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Friction in Robot Joints is the Reason for Nonlinearity in Impedance Estimation
S. I. Hwang(황성일),H. A. Kang(강현아),S. H. Kang(강상훈) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월
A stochastic estimation of arm mechanical impedance (AMI) using a low-friction robot (MIT-MANUS) under Proportional-Derivative (PD) control reported low coherence, indicating nonlinearity in AMI in the low-frequency range. It was hypothesized that the nonlinearity was due to the nonlinearity in the arm. Another study using an industrial robot under a robust impedance control (IMBIC) compensating all the nonlinearities (e.g., Friction) of the robot reported no noticeable nonlinearity. We hypothesized that the nonlinearity is not from the human arm, and the nonlinearity is due to the friction in robot joints. Mechanical impedance of the spring array was estimated using a direct-drive robot, almost identical to MITMANUS, under PD control and IMBIC, respectively. All the coherence functions obtained with IMBIC were larger than 0.9 in the frequency range of interest. The coherence functions with PD control were less than 0.8 in the low frequencies (< 5 Hz). These results indicated that the nonlinearity is due to the friction in robot joints, even though the friction was small. It is indirect but strong evidence that the human arm behaves linearly for small perturbation, and even if the robot has a low friction level, the friction should be compensated for reliable estimation.
박형필(H. P. Park),차백순(B. S. Cha),전용준(Y. J. Jeon),황병욱(B. W. Hwang),정상현(S. H. Jung),이광영(K. Y. Lee),황성일(S. I. Hwang) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
In general, precision plastic lens mold applied branched runner system of H-Type. However, filling imbalance of the mult-cavity was occurred by asymmetrical shear distribution. For this reason, the accuracy and the quality of the lens decrease. In this study, the lens mold with radial runner system of X-type lens was applied to improving the quality of lens parts. We carried out CAE analysis of lens mold with branched runner system of H-Type and radial runner system of X-type and we examined the mold temperature, temperature distribution in runner system and shrinkage distribution.