阅读说明：本技术 一种合成纸分切用固定装置 (Synthetic paper cuts uses fixing device ) 是由 唐超玉 王彬 于 2021-06-30 设计创作，主要内容包括：本发明公开了一种合成纸分切用固定装置,涉及合成纸加工设备技术领域,包括合成纸卷料、支撑底座,还包括固定组件以及转动组件,所述固定组件包括第一支轴以及第二支轴,所述第一支轴一端与第二支轴可伸缩式固定连接,另一端与合成纸卷料中心孔内筒通过插接的方式连接,将两侧第一支轴分别插接在合成纸卷料的中心孔内筒内,通过第一支轴与筒内壁间的摩擦力对其进行初步固定,其次将第二支轴远离第一支轴的一端置于支撑圆筒内,通过设置在支撑圆筒间的多组夹持部件对第二支轴进行夹持固定,转动组件通过带动支撑圆筒转动从而带动固定后的合成纸卷料进行转动,固定更加稳固,在对其进行切割时不会左右晃动。(The invention discloses a fixing device for slitting synthetic paper, which relates to the technical field of synthetic paper processing equipment and comprises a synthetic paper roll material, a supporting base, a fixing component and a rotating component, wherein the fixing component comprises a first fulcrum and a second fulcrum, one end of the first fulcrum is telescopically and fixedly connected with the second fulcrum, the other end of the first fulcrum is connected with a central hole of an inner cylinder of the synthetic paper roll material in an inserting mode, the first fulcrums at two sides are respectively inserted into the inner cylinder of the central hole of the synthetic paper roll material and are primarily fixed through the friction force between the first fulcrum and the inner wall of the cylinder, one end of the second fulcrum far away from the first fulcrum is arranged in the supporting cylinder, the second fulcrum is clamped and fixed through a plurality of groups of clamping components arranged between the supporting cylinders, and the rotating component drives the supporting cylinders to rotate so as to drive the fixed synthetic paper roll material to rotate, the fixing is more stable, and the cutting machine cannot shake left and right when being cut.)

1. The utility model provides a synthetic paper cuts uses fixing device, includes synthetic paper coil stock (1), supports base (12), its characterized in that still includes fixed subassembly and runner assembly, fixed subassembly includes first counter roll (2) and second counter roll (3), first counter roll (2) one end and second counter roll (3) retractable fixed connection, the other end is connected through the mode of pegging graft with synthetic paper coil stock (1) centre bore inner tube, fixed subassembly still includes two sets of relative support drum (21) that set up, set up multiunit clamping component between support drum (21), the clamping component is used for carrying out the centre gripping to the one end that first counter roll (2) was kept away from to second counter roll (3) and fixes, the runner assembly is used for driving synthetic paper coil stock (1) after fixed subassembly and the centre gripping to rotate so that cut.

2. The fixing device for slitting synthetic paper according to claim 1, wherein the clamping members comprise positioning rods (23) and arc-shaped clamping plates (26), the positioning rods (23) are circumferentially arranged between the supporting cylinders (21), the positioning rods (23) are slidably connected with the side walls of the supporting cylinders (21), a plurality of groups of positioning rods (23) are fixedly connected with the arc-shaped clamping plates (26) towards one side of the circle center of the supporting cylinders (21), one ends of the positioning rods (23) far away from the arc-shaped clamping plates (26) are fixedly connected with the handle (22), the outer sides of the positioning rods (23) are provided with the extension springs (24), one ends of the extension springs (24) are fixedly connected with the inner side walls of the supporting cylinders (21), and the other ends of the extension springs are fixedly connected with the arc-shaped clamping plates (26).

3. The synthetic paper slitting fixing device according to claim 1 or 2, wherein the two sides of the arc-shaped clamping plate (26) are oppositely provided with positioning bolts (25), the surface of the second fulcrum shaft (3) is oppositely provided with positioning holes matched with the positioning bolts (25), and the clamping plate (26) is fixedly connected with the second fulcrum shaft (3) through the positioning bolts (25) and the positioning holes; specifically, after the arc-shaped clamping plate (26) is used for primarily fixing the second fulcrum shaft (3), the positioning bolt (25) is inserted into the positioning hole to fix the second fulcrum shaft again.

