An intelligent frequency test system for constructing coal assemblies

Abstract

The present application relates to the field of vibration test experiment equipment, and discloses an intelligent vibration frequency test system for tectonic coal combination, when a driving cam rotates around a central shaft, the cam drives a driving lifting slider to move up and down through a transmission connecting rod, and simultaneously, the driving lifting slider drives a driven lifting slider to move up and down through a spring flexible belt, a force hammer moves synchronously with the driven lifting slider to knock the tectonic coal combination on a coal sample rack, and a vibration signal generated by the tectonic coal combination is collected by a vibration signal analyzer through an acceleration sensor. The test system builds a multi-parameter collaborative architecture of 'vibration frequency-acoustic emission-mechanical loading': multi-signal synchronous collection: the acceleration sensor collects vibration signals, and can synchronously access acoustic emission sensors and pressure sensors, to realize millisecond-level synchronous recording of vibration frequency, acoustic emission event number and coal body stress and strain data, and to completely restore the crack propagation timing.

Description

Technical Field

[0001] This invention relates to the field of vibration testing equipment, and more specifically to an intelligent vibration frequency testing system for constructing coal assemblies. Background Technology

[0002] Tectonic coal deposits are abundant and widely distributed in my country. Due to their typical characteristics such as weakened cohesive strength, significantly reduced compressive strength, and limited permeability, stress concentration easily occurs ahead of the working face during mining, leading to the superposition of vibration frequencies, increasing the degree of damage to the coal body structure, and inducing coal and gas outbursts. Studying the influence of vibration frequencies and fracture evolution in tectonic coal assemblages is crucial for ensuring safe production in coal and gas outburst mines. During coal mining, the mechanical loading environment is an important component of the stress state of the coal body, affecting not only the stability of the coal seam but also directly related to changes in the vibration characteristics of the coal. Natural frequencies, as a manifestation of the physical properties of the coal, are closely related to its internal microstructure and mechanical properties, while the loaded vibration frequency is a direct reflection of the coal's vibration response under external mechanical loading. Therefore, it is necessary to clarify the interaction between the two.

[0003] Currently, the force hammer striking method has become a common method for measuring vibration frequency due to its low cost and ease of operation. However, its reliance on manual operation makes it difficult to guarantee the accuracy of the striking force.

[0004] For tectonic coal assemblages, the heterogeneity of the coal structure exacerbates the uncontrollable impact of impact force. Tectonic coal has low strength and is sensitive to external excitation, while primary coal has higher strength, resulting in significant differences in their vibration responses. When the impact force is too high, tectonic coal regions are prone to premature formation of overdeveloped fracture networks due to stress concentration. In contrast, primary coal may have its fracture propagation underestimated due to insufficient excitation energy. This error makes it difficult to accurately analyze the fracture propagation sequence and interaction mechanism of different coal structures within the assemblage. Furthermore, the randomness of the impact force leads to a decrease in the signal-to-noise ratio of the vibration response signal, requiring researchers to spend a significant amount of time on data screening and repeated experiments, increasing the experimental cycle and manpower costs. At the same time, traditional single-parameter analysis methods are insufficient to comprehensively capture the multi-stage characteristics of coal from damage to failure. While traditional techniques such as acoustic emission (AE) and uniaxial loading can provide some mechanical parameters, they lack dynamic coupling analysis with vibration frequency, limiting the accurate characterization of the entire process of coal fracture evolution. Therefore, it is necessary to improve the accuracy of vibration frequency testing methods. Summary of the Invention

[0005] To address the aforementioned challenges, this invention aims to develop an automatic striking device capable of setting different striking forces and numbers of strikes. Through computer programming, parameters such as the stepper motor's operating speed and cycle can be precisely set, thereby accurately controlling the striking force and number of strikes on the coal sample. Furthermore, based on vibration testing methods, a multi-parameter testing method can be developed, combining vibration frequency with acoustic emission and uniaxial loading for multi-parameter collaborative monitoring. By precisely controlling the striking force and tracking micro-fracture signals and mechanical responses in real time, the accuracy of research on the evolution of coal fractures under complex conditions is improved. This is of great significance for understanding the mechanisms of coal and gas outbursts, predicting outburst risks, and developing effective prevention and control measures.

