| 摘要 |
A method and a device for controlling an electric motor arranged to serve as drive source for electrically driven hand tools or stationary machines, which during operation are made subject to varying loads. According to the invention are limit values, determined by experience and/or calculations, relating to supplied power with regard to different rotary speeds stored in one or a number of memory circuits and compared to present actual rotary speed and supplied power with use of a microprocessor. An output signal from the microprocessor is used to adjust supplied power within preset limits for each rotary speed as compensation for reductions in rotary speed due to increased load and increases in rotary speed due to reduced load. Over- or understepping stored limit values during a predetermined time period set for each group of limit values being arranged to cause disconnection of the drive voltage fed to the electric motor. Furthermore, the start operation comprises preferably of two or more during which the microprocessor step by step increases supplied power and performs comparison between to the microprocessor supplied information relating to obtained rotary speed and stored information relating to expected rotary speed for each step. A rotary speed lower than stored speed information during a predetermined time period being arranged to cause disconnection of the drive voltage fed to the electric motor. |
