Compression molding is used in making parts of complex shapes and varying sizes. Typically, the mold consists of two platens, the bottom platen being attached to the press table and the top platen operated by a hydraulic press. Metal or plastic sheets-for example, for the automotive industry-can be compression-molded in this manner. The main requirement in controlling the press is to position the top platen accurately with respect to the bottom platen (say, with a 0.001 in. or 0.025 mm tolerance), and it has to be done quickly (say, in a few seconds). How many degrees of freedom have to be sensed (how many position sensors are needed) in controlling the mold? Suggest typical displacement measurements that would be made in this application and the types of sensors that could be employed. Indicate sources of error that cannot be perfectly compensated for in this application