https://doi.org/10.35290/ro.v4n2.2023.908

Virtual reality application of an enclosed tank as a

teaching module for automatic control

Aplicación de realidad virtual de un tanque cerrado como un módulo

de enseñanza para el control automático

Fecha de recepción: 2023-04-03 • Fecha de aceptación: 2023-04-25 • Fecha de publicación: 2023-06-10

César Darío Cando Sangoquiza¹

Alfa Soluciones – Ingeniería, Ecuador

cedario93@gmail.com

https://orcid.org/0009-0006-5765-1017

Willian David Morales Chicaiza²

Alfa Soluciones – Ingeniería, Ecuador

williansmorales00@gmail.com

https://orcid.org/0009-0009-2394-5297

Edison Guillermo Mullo Mullo³

Alfa Soluciones – Ingeniería, Ecuador

edisongmullom@gmail.com

https://orcid.org/0009-0000-9268-403X

Edison David Mañay Chochos⁴

Alfa Soluciones – Ingeniería, Ecuador

edmanay@outlook.com

https://orcid.org/0000-0002-3447-2511

Abstract

In the field of engineering, Virtual Reality (VR) has emerged as a training option for students

to generate practical skills in automatic process control. The article presents a VR application

of a closed tank, which allows the introduction of control strategies for the pressure variable,

using a microcontroller and a computer. The VR interface was implemented in Unity with the

three-dimensional design of the plant shown to the user on the computer monitor, the

mathematical model that characterizes the dynamic behavior of the process and the PID

control strategy was established in the Arduino Uno module. Communication between the

Arduino and the PC was established via RS-232 protocol. The VR environment consists of a

panel for the selection and serial connection with the Arduino, also with inputs that allows to

evaluate the control strategy as the SetPoint (SP) and the manual valve (a2), which is the

actuator to introduce disturbance to the model. With the SP entered to the control system with

perturbations of 20, 60 and 90%, the PID control performed well with minimal steady state

errors. The dynamic behavior of the process is visualized in the VR environment with the

movement of the control valve stem (a1), the process variable (PV) is displayed on the PIT

100-A transmitter and the trends of the variables (SP, PV and CV). The proposal can be

replicated to other processes and different variables such as level, flow, etc.

Keywords: virtual reality, unity 3d, arduino, pid control, pressure, closed tank.

Resumen

En el campo de la ingeniería ha surgido la realidad virtual (VR) como una opción de

capacitación para que los estudiantes generen habilidades prácticas en el control automático

de procesos. El artículo expone una aplicación de VR de un tanque cerrado, que permite

introducir estrategias de control de la variable presión, haciendo uso de un microcontrolador y

un ordenador. Se logró implementar la interfaz de VR en Unity con el diseño tridimensional

de la planta que se muestra al usuario en el monitor de la computadora, el modelo matemático

que caracteriza el comportamiento dinámico del proceso y la estrategia de control PID se

estableció en el módulo Arduino Uno. La comunicación entre el Arduino y la PC se estableció

por medio del protocolo RS-232. El entorno VR consta de un panel para la selección y

conexión serial con el Arduino, también con entradas que permite evaluar la estrategia de

control como el SetPoint (SP) y la válvula manual (a2), que es el actuador para introducir

perturbación al modelo. Con el SP ingresado al sistema de control con perturbaciones de 20,

60 y 90%, el control PID tuvo un buen rendimiento con errores en estado estacionario

mínimos. El comportamiento dinámico del proceso se visualiza en el entorno VR con el

movimiento del vástago de la válvula de control (a1), se visualiza la variable de proceso (PV)

en el transmisor PIT 100-A y las tendencias de las variables (SP, PV y CV). La propuesta

puede ser replicada a otros procesos y a variables diferentes como nivel, flujo, etc.

Palabras Clave: realidad virtual, Unity, Arduino, gestión industrial, tanque cerrado

Introduction

Industries must be competitive in the market, minimize production costs, reduce pollution,

improve the quality and durability of their products. Achieving these objectives requires

appropriate methods of production control, which are possible through the application of

automatic control, therefore, in vocational training to achieve knowledge in control,

automation and instrumentation is essential. Technological progress also has a direct and

indirect impact on people's daily lives. Tipán (2022) proposed an application that allows

people with a certain degree of disability to interact through computer vision, in particular the

detection of movement with environments that simulate reality.

