Sensors and Actuators A 120 (2005) 147–153

Distributed measurement system based on networked smartsensors with standardized interfaces

Guangming Song∗, Aiguo Song, Weiyi HuangDepartment of Instrument Science and Engineering, Southeast University, Nanjing 210096, PR China

Received 6 August 2004; received in revised form 11 November 2004; accepted 11 November 2004Available online 16 December 2004

Abstract

A novel distributed measurement system (DMS) for force monitoring and control of robot wrist across Internet is presented in this paper.The DMS is a typical application of networked sensors that offers a reusable and portable design architecture for Internet-based remotemeasurement and control. The architecture covers three key areas for developing high-level distributed measurement applications, including:standardized transducer interfacing, open network communications and implementation of Internet access. With a reference to IEEE 1451,a networked sensor prototype has been developed to serve as the lowest level of the proposed architecture. Integrated with a standardizedC vided by itst an facilitatei©

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AN bus interface, the networked sensor can perform multi-axis force measuring and possesses self-identification capability proransducer electronic data sheet (TEDS). Experiment and results of the demonstration project have proved that the architecture cnterfacing smart sensors with various field buses and enable Internet access of networked sensors.

2004 Elsevier B.V. All rights reserved.

eywords:Distributed measurement system; Networked sensor; Standardized interface; Force measurement; Internet

. Introduction

In recent years, the rapid development of microelectronicnd field network technologies has made the networking ofmart sensors a very attractive and cost-effective solution forbroad range of measurement and control applications[1].he trend is moving toward distributed measurement and dis-

ributed control architecture. These distributed systems areften combined into the local area network (LAN) to improve

he interoperability by Ethernet or Internet access[2].Embedded with a microcontroller unit or microprocessor,smart sensor has much more built-in intelligence over a

raditional sensor. So it can perform more powerful functionsuch as self-identification, self-calibration, converting theaw sensor signal into a digital form, etc. However, as to theistributed measurement applications, the most attractivedvantage that a smart sensor offers is the networking

∗ Corresponding author. Tel.: +86 25 83793293; fax: +86 25 83794156.E-mail address:mikesong@seu.edu.cn (G. Song).

capability. At the lowest level of a distributed measuremsystem (DMS), smart sensors are interfaced to the netnode to sense environmental conditions[3]. The sensonetworking and DMS design are regulated by the IE1451 smart transducer interface standards[4]. The familyof standards has defined a set of common communicinterfaces for connecting transducers (sensors and actuto microprocessor-based systems, instruments andnetworks in a network-independent environment.ultimate goals of the standards are to provide the mfor achieving transducers-to-network interchangeabilitytransducer-to-networks interoperability. This will redthe industry’s effort needed to develop and migratenetworked smart transducers and will allow manufacturflexibility to add value to their products[5]. These standardspecify at least two layers between the transducer annetwork: first, the smart transducer interface module (STto interface transducers and to provide measuremencontrol functions; second, the network capable applicaprocessor (NCAP), which is a basic communication nod

924-4247/$ – see front matter © 2004 Elsevier B.V. All rights reserved.oi:10.1016/j.sna.2004.11.011

148 G. Song et al. / Sensors and Actuators A 120 (2005) 147–153

the network[6]. NCAP supports network communicationsincluding loading transducer electronic data sheet (TEDS)from STIM, remote control of STIM, and transmission ofprocessed measurement data to high-level network server.

Researchers worldwide are developing prototypes ofSTIM or NCAP with various hardware and also have es-tablished some distributed measurement and control ap-plications. National Institute of Standards and Technology(NIST) has implemented an IEEE 1451 demonstration ap-plication, a web-based machine tool coolant monitoring sys-tem. The system is still on line but some of its functionsare unavailable now[7]. University of Barcelona has real-ized a CAN bus NCAP with a 16-bit microcontroller and aSTIM with an 8-bit microcontroller[8]. Jadavpur Universityhas provided a general scheme for development of networkcapable smart transducer interface in multi-drop field busenvironment[9].

