Abstract:
An industrial robot for movement of an object in space comprising a stationary platform, a movable platform adapted for supporting the object, and a first, a second and a third arm to which the platforms are joined. The first arm comprises a first actuator, a first supporting arm influenced by the first actuator and rotatable around a first axis, and a first linkage. The second arm comprises a second actuator, a second supporting arm influenced by the second actuator and rotatable around a second axis, and a second linkage. The third arm comprises a third actuator, a third supporting arm influenced by the third actuator and rotatable around a third axis, and a third linkage. The second supporting arm is freely mounted around a cross-beam that is arranged at right angles to the second axis.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to an industrial robot comprising a manipulator and control equipment where the manipulator has three arms, each arm having a linkage supporting a movable platform. The control equipment comprises drives and means including a microprocessor and software for driving and guiding the manipulator in the desired manner. To achieve the desired movement of the platform, the linkages comprise links or rods that are articulately connected between the platform and the arms. Each joint allows a movement in three degrees of freedom. The arms are fixed to stationary actuators that allow a movement in one degree of freedom. This movement comprises both rotation and translation. The task of the platform is to directly or indirectly support tools or objects for movement, measurement, processing, machining, joining, etc.  
         BACKGROUND ART  
         [0002]    For movement and rotation of objects without changing the inclination of the objects, so-called SCARA-type robots are primarily used today. These robots are designed for the four degrees of freedom, x, y, z and rotation of an object around the z-axis. For manipulation of the object in the xy-plane, two series-connected arms are used that operate in the xy-plane, the axes thus being perpendicular to the xy-plane. The fact that the arms are connected in series implies that one arm supports the other arm, which in turn supports the object. To obtain a movement in the z-direction, a linear movement device is used. This device may be located either after the series-connected arms or before the series-connected arms in the serial kinematic chain of the robot. In the former case, the series-connected arms must move the drive package for the z-movement and in the latter case the drive package for the z-movement must move the series-connected arms. The drive package for rotating the object around the z-axis will always be located furthest out in the kinematic chain of the robot.  
           [0003]    The series connection of the arms of the SCARA robot, as well as in other robots with series-connected links, implies that the robot is given a large movable mass, that the robot structure is weak, that the accuracy is limited and that large motor torques are required to make fast movements.  
           [0004]    Several of the drawbacks that are associated with the SCARA robot are overcome by a robot that manipulates a platform with three parallel-working arms. This is referred to as a parallel kinematic structure. To obtain a rigid arm system with a large loading capacity and a low weight, the outer arms of the parallel-kinematic manipulator, nearest the manipulated platform, shall consist of six links in total, which only transfer compressive and tensile forces. A manipulator for movement of a platform in space is previously known, where the platform has the same inclination and orientation in its entire working range. The known robot has three parallel-working arms, each having its own linkage. It is known in this context that the total number of links is six and that they may be optionally distributed on the arms according to the combinations 2/2/2 or 3/2/1.  
           [0005]    To more readily describe parallel-kinematic robots comprising linkages, some definitions of different linkages are introduced here:  
           [0006]    Link: A link is a member that movably joins two elements and that, at each end, allows movement in three degrees of freedom. It usually consists of a rigid elongated member such as, for example, a rod that has a ball joint at each end. The link holds the elements at a definite distance from each other and absorbs only tensile or compressive forces. Thus, a link transfers no torsional movements.  
           [0007]    Double link: A double link is a member that movably joins two elements, that at each end allows movement in three degrees of freedom, and that transfers a moment in a plane between the elements. The double link consists of a quadrangle with, for example, two links, according to the above, that form a first pair of links and the elements that form the second pair of links. In a special case, the double link is a parallelogram, in which case the two elements are forced to move in parallel with each other. Since all joints allow movement in three degrees of freedom, this implies that the double link may twisted. Thus, the double link needs help from other linkages to remain plane.  
           [0008]    Locked double link: A locked double link is a member that movably joins two elements that, at each end, allows movement in two degrees of freedom. The locked double link consists of a double link according to the above, wherein at least one diagonal is locked. This is achieved, for example, by introducing in the quadrangle an additional link that is not parallel to any of the other links. This prevents the elements from being displaced, but still the locked double link may be twisted.  
           [0009]    Triple link: A triple link is a member that movably joins two elements, that at each end allows movement in three degrees of freedom, and that transfers a moment in two planes between the elements. The triple link usually consists of two double links, oriented in different planes, with one common link. In a special case, the triple link comprises a space parallelogram consisting of three parallel links of equal length. Such a space parallelogram may be twisted but maintains the elements oriented in parallel planes.  
           [0010]    Triangle: A triangle is a member that movably joins two elements and that at one end (the base) allows movement in one degree of freedom and at its other end allows movement in three degrees of freedom.  
           [0011]    The triangle consists, for example, of a torsionally rigid member that, at its base, is journalled to a first element through an axis and at its other end is journalled to a second element by means of a ball joint. A triangle may also consist of two links according to the above, where one of the joints is common.  
