MAE 211: Mechatronics
"A blend of mechanics and electronics, mechatronics has come to mean the synergistic use of precision engineering, control theory, computer science, and sensor and actuator technology to design improved products and processes” ME Magazine, May 1997.
Home Appliances: Controls for microwave, dishwasher, washer/dryer, oven, HVAC, musicand video systems, home security systems are all digital electronics now rather than mechanical. These are not just changes in hardware, but additions of functionality, reduction in cost, increase in reliability. Automobiles: A typical car has 5-10 microprocessors, not counting those in the stereo system. Consider the innovations and improvements in automotive performance, efficiency, safety, andreliability in the last 20 years. What advances will we see in the next 20 years? Aircraft: Similar advances in aircraft systems are on the way but have been slowed by extremely conservative regulation and approval processes. Navigation and avionics, passenger entertainment are most visible areas. Industry: Incredible strides in automation, efficiency improvement, pollution prevention, businessmanagement. Paperless factories, micro-run production, lights-out manufacturing. Medicine: MRI, CAT, digital X-rays, laser surgery, robotic surgery, artificial organs, drug delivery systems, G-I pill camera –all of these are examples of mechatronic devises.
Ramifications for Mechanical and Aerospace Engineers:
• We are entering the age of ubiquitous intelligence--smart cards, smart houses, smarthighways, smart cars …… All of it is based on embedded microprocessors, miniature sensors, micro-actuators. We have electric motors smaller than the period at the end of this sentence. You will be using, designing and building computers or objects built around computers for the rest of your life. Or not. You could be a plumber. All engineers must understand the rudiments of how computers work andhave a basic level of skill in programming them. This course is not intended to turn you into EE's, CpE's, or CS students. This course will help make sure you hire them instead of them hiring you.
Chapter 1 Mechanical Concepts
A gear train is a mechanical assembly of interacting gears that transmits motion or changes the rate or direction of motion. Gear teeth mustbe matched in shape before they will properly mate or "mesh". The important shape factors are pitch and pressure angle. You will learn about pressure angle in a later course, but gear pitch is a simple concept:
Gear Pitch (modulus) =
number of teeth pitch diameter measured in inches (mm)
In SI units, gears are specified by ‘modulus’ instead of pitch, but the concept is the same –number of teeth divided by pitch diameter.
FIGURE 1.1 The two gears pictured here have different gear pitches and will obviously not mate properly.
FIGURE 1.2 Properly mated gears have the same gear pitch (modulus)
Look at how gears mate. They don't mate with just the tips of the teeth touching, so outside diameter is not interesting; same for the root diameter (diameteracross the bottom of the teeth). What is useful is where the contact between two gears occurs—see figures 1.1 and 1.2. The pitch diameter defines an imaginary circle that cuts through the teeth. The circles thus defined for two properly mated gears are tangent to each other. For two properly mated gears, the shaft centers will be spread half the sum of the pitch diameters apart.
Example 1.1:Suppose I am building a gear train using 24-pitch gears. I want to use a 21tooth gear to drive a 72-tooth gear. How far apart will the shafts centers be? Solution: To find the distance apart, add half of the pitch diameter of both gears. Gear Pitch = # of teeth / Pitch Diameter 24 pitch = 21 teeth / x inches 24 pitch = 72 teeth / y inches (x + y) / 2 = 1.94 inches apart x = .875 inches y = 3.00...
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