US2685295A - Periodically operating controlling device - Google Patents

Description

Aug. 3, 1954 K. F. TROMP PERIODICALLY OPERATING CONTROLLING DEVICE Fild June 27, 1950 4 Sheets-Sheet 1 Aug. 3, 1954 K, TRQMP 2,685,295

PERIODICALLY OPERATING CONTROLLING DEVICE Filed June 27, 1950 4 Sheets-Sheet 2 1954 K. F. TROMP PERIODICALLY OPERATING CONTROLLING DEVICE Filed June 27, 1950 4 Sheets-Sheet 3 4 zzvnsvvrole jam: F Warn 3, 1954 K. F. TROMP 2,685,295

PERIODICALLY OPERATING CONTROLLING msvxcz Filed June 27, 1950 4 Sheets-Sheet 4 ZZ/l/EN re a Ween was Patented Aug. 3, 1954 PERIODICALLY OPERATING CONTROLLING DEVICE Klaas F. Tromp, Kerkrade, Netherlands Application June 27, 1950, Serial No. 170,521

Claims priority, application Great Britain March 14, 1950 9 Claims. 1

It is well-known in the art that any automatic controlling device comprises, in addition to means for measuring the magnitude to be controlled, means for feeling or scanning the result of the measuring operation and adjusting means adapted to be actuated by the feeler whenever the actual value of the magnitude to be controlled differs from the proper value.

The limits between which the device will be capable of keeping the actual value of said magnitude will be narrowest if the influence of the feeler on the result of the measuring means is a minimum and the adjustments effected by differences between the proper and the actual values of the magnitude to be controlled are not so considerable as to give rise to oscillation, i. e. a series of alternating positive and negative differences between the two aforesaid values. Moreover, it is essential for the adjusting means to be capable of rapid adjustment.

My present invention provides a device that fully meets the said requirements. It consists herein that the feeler is caused to operate periodically and that differences between the actual and the proper values of the magnitude cause the adjusting means to be operated between the limits of a relatively small range.

It is pertinent here to remark that the term proper value of the magnitude to be controlled does not imply one definite value only, but also a restricted range of values.

In order that my invention may be fully understood by those skilled in the art, I shall now proceed to describe it in further detail with reference to the appended drawing, which diagrammatically illustrates, in Fig. 1, Figs. 2 and 2a, Fig. 3, and Figs. 4 and 4a, respectively, four embodiments of the invention.

In Fig. 1, the numeral I designates a weighing beam. Suspended from one end of said beam is a body 2, and suspended from the other end thereof is a suitably recessed or profiled block 3 loaded by a weight 4. During swinging movement of the beam I said block 3 is movable, with a very slight clearance, across a fixed abutment 5.

A conduit 6 serves to feed a reservoir I with relatively heavy liquid, which is to be mixed with relatively light liquid supplied by a conduit Ii provided with a valve 8 for controlling the amount of liquid flowing through conduit 6 in such manner as to keep the specific gravity of the mixture in reservoir I as nearly as possible to the proper value. The conduit for discharging the mixture from reservoir I is indicated by 9. Through a valve 9 a controlled amount of the liquid mixture is fed into a vat II] enclosing the aforesaid body 2, which is thus permanently submerged in the mixture without engaging the wall of the vat. The latter is provided with a weir II, and, in the bottom, with a discharge pipe I2. The liquid discharged by the weir II and by the pipe I2 is returned to the conduit 9.

The valve 9 should be set as to ensure a permanent overflow of the liquid in vat I0, so that the surface of the liquid is kept at a constant level and the mass of weight I should be such as to hold the weighing beam I in zero position as long as the liquid in vat II) has the proper density.

The device further comprises a cam disk I3 rotatable about a horizontal axis, driven by a motor not shown and adapted to cooperate with rollers Ida, Itb pivoted to the substantially horizontal arms of bell cranks [5a and I5b, respectively, loosely mounted for independent oscillation about a common pivot I6. Said bell cranks are loaded by springs I'Ia and I'll), respectively, which tend to urge the rollers I411, I412 into engagement with cam disk I3. The substantially vertical arms of the bell cranks are provided with feelers, i. e. pointed projections I8a and I8b, respectively, adapted to cooperate with the face of block 3 in front of said feelers.

