摘要
机器人在利用高速旋转的刀具对目标材料进行铣削加工的过程中,刀具与铣削材料之间切削力的作用会使得整个铣削系统产生受迫振动.当被铣削的目标本身结构刚度较低时,铣削操作会使其产生一定的形变,不适宜利用空间位置作为控制量对铣削操作进行自动控制.由于动力工具在不同切削深度会产生不同幅值的受迫振动,并且产生的振动信号可以有效包含刀具与铣削材料之间的状态信息,能作为有效的控制量对铣削机器人进行运动控制,达到良好的自动控制效果.本文建立铣削过程中系统的振动模型,并根据振动模型列出微分方程描述动力工具的受迫振动,通过加速度传感器对振动信号进行实时采集,分析所采集信号以验证所建物理模型的准确性.利用快速傅里叶变换(FFT)对信号进行处理,提取信号中频率是刀具旋转频率的整倍数的谐波分量.由于二次谐波的FFT幅值随铣削深度的增加有较为明显特征,并且在刀具空转状态最为稳定,选其作为控制量对铣削机器人进行运动控制.采用DSP芯片作为主控制器,通过PID算法对步进电机加以控制,可以使刀具在铣削过程保持稳定的切削深度.对所建控制系统进行稳定性分析,进行实验并对铣削深度进行测量,证明刀具在铣削过程中能维持在较为稳定的深度,验证了控制算法的有效性.
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.
作者
代煜
贾宾
张建勋
曹广威
夏光明
Dai Yu;Jia Bin;Zhang Jianxun;Cao Guangwei;Xia Guangming(Institute of Robotics and Automatic Information System,Nankai University,Tianjin 300071,China)
出处
《天津大学学报（自然科学与工程技术版）》
EI
CSCD
北大核心
2020年第10期1093-1100,共8页
Journal of Tianjin University：Science and Technology
基金
国家自然科学基金资助项目(61773223)
天津市自然科学基金资助项目(18JCYBJC18800).
关键词
铣削机器人
振动反馈
FFT
DSP
PID控制
milling robot
vibration feedback
fast Fourier transform(FFT)
DSP
PID control
