Re: See what I mean about modern gizmos?

On Wed, 19 Oct 2011 09:19:26 -0700 (PDT), Ste <ste_rose0@xxxxxxxxxxx>
wrote:

On Oct 19, 1:27=A0pm, cynic_...@xxxxxxxxxxx (Cynic) wrote:
On Tue, 18 Oct 2011 06:49:03 -0700 (PDT), Ste <ste_ro...@xxxxxxxxxxx>
wrote:

Yes, those are indeed alternative solutions. =3DA0But they are both mo=
re
complex to implement
A simple electronic timed lock wouldn't be significantly more complex
to implement with off-the-shelf electronics parts. An acutator
incorporating a linear motor moving against a spring, and a store of
electrical energy with consistent behaviour such as a capacitor.

Far more complex than a metal strip wrapped in resistance wire, and
consequently more expensive and more likely to fail.

Quantify how much more expensive.

Probably an additional £20 to £40 on the retail price. In order to
get people to fork out that extra, if would need a sizeable proportion
of people thinking that the improvement in functionality made the
extra amount worthwhile - which I maintain the majority of people
would not.

Rate of failure is mainly a function of manufacturing quality.

That is only *one* of the factors. =A0There is also the MTBF of each
component part - the more parts, the lower the MTBF of the assembly.

Agreed. The point is that MTBF itself is just a synonym for "rate of
failure", and (as I say) that is mainly a function of manufacturing
quality.

You are quite simply wrong. I am a design engineer and so I work out
such things for a living. If the MTBF of a part is 5000 hours, what
is the MTBF of a machine that needs 2 such parts to work as compared
with a machine comprising of just 1 such part? Assume the exact same
quality of manufacture.

In addition, manufacturing quality is itself a function of complexity
- the more complex the part, the more likely that is will be assembled
incorrectly in the factory. =A0You can compensate by having increased
inspection and testing and better trained workers - all of which will
increase the manufacturing cost significantly.

Oh come on Cynic. I ask again, quantify how much extra cost we are
talking about.

The cost of quality control? Do a search for the price of 1000
ordiary M4 machine screws. Now do a search for the cost of 1000
identical aircraft quality M4 machine screws. the difference in price
is the cost of the additional quality control.

Yes - my point was that your solutions were no better in that regard.
Had you thought of a fail-safe design it would have had more merit.

The problem is that any "fail-safe" is going to mean your clothes are
locked in whenever failure occurs. People probably find that to be the
most unacceptable outcome, so for the lock to fail-badly is
intentional.

Of course, my design can indeed be made fail-safe. You just make the
lock closed by default, and use the motor to overcome spring pressure
when the lock is required to open (on condition that the drum is
stationary, of course), but that means the door is locked whenever the
power is off - and power failure rate is a function of many more
factors than the inherent reliability of the door lock.

Exactly my point - and another example of compromise, this time
between safety and convenience should a failure occur.

Anyway, you *could* have a fail-safe
mechanism, but due to various constraints people prefer the lock to
fail badly.

There is the law of unintended consequences at play here as well. =A0if
a mechanism caused the door to remain locked, the householder would
almost certainly attempt to get the door open. =A0Such an attempt may
well expose an untrained householder to more risk than having an
"unsafe" failure mode.

Agreed. That is exactly what I had in mind.

It might however be an idea to have a mechanism that detects that the
door is unlocked and disables the machine.

Indeed.

Which introduces another component, adding to cost. And another point
of failure that does not exist in the simpler machine. The
"improvement" will result in a lower MTBF of the machine as a whole,
which will therefore cause the machine to be perceived as less
reliable than its simpler compeditors.

You may find it frustrating to have to wait 30 seconds after the cycle
has completed, but I can assure you that finding that the machine will
not switch on at all because of a faulty door-lock sensor will be far
more frustrating.

In which case simply pause and think *before* switching the machine
on.

It is often not a case of thinking, but of going upstairs to find that
you've left a shirt on the bed, or you dropped it out the pile as you
took the pile downstairs, etc. To start scouring the house a second
time every time before you turn the machine on is absurd, because that
would be inefficient in time.

By the time you have gone upstairs to the bedroom and returned, the
machine will already be filling with water, and stopping it at that
stage is problematic. If that happens to me, I simply throw the
overlooked items into next week's wash.

If you don't remember the other items until after the machine has
filled with water, a faster door unlock would not help.

A faster door lock is certainly not the only problem. Why on Earth
isn't the program setting labelled "immediate drain" (or for cases
where the soap had been added "immediate rinse and drain")? Coupled
with the faster door lock, that would allow the machine to be opened
as quickly as possible. It's unlikely to require anything more than
additional software logic, in many of today's solid-state controlled
machines.

I can do that with my machine, and you can probably do it with yours.
Switch the machine off and on, and select the appropriate wash program
or point in the cycle. My machine has a dial that I can set to any
point in the cycle, other machines have appropriate wash cycles that
include rinse-only and spin-only. The door-lock delay doesn't come
into it because you will not be opening the door until after the end
of the new cycle.

Not that I see the need to rinse. If it is to add additional clothes,
there is no need to rinse the ones already in the machine, just drain,
add the additional clothes and start the cycle from the start on all
of them. I don't even need to drain, because my machine does not fill
above the bottom of the door until it gets to the rinse part of the
cycle.

There is almost always *some* small task that needs to be done in the
kitchen that will productively fill the time while you wait 30 seconds
or so for the door to unlock. =A0A cup to wash up. =A0 A rubbish bin to
empty. =A0A worktop or cupboard to wipe down. =A0A sugar jar to fill -
etc. =A0Try to think of positive ways to fill those seconds rather than
allowing the wait to frustrate you.

You seemed to have missed the point. My intention was precisely *not*
to devote any brainpower to the activity. I'm not bored because I've
nothing at all to do in the house. I'm bored because I'm being delayed
in getting on with what I *do* want to do.

I often think Cynic, the reason I am considered reasonably
intelligent, is precisely because I devote my brainpower to important
things.

Like engaging in a pretty pointless debate on an off-topic subject on
Usenet?

Pull the other one, ste!

--
Cynic

.

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