Interactive and Visualized Online Experimentation System for Engineering Education and Research

Summary

This work describes an online experimentation system that provides visualized experiments, including the visualization of theories, concepts, and formulas, visualizing the experimental process with three-dimensional (3-D) virtual test rigs, and visualizing the control and monitoring system using widgets such as charts and cameras.

Abstract

Experimentation is crucial in engineering education. This work explores visualized experiments in online laboratories for teaching and learning and also research. Interactive and visualizing features, including theory-guided algorithm implementation, web-based algorithm design, customizable monitoring interface, and three-dimensional (3-D) virtual test rigs are discussed. To illustrate the features and functionalities of the proposed laboratories, three examples, including the first-order system exploration using a circuit-based system with electrical elements, web-based control algorithm design for virtual and remote experimentation, are provided. Using user-designed control algorithms, not only can simulations be conducted, but real-time experiments can also be conducted once the designed control algorithms have been compiled into executable control algorithms. The proposed online laboratory also provides a customizable monitoring interface, with which users can customize their user interface using provided widgets such as the textbox, chart, 3-D, and camera widget. Teachers can use the system for online demonstration in the classroom, students for after-class experimentation, and researchers to verify control strategies.

Introduction

Laboratories are vital infrastructure for research and education. When conventional laboratories are not available and/or accessible due to different causes, for example, unaffordable purchases and maintenance cost, safety considerations, and crises such as the coronavirus disease 2019 (COVID-19) pandemic, online laboratories can offer alternatives^1,2,3. Like conventional laboratories, significant progress such as interactive features⁴ and customizable experiments⁵ have been achieved in the online laboratories. Before and during the COVID-19 pandemic, online laboratories are providing experimental services to users throughout the world^6,7.

Among online laboratories, remote laboratories can provide users with an experience similar to hands-on experiments with the support of physical test rigs and cameras⁸. With the advancement of the Internet, communication, computer graphics, and rendering technologies, virtual laboratories also provide alternatives to conventional laboratories¹. The effectiveness of remote and virtual laboratories to support research and education has been validated in related literature^1,9,10.

Providing visualized experiments is crucial for online laboratories, and visualization in online experimentation has become a trend. Different visualization techniques are achieved in online laboratories, for example, curve charts, two-dimensional (2-D) test rigs, and three-dimensional (3-D) test rigs¹¹. In control education, numerous theories, concepts, and formulas are obscure to comprehend; thus, visualized experiments are vital to enhancing teaching, student learning, and research. The involved visualizing can be concluded into the following three categories: (1) Visualizing theories, concepts, and formulas with web-based algorithm design and implementation, with which simulation and experimentation can be conducted; (2) Visualizing the experimental process with 3-D virtual test rigs; (3) Visualizing control and monitoring using widgets such as a chart and a camera widget.

Protocol

In this work, three separate visualized examples are provided to enhance teaching and learning and research, which can be accessed via the Networked Control System Laboratory (NCSLab https://www.powersim.whu.edu.cn/react).

1. Example 1: First-order system using circuit-based experimentation protocol

1. Access the NCSLab system.
   1. Open a mainstream web browser and enter the URL https://www.powersim.whu.edu.cn/react.
   2. Click on the Start Experiment button on the left side of the main page to log in to the system. User name: whutest; password: whutest.
      NOTE: This step also suits for other two examples (Example 2 and Example 3).
   3. Enter the WHULab in the left side sub-laboratory list and choose WHUtypicalLinks for experimentation.
      NOTE: Six sub-interfaces are designed and implemented for different purposes to support simulation and real-time experimentation.
   4. Enter the Algorithm Design sub-interface.
      NOTE: The user can choose a public algorithm model designed and shared by other authorized users or create a new model.
   5. Choose and click on the Create New Model button and enter the web-based algorithm interface. Build a circuit diagram using the provided blocks, as shown in Figure 1.
      NOTE: Another operational amplifier (op-amp) (Op-Amp2 in Figure 1) is used to cancel the 180° phase shift. To ensure that the input, the resistors, and the capacitor are tunable, one variable capacitor and two variable resistors in the ELECTRIC ELEMENTS library and four constant blocks from the SOURCES library are selected from the left-side block library panel.
   6. Double click the corresponding blocks to set parameters as listed in Table 1. Set the X-axis range of the chart to 8 s.
      NOTE: A popup window will be triggered after a double click to the block, which includes the descriptions of the block and can be used for setting the parameter. An example of the Resistor (R3) is illustrated in Figure 1.
   7. Click on the Start Simulation button; the simulation result will be provided in the interface, as included in Figure 1.
      NOTE: This step also suits the two other examples with other test rigs. The simulation results can provide information for users to recheck the designed circuit-based system to avoid a wrong circuit. However, a faulty circuit will cause no harm to the users or the system, so the users do not have to worry about the consequences.
   8. Click on the Start Compilation button. Wait until the designed block diagram is generated into an executable control algorithm that can be downloaded and executed into the remote controller deployed at the test rig side to implement control algorithms.
      NOTE: This step also suits the following experiments with other test rigs.
   9. Conduct real-time experiments using the generated control algorithm. Click on the Request Control button to apply for control of the circuit system.
      NOTE: "Request control" is the scheduling mechanism for the system. Once a user is granted the control privilege, the user can conduct experiments with the corresponding test rig. Only one user can occupy the test rig at a time for physical test rigs, and the queue scheduling mechanism has been implemented to schedule other potential users based on the First Come First Served rule¹¹. For virtual test rigs, a massive number of users can be concurrently supported. 500 concurrent user experimentation has been tested effectively. For the circuit-based system, 50 users can access the system at a time.
   10. Click on the Return button to the Algorithm Design sub-interface. Find the executable control algorithm under the Private Algorithm Models panel.
       NOTE: The executable control algorithm can also be found in the My Algorithm panel in the Control Algorithm sub-interface.
   11. Click on the Conduct An Experiment button to download the designed control algorithm to a remote controller.
   12. Enter the Configuration sub-interface and click on the Create New Monitor button to configure a monitoring interface, as shown in Figure 2. Four textboxes for parameter tuning and one curve chart for signal monitoring are included.
       NOTE: The chart on the right in Figure 2 is the same chart as the one in the left, which was added to demonstrate the data using the Suspend button.
   13. Link the signals and parameters with the selected widgets.
       NOTE: Parameter/ Input, Parameter/ R0, Parameter/ R1, and Parameter/ C for four textboxes, respectively, and Parameter/ Input and Signal/ Output for the curve chart.
   14. Click on the Start button to start the experiment.
       NOTE: This step also suits the following experiments with other test rigs. Users can save the configuration for future use.
   15. Set the input voltage to 0 V, tune the capacitor C to 5 µF (0.000005 in Figure 2), and then set the input voltage to 1 V; the dynamic process of the output voltage is illustrated in Figure 2.
2. Calculate the corresponding parameters K and T.
   ​NOTE: The time constant can be calculated when the output reaches 63.2% of the final value K after t = T, which is 0.632¹². From Figure 2, it can be seen that the time duration is 1 s, thus, T = 1, which is consistent with the theory in which, T = R₁C = 200000*0.000005 = 1, and K = R₁/R₀ = 200000 / 200000 = 1 (which equals the final value)¹². Thus, the first-order system can be specified as: .

