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AN APPLICATION OF REMOTELY CONTROLLED EXPERIMENTS TO PERFORM FEEDBACK-DAMPING CONTROL OF A VIBRATING BEAM M.C.Levesley1, P.Culmer1 P.Cripton2 1 School of Mechanical Engineering, University of Leeds, Leeds, U.K. 2 Department of Mechanical Engineering, University of British Columbia, Vancouver, Canada, email@example.com Abstract of a group of 20-30 students, working in pairs or small This paper presents a system developed at the University groups within a laboratory environment. To ensure each of Leeds in the UK which allows remote access to real of the students in a group has adequate access to facilities, experimental equipment (ReLOAD). The system, initially multiple copies of experimental equipment are often developed in 2000 has been in use since 2001 to provide required. The need for multiple copies of equipment improved access to experimental equipment used as part inevitably places limits on the quality of the equipment of an undergraduate engineering degree programme. that can be deployed. Even with group sizes of 20-30 Recently improvements which allow very simple students, laboratory sessions often need be repeated many expansion have prompted an increase in the number of times in a given year to ensure all students on a particular remote experiments now in use. Most recently, the system programme are exposed to the session. Even with multiple has been used as an integral part of a post graduate copies of equipment and duplicate laboratory sessions, distance delivered module in Dynamic Simulation, students can find that access to laboratory equipment is offered at the University of Leeds. Key to its operation is limited. For example, they cannot be easily repeated by the ability of the system to serve video clips that record students who may wish to collect more data, after the experiment in progress, providing essential reflecting on their initial results, or may have been ill at visualisation plus an improved sense of realism for the the time the laboratory session was being run. They can user. Both student and system evaluation has proved also be seen as being inefficient, since although expensive positive, with student feedback being particularly positive equipment is used intensively for a period, it may remain regarding the improvement in access to real data it offers. unused for most of the year. The system is shortly to be used to deliver experiments hosted at Leeds to over 200 3rd and 4th year mechanical LAN engineering undergraduates at the University of British Internet Columbia (UBC), Vancouver. The system shows huge potential to allow more efficient and collaborative use of laboratory equipment across the global engineering ReLOAD Client Computer education community. Web Server Key Words Hard Wired Connection E-Learning, Remotely Operated Experiments Equipment 1.1 1. Introduction Experiment Server 1 Engineering is by its nature a very practical subject and extensive use is made of laboratory based teaching Equipment 1.2 sessions, particularly in the first few years of a typical undergraduate degree programme. These sessions are ideally suited to develop both cognitive skills (knowledge, information analysis etc.) and psychomotor skills Experiment (physical skills, such as the use of tools and equipment). Server 2 Equipment 2.1 In addition, well designed laboratory sessions can enthuse, motivate and inspire students, as well as having the potential to allow them to work at their own pace and Equipment 2.2 take ownership of their learning material. In the UK, a typical face-to-face session may last 2-3 hours and consist Figure 1 ReLOAD Remote Experiment Structure In 2000, to overcome some of these limitations, a system 3. The ReLOAD Web Server called ReLOAD (Real Labs Operated at Distance) was developed within the School of Mechanical Engineering The ReLOAD web sever is set-up to receive and process at the University of Leeds, which allows access to requests from the client, and since the web server is a experimental equipment via a web interface. Initially it single computer, custom software can be readily created was used by level 2 undergraduates studying Vibration and installed to monitor internet requests. The client and Control using the school’s intranet but was soon computer may be one of hundreds of different PC's and adapted for more widespread access via the internet. the manner in which data is transmitted and received from Although the system cannot be used to develop the client computer has significant impact on the overall psychomotor skills, it does allow students to develop functionality and versatility of the final system. Several higher cognitive skills such as planning experiments, alternative methods have been proposed. An Active-X collecting and analysing data, and conducting further controls panel can be installed on the client computer to experiments if required. It offers greater accessibility, can send and receive information  through an Active-X be run 24 hours a day, 365 days a year and allows many enabled browser. Writing an Active-X control gives students to access a single piece of high quality maximum flexibility to place and position controls to give equipment. More recently the ReLOAD system has been the feel of some physical system, however this restricts used successfully as a key part of a distance delivered the client to using Microsoft Internet Explorer. In Masters Level module, allowing experimental validation addition, security settings may prevent these Active-X where none would otherwise have been possible. Student controls from executing. This results in a large amount of feedback has so far been very positive, with students time configuring multiple machines and inconvenience particularly appreciating the virtually unlimited access for a single user. Furthermore it is likely that users and the ability to easily visualize the output via the use of requiring a one off trial will be unable or unwilling to the video clips simultaneously with near real-time install custom software. analogue data and the reinforcement of the sense that they A Java applet can be created to run on a standard Internet are accessing real experimental data these clips provide. browser to control the experiment [3,4,5]. Java has the advantage of cross-browser and cross-platform support and the majority of today’s computers are java enabled. 