Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2000-01-19
2001-12-11
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Reexamination Certificate
active
06330095
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a beam scanning apparatus for two-dimensionally scanning over a region which is an object of measurement through use of an optical beam, such as a laser beam.
A commonly employed apparatus for measuring the distance between vehicles (hereinafter referred to simply as a “inter-vehicle distance measurement apparatus”) basically comprises an optical beam scanning device for two-dimensionally scanning over a forward region which is an object of measurement (hereinafter referred to as a “forward region”) through use of a laser beam; a light-receiving device for receiving reflected light of the thus-emitted laser beam; and a computation device for computing the distance between vehicles on the basis of the characteristics of the light received by the light-receiving device. For example, Japanese Patent Publication No. 9-274076 discloses such an apparatus for measuring the distance between vehicles.
In the related apparatus used in the inter-vehicle distance measurement apparatus, pulse light originating from a light source, such as a laser diode, is emitted as an optical beam by way of a collimator lens, and the thus-emitted optical beam is radiated onto a reflection plate which is pivotally moved within a given angular range or onto a rotating polygon mirror. The forward region is two-dimensionally scanned through use of the beam reflected from the reflection plate or the polygon mirror. For example, the inter-vehicle distance measurement apparatus described in the cited patent publication performs two-dimensional scanning operation through use of a polygon mirror.
The related apparatus is arranged so as to perform a scanning operation within a predetermined angular range through use of an optical beam, by means of pivotal movement of the reflection plate or by means of rotation of a polygon mirror. Means for deflecting an optical beam through use of such as a reflection plate or a like element requires a wider area for placement than does another constituent component, thus raising a problem in rendering the optical beam scanning apparatus compact.
Further, the related apparatus radiates an optical beam in the form of a pulse signal in synchronism with the angle of scanning. If an offset arises between the timing at which an optical beam is radiated (or illuminated) and the rotational angle (i.e., the angle of scanning) of a reflection plate or a polygon mirror, the optical beam scanning apparatus encounters a problem of inability to fully scan over the entire region which is an object of measurement. In order to work around such a problem, the first related apparatus actuates a reflection plate or a polygon mirror while maintaining a high degree of linearity relative to the timing at which an optical beam is to be radiated. To this end, a mechanism for actuating the reflection plate or the polygon mirror requires positional accuracy with a high degree of resolution.
SUMMARY OF THE INVENTION
The present invention is provided to solve the above problems. It is therefore the first object of the present invention is to provide a compact beam scanning apparatus capable of sweeping a beam, such as a laser beam, within a given angular range without involvement of optical deflection means, such as a reflection plate or a polygon mirror, and capable of appropriately sweeping a laser beam without use of a drive mechanism having a positional accuracy with a high degree of resolution.
In addition, the second object of the present invention is to provide a more practical beam scanning apparatus capable of preventing generation of heat, which would otherwise be caused by a necessity for supplying large drive power for reversing the direction of movement of optical deflection means.
In order to achieve the above objects, the apparatus of the present invention is arranged so as to directly and pivotally move a collimator lens, thorough which an optical beam originating from a light source passes, within a predetermined angular range through use of a pivot mechanism, thus obviating a necessity for optical deflection means, such as a reflection plate or a polygon mirror. Therefore, the apparatus can be made more compact than the related apparatus.
In the apparatus of the present invention, position detection means detects the position of the collimator lens actuated by the pivot mechanism. On the basis of the rotational angular position of the collimator lens, the pivotal movement of the collimator lens and the timing at which the light source is illuminated are subjected to feedback control. Accordingly, the timing at which the light source is illuminated can be accurately synchronized with the rotational angular position of the collimator lens, thus enabling appropriate scanning of a beam.
The pivot mechanism can be embodied by a magnetic drive mechanism comprising a magnet and a drive coil. In this case, in consideration of the influence imposed by inertia force or another factor, a large drive current must be supplied to the drive coil in order to reverse the direction of movement of the collimator lens being pivoted. If a large current is supplied to the drive coil, the amount of heat accumulated in the drive coil is also increased in association with the supply of the drive current. There arises a problem of deterioration of the durability of the drive coil or a problem of thermal expansion, which stems from generation of heat, thereby affecting surrounding elements.
However, according to the present invention, at the time of reversal of the moving direction during reciprocal movement, the collimator lens is imparted with urging force for mitigating the drive load in the opposite direction imposed by a collimator lens drive mechanism.
Thus, the present invention yields an advantage of the ability to diminish drive power to be supplied to the drive mechanism at the time of reversal of the moving direction of the lens, as well as an advantage of the ability to prevent heat from developing in the drive mechanism correspondingly.
REFERENCES:
patent: 5072114 (1991-12-01), Takada
patent: 5303080 (1994-04-01), O'Brien et al.
patent: 9-274076 (1997-10-01), None
Kabushiki Kaisha Sankyo Seiki Seisakusho
Robinson Mark A.
Spyrou Cassandra
Sughrue & Mion, PLLC
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