US2739030A - Electrocardiograph - Google Patents

Description

March 20,1956

Filed March 23, 1950 R. H. KRUSE ELECTROCARDIOGRAPH 2 Sheets-Sheet 1 lNVENTOR Ralph E Kruse BY M Mr (1 ATTORN 2 Sheets$heet 2 R. H. KRUSE ELECTROCARDIOGRAPH March 20, 1956 Filed Mal ch 25, 1950 m mm INVENTOR r g, ATTORNE .4!

Ralph [i Kruse BY M United States Patent C ELECTROCARBIOGRAPH Ralph H. Kruse, Pclham, N. Y., .assignor to Cambridge Instrument Company, Inc., New York, N. Y.

This invention relates to electrocardiographs or like instruments, and more in particular to electrocardiographs of the direct writing type where electrocardiograms are made by the direct contact of a stylus with the record sheet.

It is an object of the present invention to provide an improved arrangement for making records on instruments of the above-mentioned type. Ordinarily, such an instrument has a suspended recording arm or writing boom which may bea pen or other writing instrument, or a stylus, and is formed by an elongated boom portion carrying the recording or writing element, for example, a stylus element, on its projecting end. Some such prior type instruments trace a record on curved ordinates having a radius .of curvature dependent upon the effective length of the boom. Records of this character, having the arcuate form'of the curved ordinates, are objectionable; first, because the records are confusing and are difficult to read and interpret; and, second, especially in the case of-electrocardiograms and the like, because the records take on a character different from those previously known and, therefore, appear unfamiliar to the technicians interpreting them.

Records of this type have also been produced on rectilinear coordinates, by passing the paper over a knife edge and then swinging therecording element through an are which is intersected by the paper at the knife edge so that the recording element marks the paper where it crosses the knife edge.

But this introduces a tangential error which in itself is undesirable, but becomes quite objectionable because it is not apparent and, therefore, the technician will be influenced toward misinterpretation of the record. Although records of this general nature have been produced with rectangular coordinates with a straight line movement of the recording element, the arrangements for accomplishing this have been so complicated as to be impractical and they have other characteristics which interfere with their wide use. It is an object of the present invention to avoid the various difiiculties, such as those referred to above, which have been encountered in the past with records of this general character. It is a further object to provide apparatus of the above character which is sturdy in construction, accurate and dependable in accomplishing the desired result, light in weight, and inexpensive to manufacture and maintain; and, which is adaptable to meet the needs arising from special circumstances in this particular field.

In accordance with the present invention, an arrangement is provided for producing records of the above character on truly rectangular coordinates. The illustrative embodiment of the present invention is an electrocardiograph having a recording galvanometer which swings a stylus on the end of a boom through an arc across the width of a strip of moving paper. With this arrangement an accurate rectangular coordinate characteristic is obtained by curving the record paper in a cylindrical surface, the ax s f h c co nc d ith he s n i 2,739,030 Patented Mar. 20, 1956 of the stylus, which is the axis of rotation of the galvanometer coil. The paper at the zone of recording has a predetermined radius which is a fixed characteristic of the instrument.

The cylindrical curving of the paper in this accurate manner is obtained by drawing it across and in contact with the concave surface of a curved platen having the desired curvature and a fixed relationship with respect to the axis of the galvanometer coil. The recording element or stylus contacts the paper along an arc of the cylinder to which the paper is conformed by the platen and which, as indicated, has its axis coincidental with that of the galvanometer coil and the swinging axis of the stylus which is fixed thereto. In the illustrative embodiment, the boom which supports the stylus is straight and extends diagonally from the coil, but that arrangement is not essential to certain aspects of the invention. The stylus is pressed against the paper with sufiicient pressure to produce optimum recording.

Although in this specification and the accompanying drawings l have shown and described a preferred embodiment of my invention and have suggested various modifications thereof, it is to be understood that these are not intended to be exhaustive nor limiting of the invention but on the contrary, are given for purposes of illustration in order that others skilled in the art may fully understand the invention and the principles thereof and manner of applying the same in practical use and be enabled to modify and adapt it in various forms each as may be best suited to the conditions of a particular use.

In the drawings in which like reference characters refer 1 to like parts throughout;

Figure l is a fragmentary and somewhat diagrammatic perspective view of one embodiment of the invention;

Figure 2 is a typical electrocardiogram produced upon the apparatus of'Figure 1;

Figure 3 is a vertical section with certain parts shown in full of the apparatus of Figure 1 ;and,

Figure 4 is a sectional view on the line 4-4 of Figure 3.