4. The fixing device for cutting synthetic paper according to claim 3, wherein a hydraulic telescopic rod (13) is arranged between the first support shafts (2), the hydraulic telescopic rod (13) is fixedly connected with the inner wall of the first support shafts (2), clamping parts (16) are symmetrically arranged on the upper side and the lower side of the end, close to each other, of the first support shafts (2), the clamping parts (16) are movably connected with the first support shafts (2), the tail ends of output rods of the hydraulic telescopic rods (13) are symmetrically and movably connected with push rods (15), and one ends, far away from the hydraulic telescopic rods (13), of the push rods (15) are respectively and movably connected with the clamping parts (16).

5. A synthetic paper cutting fixing device according to claim 4, characterized in that the first fulcrum (2) and the second fulcrum (3) are telescopically connected through screw threads, and when the extension length of the first fulcrum (2) needs to be adjusted, the first fulcrum (2) can be telescopically arranged in the second fulcrum (3) through rotating the first fulcrum (2).

6. The fixing device for cutting synthetic paper according to claim 5, wherein the rotating assembly comprises a driving motor (18), a rotating roller (19) is fixedly installed on the side wall of the supporting cylinder (21) on one side, an annular rack (20) is installed on the outer side wall of the rotating roller (19), the annular rack (20) is meshed with a bottom end worm (27), the worm (27) is fixedly connected with the output end of the driving motor (18), supporting rods (17) are symmetrically arranged at two ends of the surface of the supporting base (12), the supporting rods (17) are rotatably connected with the supporting cylinder (21) through bearings (4), a sleeve (10) and a guide rod (9) are installed at one end of the supporting cylinder (21) on two sides close to each other, one end of the sleeve (10) and the guide rod (9) far away from each other is fixedly connected with the supporting cylinder (21) respectively, and a plurality of groups of through holes are formed in the surfaces of the sleeve (10) and the guide rod (9), the through hole is matched with the inserted rod, and the guide rod (9) and the sleeve (10) are detachably and fixedly connected.

7. The fixing device for synthetic paper slitting according to claim 6, wherein a dust collection assembly is further arranged on the surface of the supporting base (12) and used for adsorbing paper scraps generated during slitting, the dust collection assembly comprises a dust collection box (11), the dust collection box (11) is installed under a synthetic paper roll (1), a dust collection opening (28) is formed in one side, facing the synthetic paper roll (1), of the dust collection box (11), a plurality of groups of adsorption nets (29) are arranged in the dust collection box (11), a piston box (5) is arranged at one end of the supporting base (12), the piston box (5) is communicated with the dust collection box (11) through an air suction pipe (8), an exhaust pipe (7) is arranged on one side, opposite to the air suction pipe (8), of the piston box (5), a piston (6) is arranged in the piston box (5), a convex column (30) is arranged on one side of the edge of the end surface of the supporting cylinder (21), the exhaust gas purification device is characterized in that a push plate (4) which is movably connected with the convex column in a matched mode is installed on the outer side of the convex column (30), a through groove matched with the convex column (30) is formed in the push plate (4), the push plate (4) is fixedly connected with a piston (6) through a movable push rod towards one side of the piston box (5), a check valve only limited to gas inlet is arranged between a gas suction pipe (8) and the piston box (5), and a check valve only limited to exhaust is arranged between a gas exhaust pipe (7) and the piston box (5).

8. A synthetic paper cutting fixing device according to claim 7, characterized in that the support legs (14) are symmetrically arranged on both sides of the lower surface of the support base (12), and the support legs (14) are used for supporting the device.

Technical Field

The invention relates to the technical field of synthetic paper processing equipment, in particular to a fixing device for slitting synthetic paper.

Background

Synthetic paper is made by drawing synthetic polymer material (such as polyethylene, polypropylene, etc.) into sheet semi-finished product by film pressing or film blowing, and then using chemical or physical method to make it into paper, such as sand-coating can increase opacity, and using chemical to treat surface to obtain lyophobic property, etc.. Another type of synthetic paper product can be made using synthetic pulp after a pulping process.

Synthetic paper is in the production and processing process, will cut the scroll according to the in service behavior, and the installation of current equipment of cutting to synthetic scroll is put on the shelf comparatively troublesome, and is fixed insecure moreover, produces easily and rocks to influence the quality after the scroll is cut.

