EP3694669B1 - Safety device for a band saw and band saw comprising such a safety device - Google Patents

Description

The invention relates to a safety device for a band saw according to the preamble of claim 1 and a band saw according to the preamble of claim 14 and equipped with such a device.

A band saw is a machine tool in which a band-shaped saw blade is folded back on itself to form a loop. This loop is mounted on two handwheels rotatably mounted on a frame, in a mutually spaced manner. The handwheels can be rotated to cause the loop to rotate relative to the frame.

Band saws are widely used, and in a wide variety of fields. Band saws are, for example, widely used in carpentry, in particular for cutting raw wood. Saws of this type are also widely used in butchery, in particular for butchering meat carcasses.

Band saws are popular for their fast cut, which results from the high linear speed of the blade relative to the frame. This speed regularly reaches 1,800 meters per minute, and can rise up to 2,600 meters per minute.

This high speed is accompanied by a fairly long stopping time, which can reach a few tens of seconds. To reduce the time required to stop the blade, current band saws are generally equipped with a brake, most often of the electromagnetic type, coupled to the motor.

With a brake of this type, the blade stops much more quickly, typically in a few seconds, for example around 3 seconds or even less.

Increasingly, efforts are being made to improve the safety of operators working on band saws. In general, this involves detecting that the operator, and especially his hands, are approaching too close to the blade, and, if necessary, ordering this blade to stop.

One difficulty lies in the fact that the extent of the detection zone must be compatible with the work carried out on the saw: the detection zone must be sufficiently small to avoid unwanted stops, and sufficiently extended so that the blade has time to stop after the stop command, before the operator comes into contact with the blade. The extent of the detection area should also take into account the speed at which the operator is working. And this can be quite high.

The few seconds it takes for the blade to come to a complete stop by an action of the electromagnetic brake alone involves a large detection area which is generally incompatible with most operations performed on band saws. An electromagnetic brake begins to act approximately 50 milliseconds after being triggered and is not fully operational until approximately 120 milliseconds. It takes at least several hundred milliseconds to bring the blade to a complete stop. Even by being satisfied with a braked blade, and not stopped, at the time of contact with the operator, the detection zone is still too large for certain jobs: the operator sometimes works in the immediate vicinity of the blade, in particular for the cutting small pieces of wood or small pieces of carcass.

The need has thus arisen to equip band saws with specific safety devices, in addition to electromagnetic brakes intended for the normal stopping of the blade, capable of stopping the blade more quickly than the brakes. Such devices must be able to stop the blade very quickly after detection of the operator near the blade. Depending on their performance, the safety devices make it possible to reduce the detection zone to a greater or lesser extent.

In the document US 2008/245200 A1 Describing the preambles of independent claims 1 and 14, a safety device has been proposed comprising a pair of toothed jaws rotatably mounted on a frame. The frame is mounted on the frame of a band saw such that the toothed jaws are located on either side of a saw blade. The toothed jaws are interconnected by a coupling bar, which coordinates their rotation relative to the frame. An actuating rod is slidably mounted on the frame under the stress of a compression spring. One end of this rod cooperates with a portion of one of the toothed jaws shaped as a cam. The coupling bar and the cam transform a sliding of the actuating rod into a rotary and coordinated movement of the toothed jaws. The actuating rod is reversibly movable between a first and a second position relative to the frame. The toothed jaws can thus be rotated between a position where their teeth are spaced apart. from each other, when the actuator rod is in the first position relative to the frame, and a position where their teeth engage with each other, when the actuator rod is in the second position relative to the frame. to the chassis. This socket blocks the saw blade.

The actuator rod is integral with a stud which is fixedly retained relative to the frame by means of a fusible wire, with the actuator rod in its first relative position. When the presence of an operator is detected, an electric current is discharged through the wire. This melts and releases the actuating rod. The latter gains its second position under the effect of the spring return.

The device US 2008/0245200 is quite effective: it stops the saw blade very quickly. The Applicant has observed that this efficiency is due to the presence of teeth on the jaws. By engaging one in the other, these teeth suddenly and violently deform the blade. This results in an almost immediate stop of the blade. However, the blade becomes unusable: it must be changed. This results in the unavailability of the saw, the time to remove the damaged blade, fit a new one and adjust the tension of the latter. This is not satisfactory, especially since, from experience, safety stops occur several times a day for the same saw.

The Applicant has set itself the objective of improving this situation. To this end it provides a safety device for a band saw of the type comprising a frame and a pair of jaws rotatably mounted on the frame. This frame is suitable for mounting on a band saw frame with the jaws arranged on either side of a blade of this band saw. The device further comprises an actuating rod slidably mounted on the frame, and at least one elastic return member which constrains the sliding of the actuating rod. A bidirectional transmission transforms the sliding of the actuating rod into a rotation of the pair of jaws. The device also comprises an electromagnetic actuator integral with the frame and a retaining member integral with the electromagnetic actuator. The actuating rod is arranged with a receiving portion capable of coming into engagement with the retaining member when the actuating rod is in a first position relative to the frame. The bidirectional transmission is arranged in such a way that the jaws are far from each other when the actuating rod is in this first relative position. The electromagnetic actuator maintains engagement between the retainer and the receiving portion when supplied with current.

The proposed device effectively and quickly stops the blade, even in the case where the jaws are toothless. This allows the proposed device to be used without damaging the blade. The shut-off device is triggered by itself in the absence of current, in particular in the event of a power cut. The proposed device is triggered more quickly: it causes the jaws to rotate more quickly, which can, if necessary, compensate for any delay associated with the use of smooth rather than toothed jaws. The proposed device closes at the same angular position of the jaws, and at the same speed, unlike known devices. Unlike known devices, which derive their performance from the action of toothed jaws on the blade, the proposed device derives its effectiveness from a particular kinematic chain, including the release of the actuating rod by release of an electromagnetic actuator. and an associated retaining body.

