A stepper motor is a discrete motion device closely related to modern digital control technology. It is an actuator that converts electrical pulses into angular or linear displacement. When a stepper motor driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle (also known as the step angle) in a set direction. The angular displacement can be controlled by controlling the number of pulses, thus achieving accurate positioning. Simultaneously, the rotational speed and acceleration of the stepper motor can be controlled by the pulse frequency, achieving speed regulation. As can be seen, stepper motors can be directly positioned and controlled using pulse signals. Due to their high precision, simple control circuitry, ease of use, and reliability, they are widely used in industrial automatic control, CNC machine tools, combination machine tools, robots, computer peripherals (scanners, disk drives, printers), cameras (including optical and digital cameras), projectors, digital camcorders, video players (VCD, DVD, etc.), large telescopes, satellite antenna positioning systems, medical devices, barcode scanners, and various controllable mechanical tools, etc. With economic development, technological advancements, and the development of electronic technology, the application fields of stepper motors have become broader, which also places higher demands on the operating performance of stepper motors.
Microcontroller-controlled stepper motors offer advantages such as flexible and diverse functions, accurate pulse output, and strong real-time performance. Through software design, various complex controls can be implemented, resulting in relatively low system costs. In recent years, they have been widely used in various motion control systems. However, in practical applications, if the pulse frequency changes unreasonably during acceleration and deceleration, the motor may lose steps or overshoot, preventing precise positioning. Furthermore, due to the system's speed requirements, the motor needs to complete acceleration and deceleration processes quickly. This paper designs a stepper motor control system based on a PIC microcontroller, analyzes the application patterns of the exponential acceleration/deceleration curve (which offers the best speed) in practical systems, proposes an optimization method for the acceleration/deceleration curve, and employs hardware and software anti-interference techniques. Data and commands can be input via the keyboard, and the motor's speed can be easily adjusted continuously via a knob. The operating mode of the stepper motor can also be set and displayed in real time.
A stepper motor is an actuator that converts pulsed current into angular velocity. When a stepper driver receives a differential signal, it drives the stepper motor to rotate a fixed angle (lateral angle) in a set direction. Precise positioning can be achieved by controlling the number of pulses to control the angular velocity; additionally, the rotational speed and instantaneous velocity can be controlled by controlling the pulse frequency to achieve speed regulation; and the rotational direction of the stepper motor can be controlled by changing the power supply sequence of each phase.
Characteristics of stepper motors
1. The angular velocity of a stepper motor is strictly positively correlated with the pulse signal, therefore, it has no total error and has excellent tracking performance.
2. Stepper motors have a fast dynamic response, making them easy to start, stop, rotate forward and reverse, and adjust speed.
3. The speed can be smoothly adjusted within a very wide range, and a large torque can still be ensured at low speeds. Therefore, it is generally possible to drive the load immediately without the need for a speed reduction device.
4. Stepper motors can only operate with a pulse power supply system; they cannot be directly powered by AC or DC switching power supplies.
Based on the functions to be performed by the stepper motor control system, the software program mainly includes: fault interrupt handling program, timer shift interrupt program, step control signal interrupt handling program, phase sequence refresh and communication processing program, and acceleration/deceleration curve adaptive control processing program.
Since stepper motors are controlled by pulse signals, they can be controlled in an open-loop manner, which is a simple, practical, economical, and feasible technical solution for applications where high precision is not required. However, in an open-loop stepper motor drive system, the input pulses are not dependent on the rotor position but are given in advance according to a certain rule. The control system cannot adjust its control parameters according to the operating frequency and load size. This introduces some unfavorable factors to the open-loop operation of the stepper motor, especially at certain low and medium frequency points, where oscillations will occur, and in the high-frequency range, the electromagnetic torque will decrease. Both oscillations and decreased electromagnetic torque can lead to step loss and inaccurate position control.
Closed-loop feedback control plus adaptive control directly or indirectly detects the rotor's position and speed. Through feedback and adaptive processing, it automatically generates a drive pulse train according to the optimized lifting and lowering operation curve. This not only significantly improves the driving torque characteristics of the stepper motor, enabling more precise position control and higher and smoother speeds, but also gives the stepper motor greater versatility and practicality in many other fields.
