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Copyright of Journal of South China University of Technology (Natural Science Edition) is the property of South China University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Automotive Engineer (1674-6546) is the property of Auto Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Electric Drive for Locomotives is the property of Electric Drive for Locomotives Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Irrigation & Drainage is the property of Journal of Irrigation & Drainage Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Unmanned Aerial Vehicles (UAV) have widely been served as a new technology in agricultural aviation plant protection and pest control in China. However, it is highly demanded to improve the accuracy of UAV spraying pesticides and operational efficiency. In this study, a Variable Rate Application (VRA) of a centrifugal spraying system was designed for precise placement and timing of pesticide application in specific field conditions using the network Real-Time Kinematic (RTK) technology. STM32F103 single-chip microcomputer was used for the core controller. A serial port of controller was selected to obtain the global position system (GPS) information. A network modular Data Terminal Unit (DTU) was connected to realize the network RTK technology via the serial port of the controller. The control voltage was used to tailor the speeds of the centrifugal nozzle motor and peristaltic pump. A Pulse Width Modulation (PWM) was used to control the output voltage from the core controller to the armature of motors in this system. The speed of the centrifugal nozzle motor determined the output droplet size, while the speed of peristaltic pump determined the flow rate and amount of spray fog. The agricultural dataset before the system working was acquired using the airborne multispectral camera, ground object spectrometer, and handheld GPS. A prescription chart was also constructed using ArcGIS software. In the system working, the GPS modular was used to capture the location longitude and latitude data for the system to read and analyze. The system was always real-time searching the UAV geographical position during the spraying pesticides process using the GPS data, and then matching the position using the orthogonal grid. Meanwhile, the system was used to real-time tailor the changes in the duty cycle of output PWM, after matching the decision of the prescription map. The speeds of the centrifugal nozzle motor and the peristaltic pump were then to control the particle size and application amount of the UAV. The operation data was finally uploaded to the monitoring platform for real-time display and storage. Several spraying experiments were carried out in the research base of South China Agricultural University in Zengcheng City, Guangdong Province of China. The airborne spraying device was carried on the MG-1p plant protection UAV using a developed DJI Drone. The sampling points of droplets were set to match the planting density of crops, where the water-sensitive paper was used to collect the droplet data. After UAV operation, the water sensitive paper was collected into a plastic bag for later use. An hp4678 scanner was selected to map the collected water-sensitive paper after the experiment. A DepositScan software was utilized to analyze the water-sensitive paper in each sampling area after image acquisition. A detailed dataset was obtained, including the deposition amount, coverage density, and particle size of droplets. The data demonstrated that the accuracy of the device was within 0.6 m at the operating speed of 2 m/s. The application effect was finally stabilized within 2.2 m in the case of continuous operation. Particle size varied smoothly in the boundary area of prescription, as the rotating speed of the centrifugal nozzle increased. The findings can provide a sound basis for the improvement of variable application technology of plant protection UAV in precise agriculture. [ABSTRACT FROM AUTHOR]

【Objective】 This paper is to investigate experimentally the static spray characteristics of variable spray systems of centrifugal nozzles. 【Method】 A centrifugal nozzle variable spray test system was constructed by using a diaphragm pump, a high-precision turbine flowmeter, a solenoid valve and a centrifugal nozzle. Its static spray characteristics were studied for the nozzle flow rate in the range from 1.5 L/min to 13 000 r/min. For each nozzle flow rate, we measured the water droplet sizes and deposition distribution of the droplets using water-sensitive paper and droplet collection devices, respectively. 【Result】 With the increase in centrifugal nozzle flow rate, the size of droplets decreased. The deposition amount of fog droplets in the 0.5 m proximal to nozzle decreased first and then increased showing a double-peak patten, with the deposition amount increased in the second peak more than in the first peak. With the increase in the centrifugal nozzle flow rate, the peak value on the left side of the distribution center of the droplet deposition decreased, and the peak value on the left side skewed towards the droplet distribution center. The peak value on the right side remained unchanged, while the peak value on the right side moves away from the droplet distribution center. 【Conclusion】 The rotating speed of the centrifugal nozzle has a significant influence on sizes and deposition distribution of the water droplets. Reasonably controlling the droplet size to improve the uniformity of the droplet deposition distribution is a key to improving pesticide utilization and reducing its leaching to the environment.