The proposed device can operate without a pneumatic element of the cylinder type, thus avoiding any difficulty associated with a gas supply. In the event of a power cut, the proposed device goes into a state where the jaws block the blade, or remains in such a state.

The Applicant also proposes a band saw comprising a frame and a blade. The saw further comprises a safety device of the type comprising a frame and a pair of jaws rotatably mounted on the frame. This frame is mounted on the frame with the jaws placed on either side of the blade. The device further comprises an actuating rod slidably mounted on the frame, and at least one elastic return member which constrains the sliding of the actuating rod. A bidirectional transmission transforms the sliding of the actuating rod into a rotation of the pair of jaws. The device also comprises an electromagnetic actuator integral with the frame and a retaining member integral with the electromagnetic actuator. The actuating rod is arranged with a receiving portion capable of coming into engagement with the retaining member when the actuating rod is in a first position relative to the frame. The bidirectional transmission is arranged so such that the jaws are moved away from one another when the actuating rod is in this first relative position. The electromagnetic actuator maintains engagement between the retainer and the receiving portion when supplied with current.

• la figure 1A représente une scie à ruban, vue de droite ;
• la figure 1B représente la scie de la figure 1A, vue de face ;
• la figure 2 représente un détail II de la scie de la figure 1B ;
• la figure 3 représente un dispositif de sécurité à usage par exemple pour la scie des figures 1A et 1B, en perspective isométrique partiellement coupée, dans un premier état de fonctionnement ;
• la figure 4 représente le dispositif de la figure 3, vu de côté ;
• la figure 5 représente le dispositif de la figure 4, vu en coupe selon la ligne V-V ;
• les figures 6 à 8 sont analogues aux figures 3 à 5, respectivement, le dispositif de sécurité se trouvant dans un second état de fonctionnement ;
• les figures 9 à 11 sont analogues aux figures 6 à 8, respectivement, le dispositif de sécurité se trouvant dans un troisième état de fonctionnement ;
• la figure 12 représente une paire de mors à usage par exemple pour le dispositif de sécurité des figures 3 à 11 ;
• la figure 13 représente une variante de réalisation du dispositif de sécurité des figures 3 à 11, dans une vue analogue à celle de la figure 3 ;
• la figure 14 représente une variante de réalisation de la paire de mors de la figure 12, dans une vue analogue à cette figure 12 ;
• la figure 15 représente la scie des figures 1A et 1B, en vue arrière ;
• la figure 16 représente un détail XVI de la scie de la figure 15, cette scie étant dans un premier état de fonctionnement ; et
• la figure 17 représente le détail XVI de la figure 16, la scie étant dans un second état de fonctionnement.

Other characteristics and advantages of the invention will become apparent on examination of the detailed description below, and of the appended drawings in which:

• the figure 1A shows a bandsaw, seen from the right;
• the figure 1B represents the saw of the figure 1A , front view ;
• the figure 2 represents a detail II of the saw of the figure 1B ;
• the figure 3 represents a safety device for use, for example, for the saw of figures 1A and 1B , in partially cut away isometric perspective, in a first operating state;
• the figure 4 represents the device of the figure 3 , seen from the side;
• the figure 5 represents the device of the figure 4 , seen in section along the line VV;
• the figures 6 to 8 are analogous to figures 3 to 5 , respectively, the safety device being in a second operating state;
• the figures 9 to 11 are analogous to figures 6 to 8 , respectively, the safety device being in a third operating state;
• the figure 12 represents a pair of jaws for use, for example, for the safety device of figures 3 to 11 ;
• the figure 13 represents an alternative embodiment of the safety device of figures 3 to 11 , in a view similar to that of the figure 3 ;
• the figure 14 shows an alternative embodiment of the pair of jaws of the figure 12 , in a view similar to this figure 12 ;
• the figure 15 represents the saw of figures 1A and 1B , in rear view;
• the figure 16 represents a detail XVI of the saw of the figure 15 , this saw being in a first operating state; and
• the figure 17 represents detail XVI of the figure 16 , the saw being in a second operating state.

The accompanying drawings contain elements of a certain character. They can not only serve to complete the invention, but also contribute to its definition, where appropriate.

We refer to figures 1A and 1B .

They show a machine tool in the form of a band saw 1. The saw 1 comprises a frame 3 and a blade 5 in the form of a band. The saw 1 also comprises a first flywheel, or lower flywheel 7, and a second flywheel, or upper flywheel 9, each rotatably mounted on the frame 3, here in line with one another.

At least one of the lower flywheel 7 and the upper flywheel 9 is connected to a motor capable of driving the flywheel in question in rotation with respect to the frame 3. The motor is in particular of the synchronous type. A synchronous motor is easier to stop. More generally, synchronous type motors are easier to control in speed. An engine of this type can stop in a few seconds, for example in a time close to 3 seconds.

The blade 5 is folded back on itself so as to form a loop. This loop is mounted around the lower flywheel 7 and the upper flywheel 9.

The loop is moved through the flywheel. The other of the lower flywheel 7 and the upper flywheel 9 is mounted idle. At least one of the lower flywheel 7 and the flywheel upper 9 is also mounted on the frame 3 with the possibility of translation in the direction of the other of the lower flywheel 7 and the upper flywheel 9, here in an essentially vertical direction, to allow tensioning of the loop formed by the blade 5 and / or its release.

