Syringe pump abstract
A syringe pump in which a movable member is attached to a frame
so as to be movable forward and backward, a transmission roller,
transmission gear and speed increasing gear are attached to the
movable member, the drive force of a motor is transmitted to the
transmission roller through a timing belt, and a clutch mechanism
including a rotating member with teeth and a rotation preventing
member with teeth engaged with the former teeth is provided whereby
the drive force of the transmission gear is transmitted to the rotating
member through a guide member comprising a timing belt. The movable
member moves along the guide member in the state where the teeth
of the rotating member and rotation preventing member are engaged
with each other.
Syringe pump claims
What is claimed is:
1. A syringe pump which includes a casing for containing liquid
therein and a piston disposed movably in the casing for discharging
a liquid, comprising:
a frame having a mount for mounting one of the casing and piston
thereon;
a movable member supported movably on said frame and having the
other of the casing and piston attachable thereon;
a drive mechanism including a motor disposed on said frame, a drive
roller attached to an output shaft of said motor, a follower roller
attached rotatably on said frame, a transmission member attached
to said drive roller and follower roller for transmitting the torque
of said drive roller to said follower roller;
a drive force converting mechanism including a transmission roller
attached rotatably to said movable member for converting the movement
of said transmission member to rotation, a transmission gear attached
rotatably to said movable member, a speed increasing mechanism disposed
between said transmission roller and said transmission gear for
increasing the speed of transmission roller and transmitting the
increased speed of said transmission roller to said transmission
gear;
an endless guide member engaged with said transmission gear for
guiding said movable member;
a clutch mechanism including a rotating member engaged with said
guide member and a rotation preventing member disengageably engaging
said rotating member for preventing rotation of said rotating member,
the rotating member and rotation preventing member having teeth
provided on facing ends thereof and engaging each other.
2. A syringe pump according to claim 1 wherein said transmission
member includes an endless member disposed on said drive roller
and follower roller.
3. A syringe pump according to claim 2 wherein said endless member
includes a timing belt.
4. A syringe pump according to claim 1 comprising a lever supported
by said frame for fixing one of said casing and piston to said mount,
a cam member having a cam face attached to an end of said lever
and abutting on said rotation preventing member, means disposed
between said rotation preventing means and said frame for biasing
said rotation preventing means toward said cam member, and wherein
the cam face of said cam member is spaced from the center of rotation
of said cam member such that when said lever is at a position where
said lever fixes one of said casing and piston, said rotation preventing
member abuts on said rotating member while when said lever is at
a position where said lever releases one of said casing and piston
from its fixed state, said rotation preventing member is moved away
from said rotating member.
5. A syringe pump according to claim 1 comprising a radially outward
extending ear formed on said rotation preventing member, a position
restricting spring disposed between one side of said ear and said
frame for restricting the movement of said rotation preventing member
in one of opposite circumferential directions, and a stop fixed
to said frame on the opposite side of said ear from said position
restricting spring for abutting on said ear.
6. A syringe pump according to claim 5 wherein said position restricting
spring is disposed so as to prevent a circumferential movement of
said rotation preventing member occurring when said piston moves
forward relative to said casing.
7. A syringe pump according to claim 6 wherein an end of said
spring adjacent said frame is engaged with a bias adjusting screw
screwed into said frame, the screw being disposed movable axially
of said position restricting spring.
8. A syringe pump according to claim 7 comprising a detection
switch for detecting a circumferential movement of said rotation
preventing member against the action of said position restricting
spring.
9. A syringe pump according to claim 8 wherein said detection
switch is connected to a control unit which when said detection
switch detects the circumferential movement of said rotation preventing
member, the control unit receives a detection signal from said detection
switch and delivers to said motor a signal to stop said motor.
10. A syringe pump according to claim 1 wherein said speed increasing
mechanism includes a plurality of gears.
11. A syringe pump according to claim 1 wherein said guide member
includes a timing belt.
Syringe pump description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to syringe pumps which discharge
a small quantity of liquid using a syringe which includes a cylindrical
casing and a piston enclosed therein and used as a liquid discharge
unit in a medical device or an industrial device.
