Metal structure contact detection device and detection method based on capacitive sensing

Abstract

The application belongs to the technical field of capacitive sensing detection, and discloses a metal structure contact detection device and method based on capacitive sensing. The device comprises an elongated sensing electrode and an insulating sheath wrapping the electrode, the sheath forms an exposed sensing area only at one main surface and is configured to be mounted on the metal structure. The application effectively suppresses the motion interference of the metal component and the liquid bridging interference through the geometric constraint design of double isolation protection, significantly improves the reliability and accuracy of the human contact signal detection in the metal structure environment, and has the advantages of simple structure, low cost, easy installation and maintenance.

Description

Technical Field

[0001] This invention belongs to the field of detection equipment technology, specifically relating to a contact detection device and method for metal structures based on capacitive sensing. Background Technology

[0002] Capacitive sensing technology is based on the principle of capacitive coupling between conductors. When a human body approaches or touches the sensing electrode, the human body, as a conductive medium, has an induced capacitance to ground, which changes the electric field distribution between the sensing electrode and ground, thus causing a change in capacitance. By detecting this change in capacitance, non-contact or contact detection of human approach or contact can be achieved. This technology is widely used in fields such as human body induction switches, anti-pinch protection, and touch control due to its advantages of low cost, low power consumption, and no privacy leakage risk.

[0003] However, integrating capacitive sensors onto the metal structures of automated equipment presents unique technical challenges. Firstly, the metal structure itself, as a large conductor, significantly alters the electric field distribution, leading to instability in the sensor's reference capacitance value. Particularly when the metal structure contains moving parts, changes in their position cause continuous fluctuations in capacitance. The capacitance change resulting from these fluctuations is similar to that caused by human contact, making it difficult for existing technologies to effectively distinguish between them through hardware structure, easily leading to false triggering. Secondly, there is a risk of liquid intrusion in practical applications. When conductive liquid forms a bridging path between the sensing electrode and the metal structure, it generates capacitance changes similar to those caused by human contact, also leading to false triggering.

[0004] To address the aforementioned issues, existing technologies typically employ two solutions. One is to use a fully sealed structure to block liquid intrusion, but this solution cannot solve the problem of motion interference from movable metal parts and increases the structural complexity and installation and maintenance costs of the device. The other solution uses complex algorithm filtering and machine learning models to process the capacitance signal to distinguish between interference signals and valid contact signals. However, this solution significantly increases the system's computing power cost, reduces the detection response speed, and the filtering algorithm is prone to failure when both metal motion interference and liquid bridging interference are present, making it impossible to guarantee the reliability of the detection. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a metal structure contact detection device and method based on capacitive sensing. Through a geometric constraint design with dual isolation protection, it achieves highly reliable detection of human contact signals in a metal structure environment.

[0006] The technical solution adopted in this invention is as follows:

[0007] In a first aspect, the present invention provides a contact detection device for a metal structure based on capacitive sensing, comprising:

[0008] The slender sensing electrodes are used to connect to the capacitive sensing circuit;

[0009] An insulating sheath, enclosing the sensing electrode and forming an exposed sensing area only on one of its main surfaces, is provided for mounting on a metal structure.

[0010] The insulating sheath is designed to provide double isolation between the sensing electrode and the surrounding metal structure.

[0011] The first safety distance d1 is defined as the minimum distance between the sensing area and the movable metal part of the metal structure, so as to ensure that the electric field coupling strength between the movable metal part and the sensing area at the extreme position is weaker than the coupling strength when the human body touches it directly.

[0012] The second safety distance d2 is defined as the width of the insulating plane provided by the insulating sheath between the sensing electrode and the metal structure on which the device is mounted, in order to increase the creepage distance on the surface and prevent liquid from forming a continuous conductive bridging path between the sensing electrode and the metal structure.

[0013] It is worth noting that the main surface mentioned in this invention refers to the two opposite surfaces with the largest width dimension that extend along the length direction of the slender sensing electrode. This surface is the core sensing surface of the sensing electrode, and the remaining surfaces are the side surfaces and end surfaces.