           [0012]    In the following text, an arm for a robot shall mean a linkage supported by a supporting arm. By the concept supporting arm is to be understood a torsionally rigid member that movably joins two elements together and that, at both ends, allow movement in one degree of freedom. The supporting arm consists, for example, of a tube with a fork arranged at each end through which an axle passes. In a special case, the axles are parallel whereby the elements joined by the supporting arm are allowed movement in one plane only. It should be mentioned that the movement comprises rotation as well as translation. The supporting arm may, from one element to the other, transfer both tensile and compressive forces, torsional moment and bending moment.  
           [0013]    With the linkages defined above, the first of the known systems may be defined as a manipulator with three arms, each one consisting of a supporting arm and a double link. The second known manipulator may be defined as a manipulator with three arms wherein the first arm consists of a supporting arm and a link, the second arm of a supporting arm and a double link, and the third arm of a supporting arm and a triple link. It should be pointed out here that when designing according to the configuration 2/2/2, the axles of the supporting arms must cross each other to obtain an unambiguous orientation of the movable element.  
           [0014]    For a fully extended parallel-kinematic robot for movement of a platform with three degrees of freedom (e.g. in directions x, y and z in a Cartesian system of coordinates), three parallel-working arms are required. If all six degrees of freedom of the platform (x, y, z and the tool orientation) are to be manipulated, six parallel-working arms are required. Each such arm comprises an upper arm and a lower arm. In several applications, a manipulation with a combination of degrees of freedom for positioning and degrees of freedom for orientation is desired. One class of such applications is interior work in narrow spaces. In that case, it is often desired to have a robot with two degrees of freedom for tool orientation and only one degree of freedom for radial positioning.  
           [0015]    From U.S. Pat. No. 5,539,291, a parallel kinematic manipulator is previously known. A centre pillar supports a supporting arm operable around two axes. This supporting arm supports, in turn, a second supporting arm that supports a movable element. A first and a third supporting arm journalled about the same axis are connected to the movable element by means of outer arms comprising wires that, with respect to their function, may be likened to a combination of a supporting arm and a double link. The outer arms, as well as the second supporting arm, are arranged to transmit tensile and compressive forces as well as torsional moments. This entails a clumsy design of the manipulator. From the point of view of smoothness and the like, this manipulator cannot compare favourably with a corresponding manipulator where the outer arms only absorb tensile and compressive forces.  
           [0016]    From WO98/30366, a parallel kinematic manipulator is previously known. Three arms including linkages here join together a stationary element and a movable element. Three actuators fixed to the stationary element each operate an arm. A first arm includes a supporting arm with a triple link. A second arm includes a supporting arm and a double link. A third arm includes a supporting arm and a link. The links included in these linkages only need to transmit compressive and tensile stresses, which makes them very rigid, although they are designed with small dimensions and of a light material. In addition, the joints are only subjected to a normal force from the links and the bearings may therefore be made light, stiff and accurate.  
           [0017]    From WO99/58301, a further parallel kinematic manipulator is previously known. Also here, three arms including linkages join together a stationary element and a movable element. Three actuators fixed to the stationary element each operate an arm. All arms include a supporting arm with a double link, wherein the arms transmit compressive and tensile stresses only. This arm structure has been made possible by designing the manipulated platform as a frame structure in three dimensions instead of a platform in the form of a plane structure in two dimensions, as in the above known manipulator (WO98/30366).  
           [0018]    Both in the case of a two-dimensional and in the case of a three-dimensional manipulated platform according to the above-referred known manipulators, the problem arises that the arm that provides the movement of the robot in the vertical direction (in the z-direction) is influenced by large forces. In the case of large movements of the other arms (in the xy-plane), this arm will be influenced not only by torsional moments but also by strong bending moments. Especially unfavourable are forces that, in the outer end of the arm, act in an axial direction. The design implies that, when the robot is extended, said arm in the vertical direction will be located obliquely between the other two arms, as well as when the robot is folded together. Because of the kinematics, said arm for the z-manipulation will be located midway between the other two arms only within a narrow radial distance from the centre of the robot. This entails the following disadvantages:  
           [0019]    The working range is limited by the fact that the arm for z-manipulation is given an unfavourable position relative to the other arms.  
           [0020]    The rigidity of the robot will be limited by the fact that the arm for z-manipulation places at least one articulated rod in an unfavourable direction relative to the manipulated platform.  
           [0021]    The accuracy of the robot will be limited by the extra kinematic non-linearity created by the arm for z-manipulation.  
           [0022]    The dynamic properties and the rapidity of the robot are limited by the fact that the arm for z-manipulation is subjected to oblique dynamic forces.  
           [0023]    The kinematics of the robot does not automatically provide radial movement planes but a complicated mathematical compensation must be made in the control system for the curvature caused by the arm for z-manipulation.  
         SUMMARY OF THE INVENTION  
         [0024]    The object of the present invention is to suggest ways and means of producing a parallel-kinematic robot that exhibits a large working range and that prevents the arms of the robot from being subjected to unfavourable forces. This is achieved by an industrial robot with a manipulator comprising a stationary element, a movable element and three arms interconnecting the elements, each arm having a supporting arm and a linkage supported by the supporting arm, the movement plane of a central arm being adapted to intersect the movable element upon all movements.  
