SCREW DRIVING MACHINE The present invention relates to a screw driving machine comprising a rotatable shaft and a screwdriver which is supported at an outer front end of the shaft and which is carried by an outer front end of a tool holder, which is, at least to a limited extent, movable relative to the shaft, and shell-shaped with outer bound- ary walls and a hollow inner space or bore and which is supported on a shoulder portion, the screw driving ma- chine further comprising at least one spring element which acts between the shoulder portion and the tool holder and which strives to centre the tool holder on the shoulder portion so that their respective symmetry axes coincide and against the action of which the tool holder is inclinable relative to the shoulder portion.

Background Art Power screw driving machines are available in a large number of different designs and a common feature is that they have a shaft or spindle which is rotatable by means of the motor and on whose outer free end some sort of screwdriver is arranged, which has an arbitrarily designed engaging means, such as a spanner or socket or an Allen wrench. For the screwdriver to engage with the screw and perform tightening or loosening of the same it is important that the spindle and the screw be centred relative to each other. This is usually not a problem as regards hand-held screw driving machines.

For screw driving machines that are fixed or sup- ported by a frame this may, however, be a problem. This applies especially to what is referred to as multiple screw driving machines, i. e. those where a plurality of spindles or individual screw driving machines are sup- ported by a common frame and which are intended for tightening and loosening a complete screw joint with a plurality of screws which are tightened or loosened at

the same time or in immediate succession by simultaneous engagement between the individual screw driving machines and the associated screw. Owing to normal deviations, such as tolerances of manufacture for the positioning of the screws, the mutual distances between neighbouring screws may in fact differ somewhat, which means that the individual screw driving machines or their spindles must be movable at least to a limited extent so as to com- pensate for these deviations and allow that all the screw driving machines can simultaneously engage the respective screws.

DE 2,112,907 discloses a multiple screw driving machine, in which the individual screw driving machines are supported in a common body via rubber rings between the body and the front and rear end of each screw driving machine. The rubber rings allow the screw driving machines to be radially movable to a limited extent and be adjusted to any variations in the distances between the screws of a screw joint. A drawback of this screw driving machine is that each spindle must be driven by a separate motor.

A motor common to all spindles would not be feasible or would at least be combined with great expenses since it would be difficult to accomplish lateral movability and a common drive of the spindles at a reasonable cost.

US 5,609,079 discloses a screw driving mechanism in which a socket holder which holds a socket at the outer end of the screw driving machine is movably supported at the outer free end of the shaft in such manner that it is movable to a limited extent in two directions perpen- dicular to the axis of rotation and also inclinable rela- tive to the same. This is achieved by the socket holder being formed with cross-shaped ridges at its rear end which with a play engage a cross-shaped groove in the outer end of the shaft. An external collar on the shaft holds the socket holder by internally conical surfaces of the collar encompassing externally conical surfaces of the socket holder. The arrangement causes centering

of the socket holder relative to the shaft when this is oriented vertically owing to the fact that gravity in combination with the conical surfaces directs the socket holder towards the centre line of the shaft. Such a type of screw driving mechanism, however, would not function with the axis of rotation oriented, for example, hori- zontally since in that case no centering of the socket holder would be achieved and the socket holder and the socket would be suspended in a position directed ob- liquely downwards, which in practice would render opera- tion with the screw driving machine impossible.

DE-U-9,403,845 discloses a screw driving machine according to the preamble to claim 1, and also in this screw driving machine the socket is movably supported in the outer free end of the shaft. However, in this con- struction the movability of the tool holder in relation to the shaft portion is achieved by means of a pin which is inserted through the sleeve-shaped tool holder and a hole in the shaft portion. In a first plane of motion, the pin serves as a pivot. To provide movability also in a second plane of motion perpendicular to the first, the hole through the shoulder portion is formed with an ample overmeasure in relation to the pin and moreover the hole is conically widened from the centre towards each end of the hole. Such a construction has several drawbacks.