As long as rollers Ida, I4b engage the high portion of the periphery of cam I3, the feelers I 8a, I8b clear the recessed face of block 3, so that the latter has freedom of vertical movement across abutment 5. However, if the rollers reach the low portion of the cam, springs Ila, IIb urge said feelers into contact with block 3, which is thereby urged into engagement with said abutment.

As will be seen from the drawing, the portion of block 3 that is located in the plane of bell crank I5a has a recess of uniform depth through about the lower half of the block, whereas the portion that is located in the plane of bell crank I5b is similarly recessed through about the upper half of the block, it being understood that a narrow central portion of the block is unrecessed.

Fig. 1 shows the position of the various parts when the density of the liquid mixture in vat I0 exceeds the proper value. It will be seen that the weighing beam has swung through a small angular distance in clockwise direction and block 3 is suspended a small distance below zero or neutral position. Consequently, the feeler I811 of bell crank I5a engages a projecting or non-recessed portion of block 3 and the feeler I8b of bell crank I5b engages the bottom of a recessed portion. That is to say, bell crank I5b has swung in clockwise direction through a somewhat larger angular distance than bell crank l5a and has thereby closed an electric spring contact i912 with which it is adapted to cooperate, whereas contact Ilia, located in the path of bell crank Iila, is still open. Closure of contact I91) switches in an electric motor 20 to actuate, through a slip coupling (not shown), valve 8 in a direction as to increase the amount of light liquid supplied to vat [0.

Should the density of the liquid mixture in vat Ill have been too low, block 3 would have assumed a position above neutral or zero level, and its nonrecessed or projecting lower portion would have arrested bell crank I512, while its recessed lower portion would have allowed bell crank I5a to swing through an angular distance sufiicient to close spring contact I 9a, causing motor 29 to actuate valve 8 in a direction opposite that referred to above so as to decrease the amount of liquid flowing to vat Hi.

If the weighing beam I is horizontal and the low portion of cam l3 causes both bell cranks l8a, [8b to swing towards block 3 under the in fluence of springs Ila, I'Ib, said cranks are both arrested by the central, non-recessed portion of the block, so that neither contact I9a, iSb is closed.

If the shape and the rotary speed of cam l3 are properly selected and a suitable reduction gear is interposed between motor 20 and valve 8, the weighing beam will be capable freely and gradually to resume zero position whenever, owing to the density of the liquid mixture in vat Ill being too high or too low, it will have deflected in the one or the other direction. It is to be noted that in one revolution of cam I3 motor 2%) actuates valve 8 only during a comparatively very short period, during which the setting of the valve is altered only by a very small amount.

The fact that valve 8 is actuated periodically offers the advantage that the measuring means need not transmit power to the adjusting means, so that their normal operation is not impaired. Moreover, this periodic adjustment is better adapted than a continuous adjustment to reduce deviations from the proper value to a minimum. In this connection it should be borne in mind that it always takes some time for an adjustment of valve 8 to be effective in reducing or increasing the density of the liquid in vat II], for the mo ment wherein valve 3 is adjusted and, as a consequence, the density in container 1 is varied, the liquid in vat it still has the improper density and the latter is increased or reduced only gradually. If, during this time, the deflection of beam i were allowed continuously to actuate valve 8, then in the moment wherein the beam would resume its neutral position, the increase or decrease of the density of the liquid mixture in vat it would still continue, and after some time this would cause valve 8 to be actuated in the opposite direction and to give rise to a similar phenomenon, so that the actual value of the density of the liquid mixture in vat I0 would oscillate about the proper value of said magnitude. This oscillation is obviated if the feelers (I811, (812) operate periodically, provided, of course, that thefrequency and the duration of the cooperation. between the feelers and the block 3 be responsive to the length of time required for the correction of the position of beam 1.

Figs. 2 and 2a illustrate a second embodiment of the invention, Fig. 2 showing the weighing apparatus in elevation and Fig. 2d part of said apparatus, together with the means controlled thereby, in top plan view. Similar parts are designated by the same reference numerals as in Fig. l. Vat l0 and associate parts are not shown.

Whereas, in accordance with Fig. l, the pointer of the weighing apparatus is rigidly secured to the beam I, the pointer 2| illustrated in Fig. 2 is hinged to said beam by means of a pivot pin 22 in such manner as to be adapted for swinging movement in a vertical plane at right angles to plane passing through the axis of the beam. Secured to said pointer, on either side thereof, are two suitably spaced blocks 3a and 3b in vertically staggered relation. The cam disk I3 here is rotatable about a vertical axis and cooperates with the roller I l on the short arm of the horizontal bell crank I5. Spring I'I tends to hold roller [4 in engagement with the periphery of cam I3 and to move the long arm of the bell crank towards pointer 2|.

