A high-redundancy progressive failure safety type cage tennis net bag and a manufacturing method thereof

Abstract

This invention discloses a highly redundant progressive failure-safe cage-type tennis net bag and its manufacturing method. The net bag includes a bottom ring (1) and at least six independent rope loops (2). Each independent rope loop is connected to the bottom ring by a fixed structure and is evenly distributed circumferentially without crossing each other. The top rope ends of each independent rope loop are sequentially threaded onto the closed loop of a locking loop rope (22) formed by connecting the ends of a single rope. The tail of the locking loop rope (22) passes through its head to form a slip knot structure. Pulling the tail gathers the top rope ends and locks them to the top of the tennis ball. The tail and head are fixedly connected to form a unique dead knot. After the tennis ball is put into the net bag, the bottom ring is wavy, and the connection point forms a figure-eight micro-locking structure (6). The net bag also includes a movable loop rope (14) and an external device (15) for connecting an external tension source. Both the locking loop rope (22) and the external device (15) are threaded into the closed loop of the movable loop rope (14) and can move freely. The fixing strap (29) is threaded onto the movable loop rope (14) as a backup redundancy, forming double redundancy. All loop rope joints are ultrasonically welded. This invention transforms the sudden collapse of traditional mesh bags into a gradual and predictable attenuation through a three-layer progressive redundancy structure, with only one dead knot in total, resulting in a service life significantly longer than existing products.

Description

Technical Field

[0001] This invention relates to the field of tennis auxiliary equipment technology, specifically to a net bag structure for a tennis training device and its rapid manufacturing method. Background Technology

[0002] The tennis net bag is the core component of a tennis training device used to hold the tennis ball in place. The device connects the net bag to a base or stand via ropes, securing the tennis ball inside for repeated hitting by the user.

[0003] Most traditional tennis net bags use a woven mesh structure, made of multiple ropes woven into a mesh bag body, forming a uniformly distributed grid. The ropes intersect at points all over the ball's surface and are locked with knots. The connection between the tennis ball and the outside is rigid, leading to stress concentration. When the tennis ball spins at high speed, it causes the elastic ropes to spin as well, without any relief structure. In addition, these net bags generally lack redundant design; a single point breakage renders the entire bag unusable. The traditional hand-tying method is not conducive to large-scale industrial standardized production, resulting in low efficiency and poor consistency. Localized damage cannot be replaced individually, leading to the waste of the entire bag. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the shortcomings of the existing technology, the technical problem to be solved by the present invention is to provide a tennis net bag that can eliminate defects such as dead knots all over the sphere, stress concentration in rigid connections, and lack of redundant design, while eliminating the complex stress conditions at the rope crossing points, and realizing the rapid standardized production of the net bag and its repairability and replacement after local damage.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A highly redundant, progressively fail-safe cage tennis net bag includes a bottom loop and at least six individual loops.

[0009] (1) Bottom ring - geometric critical value and space avoidance design

[0010] The bottom ring is a ring-shaped reference at the bottom of the mesh bag, and is a ring structure formed by loop ropes (one or more loops, preferably two or more loops).

[0011] The outer diameter of the base ring is approximately 50mm, and it is either a regular hexagon or a regular octagon. A standard tennis ball has a diameter of 63mm (radius R = 31.5mm), and the base ring radius is r = 25mm. The height h of the contact ring between the base ring and the ball's surface from the bottom of the ball is calculated as: h = R - √(R² - r²) = 31.5 - √(31.5² - 25²) = 31.5 - √367.25 ≈ 31.5 - 19.16 ≈ 12.34mm.

[0012] The geometric calculations show that the contact ring of the approximately 50mm diameter sole is located about 12mm from the bottom of the ball—this position effectively avoids the frequent contact zone of 0-10mm from the bottom, while also avoiding the main hitting zone of the racket near the equator (31.5mm from the bottom of the ball). Approximately 50mm is the preferred value determined by the inventors after extensive geometric calculations and experimental verification: if the sole diameter is significantly smaller than 50mm (e.g., 40mm, h≈7.16mm), it is more likely to land in the bottom contact zone, increasing wear; if the sole diameter is significantly larger than 50mm (e.g., 60mm, h≈21.9mm), it is more likely to enter the equatorial hitting zone and be hit by the racket. Preferably, the outer diameter of the sole is set to 48mm to 52mm, achieving a good balance between these two values.

[0013] Preferably, the bottom ring is formed by three interlocking loops made from a 12-strand, 1.2mm PE braided rope with a length of not less than 48cm. This design has only one knot, and the rope is flat. The flat loop is further compacted by a fixing structure of six or eight independent rope loops, thereby locking the independent rope loops in place and reducing wear.

[0014] The advantage of the bottom ring is that even if one of the loops breaks at a certain point, the bottom ring is segmented and locked in place by at least six independent loops. The number of loops at the broken point is reduced, but the rest of the part is still a complete multi-loop structure. The bottom ring as a whole can still remain firm and reliable and will not fail as a whole due to a local break.

[0015] (2) At least six independent rope loops and their fixing structure to the bottom loop – a pure tension design without crossover.

[0016] Each individual rope loop is formed by connecting the ends of the rope to form a loop, and each individual rope loop is independently connected to the bottom loop and evenly distributed along the circumference of the bottom loop.

[0017] Each independent rope loop does not cross each other and only bears axial tensile load. This non-crossing design prevents the ropes from being subjected to combined stresses of bending, friction, and shear at the crossing points, thus making full use of the high axial tensile strength of the PE rope material.

[0018] Preferably, the number of independent rope loops is eight, forming eight independent rope loops.

[0019] In this invention, the method of fixing the independent rope loop and the bottom loop includes the following two parallel implementation schemes:

[0020] Option 1 (Preferred Option): Adjustable snap-lock structure

[0021] After the head of each individual rope loop passes through the bottom loop, its tail loops back through the middle of the head of the individual rope loop and is tightened, forming an adjustable snap-lock structure. This structure achieves reliable fixation without the need for winding, and can be unlocked by pulling the head, facilitating the maintenance and replacement of the individual rope loops.

[0022] Option 2 (Alternative): Ultrasonic welding fixing structure

[0023] Individual rope loops are fixedly connected to the base ring via ultrasonic welding points. During welding, the base ring is welded to each individual rope loop at 2cm intervals, ensuring that the individual rope loops are evenly distributed around the circumference of the base ring. After welding, the base ring with the welded rope loops is placed back into the positioning mold to continue subsequent processes. This method offers faster manufacturing speed, higher connection strength, and achieves the same basic function of evenly distributing and fixing the individual rope loops around the circumference of the base ring.

[0024] (3) Dead knot topology optimization - There is only 1 dead knot in total and it is located in the top safe zone.

[0025] This invention performs topology optimization on dead knots from bottom to top:

[0026] Bottom: Adjustable snap-lock structure (or ultrasonic welding) replaces dead knot;

[0027] Middle section: Independent rope loops that do not cross each other, with no dead knots;

[0028] Top: The locking loop rope (22) adopts a pre-formed loop single-point locking structure. The entire net bag has only one dead knot at the final fixed knot of the locking loop rope (22), and the knot is located in the top area of ​​the tennis ball that is only subjected to axial tension.

[0029] Concentrating the single dead knot in this area helps to effectively isolate the vulnerable parts of the mesh bag from the impact force in three-dimensional space.

[0030] (4) Locking loop rope (22) Pre-formed loop single-point locking structure

[0031] This invention employs a structure that uses a single locking loop rope (22) to lock the top ends of all independent loops at once. The specific structure and operation are as follows:

[0032] (a) Lock the loop rope (22) first connect the ends to form a closed loop;

[0033] (b) The closed loop passes through the top rope ends of each individual rope loop in sequence, so that each top rope end is hooked onto the closed loop;

[0034] (c) Pass the tail (23a) of the locking loop rope (22) through its head (23b) to form a slipknot structure (23).

