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: 10
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 and automated systems: actuators. Think about an automatic gate, a fan that rotates, or the arm of a large machine in a factory. What makes them move? The answer is actuators. In Ghana, many of our local industries, from gari processing to shea butter production, rely heavily on manual labour. This can be slow, tiring, and sometimes dangerous. By understanding actuators, we can begin to imagine and design automated solutions to make these industries more efficient, safer, and more productive, boosting our national economy.
A. The Sense-Think-Act Cycle Every automated system or robot works on a fundamental principle called the Sense-Think-Act cycle. SENSE: The system uses sensors to gather information about its environment. (e.g., a temperature sensor detects if a room is hot). THINK: A controller (like a microcontroller or a computer) processes the information from the sensors and makes a decision based on its programming. (e.g., the program says, "If the temperature is above 28°C, turn on the fan"). ACT: The controller sends a command to an actuator, which performs a physical action on the environment. (e.g., the actuator, a DC motor, receives the signal and starts spinning the fan blades).
Definition: An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system. It takes an energy source (usually an electrical signal) and converts it into some kind of physical motion (e.g., rotating, pushing, pulling). Actuators are the muscles of a machine. B. Major Types of Actuators We can classify actuators based on the type of energy they use. The three main types you will encounter are Electric, Pneumatic, and Hydraulic. Electric Actuators These use electrical energy to produce mechanical motion. They are the most common type in robotics and small-scale automation. DC Motors (Direct Current Motors): How they work: Convert electrical energy into rotational motion. The speed of rotation is proportional to the voltage applied. Characteristics: Simple, cheap, widely available. Good for continuous rotation. Ghanaian Context Example: The motor in a standing fan, a blender for grinding pepper, or the wheels of a small robotic car. Servo Motors: How they work: A special type of motor with a built-in feedback system. They can be commanded to rotate to a specific angle and hold that position precisely. Characteristics: Excellent for precise control of position. Not for continuous rotation. Ghanaian Context Example: A robotic arm designed to pick and place items (like placing bottled drinks into a crate), or a mechanism to automatically open and close a small gate or window. Stepper Motors: How they work: They rotate in a series of discrete steps. The controller can tell it exactly how many steps to turn, allowing for very precise positioning and speed control without needing a feedback sensor. Characteristics: Very precise, good torque at low speeds. Ghanaian Context Example: Used in 3D printers for building models layer by layer, or a machine that needs to precisely dispense a certain amount of grain or liquid. Solenoids: How they work: An electromagnet that produces a linear (push or pull) motion over a short distance when electricity is applied. It's usually an "on/off" type of action. Characteristics: Fast-acting, simple, provides a linear push or pull. Ghanaian Context Example: An automatic door lock, a valve to turn water on/off in an automated irrigation system, or a device to stamp a label onto a bottle. Pneumatic Actuators These use compressed air to produce motion. How they work: A compressor stores air at high pressure. When a valve is opened, the compressed air flows into a cylinder, pushing a piston to create linear or rotational motion. Characteristics: Very fast, powerful, and relatively simple mechanically. They are clean and ideal for food processing. Require a compressor, which can be noisy. Ghanaian Context Example: A machine in a sachet water factory that quickly clamps and seals the plastic bags. An automatic door on a modern tro-tro or bus. Hydraulic Actuators These use a pressurized, incompressible liquid (usually oil) to produce motion. How they work: A pump pressurizes the liquid, which is then directed into a cylinder to move a piston. Characteristics: Can generate immense force and lift very heavy loads. They are slower than pneumatic systems and can be messy if they leak. Ghanaian Context Example: The arm of an excavator or bulldozer used in construction, the hydraulic press used to extract palm oil, or a car jack. C. How to Select and Justify an Actuator Choosing the right actuator is a critical design decision. You must evaluate the requirements of the task and justify your choice based on these criteria:
| Criteria | Question to Ask | Best Suited Actuator Types | | :--- | :--- | :--- | | Type of Motion | Do I need rotation, or a straight-line push/pull (linear)? | Rotation: DC Motor, Servo, Stepper. Linear: Solenoid, Pneumatic/Hydraulic Cylinder. | | Force / Torque | How much weight must be lifted or how much resistance must be overcome? | Low: Solenoid, Small DC Motor. Medium: Servo, Stepper, Pneumatic. Very High: Hydraulic. | | Speed | How fast does the action need to happen? | Very Fast: Pneumatic, Solenoid. Variable/Moderate: DC Motor. Slower: Hydraulic, Stepper. | | Precision / Control | Do I need to control the exact position or just turn something on/off? | High Precision: Servo, Stepper. Low Precision (On/Off): DC Motor, Solenoid, Pneumatic. | | Power Source | What is available? Electricity, compressed air, or a hydraulic pump? | Depends on the system's infrastructure. Electric is most common for small projects. | | Environment | Will it be dusty, wet, or need to be very clean (like food processing)? | Clean: Pneumatic, Electric (if sealed). Dirty/Rugged: Hydraulic. | | Cost & Complexity| What is the budget? How complex is the system to build and maintain? | Low Cost/Simple: DC Motor, Solenoid. High Cost/Complex: Hydraulic Systems. |
Guided Practice (With Solutions)