US3787886A

US3787886A - Advancing mechanism for thermal print apparatus

Info

Publication number: US3787886A
Application number: US00320990A
Authority: US
Inventors: J Mccrady
Original assignee: DISPLAYTEK CORP
Current assignee: DISPLAYTEK CORP
Priority date: 1973-01-04
Filing date: 1973-01-04
Publication date: 1974-01-22
Anticipated expiration: 1991-01-22

Abstract

Disclosed is thermal printing apparatus a fixed row of thermal print heads and means for incrementally advancing thermally sensitive paper past and transverse to the thermal print heads for effecting a printout of lines of characters. The advancing mechanism advances the thermal paper while simultaneously releasing the print heads from engagement with the paper, and includes a paper gripping assembly comprising a pair of pivotally mounted, uniquely cooperating, retaining members for pulling the record material a predetermined incremental distance past the row of print heads.

Description

United States Patent [191 McCrady Jan. 22, 1974 ADVANCING MECHANISM FOR THERMAL PRINT APPARATUS [75] Inventor: John McCrady, Dallas, Tex.

[73] Assignee: Displaytek Corporation, Dallas, Tex.

[22] Filed: Jan. 4, 1973 [21] Appl. No.: 320,990

[52] 11.5. C1. 346/76 R, 197/133 R, 219/216, 226/167, 346/79, 346/136 [51] Int. Cl. G0ld 15/10, GOld 15/28 [58] Field of Search. 346/76 R, 79, 136; 197/133 R; 219/216; 226/167, 160

- [56] References Cited UNITED STATES PATENTS 1,542,129 6/1925 Hayes 226/160 2,981,587 4/1961 Kennedy 346/79 X 3,520,459 7/1970 McCrady 226/167 3,684,858 8/1972 Buck 346/76 R X Primary Examiner-Joseph W. Hartary Attorney, Agent, or Firm-Kenneth R. Glaser [57] ABSTRACT Disclosed is thermal printing apparatus a fixed row of thermal print heads and means for incrementally advancing thermally sensitive paper past and transverse to the thermal print heads for effecting a printout of lines of characters. The advancing mechanism advances the thermal paper while simultaneously releasing the print heads from engagement with the paper,

and includes a paper gripping assembly comprising a pair of pivotally mounted, uniquely cooperating, retaining members for pulling the record material a predetermined incremental distance past the row of print heads.

20 Claims, 10 Drawing Figures PAIENTED 3.787. 886

SHEET 1 BF 3 FIG. 2

PAIENTEB 3.787, 886

snmeora FIG. 3

PATENIEUJ/mmm Swan 3 or 3 ADVANCE ADVANCING MECHANISM FOR THERMAL PRINT APPARATUS This invention relates generally to thermal printing, more particularly to the thermal printing of lines of characters upon thermally sensitive record material, and even more particularly to a mechanism for incrementally advancing thermally sensitive record material past a row of thermal print heads for the sequential printing of data generated by electronic calculators or the like.

The search for new and better techniques for information display has extended the technology into an area of non-impact recording or printing utilizing heat as the'source of the printing or display energy. In accordance with this technique, a thermal print head, comprising a matrix or array of selectively energized elements, produces a predetermined pattern of hot spots in accordance with the desired form of information representation or character (letter, number, symbol, etc.); the printhead engaging thermally sensitive record material for printing the resulting character thereon. Since the thermal print operation eliminates the mechanical impacting of the printing elements upon the record material or paper, as in conventional printers, the resulting thermal printing apparatus is not only capable of operating at higher printing speeds than conventional mechanical printers, but also presents the advantage of an essentially noiseless printing operation.

Since the energizing of the heating elements of the print head is carried out electronically, thus enabling an essentially instantaneous printing operation, the rate at which data can be reproduced or printed is dependent to a large extent upon the speed at which the thermally sensitive paper and the thermal print head can be moved with respect to one another. This relative movement, for the most part, has been accomplished in prior art thermal printing systems by essentially three methods: (1) a single print head is incrementally translated along the face of the record material to produce the line of characters; (2) a row of thermal print-heads are disposed on the periphery of a drum which is rotated in cooperation with moving record material; or (3) a strip of thermally sensitive-tape is moved past a single head or past serially arranged heads in ticker tape fashion.

