Door Control Systems

This invention relates generally to door control systems and more particularly to door control systems utilized in mass transit vehicles having power operated doors, wherein it is necessary to accurately determine vehicular speed in order to properly open and close doors in order to insure passenger egress and ingress. Present systems in use are somewhat exemplified by the system disclosed in U.S. Pat. No. 2,637,009. The specification of which is hereby incorporated by reference. Wherein, in a multiple car train, operation of each door is controlled via signals from propulsion equipment and individual relays located in each door circuit. This method of door control, while providing somewhat improved performance in that each door must be closed and a propulsion signal available in order to allow the train to move, suffers from certain shortcomings. Additional door control systems involving operative vehicular interlocks are contained in U.S. Pat. Nos. 1,906,694, 2,096,043, and 1,849,516. Typical door control circuitry is also disclosed in U.S. Pat. Nos. 3,537,403, 1,906,699, 1,849,516, 3,537,403, and 3,782,034. Specification of these U.S. patents are hereby incorporated by reference.

A major shortcoming of these approaches is the ambiguity inherent in the propulsion signal and difficulties in relating car motion to the door control signal. Also possible malfunction of the individual door relay sometimes called a door control summary relay can greatly reduce system reliability. In view of the consequences of premature door opening and/or closing during rapid transit vehicle operation, there has been a substantial need for a system wherein additional checks relative to vehicle speed and condition of the propulsion system are utilized in order to more accurately determine the condition of a given vehicle and/or train prior to any door operation. Additionally, in present systems, possible electrical failures indicating incorrect door vehicle operation information have heretofore been essentially undetectable, resulting in a need for close attention by transit vehicl operators. This requirement, as in the past, resulted in reducing overall effectiveness of the door control system and increasing operation times, a highly undesirable occurrence in todays modern rapid transit systems.

Providing accurate determination of vehicular speed has also been a substantial problem with past systems. Due to the design of speed detectors, exact determination of vehicular speed due to wheel rotation has been subject to substantial error, thus substantially reducing the effectiveness of what is perhaps the best means for allowing doors to open, or in the alternative, closing open doors on start-up.

The invention disclosed here provides an improved control system and method for actuating doors which utilizes, on a time based sample basis, a number of vehicular "state" indications in addition to wheel rotation. Sampling is cyclically repeated in periods chosen to increase the reliability of door control operation.

Accordingly, it is an object of this invention to provide an improved door control system having motion and propulsion signals combined with time based checks for vehicular propulsion to enable door operating sequences.

It is a further object of this invention to provide door controller which utilizes various self-checking techniques to minimize incorrect door operation due to equipment failure.

It is a still further object of this invention to provide a door control system for mass transit vehicles wherein utilization of speed signals in combination determine through recycled logic, a most appropriate time to enable door opening and/or closing.

FIG. 1--Block diagram showing a signal flows for major functional elements of the system.

FIG. 2--A functional block diagram showing salient signal flows internal of the Low Speed Detector and No Motion Relay.

FIG. 3--Pictorial semi-schematic drawing of "typical" "A and B" car layout showing approximate physical location of major components of the disclosed invention.

FIG. 4--"Typical" door installation in a mass transit vehicle showing location of the power operator, door control panel and low speed detector.

FIG. 5--"Typical" door operator motor circuitry showing door control limit switches and associated motor control elements for a single door. Accented or bold lines indicate circuitry directly concerned with the invention.

FIG. 6--Additional "typical" door control circuitry particularly showing inter-car connections and in particular the zero speed interolock (ZIR) relay utilized in low speed detector circuitry. Accented/bold line circuits as in FIG. 5.

FIG. 7--Further "typical" door control circuitry showing connection of an individual door motor control relay. Accented/bold circuits as in FIG. 5.

FIG. 8--Initial portion of an operational flow chart for the "low speed detector" of the invention, indicating internal operating sequences and the enabling means or "no motion relay" (NMR). FIG. 8a--Second and final portion of the flow chart of FIG. 8.

