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Industrial Processes

Detecting appliance defects

   
 
Picture
The MEDEA prototype.

Mechanical defects in washing machines and dishwashers are set to be detected more quickly and accurately with a new automatic on-line system. A multidisciplinary consortium comprising six partners pooled their skills to produce and test a prototype of the system. Once commercialised, the system will help improve manufacturers' competitiveness and provide consumers with appliances that are quieter and more reliable.

 

The household appliance manufacturing sector is one of Europe's leading industries with an annual turnover of between 25 and 30 billion ECU and 250,000 in its workforce. Some say that the greatest technological breakthrough this century is in fact the washing machine. It has significantly reduced the time it takes to complete the chores of cleaning clothes. More recently, the dishwasher has released even more of our time.

Due to manufacturing faults, these machines can be noisy. We, the consumers, do not want to be disturbed from whatever it is we are doing instead of washing! We also want to put the washing machine on to run overnight when electricity is cheaper. And we want to be sure that if we buy a new machine it will work as soon as it's plugged in and carry on working for as long as possible.

Focus on quality

Manufacturers realise this and they have begun to consider quality control much more seriously. Human checks have been in operation for years but they have mainly been end-of-line checks which are inefficient and costly. If a machine comes off the line with a fault, it takes a long time for someone to detect the problem and then alter or halt production processes to fix it. What's more, only a sample of each batch of machines is tested so machines with faults could end up at the retailer.

Automatic systems for on-line testing of the functional and electrical aspects of these appliances are available. However, until recently, there were no solutions for testing the mechanical aspects of washing machines and dishwashers on-line. The solutions that were available were not reliable enough and depended too heavily on the human operator.

A team of two universities, a research institute and three SMEs decided to design and build a prototype of an automatic system that can detect a range of mechanical defects. In washing machines, this includes missing or loose screws, incorrect shock absorber or bearing assembly, misalignment of the drum and motor pulley and incorrect belt tension. In dishwashers, improper spray arm rotation can be detected.

Good vibrations

The system consists of three main blocks. The mechanical workstation automatically picks up the appliance from the assembly line, lets it go through the testing cycle and then returns it to the production line for the last stages of the manufacturing process. The second part is the non-contact optical sensor network which measures vibrations on several external points on the washing machine or dishwasher. Finally, a diagnostic expert system quickly determines whether the machine is defective or fully functioning. It uses the most advanced digital processing techniques including features extraction, neural networks and fuzzy logic. In certain cases, this final system can identify specific faults and this helps the operator repair the machine.

These computer-assisted diagnostic techniques have previously been used in medicine, the military and power generation where the technology has been used in very different ways. The appliances need to be classified one by one according to vibration measurements in the shortest possible time. In the other sectors, the system predicts faults in a continuous monitoring system.

Tapping into a pool of knowledge

Bringing together sensor specialists, system integrators, software developers, integrated optic chip manufacturers and laser vibration measurement experts provided the range of skills required to develop the new system which has been tested extensively. Gino Romiti, the project coordinator from AEA says, "We may have begun the project on our own but we wouldn't have had access to nearly as many resources and competencies without the other partners. We intend to continue to cooperate with each of the partners and we are already working with some of them on other projects." The results will feed into other work as well.

"We intend to use some of the intermediate results in similar fields, especially for on-line mechanical defects detection in other industrial products like electrical motors, compressors and pumps," continues Eng. Romiti.

All the partners have benefited from their experiences in the project. "AEA will sell the test stations worldwide after having engineered them. MIT and TUC will sell the software originating in this project to us at AEA and also directly to other markets other than electrical appliances. Similarly, LETI and CSO can do the same with their vibration sensors," explains Eng. Romiti.

Of course, once the prototype has been developed into a commercial product, the benefits will be spread more widely. Appliance manufacturers will be able to increase the quality of their production, have better control of their manufacturing processes and thus increase their competitiveness. They can get closer to their zero-defect goals. And we, the consumer, will be able to buy quieter and more reliable appliances.

 

 

Project Title:  Quality control for household appliances by on-line evaluation of mechanical defects

Programmes: Measurements and Testing
Contract Reference: SMT4-CT95-2016

Cordis DatabaseFor more information on this project,
go to the Cordis Database Record

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