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Due to its advantages of high positioning accuracy，small torque ripple and high torque density，fivephase hybrid stepping motor has been widely used. In order to further reduce its operation noise and improve the overall efficiency of the system，this paper proposes a space vector pulse width modulation（SVPWM） optimal control strategy of five-phase hybrid stepping motor which can suppress the third harmonic wave. In this paper，the decoupling control model of five-phase hybrid stepping motor considering mutual inductance is established. On this basis，SVPWM control strategy combining two adjacent large vectors and two medium vectors into a mixed voltage vector is adopted，and the corresponding dual⁃closed-loop control system of fivephase hybrid stepping motor is given. The mixed SVPWM algorithm proposed in this paper can effectively reduce the phase current ripple and harmonic content by using the large and medium vectors in the fundamental wave and the third harmonic coordinate system to suppress the third harmonic. Finally，an experimental platform based on FPGA is developed to compare the proposed strategy with the traditional hysteresis algorithm and the large vector SVPWM algorithm， and analyze the influence of the three algorithms on the phase current ripple and harmonic content，thus verifying the correctness and superiority of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Emasculation is closely associated with corn seed production, which directly affects the quality of corn seed. Mechanical emasculation with high efficiency and quality is taking the place of artificial emasculation, which is of low efficiency and poor quality. In China, mechanical emasculation is far behind developed countries, and the emasculation control system is just at the beginning stage, which restricts the development of the emasculation machines. In view of the above problems, this paper designed a set of emasculation control system, which completed adjustment of emasculation mechanism through the parallel four connecting rods driven by cylinder. In order to ensure the accuracy of the parameters, movement of four parallel connecting rods were analyzed. The hardware of the system mainly comprised a display screen, a control board and a control panel. The control board used ATmega128 chip as the control chip, used the 42GRU-9200TTL models (NPN type) photoelectric sensor to collect corn ear height, used MAX4372T chip to collect drive voltage and current, used Power MOSFET IRF4905 to drive proportional valve and used MAX232 chip to complete serial communication. The screen was used to display and set the system parameters. The control panel was used to complete the switch between manual mode and automatic mode and control the height of emasculation mechanism manually by button operation in the manual mode. In automatic mode, the system got the height of ear of corn by photoelectric sensors. The system's control algorithm was that repeatedly reading all the photoelectric sensor signals at a certain time interval, and then storing the number of occluded of up and down photoelectric sensor for the x set of data, and then making the lifting decision of emasculation mechanism according to the first set of data stored previously, and rising the emasculation mechanism only when continuous Z times lifting decision results is rising. Cylinder's movement speed was determined by the opening of proportional valve, and the PWM duty which is directly proportional to proportional electromagnet finally decides the velocity of cylinder. The system controlled the velocity of cylinder by exporting a certain duty PWM signal to control the opening of proportional valve. The system controlled the movement time of cylinder by outputting PWM signal or not, to control the closing and opening of proportional valve. The final purpose of the system is to control the movement of the emasculation mechanism. After analyzing the movement of four parallel connecting rods, combined with the vehicle operation speed and the characteristics of the hydraulic system, the parameters of the system can be obtained by calculating, and were displayed on screen. Through field tests, we found that when the emasculation machine with the emasculation control system designed in this paper rose, the motion time, displacement and maximum speed of cylinder was 150 ms, 0.007 m, and 0.1 m/s, respectively. When the emasculation mechanism went down, the motion time, displacement and maximum speed of cylinder was 180 ms, 0.007 m, and 0.15 m/s, respectively. The testing results showed that the actual movement of the hydraulic cylinder can meet the design requirements and the parameters were reasonably set, and the efficiency and accuracy can meet the castration emasculation operation requirements. [ABSTRACT FROM AUTHOR]

