US3382366A

US3382366A - Edge following device employing servosystem having bridge with complementary transistors

Info

Publication number: US3382366A
Application number: US427877A
Authority: US
Inventors: Irvin D Johnson
Original assignee: Marathon Oil Co
Current assignee: Marathon Oil Co
Priority date: 1965-01-25
Filing date: 1965-01-25
Publication date: 1968-05-07
Anticipated expiration: 1985-05-07

Description

y 1968 I. D. JOHNSON 3,382,366

EDGE FOLLOWING DEVICE EMPLOYING SERVOSYSTEM HAVING BRIDGE WITH COMPLEMENTARY TRANSISTORS Filed Jan. 25, 1965 I 2 Sheets-Sheet 1 INVENTOR j/myorm ON ATTORNZ/(Z y 1968 l. D. JOHNSON 3,382,

EDGE FOLLOWING DEVICE EMPLOYING SERVOSYSTEM HAVING BRIDGE WITH COMPLEMENTARY TRANSISTORS Filed Jan. 25, 1965 2 Sheets-Sheet 2 United States Patent EDGE FOLLOWING DEVICE EMPLOYING SERVO- SYSTEM HAVING BRIDGE WITH COMPLEMEN- TARY TRANSISTORS Irvin D. Johnson, Littleton, C0lo., assignor to Marathon Oil Company, Findlay, Ohio, a corporation of Ohio Filed Jan. 25, 1965, Ser. No. 427,877 11 Claims. (Cl. 250-202) The present invention relates to devices for the determination of physical dimensions of objects and for follow ing the edges of objects. In particular, the present invention relates to electromechanical optical devices for automatically following the edges of objects without mechanical contact.

The present invention comprises devices for the following of the edges of opaque objects, including lines drawn on paper by meanings of radiation sources, preferably electric lights, detectors so positioned that the edge of the opaque objects to be followed cut off a portion of the radiation which would otherwise fall on said detectors and means for causing movement of either or both of said detector and said radiation source so as to maintain substantially constant the amount of light cut off by said opaque object.

FIGURE 1 is an illustration of the electromechanical components of a preferred embodiment of the present invention.

FIGURES 2 and 2a are illustrations of the electromechanical components of other preferred embodiments of the present invention.

FIGURE 3 shows preferred electrical circuitry used in the controller element of the present invention.

FIGURE 3a shows a modification of the preferred circuitry for use in a specialized variation of the present invention.

In FIGURE 1 a cylinder having a somewhat irregular diameter x moves along its major axis in a direction equivalent to moving out of the paper. A source of incandescent illumination 22 shines a beam of radiation 21 upward toward a photocell 23. A carriage 24 slides along a guide bar 26 back and forth in a path approximately perpendicular to the major axis of the cylinders 20. The carriage is propelled by a screw drive which is offset from the plane of the light beam 21 so as not to interfere with the beam. The screw drive is propelled by a reversible DC motor 27, which is powered through a controller 31 which starts and stops the reverses the motor in response to electrical signals received from the photocell 23. An adjustable potentiometer 32 is turned so that no power flows to the motor 27 when approximately half of beam 21 is interrupted by the object 20. A roller support maintains the left side of the cylinder 20 in a fixed position. As the cylinde-r becomes narrower (dimension x decreases), less of beam 21 will be interrupted by the cylinder and a greater portion of the face of photocell 23 will be exposed to light, thus causing the signal fed by the photocell to controller 31 to increase. The controller will then energize motor 27 to drive carriage 24 to the left. As carriage 24 moves to the left, a greater portion of beam 21 will be interrupted by the cylinder 20 and the signal from photocell 23 will decrease. When this signal decreases to a preset value, as predetermined by adjustment of variable potentiometer tap 32, power to the motor 27 will be shut off by the controller 31. As the object grows wider (as dimension x increases), more of beam 21 will be interrupted, less of the face of photocell 23 will be exposed to light, and the signal from the photocell will decrease below the preset value. The controller with then send electrical current of reverse polarity causing the motor 27 to drive carriage 24 toward the right, until the signal from photocell 23 once again reaches the predetermined value at which point current to motor 27 will again be cut off.

