US 3637123 A
A strip feed control apparatus for controlling the size of a loop formed in a continuous strip of material extending between a strip issuing machine and a takeup or strip using machine. The apparatus comprises a photoelectric control for producing an on-off output signal alternating between two levels dependent on whether or not the photoelectric light beam is interrupted by the loop. An electrical circuit means converts this alternating on-off signal into a smoothly variable DC signal proportional to the rate of the alternating on-off signal. The variable DC signal is effective to adjust the speed of a variable DC drive motor which, in turn, adjusts the speed of the strip feed to vary the size of the loop so as to approach a predetermined optimum loop size.
Description (OCR text may contain errors)
ni States Patent Jones, Jr.
[ Jan. 25, 1972  STRlllP FEED CONTROL APPARATUS  Appl. No.: 37,217
Anderson ..226/42 X Minehart ..226/42 X Primary Examiner-Richard A. Schacher Attorney-Christel & Bean 5 7] ABSTRACT A strip feed control apparatus for controlling the size of a loop formed in a continuous strip of material extending between a strip issuing machine and a takeup or strip using machine. The apparatus comprises a photoelectric control for producing an on-off output signal alternating between two levels dependent on whether or not the photoelectric light beam is interrupted by the loop. An electrical circuit means converts this alternating on-off signal into a smoothly variable DC signal proportional to the rate of the alternating on-off signal. The variable DC signal is effective to adjust the speed of a variable DC drive motor which, in turn, adjusts the speed of the strip feed to vary the size of the loop so as to approach a predetermined optimum loop size.
13 Claims, 3 Drawing Figures PATENTEU JAN25 1972 SHEET 1 (IF 3 INVENTOR. CLAQENCE O. JONES, JR
BY W ATTOR N EYS PATENTEI] JAN25I972- SHEEI E W 3 ilkfiwwl INVENTOR. CLARENCE O. JONES J52.
ATTOQ NEYS sum 5 m '3 \J 3 C am 8 mm @Q m 2% m F Nm mm mm PATENTED M25 I972 INVENTOR. CLARENCE O. JONES, JD.
ATTOQNEYS STRIP FEED CONTROL APPARATUS BACKGROUND OF THE INVENTION This invention relates to a strip feed control apparatus and, more particularly, to an apparatus for controlling the slack in continuous strip stock advancing between two machines.
In the art of metal strip stock conditioning and utilization, wherein a continuous strip of material is advanced between various strip conditioning and/or forming machines, such as between a stock straightener and a press, for example, a certain amount of slack in the stock, which takes the form of a loop, is necessary to adjust the straighteners continuous output to the intermittent takeup of the press;
Various attempts have been made to automatically maintain a certain amount of stock slack, hereinafter referred to as a loop, between such machines and to control the size of the loop between a zero-slack condition and an excessive slack condition to insure proper functioning of the associated machines. To this end, loop controls of various types have been designed and usually comprise a pivotal mechanical element or arm having a roller at its distal end for engaging the looped portion of the stock. As the loop size varies, the arm is pivoted thereby to actuate either of a pair of limit switches at the minimum and maximum loop positions of the arm for controlling the feeding speed of the stock through the straightener thereby increasing or decreasing the loop size, as required.
While many such prior known loop control devices are available for the above purposes, they possess certain disadvantages. Because of the rapid operation of the press and consequent rapid intermittent takeup of stock, the control system may be energized and deenergized as many as 200 times per minute, causing wear and failure of the many electrical components required in such systems such as motors, limit switches, clutches, relays and the like. Also, continual contact of the mechanical arm with the advancing stock marks and scars the same, which is particularly undesirable with todays costly exotic metals.
SUMMARY OF THE INVENTION The strip feed control apparatus of the present invention, as hereinafter described, eliminates the above disadvantages by employing a single on-off switch which reverses its position each time the greatest part of the loop passes a predetermined median line in one direction or the other, or each time the greatest part of the loop reaches a predetermined limit position and each time it moves from such limit position. In one form of the invention a photoelectric cell is successively ac tivated and deactivated by the on-off. switch to produce a digital signal which is converted to an analog signal proportionate to the frequency of alternation of the digital signal.
