Method and apparatus for the control of elevator cars from a main floor during up peak traffic
BACKGROUND OF THE INVENTION 
     The present invention relates in general to a method and apparatus for the control of the dispatch of elevator cars from a main floor and, in particular, to such control during up peak traffic conditions. 
     A dispatch control for an elevator group consisting of several elevators is shown in the European Pat. No. 0 030 163, in which the dispatch interval is based on an approximate round trip time (RTT) of an elevator car, or on a mean round trip time based on the three preceding, approximate round trip times. The round trip time is divided by the number of elevator cars serving the main floor to determine a mean dispatch time interval. The approximate round trip time is the expected time which the elevator car requires for the up trip, serving the car calls registered at the main floor and the return trip to the main floor, and is calculated from building parameters, elevator installation parameters and operating condition parameters. If the elevator car has reached less than half its nominal load after expiration of the calculated dispatch interval time, the calculated interval time for the cars available at the main floor is shortened. If the elevator car reaches, after expiration of the calculated dispatch time interval, at least half its nominal load, the interval time is shortened in a similar manner, however, with different weighting of the available cars. 
     A disadvantage of the above described control is that the actual dispatching time interval is determined on the basis of approximate round trip times calculated from past data. This permits, in the best case, an estimate of the dispatching interval necessary for serving the actual traffic requirements. A further drawback is the fact that the control distinguishes only between a departure load being smaller than half the nominal load, and a departure load which is at least equal to half the nominal load, and in doing so shortens the interval time based on the number of cars available at the main floor. There results again only an approximate matching with the effective variations of the traffic requirements. A consequence of both drawbacks is that the utilization of the elevator cars is not optimized. 
     SUMMARY OF THE INVENTION 
     The present invention solves the above described problem by creating a method in which the availability of transportation is matched to the demand for transportation at the main floor of an elevator installation. In the present invention, the passengers, due to the variable conveying capacity of the elevators, profit from a service friendly to the user. The car loading is matched to the upward-peak-traffic to maintain as smooth a traffic flow at the main floor as possible. 
     In an elevator group, each elevator car is driven by a hoisting machine supplied with electrical energy by a drive system. The drive system is controlled by an elevator control for the car which controls are connected to a process computer for the system. A terminal connected to the process computer permits entry of the values for various constants used in an algorithm controller implemented in the computer. A sensor at the main floor provides information to the computer on the passengers entering the system and each car is also provided with a sensor connected to its associated control for providing data on the passengers in the associated car. 
     The algorithm is implemented as a series of steps defining a method for controlling the dispatch of the cars. In a first step sequence, the algorithm creates a transport capacity field and an interval field. In a first cycle through the first step sequence, a transport capacity and a set point or nominal time interval are calculated as a function of the set point or nominal departure load where the value of the departure load is equal to one and is incremented by one each time. The values of the calculated transport capacity and the calculated nominal time interval are stored in a field component of the transport capacity field and interval field respectively. Thus, the field components are filled with stored values as subsequent cycles through the first step sequence are completed. 
     In a second step sequence, the algorithm prepares the data necessary for the control of the dispatch of the cars. A traffic requirement is determined as a function of the destination calls received from the main floor sensor and a second traffic requirement is determined as a function of the actual departure load of the car to be dispatched. Subsequently, the algorithm calculates from the higher of the two traffic requirements the transport capacity and checks whether this value corresponds at least to the minimum transport capacity constant value. The nominal departure load, corresponding to the calculated transport capacity, is established from the transport capacity field and the nominal time interval is established from the interval field utilizing the nominal departure load. 
