Abstract:
An indusurial robot for movement of an object in space comprising a platform arranged for carrying the object, a first arm arranged for influencing the platform in a first movement and comprising a first actuator and two links, each of which comprises an outer joint arranged in the platform and an inner joint arranged in the first actuator, a second arm arranged for influencing the platform in a second movement and comprising a second actuator and two links, each of which comprises an outerjoint arranged in the platform and an inner joint arranged in the second actuator, and a third arm arranged for influencing the platform in a third movement and comprising a third actuator and a link, which comprises an outer joint arranged in the platform and an inner joint arranged in the third actuator. The first actuator comprises a first motor, a first path arranged in a first plane and a first carriage linearly movable along the first path, whereby the two innerjoints are displaceable in parallel, the second actuator comprises a second motor, second path arranged in a second plane and a second carriage linearly movable along the second path, whereby the two innerjoints are displaccable in parallel, and the third actuator comprises a third motor, a third path arranged in a third plane and a third carriage linearly movable along the third path, whereby the inner joint is linearly displaceable.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to an industrial robot comprising a manipulator and control equipment for moving an object in space. The manipulator comprises a platform jointly supported by a plurality of arms comprising linkages. Each arm is associated with an actuator with the purpose of moving the linkage of the arm in parallel such that a movement of the platform is attained. The task of the platform is to directly or indirectly support tools or objects, large as well as small, for movement, measurement, processing, working, joining, etc. In particular, the manipulator is intended to be used in the manufacturing industry but also transfer of goods and passageways for passengers in harbours and airports may come into question.  
         BACKGROUND ART  
         [0002]    A manipulator which comprises more than one arm and where at least two arms each form a chain of joints between the actuators of the manipulator and the platform which is to be manipulated is called a parallel kinematic manipulator. For a fully built-up parallel kinematic manipulator 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, and if all the six degrees of freedom of the platform are to be manipulated, six parallel-working arms are required. In many industrial applications where at present linear manipulators of a socalled gantry type are used, four degrees of freedom are normally required, which means that a corresponding parallel kinematic manipulator shall have four parallel arms.  
           [0003]    To obtain a stiff arm system with a large loading capacity and a low weight, the lower arms of the parallel kinematic manipulator nearest the manipulated platform shall have a total of six links which only transmit compressive and tenO sile forces. For a manipulator for four degrees of freedom and four arms, this implies that the four lower arms must share the six links between them and this can only be done with certain combinations, such as, for example, 2/2/1/1 or 3/1/1/1. If one of the links is used for transmitting torque in addition to compressive and tensile forces, the following possible combinations for a parallel kinematic manipulator with four degrees of freedom are also obtained: 3/2/1, 2/2/2. These combinations may also be used when only three degrees of freedom are to be manipulated in the manipulated platform.  
           [0004]    When a rectangular working range is required in manipulator applications, so-called gantry manipulators are used today. These manipulate a platform with normally four degrees of freedom: x, y, z and rotation around the z-axis. To this end these manipulators are composed of one axis of rotation and three series-connected linear paths, on which movable units are moved in the x-, y- and z-directions. The first movable unit, which is moved along a first linear path of an actuator, supports a second linear path mounted perpendicular to the first linear path. On the second linear path, there is then a second movable unit which in turn supports a third linear path, which is mounted perpendicular to both the first and second linear paths. On the third linear path there is a third movable unit, which supports an axis of rotation when the manipulator has four degrees of freedom.  
           [0005]    The series connection of the linear paths with their associated movable units and actuators impose a number of restrictions on current gantry manipulators.  
           [0006]    The manipulator becomes very heavy, which limits its speed of action and results in a need of expensive and energy-consuming actuators (motors).  
           [0007]    The manipulator becomes weak and when objects or tools are moved, a undesired oscillation of the manipulator is obtained in case of movement along the path where the movement is to be made, and especially when the movement is to be stopped, so-called overshoots are obtained.  
           [0008]    The manipulator becomes resilient when the platform is to generate forces between tools and objects, unless very expensive and complex solutions for the liner paths are used.  
           [0009]    For the movable actuators with their associated measuring sensors, movable cabling is required, which causes poor reliability in gantry manipulators.  
           [0010]    It is difficult to obtain high accuracy of the manipulator without providing expensive solutions involving, for example, air bearings, which at the same time give the manipulator limited speed of action.  
           [0011]    Two parallel linear paths are normally used for supporting the second linear path in the serial kinematic chain. This gives rise to an effect similar to that of a drawer in a chest of drawers getting wedged when being pushed it, and requires special, costly solutions to manage.  
