Optical Hole Film Punch

Abstract

A bed is provided having an aperture which is a female die with a light source below the aperture. A projecting microscope is mounted over the aperture and a marked film may be moved over the aperture so that an image of a place where a hole is to be punched is magnified on a screen. The film may then be clamped and a punch inserted through the aperture hole and punch a hole in an exact location on the film. This hole may then be used in conjunction with a guide pin to locate a second hole to thus provide two accurately located holes on the film. There may be two projectors located on a single base to enable larger magnification and to produce holes of different shape. BACKGROUND OF THE INVENTION It is highly desirable and sometimes a necessity that it be possible to locate and punch holes in sheet material at exactly predetermined places. In the art of making printed circuits it is customary to make a sheet of film on which the circuit design appears either in the form of a negative or a positive picture. Then a metal clad sheet of circuit board, the surface of which has been photosensitized, is juxtaposed to the film and light passed through the film onto the board to expose the sensitized surface which is then processed in one of the manners well known in the art to remove the portions of the metal cladding, which are undesirable, to leave the final conductive surfaces on the board. One desideratum is that the actual board and the film have a predetermined fixed relation to each other so that the conductive design on the board is placed in predetermined exact points or positions on the board. This is because the board may be subsequently used with automatic machinery to apply circuit components, or, two or more boards may be superimposed to construct the more complicated circuits. It is therefore essential that the parts on the various boards be in proper register with each other in order to assure the proper electrical connections from one board to another. Heretofore it has been the practice to take the film which is to be used to make the printed circuit and punch two or more reference holes in the film at exact points relative to each other and to the circuit depicted thereon, then these holes are aligned with holes in the board, prior to exposure by suitable pins which pass through the board and film, which thus causes the film to take an exact and always the same position relative to the board, after which exposure is made and then the two taken apart and the board further processed. In order to obtain more exact alignment of the board and film, the holes are usually placed as far apart as possible, within the limits of the borders of the board. In order to punch the holes in predetermined points, as determined by the designer of the board, the position of the points may be determined on the original drawing of the circuit, which is subsequently photographed to provide the film positive or negative, by a target marking which may be a small circle that is intersected by cross lines at right angles to each other, and which intersect each other at the center of the circle. These can be made to a high degree of accuracy because the original design is usually made on an enlarged scale and, when photographed, is reduced to the size to be used on the boards. DESCRIPTION OF THE PRIOR ART The film is then placed in an optical hole film punch which consists of a base with a hole in it and a suitable light source under the base whereby the light may be projected upward through the hole. The hole may be a female die of the proper size for the subsequent punching of the hole. Above the hole and also supported by the base is a punch holder, the bottom of which is spaced above the base sufficiently to allow the film sheet to be slid into the space. Sufficient clearance or throat space is provided that considerable lateral movement of the film in the throat may be had to permit the desired positioning of the target markings. Above the punch holder and in alignment with the hole in the female die and base there is disposed an optical system, which includes a lens system together with a suitable mirror and translucent screen (which may be a ground glass type) whereby a suitable enlargement of the image on the film may be projected on the screen in such a manner that the image is at a proper viewing angle for the operator to readily see the enlarged view. This screen is accurately marked with calibration lines and with suitable indices coordinated with the axis of the female die. With the above the film may be inserted into the throat of the apparatus and moved around until the image of the target marking is in exact alignment with the calibration or "cross hairs" on the screen. Then a male punch is inserted in the punch holder above the film and pressed downward to cause a hole to be punched in the film. The area of the throat above the film and the spacing is such that although the film may be moved to obtain registration, sufficient friction is applied to prevent accidental movement thereof and therefore once registration is effected the hole will be in the exact desired place. If desired auxiliary means may be provided to clamp the film and prevent movement thereof after registration has been effected. As previously stated the punched holes are round holes and spaced apart on the film as far as reasonably possible in order to obtain more exact subsequent uniformity of alignment, and were made independently of each other. The film, which is subject to expansion and contraction, presents a problem in that if it happens to be expanded when placed over the circuit board with reference pins, which are fixed distances apart and extend through the unexposed printed circuit board and film, tends to buckle when brought into contact with the board. This leaves a space between the film and the board which seriously affects the exposure and prevents the formation of sharp and well defined images thereon. If the film is in a contracted state, difficulty is experienced in placing the film over the reference pins and the film is either stretched to distort the image or, as sometimes happens, torn at one of the reference holes. SUMMARY OF THE INVENTION The present invention contemplates the punching of the first hole as indicated above and then using that hole as a guide for punching the second hole in exact relation to the first hole. The expansion and contraction problem is solved by making the second hole elongated so that exact lateral alignment of the two holes may be obtained and still permit a degree of expansion and contraction of the film between the holes and preventing buckling or stretching of the film. Because the one hole is round, at least one end of the film is always held in exactly the same position. Additional accuracy may be obtained by punching the round hole in the approximate center of the board and the expansion holes at approximate equal distances in opposite direction but laterally exactly aligned to thus decrease the effect of expansion or contraction by one half. A change is necessary in the apparatus to provide a second hole in the female die which is spaced from the first hole and wherein the second hole is elongated. The punch guide must also have two guide holes which necessarily requires that the holes be but slightly spaced in order to provide good guiding engagement for each male punch member and that an additional male punch member with a punch part that matches the female part be provided. Preferably the elongated punch and die have rounded ends that are of the same radius as the round punch and with an intermediate part of the same thickness as the diameter of the round punch. The distance between the ends of the hole may be approximately twice the diameter of the round punch and must be such that the maximum amount of expansion of the film will not cause the pins to engage with the ends of the hole, taking into consideration the amount of expansion and contraction for the largest sheet of film to be processed. Although the apparatus as noted above is highly satisfactory and is a great improvement over the prior art, there are certain limitations inherent in the arrangement which are overcome by another embodiment of the invention. One of the problems has been the limitations that the two stations, one for punching round holes and the other for punching elongated holes places upon the optical system. It must be remembered that an extremely high degree of accuracy of placement of the reference holes must be maintained with the two punch type of apparatus. One problem has been the obtaining of sufficient magnification to allow accurate placement of the two holes and still enable the use of two punches which are necessarily with their guide holes spaced apart at least the diameter of the punch body. Although the hole may be small, on the order of one-eighth inch, the body of the punch may be as large as three-eighths to one-half inch, therefore the field of view, which for greatest accuracy should enable the reference to be aligned with the center of the optical system, must be made large enough to cover an area of nearly 1 inch. Obviously only one of the two holes can be aligned with the center of the optical system, therefore both are placed equally spaced to one side of the center. In addition to keep the price of such a device within a reasonable price range limitations are placed upon the magnification power of such a system. Where one punch only is used it has been most practical to provide a magnification of 20 times, although 31.25 or 50 times would enable even greater accuracy of alignment to be obtained. Although a 1/8 inch field of view could be magnified as much as 40 times, with a two hole punch system and a field of 1 inch to be covered the result would be an apparatus so large and cumbersome as well as extremely expensive as to not justify the space or expense. For instance a 1 inch field of view magnified 40X would take a screen 40 inches square. Therefore it has been found that the expense and the space consumed can be reduced to a very high degree and the magnification increased to provide more accuracy by providing two optical systems whereby the greater enlargement is obtained in each one and was heretofore impractical to carry out. The round holes are punched in one station then the film transferred to the other station and the elongated hole punched. The entire system taking less than twice as much room as a single system and costing less than twice as much due to the fact that certain parts are common to each other.

