EP0418163B1 - Method and device for automatically sharpening slicing knives - Google Patents

Abstract

The invention relates to a device for sharpening an elongate cutting blade (22) having a cutting edge (23), characterised in that it comprises at least one grinding wheel (34, 35) equipped with abrasive material at least on the surface, said grinding wheel having a cylindrical body provided with a peripheral groove (46) of V-shaped profile, said grinding wheel being mounted freely rotatably about an axis (TT) contained in a plane generally parallel to the edge (23) of the blade (22) and perpendicular to the mid-plane (CXZ) of the blade, and said axis being inclined at a predetermined angle (P) relative to the normal (CY) to the mid-plane of the blade, said sharpening device comprising, furthermore, means (36) for bringing the blade and the grinding wheel into contact and means for the relative displacement of the blade and of the grinding wheel (34; 35) in a direction parallel to the edge of the blade. <IMAGE>

Description

It is known to use automatic cutting machines for cutting stacks of sheet materials such as fabric for example, in textile clothing. These machines generally consist of a cutting table on which the stack of material is deposited (commonly known as a mattress), of a mobile assembly consisting of a beam arranged transversely above the table and sliding on longitudinal guides, a cutting carriage sliding along the beam, a cutting head fixed on the cutting carriage. The various mobile elements are motorized by servo motors for example, and receive orders from a digital control. It is thus possible to move the cutting head to any point on the cutting table and following previously established trajectories. The cutting head generally consists of a mechanism making it possible to vibrate a sharp blade vertically, which mechanism can move up and down so as to make the blade penetrate or disengage at the desired location in the mattress. The blade can rotate around its vertical axis. The rotation is controlled so that the blade always remains correctly oriented relative to the path. In order for the blade to cut all the folds of the mattress, it is necessary for the blade to enter the cutting table, which therefore has a coating for this purpose.

As the cutting progresses, the blade loses its cutting power. It is therefore necessary to re-sharpen it regularly, the time between two sharpening operations essentially depending on the abrasive nature of the cut material. This sharpening must be automated so as not to disturb the automatic operating cycle of the cutting machine. There are several solutions for this, some of which have been used for a very long time on manual electric knives used in clothing (called "tip-top"): abrasive belts or small rotary cylindrical wheels. The performance of these sharpeners are relatively limited. More particularly, they are criticized for their too large bulk and their too slow sharpening speed. On the other hand, they always require a motorization of the abrasive element, whether it is a grinding wheel or a ribbon, which complicates the mechanism.

This is particularly the case of the device described in US 2,033,939 which comprises a circular blade which remains in the same vertical plane and a sharpening member. The sharpening member comprises a roller consisting of two abrasive discs mounted to rotate in a substantially vertical plane and offset with respect to the vertical plane of the blade.

Another technical problem arises for the sharpening of a movable cutting blade in rotation about its longitudinal axis.

Indeed, during cutting, the blade performs a rotation around its vertical axis imposed by the blade holder block so that one cannot predict in advance the direction of the cutting edge of the blade at the time of sharpening ; it is therefore necessary for each sharpening to correct the position of the grinding wheel relative to that of the blade.

The present invention also aims to solve this problem by imposing on the grinding wheel the same rotational movements as the blade and simultaneously.

• pas besoin de motorisation
• rapidité d'affûtage
• encombrement réduit
• compensation automatique de l'usure
• qualité d'affûtage excellente
• pas de réglage précis à effectuer.

The object of the present invention relates to a method and a sharpening device eliminating the drawbacks of traditional devices by providing the following advantages:

• no motorization required
• sharpening speed
• small footprint
• automatic wear compensation
• excellent sharpening quality
• no precise adjustment to be made.

