Disclosure of Invention
In order to solve one or more of the technical problems, the application provides a wire laying device for a ring frame composite material part and a working method thereof.
In one aspect, the invention provides a wire laying device for a ring frame composite material part,
the device comprises a fixed frame, a rotary table which is rotatably arranged on the fixed frame, a plurality of ring frame molds which are opposite to the fixed rotary table, a wire laying mechanism which is opposite to the fixed frame, and a local pressure applying mechanism which is opposite to the fixed frame;
the fiber laying mechanism comprises 0-degree fiber laying heads and a plurality of non-0-degree fiber laying heads, wherein the 0-degree fiber laying heads are used for laying the prepreg tapes in the same direction of the fiber distribution direction and the ring frame extension direction, and the non-0-degree fiber laying heads are used for laying the prepreg tapes in different directions of the fiber distribution direction and the ring frame extension direction.
The automatic ring frame composite material forming machine can automatically lay a plurality of ring frame composite material parts at one time, and greatly improves the forming quality and the forming efficiency of the complex structure. In order to simplify the production line structure and reduce the mechanism control difficulty, a basic configuration that the die rotates and reciprocates and the wire laying mechanism is fixed is adopted.
In some embodiments, the non-0 degree fiber placement head comprises a 90 degree fiber placement head having a fiber distribution direction perpendicular to the loop extension direction, a 45 degree fiber placement head having a fiber distribution direction at a 45 degree angle to the loop extension direction, and a-45 degree fiber placement head having a fiber distribution direction at a-45 degree angle to the loop extension direction.
In some embodiments, the ring frame composite material part is a Z-shaped ring frame composite material part, and the 0-degree thread paving heads comprise a vertical surface sub thread paving head for paving a vertical surface 0-degree layer, a horizontal surface sub thread paving head for paving a horizontal surface 0-degree layer, and an R-angle area sub thread paving head for paving an R-angle area 0-degree layer.
In some embodiments, the vertical surface sub-thread laying head comprises a sliding table connected with the fixed frame, two pressure roller connecting frames in sliding fit with the sliding table, an upper vertical surface laying pressure roller fixed on one of the two pressure roller connecting frames, and a lower vertical surface laying pressure roller fixed on the other of the two pressure roller connecting frames, wherein the upper vertical surface laying pressure roller and the lower vertical surface laying pressure roller are matched with two vertical surfaces of the Z-shaped ring frame composite material workpiece in a one-to-one correspondence mode.
In some embodiments, the horizontal sub-fiber laying head comprises a horizontal laying head mounting plate which is matched and connected with the fixed rack, the horizontal laying head mounting plate is provided with a horizontal laying head compression roller connecting frame, and the horizontal laying head compression roller connecting frame is provided with a horizontal laying head compression roller matched with the Z-shaped ring frame composite material workpiece.
In some embodiments, the R-corner sub-filament laying head includes an external corner press roll for external corner surface laying of the R-corner region, an internal corner press roll for internal corner surface laying of the R-corner region, an R-corner laying head mounting plate mounted to the fixed frame, and two R-corner laying head roll connection frames disposed on the R-corner laying head mounting plate and used for mounting the external corner press roll and the internal corner press roll.
In some embodiments, the non-0 degree fiber placement head comprises a fiber placement head mounting plate arranged on the fixed frame, and a fiber placement head rotary connecting frame capable of being mounted on the fiber placement head mounting plate according to different fiber placement angles, wherein the fiber placement head rotary connecting frame is provided with a prepreg tape barrel, a release paper winding shaft for taking back release paper, a clamping mechanism for realizing a function of clamping the prepreg tape, a guide groove for guiding the prepreg tape stripped from the release paper into the clamping mechanism, a prepreg tape cutter arranged between the guide groove and the clamping mechanism, and a compacting mechanism for compacting the prepreg tape on the surface of the ring frame mold.
In some embodiments, the clamping mechanism comprises a guide post, a sliding mounting table slidably mounted on the guide post, and an elastic device providing the sliding mounting table with an upward movement tendency, wherein the sliding mounting table is provided with a clamping auxiliary roller with a rotation shaft position fixed relatively, a clamping auxiliary pressing roller movably arranged with the rotation shaft position, and the sliding mounting table is provided with a guide rail part providing a rotation shaft moving section for clamping the auxiliary pressing roller.
In some embodiments, the compaction mechanism includes a bottom press block for holding down the bottom prepreg tape and a compaction roller for compacting the prepreg tape against the surface of the ring frame mold.
