Intelligent automobile pedal controller based on CAN bus

Qian WANG，Hui－zhong YANG，Zhao－bo QING

College of Mechanical Engineering，China Jiliang University，Hangzhou 310018，China

Intelligent automobile pedal controller based on CAN bus

Qian WANG†，Hui－zhong YANG，Zhao－bo QING

College of Mechanical Engineering，China Jiliang University，Hangzhou 310018，China

This paper is mainly aboutautomobile door pedalused in the production.It carried out the research of CAN bus(controller area network-bus)，analyzed its working principle，hierarchical structure and protocol.Combined with the analysis of the door pedaloperating principle，this paper designed a distributed CAN bus controlsystem.The system consists of a master CPU and four distributed control units，adopting CAN transceiver PCA82C250 to connectwith each other.The method of software imp lementation of the CAN communication system was carried out，and comparatively the algorithm of the anti-pinch and anti-collision function was analyzed.Finally it verifies the running effect of the controller with LabVIEW.

CAN bus，Intelligent car pedal controller，Anti-pinch function，Anti-collision function，PCA82C250 transceiver

† Qian WANG，E－mail:1013177030@qq.com

1.Introduction

Abroad automatic telescopic pedal is already in application on many public transport equipments，such as public bus，luxury bus，city light rail.While auto intelligent pedal system used on the cars and limos is just appeared recently，such as that of Range rover，but the installation cost is too high.The largest domestic company focusing on automobile intelligent adjustable pedal system is T－Max，whose imitation ismore，the cost is high.That requires research and development of new smart car pedal controller.Figure 1 is one kind of producing car door pedal for SUVs.This paper introduces Microchip Company's single－chip microcomputer PIC18F25K80 with internal CAN module as the core，as well as the design process of CAN bus intelligent car pedal controller hardware and software program.

2.CAN bus technology

CAN(controller area network)is a multiple hosts local network system exploited by Bosch company for automotive application.Bus adopts differential signal serial communication to work，whose anti－jamming capability is strong，which has non－destructive arbitration function based on priority，can realize multiple addressmessage transmission.In addition to automotive electronics，CAN bus has been widely used in areas，such as industrial automation and control equipment，medical instrument and environment detection.CAN bus users have become accustomed to the traditional independent CAN controller.With the development of the various application requirements and technology，more and more CAN modules of controllers appear in the form of inside and outside the chip.CAN bus communication system based on embedded microcontroller controller(MCU)has some advantages such as simple interface circuit，flexible operation，powerful features［1］.

The topology［2］of the CAN bus is a typical serial bus structure.CAN bus protocol resolves bus conflict by a way of non－destructive arbitration.CAN bus is a protocol based on message rather than site address.CAN protocol is based on the ISO/OSImodel，but only takes the physical layer of the OSI bottom，data link layer and application layer of the OSI top，whose transmission medium is the twisted－pair cable.Communication rate is up to 1 Mbps/40 m.Direct transmission distance is as far as 10 km/5 kbps.Articulated devices number can reach 110.Signal transmission of CAN adopts the short frame structure，whose effective number of bytes per frame is eight，transmission time is short，and the probability of interference is low.When nodes have seriousmistakes，it has automatic shutdown function，to cut off the node with the bus connection，which strong antiinterference ability.

Figure 1.Pedal out

In CAN system design，themost used microcontroller is external independent CAN controller，such as Philips company PCA82C200，SJA1000 and Intel's 82526，82527［3］ and other chips.Using such chip is harmful for system integration.This paper selected microcontroller PIC18F25K80 which embedded CAN controller as the CPU.

3.The Com position of Car Pedal Controller Communication Network

Electric pedal control system communication network with a total of four CAN node electronic controllers，which are left front doors controller，right front doors controller，the left rear doors controller，and right rear doors controller.The CAN bus communication technology can realize the communication between the four door controllers，as shown in Figure 2.

The way that controller realizes the function is shown as follows:function of CAN bus to send and receive data，read analog on－board network signal in the door，battery voltage signal.The basic function of normal telescopic pedal is when the pedal stretches out and meets the collision objects，it stops and reversely recovers;when the pedal takes back and meets the collision objects，it stops back，back out.Pedal has collision and clampingmaterial information completely from the feedback signal to themotor currentof the controller.For differentobstacles，themotor current curve is different.

Figure 2.Communication network structure

4.Controller hardware design

Car pedal controller ismainly composed of single chip microcomputerminimum system，power supplymodule，motor drivermodule，motor current samplingmodule，CAN bus network interface circuit.

