Design of Portal Supporting Structure Using FEM and Technical Standards

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At the backbone of the structure is fixed series of robotic arms weighing 800 kg. Distance between robotic arms during operation varies, but only sporadically. The distance between the robot axes is 2400 mm, 3000 mm and 3700 mm Figure 2. Basis on which they captured robotic arm is chosen as firmly welded to the frame structure. Attachment robotic arm on the structure of the portal is to be realized using eight screws M 24 - 100 Figure 3. Overall requested dimensions of the portal structures are height 3000 mm, a width of 5000 mm Figure 4.

3. Design Options of the Structure

Gradually was created 3 design options of the structure. These proposals differed in the types of structural elements and overall configuration. Basic design verification was carried out in the SCIA engineering software. This program allows to realize the final reviews of the design according to the relevant technical standards contained in the library program for various types of materials, but especially for steel and concrete. This applies in particular for invalid technical standard STN 73 1401 (Design of steel structures) and its replacement STN EN 1993-1-(1-12) Eurocode 3 (Design of steel structures).

Figure 2. Pitch distance of the robotic arms

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Figure 3. Gripping of the robot to the base platform

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Figure 4. Base required dimensions of the portal structure

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As part of a comprehensive assessment of a structural element was assessed: standard strength condition, plane buckling, lateral-torsional (spatial) buckling, lateral buckling, overall lateral stability, complex condition considering the axial thrust, bending and lateral buckling with relevant factor of reliability and with relevant information about fulfillment of the conditions. Finally was evaluated the maximum unity review (unity check).

Based on the preliminary results of the SCIA software was created geometric model of portal structure in SolidWorks software. This model was then subjected to static analysis performed by FEM.

3.1. Option No. 1

The main element of the structure of the option No. 1 is IPE profile. Base design verification was carried out in the program SCIA engineering. The simplified model consists of beams and columns both profile IPE 600 according to DIN 1025-5. Most adverse load combinations occurs under the effect of self-weight construction, and the force from the load robotic arms at individual positions Figure 5, where:

F_g is the force of gravity of the structure;

F_b1 and F_b1´ are the forces of gravity of the robotic arms at a distance of 3700 mm;

F_b2 and F_b2´ are the forces of gravity of the robotic arms at a distance of 3000 mm;

F_b3 and F_b3´ are the forces of gravity of the robotic arms at a distance of 2400 mm.

The force of exerted by the load robotic arm is 8 kN.

Appropriate factors of reliability (γ_M0 and γ_M1) are equal 1.15.

Figure 5. Adverse grouping of forces acting to the robot in SCIA engineering software (option No. 1)

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The review of the steel S 235, for the individual beams IPE 600 of this simplified model were very satisfying see. Consequently, there has been a change in the geometry of the beam IPE 220 and IPE 200 for columns. Re-check was also acceptable. For individual beams and columns was changed the maximum unity review from 0.04 to 0.49, from 4 % to 49 %, the change of geometry is still relevant Figure 6.

Figure 6. Display of the maximum unity review after changing cross sections (option No. 1)

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Based on the preliminary results of the SCIA engineering software was created geometric model of portal structure in SolidWorks Figure 7. Contact surfaces are connected without penetration, since it is the integral welded construction. In fact, the steel columns supporting structure are attached to concrete substrate using a base screws. In addition to self-weight construction was prescribed the load of robotic arms, which was covered the entire surface of the base.

Figure 7. The geometric model (option No. 1)

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On the geometric model was created the volume network of high quality, with the number of elements 524 135, with the number of nodes 960 654 and with the corresponding size of the element Figure 8.

Figure 8. Volume network created on the geometric model (option No. 1)

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Analytical results for option No. 1 are represented by Von Mises stress field Figure 9, by the resulting displacements field Figure 10, by field of strains Figure 11 and by layout of the safety factor Figure 12. The tables of the extreme values of reduced stress Table 1, of resulting displacement Table 2 and of strain Table 3 are also attached.

Figure 9. Von Mises stress field (option No. 1)

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Figure 10. The resulting displacements field (option No. 1)

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Figure 11. Field of strains (option No. 1)

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Figure 12. Layout of the safety factor (option No. 1)

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Table 1. The extreme values of reduced stress

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Table 2. The extreme values of resulting displacement

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Table 3. The extreme values of strain

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3.2. Option No. 2

In this case it is the all-steel (steel S 235) framed welded portal structure Figure 13. As rods there were used the tubes of size 76.1 x 4 and 33.7 x 3.2 and as material the steel S 235. Instead of mounting base is specified continuous load on the bearing rods. There were specified external load forces of robotic arms and self weight of the structure. Preliminary analysis shows that the choice of rods of size 76.1 x 4 and 33.7 x 3.2 is satisfactory Figure 14.

Figure 13. Simplified model of the structure for SCIA engineering software (option No. 2)

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Figure 14. Deformation of the rods (option No. 2)

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Static analysis of the geometric model Figure 15 was terminated unsuccessfully. The base in place of robotic arms has been separated. Thus, the whole model became unstable. Based on the results of the static analysis of the geometric model was implemented a new static study. Only the structure itself has been subjected to stability analysis. A firm grip of the structure was prescribed, self-weight and the force of size 8 kN in the selected nodes Figure 16. The geometric model itself is stable.

Figure 15. The geometric model (option No. 2)

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Figure 16. Modified geometric model (option No. 2)

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Analytical results for option No. 2 are represented by the resulting displacements field Figure 17, by values of axial forces in the rods Figure 18 and by layout of the safety factor Figure 19. The table of the extreme values of resulting displacement Table 4 is also attached.

Figure 17. The resulting displacements field (option No. 2)

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Figure 18. Axial forces in the rods (option No. 2)

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Figure 19. Layout of the safety factor (option No. 2)

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Table 4. The extreme values of resulting displacement

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3.3. Option No. 3

Simplified model of structure consisting of beam IPE 220 (according to DIN 1025-5) and of welded hollow profiles CFRHS 180x180x8 (according to EN 10219-1) forming columns of the portal structure. The loading as an option No. 1, i.e. combination of self-weight loading of the structure and the forces of gravity of the load. Designation of the applied forces as in the option No. 1 Figure 20.

Figure 20. Adverse grouping of forces acting to the robot in SCIA engineering software (option No. 3)

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According unity review in SCIA engineering software for steel S 235 were the profiles satisfactory Figure 21. Based on the preliminary results of the SCIA engineering software was created geometric model of portal structure in SolidWorks Figure 22. Power effects and material were prescribed as in option No. 1. Static analysis of the geometric model was terminated unsuccessfully. In this case the model worked unstable.

Figure 21. Display of the maximum unity review (option No. 3)

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Figure 22. The geometric model (option No. 3)

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