WO1997031412A1

WO1997031412A1 - Fixing device for detachably fastening an electric apparatus to a bar

Info

Publication number: WO1997031412A1
Application number: PCT/SE1997/000282
Authority: WO
Inventors: Lennart Sjöstedt; Patrik Söderlund; Richard Lindahl
Original assignee: Enpece Sigma Ab
Priority date: 1996-02-20
Filing date: 1997-02-20
Publication date: 1997-08-28
Also published as: PL328456A1; SE9600626L; SE9600626D0; EP0882319A1; SE509945C2

Abstract

A fixing device for detachably fastening an electric apparatus to a bar. The fixing device (1) is adapted to embrace one edge (43) of the bar (42) and comprises a spring portion (2); a fixing portion (14) which is arranged in front of the spring portion (2) and embraces said one edge (43) when the electric apparatus is fastened to the bar (42); and a rear end (17) projecting from the casing of the electric apparatus when the fixing device (1) is mounted thereon. The fixing device (1) is made in one piece and comprises a rear portion (3) including the rear end (17), and a front portion (4), between which the spring portion (2) is arranged. The rear portion (3) comprises a first engaging portion (15), for engagement in a recess (49) in the casing (41). The front portion (4) comprises a second engaging portion (12), which engages in a recess (47) in the casing (41). The spring portion (2) is biased between the first engaging portion (15) and the second engaging portion (12) when these are in engagement with the casing (41), the fixing device (1) being in a locked position. When the rear portion (3) is pressed down, the fixing device (1) is released from the locked position by the first engaging portion (15) being disengaged from the recess (49) and the spring portion (2) expanding backwards and pushing the first engaging portion (15) past the recess (49).

Description

FIXING DEVICE FOR DETACHABLY FASTENING AN ELECTRIC

APPARATUS TO A BAR

Field of the Invention

The present invention relates to a fixing device for detachably fastening an electric apparatus to a bar. The invention also concerns an electric apparatus which is adapted to utilise such a fixing device. Background Art

It is common in so-called switch cabinets or the like to arrange electric apparatus, such as connecting means, timing circuits, control units etc., adjacent to each other on a common holding bar having a standardised section. Electric connecting means include e.g. safety switches, the function of which is to quickly interrupt the current in an electric circuit which is connected to the switch when a current, which in some respect is too high, arises in the circuit. Use is often made of several circuits in close connection with each other. It is then desirable to arrange in said manner a plurality of electric apparatus together since a common phase bar can then be utilised in a simple manner to simplify the connection. Moreover, some electric apparatus can advantageously be interconnected into a block. As an example, it may be mentioned that when using safety switches in three-phase systems, blocks of three switches are used. With a view to facilitating the arrangement of a plurality of electric apparatus together, use is made of said holding bar, to which the apparatus are fastened in a row, and a common phase bar, which is connected to each of the apparatus when all the apparatus have been mounted on the holding bar. The holding bar usually has a simple section comprising two edges, which are embraced by holding means arranged in the apparatus. The holding bar may be, for example, a so-called DIN bar, and the DIN bar often has a cross-section in the form of a U with outwardly bent edges adjacent to each leg. To fix the apparatus to the holding bar, a fixing device is assigned to the apparatus to make it easy to fix the apparatus to the holding bar and remove it there¬ from. Today a number of fixing devices, or locking means, are available which are used in connection with the fix¬ ing of electric apparatus in the form of safety switches to a bar. The publication DE 35 13 762 discloses a fixing device, which uses resilience to fix the switch to the bar. The fixing device is arranged on the same side of the switch as the phase bar. One end of the fixing device protrudes from the switch and has a recess. The switch is released from the bar by the user grasping the protruding end of the fixing device and pulling it further outwards from the switch. However, this is a great drawback since the end is accessible only via a small space between the phase bar and the next row of switches. Thus, it is necessary to insert a long and narrow tool, such as a screwdriver, between the phase bar and the neighbouring row of switches, down into the recess, and then move the end of the fixing device outwards from the switch by using the lever principle against the phase bar (that part of the phase bar which is insulated). This can only be performed with great difficulty. A further known fixing device is disclosed in the publication US 5,297,002. The shown fixing device is pivotally mounted in the casing of the switch and is re¬ leased by being pivoted outwards from the switch. This does not facilitate the release of the fixing device, but also this fixing device suffers from the drawback that a large space for releasing the fixing device is necessary. There is thus a need of a fixing device for safety switches, and other electric apparatus that are mounted correspondingly, which eliminates the above-men- tioned drawbacks of the prior-art technique. Objects of the Invention

One object of the present invention is to provide a fixing device for fastening an electric apparatus to a bar, said fixing device permitting release without requiring a large space which most of the time is not accessible.

