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Elevator System Control Devices and Applications

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1 Elevator System Control Devices and Applications
Chapter 11 Elevator System Control Devices and Applications Elevator Systems • Conveyance • Calls • Access • Special Operating Modes • Elevator System Control Devices • Elevator System Control Applications

2 Conveying systems include systems to automatically transport people and/or materials between areas of a building. A conveying system is a system for the transporting of people and/or materials between points in a building or structure. Conveying systems may operate horizontally, vertically, or even diagonally. See Figure The most common type of conveying system in commercial build- ings is the elevator.

3 While passenger elevators are the most common type of elevator, other types of elevators are specifically designed for other functions. Beyond the basic function of an elevator, there are differ- ent types of elevator systems that specialize in certain types of operations. The functional types of elevators include passenger, service, freight, dumbwaiter, and con- struction elevators. See Figure 11-2.

4 Traction elevators are raised and lowered through the elevator shaft by cables operated by electric motors. The most common type of elevator is the traction ele- vator. A traction elevator is an elevator system that raises and lowers the elevator car with cables operated by an electric motor. See Figure Most designs use a set of several thick steel cables. One end of each cable attaches to the top of the elevator car and the other end wraps over a drive sheave (pulley) and attaches to the top of a counterweight. The sheave is approximately 2¢ to 4¢ in diameter and has grooves that grip the cables to move them up or down. The sheave is driven by an electric motor, either directly or through a geared trans- mission. Geared traction elevators use a worm and worm gear type reduction unit, which allows for precise control of the elevator position, though the vertical speed is limited. A typical geared traction elevator can travel at speeds of 125 fpm to 500 fpm. A typical gearless traction elevator can travel at speeds greater than 500 fpm.

5 Most of the equipment needed to operate a traction elevator is located in a machine room above the elevator shaft. Most traction elevators require a machine room. A machine room is a space directly above an elevator shaft to house the motor, sheave, and elevator controls. See Figure 11-4.

6 Machine room-less elevators use a design that reduces the size of the traction equipment enough so that it does not require a machine room. Innovations in elevator design have also produced machine room-less elevators. A machine room-less elevator is a traction elevator system using special materials and improved electric motors that require little space, eliminating the need for the machine room. See Figure This elevator design uses flat polyurethane-coated steel belts that are considerably smaller than the traditional cables, allowing the sheave to be much smaller. Reducing the size of the sheave allows the elevator drive components to be installed directly in the elevator shaft. Additionally, the controls can be installed in a more convenient area of the building. The machine room-less elevator system is suitable for applications between 2 to 30 stories and is approximately 40% more energy efficient than comparable traditional traction ele- vator systems.

7 Hydraulic elevators are raised and lowered by pistons filled with fluid.
A hydraulic elevator is an elevator that lifts the elevator car from below using a hydraulic ram. See Figure A hydraulic ram is a piston that is driven into or out of a hollow cylinder by fluid pressure. An electric motor pumps fluid into the cylinder, causing the elevator car to rise. When the car reaches the destination, the pump stops and the pressure in the cylinder holds the elevator in position. Excess hydraulic fluid is kept in a reservoir located in the elevator machine room on the lowest floor and a valve controls the amount of fluid into or out of the reservoir. To descend, the valve is opened to allow hydraulic fluid to return to the reservoir. Once the car falls to the requested level, the valve is closed and the car remains in position. A typical hydraulic elevator can travel at speeds up to 150 fpm.

8 Holeless elevators reconfigure the hydraulic pistons to the side of the elevator, reducing the amount of equipment space needed directly beneath the elevator shaft. Traditional hydraulic elevators require the hydraulic cylinder to be located underground to a depth equal to the highest level the elevator will reach, which usually limits the applications to two to seven floors. Using one or more telescoping cylinders, which nest multiple cylinder sections together, allows for shallower holes. A holeless elevator utilizes two relatively small telescoping cylinders attached directly to the sides of the steel elevator car supports, significantly reducing (though often not completely eliminating) the need for space below the lowest elevator level. See Figure Holeless ele- vators are particularly suitable for areas with high water tables or for existing building construction.

