A headrest assembly for an aircraft seat and a method of small angle adjustment and return thereof

Abstract

The application discloses an aviation seat headrest assembly and a small-angle adjusting and resetting method thereof. The assembly comprises a headrest, a headrest plate, a headrest rod, a rotating rod, an angle adjusting mechanism and a resetting mechanism. The angle adjusting mechanism is composed of a coaxially fixed ratchet wheel, a pawl and a tension spring, and can be unidirectionally locked in a range of -17° to +15° with a step of 2°±0.1°. The small rotating disc of the resetting mechanism is provided with a boss. When the headrest plate is forward rotated to +15° and then pushed by ≤5°, the boss pushes and presses the tail part of the pawl, and the pawl is unlocked within 0.3s, and the headrest plate is one-time over-reset to -17° after the hand is released. All the parts are made of 7075-T6 aluminum alloy and flame-retardant plastic, and the total weight is ≤450g. The ratchet wheel has 90 teeth, a modulus of 0.333 mm and a single-tooth meshing coincidence degree of ≥1.05, and satisfies the HIC relative 5° step reduction of ≥25% under the impact of CCAR-25.56. The application considers small-step fine support, one-hand one-key resetting, light weight and high reliability, and is suitable for batch installation of cockpit and passenger cabin seats.

Description

Technical Field

[0001] This invention relates to the field of aircraft seat technology, and in particular to an aircraft seat headrest assembly and its small-angle adjustment and reset method. Background Technology

[0002] Aircraft seat headrests provide head support for occupants, and their adjustable angle directly affects fatigue levels during long-haul flights. Current technology has the following main shortcomings:

[0003] Pilot seat headrests often use nylon sheets for friction positioning, which cannot be locked and are prone to displacement due to flight vibrations;

[0004] While the locking pin solution can fix the device, the adjustment step is generally 5° to 10°, which is too large and cannot meet the requirements for precise support.

[0005] Passenger seat headrests generally lack fore-and-aft angle adjustment, only allowing for height adjustment or side folding.

[0006] Reset requires two-handed operation and multiple adjustments, making it inconvenient to use in the cramped environment of the cockpit.

[0007] Therefore, there is an urgent need for an aviation headrest adjustment mechanism that is simple in structure, can achieve 2° small step locking, and can be reset with one hand in one go. Summary of the Invention

[0008] The purpose of this invention is to provide an aircraft seat headrest assembly and a method for adjusting and resetting the small angle thereof, thereby solving the aforementioned problems existing in the prior art.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] An aircraft seat headrest assembly includes:

[0011] Headrest;

[0012] Headrest board, used to support the headrest;

[0013] The headrest bar extends along the vertical direction of the seat and is fixed to the seat frame.

[0014] A rotating rod is horizontally fixed at the top of the headrest rod. The two ends of the rotating rod are hinged to the support on the back of the headrest plate through bushings, forming the rotation center of the headrest plate.

[0015] An angle adjustment mechanism is located between the headrest plate and the headrest rod, used to lock the headrest plate relative to the headrest rod in 2° increments within the range of -17° to +15°.

[0016] The reset mechanism is used to unlock the headrest when it continues to rotate forward to about +20° after exceeding +15°, so that the headrest can be reset to -17° in one go.

[0017] The angle adjustment mechanism includes a ratchet and a pawl that can mesh with each other. The ratchet rotates synchronously with the headrest plate, and the pawl is oscillatingly mounted on the headrest rod and remains engaged under the action of a tension spring.

[0018] In some specific embodiments, the reset mechanism includes:

[0019] A small turntable is fitted onto the top of the headrest rod;

[0020] The pawl has one end hinged to the side support of the rotating rod via a pivot, and the end away from the pivot faces the ratchet tooth surface. The pawl tooth surface can engage or disengage from the ratchet tooth surface.

[0021] The tension spring has one end attached to the hole near the pivot of the pawl, and the other end attached to the top crossbar of the rotating rod.

[0022] The ratchet is mounted on the top of the headrest and fixed coaxially with the turntable, rotating together with the turntable.

[0023] In some specific embodiments, the small turntable has a boss on its outer periphery. When the head is rotated to +20° in front of the plate, the boss pushes the tail of the pawl, forcing the pawl to separate from the ratchet, thereby unlocking the turntable.

[0024] The headrest rod is fitted with a long guide sleeve and a short guide sleeve, which are used to connect with the seat back frame and limit the up and down position of the headrest;

[0025] The long guide sleeve is located on the lower section of the headrest rod, and the short guide sleeve is located on the upper section of the headrest rod. Both of them have radial protrusions on their outer walls, which are used to engage with the keyway of the seat frame to prevent rotation.

[0026] The back of the headrest is equipped with a limiting component, which is used to engage with the fixing component on the headrest rod to limit the maximum tilt angle of the headrest to -17°.

[0027] In some specific embodiments,

[0028] The headrest is made of soft foam and covered with flame-retardant fabric. It has Velcro fasteners on the back and can be detachably attached to the front of the headrest.

[0029] The angle adjustment mechanism is enclosed in a plastic cover, which is fixed to the side of the headrest rod by a clip. Only the unlock indicator mark of the small dial is exposed on the surface of the cover.

[0030] The ratchet has 16 teeth with a tooth pitch corresponding to a 2° central angle; the pawl has 1 to 2 teeth with a tooth profile angle of 20° to 25°, used to achieve unidirectional locking and low-noise disengagement.

[0031] In some specific embodiments, all metal parts are made of 7075-T6 aluminum alloy with sulfuric acid anodizing, and the overall component weighs ≤450g, meeting the requirements for aviation weight reduction and flame retardancy.

[0032] A method for adjusting and resetting a small angle of an aircraft seat headrest based on the same concept includes the following steps: a) providing a headrest assembly; b) the passenger or pilot moves the headrest backward or forward, causing the headrest plate to rotate a ratchet; c) the pawl engages with the ratchet tooth by tooth under the action of a tension spring, achieving a 2° step-lock and meeting the condition of a sharp drop in head injury indicators.

[0033] HIC(θ)≤HIC0·e^(–k·θ)

[0034] Where θ is the step distance in degrees; k ≥ 0.28; HIC0 is the 5° step distance reference value; when θ ≤ 2°, HIC(θ) decreases by ≥ 25% relative to HIC0; d) when the headrest plate rotates forward to +15° and continues to rotate forward to about +20°, the small turntable boss pushes the pawl to separate from the ratchet, releasing the lock; e) rotate the headrest plate backward, and the ratchet freely passes over the pawl, resetting to the initial position of -17° in one go.

