Lesson Notes By Weeks and Term v4 - SHS 3
Sensors & Actuators
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Sensors & Actuators
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Robotics
Class: SHS 3
Term: 2nd Term
Week: 14
Grade code: 3.1.3.LI.2
Strand code: 1
Sub-strand code: 3
Content standard code: 3.1.3.CS.1
Indicator code: 3.1.3.LI.2
Theme: Principles of Robotic Systems
Subtheme: Sensors & Actuators
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
Welcome, future engineers and innovators! Today, we are exploring the "muscles" of robots: actuators. While sensors are the "senses" that gather information, actuators are the components that take action—they push, pull, rotate, and lift. In Ghana, many of our local industries, from gari processing plants to sachet water factories, rely on manual labour for repetitive tasks. By understanding actuators, we can design automated systems that make these processes faster, safer, and more efficient, boosting our local economy and creating new technology-focused jobs. This lesson will empower you to analyse a manual process, identify its needs, and choose the right "muscles" to automate it.
What is an Actuator? An actuator is a component in a machine or robotic system that is responsible for moving and controlling a mechanism or system. Think of it as the "muscle" of the robot. It receives a control signal (usually an electrical signal from a microcontroller like an Arduino) and converts it into physical motion. Sensor: Senses the environment (e.g., a temperature sensor feels the heat). Controller: Processes the information (e.g., a microcontroller decides it's too hot). Actuator: Takes action (e.g., a motor turns on a fan). Classification of Actuators Actuators are broadly classified based on the type of energy they convert into motion. The three main types we will study are Electric, Pneumatic, and Hydraulic. Electric Actuators These actuators use electrical energy to produce mechanical motion. They are the most common type in modern robotics due to their precision and ease of control. How they work: An electric current creates a magnetic field, which interacts with another magnetic field to produce force, causing rotation or linear movement. Common Types: DC Motors: Simple motors that spin when power is applied. Speed is controlled by voltage. Used for fans, wheels on small robots, and agitators. Servo Motors: DC motors with a feedback mechanism (a sensor) and a built-in controller. They can be commanded to move to a specific angle and hold that position precisely. Used for robotic arms, camera gimbals, and steering systems. Stepper Motors: Move in discrete, precise steps. They are excellent for applications where exact positioning is needed without a feedback sensor. Used in 3D printers, CNC machines, and document scanners. Solenoids: A coil of wire that creates a magnetic field to move a metal plunger in or out. They provide a simple, linear push-pull motion. Used in automated door locks, and valves. Advantages: High precision and accuracy. Easy to control with microcontrollers. Quiet operation. Clean (no fluid leaks). Disadvantages: Lower force and power compared to hydraulic systems. Can overheat under heavy loads. Can be more expensive for high-power applications. Ghanaian Context Example: Automating a kente weaving loom. Stepper motors could be used to precisely select and lift the correct threads (heddles) to create complex patterns, replacing the tedious manual process. Pneumatic Actuators These actuators use the energy from compressed air to produce motion, usually linear motion. How they work: A compressor fills a tank with high-pressure air. A valve releases this air into a cylinder, pushing a piston forward or backward. Components: Air compressor, reservoir tank, valves, and a pneumatic cylinder (the actuator itself). Advantages: Very fast actuation speed. Relatively low cost and simple design. Durable and reliable in harsh environments (e.g., dusty factories). Safe, as air leaks do not contaminate the environment. Disadvantages: Difficult to achieve precise position and speed control (air is compressible or "spongy"). Requires a noisy and bulky air compressor. Requires a system of pipes and hoses. Ghanaian Context Example: A sachet water ('pure water') packaging plant. A pneumatic cylinder is perfect for the fast, repetitive task of stamping the production date onto each sachet as it moves down the conveyor belt. Hydraulic Actuators These actuators use the energy from a pressurized, incompressible liquid (usually oil) to produce motion. How they work: A pump pressurizes oil, and a valve directs this oil into a cylinder, pushing a piston with immense force. Components: Hydraulic pump, fluid reservoir, valves, and a hydraulic cylinder. Advantages: Extremely high force and power output. Can lift tonnes. Robust and can operate in tough conditions. Maintains force and torque constantly. Disadvantages: Slow compared to pneumatics. Can be messy; fluid leaks are a fire and environmental hazard. Expensive to build and maintain. Requires a lot of supporting equipment (pumps, tanks, coolers). Ghanaian Context Example: A palm oil processing mill. A hydraulic press is the ideal actuator for squeezing the oil from the digested palm fruits, as this task requires enormous, sustained force that other actuators cannot provide. How to Select the Right Actuator: A Step-by-Step Guide
To "Evaluate an industrial control requirement and recommend" an actuator, follow these steps: Analyse the Motion: What kind of movement is needed? Linear: Pushing, pulling, lifting in a straight line (e.g., stamping, pressing). Rotary: Turning, spinning (e.g., mixing, driving a wheel). Oscillatory: Moving back and forth (e.g., sifting). Determine the Key Requirements (Quantify if possible): Force/Torque: How much strength is needed? (Low, Medium, High, Very High) Speed: How fast does it need to move? (Slow, Medium, Fast) Precision/Accuracy: Does it need to stop at an exact position? (Low, High) Duty Cycle: How often will it operate? (Continuously, intermittently) Consider the Environment & Constraints: Environment: Is it clean, dusty, wet, or hot? Power Source: Is electricity stable? Is an air compressor feasible? Cost: What is the budget for the system? Maintenance: How easy is it to repair? Compare and Justify: Use a simple comparison table to make your decision.
| Feature | Electric Actuators | Pneumatic Actuators | Hydraulic Actuators | | --------------- | ------------------ | ------------------- | ------------------- | | Force/Power | Low to High | Medium | Very High | | Speed | Medium to High | Very Fast | Slow | | Precision | Very High | Low | Medium | | Cost | Medium to High | Low | High | | Cleanliness | Very Clean | Clean (air leaks) | Messy (oil leaks) | | Control | Easy, Flexible | Simple On/Off | Complex |
Guided Practice (With Solutions) Scenario 1: Automating a Soap Stamping Machine A local soap producer in Accra wants to automate the process of stamping their brand logo onto each bar of soap. The process is currently done by hand with a hammer and a metal stamp. The machine needs to be fast to keep up with production.