[0035] (d) By pulling the tail, all the top ends of the individual rope loops threaded on the closed loop are brought together towards the center of the top of the tennis ball and tightened to the predetermined tension in one go;

[0036] (e) Securely connect the tail (23a) of the locking loop (22) to the head (23b) (tie a knot) (25) to maintain the locked state.

[0037] The advantage of this structure is that:

[0038] Each individual rope loop is evenly distributed along the meridian, with the top converging point located at the top of the tennis ball, avoiding the main hitting zone of the ball's equator.

[0039] All rope ends can slide freely within the closed loop, automatically balancing the tension in all directions during the tightening process;

[0040] The entire top lock can be completed with just one tightening action, making it extremely simple to operate and highly efficient.

[0041] The entire mesh bag has only one knot, which eliminates weak points to the greatest extent.

[0042] (5) The connecting structure between the movable loop rope (14) and the locking loop rope (22) and the external equipment (15)

[0043] The mesh bag also includes a movable loop rope (14) and an external device (15) for connecting an external tension source. The movable loop rope (14) is formed by sequentially threading a PE braided rope through the closed loop of the locking loop rope (22) and the connecting loop of the external device (15), and then connecting its ends together to form a closed loop rope. Both the locking loop rope (22) and the external device (15) are threaded within the closed loop of the movable loop rope (14) and can move freely along the circumference of the movable loop rope (14). This structure makes the movable loop rope (14) a flexible connector between the locking loop rope (22) and the external device (15), transforming rigid tension into flexible buffering, avoiding the problems of stress concentration and the inability to attenuate torsional waves.

[0044] The circumference of the movable loop is preferably between 5cm and 8cm. Through experiments, the inventors have found that the circumference of the movable loop within this preferred range can better exert the functions of flexible buffering and torsional wave attenuation: when it is less than 5cm, rotation is restricted and torsional waves are not easily released; when it is greater than 8cm, it is easy to swing and interfere with the top structure; within the range of 5-8cm, the functions of flexible buffering and torsional wave attenuation can be more fully exerted, resulting in a longer service life at the connection.

[0045] The movable loop rope can rotate and swing freely, transforming rigid tension into flexible buffering, which helps to fundamentally solve the problems of locking, deformation, tangling and early breakage caused by traditional rigid direct connection.

[0046] (6) Cooperative redundancy structure of movable loop rope (14), fixed belt (29), locking loop rope (22) and external equipment (15)

[0047] Preferably, the tennis ball is provided with a fixing strap (29), which is attached to the surface of the tennis ball and leaves a gap between it and the tennis ball fabric for the rope to pass through. A section of the movable loop rope (14) passes through this gap and then joins its ends to form a closed loop rope, so that the fixing strap (29) is threaded onto the closed loop of the movable loop rope (14). At the same time, the locking loop rope (22) and the connecting ring of the external device (15) are also threaded onto the closed loop of the same movable loop rope (14). The locking loop rope (22) presses over the fixing strap (29).

[0048] This structure achieves a composite force-bearing system in which the fixed belt, locking loop rope, and external equipment work together, and has the following mechanical advantages:

[0049] (a) During normal operation, the tension is transmitted to the movable loop rope (14) via the locking loop rope (22), and the fixed belt (29) is in a relaxed and unstressed state, serving only as a backup.

[0050] (b) When the individual rope loops of the net bag break due to long-term use, the fixing strap (29) automatically takes over the load as a backup tension transmission path;

[0051] (c) The fixed belt (29), the locking loop rope (22) and the external equipment (15) can slide freely along the circumference of the movable loop rope (14), avoiding the problems of stress concentration and torsional wave attenuation caused by rigid connection. In conjunction with the 5-8cm preferred range of the movable loop rope (14) itself, the connection has a longer service life.

[0052] The "one rope through three pieces" structural design transforms the fixing belt from a traditional single load-bearing structure into a "constant redundancy," achieving a synergistic gain of "1+1>1."

[0053] (7) Coupling locking mechanism between wave-shaped bottom ring and figure-eight micro-locking structure

[0054] After the tennis ball is placed in the net bag, the bottom ring (1) has a wavy structure, and the pull-up points of each independent rope loop form a figure-eight shape, forming the figure-eight micro-locking structure (6), which locks the bottom ring in place. Specifically: when the tennis ball is placed in the net bag and each independent rope loop is pulled up from the top convergence point to lock, the figure-eight micro-locking structure at each fixed structure simultaneously produces two mechanical effects—(a) the two sloping sides of the figure-eight pull the bottom ring tightly against the surface of the tennis ball; (b) multiple figure-eights act simultaneously, causing the bottom ring to naturally form a wavy undulation between adjacent fixed structures. The wavy bottom ring and the figure-eight micro-locking structure (6) form a coupled locking effect: the undulating shape of the wavy bottom ring keeps the figure-eight structure at each fixed structure in a pre-tightened state, and the impact force in any direction is dispersed by the wavy structure to multiple locking points.

[0055] The wavy bottom ring structure is a significant feature that distinguishes this invention from traditional flat woven mesh bags. Traditional mesh bags, after being filled with tennis balls, have a loose flat or spherical woven mesh at the bottom with no directional locking function. In contrast, the wavy bottom ring of this invention is an active locking structure. It is forcibly formed by the figure-eight micro-locking structure the moment the tennis ball is filled, achieving an active positioning effect of "locking upon filling".

[0056] (8) Triple progressive redundancy failure safety mechanism

[0057] The fatal flaw of traditional tennis net bags is that "single point failure leads to overall collapse"—if any string breaks in the hitting area, the entire net bag is rendered unusable without any warning, and users cannot predict when it will fail.

[0058] This invention transforms the aforementioned "sudden collapse" into "gradual and predictable decay" by constructing a three-layer progressive redundancy structure, making the failure process of the mesh bag observable, predictable, and predictable. Specifically:

[0059] The first layer of redundancy is the intrinsic dual-path backup for a single lifting rope head.

[0060] Each individual rope loop is formed by folding a single rope in half and joining the ends together, creating two parallel working branches: an upward rope segment and a downward rope segment. The two rope segments are distributed along the same meridian, serving as mirror images of each other. When one rope segment breaks due to prolonged impact, the other rope segment remains intact and independently bears the load. The overall function of this individual rope loop is unaffected, and it can continue to be used normally. Users can visually observe the rope segment breakage to determine if the net bag has entered a "redundancy reduction" stage, but its main function remains intact.

[0061] The second layer of redundancy is the independent backup between multiple lifting rope heads.

[0062] Each individual loop is physically independent, without crossing or interfering with the others. Even if any individual loop completely loses its function (both loops break), the remaining loops remain unaffected and continue to function independently, maintaining the wrapping and securing of the tennis ball. There is no cascading failure path like in traditional woven net bags where "if one fails, all fail."

[0063] The third layer of redundancy is a combined backup under geometrically critical conditions.

[0064] Through theoretical calculations and experimental verification by the inventor, four evenly distributed lifting rope ends are the critical value for maintaining the geometric stability of the tennis ball being reliably wrapped. When there are fewer than four rope ends, the tennis ball will deflect or even fall out of the net bag under high-speed hitting and spin.

[0065] This invention preferably employs eight independent loops—adding a redundancy of four loops to the four critical loops. When every other loop breaks (i.e., the 1st, 3rd, 5th, and 7th loops or the 2nd, 4th, 6th, and 8th loops break), the remaining four loops are precisely at the critical state of geometric stability, ensuring the tennis ball remains securely wrapped and will not slip out. This critical state provides the user with ample, observable warning window: the user can visually observe the gradual process of each loop breaking and replace the net bag before it completely fails, avoiding the risk of interruption caused by the "sudden failure without warning" of traditional net bags.

