Fault Diagnosis Research on Impact System of Hydraulic Rock Drill Based on Internal Mechanism Testing Method

In the production andmanufacturing process of hydraulic rock drill, there are small impact energy and low impact frequency, and a fault diagnosis method based on the internal mechanism testing and testing of the hydraulic rock drill is proposed. *is method is used to test the change law of hydraulic oil in the rock drill, by retaining the test holes on the cylinder body and other important components of the hydraulic rock drill. At the same time, the mathematical method is used to deal with the test curve, and the influence of pressure pulsation characteristics of the front and rear chambers of the impact piston and the left and right valve chambers of the reversing valve on the impact performance of the rock drill is analyzed. Based on Newton’s law, the model of the impact piston and reversing valve is established. According to the velocity and other parameters of the impact piston, the size of the impact piston switch point is calculated. *e coupling between the movement of the impact piston and the movement of the reversing valve is analyzed according to the model established. Comparing the results of the experimental data, the correctness of the fault diagnosis analysis method and model is verified. *e effect of the fault rock drill and the improved model is compared, and the theoretical basis is provided for the fault diagnosis of the rock drill and the design of a new type of rock drill.


Introduction
At present, hydraulic rock drill is widely used in mining, tunneling, and building industries.It is the core component of hydraulic drill.Its inner channel is complicated and interlaced, which brings great difficulty to the performance testing of the rock drill in the production and manufacturing process [1].
e main testing methods of the rock drill are stress wave method, photoelectric displacement method, and highspeed photography method.
e stress wave method is used to test the transmission effect of stress wave in the drill rod, and the impact energy of the hydraulic rock drill can be calculated by the stress wave test.
e photoelectric displacement method is used to paste the black and white light rod in the tail of the piston, as far as possible without changing the piston mass.e photoelectric displacement sensor is used to detect the black and white marks on the light rod.e movement law of the piston is obtained by changing the differential method, and the high-speed photography method uses the high-speed camera to shoot the tail of the piston directly and to analyze the movement law of the piston by the slow replay.e aforementioned methods focus on testing and researching the impact of piston movement and energy generation but ignore the test and analysis of the internal mechanism [2][3][4][5].
Taking the hydraulic drill with no constant-pressurized chamber as an example, through the test and analysis of the coupling between the internal impact piston and the reversing valve of the rock drill, a testing method which can be applied to the manufacturing process of the rock drill can be studied, which can provide a theoretical basis for the fault diagnosis of the rock drill and the design of a new type of rock drill.

Impact Principle of Hydraulic Rock Drill
e drilling principle of the hydraulic rock drill is shown in Figure 1. e impact piston, the damping piston, and the shank are inside the hydraulic rock drill.
e shank is connected with the drill rod through the thread, and the bit is connected to the other end of the drill rod through the thread.
In the drilling process of the rock drill, the impact piston impacts the shank to break the rock.e impact piston strikes the shank to produce the stress wave, and the stress wave is transmitted to the rock through multiple transmission, and then, the rock is broken.e re ected wave is absorbed and utilized by the damping piston [6].e impact mechanism of the hydraulic rock drill is mainly composed of cylinder body, impact piston, reversing valve, and high pressure accumulator [7].
e impact piston and the reversing valve are connected through the inner channel in the cylinder, moving under the action of hydraulic oil.e coupling between the impact piston and the reversing valve is the key factor of the working performance of the hydraulic rock drill.e structure principle is shown in Figure 2.
e impact piston movement of the hydraulic rock drill is divided into three processes: return, stroke, and impact, and the reversing valve makes a switch of direction in time with the impact piston in the three movement processes [8].But there are many key points in the three processes.e whole cycle can be divided into more than 30 movement states.In order to increase the operability of the research, the movement state is simpli ed into 8 states:

State 1:
e impact piston returns acceleration; the reversing valve is stationary.e cylinder body front chamber is at high pressure, and the rear chamber and left-right valve chambers are at low pressure.State 2: e impact piston returns acceleration; the reversing valve starts reversing.e cylinder body front chamber and right valve chambers are at high pressure, and the rear chamber and left valve chamber are at low pressure.State 3: e impact piston return trip starts; the reversing valve continues to reverse.e cylinder body front-rear chambers and left-right valve chambers are at the pressure switch point.State 4: e reversing valve completes reversing; the impact piston slows down to stop.e cylinder body rear chamber is at high pressure, and the front chamber and left-right valve chambers are at low pressure.State 5: e impact piston strokes; the reversing valve is stationary.e cylinder body rear chamber is at high pressure, and the front chamber and left-right valve chambers are at low pressure.State 6: e impact piston strokes; the reversing valve starts reversing.e cylinder body rear chamber and left valve chamber are at high pressure, and the front chamber and right valve chamber are at low pressure.State 7: e impact piston impacts the shank; the reversing valve continues to reverse.e cylinder body front-rear chambers and left-right valve chambers are at the pressure switch point.State 8: e impact piston returns acceleration; the reversing valve stops. is state is the same as state 1 and enters the second movement cycle.

