Self-balancing Recorder

Abstract

A strip chart recorder of the self-balancing type characterized by a novel index mounting, pen assembly, and linear slidewire assembly which is movable about a guide shaft for the pen assembly. The pen assembly is comprised of a molded plastic body having a cavity forming an inkwell, integral mounting structure for releasably supporting and precisely positioning a pen in the well, and integral upstanding ears supporting bearings which cooperate with a guide shaft for the pen assembly. The molded plastic body additionally supports electrical contacts of spring material which engage the slidewire and trolley of the movable slidewire assembly and supply pressure for biasing the pen into engagement with the recorder chart. The slidewire contact and pen pressures are simultaneously adjusted by setting the position of the movable slidewire assembly. Means may also be provided for separate adjustment of the pen pressure. The pen assembly additionally has a part cooperating with a portion of the slidewire assembly so that the pen may be lifted regardless of its position across the chart when the slidewire assembly is swung to a pen lift position. The index is mounted on a separate loop of a pen carriage drive cable to avoid tipping the index when the pen is lifted.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

Applicant's invention is for an improved pen and slidewire combination for a self-balancing recorder of the type which may be found in the United States Patent Office Official Class for Recorders and more particularly for Recorders including rebalancing systems. Specific features of a pen assembly per se are more likely to be found in the United States Patent Office Official Subclass directed to Recorders with Markers and/or Driving Means Therefore and in a subclass directed specifically to those with ink supply to the marker.

2. Description of the Prior Art

Strip chart recorders with linear slidewires disposed parallel to the path of travel of a pen assembly and wherein the pen assembly supports contacts which cooperate with the slidewire and/or an adjacent trolley are well known to those skilled in the art. As the speed of pen travel across the chart has been increased continuing efforts have been made to reduce the mass of the pen assembly and minimize friction. Additionally, continuing effort has been made to simplify construction for more reliable operation and cost reduction. A most pertinent example of such a recorder is found in U.S. Pat. No. 3,438,049-N. E. Polster. The Polster patent is particularly pertinent in that it is one wherein spring contacts carried by the pen assembly cooperate with a slidewire and trolley and support a component of force in a direction tending to bias a pen toward a chart. However, as will be more clearly understood from a description of applicant's invention, applicant applies the spring contact forces in a manner different from that described in the Polster patent.

It has also been known in the prior art to employ various types of pen assemblies some of which include a pen carriage in which is mounted a pen assembly including a push-in capillary pen structure such as shown in U.S. Pat. Nos. 1,347,787-H. H. Mapelsden and 2,876,740-A. Melas. However, applicant is unaware of any pen structure wherein a single fabricated unit includes a body having a cavity providing an inkwell, ear-like extensions protruding from the body and supporting bearings which cooperate with guide means for the pen, another portion protruding from the body to cooperate with pen lifting means, and means to support and precisely position a plug-in capillary pen thereby avoiding the need for a separate pen carriage.

U.S. Pat. No. 3,454,952-S. J. Harkins discloses pen lift mechanism for a strip chart recorder wherein an index is assembled on a pen carriage in a manner such that it will not move as a result of a pen lifting operation. This is accomplished in accordance with applicant's invention by utilizing a simple plastic index which snaps onto a loop of drive cable for moving the pen carriage assembly thus avoiding mounting of the index or pointer on the pen carriage.

SUMMARY OF THE INVENTION

In accordance with applicant's invention there is provided in a self-balancing recorder including a chart and drive means therefore and a pen assembly and guide means therefore, the improvement comprising a movable frame supporting a slidewire parallel to the guide means for the pen assembly. The pen assembly is rotatable with respect to its guide means and supports spring biased slidewire contact structure for engagement with the slidewire. The pen assembly additionally supports a pen for recording on the recorder chart. There is included means to position the movable frame to move the slidewire against the spring biased slidewire contact structure for developing a fixed biasing force to control slidewire contact pressure and effect rotation of the pen above its guide means to a position for recording on the chart.

Further, in accordance with applicant's invention, there is provided an integral pen assembly for a recorder. The pen assembly is comprised of a body member including an internal cavity for the storage of a supply of ink therein and integral means for cooperation with guide means for the pen assembly for limiting movement thereof to a fixed path. The body member additionally includes means releasably to retain and accurately position a plug-in pen relative to the body and in ink receiving relation with the internal cavity.

