A polishing device for building damper piston rod processing

Abstract

This invention relates to the field of piston rod grinding technology, and specifically to a grinding device for machining piston rods of building dampers. The device includes a machining base, with a headstock assembly and a tailstock assembly at each end. A reciprocating worktable is positioned between the headstock and tailstock assemblies. A longitudinal drive mechanism for moving the reciprocating worktable is mounted on the machining base. Two grinding mechanisms are symmetrically arranged on both sides of the reciprocating worktable. A constant pressure compensation mechanism is positioned between the grinding mechanisms and the reciprocating worktable. Support assemblies are located on both sides of each grinding mechanism, with the two support assemblies positioned between the grinding mechanisms and the headstock and tailstock assemblies, respectively. This invention, through the symmetrically arranged grinding mechanisms on both sides, combined with the constant pressure compensation mechanism, achieves simultaneous grinding of the piston rod of a building damper on both sides. The grinding forces on both sides cancel each other out, eliminating the elastic deflection of the workpiece caused by unidirectional radial force, and effectively solving the problem of drum-shaped or saddle-shaped deformation that easily occurs in the machining of piston rods with large length-to-diameter ratios.

Description

Technical Field

[0001] This invention relates to the field of piston rod grinding technology, and more particularly to a grinding device for processing piston rods of building dampers. Background Technology

[0002] Building dampers, as core components for energy dissipation and vibration reduction, are widely used in high-rise buildings, bridges, and large public facilities to absorb seismic energy or wind loads. The piston rod, as a key actuator of the damper, directly determines its sealing performance, friction damping characteristics, and service life based on its surface quality. Because the damper requires frequent reciprocating motion during operation, the piston rod surface must possess extremely high cylindricity, straightness, and extremely low surface roughness to ensure a precise fit with the polymer sealant and prevent leakage of the damping medium.

[0003] Currently, surface grinding is the final critical process in the production of piston rods for building dampers. Traditional grinding equipment typically references the structural design of general-purpose cylindrical grinders, where the piston rod is horizontally clamped between the rotating spindle and the tailstock center, and a grinding head arranged on one side reciprocates along the piston rod's axial direction for grinding. However, this conventional technology has significant limitations when processing piston rods specifically designed for building dampers.

[0004] First, the piston rod of a building damper typically has a very high length-to-diameter ratio and relatively weak radial rigidity. During grinding, the grinding head on one side must apply a certain radial pressure to the workpiece surface to maintain cutting efficiency. Due to the lack of symmetrical support, the piston rod is prone to elastic deflection under unidirectional radial load, resulting in stress deformation. This deformation is particularly severe in the middle of the rod, causing inconsistent grinding depth along its entire length. The outer circle of the ground piston rod exhibits a distinct waist-shaped or saddle-shaped appearance, making it difficult to achieve micron-level cylindricity. Second, during the rotation of a bent workpiece, its geometric center line oscillates continuously relative to the grinding head axis, forming periodic impact loads. This not only exacerbates the vibration of the grinding system but also easily leaves vibration marks and burn marks on the workpiece surface, directly affecting the adhesion of subsequent coatings and creating a hidden danger for sealing failure during the damper's service life. Furthermore, to avoid excessive bending of the workpiece, operators have to use extremely small cutting depths and slow feed rates, and may even need to add multiple finishing grinding processes, resulting in a significant increase in the single-piece processing cycle, low production efficiency, and difficulty in meeting the needs of large-scale production.

[0005] Therefore, developing a device that can counteract radial processing forces, suppress deformation of slender rods, and achieve high-precision uniform grinding along the entire length has become a pressing technical challenge in the field of building damper manufacturing. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art by proposing a grinding device for machining piston rods of building dampers.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A grinding device for machining piston rods of building dampers includes a machining base. A headstock assembly and a tailstock assembly are respectively provided at both ends of the machining base. A reciprocating worktable is provided between the headstock assembly and the tailstock assembly. A longitudinal drive mechanism for driving the reciprocating worktable is provided on the machining base. Two sets of grinding mechanisms are mirror-symmetrically arranged on both sides of the reciprocating worktable. A constant pressure compensation mechanism is provided between the grinding mechanisms and the reciprocating worktable. Support assemblies are provided on both sides of each grinding mechanism, and the two support assemblies are respectively located between the grinding mechanism and the headstock assembly and the tailstock assembly.

