Apparatus for equipment unit protection switching

Abstract: An equipment unit protection switch from an in-service equipment unit to a standby equipment unit is realized prior to any movement of the active equipment unit about to be removed from an equipment frame in which it is inserted. This is achieved by advantageously incorporating apparatus for generating an equipment unit removal indication signal that enables a controller to anticipate the removal of the equipment unit from the equipment frame. To this end, the equipment units employ an equipment unit latch and an associated switch to generate the equipment removal indication signal. Initial movement of the latch causes the equipment unit removal indication signal to be generated prior to any movement of the equipment unit in the frame in which it is inserted.

Description: Technical Field This invention relates to equipment unit protection switching and, more particularly, to minimizing disruption of customer service during equipment unit protection switching. Background of the Invention It has been the practice to employ redundant equipment units, e.g., plug-ins, circuit packs and the like, to enhance product reliability. The enhanced reliability has been realized by controllably switching service to a standby equipment unit upon detection of a failure of an in-service equipment unit or its removal from a connector in an equipment frame. Prior known equipment unit protection switching arrangements that were specifically directed toward removal of equipment units, relied upon the complete disengagement of the equipment unit from its connector before initializing equipment unit protection switching. Any movement of an equipment unit in its connector tends to cause transmission errors which have the potential for affecting customer service. This is especially true in relatively high digital bit rate transmission arrangements. In such prior equipment unit protection switching arrangements, the time required to effect equipment unit protection switching is directly dependent upon the speed at which the equipment unit is being removed from its connector. If the equipment unit was removed quickly, the protection switch would occur sooner than if it was removed slowly. In any event, the interval is still too long before completion of the equipment unit protection switching. Prior attemps at minimizing the time required to complete equipment unit protection switching were primarily directed toward the use of complex fault detection and isolation algorithms. Such prior algorithms required a significant amount of processing time and processing resources. US-A-4071722 and EP-A-0254456 are substantially as described in the preamble of claim 1. According to the present invention, there is provided apparatus as defined in claim 1. These and other problems and limitations of prior known equipment unit protection switching arrangements are overcome, in accordance with the invention, by controllably anticipating the removal of an in-service equipment unit from its connector to initiate equipment unit protection switching prior to any movement of the equipment unit in its connector. In one embodiment of the invention, an equipment unit latch and associated light responsive switch arrangement is advantageously employed to provide an indication that the in-service equipment unit is about to be removed from its connector. Once the latch is moved in initiating removal of the equipment unit, the associated light responsive switch provides an equipment unit removal indication signal which is employed to initiate equipment unit protection switching from the in-service equipment unit to the redundant standby equipment unit. Operation of the equipment unit protection switching algorithm is such that the protection switching is made to the redundant standby equipment unit before any movement of the in-service equipment unit has occurred toward disengaging it from its connector. In a specific embodiment of the invention, a light sensor switching arrangement including an infrared emitter and associated detector, is employed as the associated light responsive switch. A technical advantage of this invention is that an equipment unit protection switching is completed from the in-service equipment unit to the redundant equipment unit before any movement has occurred of the equipment unit being removed and consequently, only out-of-service equipment units are actually removable. Brief Description of the Drawing In the drawing: FIG. 1 is a cut-away cross section view of an equipment unit inserted into an equipment frame; FIG. 2 is another cut-away cross section view of an equipment unit about to be removed from an equipment frame; FIG. 3 shows, in simplified form, a portion of a face plate latch and a circuit diagram of the associated switch arrangement; FIG. 4 depicts, in simplified form, a system arrangement employing the invention; FIG. 5 is a flow chart illustrating steps taken utilizing the invention: and FIG. 6 graphically illustrates the time intervals at which the steps of FIG. 5 are effected. Detailed Description FIG. 1 shows a cut-away cross-section view of an equipment unit employing an equipment unit latch and an associated switch arrangement which may advantageously be employed in the invention. Shown is equipment unit 100 which, in this example, includes circuit board 101, face plate 102, latch 103, locking clip 104, alignment block 105, light emitter 106 and light detector 107. Additionally, circuit board 101 includes u one end a plurality of contacts (not shown) adapted to be inserted into a corresponding connector (not shown) supported by the equipment frame. Latch 103 is pivotally mounted to circuit board 101 at a pivot point via, for example, shoulder rivet 108. The portion of the equipment frame shown comprises upper shelf 109 including U-channel 110. Locking clip 104 is attached to alignment block 105 which, in turn, is mounted on circuit board 101. Locking clip 104 and alignment block 105 are arranged such as to affix latch 103 in place, i.e.,in a closed position, when equipment unit 100 is fully inserted in the equipment