[0066] Synergistic effect of three-layer redundancy structure:

[0067] The aforementioned three layers of redundancy are not simply an accumulation of quantities, but rather form a progressive protection chain of "level-by-level support":

[0068] In good condition (8 intact): Full performance, working normally;

[0069] Early attenuation (1-2 rope segments break): The first layer of redundancy comes into play, with a slight decrease in performance but full functionality;

[0070] Mid-term attenuation (1-2 independent loops break completely): The second layer of redundancy comes into play, performance decreases but the wrapping is secure;

[0071] Critical state (4 independent loops break at intervals): The third layer of redundancy comes into play, the tennis ball is still wrapped, and the user receives a clear replacement signal.

[0072] Extreme condition (4 consecutive fractures or critical structure failure): The mesh bag has reached the end of its service life and needs to be replaced.

[0073] When the three-layer redundant structure is exhausted layer by layer (i.e., all four independent rope loops break and another of the remaining four rope loops break), the main body of the net bag reaches its service life limit. Thus, the three-layer redundant structure transforms the "unpredictable sudden failure" of traditional net bags into a "predictable service life limit based on structural design," significantly extending the effective service life of the net bag compared to traditional single-layer structures and giving users proactive control over the equipment's condition.

[0074] (9) Full-loop rope ultrasonic welding - industrial standard manufacturing

[0075] In this invention, all joints of the looped ropes (including the bottom loop joint, each individual loop joint, and the locking loop joint, except for the movable loop joint) are pre-fixed using ultrasonic welding. For PE braided ropes with a diameter of not less than 1.2mm, ultrasonic welding parameters of 30-50kHz frequency, 0.2-1.0 seconds welding time, and 1-5kg / cm² welding pressure can be used; preferably, 35-40kHz frequency, 0.3-0.8 seconds welding time, 0.2-0.5 seconds holding time, and 2-4kg / cm² welding pressure are used; optimally, 37kHz frequency, 0.5 seconds welding time, 0.3 seconds holding time, and 3kg / cm² welding pressure are used, under which the welding strength can reach more than 90% of the strength of the base material.

[0076] The "full-loop rope structure" and "ultrasonic welding" form a deep synergy—the loop rope structure makes ultrasonic welding feasible (each joint is an independent loop closed-loop endpoint), while ultrasonic welding provides an industrialized implementation path for the loop rope structure (fast, consistent, and high-strength). The entire mesh bag production time is only 3-5 minutes, realizing a paradigm shift from "hand weaving" to "industrialized standardized production."

[0077] All PE braided ropes are cut using a hot cutter during the material preparation stage. The cutting speed is fast, the dimensions are precise, and the cutting head automatically fuses together, requiring no further processing.

[0078] (10) Rope material selection - Structural compatibility of PE braided rope

[0079] The present invention uses ultra-high molecular weight polyethylene (UHMWPE) braided rope with more than 12 braids (i.e. PE braided rope) and a diameter of not less than 1.2 mm, preferably 1.2 mm.

[0080] Reasons for material selection: Ultra-high molecular weight polyethylene (UHMWPE) fiber braided ropes have significantly higher strength than ordinary ropes of the same diameter, exhibit significantly better abrasion resistance than materials such as nylon, low elongation at break (almost no extensibility), and minimal creep. These superior properties make this material widely applicable in fields such as protective equipment. Furthermore, it is perfectly suited to the "knotless, pure tensile, and precision-locked" structural design of this invention—PE's zero creep helps maintain the dimensional stability of the wavy bottom ring and the figure-eight micro-locked structure; PE's pure tensile fatigue durability is excellent in the knotless state; and PE's high abrasion resistance helps resist friction from sand and gravel on dry, hard surfaces.

[0081] (11) Cooperative locking mechanism of independent rope loops embedded in wool fabric

[0082] After locking, the individual cord loops and sole rings embed themselves within the wool fabric, making close contact with the tennis ball bladder and forming a deep, locked position. When the tennis ball is repeatedly hit, the impact increases the contact pressure between the individual cord loops and sole rings, the wool fabric, and the bladder—the greater the impact, the deeper the embedding, and the stronger the lock (self-locking effect). Simultaneously, because the individual cord loops and sole rings are located inside the wool fabric, the wool fabric is the first to contact the racket and the ground, absorbing most of the impact and collisions. Before the wool fabric is completely worn away, the individual cord loops and sole rings experience less direct impact and friction, which helps increase their resistance to impacts. As the wool fabric gradually wears down, the individual cord loops and sole rings are gradually exposed, providing a visible wear warning.

[0083] (12) The constraint and protection of the soft skeleton on the tennis ball body

[0084] The present invention also found that the net bag has a certain restraining and protective effect on the tennis ball.

[0085] In an exemplary test conducted by the inventors, a tennis ball developed a 3cm crack in its bladder and began to leak air after approximately 1800 hits. Under normal circumstances, this tennis ball should have been unusable. However, encased in the flexible mesh bag of the present invention, the tennis ball continued to be used normally for approximately 253 more times (approximately 2053 times in total), still maintaining its basic hitting function.

[0086] This phenomenon indicates that the mesh bag structure of the present invention—a cage-like skeleton composed of multiple independent rope loops—is not merely a passive container for fixing the tennis ball, but a flexible skeleton capable of actively participating in mechanical support. When the tennis ball bladder suffers structural damage due to prolonged impact, the circumferential constraint force provided by the independent rope loops from the outside can: (a) distribute the local stress at the crack in the bladder, preventing the crack from expanding further; (b) maintain the overall shape of the tennis ball, ensuring that the ball can still bounce back when hit; and (c) help extend the lifespan of the tennis ball and reduce the frequency of replacing training equipment.

[0087] (13) Core summary of the technical solution

[0088] In summary, the core technical solution of this invention is as follows: a cage-like frame is formed by a bottom ring (1) and at least six independent rope rings (2). The locking ropes (22) are connected end to end to form a closed loop. The closed loop passes through the top rope ends of each independent rope ring in sequence, so that each rope end is hooked on the closed loop. The tail passes through the head to form a snap and is pulled tight, so that all rope ends are gathered together and locked to the top of the tennis ball at one time, forming a single-point locking structure. After the tennis ball is inserted, the bottom ring is wavy and coupled and locked with the figure-eight micro-locking structure (6). The movable rope (14) is threaded through the connecting ring of the locking rope (22) and the external device (15). The fixing strap (29) is threaded on the movable rope (14) as a spare redundancy. All rope joints are ultrasonically welded. For details of the specific structure, please refer to claims 1-10.

[0089] (III) Beneficial Effects

[0090] Compared with the prior art, the present invention has the following beneficial effects:

[0091] 1. Geometric avoidance of a base ring with an approximate 50mm polygon.

[0092] This invention, through geometric calculations, reveals that when the outer diameter of the ball's circumscribed circle is approximately 50mm, its contact ring with the tennis ball's surface is located about 12mm from the bottom of the ball. This position effectively avoids the frequent contact zone of 0-10mm at the bottom, while also avoiding the racket's main hitting zone near the equator. Comparative experiments show that a ball with a diameter of 40mm (h≈7.16mm) is more likely to land in the bottom contact zone, increasing wear; a ball with a diameter of 60mm (h≈21.9mm) is more likely to enter the equatorial hitting zone and be struck by the racket. Approximately 50mm (preferably 48-52mm) achieves a good balance between these two.

[0093] 2. Dead Knot Topology Optimization – From “Widespread on the Sphere” to “A Single Dead Knot Concentrated at the Top”

[0094] This invention reduces the dozens to hundreds of knots scattered across the surface of a traditional net bag to a single necessary fixing knot at the top (the total number of knots is only one), and this knot is located in the top region of the tennis ball, which is only subjected to axial tension and not impact. This topology optimization fundamentally eliminates the defect of knots scattered across the surface of a traditional net bag, reducing the number of weak points to a theoretical minimum.