Each of these just described approaches, while broadly accomplishing their intended objectives, suffer from the disadvantages of either limiting the speed by which a significant amount of data can-be printed, or involve complex equipment which increases not only the size, but also the expense, of the overall system. In particular, where the printer is to be incorporated in, for generating lines of characters produced by, small electronic calculators, the increased size and reduced printing speed is particularly disadvantageous.

It is therefore the primary object of the invention to provide improved thermal printing apparatus.

It is another object of the invention to provide improved thermal printing apparatus of minimum complexity for generating entire character lines of information at increased speeds.

It is an even further object of the invention to provide an improved mechanism for incrementally advancing thermally sensitive record material past thermal print head means.

mechanism for advancing thermally sensitive paper past a fixed row of thennal print heads, the advancing mechanism being particularly adapted for inclusion in an electronic calculator.

In accordance with these and other objects, the thermal print apparatus of the present invention includes a fixed row of thermal print heads, each preferably comprising an array of bar segment heating elements, and means for incrementally advancing thermally sensitive record material past and transverse to the row of thermal print heads for effecting the printout oflines of characters. A unique advancing mechanism of the apparatus advances the thermal paper while simultaneously releasing the print heads from engagement with the paper, and includes a paper gripping assembly comprising a pair of pivotally mounted, uniquely cooperating, retaining members for pulling the record material a predetermined incremental distance past the row of print heads.

Specific features of the invention, as well as further objects and advantages thereof, may best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings in which like reference numerals indicate like parts and in which:

FIG. 1 is a front perspective view of the thermal printing apparatus in accordance with the invention, with a portion of the paper advancing mechanism shown by phantom lines for clarity of illustration;

FIG. 2 is a partial perspective view of the thermal print heads and supporting substrate utilized with the apparatus illustrated in FIG. 1;

FIG. 3 is a perspective view of the front and one side of the thermal printing apparatus illustrating, in detail, the advancing mechanism in accordance with the invention;

FIG. 4 is a perspective view of the rear and opposite side from that shown in FIG. 3 of the thermal printing apparatus illustrating, in detail, the advancing mechanism in accordance with the invention;

FIG. 5 is a partial perspective'view of the gripping assembly of the advancing mechanism ilustrated in FIGS. 1 and 3, indicating the relationship between the coop erating elements of the gripping assembly; and

FIG. 6(6A-6D) is a diagrammatic representation illustrating the operating cycles of the advancing mechanism of the present invention.

It is a still further object of the invention to provide Referring now to the drawings, and particularly to FIGS. 1 and 4 thereof, a preferred embodiment of the thermal printing apparatus including the paper advancing mechanism, of the present invention, is generally depicted by the reference numeral 10, and includes a frame assembly having sidewalls 11 with oppositely disposed notches 12 in which the bosses 13 of a transversely extending spindle or shaft are removably supported. The spindle or shaft passes through the center of, and supports, a supply roll 14 of thermally sensitive record material (paper) disposed within the chamber defined by the sidewalls l1 and an arcuately shaped wall 15 joining the sidewalls 11.

The record material or thermallysensitive paper of the supply roll 14 has a viewing surface 16 adapted to change the color or shade in response to the selective application of heat thereto and may be of the type, for example, commerically available from the National Cash Register Company under the name MINIPRINT BOND. The thermally sensitive paper has a free end 17 which extends through a transversely extending slot defined between a paper guide 95 and the wall (as illustrated in FIG. 4), beneath and immediately adjacent a plurality of linearly aligned row of thermal print heads 18, and to a location forward of the print heads, as illustrated in FIG. 1. As subsequently described in greater detail, the free end 17 is incrementally advanced past the print heads 18 in the direction of the arrow 19.