     In a third step sequence, the algorithm evaluates the now known data for the control of the dispatch. The actual departure load is compared with the nominal departure load until equality prevails. Simultaneously, a comparison is made between an actual time interval and the nominal time interval. An OR-operator links both conditions, so that at equality of either comparison, the door closing command is generated by the computer to the corresponding elevator control which dispatches the car. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
     FIG. 1 is a schematic block diagram presentation of an elevator group utilizing the method according to the present invention; 
     FIG. 2 is a schematic presentation of the data sources and data sinks for the elevator group of FIG. 1; 
     FIG. 3 is a flow chart of an algorithm for the dispatch of an elevator car of the elevator group of FIG. 1; and 
     FIG. 4 is a flow chart of the algorithm for the determination of the traffic requirement for an elevator car of the elevator group of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The designations of the algorithm steps and the names of the devices in FIGS. 1 through 4, as well as the abbreviations of the constants, status variables, variables and field variables set forth in the column &#34;Memo-Code&#34; of Table 1 below, are used as reference symbols. Table 1 is a listing of the constants, status variables, variables and field variables involved in the method of according to the present invention. In FIGS. 1 through 4, reference symbols with and without indices are used. Not indexed reference symbols refer to the elevator groups consisting of &#34;n&#34; elevators. Reference symbols indexed with &#34;.1, .2 . . . n&#34; refer to the elevators &#34;1, 2 . . . n&#34;, respectively. A reference symbol indexed with &#34;.x&#34; refers to one of the elevators &#34;1, 2 . . . n&#34;. Some of the steps shown in FIGS. 3 and 4 require a determination whether constants, status variables or variables satisfy the triangularly shaped stated conditions. A positive result of a determination is characterized with the reference symbol &#34;J&#34; and a negative result of a determination is characterized with the reference symbol &#34;N&#34; in each respective step. 
     
                       TABLE 1                                                     
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Memo-Code       Constant                                                  
______________________________________                                    
CF1             calibrating factor one                                    
CF2             calibrating factor two                                    
CF3             calibrating factor three                                  
CF4             calibrating factor four                                   
CF5             calibrating factor five                                   
CF6             calibrating factor six                                    
LCC             rated load                                                
MTC             minimum transport capacity                                
NOC             number of elevators                                       
NOF             number of floors                                          
PAB             passenger access basis                                    
______________________________________                                    
Memo-Code       Status variable                                           
______________________________________                                    
CS.x            elevator start                                            
DC.x            door closing command                                      
DR.x            data inquiry                                              
______________________________________                                    
Memo-Code       Variable                                                  
______________________________________                                    
DCL             destination calls                                         
DDC             call difference                                           
IT              actual time interval                                      
IV              nominal time interval                                     
LD              passenger access difference                               
LFB.x           actual departure load                                     
PAT             passenger access time                                     
PCA             boarding passengers                                       
PCL             boarding passenger calls                                  
SL              nominal departure load                                    
TC              transport capacity                                        
UT              traffic requirement                                       
______________________________________                                    
Memo-Code       Field variable                                            
______________________________________                                    
IVA             interval field                                            
TCA             transport capacity field                                  
______________________________________                                    
 
    
     Shown in FIG. 1 is an elevator group consisting of &#34;n&#34; elevators. A hoisting machine MOTOR.1 drives an elevator car CAR.1 of the first elevator. The hoisting machine MOTOR.1 is supplied with electrical energy by a drive system SYSTEM.1, which is connected to and controlled by an elevator control CONTROL.1. The detection of the building-filling passenger traffic departing from a main floor MAIN FLOOR and entering the first elevator car is made by load measuring devices or passenger counting devices, such as a sensor SENSOR.1 mounted in the elevator car CAR.1. The SENSOR.1 is connected with and sends its signal to the elevator control CONTROL.1. The elevators two through &#34;n&#34;, with hoisting machines MOTOR.2, MOTOR.3 . . . MOTOR.n, drive systems SYSTEM.2, SYSTEM.3 . . . SYSTEM.n. elevator controls CONTROL.2, CONTROL.3 . . . CONTROL.n, sensors SENSOR.2, SENSOR.3 . . . SENSOR.n, and elevator cars CAR.2. CAR.3 . . . CAR.n (not shown) correspond in their construction and in their mode of operation to the first elevator described above. 
