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Rope Grippers & Brakes

February 18, 2009

Ascending Car Overspeed and Unintended Car Movement Protection - Section 2.19

The Code

All newly installed electric traction elevators are required to have a means to stop the car in the event of an overspeed in the up direction and to keep the car from moving when movement is not intended.  With respect to ascending car overspeed (ACO), the intent is to prevent the elevator car from from striking the hoistway overhead structure.  With respect to unintended car movement (UCM), the intent is not to permit the elevator car to move when the car and hoistway doors are not closed and locked.  This code is defined in ASME A17.1-2000/4/7, Section 2.19.  The device required is referred to as an "emergency brake." 

All altered (alteration, modernization) electric traction elevators must meet this requirement as well, provided the alteration includes one or more of the following:

  8.7.2.16.1 - Change in Type of Service
  8.7.2.16.4 - Increase in Rated Load
  8.7.2.17.2 - Increase in Rated Speed
  8.7.2.25.1 - Alteration to Driving Machines and Sheaves
  8.7.2.27.5 - Change in Type of Motion Control

As this code requirement is fairly new to the state of California, which only adopted ASME A17.1-2004 as of May 1, 2008, there have been a lot of questions raised about how and when this requirement applies, especially concerning alterations.  Must this feature be added when modernizing a winding drum elevator?  The answer is no, as the code specifically references "traction" elevators. 

The State of California has not designated the ACO & UCM protection devices as an "Approved Device" as they have for interlocks, governors, safeties, and buffers.  To my understanding, whatever means and devices are used to provide the ACO & UCM protection must simply comply with Section 2.19.

The most common alteration of an existing traction elevator is replacement of the control system.  Especially common is the removal of motor-generator sets.  For geared traction elevators, typically the DC drive motor is replaced with an VVVF-AC motor.  For existing DC gearless machines, the new control system will include an SCR drive system.  These are clear examples of a change in the type of motion control as defined in Section 1.3 - Definitions.  The original controls which included the motor-generators would be defined as "control, generator field."  Whereas the new controls would be either "control, variable voltage, variable frequency AC" or "control, static."  As such, ACO & UCM protection must be added.   

A correct reading of the code regarding a change in the type of motion control in an alteration where the new control system to be installed and the old control system to be replaced are both of the same type, ACO & UCM protection would not be required.  An example would be a gearless system where the old controls and new controls are both SCR, meaning "control, static."  There are already some early VVVF-AC elevators that are being modernized and the controls replaced with newer generation VVVF-AC systems.  Though not advised, some are replacing controls and retaining the motor-generators.  These are all examples of alterations where the type of motion control is not changed.

In the first release of this article I indicated that Mr. Paul M. Puno, Senior Engineer, DOSH, Elevator, Ride and Tramway Unit has indicated that for non-federal facilities in California, ACO & UCM protection will be required whenever an alteration to a traction elevator includes a new control system - regardless whether there is a change in the type of motion control.  This stirred up a bit of a controversy which has been resolved as of the date of this revised article by Mr. Al Tafazoli, Principal Engineer, DOSH, Elevator, Ride and Tramway Unit.  Speaking at a NAEC/NCEIG Seminar in San Mateo, CA, Mr. Tafazoli made it clear that ACO & UCM protection is not required when the type of motion control is not being changed in an alteration, as the types are defined in Section 1.3 - assuming none of the other four sections making the requirement are not triggered.  This interpretation jibes with that of other states and code authorities.

I believe it is important to recognize that the elevator code is the minimum legal requirements for elevator safety.  When technology presents new equipment and systems that enhance safety, I believe we have a professional duty - and possibly a moral duty - to at least offer the building owner the option to the add such devices.  In the case of ACO & UCM protection, adding a rope brake or equal device can possibly save lives.  It is reasonable to conclude that the death in the Ohio State University dormitory elevator case, and many others, might have been prevented if a Rope Gripper had been installed.  The condition of worn or maladjusted primary brakes on traction drive machines may be too prevalent not to require some form of a secondary brake.  It's my belief that even where the code allows control changes without adding ACO & UCM protection, it is prudent to add it anyway.   

