US3554673A

US3554673A - Syringe pump

Info

Publication number: US3554673A
Application number: US795572*A
Authority: US
Inventors: Joel M Schwartz; Daniel F Krebs
Original assignee: Sage Instruments Inc
Current assignee: Sage Instruments Inc
Priority date: 1969-01-31
Filing date: 1969-01-31
Publication date: 1971-01-12
Anticipated expiration: 1988-01-12

Abstract

THE MOTORS FOR THE SEPARATELY RECIPROCATING DRIVE MECHANISMS OF A TWO BARREL SYRINGE PUMP ARE PROVIDED WITH ELECTRIC CONTROL CIRCUITS AND SWITCHES WHICH ARE ACTUATED BY THE RECIPROCATING DEVICE MECHANISMS AND WHICH CAUSE A FULLY WITHDRAWN SYRINGE TO COMMENCE INFUSION JUST BEFORE THE OTHER SYRINGE COMPLETES INFUSION, THE SWITCHES

ALSO CAUSING SOLENOID VALVE MEANS TO OPERATE IN PHASED RELATION TO THE INFUSION OF THE SYRINGES WHEREBY THE INFUSION IS CARRIED OUT AT A CONSTANT RATE WITHOUT PERCEPTIBLE INTERRUPTIONS OR SURGES WHEN THE INFUSION OF FLUID CHANGES OVER FROM ONE SYRINGE TO THE OTHER AND BACK AGAIN.

Description

;J an-.u 12, A1971y M; scHwA-rz'. EI'AL '3,554,673

' `V`SYRINGE: -PUMP Filed Jan. ,311, 1969 2 Sheets-Sheet 1 Urt.:

FIG. 1

j(am w28.

vFIG

FIG. 3

INVENTQRS JOEL M. SCHWARTZ BY DANIEL F. KREBs 'nomnzvs SYRINGE PUMP 2 Sheets-Sheet 2 ENV v moSz/EN IOPOE CNN INVO- INVENTORS JOEL M. SCHWARTZ DANIEL F. KREBS United States Patent O 3,554,673 SYRINGE PUMP Joel M. Schwartz, White Plains, and Daniel F. Krebs, Yonkers, N Y., assignors to Sage Instruments, Inc., White Plains, N.Y., a corporation of New York Filed Jan. 31, 1969, Ser. N0. 795,572 Int. Cl. F04b 7/00, 17/00 U.S. Cl. 417-412 4 Claims ABSTRACT OF THE DISCLOSURE The motors for the separately reciprocating drive mechanisms of a two barrel syringe pump are provided with electric control circuits and switches which are actuated by the reciprocating drive mechanisms and which cause a fully withdrawn syringe to commence infusion just before the other syringe completes infusion, the switches also causing solenoid valve means to operate in phased relation to the infusion of the syringes whereby the infusion is carried out at a constant rate without perceptible interruptions or surges when the infusion of fluid changes over from one syringe to the other and back again.

BACKGROUND OF THE INVENTION (l) Field of the invention This invention relates to syringe pumps, and more particularly to two barrel syringe pumps designed to continuously infuse the iluid being pumped at a constant, predetermined rate.

(2) Prior art A typical syringe pump comprises a syringe and a reciprocating drive mechanism for moving the plunger of the syringe forwards and backwards within the barrel f the syringe. The syringe is connected by appropriate tubing and valves to a source of reservoir of the fluid being pumped and to the body or other object to which the fluid is being delivered. Movement of the syringe plunger away from the fluid opening at the bottom of the syringe barrel withdraws fluid from the fluid reservoir (hereinafter referred to as the withdrawal phase of operation of the pump) and movement of the syringe plunger toward the fluid opening of the syringe barrel delivers fluid to the body or other object (hereinafter referred to as the infusion phase of operation of the pump). The syringe of a syringe pump is usually removable so that it can be cleaned or replaced by a syringe of a different size. Such pumps provide uniform, accurate and reproducible infusion of fluids and are useful in a wide range of applications in analytical, medical, biological and industrial areas.

