Diamond grinding device with in-situ disc repairing function and in-situ disc repairing method

Abstract

The invention provides a diamond grinding device with an in-situ disc repairing function and an in-situ disc repairing method, and can be applied to the technical field of ultra-precision grinding equipment. According to the device, a sliding table support is integrated on a traditional grinding table, and a 3D printing assembly and a turning tool assembly are installed on the sliding table support in parallel. When the grinding disc is repaired, firstly, the 3D printing head is controlled to clad and deposit a metal repairing layer doped with diamond micro-powder on the abraded surface of the rotating grinding disc; and then the superhard material turning tool is controlled to conduct precise turning on the repairing layer, and the precision and smoothness of the disc face are recovered. According to the method, additive manufacturing and subtractive machining are combined, non-disassembly in-situ repair of the grinding disc is achieved, the problems that in a traditional mode, disassembly and assembly consume time, a disc body is prone to being damaged, and calibration is needed during reassembly are thoroughly solved, the maintenance efficiency and quality are remarkably improved, and long-term stability of the performance of the grinding disc is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of repair or adjustment technology for worn surfaces of grinding tools, and more specifically to a diamond grinding device and method with in-situ dressing function. Background Technology

[0002] Diamond, as the hardest known material in nature, is crucial for efficient and precise grinding and polishing in high-end manufacturing fields such as semiconductors, optical windows, and superhard cutting tools. In this process, the diamond grinding disc, as a core consumable, directly determines processing efficiency and finished product quality based on its surface condition. However, during long-term, high-load grinding operations, the surface of the grinding disc inevitably experiences uniform wear, localized deep scratches, or micro-pits. These damages not only lead to a sharp decline in grinding efficiency but also increase the surface roughness and deteriorate the surface accuracy of the processed diamond samples, even introducing subsurface damage, severely restricting product quality and production yield.

[0003] Traditional industries commonly employ offline repair methods for the maintenance of grinding discs. Specifically, when the disc's performance deteriorates to an unacceptable level, the entire grinding disc must be completely removed from its driving grinding table and transported to a specialized factory equipped with large surface grinders for repair. This method has several inherent drawbacks: First, the disassembly and assembly process is cumbersome and time-consuming, and the hoisting and transportation of heavy precision discs carries a high risk of impact, potentially causing irreversible damage to the disc or spindle. Second, the off-site repair cycle is lengthy, including waiting times, logistics, and actual processing time, significantly extending equipment downtime and severely impacting production continuity. Finally, the repair effect is limited by the external factory's technological capabilities; the conventional grinding processes used can only restore the macroscopic flatness of the disc surface, failing to specifically compensate for worn grinding media and making it difficult to guarantee optimal metallurgical bonding strength between the repair layer and the substrate. Consequently, the overall wear resistance and service life after repair are often unstable.

[0004] To overcome the shortcomings of offline finishing, the industry has tried some in-situ maintenance techniques, but all of them have significant limitations. For example, using a simple manual scraper for online "sharpening" can only slightly improve the surface shape of the disc and is powerless against severe material defects. There have also been attempts to use epoxy resin and other adhesives to embed diamond abrasives for local repairs, but the strength, heat resistance, and wear resistance of such adhesives are far lower than those of the metal substrate, and they are prone to falling off during the grinding process, resulting in short-lived effects and potential contamination of the workpiece. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] To address the problems of existing diamond grinding disc maintenance, such as the need for disassembly, low efficiency, high cost, and easy damage to the disc, this invention provides a diamond grinding device and method with in-situ disc repair functionality. The device integrates a sliding table support on a traditional grinding table, on which a 3D-printed component and a cutting tool component are mounted side-by-side. By controlling the 3D printing head to deposit a metal repair layer doped with diamond micropowder on the surface of a rotating grinding disc, and then controlling the cutting tool to precisely machine this repair layer, in-situ composite disc repair combining "additive repair" and "subtractive finishing" is achieved without disassembling the grinding disc. This method greatly simplifies the maintenance process, significantly improves disc repair efficiency and accuracy, avoids the damage risks associated with disassembly, and ensures the long-term stability and grinding performance of the grinding disc.