This general arrangement provides a simple circuit means for automatically maintaining and controlling the loop size of continuous stock advancing between two machines without the necessity of contacting the loop, thereby precluding undesired scoring or marking of the stock material. Also, because of the elimination of numerous electrical components having moving parts normally subjected to rapid operations, wear and breakdown of the control system is minimized thereby increasing efficiency and realizing a savings in costs.
Generally speaking, the strip feed control apparatus of the present invention comprises a photoelectric control for generating an on-off output signal having a frequency proportionate to interruptions of continuity in the photoelectric light beam caused by a loop of stock material extending between a stock straightener and a forming machine having an intermittent takeup. This on-off output signal frequency is converted through electrical circuit means into a variable DC signal proportional to the frequency of the on-off signal and effective to adjust the feeding speed of the straightener, as required, to decrease or increase the size of the loop. The system is preferably designed to achieve a one-half on time and one-half off time of the photoelectric output signal.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view, with portions broken away, of one form of strip feed control apparatus of the present invention shown in conjunction with a continuous strip stock straightener and a power press;
FIG. 2 is a fragmentary front elevational view, on an enlarged scale, of the upper portion of the stock straightener of FIG. 1, showing the straightening rolls and drive connections therefor; and
FIG. 3 is a diagrammatic view showing one form of electrical circuit control means employed in. the illustrated embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, there is shown in FIG. I a stock straightener, generally designated 10, for removing the curvature from a continuous strip of. stock material 11 issuing from a payoff reel (not shown). The stock 11 is fed from the straightening machine 10 in the form of a loop 12 and is intermittently fed or taken up by a power press, generally designated I3, having the usual feed roll 14, a ram 15 and bed 16 as is well known in the art. Although it will be convenient to describe the apparatus of the present invention in connection with a straightener and a press, it should be understood that the strip feed control apparatus of this invention has utility in any environment where loop control is desired, such as in connection with straighteners, reels, cradles or any combination of the above, for example.
Straightener 10 comprises a rectangular boxlike frame 18 supported on a base 19 and having a straightening head 20 mounted on the upper end of frame 18. A series of drive rolls 22 and idler rolls 23 are mounted on shafts 24 and 25, respectively, suitably journaled in head 20 for receiving the stock material 11 therebetween and straightening the same. A pair of power driven pinch rolls 26 are mounted at the entry end of head 20 and a pair of power driven pinch rolls 27 are mounted at the discharge end of head 20.
Means are provided for imparting driving force to drive rolls 22 and pinch rolls 26, 27, such means comprising a variable drive DC motor 29 mounted in frame 18 for rotating a drive shaft 30 through a suitable gear reduction mechanism 31, also mounted in frame 18. A sprocket 32 is rigidly secured to shaft 30 for engagement with an endless drive chain 33, also trained about sprockets 34 and 35, a takeup sprocket 36, and sprockets 37 and 38. As shown in FIG. 2, sprockets 34, 35, 36, 37 and 38 are rigidly secured on shafts 40, 41, 42, 43 and 44, respectively, suitably journaled for rotation in head 20 and frame 18. Shaft 40 is provided with a pinion 46 engaging a gear 47 mounted on the lower pinch roll 26, in turn engaging a gear 48 mounted on the upper pinch roll 26. Since the peripheries of the pinch rolls and the pitch circles of the gears connecting them are substantially coincident, the same dotted circles represent both in FIG. 2. Shaft 41 is provided with a pinion 49 engaging gears 50 and SI mounted on the first pair of shafts 24.
In a similar manner shaft 43 is provided with a pinion 53 meshing with gears 54 and 55 mounted on the second pair of shafts 24. Mounted on shaft 44 is a pinion 56 meshing with a gear 59 rigidly secured on the lower pinch roll 27 and a further gear 57 on shaft 44 meshes with a gear 58 mounted on the upper pinch roll 27. Thus, motor 29 transmits driving force to drive rolls 22 and pinch rolls 26, 27 by means of the sprocket and endless chain arrangement and the gears associated with such rolls. Idler rolls 23 are driven by the movement of the strip material 12. It should be appreciated that the specific straightener shown and described above is illustrative only of one type of straightener and that the number of drive rolls 22, idler rolls 23, and the specific gearing arrangement may vary within the purview of this invention.