Among other things, the tool holder will be differently movable in the two planes of motion and, as a result of the overmeasure of the hole of the shoulder portion in relation to the pin, the hinge connection will be inaccu- rate and loose. The engagement surfaces between the pin and the shoulder portion will be very small, almost punc- tiform, and this causes great wear and a short service life. Moreover, the shown construction is not suited to take up axial forces which arise, for example, when the screwdriver is made to abut against a bolt head, however, without engaging the same, owing to the fact that the screwdriver and the bolt head are displaced relative to

each other in terms of angle of rotation, and engage- ment is achieved only when the screwdriver begins to rotate. Between the tool holder and a flange portion of the shoulder portion there is arranged an elastic mate- rial in the form of a sleeve or a tube round the shoulder portion. This elastic sleeve serves as a spring element and causes centering of the tool holder round the axis of rotation of the shoulder portion but allows at the same time a limited inclination of the tool holder, if de- sired. A drawback of a spring element designed in this way is that the construction will have a large extent in the longitudinal direction. The spring element is also placed without protection and can thus easily be damaged.

Brief Description of the Invention The present invention aims at providing a screw driving machine which obviates problems and drawbacks of prior art screw driving machines of the type mentioned by way of introduction. More specifically, the invention aims at a screw driving machine in which the screwdriver is held centred in relation to the axis of rotation in- dependently of the orientation of the screw driving ma- chine, from which position the screwdriver is inclinable at an angle to the axis of rotation when engaging a screw and is then once more centred automatically when disen- gaged from the screw. Furthermore, the invention aims at a screw driving machine which affords the same movability in all directions and in which the engagement surfaces between the tool holder and the shoulder portion are large, which causes little wear and a long service life and besides makes the screw driving machine well suited to take up forces directed in the longitudinal direction of the axis of rotation. At least these objects are achieved by a screw driving machine according to claim 1.

The invention is thus based on the knowledge that the above-mentioned objects can be achieved by the tool holder being supported in a resiliently movable manner on a shoulder portion via a spring element which strives to

centre the tool holder in relation to the shoulder por- tion in such manner that the respective axes of rotation or symmetry of the tool holder and the shoulder portion coincide.

According to the invention, the tool holder is formed as a shell with outer boundary walls and an inner space or bore in which rearwards directed seats engage forwards directed seats of a shoulder portion. However, there is also a space of motion or play between the tool holder and the shoulder portion, and the spring element holds, in the starting position, the tool holder centred on the shoulder portion so that their respective axes of symmetry or rotation coincide. In the following, rear- wards or forwards directed seats relate to surfaces whose normal, i. e. a line perpendicular to the surface, has a component directed rearwards and forwards, respectively.

Thus the surfaces need not be directed strictly rearwards or forwards.

In the embodiments illustrated in the drawings, the spring element is in the form of one or two rings of an elastic material, such as rubber or plastic, and is placed between the tool holder and the shoulder portion.

On the other hand, the seats are formed as conical, annu- lar surfaces in the area about the centre of the length of the tool holder and the seats thereof are directed obliquely rearwards/inwards whereas the seats of the shoulder portion are directed obliquely forwards/out- wards. This embodiment has the further advantages of being simple with a small number of components, and durable, and besides the components included, for example a rubber ring, can easily be exchanged, if desired. Both the spring element and the seats, however, could be de- signed in many other ways within the scope of the inven- tion. For example, the spring element could consist of three or more leaf springs abutting against the outside of the tool holder. The spring element could also consist of three or more separate spring elements in the space of

motion between the shoulder portion and the tool holder, e. g. helical springs or springs of elastic material which are placed in holes formed in the tool holder or the shoulder portion. Furthermore the seats could have some other form, for example part-spherical. Their purpose is to transfer axial forces between the shoulder portion and the tool holder and at the same time allow inclination of the tool holder in relation to the shoulder portion.

In the embodiment shown in the drawings, the in- clination will occur as a combination of dislodgement of the seats and compression of the elastic material of the ring/rings. Consequently the centre of rotation in con- nection with the inclination will be somewhere between the seats and the spring element. However, the seats could be designed so that essentially no dislodgement between them takes place, but essentially just pivoting so that the entire inclination occurs by compression of the spring element. It would also be possible to reverse the position of the seats and the spring element in such manner that the seats are located rearwards from the spring element.

