CA1176934A

CA1176934A - Mechanism for screw drive and syringe plunger engagement/disengagement

Info

Publication number: CA1176934A
Application number: CA000391190A
Authority: CA
Inventors: Richard M. Bucchianeri
Original assignee: Richard M. Bucchianeri; Alaris Medical Systems, Inc.; Ivac Medical Systems, Inc.; Ivac Holdings, Inc.
Current assignee: CareFusion 303 Inc
Priority date: 1980-12-15
Filing date: 1981-11-30
Publication date: 1984-10-30
Also published as: JPS57502044A; EP0066610A4; EP0066610A1; US4424720A; WO1982001998A1

Abstract

ABSTRACT OF THE DISCLOSURE

A mechanism for screw drive and syringe plunger engagement and disengagement for a syringe infusion pump, wherein a split-nut pair are moveable into and out of engagement with a lead screw by means of rotary cam control, the rotary cam being keyed with a crank disk that is coupled to a crank arm, which operates as the syringe plunger mover. The crank arm is rotatable into and out of engagement with the syringe plunger, such rotation also causing the split-nut pair to move into and out of engagement with the lead screw. Index and cam means are carried by the crank arm to aid in proper alignment with the syringe plunger, and a sensor is provided for monitoring proper engagement of the crank arm with the plunger.

Description

~i'6934 MECHANISM FOR SCREW DRIVE AND SYRINGE PLUNGER
ENGAGEMENT/DISENGAGEMENT
.
BACKGROUND OF THE INVENTION

This invention relates generally to improve-ments in mechanisms for screw drive engagement and .disengagement, and more particularly, to a new and improved mechanical system for use in a syringe pump of the type requiring engagement and disengagement of a lead screw to facilitate installation of a syringe for parenteral admini~tration (referred to herein as ~intravenous administration~ or ~IV administration~) of medical fluids.
The usual medical procedure for the gradual IV administration of fluids into the human body, such a8 fluid replacement, liquid nutrients, blood or plasma, makes use of apparatus which is commonly referred to in the medical arts a8 an intravenous ~olution administration set. Such a set typically i8 a disposable plastic product, and comprises a drop chamber adapted to be connected to a fluid 80urce, a length of tubing extending from the chamber to the patient and a valve mechanism, such as a roller clamp on the tubing.

~ -2- ~176934 The drip chamber of the IY administration set serves a dual function of allowing a nurse or other attendant to observe the rate at which the fluid drips out of the fluid source and also creates a reservoir for the fluid at the lower end of the drip chamber to insure that no air enters the main feeding tube leading to the patient.

While observation of the rate of drop flow via the drip chamber is a simple way of controlling the amount of fluid fed to a patient over a period of time, its ultimate effectiveness requires that a relatively constant vigil be maintained on the drop flow, lest it cease entirely due to exhaustion of the fluid supply or vary unacceptably from the set rate.

. In addition to the aforedescribed difficul-ties; the IV administration of medical fluids by gravity induced hydrostatic pressure infusion of the liquid from a fluid source suspended above a patient, may be susceptible to fluid flow rate variations due to changes in the fluid level in the bottle, changes in temperature, changes in the venous or arterial pressure of the patient, patient movement, and drift in the effective setting of the roller clamp or other valve mechanism pinching the feeding tube. Moreover, there are a number of situations, ~uch as in intensive care, cardiac and pediatric patients, or where rather critical drugs are being administered, where the desired drop flow rate must be capable of rather preci8e selection and must not drift beyond certain prescribed limits in spite of varying load conditions.

In view of the foregoing, a number of electrical monitoring systems, drop flow controllers and infusion pumps have been developed in recent years ~3~ i~6934 to infuse medical fluids into patient6 at precisely regulated fluid flow rates. In particular, syringe pumps have been developed and have become popular in the IV administration of fluids into the human body, such syringe pumps typically embodying a motor driving a plunger within a syringe body to expel fluid from the syringe at a controlled rate through a length of tubing and into the patient.

One specific variety of 6yringe pump has a syringe plunger mover that is coupled for engagement with a rotary-driven lead screw for linear travel along the lead screw. These pumps are es-pecially adapted to receive a self-contained syringe, installed to have the syringe plunger mover drive the syringe plunger. Because such 6yringes are typically pre-loaded with varying amount~ of fluid and the syringe plunger mover may be in any position along its linear travel from a previous use, some mechanism is necessarily provided for selectively disengaging the syringe plunger mover from the lead screw to enable manual repo~itioning of it into alignment with the free end of the syringe plunger upon installation.

In the pa~t, 6uch syringe pumps have commonly used a spring-biased mechanism that required continuous actuation of a button or lever in order to maintain the syringe plunger mover in a state of disengagement from the lead screw while the mover was repo~itioned. Premature release of such a button or lever while attempting to reposition the syringe plunger mover, as wag prone to happen, however, caused damage to the lead screw due to thread scraping, and otherwise rendered difficult the process of alignment. Also, the spring-biasing of these mechan-isms created substantial ~hread collision forces upon .,.i .

:

, 1~76934 re-engagement of the lead screw, particularly in instances of thread misalignment, tending to cause further excess wear and damage to the instrument.

S Another common feature of existing ~yringe pumps has been ~unbalan¢ed~ engagement with the lead screw, e.g., as by utilization of a half-nut coupled to the syringe plunger mover and threadedly engaged on just one side of the lead screw. To maintain engage-ment, ~ubstantial force must be exerted by the half-nut or its equivalent on the lead ecrew, which results in relatively great friction and bowing of the lead screw. At least one solution to this latter problem has been known, but it involves use of a complex and relatively expensive collet-type collapsible nut.
In many of these pumps, moreover, syringe installation has been made even more difficult by the requirement that the mover be properly aligned before the ~yringe is installed. ~his necessitates a time consuming trial-and-error procedure in which the syringe i8 held out of the way, at least partly above or to one side of the pump, witb one hand, while the spring-biased disengagement button or lever is ac-tuated ~nd the mover is repositioned, all with the other hand. An attempt is then made to install the syringe, but if there i8 misalignment, the pro-cedure must be repeated.

Hence, those concerned with the development and use of mechanical drive 6ystems of the type ~uitable for use in IV fluid administration systems, and particularly those concerned with the design of IV
~yr~nge pumps, have long recognized the need for an improved, relatively simple, economical, durable and reliable mechani~m for engagement and disengagement with a lead ~crew that also provides for convenient . -117~934 _5_ installation of a syringe with respect to a syringeplunger mover, in order to obviate the aforedescribed difficulties. The present invention clealy fulfills this need.

,' .