This object is achieved according to the invention, by means of a cutting machine with a sharpening device, said cutting machine having an elongated cutting blade with a cutting wire mounted vertically on a rotary blade holder block, integral with '' a carriage movable relative to a cutting table, said device comprising at least one grinding wheel provided at least in surface, with abrasive material, said grinding wheel having a cylindrical body provided with a peripheral groove with V profile, said grinding wheel being mounted in free rotation around an axis, said sharpening device further comprising means for contacting the blade and the grinding wheel and means for relative displacement of the blade and the grinding wheel in a direction parallel to the edge of the blade, the grinding wheel being carried by a lifting beam, said axis of rotation of the grinding wheel being contained in a plane parallel to the edge of the blade and perpendicular to its median plane, said axis being inclined at a predetermined angle relative to normal to the median plane of the blade and the grinding wheel being fixed by means of 'A horizontal axis on a plate integral in rotation with the blade holder block so that its groove is constantly facing the cutting edge of the blade.

Another object of the invention is a sharpening method for an elongated cutting blade having a cutting wire driven in a rotational movement around its longitudinal axis and opposite a sharpening device comprising a support plate for '' at least one grinding wheel provided with at least an area of abrasive material and having a cylindrical body provided with a peripheral groove with a V-profile, in free rotation about an axis, comprising the following steps:
the axis is oriented so that it is contained in a plane parallel to the edge of the blade and perpendicular to its median plane and
it is inclined at a predetermined angle relative to the normal to the plane of the blade,
the grinding wheel support plate is slaved to the rotation movement of the blade, so that the groove of the grinding wheel is constantly facing the cutting edge of the blade,
said grinding wheel is brought into contact with the cutting edge of the blade and
the grinding wheel and the blade are relatively displaced in the longitudinal direction of the blade.

There are two ways to create the relative movement of the blade relative to the grinding wheel. The first consists in keeping the blade fixed, in the high position, and in moving the grinding wheel, first of all in a horizontal movement to come into contact with the blade and then in a vertical movement to move it along the edge of the blade. An automatic cycle can be carried out allowing several passes until the correct sharpening is achieved. The second way is, unlike the first, to keep the wheel fixed in height and to move the blade in front of the wheel. The displacement of the blade can result in particular from the longitudinal vibration of the latter. This solution has the advantage of simplifying the sharpening device by eliminating the need for a member intended to produce the vertical movement of the grinding wheel relative to the blade. Either solution will be chosen based on the design of the entire cutting head.

The sharpening is done according to the following principle: the cutting edge of the blade is brought into contact with the outer edges of the groove of the grinding wheel. Due to the inclination of the grinding wheel, the contacts are made on the two opposite sides of the blade. The relative movement between the blade and the grinding wheel creates, by friction, the rotation of the grinding wheel. The abrasive grains of the grinding wheel then machine the blade according to inclined trajectories relative to the cutting wire from where the sharpening. As the sharpening progresses, the blade wears out and progresses towards the inside of the groove of the grinding wheel.

• angle d'affûtage de la lame de coupe
• longueur de la zone à affûter
• encombrement maximal à ne pas dépasser
• amplitude du mouvement vertical relatif de la meule et de la lame.

The size of the grinding wheel depends on several elements, the main ones of which are as follows:

• sharpening angle of the cutting blade
• length of the area to be sharpened
• maximum size not to be exceeded
• amplitude of the relative vertical movement of the grinding wheel and the blade.

All the other parameters are deduced from each other. We realize that there are in fact an infinity of solutions. The solution chosen will be a compromise respecting the various constraints.

• la figure 1 est une vue de côté d'une machine de coupe, équipée d'un dispositif d'affûtage selon la présente invention,
• la figure 2 est une vue latérale prise suivant la flèche 2-2 à la figure 1,
• la figure 3 est une vue latérale analogue à celle de la figure 2, illustrant le processus d'affûtage,
• la figure 4 est une vue latérale analogue à celle de la figure 2, illustrant une variante du dispositif d'affûtage,
• la figure 5 est une vue de face d'une partie de lame et d'une meule d'affûtage selon l'invention,
• la figure 6 est une vue en coupe horizontale prise suivant la ligne 6-6 à la figure 5,
• la figure 7 est une vue schématique en perspective illustrant les relations géométriques entre la lame et la meule,
• les figures 8, 9 et 10 représentent un autre mode de réalisation du dispositif de l'invention dans lequel la meule est rendue solidaire en mouvement de la lame.

