US2538760A

US2538760A - Method and apparatus fob con

Info

Publication number: US2538760A
Authority: US
Publication date: 1951-01-23
Anticipated expiration: 1968-01-23

Description

Jan. 23, 1951 |-1 5, WN ETAL 2,538,760

METHOD AND APPARATUS FOR CONTROLLING MAGNETICALLY VIBRATED SCREENS Filed Dec. 16, 1947 2 Sheets-Sheet 1 A i i 25- f3 7 40 i 56 Z3 a9 33 33 37 l 30 v 45 I I Fy-f 1 SCREEN t nree r 13 5 IN VEN TORS.

HUGH 5: BROWN BY 67677437). GRANT A rrdezvers Jan. 23, 1951 H E BROWN m-A 2,538,760

L METHOD AND APPARATUS FOR CONTROLLING MAGNETICALLY VIBRATED SCREENS Filed Dec. 16, 1947 2 Sheets-Sheet 2 IN V EN TORS. HUGH 1 BROWN Patented Jan. 23, 1951 METHOD AND APPARATUS FOR CON- TROLLING MAGNETICALLY VIBRATED SCREENS Hugh E. Brown, Cleveland Heights, and Stewart M. Grant, Bay Village, Ohio, assignors to The W. S. Tyler Company, Cleveland, Ohio, a corporation of Ohio Application December 16, 1947, Serial No. 792,111

9 Claims.

The present invention relates to a magnetically operated vibrator for a screening machine and a method of control therefor.

Heretofore screens for screening materials have been vibrated by devices consisting of an electro-magnet and an armature attached directly or indirectly to the screen, the magnet being supplied with a pulsating or alternating current to impart oscillation to the armature and screen. In some instances resilient means were provided for causing the armature and the parts of the screen integral therewith to oscillate at a frequency the same as that of the current pulsations. The amplitudes of vibration were controlled by increasing or decreasing the voltage or current supplied to the magnet proportional to the amplitude desired. When the amplitude was relatively large, these vibrators were more or less satisfactory, but for smaller amplitudes, the reduction in current merely weakened the screen action so that a soft motion would result and the screen would readily clog. To overcome thisdisadvantage, some screens were designed so that at one end of the vibrator stroke the armature or its associated structure would strike a stop member and. thus impart a jarring action to the screen which would efiectivel shake material from the interstices of th screen.

This structure was objectionable in that it was extremely noisy and there wa considerable wear and strain on various parts thereof. Also, adjustments were necessary to maintain eflicient operation for various amplitudes and the exercise of skill was necessary in making the proper adjustments.

The object of the present invention is to provide a control circuit for a magnetic vibrator for a screening machine in which the vibrating element is mechanically freely floating but which is acted upon by the magnet to impart a quick reversal of movement of the screen throughout all ranges of amplitudes so that the screen will not clog due to lack of vigorous agitation of the screen.

Another object of the invention is to provide a method of controlling a magnetically operated Vibrator for a screening machine which will impart a jarring action to the screen during relatively small amplitudes of movement of the screen olely by the action of the magnet.

Other objects and advantages of the invention will be apparent from the following description of a preferred form of the invention, reference being made to the accompanying drawings wherein;

Fig. 1 is a fragmentary cross sectional view of a screening machine;

Fig. 2 is a wiring diagram of a control circuit for the screening machine; and

Figs. 3, 4 and 5 are wave diagrams indicating the relationship of certain currents in the control circuit and the corresponding motion of the screen.

Although the invention may be incorporated in various types of material handling or treating devices wherein rapid oscillation of certain parts is required, for the purpose of illustrating our invention we have shown a section'of a screening machine indicated generally at H] for screening or sorting materials according to particle size. The screen structure of the screening machine may be of any suitable conventional design and it is, therefore, not shown in detail. In the present embodiment of the invention the machine comprises a rectangular frame indicated at H to which is attached a skirt portion I2 which depends from the lower side of the frame. The frame I l is adapted to be supported by any suitable structure, not shown, and th skirt portion I2 is adapted to support a wire screen l3 which extends transversely of the lower open side of the skirt throughout the length thereof. The periphery of the screen [3 is secured between brackets I5 and I6 which are attached to skirt [2' so that the screen is relatively taut.

The screen is adapted to be oscillated vertically by a vibrating mechanism indicated at 20. The mechanism 20 is enclosed in a housing 2| which bridges the central portion of the frame H and which is attached to the frame by bolts 23. An electro-magnet 25 is attached to the upper wall of the housing structure and it comprises a core 26 and coil 31. The core has an opening 28 therein which is in alignment with the central opening of thecoil 2! for receiving an armature 30 of a vibrating element. The vibrating element is indicated generally at 3| and this element comprises a rigid plate 32 having the armature 30 attached integral therewith by brack-v ets 33, the connection between the brackets and plate and armature being effected by riveting. Adownwardly projecting post 35 is attached to the plate 32 and the lower end of the post is connected to the central portion of screen l3 so that p when the plate 32 is oscillated vertically the screen will be vibrated by th post.