In some embodiments, the non-0 degree fiber placement head further comprises a transverse stretching mechanism, the transverse stretching mechanism comprises a plurality of arc rollers arranged along the movement direction of the prepreg tape and a rotating arc roller driving device for driving each arc roller, each arc roller is an arc pair roller, each arc single roller in the arc pair rollers comprises an inner arc frame and a structure for sleeving an outer flexible roller surface of the inner arc frame, a plurality of bearings are arranged between the inner arc frame and the outer flexible roller surface, and the radian of the plurality of arc rollers is gradually increased in the movement direction of the prepreg tape.
In some embodiments, further comprising a length sensor disposed on the prepreg tape cartridge for measuring the length of the prepreg tape,
the device also comprises a processor which is in signal connection with the length measuring sensor, the driving mechanism of the compacting mechanism, the driving mechanism of the clamping mechanism, the driving mechanism of the rotary table and the control mechanism of the prepreg tape cutter.
On the other hand, the application also provides a working method of the wire laying equipment for the ring frame composite material part,
comprises a 0-degree silk laying procedure, a non-0-degree silk laying procedure and a rotary table position adjusting procedure;
wherein, the non-0 degree fiber-laying process comprises the following steps in sequence:
pre-conveying the prepreg tape; the prepreg tape cylinder, the release paper recovery cylinder and the length counting sensor are matched with a prepreg tape with a preset length,
clamping and cutting the prepreg tape; the bottom pressing block of the compacting mechanism compacts the tail end of the prepreg tape on one side of the surface of the ring frame die, the clamping auxiliary pressing roller is tightly attached to the clamping auxiliary roller to clamp the top end of the prepreg tape, the prepreg tape cutter finishes the cutting of the prepreg tape,
laying and compacting the prepreg tape; the compacting roller compacts the pre-impregnated tape in the outline surface of the ring frame mould in a laying mode, the bottom pressing block leaves the surface of the ring frame mould,
repeating the pre-soaking material belt pre-feeding step;
adjusting the position of the rotary table; the function of circulation operation of the circular frame die in a plurality of stations is provided, and/or the position movement of the circular frame die is provided when the silk paving process is executed.
Detailed Description
As shown in figure 1, the invention provides a wire laying device for a ring frame composite material part, which comprises a fixed rack 7,
A rotary table 1 rotatably mounted on the fixed frame 7,
A plurality of ring frame moulds 21 fixed relatively to the rotary table 1,
Thread laying mechanism relatively fixed on fixed frame 7 and
a local pressure applying mechanism 6 fixed relatively to the fixed frame 7;
the fiber laying mechanism comprises a 0-degree fiber laying head 2 with the fiber distribution direction in the same direction as the extension direction of the ring frame and a plurality of non-0-degree fiber laying heads with the fiber distribution direction different from the extension direction of the ring frame.
The automatic ring frame composite material forming machine can automatically lay a plurality of ring frame composite material parts at one time, and greatly improves the forming quality and the forming efficiency of the complex structure. In order to simplify the production line structure and reduce the mechanism control difficulty, a basic configuration that the die rotates and reciprocates and the wire laying mechanism is fixed is adopted.
The rotary table 1 is rotatably arranged on the fixed frame 7; the circular frame die 21 configured on the rotary table 1 can rotate in a reciprocating manner, and a structural foundation is laid for compact configuration of the wire laying mechanism, monitoring of wire laying quality and continuity of construction operation.
The rotary table 1 is rotatably arranged on the fixed frame 7; specifically, the fixed frame 1 is preferably provided with an arc-shaped guide rail, and the rotary table 1 is arranged in a manner of being matched with the arc-shaped guide rail;
the rotary table 1 is provided with a ring frame mold 21; specifically, the number of the ring frame molds 21 that the turntable 1 is preferably configured with may be selected according to the radian of the ring frame molds 21 and the working environment, and in the embodiment of fig. 1, the turntable 1 is configured with three ring frame molds 21, so that 3 ring frames can be automatically stacked at one time.
The local pressing mechanism 6 is used for interlaminar compaction of the prepreg tape, specifically, the local pressing mechanism 6 comprises a plurality of groups of rubber rollers and a plurality of cylinders for driving the rubber rollers, and the pressing pressure of a single roller is preferably 100-500N.