[0014] In conjunction with the first aspect, the present invention provides a first embodiment of the first aspect, wherein the second safety distance d2 and the first safety distance d1 satisfy the ratio relationship: d2 / d1≥2.

[0015] In conjunction with the first aspect, the present invention provides a second embodiment of the first aspect, wherein the surface of the sensing area is constructed as a micro-arc surface structure so that the liquid contracts into discrete droplets rather than a continuous water film under the action of surface tension.

[0016] In conjunction with the first aspect, the present invention provides a third embodiment of the first aspect, wherein the thickness of the insulating sheath in the sensing area is 0.5 mm to 2 mm, the first safety distance d1 is 1 mm to 10 mm, and the second safety distance d2 is 2 mm to 20 mm.

[0017] In conjunction with the first aspect, the present invention provides a fourth embodiment of the first aspect, wherein the cross-section of the sensing electrode is rectangular or elliptical, the thickness is 0.5 mm to 2 mm, the width is 1 mm to 5 mm, and the sensing electrode is fully wrapped by an insulating sheath through an extrusion molding process.

[0018] In conjunction with the first aspect, the present invention provides a fifth embodiment of the first aspect, wherein the bottom of the insulating sleeve is provided with a mounting buckle or adhesive layer for fixing the device to the metal structure, and the second safety distance d2 is jointly defined by the lateral width of the mounting buckle or adhesive layer and the thickness of the bottom of the insulating sleeve.

[0019] This invention provides a contact detection method using a metal structure contact detection device based on capacitive sensing as described in any one of the first to fifth embodiments of the first aspect, comprising:

[0020] Establish a baseline for basic capacitance values;

[0021] A trigger threshold is set, which is determined based on the capacitance change range defined by the first safety distance d1 and the second safety distance d2. The capacitance change generated by direct human contact is significantly greater than the capacitance change generated by the movement of movable metal parts or the capacitance change generated by liquid bridging, so as to distinguish human contact signals from environmental interference signals.

[0022] It is also worth noting that the capacitance sensing circuit described in this invention uses a dedicated capacitance-to-digital converter chip, such as the AD7147 or FDC2214. The chip's capacitance sampling channel is electrically connected to the electrical leads of the sensing electrode, and the chip's communication interface is connected to the main control unit to transmit the sampled capacitance value to the main control unit. The main control unit executes the contact detection method described above, completing the calculation of capacitance change, threshold comparison, and contact state determination. The sampling resolution of the capacitance sensing circuit is not less than 1pF, and the sampling frequency is not less than 10Hz to ensure detection sensitivity and response speed.

[0023] The beneficial effects of this invention are as follows:

[0024] By setting a first safety distance d1, this invention ensures that the movable metal part cannot form a strong electric field coupling with the sensing area even in extreme positions. The capacitance change it generates is much smaller than the capacitance change generated by direct human contact, thus providing a clear physical threshold boundary for signal differentiation and significantly improving the robustness of the detection system to mechanical motion interference.

[0025] This invention, by setting a second safety distance d2, increases the creepage distance using a wide insulating plane, effectively blocking the formation of a continuous conductive bridging path between the liquid and the metal structure. This eliminates parasitic capacitance interference caused by liquid bridging at the physical structure level and avoids false triggering caused by liquid intrusion.

[0026] This invention achieves a balance between mechanical compactness and electromagnetic compatibility by optimizing the ratio of the second safety distance d2 to the first safety distance d1, maximizing anti-interference performance within a limited installation space, and enabling the device to adapt to the installation requirements of various complex metal structures.

[0027] This invention improves detection accuracy in humid environments by setting a micro-arc surface structure on the surface of the sensing area and using surface tension to shrink the liquid into discrete droplets instead of a continuous water film. This reduces the influence of dielectric constant changes caused by the liquid simply covering the sensing surface.

[0028] This invention establishes a trigger threshold setting method based on dual isolation protection geometric parameters. By utilizing the significant differences in capacitance changes among human contact, metal part movement, and liquid bridging, it achieves a simple and reliable signal discrimination logic, reduces reliance on complex signal processing algorithms, and improves real-time detection performance. Attached Figure Description

[0029] Figure 1 This is an isometric view of the detection device in an embodiment of the present invention;

[0030] Figure 2 This is a side view of the detection device in an embodiment of the present invention.

