Automated Parking System Using OMRON PLC and HMI

[JordanCClark]

btw, I found this recently...

http://www.ebay.com/itm/10pcs-New-L...080?pt=LH_DefaultDomain_0&hash=item4614a50258

What say ?

It's a nice find, but an inductive prox likely won't work with the toy cars.


Let me back up again. I attached an animation from a presentation that I did a few years ago. One is an avi file the other is Shockwave Flash. The swf will play in a browser and automatically loop. The animation is of an inductive prox operation.

Inductive proxes have a coil of wire in the end that is attached to an oscillator. So, an AC signal of some frequency is running through it, making a magnetic field. This is like the science class experiment where you wrap wire around a nail, attach it to a battery and make an electromagnet.

When a metal objectis placed near this magnetic field an electrical current is induced into it (hence the name inductive proximity sensor) and it makes its own magnetic field.

This new magnetic field is in opposition to the original, and reduces the effect, or attenuates the original signal. The sensor circuitry monitors the amount of attenuation and triggers the PLC input.

Not all metals are created equally. Iron (or steel) works the best, but some non-ferrous stuff will work as well. For example, aluminum can get a current induced into it, but at less than half effect. Attached is a chart of correction factors. Most manufacturers tune their circuits to exclude non-ferrous metals, which is why I say that inductive proxes will not likely work for your application.

 

[kannan_kathiresan]

Not only does it act like one, it is one!


Very close! The iron in a car won't actuate a reed switch, since the car itself isn't a magnet. That's why I said you'd need a magnet in each car. Also, toy cars aren't made of iron. more on that in a bit.


That is correct.


Well... no. For the same reason I gave above. Yes there are magnets in the speakers, but magnets get exponentially weaker the further away you get. It's why you can't stick your car keys to the outside of your car door!


In real life, inductive prox sensors are used. the sensing head is essentially one very large coil of wire embedded into the pavement. There's enough iron in the car to actuate these types of sensors. In your scale model, though, you would most likely need to use a reed switch and a magnet. Die-cast toys are made of a zinc/aluminum alloy.


Reed switch: requires a magnet to actuate.
Limit switch: mechanically actuated. Something needs to physically press the switch

Hey ! wow that cleared out a lot of things. xD So, the only feasible/cheap solution would be is to use Reed switches . Limit switches don't seem practical at a parking spot. I just found out that you have reed switch magnets. So, can I get away from using a toy car with a magnet in it ?

Simple reed switches along with magnets like these would do right ? they would be able to detect metallic toy cars which I have to find next.

http://malaysia.rs-online.com/web/p/reed-switches/3622495/
http://malaysia.rs-online.com/web/p/reed-switch-magnets/3622451/

 

[kannan_kathiresan]

It's a nice find, but an inductive prox likely won't work with the toy cars.


Let me back up again. I attached an animation from a presentation that I did a few years ago. One is an avi file the other is Shockwave Flash. The swf will play in a browser and automatically loop. The animation is of an inductive prox operation.

Inductive proxes have a coil of wire in the end that is attached to an oscillator. So, an AC signal of some frequency is running through it, making a magnetic field. This is like the science class experiment where you wrap wire around a nail, attach it to a battery and make an electromagnet.

When a metal objectis placed near this magnetic field an electrical current is induced into it (hence the name inductive proximity sensor) and it makes its own magnetic field.

This new magnetic field is in opposition to the original, and reduces the effect, or attenuates the original signal. The sensor circuitry monitors the amount of attenuation and triggers the PLC input.

Not all metals are created equally. Iron (or steel) works the best, but some non-ferrous stuff will work as well. For example, aluminum can get a current induced into it, but at less than half effect. Attached is a chart of correction factors. Most manufacturers tune their circuits to exclude non-ferrous metals, which is why I say that inductive proxes will not likely work for your application.

I understand how it works now What if your toy car is made of proper iron in my case just for demonstration purposes ? because you are saying this idea would work in reality right ?

 

[JordanCClark]

If you get a Reed Switch / Magnet combination, then it should work with anything-- as long as you glue the magnet to the car...

 

[JordanCClark]

Seriously, though, if you happen to find an iron toy car, then an inductive prox will work.

Also, consider the spring idea I gave earlier. It would act as a limit switch. and springs are comparatively cheap.

 

[kannan_kathiresan]

If you get a Reed Switch / Magnet combination, then it should work with anything-- as long as you glue the magnet to the car...

hahaah ! So, should I finalize this ?? It might look funny . But, I cant afford too much time thinking now.

 

[kannan_kathiresan]

Seriously, though, if you happen to find an iron toy car, then an inductive prox will work.