[0095] 3. Top locking structure with "single tensioning and one-time locking"

[0096] This invention employs a structure where the locking loop rope (22) is pre-formed into a ring, and then the top rope ends of each independent rope loop are sequentially threaded through the head loop and tightened. This achieves a highly simplified operation where all top locking can be completed with a single tightening action. All rope ends can slide freely within the closed loop, and the tension in all directions is automatically balanced during the tightening process, avoiding stress concentration and multi-layer stacking problems caused by group locking. This significantly improves production efficiency compared to traditional grouping schemes.

[0097] 4. The optimal dynamic range of the movable loop rope (5-8cm) and its connection with the locking loop rope and external equipment.

[0098] This invention, through experiments, has shown that a movable loop rope with a circumference between 5cm and 8cm performs better in terms of flexible buffering and torsional wave attenuation: less than 5cm, rotation is restricted and torsional waves are difficult to release; greater than 8cm, it is prone to swinging and interference with the top structure. The movable loop rope transforms the traditional rigid connection into a flexible buffer, helping to fundamentally solve the problems of stress concentration and the inability to attenuate torsional waves. Simultaneously, both the locking loop rope and external equipment are fitted within the closed loop of the movable loop rope and can move freely along its circumference, achieving a truly flexible transition connection.

[0099] 5. Non-crossing pure tension design – fully leveraging the advantages of PE rope material

[0100] Each independent loop does not cross with the others and only bears axial tensile load. This design transfers the PE braided rope from the complex stress condition (bending + friction + shear) in traditional mesh bags to a pure axial tensile condition—PE rope has extremely high axial strength, excellent wear resistance, and ranks among the top in pure tensile fatigue durability. The structural design of this invention ensures that the rope always works in its strongest direction, achieving a synergistic effect of "structure adapting to material".

[0101] 6. Coupling and locking mechanism between the wavy bottom ring and the figure-eight micro-locking structure

[0102] After the diagonal pull locks in place, a figure-eight micro-locking structure naturally forms at each of the fixed structures at the bottom, resulting in a wavy bottom ring after the tennis ball is inserted. This wavy bottom ring is an active locking structure that is forcibly shaped the moment the tennis ball is inserted, achieving an active positioning effect of "locking in as soon as it's inserted"—traditional net bags have a loose flat or spherical woven mesh at the bottom after a tennis ball is inserted, without any directional locking function.

[0103] 7. Triple progressive redundancy failure safety mechanism and bidirectional collaborative protection – verified by continuous progressive experiments

[0104] This invention, through a three-layer progressive redundancy structure, transforms the sudden failure mode of traditional mesh bags—where "single-point breakage results in complete failure"—into a predictable, observable, and predictable mode where "performance gradually declines as the number of lifting rope ends decreases." Taking an eight-independent rope loop scheme as an example, the performance changes with the degree of damage to the individual rope loops as follows:

[0105] 8 individual rope loops intact 100% Normal work One rope segment breaks in an independent loop. Approximately 99% Normal use (first-level redundancy is in effect) Two rope segments broke in a single loop. Approximately 95% Normal use (second-level redundancy is in effect) Two separate rope loops broke (adjacent). Approximately 85% It can still be used normally. Four individual rope loops broke (interspersed) Approximately 70% Even in a critical state, it can still wrap around the tennis ball (third layer of redundancy is active).

[0106] The inventors fully verified the aforementioned redundancy mechanism and bidirectional collaborative protection logic through a series of progressive experiments using the same tennis ball and the same net bag. The specific experiments are as follows:

[0107] Experiment 1 (Wool Fabric Protective Net Bag Stage): A new tennis ball was placed in the net bag made according to this invention, and a standard hitting test was conducted starting from its brand-new state. After approximately 7000 hits, about two-thirds of the wool fabric of the tennis ball was worn away, at which point the PE braided rope showed no obvious pilling. This experiment demonstrates that before the wool fabric layer is completely worn away, the wool fabric, as a sacrificial layer, preferentially withstands external friction, providing effective protection for the net bag rope embedded within it.

[0108] Experiment 2 (Net Bag Protection Stage): The same tennis ball and net bag, with approximately two-thirds of the wool fabric already worn away, were continued to be hit. Starting from when the wool fabric was about two-thirds worn away, after a cumulative total of about 5428 hits, a large area of ​​the wool fabric (approximately 50%) peeled off, the PE braided rope began to show slight pilling, and some rope loop connections came loose one after another, eventually causing the tennis ball to leak out of the net bag. This experiment demonstrates that when the wool fabric layer is worn away, the cage-like skeleton of the net bag can replace the wool fabric in protecting the tennis ball.

[0109] Experiment 3 (Extreme Crack Condition): Another tennis ball was used. After approximately 1800 hits, a crack of about 3cm appeared in the bladder, and air began to leak out. Under normal circumstances, this tennis ball should have been unusable. However, under the protection of the mesh bag of this invention, the tennis ball continued to be used normally for approximately 253 times (totaling approximately 2053 times), still maintaining basic hitting function. This experiment proves that the mesh bag can still provide effective external restraint and support after the tennis ball's structure is damaged.

[0110] The progressive logic of the above three sets of experiments is clear:

[0111] Experiment 1 (7000 times) → Experiment 2 (another 5428 times) were continuous tests using the same tennis ball and the same net bag, with a total effective lifespan of approximately 12428 times (7000 + 5428).

[0112] Experiment 3 was an independent verification to demonstrate the restraining and protective effect of the mesh bag on the bladder tear.

[0113] The self-locking effect persists throughout the entire process: whether in the wool fabric protection stage or the net bag protection stage, the impact force increases the contact pressure between the individual rope loops and bottom loops and the wool fabric and bladder—the greater the impact, the deeper the embedding, and the more secure the lock. This self-locking effect continuously strengthens with the increase of the number of impacts, working synergistically with the aforementioned two-way protection mechanism to significantly extend the effective service life of both the net bag and the tennis ball.

[0114] The bidirectional synergistic protection mechanism of the "wool fabric protective mesh bag → mesh bag protecting tennis ball" of the present invention is an unexpected technical effect that has not been disclosed in the prior art, and constitutes another important creative contribution that distinguishes the present invention from traditional mesh bags.

[0115] 8. Full-loop rope ultrasonic welding – industrial standard manufacturing

[0116] All looped rope joints are ultrasonically welded, replacing traditional hand knotting. The welding strength can reach more than 90% of the strength of the base material, and the production time is only 3-5 minutes, realizing a paradigm shift from "hand weaving" to "industrialized standardized production".

[0117] Comprehensive performance test verification data

[0118] The core comparative test data of this invention and commercially available products are as follows:

[0119] wool fabric protection stage New tennis ball + new net bag, start hitting from scratch. After approximately 7000 cycles, the wool fabric was worn down by 2 / 3, while the PE rope remained intact. It fails completely after approximately 2000 uses. Mesh bag protection stage Using the same tennis ball and the same net bag, continue hitting the ball starting when the wool fabric is worn down to 2 / 3 of its original length. After being struck approximately 5428 more times, the PE rope began to fray. — Total effective lifespan Same tennis ball + same net bag, from brand new to expired. Approximately 12,428 times Approximately 2000 times Ultrasonic welding solution Standard tennis training, a fresh start The weld joints are strong after approximately 7,500 welds, but break after approximately 9,700 welds. It will fail after approximately 2000 uses. 3cm tear in tennis ball After the bladder is ruptured, it is inserted into the mesh bag of this invention. Continued normal work approximately 253 times The ball becomes invalid once it breaks.

