US2620923A - Metal detecting and sorting apparatus - Google Patents

Description

G. H. WILLIAMS Filed Dec. 23, 1949 METAL DETECTING AND SORTING APPARATUS H w 2 W i h m I N mm H QQRKNQQ T V R aw F @n v fi A a v A fi H H h A N fin Dec. 9, 1952 MM H.

Patented Dec. 9, 1952 METALTDETE CTIN G AND SORTING APPARATUS Gordon Williams, Haddohfield, N. J assignor to=Radio-Corporation of America, a corporation of'Delawai-en Application December 23, 1949, Serial No. 134,672

4 Claims. 1 t This invention relates to electrical inspection apparatus andmore particularly to the automatic inspection ofnon-metall-ic' objects for the presence therein of metal;

There has been developed asa roofing material a non-metallic composition material which-is light, fireproof and extremely weatherproof. This material is manufacturedin box-like slabs ofa iven' size which are laid end to' end to form a roof: However; '-'in order for these roofing slabs to have sufilcient strength to support a -loa'd-, it is necessary to reinforce them with a steel wire mesh orlattic'e. Such roofing materiahin a lid-- uid state, is-poured around the-steel--lattice-to completely-enclose-it.- lhis isthen baked until hard; The area of the steel lattice is slightly less than-thatoi the enveloping -material-.- In orderto--'prevent insufii'ciently reinforced slabs fron'rbeing used it is -desirable to automaticallyinspectthefinishedslabs forthepresence of suflioient steel wire-reinforcement on a continuous'production' line basis. Such inspection apparatusin view of its use on -a production line, is required to be simple in construction andmaintenance and its cost-must be a minimum-'.--

It'is therefore an object of the present invention to provide-a system for" automatically detecting, the extent ofmetal in anon-metallic body.

Itis a further object of the present invention toprovidea simple systemfor automatically detesting the extent of metal in a non-metallic body.

It is still a further object of the present in'-' venti'ontoprovide' an inexpensive system-1hr automatically detecting the extent of metal in a non-metallic body; I

These-and other objects of the'present inve'n tion are achieved by using-a metal" detector in conjunction with a system of relayswhereby the signals provided by the metal-detector responsiveto a first or' front portion ofthe body containing the reinforcing-metal-and-to a last or rearportion of the body" containing reinforcing metal areutililzed} to close a relaywhich shunts a reject "control relay to keep it from rejecting the product when'anotherrelay; which-in its non operating condition maintains the reject control relay from rejecting product,"is operated by-the body passing from "under thdmetal detector;

Should the body being inspected not'have suffic'ient'meta'l therein to actuate the metal de-* tector at proper intervals determined-by therequire'dextent of the metal in the body, then the shunting relayis not operated and the reswitch SA which is actuated and t Z ject control relay is activatedto reject the body.

The novel features-of the-invention; as well as the invention itself,- both as to its organizationand method of operation, will best-be understood from the a following description when read in connection with the accompanying drawings, in which,

Figure l is a diagrammatic representation of an arrangement of an embodiment of the'invention with a conveyor-beltand Figure'2 is acircuit diagram representative'of an embodiment of theinvention.

Referring'to Figure 1, a conveyor belt I0 driven by a motor l2, 'carriesroofing slabs pasta maintained by contaotwith a roofing slab I l.- The required metalrein-fo'rcing mesh I6 is represented by the dotted line intheslab-lk A metaldetector l8 is represented'by the'two rectangular boxes on both sidesof the conveyor belt 16'. The metal detector electromagnetic field is represented by the arrows between-the boxes andis established Withinanarea between the two boxes and normal to thecon'veyor belt. Theswitch SA is positioned a distance in advance of the metal detector field slightly less than the desired extentof the metal within theslab, which in thepresent instance is substantially the length of the-slab. Switch SA- is-th'erefore released just after the frOntmetal-including portion of the slab-has entered'the metaldetector field to actuate the metal detector.* Switch-SBis positionedaf-ter the'metal-detector at a convenient distance from the metal detector field whichis less than the length of a roofing s1ab.' The-slab must-not yet have'leftthe metal detecting field 'at-the time switchSB is activated.

