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[CENTER][SIZE=3]السلام عليكم ورحمة الله وبركاته
طبعا يسرني ان اقدم لكم هذا الشرح البسيط لما يقدمه هذا الموقع المتميز من مواضيع هامة في الهندسة الميكانيكية
الموقع ببساطة يتحدث عن
Mechanisms
اي الآليات
وهي من المواد التي تدرس حسب اعتقادي بأسم Machine Dynamics
المهم هو يقدم مواضيع متميزة وهامة في هذا المجال
وبذلك حبيت اضيفه الي قائمة مكتبة منتديات المهندس
العنوان:http://www.cs.cmu.edu/People/rapidp…lecontents.html
وهذا مثال على احد الدروس بعنوان Gears
7 Gears
Gears are machine elements that transmit motion by means of successively engaging teeth. The gear teeth act like small [/size]levers[SIZE=3].
7.1 Gear Classification
Gears may be classified according to the relative position of the axes of revolution. The axes may be [/size][/center]
[ol]
[li]
parallel,
[/li][li]intersecting,
[/li][li]neither parallel nor intersecting.
[/li][/ol]Here is a brief list of the common forms. We will discuss each in more detail later.
[ul]
[li]
Gears for connecting parallel shafts
[ol]
[li][CENTER][SIZE=3]Spur gears [/li]
The left pair of gears makes external contact, and the right pair of gears makes internal contact [/size][/center]
[li]
Parallel helical gears 
[/li][li] Herringbone gears (or double-helical gears) 
[/li][li] Rack and pinion (The rack is like a gear whose axis is at infinity.) 
[/li][/ol]Gears for connecting intersecting shafts
[ol]
[li]
Straight bevel gears
[/li][li]Spiral bevel gears
[/li][/ol]Neither parallel nor intersecting shafts
[ol]
[li]
Crossed-helical gears 
[/li][li] Hypoid gears
[/li][li]Worm and wormgear 
[/li][/ol][CENTER][SIZE=3]7.2 Gear-Tooth Action
7.2.1 Fundamental Law of Gear-Tooth Action
[/size]Figure 7-2 shows two mating gear teeth, in which [/center]
[ul]
[li]
Tooth profile 1 drives tooth profile 2 by acting at the instantaneous contact point K.
[/li][li]N1N2 is the common normal of the two profiles.
[/li][li]N1 is the foot of the perpendicular from O1 to N1N2
[/li][li]N2 is the foot of the perpendicular from O2 to N1N2.
[/li][/ul][CENTER][SIZE=3]
Figure 7-2 Two gearing tooth profiles
To obtain the expected velocity ratio of two tooth profiles, the normal line of their profiles must pass through the corresponding [/size]pitch point[SIZE=3], which is decided by the velocity ratio. The two profiles which satisfy this requirement are called conjugate profiles. Sometimes, we simply termed the tooth profiles which satisfy the fundamental law of gear-tooth action the conjugate profiles.
Although many tooth shapes are possible for which a mating tooth could be designed to satisfy the fundamental law, only two are in general use: the cycloidal and involute profiles. The involute has important advantages – it is easy to manufacture and the center distance between a pair of involute gears can be varied without changing the [/size]velocity ratio. Thus close tolerances between shaft locations are not required when using the involute profile. The most commonly used conjugate tooth curve is the involute curve (Erdman & Sandor 84)[SIZE=3]. 7.3 Involute Curve
The following examples are involute spur gears. We use the word involute because the contour of gear teeth curves inward. Gears have many terminologies, parameters and principles. One of the important concepts is the velocity ratio, which is the ratio of the rotary velocity of the driver gear to that of the driven gears.
The SimDesign file for these gears is simdesign/gear15.30.sim. The number of teeth in these gears are 15 and 30, respectively. If the 15-tooth gear is the driving gear and the 30-teeth gear is the driven gear, their velocity ratio is 2. Other examples of gears are in simdesign/gear10.30.sim and simdesign/gear20.30.sim
حيث اني هنا اخذت مقتطفات من هذا الدرس لمشاخدته بالكامل تجدوه على هذا الرابط
[/size]http://www.cs.cmu.edu/People/rapidp…isms/chpt7.html
[/center]
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