2. Description of the Related Art
Recently, demands for discharging a small quantity of liquid arise
in various fields of industries, for example, a demand for administering
a carcinostatic substance dropwise in the field of medical cares
over a long time and a demand for discharging a minimum required
quantity of soldering paste to a welded point in the field of electronic
part manufacture. Generally, a liquid such as a carcinostatic substance
to be discharged is exchanged in accordance with application and
easy exchange of such liquid is required. In the past, a syringe
pump is used to discharge a liquid accurately and to facilitate
the exchange of that liquid.
FIG. 12 shows a technique related to syringe pumps. Disposed within
a box-like frame 50 in FIG. 12 is a guide rod 51 to which a member
52 movable axially of guide rod 51 is attached. Cylindrical casing
71 of syringe 70 is fixed on top of frame 50 by syringe holder 53.
Syringe piston 72 is engaged with movable member 52 so that when
piston 72 moves forward in accordance with the movement of movable
member 52 a liquid is discharged out of cylinder 70. Screw shaft
54 is provided rotatable and parallel to guide rod 51 within frame
50. A pair of half nuts 55 is engaged on screw shaft 54. Upper half
nut 55 is connected to rod 56 attached to movable member 52. Drive
gear 57 is attached to an end of screw shaft 54 and connected to
gear 60 fixed to output shaft 59A of motor 59 through intermediate
gear 58. Therefore, when motor 59 is driven, screw shaft 54 is rotated
through gears 57 58 and 60 so that half nuts 55 and movable member
52 are moved axially. As shown in FIG. 13 intermediate gear 58
is attached rotatably to one end of swingable arm 61 the other end
of which is attached swingably to frame 50. A detection element
62A of switch 62 abuts on swingable arm 61. Spring 63 is attached
to the free end of arm 61 to which intermediate gear 58 is attached
so as to bias intermediate gear 58 against gears 57 and 60. Spring
63 switch 62 arm 61 and intermediate gear 58 constitute closure
detecting mechanism 64 which detects closure prescribed in JIS (Japanese
Industrial Standard) (6.4 in T1635-1986). If syringe 70 is closed
for some reason, the movement of movable member 52 is hindered in
spite of the operation of motor 59. If closure pressure exceeds
an allowable value, a slippage occurs between intermediate gear
58 and gear 60 attached to motor 59 so that intermediate gear 58
moves away from gears 57 60 against the action of spring 63. Switch
62 detects such movement of intermediate gear 58 and generates a
signal which causes a controller (not shown) to stop motor 59.
In order to allow syringe 70 to be replaced, piston 72 must manually
be moved freely relative to casing 71. To this end, the syringe
pump has a clutch mechanism which transmits the drive force of screw
shaft 54 to movable member 52 or releases the transmission of the
drive force of screw shaft 54 to movable member 52. In the syringe
pump of FIG. 12 the clutch mechanism has a structure in which the
pair of half nuts 55 abuts disengageably on screw shaft 54.
Another technique related to a syringe pump is disclosed in Published
Unexamined Japanese Utility Model Application Sho 63-190921 in which
the syringe pump includes a frame having a mount for a syringe,
a lever supported by the frame and fixing the syringe to the mount,
a movable member supported movably on the frame for operating the
piston in the syringe, a motor attached to the frame, a roller provided
on each of an output shaft of the motor, the movable member and
the frame, and a wire belt extending around these rollers to move
the movable member in accordance with the drive of the motor. If
the motor is driven, the wire belt causes the movable member to
be driven on the principle of a running block to discharge a liquid
from the syringe. The clutch mechanism is attached to the lever
such that when the lever is operated, the wire belt is rendered
tensile or released to transmit the drive force of the motor to
the movable member or render the movable member freely movable.
However, in the syringe pump of FIG. 12 the screw shaft and half
nuts each are a precise mechanical part to thereby render the syringe
pump expensive, disadvantageously. In order to adjust a replaced
syringe minutely, the piston can be moved by an appropriate stroke
with the syringe casing being fixed, in which case the half nuts
55 are at any position along screw shaft 54 under which condition
the clutch is actuated. Since the position of half nuts 55 relative
to screw shaft 54 is not fixed, half nuts 55 and screw shaft 54
may not coincide in thread crest in which case half nuts 55 and
screw shaft 54 are not appropriately engaged with each other and
can rotate uselessly. Therefore, the position of movable member
52 must manually be adjusted minutely such that half nuts 55 and
screw shaft 54 are appropriately engaged with each other. This adjustment
is troublesome. Even if half nuts 55 and screw shaft 54 coincide
with each other in thread crest and bottom, there may be a backlash
between the crests and bottoms, so that there occurs an error between
a quantity of drive given by motor 59 and a quantity of movement
of movable member 52 and hence an error in a discharged quantity
of liquid.