Education in various fields of engineering requires laboratories for students to receive high

quality training and practical skills in the field of process control. The advancement of

information technology has opened new horizons for learning and teaching worldwide. In

addition to field practices, virtual simulations are becoming more and more common. A

virtual environment can be a powerful tool in institutions where physical equipment is not

available to put students in "hands-on" situations, allowing for greater equity in the teaching

process (Charre-Ibarra et al., 2014).

Virtual Reality (VR) is acquiring great relevance in the educational field. It is necessary to

promote the training of future professionals in the use of these emerging technologies that

improve the teaching-learning processes (Cózar et al., 2019).

Sousa et al. (2021) proposed virtual reality as a tool for teaching and learning processes in the

field of basic and professional education. For them, VR is analyzed as an alternative to ensure

the quality of the educational process, especially in situations of physical distance due to the

pandemic.

VR is a training tool for the industrial field, because it provides virtual experiences that are

impossible in a real environment, in terms of safety in the operation of equipment and cost.

The research conducted by Montalvo et al. (2020) presents an Augmented Reality system that

allows users to train in the handling of HART instrumentation, using the Unity 3D platform

and Meta 2 glasses.

This paper proposes a Virtual Reality application of a closed storage tank as a teaching

module for automatic control, which facilitates the learning process in control engineering

fields, so that the user does not need specialized equipment or expensive computer

accessories. In this context, personal computers with Windows operating system are most

commonly used in the educational sector. A computer generally consists of a display and

input/output devices, which are used to interact with the VR system. When it comes to

development software, there are two well-known options, Unity and Unreal, both of which

offer easy-to-learn tools and large support communities for application development. When it

is required to perform automation projects at the educational level electronic boards are

widely used such as Microchip Technology and Arduino modules (Varela-Aldás et al., 2021).

Based on these criteria, the components of the virtual reality system were determined.

1.1 Mathematical model of the closed storage tank

The model originates from a mathematical proposal of the dynamic characteristics of the

process based on differential equations that describe the dynamic behavior of the process.

The flow through a valve is generally expressed by equation (1).

𝑄

𝑣

= 𝐾𝑣𝑓(𝑥) ∆𝑃

√

𝜌

(1)

Where 𝑄𝑣 is the flow through the valve, 𝐾𝑣 constant, 𝑓(𝑥) passage area, ∆𝑃 is differential

pressure across the valve, 𝜌 density of the liquid.

The final control element is considered to be a linear type valve, so 𝑓(𝑎1) = 𝑎1, (linear

opening), therefore, the inlet valve is represented in equation (2).

𝑞

𝑖

= 𝑘

𝑎1

(2)

The outlet valve 𝑓(𝑎2) = 𝑎2, 𝐾𝑣 = 𝑘2, is given in equation (3).

𝑞

𝑜

= 𝑘

∆𝑃

𝑎

√

𝜌

(3)

The differential equation describing the pressure changes of a gas inside a tank, from which

some leakage is allowed in subcritical regime, is given by equation (4) and (5).

𝑑𝑃 = − 𝑅𝑇𝐾0𝐴0 √𝑃 (𝑃 − 𝑃 ) + 𝑅𝑇 𝑢

(4)

𝑑𝑡

𝑑𝑃(𝑡)

𝑉∗𝑇

( 𝑎

𝑉

(𝑡)√𝑃 (𝑃

𝑜 𝑜

− 𝑃(𝑡)) − 𝑎

𝑉

(𝑡)√𝑃(𝑡)(𝑃(𝑡) − 𝑃 )) (5)

𝑑𝑡

𝑅 1

𝑖 𝑖 2 𝑜

Where 𝑢 is the volume of gas per unit time, with which the tank is fed using a compressor.

This value, it is assumed, does not depend on the pressure. The feeding is carried out in such a

way that the pressure changes of the gas are sufficiently slow to be considered isothermal. 𝑉

is the volume of the vessel, 𝐴0 and 𝐾0 are constants depending on the inlet valve and the gas

under consideration. 𝑅 is the universal gas constant and 𝑇 is the temperature at which the

process is carried out. 𝑃0 is also a constant (Sira-Ramirez et al., 2018).

