ES2298307T3 - SCREWING DEVICE FOR INSERTION PARTS FOR SCREWDRIVER. - Google Patents

Abstract

The screwdriver to turn a screw (4) through a drive shaft (2), of a power tool, has an inner sleeve (1) fitted to the drive shaft to take a screwdriver attachment (3) with an outer sleeve (6) around it with a restricted axial movement. It has a permanent magnet (7) at its leading side, with a passage opening (7a) through it extending from a profile tip (3a) of the attachment. A screw placed on the profile tip is held in place by the permanent magnet and, at the same time, the screw head (4a) is secured with the full extent of the profile tip into the inner screw head profile, and the outer sleeve is moved by the permanent magnet to bring the end surface (7b) against the surface of the screw head.

Description

Screwing device for parts screwdriver insert.

The present invention relates to a screwing device, of the type indicated in the preamble of claim 1.

In a known screwing device this type (for example US-PS-5,724,873) a shaft of drive, capable of being inserted by one end into a receiving jaw or a clamp insertion device motorized, for example an electroapretator, is provided in its other end of a receiver socket into which they are inserted, of interchangeable shape, screwdriver insert (Bits) Specifically, the drive shaft and the portions Bits ends usually have cross sections hexagonal exteriors and corresponding receiver bushes interior profiles.

In order to get the screws that they must be screwed by means of such a screwing device are automatically subject to the profiled tips of the screwdriver inserts, in a central area of the receiver cap is arranged a first permanent magnet, set to bar or disk mode, and in the front of the receiver socket a second permanent magnet is arranged annular, pierced by the profiled tip of the insert. Specifically, the arrangement is chosen in such a way that the first permanent magnet hold the screwdriver insert securely and axially firm in the receiver sleeve and that at insert the profiled tip into the inside profile of a head  screw both permanent magnets together take care that the extreme surfaces of the screw heads result attracted against the support surface of a magnetically disc conductor, linked with the second permanent magnet.

Although in this construction the screw is attracted with great magnetic force against the disk magnetically driver, full support of the profiled tip of the piece of screwdriver insert in the inner profile of the head of screw occurs only when the depth of the hole receiver in the receiver socket, the length of the piece of screwdriver insert and magnet thickness magnetically conductor are adapted to each other in such a way that the length of the profiled tip protruding from the disc corresponds exactly to the depth of the inner profile of the screw head. Without However, there are screws with the same inner profile, for example of Phillips star (PH) 2, whose heads have different height for different screw sizes, being correspondingly of different depth the inner profile of star. In addition, the internal profile of the screws presents, to cause of manufacturing tolerances, different depths and widths, and also the length of the insert pieces for screwdriver and tip profiles are subjected to certain manufacturing tolerances. However, on the device mentioned the axial position of the insert for screwdriver with respect to the bearing surface of the disc is invariable, and correspondingly also the length of the tip Outstanding profiling. This has as a consequence that, although in many cases the screw head rests against the face front of the magnetically conductive disk, the profile of the tip do not find all its surface inside the internal profile of the screw. This results in the tip profile being highly requested particularly in its songs, which is translates into relatively rapid profile wear, taking The entire screwdriver insert must be replaced. In the opposite case, although the profile of the tip is supported with all its surface in the internal profile of the screw, a slit free support between screw heads and face front of the magnetically conductive disk. Therefore, the magnetic field acting on the screw, and therefore the force of attraction, they are weakened. In addition it is not possible that thanks to a support of the screw heads against the front face of the magnetically conductive disk the screws are aligned coaxially with the axis of the insert for screwdriver. This is particularly true for screws with flat head surface, which is the type of bolts most commonly employed

To avoid these inconveniences another one is known screwing device of the type mentioned above (DE 199 07 837 A1), in which the second permanent annular magnet is fixed to the front end of an outer sleeve, provided with a thread inside and capable of being turned on a corresponding outer thread portion of the receiving or inner sleeve and of be thus adjusted axially exactly with respect to the piece of screwdriver insert. This is intended to achieve that always both the profile of the profiled tip is supported with its entire surface in the inner profile of the screw head as also, simultaneously, lean without any slits between yes the extreme surface of the screw head and the surface of support constituted in this case by the permanent annular magnet. However, such adjustments are too expensive in time. for practical applications, for example in the case of successive screwing of a plurality of screws, and by both of little use. And if it is assumed that the adjustment for a certain type of bolts, it is only done at start of screwing activity, tolerances in screws cause an inconvenience similar to that of the device screwing described above. It also turns out unfavorable than for the exchange of the insert for screwdriver it is necessary to completely unscrew the bushing outside and that in certain situations of tolerances the head screw exert pressure on the magnet, which can be translated in a break of this one.

According to the device according to the JP8229840A can move and adjust an outer sleeve coupled with a magnet, by axial displacement, with respect to the profiled tip, in order to ensure that the profiled tip of the screwdriver ideally penetrate the inner profile of screw head

DE-DM 1 784 695 is known a carrier for tool insertion tools screwing provided with movable guide bushes against The pressure of a spring. This carrier is built essentially in such a way that the screw to be screwed be guided, with its screw head, into the bushing guide. On the front face of the guide bushing a ring magnet During screw screwing it will rest on the final phase of the process, the guide bushing through its face front frontal against the surface on which the screw. The guide bushing is then retracted, counteracting a compression spring, until the head of screw lean against the surface and the process of Screwing is complete. In the initial state the dock of compression presses the guide sleeve forward, until the edge of said bushing rests against a ring arranged in the inside of the carrier and linked to the intermediate piece. If a screw is placed with the screw head on the surface front of the annular magnet, the screw will not be centered with respect to the profiled tip of the screwdriver insert, since that this is delayed with respect to the front surface of the ring magnet and the guide sleeve with the ring magnet is not backed up until the front surface of the guide bushing lean against the surface on which the screw is screwed. The screw has to be entered manually, before start of the screwing process, with its head in the guide bushing and be placed on the profiled tip of the screwdriver insert An additional alignment of the screw head relative to the profiled tip is produced only if the diameter of the screw head corresponds exactly to the diameter of the hole in the guide bushing. Even in this case, an alignment of the screw shape concentric with respect to the axis of the insert for screwdriver is secured only in head screws cylindrical, in which the cylindrical side wall of the head of Screw offers a support surface of a certain length.

