US3339125A - Proximity detectors - Google Patents

Description

g- 29, 1967 L. B. ALMY 3,339,125

PROXIMITY DETECTORS Filed Aug. 5, 1964 2 Sheets-Sheet 1 in Van for lawman/5. A/my 5y 72215 A #0272 a;

g- 29, 1967 B. ALMY 3,339,125

PROXIMITY DETECTORS Filed Aug. 5, 1964 2 Sheets-Sheet 2 United States Patent Gfilice 3,339,125 Patented Aug. 29, 1967 3,339,125 PROXIMITY DETECTORS Leonard B. Almy, 58 Washington St., Marblehead, Mass. 01945 Filed Aug. 3, 1964, Ser. No. 386,981 6 Claims. (Cl. 317-123) ABSTRACT OF THE DISCLOSURE This invention relates generally to proximity detectors by means of which work pieces are sensed without physical contact with a probe. More particularly the present invention relates to proximity detectors especially useful, although not exclusively so, for detecting the presence and shape of work pieces of very small dimension.

I have discovered that when the negative lead of a high voltage power supply is connected to a relatively sharp or pointed electrode and the positive lead is connected to a relatively flat electrode, a micro-ionization current flows across an air gap between the two electrodes under a voltage of three to five thousand volts if adequate current limiting resistance is introduced in series with the air gap and the spacing of the electrodes is on the order of A to /2" depending on the available supply voltage. If the current is adequately limited by appropriate resistance there is no visible corona discharge and tests with sensitive receivers placed close to the air gap have disclosed no objectionable radio frequency interference if adequate precautions are taken.

By means of a switching amplifier it is possible to actuate a relay in response to a change of as little of A1 microampere in current flow across the gap. Relay contacts by closing or opening may be employed to control devices for performing such functions as counting and inspection.

Several desirable features of the invention and many advantages will be realized from the following detailed description of an illustrative embodiment taken in connection with the accompanying drawings in which:

FIGURE 1 is a view in perspective of apparatus including three separate proximity detectors according to the present invention employed for inspecting and counting miniature lamp mounts;

FIGURE 2 is a View in perspective of a proximity detector employed for counting cans; and

FIGURE 3 is a diagram of an electric circuit associated with each detector of either FIG. 1 or 2.

Turning now to the drawings, there is illustrated in FIG. 1 an electrically conductive conveyor belt ltl-driven by suitable means in the direction of the arrow, from right to left. A-t regularly spaced intervals there are mounted on the belt a series of chucks 12 each adapted to support in upright position, a mandrel 14 having spring fingers 15 for supporting the parts of a miniature lamp mount assembly during manufacture. The mount assembly comprises a pair of lead-in wires 16 sealed in a glass bead 18 and supporting a filament 20.

In FIG. 1 the size of the mount has been exaggerated for clarity. Actually, each of the lead-in wires 16 is .004" in diameter and the spacing between the wires is approximately .040". The filament 20 is .0001 in diameter and is secured to the two lead-in wires 16.

Serving as a probe at a first inspection station in the apparatus depicted in FIG. 1 is a fiat circular disc or plate 22 having a diameter of A" to 1" and spaced from the path of the upper extremities of the lead-in Wires 16 by a distance of to /2", the diameter of the plate and the spacing being dependent upon the voltage available as will be seen. The disc 22 is connected to a positive high voltage lead 24 and the belt 10 is connected to a negative high voltage lead 26 and also grounded. Because of the presence of a high voltage direct current potential across the gap between the upper end of the lead-in wires 16 serving as one electrode and the disc 22, the other electrode, there is established in the gap, a current carrying electrostatic field 28. The presence of current flow through the filed 28 is an indication that at least one of the lead-in wires 16 is present and a current flow of 8 microamperes through the field 28 indicates the presence of both wires at their proper position. The inspection at the first station occurs before the glass bead 18 is applied to the lead-in wires 16 to secure them in predetermined relative positions.

At a later work station along the belt 10, after the bead 18 has been applied, between the lead-in wires 16, the proper positioning of the filament is checked at two more inspection stations. At the first filament inspection station there is a plate 30 similar to the plate 22 and connected to a positive high voltage lead 24, independent of that related to the plate 22. The plate 30 is fixed at a distance above the path of the filament 20 such that a current of approximately 8 microamperes flows through a field 32 established between the filament 20 and the plate 30 when the filament is present at or above its predetermined position.

