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Do You Need A Controller For A Stepper Motor?

Do You Need A Controller For A Stepper Motor?

October 25 , 2023 0

Stepper motors employ specialized control techniques to attain superior precision compared to conventional variable speed motors, all while circumventing the cost and intricacy associated with servo systems.

In the realm of industrial automation, motion control typically refers to the utilization of an electric motor to precisely manage the position, speed, and acceleration of a physical system. Pneumatics offer cost effectiveness, and hydraulics excel in delivering sheer force. However, electric motors frequently strike the ideal equilibrium between accuracy, speed, power, durability, and operational expenses.

What is stepper motor controller?

A stepper motor controller operates by converting a sequence of input pulses into precise increments in the mechanical shaft's position. Each pulse impels the shaft through a predetermined angle, allowing the motor's position to be directed to one of these steps without necessitating any feedback sensor, a configuration referred to as open loop stepper motor control. The success of this control method hinges on careful sizing of the motor in terms of torque and speed to suit the specific application. Stepper motor control utilizes this sequence of input pulses to dictate the motor's movement to attain a desired position or speed.

In stepper motor control, constant voltage drives are typically employed to apply a sustained positive or negative voltage to each winding for propulsion. However, it is crucial to recognize that it is the winding current, not the voltage, that exerts torque on the stepper motor shaft. The relationship between the current (I), applied voltage (V), winding inductance (L), and winding resistance (R) is integral to understanding these systems, and they are often referred to as L/R drives. Achieving high torque at elevated speeds necessitates a substantial drive voltage paired with low resistance and low inductance. In cases of low voltage resistive motors, a higher voltage drive can be used by simply introducing an external resistor in series with each winding, although this approach is deemed less efficient due to power wastage and heat generation.

On the other hand, constant current drives are engineered to maintain a constant current in each winding, rather than a constant voltage. With each new step, an initial high voltage is applied to the winding, leading to a swift rise in current within the winding due to the equation dI/dt = V/L, where V is significant. Stepper motor controllers typically monitor the current in each winding by measuring the voltage across a small sensing resistor in series with the windings. When the current surpasses a designated limit, the voltage is turned off, and when it falls below this limit, the voltage is reinstated. This approach ensures a relatively constant current for a specific step position. While it does require additional electronics for current sensing and control, it permits stepper motors to be driven at higher torque and swifter speeds compared to L/R drives.

For enhanced system resolution, reduced noise, and smoother motion, Portescap's Microstepping Drives offer substantial advantages. The power stage in these drives is meticulously designed to accommodate motors with low electrical time constants, resulting in exceptional dynamic performance.

Stepper specifics

Stepper motors are named as such because they are commanded by pulses received from a drive to move in small discrete steps, and they can do so rapidly. They typically work best below 1,000 rotations per minute (rpm) because torque falls off rapidly as speed increases. Stepper motors lack any overload capability, therefore one industry rule of thumb is to size stepper motors and drives so that the expected load uses only 50% of the available torque to avoid potential stalling conditions.

Stepper motors are directed by a stream of pulses originating from a controller. In the full step mode, there are typically 200 steps (or 1.8 degrees) for each complete 360 degree revolution, with each pulse advancing the motor by one step. However, full step mode is not commonly used due to its lack of precision. Instead, users often opt for half step, quarter step, or other microstepping modes, which can provide step counts ranging from 400 to as high as 50,000 steps per revolution. The crucial decision in selecting a mode lies in balancing the trade offs between accuracy and the requisite control signal bandwidth.

Despite the perception that stepper motor controller is a cost effective alternative for motion control when compared to servo motors, they offer distinct advantages. Notably, stepper motors exhibit no jitter or dither when operating at zero speed. In scenarios where the application does not entail a continuous load from forces like gravity or others, certain stepper drives can include an idle current reduction feature. This function conserves energy and minimizes motor heat generation when the shaft remains stationary.

In machinery or equipment with moving components driven by motors, potentially involving gearboxes or rack and pinion mechanisms, stepper motors emerge as an effective means to accurately position a load. While most stepper motors do not come equipped with built in motor feedback mechanisms, it is feasible to incorporate an encoder with the motor. In many applications, it is, at a minimum, essential to install sensors within the equipment to supply position feedback.

A stepper motor driver system can create motion by commanding the motor with respect to how far and how fast it should rotate. Some common motion profile examples, in order of increasing complexity, are:

Move at a fixed velocity.

Move a number of steps and then stop.

Accelerate from one velocity to another

Move a number of steps from one stopped position to another, first accelerating to a target velocity then decelerating back to zero speed at the target position, known as a trapezoidal move.

Accelerate from one velocity to another; known as an S curve move.

Stepper motors can be an advantageous choice for many applications, and when they are suitable, they will be a lower cost option than servos. For applications where accurate single axis or limited multi axis motion control is needed, stepper motors, drives, and controllers (especially PLCs) used in conjunction with position switches and/or an encoder will reliably operate machinery at about 25% the cost of servo motor systems.

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Do You Need A Controller For A Stepper Motor?

What is stepper motor controller?

Stepper specifics

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