Mechanical Point Alignment

## Mechanical Point Alignment

Alignment is performed within the physical coordinate system of the robot, using points in mechanical coordinates. The input for this module requires externally converting image points to mechanical coordinates.

## Usage Scenarios
Machine vision alignment refers to the process of using a machine vision system (cameras, lenses, lighting, image processing software) to precisely identify and measure the position and angle (pose) of a target object (workpiece), and then guide, adjust, or align it to a preset desired position and angle. The core goal is to eliminate positional and angular deviations, achieving high-precision positioning and assembly.
Simply put, the vision system tells the control system: The target is currently here (coordinates X, Y, angle θ). It needs to be at the target position (coordinates X0, Y0, angle θ0). The difference is (ΔX, ΔY, Δθ). Please move by this amount to align.
Alignment is generally used when aligning objects on two planes, commonly in film application and labeling. It is needed in situations where information captured by two cameras needs to be transformed relative to each other.

![](/media/202601/2026-01-16_103750_4119460.3507559082787539.png)

## Module Principle

In previous modules, whether correction or alignment modules, the inputs were image points, along with calibration and mapping data, finally outputting mechanical compensation. In the Mechanical Point Alignment module, both inputs and outputs are mechanical points. It performs alignment calculations directly without calibration conversion. This allows it to handle more complex mechanical models and requires users to handle the conversion between image points and mechanical points within their workflow, facilitating error tracing.

![](/media/202603/2026-03-13_115022_9151160.4043950650001191.png)

Mechanical models are divided into types that include angles (XYR, XR, YR) and types that do not include angles (XY). The calculation methods for these two types of alignment are different, and the results will also differ.
Clockwise Coordinate System:
![](/media/202601/2026-01-16_113933_0972430.8700678454763793.png)
Counterclockwise Coordinate System:

![](/media/202601/2026-01-16_113959_6188830.08372255033215326.png)

The mechanical coordinate system type corresponds to the current robot's coordinate type. When the type includes angle R, it affects the calculation results and the direction of the angle.
There are three alignment methods: Point-to-Point, Point + Angle, and Point + Line. The Point-to-Point method uses the SVD decomposition algorithm. The Point + Angle and Point + Line methods use the same algorithm. For the Point + Line method, the angle of the input line is extracted and used in the Point + Angle algorithm to calculate the result.
### Compensation Amount
For mechanical models that include angle R, compensating R will affect the XY values. (i.e., if only R is compensated, the XY position where the robot grasps the workpiece will not change, but the actual mechanical coordinates XY will change slightly to accommodate the rotation.)
The compensation amount is added to the result after the final alignment. If the alignment is not yet complete and needs to continue, the result output will not include the compensation. The compensation amount does not affect the judgment of alignment completion accuracy.
Since inputs are all mechanical points and do not require image data, the alignment can only be completed in one step.

### Advanced Parameters
Departure Pose: The mechanical coordinate position corresponding to the starting point, i.e., the position of the rotation center. This is typically the拍照 position of the bottom camera. When the mechanical type includes angle R, the拍照 pose significantly impacts the results.
Mechanical Range defines the robot's permissible motion range. It only validates the actual pose and does not restrict the offset pose. If the output actual coordinates fall outside this range, error code 5 is output.

![](/media/202603/2026-03-13_115043_7380790.10581386758666778.png)

## Usage Method

### Pre and Post Modules
Image capture from camera, feature matching, circle extraction are used to obtain points or angles for alignment. (Optimized feature matching is used to provide position correction for circle extraction.)
The departure camera and arrival camera capture departure image points and arrival image points, respectively. Departure image point data A1 is first converted to arrival camera image points via **Mapping Conversion**. Then, through **Calibration Conversion**, B1 and arrival image points B2 are converted to departure mechanical point b1 and arrival mechanical point b2. Finally, b1 and b2 are input into the Mechanical Point Alignment module, which performs the alignment calculation directly and computes the mechanical compensation.

## Parameter Configuration Description
【Mechanical Type】Select the corresponding mechanical model based on the coordinate system type of the actual robot.
【Calibration Group】Select the coordinate system group for the current equipment. The coordinate system group must be set in the Coordinate System Calibration under Global Data Management.
【Device Selection】Select the mechanical device used for mechanical alignment within the chosen coordinate system group. (Used to obtain the rotation direction and coordinate system of the robot.)
【Alignment Method】Choose from Multiple Points, Point + Angle, or Point + Line based on the different extracted features.
【Number of Point Pairs】If the Point-to-Point alignment method is selected, input the number of point pairs.
【Compensation Amount】Mechanical coordinates for compensation within the mechanical coordinate system. When subscribing, the compensation amount can be introduced via a port.
【Reference Image】The image used as a reference during processing.
#### Advanced Parameters
【Camera Departure Pose】The mechanical coordinate representing the pose of the robot end when the departure camera captures an image. When selecting subscription, the value can be introduced via a port.
【Mechanical Range】The permissible motion range of the robot.

## Output Description
The output includes two sets: Grasp Pose and Offset Pose. The Grasp Pose is the actual pose for the robot to grasp, and it is also the range checked against the 【Mechanical Range】. The Offset Pose is the offset of the robot relative to the taught position and is not checked against the mechanical range.
| Feature   | Grasp Pose       | Offset Pose              |
|------|------------|-------------------|
| Coordinate Type | Absolute Coordinates (GPS-like) | Relative Coordinates (Reference-based) |
| Safety Check | Full check against mechanical range | Range not checked |
| Primary Function | Final execution position | Position fine-tuning |
| Analogy | Detailed delivery address | "To your front left" |
| Dependency | Absolute Coordinates | Includes taught position + offset based only on taught position |
## Notes
1.  The forward operation for mapping reference is from the departure camera point to the arrival camera point. However, in integrated dual-camera and multi-camera alignment, the mapping uses an inverse operation. That is, it converts the point on the arrival camera to a point on the departure camera via mapping, and then uses the departure camera's calibration for conversion. If the actual model requires the forward operation of mapping, users need to build their own workflow and use the Mechanical Point Alignment module for calculation.

![](/media/202603/2026-03-13_115113_0878270.16348777776276713.png)
2.  The **Mechanical Coordinate System** type in the Mechanical Point Alignment module corresponds to the current robot's coordinate type. When the type includes angle R, it affects the calculation results and the direction of the angle.
## Troubleshooting
1.  When alignment is inaccurate, check if the feature matching module is accurately acquiring the image.
2.  If stable correction still cannot be achieved, test the accuracy of the calibration and mapping.
    (Method for testing calibration and mapping issues:
    Change the pick-up拍照 position by 2mm and observe if the result output changes by 2mm. If the result is incorrect in this case, it indicates a calibration error.
    Change the placement拍照 position by 2mm and observe if the result output changes by 2mm. If the result is incorrect in this case, it indicates a mapping error.)
3.  If the offset angle increases, leading to XY inaccuracies, it may be due to an incorrect calculation of the rotation center during calibration. Try re-calibrating, modifying the calibration method, or improving the rotation center calculation (add calibration verification or use the Long Radius Calibration module).
4.  If correction is accurate at the center of the field of view but shows XY deviations at the edges, consider image distortion (use the Image Distortion Correction module) or an incorrect scale calculation in the calibration (use the Calibration Check module).
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Click here to jump to the corresponding Chinese manual page: [Mechanical Point Alignment](/doc/148)