[0008] Preferably, the headstock assembly includes a headstock mounting base fixedly connected to one end of the top of the processing base, a rotary motor mounted on the headstock mounting base, and a hydraulic three-jaw chuck driven by the output shaft of the rotary motor; a longitudinal slide rail is provided on the upper surface of the processing base, and the tailstock assembly includes a tailstock mounting base slidably connected to the longitudinal slide rail, a center sleeve fixedly connected to the side of the tailstock mounting base opposite to the headstock mounting base, a movable center slidably connected inside the center sleeve, and a spring connecting the movable center and the inner bottom of the center sleeve.

[0009] Preferably, the longitudinal drive mechanism includes a servo motor and a lead screw installed inside the machining base. The lead screw is rotatably disposed within the machining base along the longitudinal direction. The output shaft of the servo motor is driven and connected to the lead screw. The reciprocating worktable is threadedly connected to the lead screw.

[0010] Preferably, mounting frames are provided on both sides of the reciprocating worktable, and the grinding mechanism includes a movable seat located on the top of the mounting frame. A grinding motor is fixedly mounted on the movable seat, and the output shaft of the grinding motor drives and connects to the grinding head.

[0011] Preferably, the top of the mounting bracket is provided with a transverse slide rail, and the constant pressure compensation mechanism includes an actuating cylinder mounted on the top of the mounting bracket. The piston rod end of the actuating cylinder is connected to the side wall of the movable seat. A pressure sensor is provided at the connection between the piston rod end of the actuating cylinder and the movable seat. The movable seat is slidably connected to the transverse slide rail, and the axis of the actuating cylinder is parallel to the axis of the transverse slide rail.

[0012] Preferably, it also includes a central controller and a proportional pressure valve, wherein the proportional pressure valve is connected in series in the air supply circuit of the first actuator cylinder, and both the pressure sensor and the proportional pressure valve are electrically connected to the central controller.

[0013] Preferably, a top plate is fixedly connected to the upper surface of the reciprocating worktable, and the support assembly includes two support seats vertically arranged on the top plate. A rotating shaft is rotatably connected between the two support seats, and a support arm is rotatably connected to the rotating shaft. A support roller is rotatably provided at one end of the support arm near the piston rod, and a counterweight section is provided at the other end of the support arm.

[0014] Preferably, the distance from the center of gravity of the support roller to the rotating shaft is 2 / 3 to 1 / 3 of the distance from the center of gravity of the counterweight section to the rotating shaft.

[0015] Preferably, the outer peripheral surface of the support roller is covered with a polyurethane elastic layer.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention utilizes a grinding mechanism arranged symmetrically on both sides, in conjunction with a constant pressure compensation mechanism, to achieve simultaneous grinding of the piston rod of a building damper on both sides. The grinding forces on both sides cancel each other out, fundamentally eliminating the elastic deflection of the workpiece caused by unidirectional radial force. This effectively solves the problem of waist-shaped or saddle-shaped deformation that easily occurs in the machining of piston rods with large length-to-diameter ratios, significantly improving cylindricity accuracy. The constant pressure compensation mechanism can adjust and maintain a constant grinding pressure in real time, avoiding grinding force fluctuations caused by workpiece surface shape errors or material inhomogeneity, ensuring consistent grinding depth throughout the entire length, and reducing surface roughness. Support components are set on both sides of the grinding mechanism to divide the long span of the piston rod into short spans, effectively suppressing the sag deflection caused by the workpiece's own weight. The longitudinal movement of the reciprocating worktable, combined with the synchronous feed of the grinding mechanism on both sides, enables continuous grinding of the entire length of the piston rod in one pass, greatly improving processing efficiency and making it suitable for the large-scale, high-precision production of piston rods for building dampers. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the present invention. Figure 1 ; Figure 2 This is a schematic diagram of the overall structure of the present invention. Figure 2 ; Figure 3 This is a partial structural diagram of the present invention; Figure 4 Partial cross-section of the present invention Figure 1 ; Figure 5 Partial cross-section of the present invention Figure 2 .