When the syringe pump comprises only one syringe and drive mechanism, the infusion of the fluidT by the pump is interrupted when the syringe plunger reaches the bottom of the syringe barrel, and infusion cannot be resumed until the plunger has been withdrawn and the syringe barrel refilled. Continuous infusion can be obtained by the use of two syringes operated by separate drive mechanisms, the infusion and withdrawal phases of the two syringes being staggered so that one syringe will always be infusing while the other syringe is withdrawing and refilling. Although such double acting, two barrel syringe pumps are capable of substantially continuous infusion, there can be a short but perceptible interruption in the infusion of fluids, or even a reversal in the direction of flow of the fluid being infused, when one syringe stops infusion, or even starts to withdraw, before the other syringe commences infusion.

It has heretofore been proposed to avoid the interruption, and especially the momentary reversal in direction,

Patented Jan. 12, 1971 ICC of the fluid being infused by providing mechanically operated valve means for the inlet and outlet tubes of the syringes of a two barrel syringe pump which delay the opening of the outlet tube of the syringe just beginning its infusion phase until this syringe has built up sucient pressure to overcome the back pressure in the infusion line 0f the pump. However, as the other syringe is beginning its withdrawal phase of operation the valve means for the outlet tubing of the latter syringe must be closed before the outlet valve of the first syringe is opened. As a result, a perceptible interruption in the infusion of liquid remains.

After an intensive investigation into the problems involved in the design of a syringe pump capable of infusing a fluid at a constant, controlled rate without interruptions or perceptible fluctuations in the rate of delivery of fluid when the infusion of one syringe stops and that of the other commences, we have discovered that a two barrel syringe pump capable of meeting these requirements must carry out alternate infusion and withdrawal phases in a prescribed and critical sequence of operational steps. Specifically, we have found that a fully withdrawn and filled syringe must start infusion before the other syringe completes its infusion phase of operation. Moreover, the closure of the inlet valve and the opening of the outlet valve of the rst syringe Imust be delayed until after this syringe has commenced infusion so that, momentarily at least, the lirst syringe isvpumping back to the fluid reservoir. Finally, we have found that the opening of the outlet valve of the first syringe and the closure of the outlet valve of the second syringe must take place at essentially the same moment.

SUMMARY OF THE INVENTION The improved syringe pump of our invention is adapted to carry out the aforementioned essential sequence of operational steps and comprises, in its basic components, two syringes each adapted alternately to infuse and to withdraw a fluid being pumped, a reciprocating drive mechanism for each syrin-ge and valve means for alternately opening and closing the fluid inlet and fluid outlet lines of each syringe in operational relationship with respect to the infusion and withdrawal phases of operation of syringes. Separately controlled eelctric motors are connected to each drive mechanism in our improved structure, and first and second motor control means actuated by the reciprocating drive mechanisms are provided for operating each of the separately controlled Imotors. Each motor control means is adapted to complete the withdrawal phase and start the infusion phase of operation of the motor to which it is connected before the other motor completes its infusion phase and starts to withdraw fluid.

In the preferred embodiment of our invention each motor control means has a controlled infusion circuit for operating the motor to which it is connected in the direction of fluid infusion at a controlled variable speed and a rapid withdrawal circuit for operating the motor in the direction of fluid withdrawal at a higher speed than the maximum speed of fluid infusion. The valve means cornprise first solenoid means for simultaneously closing the inlet of the first of the two syringes and the outlet of the second of the two syringes, and second solenoid means for simultaneously closing the outlet of the rst syringe and the 'inlet of the second syringe. Each motor control includes electric switch means actuated by the reciprocating drive mechanisms when the drive mechanisms reach each end of their reciprocating paths of travel, the switch means being connected to the controlled infusion circuits and to the rapid Withdrawal circuits of the first and second motor control means and being connected to the Ifirst and second solenoid means.

In accordance with our invention, the drive mechanism for the first syringe causes the switch means to energize the controlled infusion circuit of the second motor control before de-energizing the controlled infusion circuit of the first motor control and before energizing the second solenoid means when said first drive mechanism reaches the end of its controlled infusion direction of travel. In like manner, the drive mechanism in the second syringe causes the switch to energize the controlled infusion circuit of the first motor control before deenergizing the controlled infusion circuit of the second motor control and before energizing the first solenoid means when said second drive mechanism reaches the end of its controlled infusion direction of travel.

