973,640. Overhead conveyers. MECHANICAL HANDLING SYSTEMS Inc. Feb. 14, 1961, No. 5477/61. Heading B7L. A transfer control mechanism, Fig. 1, for a conveyer system in which load bearing trolleys T are transferred from a branch track 12 to a main track 13 at a transfer zone 15, comprises continuously driven conveyers movable along the respective tracks provided with propelling members to engage the trolleys, the conveyers being driven in synchronism, and a stop and release control device 16 to which the trolleys are driven by the branch track conveyer and means for controlling the operation of the device 16 to ensure an accurately timed transfer of the trolleys from a track 12 to the main track 13. Trolleys T moving along the track 12 are halted at the stop and release device 16 until released by operation of an empty space spotter device 14 on the main track 13, which senses when a main driving chain dog which is not pushing a trolley passes, so that the halted trolley on the track 12 is released and driven by the branch track transfer conveyer chain 70 on to the main track to be picked up by the vacant driving dog. If the driving dog passing the device 14 is already pushing a load trolley then the trolley on the track 12 will be held stationary by the device 16. The main track driving chain 61, Fig. 11, has dependent driving dogs 60 which engage with pivoted dogs 40 on the trolleys T. The transfer chain 17 is driven from the chain 61 by the provision of laterally projecting dogs 107, Fig. 9, on the transfer chain, so that the two chains are moved simultaneously and in timed relation. The transfer chain 17 also has vertically slidable driving dogs 112 with feet 113 which engage the dogs 40 of the trolleys T. The transfer chain is supported on a trackway formed of sections 23, 24, 25, 26, Fig. 1, and by an arcuate angle member 43 which is constrained to slide relative to fixed members 52, and 57 under the action of an adjustable spring 55 to control the tension of a transfer chain 17. Empty place spotter device, Figs. 1, 6, 6a.- This device is positioned adjacent the main track 13 and comprises an arm 67 pivoted at 66 to a fixed arm 64, which arm 67 carries pivotally mounted arms 71, 80. The arm 71 has a pin 73 which engages behind a fixed latch element 76, Fig. 6a, and also engages in a cam slot 74 in a lever 92 pivoted at 93, and having an end 94 adjacent the end of the arm 71 remote from the arm 67. A spring 72 serves to retain the pin 73 engaged with the latch 76. The arm 71 and end 94 of the lever 92 project into the path of the load trolleys and the pivot for the arm 80, which is of vertically disposed rod also carries on a fixed arm (not shown), which projects into the path of the driving dogs 60 of the main track driving chain. If a driving dog is pushing a trolley T along the main track 13 then the trolley will engage and move the arm 71 and the end 94 of the arm 92 to disengage the pin 73 from the latch 76 causing the arm 67 to move to the dotted line position shown in Fig. 6, thus removing the fixed arm on the pivot of the arm 80 out of the path of the driving dog 60. If, however, the driving dog is not pushing a trolley T then the arm 71 will not be moved, and the driving dog will cause the arm 80 to move to the dotted line position shown in Fig. 6, actuating a pull rod 90 through a bell-crank 88 which serves to release a halted trolley on the track 12. The end 95 of the lever 92 will also be engaged by trolley T on the track 13 and thus serves to reset the arm 71 with the pin 73 engaged by the latch 76. Trolley stop and release device, Figs. 9, 10.- This device 16, is situated on the branch track 12 and serves to stop the trolleys T on this track and release them in response to signals from the empty place spotter device as transmitted by the pull rod 90. The device 16 comprises a yoke 97, of inverted U-shape pivoted at its ends to fixed pivots 98, 99, Fig. 9. This yoke carries a cam 101 with a cam portion 103, Fig. 10, which is disposed in the path of rollers 114 which project from the top ends of the vertically slidable dogs 112. In the position shown in Fig. 10 the cam portion 103 raises the dogs 112 out of engagement with a trolley T stopped by the device 16, and by rocking the yoke about its pivots, the cam 101 is raised and the underside of the