Mechanics of Machine- Assignment.

Group 4

Question-3: What is the effect of vibration (three different examples with description) in biomedical engineering equipment and how vibration can be reduced (use at least three Journals as references)? Answer: Vibration is defined as cyclic or oscillating motion of machine or its component from its position of rest [1]. When a particle or a body or systems of connected bodies are displaced from its equilibrium position, a motion called vibration will occur. The system tends to return to this equilibrium position under the action of restoring forces (such as the elastic forces, as for a mass attached to a spring, or gravitational forces, as for simple pendulum). The system then will keep moving back and forth across its position of equilibrium [1]. Most vibrations are undesirable. There are many sources of mechanical vibrations in biomedical devices but it is difficult to determine its source of vibration [2]. Mechanical vibrations can be caused by imbalances in the rotating parts, uneven friction, the meshing of gear teeth, etc [3]. There are many effects of vibration in biomedical engineering equipments, but in this assignment only three of the effects will be discussed, which includes: Vibration leads to strain cracks of biomedical machine elements, which will consequence in its breakdown [2]; Vibrations influence machine strength and cause disturbance in the programmable motion of machine elements [2]; Vibration is one of the reasons of excessive mechanical energy dissipation in biomedical equipments [2]. First of all, large variable stresses accompanied with vibration phenomenon will lead to strain cracks of biomedical engineering equipments [1]. These will consequence in its breakdown. When a medical equipment fails or breaks down, the consequences can range from annoyance to financial disaster, or personal injury and possible lose of life. Next, vibration can influence machine strength and cause disturbances in the programmable motion of machine elements, which will create a noise source and increases friction. This will

Mechanics of Machine- Assignment. Group 4

disturb the normal machine operations and will cause a decrease in the durability of the biomedical engineering devices and machines [3]. Lastly, vibration is also one of the reasons of excessive mechanical energy dissipation in biomedical engineering equipments. This in turn will cause a decrease in the efficiency, capacity and the durability of the equipments and machines. In order to reduce the harmful effects of vibration in biomedical engineering equipments, the engineers have to imply the machine vibrations control. The main purpose of this machine vibration control includes the objective of having the most effective machine operation protection and to minimize the undesirable and harmful effects of the vibrations in the biomedical machine equipments. Attempts have been made during the last years to control vibration in machines [2]. Those tasks are known as the Vibration Control in the English literature (Kowal, 1996). In order to reduce disturbance, the following task can be considered by engineers: Protection of vibration reasons [2]; Parametric modifications [2]; Structural modifications [2]; Vibration damping [2]

Some of the methods that are included in the protection of vibration reasons are the elimination of additional energy sources, elimination or decrease in input forces (by change of P vector coordinates value Mx + Bx + Kx =P, which is the mathematical model of the system), and isolation of the system from external disturbance (can be done by substitution of rolling bearings by slide ones, decrease of colliding bodies mass, etc). As for parametric modifications, it is mainly the changes of mass and stiffness elements [2]. Structural modifications includes the introduction of additional constraints to the biomedical equipments or tearing away the existence ones (interrupting the vibration structure by introducing intermediate elements called vibroisolators) and introduction of vibration eliminators [2].

Mechanics of Machine- Assignment. Group 4

Lastly, the method of vibration damping can be introduced by engineers to reduce the vibration effects in biomedical engineering equipments, when the undesirable vibration cannot be eliminated via constructional or parameters changes [2]. Damping refers to the dissipation of mechanical energy, which is exchanged to heat. This in turn causes the decrease of general efficiency of biomedical equipments, hence it is important that engineers ensure that the medical device run with minimal damping value in order to have an ideal device performance [2]. Vibrations generally cause the efficiency of the medical device to decrease and cause the machines to get worn out earlier. Hence, it is important that biomedical engineers take the steps necessary in designing the medical devices in order to reduce the effects of vibrations on the equipments.

References: [1] Wu, J., Zhang, R. R., Radons, S., et al (2002). Vibration Analysis of medical devices with

a calibrated FEA module in Computers and Structures Journal. Retrieved on March 31, 2012 from IEEE database. [2] Barcik, M., Konieczny, J., Kowal, J., Sapinski, B., (n.d.). Vibration Control of

Mechanical Systems- introduction to the problem in Acta Montanistica Slovaca. Retrieved on April 1st, 2012 from ScienceDirect Database. [3] Poole, R. L., Simon C. Lea, Dyson John E., et al (2008). Vibration characteristics of

dental-high-speed turbines and speed-increasing handpieces in Journal of Dentistry. Retrieved on April 1st, 2012 from ScienceDirect Database.