FIG. 9--Detailed plan view of the Low Speed Detector package particularly showing operators panel and diagnostic failure code.

In accordance with the invention a control system is disclosed providing improved operation of power operated passenger doors in a mass transit vehicle. In operation, the controller of the invention provides continuous monitoring at a rate of approximately 1000 cycles per second, of the vehicle wheel speed, a signal or indication of propulsion, and absence or presence of manual request for door opening. Under prescribed conditions for each of the above factors, the system provides for manual opening and/or closing of the vehicular doors. These prescribed conditions for door opening include a wheel speed indication of more than a qualified "zero", and less than some pre-determined speed (typically 2.9 mph), the absence of a demand for vehicular propulsion, and the absence of a door opening signal.

In a preferred but not limiting embodiment of the system disclosed, utilizing micro-processor techniques well-known to those skilled in the art, the low speed detector 1 (ref. FIGS. 2 and 8) conducts a cyclic series of functional tests in order to determine the operability of the overall door control system. This sequence of tests, as indicated in detail on FIGS. 8 and 8a, along with the above mentioned vehicular operating information, conducts a series of at least six equipment operational checks shown on the above mentioned FIG. 8 and listed below.

The functional statements utilized to program the micro-computer portion of the low speed detector are contained in the Appendix.

The time based, cyclic sequential tests disclosed utilize a pre-selected time of cycle which allows self-checking of system components prior to critical functioning of the system. In this way it is possible to detect equipment failures on a continuous basis, and prior to a door opening operation which, in case of malfunction, would be either improper, interfere with efficient train operation, or result in increased difficulties in loading or unloading passengers.

In a conventional arrangement well known to those skilled in the art, two transit vehicles are arranged in what is commonly known as a "married pair". As indicated, particularly in FIGS. 1 and 3, the doors in "A" and "B" cars are controlled by the system largely centered in the "A" cars. Large trains are made up of "A-B" pair multiples.

Although the disclosed embodiment employs self-propelled "married-pair" cars as described above, the disclosed method of enabling door operation is not limited to self-propelled passenger vehicles. Therefore, the door control system disclosed here fully contemplates application on vehicles such as suburban commuter trains using locomotive traction provided by both diesel and electric prime motors. Therefore, the "propulsion systems" refer to any source of tractive effort, either at the wheel of the vehicle or as applied through drawbar pull, sometimes termed "draft".

The low speed detector comprises a micro-processor unit, typically using an 8035 central processing unit (CPU), a 2716 programmed read only memory (PROM), and (2)8212 input-output ports (I/O) such as manufactured by INTEL or equivalent.

Operation of the disclosed system is initially best understood by initial reference to functional diagram contained in FIGS. 1 and 2.

Although the door control system of the disclosed embodiment which will be described in detail below utilizes an electrically powered door actuator, other forms of door actuators are contemplated by the invention as well. Therefore, the control system disclosed can be utilized and adapted by those ordinarily skilled in the art to hydraulic, pneumatic, or any other sources of controllable power employed to move any type of door between open and closed positions.

As shown, operating signals from car wheel speed sensing element 5, traction signal/source 7, and the door open push button (DOPB) contained in both (A) and (B) cars, are supplied to low speed detector 1. The detector, as discussed above incorporates novel time based self-checking features which will be discussed in detail below. At this point, however, it is important to note that on completion of all sampling checks, the functional result is obtained through control of the output element of low speed detector 1, a no-motion relay 3. As indicated in FIGS. 1 and 6, the no-motion relay enables operation of either left hand doors of the (A) and/or (B) cars as determined by operation of the DOPB 9, 11, and/or 13, 15. Enablement by the no-motion relay (NMR) 3, in sequence enables operation of the appropriate zero (speed) interlock relay (typically, ZIR 21, 21a) indicated functionally as 17, 18, 20, or 22 in FIG. 1, and in the "typical" circuit of FIG. 6 as 21. As shown in FIG. 1 and FIG. 3, ZIR's (21, 21a) are located in each car and represent, as shown in the circuitry of FIGS. 6 and 7, the actuating means for the door operating motor armature 36, reference FIG. 5, through supplying the power through ZIR contacts 21a and 21b thereby energizing MCR relay 37 (Ref. FIG. 7).