cam portion 103 will ensure that the dogs 112 engage with the trolley T. The rollers 114 are supported on a cam track 104 so that the dogs 112 are clear of the trolleys T, Fig. 2, along the reach 23 of the transfer chain supporting track. The track 104 terminates in a downwardly inclined portion 115 and a rail 118 is disposed above the track 12 at the position of the device 16 to ensure that the dogs 112 engage with the trolleys T. The cam portion 103 is fitted in a recess 121 of this rail so that at the device 16 the dogs 112 are either forced into engagement with or disengaged from the trolleys T. The yoke 97 also has an extension arm 123, Figs. 9, 10, which carries a roller 123<SP>1</SP> to engage with and stop the wheels 42 of a trolley T when in the position shown in Figs. 9, 10. A short swingable arm 125 is pivoted to the arm 123 and carries a shoe 126 which engages with a halted trolley wheel 42, Fig. 10. The pull rod 90 is connected to one arm of a bell-crank 132, the other arm 131 of which carries a pivoted hook member 129 held by a stop 135<SP>1</SP>. When the empty place spotter causes a pull on the rod 90, the hook member engages a projecting lug on the arm 125 and this raises the stop roller 123<SP>1</SP> and pivots the yoke 97 to raise the cam position 103 so that the halted trolley T will be picked up by a dog 112 and moved on to the main track 13 to be picked up by the vacant driving dog which actuated the empty place spotter device. The dogs 112 are arranged to precede the main conveyer driving dogs at the transfer point and rollers R at this point ensure interengagement of the two driving chains. If the hook member is moved by the pull rod 90 when there is no trolley T held by the stop roller 123<SP>1</SP> then the arm 125 will be in the dotted line position shown in Fig. 10 and the lug 128 will not be engaged by the hook member, and the stop roller 123<SP>1</SP> and the cam portion 103 will remain lowered. To prevent accidental premature movement of the trolley T when released towards the track 13, an additional arm 137 is formed integral with the yoke 97, and when the stop roller is raised a stop 137<SP>1</SP> on the arm 137 is moved into the path of the wheels 42 and will prevent movement of the trolley until the dog 112 engages it. Back stop device, Fig. 17.-This device shown as 18 in Fig. 1 comprises a pivoted arm 140<SP>1</SP> with an abutment 143 which engages with a vertically journalled guide roller 41 on a trolley T stopped by the device 16. Backward movement of the trolley is then prevented by a shoulder 144. The arm 140 carries a spring steel arm 148<SP>1</SP> which will stop a following trolley T when the abutment 143 is in engagement with the roller 41. Also when in this position the arm 140 is held by a spring-loaded rod 151 which latches at 153 on to the arm 140. As the trolley moves from a position shown it engages a tappet 157 pivoted to the rod 151 and releases the arm 140 which returns to the dotted line position shown in Fig. 17 under the action of a spring 146<SP>1</SP>. The latch rod 151 may be dispensed with in a simpler embodiment. Alternative empty place spotter device, Fig. 11.-This device is an alternative to the one shown in Figs. 1, 6, and comprises a yoke-like operating member 164 mounted on a horizontal pivot 168 and having at its lower end rollers 169 to engage with the main conveyer chain driving dog 60. The dogs 60 rock the member 64 from its full line to its dotted line position shown in Fig. 11. The member 64 also has a roller 172 which engages in a notch 177 of a drawbar 175 to move a pull-rod 176 connected through a bell-crank to the pull rod 90 which operates as before described. The device also comprises a bell-crank 180 pivoted at 181 having a roller 184 to engage with trolley wheels 42. The bell-crank 180 also carries a roller 186 which engages with the underside of the drawbar 175. The trolley wheels 42 move the bell-crank from its dotted line to its full line position as shown in Fig. 11 raising the notch 177 of the drawbar clear of the roller 172. Thus only if an unoccupied dog 160 passes the device will the pullrod 90 be actuated. A spring 188 connects the member 64 and the bell-crank 180 to hold both these members in position when they are ready to be engaged by a dog 60 and a wheel 42, respectively.