The neutral-point-clamped (NPC) three-level inverter is used more and more in the grid-connected renewable energy generation system. In order to achieve the lower current harmonic, an LCL filter is also widely utilized due to its superior filtering performance. The LCL filter has the advantages of a high-frequency stopband with good performance and low-frequency compensation ability, but the parameters of LCL are hard to design. Especially the different modulation methods between three-level and two-level inverters, and the different ripple current, all these factors lead to a more difficult design of the parameters. The key of LCL design is the arm-side inductance design, due to the fact that an improper design of arm-side inductance will conduct to a completely different ripple current of the inverter, power loss of the filter components, and larger stress switch stress, thus resulting in poor performance of output current. Moreover, the control of the inverter will be affected. In the design of arm-side inductance, the most important thing is to strike a maximum ripple current. On the basis of establishing the mathematical model of a three-level grid-connected inverter, this paper takes output current control under the unity power factor into consideration, combining with the characters of space vector pulse width modulation (SVPWM) to reach the arm-side ripple current's variation regularity. The maximum ripple current could be obtained at the peak of a grid side current based on this research. There will always be three latest vectors for the synthesis of the reference vector in accordance with the principle of the Nearest Three Vectors (NTV). In addition, seven-segment modulation on the action time allocation of each vector was applied. Considering the worst case, the value of max ripple current can be obtained when the middle vector was neglected , coupled with the engineering demand for ripple current, and upper limits of arm-side inductance can be given. The lower limit of arm-side inductance can be obtained by taking the tracking requirements of grid-side current transient into account, and then the design range of arm side inductance was given. After that, with regard to the effect of LCL filter resonance and the limitation of reactive power in the system, the parameters of the filter capacitor were determined. And the grid-side inductance can be obtained according to the demand of ripple current attenuation of the grid-side current. Synthetically considering the demand for system stability and power loss, the damping resistor was designed after the LCL filter parameters were determined. At last, a simulation was performed at a 30 kW prototype in which the output current was 60A, and in contrast an experimentation was conducted at a 15 kW prototype, the output current was 30A proportionally. Simulation and experimental results validated the correctness of the ripple current in the paper. The ripple current had been well limited to the requirements of the project in the role of the arm-side inductance. At the same time, a good attenuation of ripple current had been obtained by the help of the filter capacitor and grid side inductance, leading to a high quality of output current which was displayed in both simulation and experimentation. The method of the parameter design of LCL which was employed in the paper was much more reasonable, and has a high value in practical applications. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In many high-power AC drives, with the increase of the switching frequency of the converter, the generated harmonic and electromagnetic interference(EMI)noise are getting higher and higher. Aiming at the serious problems of harmonics and EMI noise of three-level neutral-point-clamped(NPC)high-frequency converters, based on the space vector pulse width modulation(SVPWM)strategy, a random SVPWM method based on Markov chain was proposed. In this method, the random number generated by Markov chain could be applied to SVPWM strategy, so that the actual frequency change could be more randomly and evenly distributed on both sides of the theoretical switching frequency, with the output voltage harmonic noise of the actual system with also dispersed in a wide frequency band, and the EMI noise of the converter was also reduced. The simulation results show that the modulation strategy proposed in this paper has a significant improvement in the harmonic distribution compared with the traditional SVPWM strategy, and the conducted EMI noise is also reduced from 140 dB/μV to 120 dB/μV. [ABSTRACT FROM AUTHOR]