With particular reference to FIGS. 5, 6, and 7, "typical" transit car circuitry involving the door control systems are shown. As this circuitry does not constitute a part of the disclosed invention, inclusion is only for the sake of completeness. Therefore, only "salient" portions of the circuitry which involve control of the doors through the invention end element, i.e., the no-motion relay (NMR) 16 are shown. In order to facilitate disclosure, (those skilled in the art will easily understand) the above mentioned salient circuitry is disclosed in bold or accented lines while supporting and less important circuit elements such as connection type points, fuses, transient suppression diodes, are shown in light relief. Thus, circuit tracing by those skilled in the art will be directed to car circuitry associated with the invention disclosed.

FIG. 5 discloses typical single door motor actuator circuitry wherein the contacts of motor control relay (ref. 37-FIG. 5) contacts 37a and 37b are utilized in conjunction with limit switches 38a, 38b, and 38c located on the door actuating mechanism (not shown), to provide opening and closing operations of a typical transit car door set (ref. FIG. 1), i.e., doors 24, 26, 28, or 30.

As shown in FIGS. 3 and 4, a typical transit car application consists of sliding bi-parting doors 24 and as further shown in FIG. 3 doors are located at two locations on either side of each car. Returning to FIG. 4, the low speed detector 1, and its associated panel 2, as shown located adjacent to the door control station 19 and door set 24.

Returning to the circuitry of FIGS. 5, 6, and 7, the no-motion relay 3 supplies power to the coil of a zero (speed) interlock relay (ZIR) 21 as shown. Contacts 21a and 21b, of the ZIR relay, energize a MCR relay 37 and associated contacts 37a, and 37b, which as shown in FIG. 5 provides either open or closed door operations. It should be noted that as those skilled in the art will readily understand, each individual door set, i.e., left or right hand pairs, incorporates its own MCR (37) relay.

Therefore, as those skilled in the electric circuit arts will further recognize, utilization of the end element of the invention, the no-motion relay 3, is supervisory to operation of individual car doors. Therefore, initiation of car door operation via the controller 1 through actuation of the door open push-button 9, 11, 13, or 15, door operation in accordance with the invention is achieved.

Operating under control of the low speed detector (LSD) 2 and the NMR 3, door operation is enabled through pre-selected combinations of car speed, car propulsion, and a manual request for door actuation.

As indicated above, other functions are contained in the low speed detector (LSD) 1, greatly enhancing the function of the overall door control system and providing a substantial advance in the state of the art of door control systems. Chief among these functions are a series of six internal operational checks (Ref. FIG. 2) on the micro-processor 8, programmed read only memory 12, and input/output ports 14, as components of the low speed detector. As indicated in FIG. 8, and Appendix, the following series of system checks are cyclically performed;

1. A microprocessor (8) self test.

2. Continuity test of speed sensor (5) and associated circuitry.

3. Speed sensor amplifier (6) test.

4. Speed sensor (5) sensitivity test.

5. Redundant propulsion signal input circuit check.

6. NMR (3) output/feedback test.

These tests are described in substantial detail, along with micro-processor operating instructions corresponding to the block diagram tests in FIG. 8. The micro-processor program is described in detail by the Appendix. Those ordinarily skilled in the micro-processor art will readily understand the functional aspects of overall system of FIG. 8 and further operationally tabulated in the Appendix.

