Moment and angle characteristics
It refers to the relationship curve T = f between the static torque T of the stepper motor and the rotor misalignment angle θ under the condition of a single pulse and constant current.
The torque-angle characteristic is a fundamental characteristic of stepper motors, and it is very important to measure this characteristic accurately and conveniently, but this remains difficult. People have long sought to measure the torque-angle characteristic of stepper motors by using the rotational induced voltage. However, the relationship between the rotational voltage and the static torque in a stepper motor is quite complex.
Moment and angle characteristic test
When a stepper motor is given an electrical pulse signal, its rotor rotates by a corresponding angle; this angle is called the step angle of the stepper motor . Currently, the step angles of commonly used stepper motors are mostly 1.8 degrees (commonly known as one step) or 0.9 degrees (commonly known as half a step). Taking a stepper motor with a step angle of 0.9 degrees as an example, when we give the stepper motor an electrical pulse signal, it rotates 0.9 degrees; two pulse signals, and it rotates 1.8 degrees. And so on, continuously giving pulse signals allows the stepper motor to operate continuously. Due to this linear relationship between the electrical pulse signal and the stepper motor's rotation angle, stepper motors are widely used in speed control, position control, and other applications.
Reasonable range of heat generation for stepper motors:
The permissible temperature range for a motor depends primarily on its internal insulation class. Internal insulation only deteriorates at high temperatures (above 130 degrees Celsius). Therefore, as long as the internal temperature doesn't exceed 130 degrees Celsius, the motor won't be damaged, and the surface temperature will be below 90 degrees Celsius. Thus, a surface temperature of 70-80 degrees Celsius is normal for a stepper motor. A simple temperature measurement method using a spot thermometer can provide a rough estimate: if you can touch it for more than 1-2 seconds, it's below 60 degrees Celsius; if you can only touch it briefly, it's approximately 70-80 degrees Celsius; if a few drops of water vaporize quickly, it's above 90 degrees Celsius.
The main advantages of stepper motor driver microstepping are:
It completely eliminates low-frequency oscillations in the motor. Low-frequency oscillations are an inherent characteristic of stepper motors (especially reactive motors), and microstepping is the only way to eliminate them. If your stepper motor sometimes needs to operate in the resonance zone (such as traversing arcs), choosing a microstepping driver is the only option. It increases the motor's output torque. Especially for three-phase reactive motors, the torque is increased by approximately 30-40% compared to without microstepping. It improves the motor's resolution. Due to the reduced step angle and improved step uniformity, the improvement in motor resolution is self-evident.
1) Step angle α
The theoretical value of the angle through which the motor rotor rotates for each pulse signal.
Where m is the number of stator phases; z is the number of rotor teeth; k is the energizing coefficient, m phase m beats, k = 1; m phase 2m beats, k = 2.
α is generally very small, such as 3°/1.5°, 1.5°/0.75°, 0.72°/0.36°, etc.
2) Moment-angle characteristics, maximum static torque Mjmax and starting torque Mq
Static: The stepper motor is energized, and the rotor is stationary.
Static torque Mj: When a load torque M is applied to the motor shaft, the rotor will rotate through an angle θ (misalignment angle) in the load direction, and the rotor will thus be subjected to an electromagnetic torque Mj to balance the load.
Torque-angle characteristic: The curve of the static torque Mj of a single-phase stepper motor as a function of the misalignment angle θ.
3) Startup frequency fq and inertia characteristics during startup
Starting frequency or jump frequency fq: The highest frequency allowed for a stepper motor to suddenly start from a standstill and enter normal operation without missing steps under no-load conditions. Frequency exceeding the starting frequency will prevent normal starting.
Inertia frequency characteristics at startup: refers to the relationship between the starting frequency and the load's moment of inertia when the motor drives a purely inertial load.
Stepper motors start at a lower frequency under load (especially inertial load) than under no-load conditions.
4) Operating torque-frequency characteristics
Continuous operating frequency: The highest operating frequency at which the stepper motor can continuously track the command pulse frequency without missing steps after starting. Its value is much greater than the starting frequency.
Operating torque-frequency characteristic: describes the relationship between the output torque and the continuous operating frequency of a stepper motor during continuous operation.