[0120] The table above clearly shows the complete progressive protection chain of the mesh bag of this invention, from "wool fabric protective mesh bag" to "mesh bag protecting tennis balls", with a total effective life of about 12,428 cycles, which is more than 6 times that of commercially available products (about 2,000 cycles).

[0121] 9. Coordination and redundancy between fixing straps, locking loop ropes, and external equipment.

[0122] This invention achieves a composite force-bearing system with multiple components working together by fitting the connecting rings of the fixed strap (29), locking loop (22), and external device (15) on the tennis ball into the closed loop of the same movable loop (14). This structure has the following mechanical advantages: (a) During normal operation, the tension is transmitted to the movable loop (14) through the locking loop (22), while the fixed strap (29) is in a relaxed and unstressed state, serving only as a backup; (b) When the independent loop of the net bag breaks due to long-term use, the fixed strap (29) automatically takes over the load as a backup tension transmission path; (c) All three components can slide freely along the circumference of the movable loop (14), avoiding the problems of stress concentration and torsional wave attenuation caused by rigid connection, and working synergistically with the 5-8cm preferred range of the movable loop (14) itself, giving the connection a longer service life. This "one rope for three components" structural design transforms the fixed strap from a traditional single load-bearing structure into a "standby redundancy," achieving a synergistic gain of "1+1>1."

[0123] 10. Maintainability and Economy

[0124] Because each individual rope loop is independently connected to the bottom loop via a snap-lock structure or ultrasonic welding, and the top rope end is threaded within the closed loop of the same locking loop, any damaged individual rope loop can be removed and replaced individually without discarding the entire bag. With the snap-lock design, the damaged rope loop can be removed by loosening the top snap-lock, replaced with a new rope loop, and then tightened and locked again. With the welding design, the weld point of the damaged rope loop is cut off, and a new rope loop is replaced and re-welded. This maintainability design further reduces operating costs and minimizes equipment waste. Attached Figure Description

[0125] Figure 1 This is a schematic diagram of the overall structure of the high-redundancy progressive failure-safe cage tennis net bag of the present invention (taking the eight independent rope loop scheme as an example). Figure 1 The overall shape of the net bag without a tennis ball is shown, including: the bottom ring (1) is an octagonal ring structure; eight independent rope loops (2) are evenly connected to the middle of the eight sides of the bottom ring (1) through a fixing structure (sliding lock structure 5), and each independent rope loop (2) is evenly distributed in the circumference and does not cross each other; the top rope ends of each independent rope loop (2) converge at the top of the tennis ball and are locked together by locking loop ropes (22). Figure 1 The three-ring interlocking structure (7) of the bottom ring (1) is also shown.

[0126] Figure 2 This is a top view of the positioning mold and bottom ring of the present invention in the fitted state. Figure 2The structure of the positioning mold and the positioning state of the bottom ring on the mold are shown: The positioning mold includes a base plate (8) and eight rigid columns (9) fixed on the base plate. The eight rigid columns (9) are distributed along the vertices of a regular octagon. The bottom ring (1) is fitted on the outside of the eight rigid columns (9) and forms a regular octagon under the support of the rigid columns, which facilitates the positioning and fixing of the subsequent independent rope rings.

[0127] Figure 3 This is a partially enlarged schematic diagram of the "live buckle lock" structure of a single independent rope loop of the present invention. Figure 3 The specific construction of the adjustable snap-locking structure (5) between the independent rope loop (2) and the bottom loop (1) is shown: the head (3) of the independent rope loop passes through the bottom loop (1), and its tail (4) passes back from the middle of the head (3) and is tightened to form a snap. This structure can achieve reliable fixation without winding, and can be unlocked by pulling the head (3), which facilitates the maintenance and replacement of the independent rope loop.

[0128] Figure 4 This is a schematic diagram of the locking loop rope (22) of the present invention, which is pre-formed into a loop and then sequentially threaded through the top of each independent loop rope head and the tail end through the head to form a snap-lock structure. Figure 4 The core structure of the top locking structure of the present invention is shown: the locking loop rope (22) is first connected end to end to form a closed loop; the closed loop passes through the top rope head (24) of the first independent rope loop, the top rope head (26) of the second independent rope loop, the top rope head (27) of the third independent rope loop, the top rope head (28) of the fourth independent rope loop and each remaining rope head in sequence, so that each top rope head is hooked on the closed loop; the tail (23a) of the locking loop rope passes through its head (23b) to form a slip knot structure (23); by pulling the tail (23a) to gather and tighten all the rope heads, the tail and head are knotted to form a unique dead knot (25). The locking loop rope (22) and the external device (15) are looped in the closed loop of the movable loop rope (14). Figure 4 Taking four sets of diagonal rope ends as an example, in the case of eight independent rope loops, all eight rope ends are threaded onto the same closed loop.

[0129] Figure 5 This is a schematic diagram of the locked state of the top locking structure of the present invention.

[0130] Figure 5 The final structural state of the lock loop rope (22) after being pulled and locked is shown, with the top ends of each individual loop converging at the top of the tennis ball and secured by a single dead knot (25).

[0131] Specifically, Figure 5 middle:

[0132] (a) The dashed circular outline (φ16mm) of the locking loop rope (22) indicates its initial position before tightening, and the thick solid regular octagon (circumcircle φ8-10mm) indicates its final position after being tightened by force. The regular octagon is tightly clamped at the convergence root of the top rope head of each independent loop, locking the top rope head of the eight independent loops (2) to the center area of ​​the top of the tennis ball at one time.

[0133] (b) The top rope ends (24, 26, 27, 28, etc.) of each independent rope loop converge from the vertices of the regular octagon to the center point O, forming a radial tightening structure, indicating that all rope ends are tightened and fixed at once within the closed loop of the locking loop rope (22);

[0134] (c) As a specific example of the locking method between the locking loop rope (22) and the top rope ends of each independent loop, after the tail (23a) of the locking loop rope passes through the head (23b) of the locking loop rope, it is pulled and tightened to a predetermined tension. Then, the tail (23a) is pulled down from the inside of the locking loop rope (22), wrapped around twice, and then passed out from the bottom to the top through the hole in the middle of the head (23b). After being pulled tight, a dead knot (25) is formed, leaving a short tail of 3-5mm. It should be noted that this is only a preferred knotting method example. The scope of protection of the present invention is not limited to this. Any other fixed connection method that can form the unique dead knot (25) is within the scope of protection of the present invention.

[0135] (d) The unique dead knot (25) is located at the fixed connection between the tail (23a) and head (23b) of the locking loop rope, that is, at the intersection of the edge of the regular octagon and the tail (23a) - the unique dead knot (25) is the final locked end of the locking loop rope (22), and there is only one dead knot in the entire net bag, and the knot is located in the top area of ​​the tennis ball that is only subjected to axial tension and not impact;

[0136] (e) The movable loop rope (14) is shown in a circle with half solid line and half dashed line, indicating that it is looped inside the closed loop (regular octagon) of the locking loop rope (22), and the two maintain a looping connection that allows them to move relatively freely.

[0137] (f) The connecting ring of the external device (15) (figure-eight swivel) is also fitted into the closed loop of the same movable loop rope (14) for connecting to an external tension source.

[0138] Figure 5 In the middle, the locking loop rope (22) is distinguished by different line shapes to show its initial position (dashed circle) and final position (thick solid octagon), aiming to clearly show the complete locking process of "pulling the tail of the locking loop rope → closing the loop and shrinking → tightening the octagon around each rope end → fixing with a single dead knot".