           [0025]    From a first aspect of the invention, the manipulator comprises a linkage that allows the movable element a movement in space, where the orientation of the element is all the time the same irrespective of position. From a second aspect of the invention, the manipulator comprises a linkage that allows the movable element a movement along a conceived cylinder where the radius is varied. From a third aspect of the invention, the manipulator comprises a linkage that allows the movable element a movement along a spheroid where the radius is varied.  
           [0026]    The manipulator, which is common from all aspects, comprises a first supporting arm, a second supporting arm, and a third supporting arm. The second supporting arm will be referred to below also as the central supporting arm. Besides being journalled about a first axis, around which the drive system is arranged, this central supporting arm is also freely journalled about a second axis arranged substantially in a normal plane to the drive shaft. The method for imparting to the central arm only small transverse forces comprises adapting the central arm, by connections to the other arms, to adopt a position in between these.  
           [0027]    In a first preferred embodiment, the manipulator comprises an additional supporting arm, which is journalled at the central supporting arm. The end of this additional supporting arm is joined by a first link to the first supporting arm and by a third link to the third supporting arm. In a further preferred embodiment, the additional arm comprises a triangle journalled with the base to the central supporting arm. In an additional preferred embodiment, the central supporting arm comprises a rod that is fixed to the arm and on which a sleeve is running. The rod is joined to the first and third supporting arms, respectively, by a first and third link. It should also be mentioned that the further supporting arm, the triangle or the rod may equally be arranged both between the two elements and behind the stationary element.  
           [0028]    In a further preferred embodiment, the manipulator comprises a triangle, the base of which is journalled at the outer end of the central supporting arm and the top of which is journalled to the movable element. This embodiment presupposes that the linkages, which is supported by the other two supporting arms, comprise a double link and a triple link. In this embodiment, transverse forces are thereby allowed to influence the central arm. Since the central supporting arm is freely journalled in the direction of the transverse force, these forces will be moderate. In a special case, the movable element of the manipulator is formed elongated, all the link attachments thus being arranged on a straight line. The manipulator thus shaped is operated with five links only.  
           [0029]    To lock all of the six degrees of freedom of the manipulated platform, a total of at least six (in a special case five) articulated rods are used. In this way, each articulated rod will only have to transmit tensile and compressive forces, which allow the articulated rods to be made very rigid, light and accurate. Articulated rods mounted on the same supporting arm, in those cases in which they are more than one, are mounted in parallel with one another and are made equally long.  
           [0030]    The industrial robot according to the invention also comprises a control unit that handles the movements of the manipulator. The control unit comprises drives for each of the arms, power transmission, etc., and comprises a plurality of microprocessors, which are brought to operate the manipulator by means of instructions from a computer program. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0031]    The invention will be explained in greater detail by means of embodiments with reference to the accompanying drawing wherein  
         [0032]    [0032]FIG. 1 shows a known parallel-kinematic robot in which an actuator is mounted on an arm that is turned around by another manipulator and the working range and dynamic and static performance of which are therefore considerably limited,  
         [0033]    [0033]FIGS. 2A and 2B illustrate the kinematic problems that arise when the robot according to FIG. 1 is used,  
         [0034]    [0034]FIG. 3 shows a manipulator according to the invention with a mechanism that centers the central supporting arm of the manipulator between two other supporting arms, thus solving the kinematic problems associated with the embodiment of FIGS. 2A and 2B,  
         [0035]    [0035]FIGS. 4A and 4B show two advantageous embodiments of the manipulator according to the invention,  
         [0036]    [0036]FIG. 5 shows a further advantageous embodiment of the manipulator according to the invention, where the mechanism is placed in front of the centre of the robot,  
         [0037]    [0037]FIG. 6 shows an alternative advantageous embodiment of the manipulator, in which the already existing structure in the manipulator is utilized for forming a triangle,  
         [0038]    [0038]FIG. 7 shows an additional advantageous embodiment of a manipulator according to the invention, wherein the centring mechanism comprises a locked double link formed from links in combination with existing links, whereby the normal to the platform manipulated by the robot will always be directed radially outwards from the centre of the robot, and  
         [0039]    [0039]FIG. 8 shows an advantageous embodiment of the manipulator according to FIG. 7. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0040]    [0040]FIG. 1 shows a parallel-kinematic robot, which is a development of the known structures disclosed in, inter alia, U.S. Pat. No. 5,539,291. The robot is mounted on a foot  1 A, on which a column  1 B is secured. On this column there is arranged a first actuator  2  that pivots a first supporting arm  5  around a first axis, and a second actuator  3  that pivots a second supporting arm  6 A around a second axis. Both axes are parallel to each other, whereby the two supporting arms are each pivoting in respective horizontal planes shown in the figure. The actuators  1  and  2  are of the rotary type with coinciding vertical axes of rotation. On the arm  6 A, an element  1 C is secured by means of a holder  1 D, and on this element a third actuator  4  is mounted. This causes the actuator  4  to be rotated by the actuator  3  around the vertical axis of rotation of the actuator  3 . The third actuator  4  pivots a third supporting arm  7 A in a vertical plane shown in the figure. The third axis is thus oriented substantially across the other two axes. When the actuator  3  pivots the arm  6 A, the arm  7 A will thus accompany the movement of the arm  6 A and the angle between the projection of the arm  7 A (in a horizontal plane extending through the arm  6 A) and the arm  6 A will be constant.  
