fig1 shows a two - robot system comprising manipulators : two robots 1 , 3 and an external axis 2 , such as a workstation that conveys and positions work pieces mounted thereon . the external axis 2 rotates about an axis , a . robot 1 is a welding robot mounted on a mobile base . mounting a robot on a mobile base extends the reach of the robot arm and increases the size of the robot workspace . the additional degrees of freedom in the mobility of the manipulator are however not a problem if a control system according to the present invention is used to control the mobile manipulator . the additional degrees of freedom are in fact turned to advantage by using them to accomplish additional tasks specified by an operator . robot 3 is mounted on a stationary base and comprises a tool , such as a welding gun , mounted on the robot to execute specified work on work pieces mounted on the rotatable external axis 2 . the robots 1 , 3 comprise interconnected parts such as , a foot , manipulator arms , arm housing , a wrist and a turn disc . two adjoining robot parts are connected to each other so as to be rotatable in relation to each other around an axis of rotation , or are linearly displaceable in relation to each other . a first coordinate system 4 is defined to define the room . each individual manipulator : robot or work piece is defined in the first coordinate system . to control the relative positions of the interconnected robot parts in the robot programs , the parts are arranged in the first coordinate system corresponding to the physical room a first coordinate system 4 . as the manipulators , here the robots and the external axis are connected to the control system one by one ; the control system first regards the manipulators as standing in the same place in the coordinate system . to define each manipulator position according to the first coordinate system the robot system has to be calibrated . the calibration for instance is done by defining common points . one defined point on each manipulator is put together so as they meet . this is done for a number of points ; those points are defined relative to the first coordinate system . in the first coordinate system each manipulator now has an individual position . in the coordinate system each tool center point ( tcp ) that is in the point where the manipulator is working at , such as the welding gun opening point is defined relative the robot foot . after the calibration the control system has information on all manipulators positions relative to the first coordinate system and each other . for each manipulator a second coordinate system is defined . the second coordinate systems are defined in the first coordinate system , in the control system . relative to the first coordinate system a point is chosen as origin in each second coordinate system 5 , 6 , 55 . these second coordinate systems are moveable in the first coordinate system . one part of the manipulator for instance the tool center point is defined as standing still in the second coordinate system attached to that manipulator . that means that the robots are moving along with the second coordinate system , when it moves in the coordinate system . the work piece on the external axis 2 is moved during the welding and their location is also expressed in the robot programs using the second coordinate system 6 of the external axis 2 , as the second coordinate set . the two welding robots 1 , 3 are defined in two second coordinate system , 5 , 55 , one coordinate system to each robot . the second coordinate systems 5 , 6 , 55 relative positions are defined in the first coordinate system . when one of the second coordinate systems is moved in the first coordinate system the second coordinate systems keep their relative positions . the manipulators move along with the second coordinate systems . as the external axis 2 rotates , its coordinate system 6 rotates correspondingly , and the two robots move along . in this case a cartesian system is used . 1 . a robot is moving in the first - coordinate system and is moving in the second coordinate system . 2 . a robot is moving in the first coordinate system even though it is standing still in the second coordinate system . 3 . a robot is standing still in the first - coordinate system and is standing still in the second coordinate system . fig2 shows a manipulating means , in this case a handheld control tool 7 . the handheld control tool is used for manually manipulating the robot . the handheld control tool comprises a manipulator input means such as a joystick 8 , input buttons 9 and a touch display 10 . the manipulating means also comprise a communication means to communicate with the control program . each single robot has an individual set of programs in the control system . it is the same program or different programs for each robot . the control program for instance comprises basic programs such as programs comprising movement commands . to manipulate a manipulator into a preferred position , the operator use the input means to choose a movement command . the communication means then sends the input command to the control system and the control system sends the corresponding movement commands to the manipulator . although the embodiment discloses a handheld control tool the manipulating means can be any kind of man - machine interface . for instance any handheld moveable control unit such as an intelligent joystick , touch screen means , key button means or cordless communication means or even a personal computer ( pc ). the manipulating means can communicate with the control system with any input means , such as a joystick , key button means or a touch screen . during the manipulating movement an application program controlling the movements is run . during a coordinated manual movement task , when one of the manipulators , or part of a manipulator , such as a manipulator arm , is displaced or rotated , this displaces or rotates the coordinate system in which the other manipulators is attached . it is important to know exactly how the coordinate system has been displaced or rotated so that other manipulators can be directed to the programmed positions . certain tasks require two or more of the robots to move synchronously for example when moving the system in position for programming a movement instruction comprising separate movement instructions in separate manipulator - programs in order to coordinate the movements of the manipulators . fig3 shows a system of two robots , 1 , 3 , an external axis 2 , a computer means 11 , comprising at least a central processing unit ( cpu ) and a memory , and a handheld control tool 7 . the two - robot system also comprises sensor means on axis , a , to measure the rotation of the external axis 2 . after calibrating the system the control system has information on the different positions of the robots and the external axis position relative to the first coordinate system 4 . one manipulator in this case robot 1 , is chosen as the first manipulator . the origin of