The saw 1 here comprises a safety device 11 attached to the frame 3. The safety device 11 comprises a pair of jaws 13 facing one another. The safety device 11 is positioned on the frame 3 so that the blade 5 passes between the jaws 13 and is held in this position by a set of fasteners, not shown.

The frame 3 delimits a working space 15 which is crossed vertically by a portion of the blade 5. The rotation of the engine flywheel reveals in the loop of the blade 5, between the lower flywheel 7 and the upper flywheel 9, a portion , or strand, taut 5a and a soft strand 5b.

The working space 15 is crossed by the stretched end 5a while the safety device 11 is placed on the slack end 5b.

We refer to the figure 2 .

It shows the jaws 13 in a position in which they are spaced apart from one another. The jaws 13 are separated from the soft end 5b of the blade 5.

We refer to figures 3 to 5 .

They show the safety device 11 in the isolated state.

The safety device 11 comprises a frame 17 on which the jaws 13 are each mounted to rotate about respective axes parallel to each other. The frame 17 has here a pair of flat uprights, namely a first flat upright 19-1 and a second flat upright 19-2. The first flat upright 19-1 and the second flat upright 19-2 are arranged opposite each other, so as to extend parallel to one another. The first flat upright 19-1 and the second flat upright 19-2 are held one above the other in this relative position by flat cross members, namely a first end cross member 21-1 which connects one of the ends of the first upright 19-1 at the corresponding end of the second upright 19-2, a second end cross member 21-2 which connects the other end of the first upright 19-1 to the corresponding end of the second upright 19-2, and a first 21-3 and a second intermediate crosspiece 21-4 which each connect an intermediate portion of the first upright 19-1 to the corresponding portion of the second upright 19-2.

The first upright 19-1 corresponds to a front face of the safety device 11.

Each jaw 13 is mounted on a respective drive shaft 23, integrally, in rotation at least.

Each drive shaft 23 is rotatably mounted on the frame 17, guided by means of a first pair of bearings, or first bearings 25, which define a respective axis 26. Here the first bearings 25 are made in the form of plain bearings or bushings. For each shaft 23, a first bearing 25 is housed in the first upright 19-1 while the other first bearing 25 is housed in the second upright 19-2, opposite the other first bearing 25.

Each of the drive shafts 23 protrudes from the first post 19-1 away from the second post 19-2. Each of these shafts 23 protrudes from the frame 17. In each case, a jaw 13 is mounted on an end portion of a respective drive shaft 23 which projects from the first post 19-1, or first end, through the 'Intermediate of a corresponding orifice formed in the jaw 13. This first end forms a surface adapted to cooperate with a bore formed each time in a jaw 13. For example, each of these surfaces has a diameter smaller than an adjacent portion of its respective drive shaft 23. Each jaw 13 bears against one end of this adjacent portion, which forms a shoulder. Each jaw 13 is held in this position on its respective shaft 23 by a fastener, here comprising a screw 29 and a washer 31 clamped against one face of the jaw 13 by the screw 29.

Each drive shaft 23 has an end portion opposite to the first end, or second end portion 33. The second end 33 here has a reduced diameter compared to the rest of the drive shaft 23. This second end 33 is received in the first bearing 25 housed in the second upright 19-2.

Each drive shaft 23 has an intermediate portion 35 between its second end portion 33 and its opposite end portion.

The safety device 11 further comprises an actuating rod 37 mounted on the frame 17 with the possibility of translation in a first direction 38, normal to the axes of rotation 26 of the jaws 13. The actuating rod 37 is guided in translation on the frame 17 by a second pair of bearings, or second bearings 39, here in the form of plain bearings or bushings. A second bearing 39 is housed in the first intermediate cross member 21-3 while the other second bearing 39 is housed in a second intermediate cross member 21-4, opposite the first second bearing 39.

At one of its ends, the actuating rod 37 is connected to each of the drive shafts 23 by a bidirectional transmission 41 which transforms the translational movement of the rod 37 relative to the frame 17 in the first direction 38 into a rotational movement of each of the drive shafts 23 about their respective axes 26. The bidirectional transmission 41 is arranged in such a way that the rotational movements of the drive shafts 23 are mutually combined and take place in opposite directions. 'from each other.

Here, the bidirectional transmission 41 comprises a pair of connecting rods 43 of which a respective end, or small end, is attached to the corresponding end of the actuating rod 37 with the possibility of rotation about an axis parallel to the axes of rotation. 26 of the jaws 13.

The corresponding end portion of the actuating rod 37 is shaped as a yoke 45 comprising two yokes 47 which extend parallel to one another. Each of these yokes 47 is pierced with a respective orifice. The orifices of the yokes 47 and the corresponding orifices in the feet of the connecting rods 43 are traversed by the same pin forming a pin 49. The pin 49 is force-fitted into the orifices of the yokes 47 while the connecting rods 43 are each free to pivot around it. this pin 49.

The bidirectional transmission 41 further comprises a pair of cranks 51 each attached to a respective drive shaft 23 and to a head portion of a respective connecting rod 43, opposite the root portion.

The cranks 51 each have a first orifice through which the crank 51 mounts on a respective drive shaft 23. The cranks 51 each have a second orifice, opposite the first, which receives a journal 53 also received in a corresponding orifice of a respective connecting rod 43.

The translational movement of the actuating rod 37 relative to the frame 17 is constrained by an elastic return member, produced here in the form of a spring 55 working in compression. Here, the spring 55 is of the helical type.