Since the syringe pump of the Application '921 uses the wire belt
extending around the roller provided on the motor output shaft to
transmit the drive force by the frictional force occurring between
the roller and wire belt, there arises a slippage between the wire
belt and roller to thereby hinder accurate discharge of liquid disadvantageously.
Especially, if the roller rapidly rotates at high speed directly
after the actuation of the motor, the roller becomes likely to slip
relative to the wire belt due to transition from static friction
to dynamic friction. In order to eliminate such slippage, the wire
belt is required to be extend around the rollers doubly or triply.
In this case, the wire belt would be rubbed by itself and deteriorated
in durability.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a durable syringe
pump which has a simple structure to discharge a small quantity
of liquid accurately.
In order to achieve the object, the present invention provides
a syringe pump which includes a casing for containing a liquid therein
and a piston disposed movably in the casing for discharging a liquid,
comprising: a frame having a mount for mounting one of the casing
and piston thereon; a movable member supported movably on the frame
and having the other of the casing and piston attached thereon;
a drive mechanism including a motor disposed on the frame, a drive
roller attached to an output shaft of the motor, a follower roller
attached rotatably on the frame, a transmission member attached
to the drive roller and follower roller for transmitting the torque
of the drive roller to the follower roller; a drive force converting
mechanism including a transmission roller attached rotatably to
the movable member for converting the movement of the transmission
member to rotation, a transmission gear attached rotatably to the
movable member, a speed increasing mechanism disposed between the
transmission roller and the transmission gear for increasing the
speed of transmission roller and transmitting the increased speed
of the transmission roller to the transmission gear; an endless
guide member engaged with the transmission gear for guiding the
movable member; a clutch mechanism including a rotating member engaged
with the guide member and a rotation preventing member disengageably
engaging the rotating member for preventing rotation of the rotating
member, the rotating member and rotation preventing member having
teeth provided on their opposing ends and engaging each other.
The transmission member may include an endless member disposed
on the drive roller and follower roller. The endless member may
include a timing belt.
A lever may be supported by the frame for fixing one of the casing
and piston to the mount. A cam member may be attached to an end
of the lever and abutting on the rotation preventing member. Means
may be disposed between the rotation preventing means and the frame
for biasing the rotation preventing means toward the cam member.
The cam face of the cam member is spaced from the center of rotation
of the cam member such that when the lever is at a position where
the lever fixes one of the casing and piston, the rotation preventing
member abuts on the rotating member while when the lever is at a
position where the lever releases one of the casing and piston from
its fixed state, the rotation preventing member is moved away from
the rotating member.
A radially outward extending ear may be formed on the rotation
preventing member. A position restricting spring may be disposed
between one side of the ear and the frame for restricting the movement
of the rotation preventing member in one of opposite circumferential
directions. A stop may be fixed to the frame on the opposite side
of the ear from the position restricting spring for abutting on
the ear. The position restricting spring may be disposed so as to
prevent a circumferential movement of the rotation preventing member
occurring when the piston moves forward relative to the casing.
The frame side end of the position restricting spring is engaged
with a bias adjusting bolt screwed into the frame, the bolt being
disposed movable axially of the position restricting spring. In
addition, in the present invention, a detection switch may be provided
for detecting a circumferential movement of the rotation preventing
member against the action of the position restricting spring. The
detection switch may be connected to a control unit which when the
detection switch detects the circumferential movement of the rotation
preventing member, the control unit receives a detection signal
from the detection switch and delivers to the motor a signal to
stop the motor.
The speed increasing mechanism may include a plurality of gears.
The guide member may include a timing belt.
In order to discharge a liquid using the syringe according to the
present invention, the teeth of the rotational member of the clutch
mechanism are engaged with the teeth of its rotation preventing
member, namely, the clutch is actuated.
When the motor is operated under such conditions, the drive mechanism
which includes the drive roller, passive roller and transmitting
member is actuated. The movement of the transmitting member is changed
to the rotation of the transmission roller constituting part of
the drive force converting mechanism, and the rotation of the roller
is then transmitted through an acceleration mechanism to the transmission
gear.