[0006] To achieve the above objectives, the present invention provides an intelligent vibration frequency testing system for constructing coal assemblages, comprising:

[0007] The base has a supporting frame erected on it;

[0008] The driven lifting slider is mounted on the support frame and can slide up and down. It is provided with an upper elastic member facing upward and a lower elastic member facing downward.

[0009] An active lifting slider is mounted on the support frame and can slide up and down. It consists of an upper slider, a lower slider, and a connecting block fixedly connected between the upper slider and the lower slider. The upper slider is located above the driven lifting slider and contacts the upper elastic element, and the lower slider is located below the driven lifting slider and contacts the lower elastic element.

[0010] A cam is disposed below the active lifting slider. The cam has a central shaft and an eccentric shaft. The central shaft is connected to the power drive unit, and the eccentric shaft is connected to the active lifting slider through a transmission link.

[0011] A hammer is fixedly mounted on the driven lifting slider via its hammer handle;

[0012] A coal sample placement rack is positioned below the hammerhead of the hammer, and a buffer pad is provided on the rack for placing the structural coal assembly to be tested; and

[0013] A vibration signal analyzer is connected to an acceleration sensor, which is used to attach and fix to the structural coal assemblies to be tested.

[0014] As a further preferred embodiment of the present invention, the support frame is provided with a first slide groove and a second slide groove, and the left and right ends of the driven lifting slider are each installed and cooperated with a set of the first slide groove, and the active lifting slider is installed and cooperated with the second slide groove.

[0015] As a further preferred embodiment of the present invention, the support frame includes two side plates and a back plate connected between the two side plates, the first sliding groove is disposed on the side plate, and the second sliding groove is disposed on the back plate.

[0016] As a further preferred embodiment of the present invention, the power drive unit includes a servo motor, the rotating shaft of which is connected to the central shaft of the cam or connected to the central shaft of the cam via a reducer.

[0017] As a further preferred embodiment of the present invention, a crossbeam is provided on the support frame below the active lifting slider, and vertical guide sleeves are respectively provided on both sides of the crossbeam on the transmission connecting rod. Guide posts that cooperate with the guide sleeves are respectively provided on the left and right sides of the driven lifting slider.

[0018] As a further preferred embodiment of the present invention, the lower end of the guide post is connected to a limit buffer block.

[0019] As a further preferred embodiment of the present invention, a mounting hole is provided at the center of the side of the driven lifting slider, and the hammer handle of the hammer is inserted into the mounting hole and locked and fixed by a lock nut.

[0020] As a further preferred embodiment of the present invention, the coal sample placement rack includes an upright cylindrical tube, a hydraulic lifting assembly is provided inside the cylindrical tube, a placement platform is provided on the top of the hydraulic lifting assembly, a buffer pad is placed on the placement platform, the structural coal assembly to be tested is placed on the buffer pad, and at least a portion of the structural coal assembly is exposed at the upper end of the cylindrical tube.

[0021] As a further preferred embodiment of the present invention, a vertical through hole is provided on the driven lifting slider, and a spring cylindrical pin is installed in the through hole. The upper elastic element and the lower elastic element are springs installed in the spring cylindrical pin, respectively.

[0022] As a further preferred embodiment of the present invention, a computer is also included, which is connected to the vibration signal analyzer and the servo motor.

[0023] The present invention has the following beneficial effects:

[0024] 1. Automation and precise control of the excitation source: Servo motor + cam mechanism + spring cylindrical pin reset system replaces traditional manual hammers or expensive vibrators.

[0025] Traditional hammer striking methods rely on manual operation, resulting in significant randomness in striking force, frequency, and angle, and obvious secondary striking phenomena. Furthermore, multiple tests of the same coal sample show large deviations, especially given the significant strength difference between tectonically deposited and native coal, easily leading to excessive damage to tectonically deposited coal or insufficient excitation of native coal. This system achieves fully automated and precise control through a servo motor, cam-driven quick-return mechanism, and parameter mapping algorithm.

