An ultrasonic and low-frequency sound wave composite assisted high-efficiency drilling device for underground coal mines

Abstract

A high-efficiency drilling device for underground coal mines that utilizes ultrasonic and low-frequency sound waves for combined assistance. A bidirectional ultrasonic transducer and a horn are connected and installed in a housing. A splined sleeve and a rear cover are installed at the front and rear ends of the housing, respectively. A splined shaft is slidably inserted into the center of the splined sleeve, with its ends connected to the horn and a drill bit. The transducer rear cover and the housing rear cover are in axial sliding contact, with a preload spring interposed between them. A return spring is sleeved between the horn and a retaining ring at the front end of the housing. The two springs cooperate to provide a return force for the transducer. When the transducer is operating, ultrasonic vibrations generated at the front end are transmitted to the drill bit via the horn, imparting ultrasonic vibration capability. Ultrasonic vibrations generated at the rear end act on the horn via the rear cover, generating sound waves during the impact process. These waves are transmitted to the drill bit via the housing and the bidirectional ultrasonic transducer, imparting acoustic vibration capability. This device can achieve ultrasonic and acoustic composite vibration excitation of the drill bit, significantly improving drilling efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of drilling engineering, and in particular is an ultrasonic and low-frequency sound wave composite assisted high-efficiency drilling device for underground coal mines. Background Art

[0002] As shallow coal resources are depleted through intensive mining, the focus of future coal resource development in my country is gradually shifting to deeper areas. As drilling depth increases, the problem of crushing high-hardness rocks becomes increasingly prominent, placing higher demands on current rock breaking technologies.

[0003] Rock crushing efficiency significantly impacts overall operational efficiency. Traditionally, mechanical rock breaking utilizes the drill bit's high torque, high speed, and high pressure to increase penetration speed. This approach results in significant drill bit wear and a shortened service life. Furthermore, numerous issues exist, including inefficient transmission of WOB through long drill strings and complex, cumbersome connection mechanisms.

[0004] In recent years, researchers have discovered that when a rock system is excited by an external load that coincides with its natural frequency (resonance), its response amplitude reaches its maximum. This in turn increases the instability of the rock structure, favoring the expansion of cracks and further rapid rock failure. Practice has shown that when a rock specimen is in a resonant state and a certain load is applied, the mechanical effects of the impact cause significant displacement of particles within the rock, exacerbating collisions between particles. Based on this, ultrasonic vibration can be combined with low-frequency impact vibration to improve drilling efficiency while effectively reducing drill bit wear. Summary of the Invention

[0005] In response to the problems existing in the above-mentioned prior art, the present invention provides an ultrasonic and low-frequency sound wave composite assisted efficient drilling device for coal mines. The device has a compact structure, a simple installation process, a convenient maintenance process, and a low manufacturing cost. It can combine ultrasonic frequency vibrations with sound waves generated by low-frequency impact vibrations and act on the drill bit, which can realize the composite vibration excitation of sound frequency and ultrasonic frequency on the drill bit, can significantly improve the drilling efficiency, and can help extend the service life of the drill tool, which is conducive to large-scale promotion and application.

[0006] In order to achieve the above-mentioned object, the present invention provides an ultrasonic and low-frequency sound wave composite assisted efficient drilling device for coal mines, comprising a housing, a drilling tool, a spline sleeve, a bidirectional ultrasonic transducer, a housing back cover, a pre-tightening nut, a pre-tightening spring and a return spring;

[0007] The housing is a cylindrical structure with open ends, and a cylindrical mounting cavity is provided inside. An internal thread structure 1 is provided inside the rear open end of the housing, and a limiting ring is fixedly connected to the inside of the front open end of the housing.

[0008] The size of the spline sleeve is adapted to the size of the front opening end of the shell, and is fixedly packaged at the front opening end of the shell; a spline hole is opened at the axis of the spline sleeve, and the outer diameter of the spline hole is smaller than the inner diameter of the limit ring;

[0009] The bidirectional ultrasonic transducer is arranged in the middle of the installation cavity, and is composed of a pre-tightening screw, a mass block, a piezoelectric ceramic stack, a rear cover plate and a front cover plate; the pre-tightening screw is arranged at the axis center of the middle section of the installation cavity; the mass block is cylindrical, and its outer diameter is adapted to the inner diameter of the installation cavity, and a circular through hole one adapted to the pre-tightening screw is opened in its center, and is mounted on the outside of the middle section of the pre-tightening screw through the circular through hole one; the piezoelectric ceramic stack is cylindrical, and its outer diameter is adapted to the inner diameter of the installation cavity, and a circular through hole two is opened in its center; the piezoelectric ceramic stack is composed of four piezoelectric ceramic sheets and four electrode sheets arranged in sequence in an alternating and overlapping manner; the two piezoelectric ceramic stacks are respectively mounted on the outside of the pre-tightening screw through the two circular through holes in their centers , and are respectively distributed on the upper and lower sides of the mass block; the rear cover is composed of a positioning block and a positioning column, the outer diameter of the positioning block is adapted to the inner diameter of the mounting cavity, and a threaded mounting hole 1 is opened at the axis center of its front end, and the front end of the positioning column is vertically fixedly connected to the axis center of the rear end of the positioning block, and the surface of the positioning column is coated with an insulating material layer; the rear cover is fixedly sleeved on the outer side of the rear end of the preload screw through the threaded mounting hole 1 at its front end, and its front end face abuts against the rear end face of the rear piezoelectric ceramic stack; the front cover is cylindrical, its outer diameter is adapted to the inner diameter of the mounting cavity, and a threaded mounting hole 2 is opened at the axis center of its rear end, and is fixedly sleeved on the outer side of the rear end of the preload screw through the threaded mounting hole 2 at its rear end;

