Abstract:
A signal transmission apparatus from a control unit to a plurality of memory units which correspond to signal terminal means and which are connected in series with each other, wherein the memory units at the starting end and at the final end are connected to the control unit to constitute a closed loop, wherein the memory unit at the starting end or the final end receives a gate signal and stores it temporarily to open a gate, and wherein the memory units transfer gate signals to the subsequent stages successively responsive to clock pulses, and having detector means which detects whether the first gate signal has circulated the closed loop constituted by the series connected memory units, and a switch which switches the sending path of the gate signal depending upon the detected result so that the gate signal is sent from the memory unit of either the starting end or the final end.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a signal transmission apparatus for transmitting signals between a control unit and a plurality of signal terminal means. 
     2. Description of the Prior Art 
     In an elevator system, a control unit is installed in a machine room, and signals are transmitted between the control unit, platform buttons provided on each of the floors, and cage operation buttons on a board installed in the cage. The machine room is usually located just above the elevator path. The platform buttons and the cage operation board buttons, which are signal terminals, are located more remote from the control unit as the number of the floors increases. To facilitate the connection and reduce the complexity of the wiring between the control unit and the signal terminals, there has been employed an apparatus which transmits signals in series on signal lines instead of transmitting signals in parallel through such lines. 
     FIGS. 1 and 2 illustrate a conventional signal transmission apparatus employed for an elevator system in which signals are transmitted in series. 
     In the drawings, reference numeral 1 denotes a control unit which is installed in a machine room of the elevator system, and which generates clock pulse signals and reference signals to register a platform call and a cage call. Reference numeral 3 denotes a signal line for transmitting clock signals 3a that are generated maintaining a constant period (for example, 500 microseconds), 4 denotes a signal line for transmitting platform call signals 4a, 5 denotes a signal line for transmitting platform call registration signals 5a, reference numerals 61 to 69 denote platform buttons (up-call buttons and down-call buttons are not specifically shown) of the first to ninth floors, 71 to 79 denote platform call registration lamps that indicate the registration of platform call, 81 to 89 denote memory units consisting of D-type flip-flop circuits which are installed on the first to ninth floors, and to which the signal line 3 is connected through the terminals CL, 91 denotes a signal line which connects the control unit 1 to the memory unit 81, and which transmits a reference signal 91a that assumes the high level only for one period (inclusive of a delay of a short period of time) of the clock pulse signal 3a, 92 to 99 denote signal lines which connect the memory units 81 to 89, and which transmit reference signals 92a to 99a (signals 95a to 99a are not diagramed) that assume the high level only for one period (inclusive of a delay of a short period of time) of the clock pulse signal 3a, successively, being delayed in time, 111 to 119 denote D-type flip-flop circuits (hereinafter referred to as memory units) of which the terminals D are connected to the signal line 5, of which the terminals CL are connected to the terminals Q of the memory units 81 to 89, and of which the terminals Q are connected to the platform call registration lamps 71 to 79, respectively, and reference numerals 121 to 129 denote AND gates of which the input sides are connected to the signal lines 92 to 100 and to the platform buttons 61 to 69, and of which the output sides are connected to the signal line 4. 
     Reference numeral 101 denotes a signal terminal means consisting of the platform button 61, signal lamp 71, memory 111, and AND gate 121. Similarly, reference numerals 102 to 109 denote signal terminal means of the second to ninth floors. 
     Next, the operation will be described below. 
     If a clock pulse signal 3a is applied to the signal line 3 and if a reference signal 91a is applied to the signal line 91, the output 92a at the terminal Q of the memory unit 81 becomes an input 91a to the terminal D at the time when the input 3a to the terminal CL is rising. Therefore, the output 92a assumes the high level for only one period of the clock pulse signal 3a when the reference signal 91a assumes the low level. Similarly, the reference signals 92a to 94a, . . . , assume the high level successively being delayed in time as shown in FIG. 2. 
     Here, if the platform button 62 of the second floor is depressed, output of the AND gate 122 assumes the high level when the reference signal 93a assumes the high level, and is transmitted as a platform call signal 4a to the control board 1 over the signal line 4. 
