BFF3103 Vibrations

Semester 2, Session 13/14 (Section 01)

TERM PAPER:

Washing Machine: Vibration Control and Noise Reduction

Group members:

NAME ID NUMBER

Mohd Norshafiq bin Mohd Pauzi FB11015

Wong Choon Chen FB11019

Nor Haqimi bin Mohamed FB11020

Siti Aisyah binti Saahri FB11021

1.0 Introduction

Vibration control is a method to reduce the dynamic force that causes vibrations. There are some

methods to control the vibrations such as control the natural frequency of the system and avoid the

resonance, prevent excessive response of the system, reduce the transmission of the excitation forces and

reduce the response of the system. Vibration generates the noise that is not needed. Therefore, we need a

process to remove noise called noise reduction. In this research, we try to control the vibration and the

noise produced by the washing machine. There are two types of washing machines which are front

loading or drum type and top loading type. The Malaysians are famous with the top loading types while

another type is mostly used in Europe. However, regardless the types of the washing machine, vibration

and noise negatively affect the lifetime and reliability of the operation and capacity of the machine.

2.0 Vibration Control

We are focusing our goal towards the front-loading type or drum type washing machine. The

washing machine object of this work is a prototype based on the Ariston Aqualtis laundry manufactured

by Indesit Company. It is characterized by suspended tub linked to the cabinet with three springs and two

dampers, figure 1. Note that the suspended mass is linked to the top and chassis panels by three coil

springs; it is also linked to the base and chassis panel by two dampers. The suspended mass is constituted

by the drum, the motor, the fly-wheel, and by the clothes and water in the tub. The Aqualtis laundry is

equipped with two standard passive (non-electronically controlled) dampers, each providing a nominal

friction force of 100 N. The standard damper has been replaced with a sophisticated electronically-

controlled device. This is the MR Controllable Friction Damper Lord RD-1097-01. The main nominal

characteristics of the device are the following:

Maximum and minimum length: 253 mm (fully extended) and 195 mm (fully compressed), respectively;

the body diameter is 32 mm.

The delivered force does not depends on the stroke velocity but on the current command only; this

makes this device a friction actuator, which is typical of low cost dampers dedicated to washing

machine applications.

The controllable current range is 00.45 A (current peaks up to 0.6A are tolerated for a short time during

transients); the corresponding force range is 1075 N (with transient peaks of 110 N). Note that the

controllability range is very large, since the ratio between minimum and maximum force is about 1:10. As

is well known this high controllability ratio is a very important and appealing feature for semi-active

control design purposes.

Figure 1: Washing machine scheme (left) and system reference (right)

The results of the experimental are condensed in Fig.2, where performance index (1) is reported

with respect to the spin speed, for every proposed suspension configuration. The magnetorheological

configurations (1 or 2 devices) are concisely represented in the case of their best damping condition. The

results reported are very clean, and the following remarks can be done:

The spin velocity from 1200rpm to 1400rpm are the working conditions where the highest vibration

level is measured. A high level of vibrations is measured also at 1100rpm for 1-MRD-SX configuration.

However in the rest of the note we explore only the best mounting configuration, namely the 1-MRD-DX.

The no dampers configuration presents good filtering performance in the critical spin velocities range.

Unfortunately this configuration is not applicable since the drum movements are not damped in

correspondence of the natural resonance of the suspended mass. This resonance is clearly visible in term

of the cabinet vibrations at about 200rpm. Notice that in this working condition the drum hits repeatedly

the top panel with a critical stress of the entire system. This represents the classical suspension trade-off: a

low damping has a good filtering of high frequency vibration but it is not able to vanish the low frequency

resonances. So every passive damper is a compromise between best filtering and best damping.

A single MR damper positioned at motor side represents the best applicable suspension configuration in

terms of vibration level. Notice that no resonance appear around 200rpm, and furthermore this

configuration outperforms the passive configuration for every working condition.

There is no a unique current value driving the MRD which ensures the best vibration level for every spin

velocity. In other words it is not possible to fix a current a priori so that the best performance is

guaranteed.

Figure 2 : Performance index Jvib for different

mounting configuration

3.0 Noise Reduction in Washing Machine.

Compared to any other large household appliances, the washing machine definitely has more

potential noise sources due to the dynamic complexity assemblies and subsystems confined to fit within a

fixed design space. To reduce the noise emission, identifying the root cause of the noise is the first step.

By identifying what components inside the machine were the sources of noise and vibration during

regular cycle (wash, spin and dry cycle) of the washing machine, there are several possible ways noise is

generated including:

Unbalance of washing drum

Washing drum-structure borne

Washing cavity - acoustic cavity mode

Cavity between base bowl and chassis - acoustic cavity mode

Base bowl vibration

Shaft vibration (mainly bending)

Motor electro-magnetic noise and vibration

Noise leakage from underneath

Noise leakage from gap between lid and body

According to a solutions-based approach, the primary noise contributor would be the motor (D.

