Overview
On 4-axis SCARA robots, factors such as part machining, assembly, collisions and disassembly cause the actual link lengths, joint zero positions and theoretical parameters to deviate, resulting in inaccurate XY-plane positioning — and the error is amplified at far-end work positions.
The four-point DH link length calibration uses rectangular four-point geometric sampling to automatically correct the actual lengths of the upper arm and forearm as well as the zero offsets of axes 1 and 2, correcting the robot's kinematic model and improving positioning accuracy across the entire work plane.
Key Advantages
1. Four-Point Rectangular Sampling — Four Body Errors Solved in One Pass
Teach only the 4 vertices of a marked rectangle and enter its actual length and width; the length of link 1, the length of link 2, the zero offset of axis 1 and the zero offset of axis 2 are all calculated simultaneously — no need to calibrate each item separately, reducing human error from repeated operations. The rectangular geometric constraints restore the robot's true motion model.
2. Improved Positioning Accuracy Across the Entire XY Plane, Suppressing Far-End Error Amplification
Most SCARA positioning errors are concentrated in the XY plane; link length and zero errors grow as the arm extends, and the error increases with reach.
After calibration updates the DH parameters, the systematic deviation of the whole machine is compensated — accuracy is not limited to a small local area; the robot remains accurate even when extended to the far end of its work envelope.
3. No External Precision Instruments — Simple Operation, Stable Results
No high-cost inspection equipment such as laser trackers is required; calibration is performed entirely through the teach pendant.
The calibration logic is based on rectangular geometric relationships, so small teaching jitter has minimal impact on the final result, multiple calibrations are highly consistent, and operator experience requirements are low.
4. Accuracy Recovery for Assembly, Maintenance and Post-Collision Situations
After factory assembly, mechanical disassembly/maintenance or a collision, joint zero positions and relative link positions tend to shift.
This feature quickly recalibrates the body DH parameters without a full machine re-commissioning, rapidly restoring the robot's positioning accuracy.
5. One-Click Parameter Write-Back — No Manual Entry Errors
Once the calculation is confirmed, the link lengths and zero offsets are written directly into the system's DH parameters with one click and take effect immediately — no manual transcription, no human input errors.
Applicable Scenarios
4-axis SCARA robots used for component assembly, screw fastening, dispensing and loading/unloading transfer; suited to accuracy restoration after factory calibration, equipment disassembly/maintenance and collision recovery.