The objective of the article is to develop a VR instrument, which allows introducing the PID

control strategy to the pressure process, making use of a microcontroller and a computer. The

following sections describe the system design, the technologies and devices used for control

and Virtual Reality. Also, the results of the implemented system are presented.

Methodology

To carry out the development of the Virtual Reality system of a closed tank for pressure

control, it is based on the Work Breakdown Structure (WBS) methodology, which makes a

project more manageable when it is broken down into individual parts, establishes the project

boundaries and scope (Mañay et al., 2022).

Five work stages have been established for progress, which are shown in Figure 1.

Figure 1

Work Stages According to WBS Methodology

2.1 System architecture

The computer monitor displays the Virtual Reality interface to the user with the 3D model of

the plant, while the mathematical function symbolizing the dynamic behavior of the process

and the PID control strategy is located on the Arduino Uno module. The input elements

(mouse and keyboard) allow interaction with the system. The game engine selected was

Unity, which allows the development of an application with flexibility and cross-platform

features. In addition, the proposal required a three-dimensional animated character or avatars,

for which the Mixamo platform was used, which is a web application that allows

downloading prefabricated characters and avatar animations. SolidWorks software was used

to design the 3D components such as pipes, tanks, valves and transmitters.

Figure 2 shows the components required for the implementation of the VR system.

Figure 2

VR System Architecture

State of

the art

research

Virtualized

Environment

Development

Implementation

of the control

strategy

Tests and

results

Presentation

of results

Virtual Reality

Environment

3D model and animation

of the process

Communication

Microcontroller

Arduino Uno

Mathematical model

and PID control

strategy

RS-232

2.2 P&ID diagram of the process

The P&ID diagram of the pressurized storage tank process for pressure control can be seen in

Figure 3.

Figure 3

P&ID Diagram of the Closed Storage Tank

The P&ID diagram shows the control loop (100) with the respective pressure indicating

transmitter (PIT 100-A/B), pressure controller (PC), pressure indicating recorder (PIR),

current to pressure converter (PY), pressure control valve (a1), manual pressure valve (a2)

and pressure output indicator (PI 100-C).

The closed storage tank shown in Figure 3 has an inlet fluid (𝑞𝑖𝑛(𝑡)). These are piped to the

vertical tank. The fluid pressure variable in the tank is controlled by the valve (a1) and the

manual valve (a2), which are the actuators of the system.

2.3 3D virtual environment model

The 3D visualization environment, comprised of the three-dimensional model of objects in a

real plant or laboratory, can replicate and study the dynamic behaviors of a process.

It is important to point out that there are no prescriptions for designing the Virtual Reality

interface, since its structure and operation depend on the variable to be controlled. However, a

methodological proposal is proposed to develop the virtual interface, which is done by

100-A

PIT

100-B

100-A

PCV

PHV

PIT

100-A

100-C

100-A

PIR

designing the objects that make up the station in the Solidworks design software. The

designed objects are sent to the virtualization environment in a 3D template to Unity to

integrate text monitors, sounds, process animation, trend graphers and avatars that through the

use of scripts and block code control the movements of the characters and third person

interaction with the 3D objects, similar to a real industrial process.

The VR environment consists of a panel with parameters for selection and serial connection to

the Arduino Uno module (algorithm with the mathematical model of the plant and PID

control). Also, the scene offers inputs that allow modifying process variables, such as the

SetPoint (SP) value from 10 to 25 PSI and the a2 valve in the range of 20 to 90%, the a2 valve

serves as a disturbance of the plant. The variables entered to the control system vary based on

the mathematical model integrated in the microcontroller. In the VR environment, the

dynamic behavior of the process is visualized with the movement of the control valve stem

(a1) by means of the control variable (CV), the process variable (PV) is visualized in the PIT

100-A transmitter and the trends of the variables (SP, PV, CV). Figure 4 represents the

logical procedure to follow for the execution of the simulation of the plant, to avoid errors in

the execution, since the Arduino module must be connected before running the simulation.

Figure 4

Virtual Reality Environment Execution Logic Diagram

2.3 Development of the 3D virtual environment

Three-dimensional objects designed to import in FBX format to Unity and integrate with

more structure components such as panels, buttons and selectors to generate the scene in the

VR application, some objects can be modified using Canvas components. The control of the

behavior of the objects is instantiated by the execution of the programs through scripts to

create animations, vector images and two-dimensional time-dependent signals. Figure 5

shows the methodology for creating the virtualization environment.

