Low cost vision system model ST-RVSIn normal robotics the object must be in a known position - a holder or feeder or gate etc. ST Robotics offer a low cost vision system for determining the position of an object which is not in a repeatable position in the usual way. The vision system sends coordinates to the robot so it can be gripped by the robot regardless of position.
It comprises a high spec camera, C-mount lens with zoom, focus and exposure control and LED lighting with Matrox GigE interface and drivers. We can choose whichever camera size and resolution is required for the working area required. The hardware and software are easily installed in your own PC. The system includes PCIe card for PC (not suitable for laptops), all cables, CAT6 cable and camera power supply, all ready to go.
The camera and lighting should be mounted by the user about half a metre above the work area. The workspace should be shielded from stray lighting such as sunlight or fluorescent tubes. The camera is then calibrated to a disc and a rectangle of known size.
This is a high accuracy system that can measure to 0.001mm. Standard resolution is 1920 x 1200 pixels @ 41 frames per second.
While finding and picking an object does not require much precision, the ST system facilitates positioning the object to very high precision, for example as on a test fixture. It also permits inspection to very fine tolerances.
How does it work?
The PC connects to the robot controller in the usual way via serial or USB. A second serial channel (or USB converter) connects to the robot controller second serial channel. So there are now 2 serial connections between the PC and the controller. This permits you to write your program in RobWin and test out communication with the camera as you go along.
Software is provided for the controller i.e. commands or words that you can use. The simplest command is just VISION. This then sends a command to the vision system. The camera takes measurements and sends back the position of the object in X and Y coordinates plus it's angle. The robot now knows exactly where the object is and its orientation and can pick it up rotating the wrist as necessary.
Shown with the RobWin command window inset.
Final coordinates displayed and also sent to the robot. The RobWin window shows the simple command VIS and the results back from the vision system. the leading 1 means successful measurement.
The blue cross is the camera center (0,0). The mauve cross is the centre of the object, shown in this example as 7.6mm on X and 6.2mm on Y from the camera center with the object tilted to 2.7 degrees. Note that the centre of the picture is not X=0,Y=0 of the robot. These are relative positions. The robot system therefore adds offsets to reach the exact position required.
This video shows a typical application. A backing sheet feeds along a conveyor. The robot picks up a box and must place it on the backing sheet central to within 1mm. The vision system tells the robot what the X-Y position and angle of the backing sheet. The robot adjusts the box accordingly and lowers onto the sheet. Four example show how even extreme angles are handled by the system.
Parameters screen showing measured size of the object and camera settings.
Additional features in latest version:
Example of multiple objects:
The red areas are objects with parameters outside tolerance values.
Example calibration disc in a defined window with measurments and camera settings:
Capturing object of interest ignoring extraneous objects: