Parts with varied curvature features play increasingly critical roles in engineering, and are often machined under high-speed continuous-path running mode to ensure the machining efficiency. However, the continuous-pa...Parts with varied curvature features play increasingly critical roles in engineering, and are often machined under high-speed continuous-path running mode to ensure the machining efficiency. However, the continuous-path running trajectory error is significant during high-feed-speed machining, which seriously restricts the machining precision for such parts with varied curvature features. In order to reduce the continuous-path running trajectory error without sacrificing the machining efficiency, a pre-compensation method for the trajectory error is proposed. Based on the formation mechanism of the continuous-path running trajectory error analyzed, this error is estimated in advance by approximating the desired toolpath with spline curves. Then, an iterative error pre-compensation method is presented. By machining with the regenerated toolpath after pre-compensation instead of the uncompensated toolpath, the continuous-path running trajectory error can be effectively decreased without the reduction of the feed speed. To demonstrate the feasibility of the proposed pre-compensation method, a heart curve toolpath that possesses varied curvature features is employed. Experimental results indicate that compared with the uncompensated processing trajectory, the maximum and average machining errors for the pre-compensated processing trajectory are reduced by 67.19% and 82.30%, respectively. An easy to implement solution for high efficiency and high precision machining of the parts with varied curvature features is provided.展开更多
A design approach for online pre-compensation of three-axis cross-coupled contour errors with mismatched dynamics is proposed.In the context of cross-coupled contour control design,online pre-compensation of contour e...A design approach for online pre-compensation of three-axis cross-coupled contour errors with mismatched dynamics is proposed.In the context of cross-coupled contour control design,online pre-compensation of contour errors is commonly employed.However,establishing a specific relationship between contour errors is challenging for mismatched computer numerical control(CNC)systems.Therefore,the design of interpolation methods for mismatched systems remains crucial,as most existing systems struggle to be adjusted to match seamlessly.This study introduces an online pre-compensation scheme for cross-coupled contour errors in three-axis motion,which constitutes a compensation system for real-time correction of contour error estimation.The coupling control structure,based on a speed loop,comprises a proportion integration differentiation(PID)control feedback controller,a feedforward controller,and an online pre-compensation cross-coupled contour controller.The experimental results demonstrate that the proposed three-axis cross-coupled contour error pre-compensation scheme significantly enhances the contour accuracy compared to traditional cross-coupled control systems.Moreover,the proposed cross-coupled contour error pre-compensation controller exhibits superior contour performance over conventional cross-coupled controllers when tracking high-order curvature bending paths.展开更多
To meet the access demands of massive terminal users,the space-based Internet of Things(IoT)requires sufficient frequency resources for allocation.However,the frequency resources that are currently available have alre...To meet the access demands of massive terminal users,the space-based Internet of Things(IoT)requires sufficient frequency resources for allocation.However,the frequency resources that are currently available have already been allocated to a great extent.Furthermore,the utilization rate of the allocated frequency resources is low.To support massive user access under restricted frequency resources,this work proposes a scheme based on Doppler frequency offset(DFO)pre-compensation to enhance spectrum utilization efficiency.By calculating the relative motion between the satellite and the transmitting terminal,combined with the length and transmission rate of the message,the optimal compensation value of the Doppler frequency deviation is determined.The frequencyprotection interval is reduced.Simulation results show that the pre-compensation method can expand the user access volume by 90–400 times.Properly selecting the number of message splits and transmission rate to perform DFO pre-compensation calculations can increase user access by an additional 45%or more.This method improves the spectrum utilization efficiency and provides a solution to the challenge of access by a large number of users.展开更多