[0031] In the diagram: 1-Insulating sheath, 2-Induction electrode. Detailed Implementation

[0032] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0033] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0034] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0035] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0036] In the description of this application, it should be noted that the use of terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" to indicate orientation or positional relationships is based on the orientation or positional relationships shown in the accompanying drawings, or the orientation or positional relationships commonly used when the product is in use. These terms are used solely for the convenience of describing this application and for 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 application. Furthermore, the use of terms such as "first" and "second" in the description of this application is only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0037] Furthermore, the use of terms such as "horizontal" and "vertical" in the description of this application does not imply that the component is required to be absolutely horizontal or suspended, but rather that it may be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but rather that it may be slightly tilted.

[0038] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0039] Example 1:

[0040] This embodiment provides a contact detection device for metal structures based on capacitive sensing, referring to... Figure 1 and Figure 2 It includes a slender sensing electrode and an insulating sheath. The sensing electrode is made of a conductive metal material and is slender in shape that extends longitudinally. One or both ends of the electrode are electrically led out to connect to a capacitive sensing circuit for sensing changes in the electric field caused by the approach or contact of an external conductor.

[0041] The insulating sheath is made of an insulating material with a stable dielectric constant. The sheath completely encloses the sensing electrode, forming an exposed sensing area on only one main surface, while the rest of the surfaces are covered by the insulating material.

[0042] The sensing area serves as the sensitive interface for capacitive sensing, allowing an electric field to penetrate and detect external contact. The sheath isolates the sensing electrodes from the surrounding metal structure, enabling the entire device to be stably mounted on the metal surface.

[0043] The insulating sheath is specially designed to provide double isolation between the sensing electrode and the surrounding metal structure, including two safety gaps:

[0044] The first safety distance d1 is defined as the minimum distance between the sensing area and the movable metal part of the metal structure, ensuring that the electric field coupling strength between the movable metal part and the sensing area at the extreme position is weaker than the coupling strength when the human body touches it directly.

[0045] The second safety clearance d2 is defined as the width of the insulating plane provided by the insulating sheath between the sensing electrode and the metal structure on which the device is mounted. This insulating plane extends laterally along the bottom surface of the sheath to increase the surface creepage distance and prevent liquid from forming a continuous conductive bridging path between the sensing electrode and the metal structure.

[0046] It is worth noting that capacitive sensing technology faces two typical types of interference when applied to metallic structures:

[0047] First, there are electric field coupling fluctuations caused by the positional changes of movable metal parts contained in the metal structure during operation;

[0048] Second, the parasitic capacitance change caused by the bridging path formed between the sensing electrode and the metal structure when the conductive liquid enters.

[0049] The first safety distance d1 addresses motion interference from movable metal parts through spatial isolation. This distance is defined as the minimum distance between the sensing area and the movable metal parts of the metal structure. Utilizing the physical property that electric field coupling strength decreases with distance, it ensures that even when the movable metal part is in its extreme position, the electric field coupling strength between it and the sensing area is significantly weaker than that when the human body directly touches it. Therefore, the capacitance change caused by the movement of the movable metal part is suppressed to a low level, while the large capacitance change caused by human contact creates a distinguishable signal difference.

[0050] The second safety clearance d2 addresses liquid bridging interference by blocking conductive paths. This clearance is manifested as the width of the insulating plane provided by the insulating sheath between the sensing electrode and the metal structure on which the device is mounted. This plane significantly increases the creepage distance. Under the influence of surface tension, the liquid is unlikely to form a continuous conductive bridge across the wide insulating plane. Even if the liquid covers the surface of the sensing area, a stable low-resistance path cannot be established between the sensing electrode and the metal structure, thus effectively suppressing capacitive interference caused by liquid bridging.