Test System Design.
e experimental platform is designed to test the rock drill, and the pumping station 2 Shock and Vibration supplies fuel to the propulsion cylinder, the punching cylinder, and the hydraulic rock drill.e rock drill is installed on the experimental bench, which is moved by the propulsion cylinder to propel the rock drill.e rock drill is tightly pressed by the drill rod, and the punching cylinder can adjust the pressure to simulate the rock with di erent hardness.Some sensors are connected to the rock drill.e voltage signal is ampli ed by a signal ampli er.ese sensors are collected and transmitted to the computer by the data acquisition system [9].e test system is shown in Figure 3.

Test Point of Sensor Design.
According to the principle and state analysis of the hydraulic rock drill, it can be seen that the pressures in the front-rear chambers and the leftright valve chambers are the key to the impact process of the rock drill. is test will focus on the front-rear chambers and the left-right valve chambers of the rock drill so as to obtain the performance of new rock drill [10][11][12].
Design the pressure test point of the front-rear chambers; the hole diameter is not too large to increase the volume of the front and rear chambers of the cylinder body.e throughhole connection of Φ 2 mm can be selected, and the threaded holes installed by the sensor are reserved on the surface.Design the pressure test point of the reversing valve, drill the threaded hole in the center of the left and right valve cover, and install the sensor directly on the cover of the reversing valve.
e overall installations are shown in Figure 4.

Experimental Analysis
4.1.Parameter Setting.e experimental equipment is connected, and the hydraulic pump station is set up to set the propulsion pressure, in ow pressure of impact, no-load damping pressure, and other experimental parameters, as shown in Table 1.

Data Analysis.
In the experiment, four groups of data were tested, namely, the front-rear chambers of the piston and the left-right valve chambers of the reversing valve [13,14].e four sets of data were collected at the same time, as shown in Figure 5.  Shock and Vibration e characteristics of test curves are mainly analyzed from the following aspects.

Impact Point.
In the movement state analyzed earlier, the impact piston impacts the shank in state 7, and the impact time should be re ected in the curve.Before the impact, the rear chamber should be at high pressure to push the piston forward, the pressure of the rear chamber descends suddenly to 13 MPa at 108 ms, and then the pressure rises to 30 MPa. is phenomenon indicates that the impact piston impacts the shank forward (the pressure decreases) and produces the rebound (the pressure rises), and the position of the impact point is judged as shown in Figure 5.

e Change Law of Pressure in Front-Rear Chambers.
After the impact point, the pressure of the chamber continues to rise, and the impact piston has the rebound velocity after the impact is completed.To push the piston to carry out the return movement, the best conditions are reducing the rear chamber pressure to 0 MPa and increasing the front chamber pressure rapidly.

e Change Law of Pressure in Left-Right Valve Chambers.
e reversing valve should be switched and the left valve chamber pressure will drop rapidly after the impact piston is struck.But in the test curve, the continuous interval A of the right valve chamber pressure and the continuous interval B of the left valve chamber pressure of the reversing valve are too long, which means that the switch is not sensitive enough, resulting in the impact frequency of about 36 Hz, which is far from the 50 Hz standard of the design.

Abnormal Performance.
e analysis of the test curves shows that the impact frequency of the new type of rock drill is low and the impact piston velocity is small.It is necessary to further improve the internal structure design and adjust the rock drill to the best state.

Fault Diagnosis Analysis
5.1.Data Processing.Taking the impact point as the benchmark, the movement law of the impact piston is obtained by curve integral processing.Formula (1) can be obtained by momentum conservation: where F is the impact force of the impact piston in the stroke process (N), t is the action time between force F and impact piston (ms), m is the impact piston mass (kg), and v is the impact piston velocity (m/s).Among them, where P 1 is the front chamber pressure (MPa), P 2 is the rear chamber pressure (MPa), A 1 is the e ective working area of the front chamber (mm 2 ), and A 2 is the e ective working area of the rear chamber (mm 2 ).e force F of the impact piston is integrated: Formula ( 2) is substituted into (3): e velocity of each moment v i is solved by the following equation: e displacement curve is obtained after integrating the velocity curve, as shown in Figure 6.
It is clearly seen from Figure 6 that the two changes of the displacement and velocity curve in one period are 0, indicating a period of second impacts between the impact piston and the shank.At this time, the impact piston and the reversing valve are not coupled properly, and the energy is not applied e ciently to the drilling process, and the energy loss is in the second internal impacts.e second impact caused the impact piston to have insu cient rebound speed, the return distance is small, the stroke energy cannot be fully utilized, and nally, the impact energy and impact frequency cannot reach the expected target.e main reason for the second impacts is that the reversing valve is not sensitive enough.

Coupling Modeling.
e coupling relationship between the impact piston and the reversing valve is analyzed.In state 7, the impact piston impacts the shank moment, the reversing valve should be in the position shown in Figure 7, and the connection of each valve port and the pipe in the reversing valve is in a critical closing state [15][16][17].

Coupling Equation.
e best coupling relationship between the impact piston and the reversing valve is obtained when the direction is changed from state 6 to state 7, the stroke of the impact piston reaches the impact point, and the stroke of the reversing valve reaches the critical state of the reversing valve, for which the time used is the same, and the following equation is established: where x p is the impact piston displacement (mm), s p6 is the distance of the impact piston from state 6 to state 7 (mm), x v is the reversing valve displacement (mm), and s v6 is the distance of reversing valve from state 6 to state 7 (mm).