Each of the thermal print heads or modules 18 consists of an array of heating elements selectively energized or actuated to produce a predetermined pattern of hot spots in accordance with the desired character or information representation (letter, number, symbol, etc.) to be generated. The specific character is then reproduced or displayed on the viewing surface 16 of the thermally sensitive paper 14 at the location where this thermally sensitive paper contacts the print heads. Thus, for example, if the number 4 is desired to be displayed or printed on the surface 16, selected ones of the heating elements of the module 18 will be energized in a pattern corresponding to this number, the number 4 thereby being defined or printed upon the thermally sensitive record material. In accordance with a unique aspect of the present invention, an entire row of these print modules 18 are linearly disposed along the forward edge of an insulating, preferably ceramic, substrate 20 and adapted for engagement with the viewing surface 16, the essentially simultaneous energizing of this row of print heads when so engaged, reproducing or printing an entire line of characters, as depicted in FIG. 1.

The materials and fabrication of the thermal print heads 18 may be in accordance with any technique presently known in the art; for example in accordance with the description in US. Pat. No. 3,700,852, issued Oct. 24, 1972, and entitled Thermal Display Module, which patent is assigned to the assignee of the present application. Furthermore, each of the heating elements of each print head may be formed as a matrix of columns and rows, or in any other desired arrangement depending, among other things, upon the type of character to be generated. In accordance with a preferred embodiment of the present invention illustrated in FIG. 2,'however, the heating elements of each of the print modulesv 18 are formed as an array of seven bar segments 21 in a figure 8 configuration, each of the bar segments being heat dissipative elements adapted to be energized or heated by the passage of electrical current therethrough. The segments 21 are then selectively energized by way of a conductive lead or metalization pattern disposed upon one face of the insulating substrate 20, as depicted in FIG. 2, the technique for forming these interconnections being specifically described in'U.S. Pat. No. 3,700,852.

The print heads 18, while illustrated in FIG. 2 as being separate and distinct from'one another, can actually be fabricated in a manner that has two or more heads integrally joined. When these heads are so fabricated in the manner described, for example, in US. Pat. No. 3,700,852, a plurality of arrays of these bar segments are disposed in a single substrate of semiconductor material, each of the segments 21 of each array being simultaneously formed regions ofsemiconductor material. One or more of these semiconductor substrates, each having one or more arrays respectively forming the print heads 18, are then disposed upon the common ceramic substrate 20. Furthermore, it may be desirable to have selected print heads 18 of the row include arrays of elongated bar segments other than as a figure 8 configuration or, alternatively, have some of the print heads of the row comprise arrays of heating elements as bar segments and other print heads have the heating elements formed as a dot matrix in columns and rows.

The ceramic substrate 20 with the print heads 18 facing the viewing surface 16 of the paper (FIG. 1) is then secured to a mounting bar 23 by way of screws 22, for example, the mounting bar 23 being pivotally attached to the sidewalls 11 by way of pins 24. As subsequently described in greater detail, the mounting bar 23 is controllably pivoted to enable the row of print heads 18 (bar segments 21) to alternately engage with, and disv engage from, the thermal paper viewing surface 16.

A resilient pressure pad 26 disposed at the location where the row of characters to be printed extends transverse to the direction of travel of, and is disposed behind, the free end 17 of therecord material, and provides a paper supporting surface against which the print heads are urged during the print cycle. A flexible cable 27 for electrically coupling the output signals from the external circuitry (not shown) for selectively actuating the heating elements 21 can then be joined with the lead pattern 25 at the end of the ceramic substrate 20 in the manner illustrated in FIG. 2.

The entire mechanism 10 is preferably disposed within the housing of, and associated with, an electronic calculator, and enables the production of hard copy printouts from these calculators. Due to its relatively small size, and its utilization of thermal printing, it presents a virtually noiseless print apparatus for inclusion with a calculator of the hand held and battery operated variety.

After each line of characters has been printed upon the face of the thermal paper, the free end 17 is incrementally advanced past the heads 18 in the direction of arrow 19. In accordance with a specific feature of the invention, this incremental advancement is effected by an advancing mechanism which includes a gripping assembly comprising a transversely extending retaining bar 28 and a pair of retaining

fingers

29a and 29b pivotally mounted with respect to the bar 28 to clamp the free end 17 of the paper against the retaining bar 28 during the paper advance cycle, the clamping preferably being at a location forward of the print heads 18.