[0018] In the diagram: 1. Machining base; 2. Reciprocating worktable; 3. Headstock mounting base; 4. Rotary motor; 5. Hydraulic three-jaw chuck; 6. Longitudinal slide rail; 7. Tailstock mounting base; 8. Center sleeve; 9. Movable center; 10. Spring; 11. Servo motor; 12. Lead screw; 13. Mounting bracket; 14. Moving seat; 15. Grinding motor; 16. Grinding head; 17. Transverse slide rail; 18. Actuating cylinder; 19. Pressure sensor; 20. Top plate; 21. Support base; 22. Rotary shaft; 23. Support arm; 231. Counterweight section; 24. Support roller. Detailed Implementation

[0019] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0020] like Figure 1-5 As shown in the embodiment of the present invention, a grinding device for processing piston rods of building dampers is provided, including a processing base 1. A head frame assembly and a tail frame assembly are respectively provided at both ends of the processing base 1. A reciprocating worktable 2 is provided between the head frame assembly and the tail frame assembly. A longitudinal drive mechanism for driving the reciprocating worktable 2 to move is provided on the processing base 1. Two sets of grinding mechanisms are mirror-symmetrically arranged on both sides of the reciprocating worktable 2. A constant pressure compensation mechanism is provided between the grinding mechanism and the reciprocating worktable 2. Support assemblies are provided on both sides of the grinding mechanism. The two support assemblies are respectively located between the grinding mechanism and the head frame assembly and the tail frame assembly.

[0021] Specifically, the headstock assembly includes a headstock mounting base 3 fixedly connected to one end of the top of the machining base 1. A rotary motor 4 is mounted on the headstock mounting base 3, and the output shaft of the rotary motor 4 drives a hydraulic three-jaw chuck 5. A longitudinal slide rail 6 is provided on the upper surface of the machining base 1. The tailstock assembly includes a tailstock mounting base 7 slidably connected to the longitudinal slide rail 6. A center sleeve 8 is fixedly connected to the side of the tailstock mounting base 7 opposite to the headstock mounting base 3. A movable center 9 is slidably connected inside the center sleeve 8, and a spring 10 is connected between the movable center 9 and the inner bottom of the center sleeve 8. The axis of the center sleeve 8 is at the same horizontal level and strictly aligned with the axis of the hydraulic three-jaw chuck 5. The front end of the movable center 9 is conical and used to insert into the central hole at the end of the piston rod. A spring 10 in a pre-compressed state is installed between the tail end face of the movable center 9 and the bottom surface of the inner cavity of the center sleeve 8. During the grinding process, the spring 10 provides a constant axial thrust to the movable tip 9, so that the piston rod always maintains its axial position when subjected to rotation and grinding forces. It can also automatically absorb the slight axial elongation of the piston rod caused by grinding heat, preventing the piston rod from bending and deforming due to thermal expansion.

[0022] Specifically, the longitudinal drive mechanism includes a servo motor 11 and a lead screw 12 installed inside the machining base 1. The lead screw 12 is rotatably mounted in the machining base 1 along the longitudinal direction. The output shaft of the servo motor 11 drives the lead screw 12. The reciprocating worktable 2 is threadedly connected to the lead screw 12.

[0023] Specifically, mounting brackets 13 are provided on both sides of the reciprocating worktable 2. The grinding mechanism includes a movable seat 14 located on top of the mounting bracket 13. A grinding motor 15 is fixedly mounted on the movable seat 14, and the output shaft of the grinding motor 15 drives the grinding head 16. The grinding head 16 is a diamond grinding wheel, a grinding wheel, or a polishing wheel, and the plane of rotation of the grinding head 16 is perpendicular to the axis of the piston rod. The mirror-symmetrical arrangement of the two grinding mechanisms ensures that the contact points of the two grinding heads 16 are located exactly at the two ends of the diameter of the same cross-section of the piston rod, thereby forming a pair of radial forces with opposite directions and controllable magnitudes in space.