But most of these solutions have put emphasis on the hard-ware implementation of separate modules and lack high-leveldistributed applications in specific industry automation envi-ronments. The purpose of this paper is to provide a noveldistributed measurement architecture to facilitate interfacingsmart sensors with various field buses and enable Internetaccess of networked sensors. The architecture covers threekey areas for developing high-level distributed measurementapplications, including standardized transducer interfacing,o ter-n lly im-p trolt ntedi

2

roma d toi nce

with the client-server paradigm. The instruments in the localmeasurement laboratory are interfaced to the server PC viavarious bus adapters or PCI data acquisition boards. If theinstruments are equipped with CAN bus interfaces, they canbe directly added to the system by means of plug and play(PnP).

According to the interoperability in an industrial automa-tion environment[3], the system is in fact a web-based dis-tributed measurement application for robot wrist force moni-toring and control. The sensor with CAN bus interface servesas the bottom level in the control hierarchy, namely the pro-cess connection level. The sensor information is sent to thecontrol network nodes where distributed intelligence can beexecuted. Sensor data received by the processors in the net-work nodes is then broadcasted onto the network. Other nodesin the network can use the sensor data to make the appropri-ate control decision to manipulate the robot or exercise otheralgorithms.

3. Networked sensor

3.1. IEEE 1451 architecture

The IEEE 1451 family of standards is basically dividedinto two parts, the hardware-oriented standards and thes stan-d trans-d . Thes facesf uti-l ofw aveb seds rthere corea n inF

a typic

pen network communications and implementation of Inet access. The whole architecture has been successfulemented for use in robot wrist force monitoring and con

hrough Internet. Details of the architecture will be presen the Sections2–4.

. Description of the distributed measurement system

Fig. 1shows the architecture of the proposed DMS. Flogical point of view, the whole architecture is organize

mplement a two-tier communication system in accorda

Fig. 1. Hierarchical structure of

oftware-oriented standards. The hardware-orientedards define a set of hardware interfaces for connectingucers to a microprocessor or an instrumentation systemoftware-oriented standards define a set of software interor connecting transducers to different networks, whileizing existing control networking technology. At the timeriting, two standards (IEEE 1451.2 and IEEE 1451.1) heen formally published by IEEE. Four additional propotandards are being studied or balloted by IEEE for fuxtensions to the IEEE 1451 family of standards. Therchitecture of IEEE 1451 family of standards is showig. 2.

al distributed measurement system.

G. Song et al. / Sensors and Actuators A 120 (2005) 147–153 149

Fig. 2. Core architecture of IEEE 1451.

As seen in the diagram, the IEEE 1451.2 standard de-fines the sensor data model in the smart transducer interfacemodule (STIM), which consists of a transducer electronicdata sheet (TEDS) and a transducer independent interface(TII) [10]. A TEDS for a transducer contains manufacture-related data such as manufacturer name, sensor type, serialnumber, and calibration data. The TEDS is sent to a net-work or instrument at power up or upon request. Transducer(XDCR) data is converted to a digital format and sent tothe network capable application processor (NCAP) via thedigital interface TII. The IEEE 1451.1 defines a smart trans-ducer object model that describes the behaviour of the sensorsusing an object-oriented language. This object model defi-nition includes a set of object classes, attributes, methods,and behaviour that provide a concise description of a trans-ducer and a network environment to which it may connect.The standard brings a network and transducer hardware neu-tral environment in which a concrete implementation can bedeveloped.

3.2. Fabrication of a sensor with standardized interface

For the need of the specific distributed measurement ap-plications described above, here a robotic wrist force sensoris selected as a prototype to implement the networked sensor.T sorsu ents de-t ously.T ke it

network capable. Therefore, it can be directly connected tothe control network such as CAN.