Referring particularly to Figure 3 of the drawings, there is shown at the left a roll 2 of the strip of chart or record paper 4 upon which the electrocardiograms are produced (see also Figure 1). This paper has a coated recording upper surface, which is white with longitudinal and transverse markings -(see Figure 2), and is of such a character that a black line is produced if a heated stylus is moved in contact with this surface. The coatingacts somewhat as a lubricating medium and little pressure is required to make the heated stylus produce its marking; thus, the friction between the stylus and the paper is extremely small. Positioned somewhat directly above (Figure 3) the roll of paper is the galvanometer coil 6 which is supported in a manner to be more fully described below, and which has fixed to it a recording boom 8 which extends diagonally downwardly to the paper and has a stylus 10 fixed to its lower or recording end.

As shown at the right in Figure 3, the strip of paper 4 is drawn from the roll 2 which is mounted in a well in a base plate 3 by a main feed roller 12 against which it is held by a pressure roller 14. Positioned between the roll of paper 2 and the feed rollers and resiliently mounted on base plate 3 is a platen assembly 16, formed by a lower platen 18 (Figure l) and an upper platen 19. Platen 18 presents a concave surface 20 having the curvature of a cylinder the axis of which is coincident with the axis of rotation of the galvanometer coil 6. The strip of paper 4 is drawn along this surface 20 parallel to that axis and is caused to conform to the curvature of this surface by an arcuate lip 24 on the upper platen 19 which rides against the paper. This lip cooperates with platen 18 tea, in effect, form a slot through which the paper is guided without being subjected to pinching or restraining pressuresand the curvature of the paper is determined by the curvature of the lower platen. v

The-upper platen 19 is resiliently mounted onthe lower platen so that it is urged toward the position shown, although it can belifted for the purpose of threading the paper through the platen assembly. The resilient mount ing is provided by a spring bracket 21 which is generally U-shaped in a horizontal plane and'is clamped to the top surface of the upper platen by a pair of screws 22 (see also Figurie4). The two legs of this spring bracket project parallel to and are spaced from the top surfaces of the side portions of the lower platen 18, and the ends'of these legs extend downwardly and are clamped to the lower platen by screws 23. Bracket 21 has sufiicient resiliency to hold'the upper platen. in the position shown and yet this platen may be lifted with ease so that the strip. of paper 4 can be pushed through along surface 20. Thislifting movement of the upper platen is limited by a pair of screws 25 which are threaded into the top of the lower platen and have their shanks projecting loosely through openings in bracket 21. These openings are smaller than the head of screws 25 so that the heads of the screws act as stops to limit the movement of the platen. 'The upper platen is lifted only when the galvanometer and stylus assembly is raised awayvfrom the platen assembly. This lifting operation is performed by a sheet metal bracket or shield 27 which is clamped at its base to the top of the upper platen by screws 22 and which projects upwardly beneath boom 8.

' Platens 18 and 19 are of plastic but directly beneath lip 24 and embedded in the lower platen 18 is a heatconducting metal strip 26, in this embodiment of sheet aluminum. Strip 26 extends the width of the strip of paper 4 and conforms to the cylindrical curvature of surface 20 so that it is a segment of a cylinder. As will be explained more fully below, strip 26 acts to conduct heat away from the stylus at any time that the temperature in the vicinity of the stylus tends to become excessive. The upper surface of strip 26 is slightly below the curved surface 20 so that leeway. is provided in the vicinity of the lip 24 and the stylus. However, the leeway is notsuflicient to permit the paper to deviate from the true cylindrical form referred to above.

When the strip of paper is drawn from roll 2 it is in fiat form and later as it passes between rollers 12 and 14 it is again in flat form. However, during the passage between these two points it is conformed to a cylindrical shape or form so that its recording surface is contacted by stylus while this surface has a true cylindrical form and the axis is coincident with the horizontal axis of galvanometer coil 6. The paper has such characteristics that it may be diverted in the manner shown to and from this cylindrical form without buckling or wrinkling. 1