2. Example 2: Interactive and visualized virtual experimentation protocol

1. Use the NCSLab system to conduct simulation and real-time experimentation.
   1. Log in to the NCSLab system. Enter the ProcessControl sub-laboratory and choose the dualTank test rig, and then enter the Algorithm Design sub-interface.
   2. Design a proportional-integral-derivative (PID) control algorithm using the web interface provided by NCSLab following the steps described in Example 1. Figure 3 is an algorithm example for the dual tank system.
   3. Double click on the PID controller, and tune the parameters for Proportional (P), Integral (I) and Derivative (D) terms. Set P = 1.12, I = 0.008 and D = 6.6, respectively.
      NOTE: The P, I, and D terms should be tuned combined with the simulation result.
   4. Click on the Start Simulation button; the simulation result will pop up, which is included on the right side of Figure 3.
      NOTE: It can be seen that the control performance is good, and the control algorithm is ready for real-time experimentation.
   5. Generate the executable control algorithm following the previously mentioned steps.
   6. Download the control algorithm to the remote controller and configure a monitoring interface with four textboxes for Set_point, P, I, and D, respectively.
   7. Include a chart for monitoring the water level and the corresponding Set_point. Choose a 3-D widget, which can provide all angles of the test rigs and animations of water level connected with the real-time data.
   8. Click on the Start button; then, the monitoring interface will be activated as shown in Figure 4, which provides a visualized virtual experiment.
   9. Set the Set_point from 10 cm to 5 cm, and then set I = 0.1 when the height of the water level in the controlled tank reaches and stabilizes at 5 cm. Reset the set-point from 5 cm to 15 cm; it can be seen from Figure 4 that there is an overshoot.
   10. Tune I from 0.1 to 0.01 and reset the set-point from 15 cm to 25 cm. It can be seen that the overshoot has been eliminated, and the water level can quickly stabilize at the set-point value of 25 cm.

3. Example 3: Research with remote and virtual laboratories protocol

1. Conduct a real-time experiment in NCSLab.
   1. Log into the NCSLab system and choose Fan Speed Control in the Remote Laboratory sub-laboratory.
   2. Enter the Algorithm Design sub-interface. Drag the blocks to construct the internal model control (IMC) control algorithm diagram, as shown in Figure 5.
      NOTE: The F(s) and G_m(s)^-1 is designed as shown in Figure 5, in which the designed control algorithm using NCSLab is illustrated to control a fan speed control system in a remote and virtual laboratory mode.
   3. Generate the executable control algorithm and employ the fan speed control system to verify the designed IMC algorithm.
   4. Configure a monitoring interface. Link two textboxes with two parameters, namely, the Set_point and lambda (for λ which is the filter time constant) for tuning, and a real-time chart with the Set_point and Speed for monitoring. Select the 3-D model widget of the fan and the camera widget for monitoring.
   5. Click on the Start button to activate real-time experimentation. Reset the Set_point from 2,000 rpm to 1,500 rpm, and then reset it from 1,500 rpm to 2,500 rpm, the result of which is shown in Figure 6.
      NOTE: It can be concluded that when λ = 1 the system can be stabilized to a step reference.

Results

The proposed laboratory system has been used in several different disciples at Wuhan University, such as the Automation, Power and Energy Engineering, Mechanical Engineering, and other universities, such as Henan Agricultural University⁶.

Teachers/students/researchers are provided with great flexibility to explore the system using different virtual and/or physical test rigs, define their control algorithms, and customize their monitoring interface; thus, users at differ...

Discussion

The presented protocol describes a hybrid online laboratory system that integrates physical test rigs for remote experimentation and 3-D virtual test rigs for virtual experimentation. Several different block libraries are provided for the algorithm design process, such as the electrical elements for circuit-based design. Users from control backgrounds can focus on learning without programming skills. The proper design of a control algorithm that can be applied to a suitable test rig should be considered. It is also ...

Materials

Name	Company	Catalog Number	Comments
Fan speed control system	/	/	Made by our team
https://www.powersim.whu.edu.cn/react			Made by our team