In accordance with applicant's invention there is also provided an index or pointer member for a self-balancing recorder of the type having a cable for moving a pen assembly comprising an integral member including clip structure for fastening the index to the cable. The index member includes a web portion between the clip structure and a pointer portion which separates the clip and pointer portions a distance freely to receive a scale.

BRIEF DESCRIPTION OF THE DRAWINGS

For an understanding of applicant's invention the following specification and claims should be read while referring to the accompanying drawings where:

FIG. 1 is a plan view of the essential parts of a self-balancing strip chart recorder in accordance with applicant's invention with some parts broken away,

FIG. 2 is a partial perspective illustrative of the cooperation of a movable slidewire frame and a pen assembly in accordance with applicant's invention,

FIG. 3 is a side elevation with parts broken away showing the essential parts of the movable slidewire frame and pen assembly with a pen lift means positioned for the pen to be in contact with the chart,

FIG. 4 is a view similar to FIG. 3 with the parts in position for the pen to be raised from the chart, FIG. 5 is a top plan view of applicant's pen assembly,

FIG. 6 is a side elevation partly in section taken along the line 6--6 of FIG. 5,

FIG. 7 is a perspective view showing the cable drive for the pen assembly and index, and

FIG. 8 is an enlarged perspective view of the index and the manner of its connection with the drive cable.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates the essential parts of an automatic self-balancing strip chart recorder 10. Side plates 11 and 12 are part of a frame the details of which are conventional and therefore not shown. Supported for rotation in the side plates 11 and 12 is a chart metering roll for advancing a chart 14 in any customary manner. A pen 15 carried by a pen assembly 16 extends into a position overlying the chart for recording thereon. The pen assembly 16 is journaled on a guide shaft 17 and is moved back-and-forth along the shaft parallel to the chart by means of a cable 17A which is moved by a drum 18 connected to the output shaft of a recorder balancing motor 19. There is also mounted on a loop of cable 17A an index 20 which cooperates with a scale 21 to indicate to an observer the value of a condition being recorded on the chart. The operation of self-balancing strip chart recorders is well known to those skilled in the art, however, for additional information one may refer to U.S. Pat. No. 2,113,164-A. J. Williams, Jr., which is a patent describing such a recorder.

FIG. 2 is a partial perspective of the recorder 10 with parts omitted better to show features of applicant's invention. In FIG. 2 it may be observed that the pen carriage 16 has affixed thereto, as by a screw, a contact support bracket 22. This contact support bracket 22 supports a pair of contacts 23 of spring material for contacting a slidewire 24 which is supported on a support plate 27. Additionally, another pair of contacts 25 of spring material is supported by bracket 22 for engagement with a trolley 26 which is likewise supported on plate 27. As is fully described in the above mentioned Williams, Jr. patent, a slidewire is part of a measuring circuit of a self-balancing recorder and in operation a pen assembly is moved along a guide shaft by the recorder balancing motor simultaneously with positioning of a contact along the slidewire until a null condition exists in the measuring circuit thus to indicate and record the instant value of a measured quantity.

As best seen in FIGS. 2, 3, and 4, the slidewire and trolley elements 24 and 26 supported on plate 27 are in turn supported on a cross member 28 rigidly affixed to a pair of arms 29 and 31 to form a slidewire frame assembly. While various means may be utilized to fasten the arms 29 and 31 to the cross member 28, a screw through a countersunk hole in each arm into the ends of the cross member 28, such as shown in FIGS. 2-4, will be found satisfactory. The end faces of cross member 28 are parallel so that the arms 29 and 31 are disposed parallel. Each arm has a bushing 32 which serve as bearings for movement of the slidewire frame assembly about the guide rod 17 as a center. Arm 29 has a portion 29A extending to the left as viewed in FIG. 3. This portion has a bent-over tab 29B which overlies an extension 11A of sideplate 11. The tab 29B is threaded to receive a knurled adjusting screw 33 which is disposed in alignment with the extension 11A, which serves as a stop upon engagement therewith. After the desired adjustment of screw 33 has been made a lock nut 34 may be tightened to secure the screw in its adjusted position for reasons later to be described. In FIG. 3 is may be observed that the slidewire frame assembly is biased in a clockwise direction with respect to rotation about shaft 17 by means of a pen lift lever 36 which pushes a link 37 connected to arm 29 to force the adjusting screw 33 against the extension 11A of sideplate 11. The lever 36 being retained in the position shown against a stop 36B by an overcenter spring 36A which has an end fixedly related to sideplate 11 in a manner not shown.