A further object of the present invention is to pro¬ vide an electric apparatus which comprises the above-men¬ tioned fixing device and utilises all the excellent pro- perties and functions thereof. Summary of the Invention

According to the invention, a fixing device has therefore been provided for detachably fastening an elec¬ tric apparatus to a holding bar as defined in claim 1. The design of the fixing device permits very smooth and easy release thereof, and thus of the entire electric apparatus, from the bar, since only a very light pressure need be exerted on the protruding rear end of the elec¬ tric apparatus without any considerable accuracy, in con- trast to prior-art fixing devices which all require a pressure being exerted outwards from the switch in the releasing operation.

According to a preferred embodiment of the fixing device as defined in claim 4, the inventive fixing device comprises side portions, or side walls, which serve to yield rigidity such that any undesired lateral movement of the fixing device is prevented once this has been mounted. According to claim 5, the side portions comprise driving lugs which are positioned adjacent to or abut on the edge of the bar and define the position of the fixing device when the electric apparatus is mounted on a bar. This manner of achieving rigidity while the spring func¬ tion as defined in claim 3 is maintained is not to be found in e.g. the fixing device according to the publica- tion US 5,297,002, which uses a mechanism that does not afford good stability since it does not have sufficient rigidity. Since the present invention permits excellent stability, it may advantageously be used to group a plu¬ rality of electric apparatus together in blocks, as men¬ tioned before, only one fixing device being required for each block, or grouping, in order to achieve a stable fixing to the bar, in contrast to the use of e.g. the above-mentioned fixing device of US 5,297,002 for group¬ ing electric apparatus, in which case it is not suffi¬ cient to have only one fixing device, but two or more are necessary to afford any stability at all. Besides, the driving lugs serve, together with the abutment surfaces and the recesses, to embrace laterally projecting lateral lugs, which are defined in claim 6 and are positioned adjacent to the front portion, which makes the rigid side portions entrain the spring portion to prevent this from being damaged or deformed if the fixing device, after being released, is moved backwards out of the electric apparatus.

With a view to facilitating the pressing down of the rear part of the fixing device during the releasing operation, each of the side portions has, according to claim 4, been provided with a hinge portion, or connect¬ ing portion, the rear portion of the fixing device being displaceable in a direction directly opposite to the engaging direction of the first engaging portion, or locking lug, and striving to return to its position in the longitudinal direction of the fixing device.

According to a further, advantageous embodiment of the invention as defined in claim 8, the fixing device is made in one piece. This confers a number of advan- tages, for instance that production and mounting will be considerably easier and that the cost will be low.

According to one more embodiment as defined in claim 7, the fixing device is made of a plastic material, which results in a combination of, inter alia, low friction and excellent rigidity.

According to the above-mentioned embodiments, a fix¬ ing device is thus provided for electric apparatus, which obviates the above-described and also further problems with prior-art fixing devices.

According to claims 8-11, an electric apparatus is also provided, which comprises the above-mentioned fix- ing device and utilises all the excellent properties and functions thereof. Brief Description of the Drawings

The invention will now be described in more detail with reference to the accompanying drawings, in which: Fig. 1 is a schematic perspective view of a prefer¬ red embodiment of the inventive fixing device;

Fig. 2 is a schematic side view of the fixing device in Fig. 1 with the side walls cut away;

Fig. 3 illustrates schematically a side wall of the fixing device;

Fig. 4 is a schematic perspective view of safety switches with the fixing device, mounted on a holding bar;

Fig. 5 is a schematic side view of a safety switch; Fig. 6 is a schematic side view of a safety switch with a mounted fixing device and a connected phase bar. Description of a Preferred Embodiment

Let us assume in the following specification of a preferred embodiment of the apparatus according to the invention, for the purpose of exemplification, that the electric apparatus is a safety switch.

As will be evident below, the preferred embodiment is made up in such a manner that it combines in a unique fashion several desirable properties and functions, among them the following.

