Motor Drive Module Design for Electric Care Bed - inass

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Figure 2. Motor Drive Intelligent Node’s Block Diagrammunication means is the command and response mode.That is the host sends an inquiry to sub-controllers,and then sub-controllers upload the data of their ownstatus. The shortcoming of this approach is low datatransmission efficiency. As the host controller is busy,the sub-controller can’t upload data immediately andhas to wait for an order from the host. To overcomethe above shortcoming, three modules are combinedinto an intelligent network through CAN bus.Under the idea of modular design, a PnP (plug andplay) multifunctional MDM is developed. This MDMhas CAN interface that makes it possible to communicatewith HCIM, and then achieves the position closedloopand speed closed-loop.2. Intelligent CAN node-MDMIn this system, three modules are combined into anintelligent network through CAN bus. Each moduleconnects through CAN bus and among the modulesthere are multi-host communication relationships. So,each module is equipped with CAN interface, whichmakes them exchange data between each other. Figure2 is motor drive intelligent node’s block diagram.Human-computer interaction module controls the operationof actuator through CAN bus. Also the MDMtransmits real-time speed and position information tohuman-computer interaction through CAN bus. In orderto adjust the position of body, the MDM use AT90-CAN128 as the controller, and then it can rapidly andeffectively control the action of linear actuator. Theactuator drives the electric care bed’s motion mechanism,and then the function of electric care bed iscompleted. In this paperthe CAN bus interface designand MDM speed and location of closed-loop controlare mainly introduced.The actuator has complex mechanism to transfer rotarymotion to linear motion. And it has the followingfeatures such as damping and noise-reducing, fullclosedand humidity resistance design. In the processof push-pull, the linear actuator has an internal limitedswitch in order to prevent actuator from locked,and then leads speed to zero; electric current is toolarge to burn motor boards.Using Hall sensor (3144) as the feedback component,these Hall-effect switches are monolithic integratedcircuits with tighter magnetic specifications aremore stable with both temperature and supply voltagechanges. The unipolar switching characteristic makesthese devices ideal for use with a simple bar or rodmagnet. Hall sensor is identical except for magneticswitching points. Each device includes a voltage regulatorfor reverse battery protection diode, quadraticHall-voltage generator, temperature compensation circuitry,small signal amplifier, Schmitt trigger, and withsuitable output pull up, they can be used with bipolaror CMOS logic circuits.3. CAN bus interface design3.1 CAN bus communication hardware designCAN bus, which supports distributed control or realtimecontrol, is a serial controller area network. CANcommunication hardware structure is shown in figure1. The hardware mainly includes single chip microcontrollerAT90CAN128, CAN bus transceiver ATA-6660 and high-speed optocoupler 6N137, etc.AT90CAN128 is a low-power CMOS 8-bit microcontrollerbased on the AVR enhanced RISC architecture.By executing powerful instructions in a singleclock cycle, the AT90CAN128 achieves throughputsapproaching 1 MIPS per MHz allowing systemdesigners to optimize power consumption versus processingspeed. The AT90CAN128 CAN controller isfully compatible with the CAN Specification 2.0 PartA and Part B. It delivers the features required to implementthe kernel of the CAN bus protocol accordingto the ISO/OSI Reference Model.ATA6660 is a high-speed CAN transceiver. It is especiallydesigned for high speed CAN Controller differentialmode data transmission between CAN-Controllersand CAN bus. It is fully compatible to ISO11-898. In normal case the RS pin connects to grounddirectly, so baud rate can be adjusted up to 1M/s.International Journal of Intelligent Engineering and Systems, Vol.3, No.3, 2010 27
In this system, CAN bus communication nodes isa multi-host, that is, any node can not only transmitmessages to other nodes, but also receive messagesfrom other nodes through CAN bus. Thus, each nodeneeds to allocate its own ID. Nodes distribution isshown in Table 1.Figure 3. Bus ArbitrationConsidering the anti-interference ability of CAN bus,AT90CAN128 is not directly linked to the ATA6660,but through the high-speed and performance optocoupler6N137 that is good for electrical isolation betweenthe CAN nodes and can speed up to 10Mb/s.In the hardware circuit design, AT90CAN128 with8MHz crystal frequency is mainly responsible for theinitialization of CAN communication, receiving-transmittingmessages. As a result of on-chip CAN controllers,the communication hardware circuit designcan be greatly simplified and system reliability can beenhanced.3.2 CAN bus communication software designThis section uses the integrated designer environmentAVR Sutdio4 and compiler AVR-GCC. The softwaredevelopment environment is provided by AtmelCompany. In communications, CAN-usb interface cardand CAN test software ZLGCAN Test are provided byZhouLiGong Company.3.2.1 The design of CAN protocolThe CAN protocol handles bus accesses accordingto the concept called ”Carrier Sense Multiple Accesswith Arbitration on Message Priority” (shown in Figure3).During transmission, arbitration on the CAN buscan be lost to a competing device with a higher priorityCAN identifier. This arbitration concept avoidscollisions of messages whose transmission was startedby more than one node simultaneously and makes surethe most important message is sent first without timeloss.The bus access conflict is resolved in the arbitrationfield mostly over the identifier value. If a data frameand a remote frame with the same identifier are initiatedat the same time, the data frame prevails over theremote frame.Table 1. CAN Nodes ID distributionNo.ID ID ID ID ID ID ID ID Node12 11 10 9 8 7 6 5 name0 0 0 0 0 0 0 0 1 MDM1 0 0 0 0 0 0 1 0 HCIM2 0 0 0 0 0 0 1 1 PPDM3 Reserved3.2.2 The program design of CAN communicationCAN bus communication is the basic part of the motordriving module software design, mainly including:receiving and processing messages from other nodeson CAN bus; sending the state news of this controller.CAN communication module includes CAN initializingprogram, data receiving procedure and data sendingprocedure.The following mainly describes the initializing programof CAN bus and the data transmission program.CAN bus initial function: can init (U8 mode) is usedfor some parameters of CAN bus, such as the bus baudrate initialized, empty CAN message box, and CANbus enabled, etc.U8 can init(U8 mode){if ((can fixed baudrate(mode))==0)return (0);can clear all mob();Can enable();return (1);}The procedures of CAN bus transmission programare as followsinitialize the following fields before sending:Identifier tag(IDT), Identifier extension (IDE),Remote transmission request (RTRTAG), Data length(DLC), Reserved bit tag (RBNTAG), Data bytes ofmessage (MSG); set the message boxe in Tx configurationfor the Mob to send data or a remote frame;then the CAN channel scans all the message box inTx configuration, seeking for the message box havingthe highest priority and try to send it. All the parametersand data are available in the message box untila new initialization. The flowchart of AT90CAN128sending program is shown in Figure 4,International Journal of Intelligent Engineering and Systems, Vol.3, No.3, 2010 28
Page 1: International Journal ofIntelligent
Page 5 and 6: Figure 7. AT90CAN128 and LMD18200 I
Page 7 and 8: Figure 11. Hardware Design of Hall

Motor Drive Module Design for Electric Care Bed - inass

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