Low-frequency structural vibrations caused by poor rigidity are one of the main obstacles limiting the machining efficiency of robotic milling.Existing vibration suppression strategies primarily focus on passive vibra...Low-frequency structural vibrations caused by poor rigidity are one of the main obstacles limiting the machining efficiency of robotic milling.Existing vibration suppression strategies primarily focus on passive vibration absorption at the robotic end and feedback control at the joint motor.Although these strategies have a certain vibration suppression effect,the limitations of robotic flexibility and the extremely limited applicable speed range remain to be overcome.In this study,a Magnetorheological Joint Damper(MRJD)is developed.The joint-mounted feature ensures machining flexibility of the robot,and the millisecond response time of the Magnetorheological Fluid(MRF)ensures a large effective spindle speed range.More importantly,the evolution law of the damping performance of MRJD was revealed based on a low-frequency chatter mechanism,which guarantees the application of MRJD in robotic milling machining.To analyze the influence of the robotic joint angle on the suppression effect of the MRJD,the joint braking coefficient and end braking coefficient were proposed.Parallel coordinate plots were used to visualize the joint range with the optimal vibration suppression effect.Finally,a combination of different postures and cutting parameters was used to verify the vibration suppression effect and feasibility of the joint angle optimization.The experimental results show that the MRJD,which directly improves the joint vibration resistance,can effectively suppress the low-frequency vibration of robotic milling under a variety of cutting conditions.展开更多
Due to the advantages of large workspace,low cost and the integrated vision/force sensing,robotic milling has become an important way for machining of complex parts.In recent years,many scholars have studied the probl...Due to the advantages of large workspace,low cost and the integrated vision/force sensing,robotic milling has become an important way for machining of complex parts.In recent years,many scholars have studied the problems existing in the applications of robotic milling,and lots of results have been made in the dynamics,pose planning,deformation control etc.,which provides theoretical guidance for high precision and high efficiency of robotic milling.From the perspective of complex parts robotic milling,this paper focuses on machining process planning and control techniques including the analysis of the robot-workspace,robot trajectory planning,vibration monitoring and control,deformation monitoring and compensation.As well as the principles of these technologies such as robot stiffness characteristics,dynamic characteristics,chatter mechanisms,and deformation mechanisms.The methods and characteristics related to the theory and technology of robotic milling of complex parts are summarized systematically.The latest research progress and achievements in the relevant fields are reviewed.It is hoped that the challenges,strategies and development related to robotic milling could be clarified through the carding work in this paper,so as to promote the application of related theories and technologies in high efficiency and precision intelligent milling with robot for complex parts.展开更多
Hepatocellular carcinoma(HCC)is the fifth most common cancer worldwide.Significant efforts have been devoted to identify new biomarkers for molecular imaging and targeted therapy of HCC.Copper is a nutritional metal r...Hepatocellular carcinoma(HCC)is the fifth most common cancer worldwide.Significant efforts have been devoted to identify new biomarkers for molecular imaging and targeted therapy of HCC.Copper is a nutritional metal required for the function of numerous enzymatic molecules in the metabolic pathways of human cells.Emerging evidence suggests that copper plays a role in cell proliferation and angiogenesis.Increased accumulation of copper ions was detected in tissue samples of HCC and many other cancers in humans.Altered copper metabolism is a new biomarker for molecular cancer imaging with position emission tomography(PET)using radioactive copper as a tracer.It has been reported that extrahepatic mouse hepatoma or HCC xenografts can be localized with PET using copper-64 chloride as a tracer,suggesting that copper metabolism is a new biomarker for the detection of HCC metastasis in areas of low physiological copper uptake.In addition to copper modulation therapy with copper chelators,short-interference RNA specific for human copper transporter 1(h Ctr1)may be used to suppress growth of HCC by blocking increased copper uptake mediated by h Ctr1.Furthermore,altered copper metabolism is a promising target for radionuclide therapy of HCC using therapeutic copper radionuclides.Copper metabolism has potential as a new theranostic biomarker for molecular imaging as well as targeted therapy of HCC.展开更多