     A sensor SENSOR located at the main floor MAIN FLOOR detects the arriving building-filling passenger traffic and is connected to a process computer COMPUTER which in turn is connected with the elevator controls CONTROL.1, CONTROL.2 . . . CONTROL.n and with an input/output unit TERMINAL. An algorithm CONTROLLER, implemented in the process computer COMPUTER as, for example, a computer program, controls the dispatch of the elevator cars CAR.1, CAR.2 . . . CAR.n. 
     Shown in FIG. 2 are the algorithm CONTROLLER implemented in the process computer COMPUTER and the data sources (inputs) and data sinks (outputs) connected to the process computer and utilized in the method according to the present invention. Provided at the main floor MAIN FLOOR for the detection of the arriving building-filling passenger traffic are, as variants of the sensor SENSOR, light barriers, turnstiles, infrared detectors, field detectors or call registering devices which generate a destination calls signal DCL. The building-filling passenger traffic originating at the main floor MAIN FLOOR and entering and departing the cars is detected by the sensors SENSOR.1, SENSOR.2 . . . SENSOR.n, mounted in the elevator cars CAR.1, CAR.2 . . . CAR.n respectively, and is sent to the elevator controls CONTROL.1, CONTROL.2 . . . CONTROL.n respectively. 
     Constants required in the method according to the present invention can be chosen and communicated to the algorithm CONTROLLER by means of the input/output unit TERMINAL. The destination calls DCL detected by the sensor SENSOR and actual departure loads LFB.1. LFB.2 LFB.n generated by the sensors SENSOR.x in the cars are variables which are inputted as first and second traffic measurement signals to the algorithm CONTROLLER and processed further. The values of the constants, calibrating factor one CF1, calibrating factor two CF2, calibrating factor three CF3, calibrating factor four CF4, calibrating factor five CF5, calibrating factor six CF6, rated load LCC, minimum transport capacity MTC, number of elevators NOC, number of floors NOF, and passenger access basis PAB can be selected by the input/output unit TERMINAL and inputted as signals to the algorithm CONTROLLER in the process computer. The elevator controls CONTROL.1, CONTROL.2 . . . CONTROL.n generate the status variables elevator start CS.1, CS.2 . . . CS.n, the actual departure loads LFB.x from the sensors SENSOR.x, and the data inquiry DR.1, DR.2 . . . DR.n as signals to the algorithm CONTROLLER and receive from the algorithm CONTROLLER the status variables door closing command signals DC.1, DC.2 . . . DC.n. 
     There is also shown in FIG. 2 the steps of the method according to the present invention. In a first step sequence &#34;Create data fields&#34;, the algorithm CONTROLLER creates a transport capacity field TCA and a time interval field IVA each having a plurality of field components. In a first cycle through the first step sequence, a transport capacity TC is calculated as a function of a set point or nominal departure load SL, and a set point or nominal time interval IV is calculated as a function of the transport capacity and the nominal departure load SL, where the value of SL is set equal to one. The values of the calculated transport capacity TC and of the calculated nominal time interval IV are stored in associated field components of the transport capacity field TCA and the interval field IVA respectively, the field components being represented by the symbol &#34;[ ]&#34;. The symbol &#34;:=&#34; signifies an assignment of the value on the right side of the symbol to the variable on the left side of the symbol. In subsequent cycles of the first step sequence, SL is increased in each case by one. The first step sequence is repeated until SL has reached the value of the rated load constant LCC. 
     In a second step sequence &#34;Prepare data&#34;, the algorithm CONTROLLER prepares the data necessary for the control of the dispatch of a car. A traffic requirement UT is determined as a function of the destination calls DCL received from the sensor SENSOR and a second traffic requirement UT is determined as function of the actual departure loads LFB.x of the car to be used (CAR.x) as received from the elevator control CONTROL.x and as will be described in connection with FIG. 4. Subsequently, the algorithm CONTROLLER calculates, from the higher of the two traffic requirements UT, the transport capacity TC and checks whether the value of TC is greater than or equal to the minimum transport capacity MTC. The nominal departure load SL, corresponding to the transport capacity TC just determined from the traffic requirement UT, is established from values stored in the transport capacity field TCA. The determination of the nominal time interval IV takes place in an analogous manner. 