As may be seen in FIG. 3 the pen assembly 16 which is slidable along the shaft 17 is freely rotatable about the shaft 17 except for the fact that the pen 15 engaging the chart serves as one means to limit rotation of the pen assembly in a clockwise direction and the contacts 23 and 25 engaging the slidewire 24 and trolley 26 respectively serve to bias the pen assembly against counterclockwise rotation about the shaft 17. In FIG. 4 it may be observed that instead of the contact of the pen with the chart preventing clockwise rotation of the pen assembly clockwise rotation of the pen assembly is prevented by engagement of a protrusion 40B with a lip 27A in a manner later to be described.

The slidewire frame assembly comprised of the cross member 28, arms 29 and 31, the plate 27 and the slidewire 24 and trolley 26, as mentioned above, is movable about the guide shaft 17. As mentioned above, it is limited as to how far it may be moved in the clockwise direction around the shaft 17 by means of the knurled adjustment screw 33 which serves as a stop when it contacts the mating portion 11A of frame 11. Counterclockwise rotation of the slidewire frame assembly is limited by engagement of cross member 28 with an adjustable eccentric cam 35 best shown in FIGS. 3 and 4.

From the foregoing it may be observed that the range of movement of the slidewire frame assembly between its clockwise and counterclockwise positions is limited by the adjustments of the knurled screw 33 and the eccentric cam 35. The slidewire frame assembly may be moved from the position shown in FIG. 3 to the position shown in FIG. 4 wherein the pen is raised from the chart by an amount which is a function of the clearance between the protrusion 40B and lip 27A, which is dependent upon the position of adjusting screw 33, and the position of the eccentric cam 35. Moving the lever 36 to the position shown in FIG. 4 where it is releasably held against a stop 36C by the overcenter spring 36A places a spring 38 in link 37 in tension which exerts a pull to the right on link 37 thereby to pull the lower end of arm 29 and therefore the slidewire frame assembly counterclockwise about the shaft 17 and move across member 28 against the eccentric cam 35. When the slidewire frame assembly is moved counterclockwise about shaft 17 the adjustment screw at the upper end 29A of arm 29 is moved away from portion 11A of frame 11. As the lever 36 is moved to the FIG. 4 position the entire slidewire assembly moves to effect lifting of the pen 15 in a manner hereinafter set forth.

Still referring to FIG. 3 it may be noted that the support plate 27 extends upwardly beyond the cross member 28 to form the lip 27A and that the pen assembly 16 has the protrusion 40B which faces lip 27A and which, as seen in FIG. 3, is out of engagement with the lip 27A of support plate 27 by an amount which is a function of the position of adjustment screw 33. In FIG. 4 with the arm 36 in the pen lift position it will be seen that spring 38 has been placed under tension and the link 37 is pulled to the right to bias the slidewire frame assembly against the eccentric cam 35. During movement of the slidewire assembly from its FIG. 3 position to its FIG. 4 position the lip 27A engages the protrusion 40B and rotates the pen assembly 16 counterclockwise lifting pen 15 clear of the chart. From the foregoing it will be evident that no matter what the position of the pen assembly 16 relative to the width of the chart, the lip 27A of the support plate 27 which extends the full width of the chart may engage the protrusion 40B to effect a pen lift operation.