[0035] In some specific embodiments, the 2° step lock is achieved by the number of teeth Z of the ratchet and the modulus m, and satisfies:

[0036] Z=180° / θ=90

[0037] m=d / Z

[0038] Where θ = 2° is the step angle, d is the pitch circle diameter of the ratchet, and d ∈ [28 mm, 32 mm];

[0039] The pawl uses single-tooth engagement, with a tooth tip height ha=m, a tooth root height hf=1.2m, and an engagement overlap of ε≥1.05, ensuring tooth-by-tooth locking with an accuracy of 2°±0.1° within the range of -17° to +15°.

[0040] In some specific embodiments, in step d), the geometric condition for the small turntable boss to push the pawl to separate from the ratchet is satisfied:

[0041] Δθ=θmax-θrelease=15°~20°

[0042] Where θmax is the actual forward rotation angle of the headrest, θrelease is the unlocking critical angle, and:

[0043] θrelease=15°+arcsin[(s–δ) / R]

[0044] s is the boss lift, s∈[1.2mm, 1.8mm]; δ is the pawl tail clearance, δ∈[0.2mm, 0.4mm]; R is the effective radius of the boss, R∈[8 mm, 10mm].

[0045] In some specific embodiments, in step d), a pre-lubricating coating is provided between the small turntable boss and the pawl tail. During the unlocking process, the coefficient of friction between the boss and the tail is maintained between 0.10 and 0.15, so that unlocking can be completed within 0.3 seconds by pushing forward continuously with one hand.

[0046] In step d), after the head rests on the plate and rotates forward to +15°, the angle of further forward rotation shall not exceed 5°. After unlocking is completed, the boss automatically disengages from the tail of the pawl, so that the pawl immediately springs back to the engagement position under the action of the tension spring, providing overrunning space for subsequent one-time reset.

[0047] In some specific embodiments, in step e), when the headrest plate rotates backward, the back of the ratchet teeth slides along the back of the pawl teeth, and the tension spring keeps the pawl lightly touching the ratchet but not engaging, forming a one-way overrun state, so that the headrest plate returns to the initial position of -17° in one go without additional operation.

[0048] In step e), the limiting member and the fixing member abut against each other at the -17° position to prevent the headrest plate from continuing to rotate backward. At the same time, the pawl falls back into the first tooth of the ratchet under the action of the tension spring, restoring the locked state and completing the reset.

[0049] The beneficial effects of this invention are:

[0050] Fine-tuned step size: The number of ratchet teeth matches the module to achieve a step size lock of 2°±0.1°, which meets the HIC steep drop requirements under CCAR-25.562 impact conditions, and reduces head injury by ≥25% relative to a 5° step size.

[0051] One-handed reset: Continue turning forward about 5° to unlock automatically, and lean back slightly to return to -17°. No additional buttons or handles are required, and the operation time is ≤2 seconds, making it suitable for the small space of the cockpit.

[0052] Lightweight and with fewer parts: All parts are made of 7075-T6 aluminum alloy and flame-retardant plastic, with a total weight of ≤450g and ≤10 parts, reducing weight by more than 30% compared to the traditional locking pin solution.

[0053] High reliability and safety: The pawl is always in light contact with the ratchet under the action of the tension spring to prevent accidental unlocking; the limit and fixing parts are connected by metal, providing mechanical end protection, and the service life is ≥50,000 cycles.

[0054] Easy maintenance: The headrest and headrest are connected by Velcro, allowing for quick disassembly and washing; the adjustment components are fully enclosed to prevent dust from entering and reduce maintenance costs. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the small-angle adjustable and locking aviation seat headrest assembly of the present invention;

[0056] Figure 2 This is a schematic diagram of the headrest angle adjustment mechanism of the present invention;

[0057] Figure 3 This is a schematic diagram of the headrest frame structure of the present invention;

[0058] Figure 4 This is a flowchart of a method for adjusting and resetting the headrest of an aircraft seat at a small angle according to the present invention.

[0059] In the attached diagram: 1. Headrest; 2. Rotating rod; 3. Headrest plate; 4. Limiting component; 5. Fixing component; 6. Long guide sleeve; 7. Headrest rod; 8. Short guide sleeve; 9. Clip; 10. Angle adjustment mechanism; 11. Tension spring; 12. Rotating shaft; 13. Pawl; 14. Ratchet; 15. Small turntable. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0061] Reference Figure 1 , Figure 2 and Figure 3 An aircraft seat headrest assembly shown includes:

[0062] Headrest 1; headrest plate 3 for supporting headrest 1; headrest rod 7, extending along the vertical direction of the seat and fixed to the seat frame; a rotating rod 2 is horizontally fixed at the top of the headrest rod 7, and the two ends of the rotating rod 2 are hinged to the back support of the headrest plate 3 through bushings to form the rotation center of the headrest plate 3; an angle adjustment mechanism 10 is set between the headrest plate 3 and the headrest rod 7 to lock the headrest plate 3 relative to the headrest rod 7 in 2° increments within the range of -17° to +15°; a reset mechanism is used to release the lock when the headrest plate 3 continues to rotate forward to about +20° after exceeding +15°, so that the headrest plate 3 can be reset to -17° in one go; wherein, the angle adjustment mechanism 10 includes a ratchet 14 and a pawl 13 that can mesh with each other, the ratchet 14 rotates synchronously with the headrest plate 3, and the pawl 13 is oscillatingly mounted on the headrest rod 7 and kept engaged under the action of the tension spring 11.

[0063] In this embodiment, 1. The headrest 1 is located on the front of the headrest 3 and is the part that the passenger's head directly contacts. It is detachably attached to the front of the headrest 3 via Velcro fasteners on the back. Function: Provides soft support and enhances comfort; the detachable design facilitates cleaning and replacement.

[0064] 2. The headrest plate 3 is located between the headrest 1 and the angle adjustment mechanism 10, and serves as the supporting base for the headrest. The front of the headrest 1 is bonded to it; the back has a support, which is hinged to the rotating rod 2 via a bushing.

[0065] The back is also provided with a limiting member 4, which is used to block the connection with the fixing member 5.

[0066] Functions: Supports the headrest; acts as the main rotating component, driving the ratchet 14 to rotate synchronously; cooperates with the limiting component 4 to limit the maximum tilt angle to -17°.

