Control Systems

Controller

A controller serves as the brain of a mechatronics system, connecting various electrical and electronic devices to mechanical components and facilitating system operation. Its primary function is to interpret input instructions from external sources and generate the necessary outputs to activate corresponding actuators. To successfully execute the given instructions, additional elements work in conjunction with the controller, enabling the triggering of actuators and the successful completion of the controller's instructions. Depending on the system and tasks to be performed, controllers can take different forms. In simple mechanisms, the entire system is controlled using basic electrical elements, without a separate dedicated controller device. However, relatively complex mechanisms often employ a separate Microcontroller Unit (MCU) as the controller. This MCU may also be embedded within a small mechatronics device. In more complex mechatronics systems where multiple mechanisms are harmoniously coordinated within a single structure, advanced controllers such as CNC controllers, computers, or programmable logic controllers (PLCs) are utilized.

Simple control system

In a modest mechatronics system, an uncomplicated control mechanism is assembled using standard electrical elements such as relays and contactors. This system operates based on the status of input devices and subsequently activates actuators. A detailed discussion about this system will be provided later in (Chapter- ) with an example.

Microcontroller Unit or MCU

A Microcontroller Unit or MCU is a single integrated circuit utilized for specific applications, automating device management. Various mechatronics systems such as automobile engine control, washing machines, toys, cameras, security systems, etc., frequently employ microcontroller units. Most MCUs are battery-operated and require minimal power for operation. Inside a microcontroller, you will find a small central processing unit (CPU), random access memory (RAM), programmable read-only memory (ROM), and different input-output ports (parallel and serial). Since a microcontroller unit is designed for a specific function within a distinct system, its size is typically small, and all the components are assembled within a single chip. Occasionally, a small LCD or seven-segment display unit with a keypad is attached to the MCU for information retrieval and direction input. The following picture displays a simple microcontroller and its fundamental structure.

When programming a microcontroller unit, the commonly used language is 'C'. The program is stored in the microcontroller's flash memory, and in most cases, it can be reprogrammed. The MCU has ports that control the connected output elements or actuators, which are selected to turn on or off through programming. It also receives signals from different sensors connected to the programmable ports of the microcontroller. The actuators connected to the output ports of the MCU are automatically controlled based on the signals received from the sensors and the programmed instructions. In many cases, this control can be achieved without any human intervention. Below is a block diagram illustrating the automated control mechanism of an automobile engine using a microcontroller or MCU.   

Multiple microcontrollers are used for various applications in mechatronics systems, and sometimes the same MCU can be used for two separate applications, requiring different programming. Standard microcontrollers can be classified into the following basic groups based on their fabrication and utilization:

Bit size: MCUs are divided into three categories based on their bit size - 8-bit, 16-bit, and 32-bit. An 8-bit microcontroller has an 8-bit data bus, while 16-bit and 32-bit microcontrollers have 16 and 32 data lines, respectively.

Memory capacity: Different memory modules such as RAM, ROM, EPROM, EEPROM, and Flash Memory are used to store data and programs inside an MCU. Some of these memory modules are embedded within the microcontroller, while others are external. The capacity for storing data inside the memory also varies among different MCUs.

Number of input/output pins: Microcontrollers are categorized based on the number of input or output pins connected to them. This refers to the number of programmable pins or the number of input/output devices that can be managed by an MCU.

 

Difference between microcontroller and microprocessor

A microprocessor is typically used with general-purpose CPUs or computers, whereas a microcontroller itself functions as a mini-computer to control multiple devices. Unlike a microprocessor, a microcontroller includes memory devices, input/output ports, timers, and other components. A microprocessor requires additional digital components to operate, while a microcontroller functions as a standalone unit. Microprocessor-based devices are usually more complex and expensive, whereas devices operated with a microcontroller are simpler and less expensive. It is easier to program most of the pins of a microcontroller, whereas only a few pins of microprocessors can be controlled through programming. Additionally, the access time of a microprocessor is typically higher than that of a microcontroller. In summary, a microcontroller interacts directly with various sensors and attachments, whereas a microprocessor connects input/output devices through an internal bus connection that integrates multiple hardware components such as RAM and serial ports. For example, a desktop computer commonly uses a microprocessor, while a washing machine is controlled by a microcontroller.

