Crack length measuring device
By designing a photoelectric measuring device, the problems of large measurement errors of traditional rulers and high cost of high-precision equipment were solved, realizing high-precision measurement of irregular cracks and portability, adapting to harsh environments.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUDONG ZHONGHUA SHIPBUILDINGGROUP
- Filing Date
- 2026-01-28
- Publication Date
- 2026-05-12
AI Technical Summary
In existing technologies, traditional rulers have large errors when measuring irregular curved cracks, and high-precision electronic equipment is expensive and not suitable for harsh environments.
A crack length measuring device including a photoelectric measurement unit and a display unit was designed. The device uses a photoelectric sensor to detect changes in the grating, converts the signal through a microprocessor, and displays the measurement results on an LCD screen. The device adopts an adjustable housing and a spiral wire structure to adapt to different environments and spaces.
It achieves high-precision measurement of irregular cracks, reduces costs, and improves portability and environmental adaptability, making it suitable for humid and oily shipyard environments.
Smart Images
Figure CN122015654A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of ship repair and non-destructive testing technology, and in particular to a crack length measuring device. Background Technology
[0002] During the construction, use and maintenance of ships, the hull structure is prone to cracks due to various factors such as load, corrosion and fatigue. In many cases, we need to measure the length of the cracks to assess the degree of damage to the hull or to carry out some crack arrest research. At the same time, the timely detection and accurate measurement of hull cracks are also crucial to the safe operation of ships.
[0003] Currently, the measurement of hull cracks mostly relies on traditional tools such as rulers and calipers. However, this method has many drawbacks. On the one hand, the measurement accuracy is greatly affected by manual visual reading and operating techniques, making it prone to errors, especially for irregularly curved cracks, which are even more difficult to measure and whose accuracy is hard to guarantee. On the other hand, traditional measuring tools are inconvenient to carry, and their operational flexibility and durability need improvement when used in the humid and oily environment of shipyards. In addition, although some precision electronic measuring equipment can achieve high accuracy, it is expensive, difficult to distribute on a large scale to inspection personnel, and is easily damaged in harsh environments, resulting in poor adaptability. Summary of the Invention
[0004] In view of this, the present invention provides a crack length measuring device to solve the problems of large measurement error when using a ruler to measure irregular curved cracks and high cost when using high-precision electronic equipment in the prior art.
[0005] A crack length measuring device includes a housing, a photoelectric measuring unit disposed at the bottom of the housing, a power supply for powering the photoelectric measuring unit disposed inside the housing, a start switch for controlling the current flow between the power supply and the photoelectric measuring unit, and a display unit disposed on the housing for receiving signals from the photoelectric measuring unit and displaying the length signal. The photoelectric measuring unit includes a measuring wheel rotatably disposed on the housing, a grating disposed on the side of the measuring wheel, the grating being evenly spaced around the rotation axis of the measuring wheel, and a photoelectric sensor disposed on the housing for sensing the grating. A microprocessor is disposed within the photoelectric measuring unit or the display unit for receiving the photoelectric sensor signal and converting it into a length signal.
[0006] Furthermore, the photoelectric measurement unit includes a mounting base for fixing on the bottom end of the housing. The photoelectric sensor is fixedly mounted on the mounting base, and the mounting base corresponds to the side of the measuring wheel so that the sensing probe of the photoelectric sensor corresponds to the grating on the side of the measuring wheel.
[0007] Furthermore, the housing includes a separate upper shell and a lower shell, the photoelectric measurement unit is disposed in the lower shell, the display unit is disposed in the upper shell, the upper shell and the lower shell are nested together, and a locking structure for locking them is provided between the upper shell and the lower shell.
[0008] Furthermore, the outer end of the upper and lower shells is provided with a bending portion for bending inward to fix the other shell. The bending portion has a claw-like structure with an external thread at the upper end of the claw. The locking structure also includes a locking nut that is threaded to the threaded portion. One end of the locking nut has an internal thread, and the other end has a pressing portion that protrudes inward to generate a bending torque on the bending portion.