[0067] 3. The headrest rod 7 extends vertically along the seat and serves as the supporting frame for the entire headrest assembly. Its bottom end inserts into the seat back frame; a rotating rod 2 is horizontally fixed at the top; a short guide sleeve 8 is fitted onto the upper section, and a long guide sleeve 6 is fitted onto the lower section; a fixing member 5 is mounted on the rod body and cooperates with the limiting member 4. Functions: Provides overall structural support; cooperates with the guide sleeve to achieve vertical adjustment and anti-rotation of the headrest; serves as the mounting base for the angle adjustment mechanism 10 and the reset mechanism.

[0068] 4. The rotating rod 2 is horizontally fixed to the top of the headrest rod 7. The middle part is fixedly connected to the top of the headrest rod 7; both ends are hinged to the back support of the headrest plate 3 through bushings; a side bracket is provided on one side for mounting the rotating shaft 12 of the pawl 13; the top crossbar is used to hang the tension spring 11. Function: To form the rotation center of the headrest plate 3; to provide the mounting fulcrum for the angle adjustment mechanism 10 and the reset mechanism.

[0069] 5. Angle adjustment mechanism 10

[0070] 5.1 The ratchet 14 is mounted on the top of the headrest 7 and is coaxially fixed with the turntable 15. It rotates synchronously with the headrest 3 and engages with the pawl 13 to achieve locking. Function: Provides an adjustment accuracy of 2° step distance; achieves one-way locking in conjunction with the pawl.

[0071] 5.2 The pawl 13 is hinged to the side bracket of the rotating rod 2 via the pivot 12. One end is hinged to the pivot 12; the other end faces the tooth surface of the ratchet 14; a tension spring 11 is attached to the middle hole; the tail can be pushed by the boss of the small turntable 15. Function: It engages with the ratchet to lock; when pushed by the boss, it separates from the ratchet to unlock.

[0072] 5.3 Tension spring 11 connects the pawl 13 and the top crossbar of the rotating rod 2. Its two ends are respectively hooked onto the pawl hole and the crossbar. Function: To provide the elastic force for continuous engagement between the pawl and the ratchet; to allow the pawl to spring back to the engaged state after unlocking.

[0073] 6. Reset mechanism

[0074] 6.1 The small turntable 15 is mounted on the top of the headrest 7 and is fixed coaxially with the ratchet 14. It rotates synchronously with the ratchet; a boss is provided on its outer periphery for pushing the tail of the pawl. Function: When the headrest rotates forward to approximately +20°, the boss pushes the tail of the pawl to unlock; it provides a trigger mechanism for one-time reset.

[0075] 7. Guide sleeve

[0076] 7.1 A long guide sleeve 6 is fitted onto the lower section of the headrest rod 7. The outer wall has a radial key that mates with the keyway in the seat frame. Function: To limit the vertical position of the headrest; to prevent the headrest rod from rotating.

[0077] 7.2 The short guide sleeve 8 is fitted onto the upper section of the headrest rod 7. Like the long guide sleeve, it has a convex key that engages with the keyway in the frame. Together with the long guide sleeve, it enables the up-and-down adjustment of the headrest and prevents rotation.

[0078] 8. Limiting component 4 and fixing component 5

[0079] Limiting component 4: Located on the back of the headrest plate 3; it is connected to the fixing component 5; its function is to limit the maximum tilt angle of the headrest plate to -17°.

[0080] Fixing component 5: Set on the headrest rod 7; it is connected to the limiting component 4; function: to provide mechanical end protection and prevent excessive backward tilting.

[0081] 9. A plastic cover and clip 9 are mounted on the sealing angle adjustment mechanism 10. The clip 9 is fixed to the side of the headrest rod 7. Function: To protect the internal mechanism from dust and contamination; only the unlocking indicator mark of the small turntable 15 is exposed for easy operation.

[0082] In some specific embodiments, the reset mechanism includes a small turntable 15, which is sleeved on the top of the headrest 7; a pawl 13, one end of which is hinged to the side bracket of the rotating rod 2 via a rotating shaft 12, and the end away from the rotating shaft (12) faces the tooth surface of the ratchet 14, and the tooth surface of the pawl 13 can engage or disengage from the tooth surface of the ratchet 14; a tension spring, one end of which is attached to the hole of the pawl 13 near the rotating shaft 12, and the other end is attached to the top crossbar of the rotating rod 2. The ratchet 14 is sleeved on the top of the headrest 7 and coaxially fixed with the small turntable 15, and rotates together with the turntable.

[0083] In some specific embodiments, the small turntable 15 has a boss on its outer periphery. When the headrest plate 3 rotates forward to +20°, the boss pushes the tail of the pawl 13, forcing the pawl 13 to separate from the ratchet 14, thereby unlocking. The headrest rod 7 is fitted with a long guide sleeve 6 and a short guide sleeve 8, which are used to insert with the seat back frame and limit the up and down position of the headrest. The long guide sleeve 6 is located in the lower section of the headrest rod 7, and the short guide sleeve 8 is located in the upper section of the headrest rod 7. Both of them have radial protruding keys on their outer walls, which are used to cooperate with the keyway of the seat frame to prevent rotation. The back of the headrest plate 3 is provided with a limiting member 4, which is used to block the fixing member 5 on the headrest rod 7 to limit the maximum backward tilt angle of the headrest plate 3 to -17°.

[0084] In some specific embodiments, the headrest 1 is a soft foam body covered with flame-retardant fabric, and has a nylon hook and loop fastener on the back for detachable attachment to the front of the headrest plate 3; the angle adjustment mechanism 10 is encapsulated in a plastic cover, which is fixed to the side of the headrest rod 7 by a clip 9, with only the unlocking indicator mark of the small turntable 15 exposed on the surface of the cover; the ratchet 14 has 16 teeth with a tooth pitch corresponding to a 2° central angle; the pawl 13 has 1 to 2 teeth with a tooth profile angle of 20° to 25°, used to achieve one-way locking and low-noise disengagement.

[0085] In this embodiment, 1. The small turntable 15 is located at the top of the headrest rod 7, coaxial with the ratchet 14 and fitted onto the same shaft section. It is "floatingly fitted" onto the optical shaft section at the top of the headrest rod through the central hole, and axially positioned using an elastic retaining ring or step; it is rigidly connected to the ratchet 14 with two M3×5 countersunk screws evenly distributed radially at 90°, forming a "coaxial and integrated" rotating pair. Function: It rotates synchronously with the headrest plate 3; the outer peripheral boss acts as a "mechanical unlocking trigger," pushing the tail of the pawl at the +20° position to complete a one-time reset.

[0086] 2. The pawl 13 is located between the lugs of the left or right side bracket of the rotating rod 2.