[0026] (1) The striking force can be precisely controlled (by reverse-engineering the linear velocity v through the rotation speed n, and then calculating the force F);

[0027] (2) The number of taps N and the time interval T can be set to achieve fully automatic repeated testing;

[0028] (3) By using the quick-return cam-transmission link + spring cylindrical pin as an aid, the "quick-return characteristic" is achieved through the asymmetrical structure of the cam, thus completely avoiding secondary knocking.

[0029] 2. Testing Efficiency: From "Inefficient Repetition" to "Automated Batch Processing"

[0030] In traditional testing, the randomness of the striking force leads to a low signal-to-noise ratio in the vibration signal. Researchers need to spend 30%-50% of their time screening for valid data, and the testing cycle for a single sample can take several hours. At the same time, manual striking cannot achieve continuous batch testing, resulting in low experimental efficiency.

[0031] (1) Automatic data evaluation: Time domain amplitude detection, signal-to-noise ratio calculation, and secondary impact detection algorithm complete the data quality evaluation within 0.5s after each impact and automatically mark "accept / reject", reducing manual screening time by more than 80%.

[0032] (2) Batch continuous testing: Supports multiple preset parameters (such as 5 types of striking force and 10 repetitions). The system automatically completes the entire process of parameter changing, striking, and data acquisition. The single sample test cycle is shortened from the traditional 2 hours to 30 minutes, and the batch testing efficiency is increased by 3 times.

[0033] (3) Unattended operation: The computer is linked with the servo motor and vibration signal analysis block. The test plan can be preset and executed automatically, reducing the cost of manual operation and making it suitable for long-term continuous experiments (such as coal fatigue vibration test).

[0034] 3. Testing Dimensions: From "Single Parameter Isolation" to "Multi-Parameter Collaborative Monitoring"

[0035] Traditional testing methods often focus only on a single parameter, vibration frequency, and cannot be integrated with techniques such as acoustic emission (AE) and mechanical loading. This makes it difficult to comprehensively depict the entire process of coal body damage and failure, especially failing to capture the dynamic coupling relationship between the evolution of tectonic coal fractures and vibration frequency. This system constructs a multi-parameter collaborative architecture of "vibration frequency-acoustic emission-mechanical loading": Simultaneous acquisition of multiple signals: Accelerometers collect vibration signals and can simultaneously connect to acoustic emission sensors and accelerometers, achieving millisecond-level synchronous recording of vibration frequency, acoustic emission event counts, and coal body stress-strain data, thus completely reconstructing the fracture propagation timeline.

[0036] 4. Equipment adaptability: From "limited by specific scenarios" to "compatible with multiple operating conditions"

[0037] Traditional testing equipment has obvious limitations: artificial force hammers are only suitable for small laboratory samples and cannot simulate the mechanical loading environment of a coal mine; vibrator-based equipment is expensive (over 100,000 yuan per unit) and bulky, making it unsuitable for rapid on-site testing, and it can easily cause irreversible damage to fragile samples such as structural coal.

[0038] (1) Strong sample compatibility: The coal sample placement rack adopts a hydraulic lifting component (lifting range 0-100mm), which, together with the cylindrical tube accommodating cavity, can be adapted to structural coal composite samples with a diameter of 50-200mm. In addition, the buffer pad (ACF artificial cartilage material) reduces the impact damage to the sample by knocking and protects the fragile structural coal structure.

[0039] (2) Both laboratory and field use: The system is modularly designed with a base size of only 1.2m×0.8m and a weight of about 50kg. It can be disassembled for transportation and does not require complicated installation during field testing. The servo motor has a power of only 1.5kW and is compatible with the 220V voltage in coal mines, solving the problem of power supply for traditional vibrators.

[0040] (3) Cost controllable: The total cost of core components (servo motor, cam mechanism, vibration signal analyzer) is about RMB30,000, which is only 30% of the traditional exciter method, and the maintenance cost is low (the cam, guide column and other vulnerable parts can be quickly replaced, with a unit price of < RMB200). Attached Figure Description

[0041] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0042] Figure 1 This is a schematic diagram of an embodiment of the intelligent vibration frequency testing system for constructing coal assemblies according to the present invention.

[0043] Figure 2 This is a partial schematic diagram of an intelligent vibration frequency testing system, in which the support frame, base, and coal sample placement rack have been removed.

[0044] Figure 3This is a schematic diagram of the cam structure.

