Motion Control of Milling Robot Based on Vibration Feedback

During robotic milling with a tool that rotates at a high speed, the cutting force will cause the system to generate forced vibration.When the structure being milled is of low stiffness, there will be considerable deformation in the structure such that it will not be suitable to use spatial position as the measured process variable that automatically controls the milling.Because cutting at different depths generates forced vibration signals of different amplitudes, and this signal effectively contains information on the state of the tool and the milling material, this signal can be used as an effective variable in the motion control, of a robot resulting in good automation performance.In this paper, a vibration model of the system during milling was established, and a differential vibration equation was used to describe the forced vibration of the tool according to the vibration model.An accelerometer was used to collect the vibration signal in real time, and then the signal was analyzed to verify the accuracy of the constructed physical model.The signal was processed by fast Fourier transform(FFT), and harmonic components whose frequencies were integer multiples of the rotational frequency were extracted.Because the FFT amplitude of the second harmonic showed clear characteristics with increasing milling depth, and had high stability when the tool was idling, it was selected as the control variable.The DSP chip was used as the main controller, and the stepping motor was controlled by PID algorithm to maintain a constant cutting depth during milling.Stability analysis was performed on the control system, and the milling depths were measured.Experimental results proved that the tool could maintain a stable depth during milling process, thereby verifying the effectiveness of the control algorithm. © 2020, Editorial Board of Journal of Tianjin University(Science and Technology). All right reserved.