[0087] Connection method: Hinged end: A Φ4 stainless steel shaft 12 passes through the lug and the pawl shank, forming a swing pair; both ends of the shaft are riveted to prevent loosening. Elastic end: One end of the tension spring hooks into the Φ1.2 through hole of the pawl shank, and the other end hooks into the Φ2 groove of the top crossbar of the rotating rod, maintaining a preload of 12±1N. Toothed end: Engages with a single tooth of the ratchet 14, with an engagement depth of 1.2mm. Function: Maintains engagement under the action of the tension spring, achieving 2° step unidirectional locking; when pushed by the boss, it disengages within 0.3s, releasing the lock.

[0088] 3. Tension spring 11 is positioned between the top crossbar of rotating rod 2 and the pawl handle, arranged at a 25° angle. Connection method: Both ends are 90° hooks, directly hooking into pre-drilled holes and grooves; no threads, no welding, allowing for quick replacement. Function: Provides a constant tension of 10–14N to ensure low-noise engagement between the pawl and ratchet; after unlocking, it immediately springs back to the engagement angle ≤5°, preparing for the next locking.

[0089] 4. The ratchet 14 is located at the top of the headrest 7 and is coaxial with the small turntable 15 "back to back".

[0090] Connection method: The inner hole has a 0.1mm gap with the bearing section at the top of the headstock, allowing free rotation; it is rigidly connected to the small turntable via two radial screws, forming a "synchronous rotating body"; the tooth surface meshes with the 13 single teeth of the pawl. Function: With 16 teeth, a module of 0.4, and a tooth pitch of 2° central angle, it achieves a fine step distance of 2°±0.1°; the tooth back bevel angle of 22° ensures low-noise overrunning during reset.

[0091] 5. The boss is integrally set on the outer periphery of the small turntable 15, protruding 1.5mm radially and 4mm wide. It is CNC machined as an integral part of the turntable, requiring no further assembly. Function: When the head moves forward to +20°, the boss lifts 1.5mm and pushes the tail of the pawl, forcing the pawl to rotate 8°, thus completely disengaging the teeth from the ratchet and completing the mechanical unlocking.

[0092] 6. Long guide sleeve 6 position: Lower section of headrest rod 7, 80mm from the bottom of the rod. Connection method: 0.1mm gap between the inner hole and the headrest rod, radially tightened with an M4 set screw; two 180° symmetrical 3×3mm raised keys on the outer wall slide against the keyway of the seat frame. Function: Bears 70% of the lateral shear load, preventing the headrest rod from rotating or tilting under impact; also provides 40mm of vertical adjustment travel.

[0093] 7. Short guide sleeve 8 position: Upper section of headrest rod 7, 30mm from the top. Connection method: Same as the long guide sleeve, with the convex key direction consistent, forming a "double-point guide". Function: Assists the long guide sleeve in preventing rotation; provides secondary guidance during headrest lifting and lowering, reducing sway gap to ≤0.15mm.

[0094] 8. Position of limiting component 4: On the back of headrest plate 3, a 5×5mm block integrally injection molded. Connection method: No fasteners, directly serving as part of the backplate reinforcement. Function: When the headrest plate is rotated to –17°, the limiting component and the fixing component 5 engage in a metal-to-metal contact, providing a rigid endpoint, preventing excessive backward tilting and protecting the ratchet's first tooth.

[0095] 9. Fixing component 5: A 2mm thick 7075-T6 aluminum protrusion is welded to the middle section of the head resting rod 7. Connection method: An M5 threaded hole is machined on the protrusion, and it is fixed to the rod body with a countersunk screw; it is replaceable. Function: To form a hard limit with the limiting component 4, and withstand an impact torque of 50 N·m; the surface is anodized, with a hardness ≥200 HV and a service life ≥50,000 cycles.

[0096] 10. Plastic cover: Completely encloses the angle adjustment mechanism 10; dimensions: 38×32×22mm. Connection method: Attached to the side of the headrest rod 7 via clips 9; clamping force: 40N; can be installed and removed by hand. Function: Dustproof and foreign object protection; only the unlocking mark of the small turntable 15 is exposed on the surface to prevent accidental operation; meets FAR 25.853 flame retardant requirements.

[0097] 11. Clip 9 Position: Between the inside of the guard and the side of the headrest rod 7. Connection method: One-piece molded on the guard, snaps into the pre-made annular groove on the rod body, no tools required. Function: Provides a holding force of 30–50N, preventing the guard from loosening under a 9g impact; allows for quick disassembly and maintenance.

[0098] 12. Headrest 1 Position: The foremost part of the headrest panel 3, the contact area for the occupant's head. Connection method: A 50×50mm flame-retardant nylon hook-and-loop fastener is sewn onto the back and pressed against the hook-and-loop fastener on the front of the headrest panel. Peel strength ≥8N / cm. Function: Allows for manual disassembly, cleaning, or replacement within 5 seconds; meets the aviation 12-second rapid evacuation requirement.

[0099] In some specific embodiments, all metal parts are made of 7075-T6 aluminum alloy with sulfuric acid anodizing, and the overall component weighs ≤450g, meeting the requirements for aviation weight reduction and flame retardancy.

[0100] The working principle of this invention patent:

[0101] 1. When the synchronous rotating headrest is pushed by the passenger's hand, the headrest plate rotates around the center of the rotating rod, and the ratchet and small turntable fixed to the headrest plate rotate synchronously to form the same rotating body.

[0102] 2. The one-way locking pawl is always pressed against the ratchet tooth surface under the action of the tension spring; when the head plate rotates forward, the ratchet tooth tip pushes the pawl past the tooth tip and immediately falls into the next tooth root, making a "click" sound, realizing a 2° step distance one-way locking; in the opposite direction, because the tooth back angle is in contact with the pawl, it cannot move backward, thus maintaining the set angle.

[0103] 3. Unlocking the boss: After continuing to rotate forward to +15°, the boss on the outer periphery of the small turntable begins to contact the tail of the pawl; push it ≤5°, the boss lift overcomes the tension spring force, causing the pawl to swing outward as a whole, the engagement depth drops to zero, the ratchet separates from the pawl, and the entire mechanism unlocks instantly. The friction coefficient during the process is controlled at 0.10-0.15 by the pre-lubricating coating, and the unlocking time is ≤0.3 seconds, which can be completed with one hand.

[0104] 4. After the overtaking reset unlock, the passenger leans back slightly, the back of the ratchet teeth slides along the back of the pawl teeth, and the tension spring only touches lightly without engaging, forming a one-way overtaking state; the headrest can fall back freely in one go without any additional operation.

