Mechanical Engineering Flashcards
Define Mechanical Engineering:
focuses on the design, production, analysis, working and improvement of a technical object with moving parts
What is the function of guidance?
Guidance is the function of a part that directs another part along a specific path. The mechanical function performed by any component that controls the motion of one or more moving parts. A guiding component or control is a component whose mechanical function is to guide the motion of moving parts.
Guidance dictates whether the motions is….
Guidance dictates whether the motion is either rotational (wheel and axle), translational (sliding drawer) or helical (C clamp)
What to guidance and links between parts allow for?
Guidance and Links between parts allow for the restriction of motion that would otherwise impede the proper function of the mechanism.
What does Translational guidance ensure?
Ensures the straight translational motion of a moving part . ( A track at the bottom and top of a window is an example of this)
What does rotational guidance ensure?
Ensures the rotational motion of a moving part. ( An example is the axle attached tot he bicycle frame guides the wheel in a rotational motion).
What does helical guidance ensure?
Ensures the translational motion of a moving part while it rotates around the same axis. ( An example is the threads inside a C clamp controls the helical guiding of the threaded shank).
Describe motion:
If an object could exist totally independent from any other object it would have 6 degrees of motion freedom, - translation along 3 axis, and rotation around the same three axis.
2 translations and 2 rotations around 3 different axis result in 12 different potential motions.
Define linking:
As soon as a technical object contains two or more parts, an engineer must find a way to hold them together.
Linking is the mechanical function performed by any component that connects different parts of technical objects.
List the Characteristics of links and define each as you go:
1.Direct - held without a link Indirect - held with a link 2. Rigid or Flexible? - can it be deformed like a spring 3. Removable or Non-Removable? - separated without damage or not 4. Complete - prevented from moving independently Partial - move independently
Describe Motion Transmission:
Relaying a motion from one part to another without altering the nature of the motion.
A motion transmission system is a set of components that perform the function of transmitting motion.
What does the driver component do?
Receives the force
What does the driven component do?
Receives the motion and transfers it to another part.
What does the intermediate component do?
located between the driver and driven component.
Characteristics of motion in mechanical engineering systems are often applied to technical objects….
All transmit rotational motion
- The direction of the rotation of the components may be identical throughout or different.
- Clockwise or counter clockwise
- The system may or may not be reversible.
- If it is reversible then the driven component can become a driver and vice versa.
Gears are often used for one of the following reasons…
To reverse the direction of rotation
To increase or decrease the speed of rotation
To move rotational motion to a different axis
To keep the rotation of two axis synchronized
What is the gear ratio?
teeth on follower divided by # teeth on driver
teeth on follower/ # teeth on driver
1) Low gear ratio =…..
2) High gear ration=
1) Low gear ratio=more speed = less force
2) High gear ratio= less speed = more force
What does the speed change in motion transmission depend on?
Depends on the relative diameters of the driver and driven components.
What does it mean when the speed increases?
Diameter of Driver > diameter of driven
* When the diameter of the driver component is greater than the diameter of the driven component, there is a speed increase in the system.
What does it mean when there is a speed decrease?
Diameter of driver < diameter of driven
- When the diameter of the driver component is less than the diameter of the driven component, there is a speed decrease in the system.
What does it mean when there is no speed change?
Diameter of driver = diameter of driven
* When the diameter of the driver component is equal tot he diameter of the driven component, there is no speed change in the system.
Speed ratio:
The speed ratio can be used to describe the speed change for a system.
Speed ratio= diameter or number of teeth of driver component/ diameter or number of teeth of driven component.
- If speed ration= 1, then there is no change in speed
- If the speed ration is >1, then there is an increase in speed
- If the speed ration is <1, then there is a decrease in speed.
Describe “ Gear Assembly”:
- Rotational is transmitted from one gear to another
- Rotation direction is opposite in each connecting gear
- System can have more than two gear wheels
- Used in machinery where mechanical advantage is needed
- The torque ( force) of a small motor can be increased considerably through a gear train
- Requires fine machining of parts so that the teeth fit together precisely
Are gear trains reversible?
Yes
What are the advantages to gear trains?
- Will not allow slippage
- Can be connected at various angles
- Allows for large forces to transmitted
What are the disadvantages to gear trains?
- Needs lubrication
- Subject to severe damage if there is a failure in any one part of the system
- Requires elaborate machining
If the gears are no longer touching they are called…
Sprockets
Describe Sprocket and wheels chain:
- Rotational motion is transmitted from one sprocket to the other by a chain
- Rotation direction is opposite in each connecting sprocket
- System can have more than two sprockets
- Used in machinery where mechanical advantage is needed
- The teeth of sprockets must be identical so that one chain securely fits all the sprockets
- In a given system, the smaller the sprocket the faster it will rotate
Is a sprocket wheels and chain reversible?
Yes
What are the advantages of sprocket wheels and chain?
- Will not allow slippage
* Allows for large forces to be transmitted
What are the disadvantages of the sprocket wheels and chain?