Disclosure of Invention

The invention aims to provide a fixing device for slitting synthetic paper, which is used for solving the problems in the background technology.

In order to achieve the purpose, the invention provides the following technical scheme:

the utility model provides a synthetic paper is cut and is used fixing device, includes synthetic paper coil stock, support base, still includes fixed subassembly and runner assembly, fixed subassembly includes first fulcrum and second fulcrum, first fulcrum one end and second fulcrum retractable fixed connection, the other end is connected through the mode of pegging graft with synthetic paper coil stock centre bore inner tube, fixed subassembly still includes the support drum of two sets of relative settings, set up multiunit clamping component between the support drum, clamping component is used for keeping away from the one end of first fulcrum to the second fulcrum and carries out the centre gripping fixed, the runner assembly is used for driving synthetic paper coil stock behind fixed subassembly and the centre gripping and rotates so that cut.

Preferably, the clamping part includes locating lever and arc splint, locating lever circumference is arranged between supporting the drum, locating lever and supporting drum lateral wall sliding connection, and one side fixed connection arc splint of the multiunit locating lever towards supporting the drum centre of a circle simultaneously, the one end fixed connection handle of arc splint is kept away from to the locating lever, the locating lever outside sets up expanding spring, expanding spring one end and supporting drum inside wall fixed connection, the other end and arc splint fixed connection.

Preferably, positioning bolts are oppositely arranged on two sides of the arc-shaped clamping plate, positioning holes matched with the positioning bolts are oppositely arranged on the surface of the second fulcrum shaft, and the clamping plate is fixedly connected with the second fulcrum shaft through the positioning bolts and the positioning holes; specifically, after the arc-shaped clamping plate is used for preliminarily fixing the second fulcrum shaft, the positioning bolt is inserted into the positioning hole to fix the second fulcrum shaft again.

Preferably, set up hydraulic telescoping rod between the first fulcrum, hydraulic telescoping rod and first fulcrum inner wall fixed connection, both sides bilateral symmetry set up the chucking part about the one end that first fulcrum is close to each other, chucking part and first fulcrum swing joint, the terminal symmetry swing joint push rod of hydraulic telescoping rod output lever, the one end that hydraulic telescoping rod was kept away from to the push rod respectively with chucking part swing joint.

Preferably, the first fulcrum shaft and the second fulcrum shaft are telescopically connected through threads, and when the extending length of the first fulcrum shaft needs to be adjusted, the first fulcrum shaft can be telescopically arranged in the second fulcrum shaft through rotating the first fulcrum shaft.

Preferably, the runner assembly includes driving motor, one side it changes the roller to support drum lateral wall fixed mounting, change roller lateral wall installation annular rack, annular rack and bottom worm meshing, driving motor output fixed connection worm, support base surface both ends symmetry and set up branch, branch passes through the bearing and supports the drum rotation and be connected, both sides it installs sleeve and guide arm to support the one end that the drum is close to each other, the sleeve with the guide arm one end of keeping away from each other respectively with support drum fixed connection, the sleeve sets up the multiunit through-hole with the guide arm surface, through-hole and inserted bar cooperation installation can dismantle fixed connection to guide arm and sleeve.

Preferably, the surface of the supporting base is further provided with a dust collection assembly, the dust collection assembly is used for adsorbing paper scraps generated during slitting, the dust collection assembly comprises a dust collection box, the dust collection box is installed under a synthetic paper roll material, one side of the dust collection box, facing the synthetic paper roll material, is provided with a dust collection port, a plurality of groups of adsorption nets are arranged in the dust collection box, one end of the supporting base is provided with a piston box, the piston box is communicated with the dust collection box through an air suction pipe, one side of the piston box, facing the air suction pipe, is provided with an exhaust pipe, a piston is arranged in the piston box, one side of the edge of the end part of the supporting cylinder is provided with a convex column, the outer side of the convex column is provided with a push plate which is movably connected with the convex column in a matching manner, a through groove which is matched with the convex column is arranged in the push plate, one side of the push plate, facing the piston box, is fixedly connected with the piston through a movable push rod, and a one-way valve which only allows air to enter is arranged between the air suction pipe and the piston box, and a one-way valve which is only used for exhausting is arranged between the exhaust pipe and the piston box.

