relationship with the sliding direction at this end means is provided which links the front and the rear carrier 8 9 for integral movement along the slits specifically left and right hand rear brackets 13 14 are mounted within the bed 1b in alignment with the opposite ends of the rear slit 4 idlers 16 15 are pivotally mounted on the left hand rear bracket 13 and the right hand front bracket 11 respectively and a wire 17 extends around these idlers and has its opposite ends anchored to the front and rear carriers 8 9 thus following a z shaped path in this manner the wire 17 is effective to produce an integral movement of the both carriers 8 9 in the same direction if a tractive force is applied to either carrier referring to fig4 a drive force which is utilized to drive the front and rear carriers 8 9 along the slits 3 4 and thus in the direction of the x axis and to drive the traveller 7 along the y axis guide rod 5 in the direction of the y axis at a level above the bed 1b utilizing the carriers 8 9 as relay means will now be described a space is defined within the bed 1b by four brackets 10 11 13 and 14 in which an x axis servo motor 20 and a y axis servo motor 21 are supported on respective motor brackets 18 19 which are fixedly mounted in a suitable manner these servo motors.