To improve the adaptability of the multi-legged robot in rough terrain, a robotic foot capable of 3-axis force sensing is designed. The designed robotic foot is composed of five components, namely, a sensing ball, a fixed plate, 4 1-D force sensors, a base and a preloading bolt. The 4 force sensors are mounted symmetrically with 45° inclination angle in the base slots. According to the component forces detected by the force sensors in horizontal and vertical directions, the contacting force between the robotic foot and the environment can be calculated. The 3-axis force sensing principles of the robotic foot are analyzed. Based on that, an ADAMS model is established to verify the theoretical analysis. Through the sensor calibration experiment, it is found that the force exerted by preloading bolt and the material of the sensing ball have a great influence on the the 3-axis force sensing characteristics of the designed robotic foot. Finally, calibration tests of an optimized robotic foot are conducted with the selected preload and material, and the transformation matrix between voltage and force is obtained by using least square optimization method. The calibration results show that the robotic foot achieves an force sensing accuracy of ± 11.3% in X and Y directions, and ± 9.4% in Z direction.
[1] Huntsberger T, Pirjanian P, Trebi-Ollennu A, et al. CAMPOUT: A control architecture for tightly coupled coordination of multirobot systems for planetary surface exploration[J]. IEEE Transactions on Systems, Man and Cybernetics, Part A: Systems and Humans, 2003, 33(5): 550-559. [2] Huang Q J, Nonami K. Humanitarian mine detecting six-legged walking robot and hybrid neuro walking control with position/force control[J]. Mechatronics, 2003, 13(8-9): 773-790. [3] Billah M M, Ahmed M, Farhana S. Walking hexapod robot in disaster recovery: Developing algorithm for terrain negotiation and navigation[J]. International Journal of Mechanical, Aerospace, Industrial, Mechatronic and Manufacturing Engineering, 2008, 2(6): 795-800.[4] Howe R D. Tactile sensing and control of robotic manipulation[J]. Advanced Robotics, 1994, 8(3): 245-261.[5] Song A G, Wu J, Qin G, et al. A novel self-decoupled four degree-of-freedom wrist force/torque sensor[J]. Measurement, 2007, 40(9-10): 883-891. [6] Liang Q K, Zhang D, Song Q J, et al. Design and fabrication of a six-dimensional wrist force/torque sensor based on E-type membranes compared to cross beams[J]. Measurement, 2010, 43(10): 1702-1719. [7] Beccai L, Roccella S, Arena A, et al. Design and fabrication of a hybrid silicon three-axial force sensor for biomechanical applications[J]. Sensors and Actuators A: Physical, 2005, 120(2): 370-382. [8] Chuah M Y, Estrada M, Kim S. Composite force sensing foot utilizing volumetric displacement of a hyperelastic polymer[C] //IEEE/RSJ International Conference on Intelligent Robots and Systems. Piscataway, USA: IEEE, 2012: 1963-1969.[9] Ananthanarayanan A, Foong S, Kim S. A compact two DOF magneto-elastomeric force sensor for a running quadruped[C] //IEEE International Conference on Robotics and Automation. Piscataway, USA: IEEE, 2012: 1398-1403.[10] Walas K. Foot design for a hexapod walking robot[J]. Pomiary, Automatyka, Robotyka, 2013, 17: 283-287.[11] Wang D X, Guo J, Sun C C, et al. A flexible concept for designing multiaxis force/torque sensors using force closure theorem [J]. IEEE Transactions on Instrumentation and Measurement, 2013, 62(7): 1951-1959. [12] Wang D X, Yang C L, Zhang Y R, et al. A novel design of a wearable device for measuring force and torque in vascular surgery[C]//IEEE International Conference on Robotics and Automation. Piscataway, USA: IEEE, 2013: 2374-2379.[13] Wang D X, Zhang Y R, Yao C, et al. Toward force-based signature verification: A pen-type sensor and preliminary validation [J]. IEEE Transactions on Instrumentation and Measurement, 2010, 59(4): 752-762. [14] Xu Z, Kolev S, Todorov E. Design, optimization, calibration, and a case study of a 3D-printed, low-cost fingertip sensor for robotic manipulation[C]//IEEE International Conference on Robotics and Automation. Piscataway, USA: IEEE, 2014: 2749-2756.[15] Honeywell Inc. FSS low profile force sensors, FSSeries [EB/ OL]. [2015-07-05]. http://sensing.honeywell.com/index.cfm/ ci_id/0.