2D Pitch Compensation in Motion Control: Key Setup Notes
Two-dimensional (2D) pitch compensation is a powerful technique for correcting mechanical inaccuracies in motion control systems. However, improper configuration can lead to positioning errors or system instability. This article outlines the essential precautions to ensure reliable and precise compensation.
1. Axis Type Configuration and Compensation Order
Before enabling pitch compensation, the axis type (ATYPE) must be correctly set. The compensation table relies on the axis type to interpret position data and apply corrections. If you need to change the ATYPE later, always disable the compensation function first. Failing to do so can cause mismatched data and unexpected movements.
2. Axis Must Be in IDLE State
When setting up or modifying compensation parameters, ensure the axis is in a stopped (IDLE) state. Any motion during configuration can corrupt the compensation table or lead to incorrect pulse calculations. This is a fundamental safety and accuracy requirement.
3. Using MPOS Coordinates for Compensation Start Point
The starting point for the compensation grid is defined using the machine position (MPOS), not the commanded position. MPOS reflects the actual physical location, which is critical for accurate mapping of mechanical errors. Always verify that the MPOS value corresponds to the intended reference point on the machine.
4. Encoder Feedback Integrity
For axes with encoder feedback, the compensation algorithm determines the number of correction pulses based on the encoder position. Therefore, the encoder must provide accurate and stable feedback. Any noise, slippage, or misalignment in the encoder system will directly degrade compensation performance. Regular encoder diagnostics and calibration are recommended.
5. Disable Compensation Before Powering Off
Before disabling the servo drive or cutting power to the machine, always turn off the 2D pitch compensation function. If the machine moves while the drive is disabled (e.g., due to external forces or manual adjustment), the displayed position (DPOS) and machine position (MPOS) can become misaligned. This discrepancy can cause a sudden jump or fault when compensation is re-enabled.
6. Understanding the Compensation Grid
The compensation table is structured as a grid defined by a start point, spacing intervals (DisX, DisY), and the number of points in each direction. For example, if the start point is the coordinate origin (0,0), the spacing is DisX and DisY, and the grid size is 4×4, the table stores compensation data for 16 points (Point 1 to Point 16). Each point holds the correction value for that specific location. The controller interpolates between these points to smooth the compensation across the entire working area.
| Point | X Coordinate | Y Coordinate | Compensation Value |
|---|---|---|---|
| 1 | 0 | 0 | Δ1 |
| 2 | DisX | 0 | Δ2 |
| 3 | 2*DisX | 0 | Δ3 |
| 4 | 3*DisX | 0 | Δ4 |
| 5 | 0 | DisY | Δ5 |
| … | … | … | … |
| 16 | 3*DisX | 3*DisY | Δ16 |
Properly defining the grid and ensuring the machine’s coordinate system aligns with the compensation start point is crucial. Always double-check the MPOS values at the reference point before activating compensation.
⚠️ Important Reminder:
Always follow the correct sequence: set ATYPE → configure compensation → enable compensation. When modifying ATYPE, disable compensation first. Keep the axis idle during setup, and disable compensation before powering off the machine to avoid position mismatches.
By adhering to these guidelines, you can achieve high-precision motion control and extend the life of your mechanical components. Regular verification of encoder feedback and compensation tables is part of a robust maintenance routine.