Because of the fragile nature of the component parts of the work pieces, it sometimes occurs that a filament is anchored to only one of the two leadin wires 16 and the subsequent inclusion of such a lamp mount would result in a defective lamp. Such a defectively mounted filament is detected by a second filament inspection station in which a plate 34 is fixedly positioned above the path of the upper end of the lead-in wires 16 and connected to a positive high voltage lead 24 also independent of the leads associated with the plates 22 and 30. The plate 34 is sufficiently spaced from the upper end of the lead wires 16 that current flow through a field 36 established between the plate 34 and a normally positioned filament 20 reaches a low value of less than 8 microamperes. However, if the filament 20 is anchored to a single lead-in Wire 16 it has been found that, because of the operating characteristic of the filament applying apparatus, the unattached or free end of the filament tends to extend upwardly from the top of the attaching lead wire and the field 36 conducts a current in excess of 8 microamperes. Such a high current at this station indicates a defectively attached filament.

In FIG. 2 there is shown a conveyor belt 50 similar to the belt 10, but in this case connected to the positive lead 24 and grounded. The belt 50 is driven in the direction of the arrow from right to left and carries a series of electro-conductive articles such as cylindrical cans 52 either at regular or irregular intervals. Fixedly mounted near the conveyor is a probe indicated generally at 54 and consisting of a length of coaxial cable the inner conductor 56 of which is connected to the negative high voltage line 26. The free end of the conductor 56 is bared and spaced between A and /z" from the path of the cans 52 while the outer shield 58 of the probe 54 is grounded. There is accordingly established between the inner conductor 56 and each can 52 a current carrying field 60 and the spacing is such that the field carries a current of 8 microamperes.

For providing DC potential between each pair of lines 24 and 26 there is included a power supply which will now be described with reference to FIG. 3. The power supply includes a voltage regulator 62 shown as a block. The regulator power supply 62 is one of a commercially available type having an output of 117 volts AC plus or minus one or two percent for an input varying over a range of eight-five to one hundred and thirty-five volts AC at 60 cycles. The output of the supply 62 is connected to a variable auto-transformer T1 which in turn provides a variable output to the primary winding of a power transformer T2. The secondary winding of the transformer T2 has across it a voltage multiplier ladder consisting of condensers C1 to C5 which are charged through the action of diodes D1 to D inclusive. In effect, in the power supply, each condenser is charged through four diodes in series. Thus, for example, the condenser C1 is charged through a path including the diodes D1 to D4 inclusive. The positive end of the power supply at the connection of the condenser C1 and the diode D1 is connected to a microammeter typically having a full-range deflection of to microamperes and a series current limiting resistance shown as the resistors R1 to R10 inclusive. Each of these resistors is of a value of 4.7 megohms for a total series resistance of 47 megohms.

From the negative end of the power supply, the connection between the secondary winding of the transformer T2 and the condenser C5, there is a DC current path through a resistor R11 having a value of 1 megohm to the negative lead 26. The resistor R11 is in parallel with the condenser C6 which has a value of .1 microfarad and a rating of 200 volts DC. The resistor R11 is a part of a switching amplifier which will later be explained and the condenser C6 suppresses radio frequency voltages which would otherwise develop.

In operation the auto-transformer TI is adjusted so that a reading of approximately 8 microamperes is obtained on the meter M when a work piece, either a lamp mount 16 or a can 52 is in its predetermined position.

The switching circuit of which the resistor R11 and the condenser C6 are a part, includes transistors Q1, Q2, and Q3 powered by a supply comprising a transformer T3. The primary winding of the transformer T3 is connected to the output of the regulated supply 62 and the secondary is connected in a full-wave rectifier circuit comprising the diodes D11 and D12 for charging a condenser C7 to a value of volts DC. The condenser C7 is connected through a resistor R18 to a negative line 44 and the positive side of the condenser C7 is connected to the line 26.

Q1 is a PNP transistor whose emitter is connected to the line 26 through a suitable resistor R13 and whose collector is connected directly to the negative line 44. When there is no current flow through the resistor R11 there is no forward bias between the emitter and the base of the transistor Q1 and it is accordingly non-conductive. When current flows from the line 26 to the line 24 through the air gap as already described forward bias is developed across the resistor R11 and the transistor Q11 becomes conductive. It is possible that the current drop across R11 could become excessive and thus damage the transistor Q1. In order to prevent this, there is interposed between the collector and base of Q1 a diode D13 in series with a suitable current limiting resistor R12. The diode D13 becomes conductive whenever the base of the transistor Q1 becomes negative with respect to the collector and thus limits potential forward bias on the base-collector junction to a non-destructive value.

