US Patent 9829500 Speed monitoring device

There is provided a speed monitoring device which can use a low resolution position sensor and provide a high speed response without false detection. The speed monitoring device stores, in a memory unit, a permitted margin PM, a comparison distance VC which is a maximum movement distance permitted for a moving element within one cycle period, and positional data P(t−nT) (n is a natural number equal to or less than M) of the moving element obtained from the present time t to M cycles ago. During speed determination, whether |P(t)−P(t−nT)|>VC*n+PM holds true is determined for every integer n from 1 to M. When the inequality holds true, it is determined that the speed exceeds the speed limit.