4/8/2011· Elevators - Escalator - Automatic Doors
Choosing An Elevator Expert Witness
By: Ronald Creak
When choosing an expert witness, most people will agree it is vitally important to select the right one from the outset.
By: Anthony S. Boom
Electrical Engineer and Escalator Controls Expert Witness
Tel: 309-736-9844
Email Mr. Boom
Ever since the very first escalator was installed, escalator manufacturers and safety code committees have worked proactively and reactively to make escalators as safe to ride as possible. Whether manufacturers and code committees were acting proactively or reactively, as time passed, many new safety devices and rules were implemented to make escalators and auto-walks safer to ride.
In the more than 35 years that I have worked in the escalator business, I have seen the implementation of a variety of new safety devices such as missing step detectors, handrail speed sensors, comb impact devices, level step devices, over speed and under speed devices and more.
Much could be written about the addition and evolution of all the escalator safety devices, but the focus of this article is on the evolution of the most important escalator safety device - the escalator brake.
The escalator brake is the utmost important escalator safety device since every other safety device on an escalator depends on the function of the escalator brake. If there were no escalator brake then what would the value of installing an emergency stop switch or an over speed device or a comb impact device or what every safety device? The answer is, “none.” If there were no escalator brake then the escalator would not stop when a safety device activated. At best, the escalator motor would shut off and the escalator would continue to move until the weight of the passengers on the escalator was insufficient to overcome the friction of the handrails and the rolling step band.
Early escalator brakes were simple spring applied brakes, now referred to as fixed torque brakes. Tension springs and compression type springs were utilized to apply the escalator brake when required. Tension springs lost favor since; a failure of the tension spring would result in having no brake at all. Whereas a compression spring can still provide some spring force if the spring breaks.
To minimize the differences in escalator stopping distances and stopping rates, escalator manufacturers added a large flywheel to the escalator motor. Adding a flywheel to the escalator motor reduced the impact of the loading on the escalator. Essentially, the brake is working more to stop the flywheel rather than stopping the load on the escalator. The bigger the flywheel the more consistent the stopping of an escalator becomes from no load on the escalator to a heavy load on the escalator.
Adding a flywheel not only makes the escalator stop more consistently but the flywheel makes the escalator stopping rate more consistent in both directions, Up and Down directions. Without a flywheel mounted on the escalator motor, a load on the escalator will cause the escalator to stop short if the escalator is running in the Up direction and stop long if the escalator is running in the Down direction.
It may seem that the flywheel mounted on the escalator motor shaft rectified most of the issues of the fixed torque brake. However, adding a flywheel creates some new undesirable issues:
Escalator manufactures have put up with these issues for decades to gain the benefits that adding flywheel provides. However, as time went on, safety code requirements became more stringent. The code required a minimum stopping distance of 4.5”. (4.5” was calculated on a maximum deceleration rate of 3ft/s^2 for an escalator running at 90ft/min.) Stopping quicker than 3ft/s^2 was deemed to be destabilizing to passengers. However, the escalator had to be stopped in a distance no greater than about 16”. 16” was determined by the distance from the skirt switch to the comb teeth on the escalator. If someone’s shoe was entrapped between the edge of the step and the escalator skirt when tripping the skirt switch, the escalator had to be stopped before that persons’ foot was dragged into the comb teeth.
To meet the code allowed stopping distance range of 4.5” to 16”, no matter the live load on the escalator, manufacturers experimented with increasing the size of the motor flywheel to minimize the effect of the live load on the escalator. Other manufacturers explored setting the brake torque high then delaying the application of the brake to meet the minimum stop distance requirement of 4.5”.
Delaying the application of the brake helped meet the minimum stopping distance requirement but failed to meet the maximum deceleration rate of 3ft/s^2. So, the code committee added the requirement of setting the brake without delay to avoid a deceleration rate greater than 3ft/s^2.
