid stepper motors and corresponding subdivision stepper motor drivers are mainly used for stepper motor systems. However, in China, the majority of users do not particularly understand "subdivision". Some just think that subdivision is to improve the accuracy of stepper motors. In fact, subdivision is mainly to improve the operating performance of stepper motors. The following is an explanation:

　　The subdivision control of the stepper motor is achieved by the stepper motor driver precisely controlling the phase current of the stepper motor. Taking a two-phase stepper motor as an example, if the rated phase current of the stepper motor is 3A, if a conventional stepper motor driver (such as the commonly used constant current chopping method) is used to drive the stepper motor, the current in its winding will suddenly change from 0 to 3A or from 3A to 0 for each step of the stepper motor. The huge change in the phase current of the stepper motor will inevitably cause vibration and noise in the operation of the stepper motor. If a subdivision stepper motor driver is used to drive the stepper motor in a state of 10 subdivisions, the current in its winding will only change by 0.3A instead of 3A for each microstep of the stepper motor, and the current changes in a sinusoidal curve, which greatly improves the vibration and noise of the stepper motor. Therefore, the advantage in performance is the real advantage of subdivision.

　　Since the subdivided stepper motor driver needs to accurately control the phase current of the stepper motor, the stepper motor driver has very high technical and process requirements, and the cost will also be higher.

　　Note that some domestic stepper motor drivers use "smoothing" instead of subdivision, and some are also called subdivision, but this is not true subdivision. I hope that the majority of users must distinguish the essential differences between the two:

　　1. “Smoothing” does not precisely control the phase current of the stepper motor, but only slows down the rate of change of the current. Therefore, “smoothing” does not generate microsteps, while subdivided microsteps can be used for precise positioning.

　　2. After the phase current of the stepper motor is smoothed, the torque of the stepper motor will decrease. However, the subdivision control of the stepper motor driver will not cause the torque of the stepper motor to decrease. On the contrary, the torque of the stepper motor will increase.

shuangchafeng

Thank you for sharing!

freebsder

The second paragraph is interesting.

nian1206

The subdivision principle of the stepper motor driver is introduced. The stepper motor is equipped with a rotor with permanent magnets, and the stator has at least two windings. When the rotor magnetism is consistent with the stator winding, the second winding will be driven. The two windings are alternately turned on and off, which will cause the motor to lock in the desired step position. The direction of the current through the winding can also be reversed.