[0010] The drilling tool consists of a variable amplitude rod, a spline shaft and a drill bit; the variable amplitude rod is a stepped shaft structure, the large diameter section of which is located at the rear side of the small diameter section of the variable amplitude rod, and the outer diameter of the large diameter section is adapted to the inner diameter of the mounting cavity, and is axially slidably assembled in the front part of the mounting cavity, while the rear end of the large diameter section is fixedly connected to the front end face of the front cover plate; the shape and size of the spline shaft are adapted to the shape and size of the spline hole, and is axially slidable and radially limited and inserted into the spline hole, the rear end of the spline shaft penetrates into the mounting cavity and is coaxially fixedly connected to the front end face of the small diameter section of the variable amplitude rod, and the front end of the spline shaft is located outside the front end of the shell; the drill bit is located outside the front end of the shell and is coaxially fixedly connected to the front end of the spline shaft;

[0011] The shell rear cover is composed of a blocking block, a positioning sleeve and a connecting protrusion. The blocking block is cylindrical, and an external thread structure 1 is provided on the outer side of its front end, which is matched with the internal thread structure 1, and is inserted into the inner side of the rear open end of the shell through threaded cooperation; the outer side of the positioning sleeve is provided with an external thread structure 2, and the rear end of the positioning sleeve is coaxially fixedly connected to the front end face of the blocking block, the shape and size of the internal positioning hole of the positioning sleeve are matched with the shape and size of the positioning column, and the positioning sleeve can be axially slidably and radially limitedly fitted on the outside of the rear end of the positioning column; the front end of the connecting protrusion is fixedly connected to the rear end face of the blocking block;

[0012] The internal thread structure of the pre-tightening nut is adapted to the external thread structure and is installed on the outside of the positioning sleeve through thread matching;

[0013] The pre-tightening spring is arranged at the rear of the installation cavity and is sleeved on the outside of the positioning sleeve. At the same time, the rear end of the pre-tightening spring abuts against the front end surface of the pre-tightening nut, and its front end abuts against the rear end surface of the positioning block on the rear cover plate;

[0014] The return spring is arranged at the front of the installation cavity and is sleeved on the outside of the small diameter section of the amplitude transformer. At the same time, the rear end of the return spring abuts against the front end surface of the large diameter section of the amplitude transformer, and the front end of the return spring abuts against the rear end surface of the limit ring.

[0015] Furthermore, in order to efficiently transmit torque, the cross section of the positioning hole inside the positioning sleeve is a regular hexagon, and the cross section of the positioning column is a regular hexagon.

[0016] Furthermore, in order to effectively reduce the rebound resistance of the bidirectional ultrasonic transducer and effectively protect the circuit part of the bidirectional ultrasonic transducer, the inner side wall of the shell is coated with insulating lubricating oil.

[0017] Furthermore, in order to effectively enhance the rebound force, the back cover of the shell is made of a material with high hardness, density and elastic modulus.

[0018] As a preferred embodiment, the amplitude transformer and the front cover are fixedly connected by bolts.

[0019] Furthermore, in order to maximize the amplitude at the front and rear ends to achieve efficient energy conversion and thus enable both ends to have better vibration capabilities, the rear cover plate and the front cover plate are both made of metal materials with low density, good toughness and good hardness, and the mass block is made of metal materials with high density.

[0020] Furthermore, in order to enable the pre-tightening spring to provide a greater elastic force to increase the rebound force during operation, and at the same time, to enable the rear end of the bidirectional ultrasonic transducer to remain separated from the rear cover of the shell when the device is not started, so as to avoid the situation where the device cannot start normally due to impedance mismatch caused by excessive compression of the rear cover of the shell, the length of the pre-tightening spring is greater than the length of the reset spring.

