Need help with reed sensor in ferris wheel

[Lancie1]

Yes, have a freebie. There is no slow motor speed, only one speed available. The wheel is a model, and could have an electric braking mechanism, but proably not at this level. It simply coasts to a stop. Hopefully the switch magnets are strong enough to stop it at a seat as it slows to a stop.

The problem is how can I stop the reed switch activating whenever the magnet comes close to the switch, when it is going forward or backward, without wanting to load/unload. (Loading and unloading is what the reed switch is for).

The key is not to try to stop the switch from activating, but to prevent it from stopping the motor EXCEPT at the right times. Use your timers to run forward or backward until a certain time (perhaps 30 seconds) is reached THEN start looking for the next seat magnet (hopefully it will be strong enough to stick at that point or at the next seat).

It really will not matter (only a model) if it stops at any particular seat, as long as it stops at 1 of the 4 seats. To help with this, a small spring indexing drag brake could be made from a rectangle of springy sheet metal - maybe use a piece of old steel banding strap, which is very stiff and springy but also hard to cut and drill. You could use a grinder to cut it, and a titanium bit to drill holes in one end. Position the brake to drag against the wheel spokes to make sure the wheel stopped with a seat in the Unload/Load position. Also if you have an old steel tape measure that is broken, you could use a piece of the spring from that to make the brake. I have 2 or 3 broken tapes in my tool box from years past!

See Rung 007 in my last Outline R1 for one way to try to stop the seat at a magnet. It might work, depending on if the motor is geared down to turn the wheel slowly. If not, another timer will be needed to allow the wheel to coast down to a very slow speed before looking for the next reed switch closure.

 

[oldskewl]

Lancie1...you are awesome! I have two more questions however and hope that you haven't lost patience with me!

First question is with the photocell be I:2/5...how can I continue the load/unload section of the program if there is no one there? Let me explain, at the moment I:2/5 is XIO right? That means, someone is standing on it...what about if no one is standing on it or just stepped off? My experience in the past with photocell's have been almost agonizing...could I make a parallel branch in rung 0 with a timer enable/done?

second question, on the comments for rung 1...you said repeat for remaining 3 seats...does this mean repeat rungs 1 through 3?

You have been a fan-tas-tic help with this...now to load it on the PLC and practice this thing before presentation...oh, one final question- with the bits being used to latch/unlatch-they will not show up on the PLC correct and wil only interact with the model itself correct?

Thanks again!

 

[Lancie1]

First question is with the photocell be I:2/5...how can I continue the load/unload section of the program if there is no one there?

That is what the B3:0/0 STEP 1 latched realy is for: to keep things moving along once all initial conditions are met, and also to record which Step in the cyle that the machine is in.

Second question, on the comments for rung 1...you said repeat for remaining 3 seats...does this mean repeat rungs 1 through 3?

No, only Rungs 001 and 002 and they will be repeated automatically by the self-resetting timer T4:2 (which resets T4:1 and T4:2). That does the 3-second wait followed by the "RUN FORWARD" motor pulse to move the seat 1 positon. Of course, the motor pulse is actually performed by Rung 005 (located in Step 3, but serving both Steps1 and 2. Sometimes the logic cannot be divided completely into clean steps.

I was wrong about the counter setting. It needs to be set to 3, not 4. I tested the program and am still working on it, but if C5:1 = 3, Step 2 will immediately be reset (before the 3rd load wait-and-motor-pulse. So "4" works perfectly.

One final question- with the bits being used to latch/unlatch- they will not show up on the PLC, correct and will only interact with the model itself, correct?

The internal memory bits B3/0 to B3/5 will not show up on your PLC Input or Output front-panel LED indicators. But they would show up if you can go online with the program open. That is possible in the SLC 5/03's to 5/05s. What model PLC are you using?

How long do you think it will take to physically move the seat 1 position?

 

[oldskewl]

How long do you think it will take to physically move the seat 1 position?

I am taking a shot and saying that there will be about an 7 or 8 second delay between the seats.

Although, I will adjust when I apply to the program to the ferris wheel...

I am also using the Allen-Bradley SLC-500

 

[Lancie1]

Okay, I changed Timer T4:2 to 700 x 0.01 seconds. I think the attached Revision 2 fixes most of the problems. The wheel stopping time will need adjustment. I assume that it does not have a brake and will not stop instantaneously in 0 time.

 

[oldskewl]

Okay, I changed Timer T4:2 to 700 x 0.01 seconds. I think the attached Revision 2 fixes most of the problems. The wheel stopping time will need adjustement. I assume that it does not have a brake and will not stop instantaneously in 0 time.

No...it does not have a braking mechanism. Although, if I have time I will make one.

 

[Lancie1]

No...it does not have a braking mechanism. Although, if I have time I will make one.

Okay, then I made the correct assumptions by adding a COAST FORWARD T4:4 and a COAST REVERSE T4:6 timer. You need to set these for slightly more time than the longest coasting time, after cutting off power to the motor.

Here is a ZIP file with my version of the RSLogix program. You need to change the "Controller Properties" and the "IO Configuration" to match your specific physical set-up as to CPU model and what Input and Output modules are actually installed.

 

[Lancie1]

I am taking a shot and saying that there will be about an 7 or 8 second delay between the seats.

