Apparatus for controlling movement of robotic machinery relative to an object, the apparatus comprising: a controller configured to: control a first magnetic transmitter to provide a first magnetic field, the object being positioned at least partially within the first magnetic field; receive a first signal from a first magnetic field sensor mounted at a first location on the robotic machinery; determine a control signal for controlling the robotic machinery to move relative to the object using: the received first signal; stored data of the structure of the object; and a target location; and provide the control signal to the robotic machinery to cause at least the first location of the robotic machinery to move relative to the object.

A linear motor system includes a track and at least one movable member coupled to the track and configured to move along the track. The at least one movable member includes a first element, a second element relatively movable with respect to the first element, and at least one movement detector configured to transmit a movement signal. A processing unit is configured to calculate a movement of the movable member, the second element and/or the first element as a function of the movement signal received from the movement detector.