     If the platform button 63 of the third floor is depressed, output of the AND gate 123 assumes the high level when the reference signal 94a assumes the high level, and is transmitted as the platform call signal 4a over the same signal line 4. Even when the platform button 62 of the second floor and the platform button 63 of the third floor are depressed simultaneously, the platform call signals 4a are transmitted in series over the signal line 4, since the clock signals 3a have a very small period. This operation is repeated successively to obtain the conditions of the platform buttons 61 to 69. 
     As a predetermined number of pulses are sent as clock signals 3a, the data are all collected. These signals are processed by the control unit 1, and are registered as a platform call. 
     The thus registered platform call registration signal 5a is transmitted through the signal line 5, whereby the input assumes the high level at the terminal D of the memory unit 112. In this case, since the signal 93a of the high level is input to the terminal CL of the memory unit 112, the output at the terminal Q assumes the high level, and this level is maintained. Therefore, the platform call registration lamp 72 of the second floor turns on, indicating that the platform call is registered. Similarly, the platform call registration lamp 73 of the third floor also turns on. 
     The registration lamps 72, 73 can be turned off according to the same procedure as described above, though not described here in detail. That is, if the platform call registration signal 5a of the signal line 5 is rendered to assume the low level when the cage of the elevator has arrived at the second floor, the output at the terminal Q of the memory unit 112 assumes the low level when the reference signal 93a rises, and the platform call registration lamp 72 of the second floor turns off. The same also holds true for the registration lamp 73 of the third floor. 
     Namely, only four signal lines 3 to 5, and 91 are required to connect the platforms to the machine room. 
     However, although the number of signal lines can be reduced, this system is seriously affected in case, for instance, the lines are broken. For example, if the memory unit 82 becomes defective, and the signal 93a assumes the low level at all times, the memory units 83 to 89 all assume the low level, and the call is not registered by the platform buttons 62 to 69. Further, if the memory unit 81 becomes defective, the call is not registered by the platform buttons 61, 62, . . . , and the elevator is placed out of service. 
     SUMMARY OF THE INVENTION 
     The present invention is aimed to overcome the above-mentioned inconveniences, and its object is to provide a signal transmission apparatus in which in case of a fault in one of the series connected memory units or lines connecting the memory units, the signals are transmitted to the end memory unit instead of the starting memory unit and in the opposite direction between the memory units of the series in order to minimize the effect of the fault. 
     In order to achieve the above object, the present invention deals with a signal transmission apparatus which comprises: 
     a plurality of signal terminal means which are connected in parallel with signal lines running from a control unit, and which transmit signals to the signal lines via gates; 
     pulse generator means which is provided in said control unit and which generates clock pulses; 
     a counter which counts said clock pulses, and which generates a gate signal every after the clock pulses are produced in a predetermined number which is greater than the number of said signal terminal means; 
     a plurality of memory means which are corresponded to said signal terminal means, and which are connected in series with each other, wherein the memory means at the starting end and at the final end are connected to said control unit to constitute a closed loop, wherein the memory means at the starting end or the final end receives said gate signal and stores it temporarily to open the gate of the corresponding signal terminal means, and wherein said memory means transfers said gate signals to the subsequent stage successively responsive to said clock pulses; 
     detector means which detects whether said first gate signal has circulated the closed loop constituted by said memory means from the moment when said counter has generated the first gate signal to the moment when the next gate signal is generated; and 
     switching means which switches the sending path of said gate signal so that the gate signal is sent from the memory means of either the starting end or the final end, depending upon the detected result of said detector means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 illustrate a conventional signal transmission apparatus, wherein; 
     FIG. 1 is a block diagram showing the whole signal transmission apparatus; 
     FIG. 2 is a diagram for illustrating the operation; 
     FIGS. 3 to 6 illustrate an embodiment of the present invention, wherein; 
     FIG. 3 is a diagram which corresponds to FIG. 1; 
     FIG. 4 is a diagram of electric circuit connection which shows, in detail, a portion of the control unit 1; 
     FIG. 5 is a diagram of electric circuit connection which shows, in detail, a portion of FIG. 3; and 
     FIG. 6 is a diagram for illustrating the operation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the invention will be described below in conjunction with FIGS. 3 to 6. In the drawings, the same reference numerals as those of FIGS. 1 and 2 denote the same or corresponding portions. 
