US 2376791 A
Description (OCR text may contain errors)
May 2.2, 1945 J. R. LINDSAY MOTOR CONTROL Filed June 19, 1943 W W m m JAMES Ease-2T LINI'D SAY,
Patented May 22, 1945' 2,376,7itl
MOTOR CONTROL James Robert Lindsay, Bexley, Ohio, assignor to The Traylor Vibrator Company, a corporation of Colorado Application June 19, 1943, Serial No. 491,451
This invention relates to a system or circuit including a vibratory motor and more specific a vibratory electric or electromagnetic feeder circuit in which a desired average feed rate is obtained by successive periods of relatively high vibratory feeding followed by periods of relatively low or zerovibratory feeding. a An object of the invention, therefore, is to produce circuits of the type above described.
A further object of the invention is to provide anelectrical system or circuit in which the variable feed rate is provided preferably but not necessarily without shutting off completely the vibratory feeder or motor by successively altering the amplitude of vibration of the motor or feeder from a conveying condition to an essentially non-conveying condition.
Other objects of the invention will appear hereinafter, the novel features and combinations being set forth in the appended claims.
In the accompanying drawing, I v
Fig. 1 is a wiring diagram'oi' one form of the system or circuit comprising my invention;
Fig. 2 is a wiring diagram of a modified form of timer which may be substituted for the timer of Mg. 1; I
Fig. 3 is a curve illustrating atypical condition of the timer voltage applied to the grid of v the power tube of the system of Fig. l: and F18. 4 is a curve illustrating another condition of the timer voltage applied to the grid of the power tube of the system of Fig. 1 when the gamer of Fig. 2 is substituted for the .timer of s. 1.
It has been found in practice that frequently a relatively low average feed rate is desired for a vibratory feeder which may be generally of the type disclosed in the patent to James A. Flint, No. 2,094,787, dated October 5, 1937. More s ecifically, however, it has been found that in vibratory electric or electromagnetic conveyors or feeders where a cooling or drying action is to be performed, it is desired that the material be conveyed at a low average feed rate so as to afford am le time for the cooling or drying function to be carried out. Flint patents, Nos. 2,094.785 and 2,094,786 are further illustrations of these vibratory coolers and dryers to which this invention pertains; These are only two illustrations of typical devices.
It has also been found that it is 'difflcult to maintain vibratory feeding movement of the material at a satisfactory controllable rate where the average amplitude of vibration and consequently the average feed rate is low, if attempt is made to maintain the feed rate or amplitudeof vibration substantially uniform. This is believed to be because of the fact that granular material being conveyed on a conveyor, feeder, cooler or dryer, of the type generally illustrated in the above mentioned patents, tends to become substantially non-conveying at a rapid rate as the amplitude of vibration is decreased and consequently in such devices there is frequently vibration in the conveyor, feeder, cooler or dryer and there may or may not be any actual conveying of material, depending upon a very small change in the amplitude of vibration of the vibratory unit.
To overcome this difficulty and to insure that there will be a reasonably accurate average feed rate for granular material fed by one of these vibratory units, I have provided a novel control system or circuit in which the conveyor, feeder, cooler or dryer is vibrated at a relatively high conveying rate for a period of time which is preferably adjustable over a wide range, followed by a period duringwhich the vibration of the vibratory unit is appreciably reduced, preferably so as to provide no conveying action whatever.
These periods, which for shortness will be-called terminals of a transformer and may have any desired voltage such as 220 volts. The c0nduc-' tor ill leads to the center tap of the secondary of transformer I! which is the heating transformer for the filament or cathode of a power tube It which is preferably a gaseous electronic discharge tube. The filament or cathode of the tube It is heated by the transformer l2, the primary of which is energized from any available source of alternating current. The plate of the power tube It is connected to power conductor H which includes a winding or field ll of. an electromagnetic motor which is in the preferred embodiment of my invention a part of a vibratory feeder, conveyor, cooler or dryer, having the construction of one of the three above spectfied patents to James A. Flint. The power tube l3 acts as a half-wave rectifier to provide electric impulses having a frequency the same as the frequency of the source of alternating cur rent which energizes conductors l0 and ii. For example, if this frequency is cycles per second, the vibratory device having field It will vibrate at a frequency of 60 vibrations per second or 3600 vibrations per minute.
