1. How to drive a stepper motor without pulses?
However, there are some driving methods that allow a stepper motor to continue rotating without a pulse signal, for example:
Constant current drive: In this method, the phase current of the stepper motor is kept constant at a certain level. This allows the motor to rotate even without a pulse signal, but the motor speed and direction cannot be controlled.
Resonance drive: This method utilizes the resonant frequency of a stepper motor to achieve rotation. By adjusting the phase current of the motor and the inertial parameters of the mechanical load, the motor can be made to resonate at a specific speed, thereby maintaining rotation. However, resonance drive has low control precision and is prone to loss of control.
These methods allow stepper motors to continue rotating without pulse signals, but their control accuracy and reliability are relatively poor, so they are usually only used in some special applications. In most cases, pulse signals are required to control the movement of stepper motors.
II. How to reduce speed in a stepper motor
Pulse signal deceleration: The speed of a stepper motor changes according to the changes in the input pulse signal. Theoretically, giving the driver a pulse causes the stepper motor to rotate one step angle (one microstep angle in microstepping). In practice, if the pulse signal changes too quickly, the magnetic reaction between the rotor and stator will not keep up with the change in the electrical signal due to the damping effect of the internal back electromotive force, leading to stalling and missed steps.
Gearbox speed reduction: Stepper motors are used with gearboxes. The stepper motor outputs high speed and low torque. When connected to the gearbox, the reduction ratio formed by the meshing of the reduction gear set inside the gearbox reduces the high speed output of the stepper motor and increases the transmission torque, achieving the ideal transmission effect. The speed reduction effect depends on the reduction ratio of the gearbox. The larger the reduction ratio, the lower the output speed, and vice versa.
Exponential speed control: In software programming, the time constant of the exponential curve is calculated and stored in the computer's memory, and then selected during operation. Typically, the acceleration and deceleration time for a stepper motor is over 300ms. Using excessively short acceleration and deceleration times would make it difficult to achieve high-speed rotation for most stepper motors.
Encoder-controlled deceleration: PID control, as a simple and practical control method, has been widely used in stepper motor drives. It uses the given value r(t) and the actual output value c(t) to form the control deviation e(t), and then combines the proportional, integral, and derivative of the deviation linearly to form the control quantity, thereby controlling the controlled object.
