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.
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.
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.
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.
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.
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.
Richard C. Blaska
Principal
RCB Elevator Consulting, LLC
Rope Grippers & Brakes