Advantages of microcontrollers include:

·         It functions as a standalone micro-computer without the need for external digital devices.

·         Mechatronics systems coupled with an MCU are relatively easy to manage and maintain.

·         The versatility of easily programmable MCU pins enables various practical operations.

·         The operating response time is relatively low.

·         Additional memory devices and input/output modules can be easily connected to it.

·         Microcontrollers are smaller in size and relatively cheaper.

Disadvantages of microcontrollers include:

·         The structure of an MCU is more complex compared to a microprocessor.

·         Microcontrollers are limited to specific purposes.

·         They cannot directly connect to power devices.

·         They are only suitable for use with small equipment.

How are microcontrollers programmed?

In earlier days, microcontroller units were programmed using 'Assembly language'. However, nowadays, various 'High-level' languages such as C or C++, Java, Oracle, etc., are also commonly used. One major advantage of using a high-level language is that it doesn't require extensive knowledge about the hardware inside the microcontroller. The program written in a high-level language is converted into a 'Hexadecimal format' using special software called a 'Compiler'. This hexadecimal format is readable by a microcontroller or MCU. Software tools like C Compiler and Code Editor are used to compile high-level language. Once the program is written in the hexadecimal format, it is transferred to the microcontroller and stored in the machine language instructions, which consist of 'Zeros' and 'Ones' inside the MCU's memory. The following picture illustrates the programming process of a microcontroller unit.

To program a microcontroller unit, the program is first written in a high-level language on a computer. Then, it is converted into a hexadecimal format using compiler software. Finally, the program is transferred to the microcontroller, where it is typically stored in a 'Flash Memory'. Once the program is stored in the microcontroller, it operates independently from an external programmer unit or computer. The microcontroller is then connected to the mechatronics system. When powered on, the MCU executes the instructions written in its program memory. The MCU includes output ports that can be adjusted to turn on or off through programming. These output ports control actuators connected to the system. The signals from different sensors related to the mechatronics system are accepted as input signals by the microcontroller through input ports. The program written in the MCU controls the output elements associated with the mechatronics system and analyzes the signals received from the sensors.

Advanced Mechatronics Controller

Advanced mechatronics controllers are used in various types of robotic systems, CNC machines, and complex material handling systems. These controllers can perform almost every task of a mechatronics system and have the ability to store multiple programs in their memory. The main advantage of using an advanced mechatronics controller over a microcontroller is that it allows for easy programming of complex movements and the addition of other devices or elements to the system. Advanced mechatronics controllers operate primarily through two types of instructions: programming stored inside the controller's memory and instructions from a control panel directly connected to the controller. These controllers are typically designed to work with two separate devices: a Programmable Logic Controller (PLC) and a Servo Amplifier. The PLC may be embedded inside the controller or operate as a separate unit externally. Servo drives or amplifiers provide significant voltage to a Servo Motor for controlling various movements, such as axis movements in CNC machines. The PLC and Servo drive mechanism together enables complex movements and tasks in advanced mechatronics systems. Some mechatronics systems use stepper motors instead of servo motors, and the movements of these systems are controlled by a stepper motor driver unit. The following picture presents the architecture of a typical advanced mechatronics system, highlighting a controller, PLC, Servo amplifier, and servo motor.

The voltage required to rotate the stepper motor or servo motor is provided by a stepper motor driver or servo amplifier, which is commanded by the controller to achieve controlled movements. The PLC plays a significant role in supplying the necessary voltage to different actuators for performing additional work in the mechatronics system. For example, activating solenoid valves or running induction motors. The PLC constantly monitors the completion of tasks and uses various sensors and feedback elements in the mechatronics system. Continuous feedback devices like Linear Scale, Encoder, and Resolver serve as position and velocity feedback elements for servo motors, precisely measuring position. Various sensors such as proximity switches, limit switches, pressure switches, and float switches are also used to monitor different occurrences in the mechatronics system, such as the status of machine doors, the position of workpieces, the clamping of cutting tools, and the functioning of cooling systems.