[0105] 5. When the hard limit relocking head plate returns to -17°, the limit part and the fixed part collide metal and stop the movement; at the same time, the pawl aligns with the first tooth of the ratchet, and the tension spring instantly pulls it into the tooth groove, re-establishing the one-way lock and completing the reset. The entire cycle takes ≤2 seconds.

[0106] Reference Figure 4 A method for adjusting and resetting a small angle of an aircraft seat headrest, as shown, includes the following steps: S100, providing a headrest assembly;

[0107] The pre-assembled headrest assembly is then inserted into the seat back frame at the assembly station.

[0108] The 3mm×3mm protruding key on the outer wall of the long guide sleeve 6 and the short guide sleeve 8 are aligned with the keyway of the skeleton.

[0109] The insertion depth is 45 mm. Hearing a "click" indicates that the spring steel ball is locked into the groove, completing the anti-rotation positioning.

[0110] Check the unlocking mark: The triangular mark of the small turntable 15 on the surface of the plastic shield should face directly upward, with an offset ≤ ±5°.

[0111] Weight verification: Weigh with a scale with an accuracy of 0.1 g. If the overall weight ≤ 450 g, it is considered qualified and meets the aviation weight reduction index. S200, the passenger or driver pulls the headrest 1 backward or forward, causing the headrest plate 3 to drive the ratchet 14 to rotate;

[0112] One-handed operation: Place the thumb and four fingers on the front and top of the headrest respectively, and apply a torque of 0.8–1.2 N·m for calibration with a torque wrench.

[0113] Rotation direction:

[0114] The forward-facing direction is positive, up to +20°;

[0115] Backward is negative, and it is stopped by the limiting part 4 at –17°.

[0116] Synchronization verification: The clearance between the support on the back of the headrest plate 3 and the bushing of the rotating rod 2 ≤ 0.15 mm to ensure no free play; the ratchet 14 rotates synchronously with the headrest plate, and the lag angle ≤ 0.2°. S300, the pawl 13 meshes with the ratchet 14 tooth by tooth under the action of the tension spring 11, achieving a 2° step locking, and meeting the steep drop condition of the head injury index:

[0117] HIC(θ) ≤ HIC0·e^(–k·θ)

[0118] Where θ is the step angle, in degrees; k ≥ 0.28; HIC0 is the 5° step reference value; when θ ≤ 2°, HIC(θ) drops by ≥ 25% relative to HIC0.

[0119] Tooth parameters: The ratchet has 16 teeth, the tooth pitch is 360° / 16 = 22.5°; the module m = 0.4 mm, the pitch circle d = 30 mm, corresponding to a 2° central angle.

[0120] Meshing process: The pre-tightening force of the tension spring is 12 ± 1 N, ensuring that the torque required for the top of the pawl tooth to cross over the top of the ratchet tooth ≤ 0.05 N·m; a "click" sound is generated for each tooth crossed, and the sound level is 45–55 dB(A) measured at 0.3 m in an anechoic chamber. Accuracy verification: Record with a 0.01° angle encoder, and the actual step angle is 2° ± 0.1°, meeting the small step requirement of CCAR-25.562.

[0121] HIC Verification: According to the formula HIC(θ)≤HIC0·e^(–k·θ), k=0.28, θ=2°, the measured HIC(2°) decreased by ≥25% compared to the 5° baseline value, meeting the condition for a sharp drop in head injury. S400, when the headrest plate 3 rotates forward to +15° and continues to rotate forward to approximately +20°, the small turntable 15 protrusion pushes the pawl 13 to separate from the ratchet 14, releasing the lock;

[0122] The geometric condition formula is: θ_release = 15° + arcsin[(s–δ) / R]. Taking the intermediate values ​​s = 1.5mm, δ = 0.3mm, R = 9mm, θ_release ≈ 15° + 7.8° = 22.8°; after actual boss contour modification, the unlocking angle is 20° ± 1°. Operation process: The boss lifts 1.5mm, pushing the pawl tail, and the pawl rotates 8° ± 0.5°; the engagement depth decreases from 1.2mm to 0mm, and the disengagement time is ≤0.3s, verified by high-speed camera at 1000fps. Friction control: Both the boss and the pawl tail are coated with a molybdenum disulfide dry film, μ = 0.10–0.15, ensuring a continuous single-handed pushing force ≤ 15N. Automatic return: After unlocking, the boss continues to rotate 2°, and under the action of the tension spring, the pawl immediately returns, maintaining a 0.2mm gap with the back of the ratchet teeth, providing overshoot space for reset.

[0123] S500, rotate the headrest plate 3 backward, and the ratchet 14 will freely pass over the pawl 13, resetting to the initial position of -17° in one go.

[0124] Operation: Simply lean back lightly with one hand to apply a torque of 0.3–0.5 N·m; no buttons need to be pressed. Overrunning state: The ratchet tooth back slope angle is 22°, sliding with the back of the pawl tooth, with a friction coefficient ≤0.15, producing a "rustling" sound, without jamming; the tension spring maintains a light contact force of ≤1N between the pawl and the tooth back, but without meshing, achieving unidirectional overrunning.

[0125] End-point limiting: The headrest back limiter 4 collides metal-to-metal with the headrest rod fixing part 5, with a collision angle of -17°±0.2°; the angular velocity drops from 120° / s to 0 at the moment of collision, producing a "click" sound, indicating that the reset is complete. Automatic recovery to locked state: After the collision, the pawl falls into the first tooth of the ratchet under the action of the tension spring, with a meshing depth of 1.2mm, restoring the 2° step-locking capability; the entire process takes ≤2s, meeting the requirements of single-handed operation in the confined space of the cockpit.

[0126] In some specific embodiments, the 2° step lock is achieved by the number of teeth Z and the module m of the ratchet 14, and satisfies:

[0127] Z=180° / θ=90

[0128] m=d / Z

[0129] Where θ = 2° is the step angle, d is the pitch circle diameter of the ratchet, and d ∈ [28 mm, 32 mm];

[0130] The pawl 13 uses single-tooth engagement, with a tooth tip height ha=m, a tooth root height hf=1.2m, and an engagement overlap of ε≥1.05, ensuring tooth-by-tooth locking with an accuracy of 2°±0.1° within the range of -17° to +15°.

[0131] The specific operation method of this embodiment is as follows:

[0132] The first step is to convert the formula into hard dimensions. The step angle θ = 2° directly determines the number of teeth Z = 90, with no rounding margin. The pitch circle diameter d can be any value between 28mm and 32mm, and the corresponding module can be obtained from m = d / Z. Taking d = 30mm as an example, m = 0.333mm, addendum ha = m = 0.333mm, dedendum hf = 1.2m = 0.400mm, and total tooth height 0.733mm. Once these dimensions are determined, they are written into the tooling purchase order. Any subsequent changes must be recalculated using the formula to avoid step drift caused by "experience-based rounding."

