Patent Publication Number: US-2004054438-A1

Title: Manipulator to move an object in the space with at least tree arms

Description:
TECHNICAL AREA  
       [0001] The present invention relates to an industrial robot comprising a manipulator and control equipment where the manipulator has a number of arms comprising link systems where the arms together support a moveable element. The present invention in to directly or indirectly support a tool that can be used for the moving, measuring, treating, processing, etc. of objects.  
       BACKGROUND  
       [0002] A parallel robot comprises a manipulator and control equipment, where the manipulator comprises three arms, each of which is joined to pivot between a first and a second element. In the present parallel robot, the element is fixed in space. The second element consists of a manipulated platform that supports a tool or similar. In the parallel robot, there takes place a relative displacement of the second element in relation to the first element with the second element retaining its orientation/inclination. A tool is normally used when the robot is to pickup and move items between two positions/places. For picking up, the usual need is for the robot to be able to move quickly. Another need is normally that the moveable element/tool retains its orientation in space during the movement.  
       [0003] Today, the most widely used robots for moving and rotating objects without changing the inclination of the object, are those of the so called SCARA type. These robots are manufactured for the four degrees of freedom x, y, z and the rotating of objects around the z axis. Two serially coupled arms that operate in the xy-plane with axes at right angles to the xy-plane are used for manipulating the object in the xy-plane. To obtain a movement in the z-direction, a linear displacement device is used. This device can be located either after or before the serially coupled arms in the kinematic series chain of the robot. In the first case, the serially coupled arms must displace the driving means for the z-movement and in the second case the driving package for the z-movement must displace the serially coupled arms. The driving package for rotating of objects around the z-axis will always sit furthest out in the kinematic chain of the robot. A so-called SCARA robot must be able to take up the torque.  
       [0004] Serial coupling the arms of a so-called SCARA robot means, just as with all other robots with serially coupled kinematic links, that the robot acquires a large moveable mass. In addition, the serial coupling means that the structure of the robot becomes weaker. Even the precision is adversely acted and large motor moments are required to achieve rapid displacements.  
       [0005] Document WO 9958301 shows a manipulator for the relative displacement of a fist and second element. The manipulator comprises three link arrangements A, B and C that are connected between the two elements. The link arrangements A, B and C are driven by three power appliance arrangements  3 ,  4  and  5 . The link arrangements comprise upper arm and lower arm components. The lower arm components are connected to the upper arm components  6 ,  7  and  8  respectively to the second element by means of joint arrangements. The axes of rotation of the joint arrangements cut or coincide with an axis of symmetry ( 44 ) of the second element.  
       [0006] This arm structure bas been made possible through the manipulated platform being designed as a frame construction in three dimensions and by the components of all three arms closest to the moveable platform consisting of two links for transferring compressing and puling tensions from the manipulated platform.  
       [0007] Document WO 9733726 shows an industrial robot defied according to that above where the serial kinematic structure in the manipulator is replaced by a parallel kinematic structure. Three driving mechanisms are fitted with coinciding centres of rotation and each driving mechanism is joined with the moveable element in the form of a two dimensional platform via arms with five degrees of freedom. The components of the arms closest to the moveable platform comprise three, two or respectively one link and these links only need trans compressing and pulling tensions, which causes them to be very rigid, even if they are designed with small dimensions and of lightweight material. In addition, the joins are only subjected to a normal force from the links and bed can therefore be made light, rigid and precise. All driving mechanisms are mounted on the fixed element and as 2 or 3 of the driving mechanisms have a common centre axis, the whole robot structure can pivot round in the same manner as with a SCARA-robot.  
       [0008] Document U.S. Pat. No. 4,976,592 shows a manipulator for the relative displacement of a first fixed and a second manipulate element where the second element maintains its onion in space during the displacement. The manipulator comprises three arms, each of which is joined to pivot with both element. Each of the arms is joined to pivot in the fist element in single-axis joints. Each of the arms is also joined to pivot with the second element via link systems comprising two parallel links joined with elements in joints with at least three degrees of freedom. Thus, a total of all six links are joined to pivot with the second element. The aim is to set up a robot where the arms are arranged so that the second element always maintains its orientation in space and where the links are capable of transferring the torque.  
