EP2109716A2

EP2109716A2 - Multi index with stroke selector pump

Info

Publication number: EP2109716A2
Application number: EP07866152A
Authority: EP
Inventors: Rudolph Teodor BÜHRMANN; Rudolph BÜHRMANN; Frank Neimann
Original assignee: African Explosives Ltd
Current assignee: AEL Mining Services Ltd
Priority date: 2007-02-02
Filing date: 2007-11-27
Publication date: 2009-10-21
Also published as: BRPI0721207A2; AR064928A1; WO2008095205A3; WO2008095205A2; MX2009007460A; AP2009004914A0; AP2749A; ZA200904404B; CL2008000298A1; PE20081739A1

Abstract

A system for controlling a piston pump to deliver a predetermined member of pumping strokes wherein, for each stroke, an index component is moved by a defined extent which is monitored by a sensor and, once the index component is at a control position the sensor stops operation of the piston.

Description

MULTI INDEX WITH STROKE SELECTOR PUMP

BACKGROUND OF THE INVENTION

[0001] This invention is concerned with controlling the operation of a reciprocating pump.

[0002] In many applications, for example in the pumping of basic constituents to make up an explosive gel, it is important to be able to deliver an accurately controlled volume of a fluid. This ensures that the constituents are mixed in the correct proportions and that a predetermined volume of the end product is available for use. The latter aspect allows for accurate dosing and reduces wastage of the pumped material.

[0003] It is an object of the invention to provide a method of controlling the operation of a pump, and a control system, which at least partly address the aforementioned requirements.

SUMMARY OF INVENTION

[0004] The invention provides, in the first instance, a method of controlling a reciprocating pump, which includes a piston which is activated by a pressurised fluid, to deliver a predetermined number of strokes, the method including the steps, for each stroke of the piston, of moving an index component by a defined extent and monitoring the movement of the index component relatively to a sensor and, upon detecting movement of the index component to a control position, using the sensor to interrupt the supply of pressurised fluid to the piston. [0005] The sensor may be of any appropriate type and may be electrically, pneumatically or hydraulically operable. In the preferred form of the invention the sensor includes a member which is physically engageable with a formation in or on the index component which is of complementary shape to the member, when the index component is at the control position.

[0006] The index component may be moved in any appropriate way and preferably is moved in a rotational sense through an angular step about a defined axis.

[0007] The invention provides, in the second instance, a system for controlling the operation of a pump which is driven by a piston which is actuated by a pressurised fluid, the system including an index component, an actuator mechanism which is responsive to movement of the piston and which, for each stroke of the piston, causes the index component to move a defined distance, and a sensor which is responsive to movement of the index component and which, upon detecting movement of the index component to a control position, interrupts the supply of pressurised fluid to the piston.

[0008] The pressurised fluid may be drawn from any suitable source and preferably is drawn from a source of compressed air.

[0009] The index component may be moved in any appropriate way and preferably is mounted for rotational movement through a defined angular step for each stroke of the piston.

[0010] The index component may be mounted for rotational movement about a central axis of the piston. [0011] The index component and the actuator mechanism are preferably located inside a bore of a cylinder in which the piston is reciprocally movable.

[0012] The control system may include first biasing means for biasing the index component away from fixed structure towards the piston.

[0013] The actuator mechanism may include a first actuator which causes the index component to move a portion of the defined distance and a second actuator which causes the index component to move through a remaining portion of the defined distance.

[0014] "Distance" as used herein is to be interpreted in a broad sense and includes a linear distance, an angular or rotational distance or any other appropriate form of movement.

[0015] The control system may include second biasing means which acts to bias the first actuator away from the second actuator.

[0016] The index component may include a first saw tooth formation and the first actuator may include a second saw tooth formation, of similar shape to the first saw tooth formation which is engageable with a sliding action with the first saw tooth formation thereby to cause the index component to move through the portion of the defined distance referred to.

[0017] The second actuator may include a third saw tooth formation, of similar shape to the first saw tooth formation, which is engageable with the first saw tooth formation thereby to cause movement of the index component through the remaining portion of the defined distance, in the manner referred to. [0018] According to a different aspect of the invention there is provided apparatus for adjusting the length of a stroke of a reciprocating piston which is activated by a pressurised fluid, the apparatus including an adjustment member, positioned inside a cylinder in which the piston is reciprocally movable, with at least two impact formations which are axially displaced, and a striker which is movable by the piston, the adjustment member being movable, in a controlled manner, to present at least one chosen impact formation to the striker, and a sensor, responsive to movement of the adjustment member to a stroke control position for reversing movement of the piston.