The distribution directions of a plurality of fibers of the non-0-degree fiber laying heads are different from the extension direction of the ring frame, and the selection of the distribution directions of the fibers is configured according to the structural strength requirement of the ring frame composite material part.
By way of example, in the embodiment shown in FIG. 1, the non-0 degree fiber placement head comprises
A 90-degree filament laying head 3 with the fiber distribution direction vertical to the extension direction of the ring frame,
A 45-degree fiber laying head 4 with the fiber distribution direction and the extension direction of the ring frame forming an included angle of 45 degrees, and
the fiber distribution direction and the extension direction of the ring frame form a-45-degree fiber laying head 5 with an included angle of-45 degrees.
Specifically, for example, in the embodiment of fig. 1, 0-degree filament spreading heads 2, 90-degree filament spreading heads 3, 45-degree filament spreading heads 4, 45-degree filament spreading heads 5 and local pressure applying mechanisms 6 are arranged at 3 stations of the filament spreading equipment for the ring-frame composite material.
Of course, other angles or numbers of non-0 degree filament-laying heads are also within the scope of the present application.
Further, a Z-shaped ring frame composite material product is a typical ring frame composite material product, and its cross-sectional view is shown in fig. 2, which has two vertical planes, a horizontal plane and two R-angle regions (an external angle and an internal angle).
In order to improve the production efficiency of the Z-shaped ring frame composite material part, the following typical wire laying head is designed. And a plurality of groups of the Z-shaped composite material ring frames are uniformly distributed on the whole annular production line, so that a plurality of Z-shaped composite material ring frames can be automatically laid and formed at the same time.
As shown in FIG. 3, the 0-degree thread laying head comprises a vertical surface sub-thread laying head 2-1 for laying and pasting a vertical surface 0-degree layer, a horizontal surface sub-thread laying head 2-2 for laying and pasting a horizontal surface 0-degree layer, and an R-angle area sub-thread laying head 2-3 for laying and pasting a R-angle area 0-degree layer.
For 0 degree ply (ply along the length direction of the ring frame), the compaction of the prepreg tape in the R-angle area cannot be completed by a single compression roller due to the deformation capacity of the compression roller. The 0 degree shop's silk head 2 of this application has contained three sub shop's silk head, and three cooperation work accomplishes the 0 degree shop of Z shape ring frame and stacks.
The R-angle region filament-laying heads 2-3 are preferably formed by laying prepreg tows (such as 6.35mm in width). The 0 degree ply has in-plane bends and R-angle regions. In order to avoid buckling of fibers caused by excessive in-plane bending deformation of the fibers in the prepreg tape, and to ensure compaction of the prepreg tape in the R-angle area and avoid bridging, the angular ply is preferably laid by adopting an automatic filament laying process.
The vertical surface sub-thread laying head 2-1 and the horizontal surface sub-thread laying head 2-2 can be formed by laying threads in a pre-impregnated narrow band (such as the width of 12.7-24.5 mm). The molding efficiency is improved.
The vertical surface laying head 2-1 is preferably of a structure shown in figure 4 and comprises a mounting plate 9 connected with a fixed rack 7, two compression roller connecting frames 10-1 matched with the mounting plate 9, an upper vertical surface laying compression roller 2-1-1 fixed on one of the two compression roller connecting frames 10-1 and a lower vertical surface laying compression roller 2-1-2 fixed on the other one of the two compression roller connecting frames 10-1, wherein the upper vertical surface laying compression roller 2-1-1 and the lower vertical surface laying compression roller 2-1-2 are matched with two vertical surfaces of the Z-shaped ring frame composite material workpiece in a one-to-one correspondence mode.
Further, the mounting plate 7-1 is disposed between the mounting plates 9 connected to the fixed frame 7.
The vertical surface 0-degree fiber laying head compression roller connecting frame can be adjusted in a certain range (moving stroke is 10mm) along the vertical direction, so that the concentration of splicing of adjacent fiber bundles in a 0-degree laying layer in the thickness direction is avoided.
As a further improvement of the adjustment in the up-down direction, the mounting plate 9 can be provided with a plurality of mounting positions with different heights, and the compression roller connecting frame 10-1 is mounted at a certain mounting position according to the process requirement.
As another improvement of the vertical adjustment, one of the mounting plate 9 and the press roll connecting frame 10-1 is provided with at least a slide rail which slides in the vertical direction, one of the mounting plate 9 and the press roll connecting frame 10-1 is provided with a slide groove which is matched with the slide rail, and the mounting plate 9 or the press roll connecting frame 10-1 is provided with a fastening nut which is used for positioning the mounting plate 9 and the press roll connecting frame 10-1 at the position required by the process.