BRIEF DESCRIPTION OF THE DRAWINGS The improved syringe pump of our invention will be better understood from the following description thereof in conjunction with the accompanying drawings of which FIG. l is a plan view, partly broken away, of an advantageous embodiment of the two-barrel syringe pump of our invention.

FIG. 2 is a side elevation, partly broken away, of the syringe pump shown in FIG. l,

FIG. 3 is a schematic diagram of the fluid tubing layout of the pump shown in FIG. l, and

F-IG. 4 is a schematic diagram of an electrical circuit adapted to carry out the essential sequence of operations characteristic of the improved syringe pump of our invention.

DETAILED DESCRIPTION The embodiment of the syringe pump of our invention shown in FIGS. l and 2 of the drawing comprises a housing having a top plate 11 on which most of the operating elements of the syringe pump are mounted.

Adjustable syringe holders

12 and 13 are mounted on the top plate 11, each syringe holder being adapted to hold a

syringe

14 and 15 as indicated by the dotted lines in FIGS. 1 and 2. The

holders

12 and 13 are adjustable so that syringes of various sizes can be mounted therein, the

syringes

14 and 15 preferably being substantially identical in size. Separately controlled

drive mechanisms

16 and 17 are mounted on the top plate 11, each drive mechanism being adapted to move the plunger of one of the syringes backwards and forwards in a reciprocating path of travel. Also mounted on the top plate 11 are solenoid operated valve means 18 for opening and closing the inlet and outlet lines of the

syringes

14 and 15 as required for the proper operation of the syringe pump. A power line 19 and fuse holder 20 are mounted on one side of the housing 10, and the main on-off switch 21 and pilot light 22 are mounted on the other side of the housing. Also mounted on the housing are the variable speed controls (i.e., rheostats) 23 and 24 for the

drive mechanisms

16 and 17 of the device.

In the embodiment shown in the drawing, the

drive mechanisms

16 and 17 have separately reciprocating

drive carriages

26 and 27 to which the

plungers

28 and 29 of

syringes

14 and 15 are secured by

adjustable plunger clamps

30 and 31. The

drive carriages

26 and 27 each comprise a box-like structure having a longitudinal extending rack 32 and 33t, respectively, which are engaged by

drive pinions

34 and 35, respectively. Idler gears 36 and 37 are disposed on the other side of each

drive carriage

26 and 27. As shown in FIG. 2, the drive pinion of drive carriage 27 is driven through a reduction gear train 39 by a reversible, variable speed motor 41. The drive pinion 34 of drive carriage 26 is driven through a similar reduction gear train 38 and reversible, variable speed motor 40 that cannot be seen in the drawing.

The reversible,

variable speed motors

40 and 41 are each connected to motor control means which operate the motor associated therewith at a controlled variable speed when the motor is moving the drive carriage driven thereby in the direction of fluid infusion, the motor control means having a controlled infusion speed circuit for this purpose. Each motor control means also operates the motor associated therewith at a constant rate of speed that is higher than the maximum rate of speed that is higher than the maximum rate of speed in the direction of controlled infusion when the motor is moving the drive carriage in the direction of uid withdrawal, the motor control means having a rapid withdrawal speed circuit for this purpose. The controlled infusion circuits (which include the rheostats 23 and 24) and the rapid withdrawal circuits of the motor control means are conventional and are not described in detail herein. The motor control means for the motors 40 (not visible in the drawing) and 41 also include lever switches 42 (not visible in the drawing) and 43 which are operated by the

reciprocating drive carriages

26 and 27, respectively, when these drive carriages reach each end of their reciprocating paths of travel. To this end, the drive carriage 26 is provided with adjustable limit stops 44 and 45 which alternately contact and move the lever 46 of the lever switch 42, and the drive carriage Z7 is provided with

adjustable limit stops

47 and 48 which alternately contact and move the lever 49 of the lever switch 43, when the drive carriages reach each end of their reciprocating paths of travel.

