US2262958A - Potential recording mechanism - Google Patents

Description

Nov. 18, 1941. F. OFFNER POTENTIAL RECORDING MECHANISM Filed Feb. 17, 1939 3 Sheets-Sheet 1 AInp/If/ er Recorder awe/mm:

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POTENTIAL RECORDING MECHANISM Filed Feb. 17, 1939 3 Sheets-Sheet 2 Nov. 18, 1941. F. OFFNER 2,262,958

POTENTIAL RECORDING MECHANISM Filed Feb. 17, 1939 3 Sheets-Sheet 3 I 4 A29 o o 5i i I I a 2 23, 30 Q i I g (1 f Hg Q a/ z 32 33 $29 ea {2 o 0 rem-J- Patented Nov. 18, 1941 UNITED STATES PATENT; OFFICE azsaoss POTENTIAL RECORDING imcnA rsM Franklin Oifner, Chicago, 111. Application February 17, 1939,; Serial No. 257,005

(Cl. ass-5.5)

3Claims.

This invention relates to improvements in e1ec-- tric potential recorders and particularly to improvements in direct recording electrocardiov graphs.

An object of the present invention is to pro- .vide for more faithful recording at higher frequencies and with larger amplitudes than has previously been possible.

Another object of the invention is to provide a novel form of coupling between the piezo-electric crystal elements and the recording element. Other objects and advantages of the invention will be evident from the following description the line thereof adjacent each other. The piezo-electric crystal units 2| and 22 are preferably of the type disclosed in the patent to Alfred L. Williams No..

2,105,011 dated January 11, 1938, and are provided at each of three corners with metal bearing plates 23 on the front face thereof which bearing plates are formed to provide ball-like protuberances or pivot bearings 24. These pivot bearings contact the inner face of the cover plate I! of the casing-l3 and are held firmly in contact therewith by resilient rubber blocks 25 dis-.

posed between the rear wall of the casing-and each of the said three comers of the crystals' which are provided with bearing plates 23. A thin layer of rubber 28 is disposed between each of-the bearing plates 23 and the surface of the crystal elements. when the crystals are disposed in the casing as shown in Figs. 4 and 5 and the cover plate I: is applied and the screws 21 which secure the cover plate in position, are tightened, the crystal units are firmly supported between the cover plate and the rear wall of the casing, being clamped between the bearin plates 23 and the rubber blocks 25.

with three corners of each of the rectangular crystal elements 2! and 22 clamped as described Fig. 6 is a diagrammatic illustration of an electrocardiograph recording system embody g the v invention, and

Fig. 7 is an illustration of a calibration record produced by the invention.

The recording mechanism shown in Figs. 1 to 5 is mounted on a cabinet ill, the top of which is formed of a metal plate ll which forms a base for mounting the various elements of the recorder.

The recording pen assembly is mounted on the front cover plate I! of an upstanding casing ll.

Thecasing II is pivoted at one end thereof on a horizontal stub shaft l4 carried by a block ll mounted on the plate H. A bored block ll secured to the side of the casing by screws ll slides on the shaft l 4 to effect the pivotal mounting. A locking set screw ll secures the casing in axially adjusted position on the shaft II. The other end of the casing ll rests on an adjustable stop in the form of a set screw I! threaded into. the plate II which provides a means for adjusting the elevation of the casing and thus the contact pressure of the recording point on.the record tape. 7 a

The recording pen arm 20 is actuated by a pair' of piezo-electric crystal bending units II and 22 mounted in substantially the same-plane within the casing ll with the driving points above, the free corners II and 2| respectively, which are disposed adjacent each other are free to move in response to any piezo-electric deformation in the crystal units produced by the application of electrical potential thereto. The fourth and movable corners of the crystal units are provided with metal clips 3| and II, respectively, which engage over the corners and are cemented in position. Each of the clips or corner pieces Ill and II carries a phosphor bronze strip in the formof a projecting arm disposed at right angles to the face of the crystals. These arms, designated 32 and II, respectively, have connected in parallel but in such sense that when an E. M. F. is applied, the free corners II and II thereof move in opposite sense so that the arms 82 and 33 move along substantially parallel paths in opposite directions.