Among them，the power supply module is to convert the 12 V supply of the car to give standard voltage of 5 V for controller，as shown in Figure 3.Considering the cost and function need，motor driver module used the H bridge drivingmode，which saves the cost，also can achieve the required functionality，as shown in Figure 4.Motor current samplingmodule adopts the amplifier for resistance voltage，to represent themotor current feedback value.CAN bus network interfacemodule adopts PCA82C250 transceiver(TTL signals of single chip microcomputer is converted to differential signal of CAN bus).Current is limited by resistor to protect the transceiver from the impact of the flow.Small capacitance can rise to filter outhigh frequency interference and electromagnetic radiation on the bus，as shown in Figure 5.

Figure 3.Power supply module

Figure 4.Motor drivermodule

Figure 5.CAN bus interfacemodule

5.Sensorless control clip anti-collision function im p lementation

Sensorless implementation of anti－pinch and anti－collision function reliesmainly on the recognition of motor currentwaveform figure，as shown in Figure 6.There are three ways for the motor current waveform recognition:the slopemethod and amplitude method and integralmethod［4］.

Figure 6.Motor currentwaveform figure

6.The pedal control unit software design and im p lementation

The software design of the system is very important.Tools used in the design are:software MPLAB IDE，the emulator ICD2.5.In order to improve the reliability and understandability，the paper adopts modularization program design idea，and the whole program is divided into five parts:① the main program，including system initialization program and monitoring program;② the CAN communication program，includingmessage program，message receiving and sending CAN errormanagement procedures，etc;③ the clip collision prevention program，using integral algorithm，discrimination encountered obstacles，and make the right response;④ the peripheral interface program，mainly includes the current signal acquisition program，switch signal recognition，received message analysis program and display;⑤interrupt program.

The Program②，③mentioned above are the keys of the design.Figure 7 is the CAN communica－tion program(the left figure is the initial subprogram，the intermediate one is node data sending program，the right one is the node data reception procedures).Figure 8 is the clip collision prevention program.

The initialization program of the CAN interface design is important.If the design is not good，the system will notwork properly.

PIC18F25K80 MCU CAN interface initialization should set the first control registers，status register in configurationmode，the baud rate registers，I/O control register，receiving and filtering themask registers set according to requirements of the system，to ensure the smooth of CAN bus.

Figure 7.CAN communication program

Data is sent to subroutine.Data is sent automatically by the CAN controller based on CAN bus protocol.Data is sent by data query，that is，to send the information frame to sending buffer，and set up request identifier in the command register，then start the sending button.

Receiving and sending the data are similar，which are done automatically by the CAN controller.The receiving application program only receives the data read from the receiving buffer，then follows the corresponding processing.Receiving data adopts interruptmode，that is，when receiving amessage，the information will go through the filter of the acceptance，that produce a receiving interrupt，then the data received from receiving register is transferred to the specified storage area and save up，finally the interrupt returns.

Figure 8.Clip collision prevention program

Clip collision prevention program adopts integral algorithm，that is，to calculate integral value ofmotor current curve，then compare the integral value with the threshold，then make the corresponding action.

Master CPU(as shown in Figure 9)is responsible for collecting gating signals，battery voltage，determining the doors'open and close status，and sending commands to the subunit，thereafter receiving the subunit feedback information，monitoring subunit，which has the effect of the eye and brain.

Figure 9.Car stepping control themain unit

In order to guarantee the stability of the controller，it needs to monitor several key parts of the controller circuit，so dedicated test bed for signal acquisition is set up with PC software LabVIEW and USB acquisition card.PCmonitor screen is shown in Figure 10.Figure in the collection of information has a motor currentwaveform diagram，PIC18F25K80 controlmotor output pin status，control relay status，etc.So it is beneficial for finding interference problems in the circuit and optimizing the controller.

Figure 10.PCmonitor screen

7.Conclusion

Intelligent vehicle pedal based on CAN bus will become the development trend of limo and SUV，which has a broad application prospect.This design adopts the single chip microcomputer PIC18F25K80 embedded CAN controller， CAN transceiver PCA82C250，whose circuit is simple and reliable，which monitors state of the door through CAN bus communication，then accordingly reacts quickly and accurately.CAN bus communication network in the design makes the pedal controller to integrate onboard network one step further.

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基于CAN总线的智能车踏控制器

王 谦†，杨惠忠，卿兆波
中国计量学院机电工程学院，杭州 310018

以某款用于生产的汽车门踏板为例，展开了对CAN总线的研究。分析了CAN总线的工作原理、分层结构以及协议，又结合对门踏板工作原理的分析，设计了一种分布式CAN总线控制系统。系统硬件包括一个主控CPU和4个分布式控制单元，采用CAN收发器PCA82C250进行互联。系统软件提出了CAN通信的实现方法，对比分析了车踏防夹防撞算法。最后运用LabVIEW软件对控制器的运行效果进行了验证。

CAN总线;智能车踏控制;防夹功能;防撞功能;PCA82C250收发器

U270.1+4

10.3969/j.issn.1001－3881.2014.12.020

2014－01－20