The knurled screw 33 serves as an adjustment to control the amount of pressure exerted by the pen 15 on the chart 14. With the lever 36 in the position shown in FIG. 3, pressure is applied to bias the slidewire frame assembly clockwise through link 37. Backing off the adjustment screw 33 will permit the arm 29 to rotate further in the clockwise direction about the shaft 17, thus moving the slidewire 24 and trolley 26 more firmly against the spring contacts 23 and 25 to increase both the slidewire and trolley contact pressure, this in turn tends to rotate the pen assembly 16 clockwise about the guide shaft 17 and increase the pressure of pen 15 on the chart 14. Turning the adjusting screw 33 in the opposite direction so as to cause the slidewire frame assembly to move counterclockwise will reduce slidewire contact pressure and the pressure of the pen 15 on the chart 14. If this adjustment be continued it will eventually move the pen 15 clear of the chart when the distance between the protrusion 40B and the lip 27A is reduced to zero and further movement of the slidewire frame forces the pen assembly to rotate counterclockwise. Under these conditions no further reduction in slidewire contact pressure can be effected. Whether the pen be contacting the chart or be adjusted so as not to touch the chart the additional distance that the pen can be lifted from the chart after locking the adjusting screw 33 by mean of the lock nut 34 will be controlled by adjustment of eccentric cam 35 which limits counterclockwise movement of the slidewire frame assembly when lever 36 is moved to the pen-lift position shown in FIG. 4.

With applicant's arrangement the pressure of a pen or other type of marker on the chart may be set at a desired positive value or a fixed clearance may be provided between marker and chart. In either case these adjustments are independent of pen-lift operation. The distance from the center of shaft 17 to the average point of engagement of contacts 23 and 24 constitutes the length of a first lever arm and the distance from the center of shaft 17 to the point of engagement of the pen 15 with the chart 14 constitutes the length of a second lever arm. By selection of the length of these lever arms and the material and dimensions of the contacts 23 and 25 one skilled in the art can select a wide variety of pen pressures. Applicant has, for example, used an approximately one-to-one ratio for the lever arms and for the contacts 23 and 25 has used contacts obtainable from J.S. Ney Co., Bloomfield, Connecticut, U.S.A., which are described on pates 49 and 60 of their catalog R-69 as Formed Wire Brushes Type 1020, Paliney 7 (heat treated) having a basic wire diameter of 0.012-inch. The dimensions including angle of set are shown on page 49 of the catalog and the deflection force information is set forth in a Table II on page 60. The forces on the guide shaft 17 created by the action of the slidewire contacts and pen engagement with the chart are applied in a manner to achieve a good balance tending to reduce twisting of the pen assmbly 6 in a direction which would introduce friction.

In FIGS. 5 and 6 there is shown in greater detail the structure of the pen assembly 16. The pen assembly includes a body portion 40 which may desirably be made of a transparent or translucent molded plastic such as a selected one of General Electric CO.'s LEXAN polycarbonate resins. As best seen in FIG. 6 the body portion has a hollow interior 40K forming an inkwell. The body 40 has integral therewith upstanding ear portions 40A having holes to receive bushings 39 which are a good slide fit on the shaft 17. Bushings 39 may be made of phosphor bronze, a suitable plastic such as E.I. DuPont de Nemours'DELRIN, acetal resin or other material having desirable properties for use as a bearing material. As previously mentioned, the body 40 may have a protrusion 40B (FIG. 6) which may be a molded part thereof and hence integral therewith which cooperates with the lip 27A of the support plate 27 to provide a pen lift function. Each of the upstanding portions 40A may additionally have rearwardly extending ears 40C with a notch 40C' into which knotted portions of cable 17A may be captured. As may be noted in FIGS. 2 and 7 the cable 17 is knotted at spaced locations with the knots serving as stops so that an excess length of cable is left between the ears 40C so that together with the spring 17B, later to be described, the cable is a continuous loop, hence the pen assembly may be removed without losing ends of the cable.

The molded body 40 additionally includes a pair of holes 40D and 40E. The hole 40D is adapted to receive a rubber grommet 41 the center hole of which is a snug fit for the capillary pen 15. Positioned directly below the hole 40D and in line therewith is a protrusion 40F extending internally into said inkwell and having a hole therethrough to receive the lower end of the capillary pen 15. Thus it will be seen that the grommet 41 and the hole in the inwardly extending molded part 40F serve to support the pen 15 securely in a vertical position. The hole 40E receives a rubber grommet 42 having molded integral therewith a bulbous portion for priming the pen. The bulb itself may include a vent hole which is covered with an operator's finger when the pen is primed or a separate vent hole may be included adjacent the holes 40D and 40E.