The solenoid operated valve means 18 comprises a valve anvil 50 formed with two pairs of

transverse slots

51 and 52 adapted to receive the inlet and outlet lines or tubing of the

syringes

14 and 15 and with a longitudinal slot 53 adapted to receive two plate-

like valve members

54 and 55. The valve member 54 is positioned in the longitudinal slot 53 directly above the tubing disposed in the pair of transverse slots 51, and the valve member 55 is disposed in the slot 53 directly above the tubing disposed in the pair of slots 52. Moreover, the valve member 54 is connected to the armature 56 of a solenoid 57 so that when the solenoid is energized the tubes received in the slots 51 will be squeezed shut and when the solenoid 57 is deenergized the tubing received in the slots 51 will reopen. Similarly, the valve member 55 is connected to the armature 58 of a solenoid (not visible in the drawing) which when energized and de-energized cause the tubing received in the pair of slots 55 to be closed and reopened.

The arrangement of the elastomeric inlet and outlet tubing of the two

syringes

14 and 15 is shown in FIG. 3. The inlet tube `62 for syringe 14 extends through one of the slots 51 underlying the valve member 54 to the main uid withdrawal line 63 that is connected to the source of fluid being pumped, and the outlet tube 64 for syringe 14 extends through one of the slots 452 underlying the valve member 55 to the main fluid infusion line 65 that is connected to the object to which fluid is being delivered. Similarly, the inlet tube 66 of syringe 15 extends through the other of the slots 52 underlying the valve member 55 to the fluid withdrawal line 63. and the outlet tube 67 of syringe 15 extends through the other of the slots 51 underlying the valve member 54 to the uid infusion line 65. Thus, when the solenoid 57 connected to the valve member 54 is energized the inlet tube 62 of syringe 14 and the outlet tube 67 of syringe 15 will be closed, and when the solenoid connected to the valve member 55 is energized the outlet tube 64 for the syringe 14 and the inlet tube 66 for syringe 15 will be closed. Alternate energizing and deenergizing of the solenoids in operational relationship with the infusion and withdrawal phases of operation of the

syringes

14 and 15 will permit continuous uninterrupted infusion of the lluid being pumped.

The switch means 42 and 43 are connected through appropriate electrical circuitry to the controlled infusion circuits and to the rapid withdrawal circuits of the motor controls for the

motors

40 and 41, and also to the solenoids which actuate the

valve members

54 and 55 of the solenoid valve 18. The specific circuitry employed may include relays, printed circuit cards, and/or solid state components in lany suitable combination provided the circuitry is adapted to carry out the essential sequence of operational steps that are characteristic of our improved syringe pump. Specifically, the circuitry should cause the following sequence of electrical operations to be carried out when the

reciprocating drive carriages

26 and 27 contact the lever switches 42 and 43 when the drive carriages reach each end of their reciprocating paths of travel. p

(l) After the drive carriage 26 reaches its fully infused position: the rapid withdrawal circuit of the motor control for motor 40 is energized, the solenoid for valve member 54 is de-ener-gized, and the solenoid for valve member 55 is energized;

(2) When the drive carriage 26 reaches its fully withdrawn position: the rapid withdrawal circuit of the motor control for motor 40 is de-energized;

(3) As the drive carriage 27 approaches its -fully infused position: the controlled infusion circuit of the motor control for motor 40 is energized;

(4) After the drive carriage 27 reaches its fully infused position: the rapid withdrawal circuit of the motor control for motor 41 is energized, the solenoid for valve member 54 is energized, and the solenoid for valve member 55 is de-energized;

(5) When the drive carriage 27 reaches its fully withdrawn position: the rapid withdrawal circuit of the rnotor control for motor y41 is rie-energized;

(6) As the drive carriage 26 approaches its fully infused position: the controlled infusion circuit of the motor control for motor 41 is energized;

