Vibrator (mechanical)
From Wikipedia, the free encyclopedia
- For other uses of this term, see vibrator.
A vibrator is a mechanical device that is designed to generate vibrations. The vibration is often generated by an electric motor with an unbalanced mass on its driveshaft. If the motor is switched on, the rotating weight resonates.
There are many different types of vibrator. Some are components of larger products such as those in cellphones and pagers.
[edit] Vibrators as component parts
When cellphones and pagers vibrate, the vibration is produced by a small component that is built into the phone or pager. Many older, non-electronic buzzers and doorbells contain a component that vibrates for the purpose of producing a sound. Tattoo guns and some types of electric engraving tools contain a mechanism that vibrates a needle or cutting tool.
[edit] Industrial vibrators
Vibrators are used in many different industrial applications both as components and as individual pieces of equipment. Many vibrators are used to help move bulk material or small component parts. The application of vibration working with the force of gravity, can often move materials through a process more effectively than other methods. Vibration is often used to position small components so that they can be gripped mechanically by automated equipment as required for assembly etc.
Vibratory feeders and vibrating hoppers are used extensively in the food, pharmaceutical and chemical industries. Vibrating screens are used to separate bulk materials in a mixture of different sized particles. For example, sand, gravel, river rock, and crushed rock and other aggregates are often separated by size using vibrating screens.
Cement vibrators are used to shake fresh concrete so that entrapped air and excess water are released and the concrete settles firmly in place in the forms. A common type of concrete vibrator is a steel cylinder about the size of a baseball bat with a hose or electrical cord attached to one end. The vibrator head is often immersed in the wet concrete, but the concrete forms are sometimes vibrated also. Some models contain a long slender motor with an eccentric weight attached to the motor shaft. Other models have a flexible shaft connected to a motor or engine that is external to the cylindrical vibrator head. Another type is powered by a hydraulic or pneumatic unit connected to the head by a hose. In these, the internal mechanism can be either rotating or reciprocating.
Vibrating tables or shake tables are sometimes used to test products to determine or demonstrate their ability to withstand vibration. Testing of this type is commonly done in the automotive, aerospace, and defense industries. Some manufacturers of this type of industrial vibrator are Ling Electronics[1] and Unholtz-Dickie[2]. These machines are capable of producing three different types of vibration profile: sine sweep, random vibration, and synthesized shock. In all three of these applications, the part under test will typicall be instrumented with one or more accelerometers to measure how the component responds to the vibration input. A sine sweep vibration profile typically starts vibrating at low frequency and increases in frequency at a set rate (measured in hertz per minute). The amplitude (measured in gs) of the sine wave may increase or decrease as well. A sine sweep is intended to look for resonant frequencies in the part. A random vibration profile will excite different frequencies along a spectrum at different times. Significant calculation goes into making sure that all frequencies get excited to within an acceptable tolerance band. A random vibration test can be anything as short at 30 seconds up to several hours. It is intended to synthesize the effect of, for example, a car driving over rough terrain or a rocket taking off. A synthesized shock pulse is a short duration high level vibration calculated as a sum of many half-sine waves covering a range of frequencies. It is intended to simulate the effects of an impact or explosion. A shock pulse test typically lasts less than a second.
