Hello all. First off, I would like to thank you in advance for any help you are able to offer, I've done basic DC circuit design when given standard book problems but AC circuit design with real world components is what I need here.

In short: I have a pneumatic system that I need to control with a simple electrical system. Essentially, I have a 2-way air cylinder that I need to actuate using a 4-way solenoid (essentially acts as a switch). I need it to turn on and off when a distance sensor sees objects (sees object 1, on, sees object 2, off, sees object 3, on, etc., etc.). This also needs to be delayed a second or two, so I would need to know how to do that.

The use is to automate a piece of equipment that will actuate shortly after it sees the next object coming. (it sees the object as it falls onto the equipment, then actuates)

I hope this was a thorough enough explanation and again, I appreciate any help and light you can shed on this type of circuit. Thanks!

 

With the delays required and the decisions it has to contend with, it seems a microcontroller based circuit is more of what you will need, could possibly do it all with discreet components and IC's, but It would get pretty complex real quick....

B. Morse

 

I was hoping that the voltage running through the sensor could only effect the solenoid if the correct distance/object passed it, but I'm unsure of exactly how sensors work or if that would be possible (i don't need to identify specific objects, just that one is passing the sensor).

If a sensor gives off a certain voltage when an object passes it, could it be run past a resistor or series of resistors then amplified to effect the solenoid? (weed out no object readings but allow real-object readings to get through to the solenoid?).

again, i've tried reading up on how some sensors work but I'm lacking the connection with once it's plugged in. any/all help is greatly appreciated.

 

Most sensors used in these types of applications would normally not have a variable output unless it is a distance sensor of some sort, then you would still have to get the analog output and convert that to distance (Which would normally take a microcontroller to do)...
Most sensors I have used (and I have used a lot! I build automated machinery all the time) usually only have a "Go/ No Go" output, AC sensors would have to have a "load" on them, DC sensors usually come in 2 flavors of outputs an NPN or PNP type, usually these are open collector type outputs... There there is also the output trigger type that you would have to take in consideration, Dark On and Light On... some are configurable to be either (but costs more)...


You can probably achieve this with a few photoelectric retro reflective sensors, and possibly a couple of On delay relays (Some relays have built in timers for on delay, off delay, etc...)

But the way you describe its function kind of confuses me a bit, so does it only have to actuate every other item? (i.e. Detects object 1, on, detects object 2, off, etc...)


Have you done anything with PLC's (Programmable logic controllers) before?

B. Morse

 

Most sensors used in these types of applications would normally not have a variable output unless it is a distance sensor of some sort, then you would still have to get the analog output and convert that to distance (Which would normally take a microcontroller to do)...
Most sensors I have used (and I have used a lot! I build automated machinery all the time) usually only have a "Go/ No Go" output, AC sensors would have to have a "load" on them, DC sensors usually come in 2 flavors of outputs an NPN or PNP type, usually these are open collector type outputs... There there is also the output trigger type that you would have to take in consideration, Dark On and Light On... some are configurable to be either (but costs more)...

B. Morse

What I'm considering I think has to be a distance sensor, it needs to sense that a non-metal payload is passing by, but not be triggered by any background movement. If there's another way to pull this off, please let me know. And it doesn't need to be very sensitive to distance, again I just need it to know that the package is moving past.

PS - I appreciate all the help you've given so far!

 

Sorry, I was editing my post as you replied....

 

take a look here at the "Light Beam Sensing Switches with Relay Output" near the middle of the page >>> http://www.mcmaster.com/#photoelectric-switches/=813xzk
and also here for the relays with timing functions >> http://www.mcmaster.com/#catalog/116/897/=813yu5

If the object were to pass between the reflector and the sensor, then you can use these types of components for your project, they do cost a pretty penny though!

B. Morse

 

No apologies necessary!

I apologize it turns out that I've had my circuit wrong. Let me explain in more detail.

When a package passes the sensor, there needs to be a delay (as I want the package to get a certain distance before actuation), but the signal will then go to a 4-way double-solenoid valve (each solenoid will actuate the airflow to one side of a 2-way air cylinder). Here is where a new dilemma has just started. I only want one solenoid to be actuated, and i want the signal to alternate (object 1 passes sensor, solenoid 1 gets the signal, object 2 passes, solenoid 2 gets signalled, object 3 passes sensor, solenoid 1 gets signal, etc.)

I know this probably sounds really confusing as I can't really explain it much better, but i will try to draw up a diagram and schematic to match and hopefully you can help me more from there. I'll post the diagram shortly. (give me 10 mins.)

 

My terrible layout is attached here, it doesn't help much but it kind of puts everything in order as far as I see it. The more we talk about it the more im convinced I'll need some form of microcontroller but I'm not sure either. And I have heard of PLC's but have no experience with them (I'm willing to learn anything, just really looking for a best solution for this project). Thanks!

 

From what it sounds like, a PLC with a few inputs and outputs would probably the best and "easiest" to go, here is a link to some lower cost ones.... http://www.mcmaster.com/#plcs-(programmable-logic-controllers)/=814por

The ones near the bottom of the page named "Mini Programmable Logic Controllers" may work for you..... but let me think about this a bit and I will see if I can come up with an "easier" solution to implement....


Are these objects you are detecting traveling down a conveyor of some sort?

What is the 4 way solenoid rated for 110 AC?

B. Morse

 

<snip>

When a package passes the sensor, there needs to be a delay (as I want the package to get a certain distance before actuation), but the signal will then go to a 4-way double-solenoid valve (each solenoid will actuate the airflow to one side of a 2-way air cylinder). Here is where a new dilemma has just started. I only want one solenoid to be actuated, and i want the signal to alternate (object 1 passes sensor, solenoid 1 gets the signal, object 2 passes, solenoid 2 gets signalled, object 3 passes sensor, solenoid 1 gets signal, etc.)
<snip>

Instead of delaying the sensor output, why not place the sensor further down to where it will sense the object right when it needs to actuate, then you wont have to worry about any adjustments to the delay if the objects are not always exactly in the same "spot"... just a thought....

B. Morse

 

Ok, I thought these devices existed somewhere, with a little talk with my Crouzet rep, he mentioned some alternating relays >>> http://www.crouzet-usa.com/catalog/_alt_jr.shtml

the DJR2110A (or similar) might be just what you will need to toggle between the 2 solenoids.... with every input from the sensor, the relay toggles the outputs from one to the other, you could use the Common for each contact to connect to the power source and wire the solenoids on either the NO (Normally open) and NC (Normally closed)... so if solenoid one was wired to the NO contacts, when the sensor detects something, it will switch the relay and power solenoid one, next input from the sensor and the power will switch to solenoid 2....

Just shopping around for parts and racking my brain for a solution....

B. Morse

 

B Morse those sound like great ideas, I'll look into them.. Thanks again for all of the help it's GREATLY appreciated!