As long as roller HI travels on the high portion of cam I3, the long arm of the bell crank clears the pointer but the low portion of the cam allows spring I1 to urge said arm into engagement with the pointer and to cause the same to swing through a small angular distance about pin 22 towards two spring contacts I9a, I922 adapted to cooperate with the blocks 3a and 3?), respectively. If beam I is horizontal, said deflection will not bring about the closure of either contact. However, if the pointer is out of neutral position, either block So will engage contact Ida, or block 3b will engage contact 1919, so as to switch in the motor 20 and actuate the valve 8 (not shown in these figures) in the one or the other direction, all as described with reference to Fig. 1.

As will be seen from Fig. 2, those faces of blocks 3a, 3b that are adapted to engage contacts Ida, I9?) are biased, in opposite directions, relative to the vertical plane through the axis of beam I, in such manner that the period during which either contact [9a or [9b remains depressed by the bell crank i5 is proportional to the deflection of said beam. This has the advantage that relatively considerable deviations of the density in vat I8 (Fig. 1) from the proper value will be corrected a quickly as relatively small deviations, without, however, giving rise to oscillation of the actual value about the proper one.

Turning to Fig. 3, this illustrates an embodiment similar to that described with reference to Fig. l but wherein the motor for actuating the valve (8 in Fig. 1) is substituted by a mechanical drive. This renders the device especially suitable for use in installations such as coal washing plants, where rough conditions prevail.

As shown, the ends of the long arms of bell cranks Him, [511 here are connected to their springs Hoand Ill), respectively, through chains or other flexible members, sheaves around which said members are passed, and arms 28a and 287), respectively, secured to said sheaves. The feelers Illa and [8b cooperate with the block 3, which is of substantially the same configuration as block 3 illustrated in Fig. 1, it being understood, however, that the depth of each of the recesses therein increases from the non-recessed central portion towards the top and the bottom face, respectively, of the block, for reasons explained with reference to the biased blocks 3a, 311 shown in Figs. 2 and 2a.

The long arm of bellcrank [5a is further connected to one end of a belt 23w passed, in clockwise direction, around a wooden sheave 21 adapted to actuate the valve (8 in Fig. 1). The other end of belt 23a is connected to a frame 24 w urged by a spring 25w into engagement with an abutment 28a. In a similar manner, the lon arm of bell crank I52) is associated with the sheave 2'! through a belt 23?) passed around it in counterclockwise direction and secured to a frame 24b adapted, under the influence of a spring 25b, to engage an abutment 26b.

The lengths of belts 23a, 231) are such that they are slack as long as the rollers Mia, Mb engage the high portion of cam l3. If, however, the low portion of the cam reaches the said rollers, and assuming the block 3 to have moved in downward direction out of neutral position, crank 55b will be swung, under the influence of its spring I'lb, through an angular distance sufficient to pull the belt 231) tight around sheave 21 and rotate the latter through a small angular distance in clockwise direction, whereby the valve (8) is actuated so as to increase the amount of light liquid flowing to vat l0, spring 25?) preventing the belt from slipping. The other bell crank, [5a, is arrested by the non-recessed portion of block 3 and thus cannot tighten its belt 23a, which, thereby, remains idle.

Attention is drawn to the fact that each of the springs Il a, Hb should be strong enough to adjust the valve (8) to be actuated by sheave 21. As shown, said springs engage arms 23m and 2822', respectively, each of which, when assuming idle position (see arms 25a.) is nearly in parallel relation with the axis of the spring associated therewith, but at the end of the working stroke encloses an angle of about 90 with said axis. This. has the advantage that, as long as said arms are inoperative, their springs offer only a minimum of resistance to rotation of cam l3, but are fully effective the moment wherein sheave 2'! is to be rotated to adjust the valve (8).

Although the embodiment illustrated in Fig. 3 is very suitable for various purposes, it has some inconvenience owing to the fact that the moment wherein rollers M a, Mb disengage the high portion of cam IS, the feelers I811, lab are suddenly arrested by block 3 so that they forcibly strike the block 3. If, now, springs I'm, llb

have to be very strong, the noise caused by these blows could be annoying and even result in rapid wear and tear of the impacting parts.