Figure 5

Methodology for Creating the Virtual Scenario

Trend of

vaiables

Serial Port

Display

Yes

Character

animation

Mistake

Disturbance input

SetPoint input

Serial Port

Selection

Input menu display

Visualization of

trends

Start

End

Visualization and

interaction

Character Movements

Interaction

Third Person View

The set of components is coupled into a single object to form the process station, as shown in

Figure 6.

Figure 6

Virtualization of the Plant in a 3D Environment

The deployed scenario has control and visualization components, the graphical representation

of the monitoring of the variables is shown in Figure 7(a), Figure 7(b) shows the proportional

valve (a1) that allows pressure flow control.

Figure 7

Virtual Scenario, (a) Rrend of Variables, (b) Control Valve (a1)

(a) (b)

The virtual interface allows to move the character by keyboard commands through the entire

scenario composed by the objects designed and placed on the area with characteristics of a

real environment as shown in Figure 8.

Figure 8

Avatar in the Virtual Work Environment

2.4 Control strategy design

Once the Virtual Reality environment of the pressurized storage tank is implemented, the PID

control strategy for the pressure variable is designed and validated. The RS-232 protocol is

used to achieve communication between the control algorithms and the scenario. The

corresponding adjustments are made in each software and hardware, and then the

communication is established and the data exchange is validated in real time.

In industrial processes, the measurement and control of the pressure variable is essential to

achieve safe operating conditions. Any vessel or piping has a maximum working pressure and

exceeding that pressure can cause equipment failures, mainly when exposed to flammable or

corrosive liquids (Rodríguez et al., 2011). The study of control strategies is fundamental to

manage variables in closed-loop processes, Figure 9. In control theory, a control strategy

governs the dynamic behavior of a process by regulating a variable with reference to a

SetPoint by means of an input variable (Flores-Bungacho et al., 2022). There is a classical

strategy such as proportional integral derivative (PID) control, which is implemented in this

article.

Figure 9

Closed Loop Control Block Diagram

Input

Comparator

Error

signal

Control or

manipulated signal

Output

Command

signal

+ - Controller Plant

Controlled

signal

Feedback

signal

Feedback

2.4.1 Design of the PID control algorithm

The PID control strategy is the most widely used in industrial applications; it is estimated that

more than 90% of control loops use PID control, since it is a simple and effective strategy that

does not require a great theoretical foundation for its use in everyday processes (Lozano-

Valencia et al., 2012). The design of PID controllers can be achieved from different

approaches, ranging from trial-and-error methods, as based on the dynamic model of the

system. The PID algorithm can be described as shown in equation (6).

𝑢(𝑡) = (𝐾 (𝑡) + 𝐾 ∫𝑡 𝑒(𝑡)𝑑𝑡 + 𝐾𝑇

𝑑

𝑒

(𝑡)

)

(6)

𝑒

𝑇

𝑖

0 𝑑 𝑑𝑡

Where 𝑢(𝑡) is the control signal, 𝑒(𝑡) is the error, ∫𝑡 𝑒(𝑡)𝑑𝑡 is the integral of the error, and

𝑑𝑒(𝑡) is the derivative of the error. The control parameters are the proportional gain 𝐾 , the

𝑑𝑡

integral gain 𝐾 = 𝐾 where 𝑇 is the integration time, and the derivative gain 𝐾

𝑝

= 𝐾𝑇 where

𝑖 𝑇𝑖 𝑖 𝑑 𝑑

𝑇𝑑 is the derivative time (Anitha et al., 2019; Burgasi et al., 2021).

In the pressurized tank station, the PID control loop is implemented for the pressure variable,

as shown in the closed loop diagram in Figure 10.

Figure 10

Block Diagram of Implemented PID Control

Process

The pressure control loop constants are tuned with the trial-and-error method, the values of

each parameter are shown below: 𝑘𝑝 = 1.25, 𝑘𝑖 = 0.11574, 𝑘𝑑 = 0.00125.