The actuating rod 37 is produced here in the form of a shaft of circular section. The actuator rod 37 has in particular a shoulder portion 57 and a first junction portion 59 which connects the yoke 45 to the shoulder portion 57. The actuator rod 37 further comprises a second junction portion 61 which connects one end of the actuating rod 37 opposite the yoke 45 to the shoulder portion 57.

The first junction portion 59 is received in the second bearing 39 housed in the second intermediate cross member 21-4. The second junction portion 61 passes through the second bearing 39 housed in the first intermediate cross member 21-3.

A longitudinal end of the spring 55 is supported here against a large face of the first intermediate cross member 21-3 while an opposite end of the spring 55 is supported against the shoulder portion 57 of the actuating rod 37.

The end of the actuating rod 37 opposite the yoke 45 carries a backing plate 63 capable of cooperating with an actuator, here in the form of an electromagnetic suction cup 65 held fixedly relative to the frame 17. The suction cup 65 comprises a non-magnetic magnet. shown which forms a retaining member integral with the suction cup 65. The backing plate 63 forms a receiving portion of the actuating rod 37. This receiving portion is able to engage with the magnet of the suction cup 65.

Here, the suction cup 65 is attached to a large face of the second end cross member 21-2.

The safety device 11 is in a first so-called open operating state. In the open state, the actuating rod 37 is in a first position relative to the frame 17, in which the back plate 63 is engaged with the magnet of the suction cup 65. The back plate 63 is against the magnet of the suction cup. this suction cup 65. The shoulder portion 57 of the actuating rod 37 is close to the first intermediate cross member 21-3. The spring 55 is compressed between this shoulder portion 57 and this first intermediate cross member 21-3. The actuating rod 37 is retained relative to the frame 17, in this first position, by the action of the magnet of the suction cup 65 on the backing plate 63, as long as the suction cup 65 is supplied with current. The actuating rod 37 is engaged with the suction cup 65. The jaws 13, or at least an active portion thereof, are spaced apart from one another. The gap between the jaws 13 allows a passage of a saw blade, such as the blade 5 of the figures 1A, 1B and 2 .

The safety device 11 is armed.

The security device 11 here comprises an optional arming system 67.

The arming system 67 comprises an actuator, here in the form of a cylinder 69 of the electric type, the body 71 of which is fixed to the frame 17 by means of a fixing yoke 73 and of a second journal 75 housed therein and passing through an end portion of the body 71. The fixing yoke 73 is attached here against a large face of the second upright 19-2 opposite the first upright 19-1. Here, the jack 69 is of the trapezoidal screw type so that the rod 77 of the jack 69 remains stationary relative to the body 71 of this jack 69 as long as the motor of this jack 69 is not rotating.

The rod 77 of the jack 69 supports an arm 79, articulated at one of its ends on the rod 77 around a third journal 81. The arm 79 is also articulated on the frame 17, around a fourth journal 83. housed in the frame 17, here in the second upright 19-2.

Here, the arm 79 comprises a pair of elongated flanges 85 which extend parallel to one another and are held in this position by the third journal 81 and the fourth journal 83. The arm 79 is arranged such that the actuating rod 37 is located partially between these flanges 85 on a part of its second junction portion 61.

The arm 79 passes through the second upright 19-2 by a slot 80 formed in a large face thereof. The end of the arm 79 opposite the rod 77 of the cylinder 69 ends between the backing plate 63 and a large face of the first intermediate cross member 21-3. In the vicinity of this end, the arm 79 carries a pair of contact rollers 87, each mounted to rotate on a respective flange 85 of the arm 79 by a fourth journal 89.

In the first operating state of the safety device 11, the rod 77 of the cylinder 69 is deployed, and the arm 79 is in a first position relative to the frame 17, in which its end carrying the rollers 87 is remote from the counterplate. 63.

The safety device 11 is enclosed in a closed casing 91, shown here partially notched. The housing 91 is based here on the first upright 19-1, the first end cross member 21-1 and the second end cross member 21-2.

We refer to figures 6 to 8 .

The safety device 11 is in a second operating state, called closed. In the closed state, the actuating rod 37 is in a second position relative to the frame 17, in which the backing plate 63 is remote from the suction cup 65. The shoulder portion 57 of the actuating rod 37 is away from the first intermediate cross member 21-3. The spring 55 is less compressed than when the actuating rod 37 is in the first position relative to the frame 17. The actuating rod 37 is no longer in engagement with the suction cup 65. The jaws 13, or at least an active portion of these, are close to each other. The gap between the jaws 13 is such that a saw blade is blocked between them, typically the blade 5 of the jaws. figures 1A, 1B and 2 .

The arm 79 is in its first position relative to the frame 17.

The change from the open state to the closed state is caused by a cut in the power supply to the suction cup 65. The backplate 63, integral with the actuating rod 37, is no longer retained by the suction cup 65. The actuating rod 37 is no longer engaged with the suction cup 65. It leaves its first position relative to the frame 17 by a return effect of the spring 55 which relaxes. The spring 55 moves the actuating rod 37 in translation with respect to the frame 17. The bidirectional transmission 41 transforms this translation of the actuating rod 37 into a combined rotation of the jaws 13 relative to the frame 17. This rotation brings them closer together. jaws 13 from each other, at least an active part of them.