     In FIG. 3, first, reference nuemral 7 denotes a signal line which transmits a switching signal 7a that is shown in FIG. 6, and reference numerals 211 to 215 denote memory units which are provided on the first to fifth floors, to which the signal lines 3, 7 are connected commonly, and to which are further connected signal lines 91 to 96, memory units 111 to 115, and AND gates 121 to 125, correspondingly. 
     FIG. 4 shows in detail a portion of the control unit 1, wherein reference numeral 301 denotes an oscillator which generates clock pulse signals 3a shown in FIG. 6, 302 denotes a floor-number memory means which stores the number of floors where the cage will be stopped. In this embodiment, there are five floors, and a numerical value 5 is stored in the memory means 302. Reference numeral 303 denotes a counter which counts the number of pulses produced by the oscillator 301, and which produces a gate signal 303a shown in FIG. 6 every after the counted value becomes equal to the content stored in the floor-number memory means 302. Reference numeral 304 denotes a NAND element which receives the signals 3a and the gate signals 303a, and which produces a signal 304a shown in FIG. 6. Reference numeral 305 denotes a J-K flip-flop circuit (hereinafter referred to as J-K FF) which receives the signal 304a through the terminal C and which produces the switching signal 7a shown in FIG. 6 from the terminal Q. Reference numeral 306 denotes a logic element which introduces a gate signal 306a. The logic element 306 assumes a low-impedance state to invert the signal 306a to produce signals of the high and low levels, and assumes a high-impedance state or the open state to interrupt the signal 306a. Namely, the logic element 306 produces outputs of three values that will be input to terminals J, K of the J-K FF 305. Reference numeral 307 denotes a logic element which receives a gate signal 91a, and which inverts the gate signal 91a to produce outputs of three values, i.e., high level, open state, and low level that will be input to the terminals J, K of the J-K FF 305. Reference numeral 308 denotes a logic element which receives the gate signal 303a and which produces signals of three values, i.e., high level, open state and low level to the signal line 96, and 309 denotes a logic element which produces the signals to the signal line 91. Reference numeral 310 denotes an inverter element which inverts the switching signal 7a and which produces a signal of the low level to open the logic elements 307, 308. 
     The J-K FF 305 and logic elements 306, 307 constitute a detector means 320 which detects whether the gate signal 303a has circulated the memory units 211 to 215. 
     FIG. 5 shows in detail the memory units 211 to 215, wherein reference numeral 401 denotes a logic element which receives the gate signal 91a from the signal line 91 and which produces outputs of three values, i.e., high level, open state and low level to the terminal D of a memory unit 101, 501 denotes a logic element which receives a signal from the terminal Q of memory unit 101 and which produces outputs of three values, i.e., high level, open state and low level to the signal line 92, 601 denotes a logic element which receives a signal from the terminal Q of memory unit 101 and which produces outputs of three values, i.e., high level, open state and low level to the signal line 91, 701 denotes a logic element which receives the gate signal 92a from the signal line 92 and which produces outputs of three values, i.e., high level, open state and low level to the terminal D of memory unit 101, and 801 denotes an inverter element which inverts the switching signal 7a and produces a signal of the low level to open the logic elements 601, 701. 
     Memory units 212, 213, 214 and 215 are also constructed in the same manner as the memory unit 211. 
     Operation of the thus consturcted signal transmission apparatus will be described below. 
     The oscillator 301 is continuously producing clock pulse signals 3a. It is now presumed that the counter 303 produces a signal of the high level when a O-th clock pulse signal 3a is produced in FIG. 6. The output 304a of NAND element 304 assumes the low level only during a period in which the clock pulse signal 3a assumes the high level. Here, it is also presumed that the J-K FF 305 is continuously producing the switching signal 7a of the high level from the terminal Q thereof. The logic element 309 is assuming a low impedance, and the gate signal 303a is transmitted to the signal line 91. In the memory unit 211, both the logic elements 401 and 501 assume the low impedance condition since the switching signal 7a is assuming the high level. The gate signal 92a assumes the high level only for one period of the clock pulse signal 3a when the gate signal 91a assumes the low level, like in the conventional art. Likewise, the gate signal 93a assumes the high level being lagged by one period as shown in FIG. 6. 
