Vibration Frequency vs Vibration Occurrence

In everyday conversation, we often refer to single vibration effects simply as "vibrations." For example, you might mention that your phone vibrates when you receive a text message, or that the touch screen "vibrates" briefly when you tap it, and twice when you press and hold it. In reality, however, each of these effects consists of hundreds of displacement cycles occurring in a single instance.

It is crucial to realize that vibration is essentially a series of repetitive and periodic displacements. In an eccentric rotating mass (ERM) vibration motor, this displacement occurs in an angular manner as the mass rotates. In contrast, a linear resonant actuator (LRA) operates in a linear manner, with a mass moving back and forth on a spring. Therefore, these devices have vibration frequencies that reflect the oscillatory nature of their displacements.

Defining the Terms

Vibration frequency is measured in Hertz (Hz). For an Eccentric Rotating Mass (ERM) motor, motor speed in revolutions per minute (RPM) divided by 60. For a Linear Resonant Actuator (LRA), represents the resonant frequency specified in the data sheet.

It is actuators (ERMs and LRAs) that have vibration frequencies, derived from their speed and construction

Vibration occurrences are the number of times a vibration effect is activated within a given time frame. This can be expressed in terms of effects per second, per minute, per day, etc.

It is applications that have vibration occurrences, where a vibration effect might be played at specific time intervals.

How to Vary and Achieve Specific Vibration Frequency

Varying the vibration frequency is very easy.

Simply put:

The vibration frequency is directly related to the motor speed, which is affected by the applied voltage. To adjust the vibration frequency, the applied voltage can be increased or decreased. However, the voltage is constrained by the starting voltage and the rated voltage (or maximum rated voltage for a short time), which in turn limits the vibration frequency.

Different vibration motors exhibit unique characteristics based on their torque output and eccentric mass design. In addition, the vibration amplitude is also affected by the motor speed, which means you cannot adjust the vibration frequency and amplitude independently.

This principle applies to ERMs, LRAs have a fixed vibration frequency known as their Resonant Frequency. Therefore, reaching a specific vibration frequency is equivalent to making the motor run at a specific speed.