         [0041]    On the arm  5 A, an articulated-rod arrangement consisting of three articulated rods  8 A,  8 B and  8 C in a triangular configuration is mounted with the aid of joints  11   a ,  11 B and  11 C, respectively. At their other ends, the articulated rods  8 A,  8 B and  8 C are mounted with the aid of the joints  12 A,  12 B and  12 C, respectively, on the platform  17  that is to be manipulated by the robot. The articulated rods  8 A,  8 B and  8 C have equal lengths and are mounted in parallel. This arrangement forms a triple link. The platform  17  is maintained parallel to the surface that is put up by the arm  5 A and the vertical rod  5 B, which is fixedly mounted on the arm  5 A.  
         [0042]    On the arm  6 A, the vertical rod  6 B is mounted in a corresponding manner, and the arm  6 A is connected to the platform  17  via the articulated-rod arrangement consisting of the articulated rods  9 A and  9 B. The articulated rods  9 A and  9 B are at one of their ends connected to the arm  6 A and the rod  6 B through the joints  13 A and  13 B, respectively, and at their other end connected to the platform  17  through the joints  14 A and  14 B. The articulated rods  9 A and  9 B are mutually parallel and have equal lengths. This arrangement forms a double link. The platform  17  is maintained parallel to the rod  13 A. In this embodiment, the articulated-rod arrangement between the third supporting arm  7 A and the platform  17  consists of only one link, which is articulately connected to the arm  7 A through the joint  15 A and the platform  17  through the joint  16 A.  
         [0043]    All the joints may have two or three degrees of freedom. In order not to obtain inherent stresses in the structure, for each articulated rod at least one end should have a joint with three degrees of freedom.  
         [0044]    When the actuators  2  and  3  cause the arms  5 A and  6 A to pivot relative to each other, the platform  17  will be moved substantially radially outwards/inwards away from/towards the column  1 B and when the actuators  2  and  3  are run synchronously in the same direction, the arms  5 A and  6 A will pivot in the same direction with a constant mutual angle and the platform  17  will be pivoted along a circular orbit with the column  1 B in the centre. When the actuator  4  pivots the arm  7 A, the platform  17  will be moved substantially upwards/downwards, and all in all a symmetrical toroidal working range around the column  1 B is obtained, which may be compared with the working range of a conventional, so-called SCARA robot.  
         [0045]    [0045]FIG. 2 is a schematic picture of the robot in FIG. 1 seen from above, partly in a position where the platform  17  is near the column  1 B (FIG. 2A), and partly where the platform  17  is far away from the column  1 B (FIG. 2B). The arm  5  ( 5 A and  5 B in FIG. 1) is connected to the platform  17  via the articulated-rod arrangement  8  ( 8 A,  8 B,  8 C). On the articulated-rod arrangement  8 , the joints  11  ( 11 A,  11 B and  11 C) are positioned at one end and the joints  12  ( 12 A,  12 B and  12 C) are positioned at the other end. In a corresponding manner, the arm  6  ( 6 A,  6 B) is connected to the platform  17  via the joints  13  ( 13 A,  13 B), the articulated rods  9  ( 9 A and  9 B) and the joints  14  ( 14 A,  14 B). Finally, the arm  7  is connected to the platform  17  via the joint  15 , the articulated rod  10  and the joint  16 .  
         [0046]    Because of the parallel articulated rods  8  ( 8 B,  8 C), the platform  17  will always be parallel to the arm  5  ( 5 A), and in FIG. 2A, therefore, the platform  17  is angled to the left and in FIG. 2B to the right. Since the actuator  4  (see FIG. 1) is mounted on the arm  6   a , the angle between the arm  7  and the arm  6 , viewed from above as in FIG. 6, will always be constant. This means that the arm  7  in FIG. 2A will be situated nearer the arm  6  that the arm  5  and that the arm  7  in FIG. 2B will be situated nearer the arm  5  than the arm  6 . From this follows, in turn, that the working range of the robot cannot be utilized in full and that different oblique loads are imparted to the arm  7  in dependence on where in the working range the platform  17  is situated. To eliminate these problems, a robot structure is required that will ensure that the arm  7  will always be situated midway between the arms  5  and  6 .  
         [0047]    [0047]FIG. 3 shows a mechanism for forcing the arm  7  to always be situated midway between the arms  5  and  6  (viewed in a projection on the horizontal plane). The only difference between the robot in FIG. 3 and in FIG. 1 is that the coupling  1 D in FIG. 1 has been replaced by a bearing  18 . This bearing enables the element  1 C of the central column to rotate freely relative to the element  1 B of the central column and the actuators  2  and  3 . What is now required is an extra mechanism on the robot that ensures that the arm  7 A is always situated midway between the arms  5 A and  6 A or at least situated in a position with a constant angular ratio between the arms  5 A and  6 A. The simplest way of doing this is, of course, to install a fourth motor that rotates in the element  1 C relative to the element  1 B, but this results in a robot which is both more expensive and heavier. Instead, in FIG. 3, an extra articulated-rod mechanism ( 19 - 26 ) has been introduced behind the robot.  