The fixing device comprises a snap-lock function, which makes it possible, for instance, to easily attach a switch to a bar, in contrast to, for instance, the fixing device according to US 5,297,002, which certainly, theo- retically seen, has a snap-lock function, but in practice can be attached in this manner merely with great diffi¬ culty. This is due to the fact that at the same time the resilient element guarantees on its own the fixing to the bar and therefore must be made considerably more rigid than the corresponding element in the inventive fixing device. Moreover, the fixing device can, of course, be fastened after the switch has been mounted on the bar.

The fixing device also permits displacement of the entire switch transversely of the bar during removal, which means that the phase bar connected to all switches need not be released from the other switches when an indivi- dual switch is to be replaced; the fixing device accord¬ ing to e.g. DE 35 15 762 does not have this property. Since the fixing device is a separate part with good rigidity, a single fixing device can be used for an en¬ tire group of switches, in which case the fixing device is mounted on one of the switches in the group. The re¬ lease and removal of an entire group will thus be as simple as for an individual switch. Besides, it should be pointed out that since the fixing device is made in one plastic piece, the manufacture can be effected in a sim- pie manner and at a low cost.

A preferred embodiment of a fixing device 1 accord¬ ing to the invention is made in one piece and is prefer¬ ably made of plastic. A central portion of the fixing device, or the locking means, 1 is a spring portion 2, which is arranged between a rear portion 3 and a front portion 4, see Fig. 1. Moreover, the locking means 1 comprises side portions or side walls 5, 6. Each of the side walls 5, 6 is elongate and has a rear side wall por¬ tion 7, 8 which is attached to the rear portion 3, and a front side wall portion 9, 10, which is free. The side wall portions 7, 9 and 8, 10, respectively, are intercon¬ nected via a connecting portion 11.

The spring portion 2 is wave-shaped so as to be elastically compressible in the longitudinal direction of the locking means 1.

The front portion 4 comprises an engaging portion 12, which also forms the front end of the locking means 1. The front portion also has a stop portion in the form of a protruding stop lug 13 and a holding means in the form of a fixing portion 14, see Fig. 2.

The rear portion 3 has an engaging portion, which in this preferred embodiment is a projection, or a locking lug, 15 and an operating recess 16, and comprises the rear end 17 of the locking means 1.

Each of this side walls 5, 6 further has, in its front portion 9, 10, a recessed portion 18, 19 which is defined by an abutment surface 20, 21 in its rear end and a driving lug 22, 23 in its front end.

For easier understanding of the design of the fixing device 1 now follows a specification of one embodiment of a safety switch according to the invention, which is de- signed to use the inventive fixing device. The safety switch 40 has a casing 41, which is designed to be mount¬ ed on a holding bar 42, see Fig. 4. The holding bar is a DIN bar in the shape of a U with outwardly angled legs. The bar 42 has two edges 43, 44, which the casing 41 and the locking means 1, respectively, embrace. The casing 41 is provided with a fixing portion 45 having an engaging recess 46, in which one edge 43 or 44 engages when the switch 40 is mounted on the bar 42, see Fig. 5. Further¬ more, the casing has a recess 47, which is adapted to receive the engaging portion 12 of the front portion 4 of the locking means 1, a supporting projection 48, on which the front portion 4 rests when the locking means is mounted, an engaging portion, which in this preferred embodiment is a recess, 49 for receiving the engaging portion 15 of the fixing device and a displacing recess 50 which permits displacement of the switch 40 trans¬ versely of the bar 42 without any preceding raising of the switch 40. The casing 41 also comprises a locking sleeve 51. * The switch 40 can be mounted on the bar 42 in two different ways. The first alternative will be described below. The front side wall portions 9, 10 of the fixing device are forced towards each other so as to come into abutment against the spring portion 2 and the front por¬ tion 4 and are retained in this manner while the locking means 1 is inserted into the locking sleeve 51 and the front end of the locking means 1 is inserted into the recess 47. When the front end is in engagement with the recess 47, a force is applied to the rear end 17 of the locking means such that the spring portion 2 is compress¬ ed to such an extent that the engaging portion 15 of the locking means 1 can be received in the recess 49 of the casing 41. Thus, the locking means is in a first locked position, in which it is clamped between the recesses 47 and 49 or, in other words, between its engaging portions 12 and 15. A snap-lock function can now be used during mounting on the bar 42.