[0139] Figure 6 for Figure 5A magnified view (3:1) of the area indicated by the dashed circle shows the detailed structure of the unique dead knot (25) at a magnified scale. Figure 6 As shown, the closed loop of the locking loop rope (22) is an octagon, and the top ends of each independent loop (24, 27, 28, etc.) converge at the center; the tail of the locking loop rope (23a) passes through the head of the locking loop rope (23b) and is then wrapped and knotted to form a unique dead knot (25), leaving a short tail of 3-5mm; the dead knot (25) is thickened due to the multiple loops of the rope (shown as a thick solid line); the movable loop rope (14) is shown as half solid line and half dashed line, indicating that it is fitted inside the closed loop of the locking loop rope (22); the connecting ring of the external device (15) (figure-eight swivel) is also fitted inside the closed loop of the same movable loop rope (14).

[0140] Figure 7 This is a schematic diagram showing the working state of the net bag after the tennis ball is loaded into it, according to the present invention. Figure 7 The overall working state of the tennis ball (10) after being put into the net bag is shown: the tennis ball (10) is wrapped in the net bag; the independent rope loops (2) wrap around the surface of the tennis ball from the bottom along the warp direction, and the top is locked by the locking loop rope (22); the bottom loop (1) has a wave-shaped structure under the lifting action of the independent rope loops, including the crest (16) and the trough (17); the connection between each independent rope loop and the bottom loop forms a figure-eight micro-locking structure (6), so that the bottom loop is pulled tightly and adhered to the surface of the tennis ball; the tennis ball woolen fabric layer (19) wraps around the surface of the tennis ball, and the independent rope loops and the bottom loop are embedded in the woolen fabric.

[0141] Figure 8 This is a schematic diagram of the fault-tolerant state of the present invention. Figure 8 The progressive redundancy failure mechanism of the net bag is demonstrated: the figure shows the broken individual loops (12) (indicated by dashed lines) and the remaining effective individual loops (13) (indicated by solid lines). When several individual loops completely break, the remaining effective individual loops (13) still maintain the wrapping and fixation of the tennis ball, and the tennis ball will not fall out. This state corresponds to the "critical state" in the three-layer redundancy - when four individual loops break at intervals, the remaining four can still reliably wrap the tennis ball.

[0142] Figure 9 This is a schematic diagram of the connection between the movable loop rope (14) of the present invention and an external device. Figure 9 The connection structure of the movable loop rope (14) is shown: the closed loop of the locking loop rope (22) is fitted inside the closed loop of the movable loop rope (14); one end of the connecting ring of the external device (15) (figure-eight swivel) is also fitted inside the closed loop of the movable loop rope (14); both the locking loop rope (22) and the external device (15) can slide freely around the circumference of the closed loop of the movable loop rope (14). This structure achieves a flexible transition connection between the locking loop rope and the external device.

[0143] Figure 10A schematic diagram of the structure of the fixed belt (29), the locking loop rope (22) and the external equipment (15) being threaded through the movable loop rope (14) shows the collaborative working state of the three being threaded through the same movable loop rope closed loop. Figure 10 The complete structure of the fixing strap as a backup redundancy is shown: the fixing strap (29) is attached to the surface of the tennis ball (10), located between the wool layer (19) and the bladder, with a gap between them; the rope of the movable loop (14) passes through the gap between the fixing strap (29) and the wool and then connects end to end to form a closed loop, so that the fixing strap (29) is hung on the closed loop; the closed loop of the locking loop (22) and the connecting ring of the external device (15) are also simultaneously fitted into the closed loop of the same movable loop (14); the locking loop (22) is pressed on top of the fixing strap (29). This structure achieves dual redundancy, with the locking loop bearing the load during normal operation and the fixing strap automatically taking over the load when the net bag fails.

[0144] Explanation of markings in the diagram:

[0145] 1 – Bottom loop; 2 – Individual loop; 3 – Head of individual loop; 4 – Tail of individual loop;

[0146] 5 – Loop locking structure; 6 – Figure-eight micro-locking structure; 7 – Multi-loop structure (three-loop interlocking structure of the bottom ring); 8 – Positioning mold base plate; 9 – Rigid column; 10 – Tennis ball; 12 – Broken independent rope loop;

[0147] 13 – Remaining valid independent rope loops; 14 – Movable rope loops; 15 – External equipment (swivel);

[0148] 16 – Wavy bottom ring crest; 17 – Wavy bottom ring trough; 19 – Tennis tennis wool layer;

[0149] 22——Locking loop rope 23——Locking loop rope tail passing through the head to form a slip knot structure (where 23a is the tail of the locking loop rope and 23b is the head of the locking loop rope).

[0150] 24 – Top end of the first independent rope loop; 25 – Fixed connection point between the end and head of the locking loop (the only dead knot); 26 – Top end of the second independent rope loop; 27 – Top end of the third independent rope loop;

[0151] 28 – Top rope end of the fourth independent rope loop; 29 – Fixing strap. Detailed Implementation

[0152] The inventor's experimental research found

[0153] To investigate the root causes of traditional tennis net bag failures, the inventors systematically disassembled and analyzed 100 damaged tennis net bags accumulated during long-term research and development, statistically analyzing the damage at nearly 500 intersections and knots. The statistical results are as follows:

[0154] Intersections with dead knots (equatorial zone and bottom area) Approximately 90% The dead knot is a stress concentration point, located in the main hitting area of ​​the racket or the main contact area of ​​the ground, and is subjected to repeated impacts, collisions and friction; the wool fabric deteriorates rapidly after wear and tear, and is repeatedly damaged after repair. Loop rope connection intersection Approximately 5% There is localized stress concentration at the connection point of the looped rope, but there is no dead knot friction, and the damage rate is significantly lower than that of the intersection with dead knots. Top intersection and knot of the mesh bag ＜1% The top is only subjected to tensile force, without impact, collision or friction, and is not easily damaged even if there is a knot. Other locations (such as the middle of the rope) Approximately 4% Rope fatigue due to its own tensile / bending.

[0155] The above statistics show that the fundamental reason for the failure of traditional mesh bags lies in the high spatial overlap between "weak points (dead knots, cross knots) and the locations of greatest impact (primary impact zone, primary contact area)." This discovery provides experimental evidence for the "spatial avoidance" core design concept of this invention. The following embodiments are all designed based on this discovery.

[0156] Example 1 (Standard version with eight independent rope loops - slip knot solution)

[0157] Material preparation

[0158] Rope material: 12-strand PE braided rope, 1.2mm in diameter

[0159] Bottom ring rope: 1 piece, 48cm long, 1.2mm in diameter

[0160] Eight individual rope loops: 8 loops, each 16cm long and 1.2mm in diameter.

[0161] Locking loop rope (22): 1 piece, formed by joining the ends of a single rope, with a diameter of 1.2mm.

[0162] Movable loop rope (14): 1 piece (made by connecting the locking loop rope to the external equipment end to end), length determined as needed, diameter 1.2mm.

[0163] Material preparation

[0164] All PE braided ropes are cut to the required length using a hot cutter.

[0165] All joints of the rope loops (including the bottom loop joint, each individual loop joint, and the locking loop joint, excluding the movable loop joint) are pre-fixed using ultrasonic welding. For PE braided rope with a diameter of 1.2mm, ultrasonic welding parameters of 30-50kHz frequency, 0.2-1.0 seconds welding time, and 1-5kg / cm² welding pressure can be used; preferably, 35-40kHz frequency, 0.3-0.8 seconds welding time, 0.2-0.5 seconds holding time, and 2-4kg / cm² welding pressure are used; most preferably, 37kHz frequency, 0.5 seconds welding time, 0.3 seconds holding time, and 3kg / cm² welding pressure are used.

[0166] Positioning mold

[0167] Construct a regular octagon within a circle with a diameter of 5cm, and fix a rigid column with a diameter of 2mm and a height of 40mm at each corner of the regular octagon.