           [0012]    All of these limitations when using gantry manipulators can be eliminated by a parallel kinematic manipulator which is driven by parallel-working linear paths, which do not need to support each other but where all the paths may be mounted on a fixed frame structure. An example of such a parallel kinematic robot is Hexaglide, developed at the Technical Institute of Technology ETH in Zurich. The kinematics of this is clear from FIG. 1, which is described in the section DESCRIPTION OF THE PREFERRED EMBODIMENTS. Here, six movable units on three linear paths are used for guiding six degrees of freedom of the manipulated platform with the aid of six parallel links. This manipulator will have an arm system with a very low weight, will be rigid, may achieve large tool forces without yielding, has no movable cabling and may be given very high accuracy. However, this manipulator has too small a working range to replace the gantry manipulators that are used at present in various industrial applications. In addition, this parallel kinematic robot requires six actuators also when only four degrees of freedom are to be manipulated, which results in an unnecessarily high price of the manipulator. Finally, the control programs which are to attend to the movement of the manipulator become extensive.  
         SUMMARY OF THE INVENTION  
         [0013]    The present invention comprises a new base structure for parallel kinematic manipulators based on linearly driven actuators and which solve the problems which occur in the parallel kinematic manipulator described above. With the embodiments for parallel kinematic manipulators based on the new base structure described in this invention, most of the current industrial requirements of manipulators with rectangular working ranges may be solved at a lower cost and with a higher performance compared with current serial kinematic gantry structures. Examples of gantry manipulators which may be replaced by a parallel kinematic structure according to the invention are:  
           [0014]    Coordinates measuring machines for high-precision measurement of components and prefabricated products in the engineering industry.  
           [0015]    Machine tools for grinding, drilling, milling, deburring and other machining.  
           [0016]    Test machines in semiconductor manufacture, wherein semiconductor plates are to be moved to a probe station and be pressed with great force against a matrix of contacts for measuring the quality of the semiconductor material.  
           [0017]    Assembly machines for electronics, wherein the electronic components with great speed and high precision are to be moved to a correct position on, for example, a printed circuit board.  
           [0018]    Handling robots for pharmaceutical applications, for example for moving microplates during screening.  
           [0019]    Handling robots for moving components and products in the engineering industry, for example during assembly of cars.  
           [0020]    The invention comprises a manipulator which is composed of a parallel kinematic arm system which is driven by movable units on parallel linear paths. The requirement that the linear paths be parallel is due to the fact that the working range of the manipulator is to be rectangular and scalable. By choosing different lengths of the parallel linear paths, different lengths of the working range may be obtained and by choosing different distances between the parallel linear paths, different widths of the working range may be achieved. The linear paths may be floor-mounted, wallmounted, roof-mounted, or be a combination of these methods of mounting. In all of these cases, the drive system including actuators rigidly mounted on the linear paths and no movable cabling needs to accompany the movable units when these are moved along the linear paths.  
           [0021]    Thus, the invention comprises a manipulator for moving an object in space comprising a platform designed for supporting objects, a first arm adapted to influence the platform in a first movement and comprising a first actuator and two links, each of which comprises an outer joint arranged in the platform and an inner joint arranged in the first actuator, a second arm adapted to influence the platform in a second movement and comprising a second actuator and two links, each of which comprises an outer joint arranged in the platform and an inner joint arranged in the second actuator, and a third joint adapted to influence the platform in a third movement and comprising a third actuator and a link, which comprises an outer joint arranged in the platform and an inner joint arranged in the third actuator, whereby the first actuator comprises a first motor, a first path arranged in a first plane and a first carriage linearly movable along the first path, by means of which the two inner joints are displaceable in parallel, the second actuator comprises a second motor, a second path arranged in a second plane and a second carriage linearly displaceable along the second path, by means of which the two inner joints are displaceable in parallel, and that the third actuator comprises a third motor, a third path arranged in a third plane and a third carriage linearly movable along the third path, by means of which the inner joint is linearly displaceable.  
           [0022]    In an advantageous embodiment of the invention, all the outer joints are arranged along one and the same straight line of the platform.  
           [0023]    In another advantageous embodiment, the first arm comprises an additional link with an inner joint arranged in the first carriage and an outer joint arranged in the platform, whereby all the links of the first arm are arranged in parallel.  
           [0024]    In other embodiments, the paths are arranged in different ways. They are thus arranged in the same plane, in different planes, or in angled planes. The paths are also arranged jointly for several carriages.  
           [0025]    In yet another embodiment, the manipulator is arranged with a fourth arm for influencing a fourth movement of the manipulator. This movement may be rotation of the platform. The movable units, the carriages, which move with parallel linear movements on the linear paths, support the parallel kinematic arm system. To obtain a high rigidity, a high accuracy and a low weight of the arm system, this system is designed such that the platform that is to be manipulated is mounted with the aid of joints on six links (articulated rods), with one joint per articulated rod. Each joint has two or three degrees of freedom and the articulated rods are configured such that they may lock or manipulate each one of the six degrees of freedom of the platform. In their other end, the articulated rods are mounted via joints either directly on the movable units or on some type of arm which in turn is mounted on one or more of the movable units. Also at their other end, the articulated rods have joints with two or three degrees of freedom and the articulated rods are, in all cases but one, configured in such a way that they only need to transmit compressive and tensile stresses. The exception is the case where one of the articulated rods is used for transmitting a rotary movement to the manipulated platform. In this case, the articulated rod in question serves as a universal transmission.  
