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Sheet-feed switch : Why do you think it's designed this way ?

Someone suggested to me by email that the use of multiple switches might be for redundancy since they're used near a chemical bath.

At first I rejected the idea as even one switch remaining open would defeat the purpose. On second thought, if the process is activated by the transition from closed to open, but not by a steady open state, then it would work.

It would be easy to test this theory if the machine was in operating condition by wedging one or more switches open before power is applied.

However, the switch contacts are completely enclosed in plastic - probably reed types. It's actuated by a small magnet, also enclosed in molded plastic which has a pivoting lever arm. A small connector plugs on to the two external pins.

It's conceivable that the chemicals could corrode contact at the external connectors, or, as an even more remote possibility, seep inside the switch via the pin-plastic junction. But the location is such that there's very little chance for the chemicals to come in contact with the sensors. *Six* switches seem to make for an awful lot of redundancy.

Reply to
pjdd
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It would be the chemical fumes that corrode the contacts. The switches are cheap for the OEM if they prevent service calls, or even worse, in warranty failures.

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Michael A. Terrell
Central Florida
Reply to
Michael A. Terrell

Your explaination does not address *detecting* the condition.

Which in no way addresses *detecting* whether the front edge is skewed or uneven. You are making an assumption that detecting the condition would have to result in only one thing: preventing machine operation.

Ok, perhaps there is a skew roller? Its angle/position/pressure/speed could be controlled based on skewed feed detection. There could be a vacuum positioner, feed roll angling mechanism, anything, in this machine. We haven't seen it, so can only propose possibilities.

Ed

Reply to
ehsjr

OK, call it an assumption if you like. I call it a conclusion based on careful observation. See what follows.

No.

Its

There is no skew correction or positioning system of any kind. The film transport mechanism is quite straighforward. As far as film transport is concerned, there's only one motor. It drives a whole mess of rollers through a set of reduction gears, but the design is such that the action would be easily understood even by a non-technical observer.

All the rollers are parallel and run through the full width of the tanks. They are interlocked by a system of gears which are driven by a long shaft with worm gears at regular intervals. The shaft is in turn driven by the single motor via a serrated non-slip belt.

I've carefully examined the transport mechanism, including the entry side. The construction is straightforward and there are no inaccessible areas where some skew correction system might lurk unseen.

Sure, and I appreciate all the interesting feedback received. Please remember that I'm not trying to solve a repair problem here. Just trying to satisfy my curiosity.

I managed to get my hands on the operation manual of a different but closely similar model from the same company. There's plenty of warning and instructions against a skewed feed, and to make sure that the film is cut straight and perpendicular to its length.

To quote just one sentence : "Insertion must take place at right angles to the insertion rollers and the material must be kept firmly to prevent it from moving sideways until the transport rollers have a firm hold on the material".

It seems this model has only two sensors instead of six. They are referred to as input sensors and insertion sensors. The manual states in more than one place that the film must be fed so that it's over at least one sensor.

It goes without saying that since the manual is for a different model, this is not positive proof that "my" machine works in exactly the same way. But it's a strong indication, don't you think ?

Reply to
pjdd

snipped-for-privacy@rediffmail.com wrote in news: snipped-for-privacy@k70g2000cwa.googlegroups.com:

snip

snip

So why don't you share the model of the thing you are talking about, or even the similar model? Tell us WHAT IT IS! Just saying this thing that takes in a sheet of something and does something with it in a tank of some stuff and has some switches all wired in to a control board and I don't understand why they do it like this is not going to get anything but some guesses. These guesses are unlikely to satisfy what ever answer you are looking for without some information...

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