US2280948A - Inspection scheme - Google Patents

Description

April 28, 1942. F. H. GULLIKSEN INSPECTION SCHEME Filed Sept. '7, 1939 fnferzhanye and 72/66 ?6 FQVIsfOr'JE f0 hare opera/fan responsive fa decrease r'nareac o/r'ncrease of [flum/na/v'an 0/7 0/)070 fubes.

INVENTOR WITNESSES: @547; 5?;

WW m 6 m H. am MUM Patented Apr. 28, 1942 2,280,948 FFICE INSPECTION SCHEME Finn H. Gulliksen, Pittsburgh, Pa., Westinghouse Electric & Manufac Pittsburgh, Pa.,

pany, East Pennsylvania assignor turing Coma corporation of Application September 7, 1939, Serial No. 293,735 7 Claims. (01. 250-415)- My invention relates to photo-electric apparatus and is directed more specifically to a special type control system.

An object of my invention is to provide photoelectric apparatus which is responsive solely as the result of a predetermined condition of illumination occurring simultaneously on two separate light-sensitive devices.

Another object of my invention is to provide a relay which is energizable solely as the result of predetermined conductivity of an impulse control discharge tube and a static control discharge tube occurring simultaneously.

Another object of my invention is to provide a relay which is energizable solely in response to increase (or decrease) in illumination of one light-sensitive device and which is deenergizable solely as a result of increase (or decrease) in illumination of another light-sensitive device.

Other objects and advantages will become more apparent from a study of the following specification when considered in conjunction with the accompanying drawing, in which:

Figure 1 is a schematic showing of an object having a certain characteristic on a portion thereof which is to be analyzed;

Fig. 2 is a schematic showing of an optical sys tem for photo-electrically analyzing an object, such as a rivet;

Fig. 3 is a schematic showing of a control system for analyzing the presence or absence of a hole in a rivet; and

Fig. 4 is a schematic showing of a modification of the control system in Fig. 3 wherein such control system is adaptedl'or the spraying of wall boards or similar devices.

Referring more particularly to Fig. 1, numeral I denotes an object of any kind such as, for example, a letter, card, piece of sheet metal, or, in fact, any object which has a certain characteriscorrect position. Object I could likewise be a plate which is to be analyzed to determine whether or not a When such condition exists a way to an incident light beam and which is reiiective in a difl'erent way as the result 01 the absence of such characteristic.

In the past, inspections have been generally made by mechanically registering the position 01 the article. However. this scheme is slow and expensive and is not adapted for high-speed analysis of objects while in motion. Such systems, in the past, have generally involved the use oi mechanical limit switches which had to be periodically replaced because of excessive wear due to the-high number of operations required within a short period 01' time.

As an example of an object which is to be anaylzed for the presence or absence of a certain characteristic, a rivet 3 is shown in Fig. 2 which normally should have a hole 4 coaxially drilled into one end thereoi. it all previous operations have been carried out correctly. A light source mally does not illuminate a phototube P2, either when the rivet is out of the analyzing position or whenit is in the analyzing position and a hole 4 occurs therein, because in the latter instance the hole 4 disperses a light beam in some other direction than the direction 01 P2. However, if for some reason, due to faulty operation or some part of the machine which forms the rivet, hole 4 has not been made, then a reflective surface will be present at the edge of the rivet which will reflect light onto phototube P: such magnetically-operated, spring-released plunger 6 will be operated to throw rivet! into a container 1. Phototube P1 controls an impulse responsive amplifier tube T1 so that this tube will produce a control eilect controls the volti2 and II. It will thus be seen that phototube P2 can control tube T: only during the short time when P1 exercises impulse control on tube T1 which will appear more clearly hereinafter.

as shown in Fig. 3;

in impulse controlled which is connected- Assume Pi is normally continuously illumin'at'ed so that its resistance is low. This means that condenser 9 is charged as indicated. Resistor a limits the negative bias on the grid of tube Tl to a given value and the result is that tube Tl carries a predetermined current between its principal electrodes. When the light beam between L: and Pi is intercepted by the presence or a rivetjthe resistance of Pi abruptly rises and condenser 8 discharges through resistors b and c and thus places a very high negative bias on the grid oftube T1. The current between the principal electrodes tube T1 drops to some relatively low value, that is. toward zero current, for the period of discharge of condenser 8. From this analysis it is apparent that P1 and T1 are connected for dark spot operation. It takes an abrupt change from light to dark on P1 to the current in T1.