Barpanda, J. M. Tudor, 2009).The measurement on vibration of the drum motor and casing shows high

motor vibrations followed closely by the drum casing (Figure 3). In addition, the harmonic vibration

pattern, characteristic of rotating objects, is displayed in each of the vibration measurements. This

indicates that the motor vibration is driving the vibration in each of the other locations. To determine if

the radiated noise shows the same frequency harmonics as the motor vibration, the sound pressure level

(SPL) was measured (Figure 4) the harmonics of the motor vibration are also found in the radiated noise

in each of measurement locations, thereby indicating that motor vibration is resulting in high radiated

noise.

Figure 3: Vibration acceleration measurement Figure 4: SPL measurement

Various types of materials were chosen as potential candidate for noise reduction due to their

specific vibration damping and acoustical characteristics, such as PU polyurethane foams (absorber),

epoxy-based damper and thermoplastic barriers. Several unique parts were prototyped to fit within the

confined space of the washing machine. Two cast foam (PU) parts were designed for the underside (lower

foam) and back-panel (back foam) of the washing machine. A third part (enclosure) was designed as a

barrier/absorber combination for mitigating noise directly at the source. Using an optimized pattern,

epoxy-based dampers were placed on the drum casing. Through the combination of these product-neutral

approaches, the noise reductions were achieved of up to 7.2dBA which surprisingly exceed the

performance target level.

On the other hand, by a modal analysis (R. Kim, R. Lawrence, 2002) using simple noise and

vibration measurements for motor operation during a washing cycle runs at certain frequency, some of the

other machine parts also resonate at the same frequency. Hence, the need to drive away the resonance

frequency from the motor part is addressed; either by shifting the frequency lower or by adding isolator

between motor and base bowl where vibration modes are high. Vibration isolation proved to be a very

useful noise and vibration solution. The noise emission was reduced by 3dBA for the problem cycle

(Figure 5).

Figure 5: Octave Noise (Green: original, Red: modified)

4.0 Conclusion

In this work the idea of using electronically-controlled dampers for improving the vibration in a

washing machine has been developed. The actuator is a low-cost friction magnetorheological damper.

The idea is to adapt on-line the damping characteristics in order to reduce vibration level of the machine

panels. The system has been analyzed and different mounting positions of the dampers have been tested.

The design and testing procedure of two different adaptive algorithms has been proposed. The control

system has been implemented on a rapid prototyping ECU and tested on a washing machine instrumented

with three 3-axis MEMS accelerometers. Tests in an anechoic chamber have been done, in order to study

the effect of vibration control on the acoustic noise. This work has proven the effectiveness of replacing

the standard passive dampers with electronically-controlled ones. Vibration isolation proves the best way

for noise reduction.

5.0 References

1. Experiment-Based Design Optimization of a Washing Machine Liquid Balancer for Vibration

Reduction, retrieved on 20th November 2013, from

http://www.ijser.org/researchpaper%5COptimization-of-a-Drum-Type-Washing-Machine-By-

Analytical-and-Computational-Assessment.pdf

2. Vibration Reduction in a Washing Machine via Damping Control, retrieved on 20th November

2013, from http://www.nt.ntnu.no/users/skoge/prost/proceedings/ifac2008/data/papers/0320.pdf

3. H.W. Chen, Q.J. Zhang, Stability analyses of a vertical axis automatic washing machine without

balancer, Journal of Sound and Vibration, 329 (2010), pp. 21772192

4. H.H. Jeffcott, The lateral vibration of loaded shafts in the neighbourhood of a whirling speed

the effect of want of balance, Philosophical Magazine, 6 (1919), pp. 304314, D.C. Conrad, The

Fundamentals of Automatic Washing Machine Design Based upon Dynamic Constraints, PhD

Thesis, Purdue University, 1994.

5. S. Bae, J.M. Lee, Y.J. Kang, J.S. Kang, J.R. Yun, Dynamic analysis of an automatic washing

machine with a hydraulic balancer, Journal of Sound and Vibration, 257 (2002), pp. 318

6. Tudor, J. M., Barpanda, D., Solutions-Based Approach for Reducing Noise in Washing

Machine, Noise and Vibration, 2007-01-2372, May 15-17, St Charles, IL, Elsevier Science Ltd,

2009.

7. Kim, R., Lawrence, R., Structure-borne Noise Reduction in Washing Machines: noise Reduction

by Modal Analysis, New Zealand Acoustics, No, 4, Vol. 18, NZ, Fisher & Paykel Appliances

Ltd, 2002.