' As subsequently described in greater detail, after one line of characters has been printed, the retaining bar 28 and the retaining fingers 28a and 29b uniquely cooperate to incrementally advance the free end 17 to present a new blank space of the surface 16 to the print heads 18 for printing the next line of characters thereon.

Referring specifically to FIGS. 3 and 4, the retaining ,bar 28 is pivotally mounted to the sidewalls 11 by way of pins 30 passing through extensions 31a and 31b thereof. The retaining fingers 29a and 2% are respectively pivotally mounted to the bar extensions 31a and 31b by way of pins 34 passing through the integrally connected arms or

extensions

32a and 32b thereof. If

desired, springs 35 are provided for resiliently urging the,

fingers

29a and 29b against the surface of the bar 33), and toward (direction of arrow 43), the print heads 18. This pivotal movement is effected by a suspended solenoid assembly including a conventional solenoid coil 40 having leads extending to terminal portions 39 across which the actuating signal can be impressed, and a solenoid plunger 36 electromagnetically coupled thereto. The solenoid plunger 36 has a rigidly connected bracket extension 96 coupled by way of a pin 37 to a projection 35 of the extension arm 31a. Disposed around the solenoid plunger 36 and between the solenoid housing and plunger bracket is a spring 41 which is effective, when compressed, to resiliently bias or urge the retaining bar 28 in the pivotal direction represented by arrow 43.

As subsequently described in greater detail, the energizing of the solenoid coil 40 pivots the bar 28 in the direction of the arrow 33, the resulting movement incrementally advancing the free end 17 of the thermally sensitive paper. A projection or stop 87 affixed to the arm 31a and adapted to engage a side 11 limits the extent of this pivotal motion, and therefore determines the extent of the incremental advancement of the paper. As most clearly viewed in FIG. 3, the location of the retaining bar 28 in its rest" position (prior to rotation away from print heads 18) is immediately adjacent the forward edge of the pressure pad 26.

The retaining bar 28 cooperates with each of the retaining

fingers

29a and 29b to (l) firmly grip and advance the free end 17 of the paper past the row of print heads 18 as the bar 28 is pivoted in the direction of the arrow 33; and (2) release the paper from this gripping engagement while the retaining bar 28 is pivoted back to its rest position in the direction of arrow 43. To effect this result, the retaining

fingers

29a and 29b have a unique mounting relationship with the retaining bar 28. This relationship is best described by reference to FIG. 5.

Accordingly, the line X represents the radius of curvature of the are through which the transverse retaining bar 28 is constrained to pivot around its pivot point 30; and the line Y represents the radius of curvature of the are through which the retaining finger 29a (or 29b) is constrained to pivot around its pivot point 34. The line Z designates the slope of the surface of the bar 28 along which the free end 17 of the paper moves and is held. To effect the requisite advancement of the paper, the retaining finger 29a (or 29b) must be urged against the surface of the bar 28, thereby clamping the paper therebetween, as the bar 28 is rotated in the direction of the arrow 33, and must be released from this clamping arrangement when the bar rotates back to its rest position in the direction of the arrow 43. It has been determined that this dual result may be accomplished by maintaining the acute angle 6 between the radius Y and the slope line Z (thus determining the locus T of the intersection of the finger 29a with the surface of the transverse bar 28) greater than 0 and less than 90, the optimum angle 0 being from 75 to 80, inclusive. By utilizing this so-defined angular arrangement, the free end 17 of the thermally sensitive record material is firmly gripped or retained between the surface of the bar 28 and the

fingers

29a and 29b during the advance cycle (rotation of bar 28 in the direction of arrow 33); and it can slide or slip between the fingers 29 and bar 28 when the bar 28 is returned to its rest position (direction of the arrow 43) since the finger will move away from the surface of the bar 28 during this return.

Additionally, it is desirable to maintain the angle B between the radius X and the slope line Z (representing the slope of the surface of the bar 28 with respect to the arc through which the bar 28 travels) at substantially since the free end 17 of the paper is then maintained substantially tangent to this are of travel at all times, thus preventing the paper from buckling or crimping.