[0007] (II) Technical Solution

[0008] To address the aforementioned technical problems, embodiments of the present invention provide a diamond grinding device and a method for in-situ dressing.

[0009] According to a first aspect of the present invention, a diamond grinding apparatus with in-situ dressing function is provided, comprising: a grinding table including a rotatable grinding disc for grinding and polishing diamond samples; a slide support fixedly mounted on the table surface of the grinding table; a 3D printing assembly mounted on the slide support, the 3D printing assembly including a 3D printing vertical slide, a 3D printing horizontal slide, and a 3D printing head, the 3D printing vertical slide driving the 3D printing head to move vertically, and the 3D printing horizontal slide driving the 3D printing head to move horizontally; and a turning tool assembly mounted on the slide support, the turning tool assembly including a turning tool vertical slide, a turning tool horizontal slide, and a turning tool, the turning tool vertical slide driving the turning tool to move vertically, and the turning tool horizontal slide driving the turning tool to move horizontally; wherein the 3D printing assembly and the turning tool assembly are arranged side by side in space on the slide support, and the operating range of both can cover the entire surface of the grinding disc, so as to realize additive repair and subtractive finishing of the rotating disc surface sequentially without disassembling the grinding disc.

[0010] In some exemplary embodiments, the grinding table further includes a drive motor and a frequency converter, wherein the drive motor is connected to the grinding disc for driving the grinding disc to rotate; the frequency converter is electrically connected to the drive motor for adjusting and controlling the rotation speed of the grinding disc.

[0011] In some exemplary embodiments, the range of movement of the 3D printing horizontal slide and the cutting tool horizontal slide covers at least the entire radius from the center of the grinding disc to the edge of the grinding disc.

[0012] In some exemplary embodiments, the 3D printing vertical slide, 3D printing horizontal slide, lathe tool vertical slide, and lathe tool horizontal slide are precision CNC slides driven by servo motors and equipped with position encoders to achieve closed-loop precise control of the print head and lathe tool positions.

[0013] In some exemplary embodiments, the 3D printing head is a metal printing head based on a powder-feeding laser cladding process, used to deposit cast iron alloy powder doped with diamond micron powder onto the surface of a grinding disc to form a metal-based composite repair layer.

[0014] In some exemplary embodiments, the cutting tool tip is made of polycrystalline diamond or cubic boron nitride superhard material to adapt to turning repair layers containing diamond micropowder.

[0015] According to a second aspect of the present invention, an in-situ repair method for a diamond grinding disc using the above-described apparatus is provided, comprising: controlling the grinding disc to rotate at a first preset rotation speed, and simultaneously controlling a 3D printing assembly to drive a 3D printing head to deposit a metal repair layer doped with diamond micropowder on the wear area surface of the grinding disc along a preset path; controlling a cutting tool assembly to drive a cutting tool to contact the surface of the metal repair layer at a preset cutting depth, and controlling the grinding disc to rotate at a second preset rotation speed, while simultaneously driving the cutting tool to perform radial feed motion along the surface of the grinding disc to turn the metal repair layer until a disc surface that meets a predetermined flatness requirement is obtained.

[0016] In some exemplary embodiments, a first preset rotational speed is matched with the movement speed of the 3D printing head to ensure uniform deposition and good metallurgical bonding of the metal repair layer.

[0017] In some exemplary embodiments, the second preset rotational speed is matched with the radial feed rate of the cutting tool to control the roughness of the machined surface.

[0018] In some exemplary embodiments, the first preset rotation speed and the second preset rotation speed are independently adjusted by a frequency converter in the range of 5 Hz to 50 Hz according to the process stage; the moving speed of the 3D printing head and the radial feed speed of the cutting tool are independently controlled in the range of 0.1 mm / s to 0.5 mm / s.