A significant feature of the present invention is the provision of means for controlling the size of loop 12. Such means comprises a photoelectric control 60 for emitting a light beam from a suitable light source in the control 60 to a reflective target 61 and for receiving the reflected beam on the same axis onto a suitable photocell in the photoelectric control 60 to produce an output signal. The output from photoelectric control 60 to produce an output signal. The output from photoelectric control 60 is an on-off or square wave, digitaltype signal which alternates between two levels depending upon whether or not the light beam is interrupted by loop 12. This alternating on-off or digital signal is converted through circuit means, hereinafter described, to a variable DC or analogue signal to, in turn, etTect an adjustment of the speed of motor 29 for increasing or decreasing the speed of drive rolls 22, as required. In other words, as the strip material 11 is intermittently taken up by press 13 thereby decreasing loop 12 to permit passage of the light beam, the speed of drive rolls 22 tends to be increased. When the feed to press 13 is interrupted, thereby increasing loop 12 to interrupt the light beam, the speed of drive rolls 22 tends to be decreased.
FIG. 3 shows a preferred control system for regulating the speed of motor 29 and thereby the feeding speed of straightener in response to the output signal from photoelectric control 60. A portion of the control system, generally designated 59, includes a conventional closed-loop control circuit comprising an amplifier 60, the input of which is connected to the output of a summer 61 and the output of which is connected to the armature of motor 29 via line 62 having a manual forward-reverse switch 63 operatively incorporated therein. The amplifier output also is connected to the summer 61 through a resistive feedback path 64. An adjustable reference voltage developed by potentiometer 66 is applied to one input of the summer 61, and a variable DC signal voltage is applied to the other input thereof. The sum of the signal and reference voltages is present as an error voltage at the output of the summer 61 and is translated through the amplifier to drive motor 29 in a known manner.
A circuit, generally designated 68, is provided for converting the output signal of photoelectric control 60 to the variable DC signal. The photoelectric output signal is transmitted to circuit 68 via conductor 69. Circuit 68 comprises a first transistor 70 having collector, base and emitter terminals 71-73, respectively, and connected to operate as an emitter follower. In particular, collector terminal 71 is connected through a resistor 74 to a line 76 on which a reference voltage, in the present instance volts, is available. Base terminal 72 is connected to the output of photoelectric control 60 via conductor 69, and emitter terminal 73 is connected to one ter minal of a voltage divider comprising series-connected resistors 77 and 78. The junction 79 between resistors 77 and 78 is connected to one terminal of a damping potentiometer 80. The wiper arm of potentiometer 80 is connected to one terminal of a capacitor 82, the other terminal of which is connected to a line 83 on which a reference voltage, in the present instance l5 volts, is available. Line 83 also is connected to resistor 78 so as to place the other end of the voltage divider at this reference voltage. The wiper arm of potentiometer 80 also is connected through the series combination of a resistor 85 and a normally closed relay contact 86 to a line 87 on which a common or ground potential is present. A shunt or bypass thus can be provided around capacitor 82 when it is desired to operate the machine or press free of the control of the present invention, but contact 86 is opened by a suitable interlock when the control is in operation.
The circuit 68 further comprises a second transistor 88 hav ing collector, base and emitter terminals 89, 90 and 91, respectively, and connected to operate as an emitter follower. In particular, collector terminal 89 is connected to line 76 and base terminal 90 is connected to the other terminal of potentiometer 80 so as to be connected to junction 79 through potentiometer 80. Emitter terminal 91 is connected through a nected to ground potential line 87 and the wiper arm of potentiometer 94 is connected through a resistor 95 to an output voltage line 96. The variable DC signal voltage developed by circuit 68 is available between lines 96 and 87.