[0009] Furthermore, the top of the upper shell is provided with an upper support plate, and the bottom of the shell is provided with a lower support plate. The power supply is fixedly mounted on the upper support plate. The display unit is located above the upper support plate, and the photoelectric measurement unit is located below the lower support plate. The crack length measuring device also includes wires for power supply and signal transmission. Both ends of the wires are respectively provided with clamping parts for fixing the wires on the upper support plate and the lower support plate. The wires other than the two clamping parts are respectively used to connect to the display unit, the photoelectric measurement unit and the power supply.
[0010] Furthermore, the wire between the two clamping parts is spiral-shaped.
[0011] Furthermore, a lower cover plate is provided at the bottom of the lower shell, the measuring wheel is disposed between the lower cover plate and the lower shell, and an upper cover plate is provided at the top of the upper shell.
[0012] Furthermore, the outer periphery of the measuring wheel is provided with anti-slip textures, which are evenly arranged in an X-shape.
[0013] Furthermore, the housing is also equipped with a reset button for resetting the measurement results to zero.
[0014] The beneficial effects of the crack length measuring device in this invention are as follows: The housing facilitates operation; the photoelectric measuring unit, with its measuring wheel equipped with gratings and corresponding photoelectric sensors, easily converts the length signal into a photoelectric signal. The measuring wheel rotates along the crack's direction, causing the gratings to rotate sequentially. The photoelectric sensors detect these positional changes; as the measuring wheel rotates at a specific angle, a corresponding number of gratings pass through the sensor's area. By detecting the number of gratings passed sequentially, the sensor determines the wheel's rotation angle. Since the measuring wheel's diameter is fixed, the distance traveled by the wheel, i.e., the crack length, can be determined from the diameter and rotation angle. A microprocessor converts these signals, and the display unit visually presents the measurement results. In other words, this invention, with its simple structure, enables the measurement of irregular crack lengths, thus solving the problems of large errors when using rulers to measure irregular curved cracks and the high cost of high-precision electronic equipment in existing technologies.
[0015] Furthermore, upper and lower support plates are installed inside the housing to facilitate the fixing of other components.
[0016] Furthermore, by setting up an upper and lower shell arranged in a nested configuration, the length of the device can be adjusted to easily adapt to confined spaces or areas that are difficult for people to access.
[0017] Furthermore, the addition of a bend and a locking nut allows for easy fixing at any position, making length adjustment more flexible.
[0018] Furthermore, by fixing both ends of the wire, the connection between the wire and the components is prevented from being affected when the length of the housing is adjusted, thus avoiding connection point failure.
[0019] Furthermore, by setting up upper and lower cover plates, it is convenient to install the measuring wheel and maintain components such as the upper rechargeable battery.
[0020] Furthermore, by setting anti-slip textures, the measuring wheel is less likely to slip during rotation, resulting in more accurate measurement results. Attached Figure Description
[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0022] Figure 1 This is a schematic diagram of an embodiment of the crack length measuring device of the present invention; Figure 2 This is an exploded view of an embodiment of the crack length measuring device of the present invention; Figure 3 for Figure 2 A magnified view of a section at point A in the middle; Figure 4 for Figure 2 A magnified view of a section at point B in the middle; Figure 5 for Figure 2 A magnified view of a section at point C; Figure 6 This is a cross-sectional schematic diagram of an embodiment of the crack length measuring device of the present invention; Figure 7 for Figure 6 A magnified view of a section at point D; Figure 8 for Figure 6 A magnified view of a section at point E in the middle.
[0023] The labels in the diagram represent the following: 1. Housing; 11. Upper housing; 12. Lower housing; 13. Locking nut; 14. Threaded part; 15. Bending part; 16. Extrusion part; 17. Lower cover plate; 18. Upper cover plate; 19. First locking screw; 2. Photoelectric measuring part; 21. Wheel rod; 22. Measuring wheel; 23. Anti-slip texture; 24. Grating; 25. Mounting base; 26. Second locking screw; 27. Photoelectric sensor; 3. Display part; 31. Sleeve; 32. Microprocessor; 33. LCD screen; 4. Switch button; 5. Reset button; 6. Wire; 7. Rechargeable lithium battery; 8. Clamping part; 81. Plastic clamp; 82. Rubber pad; 83. Third locking screw; 9. Lower support plate; 10. Upper support plate; 101. Ear plate; 102. Fourth locking screw. Detailed Implementation
[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.