The plate 32 is resiliently mounted by two sets of coiled springs one at each end of the plate and each set comprises upper springs 31 and lower springs 38. The springs 31 abut against a cen-l tering member 39 which is attached to brackets lll on the housing structure 2 l The lower springs 38 abut a centering member M which is attached to flanges t3 formed on the housing structure. The coiled springs are centered on the plate 32 b disks it which are attached. to the plate by rivets 46 and which fit within the ends of the springs. The springs are adapted to impart a vibration frequency to the plate 32 which frequency will be the same as that of the cur ent suppplied to th coil 21 of the magnet. This frequency of vibration may be determined by the dimensions, tension and material of the springs. The tension of

springs

31 and 38 may be adjusted by interposing a suitable number of shims, indi" cated at 48, between the seating members 39 and 42 and, their respective supporting brackets and flange 43. The plate 32 will vibrate at the natural frequency, or a harmonic thereof, of the loaded springs. It will be seen that when the coil 2'! is energized armature ill will be drawn upwardly compressing the springs 31! and when the flow of current to the magnet ceases armature- 3d will move downwardly and its momentum will compress spring 33 causing this spring to return the plate upwardly. By proper timing of the en ergization of the coil 2?, oscillation of the plate and its associated structure is maintained.

Referring now to Fig. 2, we have shown the supply and control circuit for supplying a pulsat" ing current to the coil 2i of the magnet. The power supply circuit includes the two lines and iii connected with the usual or so cycle commercial current and the line lid is adapted to be connected to one side of coil 2'! through. line switch and line The opposite of the coil 21? is connected by line to the anode of a grid controlled gas filled rectifier tube and the cathode of the rectifier tube is co nected to power line 5i by lines 522 switcl and line 58. The filament of the tube RT is gized by the secondary of a power transfounn P, as indicated in Fig. 2, the transformer being connected to the lines Eli and through a witch S. It will be seen that the rectifier tube is carable of permitting cu rent impulses to flow through the coil ii'l at the rate of the frequency of the alternating current supply, fo' per second, providing the grid of the tube is not negatively biased.

The grid circuit for the tube RT is adapted to be controlled by a tuned oscillator circuit adapted to'provide an alternating current of a frequency one-half that of the power supply. An important feature of the oscillator circuit is that the phase of the current cycles thereof may be shifted relative to that of the power current by manual adjustment. This oscillator circuit includes a transformer 85?, one side of the secondary of which is connected to line 5? and the opposite side of which is connected to the grid of tube RT through a suitable resistance 5i. The primary of transformer 66 is energized by a secondary 63 of transformer P and the flow of power to the primary is controlled by a vacuum tube VT, one cathode of which is connected to one side of the secondary 63 and the anode of which is connected to one side of the primary of transformer Ell through a primary winding of a center tapped transformer M. The opposite side of the primary of transformer 65 is connected directly to one side of secondary coil 63 and a condenser at is connected in shunt with the primaries oi transformcrs 69 and H3. The grid of the v cuum e VT is connected in a circuit which includes a resistor iii having a condenser H in shunt therewith and the resistor is attached to a circuit which includes the secondary 13 of the center tapped transformer 74. The secondary circuit l3 consists of a manually variable resistor 5'5 and an inductor i6 connected in series. The center tap of secondary 13 is connected to the cathode of tubeVT. The oscillator circuit is adapted to provide the grid of tube RT with an alternating current of 30 cycles, assuming that the power circuit is 60 cycles, so that the grid will be negatively impressed thirty times per second. By adjusting the resistor '55 the wave phase of the os illator circuit can be shifted and when adjusted to one position the grid will be negatively biased during alternate positive waves of the current in the power circuit and the current passing through the tube 55 will have an impulse frequency of 30 cycles per second. This condition is indicated in .Fig. 3 wherein line 89 indicates the phase of the 60 cycle alternating power current, line 81 indicates the phase of the oscillator current and the shaded areas t2 indicate current passing through the tube RT and consequently the current through the coil 2?.

When this condition prevails the vibrator ele-- t will oscillate at its maximum amplitude which illustrated graphically by line 8d, as near be ascertained. If it is desired to reduce the amplitude of the screen for screening finer ials, for example, a current impulse is in- "posed between the normal impulses illustrated a 82 and this is accomplished by adjusting the var able resistor to cause shifting of the phase of L .-e oscillator current so that the grid of tube will be positive during all or a portion of the posltye phase of the power waves intermediate the normal waves 82, and thereby permit passage of current through the coil. This phase shifting illustrated in Fig. l wherein the shaded area 85 indicates; current flowing to the coil 2? interme dlate the normal impulses or waves This additional flow of current apparently restrains the normal downward movement of the screen be tween the normal so cycle current impulses so that the armature will more quickly respond to the succeeding normal current impulses wher by a more sudden reversal in the direction of the :reen is eiiected. not only reduces the plitude of the screen but at the same time it ases the speed at which the screen reverses direction so that a substantial jarrin action occurs in the screen. The lines 534 in Figs. 3, i ant 5 illustrate the vertical movement of the screen as plotted against the time of the current frequencies, as near as can be determined, and it will be seen that as the degree of phase shifting of the osc llator current is increased the current of the intermediate impulses are increased there by further reducing the amplitude of the screen nd increasing the vigor of its action. As the phase of grid current is shifted it will not remain positive throughout the normal waves 82, but once current starts to pass through rectifier tube VT it will continue for that wave phase although in the meantime the grid shifts to a negative bias. Thus, it is necessary to have the grid of the tube positive only at the initiation. of the normal power cycles. We have found that the amplitude is reduced in the manner deimibed, the screen action becomes sharper so that the will not clog due to its violent motion. By our control instead of reducing the current to r-duce the amplitude, the current used is actually increased and this increase results in more power being applied to the effective vibration of the screen.