[0019] (III) Beneficial Effects

[0020] As can be seen from the above technical solutions, the diamond grinding device and in-situ dressing method with in-situ dressing function provided by the embodiments of the present invention have at least the following beneficial effects:

[0021] (1) This invention revolutionizes the "in-situ" maintenance mode of grinding discs, greatly improving maintenance efficiency. The invention integrates additive manufacturing and subtractive manufacturing functional modules into the grinding equipment body, enabling online repair of the grinding discs without disassembly. This completely eliminates the long cycle of disassembly, transportation, outsourced processing, and recalibration in the traditional method, transforming maintenance from a lengthy "downtime inspection" into a "in-situ process" that the equipment can quickly perform, significantly reducing equipment downtime and improving the overall utilization rate of the equipment.

[0022] (2) By employing an additive-subtractive composite process and functional material design, the repair quality was ensured and the grinding performance was restored. This invention adopts a composite process path of "additive compensation followed by subtractive finishing." First, a metal repair layer doped with diamond micropowder is precisely deposited in the wear area using laser cladding technology, achieving selective material compensation and saving disk base material; then, the ultra-high precision of the disk surface is restored by precision turning with superhard tools. The introduction of functional diamond micropowder in the repair layer ensures the effective restoration and matching of the grinding capability of the repaired area, making the performance of the repaired disk surface as good as before or even better.

[0023] (3) An intelligent, closed-loop controlled repair process has been achieved, ensuring the reliability and consistency of the process. Through the integration of a precision CNC slide table and an online measurement and control system, this invention realizes the programmed and closed-loop control of the repair process. The system can automatically plan and execute operations based on preset or measured data, and ensure repair accuracy in real time through an iterative cycle of "processing-measurement-compensation". This fundamentally overcomes the shortcomings of traditional methods that rely on operator experience and have large quality fluctuations, enabling each repair to achieve a stable and predictable quality standard. Attached Figure Description

[0024] The above-described features, other objects, and advantages of the present invention will become clearer from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0025] Figure 1 The schematic diagram illustrates the structure of a diamond grinding apparatus with in-situ dressing function according to an embodiment of the present invention.

[0026] Figure 2 A flowchart illustrating an in-situ dressing method for a diamond grinding disc according to an embodiment of the present invention is shown.

[0027] Figure label:

[0028] 1: Grinding table; 1-1: Mainly includes grinding disc; 1-2: Table surface; 1-3: Motor; 1-4: Frequency converter; 2: Slide support; 3: 3D printing components; 3-1: 3D printing vertical slide; 3-2: 3D printing horizontal slide; 3-3: 3D printing head; 4: Lathe tool assembly; 4-1: Lathe tool vertical slide; 4-2: Lathe tool horizontal slide; 4-3: Lathe tool. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0030] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0031] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0032] Figure 1 The schematic diagram illustrates the structure of a diamond grinding apparatus with in-situ dressing function according to an embodiment of the present invention.

[0033] like Figure 1 As shown, the diamond grinding device with in-situ dressing function according to an embodiment of the present invention includes: a grinding table 1, a slide support 2, a 3D printing component 3, and a cutting tool component 4.

[0034] The grinding table 1 forms the basic platform of the entire device, including a grinding disc 1-1 for performing grinding and polishing operations, a table surface 1-2 for structural support, a drive motor 1-3 for driving the grinding disc 1-1 to rotate, and a frequency converter 1-4 for adjusting the motor speed. The drive motor 1-3 is connected to the grinding disc 1-1 via a spindle, and the frequency converter 1-4 is electrically connected to the drive motor 1-3, enabling stepless continuous adjustment of the grinding disc 1-1 speed within the range of 0-50 Hz to meet the needs of different process stages.

[0035] The slide support 2 is securely mounted on the table surface 1-2 of the grinding table 1 using bolts or other fasteners, preferably located in the diameter direction of the grinding disc 1-1. Its main body is a rigid frame structure used to support and fix subsequent functional components. This rigid frame structure provides a stable and reliable support and positioning foundation for the 3D printed components and the cutting tool assembly, effectively suppressing vibration and displacement errors during the repair process. This organic combination of the basic platform and the support not only ensures high-precision collaborative execution of additive repair and subtractive finishing processes at the same workstation, but also lays the hardware foundation for achieving fully automated control of the entire process, thereby comprehensively improving the quality and efficiency of the repair process.