Components build an advanced mechatronics controller

Different companies offer controllers with varying hardware configurations based on the requirements of the mechatronics system. However, the basic working principles are similar. In some cases, a dedicated controller is used specifically for a particular mechatronics system. Popular controller manufacturers include SIEMENS, FANUC, MITSUBISHI, ABB, YASKAWA, HEIDENHAIN, and REXROTH, among others. FANUC and SIEMENS are market leaders in the machinery industry and have the highest sales of controllers. Depending on the design and type of controller, PLCs, motor driver units, etc., can be integrated in a common and enclosed arrangement or function as separate devices coordinated with the controller from outside. The following is a list of accessories incorporated into an advanced mechatronics system:

1. A central processing unit (CPU)
2. Servo control unit
3. Operator panel
4. Motor driver unit
5. Programmable logic controller (PLC)

1. Central Processing Unit (CPU)

The central processing unit (CPU) is the controller's heart and brain. It controls and supervises the entire mechatronics system and manages crucial program information stored in the controller's memory. It decodes this information to obtain signals for specific position and velocity settings, particularly for axis movements. With complete control over the position and velocity of moving elements, such as a machine axis, the CPU constantly compares them to the programmed values. If a discrepancy occurs, the CPU takes immediate corrective measures. It also performs basic security checks and initiates remedial actions as necessary. In situations exceeding the CPU's capabilities, it decides to shut down the machine or system.

 2. Servo control unit

The CPU generates signals for position and velocity control, which serve as input command signals for the servo control unit. The servo control unit, in turn, generates suitable signals for each movement command and directly sends them to the servo drive or amplifier unit. The servo drive produces the voltage required to rotate the servo motors. Additionally, the servo control unit receives actual position signals from position feedback devices like encoders or linear scales, which are integrated with the servo motors. The feedback signal is then sent back to the CPU for further processing. Essentially, the servo control unit facilitates dual communication between the moving elements and the CPU through command and feedback. While the motor driver unit is responsible for the actual movement of a device, the rate of movement depends on the feedback system.

 3. Operator panel

The operator panel serves as a two-way communication system between the user and the machine/system. It typically consists of two main components: a video display unit and a keyboard. The video display unit provides real-time information and displays the current status of the machine or system. The keyboard is used to input different programs into the machine and select separate operating modes. Occasionally, an operator panel may lack a video display unit. Below are pictures of two operator panels frequently used with CNC machines in the machining industry, manufactured by SIEMENS and FANUC.

4. Motor driver unit

A motor driver unit is an essential component in a mechatronics system, responsible for controlling various mechanisms. For controlled movements, two types of motors are commonly used: stepper motors and servo motors. Stepper motor driver units are employed for running stepper motors, while servo motors are rotated using servo drives or amplifiers. To rotate a stepper motor, the motor driver unit generates specific voltage pulses, which rotate the motor shaft by a specific angle and provide the required torque. On the other hand, a servo amplifier produces pulse-width modulated (PWM) voltage to rotate the servo motor shaft. For a detailed explanation of the working principles of servo motors and stepper motors, please refer to the "Actuator" chapter. Below are pictures illustrating a stepper motor driver unit and a servo amplifier.

5. Programmable Logic Controller or PLC

PLCs are widely used in various advanced mechatronics systems, such as the machine tool industry, elevators, process control, and traffic light control. PLCs are typically designed by manufacturing companies with standard hardware, customizable according to specific requirements. PLCs have replaced complex relay logic circuits, offering greater versatility and easy programmability, making them compatible with modern mechatronics systems. They also facilitate more flexible circuit design changes. PLCs are usually embedded within advanced controllers and cannot be distinguished independently from the outside. However, they can also function as stand-alone units, coordinating with the controller when operating as separate devices external to the controller. PLCs supervise and sequence complex mechanisms based on the program written inside them. Further details about PLCs are discussed in a separate part of this book. Below is a picture of a stand-alone PLC coordinating with the controller.

Introduction of Arduino

Nowadays, Arduino boards are commonly used in various electronics projects and mechatronics systems. Arduino is a brand name for an open hardware advanced microcontroller that can be easily programmed externally. This means that the same Arduino board can be utilized in different projects or mechatronics systems. Different models of Arduino boards are available to cater to different system requirements, with Arduino UNO being the most popular. Arduino UNO is easy to program and operate, and it is frequently used in small mechatronics projects. The following picture shows an Arduino UNO board with multiple terminals connected to it. 