Preferably, the support base lower surface bilateral symmetry sets up the supporting leg, the supporting leg is used for supporting the device.

Compared with the prior art, the invention has the beneficial effects that: firstly, peg graft the first pivot in the centre bore inner tube of synthetic paper coil stock respectively with both sides, fix it tentatively through the frictional force between first pivot and section of thick bamboo inner wall, secondly place the one end that the first pivot was kept away from to the second pivot in the support drum, carry out the centre gripping through the multiunit clamping component who sets up between the support drum to the second pivot and fix, start the runner assembly, thereby the runner assembly supports the drum through driving and rotates and drive the synthetic paper coil stock after fixing and rotate, and is fixed more firm, can not rock about cutting it.

Drawings

Fig. 1 is a schematic structural view of a fixing device for slitting synthetic paper.

Fig. 2 is a schematic structural diagram of a supporting cylinder in a fixing device for cutting synthetic paper.

FIG. 3 is a schematic view of a first support shaft of a fixing device for slitting synthetic paper.

Fig. 4 is a schematic structural diagram of a support cylinder in a fixing device for cutting synthetic paper.

Fig. 5 is a schematic structural diagram of a push plate in a fixing device for slitting synthetic paper.

Fig. 6 is a schematic structural view of a dust suction box in a fixing device for slitting synthetic paper.

In the figure, 1-synthetic paper roll stock; 2-a first fulcrum; 3-a second fulcrum; 4-pushing the plate; 5-a piston box; 6-a piston; 7-an exhaust pipe; 8-suction pipe; 9-a guide rod; 10-a sleeve; 11-a dust collection box; 12-a support base; 13-hydraulic telescopic rod; 14-support legs; 15-a push rod; 16-a clamping member; 17-a strut; 18-a drive motor; 19-rotating the roller; 20-a ring-shaped rack; 21-a support cylinder; 22-a handle; 23-positioning rods; 24-a telescoping spring; 25-positioning a bolt; 26-arc splint; 27-a screw; 28-dust suction port; 29-an adsorption net; 30-convex column.

Detailed Description

The technical solution of the present invention will be described in further detail with reference to specific embodiments.

Referring to fig. 1-5, a fixing device for slitting synthetic paper comprises a synthetic paper roll 1, a supporting base 12, a fixing component and a rotating component, wherein the fixing component comprises a first fulcrum shaft 2 and a second fulcrum shaft 3, one end of the first fulcrum shaft 2 is fixedly connected with the second fulcrum shaft 3 in a telescopic manner, the other end of the first fulcrum shaft is connected with an inner cylinder of the synthetic paper roll 1 in an inserting manner, the fixing component further comprises two groups of supporting cylinders 21 which are oppositely arranged, a plurality of groups of clamping components are arranged between the supporting cylinders 21, the clamping components are used for clamping and fixing one end of the second fulcrum shaft 3, which is far away from the first fulcrum shaft 2, and the rotating component is used for driving the fixing component and the clamped synthetic paper roll 1 to rotate so as to facilitate slitting;

specifically, in this embodiment, at first, peg graft respectively in synthetic paper coil stock's 1 centre bore inner tube with the first counter roll 2 in both sides, fix it through the frictional force between first counter roll 2 and section of thick bamboo inner wall tentatively, secondly place second counter roll 3 in the support drum 21 is kept away from the one end of first counter roll 2, carry out the centre gripping through the multiunit clamping component who sets up between support drum 21 to second counter roll 3 and fix, start rotating assembly, thereby rotating assembly supports drum 21 through the drive and rotates synthetic paper coil stock 1 after driving the fixing and rotate, and is fixed more firm, can not rock about when cutting it.

As a further scheme of the embodiment of the invention, the clamping component comprises positioning rods 23 and arc-shaped clamping plates 26, the positioning rods 23 are circumferentially arranged between the supporting cylinders 21, the positioning rods 23 are slidably connected with the side walls of the supporting cylinders 21, a plurality of groups of positioning rods 23 are fixedly connected with the arc-shaped clamping plates 26 towards one side of the circle center of the supporting cylinder 21, one ends of the positioning rods 23 far away from the arc-shaped clamping plates 26 are fixedly connected with the handle 22, the outer sides of the positioning rods 23 are provided with telescopic springs 24, one ends of the telescopic springs 24 are fixedly connected with the inner side walls of the supporting cylinders 21, and the other ends of the telescopic springs 24 are fixedly connected with the arc-shaped clamping plates 26;