SUMMA:RY OF THE INVENTION
Briefly, and in general terms, th.e present invention resides in a new and improved mechanism for lead screw engagement and disengagement, in which a traveler mechanism, by means of selective actuation, is moved into and out of threaded engagement with the lead screw ;n a manner virtually eliminating the possibili.ty of partial thread engagement that could result in thread scraping, minimizing thread collision forces and ensuring proper thread alignment before forcing the traveler mechanism lead screw engagement.
According to one aspe.ct of the present invention, there is provided the combination comprising: a lead screw; traveler means actuable between states of threaded engagement and disengage-ment with said lead screw-, said traveler means including bia:sing means for hiasing said traveler means in said state of engagement and in said state of disengagement, said biasing means producing an over-center action during movement of said traveler means between said state of engagement and said state of disengage-ment; actuating means, selectively operable, for actuating said 20. traveler means; and means for coupling said actuating means to said traveler means to allow limited relative movement between said actuating means and said traveler means, such that said traveler means moves between said state of engagement and said sta.te of disengagement independently of said actuating means after said biasing means has moved over center, and further such that said traveler means begins to engage said lead screw in moving to state of engagement, and begins to disengage said lead screw in moving to said state of disengagement, only after said . -6-7~g~

biasing means has moved over center.
According to another aspect of the invention, there is provided the combination comprising: a lead screw; a plurality of threaded members mounted for movement into and out of engage-ment with said lead screw: control means for controlling movement of said threaded members; first biasing means for biasing said control means in a disengaged state when said threaded members are fully disengaged from said lead screw, and in an engaged state when said threaded members are fully engaged to said lead screw, said first biasing means producing an over-center action with said control means during movement between said engaged state and said disengaged state; and means for coupling said actuating means to sai.d control means to allow limited relative movement between said actuating means and said control means, such that said control means controls movement of said threaded members independently of said actuating means after said control means has travelled over center, and further such that said threaded members begin to engage said lead screw only after said control means has travelled over center towards said engaged state.
According to a further aspect of the invention, there is provided in a syringe pump for delivering a pump stroke to a syringe having a syringe plunger, the comblnation comprising:
a lead screw; traveler means actuable between states of threaded engagement and disengagement with said lead screw, said traveler means including plurality of threaded members disposed about said lead screw such that in said state of engagement th.e forces exerted by said threaded members on said -6a-G~34 lead screw are substantially balanced relative to one another;
and plunger mover means, coupled to said traveler means, for pushing against the free end of the syringe plunger, said plunger mover means beIng mounted for selective rotation between a first position, in which said plunger mover means engages the free end of the plunger and actuates said traveler means to said state of engagement wIth said lead screw, and a second position, in which said plunger mover means is disengaged from the free end of the plunger and actuates said traveler means to said state of disengagement wIth said lead screw.
The mover in the disengaged position allows for unobstructed syringe installation regardless of the linear position of the mover with respect to the plunger, and also is capable of sliding movement into proper alignment from either side of the free end of the installed plunger.
Moreover, in a further aspect of the invention, the mover serves as part of a rotary crank means for actuating the traveler mechanism, whereby rotation of the mover to its dis-engaged position with the syringe plunger causes traveler mechanism disengagement with the lead screw, and conversely, rotation of the mover into engagement with the plunger causes traveler mechanism engagement with the lead screw.
The traveler mechanism includes a biasing system for releasably biasing it in either the state of engagement or the -6b-state of disengagement with the lead screw, the biasing system preferably producing an over-center action as the traveler mechanism moves between those two states. In an important aspect of the invention, the traveler mechanism does not move into or out of engagement with the lead screw until after its biasing system has travelled over center, and because of the manner in which the traveler mechanism is coupled to its actuator, the traveler mechanism then completes its movement independent of the actuator.
Thus after initial external actuation, the traveler mechanism completes engagement or disengagement, as the case may be, due only to its own internal biasing system, with means provided to limit collision forces with the lead screw upon engagement and to cause rapid disengagement once the biasing system is over center.
More particularly, the present invention provides a new and improved mechanism in which a split nut-pair are mounted for movement into and out of engagement with the lead screw, each split nut having a projecting pin received in a cam groove formed in a rotary cam disk so that rotation of the cam disk controls movement o the split nuts. The split-nut pair is moved and locked into lead screw engagement by rotation of the cam disk in one direction to the fullest possible extent, while movement of the cam disk to the fullest extent possible in the opposite direction moves and locks the split-nut pair out of engagement, mechanical limits or stops being provided to limit rotational travel of the cam disk.
Biasing means in the form of a compression spring assembly is con-nected to the cam disk for over-center action, and an actuator mechanism is provided for bringing the spring-to-cam disk assembly from one or the other of its extreme rotational positions over `` li76934 center towards the opposite extreme position, at which point the spring assembly provides automatic rotational control of cam disk movement to the opposite extreme. In this regard, the actuator mechanism is not fixedly coupled to the cam disk, but rather is loosely keyed so that after bringing the cam disk over center, the cam disk releases from the actuator mechanism and continues to move to the opposite extreme position due solely to the biasing effect of its own spring system. Mechanical limits or stops for the actuator mechanisms are provided to help protect the split-nut pair and lead screw against damage due to overly vigorous operation of the actuator mechanism by the user, particularly during engage-ment.
The cam disk grooves each include a pair of arcuate locking portions for retaining the split-nut pins in the fully disengaged position or the fully engaged position, depending on the rotational state of the cam disk, and further include separate segments between these two locking portions, -7a-- B - ~176934 achieve prescrlbed control of the split-nut pair during engagement and rapid 6eparation of the split-nut pair during disengagement, each segment being positioned within the cam grooves so that very little, if any split-nut movement occurs until after the spring-to-cam disk assembly passes over center during rotation. The cam groove segment controlling split-nut pair engagement is configured to limit the colli~ion force between the threads of the split-nut pair and the thread6 of the lead ~crew Again, with reference to the 6yringe pump for which the aforedescribed lead screw engagement and disengagement mechanism was specifically develop-ed, the actuator mechanism comprises a crank armhaving a one end connected to a crank shaft, which in turns connects to a crank disk for keying to the cam disk. The crank arm is rotatable between closed and opened positions whereby its free end either grasps or releases, respectively, the free end (or ~thumb-rest~) of a ~yringe plunger. Another compression spring assembly ~8 connected to the crank disk for over center action tending to lock the crank arm in one or the other of its extreme rotational states.
~he opened po6ition of the crank arm corresponds to disengagement of the split-nut pair from the lead ~crew, and, conversely, the crank arm closed position corresponds to split-nut pair engagement with the lead screw. Importantly, the respective spring assembl$es for the crank disk and the cam disk automatically lock them ln the open-and-disengaged states during manual positioning of the crank arm into alignment with the thumbrest of the syringe plunger.

- 9 - ~76934 As previously mentioned, opening the crank arm provides clearance for installation of a syringe regardless of the linear position of the crank acm at the time. In particular, the crank arm may init$ally be linearly positioned forwardly of the thumbrest, it being possible with the present invention to then slide the crank arm rearwardly pas~ed the thumbrest and then forwardly into alignment for crank arm closure. In this regard, the crank arm has a beveled edge that lifts the thumbrest out of the way to permit the crank arm to pa6s by from the forward (i.e., syringe plunger) side of the thumbrest. For automatic crank arm alignment when approaching the thumbrest from the rearward side, the margin of the crank arm pushing surface catches the lip of the thumbrest a8 a manual indication of alignment, from which crank arm rotation to the closed position follows.

A fixed light source and photoelectric sensor arrangement provides a reference light beam which i8 interrupted by an opaque flag in all rota-tional positions of the crank arm, except when the crank arm is closed and properly grasping the thumb-rest, 80 that a signal can be developed to enable proper pump function.

The new and improved lead screw and syringe plunger engagement/disengagement mechanism of the present invention is extremely simple and reliable.
The mechani6m provides proper balanced-force engage ment of the lead screw, and locked disengagement of the split-nut pair to eliminate the need for continu-ous actuation of a button or lever by the user in ~176934 order to manually position the crank arm for align-ment with the plunger thumbrest. The mechani~m also provides for convenient installation of a syringe that does not require pre-alignment of the crank arm.

