![]() ![]() We measure “spin rate” in revolutions per minute (RPM) however, we measure vibration frequency in Hz (cycles per second). For ERM motors, you cannot vary the vibration frequency and amplitude independently-both increase linearly with the applied voltage.ĭC motors spin at a rate proportional to the applied voltage. ![]() There are two main characteristics of a vibration: the vibration frequency, which is how fast the mass is spinning and the vibration amplitude, which is the strength of the vibration force. When it rotates, the weight shifts causing a vibration. The idea is quite simple: attach an asymmetric or unbalanced mass to the DC motor’s axle. A video from Precision Microdrives demonstrating how eccentric rotating mass (ERM) motors work. The larger the object, the more force is needed to modulate the vibration onto the object. By attaching an ERM to an object-like a smartphone or game controller-the rotating irregular mass causes the motor and attached device to shake. When the ERM motor spins, the rotating mass’s centripetal force causes displacement. Eccentric Rotating Mass (ERM) MotorsĮccentric rotating mass (ERM) motors have an unbalanced mass attached to their axle. They require different driver circuits and actuation methods (DC for ERM and AC for LRA). Depending on their enclosure and form factor, some ERMs and LRAs can look similar even though they are fundamentally different technologies. Below, we are showing “coin” (or “pancake”) form factors of both ERM and LRA.įigure. If a vibromotor is fully enclosed in a shell, you cannot necessarily tell whether it is ERM or LRA even though the technologies are fundamentally different. Moreover, their vibration frequency is strongest at a single frequency (the resonant frequency). While LRAs are more responsive than ERMs (~15-25ms startup times), their vibration strength is more minimal and the wiring circuitry more complicated. For example, newer Apple MacBooks and iPhones feature the Apple Taptic Engine, which uses LRA technology. They are increasingly common in smartphones, watches, and trackpads to mimic the feeling of a click. LRAs require a smooth sine wave voltage signal (aka an AC signal) driven at specific resonant frequencies-usually 150-200Hz-which controls how often the mass moves and, therefore, the vibration oscillation. They linearly move a mass (up and down) attached to a spring using a magnetic voice coil. As the applied DC voltage increases, the frequency and amplitude of the vibration linearly increases, which is perceived as overall vibration intensity. ![]() For ERMs, you cannot individually control the frequency of the vibration ( i.e., how fast the mass is spinning) and the amplitude of that vibration-they are tied together. LRAs are similar in design to speakers:ĮRMs are built with DC motors and an off-centered mass: they are cheap, provide a strong vibration, and are pervasive in toys, game controllers, mobile phones, and watches however, they have a comparatively long startup time (~20-30ms) and limited controllability. ERM motors vibrate in two directions due to the centripetal force of the unbalanced mass attached to the DC motor axle. A video from Precision Microdrives showing the two most common types of vibration motors: eccentric rotating mass (ERM) motors and linear resonant actuators (LRA). The video excerpt below from Precision Microdrives shows how ERMs and LRAs vibrate. We will be using ERM motors in this lesson. ERMs vibrate along two axes while LRAs are single-axis vibrators. There are two common types of vibration motors: eccentric rotating mass (ERM) motors that have a small unbalanced mass attached to the DC motor axle that creates a displacement force when rotating and linear resonant actuators (LRA) that contain a small internal mass attached to a spring, which vibrates in a reciprocating linear motion with an applied AC signal. Images from NFP Motors and Sosav Vibromotors Examples of eccentric rotating mass (ERM) motors and linear resonant actuators (LRA) in mobile phones and watches. In this lesson, we will learn about vibration motors, which are commonly used to provide haptic feedback in game controllers, mobile phones, and smart watches.įigure. Haptic or tactile actuator technology provides feedback to the user via touch by force, motion, or temperature.
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