A further is known from EP 1 027 959 A2 screwdriving device with magnet. This device of Screwing features a screwdriver insert  with a shaft with a larger diameter and a small diameter tip, on which a spacer sleeve provided is placed, in both bases, of two annular magnets. The transition between shaft and the tip is through a step. The length of the spacer sleeve, together with the annular magnets, is sized in such a way that when supported with its back face against the step release the profile of the screwdriver tip in such a length that, when the screw is placed, it is between the screw head and front front face of the bushing spacer a slit (g). The screw head is attracted by the ring magnet against the profiled tip of the insert for screwdriver, although axial alignment does not occur additional screw with respect to the axis of the insert for screwdriver when the screw is applied, since the head Screw does not rest with its head surface against the face front of the ring magnet. This may result in the screw remain oblique in relation to the axis of the insert for screwdriver. According to a cap variant spacer, two hoops are incorporated inside it of rubber, whose dimensions are adjusted accordingly to diameter of the shaft of the tip thanks to the rubber rings produce a tension between the circumference of the tip shaft and The spacer sleeve wrap. Thanks to this tension the distance bushing is held, in an axial position preselected, on the tip shaft. In the ideal case this position must be such that, on the one hand, the screw head is rest against the front face of the anterior annular magnet and, on the other part, said head rests with its inner profile against the Tip profile of screwdriver insert. Such a preselected position would correspond to the position that fits on the "surface screwing tool magnetic support "according to DE 199 07 837 A1. Compensation automatic between tolerances in the inner profile and in the profile outside the tip of the screwdriver is not possible. He friction caused by rubber rings on the shaft is greater that the force of attraction of the annular magnets on the head of screw. In case due to corresponding tolerances between the profiled tip and the inner profile of the screw both parts do not fully support each other, the screw can not be attracted by the force of the annular magnets towards the tip profiled to full support between both profiles.

In US 3,707,894 a device is described in which are placed concentric bushings and these are fixed, by radially arranged screws, in a position  preselected with respect to the tip of the insert for screwdriver. Between the bushings at least one cap-shaped magnet. According to a way of embodiment, the screw head penetrates a recess spherical on the front face of the inner sleeve and rests against the surface of the recess. Simultaneously, the tip Bit fits the inside profile of the screw head. The bushings are fixed in preselected position on the piece screwdriver insert, so that the tip profile of the screwdriver insert take a position fixed with respect to the inner profile of the screw head, although This does not allow automatic tolerance compensation. This device therefore corresponds, in its function, essentially to the device according to DE 199 07 837 A1.

By US-PS 3,392,767 it know devices designated as "tools magnetic, "in which essentially a magnetic material in Plate shape is conformed to a cylindrical bushing and is placed concentrically between an inner bushing and a bushing steel exterior The outer cap presents, in one of the devices, in its previous hole an internal profile for the receiving a screw - or nut - hexagonal, while the inner sleeve and magnetic intermediate layer are retraced with respect to the leading edge of the outer sleeve. A penetrating screw or nut in the inner profile is there held by the magnetic field. This device is placed on a drive device, for example a head handle of bucket keys.

According to a second embodiment according to Figs. 5 to 7, the device is placed on a piece screwdriver insert. The leading edges of the outer and inner bushings are in a plane, while the magnetic material arranged in between is something backed away from those edges. Against the edges of both bushings must rest the surface of the head of a screw and be held by the magnetic field. Inner cap, cape magnetic intermediate and outer sleeve constitute a unit fixed. On the shaft of the screwdriver insert the device is attached by means of two elastic rings, the which surrounds the shaft of the insert for screwdriver or fit into a slot in said shaft. For his outer perimeter fit into an annular recess constituted between the inner sleeve, shortened at its rear end, and a rear wall of the outer sleeve, bent at the end posterior radially inward, with an opening for its mounting on the shaft of the insert for screwdriver. This recess is, in the longitudinal direction, greater than the width of the elastic rings, making it possible a limited axial displacement of the device on the shaft of the screwdriver insert. Through this displacement is intended to compensate profile tolerances inside of the screw, as well as wear of the tip of the piece screwdriver insert, and simultaneously intended ensure direct contact between the screw head and the front edges of the inner and outer bushings. A drawback of this execution consists, as well as in the device according to US 3,707,894, that the magnetic material expected elastic develops a relatively magnetic force weak, particularly when the length of the intermediate layer Magnetic is as short as it should be if the device is intended mount on an insert for a short screwdriver, usual in commerce, with a length of 25 mm. It turns out by so doubtful that the desired function of the device is automatically positioned, by scrolling axial, in a position where both the profiled tip penetrates fully in the inner profile of the screw as well as the head surface rests against the edges of the inner and outer bushings. The achievement of the function described is also doubtful by the fact that when the screw head on the profiled tip of the workpiece screwdriver insert closed magnetic field by the poles constituted by the front edges of the bushing inside and outside cap on the front face of device. In the back of the device the field magnetic is closed through the bent base crown radially inward and the subsequent inner bushing that He leans against it. Therefore, the force of attraction acts only on its anterior face, but not in the direction of the rear shaft portion of the insert for screwdriver. In practice this means that the head of screw will rest with its inner profile against the tip profiled of the screwdriver insert, and simultaneously with its head surface against the edges of the poles, only when the device is supported with the edge bottom against the elastic ring fixed by pressure on the shaft of screwdriver and separation insert resulting between the edges of the poles and the surface of the head corresponds exactly to the penetration depth of the profiled tip on the inner profile of the screw head. In all other positions, the surface of the head against the edges of the poles, and the profiled tip of the screwdriver insert will not penetrate until full support on the inner profile of the insert for screwdriver, or the reverse position will be given in between the edges of the poles and the surface of the head persist a air slit An automatic adjustment for simultaneous support of Profiles and head surface does not seem possible. He operation therefore corresponds essentially to that of device according to DE 199 07 837 A1. The necessary short length constructive also translates into a very short guided device on the hexagonal shaft of the insert for screwdriver by the remaining portion of the bushing inside, as usual screwdriver insert parts in commerce they present the hexagonal shaft only in the area of fixation, while towards the profiled tip they are turned to a circular cross section. Fig. 5 shows quite a lot Accuracy of dimensional relationships at 1: 1 scale. But nevertheless, good guidance is a precondition for the device to place and move coaxially to the axis of the insert for screwdriver and a coaxial alignment of the screw applied. Even screwdriver insert parts longer, being the next usual length in the trade of 50 mm, are turned towards the profiled tip in a long section at  circular cross section, and specifically to different diameters, depending on the size of the profiled tip. Case of the use of a device according to the principle described a suitable device should be offered for each diameter. It is also very insecure if the device can be maintained subject, in the axial position chosen on the shaft of the workpiece screwdriver insert, by the effect of imprisonment of the elastic rings, when the insert is used in electroapretadores, since in this case they act on the piece of considerable insertion vibrations. Also points to this point weak the fact that in the subsequent Patent 3,707,894 thereof Applicant is scheduled to fix such a device by radially arranged screws. However, if It aims to achieve, according to Patent 3,392,767, a secure fixation by the fact that the elastic rings fit into a groove in the shaft of the screwdriver insert is precise insert parts must be offered in a corresponding special execution, and the usual insert parts in the Commerce are not usable. A further inconvenience consists in that, because of the short shaft, the device can be fixed in a drive device, for example the receiving jaw of an electroapretator, without any impediment to the limit against the  back base. However, then an adjustment is no longer possible backwards, for example by scrolling the device on the shaft of the screwdriver insert, the fixture needs to be released, and the device has to be extracted more out.