The rotation of the transmission gear is transmitted to the guide
member which is engaged with the rotating member which is prevented
from rotating by the rotation preventing member. Therefore, the
guide member is fixed to the frame and the transmission gear moves
along the guide member. This causes the transmission gear and the
movable member to move to thereby move the piston relative to the
casing to cause the syringe to discharge a liquid.
Generally, there is a backlash between the rotation preventing
member, rotating member, guide member and transmission gear, which
backlash causes an error in the discharge of the liquid. The rotation
of the transmission roller of the drive mechanism is accelerated
by the acceleration mechanism and then transmitted to the transmission
gear, so that the error arising in the transmission gear is reduced
on the side of the drive mechanism, and hence the error in the discharge
of the liquid due to the backlash is reduced.
In order to replace the syringe after a predetermined liquid discharging
operation is ended, the rotating member and rotation preventing
member of the clutch mechanism are moved away from each other and
hence their engaging teeth are disengaged from each other, namely,
the clutch is disengaged. Under such condition, even if the motor
is actuated, only the guide member is moved and the movable member
is not. Under such conditions, the syringe is removed from the frame
mount, the movable member is manually moved to a predetermined position,
and a new syringe is placed on the frame mount.
Thereafter, in order to discharge a liquid using the new syringe,
the engaging teeth of the rotating member and rotation preventing
member are again engaged with each other and the motor is then operated.
Even if the crests of the teeth of both members abut on each other,
rotation of the rotating member causes the engaging teeth of both
the members to change their relative position circumferentially
to thereby cause the engaging teeth to engage automatically with
each other.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view of one embodiment of syringe pump according
to the present invention.
FIG. 2 is a plan view of the embodiment.
FIG. 3 is a right-hand side view of the embodiment.
FIG. 4 is a longitudinal cross-sectional view of the embodiment.
FIG. 5 is a transverse cross-sectional view of the embodiment.
FIG. 6 is a cross-sectional view taken along the line 6--6 of FIG.
1.
FIG. 7 is a cross-sectional view taken along the line 7--7 of FIG.
1.
FIG. 8 is a cross-sectional view taken along the line 8--8 of FIG.
1.
FIG. 9 is a schematic perspective view of the embodiment.
FIGS. 10(A) and 10(B) each are a plan view of a clutch mechanism.
FIG. 11 is a transverse cross-sectional view of a modification
of the present invention.
FIG. 12 is a longitudinal cross-sectional view of a syringe pump
of the art related to the present invention.
FIG. 13 is a cross-sectional view taken along the line 13--13 of
FIG. 12.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
One embodiment of the present invention will be described with
reference to the drawings.
FIGS. 1-3 shows the appearance of the embodiment.
Syringe pump 70 of the present embodiment includes a cylindrical
casing 71 which contains a liquid such as a carcinostatic substance
and a piston 72 disposed movably in casing 71. Casing 71 has at
an end flange 71A while piston 72 has at an end flange 72A.
Provided on top of an elongated box-like frame 1 in FIGS. 1-3 is
mount 2 which mounts casing 71 thereon. Mount 2 has an upper end
with U-like groove 2A fitting on casing 71. Mount 2 has groove 2B
thereon in the vicinity of the midpoint of frame 1 engaging casing
flange 71A. Piston flange 72A is engaged in the groove 3A of movable
member 3.
FIGS. 4-9 show the internal structure of the syringe pump. In FIGS.
4-9 a pair of guide rods 4 is disposed within frame 1 so as to
parallel to syringe 70. The pair of guide rods 4 supports the central
portion of movable member 3 such that the movable member is movable
along guide rods 4. Therefore, when movable member 3 moves forward
and backward along guide rods 4 piston 72 moves correspondingly
relative to casing 71.
Movable member 3 has on its lower end a pair of opposing protrusions
3B across which a pair of parallel shafts 5 is provided perpendicular
to guide rods 4. One shaft 5 has at its center first gear 6 attached
rotatably thereto. Transmission roller 7 with a plurality of external
teeth thereon is fixed coaxially to first gear 6. The other shaft
5 has second gear 8 attached rotatably thereto and engaged with
first gear 6. Transmission gear 9 is fixed coaxially to second gear
8. First gear 6 is larger in number of teeth than second gear 8.
Gears 6 and 8 constitute speed increasing mechanism 10 which increases
the speed of transmission roller 7 and transmits the increased speed
to transmission gear 9. Transmission roller 7 transmission gear
9 and speed increasing mechanism 10 constitute drive force transmission
mechanism 11.