During operation, boom 8 is swungthrough an arc of predetermined limits, due to the action of galvanome'ter coil 6 to which the boom is fixed. Coil 6 is rectangular with its sides positioned within two gaps 29 (see also Figure 4) in a magnetic core structure formed by a permanent magnet 28, two poles 30 and a stationary cylindrical core 32 positioned in the center of the galvanometer coil 6. The magnetic core structure thus forms two arcuate gaps in which the two sides of the coil are positioned and are subjected to uniform magnetic fields. Coil 6 is supported (Figure l) by four beryllium copper spring clips 34, 36, 38 and 40 which are positioned in pairs at the two ends of the coil with each clip being rigidly attached at one end to the coil and having its other end clamped by a screw 42 to the mounting frame. Each of these mounting clips is a flat strip of beryllium copper bent into an 8 form or curve at its center and having its ends extending parallel. One end of each of the springs is clamped to the coil by a band attachment 44 so that the coil is supported symmetrically at four spaced points. These clips tend to hold the coil in its exact horizontal position as shown, but yet the coil is permitted to rotate about its horizontal axis.

As shown best in Figure 3 there is positioned within the stationary core 32 a mounting sleeve structure 46 formed by a central compression spring 48 and two cylindrical end members 59. Each of the end members has an extension 52 which projects into a cylindrical opening or recess in the adjacent end wall of the galvanometer coil 6. The end members are clamped in the position shown byset screws 54 and when these set screws are loosened spring 4% urges the end members away from each other. The axis formed by end extensions 52 is coincident with the axis of coil 6 which, as indicated above, is also coincident with the cylinder of surface 20 of the lower platen. During assembly the end memhers 5% are clamped in such positions that they contact the coil only by their end extensions which project into the openings in the coil. Thus, a sleeve-bearing structure is provided for the coil, the axis of which is coincident with the axis of the coil and the recording surface. However, the coil is supported and its movementis guided by the four spring clips as discussed above, and the spring clips supply torsional control without any appreciable side or end components.

Galvanorneter coil 6 is deflected by passing signal currents through it and these currents are passed to the coil (see Figure 1) through clips 34 and 36. As has been suggested above, stylus 19 is heated and current for heating the stylus is carried by clips 38 and 40. Boom 8 is formed by two beryllium copper tubular struts 56 and 58 which are fixed to coil 6 at their upper ends and which support the two ends of the U-shaped stylus 10 at their lower ends. Struts 56 and 58 are reinforced and held in fixed relationship by three rigid transverse struts 60, 62 and 64 which are formed of glass fibers shaped as shown and are coated and cemented with a silicone cement having good-insulation properties. During use, the voltage source for heating the stylus is connected across clips 38 and 40 which are electrically connected respectively to struts 56 and 58 and the heating current flows from clip 38 down through strut 56 and thence through stylus 10 and back up strut 58 to clip 40.

As indicated above, a metal shield 27 is rigidly clamped to the upper platen 19 and projects upwardly beneath boom 8.- This metal shield acts as a lifting handle for the upper platen during the threading of the paper, but it has the important additional function of acting as a magnetic shield for boom 8. Thus, stray magnetic lines from magnet, 28 pass through the shield and are thereby diverted from the zone through which the boom swings. In this way, the electrical current which flows through struts 56 and 58 for the purpose of heating stylus 10 does not tend to cause the boom to move as it would tend to do if this shield were not provided.

Referring again to Figure 3, the galvanometer unit is mounted from its top on ,a rigid metal case '70 which providesrigid support for the galvanometer unit during use. Case has a main rectangular structure which is hinged at the left to the base plate 3 of the instrument by a hinge 72, and at the right the case has an integral forwardly projecting portion which is rigidly held to the base by a releasable clamp 74. This clamp has a cam surface latch which tightly engages and firmly holds the case in place. The case hasa window '76 through which the stylus and the strip of paper passing under it may be observed. When latch 74 is released, the case may be lifted by swinging it counterclockwise in Figure 3 around the pivot formed by hinge 72, and this lifts the galvanometer unit, and the boom and stylus, away from the platen assembly and the paper. Access may therefore be had to the paper supply and feed, for example, so that the roll of paper may be renewed and so that the paper may be threaded. As pointed out above,

during thethreading, the lower edge 24 of the'upper platen may be raised by pressing on the shield 27.

