Actuators

An actuator is responsible for moving and controlling a mechanism or system by converting energy into motion. Examples include rotating a motor or opening a valve. When an actuator receives a controlling signal, it converts the energy source into mechanical motion. In mechatronics systems, actuators enable various mechanical actions. There are two main types of actuators based on the type of movement: linear actuators, which move in a straight path, and rotary actuators, which provide rotating motion. Actuators can also be classified into three categories based on the type of energy used for motion conversion: electrically operated, hydraulically operated, and pneumatically operated. The chart below shows the categorization of different actuators.

Electrically operated actuator

Electrically operated actuators are typically represented by various types of motors. In mechatronics systems, electrically operated actuators interact with other devices associated with different mechanisms. The following is a brief list of different actuators: 

a) AC and DC motors
b) Servo motors
c) Stepper motors
d) Electric Linear Actuator or ELAs
e) Solenoid valve coils
f) Electromagnetic brakes

a) AC and DC motor

Different AC or DC motors are used in mechatronics systems depending on the system requirements. AC motors are generally preferred over DC motors due to the absence of commutation processes and carbon brushes. AC motors are available in single-phase or three-phase configurations, while DC motors are typically single-phase. Three-phase AC motors are self-starting, while single-phase AC motors require starting torque. DC motors are also self-starting. Despite the challenges, small DC motors are still used in certain applications because they provide higher starting torque compared to AC motors, and miniaturizing AC motors can be inconvenient. 3-phase induction motors of various capacities are commonly used in different machinery and mechatronics systems. The following pictures show a DC motor and an AC 3-phase induction motor.

b) Servo motor

Servo motors are special electromechanical devices used for precise and controlled movements in mechatronics systems, as well as for rotating objects at controlled speeds. These motors deliver high torque, operate at maximum efficiency with low current consumption, and are smaller in size. Servo motors are typically driven by a specialized unit called a servo drive or servo amplifier. Both DC and AC servo amplifiers can be used in mechatronics systems. Servo motors are also known as control motors because they control mechanical systems and operate on a closed-loop servo system. Earlier mechatronics systems utilized both DC and AC servo motors, but currently, AC servo motors are predominantly used due to their added advantages over DC motors. The following picture shows an AC servo motor and its interior.

A feedback sensor is always used with a servo motor. Commonly employed feedback sensors include an encoder, Inductosyn, and Resolver. In the past, servo motors used separate sensors, with encoders for position feedback and tacho generators for velocity feedback. However, encoders, resolvers, and Inductosyns can provide both position and velocity feedback as a single feedback device for servo motors. Sometimes, a braking arrangement is also incorporated inside a servo motor. The operating principle of a servo motor is explained in a separate chapter.

c) Stepper motor

A stepper motor is a brushless synchronous motor that divides a 360-degree shaft movement into multiple steps and allows accurate control of the motor shaft's speed. The name "stepper motor" comes from the fact that each electrical pulse causes a step movement of the motor shaft. Similar to a servo motor, a stepper motor is driven by a driver unit that generates the necessary electrical pulses to rotate the motor shaft. The speed of a stepper motor typically depends on the frequency of the electrical pulses. The following picture shows a stepper motor and its interior. 

Stepper motors are usually classified into three types: variable reluctance, permanent magnet, and hybrid stepper motors. These motors consist of a magnetic or toothed soft iron rotor that rotates within an electromagnetic field (see the picture). When the stators are energized by a motor driver unit, a torque is generated and applied to the rotor, causing it to start rotating while maintaining a minimum gap between the stator coils and rotor teeth or magnetic poles. If the stator coils are energized in a fixed sequence, continuous rotary movement is obtained in the stepper motor shaft. This phenomenon can be explained with the following pictures, where A-A', B-B', C-C', and D-D' coils are successively energized (dark color signifies coil excitation). As a result, the motor shaft rotates in steps of 15 degrees.

d) Electric Linear Actuator or ELA

An electric linear actuator (ELA) is typically powered by a 12V DC motor (although other types of motors can also be used) and consists of a lead-screw and nut system with a gear assembly. The rotation of the lead-screw causes linear movement on a shaft attached to the nut assembly. Compared to hydraulic or pneumatic linear actuators, electric linear actuators have the advantage of a compact design and do not require valves, pumps, pressure lines, etc., to achieve linear movement. The image below depicts an electric linear actuator.