[0025] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The singular forms “a,” “the,” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.
[0026] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various information, such information should not be limited to these terms and should not be construed as indicating or implying relative importance. These terms are used only to distinguish information of the same type from one another. For example, without departing from the scope of this disclosure, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."
[0027] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.
[0028] In the description of this invention, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "linking" should be interpreted broadly. For example, they can refer to mechanical or electrical connections, or internal connections between two components. They can be direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.
[0029] In the following description, suffixes such as "module," "part," or "unit" used to denote elements are used only for the convenience of the description of the invention and have no specific meaning in themselves. Therefore, "module" and "part" can be used interchangeably.
[0030] To better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings.
[0031] In Embodiment 1 of the crack length measuring device of the present invention: In this embodiment, the crack length measuring device includes a housing, a photoelectric measuring unit disposed at the bottom of the housing, and a display unit disposed at the top of the housing. The photoelectric measuring unit converts the length signal into a photoelectric signal, and then the display unit receives the photoelectric signal, converts the photoelectric signal back into a length signal, and displays it on the liquid crystal display screen. The device can be turned on, off, and reset using a power switch and a reset button.
[0032] Specifically, such as Figure 1 and Figure 2As shown, the device includes a housing 1, which is a slender, pen-shaped shell made of engineering plastic, convenient for gripping and capable of reaching areas difficult for personnel to access. Since the suitable length varies depending on the working conditions, the housing 1 is divided into an upper shell 11 and a lower shell 12, which are nested together. In this embodiment, at the nesting position, the diameter of the upper shell 11 is larger than the diameter of the lower shell 12, allowing the lower shell 12 to be nested inside the upper shell 11. The lower shell 12 is a smooth rod, and a locking structure for locking the lower shell 12 is provided at the lower end of the upper shell 11. Of course, in other embodiments, the lower shell can be fitted over the upper shell, in which case the locking structure would need to be provided on the lower shell.
[0033] Specifically, such as Figure 2 , Figure 4 and Figure 8 As shown, the locking structure includes a threaded portion 14 located at the lower end of the lower shell 12. The threaded portion 14 has an external thread structure. At the bottom end of the threaded portion 14, a claw-shaped bent portion 15 is also provided. The bent portion 15 has multiple protruding claws. This claw structure allows the bent portion 15 to easily deform inward, thereby clamping the lower shell 12. To facilitate the deformation of the bent portion 15, the device also includes a locking nut 13. The upper end of the locking nut 13 is provided with an internal thread that mates with the threaded portion 14, and the other end is a pressing portion 16 that gradually slopes inward into a frustum structure. When the pressing portion 16 contacts the bent portion 15, it deforms inward, thereby clamping the lower shell 12 and facilitating the fixation of the upper shell 11 and the lower shell 12. Specifically, during use, after adjusting the relative positions of the upper shell 11 and the lower shell 12, tightening the locking nut 13 upwards causes the pressing part 16 on the locking nut 13 to move towards the bending part 15 until it abuts against and deforms the bending part 15. The deformed bending part 15 then locks onto the outer periphery of the lower shell 12, thus securing the two together. Conversely, tightening the locking nut 13 downwards disengages the upper shell 11 and the lower shell 12. This extendable design expands the usability options, allowing for operation in hard-to-access areas, and also allows for easy shortening and carrying in a pocket after use. Alternatively, in other embodiments, the shell can be made as a single piece, eliminating the length adjustment function.
[0034] like Figure 2 and Figure 3As shown, a photoelectric measuring unit 2 is provided at the bottom of the lower shell 12 to facilitate the detection of irregular cracks. Specifically, the photoelectric measuring unit 2 includes a measuring wheel 22 rotatably mounted on the lower shell 12. A lower cover plate 17 is provided on the lower shell 12, and a wheel rod 21 is provided on the rotation axis of the measuring wheel 22. The wheel rod 21 passes through the lower shell 12 and the lower cover plate 17 to facilitate its rotation. The lower cover plate 17 and the lower shell 12 are fixedly connected by a first locking screw 19, which facilitates installation and also facilitates subsequent maintenance of internal components. A grating disk composed of gratings 24 is provided on the sides of both ends of the measuring wheel 22, and the gratings 24 are evenly spaced around the rotation axis of the measuring wheel 22. The measuring wheel 22 can travel along the direction of the crack. Furthermore, anti-slip texture 23 is provided on the outer periphery of the measuring wheel 22. The anti-slip texture 23 consists of X-shaped protrusions on the outside of the wheel, which increases the friction between the measuring wheel 22 and the area to be measured, preventing slippage and allowing the measuring wheel 22 to travel closer to the length of the crack. The measuring wheel 22 can also measure irregular shapes. Alternatively, in other embodiments, the entire outer periphery of the measuring wheel can be made of rubber. Alternatively, in other embodiments, a grating can be provided only on the side of one end of the measuring wheel. In this case, when installing the measuring wheel, the installation direction must be carefully considered so that the photoelectric sensor faces the side of the measuring wheel with the grating.
