Design of a teaching pendant program for a mobile shipbuilding welding robot using a PDA(49).pdf

Computer-Aided Design 42 (2010) 173–182

Contents lists available at ScienceDirect

Computer-Aided Design

journal homepage: www.elsevier.com/locate/cad

Design of a teaching pendant program for a mobile shipbuilding welding robotusing a PDAMin-jae Oh a, Sang-Moo Lee b, Tae-wan Kim a,c,∗, Kyu-Yeul Lee a,c, Jongwon Kim da Department of Naval Architecture and Ocean Engineering, Seoul National University, Seoul 151-744, Republic of Koreab Division of Applied Robot Technology, Korea Institute of Industrial Technology, Ansan 426-171, Republic of Koreac Research Institute of Marine Systems Engineering, Seoul National University, Seoul 151-744, Republic of Koread School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-744, Republic of Korea

a r t i c l e i n f o

Article history:Received 2 January 2009Accepted 26 September 2009

Keywords:Wireless teaching pendantPersonal digital assistant (PDA)Mobile shipbuilding welding robotEmbedded system

a b s t r a c t

Teaching pendant is a handheld device by which a human can control a robot. The main functions ofa teaching pendant are moving the robot, teaching it about the locations, running robot programs, andjogging the axes. A teaching pendant is usually connected to the robot by a cable. The cable connectionand the size of the teaching pendant generally do not pose a problem when the robot controller isseparate from the robot. However, a large teaching pendant connected by a cable is not suitable for a self-propelled mobile robot with an internal controller. This paper describes the communication network of apersonal data assistant (PDA) as awireless teaching pendant for amobile shipbuildingwelding robot withembedded controller system that welds and moves autonomously inside the double hull structure of aship. A double hull is a closed structure that has only a few access holes. It is very difficult and dangerous toweld components inside a double hull structure because of fumes, poisonous gas, and high temperatures.Using a wireless teaching pendant has the following advantages: (1) there are no limits to the weldingactivities that can take place, (2) the safety level increases because noworkers are in close proximity to therobot, (3) workers are far away from the dangerous environmental conditions, (4) it is possible to reducethe weight of the cable connected to the robot, and (5) it is possible to reduce the weight of the robotbecause of the reduced load of the teaching pendant and the cable. We demonstrate the functionality andperformance capabilities of our wireless teaching pendant through field-testing experiments.

© 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Arcwelding is used extensively in shipbuilding.Most of it is per-formed by humans. This is challengingwork because of the difficultworking conditions in a shipyard due to fumes, arc sparking, elec-trical hazards, and high temperatures. These conditions are evenmore intolerable inside the double hull structure of a ship. Fig. 1shows the double hull structure of a ship under construction.The double hull is a closed structure with steel plates on all

sides. International maritime regulations require that every oiltanker has a double hull to prevent oil spills. It is very difficult towork inside double hulls because there are only a few small accesspoints. There is also less light, more fumes, and higher tempera-tures than in open structures. This has driven research into the use

∗ Corresponding author at: Department of Naval Architecture and OceanEngineering, Seoul National University, Seoul 151-744, Republic of Korea. Tel.: +822 880 1434; fax: +82 2 888 9298.E-mail address: [email protected] (T.-w. Kim).

0010-4485/$ – see front matter© 2009 Elsevier Ltd. All rights reserved.doi:10.1016/j.cad.2009.09.005

of robots in shipyards and led to our development of a teachingpendant (TP) for an automatic arc welding robot.Summary of contributionWe have developed a PDA-based wireless Teaching Pendant

(PDA TP) for amobile welding robot in a double hull ship structure.We design the wireless communication network between TP andcontroller of the robot. We have conducted many welding testsin open and closed hull ship structures with the PDA TP to verifyits robustness to the welding noise. So far we have not faced anymajor problem in the use of our developed device. Fig. 2 shows awelding experiment using PDA TP in a double hull structure of aship. The PDA TP can be used for many interesting and challengingapplications, e.g. for the mobile welding robot in the shipbuildingindustry and for the other mobile robots in other industries, etc.

2. Background

2.1. Working space—Double hull

The required welding tasks inside a double hull structureinvolve U-shaped parts at the intersection of the transverse web

174 M.-j. Oh et al. / Computer-Aided Design 42 (2010) 173–182

Fig. 1. Double hull structure of a ship under construction.