While the retaining

fingers

29a and 29b can have any portion engage the surface of the bar 28, it has been found desirable to have only the edge portions 38 of these fingers contact the bar surface. Furthermore, it is to be noted that while the employment of two

separate retaining fingers

29a and 29b as illustrated, provide equalized gripping pressures of each side of the paper end 17, while at the same time, presenting an unobstructed viewing surface between the fingers, it is also contemplated that a single retaining finger may be utilized extending either partially or all the way across the surface of the paper.

Referring again to FIG. 3, the solenoid housing is also coupled to an extension 45 of the mounting bar 23 below the pivotal connection point 24 for pivoting the mounting bar 23 (and consequently the print heads 18) away from the thermal record material, a stop or extension 46 on the bar 23 disposed for engaging the wall 11 and limiting the extent of this pivotal movement. The mounting bar also includes oppositely disposed extension arms 50 having end portions terminating immediately adjacent the

finger extensions

32a and 32b, at least one of these arms 50 having a spring 51 (FIG. 4) pivoting the mounting bar 23 toward (and therefore urging the print heads 18 against) the surface 16 of the thermally sensitive paper. As a specific and unique feature, and for the reason subsequently described, the spring 51, when extended, exerts a greater resilient force than that exerted by the spring 41, when compressed.

A tab or extension 70 is also provided on the mounting bar 23, and can be coupled by any means to a button or key on the keyboard of the calculator. Manual depression of the tab 70 results not only in the pivoting of the print heads away from engagement with the thermal paper, but also enables the end portions of the extensions 50 to engage the

arms

32a and 32b and pivot the

fingers

29a and 29b from engagement with the bar 28. This then facilitates the initial threading of the free end 17 of the thermally sensitive record material when a new roll 14 of record material is to be inserted into the mechanism 10.

The method and sequence of operation of the apparatus 10 is now described. The roll 14 of thermally sensitive record material is initially loaded into the rear of the housing by disposing the shaft bosses 13 into the slots 12. The free end 17 of the roll is then threaded through the transversely extending slot between the paper guide and the wall 15, behind the substrate 20, and thereafter between the surface of the retaining bar 28 and the retaining

fingers

29a and 29b (as illustrated for example in FIG. 1 To facilitate this threading, the tab 70 may be manually depressed to release the pressure of the substrate 20 against the paper and to allow the free end 17 of the paper to slip behind the retaining fingers. Release of the tab 70 then places the mechanism in the PRINT condition illustrated in FIG. 6A.

PRINT The selected heating elements 21 of all of the print heads 18 are then energized, resulting in the printing of an entire line of characters upon the viewing surface 16. During this PRINT cycle, the solenoid coil 40 is not deenergized, the row of print heads are maintained in firm engagement by the spring 51 against the thermally sensitive paper, and the retaining bar 28 is in its rest position adjacent the pressure pad 26, the spring 41 maintaining the retaining bar 28 in this position.

ADVANCE Upon energization of the solenoid coil 40 (by application of a signal across terminals 39), the

extensions

35 and 45 are simultaneously laterally translated toward one another (in the direction of the arrows 80 illustrated in FIG. 6B), thereby pivoting the bar 28 in the direction of the arrow 33 while simultaneously pivoting the substrate 20 (and thereby the print heads 18) out of engagement with the paper (in the direction of thearrow 90). Since the retaining

fingers

29a and 29b are firmly clamped against the bar 28, as previously described, the free end 17 of the paper is advanced in the direction of the arrow 19, the stop 87 limiting the extent of pivotal rotation of the bar 28 and thereby determing the extent of the incremental advance of the paper. The stop 46 limits the extent of pivotal movement of the print heads in the direction of arrow 90 away from the paper. At this point in time, the spring 41 is fully compressed, and the spring 51 (FIG. 4) is fully extended.

RETURN Upon completion of the advancement of the paper, the solenoid coil 40 is deenergized, and the operation cycle is depicted with reference to FIG. 6C. Accordingly, since spring 51 has a greater force than that exerted by spring 41, the print head substrate 20 is initially returned to bear against the pressure pad 26 to assist in retaining the paper in its advanced position. Then, under the influence of the spring 41, the retaining bar 28 is rotated in the direction of the arrow 43, the finger 29a (and 29b) being sufficiently relieved from clamping engagement against the surface of the bar 28 to allow the gripping assembly to slide along the free end 17 of the paper to its rest position.