The switch is now easily ountable on the holding bar 42. The mounting takes place by making the fixing portion 45 embrace one edge 44 of the bar, whereupon that side of the switch on which the locking means 1 is arranged is pressed downwards against the bar 42. During this movement, the spring portion 42 is compressed fur¬ ther in the direction of the rear portion 3 of the lock¬ ing means, while the fixing portion 14 passes the edge 43 of the bar and, while passing, is moved away by the same, and expands again when the fixing portion 14 has passed the edge 43. This procedure implies in other words that the switch is snapped onto the bar. As a result, the fix¬ ing portion 14 embraces the edge 43 of the bar and the driving lugs 22, 23 are positioned adjacent to or abut against the bar and fix the position of the locking means. The locking means 1 is now in a locked position. The second alternative for mounting of the switch implies that first the locking means is inserted into the switch such that the engaging portion, or the lug, 12 is located in its rear position adjacent to an abutment sur¬ face 54 in the casing 41, the locking means 1 being in a released position, and then the switch is positioned of the bar 42, one edge 44 of the bar being in the engaging recess 46, and then the locking means 1 is clamped in the casing 41 in the same manner as in the first alternative. This alternative means that the snap-lock function is not used. Instead the displaceability transversely of the bar can be used in this manner also when mounting the switch on the bar. This displaceability will be described in more detail below.

Once the switch is mounted on the bar with the lock- ing means in its locked position, it is stably fixed even if an attempt is made to release the switch in a manner other than that described below since the side portions 5, 6 give rigidity without the spring portion 2 being loaded. A phase bar 60 is connected to a contact means 52 on that side of the switch 40 where the locking means 1 is arranged, see Fig. 6.

The releasing of the locking means 1 in order to detach the switch is a considerably simpler operation than the releasing of one of the prior-art fixing devices. It is only necessary to insert a tool in the operating recess 16 of the locking means 1 and press it slightly downwards. This operation does not require any particular accuracy. In such pressing down, the lug 15 is disengaged from the recess 49, and the spring portion 2 expands backwards. This results in the lug 15 being moved past the recess 49. The locking means is now in the re¬ leased position where it does not exert any holding force on the bar 42. It is instead displaceable backwards, i.e. out from the switch 40, along the distance which is de¬ fined by the front position of the lug 12 at the wall 53 of the recess 47 and the rear position of the lug 12 at the abutment surface 54 in the casing 41. This displace¬ ment out from the switch means that the driving lugs 22, 23 engage the lateral lugs 27, 28 of the spring portion 2 and entrain the spring portion 2 outwards, the rigidity of the side portions 5, 6 causing the spring portion 2 not to be loaded when the locking means is pulled out¬ wards. Thus, also the entire switch 40 is displaceable transversely of the bar 42 by a combination of the dis¬ placeability of the locking means and the space arranged for the edge 44 between the engaging recess 46 and an angled short side surface 55 of the projection 48.

The pressing down of the locking means 1, or more precisely the rear portion 3 of the locking means 1, is possible owing to the rear portion 7 (8) and the front portion 9 (10) of the side wall 5 ( 6) being intercon¬ nected via the hinge portion 11, which has a suitable flexural rigidity to permit bending under the action of a suitably great force, and the spring portion 2 being bendable and in this direction serving as a leaf spring, and when the action ceases, the rear portion 3 of the locking means 1 takes its position in the longitudinal direction of the locking means 1. An arrow-shaped recess 26 in each side wall 5 <6) forms a distance between the rear portion 7 (8 ) and the front portion 9 ( 10) of the side wall 5 ( 6), which permits sufficient deflection to permit release of the lug 15, but at the same time limits the deflection in order to spare the hinge portion 11.

The fixing portion 14 of the locking means 1 has an edge, which is directed towards the bar 42 and is angled to facilitate the movement past the edge 43 of the bar 42.

The inventive fixing device combines a number of properties which are each to be found in prior-art fixing devices, but are not combined in one and the same device. In addition, the present fixing device has completely new and very advantageous properties. These properties will now be summarised in order to further illustrate the many unique advantages of the invention.