As hereinbefore mentioned, the output from photoelectric control 60 is an on-off or square wave, digital-type signal which fluctuates between the two levels depending on whether or not the light beam emitting from photoelectric control 60 is interrupted by loop 12. In one exemplary illustration, the output signal voltage is at a level of about +0.2 volts or off" when the light beam is reflected by target 61 and is at a level of about +1 3.0 volts or on when the light beam is interrupted by loop 12. The system operates in such a manner as to drive motor 29 at a speed so that the output signal from photoelectric control 60 is on for one-half of the time and off for the other one-half. Stating it another way, the system drives motor 29 so that loop 12 interrupts the light beam for only one-half of a given period of operation.
Potentiometer 66 is set to develop a reference voltage corresponding to the average desired takeup speed of the press in order to drive motor 29 and thereby the straightener drive rolls at a rate of speed compatible with the press takeup. For 1 example, an 02 K range on potentiometer 66 corresponds to a press speed range of 0-250 strokes or cycles per minute. This reference voltage is applied to one input of the summer 61 in control portion 59. [f loop 12 would interrupt the light beam for only one-half of the time, a zero net average voltage would appear between lines 96 and 87 so that the other voltage input to the summer 61 would be zero and motor 29 would be driven at a constant speed corresponding to the reference voltage.
The tendency of the loop 12 to interrupt the light beam more or less than one-half the time develops an alternating or on-off signal at the output of photoelectric control 60, which has a nonzero average value and which is converted by circuit 68 to a variable DC voltage between terminals 96 and 87. This variable DC voltage is applied to the summer 61 to develop an error voltage which increases or decreases the speed of motor 29 by the necessary amount. This, in turn, drives the straightener rolls at a corresponding proportional rate of speed to increase or decrease the size of loop 12.
The on-off" or square wave signal from photoelectric control 60 is applied to base terminal 72 of transistor 70 and the voltage on emitter terminal 73 follows this voltage but is reduced by the base-emitter drop of transistor 70. By way of example, assuming transistor 70 to have a 0.6-volt drop, the voltage on emitter 73 varies between -O.4 and 12.4 volts. The voltage at junction 79 is a fraction of this voltage, as determined by the relative magnitudes of resistors 77 and 78, and this voltage appears across the combination of potentiometer and capacitor 82 since relay contacts 86 are opened in this mode of operation.
Capacitor 82 is charged to a voltage level which is the average of the voltage appearing at junction 79. The rate at which this occurs can be adjusted within the range of potentiometer 80 which affects the smoothness of the output signal. By way of example, potentiometer 80 has a range of 0-50 K and capacitor 82 is rated at 50 u.f., 50 volts. It should be understood that the specific ranges and ratings of any of the above components are exemplary only and are not intended in any manner to be restricted thereto but may vary in range and ratings as dictated by the particular application.
The relatively smoothly varying DC voltage is applied to base terminal of transistor 88, and the voltage on emitter 91 follows this voltage, but again reduced by the base-emitter drop. A certain amount of this voltage appears between lines 96 and 87, the exact amount depending on the setting of loop gain potentiometer 94. Potentiometers 80 and 94 can be adjusted against each other to achieve a desired degree of loop stability for a given adjustment in damping and to provide relatively more latitude in changing the speed of the press 13 without changing the reference voltage through potentiometer 66.
Thus, the above described circuit 68 converts the pulsating on-off" or square wave signal from photoelectric control 60 to a relatively smoothly varying proportional DC voltage appearing between lines 96 and 87. This voltage is compared to the reference voltage developed by potentiometer 66 by means of the summer 61 which generates an error voltage for increasing or decreasing the speed of motor 29, as required, to increase or decrease the rate of speed of the straightener drive rolls 22 and the pinch rolls 26 and 27 whereby the size of loop 12 is automatically controlled.
The electric circuit of FIG. 3 includes an input voltage supply to photoelectric control 60 via conductors 100 and 101, a transformer 102, and conductors 103, 104 connected to a suitable source of electric power. Conductors 103, 104 are also connected to control portion 59 to provide an input voltage supply thereto. A manually operable starting switch 105 is provided in conductor 103 for connecting photoelectric control 60 and control portion 59 to the source of electric power. Since the remainder of the circuit shown in FIG. 3 is conventional and forms no part of the present invention, it is believed that no further amplification nor'detailed illustration thereof is necessary.