[0168] Production steps

[0169] Step 1: Preparation of the bottom ring

[0170] Take a 48cm 12-strand 1.2mm PE braided rope (with pre-ultrasonic welded joints), make it into a loop rope, and then form three loops together (7) as the bottom loop.

[0171] Step 2: Upper mold for the bottom ring

[0172] The bottom ring (1) is fitted onto the outside of the eight rigid columns (9) of the positioning mold to form a regular octagon.

[0173] Step 3: Positioning the eight independent rope loops with slipknots

[0174] Take a 16cm rope (with pre-ultrasonic welded joints) and connect the ends to form an independent rope loop (2). Pass the head (3) of the independent rope loop through the middle of the bottom loop (1) on one side of the regular octagon, and then pass the tail (4) of the independent rope loop back from the middle of the head of the independent rope loop and tighten it to the predetermined tension to form an adjustable snap-lock structure (5), so that the independent rope loop is fixed in the middle of that side of the regular octagon.

[0175] Repeat the above steps to fix the eight individual rope loops to the center of each of the eight sides of the regular octagon.

[0176] Step 4: Place the tennis ball into the mold

[0177] Place a standard tennis ball (10) in the center of the mold, with eight independent rope loops radiating outwards around the ball.

[0178] Step 5: Lock the loop rope (22) at a single point.

[0179] Take the locking loop rope (22) (with pre-ultrasonic welded joints) and connect its ends to form a closed loop.

[0180] The closed loop is passed sequentially through the top ends of the 1st to 8th independent rope loops, so that each top rope end is hooked onto the closed loop.

[0181] Pass the tail (23a) of the locking loop rope (22) through its head (23b) to form a slipknot structure (23).

[0182] Pull the tail (23a) to bring all the top ends of the individual rope loops hanging on the closed loop together towards the center of the top of the tennis ball and tighten them to the predetermined tension in one go.

[0183] Tie the tail (23a) and head (23b) of the locking loop (22) together (25) to form a unique knot, and cut off any excess thread. The state after locking using the above steps is as follows: Figure 5 As shown, Figure 5 The dashed circular outline (φ16mm) of the locking loop rope (22) indicates its initial position before tightening, and the thick solid regular octagon (circumcircle φ8-10mm) indicates its final position after being tightened. The unique dead knot (25) is located at the fixed connection between the tail (23a) and head (23b) of the locking loop rope.

[0184] Figure 6 Yes Figure 5 The core area was enlarged to more clearly show the unique dead knot (25).

[0185] After the four sets of diagonal rope ends are converged and locked, eight figure-eight micro-locking structures (6) are naturally formed at the eight slip knots at the bottom, locking the bottom ring simultaneously from eight directions.

[0186] After the tennis ball is placed in, the bottom ring has a wave-shaped structure (16, 17), and the pull-up points of each individual rope loop form a figure-eight shape, forming the figure-eight micro-locking structure (6), which fixes and locks the bottom ring.

[0187] Step 6: Connect the movable loop rope (14)

[0188] Take a PE braided rope with a length of 5-8cm and thread it through the closed loop of the locking loop rope (22) and the connecting loop of the external device (15) (figure-eight swivel). Then, use ultrasonic welding to close and connect the two ends of the PE braided rope to form a loop, forming a movable loop rope (14). This allows both the locking loop rope (22) and the external device (15) to be threaded through the closed loop of the movable loop rope (14) and to move freely along the circumference of the movable loop rope (14).

[0189] Step 7: Inspect the overall structure

[0190] Confirm that the locking loop rope (22) and the external equipment (15) are both fitted inside the closed loop of the movable loop rope (14) and can move freely along the circumference of the movable loop rope (14) to achieve a flexible transition connection.

[0191] Step 8: Remove the mold

[0192] Remove the mesh bag from the mold and trim off any excess threads to obtain the finished product.

[0193] Finished product parameters

[0194] Total bag weight: Approximately 6-8 grams

[0195] Preparation time: Approximately 3-5 minutes

[0196] Bottom ring diameter: approximately 5cm

[0197] Number of individual rope loops: 8 (four sets diagonally)

[0198] Number of dead knots: 1 (located at the top of the tennis ball)

[0199] Test Results

[0200] As part of a specific embodiment of the present invention, the inventors conducted the following verification tests.

[0201] Durability progressive testing:

[0202] The test ball was a standard training tennis ball. It was first pre-hit about 7,000 times on a regular tennis ball machine (this pre-hitting process did not involve any net bag structure), which shortened the length of the wool fabric to about one-third of its original length, but did not wear it through completely, and the tennis ball was still usable.

[0203] The old ball was placed into a new net bag made according to the method of this embodiment, and the hitting test was continued starting from the point where the wool fabric was worn by about two-thirds. After a total of about 5428 impact tests, a large area of ​​the tennis ball wool fabric was detached (about 50%), a small amount of fuzzing began to appear on the PE braided rope of the net bag, the snap-lock structure was firm, the figure-eight micro-lock structure (6) was intact, and the bottom ring structure was intact.

[0204] The two sets of data above represent the continuous progressive process of the same tennis ball from brand new to final failure: 7000 pre-hit cycles (excluding the net bag) → 5428 more hits after being placed in the net bag of this invention → after a total of approximately 12428 hits, the net bag begins to show wear. During this process, the net bag only begins to directly bear friction after about 2 / 3 of the wool fabric has worn away, verifying the two-way synergistic protection mechanism of "the wool fabric first protects the net bag, and the net bag then protects the tennis ball."

[0205] During approximately 5428 tests (net bag load-bearing phase), the progressive failure data was recorded as follows: Around the 3000th test (starting from the net bag load-bearing phase), the first independent rope loop segment broke; around the 3500th test, the second independent rope loop segment broke; around the 3800th test, the first independent rope loop completely broke (both segments broke); around the 4100th test, the 1st and 7th independent rope loops completely broke; around the 4600th test, the 3rd and 5th independent rope loops completely broke. The remaining 2nd, 4th, 6th, and 8th independent rope loops maintained the tennis ball's grip until the end of approximately the 5428th test without the tennis ball falling out. This process fully verified the three-layer progressive redundancy failure safety mechanism of this invention.

[0206] Extreme crack condition test:

[0207] Another tennis ball was taken, and after about 1800 hits, the bladder developed a crack of about 3cm and began to leak air. Under normal circumstances, this tennis ball should have been unusable. However, it was placed in a new net bag made according to the method of this embodiment, and the tennis ball continued to be used normally for about 253 times (a total of about 2053 times), still maintaining basic hitting function, proving that the net bag has a restraining and protective effect on the tennis ball.

[0208] Example 2 (Combination scheme of moving loop rope and fixing strap)

[0209] Based on Example 1, a commercially available standard tennis ball with a fixing strap is taken, and the fixing strap is pasted through the tennis ball felt layer and attached to the tennis ball bladder. Following the method of Example 1, the cage-like net bag of the present invention is wrapped around the tennis ball and the fixing strap, so that the fixing strap is located directly below the locking loop rope (22).

[0210] In step 6 of Example 1, a PE braided rope with a length of 5-8cm and a braid length of 12 and a diameter of 1.2mm is taken. The fixing strap (29) is attached to the surface of the tennis ball, leaving a gap between it and the wool fabric. First, one end of the PE braided rope is passed sequentially through the connecting ring of one end of the external device (15) (figure-eight swivel), the gap between the fixing strap (29) and the wool fabric, and the closing ring of the locking loop rope (22). Then, the two ends of the PE braided rope are ultrasonically welded together to form a loop, forming a movable loop rope (14). Thus, the fixing strap (29) is hung on the closing ring of the movable loop rope (14), and the locking loop rope (22) and the connecting ring of the external device (15) are both fitted inside the closing ring of the same movable loop rope (14); the locking loop rope (22) is pressed on top of the fixing strap (29).

