Offline programming and simulation of arc welding robotic cell using RobotStudio software.
Ivan, Andrei-Mario ; Avram, Georgia-Cezara ; Nicolescu, Adrian Florin 等
1. INTRODUCTION
The works presented in this paper illustrates the possibilities and
facilities of using offline programming and simulation software for
robotic arc welding industrial purposes. In order to fully explore the
advantages of this approach, the ABB RobotStudio software was used for
the entire process, from cell layout design and application development
up to robot offline programming, as well as program optimization and
validation in the virtual environment provided by the software
(Nicolescu, 2010).
2. THE CELL STRUCTURE
The cell layout includes the following elements (see Fig. 1):
* an articulated arm industrial robot equipped with an arc welding
torch for performing arc welding operations (Nicolescu, 2005);
* four part positioners used for orienting the parts to be
processed by the robot, two types of positioners being included in the
cell structure (2 with one degree of freedom and 2 with two degrees of
freedom for part orienting) each positioner having two workstations in
order to reduce auxiliary part setting time;
* a linear tracking module in order to increase robot's work
envelope and to ensure robot's access to all positioners;
* a torch management system used to identify and allow correction
of any tool positioning and orientation errors.
[FIGURE 1 OMITTED]
Additionally, the cell includes one fume exhauster system above
each positioner, in order to evacuate the gas resulted from welding
operations.
The development of the station elements was partially made using
Catia V5 virtual prototyping environment for the walls, the fume
exhausters, the controllers, the welding source and the torch management
system (Nicolescu, 2009). After these elements have been reciprocally
constrained, the workspace and components distribution were validated
using the DMU Kinematics menu, by defining the specific motion laws for
endeffector trajectory generation and servo-assisted end-effector
orientation motions. After workscene validation, the components have
been imported in RobotStudio virtual environment, where the positioners,
the linear track and the robot have been added, as well as the
corresponding virtual controllers.
It is necessary to take into account that the manufacturing cell
includes components that are moved by other components, as is the case
for the robot, moved by the linear track and the parts, moved by the
positioners. Thus, attachment relations were defined between these
elements in order to ensure complete synchronization of different
component movements.
3. DEVELOPMENT OF APPLICATION PROGRAM
After the workscene has been completely configured, a virtual
system, representing the command unit of the station was created.
Because there are four positioners included alongside the robot and the
linear track (resulting far too many external axes for only one
controller) it became necessary to assign multiple tasks for commanding
all these units. Thus, the robot and the linear track were assigned (for
optimal coordination) to one task and the positioners were assigned each
to a different task.
Taking into account that all target points from which the paths
will be interpolated are calculated and referenced with respect to the
robot's baseframe, and that the robot is moved by the tracking
system, the virtual controller should be able to read the position
changes of the robot's baseframe. In order to ensure logical
functionality of the cell (from the controller unit's point of
view), the configuration files representing the virtual controller of
the industrial robot-linear tracking system had to be modified so that
robot's baseframe position can be updated in accordance with
robot-linear tracking system movements. After solving the baseframe
issues and setting the attachment relationship between the cell
components, the programming sequences were defined.
Because, in order to be completely processed, the part had to be
repeatedly repositioned, modular programming has proved to be the best
approach. Initially, the parts to be processed were only visually
represented in the virtual environment by the corresponding geometry,
but they were not individually linked to a particular frame. The
"Create Workobject" command allows the programmer to define a
particular frame for each processed part (***, 2007). This aspect is
important from the controller's point of view, because the robot
movements and the tool orientations are calculated with respect to both
robots' baseframe and the frame attached to the part.
The path followed by the robot's tool characteristic point was
defined by creating a set of targets. Any target has to be attached to a
workobject. Knowing that the targets created to interpolate the desired
path are positioned with respect to robot's baseframe, but are
attached to the workobject, a different workobject was created after
each reorientation of the processed part, due to the new position of its
geometry.
Each set of targets corresponding to each workobject were grouped
to form a programming module. To develop a programming module based on a
set of targets, the following steps were followed:
* for each target a set of move parameters were created, thus
resulting a move instruction, that included movement speed and accuracy,
type of movement (joint, linear or circular), tool orientation and
robot's configuration;
* the move instructions were grouped to form a path, that was
interpolated based on the targets corresponding to each instruction;
* a set of signals were configured to ensure communication and
feedback between the robot's controller and the other components of
the cells (see Fig. 2). Particularly, two types of signals were needed
for the developed application: digital output signals, used to command
the repositioning of the processed part, and digital input signals, used
to inform the robot's controller that the new position of the part
is reached, and the welding process can be restored;
* a set of action instructions were created based on the signals
and the occurring events in the station (such as reorienting a part),
these being necessary for conditioning the robot actions by the
different signal status.
After creating a target, which represents a specific position for
the tool characteristic point, the tool orientation and the robot
configuration for that target were specified (see Fig. 3 and Fig. 4).
These settings are critical to avoid singularity situations, especially
in the case of robot's configurations. The starting configuration
is very important for subsequent movements, as it limits the options for
the next target possible configurations, and this restriction can
propagate to the point that there are no valid configurations for the
next target of the path. Another important aspect of the configuration
settings is task optimization, considering that useless robot
reconfiguration between two targets increases process time (***, 2010).
After all paths have been configured, containing the necessary move
and action instructions, the final program was created by synchronizing
the paths with the virtual controller. This generated separate
procedures corresponding to each path, which could be called by creating
a main sequence of the program in the Simulation menu. The program can
be debugged and edited in text mode using the Offline menu of the
RobotStudio software (see Fig. 5).
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
4. CONCLUSION
The works included in this paper represents a part of a larger
project oriented towards optimization of industrial robotic applications
based on off-line programming and simulation techniques. Present
research explores the possibilities offered by RobotStudio offline
programming and simulation software for robotic arc welding applications
optimization, using block teaching and modular programming. Future
research will be performed in order to continue optimization for
industrial robotic assembling processes, the research strategy including
applications and simulations performed with various software, in order
to analyze and compare different software structures and programming
approaches. After fully exploring the facilities offered by the analyzed
software, methods of addressing some issues of robotic specific
applications and optimizing the different processes will be elaborated.
This stage of the research also includes validation of the simulation
results using real robotic systems.
5. REFERENCES
Nicolescu, A. (2005). Industrial Robots (in Romanian), EDP Publishing House, Bucharest, Romania
Nicolescu, A. & Ivan, A. (2009). Robotic manufacturing cells
virtual prototyping, Proceedings of the 18th International Workshop on
Robotics in Alpe-Adria-Danube Region, May 25-27, Brasov, Romania
Nicolescu, A., Ivan, A. & Marinescu, D. (2010). Advanced Part
Manufacturing using Kawasaki Robot and Off-Line Programming and
Simulation software PC Roset, Proceedings of CNC Technologies Workshop,
May 5-7, Bucharest, Romania
*** ABB (2007). RobotStudio operation manual
*** (2010) http://www.abb.com/product/ap/seitp327/6230bcade7a9d7d8[c.sub.1]2573f50042 d0a9.aspx--ABB RobotStudio Community page, Accessed
on: 2010-05-10