INTRODUCTION
Automation is the branch of technology that deals with the application of control systems to various human activities, mainly to industry. It is also defined as the action and effect of automating, that is, performing an act of production, distribution or government, without direct intervention of human conscience and will (Mataix, 2008).
Webster's online dictionary (http://www.websters-online-dictionary.org/definition/automation) defines automation as a highly technical implementation that usually involves hardware and electronic devices to replace human beings with machines in some tasks.
Another definition is made by Groover (2016), who states that automation, strictly in the field of manufacturing, is the technology involved with the application of mechanical, electronic and computer-based systems to operate and control production.
These definitions, in a general way, coincide with the idea of the use of 'certain technology' to control a production process. In addition, the first two definitions include the concept of 'replacing humans by machines', with which it agrees, but it is necessary to add that this replacement is partial and is also done for the benefit of the worker, by avoiding the performance of dangerous and routine tasks.
From these elements, it can be stated that automation is the technology that includes physical elements, like mechanical elements, electronic and computer systems (hardware and software), and theoretical knowledge, such as control engineering. This technology is implemented in various human activities, mainly in industry, in order to replace the human being in repetitive and tedious activities, which require great precision and speed or which could be dangerous or harmful to his life, leaving him a role where he can take much more advantage of his intellect, for example, as a supervisor.
The automation of industrial processes, including the agricultural industry, is a widespread practice worldwide, because it allows companies to increase their profits and competitiveness. Automation technology is expensive and some companies cannot acquire it. In the case of Cuba, the cost is not the only problem, because, even when the deficit of labor in agriculture could be solved by automation to increase production efficiency, the importation of these technologies is made difficult by the scope of the commercial, economic and financial embargo imposed by the United States government on Cuba.
The objective of this work was to propose an economical and adequate automation technology for Cuban agroindustry, considering the high costs of traditional automation technologies, the difficulty of acquiring them, the deficit of labor in agriculture and the need to develop it and its associated industry, to obtain products of high value added, suitable for consumption, exportation and tourism industry.
METHODS
A search on prices of technologies, both traditional and embedded systems is carried out on websites and commercial catalogs of some of the main manufacturers and suppliers of these technologies. In addition, a comparison is made fundamentally taking into account the economic cost. Several of the processors used in embedded systems based on their basic characteristics and their possibilities of use in the automation of the agroindustry are compared.
First, the benefits of automation in the industry are referred. According to Sharma (2017), some of the benefits of the use of automation in industrial processes are:
Reduction of production losses.
Resource optimization (saving of raw materials and energy).
Higher safety, reliability and functional safety.
Contribution to compliance with external regulatory requirements such as the environmental ones.
Flexibility in control, allowing easy adaptation to other productions.
The use of automation in agribusiness could generate a group of benefits such as those previously mentioned. Among them, saving raw material, increasing energy efficiency and compliance with environmental standards are highlighted. Nevertheless, others like obtaining a product with greater added value, increasing economic benefits, competitiveness of companies and the possibility of filling the labor deficit in agricultural production must be incorporated.
Functional Safety
In every industrial or agroindustrial plant, the processes or machines that are operated suppose a certain level of risk for the integrity of the operators, the plant or the environment. This requires adopting security measures in order to efficiently reduce risks. These measures or tasks are controlled and implemented through the automation system and are called 'Security functions'. When protection systems are implemented with automation systems, the most relevant international standard in terms of functional safety is IEC 61508, "Functional safety of electrical / electronic / programmable electronic systems related to safety". In addition to this basic standard, the specific standard IEC 61511 applies to the process industry (Smith y Simpson, 2016).
Functional safety, in some industries such as oil is mandatory, while in others that have fewer functional requirements, such as most applications of agro-industry, is only optional. Although, it is recommended for the benefits it provides such as the protection of plant personnel and equipment, when it is not a critical process in functional safety, that is, when it does not have high functional requirements, it is not commonly applied due to high costs.
Traditional Technology
The industrial solution to the problem of control of a process or plant includes the use of controllers such as Programmable Logic Controllers (PLC), and monitoring and / or monitoring systems, such as Supervisory Control and Data Acquisition Systems (SCADA).
Automation technology has a high cost, which includes the cost of the physical device, the software to configure, control and monitor these physical elements, whose cost is often higher than hardware, and training. In the opinion of the authors, the main difference between developed and developing countries is access to technology and the consequent technological dependence.
Embedded Systems
There are several definitions of embedded systems that are characterized by several specific features, such as the limited capacity of software and hardware compared to a PC, the number of functions to which they are dedicated and the reliability and security requirements (Noergaard, 2005). The same author and Holt and Huang (2018), refer the difficulty of defining the concept due to the evolution of it as a result of the constant advances in technology and the decrease in implementation costs.
For the amplitude of the concept, the one established by Noergaard (2005), is used. It defines an embedded system as a system with an applied computer, which is distinguished from other types of computers such as personal computers (PC) or supercomputers.
From this definition, and for the purposes of this work, it could be redefined as an electronic system, different from a personal computer, which uses a processor, such as the microprocessor of personal computers, in order to control a certain process.
Some of the available processors are:
Many of the embedded systems in real time use general purpose microprocessors. A microprocessor is a computer processor in an integrated circuit, which contains all, or most of the functions of the central processing unit (CPU) (Wang, 2017).
Compared to a general purpose microprocessor, a microcontroller is a self-sufficient system with peripherals, memory and a processor that is designed to perform specific tasks (Wang, 2017).
Digital signal processors (DSP) are designed for applications that require high calculation rates. DSPs implement algorithms in hardware offering high performance in repetitive calculation intensive tasks (Wang, 2017).
