High-Sensitivity and High-Stiffness Force Sensor Using Strain-Deformation Expansion Mechanism

In order to grasp and manipulate an object controllably and dexterously with a multifingered hand of robot, the sensing of fingertip force is required. To these operation, for making the controlability higher and making force sensor be proof against unexpected collisions or weights, not only the sensor’s sensibility but also its stiffness are desired as high as possible. For sensing a force acting on a force sensor, in general, some sensing elastic bodies is equipped in the force sensor. When a force is applied on the sensor, the force will pass through the sensing elastic bodies and make the bodies deform linearly so that it can be measured from the strain-deformations on the elastic bodies. So far, many researches [1]∼[7] [9] consider making the sensed force all passed through the sensing elastic bodies for force sensing. To this situation, if we want to make the sensibility higher, the stiffness of the sensing elastic bodies have to be reduced for making their deformations larger. Conversely, if we wan to make the stiffness higher, the sensibility of the sensing elastic bodies will be reduced since their deformations become to small because of the higher stiffness. Thus by using the previous sensing structures, it is hard to realize the force sensing with both of high-stiffness and high-sensitivity. For instance, about torque sensing, some strain gauges are put on an arm joint shaft to sense the torque deformation on the shaft [1]. In this way, to make the sensitivity higher, reducing the stiffness of joint shaft, for instance, using an elastic shaft as a portion of joint shaft [2], was considered. On the other hand, a joint shaft and an arm link was fixedly connected in series by an elastic body and its elastic deformation was used for joint torque sensing [3]. However this method will reduce the joint stiffness, too. Also, double-cross structure [7], double-membrane structure [6] [8] were proposed for force sensing or acceleration sensing. But these methods will reduce the sensor’s stiffness if higher sensibility is required. In general, increasing the sensitivity of joint torque sensing by reducing the joint stiffness, is not desired. This paper proposes a novel mechanism called Strain-Deformation Expansion Mechanism for 3-axis force sensing. By the force sensing mechanism, the small strain-deformation used for force sensing can be expanded while the sensor stiffness will not be reduced but will be heightened. In this paper, the force sensing principle is addressed by analyzing the O pe n A cc es s D at ab as e w w w .in te ch w eb .o rg