The foregoing sequence of electrical operations cause the following sequence of functional steps to take place:

right contact 109 also energizes the rapid withdrawal motor control 115 of the motor 116 (which corresponds to motor previously referred to), thereby causing the drive carriage 26 of the pump shown in FIG. l to move rapidly to the fully withdrawn position of the carriage. Current from the now closed contact 208 of switch 206 energizes the controlled infusion motor control 217 of the motor 216 (which corresponds to motor 41), thereby causing the drive carriage 27 of the pump shown in FIG. 1 to move at a controlled rate toward the fully infused position of the carriage. Current from the now closed contact 213 of switch 211 energizes the solenoid valve 218 (which corresponds to the valve means 55 shown in FIG. 3), thereby closing outlet tube 64 of the syringe 14 and inlet tube 66 of syringe 15. Current from the upper left contact 219 of lever switch 204 flows to the now closed contact 207 and through the holding circuit of switch 206, and current from the normally closed contact 114 of switch 111 flows to the now closed contact 212 and through the holding circuit of switch 211. Finally, current from the lower left contact 220 energizes the coil of solenoid switch 221, thereby opening the normally closed contact 222 of switch 221. All of these actions take place more or less instantaneously when the switch 101 is closed.

When the rapidly withdrawing drive carriage 26 reaches its fully withdrawn position it contacts the lever 103 of lever switch 104 and moves it from the position shown in solid lines to the position shown in dotted lines in FIG. 4, thereby opening right contacts 105 and 110 and closing left

contacts

119 and 120 of switch 104. The opening of right contacts 105 and 110 does not de-energize the coils of

solenoid switches

206 and 211 because the holding circuits of these switches are energized, and the ped d do do o Controlledinfusion do Do.

An electrical circuit that is adapted to carry out the essential seqeunce of operational steps characteristic of the syringe pump of our invention is shown in FIG. 4 of the drawing. However, the circuit sho-wn in FIG. 4 is merely illustrative of one such circuit and our invention is not limited thereto. Other circuits employing other types of lever switches, relays, printed circuit cards, solid state components and the like can readily be devised which will effect the desired sequence of operations of our two barrel syringe pump. Y

Referring now to FIG. 4, assume that the pump is turned off when one of the syringes of the pump is in the middle of the withdrawal phase of its cycle and the other syringe of the pump is in the middle of the infusion phase of its cycle of operation. lIn this situation, the main switch 101 Will be open, the pilot light 102 will be out and the

levers

103 and 203 of the lever switches 104 and 204 will be in the positions shown in FIG. 4 of the drawing.

When the switch 101 is closed, the pilot light 102 lights up and current flows to the lever switches 104 and 204 and through the circuits associated therewith. Specifically, current from upper right contact 105 of lever switch 104 energizes the coil of solenoid switch 206, thereby closing the normally

open contacts

207 and 208 and opening the normally closed contact 209 of switch 206. Current from lower right contact 110 of lever switch 104 energizes the coil of solenoid switch 211, thereby closing the normally

open contacts

212 and 213, and opening the normally closed contact 214 of switch 211. Current from the lower opening of lower right contact does not de-energize the withdrawal motor control because

contacts

114, 212 and 122 of

switches

111, 211 and 121 are closed. The closing of upper left contact 119l energizes the normally open contact 107 of switch 106. The closing of lower left contact 120 energizes the coil of solenoid switch 121, thereby opening normally closed contact 122 and thus de-energizing the withdrawal motor control 115.

When the rapidly withdrawing drive carriage 26 reaches its fully infused position it contacts the lever 203 of lever switch 204 and moves it from the position shown in solid lines to the position shown in dotted lines in FIG. 4. As the lever 204 moves from left to right it first opens lower left contact 220, thereby de-energizing solenoid switch 221 and closing contact 222. The lever 203 then contacts the arcuate extension of upper right contact 205 which energizes the coil of solenoid switch 106, thereby closing the normally

open contacts

107 and 108 and opening the normally closed contact 109 of the switch 106. Closure of contact 107 energizes the holding circuit of switch 106. Closure of contact 108` energizes the controlled infusion motor control 17 of the motor 116, thereby causing the drive carirage 26 of the pump to start to move at a controlled rate toward the fully infused position of the carriage. The moving lever 203 then opens the arcuate extension of upper left contact 219 of switch 204 which de-energizes the holding circuit of solenoid switch 206, thereby opening

contacts

207 and 208 and closing contact 209 of switch 206. The opening of contact 208 de-energizes the controlled infusion motor control 217 thereby causing the motor 216 to stop infusion. The lever 203 then contacts the lower right contact 210 which energizes the rapid withdrawal motor control 215 of the motor 216 and also the coil of solenoid switch 111.