In a preferred embodiment, the screwdriver is dis- placeable so that its axis of symmetry at the outer end of the socket deviates by up to 3 mm in all directions from the axis of rotation. In the shown embodiment, the screwdriver is a socket for screwing hexagonal bolts or nuts. The inclination of the tool holder is initiated by the screw driving machine being moved towards the screw or vice versa. If the screw and the screw driving machine are not centred, the sleeve will be made to abut with displacement relative to the bolt. Owing to a bevelled portion on the inside of the sleeve, the sleeve and the tool holder, however, will be guided obliquely and slide down over the bolt. In other types of screwdrivers, such as Allen wrenches, corresponding guide means or bevelled portions can be arranged to allow guiding of the screw- driver into engagement with the screw.

In the embodiment shown in the drawings, the screw- driver is welded to the tool holder so as to make them more or less an integrated unit. However, it should be possible to fix the screwdriver to the tool holder in many other ways, such as by means of a clamping or screw joint, and it should also be possible to form the screw- driver and tool holder in one piece.

In the preferred embodiment, the tool holder is ar- ranged on a separate shoulder portion which by means of splines is reciprocable along the rotary shaft of the screw driving machine. A helical spring presses the shoul- der portion outwards against an abutment in the form of a washer and bolt in the outer end of the rotary shaft.

When making the screwdriver abut the screw, the shoulder portion and the tool holder can thus spring back if the screwdriver does not immediately engage the engaging means of the screw. As soon as the screw driving machine is ro- tated, the screwdriver and the screw, however, will engage each other and the tool holder is then moved outwards by the helical spring. Instead of being arranged on a sepa- rate, movable shoulder portion, the tool holder could, however, also be arranged directly on a portion of the rotary shaft.

In the shown embodiment, the shoulder portion is essentially circular-cylindrical and the inner space or bore of the tool holder is formed with essentially circular-cylindrical inner surfaces. However, this is not necessary and the shoulder portion and the tool holder could have many different forms within the scope of the invention. Moreover, the tool holder need not be a continuous shell but could be formed with holes and apertures in the walls, if desired.

Brief Description of the Accompanying Drawings Fig. 1 is a top plan view of a multiple screw driving machine made up of a plurality of individual screw driving machines according to the present inven- tion,

Fig. 2 is a side view through an individual screw driving machine in section, Fig. 3 is a perspective exploded view of the front part of the screw driving machine, Fig. 4 is a part-sectional side view of the front part of the screw driving machine in a normal position, Fig. 5 is a part-sectional side view of the screw driving machine in an inclined position, Fig. 6 is a part-sectional side view of an alternative embodiment of the front part of a screw driving machine in a normal position, and Fig. 7 is a part-sectional side view of the screw driving machine according to Fig. 6 in an inclined posi- tion.

Detailed Description of a Preferred Embodiment of the Invention Fig. 1 is a top plan view of a multiple screw driving machine which is made up of a total of twelve individual screw driving machines 1. Each individual screw driving machine comprises a rotatable shaft or spindle 2 which in its outer free end supports a tool holder 3. All the screw driving machines are driven by a common motor 4 via a gear drive 5 (not shown).

Then reference is made to Fig. 2, which shows an individual screw driving machine in an enlarged lateral section. As will be seen, the rotatable shaft 2 is mounted in a body 7 by means of ball bearings 6.

For description of the inventive front part of the screw driving machine, reference is made to Fig. 2 in combination with Fig. 3. The tool holder 3 is in its rear part circular-cylindrical and has a front conical portion 8. In the front end a tool in the form of a socket 9 is supported, which is welded to the tool holder. The tool holder is shell-shaped and has an inner free space or bore 10 which is in the form of essentially three cir- cular-cylindrical bores.

The rotatable shaft 2 has a front shoulder portion or a sleeve 11 which by means of splines is non-rotation- ally connected to the shaft 2 but reciprocable along the same. A helical spring 12 is pressed between an abutment 13 on the shaft and the rear end of the sleeve 11. Thus the spring 12 strives to displace the sleeve 11 outwards to an outer end position which is defined by a stop washer 14 which is held against the outer end of the shaft 2 by means of a screw 15. The tool holder 3 has on its inside a seat 16 which is directed obliquely back- wards/inwards and is formed as a conical, annular sur- face. The seat 16 of the tool holder abuts against a corresponding seat 17 formed on the front end of the sleeve 11 and having the form of a conical, annular sur- face directed obliquely outwards/forwards. The tool holder 3 and the sleeve 11 engage each other through the seats 16,17 whereas there is a space of motion or play 18 between the tool holder and the sleeve. In the rear part of the tool holder and the sleeve, respectively, at a distance from the seats 16,17, a ring of an elas- tically yieldable material, such as rubber or plastic, is arranged in the space of motion between the outside of the sleeve 11 and the inside of the tool holder 3.

