Study on the unidirectional force sensitive beam structure with the overload protection mechanism

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A variety of force/torque sensors are used in the engineering application fields. Most of the force/torque sensors are designed to be sensitive for a weak signal, and thus, they unexpectedly lose the stiffness. Such flexible sensors tend to sense the coupled forces, and it is generally difficult to decouple them. Furthermore, the flexible sensors cause the positioning error.The objective of this study is to design and develop a unidirectional force sensitive beam structure to overcome the problems described above. In the design process, the characteristics of the H-slit and parallel beam structure was analyzed by FEA (Finite Element Analysis) and experiments. The results of this research are summarized as follows.1.From the results of experiments and FEA for the H-slit beam and parallel beam, we found that the H-slit beam was more rigid than the parallel beam if they had same sensitivity. This result indicates that the H-slit beam is an appropriate shape for the unidirectional force sensor, since it can be sensitive and stiff.2.The H-slit beam structure can be modeled by a 4-bars closed-link structure. Therefore, the structure itself can be a mechanical stopper for the overloads. The applied force decreases the width of the slit of the beam, and when the width of the slit becomes zero, the beam does not deform anymore.3.The Optimal parameter and dimensions of the H-slit beam are investigated in order to avoid the stress concentration. As a result of this study, it is found that a parabola shaped notches (minor and major axis ratio is 1:10) exhibits a relatively, adequate stress distribution.4.The H-slit force sensor is applied to the ZMP sensor for a humanoid robot. The developed ZMP sensor has 6 sensing points equipped with 12 H-slits. The sensor is attached at the sole of a humanoid robot and used for the control of the robot.