Predicting Peak Displacement in Imbalanced Rotating Drum

[Isaac0427]

Actually looking at it again, I realized that it is mostly correct, however it is a little off on the scaling and such. Also, as I said, you are integrating over time squared (i.e. add dt² to a single integral). This is why:
http://www.stankova.net/statistics_2012/double_integration.pdf

 

[madsi]

Isaac0427, thanks for your reconsideration.
And such??
Little off?
Scaling..there are no scales on the graphs.
In any case, thanks for sending the doc on how to do double integration.
If I integrate acceleration, I should get velocity(rate of change of distance over time), if I integrate velocity I should get distance as function of velocity over time.

I can understand this, but I not able to express it on paper in terms of functions/equations.

Perhaps, I know you are the wiz that mom always wanted me to be, but I would be so pleased if you chose to express your answers a little more quantitatively to make clear to me what you are saying,

I know we are all busy, so much to do, so little time(I think I read somewhere that I. Newton was laid-off while he wrote his book on Mechanics).

Please try to say what you want to say more in terms of the algebra and calculus involved.

 

[Tom.G]

How about just putting three (four?) switches, mounted on the frame, around the tub. Position them to trip when the tub wobble is greater than desired.

 

[madsi]

Thanks Tom.G,
At first the idea of using three of more switches seems to be a simple and practical approach to perhaps solving the problem.
But there are reliability and cost drawbacks to the use of limit switches, especially mechanical ones:

A switch not rated for extremely hazardous environments is otherwise cheaper, but delicate.
The interior environment of a washing machine is quite hazardous to mechanical switch contacts.
Inside the inner chambers of a washing machine enclosure there is often very high humidity and dust and lint(corrosive sw. fouling mold can thrive), not to mention the hazards of a wandering insects(spiders ants and cockroaches might find a warm, dark and humid washing machine switch enclosure an ideal oasis.)

Secondly, any switches must be carefully mounted and aligned inside a protective assembly. This assembly must also allow actuator overtravel or the switch mechanisms will be crushed or knocked out of a necessary precise alignment, either instantly or over time by collisions with the immense mass of the ballasting weights/drum asm.

Making space for added switches may increase the size, weight and cost of mfg. The size of a washing machine is somewhat standardized and if added switches take up more space, the idea of not being able to allow enclosure size to be increased even slightly translates to less suspension wandering room for the drum asm. and so the drum size would maybe need to be reduced resulting in less washing load capacity.

Adding multiple rugged switches can significantly add to the BOM of a machine and increase the cost of its design and testing, it could require a MCU to be more costly, have more control pins, and there is the cost of extra wiring and safety testing issues, etc. All this affects the bottom line in a very competitive market.

Most importantly, if the displacement achieved during an OOB condition of the drum asm. is sufficient to actuate a limit switch and even though power is then cut, the acquired momentum of the drum asm is still likely going to be more than sufficient to allow it to continue on a violent and certain trajectory towards the walls of the enclosure.

There is also the problem of nuisance tripping, the more switches, the greater the chance.

Finally, turning off power by limit switches in an OOB doesn't fix the problem, it is just a surrender to panic, it may not give the control MCU any specific feedback to redress the problem, and It just might also create and demand unwanted excessive user intervention.

 

[Nidum]

@madsi

(1)

Cutting the motor power when out of balance is detected is common practice . Even machines with complex electronic control systems do this .

The more sophisticated electronic control systems detect out of balance at lower rpm and activate load balancing procedures . Thus they usually anticipate difficulties before they become serious . Nevertheless if load suddenly goes out of balance at higher rpm the electronic system just cuts motor power in same way as cruder systems .

(2)

There are standard computational methods for processing data from an accelerometer . You could just look these up .

 

[berkeman]

Thread closed for Moderation...