[0021] In the present invention, a pre-tightening screw is used to connect the mass block and the two piezoelectric ceramic stacks located on both sides of the mass block in series, and each piezoelectric ceramic stack is composed of four piezoelectric ceramic sheets and four electrode sheets stacked in an interlaced manner. This can enable the bidirectional ultrasonic transducer to have a high-power output capability and greatly improve the overall output energy. Experiments have found that its output power can reach about 6000W; at the same time, by assembling two piezoelectric ceramic stacks, ultrasonic vibrations can be generated in both directions, and the superposition and enhancement of the vibration capacity can be achieved, which significantly improves the ultrasonic frequency vibration capacity. The front end of the rear cover plate is provided with a threaded mounting hole 1, and is fixedly mounted on the outer side of the rear end of the pre-tightening screw through the threaded mounting hole 1. In this way, the rear cover plate can be used to limit the piezoelectric ceramic stack on the rear side and press it to the rear side of the mass block; the rear end of the front cover plate is provided with a threaded mounting hole 2, and is fixedly mounted on the outer side of the front end of the pre-tightening screw through the threaded mounting hole 2. In this way, the front cover plate can be used to limit the piezoelectric ceramic stack on the front side and press it to the front side of the mass block. In this way, the two piezoelectric ceramic stacks can be pressed on both sides of the mass block through the rear cover plate and the front cover plate in conjunction with the pre-tightening screw, effectively ensuring the integrity and compactness of the bidirectional ultrasonic transducer. The shell rear cover is composed of a sealing block, a positioning sleeve and a connecting protrusion, and the sealing block is packaged in the rear open end of the shell through threaded fitting, and the positioning sleeve is axially sliding and radially limitedly sleeved on the outside of the rear end of the positioning column on the rear cover plate. This not only makes it convenient to limit the rear end of the bidirectional ultrasonic transducer, but also makes it convenient to transmit torque to the bidirectional ultrasonic transducer. At the same time, it will not cause any interference to the axial reciprocating motion process of the bidirectional ultrasonic transducer. Therefore, the bidirectional ultrasonic transducer has a certain axial reciprocating motion ability, so that the bidirectional ultrasonic transducer can generate mold plug vibration while providing mechanism vibration, so that the drilling device has dual vibration ability, which significantly enhances the drilling effect. The preload spring is sleeved on the outside of the positioning sleeve, and its two ends are respectively in contact with the preload nut on the outside of the positioning sleeve and the positioning block on the rear cover plate, which can provide an elastic force for the shell rear cover and the rear cover plate to separate from each other, effectively avoiding the impedance mismatch caused by the shell rear cover pressing the rear cover plate, thereby avoiding the device from being unable to operate normally due to the impedance mismatch; in addition, during the reciprocating motion of the bidirectional ultrasonic transducer, it can provide a reset elastic force from the rear side for the bidirectional ultrasonic transducer, thereby effectively avoiding the situation where the bidirectional ultrasonic transducer is attached to the side of the shell rear cover for a long time and cannot rebound due to insufficient reaction force when drilling into soft rock or other materials with poor hardness. Since the external thread structure 2 is provided on the outside of the positioning sleeve, the preload nut can be conveniently installed on the positioning sleeve by threaded matching. At the same time, the preload force of the preload spring can be adjusted by adjusting the height of the preload nut on the positioning sleeve, thereby adjusting the reset elastic force.The surface of the positioning column is coated with an insulating material layer to further prevent impedance mismatch problems caused by the rear cover of the housing being pressed against the rear cover, thereby ensuring that the device does not unexpectedly stop working. A spline hole is provided at the axis center of the spline sleeve fixedly encapsulated at the front end of the housing, and is axially slidable and radially limited to fit around the exterior of the spline shaft. At the same time, the rear end of the horn is fixedly connected to the front end of the front cover of the bidirectional ultrasonic transducer, facilitating the transmission of torque from the housing to the drill tool. This ensures that both the torque from the bidirectional ultrasonic transducer and the torque from the housing can be reliably transmitted to the drill tool, significantly improving torque transmission efficiency. Thus, through the combined torque transmission of the front spline sleeve and the rear end of the housing cover, the front end drill bit can rotate synchronously with the rotation of the housing, the bidirectional ultrasonic transducer, and the horn, effectively improving drilling performance. Furthermore, the bidirectional ultrasonic transducer and the horn are axially slidably assembled as a unit in the mounting cavity of the housing, allowing the housing to protect the bidirectional ultrasonic transducer. Because the horn adopts a variable diameter design and the outer diameter of the front section is smaller, the amplitude of the ultrasonic frequency vibration generated by the bidirectional ultrasonic transducer can be amplified on the smaller diameter section with a smaller wear area to reach the required working amplitude, significantly improving the vibration capacity of the drill bit. A reset spring is mounted on the outside of the small diameter section of the horn, and its two ends are respectively abutted against a limit ring fixed to the inner side of the front end of the shell and the large diameter section of the horn. This can provide a reset spring force from the front side of the bidirectional ultrasonic transducer during the reciprocating motion of the bidirectional ultrasonic transducer. In this way, the coordinated arrangement of the preload spring and the reset spring ensures that both the front and rear ends of the bidirectional ultrasonic transducer have reset spring force, effectively ensuring that the bidirectional ultrasonic transducer can continue to perform axial reciprocating motion during operation. Since both the front and rear ends of the bidirectional ultrasonic transducer have the ability to vibrate at ultrasonic frequencies, and the amplitude can exceed 50 microns, a large number of experiments have shown that under this amplitude condition, when one end of the bidirectional ultrasonic transducer contacts a fixed component with a certain hardness, the bidirectional ultrasonic transducer as a whole can rebound, and there is also contact rebound force and drilling pressure during the drilling process. Therefore, under the coupling of multiple forces, the bidirectional ultrasonic transducer and the amplitude transformer can generate large-amplitude vibration of the acoustic frequency in the shell.In this way, when the bidirectional ultrasonic transducer is connected to the ultrasonic power supply, both the front cover plate and the rear cover plate can generate high-frequency ultrasonic vibrations. Since the front cover plate is fixedly connected to the horn of the drill tool, the ultrasonic vibrations generated at the front end will be transmitted to the drill bit through the horn and the spline shaft, so that the drill bit can generate ultrasonic vibrations. The rear cover plate is axially slidably connected to the shell rear cover and will contact the shell rear cover under the action of drilling pressure. Therefore, the ultrasonic vibrations generated at the rear end will act on the end of the horn through the shell rear cover, and generate low-frequency impact sound waves during the collision between the rear cover plate and the end of the horn. The generated sound waves will be transmitted to the drill bit through the shell and the bidirectional ultrasonic transducer, so that the drill bit generates audio-frequency vibrations. In this way, ultrasonic and audio-frequency composite vibration excitations of the horn and the drill bit are realized, so that the drill bit can apply audio-frequency and ultrasonic-frequency composite vibration excitations to the rock while rotating and drilling, thereby significantly improving the impact force during drilling in a limited space, improving the drilling efficiency, and helping to extend the life of the drill bit and the horn.