2. System Overview However, writing custom java applets for experiments is not trivial and could result in an overly complex solution The essential idea of remote access to experiments is that that is difficult to maintain. the physical experimental equipment does not need to be The approach taken here was to simplify all aspects of the in the same location as the person performing the remote experiment to create a reliable, maintainable experiments. Indeed, the experimental equipment may be system. A standard web form is used at the client end to in another room, building or even country. This request experiments and retrieve and view the associated detachment from the physical system enables greater results. At the server end, LabVIEW software performs flexibility in performing experiments, but comes at the the experiments while monitoring, receiving and sending risk that the user may doubt the realism of the data or feel data across the internet to the client computer. The client detached from the experiment being performed no matter only requires standard java support to view video clips. how good the interface . The Internet or LAN network is ideal for the transfer of data in such cases and though several different methods can be employed to deliver 4. Experiment Server Computer remote experiments, the basic structure adopted here is shown in figure 1. The Experiment Servers perform the experiments and A client computer sends a request to the central ReLOAD communicate across a LAN and in turn pass the data on web server for experimental data across the Internet, from via the internet to the client PC. LabVIEW is an ideal any location with an Internet connection. Depending on platform to control experimental equipment though a data the type of experiment requested, the ReLOAD web server acquisition system. It enables intuitive design of control redirects this request via a LAN to one of several systems through a graphical user interface. Indeed, the Experiment Servers, physically connected to either a majority of undergraduate experiments within the School single or multiple pieces of experimental equipment. The of Mechanical Engineering are constructed using this Experiment Server converts the request into a series of system and it is also taught to students in several modules commands appropriate for the specific equipment being within the school. It is also a suitable and convenient run. Upon completion of the experiment, the Experiment option with which to develop the communications Server sends results in the form of data images and video functionality of the system. Using a single programming clips back to the user on the client computer via the environment and language simplifies the development ReLOAD web server, providing virtually the same level of process since no inter-language interfaces are required information as would be obtained by performing the making the system easier to adapt. experiment locally. The front panel of the Experiment Server computer is designed for use as a demonstration display, allowing staff, students and visitors at the hosting institute to The user can view the front-panel or request to control it. observe the experiments being requested remotely. When viewing, the user sees a ‘live’ representation of the Therefore all parameters used by the experiment are front panel. When controlling, the user can do everything displayed, together with a preview window for the video that would be possible if using the actual VI, for example camera and the results graph. Below this a tabbed panel altering controls, pressing buttons, etc. displays either a log of the requests submitted to the Using this method a continuous stream of information is system or the setup panel. The logs of requests shows the passed back and forth in order to synchronise the parameters submitted by users before they have been limit embedded panel with the actual VI. The number of users checked so any attempted misuse of the system will be allowed to connect to the LabVIEW Web Server is highlighted. The shutdown button should be used to close restricted by a license and as standard this is set at a single the system down. It ensures that any requests being remote user. To increase this a new license must be processed are first dealt with before the ‘shutdown’ state. purchased to cater for the number of people expected to connect at a single time. When the number of users attempting to connect to the Web Server exceeds that on 5. System Communication the license a customisable error message is returned. LabVIEW allows two alternative methods, LabVIEW Comparison of Methods : The two methods discussed HTTP Server with CGI Scripts or embedded ActiveX above are suited to different applications. The Web Server control panels, to communicate the required information and embedded front panel allow continuous interaction between computers to perform remote experiments. between the user and experiment whilst using the HTTP The LabVIEW Internet Toolkit is available as an add-on Server and CGI script allows only a single interaction in to the standard LabVIEW package. It provides an HTTP which parameters are sent and results received. server and a set of related VI’s (virtual instrument, the The LabVIEW Web Server and