[0024] Specifically, the top of the mounting bracket 13 is provided with a transverse slide rail 17, and the constant pressure compensation mechanism includes an actuating cylinder 18 installed on the top of the mounting bracket 13. The piston rod end of the actuating cylinder 18 is connected to the side wall of the movable seat 14. A pressure sensor 19 is provided at the connection between the piston rod end of the actuating cylinder 18 and the movable seat 14. The movable seat 14 is slidably connected to the transverse slide rail 17, and the axis of the actuating cylinder 18 is kept parallel to the axis of the transverse slide rail 17.

[0025] Specifically, it also includes a central controller and a proportional pressure valve. The proportional pressure valve is connected in series in the air supply circuit of the first actuator cylinder 18. Both the pressure sensor 19 and the proportional pressure valve are electrically connected to the central controller.

[0026] Pressure sensor 19 collects real-time data on the positive pressure exerted by grinding head 16 on the piston rod surface and converts this analog signal into an electrical signal, which is then transmitted to the input of the central controller. The central controller performs real-time calculations based on a preset pressure curve and adjusts the opening of the proportional pressure valve via its output, thereby precisely changing the gas pressure inside the actuator cylinder 18. This closed-loop control system enables the actuator cylinder 18 to drive the moving seat 14 for lateral feed compensation, maintaining the grinding pressure at a constant set value.

[0027] Specifically, a top plate 20 is fixedly connected to the upper surface of the reciprocating worktable 2. The support assembly includes two vertically mounted support seats 21 on the top plate 20, with a rotating shaft 22 rotatably connected between the two support seats 21. A support arm 23 is rotatably connected to the rotating shaft 22. A support roller 24 is rotatably mounted at one end of the support arm 23 near the piston rod, and a counterweight section 231 is provided at the other end of the support arm 23. The circumferential surface of the support roller 24 is radially fitted with the lower half of the piston rod. The support arm 23 rotates freely around the rotating shaft 22, and the gravitational torque generated by the counterweight section 231 generates an upward lifting force through the lever principle, ensuring that the support roller 24 remains in close contact with the bottom of the piston rod.

[0028] Specifically, the distance from the center of gravity of the supporting roller 24 to the rotating shaft 22 is 2 / 3 to 1 / 3 of the distance from the center of gravity of the counterweight section 231 to the rotating shaft 22.

[0029] Specifically, the outer circumferential surface of the support roller 24 is covered with a polyurethane elastic layer.

[0030] To enable those skilled in the art to fully understand and implement this invention, the specific implementation principles of this invention are further supplemented below with a specific application scenario.

[0031] First, the piston rod of the building damper to be processed is horizontally hoisted to the top of the processing base 1 using external hoisting equipment. The operator uses the control terminal to finely adjust the speed of the rotary motor 4 in the headstock assembly, so that the three jaws of the hydraulic three-jaw chuck 5 are fully open. The drive end of the piston rod is inserted into the clamping cavity of the hydraulic three-jaw chuck 5, and then the hydraulic station is started. High-pressure hydraulic oil enters the wedge mechanism inside the chuck, driving the three jaws to synchronously retract radially towards the center, thereby fastening the circumferential surface of the piston rod to the spindle centerline of the machine tool.

[0032] Simultaneously, the operator releases the linear guide clamp of the tailstock mounting seat 7 in the tailstock assembly, allowing it to slide along the two longitudinal slide rails 6 on the top of the machining base 1. When the conical head of the movable tip 9 contacts the center hole at the end of the piston rod, axial thrust is applied, causing the movable tip 9 to overcome the preload of the spring 10 and retract into the tip sleeve 8. During this process, the spring 10 is further compressed, and the resulting elastic restoring force acts axially on the piston rod through the movable tip 9. In the subsequent grinding process, the high-speed friction between the grinding head 16 and the piston rod generates a large amount of grinding heat. Despite the coolant spray, the piston rod still experiences a small amount of linear thermal expansion. Because the spring 10 is in a pre-compressed state, the piston rod elongates due to heat, pushing the movable tip 9 to move slightly. The spring 10 absorbs this displacement, thus preventing the piston rod from becoming unstable due to rigid constraints between the headstock assembly and the tailstock assembly. This prevents axial bending deformation of the piston rod due to thermal expansion and ensures the straightness reference during the machining process.

