Pally General - Calibration
Here is a YouTube video of the calibration steps
Calibration is only done once, and all the information Pally needs afterward will be provided in the pattern file, both product and pallet dimensions. Even if the product changes or the pallet is of a different type, you do not need to recalibrate Pally. Only if you change the gripper, move the pickup position, or change the placement of the pallets do you need to recalibrate.
Calibration box
The first step in a calibration is to find a good calibration box. This box can be any box. It does not have to be the box you plan to palletize later.
The important things to consider are that the box should be bigger than your gripper, and it should be of a quality so that it does not become deformed during the calibration process.
Measure the dimensions of the box. Remember that the length is the direction down the conveyor.
Pickup position calibration
Place the box in the position where you are going to pick up the box during palletizing, where the box is aligned with the stopper and the fixed guide.
Position the center of the gripper perfectly at the center of the box. Make sure the connector is pointing down the conveyor. Measure the distances and make sure the distance is the same on both the left and right sides of the gripper, as well as front and back. Also, make sure there is no rotation of the gripper compared to the box.
Compress the foam or the suction cups approximately 50% to ensure good contact between the box and the gripper before setting the pick position.
After calibrating the pickup position, turn on the vacuum so the box will stick onto the gripper, before calibrating the pallets.
Secondary pickup position
If your installation has a secondary pickup position, move the gripper with the box attached and place the box in the secondary pickup position. Then move (with tool view) vertically up a little more than the distance the foam or suction cups will expand. Then release the vacuum and move down again until you have compressed the foam or suction cups approximately 50%. Make sure that the center of the gripper is placed in the center of the box. Set the pickup position.
Pallet calibration
Calibrate 3 positions on each pallet.
The tool connector of the robot should point towards the front of your robot when calibrating the pallet positions. This is valid for all directions (front, left, right, or angled) of the incoming conveyor. See the picture below where the arrows show the direction of the tool connector in each position.
Keep the gripper in the same orientation for all positions. If you can not reach the far corner (position 3), don’t turn the gripper to be able to reach it. Just use a position closer to the base as the third calibration position. Keep in mind that the larger the area, the better the calibration.
Move to the first position with the box attached to the gripper. Place the box in the corner of the pallet, aligning the box with the pallet sides.
Make space between the calibration box and the pallet so that the foam or suction cup has room for expansion without causing a protective stop caused by a detected collision.
After setting the first position, move to the next position with the tool view. Move in a straight Y direction. If you see that the box starts drifting outwards or inwards on the pallet, this is an indication that you have placed the gripper on the box with a slight rotation in the pickup position calibration. Recalibrating the pickup position is recommended before returning to calibrate the pallet positions.
Remember to measure and, if necessary, adjust the height so that the distance between the box and the pallet is the same in this position as in position 1.
After setting the second position, move to the next position with the tool view. Move in a straight X direction. Make sure the box follows the edge of the pallet. Measure and maybe adjust the height so the distance between the box and the pallet is the same in this position as in position 1.
TCP check
Setting the TCP can sometimes be tricky. To verify that the TCP settings are correct, you can perform the following steps:
Move the robot to the calibrated pickup position.
Go to the Move menu, and select Tool or TCP.
Press the Y- arrow button, and the gripper should move parallel to the conveyor and in the direction where boxes arrive from.
Press the Y+ button, and the gripper should move back to the end of the conveyor.
When the gripper is above the box on the pickup position, press the RZ+ and RZ- buttons: the gripper should rotate around its own center point. Rotating by 180 degrees, the gripper should remain perfectly above the center of the box at the pickup position.
The calibration test wizard
This wizard is recommended to use to quality ensure your calibration points. The primary and secondary conveyor, left and right pallet positions, will be tested. Several different types of tests are included, which are performed sequentially.
The test wizard performs several calculation routines to identify some of the most typical mistakes usually made during calibration.
It can move the robot along a path generated based on the current calibration data and ask the user to confirm that the robot's motion appears consistent with the physical conveyor and pallet placement.
The wizard can also utilize force-controlled robot motion to measure calibration accuracy and make small adjustments based on the measurements.
Before each test step, the wizard explains the test that will be performed next. The user can start or skip the test and proceed to the next step by pressing the corresponding button.
When a test fails, a warning message appears with possible explanations of the failure. The user can stop the test wizard and fix the error, or proceed to the next step.
The test cases are divided into test groups. Currently, there are four groups:
● Testing the primary pickup position
● Testing the secondary pickup position (in projects where available)
● Testing the right pallet position (in projects where available)
● Testing the left pallet position (in projects where available)
The test cases for the primary and secondary pickup are identical.
The test cases for the left and right pallets are identical.
Testing a pickup position contains the following test cases:
● Moving parallel to the conveyor: this test can help detect calibration issues related to TCP settings.
● Moving to the pick position with 180 degrees rotation: this test can help detect calibration issues related to TCP settings.
● Automatic optimization of the pick position: this test can measure the pick position accuracy and adjust the robot position slightly up or down. (see note below)
Testing a pallet position contains the following test cases:
● Verification of the pallet size: This test can verify that the calibration box was used as required.
● Verification of the pallet shape: This test can verify that the correct pallet corners were used during calibration.
● Verification of the calibration points: This test can check that the robot’s position at each pallet corner is accurate enough.
● Automatic optimization of the pallet corner positions: this test can measure the position accuracy and adjust the robot position slightly up or down. (see note below)
NOTE: When running the tests that use force-controlled motion, the robot will firmly push the calibration box vertically down until a specific force is detected. Make sure your calibration box is made of a material hard enough to tolerate the pressure. Very soft or fragile boxes can lead to inaccurate measurements, measurement failures, or even damage to the box.
NOTE: On UR20, you’ll need to hold the 3PE button on the Teach Pendant when starting the wizard.
Pallet calibration adjustment wizard
Use the tools on the Adjustments tab to modify existing calibrations. You can move and rotate the pallet center point by pressing the corresponding button. Below is a picture from Pally for Polyscope 5.