A pendulum type rebound hammer

Abstract

The present invention relates to a pendulum-type rebound hammer, comprising a rebound hammer frame provided with a striking rod, a pendulum rotatably mounted on the rebound hammer frame via a rotating connection structure, the pendulum having an impact portion for impacting the striking rod, a pendulum driving structure for driving the pendulum toward the striking rod, and a measuring device for measuring changes in the swing speed and / or swing angle of the pendulum before and after impacting the striking rod. The present invention provides a pendulum-type rebound hammer that can reduce the influence of the friction of the hammer on the measurement during the process of the hammer impacting the striking rod.

Description

Technical Field

[0001] The invention relates to a pendulum type rebound hammer for measuring concrete strength. Background Art

[0002] The concrete rebound test uses a spring-driven hammer that strikes the concrete surface through a rod. The concrete surface elastically deforms, absorbing energy, and the hammer rebounds. The energy loss is used to characterize the concrete's hardness. The principle is that the harder the concrete, the less energy it absorbs through elastic deformation, and thus the less energy is lost during the hammer's impact.

[0003] The working process of concrete rebound test hammer is as follows Figure 1 As shown, in order to clearly illustrate the problem, the first state, the second state, the third state, the fourth state and the fifth state occur in chronological order. During operation, the height of the impact hammer 16 is first raised, as shown in the first state, the impact hammer spring 15 stores energy, and the end of the impact rod 2 away from the impact hammer contacts the concrete surface. Subsequently, the impact hammer 16 is released, and the impact hammer moves toward the impact rod under the guidance of the guide rod 19, as shown in the second state; then, the lower end surface 18 of the impact hammer hits the impact rod 2, and the impact rod hits the concrete, as shown in the third state; then, as shown in the fourth state, the impact hammer begins to rebound away from the impact rod; finally, as shown in the fifth state, the impact hammer reaches the highest rebound position.

[0004] In the prior art, there are basically two measurement methods to characterize the energy loss of the impact hammer. The first method is to measure the height difference between the impact hammer in the first state and the fifth state, and calculate the rebound value through the change in energy between the two states. The difference between the sum of the gravitational potential energy of the impact hammer in the first state and the elastic potential energy of the spring in the first state and the sum of the gravitational potential energy of the impact hammer in the fifth state and the elastic potential energy of the spring in the fifth state is the change in energy between the two states. This method obviously has the following disadvantages: 1) The change from the first state to the fifth state is not only a change in gravitational potential energy and elastic potential energy. There is sliding friction between the impact hammer and the guide rod. This friction will also cause energy loss. This friction cannot be ignored and will affect the accuracy of the rebound value characterization; 2) Since the gravitational potential energy of the impact hammer must be considered, the impact angle of the impact rod hitting the concrete surface is very critical, and the entire operation process is relatively strict.

[0005] The second method is to measure the impact velocity V0 when the hammer hits the impact rod, and the rebound velocity V when the hammer just leaves the impact rod. RThe energy loss of the hammer is characterized by the kinetic energy loss of the impact before and after the impact, and then the rebound value is calculated. This method has the following disadvantages: 1) Due to the presence of the spring, the kinetic energy loss is not complete in the two states. Only when the elastic potential energy of the spring is exactly at the potential energy zero point at the moment of impact, the kinetic energy loss can accurately characterize the energy loss of the hammer. However, it is difficult to ensure that the spring is at the potential energy zero point at the moment of impact; 2) The friction between the hammer and the impact rod is still an energy loss factor that cannot be ignored in the energy calculation process; 3) Dynamic speed measurement is not so easy and stable.

[0006] Of course, whether it is the first method or the second method, there is still a problem: the lower end face of the impact hammer is a plane. Under ideal conditions, the lower end face of the impact hammer directly contacts the upper end face of the impact rod once to complete the hardness measurement of the concrete. However, due to the guide fit tolerance between the impact hammer and the guide rod, the impact hammer cannot ensure that its lower end face is completely perpendicular to the axis of the guide rod during movement. When the lower end face of the impact hammer is not perpendicular to the axis of the impact rod, the tip of the impact hammer will first hit the impact rod once and then hit the impact rod a second time. If two impacts occur, part of the energy will be absorbed by the impact rod, and the entire measurement process will be inaccurate. Summary of the Invention

[0007] The object of the present invention is to provide a pendulum type rebound hammer which can reduce the influence of the friction force of the impact hammer on the measurement during the process of the impact hammer striking the impact rod.