The invention will now be described in detail with reference to the accompanying drawings, in which:

• FIG. 1 is a side view of a cutting machine, equipped with a sharpening device according to the present invention,
• FIG. 2 is a side view taken along arrow 2-2 in FIG. 1,
• FIG. 3 is a side view similar to that of FIG. 2, illustrating the sharpening process,
• FIG. 4 is a side view similar to that of FIG. 2, illustrating a variant of the sharpening device,
• FIG. 5 is a front view of a part of a blade and of a sharpening wheel according to the invention,
• FIG. 6 is a view in horizontal section taken on line 6-6 in FIG. 5,
• FIG. 7 is a schematic perspective view illustrating the geometric relationships between the blade and the grinding wheel,
• Figures 8, 9 and 10 show another embodiment of the device of the invention in which the grinding wheel is made integral in movement with the blade.

The cutting machine illustrated in Figure 1 comprises a fixed table 10, arranged on a frame not shown, and intended to receive sheet materials, or mattress 12, for their cutting along a predetermined path.

Above the table is arranged a beam 14, mounted in longitudinal displacement on the table 10, and driven by means not shown, in the right-left direction in Figure 1 symbolized by the arrow L.

On the beam 14 is mounted a carriage 16 which moves along the beam, using means not shown, in transverse direction relative to the table, in the front-rear direction in Figure 1, the direction right-left in FIG. 2, symbolized by the arrow T. A blade holder block 18 is mounted laterally on the carriage 16, by means of vertical movement paths 20, so as to be able to move vertically on the carriage, therefore relative to the table 10, as illustrated by the arrow H in the figure, by drive means not shown.

The blade holder block contains a gripping member 21 for a vertical cutting blade 22, means for imparting to the blade a vibratory movement in the vertical direction symbolized by the double arrow W, and means for imparting to the blade a movement of rotation around a vertical axis as symbolized by the arrow R.

The purpose of this blade rotation is to constantly keep the blade wire oriented along the tangent to the path imposed by the longitudinal and transverse drive members associated with the beam 14 and the carriage 16 respectively.

The upper face of the table is lined with a layer 24 of flexible and penetratable material, for example a carpet brush, which the tip of the blade 22 can penetrate in order to allow the cutting of the mattress 12 over its entire thickness.

Under the carriage 16 is disposed a presser foot 26 movable vertically between a raised position, illustrated in dotted lines, at a certain distance from the table 10 to allow the placement or removal of material 12 on the table 10, and a position lowered in contact with the material placed on the table.

This presser foot 26 has a dual function. The first function is to press the mattress 12 around the blade 22 to prevent the mattress from following the vertical vibration movements of the blade. The second function is to correctly guide the blade 22 as close as possible to the mattress 12 so as to avoid bending of the blade 22 due to the horizontal cutting forces.

The movement of the presser foot 26 between its raised and lowered positions is ensured by guides 28 and a drive member, not shown.

To allow simple and rapid sharpening of the blade without notably interrupting the cutting process, provision is made, in accordance with the invention, for mounting on the carriage 16 a sharpening device 30 constituted as follows:

A plate 32 is fixed to the carriage 16 on one side of the blade 22. A sharpening wheel 34 is mounted movable opposite the blade 22 and can be moved away from or closer to the latter thanks to a drive member, for example a cylinder 36 as shown.

In this embodiment, two grinding wheels 34, 35 are provided arranged one above the other and mounted idly on a lifting beam 38 at the end of the jack rod 36 in order to ensure that the grinding wheels 34, 35 are both correctly in contact with the blade 22.