         [0048]    The swinging arm  19  is mounted on an axle  20  on the element  1 C and is capable of pivoting in a vertical plane behind the robot. At the other end, the pivoting arm  19  is mounted via the joints  23  and  24  (the joint  24  is located behind the arm  19  in the figure) on the articulated rods  21  and  22 , respectively. These articulated rods are then mounted on the arms  6 A and  5 A, respectively, by means of the joints  25  and  26 , respectively. When the arms  5 A and  6 A move relative to each other, the articulated rods  21  and  22  will pivot the arm  19  up/down in a plane determined by the ratio between the articulated rods  21  and  22 . Since this ratio is constant, said plane will end up with a constant ratio between the arms  5 A and  6 A, and the arm  7 A will always pivot with this ratio between the arms  5 A and  6 A. If the ratio is chosen to be 1/1 (links  21  and  22  being of the same length and joints  25  and  26  lying in the same horizontal plane, which they do not in the figure), the arm  7 A will always be located midway between the arms  5 A and  6 A.  
         [0049]    The joints  23 ,  24 ,  25  and  26  must all have at least two degrees of freedom each. The axle  20  gives the arm  19  one degree of freedom relative to the element  1 C.  
         [0050]    [0050]FIG. 4 shows a robot viewed from behind to more clearly illustrate the mechanism for centring the arm  7 A. The parallel-kinematic robot itself differs, from the point of view of structure, from the one in FIG. 1 as far as the platform  17  is concerned. The platform in FIG. 4 consists of an axle  17  with a cross-beam  17 B. On the axle  17 , the joints  16 A,  12 A,  14 A,  12 B and  14 A are mounted along a common symmetry line. On the cross-beam  17 B, the joint  12 C is mounted. The joints  12 A,  12 B and  12 C connect the platform  17 / 17 B to the articulated rods  8 A,  8 B and  8 C, respectively, and these articulated rods are then mounted on the arm parts  5 B and  5 C by means of the joints  15 A,  15 B and  15 C, respectively. The arm parts  15 B and  15 C are secured to the arm  5 A, which is driven round by the actuator  2 , which in this figure is mounted above the motor  3  on the column  1 B. The actuator  3  drives the arm  6 A, on which the articulated rods  9 A and  9 B are mounted via the joints  13 A and  13 B, respectively. At their other ends, the articulated rods are mounted on the platform axle  17  by way of the joints  14 A and  14 B, respectively. The actuator  4  is mounted on the element  1 C, which is capable of being rotated relative to the column  1 B through the bearing  18 , which has its axis of rotation coinciding with the axes of rotation of the actuators  2  and  3 . The actuator  4  is connected to the platform  17  via the arm  7 A, the arm part  7 B, the joint  15 A, the articulated rod  10 A and the joint  16 A.  
         [0051]    The centring of the arm  7 A between the arms  5 A and  6 A is here carried out with the aid of the mechanism  19 - 26 . This mechanism has been made more rigid than that shown in FIG. 3 by mounting double pivoting arms  19 A and  19 B on the axle  20  on the platform part  1 C. When the arms  5 A and  6 A are moving relative to each other, the articulated rods  21  and  22  will, via the common joint  23 , pivot the arm pair  19 A and  19 B upwards/downwards around the axle  20 . If the articulated rods  21  and  22  are of equal length and if the joints  25  and  26  are mounted in the same horizontal plane, then the arm  7 A will be guided to end up midway between the arms  5 A and  6 A. In FIG. 4B, a variant of the centring mechanism in FIG. 4A is shown. Here, the joint  23  has been replaced by the two joints  23  and  24 , which is mounted on a system of pivoting arms that, besides the arms  19 A and  19 B, consists of a cross-beam  19 C. This design provides a somewhat lower rigidity than the design of FIG. 4A but provides a simpler joint design.  
         [0052]    For both FIGS. 4A and 4B, the joints  23 - 26  have at least two degrees of freedom each.  
         [0053]    [0053]FIG. 5 shows the same robot as in FIG. 3 but with the mechanism for centring of the arm  7 A in front of the column  1 B instead of behind as in FIGS. 3 and 4. In the same way as in FIG. 3, the joint  25  is mounted on the arm  6 A and the joint  26  on the arm SA. However, the joints  20 A and  20 B are now not directly mounted via an axle on the column segment  1 C but are now mounted on a cross-beam  7 B on the arm  7 A. The links  21  and  22  are mounted at one end on the joints  25  and  26 , respectively, and at their other ends on the common joint  23 . The links  19 A and  19 B are also mounted on the common joint  23  and at their other ends on the joints  20 A and  20 B. The common joint  23  may, of course, be divided into two or more joints in the same way as in FIG. 4B. All the joints of this centring mechanism have at least two degrees of freedom.  