As shown best in Figure 4, projecting inwardly from the opposite side walls of case 70 are two lugs 77, which are in alignment with anvil recesses in the respective sides of' the lower platen 18. When the case is swung back down again lugs 77 engage the anvil recesses in the opposite sides of the lower platen 18, and as the latch 74 (-Figure 3') is turned to clamp the frame against the base, these lugs push the platen assembly down to a predetermined position. Lugs 77 are machined during manufacture of the frame so as to have a predetermined relationship with respect to the surface upon which the galvanometer unit is mounted, and therefore the galvanometer and the boom and stylus are mounted and adjusted with a predetermined relationship with respect to these lugs. Thus, as the frame swings down to the final position shown, the lugs cause the lower platen to take a predetermined position with respect to the galvanometer coil, and this position is such that the paper-conforming surface 20 of the platen has its axis coincident with the galvanometer coil axis.

Hinge 72 is clamped to the base plate 3 of the instrument by a screw 78 which may be turned by grasping its knurled top end when the case and galvanometer unit are raised, and by loosening this screw the frame and galvanometer unit may be removed from its base plate. In view of the fact that the galvanometer unit is the part of the instrument which is most apt to require testing and service, this arrangement for ready removal and replacement of the unit has particular advantage.

It has been pointed out above that the recording element is a heated stylus supported by a boom 8, and that boom 8 is formed by two struts 56 and 58 and three transverse struts 60, 62 and 64 which are reinforcing members of glass fiber cemented with silicone cement. The heated stylus 10 is a hairpin or U-shaped element of electrical resistance wire and its ends project into the ends of the tubular struts 56 and 58 and are soldered thereto with thin films of solder. The boom with the stylus attached is given a thin gold plate, and it has been found that this protects the soldered joints between the struts and the stylus, and insures longer life. The struts diverge and have their upper ends attached to the galvanometer coil 6 at diametrically spaced points on the end wall of the coil. While the two struts 56 and 58 have some bending flexibility they are held relatively rigidly in their longitudinal extent by the reinforcing struts 60, 62 and 64. Therefore, when the galvanometer coil rotates the boom transmits the movement without flexing and the stylus follows the coil movements with great fidelity. This not only gives improved accuracy of operation but it also insures longer life of the stylus because the stylus and its junctures with the struts are not subjected to flexing actions.

It has been pointed out above that the heated stylus moves across the surface of the paper with extremely small friction and, therefore, very little force is required to move the stylus. The particular shape of stylus 10 insures that the stylus will not tend to cut into the paper or otherwise engage the paper in such a way as to interfere with the movement. The particular stylus structure has low momentum and the strut structure is such as to give maximum strength for operation with minimum Weight. This boom construction and stylus and the spring clips which support the galvanometer coil and also provide the spring follow-up are important in obtaining maximum accuracy and sturdiness. This particular shape of stylus has additional characteristics which are apparent by examining the typical electrocardiogram of Figure 2 which will now be described.

The chart paper 4 has closely spaced longitudinal lines 80 which are spaced apart a distance of one millimeter equal to one-tenth of one millivolt when the instrument is properly calibrated, and every fifth line 82 is heavier so that the distance between the heavy lines represents one-half of a millivolt. The transverse lines are some- 6 what similar and comprise closelyspaced light lines 84 with everyfifth line 86 being heavy, and the paper is moved at a predetermined speed so that these lines represent time with thev space between adjacent lines representing one twenty-fifth of a second and the space between the heavy lines representing one-fifth of a second.

The electrocardiogram 87 of Figure 2 comprises light portions 88 and heavy portions 90; the light portions are produced by stylus 10 moving transversely of the paper i. e., substantially parallel to lines 84 and 86, while the heavy portions 90 are produced by the paper moving while the stylus is relatively stationary. As will be best under stood by referring to Figure 1, the stylus 10 moves tangentially of its curved contact surface when it moves across the paper and it moves at a very rapid rate. On the other hand, the paper moves somewhat parallel to the center of curvature of the curved contact surface of the stylus so that when the stylus is stationary there is a endency for the record line to be widened by the heating effect of the portions of the stylus at the two sides (Figure 4;). of the pointed contact; and this tendency for the line to be widened is emphasized by the relatively slow movement of the paper, that is, paper moves past the stylus at a sufliciently slow rate to, permit the stylus to make a line of the width shown at 90. The variations in the width of line between the light portions 88 and the heavy portions 90 result from varied rate of movement of the stylus. This difference in the weight of the lines corresponds exactly to the difference in the weight of lines on an electrocardiogram produced by the well known standard string galvanorneter type electrocardiograph. Therefore, an electrocardiogram such as that of Figure 2, produced on the instrument herein disclosed, is similar in these characteristics to those produced on the prior standard instruments, with which physicians and technicians are familiar, and may be interpreted with reference to the more or less classical examples of electrocardiograms which appear in medical literature.