embedded panel method term used for a LabVIEW function or program). Of has several shortcomings. First is the need to purchase as particular relevance to this application are the CGI many licenses as the number of users that may be (common gateway interface) script VI’s. CGI scripts are expected on the experiment. Secondly is the provision of typically used in association with a form on a web-page. video; since continuous experimental interaction is Forms are defined using standard HTML elements and possible it would be consistent to use streaming video allow a user to enter information into a number of fields footage, giving a ‘live’ indication to the state of the and post it to a server. The server receives the post and experiment. However, video quality is dependant on invokes the relevant CGI script. The script then processes connection speed. The final factor is the reliance on the information and sends back a response (typically a proprietary plug-ins in order to embed the VI’s panel in a web-page) through the server to the user (once the user web-page. has posted a form the web-browser will await a response The HTTP Server with CGI scripts method does not from the server and display it once received). encounter these problems. The HTTP server does not By combining the LabVIEW HTTP Server and the CGI require a license dependant upon the number of users script VI’s it is possible to achieve the required interaction expected and only a widely supported, multi-platform between the user and the experiment. The experimental java plugin is required, in this case to display the video. parameters can be entered into a form on a web-page and This makes it the more attractive choice for this posted to the LabVIEW HTTP Server. This will then application. However, it is important to note that only invoke a CGI script VI that interprets these parameters experiments not requiring continuous interaction are and uses them to conduct the experiment. When the possible using this method. experiment is complete the results can be returned in the form of a web-page to the user. It should be noted that the CGI script VI’s can only be used in conjunction with the 6. Experiment Request Control Software LabVIEW HTTP Server. The communication between the web browser and HTTP The server can potentially receive multiple requests from Server can be over any network supporting HTTP traffic, clients. Each experiment requested must be performed for example a departmental LAN or the Internet. The and since each experiment requires a finite amount of latest version of LabVIEW contains tools aimed at time, a queuing system is used to ensure all experiments making it easier to control VI’s using a web-browser. The are performed in an orderly manner. front panel of a VI can be embedded into a web-page. It Two queues store and order incoming experiments and takes the form of an ActiveX component if Internet outgoing results. When the server receives data posted Explorer is being used, or a plug-in for Netscape. The from the ‘input parameters’ web-page it is added to the computer running the VI must also run the LabVIEW back of the request queue. When the experimental Web Server which controls communication between the apparatus is ready to conduct an experiment it removes embedded front panel in the web-page and the actual front the oldest request from the queue and uses the parameters panel of the VI. given. When the experiment concludes the results are placed at the back of the results queue. Both queues operate on a first in first out basis. The queue creator equipment, shown in figure 3, was designed and built by constantly waits for entries in the results queue and sends staff and students of the School of Mechanical them back to the user as soon as they are received. Engineering at Leeds and is based on equipment used in Each item in the request queue contains a number of face-to-face laboratory sessions in the second year of an elements. Firstly are the IP Address that the request was undergraduate degree programme. submitted from and the CGI connection information. The A pulse sent to the electromagnet is used to commence CGI connection information is required in order to send the experiment by displacing the free end of a cantilever the results back to the user. The experiment name is sent beam. The resulting vibrations are measured using strain as a text string to provide for the possibility of running gauges mounted to the beam surface. A signal from the multiple experiments on the same machine. Lastly, the strain gauge is used to derive a velocity signal, which is parameters sent from the web-page form are included as a fed back into an electromagnetic shaker to provide active keyed array. This is a cluster of two arrays, the first damping of the beam. The user is free to vary the containing the parameters names (called keys) and the magnitude of the feedback signal within limits, so that the second their values. An example for the vibrating beam effect of increased damping can be observed. The user experiment is given in figure 2. can also adjust the magnitude of the pulse signal sent to the electromagnet so that tests at various amplitudes of LabVIEW HTTP Server vibration can be undertaken. In addition the user can select the period of time over which the experimental data Form POST Data HMTL and reply Data is collected and whether or not they wish to see a video clip showing the movement of the beam. Queue creator Beam Displacement ( D= 0 ) CGI Read Request CGI Write Reply 0.5 0.4 0.3 Low Damping 0.2 D is p la c e m e n t 0.1 0 Strain Guages -0.1 Request Queue Results Queue -0.2 -0.3 Beam experiment -0.4 -0.5 Cantilever Beam 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Time, seconds Beam Displacement ( D= 50 ) Figure 2 The Queue Communication Process 0.5 0.4 0.3 Medium Damping