In the emitter circuit of the transistor Q2 there is a 6.8 volt Zener diode D14 which is part of a voltage divider network also including a resistor R17 and diode D15 across the amplifier power supply. In the absence of conduction through Q1 the emitter base junction of the transistor Q2 is reverse biased to the extent of the 6.8 volts across D14. When Q1 becomes conductive, however, the voltage drop across R13 is in opposition to the bias D14 and when the drop across R13 exceeds the 6.8 volts by a relatively small value the transistor Q2 becomes conductive.

Q3 is an NPN transistor whose base is connected to the collector of Q2 thru a resistor R16. While the transistor Q2 is non-conductive, the base emitter junction of Q3 is reverse biased by a voltage drop across the resistor D15 which is part of the voltage divider as already explained. When Q2 becomes conductive, the voltage drop across the resistor R15 connected between the collector of Q2 and the line 44 provides a forward bias to the emitter base junction of Q3 whose base is also connected to one side of a condenser C8. The condenser C8 has a capacity of .5 microfarad and to its other side is connected to the line 26. Forward bias to the base emitter junction of Q3 provided by the resistor R15 renders it conductive and its collector current energizes a relay coil KI to close a pair of contacts KIA. The coil K1 is one having a resistance of 11,000 ohms and has connected in parallel to it an oscillation suppressing diode D16.

When the coil K1 is energized the contacts KIA, which are bypassed by an arc suppressing condenser C9 close, thereby energizing relay coil K2 and causing the movable member of each of the switches K2A and K2B to change its position in each case opening the connection to the upper stationary contact and closing the connection to the lower contact.

The contact arrangement of the relay K2 is not mandatory and does not aifect the operation of the device nor its sensitivity since this relay is energized from the AC. line. With the circuit components already described, however, it has been found that the relay K1 is energized to close the contact KIA when the reading on the meter M is approximately 8 microamperes. Undoubtedly with modifications which are readily suggested by the present disclosure it would be possible to add stages of amplification for example and thus lower the level of current flow required to close the relay contacts KIA.

The electrical portion of the present device illustrated in FIG. 3 is necessary in connection with each of the plates 22, 30, 34, and the probe 54 and each must be individually adjusted to obtain the desired results. In the inspection arrangement illustrated in FIG. 1 the three negative lead lines 26 are connected together to the belt 10 and grounded. The plate 22 is connected to one of the positive leads 24 and adjusted at a level providing a sufficient space above the paths of normally positioned leadin wires 16 that the meter M shows a reading of approximately 8 microamperes and the relay contact KIA are closed when the lead-in wires 16 pass thru their greatest field producing position nearest the plate. In the event that one of the lead-in wires 16 is missing the field 28 will be of insufiicient intensity to cause the relay contacts KIA to close and the upper relay contacts K2A and K2B will remain closed. A time control switch which is synchronized with the conveyor 10 closed only while a pair of lead-in wires should be directly beneath the plate 22 may be employed in series with the upper relay contacts K2A for example to control an electrically controlled device for removing a mandrel 14 supporting either defectively positioned lead-in wires 16 or a single lead wire 16.

In the case of plate 30 its level is adjusted to provide the necessary 8 microamperes of current thru the field 32 when there is a properly positioned filament 20 mounted between the lead-in wires 16. It has been found that when the plate 30 is properly positioned the current flowing thru the field 32 reaches the value of 8 microamperes sufficient to energize the relay K1 to close the contact KIA only when there is a filament 20 mounted between the two lead-in wires 16. When there is no filament mounted between the lead-in wires 16, even though the lead-in wires themselves are properly positioned, the current thru the field 32 reaches a substantially lesser value and the relay contacts KIA accordingly remain open. As was suggested with reference to the inspection of the lead-in wires 16 at the plate 22, an electrically controlled device may be actuated to remove the mandrel 14 supporting a mount defective by lacking a filament 20, as indicated by the failure of the contacts KIA to close. In addition, the contacts KZB may be employed to actuate a solenoid-operated counter to aid in controlling production.

The plate 34 is positioned at a level above the path of a normally attached filament 20 such that a reading on the meter M reaches a value of 6 to 7 /2 microamperes and the relay contacts KlA are not closed by the passage of a normally positioned filament 20. However, a filament 20 attached to a single one of the lead-in wires 16 as shown in the lamp mount beneath the plate 34 causes an increase in the current carried by the field 36 and the relay contacts KIA accordingly close. For removing such a lamp mount an electrically operated device may be actuated by the closing of the normally opened lower contacts K2A. Counting of this specific type of defect may be controlled by the closing of the normally opened lower contacts K2B.

