Vibration. In its simplest form, a vibration can be thought of as the oscillation or repetitive motion of an object around an equilibrium position. The equilibrium position is the position it will reach when the force acting on it is zero.
This type of vibration is called whole-body vibration, which means that all parts of the body are moving together in the same direction at any given time.
Summary
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- 1 Features
- 2 Cause
- 3 Consequences in the human being
- 1 High frequency
- 4 vibration meters
- 5Enlace externo
- 6Fuente
Features
The vibratory movement of a whole body can be fully described as a combination of individual movements of 6 different types. Those are translations in the three orthogonal directions x, y, and z, and rotations about the x, y, and z axes. Any complex movement that the body can present can be broken down into a combination of those six movements.
Such a body is said to have six degrees of freedom. For example a ship can move from front to back (wave) from bottom to top and from portboard to triboard. It can also roll lengthwise (roll), rotate around the vertical axis (tail) and rotate around the port-triboard axis (arfar).
Assuming that an object is prevented from moving in any direction except one. For example , a clock pendulum can only move in one plane. Therefore, it is said to be a system with a single degree of freedom. Another example of a system with a single degree of freedom is an elevator that moves up and down in the elevator hub.
Cause
The vibration of an object is caused by an exciting force . This force can be applied externally to the object or it can originate from within the object. Later we will see that the rate (frequency) and the magnitude of the vibration of a given object are completely determined by the exciting force, its direction and frequency. That is why a vibration analysis can determine the exciting forces acting on a machine.
Consequences in the human being
Exposure to vibrations for prolonged periods of time, depending on their intensity and frequency , produces harmful effects on the human body. The most common effects are:
- Spinal cord injuries.
- Abdominal and digestive pain.
- Balance problems.
- visual disturbances
Depending on the frequency of vibration, they can cause the following effects:
High frequency
- Osteo-articular disorders radiologically identifiable as hyperostosating osteoarthritis of the elbow.
- Wrist injuries such as lunate malacia or osteonecrosis of the carpal scaphoid.
- Angioneurotic disorders of the hand, cramps, sensitivity disorders.
- Vascular expression manifested by crises of the type of dead fingers called Raynaud’s Syndrome.
- Increased incidence of stomach diseases.
vibration meters
Vibration meters are used to measure vibrations and oscillations in many machines and installations, as well as for product development (eg components or tools).
Vibration in machines is the result of dynamic forces produced by their moving parts. As every machine is made up of different parts, each of these will vibrate with different frequencies and amplitudes, causing wear and fatigue to the components, often being the cause of catastrophic failures.
In the absence of any instrument to measure vibration, in some plants vibration is evaluated by touch, in some cases a rod is used that transfers the vibration signal to the operator’s head, or in other cases a stethoscope is used. medical type. In each of these cases, the vibration signal is evaluated on the basis of experience, without any reference numerical value to serve for later comparison.
Mechanical objects vibrate in response to exciting forces. However, the vibration also depends on the structural characteristics of the system. This includes mass, stiffness, and damping characteristics. The mass of an object is equal to its volume multiplied by its density. Stiffness depends on the elasticity of the material and is expressed in units of force per unit deflection (lb/in). Damping is a measure of the system’s ability to dissipate energy as heat.
Excitation is usually governed by tolerances and defects within the system, its manufacture, the installation process, and the way the system was designed. The three characteristics of vibration are frequency, amplitude, and phase.
Vibration amplitude = Exciting forces / System stiffness
The measurement provides the following parameters:
- Vibration acceleration.
- Vibration speed.
- Vibration variation.
