Stepper drive has its low price and easy application. It has been widely used in various types of automation equipment. However, the stepper drive system is an open-loop system, and the phenomenon of 'inaccurate positioning' is found in the application of stepping drive.
There are generally several reasons that cause the stepper driver to have 'inaccurate positioning':
ï¬ The initial speed is too high and the acceleration is too high, causing loss of steps or even blocking.
ï¬ Improper setting of the control pulse's effective edge causes the pulse to be lost when the direction is changed. It appears to be accurate in any direction, but the stepper motor reciprocates and generates cumulative deviations, and the more the number of reciprocating times, the more the deviation becomes.
ï¬ The controller is affected by the load such as the inverter, the transmitted control signal is disturbed, causing the stepper motor to malfunction;
ï¬ The control signal line is affected by other signals of the equipment and causes the stepper motor to malfunction;
ï¬ The driver is affected by the interference signal, causing malfunction;
ï¬ Select the stepper motor torque is too small, there will be lost step in the acceleration or high speed;
ï¬ When the timing belt is used, the software compensates too much or too little, resulting in inaccurate positioning;
ï¬ The width of the pulse emitted by the controller is narrow, and the bandwidth of the control pulse of the stepping driver is narrow, resulting in lost steps at high speed;
ï¬ The temperature rise of the stepping motor is high, which causes the output torque to drop and loses in continuous operation.
ï¬ The software is defective.
The causes and solutions for the above-mentioned occurrence of the stepper motor 'positioning inaccurate' phenomenon are as follows:
1. Due to the inherent characteristics of the stepper motor, the initial speed can not be too high, especially when the load inertia is large. It is recommended that the initial speed be less than 1r/s, so that the impact is small, and the same acceleration is too large and the system has large impact. Rush, resulting in inaccurate positioning. The solution is as follows:
ï¬ reduce the initial speed and reduce the acceleration of the controller;
ï¬ The driver performs FIR filtering on the control commands. Innasys Electric Co., Ltd. of Shenzhen City launches the EZM stepper driver to provide flexible filtering of control commands to ensure that the stepper motor does not lose step at high initial speed and high acceleration.
2. There should be a certain gap time between the forward rotation and the reverse rotation of the motor. If not, it may easily cause excessive overshoot due to too large reverse acceleration.
3, the general stepper driver has certain requirements on the direction and pulse signal, such as: the direction of the signal in the first pulse rising or falling edge (different drive requirements are not the same) a few microseconds before the arrival was determined, otherwise it will One pulse runs at an angle that is opposite to the actual direction of rotation. Finally, the phenomenon of failure is manifested in the more deviation, the smaller the smaller the more obvious, the solution is mainly to use software to change the logic of the pulse or delay; 4. Stepping When the motor torque is not enough, increase the motor current and increase the driver voltage (note the optional driver). Select the motor with larger torque.
5, system interference caused by the malfunction of the controller or driver, we can only think of ways to identify the source of interference, reduce its interference capacity (such as shielding, increase the separation distance, etc.), cut off the transmission route, improve their anti-interference ability, Common measures:
ï¬ Use double-shielded shielded wires instead of ordinary wires. The signal wires in the system are separated from large-current or large-voltage change wires to reduce electromagnetic interference.
ï¬ Use the power filter to filter the interference wave from the power grid, add the power filter to the input terminals of major electrical equipment under the conditions permitting, and reduce the interference between various devices in the system;
ï¬ It is best to use optical isolation devices for signal transmission between devices. Under conditions permitting, the pulse and direction signals are preferably differentially coupled with opto-isolated signals. The inductive load (such as electromagnetic relay, solenoid valve) is added with resistance-capacitance absorption or fast bleeder circuit. The inductive load can generate 10~100 times of peak voltage at the beginning, if the operating frequency is above 20KHZ. 6, to improve the heat dissipation of the stepper motor, or select a larger stepper motor to control the temperature rise of the motor;
7. When the width of the pulse of the control signal is narrow, the response bandwidth of the stepper driver should be increased.
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