         [0054]    [0054]FIG. 6 shows the same robot as in FIG. 3 but now with a different mechanism for centring the arm  7 A between the arms  5 A and  6 A. This mechanism is based on the fact that the bearing  18  introduces another degree of freedom of the assembled robot structure and that this provides a possibility, by redundant locking of degrees of freedom of the platform  17 , of locking the new degree of freedom arisen through the bearing  18  between the column  1 B and the element  1 C. In the figure, the redundant locking is performed with the aid of the seventh articulated rod  10 B. This articulated rod is, at one end, mounted via the joint  16 A on the platform  17  and, at its other end, via the joint  15 B on the cross-beam  7 B, which is secured to the arm  7 A. In the figure, the articulated rod  10 B shares the same joint with the articulated rod  10 A, which is necessary for the platform  17  to be able to rotate around a vertical axis of rotation since it is to be maintained parallel to the arm  5 A through the articulated rods  8 B and  8 C. At its upper end the articulated rod  10 A is mounted by means of the joint  15 A in the cross-beam  7 B. The joints  15 A and  15 B may have one, two or three degrees of freedom and the joint  16 A must have at least two degrees of freedom. In the case where the joints  15 A and  15 B have only one degree of freedom, the axes of rotation of these must be coinciding. It is to be preferred that all the joints ( 15 A,  15 B and  16 A) have three degrees of freedom to prevent mechanical stresses from building up in the articulated rods and the joints.  
         [0055]    [0055]FIG. 7 shows a variant of the robot in FIG. 6. In the same way as in FIG. 6, seven articulated rods are used between the three arms ( 5 A,  6 A and  7 A) of the robot and the platform  17 , but now a different distribution of articulated rods between the arms has been made. Thus, the arms  5 A and  6 A are connected to the platform  17  through two articulated rods each ( 8 B  8 C and  9 A,  9 B, respectively). To obtain a total of seven articulated rods between the platform and the arm system, the arm  7 A must now be connected to the platform  17  by three articulated rods. In order that all the six degrees of freedom of the platform plus the degree of freedom due to the bearing  18  shall now be locked, a maximum of two of these three articulated rods ( 10 A,  10 B,  10 C) must be parallel. Thus, in FIG. 7 the articulated rods  10 A and  10 C are parallel whereas the articulated rod  10 B is diagonally mounted between the articulated rods  10 A and  10 C. The three articulated rods  10 A,  10 B and  10 C will require that a line through the joints  16 A- 16 C be parallel to a line through the joints  15 A- 15 C, and for this to be possible, the arm  5 A has been provided with a parallelogram mechanism. This mechanism adjusts the beam  34 B such that this is always parallel to the beam  7 B, whereby the platform  17  will no longer follow the orientation of the arm  5 A but will always have the same constant orientation relative to the arm  7 A that is centred midway between the arms  5 A and  6 A. The parallelogram mechanism comprises the arm  30 , which is secured to the element  1 C, the free flexible axle  31 , the parallelogram arm  33  that is parallel to the arm  5 A, the free flexible axles  35  and  36 , and the L-formed beam  34 A- 34 B. When the arm  5 A is rotated relative to the element  1 C, the beam part  34 B of the L-formed beam  34 A- 34 B will be pivoted by the parallelogram arm  33  such that the beam part  34 A is maintained parallel to the beam  30  that is secured to the column element  1 C, which, with a suitable choice of the angle between the beam parts  34 A and  34 B, means that the beam part  34 B is maintained parallel to the beam  7 B. It should be mentioned that the perspective drawing in the figure is not satisfactory, but in the figure a line through the joints  11 B and  11 C shall be parallel to a line through the joints  12 B and  12 C and parallel to a line through the joints  16 A,  16 B and  16 C as well as parallel to a line through the joints  15 A,  15 B and  15 C. It should also be pointed out that the mechanics between the beam  30  and the parallelogram arm  33  is only schematically drawn. There should actually be a frame structure here in order to obtain a rigid joint around the axle  31 .  
         [0056]    [0056]FIG. 8, finally, shows a variant of the structure in FIG. 7. With the introduction of the bearing  18 , articulated rods are required between the arm system and the platform  7 . In FIG. 7, these articulated rods are distributed among the arms  5 A,  6 A and  7 A as 2/2/3. However, there are also other functioning distributions, as, for example, 3/2/2 and 3/1/3. The case of 3/1/3 is shown in FIG. 8. The only thing that has been added here relative to FIG. 7 is that the beam angle  34 A- 34 B has been supplemented with the vertical beam  34 C, on which the articulated rod  8 A has been mounted and that the articulated rod  9 A has been removed. In the case of 3/2/2, the articulated rod  8 A according to FIG. 8 and the link  9 A according to FIG. 7 are used whereas the link  10 C is suitably removed from the arm  7 A.  
         [0057]    The joints  15 A,  15 B,  15 C,  16 A,  16 B and  16 C in both FIG. 7 and FIG. 8 may have either one, two or three degrees of freedom. In the case of one degree of freedom, the axes of rotation of the joints  15 A,  15 B and  15 C shall coincide, and likewise the axes of rotation of the joints  16 A,  16 B and  16 C shall coincide.  