The above and other objects and advantages of the present invention will become apparent from the following more detailed description, when taken ~0 in conjunction with the accompanying drawings of an illustrative embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 i6 a perspective view, partially broken away, illustrating a syringe infusion pump utilizing a mechanical engagement and disengagement system embodying the principles of the present inven-tion;

FIG. 2 is an exploded perspective view of the ~tructural components of the mechanical engagement and disengagement system, while FIG. 2a is a fragment-ary ~ide elevational view of the optical mechanism for monitoring proper engagement of the crank arm with the thumbre~t at the free end of the syringe plunger FIG. 3 is a fragmentary elevational view of the crank disk and rear housing taken from the side opposite that ~hown in FIG. 2;

FIG. 4 is a elevational view of the cam disk taken from the side opposite that shown in FIG. 2, and showing a fragmented outline of the front housing around the cam disk, while FIG. 4a is an exploded, fragmentary view of one of the cam grooves formed in the cam disk~

FIG. 5 is a view, primarily schematic in nature, taken along the axi8 of the lead screw from the left of the split-nut pair a~ shown in FIG. 2, and illustrates the interrelation~hip between the primary components of the mechanical engagement and di~engage-ment ~ystem of the invention;

, ~.
, .

'~'' `'' ''.

- 12 - ~176934 FIG. 6a - 6h i8 a series of fragmentary views, al80 primarily w hematic in nature, in which the the split-nut pair and pins, the cam grooves and the key of the cam disk, and the keyway of the crank disk are ~uperimposed and shown in a variety of positions relative to one anothers FIG. 7 is a fragmentary sectional view taken along the line 7-7 in FIG. 1, and partially 10 broken away to ~how the manner in which the crank arm grasps the thumbrest of the syringe plunger, the fully opened position of the crank arm being shown in phantom;

FIG. 8 i~ a fragmentary top plan view, 15 primarily schematic in nature and partially in section, illustrating linear travel of the crank arm, in the fully opened position, into alignment with the thumbrest; and FIG. 9 is a view similar to FIG. 0, showing 20 the crank arm rotated to the fully closed position, grasping the thumbrest.

- 13 ~ ~1~934 DESCRIPTION OF THE PREPERRED EMBODIMENT

Referring now to the drawings for the purpose of illustrating the presently preferred embodiment of the new and improved mechanical engagement/disengagement system of the present invention, and particularly to FIG. 1 thereof, there i~ shown a syringe infusion pump, indicated generally by reference numeral 10, in which the mechanical system i8 embodied. Although reference is made to the intravenous administration environment, and particularly to ~yringe pu~ps, for which the unique mechanical engagement/disengaqement ~ystem of the present invention was specifically developed, it is to be under6tood that this is by way of example only, and the system as set forth in the ensuing de6cription i8 suitable for use in other environments and for a wide variety of applications other than intravenous admini6tration.

The infusion pump 10 shown in FIG. 1 has a gyringe 11, comprising a body lla and a plunger llb, installed in it to be acted upon by the mechanical system embodied $n the pump for the controlled delivery of flu$d from the syringe through an IV tube (not shown) to the patient. The syrlnge 11 is of the self-contained variety (i.e., when in~talled it is pre-loaded with the precise volume of fluid to be infused to the patient) and the fluid is delivered by mean6 of a single, prolonged pump 6troke applied by the pump 10 to the syringe plunger llb. Typically, in use the syringe 11 does not draw fluid from another 60urce, as by cycling the syringe through alternate fill and pump strokes.

,j .. . .

- 14 - ~176934 The syringe pump 10 is contained in a gener-ally oblong housing 12 including, along one side of the ho~sing, a compartment 12a, in which various elements of the mechanical system of the present invention are disposed, and a base surface 12b ad3acent to and generally lower than the compartment. Formed on an upper surface 12c of the compartment 12a are a pair of longitudinally spaced-apart, upstanding cradle members 13a, 13b into which the cylindrical body lla of the syringe 11 is installed, with the syringe~ plunger llb extending out over the base surface 12b. Laterally adjacent to the compartment 12a and the base surface 12b, on the main housinq 12 of the syringe pump, there is shown a control panel 14 including various operating controls and indicators, which need not be described further herein for an understanding of the invention.

A traveler rod 15 extends almost the length of the syringe pump, through an end wall 12d of the compartment i2a at its intersection with the base 8urface 12b, ~o that a portion of the traveler rod is disposed within the compartment and the remaining portion of the traveler rod extends above and across the base surface. The traveler rod portion within the compartment 12a defines a lead screw 15a, while the portion outside the housing presents a smooth cylindri-cal surface. One end of the traveler rod 15 is supported by, and journalled for rotation in, an upstanding end brac~et 16 protruding from the base surface 12b, and the other end is coupled to a geared - motor (not shown), mounted within the compartment 12a for selective rotation of the traveler rod under the control of any appropriate electrical control system.

- 15 - 117693g In accordance with the invention, the thumb-rest llc at the free end of the syringe plunger llb is grasped by one end of a syringe plunger mover, which will be referred to herein as the crank arm 17. The thumbrest llc is obscured in FIG. 1 by the crank arm 17, but is clearly shown in FIGS. 7-9. The crank arm 17 has its other end fixedly attached to a hollow crank shaft 18, which is received over the traveler rod 15. The relationship between the crank shaft 18 and the traveler rod 15 is such that not only are they rotatable relative to one another, but the crank shaft is also capable of linear travel along the traveler rod. Like the traveler rod 15, the crank shaft 18 extends through the compartment end wall 12d and into the compartment 12a where the crank shaft is coupled to a traveler mechanism, indicated generally by reference numçral 19, received around the lead 6crew l5a. The traveler mechanism 19 can be 6een in ~IG. 1 through the portion of the compartment 12a that has been broken away for clarity.
!

As shown in FIG. 1, the crank arm 17 is manually rotatable about the traveler rod 15 between a~60-called ~closed~ position, in which the crank arm grasps the thumbrest llc of the syringe plunger llb, and a so called ~opened~ position (shown in phantom), in which the crank arm is rotated d~wn and away for release from the thumbrest. By means described in some detail below, rotation of the crank arm 17 between the closed and opened positions actuates the traveler mechanism 19 between states of engagement and disengagement with the lead screw 15a, respectively.

When the traveler mechanism 19 i8 engaged with the lead screw 15a, rotation of the lead screw causes the traveler mechanism, and therefore the crank shaft 18 and the crank arm 17 as well, to travel forwardly along the traveler rod (or towards the left in FIG. 1) at a rate determined by the rate of rotation and the pitch of the lead screw. The free end of the crank arm 17 in turn pushes the plunger llb forwardly into the ~yringe body lla, exerting positive pressure on the fluid contained therein and causing it to be delivered through the IV tube to the patient.

Conversely, when the traveler mechanism 19 is disenqaged from the lead ~crew 15a, the entire assembly consisting of the crank arm 17, the crank shaft 18 and the traveler mechanism 19 can be manually moved freely along the traveler rod 15 80 as to position the crank arm into alignment with the thumbrest llc prior to rotating it into the closed position.