Methods of Compliance & Products

ASME A17.1-2000/4/7, Section 2.19 defines the function, operation and requirements of ACO & UCM protection.  The emergency brake device can act upon the counterweight, car, suspension or compensation ropes, drive sheave, or brake drum or brake surface of the traction drive machine.  The code defines numerous criteria and limitations that would relate as to how the ACO & UCM protection can be accomplished.  Numerous solutions have been devised by the major elevator equipment manufacturers to meet this requirement. 

The most common new installation solution, especially for gearless and machine-room-less (MRL) type elevators, is to provide a secondary brake on the drive machine.  Most gearless drive machines now include this secondary brake as an integral part of the machine.  This solution relies upon the traction between the hoist ropes and the drive sheave to work, stopping the drive sheave and the car.  The control system includes the logic and circuitry to affect the operation, which typically includes a connection to the governor overspeed switch.

One of the early devices designed to comply with the ACO & UCM protection requirement in North America came from the Canadian company, Northern LTD, which later became ThyssenKrupp Northern Elevator.  It was called a "Sheave Jammer" and was a hydraulically activated secondary brake located under their geared machine drive sheave.  It was later recalled as it proved to be faulty.

There is a product suitable for new installation or retrofit that relies upon this same principle of stopping the drive sheave to meet the ACO & UCM protection requirement.  It is called The Sheave-Grip®, manufactured by Warner Electric Europe.  It consists of pairs of electromagnet brakes that are spring applied and electrically released onto the sides of the machine's drive sheave.  Multiple pairs of magnets may be required depending on the rated load of the elevator.  A design limitation is the magnet brakes require 2.3" [80 mm] space on each side of the sheave for a depth of approximately 4" [100 mm].  Most gearless machines don't have this space, many geared machines do.  I've yet to design a ACO & UCM protection project with the The Sheave-Grip® but expect the right job may come along...

Another solution also used in new installations but which is especially suited for retrofitting existing traction elevators is the rope brake.  This is a device that applies a brake surface directly to the elevator hoist ropes to stop the car.  It is most often mounted either directly to the hoist machine, adjacent to the machine or in the hoistway overhead.  They can typically be mounted in any orientation, most commonly on the pitched ropes between the machine drive sheave and the deflector sheave.  They can be mounted horizontally as between two overhead sheaves or inverted in the hoistway overhead beneath the machine beams.  I understand some have mounted a rope brake in the pit acting upon the compensation ropes or on the car crosshead above or between 2:1 sheaves.  These last two methods are solutions I would avoid for a host of reasons.

Rope brakes mounted in the hoistway overhead are increasingly common as, short of raising the drive machine, it is often impossible to locate a rope brake in the machine room.  Many drive machines, especially gearless, lack the necessary space and clearances to fit a rope brake.  Rope brakes mounted in the hoistway should have their controller, pumping unit, air compressor or any other supporting operational equipment mounted outside the hoistway, preferably in the machine or overhead sheave room. 

Mounting a rope brake in the hoistway requires determining that the clearances are sufficient.  Depending on whether the unit is mounted to act upon the hoist ropes that drop to the car or the counterweight, the buffer stroke, runby and 1/2 the gravity stopping distance have to be taken into account as they affect the clearances.  To allow for rope stretch, the counterweight runby varies and is typically greater than the car runby, which remains static.  For this reason and due to frequently greater clearance above the counterweight, it is often feasible to locate the rope brake at the rope drop to the counterweight when there is insufficient clearance to locate it at the rope drop to the car. 

Care must be taken in mounting the rope brake that the travel of the hoist ropes does not vary outside of the open dimension of the brake linings.  This can be an issue when the unit is mounted in the overhead either on the rope drop to the car or to the counterweight.  Some elevator companies designed and installed traction elevators where the hoist rope drops were not plumb.  This was done in some cases to eliminate the deflector sheave and the drive sheave diameter was less (or more) than the horizontal distance between the car and the counterweight rope hitches on elevators roped 1:1.  This condition also occurs on many traction elevators, especially gearless, that are roped 2:1 and standard diameter sheaves were used, resulting in the ropes travelling out of plumb. 

The survey and planning when installing in an alteration should include terminal car runs while checking the centerlines of the ropes at the point where the rope brake will be installed.  If an out-of-plumb condition exists, it must be determined that the outsides of the ropes will stay within the open dimension of the brake linings.  Note the geometrical effect that the further the vertical distance from the sheave, the greater the ropes' horizontal movement in travel.  In some cases if the rope brake can be mounted close enough to the sheave, the rope travel deviation may be within the brake lining clearances.  This may ultimately require, if possible, raising the drive machine and re-supporting it structurally, sufficiently to mount the rope brake directly below the sheave. 