Because of the relatively small deformation of the crystal units themselves and the correspondingly slight movement of the arms 32 and 33 carried by the movable corners thereof, it is-necessary to provide for a large mechanical multiplication of this motion. In orderto eflect this multiplication of the crystal motion, the forward ends ofthe arms 32-and 33 are connected to opposite sides of a rocking member in the. form of a small pulleyelement 35 which is formed with, or rigidly connected with, a coaxial larger pulley segment 36. The ends of the arms 32 and.

33 are preferably soldered to opposite sides of the pulley 359s indicated at Hand 38. The diameter of the small pulley 35- is preferably about 4 inch and that of-the large pulley segment about 1% inches. The duelpulley 35-36 is carried on a pivot shaft 39 which is. journalled in'jewel bearings 40 and 4| mounted in a supporting block 42 rigidly secured. to the face of the cover plate l2. s

The supporting arm "for the marking element is carried on a pivot shaft 43 the pointed hardened ends of which are journalled in cup jewel bearings 44 and 45 mounted-in the opposed endsof screw members 46 and 41 adjustable in the projecting arms of brackets 48 and 49 tightening of the screw 52v tends to draw: theblock 58 up to the block 42.

The screw 53. is threaded through the block 50 and its inner end bearsagainst the surface of block 42 so that tightening the screw 53 tends to force the blocks 42 and 50 apart. By relative adjustment of the screws, the position of the block 50 can be adjusted and locked due to the opposing forces exerted by the screws.

The pivot shaft 43 is parallel to the pivot shaft 39 carrying the pulleys 35 and 36 and is provided with a'small pulley 54 in horizontal alinement with the pulley segment 36. -A very thin'brass band 55 having its opposite. ends fastened to the pulley segment 36, as by small hooks 56 and 51 mounted at the ends thereof, is trained casing |3 to provide a seal at this joint.

It has been found thatthe use of two crystalline elements connected to move in opposite sense as above described possesses several advantages. First it provides double the power of a single element which allows'the amplitude of motion of the marking element to be increased by the factor the square root of two, while maintaining the same frequency response, or allows the frequency response to be increased by the same factor while maintaining the same available amplitude. Also, due to the connections employed where the amplitude of motion of each crystal element is exactly the same, a pure torque is supplied to pulley 35 and pulley segment 36 so that in theory, the shaft and bearings for these pulley elements could be dispensed with entirely, and in actual practice some slight play in these bearings will not result in any'lost motion in the system. Great care in avoidance of any possibility of lost motion in any portion of the mechanical system is particularly important'in a piezo-electric crystal actuated recording system of this type because the motion of s the crystals themselves is so minute. as compared with the final resultant motion of the marking point. Thus a lost motion of .001 inch between the crystals and the segment due to play in the segment bearings would result in lost motion of 0.1 inch at the marking point, assum- I ing a ratio of 100 tol, a representative value. It will be noted that with the mechanical system herein disclosed, all parts of the system are under tension and thus no lost motion can occur in any part thereof.

The travelingtape 65 for receiving the record 7 'is served from a roll 66 mounted within the cabinet IO, passing over tensioning guide rods 61, through a slot '68 in the base plate I and thence over the surface of the plate between upper and lower feed rolls 69 and 18, respectively. The uparound the pulley 54 on the pivot shaft 43 for The diameter of the .justin'g the-screws52 and 53 the block 56 may be disposed and locked in position to adjust the tension of the pulley band 55. I a

The supporting arm 20 for the marking element. 5'8 is;preferably made from a duralumin stamping about .002 of an inch thick and carries a 'small ink tube 59 connected to the writing point 58 mounted at the end thereof. Ink is carried to thisassembly through a fine rubber tube 60 from an ink well 6| carried on a post 52 and adjustable in height to vary the ink pressure supplied to the writing point.

Since the crystal elements may be affected by moisture, it is desirable that the container |3 be tightly sealed. To effect this, a flexible rubber opening 34in the cover plate l2 and the motion transmitting arms 32 and 33 project through per tape feeding roller 69 is mounted on a shaft 1| journalled in bearings 12 mounted on the plate while the lower roller 18 is mounted on a shaft 13 journalled between the free ends of spaced arms 14, the other ends of which are pivoted on a bracket 15 on the underside of the plate Tension adjusting screws 16, threaded into the respective arms 14 adjacent their freeends extend through openings 11 in the plate II and have springs 18 confined between the heads.

of the screws and the surface of the plate. Tightwing or loosening the screws 16 results in varying the pressure between the rollers 69 and 10.