[0008] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0009] A pendulum-type rebound hammer, a rebound hammer frame, a pendulum rotatably mounted on the rebound hammer frame via a rotating connection structure, the pendulum having an impact portion, the pendulum-type rebound hammer further comprising a pendulum driving structure for driving the pendulum to impact the impact rod, and the pendulum-type rebound hammer further comprising a measuring device for measuring changes in the swing speed and / or swing angle before and after the pendulum impacts the impact rod.

[0010] Furthermore, the rotation axis of the rotating connection structure passes through the center of gravity of the pendulum.

[0011] Furthermore, the pendulum as a whole is a centrosymmetrical structure.

[0012] Furthermore, the pendulum driving structure is a pendulum spring connected to the pendulum, and the measuring device measures the change in the swing angle of the pendulum before and after it hits the striking rod.

[0013] Furthermore, the pendulum spring is a torsion spring or a coil spring.

[0014] Furthermore, the pendulum driving structure includes a striking hammer and a striking hammer spring connected to the striking hammer. The pendulum is struck by the striking hammer and strikes the striking rod. The rotating connection structure includes a rotating shaft that rotates with the rebound instrument frame. The pendulum is fixed together with the rotating shaft. The measuring device obtains the swing speed of the pendulum by measuring the rotation speed of the rotating shaft.

[0015] Furthermore, the impact part is a ball head structure.

[0016] Furthermore, the rotation connection structure includes a bearing mounted on the rebound tester frame and a rotating shaft rotatably matched with the bearing, and the pendulum is fixed to the rotating shaft.

[0017] Furthermore, the distance between the impact portion and the rotation axis of the rotation connection structure is at least twice the radius of the rotation axis.

[0018] Furthermore, the measuring device is an absolute value encoder for detecting the rotation angle and rotation speed of the shaft.

[0019] The beneficial effects of the present invention are as follows: the pendulum driving structure in the present invention drives the pendulum to directly or indirectly impact the concrete, and the measuring device measures the speed change and / or swing angle change before and after the pendulum impact. If the measuring device measures the speed change before and after the pendulum impact, the energy loss during the pendulum impact process can be obtained through kinetic energy loss. If the measuring device measures the swing angle change before and after the pendulum impact, the energy loss during the pendulum impact process can be obtained through potential energy loss. The pendulum outputs the impact force through swinging rather than through linear movement. The influence of the friction force at the rotating connection structure on the entire impact process is affected by the distance between the impacted part and the rotation axis of the rotating connection structure. The larger the distance between the impacted part and the rotation axis of the rotating connection structure, the smaller the influence of the friction force at the rotating connection structure, thereby reducing the influence of the friction force of the impact hammer on the measurement during the impact process of the impact hammer as much as possible.

[0020] Furthermore, the rotation axis of the rotating connection structure passes through the center of gravity of the pendulum, that is, the gravitational potential energy does not change during the swing of the pendulum. Therefore, the measuring device measures the change in the swing angle of the pendulum before and after it hits the striking rod. The energy loss before and after the pendulum hits can be obtained through the change in elastic potential energy, which has nothing to do with the impact angle of the striking rod hitting the concrete, thereby reducing the difficulty of operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural diagram of the background technology of the present invention;

[0022] Figure 2 1 is a schematic structural diagram of Example 1 of the pendulum type rebound hammer of the present invention;

[0023] Figure 3 yes Figure 2Schematic diagram of the coordination of the pendulum, rotating shaft and pendulum spring;

[0024] Figure 4 yes Figure 1 A top view of

[0025] Figure 5 Schematic diagram of the structure of the pendulum in the energy storage state in Example 1;

[0026] Figure 6 2 is a schematic diagram of the principle of the pendulum type rebound hammer in the present invention;

[0027] Figure 7 Schematic diagram of the process in which the pendulum is struck by the striking hammer and strikes the striking rod in Example 2;

[0028] In the figure: 1. vertical device guide sleeve; 2. impact rod; 3. vertical device floating spring; 4. impact rod guide sleeve; 5. adjustment sleeve; 6. rebound instrument frame; 7. impact part; 8. pendulum; 9. pendulum spring; 10. rotating shaft; 11. impact rod vertical device; 12. bearing; 13. absolute value encoder; 14. pendulum limit block; 15. impact hammer spring; 16. impact hammer; 17. impact head of impact hammer; 18. lower end face of impact hammer; 19. guide rod; 20. limit outward turning edge; 21. inward turning edge of adjustment sleeve. DETAILED DESCRIPTION

