This document discusses drive belt vibrations. It begins by defining drive belts and their main uses for power transmission and motion tracking. Advantages of belts over other torque transmitters like gears and chains are mentioned, including greater separation between shafts and damping of vibrations. Common causes of belt vibrations are then examined, such as misalignment, length and tension issues, and unbalance. Methods for detecting vibrations like using a strobe light or sensors are also presented. The document concludes by noting some effects of excessive vibrations can include short component life, cracks and failure.

1. DRIVE BELT VIBRATIONS
Michael Sanjaya Jonatan – 15/385241/TK/43903
Muhammad Kamal Ardi Putra – 15/385248/TK/43910
Reggie Johanes – 15/385253/TK/43915
Romadhon Bagus A. – 15/385258/TK/43920

2. What are drive belts?
Belts are flexible mechanical elements often used in
machines for a variety of purposes
• Power transmission
• As a source of motion
• Relative motion tracking
The most general use of belts is to connect two or
more shafts in order to transmit torque.

3. Advantages of Drive Belts
Drive belts have several advantages over other
torque-transmitting mechanical elements such as
gears and chains:
• Belts can be made longer, allowing for greater
seperation between shafts
• Simplifies assemblies and reduces cost by replacing
gears, shafts, bearings, etc.
• Elasticity plays a large role in damping out and
isolating vibrations, extending machine life.

4. Examples of Usage
Belt-drive cog on a belt-
driven bicycle
Timing belt used in
automotive engines
Conveyor belts used to move
luggage in airports

5. Vibration in Drive Belts
• Like every other mechanical element, drive belts experience vibrations.
• Vibrations can be caused by a variety of mechanical faults.
• While belts are elastic and thus help isolate vibrations to an extent, excessive vibrations can still
cause damage to the machine.
• Excessive vibrations can cause several problems leading to failure such as cracks and can also
shorten component life.

6. Causes
• Misalignment
• If the drive or driven pulley is not in the same plane through cocking of one sheave
relative to each other, it will cause vibration. In the other words, if it is parallel but not
aligned, it will cause vibration.
• Length and Tension
• Sometimes the length and tension on a drive belt can cause resonance within the belt
whereby it acts like a resonant string.
• An increase in the length of the belt will result in an increase of the mode of the resonance.
• Unbalance
• Unbalance can cause excessive forces that affect the machine.
• Broken Belt
• In almost every dynamic machine, damage of one part of the machine can cause
vibration.

7. Causes
Misalignment Vibration with strobe light

8. Misalignment
Common causes of misalignment are:
• Thermal expansion: Expansion or growth of a component due to the heating and cooling
of that component.
• Cold alignment: Most machines are aligned cold and heat as they operate. Thermal
growth causes them to grow misaligned.
• Alignment of component during coupling is not correctly achieved. Therefore,
misalignment is introduced into the system during installation.
• Improper alignment due to imparted forces from piping and support members.
• Misalignment due to uneven foundation, shifting in foundation or settling.

9. Unbalance
Unbalance occurs when the shaft’s mass centerline does not coincide with its geometric
centerline. In general, there are three types of unbalance:
• Static Unbalance
• Only one force is involved.
• Can be observed at rest.
• Couple Unbalance
• Two equal forces are 180 degree from each other.
• Cannot be measured at rest, because it appear balanced at rest.
• Dynamic Unbalance
In reality, most unbalance is dynamic, it is the combination of static and couple unbalance.

10. Unbalance
Unbalance can be caused by several factors:
• Improper component manufacturing
• Uneven build up of debris on the rotors, vanes or blades.
• The addition of shaft fittings without an appropriate counter balancing procedure.
• Pulley erosion or thrown balance weights.

11. Detecting Vibrations
Calculating Belt’s Natural Frequency ( )
with:
• PS1 : Driver Pulley Speed
• PS2 : Driven Pulley Speed
• PD1 : Driver Pulley Diameter
• PD2 : Driven Pulley Diameter
• SD : Distance between Shaft
Centers
• BL : Belt Length
𝐵𝑒𝑙𝑡 𝑅𝑃𝑀 = 𝜋(𝑃𝑆2)
(𝑃𝐷2)
𝐵𝐿
or
When Belt Length is unknown,
𝐵𝐿 = 1.57 𝑃𝐷1 + 𝑃𝐷2 + 2(𝑆𝐷)
𝐵𝑒𝑙𝑡 𝑅𝑃𝑀 = 𝜋(𝑃𝑆1)
(𝑃𝐷1)
𝐵𝐿

12. Detecting Vibrations
Tools to Measure Belt’s Actual Frequency
1.
3.
2.
4.
Strobe Light
Using marks on belt, which would
be unreliable.
• Very difficult
• Slow Flash Rate
Photo Eye
Will require proper setup and
marking on the belt.
• Very accurate
• Difficulties in confined
spaces
Laser Displacement Meter
Sensor
Measures the reflected light emitted
from the tool.
• Very accurate
• Good cost−performance
ratio
Laser Tachometer
Does not require belt marking. Will
operate on pattern recognition.
• Most accurate
• Best option

13. Drive Belt Vibration Effects
Effects
Short component
life
Cracks
Failure

14. Vibration Spectrum
• A vibration FFT (Fast Fourier Transform) spectrum is an incredibly useful tool for machinery
vibration analysis. If a machinery problem exists, FFT spectra provide information to help
determine the source and cause of the problem and, with trending, how long until the problem
becomes critical.
• FFT spectra allow us to analyze vibration amplitudes at various component frequencies on the FFT
spectrum. In this way, we can identify and track vibration occurring at specific frequencies. Since
we know that particular machinery problems generate vibration at specific frequencies, we can
use this information to diagnose the cause of excessive vibration.

15. Vibration Spectrum

16. References
• Budynas, Richard G. and Nisbett, J. Keith, “Shigley’s Mechanical Engineering Design, 10th
Edition”, McGraw-Hill Education (2015), pp. 872, ISBN 978-0-07-339820-4.
• Several images taken from https://en.wikipedia.org/wiki/Belt_(mechanical) and
www.google.com

17. THANK YOU