[0133] The second step involves using a single-tooth ratchet pawl to raise the overlap ratio to above 1.05. The ratchet pawl retains only one complete tooth, with the tooth profile machined to match the ratchet wheel at a 20° pressure angle and a module of 0.333mm. The tooth tip width is controlled at 0.30mm, and the tooth root maintains a 0.02mm side clearance with the ratchet tooth tip, ensuring unidirectional locking while preventing jamming. To further increase ε, both the ratchet tooth tip and the ratchet tooth root are rounded with a radius of 0.05mm to reduce meshing impact, resulting in an actual overlap ratio calculation of 1.08, higher than the lower limit of 1.05 specified in the manual.

[0134] The third step involves writing "2°±0.1°" into the process documentation and verifying it online. A 6h-class small-module hob is used during gear hobbing, completing 90-tooth cutting in a single clamping operation. Subsequently, a laser angle encoder with 0.01° resolution is used to perform a step test on the "ratchet-pawl" assembly: the servo table records a peak torque value every 0.1° rotation, with the interval between adjacent peak values ​​required to be between 1.90° and 2.10°; otherwise, the entire batch is reworked. Another 5% of the finished products are then subjected to 50,000 cycles. Only those with tooth thickness wear ≤0.02mm and angle drift ≤0.05° are released, ensuring that any locking point within the full range of -17° to +15° maintains an accuracy of 2°±0.1°.

[0135] Through a rigid process of "fixed datum by formula → tooth profile trimming and ε increase → online measuring instrument to lock tolerance", the 90 teeth, 0.333 module, single tooth meshing, and ε≥1.05 in the instruction manual are all transformed into hard indicators that can be mass-produced and inspected, achieving aerospace-grade small step lock of "one step per tooth, 2° per tooth".

[0136] In some specific embodiments, in step d), the geometric condition for the small turntable 15 boss to push the pawl 13 to separate from the ratchet 14 is satisfied:

[0137] Δθ=θmax-θrelease=15°~20°

[0138] Where θmax is the actual forward rotation angle of the headrest, θrelease is the unlocking critical angle, and:

[0139] θrelease=15°+arcsin[(s–δ) / R]

[0140] s is the boss lift, s∈[1.2mm,1.8mm]; δ is the pawl tail clearance, δ∈[0.2mm, 0.4mm]; R is the effective radius of the boss, R∈[8mm,10mm].

[0141] At the instant of unlocking in step d), all geometric quantities must simultaneously fall on a "time-angle" curve: boss lift s, pawl tail clearance δ, and boss effective radius R. These three variables are locked by the formula θrelease = 15° + arcsin[(s–δ) / R]. Any deviation from this tolerance will push Δθ = θmax - θrelease out of the allowable window of 15° to 20°. During implementation, these three dimensions are first made into "tolerance zones," and then each piece is verified using two levels of tooling: "lower limit first, then upper limit," to ensure that the unlocking angle inevitably occurs after +15° and before +20°.

[0142] First, the variables are compressed into a given range. The boss lift s is directly formed in one step on the CNC lathe: the tool tip radius is 0.2mm, and the radial layered cutting depth is controlled at 1.2mm to 1.8mm; the pawl tail clearance δ is obtained through wire EDM shank contouring, with a kerf width of 0.1mm, keeping δ stable at 0.2mm to 0.4mm; the effective radius R of the boss is based on the pitch circle, with a 0.05mm polishing allowance during turning, and the final R falls within 8mm to 10mm. Any deviation of these three values ​​results in scrapping, preventing subsequent unlocking angle drift.

[0143] Second, use the formula to calculate the unlocking critical angle. Taking the extreme combination: minimum s 1.2mm, maximum δ 0.4mm, maximum R 10mm, we get θrelease≈15°+arcsin(0.08)≈15°+4.6°=19.6°;

[0144] Conversely, with a maximum s of 1.8 mm, a minimum δ of 0.2 mm, and a minimum R of 8 mm, we get θrelease≈15°+arcsin(0.2)≈15°+11.5°=26.5°. Since the instruction manual locks the upper limit of Δθ at 20°, the upper limit of θrelease must be reduced to ≤20°. Therefore, the lower limit of R is raised from 8 mm to 9 mm, while the upper limit of s is lowered to 1.5 mm. After recalculation, the θrelease interval is compressed to 16.1°~20.0°, which falls exactly within the 15°~20° window.

[0145] Third, online verification of the unlocking point. The assembled headrest assembly is mounted on a servo rotary table with an angle encoder resolution of 0.01°, rotating forward at a constant speed of 5° / s. When the angle exceeds +15°, the system monitors the 20με abrupt change in the strain gauge of the ratchet and pawl tooth surface contact signal in real time. The angle at the moment of the abrupt change is recorded as θrelease. Ten consecutive measurements are taken. θrelease must be between 16° and 20°, and the difference between any two measurements must be ≤0.3°; otherwise, the entire batch must be reworked. Through a three-level closed loop of "calculation first, accurate machining, and comprehensive testing," the arcsin term in the formula is solidified into repeatable process data, ensuring that the passenger can unlock the machine by pushing forward ≤5°, with a single-handed operation time ≤0.3s.

[0146] In some specific embodiments, in step d), a pre-lubricating coating is provided between the boss of the small turntable 15 and the tail of the pawl 13. During the unlocking process, the coefficient of friction between the boss and the tail is kept between 0.10 and 0.15, so that the unlocking can be completed in 0.3 seconds by pushing forward continuously with one hand.

[0147] In step d), after the headrest plate 3 rotates forward to +15°, the angle of further forward rotation does not exceed 5°, and after unlocking, the boss automatically disengages from the tail of the pawl 13, so that the pawl 13 immediately springs back to the engagement position under the action of the tension spring 11, providing overrunning space for subsequent one-time reset.

[0148] In some specific embodiments, in step e), when the headrest plate 3 rotates backward, the back of the teeth of the ratchet 14 slides along the back of the teeth of the pawl 13, and the tension spring 11 keeps the pawl 13 lightly touching but not engaging with the ratchet 14, forming a one-way overrun state, so that the headrest plate 3 returns to the initial position of -17° in one go without additional operation.

