6-Axis Robots)

This article explains how to perform manual hand-eye calibration for 4-axis, 5-axis, and 6-axis robots in an Eye-to-Hand (ETH) setup using the multiple random calibration-board poses method.

Calibration Workflow

For 4-axis, 5-axis, and 6-axis robots in an Eye-to-Hand (ETH) setup, the overall workflow for manual calibration using the multiple random calibration-board poses method is shown below:

Pre-Calibration Preparation: Complete the preparatory work before calibration.
Calibration Presettings: Configure the required settings before calibration, such as robot Euler angle type and camera mounting method.
Calibrate: Execute the calibration procedure and obtain the calibration results. This stage includes robot-side operations and requires the robot to move through a series of calibration points.
Save and Apply Calibration Result: Use the new calibration parameter group in the vision project.

The sections below explain each part of the workflow.

Pre-Calibration Preparation

Before performing hand-eye calibration, you must first complete the vision system hardware setup.

Complete Vision System Hardware Setup

Prepare the calibration board.

RVS 2.0 currently supports two types of calibration boards: the Checkerboard Calibration Board and Percipio’s custom RCCB calibration board (RCCB Calibration Board).
Install and fix the calibration board on the robot end flange. If the robot flange is equipped with a non-removable fixture, you can directly fix the calibration board on the fixture.

Attention

Please ensure the calibration board is rigidly fixed to the robot end to prevent it from shaking during calibration, which would affect calibration accuracy.
Install and fix the camera on the mounting bracket. Ensure the calibration board is within the camera’s field of view and the imaging quality is good.

Complete Pre-Calibration Checks

Before performing hand-eye calibration, the following hardware checks must be completed:

Confirm the robot base is firmly installed.
Confirm the camera bracket and camera are firmly installed.
Confirm the robot absolute accuracy meets the requirements.
Confirm the camera has been warmed up.

Calibration Presettings

Open the RVS 2.0 software and click the Camera Calibration button on the toolbar. The Calibration Presettings window pops up.
After confirming the pre-calibration checks have been completed, click the Check button, then click the Next button.
The “New Calibration” option is checked by default. Simply click the Next button.
Set the Robot Euler Angle Type parameter and select the Robot Coordinate System type according to the actual robot, and then click the Next button. If you are unsure which Euler angle type your robot uses, click “Get Euler Angle Type” and follow the instructions shown in the upper-left corner of the interface.

Attention

You can use the Get Euler Angle Type tool to obtain the robot’s Euler angle type. After clicking “Get Euler Angle Type”, follow the steps in the operating instructions in the upper-left corner of the interface.
In the Select a robot type for calibration window, select your robot type, then click the Next button.
In the Select camera setup window, select the “Eye to hand” option, then click the Next button.
The Select how to collect data window has “Multiple Random Calib Board Poses” selected by default. Click the Start Calibration button. The Calibration Window pops up.

Now, the calibration presettings are complete, and the formal calibration process will begin.

Calibrate

Select and Connect to Camera

In the Select and Connect to Camera step, click to refresh the camera list. The camera you need to connect to should now appear in the SN list.

Attention

If the target camera SN does not appear in the list, check its hardware wiring and IP settings.
Click the button to connect to the camera.
After the camera is connected, click Continuous Acquisition or Single Acquisition to verify that the camera can capture images properly. The acquired images are displayed in the ImageViewer panel on the right.
Click the Next button:
- If you clicked Single Acquisition in step 3, click the Next button on the bottom bar directly.
- If you clicked Continuous Acquisition in step 3, click Stop Acquisition first to stop capturing, and then click Next. Otherwise, the camera will keep capturing continuously and affect subsequent steps.

Mount Calibration Board and Check Intrinsic Parameters

In the 1. Select Calibration Board area, first select the image type, and then select the calibration board type.
Attention

Select the image type based on the camera’s image types (e.g., whether it supports color or IR images) and hand-eye calibration requirements:
- If the image type is “Color” or “Color; Depth”, you can select “Checkerboard Calibration Board” or “Standard Circular Calibration Board”.
- If the image type is “IR; Depth”, you can select only “Standard Circular Calibration Board”.
Configure the calibration board parameters based on the selected board type:
- For “Checkerboard Calibration Board”, enter the number of corner points in the horizontal direction, the number of corner points in the vertical direction, and the square size.
- For “Standard Circular Calibration Board”, select the calibration board model.
Manually move the robot until the calibration board is clearly and fully visible in the image view on the right.
Click the Check Intrinsic Parameters button in the 2. Check Camera Intrinsic Parameters area. The intrinsic parameters will appear in the Message box on the lower right.
- Check Success: Click the OK button in the pop-up window, then click the Next button on the bottom bar.
- Check Failure: First check whether all options and parameters in the Calibration Presettings and Mount Calibration Board and Check Intrinsic Parameters processes are set correctly. If the check still fails despite confirming the settings are correct, click the Open Percipio Viewer button in the Exception area to open the camera viewing tool and adjust camera parameters until the image quality meets the requirements.

Capture Images and Poses

In the Capture Images and Poses step, control the robot to move to different calibration points, then click the Add Image and Record Flange Pose button.

Attention

After moving the robot to different calibration points, please record the pose of each point in the robot program so that they can be directly called during recalibration.
Enter the robot flange pose in the pop-up window.

You can enter poses in any of the following ways:
- Direct modification in the pose panel: Directly adjust the coordinates (X, Y, Z) and rotation parameters.
- Adjust pose offset using the pose transformation tool: Click the Pose Tool button to open the Transform Pose tool. Adjust the pose by modifying the offset relative to the current position and orientation.
- Enter via the pose editing interface: Click the Edit Pose button and directly enter the position and rotation information in the format indicated in the pop-up window. After clicking OK, the entered value will be synchronized to the pose panel.
Attention

It is recommended to store the robot flange poses for each calibration point in a local file (.txt or .xlsx) so they can be reused during recalibration.
Repeat the above steps until the added calibration points meet the data requirements, then click the Next button on the bottom bar.

Calculate Extrinsic Parameters

In the Calculate Extrinsic Parameters step, click the Calculate extrinsic button in the 1. Calculate extrinsic and view results area.

The Message box on the lower right side of the interface will display the extrinsic parameter calculation results.

Save and Apply Calibration Results

When RMSE < 1, the calibration accuracy can generally be considered acceptable.

Click the Save button at the bottom of the Calculate Extrinsic Parameters step. The pop-up shown below indicates the extrinsic parameters have been saved successfully. The calibration results will be automatically saved to the “Calibration” directory under the project storage path.

After saving the calibration parameter group, you can select the corresponding calibration parameter group in the “ImageAcquisition” step of the project in the current solution.

The calibration workflow is now complete.