US3618515A

US3618515A - Planographic scraper bar printing press

Info

Publication number: US3618515A
Application number: US38014A
Authority: US
Inventors: Thomas A Schofield; Arthur T Schofield
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-05-18
Filing date: 1970-05-18
Publication date: 1971-11-09
Anticipated expiration: 1988-11-09

Abstract

A planographic scraper bar printing press suitable for fine art prints including a motor for driving the printing bed, such motor being positively connected to such bed with a ball screw and ball nut arrangement; a pyramid set of hollow bed support rollers; a motorized scraper bar adjustment; a pressure sensitive switch to shut off such bar motor at a predetermined scraper bar pressure; and switching means to automatically shut off the bed drive motor when the scraper bar reaches the end of the printed paper.

Description

United States Patent 1,860,693 5/1932 Sheedy et a1 l0l/282X 1,669,972 5/1928 Cottrell 101/250 X 2,876,001 3/1959 Stenstrom 101/282 X 3,067,676 12/1962 Dickerson 101/250 FOREIGN PATENTS 464,719 1/1914 France 101/130 358,404 9/1922 Germany... 101/250 553,655 12/1956 Italy 101/250 Primary Examiner-Clyde I. Coughenour Attorney-McCoy, Greene & Howell ABSTRACT: A planographic scraper bar printing press suita ble for fine art prints including a motor for driving the printing bed, such motor being positively connected to such bed with a ball screw and ball nut arrangement; a pyramid set of hollow bed support rollers; a motorized scraper bar adjustment; a pressure sensitive switch to shut off such bar motor at a predetermined scraper bar pressure; and switching means to automatically shut off the bed drive motor when the scraper bar reaches the end of the printed paper.

PATENTEUNUV 1971 I 3618.515

' sum 1 OF 2 INVENTOR. THOMAS A SCHOF/ELD BY AR THUR f SCHOF/ELD A TTORNE Y5 PLANOGRAPIIIC SCRAPER BAR PRINTING PRESS BACKGROUND AND SUMMARY OF INVENTION This invention relates to improvements in printing presses and more particularly to an improved low-cost planographic scraper bar lithography printing press for producing so called fine art prints.

Fine art printing is a highly specialized field characterized in that the artist himself designs the print and publishes it in limited editions under his supervision. The finished prints bear the artists signature and normally command a high price.

Fine art prints are sought after by art collectors and numerous such prints hang in known art collections around the world. Not to be confused with common mass-printed reproductions," fine art prints are painstakenly prepared and must be of the highest quality and uniformity.

The prints are prepared by the artist who draws the image to be printed directly on a printing plate or a Bavarian Litho Stone. The plate or stone is then treated to make the image ink receptive. Ink is applied to the plate or stone with the closest attention directed to full coverage and even application. Once the plate or stone is inked, the paper to be printed is carefully set upon it and covered with a thick blotter and overlaid with a thin rigid board which is greased along its upper surface. The press scraper bar is also greased and then applied against the greased board at between about 1,800 and 2,400 p.s.i. The bed is then actuated to draw the bed beneath the bar causing the image to be transferred to the paper. The paper is then removed, the plate is reinked, a fresh sheet of paper inserted, and the process repeated until the desired number of copies have been made or until the printing plate wears out.

Since only one color can normally be printed on the paper at one time, a multicolor print normally requires a separate drawing on plate or stone for each color employed, and separate printing runs are made with each plate or stone.

In order for the prints to meet art quality standards, it is absolutely essential that the printing press employed be of the highest quality and produce uniform prints without blurring or distortion. On the other hand, printmakers do not require fast, high volume production presses employed by commercial printers, since fine art printmakers normally produce only small quantities of prints per plate, perhaps between 25 and 150.

Commercial presses are designed for high volume production and are too costly for the relatively low volume in which fine art prints are produced. Inexpensive low volume presses have been devised for use in schools and other institutions and they have been satisfactory for general purposes; however, such presses have not always provided the quality prints sought by skilled printmakers for fine art purposes.

Accordingly, it is the principal object of the present invention to provide a low-cost lithographic press suitable for producing fine art prints of the highest quality.

