INLINE FLUID DISPENSE PUMP ASSEMBLY

An inline pump assembly for dispensing fluids, the pump assembly including a pump head, having a piston wherein movement of the piston causes the pump head to dispense a fluid. A linear actuator has a lead screw wherein actuation of the linear actuator causes the lead screw to move along a linear path. A first anti-backlash device is disposed between the linear actuator and the pump head. The anti-backlash device includes a rail having a sliding block thereon. The slide block and rail are engaged to prevent movement of the slide block about a longitudinal axis of the rail. A coupler is fixedly secured to the linear slide and having a first end connected to the lead screw and a second end connected to the piston rod.

FIELD OF INVENTION

The present invention relates generally to liquid pumping systems, wherein a fluid is moved from a supply vessel to a receiving vessel. More particularly, the present invention relates to a mechanized inline pump that can be used in various clinical analyzers.

BACKGROUND

U.S. Pat. No. 5,536,471 describes a mechanized syringe pump of the prior art that has now been in use for more than twenty-five years. Numerous design refinements have been implemented during this time without departing from the basic concepts disclosed in this patent. There are, however, several reliability problems, which continue to plague this type of mechanized syringe pump and despite considerable time and effort devoted to solving these problems, they remain troublesome.

Inline piston pumps move fluid by pulling and pushing on a piston or plunger, generally using a stepper motor to generate the linear motion. This is usually accomplished using a linear actuator electric motor, coupled to the piston/plunger. The linear actuator has a threaded rod through the center of the motor, which mates with an internally threaded cylinder inside the motor. When the motor rotates, the lead screw also rotates with the motor, unless it is prevented from rotating. If the lead screw cannot rotate, it will move linearly. Thus, a mechanism is needed to prevent the lead screw from rotating. This is usually accomplished using a shaft key inside a keyway, a splined shaft, or a ball bearing riding inside a groove. A typical problem with these designs is the play in the system, which results in inaccuracies whenever the direction of motion is reversed. This play, or slop, in the system is often termed “step loss”. It is caused by any backlash between moving components.

Such step loss has typically been addressed through the use of software and calibrating a pump system to compensate for the backlash. A software solution to achieve the target accuracy/precision, however, requires calibrating each system and has limits as to how much correction can be achieved. In addition, implanting software compensation on a pump requires modifying the existing pump control software code found on the machine in which the pump is used. However, pump manufactures/suppliers typically do not have access or control over such software. The machines on which the pumps are used are already out in the field, and thus software modifications cannot be made without significant effort.

Accordingly, it would be desirable to provide a inline pump assembly that efficiently overcomes step loss and accurately and dispensed fluid in a constant manner.

SUMMARY

In one aspect of the present disclosure, an inline fluid dispense pump assembly for aspirating and dispensing fluids is provided.

The present disclosure provides an inline pump assembly for dispensing fluids, the pump assembly including a pump head, having a piston wherein movement of the piston causes the pump head to dispense a fluid. A linear actuator has a lead screw wherein actuation of the linear actuator causes the lead screw to move along a linear path. A first anti-backlash device is disposed between the linear actuator and the pump head. The anti-backlash device includes a rail having a sliding block thereon. The slide block and rail are engaged to prevent movement of the slide block about a longitudinal axis of the rail. A coupler is fixedly secured to the linear slide and having a first end connected to the lead screw and a second end connected to the piston rod.

The present disclosure further provides an inline pump assembly for dispensing fluids, the pump assembly including a pump head, having a piston rod wherein movement of the rod causes the pump head to dispense a fluid. A linear actuator has a lead screw wherein actuation of the linear actuator causes the lead screw to move along a linear path. A linear slide is disposed between the linear actuator and the pump head. The linear slide includes a rail having a slide block thereon. The linear slide and rail are engaged to prevent rotation of the slide about a longitudinal axis of the rail. The lead screw is operably nonrotatably connected to the linear slide, and the piston is operably connected to the linear slide.

