Information
-
Patent Grant
-
6736049
-
Patent Number
6,736,049
-
Date Filed
Tuesday, October 22, 200222 years ago
-
Date Issued
Tuesday, May 18, 200420 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 092 31
- 092 187
- 403 76
- 417 319
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International Classifications
-
Abstract
A piston carrier supports an elongated, slender piston rod for reciprocation in a pump cylinder to pump fluid into and out of the cylinder. The piston rod is made of a material such as sapphire or zircon and has a diameter less than about ten millimeters, and the pump can provide flows of from about 50 nanoliters to about 250 microliters per minute at pressures of several hundred bars. A drive motor rotates a threaded screw and a drive nut of a drive system applies a linear drive force to the piston carrier. A ball and socket connection between the drive system and the piston carrier avoids the need for precise alignment to prevent breakage of the fragile piston. A magnet in the socket holds the ball in place and avoids the need for a spring or other mechanical holder. The socket also includes a ring of a low reluctance material surrounding the ball to increase the magnetic retention force.
Description
FIELD OF THE INVENTION
The present invention relates to an improved high pressure low volume pump suitable for use in high pressure liquid chromatography.
DESCRIPTION OF THE PRIOR ART
There is a need for a pump that can accurately deliver precisely measured, very small volumes of liquid at very high pressures. For example, in performing high pressure liquid chromatography (HPLC) procedures, a motor driven pump is typically used to deliver liquid solvents such as methanol, isopropyl alcohol and the like. The trend is to use smaller volumes of solvent for the mobile phase of the chromatography column and to operate at higher pressures. For example, it would be desirable to provide a pump that can deliver fluids at low flow rates in the range of from about 50 nanoliters to about 250 microliters per minute at pressures of several hundred bars.
A piston pump designed for such low flow volumes is necessarily delicate because the liquid handling components of the pump must be very small in size. Low volume HPLC pumps can benefit from the use of a small diameter piston made of sapphire or zircon or the like, because such materials can be provided to close dimensional and surface tolerances in very small sizes. However a problem exists because this material is fragile and easily broken. It is difficult to avoid breakage of a small and delicate piston during assembly and operation of the high pressure low volume pump.
SUMMARY OF THE INVENTION
A principal object of the present invention is to provide an improved high pressure low volume pump capable of providing accurately metered flows of liquids in the nanoliters per minute range at pressures as high as several hundred bars. Further objects are to provide a pump that can employ a very small piston made of a fragile material while overcoming the problem of breakage of the piston during assembly and operation of the pump; to provide a pump in which the need for mechanical piston retention, for example by a spring, is avoided; to provide a pump which does not require precise and expensive alignment of the piston with the piston drive system; and to provide a high pressure low volume pump overcoming the disadvantages of pumps that have been used in the past.
In brief, in accordance with the invention there is provided a high pressure low volume pump for high pressure liquid chromatography and the like. The pump includes a pumping section including a pump cylinder and passages for the flow of a pumped fluid into and out of the cylinder. A piston assembly includes a piston reciprocally movable in the cylinder and a piston holder supporting the piston at a first end of the piston holder. A piston drive system is connected between a motor and the second end of the piston holder for reciprocating the piston assembly in response to operation of the motor. The piston is an elongated slender rod having a diameter of less than about 10 millimeters. The interconnection of the drive system and the second end of the piston holder includes a ball-and-socket coupling with a spherical member pivotally received in a socket. A magnet in the socket holds the spherical member in the socket using magnetic force.
BRIEF DESCRIPTION OF THE DRAWING
The present invention together with the above and other objects and advantages may best be understood from the following detailed description of the preferred embodiment of the invention illustrated in the drawing, wherein:
FIG. 1
is a sectional view of a high pressure low volume pump constructed in accordance with the present invention, taken along the major axis of the pump; and
FIG. 2
is an enlarged sectional view of the piston assembly and drive system of the pump of FIG.
1
.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Having reference now to the drawing, in
FIG. 1
there is illustrated a high pressure low volume pump generally designated as
10
and constructed in accordance with the principles of the present invention. The pump
10
is useful for providing a solvent liquid mobile phase in high pressure liquid chromatographic procedures, and is capable of pumping solvents such as methanol, isopropyl alcohol, acetonitrile and others at low flow rates in the range of from about 50 nanoliters to about 250 microliters per minute at pressures of up to at least six hundred bars.