[0035] like Figure 6 and Figure 7 As shown, the travel length of the measuring wheel 22 is positively correlated with its rotation angle, and since the diameter of the measuring wheel 22 is known, the travel path of the measuring wheel 22 can be calculated simply by detecting its rotation angle, thus determining the crack length. To determine the rotation angle of the measuring wheel 22, a mounting base 25 is fixedly installed on the lower shell 12. The mounting base 25 is fixed to the lower shell 12 by a second locking screw 26. A photoelectric sensor 27 is fixedly installed on the mounting base 25. The probe of the photoelectric sensor 27 faces the light grid, accurately measuring the number of light grids 24 passing through the photoelectric sensor 27. Each time a light grid 24 passes through the photoelectric sensor 27, the photoelectric sensor 27 will excite a pulse. Crack length = number of pulses × (circumference of the measuring wheel 22 / number of light grids in one revolution of the light grid disk).
[0036] like Figure 2 and Figure 5As shown, to enable operators to intuitively obtain crack length information, a display unit 3 is also provided on the upper shell 11 in this embodiment. The display unit 3 includes a liquid crystal display screen 33 at the upper end of the upper shell 11, a microprocessor 32 is mounted on the liquid crystal display screen 33, and a sleeve 31 is mounted on the surface of the microprocessor 32, which is fitted onto the upper shell 11. The upper shell 11 has a separate upper cover plate 18, which is fixedly connected to the upper shell 11 by a first locking screw 19, facilitating the fixation of the display unit 3. The microprocessor 32 is fixedly connected to the sleeve 31, and the microprocessor 32 and the photoelectric sensor 27 are electrically connected by a wire 6; the liquid crystal display screen 33 is a 1.54-inch OLED display screen, fitted onto the upper end of the upper shell 11; the microprocessor 32 uses an STM32F103 microcontroller, which is soldered onto the circuit board of the liquid crystal display screen 33. After receiving the pulse signal from the photoelectric sensor 27, the microprocessor 32 converts it into a length signal.
[0037] Meanwhile, both the photoelectric measurement unit 2 and the display unit 3 require power to operate. Therefore, the device is also equipped with a power supply. Specifically, in this embodiment, the power supply is a rechargeable lithium battery 7, which is cylindrical and housed within the space enclosed by the upper cover plate 18 and the upper shell 11. An upper support plate 10 is also provided on the upper cover plate 18 to fix the rechargeable lithium battery 7. Specifically, an ear plate 101 is provided on the outer periphery of the rechargeable lithium battery 7. Mounting holes are provided on the ear plate 101 and the upper support plate 10, and the rechargeable lithium battery 7 can be fixedly connected to the upper support plate 10 by a fourth locking screw 102. At the same time, the upper cover plate 18 can also be easily removed to replace the battery or repair the display unit 3. In order to facilitate charging of the rechargeable lithium battery 7, an opening corresponding to the charging port on the rechargeable lithium battery 7 is also provided on the shell 1. Of course, in other implementations, the power source can also be other forms, such as lead-acid batteries or dry cell batteries. In this case, a removable battery cover needs to be installed on the casing.