[0019] The adjustment member may be movable in a second direction which is opposite to the first direction.

[0020] The adjustment member may include a plurality of impact formations which are displaced from one another in an axial sense in stepwise fashion. The striker may include a similar set of formations.

[0021] The adjustment member may be mounted for rotatable movement, in a controlled manner, in order to present one or more of the impact formations to corresponding formations on the striker.

[0022] The sensor may be of any appropriate kind. For example the sensor may be electronically, pneumatically or hydraulically based. In a preferred form of the invention the sensor includes a member which is engageable with a complementary formation in an element of the apparatus, when the adjustment member reaches the stroke control position thereby to cause reverse movement of the piston. [0023] Preferably the apparatus is provided in combination with the control system referred to and the sensor is common to the apparatus and to the system. Further, it is preferred that the second actuator is integrally formed with the stroke adjustment member.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The invention is further described by way of example with reference to the accompanying drawings in which:

Figure 1 schematically illustrates various components used for controlling the stroke length of a reciprocating piston and the number of strokes in a cycle;

Figure 2 shows a first side of an index component used in the control system;

Figure 3 shows a second, reverse side of the index component in Figure 2;

Figure 4 illustrates a first actuator which is used in the control system;

Figure 5 shows a compound device which comprises a second actuator and a stroke adjustment member;

Figure 6 is a perspective view of a piston and apparatus for controlling the length of the stroke of the piston and the number of strokes per cycle, with elements of the pump in which the piston is incorporated which are not important to an understanding of the invention being omitted;

Figure 7 is a cross sectional side view of the arrangement shown in Figure 6; and

Figure 8 is a block diagram representation of steps in controlling the operation of the piston. DESCRIPTION OF PREFERRED EMBODIMENT

[0025] The invention is concerned with controlling the number of strokes in a given cycle of operation of a piston, and with varying the stroke volume. In the following example the piston is described as being operated by compressed air but this is exemplary only and is non-limiting. The piston, in turn, is used to drive a pump of any suitable kind.

[0026] Figure 8 illustrates in general terms a control sequence which is carried out in accordance with the method of the invention. Compressed air from a source 10 passes through a control valve 12 and is used to drive a piston 14 with a reciprocating action inside a cylinder. The movement of the piston causes corresponding movement of an actuator 16 which in turn causes movement of an index component 18 in a controlled manner. A sensor 20 is used to monitor movement of the index component and when the index component reaches a control position the sensor acts on the control valve in a first mode and the valve then interrupts the flow of air to the piston 14.

[0027] It is possible to control the index component (step 22) in order to vary the number of strokes by cycle. As is explained hereinafter this is readily done by replacing the index component with another index component which will cause the piston to operate through a different number of strokes per cycle.

[0028] The piston also causes movement of a stroke adjustment member 24 which is linked to the actuator. The sensor 20 can operate in two modes. In the first mode, as has been referred to, the control valve is switched to interrupt the supply of air to the piston. In the second mode, which occurs at the end of each piston stroke in a particular direction, but excluding the stroke which comes at the end of a defined stroke cycle, the sensor operates on the control valve to cause the piston to be moved in the opposite direction.

[0029] The stroke adjustment member 24 can be set to a selected position by means of a control 26.

[0030] The control valve may be of any suitable kind known in the art. It is preferred to make use of a control system of the kind described in the applicant's co-pending application entitled "Pumping Arrangement" (South African patent application No. 2006/09692 filed 21 November 2006, the content of which is hereby incorporated into this specification) but this is not essential. The expression "control valve" is used in a general sense to designate a control function exercised on the supply of compressed air to the piston and, in practice, the control valve may be a compound system which includes a plurality of components which are interconnected to operate in a defined manner.

[0031] Figures 2 and 3 illustrate first and second sides 30 and 32 respectively of the index component 18. The first side 30 is formed with one recess 34. The number of recesses can however be varied and, in so doing, the number of piston strokes per pumping cycle can be varied accordingly. This aspect is referred to hereinafter.