To enhance the disclosure, a detailed description of salient functions keyed to micro-processor instructions follow hereinafter. It should further be noted that the Appendix program conforms to ISIS-II MCS-48/UPI-41 macro-assembler, a system well known to those skilled in the micro-processor arts.

Functional operation of the LSD 1, (ref. FIG. 2) is best understood by following the sequences shown in FIGS. 8, and 8a. It should be again noted that the numerical representation in or adjacent to the functional operating blocks correspond to the line numbers of the micro-processor operating program contained in the Appendix. As indicated earilier, those skilled in the art will recognize the format. The assembly language manual defining the programming language is INTEL manual #9800255.

Beginning at 298 on initial start-up, power is supplied to the entire door control system initiating operation of the central microprocessor unit 8. A prescribed test (500) checks for "bare minimum" operation which includes the micro-processor and associated memory. This testing establishes a minimum or "kernel" function. End points of this test are 497 for successful CPU function, and 474 for a test failure. In the event of a CPU malfunction, the NMR(3) would be de-energized at 863.

A failure code is then displayed on the system operating panel 2 at 895.

Additional NMR testing occurs at 902 in order to insure de-energization of the no-motion relay and non-enablement of the door system. The 902 test includes a group of sequential operations on the contactor to insure relay dropout or contact opening. In the event of a welded contact or other malfunction that would allow improper enablement of the door system, at 906 a "crow bar" is utilized to supply excessive current to a fuse contained in the power supply module 4. Opening of the crow bar fuse removes electrical power from the entire system and provides failure indication on the panel indicating display 2 requiring action by an operator.

It should be noted that the sequence 863, 895, 902, 906, is repeated for all test failures to be described below. Therefore, in order to avoid excessive and redundant description, the operation 863 will be described as to a low speed detector failure.

A major feature of the disclosed invention is the utilization of high speed electronic logic and associated circuitry to provide a highly reliable electro mechanical contactor wherein electronic circuitry augments a high quality electro mechanical contactor. This synergistic combination provides reliability of a much higher order of magnitude then either the circuitry and/or contactor alone. Conventional "highly reliable" contactors employ mechanical and electro mechanical designs for use in vital circuitry, through "inherent" physical characteristics. These inherent characteristics include gravity actuation of an armature in returning to a predetermined position, massive magnetic coils wherein failure due to thermal expansion and contraction is minimized, and contact material wherein certain arc handling and current interrupting features have been found to reduce the probability of failure through welding.

Although the concepts of "vital" circuitry and associated "vital" components are allied with safe and fail-safe operation of the circuitry, an exact correlation is difficult to establish. Operation of safe and/or "fail-safe" circuits imply reversion to operation having a least dangerous function or state. Therefore, although exact definitions do not exist, the concept of a conservative state can be used to define a least dangerous state. Consequence of improper door operation establishes the circuitry and objectives of the invention disclosed here as "vital", and therefore reversion to a conservative state can be considered to imply cautious or "least dangerous" modes of operation.

The above mentioned designs, while providing reasonably increased reliability, result in electro magnetic devices which are large, heavy, and substantially increased in cost. Therefore, in many cases, contactors of this type are not utilized due to the aforementioned disadvantages. In contrast, the approach provided by portions of the disclosed microprocessor control, beginning at 73 and ending at 906 provide a relatively low cost moderately sized device which incorporates all of the characteristics of the above "inherently highly reliable" device.

As disclosed the electronically augmented contactor provides frequent and repititious checks on major failure modes of an associated electro magnetic contactor. The combination, therefore, provides the synergistic combination at moderate cost and a reasonable size, thereby enhancing the probabilities of its being incorporated in equipment, and making highly reliable equipment available to designers without substantial penalties imposed by the above mentioned "inherent" devices.

