Motor Drive ICEnhancing Current Control:

bipolar stepper motors are used in a wide range of applications, from driving paper through printers to moving XY axes in industrial equipment. Typically, the motors are of low cost and stepper motor type.Motor Drive ICDrive and Control. Unfortunately, most of these ICs utilize simple current control methods, leading to imperfect motor current waveforms and suboptimal motion quality. Conducting internal bidirectional current detection within stepper motor drive ICs can enhance motion quality while simultaneously reducing system costs.

Bipolar Stepper Motor Fundamental Knowledge

The bipolar stepper motor consists of two windings. The motor moves by sequentially passing different currents through the two windings. To ensure smooth movement, the two windings can be driven by a 90° out-of-phase sine current - sine and cosine.

Steppers are typically not driven like linear amplifiers. They use PWM current regulating motor driver ICs, which provide discrete current values to represent straight line segments of a sine wave. This is known as microstepping. A sine wave can be synthesized into any number of segments, and as the number of segments increases, the waveform approaches a true sine wave. Theoretically, this can range from 4 to 2048 or more, with most IC stepper motor driver ICs completing between 4 to 64 segments. Since a sine wave produces four steps (mechanical states in the stepper motor), a 64-segment sequence is referred to as 1/8th step operation.

Why Current Control Accuracy Matters

The position of the bipolar stepper motor's rotor depends on the magnitude of the current through the two windings. Typically, when using stepper motors, precise mechanical positioning of certain mechanical systems or precise speed control is required. Therefore, the precision of the movement partly depends on the accuracy of the winding current used to drive the motor, which makes sense.

Inaccurate current control in mechanical systems can lead to two issues:

At low speeds or when stepper motors are used for positioning applications, the step size of the motor varies at each micro-step, which can lead to positioning errors.

At higher speeds, non-linearity can cause short-term speed variations within a single motor rotation. This increases unnecessary torque on the components, leading to increased motor noise and vibration.