No prior-art fixing device is releasable in the sim- pie manner as described above, i.e. by pressing only the part of the locking means projecting from the switch slightly downwards without any great accuracy. In contrast to prior-art fixing devices, the fixing device according to the present invention is easily mountable in the casing afterwards, i.e. after assembly of the casing of the actual switch, or the electric appa- ratus. This confers at least three obvious advantages, viz. that the mounting is simplified, that it is possible to select at what stage the locking means is to be mount¬ ed in the casing and, besides, that both material and mounting and dismounting time when handling blocks con- taining a plurality of switches are saved, only one fix¬ ing device being required for each block.

The fact that the fixing device besides is made in one piece confers obvious advantages.

Moreover, the fixing device according to the inven- tion makes it possible to snap the switch onto the hold¬ ing bar, if the fixing device is mounted and clamped in the switch before mounting of the switch on the bar. The fixing device also creates opportunities for an electric apparatus which is displaceable transversely of the bar, which makes dismounting much easier.

Besides, owing to the rigid side portions, the elec¬ tric apparatus mounted on the bar is stably fixed and can be broken away only if the spring is released. The side portions also protect the spring and spare it from being damaged.

Alternative Embodiments

It goes without saying that several modifications of the inventive apparatus are possible within the scope of the invention. Some examples will be mentioned below. The fixing device can, of course, be used for all types of electric apparatus which are intended to be fastened to a bar and not only for the electric apparatus described above.

Besides, the use of the fixing device is in no way restricted to bars of the appearance described above. On the contrary, ..various kinds of bars may be involved when using the fixing device within the scope of the appended claims.

Moreover, other materials than plastic can of course be used as long as they satisfy the requirements for, inter alia, rigidity and resilience.

The manufacture of the fixing device in one piece is, of course, an advantage but no necessity for achiev¬ ing the purposes of the invention. Thus, various parts of the fixing device can be manufactured separately without their positive properties in terms of function being lost.

The inventive fixing device can be designed without side portions, or side walls, in which case the function still remains. However, a design without side portions causes certain drawbacks, such as the rigidity being lost.

The first engaging portion of the fixing device and the corresponding engaging portion of the casing, which in the described embodiment are a projection and a recess, respectively, could have the reversed design, i.e. the engaging portion of the casing could be a pro¬ jection and the first engaging portion of the fixing device could be a recess. The same applies to the second engaging portion of the fixing device and its corre- sponding engaging portion in the casing. The described variant, however, is preferred.

The design of the spring portion of the fixing device is in no way restricted to that illustrated in the accompanying drawings, but other designs are possible as long as they satisfy the functionality requirements of the invention.

Claims

1. A fixing device for detachably fastening an elec- trie apparatus to a bar; the fixing device (1) being adapted to embrace one edge (43) of the bar (42) and com¬ prising a spring portion (2); a fixing portion (14) which is arranged in the vicinity of and in front of the spring portion (2) and which is adapted to embrace said one edge (43 ) when the electric apparatus is fastened to the bar (42); and a rear end (17) projecting from the casing of the electric apparatus when the fixing device (1) is mounted thereon, c h a r a c t e r i s e d in that the fixing device ( 1 ) is made in one piece and comprises a rear portion (3) including the rear end (17), and a front portion (4) , between which the spring portion (2) is arranged; that the rear portion (3) comprises a first engaging portion (15), which is adapted to engage an en¬ gaging portion (49) in the casing (41) of the electric apparatus; that the front portion (4) comprises a second engaging portion (12), which is adapted to engage in a recess (47) in the casing (41) of the electric apparatus; that the spring portion (2) is biased between the first engaging portion (15) and the second engaging portion ( 12 ) when these are in engagement with the engaging por¬ tion (49) and the recess (47), respectively, in the cas¬ ing (41) of the electric apparatus, the fixing device (1) being in a locked position; that the rear portion (3) of the fixing device ( 1 ) , for releasing the fixing device (1) from the locked position, is displaceable in a direc¬ tion directly opposite to the engaging direction of the first engaging portion (15) so as to permit sufficient displacement of the first engaging portion (15) to be released from the engaging portion (49 ) of the casing (41), and that the spring portion (2) is adapted, during the releasing operation, to expand backwards and push the first engaging portion (15) past the engaging portion (49) of the casing (41).

