Abstract
The measurement of large forces and the presence of errors due to dimensional coupling are significant challenges for multi-dimensional force sensors. To address these challenges, this paper proposes an over-constrained six-dimensional force sensor based on a parallel mechanism of steel ball structures as a measurement module. The steel ball structure can be subject to rolling friction instead of sliding friction, thus reducing the influence of friction. However, because the structure can only withstand unidirectional pressure, the application of steel balls in a six-dimensional force sensor is difficult. Accordingly, a new design of the sensor measurement structure was designed in this study. The static equilibrium and displacement compatibility equations of the sensor prototype’s over-constrained structure were established to obtain the transformation function, from which the forces in the measurement branches of the proposed sensor were then analytically derived. The sensor’s measurement characteristics were then analysed through numerical examples. Finally, these measurement characteristics were confirmed through calibration and application experiments. The measurement accuracy of the proposed sensor was determined to be 1.28%, with a maximum coupling error of 1.98%, indicating that the proposed sensor successfully overcomes the issues related to steel ball structures and provides sufficient accuracy.
Highlights
As industries such as aerospace, human body biomechanics measurement, and mechanical processing continue to push the envelope of scientific capability, the accuracy and decoupling of sensing systems has grown in importance, considering the increased interest in manned space expeditions
Once the parameters of the physical sensor size and the value of the sensor axial stiffness obtained through calculation (2 × 108 m/N baseline, varied by ±0.2 × 108 m/N to account for small stiffness differences between modules) are inserted into the equations derived earlier, the force of each measurement module can be calculated
The ideal curves produced by the measurement model of the proposed over-constrained parallel six-dimensional force sensor for each module output are shown in Figure 6, in which the generalized external force increases by 500 N at every loading point from 0 N (Point 0) to 9000 N (Point 18), and decreases by 500 N at every loading point to 0 N (Point 36)
Summary
As industries such as aerospace, human body biomechanics measurement, and mechanical processing continue to push the envelope of scientific capability, the accuracy and decoupling of sensing systems has grown in importance, considering the increased interest in manned space expeditions. The measurement model of a typical parallel six-dimensional force sensor is different from that of an over-constrained six-dimensional force sensor In this vein, Pashikevich [15] proposed a stiffness modelling method based on branch nodes for over-constrained parallel structures. For a parallel six-dimensional force sensor under heavy loads, the need to enhance the sensor range while effectively reducing the dimensional coupling poses a significant challenge in the sensor’s development. The use of a steel ball structure instead of a conventional ball pair as a measuring branch is an effective method for reducing dimensional coupling caused by friction. Based mechanism force sensor using steel ball structures to reduce dimensional coupling caused by friction. Mechanism force sensor using steel ball structures to reduce dimensional coupling caused by friction This both tension and pressure while remaining compact.
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