Patent GB-944100-A (GB)
Title: Control of endless conveyor belts
Inventor: FIRTH DONALD
IPC: B65G23/44
Filed: 1960-07-29
Abstract: 944,100. Fluid-pressure servomotor control systems. COUNCIL FOR SCIENTIFIC & INDUSTRIAL RESEARCH. Oct. 30,1961 [July 29, 1960], No. 26574/60. Heading G3P. [Also in Division B8] A hydraulic system for controlling the tension in a conveyer belt 11 is controlled by the slip of the belt on a driving roller 17. A sun wheel 15 of a differential gear is coupled by gearing 14 to a roller 12 the surface of which has a high coefficient of friction for the material of the belt 11. The other sun wheel 16 is coupled to the belt driving roller 17, and the planetary system 18 of the differential gear is coupled by a slipping clutch to a crank arm 21 which moves between stops 22 and which is linked to the sliding member 23 of a slip control valve 24. As long as the slip remains at the permitted value the arm 21 floats between the stops 22 but when the slip becomes excessive or falls below an appropriate value, the arm abuts one stop or the other and operates the valve 24. The clutch 19 enables the arm to rest against a stop 22 while the sun wheels 15, 16 rotate at different speeds, as long as the slip is outside permissible limits. The valve 24 controls a supply of fluid under pressure to a double acting hydraulic motor 25 of which a piston 27 is connected to a belt tension adjusting roller 29. To measure the tension, a loop of the belt also passes over a roller 31 on a shaft 32 one end of which is journalled in a bearing block 33 capable of slight displacement in a direction normal to the shaft in a support 34 of U-form. Pressure of liquid in a recess 35 connected by a metering orifice 37 with a passage 36 varies considerably with small changes in the position of the block 33. A further passage 38 leads from the recess to a pressure responsive valve 39, and an annular drain 41 is connected by a passage 42 to a reservoir 43. The opening of the valve 39 admits fluid under pressure into a space 44 within the slip control valve 24 to move an intermediate member 45 against the bias of a spring 46. The intermediate member incorporates ports 47, 58, 60 which move out of alignment with passages 48, 59, 61 when the member is moved by the opening of the pressure responsive valve 39. An over-riding effect on the control of pressure to the motor 25 controlling the position of the tensioning roller 29 is thus obtained. If the intermediate member 45 remains in its normal position an increase in belt slip will cause the sliding member 23 to be moved to the right, fluid will flow via the port 47 and a pipe 64 to the motor 25 and tension in the belt is increased. Belt tension is reduced if the slip falls below the normal value. If the tension in the belt rises to such a degree as to cause the valve 39 to open, the intermediate member 45 moves to the right and fluid passes via the port 60 to the motor 25 to reduce the belt tension. Opening the valve 39 also opens a switch 49 and the driving motor is switched off. The valve 39 then closes and the member 45 returns to its normal position, fluid in the space 44 being allowed to leak away through an orifice 68. A warning signal may be interconnected with the valve 39 or the switch 49 and the switching arrangement is such that when the valve returns to normal position the drive is not automatically restored and manual intervention is necessary in order to restart the driving roller 17.