[0051] Example 2:

[0052] In one specific embodiment, the sensing electrode has a rectangular cross-section, a thickness of 1 mm, a width of 2 mm, and a length customized according to the installation scenario. The electrode is made of aluminum alloy and is fully encased in an insulating sheath through an extrusion molding process, with only one main surface exposed to form the sensing area.

[0053] The insulating sleeve is made of ABS plastic and co-extruded with the induction electrode using an extrusion molding process. The thickness of the insulating sleeve is 1mm in the sensing area. The bottom of the sleeve has a flat mounting surface that fits snugly against the metal structure after installation.

[0054] The first safety distance d1 is set to 5mm to ensure that the movable metal parts in the metal structure maintain this minimum distance from the sensing area even in extreme motion positions.

[0055] The second safety clearance d2 is set to 10mm, which is limited by the lateral width of the mounting plane at the bottom of the insulating sheath and the thickness of the bottom of the sheath, satisfying the ratio relationship d2 / d1=2.

[0056] In another specific embodiment, the inductive electrode has an elliptical cross-section with a thickness of 1 mm and a width of 3 mm. The major axis of the ellipse is parallel to the surface of the sensing area, and it is fully enclosed by an insulating sheath during extrusion molding. The insulating sheath has a thickness of 0.5 mm in the sensing area. The first safety distance d1 is set to 1 mm, and the second safety distance d2 is set to 2 mm. This design is suitable for scenarios where installation space is limited but liquid protection requirements are low.

[0057] Example 3:

[0058] In one specific embodiment, the bottom of the insulating sleeve is provided with a mounting buckle, which is integrally formed with the insulating sleeve. During installation, the buckle engages with a reserved slot in the metal structure, so that the bottom of the sleeve fits tightly against the surface of the metal structure.

[0059] The second safety clearance d2 is defined by the lateral width of the mounting clip and the thickness of the bottom of the insulating sleeve. Specifically, the width of the mounting clip extending laterally is 8 mm, and the thickness of the bottom of the insulating sleeve below the electrode is 2 mm, together forming an effective insulating plane width of 10 mm.

[0060] In another specific embodiment, the bottom of the insulating sleeve is provided with an adhesive layer, which is a double-sided adhesive or silicone adhesive layer, directly pasted to the surface of the metal structure. In this case, the second safety clearance d2 is jointly defined by the lateral width of the adhesive layer and the thickness of the bottom of the insulating sleeve. The lateral width of the adhesive layer is 10mm, and the thickness of the bottom of the sleeve is 2mm, jointly defining d2 as 12mm.

[0061] Example 4:

[0062] The method for performing contact detection using the detection device of any one of Examples 1 to 3 includes:

[0063] A baseline capacitance value is established. After the system is powered on, the capacitance sensing circuit samples the reference capacitance value of the sensing electrode in a stable state. This reference value reflects the static coupling state between the metal structure and the sensing electrode in the current installation environment and is stored as a reference.

[0064] A trigger threshold is set, which is determined based on the capacitance change range defined by the first safety distance d1 and the second safety distance d2. Under this geometric constraint, the capacitance change generated by direct human contact with the sensing area is greater than the capacitance change generated by the movement of movable metal parts, and also greater than the capacitance change generated by liquid bridging, thereby distinguishing human contact signals from environmental interference signals.

[0065] In practical applications, experimental data shows that direct human contact can generate a capacitance increase greater than 50 pF; the capacitance increase generated by a movable metal part moving at the minimum distance defined by d1 is less than 15 pF; and the capacitance increase generated by liquid bridging the sheath surface is less than 8 pF. Therefore, the trigger threshold is set to 30 pF. This threshold is significantly greater than the maximum capacitance change generated by environmental interference signals, and significantly less than the minimum capacitance change generated by human contact, thus reliably detecting human contact.

[0066] Example 5:

[0067] In this embodiment, the parameter setting rules for different application scenarios are as follows:

[0068] The method for setting the first safety distance d1 is as follows: It is determined based on the maximum travel distance of the movable metal parts of the metal structure and the dimensions of the metal parts. The minimum value of d1 must satisfy the following condition: when the movable metal part is in its extreme position, the maximum capacitance change between it and the sensing area does not exceed 50% of the minimum capacitance change caused by human contact. The value of d1 ranges from 1mm to 10mm. For scenarios with large movable metal parts and high movement frequency, the upper limit of d1 is used; for scenarios with limited installation space and small movable parts, the lower limit of d1 is used.