Results

3.1 User immersion

Pressure

Output

+ -

PID

Pressure

Controlled

signal

𝑅 = 8.314472[ 0

The parameters used to describe the imprisonment process of a virtualized closed storage tank

are as follows: 𝐻 = 2𝑚; 𝐷 = 1𝑚; 𝑉 = 5;

𝐽

] ≈ 8500

;

𝑇 = 273 𝐾

𝑚𝑜𝑙∗𝐾

𝑃𝑖 = 30𝑝𝑠𝑖, 𝑃𝑜 = 10𝑝𝑠𝑖.

When entering the virtualized system, the user can: i) visualize the pressure control process of

the closed storage tank, by selecting the available serial port and pressing the "Connect" key

(1), he/she can view the values and trends of the measured and controlled variables, see

Figure 11.

Figure 11

Process in the Immersive Environment

ii) change the desired values from the user interface, (2) the SetPoint in the range of 5 to 25

PSI and (3) the perturbation from 20 to 90%, see Figure 12.

Figure 12

SetPoint Change and Disturbance

iii) The control of the implemented system makes the respective indicators and actuators

dynamic: (4) the control valve (a1) has an animation in which the stem moves depending on

the control signal, (5) the PIT-100A shows the process variable, (6) the manual valve (a2) is

the actuator that inputs disturbance to the system and (7) the PI shows the output pressure, see

Figure 13.

Connected

Disturbance

SetPoint

Time

Exit

Pressure (PSI)

Figure 13

Actuators and Process Indicators

iv) the behavior of the controlled variables, control errors and pressure actions can be

visualized in the trend graph, see Figure 14.

Figure 14

Process Variables and Trends

3.2 Process Control

The performance graph of the designed PID control law shows that the control errors tend to

zero asymptotically over time. To evaluate the control, the manual valve (a2) is kept open at

20%, 60% and 90%, the results are shown in Figure 15.

Figure 15

Performance of Process Variables, Manual Valve (a2): (a) 20%, (b) 60% and (c) 90%

Time

Pressure (PSI)

(a)

(b)

3.3 System usability

(c)

A 10-question questionnaire is established to test the usability of the virtual reality system

(SUS); it is shown in Table 1. The questionnaire applied to the users is weighted from 1 to 5;

where 1 total disagreement to 5 total agreements. The evaluation of the answers is based on

subtracting 1 from the result in the odd questions; while in the even questions the result

obtained is subtracted from 5. To obtain the SUS value, the data obtained are added and

multiplied by 2.5 to obtain 100% (Chiliquinga et al., 2021; Proaño & Andaluz, 2021). The

SUS test indicates that percentages of up to 70% will consider the system to be good

(Andaluz et al., 2018).

Table 1

Usability Questionnaire

Nº

Questions

Results

Operations

Is the information displayed on the screen what is needed to understand

what the site is about?

5-1=4

Do I understand and comprehend the screen elements presented on the

system?

5-4=1

Is the application easy to use?

5-1=4

Do I need previous knowledge to use the system?

5-1=4

Does the system provide me with the information I need to understand

the process?

4-1=3

Do the icons provide explanatory information?

5-2=3

Do the interface colors resemble those of the real world?

5-1=4

How often would you use the application?

5-4=1

Can anyone use the system?

5-1=4

Does the application offer intuitive interface control?

5-4=1

Total

72.5

Table 1 shows the evaluation of the virtual environment (SUS) of the process to determine the

percentage of usability of the project, obtained a score of 72.5%, being considered a good

system, however, the project needs to implement improvements to obtain greater results and

maximize the user experience in immersive environments.

Conclusion

The objective of creating a Virtual Reality tool for the teaching-learning process was

achieved, the project allowed to introduce variations to the PID controller through the virtual

environment and also to visualize the dynamic behavior of the pressure process in the VR

environment with the movement of the control valve stem (a1), the value of the pressure

variable in the transmitter in PIT-100A and to vary the manual valve (a2) to enter

disturbances to the process. An Arduino Uno microcontroller and a laptop computer were

used. The VR system had an investment of 910 USD: the Arduino microcontroller cost 12

USD and the computer used has the following characteristics (Intel(R) Core (TM) i7-8650U

CPU @ 1.90GHz 2.11 GHz) with a cost of 900USD, this type of computer is generally

available to university students, generating a minimum investment for the implementation of

this type of project.

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Guillermo Mullo Mullo, Edison David Mañay Chochos

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