       [0009] When a robot according to that above is used in certain applications that demand high precision, e.g. or processing material, the platform must be manufactured with great accuracy. In addition, the joints must be mounted on the platform with great accuracy and at the same time the angles of deflection of the joints must be made large.  
       [0010] Both the manipulator with a two dimensional platform and the manipulator with a three dimensional manipulator platform bring about the need for the platform to be manufactured with great accuracy as six joints each with 2 or 3 degrees of freedom are to be mounted on the manipulated platform.  
       [0011] With regard to maternal processing and other applications where large forces act on the platform, the platform mist also be made rigid and the joins be given rigid attachments in the manipulator platform without compromising accuracy. During the application of a large external torque to the platform, the platform must additionally be made so large that the joint forces that arise do not lead to age of the joint sure or the ball bearings. There is thus a need for a robot that eliminates twisting and vibrations in its construction. Furthermore, the robot should have a small moving mass to accommodate the desired cycle times.  
       [0012] When these factors are added together, the need arises for a manipulator that displays great accuracy during operation, has a large rigidity and at the same time is cheap and easy to manufacture.  
       [0013] When manufacturing and using industrial robots of the type specified above, the need thus arises for platforms that have a comparatively small extension in space, have a small moving mass and yet still have sufficient rigidity and high accuracy. They should have a minimal construction, simple and cheap attachment of the joints and yet still fufil the demand for rigidity.  
       [0014] The manipulated platforms in the documents stated above cannot fulfil these requirements.  
       DESCRIPTION OF THE INVENTION  
       [0015] The industrial robot in this present invention comprises a manipulator with control equipment. The manipulator is set up as a parallel robot with a number of arms, each of which is joined to pivot with a first and a second element. In the present parallel robot, the first element is fixed in space and the second element consists of a manipulated platform. The arm are arranged between the elements so that the second element retains its orientation/inclination in space during displacement. The arms consist of link systems comprising at least one link and joints in which the transfer of power takes place through pure compressing and pulling forces. The arms are built up of a first and a second arm part that are joined to pivot and that comprise single links, two or more parallel link arms or non-parallel multi-link systems. These allow movements between an actuator arm and a manipulated platform. The word “link” includes joint connections at the respective ends of the link.  
       [0016] The aim of the present invention is to arrange in a manipulator defined according to that above a manipulated platform that is designed with a minimal construction or the manipulated platform and with a simple attachment of the joints on the platform. Another aim is to give a fist robot with a large force that is capable of working with high precision in a large number of application areas. Another aim of the invention is to design a relatively cheap manipulator that will give a cheap and lightweight robot.  
       [0017] The solution according to the invention is characterised by the manipulator for the relative displacement of a body in space specified in claim 1. The manipulator comprises one element and at least three arms arranged to together displace an element in space with retained orientation/inclination. In addition, the manipulator comprises a fist arm that comprises two parallel links that are attached to the element with joint arrangements allowing three degrees of freedom. Furthermore, the manipulator comprises a second arm that comprises two parallel links that are attached to the element with joint arrangements allowing three degrees of freedom. The joint arrangements are arranged on a common line of symmetry of the element.  
       [0018] The manipulator with the included link set ups and joint arrangements according to the invention is arranged in accordance with the subordinate claims. The arms are arranged so that all degrees of freedom of the manipulated element, apart from the pivoting around the axis of symmetry, can be lock. The words “lock a degree of freedom” are defined as follows. A body has six degrees of freedom, three for rotation and three for translation, and if one degree of freedom is locked, the body cannot move in that degree of freedom. The manipulator according to the invention comprises arms in the form of a first and a second arm part consisting of link set-ups. The words “link set-ups” are defined as a structure consisting of joined together links where the links are connected together with joints. The connecting together of the links can be both in series and in parallel.  