frame. This is important to prevent inadvertent operation of the invention in generating an equipment unit removal indication signal. Such inadvertent operation of the invention could possibly be caused by vibration and the like. Latch 103 includes a first lever arm 111 for application of rotational force which is typically applied by a person's hand or finger. A second lever arm 112 is shown as being hook shaped and includes so-called "cam-in" surface 114 and so-called "cam-out" surface 115. Cam-in surface 114 engages the rear surface of U-channel 110 when equipment unit 100 is being inserted into the equipment frame and cam-out surface 115 engages the front surface of U-channel 110 when equipment unit 100 is being extracted from the equipment frame. FIG. 1 shows the relative position of cam-in surface 114 and cam-out surface 115 when equipment unit 100 is fully inserted into the equipment frame. The spatialplacement of U-channel 110 in shelf 109 and the dimensional spacing between surfaces 114 and 115 are important to the operation of latch 103 with the associated switch arrangement including light emitter 106 and light detector 107, in order to controllably anticipate the removal of an in-service equipment unit 100, in accordance with the invention. Latch 103 also includes so-called latch rib 116 that is physically dimensioned and is arranged, in this example, such that light emitted from emitter 106 is blocked, i.e., inhibited, from being detected by detector 107 when equipment unit 100 is fully inserted in the equipment frame. That is, when latch 103 is in a closed position. It is important to note that detector 107 must be placed in such a position so that spurious light or light other than from emitter 106 cannot be detected. Detection of such spurious light could cause generation of an inadvertent erroneous equipment removal indication signal and is extremely undesirable. In this embodiment of the invention, an infrared emitter and detector arrangement are advantageously employed for emitter 106 and detector 107, respectively. Again, the dimensions of U-channel 110, latch arm 112, cam-in surface 114, cam-out surface 115 and latch rib 116 are such that generation of an equipment unit removal indication signal is inhibited when equipment unit 100 is fully inserted in the equipment frame. Note that the space between the inner surface of cam-out surface 114 and the front surface of U-channel 110 is such as to allow appropriate movement by lever arm 112 and, hence, latch rib 116 in order to allow light from emitter 106 to be detected by detector 107 prior to any movement of equipment unit 100 in the equipment frame, in accordance with an aspect of the invention. FIG. 2 depicts a cut-away view of a portion of equipment unit 100 about to be removed from the equipment frame. Again, elements identical to those described above in relation to FIG. 1 are similarly numbered and are not described again in detail. FIG. 2 clearly illustrates that the dimensions of and placement of U-channel 110 in shelf 109 of the equipment frame and the dimensions of lever arm 112, including cam-in surface 114 and cam-out surface 115, are such as to allow sufficient movement of lever arm 111 and, hence, latch rib 116, in order to generate, in accordance with an aspect of the invention, an equipment unit removal indication signal prior to movement of equipment unit 100 in the equipment frame. In this example, the equipment unit removal indication signal is generated by detector 107 detecting light 201 emitted from emitter 106. Referring again to FIG. 1, the distance between the inner surface of cam-out surface 115 and the adjacent front surface of U-channel 110 is such as to allow the appropriate movement of latch lever arm 111 and, hence, latch rib 116, so that the equipment unit removal indication signal is generated prior to any movement of equipment unit 100 in the equipment frame. FIG. 3 shows, in simplified form, details of a portion of the latch lever arm and a circuit diagram of the associated switch arrangement employed in this example to generate the equipment unit removal indication signal for effecting equipment unit protection switching in accordance with the invention. Specifically, shown are a portion of latch lever arm 111 including latch rib 116, light emitter 106 and light detector 107. Light emitter 106 is connected, in this example, when equipment unit 100 is fully inserted into the equipment frame and its connector, to a power source in such a manner as to emit light (infrared) continuously, in well known fashion. Detector 107 is also connected to a source of potential via resistor 301 and to a reference potential, e.g., ground potential. Thus, detector 107 is arranged so that when it detects light from emitter 106, a potential transition step, i.e., the equipment unit removal indication signal is supplied as an output via buffer amplifier 302. Hysteresis is employed in the transfer function of buffer amplifier 302 to prevent so-called decision chatter when latch rib 116 moves through the cross-over point of detector 107. The equipment unit removal indication signal is supplied, for example, to a controller or the like to effect the desired equipment unit protection switching action. As indicated above the equipment unit removal indication signal, is generated when latch lever arm 103 and, hence, latch rib 116 is initially moved a sufficient distance to enable the light to pass from emitter 106 to detector 107, in accordance with an aspect of the invention. As described below, the controller is responsive to the equipment unit removal indication signal to effect an appropriate protection switching algorithm for switching signals being transmitted from the requesting active, i.e., in-service, equipment unit to its associated standby equipment unit, in accordance with the invention. FIG. 4 shows, in simplified block form, an arrangement employing an embodiment of the invention. Shown are controller 401, active equipment units 402-A, 403-A and 404-A and corresponding standby equipment units 402-S, 403-S and 404-S. It is desirable to switch from an active, i.e., in-service, equipment