[0032] The index component is of circular shape and has a central passage 36 with a small inwardly projecting rim 38 to form a surface 37 on which a biasing means such as a spring can act.

[0033] The second side 32 of the index component is formed with a first set of saw tooth formations 40 which are circumferentially positioned around the component. [0034] Figure 4 illustrates a first actuator 42 which forms part of the actuator mechanism 16. The first actuator includes a tubular component 44 with an end disc 46 in which is formed an opening 48 which is offset relatively to a centre of the disc. Formations 50 which project from the disc are used to align the disk to a housing (not shown).

[0035] A base of the tubular component is flanked by a second set of saw tooth formations 52 which extend circumferentially around the tubular component.

[0036] Figure 5 depicts a compound device 53 which includes a second actuator 54 which also forms part of the actuator mechanism 16. The second actuator comprises a body 56 with a central opening 58. A shoulder 60 projects inwardly and is sized to slide on a surface 61 of the actuator 42 and to have limited movement which is restricted in one direction by a retaining shoulder 61 A on the actuator 42. A third set of saw tooth formations 62 are positioned in a circular array on the shoulder. These formations are surrounded by a rim 64 and gear teeth 66 project radially from the rim.

[0037] The device 53 also includes a stroke adjustment member 68. The member 68 has four sections 68A, 68B₁ 68C and 68D respectively. These sections are identical. Each section projects in an axial sense from the rim 64 and is formed with three impact formations 70, 72 and 74 which are arranged in a step fashion and thus project by varying distances from the rim 64.

[0038] Figure 6 illustrates an arrangement of part of a pump which has a control system based on the components shown in Figures 2 to 5. Only those parts of the pump which are necessary for an understanding of the present invention are described herein. [0039] The pump includes a cylinder 76 with an internal bore 78 in which the piston 14 is mounted for reciprocating movement. The piston has structure 80 on a right side for actuating a pumping mechanism, not shown. This pumping mechanism may be of any appropriate form known in the art.

[0040] A striker 82 is mounted on a left side of the piston. The striker includes four identical components designated 82A, 82B, 82C and 82D respectively. The component 82B, which is clearly shown in Figure 6, includes a body 84 with a plurality of stepped striker formations 86 which are axially displaced from the left side of the piston by varying distances.

[0041] An end wall 88 fixed to the cylinder 76 bounds the bore 78. An assembly 90 of the components shown in Figures 2 to 5 is attached to this wall. The makeup of the assembly is described hereinafter with reference to Figure 7. The second actuator 54 is outermost and the gear teeth 66 are engaged with corresponding teeth on a pinion 92 fixed to a shaft 94. The shaft and pinion include mounting springs and fittings 96 which are not described in detail herein. The shaft 94 can be locked in position by means of an appropriate key (not shown), and it can be rotated using an appropriate tool (not shown). Rotation of the shaft causes rotation of the second actuator 54. In this way the impact formations 70 to 74 can be moved into alignment with different sets of the striker formations 86. The striker 82 is not rotatably movable but is only movable linearly together with the piston.

[0042] A sensing pin 100 which projects from the end wall 88 corresponds to the sensor 20 shown in Figure 8. The sensing pin can move linearly relatively to the end wall i.e. in an axial sense inside the bore, to a limited extent and is normally biased outwardly by means of a spring, not shown. Movement of the sensing pin is used to coRtrol the control valve 12 which in turn supplies air to the bore 78, either on the left side of the piston or on the right side of the piston, to cause reciprocating movement.

[0043] The nature of the control valve is not important to an understanding of the present invention and any suitable valve can be used for this purpose. The valve 12, which may be a compound device, must be able, in response to movement of the sensing pin, in a first mode, to interrupt the flow of air to the bore and, in a second mode, to switch the supply of compressed air in the bore 78 from the left side of the piston to the right side and vice versa.

[0044] Figure 7 is a cross sectional side view of the arrangement shown in Figure 6. Again structural components of the pump which are not important for an understanding of the invention have been omitted.

[0045] The piston 14 is fixed to a piston rod 14A. A pilot valve control rod 102 extends through the opening 48 and the first actuator 42. The control rod is fixed to a structure in the end wall 88 and its right end is movable into the structure 80 on the right side of the piston to allow for reciprocating piston movement. The piston is prevented from rotating by suitable means (not shown). The formations 50 in the end disc 46 of the first actuator are engaged with complementary recesses (not shown) in the end wall to ensure that the first actuator is not rotatable.