       [0019] The solution according to the invention also includes that the manipulator is produced according to the first independent method claim. The solution according to the invention even includes driving the manipulator and locking degrees of freedom according to the second independent method claim as well as using the manipulator in high precision applications according to the independent use claim.  
       [0020] According to one advantageous embodiment of the invention, the included joints each have three degrees of freedom and only five links are joined with the second element with joints that are arranged on the second element so that every pivoting axis coincides with or cuts the common line of symmetry. In this way, all degrees of freedom except for the pivoting around the axis that is constructed by the line of symmetry are locked. This means that tools such as a measurement probe, for example, always maintain a predefined with a constant inclination while pivoting around the line of symmetry is indefinite.  
       [0021] Also included in the concept of the invention is that a tool is mounted symmetrically around the line of symmetry and thereby always carries out its task with the same precision. The concept of the invention also includes that the pivoting of the tool around the line of symmetry is locked through one joint being given only two degrees of freedom.  
       [0022] It is part of the concept of the invention that the individual joints consist of universal/cardan joints, homokinetic couplings or ball joints. In the latter case, a degree of freedom is added in the form of pivoting capability of the individual link around its length axis. For links arranged parallel, this extra degree of freedom does not mean any further freedom of movement for the manipulated element in relation to the fixed element when the robot is in its assembled state.  
       [0023] In one advantageous embodiment of the invention, the included joint arrangements are designed so tat in the assembled state of the robot, they allow release movement with at least two degrees of freedom. The movement taker place between the first arm part and the manipulated element. The degrees of freedom are given by the ability to pivot in all directions by a second arm part around two angled real or in a axes, both relative to the equivalent first arm part and the manipulated element. The individual joints consist of universal/cardan joints, homokinetic couplings or ball joints. In the latter case, a degree of freedom is added in the form of pivoting capability of the second arm part around its length axis, which, as mentioned earlier, adds a further degree of freedom of the manipulated element in relation to the fixed element when the robot is in its assembled state.  
       [0024] Included in the concept of the invention is that the links of the link pairs comprised in the second arms parts have the same length and are parallel. This means that the inclination/orientation of the manipulated element does not depend on its position.  
       [0025] Included in the concept of the invention is that the second element includes a treaded rod onto which joint balls provided with through-holes and distance elements in the form of tubes are threaded and fixed. The precision of the mounting of the balls is determined by the tube parts and not in the fitting of the rod in the ball hole. This gives high precision since the fitting depends only on the precision of the balls and the dance tubes. Both can be made with high precision at a low cost by, for example, using ball-bearing balls and distance tubs with face-ground end surfaces.  
       [0026] In one advantageous embodiment of the invention, arm C with its second arm part is aged so that a link included in the arm part can pivot with large amplitude in all directions. The pivoting axes of the joint function cut or coincide with the axis of symmetry of the manipulated element. The centre of a constituent ball joint lies on the axis of symmetry of the manipulated element. To obtain the correct working area for the link associated with the joint, the attachment of the joint ball is arranged in the xy-plane in a direction towards the fixed element of the robot. In this way, both pivoting axes of the joint will be perpendicular to the axis of symmetry. Thus, a large working area for the robot is obtained since the joint function acquires a large space for swinging around the pivoting axes. The concept of the invention also includes that both of the pivoting axes named above cut the axis of symmetry.  
       [0027] In one advantageous embodiment of the invention, a joint agreement comprises spring pre-tensioned ball joints where pulling springs are used to hold together joint sockets with joint balls. The manipulated element is designed to allow two link rod pairs with pairs of opposite joint sockets to be coupled in. Equivalent joint balls are arranged on the manipulated element via rods on the lower respective up side of the joint balls so that the joint sockets can freely enclose the joint balls from the upper respective lower side. The joint sockets are then pressed against the respective joint ball with the pulling spring.  
       [0028] It is part of the concept of the invention to change the sequence between the joints arranged on the manipulated element. One embodiment with a certain sequence between the joints results in the forces along the manipulated element being more evenly distributed and thus giving a less rigid and accordingly lighter manipulated element compared with another embodiment with an alternative sequence between the joints.  
