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Subsystem: Safety
Project: 7201 - 10 kg Motor Module
Objective: Concept development of the braking system of the motor module.
Written By: Mark Kaupa
The first step in developing the concepts was to brainstorm some ideas. One main
method was to look at existing braking systems and see if they were be applicable to our
motor module. The next step was to research to find any other applicable concepts. The
concepts next were divided into subcategories.
Mechanical:
1. Drum Braking
2. Disc Braking
Electrical:
1. Dynamic Braking
2. Regenerative Braking
3. Motor Shorting
Electromechanical:
1. Magnetic Particle Braking
2. Power off Braking
3. Flange Mounting Spring Braking
For the purpose of this subsystem we are not going to discuss the electrical concepts
developed. They we integrated in the motor subsystem concept development. They are
definitely concepts that are applicable to the project but, they are assumed to be applied
and that this subsystem is a “fail-safe” system to the electrical braking that will be
applied to the project. The electrical concepts we be reevaluated at the concept selection
process.
Mechanical: Drum Braking
This system is ideal due to the emergency brake lever. This is an added safety measure to
the braking system. However, this application will need to be discussed with mechanical
subsystem to ensure that this safety concept can be used. The piston is engaged and the
discs are applied to the rotating system. The method of braking is a friction and wedging
method.
Mechanical: Disc Braking
This application is more applicable than the drum braking system. Any wheel system
will be able to utilize this braking system. A rotor is attached to the shaft and a caliper
would have to be mounted inside the yoke. There are both hydraulic and mechanical disc
brakes. The ability to lock in the brake (parking brake) is possible. However, the size of
the wheels will be an issue. If they are not large enough it might not be possible buy a
rotor and caliper to fit the motor module.
Issues with Mechanical Braking Systems:
The main issues the integration of these mechanical braking systems into an electrical
system. In addition, the size of the wheel application is needed to be determined to be
able to apply these systems. The mechanical braking system can also replace the
electrical braking system as well. Both applications can be applied and have “fail-safe”
application applied to it. However, with any friction system heat is developed. And this
can lead to failure of some mechanical systems. Therefore, maintenance is also an issue
if the application becomes very demanding of the braking system continuous
maintenance will be needed on the mechanical braking system.
Electromechanical: Electromagnetic Braking
These brakes use a single plate friction surface to engage the input and output members
of the brake. This style of brake is used in applications ranging from copy machines to
conveyor drives. They are the most common type of electromechanical brakes. Other
applications for these brakes could include packaging machinery, printing machinery,
food processing machinery and factory automation.
Electromechanical brakes operate via an electric actuation, but transmit torque
mechanically. When voltage/current is applied, the coil is energized creating a magnetic
field. This turns the coil into an electromagnet that develops magnetic lines of flux. The
magnetic flux attracts the armature to the face of the brake. The armature and hub are
normally mounted on the shaft (customer supplied) that is rotating. Since the brake coil is
mounted solidly, the brake armature, hub and shaft come to a stop in a short amount of
time.
When current/voltage is removed from the brake, the armature is free to turn with the
shaft. In most designs, springs hold the armature away from the brake surface when
power is released, creating a small air gap.
Slippage should occur only during deceleration. When the brake is engaged, there should
be no slippage once the brake comes to a full stop.
This is a variation of the mechanical disc and drum that was previously discussed.
Electromechanical: Power off Braking
Power off brakes stop or hold a load when electrical power is either accidentally lost or
intentionally disconnected. In the past, some companies have referred to these as "fail
safe" brakes. These brakes are typically used on or near an electric motor. Typical
applications include robotics, holding brakes for Z axis ball screws and holding brakes
for servo motors. Many custom designs are available and can be made for use with
different motor applications.
When no current/voltage is applied to the brake, a series of springs push against the
pressure plate, squeezing the friction disk between the inner pressure plate and the outer
cover plate. This frictional clamping force is transferred to the hub, which is mounted to a
shaft (customer supplied).
The power off brake is considered engaged when no power is applied to it. It is typically
required to hold or stop a load in the event of a loss of power, when power is not
available to run a machine.
When the brake is required to release, voltage/current is applied to the coil creating a
magnetic field. This magnetic field pulls in the pressure plate pulling against the springs,
creating an air gap between the pressure plate and the friction disk, allowing it to turn
freely with the shaft.
Electromechanical: Multiple Disks Electromagnetic Braking
Multiple disk brakes are used to deliver extremely high torque in minimal dimensional
requirements. These brakes can be used either wet or dry, which makes them ideal to run
in multiple speed gear box applications. Machine tool applications top the list where
these brakes are used.
Electromechanical brakes operate via an electric actuation, but transmit torque
mechanically. When voltage/current is applied to the coil, it creates a magnetic field. This
turns the coil into an electromagnet, which develops magnetic lines of flux. The magnetic
flux attracts the armature to the face of the brake. As it does so, it squeezes the inner and
outer friction disks together. The armature and hub are normally mounted on the shaft
(customer supplied) that is rotating. Since the brake coil is mounted solidly, the brake
armature, hub and shaft come to a stop in a short amount of time.
When current/voltage is removed from the brake, the armature is free to turn with the
shaft. Springs hold the armature away from the brake surface when power is released,
creating a minimal drag.
Slippage should occur only during deceleration. When the brake is engaged, there should
be no slippage once the brake comes to a full stop.
Electromechanical: Magnetic Particle Braking
Magnetic particle/current brakes are unique in their design from other electromechanical
brakes because of the wide operating torque range available. Like an electromechanical
brake, torque to voltage is almost linear; however, in a magnetic particle brake, torque
can be controlled very accurately (within the operating rpm range of the unit). This
makes these units ideally suited for tension control applications, such as wire winding,
foil and film tension control and tape tension control. Because of their fast response, they
can also be used in high cycle applications, such as magnetic card readers, sorting
machines and labeling equipment.
Magnetic particles (very similar to iron filings) are located in the powder cavity. Without
any voltage/current, they sit in the cavity; however, when voltage/current is applied to the
coil, the magnetic flux that is created, tries to bind the particles together, almost like a
magnetic particle slush. As the voltage/current is increased, the binding of the particles
becomes stronger. The brake rotor passes through these bound particles. The output of
the housing is rigidly attached to some portion of the machine. As the particles start to
bind together, a resistant force is created on the rotor, slowing, and eventually stopping
the output shaft.
When current voltage is removed from the brake, the input is free to turn with the shaft.
Since magnetic particle powder is in the cavity, all magnetic particle units have some
type of minimum drag associated with them.
Conclusion:
There are many electrical braking systems to apply the mechanical braking systems that
were discussed. However, the mechanical braking system cannot be ruled out. The next
issue to be applied is which application will be best for our motor module system.