Abstract: This paper introduces a design scheme for computer control experimental teaching content that reflects the characteristics of industrial control computers and is oriented towards practical applications in automation engineering. It also elaborates on the guiding ideology and main functions of the computer control experimental device adapted to the experimental teaching content.
Keywords: Automation; Industrial control computer; Experiment content; Experimental apparatus
Abstract: This article introduced a designed scheme of computer control experimental teaching contents, which could not only reflect the characteristic of IPC, but also be applied in practical automation engineering. The development idea and basic functions of this experimental apparatus of computer control correspoding with the experimental teaching contents were described.
Key words: automation; Industrial Personal Computer (IPC); experimental contents; experimental apparatus
1 Introduction
Computer Control Technology is an important professional course in the Automation major's curriculum. Its main task is to equip students with fundamental knowledge and basic application techniques regarding the composition, principles, and design of computer control systems. Laboratory sessions are a crucial component of this course, aiming to enable students to understand the basic control methods of computer control systems and master the methods of designing control systems using C programming language. The course also cultivates students' skills in independently conducting experiments on computer control systems, thereby enabling them to master the general engineering design methods of computer control systems.
As an automation major course with a strong engineering focus, the existing computer control technology experiments in our department's microcomputer principles laboratory were clearly inadequate. Therefore, starting in early 2002, our department began planning to establish a dedicated computer control technology laboratory. During the planning process, we investigated computer control experimental devices used by many universities in China or available on the market. We found that they generally had two shortcomings in their experimental teaching functions: firstly, the experimental content was outdated; secondly, they failed to reflect the characteristics of industrial control computers in practical engineering applications. Ultimately, we were unable to find a suitable computer control experimental teaching device tailored to the practical engineering needs of automation majors. In March 2003, the project leader decided to independently design computer control experimental content and develop corresponding experimental devices. After several modifications to the experimental content and prototypes, 17 computer control technology experimental devices were mass-produced and equipped in our department's computer control technology laboratory. In October 2004, they were first used for experimental teaching of the computer control technology course for undergraduate students majoring in automation in the class of 2000. Students generally reported that the experimental content was highly engineering-oriented and the experimental teaching effect was good.
2. Experimental Design
As industrial control computers are the core of computer control systems, their characteristics as industrial controllers should be reflected in experimental teaching. Only in this way can students fully understand the hardware characteristics and functions of industrial control computers. Secondly, the experiments should be geared towards automation majors, integrating experimental content with engineering practice to enhance students' learning interest and cultivate their engineering awareness. Furthermore, considering that students already have a foundation in microcomputer principles, microcontrollers, and other courses when conducting computer control technology experiments, the difficulty of the experiments should be appropriately increased, focusing on comprehensive design experiments to improve students' innovation capabilities. According to the teaching plan, computer control technology experiments consist of 6 class hours, with a one-week computer control technology course design at the end of the semester. The laboratory is open to all students on a reservation basis.
2.1 Familiarization with the experimental setup and I/O channel experiments
The computer control technology experimental device adopts a modular structure, making it very convenient to use. At the beginning of the first experiment, the instructor introduces the functions of the device to the students. Then, students spend a short time familiarizing themselves with the device and focusing on mastering the functions of the basic input/output channels. The I/O channels include 8 digital inputs, 8 digital outputs, 4 analog inputs, and 2 analog outputs. After mastering the common functions of the board, students use C language to write a subroutine to initialize the PCL812 board (its function is to initialize the PCL812 board, set the PCL board data reading mode, and set the interrupt counter) and an interrupt initialization and interrupt service subroutine. The A/D conversion is then triggered by a timer interrupt to acquire external switch signals and analog signals. Because the I/O channel functions of industrial control computers are relatively easy to understand and similar to the corresponding functions of microcontrollers, students usually master them well, thus achieving the experimental objectives.
2.2 Filtering Experiment
When a computer control system operates on the production site, the acquisition and conversion of signals are inevitably subject to various strong interferences on the production site, such as power grid fluctuations, the start and stop of high-power equipment, electromagnetic radiation from high-voltage equipment and switches, etc. These interferences will enter the I/O channel, which may cause the acquired signals to be inaccurate or even prevent the system from operating normally [1].