Description

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1, is a side elevational view of the apparatus of the invention;

FIG. 2, is a front elevational view thereof;

FIG. 3, is an enlarged plan view of a fragment of the base plate showing the light aperture and female die;

FIG. 4, is an enlarged elevational view of a punch;

FIG. 5, is a diagramatic view of an aperture and female die element showing a round and elongated hole female die.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In carrying out the invention, a base 10 is provided and an apparatus which comprises a first station is mounted on one side of the base and includes a heavy rigid pedestal 12 attached to a base plate 14 which in turn is rigidly secured to the base. Above the base 14 is smaller plate 16 which is spaced from the plate 14 to provide a throat 18 into which a film may be slipped. The base 14 supports a female die 20 below the plate 16 and in alignment with the optical system. A suitable light system indicated by the dotted crossed square 22 is disposed in or below the base 10 arranged to project rays of light upward through the female die and through the hole in a punch guide 24 into the magnifying optical system. The optical system may be conventional and include a lens tube 26 and a housing 28 which houses a mirror and enables an image to be projected on a screen 30.

With the light source 22 energized, the film to be punched is slipped into the throat 18 and the image on the film projected onto the screen 30. Exact alignment may be obtained because of the magnified image. Once the optical alignment has been obtained the film may be clamped in place and a punch such as shown in FIG. 4 is used to punch the hole in the film.

As stated before the female die could have two holes in it as shown in FIG. 5 where the outline of the die 20a is shown and has a round die hole 20b and an elongated hole 20c but they must be spaced apart, more or less as shown, in order to make room for the guide surface 20d with the result that it is impractical to have them aligned with the center of the optical system and the desired magnification is inhibited by the large screen necessary.

