Patent Publication Number: US-6986409-B2

Title: Apparatus for determining the position of an elevator car

Description:
PRIORITY CLAIM 
   This is a U.S. national stage of application No. PCT/CH03/00039, filed on 21 Jan. 2003. Priority is claimed on that application and on the following application: Country: Switzerland, Application No.: 173/02, Filed: 2 Feb. 2002. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention concerns a device for determining the position of an elevator car, including a device permanently installed in the elevator shaft which is at least as long as the total travel of the car between its uppermost and lowermost stop positions, and an additional device installed on the elevator car. 
   Devices of this type are used in elevator systems of various kinds. In these elevator systems, an elevator car is moved vertically between the floors of a building, and it is necessary to know the present position of the elevator car. Switching devices installed in the elevator shaft have a role in this. 
   2. Description of the Related Art 
   U.S. Pat. No. 4,427,095 describes a device for determining the position of an elevator car, in which a coded tape is scanned by a tape reader. Each position of the elevator car corresponds to a certain code value, which is evaluated by a microprocessor. 
   U.S. Pat. No. 6,142,259 describes a device for controlling a hydraulic elevator, in which an automatic control system for the elevator receives information about changes in the position of the elevator car by elevator shaft pulse generators. However, the travel of the elevator car is also monitored by a flowmeter, which makes it possible to regulate the speed. 
   U.S. Pat. No. 6,510,923 describes a device for controlling a hydraulic elevator, in which a flowmeter is not used. Instead, a pressure sensor installed in this line determines the pressure in the cylinder line. The change in pressure with respect to time is evaluated, and it is also stated that the acceleration of the elevator car can be computed from the pressure. From this information, it is then supposed to be possible to derive the speed of the elevator car and the distance it has traveled. It seems questionable whether the accuracy of the pressure sensors is great enough to allow sufficiently exact control of an elevator from the change in pressure as a function of time and from repeated differentiation of this data. 
   EP-A1-1 158 310 describes a device for determining the position of an elevator car, in which a sonic signal conductor is installed in the elevator shaft, and a signal coupler is installed on the elevator car. The sonic signal is in the ultrasonic range. The sonic signal conductor consists of a magnetostrictive metallic material. This system requires a transmitting unit with a signal generator and the aforementioned signal coupler, as well as at least one signal receiver and one evaluation unit. 
   SUMMARY OF THE INVENTION 
   The objective of the invention is to create a device that has a simple design and yields sufficiently exact information about the position and movement of the elevator car. 
   In accordance with the invention, this objective is achieved by the features of Claim  1 . Advantageous modifications are specified in the dependent claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a diagram of a device for determining the position of an elevator car. 
       FIG. 2  shows an advantageous embodiment, 
       FIG. 3  shows an electric circuit, 
       FIG. 4  shows a cable unit, 
       FIGS. 5   a  to  5   c  show connection points to this cable unit, 
       FIG. 6  shows a mounting device, and 
       FIG. 7  shows another electric circuit. 
   

   DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
     FIG. 1  shows an elevator shaft  1 , in which an elevator car  2  can be moved in the vertical direction. In accordance with the invention, a resistance wire  3  is installed in the elevator shaft  1  and is arranged in the vertical direction, i.e., in the direction of movement of the elevator car  2 . A first electric connecting lead  4  is connected at the upper end of this resistance wire  3 , and a second electric connecting lead  5  is connected at the lower end of the resistance wire  3 . The two electric connecting leads  4 ,  5  are routed to a position-sensing unit  6 , which is part of the automatic control and regulation unit  7 . The first electric connecting lead  4  carries an operating voltage+U B  as a signal, while the second electric connecting lead  5  carries the associated reference voltage GND. A voltage tap  8  is connected to the elevator car  2 , and the contact  9  of the voltage tap  8  rests against the resistance wire  3 . During the operation of the elevator car  2 , the contact  9  slides along the resistance wire  3 . A measuring line  10  runs from the contact  9  of the voltage tap  8  to the position-sensing unit  6 . 
   The resistance wire  3  is thus permanently installed in the vertical direction in the elevator shaft  1  and is at least as long as the total travel distance of the elevator car  2  between its lowermost and uppermost stop positions. 
   Accordingly, if the voltage +U B , for example, 10 V, is applied at one end of the resistance wire  3 , and the voltage 0 V, which represents the reference voltage GND, is applied at the other end of the resistance wire  3 , then the voltage present at the contact  9  and thus at the measuring line  10  is a direct function of the position of the elevator car  2 . The given position of the elevator car  2  can thus be clearly recognized by the position-sensing unit  6 . The voltage U Pos , carried by the measuring line  10  is a direct function of the position of the elevator car  2 :
 
 U   Pos   =f ( Pos   car ),
 
where Pos car  denotes the given position of the elevator car  2 .
 