[0038] like Figure 6 , Figure 7 and Figure 8As shown, in order to power the photoelectric measurement unit 2 and the display unit 3, and also for information exchange between the photoelectric measurement unit 2 and the display unit 3, a wire 6 is required. The photoelectric measurement unit 2 is located inside the lower shell 12, and the display unit 3 is located inside the upper shell 11. This requires the wire 6 to extend a relatively long distance along the length of the shell 1. Changes in the length of the shell 1 will also affect the wire 6. In order to reduce the impact on the wire 6 when the length of the shell 1 changes, in this embodiment, both ends of the wire 6 are fixedly mounted on the shell 1. Specifically, a lower support plate 9 is also provided inside the lower shell 12, and a clamping part 8 is provided on the wire 6. The clamping part 8 includes a U-shaped plastic clip 81, and a rubber pad 82 for clamping and fixing the wire 6 is provided on the inner side of the plastic clip 81. Both ends of the plastic clip 81 are provided with a third locking screw 83. The clamping part 8 located at the upper end of the wire 6 is fixed to the upper support plate 10 by the third locking screw 83, and the clamping part 8 located at the lower end of the wire 6 is fixed to the lower support plate 9 by the third locking screw 83. The outer ends of the wires 6 at the clamping part 8 are used to connect to the power supply, the photoelectric measurement part 2, and the display part 3, respectively. This ensures that even if the length changes, the connection between the wires 6 and the components will not be strained. Furthermore, to facilitate length variations in the wires 6, they are spirally arranged and have multiple strands. Each strand of the wire 6 can simultaneously contain both signal transmission lines and power lines.
[0039] To control the state of the device, a switch button 4 and a reset button 5 are also provided on the housing 1. The switch button 4 is installed at the upper end of the housing and is used to control the start switch in the circuit, and in turn to control the current flow between the rechargeable lithium battery 7, the photoelectric measurement unit 2, and the display unit 3, facilitating start-up and shutdown. The reset button 5 is also installed at the upper end of the housing and is used to clear the data displayed on the display unit 3, facilitating continuous measurement of multiple cracks.
[0040] Compared with existing ruler measuring instruments or high-precision instruments, this device has the following advantages: 1. Excellent portability and ease of use: The device is designed in the shape of a ballpoint pen, made of engineering plastic, making it lightweight and compact. It can be easily placed in a pocket or tool bag, making it convenient for inspection personnel to carry. The operation process is simple and intuitive; starting, stopping, and data clearing can be completed using only the power switch and reset button. No complicated professional training is required, making it widely applicable.
[0041] 2. High measurement accuracy: Utilizing the photoelectric measurement principle, the measurement data is converted by detecting changes in the grating on the measuring wheel through a photoelectric sensor, avoiding the errors of manual visual reading in traditional ruler measurement. Especially for measuring irregular curved cracks, the measuring wheel can roll closely in line with the crack trajectory, and combined with the "X"-shaped anti-slip pattern to prevent slippage, the measurement accuracy is far higher than that of traditional measurement methods.
[0042] 3. Low cost and easy to mass-produce: The device adopts a mature mechanical structure and conventional electronic components, such as photoelectric sensors, microprocessors, and LCD screens. The overall manufacturing cost is low, and there is no need for high precision machining costs, which makes it easy to mass-produce and distribute to front-line inspection personnel.
[0043] 4. Strong environmental adaptability: The pen-shaped outer shell is made of engineering plastic, which has good corrosion resistance and wear resistance; the internal wire 6 adopts a spiral structure and is fixed by the clamping part, which is not easy to be damaged by pulling; all components are firmly connected, the structure is simple and reliable, and it can adapt to the harsh shipyard working environment such as dampness and grease, and is not prone to failure.
[0044] 5. The structure is reasonably designed and easy to maintain: the upper shell and the upper cover plate, and the lower shell and the lower cover plate are connected by the first locking screw, which can be easily disassembled and assembled, facilitating the inspection and replacement of internal components such as rechargeable lithium batteries, wires, and photoelectric measurement units; the rechargeable lithium batteries are fixed by the ear plates and the fourth locking screw, making replacement convenient and reducing maintenance costs.
[0045] When in use, first adjust the length of the outer shell according to the actual measurement requirements: rotate the locking nut 13 so that it moves down along the threaded part 14 of the upper shell 11, releasing the compression part 16 from the compression of the bent part 15 of the upper shell 11. At this time, the lower shell 12 can be pulled to adjust the relative position of the upper shell 11 and the lower shell 12. After the length is adjusted properly, rotate the locking nut 13 in the opposite direction so that the compression part 16 compresses the bent part 15 of the upper shell 11. The bent part 15 deforms and sticks tightly to the outer surface of the lower shell 12, thereby achieving the locking and fixing of the upper shell 11 and the lower shell 12.