When the current in T1 is driven to zero. the junction d becomes positive and tube T: will conduct current or not conduct current depending on the conditions of lumination on P2.

Since tube P2 is of the type to be normally non-conducting, it becomes conducting only when illuminated by reason of the presence 01 a defective rivet in such position as to illuminate Pa. The negative bias produced by battery II on the grid oi tube T: will in such case be sufllcient to prevent tube T: from increasing its current between its principal electrodes even though junction d becomes more positive by reason of the sharp decrease in current through tube T1.

However, when P: is illuminated its resistance drops abruptly. Resistor R: is preferably chosen to have a larger resistance value than resistor R1. This means when tube T1 is momentarily nonconducting, that the negative bias of battery H is overcome and junction d becomes suiiiciently positive to cause an increase in current through tube T2 to thus energize solenoid 5. P: will not influence the anode-cathode circuit impedance of T2 because it is in parallel therewith; and because of the magnitude of this impedance with respect to the anode-cathode circuit impedance oi the vacuum tube T2. However the negative grid potential of T2 is decreased by virtue oi current flow through P: as the result of an IR drop through R2. This drop together with the decreased drop across Ri (due to an impulse from Pi) results in a grid voltage in tube T: which is greater than its critical voltage which therefor allows tube T2 to become conducting. The length of time tube T2 is heavily conductive depends on the constants of the elements of the circuits. I so chose the constants of condenser 9, resistors R1, R2. etc., to make certain that solenoid 5 is energized long enough to actuate plunger 6 to throw the rivet into the receptacle 1. As soon as the rivet has been sorted out the circhange than the impulse on tube T1 occurs after the time the control potential on the static controlled tube T1 is applied (and while it is still on) or at the same time thereof, in other words. both must occur simultaneously. If the impulse occurs before the static control is operative the relay will not be operated.

The wallboard spraying machine control as shown in Fig. 4 also avoids the use 01' mechanical limit switches and is arranged so that relay 20 must become energized when the trailing edge E of the wallboard W leaves position I, and the relay 20 will remain energized until the trailing edge E leaves position 11, positions I and 11 being in the paths of the respective light beams.

My control system illustrated in Fig. 4 will accomplish this control sequence without using any mechanical interlock relays. As shown in Fig. 4, two high vacuum tubes 2! and 22 and two thyratron tubes 22 and 24 are used. I Phototubes 25 and 28 control tubes 2i and 22, and are connected to give impulse control so that the current through tubes 2| and 22 will remain constant unless the illumination on the phototubes is changed abruptly. Tubes 2| and 22 have such characteristics that a normally zero grid voltage supplied by resistors 21 and 28 will produce a current through the tubes, normally near the maximum value. Due to the "impulse" capacitors 29 and 30 the current through tubes 2| and 22 will remain at maximum value, except when the illumination on the phototubes is increased suddenly, in which case the tube current will be reduced to practically zero. An alternating current source I! and a direct current source I8, 01'

a conventional type, are fed by a. transformer H are shown at the lower portion of Fig. 4. In other words serially connected tubes 22 and 23. when both conductive, apply a negative potential to tube 24 with respect to its own grid, that is. the grid voltage of tube 24 is increased to a value which exceeds its critical grid bias. This action is tantamount to connecting the cathode oi tube 24 to the cathode of tube 24, the latter being at a more negative potential than the grid of tube 24 hence the grid voltage of tube 24 is in excess of the critical grid bias thereof making tube 24 conductive providing the anode voltage is at the correct polarity and potential. Tube 24 does not conduct when 22 and 23 are non-conducting due to the negative DC voltage applied to the grid of tube 24 from the right hand section of the DC potentiometer resistor source.

Assuming now that the wallboard is in the position shown in Fig. 4, the tubes 23* and 24 will be deenergized and tubes 2| and 22 will conduct maximum current. When the wallboard moves cults are again stabilized to be ready to again operate when a defective unit is in the paths of the light beams.