Because of the integration of long term evolution （LTE） technology and mobile satellite communication systems, uplink access technology for LTE-based geo-stationary earth orbit （GEO） satellite has become a popular...Because of the integration of long term evolution （LTE） technology and mobile satellite communication systems, uplink access technology for LTE-based geo-stationary earth orbit （GEO） satellite has become a popular research topic for satellite system. In order to solve the problem of unreasonable design for physical random access channel （PRACH） signal structure and reduce the effect of time uncertainty, this paper proposes a novel random access preamble based on time pre-compensation （TPC） for LTE-Satellite （LTE-S） system. In this scheme, by applying the method of non-linear least squares, the user terminal （UT） can use and based on the transmission delay the receiving power to estimate the communication round trip delay （RTD） of the beam center and the satellite, RTD can be compensated before transmission. Therefore, the preamble length and duration can be reduced without related to the maximum of RTD. In order to verify the performance of the scheme, the MATLAB is used to build a test system. The simulation results show that the proposed preamble satisfies the requirements of LTE-S system, and the better performance than previous researches is obtained.展开更多
For a repetitive command path, pre-compen- sating the contouring error by modifying the command path is practical. To obtain the pre-compensation value with better accuracy, this paper proposes the use of a back propa...For a repetitive command path, pre-compen- sating the contouring error by modifying the command path is practical. To obtain the pre-compensation value with better accuracy, this paper proposes the use of a back propagation neural network to extract the function of systematic contouring errors. Furthermore, by using the extracted function, the contouring error can be easily pre- compensated. The experiment results verify that the proposed compensation method can effectively reduce contouring errors.展开更多
We experimentally designed dispersion-managed repeaterless transmission systems with a pre-compensation and post-compensation technique using multi-channel-chirped fiber Bragg gratings. The repeaterless transmission l...We experimentally designed dispersion-managed repeaterless transmission systems with a pre-compensation and post-compensation technique using multi-channel-chirped fiber Bragg gratings. The repeaterless transmission link supports a single channel（1548.51 nm） with a 10 Gbps repeaterless transmission system over 300 km standard single-mode fiber（SSMF）. In the system design, two distributed Raman amplifiers（DRAs） were used to improve the signal level propagated along the 300 km SSMF. The co-propagating DRA provided 15 dB on–off gain and the counter-propagating produced 32 dB on–off gain at the signal wavelength. The experiment results show that the post-compensation configuration achieves an optimal performance with a bit error rate at 1 × 10-9.展开更多
Cam-lobe radial-piston hydraulic motors are widely used in large machinery due to their excellent capability to withstand high loading at low speed.However,the line contact between the roller and cam ring generates el...Cam-lobe radial-piston hydraulic motors are widely used in large machinery due to their excellent capability to withstand high loading at low speed.However,the line contact between the roller and cam ring generates elastic deformation of the cam ring under high loading,leading to obvious speed and torque pulsations and even the detrimental crawl problem of hydraulic motors.To address this issue,we propose a deformation pre-compensated optimization design approach to compensate for the cam ring deformation in advance,thereby eliminating the influence of cam ring deformation on the hydraulic motor’s pulsation.In this approach,the design process is divided into two steps:first,the overall profile of the cam ring is optimized based on the calculated elastic deformation;second,the local profile of cam ring is further optimized until the hydraulic motor’s pulsations no longer reduce.Finally,a case study is carried out to verify the effectiveness of this approach.The result indicates the pulsation rate of a deformation pre-compensated cam ring is 40%lower than that of an uncompensated one.This study offers an easy and feasible way to design an optimized cam ring profile for low pulsation hydraulic motors.展开更多
The integration of satellite communication network and cellular network has a great potential to enable ubiquitous connectivity in future communication networks.Among numerous related application scenarios,the direct ...The integration of satellite communication network and cellular network has a great potential to enable ubiquitous connectivity in future communication networks.Among numerous related application scenarios,the direct connection of mobile phone to satellite has attracted increasing attention.However,the spectrum scarcity in the sub-6 GHz band and low spectrum utilization prevents its popularity.To address these problem,in this paper,we propose a dynamic spectrum sharing method for satellite network and cellular network based on beam-hopping.Specifically,we first develop a centralized dynamic spectrum sharing architecture based on beam-hopping,and propose a delay pre-compensation scheme for beam hopping pattern.Then,an optimization problem is formulated to maximize the overall capacity of the integrated network,with considering the service requirements,the fairness between beam positions and mixed co-channel interference,etc.To solve this problem,a polling-based dynamic resource allocation algorithm is proposed.Simulation results confirm that the proposed algorithm can effectively reduce the serious cochannel interference between different beams or different systems,and improve the spectrum utilization rate as well as system capacity.展开更多