This rest position is then depicted in FIG. 6D, all of the elements of the apparatus being in the same position as described with reference to FIG. 6A, but with the free end 17 having been incrementally advanced. The line of characters that were printed during the PRINT cycle described with reference to FIG. 6A is then in the position illustrated in FIG. 1, and the entire PRINT, ADVANCE, and RETURN" cycle can be repeated.

Various other modifications of the disclosed embodiment, as well as other embodiments of the invention, may become apparent to persons skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

What is claimed is:

1. Apparatus for incrementally advancing the free end of a supply role of thermally sensitive record material past thermal print means of the type generating a form of information representation, said thermallysensitive record material having a viewing face for indicating said information representation, said apparatus comprising:

a. first means for disposing said thermal print means at a first location adjacent said viewing face,

b. second means coupled to first means for pivotally moving said thermal print means into respective engagement with, and disengagement from, said viewing face, and

c. third means for gripping said free end of said supply roll at a location forward of said first location and incrementally advancing said record material past said thermal print means, said third means comprising a pair of cooperating retaining members pivotally mounted with respect to one another, one of said retaining members extending transverse to the direction of advancement of said record material and being pivotally mounted for respective rotation away from, and toward, said first location, the other of said retaining members having a gripping edge for engaging said viewing face and being so mounted with respect to said first retaining member to clamp the free end of said supply roll against the said one retaining member during its rotation away from said first location, and to release the free end of said supply roll from said clamping during its rotation toward said first location.

2. The apparatus as defined by claim 1, further including fourth means for pivoting said one retaining member.

3. The apparatus as defined by claim 2 wherein said second means and said fourth means comprises a solenoid.

4. The apparatus as defined by claim 2 wherein the said one retaining member is constrained to pivot through a first arc, the other of said retaining members is constrained to pivot through a second arc, and the angle between the radius of curvature of the second arc and the slope of the surface of the said one retaining member at the intersection of the said other retaining member with the surface of said one retaining member is greater than 0 and less than 90.

5. The apparatus as defined by claim 4 wherein said angle is from to 6. The apparatus as defined by claim 4 wherein the slope of the surface of the said one retaining member is substantially perpendicular to the radius of curvature of the first arc.

7. The apparatus as defined by claim 2 wherein said other retaining member comprises a pair of separate retaining fingers pivotally mounted to opposed connecting portions of said one retaining member.

8. The apparatus as defined by claim 3 wherein said other retaining member comprises a pair of separate retaining fingers pivotally mounted to opposed connecting portions of said one retaining member.

9. The apparatus as defined by claim 2 wherein said one retaining member is a transversely extending bar, and stop means is connected thereto for limiting its rotation away from said first location.

10. The apparatus as defined by claim 9 further including stop means for limiting the pivotal movement of said thermal print means away from said viewing face.

11. The apparatus as defined by claim 3 wherein said second means further includes resilient means for urging said thermal print means into respective engagement with said viewing face.

12. Thermal printing apparatus, comprising:

a. a row of thermal print heads of the type generating a form of information representation, each of said print heads comprising an array of heating elements, select ones of which, when energized, define said form of information representation,

b. first means for disposing said row of thermal print heads at a location adjacent the viewing face of thermally sensitive record material for indicating said information representation 0. second means coupled to said first means for pivotally moving said row of thermal print heads into respective engagement with, and disengagement from, said viewing face, and

d. third means for incrementally advancing said thermally sensitive record material past said row of thermal print heads simultaneous with the pivotal movement of said row of thermal print heads into said disengagement from said viewing face.

13. The thermal printing apparatus as defined by claim 12 wherein said third means comprises a pivotally mounted gripping assembly for gripping the free end of said thermally sensitive record material at a location forward of the location of engagement of said thermal print heads with said viewing face.