It will be seen that there are no rubbing or striking of parts of the vibrating mechanism so that the screen is not only practically noiseless in its operation, but there is no part subject to wear or unusual stresses. The range of amplitude of vibration is wide and the only adjustment necessary is that-of the variable resistor which can be controlled by merely turning a knob.

Although we have described but one form of the invention, it is to be understood that other forms might be adopted, all falling within the scope of the claims which follow.

We claim:

1. A control circuit for a magnetic vibrator which comprises, a grid controlled gas tube rectifier; a circuit for supplying alternating current of a predetermined frequency to the rectifier; and control means for said grid consisting of a tuned oscillator circuit, said circuit being adapted to supply an alternating current to said grid and having a frequency which is a sub multiple of the first mentioned current, and a phase shifting circuit associated with said oscillator circuit for shifting the phase of the current in the oscillator circuit relative to that of the first mentioned current.

2. A control circuit for a magneti vibrator which comprises, a grid controlled gas tube rectifier; a circuit for supplying alternatin current of a predetermined frequency to the rectifier; and control means for said grid consisting of a tuned oscillator circuit, said circuit being adapted to supply an alternating current to said grid and having a frequency of one-half that of the first mentioned current, and a phase shifting circuit associated with said oscillator circuit for shifting the phase of the current in the oscillator circuit relative to that of the first mentioned current whereby said rectifier is operative to pass one phase of alternate waves of the alternating current and fractional portions of one phase of the waves intermediate said alternate waves.

3. The method of controlling a magnetically operated material handling screen having a substantially predetermined vibration frequency, which method comprises supplying pulsating current to the magnet having a frequency substantially the same as the predetermined vibrating frequency of the screen, and introducing a pulsating current to the magnet which latter pulsating current is out of phase with the pulsations of the first mentioned current pulsations.

4. The method of controlling a magnetically operated material handling screen having a substantially predetermined vibration frequency, which method comprises supplying pulsating current tothe magnet having a frequency the same as the vibrating frequency of the screen, and reducing the amplitude of vibration of the screen by introducing an additional current to the magnet at the same frequency but out of phase with said screen.

5. A control circuit for an electro-magnetically vibrated screening mechanism comprising, a circuit including a source of alternating current for the magnet; a gas filled grid controlled tube but 6 in said circuit for controlling the fiow of current to the magnet; and a control circuit for the grid comprising an oscillator for producing an alternating current on the grid having a frequency one half that of said alternating current, said control circuit having means for shifting the phase of the alternating current on the grid relative to the first mentioned alternating current.

6. The method of controlling a magnetically operated material handling screen having a substantially predetermined vibration frequency, which method comprises supplying to the magnet pulsating current at a frequency equivalent to the vibrating frequency of the screen, and reducing the amplitude of vibration of the screen by introducing current to the magnet at the same frequency of said predetermined frequency of vibration of the screen but intermediate to said first mentioned pulsating current and out of phase with said pulsating current, said alternate intermediate impulses being of a lesser value than said first mentioned pulsation whereby Said intermediate impulses diminish the negative amplitude to accelerate the screen action.

.7. An electromagnetic vibrator for vibrating a material handling screening machine, comprising a coil, an armature, a resilient means for mounting the armature relative to the magnet for oscillating motion, means interconnecting the armature and screen, and a control circuit for said magnetic vibrator comprising, a grid controlled gas tube rectifier; a circuit for supplying alternating current of a predetermined frequency to the rectifier and coil, control means for said grid consisting of a tuned oscillator circuit being adapted to supply an alternating current to said grid and having a frequency which is a sub multiple of the first mentioned current, and a phase shifting circuit associated with said oscillator circuit for shifting the phase of the current in the oscillator circuit relative to that of the first mentioned current.

8. A magnetic vibrator of the character defined in claim 7 in which the oscillator circuit for controlling the grid of said rectifier is adapted to supply a pulsating current of one half the frequency of that of the alternating current supply.

9. In an electromagnetic vibrator having a coil and armature, rectifier tube, source of alternating current, and circuit including all of these elements, means to control amplitude of vibration of the armature comprising a phase shiftin circuit and an oscillator adjusted to introduce to the rectifier a pulsating current intermediate the pulses of the alternating current supply tocheck the impressed reciprocating movement of the armature and thereby accelerate the movement of the vibrated element.

HUGH E. BROWN. STEWART M. GRANT.

REFERENCES CITED The following references are of record in the file of this patent:

' UNITED STATES PATENTS Number Name Date