In a subsequent device according to the Patent cited the inner bushing, the magnetic bushing and the bushing  outside sit as a unit on the shaft of a long piece screwdriver insert. A coil spring in the The inside of the device rests, on the one hand, against a ring elastic, housed in a slot in the screwdriver shaft, and, on the other hand, against a ring mounted at the rear end of the inner cap. The device is located, by the dock prestressed between both rings, in a certain position with respect to the profiled tip of the insert for screwdriver. The screw is inserted into a hole in the front face of the device and leans against the edge of the inner cap In the starting position the profiled tip of the screwdriver is retracted with respect to the surface screw head, and only when the device is subjected to an axial load when applied against the screw move the bushings with the screw to such an extent that the profiled tip meshes with the inside screw profile. Dice that when the screw is applied the insert for screwdriver is often already turning - it is anyway rotation is necessary to find the gear position of the profiled tip on the inner profile of the screw head - the profiled tip and / or the inner profile in the screw head.

It is an inconvenience of the devices known that the front components continue to rotate when the device with the screw attached to its front face is supported on a surface, so that it is damaged by the further rotation of the front components.

The purpose of the present invention is to in developing a screwing device that meets the following requirements and not suffer from the inconvenience of known devices: parts of normal screwdriver insert, commercially available; immediately when the screw is applied to the device you must be achieved automatically, by the effect of the permanent magnet, both a support on the entire surface of the tip profile profiled on the inner profile of the screw head, even although the profiles have tolerances and head heights are variable, as well as a support of the extreme surface of the screw head against the front face of the device and ensure a strong adhesion of the screw to the tip profile of the screwdriver insert; should ensure that the screw attached to the device is aligned coaxially to the shaft of the screwdriver insert; when immersing screw heads on an elastic surface you must easily move the outer bushing back with the permanent magnet, with respect to the profiled tip of the screwdriver with the screw attached to it; during the screwing of embedded screws at surface level no you must continue turning the outer sleeve with the permanent magnet when the front face of the permanent magnet rests on the surface - this is intended to prevent deterioration of the surface; and finally, they should be able to easily extract the Inserts for screwdriver of the device.

The present invention provides the advantage that an exact adjustment of the outer sleeve on the inner bushing by means of a thread or screws arranged radially Thanks to the essentially free axial displacement of the outer bushing on the inner bushing, and at an arrangement and a corresponding sizing of the different parts is on the contrary, it achieves that the desired settings result from yes alone when approaching the screw heads to the front face of the screwing device.

Further advantageous features of the invention follows from the subclaims.

It will be described in more detail below. the invention by means of embodiments thereof and with relation to the attached drawings, in which:

Figs. 1 and 2 show paths seen in longitudinal section of a first embodiment of the screwing device according to the invention, in two different positions;

Figs. 3 and 4 show paths seen in section, corresponding to Figs. 1 and 2, from a second example of realization of the screwing device according to the invention;

Figs. 5 and 6 show paths seen in section, corresponding to Figs. 1 and 2, from a third example of realization of the screwing device according to the invention;

Figs. 7 and 8 show paths seen in section, corresponding to Figs. 1 and 2, from a fourth example of realization of the screwing device according to the invention;

Fig. 9 shows an elevation view of the screwing device according to Figs. 7 and 8;

Fig. 10 shows a partial section view in a modified detail with respect to Fig. 8;

Figs. 11 and 12 show paths seen in section, corresponding to Fig. 1, of a fifth and sixth example  of realization of the screwing device according to the invention;

Figs. 13 to 15 show a seventh example of embodiment of the screwing device according to the invention, in two views corresponding to Figs. 1 and 2 and in a third position, which facilitates the exchange of an insert, It can also be seen in Fig. 13a a larger scale detail of Fig. 13;

Figs. 16 to 18 illustrate an eighth example of embodiment of the screwing device according to the invention, in views corresponding to Figs. 13 to 15;

Figs. 19 and 20 illustrate a ninth example of embodiment of the screwing device according to the invention, essentially in correspondence with Figs. 13 to 15, although with another device for receiving the insert; Y

Fig. 21 illustrates a tenth example of realization of the screwing device according to the invention.

According to Figs. 1 and 2 a device screwing according to the invention comprises a receiver bushing or interior 1, made of a non-ferromagnetic material, with a hexagonal inner cross section. On the back of the an end of a drive shaft 2 is inserted, equipped with a corresponding outer cross section hexagonal, which is also fixed axially firmly in the inner sleeve 1. The front part of the inner sleeve 1 it serves to receive an insert for screwdriver 3, made of a ferromagnetic material, whose rear portion has a hexagonal outer cross section which fits in positive union, in the direction of rotation, in the inner bushing 1 and is provided, in its anterior part, with a profiled tip 3a. This presents a profile made, in this case, as a star profile, capable of being inserted in a corresponding inner star profile practiced in the 4th heads of usual 4 star screws. Alternatively it could naturally also be profiled tips with Torx profiles, or other known types for Torx screws or others. The insert 3 is axially secured, by example by means of an elastic ring 5, in the inner sleeve 1, fitting said ring into corresponding annular grooves of both sides When turning the screwing device using a motorized tightener or similar, acting on the free end of the drive portion 2, the torque exerted on the drive shaft 2 is transmitted, through the bushing inside 1, to insert 3 and, from it, to the screw Four.

On the inner bushing 1 it is guided, of axially easily movable shape, an outer sleeve 6 made of a non-ferromagnetic material, which is provided, in an anterior part that protrudes axially from the inner sleeve 1, of a permanent magnet 7 (ring magnet) inserted therein, provided with a hole 7a, and protruding axially of the inner sleeve 1. Permanent magnet 7 is preferably inserted in this way at the front end of the outer cap 6 that protrudes slightly, using a front support surface 7b, of the front face thereof, and is firmly linked with the outer sleeve 6 by stuck or otherwise. The inner cross section of the hole 7a is preferably somewhat smaller than the section outer transverse of inner bushing 1.

