This invention is useful for connection between any one of the robot parts, but it is especially advantageous for the connection of a turn disc to a rotatable arm extending from a gear.

BACKGROUND ART An industrial robot comprises a number of robot parts which are rotatably connected to one another for relative rota- tion. The first robot part is the base of the robot. Then follow one or more robot parts, which are referred to as the arms of the robot. One of the arms supports, in its outer end, a so-called tilt with a toolholder,. to which a user may connect the desired tool. The tool and the tool- holder are rotatable in relation to the arm around an axis, essentially perpendicular to the longitudinal axis of the arm. The toolholder is rotatable relative to the tilt. It is common for the toolholder to be made in the form of an essentially plane, circular disc which is provided with a number of screw holes intended to attach the tool. Such a toolholder is referred to as a turn disc. Such a robot is described in Swedish patent specification No. 516 877.

The movements of the robot are driven by a number of motors placed in the robot parts. The motor that drives a certain robot part is usually arranged in the preceding robot part.

The motor is connected to a gear which has an output shaft that is rotatable. To transmit the movement to the next robot part, the output shaft is connected to the following robot part. High demands are placed on the connection be- tween the output shaft and the next robot part. It should manage to transmit torques from the shaft to the next robot part and it should manage to take up bending moments. It is known to connect a plane surface of the output shaft to a plane surface in the next robot part by means of a screw joint. Such a screw joint comprises a number of screws that both transmit torques and take up bending moments. However, the trend is towards developing robots that manage increas- ingly higher handling weights, which implies that the num- ber of screws that are needed in the screw joint to fulfil the requirements for the connection has increased. This has also increased the time in connection with assembly of the robot. It is important from the point of view of safety that each screw is correctly tightened, which contributes to increase the time for tightening each screw. Thus, it is desirable to reduce the number of screws.

SUMMARY OF THE INVENTION The object of the present invention is to provide a device in an industrial robot which simplifies assembly of the robot and which therefore provides possibilities of automa- tic assembly of the robot.

This object is achieved with the device described in the introductory part of the description, which is characte- rized in that one of said robot parts comprises a first surface arranged with at least one projecting part and that another one of said robot parts comprises a second surface arranged with at least one corresponding recess, whereby the projecting part and the recess are arranged so as to be firmly connected to each other with respect to form. In this way, it is possible to transmit a torque from the first robot part to the second robot part when said sur-

faces are connected to each other. Because the torque is transmitted via the projecting part and the recess, the screws need not take up any torque and their number may be considerably reduced. The function of the screws is to retain the connection. Fewer screws entail, besides a simpler and faster assembly, also a saving of costs and a reduction of the weight of the robot.

According to a preferred embodiment embodiment of the in- vention, said projecting part and said recess are formed such that said surfaces can only be connected in a limited number of positions in relation to each other. Preferably, said projecting part and recess are formed such that said surfaces only fit in one position in relation to each other. To make it possible to control a robot with the desired precision, it is necessary for the robot parts to be assembled, with great precision, in a pre-defined posi- tion relative to one another. To facilitate finding this pre-defined position, the projecting part and the recess are formed so as to fit together in one way, or a few ways, only. The projecting part and the recess are shaped so as to form what can be called an interlock. In this way, auto- matic assembly of the robot with high precision is made possible. The projecting part and the recess function as a key when positioning the robot parts in connection with the assembly.

According to one embodiment of the invention, said projec- ting part has the shape of a polygon and said recess has a corresponding shape. Such a shape makes it possible to achieve, in a simple manner, a projecting part and a recess that only fit together in a limited number of ways.

According to another embodiment of the invention, the first surface comprises a plurality of elongated projecting parts extending in a radial direction in relation to a symmetry axis, whereby the parts are arranged at a distance from each other in different radial directions and said second

surface comprises a plurality of recesses with a correspon- ding shape. Instead of having a projecting part and a re- cess with an irregular shape, as in the preceding embodi- ment, the surfaces may be provided with a number of projec- ting parts and recesses which are irregularly located in relation to one another. In this way, the purpose that the surfaces shall only fit together in a limited number of ways is achieved.