   Thus, the velocity of the elevator car  2  can also be determined from the change in U Pos  with respect to time:
 
 v=dU   Pos   /dt  or  v=ΔU   Pos   /Δt 
 
where v is the velocity of the elevator car  2  and dU Pos /dt or ΔU Pos /Δt is the derivative of the voltage U Pos  with respect to time.
 
   The equipment for guiding and driving the elevator car  2  are not shown here, because they play no role at all with respect to the invention. The invention can be used in both electrically and hydraulically operated elevators, and the specific embodiment is of no consequence. 
     FIG. 2  shows an advantageous embodiment. The resistance wire  3  is mounted in the elevator shaft  1  ( FIG. 1 ) by one mounting device  11  each at the top and bottom, either on a sidewall of the elevator shaft  1  or on the roof and floor of the elevator shaft  1 . The first electric connecting lead  4  is connected to the resistance wire  3  at an upper reference point  12 , which is correlated with the uppermost position of the elevator car  2  (FIG.  1 ). The second electric connecting lead  5  is similarly connected to the resistance wire  3  at a lower reference point  13 , which is correlated with the lowermost position of the elevator car  2  (FIG.  1 ). In this way, the uppermost and lowermost positions of the elevator car  2  are determined by unique voltages. If the elevator car  2  is located in the uppermost position, then the voltage +U B , i.e., for example, 10 V, is present at the measuring line  10  (FIG.  1 ). If the elevator car  2  is located in the lowermost position, then the voltage 0 V is present at the measuring line  10 . 
   In an elevator system with four stop positions spaced an equal distance apart, a voltage U 1 =0 V is obtained for the first, i.e., the lowermost, stop position. A voltage U 2 =3.33 V is obtained for the second stop position, a voltage U 3 =6.67 V is obtained for the third stop position, and a voltage U 4 =10 V is obtained for the fourth, i.e., the uppermost, stop position. These voltages U 1  to U 4  are the reference values for the correct stop positions, by which the travel of the elevator car  2  can be regulated. Since the given voltage U Pos  during travel can be measured as an actual value, precise travel regulation is possible. The control offset must go to zero by the time the car comes to a stop. In this way, it is also possible to eliminate the use of so-called “crawling speed”, i.e., the frequently used reduced-speed approach to a stop position. The elevator car  2  can thus be moved directly to the stop position at a continuously decreasing speed until the end, which is called direct approach. This offers the advantage of reduced travel time. 
   If the supply points, i.e., the upper reference point  12  and the lower reference point  13 , do not coincide with the uppermost and lowermost stop positions, but rather the upper reference point  12  lies above the uppermost stop position, and the lower reference point  13  lies below the lowermost stop position, then different values for the voltages correlated with the stop positions are obtained for the uppermost and lowermost stop positions. Operation with direct approach is also possible here. For example, the voltage U 1  for the lowermost stop position may be 0.2 V, and the voltage for the uppermost stop position may be 9.8 V. In this case, the voltages for the other two stop positions, assuming equal distances between the stop positions, have the values U 2 =3.40 V and U 3 =6.6 V. 
     FIG. 3  shows a first embodiment of an electric circuit. The resistance wire  3  is connected with a reference voltage source  20  by the first electric connecting lead  4  and the second electric connecting lead  5 . In addition, a first sensing line  21  and a second sensing line  22  run from the reference voltage source  20  to reference point  12  and reference point  13 , respectively. This well-known method makes it possible to compensate the resistance of the connecting leads  4 ,  5 , which improves the precision of the measurements. The accuracy that can be achieved during approaches to stop positions is correspondingly improved in this way. The reference voltage source  20  is very precise. 
   The measuring line  10  runs from the contact  9  to the first input of a differential amplifier  24 . The GND signal of the second connecting lead  5  is supplied to the second input. It is advantageous for the differential amplifier  24  to have additional inputs, to which signals can be supplied to make it possible, as is already well known, to adjust the signal amplification, i.e., gain, on the one hand, and compensate the offset voltage, i.e., offset, on the other hand. Electrical errors can be minimized or even completely eliminated in this way. The output of the differential amplifier  24  is connected to a low-pass filter  25  that may be present. The output of the low-pass filter  25  is routed, on the one hand, to an operational amplifier  26 , at whose output a signal that is correlated with the position s of the elevator car  2  can be picked up, and, on the other hand, to a differentiating circuit  27 , at whose output a signal that is correlated with the velocity v of the elevator car  2  can be picked up. If a low-pass filter  25  is not used, the output of the differential amplifier  24  is routed directly to the inputs of the operational amplifier  26  and differentiating circuit  27 . 