       [0029] In one advantageous embodiment of the invention, the arm C has a second arm part that is joined to pivot with a universal/cardan coupling at each end A driving mechanism with the necessary transmission is arranged to pivot the universal/cardan coupling on the second arm part. By pivoting the universal/cardan coupling, the pivoting of the manipulated element is controlled and the rotational angle of a tool is manipulated. In accordance with embodiments described previously, the pivoting axes of all joints on the manipulated element coincide with or cut the axis of symmetry.  
       [0030] In one advantageous embodiment of the invention, the joints comprise triple-axis joints tat are connected together to form a link set-up. One such joint has a single-axis bearing arranged with the pivoting axis in the z-direction. A further two single-axis bearings are arranged on either side of the first bearing with a common pivoting axis perpendicular to the pivoting axis of the first bearing. One embodiment of the invention has joints with three single-axis bearings arranged and, to obtain a symmetric loading of the bearings, pairs of links have been introduced.  
       [0031] According to another advantageous embodiment of the invention, the robot is arranged with a fourth arm D comprising a fist arm part and a second arm part consisting of link set-ups and a fourth arm mechanism to control the angle of rotation of the manipulated element around its axis of symmetry.  
       [0032] Included in the concept of the invention is that the arms comprise translatory functioning arm parts.  
       [0033] In the embodiments described above, the manipulated element is manipulated relative to the fixed element with 3 or 4 degrees of freedom. Also included in the concept of the invention is the use of the described joint arrangements on the manipulated element to manipulate this relative to the fixed element with only two degrees of freedom. In one advantageous embodiment, the robot has arm C connected withh either arm A or arm B in the arms “AC” alternatively “BC”, which locks the degree of freedom of the manipulated element that in the embodiments described above is manipulated via link set-up C.  
       [0034] Included in the concept of the invention is that the actual driving of the moving sections relative to the stationary sections at the driving mechanism is done via transmissions such as gearboxes, and hollow axles built into the fixed element. Also included in the concept of the invention is that other cowlings are obtained between the pivoting mechanism through different transmission arrangements between the motors and the pivoting mechanism.  
       [0035] Also included in the concept of the invention is that two of the driving mechanisms either have or do not have pivoting axes that coincide. Two driving mechanisms having pivoting axes that coincide is to be preferred as the kinematics for pivoting the robot around are simplified.  
       [0036] Also included in the concept of the invention is that the tool rotates via an external power source with carriers.  
       [0037] Included in the concept of the invention is that the arms do not sit on a frame but that instead each sits on its own fixed point in space at a distance from one another. Also included in the concept of the invention is that the arms have different inclinations on the pivoting axes but have a common pivoting component.  
       [0038] This description should not be seen as a limitation of the invention but only as a guide to a fill understanding of the invention. It must thus be considered that the manipulator can be mounted on a floor, wall or ceiling. The terms horizontal plane, over, under, etc., relate to different positions depending on how the manipulator is mounted, and over can thus become under, and so on. Adaptation to manipulators that include other active parts plus the replacement of parts and details that are obvious for a person skilled in the art can naturally be made within the concept of the invention. 
     
    
    
     DESCRIPMON OF THE FIGURES  
     [0039] The invention will be described in more detail though the description of an embodiment with reference to the attached drawings where  
     [0040]FIG. 1 shows a manipulator comprising three parallel arms connected to a first and a second element according to the invention,  
     [0041]FIG. 2 a  shows a first alternative embodiment of the manipulated platform according to the invention,  
     [0042]FIG. 2 b  shows a bail joint according to FIG. 2 a,    
     [0043]FIG. 3 shows a second alternative embodiment of the manipulated platform and associated joint arrangement according to the invention,  
     [0044]FIG. 4 shows a third alternative embodiment of the manipulated platform and associated joint arrangement according to the invention,  
     [0045]FIG. 5 a  shows a fourth alternative embodiment of the manipulated platform and associated joint arrangement according to the invention,  
     [0046]FIG. 5 b  shows a ball joint according to FIG. 5 a,    
     [0047]FIG. 6 shows an alternative embodiment of joints that are included in the manipulate platform according to the invention,  
     [0048]FIG. 7 shows a first active embodiment of the manipulator according to the invention arranged with a joint arrangement according to FIG. 6,  
     [0049]FIG. 8 shows a second alternative embodiment of the manipulator according to the invention,  
     [0050]FIG. 9 shows an embodiment where two of the arms according to FIG. 1 are joined together,  
     [0051]FIG. 10 shows a second alternative embodiment with two arms according to FIG. 1 joined together. 
