Position Relative To ROBROOT or Perform Geometric Operatoration In VB or C#

PJonHar · Sep 20th 2016

Hi,

I have a situation whereby I need to know the robot position relative to robroot continuously. Currently when $ACT_BASE is set to an assigned base the $POS_ACT position is relative to the origin of the base.

I have the below code in the SPS, but occasionally the SPS stops. This is due to the fact that $POS_ACT, $ACT_TOOL or $ACT_BASE can have a state where they are uninitialised (i.e. null) and also the SPS and Robot Program run with different interpolations.

Code

IF ((VARSTATE("$POS_ACT") == #INITIALIZED) AND ($ACT_TOOL>0) AND ($ACT_BASE>0)) THEN
  TCP_ACT=BASE_DATA[$ACT_BASE]:$POS_ACT
ENDIF
IF ((VARSTATE("$POS_ACT") == #INITIALIZED) AND ($ACT_BASE==0) AND ($ACT_TOOL>=0)) THEN
  TCP_ACT=$POS_ACT
ENDIF

I have looked at doing this via an interrupt but as stated previously I need it to run continuously.
I need to try reading the variables into local SPS variables, and perform my checks on the local variables, this may improve things?
I was thinking about getting a handle on the variable $ACT_BASE and performing the calculation in my plugin?

Does anyone know of a different approach to this?

Cheers.

Spl · Sep 20th 2016

When can $pos_act be uninitialized? Anyway, why not just use $base:$pos_act_mes for both of those cases?

**SkyeFire** · Sep 20th 2016

$POS_ACT and $POS_ACT_MES can be uninitialized at almost any time, by various circumstances. A program reset/cancel is is one.

Assuming you have a KSS version of 5.6 (5.4?) or higher, you could try using ON_ERROR_PROCEED to get over the "Invalid Value" errors.

You could try using the FORWARD function with $AXIS_ACT (which is always valid), but you would need to be careful about managing Tool and base data.

The Geometric Operator is essentially just a cross-multiplication between two matrices which have been created from each of the POS/FRAME variables. So recreating the linear algebra offline is possible, but you need to have a good grasp of the underlying math and Euler rotation handling.

PJonHar · Sep 21st 2016

Thanks for your reply SkyeFire.

When you say use the FORWARD command on $AXIS_ACT, what do you mean by:

Quote

you would need to be careful about managing Tool and base data.

Spl · Sep 21st 2016

The FORWARD function is used for transforming a joint position into a cartesian position, which is called a forward transformation. And because it's calculating the cartesian position from joint values, tool transformation and base transformation is not in the result. So it gives the cartesian position of the flange in the world.

http://www.robot-forum.com/rob…m/forward-function-11842/

Fubini · Sep 21st 2016

Unfortunatly this is not totally correct:

Quote

And because it's calculating the cartesian position from joint values, tool transformation and base transformation is not in the result

You still need to set a valid $TOOL and $BASE. Cartesian positions always have a coordinate system you refer to ($BASE) and a coordinate system that is referred ($TOOL). In the special case $TOOL = $NULLFRAME and $BASE = $NULLFRAME you get from Forward($AXIS_ACT, Options) the current flange position referring zu the robot base (at least if you are not mounted on e.g. a linear unit).

Fubini

Spl · Sep 21st 2016

Maybe I explained it badly, or I'm really misunderstanding it how it works. I know that you need valid $tool and $base for cartesian motions, but when you execute the forward($axis_act, options) do you get the current tcp position in the current base, or the flange position the world, or maybe something else? Since the function doesn't seem to take tool or base arguments, does it internally use the current tool and base values to calculate the current tcp position in the current base?

Edit: Duh! It actually says in the pdf that it uses $tool, $base, $robroot and $ipo_mode. Too lazy to read until someone points out mistakes.

zitron · Sep 21st 2016

You might be interested in this: http://www.robot-forum.com/rob…relative-to-world-in-rsi/

PJonHar · Sep 21st 2016

Using the FORWARD command I could check the err_status to whether the $BASE or $TOOL values were invalid.
What do you think to the below code? (I'm not currently at a controller to try).

Code

DECL INT ERR_STATUS
...
ERR_STATUS=-1 ; Don't check against SW Limits
BASENO=$BASE ; Get the current $BASE (if any, if it isnt initialised then the FORWARD command will return -3)
TCP_ACT1=FORWARD($AXIS_ACT, ERR_STATUS) ; Assign TCP_ACT1 with the E6POS result from the FORWARD command


; If there wasnt an issue then perform the base offset to get the TCP relative to $ROBROOT
IF ERR_STATUS==0 THEN
  TCP_ACT2=BASENO:TCP_ACT1
ENDIF

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ON_ERROR_PROCEED shouldnt be needed in this case because the variables that could become uninitialised are not used in any calculations?

Spl · Sep 21st 2016

That might work. I was actually thinking of something like this

Code

temp = $base ; store current base 
$base = $nullframe
tcp_act = forward($axis_act, err_status)
$base = temp ; reset base to what it was

but I don't know if it would mess up any ongoing movements.

PJonHar · Sep 21st 2016

hmmm, so your doing it that way to save performing the geometric operation. will have to try both.

I will report back when I have tested.
Thanks!!

**SkyeFire** · Sep 21st 2016

$BASE and $TOOL cannot be manipulated from inside the SPS.

$BASE and $TOOL are FRAME type variables. $ACT_BASE and $ACT_TOOL are the Integer variables that indicate the number of the current Base and Tool.

Position Relative To ROBROOT or Perform Geometric Operatoration In VB or C#

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