HSC Encoder Zeroing with Sync input

ibrahim454

Hello friends,
In a project HSC Encoder is controlling a rotating axis shows 0-360 Degrees.

I am using Z phase of the encoder to reset counting value of HSC Counter for every revolution. The problem is the reset point of the encoder is not same with the zero point of the axis.

I am trying to use an offset value to change zero position of my encoder; I mean I am set to axis base point and sub the instant value of the encoder and this point gives me zero, but that is not work for other points of encoder.

I need to do some mathematical operations, circular shifts, may be use Mod(360). But I couldn't handle for it easly. Is there any idea about it ?

Hello.

Have a look at the attached SCL code. You did not mention all the detail required, so tags were used that needs assignment. The end result is a displacement given as a REAL number.

Does this help you?

(preview)

ibrahim454

Thanks for reply,

I am confused with encSync and degBias values, 

degBias is encoder turn position when axis goes zero actual zero point, then you convert it to pulse, But I don't understant what is encSync position? It seems same 

Hello.

Your instinct is not far off -- but allow me to fill in the detail.

The idea presented to you do not zero the encoder count that you read from the %IDxxx address. The encoder count runs continuously. The motivation is that the CPU takes a little while to zero the high speed counter. In the process you loose a few counts. The lost count vary as the rotation speed changes.

The Z-pulse from your encoder triggers a hardware driven capturing task. The absolute reading of the encoder is captured. Mathematics is used to calculate the travel. (#encRead - #encSync) represents the turn distance in pulses since the Z-pulse trigger.

The assumption is made that you are using later versions of Step7 and CPU firmware. The "Sync input" is a setting in the hardware configuration of the high speed counter. You use the CTRL_HSC_EXT to extract the captured value. Refer to the manual:
https://support.industry.siemens.com/cs/document/109772940/

The captured encoder reading (#encSync) may not be the 'zero degree' position of a turn. There may be some offset. It is set to some position in degrees (#degBias). The calculation needs that value to be in [pulse] units - that is (#encBias).

The presented idea provides for rotation in positive and negative direction in relation to the last Z-pulse. But that is in actual fact more tricky as just the mathematics. The reason why is beyond the scope of these notes.

Does this note help?

ibrahim454

Thanks for your explanation,
Unfortunately my PLC version 3.x, I can't use HSC_EXT,

I made this operation;

encPos := 2*encPPR + encRead - encBias MOD (encPPR);
encDeg := 360*encPos/ encPPR ;
Gives  me 0-360 but not sure.

Hello.

The formulas does not look correct; specifically #encPos.

Are you now making the encoder counter zero for each time the Z-pulse signal comes on? Where is it coded and how does it look like? Do you want to add a sample program here as a ZIP file?

You can make your own capture function by using a hardware interrupt function and capturing the encoder reading that happens when you make the capture. But the Z-pulse must be connected to a fast input. Do you know how to use hardware interrupts?

ibrahim454

hi,

Axis work as rotary, so I can reset count value for every turn,

I activated external sync input for Z phase and it automatically resets count value of encoder when sync input gets high every rotating.

encBias is desired zero point of the axis setted by manuel,
In the first time axis will be rotated to base point as manuel and reading value at base point, the reading value is entering as an ofset value to the encBias in the formula. so My zero angle value will be shifted the base point of the axis.

I can use hw interrupt but this seems easier :/

check attachment please.

How you used the SYNC is correct for the PLC you are using. Ignore my suggestion of before. The FW3 PLC works different than the FW4. Your input trigger is used as a 'zero'. Do know that the 'zero' happens as long as the input is true.

You have two phase encoder. I assume the specification written on the encoder is 500 pulse per turn.

When you use constant as a real number say 360.0 instead of only 360 - please. When working with encoder values, use DINT and not INT. This will avoid problems later on.

dintEncBias :=
REAL_TO_DINT(
               realDegBias / 360.0
               * DINT_TO_REAL(totalPulse)
            );

dintEncValue :=
(totalPulse + encoder - encBias) mod totalPulse;

realDegValue :=
DINT_TO_REAL(dintEncValue) / DINT_TO_REAL(totalPulse)
* 360.0;

ibrahim454

Thanks for your help, I will reform the points you mean.

I will check how the high duration of Z input will affect the position.

I work with FW3, but later on I will also work on FW4 and try to use HSC_EXT.

Thanks for code.

 I will check how the high duration of Z input will affect the position.

You still have the option of using a hardware interrupt and grab (store) the encoder value, if you see you have problems.

-- off topic --

Please mark the topic as closed when you are done with this conversation.

I value your thank you note and feedback far more than any ratings. Some of our other volunteers are motivated by ratings. Keep this in mind when someone else of this community assist you on future topics. (..but please remain realistic in your rating)

Good luck and best health.