Abstract
By combining a parallel mechanism with integrated flexible joints, a large measurement range and high accuracy sensor is realized. However, the main errors of the sensor involve not only assembly errors, but also deformation errors of its flexible leg. Based on a flexible joint 6-UPUR (a kind of mechanism configuration where U-universal joint, P-prismatic joint, R-revolute joint) parallel six-axis force sensor developed during the prephase, assembly and deformation error modeling and analysis of the resulting sensors with a large measurement range and high accuracy are made in this paper. First, an assembly error model is established based on the imaginary kinematic joint method and the Denavit-Hartenberg (D-H) method. Next, a stiffness model is built to solve the stiffness matrix. The deformation error model of the sensor is obtained. Then, the first order kinematic influence coefficient matrix when the synthetic error is taken into account is solved. Finally, measurement and calibration experiments of the sensor composed of the hardware and software system are performed. Forced deformation of the force-measuring platform is detected by using laser interferometry and analyzed to verify the correctness of the synthetic error model. In addition, the first order kinematic influence coefficient matrix in actual circumstances is calculated. By comparing the condition numbers and square norms of the coefficient matrices, the conclusion is drawn theoretically that it is very important to take into account the synthetic error for design stage of the sensor and helpful to improve performance of the sensor in order to meet needs of actual working environments.
Highlights
Compared with the traditional multi-axis force sensor, the sensor with flexible joints has advantages of fast response, small accumulated error, no mechanical friction and high measurement accuracy, so it has broad application prospects [1,2,3,4,5]
Based on the flexible joints 6-UPUR six-axis force sensor developed in the prephase, this paper focuses on establishment of the error modeling, namely, assembly error modeling and deformation error modeling
We compare it with theoretical first order kinematic influence coefficient matrix G0 and the first order kinematic influence coefficient matrix G when the synthetic error is taken into account
Summary
Compared with the traditional multi-axis force sensor, the sensor with flexible joints has advantages of fast response, small accumulated error, no mechanical friction and high measurement accuracy, so it has broad application prospects [1,2,3,4,5]. The design of sensors with flexible joints can be divided into two categories: the majority of sensors are designed and processed based on the integral structure. The other is using the assembled structure. For the former, there have been numerous research achievements. Kerr [6] proposed that the Stewart platform with instrumented elastic legs can be used as a six-axis force sensor. Gao et al [7] developed a six-axis controller based on the Stewart platform-based force sensor, and introduced the use of elastic joints to replace the real spherical joints which made miniaturization possible. Liang et al [8] designed and developed a Sensors 2017, 17, 2238; doi:10.3390/s17102238 www.mdpi.com/journal/sensors
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