What I really meant was this:

During Loading and Unloading ONLY, if the wheel is stopped with a seat at the loading position, and the motor is pulsed to make the wheel start but then coast down and stop at the next seat position, then how long would the motor need to run to cause the start-and-coast?

It should be much shorter than the total travel time, because most of the time will be coasting time when the motor is not powered. Also, this motor-pulse-time will be much shorter than the normal travel time for the regualar Step 2 Forward Run and Step 3 Reverse Run.

EDIT: I went back and added the Start/Stop switch to Rung 008, to make sure that there is a way to stop the Motor Forward, even if some of the other rungs get changed accidently. Note that the wheel will keep cycling through Steps 1 to 3 as long as the START switch is ON and I:2/5 PHOTOSWITCH is closed initially for the first Step 1.

 

[Lancie1]

No...it does not have a braking mechanism. Although, if I have time I will make one.

If your model is not too big, you could proably make a flapper brake from a piece of stiff plasitc from a bottle or jug. Plastic would be much easier to cut and fit.

My experience in the past with photocell's have been almost agonizing...could I make a parallel branch in rung 0 with a timer enable/done?

Certainly you could. But I think you would only need to bypass the photoswitch input if it is not connected or not working. In that case you can just remove it from Rung 000 (the only place it needs to appear). If you want a permanent bypass, simply install an ON/OFF toggle switch Input in a parallel branch with I:2/5 XIC, and call it "PHOTOSWITCH BYPASS. Then with BYPASS ON, the program will cycle through the 3 Steps regardless of whether anyone is waiting in line.

 

[oldskewl]

Okay, then I made the correct assumptions by adding a COAST FORWARD T4:4 and a COAST REVERSE T4:6 timer. You need to set these for slightly more time than the longest coasting time, after cutting off power to the motor.

Here is a ZIP file with my version of the RSLogix program. You need to change the "Controller Properties" and the "IO Configuration" to match your specific physical set-up as to CPU model and what Input and Output modules are actually installed.

Could you put the ZIP file into two smaller files? For some reason when I try to transfer...it won't work!

Thanks again for your help.

 

[Lancie1]

Oldskewl, I would have to use a file-splitter program to break the single RSLogix file inside the ZIP file into two parts, and you would have to then use the same file-splitter program to paste it back together again, and that is a lot of trouble for nothing.

I just tried downloading the ZIP file and extracting it and it worked perfectly. Try it again and it may work for you.

Here is a Screen Print of what shows up when I click on the file and select "OPEN" the ZIP file (using the free WinZip program). If you can't OPEN the RSS file (or the ZIP file), then you should simply save it on a flash drive and then use that to load the RSLogix program on your computer that has a copy of RSLogix500.

PS: This is the same RSLogix version that I printed out to a PDF file in Post #20.

 

[Lancie1]

I am also using the Allen-Bradley SLC-500.

Oldskewl, if you really do have one of the old SLC-500's (SLC-5/00, haven't seen one in about 25 years), then the RSLogix500 *.RSS programs will not run on that one. If you have any type of SLC from SLC 5/01 to SLC 5/05, or one of the MicroLogix units, then it should load and run okay.

 

[oldskewl]

Ok...ran program and forgot to add in one thing...the if the photocell is activated (while the ferris wheel is going forward and backward) the ferris wheel will run it's coarse and immediately start the loading/unloading cycle...can you help me with installing that part, tried all morning and I think I goobered the program more than I helped it.

 

[Lancie1]

Oldskewl, my original version R2 does just that - keeps cycling until you hit the STOP button, as long as the photocell is ON at the beginning of Step 1 (Load and Unload). For the other steps, it doesn't matter what state that Input I:2/5 is in.

If the photocell is activated (while the ferris wheel is going forward and backward) the ferris wheel will run it's coarse and immediately start the loading/unloading cycle.

Do you mean, if the photocell is activated BUT THEN DEACTIVATED while in Steps 2 and 3, then the program will keep recycling? If you want it to do that, then you need to put in another rung, and use I:2/5 to latch (OTL) an internal relay bit ON (B3:0/5), and add another rung to UNLATCH that bit at the end of Step 1. I would insert a new rung at the end of the program after rung 11 for the OTL, and use bits I:2/3 AND I:2/5, AND B3:0/2 OR B3:0/3 in a parallel OR branch, all to latch on the new "PHOTOCELL LATCHED" bit B3:0/5. I would put the Unlatch (OTU) in parallel with the other two instructions on Rung 003.

That would work, but it seems to be very unrealisitic. If a passenger shows up while the wheel is running, but then changes his mind and walks off, with the photocell latched on, you are going to stop and go into load/unload mode and then start a new cycle, even though no one is there. You would have an empty wheel running.

Please explain in more detail how the photocell is supposed to work, and I can then help you fix it to work that way. When do you want the photocell to be considered, during ALL steps, or just in Step 1 as it was in Revision 2? If you want to considered the photocell state in ALL steps, then when do you reset the Photocell Latch? How do you know when one set of people have been loaded if the photocell is always latched on?

Please post a print-out of your current version.

 

[Lancie1]

Oldskewl, Talk to me, man. Explain exactly how the photocell is supposed to work. Unless YOU understand that, then tell me, there is no way that I will know how it is supposed to work. Is it supposed to merely interrupt the cycle and start it over when the photocell is triggered, or what?

The ball is in your court, buddy. I don't know what you really have now in your program, because you haven't shared it with me lately. I am growing mushrooms in the dark here.