App. with 5 encoders 1

[Dariusch]

Hi.
I am doing a application with 5 encoder for positioning.
I have a Mitsubishi A1SH.
What is the best thing/way for handeling 5 encoder, when i have to read data for all 5 encoder at the same time?
I thought of using profibus?
Does someone have any ideas???

Thank you
Dariusch

 

[xyzz]

Do you need the quadrature mode for every encoder?
Hardware reset?

 

[Dariusch]

"Do you need the quadrature mode for every encoder?
Hardware reset?"

Im sorry, but I don't know what you mean by "quadrature mode".

It is for a machine for polishing sink/washbasin, and there are diffrent kind of these, so there have to be 10 different porgrams, one for each sink-type.
The encoder is for telling the program when the standard has to lowere the speed, in the corners.

Hadware reset? What is the benefit and is it a good idea?

 

[xyzz]

First of all, we are talking of incremental rotary encoders, rotating with speeds that requires high-speed processing by PLC.

A single direction counting requires only one pulse train from encoder to PLC.
The quadrature mode means using two phase shifted outputs of the same encoder and allows a PLC to recognize the encoder rotation direction, consequently changing the counting direction as necessary.
Not only applications with reversive movement do require this mode.
It may be necessary, for instance, in indexing application without reset, if stopping generates back-and-forth vibrations or just a single rollback. The extra pulses will be counted in wrong direction if a single direction counter is used.

The hardware reset is another pulse from encoder to PLC.
It appears in only one specific position of the encoder and resets the encoder counter value in PLC.
It is used as a zero position reference.
If such reference is taken by software from another part of equipment, you do not need a hardware reset for encoder counter.

Each pulse from encoder requires one high-speed PLC input.
Therefore, a single phase high-speed counter occupates one high-speed input, while a quadrature counter with hardware reset occupies three.

I am not familiar with Mitsubishi A1SH, but Mitsubishi FX1N and FX2N series PLCs have 6 high speed inputs.
They may be assigned to one high-speed count or reset each, with maximum of 2 quadrature counters.

 

[Dariusch]

Hi xyzz.

Thank you a lot for all the explanation.
But I have one question more.
What do you think of using profibus instead of High-speed indput??

 

[xyzz]

I cannot tell you what I think about using Profibus until you tell me what is the reason of using it in your application.
And you still have to tell me about frequencies from encoders and their mode.

Generally speaking, I usually follow the principle to use the simplest hardware architecture possible (the simplest by operation principle, not by wiring or hardware quantity).

One more point about incremental encoders.
You may use them to know the equipment relative position only, by definition.
The reference may be taken from encoder zero pulse, or from equipment.
But! The encoder counter value is not valid until the reference is found the first time.
The software must respect this.

 

[Dariusch]

Hej xyzz.

My system is of A1S, and have only 1 slof free so if I want to use High-speed indput I have to bye an extentionboard and 3 High-speed card.
So instead of that i thought of using Profibus, only 1slot.
Also there woulden be so mutch cabeling.
The frequencie is about 1 rpm./min (hydraulic actuatores)
And I think incremental encoders could do it, (but my supplyer says I can't get incremental encoder with profibus).

 

[xyzz]

With 1 rpm on encoder shaft you do not need high-speed inputs at all- just connect encoders to regular inputs.

 

[Dariusch]

Thank you xyzz!

Why didn't I think of that!
You have been very helpful thanks again.

mvh.
Dariusch