Variable spray technology is an important means to improve pesticide utilization rate and save pesticide. Fruit tree is a kind of three-dimensional space, and the densities of branches and leaves in the canopy of fruit trees at different locations are different at the same time. The ideal state of spray is to adjust the amount of spray according to local characteristics, so as to realize the application of the spray on the canopy of fruit trees as required and improve the utilization rate of pesticide. In order to achieve the effect of reducing the dosage and increasing the efficiency of pesticide application, a variable spray control system was developed and the methods for computing leaf area density parameter and pulse width modulation(PWM)'s duty ratio of actuators were proposed. As the dosage parameter, the leaf area density was derived based on the point cloud density detected by LiDAR sensor on the upper computer. Then PWM's duty ratio was calculated based on the leaf area density and sent to the slave computer-PLC in real time. The communication between upper and slave computer was carried out through RS485 standard. So the spray flow of each nozzle was controlled by the switching frequency of the solenoid valve with PWM's duty ratio signal. Key parameters were obtained by the test including the net size of spray unit, delay time of the system and the function relationship between the PWM's duty ratio and the spray flow of nozzle. The test results showed that there was a linear relationship between the PWM's duty ratio and the spray flow of nozzle under the pressure of 0.2, 0.3 and 0.4 MPa, and the linear goodness of fit were all above 0.98. Finally, the effectiveness of the variable spray system was verified by the spray test. The test results showed that the minimum number of droplets per unit area (cm²) on the water-sensitive paper was 35 drops at the sampling point, which was higher than the 25 drops defined by the common method for the spray amplitude of aerosol in the air supply spray. Under 39.9% of the canopy ratio between the target canopy area and the whole area, the variable spraying mode saved 71.96% of the pesticide dosage compared with the continuous spraying mode, and 29.72% compared with the target spraying mode, achieving the dose reduction effect. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A false target deceptive jamming method for countering UWB-SAR is proposed in this paper, which is based on dechirp processing to intercepted UWB-SAR signal, Doppler frequency modulation in phase domain and inverse dechirp to jamming signal. The jammer receiver quadrature downward converts and dechirps the intercepted UWB-SAR signal using an LFM oscillator, which could reduce the bandwidth and sample rate. And the jammer utilizes the Doppler frequency phase and back scattering coefficient template to modulate the intercepted narrowband signal. Then, the jammer uses LFM signal local oscillator to upward convert the jamming signal in order to recover the bandwidth of the jamming signal. The effects of parameter errors on the imaging position and resolution of false target in SAR image are also analyzed. Theoretical analysis and simulation indicated that the jamming signal proposed in this paper could produce a false target false. Even though the position of false target is offset and the resolution is reduce introduced by the reconnoitered parameters error, the jamming signal generated by the proposed method could still get a relatively clear image. Therefore, the proposed jamming signal generation method provides a feasible reference for countering UWB-SAR. [ABSTRACT FROM AUTHOR]

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Agricultural flexible chassis (FC) is a kind of in-wheel motor driving electric vehicle applied for greenhouse. The FC is composed of 4 identical off-centered shaft mechanisms, which can be controlled independently. Through this kind of mechanism, the FC can achieve various motion types. However, it is difficult to maintain the linkage relationship between the 2 front off-centered shaft mechanisms when the FC is in front wheel steering motion, and hard to accomplish smoothly turning. In order to solve this problem, a coupling control strategy for linkage motion was proposed in this study. Firstly, the contour error of the 2 wheel steering angle was deduced based on the Ackermann steering geometry and the cross-coupling control principle. To reduce the contour error during steering, a fuzzy PID control algorithm was designed, which could realize parameters self-tuning. As the electromagnetic friction lock was controlled by pulse width modulation (PWM) signal, the duty cycle of the PWM signal had to be adjusted according to turning situation. Thus, a fuzzy logic method was then introduced to regulate the duty cycle. Namely, the PWM signal duty cycle can be in line with the steering wheel signal size and its change rate, and the motion of the electromagnetic friction lock can match the steering speed of the off-center shaft mechanism. In this way, the coupling control of the 2 front off-centered shaft mechanisms can be achieved. The control strategy was then verified through simulation based on MATLAB/Simulink. To further verify the effectiveness of the control strategy, the control program was loaded into the steering system hardware, and tests were carried out on hard surface road. According to the traditional vehicle steering test methods, step steering test, snake steering test and random steering test were conducted. The effects of front wheel steering under the steering angle allocation control method were compared with coupling control strategy. The simulation results demonstrated that the proposed control strategy was effective and feasible. The test results on hard surface road showed that the FC had a fast steering response in step steering test. The response time of step steering was 0.8s and overshoot was 1.3° under coupling control method during front wheel steering of the FC. The overshoot under allocation control was larger than coupling control and its fluctuation was notable. From the results of the snake steering and random steering, it was obviously that the steering angles of the left and the right front wheels had good tracking performance for their target angles, respectively. The opening and closing of electromagnetic friction lock can match the steering motion of the electric wheel well. The maximum and average following errors of 3 steering modes were less than those under the allocation control method. The maximum and average contour errors of the linkage motion were 1.2° and 0.6° for step steering, 1.1° and 0.6° for snake steering, as well as 1.0° and 0.5° for random steering, respectively. All these errors were also smaller than the allocation control. Under the coupling control, the maximum steering error between simulation and test was 2.2°, and the contour error trend of them was consistent. The simulation model was reasonable and effective. The contour errors of the allocation control in these 3 kinds of tests had more fluctuations and larger range of fluctuations than coupling control. The steering performance under coupling control strategy was obviously better than the allocation control method. The steering angles of the 2 front wheels had maintained Ackerman steering geometry well. The coupling linkage control strategy proposed in this paper has good effectiveness and feasibility. This research can provide references for steering control or other applications of the FC. [ABSTRACT FROM AUTHOR]