In view of the demands for sensor networking and integra-tion, the Analog Devices ADuC812 MicroConverter is cho-sen for this implementation[11]. The ADuC812 contains an8051 compatible MCU, 8 kb of program flash/EE, 640 bytesof data flash/EE, 256 bytes of RAM, up to 32 programmableI/O lines, a SPI serial I/O port, dual DACs and an 8-channeltrue 12-bit ADC. The MicroConverter was designed with theIEEE 1451.2 model in mind. The 640 bytes of data flash/EEare ideal for re-writeable TEDS storage. With the integratedADC and DACs, it is a good choice for a modest STIM im-plementation.

With a reference to the IEEE 1451 standards, the net-worked sensor is easy to implement. The hardware architec-ture of the networked six-axis force/moment sensor is shownin Fig. 3. The force/moment sensor is referred to as a STIM.The STIM contains six independent channels, one ADuC812for raw data processing and TEDS storing, and the logic cir-cuitry to facilitate communication between STIM and NCAP.Each channel is occupied by the data stream from one of thesix force sensing elements. The NCAP is an industrial PCwith a CAN bus adapter (ADLINK PCI-7841) in this appli-cation. The NCAP connects the STIM to the specific controlnetwork and manages all the network communications. Thebasic communications between STIM and NCAP are man-a iver( TIIi andS oto-c tion,t , iti rfacei ichp andC

axisf ipleso is1 inge insidea nly

ementa

he wrist force sensor is one of the most important sensed in robot control. The networked six-axis force/momensor is this kind of device we have developed. It canect three-axis forces and three-axis moments simultanehis wrist force sensor has a CAN bus interface that ma

Fig. 3. Hardware impl

ged by a CAN controller (SJA1000) and a CAN transce82C250). According to the description in IEEE 1451.2,s in fact a 10-wire physical interface between NCAPTIM. Based on the serial peripheral interface (SPI) prol, the 10 wires are assigned to provide communicariggering, interrupts, power, etc. In this implementations unnecessary to use all of these wires. So a 4-wire intes designed based on CAN bus protocol (CAN2.0A), whrovides power, ground and two data lines (CAN HighAN Low).Fig. 4 shows the photographs of the networked six-

orce/moment sensor fabricated according to the princf the present study. As shown inFig. 4(a), the sensor00 mm in diameter and 60 mm in height. All the senslements and data processing circuits are encapsulatedn aluminium shell. The high degree of integration not o

tion of networked sensor.

150 G. Song et al. / Sensors and Actuators A 120 (2005) 147–153

Fig. 4. Photographs of the fabricated networked sensor: (a) the prototypeand (b) the internal circuit board.

greatly reduces the volume of the whole device, but also easesthe installation and maintenance.

3.3. Design of TEDS

The TEDS contains fields that fully describe the type, op-eration, and attributes of the transducer. If the transducer ismoved to a new location, it is moved with the TEDS. In thisway the information necessary for using the transducer ina system is always present. In IEEE 1451.2, eight differentTEDS sections are defined. Only two of them (Meta-TEDSand Channel-TEDS) are mandatory and must remain withthe STIM for the duration of its lifetime. The other six areoptional.

The Meta-TEDS (one per STIM) contains data that de-scribe the STIM as a whole, including revision levels, exten-sions, worst-case timing values, and channel grouping infor-mation. The Channel TEDS (one per STIM channel) definesthe functional model, calibration model, upper and lower lim-its, timing restrictions, and any other data needed to describethe functionality of each transducer channel[12].