The component parts of the traveler-mech-anism 19 are ~hown exploded apart in FIG. 2 80 that their relationship to each other can be more readily appreciated. The traveler mechanism 19 is split into a front housing 20 and a rear housing 21, and primarily comprises a split-nut pair 22, 23 a cam disk 24, a crank disk 25 and two spring assemblies 26, 27. Mounted on the outside surface of the rear housing 21, facinq towaras the crank arm 17, i8 an optical mechanism, generally indicated by reference numeral 28, for senslng whether the crank arm is in its closed position and properly grasping the thumbrest llc.

In a6sembly, the front housing 20 and the rear housing 21 fasten together ~through holes 20b, as by - 17 _ 1176934 screws (not shown). The upper ends of the front housing 20 and the rear housing 21 each have a pair of laterally extending flange6 20a, 21a, re6pectively, receivable within an extruded channel 29a formed along the bottom surface of a support member 29. The support member 29 fastens to the inside upper 6urface of the compartment 12a, and the channel 29a forms a guide for the linear movement of the traveler mechani6m 19 and holds it again6t rotation arouna the axi6 of the lead screw lSa.

On the inside of the front housing 20, there is formed a slide groove 20c with a centered clearance hole for the lead screw lSa to pass through. The slide groove 20c receives the 8pl it-nut pair 22, 23 and acts to guide movement of the split-nut pair radially inwardly or outwardly for threaded engagement or disengagement, respectively, with the lead screw lSa.
An enlarged counterbore 20d i6 al60 formed in the inside 6urface of the front hou~ing 20 and function6 as a receptacle in which the cam di6k 24 rotates, the cam dlsk being fitted with a disk roller 30 to reduce friction and eccentric rotation of the cam disk.

A~ best shown in FIG. 4, the counterbore 20d 25 iB open at the bottom to receive a downwardly extending wing 24a formed on the cam di6k 24. At the counterbore opening, the wall defining the counterbore flares outwardly on each side to define mechanical stops 20e, 20f limiting rotational movement of the cam disk 24 about the lead screw lSa to about 70 in the example of the preferred embodiment. A side of the cam disk wing 24a abuts one or the other of these stops 20e, 20f when the cam disk i6 rotated clockwi~e or counter-clock-wise, as the case may be~ to the maximum extent.

.

~176934 The rear housing 21 ~FIG. 3) also has an inwardly facing counterbore 21b in which the crank disk 25 is received for rotation, and a clearance hole concentric with the counterbore 21b through which the hollow crank shaft 18 extend6. The rear housing counterbore 21b i~ similarly open at the bottom to receive a like downwardly extending wing 25a formed on the crank disk 25 and the counterbore wall flares outwardly on each side in the same manner as on the front housing 20 to define mechanical stops 21c, 21d limiting the maximum rotational movement of the crank disk also to about 70. The crank disk 25 is fitted with two disk rollers 31.

Referring again to FIG. 4, the side of the cam disk 24 facing towards the split-nut pair 22, 23 has formed in it a pair of cam grooves 24b, 24c on diametri-cally opposite sides of a centered clearance hole 24d for the lead 6crew 15a. The split-nut pair 22, 23 each have an axially extending pin 22a, 23a received within its corresponding cam groove 24b, 24c for camming control of split-nut pair movement within the slide groove 20c of the front houging 20. The shape of each cam groove ig mirrored by the other cam groove exactly 180 aegrees opposite itself on the cam disk 24. In other words, corresponding point6 along each cam groove 24b, 24c can be found diametrically across the center of the cam disk 24.

An enlarged view of one of the cam grooves 24b, is shown in FIG. 4a. The cam groove 24b includes a pair of arcuate locking portions at the rotationally opposite ends of the groove. The radlally innermost locking portion (or uppermost groove in FIG. 4a) serves to retain the split-nut pin 23a 80 that the split nut , - lg 1176934 23 is loc~ed in the fully engaged position, and there-fore will be referred to as the engagement-locking portion 24e of the cam groove 24b. The radially outermost locking portion ~or lowermost groove in FIG.
4a) ~erves a similar purpose for the fully disengaged position of the 6plit nut 23, and will be referred to as the disengagement-locking portion 24f of the cam groove 24b.
Between point A shown in FIG. 4a, at the mouth of the disengagement-locking portion 24f, and point a, at the mouth of the engagement-locking portion 24e, the split-nut pin 23a in effect will trace one of two paths in the cam groove 24b depending on point of origin or, in other words, on the direction of rotation of the cam disk 24. The path I traced during counterclockwise rotation of the cam disk 24 is the radially outermost path indicated by the upwardly directed arrow in FIG.
4a. This corresponds to movement of the split nut 23 from disengagement towards engagement with the lead screw lSa. The cam groove along this engagement path I
comprises two segments, a first segment 249 that produces minimal split nut motion, followed by a 6econd segment 24h that causes most of the radially-inwardly directed motion of the split nut 23. The fir6t segment 249 has the purpose of ensuring that the split nut 23 will freely move, i.e., that it is not stuck in the slide groove 20c, and the ~econd segment 24h is con-figured 80 as to impact with the ~plit nut pin 23a, tending to reduce the acceleration of the cam disk 24 and, a8 a result, reducing the colli6ion force between the thread~ of the split nut 23 and the threads of the lead screw 15a.

_- - 20 - 1176934 The path II traced during clockwise rotation of the cam disk 24 i8 the radially innermost path indicated by the downwardly directed arrow in FIG. 4a, corresponding to radially outward movement of the ~plit nut 23 from engagement with the lead screw l5a to disengagement. The cam groove along this disengagement path II likewise comprises two ~egments, a first segment 24i that i~ a pure arc producing no split nut movement, and a gecond segment 24j that is steeply ramped to rapidly move the split nut 23 out of engage-ment with the lead screw 15a.

The opposite side of the cam disk 24 has an axially protruding key 24k ~FIGS. 2 and 4) which is receivable in a recessed keyway 25b (~IG. 3) formed in the side of the crank disk 25 that faces the cam disk 24. By means of the key 24k and the keyway 25b, rotation of the crank disk 25 controls rotation of the cam disk 24. The cam disk key 24k is loosely fitted in the crank disk keyway 25b in order to allow some independent motion of the cam disk 24 and the crank disk 25 relative to one another. In the preferred embodiment, the total available angular rotation between the key 24k and the keyway 25b is 30. This independent rotation iB primarily required by the cam disk 24 during ~plit-nut engagement, which occurs after the crank disk 25 has brought the spring-to-cam disk ~ystem over center. It also provides for rapid snap-action disengagement of the ~plit-nut pair 22, 23 from the lead screw 15a, as well as allowing the crank arm 17 to rotate all the way to the rub strip 33 if it mis~e~ the thumbrest llc.

~ 1176934 A main pivot pin 32 extend6 in the axial direction between the front housing 20 and the rear housing 21 and mount~ at its opposite ends in ~ertures formed near the bottoms in both housings. One 6pring assembly 26 is interconnected between the main pivot pin 32 and the cam disk wing 24a, and the other spring ~ssembly 27 is similarly interconnected between the main pivot pin 32 and the crank disk wing 25~. Each ~pring assembly 26, 27 includes a spring housing 26a, 27a in which a coil compression spring 27b (shown only for spring housing 27) is contained, and has a spring link 26c, 27c coupled to the compression spring 27b and protruding out an opening in the top of each 6pring housing. A groove 26e, 27e into which the main pivot pin 32 i6 received i~ formed in the bottom of each spring hou6ing 26, 27. The 6pring links 26c, 27c are configured to contain individual pivot pins 26d, 27d, respectively, for interconnection in grooves formed in the free ends of the cam disk wing 24a and the crank disk wing 25a, respectively. The compression springs 26b, 27b tend to bias the cam disk 24 and crank disk 25, respectively, toward one or the other of their maximum rotational ~tates, and each 6pring-to-disk assembly provides an over-center ~nap action during rotation between these state6 of engagement or dis-engagement of the 6plit-nut pair 22, 23 with the lead screw l5a.