The horizontal surface sub-thread laying head 2-2 is preferably of a structure shown in figure 5 and comprises a horizontal surface laying thread laying head mounting plate 7-2 connected with a fixed rack 7, the horizontal surface laying thread laying head mounting plate 7-2 is provided with a horizontal surface thread laying head press roll connecting frame 10-2, and the horizontal surface laying thread laying head press roll connecting frame 10-2 is provided with a horizontal surface laying head press roll 2-2-1 matched with the horizontal surface of the Z-shaped ring frame composite material part;
similarly, in order to avoid concentration of adjacent strand piece seams in different 0-degree layers on a horizontal plane in the thickness direction, the position of the connecting frame 10-2 can be adjusted within a certain range on the horizontal plane layer laying head mounting plate 7-2 along the diameter direction of the ring frame.
The connecting frame 10-2 is adjusted in a certain range along the diameter direction of the ring frame die on the horizontal plane laying and thread laying head mounting plate 7-2, and a similar implementation mode of matching of multiple mounting positions or sliding grooves of sliding rails between the mounting plate 9 and the compression roller connecting frame 10-1 can be adopted, which is not described in detail.
As shown in fig. 6, the R-corner sub-laying head 2-3 includes an external corner press roll 2-3-1 for external corner surface laying in the R-corner region, an internal corner press roll 2-3-2 for internal corner surface laying in the R-corner region, an R-corner laying head mounting plate 7-3 mounted to the fixing frame 7, and two R-corner laying head roll connecting frames 10-3 disposed on the R-corner laying head mounting plate 7-3 and used to mount the external corner press roll 2-3-1 and the internal corner press roll 2-3-2.
In order to adapt to the wire laying of the ring frames with different R angles, the press rollers used by the wire laying heads in the R angle area are detachably arranged. Furthermore, the external corner press roll 2-3-1, the internal corner press roll 2-3-2 and the R corner area fiber laying head press roll connecting frame 10-3 are detachably arranged.
For the Z-shaped ring frame composite material with the rotation diameter of 2500-3000mm, the 90/45-degree paving is preferably carried out by paving the 90/45-degree paving by using common wide prepreg tapes with the width of 150mm/300mm and the like.
When the annular structure is laid by using the prepreg tape with a certain width from inside to outside, gaps can be formed between two adjacent prepreg tapes along with the increasing of the radius. In order to avoid the gap, the prepreg tape after peeling the backing paper is subjected to deformation roller or gradual widening, and width change caused by radius change is compensated, so that full paving of the paving layer is realized.
Specifically, in the embodiment shown in fig. 7, the non-0 degree spreading head comprises a spreading head mounting plate 7-4 arranged on the fixed frame 7, and a spreading head rotary connecting frame 10-4 which can be arranged on the spreading head mounting plate 7-4 according to different spreading angles,
the silk spreading head rotary connecting frame 10-4 is provided with a prepreg tape cylinder 11, a release paper winding shaft 13 for taking back release paper, a clamping mechanism for clamping the prepreg tape, a guide groove 16 for guiding the prepreg tape stripped from the release paper into the clamping mechanism, a prepreg tape cutter 17 arranged between the guide groove 16 and the clamping mechanism, and a compacting mechanism for compacting the prepreg tape on the surface of the ring frame mold 21.
Different wire laying angles can be achieved only by rotating the wire laying head rotating connecting frame 10-4 to a target angle.
The clamping mechanism comprises a guide post, a sliding mounting table 18-3 which is slidably mounted on the guide post and an elastic device for providing the sliding mounting table 18-3 with upward movement tendency,
the sliding installation table 18-3 is provided with a clamping auxiliary roller 18-1 with a relatively fixed rotating shaft position and a clamping auxiliary press roller 18-2 movably arranged with the rotating shaft position,
the slide mount 18-3 is provided with a guide rail portion for providing a movable section of the rotation shaft for holding the auxiliary press roller 18-2.
The clamping auxiliary press roller 18-2 is preferably driven by an air cylinder, and the clamping auxiliary press roller 18-1 is tightly attached to the clamping auxiliary press roller 18-2 in the air-supply state of the air cylinder, so that the cut prepreg tape is clamped, and the clamping of the prepreg tape is realized.