[0036] The 3D printing component 3 and the cutting tool component 4 are spatially mounted side-by-side on the slide bracket 2. Details are as follows:

[0037] The 3D printing component 3 includes a 3D printing vertical slide 3-1, a 3D printing horizontal slide 3-2, and a 3D printing head 3-3. The base of the 3D printing vertical slide 3-1 is fixed to the slide bracket 2, and the 3D printing horizontal slide 3-2 is mounted on its sliding component. The 3D printing head 3-3 is mounted on the 3D printing vertical slide 3-1. The 3D printing vertical slide 3-1 drives the printing head to move up and down along the Z-axis (vertical direction) to control the printing distance, while the 3D printing horizontal slide 3-2 drives the printing head to move along the X-axis (horizontal radial direction) to cover the disk surface. Both slides are precision CNC slides equipped with servo motors and grating ruler feedback, and are controlled and linked by a unified CNC system. Optionally, the 3D printing head is a metal printing head based on a powder-feeding laser cladding process, used to deposit cast iron alloy powder doped with diamond micron powder onto the surface of the grinding disk to form a metal-based composite repair layer. The primary purpose of incorporating diamond micron powder into cast iron alloy powder and forming a metal-based composite repair layer via laser cladding is to achieve in-situ restoration of both the function and structure of the grinding disc. Specifically, diamond micron powder, as a high-hardness abrasive, plays a grinding role in the repair layer, ensuring that the repaired disc surface possesses processing efficiency and grinding capabilities comparable to the original disc, avoiding the limitation of merely restoring the geometry while losing functionality. Simultaneously, diamond particles, as a reinforcing phase, significantly improve the wear resistance and service life of the repair layer, making it less prone to wear and degradation during use. Furthermore, the laser cladding process creates a metallurgical bond between the diamond micron powder and the metal matrix, resulting in a high-strength bond between the repair layer and the disc substrate. This avoids the problems of easy detachment and poor heat resistance associated with traditional adhesive repair layers, ensuring the long-term stability of the repair layer. Although the diamond micron powder increases the hardness of the repair layer, its fine and uniform distribution, combined with superhard cutting tools (such as polycrystalline diamond or cubic boron nitride), still allows for precision turning, ensuring the final disc surface flatness and smoothness. In summary, the design incorporating diamond micropowder not only achieves in-situ compensation of the grinding media, but also enables the closed-loop completion of the composite process path of "additive repair + subtractive finishing", thereby efficiently and effectively restoring the comprehensive performance and long-term stability of the grinding disc without disassembling it.

[0038] The cutting tool assembly 4 is structurally similar to and arranged side-by-side with the 3D printing assembly 3, including a vertical cutting tool slide 4-1, a horizontal cutting tool slide 4-2, and a cutting tool 4-3. Its installation and control methods are the same as those of the 3D printing assembly 3. Optionally, the cutting tool tip is made of polycrystalline diamond or cubic boron nitride superhard material to adapt to turning repair layers containing diamond micropowder.

[0039] The turning tool assembly 4 uses superhard materials such as polycrystalline diamond or cubic boron nitride as the cutting head, enabling reliable and efficient precision turning of the diamond micropowder composite repair layer. Because the repair layer contains dispersed high-hardness diamond particles, conventional carbide tools would wear rapidly or even chip due to insufficient hardness, leading to machining failure or surface quality deterioration. Superhard material tools, with their extremely high hardness and wear resistance, can effectively cut these hard phases, ensuring the repair layer material is removed smoothly, thereby accurately restoring the geometric accuracy and surface finish of the grinding disc. This not only ensures the smooth completion of the in-situ composite grinding disc repair process path of "additive manufacturing + subtractive finishing," but also avoids efficiency losses and accuracy deviations caused by frequent tool changes through its excellent cutting stability and long lifespan, ultimately achieving high-quality, high-efficiency disc surface repair.