The spring 55 exerts a thrust force on the actuating rod 37 which is transformed into a force for clamping these jaws 13 against a saw blade. The force of the spring 55 is multiplied by a leverage effect resulting from the arrangement of the connecting rods 43 and the cranks 51. The bidirectional transmission 41 thus comprises a lever effect arrangement, adapted to act on each of the jaws 13. For a same clamping force at the jaws 13, it is necessary to generate a lower force at the spring 55 because of the cranks 51. In return, a less powerful suction cup 65 can be used, which makes it possible to release the backing plate 63 more quickly. A lower force spring 55 allows for example the use of a lower stiffness spring while maintaining the same stroke of the actuating rod 37 relative to the frame 17.

We refer to figures 9 to 11 .

The safety device 11 is in a third operating state, transient, in reset.

In the reset state, the actuating rod 37 is again in its first position relative to the frame 17.

The arm 79 is in a second position relative to the frame 17, in which the rollers 87 contact the backing plate 63. The rod 77 of the cylinder 69 is retracted. It causes the back plate 63 to push towards the suction cup 65 via the arm 79.

To go from the closed state to the reset state, the actuator 69 is controlled so that its rod 77 retracts into the body 71. This movement of the rod 77 causes a pivoting of the arm 79 relative to the frame 17, around the fourth journal 83. This pivoting brings the arm 79 first into contact with the backing plate 63 by means of the rollers 87 then pushing this backing plate 63 in the direction of the suction cup 65 This thrust is against the spring 55 which is more and more compressed as the back plate 63 approaches the suction cup 65. Finally, the back plate 63 comes into contact with the suction cup 65, the rod of. actuation 37 has regained its first position relative to the frame 17. The suction cup 65 supplied with current retains the back plate 63 and the actuating rod 37 of which the back plate 63 is integral.

The transition to the open state is done by controlling the jack 69 so that the rod 77 is deployed again. The end of the arm 79 which carries the rollers 87 moves away from the backing plate 63 by pivoting of this arm 79 on the frame 17. The backing plate 63 remains held by the suction cup 65.

We refer to the figure 12 .

It shows a pair of jaws 130 for use, for example, with the safety device 11 of the figures 3 to 11 .

Each jaw 130 comprises a body 131 and a jaw 132 pivotally mounted on the body 131, here by means of a fifth journal 133.

Each jaw 132 carries an active surface 134. The active surfaces 134 of the jaws 130 are intended to come opposite one another. These active surfaces 134 are smooth. In particular, these active surfaces 134 are devoid of teeth. These active surfaces 134 are here generally flat. These active surfaces 134 make it possible to distribute a clamping force on a blade, typically the blade 5 of the figures 1A to 2 .

Here, each jaw 132 is made in the form of a single piece, in the general shape of a rectangular parallelepiped, one face of which forms the active surface 134. Each body 131 here has an oblong profile and a groove in the shape of a mortise 135 open at one end of the body 131. Mortise 135 is arranged to receive a respective jaw 132 while allowing an angular movement of this jaw 132 relative to the body 131, for example of the order of 60 degrees.

Here, each body 131 has a longitudinal plane of symmetry. The mortise 135 has a bottom with two surfaces which extend obliquely and symmetrically with respect to the plane of symmetry of the body 131 and meet at a top. An orifice for a respective fifth journal 133 is formed in each body 131. The central axis of this orifice is in the plane of symmetry of the body 131. This arrangement of the bottom of the mortise 135 allows two identical bodies 131 to be used for make jaws 130.

Each jaw 132 is pierced with a respective hole for the fifth journal 133. This hole is spaced from the center of gravity of the jaw 132. Each jaw 132 hangs relative to a respective body 131.

At the end opposite the mortise 135, each body 131 has a bore 136 through which the body mounts to a shaft, typically the drive shaft 23 of the. figures 3 to 11 . The central axis of the bore 136 belongs to the plane of symmetry of the body 131.

In the open position, that shown here, the active surfaces 134 of the jaws 132 are moved away from each other so as to allow the passage of a blade, typically the soft end 5b of the jaws. figures 1A and 1B .

The centers of pivoting of the jaws 132 on their respective bodies 131, which correspond substantially to an intersection of the longitudinal axis of the fifth journals 133 with a transverse plane of the bodies 131, can be connected to each other by a first line virtual line 137.

The pivoting centers of the bodies 131 on the frame of a safety device, typically the frame 17 described in relation to the figures 3 to 11 , which correspond to an intersection of the longitudinal axis of the bore 136 and a transverse plane of the body 131, can be connected to each other by a second virtual straight line 138.

When the jaws 130 are in the relative open position, as shown in figure 12 , the first virtual straight line 137 and the second virtual straight line 138 extend generally parallel to each other. The first virtual straight line 137 and the second virtual straight line 138 are furthermore distant from each other by a few millimeters, here nearly ten.

First arrows 139 indicate the respective directions of rotation of the jaws 130 in the closing phase. A second arrow 140 indicates the direction of movement of the slack strand 5b. With respect to this direction of movement 140 of the blade, the first straight line 137 is located upstream of the second virtual straight line 138, with reference to the respective directions of rotation 139 of the jaws 130.

When the jaws 130 are closed, the first straight line 137 is still upstream of the second straight line 138, but close to the latter. This proximity reduces the risk of the jaws 132 bouncing off each other when closing. In addition, the closer the first straight line 137 is to the second straight line 138, the greater the pressure force of the jaws 130 on the blade 5.

The relative position of the first straight line 137 and of the second straight line 138 when closed contributes to maintaining this closure of the jaws 130, by producing a resulting force which participates in the tightening. The small spacing between the jaws 132 in the open position decreases the closing stroke, therefore the extent of the rotation of the jaws 130. This reduced stroke further reduces the risk that the jaws 132 will rebound on each other when closing. . This stroke also corresponds to the lengthening of the spring 55 between the first position and the second position of the safety device 11.

