Compact electric grinding machine

Abstract

The present invention particularly relates to a hand-held sanding machine with an outer housing ( 1 ), a tool shaft ( 2 ) and a brushless electric drive motor. In the present invention, the rotor of the drive motor is fastened to the tool shaft ( 2 ) of the sanding machine, and the stator ( 6 ) is positioned in the outer housing ( 1 ). The present invention also relates to a control method for an electric sanding machine.

1 . A hand-held sanding machine with an outer housing, a tool shaft and a brushless electric drive motor, a stator is positioned in the outer housing wherein
 the tool shaft has an eccentrically positioned tool holder, and   the rotor of the drive motor without own shaft is fastened to the tool shaft, which extends within the rotor of the drive motor.   
   
   
       2 . A sanding machine according to  claim 1 , wherein the brushless motor is slotless. 
   
   
       3 . A sanding machine according to  claim 1 , wherein the grinding disc is mounted on the tool shaft eccentrically freely rotationally. 
   
   
       4 . A sanding machine according to  claim 3 , wherein the grinding disc is with or without reduction gear mounted on the tool shaft in such a way that a rotating movement is generated. 
   
   
       5 . A sanding machine according to  claim 1 , wherein the control unit of the motor is arranged in such a way that the speed of rotation is constant irrespective of the load. 
   
   
       6 . A sanding machine according to  claim 5 , wherein the control unit is a sensorless control unit. 
   
   
       7 . A sanding machine according to  claim 6 , wherein the sensorless control unit is arranged to determine the position of the rotor in the electronic commutation by the voltage generated in the phase that is not conducting. 
   
   
       8 . A sanding machine according to  claim 6 , wherein the sensorless control unit is arranged to determine the position in the electronic commutation by the currents generated in the different phases or the relation between current and voltage in the phases. 
   
   
       9 . A sanding machine according to  claim 1  with a control unit, where the mains voltage is rectified and the following capacitor (C 2 ) is dimensioned so small that in use the voltage follows the rectified mains voltage and thus current is consumed from the network during the time when the voltage is loaded, wherein the motor is dimensioned in such a way that the nominal voltage of the motor is to be so much lower than the top value of the rectified mains voltage in relation to the required power that power correction is obtained when current is consumed during that part of the cycle when the voltage is higher than the nominal voltage of the motor and no current is consumed when the voltage is lower than the nominal voltage of the motor. 
   
   
       10 . A sanding machine according to  claim 9 , wherein the relation between current and voltage is optimized in that part of the cycle in which the voltage is higher than the nominal voltage of the motor so that smallest harmonic component possible is generated, and thus also the best possible power correction is obtained. 
   
   
       11 . A sanding machine according to  claim 9 , wherein the switched power aggregate uses only the motor's own inductance (L 1 ) as the inductive component in the switching. 
   
   
       12 . A sanding machine according to  claim 1 , wherein the motor is cooled by a blower which is mounted on the tool shaft. 
   
   
       13 . A sanding machine according to  claim 1 , wherein the cooling air cools the stator of the motor by flowing through the slot generated between the inside of the outer housing and the outside of the stator. 
   
   
       14 . A sanding machine according to  claim 1 , wherein the stator is shaped in such a way that it is, at the same time, the housing of the sanding machine. 
   
   
       15 . A sanding machine according to  claim 14 , wherein the stator has built-in cooling channels. 
   
   
       16 . A sanding machine according to  claim 1 , wherein the structure of the stator, the bearing housings and bearings, is a hermetic structure in which the cooling air passes only on the outside of the motor. 
   
   
       17 . A control method for an electric sanding machine, which method comprises rectification of the mains voltage and switched motor control, wherein the motor being dimensioned in such a way that the nominal voltage of the motor is so much lower than the top value of the rectified mains voltage in relation to the required power that sufficient power correction is obtained when current is consumed during that part of the cycle when the voltage is higher than the nominal voltage of the motor and no current is consumed when the voltage is lower than the nominal voltage of the motor. 
   
   
       18 . A control method according to  claim 17 , wherein the relation between current and voltage is optimized in that part of the cycle in which the voltage is higher than the nominal voltage of the motor so that smallest harmonic components possible are generated and, thus also the best possible power correction is obtained. 
   
   
       19 . A sanding machine according to  claim 10 , wherein power correction is carried out also during that time when the rectified voltage is lower than the nominal voltage of the motor.