Apparatus for print head retraction to facilitate paper insertion

Abstract

Print heads mounted on a carriage moveable parallel to the platen are automatically retracted away from the platen when the carriage reaches a home position to facilitate paper insertion and thereafter automatically move to the printing position as the carriage leaves the home position under a start command.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to line printers and more particularly to line printers where the print head moves parallel to the print line to complete a line of printing and still more particularly to such line printers where the print head is normally in close proximity to the platen and the paper to be printed upon is inserted directly between the print head and platen.

The invention finds particular utility in line printers used for printing upon cut forms. Insertion and removal of the cut forms must be made easy for the operator to take advantage of the high speed printing capability of a line printer.

2. Description of the Prior Art

In high speed line printers, the print heads are in close proximity to the platen to keep the travel of the printing elements to a minimum and thereby increase the speed of printing. This arrangement, however, makes it difficult to insert paper between the print heads and platen.

In the prior art, it had been the practice to move the print head into a position where it would not interfere with insertion of the paper or cut form. However, there is not always practical because when using a wide print head or multiple print heads, the width of the printer would have to be increased substantially so as to provide a home position for the print head or heads whereby they would not be in line with the paper insertion area. The present invention provides another alternative and that is to permit the print heads to overlap the paper insertion area but to automatically retract the print heads when they are moved to the paper insertion or home position.

SUMMARY OF THE INVENTION

The principal objects of the invention are to provide an improved line printer which: (a) can print upon cut forms as well as continuous forms; (b) provides a simple mechanism for automatically retracting the print heads to facilitate paper insertion and (c) automatically returns the print heads from a retracted position to a print position when a line of printing is to take place.

The above objects are achieved by mounting the print heads on a plane which is slideable relative to and moves with the print head carriage. The plate is moved to and fro by a pair of rotatable eccentrics. the shaft for rotating these eccentrics is carried by the carriage and is provided with a cam follower pin. This cam follower pin rotates the shaft and thereby rotates the eccentrics as the carriage brings the cam follower pin into engagement with a fixedly mounted rotator cam. After the print heads have been retracted and the operator has inserted a sheet of paper into the printer, the print head carriage moves away from the rotator cam whereby the cam follower pin disengages from the rotator cam and in doing so rotates the eccentrics to return the print heads automatically to the printing position.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial top plan view with the print heads in the printing position;

FIG. 2 is a partial top plan view with the print heads retracted away from the platen to facilitate paper insertion;

FIG. 3 is a partial front elevational view showing the print head carriage, the carriage drive, the print heads and the platen;

FIG. 4 is a fragmentary side elevational view showing the print heads in the printing position;

FIG. 5 is a fragmentary side elevational view showing the print heads in the retracted position; and

FIG. 6 is a schematic circuit diagram of the logic circuitry for controlling the stepper motor for driving the print head carriage.

DESCRIPTION

With reference to the drawings and particularly to FIG. 1, the invention is illustrated by way of example as being incorporated in a line printer of the type having three separate matrix print heads 10, 20 and 30. These print heads are of the type shown and described in U.S. Pat. No. 3,592,311 for Wire Printing Head by Albert S. Chou et al. Moreover, the line printer is a modified form of the type shown and described in the IBM Technical Disclosure Bulletin, Volume 15, No. 11, April 1973, on page 3370. In this invention, print heads 10, 20 and 30 are secured to slideable plate 40 by screws 11, 21 and 31 respectively. Plate 40, which serves as the printing element support means, is slideably supported by moveable carriage 80. Carriage 80 is suitably journaled on parallelly spaced shafts 100 and 110 fixed between side frames 111 and 112.

Carriage 80 is moved along shafts 100 and 110 relative to platen 115 by means of an endless belt 120 trained about driven pulley 121 and idler pulley 122. Belt 120 is attached to carriage 80 by means of plate 81 and screws 82. Pulley 121 is driven by stepping motor 125. Stepping motor 125 is operable to rotate pulley 121 both clockwise and counterclockwise so as to move carriage 80 from left to right and vice versa.

