A method for estimating, by measurements taken by an inductive sensor (25), a time for which an endothermic motor of a tool (5) has operated at predetermined rotating speeds so as to estimate a wear of the tool, said method comprising the following steps:
- arranging said inductive sensor (25) in an external acquisition device (15);
- cyclically measuring, at a pre-set sampling period (ΔC), an overall time interval (ΔT) by starting a beginning of the measuring of the overall time interval (ΔT) when a first variation peak of an electromagnetic field, generated by the endothermic motor when the tool operates, is sensed by the inductive sensor (25) and terminating the measuring of the overall time interval when a last variation peak of the electromagnetic field, generated by the endothermic motor when the tool operates, is sensed by the inductive sensor (25), where a first and a last peak are the start and tail ends respectively of a sequence of peaks having a predetermined number of successive peaks, said predetermined number of peaks being positive, whole, at least equal to six and a least common multiple at least of two and three,
- obtaining, from the overall time interval (ΔT) measured, the respective frequency thereof,
- making available a plurality of pre-set ranges of frequencies (RF1, RF2, RF3, RF4, RF5, RF6, RF7) of the overall time intervals measured which have previously stored,
- increasing the number of occurrences of a corresponding pre-set range of frequencies (RF1, RF2, RF3, RF4, RF5, RF6, RF7) by one each time the overall time interval (ΔT) having a frequency falling within the pre-set range of frequencies is measured,
- selecting, among the plurality of pre-set ranges of frequencies (RF1, RF2, RF3, RF4, RF5, RF6, RF7), the two pre-set ranges of frequencies having the largest number of occurrences, of which one with the lowest frequency represents the pre-set range of frequencies of a minimum speed and one with the highest frequency represents the pre-set range of frequencies of a maximum speed,
- calculating an overall threshold frequency by calculating an arithmetic average between at least one frequency of the range of frequencies of the minimum speed and one frequency of the range of frequencies of the maximum speed,
- determining a plurality of corrective coefficients, each obtained by dividing the number of peaks of the sequence of peaks respectively by one, and for each of the whole and positive numbers of which the number of peaks is a least common multiple,
- calculating a plurality of rotation frequencies by multiplying, for each corrective coefficient of the plurality of corrective coefficients, a frequency value of the range of frequencies of the minimum speed,
- comparing values of the calculated rotation frequencies with a pre-set reference range of frequencies indicative of an idling of the endothermic motor,
- storing a corrective coefficient of the plurality of corrective coefficients corresponding to the rotation frequency falling within the pre-set reference range of frequencies indicative of the idling of the endothermic motor, as a corrective coefficient of low speeds,
- calculating a first representative rotation frequency for each pre-set range of frequencies which are lower than the threshold frequency by multiplying the frequency value of each range by the corrective coefficient of the low speeds,
- storing the first calculated representative rotation frequencies,
- calculating a plurality of rotation frequencies by multiplying, for each corrective coefficient of the plurality of corrective coefficients, a frequency value of the range of frequencies of the maximum speed,
- comparing the values of the calculated rotation frequencies with a reference range of frequencies indicative of a maximum running of the endothermic motor,
- storing the corrective factor corresponding to the rotation frequency falling within the range of frequencies indicative of the maximum running of the endothermic motor as corrective factor of the high speeds,
- calculating a second representative rotation frequency for each pre-set range of frequencies which are greater than the threshold frequency by multiplying a frequency value of each range greater than the threshold frequency by the corrective factor of the high speeds,
- storing the second calculated representative rotation frequencies, and
- determining the operating time in which the motor has operated at the rotation frequencies of each pre-set range of frequencies by multiplying the number of occurrences of each pre-set range of frequencies by the value of the pre-set sampling period (ΔC), and indicating the wear of the tool based on the operating time.