TP

Fig. 2. Welding experiment with the developed TP in a double hull ship structure.

floor and the longitudinal stiffener. Fig. 3-¬ shows the double hullof a ship and Fig. 3-­ shows the double hull with the upper plateremoved. The U-shaped working space is shown in Fig. 3-®. Theworkers enter through the access manhole, (Fig. 3-¯).

2.2. Shipbuilding mobile welding robot—‘Rail Runner’

Because of the longitudinal stiffener, a mobile robot cannotmove freely along the U-shaped welding parts. When the robot isinserted in the open structure before the upper plate is installed,it is possible to use a crane to move the robot and the U-shapedparts to other areas. Therefore, a fixed-type welding robot can

Fig. 4. Rail Runner self-propelled shipbuilding welding robot.

be used. However it is difficult to use a crane and impossible touse a fixed-type welding robot in a double hull structure [2]. The‘Rail Runner’ is a self-propelled mobile welding robot designed forwelding the U-shaped portions of a ship’s double hull structure [1].The Rail Runner can be inserted through the access hole, weld theU-shaped part, and move automatically from one welding area toanother. The wireless TP described in this paper was developedto work with the Rail Runner controller described elsewhere [3].The Rail Runner was developed by Seoul National University andDaewoo Shipbuilding &Marine Engineering. Its structure is shownin Fig. 4. There is six-axis welding unit on the front of the robot,and the body contains a self-propulsion mechanism for sideways,frontwards, and backwards motion [3].

2.3. Teaching pendant definition and function

A TP is a handheld device for controlling a robot. It can performbasic operations such as executing robot programs, designatingrobot locations, halting the robot in an emergency, and joggingeach axis. In this paper, we show how a personal digital assistant(PDA) can be used as a TP for a mobile welding robot. A TP hasbuttons for control purposes and a liquid crystal display to showinformation such as the current location of each axis or the currentstate of the robot program (Fig. 5).A TP can send commands to the controller, receive robot status

reports from the controller, and show the current status of each

Fig. 3. Welding target in a double hull structure and access manhole [1].

M.-j. Oh et al. / Computer-Aided Design 42 (2010) 173–182 175

Fig. 5. Teaching pendant features.

axis and program. An important role of the TP is program file ad-justment. A robot program file is created by off-line programming.A robot job program file is a list of robot working commands.Fig. 6 shows the creation of a job file for robot motion. A job

file is created off-line using a computer-aided design model ofthe working space [4,5]. For the purposes of this paper, the jobis stored in the PDA TP. We will describe the job loading processand execution method later. Ideally, the job file created off-lineshould contain all of the exact information about the working part.However, it is not possible to run the robot directly using the jobfile because the working part usually contains some errors. In thiscase, a worker corrects the job file using the TP after viewing theactual working part.

2.4. Selection of wireless communications for the teaching pendant

TPs of industrial robots tend to be large. If the robot has manyaxes or functions, the TP size could be larger still. The long side ofthe TP is usually greater than 300 mm, as shown in Fig. 7.The TP is usually connected to the robot controller by a cable.

The cable connection and the size of the TP generally do notcreate a problem because the robot controller is separate fromthe robot. However, in some circumstances there are problemswith integrating the robot and its controller. A large TP and wireconnection are not suitable for a mobile robot that has an internalcontroller. It is difficult to mount a large TP on the robot becauseof the robot size, and if the TP is connected by a cable, a workermust follow the robot around. Therefore, a large wired TP is notsuitable for a self-propelled robot such as Rail Runner. To addressthis problem, we develop a wireless TP using a PDA.

Fig. 7. Existing TP of a fixed-type welding robot used in a shipyard and the PDA TP.

Table 1Specifications of a fixed-type welding robot TP and a PDA TP.

Item Existing TP PDA TP

Size (mm) 180× 350 85× 180Weight (g) 1330 410Connection Wired WirelessConnection to controller RS232C Wireless LAN (IEEE 802.3)

The benefits of the wireless PDA TP are as follows: (1) theworkers do not need to follow the robot, (2) the workers can be faraway from the difficult environmental conditions in the workingspace, (3) theworkers can be safe from the robot’smovements, and(4) the robot is easy to handle because of the PDA’s size.Table 1 compares the specifications of an existing TP for a fixed-

type welding robot used in a shipyard with those of the PDA TP.The size, weight, and absence of wired connections make the PDATP more suitable for a mobile welding robot.