When a document or cut form is to be inserted into the line printer, carriage 80 is moved under control of motor 125 into an extreme left hand or home position shown in FIG. 2. When carriage 80 is in this position, print heads 10, 20 and 30 are held in a retracted position away from platen 115.

Carriage 80 has a spaced pair of bifurcated arms 83 and 84 which rotatably support longitudinal shaft 85. Eccentrics 86 and 87 are fixed to shaft 85 between the bifurcated arms 83 and 84 respectively. Legs 41 and 42 depend from plate 40 and are held in contact with eccentrics 86 and 87 respectively by springs 43 and 44, respectively. Springs 43 and 44 are compression springs surrounding shafts 45 and 46 respectively with one of their ends bearing against legs 47 and 48 respectively and the other ends bearing against back slotted surfaces 88 and 89 of carriage 80. Shaft 45 is secured in depending legs 41 and 47 and is slideably journaled in carriage webs 91 and 92. Similarly, shaft 46 is secured in depending legs 42 and 48 and slideably journaled in carriage webs 93 and 94. By this arrangement, plate 40 moves with carriage 80 parallel to platen 115 and is moveable by eccentrics 86 and 87 transversely of carriage 80 toward and away from platen 115. Eccentrics 86 and 87 function as actuator means for moving plate 40, and thus print heads 10, 20 and 30, toward and away from the print line.

When print heads 10, 20 and 30 are in the printing position, the low sides of eccentrics 86 and 87 are in contact with depending legs 41 and 42 respectively. Shaft 85 must be rotated in order to move print heads 10, 20 and 30 to the retracted position. Shaft 85 is rotated through the cooperative action of rotator cam 130 secured to side plate 111 and cam follower pin 95 extending through shaft 85 at right angles thereto.

Rotator 130 has a central longitudinal bore 131 for receiving shaft 85 and a pair of helical grooves 132 for receiving cam follower pin 95. Thus, as pin 95 enters and follows the helical grooves 132, shaft 85 is rotated and thereby rotates eccentrics 86 and 87. The eccentrics 86 and 87 in turn move plate 40 rearwardly away from platen 115 to the retracted position. Thus, rotor 130 and cam follower pin 95 together with shaft 85 function as operator means for operating eccentrics 86 and 87 to move support plate 40 and thereby move print heads 10, 20 and 30 away from the print line when carriage 80 is in the home position and toward the print line as carriage 80 leaves the home position. The print heads 10, 20 and 30 remain in the retracted positions so long as carriage 80 is in the home position with cam follower pin 95 in the helical grooves 132 as in FIG. 2. Then as carriage 80 moves away from the home position whereby pin 95 follows helical grooves 132 to again rotate shaft 85, the print heads 10, 20 and 30 are restored to the printing position. The distance between the print heads 10, 20 and 30 and platen 115 when the print heads are in the printing position is best seen in FIG. 4. Paper insertion is then greatly facilitated by moving the print heads to the retracted position as in FIG. 5.

Printing takes place a line at a time and carriage 80 is returned to the home position after a line has been printed. Normally, a line printer is attached to a host computer system and the information to be printed is in the form of coded data which selectively operates the print heads 10, 20 and 30 to fire matrix print wires in a sequence so as to generate character patterns on the paper or cut form 15 as the print wires impact print ribbon 16. Print ribbon 16 is a conventional ribbon and is guided by print ribbon guide 17, which is attached to support arms 51 and 52 projecting upwardly from plate 40 as seen in FIGS. 2, 4 and 5.

When print head 30 approaches the right hand margin of paper 15, a permanent magnet 96, FIG. 3, attached to carriage journal 97 operates reed switch RSW1 to generate a signal for reversing stepping motor 125 and thereby moving carriage 80 to the home position. As carriage 80 is returning to the home position, magnet 96 first operates reed switch LSW2 and a signal is generated to cause stepping motor 125 to operate at a slow speed. Carriage 80 then moves to the home position at this slow speed and is stopped when magnet 96 operates reed switch LSW1. Operation of reed switch LSW1 causes a signal to be generated for stopping stepping motor 125.

