Retractable stop
BACKGROUND OF THE INVENTION 
     Selectively operable stop mechanisms for blocking and releasing articles conveyed on gravity or powered roller conveyors are common in the art and a wide variety of mechanisms have been employed for actuating such stops to blocking and retracted positions. The various criteria for completely dependable action under all possible conditions render the provision of a simple mechanism meeting all requirements a more difficult problem than apparent from initial consideration. In view of the impact and cumulative loads that may build up against the stop, there is a need for a blocking action of the stop which can withstand considerable force without yielding; since it is frequently necessary for the stop to be retracted under a highly loaded condition it is necessary to accommodate or eliminate friction in the linkage components which provide the holding resistance when it is desired to release the stop; at the same time it is desirable that the stop may be released without drag on the article which might otherwise cause wear or damage; it is desirable that any mechanism for returning the stop from retracted to blocking position be rendered automatically inoperative during any overpassing of an article while being capable of immediately moving to a stop position as soon as the trailing edge of the article has passed so as to be capable of intercepting the next article in case it is following in close proximity to that passing over the stop; it is desirable to accomplish these objectives with a simple solenoid actuation preferably de-energized when the stop is in operative position; it is desirable to stop and engage the leading edge of an article in a manner which will avoid overriding from the impact of either a single load or other loads behind it. In the end it is, of course, desirable that all of these objectives be met with a construction which is as simple and inexpensive as possible. 
     SUMMARY OF THE INVENTION 
     In the present case these objectives are met by a construction in which a cross bar extending transversely of the roller conveyor between adjacent rollers is mounted in pivotal bearings at either end with a stop member of suitable width rigidly mounted at the center having its stop engaging surface located above and ahead of the pivotal axis so that upon release the engaging surface may swing forward and downward under actuation by the leading edge of the article and be retained in a retracted position by engagement with the bottom surface of the article as it overpasses so that the stop will have a minimum distance to move in reestablishing a blocking position. A positive latch is provided which will resist any loading on the stop within the strength of the components employed which can be readily disengaged by solenoid actuation to effect a release of the stop through movement of an anti-friction roller. A spring return of the latch is inhibited by engagement of such roller with a bevelled surface angled to provide a restoring component for swinging the stop back into its operative position as soon as any article load passes off, such angle being insufficient however to cause any restoring force to raise an article having its lower surface engaging the stop in retracted position. 
    
    
     IN THE DRAWINGS: 
     FIG. 1 is a fragmentary plan view of a roller conveyor with the retractable stop of the present invention installed between adjacent rollers; 
     FIG. 2 is a sectional side elevation taken along the line 2--2 of FIG. 1; 
     FIG. 3 is a sectional side elevation taken along the line 3--3 of FIG. 1. 
    
    
     DESCRIPTION: 
     With reference to FIG. 1 a roller conveyor having rollers 10a and 10b mounted between side rails 11a, 11b driven by belts 12a, 12b for conveying articles, such as mail trays in a post office installation, along conveyor path 13 has interposed between adjacent rollers a stop assembly 14 comprising an angle stop arm 15 with a resilient stop pad 16 attached to the leading upwardly extending edge thereof. The stop arm is rigidly attached as by welding 17 (FIG. 3) to a cross shaft 18 mounted in pivot bearings 19a and 19b held respectively by a bracket 20 to side rail 11a and to housing 21 mounted on brackets 22a and 22b to side rail 11b. An extension 23 of the shaft 18 is welded at 24 to a latch plate 25 having a latch recess 26, a lower extension 27 and an upper angular extension 28 adapted for engagement by an anti-friction roller 29 mounted between a pair of side arms 30 pivotally connected at 31 to a base 32 attached to the sidewall of the housing by bolts 33. At the center of the arms 30 a link 34 is pivotally connected at 35 and the other end 36 connected to the plunger 37 of a solenoid 38 mounted with angle brackets 39 to an end wall of the housing 20. A tension return spring 40 is adjustably anchored at 41 to the other end wall of the housing connected by pin 42 to the side arms 30. 
     In operation, energizing the solenoid 38 actuates the link 34 to pivot the arms 30 to the dotted line position 30a releasing the anti-friction roller 29 from the latch recess 26 whereupon engagement with the upper end 16 of the stop arm 15 by an article, such as a mail tray 44 travelling on the surface of roller 10a, causes the stop arm to pivot around the axis of the cross shaft 18 to a retracted position where the tray will overpass the stop and move along over the roller 10b and successive rollers. The overpassing position 45 of the stop arm 15 as shown in FIG. 3 corresponds to the dotted line position 46 of the latch lever 25 as shown in FIG. 2 in which position the angle extension 28 will serve to block the return of the roller 29 to the latched recess 26 while providing an upward component of force under the tension of spring 40 when the solenoid 38 is de-energized sufficient to rotate the latch lever 25 in a clockwise direction together with the stop arm 15 as soon as the trailing edge 47 of any overpassing tray moves off the surface of the stop extension 16 whereupon the latch is reengaged before a succeeding mail tray 48 reaches the stop. 
     It will be seen in FIG. 3 that the stop arm extension 16 extends substantially above the lower surface of the tray and is angled slightly backward to assure engagement at a high enough point to prevent overriding upon impact and it will be further apparent from the geometry shown in FIG. 3 that upon initial release of the latch any retaining load on the upper end extension 16 of the stop arm will cause such extension to swing forwardly and downwardly to relieve the pressure without wear or damaging sliding movement on the forward end of the tray. 
     Thus, a simple, effective and dependable stop construction has been provided which meets all of the criteria objectives with minimal opportunity for malfunction.