3. Related work

Despite the importance of the TP in the control of robots,it has received limited research attention [4]. Sugita et al. [6]developed teaching support devices composed of threewireswornon a worker’s hand to assist in teaching. Yanagihara et al. [7]developed a teaching advisor that could show the robot’s workingenvironment to a worker. These teaching advisors were connectedto the robots by wire. Strictly speaking, these efforts are moreclosely related to the teaching advisor of a robot than to the TP.They do show, however, that the TPmust provide teaching advisorfunctions such as teaching the motion and controlling the robot.Therefore, the TP we developed has many functions to teach therobot different motions.There has been some research into wireless TP related to the

development of wireless handheld devices. d’Angelo and Corke [8]and Wu and Chen [9] proposed a wireless TP for industrial robots

Fig. 6. Creating a job process and uploading it to the PDA TP.

176 M.-j. Oh et al. / Computer-Aided Design 42 (2010) 173–182

Fig. 8. Rail Runner, wireless access point, and PDA TP.

Fig. 9. Rail Runner hardware structure, PDA TP, wireless access point, CPU board, and motion controller.

using amobile phone or PDA, and Pires and Godinho [10] proposedan industrial robot control method using a PDA. These research ef-forts were restricted to simple robot actions or were for a robotwith a fixed base. The resulting devices are not suitable for mul-tifunction self-propelled welding robots. In parallel, Comau [11]developed a wireless TP for Comau industrial robots, but this isdifficult to use with Rail Runner. Unlike previous methods, we de-velop a wireless TP for a mobile welding robot with an internalcontroller.

4. Wireless teaching pendant using PDA

4.1. System configuration for controlling the mobile robot

Fig. 8 shows the system configuration for controlling the RailRunner robot. Fig. 8-­ shows the wireless access point built intothe rear of the robot for connection with the PDA TP (Fig. 8-®).Fig. 9 shows the detailed system configuration of the PDA TP

and themain controller. Rail Runner requires an internal controllerbecause the robot is self-propelled. The controller is composed ofthe wireless access point, a CPU board for controlling the motioncontroller, and amotion controller for controlling the robotmotors.The PDA TP is connected wirelessly through the wireless access

Table 2PDA specifications.

BIP-3010 Specification

CPU Intel X-scale 400 MHzOS Windows CE.NETMemory RAM: 64 MB, ROM: 96 MBAntenna External: CDMA, Internal: WLANEnvironment IP54, 12 times 1.5 m drops on concreteOperating temp. −20 ◦C to 50 ◦CPrice $830

point. The CPU board and the motion controller are connected tothewireless access pointwith LAN cables. Fig. 10 shows the systemconfiguration of existing fixed-type welding robot. Comparingwith the Rail Runner, the TP is connected to the main controllerwith cable, and the main controller is separated from the weldingrobot.

4.2. PDA specifications

The PDA TP must be able to resist the harsh industrial envi-ronmental conditions of the double hull structure, including hightemperatures and intense fumes. Therefore, we select an industrialPDA for the TP. Table 2 shows the specifications of Bluebird Soft’s

M.-j. Oh et al. / Computer-Aided Design 42 (2010) 173–182 177

Fig. 10. Existing fixed-type welding robot hardware structure, TP, CPU board, and motion controller.

Fig. 11. Wireless access point.

BIP-3010 [12]. The most important aspect is that this PDA meetsthe IP54 standard for ingress protection. This means that a bodyof 1.0 mm diameter must not be able to penetrate the equipment.Furthermore, dustmust not be able to enter in sufficient quantitiesto prevent the equipment from operating satisfactorily, or to im-pair its safety [13]. Developing the TP program is straightforwardbecause the operating system is Microsoft Windows CE.

4.3. Access point specifications

Fig. 11 shows the wireless access point, while Table 3 lists thespecifications of thewireless access point [14]. The size andweight

Table 3Wireless access point specifications.

