HOW IT WORKS
The relevé elevator is technically classified as a “climbing elevator.” An illustrative example of another climbing elevator is the Space Elevator. The Space Elevator is envisioned as a passenger vehicle that climbs a three foot wide, paper thin, carbon nanotube ribbon, 22,000 miles into outer space. In similar fashion, the relevé elevator climbs a strong ribbon to lift passengers between the floors in their homes. Instead of a carbon nanotube ribbon, the relevé elevator uses a pair of low cost steel corded polyurethane belts as the climbing medium.
These belts are very strong with a tensile strength of over 7,500 pounds. Similar belts are currently featured in the new “Otis Gen2” commercial elevators. In the Otis elevator the belts replace conventional steel cables which are pulled upward by the drive motor at the top of the hoist way. In the relevé elevator, the belts remain stationary, suspended and locked in position. Climber drive motors, located in the floor of the cab climb the belts.
Electronic Counter Weights
Traditionally, counterweights have been an essential part of elevator design for over 150 years. Counter weights perform two functions, 1) Energy Storage, and 2) Power Reduction. When the passenger cab is lowered the counter weights are raised thus storing potential energy. This “balance” also reduces the power required to operate the system. A common technique in designing the elevator counter weights is to set the counter weight equal to the total weight of the cab plus one half the rated elevator load. This reduces the
maximum lift power at the motor by 50%.
The relevé elevator does not use physical counterweights. To accomplish this, the relevé climbing motors are twice as powerful as the motors used in the conventional approach. This is necessary since they must provide all of the force required to lift the total load including the weight of the car. Instead of storing energy in counter weights, the relevé recovers most of the lifting energy through the process of electronic regeneration. This technique is more efficient than a physical counter weighted system because the lifting energy and regenerated energy are more often in balance. In effect, the load becomes its own counter weight. The energy expended to raise the load is recovered when the load is returned to the initial level. A similar regenerative concept is used in many modern electric vehicles and hybrid cars when they go down hill or when braking.
In order for this regenerative concept to work well in practice there must exist an effective means to efficiently capture and store the high current returned by elevator operation. The very nature of elevator use creates intermittent low duty cycle, high power surges of electrical energy. In the relevé elevator this energy is stored in high compliance capacitors and batteries. Modern batteries have extremely low impedance, low weight, high efficiency, and high current surge capability.
Battery Power
There has been rapid technological growth in the field of high power density batteries and related electrical components over the last several years. This technology growth is being fueled by the mobile computer and hybrid/electric automobile industries. High tech battery power in the relevé elevator provides several advantages over standard residential line power:
1. Energy Recovery - Recharge energy from “electronic counter weight” and regenerative braking.
2. High Efficiency - The combination of low impedance, tight coupling and new DC motor technologies provide efficiencies much higher than conventional AC powered systems.
3. Emergency Power Operation - The relevé elevator can operate for several days without external power, a great advantage to disabled users during power outages.
4. Smooth Operation - Through the use of brushless DC motors, Hall position sensors, high current MOSFET technology, and “rate servo techniques,” the relevé elevator provides a very smooth acceleration, run and deceleration profile.
5. High Speed - High constant current and surge capability of modern battery power combined with high torque brushless DC motors enables high speed operation exceeding 100 feet per minute.
6. Low Power Draw - Since line power is only used to charge the batteries, external power draw is very low. Even solar power is a feasible power source for the relevé elevator.
Exterior Installation
Outdoor operation is a key feature of the relevé design. Exterior installation eliminates much of the costs associated with conventional elevator installation. However, the exterior environment poses design challenges that require special attention. The most severe challenge is protecting the guide rails from contamination that would interfere with the movement of the passenger car. Exposed guide rails run the risk of frequent contamination due to wind blown foreign materials such as leaves, paper, pine needles, and dust as well as mechanical interference due to rain, snow and ice.
The relevé solution to this contamination issue turns the conventional guide rail system inside out, thus creating a miniature enclosed elevator shaft. This is accomplished with a single aluminum extrusion measuring approximately 5 by 3 inches in cross section. Inside this extrusion are six rail surfaces for the polyurethane guide wheels. One side of the guide rail has and open slot to accommodate struts that connect the guide trucks to the passenger car. A special seal covers this slot everywhere except where the car is positioned. After the car passes, the guide rail chamber is automatically resealed.
There is an identical guide rail with an associated climber motor on both sides of the car. Each guide rail is capable of supporting the fully loaded weight of the car by itself. This dual support system is a key relevé elevator safety feature.
Safety
Elevators in general, have an incredible safety record. Statistically speaking, using an elevator is about one million times safer than riding in a car. An interesting antidote is that the number one concern of residential owners is entrapment, not falling.
Code requires phones and alarms in elevators to get help for trapped passengers. However, these provisions are insufficient abatement for some people. The relevé elevator further address fear of entrapment with its external design and large window area. Occupants can see outside thus reducing the claustrophobic effect of a small enclosed space, and outsiders can see inside. In addition, there is an emergency door in the floor of the cab providing an alternative escape and rescue option not available with internal elevator installations.
The primary safety feature in any mission critical system is redundancy. Redundancy greatly increases reliability. The two relevé guide rails and lift systems are 100% redundant with each other. Failure in either lift mechanism will not cascade to the other. Therefore, even with catastrophic component failures in one, the other is capable of lowering the car safely. The failure modes in the relevé system enable the concept of fault recovery. Component failures do not result in locking the car to the guide tracks as with most elevators. Instead, the relevé system attempts to complete its last command before actually shutting down. Only as a last resort will the emergency brakes trip and lock the cab in place.