- Needs lubrication
Give a brief explanation of the wheel and worm gear:
Worm gears are used when large gear reductions are needed. It is common for worm gears to have reductions of 20:1, and even up to 300:1 or greater.
For each 360° turn of the worm, the worm-gear advances only one tooth of the gear.
The worm is the driver. The opposite will not work.
Describe the wheel and worm gear:
- Rotational motion is transmitted from the worm gear to one or more wheel gears (sprocket)
- Used in machinery where fine adjustment is needed
- One turn of the worm gear advances the wheel by one tooth.
- Requires fine machining of parts so that the wheel gear teeth fit precisely in the worm gear.
Is the wheel and worm gear reversible?
No. If a force is applied to the wheel gear ( sprocket) the worm gear will not turn.
What are the advantages to the wheel and worm gear?
- Will not allow slippage
* Allows for fine adjustment (eg turning pegs on a guitar)
What are the disadvantages to the wheel and worm gear?
- Needs lubrication
Give a brief explanation of friction gear systems:
- Similar to a gear train, however the friction gears do not have teeth
- Less efficient than gear trains because the gears can slip.
Describe friction gears:
- Rotational motion is transmitted from one wheel to the other
- Transmission is done by friction between wheels
- Rotation direction is opposite in each connecting wheel
Are friction gears reversible?
Yes
What are the advantages to friction gears?
- easy to assemble
- inexpensive to make
- will allow slippage, protecting it from damage
- Gears can be placed perpendicular or at any angle to eachother
What are the disadvantages to friction gears?
- Wheels must always be together even as they wear away
* Wheels can slip, causing interruption in transmission of motion
What are the disadvantages to friction gears?
- Wheels must always be together even as they were away
- Wheels can slip, causing interruption in transmission of motion
- Must be kept clean (free of lubricants)
Give a brief description of the belt and pulley system:
- Similar to a chain and sprocket however, there are no teeth.
- The gear without teeth is called the pulley.
- The chain is called the belt.
Describe the belt and pulley system:
- Rotational motion is transmitted from one pulley to the other by a belt
- Rotation direction is opposite in each wheel
- System can have more than two wheels
Is the pulley and belt reversible?
Yes
What are the advantages to pulley and belt?
- easy to assemble
- will allow slippage, protecting it from damage
- allow for transmission of motion over long distance e.g ski lift
What are the disadvantages to pulley and belt?
- Slippage will occur with wear and improper tension on the belt
- Belt and Pulleys must be kept clean ( free of lubricants)
- Belt can be subject to premature wear
What are the characterisitcs of motion in transformation systems?
*Mechanical action that changes the nature of motion (rotation to translation, translation to rotation)
Describe the rack and pinion:
- Rotational motion of pinion is transformed into translational motion of rack.
- Translational motion can be applied to rack produce rotational motion in the pinion.
- The rack is really a toothed gear wheel that has been straightened.
Is the rack and pinion reversible?
Yes because rotational motion can be applied tot he pinion to produce translational motion in the rack and vice versa.
What are the advantages to the rack and pinion?
- Allows force to be applied without slippage
What are the disadvantages to the rack and pinion?
- Parts need to be lubricated
* Very precise fit needed between teeth of rack and pinion
What are the two types to the screw gear system?
Type 1) Nut is free component. Screw is fixed component.
Type 2) Screw is free component. Nut is fixed component
Is the Screw Gear system reversible?
No, because you cannot transform translational to rotational motion in this system.
What are the advantages to the screw gear system?
- Allows for precise adjustment in it’s use. Used in many types of tools and machinery.
What are the disadvantages to the screw gear system?
- Parts need to be lubricated
Give a brief description of the cam and follower systems?
Rotational motion of the cam is transformed into translational motion of the slider.
Describe the cam and follower:
- Rotational motion can be applied to cam to create translational motion on the follower. The follower must have guidance of some sort to operate properly.
- Size and shape of cam and placement of axle will determine the length and action of the stroke.
Is the cam and follower reversible?
No, because applying a force to the follower ( moving it up and down) will not cause the cam to rotate.
What are the advantages to the cam and follower?
- Allows for very precise and custom translational motion. Timing and distance of the follower can be determined by shape, size of cam and placement of axle on cam.
What are the disadvantages of the cam and follower?
- Parts need to be lubricated
* A return mechanism (e.g spring, gravity has to be built into design).
Give a brief description of the slider-crank mechanism:
- Translational motion of the piston is transformed into rotational motion of the crank. Reversible!
Define the (rotating)slider crank mechanism:
- Rotational motion is transformed to translational motion in the slide
- Translational motion of the slide is transformed into partial rotational motion in the crank.
- Provides a mechanical advantage which is determined by the size of the wheel
- Produces oscillating motion.
Is the slider crank mechanism reversible?
Yes, because rotational motion of the crank produces translational motion in the slide and translational motion of the slide produces partial rotational motion in the crank.
What are the advantages to the slider crank mechanism?
- Changes motion from translational to rotational or vice versa
What are the disadvantage s of the slider crank mechanism?
- Parts need to be lubricated
* Reversibility is only partial