FIG. 5 i~ a schematic view taken along the axi~ of the lead screw l5a and illu6trates, as an a~sembly, the aforedescribed interconnection of the cam and crank disk6 24, 25 and the spring assemblies 26, 27 between the main pivot pin 32 and the indivi-dual pivot pin6 26d, 27d. In FIG. 5, both the cam disk 24 and the cran~ aisk 25 are biased by their respective - 22 - ~1769~4 spring assemblies 26, 27 over center in the clockwise direction, with the crank arm 17 in the closed position, grasping the thumbrest llc, and the split-nut pair 22, 23 engaged with the lead screw 15a. The thumbrest llc is 6hown securely captured between the crank arm 17 and a rub strip 33 affixed along the ~djacent side wall 12e of the main pump housing lO.

With reference to FIGS. 2 and 5, the split-nut pair 22, 23 are shown abutting 80 that the generally semi-circular threaded portions of each nut register to form a threaded bore engaging the lead screw 15a as if the split-nut pair were a solid threaded nut. Thus, normal and acceptable thread fit engagement is achieved, radially balanced about the lead screw 15a. The se~i-circular threaded portions are chamfered slightly at the abutting faces of the ~plit-nut pair 22, 23 to provide full clearance around the lead screw 15a when the split nuts are disengaged.

Operation of the traveler mechanism 19 will now be explained with reference to FIGS. 6a - 6h, which illustrate in order the interaction of the various component6 as the crank arm 17 is manually rotated counterclockwise from its fully opened position through the full angular extent of its movement and then back again. FIGS. 6a - 6h are essentially en-larged views similar to FIG 5, but fragmented to show only the outlines of the cam disk 24 and the crank disk 25, and part of the crank arm 17. In addition, the split-nut pair 22, 23 and pins 22a, 23a, the cam grooves 24b, 24c and the key 24k of the cam disk 24, and the keyway 25b of the crank disk 25, are superimposed over one another in these views. The mechanical stops 20e, 20f, 21c, 21d of both the front housing 20 and the rear ~17G934 housing 21 bave also been included to aid in orienta-tion, it being appreciated that the mechanlcal stops of both housings precisely overlay one another in these views. In the description of the operation that follows, reference will be made to FIG. S for the purpose of describing the angular position of the crank arm 17 for each of the views.

In FIG. 6a the crank arm 17 i~ in its fully opened position, rotated to the maximum clockwise extent, 60 that a 6yringe can be installed in the pump 10 and the crank arm 17 can manually be moved along the traveler rod 15 into alignment with the thumbrest llc on the syringe plunger llb. Both the crank disk 25 and the cam disk 24 are correspondingly rotated to their maximum clockwise extent, each having its wing 25a, 24a abutting their respective mechanical 6tops 21d, 20e, and being biased to that state by the spring assemblies 27, 26, which are overcenter to the left in the drawing. The split-nut pair 22, 23, under the control of the cam grooves 24b, 24c in the cam disk 24, are di~engaged with the lead screw 15a and moved radially outward in the ~lide groove to the maximum ex-tent. The split-nut pins 22a, 23a are in the previously de wribed diRengagement-locking portions (see FIG. 4a) of the cam grooves 24b, 24c formed for locking the ~plit-nut pair 23, 22 in the fully disengaged position.
It ~hould al60 be noted that the cam disk key 24k is in an intermediate po~ition within the crank disk keyway 25b with 20 of available relative rotation to the left of the key in drawing and 10 of available rotation to the right.

~76934 ., .

Referring now to FIG. 6b, the crank arm 17 has been rotated 20 counterclockwise towards the closed position, or in other words 80 that the center-line of the crank arm is at 40 on the scale shown in Fig S. The crank disk 25 likewise ha~ rotated 20 in the counterclockwise direction, but due to the relationship between the key 24k and the keyway 25b, this has not resulted in any movement of the cam disk 24 or, therefore, the split-nut pair 22, 23. In other words, the 20 of relative rotation to the left of the key 24k in FIG. 6a has been consumed by this counterclockwise crank arm rotation, and the keyway 25b is ~ust now beginning to engage the key 24k. There is now 30 of available counterclockwise cam disk rotation relative to the crank disk.

As shown in FIG. 6c, an additional 15 of counterclockwise rotation of the crank arm 17 (or to the 25 mark on the scale of FIG. 5) brings the crank disk 25 and its associated spring assembly 27 to the on-center po6ition. At this po$nt, the cam di~k 24 is being driven by the crank disk 25 and thus has also rotated 15 in the counterclockwise direction. The split-nut pair 22, 23 each have moved radially inwardly towards the lead screw 15a a ~light amount, however, most of the rotation of the cam di6k 24 to this point has been devoted primarily to bringing the split-nut pins 22a, 23a ~see PIG. 4a) out of the disengagement-locking portions of the cam grooveg 24b, 24c.

Although not shown in the figures, it will be noted that further counterclockwise rotation of the crank arm 17 brings the crank disk 25 over center to the right in the drawings, 80 that thereafter the crank diQk tends to be biased by its ~pring as6embly 27 ~176934 towards the fully closed position of the crank arm 17.
Of course, rotation of the crank disk 25 will be resisted by the cam disk 24 and it6 associated sprinq 5 assembly 26, until the crank disk has rotated at least 20 in the counterclockwi~e direction past the on center position to bring the cam disk over center. As the cam disk 24 approaches and then passes the on-center position, the combined effects of spring biasing of 10 both the cam disk and the crank disk 25 will be ~uch as to automatically drive both towards the fully closed pogitions.

Continued counterclockwice rotation of the crank arm 17 (FIG. 5), brings it into engagement with 15 the thumbrest 11c of the syringe plunger llb, assuming that the crank arm and the thumbrest are properly aligned. In FIG. 6d, the center line of the syringe plunger is as shown in FIG. 5, at the O mark on the angular ~cale. In accordance with the invention, the 20 cam disk 24 i~ no longer being driven by the crank disk 25, but is instead continuing to rotate in the counter-clockwise direction due ~olely to the biasing effects of it~ ~pring assembly 26. In this regard, it will be noted in PIG. 6d that the cam di~k 24 has rotated 25 relative to the cranlc dislc 25 ~uch that the key 24k and the keyway 25b are no longer engaged, the cam disk 24 having consumed 10 of the previously available 30 of relative counterclockwise rotation FIG. 6d al~o illustrates a condition in which 30 the ~plit-nut pair 22, 23 have moved radially inwardly towards the lead screw 15a, but have not fully engaged because the threads of the ~plit-nut pair are not aligned with the threads of the lead ~crew 15a. As fre-quently occur~, the thread crests of the ~plit-nut pair , ~76934 are hung up on the thread crests of the lead screw Full engagement between the thread6 will not be possible until the lead screw l5a is rotated sliqhtly by the 6yringe pump motor.