According to a further embodiment of the invention, the second surface comprises a plurality of elongated recesses arranged in the form of grooves and the first surface com- prises a plurality of elongated projecting parts with a corresponding shape. The second surface advantageously com- prises at least two segments with elongated parallel grooves, whereby the grooves in the first segment are arranged with a longitudinal direction that differs from the longitudinal direction of the grooves in the second segment. By arranging the grooves with different longitu- dinal directions, they assist in guiding the surfaces cor- rectly during assembly. In one embodiment of the invention, the segments are arranged so as to be replaceable. In this way, a change may be made to grooves with an optional pat- tern.

According to the invention, the device comprises a joint adapted to fix the robot parts to one another. The joint is advantageously a screw joint, which comprises at least one fixing element adapted to fix the first and second robot parts to each other. The task of the joint is to absorb bending moments and to retain the robot parts. Because the projecting part and the recess take up transverse forces, the load on the joint is decreased compared with the pre- vious situation. Thus, it is sufficient with one or only a few fixing elements. This means that fewer parts have to be assembled and hence the assembly time is reduced. Other possible alternatives are a press joint and a welded joint.

According to yet another embodiment of the invention, the screw joint has a fixing element that is arranged essen- tially coaxially with the axis of rotation through the first robot part. Because the torque is absorbed in some other way, it is sufficient to join the surfaces with one screw only. If the other robot part is a turn disc, it is advantageous to arrange the fixing element in the central parts of the surfaces and to place the recesses and the projecting parts closer to the periphery of the surfaces.

Because the fixing element is placed in the centre of the turn disc instead of along its periphery, as according to the prior art, more space remains for providing screw holes intended for fixing tools. In this way, a customer require- ment, namely to have more screw holes to choose from for fixing their tools, is fulfilled.

According to one embodiment of the invention, the fixing element is provided with an axially extending through- opening. Such an opening is useful, for example, for pull- ing cabling internally of the robot.

According to one embodiment of the invention, the screw joint comprises a fixing element that has at least two portions with threads, wherein the threads in one portion has a pitch that differs from the pitch of the threads in the other portion. By cooperation between the two threads with different pitch, a considerably higher clamping force is achieved than with a conventional screw and hence the risk of the screw loosening is reduced. One pitch is formed so as to enable a rapid tightening of the screw, and the other pitch is formed so as to enable the screw to be tightened hard, although the applied force is small.

Yet another object of the invention is to provide a method for rapidly and simply connecting the first robot part to the second robot part in a device according to the inven- tion. This object is achieved with a method that is char- acterized in that the first and second surfaces are posi-

tioned in relation to each other so that the projecting part in the first surface and the recess in the second surface fit together in a connected position, whereafter the projecting part and the recess are brought into engage- ment with each other. When positioning the surfaces, the shapes of the projecting part and the recess are utilized to find the correct position. Such a method may advanta- geously be used in connection with automatic assembly of an industrial robot.

During automatic assembly of the turn disc to the shaft, it is possible, for example, to use a camera or other type of sensor for detecting the appearances and shapes of the sur- faces. Thereafter, in dependence on the shapes of the sur- faces, the surfaces are positioned in relation to each other so that the projecting part or parts of one surface is/are right opposite to the corresponding recess or re- cesses of the other surface. The surfaces are positioned so that the projecting parts and the recesses fit together when being joined together. If the projecting parts and recesses are formed so that there is only one position in which the surfaces may be mounted in relation to each other, the surfaces are oriented to this position. When the surfaces are positioned, the turn disc is moved towards the surface of the shaft so that the projecting parts are brought into engagement with the recesses. In this way a mechanical interlock of the robot parts in two degrees of freedom is achieved. Then, the turn disc is fixed to the shaft by means of any of the screw joints described above, whereby interlocking in three degrees of freedom is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be explained in greater detail by means of various embodiments described as examples, with reference to the accompanying drawings.

Figure 1 schematically shows a view from the side of an industrial robot designed according to the in- vention.

