3D machine vision based on Scorpion Vision software has been used to measure automotive bushes in random orientations.
The completion of a recent project is evidence that the advent of the latest vision systems that have 3D capability offer substantial benefits to manufacturers - including real cost savings. The ability of these new systems to build mathematical 3D models of product in real time means automation becomes simpler when processing the product on the production line, whether it is simply measuring the product in 3D for quality control or random bin picking for a materials handling system.
There are a number of reasons why 3D machine vision has now become mainstream. First and foremost of these is the evolution of software-based machine vision systems that have the ability to transform 3D calibrations from 2D images. This is highly processor-intensive and so this has been fed, in turn, by the availability of multi-core processors. Ten years ago, it could be argued that Microsoft Windows-based control systems would not have been taken seriously. But this is the case today, and the fact that Windows XP takes care of image acquisition and simultaneous processing of multiple tasks or threads at OS level without the need for any extra hardware (such as frame grabbers or additional processing) means that the application software is left to get on with the job of 3D modelling.
Measuring bushes
One such application is the measurement of automotive bushes in 3D. The host computer is a 3GHz quad-core industrial PC with Windows XP. The system utilises seven cameras producing 19 images with LED lights and a laser dot-matrix light source. The laser creates points in the images for generating point clouds and the LED lights create appropriate illumination for other 2D and 3D measurements. All cameras are individually calibrated to eliminate lens distortion and 3D calibrated using a known three-dimensional object. As a result, each camera acts as a pinhole camera with a common 3D model.
The image processing is configured using standard 2D and 3D tools in Scorpion Vision Software without any programming. The vision configuration strategy was to measure individual 3D planes on the link arm containing the bushes using stereo vision and point cloud technologies. From the 3D planes the angle difference can be measured. The planes are also used to minimise the problem due to the 45-degree camera perspective. The planes are the basis for generating virtual 3D camera systems outputting 2D image planes positioned for accurate 2D measurements on different parts of the link arm. Stereo vision technology is used to create 3D co-ordinates of 2D points and then the 3D distance can be calculated.
A key feature in Scorpion Vision Software is the easy way of creation and use of 3D models. A 3D model requires a set of 3D points that can be used for finding 3D planes and geometrical structures such as boxes and cylinders.
In this application the dot-matrix laser light source generates bright dots that are found by using a blob tool in one of the images. The output of the blob is a sequence of x and y co-ordinates of the dot centre points. The order of the co-ordinates in the sequence is not significant. The blob output is directly imported into the 'CreatPointCloud' tool in Scorpion. This tool has references to 3D calibration of all three cameras, and can use either correlation or blob search technology to find and correlate the individual bright spots in all three cameras. Finally by using the Scorpion Stereo vision technology, the output of this tool is a sequence of x, y and z co-ordinates of the dots that can be plotted and displayed as in an image.
Integration with robots
The description belies the simplicity of the system. The hardest part for the engineer is calibrating the cameras which takes a little time but is a one-off task. Building the system is a matter of using the standard non-programming tools in the Scorpion tool set. Once complete, Scorpion Vision then does all the work and outputs 3D numerical data to the associated control system. Interfacing to Scorpion is easy and can be by Ethernet, RS232, serial bus or third-party modules. Scorpion Vision has been integrated with most robot systems including Fanuc, Kuka, ABB, Denso, Bosch, Motoman, Kawaski and many more.
There are several opportunities in this field for integrator. First, it offers a commercial and technical advantage over competitors; second, it offers the ability to build complex vision systems quickly and cheaply; and the biggest opportunity of all arises through 3D vision providing a 'unique selling point' that helps integrators to win more business.
To promote 3D machine vision, Scorpion Vision is running a seminar at CenFRA in Doncaster on 10 September 2008, which is free to attend. The seminar will be promoting the use of 3D machine vision in food production, where traditional machine vision technologies struggle to cope with the non-uniformity of the product. Using 3D, food manufacturers can automate where automation was not previously possible. To download an invitation, go to www.scorpionvision.co.uk/training&support.asp.