[0029] To facilitate understanding of the present invention, the present invention will be described in more detail below with reference to the accompanying drawings and specific embodiments. Preferred embodiments of the present invention are shown in the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in this specification. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0030] It should be noted that, unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0031] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0032] Example 1 of a pendulum type rebound tester of the present invention is as follows Figures 2 to 5As shown, the rebound hammer frame 6 is provided with a striking rod 2. A pendulum 8 is rotatably mounted on the rebound hammer frame 6 via a rotating connection structure. The pendulum is a centrally symmetrical structure. One end of the pendulum is a striking portion 7 for striking the striking rod. The striking portion is a ball head structure for point contact with the striking rod. Since the pendulum is a centrally symmetrical structure, the other end of the pendulum 8 also has a similar ball head structure. The centrally symmetrical structure of the pendulum makes it easier to determine the center of gravity of the pendulum. The rotation axis of the rotating connection structure passes through the center of gravity of the pendulum 8. In this embodiment, the rotating connection structure includes a rotating shaft 10, which is rotatably engaged with the rebound hammer frame 6 via a bearing 12. The pendulum 8 is fixedly connected to the rotating shaft 10. The axis of the rotating shaft constitutes the axis of the rotating connection structure. Therefore, the axis of the rotating shaft 10 passes through the center of gravity of the pendulum.

[0033] The pendulum rebound tester also includes a pendulum driving structure for driving the pendulum to impact the striking rod. In this embodiment, the pendulum driving structure is a pendulum spring 9 connected to the pendulum. The pendulum spring 9 is a torsion spring. One end of the pendulum spring is connected to the pendulum, and the other end of the pendulum spring is connected to the rebound tester frame 6.

[0034] The pendulum rebound tester also includes a measuring device for measuring the changes in the swing speed and swing angle before and after the pendulum hits the striking rod. In this embodiment, the measuring device is an absolute value encoder 13 for detecting the rotation angle and rotation speed of the rotating shaft. The absolute value encoder 13 can detect the rotation angle of the rotating shaft 10 and the rotation angular velocity of the rotating shaft.

[0035] The rebound hammer frame includes a rebound hammer frame body and an adjustment sleeve 5 connected to the rebound hammer frame body. The adjustment sleeve 5 is threadedly connected to the rebound hammer frame. A striking rod guide sleeve 4 is fixed to the inner side of the adjustment sleeve 5. The striking rod 2 is guided and moved in conjunction with the inner hole of the striking rod guide sleeve 4. A limited outward edge 20 is provided on the striking rod 2. The adjustment sleeve 5 is provided with an adjusting sleeve inward edge 21 for cooperating with the limited outward edge 20 to limit the upward movement limit of the striking rod relative to the adjustment sleeve. The upper end surface of the striking rod guide sleeve 4 is used to cooperate with the lower end of the limited outward edge to limit the downward movement limit of the striking rod.

[0036] The adjusting sleeve 5 is used to adjust the moment when the pendulum strikes the striking rod to the moment when the pendulum spring has zero elastic potential energy. The specific use process is as follows: gently move the pendulum spring. When the pendulum automatically resets, it is the position of zero elastic potential energy of the pendulum spring. At this time, the striking rod is pressed upward by hand so that the limit outward edge of the striking rod is always in contact with the inward edge of the adjusting sleeve. The adjusting sleeve is rotated relative to the rebound test frame body to adjust the height of the adjusting sleeve so that the upper end of the striking rod contacts the striking part of the pendulum. Then, the adjustment of the adjusting sleeve is stopped. At this time, when the pendulum is rotated upward, the pendulum spring accumulates energy. When the pendulum spring carries the pendulum to strike the striking rod, the elastic potential energy of the pendulum spring is zero when the striking part contacts the striking rod. In this embodiment, an observation window can be opened at a position corresponding to the upper end of the striking rod on the rebound test frame. The observation window is blocked by a transparent material. Through this observation window, it is observed whether the upper end of the striking rod contacts the striking part.