Figure 2 shows a view from above of an outer end of the robot.

Figure 3 shows a cross section through a first embodiment of a device according to the invention compri- sing a connection between a first and a second robot part of the robot.

Figure 4 shows the surface of one of the robot parts in Figure 3 as viewed from the front.

Figure 5 shows a view, seen obliquely from the front, of the surface of one robot part according to a se- cond embodiment of a device according to the in- vention.

Figure 6 shows a view, seen obliquely from the front, of the surface of the other robot part according to the second embodiment of the device according to the invention.

Figure 7 shows a cross section through a device according to the second embodiment of the invention.

Figure 8 shows a cross section through a device according to an alternative design of the second embodi- ment of the invention.

Figure 9 shows a view, seen straight from the front, of the surface of one robot part according to a third embodiment of a device according to the invention.

Figure 10 shows a section A-A through the robot part in Figure 9.

Figure 11 shows a cross section through the third embodi- ment of the device according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 shows an example of a six-axis industrial robot, to which the invention is advantageously applied. The robot comprises a foot 1 which is fixedly mounted against a base.

The robot further comprises a stand 2, which is rotatable in relation to the foot 1 around a first vertical axis A.

At the upper end of the stand, a first robot arm 3 is rota- tably journalled in relation to the stand around a second horizontal axis B. At the outer end of the first arm, a second arm 4 is rotatably journalled in relation to the first arm around a third axis C. The second robot arm 4 comprises two parts, 4a and 4b, the outer part 4b being rotatable in relation to the inner part 4a around a fourth axis D, which coincides with the longitudinal axis of the second arm 4. The second arm 4 supports at its outer end a tilt 6, which is rotatable around a fifth axis E, which is perpendicular to the longitudinal axis of the second arm 4.

The robot also comprises a toolholder, in the form of a turn disc 7, which is rotatable in relation to the tilt around a sixth axis F. Thus, the robot comprises seven robot parts 1,2, 3,4a, 4b, 6,7, which are arranged to be rotatable in relation to one another around six axes A-F.

The invention is applicable to all six connection points between the robot parts. The following description shows, as an example, how the invention may be applied when con- necting the tilt 6 to the turn disc 7.

Figure 2 schematically shows the outer end of the robot.

The outer part 4b of the second arm comprises two formed arm parts 9,10 and is referred to as a fork. The tilt 6 is arranged between the arm parts 9,10 and is rotatable in

relation to the fork around an axis E, perpendicular to the longitudinal axis of the second arm 4b. The tilt 6 is ro- tatably connected to a disc-shaped toolholder 7. Such a toolholder is referred to as a turn disc. The turn disc 7 is arranged for rotation around an axis F, which extends axially through the tilt 6 and is essentially perpendicular to the axis E. The tilt 6 is essentially sleeve-shaped and comprises a drive unit which has an electric motor, the output shaft 12 of which sets the turn disc 7 in rotation via a reduction gear 14, for example in the form of a pla- netary gear. The tilt 6 is fixedly connected to two aligned shaft extensions 15,16, which are rotatably journalled in the arm parts 9,10 with the aid of bearings (not shown).

The turn disc 7 is secured to an end surface of the shaft 12 extending from the gear, said shaft being driven by a motor.

Figure 3 shows in cross section a turn disc 20, which is secured to an end portion of a shaft 21 extending from the gear, according to a first embodiment of the invention. The turn disc 20 is essentially annular and has an outer sur- face 22 that is provided with a number of holes or fixing elements intended for fixing various types of tools, and an inner surface 23 that is adapted to be connected to one end surface 25 of the end portion of the output shaft 21.

Figure 4 shows the inner surface 23 of the turn disc 20, that is, that surface that is intended to be connected to the end surface of the shaft 21. The inner surface 23 of the turn disc is provided with a recess 24, which coopera- tes with a projecting part 26 arranged on the end surface of the shaft 21. The recess 24 has the shape of a polygon with three sides and three smoothly rounded corners. The projecting part 26 has a corresponding shape, that is, it also has the shape of a polygon with three sides and three smoothly rounded corners. Such a polygon is called a "liktjocking"in Swedish. The projecting part 26 and the

corresponding recess 24 are formed so that they fit together in one way only and hence form an interlock.

