Recovering the home position (home position calibration)
Home position calibration aligns the 0-pulse position of each axis with the absolute encoder value. It is done before shipment, but it has to be repeated in cases like these.
When it is needed
- The combination of manipulator and controller has been changed.
- A motor or absolute encoder has been replaced.
- The stored memory has been cleared (for example because a battery ran out).
- The manipulator hit a workpiece or similar and the home position shifted.
- Main body parts such as a reducer have been replaced, or the robot has been disassembled and reassembled.
Until home position calibration is complete, you can neither teach nor play back. In a system with several robots, do it for every robot.
Four recovery methods
| Method | Idea | Caution |
|---|---|---|
| Teaching point for home position setting | While the robot is healthy, create a reference position (check point) in advance. After replacing parts, move to it and correct the offset | Cannot be created once the robot no longer moves. Create one for each axis in advance |
| Key | Record the pulse difference between the key position and the factory home position on the home position label inside the controller. If the home position is lost, set that difference from the key position as the home position | Requires the value to have been recorded on the label beforehand |
| Encoder backup error recovery function | When battery depletion has cleared the memory and an "encoder backup error" occurs, run "backup alarm recovery" on the pendant | Cannot be used after a motor or absolute encoder has been replaced |
| Robot calibration (MOTOCALV EG) | Teach 5 points × 5 postures (25 points in total) and use that position information to adjust the home position and tool data | For when no other method works. High accuracy, but every axis's home position changes |
Some models can also use the zeroing function (an option), which automates home position recovery.
Adjusting with a check point
- Preparation (while the robot is healthy): create a sharp reference that makes any offset obvious, at a place that will not move when the power is cycled or air pressure drops. Also create a check job that moves safely to it. Place the reference as far as possible from the rotation centre of the axis being aligned.
- Replacement: replace the motor or reducer.
- Provisional registration: move the replaced axis to its home position mark and register the home position provisionally.
- Find the offset: run the check job to the check point, then move only the replaced axis to line up with the reference. On the position screen, calculate "current value − command value" to get the offset in pulses.
- Final registration: move the replaced axis to the position equal to the offset in pulses, and calibrate the home position for that axis only.
- Confirmation: move to the check point again and confirm that it lines up (repeat if it does not). After checking operation with your usual jobs, write the new home position data (ABSO data) and the date on the label inside the controller.
Home position calibration on the YRC1000
- Set the security mode to management mode.
- From the main menu, select ROBOT → HOME POSITION.
- Select the control group (robot or station).
- Use the axis keys to move each axis to its home position mark, then register all axes together or one axis at a time.
- If the correct home position data is known, you can also enter the values directly.
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Source: Based on YASKAWA manuals HW1484423, HW1482733 and RE-CHO-A114.