It is surprising both the interaction between outer sleeve 6, inner sleeve 1 with the screwdriver insert 3 inserted and the permanent magnet 7 in the situation before the screw 4 is applied to the profiled tip 3a, as well as the reaction immediately after the application of the screw occurs: the outer sleeve 6 is maintained, in a first variant embodiment, preferably by the force of the permanent magnet 7, in a preselected axial position, corresponding to Fig. 1, or adjusted to this position, respectively. In this position, the hole 7a of the permanent magnet 7 is approximately in a central area of the profiled tip 3a of the insert 3 and is preferably arranged such that simultaneously the permanent magnet 7 rests against the front end of the inner sleeve 1 or against the front end of the distance bushing 8 adjacent to said inner bushing 1, respectively. This position is occupied because, on the part of the magnetic force field of the permanent magnet 7, the solid part of the insert 3, which has the hexagonal cross-section, is more strongly attracted than the profiled tip 3a, which has a considerably section minor and is surrounded by a slit of air. However, as the insert 3 is fixed inside the inner bushing 1, the freely movable outer bushing 6 is automatically moved in the direction towards the drive shaft 2, until the permanent magnet 7 stops against the front end of the inner bushing 1 or of the spacer bushing 8. By suitable axial sizing of the inner bushing 1 and of the permanent magnet 7, whose axial length is preferably shorter than that of the profiled tip 3a, it is further achieved that the profiled tip 3a protrudes forward , in this preselected position 3, with respect to the bearing surface 7b, as much as corresponds to the penetration depth prescribed in the corresponding internal profile of the screws 4 plus a preselected tolerance measure s in Fig. 1. This measurement of tolerance s is chosen in such a way that - as long as the outer sleeve 6 occupies the preselected position, illustrated in Fig. 1 - on the one hand the profiled tip 3a can always penetrate, taking into account the different head heights of the screws provided for treatment with the device, until the support in positive connection in the inner profile of the screw heads 4a, and on the other hand, a small air gap remains between the end surfaces 4b of the screw heads 4a and the bearing surface 7b, after reaching said prescribed penetration depth. However, in reality the arrangement according to the invention has as a consequence, due to the preferably very smooth axial displacement of the outer sleeve 6, that it is automatically moved immediately from the position according to Fig. 1 to the position according to Fig. 2, as soon as between the profiled tip 3a in the inner profile of a screw head 4a. This position is preferred for magnetic reasons, since the magnetic field tends to shorten the length of the field lines. Thanks to the entry of the screw head into the magnetic field, a stronger magnetic force now acts in the direction of the profiled tip 3a than in the starting position, the outer sleeve 6 moves slightly in the direction of the profiled tip with the screw applied to it until the support surface 7b of the permanent magnet 7 stops against the end surface 4b of the screw head and firmly holds the screw. Naturally, it has been assumed that screw heads 4a or screws 4 consist of a ferromagnetic material, which is taken for granted for the purposes of the invention. Since in the position according to Fig. 2 the force of attraction of the permanent magnet 7 continues to act more strongly on the solid shaft portion of the insert 3, which rests with its entire surface on the inner sleeve 1, which on the profiled tip 3a with the screw applied thereto, that is to say that a contracting force acts between the permanent magnet 7 and the rear portion of the insert 3, this results in the outer sleeve 6 with the permanent magnet 7 and the screw head 4a attached are attracted to the penetration and stop of the profiled tip 3a of the screwdriver insert 3 in the inner profile of the screw head 4a. The attractive force of the magnetic field continues to act strongly in the direction of the shaft portion, whereby the screw 4 is held firmly on the profiled tip 3a.

The axial mobility of the outer sleeve 6 in the opposite direction, that is, axially separating from the shaft of drive 2, is itself discretionary. However, the same should be limited by the projection 6a stop against the end rear of the inner bushing 1 such that the bushing exterior 6 can be returned, even from the position advanced to the maximum, only by the effect of magnetic force of back to the preselected position according to Fig. 1. This is illustrated in Fig. 2, according to which in the full position penetration of the profiled tip 3a and with simultaneous support of the extreme surface 4b against the support surface 7b only there is still a relatively small axial separation between the rear face of inner sleeve 1 and boss 6a.

In the exemplary embodiment according to Figs. 3 and 4 equal parts of the same reference numbers have been provided.  A difference from Figs. 1 and 2 consists in this case only that the insert 3 is not held in the inner sleeve 1 for elastic ring 5, but for a second permanent magnet 9 in the form of a bar or disk. The permanent magnet 9 it is for example arranged in the base of the drive shaft 2 facing the insert, linked to said shaft by glued or otherwise and provided with a cross section exterior corresponding to the outer cross section of the drive shaft 2. In this case the force must be chosen of the second permanent magnet 9 such that, although the piece of insert 3 be safely held in the inner sleeve 1, there is no essential disturbance of the function described in relation to Figs. 1 and 2.

In the exemplary embodiment according to Figs. 5 and 6, in which again equal parts have been equipped with them  reference numbers as in Figs. 1 and 2, a 10 split outer bushing instead of single piece. The cap exterior 10 comprises an anterior portion 10a, carrying the magnet permanent 7, and a posterior portion 10b, provided with a projection 10c extending radially inward and presenting a central hole, crossed by drive shaft 2, with an inner cross section that is smaller than the section outer transverse of the inner sleeve 1, that is to say the projection 10c corresponds to projection 6a in Figs. 1 to 4. The anterior portion loa and posterior portion 10b are further equipped with fitting means 11 and 12, 14, provided for establishment of an axial connection. In the embodiment example the fitting means 11 consists of an annular groove made in the outer envelope of the anterior portion 10a, while the fitting means 12, 14 comprises at least one elastic tongue 12, extending axially forward from the rear portion 10b, and a cam 14 arranged at the front end of said tab, which extends radially inward and is provided to fit in the annular groove 11. Specifically, as illustrated in Figs. 5 and 6 are planned, on the periphery of the back portion 10b, preferably several tabs 12, arranged with separation from each other and made as a whole elastic shape In addition, it is evident that the fitting means 11 could also be provided in the rear portion 10b and the lace means 12, 14 in the anterior portion 10a. Finally, other means of fitting or snap connection could be provided other than those illustrated, and instead of the fitting means 11 and 12, 14, respectively, there could naturally also be others fasteners

As further illustrated in Figs. 5 to 10, the insert 3 and the inner sleeve 1 are axially linked to each other by a pressure joint that It comprises at least one ball 15 and an annular ribbon spring 16 applied to the circumference of the inner sleeve 1. Ball 15 it is arranged in a radial recess of the inner sleeve 1 and it is limited by the spring's elastic prestressing force annular tape 16 applied radially on the outside, but it is radially inwardly moveable to such an extent that it can penetrate a notch in the outer periphery of the hexagonal portion of insert 3 and can therefore axially fix it inside the inner sleeve 1. Alternatively, a sufficient effect of imprisonment even without the existence of a notch. The job of such pressure joints can, like that of a ring elastic 5 (Fig. 1), to be advantageous with respect to the use of a second permanent or holding magnet 9 (Fig. 3), since of this The effect of the first magnet cannot be disturbed permanent 7 and, therefore, no adaptation of both is required permanent magnets 7 and 9 with each other.

Finally, in the embodiment according to Figs. 5 and 6 it is provided that, in the axial position preselected, do not stop against the front end of the bushing interior 1 the permanent magnet 7, but a projection 10d, which protrudes radially inward and is arranged in the portion anterior 10a, as illustrated in Fig. 5.