For this application, an optional End Users’ Application-Specific TEDS is added to act as a place to store any additionaldata not covered by the two mandatory TEDS sections de-scribed above, such as the location of the STIM or the namea

o bee DSs sec-t ittedf busp nsid-

Table 1Formats of the data frame from sensor to network

CAN ID field (1 byte) 0x11CAN RTR bit (1 byte) 0x00Data field (2 bytes) 0x00-0xFFTEDS address (3 bytes) 0x00-0xFFSTIM channel no. (1 byte) 0x00-0x05Sensor no. (1 byte) 0x00-0xFFPhysical unit (1 byte) 0x00-0xFF

eration. The TEDS address field stores three different TEDSaddresses and each address takes up to one-byte space. TheTEDS data blocks can be stored on the 640 bytes of dataflash/EE memory or the NCAP host. In this application, theTEDS data blocks are deployed as a separate file stored on theNCAP host, downloadable from the Internet. In this way, it isvery convenient for users to manage and update the sensor-related information. This kind of deployment does not usethe embedded memory resource, so it is also called a VirtualTEDS[13]. Detailed structure of each data block is omittedin this paper.

4. Experiment

In order to verify the feasibility of the distributed mea-surement architecture based on networked smart sensors, ademonstration project called web-enabled robot sensor lab(WERSL) has been implemented in the robot sensor lab(RSL) at Institute of Intelligent Machines, Chinese Academyof Sciences.Fig. 5shows the experiment setup of the demon-stration project. As shown inFig. 5, a Staubli PUMA 562robot manipulator has been employed to execute some typi-cal operations. The networked six-axis force/moment sensoris mounted between the end effector and the robot wrist. Ani MbS host,o rverP theR rnet.A n-n Eachp nels.A ctedt AN-e rfacec on-n f ther agec erverP lablef

plat-f on1 used

nd telephone number of the vendor.As stated above, the STIM in this application needs t

quipped with one Meta-TEDS section, six Channel TEections and one End Users’ Application-Specific TEDSion.Table 1shows the formats of one data frame transmrom sensor to network. In the formats, both the CANrotocol and the IEEE 1451.2 standard are taken into co

ndustrial PC with a Pentium III 1 GHz processor and 256DRAM serves as the NCAP host and the web servern which multiple server programs are running. The seC is directly connected to the 10 Mbps Ethernet LAN ofobot Sensor Lab, and through this same LAN, to Intedual-port CAN interface card, ADLINK PCI-7841, is co

ected to the server PC through the internal PCI bus.ort represents a stand-alone CAN node with eight chanvideo capture card, 10Moons SDK2000, is also conne

o the server PC through the internal PCI bus. The Cnabled sensor is connected to one port of the CAN inteard. A SAMSUNG Digital Color Camera SCC-131P is cected to the video capture card. The operation area oobot is monitored by SCC-131P which works in the imapture mode. The image captured is buffered on the sC and transmitted to the remote applet. It is also avai

or download using the general web server.For the entire web application development, a Java 2

orm, Sun JavaTM 2 SDK, Standard Edition (J2SE) Versi.4.202, has been employed. The HTTP web server

G. Song et al. / Sensors and Actuators A 120 (2005) 147–153 151

Fig. 5. Experiment setup of the demonstration project.

here is a third party’s product, which is Apache Tomcat Ver-sion 4.1.24. HTTP server listening at TCP port 80 sends theHTML files and class bytecodes as soon as the client re-quests arrive. The client web browser displays the web pageand loads JVM to run the applet.

We have succeeded in accessing all the service on theserver host from the same LAN of the Robot Sensor Laband from the campus LAN of University of Science andTechnology of China.Fig. 6 shows the Java applet run-ning in the client web browser. The Java applet integratesall the human–machine interfaces, including force/momenttrend panel, image panel, node function panel, image func-tion panel, TEDS panel and system info panel. Through thesepanels, remote users can monitor force/moment value trends,access sensor TEDS and watch the real-time images of robotworkspace.

