Connect incremental encoder output to three devices

[mp91]

Hi all,

I have an incremental encoder that is currently feeding into a high speed counter on a micrologix 1500. We have two new ink jet printers which originally the plan was that I would send a pulse to in order to signal I want to print.

However the printers can also take an encoder square wave to help with speed adjustments. Is it possible to simply chain the outputs from the encoder to the PLC HSP, then two printer 1, then to printer 2?

Thanks for help on a potentially stupid question

edit: all devices are within a few meters of each other

[Aabeck]

I think it would be possible.


The ABZ outputs of encoders are a voltage signal, as long as 3 sensors drawing power don't overpower the encoder output it should be fine.

[Peter Nachtwey]

Originally Posted by Aabeck

I think it would be possible.


The ABZ outputs of encoders are a voltage signal, as long as 3 sensors drawing power don't overpower the encoder output it should be fine.

Our customers do this all the time. The potential problem is with the encoder inputs. Usually there is a terminating resistor in the sensor. The encoder can probably drive 1 encoder but not 3 because the terminating resistors would be in parallel therefore 1/3 of the normal terminating resistance. Look at the documentation for the encoder inputs to see if there is an option to disable the terminating resistor except on the last encoder input.

In our case the encoder input is RS-422 with a 120 ohm impedance. However, it can be configured to have a 90K ohm impedance when daisy chaining motion controllers to a single encoder.

[Steve Bailey]

Encoder signals typically aren't rated for many milliamps of current. Check the current drawn by the printer inputs and the micrologix input against the rated current of the encoder signal.
If you find the encoder can't handle the current draw and you don't need a quadrature signal at any device consider wiring channel A to one printer and channel B to the other.

[mp91]

Thanks all.

The encoder outputs can handle 40ma. Looks like the HSC on the uL is only looking at A. So I will try to string the two printers of B and see how I go.

The printing guys somehow can't give me an answer on how much current their printer inputs use..

[_Dock_]

All I have to add is the obvious that you use a common across all three devices. This should be a given but I’ve seen many times when simple things wouldn’t work because of an isolated common.

Next question, someone enlighten me as to why this would be done? Process line labeling bottles? It still seems that a plc control would be much more reliable. Process the data and enable the printer after the logic?

[Peter Nachtwey]

Originally Posted by _Dock_

Next question, someone enlighten me as to why this would be done?

The problem is how to synchronize to one encoder so that all input devices are in phase.

This is common or it use to be. In our case it use to be very common before we could put 32 axes in one controller. Before we were limited to 8. Usually the OEM would use one controller per machine center. In the case of saw mills, there are many sawing stations synchronized to a feed chain that is turning an encoder. Everything is synchronized to the feed chain encoder. The sequence starts when the leading edge of the log or wood triggers a photo cell.

[mp91]

Originally Posted by _Dock_

Next question, someone enlighten me as to why this would be done? Process line labeling bottles? It still seems that a plc control would be much more reliable. Process the data and enable the printer after the logic?

The printers (videojet 1580's) can be sent a trigger to print from the PLC and then they use a fixed speed to work out how long the message is. Alternatively, you can give the printer an encoder pulse so that it knows exactly where to print the digits in your label.

I already have a decent encoder on the machine and these units are new. It's printing on a strip of product that's moving about 100 meters/minute but during start/stop it ramps up/down. Also different products go at different speeds and this lets you not need to update the run speed and the print speed if you need to change/add new products.

[cardosocea]

The few times I had to do something like what you're saying, I used these:

https://www.baumer.com/gb/en/product...53-154/p/29214

They're specific to isolate encoder signals and recover the square wave as well for the outputs making them pretty good should the signal degenerate between encoder and PLC.