气动下压式高速取投苗装置与吊杯时空匹配关系研究

为探索一种能实现高速取苗后无停顿快速投苗、同步接苗技术方案,分析气动下压式高速取投苗装置高速取苗后不停顿快速投苗4个阶段运动过程,得到穴盘苗运动时间。采用高速摄像机对自制高速取投苗装置无停顿快速投苗过程进行拍摄,通过PCC软件进行捕捉分析和计算,分析了穴盘苗在无停顿抛投过程中位移和时间关系。经同步接苗极限分析和交集运算得不同取苗频率吊杯同步接苗提前相位角范围,获得了高速取投苗装置高速取苗、无停顿快速投苗与吊杯同步接苗时空匹配关系。在高速移栽样机上开展吊杯同步接苗试验,试验结果表明,当取苗频率为180株/min时,吊杯同步接苗成功率为96.4%。研究结果为高速取投苗装置与吊杯时空匹配关系提供基础数据。

蔬菜移栽机气动下压式高速取苗装置设计与试验

目前,蔬菜移栽机取苗机构单行取苗频率为40~90株/min,取苗频率低已成为蔬菜高速移栽(≥90株/min)技术及装备的发展瓶颈。为实现高速取苗作业,设计了一种气动下压式高速取苗装置及配套组合式穴盘,通过"有序供盘、连续送苗、气动下压取苗、自由投苗"等作业工序,可实现120株/min的高速取苗作业。建立了取苗过程钵苗力学模型,对气动取苗机构取苗单体布置形式、取苗气缸工作压力、顶苗器运动轨迹等进行分析和计算,优化顶苗器U型末端结构,设计并构建高速取苗时序控制系统。以60 d苗龄辣椒苗为试验对象,在气缸工作压力为0.26 MPa、取苗频率为120株/min条件下,以取苗成功率、基质破损率和茎叶损伤率为取苗效果评价指标进行了取苗试验。试验表明:取苗成功率平均值为100%,基质破碎率平均值为22.46%,茎叶损伤率平均值为3.54%,能够满足蔬菜高速移栽的取苗作业要求。

气动下压式高速移栽机自动控制系统设计与试验

针对气动下压式高速移栽机有序供盘和高速取苗作业自动控制需求,本文基于Arduino微控制器设计移栽机自动控制系统。该系统包括苗盘位移监测、有序供盘、高速取苗等任务模块,以苗盘位置和苗盘位移为主要控制条件,根据供盘速度送盘速度、高速取苗间隔苗盘位移等参数匹配要求确定供盘速度和取苗间隔控制方法,建立有序供盘、高速取苗两个有限状态机,并基于动态时间片轮询算法设计控制流程,实现有序供盘、高速取苗作业过程自动控制。以供盘位置准确度和取苗位置准确度为指标开展控制系统运行准确性试验,结果表明,高速取苗时(90~150株/min),供盘位置最大相对误差1.27%,取苗位置最大相对误差12.85%,第2~6时序取苗位置最大累积相对误差分别为11.85%、5.63%、4.25%、1.94%和2.44%,均在允许误差范围内,满足作业要求。以供盘成功率、取投苗成功率为指标开展移栽性能试验,试验结果表明,高速作业时自动控制系统运行正常、性能可靠,供盘送盘有效衔接、送盘取苗精准配合,供盘成功率、取苗成功率为100%,投苗成功率不小于94.44%,实现了气动下压式高速移栽机有序供盘、高速取苗过程自动化作业。

Effects of atmospheric pressure fluctuations on hill-side coal fires and surface anomalies

This paper presents numerical studies on the effects of atmospheric pressure fluctuations on hill-side coal fires and their surface anomalies. Based on the single-particle reaction–diffusion model, a formula to estimate oxygen consumption rate at high temperature controlled by oxygen transport is proposed.Daily fluctuant atmospheric pressure was imposed on boundaries, including the abandoned gallery and cracks. Simulated results show that the effects of atmospheric pressure fluctuations on coal fires and surface anomalies depend on two factors: the fluctuant amplitude and the pressure difference between inlet(s) and outlet(s) of the air ventilation system. If the pressure difference is close to the fluctuant amplitude, atmospheric pressure fluctuations greatly enhance gas flow motion and temperatures of the combustion zone and outtake(s). If the pressure difference is much larger than the fluctuant amplitude, atmospheric pressure fluctuations exert no impact on underground coal fires and surface anomalies.

A new design of foaming agent mixing device for a pneumatic foaming system used for mine dust suppression

To overcome the drawbacks of the conventional foam technology used for dust suppression,including large pressure loss,high water pressure and low driving pressure,a new pneumatic foaming system is introduced.Then an original design of foaming agent mixing device is proposed,and its performance is investigated and evaluated under different pressure compensations.Experimental results show that the maximum absorption amount increases by 2.9-6.7 times at a pressure compensation of 0.04-0.2 MPa compared with no pressure compensation.The pressure loss and pressure fluctuation both reduce significantly with increasing pressure compensation.The critical outlet pressure increases by30.4-240%.Field application indicates that the proposed mixing device ensures the reliable addition of foaming agent used for foam dust suppression.The effect of foam on dust suppression is remarkable,and the economic cost of foam is low.Therefore,there is reason to believe that the new mixing device will greatly promote foam technology to be widely used for suppressing dust in underground coal mines.

OWC air chamber performance prediction under impulse turbine damping effects

Oscillating water columns(OWCs)are most widely used in coastal wave energy conversion.The air duct opens into the atmosphere through the air turbine,which is the power take-off device,and this results in a pressure drop across the air chamber.However,because of the complex configure of the impulse turbine and its high rotation speed,it is difficult to install it in the experimental simulator and numerical model.Therefore,the turbine damping effects on the operation of the OWC air chamber are induced to predict its performance more accurately.Orifice plates are used as a substitute for the impulse turbine as it generates a similar pressure drop and power output;the experimental and numerical pressure drops and output powers are compared.A 3D numerical wave tank based on the two-phase VOF model is established using the commercial CFD code Fluent,which can predict air flow and pressure variations in the chamber and duct.Water surface elevations,air flow velocity and pressure variation inside the chamber with the orifice plate are studied numerically,and validated by the corresponding experimental data.The air chamber of the Yongsoo OWC pilot plant is used as the engineering project case.The operating performance of the air chamber installed with a 0.428D orifice plate as the substitute for the designed impulse turbine is computed and analyzed.It is found that the turbine damping effects will cause around 30%reduction in the peak values of the pneumatic energy output of the OWC air chamber in the resonant wave domain.