[0033] After confirming that the piston rod is securely clamped, the longitudinal drive mechanism is activated. The servo motor 11 drives the lead screw 12 to rotate, moving the reciprocating table 2 to the starting grinding position of the piston rod. At this time, the two grinding mechanisms are located on the horizontal sides of the piston rod, respectively. The grinding motor 15 starts, driving the grinding head 16 to rotate at high speed. The actuator cylinder 18 begins to intake air under the control of the proportional pressure valve, pushing the moving seat 14 along the transverse slide rail 17 on the top of the mounting bracket 13 towards the central axis of the piston rod.

[0034] Since the two grinding mechanisms are mirror-symmetrically distributed on the reciprocating table 2, and the contact points of the two grinding heads 16 are on the same horizontal diameter line, when the grinding head 16 contacts the piston rod surface, the radial pressures applied by the two grinding heads 16 are opposite in direction in space vectors. Synchronous control of the proportional pressure valves on both sides by the central controller ensures that the magnitudes of the radial pressures on both sides remain consistent. According to the principle of static equilibrium, the radial resultant force on the piston rod approaches zero. The core principle of this structural design is that it completely changes the force model of the piston rod as a simply supported beam subjected to concentrated loads and undergoing flexural deformation during traditional single-sided grinding. By counteracting the radial machining force, the piston rod will not experience radial offset at the grinding point, thus ensuring the consistency of the grinding head 16's cutting depth in both the circumferential and axial directions, and physically solving the cylindricity error problem in the machining of length-to-diameter ratio rods.

[0035] During the smooth movement of the reciprocating table 2, fluctuations in the instantaneous contact force between the grinding head 16 and the piston rod surface may occur due to unevenness of the blank from the previous process or slight vibrations during rotation. At this time, the pressure sensor 19, connected in series between the actuator cylinder 18 and the moving seat 14, captures this pressure fluctuation signal. When the pressure sensor 19 detects an increase in pressure, it indicates the presence of a surface protrusion or axial oscillation towards the grinding head. After the signal is fed back to the central controller, the central controller immediately reduces the output current of the proportional pressure valve, lowering the gas pressure within the actuator cylinder 18, causing the moving seat 14 to retract outwards under the action of grinding resistance.

[0036] Conversely, when pressure sensor 19 detects a decrease in pressure, the proportional pressure valve increases the air intake, and cylinder 18 pushes the moving seat 14 inward for compensation. The principle is to maintain constant contact stress by dynamically changing the driving force, rather than maintaining a constant mechanical position. This ensures that the grinding head 16 always maintains a constant positive pressure against the piston rod surface, eliminating vibrations caused by rigid mechanical impacts and avoiding overcutting, resulting in extremely high consistency in the micro-geometry of the piston rod surface.

[0037] Due to the significant weight of the piston rod in the building damper, its middle section will naturally sag under gravity when supported at both ends. To eliminate this error, the two sets of support components move synchronously during the movement of the reciprocating worktable 2. The support arm 23 in the support component forms a lever structure with the pivot 22 as the fulcrum. The counterweight section 231 generates a downward torque under gravity, which, according to the lever balance principle, is converted into an upward lifting force by the support roller 24 through the support arm 23. The support roller 24 always abuts against the lower half of the piston rod from below. The upward support force provided by the support component precisely counteracts the gravitational component of the piston rod in the grinding area. Because the support point moves synchronously with the grinding point, the piston rod's axis remains on a theoretically horizontal straight line throughout the entire machining stroke, effectively compensating for the straightness deviation caused by its own weight. At the same time, this follow-up support enhances the local radial stiffness of the piston rod, suppressing the low-frequency oscillation of the long rod under high-speed rotation.

[0038] All contents not described in detail in the specification are existing technologies known to those skilled in the art, and the model parameters of each electrical appliance are not specifically limited; conventional equipment can be used. Electrical control components not mentioned in this technical solution are not shown in the figures because they are existing technologies, and will not be described here.