[0022] The present invention provides a new solution to the problems of low drilling efficiency, extensive damage to the drill tool, and limited available space encountered by traditional drilling tools when drilling deep hard rock in coal mines. By applying a combination of ultrasonic and acoustic frequency shocks to the horn and drill bit, the present invention provides the horn and drill bit with greater drilling impact force. This significantly improves drilling efficiency during deep hard rock drilling, helps reduce the wear rate of the drill tool, and achieves an assisted drilling effect. The present invention has a compact structure, simple installation, convenient maintenance, and low manufacturing cost. It can significantly improve drilling efficiency within a limited space and effectively extend the service life of the drill tool, making it suitable for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of the present invention;

[0024] Figure 2 Schematic diagram of the split assembly of the bidirectional ultrasonic transducer and the drilling tool in the present invention Figure 1 ;

[0025] Figure 3 Schematic diagram of the split assembly of the bidirectional ultrasonic transducer and the drilling tool in the present invention Figure 2 .

[0026] In the figure: 1. rear cover plate, 2. electrode plate, 3. piezoelectric ceramic plate, 4. mass fastener, 5. preload screw, 6. piezoelectric ceramic stack, 7. front cover plate, 8. amplitude transformer, 9. drill bit, 10. shell rear cover, 11. preload nut, 12. preload spring, 13. shell, 14. bidirectional ultrasonic transducer, 15. reset spring, 16. spline sleeve, 17. spline shaft, 18. positioning block, 19. positioning column, 20. blocking block, 21. positioning sleeve, 22. connecting protrusion, 23. mounting cavity, 24. limiting ring, 25. drilling tool, 26. spline hole, 27. circular through hole one, 28. circular through hole two. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings.

[0028] like Figures 1 to 3 As shown, an ultrasonic and low-frequency sound wave composite assisted high-efficiency drilling device for underground coal mines includes a housing 13, a drilling tool 25, a spline sleeve 16, a bidirectional ultrasonic transducer 14, a housing back cover 10, a pre-tightening nut 11, a pre-tightening spring 12, and a return spring 15;

[0029] The housing 13 is a cylindrical structure with open ends. It has a cylindrical mounting cavity 23 inside. An internal thread structure 1 is provided inside the rear open end of the housing 13. A limit ring 24 is fixedly connected to the inside of the front open end of the housing 13.

[0030] The size of the spline sleeve 16 is adapted to the size of the front open end of the housing 13 and is fixedly encapsulated at the front open end of the housing 13; a spline hole 26 is formed at the axis of the spline sleeve 16, and the outer diameter of the spline hole 26 is smaller than the inner diameter of the limit ring 24;

[0031] The bidirectional ultrasonic transducer 14 is arranged in the middle of the installation cavity 23, and is composed of a pre-tightening screw 5, a mass block 4, a piezoelectric ceramic stack 6, a rear cover plate 1 and a front cover plate 7; the pre-tightening screw 5 is arranged at the axis center of the middle section of the installation cavity 23; the mass block 4 is cylindrical, and its outer diameter is adapted to the inner diameter of the installation cavity 23, and a circular through hole 27 adapted to the pre-tightening screw 5 is opened in the center thereof, and is sleeved on the pre-tightening screw through the circular through hole 27. The outside of the middle section of the rod 5, wherein the inner diameter of the circular through hole 1 27 is adapted to the outer diameter of the preload screw 5; the piezoelectric ceramic stack 6 is cylindrical, and its outer diameter is adapted to the inner diameter of the mounting cavity 23, and a circular through hole 28 is opened in the center thereof, wherein the inner diameter of the circular through hole 28 is adapted to the outer diameter of the preload screw 5; the piezoelectric ceramic stack 6 is composed of four piezoelectric ceramic sheets 3 and four electrode sheets 2 arranged in a staggered and overlapping manner; the two The piezoelectric ceramic stacks 6 are respectively sleeved on the outside of the preload screw 5 through the circular through hole 28 in the center, and are respectively distributed on the upper and lower sides of the mass block 4; the rear cover plate 1 is composed of a positioning block 18 and a positioning column 19, the positioning block 18 is cylindrical, and its outer diameter is adapted to the inner diameter of the mounting cavity 23, and a threaded mounting hole 1 is opened at the axis center of its front end, and the front end of the positioning column 19 is vertically fixedly connected to the axis center of the rear end of the positioning block 18, and the surface of the positioning column 19 is coated with an insulating material layer; the rear cover plate 1 is fixedly sleeved on the outside of the rear end of the preload screw 5 through the threaded mounting hole 1 at its front end, and its front end face abuts against the rear end face of the rear piezoelectric ceramic stack 6; the front cover plate 7 is cylindrical, and its outer diameter is adapted to the inner diameter of the mounting cavity 23, and a threaded mounting hole 2 is opened at the axis center of its rear end, and is fixedly sleeved on the outside of the rear end of the preload screw 5 through the threaded mounting hole 2 at its rear end;