           [0026]    The main object of the invention is to suggest ways and means of manufacturing a manipulator with four degrees of freedom for positioning (x, y, z) of the manipulated platform. Additional advantages are obtained by performing rotation of the manipulated platform around an axis (the z-axis) without simultaneously giving rise to rotation of the manipulated platform around any other axis (the x- or z-axis). This manipulation is to be performed with only four movable units on parallel linear paths and should be made with only compressive and tensile stresses in the six articulated rods which connect the manipulated platform directly or indirectly to the movable units.  
           [0027]    Thus, according to the invention, the articulated rods are mounted on the manipulated platform with the aid of joints, so that two pairs of links are formed. For each pair, a mathematical line is formed through the centre of the joints of the pairs of links, the centre being defined by the mathematical point in the joint where the axes of rotation of the joint (for pivoting the link) cross each other. To attain the main object of the invention, it is now required that both of the two mathematical lines for the joints of the two pairs of links be parallel. Of special interest is the case where these mathematical lines also coincide.  
           [0028]    Starting from this basic structure of a parallel kinematic manipulator with a gantry-like working range, the invention comprises a number of advantageous embodiments.  
           [0029]    The inventive concept comprises connecting at least one of the movable units to the manipulated platform via only one of the six articulated rods. In this way, no requirements are made for orientation in any direction of the arm on which the link in question is mounted via a joint. This provides many possibilities of introducing pivotable lower arms to increase the working range of the manipulator in the z-direction. This is of particular importance when a manipulator with only three degrees of freedom (x, y, z) is to be designed.  
           [0030]    To obtain a large working range in the xy-plane, that is, in the plane in which at least two of the liner paths are mounted, according to an advantageous embodiment of the invention two of the linear paths with associated movable units are mounted such that at least four of the six links are able to move freely between the two linear paths. This makes it possible for the linkage to perform large movements in the y-direction while simultaneously performing large movements in the z-direction, since the arm system in the middle of the working range between the linear paths will have its greatest mobility in all directions. This configuration of the linear paths is the optimal one also from the point of view of rigidity of the manipulator if the linear paths are mounted such that the normal vectors to the mounting surfaces of the movable units for one of the linear paths are parallel but directed opposite to the mounting surfaces of the movable units for the other linear path.  
           [0031]    The inventive concept also comprises achieving the rotation of the manipulated platform around one, and only one, axis of rotation by means of an articulated rod connected to one of the movable units, in which case a lever arm may be used in a platform arrangement for transforming a translatory movement of the relevant link into a rotational movement of the platform. To obtain large angles of rotation of the manipulated platform, the invention also comprises the use of one of the articulated rods in a universal transmission the universal joints being mounted at both ends of the articulated rod in question and a gear wheel and a rack being used for transmitting a relative movement between two movable units on a linear path into a rotational movement of the universal transmission. In addition, the invention comprises use of a third linear path mounted between two other linear paths and with two movable units for manipulating the rotation and movement of the platform in the z-direction, in which case both of the above-mentioned embodiments for generating the rotational movement of the platform may be used.  
           [0032]    The inventive concept also comprises different designs for obtaining an extended working range of the manipulated platform with the aid of lever arms. These designs are based on relative movements between two or more movable units, with the aid of articulated couplings between the movable units, giving rise to oscillations of arms mounted on the movable units. In this way, the linear movements of the movable units will give rise to large circular movements of those joints which connect articulated rods to the oscillating arms, and large movements of the manipulated platform are obtained.  