specifically, in this embodiment, the handle 22 is held, and the handle 22 is pulled outward at the same time, the handle 22 drives the positioning rod 23 to move outward, the arc-shaped clamping plates 26 squeeze the extension springs 24 to generate elastic force, the end portion of the second support shaft 3 to be clamped and fixed is placed at the center of the supporting cylinder 21, the handle 22 is loosened, and the extension springs 24 push the plurality of arc-shaped clamping plates 26 on the periphery to move toward the second support shaft 3 at the same time through the elastic force, so as to clamp and fix the second support shaft 3.

As a further scheme of the embodiment of the invention, two sides of the arc-shaped clamping plate 26 are oppositely provided with positioning bolts 25, the surface of the second fulcrum shaft 3 is oppositely provided with positioning holes matched with the positioning bolts 25, and the clamping plate 26 is fixedly connected with the second fulcrum shaft 3 through the positioning bolts 25 and the positioning holes; specifically, after the second support shaft 3 is preliminarily fixed by the arc-shaped clamp plate 26, the positioning pin 25 is inserted into the positioning hole to fix the second support shaft again.

As a further scheme of the embodiment of the invention, a hydraulic telescopic rod 13 is arranged between the first supporting shafts 2, the hydraulic telescopic rod 13 is fixedly connected with the inner wall of the first supporting shaft 2, clamping parts 16 are symmetrically arranged at the upper side and the lower side of the end, close to each other, of the first supporting shafts 2 at the two sides, the clamping parts 16 are movably connected with the first supporting shafts 2, the tail ends of output rods of the hydraulic telescopic rods 13 are symmetrically and movably connected with push rods 15, and one ends, far away from the hydraulic telescopic rods 13, of the push rods 15 are respectively and movably connected with the clamping parts 16;

specifically, in this embodiment, after the first support shaft 2 is inserted into the inner cylinder of the central hole of the synthetic paper roll 1, the output rods of the hydraulic telescopic rods 13 on both sides move inward at the same time, and the push rods 15 push the clamping members 16 on both sides to extend outward, so that the arc-shaped portion on the top of the clamping member 16 is in full contact with the inner wall of the inner cylinder of the central hole of the synthetic paper roll 1, thereby further improving the friction between the synthetic paper roll 1 and avoiding the occurrence of shaking when the synthetic paper roll 1 is driven to rotate or cut.

As a further solution of the embodiment of the present invention, the first support shaft 2 and the second support shaft 3 are telescopically connected by a screw, when the extending length of the first support shaft 2 needs to be adjusted, the first support shaft 2 can be telescopically extended in the second support shaft 3 by rotating the first support shaft 2, which not only facilitates the assembly and disassembly of the synthetic paper roll 1, but also can fix the synthetic paper rolls 1 with different widths for slitting.

As a further scheme of the embodiment of the invention, the rotating assembly comprises a driving motor 18, a rotating roller 19 is fixedly installed on the side wall of the supporting cylinder 21 on one side, an annular rack 20 is installed on the outer side wall of the rotating roller 19, the annular rack 20 is meshed with a bottom end worm 27, the output end of the driving motor 18 is fixedly connected with the worm 27, supporting rods 17 are symmetrically arranged at two ends of the surface of the supporting base 12, the supporting rods 17 are rotatably connected with the supporting cylinder 21 through bearings 4, a sleeve 10 and a guide rod 9 are installed at one end of the supporting cylinder 21 on two sides close to each other, one ends of the sleeve 10 and the guide rod 9 far away from each other are respectively fixedly connected with the supporting cylinder 21, a plurality of groups of through holes are arranged on the surfaces of the sleeve 10 and the guide rod 9, and the through holes are matched with the inserted rods to detachably and fixedly connect the guide rod 9 and the sleeve 10;

specifically, in this embodiment, the driving motor 18 rotates, the driving motor 18 drives the worm 27 to rotate, the worm 27 drives the rotating roller 19 and the supporting cylinders 21 to rotate by meshing with the annular rack 20, and since the supporting cylinders 21 on both sides are connected through the sleeve 10 and the guide rod 9, the supporting cylinders 21 on both sides can rotate simultaneously to drive the synthetic paper roll 1 to rotate.