The present disclosure still further provides a method of dispensing fluids comprising:providing an inline pump assembly comprising:a pump head, having a piston wherein movement of the piston causes the pump head to dispense a fluid;a linear actuator having a lead screw wherein actuation of the linear actuator causes the lead screw to move along a linear path;a first anti-backlash device disposed between the linear actuator and the pump head, the anti-backlash device including a rail having a slide block thereon, the slide block and rail cooperating to prevent movement of the slide block about a longitudinal axis of the rail; anda coupler fixedly secured to the linear slide and having a first end connected to the lead screw and a second end connected to the piston rod;generating a signal from a controller;responsive to the signal, operating the linear actuator to translate the coupler a predetermined amount, the coupler advancing the pump head to dispense the fluid.

DETAILED DESCRIPTION

With reference toFIGS.1A to2, the inline fluid dispense pump assembly10may generally include a pump head12, a linear actuator20, and a pump drive assembly28, including an anti-backlash mechanism33. The pump drive assembly28is disposed between the linear actuator20and the pump head12. While the assembly10is referred to herein as a dispense pump, it is within the contemplation of the present disclosure that the assembly can both dispense and aspirate fluids.

The pump head12may be of a type know in the art and in particular of the type shown in described in U.S. patent application Ser. No. 17/602,142 filed on Dec. 9, 2020, the content of which is incorporated by reference herein in its entirety. With reference toFIG.3, the pump head12includes casing13having an internal bore14. A piston16rides within the bore14. The piston16, for example, may be made of ceramic, plastic or metal. A piston control portion17extends in a sealed manner through a sealing end21from the pump housing13. The bore14is in fluid communication with ports18aand18bin order to allow it to aspirate and dispense fluid upon axial motion of the piston. A connector19may be secured to a terminal end25of the piston control portion to facilitate connection to the assembly10as described below. It is within the contemplation of the present discloser that the pump head12may be of a variety of designs know in the art for dispensing fluid upon linear motion of a piston.

With reference toFIGS.3and6-7, the pump head12is driven by the linear actuator20that converts rotary motion to linear motion. The linear actuator includes a stepper motor22that is driven by a motor controller of a type know in the art. The stepper motor22rotates an internally threaded drive armature24in which a lead screw26, having external threads41, is disposed. Rotation of the armature24causes the lead screw26to move forward and backward along the longitudinal axis L-L of the device depending on the direction of rotation of the armature24. A spring-loaded mechanism27may be disposed on the linear actuator front end60to prevent backlash between the threads of the drive armature24and the lead screw26. The mechanism27includes a top hat-shaped cap62in which an annular bearing64is disposed. The cap62is secured to the front of the linear actuator with fasteners66such that some degree of axial movement of the cap27is permitted. A resilient gasket68may be disposed between the cap62and the linear actuator20. The gasket68provides a seal between the cap62and linear actuator but permits the requisite amount of axil movement of the cap62. A threaded sleeve70is fixedly secured within the inside diameter of the annular bearing64. The sleeve70has internal threads that engage the lead screw threads.

A biasing device31, such as a compression spring, is disposed between the cap62and the linear actuator front60. The biasing device31provides an axial force that urges the cap62away from the linear actuator. This biasing force keeps the lead screw26and the drive armature24corresponding external and internal threads in constant engagement. The force of the biasing device31also maintains thread engagement between the lead screw external threads41and the internal threads72of the sleeve. This forced engagement mitigates backlash such that the motion of the drive armature24is immediately imparted on the lead screw26.

