Simple software integration of robots in production machinery and automation systems
Automation with industrial robots is increasingly proving to be a key technology and thus an answer to current challenges. This can only be done successfully when the robots and the environment to be automated – machines, handling equipment, etc. This is where the software functions of KUKA.PLC mxAutomation come in, which, in combination with modern industrial realtime communication, allow efficient and sufficiently granular remote operation of the robot.
Robots are not an end in themselves, rather they fulfill a wide variety of tasks that contribute to an overall automation solution. They can be used, for example, for preparation or post-processing of tools or workpieces of production machinery, or for handling tasks, such as loading and unloading.
The end customer friendly automation of machine tools requires the integration of industrial robots in machining cells in such a way that modifications that have to be made by the operator, e.g. retrofits, are either applied to the robot automatically or at least ergonomically comply with machine operation requirements. Furthermore, all cell related operator actions, including those affecting the robot, must be possible from a single operator control unit in accordance with the “Single Point of Operation” principle. This includes interaction such as normal operator control, safe retraction, teaching and diagnosis.
In order to coordinate the operation of production machines and robots, communication is thus necessary between their control systems. Originally such tasks were fulfilled by signals wired in parallel, until conventional field buses took over these functions. Some industries, such as injection molding, also standardized the meaning of individual signals with the Euromap67 interface.
Only one programming interface
In order to be able to program the movements of the robot and the machine at just one location, KUKA has created the KUKA.PLC mxAutomation interface. By this means, machine builders or system integrators can essentially integrate the KUKA robot controller into their machine controller. All programming and operator tasks for the robot can be performed exclusively from the machine controller and its operator panel. Special knowledge of robot programming is no longer necessary. Operator control of the machine/robot cell can of course be carried out from one source at the familiar machine panel.
KUKA.PLC mxAutomation consists conceptionally of two main parts. A server program created by KUKA runs on the robot controller, which waits for commands for the robot to arrive via one of the field buses mentioned above. The actual robot control program runs on the machine controller; this program is created in the programming language and with the programming methods of the machine controller. In order to make this possible, KUKA provides the KUKA.PLC mxAutomation library for the individual controllers. This is integrated by the machine programmer into his programs and it then packs the programmed robot commands and their parameters into corresponding data, which are then transferred via the field bus to the KUKA.PLC mxAutomation server running on the robot controller. The server interprets the data that arrive, executes the desired robot commands and sends return parameters, status messages, etc. back to the library on the machine controller. In order for the data transfer of the robot commands and their return values to take place as quickly as possible and deterministically, the cyclical process data of the particular field bus are used exclusively for this purpose. Up to five robots can be remotely controlled simultaneously by the machine controller in this way.
The Application Programming Interface (API) of the KUKA.PLC mxAutomation library is based on the programming paradigm of PLCOpen’s Motion Control Function Blocks (MCFBs) and has been specifically expanded for KUKA robots. Nearly all functions which can be directly programmed on the robot are also available via the library. This includes general functions, such as reading of the current robot position, speed and acceleration, and also functions such as reading and writing local robot I/Os and variables. An application example for the advantageous use of system variables is sensitive gripping of workpieces or packaged goods, where the use of axis-specific torque limitation is a proven means. Within the KUKA.PLC mxAutomation configuration, the system variable TORQMON_DEF can be assigned to a KUKA.PLC mxAutomation variable, which can then be written via the KRC_SetSysVar function.
For the axis specific or Cartesian motion of the robot with LIN, PTP or CIRC, corresponding blocks are available. Here approximate positioning is also possible, as are exact time- distance functions or interrupts, for example. There are likewise functions for manual jogging of the robot and for teaching of specific points in space, which means that these operator actions can also be carried out from the machine terminal.
Advantages over other approaches
The KUKA.PLC mxAutomation approach has several advantages over other comparable solutions, in which the machine controller takes over control of the robot drives or motors, for example. The machine controller does not have to master complex robot transformations, and it does not need to know detailed machine data and metrics of the robot arms. KUKA.PLC mxAutomation works straight away with all KR C4 based KUKA robot types – from the KR AGILUS to the KR 1000 titan. KUKA has a proven, adaptable and integrated portfolio of robot arms: various reaches, payloads, shelf-mounted models, arm extensions, and optimized dead weights, etc.
There is no risk that the machine controller, due to lack of knowledge of the mechanical limits of robot motors, gear units and mechanical components, will exceed these load limits, resulting in premature failure of the robot. Additionally the machine controller retains all advantages and features of the KUKA robot controller, such as energy efficient motion algorithms adapted for the specific robot arms, loads and moments of inertia, sophisticated exception handling routines or the entire safety functions.