It should be noted that the ‘keys’ are simply the names 0.2 given to the individual fields in the web-page form. Each 0.1 D is p la c e m e n t Shaker 0 item in the Results queue consists of two elements. Firstly -0.1 the CGI connection information required to send the -0.2 -0.3 results back to the user. Secondly, a text stream -0.4 containing the results web-page location. -0.5 Electro Magnet 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Time, seconds Webcam To prevent large numbers of requests amassing under Beam Displacement ( D= 0 ) heavy demand the queue size is limited. The maximum 0.5 0.4 number of requests allowed in the queue is set by a 0.3 High Damping default value to 10, judged to be an acceptable 0.2 0.1 D is p la c e m e n t compromise between allowing multiple users and 0 minimizing the delay before results are returned. If the -0.1 -0.2 queue is full when a request is submitted, the user is sent a -0.3 ‘busy’ web-page in reply, informing them that the system -0.4 -0.5 is busy. The request is then discarded. A further check can 0 0.5 1 1.5 2 2.5 Time, seconds 3 3.5 4 4.5 5 be performed to check if the IP address of a submitted request is the same as one currently in the queue. If this is Figure 3 Experimental Equipment and Results the case the request is discarded and the user is again sent the ‘busy’ web-page. This prevents a single user from In this particular application, the equipment is used as a dominating the queue system. key part of a laboratory session for a level 2 undergraduate module in Vibration and Control. At this level the beam is treated as a 1 degree of freedom, lumped 7. Experimental Equipment parameter, mass/spring/damper dynamic system. The session is used to reinforce principals taught during the The example chosen here to demonstrate the principle of a lectures which relate the position of the roots of the typical ReLOAD enabled remote experiment is one which characteristic equation on a root locus diagram, to the implements negative velocity feedback to apply active type of free vibration response that is seen in practice. damping to a vibrating beam. This purpose made Hence visualisation of the beams motion is a crucial component, which is captured using the webcam. As the experiment and a set of standard controls allowing damping is increased students see the time taken to settle replays, rewinding, fast-forwarding etc. The video is is reduced and the frequency of oscillation is decreased. displayed using a java applet providing a consistent Careful examination of the data will however reveal to the experience across different browsers and does not require more observant students, that the roots do not follow a the user to download any special plugins. A link to the classic semicircular locus as damping is increased, since results data file is provided allowing it to be imported into the system is actually a continuous system and not a spreadsheet applications such as Excel and a copy to lumped parameter system. If the damping is increased clipboard function is also included, which serves a similar beyond a particular level the point of attachment of the purpose. The results web-page is shown in figure 5. damper becomes locked, effectively preventing the damper dissipating energy and the system reverts to a lightly damped system with an effectively shortened beam. This apparently contradictory phenomena of increasing damping resulting in a more lightly damped system is returned to in later modules, when multi degree of freedom systems are introduced. 8. The Client Computer The client computer can be any computer with appropriate Internet browser software installed and is only required to send a relatively small amount of data to the ReLOAD web server. Upon entering the experiment internet address, the user is presented with the Parameters Input web page as shown in figure 4. Figure 5 The Results Web-Page 9. Evaluation The particular remote experiment described in this paper Figure 4 The Parameter Input Web-Page has been used successfully since 2001 as an alternative to an almost identical face-to-face version of the beam A standard HTML form is used to submit information to experiment. Students are offered the option of taking the the ReLOAD Web server. Parameters are entered into the ReLOAD enabled version, in situations where they find it text boxes. In order to post the form to the server a submit impossible to attend the face-to-face session, due to button is used. Usually a submit button will directly post illness or other unavoidable circumstances. Since it was the information in a form to the defined address. However introduced, student feedback has been very positive, with in this case a java-script function first checks to see if the most appreciating the alternative approach available. user has already pressed the submit button. This is to help Many overseas students have also be able to perform the prevent the user from repeatedly clicking the submit laboratory session even when personal circumstances button, causing spurious experimental requests. The form have prevented them from being in the UK at the time of will be submitted only if the function returns a Boolean the timetabled face-to-face session. In end of session ‘true’. Note it would be possible to remove this java script examinations, the principals which are reinforced during and use the server computer to delete duplicate this laboratory session are examined. Though there is only experiment requests. a relatively small sample (around 5 students per year) The results web-page presents results from the experiment analysis of their scores suggests they perform equally well to the user in a number of ways. A graph is displayed as those who take the face-to-face version. showing the beam’s displacement and the control signal System performance evaluation