Otherwise, the configuration and arrangement of the different parts are analogous to those of Figs. 1 to 4

The bipartite variant of the outer sleeve 10 according to Figs. 5 and 6 has the advantage that the anterior portion 10a is easily configured interchangeably. Of this mode, the previous portion 10a can be replaced, in case of need, for a previous portion that is designed for another diameter or even for another shape or size of the profiled tip 3a and may for example also comprise another permanent magnet 7 with a support surface 7b greater or less. This is advantageous. particularly because of the fact that screws with the same profile interior, for example a Pozidriv profile of size 2, have different head diameters according to the diameter of the thread. For screws with smaller head diameters are chosen conveniently an annular permanent magnet 7 having a hole smaller, so that a support surface 7b is available for the screw head 4a as large as possible. Finally the Bipartite variant facilitates the exchange of parts insert 3, since the profiled tips 3a thereof can be easily caught by hand, after separation of the anterior portion 10a, and then be removed from the cap interior 1.

The exemplary embodiment according to Figs. 7 to 9, in which equal parts are designated with the same numbers of reference than in the embodiments above described, the preselected axial position of the outer bushing 10, made in correspondence with Figs. 5 and 6, by means of a spring 17, illustrated here as a spring of helical compression The spring 17 is mounted on the shaft of drive 2 and rests between the rear end of the bushing interior 1 and the front end of the rear portion 10b of the outer bushing 10. In this way the outer bushing 10 is positioned axially at such point in the direction of the shaft of drive 2 that is the same and permanent magnet 7, housed in the front end, occupy the preselected axial position with with respect to the profiled tip 3a of the insert for screwdriver.

Figs. 7 to 9 further illustrate a variant in which the preselected axial position of the outer bushing 10 is adjustable on the inner bushing 1, without it being necessary to disassemble the screwing device or possibly equip it with another spacer bushing 8 (Fig. one). For this, the drive shaft 2 is provided, in an area protruding from the projection 10c or the rear portion 10b, respectively, of an outer thread portion on which an adjustment nut 18 provided with a corresponding internal thread is threaded, against which the rear portion 17b can be supported under the effect of the spring 17. The axial displacement of the outer sleeve 10 is in this case limited, in one direction, by the stop of the rear portion 10b against the adjusting nut 18 and, in the in the opposite direction, by the stop of the rear portion 10b against the compressed spring 17. In this way, the adjusting nut 18 can be adjusted only once, during the start-up of the screwing device, so that the profiled tip 3a used in each individual case, it protrudes forward, when the outer bushing 10 is pressed against the adjusting nut 18, precisely to the same extent with respect to the permanent magnet 7 that corresponds wave at the sum of the prescribed penetration depth and the tolerance measure s described in relation to Figs. 1 and 2. This position can then be fixed by means of a locknut 19, also threaded on the drive shaft 2.

Using the spring 17, the function according to the invention in the same manner as described above in relation to Figs. 1 and 2. For this it is only  The force must be chosen (in this case the compression force) of the spring 17 so that, on the one hand, it removes the outer bushing 10, when the device is not used screwing, always to the preselected starting position, illustrated in Fig. 7, but on the other hand, when approaching a screw head 4a, said force is weaker than the force of permanent magnet traction 7. In this way the bushing exterior 10 is always automatically displaced, just like that in the case of Figs. 1 to 6, thereby approaching a screw head 4a and under the effect of permanent magnet 7, which on the one hand the end surface 4b of the screw head 4a lean against the abutment or adhesion surface 7b and, on the other part, the profiled tip 3 will penetrate the inner profile of the screw head 4a until its support in positive union.

Otherwise, the embodiment according to Figs. 7 to 9 corresponds to the realization examples and previously described.

Fig. 10 shows a variant of the example of embodiment according to Figs. 7 to 9. The outer bushing 10 is provided, in this case, with a permanent magnet 20, in which a anterior support surface 20a is provided with a sinking in cone or shell shape. Therefore, this example of embodiment is particularly suitable for screws 21 with lenticular heads 21a, whose extreme surfaces are rounded, as opposed to extreme surfaces 4b essentially flat countersunk head screws 4 normal (for example Fig. 1). The better the support surface adapts 20th with its sinking to the sphericities of the heads of screw 21a, the better the adhesion achieved by the screws 21 to the screwing device.

Otherwise, the embodiment according to the Fig. 10 corresponds to that illustrated in Figs. 7 to 9.

Figs. 5 to 10 finally show also a variant in which the screwing device can be subject and guided with the fingers, if necessary, during a screwing process. For this it is applied on the outer bushing 10 a third bushing 22, which is supported easily rotatable between a projection in the portion anterior loa and a protrusion at the anterior end of the middle of lace 11 of the rear portion 10b.

In the embodiments according to Figs. 11 and 12 the spacer sleeve 8, illustrated in Figs. 1 to 4, It is made in one piece with the outer sleeve 6 and is made as an annular projection 6b, formed at the end anterior of said outer sleeve and radially projecting inward, which is pierced, just like the bushing spacer 8, at least partially by the profiled tip 3a. To make a mounting of the screwing device possible by placing the outer bushing 6 on the bushing inner 1, at the rear end of the outer sleeve has omitted projection 6a. Instead it is planned, in the example of embodiment according to Fig. 11, an end piece 23 by way of bucket, capable of being placed under pressure on the end rear of the outer sleeve 6. This end piece 23 presents a through hole for drive shaft 2 and can be firmly linked with the outer sleeve 6, once it has been mounted on the inner bushing 1. Alternatively, and as illustrated in the exemplary embodiment according to Fig. 12, it can be provided at the rear end of the outer sleeve 6 a snap-on bushing 24, which is provided with a through hole for drive shaft 2 and be susceptible  of being mounted analogously to the end piece 23. So In addition, the two embodiments according to Figs. 11 and 12 correspond to the embodiment according to Figs. 1 and 2, for what equal parts have been endowed with the same numbers of reference.

In the exemplary embodiment according to Figs. 13 to 15, where again equal parts have been endowed with the same reference numbers as in Figs. 1 and 2, the cap spacer 8 is replaced by a spacer piece as of spring 25, in this case a helical compression spring. This spring leans, at its rear end, against a recess practiced at the front end of the inner sleeve 1, while its anterior end is intended for support against a back support surface 7c of permanent magnet 7. In addition, the inner cap 1 is conveniently shortened at its end above in this way, with respect to Figs. 1 and 2, that the shaft hexagonal screwdriver insert 3 it stands out, on the one hand, with respect to the inner sleeve more that in the construction according to Figs. 1 to 12 but, on the other hand, still penetrate as much into inner bushing 1 as necessary for the transmission of the desired torque. Alternatively, the spring 25 could for example also be arranged between the inner bushing 1 and the projection 10 of the outer bushing 10 (Figs. 5, 6) or the projection 6b of the outer sleeve 6 (Figs. 11, 12).

