1. Engineering 1040: Mechanisms & Electric Circuits Fall 2011
Power Transmission Systems:
Power Screws

2. Uses of Power Screws
Obtain high mechanical advantage in order to move large loads with a minimum effort. e.g screw jack.
Generate large forces e.g tensile testing machine, compactor press.
Obtain precise axial movements e.g. camera calibration rigs.

3. Screw Jacks

4. Toolmakers Clamp

5. X-Y Precision Table

6. Advantages of power screws
Compact design and takes less space
Large load carrying capability
Simple to design and easy to manufacture
Can obtain a large mechanical advantage
Precise and accurate linear motion
Easy maintenance
Self-locking feature

7. Thread Terminology
Pitch is the distance from the crest of one thread to the next.
When the screw rotates by one revolution the screw advances by its pitch.

8. Types of Thread

9. Ball Screws (1)

10. Ball Screws (2)

11. Advantages of a ball screw
Have very high efficiency (Over 90%)
Could be used in applications which require precise and repeatable movement
Could be easily preloaded to eliminate backlash
Smooth movement over full travel range
Can use a smaller size for same load
Has a longer life for thread

12. Disadvantages of a ball screw
Requires higher levels of lubrication
Possibility of the screw to contaminate
Additional brakes have to be used if locking is required

13. Power Screw Selection