ELAs serve various functions in mechatronics systems, with the stroke length usually dependent on the length of the lead screw. Clockwise and anticlockwise movements of the motor drive the extended or retracting movement of the shaft in the ELA. Small snap switches are typically placed inside an ELA to terminate the motor supply when it reaches both ends.

e) Solenoid valve coil

A solenoid valve coil is an electromagnetic actuator that directs hydraulic or pneumatic pressure lines when electrical power is applied. Usually, the coil is made of insulated copper wire wrapped around a hollow cylinder, creating a magnetic field inside the cylinder when an electric current passes through it. The coil is attached to a solenoid valve (hydraulic or pneumatic) in a way that a Ferro-magnetic core inside the solenoid valve, known as the Valve Plunger, fits correctly into the cylindrical part.

When a magnetic field is generated inside the cylinder, the valve plunger becomes an electromagnet and moves outward, opening an orifice inside the valve to influence the pressure line in a specific direction. Solenoid valve coils come in two different types based on actuating voltage: DC and AC voltage type. Commonly used voltages are 24V DC, 110V AC, and 220/240V AC for different mechatronics systems. Pneumatic solenoid valves typically use 24V DC coils, while hydraulic valves use 110/220V AC coils. The image below shows a 24V DC pneumatic solenoid valve in its energized and de-energized states.

f) Electromagnetic brake

Mechatronics systems use electromagnetic brakes to stall or delay the movement of electrically operated actuators. These brakes create mechanical friction or resistance through an electromagnetic force, earning them the name "electromagnetic brakes." There are different types of electromagnetic brakes, and one common type is the electrical power-off brake, which is typically fitted to a motor's shaft.

The electrical power-off brake consists of a strong permanent magnet and an electromagnetic coil attached to the motor body. A friction disk is coupled with the motor shaft, along with springs to create balance. In a normal situation, the friction plate is rigidly fastened to the permanent magnet, preventing movement of the motor shaft. When voltage is applied to the brake coil, the electromagnet neutralizes the magnetic fluxes of the permanent magnet, loosening the friction plate from spring tension. This allows the motor shaft to rotate freely. If the supply voltage is withdrawn from the braking coil, the friction plate re-attaches to the permanent magnet, halting the movement of the motor shaft. The electromagnetic brake can be energized along with the motor coil supply and de-energized by turning off the motor supply voltage. The image below illustrates a typical electromagnetic braking system commonly used with induction motors.

Hydraulic operated actuator

Hydraulic actuators convert pressurized hydraulic fluid energy into mechanical motion. A typical hydraulic system consists of a hydraulic pump driven by an induction motor, generating pressurized hydraulic fluid that passes through various valves to operate different hydraulic actuators. Hydraulic actuators perform mechanical functions such as blocking, clamping, ejecting, and power transmissions. In mechatronics systems, multiple tasks are accomplished using various hydraulically operated actuators. The functioning of a hydraulic actuator depends on factors such as hydraulic fluid pressure, flow rate, and pressure drop within the actuator. There are two basic types of hydraulic actuators: linear actuators and rotary actuators.

a) Linear hydraulic actuator

A linear actuator is used to transfer or displace an element in a straight line. The displacement depends on the stroke length of the actuator. A hydraulic cylinder is the most commonly used linear actuator in machinery. It is usually made of steel to withstand high hydraulic pressures. The movement is exerted by a piston rod inside the hydraulic cylinder, driven by pressurized fluid. The piston rod is connected to an external load and produces a pulling or pushing force in a straight line. Hydraulic cylinders are mainly categorized into two types: single-acting and double-acting cylinders.

Single-acting cylinder: A single-acting cylinder consists of a cylindrical housing, also known as a barrel, with a piston placed inside (refer to the picture below). The piston is connected to a solid rod, allowing it to move back and forth. To prevent pressurized fluid from entering the upper part of the cylinder, a rubberized piston seal is placed near the piston's diameter. The cylindrical housing features a pressure port on the side opposite to the rod and piston, enabling the entry or exit of pressurized fluid into the cylinder. The piston in the cylinder moves in only one direction due to the pressurized fluid, while a spring tension helps return the piston to its initial position. Please refer to the schematic diagram below to visualize a single-acting cylinder.

In the front of the cylindrical housing, there is a small port called the Vent port, which serves to release the accumulated air from the upper part of the cylinder into the atmosphere. The incoming pressure line, controlled by a valve, pushes the cylinder piston outward and also returns the fluid to the tank when the piston retracts. This means that the hydraulic fluid accumulated in the lower part of the cylinder's piston is also returned to the hydraulic tank through the control valve. Single-acting cylinders come in two varieties: Push-type and Pull-type. The basic function of these two cylinders is the same, with the only difference being the position of the Pressure port and Vent port, which are located in opposite directions (refer to the pictures below).

Double-acting cylinder: A double-acting cylinder operates similarly to a single-acting cylinder in terms of piston movement. However, it incorporates an additional pressure line for the reverse movement of the cylinder piston instead of relying on a spring action. As a result, a double-acting cylinder possesses two separate pressure ports at the top and bottom of the cylinder, allowing the piston to be actuated in both directions (see the picture below).