[0032] The drilling tool 25 consists of a horn 8, a spline shaft 17 and a drill bit 9; the horn 8 is a stepped shaft structure, and its large diameter section is located at the rear side of its small diameter section, so that the small diameter section of the horn 8 can be used to fit the reset spring 15. The outer diameter of the large diameter section of the horn 8 is adapted to the inner diameter of the installation cavity 23, and the axially slidable assembly is assembled in the front part of the installation cavity 23. At the same time, the rear end of the large diameter section is fixedly connected to the front end surface of the front cover 7; the spline shaft 17 is long in length and its shape is similar to the horn 8. The size of the spline shaft 17 is adapted to the shape and size of the spline hole 26, and the spline shaft 17 is axially slidable and radially limited and inserted into the spline hole 26. The rear end of the spline shaft 17 penetrates into the installation cavity 23 and is coaxially fixedly connected to the front end face of the small diameter section of the horn 8. The front end of the spline shaft 17 is located outside the front end of the housing 13; as a preferred embodiment, the outer diameter of the spline shaft 17 is consistent with the outer diameter of the small diameter section of the horn 8; the drill bit 9 is located outside the front end of the housing 13 and is coaxially fixedly connected to the front end of the spline shaft 17;

[0033] The shell back cover 10 is composed of a blocking block 20, a positioning sleeve 21 and a connecting protrusion 22. The blocking block 20 is cylindrical, and an external thread structure 1 that matches the internal thread structure 1 is provided on the outer side of its front end, and is inserted into the inner side of the rear open end of the shell 1 through threaded fitting; the outer side of the positioning sleeve 21 is provided with an external thread structure 2, and its rear end is coaxially fixedly connected to the front end face of the blocking block 20. The shape and size of the internal positioning hole of the positioning sleeve 21 are compatible with the shape and size of the positioning column 19, and it is axially slidable and radially limited to be fitted on the outside of the rear end of the positioning column 19; the front end of the connecting protrusion 22 is fixedly connected to the rear end face of the blocking block 20;

[0034] The internal thread structure of the pre-tightening nut 11 is adapted to the external thread structure and is installed on the outside of the positioning sleeve 21 through threaded fit;

[0035] The preload spring 12 is arranged at the rear of the mounting cavity 23 and is sleeved on the outside of the positioning sleeve 21. At the same time, the rear end of the preload spring 12 abuts against the front end surface of the preload nut 11, and the front end abuts against the rear end surface of the positioning block 18 on the rear cover 1.

[0036] The return spring 15 is arranged at the front part of the mounting cavity 23 and is sleeved on the outside of the small diameter section of the amplitude transformer 8. At the same time, the rear end of the return spring 15 abuts against the front end surface of the large diameter section of the amplitude transformer 8, and the front end of the return spring 15 abuts against the rear end surface of the limit ring 24.

[0037] In order to efficiently transmit torque, the cross section of the positioning hole inside the positioning sleeve 21 is a regular hexagon, and the cross section of the positioning column 19 is a regular hexagon.

[0038] In order to effectively reduce the rebound resistance of the bidirectional ultrasonic transducer and effectively protect the circuit part of the bidirectional ultrasonic transducer, the inner wall of the housing 13 is coated with insulating lubricating oil.

[0039] In order to effectively enhance the rebound force, the shell back cover 10 is made of a material with high hardness, density and elastic modulus, such as alloy steel, carbon steel, etc.

[0040] As a preferred embodiment, the amplitude transformer 8 and the front cover plate 7 are fixedly connected by bolts.

[0041] In order to maximize the amplitude of the front and rear ends to achieve efficient energy conversion and thus enable both ends to have better vibration capabilities, the rear cover plate 1 and the front cover plate 7 are both made of metal materials with low density, good toughness and good hardness, such as titanium alloy or aluminum alloy, and the mass block 4 is made of metal materials with high density, such as 45 steel.

[0042] In order to enable the pre-tightening spring to provide a greater elastic force to increase the rebound force during operation, and at the same time, to enable the rear end of the bidirectional ultrasonic transducer to remain separated from the rear cover of the shell when the device is not started, so as to avoid the device being unable to start normally due to impedance mismatch caused by excessive compression of the rear cover by the rear cover, the length of the pre-tightening spring 12 is greater than the length of the reset spring 15.