[0046] The index component 18 is engaged with the first actuator with the tubular component 44 passing through the passage 36. The first side 30 of the index component faces the end wall 88. A spring 104 is positioned on the tubular component 44 and acts between the end wall and the rim 38 of the index component. [0047] The second actuator 54 is also mounted on the first actuator. The stroke adjustment member 68 directly opposes the striker 82. The guide rod 102 passes freely through the second actuator.

[0048] The saw tooth formations 40 oppose the saw tooth formations 52 on the first actuator and the saw tooth formations 62 on the second actuator. The formations 52 and 62 are relatively narrow while the formations 40 are comparatively broad. Thus the formations 52 and 62 which are not side by side and which are axially displaced, oppose the formations 40.

[0049] A spring 106 acts between the first actuator 42 or the end wall 88 and the second actuator 54.

[0050] The principles of the invention are readily understood from the schematic illustration in Figure 1. Components shown in Figure 1 and referred to hereinbefore bear similar reference numerals.

[0051] The sensor pin 100 is located in an appropriate passage 106 in the end wall 88 and is biased outwardly by means of a spring 108. The pin carries formations, not shown, which, depending on movement of the pin and other factors, control the operation of the control valve 12. The index component 18, the first actuator 42, the second actuator 54, the stroke adjustment member 68, the striker 82 and the piston 14 are shown displaced from one another for explanatory purposes only. The piston rod 14 projects through an end wall 110 which opposes the end wall 88 and these walls, together with the cylinder 76, not shown in Figure 1 , define the volume in which the piston operates. [0052] As the piston moves towards the end wall 88, due to pressurization of the volume between the piston and the end wall 110, some of the striker formations 86 are brought into contact with the impact formations 70 to 74. The striker formations 86 which are affected by this contact are determined by the rotational displacement of the stroke adjustment member 54 and this, in turn, is set by rotating the shaft 94 shown in Figure 6. If the outermost formation 70 is aligned with a leading striker formation 86A then the piston will move only a small extent before impacting the formation 70. On the other hand if the formation 70 is aligned with a trailing formation 86B then the piston will move through the maximum length possible before the formation 70 contacts the formation 86B. This process therefore allows for the stroke length of the piston to be varied.

[0053] With the piston close to the end wall 110 the spring 104 biases the index component 18 away from the end wall 88. The formations 40 are thereby automatically brought into engagement with the formations 52 on the first actuator 42 which is fixed to the end wall. Consequently the axial movement of the. index component caused by the spring 104 is translated into a small degree of rotational movement of the index component as inclined faces of the formations 40 and 52 mesh. The rotational movement which results from this interaction is approximately half the pitch 114 of the formations 40.

[0054] When the piston reaches the end of its stroke towards the end wall 110 the movement of the piston is reversed using control techniques known in the art and the piston is again advanced towards the end wall 88.

[0055] As the piston moves towards the end wall 88 the striker 82 engages with the stroke adjustment member 68 in the manner described. Further movement of the piston causes the spring 106 to be compressed and the formations 62 are then brought into engagement with the formations 40 on the index component. (In Figure 6 the formations 62 are shown as a number of discrete formations displaced from each other). This is to simplify the illustration.

[0056] When the formations 62 engage with the corresponding formations 40 the index component is moved through the remaining portion of the pitch 114. The stroke adjustment member 68 is constrained against rotational movement by the action of the pinion 92 which is locked in position.

[0057] Further movement of the piston brings the index component 18 into abutment with the sensor pin 100. If the pin is not aligned with the recess 34 then the pin is pushed into the end wall 88 and this causes switching of the control valve thereby to introduce compressed air into the bore 78 between the piston and the end wall 88. The piston then moves on its reverse stroke. The striker 82 is disengaged from the stroke adjustment member 68 and the spring 106 moves the member 68 away from the first actuator 42. The spring 104 can then act on the index component and urge the component away from the end wall 88. The index component then interacts with the formations 52 on the first actuator and, as explained, the index component is moved through a portion of the pitch 114.

