1. Field of the Invention
The present invention relates to a scanning type laser radar system for a vehicle, including a laser beam source, and a mirror for forming a beam directed forwardly by reflection of a laser beam from said laser beam source. A driving device or driving means is provided for driving the mirror for turning movement about an axis vertical to a road surface to laterally scan the beam from said mirror, and a light receiver is provided for receiving the beam reflected from an object.
2. Description of the Prior Art
Such a system is conventionally known, for example, from Japanese Patent Application Laid-open No. 203975/84.
In the known system, as shown in FIG. 5, a beam having a vertically constant angle .alpha. and a decreased width in consideration of a vertical pitching caused by an acceleration or deceleration of the vehicle is radiated to conduct a scanning laterally through a predetermined angle to detect an object such as a preceding vehicle V.sub.c existing ahead of the subject vehicle V, thereby judging whether an actuator should be operated for avoiding the collision. In the above known system, however, the mirror has a reflectance which is constant over its entire surface and hence, the range detectable by the outgoing beam is of a substantially fan shape, as shown by a dashed line in FIG. 5. For this reason, if a foreign matter 7 or the like which is undesirable to be detected as an obstacle exists on a road surface 6 between the subject vehicle V and the preceding vehicle V.sub.c, there is a possibility that beam reflected from the foreign matter 7 may be detected before detection of beam reflected from the preceding vehicle V.sub.c, thereby causing a mis-operation. Further, when a bridge 8, a traffic sign or the like causing no interference with the traveling of the vehicle V exists above the preceding vehicle V.sub.c, there is also a possibility that the bridge 8 or the like may be detected as an obstacle to cause a mis-operation.