Refrence Encoder, what does it do?

[bornwild]

Hey folks.

I want to know what does refrencing encoder mean. Does it mean we are resetting encoder? In our plant when there is a problem with encoder positions. We always reference it. The way we do is that we press some push buttons as in the program and reference it. I don't understand what does it actually do?

 

[HJTRBO]

In the past I have worked on Corrugated cardboard equipment and every job change a machine homing sequence was executed. Unfortunately the older Mitsubishi Summits / Esprits and Martin Die Cutters were fitted with incremental encoders.
Maybe your position feedback is similar in that after many mechanical movements with no absoloute reference (i.e no reference to a home limit or prox etc after or during every mechanical movement) the machine control system suffers an accumulation of binary and mechanical errors. As this is the case then for many an application, you are required to "reference" the machine to "reset" the internal high speed counter accumulator.

 

[xzen]

Walk that walk

Imagine finding yourself waking up blindfolded in a dark corridor. There is a railing that you can follow along one of the long walls. You know that the exit door is located on the other long wall 200 "calibrated" steps from one end of the corridor. If you want to find the exit door, you first have to go to the end of the corridor. That's your reference point. The railing tells you which direction to go.
This is called referencing

Since you don't know how far from the end wall, you will probably do your reference walk slowly not to crash full speed into the wall.

After referencing you can walk full speed 200 steps and find the exit door -- or any other door if you know the distance (how many steps).

An incremental encoder can count up and down and tell which direction it travels, but the control system (PLC, counter, servo controller…) need to know where is the zero point. The zero point is often defined by a reference sensor near the end of the axis.

The control system may also use the encoder's own zero pulse together with the reference signal to define a more accurate zero point. The encoder has one zero pulse for each turn. So if the zero pulse is used in referencing, the orientation of the encoder rotor becomes important!

Shutting down and restarting the control system is analoge to waking up blindfolded in the dark corridor. You have to do the reference walk.

There may also be other situations like typically a machine reset that the programmer has considered inconclusive and therefore requiring a reference run (walk).

 

[bernie_carlton]

To Xzen - an excellent analogy! Thank you for your contribution.

 

[mjoubert]

Reference Encoder Vs. Homing

What has been described is the homing process. A reference encoder usually refers to the encoder situated on the machine that the slave drive/s should follow. Both the master & slave drives should also have feedback encoders if it is a closed loop system.

 

[Mrslipmat]

By the sounds of it you are setting the zero point with a manual pushbutton... Does your machine have to be in a certain position before you referance or reset the encoder ?

regards

 

[bornwild]

Thanks for the replies. But now i am confused between referencing and homing? I think referencing has something to do what mjoubert writes, but i am not sure. Can you please explain?

 

[bornwild]

By the sounds of it you are setting the zero point with a manual pushbutton... Does your machine have to be in a certain position before you referance or reset the encoder ?

regards

ya that is right

 

[Jeebs]

It depends which manual you use.
Some say homing, other say referencing, but both mean the same. (in these manuals that is)

Your descprition is pretty vague.
From what you wrote it could be anything from Homing, to referencing as mjoubert meant, to simply setting target values.
If you want a nice and correct answer, your question needs to be more detailed.

 

[bornwild]

Let me put this . We have two encoders one on the motor and other one is external. we define a refrence point and do some math so both encoder have the same value.

 

[mjoubert]

In your case, it sounds like the external encoder is the reference encoder. The motor encoder is your feedback encoder.

When you move your machine to the correct position and make the digital input for home, the reference encoder actual position is set in the drive / plc as the new zero point. The feedback encoder on the motor is used to provide the closed loop feedback to the drive so that it knows that the target positions have been reached.