基金Supported by National Natural Science Foundation of China(Grant Nos.51575087,51205041)Science Fund for Creative Research Groups(Grant No.51321004)+1 种基金Basic Research Foundation of Key Laboratory of Liaoning Educational Committee,China(Grant No.LZ2014003)Research Project of Ministry of Education of China(Grant No.113018A)
文摘Parts with varied curvature features play increasingly critical roles in engineering, and are often machined under high-speed continuous-path running mode to ensure the machining efficiency. However, the continuous-path running trajectory error is significant during high-feed-speed machining, which seriously restricts the machining precision for such parts with varied curvature features. In order to reduce the continuous-path running trajectory error without sacrificing the machining efficiency, a pre-compensation method for the trajectory error is proposed. Based on the formation mechanism of the continuous-path running trajectory error analyzed, this error is estimated in advance by approximating the desired toolpath with spline curves. Then, an iterative error pre-compensation method is presented. By machining with the regenerated toolpath after pre-compensation instead of the uncompensated toolpath, the continuous-path running trajectory error can be effectively decreased without the reduction of the feed speed. To demonstrate the feasibility of the proposed pre-compensation method, a heart curve toolpath that possesses varied curvature features is employed. Experimental results indicate that compared with the uncompensated processing trajectory, the maximum and average machining errors for the pre-compensated processing trajectory are reduced by 67.19% and 82.30%, respectively. An easy to implement solution for high efficiency and high precision machining of the parts with varied curvature features is provided.
文摘A design approach for online pre-compensation of three-axis cross-coupled contour errors with mismatched dynamics is proposed.In the context of cross-coupled contour control design,online pre-compensation of contour errors is commonly employed.However,establishing a specific relationship between contour errors is challenging for mismatched computer numerical control(CNC)systems.Therefore,the design of interpolation methods for mismatched systems remains crucial,as most existing systems struggle to be adjusted to match seamlessly.This study introduces an online pre-compensation scheme for cross-coupled contour errors in three-axis motion,which constitutes a compensation system for real-time correction of contour error estimation.The coupling control structure,based on a speed loop,comprises a proportion integration differentiation(PID)control feedback controller,a feedforward controller,and an online pre-compensation cross-coupled contour controller.The experimental results demonstrate that the proposed three-axis cross-coupled contour error pre-compensation scheme significantly enhances the contour accuracy compared to traditional cross-coupled control systems.Moreover,the proposed cross-coupled contour error pre-compensation controller exhibits superior contour performance over conventional cross-coupled controllers when tracking high-order curvature bending paths.
基金Project supported by the Proximity Space Science,Technology and Industry Guidance Fund(No.LKJJ-2023022-01)。
文摘To meet the access demands of massive terminal users,the space-based Internet of Things(IoT)requires sufficient frequency resources for allocation.However,the frequency resources that are currently available have already been allocated to a great extent.Furthermore,the utilization rate of the allocated frequency resources is low.To support massive user access under restricted frequency resources,this work proposes a scheme based on Doppler frequency offset(DFO)pre-compensation to enhance spectrum utilization efficiency.By calculating the relative motion between the satellite and the transmitting terminal,combined with the length and transmission rate of the message,the optimal compensation value of the Doppler frequency deviation is determined.The frequencyprotection interval is reduced.Simulation results show that the pre-compensation method can expand the user access volume by 90–400 times.Properly selecting the number of message splits and transmission rate to perform DFO pre-compensation calculations can increase user access by an additional 45%or more.This method improves the spectrum utilization efficiency and provides a solution to the challenge of access by a large number of users.