As stated previously the roofing slab- Hlbeing inspected is --composed of substantially nonmetallic material-having a suitable-rectangular area and-thickness and completelyenclosing a reinforcing metal mesh lB which extends substantially throughout the roofing slab area:

Metal detectors of the type herein employed are wellknown to the-art and essentially include means toestablish a balanced metal detecting field and means to detect an unbalance in said field caused by metalmoving through '-it.- A pair of fieldcoils exoitedby an RIF. oscillator may be'usedto'set up a balanced'field These coils may be positioned below and proximal to the com veyor be'ltand maybe-contained in the' lower box. A detecting coil may "bepositioned above the conveyor belt and may lie-contained in the upper'box: As long as the metal detecting field is balanced, a minimum or null voltage is induced in the detecting coil. However, when metal is first moved into the field or when metal is moved out of the field a large unbalance voltage is induced in the detecting coil due to the large changes created in the field by the entering or departing metal. While metal is moving through the entire field area, although the field may be unbalanced, the voltage induced in the detector coil is not as large as the voltage induced when metal is entering or leaving the field since the changes occurring in the field are not as great. A metal detector such as may be used herein is described and claimed in an application by J. H. Reynolds, Serial No. 568,045, for a Metal Detector, filed December 13, 1944, now Patent No. 2,513,745. issued July 4, 1950.

Referring to Figure 2, there may be seen represented diagrammatically three motor driven time delay relays, TA, TB and TC. These relays are of the type wherein the sequence of operation of the contacts is adjustable. Upon excitation of the time delay relay any pairs of contacts may be made to close immediately and upon operation of the relay after the predetermined time delay interval the remaining contacts are closed. Of course, if the time delay relay contacts are set to be normally closed, upon excitation, any desired pairs of contacts may be made to open and, after an elapse of the predetermined time interval, the remaining contacts are opened. Time delay relays of this type are described and claimed in Patent No. 1,794,762, issued to John Albert Garell on March 3, 1931, for Circuit Controlling Device, Patent No. 2,175,864, for a Multicircuit Timing Switch, issued October 10, 1939, to Carl Ludwig Anderson, and Patent No. 2,175,865 for a Timing Switch and Mechanism, issued October 10, 1939, to Carl Ludwig Anderson.

Also represented diagrammatically in Figure 2 are two latching relays LA and LB which are of the well known type which, when they are operated, remained latched and will not release or become non-operative until a current is applied to the respective releasing coils LAR and LBR.

Switch SA is a two-position switch. As the front portion of a slab is carried under switch SA by the conveyor belt, the switch is operated to close contacts SAI. This excites time delay relay TA, and after a time interval, determined by the time it takes the conveyor belt to move the front portion of the slab, "which is supposed to have reinforcing metal, from its position when SA is operated to just prior to its entering the field of the metal detector, contacts TA2 are closed.

The output signal of the metal detector is shown being applied to a thyratron 20. This signal, as briefiy explained above, is a voltage whose amplitude is greatest upon the entry of metal into the metal detecting field or its departure therefrom. By adjusting the bias applied to the thyratron grid from the variable bias source 22 it is possible to make the thyratron 20 fire only when a leading edge signal and a trailing edge signal is received from the roofing slab It. The thyratron anode supply is alternating current derived from a transformer 24 and permits deionization of the thyratron 20 almost immediately after a signal is removed from its grid. Included in the thyratron anode circuit is a normal- 1y open relay A. Contacts Al and A2 are closed whenever the thyratron fires responsive to signals from the metal detector.

