Article: A Distance PLC Programming Course Employing a Remote Laboratory Based on a Flexible Manufacturing Cell
The overwhelming developments of the internet technologies are becoming enabling agents of new teaching methods. Among them the remote laboratories are increasedly being considered as a serious alternative to the classical local laboratories. In the CITCEA-UPC (Center of Technological Innovation in Static Converters and Drives, Polytechnical University of Catalonia) located in Barcelona (Spain), a remote laboratory experience with a flexible manufacturing cell has been carried out with the collaboration of Schneider Electric and its Training Centre. The flexible cell is a small-scale industrial system where the students can learn and become familiar with real industrial components, such as position sensors, pneumatic and electrical actuators, drives, PLCs and industrial communication networks. Such skills can be better acquired allowing the students to connect directly to all the devices by means of Ethernet cards, with no need for computers working as servers. Hence, there are no differences in the connection, programming and debugging procedures between the local and the remote students, since all of them connect to the same Ethernet card of the PLC). The remote laboratory is used in the subject Electrical Workshop of Automation. Such a subject belongs to the Electrical Engineering degree and is optional in the student curriculum. Although the subject Electrical Workshop of Automation can be done in any course, most of the students are in the 3rd or 4th course of the degree.
Students can choose to do either local or remote exercises. The present work focuses on the second option. In any case the laboratory exercises are geared towards project based learning, the practices are not considered as isolated problems to be solved, but as a general project to be developed. The theoretical background is given in a Moodle based web-site. This background includes the basics of electrical and pneumatic actuators, drives, position sensors, PLC programming (GRAFCET, GEMMA, ladder language, structured language, etc.), communications between systems (Ethernet), etc. After ensuring (by means of auto-evaluation questionnaires) that they have acquired the required background, the problems are presented and the students need to develop remotely the control of one of the four different sub-cells. They will be moved through the different sub-cells in different exercises until they have finished properly all of them. The students receive the needed software with the corresponding instructions and they install it in their computer. To supervise the evolution of the cell they use an IP camera.
Although the practical course is organized in eight sessions or exercises, there is only one general problem to be solved by the students”>the entire automation of the cell. This approach fits into project-based learning methods, where the students have to deal with general projects instead of single sessions. After the eight sessions, the students have to write a report where the entire project is to be documented.
The platform has been tested by twenty-five volunteer students, divided in two different groups: the local group, composed of fourteen students and the remote group, composed of eleven students. All the students had the same initial level, since none of them had neither ever attended a PLC programming course nor programmed a PLC.
The students belonging to both groups have been able to implement the programs and make the cell work, but achieving different complexity levels. Although the course has been valued in general terms very positively, three students enrolled in the remote group have pointed out that the major drawback is the necessity of a good Internet connection to watch the real-time IP camera at an acceptable rate.
Two different assessments have been undertaken, resulting in the continuous evaluation and final marks. The first one considers the work done during the whole course, mainly shown in the final report submitted to the instructors. The final mark is obtained as the result of averaging the continuous evaluation and final examination marks. All the students including those who have undertaken the local practices have been requested to answer (with marks 1-5) an anonymous questionnaire and submit it to the instructors. The final report has been assessed according to the following criteria (each criterium one point):
1) The student has submitted the report and has undertaken it as described in the bases.
2) The documentation included in the program is clear and helps to understand and follow the program.
3) The cell works in the more favorable cases.
4) The student has delved into the GEMMA guide capabilities and hence he/she considers some of the problems that appear when the operation mode (automatic/manual)
is eventually changed.
5) The cell works in all the different scenarios described (emergency stops, sensors failure, etc.).
In the final exam the students have answered a test covering the contents studied in the course and has implemented a program similar to the practices carried out. They have been assessed according to the criteria described above. The survey questions and results allow the comparison of the results between the two groups. It shows no significant differences, neither in the survey answers nor in the qualification marks. The remote group continuous evaluation mark is a bit higher, but the final mark is slightly better for the local group. Although some conclusions can be extracted from such results, the overall differences shown seem to obey more the different student abilities than differences in the teaching methods employed. The authors believe that the drawbacks of distance learning (mainly the partial perception of the laboratory, the technical requirements and the more reduced communication between the students and with the instructor) are balanced with the advantages (extra motivation of the students, time and space laboratory constraints removal) so that the final outcome is not significantly different. Forthcoming improvements in information technologies can minimize the drawbacks of distance learning and boost it even further.
Regarding further improvements to be done, the main challenge is the Internet connection dependence of the users. The lack of high speed Internet creates a technological boundary. With the scope of international cooperation with some developing countries, this is becoming a very relevant issue and some actions have been and are being taken. Among them the use of a SCADA (Supervisory Control And Data Acquisition) system which does not need a large amount of data to transmit is appearing as a reliable alternative.
The authors acknowledge the support received from Schneider Electric Spain, its Training Centre, CCD-UPC and the ALFA II-0341-A project.
Author 1: Oriol Gomis-Bellmunt [email protected]
Author 2: Daniel Montesinos-Miracle [email protected]
Author 3: Samuel Galceran-Arellano [email protected]
Author 4: Andreas Sumper [email protected]
Author 5: Antoni Sudria-Andreu [email protected]
Article Link:
http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?puNumber=13