In order to improve the reliability of computer control system, various anti-interference measures must be taken in system design. If the content of anti-interference of I/O channel is not arranged in the experimental teaching, it will be detrimental to students’ true understanding of the composition and characteristics of computer control system. There are two common methods to suppress crosstalk interference: one is to select analog input filter according to the characteristics of interference signal; the other is to use digital filtering technology, such as average value method, median method, first-order inertial filtering and other algorithms to filter out interference signal[1]. In comparison, digital filter can better help students understand the characteristics of computer control system. When students are doing experiments, they are required to first understand the board initialization and interrupt subroutine with detailed comments, and then refer to the introduction of digital filter implementation in the edited "Computer Control Technology Experiment Guide" to analyze the program flowchart of digital filtering algorithm. Students are required to write various digital filtering algorithm programs themselves, and then input the mixed signal collected by A/D channel to verify the filtering effect of digital filter. This experiment is mainly to help students become familiar with the implementation method of digital filter, understand the hardware characteristics of industrial control computer, and understand the relevant driver program and board settings of board. Because the laboratory is fully open, students with extra capacity or interest can also conduct experiments on other advanced filtering algorithms, design the transfer function of a digital filter system, and program the digital filter.
2.3 Experiment on Digital PID Algorithm
This experiment requires students to design the controller transfer function for the controlled object based on its transfer function. Control of the controlled object is achieved using PID positional recursive formulas, PID incremental recursive formulas, and anti-integral saturation PID control algorithms. The P, I, and D parameters are determined according to the PID control object tuning method. Connecting the components helps students gain a holistic understanding of the structure of the computer control system.
In the experiments, students generated a useful signal with high-frequency noise interference, passed it through an analog low-pass filter, and then used the filter output as the given input of the closed-loop system for data acquisition via analog input channel one. The output of the simulated object was used as a unity negative feedback signal and also acquired via analog input channel one. After the board acquired the given and feedback signals, students were required to call their self-written PID control algorithm subroutine to calculate the control quantity based on the deviation value at the sampling time. The control quantity was output through analog output channel 1 and applied to the input of the simulated object for closed-loop control. A written display subroutine was then called to display the control results and parameters in real time. In summary, the first three experiments were both independent and interconnected. Through these experiments, students strengthened their understanding of the data acquisition process using the board, laying a foundation for applying industrial control computers to practical computer control system engineering.
2.4 Comprehensive Experimental Design
Industrial control computers have a wide range of applications in industrial control. They can be applied to systems such as motor control and temperature control, and also in distributed control systems that have emerged with the development of automation in modern large-scale industrial production and the increasing complexity of process control requirements. Because the actual application systems of industrial control computers in industrial production are usually quite complex, and experimental teaching time is very limited, it is unrealistic to design truly practical systems within the limited experimental teaching time. Therefore, comprehensive design experiments such as "Design of an Industrial Control Computer-Controlled DC Servo System," "Design of an Industrial Control Computer-Controlled Temperature Control System," and "Design of an Industrial Control Computer-Controlled Distributed Control System" are extracted from actual engineering application systems. These experiments not only demonstrate the advantages of industrial control computers and closely resemble the engineering realities that automation students will face in their future work, but can also be completed within a limited time. Through the comprehensive design experiments offered in the end-of-semester course design, students' understanding of the application of industrial control computers in practical engineering is enhanced, their engineering interest is cultivated, and their ability to comprehensively apply their knowledge to solve practical problems is improved. The comprehensive design experiments require multiple experimental topics. Each class is divided into several groups, with 2-3 students in each group. The boxes used in the first three experiments can mostly be directly reused in the comprehensive design experiment. This allows students to understand the engineering value of the previous experiments while reducing the time spent on the comprehensive experiment. Students are generally able to complete a comprehensive design experiment within the one-week course design period.
3. Development of the experimental apparatus
To meet the requirements of experimental teaching in the automation major, a computer control technology experimental device was developed. Simultaneously, based on the needs of the course design, several typical controlled objects were designed, such as a self-made DC generator and a soldering iron. The Advantech IPC-610L industrial control computer, manufactured by Advantech Corporation of Taiwan, is specifically designed for industrial control systems and is widely used in the industrial computer and automation market. Our department's computer control technology course selects industrial control computers as the teaching model; therefore, this experimental device was developed using an Advantech industrial control computer.
