For years, spring set/electrically released brakes have provided failsafe braking and holding in a multitude of applications. Generally mounted on a motor or drive shaft, the brakes offer holding and dynamic stopping in applications ranging from large wind turbines to small servo motors. Specially designed brake controls are a critical factor of brake performance in any application.
A key operational aspect of the controls is the detection of armature motion during brake disengagement. With standard controls, users must estimate the time interval between the initial application of voltage and full disengagement. Required to be conservative to avoid excess wear and total loss of operation, these estimates are unable to fully optimize performance. Standard controls are also unable to notify the user when the brake disengages or provide any information about the condition of the brake.
Newly developed smart control spring set/electrically released brake control technology not only optimizes brake performance but also provides previously unavailable real-time brake outputs to the user. By monitoring the current supplied to the brake during disengagement, the new controls reliably detect armature motion to accurately determine the point of brake disengagement and respond by reducing the activation voltage to a holding voltage, taking the guesswork out of the determination. By conveying real-time data about brake disengagement and performance to other controllers or computers with monitoring software, the smart controller serves as a diagnostic tool to maintain overall drive system health. Interchangeable with existing brake controls and able to be seamlessly integrated into the Industrial Internet of Things (IIoT), this innovation takes spring set/electrically released brake controls to the next level.
Standard Brake Controls
In all spring set brakes, an armature is biased against the friction elements by a set of springs between the brake housing and the armature. The spring force pushing against the armature squeezes the brake rotational friction elements against the stationary friction elements, thereby stopping the rotational friction elements, creating torque. The brake is disengaged by applying DC current to the brake coil. The coil produces an electromagnetic field in the brake housing that pulls the armature against the springs and across a preset air gap until the armature abuts the housing. At this point, the brake is fully disengaged. Holding the armature against the housing requires a lower-strength magnetic field because of the elimination of the air gap, allowing the activation voltage to be reduced to a holding voltage.
The manually set lower holding voltage allows the brake to run cooler, requiring lower power consumption and causing less wear of the brake. Generally, the required holding voltage varies negligibly with changes in environmental conditions and does not vary with brake wear.
In standard brakes, the time interval between the initial activation voltage and the reduced holding voltage, or brake disengagement time, is also set manually. Environmental and operating variables that are application specific — such as temperature, vibration, shock loading, contamination, cycle rates, and wear — affect the brake disengagement time from cycle to cycle and over the life of the brake. If the disengagement time is underestimated, the motor engages before the brake is fully disengaged, causing the two to work at cross purposes, resulting in increased wear and excessive heat generation. An overestimate of disengagement time causes, at a minimum, longer cycle rates and higher power consumption.
For the best performance and longevity, the user establishes the disengagement time based on the maximum amount of time required for disengagement at the end of the brake’s operational life, accounting for all environmental variations and adding a safety factor. The safety factor assures that the controls do not reduce the applied voltage to the holding voltage prior to the brake fully disengaging. At any point in the life of the brake, the amount of time beyond the full disengagement before the voltage is reduced to the holding voltage is shown in Figure 1 as Wasted Time.
Standard brake controls are unable to respond to the condition of the brakes and do not provide the user with information about brake performance. The controls will continue to operate regardless of whether the brake is operational. The brake will operate until it can no longer disengage, resulting in catastrophic failure that may also adversely affect other drive system components. Only through frequent visual inspections of the brake friction elements could a user assess the worn condition of a brake and often, such inspections are not feasible or cost-effective.
New Smart Control Technology
The new smart IloT brake controller detects motion in the brake armature and utilizes this information to accurately determine when the brake is disengaged, then automatically reduces the full activation voltage to the preset holding voltage. The detection of the armature motion is communicated to the user in real time. In addition, data is collected and analyzed from cycle to cycle to assess the overall condition of the brake and drive system, with abnormalities reported to the user. Providing such otherwise unavailable data allows the user to maximize efficiencies while minimizing failure risk.
The standard brake user’s overestimate or underestimate of time to full disengagement is eliminated with the new smart brake controls. Precise tracking of armature motion allows the smart sense controls to reduce the voltage to the holding voltage with negligible (t+) response delay. The voltage reduction occurs when the brake armature moves, regardless of variations in temperature, operation, environmental conditions, or brake wear. Figure 2 illustrates smart brake control disengagement of a new brake (green line) and a worn brake (red line). The time before the controls reduce the activation voltage to the holding voltage accurately tracks by (t+) the actual disengagement time from the brake’s new condition to its fully worn condition.
For example, operational temperature changes may result from factors such as cycle rate variations, torsional load changes, and environmental conditions. The temperature changes affect the brake’s capability to thermally expel heat and consequently affect brake disengagement time. The smart brake controls automatically adjust for any disengagement time variations by accurately reading the actual disengagement time.
The precise tracking feature of smart controllers, in combination with its digital signal output, resolves a performance issue specific to holding brakes. When a holding brake releases its torsional load, the motor takes control of the load. An overestimate of the release time causes “drift” of the load before the motor takes control. By digitally notifying the motor controller in real time when the brake is fully released, the smart controller effectively eliminates any drift.
Beyond notifying the user of brake disengagement, the controls offer several other digital and analog outputs in real time. For example, the smart controller communicates abnormal brake cycles, which may be an indication that the drive system’s bearings are approaching failure. The controls also estimate brake life based on the wear generated from prior cycles and notify the user of the worn condition of the brake. The information may be used to schedule brake maintenance to avoid brake failure.
In some cases, catastrophic system failure may also be avoided. For example, a system that is being operated beyond its means with high cycle rates or excessive loads will generate extreme heat, causing the brake to cease disengaging. With a standard brake control, the user would not be able to identify the issue until the drive system failed. With new brake controls, if a brake is no longer able to disengage, by monitoring the controls, the brake failure can be determined by the user.
Ease of installation and integration further enhance the value of the new technology. Free of external sensors, the smart sense controls are fully interchangeable with existing standard controls. The smart brake controls provide analog (brake wear) and digital (brake disengagement and 80% worn condition) outputs that may be connected to smart motor controllers and/or monitoring software such as HMI or IoT-enabled software.
The new, innovative smart controller internally senses, captures, and makes use of brake armature movement to provide sensorless optimization of spring set/electrically released brakes, conserving power and maximizing brake life. Previously unavailable analog and digital outputs allow users to monitor armature position and movement, providing key insights into brake wear that help the user get the most out of the brake and improve the drive system. The controls may be seamlessly integrated with monitoring software to provide complete remote monitoring of critical systems.
This article was written by Michael Gamache, President, Carlyle Johnson Machine Company and Regent Controls, Greenville, RI. For more info, visit here .