• on stoppe les déplacements longitudinaux et transversaux de la poutre 14 et du chariot 16,
• on stoppe la vibration (w) verticale de la lame 22,
• on fait pivoter (R) la lame 22 jusqu'à amener le fil 23 de celle-ci face aux meules 34, 35 d'affûtage,

The structure and arrangement of the grinding wheels will be described in detail below. As illustrated in FIG. 3, the blade 22 is sharpened at regular intervals as follows:

• the longitudinal and transverse displacements of the beam 14 and of the carriage 16 are stopped,
• the vertical vibration (w) of the blade 22 is stopped,
• the blade 22 is made to rotate (R) until the wire 23 thereof is brought in front of the grinding wheels 34, 35,

• on amène les meules 34, 35 en contact avec le fil 23 de la lame 22,
• on fait effectuer à la lame 22 au moins une course verticale (H) ascensionnelle d'amplitude désirée, en montant le bloc porte-lame 18 par rapport au chariot 16, afin d'affûter la lame 22 sur une longueur désirée à partir de sa pointe 21,
• on éloigne les meules 34, 35 de la lame 22,
• on réoriente la lame dans sa position initiale
• on redescend la lame 22 dans le matériau 12 à couper,
• on redémarre la vibration verticale (W) de la lame 22,
• on redémarre les déplacements longitudinaux et transversaux de la poutre 14 et du chariot 16.

This is all the more difficult as the material is hard and thick.

• the grinding wheels 34, 35 are brought into contact with the wire 23 of the blade 22,
• the blade 22 is made to carry out at least one vertical upward stroke (H) of desired amplitude, by mounting the blade holder block 18 relative to the carriage 16, in order to sharpen the blade 22 over a desired length from its point 21,
• the wheels 34, 35 are moved away from the blade 22,
• we redirect the blade to its initial position
• the blade 22 is lowered into the material 12 to be cut,
• the vertical vibration (W) of the blade 22 is restarted,
• the longitudinal and transverse displacements of the beam 14 and of the carriage 16 are restarted.

As illustrated in FIG. 4, it can alternatively be provided that the blade 22 remains fixed during sharpening, and that the grinding wheels 34, 35 move vertically.

To this end, the plate 32 and the jack 36 for moving the grinding wheels 34, 35 are mounted movable along vertical guides 40 of the carriage 16, under the control of a motor member, for example also a jack 42.

When the blades 22 are relatively thin and capable of bending significantly under the contact of the grinding wheels 34, 35, provision will advantageously be made against the blade and opposite the grinding wheels a rear stop 44 against which the blade comes to bear, which prevents it from sagging.

As illustrated in FIG. 2, it may be a simple stop with a flat surface made of wear-resistant material, against which the edge of the blade 22 opposite the wire 23 slides during sharpening.

According to a variant not shown, this stop may be produced in the form of a roller.

In the case of the variant of Figure 4, it will be necessary to mount the rear stop 44 on a vertically movable support jointly with the plate 32 and the cylinder 36 wheel holder.

As illustrated schematically in Figure 5, each grinding wheel 34, 35 has the shape of a flattened cylinder and has a groove 46 in V at its periphery. It is mounted so that its axis TT is inclined relative to the horizontal. Thus, when the grinding wheel is brought closer to the blade 22, it comes into contact with the opposite flanks 48, 50 on either side of the wire 23 of the blade at two points B, B 'spaced vertically from the lateral edges of the groove .

The grinding wheel 34, 35 is produced so as to include abrasive grains at least on the surface at the level of the external edges of the groove 46. To do this, it is possible either to produce a grinding wheel in a material containing abrasive grains in a binder, or fix by any suitable method a coating containing abrasive grains on the surface of a blank of non-abrasive material.