The arrangement shown in FIG. 2 is useful either for counting cans 52 for verifying the presence of a can in a particular position at a given time. The wire 56 is fixedly positioned so that when a can 52 being moved by the belt 50 is directly in line with the probe 54, approaching it most closely, the current reading on the meter M reaches a value of 8 microamperes and the contacts KIA are closed. Resultant closing of the lower contacts K2A and K2B may be employed for counting and for verifying the presence of a can at a particular place and time.

In the foregoing examples it has been seen that the lamp mount parts consisting of the lead-in wires 16 and the filament 20 of small end dimension are connected to the negative lead of the power supply 26 while a relatively flat plate 22, 30 or 34 is connected to a positive lead 24. On the other hand in the case of the cans 52 the probe 54, which is sharply pointed, is connected to the negative lead 26 and the cans, which are relatively fiat and present a relatively broad area, are connected to the positive lead 24. It has been found experimentally that with the width of the gap and applied voltage remaining constant, the current flow thru the microionization field is greater by a factor of between 5 and to 1 when current fiow is from a relatively sharp negative member to a relatively broad positive member than when the polarity is reversed.

Having thus disclosed my invention and described illustrative embodiments, what I claim as new and desire to secure by Letters Patent of the United States is:

1. A proximity detector for sensing an article comprising a high voltage power supply having one pole connected to the article, an electrode connected to the other pole of the power supply and positioned near the path of the article, means for moving the article into a position along the path wherein a current carrying microionization field is established in an air gap between the electrode and the article, the connections between the article and the power supply and between the electrode and the power supply being established between the negative pole and the sharper of the article and the electrode, a switch, and means responsive to current flow through the air gap for actuating the switch.

2. A proximity detector for sensing an article comprising a high voltage power supply having one pole connected to the article, an electrode connected to the other pole of the power supply and positioned near the path of the article, means for moving the article into a position wherein a current carrying microionization field is established in an air gap between the electrode and the article, the connections between the article and the power supply and between the electrode and the power supply being established between the negative pole and the sharper of the article and the electrode, a switch, a switching amplifier current limiting resistance in series with the air gap including a resistor for coupling current flow through the power supply to the amplifier whereby to actuate the switch in response to a pre-determined value of current flow through the air gap.

3. A proximity detector for sensing an article at a predetermined position comprising a high voltage power supply having a positive and a negative pole, a probe spaced from the article at a pre-determined position to provide an air gap between the article and the probe, the article and the probe being a pair of electrodes defining the air gap between them, connecting means including a negative line from the power supply to the electrode having the smaller area at the gap and a positive line to the other electrode, a switch, and means for actuating the switch in response to a pre-determined current through the gap.

4. A proximity detector according to claim 3 in which the article is one having a small area at the gap relative to the electrode and the electrode is a flat circular disc having a diameter between A" and /2" spaced between and from the article.

5. A proximity detector according to claim 3 in which the last mentioned means includes a switching amplifier comprising a switch actuating coil energized to operate the switch when current flow through the gap reaches a value of 7 /2 to 8 /2 microamperes.

6. A priximity detector according to claim 3 in which the output of the high voltage power supply is regulated and adjustable to provide the necessary current flow through the gap of a given dimension.

References Cited UNITED STATES PATENTS 9/ 1957 Rockafellow. 6/1966 Jarvis et al 317-262

Claims (1)

1. A PROXIMITY DETECTOR FOR SENSING AN ARTICLE COMPRISING A HIGH VOLTAGE POWER SUPPLY HAVING ONE POLE CONNECTED TO THE ARTICLE, AN ELECTRODE CONNECTED TO THE OTHER POLE OF THE POWER SUPPLY AND POSITIONED NEAR THE PATH OF THE ARTICLE, MEANS FOR MOVING THE ARTICLE INTO A POSITION ALONG THE PATH WHEREIN A CURRENT CARRYING MICROIONIZATION FIELD IS ESTABLISHED IN AN AIR GAP BETWEEN THE ELECTRODE AND THE ARTICLE, THE CONNECTIONS BETWEEN THE ARTICLE AND THE POWER SUPPLY AND BETWEEN THE ELECTRODE AND THE POWER SUPPLY BEING ESTABLISHED BETWEEN THE NEGATIVE POLE AND THE SHARPER OF THE ARTICLE AND THE ELECTRODE, A SWITCH, AND MEANS RESPONSIVE TO CURRENT FLOW THROUGH THE AIR GAP FOR ACTUATING THE SWITCH.

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