Abstract
Nowadays improving the accuracy and enlarging the measuring range of six-axis force sensors for wider applications in aircraft landing, rocket thrust, and spacecraft docking testing experiments has become an urgent objective. However, it is still difficult to achieve high accuracy and large measuring range with traditional parallel six-axis force sensors due to the influence of the gap and friction of the joints. Therefore, to overcome the mentioned limitations, this paper proposed a 6-Universal-Prismatic-Universal-Revolute (UPUR) joints parallel mechanism with flexible joints to develop a large measurement range six-axis force sensor. The structural characteristics of the sensor are analyzed in comparison with traditional parallel sensor based on the Stewart platform. The force transfer relation of the sensor is deduced, and the force Jacobian matrix is obtained using screw theory in two cases of the ideal state and the state of flexibility of each flexible joint is considered. The prototype and loading calibration system are designed and developed. The K value method and least squares method are used to process experimental data, and in errors of kind Ι and kind II linearity are obtained. The experimental results show that the calibration error of the K value method is more than 13.4%, and the calibration error of the least squares method is 2.67%. The experimental results prove the feasibility of the sensor and the correctness of the theoretical analysis which are expected to be adopted in practical applications.
Highlights
With the ability of measuring three force components and three torque components, the six-axis force sensor is one kind of the most important and challenging sensors, used widely in many research areas such as wind tunnel balances, thrust stand testing of rocket engines, and in robotics, the automobile industry, aeronautics, etc. [1]
Considering the traditional spherical joints are difficult to processed into flexible joints in a large measurement range situation, and the measurement accuracy will be affected, which restricts its application in six-axis force sensors based on flexible parallel mechanism, this paper proposes a kind of structure model of six-axis force sensor based on a parallel 6-UPUR mechanism
A, B, C, joints the center distance l1 ofrange the U situation, joint and location center distance l2 ofaccuracy the R joint,will as shown in Figurewhich measurement and the measurement be affected, restricts its application in six-axis force sensors based on flexible parallel mechanism, this paper proposes a kind of structure model of six-axis force sensor based on a parallel 6-UPUR mechanism
Summary
With the ability of measuring three force components and three torque components, the six-axis force sensor is one kind of the most important and challenging sensors, used widely in many research areas such as wind tunnel balances, thrust stand testing of rocket engines, and in robotics, the automobile industry, aeronautics, etc. [1]. With the ability of measuring three force components and three torque components, the six-axis force sensor is one kind of the most important and challenging sensors, used widely in many research areas such as wind tunnel balances, thrust stand testing of rocket engines, and in robotics, the automobile industry, aeronautics, etc. Since the Stewart platform was applied to the measurement of space six-axis forces by measuring the forces in the six legs with convection elements in 1983 [3], parallel structure have been widely used in six-axis force sensors [4], stimulated by the advantages of good stiffness, symmetric and compact. Sensors 2016, 16, 1271 structure, and straightforward mapping expression between the wrenches applied on the platform and the measured leg forces. Nguyen et al [5] developed a Stewart platform-based sensor with LVDT’s mounted along the legs for force/torque measurement in the presence of passive compliance. Durand changed the traditional Stewart structure and put piezoelectric quartz inside the Stewart structure and pre-tightened it [6], the sensor was more compact and could be used to measure tensions
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