By virtue of the vertical relative movement of the blade 22 and of the grinding wheel 34, 35, the latter is rotated and exerts on the blade a machining by the abrasive grains at the level of the contact zones following paths inclined relative to the wire 23 which achieves sharpening.

We will now show the calculation method allowing optimal sizing of the grinding wheel 34, 35 for a blade 22 of given dimensions.

If we refer to the schematic perspective of Figure 7, point C corresponds to the center of the grinding wheel; the axis CX is the horizontal axis which intersects the bottom groove circle 46 and the wire 23 of the blade at a point D, the axis CY is the horizontal axis perpendicular to the previous one; the axis CZ is the vertical axis passing through the center C; the plane CXZ therefore representing the median plane of the blade 22. The axis TT of the grinding wheel 34 is contained in the plane CYZ and forms an angle P with the axis CY.

The V-shaped groove defines a circle 52 at the bottom of the groove of radius Ri and two circular edges 54, 56 of radius R and spaced by a distance a, the wire 23 of the blade 22 making contact with both edges at two points B and B ′ vertically distant by a distance e.

The point B is projected on the axis CZ at a point A distant from the center C by a distance e / 2 and on the axis TT at a point G distant from the center C by a distance a / 2.

The truncated cone defining the groove wall on which the point B is located has a point E on the top on the axis TT, at a distance b from the center C.

This point E is projected in a horizontal plane containing the line AB at a point F.

The point H is located at the intersection of the generator EB and the circle 52 at the bottom of the groove and the point J is the projection of the point H on the segment BF.

Q is called the half-angle of opening of the groove 46, Xt the horizontal distance between the axis CE and the wire 23 of the blade; Ri the radius of the circle 52 at the bottom of the groove; Qa the apparent half-angle of the groove 46 of the grinding wheel, seen vertically by the blade 22; and N is the half cutting angle of the blade 22.

1 - Relationship between the dimensions of the grinding wheel:

soit $$\text{R = Ri +}\frac{\text{a}}{\text{2 Tg Q}}$$

Based on the CGBH rectangular trapezoid
we have the relationship $$\text{GB = CH +}\frac{\text{at}}{\text{2}}\frac{\text{1}}{\text{Tg Q}}$$

is $$\text{R = Ri +}\frac{\text{at}}{\text{2 Tg Q}}$$

2 - Distance between the two contact points of the blade wire:

From the ACG triangle $$\begin{gathered} \text{CG / AC = sin P} \\ \text{let a = e sin P} \end{gathered}$$

3 - Distance between the blade wire and the vertical axis:

   soit $$\text{Xt² + (e/2)² = (a/2)² + R²}$$

et en y remplaçant a par e sin P d'après la relation (2) : $$\text{Xt =}\text{(}\text{R²-(e/2 cos P)²}{\text{)}}^{\text{1/2}}$$

From triangles ABC and BCG $$\text{CB² = AB² + AC² = GB² + CG²}$$

is $$\text{Xt² + (e / 2) ² = (a / 2) ² + R²}$$

and by replacing a by e sin P according to the relation (2): $$\text{Xt =}\text{((}\text{R²- (e / 2 cos P) ²}{\text{)}}^{\text{1/2}}$$

4 - Apparent angle of the throat

   soit $$\text{a/2 + b = R tg Q}$$

   ou $$\text{b = R tg Q - a/2}$$

From the triangle BGE $$\text{GE = GB tg Q}$$

is $$\text{a / 2 + b = R tg Q}$$

or $$\text{b = R tg Q - a / 2}$$

   et $$\text{tg Qa =}\frac{\text{AF}}{\text{Xt}}\text{=}\frac{\text{b cos P}}{\text{Xt}}$$

d'où, en y reportant l'expression de b donnée par la relation (3) : $$\text{tg Qa = (R tg Q - a/2) cos P/Xt}$$

