Design and implementation of mobile robot based on

· weight: 130g

3.2 drive module

the drive motor and steering motor have the same drive principle, both of which adopt pulse width modulation (PWM) mode for speed regulation, and the PWM signal is generated by f2407. The drive circuit adopts h full bridge mode, which is composed of four Darlington tubes (two TIP132 and two TIP137), four in4001 diodes and NAND gates. The circuit schematic diagram is shown in Figure 2. When pwm2 and pwm4 are at low level and pwm1 and pwm3 are at high level, T1 and T4 are saturated and conductive, T2 and T3 are cut off, the current changes from T1 → motor → T4, and the motor rotates forward; On the contrary, when pwm1 and pwm3 are at low level and pwm2 and pwm4 are at high level, T2 and T3 are saturated, T1 and T4 are cut off, and the current is from T2 → motor → T3, and the motor is reversed

in order to prevent T1, T3 or T2, T4 from conducting at the same time, forming a short circuit and breaking down the device, a pair of non overlapping PWM outputs should be used to correctly open and close these two tubes. Add a dead time between the shutdown of one pipe and the opening of another pipe, so that the other pipe has been completely shut down before one pipe is opened. F2407 has a dead time control unit, which is a major feature of f2407. Therefore, software can be used to ensure that the opening intervals of the upper and lower bridge arm switching elements of the power circuit do not overlap, simplifying the hardware circuit design and improving the reliability

3.3 4-turn-1 serial port communication module

because DGPS receiver, magnetic compass, odometer and MC35 communication module all adopt RS-232 asynchronous serial communication, while f2407 has only one serial port, so the serial port communication with f2407 must be completed by converting the four serial port data. Therefore, a 4-to-1 serial communication module based on time-sharing multiplexing method is developed. When f2407 needs the data of a sensor (or wireless communication module), it will gate the sensor through the circuit and occupy the f2407 serial port for communication; When the data of another sensor or wireless communication module is required, turn off the gating of the last sensor and gate the sensor or wireless communication module at the same time. The 4-to-1 serial port communication module is composed of a decoder 74LS138, a three state output four bus buffer gate 74ls125, and a level converter MAX232. Its circuit schematic diagram is shown in Figure 3

3.4 positioning sensor

3.4.1 DGPS receiver

gps (Global Positioning System) is a satellite based radio navigation system, which provides a cheap and practical tool that can determine position, speed and time on a global scale. GPS consists of 24 satellites (21 working stars and 3 backup stars). The constellation is distributed on six orbital planes with an inclination of 55 ° to the equatorial plane of the earth. Its operation cycle is 11 hours and 58 minutes, the orbital radius is 20200km, and the included angle of each orbital plane is 60 °. Each satellite transmits L-band ultra-high continuous wave to the earth and modulates two kinds of pseudo-random codes (military high-precision secret P code and civil c/a code). This distribution ensures that users can continuously receive navigation signals from at least four satellites at any place and at any time on the earth, so as to calculate the three-dimensional coordinates of the receiver and the time offset between the receiver and GPS simultaneously. The three-dimensional coordinate system adopts ECEF Cartesian coordinate system or geodetic coordinate system, such as WGS84

although the U.S. government canceled the optional protection of civil c/a code in May 2001, the single point real-time positioning accuracy of civil navigation GPS receiver can only reach about 25m, which can not meet the positioning and navigation requirements of the system. With real-time differential GPS (DGPS), the positioning accuracy can reach 2 ~ 5m, which can meet the requirements of system positioning and navigation

for this purpose, a single base station DGPS (srdgps) system is developed, and its structural block diagram is shown in Figure 4. The reference station is composed of allstar base GPS receiver, antenna, MDS radio transmitter and antenna, and the mobile station is composed of superstar GPS receiver, antenna, mdx radio receiver and antenna. Among them, the reference station is installed on the roof of the first floor of teaching in Xujiahui campus of Shanghai Jiaotong University. The reference station can cover a radius of 30 kilometers, and the mobile station is installed on the vehicle unit

3.4.2 digital compass and speed sensor

HMR 3300 digital compass of Honeywell company is used as the direction detection sensor of mobile robot. Its main technical indicators are: (1) 1 degree heading accuracy, 0.1 degree resolution; (2) 0.5 degree repeatability; (3) ± 60 degree tilt and pitch range; (4) 15Hz response time; (5) -40 ± 85 ℃ working temperature; (6) 6 ~ 15V DC voltage

at the same time, the Hall speed sensor for Volkswagen Santana 2000 car is used as the speed sensor of mobile robot. Its working principle is that the hall sensor is used as the conversion element to convert the mechanical rotation into electrical pulse signal output. The main technical indicators are: (1) the output waveform is rectangular pulse, and the duty cycle is 50%; (2) Generate 6 pulses per revolution; (3) The rated voltage is 12V

4 power module

the power module needs to supply power to each sensor, DSP chip, other chips and motor respectively. Among them, after the magnetic compass, code disk and DG are amplified by high-speed amplifier, the PS receiver uses 12V DC voltage, the DSP chip uses 3.3V DC voltage, other chips use 5V DC voltage, and the motor power supply uses 12V DC voltage. Therefore, a 12V DC battery (4ah) is used, and the DC 5V is realized by the l7805 of St semiconductor company and the power tube for current expansion. The 3.3V power supply for DSP chip is realized by the 1smb5913bt3 of on semiconductor company. When f2407 works normally, all power pins are 3.3V; When writing flash memory, vccp pin supplies 5V power; During reset, the reset circuit will generate a 10 μ The continuous low level of s width resets the chip

5 controller program structure

dsp program is composed of five functional modules, including system initialization module, serial port communication module, path guidance module, drive motor control module and steering motor control module. Ti provides CC and CCS platforms for C language development. The platform includes ANSI C optimization compiler, which can be developed and debugged at the source program level. This method greatly improves the development speed and readability of the software, and facilitates the modification and transplantation of the software. However, in some cases, the efficiency of the code cannot be compared with the efficiency of manually written assembly code. In addition, using C language to realize some hardware control of the chip is not as convenient as assembler, and some can't even be realized in language. In order to make full use of chip resources and give better play to C language and assembly language