In order to achieve these desirable performance characteristics, the pump
10
includes a piston
12
in the form of an elongated slender rod having a diameter of less than about ten millimeters, and preferably having a diameter in the range of from about one to about three millimeters. The piston
12
is made of a crystalline material, preferably sapphire, or of a material having similar characteristics, such as a mineral, preferably zircon. The advantages of such materials is that they can be provided in the very small sizes needed for the present invention with precise tolerances and surface characteristics. A potential disadvantage of a piston
12
made of this material and size is that it is fragile and subject to breakage when the pump
10
is assembled and operated. The present invention overcomes this potential disadvantage and solves the problem of breakage of the pump piston
12
.
Proceeding to a more detailed description of the pump
10
, it includes a pump body
14
carrying an end cap
16
to which is secured a drive motor
18
. Drive motor
18
is a stepper motor that can be precisely rotated under the control of a microprocessor that receives position feedback signals provided over a cable
20
from a detector
22
that receives signals from an encoder at the back of the motor
18
.
A piston assembly
24
including the piston
12
is linearly reciprocated by a piston drive system
26
that is coupled to the motor
18
by a drive transmission
28
that converts rotary motion of the motor
18
to linear motion of the piston drive system
26
and piston assembly
24
. The piston
12
reciprocates in a pumping cylinder
30
that is part of a pumping section
32
machined in a pump head
34
attached to a piston housing
36
including a cap
38
secured to the pump body
14
and a spacer body
40
between the cap
38
and the pump head
34
.
The pumping section
32
in the pump head
34
includes a fluid inlet passage
42
and a fluid outlet passage
44
, both communicating with the pump cylinder
30
. There is sufficient clearance around the piston
12
for fluid to flow within the cylinder
30
along the surface of the piston
12
, and the passages
42
and
44
may be located if desired at other points along the length of the cylinder, for example to permit inlet and outlet valves to be mounted directly within or on the pump head
34
. An inlet flow valve (not shown) located at the pump head
34
or remote therefrom is opened to admit fluid to
1
the passage
42
and cylinder
30
when the piston is moved out from the cylinder
30
(to the right as seen in FIG.
1
). An outlet flow valve (not shown) located at the pump head
34
or remote therefrom is opened when the piston is moved into the cylinder
30
(to the left as seen in FIG.
1
). The inlet and outlet flow valves can be check valves or microprocessor controlled valves such as solenoid valves. To provide continuous mobile phase flow in a HPLC system, an assembly of a plurality of valves
10
can be used so that outlet flow is provided by at least one valve
10
at all times.
The piston assembly
24
includes a piston holder
46
having an elongated, axially extending hole at one end into which the piston
12
is inserted and secured. The holder
46
reciprocates in a rinse chamber
48
within the spacer body
40
. A rinse liquid flowing through rinse ports
50
can flow through the chamber
48
. The pumped fluid is isolated from the rinse liquid by a collapsible bellows seal
52
having one end in a groove
54
in the piston holder
46
and another end captured between the cap
38
and spacer body
40
. The fully extended position of the piston
12
seen in
FIG. 1
is determined by engagement of a stop flange
56
of the holder
46
against the pump head
34
.
Drive transmission
26
includes a threaded screw
58
that is axially aligned with and secured to a drive shaft
60
of motor
18
by a shaft coupling
62
. The drive system
26
includes a hollow drive collar
64
axially receiving the drive screw
58
. A radially extending projection
66
of the collar
64
is received in an axially extending slot
68
in the pump body
14
to prevent rotation of the drive collar
64
. A threaded drive nut
70
is mounted within the collar
64
and mates with the drive screw
58
. A bearing
72
supports the collar
64
for linear motion along the axis of the pump
10
. When the motor
18
rotates the shaft
60
, rotation of the screw
58
results in precisely controlled linear motion of the mating drive nut
70
and the drive collar
64
.
In accordance with the invention a ball and socket connection
74
transmits drive force between the drive collar
64
and the piston holder
46
. The end of the piston holder
46
opposite the piston
12
is spherical in shape to provide a coupling ball
76
. The end of the drive collar
64
is provided with a socket
78
receiving the ball
76
. The use of the ball and socket connection
74
avoids the need for exact alignment of the axis of the drive system
26
with the axis of movement of the piston assembly
24
. The cost of precise tolerances is eliminated, and breakage of the piston
12
due to misalignment is prevented.