The reliability of the motor has been the focus of research in related fields. The negative effects of PWM control technology further increases the complexity and difficulty of the motor reliability analysis. Currently there are no systematic analyses on the influences and failure mechanism caused by PWM pulses. Winding insulation and bearing are two vulnerable parts in motor. In the paper, firstly the failure mechanism caused by PWM pulses is expounded, and some typical results are introduced in winding insulation and bearing reliability, and the research status of the overall motor life prediction techniques is summarized. Finally the unresolved problems is dicussed, and the possible domains in future are also analyzed. [ABSTRACT FROM AUTHOR]

In order to design a low-cost, small-size and light-weight brushless DC motor (BLDCM) controller, the paper introduces the advantages of BLDCM and discusses related position detecting methods, compares the control methods of BLDCM with position sensors with that without position sensors, and analyzes the operation status of BLDCM controller. The paper designs a sensorless BLDCM controller based on back-EMF, and employs a double-closed-loop speed regulating system to get good dynamic performance. Besides, based on the excellent performance of MCU in interruption processing, the designed controllr could achieve real-time current monitoring and fast over-current protection. The paper also designs a communication protocol, on the basis of RS232, to strengthen the communication stability between PC and motor controller and to monitor the status of speed regulating system in real time. Finally, experiment is designed and cnried out to validate the proposed system. [ABSTRACT FROM AUTHOR]

In this paper a Novel Direct Torque Control (DTC) algorithm for Open End Winding Induction Motor (OEWIM) drive is proposed and simulated. This algorithm gives simple generation of the reference vector for the stator voltage with constant inverter switching frequency. Compared to the other SVPWM algorithm based DTC methods, this algorithm is very simple and has very less mathematical operations, and can be implemented on most existing digital drive controllers. In this new controller technique, torque and stator flux errors are used together with the stator flux angular frequency to generate a reference voltage vector. Simulated results of the novel system are presented and discussed, which shows the simplicity of the algorithm. [ABSTRACT FROM AUTHOR]

