Читать книгу People Flow in Buildings - Marja-Liisa Siikonen - Страница 29

In buses, the weigh in motion (WIM) systems enable the estimation of the number of passengers through the ground loading of the vehicle detected before and after the stops. The counting is performed by load sensors either on the ground or on the suspensions. The dead weight of the vehicle load on the ground is measured. The difference between the dead weight and the vehicle with passenger load is measured, and the number of people is calculated by dividing the difference by the average weight of a person (Pinna et al. 2010 ).

In elevators, a car load weighing device (LWD) is always required for safety reasons. At least 80% load for comfort reasons, 100% for full load and 120% for overload limit load values should be detected. Several methods exist to measure car load. One of them is to use elastomer pads below the cabin platforms. The deflections of the pads are measured with various loads which are actuated by micro switches as shown in Figure 2.5a (Strakosch 1983 ). A strain gauge LWD can be mounted on the crosshead beam on the top of the car, or other place in the support structure (Wittur 2002 ). The device measures the strain on an object, which consists of an insulating flexible backing that supports a metallic foil pattern. As the foil is deformed, its electrical resistance changes, which is then measured, see Figure 2.5b. One type of LWD load uses inductive proximity sensors to detect linear movements of the car platform when it is loaded or unloaded. An object plate and a sensor are placed under the car platform where the distance between the sensor and the object plate is transformed to analog signal (KONE 2006 ).

Figure 2.5 Load‐weighing by platform deflection

(Source: Strakosch (1983 ). © 1983, John Wiley & Sons) (a), and strain gauge techniques (b)

(Source: Wittur (2002 ). © 2002, WITTUR Austria GmbH).

Measurement of the car load gives only a hint of how many passengers are inside the car. The usual method is to measure load difference during a stop, and convert it to passenger counts by dividing it by the average passenger mass, e.g. 75 kg. The simplest approach to estimate passenger transfers is to measure the difference between the arrival and the departure load during a stop. This assumption produces error in the passenger counting since the passenger weights can vary from a few kilograms to more than 100 kg. People may also carry heavy objects, such as suitcases or shopping bags, causing even more error in the counting. A second method uses accurate LWD information to distinguish the difference of car loads between the car arrival to the floor, minimum load during the stop, and the departure load when it leaves the floor. This method assumes that the people first exit the car, and then new people enter in the car. The load difference between the arrival and minimum load correlate with the passenger mass of those who have exited the car. The difference between minimum load and the departure load correlates with the passenger mass entered in the car. A third method uses accurate load information during a stop to distinguish incremental and diminishing steps in the car load (Siikonen 1997 ). An incremental step in car load indicates that a passenger has entered the car, and a diminishing step that someone has exited the car, respectively. The method does not pay attention to the passenger mass, it only counts the stepwise changes in the load during the stop. Passenger transfers in and out from the car can occur in mixed order.

Figure 2.6 Step‐counting method to count the number of entering and exiting passengers during an elevator stop

(Source: Based on Siikonen (1997 ). © John Wiley & Sons).