Double-acting cylinders are further categorized into two types: one with a piston rod on one side and another with a piston rod on both sides. This means that the piston can be located on either side of the cylinder or on both sides. In most cases, a double-acting cylinder with a one-sided piston rod is used in mechatronics systems and specific applications, while a double-acting cylinder with a piston rod on both sides is more commonly seen. The image below illustrates a double-acting hydraulic cylinder with a piston rod on one side, commonly found in various mechanisms for linear movement.

b) Rotary hydraulic actuator

When high torque and heavy-duty rotary motions are required in a mechatronics system, a hydraulic rotary actuator is preferable over an induction motor. Hydraulic actuators are more efficient for shifting, rotating, or indexing heavy loads. There are two types of hydraulic rotary actuators: limited movement rotary actuators and continuous movement rotary actuators, also known as hydro-motors.

Limited movement rotary actuators come in various types, including rack and pinion, crank-lever, vane, parallel piston, etc., depending on the specific movement and application. The images below illustrate a rack and pinion type and a vane type of limited movement hydraulic rotary actuator, commonly used in different mechatronics systems.

For applications requiring slow and continuous rotary motion of heavy loads, a continuous movement hydraulic rotary actuator or hydro-motor is typically employed. Hydro-motors offer advantages over induction motors in terms of size, as they are smaller while performing the same work. Different types of hydro-motors are available, including gear, piston, and vane types. The image below shows a vane-type hydro-motor commonly found in various mechatronics systems.

Pneumatic operated actuator

A pneumatic actuator converts compressed air energy into mechanical motion. When a gaseous substance like air is compressed, its volume decreases, causing an increase in pressure. This enhanced pressure can be utilized to perform various mechanical tasks. Compressed air can be stored in a reservoir for later use. Pneumatic actuators are used in applications such as automatic machine door opening and closing, and arm movement of cutting tools. Pneumatic actuators are designed to handle light loads, typically between 5 to 7 kg of pneumatic pressure. To handle larger loads, a pneumatic actuator requires a cylinder piston with a bigger diameter. The body of a pneumatic cylinder is usually made of aluminum or its alloy, which makes it lighter compared to a hydraulic cylinder. Pneumatic actuators can be either linear or rotary, similar to hydraulic actuators.

a) Pneumatic linear actuator

Pneumatic linear actuators refer to a range of pneumatic cylinders. Pneumatic cylinders come in different types and structures depending on their function. Since compressed air pressure is lower than hydraulic pressure, the mechanical power available with a pneumatic cylinder is also less. Therefore, the structure of a pneumatic cylinder is lighter compared to a hydraulic cylinder. If the same amount of work is performed using a pneumatic cylinder instead of a hydraulic cylinder, the barrel diameter of the pneumatic cylinder will be larger. Pneumatic cylinders are more convenient to use in mechatronics systems. However, when a steady force is required or when dealing with fluctuating loads, a hydraulic cylinder is preferable over a pneumatic cylinder. The following picture shows a pneumatic cylinder and its interior, commonly used in mechatronics systems.

The response time of a pneumatic cylinder is instantaneous, but it also has some disadvantages. When the cylinder completes its stroke, the piston thrusts extensively against the end covers of the cylinder, which can lead to damage. To overcome this problem, most pneumatic cylinders are equipped with a cushioning system. The cushioning system reduces the piston movement when it strikes the cylinder edge. Pneumatic cylinders have two types of cushioning systems: fixed type and adjustable type cushioning. The fixed cushioning system is commonly found in lower-diameter pneumatic cylinders, while the adjustable cushioning system is used when the cylinder piston speed is higher. Different types of cylinders are usually found in various mechatronics systems.

• Single-acting pneumatic cylinder
• Double-acting pneumatic cylinder
• Rodless pneumatic cylinder

Single-acting Pneumatic Cylinder - The functioning of a single-acting pneumatic cylinder is similar to a single-acting hydraulic cylinder. It consists of a piston placed inside a cylindrical barrel with a rod attached to it, allowing it to move with the piston. The displacement of the cylinder's piston is achieved by air pressure and retracted by compression or expansion of spring tension. These cylinders also have a fixed or adjustable cushioning system. Like hydraulic cylinders, pneumatic single-acting cylinders are available in two varieties: push-type and pull-type. The following picture shows a push-type single-acting pneumatic cylinder.

Double-acting Pneumatic Cylinder - Double-acting pneumatic cylinders function similarly to hydraulic cylinders. They can have a piston rod on one side or on both sides. Both types of cylinders are equipped with a cushioning system. The following pictures show both types of double-acting pneumatic cylinders. 