The axially acting force of the spring 25 is so adapted to the magnetic force of the permanent magnet 7 that in the equilibrium position illustrated in Fig. 13 the magnet permanent 7, which bumps against the front end of the spring helical 25, and thus also the outer bushing 6 occupy the preselected axial positions described above in relationship with Figs. 1 and 2. Specifically, the spring 25 is preferably in an essentially relaxed state, so that its anterior end serves, as in Fig. 1 of the front end of spacer sleeve 8, essentially only as a stop for the permanent magnet 7. Therefore, if the tip profile 3a of the insert 3 is inserted analogously to Fig. 2, in the inner profile of the screw head 4a (Fig. 14), then the magnetic force automatically gives rise to an axial displacement of the outer sleeve 6 such that, on the one hand, the profiled tip 3 fully penetrates the internal profile of the screw head 4a and, on the other hand, the screw head 4a leans against the support surface front 7b of the permanent magnet 7. The rear support surface 7c of the permanent magnet can then, as illustrated in the Fig. 14, axially separate from the front end of the spring helical compression 25, which in this case loses its function.

An essential advantage of the spring 25 consists in that the outer sleeve 6 can move with the fingers, and by compression of the spring 25, from the position according to Fig. 13 subsequently backwards in the axial direction, that is to say in the direction towards drive shaft 2, as illustrated in Fig. 15. With this the front end of the bushing is retracted external 6 axially to such an extent, behind the tip profiled 3a of insert 3, which profiled tip 3a is almost completely uncovered or at least stands out both forward, with respect to permanent magnet 7, that the it can be easily grasped with the fingers and removed from the device. This would not be possible if the outer sleeve 6 I could only move backwards, just as in the case of Examples of embodiment according to Figs. 1 to 12, in such a measure that the profiled tip 3a protrudes from the device screwing just as much as illustrated in Fig. 1. In the moment when the pressure on the spring 25 is canceled again, it automatically returns the outer sleeve 6 to the position according to Fig. 13.

As further improvement is provided in the example according to Figs. 13 to 15, as illustrated particularly in Fig. 13a, that the axial positions of a annular groove 5a practiced in inner sleeve 1, with ring elastic inserted in it, and of notches 5b made in the hexagonal shaft of insert 3, be chosen as such so that the elastic ring 5 does not fit fully in the notches 5b, the insert 3 being inserted until it stops in the inner cap 1, otherwise. to lean partially against a oblique surface of the annular groove 5b. This way it turns out facilitated the axial extraction of the insert 3 towards in front, with your fingers, without the need to use pliers or similar. This applies even when at the ends of the wire of the elastic ring 5 there are, for manufacturing reasons, small burrs Despite this, even in this provision, the clamping force caused by elastic ring 5 large enough to hold securely during work, insert 3 inside the inner sleeve one.

For the rest, on the outer sleeve 6 can be supported, preferably rotatably, a third bushing 22, corresponding to bushing 22 in Figs. 4 to 10, or else the outer sleeve may comprise an envelope 26 of plastic.

The exemplary embodiment according to Figs. 16 a 18 corresponds to the exemplary embodiment according to Figs. 13 to 15, with the difference that the helical compression spring is missing 25. In this case, the strength of the permanent magnet 7 and the measures of the inner bushing 1 and outer bushing 6 are designed of such that the function described in relation to the above Examples of embodiment are established when the outer bushing 6 occupy, in its state of disuse, approximately one position intermediate as seen in Fig. 16. However, this intermediate position does not constitute a stable position, determined by a career limiting means for permanent magnet 7 or for the outer sleeve 6, which adjusts automatically in case of disuse of the device, but of a basically labile position. Between this intermediate position and a position fully backward, given by the top of the permanent magnet 7 against the inner bushing 1 (Fig. 18) and that, as in the case of Figs. 13 to 15, serves to facilitate the extraction of the piece insert 3 of the inner sleeve 1, are practically possible All axial positions. This could result in that, as the device approaches a screw head 4a, the permanent magnet 7 will not automatically move to position according to Fig. 17. However, this position can be achieved easily due to the fact that the outer sleeve 6 is advanced  with the fingers, when using the device, from the position according to Fig. 18 axially towards the position according to the Fig. 16, until the magnetic effect begins analogously to Figs. 13 to 15 and then be given, in the subsequent course, automatically the operation described in relation to the Figs. 1 to 12

In the embodiments so far described the hexagonal shaft 3 of the insert is held in the inner sleeve 1 either by an elastic ring 5, a permanent magnet 9 or ball 15, prestressed by the spring cancel 16. According to a further embodiment according to Figs. 19 and 20, the hexagonal shaft of insert 3 is held by a ball 27, which is guided in a radial bore in the anterior zone of the prolongation the. Through a further bushing 29, axially movable, the ball is moved radially towards inside, until it fits into the notch in the contour outside of the hexagonal portion of the insert 3. The radial movement is generated by a cone 30 that is machined in the anterior area of the axial bore of the bushing 29 and which, in its contact position with the ball 27, transforms the axial force, acting by a spring 28 on the bushing 29, in a radial effect force. Instead of the ball can also be provided a locking element configured differently, which travel essentially radially in a slot radially in extension 1a.

If the axial movement of the bushing 29 is not limited by tensioning with the clamping element, that is when no insert is found in the carrier, the axial movement is limited forward by the safety ring 31. The spring 28 is supported by its rear end against a recess practiced at the transition point of the inner sleeve 1 to the prolongation the. The outer bushing 6 is guided in a way axially movable essentially on the inner sleeve 1, although as an additional guide the envelope of the bushing 29. On the base of bushing 29, spring 25 is supported, which moves the outer sleeve 1 with the ring magnet 7 to the preselected position with respect to the tip 3a of the piece of insertion.

In combination with the device screwing according to the invention, the retrocession of the bushing 29 it is achieved by the fact that the outer sleeve 6 is backward until spring 25 is so tensioned or completely  compressed that the force acting from the front on the bushing 29 is greater than the force of spring 28 and bushing 29 can be retracted to such an extent that ball 27 or other clamping element yield radially outward and result released the imprisonment of the hexagonal portion of the piece of insert 3.

The dimensions of the extension the, the separation between its anterior face and the annular magnet 7, the lengths of springs 25 and 28 in their compressed state and the bushing length 29 are adapted to each other such that,  the outer sleeve 6 being retracted as far as it will go against the compressed springs 25 and 28, the insert for 3 screwdriver protrudes with its anterior portion widely from the screwing device, can be easily grasped with fingers and can be removed from the device screwing.