           [0033]    In an advantageous embodiment of the invention, at least four of the joints between the manipulated platform and the six articulated rods are mounted along a common symmetrical line, which corresponds to the previously mentioned mathematical lines coinciding. If, in addition, a fifth joint for manipulating the platform in the z-direction is mounted on this symmetry line, the platform will be constituted by a rod or a shaft, which may then be rotated around by the sixth articulated rod via a lever arm or via a universal transmission. This gives a very compact platform, which is easy to manufacture with high precision. In addition, this platform provides a possibility of simply using ordinary ball or roller bearings to implement the joints in question. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]    The invention will be explained in greater detail by description of an embodiment with reference to the accompanying drawings, wherein  
         [0035]    [0035]FIG. 1 is a manipulator designed according to the prior art, with parallel linear paths comprising six movable units with six links between these units and the platform which is to be moved and rotated by the manipulator,  
         [0036]    [0036]FIG. 2 is a manipulator according to the invention for manipulating the position of a platform under constant tilting and orientation, using only three movable units on only two parallel linear paths via six links,  
         [0037]    [0037]FIG. 3 is a modification of the manipulator according to FIG. 2 with the aim for manipulating, in addition to the position of the platform, also the orientation of the platform, using an additional movable unit on only two parallel linear paths,  
         [0038]    [0038]FIG. 4 is an advantageous embodiment of the manipulator according to FIG. 4, wherein only four movable units on only two linear paths manipulate the position and orientation of the platform around only one axis,  
         [0039]    [0039]FIG. 5 a  and FIG. 5 b  are advantageous implementations of the joint arrangement of the manipulator according to FIG. 4,  
         [0040]    [0040]FIG. 6 is another advantageous implementations of the joint arrangement of the manipulator according to FIG. 4, and then in particular when the platform is subjected to great forces and torques,  
         [0041]    [0041]FIG. 7 is a modification of the manipulator in FIG. 4 with three movable units for manipulating the position of the platform only, whereas the inclination and orientation thereof are maintained constant,  
         [0042]    [0042]FIG. 8 is a wall-mounted manipulator of the same type as the manipulator according to FIG. 4,  
         [0043]    [0043]FIG. 9 is a modified wall-mounted manipulator for obtaining a larger working range for the positioning of the platform,  
         [0044]    [0044]FIG. 10 is an advantageous configuration of the linear paths for obtaining a large working range of the manipulator in the horizontal plane in the case of floor mounting,  
         [0045]    [0045]FIG. 11 is a first embodiment of the manipulator for obtaining a large working range also in the vertical plane with a configuration of the linear paths according to FIG. 10,  
         [0046]    [0046]FIG. 12 is the working range in the horizontal plane which is obtained with a configuration of the linear paths according to FIGS. 10 and 11,  
         [0047]    [0047]FIG. 13 is a variant of the embodiment of the manipulator in FIG. 11 for obtaining a large working range also in the vertical plane,  
         [0048]    [0048]FIG. 14 is an embodiment of the manipulator according to FIG. 13 for obtaining a large working range also in the case of rotation of the platform around an axis,  
         [0049]    [0049]FIG. 15 is an alternative embodiment with a third linear path for obtaining a large working range also in the case of rotation of the platform,  
         [0050]    [0050]FIG. 16 is an advantageous alternative embodiment of the manipulator for obtaining a large working range of the manipulated platform, both with regard to positioning and rotation around an axis, using two linear paths and four movable units,  
         [0051]    [0051]FIG. 17 is a variant of an embodiment of the manipulator in FIG. 16 when a simple design is more important than a large working range for rotation of the platform, and  
         [0052]    [0052]FIG. 18 is an alternative embodiment of the manipulator for illustrating the problems that arise when the main object of the invention is not fulfilled. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0053]    [0053]FIG. 1 shows the prior art for manipulating, on linear paths  10 ,  11  and  15 , a platform  1  by means of links  13 - 18 , which only transmit compressive and tensile stresses. The six links  13 - 18  are provided at each end with joints  13   a - 18   a  and  13   b - 16   b , respectively. The joints have two or three degrees of freedom and the links are mounted, via the joints  13   a - 18   a , on the platform  1  that is to be manipulated. With the joints  13   b - 18   b , the links are mounted on the movable units  2 ,  3 ,  4 ,  5 ,  26 ,  27  with one link for each movable unit. The movable units are controlled by actuators  6 ,  7 ,  8 ,  9 ,  29  and  28  and may be positioned along the linear paths  10 ,  11 ,  25  independently of each other. By performing this positioning in a certain pattern given by the kinematics of the manipulator, the platform may be caused to move in the x-, y- and z-directions and to obtain rotations around the z-axis (Vz). It is also possible to obtain rotations around the x- and y-axes, but there is no need for that in most of the gantry applications that are being used today.  
         [0054]    [0054]FIG. 2 shows how a manipulator with three linear actuators may be used for manipulating the position of an object  12 , the largest movements being obtained in the y-direction (the y-direction according to the coordinate system written in the figure). The object  12  is placed on a platform  1 , which is retained by the six links  13 - 18 . The links  13 - 15  are mounted at their lower ends on the movable unit  2 , which is caused to move along the linear path  11  with the aid of the drive device  7 . In a corresponding way, the lower end of the link  16  is mounted on the unit  3 , which on the path  10  is connected to the drive device  6 . Further, the links  17  and  18  are mounted on the unit  4  with the drive device  8 . Each link has, at both ends, joints  13   a - 18   a  and  13   b - 18   b , respectively, each having two degrees of freedom (e.g. a universal joint) or three degrees of freedom (e.g. a ball joint). The links  13 ,  14 , and  15  have the same length and are mutually parallel and mounted such that the joints  13   a ,  14   a ,  15   a  and  13   b ,  14   b ,  15   b , respectively, form triangles. The links  17  and  18  are also mutually parallel and have the same length. On the other hand, the links  13 ,  14 ,  15  need not have the same length as the links  17 ,  18 , nor the same length as the link  16 , and the link  16  need not have the same length as the links  17  and  18 . For high precision and high rigidity, the links are suitably manufactured of carbon-fibrereinforced epoxy tubes, which are glued to holders for the joints. The units  2 ,  3 ,  4  may be driven by ball screws with motors  6 ,  7 ,  8  in the ends of the linear units  10 ,  11 . As an alternative, belt transmissions may be used and if very high stiffness and accuracy are required, it is also possible to use linear motors. In the linaear-motor case, the winding should be placed on the stationary part to avoid movable cabling, but this implies that two parallel linear motors are needed for the linear path  10  with two movable units. It should be pointed out that the linear paths  10  and  11  in the embodiment shown in the figure are adjacent to each other (in the x-direction) and at different levels (in the zdirection). The reason for the path  10  being at a higher level than the path  11  is that the distance between the movable units  3  and  4  then becomes smaller and that these units need not be moved to the same extent to obtain a given transfer of the platform  1 , which allows the linear path  10  to be made shorter than if all the links had been of equal length.  