基金sponsored by the Science and Technology on Information Transmission and Dissemination in Communication Networks Laboratory (ITD-U13007/KX132600014)the National Natural Science Foundation of China (91438114)the Fundamental Research Funds for the Central Universities (2014RC0202)
文摘Because of the integration of long term evolution （LTE） technology and mobile satellite communication systems, uplink access technology for LTE-based geo-stationary earth orbit （GEO） satellite has become a popular research topic for satellite system. In order to solve the problem of unreasonable design for physical random access channel （PRACH） signal structure and reduce the effect of time uncertainty, this paper proposes a novel random access preamble based on time pre-compensation （TPC） for LTE-Satellite （LTE-S） system. In this scheme, by applying the method of non-linear least squares, the user terminal （UT） can use and based on the transmission delay the receiving power to estimate the communication round trip delay （RTD） of the beam center and the satellite, RTD can be compensated before transmission. Therefore, the preamble length and duration can be reduced without related to the maximum of RTD. In order to verify the performance of the scheme, the MATLAB is used to build a test system. The simulation results show that the proposed preamble satisfies the requirements of LTE-S system, and the better performance than previous researches is obtained.
文摘For a repetitive command path, pre-compen- sating the contouring error by modifying the command path is practical. To obtain the pre-compensation value with better accuracy, this paper proposes the use of a back propagation neural network to extract the function of systematic contouring errors. Furthermore, by using the extracted function, the contouring error can be easily pre- compensated. The experiment results verify that the proposed compensation method can effectively reduce contouring errors.
基金supported by the Telekom Malaysia Berhad(TM)and TM Research & Development Sdn Bhd(RDTC/110782 and RDTC/140859)
文摘We experimentally designed dispersion-managed repeaterless transmission systems with a pre-compensation and post-compensation technique using multi-channel-chirped fiber Bragg gratings. The repeaterless transmission link supports a single channel（1548.51 nm） with a 10 Gbps repeaterless transmission system over 300 km standard single-mode fiber（SSMF）. In the system design, two distributed Raman amplifiers（DRAs） were used to improve the signal level propagated along the 300 km SSMF. The co-propagating DRA provided 15 dB on–off gain and the counter-propagating produced 32 dB on–off gain at the signal wavelength. The experiment results show that the post-compensation configuration achieves an optimal performance with a bit error rate at 1 × 10-9.
基金supported by the National Key R&D Program of China(No.2021YFB3400501)the National Science Foundation of China(Nos.52105070 and U21B2074)。
文摘Cam-lobe radial-piston hydraulic motors are widely used in large machinery due to their excellent capability to withstand high loading at low speed.However,the line contact between the roller and cam ring generates elastic deformation of the cam ring under high loading,leading to obvious speed and torque pulsations and even the detrimental crawl problem of hydraulic motors.To address this issue,we propose a deformation pre-compensated optimization design approach to compensate for the cam ring deformation in advance,thereby eliminating the influence of cam ring deformation on the hydraulic motor’s pulsation.In this approach,the design process is divided into two steps:first,the overall profile of the cam ring is optimized based on the calculated elastic deformation;second,the local profile of cam ring is further optimized until the hydraulic motor’s pulsations no longer reduce.Finally,a case study is carried out to verify the effectiveness of this approach.The result indicates the pulsation rate of a deformation pre-compensated cam ring is 40%lower than that of an uncompensated one.This study offers an easy and feasible way to design an optimized cam ring profile for low pulsation hydraulic motors.
基金supported in part by the National Key Research and Development Program of China under Grant 2018YFA0701601in part by the National Natural Science Foundation of China under Grant 61922049 and Grant 61941104in part by the Tsinghua University-China Mobile Communications Group Company Ltd.,Joint Institute.
文摘The integration of satellite communication network and cellular network has a great potential to enable ubiquitous connectivity in future communication networks.Among numerous related application scenarios,the direct connection of mobile phone to satellite has attracted increasing attention.However,the spectrum scarcity in the sub-6 GHz band and low spectrum utilization prevents its popularity.To address these problem,in this paper,we propose a dynamic spectrum sharing method for satellite network and cellular network based on beam-hopping.Specifically,we first develop a centralized dynamic spectrum sharing architecture based on beam-hopping,and propose a delay pre-compensation scheme for beam hopping pattern.Then,an optimization problem is formulated to maximize the overall capacity of the integrated network,with considering the service requirements,the fairness between beam positions and mixed co-channel interference,etc.To solve this problem,a polling-based dynamic resource allocation algorithm is proposed.Simulation results confirm that the proposed algorithm can effectively reduce the serious cochannel interference between different beams or different systems,and improve the spectrum utilization rate as well as system capacity.