    
    
     DESCRIPTION OF AN EMBODIMENT  
     [0052] An industrial robot comprises a manipulator (FIG. 1) for the relative displacement of a first element  1  and a second manipulated element  2 . The manipulator comprises three arms, A, B and C, that were and are arranged in parallel and that join together the first  1  and second  2  element. In this embodiment, the fist element  1  is firmly attached to a frame. The second element  2  can be regarded as a platform  2  that in this embodiment, consists of a rod-like element. Each one of the arms A, B and C respectively comprises partly a first arm part  6   a ,  7   a  respectively  8   a  and partly a second arm part  6   b ,  7   b  respectively  8   b.  The second arm part  6   b  consists of two parallel links  14  and  15 , the second aim part  7   b  consists of two parallel links  16  and  17 , and the second arm part  8   b  consists of one link  18 .  
     [0053] The parallel links  14  and  15  respectively  16  and  17  have the same length and are parallel so that the inclination of the second element  2  shall not depend on its position.  
     [0054] The links  14  respective  15  included in the arm A are joined to pivot with the first arm part  6   a  at the joints  20  respectively  21  and with the platform  2  at the joints  22  respective  23 .  
     [0055] The links  16  respectively  17  included in the arm B are joined to pivot with the first arm part  7   a  at the joints  24  respectively  25  and with the platform  2  at the joints  26  respectively  27 .  
     [0056] The link  18  of the arm C is joined to pivot with the fist arm part  8   a  at the joint  28  and with the platform  2  at the joint  30 .  
     [0057] Here, the manipulated platform  2  consists of a rod-like element  2  that has a line of symmetry  44 . The joints  22 ,  23 ,  26 ,  27  and  30  are arranged on the rod-like element. The joints  22 ,  23 ,  26 ,  27  and  30 , which have three degrees of freedom, are arranged with every pivoting axis to coincide with or cut the common line of symmetry  44 . This means that a tool such as a measurement probe  36 , for example, always acquires a predefined position with a constant inclination while its pivoting around the line of symmetry  44  is indefinite. The measurement probe  36  is fitted symmetrically around the line of symmetry  44 . FIG. 3 shows that even the pivoting of the tool  36  around the line of symmetry  44  can be locked if the joint  30  is given only two degrees of freedom.  
     [0058] Driving mechanisms  3 ,  4  and  5  are arranged to bring respective arms A, B and C into movement and to in this way achieve a relative displacement of the platform  2  in x, y and z directions in relation to the first element  1 .  
     [0059] The driving mechanisms  3 ,  4  and  5  are arranged with a stationary section  3   a ,  4   a  restively 5a as well as a section  3   b ,  4   b  respectively  5   b  that is moveable in relation to this. The driving mechanisms are design as pivoting mechanisms, ie. their moving parts  3   b ,  4   b  respectively  5   b  can pivot or rotate. The driving mechanisms  3  and  4  have their stationary sections  3   a ,  4   a  firmly attached to the first element  1 . In FIG. 1, the fixed section  5   a  of the driving mechanism  5  is firmly attached to the pivotable part  4   b  of the driving mechanism  4 . It is thus possible to pivot the whole of the robot structure around a column-shaped part  1   a  of the fixed element  1 .  
     [0060] The assembled state of the manipulator allows relative movement with at the most two degrees of freedom between the first arm part  6   a ,  7   a  respectively  8   a  and the second element  2 . For arm A, the degrees of freedom for swiveling in all directions are obtained from the links  14  and  15  around two angularly set-up real or imaginary axes both relative to the fist arm part  6   a  and the second element  2 . The joints  20 ,  21 ,  22  and  23  consist of ball joints, which give a degree of freedom in the form of pivoting capability at the individual links  14  and  15  around their length axes. One consequence of the parallel arranged links  14 ,  15  is that this additional degree of freedom does not give any additional freedom of movement at the second element  2  in relation to the first element  1  when the robot is in its assembled state.  