has been encouraging, of the damper. Alongside are the embedded video clip of with tests being performed by multiple users at various global locations showing minimal delay in results being Students are familiar with the webcam, accelerometers served to the client computer, usually within less than 20 and other hardware associated with the ReLOAD seconds, depending on the queue size and internet speed. experiment but they stills consider this approach to delivering an experiment to be "high tech" (even though the actual equipment is exactly equivalent to that students 10. Delivering Additional Experiments have used in past years in these courses). As a way to augment the face-to-face and hands-on experiments then, The solution to performing remote experiments outlined the ReLOAD system appears ideal. Students in Mech 364 here uses a vibrating beam experiment as an example. The and 465 will cycle the through a version of the ReLOAD system provides a method of performing any remote beam experiment during March 2006 and will be polled at experiment not requiring real-time video feedback or data the end of the term regarding the effectiveness of transfer. The system allows for multiple pieces of ReLOAD to deliver the experiment. equipment to be connected to a single Experiment Server and numerous variants of an experiment to run on each 11. Conclusions piece of equipment. In addition the ReLOAD web server supports access to multiple Experiment Server computers The solution presented in this paper allows remote control allowing a highly flexible and reconfigurable system. This of an experiment using only a typical java enabled web option is especially useful if few experiments are browser. The solution does not offer continuous control; performed, or if demand for a particular experiment is once a set of parameters have been submitted to the focused around a specific time period. For example, a two experiment the user must wait until the experiment week time slot to complete module course work. It is now terminates before resubmitting revised values. Continuous straightforward to create new ReLOAD enabled control is possible at the current time but was not experiments, since each experiment is controlled using a considered necessary or viable due to the limitations of standard LabVIEW VI. A set of tools is used to create the the streaming video that would be needed to support it. necessary webpages with minimal intervention required. However, improvements in video streaming technology, This has resulted in a relatively straightforward and rapid coupled with inevitable increases in network bandwidth expansion of the system. Numerous new experiments are and processing power may soon make this a more realistic currently under development, one being in collaboration option. The current solution offers a simple, easily with the University of British Columbia (UBC), this being adaptable system based upon well-established Internet an excellent transatlantic test case for the ReLOAD technology and makes most use of available time, while system. one person is analysing their data numerous other UBC currently maintains two vibrations courses in the experiments can be performed for other users. Both undergraduate Mechanical Engineering curriculum. One student and system evaluation has so far proved very is at the third year level (Mech 364) and one is at the encouraging, and based on initial success additional fourth year level (Mech 465). Both courses incorporate experiments are currently being commissioned. laboratory experiments and both courses are large with more than 90 students registered in each. Classes this size render classic face-to-face experiments with small group References sizes and adequate instruction, time-consuming and logistically challenging. The acquisition of psychomotor  A. Selmer, M. Goodson, M. Kraft, S. Sen, V. skills and "mechanical intuition" associated with face-to- McNeill, B. S. Johnston, C.K. Colton, Process Dynamics face experiments is a priority at UBC but the requirement and Control Experiments Performed Across the Atlantic for small group sizes and adequate supervision combined Workshop on Internet Accessible Laboratory Experiments with the large class sizes means that providing more than in Chemical Engineering Ed., Cambridge, UK 2005. two face-to-face experiments in a four month semester is  M. Hites, Creating and running undergraduate not plausible. Ideally, it would be possible to augment experiments controlled through the internet, Proc. IL/IN these experiments with additional experiments that could Conf. of American Soc. of Eng. Ed., 2002, 192-198 be performed individually by each student and at each  C. Rohrig, A. Jochheim. The virtual Lab for student's own pace. The ReLOAD system offers an ideal controlling real experiments via Internet, Proc. IEEE method to provide extra experiments that can be done International symposium on computer aided control individually and as part of the students' own timetable. system design. 1999 279-284. The same detailed lab reports and documentation of  J. Sanchez, F. Morilla, S. Dormido, J. Aranda, P. methods and results that is provide for face-to-face Ruiperez. Virtual and remote control Labs using Java: A experiments will be required from the ReLOAD qualitative approach, IEEE Control systems magazine, experiments. In addition, the ReLOAD experiments can be April 2000, 8-20. demonstrated in a class or tutorial session with the same  C. Rohrig, A.Jochheim, Java-based framework for procedures and software as the students themselves will remote access to laboratory experiments, Proc. IFAC/ use. In-classroom laboratory instruction of this type is IEEE Symp. on Advances in Control Ed., Australia, 2000. often not plausible with the face-to-face experiments.
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