Also, consider the spring idea I gave earlier. It would act as a limit switch. and springs are comparatively cheap.

Okay, let me first check if i can find a iron toy car. If so then them ebay sensors might come in to play.

I really liked your spring idea. I might even give that a shot if I fail to get the reed switch idea going.

Just using the reed switch + magnet glued to car would work for my parking system right?

Objectives(using sensor) :
- Open entrance gate
- Make sure car is within the lift boundary
- Check if a parking spot is free
- Open the exit gate

Anything else that I might have missed ?

 

[JordanCClark]

Just using the reed switch + magnet glued to car would work for my parking system right?

Yes. Just be aware of the sensing distances involved with whatever you get.

Objectives(using sensor) :
- Open entrance gate
- Make sure car is within the lift boundary
- Check if a parking spot is free
- Open the exit gate

Anything else that I might have missed ?

Looks like a good start for the basics.

 

[kannan_kathiresan]

Yes. Just be aware of the sensing distances involved with whatever you get.


Looks like a good start for the basics.

http://malaysia.rs-online.com/web/p/reed-switches/3622495/

This doesn't mention the sensing distance :s and are the current rating etc compatible with my PLC ?

 

[JordanCClark]

Yeah, ratings get odd for the glass switches. These are rated in Pull-in Sensitivity and Drop-out Sensitivity. This is measured in Ampere Turns which is a measure of magnetic strength. The lower the number, the more sensitive the sensor is. You may have to experiment a bit to see what woks best for you.

EDIT: Forgot to add, the ratings are okay to use for PLC inputs.

 

[Lancie1]

Don't forget that if you can find a metal car (any metal will work), then the chepest, easiest solution is two pieces of spring steel (like you find used for pallet banding or in pallet shipping), or in the spring for a roll-up measuring tape, and many other places). Basically, two pieces of metal that contact the bottom of a car, and allow the car to become the conductor that closes the switch, sending a 24 volt signal to your PLC.

I wil try to draw a picture of how it would work, but very similar to Jordan's drawing with the two springs. (I borrowed Jordan's car picture). If you can't find metal cars, you could could glue a piece of heavy foil to the bottom center of each car. In fact, a plastic car might work better, because then you could locate a metal "target" so that the car has to be centered in the parking space before the switch will close.

 

[gtsuport]

Just scanned this post quickly.
The CP1L 24vdc supply is rated at .3 amps.

I am hoping the OP understands a separate supply will be required to run the 15 volt motors.

The inputs can be wired either sinking or sourcing, but all must be the same. This is determined by the COM connection on the terminal strip.

Hope this will help.

 

[Lancie1]

I am hoping the OP understands a separate supply will be required to run the 15 volt motors.

I don't think he does. He still thinks that the small 0.3 Amp power supply in his Omron PLC will be enough to power relays, motors and the PLC too. NOT! I think he needs to purchase a 24 volt external power supply, rated for 5 or 10 AMPS, not tenths of Amps. As Jordan pointed out earlier, one large 10 Amp supply with both 24 and 12 volt DC oututs would probably do the job of powering both the 15 volt motors and all the other 24 VDC stuff.

 

[Lancie1]

I have these two motors in my lab already . Can it be used for the lift system ?

Motor 1
Make : Como Drills
Current rating : 2.85A
Output speed : 13360 rpm
power rating: 21.2W
supply voltage: 4.5V - 15V

The 13360 Revolutions per Minute will tear the roof out of your lift before you can stop it. If you use this motor, you will have to limit your voltage to about 5 volts so that is does not run away and destroy your lift before you can stop it. 100 RPM max would be better!

Also the power rating is 2.85 Amps. You need a power supply for 2 motors at 2.85 Amps. I don't think 0.3 Amps is going to do the job!

 

[kannan_kathiresan]

Don't forget that if you can find a metal car (any metal will work), then the chepest, easiest solution is two pieces of spring steel (like you find used for pallet banding or in pallet shipping), or in the spring for a roll-up measuring tape, and many other places). Basically, two pieces of metal that contact the bottom of a car, and allow the car to become the conductor that closes the switch, sending a 24 volt signal to your PLC.

I wil try to draw a picture of how it would work, but very similar to Jordan's drawing with the two springs. (I borrowed Jordan's car picture). If you can't find metal cars, you could could glue a piece of heavy foil to the bottom center of each car. In fact, a plastic car might work better, because then you could locate a metal "target" so that the car has to be centered in the parking space before the switch will close.

Using reed switches with magnets wont cost me much either I guess ? Obviously spring idea is much cheaper. I shall try and implement the reed switch idea initially.. so It looks like I have done something atleast I will post the pictures of my design which I did on PROE