Figs. 4 and 4a illustrate mechanism which, although somewhat more complicated, is devoid of the inconveniences just stated. Also in accordance with these figures, sheave 2? serves to actuate valve (8). Secured to the end of lever arm lSa (Fig. 4) is one end of belt 23a, the other end of which is secured to the lever arm 24c. Arm l5a is further connected, through a chain 35a, to one arm of a lever 30, which is rotatably mounted on a fixed pivot 33, and the diametrically opposed arm 3| of said lever is connected, through chain 34a, to lever arm 24a. The third arm 32 of said lever is engaged by a strong coiled spring l1.

Lever arm a is keyed to pivot pin l6 mounted for rotation in the frame (not shown) and is provided with a roller Ida, for engagement with the periphery of cam 13. The lever arm 24a is loosely mounted on pivot 16 and connected, through a spring c, with a lever arm 26a also freely rotatable about pin l6. Secured to lever arm 26a is the feeler 181w, which is arranged for cooperation with block 3 suspended from one arm of the weighing beam from the other arm of which is suspended the body 2.

As long as roller [4a engages the high portion of cam l3, belt 23a is slack and lever arm 26: engages, through a nose 29a, lever arm 24a to which it is connected by spring 25a. The moment wherein roller Ma reaches the "low portion of cam i3, and assuming the density of the liquid in the vat ([0) to have the proper (or a lower) value, spring I! pulls lever arm Ida and, thereby, the left hand side part of belt 23a upwards, but simultaneously it allows lever arm 24a to swing downward and to lower the right hand part of belt 2311 by the same amount, so that this belt remains slack. The lever arm 26m and the feeler I804 simply follow the downward swinging movement of lever arm 24a, since, under the conditions stated, block 3 assumes a position wherein its recessed lower portion faces feeler Illa, so that the swinging movement of the latter is not interfered with.

If, however, the actual value of the density of the liquid in the vat (l9) exceeds the proper value, so that block 3 assumes a position on a lower level, feeler law will, during its aforesaid swinging movement, be arrested by the projection or non-recessed upper portion of block 3, which itself is thereby urged against the abutment 5, owing whereto lever arm 26a is also arrested and, through spring 25a, brakes lever arm 24a, the consequence being that chain 34a will get slack and belt 23a is pulled tight around sheave 2? under the upward pull of lever arm 30 by spring 11 in combination with the upward pull of lever arm 24a by spring 251a. This causes the sheave 27 to be rotated through a small angular distance, in clockwise direction, under the influence of spring I7, since, as it is pertinent here to state, spring I! is stronger than spring 25c.

When roller Ma is thereupon urged downward by the high portion of cam i3, lever arm We is swung in counterclockwise direction so as to tension spring [1, lever arm 24a is swung upwards under the pull of chain 34a and lever arm 26a together with the feeler l8a will follow this upwards swinging movement owing to the engagement of arm 24a, with nose 29a.

When the density of the liquid in the vat I!) is subnormal, the sheave 2'! is rotated counterclujockwise by the mechanism shown in Fig. 4a, it being understood that the parts i, 2, 3, 5, IE, IT, 30, 3|, 32, 33 are common to this mechanism and the one just described with reference to Fig. 4, and that the parts marked by reference numerals indexed a in Fig. 4, are duplicated in the mechanism shown in Fig. 4a, wherein their references are indexed 1).

Passed around sheave 27 is a second belt 231), whose ends are connected to lever arms 15b and 2412, respectively. As shown, the positions of these arms correspond to those of arms 24a and I5a, respectively, and feeler [8b cooperates with that part of block 3 whose upper portion is recessed. Since lever arm 15b is keyed to pivot pin IE and, consequently, is rigidly secured to lever arm l5a (Fig. 4), it is clear that movement imparted by cam I3 (Fig. 4) to lever arm [5a will be transmitted to lever arm 15b.

In view of the explanations given hereinbefore it is believed that the operation of the mechanism shown in Fig. la does not require further description.

Attention is drawn to the fact that, with an arrangement as illustrated in Figs. 4 and 4a, the feelers (I8c, I8b) are caused to engage block 3 only under the influence of the weight of lever arms 24 and 26. By suitably balancing said weight, the force of the impact can still be reduced. As a matter of course, the pressure exerted by the feelers 0n the block once they have engaged the same, is thereupon increased by the tension of spring 25, but this pressure is static and, moreover, considerably lower than the one brought about by the springs I'Ia, Ilb in the arrangement described with reference to Fig. 3.