[0045] The markings in the image are as follows:

[0046] 1. Support frame; 2. Driven lifting slider; 3. Active lifting slider; 301. Upper slider; 302. Lower slider; 303. Connecting block; 4. Guide column; 5. Guide sleeve; 6. Transmission link; 7. Servo motor; 8. Cam; 81. Central shaft; 82. Eccentric shaft; 9. Limiting buffer block; 10. Spring cylindrical pin; 101. Spring; 11. First slide groove; 12. Force hammer; 13. Crossbeam; 14. Structural coal assembly; 15. Accelerometer; 16. Buffer pad; 17. Hydraulic lifting assembly; 18. Cylindrical tube; 19. Vibration signal analyzer; 20. Computer.

[0047] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0048] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Terms such as "upper," "lower," "left," "right," "middle," and "one" used in the preferred embodiments are merely for clarity of description and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0049] like Figure 1 , Figure 2 and Figure 3 As shown in this embodiment, an intelligent vibration frequency testing system for constructing coal assemblies includes:

[0050] The base has a support frame 1 erected on it. The support frame includes two side plates and a back plate connected between the two side plates. The side plates have a vertical first sliding groove 11, and the back plate has a vertical second sliding groove.

[0051] The driven lifting slider 2 is mounted on the support frame 1 by engaging with the first slide groove 11 at its left and right ends. The driven lifting slider 2 has two vertical through holes symmetrically opened on its center. A spring cylindrical pin 10 with a spring 101 is fixedly installed in the through hole. Both ends of the spring 101 extend out of the spring cylindrical pin 10 so that both ends of the spring cylindrical pin 10 are elastic.

[0052] The active lifting slider 3, through cooperation with the second sliding groove, is mounted on the back plate of the support frame 1 in a reciprocating up-and-down sliding manner. It consists of an upper slider 301, a lower slider 302, and a connecting block 303 fixedly connected between the upper slider 301 and the lower slider 302. The upper slider 301 is located above the driven lifting slider 2 and contacts the upper end spring 101 of the spring cylindrical pin 10. The lower slider 302 is located below the driven lifting slider 2 and contacts the lower end spring 101 of the spring cylindrical pin 10. When the active lifting slider 3 descends, the upper slider 301 compresses the spring 101 above the spring cylindrical pin 10 downwards to push the driven lifting slider 2 downwards. When the active lifting slider 3 rises, the lower slider 302 compresses the spring 101 below the spring cylindrical pin 10 upwards to push the driven lifting slider 2 upwards.

[0053] Cam 8 is located below the active lifting slider 3. Cam 8 has a central shaft 81 and an eccentric shaft 82. Its central shaft 81 is connected to the rotating shaft of the servo motor 7 fixed on the base. A transmission link 6 is connected to the eccentric shaft 82. The other end of the transmission link 6 is hinged to the lower slider 302 of the active lifting slider 3. When cam 8 rotates around the central shaft 81, it drives the transmission link 6 to move through the eccentric shaft 82, thereby driving the active lifting slider 3 to move up and down.

[0054] The hammer 12 is inserted into the mounting hole in the center of the side of the driven lifting slider 2 through its hammer handle and locked in place by the anti-loosening nut. Its hammer handle is horizontal or the hammer head is slightly tilted downward so that the hammer 12 can perform a striking action as it follows the driven lifting slider 2.

[0055] A coal sample placement rack includes an upright cylindrical tube 18, inside which a hydraulic lifting assembly 17 is provided. The top of the hydraulic lifting assembly 17 supports a placement platform with a buffer pad 16. The structural coal assembly 14 to be tested is placed on the buffer pad 16 and located below the hammer head of the hammer 12. The upper end of the cylindrical tube 18 and the placement platform form a receiving cavity, and at least a portion of the structural coal assembly 14 is exposed in the receiving cavity.

[0056] The vibration signal analyzer 19 is connected to an acceleration sensor 15, which is fixed to the structural coal assembly 14 to be tested by a cable tie. When the servo motor 7 drives the cam 8 to rotate around its central axis 81, the cam 8 drives the active lifting slider 3 to move up and down through the transmission link 6. At the same time, the active lifting slider 3 flexibly drives the driven lifting slider 2 to move up and down through the spring 101. The hammer 12 moves synchronously with the driven lifting slider 2 to strike the structural coal assembly 14 on the coal sample placement rack. The vibration signal generated by the structural coal assembly 14 is collected by the vibration signal analyzer 19 through the acceleration sensor 15.

