Research Papers

Development of n-DoF Preloaded Structures for Impact Mitigation in Cobots

[+] Author and Article Information
S. Seriani

Department of Architecture and Engineering,
University of Trieste,
via A. Valerio 10,
Trieste 34127, Italy
e-mail: sseriani@units.it

P. Gallina

Department of Architecture and Engineering,
University of Trieste,
via A. Valerio 10,
Trieste 34127, Italy
e-mail: pgallina@units.it

L. Scalera

Polytechnic Department of Engineering
and Architecture,
University of Udine,
via delle Scienze 206,
Udine 33100, Italy
e-mail: scalera.lorenzo@spes.uniud.it

V. Lughi

Department of Architecture and Engineering,
University of Trieste,
via A. Valerio 10,
Trieste 34127, Italy
e-mail: vlughi@units.it

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANISMS AND ROBOTICS. Manuscript received November 24, 2017; final manuscript received May 31, 2018; published online July 18, 2018. Assoc. Editor: Raffaele Di Gregorio.

J. Mechanisms Robotics 10(5), 051009 (Jul 18, 2018) (10 pages) Paper No: JMR-17-1395; doi: 10.1115/1.4040632 History: Received November 24, 2017; Revised May 31, 2018

A core issue in collaborative robotics is that of impact mitigation, especially when collisions happen with operators. Passively compliant structures can be used as the frame of the cobot, although, usually, they are implemented by means of a single-degree-of-freedom (DoF). However, n-DoF preloaded structures offer a number of advantages in terms of flexibility in designing their behavior. In this work, we propose a comprehensive framework for classifying n-DoF preloaded structures, including one-, two-, and three-dimensional arrays. Furthermore, we investigate the implications of the peculiar behavior of these structures—which present sharp stiff-to-compliant transitions at design-determined load thresholds—on impact mitigation. To this regard, an analytical n-DoF dynamic model was developed and numerically implemented. A prototype of a 10DoF structure was tested under static and impact loads, showing a very good agreement with the model. Future developments will see the application of n-DoF preloaded structures to impact-mitigation on cobots and in the field of mobile robots, as well as to the field of novel architected materials.

Copyright © 2018 by ASME
Your Session has timed out. Please sign back in to continue.


