Transcript:
[0m:00s] Hey, I’m Mitchell and welcome to another video in the RSP Education Series. Imagine your robotic arm jitters when placing a microchip or your CNC mill leaves ripples on a precision machined surface. The culprit isn’t poor programming or sloppy hardware. It’s torque ripple, the silent saboteur of motion control. Whether you’re using stepper motors or brushless DC drives, torque ripple can quietly degrade your performance, your profits, and your precision. Let’s break down what causes it and how to fight back. This video is for educational purposes only. Consult a professional for your application. RSP Supply is not liable for any misuse of this information. Let’s get into it.
[0m:50s] A stepper motor is a type of electric motor that doesn’t spin freely. It moves in small, precise steps, like a clock’s second hand ticking forward instead of sweeping smoothly. Each time the motor gets an electrical pulse, it rotates a fixed amount, usually 1.8 degrees per step, meaning 200 steps equals one full turn. Stepper motors are used in automation when precise, repeatable movement is required. Examples include robotic arms moving to specific locations, label feeders positioning products, or lifts raising objects to exact heights.
[1m:27s] Stepper motors are great because they’re affordable and simple to control. In many cases, they don’t need position sensors because their movement is predictable. They can also hold position without moving, which is useful for tasks like holding a valve open. Torque ripple happens in stepper motors because each step generates slightly different torque levels. Between steps, torque drops, creating a pulsed, uneven torque profile known as torque ripple.
[1m:58s] Torque ripple causes vibrations in precise machinery like CNC mills or laser cutters, reduces accuracy in low speed applications such as linear stages, and increases noise and resonance that can damage components. Ways to minimize ripple include microstepping, which breaks full steps into smaller increments using sine and cosine currents for smoother torque. Another method is using damped stepper drivers that actively reduce vibration and resonance with internal algorithms. Closed loop feedback, also called hybrid stepper control, adds an encoder for position feedback, reducing errors and smoothing torque output.
[2m:50s] Now let’s talk about BLDC motors, or brushless DC motors, and PMSMs, or permanent magnet synchronous motors, and how torque ripple affects them. Brushless motors rotate using a magnetic field generated electronically. With no brushes, they require less maintenance and operate smoothly, but torque ripple still exists. Torque ripple in these motors mainly comes from cogging torque, which is the interaction between rotor magnets and stator teeth, and from non-ideal commutation, which is how current is switched between motor phases. This ripple causes speed fluctuations at low RPMs, which can affect conveyor belt control, label printers, or robotic end effectors. In robotic arms, even tiny torque variations can create oscillations or misalignment. Ways to minimize ripple include field-oriented control (FOC), an advanced technique that aligns current with the rotor field for smoother torque; high-resolution encoders, which provide real-time feedback for precise phase current adjustments; sine wave commutation, which uses smooth sinusoidal current instead of blocky trapezoidal signals; and skewed stator slots or rotor magnets, a mechanical design tweak that reduces magnetic snapping effects.
[4m:08s] In a factory, precision equals profit, downtime equals lost money, and component wear means more maintenance. Torque ripple affects all three. In robotics, smooth joints are critical for pick and place or welding. In packaging lines, speed inconsistencies throw off labeling and sorting. In machining, torque ripple can appear as visible surface ripples on finished parts. In inspection and vision systems, small vibrations distort image quality.
[4m:44s] Torque ripple isn’t just an academic concept. It’s a real-world issue for anyone dealing with precision motion. From stepper motors clicking unevenly to brushless motors fighting cogging torque, ripple introduces vibration, inaccuracy, and wear. But with the right strategies like microstepping, field-oriented control, feedback loops, or clever mechanical design you can regain control of your torque and achieve smooth, efficient motion. In automation, precision pays and ripple costs. For hundreds of thousands of industrial automation products, visit rspsupply.com, the internet’s top source for industrial hardware.