How does PLC control the speed and direction of a stepper motor?

As an industrial control computer, PLC has a modular structure, flexible configuration, high-speed processing speed, precise data processing capabilities, and PLC also has good control capabilities over stepper motors. By utilizing its high-speed pulse output function or motion control function, it can achieve control over stepper motors.

For those specific devices whose moving distance and speed are determined during operation, it is considered that using PLC to control the operation of the stepper motor through the stepper motor driver is also a technical solution.

Features of stepper motors:

(1) The angular displacement of the stepper motor is strictly proportional to the number of input pulses. There is no cumulative error after the motor runs for one circle, and it has good followability.

(2) The open-loop digital control system consisting of a stepper motor and a driver circuit is very simple, cheap, and reliable. At the same time, it can also form a high-performance closed-loop digital control system with an angle feedback link.

(3) The stepper motor has fast dynamic response and is easy to start and stop, reverse and change speed.

(4) The speed can be smoothly adjusted within a fairly wide range, and high torque can still be obtained at low speed.

(5) The stepper motor can only operate by being powered by a pulse power supply. It cannot directly use AC power or DC power.

The highest stepping frequency that a stepper motor can respond to without losing steps is called the "starting frequency"; similarly, the "stopping frequency" refers to the highest stepping frequency at which the stepper motor does not rush past the target position when the system control signal is suddenly turned off. The starting frequency, stopping frequency and output torque of the motor must be adapted to the rotational inertia of the load. With these data, the stepper motor can be effectively controlled at variable speed.

When using PLC to control stepper motors, the pulse equivalent, pulse frequency upper limit and maximum pulse number of the system should be calculated according to the following formula, and then the PLC and its corresponding functional modules can be selected. The required frequency for PLC high-speed pulse output can be determined based on the pulse frequency, and the bit width of the PLC can be determined based on the pulse number.

Pulse equivalent = (stepping motor step angle × pitch) / (360 × transmission speed ratio)

Pulse frequency upper limit = (moving speed × stepper motor subdivision number) / pulse equivalent

Maximum number of pulses = (moving distance × stepper motor subdivision number) / pulse equivalent

Pulse equivalent = (stepping motor step angle × pitch) / (360 × transmission speed ratio)

Pulse frequency upper limit = (moving speed × stepper motor subdivision number) / pulse equivalent

Maximum number of pulses = (moving distance × stepper motor subdivision number) / pulse equivalent

The PLC must first establish a coordinate system for the control of the stepper motor. It can be set as a relative coordinate system or an absolute coordinate system. The coordinate system is set in the DM6629 word, with bits 00-03 corresponding to pulse output 0 and bits 04-07 corresponding to pulse output 1. When set to 0, it is a relative coordinate system; when set to 1, it is an absolute coordinate system.

PLC is used to control the operation of stepper motors through stepper drivers, so that PLC is more widely used in stepper electric control. For example, in the process of controlling single and double axis motion, parameters such as moving distance, speed and direction are set on the control panel.

After the PLC reads these set values, it generates pulse and direction signals through calculation to control the stepper motor drive to achieve the purpose of distance, speed and direction control. The system operation results are proven to be reliable, feasible and effective through actual measurements.