Colgate, J. , Wannasuphoprasit, W. , and Peshkin, M. A. , 1996, “ Cobots: Robots for Collaboration With Human Operators,” Proc. ASME Dyn. Syst. Control Div., 58, pp. 433–439. https://pdfs.semanticscholar.org/5435/3022659475f2cbdc67f051a61e2fef7f82e9.pdf
Yamada, Y. , Hirasawa, Y. , Huang, S. , Umetani, Y. , and Suita, K. , 1997, “ Human-Robot Contact in the Safeguarding Space,” IEEE/ASME Trans. Mechatronics, 2(4), pp. 230–236. [CrossRef]
Lim, H.-O. , and Tanie, K. , 2000, “ Passive Viscoelastic Trunk and Passively Movable Base,” Int. J. Rob. Res., 19(4), pp. 307–335. [CrossRef]
Seong-Sik, Y. , Sungchul, K. , Seung-Kook, Y. , Seung-Jong, K. , Young-Hwan, K. , and Munsang, K. , 2005, “ Safe Arm Design With MR-Based Passive Compliant Joints and Visco-Elastic Covering for Service Robot Applications,” J. Mech. Sci. Technol., 19(10), pp. 1835–1845. [CrossRef]
Park, J.-J. , Kim, B.-S. , Song, J.-B. , and Kim, H.-S. , 2008, “ Safe Link Mechanism Based on Nonlinear Stiffness for Collision Safety,” Mech. Mach. Theory, 43(10), pp. 1332–1348. [CrossRef]
Park, J.-J. , Kim, H.-S. , and Song, J.-B. , 2009, “ Safe Robot Arm With Safe Joint Mechanism Using Nonlinear Spring System for Collision Safety,” IEEE International Conference on Robotics and Automation, Kobe, Japan, May 12–17, pp. 3371–3376.
Park, J.-J. , and Song, J.-B. , 2010, “ A Nonlinear Stiffness Safe Joint Mechanism Design for Human Robot Interaction,” ASME J. Mech. Des., 132(6), p. 061005. [CrossRef]
Park, J.-J. , and Song, J.-B. , 2010, “ Safe Joint Mechanism Using Inclined Link With Springs for Collision Safety and Positioning Accuracy of a Robot Arm,” IEEE International Conference on Robotics and Automation, Anchorage, AK, May 3–7, pp. 813–818.
López-Martínez, J. , Blanco-Claraco, J. L. , García-Vallejo, D. , and Giménez-Fernández, A. , 2015, “ Design and Analysis of a Flexible Linkage for Robot Safe Operation in Collaborative Scenarios,” Mech. Mach. Theory, 92, pp. 1–16. [CrossRef]
Medina, J. , Lozano, P. , Jardòn, A. , and Balaguer, C. , 2016, “ Design and Characterization of a Novel Mechanism of Multiple Joint,” IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Daejeon, Korea, Oct. 9–14, pp. 2444–2451.
Lauzier, N. , and Gosselin, C. , 2015, “ A Comparison of the Effectiveness of Design Approaches for HumanFriendly Robots,” ASME J. Mech. Des., 137(8), p. 082302. [CrossRef]
Park, J.-J. , Song, J.-B. , and Haddadin, S. , 2015, “ Collision Analysis and Safety Evaluation Using a Collision Model for the Frontal Robot–Human Impact,” Robotica, 33(7), pp. 1536–1550. [CrossRef]
López-Martínez, J. , García-Vallejo, D. , Giménez-Fernández, A. , and Torres-Moreno, J. , 2014, “ A Flexible Multibody Model of a Safety Robot Arm for Experimental Validation and Analysis of Design Parameters,” ASME J. Comput. Nonlinear Dyn., 9(1), p. 011003. [CrossRef]
Courreges, F. , Laribi, M. A. , Arsicault, M. , and Zeghloul, S. , 2016, “ Designing a Biomimetic Model of Non-Linear Elastic Safety Mechanism for Collaborative Robots,” IEEE 14th International Conference on Industrial Informatics (INDIN), Poitiers, France, July 19–21, pp. 231–236.
Wolf, S. , and Hirzinger, G. , 2008, “ A New Variable Stiffness Design: Matching Requirements of the Next Robot Generation,” IEEE International Conference on Robotics and Automation, Pasadena, CA, May 19–23, pp. 1741–1746.
Tonietti, G. , Schiavi, R. , and Bicchi, A. , 2005, “ Design and Control of a Variable Stiffness Actuator for Safe and Fast Physical Human/Robot Interaction,” IEEE International Conference on Robotics and Automation, Barcelona, Spain, Apr. 18–22, pp. 526–531.