[0058] Thus with each stroke of the piston the index component is moved as the piston moves away from the end wall 88 through part of the pitch 114 and, as the piston moves towards the end wall 88, through the remaining portion of the pitch 114. The index component is thereby rotated through a precisely controlled angle which depends, at least, on the pitch 114. [0059] The process continues in this way until the recess 34 is rotated to a position at which it is aligned with the sensor pin 100. On this piston stroke the sensor pin enters the recess 34. The control valve is responsive to this particular situation and interrupts the supply of air to the bore 78.

[0060] The index component thus regulates the number of strokes of the piston in a particular cycle. The index component could for example carry two or more recesses spaced from each other with the angular displacement between adjacent recesses then determining the number of strokes in the cycle.

[0061] By rotatably moving the adjustment member 68 to bring different striker formations 86 into contact with the impact formations 70 to 74 the stroke length of the piston is adjustable.

[0062] The invention thus makes it possible to adjust the volume of fluid which is pumped in a given cycle, by the action of the piston, by varying the stroke length of the piston and by varying the number of piston strokes in the cycle.

Claims

1. A method of controlling a reciprocating pump, which includes a piston which is activated by a pressurised fluid, to deliver a predetermined number of strokes, the method including the steps, for each stroke of the piston, of moving an index component by a defined extent and monitoring the movement of the index component relatively to a sensor and, upon detecting movement of the index component to a control position, using the sensor to interrupt the supply of pressurised fluid to the piston.

2. A method according to claim 1 wherein the sensor includes a member which is physically engageable with a formation in or on the index component which is of complementary shape to the member, when the index component is at the control position.

3. A method according to claim 1 or 2 wherein the index component is moved in a rotational sense through an angular step about a defined axis.

4. A system for controlling the operation of a pump which is driven by a piston which is actuated by a pressurised fluid, the system including an index component, an actuator mechanism which is responsive to movement of the piston and which, for each stroke of the piston, causes the index component to move a defined distance, and a sensor which is responsive to movement of the index component and which, upon detecting movement of the index component to a control position, interrupts the supply of pressurised fluid to the piston.

5. * A system according to claim 4 wherein the pressurised fluid is drawn from a source of compressed air.

6. A system according to claim 4 or 5 wherein the index component is mounted for rotational movement through a defined angular step for each stroke of the piston.

7. A system according to any one of claims 4 to 6 wherein the index component is mounted for rotational movement about a central axis of the piston and is located, together with the actuator mechanism, inside a bore of a cylinder in which the piston is reciprocally movable.

8. A system according to any one of claims 4 to 7 wherein the actuator mechanism includes a first actuator which causes the index component to move a portion of the defined distance and a second actuator which causes the index component to move through a remaining portion of the defined distance.

9. A system according to claim 8 wherein the control system includes first biasing means for biasing the index component away from fixed structure towards the piston and second biasing means which acts to bias the first actuator away from the second actuator.

10. A system according to claim 8 or 9 wherein the index component includes a first saw tooth formation and the first actuator includes a second saw tooth formation, of similar shape to the first saw tooth formation, which is engageable with a sliding action with the first saw tooth formation thereby to cause the index component to move tnrougπ me portion υι me UBHHBU distance.

11. A system according to claims 8, 9 or 10 wherein the second actuator includes a third saw tooth formation, of similar shape to the first saw tooth formation, which is engageable with the first saw tooth formation thereby to cause ^" movement of the index component through the remaining portion of the defined distance.

12. Apparatus for adjusting the length of a stroke of a reciprocating piston which is activated by a pressurised fluid, the apparatus including an adjustment member, positioned inside a cylinder in which the piston is reciprocally movable, with at least two impact formations which are axially displaced, and a striker which is movable by the piston, the adjustment member being movable, in a controlled manner, to present at least one chosen impact formation to the striker, and a sensor, responsive to movement of the adjustment member to a stroke control position, for reversing movement of the piston.

13. Apparatus according to claim 12 wherein the adjustment member is movable in a second direction which is opposite to the first direction.

14. Apparatus according to claim 12 or 13 wherein the adjustment member includes a plurality of impact formations which are displaced from one another in an axial sense in stepwise fashion and the striker includes a similar set of formations.

15: Apparatus according to claim 14 wherein the adjustment member is mounted for rotatable movement, in a controlled manner, in order to present one or more of the impact formations to corresponding formations on the striker.

16. A combination of apparatus according to any one of claims 12 to 15 and a control system according to any one of claims 4 to 11 , wherein the sensor is common to the apparatus and to the control system.