Because the cre6ts of threads in general are relatively weak, those of ordinary skill will appre-ciate that in the condition represented, there would be a possibility of damaging the threads of the split-nuts 22, 23 and the lead 6crew 15a if any significantforce were applied to the 6plit nut6 in an attempt to complete engagement. With the mechanical engagement and drive system of the pre6ent invention, however, this does not occur because the ~pring assembly 26 of the cam di6k 24, which is the only element exerting force on the cam disk, is only 15 over center to the right, 60 that minimal inwardly-directed force is being exerted on the 6plit-nut pair 22, 23, through the cam grooves 24b, 24c in the cam disk 24.

Moreover, a6 previou61y explained in connection with FIG. 4a, the split-nut pin 23b engage6 the second segment 24h of the cam groove 24b along the engagement path I 80 a8 to reduce the colli6ion force of the split-nut threads with the lead ~crew threads for further protection again6t damage and therefore pre-venting premature thread wear.

Slight rotation of the lead screw l5a permits full engagement of the split-nut pair 22, 23 through the biasing of the ~pring as6embly 26 on the cam di6k 24. Thus, in re~pon~e to such lead screw rotation, as shown in FIG. 6e, the cam disk key 24k has consumed the remaining 20 in the keyway 25b available for counter-clockwise rotation of the cam disk 24 relative to the ..

~76934 crank disk 25, bringing the cam disk 35 over center to the right. This rotation of the cam disk 24 brings the split-nut pins 22a, 23a into the engagement-locking portions of the cam grooves, which serve to lock the split-nut pair 22, 23 in engagement with the lead screw lSa. The cam disk spring assembly 26 now holds the cam disk wing 24a against the mechanical stop 20f, assuring that the split-nut pair 22, 23 will be held in engagement with the lead screw l5a and the crank arm 17 will travel forward along the traveler rod 15 as the lead screw 15a rotates, to result in a pump stroke being applied to the syringe 11.

Of course, in those cases in which the re6pective threads of the split-nut pair 22, 23 and the lead screw lSa happen to be aligned as the crank arm 17 i8 rotated $nto engagement with the thumbrest llc on the syringe plunger llb, the relative positions of the components represented by FIG. 6d will be transitory and the cam disk 24 will continue to rotate directly to the state represented by FIG. 6e.

FIG. 6f represents a condition in which the crank arm 17 has not grasped the thumbrest llc, but has instead rotated fully into the contact with the rub strip 33 on the ad~acent sidewall 12e. This occurs under conditions where the syringe 11 is entirely absent from the apparatus, the crank arm 17 is misaligned behind or rearwardly of the thumbrest llc, or an improperly sized ~yringe has been in~talled, such syringe having an undersized thumbrest. The relationsh~p between the key 24k and the keyway 25b permits the crank disk 25 to regain 10 of counterclockwise rotation relative to the cam disk 24, to allow the crank arm 17 to rotate past it~ O position into contact with the rub strip - 1~76934 33. As shown in FIGURE 6f, this extra 10 of rotation of the crank disk 25 brings it into phase with the cam disk 24, with the wings of each abutting their respective mechanical stops 21c, 20f on their respective housings 21, 20.
It should be appreciated from Figures 6a-6f that the mechanical stops 21c for the crank disk wings 25a, together with the relative play between the key 24k and the keyway 25b, combine to help protect the split-nut pair 22, 23 and the lead screw 15a against damage even as a result of overly vigorous operation of the crank arm 17 by the user during the engagement process. As previously mentioned, in normal operation once the cam disk 24 is driven over center by the crank disk 25, the cam disk disengages the crank disk 25 and tends to continue rotating solely as a result of its own spring assembly 26. If the crank arm 17 is very sharply rotated towards the closed position, it is theoretically possible such disengagement of the cam disk 24 from the crank disk 25 will not occur as soon as the cam disk passes center. Even under the worst circumstances, however, the cam disk 24 will disengage when it is no more than 15 over center, because the crank disk 25 itself would be a maximum 35 over center, leading the cam disk by 20 at this point, and could rotate no further because of the mechanical stop 21c (i.e., assuming the crank arm 17 contacted the ru~ strip 33, which incidentally also serves as a stop). Since this worst-case disengagement of the cam disk 24 from the crank disk 25 coincides with the earliest possible contact between the split-nut pair 22, 23 and the lead screw 15a at their respective thread crests (see Figure 6d), the user cannot exert undue engage-ment forces on the threads in this manner.

1~76934 Turning now to the operation of the traveler mechanism 19 during the process of rotating the crank arm 17 towards the opened position, it will be appreciated by reference to FIGURE 6e, that the crank disk 25 leads the cam disk 24 in the clockwise direction over the initial portion of clockwise rotation because of the relationship between the key 24k and the keyway 25b. This lead phase amounts to 10 of clockwise rotation. Thus, it will be apparent that the crank disk 25 will pass its on-center position 10 ahead of the cam disk 24.
The paths that the split-nut pins 22a, 23a follow within the cam grooves 24c, 24b during clockwise rotation are such that the spring-to-cam disk system must rotate about 10 past its on-center position before there is any outward radial movement of the split-nut pair 22, 23 for disengaging the lead screw 15a. This may be seen in FIGURE 6g, where it is apparent that the split-nut pins 22a, 23a thus far have traced a path in the groove defined as a pure arc relative to the center of the disk 24 so that no radial movement of the split-nut pair 22, 23 has occurred.
The condition of the mechanism shown in FIGURE 6g is transitory and has been included to illustrate the foregoing point At the position of rotation of the cam disk 24 shown in Figure 6g, the split-nut pins 22a, 23a are just engaging steep ramp portions 24j (see FIGURE 4a) of the cam grooves 24b, 24c which will tend to drive the split-nut pair 22, 23 very rapidly in the outward radial direction for disengagement of the lead screw 15a. The steep ramp portions 24j (see FIGURE 4a) leads directly back to the disengage-ment-locking portion 24f of the cam grooves 24b, 24c provided for locking the split-nut pair 22, 23 in the fully disengaged position -`~ -29-.
, .

.

.~

Significantly, in the transitory state shown in FIGURE
6g, the cam disk 25 is over center so that split-nut pair disengage-ment has become automatic regardless of whether the user continues to rotate the crank arm 17 to its fully opened position. In this regard, it will be noted that the cam disk 24 is 10 over center to the left and 25 away from the left most mechanical stop 20f, and that there is 25 of available clockwise rotation of the cam disk key 24k relative to the crank disk keyway 25b. This is also apparent by comparing FIGURE 6g to FIGURE 6b.
It is thus impossible for the user, by rotating and holding the crank arm 17 in a partially opened position, to hold the split-nut pair 22, 23 in a condition of only partial disengage-ment with the lead screw 15a. The split-nut pair 22, 23 either are fully engaged with the lead screw 15a or rapidly disengage it completely so that no damaging thread scraping can occur during manual repositioning of the crank arm 17.
FIGURE 6h corresponds to FIGURE 6a and has been included to illustrate that the various components resume their original positions upon rotation of the crank arm 17 to the fully opened position.
In a further aspect of the invention, the mechanical engagement and disengagement system has been designed so that the syringe 11 can be installed in the infusion pump 10 without first attempting to align the crank arm 17 with the thumbrest llc on the syringe plunger llb. In this regard, it will be appreciated by -29a-, - 30 ~ 7693g viewing FIGS. 1 and 7 that when the crank arm 17 i8 in the fully opened posit$on, there is sufficient clearance in the space above it to receive the syringe plunger llb due to the fact that the crank arm rotates out of the way. As previously described, the crank arm 17 is, in fact, biased or ~locked~ to the opened position due to the biasinq force of the crank disk spring assembly 27.