[0069] The method for setting the second safety distance d2 is as follows: it is determined according to the liquid contamination risk level of the application scenario. The minimum value of d2 must satisfy d2 / d1≥2. For scenarios with high humidity and risk of liquid splashing, a ratio of d2 / d1≥3 is taken; for dry indoor scenarios without liquid contamination, a basic ratio of d2 / d1=2 can be taken; the value range of d2 is 2mm to 20mm.

[0070] The method for setting the insulation thickness of the sensing area is as follows: it is determined according to the detection sensitivity requirements. The smaller the thickness, the higher the sensitivity; the larger the thickness, the better the scratch resistance and wear resistance. The value range is from 0.5mm to 2mm.

[0071] In other embodiments, the second safety distance d2 and the first safety distance d1 satisfy the ratio relationship d2 / d1≥2.

[0072] As one implementation method, d2 / d1=2, where d1=5mm and d2=10mm, achieving a basic balance between mechanical compactness and anti-interference performance, suitable for general industrial environments.

[0073] As another implementation, d2 / d1=3, where d1=4mm and d2=12mm. By increasing the width of the insulating plane, the anti-bridging capability in humid or dusty environments is further improved, making it suitable for outdoor or high-humidity industrial environments.

[0074] As another implementation method, d2 / d1=4, where d1=3mm and d2=12mm. This maximizes the creepage distance while maintaining a small mechanical clearance, making it suitable for scenarios where there is a risk of liquid splashing but limited installation space.

[0075] It should be understood that the ratio selection should be within the allowable range of installation space, but all should meet the basic constraint of d2 / d1≥2 to ensure that the second safety distance has a stronger effect on suppressing liquid bridging than the first safety distance has on suppressing metal movement interference.

[0076] In other embodiments, the surface of the sensing area is constructed as a micro-arc surface structure, which has a gently convex shape in the transverse direction and a radius of curvature of 10 mm. Under the influence of surface tension, the liquid on this surface tends to contract into discrete droplets rather than a continuous water film, reducing the impact of uniform changes in dielectric constant caused by simply covering the sensing surface, and further improving detection accuracy in humid environments.

[0077] As another implementation, the surface of the sensing area is constructed as a rough surface, with the surface roughness Ra controlled within the range of 1.6 μm. The micro-uneven structure disrupts the tendency of the liquid to spread continuously.

[0078] As another implementation, the surface of the sensing area is coated with a hydrophobic coating with a contact angle greater than 120 degrees, causing the liquid to roll off in a spherical shape or remain in a discrete state.

[0079] In other embodiments, the cross-sectional shape of the sensing electrode can be varied. As one implementation, the sensing electrode has a circular cross-section with a diameter of 1.5 mm, suitable for scenarios requiring isotropic sensing sensitivity. As another implementation, the sensing electrode is made of copper foil with a thickness of 0.5 mm and a width of 5 mm, bonded to an insulating sheath via a lamination process.

[0080] Regarding the installation method, as one implementation method, the insulating sleeve is fixed to the magnetic metal structure by magnetic attraction, and a permanent magnet is embedded at the bottom of the sleeve. In this case, the second safety distance d2 is limited by the extension width of the insulating sleeve outside the magnetic attraction component.

[0081] In another embodiment, the bottom of the insulating sheath is provided with elastic claws, which clamp the edge of the metal structure. In this case, d2 is defined by the lateral width of the insulating material at the root of the claws.

[0082] In this embodiment, the second safety distance d2 and the first safety distance d1 satisfy the ratio d2 / d1≥2. The effectiveness of this ratio relationship is verified through comparative testing below:

[0083] Test conditions: Standard electrode structure (aluminum alloy rectangular cross section, 1mm thickness, 2mm width), 1mm insulation thickness in the sensing area, and laboratory environment with temperature of 25℃ and humidity of 60%RH.

