Eye-in-Hand Calibration for Six-Axis Robots

About 4258 wordsAbout 14 min

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

1. Random Pose Sampling 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) 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, 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.

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
For Camera Installation Method, select Eye-in-Hand
For 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 Type	Camera Mounting Height	Select Calibration Board
Six-axis Robot	Below 0.5 m	A6 Multi-concentric-circle Calibration Board
	Below 1.5 m	A5 Multi-concentric-circle Calibration Board
	1.5 m -- 2.5 m	A4 Multi-concentric-circle Calibration Board
	Above 2.5 m	A3 Multi-concentric-circle Calibration Board
Three-axis/Four-axis Robot	Below 0.5 m	A6 Multi-concentric-circle Calibration Board
	Below 1.5 m	A5 Multi-concentric-circle Calibration Board
	1.5 m -- 2.5 m	A4 Multi-concentric-circle Calibration Board
	Above 2.5 m	A3 Multi-concentric-circle Calibration Board

For Calibration Method, select Random Pose Sampling 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

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

1.4.1 Collect Multiple Sets of Calibration Board and Robot Coordinates

(1) Control the Robot carrying the Camera to move so that the Calibration Board is at the center of the Camera field of view and parallel to the Camera imaging plane.

(2) Click Start Sampling. The Start Sampling button changes to Stop Sampling. Two types of detections, Camera and Robot, appear in the Detection Results Panel below. If all Camera and Robot detections are green icons, the detection passes. If there is a red icon, it indicates failure and should be checked.

(3) Camera detection is divided into 4 aspects:

(4) Robot detection is divided into 3 aspects:

(5) If coordinate axes appear on the Calibration Board in the visualization window and the center of each concentric circle is green, the current pose meets the requirements.

(6) Click Add Sample. If the sample is valid, a Sample Validity Check Passed popup appears. After clicking OK, a Sample 1 label appears under Collected Samples. Click Sample 1 to view the saved sample, and click the close button after Sample 1 to delete the sample.

If the sample is close to an existing sample, the sample is invalid. A Sample Validation Failed popup appears, prompting Close to Existing Samples. After clicking Back, control the Robot carrying the camera to move and collect the sample again.

(7) Control the Robot carrying the Camera to move so that the Calibration Board is located at the four corners of the Camera field of view, and the rotation angles around the X, Y, and Z axes are all greater than 10°. Repeat the above sample collection steps until at least 5 samples are saved.

(8) After saving at least 5 valid samples, click Finish Collection to enter the Calculation Results page.

1.4.2 Calculate the Calibration Result

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

1.5 Calibration Result Inspection and Analysis

If Calibration Error exceeds the normal range, the cause of the error needs to be identified. Click Calibration Diagnosis, and refer to Calibration Result Inspection and Analysis to analyze the calibration result, solve the problem, and check again until the calibration result accuracy meets the scenario requirements.

1.6 Select the Eye-Hand Calibration Configuration

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

2. Needle-tip Tool Touch Calibration

2.1 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) 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, 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.

2.2 Calibration Information Configuration

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

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
For Camera Installation Method, select Eye-in-Hand
For Calibration Board Type, select the current Calibration Board type

Robot Type	Camera Mounting Height	Select Calibration Board
Six-axis Robot	Below 0.5 m	A6 Multi-concentric-circle Calibration Board
	Below 1.5 m	A5 Multi-concentric-circle Calibration Board
	1.5 m -- 2.5 m	A4 Multi-concentric-circle Calibration Board
	Above 2.5 m	A3 Multi-concentric-circle Calibration Board
Three-axis/Four-axis Robot	Below 0.5 m	A6 Multi-concentric-circle Calibration Board
	Below 1.5 m	A5 Multi-concentric-circle Calibration Board
	1.5 m -- 2.5 m	A4 Multi-concentric-circle Calibration Board
	Above 2.5 m	A3 Multi-concentric-circle Calibration Board

For Calibration Method, select Pin-Tip 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.

2.3 Pre-calibration Check

Ensure that the Robot base is securely installed

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;

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

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, please place the Calibration Board on the work platform and ensure that it is 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.

2.4 Collect Samples

2.4.1 Collect the 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, a Saved Successfully popup appears; if the sample is close to an existing sample, the sample is invalid and a save failure popup appears.

(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, the current pose meets the requirements.

Camera detection is divided into 4 aspects:

2.4.2 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 Add Sample to collect the Robot coordinates during touch-point sampling.

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

Click Next

2.4.3 [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 Add Position to add a new calibration position, and repeat 2.4.1 Collect the Calibration Board and Robot Coordinates and 2.4.2 Touch the Calibration Board with the Needle Tip to collect calibration samples and Calibration Board touch points.

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