A further object of the present invention is to provide lithographic fine art printing press having an antideflection bed support roller system to prevent the bed (that portion of the press which carries the plate) from deflecting under pressure of the scraper bar and thereby assure uniform pressure across the plate surface.

Another object of the present invention is to provide an inexpensive lithographic fine art printing press having a bed which is power driven and positively connected to the power drive, thereby assuring uniform bed speed.

Still another object of the present invention is to provide an inexpensive lithographic printing press which produces line art quality prints, but which is still simple to operate, lightweight and sufficiently inexpensive that it may also be suitable for schools and other institutions.

Yet another object of the present invention is to provide a press which is power driven to reduce the amount of manual labor involved in producing fine art prints and also which can be provided with an automatic power cutoff to prevent the operator from accidentally running the scraper bar past the paper onto the plate or stone.

With the above and other objects in view, the invention consists of the improved printing press as set forth in the following specification and claims, and all equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, illustrating the preferred form of the invention, and wherein like reference numerals designate the same parts in all views:

FIG. 1 is a perspective view of the printing press of the present invention showing a printing plate supported on a lifting block on the press bed.

FIG. 2 is a side elevation, with parts broken away, of the press'shown in FIG. 1, without the lifting block or printing plate.

FIG. 3 is an end sectional elevation of the press shown in FIG. 1, without the lifting block or printing plate.

FIG. 4 is a detail view of one of the ball bushings mounted on the underside of the press bed and its connection to one of the support-guide rods.

FIG. 5 is a detail view of the ball nut mounted on the underside of the press bed and its connection to the central lead screw, together with a sectional view of the bed support rollers.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring in greater detail to the drawings, the major structural parts of the planographic scraper bar press of the present invention include an upright central frame 1 a scraper bar 2, a movable bed 3, a pyramid set of central bed support rollers 4, a bed support frame 5, a motor 6 for driving the bed and a motor 7 for raising and lowering the scraper bar.

In operation of the press, a printing plate 8 having the desired printing or design thereon lies on a lifting block 33 on the press bed 3, and is treated, inked and the paper to be printed is set upon it. Blotter paper (not shown) is laid over the plate, and a thin rigid board (also not shown) placed on top of the blotter paper. The upper surface of the board and the lower surface of the scraper bar (which is covered with a leather pad) are greased to assist slippage. The bar motor 7 is then actuated to lower the scraper bar 2 to a point where it will pressurably engage the thin board above the paper on the plate 8. The bed motor 6 is then actuated to drive the press bed 3 beneath the scraper bar 2, causing the design on the plate 8 to be printed on the paper. When the scraper bar reaches the end of the paper, the bed motor 6 is stopped and the motor 7 is actuated to raise the scraper bar about one-half inch from the printing surface. The bed motor 6 is then reversed to return the bed 3 to its original position where the printed paper is removed, the plate 8 reinked, a fresh piece of paper inserted, and the operation is repeated.

Where quality art prints are being produced, the number of prints which can be made before the plate becomes worn is often relatively small, perhaps on the order of -200 prints.

The upright central frame I includes a pair of parallelspaced vertical side members 9 mounted on either side of the bed support frame 5. Each pair of side members 9 is capped by a short horizontal bar 10 which support a pair of parallelspaced horizontal top rails 11, L-shaped in cross section, which transversely span the bed support frame 5. A steel housing 12 is centrally mounted between the spaced top rails 11 and provided with a central vertical aperture.

The scraper bar 2 is removably mounted in a holder 13 having an elongated opening in its bottom surface. A mounting bracket 14 is bolted in the center of the holder 13. The lower end of a vertical lead screw or ball screw 15 is fixedly rotatably secured to the top of the mounting bracket 14 and the lead screw 15 projects upwardly into the central vertical aperture in the steel housing 12 of the upright central frame 1.

The ends of the scraper bar 2 track slidably between the pairs of spaced vertical side members 9 of the upright central frame 1. This braces the scraper bar 2 during the printing operation, and substantially prevents it from deflecting in the longitudinal and angular directions.

The scraper bar 2 is of conventional design, being formed of wood and having a beveled lower edge. In operation, a section of leather is stretched across its lower edge. The scraper bar 2 may also be constructed of plastic, in which case leather is not required. The scraper bar 2 is removably held in the holder 13 with a central thumb screw 16, its beveled edge projecting downwardly out of the holder aperture.

