{ "cells": [ { "cell_type": "markdown", "id": "aeba632d-321b-4f5d-8333-0016a715a925", "metadata": {}, "source": [ "# 10 Component of Robot: Actuator\n", "November 8, 2024\n", "\n", "In this article discussion is done on Actuator, another important component of robot. The previous articles \"Component of Robot: Sensor-I\" and \"Component of Robot: Sensor-II\" focused on the sensor component of the robot.\n", "\n", " \n", "\n", "Actuators\n", " \n", "\n", "Known as the “Muscles of the Robots”, actuators are the crucial components of robots which help in the motion of the robotic links and joints and thus help in the desired interaction of the robots with the physical world. They basically transform electrical, pneumatic or hydraulic energy into mechanical motion and thus actively impacting the physical actions and functionality of the robots. So, they are also called as active components of the robots.\n", "\n", " \n", "\n", "## 10.1 Electric Actuators\n", " \n", "\n", "Electrical actuators are the most common types used in robotics for their efficient and precise motion control. They are easily available, versatile and affordable and thus finds applications in most cases. They convert electrical energy into mechanical motion with the help of different types of motors. These motors are described as below.\n", "\n", " \n", "\n", "### 10.1.1 DC Motor\n", " \n", "\n", "Direct Current (DC) motors are simple, efficient and cost-effective electric actuators which converts electrical energy (direct current) into smooth rotational motion. They can be precisely controlled using feedback loops.\n", "\n", "```{figure} _static/DC_Motor.png\n", ":alt: Robota10.1 robot design\n", ":width: 300px\n", "\n", "DC Motor (Source: Freepik)" ] }, { "cell_type": "markdown", "id": "72d14712-5b5d-47b8-9133-405ad1148d87", "metadata": {}, "source": [ "***Working Principle of DC Motor***\n", " \n", "The construction of the DC motor consists of a stator which is basically the magnets (curved permanent or electromagnets) for providing the magnetic field and a rotor or armature which is basically the coils wrapped around a frame.\n", "\n", " \n", "\n", "```{figure} _static/DC_Motor_Construction.png\n", ":alt: Robota10.2 robot design\n", ":width: 300px\n", "\n", "Construction of DC Motor (Source: Image by Author)" ] }, { "cell_type": "markdown", "id": "b8e0b4c9-e0c7-4143-baca-2c07030f541f", "metadata": {}, "source": [ "When the current flows through the rotor coils, then due to magnetic field, they experience forces which make them rotate for half way, and by using a commutator ring, the polarity is reversed so that the rotation is maintained in the same direction. DC motors can be controlled by adjusting the voltage and thus change the speed of rotation or through pulse-width modulation (PWM). The working principle is explained in this video.\n", "DC motors can of two types-Brushed DC motor which uses brushes for commutation and Brushless DC motor (BLDC) which uses electronic commutation.\n", " \n", "\n", "***Advantages of DC Motor***\n", " \n", "\n", "They are simple to control just by adjusting the input voltage, smooth operation, compact and lightweight.\n", "\n", " \n", "\n", "***Disadvantages of DC Motor***\n", " \n", "\n", "Requires feedback mechanism for precise control and thus makes it complex and heavy, can overheat, need maintenance due to wear and tear of brushes in Brushed DC motors, high cost for brushless DC motor.\n", "\n", " \n", "\n", "***Applications***\n", " \n", "\n", "DC motors are used in mobile robots, robotic arms, small industrial robots requiring continuous or variable speed, drones and UAVs, etc.\n", "\n", " \n", "\n", "### 10.1.2 Stepper Motor\n", " \n", "\n", "For precise incremental position control, stepper motors play a huge role as they rotate in discrete or fixed steps without requiring any feedback mechanisms.\n", "\n", " \n", "\n", "***Working Principle of Stepper Motor***\n", " \n", "\n", "The construction of a stepper motor consists of a stator and a rotor. The stator basically has number of coils arranged in a specific pattern and provides the necessary magnetic field by energizing these coils. And the rotor is made up of either a permanent magnet which is diametrically polar, a variable reluctance material like soft iron core, or a toothed permanent magnet which axially polar (hybrid).\n", "\n", " \n", "\n", "```{figure} _static/Stepper_Motor_Construction.png\n", ":alt: Robota10.3 robot design\n", ":width: 300px\n", "\n", "Construction of Stepper Motor with Permanent Magnet rotor (Source: Image by Author)" ] }, { "cell_type": "markdown", "id": "d477cc16-fef2-46c4-8c81-ff22d116c00b", "metadata": {}, "source": [ "When stator coil patterns are energized sequentially by some electronic pulse, then the rotor magnetic poles (or ferromagnetic material) are attracted towards the opposite poles of the stator electromagnetic coils and thus, continuous rotation is obtained through discrete steps or angle of rotation. The magnitude of torque and speed are dependent on the number of phases of the stator coils, or poles of the magnets in the rotor, etc.