I. What is the working principle of a stepper motor?
Generally, all kinds of motors have an iron core and winding coils. If the windings have resistance, current will flow and cause losses. The amount of loss is positively correlated with the resistance and the square of the current. This is what we commonly call copper damage. When the current is not standard DC or a sine wave, harmonic losses will also occur; at the same time, due to the hysteresis eddy current effect of the iron core, losses will also occur in the alternating magnetic field. Its size is related to the material, current, frequency, and voltage, and is called iron damage.
Both of these losses lead to heat generation, which in turn affects the motor's efficiency. Stepper motors draw more current and have higher harmonic content than regular motors in pursuit of high precision and output torque; therefore, stepper motors tend to generate more heat than regular motors.
An electric motor converts electrical energy into mechanical energy, and a stepper motor is an open-loop control element that converts electrical pulse signals into angular velocity or linear displacement. Under non-overload conditions, the motor's speed and stopping position depend only on the number and magnitude of the pulse signals, unaffected by load changes; that is, adding pulse signals to the motor results in a step angle rotation. This linear correlation, coupled with the stepper motor's characteristic of only having periodic deviations and no cumulative errors, makes stepper motors very simple to use in applications such as speed and position control.
II. Working Principle of Servo Motors
1. A servo mechanism is an automatic control system that allows the position, orientation, and status of a measured object to change arbitrarily according to the input target (or given value). The positioning function of a servo system is mainly achieved through pulses. After receiving a pulse, the servo motor will rotate to the corresponding angle to achieve offset. Relying on the pulse transmission function of the servo motor, it sends out a corresponding number of pulses, and the sent pulses are the same as the received pulses. Therefore, the system knows how many pulses the servo motor has sent and received, thus accurately controlling the motor's rotation and achieving accurate positioning down to 0.001mm.
DC servo motors are generally divided into brushed and brushless types. Brushed motors have a more compact structure, higher starting torque, are easier to operate, and are less expensive. However, they are more difficult to maintain and are prone to signal interference, thus requiring specific environmental conditions. Brushed motors are typically used in cost-sensitive civilian or industrial environments.
Brushless motors are smaller and lighter, achieving high speed, fast response, low inertia, stable torque, and smooth rotation even at high output. While complex to operate, they are easily made intelligent, with flexible electronic commutation methods that allow for waveform or sine wave switching. Motor maintenance is simpler, lifespan is longer, and efficiency is higher, with less battery radiation and lower operating temperatures, allowing for use in various environments.
2. AC servo motors, also known as brushless motors, generally come in asynchronous and synchronous types. Synchronous motors are typically used for motion control, offering a wide power range and high power output. They have high inertia and a low maximum rotational speed, which decreases rapidly with increasing power. Therefore, they are suitable for low-speed, stable operation.
3. The servo motor uses a permanent magnet as its internal rotor. The controller controls the three-phase electricity (U/V/W) to generate a magnetic field, and the rotor rotates under the influence of this magnetic field. Simultaneously, the motor provides encoder feedback signals to the controller. The controller compares the feedback value with the target value and adjusts the rotor's rotation angle accordingly. The accuracy of the servo motor is determined by the encoder's accuracy (line count).
The functional differences between AC servo motors and brushless DC servo motors: AC servo motors are better because they operate with a sine wave, resulting in smaller torque pulses. DC servo motors use trapezoidal wave control. Generally speaking, DC servo motors have a simpler structure and are less expensive.