[0057] Computer 20 is connected to the vibration signal analyzer 19 and the servo motor 7. Through programming of computer 20, parameters such as the running speed, number of rotations, and number of taps of the servo motor can be precisely set. After tapping, the vibration data is collected by the acceleration sensor 15 and then fed back to computer 20 by vibration signal analyzer 19 for recording and analysis.

[0058] The function of the hydraulic lifting component 17 is to adjust the placement height of the platform within the cylindrical tube 18, thereby aligning the top striking surface of the constructed coal assembly 14 in the experiment with the optimal striking point of the hammer 12. The hydraulic lifting component 17 is a conventional structure, such as a jack.

[0059] In specific implementation, a crossbeam 13 is provided on the support frame 1 below the active lifting slider 3. Vertical guide sleeves 5 are provided on both sides of the crossbeam 13, located on the transmission connecting rod 6. Guide posts 4, which cooperate with the guide sleeves 5, extend downwards from the left and right sides of the driven lifting slider 2. During the up-and-down movement of the driven lifting slider 2, the guide posts 4 move within the guide sleeves 5, thus effectively guiding the movement of the driven lifting slider 2, ensuring smooth and stable motion. A silicone limiting buffer block 9 is connected to the lower end of the guide post 4 as a mechanical limiting device to prevent the driven lifting slider 2 from moving downwards beyond its maximum stroke. That is, when the driven lifting slider 2 moves downwards beyond the preset maximum stroke (such as due to improper installation height or other special circumstances), the limiting buffer block 9 contacts the base surface, mechanically limiting the continued descent of the driven lifting slider 2, thereby protecting the equipment.

[0060] This invention innovatively employs an asymmetric cam 8 as the main component and a spring 101 carried by a spring cylindrical pin 10 as an auxiliary component in a quick-return structure as a solution for secondary impact. The quick-return device of cam 8 uses a servo motor 7 as the main power source. With the help of an asymmetric contour design (large difference in the slope of the working section and the return section), the rotational motion of the motor is converted into the linear reciprocating motion of the driven lifting slider 2 driving the power hammer 12 through the transmission link 6, which dominates the motion mode and rhythm of "slow advance for impact, fast retreat for reset". The elastic component of the spring cylindrical pin 10 does not actively pull the driven lifting slider 2, but assists in the motion sequence of cam 8 - when the transmission link 6 pulls the driven lifting slider 2 downward, it compresses the upper spring 101 to generate a downward thrust, thereby accelerating the downward movement of the power hammer 12 (without affecting the overall speed). The thrust is greatest when the coal sample is struck at the lowest point of the downward movement; when rising, it compresses the lower spring 101 to generate an upward thrust, which accelerates the upward movement of the power hammer 12 (without affecting the overall speed). During the striking phase, the system maintains full compression to ensure precise force application. In the rapid return phase, it releases elastic potential energy as cam 8 enters the return segment, providing support for the rapid retraction of the driven lifting slider 2. Simultaneously, it eliminates mechanical clearance between cam 8 and the driven component, preventing impact vibration. The two work together in a "cam 8-driven, spring 101-assisted optimization of the return effect" mode to achieve efficient rapid return of the hammer 12 without secondary striking. The striking frequency of this test system is determined by the rotational speed of cam 8; one revolution of cam 8 results in one striking.

