User Manual

ManualsBrandsRoboception ManualsCamera & Photo3D camera

Warning: A large error during veriﬁcation can be due to miscalibrated cameras, an inaccurate calibration

grid, or wrong grid width or height. Please make sure that the grid is accurate and the entered grid width and

height are correct. Otherwise, manual calibration will actually decalibrate the cameras!

Step 3: Performing calibration

The camera’s exposure time should be set appropriately before starting the calibration. To achieve good calibration

results, the images should be well-exposed and image noise should be avoided. Thus, the maximum auto-exposure

time should be great enough to achieve a very small gain factor, ideally 0.0 dB. The gain factor is displayed below

the camera images as shown in Fig. 6.6.3.

Fig. 6.6.3: Starting the calibration procedure

For calibration, the grid has to be held in certain poses. The arrows from the grid corners to the green areas

indicate that all grid corners should be placed inside the green areas. The green areas are called sensitive areas.

The Size of Sensitive Area slider can control their size to ease calibration as shown in the screen shot in Fig. 6.6.3.

However, please be aware that increasing their size too much may result in slightly less calibration accuracy.

6.6. Camera calibration 51

Summary of content (11 pages)

PAGE 1
Warning: A large error during verification can be due to miscalibrated cameras, an inaccurate calibration grid, or wrong grid width or height. Please make sure that the grid is accurate and the entered grid width and height are correct. Otherwise, manual calibration will actually decalibrate the cameras! Step 3: Performing calibration The camera’s exposure time should be set appropriately before starting the calibration.
PAGE 2
Holding the grid upside down is a common mistake made during calibration. Spotting this in this case is easy because the green lines from the grid corners into the green areas will cross each other as shown in Fig. 6.6.4. Fig. 6.6.4: Wrongly holding the grid upside down leads to crossed green lines. Note: Calibration might appear cumbersome as it involves holding the grid in certain predefined poses. However, only this can ensure an unbiased, high-quality calibration result.
PAGE 3
First, the grid should be held closer than 40 cm from the sensor. It must be fully visible in both images and the cameras should look perpendicularly onto the grid. A green outline that stays in the image indicates the images’ acceptance. Fig. 6.6.6: Holding the grid closer than 40 cm during stereo calibration Next, the grid should be held at least 1 m from the cameras. The small cross in the middle of the images should be inside of the grid and the cameras must look perpendicularly onto the grid.
PAGE 4
Note: The camera calibration component’s available parameters and status values are for internal use only and may change in the future without further notice. Calibration should only be performed through the Web GUI as described above. 6.6.4 Services Note: The camera calibration component’s available service calls are for internal use only and may change in the future without further notice. Calibration should only be performed through the Web GUI as described above. 6.
PAGE 5
b. The rc_visard is not mounted on the robot but is fixed to a table or other place in the robot’s vicinity and remains at a static position w.r.t. the robot. While the general Calibration routine (Section 6.7.3) is very similar in both use cases, the calibration process’s output, i.e., the resulting calibration transform, will be semantically different, and the fixture of the calibration grid will also differ.
PAGE 6
Warning: It is extremely important that the calibration grid is attached securely to the robot such that it does not change its relative position w.r.t. the user-defined robot frame during step 2 of the Calibration routine (Section 6.7.3). Securely preventing unintended position changes such as those caused by vibrations, for example by mounting the calibration grid itself on a wooden support (suggested thickness min. 1 cm), which can then be screwed to the robot structure, e.g.
PAGE 7
6.7.3 Calibration routine The general hand-eye calibration routine consists of three steps, which are illustrated in Fig. 6.7.4. These three steps are also represented in the Web GUI’s guided hand-eye-calibration process (Section 4.5). 1. Set parameters e.g., grid width, height. Slots with robot poses and corresponding camera images 2a. Move robot + to new calibration position. repeat 3x or more (diﬀerent views on calibration grid) (x,y,z) (qx,qy,qz,qw) (x,y,z) (qx,qy,qz,qw) + slot_0 2b.
PAGE 8
Fig. 6.7.5: Defining hand-eye calibration settings via the rc_visard’s Web GUI Step 2: Selecting and reporting robot calibration positions In this step (2a.), the user defines several calibration positions for the robot to approach. These positions must each ensure that the calibration grid is completely visible in rc_visard’s left camera image. Furthermore, the robot positions need to be selected properly to achieve a variety of different perspectives for the rc_visard to perceive the calibration grid.
PAGE 9
After the robot reaches each calibration position, the corresponding pose Text robot of the user-defined robot frame in the user-defined external reference frame ext needs to be reported to the hand-eye calibration component (2b.). For this purpose, the component offers different slots to store the reported poses and the rc_visard’s corresponding left camera images.
PAGE 10
Fig. 6.7.7: First sample image in the hand-eye calibration process for a statically mounted rc_visard Once the suggested view is achieved, the user-defined robot frame’s pose needs to be entered manually into the respective text fields, and the corresponding camera image is captured using the Take Picture to Proceed button. Note: The user’s acquisition of robot pose data depends on the robot model and manufacturer – it might be read from a teaching or handheld device, which is shipped with the robot.
PAGE 11
This procedure is repeated four times in total. Complying to the suggestions to observe the grid from above, left, front, and right, as sketched in Fig. 6.7.6, in this example the following corresponding camera images have been sent to the hand-eye calibration component with their associated robot pose: Fig. 6.7.