[0043] In the present invention, a pre-tightening screw is used to connect the mass block and the two piezoelectric ceramic stacks located on both sides of the mass block in series, and each piezoelectric ceramic stack is composed of four piezoelectric ceramic sheets and four electrode sheets stacked in an interlaced manner. This can enable the bidirectional ultrasonic transducer to have a high-power output capability and greatly improve the overall output energy. Experiments have found that its output power can reach about 6000W; at the same time, by assembling two piezoelectric ceramic stacks, ultrasonic vibrations can be generated in both directions, and the superposition and enhancement of the vibration capacity can be achieved, which significantly improves the ultrasonic frequency vibration capacity. The front end of the rear cover plate is provided with a threaded mounting hole 1, and is fixedly mounted on the outer side of the rear end of the pre-tightening screw through the threaded mounting hole 1. In this way, the rear cover plate can be used to limit the piezoelectric ceramic stack on the rear side and press it to the rear side of the mass block; the rear end of the front cover plate is provided with a threaded mounting hole 2, and is fixedly mounted on the outer side of the front end of the pre-tightening screw through the threaded mounting hole 2. In this way, the front cover plate can be used to limit the piezoelectric ceramic stack on the front side and press it to the front side of the mass block. In this way, the two piezoelectric ceramic stacks can be pressed on both sides of the mass block through the rear cover plate and the front cover plate in conjunction with the pre-tightening screw, effectively ensuring the integrity and compactness of the bidirectional ultrasonic transducer. The rear cover of the shell is composed of a blocking block, a positioning sleeve, and a connecting protrusion. The blocking block is encapsulated at the rear open end of the shell through threaded engagement, and the positioning sleeve is axially slidably and radially limitedly sleeved on the outside of the rear end of the positioning column on the rear cover plate. This not only facilitates limiting the rear end of the bidirectional ultrasonic transducer, but also facilitates transmitting torque to the bidirectional ultrasonic transducer. At the same time, it does not cause any interference with the axial reciprocating motion process of the bidirectional ultrasonic transducer. As a result, the bidirectional ultrasonic transducer has a certain axial reciprocating motion capability, so that the bidirectional ultrasonic transducer can generate mold plug vibration while providing mechanism vibration, so that the drilling device has dual vibration capabilities, which significantly enhances the drilling effect. The preload spring is sleeved on the outside of the positioning sleeve, and its two ends are respectively in contact with the preload nut on the outside of the positioning sleeve and the positioning block on the rear cover plate, which can provide an elastic force for the shell rear cover and the rear cover plate to separate from each other, effectively avoiding the impedance mismatch caused by the shell rear cover pressing the rear cover plate, thereby avoiding the device from being unable to operate normally due to the impedance mismatch; in addition, during the reciprocating motion of the bidirectional ultrasonic transducer, it can provide a reset elastic force from the rear side for the bidirectional ultrasonic transducer, thereby effectively avoiding the situation where the bidirectional ultrasonic transducer is attached to the side of the shell rear cover for a long time and cannot rebound due to insufficient reaction force when drilling into soft rock or other materials with poor hardness. Since the external thread structure 2 is provided on the outside of the positioning sleeve, the preload nut can be conveniently installed on the positioning sleeve by threaded matching. At the same time, the preload force of the preload spring can be adjusted by adjusting the height of the preload nut on the positioning sleeve, thereby adjusting the reset elastic force.The surface of the positioning column is coated with an insulating material layer to further prevent impedance mismatch problems caused by the rear cover of the housing being pressed against the rear cover, thereby ensuring that the device does not unexpectedly stop working. A spline hole is provided at the axis center of the spline sleeve fixedly encapsulated at the front end of the housing, and is axially slidable and radially limited to fit around the exterior of the spline shaft. At the same time, the rear end of the horn is fixedly connected to the front end of the front cover of the bidirectional ultrasonic transducer, facilitating the transmission of torque from the housing to the drill tool. This ensures that both the torque from the bidirectional ultrasonic transducer and the torque from the housing can be reliably transmitted to the drill tool, significantly improving torque transmission efficiency. Thus, through the combined torque transmission of the front spline sleeve and the rear end of the housing cover, the front end drill bit can rotate synchronously with the rotation of the housing, the bidirectional ultrasonic transducer, and the horn, effectively improving drilling performance. Furthermore, the bidirectional ultrasonic transducer and the horn are axially slidably assembled as a unit in the mounting cavity of the housing, allowing the housing to protect the bidirectional ultrasonic transducer. Because the horn adopts a variable diameter design and the outer diameter of the front section is smaller, the amplitude of the ultrasonic frequency vibration generated by the bidirectional ultrasonic transducer can be amplified on the smaller diameter section with a smaller wear area to reach the required working amplitude, significantly improving the vibration capacity of the drill bit. A reset spring is mounted on the outside of the small diameter section of the horn, and its two ends are respectively abutted against a limit ring fixed to the inner side of the front end of the shell and the large diameter section of the horn. This can provide a reset spring force from the front side of the bidirectional ultrasonic transducer during the reciprocating motion of the bidirectional ultrasonic transducer. In this way, the coordinated arrangement of the preload spring and the reset spring ensures that both the front and rear ends of the bidirectional ultrasonic transducer have reset spring force, effectively ensuring that the bidirectional ultrasonic transducer can continue to perform axial reciprocating motion during operation. Since both the front and rear ends of the bidirectional ultrasonic transducer have the ability to vibrate at ultrasonic frequencies, and the amplitude can exceed 50 microns, a large number of experiments have shown that under this amplitude condition, when one end of the bidirectional ultrasonic transducer contacts a fixed component with a certain hardness, the bidirectional ultrasonic transducer as a whole can rebound, and there is also contact rebound force and drilling pressure during the drilling process. Therefore, under the coupling of multiple forces, the bidirectional ultrasonic transducer and the amplitude transformer can generate large-amplitude vibration of the acoustic frequency in the shell.In this way, when the bidirectional ultrasonic transducer is connected to the ultrasonic power supply, both the front cover plate and the rear cover plate can generate high-frequency ultrasonic vibrations. Since the front cover plate is fixedly connected to the horn of the drill tool, the ultrasonic vibrations generated at the front end will be transmitted to the drill bit through the horn and the spline shaft, so that the drill bit can generate ultrasonic vibrations. The rear cover plate is axially slidably connected to the shell rear cover and will contact the shell rear cover under the action of drilling pressure. Therefore, the ultrasonic vibrations generated at the rear end will act on the end of the horn through the shell rear cover, and generate low-frequency impact sound waves during the collision between the rear cover plate and the end of the horn. The generated sound waves will be transmitted to the drill bit through the shell and the bidirectional ultrasonic transducer, so that the drill bit generates audio-frequency vibrations. In this way, ultrasonic and audio-frequency composite vibration excitations of the horn and the drill bit are realized, so that the drill bit can apply audio-frequency and ultrasonic-frequency composite vibration excitations to the rock while rotating and drilling, thereby significantly improving the impact force during drilling in a limited space, improving the drilling efficiency, and helping to extend the life of the drill bit and the horn.

