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Frequently Asked Questions
When using a motor with a brake installed on the vertical Z-axis, the spindle drops slightly when the servo is off before the brake engages. How can this issue be resolved?
Under the correct wiring method, the motor brake is controlled to open and close by the driver's DO signal BRK-OFF. When servo is on, the driver outputs a signal to release the brake; when servo is off, the brake is applied. Before turning off the servo on, the brake is engaged first to prevent the machine head from dropping. (The brake must be controlled by an intermediate relay)
When powering on during servo test, the motor vibrates and makes a loud noise, then the servo alarm goes off. How to solve this?
This phenomenon is caused by the driver gain being set too high, resulting in self-excited oscillation. Please adjust the parameters to reduce the system stiffness.
During normal use, the motor temperature becomes very high due to frequent start-stop cycles. Will long-term use under these conditions damage the motor?
The servo motor encoder will be damaged when the temperature reaches above 85 degrees Celsius. The rotor temperature of the servo motor will experience demagnetization when it exceeds 130 degrees Celsius. Due to the temperature difference inside and outside the servo motor, when the surface temperature of the motor body is about 85 degrees Celsius, the internal temperature of the motor reaches 130 degrees. In situations where the servo motor starts and stops frequently, the temperature of the servo motor may become very high. At this time, forced cooling measures need to be taken externally, such as adding cooling fans, removing the internal regenerative resistor, and installing a higher power regenerative resistor externally.
What are the functions and differences of ordinary encoders, single-turn absolute encoders, and multi-turn absolute encoders?
A standard encoder provides a fixed number of pulses per revolution and cannot record the motor's stopping angle within one revolution. A single-turn absolute encoder, in addition to providing a fixed number of pulses per revolution, can record the stopping angle within a single revolution but cannot record the number of revolutions the motor has run. A multi-turn absolute encoder can record the number of revolutions based on the single-turn absolute encoder but requires a built-in battery or other power supply devices.
What types of stepper motors are there?
Stepper motors are divided into three types: Permanent Magnet (PM), Variable Reluctance (VR), and Hybrid (HB). Permanent magnet stepper motors are generally two-phase, with smaller torque and size, and a step angle usually of 7.5 degrees or 1.5 degrees; variable reluctance stepper motors are generally three-phase, capable of high torque output, with a step angle usually of 1.5 degrees, but they have high noise and vibration. Hybrid stepper motors combine the advantages of permanent magnet and variable reluctance types. They are further divided into two-phase and five-phase: the two-phase step angle is generally 1.8 degrees, while the five-phase step angle is generally 0.72 degrees. This type of stepper motor is the most widely used.
What is Holding Torque?
Holding torque refers to the torque that locks the rotor when the stepper motor is powered but not rotating. It is one of the most important parameters of a stepper motor. Typically, the torque of a stepper motor at low speed is close to the holding torque. Since the output torque of a stepper motor decreases continuously as speed increases, and the output power also changes with speed, holding torque becomes one of the most important parameters for measuring a stepper motor. For example, when people refer to a 2N.m stepper motor without special explanation, it means a stepper motor with a holding torque of 2N.m.
What is the allowable surface temperature of the stepper motor?
Excessive temperature in a stepper motor will first cause the motor's magnetic materials to demagnetize, leading to a decrease in torque and even loss of steps. Therefore, the maximum allowable surface temperature of the motor should depend on the demagnetization point of the magnetic materials used in different motors. Generally, the demagnetization point of magnetic materials is above 130 degrees Celsius, and some can be as high as over 200 degrees Celsius. Thus, a surface temperature of 80-90 degrees Celsius for a stepper motor is completely normal.
Why can a stepper motor operate normally at low speeds, but fail to start above a certain speed, accompanied by a whining noise?
A stepper motor has a technical parameter: no-load starting frequency, which is the pulse frequency at which the stepper motor can start normally under no-load conditions. If the pulse frequency exceeds this value, the motor cannot start properly and may experience missed steps or stall. Under load conditions, the starting frequency should be lower. To achieve high-speed rotation, the pulse frequency should have an acceleration process, starting at a lower frequency and then increasing at a certain acceleration to the desired high frequency (motor speed increases from low to high).
How to overcome the vibration and noise of a two-phase hybrid stepper motor during low-speed operation?
The inherent drawback of stepper motors is large vibration and noise at low speeds, which can generally be overcome by the following methods:
A: If the stepper motor operates exactly in the resonance region, the resonance can be avoided by changing the reduction ratio or other mechanical transmissions;
B: Use a driver with subdivision function, which is the most common and simplest method;
C: Replace with a stepper motor with a smaller step angle, such as three-phase or five-phase stepper motors;
D: Replace with an AC servo motor, which can almost completely overcome vibration and noise, but the cost is higher;
E: Add a magnetic damper on the motor shaft; such products are available on the market, but the mechanical structure changes significantly.
Why does the torque of a stepper motor decrease as the speed increases?
When the stepper motor rotates, the inductance of each phase winding of the motor generates a back electromotive force; the higher the frequency, the greater the back electromotive force. Under its influence, as the frequency (or speed) increases, the phase current of the motor decreases, resulting in a reduction in torque.
Does the number of microsteps of a microstepping driver represent its accuracy?
The subdivision technology of stepper motors is essentially an electronic damping technology (please refer to relevant literature). Its main purpose is to reduce or eliminate low-frequency vibrations of the stepper motor. Improving the motor's operating accuracy is only an incidental function of the subdivision technology. For example, for a two-phase hybrid stepper motor with a step angle of 1.8°, if the subdivision number of the subdivision driver is set to 4, then the motor's operating resolution is 0.45° per pulse. Whether the motor's accuracy can reach or approach 0.45° also depends on other factors such as the subdivision driver's subdivision current control accuracy. The accuracy of subdivision drivers from different manufacturers may vary greatly; the larger the subdivision number, the harder it is to control accuracy.
How to determine the DC power supply for a stepper motor driver?
A. Determination of Voltage
The supply voltage of a hybrid stepper motor driver generally has a wide range (for example, the supply voltage of MC425 is 12 to 36 VDC). The power supply voltage is usually selected based on the motor's operating speed and response requirements. If the motor operates at a higher speed or requires a faster response, the voltage value is also higher. However, note that the ripple of the power supply voltage must not exceed the maximum input voltage of the driver, otherwise it may damage the driver.
B. Determination of Current
The supply current is generally determined based on the driver's output phase current I. If a linear power supply is used, the supply current can generally be 1.1 to 1.3 times I; if a switching power supply is used, the supply current can generally be 1.5 to 2.0 times I.
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