Returning now to 497, signifying a successful central processing unit test. The program at 517 tests for car speed less than 2.9 miles per hour. It should be pointed out that those skilled in the art will recognize that the speed tested for, as well as other numerical constants disclosed herein, is "programmable" and may vary depending on the particular embodiment of the invention. Car speed indications less than 2.9 miles per hour, proceed to a check for speed "zero" at 339. It should be noted that the term "zero" is qualified to include indications from the car speed sensor 5 less than 0.5 miles per hour, due to the unreliability of wheel speed sensors at very low speeds.

Continuing on in the functional program: at test 339, assuming that speed were in excess of 0.5 miles per hour, a second test at 689 would be applied so as to check for a second consecutive low speed. Assuming that on re-cycling, two consecutive speeds above 0.5 miles per hour but below 2.9 miles per hour were encountered a low speed flag would be set at 695, thereby establishing a low speed indication for the subsequent test at 793. In the alternative, assuming that the indicated speed between 2.9 and 0.5 miles per hour was not the second consecutive such speed, the low speed flag would not yet be set. This essentially forces a second pass through the system establishing additional reliability of the low speed sensing.

If the indicated car speed is "zero", a check for counts, i.e., pulses from the wheel speed sensor (5) indicating speeds less than 0.5 miles per hour for three seconds is accomplished in 593. Assuming the speed is held for three seconds, at 594 an operation check on the wheel speed indicator (5), and its associated amplifier and inter-connecting cables is performed. These tests include connecting cable continuity, wheel speed sensor resistance, and amplifier frequency response.

It should be noted that the three second check period provides for attainment of speeds low enough to prevent generation of current by the wheel speed sensor which would interfere with the subsequent electrical test.

Returning to FIG. 8, at the 517/676 test for speeds less than 2.9 miles per hour, an additional test at 678 tests for speed greater than 3.2 miles per hour; therefore, in a situation where indicated speed excess of 2.9 miles per hour might be less than 3.2 miles per hour, the low speed indication is unaffected. These two tests are essential in that possibilities for variation in speed sensor speed pulses, gear back lash, and wheel/gear eccentricity can combine to "loop" the system around a single given speed. Therefore, it has been found necessary to provide "hysteresis" which is a substantial factor in stabilizing the system and providing consistant indications for proper door operation.

In the event that a speed of 3.2 MPH, or greater, is detected, the low speed flag is removed at 679.

At test 593, assuming the prior indicated "zero" speed were not maintained for three seconds, program operation would bypass the sensor, cable, and amplifier test of 594. At test 594, in the event that tests of the speed sensor, cable, and amplifier are unsatisfactory the program proceeds to 863, where a no-motion relay is de-energized and subsequent tests discussed above are conducted to again inhibit door operation. A flag indicating failure is set in 615-629.

Upon completion of the above wheel speed functions, operation continues with testing of the door open push button (DOPB) signal or operating any one of switches 9, 11, 13, 15 at 710. De-actuation, i.e. opening a normally closed switch, is a function of the continuous current circuitry employed. In use, failure of any component in the DOPB circuit carrying current will be detected since a door opening signal out of sequence will fail subsequent tests.

If the signal indicates de-actuation of the DOPB, i.e. a requirement for door opening, a "NOT-DOPB" flag is set for subsequent test at 793. If the signal indicates actuation of the DOPB, a further check is made, at 713, of the low speed status. If the vehicle speed is above "low speed", the "NOT-DOPB" flag is cleared at 715. As can be seen in the logical flow of this operation, continuous actuation of the DOPB, while the vehicle is decelerating from a "high speed" to a "low speed", will pre-empt the setting of the "NOT-DOPB" flag which in turn will inhibit door operation via the subsequent test at 793. Since operation of the DOPB must accompany a low speed condition on each program sequence to initiate the "energize NMR" phase at 793/803. Those familiar with mass transit operation will recognize the desirability of this feature as it prevents the "automatic" opening of doors at attainment of low speed should the DOPB be "plugged" or otherwise artificially maintained in the actuated or "door open" state resulting in a substantial improvement in passenger handling and door system reliability.

