The self-aligning receiver in wmps system for AGV positioning

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A kind of self-aligning photoelectric signal-receiving sensors is proposed driven by servo motors from the application of workshop Measurement Positioning System( wMPS) for the high-precision navigation and positioning project of Automated Guided Vehicle( AGV) . The photoelectric signal-receiving sensors lost the optical signal abnormally because of the complex measurement environment. In order to enable the sensor to receive enough light signals at all times,the control program were designed. Real-time control effect can be achieved only by using the body posture measured by the wMPS as the program input amount. The experimental shows that this new type of sensor ensures that signals from the specific transmitter can always be received. The measurement range and continuity of the AGV positioning navigation system adopting this optimization method is greatly increased by using this new type of sensor.

0 Introduction

AGV (automated guided vehicle), as an automatic intelligent handling equipment and platform, can drive along a specific path, thus realizing the automation of goods handling and taking in the factory. As an effective means and key equipment of modern logistics processing automation, it can effectively improve production efficiency and reduce labor intensity. With the rapid development of e-commerce industry, the demand for efficient, flexible and energy-saving automatic logistics system is more and more strong. As one of the key technologies of AGV, the importance of navigation technology has also attracted great attention of the industry.

In recent years, many AGV navigation methods have been proposed, such as magnetic stripe navigation, optical navigation, lidar navigation and visual navigation. Magnetic stripe navigation sets magnetic tape, magnetic nail and other guidance devices in the navigation field in advance, and installs corresponding induction elements on AGV to identify and track, so as to realize positioning and navigation on the determined path. This method has the advantages of single path, low precision and poor flexibility; optical navigation is similar to magnetic stripe navigation, in which the magnetic stripe is replaced by painting or color band, and the ground image is processed and recognized by the camera installed on AGV. This method has good flexibility, but it is sensitive to the pollution and wear of color bands, with poor reliability and low accuracy; the lidar navigation technology is relatively mature, with the highest repetition positioning accuracy of ± 4mm and data update rate of about 8Hz; Vision navigation is to collect images with CCD camera during AGV driving, process the image information, build real-time map, and determine the change of position and posture. However, due to the limitation of image quality and computing speed, the real-time positioning accuracy and response speed can not meet the needs of users.

With the application of wmps (workshop measuring positioning system, wmps) to AGV (automated guided system) The theory and application of AGV positioning are becoming more and more mature. An AGV positioning and navigation method combined with fuzzy control takes the relationship between the vehicle body position and the position of the target point measured by wmps system as the control input. The positioning accuracy of AGV moving to the target point is better than 2.5mm. Wmps is a large-scale three-dimensional coordinate measuring system based on photoelectric scanning, which is independently developed by the scientific research team of the State Key Laboratory of precision testing technology and instruments of Tianjin University. It has the characteristics of high precision, large measurement space and flexible layout. As a sensor used for measuring coordinate point, wmps spherical receiver can be fixed on AGV vehicle body as coordinate measuring point. The position and pose information of the vehicle is fitted by the position relationship between these points.

In the experiment of AGV positioning and navigation using wmps system, in order to realize the continuity of positioning process, the reasonable layout of transmitter station in measurement field has always been discussed. The purpose is to realize that each receiver on the car body can measure the coordinates of each position in the measurement field. However, because the photosensitive element of the receiver is not omni-directional design, at the same time, it can only receive part of the light signal incident in the space. A servo motor driven self-adjusting receiver is designed. Starting from the improvement of AGV positioning method and the design of direction adjustment method, the tracking, aiming and transmitting function of the new receiver is realized to achieve better dynamic positioning effect.

1 Optimization of AGV positioning principle

At present, the wmps measurement system is used for AGV positioning, and the mathematical model of optical signal intersection measurement of multiple transmitting stations is used. In order to reduce the number of optical signals needed to calculate the real-time sitting position information of AGV, this paper first proposes a pseudo rendezvous measurement positioning method based on the optimization of AGV positioning calculation principle. With this method, the receiver only needs to receive the signal from one transmitting station to achieve the same positioning effect.

1.1 wmps measurement model and principle

This chapter first introduces the wmps measurement system to further explain the AGV positioning principle. Wmps measurement system is composed of laser transmitting base station (hereinafter referred to as transmitting station), photoelectric receiving sensor (hereinafter referred to as receiver), signal processor and computer. The receiver obtains optical signal from the transmitting station and generates analog electrical signal, which is converted into digital signal by signal processor, and the space coordinate of receiver is calculated by computer.

The self-aligning receiver in wmps system for AGV positioning

Fig. 1 working principle of wmps transmitting station

As shown in Fig. 1, the transmitting station constructed by cylinder combination can be abstracted into a mathematical model composed of two scanning light planes with a certain angle to each other and a rotating axis (Z axis). Select the appropriate origin on the rotating axis to construct the corresponding instrument coordinate system of the transmitting station. The parameters (unit normal vector) of the scanning light plane in the coordinate system of the transmitting station can be expressed as (AKI, bki, CKI, DKI) t (I is the serial number of the optical plane, and K is the serial number of the transmitting station). When the transmitting station is working, the rotor of the turntable drives two line lasers emitting scanning light planes to rotate together at a certain angular velocity ω K (generally, the value of ω K is 25-50 revolutions per second). At the same time, when the turntable rotor of the transmitting base station rotates to a certain position as the initial position, the synchronous light laser installed on the transmitting station sends synchronous light signal to space as the timing starting point. The color circles shown in the figure are receivers. The receiver measures the angle of the scanning light plane around the rotation axis when the scanning light plane reaches the measuring point by timing. When the turntable turns to the initial position, the time when the receiver receives the synchronous light signal is recorded as

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