This invention relates to a positioning system for positioning a positioning unit along a longitudinal axis. The positioning system comprises a linear guide arrangement for enabling a linearly guided motion parallel to said axis, wherein the positioning unit is operatively connected to said guide arrangement. Furthermore, the positioning system comprises a motor, wherein the motor comprises a moving motor member operatively connected to said linear guide arrangement and an elongated stationary motor member extending parallel to said axis. The moving motor member is adapted to move along the stationary motor member for providing motion parallel to said axis. Moreover, the positioning system further comprises a force transmission arrangement which operatively connects said moving motor member to the positioning unit. The force transmission arrangement is arranged to provide an engagement between said positioning unit and said moving motor. The engagement is rigid in a direction parallel to said axis for instantaneous transmission of a linear force, and is resilient in directions other than said direction parallel to said axis, whereby transmission to the positioning unit of forces arising from thermal expansion of the motor is reduced or eliminated.