| Bolt is an important part of support system of coal mine roadway.At present,most coal mines use bolt support system to support coal mine roadway.However,due to the strong masking of bolt support,the disturbance of excavation of shearer and roadheader,harsh environment and erosion of groundwater on bolt support,the increase of the axial force of bolt in bolt support system causes the failure of coal mine roadway support,leading to roof fall accidents in coal mine roadways from time to time,resulting in serious economic and casualties of coal miners.The change of the bolt's axial force is an important index to measure the working conditions of bolts.Real-time detection and monitoring of the change of the axial force of bolts can timely grasp and predict whether the prestressing force corresponding to the bolts is relaxed or not,and whether the rock mass of coal mine roadway is stable and safe plays an important role.Research on a sensor which can quickly and conveniently detect the change of the bolt's axial force is of great economic and scientific value for the detection of the bolt's axial force.At present,the devices used in coal mines to detect the axial force of bolts can be divided into the following two categories: one needs to be installed between fastening nuts and ball cushions,which increases the cost of bolt supporting materials and reduces the effective anchorage length of bolts;the other needs to install strain gauges or optical fibers on the bolts,which will lead to grooving or drilling and weaken the strength of bolts,while a large number ofinstallation increases the cost of bolt support.On the basis of summarizing the existing results of bolt detection devices,aiming at the shortcomings of the above bolt detection devices,this paper proposes that the combination of amorphous alloy strip piezomagnetic effect and electromagnetic induction can be effectively applied to the bolt axial force detection.A piezomagnetic bolt axial force sensor is designed,and the output value of the induction coil of the sensor is used to detect the bolt axial force.Firstly,the finite element analysis of the bolt tail thread connection part is made,and the rule that the stress state of the bolt fastening nut surface can be used to feedback the change of the bolt axial force is determined;secondly,the structure of the piezomagnetic bolt axial force sensor and the parameters of the key components are determined,the magnetic circuit equation of the sensor and the output characteristic equation of the sensor are analyzed;once again the sensor is established.The magnetic field simulation model analyzed the influence of air gap size,excitation voltage amplitude and excitation frequency on the magnetic induction intensity of the output coil of the sensor,and determined that the sensitivity of the sensor could be improved by adhering amorphous alloy ribbon to the surface of the fastening nut.Finally,a system platform was built to test the static characteristics of the sensor,and the air gap size was analyzed from several indicators of the static characteristics of the sensor.The static calibration test of the sensor under the conditions of 0 mm air gap,400 mv excitation voltage and 10 KHz excitation frequency shows that the sensitivity of the sensor is-0.2151 mv/KN under loading,0.2189mv/KN under unloading,8.826% linearity and 1.67% hysteresis error.It basically meets the requirement of detecting the axial force of bolt under mine. |
PDF Full Text Request