1. Field of the Invention
The present invention relates to a galvanoscanner and a laser processing machine for optically writing data into a to-be-written medium. Particularly, it relates to a galvanoscanner in which permanent magnets disposed around a shaft and polarized into poles in a circumferential direction of the shaft are used as a rotor, and a laser processing machine equipped with the galvanoscanner.
2. Description of the Background Art
A device for drilling a printed wiring board is roughly classified into a drilling processing machine which performs drilling with a drill and a laser processing machine which performs drilling with a laser beam. On the other hand, a printed wiring board has been multi-layered recently and holes for mounting elements or the like or interlayer connection holes have been arranged densely so that the number of holes per sheet has been increasing. For this reason, the drilling device is shifting from a drilling processing machine to a laser processing machine. Increase in drilling speed is required of the laser processing machine in accordance with increase in the number of holes.
As shown in FIG. 26, the laser processing machine generally performs drilling in such a manner that laser light 111 emitted from a laser light source 110 is deflected and scanned by galvanoscanners 1 and condensed onto a printed wiring board 113 by an fθ lens 112. On this occasion, it is necessary to increase the response speed of each galvanoscanner 1 in accordance with the increase in drilling speed, and it is necessary to increase the current flowing in a coil to increase the response speed of each galvanoscanner 1. However, Joule heat produced in the coil increases as the current flowing in the coil increases. Incidentally, each galvanoscanner 1 is provided with a galvanomirror 100 attached to one end of a shaft of the galvanoscanner 1, so that laser light 111 is deflected by swinging of the galvanomirror 100 so as to be scanned on the printed wiring board 113.
The Joule heat produced in the coil is transmitted to a permanent magnet used as a rotor through a clearance, so that the temperature of the permanent magnet increases. In the case of high-speed response, the temperature of the permanent magnet further increases because the eddy current flowing in the permanent magnet increases. The temperature rise demagnetizes the permanent magnet to reduce rotating torque. As a result, electric power consumption at driving time increases. That is, increase in electric power consumption at the time of driving the galvanoscanner was unavoidable in accordance with increase in response frequency.
Therefore, for example, techniques to suppress such increase in electric power consumption have been proposed in JP-A-Hei-11-252835, JP-A-2008-43133 and JP-A-2007-6626. Of these, JP-A-Hei-11-252835 has disclosed an invention of a rotor of a permanent magnet type electric rotating machine having a rotating magnetic field formed from an iron-containing permanent magnet on a rotor core fixed to a rotation shaft to reduce eddy currents generated in a surface of the permanent magnet forming the rotating excitation field, wherein: the rotating excitation field includes a plurality of parted permanent magnet units arranged in the axial direction of the rotation shaft, and an electrically insulating layer is disposed between adjacent end surfaces of adjacent two of the parted permanent magnet units so as to prevent eddy currents from flowing straddle the adjacent two parted permanent magnet units.
JP-A-2008-43133 has disclosed an invention of a rotary actuator device including: a rotor having a rotation shaft and permanent magnets disposed around the rotation shaft; a stator disposed around the rotor and having coils and a yoke; and a housing for receiving the rotor and the stator to suppress increase of the temperature of the permanent magnets in the movable magnet type actuator device to prevent deterioration of hole position accuracy so that the rotor is swung in a predetermined angle range; wherein: radial grooves opened toward the stator and having a depth not smaller than a skin depth represented by a function of the volume resistivity and permeability of the permanent magnets and the fundamental frequency of the current flowing in the coils are formed in the permanent magnets.
JP-A-2007-6626 has disclosed an invention of a scanner including: a rotor having a shaft and permanent magnets attached to an outer circumferential side of the shaft; and a stator disposed in the outside of the rotor and having a casing, a yoke held in an inner circumferential side of the casing and coils disposed in an inner circumferential side of the yoke to uniformize the torque constant of the scanner to attain improvement in positioning accuracy; wherein: the permanent magnets of the rotor are provided with grooves formed in the outer circumferential portions of the permanent magnets so as to be radially concavely curved so that the torque constant of the scanner is uniformized circumferentially by the grooves.
As described above, JP-A-Hei-11-252835 has described that an electrically insulating layer is disposed between adjacent end surfaces of adjacent two of parted permanent magnet units so as to prevent eddy currents from flowing straddle the adjacent two parted permanent magnet units. JP-A-2008-43133 has described that radial grooves are formed in permanent magnets to suppress generation of eddy currents. JP-A-2007-6626 has described only circumferential uniformization of the torque constant. In any case, each of these aforementioned inventions intends to attain reduction of power consumption. However, the ratio of the torque constant to the moment of inertia in the galvanoscanner presents a problem in order to attain reduction of power consumption.
However, in the inventions described in JP-A-Hei-11-252835, JP-A-2008-43133 and JP-A-2007-6626, there is no particular consideration about the ratio of the torque constant to the moment of inertia.