The tape feeding roller 69 is driven, by a synchronous motor 19 through a variable speed .drive. The motor 19 is provided'with a built on reduction gear drive 80 on the output shaft 8| of which gears 82 and 83 are mounted. The gear 82 is the larger of the two and is adapted to mesh with a smaller gear 84 on the shaft 1| of roller 69 while the gear '83 is smaller and is thisdiaphr'agm, being sealed-thereto by rubbercement. A suitable gasket 64 is also disposed beadapted to mesh with a larger gear 85 also mounted on shaft 1|, as shown in Fig. 1.

In order to provide for shifting the gears 82 and 83 selectively to engage them with the respective gears 84 and 85, themotor 19 is mounted on parallel links 86 and 81, pivoted at one end on the plate H as indicated at 88 and having pivotal connection to the'motor base as indicated at 89.

serves for swinging the linkage mechanism to shift the motor and gear assembly including the The link 81 extends beyond theedge of the plate I to provide a handle 98 which.

, between 90 and M. A series of switches 93, 04,

.is interposed between the primary and secondary.

I I capacity coupled: type having a variable voltage gears 82 and v83 so that either one of the latter may be engaged selectively with its associated gear 04 or 85.

;The electrical circuit connections for use of this potential recording marker in electrocardiog- 5 raphy are shown in Figure 6. Here 90 represents the writing mechanism described above, a thermionic vacuum tube amplifier, and 92 a variable series resistance element placed in series 85 and Stare used to connect the proper pairs of patient electrodes from the four standard electrical lead positions, right arm, left arm, chest and left-leg, to the amplifier input terminals.

These patient electrodes are numbered 91, 98, 99 and ill, respectively.'

A calibrating means MI is interposed in series .with the amplifier input. This is so arranged that direct potential pulses of l millivolt amplitude or an alternating potential of'l millivolt peak amplitude may be alternatively introduced.

One way of constructing such a calibrating means is indicated in Fig. 6. A resistor I0! is interposedin series with the input of the amplifier and either a direct current or an alternating current; may alternatively be passed through this resistor by throwing switch I03. The D. C. is obtained from'battery- I04 and the current as read on meter H4 is adjusted by variable resistor I05 so thatits value is sumcient to give the proper voltage drop in resistor I02. The A. C. is obtained from transformer I06, the primary of which'is connected to a 60 cycle A. C. supply line. A grounded electrostatic shield Ill 30 Here againthe current'jwhich is" passed through resistor lill-"isadjusted to the proper value as read on meter I ll, by a 'variable resistor I08. Now when switch-J03 is rapidly opened and closed in the down; position a series of D. C. pulses is 40 applied to thezamplifier input, while throwing the switch in the'up;position will apply an alternating current. "The function of this will be discussedlater.

Theamplifierfis'preferably of the resistance 4:;

gain of. up tofabout three hundred thousand times and an overall time constant of approximately one totwoseconds. It should be capable of. delivering a peak output voltage of about six hundred volts and its output impedance should be under approximately forty thousand ohms. The purpose of the variable series resistance element 9! is to provide damping of the motion of the recorder. The leads I" and H0 from the amplifier may be connected to the crystals through binding posts HI and H2.

Damping is required in this recorder because the moving mechanical system attached to the crystals has such relatively large inertialeffect it will reduce the resonant frequency of the system composed of the crystals andmechanical system to a frequency approaching that which it is desired to record. Although this moving sys-' tem be made as light as practicable, such an in- 05 ertial effect will still be produced, forthe amplitude of motion of. portions of the system, and especially of member 20 and associated marking element and ink tube, is relatively very great as compared with the motion of the crystals. The 70 effective inertia of any portion of the system is found by multiplying; its actual mass by the square of its amplitude of motion; and thus it is seen that the mass of the marking element may be 100 or 10,000 times as important as an equal mass at the driving point' of the crystal itself. The total inertial efiect of the moving mechanical system in the instrument as here described, is such that the mass of the crystals themselves is negligible in comparison therewith.