3.1 Guiding Principles of Research and Development
(1) Facilitates the implementation of comprehensive and design-oriented experiments. Design-oriented and comprehensive experiments are important means to improve students' innovative abilities. Computer-controlled technology experimental devices are multifunctional and have strong input and output interface functions, which facilitates the implementation of comprehensive and design-oriented experiments.
(2) Facilitates open-ended experimental teaching. The computer-controlled technology experimental device adopts a modular structure, which is easy to operate, safe, and facilitates the implementation of open-ended experimental teaching.
(3) Experimental teaching is geared towards engineering practice. Emphasis is placed on implementing the idea that experimental teaching is geared towards engineering practice. Based on the designed experimental teaching content, students understand the uses and methods of industrial control computers in their actual work after graduation, thereby cultivating students' engineering interest and improving the effectiveness of experimental teaching. The above guiding principles were established at the beginning of the development of the computer control technology experimental device. During the development process, after multiple improvements to the prototype, the final experimental device used for student experiments basically embodies these guiding principles.
3.2 Basic Functions of the Device
This experimental setup consists of an industrial control computer, UNIT1 to UNIT4 enclosures, and typical controlled object models. The industrial control computer is the core component of the setup, and it also contains two ISA interface boards, PCL-812PG and PCL-833. The PCL-812PG board is a comprehensive board with A/D, D/A, DI, and DO functions, and it is inserted into the ISA10 slot; the PCL-833 board is used to count the pulses of the photoelectric encoder and is inserted into the ISA7 slot.
Each unit from UNIT1 to UNIT4 can be easily detached by unplugging the rear connector. The units can be flexibly combined, are easy to operate, intuitive, and versatile. The UNIT1 panel consists of three parts: power control, signal source, and channel experiment. The signal source includes a noise source, a step signal source, and a mixing circuit. The noise source switches between pulse noise and uniform noise via a DIP switch on the printed circuit board inside the UNIT1 unit. The step signal source provides a DC output of -10 to 10V via a manually adjustable potentiometer, and a ping-pong switch controls the DC power supply to provide a step input signal. The mixing circuit is a two-way in-phase summing circuit. The channel experiment section includes 8 digital inputs, 8 digital outputs, 4 analog inputs, and 2 analog outputs.
The main function of the UNIT2 module is to conduct filtering experiments and digital PID algorithm experiments. It consists of three parts: an analog filtering circuit, a digital filtering circuit, and an analog object circuit. The analog filtering circuit diagram is shown in Figure 1.
Figure 1 Analog filter circuit diagram
The digital filter circuit in the UNIT2 enclosure is only a schematic diagram and does not contain an actual circuit. The schematic indicates that the filter input enters the industrial control computer via A/D channel 1, and the filter output is output from the industrial control computer via D/A channel 1. Both channels are connected to the I/O interface circuit. During the experiment, students simply need to insert the mixed signal into the designated A/D channel port to observe the filtering effect. The analog object circuit mainly consists of an operational amplifier and several capacitors and resistors. Students can select between first-order and second-order analog objects using the ping-pong switch on the UNIT2 enclosure panel. The circuit diagrams for each analog object are shown in Figure 2.