Motor 12 is attached to one internal side of frame 1 and includes
a stepping motor which causes a liquid to be discharged with an
accuracy of one pulse in accordance with a motor drive signal. Output
shaft 12A of motor 12 is disposed parallel to shafts 5. Drive roller
13 with a plurality of external teeth thereon is attached to output
shaft 12A. Shaft 14 is provided parallel to shafts 5 in the vicinity
of the other internal side of frame 1 and has follower roller 15
with a plurality of external teeth thereon attached rotatably thereto.
First timing belt 16 comprising a transmission member extends around
drive roller 13 and follower roller 15 and is engaged with transmission
roller 7. Motor 12 drive roller 13 follower roller 15 and first
timing belt 16 constitute drive mechanism 17.
Shaft 18 is disposed parallel to shaft 14 between motor 12 and
movable member 3 below mount 2 and has rotating member 19 with a
plurality of external teeth thereon rotatably attached thereto.
Shaft 14 has third gear 20 attached rotatably thereto. Second timing
belt 21 as a guide member extends around rotating member 19 and
third gear 20. Second timing belt 21 is engaged with transmission
gear 9 to thereby guide movable member 3 along a linear path. Rotation
preventing member 22 is attached rotatably to shaft 18 and disengageably
to rotating member 19 which cooperates with rotation preventing
member 22 to constitute a clutch mechanism. Members 19 and 22 have
at at opposing ends engaging teeth 19A and 22A, respectively, engaging
with each other. Spring 23 is provided as biasing means between
a side of frame 1 and the opposite end of rotating preventing member
22 from engaging teeth 22A. It biases rotating preventing member
22 toward rotating member 19 to ensure the engagement of engaging
teeth 19A and 22A. Rotation preventing member 22 has a pair of radially
outward extending ears 22B and 22C at the spring 23 side end thereof.
A lower surface of left-hand ear 22B of FIGS. 4 and 5 abuts on stop
24 fixed to frame 1 while an upper surface of ear 22B is engaged
with a lower end of coil spring 25 which biases ear 22B toward
stop 24. Namely, rotation preventing member 22 is normally fixed
by stop 24 and coil spring 25. Under such condition, if motor output
shaft 12A is rotated counterclockwise in FIG. 9 rotating member
19 tries to rotate clockwise, but rotation preventing member 22
prevents rotating member 19 and second timing belt 21 from rotating,
so that movable member 3 moves leftward in the figure along timing
belt 21 to thereby advance piston 72. If motor output shaft 12A
rotates clockwise in FIG. 9 movable member 3 moves rightward to
thereby move piston 72 backward.
Disposed below right-hand ear 22C in FIGS. 4 and 5 is detection
switch 26A which detects closure prescribed in JIS (6.4 T1635-1985).
If casing 71 has been closed when piston 72 moves forward, rotation
preventing member 22 tries to rotate clockwise against the action
of coil spring 25. Detection switch 26A detects such rotation of
member 22. Detection switch 26A is connected to control unit 26B,
which receives a detection signal from detection switch 26A when
same detects the movement of rotation preventing member 22 and sends
to motor 12 a signal to stop the operation of the motor. An upper
end of coil spring 25 abuts on a lower end of adjusting screw 27
screwed into the upper portion of frame 1. Adjusting screw 27 is
movable axially of coil spring 25. By adjusting a quantity of movement
of coil spring 25 the biasing force of coil spring 25 and hence
a set value of the closure pressure to be sensed is adjusted.
Rod 28 is disposed movable vertically and circumferentially in
the upper end of frame 1. Rod 28 has a cam member 29 at a lower
end and a syringe hold lever 30 at an upper end. Cam member 29 has
a linear cam face 29A and an arc cam face 29B. Linear cam face 29A
is spaced from the cam rotation center such that when syringe hold
lever 30 is at a position where syringe casing 71 is fixed, rotation
preventing member 22 abuts on rotating member 19. Arc cam face 29B
is spaced from the center of rotation of the cam member such that
when syringe hold lever 30 is at a position where casing 71 is released
from its fixed state, rotation preventing member 22 is away from
rotating member 19. Spring 31 is provided between the upper surface
of cam member 29 and an upper end of frame 1 so as to urge syringe
hold lever 30 and hence casing 71 downward.