This embodiment of the jaws 130 allows efficient and rapid braking of a blade, without damaging the latter. The effectiveness of the braking results in particular from the absence of rebound of the active surfaces 134 one on the other when the jaws 130 are closed. This absence of rebound is due in particular to the conformation of the active surfaces 134 and to the low rotary travel of the bodies 131. The force to be generated by the spring 55 is also reduced, owing to the fact that the forward movement of the blade contributes to the clamping of the jaws 130. A lower force in the spring 55 allows a smaller dimensioning of the electromagnetic actuator.

The bidirectional transmission 41 produced from pairs formed of connecting rods and cranks causes a small angular displacement of the jaws 130 between their open position and their closed position. This low travel contributes to obtaining contact between the jaws 130 and the blade which is always made in the axis of the blade and to reduce the risk of rebound.

We refer to the figure 13 .

It monsters a second safety device 110 for use in particular with the band saw 1 of the figures 1A and 1B .

• chaque arbre d'entraînement 23 présente une portion d'extrémité non référencée et une portion d'épaulement 27 adjacente à la portion d'extrémité ;
• chaque mors 13 vient en appui contre la portion d'épaulement 27 de son arbre d'entraînement 23 respectif et se trouve maintenu dans cette position par une fixation respective, comprenant la vis 29 et la rondelle 31 serrée contre une face du mors 13 par la vis 29.

The second safety device 110 is analogous to the safety device 11 described in relation to the figures 3 to 11 , with the following exceptions (identical reference numbers designate structurally and / or functionally similar elements):

• each drive shaft 23 has a non-referenced end portion and a shoulder portion 27 adjacent to the end portion;
• each jaw 13 bears against the shoulder portion 27 of its respective drive shaft 23 and is held in this position by a respective fixing, comprising the screw 29 and the washer 31 clamped against one face of the jaw 13 by the screw 29.

We refer to the figure 14 .

It shows a pair of jaws of a second type, or second pair of jaws 230 for use, for example, with the safety device 11 of the figures 3 to 11 or the second safety device 110 of the figure 13 .

The second jaws 230 are profiled. In profile, each second jaw 230 has a curved edge carrying an active surface 234. The active surfaces 234 of the second jaws 230 are intended to come opposite one another. These active surfaces 234 are smooth. In particular, these active surfaces 234 are devoid of teeth.

The profile of the active surfaces 234 is such that a contact area 241 with a saw blade, typically the soft strand 5b of the figures 1A and 1B , or practically one-off. This contact zone 241 is also slightly offset from the second virtual straight line 138 which connects the centers of rotation corresponding to the intersection of the axes of rotation 26 with the profile of the second jaws 230.

The second jaws 230 have a profile arranged such that the active part of the active surfaces 234 of these second jaws 230, formed of the contact zone 241, is located in advance with respect to the second virtual straight line 138, with reference to to the directions of rotation of the second jaws 230. The offset is of the order of a millimeter, here 2 millimeters for example.

The first arrows 139 indicate the respective directions of rotation of the second jaws 230 in the closing phase. The second arrow 140 indicates the direction of movement of the slack strand 5b. With respect to these directions of movement, the contact zone 241 is located before the second virtual straight line 138. The rest of the active surfaces 234 is shaped such that the contact between the active surfaces 234 of the second jaws 230 with the blade is always offset by the same distance with respect to the second virtual straight line 138, regardless of the thickness of the blade 5. The active surfaces 234 are shaped according to a snail curve.

This allows efficient and rapid braking of the blade, without damaging it. This effective braking results in particular from the absence of rebound of the active surfaces 234 one on the other during the closing operation, due in particular to the shaping of the active surfaces 234. The force to be generated is also reduced. by the spring 55, due to the fact that the forward movement of the blade contributes to the tightening of the second jaws 230. A lower force allows a smaller dimensioning of the electromagnetic actuator.

We refer to the figure 15 .

The saw 1 here comprises a disengagement system 93 by means of which at least one of the lower flywheel 7 and the upper flywheel 9 is mounted on the frame 3 of the saw 1. Here, the disengaging system 93 is added to that of the lower flywheel 7 and the upper flywheel 9 which is mounted loose on the frame 3, for example the upper flywheel 9.

The disengagement system 93 can be controlled so as to release the tension of the blade 5, simultaneously with the triggering of a safety device. The blade 5 can thus slide relative to the lower flywheel 7 and the upper flywheel 9, so that the blade 5 stops before these flywheels. As the control of the disengagement system 93 and of the safety device is simultaneous, the forces to be applied to the blade 5 to stop it are also limited.

We refer to the figure 16 .

The upper flywheel 9 is rotatably mounted on a support shaft 95, via a hub 97.

The disengaging system 93 comprises a main rod 99 by means of which the hub 97 is supported on the frame 3. The disengaging system 93 further comprises a second arm 101 articulated on the frame 3, here by thanks to a pivot 102 disposed at one end of the second arm 101. The system 93 further comprises a second electromagnetic suction cup 103 fixed to the frame 3 and a second backing plate 105, able to cooperate with the second suction cup 103. This second backing plate 105 is fixed to one end of the second arm 101 opposite the pivot 102. The second back plate 105 is engaged in the second suction cup 103. As long as it is supplied with current, the second suction cup 103 maintains the back plate 105 in this engaged state.