In the machining of complicated surfaces,the cutters with large length/diameter ratios are used widely and the deformation of the machining system is one of the principal error sources.During the process planning stag...In the machining of complicated surfaces,the cutters with large length/diameter ratios are used widely and the deformation of the machining system is one of the principal error sources.During the process planning stage,the cutting direction angle,the cutter lead and tilt angles are usually optimized to minimize the force induced error.It may lead to a low machining efficiency for bullnose end mills,as the material removal rates are different largely for different machining angles.In this paper,the influence mechanism of the machining angles on the force induced error is studied based on the models of the instantaneous cutting force when the cutter flute traveling through the cutting contact point and the stiffness of the machining system.In order to evaluate the machining angles,the force induced error/efficiency indicator(FEI)is defined as the division of the force induced error and the equal volume sphere of the removed material.FEI is dimensionless,with the lower FEI,the lower force induced error and the higher machining efficiency.For optimal selection of the machining angles,the critical FEI is calculated with the constraint of force induced error and the desired material removal rate,and the critical FEI separate the set of the machining angles into two subsets.After the feed rate scheduling process,the machining angles in the optimal subset would have higher machining accuracy and efficiency,while the machining angles in the other subset have lower machining accuracy and efficiency.Through the machining experiment of five axis machining and freeform surface machining,the effectiveness and superiority of the proposed FEI method is verified with a bullnose end mill,which can improve the machining efficiency with the constraint of force induced error.展开更多
Robot teleoperation plays an important role in industrial manufacturing in unknown and dangerous environments beyond human reach.In telerobotic manufacturing tasks,environmental interaction forces may vary significant...Robot teleoperation plays an important role in industrial manufacturing in unknown and dangerous environments beyond human reach.In telerobotic manufacturing tasks,environmental interaction forces may vary significantly from task to task.Therefore,it is crucial to provide operators with the specific proportional feedback of environmental interaction forces to enhance their environmental awareness and manipulation capabilities.However,variable time delays and various scales of environmental interaction force feedback seriously affect the system stability,which should be rigorously addressed when designing control parameters.To cope with these difficulties,a position and scaled force tracking control framework is proposed and the LyapunovKrasovskii theory is used to obtain a simple algebraic stability criterion with the scaling factor of the environmental interaction force feedback.In addition,a low-pass filter-based radial basis function neural network is designed to avoid the effect of the measurement noise and the sudden change of the non-passive environmental interaction force on the system stability.Compared with different controllers in various telerobotic manufacturing tasks such as heavy lifting,cutting,and polishing,our proposed method achieves better position and scaled force tracking performance.展开更多
Dear Editor,Biomolecular condensates have emerged as key players in cellular processes and responses to stress(Alberti and Hyman,2021).Recent studies have revealed that most biomolecular condensates arise from liquid-...Dear Editor,Biomolecular condensates have emerged as key players in cellular processes and responses to stress(Alberti and Hyman,2021).Recent studies have revealed that most biomolecular condensates arise from liquid-liquid phase separation(Banani et al.,2017;Shin and Brangwynne,2017),a process that has been described in the field of polymer chemistry.展开更多
This study proposes an algorithm for max- imizing strip width in orthogonal tum-miUing based on variable eccentric distance. The machining error model is first established based on the local cutting profile at the con...This study proposes an algorithm for max- imizing strip width in orthogonal tum-miUing based on variable eccentric distance. The machining error model is first established based on the local cutting profile at the contact line. The influencing factors of the strip width are then investigated to analyze their features and determine an optimizing strategy. The optimized model for maximum machining strip width is formulated by adopting a variable eccentric distance. Hausdorff distance and Fr6chet distance are introduced in this study to implement the constraint function of the machining error in the optimized model. The computing procedure is subsequently provided. Simulations and experiments have been conducted to verify the effectiveness of the proposed algorithm.展开更多
基金supported by the National Natural Science Foundation of China(No.U20A20294)the National Natural Science Foundation of China(No.52322511)the National Natural Science Foundation of China(No.52188102).
