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Eye in hand Three-axis Robot Calibration

About 1998 wordsAbout 7 min

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

For Eye in hand three-axis Robot calibration, the needle-tip Tool touch calibration method is recommended

1. Needle-tip Tool Touch Calibration

1.1 Pre-calibration Preparation

Before eye-hand calibration, the following preparations must be completed:

（1）Complete the hardware setup of the 3D vision guidance kit

Please refer to 3D Vision Guidance Kit Hardware Setup to complete the installation and connection of the Robot, camera, and industrial PC

（2）Complete creating a new Project and a new task

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

（3）Complete camera connection and parameter adjustment and configure them into task information

Please refer to Camera Connection and Parameter Adjustment Guide to connect the camera, adjust camera imaging quality, verify camera accuracy, and configure them into 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, without obvious scratches, stains, bends, or deformation

  • If the calibration method is Random Pose Sampling Calibration, please ensure that the Calibration Board is placed on the work platform and located within the camera field of view.

1.2 Calibration Information Configuration

Enter the eye-hand calibration page, click Add Eye-Hand Calibration, and enter the calibration information configuration page

For reference only. The figure shows an Eye to hand scenario. For the Eye in hand scenario, follow the description.

  • Calibration Name can be used to freely 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

  • Camera Installation Method select Eye-in-Hand

  • Calibration Board Type select the current Calibration Board type

The appropriate Calibration Board is mainly determined by the Robot type and camera height. Please refer to the table below and select an appropriate Calibration Board according to actual scenario requirements.

Robot TypeCamera Installation HeightSelect Calibration Board
Six-axis RobotBelow 0.5 mA6 Multi-concentric-circle Calibration Board
Below 1.5 mA5 Multi-concentric-circle Calibration Board
1.5 m -- 2.5 mA4 Multi-concentric-circle Calibration Board
Above 2.5 mA3 Multi-concentric-circle Calibration Board
Three-axis/Four-axis RobotBelow 0.5 mA6 Multi-concentric-circle Calibration Board
Below 1.5 mA5 Multi-concentric-circle Calibration Board
1.5 m -- 2.5 mA4 Multi-concentric-circle Calibration Board
Above 2.5 mA3 Multi-concentric-circle Calibration Board

  • Calibration Method select Needle-tip Tool Touch Calibration

  • If the Robot has a corresponding calibration program and 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 Pre-calibration Check

For reference only. The figure shows an Eye to hand scenario. For the Eye in hand scenario, follow the description.

  • Ensure that the Robot base is securely installed

Before performing eye-hand calibration, carefully check the installation of the Robot base. If the Robot base is not firmly installed, the Robot will shake noticeably during movement, affecting Robot accuracy and thus the calibration result.

Check whether the installation of the Robot base meets the requirements according to the following steps:

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

Second, operate the Robot to translate or rotate significantly at 100% speed and observe whether there are signs of shaking. If there is shaking, readjust and secure the Robot base to ensure that no displacement, tilting, or similar problems occur 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 performing eye-hand calibration, carefully check the installation of the camera and its bracket. If the camera and its bracket are not firmly installed, camera imaging quality will be affected, thereby affecting the calibration result.

Check whether the installation of the camera and its bracket meets the requirements according to the following steps:

First, check whether the camera bracket is a machined part; aluminum profiles should be avoided for the bracket material;

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

Third, shake the camera and observe whether there is obvious shaking to ensure that the camera is securely 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 needs to be placed on the work platform and be 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, please refer to Calibration Verification to correct the Robot accuracy.

1.4 Collect Samples

For reference only. The figure shows an Eye to hand scenario. For the Eye in hand scenario, follow the description.

1.4.1 Collect the Calibration Board and Robot Coordinates

（1）Adjust the position of the Calibration Board, place it within the area where the workpiece is placed, and click Start Sampling.

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

For reference only. The figure shows an Eye to hand scenario. For the Eye in hand scenario, follow the description.

（3）Check the detection results. If all detection items are green icons, coordinate axes and feature points appear in the visualization window, and all circle centers are green, it indicates that the current Calibration Pose meets the requirements.

Camera detection is divided into 4 aspects:

1.4.2 Touch the Calibration Board with the Needle Tip

（1）Click Start Sampling, control the Robot to move, and let the needle tip touch the center of the corresponding concentric circles in sequence according to the numbers marked in the visualization window.

（2）Click New Sample to collect the Robot coordinates when touching the point.

（3）Repeat the above steps to collect at least 3~6 concentric-circle touch-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 deviations caused by changes in depth of field in wide-angle vision systems, layered sampling along the Z-axis can effectively balance the error distribution of different focal planes;

  • For work environments with limited space, when placing the Calibration Board once cannot complete the collection of more than 3 feature points, a multi-position Calibration Board placement and batch sampling method can be used to meet the minimum sample size requirement through accumulation.

Click New Position to add a new calibration position, and repeat 1.4.1 Collect the Calibration Board and Robot Coordinates and 1.4.2 Touch the Calibration Board with the Needle Tip to collect calibration samples and Calibration Board touch points.

For reference only. The figure shows an Eye to hand scenario. For the Eye in hand scenario, follow the description.

1.4.4 Calculate the Calibration Result

Click 计算结果 . Pickwiz calculates the calibration result based on the collected samples. If the Calibration Error does not meet the requirements, please perform Calibration Result Inspection and Analysis.

1.5 Select the eye-hand Calibration Configuration

After the Calibration Process is completed, return to the Run Configuration page, click Task Information, click the drop-down list of Eye-Hand Calibration, and select the corresponding eye-hand calibration configuration.