Another advantage of the device shown in Figs. 4, 4a is that the motor for driving cam 13 has to tension only one spring I! of the same strength as each of the two springs He, no shown in Fig. 3.

In the device in accordance with Figs. 4, 4a,, the power required for rotating sheave 21 is furnished by spring H, which is periodically loaded by the motor for driving cam 13. Said power could, however, also be furnished by the motor directly, for instance so that cam I3 directly engages lever arm 32 and lever arms 15a, 151) are loaded by a spring, which, then, could be essentially weaker than each spring I! in the device shown in Fig. 3. This is an advantage when rotation of sheave 21 requires a considerable amount of energy.

My invention thus provides simple and reliable means for controlling the density of liquid media, although it is also suitable, inter alia, for checking the weight of packages, dosed solids, etc. As stated before, it is primarily intended for use in coil preparation and, generally spoken, in ore dressing plants, for instance, for controlling a uniform supply both of liquid and of solid material to flotation machines, for controlling the solid to liquid ratio of pulp in thickeners, for controlling the density of coarse ore pulp returned from a classifier to a ball mill whose output is passed through said classifier, for substituting the usual automatic controlling devices of jigs wherein the jig-stroke is adjusted in accordance with the thickness of the layer of sinks, etc.

What I claim is:

1. A system for producing a suspension having a predetermined density by mixing a suspension of variable density with a density adjusting liquid, said system comprising in combination a supply conduit for suspension of variable density, a supply conduit for the density adjusting liquid, a reservoir adapted to receive the liquids supplied by both said conduits and provided with a discharge conduit, control valve means in the supply conduit for the density adjusting liquid, actuating means operable to increase and to decrease the passage of said control valve means, a weighing beam, means for swingably supporting said beam, means for loading one arm of said beam responsive to the density of the mixture in said reservoir, means for balancing said beam so that the latter is maintained in a balanced position when the density of the mixture in said reservoir is at a predetermined value, two check members ofiset and fixed relative to one another and connected to said weighing beam so as to follow movement of said beam from said balanced position, two feeler means each adapted to cooperate with a related one of said check members, means for periodically causing movement of said check members and said feelers relative to one another, and means efiective during the periodic relative movement of said feelers and check-members for operating said actuating means in response to the cooperation of said feeler means and said check members when said check members are displaced by movement of said beam from its balanced position.

2. A system in accordance with claim 1, wherein said check members are profiled as to hold said actuating means in operative position during a period proportional to the deflection of the weighing beam.

3. A system in accordance with claim 2, wherein the feeler means are loaded by spring means tending to urge them into engagement with the profiled check members.

4. A system in accordance with claim 1, wherein the feeler means are operatively coupled with the actuating means through mechanical means.

5. A system in accordance with claim 1, wherein the feeler means are coupled through spring means with periodically operated mechanical means for imparting movement to the actuating means.

6. A system in accordance with claim 4, wherein said mechanical means comprise a sheave for imparting movement to the actuating means, and a belt passed around said sheave, said belt being operative only when said check members interfere with the periodic movement of the feeler means.

7. A system according to claim 1 in which said check members have surfaces normally spaced from said feeler means, said surfaces being non-parallel to the general plane of deflection movement of said members and in which said feeler means engage said surfaces for a period of time proportional to amount of deflection of said check members resulting from the deflection of said beam.

8. A system according to claim 1, wherein said means for operating the actuating means includes a sheave for imparting movement to said actuating means, at least one belt passed around said sheave, said belt being connected to and movable by said periodical movement causing means, and means connected to said feelers for tighten- ,ing and loosening said belt on said sheave according to the position of said check members.

9. A system according to claim 1, wherein said means for operating the actuating means includes switch means for causing energization of said actuating means, said switch means being actuated by said feeler means.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,178,193 Trimbey Apr. 4, 1916 1,210,180 Logan 1 Dec. 26, 1916 1,664,840 Wermine Apr. 3, 1928 1,892,839 Howard a- Jan. 3, 1933 1,966,638 Morgan July 1'7, 1934 2,332,953 Tromp Oct. 26, 1943 2,490,634 Keene Dec. 6, 1949

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