     [0061] The same conditions regarding ball joints apply or arm B. Two degrees of freedom or arm B are given by the pivoting capability in all directions of links  16  and  17  around two angularly set-up real or imaginary axes both relative to the first arm part  7   a  and the second element  2 . The joints  24 ,  25 ,  26  and  27  consist of ball joints, which give a degree of freedom in the form of pivoting capability at the individual links  16  and  17  around their length axes. One consequence of the parallel arranged links  16 ,  17  is that this additional degree of freedom does not give any additional freedom of movement at the second element  2  in relation to the first element  1  when the robot is in its assembled state.  
     [0062] For arm C, ball joints  28  and/or  30  give a further degree of freedom at the first arm part  8   a  relative to the second element  2 , namely pivoting capability around the line of symmetry  44  of the platform  2 . Arm C requires that the link  18  be joined with the first arm part  8   a  by means of ball joint  28  and, with the aid of ball joint  30 , joined to the second element  2 . These joist arrangements are designed so that in the assembled state of the robot they allow relative movement with three degrees of freedom between the first arm part  8   a  and the second element  2 . These degrees of freedom are given by a the pivoting capability in all directions of the link  18  around two angularly set-up real or axes both relative to the first arm part  8   a  and the second element  2 , as well as a degree of freedom in the form of pivoting capability of link  18  around its length axis.  
     [0063] Driving mechanism  4  has its moving part  4   b  joined to the first arm part  7   a  on arm B so that the driving mechanism  4  is capable of imparting a swinging movement in the xy-plane to the first arm part  7   a . In an equivalent manner, driving mechanism  3  has its moving part  3   b  joined to the first arm part  6   a  on arm A so that the driving mechanism  3  is capable of imparting a swinging movement in the xy-plane to the fist arm part  6   a.  Both driving mechanisms  3  and  4  have pivoting axes that coincide, as shown in FIG. 1.  
     [0064] The main task of driving mechanism  5  is to give the second element  2  an upwards and downwards movement and the pivoting axis for driving mechanism  5  is thus at right angles to the pivoting axes for driving mechanisms  3  and  4 . For the robot to be able to swing round the first element  1 , the fixed part  5   a  is mounted on the driving mechanism  5  in such a manner that the pivoting axis of driving mechanism  5  accompanies the pivoting of any of the first arm parts  6   a  or  7   a  or is coupled to both the first arm parts  6   a  and  7   a  via transmission so that the first arm part  8   a  always finds itself in the middle between the first arm parts  6   a  and  7   a.  In FIG. 1, the fixed part  5   a  of driving mechanism  5  is firmly attached to the moveable part  4   b  of driving mechanism  4 .  
     [0065] The critical aspect in the design of the robot according to FIG. 1 is to obtain a joint arrangement for the joints  22 ,  23 ,  26 ,  27  and  30  so that all degrees of freedom of the second element  2  except for pivoting around the axis of symmetry  44  are locked by the links  14 ,  15 ,  16 ,  17  and  18 . In the figure, the joints are arranged in the following order from the top downwards;  30 ,  22 ,  26 ,  23  and  27 .  
     [0066]FIG. 2 a  shows an embodiment where the joints in the manipulator according to FIG. 1 are arranged according to an alternative sequence on the second element  2 , namely  30 ,  26 ,  22 ,  23  and  27 . All joints consist of ball joints where the respective joint balls  30   a ,  26   a ,  22   a ,  23   a  and  27   a  have been mounted through a threaded rod  2   g  with a nut  2   f  pulling together the joint balls and the distance tubes  2   a ,  2   b ,  2   e ,  2   d  and  2   e  that lie between them. At one of its ends, rod  2   g  is attached to joint ball  30   a  and passes freely through hole  44   a  that is made in the other joint balls. The tool  36  is mounted at the lower end of the rod  2   g  on an extra platform, which even supports an external driving source to rotate the tool.  