The punch includes a male punch member 32a which matches with the hole 20b, and a body 32b from which the punch projects and which in turn is supported by a body 32c that is guided in the guide 24. A suitable handle or knob 32d is provided for handling the punch thus making it unnecessary to touch the punch or guiding parts with the hands.

Therefore as can best be seen from FIG. 2 there is provided two optical systems mounted on the same base 10 to provide two stations with one designed to punch round holes and the other elongated holes. The second system may be substantially the same as at the first station except that an elongated punch and die are used and there is a difference in the base that enables another phase of the invention to be carried out. At the second station the base 14 is provided with a groove or slot 40 extending from the forward edge of the base back to the pedestal 12. This slot so placed that it is in alignment with the center of the die system and is wide enough to receive a reference pin which may be slidable therein. A plain slot is illustrated, but it could be of inverted T shape to allow a headed pin to be used.

The two punches, as shown in FIG. 2, include a round punch 32 for matching with a round hole such as 20b, and an elongated (crosswise) punch 32' for matching with a hole such as shown at 20c, FIG. 5. The two punches are conveniently stored in a storage block 42 disposed between the two stations.

In operation the film is placed in the first station and after optical alignment has been effected, held or clamped and a round hole is punched. The clamping can be by magnetic means if desired. Then the film is transferred to the second station and the round hole placed over a slidable pin 46 disposed in the slot 40. This base is sufficiently long that the second reference point can be aligned with the optical system while the film at the previously punched end is prevented from lateral movement at that end by the pin in the slot 40 projecting through the round hole in the film sheet. The reference point on the film having been properly located on the screen according to the screen marking, it is clamped and the film is punched with the elongated punch. By this system it will be noted that the second reference point may be more quickly moved into location because the pin and slot combination holds the film against lateral movement. Also, because the one end of the film is held, there is positive assurance that the elongated hole will be punched with its longer diameter exactly aligned with the diameter of the first hole and that there is no tendency of the elongated hole to slant, and therefore if expansion or contraction occurs the side walls of the longer hole are tangent to the reference pin and lateral alignment is positively assured to an extremely high degree of accuracy.

The throat 18 is sufficiently deep that the round hole may be centrally located in the film and elongated holes punched on opposite sides.

Inasmuch as two stations are used, with two optical systems, it is possible to obtain the larger image magnifications at each station without the need of an inordinately large screen. This fact alone, although increasing the cost of a single optical system as used conventionally in the past, is less than the cost of a system with larger magnification because the base 10 and the controls are common to both stations. What is more important is the fact that large magnification can be obtained on a screen of small size and it is cheaper to make two small systems than one large system. Finally it enables a more compact arrangement with easier viewing.

Claims

I claim:

1. An apparatus for punching guide holes in a sheet of film having an image of a printed circuit thereon to enable said film to be placed over guide pins extending in fixed relation to a circuit board to be exposed for forming a printed circuit thereon and wherein said film has markings thereon to indicate where said holes are to be punched which comprises: a first station including a base, a light source below the base and said base being formed with an aperture for allowing light to pass therethrough and to guide a punch, a magnifying optical system disposed above the base, and having a screen with markings thereon for correlating the image on the film with the markings on the screen, means for enabling said film to be disposed between said light source and said optical system for projecting an enlarged image of a marking where the hole is to be punched and a first punch means for insertion in and to be guided by said aperture for said light source, to punch a hole in the film, a second station disposed on said base, a second light source below the base, said base being formed with an aperture for passing light from the second source through the base and for the reception of a punch, and a second magnifying optical system disposed above the base and having a screen with markings thereon for correlating an image on the film with the markings on the screen, means for enabling said film to be disposed between the light source and said optical system for projecting an enlarged image of a marking where a hole is to be punched and a second punch means for insertion in and to be guided by the walls of said aperture for punching a second hole in said film.

2. An apparatus as described in claim 1 wherein said base is formed with means for the reception of a slidable guide means, said guide means is engaged in the first punched hole to hold said film at the place where the hole has been punched against lateral movement.

3. An apparatus as described in claim 2 wherein said guide means extends from a forward end of the base toward, and in diametrical alignment with said aperture.

4. An apparatus as described in claim 3 wherein said guide means is a groove in said base having parallel side walls and a pin is slidably disposed in said groove and of the same diameter as the first punched hole and said film is engaged with the first punched hole over said pin.

5. An apparatus as described in claim 4 wherein said first punch means is a round punch for punching a round hole and said second punch means is one for punching a hole having one diameter the same as the diameter of the first punch and a second diameter normal to the first diameter larger than the diameter of the first punch.

6. An apparatus as described in claim 5 wherein the second diameter of the second punch is at least twice the length of its first diameter.