文摘Low-frequency structural vibrations caused by poor rigidity are one of the main obstacles limiting the machining efficiency of robotic milling.Existing vibration suppression strategies primarily focus on passive vibration absorption at the robotic end and feedback control at the joint motor.Although these strategies have a certain vibration suppression effect,the limitations of robotic flexibility and the extremely limited applicable speed range remain to be overcome.In this study,a Magnetorheological Joint Damper(MRJD)is developed.The joint-mounted feature ensures machining flexibility of the robot,and the millisecond response time of the Magnetorheological Fluid(MRF)ensures a large effective spindle speed range.More importantly,the evolution law of the damping performance of MRJD was revealed based on a low-frequency chatter mechanism,which guarantees the application of MRJD in robotic milling machining.To analyze the influence of the robotic joint angle on the suppression effect of the MRJD,the joint braking coefficient and end braking coefficient were proposed.Parallel coordinate plots were used to visualize the joint range with the optimal vibration suppression effect.Finally,a combination of different postures and cutting parameters was used to verify the vibration suppression effect and feasibility of the joint angle optimization.The experimental results show that the MRJD,which directly improves the joint vibration resistance,can effectively suppress the low-frequency vibration of robotic milling under a variety of cutting conditions.
基金supported by National Science Fund for Distinguished Young Scholars of China(No.51625502)Innovative Group Project of National Natural Science Foundation of China(No.51721092)Innovative Group Project of Hubei Province of China(No.2017CFA003)。
文摘Due to the advantages of large workspace,low cost and the integrated vision/force sensing,robotic milling has become an important way for machining of complex parts.In recent years,many scholars have studied the problems existing in the applications of robotic milling,and lots of results have been made in the dynamics,pose planning,deformation control etc.,which provides theoretical guidance for high precision and high efficiency of robotic milling.From the perspective of complex parts robotic milling,this paper focuses on machining process planning and control techniques including the analysis of the robot-workspace,robot trajectory planning,vibration monitoring and control,deformation monitoring and compensation.As well as the principles of these technologies such as robot stiffness characteristics,dynamic characteristics,chatter mechanisms,and deformation mechanisms.The methods and characteristics related to the theory and technology of robotic milling of complex parts are summarized systematically.The latest research progress and achievements in the relevant fields are reviewed.It is hoped that the challenges,strategies and development related to robotic milling could be clarified through the carding work in this paper,so as to promote the application of related theories and technologies in high efficiency and precision intelligent milling with robot for complex parts.
基金Supported by(in part)A faculty research start-up fund to Peng F from the Carman and Ann Adams Foundation,Detroit,Michigan,United StatesHarold C Simmons Comprehensive Cancer Center,University of Texas Southwestern Medical Center,Dallas,Texas,United States.
文摘Hepatocellular carcinoma(HCC)is the fifth most common cancer worldwide.Significant efforts have been devoted to identify new biomarkers for molecular imaging and targeted therapy of HCC.Copper is a nutritional metal required for the function of numerous enzymatic molecules in the metabolic pathways of human cells.Emerging evidence suggests that copper plays a role in cell proliferation and angiogenesis.Increased accumulation of copper ions was detected in tissue samples of HCC and many other cancers in humans.Altered copper metabolism is a new biomarker for molecular cancer imaging with position emission tomography(PET)using radioactive copper as a tracer.It has been reported that extrahepatic mouse hepatoma or HCC xenografts can be localized with PET using copper-64 chloride as a tracer,suggesting that copper metabolism is a new biomarker for the detection of HCC metastasis in areas of low physiological copper uptake.In addition to copper modulation therapy with copper chelators,short-interference RNA specific for human copper transporter 1(h Ctr1)may be used to suppress growth of HCC by blocking increased copper uptake mediated by h Ctr1.Furthermore,altered copper metabolism is a promising target for radionuclide therapy of HCC using therapeutic copper radionuclides.Copper metabolism has potential as a new theranostic biomarker for molecular imaging as well as targeted therapy of HCC.