         [0058]    The articulated rods  8 A,  8 B,  8 C,  9 A,  9 B,  10 A,  10 B are mounted on the platform  17  by means of the joints  12 A,  12 B,  12 C,  14 A,  14 B,  16 A. In a corresponding manner, the articulated rods  8 A,  8 B,  8 C,  9 A,  9 B,  10 A,  10 B are mounted by means of joints  11 A,  11 B,  11 C,  13 A,  13 B,  15 A on the three pivoting arms  5 A,  6 A,  7 A in order to form kinematic chains. Thus, a first kinematic chain is obtained consisting of a first element  1 C, on which the third pivoting arm  7 A is mounted, the third pivoting arm itself  7 A and the articulated rods  10 A,  10 B connected to the third pivoting arm  7 A. A second kinematic chain is defined by a second element  1 B, on which the first two pivoting arms  5 A,  6 A are mounted, one  5 A of the first two pivoting arms  5 A,  6 A, the articulately rods  8 A,  8 B,  8 C connected to said one  5 A of the first two pivoting arms, the manipulated platform  17 , the articulated rods  9 A,  9 B connected to the other  6 A of the said first two pivoting arms mounted on said element  1 B, and the other  6 A of said first two pivoting arms  5 A,  6 A.  
         [0059]    The articulated rods mounted on the same pivoting arm are mounted, in those cases where there are more than one, parallel to one another and are made with equal lengths. The joints  11 A,  11 B,  11 C,  12 A,  12 B,  12 C,  13 A,  13 B,  14 A,  14 B of the articulated rods  8 A,  8 B,  8 C,  9 A,  9 B that are included in the second kinematic chain have two or three degrees of freedom whereas the joints  15 A,  15 B,  15 C,  16 A,  16 B,  16 C of the articulated rods  10 A,  10 B,  10 C that are included in the first kinematic chain may also have one degree of freedom.  
         [0060]    To obtain a robot with a large working range and with good dynamic properties, the axes of rotation, around which the above-mentioned first two pivoting arms  5 A,  6 A are pivoting, must not be perpendicular to each other and the best performance is obtained if these axes of rotation are parallel and preferably coinciding. For the third pivoting arm  7 A, its axis of rotation must not be parallel to any of the axes of rotation of the first two pivoting arms  5 A,  6 A, and the best performance is obtained if the axis of rotation of the third pivoting arm  7 A is perpendicular to the axes of rotation of both of the first two pivoting arms  5 A,  6 A.  
         [0061]    The invention comprises a robot in which the above-mentioned first element  1 C is connected to the above-mentioned second element  1 B via a bearing  18  such that the first element  1 C may be freely rotated relative to the second element  1 B. This implies that the third pivoting arm  7 A, which is mounted via a joint or a rotating actuator  4  on the first element  1 C, may pivot in different directions relative to the second element  1 B. With the introduction of said bearing  18 , an extra degree of freedom has been introduced between said first kinematic chain and said second kinematic chain, which may be utilized for guiding the first kinematic chain such that a favourable position of the components thereof  1 C,  4 ,  7 A,  7 B,  15 A,  10 A is obtained relative to the components  5 A,  5 B,  5 C,  11 A,  11 B,  11 C,  8 A,  8 B,  8 C,  12 A,  12 B,  12 C,  17 ,  17 A,  14 A,  14 B,  9 A,  9 B,  13 A,  13 B,  6 A,  6 B in the second kinematic chain when said platform  17  is manipulated by the robot in its working range.  
         [0062]    The inventive concept comprises guiding the above-mentioned kinematic chains relative to each other by introducing a bridge between these kinematic chains. This bridge comprises one or more extra articulated rods  10 B,  10 C,  21 ,  22  connected to joints  15 B,  16 A,  15 C,  16 C,  23 ,  24 ,  25 ,  26  directly or via pivoting arms  19 ,  19 A,  19 B and/or other extra articulated rods  19 A,  19 B. Since said kinematic chains are separated by the previously mentioned bearing  18 , said bridge will lock the degree of freedom of rotation provided by said bearing  18 .  
         [0063]    The inventive concept also comprises mounting said bearing  18  such that its axis of rotation is not perpendicular to the axes of rotation of said first two pivoting arms  5 A,  6 A and not parallel to the axis of rotation of said third pivoting arm  7 A. To obtain the largest possible working range and optimum dynamic properties of the robot, said bearing  18  is mounted such that its axis of rotation becomes parallel to and preferably coinciding with the axes of rotation of said first two pivoting arms  5 A,  6 A and at the same time perpendicular to the axis of rotation of said third pivoting arm  7 A.  