In order to retain the ball
76
within the socket
78
and to permit the drive system
26
to both push and pull the piston assembly, a magnet
80
is incorporated into the socket
78
. The ball
78
is held by magnetic force rather than mechanically by a spring or other retention device. The socket
78
is generally cup shaped and includes a base wall
82
providing a nest for holding the magnet
80
and a side wall
84
surrounding the ball
76
. The piston holder
46
including the ball
76
is formed of a magnetic, preferably ferrous, material attracted by the magnet
80
. A nonmagnetic spacer
86
, preferably of plastic, at the surface of the magnet
80
locates the ball
76
in close proximity to the magnet
80
and permits universal pivotal motion of the ball
76
in the socket
78
. Although the magnet
80
can be of other materials, it is preferably a rare earth, neodymium-iron-boron magnet.
The magnetic retention force is maximized by a ring
88
of low magnetic reluctance material, such a soft iron, supported in the side wall
84
and surrounding the central plane of the ball
76
. The ring
88
contributes to a low reluctance path including the magnet
80
and the ball
76
and increases the magnetic holding force by changing an open ended flux path to more of a closed flux path.
In assembling the pump
10
, when the cap
38
is joined to the pump body
14
, the ball
76
enters into the socket
78
and is urged by the magnet
80
to the fully seated position seen in FIG.
1
. This is a gentle and smooth motion that does not apply shocks or stresses to the piston
12
, thus avoiding breakage. If a mechanical retention system were used, the insertion of the piston
12
into the socket
78
would tend to cause breakage due to shocks and stresses arising from abrupt motions or from non axial forces applied to the piston holder
46
.
While the present invention has been described with reference to the details of the embodiment of the invention shown in the drawing, these details are not intended to limit the scope of the invention as claimed in the appended claims.
Claims
- 1. A high pressure low volume pump for high pressure liquid chromatography and the like comprising:a pumping section including a pump cylinder; passages for the flow of a pumped fluid into and out of said cylinder; a piston assembly including a piston reciprocally movable in said cylinder; said piston assembly including a piston holder supporting said piston at a first end of said piston holder; a motor; and a piston drive system connected between said motor and the second end of said piston holder for reciprocating said piston assembly in response to operation of said motor; said piston being an elongated slender rod having a diameter of less than about 10 millimeters; the interconnection of said drive system and said second end of said piston holder including a ball-and-socket-coupling with a spherical member pivotally received in a socket; said socket being cup-shaped with a base and a side wall at least partly surrounding said spherical member; said pump being characterized by: a magnet in said socket for holding said spherical member in said socket using magnetic force, said magnet being located in said base adjacent to said spherical member, and said socket further including a ring of low reluctance magnetic material supported in said side wall and surrounding said spherical member.
- 2. A high pressure low volume pump as claimed in claim 1, said piston being made of a crystalline material.
- 3. A high pressure low volume pump as claimed in claim 2 said piston being made of sapphire.
- 4. A high pressure low volume pump as claimed in claim 1, said piston being made of a mineral.
- 5. A high pressure low volume pump as claimed in claim 4, said piston being made of zircon.
- 6. A high pressure low volume pump as claimed in claim 1, said spherical member being said second end of said piston holder, and said socket being part of said drive system.
- 7. A high pressure low volume pump as claimed in claim 6, said motor including a rotatable drive shaft and said drive system including a drive transmission for converting rotary shaft motion into linear motion of said socket.
- 8. A high pressure low volume pump as claimed in claim 7, said drive transmission including a threaded shaft rotatably driven by said motor drive shaft and a threaded drive nut carried by said drive system.
- 9. A high pressure low volume pump as claimed in claim 1, said piston having a diameter in the range of from about one millimeter to about three millimeters.
Priority Claims (1)
Number |
Date |
Country |
Kind |
00403469 |
Dec 2000 |
EP |
|
PCT Information
Filing Document |
Filing Date |
Country |
Kind |
PCT/US01/44927 |
|
WO |
00 |
Publishing Document |
Publishing Date |
Country |
Kind |
WO02/48582 |
6/20/2002 |
WO |
A |
US Referenced Citations (3)
Number |
Name |
Date |
Kind |
4753581 |
Hiscock |
Jun 1988 |
A |
5312233 |
Tanny et al. |
May 1994 |
A |
5415489 |
Hutchins et al. |
May 1995 |
A |