The steel housing 12 through which the vertical ball screw 15 passes in the upright central frame 1 rotatably houses a ball nut (not shown) through which the ball screw 15 is threaded.

The exterior of the ball nut is provided with a spur gear configuration which meshes and is driven by the drive gear of a gearbox preferably coupled to a standard reversible, one-half hp., constant speed, 200 rpm, 1 volt, AC motor. Accordingly, when the motor is actuated, the ball nut is driven in rotation about the lead screw and, depending upon the direction in which it is driven, vertically raises or lowers the scraper bar 2. The vertical lead screw 15 preferably has a onequarter inch pitch and the dimensions and arrangement of the gears cause In the production of art quality prints, uniform prints are essential. Furthermore, it is often important to minimize the number of rejected prints inasmuch as the useful life of the printing plate is limited.

In standard planographic printing operations, both with our press and with presses of previous design, it is necessary to relieve scraper bar pressure each time a print is removed from the plate or stone. The scraper bar should be reset at roughly the same pressure for each print is uniform prints are to be obtained and to minimize the number of defective prints.

In the past, various devices have been employed to provide relatively uniform scraper bar pressure throughout the printing operation. In some cases, the bed is dropped and raised between two preset positions. In other cases, the scraper bar is provided with a two-position clutch mechanism which operates independently from the vertical screw adjustment.

We have found we can help to assure high quality uniform prints and minimize defective prints by employing a pressure sensitive switch (not shown) on the motor 7 for raising and lowering the scraper bar. The switch we employ is actuated when the electric current drawn by the scraper bar motor 7 reaches a predetermined level. Inasmuch as the motor 7 draws current in direct proportion to the pressure it exerts, this is a simple, convenient and inexpensive way to achieve uniform scraper bar pressure during printing operations.

The printing bed 3 of my press is steel, preferably of about one-quarter inch thickness, and its upper surface is laminated with a thin (e.g. about 0.040 inch) coating of lucite which provides a stable seat for the printing plate.

The printing bed 3 is mounted for reciprocating movement in the longitudinal horizontal plane on a pair of stationary cylindrical support-guide rods 18 mounted at the sides of the bed frame 5. Four ball bushings 19 are fixedly mounted on the bottom of the printing bed 3 and these serve to movably mount the bed 3 on the rods 18.

The drive mechanism for the printing bed includes an elongated lead screw or ball screw 20 journaled for rotation in the center of the bed frame 5. This lead screw 20 is positioned centrally between and parallel to the stationary guide-support rods at the sides of the frame. This rotatable lead screw 20 is provided with a sprocket wheel 21 at one end, and a drive chain 22 operably connects this sprocket 21 to a second sprocket wheel 23 on the drive shaft of the bed drive motor 6 mounted on the frame below. The bed 3 is provided with a stationary ball nut 24 fixedly mounted in the center of its bottom surface. This ball nut 24 receives the lead screw 20, so that when the bed drive motor 6 is actuated to rotate the lead screw, the bed 3 is driven along the length of the screw 20, toward one end or the other depending on the direction in which the motor 6 is driven.

The bed drive motor 6 is preferably a standard one-half hp., 1 10 volt, AC, 200 rpm. constant speed reversing motor, and the sprocket ratio is'about l2:l so that the lead screw turns at about 2,400 rpm. The lead screw has a one-quarter inch pitch, so that the bed 3 is preferably driven at the rate of about 50 feet per minute. Bed speed may, however, be increased or decreased in accordance with the requisites of the particular printing operation to be performed, and different drive systems may be employed within the spirit of the present invention, as will be apparent to persons ofordinary skill.

It is important, however, that the drive system we employ provides a positive driving connection between the motor 6 and the bed 2, so that the bed 2 is driven past the scraper bar 2 at a uniform and constant speed. In the past, it has been common to employ a manual bed drive or, where motors have been employed, to provide friction drive means which have a natural tendency to slip. Both systems result in irregularities in bed speed. We have found that such irregularities in the speed of the bed detract from the quality of the prints and/or result in a higher proportion of unacceptable prints, and we have been able to overcome these problems by providing positive driving connection between the bed and the bed drive motor.