[0149] In step e), the limiting member 4 and the fixing member 5 abut against each other at the -17° position, preventing the headrest plate 3 from continuing to rotate backward. At the same time, the pawl 13 falls back into the first tooth of the ratchet 14 under the action of the tension spring 11, restoring the locked state and completing the reset.

[0150] In this embodiment, the unlocking cycle of step d) is constrained by two rigid parameters: a friction coefficient of 0.10-0.15 and a total time of 0.3s. During implementation, a molybdenum disulfide dry film coating with a thickness of 1.5μm is applied simultaneously to both the boss and the tail of the pawl, with a curing temperature of 120℃. Then, a closed-loop torque table is used for verification: when θ>15°, the servo motor continues to push 5° with a constant torque of 30 N·mm. The coating reduces the sliding friction to 0.12, with the entire process taking 220ms. The remaining 80ms is reserved for the spring rebound, completing the unlocking within 0.3s. After 5000 wear cycles, the μ remains ≤0.18; exceeding this limit requires re-spraying the entire batch.

[0151] Once unlocking is complete, the boss contour immediately separates from the pawl tail: the outer edge of the boss is cut at a 3° rear angle at a 20° position to ensure zero contact within 0.05s after turning past the critical point; the tension spring is preloaded at 12N, has a free length of 20mm, and a rebound stroke of only 2mm, which can drag the pawl back to the engagement angle within 30ms, and maintain a 0.2mm gap between the tooth back and the ratchet, forming an overrun space, clearing obstacles for subsequent one-time reset.

[0152] Step e)'s "one-way overtaking" is achieved through the tooth back chamfer: the ratchet tooth back is made with a 22° chamfer, and the pawl tooth back has the same angle but with a 0.05mm negative chamfer. When the passenger leans back slightly, the two tooth backs slide together, and the tension spring gently presses the pawl against the tooth surface without engaging it. The sliding resistance torque is ≤0.02 N·m, and the headrest can fall back freely. At the instant of reaching -17°, the limiting part and the fixing part collide metal-to-metal, making a "click" sound and absorbing the remaining kinetic energy; at the same time as the collision, the pawl is exactly aligned with the first tooth of the ratchet, and the tension spring contracts in the last millimeter, pulling the pawl into the tooth groove with a meshing depth of 1.2mm, restoring the lock. The entire reset process does not require the hand to leave the headrest, and the time is ≤1s.

[0153] Example

[0154] Cockpit layout: Insert the entire headrest assembly along the guide groove of the seat back frame until the 3 mm × 3 mm protrusions on the outer wall of the long and short guide sleeves are fully engaged with the keyway of the frame. When you hear the "click" sound of the spring steel ball, the anti-rotation positioning is completed. At this time, the unlock mark arrow is pointing straight up, with an offset of ≤ ±5°.

[0155] Angle adjustment: The driver can use one hand to pull the headrest forward with a torque of 0.8-1.2 N·m, and the headrest will drive the ratchet to rotate synchronously; the pawl will pass over the 90-tooth ratchet tooth by tooth under the action of a 12 N tension spring, with each tooth at 2°±0.1°, emitting a light sound of 45dB, and can be locked at any position within the range of -17° to +15°.

[0156] Unlocking and Resetting: When pushing forward to +18°, the small turntable boss s=1.5mm, R=9mm pushes the tail of the pawl, overcoming the tension spring force within 0.3s to reduce the engagement depth to zero, thus unlocking the mechanism; then lean back slightly, the back of the ratchet teeth slides along the back of the pawl teeth, forming a one-way overrun, and falls back to -17° within 1 second, the limit part and the fixed part collide metal to stop the movement, and at the same time the pawl falls back into the first tooth, returning to the locked state.

[0157] In terms of component materials, small parts such as pawls, ratchet wheels, shafts, turntables, and limiters are all made of stainless steel, while the fixing parts and headrest rotating rods are made of 7075 aluminum alloy, the springs are made of 65Mn spring steel, the headrest rods are made of carbon fiber, and the guide sleeves are made of nylon.

[0158] Weight verification: The entire assembly is made of 7075-T6 aluminum alloy and flame-retardant plastic, with a total weight of 445g, and has passed the airworthiness weighing test; after 50,000 cycles, the tooth thickness wear is ≤0.02mm and the angle drift is ≤0.05mm, requiring no part replacement and achieving maintenance-free use.

[0159] By adopting the above-disclosed technical solution of this invention, the following beneficial effects are obtained:

[0160] This invention combines "fine adjustment with small step size" and "one-handed one-time reset" into one, bringing multiple quantifiable benefits: First, it compresses the headrest angle step size from the traditional 5°~10° to 2°±0.1°, reducing the head injury index by ≥25% relative to the 5° baseline under the CCAR-25.562 impact conditions, significantly improving occupant protection; Second, the unlocking angle is only ≤5° greater than the maximum operating angle, the disengagement is completed within 0.3 seconds, and the automatic return to -17° within 1 second when leaning back slightly, all with one-handed operation, completely solving the pain point of "multiple lever movements with both hands" in the confined space of the cockpit; Third, the all-aluminum alloy + flame-retardant plastic structure keeps the component weight below 450g and the number of parts ≤10, reducing weight by more than 30% compared to traditional locking pin solutions, directly reducing the overall weight of the seat system and bringing additional payload benefits to airlines. Fourth, the ratchet-pawl one-way overtake design provides mechanical endpoint protection, with an angle drift of ≤0.05° after 50,000 cycles. Maintenance only requires wiping the coating, and it does not need to be replaced during its lifespan, significantly reducing operating and maintenance costs. Fifth, the plastic cover provides overall encapsulation, preventing dust and foreign objects from entering, and the headrest and headrest panel can be quickly removed and cleaned in 5 seconds using Velcro, improving cabin hygiene and maintenance efficiency. In summary, this invention simultaneously delivers verifiable gains in five dimensions: safety, operability, weight, reliability, and ease of maintenance, making it suitable for mass installation in pilot and passenger seats.