         [0064]    The inventive concept also comprises mounting an extra articulated rod  10 B between the manipulated platform  17  and the third pivoting arm  7 A to obtain said bridge that is to lock the degree of freedom of rotation provided by said bearing  18 . This extra articulated rod is mounted at an angle relative to the already existing articulated rod  10 A between the platform  17  and the third pivoting arm  7 A. At one end the extra articulated rod  10 B is mounted on the platform  17  by a common joint  16 A with the already existing articulated rod  10 A and at its other end the extra articulated rod  10 B is mounted on a beam  7 B some distance away from the existing articulated rod  10 A. The beam  7 B is secured to the third pivoting arm  7 A and is mounted so as not to become parallel to the third pivoting arm  7 A but preferably perpendicular thereto. In that way, a movement of the platform  17  in the lateral direction will force the third pivoting arm and the first element  1 C to rotate on said bearing  18  and thus to accompany the movement of the platform in the lateral direction, which, in turn, means that the third pivoting arm will be situated in the centre of the working range between the first two pivoting arms  5 A,  6 A. The extra articulated rod  10 B and the existing articulated rod must have a common rod  16 A towards the platform  17  to allow this to rotate when being manipulated in the radial direction relative to the centre of the robot.  
         [0065]    The inventive concept also comprises using a kinematic bridge that does not need a common joint  16 A towards the platform  17 . To this end, a parallelogram mechanism  30 ,  31 ,  33 ,  35 ,  34 A,  36  is introduced in one of the first two pivoting arms. By connecting this parallelogram mechanism between the first element  1 C and the articulated rods  8 A,  8 B,  8 C belonging to the current one  5 A of the first two pivoting arms, the platform  17  will always be capable of being maintained parallel to a cross-beam  7 B to the third pivoting arm  7 A. This makes it possible to use two or more articulated rods between the manipulated platform  17  and the cross-beam  7 B to the third pivoting arm  7 A without a common joint being required at the platform  17 . For example, when using two articulated rods when connecting the third pivoting arm  7 A to the platform  17 , a triangular configuration of the articulated rods, with its base on the platform  17 , may be used. Further, when two articulated rods are used, a parallelepipedic configuration may be used. When two articulated rods are used between the third pivoting arm  7 A and the platform  17 , the first two pivoting arms  5 A,  6 A will need together five articulated rods to the platform  17 , in which case the distribution between the pivoting arms is three for one of the pivoting arms and two for the other. If instead three articulated rods  10 A,  10 B,  10 C are mounted between the cross-beam  7 B of the third pivoting arm  7 A and the platform  17 , only four articulated rods altogether will be required for the first two pivoting arms  5 A,  6 A, and these may then be distributed in two different ways, either two articulated rods each for the first two pivoting arms  5 A,  6 A or three articulated rods for one and one articulated rod for the other of the first two pivoting arms. When three articulated rods are used between the third pivoting arm and the platform, all the three articulated rods may not be mounted in parallel but at least one articulated  10 B must be mounted at an angle relative to the other articulated rods  10 A,  10 C. In fact, none of these articulated rods  10 A,  10 B,  10 C need to be parallel. On the other hand, all the joints  16 A,  16 B,  16 C of the articulated rods towards the platform must be situated along a line that is parallel to a line through the joints  15 A,  15 B,  15 C of the articulated rods towards said cross-beam  7 B. These lines should, in addition, be parallel to the axis of rotation of the third pivoting arm  7 A. It should be pointed out that the joints  15 A,  15 B,  15 C,  16 A,  16 B,  16 C may have one, two or three degrees of freedom, and in the case of one degree of freedom all the joints at the same end of the articulated rods shall have coinciding axes of rotation. Preferable is to have three degrees of freedom at one end of the articulated rods and two or three degrees of freedom at the other end of the articulated rods in order not to build mechanical stresses into the articulated rods and the rest of the robot structure. For an optimum design, there should be no redundancy as far as locking of degrees of freedom in the previously mentioned kinematic chains is concerned.  
         [0066]    The inventive concept comprises supplementing the extra articulated rods  21 ,  22  by extra pivoting arms  19 ,  19 A,  19 B and/or additional extra articulated rods  19 A,  19 B. The pivoting arms and the additional extra articulated rods are connected either to the above-mentioned first element  1 C or to the third pivoting arm  7 A. The extra pivoting arm  19  is suitably mounted on the other element  1 C via a joint with one degree of freedom so that the axis of rotation of the extra pivoting arm  19  is essentially parallel to the axis of rotation of the third pivoting arm  7 A. The additional extra articulated rods  19 A,  19 B are mounted on a cross-beam, either on the third pivoting arm  7 A or on the second element  1 C. One  21  of the extra articulated rods  21 ,  22  is mounted at one end via a joint  25  with two degrees of freedom on one  6 A of the first two pivoting arms and at its other end via a joint  23  with two degrees of freedom on said pivoting arms and/or additional articulated rods. The other  22  of the extra articulated rods  21 ,  22  is mounted at one end via a joint  26  with two degrees of freedom on the other  5 A of the first two pivoting arms and at its other end via a joint  24  with two degrees of freedom on said pivoting arms and/or additional articulated rods. In this way, said first kinematic chain is connected to said second kinematic chain and the extra degree of freedom through said bearing  18  is locked. This locking may easily be made such that the third pivoting arm  7 A will always be situated midway between the first two pivoting arms  5 A,  6 A.