Ithas been pointed out above that case may be released at its forward end and lifted from the base plate and this raises the stylus and boom away from the paper and platen assembly. When the case is swung back so as to return it to the position shown, the stylus may engage the paper initially with very light pressure, but when the case is clamped down and the galvanometer unit is moved to its position wherein the axis of the galvanometer coil coincides exactly with that of the axis of surface 20, this final positioning movement tends to stress or tension the boom and the stylus is then pressed against the paper with the desired pressure. While the boom is not deformable in its longitudinal direction, it has sufiicient flexibility to permit this tensioning action and the stylus is held resiliently against the recording surface.

The strip 26 of aluminum beneath lip 24 and the Zone within which the stylus contacts the paper insures that the stylus will not be overheated, and the platen will not be damaged. During normal operation the stylus contacts the record paper with the paper riding somewhat in air, that is, it is supported by the platen surface 20 and is held slightly above the upper surface of the strip 26 with the result that the recording action of the heated stylus is not interfered with by the strip conducting the heat away from the stylus. However, if the paper supply should become exhausted without the operator being aware of that fact, the stylus drops onto strip 26 and the heat of the stylus is conducted'therefrom by the strip and this keeps the stylus temperature within acceptable and safe limits. Furthermore, the strip will withstand relatively high temperatures without injury.

In this embodiment the heating current to the stylus is turned off when the paper feeding operation stops. Furthermore, the heating current and the coil deflecting current circuits are disconnected when the galvanometer is lifted by swinging case 70 on hinge 72.

As various embodiments may be made of the above invention and as changes might be made in the embodiment above set forth,-it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense. I

I claim:

1. In an electrocardiograph of the type having a galvanometer unit,- a stylus assembly associated therewith, and a record chart and platen assembly adapted to form the record chart into a curved surface having its axis coincident with the axis of rotation of the stylus assembly, the combination of a coil in said galvanometer unit adapted to be rotated about a predetermined axis, an electrically heated stylus element and a boom secured to said stylus element and said coil including electrical circuit connections for said element and mounting means for said galvanometer coil comprising a plurality of spring strips each of which has a curved central portion with one end fixed to the coil and the other end fixed to the stationary frame of the instrument and arranged to provide both mechanical support and electrical connection for said coil and stylus assembly.

2. An instrument as described in claim 1 wherein said mounting means comprises four of said springs individually mounted in pairs at opposite ends of said coil, one of said pair providing electrical connections to said stylus assembly and the other providing electrical connections to said coil. C

3. An instrument as described in claim 2 wherein said boom comprises two tubular metal struts which have their ends adjacent each other where they are attached to said heated stylus element, the opposite ends of said struts being spaced from each other and supported by the coil adjacent and electrically connected to the springs providing the electrical circuit to and from said heated element.

4. In an electrocardiograph of the type having a galvanometer unit and a record chart and platen assembly adapted to form the record chart into a portion of a cylindrical surface, the combination of a coil in said galvanometer unit adapted to turn about a predetermined axis, a stylus assembly comprising a'heated stylus element, a truss rigidly connected at one end to said stylus element and rigidly fixed to said coil at the other end to form a stylus boom flexible in a first plane which is longitudinal of said truss and passes through the axis of said coil and is rigid in a second plane which is the plane of the truss and is perpendicular to said first plane whereby said stylus element precisely tracks the rotary movements of said coil but may flex to and from the record chart surface, mounting means for said coil comprising a plurality of spring strips each having one end fixed to said coil and the other end fixed to the stationary frame of the instrument and arranged to provide both mechanical support and electrical connection for said coil and stylus assembly.

5. A device as described in claim 4 wherein said stylus boom comprises a pair of conducting members joined together in a gradually diverging manner from said stylus element and a plurality of spaced insulating members connecting said conducting members whereby the electrical heating circuit for said stylus element is down one conducting member through the stylus element and back up the other conducting'membcr to a pair of said spring strips.

6. A device as described in claim 5 wherein there are four of said spring strips, each having an S curved cen tral portion, and one pair is connected to provide electrical connection to said conducting members and the other pair is connected to provide electrical connection to said coil.

