Application of triaxial acceleration sensor in intelligent vehicle control and road recognition (I)

The three-axis acceleration sensor MMA7260Q can measure the inertia of the smart car, select the best center of gravity, and accurately locate the smart car in a straight line, curve, ramp, drift and other running states; the acceleration sensor can predict the path in advance and determine when the braking effect is best. It also solves the balance and direction recognition of the upright walking car model.

　　Therefore, a design based on three-axis acceleration sensor in smart car control and path recognition is proposed. This design uses three-axis acceleration sensor MMA7260Q to measure the acceleration signal of the smart car in motion, and uses embedded single chip MC9S12XSl28B as the core controller to sample the acceleration signal, A/D conversion, and then store the characteristic data in EEPROM. It solves the problem of smart car motion path analysis and obtains the car acceleration in real time, so as to obtain the running status of the car more comprehensively, which provides the possibility for smooth control and better road condition recognition.

　　In the upright walking car model, applying the same principle and selecting the optimal center of gravity can effectively solve the balance and direction recognition of the upright walking car model, thereby speeding up the driving speed of the car model.

　　The experimental results prove that the acceleration sensor has strong anti-interference ability and can extract angle information more accurately, ensuring that the smart car can travel at a higher speed on a straight road and can turn smoothly on a curve without stalling.

　　1. Existing problems of smart cars

　　During the operation of the car model, people cannot judge the running state of the car. Using an acceleration sensor to monitor the acceleration of the car can more accurately know the running state of the car, and can distinguish between ramps and non-ramp roads by detecting the change of acceleration in a certain direction. So as to make corresponding strategic responses. Avoid the car from stopping and overturning during the competition. And it also solves the balance of the upright walking car model during the walking process.

　　2. MMA7260Q Introduction

　　The accelerometer is MMA7260Q produced by Freescale.

　　Figure 1 Chip pin definition

　　2.1 Features of MMA7260Q:

　　It provides three-axis XYZ detection sensitivity in one device, with optional sensitivity: 1.5g, 2g, 4g and 6g; low power consumption, sleep mode, low voltage operation generally at 2.2V~3.6V, fast startup, generally startup time is 1ms; it has low noise, and the package is generally a 16-pin 6mm x 6mm x 1.45mm pinless quad flat package (QFN).

　　2.2 Advantages of MMA7260Q

　　Provides flexible optional ranges for multi-functional applications: including 1.5g, 2g, 4g and 6g; low power consumption, which can extend battery life Short power-on response time, best suited for sleep mode of battery-powered handheld devices, small number of components - saving cost and space Low noise, high sensitivity, with adaptive function, high frequency and resolution, providing accurate fall, tilt, move, place, vibration and swing sensing sensitivity Recommended gravity acceleration levels for different applications Free fall detection: 1g~2g Tilt control: 1g~2g.

2.3 Analysis of Acceleration Sensor Applications

　　2.3.1 Analysis of interference factors

　　The chip can test the acceleration change in one direction. Therefore, different installation methods are adopted, and more interference factors must be considered during the process.

　　1. Mechanical vibration of the vehicle during movement

　　2. The impact of uneven speed control on the vehicle's motion state

　　3. The difference between the error under normal circumstances and the output generated by the acceleration sensor under normal circumstances

　　2.3.2 Installation method analysis

　　If it is installed on the pole where the camera is installed, the pole will shake left and right when the car accelerates or decelerates. Through Labview observation, it is found that the interference is too large. If it is installed at the rear of the car, the impact on MEMS will be more obvious than before due to the vibration of the motor itself.

　　After testing, it is found that if the acceleration in the horizontal X direction is measured, the circuit board with MMA2260 should be mounted on the front of the vehicle.

　　Figure 2 Acceleration sensor installation method

　　If it is installed on an upright walking car model, the acceleration in the vertical Z direction should be measured.

　　Figure 3 Schematic diagram of upright walking car model installation