\n", "\n", " \n", "\n", "***Advantages of Stepper Motor***\n", " \n", "\n", "As they move in steps, so a precise control can be done without the need of additional feedback mechanisms. They have the characteristic of high-torque low-speed applications and thus can hold load in a particular position.\n", "\n", " \n", "\n", "***Disadvantages of Stepper Motor***\n", " \n", "\n", "Generate heat due to high consumption of power continuously and may lose steps if overloaded. They are also not suitable for high-speed applications.\n", "\n", " \n", "\n", "***Applications of Stepper Motor***\n", " \n", "\n", "Mainly used for 3D printers, CNC machines, robotic arms, camera and scanners requiring precise positioning.\n", "\n", " \n", "\n", "### 10.1.3 Servo Motor\n", " \n", "\n", "Servo motors are those actuators which can be controlled accurately by using some feedback loop mechanisms. Typical servo motor consists of a motor, sensor (often a hall-effect encoder) and a control circuit. They can be both AC and DC types.\n", "\n", " \n", "\n", "***Working Principle of Servo Motor***\n", " \n", "\n", "The closed loop feedback mechanism of the servo motor is operated as the desired position or speed is commanded to the motor, the sensor (encoder or potentiometer) senses the actual position or speed which is then compared with the commanded input. Then the motor is adjusted to minimize the difference and thus error is reduced to ensure precise and repeatable motions.\n", "\n", " \n", "\n", "***Advantages of Servo Motor***\n", " \n", "\n", "Servo motors are used in applications requiring accurate position and speed control as it is feedback looped, stability and higher torque control as well as tasks requiring repetitive and precise movements.\n", "\n", " \n", "\n", "***Disadvantages of Servo Motor***\n", " \n", "\n", "They are complex and costly, draw high current leading to overheating, limited range of motion, etc.\n", "\n", " \n", "\n", "***Applications of Servo Motor***\n", " \n", "\n", "Huge application in robotic arms, humanoids, drones and aerospace, industrial automation, etc.\n", "\n", " \n", "\n", "## 10.2 Pneumatic Actuators\n", " \n", "\n", "Pneumatic actuators are devices that operate by converting compressed air to mechanical motion. They are simple, robust and fast and are used where electric actuators are to slow and hydraulic are too complex or too powerful.\n", "\n", " \n", "\n", "```{figure} _static/Pneumatic_Actuator2.jpg\n", ":alt: Robota10.4 robot design\n", ":width: 300px\n", "\n", "Pneumatic Actuator (Source: Freepik)" ] }, { "cell_type": "markdown", "id": "9a6b4106-427a-45c3-bedf-b3339b493a65", "metadata": {}, "source": [ "***Working Principle of Pneumatic Actuator***\n", " \n", "\n", "The pneumatic actuators typically consist of compressor, air reservoir, valve, piston-cylinder. When the compressed air from the reservoir is forced into the cylinder or chamber, then pressure exerted on the piston results in the desired output motion (linear or rotation). The valve is used for controlled the air flow in the chamber and thus the motion and direction of the piston are controlled by adjusting the valve. This motion can be used for pushing, pulling, lifting or rotating, etc.\n", "Pneumatic actuators may be either linear (single-acting, double-acting cylinders) or rotary (vane actuators, rack-and-pinion actuators).\n", " \n", "\n", "***Advantages of Pneumatic Actuator***\n", " \n", "\n", "Pneumatic actuators are fast and repetitive, lightweight, can operate in hazardous environments and are cost effective than electric or hydraulic actuators.\n", "\n", " \n", "\n", "***Disadvantages of Pneumatic Actuator***\n", " \n", "\n", "Less precise and noisy operation, need consistent supply of compressed air, leaks and energy loss thereby less efficiency, limited range of motion, harder to control, etc.\n", "\n", " \n", "\n", "***Applications of Pneumatic Actuator***\n", " \n", "\n", "Extensively used in applications involving pick-and-place, material handling, packaging, assembly line sorting, clamping, automotive industry for painting, welding, food and beverage industry, medical industry as well as aerospace and defense, etc.\n", "\n", " \n", "\n", "## 10.3 Hydraulic Actuators\n", " \n", "\n", "Hydraulic actuators use pressurized fluid to generate motion and thus are extremely powerful and can provide huge force relative to their size. So, these actuators find application in heavy-duty industrial robots or exoskeletons requiring significant force and torque.