Therefore, when the front portion of the roofmg slab which is supposed to include reinforcing metal arrives under the metal detecting field, contacts Al and A2 are closed and locking relay LA is operated through contacts Al and TA2. The closing of contacts LAI prepares a circuit for the operation of time delay relay TB. When the slab has passed switch SA the switch is returned to a position where contacts SA2 are closed. This energizes time delay relay TB. Contact TB3 is closed immediately. The delay interval between energization and operation of time delay relay TB is determined as the interval required for all but the rear end portion of the slab containing the desired reinforcing metal to be carried out from under the metal detecting field. When contacts SAI are opened time delay relay TA is rendered inoperative.

Time delay relay contacts TB2 close just prior to the metal detector relay A being operated by a signal received from the rear portion of the slab which contains reinforcing metal. This serves to energize release coil LAR of latching relay LA which is then rendered inoperative. However, relay TB is held operated through its contact TB3 being connected to the power source through normally closed contacts TC2 of time delay relay TC.

Due to its positioning, the leading edge of the slab is carried under and operates switch SB before the metal detector operates responsive to the metal in the rear portion of the slab leaving the metal detector field but after relay LB is operated. Relay TC is energized through the closing of contacts SBI. Contacts TC3 are opened immediately upon such energization. The metal detector relay A is then operated by the signal generated by the metal being in the rear portion of the slab. Latching relay LB is then operated through closed contacts A2 and TB2.

Time delay relay TC has an interval between energization and operation which is determined as the interval between operation of switch SB! and operation of latching relay LB. Relay D is a reject control relay which is normally held operated through the normally closed contacts TCI and its own closed contacts D2. Contacts DI, when closed, keep the conveyor motor circuit 26 operating. Should contacts DI be opened the conveyor motor will stop. Contacts TCI are shunted or paralleled by contacts LBI when latching relay LB is operated. Therefore when time delay relay TC is operated and contacts TCI are opened, if relay LB was previously operated, relay D is maintained closed and the roofing slab is accepted. If relay LB was not previously operated, relay D is opened when contacts TCI are opened and the conveyor motor circuit is opened. The conveyor belt then stops and the slab I4 is rejected.

Opening of contacts TC2 renders time delay relay TB inoperative. When an accepted slab has been carried past switch SB, the switch contacts SBI are opened and time delay relay TC is thus rendered inoperative. Its normally closed contacts TCI, 2 and 3 are then closed again. Upon closure contacts TC3 through contacts LB2 energize release coil LBR. and relay LB is deenergized. Push button TB is used for the purpose of shunting contacts D2 so that relay D may be closed and the conveyor belt started again after a rejected slab has been removed from under switch SB and relay TC has been rendered inoperative again.

If a slab contains no metal or contains metal which does not extend through the desired inspection' areas of the slab, then switch. SA and relay TA may be operatedbut since the metal detector signal is-absent at the proper time, relays TB and LB will not operate; Therefore the opening contacts of -TCI will open relay D and stop the conveyor belt Ill with the defective slab under switch SB. Time delay relay TC is held energized and-the conveyor belt cannot bestarted again until th removal-of the defecti-ve slab from under switch 83- If a slab-contains reinforcing metal inthe front portionandnotin the rear portion then switch SA, time delay relayTA, latching relay LA and timedelay relay TB are operated but not latchingrelayLB in view of the absence of the metal-detector signal at-the proper time. The'slab is thenrejected.-

It hasbeen found that inspection of th designated front and rear areas by the metal detector are all that is required --to determine whether or'not the reinforcing "metal hasthe proper'extent within the roofing slab; Furthermore, it isextremely unlikely that two pieces of tramp-metalwould be'positioned in the precise inspected areas to cause acceptance; The use of. this inspection apparatus need not be limited to roofingslabs but can be'used in any-case where the presenceof metal indesired areasof a non metallic enclosing substance-is desired to be inspected;

From'the foregoing description it willbe'rea-dily apparentthat I have provided an improved apparatus for automatically and continuously detecting the extent of metal 'ina non-metallic body. Althoughfa single embodiment of 'my present invention has been shown and described, it should belapparent that many-changes'may be made, and manyxother embodimentsiare possible, all within the spirit and scope of my invention; I therefore desire that the foregoing description shall be taken as illustrative and not aslimiting.