[0046] Pressing the switch button 4 powers the photoelectric measurement unit 2 and the display unit 3 via the rechargeable lithium battery 7, putting the device into operation. The anti-slip texture 23 of the measuring wheel 22 is placed against the starting position of the crack in the hull. The measuring wheel 22 is then rolled along the crack. The rotation of the measuring wheel 22 causes the gratings 24 on both sides to rotate synchronously. The photoelectric sensor 27 detects the positional changes of the gratings 24 in real time and converts the detected light signal into an electrical signal, which is transmitted to the microprocessor 32 via the spiral wire 6. The microprocessor 32 processes the electrical signal, calculates the length of the crack based on the circumference of the measuring wheel 22 and the number of rotations, and transmits the measurement data to the LCD screen 33 for display. When the next measurement is needed, pressing the reset button 5 clears the data on the LCD screen 33, allowing the measurement to restart.
[0047] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
Claims
1. A crack length measuring device, characterized in that: The device includes a housing, a photoelectric measuring unit located at the bottom of the housing, a power supply inside the housing to power the photoelectric measuring unit, a start switch between the power supply and the photoelectric measuring unit to control the current flow, and a display unit on the housing for receiving signals from the photoelectric measuring unit and displaying them as length signals. The photoelectric measuring unit includes a measuring wheel rotatably mounted on the housing, with a grating on the side of the measuring wheel, the grating being evenly spaced around the rotation axis of the measuring wheel. The photoelectric measuring unit also includes a photoelectric sensor mounted on the housing to sense the grating. A microprocessor is also located inside the photoelectric measuring unit or the display unit for receiving signals from the photoelectric sensor and converting them into length signals.
2. The crack length measuring device according to claim 1, characterized in that: The photoelectric measurement unit includes a mounting base for fixing on the bottom end of the housing. The photoelectric sensor is fixedly mounted on the mounting base, and the mounting base corresponds to the side of the measuring wheel so that the sensing probe of the photoelectric sensor corresponds to the grating on the side of the measuring wheel.
3. The crack length measuring device according to claim 1 or 2, characterized in that: The housing includes a separate upper shell and a lower shell. The photoelectric measurement unit is located in the lower shell, and the display unit is located in the upper shell. The upper shell and the lower shell are nested together, and a locking structure is provided between the upper shell and the lower shell for locking them together.
4. The crack length measuring device according to claim 3, characterized in that: The outer end of the upper and lower shells is provided with a bending portion for bending inward to fix the other shell. The bending portion has a claw-like structure with an external thread at the upper end of the claw. The locking structure also includes a locking nut that is threaded to the threaded portion. One end of the locking nut has an internal thread, and the other end has a pressing portion that protrudes inward to generate a bending torque on the bending portion.
5. The crack length measuring device according to claim 4, characterized in that: The top of the upper shell is provided with an upper support plate, and the bottom of the shell is provided with a lower support plate. The power supply is fixedly mounted on the upper support plate. The display unit is located above the upper support plate, and the photoelectric measurement unit is located below the lower support plate. The crack length measuring device also includes wires for power supply and signal transmission. Both ends of the wires are respectively provided with clamping parts for fixing the wires on the upper support plate and the lower support plate. The wires other than the two clamping parts are respectively used to connect to the display unit, the photoelectric measurement unit and the power supply.
6. The crack length measuring device according to claim 5, characterized in that: The wire between the two clamping parts is spiral-shaped.
7. The crack length measuring device according to claim 3, characterized in that: The bottom of the lower shell is provided with a lower cover plate, the measuring wheel is disposed between the lower cover plate and the lower shell, and the top of the upper shell is provided with an upper cover plate.
8. The crack length measuring device according to claim 1 or 2, characterized in that: The outer circumference of the measuring wheel is provided with anti-slip texture, and the protective texture is evenly arranged in an X shape.
9. The crack length measuring device according to claim 1 or 2, characterized in that: The housing is also equipped with a reset button for resetting the measurement results to zero.