     [0067] The joint function can be obtained in a number of ways and FIG. 2 b  shows one example with a joint socket  55  and a holder-on  56 . In FIG. 2 b , joint ball  26   a  is seen from above and in the centre of the joint ball in this perspective there is the hole  44   a  for the rod  2   g . The joint function is obtained through a joint socket  55 , which abuts ball  26   a  at at least three points, being pressed firmly against the ball with a holder-on  56  that abuts the ball at at least one point. The joint socket and holder-on are mounted on link  16  with the aid of the holder  57  that is sprung to obtain a predefined force between the holder on and the joint socket. The joint according to FIG. 2 b  is also used for the joints  22   a ,  23   a , and  27   a.    
     [0068] Link  16  can pivot with large amplitude in all directions, and this is made possible by the joint function in FIG. 2 b  acquiring a large space for pivoting around the pivoting axes  58  and  2   g . To obtain the correct working area for link  18 , the attachment of joint ball  30   a  is arranged in the xy-plane in a direction towards the fixed element  1  of the robot, whereby both pivoting axes of the joint become perpendicular to the axis of symmetry  44 . For the best function of the robot, both of these pivoting axes cut the axis of symmetry.  
     [0069]FIG. 3 shows a joint arrangement with pre-tensioned sprung ball joints, where pulling springs  40 ,  41  are used to hold ball sockets and ball joints together, constructed for the connection between the arms A respectively B and element  2 . The second element  2  is designed to allow the connecting of the link rod pairs  14 ,  15  respectively  16 ,  17  with opposite pairs of joint sockets  22   b ,  23   b  respectively  26   b,    27   b . The joint balls  22   a  and  23   b  are ranged against the second element  2  via rods on the upper respective lower sides so that the joint sockets  22   b  respective  23   b  can freely enclose the joint balls  22   a  and  22   b  from the per respective lower sides. The joint sockets are then pressed against the respective joint ball with the pulling spring  41 . The equivalent arrangement is made for the link rods  16  and  17  where the joint sockets  26   b  respective  27   b  then press against the joint balls  26   a  respective  27   a  with the aid of spring  40 .  
     [0070] For the complex designed second element  2  to acquire a well-defined orientation around its symmetry/rotation axis  44 , the ball joint  30  in FIG. 1 a  is replaced by a universal/cardan coupling  42  that does not allow element  2  to rotate. Universal/cardan coupling  42  consists of the cross  42   e  tat binds the pair of is  42   a    42   b  with the pair of bearings  42   c ,  42   d  mounted at right angles to them. Link  18  is coupled to the pair of bearings  42   c    42   d  via an upper yoke, and the second element  2  is coupled to the pair of bearings  42   a ,  42   b  via a lower yoke.  
     [0071]FIG. 4 shows an alternative joint arrangement. The only difference with the arrangement shown in FIG. 3 is that the joints to the link pairs  14 ,  15  and  16 ,  17  have another sequence along the axis of rotation  44 , namely the sequence that was used in FIG. 1 a.  As such, the joints now come in the order  22 ,  26 ,  23  and  27  in the direction towards the tool.  
     [0072]FIG. 5 a  shows an alternative joint arrangement where several link rods share the same joint ball. The joints  22 ,  26  and  30  in FIG. 1 share a first common relatively larger ball joint  45  in FIG. 5 a  and the joints  23  and  27  share a second common relatively larger ball joint  46 . This means that the joint axes for the links  14 ,  16  and  18  cut one another at a common point that lies on the axis of symmetry  44  of the second element  2 . In an equivalent manner, the joint axes for the links  15  and  17  cut one another at a common point that also lies on the line of symmetry  44 . Joint balls  45 , 46  and the tool  36  are arranged with the use of distance casings  2   a  and  2   b  and a threaded rod in the same manner as shown previously in FIG. 2 a.    
