The present invention relates to a tilt detecting device capable of stably detecting tilt and horizontality.
As a device for detecting the horizontality and the tilt, a tilt sensor, for instance, is known and as conventional tilt sensors and the following two types can be cited.
A first one is a device where a liquid is sealed in a container so that a free liquid surface is formed, an absolute pattern is projected by a telecentric optical system to a liquid surface of the liquid, and a reflection image of the absolute pattern obtained by a rear-surface reflection on the liquid is projected to a photodetection element.
In the case of the sensor described above, since the liquid surface of the liquid is horizontal at all times, when the sensor is tilted, a reflection image projected to the photodetection element moves, and by detecting an amount of moving of the reflection image, the tilt of the sensor is detected.
As the liquid sealed in the container, an oil with viscosity or the like is used so that recognition of the absolute pattern can be performed normally even under vibrating, and the absolute pattern can be stably recognized by damping of the oil. However, since the viscosity of the oil rises under a low temperature, in order to detect the tilt under a low-temperature environment, there is a problem that follow-up properties deteriorate.
Further, a second one is a device where an image of penetrating type circular bubble tube is projected to an element split in four parts and the tilt of the sensor is detected from changes of light amount. In the case of the second sensor, since a light quantity difference caused by a shade of air bubbles is seen, a displacement by vibrating can be processed by averaging, and as the liquid to be sealed in the bubble tube, alcohol with a low viscosity or the like is used.
However, in the case of the sensor described above, since a movement of the air bubbles directly depend on an accuracy of a glass inner surface, a range where the movement of the air bubbles follows up the tilt of the sensor with the good sensitivity is limited. Further, an influence by a deformation of the air bubbles caused by a temperature change can be easily applied, and there is a problem that an offset at a zero point is difficult.