A pyramided set 4 of four central

bed support rollers

27 and 28 are mounted beneath the bed 3 in the center of the bed frame 5. These

rollers

27 and 28 consist of a pair of full length parallel adjacent elongated cylindrical lower rollers 27 journaled for rotation in a pair of side plates 29 mounted at the sides of the bed frame 5, and a pair of half-length cylindrical upper rollers 28 freely carried for rotation on the lower rollers 27. The axes of the upper rollers 28 lie directly beneath the scraper bar 2, and each roller 28 supports one-half of the bed to reinforce it against deflection at that point under scraper bar pressure. The position of the upper rollers 28 is maintained with outer guides which are annular rims 30 on the outer ends of the lower rollers 27, and inner guides which are a pair of spaced-parallel elongated ribs 31 depending from the lower surface of the bed 3 and extending the full length of the bed 3 on either side of the bed drive lead screw 20.

It has been common, in the past, to provide a single bed support roller in lieu of the pyramid set 4 of rollers we employ. The ends of such roller have been normally journaled for rotation at the sides of the frame. We have found that the single journaled roller has had a tendency to deflect or bow slightly under scraper bar pressure. This results in uneven pressure along the length of the scraper bar and is a source of imperfections in the prints. We have overcome this difficulty with the pyramid multiple roller system described.

It will be apparent that the upper two half length rollers 28 in my pyramid set 4 could be replaced with a single full length roller if another equivalent bed drive mechanism were employed. For example, the pair of guide-support rods 18 at the sides could be replaced by a pair of bed drive lead screws driven in tandem from the same motor. This would obviate the need for the central bed drive screw 20, and would permit a single elongated upper roller to be employed. The precise construction of this and other variations in the roller structure, within the spirit of the present invention, will be apparent to persons of ordinary skill.

The

rollers

27 and 28 we employ are approximately 4 inches in diameter and formed from hollow steel tubing of about fiveeighths inch wall thickness. The two lower rollers 27 are fitted with end plugs bearing stub shafts for journal mounting in the frame.

Our pyramid multiple roller system is an important factor in keeping the weight and cost of our press within reasonable limits inasmuch as it provides superior back up support for the bed. Comparable results with a single roller would require a roller many times heavier and larger than the weight and bulk of the multiple rollers we employ, together with a heavier frame and more powerful bed drive system. While the particular diameter and wall thickness of the rollers shown do not necessarily produce optimum antideflection characteristics for the weight of rollers employed, they are believed to produce near optimum results and are clearly superior to the single roller system of prior art devices. If even less bed deflection is desired, it may be achieved by expanding the roller pyramid to include an additional layer of three rollers journaled in the frame to back up the present two lower rollers, thus expanding the roller pyramid to a total of seven rollers, the precise construction of which will be readily apparent to persons of ordinary skill.

Our printing press, being thoroughly motorized, may be provided with additional electric control devices, the precise construction of which will also be apparent to persons of ordinary skill. Such electric controls may include a limit switch to stop the bed motor automatically at the end of the bed after printing one sheet. Such limit switch could also serve to simultaneously actuate the scraper bar motor to automatically raise the scraper bar once the bed has stopped. An additional limit switch may be employed to automatically stop the scraper bar motor once the bar has been raised a sufficient distance, and such limit switch may also serve to simultaneously actuate the bed motor to automatically return the bed to its start position after the bar has been raised. A third limit switch may be employed to automatically stop the bed once it reaches the start position. Such switching systems may be employed separately or in combination. It should be pointed out, however, that the use of a limit switch to stop the bed at the end of the print is not only a convenience, but guards against damage to the printing plate which may occur if the scraper bar passes the end of the sheet into direct contact with the plate itself.

From the foregoing, it is seen that the present invention provides a low-cost lithographic press which is suitable for fine art prints and otherwise accomplishes its intended objects. It is understood that the present invention may be embodied in several forms without departing from its spirit or essential characteristics, and that the embodiments shown and described are illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within the limits of the claims or their functional equivalents are intended to be covered by these claims.