     In a third step sequence &#34;Evaluate data&#34;, the algorithm CONTROLLER evaluates the now known data for the control of the dispatch. The actual departure load LFB.x is compared with the nominal departure load SL, until enough passengers have entered the car and equality prevails between the actual and the nominal values. Simultaneously, a comparison is made between an actual time interval IT and the nominal time interval IV. An OR-operator links both conditions. so that either at the equality LFB.x= SL or at the equality IT= IV, the door closing command DC.x is generated to the elevator control CONTROL.x, which dispatches the associated car CAR.x. 
     FIG. 3 shows the structure and the sequence of the flow chart of the algorithm CONTROLLER. In a step S1 &#34;Initialize&#34;, all constants and variables used in the algorithm CONTROLLER are set to the initial state. In a step S2, an iteration procedure comprising steps S3 through S6 for the calculation of the transport capacity TC and the nominal time interval IV, as well as for the creation of the data fields, transport capacity field TCA and interval field IVA, is carried out. In a first cycle of the iteration procedure shown in the step S2, the value of the nominal departure load SL is set to one, in a second cycle to two, and so on until the iteration procedure has been cycled LCC times. In the step S3, the transport capacity TC is calculated as function of the nominal departure load SL. The calculation of the inclusive acceleration, deceleration, door and exiting losses is estimated at &#34;m&#34; seconds. From the number of stops and the stopping times, the round trip time can be calculated. The formula used in the step S3 for the calculation of the transport capacity TC results from the relation: transport capacity equals departure load divided by round trip time. 
     The calculation of the nominal time interval is carried out in the step S4, as a function of the calibrating factor two CF2, the nominal departure load SL, the transport capacity TC and the number of elevators NOC. In the step S5 and in the step S6, the transport capacity TC calculated in the step S3 and the nominal time interval IV calculated in the step S4 respectively are stored in the transport capacity field TCA and in the interval field IVA respectively. Thus, the calculated values are assigned to the field components, indexed with SL, of the one dimensional data fields at every cycle of the iteration procedure. 
     The control &#34;loop&#34; starts with a step S7 in which it is checked whether the status variables elevator start CS.1, CS.2 . . . CS.n, linked with the OR-operator &#34;V&#34; and generated from the elevator controls CONTROL.1, CONTROL.2 . . . CONTROL.n, have a value of one. A positive result of the check, that is at least one elevator start signal CS.x is present indicating the start of the previous car, justifies the start of the actual time interval IT shown in a step S8. In a step S9, it is checked whether data is requested from one of the elevator controls CONTROL.1, CONTROL.2 . . . CONTROL.n by means of the status variable data inquiry DR.1, DR.2 . . . DR.n and the data requesting elevator control CONTROL.x is identified. Thereby the algorithm CONTROLLER identifies the index &#34;.x&#34; of the actual departure load LFB.x to be received in subsequent steps and the door closing command DC.x to be generated in subsequent steps. A positive result of the check justifies the execution of steps S10, S11 . . . S28, explained in FIG. 4, in which the traffic requirement UT is determined independently of the building-filling passenger traffic. 
     The traffic capacity TC is calculated in a step S29 from the calibrating factor five CF5 and the traffic requirement UT determined by the method shown in FIG. 4. The transport capacity TC, dependent on the traffic requirement UT, is checked in a step S30 as to whether it equals or exceeds the value of the minimum transport capacity MTC. A negative result of the check justifies the execution of a step S39 wherein predetermined values of one and infinity are assigned to the nominal departure load SL and to the nominal time interval IV respectively. After the conclusion of the step S39, the algorithm CONTROLLER continues the control loop in a step S36. A positive result of the check performed in the step S30 justifies the execution of a step sequence S31, S32 . . . S38. In the step S31, the nominal departure load SL is reset to zero. 
