How a Rotary Incremental Encoder Works. Direction and Position.
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- เผยแพร่เมื่อ 2 มิ.ย. 2024
- In this video we go through how a rotary incremental encoder works, what it means to quadrature count, how counters determine direction, and go through an exercise to program a high speed counter in ladder logic to better understand how these high speed counters work.
Items used in this video:
PLC Tools SIM-EOC Encoder Simulator plctools.com/encoder-pulse-fr...
Allen Bradley Micro850 PLC Trainer twcontrols.com/plc-trainers
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Hey Tim, That was very informative, just need one clarification--Suppose I am using an encoder which generates 1000 pulses per revolution. Now If i use a HSC to count the signals, its going give 4000 pulses per revolution of the encoder or 2000 (if I am not using the B channel).So do I need to divide the no. of pulses by 4 (or 2 in case of no B channel) to get the actual no. of revolutions??
You sir are an excellent teacher. I greatly appreciate your videos. I am planning on an encoder geared to a line shaft for measurement and this takes away some of the mystery. It's all new to me yet but it's a start and is going g to be a fun (and I'm sure frustrating at times) adventure!! Every days a school day! Thanks again! Keep up the great vids!!
You are right, learn something new every day!
exelente video sobre encoderes, estão de parabéns, esta me ajudando bastante com as minhas duvidas
Glad I could help
Thank you Mr.
You are welcome Antonio
Hello, Thank you for your presentation, one funny thing I noticed is that there seems to be only one set of Marks, spread uniformly around the outer circle, but where are the two (2) object 90 degrees apart? Ninety degrees is sizeable, that's about a quarter of the outer circle, can you point them out in your picture of the slotted disc?
Thank you for your help.
There are two sensors that look at the same set of marks. The second sensor is 90° out of phase, which is different from 90 rotational degrees. This way it can look at if the a or b is rising first to determine direction.
Good discussion on the basics, especially helpful to show how you can lose counts. And I have seen them go backwards as well because of lost counts.
But two things:
1) Don't forget the marker pulse, and the difference between single-ended and differential outputs. Really important to know if you have to go out and troubleshoot an unknown encoder (like I had to this week) .Maybe for another video.
2) Those have got to be some of the most out of trim probes that I have seen in ages. I don't trim mine up often either, but dang! :)
Surprise, I have one coming on single ended and differential outputs :)
Yes I need to spend some time and study on the in's and out's of that scope. It is handy but some things are not that intuitive.
@@TimWilborne There should be a tiny cap on the handle of your probe, so find a source for a clean square wave, say, from the output from a handy encoder, and tweak the cap until the wave squares up. Go easy, they are fragile.
I just got finished reverse engineering an encoder from the dark days of the 80's that had no documentation on it whatsoever. The first thing was to determine the voltage to the encoder, this machine has a mix of 5 and 12 volt encoders so it's certainly not a case of being overcautious on my part. Popping the Amphenol connector off allowed me to peek inside to see a 10 VDC electrolytic cap, so it appeared to be a 5 VDC encoder.
I used a cheap transistor tester to look back into the outputs of the encoder, and it showed a pair of back-to-back diodes. So maybe it was a differential encoder? Hooked it up and sorted out which pair was which using my scope and that was that.
BTW, your kids might enjoy building their own transistor testers, and they are super handy:
www.ebay.com/itm/Signal-Generator-Tools-Component-Tester-Transistor-Diode-Capacitance-ESR-Meter/253263691903?_trkparms=ispr%3D1&hash=item3af7b1407f:m:mG8hJvfWRDcZleWVEcwbNZA&enc=AQAEAAACcIQvEcHUrT7nmUC3yY5qbPyaBN1nJEDYW8MyypsJPgXK3AqiNsU0sSphPu4g6Qid36H5LLoReq5x%2B17SM4jyBpSuOJZ%2FGkjqXhYQWm2HDi3U%2FoWbFactomqtF8GY4UtMyNLMGDG%2FhtBJQV40mkJrymWJkIFsanata4ffDp6wyLDdZyxl4ndioHjDfk9rQ6jfO4vwModcINPKFrlaXmE26wfCrO%2Fv%2Fxo1x5pulZ0MkJlcV%2FDCPT127SucPQPrkmoGVrgYD6tN6IgBDD5UmunRX7Wo6XsKnqdREiWwGRKwak4805LTvq0VlphH7lDzQbvHKDwEEzkvkh20Txk83uYR6d1flHdqHfBfh%2FHRrX4Yv3go8iyfteGwe5KOGGbCfW%2BQeB4pvuZQO9XpFApK3hFZ%2FHl8XspiSMSuu8jaxkLvP5IbLh65eCY6ypo6rH25Gn7jqz5OP7qwSS50aMtu4jm1IXnmTR1oyTUh0IcFxfgIjyFD0g8m524K%2Ff7H1kcVHs8pDaOgPi73Pz1PGECEVq0E6vvflSTRgf%2Bmn1rUiMqgKrCXk1jdS%2F4hoHp6jtf8AS8mzTheTE00A9H%2F2%2BPMT9krPSxDYu4KMFbLuvitlPMkAZdstKaE6HaSr9a8u8%2BTeIbNAzZcWF%2B%2BoayzWqM2%2FORXPJd1iw8aB5BT5nJIIN8TaOZLenkHtrKRm68KazM2jhTLWghcQaP4T37oYuwpqhYY6cHNu44ROvQjYHjNSMeRx9mIJ0NtRac5zuxB9buo0Kmv%2FBq26dW0lYYuDwsR1uX66qxQHQ9N1x8Gu2%2BTliwwoftHyGgBHMX8Y2WeXVtEecwG7Q%3D%3D&checksum=253263691903c8a55cb0d76a48839588a1180f0dd680
Looking forward to the single-ended and differential outputs video. :)
Two on the encoders on this thing are 12 volt single-ended encoders and the inputs to the new motion controller were set up as differential inputs. Grrr...
