What Is a Vibration Generator?
A vibration generator is a device that generates mechanical vibration.
They range from tiny devices built into cell phones to large devices used to reproduce earthquakes. Some of these devices can accurately generate the target vibration and can be used in a variety of ways.
There are a wide variety of conditions for the frequency, amplitude, and direction of the vibration to be generated, as well as a wide variety of drive methods, including electric, pneumatic, and hydraulic. The appropriate device for each condition is incorporated as needed.
Uses of Vibration Generators
The most familiar vibration generators are used to transmit something to a person through vibration, such as the vibration generator within a cellular phone.
In industrial equipment, vibration generators are mainly used in devices that convey or align parts by applying vibration, as well as in parts feeders and powder cutters.
Other applications include testing equipment that simulates the transportation of goods by truck, and testing equipment that simulates a major earthquake to check the strength of buildings and other structures.
Principle of Vibration Generators
Vibrations in cell phones, for example, are based on the principle that an eccentric weight is attached to the tip of a motor and rotated, causing vibrations when the motor cannot rotate stably. In industrial applications, vibration generators are often combined with a single axis vibration generator in multiple directions to generate the desired vibration, since the reproducibility of vibration is important.
Vibration generators that use hydraulic pressure can generate large forces and amplitudes, but at higher frequencies, the oil movement cannot keep up. Pneumatic vibration generators are simple, easy to install, and can be used in clean environments, but they are not suitable for generating precise vibrations due to the compressibility of the air itself. Vibration generators using electromagnetic coils can handle high frequencies, but the amplitude generated is small.
In order to generate vibration generators accurately, test equipment, for example, can be fitted with sensors to provide feedback to accurately reproduce the desired vibration.
Types of Vibration Generators
Vibration generators are classified into three types: hydraulic, electrodynamic, and unbalanced mass types.
1. Hydraulic Type
Hydraulic vibration generators use hydraulic pressure to drive a piston to generate vibration.
2. Electrokinetic Type
Electrokinetic vibration generators generate vibration by applying an electric current to a coil and using the force generated in a magnetic field. It is based on the same principle as a speaker and is called Fleming’s left-hand rule. Fleming’s left-hand rule is a method of memorizing electromagnetic phenomena, which was invented by John Ambrose Fleming, and is shown by the fingers of the left hand, in which an electric current flowing through a conductor in a magnetic field causes the conductor to move in a certain direction due to the Lorentz force acting on it.
3. Unbalanced Mass Type
The unbalanced-mass vibration generator is a motor with eccentric weights attached to it that rotates and generates vibration by centrifugal force. The unbalanced-mass type is based on the same principle as the vibration of a cellular phone and is often used for aligning machines.
How to Select a Vibration Generator
1. Hydraulic Type
Hydraulic vibration generators can easily generate large forces. They can be large enough to build a house on top of the vibration generator and can be driven in the mid-range, as high as 1,000 Hz. On the other hand, smaller vibration generators are impossible to manufacture, and large hydraulic pumps are difficult to maintain, difficult to use, and unsuitable for high-frequency applications.
2. Electrokinetic Type
Electrokinetic vibration generators can be driven without contact and produce a broadband, distortion-free waveform. They can also accommodate a wide variety of external input signals. Furthermore, they can be manufactured from very small to large devices, and can be easily installed in laboratories with only a power supply. However, large amplitude and large output are difficult to achieve, and a signal source and power amplifier are required to drive the system, making the system very expensive.
3. Unbalanced Mass Type
Unbalanced-mass vibration generators are simple and inexpensive, and can be driven by a power source alone. However, it is not suitable for vibration testing due to its nature of rotational motion and poor reproducibility. The frequency limit is low and cannot be driven by external signals, such as seismic waves, random waves, or shock waves.