unit to a standby equipment unit prior to removal of the active equipment unit and, by employing the invention, prior to any movement of the active equipment unit in an equipment frame. This is realized in the system of FIG. 4, in accordance with the invention, by each of equipment units 402-A, 403-A, 404-A, 402-S, 403-S and 404-S, including a latch and an associated light-responsive switch arrangement. Upon any movement of the latch toward an attempted removal of the equipment unit the associated switch arrangement advantageously generates an equipment unit removal indication signal prior to any movement of the equipment unit from a corresponding equipment frame and, more particularly, from a connector therein. The equipment unit removal indication signal is supplied from each of equipment units 402-A, 403-A, 404-A, 402-S, 403-S and 404-S, via circuit paths 405 through 410, respectively, as appropriate to controller 401. In turn, controller 401 is connected via bus 411 to each of equipment units 402-A, 403-A, 404-A, 402-S, 403-S and 404-S. Bus 411 supplies signals to and receives signals from each of the equipment units indicating whether a switching is to be made and/or whether it is an active or a standby equipment unit. It should be noted that upon effecting equipment unit protection switching the appropriate standby unit is the "active" unit and the previously active unit is in a standby or out-of-service mode. Thus, upon receiving an equipment unit removal indication signal from an active equipment unit controller 401 initiates an equipment protection switching algorithm which causes switching of the transmission of signals from the requesting in-service equipment unit to its corresponding standby equipment unit For example, if active equipment unit 403-A supplies an equipment unit removal indication signal to controller 401, controller 401 would cause the signals being supplied to equipment unit 402-A and to equipment unit 404-A to be selected from equipment unit 403-S rather than equipment unit 403-A. The signals from equipment unit 403-A would appropriately be inhibited at equipment unit 402-A and equipment unit 404-A. FIG. 5 is a flow chart showing steps in the operation of the invention. Specifically, step 500 indicates a need to remove an equipment unit. This removal is initiated by lifting the latch as indicated in step 501. Step 502 indicates that the associated light responsive switch arrangement, in this example including light emitter 106 and light detector 107, generates the equipment unit removal indication signal. In response to reception of the equipment unit removal indication signal, the controller anticipates the removal of the corresponding equipment unit and forces equipment unit protection switching to the appropriate standby equipment unit, as indicated in step 503. Step 504 indicates that the protection switching has been completed, usually in a relatively short interval. In this example, an equipment protection switching is typically effected in about five (5) msec. Step 505 indicates that the requesting equipment unit is now inactive. Step 506 indicates that the requesting equipment unit now first begins to move in the equipment frame and, hence, in any corresponding connector that it is inserted in. Step 507 indicates complete removal of the requesting equipment unit from the equipment frame. Step 508 then indicates that the physical removal of the equipment was not service-affecting and there were no transmission errors during the removal FIG. 6 depicts a timing diagram illustrating the approximate time intervals at which the steps of FIG. 5 occur. Specifically, the initial movement of the latch occurs at time zero (0). The equipment unit removal indication signal is supplied to the controller at about the 50 msec point and an equipment unit protection switching is typically effected at about the 55 msec point. The previously in-service equipment unit requesting the switching is now also inactive. From this point on (time after about 55 msec), the controller considers that the requesting equipment unit has been removed and ignores any associated fault indications caused by the physical removal. Normally, the now inactive service unit begins to move in its connector at about the 150 msec point. The requesting equipment unit is electrically disengaged from its connector at about the 400 msec point. Thus, in this manner equipment protection switching is made from a in-service active unit to an out-of-service standby unit without transmission errors possibly caused by movement of the in-service equipment unit is its connector. Again, this is realized by advantageously employing the invention to effect equipment unit protection switching prior to any movement of the requesting equipment unit in the equipment frame and, hence, in its corresponding connector. The above described arrangements are, of course, merely illustrative of the application of the principles of the invention. Although a central controller is employed in the disclosed embodiment, it will be apparent that individual controllers in the equipment units could be equally employed. Moreover, it will be apparent that other positions of light sensor arrangements may be employed. For example, an integral light emitter-detector arrangement could be used in which light from the emitter is normally reflected off a surface either on the latch assembly or the circuit board and supplied to the detector. Then, an equipment unit removal indication signal would be generated by movement of the latch assembly causing the light from the emitter not to be supplied to the detector. It will also be apparent that the switch arrangements could be placed at other locations on the circuit board or equipment frame to realize the generation of the desired equipment unit removal indication signal. Again, it is important to note in this additional example, the generation of the equipment unit removal indication signal must occur at an appropriate instant after movement of the latch assembly, but prior to any movement of the equipment unit in the equipment frame, in accordance with an aspect of the invention.