The network environment is 10 Mbps Ethernet LAN. Therobot moves under control of a preset routine. The remotesensor data acquisition is performed on a client host in thesame subnet. By setting parameters and sending commandsthrough the node function panel, the remote sensor node startsthe distributed measurement task. The data is immediatelytransferred to the client applet by TCP connections.Fig. 7shows the results of remote experiment. The trends of re-mote data acquired by the networked sensor are in accordancewith the actual force status of the robot wrist. Although thenetwork delay on the wire can be small enough, differencebetween the computing abilities of any two-client computerwill sometimes have an influence on the repeatability. Theremote data can be directly used in the distributed control ap-plications such as Web Telerobotics and other force feedbackcontrol through web.

Fig. 6. Java applet in the client browser window

serving as a remote human–machine interface.

152 G. Song et al. / Sensors and Actuators A 120 (2005) 147–153

Fig. 7. Trends of the remote experiment results of (a) force value and (b)moment value.Fx, Fy andFz represent force vectors parallel tox-, y- andz-axes, respectively.Mx,My andMz represent moment vectors aroundx-, y-andz-axes, respectively.

5. Conclusions

In this paper, a distributed measurement system devotedto the sensor application over Internet has been described.The system provides a reusable and portable architecture forInternet-based distributed measurement applications. It cov-ers some important areas that will play critical roles in futureDMS development, including standardized transducer inter-facing, open network communications, and implementationof Internet access. The networked sensor serves as the loweslevel of the proposed architecture. With a reference to IEEE1451, a networked sensor prototype has been developed forforce measurement and control of robot wrist. The networkedsensor is integrated with a standardized CAN bus interfaceand possesses self-identification capability provided by itsTEDS.

The whole architecture has been successfully imple-mented by a demonstration project for use in robot wrist forcemonitoring and control through Internet. Experiments havebeen done in the Ethernet LAN environment of Robot SensorLab and China Education and Research Network (CERNET).

The experiment results show that sensor data and TEDS infocan be accessed on line with small delay. The system archi-tecture is open to future expansion. It is easy to add othernetworked sensors and software components. So the systemwill be good enough for other high-level applications such assensor fusion and Web Telerobotics.

Acknowledgements

The authors gratefully acknowledge Prof. Yunjian Ge andDr. Zhongcheng Wu (Institute of Intelligent Machines, Chi-nese Academy of Sciences) for enlightening advices anddiscussions. The authors would like to thank Yiwen Bian,Lifu Gao, Min Zhu and Yi Tang (University of Science andTechnology of China) for providing great technological sup-ports. This work was supported in part by 973 Program(No.2002CB312102) from the Ministry of Science and Tech-nology of China.

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Biographies

Guangming Songreceived the PhD degree in control science and engi-neering from the University of Science and Technology of China, Hefei,China, in 2004. He is presently a postdoctor of the Department of In-strument Science and Engineering, Southeast University, Nanjing, China.His current research interests include web-based distributed measurementand control, networked sensor and telerobotics.

Aiguo Song received the BS degree in automatic control in 1990, theMS degree in measurement and control in 1993 from Nanjing Aeronau-

tics and Astronautics University, Nanjing, China, and the PhD degree inmeasurement and control from Southeast University, Nanjing, China, in1996. From 1996 to 1998, he was an Associate Researcher with the In-telligent Information Processing Laboratory, Southeast University, China.From 1998 to 2000, he was an associate professor with the Department ofInstrument Science and Engineering, Southeast University, China. From2000 to 2003, he was the Director of the Robot Sensor and Control Lab,Southeast University, China. From April 2003 to April, 2004, he was avisiting scientist with the Lab for Intelligent Mechanical Systems (LIMS),Northwestern University, Evanston, USA. He is currently a professor withthe Department of Instrument Science and Engineering, Southeast Uni-versity, China. His current interests concentrate on teleoperation, hapticdisplay, Internet telerobotics, distributed measurement systems.

Weiyi Huang graduated from Nanjing Institute of Technology, China in1953. He is now a professor at the Department of Instrument Scienceand Engineering, Southeast University, China. He has been engaged inresearch work on gyro navigator, multi-axis force sensor, etc.