[0061] This invention achieves automated and precise control of the excitation source: the servo motor 7 is controlled in software to perform simple rotational cycles, while the mechanical structure resolves the inherent contradictions. The core of the servo motor 7 control strategy of this invention includes two parts: target parameter calculation and motion execution. First, the integrated control unit calculates the parameters based on the user-defined target striking force F, striking frequency N, and time interval T. Based on the formula... The required impact velocity is derived, and then... The target rotational speed n of the servo motor 7 is calculated. Then, the integrated control unit sends a command to the servo driver, driving the servo motor 7 to execute a preset striking cycle: first, rotating at a fixed angle θ_impact at rotational speed n, driving the impact hammer to complete one strike; then, via the cam 8 and transmission link 6, the impact hammer is quickly reset. This action constitutes a complete striking cycle. The system accumulates the number of cycles using an internal counter and compares it with the user-set target number of strikes N, repeating this process until all strikes are completed. The entire process automatically alternates and cycles, with a high-precision timer strictly controlling the time interval T between each strike, ultimately achieving precise, automatic, and programmable control of the striking force, number of strikes, and time interval. Although specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is limited only by the appended claims.

Claims

1. An intelligent vibration frequency testing system for constructing coal assemblages, characterized in that, include: The base has a supporting frame erected on it; The driven lifting slider is mounted on the support frame and can slide up and down. It is provided with an upper elastic member facing upward and a lower elastic member facing downward. An active lifting slider is mounted on the support frame and can slide up and down. It consists of an upper slider, a lower slider, and a connecting block fixedly connected between the upper slider and the lower slider. The upper slider is located above the driven lifting slider and contacts the upper elastic element, and the lower slider is located below the driven lifting slider and contacts the lower elastic element. A cam is disposed below the active lifting slider. The cam has a central shaft and an eccentric shaft. The central shaft is connected to the power drive unit, and the eccentric shaft is connected to the active lifting slider through a transmission link. A hammer is fixedly mounted on the driven lifting slider via its hammer handle; A coal sample placement rack is located below the hammerhead of the hammer, and a buffer pad is provided on the coal sample placement rack for placing the structural coal assembly to be tested on the buffer pad; as well as A vibration signal analyzer is connected to an acceleration sensor, which is used to attach and fix to the structural coal assemblies to be tested.

2. The intelligent vibration frequency testing system for constructing coal assemblies according to claim 1, characterized in that, The support frame is provided with a first slide groove and a second slide groove. The left and right ends of the driven lifting slider are each installed and cooperate with a set of the first slide groove, and the active lifting slider is installed and cooperated with the second slide groove.

3. The intelligent vibration frequency testing system for constructing coal assemblies according to claim 2, characterized in that, The support frame includes two side plates and a back plate connecting the two side plates. The first sliding groove is disposed on the side plate, and the second sliding groove is disposed on the back plate.

4. The intelligent vibration frequency testing system for constructing coal assemblies according to claim 1, characterized in that, The power drive unit includes a servo motor, the shaft of which is connected to the central shaft of the cam or to the central shaft of the cam via a reducer.

5. The intelligent vibration frequency testing system for constructing coal assemblies according to claim 1, characterized in that, The support frame is provided with a crossbeam below the active lifting slider. Vertical guide sleeves are provided on both sides of the crossbeam on the transmission connecting rod. Guide posts that cooperate with the guide sleeves are provided on the left and right sides of the driven lifting slider.

6. The intelligent vibration frequency testing system for constructing coal assemblies according to claim 5, characterized in that, The lower end of the guide post is connected to a limit buffer block.

7. The intelligent vibration frequency testing system for constructing coal assemblies according to claim 1, characterized in that, The driven lifting slider has a mounting hole at its center on its side, and the hammer handle of the hammer is inserted into the mounting hole and locked in place by a lock nut.

8. The intelligent vibration frequency testing system for constructing coal assemblies according to claim 1, characterized in that, The coal sample placement rack includes an upright cylindrical tube, a hydraulic lifting assembly is provided inside the cylindrical tube, a placement platform is supported on the top of the hydraulic lifting assembly, a buffer pad is placed on the placement platform, the structural coal assembly to be tested is placed on the buffer pad, and at least part of the structural coal assembly is exposed at the upper end of the cylindrical tube.

9. The intelligent vibration frequency testing system for constructing coal assemblies according to claim 1, characterized in that, The driven lifting slider has a vertical through hole, and a spring cylindrical pin is installed in the through hole. The upper elastic element and the lower elastic element are springs installed in the spring cylindrical pin, respectively.

10. The intelligent vibration frequency testing system for constructing coal assemblages according to any one of claims 1-9, characterized in that, It also includes a computer, which is connected to the vibration signal analyzer and the servo motor.

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