Claims: Apparatus for use in effecting equipment unit (402A, 403A or 404A) protection switching from an equipment unit (100) being removed from an equipment frame in which it is inserted to a standby equipment unit (402S, 403S or 404S), the apparatus including an equipment unit (100), said equipment unit (100) including a circuit board (101) inserted in a connector in the equipment frame and a latch (103) pivotally mounted on said circuit board (101) at a pivot point (108) for securing the equipment unit in the equipment frame, the apparatus further being CHARACTERIZED BY, said latch (103) having a first lever arm (111) and a second lever arm (112), the first lever arm (111) extending from the pivot point (108) in a first direction and the second lever arm (112) extending from the pivot point in a second direction, the first lever arm (111) being used for application of a first force for causing rotational movement of the latch about the pivot point (108), the second lever arm (112) having a cam out surface (115) for applying a second force toward removal of the circuit board (101) from the connector in the equipment frame when the circuit board (101) is fully inserted in the connector and when the first force is applied to the first lever arm (111) in a direction toward removing the circuit board from the connector, the cam out surface (115) being arranged such as to allow initial movement of the first lever arm (111) from a closed position prior to applying a second force toward removing the circuit board from the equipment frame so that the first lever arm (111) of the latch (103) is allowed to move freely prior to the cam out surface applying the second force (on 110) toward removing the circuit board (101) from the connector in the equipment frame, a light responsive switch (106, 107) associated with said latch (103) and being responsive to said initial movement of said latch (103) for generating an equipment unit removal indication signal for initiating the equipment unit protection switching prior to any movement of said circuit board (101) in its connector, and a controller (401) responsive to said equipment unit removal indication signal for effecting the protection switching. Apparatus as defined in claim I wherein said latch (103) is positioned to disable said light responsive switch (106, 107) from generating said equipment unit removal indication signal when the equipment unit is fully inserted in the equipment frame and said latch (103) is in a closed position. Apparatus as defined in claim 2 wherein said light responsive switch includes a light emitter (106) and a light detector (107). Apparatus as defined in claim 3 wherein said light emitter (106) comprises an infrared light emitter and said light detector (107) comprises an infrared light detector. Apparatus as defined in claim 3 wherein said light responsive switch further includes an amplifier (302) in circuit with said light detector (107) for supplying said equipment unit removal indication signal as an output, said amplifier having a transfer function employing hysteresis. Apparatus as defined in claim 2 wherein said first lever arm (111) includes a protruding member (116) which inhibits generation of said removal indication signal the when the latch (103) is in the closed position. Apparatus as defined in claim 6 wherein said light responsive switch includes a light emitter (106) and a light detector (107). Apparatus as defined in claim 7 wherein said light responsive switch (106, 107) further includes an amplifier (302) in circuit with said light detector (107) for supplying said equipment unit removal indication signal as an output, said amplifier having a transfer function including hysteresis. Apparatus as defined in claim 7 wherein said light emitter (106) comprises an infrared light emitter and said light detector (107) comprises an infrared light detector. Apparatus as defined in claim 7 wherein said light emitter (106) and said light detector (107) are mounted on the circuit board (101) in prescribed spatial alignment relationship to each other and to said first lever arm (111) of said latch (103) and wherein said protruding member (116) of said first lever arm (111) of said latch (103) is positioned to inhibit light being emitted from said light emitter (106) from reaching said light detector (107) when the equipment unit is fully inserted in the equipment frame and the latch (103) is in a closed position and such that said light detector (107) is able to detect light from said light emitter (106) upon the first lever arm (111) of said latch moving a prescribed distance upon initiation of removal of the equipment unit (100) from the equipment frame, but prior to any movement of the equipment unit (100) in the equipment frame. Apparatus as defined in claim 9 wherein said protruding member (116) of said first lever arm (111) comprises a protruding element (116) having prescribed dimensions and being such as to be positioned between said light emitter (106) and said light detector (107) when said latch (103) is in a closed position to inhibit light emitted by said light emitter (106) from reaching said light detector (107) when the equipment unit (100) is fully inserted in the equipment frame and the latch (103) is in a closed position and such that said light detector (107) is enabled to detect light from said light emitter (106) upon the protruding element (116) of the first lever arm (111) of said latch (103) moving a prescribed distance upon initiation of removal of the equipment unit (100) from the equipment frame, but prior to any movement of the equipment unit in the equipment frame.

Inventors: BROCKWAY ROBERT C, DIETZ PHILIP S, NGUYEN LO C, BROCKWAY, ROBERT C., DIETZ, PHILIP S., NGUYEN, LO C.
Applicants: AT & T CORP, AT&T CORP.
Application year: 1992
Main classification: H05K7
IPC codes: H05K7, H01H35