As a result of this invention, an improved strip feed control apparatus is provided for automatically maintaining a slack loop in strip stock in an improved and more efficient manner and without the usual abrupt speed adjustments of the strip feed mechanism. By the provision of a photoelectric control and an electric control system, the feeding speed of the stock drive rolls is increased or decreased smoothly as required to maintain the loop size within a tolerable range. Moreover, the loop control means does not contact the loop thereby avoiding undesired marking or scoring of the stock.
While interruption of a light beam by the loop as it changes in magnitude has been described herein as the preferred method of aggravating the on-off switch which provides a digital control signal, it is to be understood that other means may be employed in place of the photoelectric means within the purview of the invention. For instance, a floor plate may be provided beneath the loop 12 with circuit connections such that an electric circuit is made each time the loop increases in size to a point where it contacts the floor plate and which circuit is broken each time the loop, upon decrease in mag nitude, moves out of contact with the floor plate. The on-off signal thus generated may be connected into the control cir' cuitry of FIG. 3 in the same manner as the output signal of the photoelectric control 60 is applied in the principal embodiment.
A preferred embodiment of this invention having been described and illustrated in the drawings, it is to be realized that modifications thereof may be made without departing from the spirit and scope of this invention.
1 claim: I
1. Strip feed control apparatus comprising: means for feed ing a continuous strip of material having a loop of slack material formed therein beyond the discharge end of said feeding means, means for sensing an increase or decrease in the size of said loop relative to a reference size, means responsive to said sensing means for generating a digital signal having a frequency determined by the number of times the size of said loop increases or decreases relative to said reference size, means converting said digital signal to an analogue value proportional to the frequency of said digital signal, and means responsive to said analogue value for adjusting the speed of said feeding means to maintain the size of said slack loop within predetermined limits.
2. A strip feed control apparatus according to claim 1 wherein said sensing means comprises photoelectric means.
3. Strip feed control apparatus according to claim 2 wherein said last mentioned means includes a variable speed electric motor and drive means connecting said :motor to said feeding means.
4. Strip feed control apparatus according to claim 1 wherein said last-mentioned means includes a variable speed electric motor and drive means connecting said motor to said feeding means.
5. Strip feed control apparatus according to claim 1 wherein said feeding means comprises a plurality of rolls for advancing said continuous strip of material.
6. Apparatus according to claim 1 wherein said photoelectric means includes a light source for emitting a light beam in the path of said loop and a photocell for sensing said light beam, whereby interruption of said light beam by an increase in the size of said loop tends to effect a decrease in the rate of speed of said feeding means and reestablishment of said light beam by a decrease in the size of said loop tends to effect an increase in the rate of speed of said feeding means.
7. Apparatus for controlling the size of a loop formed in a continuous strip of material issuing from a first machine and taken up by a second machine comprising: means mounted on one of said machines for feeding said strip, means for sensing an increase or decrease in the size of said loop relative to a reference size, means responsive to said sensing means for producing an alternating on-off signal having a frequency determined by the number of times the size of said loop increases or decreases relative to said reference size, electrical circuit means for variably converting said alternating on-off signal to a DC signal proportional to the frequency of alternation of said on-off signal, and means responsive to said variable DC signal for adjusting the rate of speed of said feeding means to vary the size of said loop to approach said reference size.
8. Apparatus according to claim 7 wherein said sensing means comprises photoelectric means.
9. Apparatus according to claim 8 wherein said photoelectric means comprises a light source for emitting a light beam across the general path of said loop, and a photocell for sensing said light beam.
10. Apparatus according to claim 9 wherein an increase or decrease in the size of said loop interrupts or reestablishes said light beam and thereby actuates said on.-off-signal-producing means.
11. Apparatus according to claim 8 wherein said photoelectric means includes a light beam which is interrupted by an increase in the size of said loop and reestablished by a decrease therein, whereby said increases and decreases produce said on-off signal.
12. Apparatus according to claim 7 wherein said last-mentioned means includes a variable speed DC electric motor and drive means connecting said motor to said feeding means.
13. Apparatus according to claim 7 wherein said feeding means comprises a plurality of rolls for advancing said continuous strip of material.