Another portion of the molded body 40 is an upstanding ear 40G terminating in a thickened portion 40H. The portion 40H has a hole therethrough and a slot 40J which provides a resilient clamp to receive the horizontal portion of the capillary pen 15. When the pen 15 is snapped into the slot in this resilient plastic material it is securely held and retained against motion vertically and against rotation with respect to the body 40. As best seen in FIG. 5 the pen 15 is held securely at right angles with respect to the longitudinal axis of the guide shaft 17 and as best seen in FIG. 6 the pen 15 is held securely against vertical motion with respect to the body 40 and with respect to the longitudinal axis of the guide shaft 17. Since the position of rotation of the body 40 about the longitudinal axis of 17 is precisely controlled by means of the knurled adjusting screw 33 and the eccentric cam 35, as shown in FIGS. 3 and 4, and dependent upon the position of lever 36, it will be understood that application has provided a very simple pen assembly which when locked in the groove 40J holds the tip of the pen 15 securely in its writing position. Nevertheless the pen is readily removable for cleaning by operating the lever 36 of FIGS. 3 and 4 to the pen lift position and swinging the pen 15 clockwise as viewed in FIG. 5 by unsnapping it from the groove 40J, shown best in FIG. 6, and drawing the pen vertically from the body 40. When the pen is replaced by performing the removal operations in reverse the pen will always come back to its precise position with respect to the chart to record correct values of measured quantities and with the same adjusted pen pressure until such adjustment be changed by an operator.

As may be seen in FIG. 6 the writing tip 15A of pen 15 is supported in a sleeve 15B which is removable to permit changing the writing tip. In the above described modification of applicant's invention a sapphire writing tip was employed which requires a pen pressure in excess of 15 grams. In order to make it possible to utilize writing tips of other materials, such as a felt tip which functions with a much lower pen pressure, the pen assembly 16 may include a spring 40L with a slide 40M of low friction material to engage and move along member 28 and apply a force in opposition to that of spring contacts 23 and 25. The body 40 may include an inwardly extending threaded boss 40N for supporting the spring 40L as by a capscrew 40P. Also if desired the rider 40M may be mounted on a threaded adjusting screw not shown to provide a fine adjustment for the reduced pen pressure. If desired the member 28 may support a retransmitting slidewire in this location and the slide 40M may comprise spring contact structure for engagement therewith. The structures described enable one skilled in the art by selection of contact spring configurations and materials, the distances between the center of shaft 17 and the points of engagement of the contacts 23 and 25 with the slidewire and trolley and the writing tip of pen 15 with the chart, and the material and dimensions of spring 40L to obtain slidewire contact and pen or other marker pressures or spacing over a wide range and accurately control them during recording and pen lift operations.

It is another feature of applicant's invention, as best shown in FIG. 7, to so mount an index 20 relative to the pen 15 so that there will be no interaction between the two when the pen is lifted. It has been customary in prior art recorders to mount an indicator on the pen carriage in a manner shown, for example, in U.S. Pat. No. 2,113,748. Mounting an indicator on the pen carriage in a manner such that it moves when a pen is raised or lowered with respect to writing engagement on the chart causes the pen to move relative to a fixed scale in a manner such as to introduce a parallax error when reading the relationship between pointer and scale. In FIG. 7 there is shown a stringing arrangement for the cable 17A wherein there is provided an extra loop of cable on which may be mounted separately and apart from the pen assembly the indicator 20.

Referring to FIG. 7 it may be seen that the cable 17A has a pair of knots 17C, only one of which shows in FIG. 7, between which there is a slack portion 17D. With the cable secured as shown in FIGS. 2 and 6 in the grooves 40C' in the ears 40C of the pen body 40, the cable 17A, due to the action of a tension spring 17B, forms a continuous closed loop securely fastened to the pen assembly 16. For a better understanding of the cable stinging arrangement, in FIG. 7 reference numbers have been applied to the various strands of cable 17A as well as to the pulleys around which the cable is passed. If the drum 18 be rotated clockwise by the recorder balancing motor the cable 17A is paid out around a pulley 50 and element 51 of cable 17A will move to the left as shown in FIG. 7. The cable continues around pulley 52 and the cable element 53 moves in the direction of the arrow and around pulley 54. Element 55 of the cable 17A moves to the right as viewed in FIG. 7 and around pulley 56. Element 57 of cable 17A moves parallel to and in the same direction as element 51, that is to say, to the left as viewed in FIG. 7 and around pulley 58. Element 59 moves in the direction of the arrow around pulley 60. Element 61 with the spring connector 17B moves to the right around pulley 62 and is wound up on drum 18. From the foregoing it will be clear that elements 51 and 57 of the cable 17A will at all times move in the same direction and at the same speed.