In operation, in order to cause syringe 70 to discharge a liquid,
engaging teeth 19A and 20A of rotating member 19 and rotation preventing
member 22 of the clutch mechanism are engaged with each other or
the clutch is engaged.
Under such condition, if motor 12 is operated, drive mechanism
17 comprising drive roller 13 passive roller 15 and first timing
belt 16 is actuated. The movement of first timing belt 16 is converted
to rotation of transmission roller 7 constituting a part of drive
force converting mechanism 11 and this rotation is transmitted to
transmission gear 9 through speed increasing mechanism 10 comprising
two gears 6 and 8.
Rotation of transmission gear 9 is intended to be transmitted to
second timing belt 21 and rotating member 19. However, rotating
member 19 is prevented from rotating by rotation preventing member
22. Therefore, second timing belt 21 is fixed to frame 1 and transmission
gear 9 moves along second timing belt 21 and hence movable member
3 also moves back and forth along guide rod 4. Piston 72 engaged
with movable member 3 is then moved back and forth relative to casing
71 engaged with mount 2 to thereby cause syringe 70 to discharge
a liquid.
Generally, there is a backlash among rotation preventing member
22 rotating member 19 second timing belt 21 and transmission gear
9. However, the rotational speed of transmission roller 7 is increased
by speed increasing mechanism 10 and then transmitted to transmission
gear 9 so that an error occurring in transmission gear 9 is reduced
on the side of drive mechanism 17.
When an abnormal pressure exceeding a set value occurs within casing
71 in the liquid discharging operation, rotation preventing member
22 rotates clockwise in FIG. 4 against the action of coil spring
25. Detection switch 26A detects such rotation to thereby cause
control unit 26B to stop motor 12.
In order to exchange syringe 70 after a predetermined liquid discharging
operation is ended, syringe hold lever 30 is rotated until it aligns
with the longitudinal axis of frame 1. Cam member 29 also rotates
in accordance with rotation of lever 30 and arc cam face 29B abuts
on rotation preventing member 22 as shown in FIG. 10(B) by which
operation rotation preventing member 22 is moved away from rotating
member 19 to disengage engaging teeth 19A and 22A from each other
and hence the clutch is disengaged. Under such condition, rotating
member 19 only rotates and movable member 3 will not move even if
motor 12 is operated.
When the clutch is disengaged, movable member 3 is manually moved
to an appropriate position such that syringe 70 is insertable between
mount 2 and movable member 3. Under such condition, syringe casing
71 is inserted into U-like groove 2A in mount 2 and flange 71A of
piston 72 is engaged in groove 3B in movable member 3.
Thereafter, lever 30 is turned through 90 degrees to fix same to
mount 2 of casing 71. Cam member 29 is also rotated in accordance
with the turning of lever 30 and linear cam face 29A abuts on rotation
preventing member 22. Thus, as shown in FIG. 10(A), rotation preventing
member 22 abuts on rotating member 19 and hence engaging portions
19A and 16A are engaged with each other and hence the clutch is
engaged.
Thereafter, in order to cause replaced new syringe 70 to discharge
a liquid, motor 12 is again operated. Even if the crests of engaging
teeth 19A and 22A of both members 19 and 22 abut on each other and
the clutch is not completely engaged, the operation of motor 12
causes rotating member 19 to rotate to thereby change the relative
circumferential position of engaging teeth 19A and 22 of both the
members 19 and 22 and hence to cause these teeth to automatically
engage each other.
According to such structure of the present embodiment, the clutch
mechanism is composed of rotating member 19 and rotation preventing
member 22 with engaging teeth 19A and 22A, respectively, so that
the operation of motor 12 causes teeth 19A and 22A to automatically
engage each other and rotating member 19 will not rotate uselessly
relative to rotation preventing member 22. In addition, since speed
increasing mechanism 10 which increases the speed of transmission
roller 7 and transmits the increased speed to transmission gear
9 is disposed in drive force converting mechanism 11 an error transmitted
to transmission gear 9 is reduced even if there is a play between
members 19 and 22 due to backlash between engaging teeth 19A and
22A, etc. The error can be made to approach 0 limitlessly by adjusting
the speed increase rate of speed increasing mechanism 10. Provision
of a clutch on motor output shaft 12A would be conceivable. However,
according to such structure, a possible error arising in the clutch
would be transmitted to transmission gear 9 intactly or in an amplified
manner. Therefore, in the present embodiment, a liquid is discharged
accurately with syringe 70.