What is claimed is.

, l.-A system for inspecting the extent of metal enclosed in non-metallic bodies being carried on a conveyor belt comprising in combination a metal detector having, a balanced metal detecting electromagnetic field through which said conveyor belt carries said bodies, said metaldetector including a normally open relay which is operated in' response to an unbalance of the metal detecting field caused by the entry of a front portion of one of said bodies having metal therein and in response to an unbalance caused by the departure of a rearward portion of said one of said bodies having metal therein, a reject control switch, first switch means to hold-said reject control switch inoperative when said first switch means is inoperative, relay means to couple a .circuit .in parallel with said first switch means aorossesaid reject control switch responsive to operation of said metal detector relay by detection of metal in said body front portion and rear portion, and second switch means to operate said first switch means, said second switch means being positioned to be operated by passage of said body from said metal detector whereby said relay means maintains said reject control switch inoperative when said body contains sufiicient metal and said reject control switch is permitted to operate when said body contains insuificient metal.

2. A system for inspecting the extent of metal enclosed in non-metallic bodies being carried on a conveyor belt comprising in combination a metal detector having a balanced metal detecting electromagnetic field through which said conveyor belt carries .sa-id bodies, said-metal de tector including a normally open relaywhich is closed in-responseto an unbalance-of said-metal detecting field caused by the entry of a front portion ofone of said bodies havingmetal therein and in response to an unbalance caused by the departure of a rearward portion cfsa-id oneof said bodies having metal-thereina reject control switch, first switch means to holdsaid reject control-switch inoperative when said first-switch means is inoperative, second switch means' operated in response to th 'closi-ng of said-metal detector relay inresponse to the entry of sa-id front-portion-of said one of saidbodies-into said metal detector field, third switch means operated through *said second switch'means in-response to the closing-of said metal detector relay-in're sponse to thedeparture of a rearwardportion-of said one ofsaid bodies; said third switchmeans when operated being connected in parallel "with said first switch means across said reject-control switch, fourth switch meanstooperate said first switch means; saidfourthswitch means-be'ingpo sitioned to be operated by the passage ofsaid body away from said metal detector, whereby said third switch means maintains said'rejectcontrol switch inoperative when said-body contains sufii= cient reinforcing metal; and said' reject'switch is operatedto reject said body; when said" second and third switches are not operated due to'said body not containing sufficient metal:

3. A system for inspecting the extent'of metal enclosed in non-metallic bodies being carried on a dielectric conveyor belt comprising in combination a metal detector having a balanced metal detecting electromagnetic field through which said conveyor belt carries said bodies, said metal detector including a normally open relay which is closed in response to" an unbalance of said metal detecting field caused by the entry-of a .front portion of one of said bodies havingme'taltherein and in response to'an unbalance caused by the departure of a rearward portion of said one of said bodies having metal therein, a two position switchpositioned along said conveyor belt in advance of said: metal detector field to "be operated to a first of its two positions by the passage, of a front portion of one of said bodies therebyan'd returning to a second of its two positions after passage ofrarear portion of said body; a first time delay relay energized in response tosaidfitiwo position switch being operated to its first posi-.- tion, the delay interval between energization and operation of said first time delayrelay being de-,- termined as slightly less than the interval. requiredv for said body front portion toarrive at said metal detector field from said two position switch,.a first latching relay operatedthrough said operated first time delayrelay in response to the closingof said metal detector relay. responsive to, the entry of a front metalcontaining portion of said body into said metal detector field, a second time delay relay energized through said latching relay in response to said two position switch being operated to the second of its two positions, the delay interval between energization and operation of said second time delay relay being determined as slightly less than the interval required for said body rear portion to arrive at said metal detector field from said two position switch, a second latching relay operated through said operated second time delay relay in response to the closing of said metal detector relay responsive to the passing of a rear metal containing portion of said body through said metal detector field, a reject control relay, a third time delay relay connected to said reject control relay to hold it inoperative when said third time delay relay is inoperative, said second latching relay being connected to parallel said third time delay relay connections to said reject control relay when said second locking relay is operated, and a single position switch positioned along said conveyor belt after said metal detector to be operated by the passage of a front portion of said body thereby, said third time delay relay being energized responsive to operation of said single position switch, said third time delay relay interval being determined as the interval required for said body rear portion to pass completely from said metal detector field, whereby operation of said third time delay relay does not operate said reject control relay when sufiicient metal is in said body, said second latching relay holding said reject control relay inoperative when said third time delay relay is operated.

