A stacker retrieval system includes an encoder, brake, and motor. The brake housing is modified to provide a mount register for the encoder and extended shaft.

Because brake-engaging springs immediately jump into action when power is cut, spring-set brakes are especially suitable for backup and protection applications. Widely used for static holding, general load stops, and occasional emergency stops, they’re also effective where VFDs, servos, and stepmotors slow loads first. While some use a diaphragm or bladder arrangement, most fluid power and electrically released types use springs for clamping when power is removed. The latter can be categorized into two groups.

Electrically released armature-activated brakes use springs to clamp the rotor (with attached friction pads) between a stationary end plate and a non-rotating armature. In these units a simple, fixedvoltage power supply keeps the brake released. With power applied to the brake coil, its magnetic force attracts the armature to compress the springs and release their hold.

Generally coils are rated for continuous duty and can be continually energized without overheating. When coils do heat up, they get hottest at coil engagement due to engaging, or pull-in amperage. For UL Class A insulation, coil temperatures shouldn’t exceed 105°C; Classes B and H limits are 130° and 180°C respectively. A high ambient temperature where the brake is actually mounted may limit the coil cycle rate. A coil temperature rating should include the wire, tape, insulation, and any coating materials.

Solenoid-actuated brakes are the second type of electrically activated springset brake. They come with either single or dual-voltage coils and can be wired to either single or three-phase motors. Compared to armature-actuated brakes, solenoid-actuated brakes have a crisp electrical response time. However, instantaneous rated voltage must be supplied to coils to ensure proper solenoid pull-in and maximum coil cycle rate.

It’s important to remember that these brakes must be wired separate from drives for proper control of each. Solenoid-actuated brakes are designed to a typical NEMA voltage range of
10% of the rated voltage and frequency. Equipment and system installers accustomed to typical NEMA design B motors may try to wire the coil across the motor windings; however, by design VFDs vary frequency, and that doesn’t work with a fixed-frequency product. An installation rule of thumb: Confirm wiring before powering. For example, suppose a brake is mounted to the accessory end of a drive intended for field-wire. An installer, familiar with standard motors, might assume the brake has been pre-wired, and begin to troubleshoot a faulty operation. In fact, in this situation the brake is not getting any electrical power. To prevent these misunderstandings, some drive manufacturers have a fixed voltage tap in their power box, which is a convenient arrangement for wiring a brake into the motor power box.

How big?

Emergency brakes cannot protect if they’re improperly selected; ISO and ANSI safety factors must be applied. So exactly how powerful should a specified brake be? It depends on whether the desired reaction is a very rapid emergency stop, or softer stop that sacrifices brakes to prevent disturbing loads or the overall system. Establishing maximum as well as typical conditions — from typical situations to worst-case scenarios — also influence requirements. The entire system (and not just one component) must have enough torque to meet the dominant prescribed condition: braking, clutching, tensioning, or limiting. The trick is knowing that condition ahead of time.

Some brakes are modified for outdoor environments and include lock-out manual releases for use in oil-rig equipment. Going clockwise, the system includes a large pinion, gearbox, parallel-shaft chain drive, motor, and the brake.

The easiest and most common method is to size a brake’s dynamic torque to the system’s motor torque. This technique does have limitations; motors can draw extra current for short bursts to provide more torque than their 100% rating. (This is especially important to remember for vertical applications, as brakes must be able to stop any falling of whatever items the motor lifts.) Even so, sizing to the system’s motor torque is a suitable method for the majority of cases.

Whether torque selection is robust or lean depends on design Driving a conveyor system intent. Because of the potential for fatigue or early wear of other system components (such as gearboxes or leadscrews) overdesigning is actually just as risky as under-designing. Specific industry standards — for automotive, packaging, medical, and general material hoisting applications — play a role in the type of planning required. In fact, each industry has different recommended sizing schedules. Motor manufacturer’s performance curves can be consulted for dynamic torque ratings at operating speeds that meet or exceed peak torques developed by the motor. Sometimes if the brake is small enough, the motor and load can drive through the brake.

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