A positioning device (13) for producing a light signal (32) to position a robot tool (2) relative to a workpiece (14) is provided. The positioning device (13) comprises a frame (16) and a pair of light sources (22, 24) mounted at the free end of the frame and arranged to direct a pair of light beams (28, 30) therefrom in converging directions which intersect with each other and provide a light signal (32) at a predetermined distance from the free end of the frame (16). The positioning device (13) can include two pairs of light sources to generate two pairs of intersecting light beams (28, 30; 29, 31, ). The two pairs of light sources can be arranged so that the two pairs of light beams (28, 30; 29, 31) are located substantially 90 degrees apart.