External rotary calibration in Robotmaster V7 - Part 1
Previous Considerations:
Before starting the calibration procedure in the hardware, it is important to ensure that the robot TCP is properly calibrated.
The dual rotary has to be considered as a rigid body, where the R1 axis is perfectly perpendicular to the R2 axis. Cases where R1 and R2 are not perfectly perpendicular are not supported. (See Figure 1)
Figure 1: Example of perpendicular R1 and R2
Case 1 – Calibrated frames can be retrieved from the controller
In some brands (ABB, Kuka, etc.) the calibration procedure provides the calculated rotary frames.
Some cases, the provided frame is directly the one corresponding to the root (i.e. the base) of the dual rotary positioner.
Other cases, the frames are provided separately.
Figure 2: ABB robot with Calibrated frames for R1 and R2
When the frames are provided separately, we will need to merge them to obtain our calibrated positioner frame:
The machined surface of the rotary plate (R2_dynamic) will be located at the X-Y plane of the R2 Frame
We have constrained the plane and the center of the rotary plate, but we still need to orient the whole positioner around the Z axis of the R2 Frame
To do this, we will align the X axis of the calibrated positioner frame to the Z axis of the R1 frame (i.e. the dual positioner tilting axis)
Instructions on how to merge frames to obtain calibrated positioner frame:
We import a dummy cube, which will be useful for aligning the frames.
We align the dummy cube to the R1 frame obtained from the controller:
Figure 3: Dummy Cube aligned to R1 frame.
3. We translate (NOT ROTATE) the dummy cube from R1 to R2:
Figure 4: Dummy Cube translated to R2 frame.
4. Now we can create a new Frame (in this case, it will be named CalibratedFrame)
5. We align this new frame to the R2 frame:
Figure 5: “Calibrated Frame” aligned to R2 frame.
6. Now we start a rotation of the frame around the XY plane by grabbing the gnomon from the tip of the blue rotation arc…
Figure 6: Rotating gnomon around XY plane.
7. …and release it along the dummy cube edge. Once this is done, we can remove the dummy cube and forget about it.
Figure 7: X axis aligned to edge of Dummy Cube.
8. Now we can grab the whole rotary from a gnomon attached to the center of the rotary plate, and align it to CalibratedFrame:
Figures 8-10: Moving the Rotary table to “CalibratedFrame”
9. The CAD model of the positioner is calibrated. Now we can go ahead and create the rest of the cell.
Case 2 - Manual best fit calibration, described in:
External rotary calibration in Robotmaster V7 - Part 2