     In a first cycle of an iteration procedure represented by the step S32 and the step S33, the nominal departure load SL is set to one and the field component is indexed with SL. The transport capacity field TCA is compared with the transport capacity TC calculated on the basis of the traffic requirement UT. At every cycle of the iteration procedure, the nominal departure load SL, the running variable, is increased by one and thereby the selected field component indexed with SL. The iteration procedure of the step S32 is repeated until the transport capacity TC stored in the transport capacity field TCA corresponds to the transport capacity TC calculated on the basis of the traffic requirement UT. In the step S34, the field component indexed with SL is the interval field IVA which is addressed and the stored component value  assigned to the variable nominal time interval IV. 
     The nominal time interval IV, addressed on the basis of the departure load SL and determined in the interval field IVA in the steps S32 and S33, is calibrated in the step S35 with the calibrating factor six CF6. The iteration procedure shown in the step S36 checks, in the step S37, the actual departure load LFB.x of the selected car CAR.x and the actual time interval IT until either the actual departure load LFB.x is equal to the nominal departure load SL or the actual time interval IT is equal to the nominal time interval IV. As soon as either one of the conditions is satisfied, the door closing command DC.x is generated in the step S38 to the elevator control CONTROL.x, which dispatches the associated car CAR.x. Thereby, the control loop of the algorithm CONTROLLER is terminated. 
     FIG. 4 shows the structure and the sequence of the flow chart of the algorithm CONTROLLER for the determination of the traffic requirement UT. In the steps S10, S11, . . . S14, the variables necessary for the determination of the traffic requirement UT are prepared by resetting in the steps S10 and S11 a variable boarding passenger calls PCL and a variable boarding passengers PCA to zero. In the step S12, the algorithm CONTROLLER receives the destination calls DCL detected by the sensor SENSOR. In the steps S13 and S14, values are assigned to the variables old destination calls DCL ALT  and old actual departure load LFB.x ALT , used for the determination of the traffic requirement UT, which are the value of the actual destination calls DCL and the value of the actual departure load LFB.x (zero) respectively. The detection of the traffic requirement UT is initiated in the step S15 with the start of a passenger access time variable PAT. Carried out in the step S16 is an iteration procedure compromising the steps S17, S18 . . . S24 for the detection of changes, with respect to the destination calls DCL and the actual departure load LFB.x, having occurred during the access time PAT. 
     In the first cycle of the iteration procedure illustrated in the step S16, the destination calls are received in the step S17 from the SENSOR at the main floor and a call difference DDC is calculated in the step S18 from the current destination calls DLC  and the old destination calls DCL ALT . Subsequently, the current value of the destination calls DCL is assigned to the old destination calls DCL ALT  in the step S19. In the step S20, the call difference DDC is summed with the already detected boarding passenger calls PCL to generate a new value for PCL. In the steps S21, S22 . . . S24, a cycle is performed which is identical with the cycle shown in the steps S17, S18 . . . S20 and in which a passenger access difference LD is calculated and is summed with the already detected boarding passengers. PCA. The iteration procedure illustrated in the step S16 is cycled until either the boarding passenger calls PCL or the boarding passengers PCA equal the value of the passenger access basis constant PAB received from the input/output unit TERMINAL. The detection of the traffic requirement UT is concluded at a step S25. 
     In a step S26, a check is made whether, during the passenger access time PAT, more boarding passenger calls PCL were detected than boarding passengers PCA. A positive result of the check justifies execution of a step S27, in which the traffic requirement UT is precalculated, for example for five minutes, from the boarding passenger calls PCL and the passenger access time PAT. A negative result of the check of the step S26 justifies execution of a step S28, in which the traffic requirement is precalculated, for example for five minutes, from the boarding passengers PCA and the passenger access time PAT. After the conclusion of the step S27 or the step S28, the algorithm CONTROLLER continues with the control loop at the step S29 in FIG. 3. 
     Although the algorithm shown in FIGS. 2-4 has been described in terms of a computer program for a general purpose programmed computer, it also could be implemented in discrete analog or digital circuitry. Each of the arithmetic and comparison functions can be performed by circuit elements which are well known. The present invention combines these known arithmetic and comparison functions into a new and unique method and apparatus for controlling the dispatch of elevator cars from a main floor, particularly during up peak traffic conditions. 
     In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.