As a further solution of the embodiment of the present invention, referring to fig. 1-6, a dust collection assembly is further disposed on the surface of the supporting base 12, the dust collection assembly is used for adsorbing paper scraps generated during slitting, the dust collection assembly includes a dust collection box 11, the dust collection box 11 is installed under the synthetic paper roll 1, a dust collection port 28 is disposed on one side of the dust collection box 11 facing the synthetic paper roll 1, a plurality of sets of adsorption nets 29 are disposed in the dust collection box 11, a piston box 5 is disposed at one end of the supporting base 12, the piston box 5 is communicated with the dust collection box 11 through an air suction pipe 8, an exhaust pipe 7 is disposed on one side of the piston box 5 opposite to the air suction pipe 8, a piston 6 is disposed in the piston box 5, a convex pillar 30 is disposed on one side of an edge of an end surface of the supporting cylinder 21, a push plate 4 movably connected to the convex pillar 30 is mounted on an outer side of the convex pillar 30, a through groove matched with the convex pillar 30 is disposed in the push plate 4, one side of the push plate 4 facing the piston box 5 is fixedly connected with a piston 6 through a movable push rod, a one-way valve limited to air inlet is arranged between the air suction pipe 8 and the piston box 5, and a one-way valve limited to air exhaust is arranged between the exhaust pipe 7 and the piston box 5;

specifically, in this embodiment, the supporting cylinder 21 pushes the piston 6 to reciprocate in the piston box 5 through the cooperation of the pushing plate 4, the through groove and the protruding column 30 in the rotating process, external air is sucked into the piston box 5 through the dust suction port 28, the dust suction box 11 and the air suction pipe 8 and is discharged through the air discharge pipe 7, and the suction net 29 adsorbs and filters dust and paper dust in the air sucked into the dust suction box 11, so as to prevent the paper dust from scattering in the air.

As a further scheme of the embodiment of the invention, support legs 14 are symmetrically arranged on two sides of the lower surface of the support base 12, and the support legs 14 are used for supporting the device.

The working principle of the invention is as follows: firstly, the first fulcrum shafts 2 at two sides are respectively inserted into the inner cylinder of the central hole of the synthetic paper roll 1 and are primarily fixed through the friction force between the first fulcrum shafts 2 and the inner wall of the cylinder, secondly, one end of the second fulcrum shaft 3 far away from the first fulcrum shafts 2 is arranged in the supporting cylinder 21, the output rods of the hydraulic telescopic rods 13 at two sides simultaneously move inwards, the clamping components 16 at two sides are pushed by the push rod 15 to extend outwards, so that the arc-shaped part at the top end of the clamping component 16 is fully contacted with the inner wall of the inner cylinder of the central hole of the synthetic paper roll 1, the friction force between the output rods and the synthetic paper roll 1 is further improved, the phenomenon that the synthetic paper roll 1 is shaken when being driven to rotate or cut is avoided, the handle 22 is held, the handle 22 is pulled outwards at the same time, the handle 22 drives the positioning rod 23 to move outwards, the arc-shaped clamping plates 26 extrude the telescopic springs 24 to generate elastic force, and the end part of the second fulcrum shaft 3 to be clamped and fixed is arranged at the center of the supporting cylinder 21, the handle 22 is loosened, the extension springs 24 push the plurality of peripheral arc-shaped clamping plates 26 to move towards the second support shaft 3 through the elastic force, the second support shaft 3 is clamped and fixed, the rotating assembly is started, the rotating assembly drives the supporting cylinder 21 to rotate so as to drive the fixed synthetic paper roll stock 1 to rotate, the fixing is more stable, the synthetic paper roll stock cannot shake left and right when the synthetic paper roll stock is cut, the supporting cylinder 21 pushes the piston 6 to reciprocate in the piston box 5 through the matching of the push plate 4, the through groove and the convex column 30 in the rotating process, outside air is sucked into the piston box 5 through the dust suction port 28, the dust suction box 11 and the air suction pipe 8 and is discharged through the exhaust pipe 7, and the suction net 29 absorbs and filters dust and paper scraps in the air sucked into the dust suction box 11, so that the paper scraps are prevented from floating in the air.

While the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art.