I designate tube T1 an impulse tube grid bias, for the operations hereinbefore discussed, changes solely in proportionto the rate of change of illumination of P1, whereas tube T: I designate as a static control tube because its grid bias changes only in accordance with the change of illumination of P2. The grid of tube T: may have a small positive bias so that T2 carries a because its t small current not sufficient to operate solenoid 5. When tubes Pi, P2, and T1 produce their effect, I

the grid characteristics as to polarity, but not as to value. remain the same. It is necessary either toward the right, conditions remain unchanged until the trailing edge E leaves position I. At this instant the current through tube 2| is momentarily reduced to zero and thyratron tube}! becomes ionized through tube 22, thus eflecting conduction of tube 24 and energizing relay 2!]. The relay now remains energized until edge E leaves position II, when, due to the impulse action of capacitor 30 the current through tube 22 is momentarily reduced to zero, thus de-ionizing tube 23 and deenergizing tube 24 and relay 20. When relay 20 is energized it operates a valve '.(not shown) which opens a nozzle 2| .which sprays paint on the wallboard. It will be obvious that instead of operating a nozzle. relay 20 could operate any other means such as a machining tool, saw or any other device which performs an operation on the wallboard only during the period starting when trailing edge E leaves position I until it leaves position II on its movement to the right.

To briefly summarize the operation in Fig. 4, it will be seen that only upon increase in illumination falling on phototube 25 does relay become energized, and only upon increase of illumination of phototube 26 does relay 20 become deenergized. Decreasing of illumination of either tube has no eflect. Ii, however, it were desired to have a system in which a decrease in illumination on phototube energizes relay 20 and a decrease in illumination of phototube 26 26 and resistor 32.

I am, 0! course, aware that others, after having had the benefit oi the teachings of my invention, may devise other devices embodying my invention, and I, therefore, do not wish to be limited to the specific showings made in the drawing and the descriptive disclosure hereinbefore made, but wish to be limited only by the scope oi! the appended claims and such prior art that may be pertinent.

I claim as my invention:

1. An electrical control system comprising, in combination, a light source, a light responsive device cooperating therewith to detect the presparticularly control system for analyzing obiects mined characteristic thereon.

4. Apparatus as set forth in claim 3 in which said second electric discharge device is statically controlled by said second photoelectric device, that is, it is responsive to a change of illumination thereof.

5. An electrical control system comprising, in

combination, a light source, a light sensitive device cooperating therewith operating therewith so as to detect the presence of a certain characteristic on a portion of said object, and a second electric discharge device having an anode and a cathode and a control grid, and the anode of the first discharge device being connected to the grid 01 the second tube, a resistor connected im parallel with first discharge device thereby controlling the potential 01' the grid 0! said second discharge device. first light sensitive device being in the grid ciranode-cathode circuit of said second discharge device, a source oi. direct current potential connected across said first discharge device and said resistor in series relationship, a second source of direct current potential connected across said second discharge device, a relay connected in series with said second discharge device and which is operable solely in response to simultaneous presence 01 the object in said first light beam and the presence of a certain characteristic of said object in the second light beam.

6. An electrical control system comprising, in combination, a light source, a light sensitive d vice cooperating therewith to detect the presence of an object, a condenser, an impulse controlled electrical discharge tube connected with said light sensitive device and condenser so as to be responsive solely to the rate of change of illumination on said light sensitive device, a second light source, a second light sensitive device cooperating therewith so as to detect the presence of a certain characteristic on a portion of said which is deenergized solely in response and change of illumination in a predetermined direction of the other of said impulses controlled tubes.

7. An electrical control system comprising, in combination, a light of a certain characteristic on a portion of said object, a second impulse controlled electric discharge tube, a thyratron amplifier tube having a grid whose potential is controlled in accordance with the plate current of one of said impulse controlled discharge tubes. a second thyratron amplifier tube having a grid whose potential is controlled in accordanc with the plate current controlled discharge tubes. a source or direct current potential, the grid-cathode circuits of said amplifier tubes being connected in series relationship with respect to said source or direct current potential.-

FINN H. G LIKBEN.

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