9 The governor sheave engages the emergency brake system if the elevator falls too rapidly.
The governor system is built on a separate sheave located in the machine room. The elevator car is con- nected to a loop of cable that goes around the governor sheave and another sheave at the bottom of the elevator shaft. As the elevator car travels up and down, the cable turns the governor sheave accordingly. See Figure A pair of hooked flyweights (weighted arms) is attached to the face of the governor sheave. In normal operation, the spinning flyweights remain near the center of the sheave because the rotation is relatively slow. However, if the elevator speed reaches the maximum allowable speed, the fast-spinning flyweights extend outward due to centrifugal force and the arms hook onto stationary ratchets. This locks the governor sheave, jerking on the governor cable connected to the elevator car brake sys- tem, which engages the emergency brakes.

10 When engaged, emergency elevator brakes wedge up against the rails guiding the elevator car, slowing it to a stop. The brakes on the elevator car use brake pads that squeeze up against the guide rails to slow and stop the car. The pads are mounted on sets of wedge-shaped blocks on each side of the car. See Figure Normally, there is a gap between the brake pads and the guide rail. However, when the governor cable jerks suddenly to a stop, a linkage in the elevator shaft is ac- tuated that pulls up on the car’s brake assemblies, wedging the brakes tightly up against the guide rails. The linkage is designed to brake both sides of the car at the same time and with the same force, bringing the car to a controlled stop.

11 When the elevator car is in the correct position, the door operating system unlocks and pulls open both the car doors and the elevator shaft doors. The elevator car doors are opened with an electrical motor and linkage assembly mounted to the top of the elevator car. See Figure When the car reaches the correct position, the motor turns 180° in one direction, moving a pair of arms that pulls the doors open. Each set of doors rides along a set of rails and may consist of two separate panels.

12 The elevator system can respond to signals from other building systems to add calls, control access, and change elevator operating modes. The controller may be added to a building automation network to share information with and receive external inputs from other building systems. This integration can involve sending additional call signals to the elevator controller, controlling access with elevators, and changing the elevator’s operating mode. See Figure For example, an access control system may request an ele- vator car to a certain floor, or a fire alarm system disables an elevator system for occupant use for safety reasons.

13 The normal operating algorithm of an elevator system determines the best sequence of stops in order to minimize passengers’ waiting time. A call is a request for an elevator to stop at a certain floor to either pick up or drop off passengers. Calls are typically activated from inside the elevator, where riding passengers press buttons corresponding to the desired drop-off floors, or from an elevator lobby on any floor the elevator serves, where waiting passengers typically press buttons for the desired direction (up or down). The elevator controller constantly monitors the car position and the calls from all sources and controls the elevator’s direction and stops according to a preprogrammed algorithm. See Figure An algorithm is a sequence of instructions for producing the optimal result to a problem. In this case, the optimal operation of the ele- vator minimizes the waiting times for all the passengers riding and waiting for the elevator.

14 Elevators can be used to control access to certain areas of a building by either controlling the access to the elevator or controlling where the elevator can stop. Smaller buildings with fewer elevators may not want to dedicate an entire elevator for special access situations. If the secure areas require access only occasionally, then this elevator would be idle much of the time, wasting this building resource. Instead, one or more of the elevators providing regular service to unsecured floors may include a means to also transport authorized passengers to secure floors. In this situation, the access control device is located inside the elevator. See Figure In ad- dition to selecting the desired secure floor, a pas- senger must also use the necessary key, code, or other authorizing means, depending on the access control device. Only when the passenger has confirmed his or her authorization will the elevator travel to the secure floor. This system is commonly used for lower security applications, however, since it is relatively easy for unauthorized passengers riding in the same elevator car to also gain access to secure areas.

