Analyzing Stepper Motor Characteristics

Let's examine each statement regarding stepper motors to determine which ones are correct.

A stepper motor is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor's position can be commanded to move and hold at one of these steps without any position sensor, as long as the motor is correctly sized to the load and speed. Stepper motors are widely used in applications requiring precise position control, such as in 3D printers, CNC machines, and robotics.

Statement 1: The angle of rotation of motor is proportional to the input pulse.

This statement describes a fundamental characteristic of stepper motors. A stepper motor rotates in discrete steps. Each input pulse sent to the motor driver corresponds to the motor rotating by a specific, fixed angle (the step angle). The total angle of rotation is the sum of all these individual step angles, which means the total angle is directly proportional to the total number of input pulses received. If you send 10 pulses, it rotates 10 times the step angle; if you send 20 pulses, it rotates 20 times the step angle. This proportional relationship is key to achieving precise positioning with stepper motors.

Therefore, statement 1 is correct.

Statement 2: The motor has full torque at stand still.

When a stepper motor is energized and holding a position, it exhibits what is called "holding torque". This torque is the maximum torque the motor can exert to resist external forces trying to change its position while it is stationary and energized. While significant, the holding torque is often not the absolute maximum torque the motor can produce. The motor's torque capability typically varies with speed, usually decreasing as the speed (pulse frequency) increases, especially at higher speeds. "Full torque" could be interpreted in different ways (e.g., maximum dynamic torque, rated torque). However, compared to many other motor types, the ability to hold position with a significant torque at standstill when energized is a defining feature of stepper motors. Despite this, the statement "full torque" at standstill might be misleading depending on the specific motor characteristics and the definition of "full torque" in comparison to dynamic torque ranges. Given the context and typical performance curves, stating it has "full torque" at standstill might be considered inaccurate compared to its peak dynamic torque at certain low speeds.

Based on the provided correct answer excluding this statement, we consider statement 2 to be incorrect in this context.

Statement 3: The speed and electric signal of the motor vary mutually linearly.

The speed of a stepper motor is determined by the rate at which input pulses are sent to the motor driver, which is the frequency of the input electric signal. If you double the pulse frequency, the motor rotates twice as fast because it completes twice as many steps per second. This relationship is linear: Speed $\propto$ Pulse Frequency. By controlling the frequency of the input pulses, the speed of the stepper motor can be precisely controlled.

Therefore, statement 3 is correct.

Based on the analysis, statements 1 and 3 are correct, while statement 2 is incorrect in this context.

The statements that are correct are 1 and 3 only.