[0161] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An aircraft seat headrest assembly, characterized in that, include: Headrest (1); Headrest (3) is used to support the headrest (1); The headrest rod (7) extends along the vertical direction of the seat and is fixed to the seat frame; The headrest rod (7) has a rotating rod (2) fixed horizontally at its top end. The two ends of the rotating rod (2) are hinged to the back support of the headrest plate (3) through bushings, forming the rotation center of the headrest plate (3). An angle adjustment mechanism (10) is provided between the headrest plate (3) and the headrest rod (7) to lock the headrest plate (3) relative to the headrest rod (7) in 2° increments within the range of -17° to +15°. A reset mechanism is used to unlock the headrest (3) when it continues to rotate forward to about +20° after exceeding +15°, so that the headrest (3) can be reset to -17° in one go; The angle adjustment mechanism (10) includes a ratchet (14) and a pawl (13) that can mesh with each other. The ratchet (14) rotates synchronously with the headrest plate (3), and the pawl (13) is swayably mounted on the headrest rod (7) and remains engaged under the action of the tension spring (11). The reset mechanism includes: The small turntable (15) is fitted onto the top of the headrest rod (7); Pawl (13), one end of which is hinged to the side support of the rotating rod (2) via a pivot (12), and the other end away from the pivot (12) faces the tooth surface of the ratchet (14). The tooth surface of the pawl (13) can engage or disengage from the tooth surface of the ratchet (14). One end of the tension spring is attached to the hole of the pawl (13) near the rotating shaft (12), and the other end is attached to the top crossbar of the rotating rod (2). The ratchet (14) is fitted onto the top of the headrest (7) and fixed coaxially with the small turntable (15), rotating together with the turntable; The small turntable (15) has a protrusion on its outer periphery. When the head rest plate (3) rotates forward to +20°, the protrusion pushes the tail of the pawl (13), forcing the pawl (13) to separate from the ratchet (14) and thus unlocking the device. The ratchet (14) has 16 teeth with a tooth pitch corresponding to a 2° central angle; the pawl (13) has 1 to 2 teeth with a tooth profile angle of 20° to 25°, which is used to achieve one-way locking and low-noise disengagement.

2. The headrest assembly according to claim 1, characterized in that: The headrest rod (7) is fitted with a long guide sleeve (6) and a short guide sleeve (8) for connecting with the seat back frame and limiting the up and down position of the headrest; The long guide sleeve (6) is located in the lower section of the headrest rod (7), and the short guide sleeve (8) is located in the upper section of the headrest rod (7). Both of them have radial protruding keys on their outer walls for anti-rotation cooperation with the keyway of the seat frame. The headrest plate (3) has a limiting member (4) on the back, which is used to block the fixing member (5) on the headrest rod (7) to limit the maximum backward tilt angle of the headrest plate (3) to -17°.

3. The headrest assembly according to claim 2, characterized in that: The headrest (1) is a soft foam body covered with flame-retardant fabric, and has a nylon hook and loop fastener on the back, which can be detachably attached to the front of the headrest (3). The angle adjustment mechanism (10) is encapsulated in a plastic cover. The cover is fixed to the side of the headrest rod (7) by a clip (9). Only the unlocking indicator mark of the small turntable (15) is exposed on the surface of the cover.

4. The headrest assembly according to any one of claims 1-3, characterized in that: All metal parts are made of 7075-T6 aluminum alloy with sulfuric acid anodizing. The overall component weighs ≤450g, meeting aviation weight reduction and flame retardant requirements.

5. A method for adjusting and resetting the headrest of an aircraft seat at a small angle, characterized in that, The headrest assembly according to any one of claims 1-3 includes the following steps: a) providing a headrest assembly; b) the passenger or driver moves the headrest (1) backward or forward, causing the headrest plate (3) to rotate the ratchet (14); c) the pawl (13) engages with the ratchet (14) tooth by tooth under the action of the tension spring (11), achieving a 2° step lock and satisfying the condition of a sharp drop in head injury indicators: HIC(θ)≤HIC0·e^(–k·θ) Where θ is the step distance in °; k ≥ 0.28; HIC0 is the 5° step distance reference value; when θ ≤ 2°, HIC(θ) decreases by ≥ 25% relative to HIC0; d) when the headrest plate (3) rotates forward to +15° and continues to rotate forward to about +20°, the small turntable (15) boss pushes the pawl (13) to separate from the ratchet (14) and release the lock; e) rotate the headrest plate (3) backward, and the ratchet (14) freely passes over the pawl (13) and resets to the initial position of -17° in one go.

6. The method for adjusting and resetting the small angle of the aircraft seat headrest according to claim 5, characterized in that, The 2° step lock is achieved by the number of teeth Z and the module m of the ratchet (14), and satisfies: Z=180° / θ=90 m=d / Z Where θ = 2° is the step angle, d is the pitch circle diameter of the ratchet, and d ∈ [28 mm, 32 mm]; The pawl (13) adopts single-tooth meshing, with tooth tip height ha=m, tooth root height hf=1.2m, and meshing overlap ε≥1.05, ensuring tooth-by-tooth locking with an accuracy of 2°±0.1° within the range of -17° to +15°.

7. The method for adjusting and resetting the small angle of the aircraft seat headrest according to claim 5, characterized in that, In step d), the geometric condition for the small turntable (15) boss to push the pawl (13) and ratchet (14) to separate is satisfied: Δθ=θmax-θrelease=15°~20° Where θmax is the actual forward rotation angle of the headrest, θrelease is the unlocking critical angle, and: θrelease=15°+arcsin[(s–δ) / R] s is the boss lift, s∈[1.2mm,1.8mm]; δ is the pawl tail clearance, δ∈[0.2mm, 0.4mm]; R is the effective radius of the boss, R∈[8mm,10mm].

8. The method for adjusting and resetting the small angle of the aircraft seat headrest according to claim 5, characterized in that, In step d), a pre-lubricating coating is provided between the boss of the small turntable (15) and the tail of the pawl (13). During the unlocking process, the coefficient of friction between the boss and the tail is kept between 0.10 and 0.15, so that the unlocking can be completed in 0.3 seconds by pushing forward continuously with one hand. In step d), after the headrest plate (3) rotates forward to +15°, the angle of further forward rotation does not exceed 5°, and after unlocking, the boss automatically disengages from the tail of the pawl (13), so that the pawl (13) immediately rebounds to the engagement position under the action of the tension spring (11), providing overrunning space for subsequent one-time reset.

9. The method for adjusting and resetting the small angle of the aircraft seat headrest according to claim 5, characterized in that, In step e), when the headrest plate (3) rotates backward, the back of the teeth of the ratchet (14) slides along the back of the teeth of the pawl (13), and the tension spring (11) keeps the pawl (13) and the ratchet (14) lightly touching but not engaging, forming a one-way overrunning state, so that the headrest plate (3) returns to the initial position of -17° in one go without additional operation. In step e), the limiting member (4) and the fixing member (5) abut against each other at a position of -17° to prevent the headrest plate (3) from continuing to rotate backward. At the same time, the pawl (13) falls back into the first tooth of the ratchet (14) under the action of the tension spring (11), restoring the locked state and completing the reset.

Images