Rodless Pneumatic Cylinder - The function of a rodless pneumatic cylinder differs from that of a basic cylinder. In this type of cylinder, there is no piston rod connected to the cylinder piston. Instead, the piston is coupled with an outer load-carrying cartridge through a magnetic or mechanical coupling. Rodless pneumatic cylinders come in three types: cable cylinder, sealing band cylinder with a slotted cylinder barrel, and magnetically coupled slide cylinder. Among them, sealing bands and magnetically coupled cylinders are commonly used in mechatronics systems. The following pictures show a magnetically coupled rodless pneumatic cylinder and its interior. 

b) Pneumatic rotary actuator

A pneumatic rotary actuator utilizes pneumatic energy or air pressure to achieve rotary movement. Pneumatic rotary actuators are available in two types: continuous rotary movement and limited rotary movement. A continuous rotary motion pneumatic actuator is sometimes referred to as a pneumatic motor. This motor delivers constant rotary motion by utilizing a pneumatic pressure line. According to their structure and working principles, pneumatic motors can be categorized into three types: piston motor, sliding vane motor, and gear motor. The following picture shows a sliding vane pneumatic motor.

A limited movement pneumatic rotary actuator allows for higher torque. The standard rotations of these actuators are usually 90°, 180°, and 270°. There are three types of rotary actuators available: vane type, rack & pinion type, and helix spine type pneumatic rotary actuator. The following pictures show a rack & pinion type limited movement rotary actuator. 

Continuous measuring equipment

Continuous measuring equipment is a specialized tool used to precisely measure linear or angular position, displacement, and sometimes speed and other parameters in a mechatronics system. These measuring tools continuously provide real-time position information of a moving object in the form of an electrical signal to the controller. Measuring equipment can be classified into two primary groups: rotary measuring tools (such as encoders, resolvers, and tacho generators) and linear measuring tools (such as Linear Scales and Inductosyns). The basic function of these measuring devices is to create a constant electronic signal and transmit it to the controller. The following are some commonly used measuring devices or equipment found in various mechatronics systems.

Optical Encoder

The optical encoder is the most commonly used rotary measuring device in mechatronics systems. It is used to measure the position and speed of various elements, such as the location of an axis or spindle speed feedback in CNC machines. Typically, the encoder is integrated inside a servomotor and connected to the motor shaft through a coupling. Alternatively, it can be attached separately to a ball screw or coupled to a spindle unit using a timing belt. Inside the optical encoder, a graduated glass disc is attached to the shaft, which is fixed to the encoder body flange with preloaded ball bearings. The glass disc can rotate freely along with the shaft. The disc is designed with opaque and transparent sections. Photo-electric cells and light sources are positioned on either side of the glass disc in a way that allows the light to pass through and strike the photo-electric cells.

As the servo motor shaft or ball screw rotates, the glass disc attached to the encoder's shaft also rotates. This is because the encoder shaft is affixed to the motor shaft or ball screw. The transparent and opaque sections of the glass disc cause the emitted light from the light source to intermittently reach or miss the photo-electric cells. The output signal from the photo-electric cell is then passed through an electronic circuit, which converts the sinusoidal signal into a rectangular waveform. This waveform is transmitted to the controller via a signal cable. There are two types of optical encoders commonly used in mechatronics systems: the incremental rotary encoder and the absolute rotary encoder. The image below depicts an optical encoder that is widely used in mechatronics systems.

Incremental rotary encoder

The concept of incremental measurement involves computation through counting. In the case of an incremental rotary encoder, its output signal is directed to an electronic counter located inside the Controller. This counter keeps track of each increment in the encoder's output signal, providing a comprehensive measurement. The following diagram illustrates the functioning of an incremental rotary encoder.

The primary distinction between an incremental rotary encoder and an absolute rotary encoder lies in the structure of the graduated glass disk contained within the encoder. As depicted in the preceding diagram, the graduations on the glass disk of an incremental encoder are marked radially, ranging from 200 to 18000 PPR (parts per revolution). The PPR value signifies the number of pulses generated by the encoder as the shaft completes a 360-degree rotation, depending on the markings on the glass disk. Additionally, a reference mark is present in a specific location on the graduated glass disk, serving as the starting point for measurement counting.

Absolute rotary encoder

The working principle of an absolute rotary encoder is similar to that of an incremental rotary encoder. However, the construction of the glass disc differs. In an absolute encoder, multiple tracks are formed on the glass disc instead of a single track as in the incremental encoder. Each track has transparent and opaque sections arranged in a unique pattern. The signals received from the photo-electric cells create a unique pattern for each specific position of the encoder shaft. The signals from different positions of the encoder shaft are commonly expressed using Binary or Gray code. The image below illustrates the structure of a glass disc in an absolute rotary encoder.