     [0073] The joint function according to the joints  45  respectively  46  is shown in FIG. 5 b . A magnet  35  holds firmly the end surface of link  16  against joint ball  45 . In the same way, links  14  and  18  are arranged on joint ball  45  and links  15  and  17  are arranged on joint ball  46 .  
     [0074]FIG. 6 shows how single axis bearings can be coupled together to form the second arm part  7   b . The joint arrangements  24  and  25 , which connect the first arm part  7   a  to the links  16  and  17 , consist of 3 single-axis bearings  24   a ,  24   b ,  24   c  respectively  25   a,    25   b ,  25   c . The bearings  24   c  and  25   c  have a pivoting axis in the z-direction and are mounted on the part of the first arm part  7   a  that extends in the z-direction. On either side of the bearings  24   c  and  25   c , bearings  24   d ,  24   e ,  25   d ,  25   e  are arranged with pairs of common pivoting axes at right angles to the pivoting axes for beans  24   c  respectively 25c. The same bearing configuration is used to join links  16  and  17  to the second element  2  with joints  26  and  27 . To obtain a symmetric loading of the bearing link pairs  16   a ,  16   b  and  17   a ,  17   b  have been introduced. In the same manner as in FIGS. 3 and 4, a universal/cardan coupling is used to join link  18  to element  2 .  
     [0075] With the bear arrangement for the second arm part shown in FIG. 6, a robot can be built up according to FIG. 7. The figure shows how both the arm parts  8   a  respectively  6   a  are arranged with the joint arrangement according to FIG. 6.  
     [0076] To steer the rotation angle of the second element  2  around its axis of symmetry  44 , an additional arm D is joined to pivot with the first element in a single-axis joint in the form of a driving mechanism  46 . The arm D comprises a first arm part  47 , the parallel link  49  and the arm  51 . The link  49  is joined to pivot with the first arm part  47  via the joint  48  and with the arm  51  via joint  50 . The joints  48  and  50  are designed so that the link  49  can pivot in all directions relative to arm  47  and similarly can pivot in all directions relative to arm  51 , which means that the joints  48  and  50  have at least 2 degrees of freedom. In FIG. 7, the same type of joint arrangement is used for joints  48  and  50  as is used for the joints  24 ,  25 ,  26 ,  27 ,  20 ,  21 ,  22  and  23  in FIG. 6. This type of joint arrangement works for the arm D as long as the arms  47  and  51  pivot in the same plane.  
     [0077] The joints  28  respective  30  connect link  18  with the first arm part  8   a  respectively a part  52  of the second element  2  and are executed as universal/cardan couplings. For arm D to be able to pivot the second element  2  around the axis of symmetry  44 , at least one of the universal/cardan joints is complemented with a bearing  53  so that the second element  2  can pivot relative to the first am part  8   a.    
     [0078] In FIGS.  1 - 7 , the second element  2  is manipulated relative to the first element  1  with three or four degrees of freedom. However, it is also possible to carry out this manipulation  2  relative to the first element  1  with only two degrees of freedom, as is shown in FIG. 8.  
     [0079] Here, arm C is built together with arm B. The arm A is unchanged B has been complemented with. The link  18  from the arm C is arranged in the link system of the second arm part  7   b  between the parallel links  16  and  17 . The link  18  is ranged diagonally between the first arm part  7   a  and the second element  2  via the joints  28  and  30  to lock the degree of freedom of the second element  2  that is manipulated via the arm C in FIG. 1. The length of the link  18  between the joints  28  and  30  is adjusted with a built-in adjustment device  28   a.  In this manner, the inclination of the second element  2  can be steered separately from the arms A and B.  
     [0080] In FIG. 9, the pivoting mechanism  5  and thereby the attachment for the arm C has been moved and connected to the first arm part  7   a.  The second arm part  8   a  costs of a single link  18  joined to pivot with the second element  2  in the tripe-axis joint  30 . FIG. 10 shows a manipulator according to FIG. 9 where the single link  18  is replaced by the parallel links  18   c  and  18   d . The manipulators according to FIGS. 9 and 10 give a manipulation of the second element in only three degrees of freedom.