Energizing of switch 111 closes normally

open contacts

112 and 113 and opens normally closed contact 114. Closure of contact 113 energizes solenoid valve 118 (which corresponds to the valve means 54 shown in FIG. 3), thereby closing the inlet tube 62 of syringe 14 and the outlet tube 67 of syringe 15. Opening7 of contact 114 de-energizes the holding circuit of switch 211, thereby opening

contacts

212 and 213 and closing contact 214 of switch 211. Opening of contact 213 de-energizes solenoid valve 218, thereby opening the inlet tube 66 of syringe and the outlet tube 64 of syringe 14. Closure of contact 214 energizes the holding circuit of switch 111. The commencement of the rapid withdrawal phase of operation of motor 216 and the associated syringe 15, the closure of solenoid valve 118 and the opening of solenoid valve 218 take place essentially simultaneously.

The drive carriage 26 of the syringe 14 moves at a controlled, relatively slow rate toward the fully infused position of the carriage while the drive carriage 27 of the syringe 15 moves relatively to the fully withdrawn position of the carriage. When the rapidly moving drive carriage 27 reaches its fully withdrawn position it moves the lever 203 of lever switch 204 from right to left, thereby de-energizing the rapid withdrawal motor control 215 and stopping the motor 216. The drive carriage 26 of the syringe 14 continues in the meantime to move at a controlled rate toward its fully infused position. When the drive carriage 26 reaches its fully infused position it moves the lever 103 of lever switch 104 from left to right,

thereby sequentially energizing the controlled infusion g motor control 217, then de-energizing the controlled infusion motor control 117, and then essentially simultaneously energizing the rapid withdrawal motor control 115, energizing the solenoid valve 218 and de-energizing the solenoid valve 118. When the rapid withdrawal motor control 115 and motor 116 move the drive carirage 26 to its fully withdrawn position the lever 103 will be moved from right to left, and when the controlled infusion motor control 217 and motor 216 move the drive carriage 27 to its fully infused position the lever 203 will be moved from left to right, thereby effecting the sequences of operations previously described. The cyclic operation of the syringe pump continues in the manner described until the main switch 101 is opened.

As noted, the specific drive mechanism and the electrical circuitry associated therewith herein described comprise an advantageous, but by no means the only, means of carrying out the cyclic sequence of operations characteristic of the syringe pump of our invention. For example, the desired series of operational steps could be carried out by the use of a single electric motor which runs in one direction only and which is provided with a variable speed control. In this embodiment gears would be switched in and out of engagement by means of solenoids and clutches operated by the switch means of the apparatus. The solenoid operated gears and clutches would be adapted to change the direction of travel of the drive carriage and to control the speed of infusion and withdrawal so that withdrawal is always faster than infusion. Other drive mechanisms adapted to carry out the required sequence of operational steps characteristic of our syringe pump could be devised.

In addition to the use of our syringe pump to continuously infuse a single iiuid into an object or body, the syringe pump of our invention can be employed as a proportioning pump. In this application the intake line of each syringe is connected to a separate fluid supply reservoir. In operation, fluid withdrawn alternately from each fluid supply reservoir would be infused sequentially into the object or body to which the uid is being delivered.

The amount of fiuid infused into the body by each syringe of the pump is controlled by adjustment of the stroke length and selection of syringe size.

We claim:

1. In a syringe pump comprising two syringes each adapted alternately to infuse and to withdraw a fluid being pumped, a reciprocating drive mechanism for each syringe and valve means for alternately opening and closing the fluid inlet and fiuid outlet lines of each syringe in operational relationship with the infusion and withdrawal phases of operation of said syringes, the improvement which comprises:

a separately controlled electric motor connected to each drive mechanism,

first and second motor control means actuated by the reciprocating drive mechanisms for operating each of said separately controlled motors, each motor control means having a controlled infusion circuit for operating the motor to which it is connected in the direction of fluid infusion at a controlled variable speed and a rapid withdrawal circuit for operating said motor in the direction of fluid withdrawal at a higher speed than the maximum speed of iiuid infusion,

valve means comprising first solenoid valve means for simultaneously closing the inlet of the first of the two syringes and the outlet of the second of the two syringes, and second solenoid valve means for simultaneously closing the outlet of the first syringe and the inlet of the second syringe, and

electric switch means for the controlled infusion circuits and the rapid withdrawal circuits of the first and second motor control means and for the first and second solenoid valve means, said switch means being actuated by the reciprocating drive mechanisms when the drive mechanisms reach each end of their reciprocating paths of travel.

