On Wed, 14 Nov 2007 12:33:41 -0500, "Tom Gardner" wrote:

Our newest machine has a logic problem. The machine has two nail guns that
assemble a handle onto a wooden block brush. The operator loads a handle
and brush into the fixture and presses two palm switches. The palm switches
energize a relay that latches and energizes the solenoid valve that controls
an air cylinder that lifts the fixture to the nail guns until the fixture
hits a limit switch. The NC contacts on the limit switch then open and the
relay unlatches. The NO contacts close and energize a solenoid valve that
supplies air to the triggers on the nail guns. (There is also a limit switch
at the bottom of the stroke that powers the palm switches only at the bottom
position.)

The problem is that when the fixture hits the limit switch it reverses
direction immediately. The gun trigger air solenoid only gets that quick
hit and doesn't have enough time to build up enough pressure to trigger the
guns. I need to delay the fixture at the top of the stroke long enough to
fire the guns.

A few tenths of a second should be enough. An off-delay timed relay should
do it, right? As I look through the Grainger catalog and McMaster-Carr I
get a bit confused.

What is a "Off delay Retrigerable, one shot" relay? I don't think that this
is what I want but I'm not sure. I think I want just an "Off Delay" relay.

Trying to wrap my mind around the difference between on and off delay
here, but just happened to be looking up this little beast for my work
today.
http://www.marshbellofram.com/ATC/339A_series.htm

Other than being the opposite 'on-ness' think it is about what your
looking for. A local supplier claims to have them in stock for around
$32.

We have a small automatic router that was built in house years ago and
uses several of these timers. (Simply cuts a rectangular hole in the top
of small plastic boxes) Yours truly been tasked with building a new
one... Hopefully a bit less kludgie than the original

The old timers have held up well despite the rough treatment they have
received so I plan on using the closest one still available in that
series.
--
William