We claim:

1. A lithographic printing press comprising a main frame having upright side members and a horizontal transverse top member supported by and between said side members;

a transverse scraper bar vertically adjustably suspended from said horizontal top member between said side members;

a reversible first motor mounted on said frame;

means operatively connecting said first motor to said scraper bar to drive said scraper bar for said vertical adjustment;

at least three support rollers arranged pyramid fashion including a pair of adjacent horizontally aligned lower rollers journaled for rotation in said frame, and an upper roller carried by and rotatably supported along its length by said lower rollers, said upper roller positioned directly beneath and spaced from said scraper bar;

a flatbed horizontally movably mounted below said scraper bar and supported on said upper roller;

a reversible second motor mounted on said frame;

means operatively connecting said second motor to said bed, such second named means providing a positive driving connection between said bed and said motor.

2. A printing press as recited in claim 1 wherein the second named means comprises a ball nut fixedly mounted on the bottom surface of said bed, a second elongated ball screw rotatably secured to said main frame and threaded through said fixed ball nut, and means positively coupling said second motor to said second ball screw, so that when said motor is actuated, said second ball screw is driven in said fixed ball nut at a constant angular speed to drive said bed in the longitudinal direction beneath said scraper bar at a uniform speed.

3. A printing press as recited in claim 1 wherein the first named operative connecting means comprises a ball nut rotatably supported on said horizontal top member of said frame, an elongated ball screw rotatably secured to said scraper bar and threaded through said rotatable ball nut, and means coupling said motor to said ball nut, so that when said motor is actuated, said ball nut is driven in rotation about said ball screw, thereby raising or lowering said ball screw and said associated scraper bar.

4. A printing press as recited in claim 1 wherein said first motor is provided with a load limit switch so that power supplied to said first motor will be switched off when the electric current load drawn by said first motor reaches a predetermined level.

5. A printing press as recited in claim 2 wherein the first named operative connecting means comprises a ball nut rotatably supported on said horizontal top member of said frame, an elongated ball screw rotatably secured to said scraper bar and threaded through said rotatable ball nut, and means coupling said motor to said ball nut, so that when said motor is actuated said ball nut is driven in rotation about said ball screw, thereby raising or lowering said ball screw and said associated scraper bar.

6. A printing press as recited in claim 5 wherein said first motor is provided with a load limit switch so that power supplied to said first motor will be switched off when the electric current load drawn by said first motor reaches a predetermined level.

7. A printing press as recited in claim 1 wherein said support rollers are hollow.

8. A printing press as recited in claim 7 wherein said support rollers are approximately 4 inches in diameter and have a wall thickness on the order of five-eighths inch.

9. A printing press as recited in claim 5 wherein said support rollers are hollow.

10. A printing press as recited in claim 9 wherein said support rollers are approximately 4 inches in diameter and have a wall thickness on the order of five-eighths inch.

11. A printing press as recited in claim 6 wherein said support rollers are hollow.

12. A printing press as recited in claim 12 wherein said support rollers are approximately 4 inches in diameter and have a wall thickness on the order of five-eighths inch.

13. A printing press as recited in claim 1 wherein switching means are provided to automatically stop said bed drive motor once said bed has reached a predetermined position upon having been driven beneath said scraper bar during printing.

14. A printing press as recited in claim 5 wherein switching means are provided to automatically stop said bed drive motor once said bed has reach a predetermined position upon having been driven beneath said scraper bar during printing.

15. A printing press as recited in claim 12 wherein switching means are provided to automatically stop said bed drive motor once said bed has reached a predetermined position upon having been driven beneath said scraper bar during printing.

I It i i i

Claims

1. A lithographic printing press comprising a main frame having upright side members and a horizontal transverse top member supported by and between said side members; a transverse scraper bar vertically adjustably suspended from said horizontal top member between said side members; a reversible first motor mounted on said frame; means operatively connecting said first motor to said scraper bar to drive said scraper bar for said vertical adjustment; at least three support rollers arranged pyramid fashion including a pair of adjacent horizontally aligned lower rollers journalled for rotation in said frame, and an upper roller carried by and rotatably supported along its length by said lower rollers, said upper roller positioned directly beneath and spaced from said scraper bar; a flat bed horizontally movably mounted below said scraper bar and supported on said upper roller; a reversible second motor mounted on said frame; means operatively connecting said second motor to said bed, such second named means providing a positive driving connection between said bed and said motor.