Fig. 21 shows a device according to the invention, which essentially corresponds to the embodiment according to Fig. 13. Unlike the embodiment according to the Fig. 13, the embodiment according to Fig. 21 comprises, in the rear area of the device, a cap 32 that is attached to the shaft 2 or slid over it and fixed with the elastic ring 35, and which with its front end 33 bumps against the rear end of inner sleeve 1, through hole expanded in the projection 6a of the outer sleeve 6, 10 and determines with its rear end 34 a stop that prevents the shaft 2 of the device is inserted excessively in the reception, by example a tripartite jaw, of an electroapretador and the face front of the tripartite jaw can come up against the back face of outer bushing 6, 10, so not an axial movement of the outer sleeve would be possible backward. Instead of the bushing, shaft 2 could comprise in this place a flange as a stop. The cap 32, as well as well as a flange, they preferably have an outline circular peripheral, so that the outer bushing 6, 10 can turn on inner bushing 1 and stop bushing 32. In a very simple embodiment the stop is constituted by an elastic ring, housed in a groove in shaft 2 in the corresponding place and whose peripheral diameter is greater than the shaft diameter

It is clear that they can also endow themselves with a cap or flange all the variants of embodiment illustrated in the drawings.

All the described embodiments have in common, on the one hand, the desired function, that is to say that the screw 4, 21 is secured securely and in a coaxial position with the screwdriver insert 3 at the front end of the screwing device and simultaneously the profiled tip 3a will penetrate the screw heads 4a, 21a to the support with the entire surface in the inner profile. The coaxial position of the screw 4 is achieved by the fact that the outer bushing 6 has a precise and relatively long guide on the inner bushing 1, whereby the bearing surface 7b on the front face of the permanent magnet 7 is always in right angle with respect to the axis of the screwdriver insert 3 and the screw is not attracted by a support surface 7b possibly not perpendicular to the axis to an oblique position, remaining therein, which would no longer produce a coaxial centering of the screw through the inner profile in the screw head 4a on the profiled tip 3a. In all embodiments, the subsequent behavior of the outer sleeve 6, 10 during screwing of a screw 4, 21 is basically unimportant. In fact, during the screwing of the screw 4, 21, as usual, the axial forces exerted by the motorized tightening device or the like act through the screwdriver insert 3 and the profiled tip 3a thereof, directly on the screw heads 4a, 21a, so that the axial position of the outer sleeve 6, 10 that is then established is not essential. It is, however, advantageous, in all embodiments, that the axial load during screwing of a screw acts only on the tip of the insert 3, but not also on the permanent magnet 7, although although it is supported against The screw head can axially yield together with the outer sleeve 6, 10. This eliminates the risk that the permanent magnet 7, made as a ring magnet and generally made of a brittle material, may break during the course of the time because of excessive load. Furthermore, as required by the purposes of the invention, thanks to the ability to yield axially or to retract from the outer sleeve 6, 10 it is possible to sink
screws

Since the outer sleeve 6, 10 can rotate on the inner bushing, the rotation of the outer bushing 6, 10 is finished as soon as support surface 7b of the front face of the permanent magnet 7 on the surface on which the screw is screwed, and act a friction on said support surface 7b. This practically avoids a surface deterioration. Although at this moment there is a relative rotating movement of the end surface 4b of the screw head 4a with respect to the support surface 7b of the permanent magnet, this only happens until the screw is Something sunk

The main constructive characteristics of the device, in the various variants of embodiment, consist in that the outer bushing 6, 10, with the permanent magnet 7 inserted in its front part, is easily guided axially movable in two directions and rotatable on the bushing. interior 1, in which the dimensions and shapes of the inner sleeve 1 and the outer sleeve 6, 10 as well as the magnetic force are chosen such that under the effect of the magnetic force and / or the elements that influence the positioning of the bushings with each other, such as springs, spacer bushing, the outer bushing adopts a position in which the screwdriver insert 3, conventional in commerce and inserted in the inner bushing, in a starting position 1, protrudes with its profiled tip 3a from the passage hole of the permanent magnet surrounding said profiled tip to such an extent that a protruding length exceeds the extent of tolerance s maximum possible depth of the inner profile in the screw type associated with the profiled tip 3a.

The invention is not limited to the described embodiments, which allow multiple variants. This applies, first of all, to the type of screwdriver insert used, particularly the profiled tips thereof, as well as the corresponding screws. Instead of screws with internal star profiles, Torx, Pozidriv and other screws, as well as corresponding insert pieces, can also be provided. In addition, the invention is not limited to the described configuration of the inner and outer bushings. If the advantages of the rotating outer sleeve can be dispensed with, it could also be guided on the inner sleeve in a non-rotating manner by means of a cross section other than the cylindrical. In addition, the bearing surfaces for the screw heads do not necessarily need to be configured in the permanent magnets themselves 7, 20. On the contrary, it would also be possible to arrange the front front surfaces of the permanent magnets 7, 21 and of the outer bushes 6 , 10 in one plane and support the screw heads at least partially also with the front front surfaces of the outer bushings. Specifically, constructions are also conceivable in which the support surfaces are constituted by the front front surfaces of a polar plate disposed on the permanent magnets. In addition, the outer and inner bushings do not necessarily need to consist of non-ferromagnetic materials, although materials such as, for example, stainless steel, brass or aluminum, or the like are preferred. Finally, it is understood that the different characteristics can also be applied in combinations and variants other than those illustrated and described. The screwing device according to the invention can be manufactured, according to the construction principle described in the various variants, of course, in different sizes. The most common and usual commercial screwdriver insert parts are manufactured with a cross section of the 4 mm, 6.35 mm (1/4 '') and 8 mm hexagonal shaped shank. The parts of the device intended for receiving screwdriver shafts must naturally adapt to the various measures, as well as the amplitude of the passage hole in the permanent magnet, while other parts may eventually remain unchanged. However, it is considered convenient to adapt the screwing device as a whole to the sizes of the different screwdriver insert sizes. For special application purposes, for example in assembly lines, screwing devices can be adapted according to the construction principle according to the invention, also as special execution, to special executions of screwdriver insert parts, also for example to such with a cross section of the circular shaft and a surface of
drag

Claims (23)