However, if the horizontal distance between the drive sheave and the hitch for 1:1 or car/counterweight sheave for 2:1 is too great, the rope brake cannot be installed without adding a deflector sheave.  Adding a traditional iron deflector sheave typically requires a minimum 5 inches of rope deflection to provide sufficient tangential force on the deflector sheave to prevent loss of traction.  If the deflection is less than 5 inches, the choices are to use a plastic deflector sheave which requires less torque to rotate or to shift the drive machine to obtain 5 inches of deflection.  Many machines are fairly easy to shift with the advantage of bringing both rope drops plumb. 

A similar impediment to mounting a rope brake in a location other than between the machine drive sheave and a deflector sheave is the line of ropes' rotation in plan which occurs in 2:1 roping arrangements.  It is rare in a layout that the drive or deflector sheaves and the car or counterweight sheaves are on parallel axes.  Typically the axes of these sheaves are rotated, sometimes up to 90 degrees.  The result is that the line of hoist ropes rotate in plan through their travel.  The degree of rotation at a given point vertically from the sheaves will vary depending on where the car or counterweight is in its travel in the hoistway.  The closer the 2:1 travelling sheave is to the stationary sheave, the greater the degree of rotation.  Like the out-of-plum condition described above, this line of rope rotation effect must be taken into account when planning the installation of a rope brake.  Locating the rope brake closer to the stationary sheave will mitigate this effect.  In many installations, however, this rotation is too great to fit within the brake lining clearance.  

Yet another complication in mounting a rope brake in a location other than between the machine drive sheave and a deflector sheave, is the hoist rope splay which occurs in 1:1 roping near the shackles.  The car or counterweight hitch plates typically include a hole pattern that is dimensionally staggered so as to allow sufficient space for the rope shackles.  In many instances with a hoistway overhead rope brake installation the vertical clearance is such that the rope splay exceeds the brake lining clearance.  If this will occur, a solution may be to provide a rope collector to bring the ropes into alignment below the brake linings.  The design of the collector must comply with the code, including Section 2.20.9.2 in so far as it does not grip the ropes or impede the individual adjustment of the rope tensions.  We've designed such a system using halved wood blocks with oversized holes for the ropes, tethered to the crosshead.  This product is available from my sister company, Smart Elevator Tech, LLC, the Rope Align Blockhttp://smartelevatortech.com/RopeAlignBlock.htm

Rope Brakes Available

There are several elevator rope brake products on the market.  The most common one used in North America is the Rope Gripper™, manufactured by Hollister-Whitney Elevator Corporation, Quincy, IL.  The current models are spring closed and hydraulically opened.  There are five models used in North America for a full range of speed and load duties.  Mounting is simplified by its pivoting base.  As stated above, the unit can be mounted in any orientation, including vertical, a pitched angle, horizontal and inverted.  I'm advised by their engineers that the maximum allowed open dimension between the brake linings is equal to the diameter of the hoist rope plus 5/8". 

Hollister-Whitney provides a very detailed installation manual and guidelines that must be followed to properly install, wear-in and inspect the Rope Gripper™ rope brake.

I understand Hollister-Whitney will soon be releasing a complete new series of their Rope Gripper™ which will be electrically driven, eliminating the separate hydraulic pumping unit. 

Another rope brake commonly used is the BODE Rope Brake, manufactured by BODE Components GmbH, Düsseldorf, Germany.  This unit is actuated using compressed air and is spring released.  As such, one or more air compressors are required, which must be located in the machine room or overhead sheave room.  The physical configuration and mounting of the BODE Rope Brake is different in that it consists of a stationary steel back plate and brake lining inline with the hoist ropes and a bell type air cylinder on the front which drives a plate and brake lining. 

This configuration can have the advantage of being able to fit where other rope brakes don't.  The dimension from the inside face of the brake lining to the back side of the stationary plate is only 1.1" [28 mm].  This allows for a very close clearance fit to a drive machine, such as with many gearless machines where other rope brakes won't fit.  Designing the structural mounting for the BODE is a little more involved as the typical pitched vertical connection must be accommodated.  Either the angle must be measured very accurately for a rigid support or an adjustable angle support is needed. 