With specific reference toFIGS.3to5, the anti-backlash mechanism33is disposed between the lead screw26of the linear actuator20and the pump head12. The anti-backlash mechanism33mitigates backlash between the linear actuator20and the piston16such that the pump head12repeatedly and constantly dispenses and/or aspirates the correct amount of fluid. The anti-backlash mechanism33is disposed in the rigid housing29of the pump drive assembly28. The anti-backlash mechanism33includes a linear slide30including a precision ground rail32and a slide block34riding thereon. The linear slide30may of a type known in the art for providing precision linear guided motion. The rail32is fixedly secured to the housing29by fasteners35such that it is aligned along the longitudinal axis L-L. The rail32includes longitudinally extending grooves36running along opposed sides thereof. The slide block has a C-shaped channel38with opposed sidewalls40. Longitudinally extending recesses42in sidewalls40extend along the length of the sidewalls40. A plurality of ball bearings37are disposed in the recesses42and extend into the rail grooves36to help provide smooth motion between the slide block34and the rail32as well as to restrict any nonlinear axial motion. The engagement between the slide block34and the rail32is such that rotational movement of the slide block34about the longitudinal axis L-L is prevented. In addition, rotation about an axis Y-Y running perpendicular to the rail is also prevented. Thus, there is no backlash between the linear slide30and rail32.

With reference toFIGS.1B,1C, and3to5, a coupler50is disposed in the housing29and fixedly secured to the top surface of the slide block34by fasteners53. The coupler50has first and second opposed ends52and54, respectively, each having and opening56therein. The coupler first end52is attached to the piston connector19. The piston connector19is inserted in the opening and retained therein by a fastener such as a set screw58. The coupler second end54is connected to the lead screw26. The lead screw26may be inserted into opening56in the coupler and nonrotatably secured thereto by a set screw58of other type of fastening means know in the art. The connection between the lead screw26and coupler50prevents rotation of the lead screw26. Therefore, when the drive armature24rotates, the lead screw26only moves linearly. The coupler50may include a trigger flag55in the form of a set screw extending outwardly from a top surface of the coupler. The trigger flag55may cooperate with an optical, or other type of proximity sensor (not shown), to permit the location of the coupler50to be ascertained. The housing29may include a longitudinally extending slot39on and through its top surface. The slot39permits the position of the coupler50and the trigger flag55thereon to be viewed and to be accessible to trigger the proximity sensor.

In operation, a system controller emits a signal to the stepper motor controller which results in the stepper motor22turning and rotating the drive armature24. The drive armature's motion is imparted on the lead screw26that is secured against rotation, therefore, the lead screw26begins to translate. Since the slide block and rail prevent any rotational movement there is no backlash resulting from the movement of the lead screw26. The lead screw's linear motion is imparted on the coupler50which is secured to the linear slide30. The linear slide30prevents any rotational movement of the coupler50. Therefore, all the movement of the lead screw26is converted into linear motion of the coupler50. The coupler50moves in a guided manner and translates the piston16in a forward direction a predetermined amount to actuate and drive the pump head12and dispense a predetermined amount of fluid.

When the direction of movement is to be reversed, the system controller emits a signal causing the motor22to reverse direction. The resultant motion of the lead screw26, through engagement with the coupler50, is directly imparted on the piston16without any play or backlash and the piston16moves in a reverse direction. Therefore, the pump head12can be repeatedly driven in both directions without any backlash and without any resultant loss of dispensing accuracy. There is no need to use software, sensors or other complex devices to compensate for backlash in an attempt to achieve a desired accuracy. With this pump assembly, dispense accuracy of +/−10 picoliters can be achieved.

The present invention addresses the shortcomings of the prior designs by eliminating the backlash from the system using mechanical means instead of relying on the software. Thus, there is no need to modify or update software code which can be impractical especially in the field. To accomplish this, both areas of known backlash are addressed. The spring-loaded mechanism27acts as an anti-backlash mechanism that is incorporated directly onto the motor lead screw to eliminate backlash from the threads. In addition, a further backlash mechanism28in the form of the linear slide block with roller ball bearings is used to prevent any rotation of the lead screw26. By incorporating both an anti-backlash mechanism33on the lead screw, and a slide block, any and all mechanical backlash in the system is removed and step loss is effectively eliminated. These system improvements eliminate the inaccuracies seen whenever direction of motion is reversed, and are entirely independent of the driver hardware and software.

While various embodiments of the present invention are specifically illustrated and/or described herein, it will be appreciated that modifications and variations of the present invention may be effected by those skilled in the art without departing from the spirit and intended scope of the invention.