Patent ID: 6293388
Filing Date: 2001-09-25
Classification: B65G

Abstract:
An overhead conveyor system, comprising:a plurality of trolleys for suspending loads;an overhead powered conveyor for suspending said trolleys and transporting said trolleys serially in a conveying direction along at least one powered conveying path;said overhead powered conveyor having at least one drive having a rotational power output, cylindrical drive shafts mounted for rotation about respective shaft axes parallel to respective portions of said conveying path, and a power connection between said drive power output and said drive shafts for driving said drive shafts about said shaft axes, respectively;said trolleys each having a skewed driven wheel mounted for rotation about a driven wheel axis nonparallel and non-perpendicular to a corresponding one of said shaft axes, and said driven rollers engaging a top portion of said drive shafts with sufficient traction so as to form a helical loci of engagement about the periphery of said drive shafts during rotation of said drive shafts about said shaft axis to power said trolleys along the conveying path in the direction of the powered conveying path dependent upon a direction of rotation of said drive shafts and the skew of said rollers;said trolleys suspending the loads vertically below said drive shafts;an overhead gravity line conveyor having a gravity rail for suspending said trolleys and transporting said trolleys serially along at least one gravity line conveying path that is operatively adjacent a powered conveying path to form together a mixed powered and gravity rail conveyor;each of said trolleys having a gravity wheel to engage with said gravity rail to support respective ones of said trolleys on said gravity line conveyor with said driven rollers disengaged from said drive shaft;said overhead gravity line conveyor having a step feeder mounted adjacent said gravity rail, said step feeder having a pivot arm that is pivotally mounted about a pivot axis at right angles to the conveying path for pivotal movement between a gravity wheel receiving and holding position that engages and thereby prevents a wheel of a lead trolley on said gravity rail from continuing in the conveying direction along the conveying path, and a release position that is free of said lead trolley in the conveying direction to thereby permit said lead trolley to continue in the conveying direction along the conveying path;said pivot arm having an escapement dog above and vertically aligned with said rail, said dog having a downstream leg that engages with the downstream portion of said wheel of said lead trolley in the receiving and holding position and is clear of the path of travel of said wheel of said lead trolley moving downstream in the release position of said pivot arm, and an upstream leg that engages with the downstream portion of said wheel of said following trolley in the release position and is clear of the path of travel of said wheel of said following trolley moving downstream to become said next lead trolley in the receiving and holding position of said pivot arm;said step feeder further having a release sensor mounted at a switch position in the path of said trolleys below said gravity rail and thus at a substantial radial distance from said axis of rotation of said wheel of both said lead trolley and said following trolley, which axis of rotation is also said axis of swinging of the respective one of said trolleys, thereby to normally sense a lead trolley on said gravity rail in the release position when said pivot arm is in the receiving and holding position, and in response thereto provide a release signal;said release sensor mounted position being such that it would abnormally sense said following trolley as it normally swings about its wheel axis of rotation due to pressure from further upstream trolleys engaging if there was no lead trolley in the release position to prevent such swinging and if said following trolley did not move upstream a sufficient distance when said pivot arm is pivoted from the receiving and holding position to the release position;said step feeder further having an actuator engaging said pivot arm to thereby, when actuated by an actuator signal that is dependent upon the release signal, pivot said pivot arm including said dog about the pivot axis from the receiving and holding position to the release position, to thereby release lead ones of said trolleys one at a time along the conveying path in dependence upon the actuator signal; andsaid escapement dog having a cam shaped retention abutment to engage and force back at least said sufficient distance in a direction counter to the conveying direction said following trolley while said pivot arm rotates from the receiving and holding position into the release position, and thereby prevent said following trolley from actuating said release sensor during the normal swinging while said gravity line is exposed to significant back pressure from subsequent trolleys.