The main rod 99 is supported on the frame 3 by the second arm 101, under the stress of an elastic return member, here in the form of a second spring 106, for example a helical spring working in compression. One end of the second spring 106 rests on a face of the second arm 101 while an opposite end bears against a washer 107 stopped in translation with respect to the main rod 99 by a nut 108. The nut 108 is engaged. on a threaded portion of the main rod 99. The tension of the blade 5 depends on the state of compression of the second spring 106. This tension can be adjusted by acting on the nut 108.

We refer to the figure 17 .

Unlike the state of the figure 16 , the second suction cup 103 is no longer supplied with current. The suction cup 123 no longer maintains the engagement between the backing plate 105 and the suction cup 103. Under a return effect of the second spring 106, the second arm 101 pivots around the pivot 102. The main rod 99 accompanies this pivoting by moving relative to it. to frame 3. The blade 5 is relaxed.

The disengaging system 93 and the safety device are preferably connected to the same electric power supply so that an interruption of this power supply simultaneously triggers the safety device and the disengaging system. This results in a combined effect due to a lower tension of the blade to be stopped.

• La ventouse 65 est un exemple d'actionneur électromagnétique. D'autres réalisations de cet actionneur peuvent être envisagée. En particulier, ou peut prévoir un moteur et un doigt solidaire de celui-ci en tant qu'organe de retenue. Une partie de la tige d'actionnement est agencée de manière à recevoir une extrémité du doigt, par exemple avec une gorge. Alimenté électriquement, le couple du moteur maintient le doigt dans la gorge. En l'absence de courant, la tige d'actionnement est rappelée par l'organe élastique et ce mouvement de rappel fait sortir le doigt hors de la gorge. Le moteur peut agir de manière inverse en rappelant le doigt dans la gorge, à l'encontre de l'organe de rappel élastique. Le moteur agit ainsi également en tant que système de réarmement.
• Le ressort 55 peut être remplacé par un ou plusieurs organes de rappel élastique de type différent. Par exemple, on peut prévoir, en remplacement ou en complément du ressort 55, un couple de ressorts de torsion agencés chacun entre un arbre d'entraînement 23 respectif et le châssis 17.
• La transmission bidirectionnelle 41 peut comprendre une crémaillère et un couple de pignons solidaires des arbres d'entraînement 23. Ces pignons viennent en prise chacun sur cette crémaillère ou un premier sur cette crémaillère et l'autre sur le premier. Plus généralement, les mouvements rotatifs des arbres d'entraînement 23 peuvent être mutuellement synchronisés, par exemple par engrenage ou pignon crémaillère.
• Le dispositif de sécurité peut être équipé d'un ou plusieurs capteurs de position disposé de manière à déterminer si la tige d'actionnement 37 se trouve dans sa première position. Une électronique de commande peut être configurée de manière à interdire la mise en marche d'une scie tant que la tige d'actionnement 37 ne se trouve pas dans sa première position. Le capteur de position peut être complété par une détection du maintien de l'engagement de la tige d'actionnement 37 par l'organe de retenue. On peut également détecter la position de la tige 77 du vérin 69 et conditionner le démarrage de la machine au fait que la tige 77 soit rétractée.
• Les premiers paliers 25 peuvent être de types différents l'un de l'autre. Par exemple l'un des premiers paliers 25 est de type général palier lisse tandis que l'autre de ces paliers est du type général à éléments roulants. Selon un autre exemple, l'un des premiers paliers 25 est de type à bille tandis que l'autre est de type à aiguilles. Il en est de même des seconds paliers 39.
• On a décrit un organe de rappel élastique ici sous la forme d'un ressort 55 en appui sur une grande face de la première traverse intermédiaire 21-3 et travaillant en compression. En remplacement ou en complément, l'organe de rappel élastique peut prendre la forme d'un ressort hélicoïdal intercalé entre la portion d'épaulement 57 et une grande face de la seconde traverse 21-4 et travaillant en traction. On peut également utiliser des ressorts de type différent, en particulier des ressorts à gaz.

The proposed device is not limited to the embodiment described further, but encompasses all the variants that a person skilled in the art may envision. Specifically :

• The suction cup 65 is an example of an electromagnetic actuator. Other embodiments of this actuator can be envisaged. In particular, or may provide a motor and a finger secured thereto as a retaining member. Part of the actuating rod is arranged so as to receive one end of the finger, for example with a groove. Electrically powered, the torque of the motor keeps the finger in the throat. In the absence of current, the actuating rod is returned by the elastic member and this return movement causes the finger to come out of the groove. The motor can act in the opposite way by returning the finger in the groove, against the elastic return member. The motor thus also acts as a rearming system.
• The spring 55 can be replaced by one or more elastic return members of a different type. For example, it is possible to provide, replacing or in addition to the spring 55, a pair of torsion springs each arranged between a respective drive shaft 23 and the frame 17.
• The bidirectional transmission 41 may include a rack and a pair of pinions integral with the drive shafts 23. These pinions each engage this rack or a first on this rack and the other on the first. More generally, the rotary movements of the drive shafts 23 can be mutually synchronized, for example by gear or rack pinion.
• The safety device may be equipped with one or more position sensors arranged so as to determine whether the actuating rod 37 is in its first position. Control electronics can be configured so as to prevent the starting of a saw as long as the actuating rod 37 is not in its first position. The position sensor can be supplemented by a detection of the maintenance of the engagement of the actuating rod 37 by the retaining member. It is also possible to detect the position of the rod 77 of the jack 69 and to condition the starting of the machine to the fact that the rod 77 is retracted.
• The first bearings 25 can be of different types from one another. For example, one of the first bearings 25 is of the general plain bearing type while the other of these bearings is of the general type with rolling elements. According to another example, one of the first bearings 25 is of the ball type while the other is of the needle type. The same applies to the second stages 39.
• An elastic return member has been described here in the form of a spring 55 bearing on a large face of the first intermediate cross member 21-3 and working in compression. As a replacement or in addition, the elastic return member can take the form of a helical spring interposed between the shoulder portion 57 and a large face of the second cross member 21-4 and working in tension. It is also possible to use springs of a different type, in particular gas springs.