In the ABF triangle, $$\text{AF = b cos P}$$

and $$\text{tg Qa =}\frac{\text{AF}}{\text{Xt}}\text{=}\frac{\text{b cos P}}{\text{Xt}}$$

hence, by transferring the expression of b given by the relation (3): $$\text{tg Qa = (R tg Q - a / 2) cos P / Xt}$$

5 - Conditions to be fulfilled for proper operation:

• 1) The half cutting angle of the blade must be less than the apparent angle of the groove:
  is $$\text{N <Qa}$$
  
• 2) The blade thread must not be in contact with the back of the throat,
  is $$\text{Xt> Ri}$$
  

6 - Numerical example:

We take here numerical values corresponding to a concrete case.

Initially, we arbitrarily set wheel sizes compatible with the available environment. We then perform all the calculations with these values: depending on the results obtained, we can slightly modify some values and repeat the calculation until obtaining the satisfactory values.

d'après (3), on calcule Xt $$\text{Xt = 12,4 mm}$$

d'après (5) N < Qa ou encore tg N < tg Qa
La condition devient donc, en se servant de (4) : $$\text{tg N <}\frac{\text{(R. tg Q - a/2).cos P}}{\text{Xt}}$$

d'où l'on extrait : $$\text{tg Q >}\frac{\text{1}}{\text{R}}\text{(}\frac{\text{tg N Xt}}{\text{cos P}}\text{+}\frac{\text{a}}{\text{2}}\text{),}$$

soit tg Q > 0,384 ou encore Q > 21° d'après (6), Xt > Ri
d'après (1), $$\text{Ri = R -}\frac{\text{a}}{\text{2.tg Q}}$$

donc $$\text{Xt > R -}\frac{\text{a}}{\text{2. tg Q}}$$

ou encore, $$\text{tg Q <}\frac{\text{a}}{\text{2.(R - Xt)}}\text{,}$$

d'où tg Q < 0,674 soit Q < 34°
l'angle Q est donc borné par : $$\text{21° < Q < 34°}$$

So for our example, we will take:
N = 15 °
P = 15 °
e = 24 mm
R = 17 mm
according to (2), we deduce:
a = 24 x sin 15 = 6.2 mm $$\text{a = 6.2 mm}$$

according to (3), we calculate Xt $$\text{Xt = 12.4 mm}$$

according to (5) N <Qa or even tg N <tg Qa
The condition therefore becomes, using (4): $$\text{tg N <}\frac{\text{(R. tg Q - a / 2) .cos P}}{\text{Xt}}$$

from which we extract: $$\text{tg Q>}\frac{\text{1}}{\text{R}}\text{((}\frac{\text{tg N Xt}}{\text{cos P}}\text{+}\frac{\text{at}}{\text{2}}\text{),}$$

either tg Q> 0.384 or Q> 21 ° according to (6), Xt> Ri
according to (1), $$\text{Ri = R -}\frac{\text{at}}{\text{2.tg Q}}$$

so $$\text{Xt> R -}\frac{\text{at}}{\text{2. tg Q}}$$

or, $$\text{tg Q <}\frac{\text{at}}{\text{2. (R - Xt)}}\text{,}$$

hence tg Q <0.674 or Q <34 °
the angle Q is therefore bounded by: $$\text{21 ° <Q <34 °}$$

In order to have a maximum duration of use of the blade, it is advantageous for the difference (Xt - Ri) to be as large as possible, which amounts to choosing Q closer to 21 ° than to 34 °.

Take for example Q = 22.5 °

We can then calculate Ri = 9.5 mm

The exact dimensions of the grinding wheel are then:
R = 17 mm
a = 6.2 mm
Q = 22.5 °
Ri = 9.5 mm
P = 15 °

During sharpening, the blade 22 sinks slightly into the groove 46 but the wire 23 theoretically remains at the distance Xt from the axis OZ. In fact, as the edges of the groove 46 undergo slight wear, there is in practice a slight reduction in this distance Xt as and when used, but which is not a problem since values are chosen. such that Xt - Ri is as large as possible.