Referring now to FIG. 8, wherein the crank arm 17 i8 shown schematically in cross-section, the crank arm is provided with a bevelled edge 17a permitting installation of the syringe regardless of the linear position of the crank arm relative to the thumbrest llc at the time of installation. More specifically, if the crank arm 17 happens to be forward, or to the left in FIG. 8, of the thumbrest llc the crank arm can be manually moved rearwardly, or to the right in FIG. 8, and as the bevelled edge 17a on the crank arm contacts the plunger side of the thumbrest it will cam the plunger llb to be lifted over the crank arm. After the crank arm passes by, the syringe plunger llb then will typically return to its original position by force of gravity, and the crank arm is then moved forwardly into proper alignment with the end of the thumbrest. Auto-matic alignment is achieved due to the fact that the margin of the pushing surface 17b of the crank arm 17 most nearly adjacent the thumbrest llc has a slight interference fit with the thumbrest when approaching it from the rear (or right, in FIG. 8). Thus, alignment of the crank arm 17 will be indexed when the margin of the syringe plunger pushing surface 17b contacts the thumbrest llc. At this point, the crank arm 17 is in position to be rotated inwardly and upwardly to grasp the thumbrest llc in an anti-syphon groove 17c formed - 31 _ ~176934 in the crank arm. Of cour6e, lf the crank arm 17 iB
initially rearward (or to the right) of the thumbrest llc at the tine of 6yringe installation, the crank arm 18 simply slid forward until properly indexed with the thumbrest.

As best shown by the enlarged framentary end vie~ in FIG. 2a, proper engagement of the crank arm 17 with the thumbrest llc is electro-optically monitored by the optical mechanism 28 which includes a combined light source and photoelectric sensor assembly 28a affixed to the outer surface of the rear housing 21. A
torsional spring 28b iB coiled about a first post 21f that extends axially outward from one of the holes in the rear housing 21 used to fa6ten it to the front housing 20 (~IG. 2), and one estended portion 28b' of the spring iB directed across the top of the rear housing and fastens to a second post 219 axially protruding from the other mounting hole. An opposite extended portion 28b~ of the spring is directed down-wardly from the first post 21f and carries an opaque flag 28c mounted normal to the spring wire. A collar 18a, on which a cam lobe 18a' is formed, is fixed on the hollow crank shaft 18 immediately ad~acent the outer surface of the rear housing 21, a8 by a pin.

As shown in ~IG. 2, when the crank arm 17 is fully engaged with the thumbrest llc, the cam lobe 18a' cams the downwardly extending spring portion 28b~
outwardly ~o that the opaque flag 28c doee not interrupt the reference llght beam between the llght source and photoelectric sensor 28a. In any other angular position of the crank arm 17, the cam lobe 18a' 18 rotated out of engagement ~ith the spring wire port$on 28b~ ~o that lts natural pring bias mpves the opague flag 28c -'~" llq6934 inwardly to interrupt the reference light beam. A
corresponding electrical signal is generated to indicate the angular ~tate of the crank arm 17 to the control system of the infusion pump 10. The control system in turn can use this signal as one of many enabling signal6 for pump operation and to trigger appropriate alarms or otherwise indicate t~e state of the crank arm to medical personnel using the pump.
The mechanical engagement and disengagement sy6tem of the present invention satisfies a long ex-isting need for improved, relatively simple, economical and reliable mechanisms for screw drive and syringe pump engagement and disengagement. The 6ystem tends to ensure against undue wear and damage to the threads of both lead screws and traveler mechanisms, and provides simplified syringe installation and plunger mover alignment It will be apparent from the foregoing that, while particular forms of the invention have been illustrated and described, various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The combination comprising:
a lead screw;
traveler means actuable between states of threaded engagement and disengagement with said lead screw, said traveler means including biasing means for biasing said traveler means in said state of engagement and in said state of disengagement, said biasing means producing an over-center action during movement of said traveler means between said state of engagement and said state of disengagement;
actuating means, selectively operable, for actuating said traveler means; and means for coupling said actuating means to said traveler means to allow limited relative movement between said actuating means and said traveler means, such that said traveler means moves to said state of engagement independently of said actuating means after said biasing means has moved over center, and further such that said traveler means begins to engage said lead screw in moving to said state of engagement only after said biasing means has moved over center.

2. A combination as set forth in Claim 1, and further including:

means for limiting collision forces between said traveler means and said lead screw as said traveler means moves to said state of engagement.

3. The combination comprising:
a lead screw;
traveler means actuable between states of threaded engagement and disengagement with said lead screw, said traveler means including biasing means for biasing said traveler means in said state of engagement and in said state of disengagement, said biasing means producing an over-center action during movement of said traveler means between said state of engagement and said state of disengagement;
actuating means, selectively operable, for actuating said traveler means; and means for coupling said actuating means to said traveler means to allow limited relative movement between said actuating means and said traveler means, such that said traveler means moves to said state of disengagement independently of said actuating means after said biasing means has moved over center, and further such that said traveler means begins to disengage said lead screw in moving to said state of disengagement only after said biasing means has moved over center.

4. A combination as set forth in Claim 3, and further including:
means for rapidly moving said traveler means to said state of disengagement after said biasing means has moved over center.

5. The combination comprising:
a lead screw;
traveler means actuable between states of threaded engagement and disengagement with said lead screw, said traveler means including biasing means for biasing said traveler means in said state of engagement and in said state of disengagement, said biasing means producing an over-center action during movement of said traveler means between said state of engagement and said state of disengagement;
actuating means, selectively operable, for actuating said traveler means; and means for coupling said actuating means to said traveler means to allow limited relative movement between said actuating means and said traveler means, such that said traveler means moves between said state of engagement and said state of disengagement independently of said actuating means after said biasing means has moved over center, and further such that said traveler means begins to engage said lead screw in moving to state of engagement, and begins to disengage said lead screw in moving to said state of disengagement, only after said biasing means has moved over center.

6. A combination as set forth in Claim 5, and further including:
means for limiting collision forces between said traveler means and said lead screw as said traveler means moves to said state of engagement.

7. A combination as set forth in Claim 5, and further including:
limit means for limiting the range of operation of said actuating means.

8. A combination as set forth in Claim 5, and further including:
means for rapidly moving said traveler means to said state of disengagement after said biasing means has moved over center.

9. The combination comprising:
a lead screw;
a pair of split nuts disposed on opposite sides of said lead screw and mounted for movement into and out of engagement with said lead screw;
rotary cam means for controlling the movement of said split nuts;
actuating means, selectively operable, for actuating said rotary cam means;
first biasing means for biasing said rotary cam means in either one of opposite rotational states, said first biasing means producing an over-center action with said rotary cam means during rotation between said opposite rotational states; and means for coupling said actuating means to said rotary cam means to allow limited relative movement between said actuating means and said rotary cam means, such that said rotary cam means controls movement of said split nuts independently of said actuating means after said rotary cam means has travelled over center, and further such that rotation of said rotary cam means in a first direction between said opposite rotational states causes movement of said split nuts into engagement with said lead screw only after said rotary cam means has travelled over center.