2. A fixing device as claimed in claim 1, c h a r ¬ a c t e r i s e d in that, during the releasing opera- tion, the engaging portion (14) disengages the bar (42) and the fixing device (1) is put in a released position, and that the fixing device ( 1 ) is displaceable in the released position to permit displacement of the entire electric apparatus transversely of the bar (42) .

3. A fixing device as claimed in claim 1 or 2, c h a r a c t e r i s e d in that the engaging portion (14) is connected to the front end of the spring portion (2); and that, when the fixing device (1) is in its lock¬ ed position and the electric apparatus is being fixed to the bar (42), the spring portion (2) is adapted to be compressed backwards as the fixing portion ( 14) passes and, while passing, is moved away by the edge (43) of the bar (42) and again to expand when the fixing portion (14) has passed the edge (43), such that the fixing portion (14) embraces the edge (43), the electric apparatus being fixed to the bar (42) .

4. A fixing device as claimed in any one of claims 1-3, c h a r a c t e r i s e d in that side walls (5, 6), each comprising a rear side wall portion (7, 8) connected to the rear portion (3) of the fixing device (1 ) , and a front side wall portion (9, 10) connected to the rear side wall portion (7, 8) via a connecting portion (11).

5. A fixing device as claimed in any one of claims 1-4, c h a r a c t e r i s e d in that driving lugs (22, 23) are arranged at the front end of the side walls (5, 6) and are located adjacent to or abuts on the bar (42 ) and define the position when the electric apparatus is fastened to the bar (42) by means of the fixing device

(1).

6. A fixing device as claimed in any one of claims 1-5, c h a r a c t e r i s e d in that the front portion (4) of the. fixing device (1) comprises laterally project- ing lateral lugs (27, 28), with which the driving lugs (22, 23) engage and which they pull along when the fix¬ ing device ( 1 ) is being pulled outwards from the electric apparatus.

7. A fixing device as claimed in any one of claims 1-6, c h a r a c t e r i s e d in that the fixing device (1) is made of a plastic material.

8. An electric apparatus which is adapted to be detachably fastened to a bar, comprising a fixing device (1), which is adapted to embrace one edge (43) of the bar (42) and which comprises a spring portion (2), a fixing portion (14) which is arranged in front of the spring portion (2) and adapted to embrace said one edge (43) when the electric apparatus is fastened to the bar (42), and a rear end (17) projecting from the casing (41) of the electric apparatus; and a recess (46) which is formed in the casing ( 1) of the electric apparatus and which is adapted to embrace the other edge (44) of the bar (42) , c h a r a c t e r i s e d in that the fixing device (1 ) is made in one piece and comprises a rear portion (3) including the rear end (17), and a front portion (4), between which the spring portion (2) is arranged; that the rear portion (3) comprises a first engaging portion (15), which is adapted to engage an engaging portion (49) in the casing (41) of the electric apparatus; that the front portion (4) comprises a second engaging portion (12), which is adapted to engage in a recess (47) in the casing (41) of the electric apparatus; that the spring portion (2) is biased between the first engaging portion (15) and the second engaging portion (12) when these are in engagement with the engaging portion (49) and the recess (47), respectively, in the casing (41) of the electric apparatus, the fixing device being in a locked position, that, for releasing the fixing device (1) from the locked position, the rear portion (3) of the fixing device (1) is displaceable in a direction directly oppo¬ site to the engaging direction of the first engaging portion (15), to permit sufficient displacement of the first engaging portion (15) to be released from the engaging portion (49) of the casing; and that, during the releasing operation, the spring portion (2) is adapted to expand backwards and push the first engaging portion (15) past the engaging portion (49) of the casing.

9. An electric apparatus as claimed in claim 8, c h a r a c t e r i s e d in that, during the releasing operation, the fixing portion (14) disengages the bar (42) and the fixing device (1 ) is put in a released position, and that the fixing device ( 1 ) is displaceable in the released position to permit displacement of the entire electric apparatus transversely of the bar (42) .

10. An electric apparatus as claimed in claim 8 or 9, c h a r a c t e r i s e d in that the casing comprises a locking sleeve ( 51 ) , in which the fixing device ( 1 ) is arranged, said locking sleeve (51) comprising the engag¬ ing portion (49) and the recess (47).

11. An electric apparatus as claimed in any one of claims 8-10, c h a r a c t e r i s e d in that the fixing device ( 1 ) is mountable and dismountable in the locking sleeve (51).