The advantage of having two or more grinding wheels in the direction of the thread is to allow sharpening over a sufficient length while reducing the amplitude of the relative movement of the blade.

These wheels will be carried by an appropriate number of spreaders.

FIGS. 8 to 10 show another embodiment of the invention in which the blade holder block 18 is made integral in movement with the grinding wheel 34.

For this purpose, the grinding wheel 34 (or the grinding wheels mounted in series on the lifter 38) is fixed to the plate 52 by means of a horizontal axis 54; in addition, this plate 52 has a device for guiding the blade 22 and carries the presser foot 26 which can be actuated by means of a jack 58. During cutting, the plate 52 is driven by the same rotational movement as that imposed by the blade holder block 18 on the blade 22 and thus drives in this movement the sharpening system. The groove of the grinding wheel 34 is therefore constantly facing the cutting edge of the blade. In FIG. 9, just before sharpening, the presser foot 26 rises against the plate 52 thanks to the jack 58, which requires the cam 60 to compress the return spring 62 located on the guide 54. The sharpening system in this way is positioned correctly facing the edge of the blade. The sharpening can then take place in the position shown in FIG. 10.

According to this advantageous variant, the sharpening process takes place in the following manner: the blade 22 is placed in the high position and is then automatically oriented with its cutting wire facing the groove of the grinding wheel.

The grinding wheel 34 is automatically arranged by slaving the rotation of the grinding wheel to that of the blade as shown in FIG. 9.

The blade 22 is then vibrated in exactly the same way as during cutting; the grinding wheel 34 is then brought in a horizontal movement into contact with the blade, and is kept in this arrangement for a very short time.

Finally, after having cleared the grinding wheel 34, the cutting process can be resumed without the need to stop the vibration of the blade 22.

Since the sharpening is done according to this method with the blade in the high position, we can therefore take advantage of the dead times of the cut (for example during the movement between two pieces), where the blade is necessarily in the high position to perform the sharpening . The sharpening is thus in "masked time", which avoids loss of time and optimizes the speed of the machine.

The relative movement of the blade 22 and the grinding wheel 34 is, according to this method, directly linked to the amplitude of longitudinal vibration of the blade, it is therefore necessary to take this data into account in calculating the optimal dimensioning of the system. The other operating constraints mentioned in the presentation general remain naturally applicable.

Let W be the amplitude of the blade's longitudinal vibration. Each contact point (B and B ′) sharpens on both sides of the blade a length equal to W. As we want a "covering" of the two sharpened zones, we must respect the following condition: $$\text{e <W}$$

It will suffice to take for example a "covering" of 1 mm: $$\text{e = W - 1 (e and A in mm)}$$

The cutting constraints fix:
W = 25 mm
N = 15 °

Then e = 24 mm (value used previously during the numerical application made as part of the general method).

Another parameter involved in the sizing and configuration of the system is the length of the sharpened blade. Let L be the length of the sharpened blade. Since there is an "overlap", we therefore have: $$\text{L = e + W}$$

Knowing that e depends only on the dimensions and the inclination of the grinding wheel which can be chosen, we can adjust e according to the length of blade that we wish to sharpen, as long as this length remains less than 2W, since a must not exceed W. If on the other hand L exceeds 2W, provision is made to place in series a number n of grinding wheels so that the length of the sharpened blade reaches the desired value. The distance between two successive grinding wheels is such that the "overlap" of two sharpened zones by different grinding stones is equal to the "overlap" of two zones sharpened by the same grinding wheel. The total length of the sharpened blade is then given by the formula: $$\text{L = (2n-1) e + W}$$

Again, the parameter e can be adapted so as to obtain the desired length of sharpened blade.