Figure 2 Schematic diagram of the simulated object
The transfer function of the simulated object corresponding to Figure 2 is:
UNIT3 is primarily used for motor position and speed control experiments, with an additional schematic diagram of a distributed control system. The motor control principle diagram is shown in Figure 3. Motor position control essentially involves constructing a position loop. The input pulse sequence and feedback pulse sequence generate a position error pulse sequence signal. This error pulse sequence signal is applied to the driver board, driving the DC servo motor to rotate at low speed and high torque using an H-type bipolar reversible PWM method to reach the desired position. In Figure 3, both the A/D and D/A converters are implemented using the PCL-812PG board. The pulse board is inserted into the PCL-833 board in the ISA10 slot of the industrial control computer. The driver board is located inside the UNIT3 enclosure; it is an H-type bipolar reversible PWM drive system. The incremental photoelectric encoder can output 1024 A-phase and B-phase pulses and 1 zero-position pulse per revolution, with a 90-degree phase difference between the A and B phase pulse signals. All three pulse signals are differential signals, input to the PCL833 pulse board for pulse counting. During the experiment, students can directly connect the given signal to the corresponding A/D channel on the UNIT1 panel. The industrial control computer outputs the control voltage through the D/A channel. When the control voltage is -10 to 10V, the armature voltage output by the driver board allows the speed of the self-made DC motor to vary within the range of -1500 to 1500 rpm. This design primarily considers that students are conducting computer control technology experiments, and the focus of training should be on mastering the control algorithm, minimizing the time students spend on other design and debugging tasks. The circuit diagram of the experimental setup is appended to the end of the experimental manual for students' reference.
Figure 3 Motor control principle diagram
The distributed control system experiment does not include actual circuitry within the UNIT3 enclosure. The distributed control system employs an industrial Ethernet card and a fieldbus based on the TCP/IP protocol. This fieldbus connects the host computer and the slave computers, forming the distributed control system. The slave computers exchange data with the host computer via a hub. The experimental software consists of two parts: the host computer displays the monitoring interface for the distributed control system, running in KingSCADA 6.5 software under Windows 2000; the slave computers serve as the field data acquisition interface, also running in the KingSCADA 6.5 environment.
The experimental structure diagram of the distributed control system is shown in Figure 4.
Figure 4. Experimental structure diagram of distributed control system
UNIT4 is primarily used for temperature control experiments and displaying the experimental setup. The ADAM4016 is a key component in temperature control. The ADAM4016 sends three switching signals to control three solid-state relays. These relays control the AC power supply to regulate the actual power of the heating element, which consists of three 20W soldering iron tips tightly bound together. The temperature sensor is a Pt100. The temperature signal is converted into a current signal by an integrated transmitter (0–200℃ corresponds to 4–20mA). The transmitter can also display the heating element temperature in real time. The experimental setup uses a Samsung 15-inch LCD screen to display the experimental results.
Figure 5 Temperature control principle diagram
To meet the needs of comprehensive design experiments, corresponding typical control object models were designed, such as self-made DC generators and heating elements. These control object models are similar to the system characteristics in actual engineering, only smaller in size and with simplified auxiliary circuits. During experiments, students can assemble different mounting boxes on the experimental setup as needed and connect these control objects to the computer control system through input/output channels.
The computer control technology experimental device, shown in Figure 6, has passed the evaluation of school experts. The experts unanimously agreed that the experimental device, with an industrial control computer as its core, adopts a modular structure and is designed according to the standards of actual industrial control systems. It is easy to use, offers rich experimental content, and helps improve students' hands-on skills, ability to use industrial control computers, and software programming skills. It comprehensively improves students' application level of computer control technology and provides a platform for teachers and graduate students to conduct scientific research and product development. Its comprehensive design concept is advanced and has reached the leading level in China.
Figure 6. Computer Control Technology Experimental Device
References:
[1] Lai Shouhong. Microcomputer Control Technology [M]. Beijing: Machinery Industry Press, 2000. 82-83.
[2] Xu Peiya, Zhang Xining. Reforming experimental content to improve teaching effectiveness [J]. Laboratory Research and Exploration, 1995, (4): 21-22.
[3] Zhang Hongjun, He Jianjun. Experimental device for computer network control system [J]. Automation Technology and Application, 2005, 24 (9): 54-57.
[4] Xiang Benxiang, Yu Shouyi. Experimental device for computer decoupling control system [J]. Microcomputer Information, 2005, 21 (1): 25-26, 38.
[5] Xue Yingcheng. Microcomputer control systems and their development trends [J]. Teaching and Management, 2005, (4): 91-92.
[6] Nie Zhigang, Liu Zhengdong. Comprehensive design experiments in experimental teaching [J]. Experimental Technology and Management, 2008, 25 (3): 140-141.
[7] He Jianqiang, Xue Yingcheng. Reform practice of teaching system of industrial control computer course [J]. Industrial Control Computer, 2006, 19 (12): 87-87, 78.