Magnetic Encoder

In situations where using an optical encoder with a glass disc is inconvenient, such as in environments with vibration, extreme heat, or humidity, a magnetic encoder is used. The magnetic encoder operates using Hall Effect technology and provides accurate feedback even in harsh conditions. Both rotary and linear types of magnetic encoders are used in mechatronics systems. The images below depict two types of magnetic encoders.

A magnetic rotary encoder consists of three main components: a magnetic disk, a sensor, and a conditioning circuit. The encoder disk is designed with tiny magnetic poles arranged alternately along the circumference. When the disk rotates, a sensor inside the sensing head detects changes in the magnetic field and converts them into a sine wave signal. The sensor used is typically a Hall Effect device or sometimes a Magneto-resistive element. The signals from the sensor pass through a conditioning circuit to make them understandable to the mechatronics controller. The sensor and conditioning circuit are usually housed inside the sensing head and connected to the controller with a signal cable. The working principle of a linear magnetic encoder is similar to that of a rotary magnetic encoder, but a magnetic tape is used instead of a magnetic disk. The magnetic tape is magnetized with alternating poles along its length.

Linear Scale

A linear scale, also known as a linear encoder, precisely measures the linear displacement of an object, such as the linear axis movements of a CNC machine. In CNC machines, a linear scale is typically installed along with the machine's slide to provide accurate and precise position measurement compared to an encoder, which is usually fitted with a motor encoder. Backlash is always present when there is a conversion from linear displacement to rotary movements, such as with a motor. Therefore, a linear scale offers better accuracy than an encoder. The image below illustrates a linear scale and its internal components.

A linear scale consists of two separate parts: the glass scale and the reading head. One of these components (either the glass scale or the reading head) is affixed to a moving body, while the other remains stationary. The glass scale features alternate gratings, similar to an encoder's glass scale, with transparent and opaque sections. The reading head, like an encoder, contains a light source, lens, scanning reticle, and photoelectric cells assembled inside it (as seen in the previous image). When the reading head moves over the glass scale, the transparent and opaque grating parts on the scale align alternately with a scanning reticle index. This alignment causes the light passing through the lens to reach the scanning reticle and glass scale, ultimately reaching the photoelectric cells. Consequently, the light fluctuates alternately over the photoelectric cells, generating a sinusoidal signal based on these fluctuations. The sinusoidal signal output from the photoelectric cells is converted into a rectangular waveform using an electronic circuit inside the reading head. Finally, it is transmitted to the controller through a flexible cable.

Resolver

A resolver is a rotary measuring device that is attached to a motor shaft. It provides position and velocity feedback for a rotating device. A resolver consists of two stator windings and a rotor winding. The stator windings are typically wound in a manner that creates a 90° phase shift between them. The rotor winding and stator windings are integrated within the resolver, functioning as primary and secondary windings of a transformer. If a sinusoidal signal is passed through the stator windings (with a 90-degree phase shift), a sinusoidal signal is also induced in the rotor winding. As the rotor shaft rotates, the output signal changes based on the reference signal, and the magnitude of the output signal depends on the extent of rotation of the resolver shaft. The phase of the output signal changes from 0° to 360° when the resolver shaft rotates continuously. Since controllers only recognize digital information, the resolver's output signal is usually converted into a digital signal before being sent to the controller. The image below illustrates a resolver.  

Tachogenerator

A tachogenerator is a rotary measuring device used to obtain speed feedback from a rotating element. It was commonly used in earlier mechatronic systems, but with advancements in technology, it has become almost obsolete, as optical encoders now provide both speed and positional feedback. A tachogenerator is a simple permanent magnet DC generator typically installed on the same shaft as a servomotor or a rotating object. It generates a DC voltage, which serves as the signal output. The analog DC voltage generated varies with the motor's RPM, and a controller retrieves information about the motor's speed or RPM by measuring the analog voltage from the tachogenerator. The image below displays a simple DC tachogenerator.

Inductosyn

Inductosyn is an analog type of precision measuring equipment and can be considered one of the world's most accurate position-measuring devices. It comes in two main types: linear and rotary. Both types consist of two non-contacting elements. In the case of linear Inductosyn, these elements are a scale and a slider, while for the rotary type, they are a rotor and a stator. Inductosyn is commonly used for high-accuracy measurement and functions reliably even in harsh environments. One significant advantage of using a linear Inductosyn over a linear scale is that the scale can be easily expanded and is suitable for measuring long distances. The following images illustrate linear and rotary Inductosyn devices.