In the system of my invention, the amplitude of vibration of the vibratory motor, which may be generally referred to by the reference character I4, is controlled by what is known as phase shift mechanism, that is, the input or control voltage of the tube It is shifted with respect to the plate, output, or anode voltage of the tube II and this phase .relation will determine the amplitude of vibration of the motor I4 in a manner well understood in this art.
To provide for automatic and periodic adjustment of the feed rate of the vibratory motor '4 I provide a control circuit for the tube II in which the phase relation between the input voltage and the output voltage is cyclically adjusted during succeeding periods in which the amplitude of vibration of the motor I4 is alternately relatively high and relatively low. Ialso provide means to adjust the actual time of each cycle of successive high and low periods as well as the ratio of the high periods to the low periods and consequently the time of the high period and of the low period of each cycle.
The input circuit of the tube It extends from its filament or cathode to the center tap of the secondary of transformer i2, thence by conductor II to the secondary of transformer l0, thence by conductor I I to variable resistor l8 and from a variable tap thereof by way of conductor I! through current limiting grid resistor 20 to the grid of tube II. There is an electric network which provides for the adjustment of the phase relation of the grid voltage to the plate voltage of the tube It which includes a source of phase shift control voltage 2| energized from the same source which energizes conductors l and H and which energizes transformer It. This phase shift control voltage 2| is so adjusted as to provide,
without other influence, such a phase relation between the grid voltage and plate voltage of tube ll as to give a normally desired amplitude of vibration of the motor i4. It may be stated at this point that this amplitude of vibration provided by the phase shift control 2 i independently of the other control, may be either the so-called "high" vibration or the so-called "low" vibration and the selection of whether it is "high" or "low" will normally depend upon whether during each cycle of alternate high" or low vibrations the proportion of "high vibration is greater or less than the proportion of low vibration. For example, referring to Fig. 3 of the drawing, let it be assumed that the curve ABC represents a cycle of operation of successive high and "low periods of vibration and for illustration we will assume that the time represented by curve ABC is ten seconds. In other words, every ten seconds there will be a cycle of successive "high" and "low" periods of vibration of the motor l4.
As illustrated in Fig. 3 of the drawing, the period from A to B is designated as high vibration and this period is approximately 25% of the complete cycle, the "low" period being approximately 75% of the cycle. Under such conditions the vibratory motor l4 will vibrate with a "high" vibration for 2% seconds, followed by a low vibration of 7% seconds and this will be repeated in cycles. Under these conditions the phase shift control 2|, if alone in control, preferably would provide the "low" amplitude of vibration. It may be stated that the curve of Fig. 3 actually illustrates the voltage'applied to conductors l1 and I9, which is the supplemental control voltage for tube It,
superposed by the timer mechanism, hereinafter described, on the resistor ll, this "high period may be adjusted to any portion of the cycle. In other words, the point B on the curve of Fig. 3 may approach the point A as one limit and the point C as the other limit. It is, of course, obvious that as the high[ period is adjusted, the ratio of the "high" to low is varied and the actual time of the "low" is also varied unless the overall time from A to C is also adjusted.
To provide the supplemental control for the tube It I provide a timer 22 which, as illustrated in Fig.1 of the drawing, is in the form of a simple thermal flasher relay whichcontrols a periodic application of an A. C. voltage to the resistor ll followed in each instance by a short circuiting of said resistor ll. As illustrated, the timer 22 is provided with a heater 2! and bi-metallic strip 24 which controls a switch 2!. The timer or relay 22 is energized from a transformer 28 through a variable resistor 21. The resistor II is connected across the terminals of the switch 2| and when said switch 25 has its contacts closed, the resistor I8 is short circuited.