Continuing with the operation, the propulsion input signal is sampled 734 (reference Appendix program). At the signal interface 7, the propulsion signal is applied to two identical legs of a redundant signal processing circuit. If the results of these redundant circuits are not identical, a malfunction may have occurred at 767. To allow for variations in response times for the two circuits a temporary flag is set and a delay of ten "program loops " is introduced (772) before action is taken. If the two results are reconciled before the completion of the delay, the temporary flag is cleared and the delay process is terminated 764 (reference Appendix program) in preparation for possible invocation at a later time.

If, however, the delay proceeds to completion (also program) the discrepancy is recognized as a circuit malfunction and appropriate action is taken (863) by disabling the NMR as previously described.

When the two circuits give identical results, these will indicate either propulsion or not-propulsion. In the case of "not-propulsion", a flag will be set establishing a "not-propulsion" indication (758) for subsequent testing at 793. In the case of propulsion, not only will the "not-propulsion" flag be cleared (749), but a further test will be performed that checks for the transistion from not-propulsion to propulsion (738). The transition (or vehicled start-up) begins a delay sequence of approximately 12 seconds (741 program and 390-395) to allow sufficient acceleration of the vehicle to detect wheel pulses. If, during the 12 second delay, speed pulses are detected, the delay sequence is terminated (568). If, however, no speed pulses are detected and the delay proceeds to completion, a malfunction has occurred. A speed sensor sensitivity failure is indicated (with pickup sensitivity failure code--FIG. 9) (397) and the NMR is de-energized (863) as described earlier.

Continuing on in the sequence, at 793 a comprehensive check of information (i.e. flags) developed earlier regarding proper low speed, lack of door opening push button signal, i.e., actuation of the DOPB switch, and no propulsion is conducted to insure that all three situations are present. Assuming a positive result, at 803 a signal to energize the no motion relay 3 is developed)i.e., coil command at 800) and the relay itself is tested for operation via 824-838.

It should be noted that the extremely high cycling speeds of this portion of the system operate well inside the operating time of the no-motion relay 3 and, therefore, at 805 and 818 it is necessary to establish a delay as indicated in FIG. 2 at element 16, to provide additional time for relay contacts to operate. Therefore, recycling through 824-838, and back to 517, returning to 803 until the delay terminates before checking the status of the NMR contacts. After maintaining the appropriate control signal for the NMR coil, (at 805 or 818) an additional check for termination of the delay is conducted at 824 and 825, which if successful, moves the program to 828. Step 828 provides an indication of contact status in the no-motion relay 3 as signified on FIG. 2 by the functional connections between blocks (3) and (7). Further, testing of the NMR contacts for either pick up or drop out action is conducted at 831 and 836 respectively. Alternately, failure of NMR contacts to "make" establish an output failure at 840 with attendant failure code at 895. This provision signals a "non opening" failure in the controller end element on panel 2, for appropriate action by train operating crews.

Assuming pick up of the NMR (3) is desired, the 831 leg proceeds to further check for presence of a coil command provided earlier by the low speed, door open push button, and propulsion checks at 793. Assuming a positive result at 834, operations return to 517, reinitiating the entire cycle beginning with the low speed check.

It should be noted that the above description assumed that all requirements for door opening were present, and terminated in enabling the door opening via the ZIR (21) contact, i.e., elements 17, 18, 20, and 22 in the appropriate cars. As indicated earlier, and shown in FIG. 3, actuation of the door opening push button in a train attendant is accomplished for either one side of the car or the other. Thus, in the above example assuming a pair of "A" and "B" cars either elements 28, 30, 36, and 38, or 24, 26, 32, and 34 would be enabled and opened for passenger traffic.

