Research of System Structure and Precision of Measurement Robots

This paper analyzes the system structure and precision of measurement robots.The automatic principle is also discussed.The key technique to measurement robots is that the CCD camera is used to catch the image of targets and the image will be enhanced and processed to extract the features needed for matching, then the accurate motor will rotate the theodolite part to point to the target, so the whole operating and measuring are automatic. According to the number of instruments used, we can divide them into two kinds.One is the single instrument robot, including one computer and one prism.Based on the polar coordinate positioning method, we can determine the points by the slope distance, horizontal angle and vertical angle measurements.It is high efficiency to catch points and very easy to operate the instrument, but due to the limit of the precision to measure distance by the instrument, the position precision is about 1mm.The other is the multiple instrument system.It consists of two or more measurement robots, a computer and software.Because we can calculate the 3D coordinates from the horizontal angles and vertical angles measured from two stations by space intersection, the distance measurement is not necessary, so the prism is optional and natural points can be used.With the help of image processing software, the system can look for the same point automatically.Because the absolute and relative position elements (the horizontal distance, height difference between the instruments and the direction between them) can be determined accurately, the precision of multiple measurement robots system is very high, even up to 0.07 mm.Due to the high precision, it can be used to monitor the shape of some industrial structure.The mathematic formulae were derived according to error propagation principle for the coordinates.Typical parameters were used to calculate the influence of known elements to the result. A Leica TCA1100 measurement robot was used to do some experiments.We developed a software with VB for it.The surveyor can make a surveying plan through the dialog window displayed on the screen of the computer.For example, the surveyor can determine the number of measuring rounds according to the project demanding and give searching scope of targets as well as the start time and waiting time between adjacent rounds.Some instruments use a special target which send out signal, so the measurement robot can find it without the approximate position, while others which use the common prism as target have to get approximate positions of the targets from the surveyor.After all of the initial information was entered to the computer, it would control the instrument to do the whole surveying work automatically according to your plan.The horizontal di-rections, vertical angles and slope distances from the instrument to the targets or the 3D coordi-nates of the targets will be recorded to the data base in the computer.The surveyor can view the data base at any time.By the help of the software, the surveyor can draw the shape of an industrial product or the deformation graph of a civil building.Some experiment results are presented in this paper.