Thus, in operation, carriage 24 continuously follows the right edge of the cylinder 20. Since the left edge of the cylinder 20 is always held against roller support 30, the position of carriage 24 is proportional to the thickness x of the cylinder at any point along its major axis which is passing through the light beam 21. A sensitive slide-wire potentiometer 28 mounted in contact with the screw feed 25 continuously varies in resistance in proportion to the position of the carriage 24, and therefore, in proportion to the thickness of the cylinder 20.

The resistance of the slide-wire potentiometer 28 may be digitized, as by, a power supply and a digital volt meter, or recorded as on a conventional linear chart drive recorder coupled with a mechanism which advances a cylinder 20 along its major axis, or shown on an oscilloscope or other display device. Alternatively, the resistance of slide-wire potentiometer 28 may be run through a time delay and used to operate a trimming tool which grinds or otherwise removes material from the cylinder 20 in order to achieve uniform thickness along its major axis.

FIGURE 2 shows a second preferred embodiment of the present invention operating in a manner similar to the embodiment shown in FIGURE 1, except that the light 22 and the photocell 23 are mounted on the same portion of carriage 24 and the beam from the light projects downward toward mirror 29 which reflects the beam upward to the photocell 23. FIGURE 2a shows a further modification which may be made by mounting the photocell 23 and the light 22 on a wheel 32 connected by gear drive 33 which rotates the wheel when it is turned by motor 27. As in the previously discussed embodiments, motor 27 is controlled by a controller 31 which receives signals from the photocell 23. Slide-wire potentiometer 28 is moved in relation to the rotation of the wheel 33.

FIGURE 3 shows preferred electrical circuitry for the controller 31. This circuitry is itself inventive, and it is discussed more fully and claimed in my copending application of the same assignee, Ser. No. 420,970, filed Dec. 24, 1964, now abandoned.

The basic elements of the electrical circuitry illustrated in FIGURE 3 are a DC power supply 33, a rebalanceable bridge circuit formed by resistance elements R R R and R and a reversible DC motor 27. R is the photocell 23 shown in FIGURES 1, 2, and 2a, and R is the variable potentiometer resistance controlled by turning tap 32 shown in FIGURE 1. R and R are fixed resistances. Two pairs of complementary transistors are connected across two junctions of the bridge. When the resistance of R (photocell 23) is just sufiicient to balance the bridge, no current flows to motor 27. When the resistance of R decreases so that the bridge is unbalanced, a path of current flow from power source 33 is open d through

transistors

33, 34, 40, 39 and 42 to motor 27 driving the motor in a direction which tends to cause the edge of the object being measured 20 to interrupt a lesser portion of light beam 21. Conversely, when the resistance of R (photocell 23) increases, the current path is opened from the power supply 33 through

transistors

35, 36, 38, 37, and 41 to drive motor 27 in the opposite direction and cause a greater portion of light beam 21 to be interrupted.

FIGURE 3a shows a modification which may readily be made to the circuitry of FIGURE 3. An additional sensing element 23a is substituted for fixed resistor R Thus modified, the circuit will respond to differences in the resistance of

sensing elements

23 and 23a. This modification is useful where some ambient light falls on element 23, since variations in the intensity of such background radiation can be corrected for by pointing element 23a toward such radiation.

It should also be understood that the devices of the present invention may be used in pairs. For example, the roller 30 of FIGURES 1 and 2 could be replaced with a second optical caliper system and the outputs from both of the slide-wire potentiometer 28 could be algebraically added in a conventional electrical adder circuit so that a thickness of the object 20 was continuously measured without any contact whatsoever. In such applications, the object could be hanging rope or extruded plastic and the invention would be particularly valuable where mechanical contact would be likely to cause markings where the plastic had not yet hardened. A further variation utilizing a pair of the devices of the present invention is to mount the devices at approximately right angles so that their slide wires describe two coordinates locating the points on the edge of object 20 on a two dimensional grid system. Such a system may be utilized to create an electro-mechanical pantagraph where the template is followed by the two devices of the present invention and the output from their potentiometers 28 drives a pair of motors which in turn move an arm to trace a pattern geometrically similar to the edge of the template. In specialized applications, three devices of the present invention may be utilized so as to locate all three geometric coordinates of points on the edge of object 20.