A schematic diagram of the circuitry for operating stepping motor 125 is shown in FIG. 6. Motor 125 is started under control of the operator depressing a start key to apply a start signal to start terminal 150 or is started by the host computer applying a start signal to terminal 150. The start signal from either source is applied to motor drive control circuit 151 which includes conventional logic for generating forward and reverse sequences of stepper motor pulses. The forward sequence of stepper motor pulses is applied to AND circuit 152 which controls the advancement of stepping motor 125 in the forward direction. Motor drive control 151 supplies a reverse sequence of pulses for stepping motor 125 to AND circuit 154 which will pass the reverse sequence pulses to motor 125 via OR circuit 155 only when it is conditioned by a reverse signal from direction control logic 153. Direction control logic 153 generates a reverse direction control signal when magnet 96 operates switch RSW1. The start signal initially causes direction control logic 153 to generate a forward control signal for conditioning AND circuit 152.

When magnet 96 operates switch LSW2 and the reverse control signal is present, the motor drive control logic 151 provides the reverse sequence of stepping pulses at a slower rate to AND circuit 154 whereby motor 125 operates at a slower speed. Thereafter, magnet 96 operates switch LSW1 and motor drive control logic 151 ceases to provide a sequence of stepping pulses to either AND circuit 152 or AND circuit 154.

This causes stepping motor 125 to stop and it remains stopped until a start pulse is again applied to start terminal 150. During the time that the motor is stopped, the print heads 10, 20 and 30 are held in the retracted position and the operator can insert a new form in the manner described in the aforementioned IBM Technical Disclosure Bulletin.

From the foregoing it is seen that the invention provides a combination of apparatus for automatically retracting the print heads from the printing position to a paper insertion position when the print carriage reaches the home position. It is further seen that as the print carriage moves away from the home position to start a new line of printing, the print heads automatically move from the retracted position to the printing position.

Claims

We claim:

1. In a line printer having printing means mounted on a carriage moveable along a carriage path relative to the print line from a home position located at one extreme end of said carriage path to a return position located at another extreme end of said carriage path and back to the home position, said printing means being moveable relative to said carriage toward and away from said print line the improvement comprising:

means normally holding said printing means in a print position relative to said print line, and

means operable in response to said carriage coming into said home position for retracting said printing means away from said print line and holding said print means in the retracted position so long as said carriage remains in said home position and for restoring said printing means toward said print line when said carriage is moved away from said home position.

2. In a line printer having a carriage moveable along a carriage path relative to the print line from a home position located at one extreme end of said carriage path to a return position located at another extreme end of said carriage path and back to the home position, the improvement comprising:

printing element support means moveably mounted to said carriage to move toward and away from said print line,

actuator means for moving said support means toward and away from said print line, said actuator means normally holding said support means toward said print line, and

operator means for operating said actuator means to move said support means away from said print line when said carriage is in said home position and to move said support means toward said print line when said carriage leaves said home position.

3. The line printer of claim 2 wherein said means for operating said actuator means causes said actuator means to hold said support means away from said print line while said carriage is in said home position.

4. The line printer of claim 2 wherein said actuator means is mounted on said carriage to move therewith.

5. The line printer of claim 2 wherein said operator means for operating said actuator means is stationary.

6. The line printer of claim 4 wherein said actuator means comprises

a rotatable shaft journalled in said carriage,

at least one eccentric mounted on said shaft in a position to bear upon said support means, and

means carried by said shaft for engaging said operator means when said carriage moves into said home position.

7. The line printer of claim 6 wherein said means carried by said shaft is a cam follower pin projecting radially outward from said shaft.

8. The line printer of claim 5 wherein said operator means is a fixedly mounted cam having a hollow interior for receiving said actuator means.

9. The line printer of claim 8 wherein said cam has a pair of longitudinal helical grooves for receiving said actuator means.