         [0055]    For most applications where so-called gantry manipulators are currently used, a fourth degree of freedom is required to also be able to rotate the platform  1  around the z-axis. One possibility of doing so with the structure according to FIG. 2 as a base is to connect the links  17  and  18  to different movable units, which is shown in FIG. 3. Thus, the link  18  has here been connected to a new movable unit  5  via a rod  6 , such that the links  17  and  18  can be manipulated independently of each other. The movable unit  5  is moved on the linear path  11  by the drive unit  9 . With this modification of the original manipulator in FIG. 2, a rotation of the platform  1  may be obtained by adjusting the relationship between the positions of the movable units  4  and  5 . This gives rise to a pure rotation around the z-direction (Vz) when the links  13 ,  14  and  15  are perpendicular to the movable unit  1 , but if the angle of the these links relative to the movable unit  1  deviates from 90 degrees, the rotation of the platform  1  will be accompanied by a change of the inclination of the platform. The greater the deviation from 90 degrees, the greater will be the change of inclination as a function of the rotation of the platform, and therefore the manipulator in FIG. 3 has a limited use.  
         [0056]    [0056]FIG. 4 shows a structure that does not involve the disadvantage that a rotation of the platform  1  may give rise to a change of the inclination of the platform. Here, the platform  1  is mounted on a vertical platform rod ( 1   a - 1   f ), on which the joints  13   a ,  14   a ,  17   a ,  15   a  and  16   a  are mounted. The platform rod also includes a horizontal lever arm  1   g , at the end of which the joint  18  is mounted. The joints  13   a  and  14   a  connect the parallel and equally long links  13  and  14  to the vertical platform rod and at their other ends these links are connected via the joints  13   b  and  14   b  to the rod  2 B, which is parallel to the platform rod and which is mounted on the movable unit  2 . In the same way, the joints  15   a  and  16   b  connect the parallel and equally long links  15  and  16  to the platform rod. At their other ends, the parallel links  15  and  16  are mounted on the rod  3 B via the joints  15   b  and  16   b . The rod  3 B is parallel to the platform rod and is mounted on the movable unit  3 . The joint  17   b  is used for the link  17 , which, via the joint  17   b , is manipulated by the movable unit  5 . The links  13 - 17  lock all the degrees of freedom of the platform rod except the rotation around its symmetry axis. To lock (and manipulate) this degree of freedom, the link  18  is used which, via the joint  18   a  and the lever arm  1   g , can rotate the lever arm rod and hence the platform  1 . At its other end, the link  18  is mounted, via the joint  18   b , on the movable unit  4 , which thus controls the orientation of the platform  1  without influencing the inclination of the platform (the inclination being determined by the rods  2 B and  3 B via the links  13 ,  14 ,  15  and  16 ).  
         [0057]    The joints on the platform rod may be implemented as universal joints, ball joints or with suitably arranged ball bearings. FIG. 5 a  shows an implementation using ball joints. The balls for the joints  13   a ,  14   a ,  15   a ,  16   a  and  17   a  have a vertical hole through which a shaft  20  extends which connects the platform  1  to the lever arm  1   g . Between the ball to the joint  13   a  and the platform  1 , a sleeve  1   a  is mounted, and between the balls to the joints  14   a - 16   a  the sleeves  1   a - 1   e  are mounted, and below the ball to the joint  16   a  the sleeve lf is mounted. With the nut  21  on the shaft  20 , the balls  13   a - 17   a  with the intermediate sleeves are clamped in the platform  1 , thus forming a platform rod. In the shaft  10 , the lever arm  1   g  is fixedly mounted such that a movement of the link  18  gives rise to a rotation of the platform rod, which is journalled in the joints  13   a - 17   a . The design of the joints  13   a - 17   a  is shown in FIG. 4 b , exemplified by the joint  17   a . The joint is seen in cross section from above with the shaft  20  inside the perforated ball. On the link  17 , a joint holder  22  is mounted. The joint holder presses the angle  23  against one side of the ball and the plate  24  against the other side of the ball. The angle  23  gives at least three contact surfaces with the ball and the plate  24  at least one contact surface. The corresponding joint design may also be implemented on the rods  2 B and  3 B in FIG. 4.  
