Standard braking systems could not meet the difficult speed, energy, and dynamic torque constraints.
A manufacturer of low- and high-rise elevators faced a challenge when
customers began calling for a flexible elevator to meet the needs of the
growing mid-rise, mixed-use building market. The global construction
boom of mid-rise buildings can be attributed to several factors.
Developers are more apt to build “short” because it requires less capital
and the time to get permits approved is reduced considerably, especially
in developing countries.
In response to this growing demand, the elevator OEM began
developing a new elevator design that was adaptable for a variety of
mid-rise buildings including apartments, hotels, offices, and shopping
centers. To ensure global acceptance, the new flexible elevator was
designed to meet building codes around the world.
Increased Constraints
The technology of elevator manufacturing is changing as OEMs
migrate from using standard steel ropes to using innovative belts. One
consequence of the change is increased constraints for the braking
system, resulting in a difficult specification for this design. The
company called on Warner Electric, part of Altra Industrial Motion, to
develop a braking system for the challenging gearless motor elevator
application that required dynamic torque less than 160% of nominal
torque, noise lower than 54 dB, and very high energy up to 57 kJ
(Figure 1).
The braking system had to provide the following three functions:
- Parking brake: maintain elevator car in position when not used
(at a floor or during night).
- Ascending car overspeed protection: stop the car or reduce the
speed of the counterweight if falling.
- Protection against unintended car movement: stop the car if
there is abnormal movement with open doors.
The elevator design process spanned several years, and Warner
Electric engineers worked closely with the customer’s engineering team
as the elevator design evolved. Initially, the request was for a standard
elevator brake, but the specifications became more challenging over
time. The leading constraints were increased speed (x3), increased
energy (x10), and the previously mentioned maximum torque
limitation.
Warner Engineers developed a solution that had low wear but
high energy, noise dampening with low torque impact, and torque
stability and precision. To meet the criteria, two modified ERS VAR15
spring set/electrically released brakes with fixed magnets and a floating
disc were designed. The floating disc is connected to the shaft that
rotates to move the elevator up or down, and a set of springs inside.
the brake module can press a plate against the disc. With power, the
magnetism pulls the plate away from the disc, compressing the springs
and allowing the disc to rotate. This allows the elevator to move. When
power is cut, the springs compress the plate against the rotating disc to
stop or hold the elevator in place.
The disc is splined and mounts to a mated splined hub so that
it can move slightly along the hub. When the brake engages the disc,
it does so on both sides. Since the plate floats, it can receive equal
compression from both sides of the brake.
Tight Footprint
Figure 2: A new, multi-station robotized cell is
also incorporated into the production process
to provide friction disc burnishing, static torque
adjustment, electrical adjustment, dynamic torque
measuring, and component crimping to secure the
adjustment.
The modular, compact units allowed the configured system to fit
within the customer’s tight footprint. Units are microswitch equipped
and conform to European Lift Directive 2014/33/EU (EN 81-20 and
EN 81-50 certified). To meet the tight footprint, the design team needed
to choose the best compromise between maximum energy versus wear,
maximum torque limit versus noise, and 100% adjusted brake
(6 sigma oriented) versus production cost.
Thermal control was a key issue due to the system’s high-energy
braking. Heat is not dissipated, but must instead be absorbed by the
system. This was a major criterion that impacted the overall brake
design and friction material selection.
The OEM team was in regular contact with Warner Electric’s
engineering team during all the development phases of the project,
including many meetings in person. Various performance curves,
statistical analysis, and test reports were provided to the customer to
validate the brake design and performance.
The brakes were subjected to a full array of lengthy testing
including energy, life cycle, climatic, aging and destruction tests.
Pre-packaged brake assemblies were delivered to the customer with
ready-to-mount paired magnets and burnished discs.
Manufacturing Technology
Warner Electric has recently invested in new manufacturing
technology while optimizing their elevator brake manufacturing
workflow for improved quality and efficiency (Figure 2).
Manufacturing upgrades include a new production line divided into two
new work cells. The primary work cell allows for semi-automatized
assembly utilizing conveyors. Components and brakes are traceable via
bar codes. Visio software is used for component presence and profile
detection. A slaved system has also been incorporated for screwdrivers,
di-electrical tests, etc.
A new, multi-station robotized cell is also incorporated into
the production process to provide friction disc burnishing, static
torque adjustment, electrical adjustment, dynamic torque measuring,
and component crimping to secure the adjustment. All production
parameters are stored in a custom software program developed
exclusively for Warner Electric. The program provides traceability for
future analysis and continuous improvement.
The new production enhancements to the Warner Electric plant
in Angers, France will allow Warner to more effectively meet the
anticipated demand for the new elevator brake from Europe, Asia
Pacific, and Latin America.
For more information about the Warner Electric products used in
this application, visit www.warnerelectric.com.