[0084] The metal structure is simulated by an aluminum plate measuring 200mm × 200mm, and the movable metal parts are simulated by aluminum sheets measuring 100mm × 50mm, with the spacing controlled by a precision displacement stage.

[0085] Test Plan A:

[0086] The first safety clearance d1 is set to 4mm, and the second safety clearance d2 is set to 6mm.

[0087] Test results show that when the movable metal part moves to a distance of 4mm from the sensing area, the capacitance change is 18pF; when 5ml of water droplets are sprayed onto the surface of the sensing area to form a local water film, the liquid climbs along the insulating plane to form a bridge, and the capacitance change is 25pF. At this time, the liquid interference signal of 25pF is greater than the metal movement interference of 18pF, and close to the human contact signal of 55pF, making it difficult to set a reliable threshold and posing a risk of false triggering.

[0088] Test Plan B:

[0089] The first safety clearance d1 is set to 5mm, and the second safety clearance d2 is set to 10mm.

[0090] Test results show that the capacitance change caused by the movement of a movable metal part at a distance of 5mm is 12pF; after spraying an equal amount of water droplets, due to the 10mm wide insulating plane blocking the continuous water film, the liquid cannot form an effective bridge, and the capacitance change is only 8pF; direct human contact produces a capacitance change of 60pF. A clear gradient is observed among the three: liquid interference 8pF < metal interference 12pF << human contact 60pF, and a reliable 30pF threshold can be set for differentiation.

[0091] Test Plan C:

[0092] The first safety clearance d1 is set to 3mm, and the second safety clearance d2 is set to 9mm.

[0093] Test results show that a movable metal part moving 3 mm produces a capacitance change of 22 pF; liquid bridging produces a capacitance change of 6 pF; and human contact produces a capacitance change of 58 pF. Although the smaller d1 leads to increased metal interference, the wide insulating plane with d2 / d1=3 effectively suppresses liquid bridging, and the three can still be distinguished.

[0094] Test Plan D:

[0095] The first safety clearance d1 is set to 2mm, and the second safety clearance d2 is set to 8mm.

[0096] Test results show that a movable metal part moving 2mm generates a capacitance change of 35pF; liquid bridging generates a capacitance change of 5pF; and human contact generates a capacitance change of 55pF. At this point, the difference between the 35pF interference from metal and the 55pF interference from human contact is reduced to 20pF, but a threshold of 45pF can still be set for differentiation, and the 5pF interference from liquid is completely suppressed.

[0097] The above comparative tests show that the ratio of d2 / d1≥2 ensures that liquid bridging interference is always suppressed under metal motion interference, forming a stable interference hierarchy: liquid interference < metal interference < human contact. This is an important physical basis for achieving reliable threshold discrimination.

[0098] Parallel schemes and comparative tests of surface structures of the sensing area:

[0099] In other embodiments, the surface of the sensing area is configured with different morphologies to optimize liquid behavior. The following comparative tests verify the effectiveness of the micro-arc surface structure:

[0100] Test conditions: The standard electrode and sheath structure from Example 2 were used, with d1=5mm and d2=10mm. 3ml of tap water was evenly sprayed onto the surface of the sensing area to simulate moderate liquid contamination.

[0101] Planar structure: The surface of the sensing area is a flat plane. After spraying, the liquid spreads on the surface to form a continuous water film, covering approximately 80% of the sensing area. The measured capacitance change was 18pF. This relatively large value is because the continuous water film alters the dielectric constant distribution on the surface of the sensing area, creating a near-conductive surface.

[0102] Micro-arc surface structure: The surface of the sensing area is constructed as a micro-arc surface, which has a gently convex shape along the transverse direction, with a radius of curvature of 10 mm and an arc height of 0.3 mm. Under the influence of surface tension and gravity, the liquid on this surface tends to contract and accumulate towards the bottom of the arc, forming discrete droplets rather than a continuous water film. The coverage area is reduced to approximately 30%, and the measured capacitance change is 9 pF, a 50% reduction compared to the planar structure.

