Repeatability Error

Hello,

I am working on 6 axis robot arm project & now in final stage.
My teaching method is jogging and record all position values then convert it to g-code manually and run it.

I mention the my problem as follows:

Lets consider only 1st AXIS, "X" and route is A ---> B
First, i record two position values by jogging the X axis manually to point A and B. Then i make the G-code and run it.

At the first run after homing,
"A" point shift some distance and " B" also shifted in same value.
When i run it continuously, both point shifted every time.

I still couldn't find the reason for this issue.
Please reply with your recommendations.

thanks Lakshan.

Both end point and start point shift every time when it make moves. Not only after homing. Please see the attachment.
(shifting distance is same in every time)

My best guess is you have a mechanical problem, possibly a coupling is slipping.

No. I already checked it.
when it moving in shifting distance area, G-code still running. So, i confirmed this is not a mechanical error.
Other thing is i am using HD harmonic drives for joints. No any backslash.

You need to check the above things. Tell us what kind of motors you have, steppers or servos. Steppers can be very prone to missing steps and loosing position if not properly configured. Servos can lose position to, but for different reasons, that you must also trouble shoot.

If it isn't a motor positioning problem, and it isn't a mechanical problem (slipping shaft coupling...) then it may be a bug in your kinematics (this seems unlikely), and I think is why Andy was asking if your Joint positions are reading correctly. Such that if joint0 (joint1,joint2...) is commanded to move from A to B and back does it in fact do that and do the physical machine movements match what is shown in Linuxcnc. (As you probably know this is not the same as commanding a move in Cartesian space such as X0 to X2.)

I am using servo motors. but not use encoder signal with LInuxCNC. and I do not use kinematics. I simply jog each axis and record position values. then make G-code accordant and run the code. actually, It was success at my first 2-3 runs. i couldn't find how its going to wrong. Any possibility of fault in my PC?
Anyway 100% sure it is not a mechanical problem. joints works without any backslash or loose.

I tried reducing the scale each axis separately. shift distance became low. not zero. But when i run the whole system at once shifting occur as earlier. confused with this.

and I observed that this problem occur due to LinuxCNC. because my machine hasn't any delay with the PC. I checked it with very slow speed. when each axis run on shifting distance linuxcnc send pulse. (g code is still running.)

what kind of servos? How are they interfaced with the PC?

AC servo . i am using 3 parallel ports.