15 Some special elevator operating modes help the elevator system serve passengers more efficiently during certain periods of the day. These special modes can be activated in a variety of ways. Some require manual activation, such as by a keyswitch. Some may be activated by an automated means within the elevator controller. For example, the controller may be programmed to switch to a different mode by analyzing the pattern of passenger calls and their locations, or it may be programmed to switch modes at certain times of the day. See Figure Alter- natively, some special elevator operating modes can be activated by systems outside of the elevator system, such as an access control system or fire alarm system. This can be the case if these systems are integrated together in a building automation network to share con- trol signals.

16 Phase two fire service mode functions are activated by a keyswitch, typically inside the elevator car. If the fire department personnel decide that the elevator is safe to use under the circumstances, they can manually override the otherwise disabled elevator. Phase two mode is an elevator system operating mode that enables rescue personnel to manually operate an ele-vator that is in phase one mode. This mode is activated by fire department personnel with a special key switch inside the elevator car. See Figure While in this mode, automatic functions such as doors opening and closing do not operate normally. For example, to open the door, the door open button must be pressed and held until the door is fully open. Likewise, the door close button must be pressed and held until the door closes completely. Once the door is closed completely, the elevator will move to the requested floor. If the firefighter wants the elevator to remain on a specified floor, the hold position on the key switch is used. When the firefighter wishes to return to the recall floor, the phase two keyswitch is simply turned off.

17 Elevator controllers are connected to numerous elevator-specific control devices to operate the elevator system independently. The dedicated elevator controller makes all decisions on elevator stops and directions during normal operation, so a building automation system does not need to manage normal elevator system operations. Elevator controllers include a means to accept inputs from sensors and call buttons, microprocessors to make control decisions based on operating algorithms and modes, and a means to directly control output devices, particularly the electric motor or drive that moves the elevator. See Figure The con- troller adjusts the speed of the elevator as it approaches a destination floor, determines where to send an elevator car next, changes its direction, continuously monitors the posi- tion of each elevator car, and dispatches elevator cars to certain locations where peak usage is likely.

18 Call buttons are the typical method for passengers to select their desired travel direction or floor. Elevator controllers are connected to various call buttons throughout the building. A call button is a user-operated pushbutton input device that sends a call signal to an elevator controller. Call buttons for riding passengers are located inside the elevator car and correspond to each floor accessible by that elevator. Call buttons for waiting passengers are located on each floor served by the elevator and typically correspond only to the desired direction of travel (up or down). Call buttons are fairly consistent among all elevators in both function and ap- pearance, regardless of manufacturer. See Figure

19 Telephones or similar two-way communication devices are installed inside elevator cars for emergencies. All elevators require a method to communicate with the outside world in the event of an elevator problem, par- ticularly if the elevator becomes stuck between floors. Therefore, elevator cars include a dedicated telephone that automatically connects to either on-site or off-site security or maintenance personnel. A telephone may be mounted within a closed cabinet in the elevator car or the telephone line may be connected to a digital com- municator. The telephone connection may be activated by picking up the receiver or pushing a “call for assis- tance” button. See Figure

20 In emergency fire situations, the fire alarm control panel signals to the elevator controller to recall the elevator car(s) to a designated floor. Emergency elevator recall is a critical life safety appli- cation that integrates an elevator system with a fire alarm system to completely override normal operations. Signals from the fire alarm control panel (FACP) cause the ele- vator controller to initiate phase one mode, which recalls all elevator cars to a designated floor. See Figure Once there, the elevators are shut down, unless they are used by firefighting personnel in phase two mode.

21 Inputs from access control systems can be used by elevator controllers to anticipate waiting passengers and automatically call elevators to certain floors. This anticipation of elevator calls requires inputs from other building systems, such as access control or secur- ity systems, that can monitor entry into the areas near the elevators. See Figure

22 Access control systems can be used to admit only authorized personnel to elevators serving secure building areas. Integration with access control systems is commonly used for applications that require authorization to access certain floors. This can be done either in the elevator lobby or inside the elevator car. See Figure

23 When integrated with access control systems, elevators can be used to secure individual building floors by requiring authorization for certain floor calls from inside the elevator car. In this application, a call for the desired floor or direction is sent to the elevator controller only when the access con- trol device verifies an authorized user. See Figure

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