[0103] Rough surface structure: The surface of the sensing area is sandblasted to form a rough surface with a surface roughness Ra of 1.6 μm. The micro-uneven structure disrupts the continuous spreading tendency of the liquid, and the liquid is distributed in an island-like pattern. The measured capacitance change is 11 pF, which is between that of a plane and a micro-arc surface.

[0104] Hydrophobic coating structure: A fluorocarbon hydrophobic coating is applied to a planar structure with a contact angle of 130 degrees. Liquid rolls off in a spherical shape or remains in a discrete spherical shape, covering an area of ​​less than 20%, and the measured capacitance change is 6pF, demonstrating the best anti-liquid interference effect.

[0105] The test data above show that the micro-arc surface structure effectively reduces the capacitance change caused by simple liquid coverage by changing the distribution pattern of liquid on the surface, and further improves the detection accuracy in humid environments.

[0106] To verify the effectiveness of the first safety clearance d1 within the range of 1mm to 10mm, the following boundary tests were performed:

[0107] Lower limit test: The distance between the movable metal part and the sensing area was adjusted to 1mm. The maximum capacitance change generated when the metal part moved was measured to be 20pF, while the capacitance change generated when the human body came into contact with it was 52pF. The difference was 32pF. A threshold of 30pF can still be set to distinguish between them, but the safety margin is relatively small.

[0108] If d1 < 1 mm, the measured metal interference reaches 35 pF, while the difference between 55 pF and human contact interference is only 20 pF. Furthermore, the interference can fluctuate by ±5 pF due to the influence of ambient temperature, posing a risk of misjudgment. Therefore, d1 ≥ 1 mm is necessary.

[0109] Upper limit test: With the distance between the movable metal part and the sensing area adjusted to 10mm, the maximum capacitance change generated when the metal part moves was measured to be 3pF, while the capacitance change generated when the human body contacts it was 48pF, a difference of 45pF, indicating extremely reliable differentiation. However, an excessively large d1 would occupy too much installation space, making it difficult to implement in compact automated equipment. Therefore, d1≤10mm is a balance between reliability and installation feasibility.

[0110] To verify the effectiveness of the second safety clearance d2 within the range of 2mm to 20mm, the following boundary tests were performed:

[0111] Lower limit test: The bottom plane width of the insulating sheath is 2mm. After spraying water droplets in the sensing area, the liquid climbs along the surface and forms a continuous bridging path within a 2mm width. The measured capacitance change is 28pF, which is close to the human contact signal (above 50pF), making it difficult to reliably distinguish. Therefore, d2≥2mm is necessary and must be used in conjunction with a ratio of d2 / d1≥2.

[0112] Upper limit test: The bottom plane width of the insulating sleeve is 20mm. Under the action of surface tension, the liquid can only climb up to 8mm to 10mm before stopping, unable to cross the 20mm width to form a bridge. The measured capacitance change is only 4pF, and liquid interference is completely suppressed. However, an excessively wide d2 will increase the lateral size of the device, making it difficult to install in space-constrained scenarios. Therefore, d2≤20mm is the upper limit for engineering practicality.

[0113] Full-condition environmental adaptability test:

[0114] The detection device of this embodiment was tested under full operating conditions within a temperature range of -20℃ to 60℃ and a humidity range of 10%RH to 95%RH.

[0115] Test results show that, within the full temperature and humidity range, the drift of the baseline capacitance value does not exceed ±3pF, the maximum capacitance change caused by the movement of movable metal parts does not exceed 15pF, the maximum capacitance change caused by liquid bridging does not exceed 8pF, the capacitance change caused by human contact is always greater than 50pF, and when the trigger threshold is set to 30pF, there are no false triggers, and the detection accuracy reaches 100%.

[0116] Long-term stability test: The detection device was installed on the metal structure of industrial automation equipment and operated continuously for 500 hours. During this period, it was subjected to repeated reciprocating motion of metal parts and liquid splash contamination. The test results showed that the detection performance of the device did not decrease, and there were no missed or false detections, demonstrating excellent long-term stability.