[0040] In embodiments of the present invention, the effective strokes of both the 3D printing horizontal slide 3-2 and the cutting tool horizontal slide 4-2 are not less than the radius of the grinding disk 1-1, thereby ensuring that the print head and the cutting tool can move from the center of the grinding disk to its outer edge, achieving operation coverage of the entire disk surface area. This design avoids repair blind spots caused by insufficient stroke, allowing the printing and turning paths to continuously traverse the entire disk, helping to ensure uniform repair layer thickness and a smooth turning surface, thereby improving the geometric accuracy and surface quality after repair. Simultaneously, since there is no need to move or reposition the grinding disk during the repair process, the control flow is simplified, significantly enhancing the automation level and operational convenience of the process, providing key hardware support for the efficient collaboration of additive repair and subtractive finishing at the same workstation and in the same coordinate system.

[0041] Figure 2 A flowchart illustrating an in-situ dressing method for a diamond grinding disc according to an embodiment of the present invention is shown.

[0042] like Figure 2 The in-situ dressing method for diamond grinding discs according to an embodiment of the present invention includes steps S1 to S5.

[0043] Step S1: Install the 3D printing head.

[0044] Mount the 3D printing head 3-3 onto the 3D printing vertical slide 3-1, and connect the powder feeding line to the laser path (if laser cladding is used).

[0045] Step S2: Install the cutting tool.

[0046] Install and secure the cutting tool 4-3 onto the tool post of the cutting tool vertical slide 4-1. Drive both components to their respective initial safe positions using the CNC system.

[0047] If the 3D printing head 3-3 and the cutting tool 4-3 have already been installed on the device, steps S1 and S2 can be skipped, and the process can start directly from step S3.

[0048] Step S3: 3D printing the replacement disc. The specific steps are as follows:

[0049] S3.1 Grinding disc rotation: Start the motor 1-3 of grinding disc 1-1, adjust the frequency converter 1-4, and set the rotation frequency of grinding disc 1-1 to 10 Hz.

[0050] S3.2 3D Printing: Control the vertical slide 3-1 of the 3D printing machine to make the 3D printed component 3 lightly touch the surface of the grinding disk 1-1. Then, control the horizontal slide 3-2 of the 3D printing machine to make the 3D print head 3-3 move back and forth at a uniform speed of 0.1-0.5 mm / s. At the same time, the 3D print head 3-3 prints a thin layer of cast iron mixed with diamond powder on the surface of the grinding disk 1-1, so that the thin layer of cast iron mixed with diamond powder completely covers the surface of the grinding disk 1-1. The printing thickness is set between 0.1 mm and 2 mm depending on the degree of damage to the disk surface.

[0051] S3.3 End 3D printing: Adjust the frequency converter to set the rotation frequency of grinding disc 1-1 to 0Hz, and stop the grinding disc from rotating.

[0052] Step S4: Turning and dressing the disc, the specific steps are as follows.

[0053] S4.1 Positioning the cutting tool: Control the vertical slide 4-1 of the cutting tool so that the cutting tool 4-3 lightly touches the surface of the grinding disc 1-1, and record the scale value H1 of the vertical slide 4-1 of the cutting tool (lifting is negative, lowering is positive). Then lift the cutting tool 4-3 to H1-ΔH1 (ΔH1=5.0 mm, to avoid instantaneous damage to the cutting tool and the grinding disc when the grinding disc starts).

[0054] S4.2 Grinding disc rotation: Start the motor 1-3 of grinding disc 1-1, adjust the frequency converter 1-4, and set the grinding disc rotation frequency to 10Hz.

[0055] S4.3 Turning: Determine the turning depth ΔH2 (e.g., ΔH2=0.5mm), control the vertical slide 4-1 of the cutting tool to move down to the turning depth H1+ΔH2, and then control the horizontal slide 4-2 of the cutting tool to make the cutting tool 4-3 move back and forth at a constant speed of 0.1~0.5 mm / s, turning the surface of the grinding disc 1-1 until the surface of the grinding disc is flat.

[0056] S4.4 End turning: Raise the cutting tool 4-3, adjust the frequency converter to set the rotation frequency of the grinding disc 1-1 to 0 Hz, and stop the grinding disc from rotating.

[0057] Step S5: End the repair process.

[0058] Once the grinding disc has been properly dressed, stop its rotation. Control the cutting tool assembly 4 and the 3D printing assembly 3 to raise and move the cutting tool 4-3 and the print head 3-3 to a preset "avoidance" position away from the grinding disc, preventing interference with subsequent normal grinding operations. Clean up any debris and dust generated during the dressing process.

