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Eye-in-Hand Calibration for Three-Axis Robots

About 1977 wordsAbout 7 min

This article describes how to perform eye-hand calibration for a three-axis Robot in an Eye-in-hand scenario.

For Eye-in-hand three-axis Robots, the pin tool contact-point calibration method is recommended.

1. Pin Tool Contact-Point Calibration

1.1 Preparation Before Calibration

Before starting eye-hand calibration, complete the following preparations:

(1) Complete the 3D Vision Guidance Kit hardware setup

Please refer to 3D Vision Guidance Kit Hardware Setup to complete the installation and connection of the Robot, Camera, and IPC

(2) Create a Project and a task

Please refer to Project Operation Guide and Task Operation Guide to create a Project and a task.

(3) Complete Camera connection and parameter adjustment, and configure it in the task information

Please refer to Camera Connection and Parameter Adjustment Guide to connect the Camera, perform camera imaging quality adjustment, verify Camera accuracy, and configure it in the task information.

(4) Complete Robot communication configuration

Please refer to Robot Configuration and Communication Operation Guide to establish communication between the Robot and PickWiz.

(5) Prepare the materials required for calibration

  • Please ensure that the Calibration Board is flat and clear, with no obvious scratches, dirt, bending, or deformation

  • If the calibration method is random pose sampling calibration, please ensure that the Calibration Board is placed on the work platform and is within the Camera field of view.

1.2 Calibration Information Configuration

Enter the eye-hand calibration interface, click Add Eye-Hand Calibration, and go to the calibration information configuration interface.

For reference only; the image shows an Eye to hand scenario. For an Eye in hand scenario, follow the description.

  • Calibration Name can be used to name the current calibration configuration

  • Calibration ID is used by the Robot to switch calibration configurations

  • Camera is the IP address of the currently connected Camera

  • Camera Brand is the brand of the currently connected Camera

  • Robot Type must be consistent with the Robot type in Robot Configuration

  • For Camera Installation Method, select Eye-in-Hand

  • For Calibration Board Type, select the current Calibration Board type

The appropriate Calibration Board mainly depends on the Robot type and Camera height. Please select a suitable Calibration Board according to the actual application scenario and the table below.

Robot TypeCamera Mounting HeightSelect Calibration Board
Six-axis RobotUnder 0.5 mA6 Multi-Concentric-Circle Calibration Board
Under 1.5 mA5 Multi-Concentric-Circle Calibration Board
1.5 m -- 2.5 mA4 Multi-Concentric-Circle Calibration Board
Over 2.5 mA3 Multi-Concentric-Circle Calibration Board
Three-axis/Four-axis RobotUnder 0.5 mA6 Multi-Concentric-Circle Calibration Board
Under 1.5 mA5 Multi-Concentric-Circle Calibration Board
1.5 m -- 2.5 mA4 Multi-Concentric-Circle Calibration Board
Over 2.5 mA3 Multi-Concentric-Circle Calibration Board

  • For Calibration Method, select Pin-Tip Touch Calibration

  • If the Robot has a corresponding calibration program, and the Robot needs to run that calibration program to send the pose to PickWiz when sampling the Calibration Board, then for Get Coordinates Online** select Yes; if the Robot does not have a corresponding calibration program, and the pose of the Robot end Tool needs to be entered manually when sampling the Calibration Board, then for Get Coordinates Online **select No.

1.3 Checks Before Calibration

For reference only; the image shows an Eye to hand scenario. For an Eye in hand scenario, follow the description.

  • Ensure that the Robot base is securely installed

Before starting eye-hand calibration, carefully inspect the installation of the Robot base. If the Robot base is not firmly installed, the Robot may shake noticeably during movement, affecting Robot accuracy and therefore the calibration result.

Check whether the Robot base installation meets the requirements as follows:

First, the surface where the Robot base is installed must be flat and kept clean;

Second, operate the Robot at 100% speed with large translational or rotational movements and observe whether there are signs of shaking. If shaking is present, readjust and secure the Robot base to ensure that no displacement or tilting occurs during Robot movement;

Third, check whether the Robot body and the base are tightly connected, and tighten the screws to prevent loosening.

  • Ensure that the Camera and its bracket are securely installed

Before starting eye-hand calibration, carefully inspect the installation of the Camera and its bracket. If the Camera or its bracket is not firmly installed, Camera imaging quality will be affected, which in turn will affect the calibration result.

Check whether the Camera and its bracket installation meets the requirements as follows:

First, check whether the Camera bracket is a machined part, and avoid using aluminum profiles as the bracket material;

Second, shake the bracket and observe whether there is any obvious wobbling. If so, readjust and secure the bracket;

Third, shake the Camera and observe whether there is any obvious wobbling to ensure that the Camera is firmly installed.

  • Ensure that the Calibration Board is stably placed within the Camera field of view

When the Camera installation method is Eye in hand, the Calibration Board must be placed on the work platform and kept within the Camera field of view.

  • Ensure that the Robot accuracy meets the project requirements

If the Robot accuracy does not meet the project requirements, refer to Calibration Verification to correct Robot accuracy.

1.4 Collect Samples

For reference only; the image shows an Eye to hand scenario. For an Eye in hand scenario, follow the description.

1.4.1 Collect Calibration Board and Robot Coordinates

(1) Adjust the position of the Calibration Board, place it within the target object placement area, and click Start Sampling.

(2) Click Add Sample. If the sample is valid, Saved Successfully is displayed. If the sample is close to an existing sample, the sample is invalid and a save failure message is displayed.

For reference only; the image shows an Eye to hand scenario. For an Eye in hand scenario, follow the description.

(3) Check the detection result. If all inspection items show green icons, coordinate axes and feature points appear in the visualization window, and all circle centers are green, the current Calibration Board Pose meets the requirements.

Camera detection is divided into 4 aspects:

1.4.2 Touch the Calibration Board with the Pin Tip

(1) Click Start Sampling, control the Robot to move, and have the pin tip touch the center of each corresponding concentric circle in the numerical order marked in the visualization window.

(2) Click Add Sample to collect the Robot coordinates at the moment of contact-point sampling.

(3) Repeat the above steps to collect at least 3~6 concentric-circle contact-point samples.

  • Click Next

1.4.3 [Optional] Add a New Calibration Position

During the calibration sampling stage, the system uses a single-pose calibration mode by default. However, in specific application scenarios, it can be extended to a multi-position calibration strategy, improving calibration robustness and system adaptability under complex working conditions:

  • To address accuracy deviation caused by depth-of-field changes in wide-angle vision systems, layered sampling along the Z-axis can effectively balance the error distribution across different focal planes;

  • For space-constrained work environments, when a single Calibration Board placement cannot complete the collection of more than 3 feature points, a multi-position Calibration Board placement and batch-by-batch sampling method can be used to cumulatively satisfy the minimum sample size requirement.

Click Add Position to add a new calibration position, then repeat **1.4.1 Collect Calibration Board and Robot Coordinates **and **1.4.2 Touch the Calibration Board with the Pin Tip **to collect calibration samples and perform Calibration Board contact-point sampling.

For reference only; the image shows an Eye to hand scenario. For an Eye in hand scenario, follow the description.

1.4.4 Calculate Calibration Results

Click Calculate Result. PickWiz calculates the calibration result based on the collected samples. If the calibration error does not meet the requirements, perform Calibration Result Inspection and Analysis.

1.5 Select the Eye-Hand Calibration Configuration

After Calibration Workflow is completed, return to the Run Configuration interface, click Job Information, click the dropdown list for Eye-Hand Calibration, and select the corresponding eye-hand calibration configuration.