Control system for a decanter centrifuge

Abstract

A torque sensing device capable of measuring the force exerted by a torque arm on a lever is positioned between the torque arm and the lever. The torque arm is connected to the pinion of a planetary gearbox for rotating the bowl and screw conveyer of a decanter centrifuge at different speeds. The torque sensing device measures the torque between the pinion gear and the planetary gearbox. The sensor can be connected to a controller which can reduce the flow of the liquid/solid mixture to the decanter centrifuge thereby/reducing the torque and avoiding substantial damage to the planetary gearbox.

Claims

1. A method of controlling the liquid/solid mixture flow rate to a decanter centrifuge, the decanter centrifuge including a planetary gearbox having a central pinion gear, a torque arm fixed to the pinion gear, and a pivoted lever arm connected at one end to an over center spring mechanism and engaging the torque arm at a second portion comprising: positioning a torque sensor between the torque arms fixed to the pinion gear and the second portion of the lever arm; measuring the torque force applied to the lever arm; and varying the flow rate of the liquid solid mixture to the decanter centrifuge in response to the force applied to the lever arm.

2. The method of claim 1 including varying the flow rate of the liquid/solid mixture by varying the speed of a variable speed pump which pumps the liquid/solid mixture to the decanter centrifuge.

3. The method of claim 1 including varying the flow rate of the liquid/solid mixture by controlling an adjustable valve.

4. The method of claim 1 including the terminating the flow of the liquid/solid mixture to the decanter centrifuge, at a predetermined maximum torque load.

5. The method of claim 1 including the step of establishing a range of acceptable torque force levels applied to the lever arm and varying the flow rate of the solid/liquid mixture so that the torque force level is maintained within the predetermined range.

6. The method of claim 1 further comprising the step of providing a remote monitor including a display device for displaying the measured torque force and varying the flow rate of the liquid/solid mixture in response to force measurements displayed on the monitor.

7. The method of claim 1 wherein the pivoted lever arm includes a circular ring member and the torque sensor includes a reduced diameter stem portion which is positioned within the circular ring member.

8. The method of claim 7 wherein the torque sensor also includes an enlarged portion which presses against an end portion of the torque arm.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

(1) FIG. 1 is a perspective view of a conventional decanter centrifuge with a torque sensor.

(2) FIG. 2 is a side elevation view of the bowl and a screw conveyor positioned within the housing shown in FIG. 1.

(3) FIG. 3 is a schematic view of a planetary gear box.

(4) FIG. 4 is a perspective view of a torque sensor according to an embodiment of the invention.

(5) FIG. 5 is a perspective view of a torque sensor according to an embodiment of the invention connected to the centrifuge torque sensing mechanism.

(6) FIG. 6 is a diagram of a flow control system for the liquid to be treated.

DETAILED DESCRIPTION OF THE INVENTION

(7) As shown in FIG. 1, a typical prior art decanter centrifuge 10 includes a base support 11 and cover 12 pivoted to the base support. A planetary gearbox housing 13 houses a planetary gear system for example as shown in FIG. 3. A torque sensing assembly 17 is connected to the base and includes a spring loaded over center assembly 81 as discussed below and a lever arm 15 pivotally connected to the over center assembly 81 and pivoted about a support pin 55 shown in FIG. 5.

(8) Lever arm 15 includes a rest pad 18 which is adapted to be engaged by a torque sensor arm 14 which is attached to the fixed center pinion of the planetary gear system. As discussed above, when the torque on the fixed center pinion of the drive planetary gearing exceeds a predetermined maximum, the distal portion of the torque sensor arm 14 will exert a force on lever arm 15 sufficient to cause the over center mechanism to trip. At this point lever arm 15 will rotate downwardly as seen in FIG. 5 which allows the torque sensor arm 14 and pinion gear to rotate freely with the ring gear, thus reducing the differential speed to zero and thus eliminating the load on the planetary gearbox.