[0037] The adjustment sleeve 5 is mounted with a vertical impact rod 11, which is used to ensure that the impact rod is perpendicular to the concrete surface. The impact rod includes a vertical impactor floating spring 3 and a vertical impactor guide sleeve 1. The vertical impactor guide sleeve is arranged to guide the movement of the adjustment sleeve. The vertical impactor floating spring 3 is arranged between the vertical impactor guide sleeve 1 and the adjustment sleeve 5. The lower end surface of the vertical impactor guide sleeve is a plane perpendicular to the axis of the impact rod. During use, the lower end surface of the vertical impactor guide sleeve contacts and cooperates with the concrete surface to be tested. The adjustment sleeve is pressed until the lower end surface of the impact rod also contacts and cooperates with the concrete surface. At this time, the limit outward edge of the impact rod and the inward edge of the adjustment sleeve on the adjustment sleeve are blocked. The rebound value test can be carried out. The pendulum is rotated upward, the pendulum spring stores energy, and then the pendulum is released. Driven by the pendulum spring, the pendulum's impact part strikes the impact rod. After the impact, the concrete absorbs energy, and the pendulum loses energy. The pendulum limit block 14 in the figure is used to limit the clockwise rotation limit of the pendulum.

[0038] The absolute value encoder in the present invention can measure the rotation angle of the rotating shaft, and can also measure the rotation angular velocity of the rotating shaft. When the rotation angle of the rotating shaft is selected as the measurement data, the energy loss before and after the pendulum impact can be calculated through the potential energy loss. It is simple and convenient because during the entire impact process, the gravitational potential energy of the pendulum does not change, and only the elastic potential energy of the pendulum spring changes. Therefore, it is not limited to the impact angle of the striking rod and is not related to the striking angle. It is easy to operate, and the energy loss before and after the pendulum impact can be easily obtained, and then the rebound value can be obtained.

[0039] When the angular velocity of the rotating shaft is selected as the measurement data, the energy loss before and after the pendulum impact can be calculated by kinetic energy loss. The speed of the impact part before and after the impact of the rebound rod can be converted into the angular velocity of the rotating shaft. Since the elastic potential energy of the pendulum spring is zero when the impact part impacts the rebound rod, the pendulum moves at a constant speed when there is no pendulum spring force involved. Therefore, the energy loss before and after the pendulum impact can be easily obtained, and then the rebound value can be obtained. The present invention can use potential energy to calculate the energy loss of the pendulum, and can also calculate the energy loss of the pendulum by kinetic energy.

[0040] Since the guidance is through the rotating connecting structure, the guiding structure does not need to pass through the pendulum, so the impact part can be a ball head structure for point contact cooperation with the impact rod. The impact part and the impact rod complete the test with one collision, ensuring the accuracy of the test.

[0041] After the rotating pendulum is used to strike the striking rod, the rotating shaft fixed with the pendulum has the same angular velocity as the pendulum. Compared with the linear velocity measurement in the prior art, the measurement of the rotating shaft speed is simple and convenient.

[0042] Moreover, whether calculating the energy loss before and after the pendulum impact using potential energy or kinetic energy, the work done by friction at the rotating shaft can be almost ignored due to the use of a pendulum structure. The principle is that the friction coefficient of the bearing is 0.001-0.003. In this embodiment, it is assumed that the rolling friction coefficient of the bearing is 0.002. The friction coefficient is represented by μ, the radius of the rotating shaft is r, the distance between the impact part and the rotating shaft axis is d, the mass of the pendulum is m, the stiffness of the pendulum spring is D, and the impact angular displacement of the pendulum spring from the energy storage state to the zero elastic potential energy state is S. The friction force f=mg*μ generated by the gravity of the pendulum, and the friction torque w=mg*μ*r generated by this friction force. This friction torque generates a corresponding reaction force F at the collision point. The reaction force F=mg*μ*r / d. This force produces a deviation in the spring stretching length, and the deviation =F / D. This deviation has a relatively small effect on the overall energy loss of the pendulum, and the deviation depends on the r / d value. That is to say, the greater the ratio of the radius of the impact part to the axis of rotation and the axis of rotation, the smaller the deviation.

[0043] Assuming D = 785 N / m, S = 75 mm, m = 0.37 kg, μ = 0.002, r = 5 mm, and d = 86 mm, the friction force generated by the weight of the pendulum is f = 0.37 * 10 * 0.002 = 0.0074 N, resulting in a friction torque w = 0.0074 N * 0.005 = 0.000037 Nm. This friction torque generates a corresponding reaction force F = 0.000037 Nm / 0.086 = 0.00043 N at the point of impact. This force produces a deviation in the spring's stretched length: 0.00043 N / 785 N / m = 0.00000055 m = 0.00055 mm. This length deviation has a relatively small impact on the energy loss caused by the pendulum's impact, with a maximum deviation of less than 2 / 10,000.