     When the gate signal 92a is assuming the high level, a signal of platform button 61 is sent to the control unit 1 and when the gate signal 93a is assuming the high level, a signal of platform button 62 is sent to the control unit 1. Further, when the gate signals 92a, 93a are assuming the high level, a signal sent to the signal line 5 is stored by the memory units 111, 112, respectively. The memory units 111, 112 produce signals of the high level through the terminals Q thereof, and registration lamps 71, 72 are turned on by these outputs. 
     It is now supposed that the signal line 93 is broken at a point E shown in FIG. 3. The signal 93a is not input to the memory unit 213, and the memory units 213, 214 and 215 do not operate any more. As a fifth clock pulse signal 3a is produced in FIG. 6, the gate signal 303a assumes the high level, and the signal 304a assumes the low level. Since the memory unit 215 does not operate, the gate signal 96a remains at the low level. Therefore, the logic element 306 produces an output of the high level which will be input to the terminals K, J of the J-K FF 305. As the signal 304a assumes the high level again after a half period of the clock pulse signal 3a,the J-K FF 305 produces the switching signal 7a of the low level. Therefore, the logic elements 306, 309 assume the high-impedance condition, and the logic elements 307, 308 assume the low-impedance condition. As the logic element 309 assumes the high impedance, the gate signal 91a assumes the low level after a half period of the clock pulse signal 3a. Further, as the logic element 308 assumes the low impedance, the gate signal 303a is allowed to pass through for only a half period, and a gate signal 96a assumes the high level. 
     In FIG. 5, the switching signal 7a is assuming the low level. Therefore, the logic elements 405, 505 assume the high-impedance state, and the logic elements 605, 705 assume the low-impedance state. As the sixth clock pulse signal 3a rises, the memory 101 produces an output of the high level, whereby a gate signal 95a of the high level is transmitted to the memory unit 214 via the logic element 605 and the signal line 95. While the gate signal 96a is assuming the high level, the signal of the signal line 5 is received by the memory unit 115 and is stored therein. At the same time, a signal produced by the platform button 65 is transmitted to the control unit 1 via the element 125 and the signal line 4. This point is the same as that of the conventional art. Similarly, the memory unit 214 operates responsive to the gate signal 95a and produces a gate signal 94a that will be transmitted to the memory unit 213. Although the memory unit 213 operates properly, the signals are not transmitted between the control unit 1 and the memory 112 or the platform button 62, since the line is broken at the point E. The signals are not transmitted to the memory units 212, 211, either. 
     As the tenth clock pulse signal 3a is produced in FIG. 10, the gate signal 303a assumes the high level, and the gate signal 304a assumes the low level. Further, since the gate signal 91a is assuming the low level, a signal of the high level is input to the terminals J, K of the J-K FF 305 via the logic element 307. Therefore, as the signal 304a  assumes the high level, the switching signal 7a is inverted to assume the high level. Due to this inversion, the logic elements 306, 309 assume the low-impedance state, and the logic elements 307, 308 assume the high-impedance state. Therefore, the gate signal 91a assumes the high level via the logic element 309. As mentioned earlier, the gate signal 91a operates the memory units 211, 212, successively. 
     According to the above-mentioned embodiment, the signals can be sent to and received from the platform button and the registration lamp, even when the signal line is broken. 
     Although the above-mentioned embodiment has dealt with the case where the signal line is broken, the same also holds true even in case defect has developed in the memory unit and the signals are not transmitted to the subsequent units. Namely, the signals are alternatingly transmitted from both the memory unit 211 and the memory unit 215, enabling the platform buttons and the signal lamps to operate properly. 
     Further, although the above-mentioned embodiment has dealt with the elevator system, it should be noted that the invention is in no way limited thereto only, but can be adapted to any system where signals are transmitted in series to a plurality of places, to achieve the desired objects. 
     In the above embodiment, furthermore, the gate signal 303a is generated every after the number of clock pulse signals becomes equal to the number of the platform buttons. The invention, however, should not be limited thereto only. Namely, desired objects can be accomplished even when a gate signal is generated every after the clock pulse signals are generated in a predetermined number which is greater than the number of the platform buttons.