[0211] This embodiment has been verified through actual testing: when the cage net is intact, the hitting force is completely transmitted to the movable loop rope and the figure-eight swivel through the locking loop rope (22), and the fixing strap is in a relaxed and stress-free state. When the independent loop rope of the cage net breaks after approximately 9700 impacts, the fixing strap automatically begins to bear the tension alone, and the tennis ball remains firmly fixed without coming off. This embodiment achieves a composite force-bearing system in which the fixing strap, locking loop rope, and swivel work in synergy.

[0212] Example 3 (Eight Independent Rope Loops - Welding Scheme)

[0213] Based on Example 1, the fixing method between the individual rope loops and the bottom ring in step 3 is changed from adjustable snap-lock to ultrasonic welding: the predetermined connection points of each individual rope loop are directly fixed to the middle of the bottom ring through ultrasonic welding points, and the welding parameters are the same as those described in the material preparation stage. After welding is completed, the bottom ring with the welded individual rope loops is placed back into the positioning mold, and the subsequent steps are performed. The remaining steps are the same as in Example 1.

[0214] In an exemplary durability test conducted by the inventors, the net bag using the above-mentioned preferred parameters, using a standard training tennis ball (such as Teloon, approximately 6.3 cm in diameter), showed no obvious loosening of the weld points after more than approximately 7,500 impact tests; at approximately 9,700 impact tests, the first independent rope loop was observed to break, while the wavy bottom loop and the figure-eight micro-locking structure (6) remained intact, demonstrating the effectiveness of the progressive failure safety mechanism.

[0215] Example 4 (Basic version with six independent rope loops - slip knot solution)

[0216] Based on Example 1, the eight independent rope loops are changed to six independent rope loops, and the positioning mold is changed to a regular hexagon. After the locking loop rope (22) is pre-formed into a ring, it is passed through the top rope ends of the six independent rope loops in sequence, and the tail is passed through the head buckle to tighten and lock. The remaining steps are the same as in Example 1.

[0217] Industrial applicability

[0218] This invention enables industrial production through standard weaving, ultrasonic welding, and assembly processes. The cage-like mesh bag can be produced using a 16-column weaving mold in conjunction with manual or semi-automatic weaving equipment; the joints of each loop rope are fixed using ultrasonic welding, resulting in high welding strength; the movable loop ropes and elastic ropes can be cut and connected using ordinary rope processing equipment; and the overall assembly can be completed using an assembly line method. This invention is applicable to various single-person tennis training devices, ball practice equipment, and other products.

Claims

1. A highly redundant, progressively fail-safe cage-type tennis net bag, characterized in that, include: Bottom ring (1): A ring structure formed by loop ropes, forming a ring reference at the bottom of the net bag; at least six independent loop ropes (2): each independent loop rope is formed by connecting the ends of the ropes to form a loop rope, and each of the independent loop ropes is connected to the bottom ring by a fixed structure and is evenly distributed along the circumference of the bottom ring; the top rope ends of each of the independent loop ropes are sequentially threaded onto the closed loop of a locking loop rope (22) formed by connecting the ends of a rope, and the tail of the locking loop rope (22) passes through its head to form a snap structure. By pulling the tail, the top rope ends are gathered and locked to the top of the tennis ball. The tail of the locking loop rope (22) is fixedly connected to the head to maintain the locked state; the independent loop ropes do not cross each other; after the net bag is filled with tennis balls, under the lifting action of each of the independent loop ropes, the bottom ring (1) has an undulating wave-shaped structure between adjacent fixed structures, and the connection between each independent loop rope and the bottom ring forms a figure-eight micro-locking structure (6) due to the lifting action.

2. The high-redundancy progressive failure-safe cage-type tennis net bag according to claim 1, characterized in that, The outer diameter of the bottom ring (1) is 48mm to 52mm, and the vertical distance between the contact ring of the bottom ring and the bottom of the tennis ball is 11mm to 13mm; the total number of dead knots in the net bag is only 1, and the dead knot is located in the top area of ​​the tennis ball.

3. The high-redundancy progressive failure-safe cage-type tennis net bag according to claim 1, characterized in that, The number of independent rope loops is eight, and the eight independent rope loops are distributed in pairs opposite each other in four diagonal directions on the bottom ring; each independent rope loop is formed by folding a rope line in half to form two rope segments.

4. The high-redundancy progressive failure-safe cage-type tennis net bag according to claim 1, characterized in that, The fixing structure is an adjustable snap-locking structure (5): the head (3) of each independent rope loop passes through the bottom ring, and the tail (4) of the independent rope loop passes back from the middle of the head of the independent rope loop and is tightened, and can be unlocked by pulling the head; or, the fixing structure is an ultrasonic welding structure, and the independent rope loop (2) is fixedly connected to the bottom ring (1) through ultrasonic welding points.

5. The high-redundancy progressive failure-safe cage-type tennis net bag according to claim 1, characterized in that, It also includes a movable loop rope (14) and an external device (15) for connecting an external tension source; the locking loop rope (22) and the connecting ring of the external device (15) are both fitted inside the closed loop of the movable loop rope (14) and can move freely along the circumference of the movable loop rope (14).

6. The high-redundancy progressive failure-safe cage-type tennis net bag according to claim 5, characterized in that, The circumference of the movable loop cord (14) is 5cm to 8cm; it also includes a fixing strap (29) set on the tennis ball, and there is a gap between the fixing strap (29) and the tennis ball fabric for the cord to pass through; a section of the movable loop cord (14) passes through the gap and then the ends are joined together to form a closed loop, so that the fixing strap (29) is hung on the closed loop of the movable loop cord (14); the locking loop cord (22) is pressed on top of the fixing strap (29), so that the fixing strap (29) serves as a backup tension transmission path when the net bag fails.

7. A rapid manufacturing method for a highly redundant, progressively fail-safe cage-type tennis net bag, characterized in that, Includes the following steps: Preparation: All joints of the loops are pre-fixed by ultrasonic welding; a positioning mold is provided, which has several positioning posts distributed along the circumference, the number of which is the same as the number of independent loops; the bottom ring (1) is fitted over the outside of the positioning posts to form a regular polygon; each independent loop (2) is connected to the middle of the bottom ring on each side of the regular polygon through a fixing structure, so that each independent loop is evenly distributed along the circumference of the bottom ring; the tennis ball (10) is placed in the center of the mold; a rope is taken and connected end to end to form a closed loop locking the loop (22), and the closed loop is... The loops pass through the top ends of each individual rope loop in sequence, so that each top rope end is hooked onto the closed loop; the tail of the locking loop rope (22) passes through its head to form a snap structure, and the tail is pulled to gather and lock the top rope ends to the top of the tennis ball, thus fixing the tail and head together; a rope is threaded through the closed loop of the locking loop rope (22) and the connecting loop of the external device (15) and then connected end to end to form a movable loop rope (14), so that the locking loop rope (22) and the external device (15) are both threaded through the closed loop of the movable loop rope (14); the mold is removed to complete the production.

8. The method according to claim 7, characterized in that, The number of positioning posts is six or eight.

9. The method according to claim 7, characterized in that, The fixing structure is an adjustable snap-locking structure (5): the head (3) of each independent rope loop is passed through the bottom ring, and the tail (4) of the independent rope loop is passed back from the middle of the head of the independent rope loop and tightened; or, the fixing structure is an ultrasonic welding structure: each independent rope loop (2) is fixedly connected to the bottom ring (1) through ultrasonic welding points.

10. The method according to claim 7, characterized in that, The method further includes: before or simultaneously threading the rope through the closed loop of the locking loop (22) and the connecting loop of the external device (15), passing one end of the rope through the gap between the fixing strap (29) and the wool fabric on the tennis ball, so that the fixing strap (29) is hooked onto the closed loop of the movable loop (14).

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