Out-of-step should be a missed pulse does not move to the specified position. Overshoot should be the opposite of out-of-step, moving beyond the specified position.
Stepper motors are often used in motion control systems where the control is simple or where low cost is required. The biggest advantage is that the position and speed are controlled in an open-loop manner. But precisely because it is open-loop control, the load position has no feedback to the control loop, and the stepper motor must respond correctly to each excitation change. If the excitation frequency is not selected correctly, the stepper motor will not be able to move to the new position. The actual position of the load appears to be in permanent error relative to the position expected by the controller, i.e., an out-of-step phenomenon or an overshoot is imagined. Therefore, in the stepper motor open-loop control system, how to prevent the loss of step and overshoot is the key to the normal operation of the open-loop control system.
Out-of-step and overshoot phenomena occur when the stepper motor starts and stops, respectively. In general, the limit of the system start frequency is relatively low, while the required operating speed is often relatively high. If the system is started directly at the required running speed, because the speed has exceeded the limit, the starting frequency and can not be started properly, starting with a lost step, heavy can not start at all, resulting in blocked rotation. After the system is running, if the end point is reached immediately stop sending pulses, so that it stops immediately, then due to the inertia of the system, the stepper motor will turn over the balance position desired by the controller.
In order to overcome the stepping out of step and overshoot phenomenon, should be added to the start-stop appropriate acceleration and deceleration control. We generally use: motion control card for the upper control unit, PLC with control functions for the upper control unit, microcontroller for the upper control unit to control the movement acceleration and deceleration can overcome the phenomenon of lost step overshoot.
In layman's terms: when the stepper driver receives a pulse signal, it drives the stepper motor to turn a fixed angle (and step angle) in the set direction. You can control the number of pulses to control the amount of angular displacement, so as to achieve the purpose of accurate positioning; at the same time, you can control the pulse frequency to control the speed and acceleration of motor rotation, so as to achieve the purpose of speed regulation. Stepper motor has a technical parameter: no-load start frequency, that is, the stepper motor in the case of no-load pulse frequency can start normally. If the pulse frequency is higher than the no-load start frequency, the stepper motor can not start properly, may occur to lose steps or blocking phenomenon. In the case of a load, the starting frequency should be lower. If the motor is to rotate at high speed, the pulse frequency should have a reasonable acceleration process, i.e., the starting frequency is low and then ramps up to the desired high frequency at a certain acceleration (motor speed ramps up from low to high speed).
Starting frequency = starting speed × how many steps per revolution. No-load starting speed is the stepper motor without acceleration or deceleration without load directly rotate up. When the stepper motor rotates, the inductance of each phase of the motor winding will form a reverse electric potential; the higher the frequency, the greater the reverse electric potential. Under its action, the motor with the frequency (or speed) increases and the phase current decreases, which leads to a decrease in torque.
Suppose: the total output torque of the reducer is T1, the output speed is N1, the reduction ratio is 5:1, and the stepping angle of the stepper motor is A. Then the motor speed is: 5*(N1), then the output torque of the motor should be (T1)/5, and the operating frequency of the motor should be
5*(N1)*360/A, so you should look at the moment-frequency characteristic curve: the coordinate point [(T1)/5, 5*(N1)*360/A] is not below the frequency characteristic curve (starting moment-frequency curve). If it is below the moment-frequency curve, you can select this motor. If it is above the moment-frequency curve, then, you cannot select this motor because it will miss-step, or not turn at all.
Do you determine the working state, you need the maximum speed determined, if determined, then you can calculate according to the formula provided above, (based on the maximum speed of rotation, and the size of the load, you can determine whether the stepper motor you choose now is suitable, if not you should also know what kind of stepper motor to choose).
In addition, the stepper motor in the start after the load can be unchanged, and then increase the frequency, because the stepper motor moment frequency curve should actually have two, you have that should be the start moment frequency curve, and the other is off the moment frequency curve, this curve represents the meaning of: start the motor at the start frequency, after the completion of the start can increase the load, but the motor will not lose step state; or Start the motor at the starting frequency, in the case of constant load, you can appropriately increase the running speed, but the motor will not lose step state.
The above is the introduction of stepper motor out-of-step and overshoot.
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Post time: Apr-03-2023