The projecting part 26 has an edge 28 that is slightly conically shaped, and the recess 24 has a corresponding edge 29 that is also slightly conically shaped in order to obtain a connection free from play. The edges 28 and 29 need not be conical, but may in an alternative embodiment be straight. The projecting part 26 and the recess 24 transmit torque from the shaft 21 to the turn disc 20 when the shaft and the turn disc are connected to each other.

The projecting part 26 is provided with an inward bend and the recess 24 is provided with a corresponding outward bend 27, the outward bends being intended to function as a key so that the surfaces can only be mounted in one position in relation to each other.

An essentially circular through-opening 30 is provided through the centre of the turn disc 20. To attach the turn disc 20 to the output shaft 22, a screw joint 31 is ar- ranged. The screw joint 31 comprises a fixing screw 32 that extends through the central opening 30 in the turn disc and engages with threads 34 into corresponding threads provided internally in a countersunk portion 35 in the shaft 22. The fixing screw 32 is formed at one end with threads and at its other end provided with a flange 36 that is adapted to make contact with a corresponding flange 38 extending around the opening 30 in the turn disc. The fixing screw 32 is provided with an axially extending through-hole 39 in- tended to pull cables between the robot parts. The fixing screw 32 is designed so that its diameter is essentially larger than its axial length. This embodiment of the inven- tion means that only a small number of parts need be assem- bled, which entails a faster assembly work than previously.

Figure 5 shows an inner surface 44 of a turn disc 40, and Figure 6 shows an end surface 46 of a shaft 42, according to a second embodiment of the invention. The turn disc 40

and the shaft 42 are intended to be connected to each other and to form a so-called key joint of the claw-clutch type.

The turn disc 40 has a surface 44 that is intended to be connected to the end surface 46 of the shaft 42. The sur- face 44 is provided with an annular projecting part 48 and the surface 46 has a corresponding annular recess 50. The projecting part 48 acts as a guiding edge and centres the turn disc in relation to the shaft. A plurality of projec- ting parts 52, extending radially inwardly towards the centre of the turn disc, extend from the annular guiding edge 48. The projecting parts 52 are arranged in spaced relationship along the guiding edge 48. The distance be- tween the projecting parts 52 should be different to achieve a unique fit of the turn disc to the shaft. In an alternative embodiment, the guiding edge 48 and its corre- sponding recess 50 may be eliminated by increasing the number of projecting parts 52 and their corresponding re- cesses 54.

The number of projecting parts 52 is adapted such that self-centring arises. The projecting parts 52 are wedge- shaped and have an angle of clearance varying between 1 and 12 degrees. The surface 46 is provided with corresponding recesses 54, which have a shape and location corresponding to the shape and location of the projecting parts 52 in the turn disc. The turn disc 40 is provided with a through- opening 56 arranged at the centre of the turn disc. The shaft 42 is provided with a circular countersunk portion 57 with a diameter essentially corresponding to the diameter of the opening 56 in the turn disc. The opening 56 is pro- vided on the inside with threads 58 and is intended to re- ceive a fixing screw. The countersunk portion 57 is provi- ded on the inside with threads 59 and is intended to re- ceive the same fixing screw.

Figure 7 shows the turn disc 40 connected to the shaft 42 by means of a screw joint. The screw joint comprises a clamping screw 60 and threads 58 arranged on the inside of

the opening 56 in the turn disc 40 and threads 59 arranged on the inside of the countersunk portion 57 in the shaft 42. The clamping screw 60 is provided with two types of threads with two different pitches. The clamping screw 60 has an envelope surface that is divided into an upper por- tion 66 that has threads with a first pitch and a lower portion 68 that has threads with a second pitch. The first pitch is smaller than the second pitch. For example, the first pitch is 2 mm, and the second pitch 3 mm. The upper portion 66 of the clamping screw 60 is intended to engage with the threads 58 in the opening 56 in the turn disc and the lower portion 68 of the clamping screw 60 is intended to engage with the threads 59 in the countersunk portion 57 in the shaft. By cooperation of the two threads with diffe- rent pitch, a considerably higher clamping force is ob- tained than with a conventional screw, which reduces the risk of loosening of the screw. The clamping screw 60 has a diameter that essentially corresponds to the opening 56 in the turn disc 40. The diameter is, for example, 110 mm. At its upper end, the clamping screw is provided with a hexa- gon hole 62 intended for an Allen key.