In the 1980’s, the company that I worked for paired a permanent magnetic brake (PM brake) with a novel method of applying a fixed brake torque proportional to the load on the escalator. The advantage of the PM brake was and is that it is a variable torque device. The PM brake produces a torque that is inversely proportional to the current flowing though the PM brake coil. If the load on the escalator was heavy then the brake controller could increase the brake torque by reducing the PM brake current . If the load on the escalator was light then the brake controller could decrease the brake torque by increasing the PM brake coil current.
Now this brake controller determined the load on the escalator by measuring the phase angle between the escalator motor voltage and the escalator motor current. A larger phase angle implies a lighter load on the escalator while a smaller phase angle implies a heavier load on the escalator. If the phase angle were small then the escalator brake controller would reduce the PM brake coil current to apply more braking force while the escalator was stopping. When the phase angle was larger the escalator brake controller would increase the PM brake coil current to decrease the braking torque.
Applying brake torque proportional to the load on the escalator eliminated the need for a flywheel while being able to meet the code requirements for deceleration rate and stopping distances. However, this brake controller required a fairly complex control setup that varied depending on motor size and motor manufacture. Additionally, the PM brake torque was not consistent from brake to brake for a given brake coil current. Consequently, additional setup adjustments had to be made from time to time or whenever the brake was replaced with a new brake.
In 1988, the same company came up with a new brake control that was simpler to set up and was independent from motor size, motor manufacture, and variations in brake torque for a given brake coil current. This new method utilized “velocity feedback” with the same PM brake. The “velocity feedback” brake controller compared a predefined voltage ramp to the voltage of a tachometer driven by the escalator motor. The brake controller would vary the brake torque depending on how the tachometer voltage was following the predefined voltage ramp. If while the escalator was stopping, the tachometer voltage was less than the predefined voltage ramp voltage then the escalator was stopping quicker than desired. So, the brake controller would reduce the braking torque to decrease the stopping rate of the escalator. However, if the tachometer voltage was greater than the predefined voltage ramp then the escalator was stopping slower than desired. So, the brake controller would increase the braking torque to decrease the stopping rate of the escalator.
As long as the brake could produce ample torque to stop the rated load velocity feedback functioned fairly well.
It should be noted that to prevent an unsafe situation, the escalator controller would not allow the escalator to run if the voltage on the tachometer was too low.
In 1993, the same company came up with another new brake controller that had all of the advantages of the “velocity feedback” brake controller but was even simpler set up and did not have to be “tuned” or “re-tuned”. This new method utilized “deceleration feedback” with the same PM brake. This brake controller utilized an encoder instead of a tachometer to determine velocity and to calculate the real time escalator deceleration. The calculated real time escalator deceleration rate was then compared to a desired deceleration setpoint. The brake controller utilized a PI (Proportional and Integral) control to vary the brake torque depending on how close the real time escalator deceleration rate was to the desired set point. If while the escalator was stopping, the real time escalator deceleration rate was greater than the setpoint then the escalator was stopping quicker than desired. So, the brake controller would reduce the braking torque to decrease the stopping rate of the escalator. However, if the real time escalator deceleration rate was less than the setpoint then the escalator was stopping slower than desired. So, the brake controller would increase the braking torque to increase the stopping rate of the escalator.
As long as the brake could produce ample torque to stop the rated load deceleration feedback functioned well.
One of the major drawbacks of deceleration feedback brake control is on an Up running escalator. A loaded Up running escalator will always stop quicker than the desired deceleration setpoint if there is no flywheel mass mounted on the escalator motor. However, at this time, the Escalator Safety Code does not require a maximum deceleration rate when the escalator is running in the Up direction.
Earlier this year, 2024, I finished testing a new hybrid braking system for escalators and auto-walks. This hybrid braking system incorporates deceleration feedback braking control with another type of brake control recently permitted by the ASME A17.1-2019 and 2022 Escalator safety code Rule 6.1.5.3.4. The Escalator Safety code refers to this new braking system as, “Motor-Controller Dynamic Braking.” Motor Controlled Dynamic Braking requires power to remain connected to the escalator motor during the braking process because the motor is being utilized for braking.
