The vibration motors are crucial components of cell phones, providing haptic feedback through vibrations, thereby enhancing user engagement and interaction.
These motors are tiny permanent magnet DC brushed motors that allow a cell phone to vibrate. They are one of the micro motors and they range from a few to several millimeters in size. A vibration motor comes into play when a phone call or text message is received, activating the motor to work rapidly and produce a vibrating alert in silent mode.
There are two types of vibration motors, eccentric rotating mass and linear resonant actuators.
Image Source: Precisionmicrodrives & Ebay & Unsplash & Pixabay
Eccentric Rotating Mass
The eccentric rotating mass uses an electric current to drive a rotor, creating a vibrating effect. This motor type can be classified into ordinary vibration motors and coin vibration motors.
The ordinary vibration motor has an asymmetrical semicircular cam mounted on a shaft. When the motor drives the shaft to rotate, the off-centered gravity of the cam causes a varying centrifugal force, generating vibration. Despite producing strong vibrations, the eccentric rotating mass doesn’t provide a satisfying user experience.
In addition, there is another type of eccentric rotating mass, also known as a coin vibration motor. Its principle is similar to that of a conventional vibration motor, both of which use centrifugal force to drive the vibration of the phone. The former will continue to rotate for some time even if the current is no longer driving it due to its rotational inertia, while the latter will cause the vibration to increase and emit a “buzzing” sound due to its increased speed. The coin-type vibration motor is very thin, and it can reach 1.8mm, which is suitable for thin and light smartphones.
Rotor motors are advantageous for their small size and low cost. However, their limitation is a lack of control of the vibration, The eccentric rotating mass continues rotating due to rotational inertia even when the electric current stops. That is why they are mainly used in low-end cell phones and smart bracelets.
Image source: Linkedin & Precisionmicrodrives
Linear Resonant Actuators
The advent of linear resonant actuators effectively resolves the monotony issue of rotor motors. The vibration of this type of motor comes from the vibration of the vibration element in the horizontal or vertical direction. It does not require any rotation to start and stop and it takes only 50ms from the standstill to the highest vibration level, while the eccentric rotating mass needs 100ms~200ms. So the user experience is very good.
With customized control routes, linear resonant actuators can realize independent control of vibration intensity or frequency, bringing richer vibration feedback. Linear resonant actuators are divided into two types according to the vibration direction: vertical linear motors and horizontal linear motors. The principle of these two linear vibration motors is to directly convert electrical energy into kinetic energy through the linear motion of the vibration element.
Vertical linear resonant actuators | also known as circular linear motors or Z-axis linear motors, move in the up and down directions of the phone. The movement distance is limited by the thickness of the phone, so the volume is small and the vibration is relatively weak. However, it has a faster start-up and braking speed than a rotor motor. The sound it makes is generally “squeaky”. The cost of a vertical linear resonant actuator is around $5, which is a good balance between cost and experience.
Horizontal linear resonant actuator | due to the limited vertical movement range of the vertical linear resonant actuator, the horizontal linear resonant actuator was born. It is also known as the X/Y axis linear vibration motor. Through the optimization of the phone algorithm, the horizontal linear resonant actuator has a higher upper limit of vibration intensity and can realize more vibration modes. For example, the different vibration feedback of different operations realized by high-end phones fully reflects the precise control of the linear resonant actuator.
However, due to the large size of the horizontal linear resonant actuator, it will occupy a larger space in the internal space of the phone. It has high requirements for the layout design of the phone motherboard, and it will also squeeze the space of the battery to a certain extent. In addition, the cost of the horizontal linear resonant actuator is between $8 and $10, which is far higher than that of the eccentric rotating mass and vertical linear resonant actuator.
Image source: Amazon and Gif source: Web
Some Datasheets of Vibration Motors for Reference
| Linear Vibration Motor | |
| Item | Specifications |
| Motor Length | 12±0.1 mm |
| Motor Width | 6±0.1 mm |
| Motor Height | 2.8±0.1 mm |
| Weight | 1.36±0.1 Gram |
| Resistance | 16±2 Ω |
| Rated Current Max. | 135 mA |
| Vibration Acceleration | Min0.65Grms |
| Operating Frequency | 200±10 Hz |
| Rising Time Max. | 50 msec |
| Falling Time Max. | 60 msec |
| Mechanical Noise Max. | 50 dB(A) |
* Image source: Phonepartworld
| Coin Vibration Motor | |
| Item | Specifications |
| Rated Voltage | 3.0V DC |
| Operating Voltage | 2.3~4.0V DC |
| Rotation | clockwise or Contrary clockwise |
| Operating Environment | -20~+60°C,Ordinary Humidity |
| Rated Speed | 15500±2500rpm min |
| Rated Current | 90mA Max |
| Starting Current | 150mA Max |
| Starting Voltage | 2.3V DC Max |
| Insulation Resistance | 10MΩ Min |
| Bracket Deflection Strength | 9.8N or more |
| Mechanical Noise | 50dB(A)Max |
* Image source: Amazon