Operation of the timer 22 is as follows: To start operation, the transformer 2| is energized and an obvious circuit is provided from the secondary thereof to the heater 2', normally closed switch 25, bi-metallic strip 24 and variable resistor 2I. Theheater 2! begins to heat under the influence of the electric current and after a predetermined time which may be adjusted by controlling the variable resistor 21, bi-metallic strip 24 deflects sufficient to open the contacts of switch 2!. when this is done the circuit to the heater 23 isbroken and the bi-metallic strip 24 starts to cool and after suflicient cooling time recloses the contacts of switch 25, repeating this cycle of operation. When the contacts of switch 25 are closed, period B--C of the curve of Fig. 3 maintains, and no control voltage is applied to conductors i1 and I9. Upon the opening of the contacts of switch 2|, point A in the cycle of the curve of Fig. 3 is reached and a voltage is applied from the sec-- ondary of the transformer 2| through an obvious circuit to the resistor i8 including the heater 2! and resistor 21. The current flow at this time, however, is very small. due to the value of resistors ll and 21 and consequently the heat generated in heater 23 under such circumstances is insufiicient to maintain the switch 28 open.
=It is obvious that by controlling the resistor 21,
the time of the cycle A-B-C may be adjusted.
and this also adjusts the time that the switch 2| is closed which. also adjusts the actual time of the period 3-0. The time of the 'period A-B may be controlled by changing the bi-metallic strip 24 or by changing the adjustment of the contacts of switch 25.
As previously indicated, when the contacts of switch 25 open and remove the short circuit of resistor I! an alternating current voltage is applied to resistor I8 and by it superposed on the normal phase shift voltage of the input circuit of tube i3, whereby a phase shift will take place so as to give a period of "high" vibration. The change in the vibration effected by this appearance of alternating current voltage on resistor ll may be adjusted by adjusting the position of the variable contact associated therewith. Furthermore, as previously mentioned, if desired, the
phase shift control apparatus 2| may be normally set so that when resistor II is short-circuited, the amplitude of vibration of the motor i4 will be "high" and when the particular phase mam shiit voltage appears on resistor It. the amplitude of vibration or motor Il may thereby be reduced. Turning to Fig. 2 of the drawing. there is illustrated an electronic timer which may be substituted for thetimer 22, resistor ll andassociated parts. In making this substitution it is to be. understood that conductors I I and It are merely connected to the timer oi'Fig. 2as illustrated and-everything above the conductors I1 and II oi Fig. 1 is eliminated by the substitution.
the timer of Fig. l. Transformer "has a double secondary winding. one winding oiiwhich energizes the filament of anelectronicdischarge tube It, preierably oi the gaseous type. The tube It has an indirectly heated cathode and may have two grids, one of which is a control grid, the other a stabilizing grid. Bald tube 2! is connected as a relatively low irequency relaxation oscillator. v
The plate or output circuitoi the tube It extends from the left-hand terminal of the main secondary winding of transformer II by way oi conductor 32 thro gh a. control switch ll and condenser 8| which is connected to the plate or anode of said tube 20. Theother or right-hand terminal oi the main secondary winding oi trans former I8 is connected to a terminal II and then through variable resistor 34 to a terminal it to which the indirectly heated cathode oi tube 29 is directly connected. The stabilizing grid of the tube 29 is also connected to terminal II. A condenser 80 is connected across the terminals 88 and II. The control grid oi the tube 2! is also connected to the terminal ll through protecting resistor It. It may also be mentioned that connected across the terminal of condenser Ii is a pair of resistors l1 and II, the latter of which has a variable tap associated with it which is connected to conductor ll.
The operation of the timer of Pig. 2 will now be described. Assuming switch it is closed, a surge oi current will flow in the plate circuit of the tube II the circuit being from the right-hand end oi main secondary it to terminal I8, through resistor It. terminal 3!, through the cathode oi tube 2! to the plate of'tube II and thence throughconductor 81, condenser II and switch I. to the lert-hand terminal or said winding. This surge of current will charge the condenser ll. When this occurs, voltage will appear between the terminals II and ll which will charge condenser I. connected between them. This voltage, acting through resistor it and the control grid oi the tube 29, will immediately shut off the iiow of current through said tube 29 by automatic action.