Impact Piston Movement Di erential Equation.
e impact mechanism model is as shown in Figure 8. e key parts of the coupling between the impact piston and the where m p is the mass of the impact piston (kg), K p is the coe cient of viscous resistance, and F l is the friction force of seal (N).

Reversing Valve Movement Di erential Equation.
e reversing valve model is as shown in Figure 9. e key parts of the coupling between the impact piston and the reversing valve are the circled parts 1, 2, 3, 4, 5, 6, and 7, and the following di erential equation is established: where m v is the mass of the reversing valve (kg), x v is the displacement of the reversing valve (mm), K v is the coe cient of viscous resistance, P 3 is the pressure of the left valve chamber (MPa), P 4 is the pressure of the right valve chamber (MPa), P 5 is the initial return pressure in the left side (MPa), P 6 is the initial return pressure in the right side (MPa), P 7 is the damping pressure in the left side (MPa), P 8 is the damping pressure in the right side (MPa), and A v1 , A v2 , and A v3 are the compression areas of the reversing valve (m 2 ).

Fault Diagnosis.
e internal parameters of the rock drill are incorporated into the model, and the coupling parameters Δt 1 and Δt 2 are obtained by the following equation:   6 Shock and Vibration e reversing time is nearly twice as much as the impact time.At this time, the coupling between the impact piston and the reversing valve is extremely poor, and the structural design of the key position of the reversing valve is analyzed.Figure 10 shows the magni ed image of the circled key part 3 shown in Figure 9.
e structure mainly controls the speed of the reversing valve, neither too fast nor too slow.If the reversing speed is too fast, the pressure oil of the front chamber is switched to high pressure when the impact piston does not impact the shank, which will reduce the impact velocity of the shock piston.e impact piston impacts the high pressure oil of the front chamber at the highest speed, not the shank.If the velocity of the reversing valve is too slow, the pressure of the rear chamber is still high, the high pressure will cause second impact after the impact piston rebound, and the return energy will be lost.is is the problem of the product.
e clearance ow equation of the structure is established by the following equation: where the C d is the ow coe cient, ε is the gap between the cylinder and the reversing valve, which controls the valve velocity (mm), P 0 is the return oil pressure (MPa), R vi and L vi are the radius and length (mm) of each segment on the reversing valve, respectively, as shown in Figure 10, and Δt is the time (ms) for all the oil discharge from damping chamber.Formula ( 10) is combined with (11): Equations ( 12), (7), and (8) are used to solve Δt. e gap between the velocity control structure and cylinder body is modi ed to make Δt equal to Δt 2 , and the optimal clearance amount ε is 0.036 mm.

Validation.
e speed control structure clearance of the reversing valve is modi ed and processed to 0.036 mm, and the curve data are obtained as shown in Figure 11.
After the structure modi cation, the pressure switching time of the left-right valve chamber pressure is obviously reduced, the pressure duration of the left valve chamber is 2.6 ms, the pressure of the right valve chamber is 2.3 ms, the impact frequency increases to 48 Hz, the impact piston is directly rebound after the piston collision, the front-rear chamber pressure switches in time and there are no second collisions, and the high speed of the impact piston stroke is the fastest, which is increased to 12.1 m/s.

Conclusions
(1) e mechanism testing method of the hydraulic rock drill is designed, including calculation method and location of sensor installation.Test the data of the rock drill, analyze the test data, and complete the fault diagnosis of the rock drill according to the characteristics of the test data.(2) e mathematical model of the impact and reversing mechanism of the hydraulic rock drill is established.e coupling condition of the impact piston and the reversing valve of the hydraulic rock drill is put forward.According to the optimum coupling condition, the optimum time for the movement of the reversing valve is obtained, and the best clearance Shock and Vibration between the speed control structure of the reversing valve and the cylinder body is designed.(3) e experiment is carried out based on the optimal clearance of the new reversing valve.rough the experimental data, it can be seen that the impact frequency of the rock drill is increased from 36 Hz to 48 Hz, the velocity of the impact piston is increased from 9.7 m/s to 12.1 m/s, and the overall performance of the rock drill is greatly improved.e internal mechanism testing method reacts more intuitively to the change law of the internal mechanism of the rock drill and provides a more direct and e ective method for the design and production of a new rock drill, the study of the correctness of the design theory, and the actual use e ect.
Data Availability e data used to support the ndings of this study are available from the corresponding author upon request.

Figure 4 :
Figure 4: Sensor installation location in impact and reversing mechanism.

Figure 6 :
Figure6: Pressure curves of chamber and integral curves of piston velocity and displacement.FC: front chamber; RC: rear chamber; LVC: left valve chamber; RVC: right valve chamber; IPD: impact piston displacement; IPV: impact piston velocity.

Figure 7 :l 12 l 13 l 14 l 15 l 16
Figure 7: Impact piston and valve position in state 7.

Table 1 :
Test initial data setting.