Mathijssen, G. , Brackx, B. , Damme, M. V. , Lefeber, D. , and Vanderborght, B. , 2013, “ Series-Parallel Elastic Actuation (SPEA) With Intermittent Mechanism for Reduced Motor Torque and Increased Efficiency,” IEEE/RSJ International Conference on Intelligent Robots, Tokyo, Japan, Nov. 3–7, pp. 5841–5846.
Bely, P. Y. , 2003, “ The Design and Construction of Large Optical Telescopes,” Astronomy and Astrophysics Library, Springer-Verlag, New York.
Olivieri, L. , Antonello, A. , Savioli, L. , and Francesconi, A. , 2014, “ Dynamic Behavior of a Semi-Androgynous Small Satellite Docking Interface,” 65th International Astronautical Congress, Toronto, ON, Canada, Sept. 29–Oct. 3.
Wu, Y.-S. , and Lan, C.-C. , 2014, “ Linear Variable-Stiffness Mechanisms Based on Preloaded Curved Beams,” ASME J. Mech. Des., 136(12), p. 122302. [CrossRef]
Qin, Z. , Yan, S. , and Chu, F. , 2010, “ Dynamic Analysis of Clamp Band Joint System Subjected to Axial Vibration,” J. Sound Vib., 329(21), pp. 4486–4500. [CrossRef]
Liguori, C. , Paciello, V. , Paolillo, A. , Pietrosanto, A. , and Sommella, P. , 2013, “ Characterization of Motorcycle Suspension Systems: Comfort and Handling Performance Evaluation,” IEEE International Instrumentation and Measurement Technology Conference (I2MTC), Minneapolis, MN, May 6–9, pp. 444–449.
Baronti, F. , Lenzi, F. , Roncella, R. , Saletti, R. , and Di Tanna, O. , 2007, “ Embedded Electronic Control System for Continuous Self-Tuning of Motorcycle Suspension Preload,” Mediterranean Conference on Control and Automation, Athens, Greece, June 27–29, pp. 1–6.
Nirmal, M. D. , Mandal, K. , and Sun, Y. Q. , 2014, “ Impact Forces at Dipped Rail Joints,” J. Rail Rapid Transit, 230(1), pp. 271–282.
Pashkevich, A. , Klimchik, A. , and Chablat, D. , 2011, “ Enhanced Stiffness Modeling of Manipulators With Passive Joints,” Mech. Mach. Theory, 46(5), pp. 662–679. [CrossRef]
Dwivedy, S. K. , and Eberhard, P. , 2006, “ Dynamic Analysis of Flexible Manipulators, a Literature Review,” Mech. Mach. Theory, 41(7), pp. 749–777. [CrossRef]
Shabana, A. A. , 1997, “ Flexible Multibody Dynamics: Review of Past and Recent Developments,” Multibody Syst. Dyn., 1(3), pp. 189–222. [CrossRef]
Bauchau, O. A. , 2011, Flexible Multibody Dynamics, Springer, Dordrecht, The Netherlands. [CrossRef]
Boscariol, P. , Gallina, P. , Gasparetto, A. , Giovagnoni, M. , Scalera, L. , and Vidoni, R. , 2017, “ Evolution of a Dynamic Model for Flexible Multibody Systems,” Advances in Italian Mechanism Science, Springer, Cham, pp. 533–541. [CrossRef]
Vanderborght, B. , Albu-Schaeffer, A. , Bicchi, A. , Burdet, E. , Caldwell, D. , Carloni, R. , Catalano, M. , Eiberger, O. , Friedl, W. , Ganesh, G. , Garabini, M. , Grebenstein, M. , Grioli, G. , Haddadin, S. , Hoppner, H. , Jafari, A. , Laffranchi, M. , Lefeber, D. , Petit, F. , and Strami, S. , 2013, “ Variable Impedance Actuators: A Review,” Rob. Auton. Syst., 61(12), pp. 1601–1614. [CrossRef]
Lauzier, N. , and Gosselin, C. , 2011, “ Series Clutch Actuators for Safe Physical Human-Robot Interaction,” IEEE International Conference on Robotics and Automation (ICRA), Shanghai, China, May 9–13, pp. 5401–5406.
Schaedler, T. A. , and Carter, W. B. , 2016, “ Architected Cellular Materials,” Annu. Rev. Mater. Res., 46(1), pp. 187–210. [CrossRef]
Bauer, J. , Meza, L. R. , Schaedler, T. A. , Schwaiger, R. , Zheng, X. , and Valdevit, L. , 2017, “ Nanolattices: An Emerging Class of Mechanical Metamaterials,” Adv. Mater., 29(40), p. 1701850. [CrossRef]
Valdevit, L. , 2016, “ 3D Manufacturing of Micro and Nano-Architected Materials,” Proc. SPIE, 9738, p. 97380K.