   The reference voltage source  20 , the differential amplifier  24 , the possibly present low-pass filter  25 , the operational amplifier  26 , and the differentiating circuit  27  are, for example, components of the automatic control and regulation unit  7  shown in  FIG. 1 , such that the differential amplifier  24 , the possibly present low-pass filter  25 , the operational amplifier  26 , and the differentiating circuit  27  are components of the position-sensing unit  6  ( FIG. 1 ) contained in the automatic control and regulation unit  7 . 
     FIG. 4  shows an embodiment of a cable unit  30  in a cutaway oblique view, which is equipped with the resistance wire  3  and other conductors. The base of the cable unit  30  is a plastic support  31 , on one side of which the resistance wire  3  is form-fitted to the plastic support  31 . Three conductors are mounted on the opposite side, namely, a feed conductor  32 , a sensing conductor  33 , and a feedback conductor  34 . For the sake of simplicity, the resistance wire  3  and the three conductors  32 ,  33 ,  34  are shown here as flat wires, but they may have any desired form. The arrangement of the conductors should be regarded merely as an example. Other embodiments are possible within the general scope of the idea of the invention. For example, the feed conductor  32  and the sensing conductor  33  may be embedded in the plastic support  31 , i.e., they may be surrounded by insulating material. 
     FIGS. 5   a  to  5   c  show how the cable unit  30  is connected. In  FIG. 5   a , the upper connection point  12  ( FIG. 2 ) is shown schematically in a special embodiment. Here an upper connecting piece  40  is fastened to the cable unit  30  in a position on the cable unit  30  that corresponds to the uppermost position of the elevator car  2  (FIG.  1 ). The bridge  40  consists of a bracket  41  with an inserted electrically conductive web  42 . The resistance wire  3 , the feed conductor  32 , and the sensing conductor  33  are electrically connected with one another by the web  42 . It is advantageous for the mounting device  11  ( FIG. 2 ) for the upper end of the cable unit  30  to be located directly above the connecting piece  40 . However, the mounting device  11  and the connecting piece  40  may also be combined into a single component. 
     FIG. 5   b  is a schematic representation of a tapping unit  50 , which is connected by a bracket  51  to the elevator car  2 , which is not shown here (see FIG.  1 ). Therefore, as the elevator car  2  travels, the tapping unit  50  slides along the cable unit  30 . The tapping unit  50  consists of a mounting fixture  52  and a spring bracket  53  supported in the mounting fixture  52 . The spring bracket  53  is shaped in such a way that it creates a permanent connection between the resistance wire  3  and the feedback conductor  34 , so that, at any given location, the potential present at the feedback conductor  34  is the same as the potential that prevails at the contact point of the spring bracket  53  on the resistance wire  3 . This is the potential that is correlated with the position of the elevator car  2  ( FIG. 1 ) at any given time. 
     FIG. 5   c  shows a connection unit  60  with which the lower connection point  13  ( FIG. 2 ) is formed in a special embodiment. The connection unit  60  again surrounds the cable unit  30  and is fastened to it. The connection unit  60  consists of a support  61 , in which four contacts are embedded. The first of these contacts is a position signal contact  62 , which is in contact with the feedback conductor  34 . As was explained in connection with  FIG. 5   b , the feedback conductor  34  has the potential that corresponds to the position of the elevator car  2  ( FIG. 1 ) at any given time, i.e., the voltage U Pos . Therefore, the measuring line  10  described earlier in connection with  FIG. 1  is connected to the position signal contact  62  and leads to the position-sensing unit  6  of the automatic control and regulation unit  7  (FIG.  1 ). The advantageous solution resulting from  FIGS. 5   b  and  5   c  avoids a separate cable connection of the elevator car  2  to the position-sensing unit  6 , as would be necessary according to the drawing in FIG.  1 . 
   The connection unit  60  also contains a sensing positive contact  63 , which is in electrical contact with the sensing conductor  33 . The first sensing line  21  described earlier in connection with  FIG. 3  is connected to the sensing positive contact  63 . A power supply voltage contact  64  installed in the connection unit  60  creates electrical contact with the feed conductor  32 . The first electric connecting lead  4  known from  FIGS. 1 and 3  is connected to it and supplies the operating voltage +U B . Furthermore, the connection unit  60  contains a GND contact  65 , which creates electrical contact with the resistance wire  3 . The GND contact  65  is connected to the second electric connecting lead  5 , which carries the reference voltage GND associated with the operating voltage +U B , as well as to the second sensing line  22  shown in FIG.  3 . 
   If, as was mentioned earlier, the feed conductor  32  and the sensing conductor  33  are embedded in the plastic support  31 , the insulation must be removed in the region of the connecting piece  40  and the connection unit  60 . 