         [0058]    The embodiment of the joints according to FIGS. 5 a  and  5   b  is primarily suited for applications where not too large forces are to be applied to the platform  1 . In those cases where larger forces influence the platform  1 , universal joints or angularly adjusted ball or roller bearings according to FIG. 6 may be used. The figure exemplifies the joint arrangement with the links  15  and  16 . The implementation of the joints themselves is explained starting from the joint  16   b . On the rod  3 B a bearing  16   b III is mounted, and on both sides of this bearing, two other bearings  16   b II and  16   b I are mounted. In the figure, the axis of rotation for the bearing  16   b III is vertical and for the bearings  16   b I and  16   b II horizontal. On the bearings  16   b I and  16   b II, a bridge  16 B is mounted (the bridge  16 A at the other end of the link  16  being more clearly shown), and on this bridge the link  16  is mounted. With this design, the platform rod interconnects the joints by simply mounting the bearings with a vertical axis of rotation on the rods, and the parts  1   d ,  1   e , etc., of the rod are thus in this case a continuous shaft.  
         [0059]    The manipulator in FIG. 4 manipulates the platform  1  with four degrees of freedom. For the sake of completeness, FIG. 7 shows the base structure for manipulation with three degrees of freedom. The links  13 ,  14 ,  15 ,  16  and  17  are mounted in exactly the same way as in FIG. 4. The only difference is that the link  18  is now mounted on the movable unit  3  and that the movable unit  4  with the associated actuator  9  has been removed. The link  18  is chosen with the same length as the links  15  and  16  and is mounted so as to become parallel to these links. To this end, the movable unit  3  is provided with an arm  3 C, which together with the lever arm  1   g  ensures that the link  18  is parallel to the links  15  and  16 . Alternatively, the link  18  is mounted on the movable unit  2  or  5  and then parallel to the links  13 ,  14  and  17 , respectively. By moving the units  2 ,  3  and  5 , the position in the x-, y- and z-directions of the platform  1  can now be controlled.  
         [0060]    In FIGS. 4 and 7, the platform rod is perpendicular to the surface, which is clamped by the linear paths  10  and  11 . However, the platform rod may be given a different angle relative to the linear paths by inclining the rods  2 B and  3 B, provided, however, that the rods  2 B and  3 B are still parallel. In an extreme case, the rods  2 B and  3 B are chosen to be parallel to the plane that is clamped by the linear paths, and such a configuration is shown in FIG. 8. Here, the linear paths are wall-mounted above each other and approximately at the same plane, which, however, is not necessary. The tilt angles of the platform  1  are locked by the links  13 ,  14 ,  15  and  16 , which also substantially control the movement of the platform in the xy-plane. The link  17  substantially controls the movement of the platform in the z-direction, and the link  18  controls the rotation of the platform around the z-axis (Vz). In the same way as in FIG. 7, the rotation of the platform around the z-axis may be maintained constant by mounting the link  18  on the unit  2  or the unit  3  or the unit  5 . In all three cases, the link  18  is mounted parallel to the link/links which is/are already on the platform in question and is made with the same length as this link/these links.  
         [0061]    [0061]FIG. 9 shows an arrangement, which has the advantage that the manipulator may be given a larger working range relative to the length of the linear paths  10  and  11 . This is achieved by providing the manipulator with an extra set of arms  62 ,  68  and  72  with the task of imparting to the links  13 ,  14  and  15 ,  16  and  17 , respectively, larger movements than in previous embodiments where these links are directly mounted on the movable units of the linear paths. However, this advantage entails the disadvantage that the mechanics becomes more complex and that the manipulator becomes mechanically less rigid. The links  13  and  14  are here mounted, via the joints  13   b  and  14   b , on a vertical beam  61  which may be pivoted in the horizontal plane by being fixedly mounted on the swinging arm  62 . This swinging arm is mounted, via the joint  65  (1 degree of freedom), on the block  66  which is mounted on the movable unit  66 . In a corresponding way, the links  15  and  16  are mounted on the beam  67 , which is secured to the swinging arm  68 . This swinging arm is mounted on the movable unit  2  via the joint  70  and the block  71 . Between the swinging arms  62  and  68 , there is a bar  64 , which is articulately connected to the swinging arms through joints  63  and  69 . This bar causes a relative movement between the movable units  2  and  3  to give rise to a pivoting movement of the swinging arms  68  and  69 , which in turn entails a movement in the y-direction of the platform  1 . To obtain upward and downward movements of the platform  1 , the link  17  is mounted, via the joint  17   a , to a swinging arm  72 , which is substantially adapted to swing in the vertical plane. The arm  72  is connected, via the joint  73 , to the block  74  on the movable unit  2 . The arm  72  is caused to swing by the relative movement between the movable unit  2  and the movable unit  4 . This is made possible through the link  75 , which connects the movable unit  4  to the swinging arm  72  by means of the joints  75   b  and  75   a . The rotation of the platform  1  is obtained in the same way as in FIG. 8 with the aid of the lever arm  1   e  and the link  18 .  
