Pneumatics
Pneumatics engineers have developed an amazing suit that can be worn over the body that assists the muscles as they move. Using blasts of air, tubes in the suit expand and act like muscles moving the arms with more strength.
A similar kind of technology was used to assist Seiji Uchida, a paralyzed climber. Seji was able to climb part way up the Matterhorn riding on the shoulders of his friend, Takeshi Matsumoto. Takeshi wore a special suit which is a wearable robot known as HAL, or "Hybrid Assistive Limb.” HAL allows someone who could normally push 220 pounds with their legs to carry an amazing 396 pounds. The inventor, Yoshiyuki Sankai, said, "The most important thing is that we try to support handicapped persons' dreams. ...and now we're going to build a better version."
Another application of this kind of robotic design helps stroke survivors regain the ability to do basic tasks. The robotic arm shown in the photo at right provides assistive therapy by giving the patient support for repetitive functions. RUPERT, the robotic arm, is powered by four pneumatic muscles to assist movement at the shoulder, elbow and wrist.
One common element in each of these designs is the use of pneumatic devices. Pneumatic means “air” or “breath.”
Pneumatics are not usually part of the curriculum in either elementary or high school. It seems strange that a ubiquitous application of a physical principle in science would be overlooked by curriculum writers! Pneumatic systems are common elements of many machines. So are hydraulics. If you put a liquid in a pneumatic system, it becomes a hydraulic system. Pneumatic and hydraulic devices are simple machines. They trade distance for force.
Exploring
Start with three syringes and a piece of aquarium tubing. Take time to experiment with the syringes to see the interactions.
• Connect one small syringe to one small syringe. How far does each plunger move?
• Connect one small syringe attached to one large syringe. How far does the large plunger move when you press on the small syringe? Try the reverse: How far does the small plunger move when you press on the large syringe?
Troubleshooting
Syringes are easy to work with. The rubber plunger will sometimes get dry and sticky, so a bit of silicon lubricant will soften the materials. Pressing too hard on the syringe will pop the tubing off the tip of the plastic syringe.
Students will learn the limits of the materials by manipulating the various combinations of small and large syringes. The main thing that students should learn from these examples is that pneumatic cylinders can be used to apply forces.
1) To change direction of a force only: The syringe sizes will be the same dimensions.
2) To apply a small force and expect a larger force to act: Use a small syringe to activate a larger syringe.
3) To apply a larger force and expect a longer movement: Use a large syringe to activate a smaller syringe.
Principles of Pneumatic Simple Machines Using Syringes
• With two syringes of equal size, the distance that one plunger is moved should equal the other plunger distance. There is conservation of work because the force and distance on each syringe is the same. This would be the same as a lever with equal arms or a fixed pulley that simply changes direction. The advantage of a pneumatic system like this is that it can apply a force at a distance--around a corner, through a small opening, or at a remote location.
The robotic hand is an example of this application. Many small pistons move each part of the fingers. An operator can control the hand from a distance.
When a small syringe moves a large syringe, the distance that the large syringe moves is smaller--but the force is greater. This is the same principle as with all simple machines. In this case, if the small syringe moves 10 cc, and the large syringe only moves 5 cc. The force the large syringe can exert is twice the force that was applied by the small syringe. Mathematically, the same formula that is used with other simple machines (levers, planes and pulleys) can be applied here.
F1 X d1 = F2 X d2
If we press on piston at F1 and move it 10 centimeters, the larger piston will move 5 centimeters in this case. The force at F2 will be two times that of F1.
A jack hammer uses this principle. Air is pushed through a small piston a long distance. This activates a large piston that moves a short distance but that applies a great amount of pressure--enough to break concrete!
When a large syringe moves the small syringe, the small syringe will move much faster and further than the large syringe. If students are careful to notice, it is harder to push on the large syringe to move the small syringe. In this case a larger force is required on the large syringe to move the small syringe.
An application that uses a large force to move a piston a long distance is a boom lift. In this case the piston that moves the person in the bucket travels a long distance.