4. A system for inspecting the extent of metal enclosed in non-metallic bodies being carried on a dielectric conveyor belt comprising in combination a metal detector having a balanced metal detecting electromagnetic field through which said conveyor belt carries said bodies, said metal detector including a normally open relay which is closed in response to an unbalance of said metal detecting field caused by the entry of a front portion of one of said bodies having metal therein and in response to an unbalance caused by the departure of a rearward portion of said one of said bodies having metal therein, a two position switch positioned along said conveyor belt in advance of said metal detector field to be operated to a first of its two positions by the passage of a front portion of one of said bodies thereby and returning to a second of its two positions after passage of a rear portion of said body, a first time delay relay having normally open contacts, said first time delay relay being energized in response to said two position switch being operated to its first position, the delay interval between energization and operation of said first time delay relay being determined as slightly less than the interval required for said body front portion to arrive at said metal detector field, a first latching relay having normally open contacts, said first latching relay being operated in response to the closing of the contacts of said first time delay relay and said metal detector relay responsive to the entry of a front metal containing portion of said body, a second time delay relay having normally open contacts, said sec,-

ond time delay relay being energized and said first time delay relay being rendered inoperative in response to said two position switch being operated to the second of its two positions, said second time delay relay being of the type wherein one pair of its normally open contacts are closed upon excitation and the other of its normally open contacts are closed upon operation, said second time delay relay being maintained energized through said one pair of contacts, the delay between energization and operation of said second time delay relay being determined as slightly less than the interval required for said body rear portion to arrive at said metal detector field from said two position switch, said first latching relay being rendered inoperative responsive to the closing of said second time delay relay contacts, a second latching relay having normally open contacts, said second latching relay being operated in response to a closing of the second time delay relay contacts and said metal detector relay contacts responsive to the passing of a rear metal containing portion of said body through said metal detector field, a third time delay relay having normally closed contacts, said third time delay relay being of the type wherein one pair of its contacts are opened upon excitation and the remainder of its contacts are opened upon operation, a single position switch placed along said conveyor belt after said metal detector to be operated by passage thereby of one of said bodies prior to the arrival of a rear portion of said body under said metal detector field, said third time delay relay being excited responsive to operation of said single position switch, the interval between excitation and operation of said third time delay relay being determined as the time required for said body rear portion to pass from said metal detector field, a reject control relay having normally open contacts, said reject control relay being held in an operated position to close its contacts and to maintain said conveyor operating through its closed contacts, said reject control relay being held operating through the normally closed contacts of said third time delay relay, the contacts of said second latching relay when operated serving to parallel said third time delay relay contacts maintaining said reject control circuit operating, passage of said body away from said single position switch rendering said single position switch non-operating, said third time delay relay being rendered non-operating responsive to said single position switch being rendered non-operating, said second latching relay being rendered non-operating responsive to the closing of said one pair of contacts of said third time delay relay.

GURDON H. WILLIAMS.

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

UNITED STATES PATENTS Number Name Date 1,957,222 Mershow May 1, 1934 2,138,645 Rey Nov. 29, 1938 2,504,731 Rose Apr. 18, 1950

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