14. The apparatus as defined by claim 13 including fourth means coupled to said pivotally mounted gripping assembly and to said second means for simultaneously pivoting said gripping assembly away from said row of thermal print heads while pivoting said row of thermal print heads away from said viewing face.

15. The apparatus as defined by claim 14 wherein said fourth means comprises solenoid means.

16. The apparatus as defined by claim 14 wherein said gripping assembly comprises a retaining bar extending transverse to the direction of advancement of said thermally sensitive record material and a pair of retaining fingers pivotally mounted to opposed extension portions of said retaining bar, said retaining fingers being so mounted with respect to said retaining bar to clamp the free end of the thermally sensitive record material against the face of said retaining bar during the rotation of said retaining bar away from said row of thermal print heads, and to release the free end of said thermally sensitive record material from said clamping during the rotation of said retaining bar towards said row of thermal print heads.

17. The apparatus as defined by claim 16 wherein the said retaining bars constrain to pivot through a first arc, the retaining fingers are constrained to pivot through a second arc, and the angle between the radius of curvature of the second arc and the slope of the surface of the retaining bar at the intersection of the retaining fingers with the surface of the retaining bar is greater than 0 and less than 18. The apparatus as defined by claim 17 wherein said retaining bar has stop means connected thereto for limiting its pivotal movement away from said row of thermal print heads.

19. The apparatus as defined by claim 18 further including stop means for limiting the pivotal movement of said row of thermal print heads away from said viewing face.

20. The apparatus as defined by claim 18 wherein said second means includes resilient means for urging said row of thermal print heads into engagement with said viewing face.

Claims

1. Apparatus for incrementally advancing the free end of a supply role of thermally sensitive record material past thermal print means of the type generating a form of information representation, said thermally sensitive record material having a viewing face for indicating said information representation, said apparatus comprising: a. first means for disposing said thermal print means at a first location adjacent said viewing face, b. second means coupled to first means for pivotally moving said thermal print means into respective engagement with, and disengagement from, said viewing face, and c. third means for gripping said free end of said supply roll at a location forward of said first location and incrementally advancing said record material past said thermal print means, said third means comprising a pair of cooperating retaining members pivotally mounted with respect to one another, one of said retaining members extending transverse to the direction of advancement of said record material and being pivotally mounted for respective rotation away from, and toward, said first location, the other of said retaining members having a gripping edge for engaging said viewing face and being so mounted with respect to said first retaining member to clamp the free end of said supply roll against the said one retaining member during its rotation away from said first location, and to release the free end of said supply roll from said clamping during its rotation toward said first location.

4. The apparatus as defined by claim 2 wherein the said one retaining member is constrained to pivot through a first arc, the other of said retaining members is constrained to pivot through a second arc, and the angle between the radius of curvature of the second arc and the slope of the surface of the said one retaining member at the intersection of the said other retaining member with the surface of said one retaining member is greater than 0* and less than 90*.

5. The apparatus as defined by claim 4 wherein said angle is from 75* to 80*.

6. The apparatus as defined by claim 4 wherein the slope of the surface of the said one retaining member is substantially perpendicular to the radius of curvature of the first arc.

12. Thermal printing apparatus, comprising: a. a row of thermal print heads of the type generating a form of information representation, each of said print heads comprising an array of heating elements, select ones of which, when energized, define said form of information representation, b. first means for disposing said row of thermal print heads at a location adjacent the viewing face of thermally sensitive record material for indicating said information representation c. second means coupled to said first means for pivotally moving said row of thermal print heads into respective engagement with, and disengagement from, said viewing face, and d. third means for incrementally advancing said thermally sensitive record material past said row of thermal print heads simultaneous with the pivotal movement of said row of thermal print heads into said disengagement from said viewing face.

17. The apparatus as defined by claim 16 wherein the said retaining bars constrain to pivot through a first arc, the retaining fingers are constrained to pivot through a second arc, and the angle between the radius of curvature of the second arc and the slope of the surface of the retaining bar at the intersection of the retaining fingers with the surface of the retaining bar is greater than 0* and less than 90* .

18. The apparatus as defined by claim 17 wherein said retaining bar has stop means connected thereto for limiting its pivotal movement away from said row of thermal print heads.