[0059] Those skilled in the art will understand that the features described in the various embodiments of the present invention can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in the present invention. In particular, the features described in the various embodiments of the present invention can be combined and / or combined in various ways without departing from the spirit and teachings of the present invention. All such combinations and / or combinations fall within the scope of the present invention.

Claims

1. A diamond grinding device with in-situ dressing function, characterized in that, include: A grinding table, including a rotating grinding disc, is used for grinding and polishing diamond samples; A slide support is fixedly installed on the surface of the grinding table; A 3D printing component is mounted on the slide bracket. The 3D printing component includes a 3D printing vertical slide, a 3D printing horizontal slide, and a 3D printing head. The 3D printing vertical slide is used to drive the 3D printing head to move in the vertical direction, and the 3D printing horizontal slide is used to drive the 3D printing head to move in the horizontal direction. A cutting tool assembly is mounted on the slide bracket. The cutting tool assembly includes a cutting tool vertical slide, a cutting tool horizontal slide, and a cutting tool. The cutting tool vertical slide is used to drive the cutting tool to move in the vertical direction, and the cutting tool horizontal slide is used to drive the cutting tool to move in the horizontal direction. The 3D printing component and the cutting tool component are arranged side by side in the slide bracket, and the operating range of both can cover the entire surface of the grinding disk, so as to perform additive repair and subtractive finishing on the rotating disk surface in sequence without disassembling the grinding disk.

2. The diamond grinding apparatus according to claim 1, characterized in that, The grinding table also includes a drive motor and a frequency converter. The drive motor is connected to the grinding disc for driving the grinding disc to rotate. The frequency converter is electrically connected to the drive motor for adjusting and controlling the rotation speed of the grinding disc.

3. The diamond grinding apparatus according to claim 1, characterized in that, The range of motion of the 3D printing horizontal slide and the lathe tool horizontal slide covers at least the entire radius from the center of the grinding disc to the edge of the grinding disc.

4. The diamond grinding apparatus according to any one of claims 1 to 3, characterized in that, The 3D printing vertical slide, 3D printing horizontal slide, lathe tool vertical slide, and lathe tool horizontal slide are precision CNC slides driven by servo motors and equipped with position encoders to achieve closed-loop precise control of the print head and lathe tool positions.

5. The diamond grinding apparatus according to claim 1, characterized in that, The 3D printing head is a metal printing head based on a powder-feeding laser cladding process, used to deposit cast iron alloy powder mixed with diamond micron powder onto the surface of the grinding disc to form a metal-based composite repair layer.

6. The diamond grinding apparatus according to claim 1 or 5, characterized in that, The cutting tool is made of polycrystalline diamond or cubic boron nitride superhard material to adapt to turning repair layers containing diamond micropowder.

7. A method for in-situ dressing of a diamond grinding disc using the apparatus described in any one of claims 1 to 6, characterized in that, The method includes: The grinding disc is controlled to rotate at a first preset speed, and the 3D printing component is controlled to drive the 3D printing head to deposit a metal repair layer containing diamond micro powder on the surface of the worn area of ​​the grinding disc according to a preset path. The tool assembly is controlled to drive the tool to contact the surface of the metal repair layer at a preset cutting depth, and the grinding disc is controlled to rotate at a second preset speed. At the same time, the tool is driven to perform radial feed motion along the surface of the grinding disc to turn the metal repair layer until a disc surface that meets the predetermined flatness requirements is obtained.

8. The method according to claim 7, characterized in that, The first preset rotation speed is matched with the moving speed of the 3D printing head to ensure uniform deposition and good metallurgical bonding of the metal repair layer.

9. The method according to claim 7, characterized in that, The second preset rotational speed is matched with the radial feed speed of the cutting tool to control the roughness of the machined surface.

10. The method according to claim 7, characterized in that, The first preset speed and the second preset speed are independently adjusted by the frequency converter within the range of 5 Hz to 50 Hz according to the process stage; The moving speed of the 3D printing head and the radial feed speed of the cutting tool are independently controlled within the range of 0.1 mm / s to 0.5 mm / s.

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