1. Screwing device suitable for tightening screws (4, 21) of ferromagnetic material, which have screw heads (4a, 21a) provided with internal profiles, comprising an inner bushing (1) for fixed reception against rotation and axially secured by a screwdriver insert (3) consisting of a ferromagnetic material, which has a profiled tip (3a) protruding from the front of the inner sleeve (1) and intended to be inserted into the inner profiles of the heads of screw (4a, 2la), a drive shaft (2) linked with said inner bushing and an outer bushing (6, 10) that at least partially surrounds the inner bushing (1) and in whose front part an annular permanent magnet is incorporated (7, 20), which is provided with a hole (7a) crossed by the profiled tip (3a) of the screwdriver insert (3) and has a magnetic support surface (7b, 20a) active, intended for the support of the screw heads (4a, 21a), characterized in that the outer bushing (6, 10) is supported and guided on the inner bushing (1) in a limitedly movable way in an axial direction and, being inserted The screwdriver insert (3) is capable of being placed automatically or manually in a preselected axial position which, when a screw (4) is placed on the profiled tip (3a), due to the magnetic force of the permanent magnet (7, 20) not only the outer sleeve (6, 10) with the permanent magnet (7, 20) be attracted against the screw head (4a) to the front surface support (7b) of the permanent magnet against the end surface (4b) of the screw head, but the screw head (4a) is also attracted against the profiled tip (3a) to the support with its entire surface of the profiled tip on the inner profile of the head of screw (4a). 2. Screwing device according to claim 1, characterized in that between the permanent magnet (7, 20) and the inner sleeve (1) there is arranged a spacer (8), coaxial with said sleeve and consisting of a non-ferromagnetic material. 3. Screwing device according to claim 2, characterized in that the distance piece consists of a distance bushing (8) arranged at the front end of the outer bushing (6). 4. Screwing device according to claim 2, characterized in that the spacer part (8) consists of a projection (6b, 10d) made in one piece with the outer sleeve (6, 10). 5. Screwing device according to claims 1 to 4, characterized in that the shaft (2) comprises a stop consisting of either a stop bushing (32), mounted on the shaft (2) or arranged with sliding adjustment on said shaft and axially secured by means of an elastic ring (35) and bumping with its front end (33) against the rear end of the inner sleeve (1), or of a flange integrated in the shaft (2), which exceeds in its diameter the hexagonal profile and corresponds in its extension and cross section to the stop bushing, or else the stop consists only of an elastic ring inserted in a groove in the shaft (2) and protruding from the profile of the shaft. 6. Screwing device according to claim 5, characterized in that the outer sleeve (6) is made of a single piece and is provided, at a rear end, with a projection (6a, 10c) intended to limit its axial displacement. 7. Screwing device according to claim 6, characterized in that the outer bushing (10) is made in a bipartite manner and the projection (10c) constitutes a part of a rear portion (10b) capable of being releasably linked with an anterior portion (10a) of the outer sleeve (10), the front portion (10a) and the rear portion (10b) being provided with engaging means (11; 12, 14) intended for establishing an axial connection. 8. Screwing device according to claim 7, characterized in that the engagement means comprise an annular groove (11), in a portion (10a), and elastic tabs (12) with cams (14), intended to fit into the groove annular (11), in the other portion (10b). 9. Screwing device according to one of claims 1 to 8, characterized in that the insert (3) and the inner sleeve (1) are provided with fitting means (15, 16, 27, 28, 29, 30) intended to the establishment of an axial connection. 10. Screwing device according to one of claims 1 to 9, characterized in that the arrangement and adaptation of the construction components together are such that the outer bushing (6, 10) is adjusted to a preselected position on the inner bushing (1 ) by effect of the magnetic force of the permanent magnet (7, 20) and possibly of a second permanent magnet (9). 11. Screwing device according to one of claims 7 to 10, characterized in that the outer bushing (10) is positioned in the axial position preselected at least in part by a coil spring (17) disposed on the drive shaft (2) and supported between a rear face of the inner sleeve (1) and the projection (10c). 12. Screwing device according to one of claims 7 to 11, characterized in that the preselected position is adjustable by the fact that the drive shaft (2) has, in an axially projecting area of the projection (10c), a thread section outside on which an adjusting nut (18) is supported against the stop (10c) and equipped with an internal thread. 13. Screwing device according to one of claims 10 to 12, characterized in that the preselected axial position is adjusted such that the profiled tip (3a) protrudes forward with respect to the bearing surface (7b), in this position of the bushing. outside (6, 10), in a measure corresponding to the maximum penetration depth in the inner profile in the screw head (4a) plus a measure of tolerance (s), as long as the outer sleeve (6, 10) continues being axially movable. 14. Screwing device according to one of claims 1 to 13, characterized in that the outer sleeve (6, 10) is axially movable in the direction of the drive shaft (2), the insert (3) being fully inserted in the inner sleeve (1), in such a measure beyond the preselected position that the profiled tip (3a) protrudes forward, with respect to the support surface (7b) of the permanent magnet (7), in more than what corresponds at maximum penetration depth plus a measure of tolerance (s). 15. Screwing device according to claim 14, characterized in that the spacer part consists of a spring (25) arranged in front of the front face of the inner sleeve (1). 16. Screwing device according to claim 15, characterized in that the length and / or force of the spring are chosen such that the outer bushing (6) adopts the preselected position in a state of the spring (25) essentially relaxed. 17. Screwing device according to one of claims 1 to 16, characterized in that the support surface (7b, 20a) is constituted by an anterior front surface of the permanent magnet (7, 20) and is flat or adapted to the shape of the end surfaces of the screw heads (21a) and is for example configured correspondingly concavely. 18. Screwing device according to one of claims 1 to 17, characterized in that the outer sleeve (6) comprises a plastic covering (26). 19. Screwing device according to one of claims 1 to 18, characterized in that the insert (3) is provided with notches (5b) and the inner sleeve (1) is provided with an annular groove (5a) for the housing of an elastic ring (5) for securing the insert (3), the position of the elastic ring (5) in the inner sleeve (1) being displaced axially in such measure with respect to the position of the notches (5b) in the insert (3), with the insert (3) resting against the front surface of the drive shaft (2), that the elastic ring (5) fits only partially in the notches (5b). 20. Screwing device according to one of claims 1 to 19, characterized in that an axial end position of the outer sleeve (6) with respect to the inner sleeve (1) is limited, on a rear part of the device, by a projection (6a) or a ring (24) at a rear end of the outer sleeve (6) and, at a front part of the device, by the permanent magnet (7) or a projection (6b) shortened in its axial extension. 21. Screwing device according to claims 1, 2, 5, 6 and 18 to 20, characterized in that a hexagonal shaft of the insert (3) is housed in an extension (1a) of the inner sleeve (1), because over said extension (1a) is arranged an axially displaceable bushing (29) and at least one clamping element (27) is supported by a radial bore or a radial notch in the extension (1a) and is pressed radially against the shaft hexagonal by a cone (30) practiced in the anterior area of the bushing (29) and under the effect of a spring force (28) acting axially on the bushing (29), because a spring (25) is arranged in the space intermediate between the front face of the bushing (29) and the permanent magnet (7), whose dimensions and / or force are on the one hand sized in such a way that in the essentially relaxed state of the spring (25) the outer bushing (1) with the permanent magnet (7) adopt the preselected position with respect to the profiled tip (3a), and on the other hand in its compressed state the spring (25) presses the bushing (29) in such a way that the widened part of the cone (30) made in the bore of the bush come to be placed on the clamping element (27). 22. Screwing device according to claim 21, characterized in that the dimensions of the extension (1a), the separation between its front face and the annular magnet (7), the lengths of the springs (25) and (28) in the state compressed and the length of the bushing (29) are adapted in such a way that the outer bushing (6) is capable of being displaced backwards in such a way that the screwdriver insert (3) protrudes with its front part in such measurement of the screwing device that can be easily grasped with the fingers and removed from the screwing device. 23. Screwing device according to claims 1 to 22, characterized in that the outer bushing (6, 10) is rotatably supported on the inner bushing (1).