Based on infrared sensors to guide the AGV design
Automatic Guided Vehicle (AGV-Automated Guided Vehicle) is a modern logistics system in manufacturing enterprises and important equipment is a kind of micro-control processor as the core, battery-powered, non-contact guiding device with an unmanned automatic oriented transportation vehicle. It can be issued in accordance with the command control system, based on pre-design process, according to the sensor to determine vehicle location information, driving along the prescribed route and stop location of the autopilot. AGV has a high transport efficiency, energy saving, reliable, pollution-free, flexible delivery, etc., have been widely used in many fields. From supermarkets, the workshop expanded to large automated warehouses, hospitals and distribution centers, AGV to become one of the main indicator of industrial automation. In this paper, scale models simulate the actual production line vehicles AGV, and uses infrared sensor technology to guide AGV movement.
2 Hardware System
2.1 The overall design
Automatic guided vehicle including the body, controls, sensors and power devices, etc. 4. Among them, the body by reducing the proportion of 200 mm × 300 mm, with a differential rear-wheel drive model car simulation. Controller is based on SCM MC9S12DG128 as the core, with the body's sensors and power devices to control the AGV and stable operation. The infrared sensor consists of measuring the Hall sensor and speed sensor. Battery-driven power plant is a DC motor and steering gear constitute, respectively, control speed and steering. This coupled with the corresponding 4 drive circuit, the path to self-identify, control model car stable operation. AGV model car shown in Figure 1.
AGV and the MCU can be seen as an automatic control system is composed of sensors, information processing, control algorithms, actuator 4 parts. The hardware is a microcontroller as the core, equipped with sensors, actuators and the corresponding drive circuits control system; information processing and control algorithms by the control software. Figure 2 shows the hardware circuit diagram.
2.2 MCU Introduction
AGV system controller using MC9S12DGl28 as the device built-in 128 KB of Flash, 8 KB of RAM, 2 KB of EEPROM, 8 loser who capture and output compare channel, two 8-bit or 16-bit pulse accumulator, 8 PWM wave generator channel, 8 channel 10-bit ADC or 16-channel 8-bit ADC, 2 SCI, SPI communication interfaces, 80 to 112 programmable I / O ports.
2.3 Power Module
AGV model car powered by a 7.2 V, 2 A / h batteries available. Different modules in the circuit work required voltage and current are different, requiring multiple voltage regulator circuit the battery voltage into the required voltage for each module. LM7805 is a series regulator, the output voltage is 5 V, the main microcontroller, infrared sensor, speed sensor and part of the interface circuit to provide power. The LM1117-ADJ output of 2.85 V ~ 6 V adjustable power supply. By adjusting the potentiometer for the steering gear to 6 V supply voltage. 7.2 V battery power directly to the ACV model car rear wheel motor.
Speed Detection Module 2.4
CS3020-based speed sensor with Hall element. Hall element easy to use, just a pull-up resistor connected to the power output can work. Inside the tire glue 4 magnets, the magnets are fixed on the direction of Hall elements choose the right place. When the tires around every turn, the Hall element output 4 signals, tire circumference 17 cm, so the time difference of two signals each for the T, AGV traveling 4.25 cm. By measuring T, calculate the speed of AGV V = 4.5 cm / T.
Infrared Detection Module 2.5
AGV model car boot way for ultrasound guidance, electromagnetic induction guidance, image recognition guidance, inertial navigation, infrared sensors to guide and so on. As easy to use infrared sensors, low cost, and guide precision, fast response, etc., so the system uses infrared sensor technology to guide AGV model car traffic. Large selection of transmit power, receive sensitivity of the infrared sensor infrared detection circuit to ensure reliable operation of the foundation. The infrared sensor system design, selection of reflective photoelectric TSL600. Shown in Figure 3, the right is the infrared receiver infrared light-emitting diodes and transistors, which, VCC is 5 V, and R1 = 510 Ω and R2 = 20 kΩ resistor to limit, OUT is the output signal. Infrared emission of infrared light emitting diode reflector according to the media reflected the depth of color to the amount of light receiving transistor different. Receive transistor is a phototransistor, the amount of light received more output current increases. The design of the AGV model of 10 cm at the front 7 on the horizontal installation of infrared sensors, AGV is installed on the central axis direction 1 on the central axis of the left and right sides of the installation of 3 pairs. According to 7 on the sensor output signals to determine the black guide lines and the position relationship between AGV model cars, to guide towards the provision of reliable data. Infrared receiver receives the reflected infrared light path changes the voltage generated to reflect the location of the track centerline. Infrared sensor output is analog, through the MCU's ADC to convert analog to digital, not only simplify the external circuit design, while retaining the continuous changes in infrared receiver voltage information, the software algorithm more precise location information and eliminate ambient light effects. MC9S12DG128 10-bit ADC with 8 or 16 8-bit ADC, 8-bit effective value taking into account the system accuracy requirements have been met, the system 8-bit ADC with 16 channels in 7.
2.6 Drive Control Module
Motor start using PC33886 as the drive and the left part of the circuit shown in Figure 3. PWM3 generated by MCU IN1 pin to adjust the PC33886 the OUT1 port output voltage, and ground to IN2 OUT2 output is 0, so OUT1 and OUT2 produces a pressure differential between, MCU by changing the duty cycle to regulate PWM3 motor speed.
3 System Software Design
3.1 Control Algorithm
In the continuous control system, according to the ratio of deviation (P), integral (I), differential (D) of the PID control algorithm to control access to a wide range of applications. The digital PID control algorithm is simple and easy to adjust parameters, adaptable. The system design, an incremental digital PID control algorithm, PWM DC motor speed control.
3.2 Program flow
The system's main program flow chart shown in Figure 4. System first initialize the device, and then modify the program parameters into the parameter set to open after the break, the last loop position, velocity control procedures.
Experiment was 5 000 min × 6 000 mm in the region to build roads in the U-driving, middle of the road marked with 20 mm wide black boot line. Under normal circumstances, given the speed of AGV model car ceiling 1 m / s, AGV hug the road in the boot line, starting from the starting point to identify the destination and stop consuming the entire total of 22 s; for a given model of vehicle speed AGV limit of 1.5 m / s when, AGV traveling relatively smooth line in the boot, the whole time-consuming a total of 16 s; for a given maximum speed of AGV model car 2 m / s when, AGV driving instability, sometimes in the red corner a guide wire, the entire process took a total of 12 s. According to the above experiment, AGV stability of the average velocity of 1 m / s. AGV is not racing cars, industrial field generally stable and secure is the major consideration, so the design of the stability of the model car in full compliance with the norms AGV vehicles to reach the independent guide, transportation efficiency, energy saving, reliable, pollution-free requirements.