Protection device

A robot monitoring system comprising a safety system for safety functions, which system prevents that an error in one control circuit does not result in a function failure by using supervising functions comprising at least two sensors connected to a monitoring unit, which receives and processes information about a position of a machine from both sensors and compares the results with stored values and a number of input conditions for the monitoring unit, whereby said sensors comprise means for generating data with respect to a position of a robot part's movement and said monitoring unit comprises means, which with respect to the result of the comparison is arranged to stop a parts movement if conditions for a stop are fulfilled,

• wherein the
• sensor is an absolute encoder, which in every position of movement of said robot part provides a position value to the monitoring unit through a common buss, which monitoring unit is arranged to process information about the position of said robot part and also said part's speed and direction and that said monitoring unit is arranged to compare values from said sensors and when detecting deviating value from either one of the sensors, to detect a functional error with the sensors.