Now assuming that there were no damping introduced in the electro-mechanical system, as the resonant frequency is approached the amplitude of motion produced by a constant input voltage would greatly increase, and thus give distorted records of waveform. However, by properly introducing damping means, either electrical or mechanical, it is possible to dissipate relatively more power in such means as the resonant frequency is approached, and by careful adjustment of this means a relatively uniform response amplitude may be obtained, independent of frequency, even up to frequencies slightly surpassing the -first electro-mechanical resonant frequency of thesystem. As previously disclosed, it is possible to obtain such damping by the use of such a series resistance, and applicant has found that in the present invention is is desirableto obtain damping. of the motion by this 7 means in preference to mechanical damping. Applicant has found that the optimum value of this resistance may be very simply found by the use of calibrator Ill. A direct potential of 1 millivolt is introduced and the response amplitude adjusted to a suitable value (c. g. 1 cmas standard for electrocardiography) by varying the amplifier gain. Now an alternating potential of this same peak amplitude is introduced and the damping resistor 92 is adjusted until the re sponse amplitude obtained from the alternating potentials is equal to that obtained with the direct potential. The appearance of records when properly damped is shown in Fig. 7. Here H6 represents the form of tracing which would be obtainedwith the direct current pulses and Ill that-obtained with the alternating current. The

- frequency of alternating current to be here used is not critical but should lay in the middle range of the instrument. 60 cycles per second is a suitable value. Thejustification for this method of damping is as follows: The most desirable form of frequency response for a recorder is one in which all frequencies are recorded with equal amplitude (assuming they are of the same voltage). Applicant has found that if direct current pulses (in effect very low frequencies) and medium frequency potentials (as here 60 cycles per second) are recorded with the same amplitude-the frequency response curve of the instrument is made as nearly flat as possible. A variation of the damping resistor 92 will not affect appreciably the amplitude of the direct current pulses because of the relatively high impedance of the recorder to direct current, and thus the calibration need not be reset after adjusting the damping control. Although the voltages supplied for adjusting the damping are'here shown in series with the input they may be alternatively inserted in any positions in the system so long as they introduce equal voltages in series with the the body in the four positions indicated, and a pair of the switches 63- are closed to connecta selected pair of electrodes to the input terminals of the amplifier. The recording point will mark a direct record of the wave form of the body potentials as modified by the heart action so as to produce a cardiogram suitable for diagnosing the condition of the heart. Calibration may also be performed with the patient in the circuit, with switch 3 open.

Although a preferred embodiment of the invention and manner of employing the same have been illustrated and described by way of example, it will be understood that various modifications of the details of construction and mode of opera- .tion may be resorted to without departing from the spirit of the invention within the scope of the appended claims.

I claim:

1. In a potential recording mechanism of the character described, a pair of piezo-electric crystalline elements supported with the driving points thereof adjacent each other and connected to a current source in such manner that said driving points move in opposite directions under the V axis of said rocking member, said connections each comprising a relatively stiff link rigidly fastened at one end to one of said driving points and rigidly fastened at its other end to said rocking member, a 'pivot shaft spaced from the axis of said rocking member and substantially parallel thereto, a small diameter pulley member on said pivot shaft, a flexible band providing a driving connection between said rocking member and said pulley member, a recording arm carried by said pivot shaft and a marking element adjacent the free end of said am.

3. In a device for making direct legible marked records of the wave form of varying electricalpotentials, a plurality of piezo-electric'crystal elements connected in reverse parallel relation with the source of said potentials, and having movable portions adjacent each other, apivoted recording arm, motion multiplying means pro: viding a driving connection between said crystal elements and said recording arm, said driving connection comprising a rocking unit including a pair of coaxial rocking pulley members of differpivoted recording arm, and tensioned driving connections between said said recording arm.

2. In a device for making legible marked records of the wave form of varying electrical potentials, a pair of piezo-electric crystal units supported with the free ends thereof adjacent and connected with the current source in reverse relation so as to respond in opposite sense under the influence of applied electrical potential, a

rocking member and ent diameters, a relatively stiff projecting arm rigidly secured at one end thereof to the movable portion of eachof said crystal elements, said arms being rigidly connected at the other end thereof to the pulley member of smaller diameter on opposite sides of the axis thereof to provide a positive two-way drive connection between'the movable portion of each .crystal element and the rocking unit whereby said crystal elements mutually aid each other in imparting a rocking pivoted rocking member, two-way motion trans- I mitting connections'from the free ends of said crystal units to points on opposite "sides of the action without lost motion to said pulley members, a pivot shaft for said recording arm disposed substantially parallel with the axis of said pulley members, a pulley member carried by said pivot shaft having a diameter less than that of the larger of said first mentioned pulley members,

and a flexible driving connection between the peripheries of the larger of said first mentioned pulley members and the pulley on said pivot shaft.

FRANKLIN OFFNER.

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