It should be understood that while the above specific embodiments have employed incandescent radiation, infrared, ultraviolet, nuclear or other forms of radiation which may be projected in a reasonably directional beam may readily be employed with the present invetnion. Further, an AC motor with phase reversal could be employed. Also, the objects with which the invention is utilized need not be solids, but can also be printed darker or lighter spaces on paper or celluloid, etc. These and other variations of the devices and procedures described are to be included within the invention.

The present invention also comprises a bridge-controlled servosystern including a reversible motor for maintaining a condition and a desired value comprising a power supply, a motor-controlled circuit connected to said power supply, a bridge circuit connected to said power supply and having four arms forming four junctions, a transistor switching circuit connected between two opposite junctions of said bridge and having first and second outputs connected to said motor control circuit, said switching circuit comprising two pairs of complementary transistors, means connecting the base electrodes of the transistors of one conductivity type of each pair to diiferent forms of said opposite junctions, and means connecting the base electrode of each of the transistors of the opposite conductivity type of each pair to the opposite junction different from that to which its complementary transistor base electrode is connected, condition responsive variable impedance means in one arm of said bridge for varying electrical potential at one of said opposite junctions in accordance with a condition, an adjustable impedance means in another arm of said bridge for adjusting the electrical potential of the other of said opposite junctions to correspond to a desired value of the condition whereby said bridge is balanced when the potentials at said opposite junctions are equal so that no signal appears at either of said outputs, and the bridge is unbalanced when said potentials are unequal to provide an output signal on a selected one of said outputs as determined by the sense of the bridge unbalance to connect the motor to said power supply, thereby driving said motor in the direction to return the condition to the desired value to rebalance the bridge and disconnect the motor from said power supply.

Further discussion of the electrical aspects of the present invention will be found in the file of US. patent application 420,970 of Irvin D. Johnson, filed Dec. 24,

1964, for Bridge-Controlled Servosystem, now abandoned.

What is claimed is:

1. Electro-optical devices for automatically following the periphery of objects substantially opaque to radiation which objects are moving in relation to the devices, said devices operating without mechanical contact with said objects, said devices comprising in combination a source of radiation, a relatively directional radiation detector generating a quantitative electrical signal indicative of the amount of radiation to which the face of said detector is exposed positioned some distance from said source, said detector being positioned to receive radiation from said source and having a substantial area exposed to said radiation, movable support means for positioning said detector and said source in relation to said object so as to expose only a predetermined portion of said face of said detector to said radiation, reversible and stoppable drive means for moving said support in relation to said object to alternate positions so as to successively expose greater and lesser portions of the face of said detector to said radiation, a controller for operating said drive means in response to said quantitative signals generated by said detector, said controller comprising an electrical bridge circuit connected to a power supply and having four arms forming four junctions, a transistor switching circuit con nected between two opposite junctions of said bridge and having first and second outputs connected to energize said drive means, said switching circuit comprising two pairs of interconnected transistors, said detector comprising a variable impedance electrically connected in one arm of said bridge for varying the electrical potential at one of said opposite junctions in proportion to the radiation b ing received by said detector, and adjustable impedance means in another arm of said bridge for adjusting the electrical potential at the other of said opposite junctions to correspond to said preset level of the signal received from said detector, whereby said control means controls said drive means so as to decrease the area of said detector face whenever said bridge is unbalanced by a quantitative signal from said detector which exceeds a preset value which preset value corresponds to the exposure of said predetermined area of said detector to said radiation, said controller stopping said drive means whenever said bridge is balanced by a signal from said detector equal to said preset value and said controller reversing said drive means whenever said bridge is unbalanced by a signal from said detector less than said preset value wherein each of said transistor pairs comprises complementary transistors and wherein the base electrode of one transistor of each pair of complementary transistors is connected to one of said opposite junctions and the base electrode of the other transistor of each pair is connected to the opposite junction.

2. The devices of claim 1 wherein the drive means comprises a direct current motor which is electrically connected to one arm of the bridge circuit so that said motor and said bridge circuit are powered by a single direct current power supply.