[0044] The present invention provides a new solution to the problems of low drilling efficiency, extensive damage to the drill tool, and limited available space encountered by traditional drilling tools when drilling deep hard rock in coal mines. By applying a combination of ultrasonic and acoustic frequency shocks to the horn and drill bit, the present invention provides the horn and drill bit with greater drilling impact force. This significantly improves drilling efficiency during deep hard rock drilling, helps reduce the wear rate of the drill tool, and achieves an assisted drilling effect. The present invention has a compact structure, simple installation, convenient maintenance, and low manufacturing cost. It can significantly improve drilling efficiency within a limited space and effectively extend the service life of the drill tool, making it suitable for large-scale promotion and application.

[0045] During use, the housing 13 is driven to rotate via the connecting protrusion 22. During this process, the radial limiting cooperation between the positioning sleeve 21 on the rear cover 10 and the positioning column 19 on the rear cover plate 1, and the radial limiting cooperation between the spline sleeve 16 and the spline shaft 17 on the drill tool, synchronously drives the bidirectional ultrasonic transducer 14, the horn 8, the spline shaft 17, the drill bit 9, the preload spring 12, and the return spring 15 to rotate. At the same time, the bidirectional ultrasonic transducer 14 is connected to the ultrasonic power supply, causing the front cover plate 7 and the rear cover plate 1 to generate ultrasonic frequency vibrations. Since the front cover plate 7 is fixedly connected to the horn 8, the ultrasonic frequency vibrations generated at the front end of the bidirectional ultrasonic transducer 14 are transmitted to the drill bit 9 via the horn 8 and the spline shaft 17, thereby endowing the drill bit 9 with ultrasonic frequency vibration capability, further improving the drilling capability of the drill bit 9. Since the rear cover plate 1 is slidingly connected to the shell rear cover 10, the rear cover plate 1 will contact the shell rear cover 10 under the action of drilling pressure. Therefore, the ultrasonic frequency vibration generated by the rear end of the bidirectional ultrasonic transducer 14 will act on the end of the horn through the shell rear cover 10, and will generate sound waves during the collision between the shell rear cover 10 and the end of the horn. The generated sound waves will be transmitted to the drill bit 9 through the shell 13 and the bidirectional ultrasonic transducer, causing the drill bit 9 to generate audio frequency vibrations. In this way, ultrasonic frequency and audio frequency composite vibration excitation of the horn 8 and the drill bit 9 is realized. At the same time, through the coordinated arrangement of the preload spring 12 and the return spring 15, it can be ensured that the front and rear ends of the bidirectional ultrasonic transducer 14 have a return elastic force, and then during the drilling process, under the coupling action of the return elastic force of the springs at both ends, the rebound force of the drilling contact and the drilling pressure, the bidirectional ultrasonic transducer 14 and the amplitude transformer 8 can continuously generate large-amplitude reciprocating vibrations of the acoustic frequency in the shell 13, ensuring that the ultrasonic frequency and acoustic frequency composite vibration excitation can be continuously applied to the drill bit 9 during operation, significantly improving the stability and reliability of the drilling device.

