Photoelectric inclination sensor and its application to the measurement of the shapes of 3D objects

A method for obtaining the tilt angle and direction in a two-dimensional plane, by using a photoelectric inclination sensor consisting of an LED, a hemispherical spirit level, and a photodiode array is explained. An application of the sensor to the measurement of the shape of a 3-D object is also described. Light from the LED projects a bubble in the spirit level and throws a shadow onto the surface of an array composed of four equivalent p-n junction diodes, isolated from each other by a cross on a wafer. The tilt angle and direction in a two-dimensional plane are obtained by combining the diode outputs. By positioning the sensor on the crosspoints of the lines drawn longitudinally and latitudinally at an interval on the surface of a small mountain in a Japanese garden, the x and y components of the tilt angle can be obtained and its shape is reconstructed by a computer. The principle of the sensor, the system to display the tilt angle and its x and y components, and the application of the system to the measurement of the shape of a mountain are explained.>