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.

Claims

1.-18. (canceled)

19. A compact hand-held sanding machine comprising: an outer housing; a tool shaft; a brushless electric drive motor; a stator being positioned in the outer housing; a rotor having a central aperture, said rotor being received within the stator; said tool shaft extending within said aperture in said rotor and fastened thereto; and wherein the tool shaft includes an eccentrically positioned cavity, and wherein an eccentric bearing is received within said cavity.

20. A sanding machine according to claim 19, wherein the eccentrically positioned cavity is formed with the tool shaft.

21. A sanding machine according to claim 19, wherein the grinding disc is mounted on the tool shaft eccentrically freely rotationally.

22. A sanding machine according to claim 21, 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.

23. A sanding machine according to claim 19, wherein the control unit of the motor is arranged in such a way that the speed of rotation is constant irrespective of the load.

24. A sanding machine according to claim 23, wherein the control unit is a sensorless control unit.

25. A sanding machine according to claim 24, 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.

26. A sanding machine according to claim 24, 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.

27. A sanding machine according to claim 19 with a control unit, where the mains voltage is rectified and the following capacitor (C2) 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.

28. A sanding machine according to claim 27, 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.

29. A sanding machine according to claim 27, wherein the switched power aggregate uses only the motor's own inductance (L1) as the inductive component in the switching.

30. A sanding machine according to claim 19, wherein the motor is cooled by a blower which is mounted on the tool shaft.

31. A sanding machine according to claim 19, 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.

32. A sanding machine according to claim 19, wherein the stator is shaped in such a way that it is, at the same time, the housing of the sanding machine.

33. A sanding machine according to claim 32, wherein the stator has built-in cooling channels.

34. A sanding machine according to claim 19, 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.

35. A compact hand-held sanding machine having a grinding disk comprising: an outer housing; a tool shaft and a brushless electric drive motor, a stator being positioned in the outer housing wherein the tool shaft extends within and is fastened to a rotor of the drive motor, and has an eccentrically positioned tool holder cavity; and a shaftless rotor of the drive motor is fastened to the tool shaft, said tool shaft extending within the rotor of the drive motor; wherein a grinding disc is fastened freely rotationally to the tool shaft via an eccentric bearing, the eccentric bearing being received into the eccentrically positioned cavity of the tool shaft; thereby creating a compact sanding machine.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0016] The invention is described in more detail in the following with reference to the attached drawings, in which

[0017] FIG. 1 shows a top view of the sanding machine;

[0018] FIG. 2 shows a side view of the sanding machine;

[0019] FIG. 3 shows a cross-section along line A-A;

[0020] FIG. 4 shows a cross-section along line B-B;

[0021] FIG. 5 shows an electricity drawing of prior art control;

[0022] FIG. 6 shows prior art power correction;

[0023] FIG. 7 shows a first embodiment of new motor control; and

[0024] FIG. 8 shows a second embodiment of the motor control.

PREFERRED EMBODIMENTS

[0025] The sanding machine shown in FIGS. 1 to 4 is formed of a housing 1 enclosing all parts of the motor. The motor is formed of a stator 6, including a casing with cooling fins 12 and a rotor 7. These parts are integrated with the parts keeping a tool shaft 2, a bearing housing at both ends 4, 11 and a bearing 10 in place, in such a way that the rotor 7 is fastened to the tool shaft 2. The casing and cooling fins of the stator 6 are shaped in such a way that an air slot is generated which is limited by the casing, the housing of the sanding machine and the cooling fins. The grinding disc 3 is fastened freely rotationally to the tool shaft 2 via an eccentric bearing 8. The blower 9, which is fastened to the tool shaft 2 preferably at the same height as the balance weights, sucks in air through the hole 14. The air cools the control unit 15 and then the motor via the cooling fins 12. The air is blown out through the hole 5. The shroud 16 collects the grinding dust that is sucked out through the grinding disc 3 and further out through the extraction pipe 17. The switch 13 is in connection with the control unit and attends to the switching on and switching off ergonomically. A soft part 18 around the casing makes the machine grip-friendly. In another embodiment, the disc is not freely rotating, but the disc is rotating with or without eccentric movement through a connection to the tool shaft 2.

[0026] The rotor is prevented to rotate in respect to the shaft with a woodruff key where the corresponding slot is shown in the rotor in picture 4. The rotor can also be prevented to rotate with other kind of keys or with splines.

[0027] The balance weights that are integrated in the tool shaft are so large that the bearing 10 (lower part) has to be mounted before the rotor is fastened to the tool shaft.

[0028] To enhance the compactness the bearings 10 and the bearing housings 4, 11 are partly or fully inside the stator 6 or the windings.

[0029] In another embodiment, the dust extraction also attends to the cooling of the motor in such a way that part of the air is sucked via the motor and the cooling fins, and in this way the motor cools off without a separate blower.

[0030] Functioning of the power correction of the control unit in a first embodiment is described in FIG. 7. The mains voltage is rectified and the following capacitor C2 is so small that the voltage follows the rectified voltage. The motor is 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 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. The control unit utilizes the well-known step-down topology in such a way that the relation between current and voltage is optimized so that smallest harmonic components possible are generated, and thus also the best possible power correction is achieved in that part of the cycle in which the voltage is higher than the nominal voltage of the motor. If the voltage is lower than the nominal voltage, no power is taken to the motor. If the time when the current corresponds to the optimal load in relation to the whole cycle is sufficiently long in relation to the required power, the harmonic components generated back to the electric network will be within allowed values. If the self-inductance L1 of the motor is sufficiently great, the control unit can preferably be made without external inductances. The motor in FIG. 7 has been simplified in such a way that only one switch SW1 is shown. In practice, electronically commutated 3-phase control is directly carried out for the motor.

[0031] If the power correction obtained is not sufficient, the function can be further improved according to the embodiment in FIG. 8. Here, an external inductance L1 and an extra switch according to step-up topology have been incorporated to carry out power correction also during the time when the voltage is lower than the nominal voltage of the motor. The connection is still preferable because the current and the voltage are lower than in a case where the power correction should be carried out during the whole cycle. Above all, the value at the external inductance L1 may be lower because the voltage is lower when the switching is carried out.

[0032] The above description and the related figures are only intended to illustrate a present solution for the structure of a sanding machine. Thus, the solution is not confined merely to the above or the embodiment described in the attached claims, but a plurality of variations or alternative embodiments are feasible within the idea described in the attached claims.