7. An electrocardiograph instrument of the type having a galvanometer unit and a record chart and platen assembly positioned to form the record chart into a portion of a cylindrical surface, comprising a'coil in said galvanometer unit, a stylus assembly operatively connected to said coil at one end and carrying at its other end a stylus mounted to contact said record chart, supporting means for said coil comprising a plurality of spring strips each having one end'thereof fixed to'said coil and the other end thereof fixed to the stationary frame portion of the instrument and arranged to aid in the support of said coil in a predetermined central position with respect to said pivots whereby signals of equal magnitude but opposite polarity will produce equal but oppositely directed deflections of said stylus element.

3. A device as described in claim 7 wherein said stylus assembly is rigidly fixed to said coil and said supporting means comprises four spring clips having an S curved central portion and one pair is connected to provide the electrical connection for said stylus and the other pair is connected to provide the electrical connection forsaid coil. l

9. A device as described in claim 8 wherein the platen assembly includes a canopy portion of magnetic material extending upwardly between said stylus boom and said galvanometer unit and shielding said boom and preventing damping of the deflections.

10. An electrocardiograph of the type having a galvanometer unit and a record chart and platen assembly mounted to form the record chart into a portion of a cylindrical surface, the combination of a' magnetic core structure comprising a pair of oppositely disposed pole pieces having concave pole faces, a stationary cylindrical core portion centrally positioned between said pole pieces to form two equal arcuate gaps in the magnetic circuit of said galvanometer unit; a rectangular coil loosely mounted about said stationary cylindrical element on a pair of pivots so that the side portions of said coil are positioned in said gaps; a stylus assembly comprising a heated stylus element and a stylus boom connected thereto at one end and rigidly mounted on said coil at the other end; supporting means for said coil comprising a plurality of spring strips having one end fixed to said coil and the other end fixed to the stationary frame portion of said instrument and arranged to maintain said coil in a central position within said arcuate gaps to subject each side of said coil to a uniform magnetic field whereby equal deflections in either direction are obtained for signals of equal magnitude.

ll. In a direct-writing electrocardiograph, a writing assembly including means for producing a magnetic field, a coil positioned within the field and having an axis of rotation, resilient means for supporting the coil for partial rotation within the field an about said axis including four strips of resilient material mechanically connected to said coil at spaced points around its periphery and in pairs with two of said points being spaced from said axis on one side of said coil and the other two points being spaced from said axis on the other side of said coil, a stylus-supporting boom mechanically coupled to said coil at two points spaced from the axis of rotation of said coil, and stylus means carried by said boom.

12. Au electrocardiograph writing mechanism comprising a permanent magnet having pole pieces with spaced opposing arcuate surfaces, a coil form of generally rectangular cross section positioned between said pole pieces, four S-shaped coil-supporting members formed of beryllium copper strips each secured at one end to said coil form, two of said members being secured at spaced points to one end of the coil form and the other two at spaced points to the opposite end of the coil form, frame means supporting the other ends of said members, a coil extending around and carried by said coil form, two metal boom-supporting strips secured to two of said coil-supporting members immediately adjacent said coil and extending outwardly in opposite directions, a generallyV- shaped stylus-supporting boom having two converging legs each joined at the base of the V to one of said boomsupporting. strips, stylus means carried by said bo'om at the apex of the V, and chart-supporting means adjacent said stylus means for supporting a moving chart strip.

13. In an electrocardiogranh for producing directly a visible trace on a chart strip, apparatus comprising a frame, a Writing assembly swingably secured to said frame and including means for producing a magnetic field, coil movably supported in said field, and stylus means mechanically secured to and extending from said coil, chart positioning means for guiding and positioning said chart strip with respect to said stylus means near the region engaged by said stylus means, means supporting said chart-positioning means on said frame and permitting limited relative movement between said frame and said chart-positioning means, and means rigidly secured to said writing assembly and arranged to releasably engage said chart-positioning means and hold it in predetermined fixed position relative to said writing assembly. 14. In an electrocardiograph for making a visible trace on a chart strip, apparatus comprising a base, a writing assembly including means producing a magnetic field, 2

a movable coil positioned in said field, and stylus means mechanically coupled to said coil and arranged to be deflected by movement of the coil, a platen secured to said base for supporting said chart strip, said platen being arranged for limited freedom of movement with respect to said base, supporting means secured to said writing assembly and swingabiy secured to said base and movable between a closed position wherein said stylus means is positioned near the platen and an open position wherein the stylus means is removed from the proximity of said platen, and positioning means on said writing assembly arranged to engage and position said platen relative to said writing assembly when said supporting means is in its closed position.