2. The syringe pump according to claim 1 in which the drive mechanism for the first syringe causes the switch means to energize the controlled infusion circuit of the second motor control before de-energizing the controlled infusion circuit of the first motor control and before energizing the second solenoid means when said first drive mechanism reaches the end of its controlled infusion direction of travel, and in which the drive mechanism for the second syringe causes the switch means to energize the controlled infusion circuit of the first motor control before de-energizing the controlled infusion circuit of the second motor control and before energizing the first solenoid means when said second drive mechanism reaches the end of its controlled infusion direction of travel.

3. The syringe pump according to claim 1 in which the switch means (a) energizes the controlled infusion circuit of the second motor control before de-energizing the controlled infusion circuit of the first motor control, and then energizes the second solenoid means and the rapid withdrawal circuit of the first motor control and de-energizes the first solenoid means, when said first drive mechanism reaches the end of its controlled infusion direction of travel, (b) de-energizes said first rapid withdrawal circuit when said first drive mechanism reaches the end of its rapid withdrawal direction of travel, (c) energizes the controlled infusion circuit of the first motor control before de-energizing the controlled infusion circuit of the second motor control, and then energizes the first solenoid means and the rapid withdrawal circuit of the second motor control and de-energizes the second solenoid means, when said second drive mechanism reaches the end of its controlled infusion direction of travel, and (d) de-energizes said second rapid withdrawal circuit when said second drive mechanism reaches the end of its rapid withdrawal direction of travel.

4. The syringe pump according to claim 1 in which the reciprocating drive mechanisms for the first and second syringes cause the switch means to effect the following sequence of electrical operations:

(a) as the first drive mechanism approaches its fully infused position: controlled infusion circuit of second motor control energized;

(b) after the irst drive mechanism reaches its fully infused position: rapid Withdrawal circuit of first motor control energized, first solenoid means de-ener gized, and second solenoid means energized;

(c) when the irst drive mechanism reaches its fully withdrawn position: rapid Withdrawal circuit of first motor control de-energized;

(d) as the second drive mechanism approaches its fully infusedposition: controlled infusion circuit of first motor control energized;

I (e) after the second drive mechanism reaches its fully infused position: rapid withdrawal circuit of second motor control energized, rst solenoid means energized, and second solenoid means de-energized;

(f) when the second drive mechanism reaches its fully withdrawn position: rapid Withdrawal circuit of second motor control de-energized.

References Cited UNITED STATES PATENTS 2,419,993 5/1947 Green et al 103-152 10 3,259,077 7/1966 Wiley et al 103-227 ROBERT M. WALKER, Primary Examiner U.S. C1. X.R. 15 417-515 gjg t UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,554 ,673 Dated Jantla'ry`l2L 1971 lnvcntods) Joel M. Schwartz and Dan'el P. Krel'ns It :ls certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r- Column 1 llne. 39,' "of" should read or --v r Column 1, 1ne.55, "of the should read o'vf cu; Columm 2, line 4S; l "',eelectrid should read electric Column 3., Alne, "longitudinal" lshould n read 'lo'ngtixdna .Column 4,- 1ines 7 and 8, "that is h'irgher than the maximum t rate of speed" is repeated and the second -occurence should be deleted.

Coluxrn 5, line 47, "electrical" should' readllelectric Column1 6, line SS', "when the rapidly vrthdrawng drive. carriage 26" should read 4when the moreslowljr moving drive carrageZ? Column 6, line 68', "1 7" should read 117 ;l

'Column 7. `1ine 25. "relatively to" should red relatively rapidly to Column 7, l'ne 41, "carirage" sho'uld read ca rrage Signed and sealed this 11th day of May" 1971 (SEAL) Attest: l EDWARD mrmamcfum,Jn.l WILLIAM E. scHUYLER Jn. Attesting officer cummiasioner or Patnca.