So we are going to use a couple of these to convert the signals:
www.usdigital.com/products/accessories/interfaces/EA
Only good for 5 VDC outputs, so I will have to add 5.1 volt Zeners as well as current limiting resistors to the input. But such is life. :)
regards Tim i have multiple allen bradley 845T series encoders my question: is it normal to get hot even without operating? I thought it was faulty and bought others but it also gets hot over 40 degrees centigrade without being in operation
I can't say I've ever noticed one getting hot but I doubt I've ever checked. One thing to think about when you say it isn't "running", the encoder is always running. Half of it's outputs are on and the other half are off. It also does have a small current consumption to power its circuits. I wouldn't be alarmed over 40 degrees centigrade.
Tim Wilborne Thanks
Can I get some information on the small scope you were using? Thanks.
Hi Dan, see the following link, this is a very handy scope for the size and the cost. amzn.to/2YY0LQd
I have a Seed DSO Nano v3 somewhere. It was cool and nerdy to have a scope that fit in my shirt pocket, but it's not all that useful. I prefer my Rigol 1054Z.
One thing that isn't obvious is that you need to be really careful about plugging the scope into a USB port while using it. The reason for this is that you just created a ground path for the scope through the USB port.
@@MrWaalkman Good tip, I'll remember that.
@@TimWilborne I found out by taking down a DeviceNet network when I plugged it in. No harm done, but it was a bit scary. :)
thanks Mr
You are welcome!
very handy scope indeed you have there, can the scope be used on analog signals and can it identify signal interference. oh and thanks again tim.
Yes it can be used for that. We're going to do some videos on using it in industrial applications
@@TimWilborne looking forward to that🤟
Great Video, Thank You!!
Do you have a similar solution for detecting direction using RSLogix500 where there detecting the rising and falling edge of an input is not as simple?
For the Micrologix you use the HSC function file. See link below.
twcontrols.com/lessons/rslogix-500-training-allen-bradley-micrologix-high-speed-counter-rslogix-500-function-file-configuration-for-an-encoder
Show us how to troubleshoot a faulty encoder, out in the wild...
What are the mechanical things that would interfere with the encoder?
Bad bearings? Dust? lack of lube on bearings?
Take one apart and show us the insides...
What is the difference between HTL & TTL types encoders.Can you please explain?
An HTL is a sourcing output or will provide whatever the input voltage is on the channel. A TTL is a sinking output of will take whatever input voltage is applied to common.
I remember ball mice from the 1990s that had optical encoders, but with only one sensor pair (ie led / phototransistor). I'm sure of this, because it confused me, as to how it would detect direction with only one set of sensors. So how could it? My theory is it might have used 2 levels of light, to encode movement as off / dim / bright / off / dim / bright. That same sequence in reverse would be distinguishable. Where a simple on / off / on / off sequence couldn't provide direction information.
That would be more work to detect the 3 levels, but stuff inside the controller chip could handle it, and I think at that point they manufactured actual mouse chips for just that purpose rather than a more general MCU.
So how did they work? My guess is the only solution I can think of, but I'd like an expert to actually tell me! There were in the cheapest mice but worked fine.
I'm not the "expert" on these, but my understanding was that they were not simply phototransistors, but optical sensors,. Think more of a crude camera that tracks movement of a picture.
I bought a similar scope.
Did not come with an assistant.
Please advise.
Assistant?
What scope is that
I’m trying to make a rotary encoder using two infrared switches but I’m having a hard time getting it to work correctly
It probably has to do with your response time of your switches. Standard switches will not respond fast.
@@TimWilborne possibly. it does seems to work but it’s not very accurate on knowing the direct and it resets on every tick. I’m not sure if I need to get my measurements better or something. The rotor plate has 3mm gaps and then I have the body that holds the sensors in place. I’ll keep tinkering on fusion360 see if I can get better results. I can’t really look at the wave form because my oscilloscope only has 1 input
@@TimWilborne I’m guessing a normal rotary clicks into a zero point on both clk and dit. That’s not really going to work with this so maybe I need to alter the code to make it force a 0 if it’s not moving. Cheers for the reply
Did you see this one where we talked about the input filters?
th-cam.com/video/vBNCUFao2jQ/w-d-xo.html
@@TimWilborne watching it now, this is an interesting watch and something to bare in mind. Im not really doing it fast it’s hand spun