The operating principle of an Inductosyn is similar to that of a multi-pole wire-wound resolver. A resolver operates as a rotating transformer with two windings, while in a rotary Inductosyn, the windings are in the form of printed circuit patterns on the rotor and the stator. An AC signal is applied as excitation to the winding on the rotor element, and the current flowing through the rotor induces a current in the stator winding. The output amplitude varies cyclically as the rotor rotates relative to the stator, producing the signal output. The output signal is then amplified and transmitted to an analog-to-digital converter circuit to obtain a suitable signal for the controller.

A linear Inductosyn can be considered a resolver that has been unwound onto a flat surface. In this analogy, the stator of a resolver corresponds to the scale of a linear Inductosyn, while the rotor corresponds to the slider. The linear Inductosyn scale is typically attached to the machine bed, and the slider is fitted to the moving element. The slider moves over the scale, maintaining a small gap (usually 200 microns). Similar to a resolver, the slider of an Inductosyn contains two windings, and a sinusoidal voltage is applied to these windings with a 90-degree phase difference. This voltage induces a voltage in the winding across the slider. The induced voltage within the slider changes with the slider's movements, which is considered as the signal. The induced voltage has a very low value (microvolts), so a suitable pre-amplifier is always used with an Inductosyn to amplify this voltage. This allows the signals from the Inductosyn to be directly interfaced with the controller.

Motion Control & Controlling of Elements

Motion Control with Mechatronics

Motion Control is the integration of mechanical mechanisms with electronics or electrical components, along with a control system. The mechanism being controlled is purely mechanical, while the control system typically consists of electronic or electrical elements. In simpler terms, motion control in a mechatronics system involves managing the supply voltage provided to an electrical or electronic device to control a particular mechanism. These mechanisms can be operated or driven by hydraulic or pneumatic systems, as well as servo drives and motors. In some cases, a controller is used, and occasionally a PLC (Programmable Logic Controller) is employed for control. This article will discuss various movements and support functions associated with mechatronics systems.

Different Types of Movements

Comprehensive control over various movements is required in any automated system. Mechatronics systems primarily involve three types of movements: controlled movement, preset movement, and continuous rotary movement.

Controlled Movement Controlled movement involves precise position control, such as the movement of a robotic arm or the axes movements of a CNC machine. Stepper motors or servo motors are commonly used to achieve controlled movement in mechatronics systems. These motors ensure accurate and controlled movement within fine tolerances.

Preset Movement Preset movement refers to a mechanism that moves or shifts a certain distance along a predefined path. Examples of preset movements include automatic door open/close systems in machines or the clamp/de-clamp mechanism of a material-collecting robotic arm. These movements are typically executed using hydraulic or pneumatic cylinders.

Continuous Rotary Movement Continuous rotary movement is observed in mechanisms like the spindle and tool magazine movements of CNC machines. This type of movement is usually achieved using AC or DC motors, sometimes assisted by pneumatic or hydraulic systems.

The image below illustrates multiple movements of a robotic arm, where servo motors are employed for different controlled movements, and a hydraulic cylinder is used for the material clamping system.

Types of Movements in Mechatronics Systems:

1. Controlled Movement

• Linear Controlled Movement
• Rotary Controlled Movement

2. Limited Movement

• Limited Linear Movement
• Limited Rotary Movement

3. Continuous rotary movement

1. Controlled Movement

Controlled movements are commonly found in mechatronics systems, such as the axes movements in CNC machines, arm movements in robotic systems, and material handling systems. These movements are often accomplished using stepper motors or servo motors. The controlled movement aims to establish precise movement paths with accurate measurements and the ability to stop at specific distances as required. In mechatronics systems, controlled movement can be categorized into two types: linear controlled movement and rotary controlled movement.

Linear-controlled movement involves the straight-line movement of an element or equipment, while rotary-controlled movement positions the element along a circular path. Ball-screw and nut systems are commonly used for controlled linear movements, while worm and worm wheel systems are used for controlled rotary movements. Refer to the images below for illustrations of controlled linear and rotary movements commonly found in mechatronics systems. 

In the image on the left, a ball screw is coupled with a motor shaft to achieve linear movement. When the motor shaft (servo or stepper motor) rotates, the ball screw also revolves, causing the connected "Bed" to move in a linear or straight line. Precise control of the motor shaft displacement enables accurate linear movement of the bed. This means that the linear controlled movement in a mechatronics system is achieved by controlling the servo or stepper motor shafts. The image on the right shows a similar setup, but with a worm shaft connected to the motor shaft, resulting in the rotary motion of the worm wheel. By controlling the position of the motor shaft precisely, the rotary movement of the wheel can also be controlled accurately. Chapter VII of this document discusses in detail the use of ball-screw and worm and worm wheel systems for linear and rotary movements.