(9) FIG. 2 illustrates the internal parts and function of a typical decanter centrifuge. The liquid solid mixture is fed through inlet 22 of a rotating screw conveyor 23 while supported by suitable bearings. A rotating bowl 21 is also rotatably supported by suitable bearings. Gearbox 13 drives screw conveyor 23 and bowl 21 of the centrifuge as discussed above. An inlet distributor 31 allows the liquid to be treated to enter the space between screw conveyor 26 and bowl 21. Solids are directed toward the inner surface 24 of bowl 21 and are moved toward solids outlet 27 while the liquid exits the centrifuge via outlet 28.

(10) FIG. 3 shows a typical planetary gear system including ring gear 41, planet gears 42 and a sun or pinion gear 43.

(11) FIG. 4 illustrates a torque sensor 50 according to an embodiment of the invention. The sensor includes a first cylindrical stem portion 61 and a cylindrical head portion 52 having a diameter larger than that of stem portion 61. Embedded within head portion 52 is a flexsensor 53. A suitable flexsensor is available from Teksan, Inc. and is known as a Flexiforce sensor which is a thin printed circuit that senses contact force. Sensor 50 includes a pair of electrical leads 54 and 55 which are connectable to a wire pigtail 82. Torque sensor 50 can be formed by encasing the flexsensor in a housing of a polyurethane elastomer, for example, by molding.

(12) FIG. 5 illustrates the manner in which the torque sensor 50 can be connected to a conventional torque sensor assembly used for decanter centrifuges.

(13) The torque sensor assembly includes a torque sensor arm 51 which is fixedly attached to the pinion gear of the planetary gearbox. Lever arm 56 has one end pivotably attached to over center mechanism 54 and a central portion 70 that is pivotably supported by a pin 85. Pin 85 is attached to a support block 83 which is secured to base 11. The other end 58 lever arm 56 includes a circular ring member 57 which is adapted to receive stem portion 61 of the torque sensor 50. With torque sensor 50 positioned at the end portion 57 of lever arm 56, the lower portion 63 of torque arm 51 will press against head portion 52 of the torque sensor. As the torque on the pinion gear increases, the force on the torque sensor will increase and can be monitored by a suitable monitor connected to the force sensor via wire pigtail 51.

(14) By suitable observation and experimentation, it is possible to determine the safe operating ranges of torque on the pinion gear. As the torque approaches this range, rather than having the torque arm trip, which will cause the centrifuge to plug and require downtime to unplug the centrifuge, an operator can adjust the flow rate of the liquid/solids mixture delivered to the centrifuge. This could be done manually by adjusting valves or the speed of the liquid/solid supply pump.

(15) Alternatively, the signal from the torque sensor could be used to automatically control the flow rate to the centrifuge by automatically adjusting a valve in a bypass loop or the speed of the supply pump.

(16) FIG. 6 illustrates such a system in which an inlet line 71 is connected to a variable speed pump 72 which is connected to a valve 73 having an outlet line 74 and a return line 75.

(17) Outlet conduit 74 is connected to decanter centrifuge 10. The amount of liquid delivered to centrifuge 10 can be varied by a signal from sensor 50 to a controller 74 that varies either the speed of the pump 72 or controls the amount of liquid recirculated through valve 73 via conduit 75 as is known in the art. If the torque falls below the safe operating range, the controller can increase the flow rate by increasing the speed of the pump or reducing the amount of liquid recirculated via the valve.

(18) The torque sensor 50 can be designed to replace an existing torque pad on a machine already in the field or it can be installed in a new machine prior to use.

(19) Also the method of controlling the flow rate does not require the use of a lever arm that is connected at one end to a center trip mechanism. The torque sensor could be placed between the torque arm connected to the pinion and a resistance member without the trip mechanism so that the force applied to the resistance member is measured and used to vary the flow rate of the liquid to the decanter centrifuge. The resistance member could be fixed to base 11.

(20) Although the present invention has been described with respect to specific details, it is not intended that such details should be regarded as limitations on the scope of the invention, except to the extent that they are included in the accompanying claims.