[0117] In other embodiments, the trigger threshold may be set using an adaptive algorithm.

[0118] As one implementation method, the system periodically updates the baseline base capacitance value to compensate for slow drift caused by changes in ambient temperature.

[0119] As another implementation method, the trigger threshold is set as a floating threshold, which is dynamically adjusted according to the periodic movement law of the movable metal part. When the metal part is stationary, the threshold is lowered to improve sensitivity, and when the metal part is moving, the threshold is raised to prevent false triggering.

[0120] Those skilled in the art will understand that, in addition to the above-described embodiments, the detection device may employ a variety of alternative configurations.

[0121] In addition to aluminum alloy and copper foil, the induction electrode can also be made of stainless steel strip or conductive polymer, as long as it meets the basic function of a slender conductor. The insulating sheath can be made of PVC, PP, PE, or silicone, in addition to ABS, and its dielectric constant should be in the range of 2 to 4 to ensure electric field penetration.

[0122] The first safety distance d1 can be selected within the range of 1mm to 10mm based on the maximum range of motion of the movable metal parts, and the second safety distance d2 can be selected within the range of 2mm to 20mm based on the risk level of liquid contamination, as long as the basic relationship of d2 / d1≥2 and d2 is always greater than d1 is met.

[0123] The thickness of the insulating sheath in the sensing area can be adjusted from 0.5mm to 2mm according to the sensitivity requirements.

[0124] The above embodiments are merely examples and not limitations. Any equivalent substitutions or modifications to the technical features based on the core concept of dual isolation protection, inspired by this invention, should fall within the protection scope of this invention. The protection scope of this invention is defined by the claims.

Claims

1. A contact detection device for metal structures based on capacitive sensing, comprising: The slender sensing electrodes are used to connect to the capacitive sensing circuit; An insulating sheath encloses the sensing electrode and forms an exposed sensing area on only one of its main surfaces; the device is configured to be mounted on a metal structure. Its features are: The insulating sheath is designed to provide double isolation between the sensing electrode and the surrounding metal structure. The first safety distance d1 is defined as the minimum distance between the sensing area and the movable metal part of the metal structure. The second safety clearance d2 is defined as the width of the insulating plane provided by the insulating sheath between the inductive electrode and the metal structure on which the device is mounted.

2. The metal structure contact detection device based on capacitive sensing according to claim 1, characterized in that, The second safety distance d2 and the first safety distance d1 satisfy the ratio relationship: d2 / d1≥2.

3. The metal structure contact detection device based on capacitive sensing according to claim 1, characterized in that, The surface of the sensing area is constructed as a micro-arc surface structure.

4. The metal structure contact detection device based on capacitive sensing according to claim 1, characterized in that, The thickness of the insulating sheath in the sensing area is 0.5 mm to 2 mm, the first safety distance d1 is 1 mm to 10 mm, and the second safety distance d2 is 2 mm to 20 mm.

5. The contact detection device for metal structures based on capacitive sensing according to claim 1, characterized in that, The cross-section of the sensing electrode is rectangular or elliptical, with a thickness of 0.5 mm to 2 mm and a width of 1 mm to 5 mm. The sensing electrode is fully enclosed by an insulating sheath through an extrusion molding process.

6. The contact detection device for metal structures based on capacitive sensing according to claim 1, characterized in that, The bottom of the insulating sleeve is provided with a mounting buckle or adhesive layer for fixing the detection device to the metal structure, and the second safety distance d2 is defined by the lateral width of the mounting buckle or adhesive layer and the thickness of the bottom of the insulating sleeve.

7. A contact detection method, using the metal structure contact detection device based on capacitive sensing as described in any one of claims 1 to 6, characterized in that, include: Establish a baseline for basic capacitance values; A trigger threshold is set, which is determined based on the capacitance change range defined by the first safety distance d1 and the second safety distance d2, wherein the capacitance change generated by direct human contact is greater than the capacitance change generated by the movement of movable metal parts or the capacitance change generated by liquid bridging, so as to distinguish human contact signals from environmental interference signals.

Images