3. The devices of claim 1 wherein each of said transistor pairs comprises complementary transistors and wherein the base electrode of one transistor of each pair of complementary transistors is connected to one of said opposite junctions and the base electrode of the other transistor of each pair is connected to the opposite junction;

4. The devices of claim 1 wherein a second detector is electrically connected to an arm of said bridge circuit different from the arm to which the first of said detectors is connected and wherein said second detector is located to sense background radiation, said detectors being so arranged that said drive means is controlled in response to the difference between the radiation striking the two detectors.

5. A system comprising two devices of claim 1 in substantially opposed relationship, each of said devices following a different side of an object and output means indicative of the relative distance between the detectors of the devices, whereby the combined signal from said output means is indicative of the thickness of said object.

6. A system wherein a plurality of the devices of claim 1 are utilized so as to triangulate the locations of points on the periphery of the object, with the output means providing suflicient information to locate such positions on a grid.

7. The system of claim 6 wherein at least three of said devices are utilized so as to provide sufiicient information to locate positions in a three-dimensional coordinate system.

8. A bridge-controlled servosystem including a reversible motor for maintaining a condition at a desired value comprising a power supply, a motor controlled circuit connected to said power supply, a bridge circuit connected to said power supply and having four arms forming four junctions, a transistor switching circuit connected between two opposite junctions of said bridge and having first and second outputs connected to said motor control circuit, said switching circuit comprising two pairs of complementary transistors, means connecting the base electrodes of the transistors of one conductivity type of each pair to dilferent forms of said opposite junctions, and means connecting the base electrode of each of the transistors of the opposite conductivity type of each pair to the opposite junction diiferent from that to which its complementary transistor base electrode is connected, condition responsive variable impedance means in one arm of said bridge for varying electrical potential at one of said opposite junctions in accordance with a condition, an adjustable impedance means in another arm of said bridge for adjusting the electrical potential at the other of said opposite junctions to correspond to a desired value of the 3,

condition, whereby said bridge is balanced when the potentials at said opposite junctions are equal so that no signal appears at either of said outputs, and the bridge is unbalanced when said potentials are unequal to provide an output signal on a selected one of said outputs as determined by the sense of the bridge unbalance to connect the motor to said power supply, thereby driving said motor in the direction to return the condition to the desired value to rebalance the bridge and disconnect the motor from said power supply.

9. A transistor control circuit as defined in claim 8 further comprising a power supply connected to said bridge circuit and transistors, said bridge being balanced when the potentials at said opposite junctions are equal so that said transistor pairs are non'conducting, and means rendering said potentials unequal to balance the bridge whereby one of said transistor pairs becomes conducting while the other remains nonconducting.

10. A transistor control circuit as defined in claim 9 wherein the emitters of the transistors in each complementary pair are connected in series.

11. A transistor control circuit as defined in claim 10 wherein when one bridge is unbalanced, the unequal bridge junction potentials cause One transistor pair to be forward-biased and the other reverse-biased.

References Cited UNITED STATES PATENTS 1,976,298 10/1934 Richter 250202 2,117,878 5/1938 Friedemann 250219 2,674,151 4/ 1954 Garrett et a1 250-202 2,273,920 4/1942 Evans et al. 250210 2,810,316 10/1957 Snyder 250202 3,204,109 8/1965 Goodwin 250--219 RALPH G. NILSON, Prinmry Examiner.

' M. ABRAMSON, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,382,366 May 7, 1968 Irvin D. Johnson It is certified that error appears in the ahoveidentified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 43, "cylinders" should read cylinder line 48, "the reverses" should read and reverses line 70, "with then" should read will then Signed and sealed this 25th day of November 1969.

@EA Attest:

WILLIAM E. SCHUYLER, IR.

Edward M. Fletcher, Jr.

