Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Patent
1990-04-06
1992-04-21
Ben, Loha
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
359221, 359223, G02B 2608
Patent
active
051073650
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a rotary laser scanner device which is used in, for example, a laser processing apparatus and which is capable of deflecting, through rotation of a deflection mirror, an incident laser beam so as to position the laser beam. More particularly, the present invention is concerned with a rotary laser scanner device having improved driving and detection mechanisms for the rotation of the deflection mirror.
BACKGROUND OF THE INVENTION
Laser beams are finding wide use in various fields such as optical office equipments and video devices, besides fields such as laser markers, laser trimmers and so forth. When a laser beam is used, it is necessary to properly position the laser beam, i.e., to effect deflection and scanning of laser beam. To this end, hitherto, laser scanner devices of galvanometer-type have been used popularly.
A galvanometer-type laser scanner device has, as shown in Japanese Patent Unexamined Publication No. 53-143910 for example, a mirror attached to the rotor shaft of an electric motor having a stator and a rotor capable of performing a limited rotation. The scanner device also has a position sensor of electrostatic capacitance type arranged around the rotor shaft of the motor, and output from this sensor is fed back to the instruction signal given to the motor, thereby to position the mirror.
This known laser scanner device, however, has suffered from the following disadvantages:
(1) A positional drift of 600 .mu.rad/.degree.C. or so is caused by a change in the ambient temperature.
(2) Response speed is low because the drive relies upon magnetic force. In particular, response speed is low at start-up of the motor (start-up time 3 to 4 msec).
Some of the known laser scanner devices of the type described above employ, as the rotation angle sensor for positioning the mirror, a low-inertia type device in which an electrostatic capacitance type sensor b is arranged to surround the rotation shaft a of the mirror. This type of rotation angle sensor is superior in that the rotation angle is sensed with a high resolution of 0.005.degree. or so, but undesirably exhibits a large temperature drift of 0.03.degree./.degree.C. or so. FIG. 2 shows another known rotation angle sensor for positioning the mirror, in which a light-emitting element d and a light-receiving element e are arranged spaced apart from the mirror rotation shaft c, so that the angular displacement of the shaft c is sensed by the light-receiving element e. This type of rotation angle sensor also exhibits high resolution and low inertia, but suffers from impractically narrow sensing coverage and inferior linearity.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a laser scanner device which can operate with a high response speed, particularly at start-up, and which can always maintain a constant high level of mirror positioning accuracy regardless of change in ambient air temperature.
Another object of the present invention is to provide a laser scanner device which can improve the linearity of sensing output representing the sensed rotation angle of the output shaft.
To this end, according to the present invention, there is provided a laser scanner device for deflecting a laser beam by a deflection mirror which is rotated at high speed, comprising: a piezoelectric actuator capable of producing a linear displacement corresponding to an input drive signal; a motion converting member for converting the linear displacement produced by the piezoelectric actuator into a rotational displacement; a displacement amplifying mechanism having an output shaft to which the rotation shaft of the deflection mirror is coupled, the displacement amplifying mechanism being capable of amplifying the rotational displacement output from the motion converting member; and control means for inputting a drive signal, for rotatingly driving the deflection mirror, to the piezoelectric actuator.
Thus, according to the invention, a piezoelectric actuator havi
REFERENCES:
patent: 4660941 (1987-04-01), Hattori et al.
patent: 4708420 (1987-11-01), Liddiard
patent: 4778233 (1988-10-01), Christenson et al.
Ben Loha
Kabushiki Kaisha Komatsu Seisakusho
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