   This embodiment of the cable unit  30 , in conjunction with the upper connecting piece  40  in accordance with  FIG. 5   a , the tapping unit  50 , and the connection unit  60 , results in the advantageous situation that all of the connections to the resistance wire  3  that are shown in  FIGS. 1 ,  2 , and  3  are present in the connection unit  60 . This allows simple wiring and thus significantly reduces the assembly work. 
   Since the cable unit  30  has a plastic support  31 , and the plastic can undergo thermal expansion that is not negligible, a problem can arise if the temperature in the elevator shaft  1  is subject to fluctuation. To absorb the thermally produced change in length of the cable unit  30 , it is advantageous to anchor the cable unit  30  permanently at the upper end of the travel range of the elevator car  2  (FIG.  1 ), and to provide a flexible mount for the lower end of the cable unit  30 . It would also be possible to permanently mount the lower end of the cable unit  30  and to provide a flexible mount for the upper end. It is advantageous for the connection unit  60  to be installed at the lower end of the cable unit  30 , because the other elevator system equipment, such as a control box and the drive machinery, are also usually located at the bottom of the building. 
     FIG. 6  is a schematic representation of a spring mounting. The lower end  70  of the cable unit is connected to a cable clamp assembly  71 , which is attached to one end of an extension spring  72 , whose other end is attached to a mounting device  73 , which is connected to a wall  74  or the floor of the elevator shaft  1  by positive locking. The situation at a certain temperature is shown with solid lines. If the temperature is significantly higher, the cable unit  30  lengthens accordingly, but it remains under tension due to the action of the extension spring  72 . However, the lower end  70  with the cable bearer  71  is then located in a lower position, which is shown in  FIG. 6  with broken lines. 
   To ensure that these temperature-related changes in the length of a cable unit  30  do not lead to errors in the determination of the position of the elevator car  2  (FIG.  1 ), it is advantageous to fix the connection unit  60  in its position relative to the elevator shaft  1  ( FIG. 1 ) by rigidly connecting the connection unit  60  to the wall  74  by means of a mounting element  75 . This guarantees that the distance between the bridge  40 , which defines the uppermost position of the elevator car  2  (FIG.  1 ), and the connection unit  60  remains constant. The connection unit  60  is thus fixed on the elevator shaft  1  ( FIG. 1 ) and not on the cable unit  30 . The contacts  62 ,  63 ,  64 , and  65  slide along the corresponding conductors, when the entire length of the cable unit  30  changes as a result of changes in temperature. This guarantees accuracy of measurement at all temperatures. 
     FIG. 7  shows a second embodiment of an electric circuit. As in the embodiment shown in  FIG. 3 , a reference voltage source is also present here. However, it is labeled with reference number  20 ′ here, because although it is functionally similar, it is not the immediate source of the voltage supply for the resistance wire  3 . The voltage supply for the resistance wire  3  is provided by the amplifier  80  in this case, which is controlled by the reference voltage source  20 ′. The amplifier  80  is connected with the resistance wire  3  by the first electric connecting lead  4  and the second electric connecting lead  5  as well as by the first sensing line  21  and the second sensing line  22 . 
   An analog-to-digital converter  81  is connected to the measuring line  10  in this case. Like the amplifier  80 , the analog-to-digital converter  81  is operated on the reference voltage source  20 ′. This has the significant advantage that the reference voltage source  20 ′, unlike the reference voltage source  20  (FIG.  3 ), does not have to be extremely precise. If the voltage of the reference voltage source  20 ′ changes, this does not result in a measuring error in the position determination, because the amplifier  80  and the analog-to-digital converter  81  are connected to the same voltage source. Therefore, the requirements placed on the reference voltage source  20 ′ are not as great. The analog-to-digital converter  81  produces a digital signal at its output that corresponds to the position of the elevator car  2  (FIG.  1 ). This signal is fed to a microprocessor  82 , which is part of the automatic control and regulation unit  7  and contains the functionality of the position-sensing unit  6  (FIG.  1 ). The microprocessor  82  processes the digital signal of the analog-to-digital converter  81  in such a way that it determines the position s and the velocity v of the elevator car  1 . Therefore, some of the components shown in  FIG. 3  are not needed, namely, the differential amplifier  24 , with the ability to adjust the signal amplification (gain) and the offset voltage (offset), the operational amplifier  26 , and the differentiating circuit  27 . Since both the amplifier  80  and the analog-to-digital converter  81  are controlled by the reference voltage source  20 ′, the operating voltage +U B  at the resistance wire  3  also depends on the reference voltage U Ref  of the reference voltage source  20 ′. Therefore, changes in the reference voltage U Ref  do not cause any measuring errors. 
   It is advantageous to combine the analog-to-digital converter  81  and possibly the reference voltage source  20 ′ and the amplifier with the connection unit  60  to form a single assembly unit. This reduces the assembly work.