Claims (11)

1. Cutting machine comprising a sharpening device, said cutting machine having an elongated cutting blade (22) presenting a sharp edge (23) mounted vertically on a rotary blade-holder unit (18), fast with a carriage (16) which moves with respect to a cutting table (10), said device comprising at least one grinding wheel (34, 35) provided at least on the surface with abrasive material, said grinding wheel having a cylindrical body presenting a V-sectioned peripheral groove (46), said grinding wheel being mounted to rotate freely about an axis (TT), said sharpening device further comprising means (36) for placing the blade and the grinding wheel in contact and means for relative displacement of the blade and of the grinding wheel (34, 35) in a direction parallel to the sharp edge of the blade, the grinding wheel being borne by a bifurcated support (38), said axis of rotation (TT) of the grinding wheel (34, 35) being contained in a plane which is parallel to the sharp edge (23) of the blade (22) and perpendicular to its median plane (CXZ), said axis being inclined by a predetermined angle (P) with respect to the normal (CY) to the mediane plane of the blade and the grinding wheel (34, 35) being fixed by means of a horizontal spindle (54) on a plate (52) fast in rotation with the blade-holder unit (18) with the result that the groove of the grinding wheel is constantly opposite the sharp edge (23) of the blade (22).
2. Machine according to claim 1, characterized in that the means for relative displacement of the blade (22) and of the grinding wheel (34, 35) comprise a means for displacing the blade in the direction of its sharp edge (23) opposite a fixed grinding wheel.
3. Machine according to any one of claims 1 or 2, characterized in that the means for relative displacement of the blade (22) and of the grinding wheel (34, 35) comprise a means (42) for displacing the grinding wheel (34, 35) in the direction of the sharp edge (23) of the blade.
4. Machine according to any one of claims 1 to 3, characterized in that said blade-holder unit (18) is provided with means for orientation of said blade in rotation and with means for driving the blade in the longitudinal direction.
5. Machine according to any one of claims 1 to 4, characterized in that it comprises a rear stop (44) on that side of the blade (22) opposite said grinding wheel (34, 35).
6. Machine according to claim 2, characterized in that the means for relative displacement of the blade (22) and of the grinding wheel (34, 35) comprise means (W) for vibrating the blade.
7. Machine according to one of the preceding claims, characterized in that the means for placing the blade (22) and the grinding wheel (34, 35) into contact comprise a jack (36) whose rod is fast with the bifurcated support (38).
8. Machine according to claim 3, characterized in that the means for displacement of the grinding wheel (34, 35) in the direction of the sharp edge of the blade (22) comprise a jack (42) associated with the vertical guides (40) mounted on the carriage (16).
9. Machine according to one of the preceding claims, characterized in that it comprises two grinding wheels (34, 35) juxtaposed in the direction of the sharp edge of the blade (22) by being borne by at least one bifurcated support (38).
10. Process for sharpening an elongated cutting blade (22) presenting a sharp edge (23) animated by a movement of rotation about its longitudinal axis and opposite a sharpening device comprising a plate (52) supporting at least one grinding wheel (34) provided at least on the surface with abrasive material and having a cylindrical body presenting a V-sectioned peripheral groove (46), mounted to rotate freely about an axis (TT), comprising the following steps:
       orienting axis (TT) so that it can be contained in a plane which is parallel to the sharp edge (23) of the blade and perpendicular to its median plane and
       inclining it by a predetermined angle (P) with respect to the normal to the plane of the blade,
       servo-controlling the plate (52) supporting the grinding wheel (34) by the movement of rotation of the blade (22), with the result that the groove (46) of the grinding wheel (34) is constantly opposite the sharp edge (23) of the blade (22),
       bringing said grinding wheel (34, 35) in contact with the sharp edge (23) of the blade and
       relatively displacing the grinding wheel and the blade in the longitudinal direction of the blade.
11. Process according to claim 10, characterized in that the grinding wheel (34, 35) and the blade (22) are displaced relatively by placing the latter in longitudinal vibration (W).

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