Item Specification

Model number WRT54GCStandards IEEE 802.3, IEEE 802.3u, IEEE 802.11g, IEEE 802.11bPorts Internet: One 10/100 RJ-45 Port, LAN: Four 10/100

RJ-45 Switched portsWireless security Wi-Fi Protected Access (WPA/WPA2 Personal), WEP,

Wireless MAC filteringDimensions 98× 98× 25 mmWeight 0.141 kgStorage temp. −20 ◦C to 70 ◦C

of the access point are important. Because Rail Runner is self-propelled, the robot’s size and weight are critical, and a small andlight access point is important. The size and weight of the LinksysWRT54GC make it suitable for our robot.

4.4. Structure of message passing among the PDA TP, main controller,and robot

The program structure of message passing is defined by therelationship of the TP, the main controller, and the robot. Fig. 12shows a sequence diagram of the communication network amongthe TP, main controller, and robot. First, the PDA TP sends acommand to themain controller through thewireless LAN (Fig. 12-¬, ­). Then the main controller sends a command related to themessage from the TP to the robot (Fig. 12-®) and the robot starts

Fig. 12. Communication network among the TP, main controller, and robot.

178 M.-j. Oh et al. / Computer-Aided Design 42 (2010) 173–182

Fig. 13. Program structure of the main controller.

Fig. 14. Sequence diagram of loading and executing job among the TP, main controller, and robot.

Table 4PDA TP functions.

Menu Function

WORK menu Load job, make new job, save job, load job list, run joblist, etc.

WELD menu Set welding condition, set ending condition, setwelding sensor data, etc.

USER menu Set home position, set software limit, set digital in/out,etc.

ENV menu Load environment condition, set offset, set motorbreak, set motor gain, etc.

JOG menu Jog each axis

to move (Fig. 12-¯). Once it is motion, the robot sends the statusof each joint to the main controller (Fig. 12-°, ±). Next, the maincontroller sends the current status to the TP through the wirelessLAN (Fig. 12-², ³). The command for each step is in the form of amessage.Fig. 13 shows the structure of the main controller program. The

main controller waits for a message. When it receives a messagefrom the PDATP, it analyzes themessage and sends the appropriaterobot motion commands to the robot. The motion controller thengoes into a waiting state. Since the main controller’s operatingsystem is a real-time OS (QNX) with embedded system, we canguarantee real-time operation. With this structure, we developedthe PDA TP program module and the main controller programmodule using message passing. The program structure of the maincontroller and robot are described in greater deal elsewhere [2].

4.5. PDA TP functions

The PDATPhas functions related to jobs (WORKMenu),welding(WELD Menu), the user (USER Menu), the environment (ENV

Menu), and jogging (JOG Menu). These functions are explained inTable 4. The functions in the WORK menu are related to the jobsthat are required to run the robot. The functions in the WELDmenu are for welding tasks such as setting welding and sensingconditions. The functions in the ENV menu are for adjusting therobot environment, e.g., tuning the gain and setting breaks. The JOGfunction are related to jogging axes.In the next section, we present an example of loading and exe-

cuting a job using the PDA TP as this is themost important functionof robot operation.

4.6. Message passing process between the PDA TP and controller

To explain the message passing process, we present someexamples such as loading, executing, and jogging. Fig. 14 is asequence diagramof loading and executing a job. Since the PDAhasmemory for storing data, the job file is created off-line and savedin the PDA TP memory (Fig. 14-¬). The PDA TP uploads the jobfile to the hard disk of the robot main controller through wirelessFTP (Fig. 14-­). Next, the TP sends the upload job command tothe memory of the main controller (Fig. 14-¯) and then the maincontroller sends a job information message to the TP (Fig. 14-²). When the TP sends the execute job command to the maincontroller (Fig. 14-´), the main controller analyzes each job lineand sends the appropriate motion commands to the robot (Fig. 14-).When themain controller receives information about the robotstatus (Fig. 14- ), it sends this to the TP (Fig. 14- ), and theTP displays the current job line. The actions of the PDA TP aredescribed in Section 5.Fig. 15 shows the interaction of the TP, main controller and

robot when executing a job command. In this example, the jobhas three lines: WEAVE, MOVJ, and WEAVE. WEAVE is a vertical

M.-j. Oh et al. / Computer-Aided Design 42 (2010) 173–182 179

Fig. 15. Sequence diagram of message passing for executing a job which has three lines of command (WEAVE, MOVJ, WEAVE).

Fig. 16. Sequence diagram of jogging the axis for the same amount of time.

