Mechanical and Pneumatic Control Systems (Option B)

Mechanical and pneumatic systems

Machines move, and behind every moving product is a mechanism, a device that changes one kind of motion or force into another. This module covers two families of control. Mechanical systems use parts such as levers, gears, pulleys, cams and linkages to change the size, direction or type of a movement, and they let a small effort shift a large load. Pneumatic systems instead use compressed air to create a strong, clean, repeatable push, driving pistons inside cylinders. Along the way you meet the four types of motion, the idea of mechanical advantage, and the simple sums that describe how gears change speed and force. Understanding these lets you look at any machine and work out how it does its job.

Words for mechanisms

Learn these terms before the mechanisms are matched up. They name the ideas used in mechanical and pneumatic systems.

Match each mechanism to what it does

Rotary against reciprocating motion

There are four types of motion, and two of the most common are easy to mix up. Naming the motion correctly is the first step in describing a mechanism.

Which mechanism is needed?

A designer needs to turn the round-and-round motion of a motor into the up-and-down motion of a needle. Which mechanism does this?

• A cam
• A pulley on its own
• A pair of gears on their own
• A single fixed bar

How a pneumatic cylinder works

Pneumatic systems use compressed air to create movement, and they are common where a strong, clean, repeatable push is needed. Air is squeezed by a compressor and stored, then released through a valve into a cylinder. Inside the cylinder a piston is pushed along, and that push does the work, such as clamping a part or stamping a shape. A single-acting cylinder is driven out by air and returned by a spring; a double-acting cylinder uses air to drive the piston both ways, giving more control. Pneumatics is safe, since it uses only air, and reliable, which is why factories rely on it for repeated tasks all day long.

Pick the true facts about mechanisms

Select every statement about mechanisms that is true.

• A lever turns about a pivot
• Gears pass on turning motion
• A cam can change rotary motion into up-and-down motion
• A machine creates energy from nothing
• Mechanisms cannot change a force

Order how a pneumatic system works

Put the stages of a simple pneumatic system into the order the air flows.

• A compressor squeezes the air
• The compressed air is stored in a receiver
• A valve controls when the air is released
• The air pushes a piston inside a cylinder
• The piston does the work, such as clamping

Complete the mechanisms facts

A device that changes one kind of motion or force into another is a _____. A stiff bar that turns about a pivot to move a load is a _____. Toothed wheels that mesh to pass on turning motion are _____. Motion that spins round and round, like a wheel, is called _____ motion.

Tap the two examples of rotary motion

Read these four movements. Tap the TWO that are examples of rotary motion.

• a car wheel turning
• a fan blade spinning round
• a piston moving back and forth
• a pendulum swinging side to side

A seesaw in a playground

Think of a seesaw in a playground. A small child can lift a much heavier adult if the adult sits close to the middle and the child sits right out at the end. Nothing magic has happened; the distance from the pivot has done the work, trading a longer push for a bigger lift. Machines are full of this same trade. Move something a greater distance with less force, or a shorter distance with more force, and you can shift loads that a bare hand never could. Once you spot the pivot, the wheel or the slope doing the trade, a complicated-looking machine suddenly makes sense.

Work out the gear ratio

A driver gear has twenty teeth and it turns a driven gear with sixty teeth. What is the gear ratio, found by dividing the driven teeth by the driver teeth? Give the number only.

Choose the right mechanism

Read each situation and choose the best answer.

• You need to lift a heavy flag to the top of a pole using a rope. Which mechanism helps?
• You want a small effort to move a large load on a bar. What should you use?
• A factory needs a strong, clean, repeated push to clamp parts. What suits it?

Build a mechanisms point

Choose the word for each gap to complete one point about mechanisms.

Explain mechanical and pneumatic systems

A friend is studying design and asks how mechanical and pneumatic systems make things move. Using what you have learned, explain the main ideas.

• Explain what a mechanism is
• Explain two mechanisms, such as the lever and gears, and what they do
• Explain the main types of motion
• Explain how a pneumatic cylinder creates movement
• Explain what mechanical advantage or a gear ratio tells you