基金supported by National Science Fund for Distinguished Young Scholars of China(No.51625502)Innovative Group Project of National Natural Science Foundation of China(No.51721092)Innovative Group Project of Hubei Province of China(No.2017CFA003)。
文摘In the machining of complicated surfaces,the cutters with large length/diameter ratios are used widely and the deformation of the machining system is one of the principal error sources.During the process planning stage,the cutting direction angle,the cutter lead and tilt angles are usually optimized to minimize the force induced error.It may lead to a low machining efficiency for bullnose end mills,as the material removal rates are different largely for different machining angles.In this paper,the influence mechanism of the machining angles on the force induced error is studied based on the models of the instantaneous cutting force when the cutter flute traveling through the cutting contact point and the stiffness of the machining system.In order to evaluate the machining angles,the force induced error/efficiency indicator(FEI)is defined as the division of the force induced error and the equal volume sphere of the removed material.FEI is dimensionless,with the lower FEI,the lower force induced error and the higher machining efficiency.For optimal selection of the machining angles,the critical FEI is calculated with the constraint of force induced error and the desired material removal rate,and the critical FEI separate the set of the machining angles into two subsets.After the feed rate scheduling process,the machining angles in the optimal subset would have higher machining accuracy and efficiency,while the machining angles in the other subset have lower machining accuracy and efficiency.Through the machining experiment of five axis machining and freeform surface machining,the effectiveness and superiority of the proposed FEI method is verified with a bullnose end mill,which can improve the machining efficiency with the constraint of force induced error.
基金supported by the National Natural Science Foundation of China(Grant Nos.52188102,52105515,62373161)。
文摘Robot teleoperation plays an important role in industrial manufacturing in unknown and dangerous environments beyond human reach.In telerobotic manufacturing tasks,environmental interaction forces may vary significantly from task to task.Therefore,it is crucial to provide operators with the specific proportional feedback of environmental interaction forces to enhance their environmental awareness and manipulation capabilities.However,variable time delays and various scales of environmental interaction force feedback seriously affect the system stability,which should be rigorously addressed when designing control parameters.To cope with these difficulties,a position and scaled force tracking control framework is proposed and the LyapunovKrasovskii theory is used to obtain a simple algebraic stability criterion with the scaling factor of the environmental interaction force feedback.In addition,a low-pass filter-based radial basis function neural network is designed to avoid the effect of the measurement noise and the sudden change of the non-passive environmental interaction force on the system stability.Compared with different controllers in various telerobotic manufacturing tasks such as heavy lifting,cutting,and polishing,our proposed method achieves better position and scaled force tracking performance.
基金supported by grants from the National Natural Science Foundation of China(32161133001)the Beijing Natural Science Foundation(JQ21020).
文摘Dear Editor,Biomolecular condensates have emerged as key players in cellular processes and responses to stress(Alberti and Hyman,2021).Recent studies have revealed that most biomolecular condensates arise from liquid-liquid phase separation(Banani et al.,2017;Shin and Brangwynne,2017),a process that has been described in the field of polymer chemistry.
文摘This study proposes an algorithm for max- imizing strip width in orthogonal tum-miUing based on variable eccentric distance. The machining error model is first established based on the local cutting profile at the contact line. The influencing factors of the strip width are then investigated to analyze their features and determine an optimizing strategy. The optimized model for maximum machining strip width is formulated by adopting a variable eccentric distance. Hausdorff distance and Fr6chet distance are introduced in this study to implement the constraint function of the machining error in the optimized model. The computing procedure is subsequently provided. Simulations and experiments have been conducted to verify the effectiveness of the proposed algorithm.