\n", "\n", " \n", "\n", "```{figure} _static/Hydraulic_actuator.jpg\n", ":alt: Robota10.5 robot design\n", ":width: 300px\n", "\n", "Hydraulic Actuator (Source: Wikimedia Commons)" ] }, { "cell_type": "markdown", "id": "6633c71e-9694-4880-bcb7-aea7dc3c193d", "metadata": {}, "source": [ "***Working Principle of Hydraulic Actuator***\n", " \n", "\n", "The key components of hydraulic actuators include hydraulic pump for pressurizing the hydraulic fluid, reservoir for storage of the fluid, control valves to adjust the flow by changing the force, speed or direction of the fluid motion, cylinder or chamber where the pressure is converted to linear or rotational motion, and finally the piston or rotor which basically converts the pressure into linear or rotary motion. \n", "So hydraulic actuators are two types- linear and rotary.\n", " \n", "\n", "***Advantages of Hydraulic Actuator***\n", " \n", "\n", "Hydraulic actuators have high force and power output, smooth and precise control, durable and reliable in harsh conditions, compact design and provide required strength and reliability for heavy-duty applications.\n", "\n", " \n", "\n", "***Disadvantages of Hydraulic Actuator***\n", " \n", "\n", "Complex and bulkier in size, require regular maintenance, leakage problem, dangerous fluid leading to pollution, etc., are some of the limitations of hydraulic actuators.\n", "\n", " \n", "\n", "***Applications of Hydraulic Actuator***\n", " \n", "\n", "Usually used for heavy-duty construction equipment like excavators, bulldozers, cranes and backhoes; aerospace and defense like landing gears, flight controls, braking system, naval ships, artillery; marine applications like underwater robots, subsea valves, etc.\n", "\n", " \n", "\n", "## 10.4 Soft Actuators\n", " \n", "\n", "Soft actuators are advanced actuation systems used to mimic biological muscles and are usually made of flexible materials like elastomers. They are used in applications requiring adaptability and delicate or fragile handling.\n", "\n", " \n", "\n", "### 10.4.1 Pneumatic Soft Actuator\n", " \n", "\n", "The flexible actuator is expanded or contracted through the application of compressed air. And thus, these actuators can apply force gently and handle fragile objects.\n", "\n", " \n", "\n", "### 10.4.2 Electroactive Polymers (EAPs)\n", " \n", "\n", "The shape of these actuators is changed using electric fields (e.g., piezoelectric materials). They are flexible, lightweight and energy-efficient.\n", "\n", " \n", "\n", "### 10.4.3 Shape Memory Alloys (SMAs)\n", " \n", "\n", "Shape memory alloys are special substances which remember their original shape. When the temperature changes, SMAs changes their shape and thus motion can be generated by these actuators. They are lightweight, compact and silent and are applied in small-scale actuation works.\n", "\n", " \n", "\n", "```{figure} _static/Shape_memory_effect.jpg\n", ":alt: Robota10.6 robot design\n", ":width: 300px\n", "\n", "Shape Memory Effect (Source: Wikimedia Commons)" ] }, { "cell_type": "markdown", "id": "25624345-b775-45d1-b438-5711a812d087", "metadata": {}, "source": [ "***Advantages of Soft Actuator***\n", " \n", "\n", "These actuators are highly flexible, capable of conforming to complex shapes, offer fragile force, silent (SMAs), compact size.\n", "\n", " \n", "\n", "***Disadvantages of Soft Actuator***\n", " \n", "\n", "Strength and force output is small, challenging to control, durability is also less, slow movements, can fatigue over time and high amount of energy consumption, overheating, etc.\n", "\n", " \n", "\n", "***Applications of Soft Actuator***\n", " \n", "\n", "Soft actuators are mostly used in medical robots where gentle interactions with human tissues are required. Also to handle perishable or delicate materials like in food industry, in wearable technology like robotic exoskeleton, prosthetic devices, micro-robots, satellite deployment mechanisms, etc.\n", "\n", " \n", "\n", "The next article is about the control system and their role as a component of robotics system." ] }, { "cell_type": "code", "execution_count": null, "id": "066a9169-ae21-4f29-b3e0-8c719f04201b", "metadata": {}, "outputs": [], "source": [] } ], "metadata": { "kernelspec": { "display_name": "Python 3 (ipykernel)", "language": "python", "name": "python3" }, "language_info": { "codemirror_mode": { "name": "ipython", "version": 3 }, "file_extension": ".py", "mimetype": "text/x-python", "name": "python", "nbconvert_exporter": "python", "pygments_lexer": "ipython3", "version": "3.11.9" } }, "nbformat": 4, "nbformat_minor": 5 }