Controlled movement in mechatronics systems can be further classified into two groups: open-loop systems and closed-loop systems. Open-loop systems are rarely used because they lack feedback devices. In an open-loop system, the controller sends commands for movement without verifying whether the actual movement has been executed. Stepper motors are commonly used in open-loop systems, driven by special driver modules that receive digital pulse signals. Since there is no real-time information about the movement and position of the device, open-loop systems cannot account for obstructions or resistance during movement. These systems are suitable for mechatronics systems with small and uniform loading torque requirements that involve repetitive work. The image below illustrates the architecture of an open-loop system with linear controlled movement. 

 In line with the earlier image, the controller sends a reference or command voltage to the "Motor Driver" unit, which provides the necessary supply voltage to the stepper motor. The driver unit controls the voltage for motor shaft movement according to the command voltage. The driver unit also establishes the displacement of the machine bed and the speed of the motor. Once the movement command is conveyed to the motor, the controller does not verify the movement of the motor shaft or bed position. Chapter IV provides detailed information on the working principle of stepper motors.

On the other hand, most advanced mechatronics systems operate using closed-loop systems, which incorporate various feedback components. In a closed-loop system, the controller generates movement instructions and continuously monitors the results using different feedback devices. This ensures that the controller always has accurate and definite position information of a moving element. A closed-loop control system typically utilizes two types of feedback arrangements: position feedback and velocity feedback. Continuous feedback devices such as encoders and linear scales are used to obtain this feedback. A separate Chapter comprehensively discusses these feedback devices, known as continuous measuring sensors. The image below demonstrates the design of a closed-loop movement system using a ball screw and servo motor for movement on the axis of a CNC machine. 

In the closed-loop system shown in the previous image, the command or reference voltage from the controller is sent to the servo amplifier unit, which generates the necessary supply voltage for the servo motor. The servo amplifier unit ensures that the servo motor receives the exact voltage required for precise control of the motor's movement, based on the specific movement command for the ball screw. The basic working principle of a servomotor is discussed in Chapter IV. In a closed-loop control system, the controller continuously monitors whether the movement of the motor shaft or the machine bed corresponds to the command. Feedback devices such as encoders and linear scales are connected to the servo motor or directly coupled with the moving element to provide real-time position information to the controller and velocity information to the servo amplifier. A detailed discussion of different feedback elements used in mechatronics systems is presented in a separate chapter.

2. Limited Movement

Limited movement refers to the movement of an element within a specific distance, usually in a bidirectional manner. In a limited movement process, the moving element cannot stop at any position within its movement path. Once the starting command is given to a moving device, it will shift to one end of the movement track, and there is no way to stop it at an intermediate position. For example, the open/close mechanism in a machine door demonstrates limited movement. The stroke length of an actuator is restricted to open or close the door as required.

Mechatronics systems employ two types of limited movements: linear and rotary. Linear limited movements in mechatronics systems typically utilize different cylinders, which are selected based on the required movement stroke and the type of load to be overcome. Hydraulic cylinders are commonly used to overcome greater barriers or transport heavy loads, while pneumatic cylinders are suitable for lighter loads. For instance, pneumatic cylinders are used for the open/close mechanism of a machine door, while hydraulic cylinders are employed for work-piece clamping mechanisms in robotic arms that carry heavy loads. Rotary-limited movements are achieved using hydraulic and pneumatic rotary actuators, which have restricted movement paths. CNC machine pallet changing systems often utilize this type of limited rotary movement.

In an advanced mechatronics system, limited movement is usually controlled by a PLC (Programmable Logic Controller). The movement command is sent from the controller to the PLC, which verifies the entire situation and generates the required signal. The PLC then sends this signal to an actuator for the movement of the element. Advanced mechatronics systems often interface with various sensors (feedback elements), and the signals from these sensors are directly sent to the PLC to ensure proper completion of the element's movement. The working principles of different sensors and actuators employed in mechatronics systems are discussed in a separate chapter. The following picture shows a basic configuration of a limited linear movement, where a pneumatic cylinder's piston is controlled by the PLC.

If you examine the previous picture, you will notice that after issuing the movement command (in this case, throwing out or retracting the pneumatic cylinder's piston), the controller sends it directly to the PLC for decisive action. The PLC generates the desired voltage to energize the solenoid valve coil according to the command. Both ends of the double-acting pneumatic cylinder are connected to an air pressure line through solenoid valves, allowing extension or retraction of the cylinder piston. By activating the solenoid coil on the right side, air pressure reaches the rear side port of the cylinder through a solenoid valve, moving the piston to an extended position. Similarly, activating the solenoid coil on the left side allows air pressure to reach the front port of the cylinder through the left-side solenoid valve, retracting the piston. Two magnetic sensors are fitted on the cylinder to identify the piston's front and rear positions, and these feedback signals are sent to the PLC. The PLC can determine whether the actual movement of the cylinder piston (extension and retraction) is correct based on these signals.