         [0062]    [0062]FIG. 10 shows an alternative configuration for obtaining a larger working range. The linear paths  10  and  11  are here located on the side, facing each other, and are mutually parallel (distorted perspective in the figure). The link pairs  13 ,  14  and  15 ,  16  are mounted on the movable units  2  and  3 , respectively, the single link  17  is mounted on the movable unit  5  and the link  18 , which is responsible for the rotation of the platform  1  around the z-axis, is mounted on the unit  4 . By connecting the unit  18  to any of unit  2 ,  3  or as previously described, the platform  1  may be positioned under a constant angle or rotation.  
         [0063]    The configuration with the link pairs  13 ,  14  and  15 ,  16  manipulated between the linear paths  10  and  11  opens up new possibilities for obtaining a parallel kinematic gantry manipulator with a very large working range. To be successful in doing so, however, an arrangement of link  17  different from that in FIG. 10 is required. An example of such an arrangement is shown in FIG. 11. The link  17  is here manipulated by the movable unit  4  via the joint  17   b , the link  17 D and the joint  17   e . When the joint  17   e  is moved by the movable unit  4  along the linear path  11 , the joint  17   b  will be swung around an axis, which extends between the joints  17   c  and  17   d . This oscillation gives rise to large vertical movements of the joint  17   a , resulting in the platform  1  being manipulated with a large working range in the z-direction. The joint  17   b  is connected to the joints  17   c  and  17   d  with the aid of the links  17 B and  17 C and the platform  1  will be manipulated in the z-direction as soon as any of the movable units  2 ,  3  and  4  are moved relative to one another. In other respects, the manipulator in FIG. 11 is identical with that shown in FIG. 10.  
         [0064]    As mentioned above, a parallel kinematic gantry robot with parallel links operating between the linear paths will be given a very large working range. This is illustrated in FIG. 12, which is a simplified projection of the manipulator according to FIG. 11, viewed from above. Only the movable units  2  and  3 , which determine the working range in the xy-plane, are shown together with associated upper links  13  and  15  as well as one of the joints ( 13   a ) on the platform rod and the joints  13   b  and  15   b  on the movable units. If the links  13  and  15  are each made longer than the distance between the parallel linear paths, the working range of the manipulator in the xy-plane will be able to cover a surface almost as large as the surface between the linear paths. With a suitable arrangement for manipulation of the platform  1  in the z-direction, this working range in xy-plane will apply also to a relatively large depth in the z-direction, even if the working range will always become narrower below and above the plane formed by the linear paths  10  and  11 .  
         [0065]    A somewhat simpler arrangement for obtaining a large working range in the z-direction is shown in FIG. 13. Here, the link  17  is mounted on the arm  36  via the joint  17   b  (with two or three degrees of freedom), the arm  36  in turn being connected to the movable unit  4  through the joint  35  (with one degree of freedom). The arm  36  is caused to swing around the axis of the joint  35  when the movable units  3  and  4  move relative to each other. This function is achieved by the fact that the arm  36  has a lever arm  34 , which, via the joint  33 , is connected to the movable unit  3  via the arm  32 . The arm  32  is fixedly mounted on the movable unit  3  with the aid of the joint  31 , which allows the arm  32  to swing in the vertical plane. The links  13 - 16  are arranged in the same way as in FIGS. 10 and 11. On the other hand, the link  18  is configured to maintain a constant angle of rotation of the platform  1 . This is achieved by allowing the link  18  to form a parallelogram with the links  13  and  14 , which is achieved with the arm  2 A fixedly mounted on the movable unit  2 . As an alternative, the link  18  may be mounted in a corresponding way on the movable unit  3 .  
         [0066]    In several cases it is desired to rotate the platform  1  at least one full turn around the z-axis. FIG. 14 shows one way of doing this. The link  17  here has a universal joint at each end, whereby the link will function as a universal driving shaft transmission. The universal joint  17   b  is connected to the gear wheel  38  via the shaft  37 . The shaft  37  is maintained single-axis-articulated by the arm  36 , which also holds the slide  40  for the rack  39 . The rack  39 , in turn, is mounted on the movable unit  5  via the joint  41 , the fork  42 , the arm  43  and the joint  44 . The device for controlling the arm  36  is the same as in FIG. 13. When the movable unit  5  is moved relative to the movable unit  4 , the rack  39  will move in the slide  40  and hence rotate on the gear wheel  38 , which in turn results in the universal transmission  17   b ,  17  and  17   a  imparting to the platform rod  1   a - 1   e , and hence to the platform  1 , a rotational movement around the z-axis.  
