On Nov 14, 9:33 am, "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.

Some guns we used, notably Bostich, were very slow to respond.
If a customer felt it was in their best interest to stay with the
Bostich
we would add a small poppet valve right on the gun, and just use
the brief trigger pulse to fire the valve which fired the gun; this
was
much more reliable. When using other guns we always made sure
the firing valve was as close to the gun as possible (1 to 2 feet) and
this was always enough to get fast firing times (while the guns were
in motion by the way). The small poppet valve was a Humphry and
supplied by Bostich. The main firing valves we used were ARO 3/8".

Although you don't mention specifics, another idea Engineering came
up with was to use a coil of vinyl tubing before the item you wanted
to delay the return of. The idea was to delay the movement of the
cylinder until the entire coil/reservoir/cylinder pressure had dropped
sufficently to allow the assembly to move. It worked fairly well in
non-critical applications.

Good luck.

dennis
in nca