Actually, Motor Controlled Dynamic Braking is not new but until recently was not permitted for use on escalators and power walks because the Escalator Safety code has always required the removal of power from the driving machine motor and brake whenever a safety device is activated. The escalator safety code now permits the use of Motor Controlled Dynamic Braking provided several other rules are followed.
To overcome the disadvantages of the Motor Controlled Dynamic Braking I paired Dynamic braking with Deceleration Feedback control to form a hybrid system. For most safety devices, Motor Controller Dynamic Braking is utilized. Where Motor Controlled Dynamic Braking cannot be utilized the hybrid system utilizes Deceleration Feedback control.
Ever since the very first escalator was installed, escalator manufacturers and safety code committees have worked proactively and reactively to make escalators and auto-walks as safe as possible by adding and improving safety devices.
The most important safety device on the escalator is the escalator brake. All other safety devices depend on the escalator brake to stop the escalator when a safety device is actuated. The brake must not only stop the escalator or auto-walk, but the brake must stop the escalator in a manner that is as safe as possible.
As previously discussed, escalator brakes started out as fixed torque brakes. Then improvements came with the addition of flywheels, variable fixed torque brakes, velocity feedback, deceleration feedback, and now Motor Controlled Dynamic Braking.
The braking system that I recently finished testing is a hybrid system which combines Motor Controlled Dynamic Braking with deceleration feedback braking for when Motor controlled Dynamic Braking cannot be utilized.
ASME A17.1-2019/CSA B44:19 Rule 6.1.5.3 Brakes
Anthony S. Boom, is an Electrical Engineer and Escalator Controls Expert Witness with over 35 years in the escalator business. Currently providing expert witness services though Cetek, Inc., he spent the last three decades working as an Electrical Engineer with Montgomery Escalator and KONE R&D, escalator division. Mr. Boom offers expert witness services to attorneys representing plaintiff and defense. Services include expert witness testimony, written or oral affidavits, site inspections, technical investigations, technical review documentation, etc.
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4/8/2011· Elevators - Escalator - Automatic Doors
Choosing An Elevator Expert Witness
By: Ronald Creak
When choosing an expert witness, most people will agree it is vitally important to select the right one from the outset.
8/22/2014· Elevators - Escalator - Automatic Doors
Garage Doors: A Brief Tutorial on Garage Door Safety & Installation
By: Michael Panish
As a door expert, I am called upon many times a year to evaluate garage door injuries. In my professional career as a general contractor and door & hardware contractor, I have installed many different types of garage doors. I have been involved with roll up doors, both for commercial warehouse applications and automotive repair facilities that allow the passage of a motor vehicle. I have installed and serviced life safety/fire drop doors typically seen in hospitals, pharmacies, labs, shopping centers and other commercial venues. I have placed sectional doors in apartment buildings, single family homes and condominiums. My company has custom built many types of garage enclosures that have had special cosmetic concealed purposes for themed attractions. Working on historic buildings has given me the opportunity to work on sliding barn type doors, hinged parting doors and old carriage style swinging doors. I have removed and replaced the older style, overhead vintage single panel pivoting hinged garage door from commercial and residential locations, and have installed a variety of newer and safer products.
5/7/2014· Elevators - Escalator - Automatic Doors
Door Defects & Door Related Injury Claims
By: Michael Panish
We are all used to opening and closing doors on a daily basis. Unless you encounter a problem with the function of your doors, you probably don't give their operation and component make up much thought. I am continually contacted by attorneys seeking my advice on an injury that took place because of an improperly adjusted or malfunctioning door. In this article, I am simply discussing manually operated doors. Nothing fancy or automatic about them, the kind where you grab a lever, push a plate or bang on a bar to enter or leave a room or building. So, if you want to learn to communicate professionally and simply with your door expert or even your building manager, read on.