Since drive mechanism 17 drive force transmission mechanism 11
and the guide member are constituted by a plurality of gears and
timing belts to drive movable member 3 in the present embodiment,
the present embodiment produces the following advantages. Since
the use of the screw shaft and nuts is eliminated, the cost of the
syringe pump is reduced. In addition, no wire belt is used and hence
the durability of the syringe pump is improved.
In the present embodiment, closure of syringe 70 prescribed in
JIS is detected accurately irrespective of the kind of the syringe
pump. When syringe 70 is closed in closure detection mechanism 64
shown in FIGs. 12 and 13 gear 60 slides relative to intermediate
gear 58 which moves away from other gears 57 and 60 against the
action of spring 63. The force of intermediate gear 58 to move against
the action of spring 63 is influenced by the slide surface of the
gear or the finished state of the curved gear tooth face. However,
the degree of curved tooth face finish varies from one gear to another,
so that the force of intermediate gear 58 to move differs from one
syringe pump to another. In contrast, the closure detection mechanism
in the present embodiment is arranged such that stop 24 and position
restricting spring 25 are disposed in opposed relationship with
respect to rotation preventing member 22 and that detection switch
26A is disposed which detects the rotation of rotation preventing
member 22 against the action of position restricting spring 25.
Therefore, the closure in syringe 70 is detected without using slippage
between the gears, so that closure in syringe 70 can be detected
irrespective of the kind of the syringe pump used. In addition,
provision of control unit 26B in the present embodiment causes the
discharging of a liquid by syringe 70 to be automatically stopped.
Since the end of position restricting spring 25 is engaged with
bias adjusting screw 27 screwed into frame 1 adjustment of a quantity
of movement of bias adjusting screw 27 causes the biasing force
of spring 25 and hence the set value of closure pressure to be detected
to be changed.
Since cam member 29 with linear cam face 29A and arc cam face 29B
is attached at the end of lever 30 turning lever 30 to remove and
attach syringe 70 causes the clutch mechanism to operate automatically.
Therefore, syringe 70 can be replaced rapidly and easily.
While in the above embodiment the transmission member is illustrated
as including timing belt 16 and roller 13 passive roller 15 and
transmission roller 7 are illustrated in the form of a gear, the
transmission member may be replaced with a chain, and drive roller
13 and passive roller 15 and transmission roller 7 may take the
form of a sprocket structure. As shown in FIG. 11 the transmission
member may be wire belt 36 and drive roller 13 and passive roller
15 each may be a cylindrical member to which an end of wire belt
36 is attached, and transmission roller 37 may be a cylindrical
member around which the middle portion of wire belt 36 extends.
If a timing belt is used as the transmission member as in the previous
embodiment, it is ensured that the drive of motor 12 is transmitted
to speed increasing mechanism 10.
The mechanism for detecting closure in syringe 70 may have a structure
shown in FIG. 11 in which stops 24 abut on corresponding ears 22B
and 22C of rotation preventing member 22 a distortion gage 40 which
detects pressure exerted on rotation preventing member 22 when rotation
member 22 rotates is attached to right-hand ear 22C in FIG. 11
and motor 12 is stopped by a control unit (not shown) when distortion
gage 40 detects a pressure exceeding a predetermined value.
Alternatively, rotating member 19 and rotation preventing member
22 may be attached to shaft 14 and third gear 20 may be attached
to gear 18.
Motor 12 is not necessarily required to be a stepping motor, but
may be a third motor such as a pulse motor or a regular motor. Preferably,
a motor the speed of which is controlled is used.
Piston 72 and casing 71 may be attached to mount 2 and movable
member 3 respectively.
A plurality of syringes 70 may be mounted on the pump in which
case all the syringes may be attached on mount 2 and single movable
member 3. Alternatively, a plurality of movable members 3 may be
used to which corresponding syringes are attached and driven separately.
As described above, the inventive syringe pump has a simple durable
structure to permit an accurate small quantity of liquid to be discharged.
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