How Arduino works: The basic operating system of an Arduino board is similar to a microcontroller board. As shown in the earlier picture, an Arduino UNO board consists of different ports/terminals that connect various external components. The board is supplied with voltage through a power connector, which also powers the elements connected to it, such as sensors and LEDs. Depending on the system requirements, different sensors are used in mechatronics systems, including general switches, proximity switches, magnetic sensors, etc. These sensors are connected to input pin terminals and specified in the programming. The output pin terminals of the board are connected to various output elements like lamps, motors, actuators, etc. These output pin terminals are also controlled through programming. Additionally, analog sensors like temperature sensors, light sensors, humidity sensors, etc. can also be connected to an Arduino board. Input and output pin terminals and their logical applications or operations are defined using special instructions within a program. Depending on the status of the input pins, the status of the output pins can automatically change. This means that devices connected to output pins are activated or deactivated based on the input pin status. The board includes a USB connector that allows an external computer to download or upload programs to the microcontroller chip inside the board. Additionally, Arduino boards contain various small components like oscillators and voltage regulators.

Advantages of using Arduino: There are several advantages to using Arduino boards. They are cost-effective and can be easily utilized in different electronics projects. The Arduino software, known as Arduino IDE, is versatile and compatible with different operating systems such as Windows, Macintosh, and Linux. Arduino IDE uses a simplified language, making it suitable for beginners as well as advanced users for complex programming. Since Arduino IDE is an open-source tool, experienced programmers can easily extend its functionalities through C++ programming. Arduino boards also offer extensible hardware, allowing experienced circuit designers to modify the board's hardware.

Programming an Arduino: As mentioned earlier, Arduino boards are programmed using software called Arduino IDE, which is an open-source program. The IDE provides a special environment with syntax highlighting and other features to make coding easier. Arduino programming is typically based on processing programming and includes different instructions such as "and" and "if" for programming the board. Below is a simple example that demonstrates how programming is written for an Arduino board.

Blinking LED program

The following picture illustrates a simple circuit for creating a blinking LED using an Arduino board. In this circuit, the LED's positive terminal is connected to the digital output port "PIN 10," and the negative terminal is connected to the ground.

To make the LED blink, we will turn it on and off for a duration of 1 second. By setting the status of PIN 10 to high or low, the LED will blink accordingly. The program instructions for blinking an LED are provided below. 

What is Raspberry Pi?

Raspberry Pi is a low-cost, credit card-sized single-board computer. It can be used as a regular computer by connecting it to a monitor, keyboard, mouse, etc. Raspberry Pi is also commonly used in gaming systems, small robotic systems, and as a controller for various mechatronics systems. Unlike other controllers used in mechatronics systems, Raspberry Pi integrates multiple components and ports into a single board, making it highly adaptable. The following picture shows a Raspberry Pi board with different integrated ports.   

A Raspberry Pi board features various ports, including USB, HDMI, Ethernet, etc. These ports allow connection with different peripherals and devices. USB ports can be used to connect peripherals such as keyboards, digital cameras, and flash drives. The Ethernet port enables a wired connection to a computer network using an RJ45 connector. An audio jack can be used for better sound by connecting amplified speakers. The camera connector, also known as the Camera Serial Interface (CSI), is used to connect a specially designed Raspberry Pi camera module. The HDMI port can carry audio and video signals to display devices like computer monitors, TVs, or projectors. The Display Serial Interface (DSI) connector is used to interface a specially designed Raspberry Pi Touch Display. GPIO (general-purpose input/output) is a connector with 40 metal pins, split into two rows of 20. Through GPIO, additional hardware and elements such as LEDs, switches, temperature sensors, joysticks, and pulse-rate monitors can be connected. To operate, a Raspberry Pi requires peripheral devices such as a Micro SD card for storage, a monitor for displaying activities, a keyboard, a mouse for giving commands, and a 5-volt DC power supply.

Before using Raspberry Pi, it needs to be equipped with special software, including its operating system. The software can be installed via a Micro SD card or downloaded from the Internet. Raspberry Pi supports a wide range of software, including various operating systems. The official operating system of the Raspberry Pi Foundation, called "Raspbian," is the most popular choice. Raspberry Pi is not limited to using pre-existing software; it also provides the capability to create its own programming or coding. It serves as a powerful and fully functional programming tool for creating games, animations, operating mechatronics systems, and even complex robotics projects.