Referring now to Fig. 4 or the drawing, immediately upon the ilrlng oi the tube II, or in other words, on the surge or current therethrough. the Point D in the cycle is at hand and between the point D and the point E the condenser Ii has a charge which is indicated bythis portion of the curve. This charge on condenser Ii is applied in an amount determined by the position or the variable contact associated with conductor I! to said conductors I1 and I0, since the conductorll is connected by way of conductor I! Due, to the iact that condenser it has a high resistantshunt permanently connected across its terminal. provided by resistors 31 and II, it will discharge at a. desired rate following its being charged, as above described.
litter the voltage on condenser II has bee substantially discharged, the point E of curve or and there is no supplemental voltage produced by the timer oi Fig. 2 applied to the conductors i1 20' Pig. 4' is reached. This time period D--E oi said curve is indicated as representing the period of "high" vibration, though as previously indicated in discussing Fig. 1 it may be indicated ,as low,"
depending upon the setting or the phase shiit control deviceoiFig. 1. a v v Frompoint it to point P of the curve is the "low' period in the illustration, given, during which c ndenser II is substantially. discharged II. In other words, during this flow period, the control or the amplitude of vibration oi'motor i4 is that determined by the phase shift control apparatus 2i. i i The elective height of the curve I) and E may be controlled and thus the value of the "high" amplitude may be controlled, by adjusting the variable tap associated with conductor II and resistor It. The time of the cycle from Dto l",
may be variably controlled by controlling the discharge rate of the condenser 8|, because this condenser ll shuts oi! the current ilow through tube ll very shortly alter it is initiated by placing a high negative bias on the control grid thereoi and maintaining this bias until the condenser 80 has discharged. The time interval of this discharge of condenser 8| is controlled by controlling the ed'ective value of variable resistor I4. It is. of course, evident that this time discharge 0! condmser II must be greater than the time oi discharge or condenser II and as these two times apmuch each other the points E and l" of the curve of Hg. 4 approach each other. The ratio oithe "'high to the "low" period in the timer 0! Fig. 2
can, of course, be adjusted by adjusting the resistor 8i.
It may be further pointed out that the timers oi both Figs. 1 and 2 are extremely flexible as, for
example, the "high" period oi eithercan be almostaslowasilt orashighasiwtt oieach cycle and the same, oi course, istrue for the "low period of each. Furthermore. the high period can be obtained by placing a supplemental volttion or the conveyor, ieeder, cooler or dryer operinfluencing the input circuit oi tube II, the phase relation between the input and output voltage thsreoi' would provide a "low" amplitude of vibraated by the motor ll. This vibration may be insuiiicient to produce any conveying action whatever though it may produce some conveying action. It may be stated that the advantage of maintaining some vibration on the vibratory'unit as against completely shutting iton is that some materials while being cooled or dryed or merely convesedtend tosticktothedeckoithevibratory to one terminal or .Il.
lied. Periodically there will be successive periods of "hish and "low vibration and the ratio of the two may be adjusted over an extremely wide range as above indicated. During the periods of high or working conveying vibration the material will be conveyed at a rather definite. rate. As a consequence, in the operation or a conveyor, feeder, cooler or dryer, an operator can be assured that the material will be conveyed over a given distance in an approximate predetermined time. yet this time may be such that the average reed rate is appreciably below that which could be sustained by the vibratory unit, that is, the conveyor, feeder, cooler or dryer. I have therefore provided a system for conveying either alone or while conditioning granular material, one illustration of which is plastic material in granular form, in which the average rate of feed is'below that at which the vibratory unit can dependably continuously convey material. The operation of the system oi Fix. 1 when modified by substitutin: the timer of Fig. 2 is essentially the same, the diiference being that the timer of Fig. 2 has a greater flexibility than the timer 011 1;. 1.
Obviously those skilled in the art may make various changes in the details and arrangement of parts without departing from the spirit and scope of the invention as defined by the claims hereto appended, and I wish therefore not to be restricted to the precise construction herein disclosed.
Having thus described and shown an embodiment of my invention, what I now desire 'to secure by Letters Patent of the United States is:
1. In combination, a feeder of the vibratory electric type. a source of current for energizins said feeder, a continuous circuit connecting said feeder and said source whereby said feeder is always energized, and automatically operable electrical control means connected to control the rate of current flow in said continuous circuit, said control means including mechanism operable to adjust cyclically the current how in said continuous circuit to values successively below and above that at which said feeder will continue to feed material. Y
2. Incombination, a feeder of the vibratory electric type, a source of current for energizing