Cominissioner of Patents Atteating Officer

Claims

1. ELECTRO-OPTICAL DEVICES FOR AUTOMATICALLY FOLLOWING THE PERIPHERY OF OBJECTS SUBSTANTIALLY OPAQUE TO RADIATION WHICH OBJECTS ARE MOVING IN RELATION TO THE DEVICES, SAID DEVICES OPERATING WITHOUT MECHANICAL CONTACT WITH SAID OBJECTS, SAID DEVICES COMPRISING IN COMBINATION A SOURCE OF RADIATION, A RELATIVELY DIRECTIONAL RADIATION DETECTOR GENERATING A QUANTITATIVE ELECTRICAL SIGNAL INDICATIVE OF THE AMOUNT OF RADIATION TO WHICH THE FACE OF SAID DETECTOR IS EXPOSED POSITIONED SOME DISTANCE FROM SAID SOURCE, SAID DETECTOR BEING POSITIONED TO RECEIVE RADIATION FROM SAID SOURCE AND HAVING A SUBSTANTIAL AREA EXPOSED TO SAID RADIATION, MOVABLE SUPPORT MEANS FOR POSITIONING SAID DETECTOR AND SAID SOURCE IN RELATION TO SAID OBJECT SO AS TO EXPOSE ONLY A PREDETERMINED PORTION OF SAID FACE OF SAID DETECTOR TO SAID RADIATION, REVERSIBLE AND STOPPABLE DRIVE MEANS FOR MOVING SAID SUPPORT IN RELATION TO SAID OBJECT TO ALTERNATE POSITIONS SO AS TO SUCCESSIVELY EXPOSE GREATER AND LESSER PORTIONS OF THE FACE OF SAID DETECTOR TO SAID RADIATION, A CONTROLLER FOR OPERATING SAID DRIVE MEANS IN RESPONSE TO SAID QUANTITATIVE SIGNALS GENERATED BY SAID DETECTOR, SAID CONTROLLER COMPRISING AN ELECTRICAL BRIDGE CIRCUIT CONNECTED TO A POWER SUPPLY AND HAVING FOUR ARMS FORMING FOUR JUNCTIONS, A TRANSISTOR SWITCHING CIRCUIT CONNECTED BETWEEN TWO OPPOSITE JUNCTIONS OF SAID BRIDGE AND HAVING FIRST AND SECOND OUTPUTS CONNECTED TO ENERGIZE SAID DRIVE MEANS, SAID SWITCHING CIRCUIT COMPRISING TWO PAIRS OF INTERCONNECTED TRANSISTORS, SAID DETECTOR COMPRISING A VARIABLE IMPEDANCE ELECTRICALLY CONNECTED IN ONE ARM OF SAID BRIDGE FOR VARYING THE ELECTRICAL POTENTIAL AT ONE OF SAID OPPOSITE JUNCTIONS IN PROPORTION TO THE RADIATION BEING RECEIVED BY SAID DETECTOR, AND ADJUSTABLE IMPEDANCE MEANS IN ANOTHER ARM OF SAID BRIDGE FOR ADJUSTING THE ELECTRICAL POTENTIAL AT THE OTHER OF SAID OPPOSITE JUNCTIONS TO CORRESPOND TO SAID PRESENT LEVEL OF THE SIGNAL RECEIVED FROM SAID DETECTOR, WHEREBY SAID CONTROL MEANS CONTROLS SAID DRIVE MEANS SO AS TO DECREASE THE AREA OF SAID DETECTOR FACE WHENEVER SAID BRIDGE IS UNBALANCED BY A QUANTITATIVE SIGNAL FROM SAID DETECTOR WHICH EXCEEDS A PRESET VALUE WHICH PRESET VALUE CORRESPONDS TO THE EXPOSURE OF SAID PREDETERMINED AREA OF SAID DETECTOR TO SAID RADIATION, SAID CONTROLLER STOPPING SAID DRIVE MEANS WHENEVER SAID BRIDGE IS BALANCED BY A SIGNAL FROM SAID DETECTOR EQUAL TO SAID PRESET VALUE AND SAID CONTROLLER REVERSING SAID DRIVE MEANS WHENEVER SAID BRIDGE IS UNBALANCED BY A SIGNAL FROM SAID DETECTOR LESS THAN SAID PRESET VALUE WHEREIN EACH OF SAID TRANSISTOR PAIRS COMPRISES COMPLEMENTARY TRANSISTORS AND WHEREIN THE BASE ELECTRODE OF ONE TRANSISTOR OF EACH PAIR OF COMPLEMENTARY TRANSISTORS IS CONNECTED TO ONE OF SAID OPPOSITE JUNCTIONS AND THE BASE ELECTRODE OF THE OTHER TRANSISTOR OF EACH PAIR IS CONNECTED TO THE OPPOSITE JUNCTION.