Index 20, as best seen in FIG. 8, is comprised of a molded element which may be made of a colored resilient plastic such as one of the General Electric Co.'s LEXAM polycarbonate resins. An upstanding portion 20A of the molded plastic part has a shape similar to an inverted T. The cross member of the T-includes a pair of U-shaped clips 20B as integral parts of the molding. These clips are a snug fit on element 57 of cable 17A. At the top of the T-shaped portion is a U-shaped part 20C with the legs of the U-spaced apart a distance freely to pass element 55 of cable 17A. As is readily evident from FIG. 8, the T-shaped portion extends upwardly from a flat bottom portion 20D which has an upwardly projecting pointer portion 20E. The width of the flat bottom web portion between the upstanding T and the pointer is sufficient freely to accommodate a scale interposed between the pointer and the T-shaped portion.

As will be more clearly understood by referring back to FIG. 7, the index 20 is secured to cable element 57 by snapping the close fitting clips 20B onto the cable with the index portion 20E positioned in line with the pen 15. The upper U-shaped element which straddles the cable element 55 merely serves to steady the index in an upright position, and as best shown in FIG. 1 the scale fits freely between the upstanding portion 20A and 20E shown in FIG. 8. As will be understood, th index will move back-and-forth in alignment with the pen 15, however the pen 15 may be raised or lowered without in any way affecting the position of the index 20.

Whle applicant's invention has been illustrated utilizing specific examples of structure and materials it will be apparent that the structures may take different forms and various materials may be used which will be found suitable for the practice of applicant's invention. Additionally, it is believed clear that some features of applicant's invention may be employed without the use of other features within the scope of applicant's claims.

Claims

What is claimed is:

1. A self-balancing recorder including a chart and drive means therefore and a pen assembly and guide means therefore, with the improvement comprising:

a movable frame supporting a slidewire parallel to said guide means for said pen assembly,

said pen assembly being rotatable with respect to its guide means and supporting spring biased slidewire contact structure for engagement with said slidewire and a pen for recording on said chart, and

means to position said movable frame with said slidewire against said spring biased slidewire contact structure for developing a fixed biasing force to control slidewire contact pressure and effect rotation of said pen assembly about its guide means to move said pen to a position for recording on said chart.

2. A self-balancing recorder according to claim 1 wherein an adjustable stop is provided to limit movement of said movable frame to control the pressure of said pen on said chart.

3. A self-balancing recorder according to claim 1 wherein said guide means for said pen assembly is a round shaft about the longitudinal axis of which both said pen assembly and said movable frame rotate.

4. A self-balancing recorder according to claim 1 wherein said pen assembly is comprised of an integral body member including:

an internal cavity for the storage of a supply of ink,

means to support said spring biased slidewire contact structure for engagement with said slidewire

means for supporting bearing structure for cooperation with said guide means therefore, and

means releasably to retain and accurately position said pen relative to said body and in ink recieving relation with said internal cavity.

5. A self-balancing recorder according to claim 4 wherein the integral body member of said pen assembly additionally includes spaced apart slotted structures for reception of a length of cable and cable stops for moving said pen assembly relative to said chart.

6. A self-balancing recorder according to claim 4 wherein the integral body member of said pen assembly additionally includes means to support a spring mounted slider for engagement with an element of said movable frame disposed parallel to said slidewire.

7. A self-balancing recorder according to claim 1 wherein said pen assembly additionally supports spring means for application of a force on said slidewire assembly in opposition to that of said spring biased slidewire contact structure for reduction of the pressure of said pen on said chart.

8. A self-balancing recorder according to claim 1 including a cable for moving said pen assembly along said guide means therefor and an index attached to a loop of said cable for movement in alignment and together with said pen of said pen assembly.

9. A self-balancing recorder according to claim 1 wherein said movable frame includes lip structure and said pen assembly includes means cooperating with said lip structure to oppose the spring bias of said slidewire contact structure.

