Electric Brake and Clutch Assemblies Information
Electric brake and clutch assemblies are equipment drive components that consist of electric brakes for slowing or stopping shafts and electric clutches for connecting or disconnecting shafts. Battery-powered load cells apply voltage signals to a web and compare the resulting web tension to a tension set point. Correcting the current output produces a braking torque that is proportional to the supplied current. Engaging the clutch transfers power from an engine to devices such as a transmission and drive wheels. Disengaging the clutch stops the power transfer, but allows the engine to continue turning. Braking slows or stops the movement of the coupled shafts by using permanent magnets, hysteresis, eddy current, or magnetic particles. Typically, electric brake and clutch assemblies are used in applications that require fast response times and precise tension control.
Clutch specifications for electric brake and clutch assemblies include torque rating, power, rotational speed, and operating voltage. Spring-return clutches require power to engage. Spring-actuated clutches require power to disengage. A variety of engagement methods are available. Non-contact clutches uses methods such as magnetic fields and eddy currents. Friction clutches generate friction between contact surfaces. Wrap spring clutches transmit torque from the input to the output through a wrapped spring that uncoils to disengage the clutch. Oil shear clutches achieve drive engagement through the viscous shear of transmission fluid between the clutch plates. Sprags, steel wheels that tip in one direction to wedge between inner and outer races, are clutches that can often transmit more torque than other slip or overrunning devices. Ball detent clutches feature a slip mechanism in which, upon overload, seated balls are dislodged and overcome springs or air pressure engagement. Similarly, pawl clutches overcome spring or air pressure engagement and rotate out of their detent. With roller detent clutches, rollers that are held in place by springs wedge between the inner and outer races to engage the clutch.
Brake specifications for electric brake and clutch assemblies include torque rating, power, speed, and operating voltage. Spring-return brakes require power to engage. Spring-actuated brakes require power to disengage. A variety of brake engagement methods are available, including friction, wrap spring, oil shear, toothed surface, and non-contact methods. Band brakes, the simplest brake configuration, have a metal band lined with heat and wear resistant friction material. Drum brakes, which are commonly used on automobile rear wheels, work when shoes press against a spinning surface called a drum. Disc breaks are constructed of brake pads, a caliper, and a rotor. During operation, the brake pads are squeezed against the rotor. Cone brakes are made with a cup and a cone, which is lined with heat and wear resistant material. During actuation, the cone is pressed against the mating cup surface.
How to Select a Clutch or a Brake
Selecting electric brake and clutch assemblies requires an analysis of measurements, shaft configurations, and special features. Important measurements for electric brake and clutch assemblies include diameter, the cross-sectional width of the assembly; length, the dimension along the axis of rotation; and weight. Shaft configurations can be in-line along the axis of the load, parallel but offset from the axis, or perpendicular (right angle) to the axis. Special features include adjustable torque, zero backlash, feedback, automatic re-engagement, and bidirectional rotation.
JIS B 0152 - Clutches and Brakes - Vocabulary