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I was trying to think of a clever title for this post, but it's
the Friday before a long weekend and I'm excited for a vacation. The electric
breaks selection guide was one of the first guides I completed at GlobalSpec;
it was a labor of love and I learned a lot! Now I would love to share an
abridged version with you.
Electric brakes are actuator devices that use an electrical
current or magnetic actuating force to slow or stop the motion of a rotating
component. They are used in industrial and vehicular braking applications that
require fast response times and precise tension control.
There are two main types of electric brakes: magnetic and
friction. Each has various subtypes. As described below, the way an electric
brake works depends upon these characteristics.
Spring Applied Brakes. Image
Credit: Hillard
Types of Magnetic Brakes
Magnetic brakes are non-contact brakes that use magnetic fields to
actuate the braking components. There are four types.
This table compares
the different types of magnetic brakes.
|
Type |
Application |
Advantages |
Disadvantages |
|
Permanent
magnetic brake |
For
electric motors, robotics, holding brakes for Z axis ball screws and servo
motor brakes |
High
and accurate torque, long life, unaffected by power supply, safe and easy to
use |
Require
a constant current control to offset the permanent magnetic field |
|
Electromagnetic
brake |
Copy
machines, conveyor drives, packaging machinery, printing machinery, food
processing machinery and factory automation |
Fast
response time, smooth, reliable, and backlash free operation, produce high
torque, automatic air gap available |
Braking
force diminishes as speed diminishes, load cannot be held at a standstill
causing safety concern. |
|
Eddy current
brakes |
Train
and roller coaster brakes |
Noncontact,
Frictionless, resettable, light weight, few moving parts |
Unusable
at low speeds, generates heat |
|
Hysteresis
powered brakes |
Food
and drug packaging operations, clean rooms, environmental test chambers, load
simulation for life testing on rotating devices, capping, bolting and other
screwing applications |
Long,
maintenance-free life, cost effective, operational, smoothness, torque
repeatability, broad speed range, environmental stability, high-dissipation
capability. The torque remains constant and smooth and responds with
increases and decreases in current. |
Experience
a salient-pole phenomenon called "cogging", an undesirable,
pulsating output torque which prevents smooth and efficient operation of these
systems |
Types of Electrically Actuated Friction Brakes
Although many electric brakes use mechanical methods for
actuation, others rely upon friction. There are several types of frictional
brake devices. Each is described below.
This table compares different types of friction brakes.
|
Mechanism |
Application |
Advantages |
Disadvantage |
|
Band |
Automatic
transmissions, backstops, bucket conveyors, hoists |
Simple,
inexpensive, easy to make, reliable, low maintenance |
Poor
heat dissipation capacity, wear friction lining is uneven from one end to the
other. |
|
Drum |
Rear
automobile brakes |
Shoe
mounting can be designed to assist their own operation (self-actuating),
don't need a break booster |
The
friction area is covered by lining, so most of the heat must be conducted through
the drum to reach the outside air to cool, difficult to get water out of the
drum if driven through water, not as efficient in reverse |
|
Disc |
Automobile
brakes, often front wheel |
Brake
fade is rare, can operate after being exposed to water |
Generate
high heat from friction, no self-servo effect |
Friction brakes are used in industrial applications such as in
agriculture, ATVs, aerospace and construction equipment, or mining, milling and
manufacturing projects.
Image Credit:
How Stuff Works
Operating Specifications
Specifications for electric brakes include the torque rating and
power. The torque rating is the turning force of an object and should be
greater than or equal to what is required by the application. Power is defined as the rate of
doing work.
The brake capacity depends on five factors:
- Unit pressure between brakes
- Contacting area of braking surface
- The radius of the brake drum
- The coefficient of friction
- The ability of
the brake to dissipate heat that is equivalent to the energy being
absorbed.
So
there you have it, how to select electric brakes. The full guide can be found
on GlobalSpec - How to Select Electric Brakes.
It
is the Editorial Team's desire that we provide you with quality content that is
helpful. So let us know what you think!
Enjoy
the holiday!
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Re: How to Select Electric Brakes
