Patent GB-714835-A (GB)
Title: Improvements in or relating to conveyor systems
IPC: B65G23/36
Filed: 1951-02-08
Abstract: 714,835. Electric motor control systems. ROBINS, S. D. Feb. 8, 1951 [Feb. 11, 1950], No. 3093/51. Class 38(3) [Also in Groups XXX and XXXV]  In a conveyer system consisting of an endless belt extending between head and tail pulleys and having more than one drive unit for driving the belt, at least one of which drive units is disposed at a point in the working run between the head and tail pulleys, at least one of the drive means is controlled by belt tension feeler means which are adapted to respond to variation of belt tension independently of the variation of the weight of material supported by the belt, whereby the distribution of driving force along the belt is such that the working run of the belt is subjected to the same means tension when running empty as when under normal load. As shown, Fig. 16, a conveyer belt 60 is driven by several drive units 65-69, each consisting of an electric motor driven endless driving member (see Group XXX), and tension controlling means is provided comprising sag-responsive units 81-85 on the downstream side of each of the drive units, for controlling through switches opened by under-tension the motors of these drive units, and units 80, 112 on the downstream side of the head and tail pulleys for similarly controlling motors driving the latter. Each of these units except unit 112 also controls through switches opened by over-tension the motor of the following unit as shown so that a substantially uniform tension is maintained by actuation of the change-over switches 98-109. Switch 110 associated with the unit 112 is actuated only when a blockage occurs or when one of the motors is stopped, e.g. by opening one of the switches 118-124, whereby tension weight 64 rises abnormally and this stops all the motors in sequence. The motors are restarted in sequence upon reclosing the opened switch. The weight 64, unit 112 and switch 110 may be replaced if desired by a drive unit and switches similar to the remaining units and switches. Instead of opening the under-tension and overtension switches. it may be preferred to close these whereby instead of stopping the motors, the motors are caused to operate at a slower or faster speed by actuating retarder or accelerator motors 135, Fig. 17, each of which acts through a worm gear 133, 134 to rotate the housing of the associated drive motor 130 in reverse, or the same, direction with respect to that of its driving shaft 131 whereby to reduce or increase, the speed of the latter. In order that the sag-responsive devices may be responsive to variation of belt tension independently of the variation of the weight of material supported by the conveyer belt, each sag-responsive device, shown diagrammatically in Figs. 16 and 17, consists, as shown in Fig. 18, of a feeler arm 157 pivoted to a fixed support at 158 and provided with a roller 159 engaging the underside of the belt 145 between adjacent idler rollers 146, 147 which are themselves movably carried by parallel links 150, 151, lever 157 being connected centrally with the idler 146 by a link 155. The idlers 146, 147 are resiliently pressed upwardly against the underside of the belt, by springs 152, 153 while smaller springs 160, 161 act on the link 155 to cause roller 159 on the lever 157 to be pressed upwardly against the underside of the belt, the arrangement being such that with a uniform loading of the belt the effect on the link 155 of a change in belt loading is to move it down or up while maintaining its horizontal disposition. Thus two plungers 168, 169 operating in chambers 166, 167 interconnected by an orifice 165 are unaffected by change in belt loading whereas change in belt tension independent of belt loading causes link 155 and hence a mercury switch 162 carried thereby to be tilted, the latter movement being damped by the action of the orifice 165 restricting passage of fluid between the chambers 166, 167. In a modified arrangement of the drive units and sag-responsive units, Fig. 20 (not shown), the take-up loop incorporating the weight 64. Fig. 16, is re-located so as to provide a drive unit between it and the head pulley which now has a feeler mechanism on its downstream side. The drive unit interposed between the take-up loop and the head pulley is driven at slightly less than synchronous speed so that the function of controlling the belt is thrown on the undertension switches except when the belt is stopped at some point in the system e.g. in an emergency. Other drive units in the system can similarly be used as the " standardizer by driving the chosen unit at the just under synchronous speed.