Grahic Jump Location
Fig. 1

Behavior of cobots during a collision: in (a), a rigid-link cobot is shown in its initial position with respect to an obstacle; in (b), the collision between the two is shown;in (c), a cobot with compliant links is shown; and in (d), the collision is shown to cause an elastic deformation of the first link

Grahic Jump Location
Fig. 2

Difference between linear and preloaded elastic structures: in (a), a simple linearly elastic structure is shown, while in (b) a preloaded elastic mechanism is visible in series to the structure; preload is defined by the pair of outward-looking triangles, indicating a compressed spring. Respectively, in (c) and (d), the force–displacement relations between linear and preloaded structures are illustrated, whereas in (e) and (f) the stored elastic energies E1,2 are represented for the two cases.

Grahic Jump Location
Fig. 3

Definitions of the fundamental preloaded elements and their elementary combinations, along with an illustration of the nominal elastic behavior: in (a), a translational traction element is shown. The mechanical limit is shown in blue, where the spring preload direction is indicated by the inward facing triangles, meaning that a traction preload is present; in (b), the compression counterpart is shown, in this case the preload is compressive; in (c), the combination of (a) and (b) is visible; in (d)–(f), the same is illustrated for the rotational case. The plots in (g)–(i) show the elastic law for the solutions above each one.

Grahic Jump Location
Fig. 4

Some examples of preloaded structures, from one-dimensional (1D) element to 3D arrays. The first row shows the fundamental preloaded elements: translational and rotational. Combinations of monodimensional preloaded structures are visible in the second row: a translational compression-traction solution, a 2DoF rotational one, and a combined translational-rotational structure. The third row shows planar 2D arrays of translational preloaded elements and of combined translation-rotation elements. The last row shows a 3D translation-rotation array.

Grahic Jump Location
Fig. 5

Multiple-DoF model for a serial preloaded structure: in (a), the kinematics is shown; in (b), the boundary constraints and loading conditions are shown: the elastic “ground” implementation and the impactor of mass md; and in (c), the shape of the nonlinear preloaded stiffness curve is shown for the general joint i; note that the relation is symmetric with respect to zero

Grahic Jump Location
Fig. 6

Diagram of the fundamental unit of the s-structure: in (a), a general “at rest” view is shown, along with labels to the main components; in (b), the upward configuration is shown; and in (c), the downward one

Grahic Jump Location
Fig. 7

Prototype segment: in (a), the structure can be seen from the outside and in (b), a section view is shown, with the main internal components

Grahic Jump Location
Fig. 8

Experimental prototype and capture system. The complete system is shown in (a), along with the impactor and the impact spring. The reader can appreciate the different visible portion of the screws on the joints' springs, signaling different preload values. In subfigures (b)–(e), some snapshots of the beam are visible during the impact experiment. In this case, time is referred to the instant when impact happens (t=0s).

Grahic Jump Location
Fig. 9

Error analysis: in the first plot from the top, the cable length error due to the asymmetric effect of the pulley on the cable can be seen; in the second plot, the y-coordinate of point Qn is shown against time in both the nominal and small-angles approximation, whereas in the last plot the relative error εn,rel can be seen

Grahic Jump Location
Fig. 10

Static stiffness plot of the beam. The displacement Δy is measured at point P6 in the model and at the corresponding point in the prototype. On the left, the numerical and experimental curves are shown, while on the right the displacement error is reported.

Grahic Jump Location
Fig. 11

Coordinate y of the barycenter Qi of the links over time following impact at t=0.225s of the impactor. A comparison between results of the numerical (solid line, Δt=10−5) and experimental (dashed line, Δt=10−3) runs is shown.

Grahic Jump Location
Fig. 12

Relative error between experimental and numerical results for the five links; the values are relative to the maximum absolute Qy,i of each link's experimental result. Error values are bound to the 0–1 interval.



Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In