Claims (15)

1. Safety device for a bandsaw (1), said safety device being of the type comprising a frame (17) and a pair of jaws (13) rotatably mounted on the frame (17), this frame (17) being suitable for being mounted on a framework (3) of the bandsaw (1) with the jaws (3) disposed on either side of a blade (5) of this bandsaw (1), the device further comprising an actuating rod (37) slidably mounted on the frame (17), and at least one elastic return member (55) constraining the sliding of the actuating rod (37), whereas a two-way transmission (41) transforms the sliding of the actuating rod (37) into a rotation of the pair of jaws (13), characterised in that the device further comprises an electromagnetic actuator (65) rigidly connected to the frame (17) and a retaining member rigidly connected to the electromagnetic actuator (65), in that the actuating rod (37) is arranged with a receiving portion (63) which is capable of engaging with the retaining member when the actuating rod (37) is in a first position relative to the frame (17), the two-way transmission (41) being arranged so that the jaws (13) are distant from one another when the actuating rod (37) is in this first relative position, and in that the electromagnetic actuator (65) maintains the engagement between the retaining member and the receiving portion (63) when it is supplied with current.
2. Device according to claim 1, wherein the electromagnetic actuator (65) releases the engagement between the retaining member and the receiving portion (63) when it is no longer supplied with current.
3. Device according to one of claims 1 and 2, wherein the elastic return member (55) is capable of displacing the actuating rod (37) from the first relative position thereof to a second relative position, and the two-way transmission (41) is arranged so that the jaws (13) are close to one another when the actuating rod (37) is in this second relative position.
4. Device according to one of the preceding claims, wherein the two-way transmission (41) includes at least one leverage arrangement, and this leverage arrangement is adapted to act on each of the jaws (13).
5. Device according to claim 4, wherein the leverage arrangement includes a pair of connecting rod (43) and crank (51) pairings, each crank (51) being rigidly connected to a respective jaw (13) whereas each connecting rod (43) connects a respective crank (51) to the actuating rod (37).
6. Device according to one of the preceding claims, wherein the electromagnetic actuator (65) comprises a lock (65), one magnet whereof forms the retaining member, and the receiving portion (63) of the actuating rod (37) is in the form of a backplate (63), the shape whereof corresponds to the magnet.
7. Device according to one of the preceding claims further comprising an arming mechanism (67) capable of displacing the actuating rod (37) from the second relative position to the first relative position, against the elastic return member (55).
8. Device according to claim 7, wherein the arming mechanism (67) comprises a hinged arm (79)to the frame (17), the hinged arm (79) being capable of being displaced from a position wherein it is separate from the actuating rod (37) to a position wherein it cooperates with at least a part of this actuating rod (37).
9. Device according to claim 8, wherein the arming mechanism (67) comprises an electric cylinder (69) with a body (71) and a rod (77), the cylinder body (71) is fastened to the frame (17) whereas the rod (77) is hinged to said arm (79).
10. Device according to one of the preceding claims, wherein the jaws (13, 130, 230) comprise an active part (134, 234), at least one part whereof comes into contact with the blade (5) of the saw when the actuating rod (37) is located in the second relative position thereof and the active part (134, 234) of these jaws (13, 130, 230) is devoid of teeth.
11. Device according to claim 10, wherein the jaws (13, 130, 230) have a profile arranged such that said part of the active part (134, 234) of these jaws (13, 130, 230) is located further ahead relative to a virtual line (138) connecting the centres of rotation of the jaws (13) to one another.
12. Device according to one of the preceding claims, wherein each of the jaws (13, 130) has a body (131) and a grip jaw (132), the grip jaw being rotatably mounted on the body.
13. Device according to claim 12, wherein each grip jaw (132) carries an active surface that is planar as a whole.
14. Bandsaw (1) comprising a framework (3) and a blade (5), the saw further comprising a safety device of the type comprising a frame (17) and a pair of jaws (13) rotatably mounted on the frame (17), this frame (17) being mounted on the framework (3) with the jaws (3) disposed on either side of the blade (5), the device further comprising an actuating rod (37) slidably mounted on the frame (17), and at least one elastic return member (55) constraining the sliding of the actuating rod (37), whereas a two-way transmission (41) transforms the sliding of the actuating rod (37) into a rotation of the pair of jaws (13), characterised in that the device further comprises an electromagnetic actuator (65) rigidly connected to the frame (17) and a retaining member rigidly connected to the electromagnetic actuator (65), in that the actuating rod (37) is arranged with a receiving portion (63) which is capable of engaging with the retaining member when the actuating rod (37) is in a first position relative to the frame (17), the two-way transmission (41) being arranged so that the jaws (13) are distant from one another when the actuating rod (37) is in this first relative position, and in that the electromagnetic actuator (65) maintains the engagement between the retaining member and the receiving portion (63) as long as it is supplied with current.
15. Saw according to claim 14, wherein the blade (5) is mounted on the framework (3) via a pair of flywheels (7; 9), the saw further comprising a disengaging system (93) via which at least one of these flywheels (7; 9) is mounted on the framework (3), and the disengaging system (93) is actuated by a second electromagnetic actuator (103) arranged so as to trigger said system in the absence of the feed current.

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