Figure 8 shows an alternative embodiment of the screw joint in Figure 7. The screw joint comprises, in addition to the clamping screw 70 with two threads 72,74 with. different pitch, also an annular element 72 which is arranged between an upper part 76 of the clamping screw and the turn disc 40. The annular element 72 is provided on its inside with threads that fit the threads 72 in the upper part 76 of the clamping screw 70. The inside of the countersunk portion 57 in the shaft 42 is provided with threads that fit the threads 74 in the lower part 78 of the clamping screw 70.

The pitch of the thread 72 is smaller than the pitch of the thread 74. One advantage of this embodiment is that it is simpler and less expensive to manufacture threads in the annular element than to manufacture threads direct in the turn disc, which is large and heavy.

Figure 9 shows a turn disc 80 according to a third embodi- ment of the invention. The surface that is intended to be connected to a surface of the shaft is provided with elon- gated grooves in the form of alternately ridges 81 and valleys 82. Such a valley 82 will hereinafter be referred to as a groove. An axially directed surface, facing the turn disc, of an outer portion of the shaft is provided with corresponding grooves. The grooves on the surface of the shaft are formed to fit to the shape of the grooves on the turn disc in such a way that a ridge on one surface meets a corresponding valley on the other surface. The surface is divided into three segments 83a, 83b, 83c, each of which includes a portion with parallel grooves. The grooves within one segment are arranged with a longitudinal direction that differs from the longitudinal direction of the grooves in the other segments. Thus, the grooves within one segment are arranged with parallel longitudinal axes, but the grooves are arranged with a longitudinal axis that intersects the longitudinal axes of the grooves in the other segments. The angle between the longitudinal axes of the grooves in two adjacent segments is preferably within the interval of 70 to 120 degrees. The advantage of having different segments with different directions of the grooves is that the turn disc and the shaft become self-centring during assembly. Thus, there is only one possible position in which to mount the turn disc in relation to the axis. In one embodiment of the invention, the grooved segments are replaceable such that they can be replaced by other seg- ments with other longitudinal directions.

Figure 10 shows, on a larger scale, the appearance of the grooves in a section A-A across the longitudinal direction of the grooves in Figure 9. The valleys or grooves 82 may be regarded as elongated recesses in the turn disc, and the surface of the shaft has corresponding projecting parts in the form of ridges that fit into the grooves 82. The grooves 82 are formed so as to taper off downwards towards the bottom of the valleys for the purpose of providing a

fit, free from play, between the turn disc and the output shaft. The grooves have a clearance a, which is preferably in the interval of 1-12 degrees.

The turn disc 80 is fixed to the surface of the output shaft 86 of the gear by means of a screw joint, as shown in Figure 11. The screw joint comprises six screws 84 exten- ding through axially directed holes in the turn disc and engaging with their threads into threaded screw holes in the outer portion of the shaft 86. The screws 84 are not intended to take up any torque. The torque is instead taken up by the ridges 81 and the grooves 82. The screws 84 are arranged symmetrically along the surface at the same radial distance from the centre.

The invention is not limited to the embodiments shown but may be varied and modified within the scope of the appended claims. The projecting parts and the recesses may be formed in many other ways than those shown here. Which shape to choose depends on the type of robot and on what robot parts of the robot are to be connected to one another. The shape may vary depending on how much torque the connection is supposed to manage to transmit between the robot parts.

Each one of the surfaces may either be provided with re- cesses, projecting parts or with both recesses and pro- jecting parts.