“The autonomous mobile robot system refers to an intelligent system that performs autonomous path planning according to the command task and environmental information, and continuously collects local environmental information and makes decisions during the task execution process, so as to achieve safe driving and accurately reach the target location. This paper takes LPC2119 as the control core and introduces a design scheme of a wheeled mobile robot. The robot system uses ultrasonic sensors, photosensitive sensors, and collision sensors to collect external environmental information, and uses PTR2000 to realize the communication between the mobile robot and the computer, so as to realize the feedback of on-site information and the sending of computer control commands.
The autonomous mobile robot system refers to an intelligent system that performs autonomous path planning according to the command task and environmental information, and continuously collects local environmental information and makes decisions during the task execution process, so as to achieve safe driving and accurately reach the target location. This paper takes LPC2119 as the control core and introduces a design scheme of a wheeled mobile robot. The robot system uses ultrasonic sensors, photosensitive sensors, and collision sensors to collect external environmental information, and uses PTR2000 to realize the communication between the mobile robot and the computer, so as to realize the feedback of on-site information and the sending of computer control commands.
LPC2119 is an arm7TDMI-S microprocessor that supports real-time simulation and tracking introduced by Philips, embedded with 128KB high-speed Flash memory. It adopts 3-stage pipeline technology, fetching, decoding and executing at the same time, which can process instructions in parallel and improve the running speed of CPU. Due to its very small size and extremely low power consumption, it is ideal for miniaturization applications. On-chip up to 64KB of SRAM, with large buffer size and powerful processing capabilities. LPC2119 integrates 2 CAN controllers, 2 32-bit timer counters and 4 ADC unit circuits.
Design of PWM Control Circuit for Motor
IR2110 is a dual-channel, high-voltage, high-speed power device gate drive monolithic integrated driver introduced by IR Company of the United States. It integrates most of the functions required to drive high-side and low-side MOSFETs or IGBTs in a high-performance package, providing extremely fast switching speeds and extremely low power consumption with few external discrete components. Its characteristics are: convert the input logic signal into the same-phase low-impedance output drive signal, which can drive 2 outputs on the same bridge arm, with strong driving ability and fast response speed; high operating voltage, up to 600V; built-in undervoltage Blocking; low cost, easy to debug; small size of the circuit chip, DIP14 package. The high-voltage side driver is powered by an external bootstrap capacitor. Compared with other IC driver circuits, the design greatly reduces the number of driving transformers and capacitors, reduces product cost, reduces volume, and improves system reliability. This bootstrap integrated circuit suitable for driving power MOSFETs and IGBTs has been widely used in power drive fields such as power conversion and motor speed regulation.
The PWM function of the LPC2119 microcontroller is based on a standard timer. It has a 32-bit timing controller, a prescaler controller, and 7 matching controllers. It can realize 6 single-sided PWM or 3 bilateral PWM outputs, and can also use Mixed output of these two types. This system uses ports PWM0 and PWM1 to output two PWM signals to control the two drive motors of the mobile robot respectively. The PWM signal forms two signals with a phase difference of 180° through the optocoupler and is added to the HIN and LIN pins of the IR2110 to realize the control of the two MOSFET switches on the same bridge arm. The principle is shown in Figure 1.
When HIN is at high level, Q1 and Q4 are turned on, and the forward working voltage is applied to the DC motor; when HIN is at low level, the LIN terminal inputs a high level, Q2 and Q3 are turned on, and reverse is applied to the DC motor Operating Voltage. Therefore, the working voltage on the armature is a bipolar rectangular pulse waveform. Due to the action of mechanical inertia, the average value of the rectangular pulse voltage determines the direction and speed of the motor.
Ultrasonic Sensor System
In order to reduce the burden of the controller LPC2119, the ultrasonic sensor system is controlled by the AT89C1051 microcontroller of Atmel Company. 1051 microcontroller is a high-performance microcontroller containing a 1KB programmable E2PROM, which is compatible with the instructions and pins of the industry standard MCS-51. It provides a highly flexible and efficient solution for many embedded control applications. AT89C1051 has the following features: 1KB E2PROM, 128B RAM, 15 I/O lines, 2 16-bit timers/counters, 5 two-level vector interrupt structures, 1 full bidirectional serial port and contains precision analog comparison It has a voltage working range of 4.25~5.5V and a working frequency of 24MHz, and also has a secondary program memory lock, power-down and clock circuit of the encrypted array. In addition, AT89C1051 also supports two software-set power saving methods. When idle, the CPU stops, while the RAM, timer/counter, serial port and interrupt system continue to work. When power is off, the contents of RAM are saved, but the oscillator is stopped to disable other functions of the chip until the next hardware reset.
1051 controls to send an ultrasonic wave every 60ms, detects the echo time, and completes the calculation of the distance. In this way, the 16-channel ultrasonic cycle detection is about 1s, and the ultrasonic speed at room temperature is about 344m/s, the distance of the obstacle can be calculated, and finally the ultrasonic sensor number and distance information are transmitted to the LPC2119. The ultrasonic transmitting and receiving subsystem is shown in Figure 2. 1051 uses the P1.0 pin to send a 40kHz pulse signal, this signal is used as the enable signal of the 4-16 decoder 74HC154, and the pins P1.1~P1.4 are used as decoding signals, corresponding to numbers 0~15 respectively. of ultrasonic sensors. This signal is amplified by the 9013 and pushes the transducer to generate a 40kHz ultrasonic signal.
LM567 is a phase-locked loop circuit. The external resistors and capacitors on pins 5 and 6 determine the center frequency f2 of the internal voltage-controlled oscillator, and f2≈1/1.1RC. Its 1 and 2 feet are grounded through capacitors to form an output filter network and a loop single-stage low-pass filter network. The capacitor connected to pin 2 determines the capture bandwidth of the phase-locked loop: the larger the capacitor value, the narrower the loop bandwidth. The working voltage of LM567 is 4.75~9V, the working frequency is from DC to 500kHz, and the quiescent working current is about 8mA.
This design is a vehicle-mounted embedded system based on the arm7 microprocessor, which not only meets the requirements of the mobile robot control system but also provides a good technical support for the transformation application of the robot. On this basis, various advanced control algorithms can be added to realize the intelligence of mobile robots.