Returning to the above discussed operating sequence and FIG. 7, a particularly useful and novel function is included involving the "crow bar" 38 actuated by the system in the event of failure to control the operation of the NMR. In one sequence of operations (reference FIG. 8) assuming that at 594 testing of the speed indicator and associated equipment have been unsuccessful at 616-629, indication of this failure is noted and stored and the program proceeds to 863. In keeping with the major thrust of this invention, the primary enabling element, that is the no-motion relay 3, is to be de-energized in order to prevent improper door opening. 863 also provides for the failure indication code to the operating panel 2 providing convenient diagnosis of the specific failure for action by the operator.

At this point it is still possible for the end element, i.e., the no-motion relay to remain energized due to mechanical or a combination of electrical and mechanical failures. Therefore, at 895 a delay is conducted for a sufficient length of time to insure that the rapid program cycle has not indicated failure due to the slow drop out time of the relay. Assuming this built in time delay is exceeded, and the feedback monitoring loop (902) indicates closed NMR contacts, at 906 the "crow bar" 38 is operated or fired. As indicated above, operation of the "crow bar" potentially shuts down the entire door system and provides indication of the shut down on the panel 2 since as shown "NO LED's ON POWER LOSS" is displayed.

A further novel and advantageous feature of the invention involves availability of quick diagnosis of system failures other than the above described NMR remaining energized in the absence of prescribed car operating requirements. A diagnostic code provides a series of unique indications by light emitting diodes or other display lamps on the control panel 2.

In operation, the failure code is initiated for each test not resulting in a successful outcome. These include: at 616-629, the speed input and associated equipment; the propulsion inputs at 779, and possible failure in the no-motion relay at 842. Therefore, using the panel shown in FIG. 8, it is possible for train attendant to quickly determine the source of difficulty and act accordingly. Those skilled in the mass transportation field will readily recognize that under the operating conditions present in train operation, availability of this kind of system will greatly improve car reliability and decrease the possibility of improper door opening.

An additional advance in the door control art provided by the invention improving the utilization of a micro-processor, is provided by the "power-on" test of the central processor. This feature insures that prior to any door enablement the probability of failure of the CPU and associated memory is greatly reduced. In particular, the test sequence contained in the power reset system test, lines 412 to 472 of Appendix, result in frequent and regular tests of the microprocessor function.

On initial power turn-on, the NMR will be energized given the speed indication of zero miles per hour as opposed to a speed less than 2.9 miles per hour maximum, on satisfactory completion of the tests indicated earlier. This "lack" of speed signal will result in a valid low speed indication only until the first speed pulse is detected. From that time on, the speed requirements are set forth earlier dictate the status of the low speed indication.

Remaining system functions shown in the loops, while not described in the detail utilized above, will be readily understood by those skilled in the art. Complimentary tests, disclosed by correlation of the functional flow diagram with indicated steps in the program disclosed in the appendix, can be easily followed.

Certain novel aspects of the above system-check features provided by the LSD (1) are described below.

Utilizaton of a micro-processor and associated programmable memory devices in a novel combination with elements of car propulsion and power door operating equipment provides additional and novel advantages in door control. In particular, high speed repetitious functional "validity" checks of both car operating conditions and associated input and interface devices provides substantial improvements in overall system reliability and further provides detection of possible hazards to passengers prior to door operation. These novel functions, although somewhat inter-related can be distinguished as:

1. Functional interrogation of the overall system, assuming proper component operation.

2. Functional tests independent of car operating functions of system components at the predetermined time relationship with car functions indicated above so as to provide clear indications of failure prior to door operation.

These predetermined failure modes are clearly indicated (ref. FIG. 9) on the low speed detector panel indicating display 2. As shown, the series of four indicators provide rapid diagnosis of system malfunction at any time. The panel and indicators 2 are located as shown in FIG. 4, prominently displayed on the conductors door control panel.

Thus it is apparent that there has been provided, in accordance with the invention, a system for controlling power operated doors for transit vehicles, that fully satisfies the objects, aims, and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. ##SPC1## ##SPC2## ##SPC3##