Today, electromechanical actuator systems are used in a variety of applications,of which some are more safety critical than others. Likewise, they are used ina wide range of applications where the safety of persons often to a higher or lesserextent depends on that the actuators remains safe both during normal use and inthe fault conditions, which may occur. By an actuator comprising a DC motor (2)equipped with a worm drive and a spindle (4), the typical wearing components arethe bearing, which carries the spindle (4), the spindle nut (5) and the worm wheel(9) in the worm drive. Common to the described defect situations is that they inthe time leading up to the occurrence of the defect will show a decrease in the ratioof efficiency. Whether it is the spindle bearing, the worm drive, the spindlenut (5) or for that matter the motor, which is getting worn, the proportion betweenthe current which the motor absorbs and the force the actuator performs will change.The purpose of the present invention is thus to monitor the ratio of efficiencyof the actuator. When this begins to change, becomes worse, it is time to replacethe actuator before it becomes defective. For this purpose a load cell can forinstance be incorporated in the actuator, for measuring the force on the rearmounting. This force is compared with the power consumption and an indicatorfor the ratio of efficiency can thus be calculated as force/current.