For limited rotary movement, a similar mechanism is applied in mechatronics systems, but rotary actuators are used instead of cylinders. The electrical connections between the PLC, solenoid valve coil, and the controller remain the same, but the output pressure line of the solenoid valve is connected to both ends of the rotary actuator. As mentioned before, the selection of a rotary actuator depends on the desired movement path. For example, if a robotic arm requires a rotary movement from 0 to 90 degrees, the selected rotary actuator's movement will be restricted to this range, and it will not be possible to stop the actuator at any intermediate position. Feedback systems can also interface with limited-movement rotary actuators to ensure the correct rotary movement between the two ends. The following picture shows a 315-degree limited movement hydraulic rotary actuator and its control mechanisms (no feedback system is shown). 

3. Continuous rotary movement

Continuous rotary movement refers to the uninterrupted rotation of a moving element, which can be both controlled and uncontrolled. Controlled continuous rotary movement involves speed control and is commonly achieved using servomotors and servo amplifiers, eliminating the need for gear mechanisms. Servomotors offer different RPM options without requiring additional attachments (the operation and working principle of a servomotor are discussed in a separate chapter).

In mechatronics systems where controlled continuous rotary movement is not necessary, fixed RPM DC or AC motors are used to achieve continuous rotary movements at specific speeds. Hydro-motors and pneumatic motors are also utilized for continuous rotary movement in mechatronics systems. The advantage of using hydro-motors or pneumatic motors is that they provide a large starting torque compared to traditional electric motors. For example, a hydro-motor may be used for the tool arm movement of a CNC machine when continuous rotation with a high starting torque is required. In certain situations where using electricity is inconvenient, such as in the mining industry, pneumatic motors are employed to achieve high rotational speeds. PLCs typically control the continuous rotary movement of hydro-motors or pneumatic motors in advanced mechatronics systems, using a control method similar to that of limited movement systems discussed earlier. Instead of cylinders, hydro-motors or pneumatic motors are used. The working processes of hydro-motors and pneumatic motors are addressed in a separate chapter. The following picture shows the control mechanism of a hydro-motor with a PLC unit.  

Control of elements

In addition to controlled and preset movements in mechatronics systems, various electro-mechanical elements need to be controlled. For example, starting a cooling system, operating a three-phase induction motor, or controlling a lighting system. The PLC supplies voltage to devices like relays and contactors to make them operational within automated systems. Feedback systems are sometimes employed as well. The following picture represents a three-phase induction motor-driven pump controlled by a PLC. Upon receiving a command from the controller, the PLC sends the necessary voltage to activate the motor contactor. A three-phase AC voltage is then supplied to start the induction motor, drawing water through the attached pump unit and delivering it through the outlet. A flow switch is connected to the outlet line, providing a feedback signal to the PLC, allowing the controller to immediately detect any interrupted flow of water.

Most PLCs used in mechatronics systems operate on 24V DC voltage. Sensors and actuators with different voltage ratings connected to the mechatronics system are supplied through relays to obtain the desired voltages for those devices. In the previous example, if a 220V AC coil voltage contactor is used instead of a 24V DC coil voltage, it would not be possible to control that voltage directly from the PLC. However, by using a 24V DC relay, the required voltage (220V AC) can be obtained to activate the motor contactor. The following image explains how a 220V AC voltage is obtained using a 24V DC relay controlled by an output signal from the PLC.

A relay is an electromagnetic switch commonly used to turn an electric circuit on or off. It controls a large amount of current in a circuit by regulating a relatively small current. There are two main types of relays: electro-mechanical and solid-state relays. Electro-mechanical relays use magnetic force to turn electrical contacts on or off, while solid-state relays employ electronic circuits. A relay typically has multiple switching elements, each with three terminals: normally closed (NC), normally open (NO), and common (C). When a relay is deactivated, the NC and common terminals are connected, whereas in the activated state, the common terminal is connected to the NO terminal. This enables the relay to switch an electrical circuit on or off by connecting or disconnecting the NC, NO, and common terminals. The active and deactivate states of a relay are shown in the following pictures.

Multiple types of relays are used in mechatronics systems for controlling various electrical circuits and creating logical circuits. In simple mechatronics systems without a PLC, relays are used to create simple logical operation circuits. The following picture illustrates the control of different-rated electrical elements. A 24V DC voltage is supplied from a PLC to activate or deactivate each relay, and the common terminals of the relays are connected to 24V DC, 110V AC, and 220V AC, respectively. As a result, different-rated lights connected to the NO terminals of the relays will illuminate according to the activation of the respective relay.