tailieunhanh - Control of Redundant Robot Manipulators - R.V. Patel and F. Shadpey Part 12

Tham khảo tài liệu 'control of redundant robot manipulators - . patel and f. shadpey part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 158 6 Experimental Results for Contact Force and Compliant Motion Control Selection of PD Gains In the modified AHIC scheme see Figure a PD controller was implemented to ensure that the reference error error between the target trajectory generated by the AHIC controller and tool frame trajectory converges to zero. Therefore in order for the robot to act as closely as possible to the ideal impedance system specified by and the PD gains need to be selected as high as possible. Different experiments were conducted to find the best values for the PD gains. The maximum values that do not excite the unmodeled dynamics were obtained experimentally as kp 400 kv 40. Figure Plot of magnitude versus frequency for the second-order filter in Equation . Preparation and Conduct of the Experiments 159 Selection of the Force Filter The force sensor data usually contain a high level of noise which needs to be filtered out by implementation of a low-pass filter. The selection of the filter is a trade-off between noise rejection and stability requirements as the low-pass filter introduces a delay in the sensor loop which can cause instability. The JR3 force-sensor interface card provides a cascade of low-pass filters. Each succeeding filter has a cutoff frequency that is 1 4 of that of the preceding filter. For the JR3 sensor with a sample rate of 8 kHz the cutoff frequency of the first filter is 500Hz. The subsequent filters cutoff at 125 Hz Hz Hz and so on. The optimal filter has been selected experimentally. Figure shows the force measurements with different filters for the test scenario of Figure . As one may notice the filter with Hz cutoff frequency gives the best tracking fd 15N with maximum noise reduction. Effect of Kinematic Errors Robustness Issue The AHIC scheme may suffer from two major sources of kinematic errors The kinematic parameters of the arm In the absence of an accurate kinematic calibration