15. In an electrocardiograph for making a visible trace on a chart strip, apparatus comprising a base, a writing assembly including means producing a magnetic field, a movable coil positioned in said field, and stylus means mechanically coupled to said coil and arranged to be deflected by movement of the coil, chart positioning means for positioning said chart strip adjacent said stylus means, means supporting said chart-positioning means for limited movement with respect to said base, resilient means urging said chart-positioning means toward a predetermined position, supporting means secured to said writing assembly and swingably secured to said base and movable between a closed position wherein said stylus means is positioned near the platen and an open position wherein the stylus means is removed from the proximity of said platen, and means on said cover engaging said chart-positioning means and moving it against the force of said resilient means when said supporting means is in its closed position thereby to position said stylus means precisely with respect to said chart strip.

16. Electrocardiograph apparatus for producing a visible trace on a chart strip comprising a base, a cover swingably mounted on said base and movable between open and closed positions, a writing assembly secured to said cover and including a permanent magnet having pole pieces with spaced opposing arcuate surfaces, a coil form of generally rectangular cross section positioned between said pole pieces, four S-shaped coil-supporting members formed of beryllium copper strips each secured at one end to said coil form, two of said members being secured at spaced points to one end of the coil form and the other two to spaced points at the opposite end of the coil form, frame means supporting the other ends of said members, a coil extending around and carried by said coil form, two metal boom-supporting strips secured to two of said coil-supporting members immediately adjacent said coil and extending outwardly in opposite directions, a generally V-shaped stylus-supporting boom having two diverging legs each joined at the base of the V to one of said boom-supporting strips, and stylus means carried by said boom at the apex of the V, and chart-supporting means on said base for supporting said chart strip adjacent the stylus means when the cover is in its closed position.

17. Electrocardiograph apparatus for producing a visible trace on a chart strip comprising a base, a cover swingably mounted on said base and movable between open and closed positions, a writing assembly supported by said cover and including a permanent magnet having pole pieces with spaced opposing arcuate surfaces, a coil form of generally rectangular cross section positioned between said pole pieces, four S-shaped coil-supporting members formed of beryllium copper strips each secured at one end to said coil form, two of said members being secured at spaced points to one end of the coil form and the other two to spaced points at the opposite end of the coil form, frame means supporting the other ends of said members, a coil extending around and carried by said coil form, two metal boom-supporting strips secured to tWo of said coil-supporting members immediately adjacent said coil and extending outwardly in opposite directions, a generally V-shaped stylus-supporting boom having two diverging legs each joined at the base of the V to one of said boom-supporting strips, and stylus means carried by said boom at the apex of the V, chartsupporting means on said base for supporting said chart strip, adjacent said stylus when the cover is in its closed position and including a lower platen movably supported by said base, and means on said cover arranged to engage said platen for positioning said platen accurately with respect to said writing assembly when the cover is in its closed position.

1.8. In an electrocardiograph for producing directly a Visible trace on a chart strip, apparatus comprising a frame, a Writing assembly swingably secured to said frame and including means for producing a magnetic field, a coil movably supported in said field, and stylus means mechanically secured to and extending from said coil, said stylus means being heated, chart positioning means for guiding and positioning said chart strip with respect to said stylus means near the region engaged by said stylus means, means supporting said chart-positioning means on said frame and permitting limited relative movement between said frame and said chart-positioning means, and means rigidly secured to said writing assembly and arranged to releasably engage said chart-positioning means and hold it in predetermined fixed position relative to said writing assembly, said chart positioning means containing a strip of metal of high heat conductivity opposite the place on said chart engaged by said heated stylus means.

19. In an electrocardiograph, apparatus as claimed in claim 18 and wherein the surface of said metal strip is spaced slightly below the surface of the chart positioning means.

References Cited in the file of this patent UNITED STATES PATENTS 1,071,192 Von Voss Aug. 26, 1913 1,782,519 Sutton Nov. 25, 1930 1,901,921 Means Mar. 21, 1933 2,003,913 Wente June 4, 1935 2,412,639 Traugott Dec. 17, 1946 2,606,093 Reason Aug. 5, 1952 FOREIGN PATENTS 612,619 Great Britain Nov. 16, 1948

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