Fig. 17. Rail Runner jogging test using the PDA TP.

zigzag welding process and MOVJ is a movement from one pointto another with linear interpolation of the angles of each axis.When the operator executes the job (Fig. 15-¬), themain controllersend move commands to the robot (Fig. 15-­), and the robotexecutes the first line of the job (Fig. 15-®). At this point, the TPrequests the current status from the main controller to determinethe current job status (Fig. 15-¯). The main controller requeststhe current joint status of the robot (Fig. 15-°) and the robotreplies with the current status of all its joints (Fig. 15-±). After that,

the main controller analyzes the current joint status comparedto what the job dictates, and sends the current job line numberto the TP (Fig. 15-²). The TP highlights the current job lineand these sequences are repeated. The WORK, WELD, USER, andENV functions have sequences similar to Figs. 14 and 15. Thejog function is also somewhat similar, although there are somedifferences.Fig. 16 is a jog sequence diagramof the communication network

among the TP, main controller, and robot (Fig. 16). The jog function

180 M.-j. Oh et al. / Computer-Aided Design 42 (2010) 173–182

Fig. 18. PDA TP menus.

Fig. 19. PDA TP functions.

does not have a return value and stops immediately when the jogstop button is pushed. The TP sends a JOG FLAG ON message tothe controller every 1/100 s (Fig. 16-¬, ³). In this short time, thecontroller runs the robot motors (Fig. 16-®, ¯) and immediatelysets the JOG FLAG off (Fig. 16-°, ±). Then, the motors decelerate(Fig. 16-²). If the JOG FLAG is not on when this happens, allthe motors will stop. However, if the TP sends the JOG FLAG ONmessage again (Fig. 16-³), the controller turns the motors on(Fig. 16-µ, ).

5. Results

Fig. 17 shows the Rail Runner jog motion using the PDA TP. Therobot is controlled precisely by the PDA TP.Fig. 18 shows the PDA TPmenus, including details of theWORK,

WELD, USER, ENV, and JOG menus. Fig. 19 shows the PDA TPfunctions. Since, we have included commercial TP functionality inthe PDA TP we develop, it is easy to program new functions.Fig. 20 shows the process of loading and executing a job on the

PDA TP. The TP is first connected to the robot main controller, as

shown in Fig. 20-¬–®. Next, the operator chooses the LOAD menuto load the job. A window appears in which the operator can selectthe appropriate job file (Fig. 20-±).When the operator selects a job,a message is displayed about loading the job successfully (Fig. 20-²). The TP then displays the current job information received fromthe main controller (Fig. 20-³). At that point, the robot is readyto start moving. When the operator pushes the AUTO button onthe EXEC mode tab (Fig. 20-´), the robot starts to move. The TPhighlights each job line of the current robot status.Fig. 21 shows a welding experiment. This actual industrial en-

vironment test demonstrates that the wireless PDA TP works fine.

6. Implementation

The PDA used in this paper has the Microsoft Windows CE.NET4.2 operating system. We develop the PDA TP program usingEmbedded Visual C++ 4.2 and MFC.

M.-j. Oh et al. / Computer-Aided Design 42 (2010) 173–182 181

Fig. 20. Example of job loading and execution.

Fig. 21. Rail Runner welding experiment.

Fig. 22 shows the structure of the PDA TP program. CTeach-ingPendant is the main class. There are also two other classes:CTPEditMode and CTPExecMode. Each class has subclasses thatexecute the proper tasks. Each subclass works in the form of send()and receive() functions. All functions, e.g., CWork, CWeld, CJog,CRunMode, etc., are inheritance classes of the CNetInfo class. TheCNetInfo class has a sending data variable (m_SendData) and a re-ceiving data variable (m_ReceiveData), as well as a sending mes-sage function (SendMessage()) and a receiving message function(ReceiveMessage()). All inheritance classes save their data to thesending data, send the data to the main controller using theSendMessage() function, and receive data from themain controllerusing the ReceiveMessage() function. For example, when the TPsends a JOG commandwith 80% speed and second axis to the maincontroller, firstly, the value of the speed and axis number are savedin m_SendData variable. Next, the user pushes the JOG button, andthen the data are sent to the motion controller by SendMessage()function. The program structure of the main controller is same asthe TP’s. Therefore, when the main controller sends the message

to the TP, the TP can receive the message using ReceiveMessage()function and m_ReceiveData variable.