A Field Programmable Gate Array (FPGA) is a device that contains a network of cells or logic gates that can be quickly reconfigured, which facilitates the rapid creation of prototypes of embedded systems (Wang, 2017).
RESULTS AND DISCUSSION
Microprocessor
Microprocessors find their applications when the tasks are not specific. For example, personal computers use these as a processor, which allows performing a variety of complex tasks such as software development, games, and websites. In these cases, the relationship between inputs and outputs is not defined. They need a lot of resources, such as RAM, ROM and Input/Output (I /O) ports. Embedded software can be tailored to specific tasks that are designed for embedded systems.
Microcontroller
Microcontrollers are used in systems where the relationship between inputs and outputs are usually clearly defined. Some examples are: the computer mouse, washing machines, digital cameras, microwave ovens, cell phones and digital clocks. As the applications are very specific, they have little demand for resources such as RAM, ROM, I/O ports, and therefore can be embedded in a single chip with the processor. This reduces the size and the cost. A microcontroller is very easy to replace, while microprocessors are 10 times more expensive. In addition, microcontrollers generally consume less energy and are more immune to power peaks compared to other techniques (Wang, 2017).
Digital Signal Processors (DSP)
Digital signal processors are two to three times faster than signal processing applications based on general purpose microprocessors, including audio, video and communications. According to Wang (2017), among its disadvantages, it can be mentioned that they generally have a high cost and that some commercially available DSPs lack adequate support for the compiler.
Field-Programmable Gate Array (FPGA)
FPGAs are commonly used in the design stage and are usually replaced in the final product with custom circuits, due to higher performance and lower cost. When reconfiguration is an essential part of the functionality of an embedded system, FPGAs appear in the final product.
In the most common applications that require data processing, microprocessors, microcontrollers, DSP or FPGA are generally used. The microprocessors find their applications when the tasks are not specific. Microprocessor-based designs require a lot of resources, are complex and expensive compared to microcontrollers. Microcontrollers are self-sufficient systems with peripherals, memory and a processor that is designed to perform specific tasks. In the vast majority of cases, a design based on microcontroller is sufficient. In addition, it is simpler and less expensive than the microprocessor-based design. DSPs are used when it is necessary to implement certain algorithms in hardware, for example for signal processing, which allows higher processing speeds by decreasing the processor load. FPGAs are reconfigurable hardware, very expensive, which are generally used in the design stage of new products, but also and perhaps the most important application, is when reconfiguration is required in real time, which is an unusual requirement in the majority of the applications.
Particularly for control and automation applications in the agroindustrial sector, which do not have large processing and functional safety requirements, it is recommended to use microcontrollers over the microprocessor-based option, due to its simplicity and cost. When it is required to perform signal processing, which requires great processing power; it is recommended to use the DSP, since they implement some algorithms in hardware. Also, when reconfiguration is required in real time, an unusual requirement, it is recommended to use FPGA.
Embedded Systems in Agriculture Worldwide
Embedded systems have been widely used in various fields of agriculture. A study by Zhang & Pierce (2013) reported several applications during that year, as shown in Table 1.
TABLE 1.
Some reports of the use of embedded systems in agriculture during the year 2013
| Application | Authors |
|---|---|
| Agricultural robotic vehicles | (Noguchi, 2013) |
| Agricultural infotronic systems | (Zhang et al., 2013) |
| Precision agriculture | (Yang y Lee, 2013) |
| Automated crop production | (Shearer y Pitla, 2013) |
| Mechanization, monitoring and control in cotton production | (Sui y Thomasson, 2013) |
| Automated production in orchards and vineyards | (Burks et al., 2013) |
| Automated enclosures and animal production | (Purswell y Gates, 2013) |
| Automation and nutrition management | (He et al., 2013) |
| Automated pesticide application systems | (Karkee et al., 2013) |
| Automated irrigation management | (Wang et al., 2013) |
| Post-harvest automation | (Kondo y Kawamura, 2013) |
Among the main results of the research process, Table 2 shows the prices of some of the products of SIEMENS*, a manufacturer of great prestige in the field of automation, and Table 3, those of some Microchip† microcontrollers, also a prestigious company and very popular among embedded system developers.
TABLE 2.
Selection of some low and medium-range PLCs (with software) (Siemens, 2016)
| PLC | Characteristics | Price |
|---|---|---|
| LOGO! 8 12/24RCE |
| 241.66 USD |
| SIMATIC S7-1200 + KTP300 Basic |
| 605.23 USD |
| SIMATIC S7-1200 + KTP700 Basic |
| 1128.38 USD |
| SIMATIC S7-1511-1PN Compacto |
| 2281.25 USD |
TABLE 3.
Selection of some microchip microcontrollers (Microchip, 2017)
Table 4 compares the prices of some of the previously mentioned PLCs and microcontrollers.
TABLE 4.
Price comparison
It is necessary to clarify that the function of the microcontroller in the control system is to execute the control algorithms, so it can be considered as the 'core' of the system. In addition, it must be taken into account that this comparison is made considering only the cost of the processor.
As it can be seen, from the point of view of economic cost of the processor and for applications with low functional requirements, automation based on microcontrollers is much more economical than that used by traditional technology based on PLC and SCADA. This represents an alternative or opportunity to explore for developing countries or companies with low economic resources, and specifically for the Cuban agroindustry.
CONCLUSIONS
A search and comparison of the available automation technologies was carried out, which took into account the technology based on Programmable Logic Controllers (PLC) and Supervision, Control and Data Acquisition Systems (SCADA) that is traditionally used in the industry worldwide, and technology based on embedded systems, developed for example from microcontrollers.
It was determined that the development of proprietary technology from embedded systems is more economical and is considered more appropriate for the conditions of Cuban agribusiness.