10. A self-balancing recorder according to claim 9 wherein said means to position said movable frame includes mean to move said movable frame in a direction causing said lip structure to push against said means cooperating with said lip structure to raise said pen from the chart.

11. A self-balancing recorder according to claim 1 wherein said pen assembly additionally supports a spring biased slider for engagement with an element of said movable frame supporting a slidewire parallel to said guide means for said pen assembly, said spring biased slider exerting a force in opposition to that of said spring biased slidewire contact structure.

12. An inkwell, for recorder pen assembly, comprised of molded plastic forming wall structure of a supply of ink therein, a portion of said plastic projecting outwardly from said wall structure for cooperation with guide means for limiting movement of said body member to a fixed path relative to a recorder chart, said wall structure of molded plastic including one of more portions for receiving and supporting a plug-in pen, and a portion of said molded plastic projecting outwardly from said wall structure forming a resilient clamp to receive a pen portion releasably to retain and accurately position a plug-in pen relative to said body member in ink recieving relation with said internal cavity and prevent rotation of said pen with respect to said body.

13. An inkwell, for a recorder, having means releasably to retain a plug-in pen in said well comprising support means in the top of said well in alignment with support means in a protrusion extending internally into said well, and an ear portion including a pen engaging slot securely to hold a pen in vertical alignment in said support means and against rotation about an axis defined by a line through the centers of said support means.

14. An inkwell, for a recorder pen assembly, comprised of molded plastic forming wall structure of a body member including an internal cavity for the storage of a supply of ink therein, portions of said plastic projecting outwardly from said wall structure and forming a pair of spaced apart ear portions having aligned holes for cooperation with a guide rod for limiting movement of said body member to a fixed path relative to a recorder chart, said wall structure of molded plastic including means for supporting a plug-in pen in ink receiving relation with said internal cavity, and a portion of said molded plastic projecting outwardly from said wall structure and having a pen engaging portion providing means releasably to retain and accurately position a plug-in pen relative to said body member.

15. An index member for a self-balancing recorder of the type having a cable for moving a marker assembly comprising an integral member including clip structure for fastening said index to a cable, a web portion having said clip structure associated with one edge of said web portion and a pointer portion associated with the other edge of said web portion and with the width of said web separating said clip portion and said pointer portion a distance to receive a scale.

16. An index member according to claim 15 wherein said web portion includes an upstanding portion supporting a U-shaped cable receiving element which serves to steady said index member in an upright position.

17. A marker assembly for a self balancing recorder of the type having a cable for moving the marker assembly, said assembly including a pair of spaced apart slotted elements for reception therebetween of an element of said cable having a pair of cable stops separated by a distance greater than that between said spaced apart slotted elements thereby to permit separation of said cable from said marker assembly without losing ends of cable.

18. A self-balancing recorder including a chart and drive means therefore, a marker assembly and guide means therefore, and a cable actuated by a balancing motor to move said marker assembly relative to said chart with the improvement comprising:

spaced apart slotted elements supported by said marker assembly,

said cable including stop structure spaced along the length thereof a distance greater than that between said spaced apart slotted elements, and cable tensioning means fo holding said cable with said stop structure against said slotted elements.

19. A self-balancing recorder including a chart and drive means therefore and a marker assembly and guide means therefore with the improvement comprising:

a movable frame swingable about the guide means for said marker assembly, said movable frame supporting a slidewire parallel to said guide means,

said marker assembly being rotatable with respect to said guide means and supporting; spring biased slidewire contact structure for engagement with said slidewire, marking means for recording on said chart, and a marker lift element for cooperation with said movable frame, and

spring controlled marker lift means in one position applying a force to said movable frame to press said slidewire against said spring biased slidewire contact structure to bias said marker toward said chart and in another position pulling said movable frame in a direction away from said spring biased slidewire contact structure and against said marker lift element to move said marker away from said chart.

20. A self-balancing recorder according to claim 19 wherein an adjustable stop is provided for limiting the extent of movement of said movable frame toward said spring biased slidewire contact structure for regulation of the pressure of the contacts on the slidewire and the pressure of the marker on the chart.

21. A self-balancing recorder according to claim 19 wherein an adjustable stop is provided for limiting the distance that the marker may be lifted from the chart.