In order to ensure that the prepreg tape of the clamping section has tension all the time during laying, the sliding installation table 18-3 installed on the auxiliary clamping roller 18-1 and the auxiliary clamping roller 18-2 has a tendency of moving upwards under the action of an elastic device (for example, a scheme that a guide pillar is sleeved with a pre-compression spring is adopted), so that a certain tension can be applied to the prepreg tape of the clamping section, and meanwhile, the length of the clamping section of the prepreg tape can be automatically adjusted along with continuous laying of wires.
The compacting mechanism includes a bottom press block 20-1 for compressing and fixing the bottom prepreg tape
And a compaction roller 20-2 for compacting the prepreg tape in the ring frame mold 21.
The compaction roller 20-2 is movable along the contour of the ring frame mould to compact the prepreg tape against the mould surface.
Furthermore, the bottom pressing block 20-1 and the compacting roller 20-2 are preferably both flexible rubber rollers,
further, the compacting mechanism preferably further comprises a bottom compact driving cylinder for driving the bottom compact 20-1, and a compacting roller driving cylinder for driving the compacting roller 20-2.
As shown in fig. 8, in the fiber spreading equipment for the ring frame composite material part provided by the present invention, the non-0 degree fiber spreading head further includes a transverse stretching mechanism, and the transverse stretching mechanism is located between the holding mechanism and the compacting mechanism along the movement direction of the prepreg tape.
The method is used for transversely widening the cut backing-free prepreg tape step by step, and widening the prepreg tape in advance according to the actual filament laying position during filament laying so as to compensate for the gap increasing along with the radius. (the preferred case of 90/+ -45 degree plies are laid down diametrically from the inside to the outside of the Z-shaped ring frame).
Furthermore, the transverse widening mechanism comprises a plurality of arc-shaped rollers 19-1 arranged along the moving direction of the prepreg tape and an arc-shaped roller driving device 19-2 for driving the arc-shaped rollers 19-1 to rotate.
Under the action of tension, the unidirectional prepreg tape generates certain transverse deformation after deformation, and transverse widening of the prepreg tape is realized. The transverse widening mechanism can adjust the width of the prepreg tape on line, the required change of the prepreg tape width along with the increase of the radius is compensated in 90/+/-45-degree paving, and the forming quality and the forming efficiency of the complex structure are improved to a great extent.
Each arc-shaped roller 19-1 is preferably in an arc-shaped double-roller structure form and has a good shaping effect.
Each arc single roller of the two arc pair rollers is suitable to adopt a structure that an inner arc frame is sleeved with an outer flexible roller surface, and a plurality of bearings are arranged between the inner arc frame and the outer flexible roller surface.
The plurality of arc-shaped rollers 19-1 have gradually increased radian in the moving direction of the prepreg tape.
The prepreg tape is gradually widened by the multistage arc-shaped rollers 19-1 under the action of certain tension so as to realize compensation of the gap increasing along with the radius.
The wire laying equipment for the ring frame composite material part also comprises
A length measuring sensor 15 for measuring the length of the prepreg tape. A length measuring sensor 15 is disposed on the prepreg tape drum 11;
the wire laying equipment for the ring frame composite material part further comprises a processor 8 which is in signal connection with the length measuring sensor 15, the driving mechanism of the compacting mechanism, the driving mechanism of the clamping mechanism, the driving mechanism of the rotary table 1 and the control mechanism of the prepreg tape cutter 17.
The processor is suitable for various UMAC controllers, and the upper computer realizes data storage, motion planning and the like.
In the actual working process, according to the laying design requirement, designing a corresponding thread laying program, and selecting a working thread laying head to finish the manufacture of the ring frame composite material part.
Further, the wire laying equipment for the ring frame composite material part further comprises a wire laying quality detection mechanism in signal connection with the processor 8.