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Electromagnetic friction lock is an important part of agricultural flexible chassis. When it is closed, flexible chassis will be driven forward, and will steer when opened. In engineering practice, flexible chassis needs to steer while advancing. Therefore, there is conflict between the opening and the closing of electromagnetic friction lock when the 2 motions need to be carried out at the same time. In order to solve this problem, a method based on pulse width modulation (PWM) technology was proposed to control the opening and the closing in this paper. The opening was achieved during low level of PWM wave, while the closing was achieved during high level of PWM wave. In this way, flexible chassis can be driven forward during steering. Further, some experiments were conducted to investigate the influences of PWM frequency and duty cycle on driving and steering performance of flexible chassis. Firstly, based on off-centered steering shaft test bench, two-factor experiments were performed to study the effects of frequency and duty cycle on pulse tightening torque, using a traction device which was composed of a lever and a force sensor. Then tightening torque was calculated from force sensor measurement and arm length value. Secondly, for the purpose of examining the characteristics of time-sharing steering related with the influence of frequency, duty cycle and initial speed of electric wheel, a quadratic orthogonal regression experiment was conducted on off-centered steering shaft test bench. In this test, steering motion was simulated by controlling the speed of horizontal turntable of test bench and electric wheel. Average steering angular velocity was taken as the evaluating indicator of steering characteristics, and it can be attained by measuring the steering time due to the same target angle of steering. Afterwards, results of two-factor experiment showed that frequency, duty cycle and their interaction had highly significant influences on tightening torque (P<0.01). In the process of rotation, the curve of tightening torque showed a pulse change, and the rotation angle of steering arm displayed a step-like rise. When frequency was 4-24 Hz and duty cycle was 20%-80%, the tightening torque of off-centered steering shaft varied from 6.822 to 40.046 N·m. The tightening torque declined as frequency increased when duty cycle was 20%-80% except a few duty cycles. Meanwhile, for the frequency ranging from 4 to 24 Hz, tightening torque rose with the increasing of duty cycle. Then regression analysis was carried out according to the results and a regression model was presented. Results of quadratic orthogonal regression experiment illustrated that the average steering angular velocity was remarkably influenced by the PWM frequency, duty cycle and their interaction as well as the initial rotation speed of in-wheel motor (IWM) (P<0.05). With the increment of duty cycle and the initial speed of IWM, the steering average angular velocity decreased rapidly but slowly increased with the increasing of frequency. When the frequency was 4-24 Hz and the duty cycle was 20%-80%, and the initial speed of IWM was 30-120 r/min, the average steering angular velocity varied from 0 to 0.514 rad/s. Therefore, through changing the PWM frequency, duty cycle and the initial speed of IWM, the process of pulse-driven and time-sharing steering for flexible chassis is able to be well achieved, and these results can provide a basis for cooperative control of flexible chassis [ABSTRACT FROM AUTHOR]

Due to the nonlinearity of the digital pulse width modulation ( PWM ) generators in digital class D power amplifiers, this paper proposed an improved nonlinear error precorrection method for digital PWM generators. The proposed method took advantage of the characteristics of Σ-Λ modulators to modify the correction factor expression of the original method. Phis method not only can correct the nonlinear error produced by the digital PWM generator, hut also can solve the original method’s problem that the energy of the correction factors adding to the Σ-Λ modulator is too big to cause the integrator outputs saturate and oscillate, so it can degrade the performance of the power amplifier system. The experimental results indicate that the energy of the correction factors calculated from this method is far less than that calculated from the original nonlinear error precorrection method and that the proposed method can basically eliminate the nonlinear error produced by the digital PWM generator. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Guangdong University of Technology is the property of Journal of Guangdong University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Variable spray technology is an important means to improve pesticide utilization rate and save pesticide. Fruit tree is a kind of three-dimensional space, and the densities of branches and leaves in the canopy of fruit trees at different locations are different at the same time. The ideal state of spray is to adjust the amount of spray according to local characteristics, so as to realize the application of the spray on the canopy of fruit trees as required and improve the utilization rate of pesticide. In order to achieve the effect of reducing the dosage and increasing the efficiency of pesticide application, a variable spray control system was developed and the methods for computing leaf area density parameter and pulse width modulation(PWM)'s duty ratio of actuators were proposed. As the dosage parameter, the leaf area density was derived based on the point cloud density detected by LiDAR sensor on the upper computer. Then PWM's duty ratio was calculated based on the leaf area density and sent to the slave computer-PLC in real time. The communication between upper and slave computer was carried out through RS485 standard. So the spray flow of each nozzle was controlled by the switching frequency of the solenoid valve with PWM's duty ratio signal. Key parameters were obtained by the test including the net size of spray unit, delay time of the system and the function relationship between the PWM's duty ratio and the spray flow of nozzle. The test results showed that there was a linear relationship between the PWM's duty ratio and the spray flow of nozzle under the pressure of 0.2, 0.3 and 0.4 MPa, and the linear goodness of fit were all above 0.98. Finally, the effectiveness of the variable spray system was verified by the spray test. The test results showed that the minimum number of droplets per unit area (cm2) on the water-sensitive paper was 35 drops at the sampling point, which was higher than the 25 drops defined by the common method for the spray amplitude of aerosol in the air supply spray. Under 39.9% of the canopy ratio between the target canopy area and the whole area, the variable spraying mode saved 71.96% of the pesticide dosage compared with the continuous spraying mode, and 29.72% compared with the target spraying mode, achieving the dose reduction effect.

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)