10. A combination as set forth in Claim 9, wherein said split nuts and said rotary cam means are freely moveable along said lead screw as a unit when said split nuts are disengaged from said lead screw.

11. A combination as set forth in Claim 9, wherein rotation of said rotary cam means in a second direction between said opposite rotational states causes movement of said split nuts out of engagement with said lead screw only after said rotary cam means has travelled over center.

12. A combination as set forth in Claim 9, and further including:
limit means for limiting the range of operation of said actuating means.

13. A combination as set forth in Claim 9, wherein said means for actuating said rotary cam means comprises rotary crank means for rotating said rotary cam means.

14. A combination as set forth in Claim 13, and further including:
second biasing means for biasing said rotary crank means towards either one of opposite rotational states, said second biasing means producing an over-center action with said rotary crank means during rotation between said opposite rotational states.

15. The combination comprising:
a lead screw;
a plurality of threaded members mounted for movement into and out of engagement with said lead screw;
control means for controlling movement of said threaded members:
first biasing means for biasing said control means in a disengaged state when said threaded members are fully disengaged from said lead screw, and in an engaged state when said threaded members are fully engaged to said lead screw, said first biasing means producing an over-center action with said control means during movement between said engaged state and said disengaged state; and means for coupling said actuating means to said control means to allow limited relative movement between said actuating means and said control means, such that said control means controls movement of said threaded members independently of said actuating means after said control means has travelled over center, and further such that said threaded members begin to engage said lead screw only after said control means has travelled over center towards said engaged state.

16. A combination as set forth in Claim 15, wherein said threaded members, said control means, said first biasing means and said actuating means are freely moveable along said lead screw as a unit when said split nuts are disengaged from said lead screw.

17. A combination as set forth in Claim 15, wherein said control means includes means for limiting collision forces between said threaded members and said lead screw upon engagement.

18. A combination as set forth in Claim 15, wherein said control means comprises a rotary cam and said actuating means comprises a rotary crank.

19. A combination as set forth in Claim 15, wherein said threaded members begin to disengage said lead screw only after said control means has travelled over center towards said disengaged state.

20. A combination as set forth in Claim 19, wherein said control means includes means for rapidly disengaging said threaded members from said lead screw after said control means has travelled over center.

21. A combination as set forth in Claim 19, wherein said control means comprises a rotary cam and said actuating means comprises a rotary crank.

22. In a syringe pump for delivering a pump stroke to a syringe having a syringe plunger, the combination comprising:
a lead screw;
a pair of split nuts disposed on opposite sides of said lead screw and mounted for movement into and out of engagement with said lead screw;
control means for controlling the movement of said split nuts; and plunger mover means, coupled to said control means, for pushing against the free end of the syringe plunger, said plunger mover means being mounted for selective rotation between a first position, in which said plunger mover means engages the free end of the plunger and actuates said control means to an engaged state in which said split nuts are engaged to said lead screw, and a second position, in which the plunger mover means is disengaged from the free end of the plunger and actuates said control means to a disengaged state in which said split nuts are disengaged from said lead screw.

23. A combination as set forth in Claim 22, wherein said split nuts, said control means and said plunger mover means are freely moveable along said lead screw as a unit when said split nuts are disengaged from said lead screw.

24. A combination as set forth in Claim 23, and further including:
first biasing means for biasing said control means in said engaged state and in said disengaged state, said first biasing means producing an over-center action with said cam means during movement between said engaged state and said disengaged state.

25. A combination as set forth in Claim 24, wherein movement of said control means from said disengaged state towards said engaged state causes movement of said split nuts into engagement with said lead screw only after said control means has travelled over center, and further including:
means for coupling said plunger mover means to said control means to allow limited relative movement between said plunger mover means and said control means, such that said control means controls movement of said split nuts into engagement with said lead screw independently of said plunger mover means after said control means has travelled over center, said control means including means for limiting collision forces between said split nuts and said lead screw upon engagement.

26. A combination as set forth in Claim 24, wherein movement of said control means from said engaged state towards said disengaged state causes movement of said split nuts out of engagement with said lead screw only after said control means has travelled over center, and further including:
means for coupling said plunger mover means to said control means to allow limited relative movement between said plunger mover means and said control means, such that said control means controls movement of said split nuts out of engagement with said lead screw independently of said plunger mover means after said control means has travelled over center, said control means including means for rapidly disengaging said split nuts from said lead screw after said control means has travelled over center.

27. A combination as set forth in Claim 24, wherein said control means comprises a cam and said plunger mover means comprises a crank arm.

28. A combination as set forth in Claim 24, and further including:
sensing means for sensing if said plunger mover means is in said first position.

29. A combination as set forth in Claim 24, and further including:
second biasing means for releasably biasing said plunger mover means in said first position and in said second position.

30. In a syringe pump for delivering a pump stroke to a syringe having a syringe plunger, the combination comprising:
a lead screw;
traveler means actuable between states of threaded engagement and disengagement with said lead screw, said traveler means including plurality of threaded members disposed about said lead screw such that in said state of engagement the forces exerted by said threaded members on said lead screw are substantially balanced relative to one another; and plunger mover means, coupled to said traveler means, for pushing against the free end of the syringe plunger, said plunger mover means being mounted for selective rotation between a first position, in which said plunger mover means engages the free end of the plunger and actuates said traveler means to said state of engagement with said lead screw, and a second position, in which said plunger mover means is disengaged from the free end of the plunger and actuates said traveler means to said state of disengagement with said lead screw.

31. A combination as set forth in Claim 30, wherein said traveler means and said plunger mover means are freely moveable along said lead screw as a unit when said plunger mover means is in said second position and said traveler means is in said state of disengagement.

32. A combination as set forth in Claim 31, wherein said traveler means includes first biasing means for releasably biasing said traveler means in said state of engagement and in said state of disengagement.

33. A combination as set forth in Claim 32, wherein said first biasing means produces an over-center action during actuation of said traveler means between said state of engagement and said state of disengagement.

34. A combination as set forth in Claim 33, and further including:
second biasing means for releasably biasing said plunger mover means in said first position and in said second position.

35. A combination as set forth in Claim 34, wherein said second biasing means produces an over-center action during rotation of said plunger mover means between said first position and said second position.

36. A combination as set forth in Claim 35, wherein said traveler means is actuated into said state of engagement only after said first biasing means has travelled over center.

37. A combination as set forth in Claim 35, wherein said traveler means is actuated into said state of disengagement only after said first biasing means has travelled over center.

38. A combination as set forth in Claim 35, and further including:
means for coupling said plunger mover means to said traveler means to allow limited relative movement between said plunger mover means and said traveler means, such that said traveler means moves between said state of engagement and said state of disengagement independently of said plunger mover means after said first biasing means has travelled over center.

39. A combination as set forth in Claim 38, and further including:
means for limiting collision forces between said traveler means and said lead screw as said traveler means moves to said state of engagement; and means for rapidly moving said traveler means to said state of disengagement after said first biasing means has moved over center.

40. A combination as set forth in Claim 30, and further including:
sensing means for sensing if said plunger mover means is in said first position.