There are rope brakes that I've not yet worked with, including the "VGRB2 Rope Brake & UMD" manufactured by Atwell International Limited, Worcester, UK. From the information on the Internet, their device consists of either separate up and down units or a combined up & down unit.  It's an electromechanical failsafe design and is physically mounted similar to the Hollister-Whitney Rope Gripper™.  According to the duty charts, the Atwell rope brake is limited to the lower capacities common to Europe and Asia.  The brake linings are pre-formed for the rope size and pitch.

Other rope brakes are made in the Far East, also similar in design to Hollister-Whitney Rope Gripper™.  There is the Rope Brake Model JSQ as sold by Jinan China-Australia Imp. & Exp. Service Co., Ltd. as well as DIYSite.com Limited.  Another one is the Rope Brake Model PB298 as sold by China Ningbo Xinda Group Co., Ltd.  I have no experience with these devices.

Draka offers its rope brake, the Sure Stop™ RB500 Rope Brake. This is a self contained electrically driven device.  It is limited to maximum 1/2" hoist ropes and 350 FPM for 2:1 roping. 

Design & Engineering

The mounting of a rope brake must comply with Section 2.19.4 and as such, is considered a structural element of the elevator system.  In a new elevator installation the elevator engineer designing the package would presumably design the mounting of the rope brake along with sizing the machine beams, guiderail stacks, etc.  All too often, however, in an alteration project the mechanic in the field is left to figure out how to structurally mount the rope brake.  Some mechanics are very good seat-of-the-pants designers and will build a very solid structure and mounting for the device.  Not all mechanics are capable of doing this, nor, I would argue, should they do it.  There have been numerous instances where the newly installed rope brake mounting has failed, resulting in the device ending up wrapped around the machine drive sheave still firmly gripped to the hoist ropes. 

Shortly after California adopted A17.1-2004 last May, Mr. Al Tafazoli, Principal Engineer, DOSH, Elevator, Ride and Tramway Unit responded to a question of whether engineering proof or submittals would be required for the installation of rope brakes.  The answer was not normally, unless there were special circumstances that would require it.  In other words, if during an inspection a ERT inspector upon looking at the mounting thought that it might be suspect, she/he could require that engineering be performed to prove the structural integrity of the installation.  This is something the inspectors commonly do on such other things as car sling modifications, machine motor plate adapters, etc.

This may have changed, however.  It is our (Ronald Eddington, SE and my) understanding that all Cal/OSHA – Elevator Unit offices in Southern California have been requiring full engineering, signed and stamped by a California licensed professional engineer, for non-factory mounted rope brakes.  From a recent email sting I've seen, this my now apply to all of California.  I would recommend that you check with you local Cal/OSHA – Elevator Unit office to be sure.

We believe it's better to properly engineer the mounting of the rope brake or added machine brake, especially in a retrofit.  A few of the reasons and benefits of engineering include:

  Verification of field measurements of the locations, clearances, and viability of the installation. 
  Certify the runbys, clearances, rope line movement or rotation, etc. for hoistway installations.
  Assurance that the mounting, support, fastening, etc. are done correctly structurally in compliance with the code and proper engineering standards.
  Certify the acceptability of the loading and duty of the rope brake and the strength and deflection criteria of the supporting structure.
  Produce accurate drawings that can serve for submittal approval, equipment sizing, mounting material fabrication and installation guidance.
  All materials, including mounting structure, supporting steel, hardware and fasteners can be sourced in advance of the job.
  Reduce field labor expended in the design, sourcing and fabrication of the mounting structure and hardware.
  More creative solutions and options can be considered due to experience, often resulting in savings.
  California licensed structural engineering provided if preferred or required.

Providing full engineering services in support of the installation of ACO & UCM protection is one of the many services provided by RCB Elevator Consulting, LLC.  If you have any questions about a ACO & UCM protection project or if we can be of assistance, please feel free to call.

Note:  The italicized text above has been added on February 14, 2011 to this previously authored article.

Richard C. Blaska
Principal
RCB Elevator Consulting, LLC


Comments:  All comments and suggestions are welcome.  Feel free to write, call or email the author.


Disclaimer:  Any use of information contained herein is solely the responsibility of the user.  RCB Elevator Consulting, LLC and its associates accepts no liability for any information contained herein.

 

 

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