         [0067]    The arrangement with the arms  36  and  43  in FIG. 14 may result in certain problems as regards the rigidity of the platform to forces in the z-direction and torque around the z-axis. One way of increasing the rigidity With regard to these components is to introduce another linear path  47  according to FIG. 15. The linear paths  10  and  11  now only have the movable units  2  and  3  whereas the movable units  4  and  5  are located on the linear path  47 . It should be pointed out here that a linear path may very well consist of two separate tracks, one for each movable unit. However, there is never any need of the movable units passing each other, so the most economical solution is to allow two units to share the same track but have different drive transmissions such as, for example, ball screws and belts. The linear path  47  is responsible for the movements of the platform in the z-direction and its rotation around the z-axis. The movement in the z-direction is achieved by movement of the movable unit  4 , whereby the link  17  moves the platform rod  1   a - 1   e  up or down. The rotation around the z-axis is achieved by moving the movable unit  5  relative to the movable unit  4 . This will cause the rack  39  to rotate the gear wheel  38 , which in turn rotates the universal transmission  17   b ,  17 ,  17   a , resulting in the platform rod and hence the platform  1  rotating. The gear wheel  38  is fixedly journalled in the movable unit  4  and the rack  39  is fixed in the movable unit  5  by means of the joint  41 . The slide  40  for holding the rack  39  against the gear wheel  38  is mounted on the movable unit  4 .  
         [0068]    In principle, the universal transmission for transmitting a rotational movement to the platform  1  may be implemented by any of the links included in the manipulator. FIG. 16 illustrates this fact. Here, the link  16  is used for the universal transmission, and for obtaining the correct direction of the rotational movement to the platform  1 , a bevel gear pair with the wheels  48  and  49  is used. The platform  1  is here mounted on a shaft  1   a , which is mounted in a bearing in the gear wheel holder  58 . The orientation and the position of the gear wheel holder  58  are determined by the links  13 - 18 , where the link  16  is at the same time used for transmitting the rotational movement. The universal joint  16   a  is in direct connection with the bevel wheel  49  via the shaft  50  which is fixedly journalled to the gear wheel holder  58 , the bevel wheel  49  in its turn driving the bevel wheel  48  and hence the platform  1 . At its other end the link  16  is in direct connection, via the universal joint  16   b , with the gear wheel  38  by means of the shaft  37 , which gear wheel  38  is journalled in the movable unit  3 . In the same way as in FIG. 15, the gear wheel is driven round by a rack  39 , which is fixed to the movable unit  4  with the joint  41 . On the movable unit  3 , the rack  39  is pressed against the gear wheel  38  by a bearing  40 , whereby a relative movement between the movable units  3  and  4  gives rise to a rotation of the gear wheel  38 . For the manipulation in the z-direction, the link  17  is connected at its other end, via the joint  17   b , to the arm  53  which, by means of the joint  52 , is mounted on an angle holder  51  on the movable unit  2 . The arm  53  is caused by the link  56  to swing around the joint  52  when the movable unit  5  moves relative to the movable unit  2 .  
         [0069]    [0069]FIG. 16 also shows the two mathematical lines  80  and  81 . These are defined by centre points for the joints  13   a ,  14   a  and  15   a ,  16   a , respectively. Common to the manipulators which have been described so far and which characterize the invention is that these mathematical lines ( 80 ,  81 ) are parallel. In FIGS. 4, 5,  7 ,  8 ,  9 ,  10 ,  11 ,  13 ,  14  and  15 , these lines are, in addition, coinciding.  
         [0070]    It is necessary that the mathematical lines  80  and  81  be parallel for the platform  1  to be able to rotate without obtaining a simultaneous change of the inclination. This is exemplified by FIGS. 17 and 18. In FIG. 17, the lines  80  and  81  are parallel and the platform  1  is given a pure rotational movement when the movable unit  4  moves relative to the movable unit  3 . In FIG. 18, however, the lines  80  and  81  are not parallel and when the movable unit  4  moves relative to the movable unit  3  in this case, the inclination of the platform  1  will at the same time be changed, which is not desirable in the majority of applications.  
         [0071]    [0071]FIG. 17 is a variant of the basic structure in FIG. 16. The rotation of the platform  1  is carried out in FIG. 17 by the link  18  instead of by means of the universal transmission and the bevel gear pair as in FIG. 16. This provides a simpler manipulator design, but at the expense of a smaller number of rotations of the platform being carried out.  
         [0072]    In FIG. 18, the platform  1  is in the form of a frame such that the mathematical line  80  becomes vertical and the mathematical line  81  horizontal. The links  17  and  18  are so mounted that the joints  17   a  and  18   a  form a mathematical line in the horizontal plane, which may not be parallel to the line  81 . The links  17  and  18  are manipulated by the movable unit  4  on the linear path  47  mounted horizontally over the working range, the link  15  is manipulated by the movable unit  4  and the link  16  by the movable unit  4 , both on the vertically angled path  11 , and the links  13  and  14  are manipulated by the movable unit  2  on the vertically angled opposite path  10 . To obtain the desired geometrical relationships between the points of mounting of the link  17  and  18 , an angled beam  4 B is used on the movable unit  4 . If the links  15  and  16  are held parallel provided that they are of equal length, the platform  1  may be manipulated with a constant inclination.