[0044] In other embodiments of the present invention, a suitable value of r / d can be selected as needed, and the distance between the impact part and the rotation axis of the rotating connection structure is at least twice the radius of the rotation axis, which can reduce the influence of friction; when only potential energy is needed to calculate the energy loss value of the pendulum, the measuring device only needs to measure the swing angle of the pendulum before and after the impact process; when only kinetic energy is needed to calculate the energy loss value of the pendulum, the measuring device only needs to measure the speed change of the pendulum before and after the impact of the impact rod; the swing spring can also be a torsion spring or a cylindrical spring, etc.; the impact rod can also be omitted, and the adjustment sleeve and the impact rod vertical device can be omitted. At this time, the pendulum can directly contact and impact the concrete.

[0045] Example 2 of a pendulum type rebound tester of the present invention is as follows Figures 6 and 7 As shown in the figure, Example 2 differs from Example 1 in that no pendulum spring is connected to the pendulum 8. The pendulum drive structure includes a snap hammer 16 and a snap hammer spring 15 connected to the snap hammer. The snap hammer 16 has a snap hammer impact head 17 for impacting the pendulum. The pendulum 8 is impacted by the snap hammer 16 and impacts the impact rod 2. The measuring device can measure the change in speed of the pendulum before and after impacting the impact rod. During use, the height of the snap hammer 16 is raised, the snap hammer spring 15 stores energy, and then the snap hammer spring 15 is released, causing the snap hammer 16 to impact the pendulum 8. Then, the impact portion 7 of the pendulum 8 impacts the impact rod 2, and the impact rod impacts the concrete. Figure 7 From left to right in the middle, the first picture shows the moment when the striking hammer hits the inverted pendulum, and the second picture shows the moment when the pendulum hits the striking rod.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A pendulum type rebound hammer, comprising a rebound hammer frame, characterized in that: The rebound hammer frame is also rotatably equipped with a pendulum through a rotating connection structure. The pendulum has a striking portion. The pendulum rebound hammer also includes a pendulum driving structure for driving the pendulum to strike the striking rod. The pendulum rebound hammer also includes a measuring device for measuring the change in the swing angle of the pendulum before and after the impact. The rotation axis of the rotating connection structure passes through the center of gravity of the pendulum. The pendulum driving structure is a pendulum spring connected to the pendulum. The rotating connection structure includes a bearing mounted on the rebound hammer frame and a rotating shaft rotatably matched with the bearing. The pendulum is fixed to the rotating shaft, and the striking portion is 1 / 4 of the distance from the rotating connection structure to the impact portion. The distance between the rotation axes is at least twice the radius of the rotation axis. The rebound hammer frame includes a rebound hammer frame body and an adjusting sleeve connected to the rebound hammer frame body. The adjusting sleeve is threadedly connected to the rebound hammer frame. A striking rod guide sleeve is fixed to the inner side of the adjusting sleeve. The striking rod is guided and moved in cooperation with the inner hole of the striking rod guide sleeve. A limited outward turning edge is provided on the striking rod, and an adjusting sleeve inward turning edge is provided on the adjusting sleeve for cooperating with the limited outward turning edge to limit the upward movement limit of the striking rod relative to the adjusting sleeve. The upper end surface of the striking rod guide sleeve is used to cooperate with the lower end stop of the limited outward turning edge to limit the downward movement limit of the striking rod.

2. The pendulum type rebound hammer according to claim 1, characterized in that: The pendulum as a whole is a centrosymmetrical structure.

3. The pendulum type rebound hammer according to claim 1, characterized in that: The pendulum spring is a torsion spring or a coil spring.

4. The pendulum type rebound hammer according to claim 1, characterized in that: The pendulum driving structure includes a striking hammer and a striking hammer spring connected to the striking hammer. The pendulum is struck by the striking hammer and strikes the striking rod. The rotating connection structure includes a rotating shaft that rotates with the rebound instrument frame. The pendulum is fixed together with the rotating shaft. The measuring device obtains the swing speed of the pendulum by measuring the rotation speed of the rotating shaft.

5. The pendulum type rebound hammer according to claim 4, characterized in that: The measuring device is an absolute value encoder for detecting the rotation angle and rotation speed of the rotating shaft.

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