the movable second coordinate system 5 is defined as moving along with the tcp of robot 1 and the origin of the movable second coordinate system 55 is defined as moving along with the tcp of robot 12 . the manipulator and the external axis are now handled as a system that is controlled and moved synchronized . the manipulators are placed in a work position and the second coordinate systems are defined relative to each other . now when the first manipulator is activated , the first manipulator moves all three second coordinate systems . that is each manipulator is moved synchronized and accompanying when a point in the second coordinate system is moved . within the second coordinate system each manipulator tool center point is fixed for instance relative the work piece as if the manipulators : the robots and the work piece were a single system . thus the manipulators move together in a synchronized motion , like if they were attached to each other , as one single unit comprising the same number of axes as the robots and the external axes together . when moving the first manipulator robot 1 , robot 3 is therefore able to move to the corresponding positions relative axis 2 , the work piece , and the first coordinate system . the work piece is active also when manipulating the system , enabling all robots to maintain orientation in relation to work piece . tools held by the robots will thus have the right orientation and they will be guided to the right place on the work piece . fig4 shows a controls system 21 installed on a computer and a manipulating means . the control system controls a three - mechanical unit system such as the systems shown in fig1 and 3 comprising three manipulators , two robots and an external axis . the picture also shows the communication between the control system 21 and the manipulating - means 7 . the control system 1 comprises three mechanical - unit programs c , d , e containing instructions such as “ stop ”, “ start ” and “ wait ” and also movement instructions such as “ move to ” for each mechanical unit . the control system 1 also comprises a plurality of program planners 30 , 31 , 33 that tell said at least one mechanical unit how to move in order to be able to execute a programmed task . each manipulator - program c , d , e , is connected to only one path planner 30 , 31 , 33 , at any given time . arrows 12 , 13 , 14 in fig2 show that each manipulator - program c , d , e , is connected to a different path planner 30 , 31 , 33 , so when the manipulator - programs are run , each manipulator will move independently . the control system 1 comprises means to switch the manipulators from independent to synchronised movement . if the manipulator - programs c and d are to be synchronised , the control system disconnects manipulator - program e from path planner 10 and connects program d to path planner 30 . when manipulator - programs c and d need to be synchronised , they are both connected to path planner 30 as indicated by arrows 12 and 15 in fig2 . the path planners 30 , 31 , 33 , communicate with a central data storage means 16 that contains position and status data transmitted from each of the three manipulators . the manipulating means also communicate with the central data storage means . the message exchanging , or communication , between the path planners and the central data storage means or by the manipulating means and the central data storage is indicated by double - headed arrows in fig4 . in this way the path planners 30 , 31 , 33 receive updated information on whether , and how , the three manipulators have moved as well as about the status of the manipulators . after a manipulator has been displaced and / or rotated the path planner calculates the position and / or orientation of that manipulator &# 39 ; s coordinate system before providing manual movement instructions for a manipulator working in that coordinate system . movement instructions are then transmitted to drive modules 18 , 19 , 20 associated with each manipulator via a main computer interface 17 so that the corresponding manipulators are able to move to the manual manipulated positions . fig5 shows a flow chart describing the method according to an embodiment of the invention . create a memory list for all manipulators that will move . ( 100 ) select first manipulator , go to 100 then 120 . ( 110 ) is a second coordinate system moved by first manipulator , ( 120 ) go to 130 else go to 150 . loop thru remaining manipulators , ( 130 ) is a second manipulator moved by a second coordinate system ( 140 ) go to 100 else go to 130 . create move order for first manipulator with end - positions as : ( 150 ) current position and man - machine interface contribution . will other manipulators move ? go to 170 else 180 , ( 160 ) create move order for remaining manipulators with ( 170 ) end - positions as : current position fixed to second coordinate system . send move orders to path planners . ( 180 ) one feature of the method according to the invention is that a manipulator can be moving although it in the second coordinate system stands still . the first manipulator can be chosen as any manipulator of the system . the leading manipulator can also be changed at any time during the manipulation of the system . a manipulator can be disconnected from the system , the control program then has access to information of the number of active manipulators . if one robot is disconnected , it stands still relative to the first coordinate system . a system according to a preferred embodiment of the invention comprises one or several manipulators , a manipulating means , and a computer means : more than one robot , for example 2 , 3 or 4 robots , more then one work pieces , more then one manipulating means . for instance two robots are holding a work piece and two robots are working on the work piece or one robot and one manipulator . the work piece is for instance a car body . the first coordinate system origin can be chosen as any point . the use of the equipment according to the present invention is in industrial processing such as but not limited too spot welding , arc welding , lifting heavy units , laser processes and any mechanical work : drilling , driving in rivets , to maximize the use of the robots performance during said processing . the use of the equipment according to the present invention is also for instance as programming tool . although the embodiments disclosed describe a three - manipulator - system , the control system according to the present invention can be used to control any number of manipulators from a single controller . addition of a manipulator to a particular system requires only the addition of a configuration file into the inventive control system . the invention is of course not in any way restricted to the preferred embodiments thereof described above , but many possibilities to modifications thereof would be apparent to a man with ordinary skill in the art without departing from the basic idea of the invention as defined in the appended claims .