Packaging
Flexible picking needs clever controls
Wednesday 30. April 2008 - Even the most complex robotics applications can now be developed as easily as using a word processor.
Imagine a machine that has four axes of motion; operates at up to 180 cycles a minute, accurately and with high repeatability; is capable of operating 24/7 reliably and has a mean time between failures (MTBF) of 250,000 hours. This describes ABBs new FlexPicker IRB360 delta robot, found increasingly in all sorts of food, packaging, pharmaceutical and other product picking applications.
With simplicity and ease of use being key considerations, as much as possible in the programming of the new robots is performed in the background. As a result, the end user can simply program the machines by defining the load point positions, the rest lies within the controls.
It starts with the line concept
The simplification starts with the production line concept. ABB has developed a suite of software called PickMaster that enables robot automation to be built on screen in minutes and then transferred to the line itself.
PickMaster runs within a familiar MS Windows environment and uses similar file structures – making compiling and storing files as simple as when word processing. Drop down menus and drag and drop features enable even complicated set ups to be developed very quickly. Any industrial PC will provide a suitable hardware platform.
Two fundamental files are created: a Line File and a Project File. There are also separate modules for configuring the vision system and the robots themselves.
The Line File contains the details of all the fixed assets/static structures in the system including number of robots, camera position, camera calibration, robot calibration and so forth. If any of these parameters change, it clearly affects any other project files configured to run on that line.
Line files are very simple to compile by dropping in rudimentary icons to represent the conveyors, robot work areas, fixed work areas, cameras, sensors, robot controllers and so on. Behind each icon sits the detailed data about that object.
In practicality, the user typically first defines the work areas. Cameras are then added together with their configurations and communications channel numbers (e.g. channel 1 and channel 2). These cameras can be calibrated using standard “blob” matrix or a more accurate “checkerboard” approach favoured by the world leading vision provider Cognex. The checkerboard enables a warp to be applied to allow compensation for perspective as well as 3D orientation in the product being picked. Objects can be defined from an open interface so that sensors, for example, can be added. Once complete, the Line file is simply named and stored in an appropriately titled folder.
The project file contains the actual process or production details including data about the product to be picked, tray types, placement and other information. These files are effectively recipes for the line and the vision system files must also know what the projects consist of, so that a broad variety of processes can be carried out on a single line configuration. Indeed, many projects can be carried out alongside, but independent of, each other on the line – for example, robots and vision system cameras can do separate tasks.
Vision systems can be set up through PickMaster. For example, the field of view (search region) can be set and the orientation parameters of the product being picked can be selected. Accurate geometric shape recognitions can be deployed for a large quantity of consistently shaped products, or for irregularly shaped items simple blob recognition may be all thats required. Again, all vision information is stored in the Project and Line Files.
Where multiple robots work in co-ordinated cells, the PickMaster software can treat the project as a single project for multiple robots or as discrete projects – one per robot for example, up to eight robots and eight cameras.
Once the Line file and the associated recipe, vision, robot, inspection and container files have been defined and saved, the line start up from PickMaster by a single button click. In doing so, the connection to the PickMaster runtime process in the robot controllers is established via a direct Ethernet link and position data is processed through these efficient communication channels
Files created within PickMaster are remarkably small which means they can be transferred easily and even e-mailed for diagnostics and fault-finding analysis. On the topic of diagnostics, one very useful facet of the PickMaster software is its in-built vision recorder. This allows the user to review the camera captures with all the hits on the line and, if required, remodel lines to achieve maximum efficiency.
Within the controller, two established software tools aid ABB in attaining its performance: TrueMove and QuickMove. TrueMove ensures that the motion path followed by the robot is the same as the programmed path – regardless of the robot speed. QuickMove is a unique self-optimizing motion control feature. It keeps cycle times at a minimum by ensuring maximum acceleration at every moment. Tests have shown that ABB robots can reach more than 25% shorter cycle times than competitors.
Finally, the controller has to be flexible enough to communicate with a host of other peripheral or associated controls or feedback devices. For example, a commonly encountered need is to be able to track products to be picked at the conveyors speed; or to accept data from sensors, vision systems or external PLCs.