7. Conclusion and future work

We have presented a PDA-based wireless TP for a mobile weld-ing robot in a double hull ship structure. Wireless communicationbetween the TP and the robot is possible through the wireless ac-cess point on the mobile robot’s main controller. Also we havedeveloped amessage passing system among the PDA TP,main con-troller, and robot. We tested the functions for jogging and loadingand executing jobs and alsowehave verified thewireless TP’s func-tions and performance experimentally. Using this wireless TP hasthe following advantages: (1) there are no limits to a worker’s ac-tivity, (2) it is safe because the operator is not close the robot beingcontrolled, (3) workers are far away from the dangerous workingconditions, (4) it is possible to reduce the weight of the cable thatis connected to the robot, and (5) it is possible to reduce theweightof the robot because of the elimination of the cable.Future work will involve verifying the emergency stopping

function and controlling several robots using one PDA TP. Themostimportant function of a TP is to stop the robot in an emergencysituation. The PDA TP does not seem to cause any delay, but thismust be tested. Other future works will involve investigation ofa noise-free PDA TP. Electrical noise can be a big problem inindustrial welding, and the motion controller or CPU board canfail when the robot is in the midst of a welding operation. Thenoise problem is particularly serious in a wireless environmentwhere the communications between the wireless device andthe controller can be interrupted. Therefore, we have conductedseveral tests to verify the noise-free performances of the wirelessTP in the actual construction process of double-hulled ships. Wehave already welded more than 70 U-shaped parts in the double-hulled ship. For the present there does not seem any problem inusing the newly-developed TP. However, further tests or specialmeasurements are required to secure our noise-free wireless TP.The last area of future work is indicated in Fig. 23, which shows

182 M.-j. Oh et al. / Computer-Aided Design 42 (2010) 173–182

Fig. 22. PDA TP program structure.

Fig. 23. Multiple connections of the PDA TP and the Rail Runner.

one PDA TP connected to multiple Rail Runners. We believe that itis possible to control several Rail Runners using one PDA TP.

Acknowledgement

This work was supported by the Self-propelled Welding RobotProject at Daewoo Shipbuilding & Marine Engineering Co., Ltd.

References

[1] Lee K-Y, Kim J, Kim T-W, Lee S, Lee D, Ha S, et al. Development of amobile welding robot for double hull structure in shipbuilding. Robotics andApplications 2007;29–31.

[2] Lee K-Y, Kim T-W, Kim J, Ku N-K, Lim H, Woo J. et al. Real-time controlarchitecture of embedded controller for mobile welding robot in shipbuildingindustry. In: Proceeding of IFAC 2008. 2008.

[3] Kim J, Lee K-Y, Kim T-W, Lee D, Lee S. Development and application ofautonomous traveling mechanism in the double hull structure of the ship. In:Proceeding of IFAC 2008. 2008.

[4] Morley EC, Syan CS. Teach pendants: How are they for you? Industrial Robot1995;22(4):18–22.

[5] Jacobsen NJ. Three generation of robot welding at odense steel shipyard. In:Proceeding of ICCAS 2005. 2005. p. 289–300.

[6] Sugita S, Itaya T, Takeuchi Y. Development of robot teaching support devices toautomate deburring and finishing works in casting. The International Journalof Advanced Manufacturing Technology 2004;23(3–4):183–9.

[7] Yanagihara Y, Muto S, Kakizaki T. Evaluating user interface of multimodalteaching advisor implemented on a wearable personal computer. Journal ofIntelligent and Robotic Systems 2001;31:423–38.

[8] d’Angelo P, Corke P. A robot interface using wap phone. In: Australianconference on robotics and automation. 2001.

[9] Wu S, Chen Y. Remote robot control using intelligent hand-held devices.In: Proceedings of the fourth international conference on computer andinformation technology. 2004.

[10] Pires JN, Godinho T. Robot control using a simple wireless pda. http://robota.dem.uc.pt/. 2005.

[11] Comau. Comau. http://www.comau.com/. 2006.[12] Blubird. Blubird. http://www.bludbird.com. 2007.[13] IP54. Ip54. http://www.wikipidia.com/IP54. 2007.[14] Linksys. Linksys. http://www.linksys.com. 2007.