Claims

1. An ultrasonic and low-frequency sound wave composite assisted high-efficiency drilling device for underground coal mines, comprising a housing (13) and a drilling tool (25), characterized in that: It also includes a spline sleeve (16), a bidirectional ultrasonic transducer (14), a shell back cover (10), a pre-tightening nut (11), a pre-tightening spring (12) and a return spring (15); The housing (13) is a cylindrical structure with open ends, and has a cylindrical mounting cavity (23) inside. An internal thread structure is provided inside the rear open end of the housing (13), and a limiting ring (24) is fixedly connected to the inside of the front open end of the housing (13). The size of the spline sleeve (16) is adapted to the size of the front opening end of the housing (13), and is fixedly encapsulated at the front opening end of the housing (13); a spline hole (26) is provided at the axis of the spline sleeve (16), and the outer diameter of the spline hole (26) is smaller than the inner diameter of the limiting ring (24); The bidirectional ultrasonic transducer (14) is arranged in the middle of the installation cavity (23), and is composed of a pre-tightening screw (5), a mass block (4), a piezoelectric ceramic stack (6), a rear cover plate (1) and a front cover plate (7); the pre-tightening screw (5) is arranged at the axis center of the middle section of the installation cavity (23); the mass block (4) is cylindrical, and its outer diameter is adapted to the inner diameter of the installation cavity (23), and a circular through hole adapted to the pre-tightening screw (5) is opened in the center thereof. One (27), and is sleeved on the outside of the middle section of the preload screw (5) through the circular through hole one (27); the piezoelectric ceramic stack (6) is cylindrical, its outer diameter is adapted to the inner diameter of the mounting cavity (23), and a circular through hole two (28) is opened in the center; the piezoelectric ceramic stack (6) is composed of four piezoelectric ceramic sheets (3) and four electrode sheets (2) arranged in an interlaced and overlapping manner; the two piezoelectric ceramic stacks (6) are respectively connected through the circular through hole two (28) in the center It is sleeved on the outside of the pre-tightening screw (5) and is respectively distributed on the upper and lower sides of the mass block (4); the rear cover (1) is composed of a positioning block (18) and a positioning column (19), the outer diameter of the positioning block (18) is adapted to the inner diameter of the mounting cavity (23), and a threaded mounting hole 1 is provided at the axis center of the front end thereof, the front end of the positioning column (19) is vertically fixedly connected to the axis center of the rear end of the positioning block (18), and the surface of the positioning column (19) is coated with an insulating material layer; the rear cover (1) is fixedly sleeved on the outer side of the rear end of the pre-tightening screw (5) through the threaded mounting hole 1 at its front end, and its front end face abuts against the rear end face of the rear piezoelectric ceramic stack (6); the front cover (7) is cylindrical, the outer diameter of which is adapted to the inner diameter of the mounting cavity (23), and a threaded mounting hole 2 is provided at the axis center of the rear end thereof, and is fixedly sleeved on the outer side of the rear end of the pre-tightening screw (5) through the threaded mounting hole 2 at its rear end; The drilling tool (25) is composed of a variable amplitude rod (8), a spline shaft (17) and a drill bit (9); the variable amplitude rod (8) is a stepped shaft structure, the large diameter section of which is located at the rear side of the small diameter section, and the outer diameter of the large diameter section is adapted to the inner diameter of the mounting cavity (23), and the large diameter section is axially slidably assembled in the front part of the mounting cavity (23), and at the same time, the rear end of the large diameter section is fixedly connected to the front end surface of the front cover plate (7); the shape and size of the spline shaft (17) are consistent with those of the spline shaft (17). The key hole (26) is adapted in shape and size and is inserted into the spline hole (26) in an axially slidable and radially limited manner. The rear end of the spline shaft (17) penetrates into the mounting cavity (23) and is coaxially fixedly connected to the front end face of the small diameter section of the amplitude transformer (8). The front end of the spline shaft (17) is located outside the front end of the housing (13); the drill bit (9) is located outside the front end of the housing (13) and is coaxially fixedly connected to the front end of the spline shaft (17); The shell rear cover (10) is composed of a blocking block (20), a positioning sleeve (21) and a connecting protrusion (22). The blocking block (20) is cylindrical, and an external thread structure 1 is provided on the outer side of its front end, which is matched with the internal thread structure 1, and is inserted into the inner side of the rear open end of the shell (13) through threaded matching; the external thread structure 2 is provided on the outside of the positioning sleeve (21), and the rear end is coaxially fixedly connected to the front end face of the blocking block (20); the shape and size of the internal positioning hole of the positioning sleeve (21) are matched with the shape and size of the positioning column (19), and the positioning sleeve is axially slidable and radially limited and is fitted on the outside of the rear end of the positioning column (19); the front end of the connecting protrusion (22) is fixedly connected to the rear end face of the blocking block (20); The internal thread structure of the pre-tightening nut (11) is adapted to the external thread structure and is mounted on the outside of the positioning sleeve (21) through threaded matching; The preload spring (12) is arranged at the rear of the mounting cavity (23) and is sleeved on the outside of the positioning sleeve (21). At the same time, the rear end of the preload spring (12) abuts against the front end surface of the preload nut (11), and the front end abuts against the rear end surface of the positioning block (18) on the rear cover plate (1); The return spring (15) is arranged at the front of the installation cavity (23) and is sleeved on the outside of the small diameter section of the amplitude changing rod (8). At the same time, the rear end of the return spring (15) abuts against the front end surface of the large diameter section of the amplitude changing rod (8), and the front end of the return spring (15) abuts against the rear end surface of the limiting ring (24); When the bidirectional ultrasonic transducer (14) is connected to the ultrasonic power supply, the front cover (7) and the rear cover (1) can both generate high-frequency ultrasonic vibrations. The ultrasonic vibrations generated at the front end are transmitted to the drill bit (9) via the amplitude transformer (8) and the spline shaft (17), causing the drill bit (9) to generate ultrasonic vibrations. The ultrasonic vibrations generated at the rear end act on the end of the amplitude transformer (8) via the shell rear cover (10), and generate low-frequency impact sound waves during the collision between the rear cover (1) and the end of the amplitude transformer (8). The generated sound waves are transmitted to the drill bit (9) via the shell (13) and the bidirectional ultrasonic transducer (14), causing the drill bit (9) to generate sound-frequency vibrations.

2. The high-efficiency drilling device for coal mines using ultrasonic and low-frequency sound wave composite assistance according to claim 1, characterized in that: The cross section of the internal positioning hole of the positioning sleeve (21) is a regular hexagon, and the cross section of the positioning column (19) is a regular hexagon.

3. The high-efficiency drilling device for coal mines using ultrasonic and low-frequency sound wave composite assistance according to claim 1 or 2, characterized in that: The inner side wall of the housing (13) is coated with insulating lubricating oil.

4. The high-efficiency drilling device for coal mines using ultrasonic and low-frequency sound wave composite assistance according to claim 3, characterized in that: The shell back cover (10) is made of a material with high hardness, density and elastic modulus.

5. The high-efficiency drilling device for coal mines using ultrasonic and low-frequency sound wave composite assistance according to claim 4, characterized in that: The amplitude transformer (8) and the front cover plate (7) are fixedly connected via bolts.

6. The high-efficiency drilling device for underground coal mines using ultrasonic and low-frequency sound wave composite assistance according to claim 5, characterized in that: The rear cover plate (1) and the front cover plate (7) are both made of metal materials with low density, good toughness and good hardness, and the mass block (4) is made of metal materials with high density.

7. The high-efficiency drilling device for coal mines using ultrasonic and low-frequency sound wave composite assistance according to claim 6, characterized in that: The length of the preload spring (12) is greater than the length of the return spring (15).

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