On the other hand, the invention also provides a working method of the wire laying equipment for the ring frame composite material part, which comprises a 0-degree wire laying process, a non-0-degree wire laying process and a rotary table position adjusting step;
wherein, the non-0 degree fiber-laying process comprises the following steps in sequence:
pre-conveying the prepreg tape; the prepreg tape cylinder 11, the release paper recovery cylinder 13 and the length measuring sensor 15 are matched with a prepreg tape with a preset length,
clamping and cutting the prepreg tape; the bottom pressing block 20-1 of the compacting mechanism compacts the tail end of the prepreg tape on one side of the surface of the ring frame mould 21, the clamping auxiliary pressing roller 18-2 is tightly attached to the clamping auxiliary roller 18-1 to clamp the top end of the prepreg tape, the prepreg tape cutter 17 finishes the cutting of the prepreg tape,
laying and compacting the prepreg tape; the compacting roller 20-2 is used for laying and compacting the prepreg tape on the contour surface of the ring frame mold 21, the bottom pressing block 20-1 is separated from the surface of the ring frame mold 21,
repeating the pre-soaking material belt pre-feeding step;
adjusting the position of the rotary table; the function of providing the circular frame die 21 to circulate in a plurality of stations and/or the position movement of the circular frame die 21 when the wire laying process is executed is provided.
In the step of laying and compacting the prepreg tapes, the compacting roller 20-2 compacts the prepreg tape laying yarns on the contour surface of the ring frame mold 21, and the method comprises the steps that the compacting roller 20-2 lays the prepreg tapes on the contour surface of the ring frame mold 21, the clamping mechanism continuously moves downwards along with the laying yarns, when the prepreg tape clamping mechanism reaches a lower limit position, the clamping mechanism gives up clamping and resets, and the prepreg tapes of the residual free sections are continuously compacted on the contour surface of the ring frame mold 21 under the action of the compacting roller 20-2.
The clamping mechanism abandons clamping, and in the case of adopting a pneumatic mechanism for the clamping auxiliary pressing roller 18-2, the air cylinder can be selected to exhaust air to realize abandoning clamping.
In an embodiment with a widening means, the laying process further comprises a transverse widening step before the prepreg tape laying compaction step;
selecting the working time of a prepreg tape transverse widening mechanism according to the prepreg tape widths required by different positions to transversely widen the prepreg tape;
according to the silk spreading method provided by the invention, 90-degree and +/-45-degree layers are automatically spread by adopting a tape spreading mode, and the wide prepreg tape (such as 150mm) is spread and pasted by the processes of precutting, transverse deformation and hot-pressing silk spreading.
When the device works, the rotary table 1 does circular motion, and the sub-fiber laying heads of the 0-degree laying layer work cooperatively to complete the 0-degree laying layer laying of the Z-shaped ring frame. The ply lay-up flow of the non-0 degree laying head is shown in figure 9.
In the thermal diaphragm forming process, when the existing flat plate lamination deforms in a curvature change mode, slippage deformation among prepreg tape layers and fiber wrinkles can occur. The molding process is also not ideal for forming the female corner of a Z-shaped ring frame member, for example. In addition, the forming process is not suitable for a thick-layer plate, and the die pressing deformation forming process developed on the basis of the thermal diaphragm converts vacuum negative pressure of the thermal diaphragm into mechanical pressure and is suitable for deformation of the thick-layer plate. However, the cross-sectional dimension of the component with double-curved features, such as the Z-shaped ring frame, is changed, and when the flat-deformation-profiling process is adopted, the accumulation of redundant materials and the corrugation of fibers are necessarily caused. The automatic forming equipment of the frame-shaped structure provided by the application provides independent thread laying heads for each forming working section, and combines an integral operation process, so that the technical problem is well solved.
Up to this point, the present embodiment has been described in detail with reference to the accompanying drawings. From the above description, one skilled in the art should clearly recognize the present application.
It is to be noted that, in the attached drawings or in the description, the implementation modes not shown or described are all the modes known by the ordinary skilled person in the field of technology, and are not described in detail. Furthermore, the above definitions of the various elements and methods are not limited to the specific structures, shapes, or configurations shown in the examples.
It is also noted that the illustrations herein may provide examples of parameters that include particular values, but that these parameters need not be exactly equal to the corresponding values, but may be approximated to the corresponding values within acceptable error tolerances or design constraints. Directional phrases used in the embodiments, such as "upper", "lower", "front", "rear", "left", "right", etc., refer only to the orientation of the drawings and are not intended to limit the scope of the present application. In addition, unless steps are specifically described or must occur in sequence, the order of the steps is not limited to that listed above and may be changed or rearranged as desired by the desired design. The embodiments described above may be mixed and matched with each other or with other embodiments based on design and reliability considerations, i.e., technical features in different embodiments may be freely combined to form further embodiments.
The above-mentioned embodiments are further described in detail for the purpose of illustrating the invention, and it should be understood that the above-mentioned embodiments are only illustrative of the present invention and are not to be construed as limiting the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.