A flange 20 with four recesses 21 is arranged in the rear end of the sleeve 11. It serves to retain the ring 19 and to prevent the tool holder 3 from rotating by projections 22 in the rear end thereof being inserted into the recesses 21 and preventing rotation of the tool holder 3 in relation to the sleeve 11.

The Figures also show a screw 23 which is inserted in a threaded hole 24 in the sleeve 11 while an opposite end of the screw 23 extends at least partially into a hole 25 which is formed in the tool holder 3 and has a significantly greater diameter than the screw 23. This arrangement serves as a locking means which prevents the tool holder from being pulled away from the sleeve 11 but which allows, owing to the difference in diameter between

the screw 23 and the hole 25, a limited motion of the tool holder 3 in relation to the sleeve 11.

Reference is now also made to Figs 4 and 5 for de- scription of the function of the inventive screw driving machine. Fig. 4 shows the tool holder 3 and the sleeve 11 in a starting position, in which the tool holder 3, be- cause of the elastic ring 19, is centred on the sleeve 11 and the rotatable shaft 2 so that their respective axes of symmetry or rotation coincide. By moving the screw driving machine towards a workpiece, the socket 9 is made to abut against a screw head 26 in the workpiece. In the embodiment shown in Fig. 5, the screw head has the form of a hexagonal bolt head. If the socket 9 does not imme- diately engage the bolt head 26, the tool holder 3 and the sleeve 11 will be displaced rearwards on the shaft 2 by means of the splines and against the action of the spring 12. Immediate engagement can be prevented even if the bolt head is aligned with the axis of rotation of the screw driving machine as is the case with the bolt head 26. In that case, this depends on the lateral faces of the bolt head 26 not coinciding with corresponding en- gagement surfaces of the socket 9. As soon as the screw driving machine is rotated, these will reach a position where they coincide and the spring 12 pushes the socket 9 over the bolt head 26.

If the bolt head is not centred relative to the axis of rotation of the screw driving machine, as is the case with the bolt head 26', the socket 9 will be made to abut, with displacement, against the bolt head. By the socket 9 being formed with a bevelled portion 27 on the inside of the area of its outer edge and thanks to the tool holder being supported on the sleeve 11 in a manner movable to a limited extent, the tool holder 3 will be inclined when pressed against the bolt head, as illus- trated in Fig. 5 and thus engagement between the socket 9 and the bolt head 26'is made possible. The inclination is achieved by a combination of displacement between the

seats 16 and 17 and compression of the elastic ring 19.

In the shown embodiment, the centre of pivoting will be somewhere between the seats and the elastic ring. Engage- ment between the socket 9 and the bolt head 26'is pos- sible in spite of a certain deviation between the axis of rotation of the screw driving machine and the centre axis of the screw. However, the inclination between the socket 9 and the bolt head 26'may cause a very tight engagement between them. However, the locking means in the form of the screw 23 prevents the tool holder 3 from being pulled away from the sleeve 11 when the screw driving machine is removed from the screw.

Figs 6 and 7 show an alternative embodiment of the screw driving machine according to the invention. In this embodiment, the spring function is accomplished by two separate elastic rings 19,19' ; on the one hand an elas- tic ring 19 in the same position as in the previous em- bodiment, i. e. in the rear part of the tool holder, and on the other hand an elastic ring 19'between the seats 16,17 and the locking means 23, i. e. essentially in the area where the centre of rotation of the tool holder is positioned. In this embodiment, the circumferential sur- face of the tool holder is formed with a total of three particle-removing holes 28, of which two are to be seen in the Figures. They serve to allow removal of chips and fibres entering through the socket, from the inside of the shell-shaped tool holder.