[0039] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A grinding device for building damper piston rod processing, characterized in that, The equipment includes a processing base (1), with a headstock assembly and a tailstock assembly at both ends. A reciprocating worktable (2) is provided between the headstock assembly and the tailstock assembly. A longitudinal drive mechanism for driving the reciprocating worktable (2) to move is provided on the processing base (1). Two grinding mechanisms are mirror-symmetrically arranged on both sides of the reciprocating worktable (2). A constant pressure compensation mechanism is provided between the grinding mechanism and the reciprocating worktable (2). Support assemblies are provided on both sides of the grinding mechanism. The two support assemblies are located between the grinding mechanism and the headstock assembly and the tailstock assembly, respectively.

2. The polishing device for building damper piston rod machining according to claim 1, characterized in that, The headstock assembly includes a headstock mounting base (3) fixedly connected to one end of the top of the processing base (1). A rotary motor (4) is mounted on the headstock mounting base (3). The output shaft of the rotary motor (4) drives a hydraulic three-jaw chuck (5). A longitudinal slide rail (6) is provided on the upper surface of the processing base (1). The tailstock assembly includes a tailstock mounting base (7) slidably connected to the longitudinal slide rail (6). A center sleeve (8) is fixedly connected to the side of the tailstock mounting base (7) facing the headstock mounting base (3). A movable center (9) is slidably connected inside the center sleeve (8). A spring (10) is connected between the movable center (9) and the inner bottom of the center sleeve (8). A linear guide clamp is provided between the tailstock mounting base (7) and the longitudinal slide rail (6).

3. The polishing device for architectural damper piston rod machining according to claim 1, characterized in that, The longitudinal drive mechanism includes a servo motor (11) and a lead screw (12) installed inside the processing base (1). The lead screw (12) is rotatably disposed in the processing base (1) along the longitudinal direction. The output shaft of the servo motor (11) drives and connects to the lead screw (12). The reciprocating worktable (2) is threadedly connected to the lead screw (12).

4. The polishing device for architectural damper piston rod machining according to claim 1, characterized in that, The reciprocating worktable (2) is provided with mounting brackets (13) on both sides. The grinding mechanism includes a movable seat (14) located on the top of the mounting bracket (13). A grinding motor (15) is fixedly installed on the movable seat (14). The output shaft of the grinding motor (15) drives the grinding head (16).

5. The polishing device for architectural damper piston rod machining according to claim 4, characterized in that, The top of the mounting bracket (13) is provided with a transverse slide rail (17). The constant pressure compensation mechanism includes an actuating cylinder (18) installed on the top of the mounting bracket (13). The piston rod end of the actuating cylinder (18) is connected to the side wall of the movable seat (14). A pressure sensor (19) is provided at the connection between the piston rod end of the actuating cylinder (18) and the movable seat (14). The movable seat (14) is slidably connected to the transverse slide rail (17). The axis of the actuating cylinder (18) is parallel to the axis of the transverse slide rail (17).

6. The polishing device for architectural damper piston rod machining according to claim 5, characterized in that, It also includes a central controller and a proportional pressure valve, the proportional pressure valve being connected in series in the air supply circuit of the first actuator cylinder (18), and the pressure sensor (19) and the proportional pressure valve being electrically connected to the central controller.

7. The polishing device for architectural damper piston rod machining according to claim 1, characterized in that, The upper surface of the reciprocating worktable (2) is fixedly connected to a top plate (20). The support assembly includes two support seats (21) vertically arranged on the top plate (20). A rotating shaft (22) is rotatably connected between the two support seats (21). A support arm (23) is rotatably connected on the rotating shaft (22). A support roller (24) is rotatably arranged at one end of the support arm (23) near the piston rod. A counterweight section (231) is provided at the other end of the support arm (23).

8. The polishing device for architectural damper piston rod machining according to claim 1, characterized in that, The distance from the center of gravity of the support roller (24) to the shaft (22) is 2 / 3 to 1 / 3 of the distance from the center of gravity of the counterweight section (231) to the shaft (22).

9. The polishing device for architectural damper piston rod machining according to claim 1, characterized in that, The outer circumferential surface of the support roller (24) is covered with a polyurethane elastic layer.

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